JPH03182357A - Hot melt ink jet recording head - Google Patents

Abstract

PURPOSE:To secure sufficient pressuring force and to record with small drops of ink stably at high density by providing a cooling/heating means separately for each of a plurality of nozzles and using an ink pressuring chamber and an ink pressuring means in common to a plurality of the nozzles. CONSTITUTION:A hot melt ink 15 at the side of an ink nozzle 3 is kept solid. An exciting voltage is impressed to an electrode 14 by an image signal from outside, and also to electrodes 10, 11 in an opposite direction, so that a bonding part of Peltier thin films 8, 9 starts heating. Accordingly, the hot melt ink 15 at the side of the ink nozzle 3 is melted. At the same time, the volume in an ink pressuring chamber 2 is changed by the action of a piezoelectric vibrator 13 thereby to press the ink. As a result, small drops of liquid ink are discharged from the ink nozzle 3. Thus, recording is carried out. The voltage impressed to the piezoelectric vibrator 13 is finely adjusted in accordance with hot many of a plurality of the corresponding ink nozzles 3 receive discharging instructions. Therefore, the ink drops can be discharged stably at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is an on-demand type inkjet printer used to eject ink droplets in accordance with an image signal to form dots on a recording medium to record characters, figures, etc. The present invention relates to a hot melt inkjet recording head.

BACKGROUND OF THE INVENTION Conventionally, various methods have been proposed for inkjet recording heads, which are a means of ink recording technology. Hot-melt inkjet recording heads are known in which ink is formed into droplets and adhered to a recording medium. In the recording method using this hot melt inkjet recording head, after the hot melt ink adheres to the recording medium,
Because it cools and solidifies immediately, there is no problem of bleeding that often occurs when liquid ink is used, and it has the advantage that the recording state on the recording medium is less affected by the material of the recording medium, so its application to recording devices is being considered. There is. The conventional hot melt inkjet recording head mentioned above is as follows:
For example, a configuration described in Japanese Unexamined Patent Publication No. 61-98547 is known. The conventional example will be described below with reference to the drawings.

2(a), 2(b), and 2(c) show a conventional hot melt inkjet recording head, FIG. 2(a) is an external perspective view, and FIG. 2(b) is the same as that of FIG. 2(a). 2(c) is a partially enlarged sectional view taken along the line lIc-lIc in FIG. 2(b).

As shown in FIGS. 2(a) to 2(C), a plurality of ink pressurizing chambers 61 are horizontally divided on the front side of the upper part of the head base 60, and each ink pressurizing chamber 61 is divided on the front side of the head base 60. An ink nozzle 62 that opens to the outside is formed. An ink chamber 63 is formed below the ink pressurizing chamber 61, and these ink pressurizing chamber 51 and ink chamber 63 are connected to a narrow ink flow path 6.
4. An ink replenishment chamber 66 is formed on the rear side of the head base 50, and the lower part of each ink replenishment chamber 66 is communicated with the lower part of the ink chamber 63 through an ink flow path 66 formed horizontally in the lower part of the head base 60. There is. A cartridge 67 is loaded into the upper opening of each ink supply chamber 66, and hot melt ink 68 is injected into the cartridge 67. head base 60
A hole 69 communicating with each ink pressurizing chamber 61 in the horizontal direction is formed in the upper part of the ink pressurizing chamber 61 , a rod-shaped piezoelectric vibrator 60 is provided in the multi-hole 69 , and a suppressing part 61 is provided in the front side of the piezoelectric vibrator 60 . It is being

The operation of the above configuration will be described below.

The hot melt ink 68 in the cartridge 67 is heated and melted, and the liquid ink 58a is supplied to the ink pressurizing chamber 61 through the ink supply chamber 66, the ink channel 66, the ink chamber 63, and the ink channel 64. Then, when an image signal is applied to the electrode 62 of the rod-shaped piezoelectric vibrator 60, the rod-shaped piezoelectric vibrator 60 expands and contracts in the length direction, and the volume of the ink pressurizing chamber 610 is changed by the suppressing part 61, and the ink is By pressurizing and ejecting ink droplets from the ink nozzle 62, characters, figures, etc. can be recorded on the recording medium.

