JPH10193649A - Method and apparatus for ink jet printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimally print with high gradability or in response to recording density without complicating a discharge mechanism or a control system by controlling a driving pulse to a printing element in response to an image signal, an altering number of secondary droplets separated from ink droplet after discharging. SOLUTION: To record, a record signal, i.e., an electric signal is applied as a driving pulse for discharging ink from a discharge signal generating means from a board to a heater of a head. When a method for applying the pulse to be applied to the heater in an ink channel is altered, shot dot area becomes an area obtained by adding dots formed of main droplets Da, Db (including Db-1, Db-2, Db-3), and shot dot Db of secondary droplet is introduced within the dot Da of main droplet to become total area of them. Accordingly, applying condition of the pulse signal is altered in response to gradation information of the input image signal to control ink amount to be discharged and number of secondary droplets, and dot area per one pixel can be altered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printing method and apparatus for printing by attaching ejected ink droplets to a printing medium such as paper, and more particularly, to printing with gradation and recording density. The present invention relates to an ink jet printing method and apparatus capable of performing optimal printing according to, for example, the present invention.

[0002]

2. Description of the Related Art An ink jet printing apparatus is a non-impact recording method, so that it is excellent in quietness at the time of recording, and is capable of high-speed recording and obtains a highly saturated color image. I am collecting.

[0003] Among the ink jet printing apparatuses, a printing apparatus using a printing element which discharges ink from an ink discharge port by causing film boiling of ink by using thermal energy is compact and multi-office. There is an advantage that high density offices can be achieved.

As described above, the ink-jet printing apparatus utilizing thermal energy has many advantages. However, when a high-resolution and high-quality image is to be recorded, a gradation property is required for the recording pixels. It is desirable to perform image recording including halftone (halftone) information.

Conventionally, as a method of gradation expression used in an ink jet printing apparatus, a plurality of types of inks corresponding to each of a plurality of ejection ports are ejected in accordance with the tone information of an image signal, and formed by using them. Overlapping the dots on the print medium to be printed, or
A method of providing a plurality of heaters forming a print element in one discharge port and controlling the drive timing of the heaters has been adopted, and the gradation has been expressed by these methods.

[0006]

However, in the above-described conventional example, a plurality of inks, ink supply systems, drive circuit systems, and the like are required to express the gradation of one pixel.
As a result, there has been a problem that the device configuration is complicated and the manufacturing cost is relatively high.

[0007] The object of the present invention is to solve these problems,
Provided is an ink jet printing method and apparatus capable of performing printing with high gradation and optimum printing according to recording density without increasing the complexity of an ink ejection mechanism and a control system and increasing manufacturing costs. It is in.

[0008]

According to a first aspect of the ink jet printing method of the present invention, an ink droplet for printing an image on a printing medium is ejected from a discharge port by applying a driving pulse to a printing element. In the inkjet printing method for ejecting, the number of sub-droplets separated from the ejected ink droplet is changed by controlling the driving pulse according to an image signal.

A second embodiment of the ink jet printing method according to the present invention is directed to an ink jet printing method in which a drive pulse is applied to a printing element to discharge ink droplets for printing an image on a printing medium from a discharge port. Controlling the drive pulse in accordance with an image signal to vary the area of the landing dot formed on the print medium by the main droplet and the sub droplet separated from the ink droplet after ejection. A first aspect of the inkjet printing apparatus of the present invention is
By applying a drive pulse to the print element,
In an ink jet printing apparatus that prints an image on a print target medium by using a print head capable of discharging ink droplets divided into main droplets and sub-droplets from discharge ports, by controlling the drive pulse according to an image signal, The ink jet recording apparatus further comprises control means capable of changing the number of the sub-droplets from which the ink drops after ejection are separated.

In a second embodiment of the ink jet printing apparatus according to the present invention, an image is printed on a printing medium by using a print head capable of discharging ink droplets from a discharge port by applying a driving pulse to a printing element. In the inkjet printing apparatus, by controlling the driving pulse according to an image signal, it is possible to change an area of a dot formed on the print medium by a main drop and a sub drop separated from the ink drop. A control means is provided.

