JPH02111551A - Ink jet recording head and manufacture of ink jet recording head - Google Patents

Abstract

PURPOSE:To enable ink jet recording which is excellent in discharge stability, removability of a bubble in a head, a gradation property, frequency response, etc., to be performed by a method wherein a junction part on an ink pressure chamber side is compactly joined. CONSTITUTION:Since a filter 6 and a glass nozzle 1 are joined by thermal deposition near an end face 9 on an ink pressure chamber 3 side of a filter 6, there is no clearance between both at said part and therefore a clearance between the joined surfaces disappears on the ink pressure chamber 3 side. Then, a clearance in which a bubble remains is gone, and a risk in which pressure in the ink pressure chamber 3 is absorbed by the bubbles remaining in the clearance and the discharge amount and discharge direction of ink become unstable or the like are prevented. Further, even though any clearance exists on a rear side of the filter 6, there is no affection. It is become that the ink pressure chamber 3 is distant from the clearance on the rear side of the filter 6 and a ratio in which the pressure in the ink pressure chamber 3 is absorbed by the bubbles remaining in the clearance on the rear side of the filter 6 is little.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is applicable to inkjet recording. Specifically, the tip of a tubular nozzle has an orifice through which ink droplets are ejected, and the rear end of the tubular nozzle The present invention relates to an inkjet recording head comprising a plurality of structural members, which has a filter, and is configured to eject ink by applying pressure to an ink pressure chamber using an electromechanical conversion means.

The present invention also relates to a method of manufacturing an inkjet recording head.

[Conventional technology]

Conventionally, there are many types of inkjet recording apparatuses. Broadly speaking, there are three types: 1) Continuous injection type, 2) On-demand type, and 2) Electrostatic suction type.

In the continuous ejection type, recording is performed by charging and deflecting ink that is continuously ejected, so the device is complicated), and ink recovery and cleaning devices are also required.

Furthermore, although the structure of the electrostatic suction type is relatively simple, it requires a high voltage and is dangerous. Furthermore, there are many restrictions on the physical properties of the ink such as conductivity, and the frequency response is poor.

However, with on-demand printing, ink droplets are ejected only when necessary using the pressure of an ejection energy generating element such as a piezoelectric element, and the structure is very simple.
It is highly anticipated as a recording device.

In order to realize a full-color printer using these recording methods, it is necessary to achieve high resolution and faithful halftone expression.

For midtone expression, digital methods such as the dip method,
2. An analog type that changes the recording dot size.
) can be considered. However, in digital halftone representation methods, resolution must be sacrificed in order to increase the number of tones. For this reason, there are expectations for analog recording in which the recording density is controlled by changing the recording dot size.

In an on-demand head, the recording dot size can be easily changed by changing the voltage and pulse width applied to the piezoelectric element.

[Problem that the invention seeks to solve]

However, when on-demand type ink is continuously ejected, minute air bubbles may be generated within the head. If you try to eject ink in this condition, the amount and direction of ink ejection will not be determined, and furthermore, all the ejection energy will be absorbed by the air bubbles in the head, resulting in a situation where no ink droplets will be ejected at all. There is. One of the factors that causes such a phenomenon to occur is air dissolved in the ink. That is, it is thought that by continuously driving the head, dissolved air becomes bubbles due to cavitation, etc., and grows into larger bubbles, which disturbs the ejection. Another factor is that air may be injected into the pressure chamber from the orifice tip due to subtle differences in various conditions during continuous ejection, and furthermore, air may be injected into the pressure chamber from the ink supply side as microbubbles in the ink. It is also possible to take it internally.

Therefore, when fishing by boat, inkjet recording apparatuses are equipped with a pressure or depressurization pump as a recovery system when bubbles are trapped, and this is used as a means to remove air bubbles within the head. For example, a capping device is installed at the pace point position, and in order to prevent the ink from drying out when not in use, the capping device seals the orifice of the recording head, but a vacuum pump is installed in the capping device. When bubbles are trapped, the head is attached to a capping device and a vacuum pump is activated to suck out the bubbles.

However, inkjet recording heads are small and consist of several parts such as orifices, pressure chambers, ink supply channels, bubble and dust filters, etc.
A gap may be formed between the parts that make up the head. Microbubbles generated by cavitation layers, etc. tend to stay in such gaps, and since there is almost no ink flow in the gaps, microbubbles that have entered directly into the gap must be removed by operating the recovery system. However, it was very difficult to remove.

[Means for solving problems]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an inkjet recording head capable of performing inkjet recording with excellent ejection stability, ability to remove air bubbles within the head, gradation, frequency response, etc. It is in.