Next, for comparison with the hot melt ink jet recording head described above, an example of a typical ink jet recording head using liquid ink at room temperature will be described with reference to an exploded perspective view shown in FIG. As shown in the figure, the head base 71 consists of a substrate 72 and an upper plate 73, and the substrate 72 has an ink pressurizing chamber 74, an ink flow path 76, an ink nozzle 76, and an ink chamber 77 formed in a horizontal plane. There is. The ink nozzles 76 are arranged at a high density (for example, 8 nozzles/Il) by gathering the ink channels 76 at the tip side.

A piezoelectric vibrator 78 is provided on the upper plate 73 above the ink pressurizing chamber 2o.

The structural difference between the two is due to the viscosity of the ink. That is, while the viscosity of liquid ink is 2 to 3 cp, the viscosity of hot melt ink is
) is also about 10 cp, and the flow resistance is large.

Therefore, hot melt ink requires a large force to be ejected from the ink nozzle 62, and a piezoelectric vibrator 60 with a large shape as shown in FIG. 2 is used to minimize the distance between the ink pressurizing chamber 61 and the ink nozzle 62. Designed to be short. In other words, as shown in FIG.
A design in which an ink flow path 76 is provided between the ink pressure chamber 6 and the ink pressurizing chamber 74 to centralize the ink flow path 76 cannot be adopted in the case of a head using hot melt ink. Furthermore, a planar flow path configuration as shown in FIG. 3 is also not possible.

Therefore, a head configuration as shown in FIG. 2 has been proposed.

Problems to be Solved by the Invention However, in the configuration of the conventional hot melt inkjet recording head as described above, the ink pressurizing chamber 51 is provided independently corresponding to each ink nozzle 62, and furthermore, the ink pressurizing chamber 51 In order to shorten the distance between the ink nozzles 620 and the ink nozzles 620, there is a limit to the high-density arrangement of the ink nozzles 62.

Furthermore, it is necessary to form a long distance and a three-dimensional flow path between the ink supply chamber 65 and the ink pressurizing chamber 61. On the other hand, when hot melt ink 68 is used, a heat cycle between normal temperature and operating temperature is required. The hot melt ink 68 applied to the head expands in volume by about 10 to 20% when melted. For this reason, the hot melt ink 68 thermally contracts when cooled, creating spaces everywhere in the flow path, allowing air to enter and remaining as bubbles when the hot melt ink 68 is heated and melted, causing problems such as ink shortage.

The present invention solves the problems of the prior art as described above, and allows ink nozzles to be arranged with high density, and also prevents the occurrence of ink shortage phenomenon, thus achieving a stable ink volume. It is an object of the present invention to provide a hot melt inkjet recording head that can realize high-density recording of droplets.

Means for Solving the Problems The technical solution of the present invention for achieving the above object is as follows:
A plurality of nozzles, an ink pressurizing chamber provided in common to the plurality of nozzles, a pressurizing means for pressurizing ink in the ink pressurizing chamber, an ink reservoir communicating with the ink pressurizing chamber, and each of the above. It is equipped with cooling and heating means provided for each nozzle.

Preferably, the nozzle, the ink pressurizing chamber, and the flow path communicating with the ink reservoir are arranged essentially in a substantially flat plane.

Furthermore, it is possible to provide a plurality of sets of the ink pressurizing chamber and pressurizing means, and to make each set of ink pressurizing chamber and pressurizing means correspond to a plurality of nozzles.

Further, the height of the nozzle side is formed at least lower than the ink reservoir side, and the head base is inserted into the recording apparatus main body from the nozzle side, and the bottom surface of the head base is brought into thermal contact with the heating means provided on the recording apparatus main body, and the head base is replaced. can be configured for use.

Further, a Peltier element can be used as the cooling and heating means, and the head base is formed of a thermally conductive metal material, and the outer surface of the nozzle on the discharge side of the head base is covered with a heat-resistant resin thin film. A thin Peltier element can be formed on this heat-resistant resin thin film, and a resin thin film having heat resistance and a property of repelling liquefied ink is coated on the Peltier element. be able to.

To drive the hot-melt inkjet recording head, the head base is heated from the outside to first melt the ink in the ink pressure chamber, and the melting progresses from this part toward both the nozzle side and the ink reservoir side. Finally, the ink at the top of the ink reservoir is melted, and during this time the nozzle tip is kept in a solid state by cooling means. Thereafter, in response to an image signal from the outside, the common pressure means is operated, and the nozzle cooling means is selectively stopped and the nozzle heating means is operated to melt and eject the ink at the tip of the nozzle.
After the operation is completed, the overall heating is stopped when the ink at the tips of all the nozzles is in a solid state, and the ink is solidified from the top surface in the ink reservoir, and finally the ink in the ink pressurizing chamber is solidified. During the above driving, the power input to the ink pressurizing means is finely adjusted depending on the number of nozzles that eject ink.

