JPH1081015A - Ink jet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the length of a recording head, reducing the occupation space in the direction, and thereby obtaining images with a high density and good gradation by arranging a first head portion and a second head portion together in parallel along a line intersecting with the scanning direction aslant. SOLUTION: Each head assembly 10 is such that the nozzle arrangement straight lines 34a of small-diameter head portions 12 and nozzle arrangement straight lines 34b of large-diameter head portions 14 are set at a predetermined angle θ1 with respect to a main scanning direction 6, and are secured on a base 8 by appropriate securing means such a s screws. Accordingly, the length in an auxiliary scanning direction occupied by a head 2 is shortened. Also, in the ink jet recording head 2, since the pitches are made narrower with respect to the auxiliary scanning direction of nozzle 32 by arranging the head portions 12, 14 relative to the main scanning direction, images can be formed with a high density. Then, desired gradation images can be obtained by discharging ink droplets with different sizes from the small-diameter head portions 12 and large-diameter head portions 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an ink jet recording head.

[0002]

2. Description of the Related Art Conventionally, an ink jet recording head shown in FIG. 9 is known. This ink jet recording head 100 includes four head units 102 and a substrate 104 that holds these head units 102. Each head unit 102 is provided with a plurality of nozzles 112 at equal intervals along a line 110 extending in a sub-scanning direction 108 (moving direction of the recording medium) orthogonal to the main scanning direction 106 (scanning direction) of the head 100. Ink (not shown) is ejected from these nozzles 112.

[0003]

However, the ink jet recording head 100 has a problem in that the head section 102 is long in the sub-scanning direction 108, and the occupied space in that direction is large. Further, in the above-described ink jet recording head 100, there is a limit in reducing the pitch of the nozzles 112 due to manufacturing restrictions, and there is also a limit in obtaining a high-density image by further reducing the nozzle pitch. Further, reproduction of gradation was not sufficient.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the above-mentioned problems, and has a structure in which an ink jet recording head is provided with a predetermined interval along a first line obliquely intersecting the scanning direction. A first head portion in which a plurality of first nozzles are arranged, and a second nozzle having a larger diameter than the first nozzle is arranged at the same interval as the first nozzle along a second line parallel to the line And a second head portion.

[0005]

In the above-mentioned ink jet recording head, both the first head portion and the second head portion are arranged along a line obliquely intersecting with the scanning direction. The length of the recording head in the moving direction is short, and the space occupied in that direction is small. Further, since the nozzle pitch in the sub-scanning direction is narrow, an image with a higher density can be obtained as compared with a conventional head. Further, since the nozzles of the second head portion can discharge ink droplets larger than those of the first head portion, ink droplets having different sizes are discharged from these two types of nozzles to achieve high-density gradation. Excellent images can be obtained.

[0006]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, an ink jet recording head 2 is a carriage (not shown) that reciprocates in a printing unit such as a printer in a direction (main scanning direction 6) orthogonal to a conveying direction (sub-scanning direction 4) of a recording medium such as paper. ). Head 2
Consists of a base 8 and four head assemblies 10 fixed thereto. Each head assembly 10 includes a first ink droplet ejection head unit 12 that ejects ink droplets of a predetermined size, a second ink droplet ejection head unit 14 that ejects ink droplets having a diameter larger than this. Are integrally combined. Hereinafter, the first ink droplet discharging head unit 1
2 is referred to as “small diameter head section 12”, and the second ink droplet ejection head section 14 is referred to as “large diameter head section 14”. Further, since the small-diameter head portion 12 and the large-diameter head portion 14 have substantially the same configuration, the same portions are denoted by the same reference numerals, and the description will not be repeated.