Another object of the present invention is to provide a method for manufacturing such an inkjet recording head.

In order to achieve the above object, the tip of the tubular nozzle has an orifice from which ink droplets are ejected, the rear end of the tubular nozzle has a filter, and an electromechanical transducer applies pressure to the ink pressure chamber. An inkjet recording head comprising a plurality of structural members configured to be able to eject, wherein at least a joint of the plurality of structural members on the ink pressure chamber side is joined without a gap. A recording head is provided.

Further, the heating center of a heater for heat welding is set at a portion of the tubular nozzle corresponding to the vicinity of the end face of the filter on the side of the ink pressure chamber, and the tubular nozzle and the filter are joined by heat welding. There is provided a method for manufacturing the ink jet recording head described above.

〔Example〕

The present invention will be explained in detail below using the drawings.

FIG. 1 shows an example of the configuration of a Gould type on-demand inkjet recording head.

In the figure, 1 is a straight glass nozzle, 2 is a cylindrical piezoelectric element placed outside the nozzle 1, and the part of the nozzle 1 where this piezoelectric element is placed is the ink pressure chamber 3. becomes. 4 is an orifice. In this embodiment, the orifice 4 is formed by narrowing the tip of a straight glass nozzle, and the glass nozzle 1 and the orifice 4 are one body. By supplying an electric signal from the drive unit 7 to the piezoelectric element 2, the volume of the ink pressure chamber 3 is decreased or increased, so that ejection energy is generated, and the i/r droplet 5 is ejected from the orifice 4. . The ejected ink droplets 5 are attached to a recording medium (not shown) such as paper, and information is recorded. In addition, 6 is a ceramic filter, which has a small diameter straight hole for boat fishing.
It not only prevents dust and air bubbles in the ink from entering the nozzle, but also acts as a fluid resistance element.
Balances the fluid resistance. When assembled as a printer, the rear end of the glass nozzle 1 is connected to an ink tank (not shown) to supply ink.

According to the above configuration example, the joint part 8 is only between the glass nozzle 1 and the filter 6. Therefore, in the recording shown in FIG. This prevents the pressure in the ink pressure chamber from being absorbed by the air bubbles remaining in the gap.

Glass nozzle 1 and filter 6 are usually joined together by thermal welding. For example, an annular heater is attached to the outside of the glass nozzle 1 at the joining part, and the heater is heated to melt the glass nozzle 1 to form a neck, thereby thermally welding the glass nozzle 1 and the filter 6 together.

FIG. 2 is a view of the rear part of the recording head 8 to show the divided heater installation locations.

In the figure, A is near the end face 9 of the filter 6 on the ink pressure chamber 3 side, B is the front part from A, C-1 is near the center of the filter 6, and C-2 is the back part from C-1. It is a part.

Heat by placing the center position of the heater within the range of A,
Figure 3 shows a diagram of the product in a heat bath. As shown in the figure, since the filter 6 and the glass nozzle 1 are joined (by thermal welding) near the end surface 9 of the filter 6 on the ink pressure chamber 3 side, there is no gap between them at that part. Therefore, there is no gap between the mating surfaces on the ink pressure chamber 3 side. Therefore, there is no gap in which air bubbles can accumulate, and the pressure in the ink pressure chamber 3 is absorbed by the air bubbles accumulated in the gap, thereby preventing the ink ejection amount and ejection direction from becoming unstable. Note that even if there is a gap on the rear end side of the filter 6, it will not have any effect. There is a distance between the ink pressure chamber 3 and the gap on the rear end side of the filter 6.
This is because the rate at which the pressure in the ink pressure chamber 3 is absorbed by the air bubbles staying in the gap on the rear end side of the filter 6 is small.

Note that conventionally, the center position of the heater was placed at the C-1 portion for thermal welding. FIG. 5 shows a state in which multiple parts are joined by this method. As shown in the figure, in this method, C
-1 part is the center part of the filter 6 which has a large heat capacity;
The glass in this part does not melt, but begins to melt from the glass near both ends of the filter where the amount of heat is small, so the filter 6-
are welded together with a gap remaining between the two nozzles and one.

In such a welding method, a small hole such as H is formed due to subtle differences in various conditions, which communicates with the gap between the filter 6 and the nozzle 1, and may create a nest of air bubbles.

Furthermore, if the center position of the BK heater is located at the front side of the range A, the glass at position B will melt before the filter is welded to the glass and become constricted as shown in Figure 4. Note that as the diameter of the glass nozzle 1 gradually decreases with the constriction, the glass nozzle 1 and the filter 6
Although they appear to be layered on the upper surface, they are not thermally welded, and therefore there are many gaps between the glass nozzle 1 and the filter 6.

Furthermore, if the center of the heater is placed at position C-2, it will be welded as shown in FIG. Create a bubble nest.

From the above, by setting the center of the heater in the range A, heating it, and joining the glass nozzle 1 and filter 6 by thermal welding, a gap is created between the joining surfaces on the ink pressure chamber 3 side. can be prevented.

FIG. 7 shows a diagram in which, in the recording head 8 shown in FIG. 1, the filter 6 is made to protrude from the rear end surface of the glass nozzle 1 by a predetermined length, and the two are joined by heat welding. The center point of the heater is near the front end surface 9 of the filter 6, as in the case of FIG. By causing the filter 6 to protrude beyond the rear end surface of the glass nozzle 1 by a predetermined length, the rear end portion of the glass nozzle 1, which has been exposed to force U heat, is prevented from wrapping around the outside of the rear end surface of the filter 6. Can be done at&,
Since the portion close to the rear end surface of the glass nozzle 1 is heated, the glass nozzle 1 is sufficiently melted, and the glass nozzle 1 and the filter 6 are sufficiently thermally welded to prevent the generation of a gap between the two.

Next, a case where a recording head was actually manufactured (by the method for manufacturing the recording head) and a comparative example will be described.

(Specific Example 1) Length: 40 mm, inner diameter: 6601 tm, outer diameter: 760 μm.

Using a No4 Ilex glass nozzle with a ground ice diameter of 50 μm1 and a ceramic filter with a lotus root-shaped hole of 1 m in length and 620 μm in outer diameter, align the rear end surface of the glass nozzle with the rear end surface of the filter, and place the outside of the glass nozzle. An annular heater was installed in the filter, and the heating center of the heater was set at the front end surface of the filter. It was heated at 720°C for about 13 seconds. Glass nozzles are soft only near the front end of the sifter due to heat, and surface tension causes the large diameter to gradually weld from the front end of the sifter to the rear, which is narrow, creating a pressure chamber that affects discharge. Neighboring gaps can be completely eliminated9.

Even if continuous printing was performed, normal ejection could be performed for more than 3 hours.

Even if air bubbles are forcibly mixed in from the Oriice side and the discharge direction becomes uneven, the discharge will return to normal after a few seconds if the amount is small. Even if the discharge did not recover naturally, it was possible to immediately return to normal discharge conditions by using the vacuum pump inside the printer.

(Specific Example 2) Example 1 except that the same members as Example 1 were used, and the heater was installed 0.3 degrees behind the front end of the filter.
When welding was carried out in the same manner as above, it was possible to create a bath coat with no gaps.

In the evaluation of ejection stability by continuous printing, it lasted for more than 3 hours, and the results of the forced bubble inclusion test were also good as in Example 1.

(Specific Example 3) When welding was carried out in the same manner as in Example 1 except that the same members as in Example 1 were used and the heater was installed 1 m in front of the front end of the filter, there was no gap. Welding was completed.

In the evaluation of ejection stability by continuous printing, it lasted for more than 3 hours, and the results of the forced bubble inclusion test were also good as in Example 1.

(Specific Example 4) Using the same members as in Example 1, the filter was arranged with the glass nozzle also protruding as shown in Fig. 7, and bathing was carried out in the same manner as in Example 1 except for the above. However, we were able to weld without any gaps.

In the evaluation of ejection stability by continuous printing, it lasted for more than 3 hours, and the results of the forced bubble inclusion test were also good.

(Comparative example) When welding was carried out in the same manner as in Example 1 except that the same members as in Example 1 were used and the heater was installed in front of the filter, the heat from the heater was transferred to the vicinity of the filter. Because it was difficult to clean, the glass nozzle on the front side of the filter was melted badly, and the filter and glass nozzle were mostly welded together, leaving a lot of gaps.

20~20 in evaluation of ejection stability by continuous printing
After 30 minutes, the discharge became defective, and even if the discharge was continued, the discharge did not recover, and finally the discharge failed. Even if you perform a recovery operation using the recovery pump installed in the printer, it is extremely difficult to remove air bubbles that have entered the gap.
The condition did not return to normal and the recovery rate was very poor.

(Comparative Example 2) Using the same members as in Example 1, the heater was installed at a distance of 0.5 m from the front end of the filter, i.e., at the center of the filter, and the rest was the same as in Example 1. When the filter was welded, there was a hole in a part of the welded glass near the front end of the filter, leaving a gap.

20~20 in evaluation of ejection stability by continuous printing
After 30 minutes, the discharge became defective, and even if the discharge was continued, the discharge did not recover, and finally the discharge failed. Even when a recovery operation was performed using the recovery pump installed in the printer, the printer did not recover to normal condition at all, and the recovery performance was also very poor.