Therefore, according to the present invention, the flow paths between the ink pressurizing chamber and the nozzle and between the ink reservoir and the ink pressurizing chamber can be made short and have a flat configuration, and the resistance to the ink flow is small, so that a large No ejection force is required, and the ink pressure chamber
Since the pressurizing means is shared, a sufficient ejection force can be ensured even if the nozzles are arranged in a high density arrangement. In addition, as mentioned above, the flow path is short and has a flat configuration, so even if air bubbles get mixed in, they can be easily pushed out and removed. It solidifies when there is positive pressure in the discharge direction, and airtightness is maintained without creating any gaps due to cooling contraction, so air can enter from there when cooling after use. This eliminates the problem of air bubbles.

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

Figure 1 (aJ to (C1) shows a hot melt inkjet recording head in one embodiment of the present invention;
) is a plan view, and FIG. 1(b) is Ib-Ib in FIG. 1(a).
The cross-sectional view of the arrow quiver (FIG. 1C) is a front view.

As shown in FIGS. 1(a) to (C), the head base 1 is made of a metal material with excellent thermal conductivity, and an ink pressurizing chamber 2 is formed in the front side thereof. The front side portion is formed into a gradually converging shape as it reaches the tip side, and is opened outward by an ink nozzle 3 formed on the front surface of the head base body 1. An ink reservoir 4 is provided on the rear side of the hecht base 1.
The ink reservoir 4 is connected to the ink pressurizing chamber 2 at the bottom of the head base 1 through an ink replenishment channel 6. An air hole 6 is formed at the top of the ink reservoir 4. An insulating thin film 7 made of electrically and thermally insulating Teflon or the like is formed on the front side of the head base 1 so as to surround the ink nozzles 3 . As cooling and heating means, Peltier element thin films 8 and 9 made of two types of semiconductor materials are formed by vapor deposition. These Peltier element thin films 8 and 9 are overlapped on the front surface of the head base 1, that is, on the open side of the ink nozzle 3, forming a joint that causes cooling and heating phenomena (note that
This joint does not necessarily require that the two conductor materials overlap, and may be formed using a metal that is a good electrical conductor.)

Metal electrodes 10.11 for voltage application are provided on the Peltier element thin film 8.9, and these electrodes 10.11 are connected to the main body of the recording apparatus (not shown). As the Peltier element material, for example, a deposited film of an alloy of bismuth, tellurium, and antimony is used as a positive thermoelectric coefficient material, and a deposited film of an alloy of bismuth, tellurium, and selenium is used as a negative material. The electrical resistivity of these is 10 Ω·m, and the thermal conductivity is about 2×1 ow/(α·deg). here,
When a current is applied from the side of the material with a negative thermoelectric coefficient, an endothermic cooling phenomenon occurs under this setting, and when an electric current is applied from the opposite direction, an exothermic phenomenon occurs.

The ink pressurizing chamber 2 is formed to be common to all the ink nozzles 3. The upper part of the ink pressurizing chamber 2 is formed by a metal movable plate (diaphragm) 12, a piezoelectric vibrator 13 is provided on the movable plate 12, and an electrode 14 is provided on the piezoelectric vibrator 13.
is provided.

The movable plate 12 also serves as a ground electrode, and when an excitation voltage is applied to the electrode 14, the piezoelectric vibrator 13 vibrates, the movable plate 13 is moved, and the volume of the ink pressurizing chamber 2 is changed. These act as pressure vibrators common to all ink nozzles 3.

Electrical connection with the main body of the recording device is made through contact with the electrode 14.

The ink nozzle 3, ink pressurizing chamber 2 and ink reservoir 4
The flow channels leading to are arranged essentially in a substantially planar manner. Further, the height of the nozzle 3 side is at least lower than that of the ink reservoir 4 side, and the heating means is inserted into the recording apparatus main body from the ink nozzle 3 side, and the bottom and side surfaces of the head base 1 are provided in the recording apparatus main body. It is designed to be in thermal contact with.

The hot-melt ink jet recording head configured as described above can also be used as a disposable head that is replaced with a new one when the hot-melt ink in the ink reservoir 4 is used up.