The small diameter head section 12 and the large diameter head section 14
As shown in FIG. 2 to FIG. 4 which show the components of the head assembly 10 and the cross sections in the vertical and horizontal directions, respectively, a substrate 16, a vibration plate 18, and a top plate 20 are provided. The substrate 16 is made of a material such as metal or synthetic resin. The vibration plate 18 is made of a well-known piezoelectric material, and has electrode layers (not shown) on the upper surface and the lower surface. Also, the diaphragm 18
A plurality of slits 22 are formed in parallel at a predetermined interval from one end thereof, and a space between adjacent slits 22 is alternately used as a piezoelectric member 24 and an upright wall portion 25. The piezoelectric member 24 is polarized by applying a high voltage between the upper and lower electrodes at a high temperature.
It can be expanded in the direction opposite to. Top plate 20
Is made of a material such as a metal or a synthetic resin, is finely processed by photolithography or the like, and has a long groove-shaped ink cavity 26 facing each piezoelectric member 24, and an ink distribution chamber 28 disposed at one end of the ink cavity 26. A communication port 30 for communicating the ink distribution chamber 28 with each of the ink cavities 26 is provided. In addition, a plurality of nozzles 32 communicating with each ink cavity 26 are provided at an end of the top plate 20.
Is a straight line 34 (34a, 34b) by laser processing (FIG. 1).
(See Reference). The size of the nozzle 32 of the small diameter head 12 and the size of the large diameter head 14 are different, and the nozzle diameter of the large diameter head 14 is larger than the nozzle diameter of the small diameter head 12. Further, as shown in FIG. 3, the end of the diaphragm on the nozzle side is covered with a cover 36.

[0008] The substrate 16 and the diaphragm 1 having the above configuration
8 and the top plate 20 are the ink cavities 26 of the top plate 20.
Are opposed to the piezoelectric members 24 and integrally connected and fixed by an adhesive. Further, as best shown in FIG.
2 and the large-diameter head portion 14 are integrally connected by an adhesive or the like with their substrates 16 back to back. As shown in FIG. 1, each head assembly 10 has a nozzle arrangement straight line 34 (34a) of the small diameter head unit 12 and a nozzle arrangement straight line 34 (34b) of the large diameter head unit 14 in the main scanning direction 6.
And is fixed to the base 8 by an appropriate fixing means such as a screw or an adhesive. Therefore, the length of the sub-scanning direction 4 occupied by the head 2 is shorter than that of the conventional inkjet recording head shown in FIG.

As shown in FIG. 3, the length of the diaphragm 18 in the longitudinal direction of the ink cavity 26 is
Longer than the piezoelectric member 24 on the opposite side of the nozzle 32.
Protrudes from the top plate 20, and at this protruding portion, each electrode on one surface of the piezoelectric member 24 is connected to the ground, and each electrode on the other surface is connected to a flexible wiring board 38 (see FIG. 2) for signal output. Unit (not shown).
Further, an ink supply pipe 40 is connected to the ink distribution chamber 28. Then, ink of a different color is supplied and filled into the ink cavity 26 via the ink supply pipe 40, the ink distribution chamber 28, and the communication port 30 for each head assembly 10. For example, four head assemblies 1 shown in FIG.
0 is yellow, magenta, cyan,
Black ink is supplied.

The nozzles 32 of the small-diameter head section 12 and the corresponding nozzles 32 of the large-diameter head section 14 may be arranged on the same straight line parallel to the main scanning direction 6 or slightly shifted in the sub-scanning direction. Alternatively, in the present embodiment, FIG.
.., The second, third,..., Nozzles 32 from the top of the small-diameter head unit 12 are on straight lines 42 parallel to the first, second,. Are located. In FIG. 5 and FIG. 6 in which a part thereof is enlarged, the nozzle arrangement straight line 34 (34a) of the small diameter head unit 12 and the nozzle arrangement straight line 3 of the large diameter head unit 14 are shown.
4 (34b) is D, the nozzle pitch in each of the head sections 12 and 14 is n, the distance between the arrangement straight lines 34a and 34b in the main scanning direction is m, and the main scanning direction line 42 and the small diameter head section 12 The nozzle array straight line 34a, the nozzle 32 of the small diameter head section 12, and the corresponding large diameter head section 1
A formed by a line 44 connecting the fourth nozzle 32
When BC is assumed, angles ABC and ACB are set to θ, respectively.
Assuming that 1, θ2, the nozzle arrangement straight lines 34a and 34b are arranged so as to satisfy the following relationships of Expressions 1 to 3. FIG. 7 shows the relationship between θ1 and L when n = 250 μm (corresponding to 100 dpi).

