JP2919641B2 - Inkjet recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording method for recording a monochrome or color image using an ink jet recording head having a plurality of ink discharge ports, and more particularly to a method for ejecting a plurality of liquid droplets having different liquid amounts by a plurality of scans. The present invention relates to an ink jet recording method in which one pixel is formed by landing on substantially the same location on a recording material to form a clear image with excellent gradation.

[0002]

2. Description of the Related Art In recent years, a plurality of ink droplets (droplets) are landed on substantially the same location on a recording material to form one dot (pixel), and gradation is changed by changing the number of ink droplets landed. A so-called multi-droplet method has been developed. The multi-droplet method is expected to be extremely effective as a method for obtaining a high-density and high-gradation image, particularly in inkjet recording in which it is difficult to greatly modulate the size of one ink droplet itself.

However, in the conventional multi-droplet method, since one pixel is formed by a plurality of ink droplets ejected from one ink ejection port during one scan, the variation of the volume of the ink droplet for each ejection port varies. If there is, there is a problem that streaks (streaks) and density unevenness (spots) occur in an image that should be uniform.

In order to avoid these problems, in the conventional multi-droplet system, the recording head must be manufactured very precisely in order to minimize the variation in the volume of the ink droplets between the discharge ports. As a result, there have been problems such as an increase in manufacturing cost and a decrease in manufacturing yield. In addition, as a method of eliminating density unevenness by software, a method of changing the number of ejected ink droplets by using an image processing such as an error diffusion method so as to slightly cancel the volume of the ink droplet between the ejection ports is also proposed. However, when such image processing is incorporated, there is a problem that the production cost of the system is increased. Further, even if such an image processing method is used, it is necessary to readjust the number of ink droplets to be ejected when the variation in the volume of the ink droplets between the discharge ports changes with time, which causes a problem that the maintainability is poor. Had.

[0005]

SUMMARY OF THE INVENTION U.S. Pat.
In JP-A-6-935, a multi-tone inkjet printer is proposed in which one pixel expresses gradation by combining a plurality of ink droplets having different liquid volumes of 1 pl (picoliter), 2 pl, and 4 pl. According to this proposal,
0, 1, 2, 1 + 2 (= 3), 4, 1 + 4 (=
5) Eight types of ink droplet volumes of 2 + 4 (= 6) and 1 + 2 + 4 (= 7) can be obtained by overlapping three ink droplets, and the printing speed can be improved as compared with the system in which one ink droplet is overlapped seven times. Have been. However, as shown in FIG. 5, the relationship between the total volume of ink droplets forming one pixel and the reflection density is generally an upwardly convex curve with a sharp rise. Therefore, even if the intervals of the possible values of the total volume of ink droplets forming one pixel are equal, the intervals of the possible values of the reflection density corresponding thereto are not equal. Therefore, in a region where the volume of the ink droplet forming one pixel is small, the interval of the possible values of the reflection density is wide, and in a region where the volume of the ink droplet forming one pixel is large, the interval of the possible values of the reflection density is large. Becomes narrower. That is, the magnitude of the volume of the ink droplet in the region where the volume of the ink droplet forming one pixel is large does not contribute much to the gradation. In addition, since the number of combinations of ink droplets forming one pixel is large (eight types in the case of 1 pl, 2 pl, and 4 pl), the circuit of the image processing system is complicated, and the design cost and the manufacturing cost are significantly increased. .

Further, another problem of the invention disclosed in the above-mentioned US Patent Publication is that the volume of ejected ink droplets is four times as large as 1 pl to 4 pl (or eight times as large as 1 pl to 8 pl) and the ejection amount is different. The head structure must be formed in the same recording head, which is a very serious obstacle that involves difficulty in producing the recording head. In general,
The parameters of the recording head for changing the volume of the ink droplet to be ejected include the distance between heater ejection ports, the size of the heater, the shape of the ejection port or barrier, and the area of the ejection port. In order to change the volume of the ink droplet to be discharged from 1 to 4, it is necessary to change the distance between heater discharge ports, the area of the heater, and the area of the discharge port, and it is difficult to produce the same only by a conventional production process. Accordingly, in order to actually achieve this, a new manufacturing process needs to be added, and the manufacturing cost of the recording head becomes considerably high.

