JP3215134B2 - Inkjet recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

[0003] As one of the ink jet recording heads capable of performing gradation recording, a so-called thermal ink jet technology in which bubbles are generated in a recording liquid and the recording liquid is ejected from fine nozzles by pressure due to expansion of the bubbles. Is disclosed in Japanese Patent Publication No. 59-3194.
There is No. 3 publication. This publication discloses that gradation recording is performed by applying a signal having gradation information to an electrothermal converter having a heating portion having a heating value adjustment structure and generating a heat amount corresponding to the signal in the heating portion. It is characterized by the following.
Specifically, it has a structure in which the thickness of the protective layer, the heat storage layer, or the heating element layer changes gradually, or a structure in which the pattern width of the heating element layer changes gradually.

On the other hand, Japanese Patent Application Laid-Open No. 63-42872 discloses a similar gradation recording technique. This is also Japanese Patent Publication 59-
As in the technology of Japanese Patent No. 31943, a feature is that the heating element layer has a three-dimensional structure. Other gradation recording techniques are disclosed in JP-B-62-46358 and JP-B-6-64.
JP-A-2-46359 and JP-B-62-48585 disclose such a technique. Each of them selects a predetermined number of heating elements from a plurality of heating elements arranged in one flow path, or selects one from a plurality of heating elements having different heating values to generate bubbles. The size is changed or the ejection amount is changed by variably controlling the shift of the input timing of the drive signal to the plurality of heating elements.

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

Further, US Pat. No. 4,503,444 discloses that a minute ink droplet is 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. A technique for changing the diameter is disclosed. As described above, in order to achieve higher image quality than before, various gradation recording techniques have been proposed, and these techniques are themselves techniques having excellent characteristics. However, it cannot be said that the features of the technology are fully utilized in terms of point of view, and the images are not as high as expected.

[0007] As a result of studying and investigating the reason why high image quality has not been obtained in the prior art, the present applicant has noticed the following. That is, when each obtained pixel is enlarged and viewed with a microscope, the shape of the pixel is not a beautiful circle but an ellipse even though the size of the pixel has changed almost as intended. In addition, attention has been paid to the fact that the image quality is disturbed due to the trailing state from a round pixel or the trailing state, or the presence of a minute pixel near one pixel.

[0008]

SUMMARY OF THE INVENTION The present invention is based on the premise that high image quality cannot be obtained as described above, in which the relative speed between the recording head and the recording medium is constant, and when performing gradation recording, It is an object of the present invention to provide a recording method capable of realizing high quality as originally intended by making the relative speed variable.

[0009]

According to the present invention, in order to achieve the above object, a liquid is ejected on a recording medium as liquid droplets,
In an ink jet recording method for recording binary recording information and multi-value recording information on a recording medium, when image information input to a recording head is multi-value recording information, the recording information is higher than the recording head drive frequency in the binary recording information. and records a slow recording head driving frequency, the recording heads at the time of multi-value recording
The relative speed between the recording medium and the recording medium in the range of 0.1 to 0.5 m / s.
It is characterized by being enclosed .

According to the present invention, there is provided an ink jet recording method for giving a state change due to heat to a liquid by thermal energy, causing the liquid to fly on a recording medium as liquid droplets, and recording binary recording information and multi-value recording information on the recording medium. In the case where recording is performed by changing the mass of the liquid, the frequency of forming one pixel is changed with respect to the frequency of forming one pixel when the recording is performed with the mass of the liquid for forming one pixel constant.
The pulse width in the case where recording is performed with the frequency of forming one pixel delayed and the recording is performed while changing the liquid mass is electric energy having a pulse width smaller than the pulse width in the case where recording is performed while maintaining the liquid mass constant. The recording is performed by changing the mass of the liquid by inputting a pulse.

Also, the present invention provides a method for applying heat energy to a liquid.
In the ink jet recording method of giving a state change due to heat, causing the liquid to fly on a recording medium as liquid droplets, and recording binary recording information and multi-value recording information on the recording medium, the mass of the liquid for forming one pixel is reduced. 1 pixel type when recording at a constant
Against adult frequency, by varying the mass of the liquid slows down the 1 pixel formation frequency of recording record to, the plurality when recording by changing the liquid mass is arranged in one flow path from the heating element, Ru der those characterized in that by selecting a predetermined number of heating elements for recording by changing the mass of the liquid.