In this embodiment, the piezoelectric vibrator 13 is vibrated at a frequency of, for example, 2 kHz, and the Peltier element thin film 8.9 is driven in synchronization with this and with an appropriate phase difference. The Peltier element thin film 8.9 can cool or heat the ink 16 at the tip of the ink nozzle 3 according to a discharge command. Ink 1 at the tip of heated ink nozzle 3
6 melts and is ejected as ink droplets as the volume of the ink pressurizing chamber 2 changes due to the vibration of the piezoelectric vibrator 13.

When cooled, the ink 16 solidifies and stops being ejected.

The operation of the above configuration will be described below.

Now, it is assumed that the hot melt ink 16 in the ink reservoir 4 is filled into the ink pressurizing chamber 2 through the ink supply channel 6, and in this state, the hot melt ink 15 is maintained in a solid state. First, when the power is turned on to the recording apparatus main body, the external heating means on the recording apparatus main body side starts operating to warm the bottom and side surfaces of the head base 1, and at the same time, voltage is applied to the electrodes 1o and 11. and Peltier element thin film 8.9
The joint begins its cooling action. As a result, the solid hot melt ink 15 is melted from inside the ink pressurizing chamber 2, and the melting progresses from this part toward both the ink nozzle 3 side and the ink reservoir 4 side, and finally reaches the top of the ink reservoir 4. hot melt ink 16 is melted. During this time, the hot melt ink 16 on the side of the ink nozzle 3 is maintained in a solid state at a temperature below its melting point. Here, an excitation voltage is applied to the electrode 14 by an external image signal, and at the same time, a voltage is applied in the opposite direction to the electrode 10.11, so that the joint portion of the Peltier element thin film 8.9 starts heating.

As a result, the hot melt ink 16 on the ink nozzle 3 side
As the ink is melted, the volume inside the ink pressurizing chamber 2 changes due to the drive of the piezoelectric vibrator 13, and the ink inside the ink pressurizing chamber 2 is pressurized. The liquid is ejected, and characters, figures, etc. are recorded on the recording medium. Here, the voltage applied to the piezoelectric vibrator 13 is finely adjusted depending on the rate at which the corresponding plurality of ink nozzles 3 receive ejection commands, so that a stable ink droplet ejection state can always be maintained. That is, for example, when fully open, the maximum applied voltage is set, and when fully opened, the minimum applied voltage is set to 60
%, the applied voltage is between the two. The ejected ink 16 is replenished via the ink flow path 6 to the ink reservoir 4.
This can be achieved by supplying the ink 16 inside. Although the space within the ink reservoir 4 increases as ink is consumed, air is supplied through the air holes 6 and a reduced pressure state is prevented.

After recording is complete, when the power to the recording device is turned off,
At the same time as the external heating means stops heating, the joint of the Peltier element thin film 8.9 starts cooling, and the ink 16 in the head is transferred to the part that is in contact with the outer wall of the ink reservoir 4 and the ink nozzle 3 side. The central portions of the ink 16 in the ink pressurizing chamber 2 and the ink 15 in the ink reservoir 4 are finally solidified. As the ink solidifies, a thermal contraction phenomenon occurs and a gap is created within the head, but since the ink 16 at the tip of the ink nozzle 3 is in a solid state, air hardly ever enters the gap. Even in the unlikely event that air bubbles get mixed in, as shown in FIG. 16, it can be easily removed. In addition, the air mixed in or melted in the ink 16 is heated and melted in a vacuum to remove the air before filling it into the cartridge, so as long as air is not mixed in from the outside, ink shortages due to air bubbles will not occur. .

In the above embodiment, the spacing between the ink nozzles 30 is 260 μm between center points, and the 48 nozzle configuration is approximately 1 mm in the horizontal direction.
2 friends. In addition, when installed in the recording device main body, 4
The nozzle positions were determined diagonally upward to the right in FIG. 1(c) so that eight nozzles would be arranged at equal intervals within the vertical width of 311. Therefore, in the figure, the left end nozzle, which is omitted, has a height difference of three degrees from the right end nozzle. The difference between the ink level and the ink level in the ink reservoir 4 is the worst at the left end, but this pressure difference is so small that it can be almost ignored. The size of the piezoelectric vibrator 13 is 1211rN
The amount of ink was set to 1 nl to ensure a sufficient ink ejection force.