Further, in the invention disclosed in the above-mentioned US Patent Publication, a plurality of series of ink ejection ports having different ejection ink droplet volumes such as 1 pl, 2 pl, 3 pl, and 4 pl along the main scanning direction in which the recording head reciprocates. Are arranged close to each other on the front surface of the recording head, and are configured to discharge a plurality of ink droplets to the pixel of interest in one main scan. Penetration,
During the time when the fixation is hardly performed, the ink droplets successively overlap the ink droplets. Therefore, in an image area where the number of droplets to be superimposed on the recording material is large, the droplets of the adjacent pixels come into contact with each other to form an image. Bleeding is likely to occur, resulting in loss of sharpness of character parts and the like, and in color images, the outline of the image is blurred due to bleeding due to color mixture of ink before fixing, especially at the boundary of a single color region, and recording quality is greatly reduced. There was a serious problem to be solved.

The present invention has been made to solve the above-mentioned various problems of the prior art, and is relatively inexpensive and excellent in gradation without lowering the recording speed. It is an object of the present invention to provide an ink jet recording method capable of obtaining a clear image.

[0009]

In order to achieve the above object, the present invention provides an ink jet recording method for forming a gradation image using an ink jet recording head having a plurality of ink ejection ports. Droplets discharged from different discharge ports land on substantially the same location on the recording material according to the gradation level to form one pixel, and each gradation per pixel recorded on the recording material The volume of droplets discharged from at least one of the different outlets is made different from the volume of droplets discharged from other outlets so that the density between levels is substantially equal. Is set.

According to one aspect of the present invention, the plurality of ink ejection ports are arranged in a direction substantially perpendicular to the scanning direction of the ink jet recording head, and a group of droplets ejected from the ink ejection ports is provided. Among them, a droplet having a large volume is ejected so as to be overprinted with a droplet having a small volume.

Further, the present invention provides, in another form,
The ink jet recording head may include an electrothermal converter as an element for generating energy for discharging the droplets, for applying thermal energy for causing film boiling on the droplets. .

[0012]

According to the present invention, ink droplets are overprinted on one pixel in a plurality of scans (scans), so that the ink that has landed previously permeates and is fixed by the ejection of ink droplets in each scan. Since the ink is almost completely dried, bleeding of ink, color mixing, blurring of image outline, and the like are eliminated, and as a result, a clear image excellent in gradation is obtained.

Further, in the present invention, the ejection port groups are arranged in different scanning directions, and one pixel is formed by over-printing with a series of ink droplets from the ejection port groups, each of which has a different volume of ink droplets. The number of scans for forming one pixel is reduced, and the image quality of the highlight area as well as the image quality of the high density area can be improved with almost no decrease in the recording speed.

Further, according to the present invention, the volume ratio of the ejected ink droplets is appropriately set so that the gradation levels per overprinted pixel are substantially equal, and the ink droplet having a large volume is replaced with the ink droplet having a small volume. Since the ink droplets are always overprinted, the volume ratio of the maximum ink droplet to the minimum ink droplet of the ejected ink can be made relatively small. Image signal processing is also facilitated. As a result, a good halftone image can be obtained at a relatively low price without increasing the manufacturing cost of the head and the main unit.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, a recording method on which the present invention is based will be described. This is because, by forming one pixel by ink droplets ejected from a plurality of ink ejection ports by a plurality of scans, variation in the volume of the ink droplets ejected from the ejection ports between the ejection ports is reduced, This is a recording method that hardly causes unevenness (hereinafter, referred to as a multi-scan method).

It has been confirmed that this multi-scan method can reduce the deterioration of image quality due to streaks and unevenness and can obtain a clear image. However, although the image quality is improved by introducing such a multi-scan method,
A problem to be solved further arises that the printing time increases. Hereinafter, this point will be described.

Generally, as the volume of one ink droplet constituting one pixel is reduced, the granularity in a highlight region of an image becomes less visible.
The image quality in the highlight area is improved. But,
If the volume of the ink droplet is reduced, the reflection density on the paper (recording material) is reduced. Therefore, in order to improve the image quality in the high density region of the image, a large number of ink droplets must be overlapped on the same pixel. Overlapping a large number of ink droplets on the same pixel in this manner means an increase in the number of scans for the one-pixel format, so that the image quality in the highlight region and the image quality in the high-density region are improved at the same time. If so, the printing time will be greatly increased. On the other hand, when one pixel is formed by superimposing about three ink droplets at the maximum, it is difficult to improve the image quality in the highlight area.