[0011]

L = n · sin (θ1)

## EQU2 ## n = m · sin (θ2)

## EQU3 ## sin (θ1) + sin (θ2) = 1

The ink jet recording head 2 configured as described above reciprocates in the main scanning direction 6 with the movement of a carriage (not shown). A recording medium such as paper is conveyed in the sub-scanning direction 4. In each of the heads 12 and 14,
When a printing pulse is applied between the electrodes, the piezoelectric member 24 vibrates and pressurizes the ink in the ink cavity 26. As a result, ink is ejected through the nozzle 32. In this embodiment, for example, no voltage is applied from the uppermost nozzle 32 of the small-diameter head portion 12 and the lowermost nozzle 32 of the large-diameter head portion 14 in FIG. Thus, ink droplets are not ejected.

Further, in the ink jet recording head 2, the pitch of the nozzles 32 in the sub-scanning direction is narrowed by arranging the heads 12 and 14 obliquely with respect to the main scanning direction. Is possible. In addition, desired gradation images can be obtained by ejecting ink droplets of different sizes from the small diameter head section 12 and the large diameter head section 14.

In the above embodiment, the small diameter head 1
By making the nozzle diameter in 2 smaller than the nozzle diameter of the large-diameter head portion 14, the small-diameter ink droplet and the large-diameter ink droplet are ejected, respectively. By adjusting the voltage and / or the application time of the signal pulse applied to the large-diameter head 24, the large-diameter head unit 14 may eject larger-diameter ink droplets than the small-diameter head unit 12, or may have an ink-repellent coating. May be applied to the nozzles so that the sizes of the ink droplets ejected from the heads 12 and 14 may be different.

The head assembly 1 of the above embodiment
0, the piezoelectric member 24 is in contact with the ink. However, as in the other embodiment shown in FIG.
A partition 50 made of a thin metal film or a resin film is provided between the piezoelectric member 24 and the top plate 20.
0 may be applied to pressurize the ink. According to this embodiment, since the piezoelectric member 24 and the ink are separated by the partition wall 50, there is an advantage that the ink does not penetrate the piezoelectric member 24 and the deformability thereof is not reduced.

[Brief description of the drawings]

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

FIG. 2 is an exploded perspective view of a head assembly in the inkjet recording head shown in FIG.

FIG. 3 is a vertical sectional view of a head unit.

FIG. 4 is a sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a diagram showing an arrangement of a small diameter nozzle and a large diameter nozzle in the head assembly.

FIG. 6 is a partially enlarged view of FIG. 5;

FIG. 7 shows θ1 when the nozzle pitch is 250 μm.
FIG. 4 is a diagram showing a relationship between L and L.

FIG. 8 is an exploded perspective view of a head assembly according to another embodiment.

FIG. 9 is a front view of a conventional inkjet recording head.

[Explanation of symbols]

2 ... inkjet recording head, 4 ... sub-scanning direction, 6 ...
Main scanning direction, 10: head assembly, 12: small diameter head, 14: large diameter head, 32: nozzle, 34a, 3
4b: nozzle array straight line.

Claims (1)

[Claims] 1. A first head portion having a plurality of first nozzles arranged at predetermined intervals along a first line obliquely intersecting a scanning direction, and an ink droplet having a diameter larger than that of the first nozzle. An ink jet recording head comprising: a second head portion in which second nozzles capable of discharging ink are arranged along a second line parallel to the first line and at the same interval as the first nozzle.