JPH05338143A - Ink jet head - Google Patents

Abstract

PURPOSE:To discharge a certain quantity of ink stably by a method wherein a temperature control means is formed over the whole region of an inner peripheral surface of a nozzle in an ink jet head wherein the ink is frozen with a nozzle part when the ink is made not to be discharged and the ink is melted by heating when discharged. CONSTITUTION:A nozzle 8 is constructed in a tapered form so that a dis-discharge opening 8a side becomes narrow, its peripheral wall surface is covered by a heating element 9 of a temperature control means, and an thermal insulating material 11 layer is laid between an inside of the heating element 9 and a nozzle base material 10. An individual electrode 12 is formed to each heating element 9, and a heat plate 14 jointly used as a common electrode is arranged to a discharge opening 8a side of the nozzle 8. The heating element 9 is used as an ink melting and temperature detecting means. The nozzle 8 from which the ink is desirous to be discharged is selectively operated with a driving IC. Though the nozzle 8 is blocked up ordinarily since liquid ink supplied from a second ink tank 6 is frozen, the ink is heated to be melted by conducting the heating element 9, and discharged by inertial force. When applied voltage is turned off with the driving IC, heat of the heating element 9 is radiated with the heat plate 14. A neighborghhood of the nozzle discharge opening 8a is quickly cooled to freeze the ink.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head using a heat-meltable ink (an oil-based ink which is also generally called a solid ink). More specifically, according to the present invention, a common ink tank having a plurality of nozzles stores ink that has been heated and melted into a liquid state, and when the ink is not ejected, the nozzle is solidified at the nozzle portion to eject the ink. The present invention relates to an improvement in a nozzle portion of an ink jet head that heats and melts ink that has solidified.

[0002]

2. Description of the Related Art As an ink jet head using a heat-meltable ink, there is a multi-nozzle recording type ink jet head as disclosed in Japanese Patent Publication No. 62-41112. In this multi-nozzle inkjet method, as shown in FIG. 11, a plurality of nozzles 102 are opened in a common ink tank 101, and at each nozzle 102, a Peltier element 103, ...
03, and selectively Peltier elements 103, ..., 103
The nozzle 102 is heated or cooled to select a nozzle for ejecting ink, and a desired character or image is recorded. That is, this inkjet head is
The melted ink is stored in a common ink tank, while the ink is solidified at each nozzle portion, and the solidified ink in the nozzle portion is heated and melted only when ejected. Peltier element 103, ..., Near the nozzle outlet
By locally heating or cooling by 103,
It is provided so as to melt a mass of ink filling the inside of the nozzle or solidify the melted ink. The ink 104 is always heated and melted in the shared ink tank 101, but is solidified by the forced cooling in each nozzle 102 portion, and the nozzle 102 is blocked. This multi-nozzle head uses an exciting element 105 composed of a piezoelectric element or an ultrasonic vibrator to form an ink tank 101.
The wall of the ink is pressure-excited to apply pressure to the entire molten ink 104 in the ink tank 101 to eject the ink in the selected nozzle 102.

[0003]

However, in this multi-nozzle head, the Peltier element 103 is fixed around the ejection opening of the nozzle 102, and the nozzle ejection opening is locally heated to solidify inside the nozzle. Since the ink is melted, it takes time to transfer the heat applied from the nozzle ejection port surface to the inner part of the nozzle and to melt all the ink in the nozzle.
That is, the response speed becomes slow. In addition, since this multi-nozzle head locally applies heat on the surface of the nozzle outlet,
A uniform melt cannot be expected in the nozzle axis direction, and stable ejection cannot be obtained.

Further, since the Peltier element 103 is arranged around the ejection port of the nozzle 102 in the same head, the nozzle interval is influenced by the size of the Peltier element 103, which hinders the downsizing of the head. This is because a minimum amount sufficient to obtain the amount of heat for melting the entire amount of ink in the nozzle on the order of 0.5 ms is required.

An object of the present invention is to provide an ink jet head having a fast response speed and stable ink ejection.

