JPH03208661A - Ink jet recording head and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to easily remove bubbles in a nozzle by forming a joint section of the rear end of the nozzle in contact with a filter into an edgeless shape. CONSTITUTION:A plurality of holes 6A are formed in the central section of a filter 6, while the section 6B having no hole therein surrounding the central section serves as an reinforcement. The inner end surface of the section 6B on the side of a nozzle is covered by an extended section, as designated by 1A, of a member of the nozzle to prevent an edge-shaped corner from being formed within the nozzle. As a result, ink flows smoothly from the filter 6 toward the nozzle 1, preventing thereby bubbles from remaining in the nozzle. Further, the extended section 1A which covers the section 6B is formed by heating glass material composing the nozzle 1 at the end of the filter 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording head and a method for manufacturing the recording head, and more specifically, an inkjet recording head configured to eject ink droplets by mechanical pressure means. and its manufacturing method.

[Prior Art] Various configurations of inkjet recording heads have been known in the past, depending on the method of ejecting ink droplets, the method of generating ejection energy, and the like. Among these, a so-called on-demand recording head is often used, in which the application of an ejection signal corresponds to the ejection of ink droplets, and the ink droplets can be ejected only when necessary.

One configuration of this on-demand type recording head is a recording head configured to eject ink droplets using pressure generated by an electromechanical transducer such as a Vieso element. The general configuration of this recording head is that ink is filled in a tubular nozzle with a tapered tip where the ejection port is opened, and ejection pressure is generated by applying mechanical deformation to this nozzle using a Viezo element. Then, ink droplets are ejected from the ejection port.

This so-called Viezo recording head has the advantage of being able to easily express halftones when recording full-color images and the like. That is, by changing the voltage and pulse width of the electric pulse applied to the Viezo element, it is possible to change the size of the ink droplet (the amount of ink) ejected in response to the electric pulse. Thereby, it is possible to control the recording density by changing the size of the dots formed on the recording paper by the ink droplets.

[Problems to be Solved by the Invention] However, in the above-mentioned Viezo recording head, when ink droplets are continuously ejected, minute bubbles may be generated in the nozzles. If ink droplets are ejected under such conditions, the size (ink amount) and ejection direction of the ejected ink droplets may not be determined due to the influence of air bubbles, and furthermore, the ejection energy generated by the Viezo element may be In some cases, the kinetic energy of the bubbles is absorbed and it becomes impossible to eject at all.

One of the causes of such bubbles is cavitation when ink flows in a nozzle as ink droplets are ejected.

In particular, dissolved gas is generally present in the ink, and the formation of bubbles generated by cavitation is facilitated by the dissolved air bubbles serving as the nucleus.

Another cause of bubble generation is that air is taken in from the ejection opening or the ink supply path as the ink droplets are ejected.

Therefore, conventionally, inkjet recording apparatuses have been equipped with a so-called ejection recovery system that pressurizes the inside of a nozzle to eject air bubbles together with ink, or that sucks ink inside a nozzle and sucks out air bubbles along with the ink.

However, in conventional nozzle configurations, even with such a recovery system, it is not possible to completely remove air bubbles that get mixed into the ink inside the nozzle, and the unremovable air bubbles accumulate, causing ejection failures as described above. There were cases.

FIG. 3 is a schematic cross-sectional view showing a part of a conventional nozzle configuration. The figure shows the rear end of the nozzle, where 1 is the nozzle and 6 is a filter. In general, a nozzle has a tubular shape from the tip end where the discharge port opens to the rear end, and for example, an annular piezo element is provided around a part of the nozzle. Further, as shown in the figure, a filter 6 is joined at the rear end.

By joining this filter 6, the shape inside the nozzle 1 is
An edge-like corner portion as shown by IB in the figure is formed.

This part is a stagnation part where the flow velocity of the ink is extremely low, and the above-mentioned bubbles stay in this part, that is, the shaded part in the figure, and gradually become larger bubbles. It is difficult to remove such air bubbles that remain in this area, even with the above-mentioned discharge recovery system, because the flow velocity in this area cannot be sufficiently increased. As a result, the bubbles that grow in this area may block the filter or have an adverse effect on the propagation of pressure waves generated by the viezo element, resulting in ejection failure as described above.

The present invention has been made to solve the above-mentioned problems, and its purpose is to form the joint part of the rear end of the nozzle with the filter into a shape that eliminates the edge-like corner part. Accordingly, an object of the present invention is to provide an inkjet recording head that eliminates the accumulation of air bubbles and allows easy removal of air bubbles in nozzles, and a method for manufacturing the recording head.