In the present invention, by controlling the drive pulse applied to the print element according to the image signal, the number of sub-droplets can be reduced when the ink drops are divided into main drops and sub-droplets from the discharge ports. Alternatively, the dot area on the print medium formed by the main droplet and the sub-droplet is changed to realize printing of an image with high gradation and optimum printing corresponding to the recording density.

[0012] Thus, for example, per pixel, a small and simple unit using a single ejection port, a single recording element such as a heater, a single ink supply system, and a single drive circuit system. According to the configuration, the area of dots per pixel is controlled, and printing with high gradation can be reliably performed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a perspective view of an essential part of an ink jet printing apparatus of the present invention in which an ink jet print head is incorporated, FIG. 2 is a sectional view of the ink jet print head, and FIG. It is a perspective view of a head.

In FIG. 1, reference numeral 1 denotes an integrated ink jet print head in which an ink jet head and an ink tank are integrated, and can be mounted on a carriage 5 which reciprocates in a main scanning direction along a guide rod 10. I have. Reference numeral 2 denotes a cap used for a suction recovery process for sucking ink from the ink discharge port 8 of the head 1 (see FIG. 2) and capping for preventing the head 1 from drying, and 3 denotes a recovery pump communicating with the cap 2. . Reference numeral 4 denotes an electric wiring section, which supplies an ink ejection signal to a heater 6 serving as a print element for applying thermal energy to ink in an ink flow path (see FIG. 2) communicating with the ejection port 8 of the head 1. A flexible printed circuit board (hereinafter, referred to as "FPC") for applying an electric signal as a driving pulse from the generating means.

In order to perform recording using this printing apparatus, a recording signal, that is, an electric signal as a driving pulse for ink ejection from an ejection signal generating means is applied from the FPC 4 to the heater 6 of the head 1 via an electrode. . As a result, the heater 6 generates heat, and the heat energy is applied to the ink existing in the ink flow path 7 near the heater 6. As described above, when the thermal energy is applied to the ink from the heater 6, bubbles are generated in the ink with an instantaneous increase in the volume of the ink in that portion. As a result, ink existing downstream of the heater 6 is ejected from the ejection port 8 as droplets. Head 1
The ink droplets which move in the main scanning direction together with the carriage 5 and which are ejected from the ejection ports 8 are caused to land on and adhere to a recording material as a printing medium such as paper sent to the front of the print head 1. The desired image is recorded.

FIG. 8 is a block diagram showing a configuration of a control system of the ink jet printing apparatus shown in FIG.

In FIG. 8, a CPU 100 executes control processing, data processing, and the like for each operation unit in the apparatus. The processing procedure and the like are stored in the ROM 100A.
RAM 100B is used as a work area for executing the processing. Ink is ejected from the print head 1 by the CPU 100 supplying drive data and a drive control signal for the heater 6 as an electrothermal transducer to the head driver 1A. CPU1
00 controls the waveform of the drive pulse for the heater 6 as described later. Further, the CPU 100 controls a carriage motor 20 for moving the carriage 5 via a motor driver 20A, and feeds a paper for rotating a roller for conveying a recording material in a sub-scanning direction orthogonal to the main scanning direction. (PF) The motor 50 is controlled via the motor driver 50A.

FIG. 4A shows how an ink droplet flies when the method of applying an input pulse (drive pulse) applied to the heater 6 in the ink flow path 7 is changed by an experiment performed by the present inventor.
6 (a) to 6 (d), and FIG. 6 shows the discharge modes of FIGS. 4 (a) to 4 (d).
(C), (d) ”), the input pulse waveform, the ejection state, the ejection amount, and the landing dot area. Here, the landed dot area is the area of a dot formed by landing an ink droplet on a recording material,
The area is the sum of the dots formed by the main droplets D _a and D _b (including D _b−1 , D _b−2 and D _b−3 ) described later.
In this experiment, the driving frequency for driving the heater 6 to discharge ink from the discharge port 8 was 14 kHz,
The distance between the sheet and the recording material is 2 mm.

[0019] First, in the discharge mode (a), the input pulse width is 4.5Myusec, ink droplets ejected from the ejection port 8, as shown in FIG. 4 (a), the main droplet D _a and sub-droplets D _b
It was confirmed that the aircraft would fly separately. Ejection speed of the main droplet D _a is 9m / sec, the ejection speed of the sub-droplet D _b is 8.5m
/ A sec, impact point distance difference between the main droplet D _a and sub-droplets D _b on the recording material is 13 .mu.m. Dot area of the main droplet D _a at this time 4300μm ^2, the dot area of the sub-droplet D _b is 460 .mu.m ^2. FIG. 5A is a plan view of dots formed on the recording material by the ink droplets D _a and D _b . In FIGS. 5A to 5D, the same dots are formed by the main droplets _Da and _Db (including _Db-1 , _Db-2 , and _Db-3 described later). reference numeral, and a solid line in FIG. 5 (a) ~ (d) are those of the dot D _a, it represents the contour of the deposited dots total area of the D _b, the dotted line in 5 the figure, the dot D _a, representing the trace when the D _b has landed. The FIGS. 5 (a) As is apparent from, deposited dots D _b of the sub-droplet enters the dot D _a main droplet landing dot area of their total approximately to the area of the dots D _a of the main droplet It becomes the same 4300 μm ² .

Next, the input pulse in the ejection mode (a) is
As shown in FIG. 6B, a pre-heat pulse of 1.5 μsec, a rest time of 1.5 μsec, and a main pulse of 3.0 μsec, and the ink droplet ejected from the ejection port 8 is shown in FIG. 4B. it was confirmed that flies divided into a main droplet D _a and the sub-droplet D _b as. Ejection speed of the main droplet D _a is 10 m / sec, the ejection speed of the sub-droplet D _b is 8.5 m / s
an ec, impact point distance difference between the main droplet D _a and sub-droplets D _b on the recording material is 35 [mu] m. Dot area D _a of FIG. 5 (b) formed by the main droplets D _a at this time is 630
0 .mu.m ^2, the area of the dot D _b in FIG. 5 (b) formed by the sub-droplet D _b is 460 .mu.m ^2. This figure 5
As is clear from (b), the dot D _b of the sub-droplet enters almost main droplet in dots D _a of the landing dot area of their total approximately the same 6500 as the area of the dots D _a of the main droplet
μm ² .

The input pulse of the ejection mode (c) is shown in FIG.
(C) a preheat pulse of 1.5 μsec,
Downtime 3.0Myusec, made from the main pulse 3.0Myusec, ink droplets discharged from the discharge port 8, a main droplet D _a and two sub-droplet D _b-1, as shown in FIG. 4 (c), D
It was confirmed that it flew separately from _b-2 . Main drop D _a
Is 11.5 m / sec, the ejection speed of the sub _- drop D _b-1 is 9.0 m / sec, and the ejection speed of the sub _- drop D _b-2 is 8.5.
m / sec, the main droplet D _a and the sub droplet D on the recording material.
impact point distance difference between _b-1 is 48 [mu] m, the sub-droplet D _b-1 and sub-droplets D
The landing point distance difference from _b-2 is 13 μm. Figure 5 (c) dot D area _a is 5100Myuemu ² in which is formed by the main droplets D _a at this time, and FIG. 5 (c) in the dot D _b-1 that are formed by the sub-droplet D _b-1 area 3300μm ^2, the dot D in FIG. 5 (c) which is formed by the sub-droplet D _b-2
area _b-2 is 460 .mu.m ^2, landed dot area of their total becomes 7800μm ^2.

The input pulse of the ejection mode (d) is shown in FIG.
(D) a pre-heat pulse of 1.5 μsec,
Downtime 5.0Myusec, made from the main pulse 3.0Myusec, ink droplets discharged from the discharge port 8, a main droplet D _a and three sub-droplet D _b-1, as shown in FIG. 4 (d), D
It was confirmed that it flies separately into _b-2 and _Db-3 .
Ejection speed of the main droplet D _a is 15.5 m / sec, the sub-droplet D _b-1
Is 11.5 m / sec, the discharge speed of the sub _- drop Db _-2 is 9.0 m / sec, and the discharge speed of the sub _- drop Db _-3 is 8.5.
m / sec, the main droplet D _a and the sub droplet D on the recording material.
impact point distance difference between _b-1 is 44 .mu.m, the sub-droplet D _b-1 and sub-droplets D
impact point distance difference between _b-2 is 48 [mu] m, the sub-droplet D _b-2 and sub-droplets D
The landing point distance difference from _b-3 is 13 μm. Figure 5 (d) dot D area _a is 5100Myuemu ² in which is formed by the main droplets D _a at this time, FIG. 5 (d) in the dot D _b-1 that are formed by the sub-droplet D _b-1 area 3300μm ^2, the sub-droplet D dots D in FIG. 5 (d) which is formed by _{b-2 b-2}
The area of 2800μm ^2, the area of the sub-droplet D _b-3 in FIG. 5 (d) which is formed by dots D _b-3 is 460 .mu.m ²
And their total landing dot area is 9600
μm ² .

As described above, under the condition that the distance between the head 1 and the recording material is 2.0 mm and the driving frequency is 14 kHz, the ejection condition is changed by changing the application condition of the pulse signal applied to the heater 6. The amount of ink and the number of sub-droplets can be controlled, and the dot area per pixel can be changed.

Therefore, according to the method of this embodiment,
By changing the application condition of the pulse signal in accordance with the gradation information of the input image signal, the dot area per pixel can be controlled and gradation recording can be easily performed.

(Second Embodiment) This embodiment relates to the ink jet printing apparatus of the first embodiment,
When a pulse signal is applied to the heater 6 as the thermal energy generating means to eject ink droplets from the ejection port 8, the number of sub-droplets is changed by changing the application condition of the pulse signal according to the resolution of the recorded image. By controlling the amount of the sub-droplets and the amount of the sub-droplets, the dot area on the recording material formed by the main drops and the sub-droplets is changed, whereby the dot area per pixel is optimally obtained.

Specifically, 360 dpi and 720 dpi
The ink is ejected under the conditions as shown in FIGS. 7A and 7B according to each of the recording densities. In this experiment, the ink ejection frequency was 14 kHz, and the distance between the head 1 and the recording material was 2 mm.

FIG. 7A shows pulse signal application conditions when performing 720 dpi image recording.
This corresponds to the ejection mode (a) in (a). Thus, the input pulse width is 4.5Myusec, ink droplets discharged from the discharge port 8, it flies divided into a main droplet D _a and the sub-droplet D _b as shown in FIG. 4 (a) described above Was confirmed. Ejection speed of the main droplet D _a is 9m / sec, the ejection speed of the sub-droplet D _b is 8.5 m / sec, impact point distance difference between the main droplet D _a and sub-droplets D _b on the recording material 7 μm. At this time, the dot area of the main droplet D _a is 4300 μm ² , and the sub droplet D _b
Has a dot area of 460 μm ² . Accordingly, as shown in Fig. 5 described above (a), the dot D _b of the sub-droplet enters landed within the dots D _a main droplet landing dot area of their total approximately to the area of the dots D _a of the main droplet Same 4300μ
m ² .

FIG. 7 (b) shows the pulse signal application conditions when recording an image at 360 dpi.
This corresponds to the ejection mode (b) in (b). Therefore, the input pulse width is 1.5 μsec preheat pulse, 5.0 μsec.
μsec downtime, made from the main pulse 3.0Myusec, ink droplets ejected from the ejection port 8, the three and the main droplet D _a, as shown in FIG. 4 (b) described above sub-droplet D _b-1,
It was confirmed that it flies separately into D _b-2 and D _b-3 . Ejection speed of the main droplet D _a is 15.5 m / sec, sub-droplets D
The ejection speed of _b-1 is 11.5 m / sec, the ejection speed of sub _- drop D _b-2 is 9.0 m / sec, and the ejection speed of sub _- drop D _b-3 is 8.5 m / sec. impact point distance difference between the main droplet D _a and the sub-droplet D _b-1 in the above 44 .mu.m, the sub-droplet D _b-1 and the landing point distance difference between the sub-droplet D _b-2 is 48 [mu] m, sub-droplets D _b- The landing point distance difference between ₂ and the sub _- drop Db _-3 is 13 μm. At this time, the dot area of the main droplet D _a is 5100 μm ² , the dot area of the sub droplet D _b-1 is 3300 μm ² , the dot area of the sub droplet D _b-2 is 2800 μm ² , and the dot area of the sub droplet D _b-3 is 460μ
m ² . Therefore, as shown in FIG. 5B, the total area of the landing dots is 9600 μm.
It becomes ² .

As described above, the amount of ink to be ejected and the number of sub-droplets are controlled by changing the pulse signal application condition with the paper interval 2.0 mm and the ink ejection frequency being 14 kHz, so that the desired resolution is obtained. , It is possible to change the dot landing area per pixel.

Further, according to the ejection method of the present embodiment, it is possible to control the dot landing area per pixel according to the resolution of the recorded image, and to perform recording with the optimum dot landing area at each resolution. Become.

(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 performing ink ejection, particularly in an ink jet recording system. An excellent effect is obtained in a print head (hereinafter, also referred to as a "recording head") and a printing apparatus (hereinafter, also referred to as 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,
Although it can be applied to any type of continuous type, in particular, in the case of the on-demand type, it can be applied to a sheet holding liquid (ink) or an electrothermal converter arranged corresponding to the liquid path. By applying at least one drive signal corresponding to the recorded information and providing a rapid temperature rise exceeding nucleate boiling, heat energy is generated in the electrothermal transducer, and film boiling occurs on the heat acting surface of the recording head. Liquid (ink) corresponding to this drive signal on a one-to-one basis.
This is effective because air bubbles inside can be formed. The liquid (ink) is ejected through the ejection opening by the 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. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 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 (straight liquid flow path or right-angle liquid flow path) of the discharge port, liquid path, and 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 in which a common slit is used as a discharge portion of an electrothermal converter for a plurality of electrothermal converters. The effect of the present invention is effective even if the configuration is based on JP-A-59-138461, which discloses a configuration 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.

Further, the present invention can be effectively applied to a full-line type recording head having a length corresponding to the maximum width of a recording medium on which a recording apparatus can record. Such a recording head may have a configuration that satisfies the length by a combination of a plurality of recording heads, or a configuration as one integrally formed 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 or ink from the apparatus main body by being attached to 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. If these are specifically mentioned, the recording head is heated using capping means, cleaning means, pressurizing or suction means, an electrothermal transducer, another heating element or a combination thereof. Pre-heating means for performing the pre-heating and pre-discharging means for performing the discharging other than the recording can be used.

The type and number of recording heads to be mounted are, for example, not only one provided for single color ink, but also 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.

In addition, in the embodiments of the present invention described above, the ink is described as a liquid. However, an ink which solidifies at room temperature or lower and which softens or liquefies at room temperature may be used. In general, the ink jet method generally controls the temperature of the ink itself within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range. Sometimes, the ink may be in a liquid state. In addition, in order to positively prevent temperature rise due to thermal energy by using it as energy for changing the state of the ink from a solid state to a liquid state, or to prevent evaporation of the ink, the ink is solidified in a standing state and heated. 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
As described in Japanese Patent Publication No. 1260, it is also possible to adopt a form in which the sheet is opposed to the electrothermal converter in a state where it is held as a liquid or solid substance in the concave portion or through hole of the porous sheet. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

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

[0040]

As described above, according to the present invention, ink droplets are divided into main droplets and sub-droplets by controlling the driving pulse applied to the print element according to the image signal, and the ink droplets are discharged from the discharge ports. At this time, by changing the number of sub-droplets or the dot area on the print medium formed by the main drop and sub-droplet, it is possible to print an image with high gradation and an optimal print according to the recording density. Can be realized.

Accordingly, for example, a single discharge port, a single recording element such as a heater, a single ink supply system, and a single drive circuit system can be used for one pixel, and the size is small and simple. With the configuration, it is possible to control the area of the dots per pixel and to surely perform printing with high gradation.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of an inkjet printing apparatus as an embodiment of the present invention.

FIG. 2 is a sectional view of the print head shown in FIG.

FIG. 3 is a perspective view of the print head shown in FIG.

FIG. 4 is an explanatory diagram of a flying ink droplet when a drive pulse is changed in the first embodiment of the present invention.

FIG. 5 is a plan view of dots formed on a recording material by the ink droplets shown in FIG.

6 is an explanatory diagram of a driving pulse for forming the flying ink droplet shown in FIG.

FIG. 7 is an explanatory diagram of a driving pulse according to a second embodiment of the present invention.

FIG. 8 is a block diagram of a control system of the inkjet printing apparatus shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Print head 2 Cap 3 Recovery pump 4 Flexible printed circuit board 5 Carriage 6 Motor (electric heat conversion body) 7 Ink flow path 8 Discharge port

Claims (13)

[Claims] 1. An ink jet printing method in which an ink droplet for printing an image on a print medium is ejected from an ejection port by applying a drive pulse to a print element, wherein the drive pulse is controlled according to an image signal. A method of changing the number of sub-droplets separated from the ink drops after ejection. 2. An ink-jet printing method in which an ink droplet for printing an image on a print medium is ejected from an ejection port by applying a drive pulse to a print element, wherein the drive pulse is controlled according to an image signal. An ink jet printing method, wherein the area of the landing dots formed on the print medium is changed by the main droplet and the sub droplet separated from the ink droplet after ejection. 3. The ink jet printing method according to claim 1, wherein the driving pulse is controlled according to gradation information of an image signal. 4. The ink jet printing method according to claim 1, wherein a waveform of the driving pulse is controlled according to a recording density of an image on the print medium. 5. The method according to claim 5, wherein the position of the discharge port is moved, the ink droplet discharged from the discharge port is separated into a main drop and a sub-drop, and the discharge direction of the main drop and the sub-drop is changed. 5. The ink jet printing method according to claim 1, wherein the center positions of the main droplet dots and the sub droplet dots formed on the printing medium are shifted. 6. The printing element according to claim 1, further comprising: an electrothermal converter that generates thermal energy for causing film boiling of the ink as energy used for discharging the ink droplet from the discharge port. The inkjet printing method according to claim 1. 7. An ink-jet printing method for printing an image on a printing medium by using a print head capable of discharging ink droplets divided into main droplets and sub-droplets from a discharge port by applying a driving pulse to a print element. The apparatus according to claim 1, further comprising a control unit configured to control a number of the sub-droplets from which the ejected ink droplet is separated by controlling the driving pulse according to an image signal. 8. An ink jet printing apparatus which prints an image on a printing medium by using a print head capable of discharging ink droplets from a discharge port by applying a drive pulse to a print element, An ink jet apparatus comprising: a control unit capable of changing an area of a dot formed on the print medium by a main drop and a sub drop separated from the ink drop by controlling according to a signal. Printing device. 9. The ink jet printing apparatus according to claim 7, wherein the control unit controls the driving pulse according to gradation information of an image signal. 10. The ink jet printing apparatus according to claim 7, wherein the control unit controls the driving pulse in accordance with a recording density of an image on the print medium. 11. A printing apparatus comprising: a moving unit capable of moving the print head in a main scanning direction; and a conveying unit capable of conveying the print medium in a sub-scanning direction substantially orthogonal to the main scanning direction. The inkjet printing apparatus according to any one of claims 7 to 10, wherein: 12. The moving unit, when moving the print head in the main scanning direction, separates the ejected ink droplet into a main droplet and a sub-droplet, and discharges the main droplet and the sub-droplet. 12. The ink jet printing apparatus according to claim 11, wherein the center positions of the main droplet dots and the sub droplet dots formed on the printing medium are shifted by changing the center position of the ink droplet. 13. The printing element of the print head, further comprising: an electrothermal converter that generates thermal energy that causes film boiling of the ink as energy used for discharging the ink droplet from the discharge port. The inkjet printing apparatus according to any one of claims 7 to 12, wherein: