JP6806144B2 - Inkjet head, head module and inkjet recorder - Google Patents

Description

The present invention relates to an inkjet head, a head module, and an inkjet recording device.

Conventionally, there is known an inkjet recording device that ejects ink droplets from a plurality of nozzles provided in an inkjet head to form an image on a recording medium. The inkjet head is provided with an actuator that serves as a pressure generating means for ejecting droplets from the nozzle, a driving unit of the actuator, and the like.

In such an inkjet head, the heat generated by driving the actuator heats the inkjet head and raises the temperature of the ink inside the head. As a result, if the temperature of the ink inside the head becomes uneven, the viscosity of the ink becomes uneven, so that the injection speed of the ink varies, which may cause image quality deterioration such as printing unevenness.

Further, in recent years, since it has become possible to drive the actuator at a high frequency, the amount of heat generated from the actuator and the drive IC tends to increase. Furthermore, due to the recent miniaturization of inkjet heads, these actuators are often arranged at high density. In an inkjet head equipped with such an actuator, temperature unevenness of ink is likely to occur inside the head. Therefore, it is required to reduce the temperature unevenness of ink by designing the head itself to easily dissipate heat. ing.

Therefore, Patent Document 1 discloses an inkjet head including a nozzle plate having three or more rows of nozzles, and the nozzle plate is provided with heat-dissipating portions having different heat dissipation rates for each nozzle row. There is. In this inkjet head, since the central nozzle row portion, which tends to have a high temperature, is easily dissipated, it is easy to keep the ink temperature between the nozzle rows uniform.

Japanese Unexamined Patent Publication No. 2012-196880

However, in recent years, in an inkjet recording device equipped with a large number of inkjet heads, the drive rate of the actuator differs greatly depending on the image to be printed, so that there are many cases where a large difference in ink temperature occurs between the heads. .. In such a case, since the viscosity of the ink between the heads is different, the ink ejection speed between the heads is different, which may cause image quality deterioration such as printing unevenness described above.

Further, in an inkjet recording device that draws using a highly viscous ink such as UV ink, the heater built in the inkjet head may be used while heating the ink so that the ink viscosity is suitable for the injection characteristics. .. The inkjet head mounted on such a device needs to be designed to make it difficult for heat to escape to the outside, contrary to the conventional design that easily dissipates heat. Therefore, particularly in this inkjet recording device, a new problem-solving means for controlling the ink temperature in the inkjet head with high accuracy and making the ink between the heads uniform has been required.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an inkjet head, a head module, and an inkjet recording device capable of controlling an ink temperature with high accuracy.

In order to solve the above problems, the invention according to claim 1 is an inkjet head mounted on a head module of an inkjet recording device.
A head tip having a plurality of pressure generating means for ejecting ink from the plurality of nozzles by causing a pressure change in a plurality of pressure chambers communicating with each of the plurality of nozzles.
A common ink chamber for storing ink supplied to the plurality of pressure chambers, and
An exterior frame provided outside the common ink chamber and having a heat radiating portion capable of dissipating heat from the inkjet head.
A drive unit for driving the pressure generating means, which is attached to a housing provided on the outside of the exterior frame.
A detection means for detecting the temperature of the head chip and
A first heater that is driven based on the temperature detected by the detection means and heats the exterior frame is provided.
The thermal resistance of the thermal resistance from the center of gravity of the head chip and the center of gravity of the heat radiating portion Ra (℃ / W), from the center point of the contact portion between the housing and the drive unit and the center of gravity of the heat radiating portion Is Rb (° C./W), and the thermal resistance from the center of gravity of the contact point between the first heater and the exterior frame to the center of gravity of the heat radiating portion is Rc (° C./W). ) Is satisfied.
Equation (1): Rc <Rb <Ra

The invention according to claim 2 is the inkjet head according to claim 1.
It is characterized by including a second heater for heating the common ink chamber.

The invention according to claim 3 is the inkjet head according to claim 1 or 2.
The side surface of the inkjet head is characterized by having a plurality of convex portions protruding from the side surface.

The invention according to claim 4 is the inkjet head according to any one of claims 1 to 3.
The heat radiating portion is characterized in that it is formed of aluminum or an aluminum alloy.

The invention according to claim 5 is the inkjet head according to any one of claims 1 to 4.
The head chip is characterized by having a silicon substrate.

The invention according to claim 6
A head module having a mounting member for mounting the inkjet head according to any one of claims 1 to 5.
Two or more of the inkjet heads are attached to the attachment member so that the heat radiating portion of the inkjet head comes into contact with the attachment member.
The mounting member is made of metal.

The invention according to claim 7
The head module according to claim 6 and
A control unit that controls the drive of the first heater based on the temperature detected by the detection means.
It is an inkjet recording apparatus characterized by the above.

According to the present invention, it is possible to provide an inkjet head, a head module, and an inkjet recording device capable of controlling the ink temperature with high accuracy.

