JPH04361055A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To materialize an ink jet recording method capable of providing clear images in excellent gradation at low cost without decreasing recording speed. CONSTITUTION:A number of ejection port groups 101, 102, 103 ejecting ink droplets in different volumes are arranged on a recording head 1 along the vertical scanning direction intersecting at a right angle to the direction in which the recording head moves for scanning. The ink droplets in different volumes are ejected by scannings executed in a number of times and are shot in overlaying approxi-mately onto the same spot for formation of one pixel, and thereby gradation density is expressed in halftone image. The volumes of the ink droplets to be ejected are determined, for instance, to be 5p1, 8p1, 11p1 so that the gradation level for each of the pixels whereon the shooting in overlaying is executed can be set approximately at equal intervals, and then the shooting in overlaying is made so that the ink droplet in larger volume comes without fail over the ink droplet in smaller volume.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an inkjet recording method for recording monochrome or color images using an inkjet recording head having a plurality of ink ejection ports, and in particular, the present invention relates to an inkjet recording method for recording monochrome or color images using an inkjet recording head having a plurality of ink ejection ports. The present invention relates to an inkjet recording method in which a single pixel is formed by landing on substantially the same location on a recording material to form a clear image with excellent gradation.

0002

[Prior 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 achieved by varying the number of ink droplets that land. A so-called multi-droplet method has been developed to express This multi-droplet method is expected to be extremely effective as a method for obtaining high-density and high-gradation images, especially in inkjet recording where it is difficult to greatly modulate the size of a single ink droplet itself.

However, in the conventional multi-droplet method, one pixel is formed by multiple ink droplets ejected from one ink ejection port during one scan, so the volume of ink droplets for each ejection port varies. If this is the case, there is a problem in that streaks or density unevenness (spots) occur in images that should originally be uniform.

[0004] In order to avoid these problems, in the conventional multi-droplet method, the recording head must be manufactured with great precision in order to minimize variations in the volume of the ejected ink droplets between the ejection ports. As a result, there have been problems such as increased manufacturing cost and poor manufacturing yield. In addition, as a software-based method to eliminate density unevenness, we have proposed a method that uses image processing such as error diffusion to change the number of ink droplets to be ejected so as to more or less cancel out the volume of ink droplets between the ejection ports. However, there is a problem in that incorporating such image processing increases the production cost of the system. Furthermore, even if such an image processing method is used, it is necessary to readjust the number of ejected ink droplets when the dispersion of ink droplet volume between ejection ports changes over time, resulting in the problem of poor maintainability. had.

[0005]

[Problem to be solved by the invention] U.S. Patent No. 4,746
, No. 935 proposes a multi-tone inkjet printer that expresses gradation by combining a plurality of ink droplets with different liquid volumes of 1 pl (picoliter), 2 pl, and 4 pl for each pixel. According to this proposal, the pair ratios are 0, 1, 2, 1+2 (=3), 4, 1+4 (=5
), 2 + 4 (= 6), 1 + 2 + 4 (= 7), eight types of ink droplet volumes can be obtained by stacking three ink droplets, and printing speed is improved compared to the method of stacking one ink droplet seven times. ing. 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 steep rise. Therefore, even if the possible values of the total volume of ink droplets forming one pixel are set at equal intervals, the corresponding possible values of the reflection density are not equally spaced. Therefore, in areas where the volume of ink droplets forming one pixel is small, the interval between possible values of reflection density becomes wide, and in areas where the volume of ink droplets forming one pixel is large, the interval between possible values of reflection density becomes wider. becomes narrower. In other words, the size of the ink droplet volume in a region where the volume of ink droplets forming one pixel is large is as follows:
It does not contribute much to the gradation. In addition, since there are many combinations of ink droplets that form one pixel (eight types in the case of 1 pl, 2 pl, and 4 pl), the image processing circuit becomes complicated, which significantly increases design and manufacturing costs. .