(Comparative Example 3) When welding was carried out in the same manner as in Example 1 except that the same members as in Example 1 were used and the heater was installed near the rear end of the filter, a gap was created near the front end of the filter. was.

20~20 in evaluation of ejection stability by continuous printing
After 30 minutes, the discharge became defective, and even if the discharge was continued, the discharge did not recover, and finally the discharge failed. Even when a recovery operation was performed using the recovery pump installed in the printer, the printer did not recover to normal condition at all, and the recovery performance was also very poor.

In the record shown in FIG. 1, since the do 8 is a Gould type in which the joining surface is only between the glass nozzle 1 and the filter 6, these joining members are joined so that there is no gap on the ink pressure source 3 side. However, if there are other joining surfaces such as Kaiser type, it is necessary to join those other joining surfaces so that there is no gap on the ink pressure chamber side, that is, on the ink pressure chamber side. The chamber has a structure with a lot of gaps where the pressure of the chamber can easily be transmitted, so even if microbubbles occur, they will immediately escape along with the ink droplets.

Even if a large number of bubbles are generated that cannot be removed naturally, they can be immediately recovered by using the recovery system ponder inside the printer.

Note that the area A in FIG. 2, ie, the vicinity of the front end face of the filter, is the area where the ink that has passed through the filter and exited into the recording nozzle swirls, and is particularly prone to bubbles. Therefore, even if there are multiple joints, by creating a structure where only the joint between the glass nozzle and the filter has no gaps, especially on the ink pressure chamber side, the air bubbles can absorb pressure energy, thereby preventing ink ejection. Instability in the amount of ink and the direction of ink ejection can be significantly improved.

〔Effect of the invention〕

In the inkjet recording head according to the present invention, at least the joint part on the ink pressure chamber side among the joint parts of the plurality of structural members is joined without any gap, so that the pressure in the ink pressure chamber is directly transmitted and the pressure in the ink pressure chamber is There is no gap between KVi and the area where the ink is absorbed and tends to cause instability in the amount of ink ejected and the direction of ink ejected. Therefore, the gap does not become a nest of air bubbles, and even if small air bubbles occur, they will immediately escape together with the ink droplets.Also, even if a large number of air bubbles occur that cannot be removed naturally, the printer's internal recovery system Immediate recovery can be achieved by using a pump, etc.

Further, in the case where a tubular nozzle and a filter are joined by thermal welding, the inkjet recording head manufacturing method according to the present invention includes a heater for thermal welding in a portion of the tubular nozzle corresponding to the vicinity of the end surface of the filter on the ink pressure chamber side. The heating center of the tubular nozzle and the filter are set and the tubular nozzle and the filter are joined by thermal welding.9th, there is no gap on the ink pressure chamber side at the joint between the two.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing an example of the configuration of a Goolby type of on-demand inkjet recording head, and Fig. 2 shows a glass nozzle and a filter joined by thermal welding for explanation of Figs. 3 to 6. In this case, the setting position of the center of the heater is divided into ranges. Figs. 3 and 7 show the state in which the glass nozzle and filter are joined by the method of the present invention, and Figs. FIG. 7 is a diagram showing a state in which a glass nozzle and a filter are joined by another method. DESCRIPTION OF SYMBOLS 1... Glass nozzle, 2... Piezoelectric element, 3... Ink pressure type, 4... Orifice, 5... Ink droplet,
6... Filter, 8... Inkjet recording head, 9... End face of filter on ink pressure chamber side, A...
Near the end face of the filter on the ink pressure chamber side.

Claims (4)

[Claims] (1) The tip of the tubular nozzle has an orifice through which ink droplets are ejected, the rear end of the tubular nozzle has a filter, and the ink droplets can be ejected by applying pressure to the ink pressure chamber using electromechanical conversion means. An inkjet recording head comprising a plurality of structural members, characterized in that among the joints of the plurality of structural members, at least the joint on the ink pressure chamber side is joined without a gap. (2) The joint between the tubular nozzle and the filter is formed by thermal welding of the heated and constricted tubular nozzle and the filter.
The inkjet recording head described. (3) The inkjet recording head according to claim 1 or 2, wherein the filter protrudes from a rear end surface of the tubular nozzle. (4) The heating center of a heater for heat welding is set at a portion of the tubular nozzle corresponding to the vicinity of the end face of the filter on the side of the ink pressure chamber, and the tubular nozzle and the filter are joined by heat welding. The method for manufacturing an inkjet recording head according to claim 2 or 3, characterized in that: