JPH05177845A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To record the image data inputted to a recording head at a recording speed slower than that of binary recording data when said image data is multivalue recording data. CONSTITUTION:In an ink jet recording method of emitting particles of a liquid to a recording material to record binary recording data or multivalue recording data, when gradation recording is performed, a defect such that high image quality is not obtained by a tailing phenomenon or an oval pixel is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording method, and more particularly to an inkjet recording method suitable for gradation recording in an inkjet printer.

[0002]

2. Description of the Related Art Ink jet recording means have the advantages that noise during recording is extremely low and that recording can be performed on plain paper without requiring a special fixing process.
Since high-speed recording is possible, it has attracted attention as a recording means. In particular, in recent years, from the demand of users who desire higher image quality, the conventional binary recording image is not satisfactory, and gradation recording, which is a multi-value recording image, is expected. Therefore, various inkjet recording heads capable of performing gradation recording have been proposed.

As one of the ink jet recording heads capable of performing gradation recording, so-called thermal ink jet technology in which bubbles are generated in the recording liquid and the recording liquid is ejected from fine nozzles by the pressure due to the expansion of the bubbles. Is disclosed as Japanese Patent Publication No. 59-3194.
There is a publication No. 3. In this publication, a gradation recording is performed by applying a signal having gradation information to an electrothermal converter having a heating portion having a heating amount adjusting structure and generating a heat amount according to the signal in the heating portion. It is characterized by.
Specifically, the structure is such that the thickness of the protective layer, the heat storage layer, or the heating element layer gradually changes, or the pattern width of the heating element layer gradually changes.

On the other hand, Japanese Patent Laid-Open No. 63-42872 discloses a similar gradation recording technique. This is also the Japanese public Sho 59-
Similar to the technique of Japanese Patent No. 31943, the heating element layer is characterized by having a three-dimensional structure. Other gradation recording techniques include Japanese Patent Publication No. 62-46358 and Japanese Patent Publication No. 6-6.
2-46359 and JP-B-62-48585 disclose such techniques. They select a predetermined number of heating elements from a plurality of heating elements arranged in one flow path, respectively, or select one of a plurality of heating elements having different heating values to generate bubbles. The size has been changed, and the discharge amount has been changed by variably controlling the deviation of the input timing of the drive signals to the plurality of heating elements.

Further, Japanese Patent Application Laid-Open No. 59-124863,
Japanese Unexamined Patent Publication No. 59-124864 discloses a technique for controlling the discharge amount, which has a heating element and a bubble generating section different from the heating element for discharging. Furthermore, JP-A-63-4286
Japanese Unexamined Patent Application Publication No. 9 discloses a technique of controlling the discharge amount by changing the number of times the bubbles are generated by changing the time for energizing the resistor.

Further, in US Pat. No. 4,053,444, minute ink droplets are generated at a very high driving frequency, and the number of minute ink droplets forming one pixel is changed in accordance with image density information. Techniques for changing the diameter are disclosed. As described above, various gradation recording techniques have been proposed in order to achieve higher image quality than in the past, and these techniques have excellent characteristics in their own right. In that sense, it cannot be said that the features of the technology have been fully utilized, and the image quality has not been as high as expected.

As a result of examining and investigating the reason why high image quality is not obtained in the conventional technique, the applicant has found the following points. In other words, when each of the obtained pixels was magnified and viewed with a microscope, the shape of the pixel was an ellipse instead of a clean circle, although the size of the pixel changed as expected. It is noted that the image quality is disturbed by the rounded pixels, the trailing state, or the presence of minute pixels in the vicinity of one pixel.

[0008]

SUMMARY OF THE INVENTION The present invention is premised on the reason that high image quality cannot be obtained as described above, and when the relative speed between the recording head and the recording medium is constant and gradation recording is performed, It is an object of the present invention to provide a recording method that can realize high image quality as originally intended by making the relative speed variable.

[0009]

In order to achieve the above-mentioned object, the present invention causes a liquid to fly as droplets onto a recording medium,
In an inkjet recording method for recording binary recording information and multi-valued recording information on a recording medium, when image information input to a recording head is multi-valued recording information, recording is slower than the recording speed in the binary recording information. It is characterized by recording at speed.