[Means for Solving the Problems] To this end, in this description, a nozzle is provided which has an ejection opening for forming ink droplets at its tip, and the ink droplets are formed by applying pressure to the ink inside the nozzle. An inkjet recording head for recording by ejecting an inkjet recording head, comprising a filter that is joined at the rear end of the nozzle and has a hole that communicates the inside and outside of the nozzle, and the inside of the nozzle of the filter is It is characterized in that the member constituting the inner wall of the nozzle extends to the vicinity of the portion where the hole is provided.

Also, manufacturing an inkjet recording head that is equipped with a nozzle having an ejection opening for forming ink droplets at its tip and performs recording by ejecting ink droplets by applying pressure to the ink inside the nozzle. In the method, a filter having a hole for communicating the inside and outside of the nozzle is joined to the rear end of the nozzle, and the nozzle and the filter are connected by heating the vicinity of the joining part of the nozzle. It is characterized by comprising the steps of welding and, accompanying the welding, extending the member forming the nozzle to the vicinity where the holes of the filter are arranged.

[Function] According to the above-mentioned precautions, the connection between the nozzle and the filter eliminates the formation of edge-like corners in the ink flow, and prevents the accumulation of air bubbles mixed in the ink inside the nozzle. As a result, air bubbles present in the ink are quickly removed from the nozzle during ink ejection or ejection recovery operation.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing the main parts of an inkjet recording head according to an embodiment of the present invention. In the figure, 1 is a nozzle, and the nozzle l has an opening as a discharge port 4 at its tip, a part whose cross-sectional area gradually increases from this opening, and a part that continues from this part to the rear end. It is made of a tubular glass material having a section with a similar cross-sectional area. Reference numeral 2 denotes a piezo element (piezoelectric element) provided in a part of the uniform cross-sectional area of the nozzle 1. The piezo element 2 has an annular shape and is joined around the nozzle l. In response to this, an electric pulse is applied by the activation unit 7, which distorts the vieso element 2, thereby deforming the nozzle 1 in the part where the vieso element 2 is attached.This deformation of the nozzle 1 causes this in the nozzle l The ink in the ejection energy application area corresponding to the deformed part is compressed.This compression causes pressure waves to propagate within the nozzle toward the leading and trailing ends, and the behavior of this pressure wave and its reflected waves causes the leading end to become compressed. Ink droplets are ejected from the ejection port 4, and
Ink is supplied from an ink supply path (not shown) at the rear end.

6 is a filter attached to the rear end of the nozzle 1;
Made of ceramic material. The filter 6 has a cylindrical shape that matches the shape of the nozzle 1, and a plurality of tubular holes are formed through both end surfaces of the cylindrical column. This hole is
It not only functions as a filter to prevent dust and bubbles in the ink from entering the nozzle, but also functions as a fluid resistance against the ink and maintains the ink pressure within the nozzle 1 at an appropriate level. Furthermore, due to the presence of these holes, pressure waves generated within the nozzle 1 due to ink droplet ejection are quickly attenuated, reducing the influence on the next ink droplet ejection.

FIG. 2 is a schematic sectional view showing a part of the nozzle shown in FIG. 1, and shows the matching portion between the nozzle 1 and the filter 6 in detail.

As shown in the figure, a plurality of holes 6A described above are formed around the center of the filter 6, and the area around which these holes are formed is a hole-free portion 6B.

This non-porous part 6B exists for reasons such as maintaining the strength of the filter 6, and as shown in FIG. 3, in the conventional nozzle, an edge-like corner part is formed due to the presence of this non-porous part. It had been.

In this embodiment, by extending the member forming the nozzle l on the inside of the nozzle of the non-porous part 6B (in FIG. 2, I
(A) Cover the nozzle to prevent edges from forming inside the nozzle.

As a result, the ink flows smoothly from the filter 6 to the front of the nozzle 1, and air bubbles are not retained in the nozzle.

In this embodiment, a portion I covering the above-mentioned extended area and the non-porous portion 6B is
A is formed by heating the glass material constituting the nozzle 1 at the end of the filter 6, as will be described later. That is, the glass material is melted by heating (the molten glass material moves to the inside of the nozzle 1 while passing through the non-porous part 6B of the filter 6 due to its surface tension and is welded to the non-porous part 6B. The nozzle according to the method
The shape allows a narrowed portion, and the fluid resistance of this portion increases, so that it is possible to have the advantage that the diameter of the pores of the filter 6 does not have to be made so small. Further, when the nozzle is narrowed down, the thickness of the welded part of the nozzle to the filter 6 becomes thicker, so the strength increases.

In the above embodiment, in order to prevent the formation of an edge-like corner part, the member constituting the nozzle was made to extend to the non-porous part of the filter, but this non-porous part was made with a separate member from the nozzle member. The filter may cover the hole, or the filter may have a shape in which no edge-like corners are formed in advance.