Furthermore, another problem with the invention disclosed in the above-mentioned US patent publication is that the volume of the ejected ink droplets differs by four times, 1 pl vs. 4 pl (or 8 times, 1 pl vs. 8 pl). The head structure has to be built into the same recording head, which is a very big problem and makes it difficult to manufacture the recording head. in general,
Recording head parameters for changing the volume of ink droplets to be ejected include the distance between heater ejection ports, the size of the heater, the shape of the ejection ports or the shape of the barrier, and the area of the ejection ports. In order to change the volume of the ink droplet to be ejected from 1 to 4, it is essential to change the distance between the heater ejection ports, the heater area, and the ejection port area, which is difficult to manufacture using only conventional manufacturing processes. Therefore, in order to actually achieve this, it is necessary to add a new manufacturing process, and the manufacturing cost of the recording head becomes considerably high.

Moreover, in the invention disclosed in the above-mentioned US patent publication, a series of ink ejection ports each having a different volume of ejected ink, such as 1 pl, 2 pl, 3 pl, and 4 pl, are arranged along the main scanning direction in which the recording head reciprocates. The ink droplets are arranged close to each other on the front surface of the recording head, and are configured to eject multiple ink droplets to the target pixel in one main scan. penetration,
Ink droplets overlap one after another while almost no fixing is performed, and as a result, in image areas where there are a large number of overlapping droplets on the recording material, droplets of adjacent pixels come into contact with each other, causing the image to deteriorate. Smearing is likely to occur, which impairs the clarity of text, etc. In addition, in color images, the outline of the image becomes blurred due to smearing due to color mixing of ink before fixing, especially at the boundaries of monochromatic areas, which significantly reduces the recording quality. There were serious issues that needed to be resolved.

The present invention has been made to solve the above-mentioned problems of the prior art, and provides a method that is relatively inexpensive, has excellent gradation, and does not reduce the recording speed. The object of the present invention is to provide an inkjet recording method that can produce clear images.

[0009]

Means for Solving the Problems In order to achieve the above object, the present invention utilizes an inkjet recording head having a plurality of ink ejection orifices so that a plurality of droplets having different amounts of liquid are applied to the recording head in a plurality of scans. The particles land on substantially the same location on the recording material to form one pixel, and the gradation levels per pixel recorded on the recording material are approximately equally spaced;
It is characterized in that the volume ratio of the droplets is set respectively.

Further, in 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 inkjet recording head, and a group of droplets ejected from the ink ejection ports is arranged. A droplet having a large volume may be output so as to be overlaid with a droplet having a small volume.

[0011]Furthermore, the present invention has another form,
The inkjet recording head may be characterized by having an electrothermal transducer for applying thermal energy to cause film boiling on the droplets, as an element that generates energy for ejecting the droplets. .

0012

[Operation] In the present invention, since ink droplets are overlaid on one pixel by multiple scans, the ink that landed first permeates and fixes with the ejection of ink droplets for each scan. Since the ink dries almost completely, there is no ink bleeding, color mixing, blurring of the image outline, etc., and as a result, a clear image with excellent gradation can be obtained.

Furthermore, in the present invention, the ejection port groups are arranged in different scanning directions, and one pixel is formed by overlapping ink droplets from a series of ejection port groups, each having a different volume of ejected ink droplets. The number of scans required to form one pixel is reduced, and image quality in high-density areas as well as in highlight areas can be improved with almost no reduction in recording speed.

Furthermore, in the present invention, the volume ratio of the ejected ink droplets is appropriately set so that the gradation levels per overprinted pixel are approximately equally spaced, and the ink droplets with a large volume are replaced with the ink with a small volume. Since the ejected ink droplets are always overlapped, the volume ratio of the largest ink droplet to the smallest ink droplet can be made relatively small, and the number of combinations of ink droplets has been halved compared to conventional methods, making it easier to select ejection ports. Image signal processing is also facilitated, and as a result, a good halftone image can be obtained at a relatively low cost without increasing the manufacturing costs of the head and main body device.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, the recording method that is the premise of the present invention will be explained. By scanning multiple times to form one pixel with ink droplets ejected from multiple ink ejection ports, this reduces variations in the volume of ink droplets ejected from the ejection ports, thereby reducing streaks and This is a recording method that is less likely to cause unevenness (hereinafter referred to as the multi-scan method).