The present invention provides an ink jet recording method in which a liquid is subjected to a state change due to heat due to heat energy, and the liquid is ejected as droplets onto a recording medium to record binary recording information and multilevel recording information on the recording medium. In the above, in comparison with the recording speed in the case where the mass of the liquid for forming one pixel is made constant, the recording speed is made slower when the mass of the liquid is changed to perform the recording, and the liquid mass is changed. The pulse width in the case of recording is electric energy with a pulse width smaller than the pulse width in the case of recording with the liquid mass kept constant,
One or more pulses are input and the mass of the liquid is changed and recorded.

Further, according to the present invention, the liquid is drawn out by the recording electrode by electrostatic force and is made to fly to the recording medium as a droplet,
In an ink jet recording method for recording binary recording information and multi-valued recording information on a recording medium, the mass of the liquid is changed with respect to the recording speed when recording is performed with the mass of the liquid for forming one pixel being constant. In order to change the mass of the liquid by recording at a slower recording speed in the case of recording, the pulse width or pulse voltage input to the recording electrode is changed.

[0012]

According to the structure of the present invention, in various ink jet recording means such as an ink jet printer, when performing gradation recording, the speed is reduced in the case of multi-valued recording as compared with binary recording of high speed recording to form an image. Can be of high quality.

[0013]

First, the operation of a bubble jet head as an example of an ink jet head to which the present invention is applied will be described with reference to FIG. 2 is a perspective view of the bubble jet head shown in FIG. 1, and FIG. 3 is a perspective view of the head of FIG. 2 disassembled into a lid substrate (FIG. 3A) and a heating element substrate (FIG. 3B). FIG. 4 is a perspective view of the lid substrate shown in FIG. 3A as viewed from the back side. In the figure, 1 is a lid substrate, 2 is a heating element substrate, 3 is a recording liquid inflow port, 4 is a discharge port, 5 is a flow path, 6 is a region for forming a liquid chamber, 7 is an individual (independent) electrode, 8
Is a common electrode, 9 is a heating element (heater), 10 is ink, 1
Reference numeral 1 is a bubble, and 12 is a flying ink liquid.

First, ink ejection by a bubble jet will be described with reference to FIG. (A) is a steady state, in which the surface tension of the ink 10 and the external pressure at the ejection port 4 are in equilibrium. (B) shows a state in which the heating element 9 as a heater is heated, the surface temperature of the heating element 9 rises sharply, and is heated until the boiling phenomenon occurs in the adjacent ink layer, and the minute bubbles 11 are scattered.

(C) shows a state in which the adjacent ink layer that has been rapidly heated on the entire surface of the heating element 9 is instantly vaporized to form a boiling film, and the bubble 11 has grown. At this time, the pressure in the nozzle rises as much as the bubbles grow, the balance with the external pressure on the ejection port surface is lost, and the ink column starts to grow from the ejection port 4. In (d), the bubble 11 has grown to the maximum, and the ink 10 corresponding to the volume of the bubble is pushed out from the ejection port surface. At this time, no current is flowing through the heating element 9, and the surface temperature of the heating element 9 is decreasing. The maximum value of the volume of the bubble 11 is slightly delayed from the timing of applying the electric pulse.

(E) shows a state in which the bubble 11 is cooled by ink or the like and starts to contract. At the front end of the ink column, the ink column moves forward while maintaining the pushing speed, and at the rear end of the ink column, the internal pressure of the nozzle decreases due to the contraction of the bubble 11, and the ink flows backward from the ejection port surface into the nozzle, thus constricting the ink column. Is occurring.

In the state (f), the bubble 11 is further contracted, the ink contacts the surface of the heating element, and the surface of the heating element is further rapidly cooled. On the orifice surface, the external pressure is higher than the internal pressure of the nozzle, so a large meniscus has entered the nozzle. The tip of the ink column becomes a droplet and flies toward the recording paper at a speed of 5 to 10 m / sec.
(G) is a process in which the ink is supplied to the ejection port again by the capillary phenomenon and returns to the state of (a), and the bubbles are completely extinguished.

FIG. 5 is an embodiment for explaining the construction of the main part of the above-mentioned liquid jet recording head. FIG. 5A is a detailed front partial view seen from the ejection port side of the bubble jet head.
(B) is a partial cross-sectional view taken along the alternate long and short dash line xx in (a). Recording head 13 shown in this drawing
The structure is formed by arranging and bonding a grooved plate 16 having a predetermined number of grooves of a predetermined linear density and a predetermined width and depth on a substrate 15 having the electrothermal converter 14 provided on the back surface. A liquid ejection portion 18 including an ejection port 17 for ejecting the liquid is formed at the end of the recording head.