As mentioned above, ink droplets can be ejected from the plurality of ink nozzles 3 that are almost directly connected from the common ink pressurizing chamber 2 by applying a slight pressure because the flow path resistance is small. Therefore, replenishment of the ink 15 through the common passage 5 could be realized with slight flow path resistance, and ink droplets could be stably ejected with sufficient ejection force.

Note that the ink pressurizing chamber 2 and the piezoelectric vibrator 13 do not have to correspond to all the ink nozzles 3 in common.

A plurality of ink pressurizing chambers 2 and piezoelectric vibrators 13 are prepared, and each ink pressurizing chamber 2 and piezoelectric vibrator 1301 pair is made to correspond to a plurality of ink nozzles 3, while ensuring the pressure necessary for ink ejection. The ink nozzles 3 can be operated simultaneously. Although not shown in FIG. 1, ink leakage and chemical reactions with ink from the Peltier element thin film 8.9 are not a problem, but there is a heat resistant layer on the Peltier element thin film 8.9. , and may be coated with a thin resin film made of Teflon or the like that has the property of repelling liquefied ink.This completely eliminates the problem with ink, reduces thermal bonding with air, and reduces heat resistance. Design is also advantageous.

Effects of the Invention As described above, according to the present invention, a plurality of nozzles are individually provided with cooling and heating means, and an ink pressure chamber and an ink pressure means common to the plurality of nozzles are combined to improve the flow. It is possible to form flow channels that are short and arranged on a flat surface, and even if the nozzles are arranged in a high density, a sufficient pressurizing area can be secured, and a sufficient pressurizing force can be secured. Moreover,
The ink at the tip of the nozzle is always in a solid state except when the ink is being ejected, and air never enters from the nozzle, and there is almost no air bubbles mixed in due to thermal expansion and contraction of the ink. Therefore, stable ink droplet recording is possible at high density.

[Brief explanation of drawings]

1(a) to 1(c) show a hot melt inkjet recording head according to an embodiment of the present invention, and FIG.
) is a plan view, and FIG. 1(b) is Ib-Ib in FIG. 1(a).
1(C) is a front view, FIG. 2(a)-(
C) shows a conventional hot melt inkjet recording head, FIG. 2(a) is an external perspective view, and FIG. 2(b) is a second
A sectional view taken along arrows ■b-■b in Figure (a), and Figure 2 (c) shows the second
FIG. 3 is an exploded perspective view showing a conventional inkjet recording head using liquid ink at room temperature. DESCRIPTION OF SYMBOLS 1...Head base, 2...Ink pressure chamber, 3...
Ink nozzle, 4... Ink reservoir, 6... Ink supply channel, 7... Insulating thin film, 8.9... Peltier element thin film, 12... Movable plate, 13... Piezoelectric vibrator , 16・
・Hot melt ink.

Claims (7)

[Claims] (1) a plurality of nozzles, an ink pressurizing chamber provided in common to the plurality of nozzles, a pressurizing means for pressurizing the ink in the ink pressurizing chamber, and an ink reservoir communicating with the ink pressurizing chamber; A hot melt inkjet recording head comprising cooling and heating means provided for each nozzle. (2) The hot melt ink jet recording head according to claim 1, wherein the nozzle, the ink pressurizing chamber, and the flow path leading to the ink reservoir are arranged essentially in a substantially flat plane. (3) The hot melt inkjet recording head according to claim 1 or 2, wherein a plurality of sets of ink pressurizing chambers and pressurizing means are provided, and each set of ink pressurizing chambers and pressurizing means corresponds to a plurality of nozzles. (4) The height of the nozzle side is formed to be lower than at least the ink reservoir side, the head is inserted into the recording apparatus main body from the nozzle side, and the bottom surface of the head base is in thermal contact with heating means provided on the recording apparatus main body, The hot melt ink jet recording head according to any one of claims 1 to 3, which is configured to be used interchangeably. (5) The hot melt inkjet recording head according to any one of claims 1 to 4, wherein a Peltier element is used as the cooling and heating means. (6) The head base is made of a thermally conductive metal material, the outer surface of the head base on the discharge side of the nozzle is covered with a heat-resistant resin thin film, and a thin-film Peltier element is formed on the heat-resistant resin thin film. 7. The hot melt ink jet recording head according to claim 6. (7) The hot melt ink jet recording head according to claim 5 or 6, wherein the Peltier element is coated with a resin thin film having heat resistance and a property of repelling liquefied ink.