[0017] It has been confirmed that this multi-scan method improves the deterioration of image quality due to streaks and unevenness and provides clear images. However, although the introduction of such a multi-scan method improves image quality,
A further problem to be solved was that the printing time increased. This point will be explained below.

Generally speaking, the smaller the volume of each ink droplet constituting one pixel, the harder it becomes to see the graininess in the highlight area of the image.
Image quality in highlight areas is improved. but,
As the volume of the ink droplets decreases, the reflection density on the paper (recording material) decreases, so in order to improve the image quality in high-density areas of the image, it is necessary to overlap many ink droplets on the same pixel. In this way, overlapping a large number of ink droplets on the same pixel means an increase in the number of scans for a single pixel format, so it is possible to improve the image quality in highlight areas and at the same time improve the image quality in high density areas. This would significantly increase printing time. On the other hand, when one pixel is formed by overlapping a maximum of about three ink droplets, it is difficult to improve the image quality in the highlight area.

By the way, the frequency fkHz that forms one pixel in the binary recording method using only "0" and "1" (in the binary recording method, the frequency that forms one pixel and the frequency that ejects ink droplets are the same) ), then in order to obtain the same printing speed as the binary recording method using the multi-scan method in which a maximum of n ink droplets are overlapped on the same pixel, a frequency of at least f x n kHz for ejecting ink droplets is required. It is said that However, even though the volume of one ink droplet is smaller than that in binary recording, there are still many practical technical problems in increasing the recording head drive frequency by n times. The larger the number, the more difficult it is to achieve.

FIG. 1 schematically shows the main structure of a serial type ink jet recording apparatus according to an embodiment of the present invention. Reference numeral 1 denotes an inkjet recording head that ejects ink droplets in response to an input signal (drive signal) supplied through a flexible cable 4, and it prints a series of ink droplets with different ejected ink droplet volumes as shown in FIG. 3 or FIG. 6, which will be described later. It has a discharge port. The head 1 is mounted and fixed on a carriage 5, and is reciprocated in a horizontal main scanning direction along a pair of guide rails 9 by driving a carriage feed motor (see FIG. 2), which will be 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 ejecting ink droplets from each of the ejection ports (to be described later) toward the recording material 11 (generally paper). The recording material 11 is wound around a platen roller 13, and driven by a paper feed motor (see FIG. 2), which will be described later, which rotates the platen roller 11, the recording material 11 is moved at a predetermined pitch in a sub-scanning direction perpendicular to the main scanning direction. Sent.

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

(First Embodiment) FIG. 3 shows a schematic structure of the head 1 in one embodiment of the present invention. In order to simplify the explanation, the ejection ports in the figure are shown as three types of ejection port groups 101, 102, and 103, which are obtained by dividing a series of ejection ports into three groups of four ejection ports each. 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 (picoliters),
The second ejection port group 102 is 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 outlet group 103 is 11
This is a group of a series of ejection ports (ejection port numbers 9 to 12) each designed to eject an ink droplet with a volume of pl. These ejection groups 101 to 103 are arranged in a line along the vertical direction of the head 1, that is, the sub-scanning direction that is substantially perpendicular to the main-scanning direction in which the head 1 reciprocates. The head 1 consists of a substrate 2 and a base 3, and the ejection ports are opened on the surface of the substrate 2 facing the recording material 11. By the way, in order to manufacture the head 1 at a low cost, it is necessary to be able to use the conventional manufacturing process almost as is.
The following are desirable. The maximum ink droplet in this example is 11 pl, and the minimum ink droplet is 5 pl, so the volume ratio is 2.2, which satisfies the above conditions, and in this respect, the head
can be manufactured relatively inexpensively.

FIG. 4 shows the printing state in this embodiment. The large square outer frame in the figure is a recording material 11 that is printed by multiple scans of the carriage 5 (hereinafter referred to as scans).
The entire recording area is shown. Five recording areas (A,
B, C, D, and E) correspond to each ejection port group that ejects the three types of ink droplet volumes described above, and the width in the vertical direction corresponds to the amount of one feeding of the recording material 11. are doing. In the first scan, the ejection ports with ejection port numbers 1 to 4 (
101) to eject 5 pl ink droplets onto the most advanced area A according to the gradation of the image data (gradation data) to print dots. Next, the recording material 11 is sent upward in FIG. 4 by 63.5 μm (ejection port pitch)×4 (number of ejection ports)=254 μm, and a second scan is started.

In the second scan, from the ejection ports (101) of ejection port numbers 1 to 4 that have moved to the next area B, 5 pl is emitted according to the gradation of the image data, as in the first scan.
Ink droplets are ejected to print dots. At the same time, ink droplets of 8 pl are ejected from the ejection ports (102) with ejection port numbers 5 to 8 that have moved to area A to the image of area A printed in the first scan according to the gradation of the image data. The ink droplets are piled up. At this time, the 8 pl ink droplet is not applied to a location where the 5 pl ink droplet was not applied during the first scan. After the second scan is completed, the recording material 11 is fed in the direction shown in FIG. 4 by the same distance of 254 μm as described above, and a third scan is started.

In the third scan, ink is ejected from the ejection ports (101) with ejection port numbers 1 to 4 that have moved onto the third area C and from the ejection ports (102) with ejection port numbers 5 to 8 that have moved to area B. Droplets are ejected and printing is performed in the same manner as in the second scan. Discharge port numbers 9 to 1 that moved to area A at the same time
Printing is performed by ejecting ink droplets with an ink droplet volume of 11 pl from the second ejection port (103) according to the image data. At this time as well, the 11 pl ink droplet is not applied to areas where the 5 pl and 8 pl ink droplets are not applied in the first and second scans.

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

By sequentially repeating the fourth scan and fifth scan in the same manner as above, dot printing is performed on the recording material 11 according to the gradation of the image data, and the recording state of area A is changed to the recording material 11. It spreads over the entire area to be recorded on the material 11, and the ejection ports numbered 8 to 12 of the head 1 (10
3) reaches area E and printing is performed, this recording work ends.

In this embodiment, a configuration is adopted in which a block is formed for a series of ejection ports each having a different volume of ink droplets. It goes without saying that the recording effect will be the same even if they are arranged adjacent to each other alternately.

FIG. 5 shows the relationship between the ink volume per pixel of a recorded image printed on the recording material 11 as explained in FIG. 4 and its reflection density. In this embodiment shown in FIGS. 3 and 4, the reflection density is 0.05 at the 0th level without ink (the reflection density of the paper itself, which is the recording material 11), and the first level (I) with an ink amount of 5 pl.
The reflection density is 0.47, 1.02 at the second level (II) with an ink amount of 13 pl, and 1.38 at the third level (III) with an ink amount of 24 pl. This means that, compared to the conventional multi-scan method and the method proposed in US Pat. It shows. In addition, the reflection density at the first level (I) is 0.47, which is almost the same as the value obtained by the conventional multi-scan method of stacking up to 5 ink droplets per pixel (although , if the maximum values of reflection densities in the images are equal). Therefore, the image obtained in this embodiment has a density level that is comparable to that of an image printed by overlapping up to five ink droplets per pixel using the conventional multi-scan method. Furthermore, in terms of printing speed, in this embodiment, a maximum of three ink droplets need to be overlapped per pixel, so it is possible to reduce the printing time by about 20%.

Note that the above image data (gradation data) in this embodiment is obtained by performing processing such as logarithmic conversion and γ correction on the data obtained by reading the original image with a Morocross scanner, 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 in another embodiment of the present invention. The series of outlets in this embodiment is divided into two outlet groups 111 and 112,
The ejection ports 111 and 112 are designed to eject ink droplets of 5 pl and 14 pl, respectively. The number of ejection ports is 8 ejection ports that eject 5 pl ink droplets forming the first ejection port group 111, and 4 ejection ports that eject 14 pl ink droplets forming the second ejection port group 112. be. This head 1 is mounted on the carriage 5 of the serial printer shown in FIG. 1 in the same way as the first embodiment shown in FIG.
As shown in FIG. 4, the recording scan is performed to print a halftone image corresponding to the image data on the recording material 11.