The liquid discharge part 18 is a place where the heat energy generated from the discharge port 17 and the electrothermal converter 14 acts on the liquid to generate bubbles, which causes a rapid state change due to expansion and contraction of the volume. And a certain heat acting part 19. The heat acting portion 19 is the heat generating portion 20 of the electrothermal converter 14.
The heat acting surface 21, which is located on the upper part of the heat generating portion 20 and is in contact with the liquid, is a lower surface thereof. Heat generation part 20
Is a lower layer 22 provided on the substrate 15 and the lower layer 22.
The heating resistor layer 23 is provided on the heating resistor layer 23, and the protective layer 24 is an upper layer provided on the heating resistor layer 23.

The heating resistance layer 23 is provided with electrodes 25, 26 on its surface for energizing the heating layer 23 in order to generate heat, and the heat generation part is provided between these electrodes by the heating resistance layer 23. 20 are formed. The electrode 25 is an electrode common to the heat generating portion 20 of each liquid ejecting portion 18, and the electrode 26 is a selection electrode for selecting the heat generating portion 20 of each liquid ejecting portion 18 to generate heat. It is provided along the liquid flow path of the discharge part 18.

The protective layer 24 fills the heat generation resistance layer 23 and the liquid flow path of the liquid discharge part 18 in order to protect the heat generation resistance layer 23 in the heat generation part 20 chemically and physically from the liquid used. It has a role of separating the existing liquid, preventing a short circuit between the electrodes 25 and 26 through the liquid, and further preventing an electric leak between the adjacent electrodes. The liquid flow path provided in each liquid discharger 18 constitutes a part of the liquid flow path upstream of each liquid discharger, and
Communication is performed via a liquid passage chamber (not shown). Electrode 2 connected to electrothermal converter 14 provided in each liquid discharger
5, 5 and 26 are protected by the protective layer 24 which is the upper layer due to the design convenience thereof, and on the upstream side of the heat acting portion,
It is provided so as to pass under the common liquid chamber.

FIG. 6 is a detailed view for explaining the structure of the bubble generating portion using a heating resistor, in which 27 is a heating resistor, 28 is an electrode, 29 is a protective layer, and 30 is a power supply device. Shows. A useful material for the heating resistor 27 is, for example, a tantalum-SiO ₂ mixture,
Examples thereof include tantalum nitride, nichrome, silver-palladium alloy, silicon semiconductor, and borides of metals such as hafnium, lanthanum, zirconium, titanium, tantalum, tungsten, molybdenum, niobium, chromium and vanadium. 27 heating resistor 28 electrode 29 protective layer 30 power supply device

Among the materials forming these heating resistors 27, metal borides can be cited as particularly excellent ones, and among them, hafnium boride has the most excellent characteristics, and then, The order is zirconium boride, lanthanum boride, tantalum boride, vanadium boride, and niobium boride. The heating resistor 27 can be formed by using a method such as electron beam vapor deposition or sputtering using the above materials. The film thickness of the heating resistor 27 is determined according to the area, the material, the shape and size of the heat acting portion, and the actual power consumption so that the amount of heat generated per unit time becomes a desired value. In general, it is 0.001 to 5 μm, preferably 0.01 to 1 μm.
It is said that.

As the material forming the electrode 28, many of the commonly used electrode materials can be effectively used.
Specifically, for example, Al, Ag, Au, Pt, Cu, and the like are used, and these are provided in a predetermined position, with a predetermined size, shape, and thickness by means such as vapor deposition.

The characteristic required for the protective layer 29 is that it does not prevent the heat generated by the heating resistor 27 from being effectively transferred to the recording liquid, and protects the heating resistor 27 from the recording liquid. is there. Examples of useful materials for forming the protective layer 29 include silicon oxide, silicon nitride, magnesium oxide, aluminum oxide, tantalum oxide, zirconium oxide and the like. These can be formed using a technique such as electron beam evaporation or sputtering. The thickness of the protective layer 29 is usually 0.01 to
10 μm, preferably 0.1-5 μm, optimally 0.1
It is desirable that the thickness is formed to be about 3 μm.

FIG. 7 is an explanatory diagram of a case where ink is ejected from nozzles using the above-described ink jet head.
(A) shows the case of binary recording, and (b) shows the case of multi-valued recording. (A) showing the case of binary recording is the same as the description of ink ejection by the bubble jet in FIG. 1, in which input energy is input to the heating element and one of the bubbles is generated by the heated heating element, Ink droplets 31A for forming recording pixels are ejected from the ejection ports 32 by the generation of the bubbles. In this case, bubbles are generated once, and the film of the bubbles covers the heating element, which prevents the heat of the heating element from propagating to the ink side. Therefore, even if the input energy is increased or decreased, the size of the bubble is affected. , The size of the ejected ink drop is substantially constant, and so-called binary recording is obtained.

On the other hand, FIG. 7B shows the case of so-called multi-value recording in which the mass of the ejected ink droplets changes. This multi-value recording cannot be performed simply by the ink jet head described with reference to FIG. In order to perform multi-valued printing, the size of the bubble generated changes according to the size of the input energy, the mass of the ink droplet ejected from the nozzle changes according to the size of the bubble, and the size of the recording pixel changes. It can be a means. Here, in FIG. 7B, the ink droplet 31 ejected from the ejection port 32 is generated as a result of the generation of a large bubble.
The case where the mass of B is larger than the mass of the ink 31A of FIG. 7A is illustrated. 31A, B Flying ink droplet 32 Ejection port

Since the ink jet head is provided with means capable of changing the mass of the ejected ink, one print P as shown in FIG.
In the case where the character information M and the image information G coexist in the inside, suitable recording can be performed. In other words, when printing character information, it is possible to eject almost uniform ink droplets and
When the value recording is performed and the image information G is printed, the mass of the ejected ink droplets is changed to perform multi-value recording with rich gradation and so-called photograph-like information can be printed.

Binary printing and multi-valued printing can be performed using the same head as the ink jet head, but since the size of the nozzle is the same, the difference in the mass of the ejected ink is: As shown in FIGS. 7A and 7B, the length of the ink droplets 31A and 31B in the ejection direction (l
It appears as a difference between a) and (lb). Therefore, in the case of multi-valued recording (see FIG. 7) at the same frequency (head drive frequency) as in the case of binary recording (FIG. 7A).
Injecting ink droplets in (b) may cause inconvenience.

In general, the ink jet head is driven at the maximum speed when it is continuously driven in order to fully exhibit its capability. By the way, when the multi-valued recording (FIG. 7B) is performed similarly to the maximum speed in the binary recording (FIG. 7A), the mass of the ejected ink droplet in the binary recording is increased. There is no problem when the mass of the ink droplet of multi-valued recording is smaller than that of the above, but when the mass of the ink droplet is large, the length (lb) of the ink droplet becomes long, and therefore the preceding ink droplet Before the ink is separated from the nozzle portion, the next ink droplet may be ejected, and the ink droplets before and after may be integrated. In such a case, the ink droplets ejected onto the paper surface cannot form a pixel at a desired position on the paper surface, resulting in image disturbance.

From the above, when binary recording and multi-value recording are performed using the same head, in order to obtain a good image on the paper surface, the mass of the ejected ink droplets is binary recording. When the multi-valued recording is larger than that, the driving speed in the multi-valued recording needs to be slower than that in the binary recording.

Next, another problem in the case where the character information (binary recording information) M and the image information (multivalue recording information) G as shown in FIG. 8 are mixed on one sheet will be described. In general, when recording is performed, the recording head and a recording medium such as paper or OHP paper make relative motion. In the case of a small printer, the recording head performs shuttle movement, and in the large printer, the recording head is fixed and the recording medium moves. In any case, since the recording is performed while the recording head and the recording medium perform relative movement, the relative speed between the recording head and the recording medium is an important factor in performing high-quality recording. For example, in order to perform high-quality recording even when the binary recording of FIG. 7A is obtained or the multi-valued recording of FIG. 7B is performed, a neat circle at a desired position on the paper surface. It is necessary to get pixels.

