JPH1086363A - Ink jet recording head and ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording head having nozzle arrangement capable of taking a time lag long between the adhesion times of respective ink drops in order to prevent that respective inks are mixed in a liquid state to deteriorate color development when large and small ink drops different in color are superposed on a recording medium. SOLUTION: Recording heads 3C, 3M, 4Y, 4BK move in a main scannting direction while ink drops are emitted from a plurality of the nozzles opposed to a recording medium and the ink drops are bonded to a recording medium to record an image. The first nozzle row 16 having a plurality of nozzles 15 emitting ink drops arranged thereto and a second nozzle row 18 having a plurality of nozzles 17 emitting ink drops larger than those emitted from the first nozzle row 16 are arranged in series along the sub-scanning direction crossing the main scanning direction at a right angle.

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 (DOD) type ink jet recording head for recording an image by discharging an ink drop from a nozzle in accordance with an image signal and attaching the ink drop to a recording medium such as recording paper. The present invention relates to an inkjet recording apparatus.

[0002]

2. Description of the Related Art Conventionally, a plurality of nozzles are provided in an ink jet recording head of the above-mentioned DOD type, and large and small ink drops are ejected from these nozzles as appropriate. There is known a method of expressing gradation by combining formed large diameter ink dots and small diameter ink dots.

In the case of forming a multi-color gradation image using three or four colors of ink, two ink dots having different colors and sizes are formed at the same position and are superimposed on each other. Are formed at a small distance within a fixed area on a recording medium, and various colors can be expressed by a method such as visually mixing color stimuli of each dot. It should be noted that comparing the two, overlapping the ink dots is more advantageous in expressing the intermediate colors.

In the above ink jet recording head,
One method of changing the size of the ink drop is to change the size of the nozzle. As an example, U.S. Pat. No. 5,208,605 discloses a nozzle array 62 composed of a plurality of large-diameter nozzles 61 for discharging large ink drops and a small ink drop, as shown by a solid line in FIG. A print head 60 is disclosed in which a nozzle row 64 including a plurality of small-diameter nozzles 63 for discharging is arranged in parallel. In U.S. Pat. No. 5,412,410, a plurality of large-diameter nozzles 71 and small-diameter nozzles 72 are respectively arranged along a sub-scanning direction orthogonal to the main scanning direction of the head, as indicated by solid lines in FIG. An alternately arranged printhead 70 is disclosed. In the former, the main scanning direction is not specifically shown in the drawings and the like, but it is assumed that the nozzle row is formed to be orthogonal to the main scanning direction in accordance with a general configuration of an ink jet recording head.

[0005]

Since each of the print heads 60 and 70 is for a single color, for example, four color inks of cyan (C), magenta (M), yellow (Y), and black (Bk) are used. In order to form a multi-color gradation image by using four print heads 60, 7 corresponding to each ink, as shown by dotted lines in FIGS.
0 must be arranged on the carriage (not shown) along the main scanning direction.

However, when the large and small ink drops of different colors are superimposed on the print heads 60 arranged as shown in FIG. 7, the ink drops attached to the recording medium are absorbed and dried before being dried. There is a risk that the ink drops may land, and the respective inks are mixed in a liquid state, and the color tends to be turbid, so that a desired color expression cannot be obtained. Specifically, when a small ink drop of cyan (C) is superimposed on a large ink drop of magenta (M), the time between landing of these two ink drops is determined by the large-diameter nozzle row of the magenta head 60. There is only a small time required for the carriage to move the distance x between the nozzle array 62 and the small-diameter nozzle array 64 of the cyan head 60, and the above-described color mixing may occur in the case of ink that dries relatively slowly. Is high.