Perspective view showing a schematic configuration of an inkjet recording device Bottom view showing the head module Perspective view showing an inkjet head Enlarged cross section of a part of the cross section of the head tip Perspective view of a cross section cut along VV in FIG. Sectional view cut along VV of FIG. Right side view of the inkjet head Sectional view cut along VIII-VIII of FIG. Sectional view cut along IX-IX of FIG. A cross-sectional view showing the positional relationship of the head chip, the exterior frame, and the housing in the cross section along VIII-VIII of FIG. A perspective view showing the positional relationship between the head chip, the exterior frame, and the housing in the cross section along VIII-VIII of FIG. Block diagram schematically showing the functional configuration of an inkjet recording device Model diagram for calculating thermal resistance value Perspective view of a modified example of an inkjet head

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

[Outline of Inkjet Recording Device]
The inkjet recording device 100 includes a platen 101, a transfer roller 102, line heads 103, 104, 105, 106 and the like (FIG. 1).
Further, in the following description, as shown in FIG. 1, the transport direction of the recording medium R is defined as the front-rear direction, the width direction orthogonal to the transport direction on the transport surface of the recording medium R is defined as the left-right direction, and is perpendicular to the front-rear direction and the left-right direction. This direction will be described as the vertical direction (ink ejection direction).

The platen 101 supports the recording medium R on the upper surface, and when the transport roller 102 is driven, the platen 101 transports the recording medium R in the transport direction (front-back direction).
The line heads 103, 104, 105, and 106 are provided in parallel in the width direction (horizontal direction) orthogonal to the transport direction from the upstream side to the downstream side in the transport direction (front-back direction) of the recording medium R. A head module 200 is provided inside the line heads 103, 104, 105, 106, and the head module 200 is provided with at least one inkjet head 10.

[Head module]
In the head module 200, a plurality of inkjet heads 10 are attached to a mounting member 201 having an opening so that the head chip 20 is exposed from the opening (FIG. 2). Further, the heat radiating portion 51 of the inkjet head 10 is attached to the attachment member 201 so as to be in contact with the attachment member 201. Further, the plurality of inkjet heads 10 are provided so as to be parallel to each other in two rows in the left-right direction, and are attached in a positional relationship in which they are arranged in a houndstooth pattern as a whole. Since the heat radiating portion 51 of the inkjet head 10 is in contact with the upper surface side of the mounting member 201, the heat radiating portion 51 is shown by a broken line in FIG.
Then, for example, the line heads 103, 104, 105, and 106 are provided with an inkjet head 10 that ejects cyan (C), magenta (M), yellow (Y), and black (K) inks, respectively. The head module 200 is provided.

The mounting member 201 is preferably made of metal from the viewpoint of high thermal conductivity. By setting the mounting member 201 to have high thermal conductivity, it is possible to easily dissipate heat from the heat radiating portion 51 of the inkjet head 10 to the mounting member 201. Then, the attachment member 201 is warmed by the heat, and heat exchange is performed with the other inkjet heads 10, so that the temperatures of the plurality of inkjet heads 10 attached to the attachment member 201 can be easily made uniform.
As the metal, the type is not particularly limited because it generally has high thermal conductivity, but for example, 42 alloy, nickel, Kovar, Invar, stainless steel, copper, aluminum, aluminum alloy and the like can be used.

[Inkjet head]
The inkjet head 10 includes a head chip 20, a holding unit 30, a common ink chamber 40, an exterior frame 50, a housing 60, a cover member 70, a temperature detecting unit 80 as a temperature detecting means, and the like (see FIGS. 3 to 11). ..
In addition, in FIGS. 10 and 11, in order to explain the positional relationship between the head tip 20, the exterior frame 50, and the housing 60, other components such as the connecting member 21, the cap portion 22, and the common ink chamber 40 are omitted. It is described as.

The head chip 20 is composed of a nozzle substrate 1, a first adhesive substrate 2, a pressure chamber substrate 3, a second adhesive substrate 4, a piezoelectric element 5 as a pressure generating means, and a wiring substrate 6 laminated in this order. (Fig. 4).

The nozzle substrate 1 is located at the bottom layer of the inkjet head 10. Further, the nozzle substrate 1 is, for example, a substrate made of silicon. The lower surface of the nozzle substrate 1 is a nozzle forming surface facing the recording medium R, and a plurality of nozzles n are formed so as to vertically penetrate the nozzle substrate 1.

The first bonding substrate 2 is laminated and joined on the upper surface of the nozzle substrate 1. The first adhesive substrate 2 is, for example, a glass substrate. The first bonding substrate 2 is formed with a through hole 2a that communicates with the nozzle n of the nozzle substrate 1 and forms an ink flow path.
The pressure chamber substrate 3 is laminated and joined to the upper surface of the first bonding substrate 2.