[0006]

In order to achieve such an object, the present invention stores ink which is heated and melted into a liquid state in a common ink tank having a plurality of nozzles, and when the ink is not ejected, the nozzle portion In the ink jet head that heats and melts the solidified ink in the nozzle portion when the ink is solidified and ejected, the temperature control means is formed over the entire inner peripheral surface of the nozzle.

Here, the temperature control means is preferably a heating element, and more preferably, a heat insulating material layer is provided between the layer of the heating element and the base material forming the nozzle.

[0008]

Therefore, the entire inner peripheral surface of the nozzle is heated at the same time, and the entire mass of ink blocking the nozzle is heated and melted at the same temperature. For this reason, it takes a short time for the ink to reach a molten state and is uniformly melted.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 4 shows an embodiment of the ink jet head of the present invention. The inkjet head of this embodiment is a so-called multi-nozzle head that ejects a plurality of types of ink, but the description will mainly focus on one inkjet head. This inkjet head 1 is a head 2 provided with a plurality of nozzles capable of storing ink and controlling ejection.
A vibrating means 3 for supporting the head 2 portion and vibrating the whole by resonance, an ink introducing means 4 for accommodating the solid ink 39s and melting it as necessary, and the melted ink 3
A first ink tank 5 that stores a fixed amount of 9r, the first ink tank 5, and a second ink tank 6 on the head side.
It is mainly composed of an ink supply pipe 7 for connecting with.

The head 2 is, as shown in FIGS. 1 and 3,
A plurality of ink ejection nozzles, for example, 48 nozzles 8, 8, ..., 8 in the present embodiment are set as one set in the bottom of the second ink tank 6, and four sets are arranged in a zigzag pattern with each 6 rows in a line.
They are arranged in columns. In the inkjet head 1 of the present embodiment, which is intended to eject four types of ink, four nozzle groups are arranged, but it goes without saying that one nozzle group is used as the minimum unit. A second ink tank 6 that stores the melted ink 39r is arranged above the nozzle 8.

The nozzle 8 is composed of a tapered hole which becomes narrower on the discharge port 8a side, and its peripheral wall surface is covered with a heating element 9 serving as a temperature control means. The heating element 9 is made of, for example, a thin film of tungsten or the like formed by a known thin film forming technique, and a layer of a heat insulating material 11 is interposed between the heating element 9 and a nozzle base material 10 made of ceramic or the like.
Due to the presence of the heat insulating material 11, the heat of the heating element 9 is transferred to the nozzle base material 1.
Prevents escape to the 0 side and improves heat generation efficiency. Each heating element 9
An individual electrode 12 is formed in the nozzle, and is provided so as to energize and heat only the heating element 9 of an arbitrary nozzle 8. The electrode 12 is formed in a disc shape surrounding the hole of the nozzle 8. Further, the electrode GN is provided on the ejection port 8a side of the nozzle 8.
A heat dissipation plate 14 also serving as D (common electrode) is arranged.
The heat radiating plate 14 radiates the heat generated in the heating element 9 to cool it rapidly. As the heat dissipation plate 14, it is preferable to use, for example, a material excellent in both electrical conductivity and thermal conductivity such as copper. Usually, the heat dissipation plate 14 has a large number of nozzles 8, ..., 8
The entire surface (the entire surface of the head) of the nozzle substrate 10 for forming the nozzles is covered and only the periphery of the nozzle ejection port 8a is opened. In general,
The ink ejection force depends on the acceleration of the vibration of the head and the opening area of the nozzle. On the other hand, the ejection repulsion force is determined by the surface tension of the ink and the shape of the nozzle 8. Then, stable ejection is obtained when the ink ejection force exceeds the ejection repulsion force. However, since the nozzle 8 used in the inkjet head is a very small hole having a diameter of about 50 μm, stable ink ejection is difficult only by vibration of the nozzle portion. However, in this embodiment, by arranging the second ink tank 6 on the nozzle 8, the nozzle 8
It is provided so as to obtain a sufficient ejection force by the inertia of the ink inside and the inertia of the ink inside the second ink tank 6. Moreover, as shown in FIG. 1B, the nozzle shape is formed in a taper shape such that the diameter gradually becomes smaller toward the discharge port 8a, and the opening area is made larger toward the upper part of the nozzle 8 so that the discharge pressure is increased. Becomes bigger.

The second ink tank 6 constitutes the head 2 together with the nozzle 8 and is vibrated together with the nozzle 8 by the vibrating means 3. Further, a heating member (not shown) is installed on the lid member 16 that closes the second ink tank 6,
The ink 39r in the second ink tank 6 is kept at a constant temperature so as not to harden. A liquid retaining material 17 that holds the ink 39r is housed in the second ink tank 6. The liquid retaining material 17 suppresses the free movement of the ink in the molten state to prevent the ink from jumping out due to vibrations, and also functions as a filter for removing foreign matters that may cause nozzle clogging. As a result, even if the head 2 vibrates due to resonance, only the required amount of ink is ejected from the nozzles 8.
Is supplied and discharged. The liquid retaining material 17 is not particularly limited, but it is preferable to use felt or moltoprene.

The vibrating means 3 for vibrating the head 2 is not particularly limited, but in the present embodiment, a vibrating means such as a tuning fork utilizing the resonance action is adopted. For example, as shown in FIG. 4, a first vibrating body 20 having a vibration generating coil / electromagnet 29 at its tip and a second vibrating body 21 facing the first vibrating body 20 are connected to a fixing member 22 at their base ends. The first vibrating body 20 and the second vibrating body 21 are attracted to each other by the actuation of the electromagnet 29, and when they are released, the first vibrating body 20 and the second vibrating body 21 are resonated with each other by their elastic force. The head 2 is mounted on the tip of the second vibrating body 21 and is designed so that the masses of the first vibrating body 20 and the second vibrating body 21 are substantially equal.
The first vibrating body 20 and the second vibrating body 21 are provided with a center-of-gravity adjusting means 30 for adjusting the positions of their centers of gravity. In the case of the present embodiment, the center of gravity adjusting means 30 is the first
And the bracket 3 fixed to the second vibrating body 20, 21.
1 and a screw 32 screwed to the bracket 31. Therefore, the position of the center of gravity can be easily adjusted by adjusting the screwing amount of the screw 32. In the case of this embodiment, the center-of-gravity adjusting means 30 is provided at both ends of the vibrating bodies 20, 21 on which the head 2 having four nozzle groups is mounted, as shown in FIGS. Further, the electromagnet 29 that induces the resonance action is arranged at a uniform position slightly outside the centers of the vibrating bodies 20 and 21. This state is shown in FIGS.

The ink supply pipe 7 for supplying ink from the first ink tank 5 side on the base end side to the second ink tank 6 on the head 2 side is made of a material having a good thermal conductivity such as copper. An inverted U-shaped pipe is used. The ink supply pipe 7 is provided with an ink injection port 18 formed in a lid member 16 of the second ink tank 6 on the head 2 side.
Has been inserted inside. Ink supply pipe 7 and ink inlet 1
A gap is formed between the ink supply pipe 8 and the head 8 so that the ink supply pipe 7 does not interfere with the vibration of the head 2. The ink supply pipe 7 is filled with a material 19 such as felt or maltoprene that causes or assists the capillary phenomenon, and the ink 3 in the melted state in the first ink tank 5 is filled.
9r is provided so as to be supplied into the second ink tank 6 on the head side by utilizing the capillary phenomenon. The felt 19 that causes or assists the capillary phenomenon is connected to at least the liquid retaining material 24 in the first ink tank 5, but is not necessarily connected to the liquid retaining material 17 in the second ink tank 6. good. Rather, from the viewpoint of vibration transmission, it is preferable that the felt 19 and the liquid retaining material 17 in the second ink tank 6 are not connected, but when a material having high elasticity is used. Even if connected, it does not particularly affect the vibration system.

The first ink tank 5 is supported by a support plate 15 and is fixed to a fixing member 22 for connecting and fixing the first and second vibrating bodies 20 and 21. The first ink tank 5 is left stationary regardless of the resonance action of the vibrating means 3,
The ink 39r in a molten state is stably supplied to the vibrating head 2. As shown in FIGS. 4 and 5, the first ink tank 5 is partially partitioned by the partition wall 23 into two large and small chambers 5a and 5b, and one large chamber 5
A felt 24 as a liquid retaining material is accommodated in a.
Also, the thermistor 25 is installed in the small room 5b,
The amount of ink stored decreases and the thermistor 2
It is provided to detect the remaining amount of ink by utilizing the fact that the resistance value of the thermistor 25 changes when 5 is exposed. The felt 24 is not housed in the room 5b in which the thermistor 25 is arranged, and only ink is stored. Therefore, when the ink is supplied to the second ink tank 6 on the head 2 side and the ink in the first ink tank 5 decreases, the ink in the chamber 5b of the thermistor 25 is preferentially absorbed by the felt 24. , The amount of ink contained in the felt 24 can be shown before the amount of ink is significantly reduced. A sheet-shaped heating element (not shown) is provided on the ceiling surface of the first ink tank 5 for maintaining the molten state of the stored ink 39r.

Ink introducing means 4 is connected to the first ink tank 5. The ink introducing means 4 is, as shown in FIG. 7, an ink cylinder 26 containing a rod-shaped solid ink 39s.
A supply hole 27 for communicating the bottom of the ink cylinder 26 with the first ink tank 5, and a built-in heater 28 for heating the bottom of the ink cylinder 26 to melt the solid ink 39s in the ink cylinder 26 from the bottom. It consists of Heater 2
The drive of 8 is controlled by the thermistor 25 installed in the first ink tank 5. That is, when the remaining amount of ink in the first ink tank 5 is reduced and the thermistor 25 is exposed from the ink 39r, the fact is detected.
It can be detected by the change of the resistance value of. Therefore, the heater 28 is controlled by detecting a change in the resistance value of the thermistor 25, and when the ink remaining amount in the first ink tank 5 becomes less than the set value, the heater 28 is automatically energized to set the solid state. It is provided so that the ink 39s is melted and the melted ink 39r is replenished.

The heating element 9 of each nozzle 8 is driven by a nozzle driving IC 13. The nozzle driving IC 13 is mounted on the ceramic substrate 10 of the head 2 of the second vibrating body 21 and is connected by the nozzle electrode 12, the copper wiring 12a and the wire bonding 13a. Although the input terminals of the drive IC are common in this embodiment, they may be individually drawn out. The heat generation temperature of the heating element 9 is measured by detecting the resistance value of the heating element 9. Therefore, the energization of the heating element 9 can be controlled based on this measured temperature. Here, the nozzle 8 and the driving IC 13 are copper wiring 1
2a and wire bonding 13a. The drive IC 13 is sealed with a sealing material such as silicone or epoxy resin in order to improve reliability.
The temperature control means including the driving IC 13 and the heating element 9 driven by the driving IC 13 has two functions, an ink ejection function and a nozzle temperature control function (preheating function) when not operating. Here, the nozzle temperature control function refers to a function of keeping the heating element 9 of each nozzle 8 at a certain constant temperature. If the heating element 9 is preheated to a certain constant temperature in this way, the solidified ink can be melted and ejected by slight heating, so that the responsiveness can be improved and stable regardless of changes in the environmental temperature. Ink ejection is possible.

Further, regarding the nozzle temperature control function, FIG.
A description will be given based on an example shown in FIG. The nozzle temperature control includes a nozzle control unit 33, a nozzle driver 34, an output control unit 35, a temperature detection unit 36, a comparison unit 37, and a reference data unit 38 that outputs a reference value. These are formed by the IC chip 13, for example. The data signal output from the control unit such as the printer main body or the computer is input to the nozzle control unit 33, drives the nozzle driver 34, and causes the output control unit 35 to correspond to the heating elements 9 of the nozzles 8.
Control the output that activates. This output control detects the change in resistance of the heating element 9 itself to detect the heating temperature of the heating element 9, and determines this by the reference temperature value at the time of operation for each nozzle position or the nozzle determined in advance by the reference data section 38. It is compared with a reference temperature value during operation (that is, the temperature set based on the temperature at which the solid ink melts) determined regardless of the position, and based on the comparison result, it is determined whether or not to continue energization. Nozzle control section 3
3 is operated or compared with a reference temperature value at the time of non-operation (that is, a temperature set based on the temperature at which the molten ink is solidified) determined for each nozzle position or irrespective of the nozzle position, and whether to energize After determining whether or not, the nozzle control unit 33 is operated based on the comparison result.

Since the ink jet head of the present invention is constructed as described above, it operates as follows.

First, the head 2 is vibrated. This causes the first vibrating body 20 and the second vibrating body 21 to vibrate by passing a current of a desired frequency through the vibration generating coil / electromagnet 29 of the first vibrating body 20. For example, when a sine wave of about 2000 Hz is applied to the coil 29, the first vibrating body 20 and the second vibrating body 21 resonate like a tuning fork with the connecting member 22 as the vibration neutral point. At this time, the nozzle 8 of the head 2 attached to the tip of the second vibrating body 21 also vibrates integrally with the second vibrating body 21. Moreover, the nozzle 8 vibrates by the resonance of the second vibrating body 21 so as to move in parallel. In this state, the ink 39r already supplied into the first ink tank 5 via the ink introducing means 4 is held in the ink supply pipe 7 while being held by the felt 24 of the liquid retaining material in the first ink tank 5. Is supplied to the second ink tank 6 on the side of the head 2 through the felt 19 by the capillary phenomenon. The ink 39r stored in the second ink tank 6 vibrates while being held by the felt 17 as a liquid retaining material, with the same acceleration applied to the entire ink.

Therefore, the nozzle 8 from which ink is desired to be ejected is selectively operated by the drive IC 13. The nozzle 8 is normally closed by solidification of the liquid ink 39r supplied from the second ink tank 6, but is heated and melted by energizing the heating element 9 which is the temperature control means, and ejected by inertial force. The heating element 9 generates heat at a temperature at which ink is melted, for example, in the range of 120 ° C. to 150 ° C., at least over the entire inner peripheral surface of the nozzle 8. As a result, the solid ink blocking the nozzle 8 is simultaneously heated and melted on the entire surface, and is ejected by the above-described vibration. Assuming that the head is vibrating as shown in FIG. 10, if the ink is melted when the vibration acceleration is downward, the ink is ejected from the nozzle 8 when the vibration acceleration direction changes upward. Then, when the applied voltage is turned off by the drive IC 13, the heat of the heating element 9 forming the nozzle 8 is dissipated by the heat radiating plate 14, and the vicinity of the nozzle ejection port 8a is rapidly cooled and the ink is solidified. That is, the state before heating the heating element 9 is obtained.
The timing of turning off depends on the time required for cooling. For example, if the solidification timing is completed when the acceleration of vibration is in the upward direction, ink can be ejected and solidified in one cycle of vibration. For this reason, theoretically, it is possible to print at a frequency of 1 second. Therefore, the drive IC 13
The nozzles 8 selectively generate heat based on the image data or the character data input to, so that the melted ink is ejected only from the selected nozzle 8. The ink in the nozzles 8 that has not been selected is cooled and solidified by natural heat dissipation. When the remaining amount of the melted ink in the first ink tank 5 becomes small, the solid ink in the ink cylinder 26 is melted by the heating of the built-in heater 28 and the ink is automatically stored in the first ink tank 5. Will be replenished.

The temperature of each nozzle can be controlled by the drive IC 13 even when it is not operating. Then, by measuring the resistance of the heating element 9 forming the nozzle 8,
The temperature is detected, the temperature is heated to the optimum temperature by the heating element 9 to an appropriate temperature immediately before the solidified ink is melted, and when the temperature is reached, the operation of stopping the heating is repeated to prevent defective ink ejection due to insufficient melting. That is, the print quality is stabilized. Further, since the above-mentioned optimum temperature is slightly different depending on the type of ink or the type of color, it is preferable to change the set preheating temperature according to the color or type of ink.

Incidentally, the higher the vibration frequency of the head 2, the faster the printing speed but the larger the printing noise (print stain), and the smaller the frequency, the slower the printing speed but the printing noise tends to decrease. According to experiments by the present inventors, the optimum frequency is considered to be around 2000 Hz. Moreover, it is preferable to use the resonance frequency as the frequency to be used.

The above-mentioned embodiment is an example of the preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, although the nozzle of the head in the case of ejecting the ink downward by mainly utilizing the vibration of the vibrating body has been described in the present embodiment, the invention is not particularly limited to this, and the multi-head nozzle shown in FIG. As described above, it is possible to apply the ink to a nozzle that ejects ink using one excitation element, or to eject the ink laterally with the vibrating body facing sideways.

Further, the ink jet head configured as described above can be used in a state in which one kind of ink is stored in the second ink tank 6 as one common tank, or a plurality of inks, for example, four inks. May be discharged. Such a printer is shown in FIG. This printer comprises a platen 41 driven by a paper feed motor 40, a lateral feed motor 42 for axially moving the print head 1 along the platen 41, a belt 43, and a guide rod 44. Further, the print head 1 and the control means (not shown) are connected by a cable 45. The print head 1 has a transverse feed motor 42.
The lateral movement can be controlled by the guide 44 or the like. On the other hand, the paper 46 can be controlled to move vertically by the paper feed motor 40. In the print head 1, four ink cylinders 26, 2
The four color inks accommodated in 6, 26, and 26 are repeatedly melted and solidified (controlled by the IC installed in the head), and full-color output is performed.

[0027]

As is clear from the above description, the ink jet head of the present invention is provided with a plurality of nozzles and stores the ink which is heated and melted into a liquid state in a common ink tank, and when the ink is not ejected, the nozzle is ejected. In an inkjet head that heats and melts the ink that has hardened in the nozzle portion when the ink is solidified in the part and ejected, the temperature control means is formed over the entire inner peripheral surface of the nozzle, so that the entire inner peripheral surface of the nozzle is heated simultaneously. The entire block of ink blocking the nozzle is heated and melted at the same temperature. For this reason, it takes a short time for the ink to reach a molten state and is uniformly melted. In addition, according to the present invention, since the ink applied to the nozzle has a uniform temperature distribution and is solidified, the nozzle is not clogged, so that a constant amount of ink is stably ejected.

Further, in the present invention, when a heating element is used as the temperature control means and a layer of a heat insulating material is formed between the heating element and the base material forming the nozzle, the heat generation efficiency can be improved with a simple structure. ..

Further, according to the present invention, since the temperature control means is provided on the inner peripheral surface of the nozzle, the nozzle interval substantially depends on the nozzle processing technique, and the nozzle interval can be narrowed to enable downsizing of the head.

[Brief description of drawings]

FIG. 1 is an enlarged view showing an embodiment of a nozzle portion of an inkjet head of the present invention, (A) is a plan view, (B) is a vertical sectional view, and (C) is a bottom view.

FIG. 2 is a block diagram of a nozzle temperature control unit.

3A and 3B are diagrams showing an arrangement example of nozzles of the inkjet head of FIG. 1, in which FIG. 3A is a plan view, FIG. 3B is a front view, and FIG.
FIG. 3 is an enlarged plan view of one nozzle group.

FIG. 4 is a side view showing an embodiment of the inkjet head of the present invention.

5 is a plan view of the inkjet head of FIG. 4. FIG.

6 is a front view of the inkjet head of FIG. 4. FIG.

7 is a cross-sectional view taken along line VII-VII of the inkjet head of FIG.

8 is a cross-sectional view taken along the line VIII-VIII of the inkjet head of FIG.

FIG. 9 is a mechanism diagram of a printer using the head.

FIG. 10 is a vibration cycle diagram of the head.

FIG. 11 is a perspective view showing a conventional multi-nozzle.

[Explanation of symbols]

 6 Second Ink Tank (Shared Ink Tank) 8 Nozzle 9 Heating Element as Temperature Control Means 10 Nozzle Base Material 11 Thermal Insulation Material 12 Electrode 39r Liquid Ink

Claims (2)

[Claims] 1. A common ink tank having a plurality of nozzles stores ink that has been heated and melted into a liquid state, and when the ink is not ejected, the nozzle portion is solidified and when the ink is ejected, the nozzle portion is solidified. An ink jet head for heating and melting ink, wherein temperature control means is formed on the entire inner peripheral surface of the nozzle. 2. The ink jet head according to claim 1, wherein the temperature control means is a heating element, and a heat insulating material layer is provided between a layer of the heating element and a base material forming the nozzle. ..