On the other hand, when large and small ink drops of different colors are overlapped by the print heads 70 arranged as shown in FIG. 8, the carriage is moved in the sub-scanning direction by the distance y between the large-diameter nozzle 71 and the small-diameter nozzle 72. It takes time to move. Therefore, the time difference between the landing of the two ink drops is larger than that of the print head 60 described above. However, in order to sufficiently prevent the above-described color mixing, it is desired that the nozzle arrangement be such that the time difference can be further increased without reducing the moving speed of the carriage.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for ejecting ink drops from a plurality of nozzles facing a recording medium and moving the ink drops in a main scanning direction to record the ink drops. In an ink jet recording head for recording an image by adhering to a medium, a first nozzle row in which a plurality of nozzles from which ink drops are respectively discharged is arranged, and an ink drop larger than that discharged from the first nozzle row. Are arranged in series along a sub-scanning direction orthogonal to the main scanning direction with a second nozzle row in which a plurality of nozzles respectively ejected are arranged. Further, the present invention provides an ink jet recording head for recording an image by ejecting ink drops from a plurality of nozzles facing a recording medium and attaching the ink drops to the recording medium, and moving the recording head in the main scanning direction. An ink jet recording apparatus comprising: a first moving unit; and a second moving unit that moves a relative position between the recording head and the recording medium in a sub-scanning direction orthogonal to the main scanning direction. Has a first nozzle row in which a plurality of nozzles from which ink drops are respectively ejected are arranged, and a second nozzle in which a plurality of nozzles from which ink drops larger than those ejected from the first nozzle row are respectively ejected are arranged. The two nozzle rows are arranged in series along the sub-scanning direction. here,
The "main scanning direction" refers to the actual moving direction of the head, the "sub-scanning direction" refers to a direction orthogonal to the main scanning direction, and the "arranged in series" refers to the first and second nozzle rows. Are arranged on the same straight line as well as the case where the nozzle rows are slightly shifted in the main scanning direction.

[0009]

When printing is performed using the ink jet recording head according to the present invention, in order to superpose large and small ink drops on the recording medium, the carriage must be positioned at the end of each nozzle row in the same direction. At least time is required to move the distance between the nozzles in the sub-scanning direction. That is, the time that elapses before the ink drops are superimposed becomes longer than in the above-described related art. Therefore, during the movement, the ink drop that has previously adhered is absorbed by the recording medium and is dried, and even if the next ink drop adheres on it, each ink is prevented from being mixed in a liquid state. Is done. Therefore, for example, when a plurality of the heads are provided in the main scanning direction and a multicolor image is formed by ejecting inks of different colors from the respective heads, color development is performed without impairing the unique color stimulus of each ink drop. Color expression can be improved, and the image quality can be improved.

The same effect can be obtained also when large and small ink drops having different colors are closely attached to a recording medium to express colors. That is, if the next ink drop lands in the vicinity of one of the ink drops before it dries, the ink drops may be connected and mixed, but according to the head having the nozzle arrangement according to the present invention, the size is large. After the ink drop dries, you can land a small ink drop in close proximity,
Each dot can be formed as a completely independent dot, and even in this color expression method, high image quality with good coloring can be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view of a main part of an ink jet recording apparatus for color printing according to an embodiment of the present invention. As shown in FIG. 1, the ink jet recording apparatus 100 includes a base 50. Base 5
A pair of side walls 51 facing each other at a predetermined interval are provided on the upper side. A backup roll 5 is provided between the side walls 51.
4. The guide rod 53 and the ball screw 52 are bridged in parallel. The backup roll 54 and the ball screw 52 are each rotatable, and are drivingly connected to motors 56 and 55, respectively. The carriage 2 is provided so as to engage with the guide rod 53 and the ball screw 52. The carriage 2 has a screw hole (not shown), and the combination of the screw hole and the ball screw 52 causes the carriage 2 to move along the guide rod 53 and the ball screw 52 along the arrow a based on the rotation of the ball screw 52. It can reciprocate in a direction (hereinafter, referred to as “main scanning direction”). The carriage 2 also has an ink jet head described later on a surface facing the backup roll 54, and prints ink from the ink jet head on a recording medium such as paper conveyed in the circumferential direction along the outer peripheral surface of the backup roll 54. An image is formed on a recording medium by discharging a drop. When forming an image, the carriage 2 moves at a constant speed in the main scanning direction.