The pressure chamber substrate 3 is composed of a pressure chamber layer 3a and a diaphragm 3b.
The pressure chamber layer 3a is laminated and joined on the upper surface of the first bonding substrate 2. The pressure chamber layer 3a is made of a silicon substrate. In the pressure chamber layer 3a, a pressure chamber 3c for storing ink ejected from the nozzle n is formed so as to penetrate the pressure chamber layer 3a.
The pressure chamber 3c is provided above the through hole 2a and the nozzle n, and communicates with the through hole 2a and the nozzle n.
The diaphragm 3b is laminated and joined to the upper surface of the pressure chamber layer 3a so as to cover the opening of the pressure chamber 3c. That is, the diaphragm 3b constitutes the upper wall portion of the pressure chamber 3c. Further, for example, an oxide film is formed on the surface of the diaphragm 3b.
A second adhesive substrate 4 is laminated and joined to the upper surface of the diaphragm 3b.

The second adhesive substrate 4 is laminated on the upper surface of the diaphragm 3b. Further, the second adhesive substrate 4 is made of, for example, a photosensitive resin. A space 4a for accommodating the piezoelectric element 5 is formed inside the second adhesive substrate 4. The space portion 4a is formed above the pressure chamber 3c so as to penetrate the second adhesive substrate 4.

The piezoelectric element 5 is formed in a plan view shape substantially the same as that of the pressure chamber 3c, and is provided at a position facing the pressure chamber 3c with the diaphragm 3b interposed therebetween. The piezoelectric element 5 is an actuator made of PZT (lead zirconium titanate) for deforming the diaphragm 3b. Further, an electrode (not shown) provided on the lower surface of the piezoelectric element 5 is connected to the diaphragm 3b. Then, the piezoelectric element 5 can eject ink from the nozzle n by causing a pressure change inside the pressure chamber 3c.

Further, in the second adhesive substrate 4, a through hole 4b that communicates with the communication hole 3d of the pressure chamber substrate 3 is formed independently of the space portion 4a.
The wiring board 6 is laminated and joined to the upper surface of the second bonding board 4.

The wiring board 6 includes, for example, an interposer 6a, which is a board made of silicon. For example, the lower surface of the interposer 6a is coated with two layers of silicon oxide insulating layers 6b and 6c, and the upper surface thereof is also coated with the silicon oxide insulating layer 6d. Then, of the two insulating layers 6b and 6c below the interposer 6a, the insulating layer 6c located on the lower side is laminated and joined to the upper surface of the second adhesive substrate 4.

Further, a through hole 6e is formed in the interposer 6a in the stacking direction, and a through electrode 6f is inserted through the through hole 6e. One end of the lower wiring 6g extending in the horizontal direction is connected to the lower end of the through electrode 6f. At the other end of the lower wiring 6g, an exposed stud bump 6h is provided in the space 4a, and is connected to the conductive paste 5a provided on the electrode (not shown) on the upper surface of the piezoelectric element 5. Further, the lower wiring 6g is sandwiched and protected by two insulating layers 6b and 6c below the interposer 6a.
Further, the interposer 6a is formed so that an inlet 6i communicating with the through hole 4b of the second adhesive substrate 4 penetrates the interposer 6a in the vertical direction.

Further, on the upper surface of the wiring board 6, an upper wiring 6j is provided, one end of which is connected to the upper end of the through electrode 6f and the other end of which is connected to the connecting member 21 at the end of the wiring board 6 in the front-rear direction. ing. The connection member 21 is a wiring member made of a flexible printed circuit board or the like, and is pulled out from the upper part of the head chip 20 and connected to a drive unit 61 described later (see FIG. 6 and the like). Then, electricity is supplied to the piezoelectric element 5 from the drive unit 61 through the connecting member 21, the upper wiring 6j, the through electrode 6f, and the lower wiring 6g.

Further, an adhesive layer 6k is formed so as to cover the upper surface of the upper wiring 6j on the upper surface of the wiring board 6 and the upper surface of the insulating layer 6d of the interposer 6a. The adhesive layer 6k is made of, for example, a photosensitive resin for adhering the inkjet head 10 to the holding portion 30. Further, the adhesive layer 6k constitutes a protective layer that protects the upper wiring 6j. Further, the adhesive layer 6k is formed with a through hole 6l that communicates with the inlet 6i.

Further, as shown in FIG. 6 and the like, a cap portion 22 for closing the lower side of the inkjet head 10 is provided at the end portions of the head chip 20 in the left-right direction and the front-rear direction. It is preferable from the viewpoint of protecting the inside of the device.

The holding portion 30 is joined to the upper side of the head chip 20 and holds the common ink chamber 40, the exterior frame 50, and the like.

The common ink chamber 40 is provided on the wiring board 6, and stores ink for supplying ink from each through hole 6l on the upper surface of the head chip 20 to the pressure chamber 3c in each head chip 20. Further, on the side surface of the common ink chamber 40, a second heater 41 and a heat transfer plate 43 capable of heating the common ink chamber 40 are provided.

The second heater 41 is connected to the input lead wire 42a and the output lead wire 42b, and the drive is controlled by the control unit 300 (see FIG. 12), and electricity is supplied to the second heater 41 through the input lead wire 42a. It is designed to heat. Then, by heating the common ink chamber 40 with the heat generated in the second heater 41, the ink in the common ink chamber 40 can be heated.