Hereinafter, a method for manufacturing the above-mentioned nozzle and a recording experiment using this nozzle will be explained.

[Experiment Example 1] Glass nozzle (length 40 mm, inner diameter 660 μm, outer diameter 7
60μtn. A ceramic filter with a discharge port diameter of 50μII1) and a pore diameter of 504n+ (length 0.8nua
．． After inserting a ceramic filter into the rear end of the glass nozzle, the tube was heated at 720° C. for about 30 seconds using a heater. In the glass nozzle, the vicinity of the filter was melted by the heat, and the inner wall of the constriction moved inward due to surface tension, so that the non-porous part with a width of 50 μm was covered with glass.

When continuous recording was performed using an inkjet recording head equipped with nozzles made in this way, it was possible to perform normal ejection for three hours or more.

Even if air bubbles are forcibly mixed in from the discharge port side, resulting in a discharge failure where the discharge direction is temporarily uneven,
If the amount of air bubbles mixed in is small, normal ejection will return to normal ejection within a few seconds after normal ejection.Also, even if the amount of air bubbles is large and does not recover naturally, use the suction bomb inside the recording device. Therefore, it was possible to immediately return to a normal discharge state.

[Experiment Example 2] Same glass nozzle as Experiment Example 1 and length 0.7 mm
Other than that, the same ceramic filter as in Experimental Example 1 was used, and it was heated for about 40 seconds with a heater in the same manner as in Experimental Example 1.

In evaluating the ejection stability through continuous recording using a recording head equipped with such a nozzle, normal ejection could be performed for more than 3 hours, and the results of the forced bubble inclusion test were also good as in Experimental Example 1. Ta.

[Experimental Example 3] Same glass nozzle as Experimental Example 1, and hole diameter of 60 μm
Other than that, the same ceramic l 5 filter as in Experimental Example 1 was used, and the heater was used in the same manner as in Experimental Example 1.
Heated for seconds.

In evaluating the ejection stability of such a head,
Normal discharge could be performed for 3 hours or more, and the results of the forced bubble mixing test were also good as in Experimental Example 1.

[Comparative Example] Using the same nozzle and filter as in Experimental Example 1, the filter was welded to a glass nozzle in the same manner as in Experimental Example 1, except that the heating time by the heater was about 13 seconds.

In evaluating the ejection stability of a recording head equipped with such a nozzle through continuous recording, the ejection failure state occurred after 20 to 30 minutes, and even if ejection continued, the condition did not recover, and finally the ejection failure state occurred.

Furthermore, even when a recovery operation was performed using a recovery bomb, the normal state could not be recovered at all, and the recovery performance was also very poor.

l 6 [Effects of the Invention] As is clear from the above description, according to the present invention, by joining the nozzle and the filter, the formation of edge-like corners in the ink flow is eliminated, and the inside of the nozzle is reduced. There is no place for air bubbles that get mixed into the ink to accumulate. As a result, air bubbles present in the ink can be removed by ink ejection.
Alternatively, it is quickly removed from the nozzle with the ejection recovery operation.

As a result, a recording head with improved ejection stability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing an inkjet nozzle according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing details of the joint between the nozzle and filter shown in FIG. 1 according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a conventional example of a joint between a nozzle and a filter. DESCRIPTION OF SYMBOLS 1... Nozzle, 2... Viezo (piezoelectric) 3... Pressure action part, 4... Discharge port, 6... Filter, 6A... Hole, 6B... Non-porous part. element,

Claims (1)

[Claims] 1) A nozzle having an ejection opening for forming ink droplets at its tip, and recording by ejecting ink droplets by applying pressure to the ink inside the nozzle. The inkjet recording head includes a filter that is joined at the rear end of the nozzle and has a hole that communicates the inside and outside of the nozzle, and the inside of the nozzle of the filter constitutes an inner wall of the nozzle. An inkjet recording head characterized in that the member extends close to a portion where the hole is provided. 2) Manufacture of an inkjet recording head that is equipped with a nozzle having an ejection opening for forming ink droplets at its tip and performs recording by ejecting ink droplets by applying pressure to the ink inside the nozzle. In the method, a filter having a hole for communicating the inside and outside of the nozzle is joined to the rear end of the nozzle, and the nozzle and the filter are connected by heating the vicinity of the joining part of the nozzle. A method for manufacturing an inkjet recording head, comprising the steps of welding and, accompanying the welding, extending a member forming the nozzle to a vicinity where the hole of the filter is provided. 3) The inkjet recording head according to claim 1, wherein the member constituting the inner wall of the nozzle is a member integrated with the nozzle. 4) The member constituting the inner wall of the nozzle extends to a portion where the hole is provided by melting a part of the nozzle by heating.
The inkjet recording head described in .