FIG. 2 is a perspective view showing the configuration of the recording medium facing portion of the carriage 2. As shown in FIG. 2, the adjustment plate 5 is rotatably attached to the carriage 2 by a retaining screw 7. The adjusting plate 5 is provided with a retaining screw 7.
On the side opposite to the mounting portion, the engaging portion 8 is fixed to the engaging portion 8 fixed to the carriage 2 and is pressed so as to be in close contact with the carriage 2. Further, a bent portion 9 is formed on the adjustment plate 5 above the engagement portion 8. The tip of the adjusting screw 10 penetrating the bent portion 9 is screwed into a screw hole of a protruding portion 12 protruding from the carriage 2. A spring 11 is mounted around the adjustment screw 10 between the bent portion 9 and the protruding portion 12. The spring 11 urges the bent portion 9 in a direction away from the protrusion 12. Adjustment plate 5
, Two multi-heads 3 and 4 are fixed parallel to each other and at substantially the same height in the sub-scanning direction. The multi-heads 3 and 4 may be formed integrally.

As shown in FIG. 3, the multi-head 3 integrally includes a cyan head portion 3C and a magenta head portion 3M, which are ink jet recording heads according to the present invention, symmetrically with respect to a central cross section X thereof. . Similarly, the multi-head 4 integrally includes a yellow head portion 4Y and a black head portion 4Bk. Since the multi-heads 3 and 4 have the same configuration except that the supplied ink is different, only the multi-head 3 will be described below.

The multi-head 3 has a channel plate 20 at a portion facing the recording medium. Channel plate 2
Reference numeral 0 denotes a flat plate made of resin, metal, or the like, and a plurality of recesses are formed on the back surface thereof. This channel plate 20
As shown in FIG. 4, a partition 21 made of a thin film of metal, resin, or the like is adhered to the concave portion forming surface as shown in FIG. Channel plate 2 covered with this partition 21
The ink channel 22, the inlet 23, and the ink supply chamber 24 are respectively formed in the insides of the respective recesses of No. 0.

A plurality of ink channels 22 are arranged along the main scanning direction and at equal pitches in the sub-scanning direction.
Each of the ink channels 22 accommodates ink supplied from an ink supply chamber 24 via a corresponding inlet 23.

A plurality of small-diameter nozzles 15 and large-diameter nozzles 17 are formed on the recording medium facing surface of the channel plate 20 so as to communicate with the respective ink channels 22.
The small-diameter nozzle 15 discharges a small ink drop, and the large-diameter nozzle 17 discharges a larger ink drop than that discharged from the small-diameter nozzle 15. The plurality of small-diameter nozzles 15 are arranged linearly to form a small-diameter nozzle row 16, and the plurality of large-diameter nozzles 16 are arranged linearly to form a large-diameter nozzle row 18. The nozzle rows 16 and 18 are arranged in a straight line in the sub-scanning direction. The nozzles 15 and 17 may be arranged not in a straight line but in a staggered manner along the sub-scanning direction to form the nozzle rows 16 and 18, or the small-diameter nozzle row 16 and the large-diameter nozzle row may be configured. The nozzle rows 18 may be arranged slightly shifted in the main scanning direction.

As shown in FIG. 4, on the lower surface of the partition 21,
It is fixed to a substrate 33 made of a highly rigid material such as ceramic through spacer members 30, 31, and 32. A plurality of piezoelectric members 25 are fixed on the substrate 33 so as to be opposed to the ink channel 22 via the partition wall 21 and arranged along the longitudinal direction of the ink channel 22. The piezoelectric member 25 is a pressurizing unit that presses the ink contained in the ink channel 22 through the partition 21 based on the deformation at the time of applying a voltage, and ejects ink drops from the nozzles 15 and 16.

The piezoelectric member 25 has a rectangular body made of a piezoelectric material such as lead zirconate or lead titanate, for example, having electrodes formed on the upper and lower surfaces, respectively, and has a length and width smaller than those of the ink channel 22. It is formed small.
The piezoelectric member 25 is polarized, and is deformed by applying a voltage to electrodes provided above and below. The electrode on the upper surface of each piezoelectric member 25 is connected to ground via a conductive partition 21 that comes into contact with the electrode. On the other hand, the lower electrode
It is electrically connected to individual lead lines formed on the substrate 33 in a pattern corresponding to the respective piezoelectric members 25, and connected to drivers (not shown) via the lead lines.
The driver applies a voltage to the piezoelectric member 25 according to an image signal. The piezoelectric member 25
The method of extracting each electrode described above is not limited to that of the present embodiment, and can be variously changed.