A heat transfer plate 43 is provided on the outside of the second heater 41. The heat transfer plate 43 protects the second heater 41 provided on the outer periphery of the common ink chamber 40, and also has a role of transferring heat to the common ink chamber 40 by warming the heat transfer plate 43 itself.

Further, above the common ink chamber 40, an ink supply unit 44 that supplies ink to the common ink chamber 40 and an ink discharge unit 45 that discharges the ink of the common ink chamber 40 are provided.

The exterior frame 50 is formed of, for example, an aluminum alloy in a long shape in the left-right direction, and heat-dissipating portions 51 and 51 are provided at its left end and right end (FIGS. 10 and 11).
The heat radiating portions 51 and 51 are fixed so as to come into contact with the mounting member 201 of the head module 200 by screws or the like, whereby the inkjet head 10 is mounted and fixed to the head module 200 (FIG. 2). Then, the heat of the inkjet head 10 can be dissipated from the heat radiating unit 51 to the mounting member 201 of the head module 200.
It is preferable that the heat radiating portion 51 is made of aluminum or an aluminum alloy from the viewpoint of high thermal conductivity and excellent corrosion resistance.
The heat radiating portion 51 may be formed of at least a material having a high thermal conductivity. If a material having low corrosion resistance is used, the surface thereof should be coated with a parylene film, chrome plating, fluororesin, or the like. And it is sufficient.
Further, although the heat radiating portion 51 is provided on the exterior frame 50, it may be integrally molded with the exterior frame 50, or may be adhered to the exterior frame 50 with an adhesive or the like.

Further, a first heater 52 is provided on the inner surface of the exterior frame 50 (FIGS. 5 and 6). The first heater 52 can heat the exterior frame 50 by the heat generated in the first heater 52. Further, the first heater 52 is pulled out from the lower part of the heat transfer plate 43 from the inside to the outside of the heat transfer plate 43 and is connected to the second heater 41 (not shown), and the first heater 52 and the second heater 41 Is designed to be heated at the same time.
The first heater 52 and the second heater 41 are connected to each other and are heated at the same time. However, the present invention is not limited to this configuration, and the first heater 52 and the second heater 41 are provided separately and independently. , Each heater may be controlled separately.

The housing 60 is formed of, for example, an aluminum alloy in a long shape in the left-right direction, and a common ink chamber 40, a heat transfer plate 43, a connecting member 21, and the like are arranged inside the housing 60. Further, support portions 62, 62 in which drive portions 61, 61 are installed are provided in the upper portion of the common ink chamber 40 on the front side and the rear side inside the housing 60.
Further, the housing 60 and the exterior frame 50 may be formed as separate bodies, and they may be bonded to each other by an adhesive or the like, but the housing 60 and the exterior frame 50 are formed as an integral part. It may be configured.
The drive unit 61 is an integrated circuit made of silicon, and is connected to a connecting member 21 drawn from the front-rear end of the head chip 20 through between the exterior frame 50 and the housing 60 toward the upper part. There is. Since the drive unit 61 is provided at a position far from the head chip 20, the heat generated from the drive unit 61 is less likely to affect the head chip 20.
Further, the front and rear connection members 21 connected to the front and rear drive units 61 and 61 are gathered near the central portion of the housing 60, and finally, the control is installed outside the head chip. It is connected to the unit 300 (see FIG. 12).

The cover member 70 is attached to the upper part of the housing 60 and protects the components inside the inkjet head 10 together with the housing 60 (FIG. 3). In addition, except for FIGS. 3, 7, and 14, for convenience of explanation, the inkjet head 10 in a state where the cover member 70 is removed is shown.

The temperature detection unit 80 is, for example, the tip portion of the thermistor, which is adhered to the central portion of the front end portion of the head tip 20 by an adhesive, and detects the temperature by the resistance value thereof. Further, the temperature detection unit 80 is finally connected to the control unit 300 outside the inkjet head 10 by the flexible printed circuit board 81.

[Control unit]
The inkjet recording device 100 includes a control unit 300 as a control means for controlling each unit constituting the device (FIG. 12).

The control unit 300 includes a CPU (Central Processing Unit) 301 and a RAM (Random Access).
It is configured to include Memory) 302, ROM (Read Only Memory) 303, and the like.
Various processing programs are stored in the ROM 303, and the CPU 301 reads various programs stored in the ROM 303 and expands them in the RAM 302, and controls the operation of each part of the inkjet recording device 100 according to the expanded programs.

For example, the control unit 300 drives a drive motor (not shown) to rotate the transport roller 102, and transports the recording medium R from the rear to the front while being supported by the platen 101 (FIG. 1).
Further, the control unit 300 drives the drive unit 61 of the piezoelectric element 5 to supply electricity to the piezoelectric element 5 inside the head chip 20, and the piezoelectric element 5 is displaced to pressurize the pressure chamber 3c, whereby the nozzle n Inject ink from.

Further, the control unit 300 detects the temperature of the head chip 20 by the detection signal from the temperature detection unit 80, and determines whether or not to supply electricity to the first heater 52 and the second heater 41 based on the temperature. Then, the temperature of the inkjet head 10 is controlled.

The control unit sets a temperature range of 300, for example, the head chip 20 in which ink ejection is stable, sets the average value of the temperature range as the reference temperature, and when the head chip 20 is below the reference temperature, the temperature range is set. , The first heater 52 and the second heater 41 are heated, and on the other hand, when the reference temperature is exceeded, the first heater 52 and the second heater 41 are turned off to dissipate the heat of the inkjet head 10. As a result, the temperature of the head chip 20 in which the ink immediately before being ejected is stored can always be maintained near the reference temperature. Here, if the temperature range in which the above-mentioned ink ejection is stable is set under the same conditions for all the inkjet heads 10 mounted on the head module 200, the head chips 20 of all the inkjet heads 10 will be predetermined. As the temperature is kept near the reference temperature, the temperature difference between the heads becomes small as a result. As a result, the ink ejection speed between the heads is less likely to vary, and printing unevenness and the like are less likely to occur.

Here, the temperature range in which the above-mentioned ink ejection is stable is, for example, the resolution of the drawn image (for example, 600 dpi), the drive frequency of the piezoelectric element 5 (for example, 40 kHz), and the recording when forming an image using a certain ink. The distance between the medium and the nozzle n (for example, 1.0 mm), the reference value of the ink ejection speed (for example, 6.0 mm / sec), and the increase in the ink ejection speed per 1 ° C. increase of the head chip 20 (for example, 0.2 m / sec). Based on information such as sec), it can be defined and calculated according to the temperature range of the head chip 20 when the landing deviation is within half a pixel.

Further, as another example of the temperature control method, the temperature of the head chips 20 of all the inkjet heads 10 mounted on the head module 200 is detected, the average temperature thereof is used as a reference temperature, and the head chip 20 is the reference. If the temperature is lower than the temperature, the first heater 52 and the second heater 41 are heated, and if the temperature is higher than the reference temperature, the first heater 52 and the second heater 41 are turned off and the inkjet head 10 is used. Dissipate heat. As a result, it is possible to suppress variations in the temperature of the head chip 20 between the inkjet heads 10 mounted on the head module 200, so that variations in the ink ejection speed between the heads are reduced and printing unevenness and the like are less likely to occur. Become.

Not limited to the above-mentioned example, the control method can be appropriately changed as long as the temperature of the head chip 20 can be controlled to be uniform among the plurality of inkjet heads 10 attached to the head module 200.

[Relationship of thermal resistance values between predetermined members of an inkjet head]
In the inkjet head 10 of the present embodiment, the thermal resistance from the head chip 20 to the heat radiating unit 51 is Ra (° C./W), the thermal resistance from the drive unit 61 to the heat radiating unit 51 is Rb (° C./W), and the first. When the thermal resistance from the heater 52 to the heat radiating portion 51 is Rc (° C./W), the relationship of the following formula (1) is satisfied.
Equation (1): Rc <Rb <Ra

The thermal resistance R (° C./W) referred to in the present specification indicates a thermal resistance value between two points, and the temperature difference ΔT (° C.) with respect to the heat transfer amount Q (W) between the two points is ΔT. It is R when = RQ is set. Here, it can be considered as an electric circuit (FIG. 13) in which the temperature difference (° C.) is a voltage, the heat transfer amount (W) is a current, and the thermal resistance (° C./W) is a resistance. Similar to Ohm's law, the series and parallel laws of thermal resistance can be applied.

Further, as can be seen from the relationship of the equation (1), the inkjet head 10 of the present embodiment is formed so that the thermal resistance Ra from the head chip 20 to the heat radiating portion 51 is larger than Rb and Rc, and the ink is ejected. The temperature of the ink inside the head chip 20, which is the ink immediately before, is less likely to fluctuate. As described above, by using the head chip 20 as a substrate having a silicon substrate, the temperature of the entire head chip 20 can be easily made uniform.

Further, the thermal resistance Rb from the drive unit 61 to the heat radiation unit 51 is smaller than the thermal resistance Ra, and the thermal resistance Rc from the first heater 52 to the heat radiation unit 51 is smaller than the thermal resistance Rb. Therefore, heat is most easily conducted from the first heater 52 to the heat radiating section 51 through the exterior frame 50, and the heat of the exterior frame 50 is radiated directly from the heat radiating section 51 to the outside of the inkjet head 10 to the drive section 61 side and the drive section 61 side. It is difficult to transfer heat to the head chip 20 side.
As a result, for example, when the temperature of the head chip 20 is higher than the above-mentioned reference temperature and it is desired to release the heat of the inkjet head 10, the first heater 52 is turned off and the heat radiating unit 51 is passed through the exterior frame 50. Heat can be efficiently dissipated from. On the other hand, for example, when the temperature of the head chip 20 is lower than the above-mentioned reference temperature and the heat of the inkjet head 10 is not to be released, the first heater 52 is turned on to warm the exterior frame 50. Therefore, it is possible to make it difficult for heat to escape from the heat radiating portion 51. In that case, since the second heater 41 is also turned on, the ink in the common ink chamber 40 is heated, and the ink enters the head chip 20 to heat the head chip 20 as well.

Further, the thermal resistance Rb from the drive unit 61 to the heat radiation unit 51 is larger than the thermal resistance Rc from the first heater 52 to the heat radiation unit 51. As a result, for example, when the temperature of the head chip 20 is higher than the above-mentioned reference temperature and it is desired to dissipate the heat of the inkjet head 10, the heat generated by the drive unit 61 is in contact with the drive unit 61. Heat can be released from the body 60 to the outside of the inkjet head 10 from the heat radiating portion 51 through the contact point M3 (see FIG. 13) between the housing 60 and the exterior frame 50. On the other hand, for example, when the temperature of the head chip 20 is lower than the above-mentioned reference temperature and the heat of the inkjet head 10 is not to be released, the first heater 52 is turned on and the exterior frame 50 is used. By heating, the heat generated by the drive unit 61 can be retained in the housing 60 portion without escaping, so that it can be used as a heat source for heating the inkjet head 10.

Further, the thermal resistance Ra from the head chip 20 to the heat radiating unit 51 has a resistance value sufficient to dissipate the heat generated by the piezoelectric element 5 as the pressure generating means from the heat radiating unit 51. This resistance value is, for example, the resolution of the drawn image (for example, 600 dpi), the drive frequency of the piezoelectric element 5 (for example, 40 kHz), the distance between the recording medium and the nozzle n (for example, 1.0 mm), and the reference value of the ink ejection speed (for example, 1.0 mm). For example, 6.0 mm / sec), based on information such as an increase in ink ejection speed per 1 ° C increase of the head chip 20 (for example, 0.2 m / sec), for example, allowance when the landing deviation is within half a pixel. The possible temperature rise value can be calculated, and the thermal resistance Ra can be determined from this temperature rise value.

[Calculation method of thermal resistance value]
The thermal resistance R (° C./W) of the heat transfer member is the length L (m) of the heat transfer member, the thermal conductivity λ (W / (m · K)) of the heat transfer member, and the cross-sectional area A of the heat transfer member. When (m ² ), it can be expressed as R = L / λA. Therefore, the thermal resistance value R between the predetermined two points can be calculated as the combined resistance of the series circuit and the parallel circuit by the circuit model as shown in FIG.

An example of the method of calculating the thermal resistance value will be described with reference to the circuit model diagram of FIG. Here, in the calculation of the thermal resistance value, the inkjet head 10 is calculated for a cross section half of the center, assuming that it is symmetrical. Further, in the calculation of the thermal resistance, the thermal resistance due to convection and radiation is excluded as a minute one, and the calculation is performed only by the heat conduction between the members.

In FIG. 13, in a cross section cut along a plane parallel to the front-rear direction at the center of the inkjet head 10 in the left-right direction, the center of gravity of the contact point between the front drive unit 61 and the housing 60 is set to S1a, and the rear drive unit 61 is shown. The center of gravity of the contact point between the housing 60 and the housing 60 is S1b, the center of gravity of the contact point between the front first heater 52 and the exterior frame 50 is S2a, and the contact point between the rear first heater 52 and the exterior frame 50. The position of the center of gravity is represented by S2b, and the position of the center of gravity of the head tip 20 is represented by S3.

Here, since the housing 60 is separated into two in the front-rear direction, the front side and rear side housings 60 are regarded as a parallel circuit. Further, in the following description, S1a and S1b are collectively referred to as S1 (FIG. 13).
Similarly, since the exterior frame 50 is separated into two in the front-rear direction, the front and rear exterior frames 50 are regarded as a parallel circuit. Further, in the following description, S2a and S2b are collectively referred to as S2 (FIG. 13).

Further, the position of the center of gravity of the heat radiating portion 51 provided at the left end portion of the inkjet head 10 is represented as E1.
Further, since heat is transferred to the same region on the way from each of S1, S2 and S3 to E1 and finally reaches E1 (heat dissipation part), the position of the same region on the way is determined. It is expressed as M3.

As shown in FIG. 13, the thermal resistance Ra (° C./W) from the head chip 20 to the heat radiating portion 51 is calculated as the thermal resistance between S3 and E1. Further, the thermal resistance Rb (° C./W) from the drive unit 61 to the heat radiation unit 51 is calculated as the thermal resistance between S1 to E1. Further, the thermal resistance Rc (° C./W) from the first heater 52 to the heat radiating portion 51 is calculated as the thermal resistance between S2 to E1.

Here, between S1 to E1, between S2 to E1 and between S3 and E1, can be represented as a circuit model in which a series circuit and a parallel circuit are combined, respectively. Also, since the thermal resistance value changes when the cross-sectional area is different even for the same member, the thermal resistance calculation is divided at the change point of the cross-sectional area, regarded as a series circuit, and each is calculated separately and then added. It is calculated.

Specifically, the thermal resistance between S1 to M3 is the same member, but there is a change point M1 in the cross-sectional area in the middle. The thermal resistance R1 between S1 to M1 is the thermal resistance of the housing 60 portion on the front side and the rear side, and the respective thermal resistances are regarded as a parallel circuit arranged in parallel, and the sum of their reciprocals (1 / (R1a)). It is calculated by + 1 / (R1b)). The thermal resistance between S1 to M3 is calculated by the sum of the thermal resistance R1 between S1 and M1 and the thermal resistance R2 between M1 and M3 (R1 + R2).

The thermal resistance between S2 and M3 is obtained by R3 because there is no change point. R3 is the thermal resistance of the front and rear exterior frame 50 parts, and each thermal resistance is regarded as a parallel circuit arranged in parallel, and the sum of their reciprocals (1 / (R3a) + 1 / (R3b)) It is calculated.

The thermal resistance between S3 and M3 is calculated by the sum (R4 + R5) of the thermal resistance R4 of the head tip 20 portion corresponding to S3 to M2 and the thermal resistance R5 from the end of the head tip to M3 (between M2 and M3). doing.
Here, in the calculation of R4, since the head chip 20 is a laminated body of a plurality of (for example, n) substrates, the thermal resistance of each substrate is regarded as a parallel circuit as shown in FIG. It is calculated as the sum of the reciprocals of the resistance of each substrate by the equation (2). The thermal resistance of the substrate is calculated using the above-mentioned R = L / λA, and the numbers in parentheses indicate the number of layers of the substrate from the bottom.
Equation (2): R4 = (1 / R4 ₍₁₎ ) + (1 / R4 ₍₂₎ ) + ... + (1 / R4 _(n) )

Further, since the thermal resistance between M3 and E1 has a change point having a different cross-sectional area between M3 and E1, the point of the change point is represented as M4. Therefore, the thermal resistance between M3 and E1 is calculated by the sum of the thermal resistance R4 between M3 and M4 and the thermal resistance R5 between M4 and E1 (R4 + R5).

The thermal resistance at each interval can be calculated by the above calculation method. Then, the thermal resistance Ra from the head chip 20 to the heat radiating unit 51, the thermal resistance Rb from the driving unit 61 to the heat radiating unit 51, and the thermal resistance Rc from the first heater 52 to the heat radiating unit 51 satisfy the equation (1). As described above, each component is selected so as to increase in the order of Rc, Rb, and Ra.
In the comparison of the thermal resistance values of Ra, Rb and Rc, since the path between M3 and E1 is the same, the thermal resistance between S3 and M3, the thermal resistance between S1 and M3 and the thermal resistance between S2 and M3 It may be obtained by comparing the values.

[Modification example]
The inkjet head 10 of the present embodiment is provided with a heat radiating portion 51 capable of dissipating the heat of the inkjet head 10. However, in order to further enhance the heat radiating effect, the inkjet head 10 projects from the side surface portion. It may have a plurality of convex portions 63. Further, from the viewpoint of increasing the surface area and enhancing the heat dissipation effect, as shown in FIG. 14, it is preferable to have a heat sink shape in which a large number of a plurality of convex portions 63 along the vertical direction are arranged in the front-rear direction.
By improving the heat dissipation of the inkjet head 10 in this way, it is possible to use, for example, a resin substrate having a thermal conductivity inferior to that of metal as the mounting member 201 of the head module 200.
In the case of the inkjet head 10 having such a convex portion 63, it is necessary to include the thermal resistance due to convection of the portion provided with the convex portion 63 in the calculation of the thermal resistance. In this case, the required thermal resistance under the conditions of the assumed usage environment may be calculated, the required surface area of the heat sink shape may be obtained, and the shape may be designed to have that surface area.

[Technical Effect of the Present Invention]
As described above, the inkjet head 10 of the present embodiment has an exterior frame 50 having a heat radiating portion 51 capable of dissipating the heat of the inkjet head 10 and a driving unit 61 for driving a piezoelectric element 5 attached to the housing 60. A first heater 52 that heats the exterior frame 50, a temperature detection unit 80 that detects the temperature of the head chip 20, and a control unit 300 that controls the drive of the first heater 52 based on the detected temperature. The thermal resistance from the head chip 20 to the heat radiating unit 51 is Ra (° C./W), the thermal resistance from the drive unit 61 to the heat radiating unit 51 is Rb (° C./W), and the heat resistance from the first heater 52 to the heat radiating unit 51. When the thermal resistance up to is Rc (° C./W), the relationship of Rc <Rb <Ra is satisfied. As a result, the temperature of the head chip 20 can be controlled with high accuracy, and the printing speed can be kept within the range of the ink ejection speed at which printing unevenness does not always occur during printing.