Next, the operation of this embodiment will be explained with reference to FIG. First, in the first scan, the ejection port numbers 1 to 4 are
Using the ejection port (111), 5 pl ink droplets are landed on the pixel positions in area A where 24 pl/pixel and 10 pl/pixel ink droplets are to be overlapped, and 5 pl/pixel ink droplets are simultaneously applied.
Ink droplets of 5 pl are landed on approximately 50% of the pixel positions of pl/pixel. Next, the recording material 11 is sent upward in FIG. 4 by 254 μm, and a second scan is started.

In the second scan, printing is performed by ejecting ink droplets from the ejection ports (111) of ejection port numbers 1 to 4 that have moved to area B in the same manner as in the first scan. At the same time, the discharge ports with discharge port numbers 5 to 8 (11
From 1), printing is performed by ejecting ink droplets to the pixel positions of 5 pl/pixel that were left unprinted by the ejection ports numbered 1 to 4 in the first scan, and 24 pl/pixel and 1
Printing is also performed by landing 5 pl ink droplets from the ejection ports numbered 5 to 8 on pixel positions where ink droplets of 0 pl/pixel are to be overlapped. Then, the recording material 11 is moved upward 2 in FIG.
Move by 54 μm and start the third scan.

In the third scan, the ejection ports numbered 1 to 4 and 5 to 8 (
111), printing is performed by ejecting 5 pl ink droplets as in the second scan. At the same time, from the ejection ports (112) with ejection port numbers 9 to 12 that have moved relative to area A, 14 pl ink droplets are ejected only at pixel positions where 24 pl/pixel ink droplets should be overlapped according to the image data. and then layer them on top of each other.

At the stage when this third scan is completed, in area A, 0 per pixel is generated due to overlapping ink droplets.
4 of pl (without ink), 5pl, 10pl, 24pl
The printing of the seed ink droplet amount is completed. In addition, in area B, ink droplets of 0 pl, 5 pl, and 10 pl are overprinted per pixel, and in area C, 0 pl, 5 pl ink droplets are printed over each pixel.
l ink drops are printed per pixel.

[0036] In the fourth and fifth scans, printing is performed sequentially in the same manner as described above, and when the state of area A reaches all of the areas to be recorded, the printing operation is completed. Note that in this example, the ink volume per pixel is 0 pl, 5 pl, and 10 p.
l, 24pl, so as can be seen from Figure 5, the first
An image with substantially the same quality as in the example is obtained.

In particular, in this embodiment, the first
An ejection port group for ejecting ink droplets (ejection port numbers 1 to 4) and an ejection port group for ejecting second ink droplets (ejection port numbers 5 to 8)
) are used selectively (e.g. randomly). This is to reduce density unevenness in the ejection port array direction that occurs due to variations in head manufacturing. That is, in a pixel area of 5 pl/pixel, printing is performed using only ink droplets ejected from a single ejection port per pixel. Therefore,
When printing is performed using only the first ink droplet for all pixels of 5 pl/pixel, unevenness may become noticeable depending on the image. In this embodiment, the reason why the first ink droplet and the second ink droplet form 5 pl/pixel is to eliminate the unevenness. Therefore, according to this embodiment, it is possible to provide an image with no density unevenness and excellent gradation as described above.

Note that in both Examples 1 and 2, the ejection opening group with a small ejection volume is located below the head, and when recording droplets with a large ejection volume and small droplets overlapping, the droplets with a small ejection volume are However, the order in which droplets with different ejection volumes are recorded is not limited to this, and the order in which the ejection port groups are arranged may be different, for example, even if the ejection port with a large ejection volume is located below the head. good.

It goes without saying that the present invention can also be applied to color inkjet recording.

(Others) The present invention is particularly applicable to inkjet recording systems, in which means for generating thermal energy as the energy used to eject ink (
For example, the present invention provides an excellent effect in a recording head or recording apparatus that is equipped with an electrothermal converter (for example, an electrothermal converter, a laser beam, etc.) and uses the thermal energy to cause a change in the state of the ink. This is because such a system can achieve higher recording density and higher definition.

For its typical configuration and principle, see, for example, US Pat. Nos. 4,723,129 and 4,740.
Preferably, it is carried out using the basic principles disclosed in the '796 specification. This method is the so-called on-demand type.
It can be applied to any continuous type, but in particular, in the case of an on-demand type, it is applicable to the electrothermal converter placed corresponding to the sheet holding the liquid (ink) or the liquid path. , by applying at least one drive signal that corresponds to recorded information and provides a rapid temperature rise exceeding nucleate boiling, the electrothermal transducer generates thermal energy to produce film boiling on the thermally active surface of the recording head. As a result, liquid (ink) is generated in one-to-one correspondence with this drive signal.
This is effective because air bubbles can be formed inside. Due to the process of growth and contraction of the bubbles, liquid (ink) is ejected through the ejection opening (ejection port) to form at least one droplet. It is more preferable to use this drive signal in a pulse form, since the growth and contraction of bubbles can be carried out immediately and appropriately, making it possible to eject liquid (ink) with particularly excellent responsiveness. As this pulse-shaped drive signal, US Pat. No. 4,463,359
Suitable materials are those described in No. 4,345,262. Furthermore, if the conditions described in US Pat. No. 4,313,124 concerning the invention regarding the temperature increase rate of the heat acting surface are adopted, even more excellent recording can be performed.

[0042] In addition to the configuration of the recording head that combines ejection ports, liquid paths, and electrothermal converters (straight liquid flow path or right-angled liquid flow path) as disclosed in the above-mentioned specifications, U.S. Pat. No. 4,558,333 and U.S. Pat. No. 44 disclose a configuration in which a heat acting part is arranged in a bending region.
A configuration using the specification of No. 59600 is also included in the present invention. In addition, JP-A-59-123670 discloses a configuration in which a plurality of electrothermal transducers have a discharge section having a common slit as a discharge opening, and a hole absorbing pressure wave of thermal energy is disclosed. The effects of the present invention are also effective even with a configuration based on Japanese Patent Application Laid-Open No. 138461/1983, which discloses a configuration in which a discharge portion is provided corresponding to a discharge portion. That is, regardless of the form of the recording head, according to the present invention, recording can be performed reliably and efficiently.

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

Further, it is preferable to add ejection recovery means for the recording head, preliminary auxiliary means, etc. to the configuration of the recording apparatus of the present invention, since this further stabilizes the effects of the present invention. Specifically, these include capping means, cleaning means, pressure or suction means for the recording head, electrothermal transducers that generate thermal energy to eject ink droplets necessary for recording, and Preheating means that performs preheating using a different heating element or a combination thereof, and preliminary ejection means that performs ejection other than recording.

Regarding the type and number of recording heads to be mounted, for example, in addition to a single head that corresponds to a single color ink, there are also systems that correspond to a plurality of inks of different recording colors and densities. A plurality of them may be provided. That is, for example, the recording mode of the recording apparatus is not limited to a recording mode for only a mainstream color such as black, but may also be a recording mode in which the recording head is configured integrally or in a combination of multiple colors, Alternatively, the present invention is extremely effective for an apparatus equipped with at least one of the full-color recording modes using color mixing.

[0046] Furthermore, the ejection port array is not limited to one row, but may be configured to have a plurality of rows (for example, one row has 20 ejection ports, and four rows of these are arranged).