However, as is clear from FIGS. 7A and 7B, the difference in the mass of the ejected ink droplets causes the difference in the lengths la and lb of the ink droplets. From a microscopic view of the time taken for one pixel to be formed, the binary recording of FIG. 7A is faster than the multivalued recording of FIG. 7B. That is, the time from when the front end of the ink droplet reaches the paper surface to when the rear end portion of the ink drop reaches the paper surface becomes longer as the ink droplet is longer. In this case, if the relative speed between the recording head and the recording medium is relatively slow,
In both the case of (a) and the case of FIG. 7 (b), substantially uniform round pixels are formed, but when the relative speed is high, the trailing edge of the ink droplet is round. This causes the so-called tailing phenomenon, which is a phenomenon that the image quality is disturbed by being projected to the outside of the pixel.

Further, as shown in FIG. 9, there is a case where a small ink droplet called a satellite 33 flies at the trailing end of the ejected ink droplet 31C, and in such a case, the above recording is performed. When the relative speed between the head and the recording medium is high, the satellite adheres to the periphery of the pixel, which deteriorates the image quality.

Generally, when performing ink jet recording,
At least for binary recording, the relative speed between the recording head and the recording medium during printing is set to the maximum or within the range in which good round pixels can be obtained and considering the cost for configuring the printer. The speed is set according to. When performing multi-valued recording using the same recording head,
There is no problem when the mass of the ejected ink droplet is smaller than that in the case of binary recording, but when the mass of the ejected ink droplet is large,
Since the trailing edge of the ink drop causes a trailing phenomenon on the paper surface and causes a deterioration in image quality, the relative speed between the recording head and the recording medium during printing in multi-value recording is slower than in binary recording. It is important to record it.

FIG. 10 is a drawing for explaining another gradation recording means using a thermal ink jet. In the drawing, 31 is a flying ink drop, 34 is the shape of a pixel on the paper,
Reference numeral 35 indicates a drive pulse. FIG. 10 (a) shows FIG.
Similar to (a), the flying ink droplets have a uniform ink amount,
This is a case where binary recording is performed. In FIG. 10B, one or more pulse energies are applied at fine intervals, and one or more micro ink droplets 31 ₁ to
31 ₄ is formed.

Further, depending on different conditions, it is possible that these minute ink droplets are not independent but can fly as one continuous ink droplet having a bump-shaped bulge according to the input pulse energy number. The pulse energy input in the case of FIG. 10B is as shown in FIG.
The pulse energy is smaller than the pulse energy of, and thus the ink droplet formed is also small.

Since this small pulse energy has a high frequency (several to several tens of kHz) and one to several pulses are applied, minute ink droplets continue as shown in FIG. 10 (b). Alternatively, by ejecting and flying as one ink column in which they are connected, the pixel 34 is formed by adhering to the paper surface. And these fine ink droplets 31 _{1-31 4} for attachment to the paper surface in a short time, to form the one pixel of a plurality of ink droplets. That is, gradation recording is performed by changing the pixel size according to the number of ink drops.

In short, one recording head is used, the operation shown in FIG. 10A is performed for the character information (binary recording information), and the image information (multivalue recording information) is used. , And can be used to perform the operation shown in FIG. 10B, and can handle all kinds of image information. In the case of FIG. 10 as well, in the same manner as described with reference to FIG. 7, the ink droplet length la in the case of performing binary recording, and in the case of multi-level recording, in particular, a plurality of pulses are input, and the ink mass is large. The total length lb of the minute ink drop row in the case
Since the total length lb of the latter minute ink droplet array may be longer than the former ink droplet length la, the frequency of forming one pixel when performing multi-valued recording is It is necessary to perform the recording at a slower recording speed than when performing binary recording.

FIG. 11 shows, as another gradation recording means, an ink jet head of a type in which ink is sucked and ejected by using an air flow and an electrostatic force. Recording head 3
6, an air chamber 37 and an ink chamber 38 are provided, an air ejection port 39 is provided on the recording paper side of the air chamber 37, and an ink ejection port 40 is provided on the recording paper side of the ink chamber 38. ing. The air outlet 39 has a diameter of about 100 μm,
The ink ejection port 40 has a diameter of about 50 μm. The number of each discharge port 39, 40 is 24, respectively. Also,
A common electrode 41 is attached to the wall surface where the air ejection port 39 is opened, and a control electrode 42 is attached to each ink ejection port 40. Reference numeral 46 is an ink tank.

The operating principle of the ink jet head 36 will be described. First, 10 to 15 MPa (0.1 to 0.15 kgf / cm ² ) is supplied to the air chamber 37 by the air pump 43.
Apply pressure and blow out air. At the same time, a bias voltage of about 500 V is applied between the ink and the common electrode 42. Therefore, an electrostatic force is generated by the bias voltage, and the ink discharge port 40 is discharged from the ink discharge port 40 shown in FIGS.
Ink bulge (meniscus) 4
You can do 4.

Here, between the ink and the control electrode 42,
When a pulsed signal voltage of −400 V is applied, a stronger electrostatic force is generated and the meniscus 44 is stretched. Then, the ink flows along with the air flow, and a thin ink beam 45 is generated as shown in FIG. The diameter of the beam 45 of this ink is 10 μm or less, and the ink ejection port 4
It becomes much thinner than 0. Although the ink beam 45 can fly about 10 to 20 mm, the recording paper is actually installed at a position within 3 to 4 mm from the nozzle.

The amount of ejected ink is controlled by the pulse width of the signal voltage. In addition to the pulse width, it may be controlled by a pulse voltage. With such a configuration, the mass of the ejected ink can be controlled in a wide range of 1: 200, and the pulse width for ejecting the minimum amount of ink is 50 to 60 μs. With this method, the size of the pixels to be recorded on the recording paper can be easily changed.
Gradation control is also possible.

FIG. 12 shows the nozzle shape and the meniscus shape in the vicinity of the discharge port in FIG. 11 and the ink discharge state. (A) is a state in which no air flow is flowing, and the meniscus has a concave shape 44a. This is because the ink surface in the ink tank 46 is arranged below the nozzle. In (b), an air flow is generated,
In the state where no signal is applied, the meniscus has a convex shape 44b.

Since the air pressure is also applied to the ink tank 46, the ink pressure Pi is stored in the ink chamber 38 of the head.
However, the pressure Pi and the air pressure Pa near the ink ejection port generated by the air flow sent to the head are balanced to form the meniscus 44b. On this occasion,
The air pressure Pa is smaller than the air pressure Pi applied to the ink tank 46 due to the pressure loss in the air flow path, and Pi
Since> Pa, the meniscus 44b is formed in a convex shape.

(C) shows that a voltage is applied between the electrodes, the meniscus 44b is stretched, and the meniscus 44b flies while being accelerated by an air flow. After that, when the signal voltage between the electrodes is released, the ink stretched in the form of a string is cut, and the ink having a thin liquid column flies. Then, when the air flow is released, the state of (a) is restored.

In the case of the ink jet system using the air flow and the electrostatic force shown in FIGS. 11 and 12, the same pixel diameter is printed, binary recording, and different pixel diameter is printed, multivalued recording. And are possible. In the case of multi-valued printing in which large pixels are formed, the ink is stretched and slender due to the shape of a string and flies, so that the ink column becomes longer than in the case of binary printing.

Therefore, also in this system, when performing multi-valued recording, the front end of the next ink column does not adhere to the rear end of the preceding ink column, and the rear end portion of the ink column on the paper surface. This can be solved by making the recording speed slower than the recording speed when performing binary recording in order to prevent the trailing phenomenon from occurring.

Although the case of the ink jet system using the air flow and the electrostatic force has been described above, it is also possible to fly the ink only by the electrostatic force without flowing the air flow. In that case, a bias voltage of, for example, 2 to 3 kV is required to fly the ink, and it is necessary to increase the driving energy. However, since an air flow is not required, an air pump or the like is unnecessary and the structure is simple.

The present invention will be described below with reference to experimental examples. Experimental Example 1 In FIG. 13, ink droplets are ejected by the action of thermal energy.
It is a heating element related to the recording head, and is input to the heating element.
A configuration that can control the temperature distribution according to the signal level
FIG. 1 shows an example of the plane shape of the heating element pattern.
It Reference numeral 47 is a heating element, and electrodes 48 and 49 are provided at both ends thereof.
And the heating element 47 has a width B on the electrode 48 side. ₁Narrow the electrode
92 side width B₂Wide, width B₁Part and width B₂part
Change the current density at, and thus per unit time
There is a difference in the calorific value of. The shorter width of the heating element 47
Width B₁15 μm, the longer width B₂To 40 μm
However, the length L of the heating element 47 is set to 100 μm, and the resistance of the heating element is set to
A resistance value of 120Ω was used.

A heating element substrate having such a heating element 47 and a flow path plate formed by etching a photosensitive glass are combined to form an ink jet head as shown in FIG. 2, and the driving conditions of the head are changed. Then, the printed pixel diameter dimension and its pixel shape were evaluated. The results are shown in Table 1. The nozzle size of the head is 40 μm × 30 μ
m. The ink used was DeskJet ink manufactured by Hewlett-Packard Company, and the recording paper used was matte coated paper NM manufactured by Mitsubishi Paper Mills Ltd.

[0052]

[Table 1]

In Table 1, No. No. 1 is a condition for performing binary recording. 2 to No. Reference numeral 12 represents a case of multi-valued recording in which the mass of ejected ink is changed by utilizing the characteristics of the head. The pixel diameter is an average value of n = 10. The circles in the pixel shape indicate the case where a good round pixel was obtained, and the crosses indicate the case where a clean round shape was not obtained.

As is clear from Table 1, in the case of multi-value recording, when a particularly large pixel diameter is obtained, 2
It can be understood that a good round pixel is formed by driving at a speed lower than the driving speed of the head at the time of value recording.

Experimental Example 2 The size of the heating element in this case is the width B of the heating element 47.
Is constant, the width size is 28 μm, and the heating element 9
The length L of 0 is 140 μm, and the resistance value of the heating element is 128
Ω was used. And the size of the head isle is
The size was 28 μm × 29 μm. The conditions of ink, recording paper, etc. are the same as in Experimental Example 1 above. When the number of pulses is plural, the pulse generation frequency in the pulse group is set to 30 kHz.

The results are shown in Table 2.

[Table 2]

As is apparent from Table 2, the normal binary recording is No. No. 1, which is a multi-valued record, the number of pulses is 1. 2 to No. In 24, the number of pulses (2 to 10) is changed by a plurality of pulse groups to change the pixel diameter. Then, the multi-value recording, in order to obtain a larger pixel size than the pixel size of the binary recording, the drive frequency f ₀ as the group of pulses, the driving frequency f at the time of binary recording ₀
By making it slower, good round pixels can be obtained.

Experimental Example 3 An experimental example in which ink is ejected by using an ink jet type head using an air flow and an electrostatic force as shown in FIG. 11 will be described. The input energy was changed by changing the pulse width. In this head, the diameter of the ink ejection port is φ60 μm, and the diameter of the air ejection port is φ
The ink was 120 μm, the control voltage was −420 V, the bias voltage was 500 V, the air pressure was 0.1 kg / cm ² , and the ink used was a dispersion of pigment in Isopar.

The results are shown in Table 3.

[Table 3]

No. 1 in Table 3 1 is a case where a condition that a stable and uniform pixel diameter is obtained is provided, and binary recording is performed under this condition. As is clear from Table 3, when gradation recording (multi-value recording) is performed by ejecting ink by electrostatic force (No. 2 to No. 12), the one having a pixel diameter larger than that of binary recording is selected. To get that drive frequency 2
It can be understood that a good pixel shape can be obtained by making the value slower than the value recording.

Experimental Example 4 In this experimental example, a recording head having the same structure as that used in Experimental Example 1 was used, and the pixel shape was examined by changing the relative speed between the head and the recording paper. The size of the recording head is such that the shorter width B ₁ of the heating element is 10 μm and the longer width B ₂ is 35 μm.
The length L of the heating element was 90 μm, and the resistance value of the heating element was 118Ω. The nozzle size of the recording head was 35 μm × 25 μm.

The relative speed between the recording head and the recording paper was fixed by fixing the recording paper and changing the speed of the carriage carrying the recording head. Other conditions are Experimental Example 1
It is similar to the case of. The results are shown in Table 4.

[Table 4]

As is clear from Table 4, when gradation recording (multi-value recording) is performed by changing the mass of ink ejected from the nozzles, in order to obtain a pixel larger than the pixel in binary recording, binary It can be understood that good round pixels can be obtained by setting a speed slower than the relative speed (0.5 m / s) between the print head and the printing paper at the time of printing.