By the way, the frequency fkHz at which one pixel is formed in the binary recording method of only "0" and "1" (in the binary recording method, the frequency at which one pixel is formed and the frequency at which ink droplets are ejected are the same. In the multi-scan method in which a maximum of n ink droplets are overlapped on the same pixel, at least a frequency for ejecting an ink droplet of f × n kHz is necessary to obtain the same printing speed as that of the binary recording method. It is said. However, although the volume of one ink droplet is smaller than that in binary recording, increasing the drive frequency of the recording head by n times actually has many technical problems. The higher the number, the more difficult it is to achieve.

FIG. 1 shows a schematic configuration of a main part of a serial type ink jet recording apparatus according to an embodiment of the present invention. Reference numeral 1 denotes an ink jet recording head that discharges ink droplets in accordance with an input signal (drive signal) supplied through the flexible cable 4, and a series of inks having different discharged ink droplet volumes as shown in FIG. Has a discharge port. The head 1 is mounted and fixed on a carriage 5 and reciprocates in a horizontal main scanning direction along a pair of guide rails 9 by driving a carriage feed motor (see FIG. 2) described later using a timing belt 7 as a transmission means. A halftone image corresponding to an input signal is formed on the recording material 11 by selectively discharging ink droplets from each of the ejection ports described below toward the recording material (generally paper) 11. The recording material 11 is wound around a platen roller 13, and is driven by a paper feed motor (see FIG. 2) which rotates the platen roller 11 in a sub-scanning direction perpendicular to the main scanning direction by a predetermined pitch at a predetermined pitch. Sent.

FIG. 2 shows a schematic configuration of a control system circuit of the apparatus according to the embodiment of the present invention. Reference numeral 21 denotes a main controller that controls the entire apparatus such as a discharge timing.
A one-chip microprocessor or the like having a built-in (central processing unit), a program ROM (read only memory), a work RAM (random access memory) and the like is usually used. The main controller 21 transmits an image data signal to a host computer 23 such as a color image reader.
, And stores it in the frame memory 25 for the buffer in units of one frame. During recording, the main controller 21 controls the drive of the carriage feed motor 29 through the motor driver 27 and controls the drive of the paper feed motor 33 through the motor driver 31. With this,
Based on the image data read from the frame memory 25,
Convert to gradation data according to this system (recording device),
The ejection control of the head 1 is performed at the timing of the present invention via the driver controller 35 and the head driver 37, whereby high-quality color image recording is obtained.

(First Embodiment) FIG. 3 shows a schematic configuration of the head 1 according to an embodiment of the present invention. The discharge ports in the figure are shown as three types of discharge port groups 101, 102, and 103 in which a series of discharge ports are divided into three groups of four for ease of description. The first ejection port group 101 is a group of a series of ejection ports (ejection port numbers 1 to 4) designed to eject ink droplets each having a volume of 5 pl (picoliter).
The second ejection port group 102 has a series of ejection ports (ejection port number 5) designed to eject ink droplets each having a volume of 8 pl.
8), and the third discharge port group 103 is 11
pl is a group of a series of discharge ports (discharge port numbers 9 to 12) designed to discharge ink droplets having a volume of pl. These ejection groups 101 to 103 are arranged in a line in the vertical direction of the head 1, that is, in the sub-scanning direction substantially perpendicular to the main scanning direction in which the head 1 reciprocates. The head 1 includes a substrate 2 and a base 3, and the above-described discharge port is opened on the surface of the substrate 2 facing the recording material 11. By the way, in order to manufacture the head 1 at low cost, it is necessary to be able to use the conventional manufacturing process almost as it is. For this purpose, the volume ratio between the maximum ink droplet and the minimum ink droplet is 3.
0 or less is desirable. The maximum ink drop of this embodiment is 11 pl
Since the minimum ink droplet is 5 pl, the volume ratio is 2.2, which satisfies the above condition, and the head 1 can be manufactured at a relatively low cost in this respect as well.

FIG. 4 shows a printing state in this embodiment.
A large rectangular outer frame in the figure indicates a recording material 11 to be printed by scanning the carriage 5 a plurality of times (hereinafter, referred to as scanning).
2 shows the entire recording area. Five recording areas (A,
B, C, D, and E) respectively correspond to the above-described three orifice groups for discharging the three types of ink droplet volumes, and the width in the vertical direction corresponds to one feed amount of the recording material 11. doing. In the first scan, 5 pl ink droplets are ejected to the forefront region A using the ejection ports (101) of ejection port numbers 1 to 4 according to the gradation of image data (gradation data), and dot printing is performed. . Next, the recording material 11 is 63.5 μm (ejection port pitch) × 4 (the number of ejection ports) = 254 μm in FIG.
And the second scan is started.