Next, a description will be given of an ink drop ejection operation when multicolor printing is performed by the ink jet recording apparatus 100 having the above configuration. The cyan head 3C and the magenta head 3M of the multi-head 3 include:
The ink supply chambers 24, 2 are provided via the ink supply ports 26, 26.
4, cyan and magenta inks are supplied, respectively.
Each ink channel 22 is accommodated via an inlet 23. Similarly, the yellow and black inks are stored in the respective ink channels 22 in the yellow head portion 4Y and the black head portion 4Bk of the multi-head 4.

In this state, first, before starting printing, the carriage 2 is moved in the main scanning direction, and a voltage is applied to the piezoelectric member 25 to cause ink drops to be ejected, thereby forming ink of each color formed on the recording medium. The degree of dot overlap is confirmed, and the positions of the heads 3C, 3M, 4Y, and 4Bk are adjusted. Specifically, for example, at the timing when the ink drops are attached to the same position on the recording medium from the large-diameter nozzles 17 located on the most upstream side in the sub-scanning direction of the yellow head unit 4Y and the cyan head unit 3C, respectively. Each is discharged. It is sufficient that the dots formed on the recording medium by these two ink drops completely overlap. However, as shown in FIG. 5A, the cyan dot (C) is shifted above the yellow dot (Y). If it is, loosen the retaining screw 7 and the adjusting screw 10
The adjustment plate 5 is slightly rotated in the direction of arrow A in FIG. Conversely, as shown in FIG. 5B, when the cyan dot (C) is shifted below the yellow dot (Y), the adjusting screw 10 is tightened to move the adjusting plate 5 in the direction of arrow B in FIG. Turn slightly. In this way, the adjustment is performed so that the two dots are accurately overlapped, the retaining screw 7 is tightened, and then printing is started.

In multicolor printing by the ink jet recording apparatus 100, when color expression is performed by superposing large and small ink drops, for example, when superposing a small cyan ink drop on a large yellow ink drop, first, A large ink drop is ejected from the large-diameter nozzle 17 located on the most upstream side in the sub-scanning direction of the large-diameter nozzle row 18 of the yellow head unit 4Y, and a yellow dot is formed on the recording medium.

Thereafter, the carriage 2 gradually moves in the sub-scanning direction while reciprocating between both ends of the recording medium in the main scanning direction. When the small-diameter nozzle 15 located on the most upstream side in the sub-scanning direction of the small-diameter nozzle row 16 of the cyan head portion 3C comes to the position of the yellow dot, a small ink drop is ejected from the small-diameter nozzle 15 to discharge the ink. Overlay on the yellow dot. At this time, the time difference between the two ink drops adhering to the recording medium is determined by the distance z between the large-diameter nozzle 17 and the small-diameter nozzle 15 located at the most upstream side in the sub-scanning direction. The time is almost equal to the time required to move. This time is a time sufficient for the yellow ink drop previously attached to be absorbed by the recording medium and dried.

Therefore, even if small ink drops of different colors adhere to the ink, each ink does not mix in a liquid state. Further, since a small cyan dot is superimposed on a large yellow dot, the yellow dot is not obstructed. As a result, the unique color stimulus of each ink dot is not impaired, so that color expression with good color development is possible, and the image quality can be improved.

The same effect as described above can be obtained also in the case where two large and small ink drops of different colors are not overlapped but are attached close to each other on a recording medium to express colors. That is, for example, if a small cyan ink drop is attached close to the large yellow ink drop that has previously adhered before it dries, the ink drops may be connected to each other and mixed, but the head according to the present embodiment may not be used. According to the inkjet recording apparatus 100 having a large ink drop, after a large ink drop is dried, a small ink drop can be attached close to the ink drop. Therefore, the ink drops can be formed as completely independent dots. High image quality can be obtained.

Further, by depositing a large ink drop first, drying it, and overlaying a small ink drop of the same ink, ink dots having the same color but different densities can be formed. Conversely, even if the next ink drop is overlapped before the previously attached ink drop dries, the two ink drops are mixed in a liquid state, which is different from the color of the dot formed by one ink drop. Disappears. According to the head according to the present embodiment, since the next ink drop can be overlapped after the previously attached ink drop is sufficiently dried, it is possible to form ink dots having different densities even in the same hue, The gradation width can be widened. In addition, the problem that the intended dot shape cannot be obtained when ink drops are superimposed due to the ink drops that have landed earlier not being sufficiently dried is also solved.