Further, the inkjet head 10 of the present embodiment is provided with the second heater 41 for heating the common ink chamber 40, so that when the temperature of the ink is desired to be raised, the temperature can be raised to a target temperature more quickly, and the inside of the head can be raised. The temperature of the ink entering can be made uniform.

Further, the inkjet head 10 of the present embodiment can improve the heat dissipation efficiency of the inkjet head 10 by having a plurality of convex portions protruding from the side surface of the inkjet head.

Further, in the inkjet head 10 of the present embodiment, the heat dissipation efficiency of the inkjet head 10 can be improved by forming the heat radiating portion 51 with aluminum or an aluminum alloy.

Further, the inkjet head 10 of the present embodiment has a configuration in which the head chip 20 has a silicon substrate, so that the temperature of the entire head chip 20 can be easily made uniform.

Further, the head module 200 equipped with the plurality of the inkjet heads 10 of the present embodiment is attached to the attachment member 201 so that the heat radiating portion 51 of the inkjet head 10 is in contact with the attachment member 201, and the attachment member 201 is formed of metal. There is. As a result, the mounting member 201 has a high thermal conductivity, so that it is possible to easily dissipate heat from the heat radiating portion 51 of the inkjet head 10 to the mounting member 201. Then, the attachment member 201 is warmed by the heat, and heat exchange is performed with the other inkjet heads 10, so that the temperatures of the plurality of inkjet heads 10 attached to the attachment member 201 can be easily made uniform.

Further, the inkjet recording device 100 of the present embodiment includes a head module 200 and a control unit 300 that controls the drive of the first heater 52 based on the temperature detected by the temperature detection unit 80. The ink temperature of the inkjet head 10 provided in the recording device can be controlled with high accuracy.

[Other]
It should be considered that the embodiments of the present invention described above are exemplary in all respects and not restrictive. That is, the scope of the present invention is shown not by the above description but by the scope of claims, and it is intended that all modifications within the meaning and scope equivalent to the scope of claims are included.

For example, as the inkjet recording apparatus 100, an example of a one-pass drawing method in which drawing is performed only by transporting a recording medium using line heads 103, 104, 105, 106 has been described, but it can be applied to an appropriate drawing method. A drawing method using a scanning method may be used.

Further, the temperature detection unit 80 can be appropriately changed if the temperature of the head chip 20 can be detected, and the position and number of detections can be appropriately changed.

Further, although one heat radiating portion 51 is provided at each of the left end portion and the right end portion of the exterior frame 50, the position and number of the heat radiating portions 51 can be appropriately changed.

The present invention can be used for an inkjet head, a head module, and an inkjet recording device.

n Nozzle 5 Piezoelectric element (pressure generating means)
3c Pressure chamber 10 Inkjet head 20 Head chip 40 Common ink chamber 41 Second heater 43 Heat transfer plate 50 Exterior frame 51 Heat dissipation unit 52 First heater 60 Housing 61 Drive unit 63 Convex portion 80 Temperature detection unit (detection means)
100 Inkjet recording device 200 Head module 201 Mounting member 300 Control unit (control means)

Claims (7)

An inkjet head mounted on the head module of an inkjet recording device.
A head tip having a plurality of pressure generating means for ejecting ink from the plurality of nozzles by causing a pressure change in a plurality of pressure chambers communicating with each of the plurality of nozzles.
A common ink chamber for storing ink supplied to the plurality of pressure chambers, and
An exterior frame provided outside the common ink chamber and having a heat radiating portion capable of dissipating heat from the inkjet head.
A drive unit for driving the pressure generating means, which is attached to a housing provided on the outside of the exterior frame.
A detection means for detecting the temperature of the head chip and
A first heater that is driven based on the temperature detected by the detection means and heats the exterior frame is provided.
The thermal resistance of the thermal resistance from the center of gravity of the head chip and the center of gravity of the heat radiating portion Ra (℃ / W), from the center point of the contact portion between the housing and the drive unit and the center of gravity of the heat radiating portion Is Rb (° C./W), and the thermal resistance from the center of gravity of the contact point between the first heater and the exterior frame to the center of gravity of the heat radiating portion is Rc (° C./W). ) Is satisfied with the inkjet head.
Equation (1): Rc <Rb <Ra The inkjet head according to claim 1, further comprising a second heater for heating the common ink chamber. The inkjet head according to claim 1 or 2, wherein the side surface of the inkjet head has a plurality of convex portions protruding from the side surface. The inkjet head according to any one of claims 1 to 3, wherein the heat radiating portion is formed of aluminum or an aluminum alloy. The inkjet head according to any one of claims 1 to 4, wherein the head chip has a silicon substrate. A head module having a mounting member for mounting the inkjet head according to any one of claims 1 to 5.
Two or more of the inkjet heads are attached to the attachment member so that the heat radiating portion of the inkjet head comes into contact with the attachment member.
A head module characterized in that the mounting member is made of metal. The head module according to claim 6 and
A control unit that controls the drive of the first heater based on the temperature detected by the detection means.
An inkjet recording device characterized by comprising.

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