In the second scan, the discharge ports (101) of the discharge port numbers 1 to 4 that have moved to the next area B have 5 pl in accordance with the gradation of the image data in the same manner as in the first scan.
Is ejected, and dot printing is performed. At the same time, 8 pl of ink droplets are ejected from the ejection ports (102) of ejection port numbers 5 to 8 that have moved to the area A to the image of the area A printed in the first scan in accordance with the gradation of the image data. And add ink drops. At this time, the 8 pl ink drop is not hit at a place where the 5 pl ink drop is not hit during the first scan. After the end of the second scan, the recording material 11 is fed in the direction of FIG. 4 by 254 μm as described above, and the third scan is started.

In the third scan, ink is ejected from the ejection ports (101) of ejection port numbers 1-4 moved to the third area C and the ejection ports (102) of ejection port numbers 5-8 moved to the area B. The droplets are ejected and printing is performed in the same manner as in the second scan. Discharge port numbers 9-1 moved to area A at the same time
Printing is performed by discharging ink droplets having an ink droplet volume of 11 pl according to image data from the second discharge port (103). Also at this time, the 11 pl ink droplet is prevented from being hit where no 5 pl or 8 pl ink droplet is hit in the first scan and the second scan.

At the end of the third scan, there are two states where 0 pl (no ink is attached) and 5 pl of ink droplets are attached in pixel units in the area C, and 0 pl in the area B. And 5pl and 13pl (= 5pl
+8 pl) ink droplets adhered in pixel units, and the area A has 0 pl, 5 pl, and 13 pl
pl (= 5pl + 8pl) and 24pl (= 5pl + 8p)
There are four states in which ink droplets of (l + 11 pl) adhere to each pixel.

By sequentially repeating the fourth scan and the fifth scan in the same manner as described above, dot printing corresponding to the gradation of the image data is performed on the recording material 11, and the recording state of the area A is recorded. Spreading over the entire area to be printed on the material 11, the ejection openings (10
After 3) reaches area E and printing is performed, this recording operation ends.

In the present embodiment, a configuration is adopted in which a block is formed for each series of ejection ports each time the volume of ink droplets differs, but the ejection ports for ejecting ink droplets of different volumes are used. It goes without saying that the recording effect is the same even if they are arranged alternately adjacently.

FIG. 5 shows the relationship between the ink volume per pixel (pixel) of the recorded image printed on the recording material 11 and the reflection density thereof as described with reference to FIG.
In the present embodiment shown in FIGS. 3 and 4, the reflection level at the 0th level without ink is 0.05 (the reflection density of the paper itself as the recording material 11), and the first level (I) at 5 pl of ink amount.
, The reflection density is 1.02 at the second level (II) with the ink amount of 13 pl, and 1.38 at the third level (III) with the ink amount of 24 pl. This is because, compared to the conventional multi-scan method and the method proposed in the above-mentioned US Pat. No. 4,746,935, the intervals between the reflection densities between the levels are closer to equal intervals, and the gradation characteristics are also improved. Is shown. The reflection density at the first level (I) is also 0.47, which is almost the same as the value obtained by the method of superimposing a maximum of five ink drops per pixel in the conventional multi-scan method (however, , When the maximum value of the reflection density in the image is equalized). Therefore, the image obtained in the present embodiment can obtain a density level comparable to an image printed by superimposing a maximum of five ink droplets per pixel by the conventional multi-scan method. In the present embodiment, the printing speed can be reduced by about 20% since only three ink droplets can be overlapped per pixel in this embodiment.

The image data (gradation data) in this embodiment is obtained by subjecting data obtained by reading an original image with a Morrokuro scanner to logarithmic conversion, gamma correction, etc., and then performing four-value error diffusion. It was created by applying the law.

(Second Embodiment) FIG. 6 shows a schematic configuration of a head 1 according to another embodiment of the present invention. In this embodiment, a series of outlets is divided into two outlet groups 111 and 112,
The ejection opening 111 is designed to eject 5 pl ink droplets, and the ejection opening 112 is designed to eject 14 pl ink droplets. The number of ejection ports indicates that eight ejection ports that eject 5 pl ink droplets forming the first ejection port group 111 and four ejection ports that eject 14 pl ink droplets that constitute the second ejection port group 112 are shown. is there. The head 1 is mounted on the carriage 5 of the serial printer shown in FIG. 1 as in the first embodiment shown in FIG.
As shown in FIG. 4, the printing scan proceeds, and a halftone image corresponding to the image data is printed on the recording material 11.

Next, the operation of this embodiment will be described with reference to FIG. First, in the first scan, the ejection port numbers 1 to 4
5l ink droplets are landed on pixel positions where 24 pl / pixel and 10 pl / pixel ink droplets are to be superimposed in the area A by using the ejection port (111) of
An ink droplet of 5 pl is landed on about 50% of the pixel position of pl / pixel. Next, the recording material 11 is moved upward by 254 μm in FIG. 4, and the second scan is started.

In the second scan, printing is performed by discharging ink droplets from the discharge ports (111) of the discharge port numbers 1 to 4 that have moved to the area B in the same manner as in the first scan. At the same time, the ejection ports of ejection port numbers 5 to 8 (11
From 1), printing is performed by ejecting ink droplets to the pixel positions of 5 pl / pixel left unprinted by the ejection ports 1 to 4 in the first scan, and printing is performed at 24 pl / pixel and 1 pixel.
Printing is performed by ejecting 5 pl ink droplets from the ejection ports of ejection port numbers 5 to 8 at pixel positions where ink droplets of 0 pl / pixel are to be superimposed. Then, the recording material 11 is moved upward in FIG.
The third scan is started by feeding by 54 μm.

In the third scan, 5 pl of ink droplets are ejected from the ejection ports (111) of the ejection port numbers 1 to 4 and 5 to 8 which have relatively moved to the area C and the area B, as in the second scan. To print. At the same time, 14 pl ink droplets are ejected only from the pixel positions where 24 pl / pixel ink droplets are to be overlapped from the ejection ports (112) of ejection port numbers 9 to 12, which have relatively moved to the area A, according to the image data. And repeat.

At the stage where the third scan is completed, in the area A, 0 per pixel is obtained due to the overprinting of ink droplets.
pl (no ink), 4 of 5pl, 10pl, 24pl
The printing of the seed ink droplet amount is completed. In area B, 0 pl, 5 pl, and 10 pl ink droplets are overprinted per pixel, and in area C, 0 pl, 5 p
1 ink drop is printed per pixel.

In the fourth scan and the fifth scan, printing is sequentially performed in the same manner as described above. When the state of the area A reaches all the areas to be recorded, the printing operation is completed. In this embodiment, the ink volume per pixel is 0 pl, 5 pl, and 10 p.
1 and 24 pl, as can be seen from FIG.
An image of almost the same quality as that of the embodiment can be obtained.

In particular, in the present embodiment, the first position is determined for a pixel position at which a 5 pl ink droplet is supplied per pixel.
A group of discharge ports for discharging ink droplets (discharge port numbers 1 to 4) and a group of discharge ports for discharging second ink droplets (discharge port numbers 5 to 5)
8) are selectively (eg, randomly) used. This is to reduce density unevenness in the ejection port array direction caused by variations in head manufacturing and the like. That is, in the pixel area of 5 pl / pixel, printing is performed using only ink droplets discharged from a single discharge port per pixel. Therefore, if printing is performed using only the first ink droplet for all the pixels of 5 pl / pixel, unevenness may be noticeable depending on the image. In this embodiment, the reason why 5 pl / pixel is formed by the first ink droplet and the second ink droplet is to eliminate the unevenness. Therefore, according to the present embodiment, it is possible to provide an image having no gradation unevenness and excellent gradation, as described above.

In each of the first and second embodiments, a discharge port group having a small discharge volume is provided below the head. The recording order of the droplets having different ejection volumes is not limited to this, and the arrangement order of the ejection port group may be, for example, even if an ejection port having a large ejection volume is below the head. good.

The present invention can of course be applied to color ink jet recording.

(Others) It should be noted that the present invention includes a means (for example, an electrothermal converter or a laser beam) for generating thermal energy as energy used for discharging ink, particularly in an ink jet recording system. An excellent effect is obtained in a recording head and a recording apparatus of a type in which the state of ink is changed by the thermal energy. This is because according to such a method, it is possible to achieve higher density and higher definition of recording.

The typical configuration and principle are described in, for example, US Pat. Nos. 4,723,129 and 4,740.
It is preferable to use the basic principle disclosed in the specification of Japanese Patent No. 796. This method is a so-called on-demand type,
It can be applied to any type of continuous type, but especially in the case of on-demand type, it can be applied to the sheet holding liquid (ink) or the electrothermal converter arranged corresponding to the liquid path. By applying at least one drive signal corresponding to the recorded information and giving a rapid temperature rise exceeding the nucleate boiling, heat energy is generated in the electrothermal transducer, and film boiling occurs on the heat acting surface of the recording head. As a result, the liquid (ink)
This is effective because air bubbles can be formed inside. The liquid (ink) is ejected through an ejection opening (ejection port) through the process of growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of a liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable. US Pat. No. 4,463,335 discloses a pulse-shaped drive signal.
No. 9 and No. 4,345,262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.

As the configuration of the recording head, in addition to the combination configuration (a linear liquid flow path or a right-angle liquid flow path) of a discharge port, a liquid path, and an electrothermal converter as disclosed in the above-mentioned respective specifications. U.S. Pat. No. 4,558,333 and U.S. Pat. No. 44,558 which disclose a configuration in which a heat acting portion is arranged in a bending region.
A configuration using the specification of Japanese Patent No. 59600 is also included in the present invention. In addition, Japanese Unexamined Patent Application Publication No. 59-123670 discloses a configuration having a discharge section having a common slit as a discharge opening for a plurality of electrothermal transducers, and an aperture for absorbing pressure waves of thermal energy. The effect of the present invention is effective even if the configuration is based on JP-A-59-138461, which discloses a configuration in which is provided corresponding to a discharge unit. That is, according to the present invention, recording can be reliably and efficiently performed regardless of the form of the recording head.

In addition, even in the case of the serial type as described above, a recording head fixed to the apparatus main body or an electric connection with the apparatus main body and ink from the apparatus main body can be provided by being mounted on the apparatus main body. The present invention is also effective when a replaceable chip-type recording head that can be supplied or a cartridge-type recording head in which an ink tank is provided integrally with the recording head itself is used.

It is preferable to add a recording head ejection recovery unit, a preliminary auxiliary unit, and the like as the configuration of the recording apparatus of the present invention since the effects of the present invention can be further stabilized. To be more specific, capping means for the print head, cleaning means, pressurizing or suction means, an electrothermal transducer or a heat generating element for generating thermal energy for discharging ink droplets necessary for printing. Preheating means for performing preheating using a different heating element or a combination thereof may be used, and predischarge means for performing discharge different from recording.

The type and number of recording heads to be mounted are not limited to those provided only for one color ink, for example, and for a plurality of inks having different recording colors and densities. A plurality may be provided. That is, for example, the printing mode of the printing apparatus is not limited to a printing mode of only a mainstream color such as black, but may be any of integrally forming a printing head or a combination of a plurality of printing heads. The present invention is also very effective for an apparatus provided with at least one of the recording modes of full color by color mixture.

The number of discharge ports is not limited to one, but a plurality of rows (for example, a configuration in which one row has 20 discharge ports and four rows are arranged) can be used.

In addition, in the embodiments of the present invention described above, the ink is described as a liquid. However, even if the ink is solidified at room temperature or lower, it can be softened or liquefied at room temperature. Since it can be used in liquid form when recording is performed, it can be used in the present invention. Alternatively, in the ink jet system, in some cases, the temperature is adjusted so that the ink itself is kept within a range of 30 ° C. or more and 70 ° C. or less, and the temperature is controlled so that the viscosity of the ink is in a stable ejection range. 30 ° C in this case
An ink that is liquid at a temperature of 70 ° C. or lower can be used. In addition, the ink is liquefied for the first time by heating in order to positively prevent the temperature of the ink itself from rising due to thermal energy or to prevent the ink from evaporating by using the energy as the energy of the state change from the solid state to the liquid state of the ink. May be used. In any case, the application of heat energy causes the ink to be liquefied by the application of the heat energy according to the recording signal and the liquid ink to be ejected, or to start solidifying when it reaches the recording medium. The present invention is also applicable to a case where an ink having a property of liquefying for the first time is used. In such a case, the ink
JP-A-54-56847 or JP-A-60-7
It may be used for recording while being held as a liquid material or a solid material in concave portions or through holes of a porous sheet as described in JP-A-1260. In the present invention, it is most effective to execute the above-described method of causing film boiling for each ink.