By the way, each of the heads 3C, 3M, 4
In Y and 4Bk, the large-diameter nozzle row 18 is
In this nozzle arrangement, a large ink drop is first attached to the recording medium because the ink droplets are arranged on the downstream side in the sub-scanning direction. Conversely, for example, when using ink that dries relatively slowly, for example, the small-diameter nozzle row 16 is arranged upstream in the sub-scanning direction,
You may make it attach a small ink drop first. In this case, the small ink drop dries faster than the large ink drop, and the large ink drop can be overlaid after being completely dried. Good color expression can be achieved.

In the head of the present embodiment, the nozzle diameter is changed in order to eject large and small ink drops. However, the size of the ink drop may be changed by another method. For example, while all the nozzles are formed to have the same size, the ink channel 22 and the piezoelectric member 25 for ejecting a large ink drop may be formed larger than those for ejecting a small ink drop, or the same color ink may be used. Even if the same pressure is applied, the size of the ink drop to be ejected changes by changing the physical properties such as viscosity and surface tension. The physical properties of the ink contained in the ink channel 22 and the ink may be different.

The ink jet recording head of this embodiment is also effective when a single color gradation image is formed by providing only one in the recording apparatus. Furthermore, if the large and small ink drops are formed of oil-based ink and water-based ink, respectively, and are overlapped, color mixing in a liquid state can be more effectively prevented, and the above-described effect can be further ensured.

In the present embodiment, the piezoelectric member is used as the ink pressurizing means. However, the present invention is not limited to this. Any member may be used as long as it ejects ink from nozzles. Bubbles may be generated to pressurize the ink.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of an ink jet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of an inkjet recording head for multicolor printing.

FIG. 3 is a front view of a multi-head in which two inkjet recording heads are integrally formed.

FIG. 4 is a cross-sectional view of the multi-head of FIG. 2, taken along the line III-III.

FIG. 5 is a diagram showing a state in which two ink drops having different colors and the same size are superimposed on a recording medium, and their adhesion positions are shifted.

FIG. 6 is a diagram illustrating position adjustment of each head for correcting a position shift between two ink drops.

FIG. 7 is a diagram illustrating an example of a conventional inkjet recording head in which large and small nozzles are arranged.

FIG. 8 is a diagram showing another example of a conventional ink jet recording head in which large and small nozzles are arranged.

[Description of Signs] 2 ... Carriage, 3 ... Multi head, 3C ... Cyan head section, 3M ... Magenta head section, 4 ... Multi head, 4Y ... Yellow head section, 4Bk ... Black head section, 15 ... Small diameter Nozzle, 16 ... small-diameter nozzle row (first
Nozzle row), 17 large diameter nozzle, 18 large diameter nozzle row (second nozzle row), 52 ball screw, 54 backup roll, 55, 56 motor, 100 ink jet recording apparatus, 101 ink jet Recording head.

Claims (2)

[Claims] 1. An ink jet recording head that moves in a main scanning direction while ejecting ink drops from a plurality of nozzles facing a recording medium and attaches the ink drops to a recording medium to record an image. A first nozzle row in which a plurality of nozzles to be ejected are arranged, and a second nozzle row in which a plurality of nozzles to which ink drops larger than those ejected from the first nozzle row are respectively ejected are arranged. An ink jet recording head, which is arranged in series along a sub-scanning direction orthogonal to a main scanning direction. 2. An ink jet recording head which discharges ink drops from a plurality of nozzles facing a recording medium and causes the ink drops to adhere to the recording medium to record an image, and a method of moving the recording head in a main scanning direction. A second moving means for changing a relative position of the recording medium with respect to the recording head to a sub-scanning direction orthogonal to the main scanning direction;
An ink jet recording head comprising: a first nozzle row in which a plurality of nozzles from which ink drops are respectively ejected are arranged; and an ink jet head ejected from the first nozzle row. An ink jet recording apparatus, wherein a second nozzle row in which a plurality of nozzles from which a larger ink drop is respectively ejected is arranged in series along the sub-scanning direction.