[0012]

According to the constitution of the present invention, in various ink jet recording means in an ink jet printer or the like, when performing gradation recording, the speed is reduced in the case of multi-value recording as opposed to the high-speed binary recording, and the image is reproduced. High quality can be achieved.

[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. FIG. 2 is a perspective view of the bubble jet head shown in FIG. 1, 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. In the figure, 1 is a cover substrate, 2 is a heating element substrate, 3 is a recording liquid inlet, 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
1 is a bubble and 12 is a flying ink liquid.

First, ink ejection by bubble jet will be described with reference to FIG. 3A shows a steady state, in which the surface tension of the ink 10 and the external pressure at the discharge port 4 are in an equilibrium state. (B) shows a state in which the heating element 9 serving as a heater is heated, the surface temperature of the heating element 9 rises sharply, the adjacent ink layer is heated until a boiling phenomenon occurs, and minute bubbles 11 are scattered.

FIG. 3C shows a state in which the adjacent ink layer heated rapidly over the entire surface of the heating element 9 is instantaneously vaporized to form a boiling film, and the bubbles 11 grow. At this time, the pressure in the nozzle rises by the amount of the bubble growth, 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. (D) shows a state in which the bubble 11 has grown to a 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 leading end of the ink column, the ink moves forward while maintaining the extruded speed, and at the trailing end, the ink flows backward from the discharge port surface into the nozzle due to the decrease in the internal pressure of the nozzle due to the contraction of the bubble 11, and the ink column is constricted Has occurred.

FIG. 3F shows a state in which the bubbles 11 are further contracted, the ink comes into contact with the surface of the heating element, and the surface of the heating element is cooled more rapidly. On the orifice surface, the external pressure is higher than the internal pressure of the nozzle, so that a large meniscus has entered the nozzle. The tip of the ink column becomes a droplet and flies in the direction of the recording paper at a speed of 5 to 10 m / sec.
(G) is a process in which the ink is supplied again to the ejection port by capillary action and returns to the state of (a), and the bubbles have completely disappeared.

FIG. 5 is an embodiment for explaining the structure of the main part of the above-described liquid jet recording head. FIG. 5 (a) is a detailed partial front view of the bubble jet head viewed from the ejection port side.
FIG. 3B is a partial cross-sectional view taken along a dashed-dotted line xx in FIG. Recording head 13 shown in this drawing
Is formed by arranging and joining a grooved plate 16 provided with a predetermined number of grooves having a predetermined width and a predetermined depth at a predetermined linear density on a substrate 15 provided with an electrothermal converter 14 on the back surface. At the end of the recording head, a liquid discharge section 18 including a discharge port 17 for causing the liquid to fly is formed.

The liquid discharge section 18 is a place where the thermal energy generated from the discharge port 17 and the electrothermal transducer 14 acts on the liquid to generate bubbles, which cause a sudden state change due to expansion and contraction of the volume. And a certain heat acting portion 19. The heat acting section 19 is a heat generating section 20 of the electrothermal converter 14.
Of the heat generating portion 20 as a surface in contact with the liquid, is a lower surface thereof. Heat generator 20
Is a lower layer 22 provided on the base 15,
It comprises a heating resistance layer 23 provided thereon and a protective layer 24 as an upper layer provided on the heating resistance layer 23.

The heating resistor layer 23 is provided on its surface with electrodes 25 and 26 for supplying electricity to the layer 23 in order to generate heat. 20 are formed. The electrode 25 is an electrode common to the heat generation units 20 of the liquid discharge units 18, and the electrode 26 is a selection electrode for selecting the heat generation units 20 of each liquid discharge unit 18 to generate heat, and It is provided along the liquid flow path of the discharge unit 18.

The protective layer 24 fills the liquid flow path of the heat generating resistance layer 23 and the liquid discharge unit 18 in order to protect the heat generating resistance layer 23 in the heat generating part 20 chemically and physically from the liquid to be used. It has a function of isolating a liquid that is present, preventing a short circuit between the electrodes 25 and 26 through the liquid, and preventing electrical leakage between adjacent electrodes. The liquid flow path provided in each liquid discharge part 18 constitutes a part of the liquid flow path upstream of each liquid discharge part,
They are communicated via a liquid passage chamber (not shown). Electrodes 2 connected to electrothermal transducers 14 provided in each liquid discharge section
5 and 26 are protected by the protective layer 24, which is the upper layer, on the upstream side of the heat acting portion due to the design convenience.
It is provided so as to pass below the common liquid chamber.

FIG. 6 is a detailed view for explaining the structure of a bubble generating section using a heating resistor. In the drawing, 27 is a heating resistor, 28 is an electrode, 29 is a protective layer, and 30 is a power supply device. Is shown. Useful materials for forming the heating resistor 27 include, for example, a tantalum-SiO ₂ mixture,
Examples include tantalum nitride, nichrome, silver-palladium alloy, silicon semiconductor, and boride of metal such as hafnium, lanthanum, zirconium, titanium, tantalum, tungsten, molybdenum, niobium, chromium, and vanadium. 27 Heating resistor 28 Electrode 29 Protective layer 30 Power supply

Among the materials constituting the heating resistor 27, metal borides can be cited as being particularly excellent. Among them, hafnium boride has the most excellent characteristics. The order is zirconium boride, lanthanum boride, tantalum boride, vanadium boride, and niobium boride. The heat generating resistor 27 can be formed using the above-mentioned materials by a technique such as electron beam evaporation or sputtering. The thickness of the heating resistor 27 is determined according to its area, material, shape and size of the heat acting portion, and furthermore, power consumption in an actual plane, so that the amount of heat generated per unit time becomes a desired value. Usually, 0.001-5 μm, preferably 0.01-1 μm
It is said.

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 can be cited, and they are provided in a predetermined size, shape, and thickness at a predetermined position by means such as vapor deposition using these.

The properties required for the protective layer 29 are that they do not prevent the heat generated by the heating resistor 27 from being effectively transmitted to the recording liquid, and that the heating resistor 27 is protected from the recording liquid. is there. Useful materials for forming the protective layer 29 include, for example, 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
Preferably, it is formed to a thickness of about 3 μm.

FIG. 7 is a diagram illustrating the 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-level recording. (A) showing the case of binary recording is the same as the description of the ink jet 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. The ink droplet 31A for forming a recording pixel is ejected from the ejection port 32 by the generation of the bubble. In this case, bubbles are generated once, and the film of the bubbles covers the heating element, thereby preventing 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 bubbles is affected. , And the size of the ink droplet does not change, so that the mass of the ejected ink droplet becomes substantially constant, so that a so-called binary recording is obtained.

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

The ink jet head is provided with means for changing the mass of the ink to be ejected, so that a single print P as shown in FIG.
In the case where the character information M and the image information G are mixed in the information, suitable recording can be performed. In other words, when printing character information, a substantially uniform ink droplet is ejected to print the character information.
When printing the image information G by performing the value recording, it is possible to perform multi-value recording with rich gradation by changing the mass of the ink droplet to be ejected, and print information such as a so-called photograph.

[0029] Binary recording and multi-value recording can be performed using the same head as the ink jet head. However, since the size of the nozzle is the same, the difference in the mass of the ejected ink is as follows. As shown in FIGS. 7A and 7B, the length (l) of the ink droplets 31A and 31B in the ejection direction is shown.
It appears as a difference between a) and (lb). Therefore, the same frequency (head drive frequency) as in the case of performing binary recording (FIG. 7A) and the case of multi-level recording (FIG. 7A).
Injecting ink droplets in (b)) may cause inconvenience.

In general, the ink-jet head is driven at the maximum speed when driven continuously in order to make full use of its ability. By the way, similarly to the maximum speed in the case of binary recording (in the case of FIG. 7A), when the multi-value recording (FIG. 7B) is performed, the mass of the ink droplet ejected in the case of the binary recording Although there is no problem when the mass of the ink droplet for multi-value recording is small, the length (lb) of the ink droplet becomes long when the mass of the ink droplet is large. Before the ink droplets are separated from the nozzle portion, the ejection of the next ink droplet is started, and the ink droplets before and after are integrated. In such a case, the ink droplet ejected on the paper cannot form a pixel at a target position on the paper, and the image is disturbed.

From the above, when performing binary recording and multi-value recording using the same head, in order to obtain a good image on the paper surface, the mass of the ink droplet to be ejected must be equal to the binary recording. When multi-level printing is larger than multi-level printing, the driving speed in multi-level printing needs to be slower than in binary printing.

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

However, as is clear from FIGS. 7A and 7B, the difference in the mass of the ejected ink droplet appears as the difference in the length of the ink droplet la, lb, and therefore, the paper surface Looking microscopically at the time when one pixel is formed, binary recording in FIG. 7A is faster than multi-level recording in FIG. 7B. In other words, the time from when the leading end of the ink droplet reaches the paper surface to when the trailing end portion of the ink droplet 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 low, FIG.
In both the case of FIG. 7A and the case of FIG. 7B, a substantially uniform round pixel is formed, but when the relative speed is high, the trailing end of the ink droplet is round. It protrudes outside the pixel and causes a so-called tailing phenomenon, which causes image quality to be disturbed.

As shown in FIG. 9, the ink droplet 31C may fly with a small ink droplet called a satellite 33 at the rear end of the ejected ink droplet 31C. When the relative speed between the head and the recording medium is high, the satellite adheres to the periphery of the pixel, thereby deteriorating the image quality.

Generally, when performing ink jet recording,
In at least binary recording, the relative speed between the recording head and the recording medium during printing is set to the maximum, or the speed, within a range where good round pixels can be obtained and in consideration of the cost in configuring the printer. The speed is set according to. Then, when performing multi-value recording using the same recording head,
There is no problem when the mass of the ejected ink droplet is smaller than in the case of binary recording, but when the mass of the ejected ink droplet is larger,
Since the trailing edge of the ink droplet on the paper surface causes a trailing phenomenon 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 set to be slower than in binary recording. It is important to record.

FIG. 10 is a view for explaining another gradation recording means by thermal ink jet. In the drawing, 31 is a flying ink droplet, 34 is the shape of a pixel on the paper,
Reference numeral 35 denotes a drive pulse. FIG.
As in (a), the flying ink droplet has a uniform ink amount.
This is a case where binary recording is performed. FIG. 10B shows that one or more pulse energies are applied at small intervals, and one or more micro ink droplets 31 ₁ to 31 ₁ to 31 〜 depending on the energy.
31 ₄ are formed.

Further, depending on different conditions, these fine ink droplets can fly independently as one continuous ink droplet having a bump-like bulge corresponding to the number of input pulse energies. The pulse energy input in the case of FIG.
Is smaller than the pulse energy, and the ink droplets formed are also smaller.

This small pulse energy has a high frequency (several to several tens of kHz), and since one to several pulses are applied, as shown in FIG. Alternatively, they are ejected and fly as one connected ink column, thereby adhering to the paper surface to form the pixel 34. Since these minute ink droplets 31 _{1 to} 31 ₄ adhere to the paper surface in a short time, one pixel is formed by a plurality of ink droplets. That is, gradation recording is performed by changing the size of a pixel according to the number of ink droplets.

In short, using one recording head, the operation shown in FIG. 10A is performed for character information (binary recording information), and for image information (multi-value recording information). 10 (b), and can correspond to all kinds of image information. In the case of FIG. 10 as well, as described with reference to FIG. 7, the length la of the ink droplet in the case of performing the binary printing and the input of a plurality of pulses particularly in the case of performing the multi-value printing, and the ink mass is large. Length lb of the minute ink drop row in case
This means that the whole length lb of the latter minute ink droplet row may be longer than the former ink droplet length la, so that the frequency of forming one pixel when performing multi-valued printing is It is necessary to perform recording at a lower recording speed than when performing binary recording.

FIG. 11 relates to another type of ink jet head of a type in which ink is sucked and fly using an air flow and electrostatic force as another gradation recording means. 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 discharge port 40 has a diameter of about 50 μm. The number of each of the discharge ports 39 and 40 is 24 each. Also,
A common electrode 41 is attached to the wall surface where the air outlet 39 is opened, and a control electrode 42 is attached to each ink outlet 40. 46 is an ink tank.

The principle of operation 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 air 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 ejection port 40 is connected to the ink ejection port 40 from FIG.
As shown in the figure, the ink bulge (meniscus) 4
4 can be done.

Here, between the ink and the control electrode 42,
When a pulse signal voltage of -400 V is applied, a stronger electrostatic force is generated, and the meniscus 44 is stretched. Then, the ink jumps on the air flow, and a thin ink beam 45 is generated as shown in FIG. The diameter of the ink beam 45 is 10 μm or less,
It is much thinner than 0. Further, the ink beam 45 can fly about 10 to 20 mm, but the recording paper is actually set at a position within 3 to 4 mm from the nozzle.

The amount of ink ejected is controlled by the pulse width of the signal voltage. Control may be performed by a pulse voltage in addition to the pulse width. With such a configuration, the mass of the flying ink can be controlled in a wide range of 1: 200, and the pulse width for flying the minimum amount of ink is 50 to 60 μs. In this method, the size of the pixel to be recorded on the recording paper can be easily changed, and 256 pixels can be used.
Control of gradation is also possible.

FIG. 12 shows the nozzle shape, meniscus shape, and ink discharge state near the discharge port in FIG. (A) is a state in which the air flow is not flowing, and the meniscus has a concave shape 44a. This is because the ink liquid level in the ink tank 46 is located below the nozzle. In (b), an air flow is generated,
In this state, no signal is applied, and 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 meniscus 44b is formed while maintaining the balance between the pressure Pi and the air pressure Pa generated near the ink ejection port by the air flow sent to the head. 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.
> Pa, the meniscus 44b is formed in a convex shape.

(C) shows a state in which a voltage is applied between the electrodes, the meniscus 44b is stretched, and flies while being accelerated by the air flow. Thereafter, when the signal voltage between the electrodes is released, the ink stretched in a string form is cut, and the thin liquid columnar ink flies. Then, when the air flow is released, the state shown in FIG.

In the case of the ink jet system using the air flow and the electrostatic force shown in FIGS. 11 and 12, binary recording in which the same pixel diameter is printed and printing in which the pixel diameter is different, multi-value recording are performed. And it is possible. In the case of multi-value recording in which a large pixel is formed, the ink is elongated and flies in the form of a thread and flies, so that the ink column becomes longer than in the case of binary recording.

Therefore, also in this method, when multi-value recording is performed, the front end of the next ink column is not attached to the rear end of the preceding ink column, and the rear end of the ink column is In order to prevent the trailing phenomenon from occurring, the problem can be solved by making the recording speed slower than the recording speed when performing binary recording.

As described above, the case of the ink jet system using the air flow and the electrostatic force has been described. However, it is also possible to fly the ink only by the electrostatic force without flowing the air flow. In that case, in order to fly the ink, a bias voltage of, for example, 2 to 3 kV is required, and it is necessary to increase driving energy. However, since no air flow is required, an air pump or the like is not required, and the configuration is simplified.

Hereinafter, the present invention will be described with reference to experimental examples. Experimental Example 1 FIG. 13 shows that an ink droplet flies by the action of thermal energy.
Heating element related to the recording head
Configuration that can control the temperature distribution according to the signal level
And shows an example of the planar shape of the heating element pattern.
You. 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 electrodes
92 side width B_TwoIs formed wider and the width B₁Part and width B_Twopart
Change the current density at
Are different from each other. The shorter width of the heating element 47
Width B₁Is 15 μm, the longer width B_TwoWith 40 μm
The length L of the heating element 47 is set to 100 μm, and the resistance of the heating element is set to 100 μm.
The resistance value used was 120Ω.

A heating element substrate having such a heating element 47 and a flow path plate formed by etching 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 diameter of the printed pixel and the shape of the pixel were evaluated. Table 1 shows the results. The nozzle size of the head is 40 μm × 30 μm.
m. The ink used was DeskJet ink manufactured by Hewlett-Packard Company, and the recording paper used was mat-coated paper NM manufactured by Mitsubishi Paper Mills.

[0052]

[Table 1]

In Table 1, No. No. 1 is a condition for performing binary recording. 2-No. Reference numeral 12 denotes a case of multi-value recording in which the mass of the ejected ink is changed by utilizing the characteristics of the head. Note that the pixel diameter is an average value of n = 10. The mark “○” in the pixel shape indicates a case where a good round pixel was obtained, and the mark “X” indicates a case where a clean round shape was not obtained.

As is apparent from Table 1, in the case of multi-value recording, especially when a large pixel diameter is obtained, two pixels are required.
It can be understood that good round pixels are formed by driving the head at a speed lower than the driving speed of the 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 size of the width 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 head ’s idle size is
It was 28 μm × 29 μm. The conditions for ink, recording paper, and the like are the same as those in Experimental Example 1. When the number of pulses is plural, the pulse generation frequency in the pulse group was 30 kHz.

Table 2 shows the results.

[Table 2]

As is clear from Table 2, the normal binary recording is No. 1, the number of pulses is 1, and No. 1 is a multi-value recording. 2-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 jetted using an ink jet type head using an air flow and 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 discharge port is φ60 μm, and the diameter of the air discharge port is φ60 μm.
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.

Table 3 shows the results.

[Table 3]

No. 3 in Table 3. 1 is a case where a condition for obtaining a stable and uniform pixel diameter is provided, and binary recording is performed under this condition. As is clear from Table 3, in the case where gradation recording (multi-value recording) is performed by causing ink to fly by electrostatic force (No. 2 to No. 12), a pixel having a pixel diameter larger than that of binary recording is used. In order to obtain, its driving frequency is 2
It can be understood that a good pixel shape can be obtained by making the recording time slower than when recording the value.

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 recording head dimensions were such that the shorter width B ₁ of the heating element was 10 μm and the longer width B ₂ was 35 μm.
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 determined by fixing the recording paper and changing the speed of the carriage on which the recording head was mounted. Other conditions were as in Experimental Example 1.
Is the same as Table 4 shows the results.

[Table 4]

As is apparent from Table 4, when gradation recording (multi-value recording) is performed by changing the mass of ink ejected from the nozzles, it is necessary to use a binary method in order to obtain a pixel larger than that in binary recording. Relative speed between recording head and recording paper during recording
Degrees by remote, by recording is set to a slow speed, it can be understood that good round pixel is obtained.

[0064]

According to the structure of the present invention, when performing gradation recording in various ink jet recording means in an ink jet printer or the like, tailing or oblong pixels conventionally observed in the case of multi-value recording are eliminated. This has the effect of obtaining good round pixels and enabling high-quality gradation recording.

[Brief description of the drawings]

FIGS. 1A to 1G are explanatory views of the operation 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 exploded into a lid substrate and a heating element substrate.

FIG. 4 is a perspective view of the lid substrate shown in FIG.

FIGS. 5A and 5B are diagrams for explaining a configuration of a main part of the liquid jet recording head, wherein FIG. 5A is a detailed front view viewed from the ejection port side, and FIG. 5B is a dashed line xx in FIG. It is sectional partial drawing in the part shown by.

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

FIGS. 7A and 7B are explanatory diagrams of a case where ink is ejected from an ejection port using the ink jet head shown in FIGS. 5 and 6, wherein FIG. 7A shows a case of binary recording, and FIG. Is the case.

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

FIG. 9 is an explanatory diagram illustrating a state where satellites are generated at the rear end of the ejected ink droplets.

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

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

12 (a) to 12 (c) are drawings for explaining the operation of the ink jet head shown in FIG.

FIG. 13 shows 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]

 REFERENCE SIGNS LIST 1 cover substrate 2 heating element substrate 3 recording liquid inflow port 4 orifice 5 flow path 6 area 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 Discharge port 33 Satellite 34 Pixel shape 35 Drive pulse 37 Air chamber 38 Ink chamber 39 Air discharge port 40 Ink discharge port 41 Common electrode 42 Control electrode 43 Air pump 44 Meniscus 45 Ink beam 46 Ink tank 47 Heating element 48, 49 Electrode

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/205 B41J 2/05

Claims (3)

(57) [Claims] 1. A liquid is made to fly on a recording medium as a liquid droplet,
In an ink jet recording method for recording binary recording information and multi-value recording information on a recording medium, when image information input to a recording head is multi-value recording information, the recording information is higher than the recording head drive frequency in the binary recording information. and records a slow recording head driving frequency, the recording heads at the time of multi-value recording
The relative speed between the recording medium and the recording medium in the range of 0.1 to 0.5 m / s.
An ink jet recording method characterized by the囲内. 2. An ink jet recording method in which a state change due to heat is given to a liquid by thermal energy, the liquid flies as droplets on a recording medium, and binary recording information and multi-value recording information are recorded on the recording medium. In contrast to the one-pixel formation frequency in the case where recording is performed with the mass of the liquid for forming one pixel constant, the one-pixel formation frequency in the case where recording is performed while changing the mass of the liquid is slowed down, and the liquid mass is reduced. The pulse width when changing and recording is the electric energy having a pulse width smaller than the pulse width when recording while keeping the liquid mass constant. Characteristic ink jet recording method. 3. An ink jet recording method for giving a state change due to heat to a liquid by thermal energy, causing the liquid to fly on a recording medium as droplets, and recording binary recording information and multi-value recording information on the recording medium. In contrast to the one-pixel formation frequency in the case where recording is performed with the mass of the liquid for forming one pixel constant, the one-pixel formation frequency in the case where recording is performed while changing the mass of the liquid is slowed down, and the liquid mass is reduced. An ink jet recording method in which when changing recording, a predetermined number of heating elements are selected from a plurality of heating elements arranged in one flow path and recording is performed while changing the mass of the liquid.