JPH1044436A - Jet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a smooth multilevel halftone image by providing an ink jet head with a plurality of heads, forming the member constituting the nozzle at each head part of a different ink-repelling material and jetting an ink droplet of different size depending on the difference of ink-repellency. SOLUTION: Since a top plate 16a constituting a nozzle at a large diameter head part is made of stainless steel having a small ink contact angle while a top plate 16b constituting a nozzle at a small diameter head part is made of fluororesin having a large ink contact angle, wettability to ink is improves at the large diameter head part as compared with the small diameter head part. Consequently, an ink droplet 26b being jetted from the nozzle at the small diameter head part has a diameter substantially equal to the nozzle diameter but an ink droplet 26a larger than the ink droplet 26b is jetted from the nozzle at the large diameter head part. The large diameter head part or the small diameter head part can be selected appropriately depending on the image conditions and a multilevel halftoning can be realized by varying the voltage being applied to a piezoelectric part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drop-on-demand type ink jet recording head for recording an image by ejecting ink droplets in response to a print signal and attaching the ink droplet to a recording medium such as recording paper.

[0002]

2. Description of the Related Art In order to perform high-quality printing at high speed using an ink jet recording head, it is effective to express gradation by changing the diameter of printing dots. For that purpose, it is necessary to change the amount of ink ejected from the nozzle in accordance with the gradation level. Therefore, conventionally, a head having a plurality of heads and a nozzle diameter in each head different from a nozzle diameter in other heads is known.

[0003]

However, simply changing the nozzle diameter of each head portion to another nozzle does not greatly increase the width of the gradation, and it is necessary to create a smooth halftone image such as a photograph. It was not enough.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. A plurality of heads are provided in an ink jet recording head, and members constituting nozzles of each head portion are made of materials having different ink repellency. It is formed. In addition,
It is preferable that the ink repellency of each head part is different from the ink repellency of the other head parts by a contact angle of 5 ° or more. The nozzle diameter of each head may be the same. Further, the nozzles of each head may be formed in a tapered shape expanding toward the discharge port.

[0005]

In the above-mentioned ink jet recording head, the members constituting the nozzles in the respective head portions have different ink repellency, and eject ink droplets of different sizes based on the difference in the ink repellency. . That is, a nozzle made of a member having a smaller contact angle with ink ejects an ink droplet having a larger diameter than a nozzle made of a member having a larger contact angle. Therefore, by appropriately ejecting ink from each of the head portions having nozzles made of different ink-repellent members, a smooth halftone image with high gradation can be obtained.

[0006]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 3 show an ink jet recording head according to the present invention. The head 10 includes a large-diameter ink droplet ejection head unit 12 (hereinafter, referred to as a “large-diameter head unit 12”) and a small-diameter ink droplet ejection head unit 14 (hereinafter, referred to as a “small-diameter head unit 14”). The large-diameter head section 12 and the small-diameter head section 14 include a top plate 16, a partition 18, a frame 20, a piezoelectric member 22, and a substrate 24.
And are integrally configured.

The top plate 16 is a top plate 16a for a large diameter head.
And a top plate 16b for the small diameter head. Top plate 16a
Is made of a stainless steel material having a small contact angle with ink, and the top plate 16b is provided with a P having a large contact angle with ink.
Made of FA fluororesin. These top plates 16a,
16b, a plurality of ink cavities 28 for accommodating the ink 26 by finely processing a portion (opposing surface) facing the partition wall 18;
And a nozzle 30 for discharging the ink 26 in each ink cavity 28, an ink supply chamber 32 for accommodating the supply ink 26, and an ink inlet 34 for connecting each ink cavity 28 to the ink supply chamber 32. . As shown in FIG. 1, the ink cavities 28 of the large diameter head section 12 and the small diameter head section 14
2, 14 are formed in parallel and in the shape of a long groove extending toward the facing direction. The ink supply chamber 32 is formed on the opposite side of the center line 36 across the ink cavity 28, and is connected to an ink tank (not shown).
In the present embodiment, the nozzle 30 of the large diameter head 12 is
And the small diameter head portion 14 have the same diameter. The shapes and sizes of the ink cavities 28, the ink inlets 34, the piezoelectric members 22 and the like are the same for each of the head portions 12 and 14. That is, the head 10 is
The heads 12 and 14 have the same configuration except that the material of the head 6 is different, and are formed symmetrically about the center line 36.