In addition, the form of the ink jet recording apparatus according to the present invention is not only used as an image output terminal of an information processing apparatus such as a computer, but also a copying apparatus combined with a reader or the like, and a facsimile having a transmission / reception function. It may be in the form of an apparatus.

[0049]

As described above, according to the present invention,
Since the ink droplets are overprinted for one pixel in a plurality of scans (scans), the ink that has landed earlier permeates and is fixed by the ejection of the ink droplets in each scan, and is almost completely dried. Blurring, color mixing, blurring of image outline, etc. are eliminated, and as a result, a clear image with excellent gradation is obtained.

Further, according to the present invention, the ejection port groups are arranged in the sub-scanning direction, and one pixel is formed by overprinting with a series of ink droplets from the ejection port groups each having a different volume of ink droplets. The number of scans for forming one pixel is reduced, and the image quality of the highlight area as well as the image quality of the high density area can be improved with almost no decrease in the recording speed.

Further, in the present invention, the volume ratio of the ejected ink droplets is set appropriately so that the gradation levels per overprinted pixel are substantially equal, and the large-volume ink droplet is replaced with the small-volume ink droplet. Because the ink is always overprinted on the droplet, the volume ratio between the maximum ink droplet and the minimum ink droplet of the discharged ink can be made relatively small. Image signal processing becomes easy, and as a result, a favorable halftone image can be obtained at a relatively low price without increasing the manufacturing cost of the head and the main body device.

Further, in the present invention, a plurality of (two in the embodiment) ejection port groups for ejecting ink droplets of the minimum volume are provided.
By selectively using both of the divided ejection port groups for the pixels forming one pixel with one ink droplet of the minimum volume, for example, alternately for adjacent pixels, the head production is improved. Density unevenness in the ejection port array direction caused by variation or the like can be reduced.

Further, according to the present invention, the volume of the ink droplets used in the low-density region can be made smaller than the average of the volume of the n ink droplets ejected from the n different ejection ports forming one pixel. Therefore, it is possible to reduce the gradation level of the high density part which does not significantly affect the gradation characteristic in the image, and appropriately set the gradation level of the low density part which is important in the gradation characteristic. Good images can be obtained at low cost even with a small number of tones.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a main configuration of an ink jet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a circuit configuration of a control system of the inkjet recording apparatus according to the embodiment of the present invention.

FIG. 3 is a perspective view illustrating a schematic configuration of a recording head according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a recording operation by a recording head according to one embodiment of the present invention.

FIG. 5 is a graph showing a relationship between an ink volume per pixel and a reflection density in the embodiment of the present invention.

FIG. 6 is a perspective view illustrating a schematic configuration of a recording head according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording head 2 Substrate 3 Base 4 Flexible cable 5 Carriage 7 Timing belt 9 Guide rail 11 Recording material 13 Platen roller 21 Main controller 25 Frame memory 35 Driver controller 37 Head driver 101 5pl ejection port group 102 8pl ejection port group 103 outlet group for 11 pl 111 outlet group for 5 pl 112 outlet group for 14 pl

Claims (3)

(57) [Claims] 1. An ink jet recording method for forming a gradation image using an ink jet recording head having a plurality of ink ejection ports, wherein droplets ejected from different ejection ports in a plurality of scans according to a gradation level. And landed on substantially the same location on the recording material to form one pixel, and the density of each pixel recorded on the recording material is substantially the same between the gradation levels. An ink jet recording method, wherein the volume of droplets discharged from at least one of the different discharge ports is set to be different from the volume of droplets discharged from other discharge ports. 2. The ink jet recording apparatus according to claim 1, wherein the plurality of ink ejection ports are arranged in a direction substantially perpendicular to a scanning direction of the ink jet recording head, and a droplet having a large volume in a droplet group ejected from the ink ejection ports. 2. The ink jet recording method according to claim 1, wherein the ink is ejected so as to be overprinted with a small volume droplet. 3. The ink jet recording head according to claim 1, further comprising an electrothermal transducer for applying heat energy for causing the liquid droplets to generate film boiling, as an element for generating energy for discharging the liquid droplets. The inkjet recording method according to claim 1 or 2, wherein