In addition, in the embodiments of the present invention described above, the ink is described as a liquid, but even if the ink solidifies at room temperature or lower, it may be softened or liquefied at room temperature. , can be liquefied and used during recording, so it can be used in the present invention. Alternatively, in the inkjet method, in some cases, the temperature is adjusted so that the ink itself is kept within a range of 30° C. to 70° C., and the temperature is controlled so that the viscosity of the ink is within a stable ejection range. In this case 30℃
An ink that becomes liquid at temperatures above 70° C. or below can be used. In addition, in order to actively prevent the temperature of the ink itself from rising due to thermal energy by using the energy to change the state of the ink from a solid state to a liquid state, or to prevent the ink from evaporating, it is first liquefied by heating. You may also use ink. In any case, by applying thermal energy in accordance with the recording signal, the ink is liquefied and the liquid ink is ejected, or the ink has already begun to solidify by the time it reaches the recording medium. The present invention is also applicable when using ink that is liquefied for the first time. The ink in this case is
JP-A-54-56847 or JP-A-60-7
The material may be used for recording while being held as a liquid or solid material in the recesses or through holes of a porous sheet, as described in Japanese Patent No. 1260. In the present invention, the most effective method for each of the above-mentioned inks is to perform the above-mentioned method of causing film boiling.

In addition, the inkjet recording device according to the present invention can be used as an image output terminal for information processing equipment such as a computer, a copying device combined with a reader, etc., and a facsimile machine having a sending/receiving function. It may also take the form of a device.

[0049]

[Effects of the Invention] As explained above, according to the present invention,
Since ink droplets are overlaid on one pixel by multiple scans, the ink that landed first permeates and fixes with each ink droplet ejected for each scan, and dries almost completely. This eliminates bleeding, color mixing, blurring of image outlines, etc., and as a result, a clear image with excellent gradation is obtained.

Furthermore, in the present invention, the ejection port groups are arranged in the sub-scanning direction, and one pixel is formed by overlapping ink droplets from a series of ejection port groups each having a different volume. The number of scans required to form one pixel is reduced, and image quality in high-density areas as well as in highlight areas can be improved with almost no reduction in recording speed.

Furthermore, in the present invention, the volume ratio of ejected ink droplets is appropriately set so that the gradation levels per overprinted pixel are approximately equal intervals, and ink droplets with a large volume are replaced with ink with a small volume. Since the droplets are always overprinted, the volume ratio of the largest and smallest ink droplets can be made relatively small, and the number of combinations of ink droplets has been halved compared to conventional methods, making it easier to select the ejection port. Image signal processing is also facilitated, and as a result, a good halftone image can be obtained at a relatively low cost without increasing the manufacturing costs of the head and main unit.

Furthermore, in the present invention, a plurality of ejection port groups (two in the embodiment) for ejecting ink droplets of minimum volume are provided.
By dividing the ink droplet into two groups and using both of the divided ejection port groups selectively, for example, alternately in adjacent pixels, for a pixel in which one pixel is formed by one ink droplet with the minimum volume, it is possible to improve head fabrication. It is possible to reduce density unevenness in the direction of the ejection port array caused by variations or the like.

Furthermore, according to the present invention, the volume of the ink droplet used in the low density region can be made smaller than the average volume of n ink droplets ejected from n different ejection ports forming one pixel. From this, it is possible to reduce the gradation level of the high-density part of the image, which does not have much influence on the gradation characteristics, and to appropriately set the gradation level of the low-density part, which is important for the gradation characteristic, so that the gradation level per pixel can be reduced. Good images can be obtained at low cost even with a small number of keys.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the main part configuration of an inkjet recording apparatus according to an embodiment of the present invention.

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

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

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

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

FIG. 6 is a perspective view showing a schematic configuration of a recording head in another embodiment of the present invention.

[Explanation of symbols]

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

Claims (3)

[Claims] [Claim 1] Using an inkjet recording head having a plurality of ink ejection ports, a plurality of droplets each having a different amount of liquid are landed on substantially the same location on a recording material in a plurality of scans to form one pixel. An inkjet recording method, characterized in that the volume ratios of the droplets are set so that the gradation levels per pixel recorded on the recording material are approximately equally spaced. 2. 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 droplet having a large volume among a group of droplets ejected from the ink ejection ports. 2. The inkjet recording method according to claim 1, wherein the inkjet recording method is outputted so as to be overlaid with a droplet having a small volume. 3. The inkjet recording head includes, as an element that generates energy for ejecting the droplets,
3. The inkjet recording method according to claim 1, further comprising an electrothermal converter for applying thermal energy to cause film boiling on the droplet.