The partition 18 is made of a thin film made of a material such as metal or synthetic resin.
It is fixed between 0. It is desirable that the partition wall 18 be fixed with a predetermined tension applied thereto.

The frame 20 is made of metal, synthetic resin, or ceramic, and is fixed between the partition 18 and the substrate 24. The frame body 20 has a frame portion along the outer edge of the head 10 and a frame portion along the center line 36, and two spaces are formed by being surrounded by each frame portion. One of the two spaces corresponds to the large-diameter head portion, and the other corresponds to the small-diameter head portion. Large diameter head 1 surrounded by this frame 20
A plurality of piezoelectric members 22 are arranged in parallel with each other along the ink cavity 28 in a space between the small-diameter head portion 1 and the small-diameter head portion 12.

The piezoelectric member 22 is a well-known laminated piezoelectric member in which thin piezoelectric sheets and electrode layers are alternately stacked. Further, a partition wall 38 is disposed between the adjacent piezoelectric members 22. The piezoelectric member 22 and the partition wall 38 are formed by fixing one laminated piezoelectric member to the substrate 24 and then performing slice cutting by dicing.

The substrate 24 is made of ceramic, metal, synthetic resin, or the like, and is fixed to the frame 20 with an adhesive.

In the head 10 configured as described above, the ink 26 is supplied to the ink supply chamber 32 from an ink tank (not shown). The ink 26 in the ink supply chamber 32 is distributed to each ink cavity 28 via an ink inlet 34. When a predetermined voltage (print signal) is applied to the piezoelectric member 22 from a print signal control circuit (not shown), the piezoelectric member 22 is deformed toward the ink cavity 28. Further, the deformation of the piezoelectric member 22 is transmitted to the partition wall 18, whereby the ink 26 in the ink cavity 28 is pressurized, and the ink droplet flies through the nozzle 30.

As described above, the stainless steel material having a small ink contact angle is used for the top plate 16a forming the nozzle 30 in the large diameter head unit 12, and the top plate 16b forming the nozzle 30 in the small diameter head unit 14 is used for the top plate 16a. Fluorine resin with a large ink contact angle is used, and a large diameter head 1
The wettability with respect to the ink of No. 2 is better than the wettability with respect to the ink of the small diameter head portion 14. Therefore, as shown in FIG. 4A, in the large-diameter head portion 12, the free ink surface exists outside the nozzle 30. On the other hand, FIG.
As shown in (b), in the small-diameter head portion 14, the free ink surface exists inside the nozzle 30. As a result, the diameter of the ink droplet 26b discharged from the nozzle 30 of the small-diameter head unit 12 is substantially equal to the nozzle diameter, whereas the large-diameter head unit 1
The ink droplet 26a ejected from the second nozzle 30 is larger than the ink droplet 26b ejected from the small diameter head unit 14. Accordingly, by appropriately selecting the large-diameter head unit 12 and the small-diameter head unit 14 according to the conditions of the image to be created, and by changing the voltage applied to the piezoelectric member, the gradation can be changed widely, and Such a smooth halftone image can also be created. In the present embodiment, the nozzle 30 of the large-diameter head section 12 and the small-diameter head section 14 have the same diameter.
If it is larger than that of, the gradation width is further increased.
In the present embodiment, since the shape and size of the nozzles are all the same, when forming the nozzles of each head by machining or molding, it is only necessary to change the material for each head. Often, it is not necessary to change production equipment and jigs.

Using the ink jet recording head shown in FIGS. 1 to 4, the relationship between the diameters of ink droplets ejected from the large-diameter head portion and the small-diameter head portion and the applied voltage was examined by performing the following experiments 1 and 2.

Experiment 1: A 100 μm thick plate made of SUS304 stainless steel (material A) having a contact angle of about 60 ° with the aqueous standard ink was used for the top plate of the large diameter head. A 100 μm thick plate made of a PFA-based fluororesin (material B) having a contact angle of about 100 ° with the aqueous standard ink was used. In this experiment, a hydrophilic coating was applied to the entire surface of the fluorocarbon resin plate on the ink cavity side by gold vapor deposition so as not to prevent ink from flowing into the ink cavity. The nozzle diameter of both heads was 40 μm. A pulse having a frequency of 4 kHz and a voltage of 10 to 50 V was applied to the piezoelectric member. The results of Experiment 1 are shown in the table of FIG. As is clear from this table, even when the voltage of the print signal is the same, the ink droplet ejected from the large-diameter head portion of the material A having a small contact angle with the ink and having good wettability has a smaller contact angle with the ink. Is larger than the ink droplet ejected from the small diameter head portion of the material B which is inferior in wettability. When the nozzle is made of the material A, the ink droplet can be changed by about 5 gradations, and when the nozzle is made of the material B, the ink drop can be changed by about 4 gradations. Change is possible.

Experiment 2: The nozzle diameter of the material B used in Experiment 1 was changed to 20 μm. Other experimental conditions are the same as those in Experiment 1. The results of Experiment 2 are shown in the table of FIG. As is clear from this table, three types of top plates (top plate 1: material A, nozzle diameter 40 μm, top plate 2: material B, nozzle diameter: 40 μm, top plate 3: material B, nozzle diameter 20 μm)
If m) is used, an ink droplet change of 8 to 9 gradations can be obtained.

As described above, by forming the top plate of each head portion from a material having a different ink repellency and varying the nozzle diameter of each head portion, a wide range of gradations can be obtained, and a halftone image such as a photographic image can be obtained. Can also be obtained.

The material of the top plate may be changed by adding another material to the same base material. For example, as the material A, a polysulfone resin having a standard contact angle of about 60 ° is used, and as the material B, fine glass beads are dispersed in the polysulfone resin and a fluorosilicone-based coupling treatment (surface treatment) is performed to reduce the contact angle. You may use what was raised to about 90 degrees. As described above, the wettability of a material can be controlled by filling or dispersing a material having a good wettability or a material having a poor wettability in a resin material or an electroformed material.

The nozzle shown in the above embodiment has a tapered shape in which the cross-sectional area decreases toward the discharge side. However, as shown in FIG. 7, the nozzle has an inverted tapered shape expanding toward the discharge side. Is also good. In this case, the size of the ink droplet can be changed more widely.

Further, in order to make the size of ink droplets ejected from each head part have a clear difference and increase the number of gradation steps as a whole, the ink contact angle of the nozzle constituting member in each head part is 5 °. It is desirable that the angle be different by more than 10 degrees.

[Brief description of the drawings]

FIG. 1 is a partial plan view of an ink jet recording head according to the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG. 1 and a partially enlarged sectional view.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a partially enlarged sectional view of a large-diameter head portion and a small-diameter head portion showing a state in which ink is ejected from a nozzle.

FIG. 5 is a chart showing the relationship between the applied voltage and the ink droplet diameter when the nozzle diameter of the large diameter head section is the same as the nozzle diameter of the small diameter head section.

FIG. 6 is a table showing the relationship between the voltage applied to the electrode and the dot diameter when the nozzle diameter of the small-diameter head section is different.

FIG. 7 is a partially enlarged cross-sectional view of a large-diameter head and a small-diameter head showing a state where ink is ejected from nozzles of other shapes.

[Explanation of symbols]

Reference numeral 10: head, 12: large-diameter head, 14: small-diameter head, 16, 16a, 16b: top plate, 18: partition wall, 20:
Frame, 22: piezoelectric member, 24: substrate, 26: ink, 2
8 ... ink cavity, 30 ... nozzle.

Claims (4)

[Claims] 1. An ink jet recording head for ejecting ink from nozzles in response to a print signal and attaching the ink to a recording medium, the inkjet recording head having a plurality of ink ejection heads, and a member constituting a nozzle of each head being: An ink jet recording head made of materials having different ink repellency. 2. The ink repellency of each head part differs from the ink repellency of other head parts by a contact angle of 5 ° or more.
Inkjet recording head. 3. The ink jet recording head according to claim 1, wherein the nozzle diameter of each head portion is the same. 4. An ink jet recording head according to claim 1, wherein the nozzle of each head portion is formed in a tapered shape expanding toward the discharge port.