[0064]

With the structure of the present invention, when various types of ink jet recording means such as an ink jet printer are used for gradation recording, the tailing and oval pixels which have been conventionally seen in the case of multi-valued recording are eliminated. Therefore, it is possible to obtain a good round pixel and to perform high-quality gradation recording.

[Brief description of drawings]

1A to 1G are operation explanatory views of a bubble jet head to which the present invention is applied.

FIG. 2 is a perspective view of the bubble jet head shown in FIG.

3A and 3B are perspective views of the head of FIG. 2 disassembled into a lid substrate and a heating element substrate.

FIG. 4 is a perspective view of the lid substrate shown in FIG. 3A as viewed from the back side.

5A and 5B are drawings for explaining a configuration of a main part of a liquid jet recording head, in which FIG. 5A is a detailed front partial view seen from the ejection port side, and FIG. 5B is a dashed-dotted line xx in FIG. FIG. 4 is a partial sectional view of a portion indicated by.

FIG. 6 is a cross-sectional view for explaining the structure of a bubble generating portion that uses a heating resistor in the recording head.

FIG. 7 is an explanatory diagram of a case where ink is ejected from an ejection port using the inkjet head of FIGS. 5 and 6, where (a) is for binary recording and (b) is for multi-valued recording. This is the case.

FIG. 8 is an explanatory diagram of a case where character information M and image information G are mixed in one print P.

FIG. 9 is an explanatory diagram showing a state in which satellites are generated at the trailing ends of ejected ink droplets.

10A and 10B are drawings for explaining another gradation recording means using a thermal ink jet, where FIG. 10A shows a case of binary recording and FIG. 10B shows a case of multi-value recording.

FIG. 11 is a diagram showing an outline of an ink jet head of a type in which ink is sucked and ejected by using an air flow and electrostatic force as another gradation recording means.

12A to 12C are views for explaining the operation of the inkjet head shown in FIG.

FIG. 13 is a heating element relating to a recording head that causes ink droplets to fly by the action of thermal energy, and shows a planar pattern of the heating element.

[Explanation of symbols]

 1 Cover Substrate 2 Heating Element Substrate 3 Recording Liquid Inlet 4 Orifice 5 Flow Path 6 Region for Forming Liquid Chamber 7 Individual (Independent) Electrode 8 Common Electrode 9 Heating Element (Heater) 10 Ink 11 Bubble 12,31 Flying Ink Drops 13, 36 Recording heads 31A, B, C Flying ink drops 32 Ejection port 33 Satellite 34 Pixel shape 35 Driving pulse 37 Air chamber 38 Ink chamber 39 Air ejection port 40 Ink ejection port 41 Common electrode 42 Control electrode 43 Air pump 44 Meniscus 45 Ink beam 46 Ink tank 47 Heating element 48, 49 Electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H04N 1/23 Z 9186-5C

Claims (4)

[Claims] 1. A liquid droplet is caused to fly onto a recording medium,
In an inkjet recording method for recording binary recording information and multi-valued recording information on a recording medium, when image information input to a recording head is multi-valued recording information, recording is slower than the recording speed in the binary recording information. An ink jet recording method characterized by recording at a speed. 2. An ink jet recording method for imparting a state change due to heat to a liquid by thermal energy, causing the liquid to fly as a droplet onto a recording medium, and recording binary recording information and multilevel recording information on the recording medium, Recording is performed at a slower recording speed when changing the mass of the liquid for recording than when changing the mass of the liquid for forming one pixel for recording, and changing the liquid mass when recording. The pulse width in the case of performing is electric energy having a pulse width smaller than the pulse width in the case of recording with the liquid mass kept constant, and an ink jet recording characterized by changing the mass of the liquid by inputting one or more pulses. Recording method. 3. An ink jet recording method for recording a binary recording information and a multi-value recording information on a recording medium by drawing liquid by electrostatic force by a recording electrode and causing the liquid to fly as droplets to the recording medium. In contrast to the recording speed when recording with the liquid mass kept constant, the recording speed is reduced when recording by changing the mass of the liquid.
The inkjet recording method is characterized in that, in order to change the mass of the liquid, a pulse width or a pulse voltage input to the recording electrode is changed. 4. The ink jet system according to claim 1, wherein, when recording is performed at a slower recording speed, the relative speed between the recording head and the recording medium is slower than 0.5 m / s. Recording method.