JPH0717062B2 - Image recording method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image recording method of recording an image on a recording member by flying a liquid colorant such as ink.

“Prior Art” The so-called non-impact recording method is attracting attention as a method for making hard copy of image information converted into an electrical signal because it generates less noise during recording.

Among them, the inkjet method, which can use plain paper and can perform recording without special processing such as fixing, is considered to be a very useful recording method.

Conventionally, the ink jet method which has been put into practical use has been one in which ink is contained in a hermetically sealed container, a pressure pulse is applied to the container, and the ink is ejected from an ejection port (orifice) of the container for recording. In this method, the ink ejecting device cannot be downsized due to its operating mechanism. Therefore, when recording the required image density, it was necessary to mechanically scan the ink ejecting device. Therefore, the recording speed is reduced.

On the other hand, some techniques have been proposed as methods for improving the above-mentioned drawbacks of the inkjet method and enabling high-speed recording.

One of them is a magnetic ink jet method in which magnetic ink is arranged in the vicinity of the magnetic electrode array, ink is ejected corresponding to pixels by utilizing the ink rise due to a magnetic field, and the magnetic ink is ejected by an electrostatic field. This method allows high-speed recording because electronic scanning is possible, but it has the drawback that it is difficult to select ink and it is difficult to colorize, which is an original feature of inkjet.

Separately from this, the ink is arranged in a slit-shaped ink reservoir parallel to the electrode array, and the ink is caused to fly according to the electric field pattern formed between the opposing electrode and the electrode array through the recording paper. A method called a plane inkjet method is also well known. This method does not require a fine orifice or the like for storing ink, and can improve ink clogging, but since the voltage applied for ink flight is high, in order to prevent voltage leakage between adjacent and neighboring electrodes, Since the electrode array needs to be driven in a time division manner, there is a drawback that the speed cannot be increased so much.

A so-called thermal bubble jet method has also been proposed, in which ink is ejected from an ejection port by thermal energy.
In this method, the ink is rapidly heated to cause the film surface boiling, and the ink is ejected from the orifice by the pressure increase caused by the rapid formation of bubbles in the orifice. However, the temperature at which film surface boiling occurs is 5 to 60
Since the temperature is as high as 0 ° C., there is a practical defect that thermal deterioration of the ink and thermal deterioration of the heating resistor protective layer provided as a heating means are likely to occur.

“Problems to be Solved by the Invention” As described above, in the conventionally developed inkjet methods, it is difficult to sufficiently increase the recording speed, use of special ink, and drive Therefore, there is a problem that a certain measure is required or that the ink or the heating means is thermally deteriorated, and any of the methods still has a problem that must be solved in practical use.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an image recording method and an image recording apparatus in which ink selection is easy and high-speed recording is possible.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image recording method in which ink selection is easy and high-speed recording is possible.

“Means for Solving Problems” In the present invention, an ejection unit for ejecting a liquid colorant,
A supply path for supplying the liquid colorant to the discharge section, a heating element provided in the vicinity of the discharge section of the supply path, a first electrode provided in a direction to fly the liquid colorant from the discharge section, A second electrode for forming an electric field between the first electrode and the first electrode, the electric field passing through the liquid surface of the liquid colorant in the ejection portion, and the second electrode and the first electrode A first voltage applying means for applying a pulsed voltage only when the liquid colorant is flown between the first and the second voltage applying means, and the pulsed voltage is applied when the voltage is applied by the first voltage applying means. The image recording apparatus is provided with a second voltage applying means for applying a pulsed voltage to the heating element, which overlaps with the heating element for a predetermined period.

This applies the pulsed electrical energy by applying a uniform electric field to the entire liquid colorant for a short time,
Further, the pulsed heat energy is locally applied to the liquid colorant to fly the liquid colorant in the region to which both the energy are applied.

Alternatively, or alternatively, the pulsed thermal energy is applied by uniformly heating the entire liquid colorant for a short time, and further the pulsed electrical energy is locally applied to the liquid colorant. Then, the liquid colorant in the region to which both the above-mentioned energies are applied is caused to fly.

"Operation" In the image recording method of the present invention, electric energy and thermal energy are applied to the liquid colorant so that the liquid colorant in the region where both are applied is flown.

This method is implemented in the following manner, for example.

First, a uniform electric field is applied to the liquid colorant. This alone does not cause the liquid colorant to fly. Here, heat energy is locally applied to this liquid colorant. As a result, the liquid colorant in the area to which the thermal energy is applied flies.

The same thing occurs when the liquid colorant is uniformly heated at a temperature at which flight does not occur and a local electric field is applied to the liquid colorant.

An apparatus for carrying out such a method includes the following modes.

For example, a plurality of heating elements are arranged in an array. Then, these heating elements are brought into contact with the liquid colorant. Then, the heating elements located at the positions corresponding to the recording pixels are selectively heated, and a uniform electric field is applied. In this way, the liquid colorant is made to fly toward the recording member. One pixel can be recorded in one flight.

By repeating this to record a pixel array in a line shape and further scan the recording member, an image can be recorded.

Similar recording can be performed when the liquid colorant is heated to a uniform temperature and a plurality of electric field forming elements for locally applying an electric field are provided.

Here, when the pulsed electric energy is applied to the liquid colorant at the same time as the pulsed thermal energy is applied, even if the liquid colorant flies in the region where both energy are applied, False flight does not occur in other areas before and after. Further, since the electric field or the like is not constantly applied, the liquid level of the liquid colorant is stabilized, and the liquid colorant quickly returns to the stable liquid level after the flight. Therefore, stable and high-speed recording can be performed.

[Example] (Principle of Operation) The principle of recording operation of the image recording method of the present invention will be described with reference to FIG.

First, as shown in FIG. 1A, the liquid colorant 1 is disposed between the base electrode 2 and the counter electrode 3. Liquid colorant 1
For example, an ink which is liquid at room temperature and whose composition is adjusted so as to give a suitable electric resistance is used. Hereinafter, the liquid colorant 1 will be simply referred to as the ink 1, and the description will be continued. Both the base electrode 2 and the counter electrode 3 are conductive plates.

A predetermined voltage from the DC power supply 4 is applied between the electrodes 2 and 3. At this time, a constant electrostatic field is applied to the ink 1, and due to the electrostatic induction action, the Coulomb force given by the product of the induced charge and the electrostatic field generated here acts on the free surface of the ink. This force causes the ink 1 to fly in the direction of arrow 5.

On the other hand, the surface tension of the ink, the interfacial tension, and the viscous resistance to the ink that is about to fly act as drag forces. FIG. 1a shows a state in which this drag force is larger than the Coulomb force and the ink surface is kept horizontal.

Here, the ink 1 is locally heated. That is,
In the figure, the temperature T1 of the region S1 is made higher than the temperature T0 of the other regions (Fig. 1b). As a result, in the area S1, the first
The ink surface rises as shown in FIG. That is, in the area S1, the drag decreases due to the temperature rise of the ink, and the action of the Coulomb force locally increases. An electric field is concentrated on the raised ink 1 ', and the Coulomb force acts strongly. Thus, finally, as shown in FIG. 1C, a part of the ink 1 ′ in the region S1 grows in a columnar shape, is torn and flies toward the counter electrode 3.

This phenomenon can be caused without rapidly heating the ink as it approaches a phase change such as film surface boiling.

That is, electric energy is applied to the ink by the electric field, and heat energy is further applied by heating. The amount of electric energy and thermal energy to be applied is selected so that the ink is ejected only in the area where both energies are applied. As a result, it is possible to practically control the flight location and the flight timing of the ink.

In addition, this principle could be verified by the following experiments.

First, as shown in FIG.
It is arranged on the upper side, and the voltage of the power source 4 is gradually increased while keeping the temperature constant. When this voltage exceeds a certain voltage, an ink column 1'as shown in FIG. 1c grows randomly from the ink surface toward the counter electrode 3.

This phenomenon is, for example, by JR MELCHER (published by MITPRESS, USA) "FIELD COUPLED SURFACE WAVES" (P61-P66)
It can be interpreted as an unstable electrohydrodynamic wave growth phenomenon described in (1).

That is, when the Coulomb force acting in the upward direction and the drag force acting in the downward direction maintain a certain equilibrium perpendicular to the liquid surface of the ink, a certain perturbation (deformation of the liquid surface or local part of the electric field) that may occur naturally Non-uniformity) causes the Coulomb force to concentrate locally. There, the Coulomb force overcomes the drag force and the ink column grows.

In the present invention, for example, the electric field is selected to have a strength insufficient for growing the disordered ink column and applied to the ink. When the ink is heated in this state, the surface tension, the viscosity, etc. of the ink in the heated area are lowered.
As a result, an unstable surface wave is generated even in the above electric field, and the ink column grows in that area.

By guiding the ink thus ejected to the surface of a recording member such as recording paper, one dot can be recorded. Further, if these dots are regularly arranged, an image can be recorded.

Here, when the voltage of the power supply is further increased, the ink temperature rises to T1 in the area S1 to which the heat energy is applied, and the ink column 1'is generated. There were signs of "" growth (Fig. 1d).

Therefore, the following experiment was conducted in order to investigate what kind of physical properties of the ink the growth of the liquid column from the ink surface in the ink heating region depends on.

The solid line in the graph of Fig. 2a indicates that the volume resistivity is 10 at room temperature.
^The results of measuring the values of the threshold electric fields of the respective inks of ³ , 10 ⁴ , 10 ⁵ , and 10 ⁶ Ω · cm are shown. Also, the liquid column growth time in that case was taken, and the results as shown by the broken line were obtained.

Similarly, for inks having different surface tensions, the results shown in FIG. 2b are obtained, and for inks having different viscosities,
The result shown in FIG. 2c was obtained. The ink liquid column growth time is the time until the ink comes into contact with the counter electrodes separated by 300 μm.

That is, the threshold electric field decreases as the surface tension and viscosity increase, and the liquid column growth time tends to increase as the ink volume resistivity increases.

From the above experimental results, it is considered that the generation of the liquid column due to the cooperative action of the thermal energy and the electric energy is mainly caused by the temperature change of the surface tension of the ink in the heating region. However, the temperature change of the surface tension itself is not so large. Therefore, the liquid surface may be perturbed due to other factors, which may cause erroneous flight. In particular, if the growth speed of the ink column is increased and the strength of the applied electric field is increased in order to improve the recording speed, this false flight easily occurs.

Therefore, in the present invention, electrical energy and thermal energy are applied in pulses to prevent erroneous flight.

FIG. 3 is a time chart showing aspects of the application timing of the electric energy E and the application timing of the thermal energy H.

In the case of FIG. 3a, electric energy and thermal energy are applied at the same timing and for the same time. In FIGS. 3b and 3c, the energy of the other is applied for a short period of time during the application of either one. Further, regarding FIGS. 3D and 3E, although both electric energy and thermal energy are applied for substantially the same time, either one precedes.

When the electric energy is made to precede the heat energy, the ink can be made to fly easily before the heat energy is applied, and the amount of heat generation can be reduced. Moreover, if the period to be preceded is appropriately selected, no false flight will occur. On the contrary, if the thermal energy is applied first and the electric energy is applied after the viscosity of the ink is sufficiently lowered, the timing of ejecting the ink can be accurately controlled by the timing of applying the electric energy. That is, even if the time from the heat generation due to the difference in the temperature of the ink before applying the heat energy and the ambient temperature to the decrease of the viscosity of the ink to the value required for the flight or less fluctuates, the timing of ejecting the ink is It is not affected and can be controlled by the timing of applying the electric field.

In any of the above cases, when both energies are applied to the liquid colorant, the liquid colorant flies in the areas to which both energies are applied.

(Example of Recording Head) FIG. 4 is a cross-sectional view showing an example of the recording head and its peripheral portion of the image recording apparatus embodying the present invention.

Here, a pair of wall members 10 and 11 have one edge thereof as a recording member.
It is arranged toward 12 directions. The recording member 12 is plain paper used for recording in a general copying machine or the like.

The pair of wall members 10 and 11 are arranged at a predetermined interval, and the liquid colorant 13 is contained between them. Wall member 1
Each of 0 and 11 has a slit having a certain width in the direction perpendicular to the paper surface, which is formed at one edge facing the recording member 12. In the present invention, this portion is called the discharge portion 14. Liquid colorant
In the discharge part 14, 13 forms a convex curved surface 13 'due to its surface tension.

On the inner surface of one wall member 11, a large number of heating resistors 16 arranged in an array in a direction perpendicular to the plane of the drawing are provided, and each of them has a common electrode 17 at one end and a lead electrode at the other end.
18 connected.

An electric field forming electrode 19 is formed on the inner surface of the other wall member 10 over substantially the entire surface thereof.

FIG. 5 shows a perspective view of the main part.

The portion of the heating resistors 16 arranged in this array has, for example, a structure similar to that of a thermal head which has been generally used for thermal recording in the past. In the case of this embodiment, a so-called edge type thermal head is used, and the coloring temperature is about
It is possible to record at a recording density of 8 dots / mm on a 90 ° C. thermosensitive recording paper. When recording on this thermal paper,
0.5 W / dot of power is applied to each heating resistor for 1 msec.

The distance D between the pair of wall members 10 and 11 was set to 100 μm.

Returning to FIG. 4 again, the interval 1 between the discharge unit 14 and the recording member 12 was set to 200 μm. Further, a counter electrode 21 was provided on the back surface of the recording member 12, and a power source 22 for applying a predetermined voltage was connected between the counter electrode 21 and the electric field forming electrode 19. In this embodiment, the electric field forming electrode 19 is grounded and the counter electrode 21 is +
A voltage of 1500 V was applied. These constitute electric energy applying means.

Further, the electrodes 17 and 18 at both ends of the heating resistor 16 are connected to the power source 23.
Connected. Heat energy applying means is constituted by these.

A control means 24 is connected to the power sources 22 and 23 so that the application of energy is turned on / off by an image signal of an image to be recorded. The control means 24 is composed of a circuit including a shift register driver for driving a known thermal head.

In this example, the liquid colorant 13 was an ink in which a carbon black pigment was dispersed in liquid paraffin in an amount of about 15 weight percent. Its volume resistivity at 20 ° C. is 1.0 × 10 ⁶ Ω · cm, and its viscosity is 300 cp. Surface tension is 70 dyn
It was e / cm.

In the recording head having the above structure, when a voltage from the power supply 22 is applied between the electric field forming electrode 19 and the counter electrode 21, a uniform electric field is applied to the liquid colorant 13 near the ejection portion 14. .

In this state, current is selectively supplied to the heating resistor 16.
In the case of this example, energization was performed at 25 V and 25 mA for 1 msec.

As a result, the ink 13 flies toward the recording member 12 only near the heating resistor 16 to which the current is supplied, and a circular dot having a diameter of about 150 μm is recorded on the recording surface. Even if this energization time was shortened to 200 μsec, similar recording could be performed.

When the above operation was performed without applying a voltage between the electric field forming electrode 19 and the counter electrode 21, the ink did not fly.

On the contrary, when the voltage applied between the electric field forming electrode 19 and the counter electrode 21 is increased without energizing the heating resistor 16, when the voltage exceeds 3000 V, the ejection is performed. Ink 13 was seen flying randomly all over Part 14.

Here, when the voltage of the power supply 22 is 1500 V, the heating resistor 1
Ink column growth started about 100 μsec after the start of energization to 6. Then, the ink adheres to the recording member 12,
It took about 1 msec until the ink surface 13 'returned to its original state.

The next recording operation must be performed after the ink surface 13 'is restored, but if it is left as it is, it is difficult to increase the speed to a certain extent or more.

On the other hand, when the voltage of the power supply 22 was raised to 2500 V, the time until the start of growth of the ink column was shortened to about 50 μsec. However, the recovery time of the ink surface 13 'does not change. Moreover, erroneous ink jetting occurs in areas other than the heating area.

On the other hand, the voltage of the power supply 22 is raised at the same time when the heating resistor 16 is energized, and is cut off again after about 100 μsec to 1 msec.

As a result, erroneous flight does not occur even when the power supply voltage is 2500 V, and the ink surface returns in about 200 μsec.

That is, in the state where electric energy is not applied, the liquid surface is stable because it receives no Coulomb force, and is stabilized more quickly even after the ink is ejected.

Further, when electric energy and heat energy are suddenly applied locally from such a stable state, ink flying occurs only in that portion. If the application of both energies is stopped immediately thereafter, there is no room for false flight.

In this way, the control means 24 drives the power supply 22 and the power supply 23 at predetermined timings for a predetermined time so that pulsed electrical energy and thermal energy are applied. The application timing can be selected variously as described in FIG.

(Ink Flying Condition) In the present invention, since electric energy and thermal energy are applied to the liquid colorant to fly it, it is necessary to stably control the ink flying condition and the ink flying. It is necessary to clarify the limit value (threshold value) at which

FIG. 6 is a graph showing the results of an experiment conducted to find this threshold value.

From the data shown in FIG. 6a, it can be seen that the threshold electric field value decreases as the ink temperature increases.

Further, according to FIG. 6B, the viscosity of the ink is curved, but it decreases with the temperature rise of the ink, similarly to the threshold electric field. Similar tendencies are observed in the surface tension (c in the same figure) and the volume resistivity (d in the same figure).

Therefore, it is clear that these are largely involved in the value of the threshold electric field.

That is, it is considered that the value of the threshold electric field decreases as the temperature rises due to the combined effect of changing the physical properties such as the viscosity, surface tension, and electrical conductivity of the ink.

From this, when an electric field that does not cause the ink to fly at room temperature is applied and the ink is locally heated, the ink flies due to the cooperative action of the heat and the electrostatic field, and pixel-shaped recording can be performed. Of.

“Modification” (Modification of Electrical Energy Applying Means) FIG. 7 shows a modification of the main part of the recording head described above according to the present invention.

In the figure, a large number of electric field forming electrodes 33 are arranged in an array on the inner surface of one of the pair of wall members 30 and 31. Ink (not shown) is accommodated between the wall members 30 and 31, but this is uniformly heated by the heat energy applying means (not shown).

A counter electrode 21 is provided on the back surface of the recording member 12, and a power source for applying a voltage between the counter electrode 21 and the electric field forming electrode 33.
34 is connected. The power source 34 selectively applies a predetermined voltage to a large number of electric field forming electrodes 33 according to an image signal. As a result, an electric field is formed between the electric field forming electrode 33 to which the voltage is applied and the counter electrode 21 to the extent that ink flying occurs. In this way, recording according to the image signal can be performed on the recording member 12. In this way, similar recording can be performed by controlling the position where the electric energy is applied. In this case, since the ink is heated, there is an advantage that the ink can be ejected at a relatively low voltage.

(Modification of Heat Energy Applying Means) FIG. 8 shows still another embodiment of the main part of the recording head.

In this embodiment, the heating resistors 16 having the same structure as that shown in FIG. 8 are arranged in an array on a horizontally arranged substrate 40.
The ink 13 is held above the heating resistor 16 by dam members 41 and 42 provided on the left and right sides of the ink 13.

The recording member 12 is arranged above the ink 13 with its recording surface facing downward. Further, an electric energy applying means (not shown) forms an electric field in a direction perpendicular to the substrate 40.

In such a recording head, when current is supplied to the heating resistor 16 to generate heat, the ink 13 flies in the vertical direction by the same principle as described above, and recording can be performed on the recording member 12. The present invention can also be implemented by such a configuration.

(Others) The image recording method of the present invention is not limited to the above embodiments.

For example, a laser oscillator can be used as the heat energy applying means. In this case, the laser light is modulated according to the image information to be recorded, and the laser light is radiated onto the ink to selectively heat the ink.

Also, an example in which one of the electric energy applying means and the thermal energy applying means is always driven has been shown, but both may be simultaneously driven locally and only for a short time for ejecting ink. Absent.

[Advantages of the Invention] According to the image recording method of the present invention described above, the temperature at which the ink, the heating resistor, and the like do not undergo significant thermal deterioration,
Ink jetting is caused by an electric field that does not cause leakage between electrodes, and high-speed and high-density recording can be performed.

Moreover, the means for holding the ink may have a relatively simple structure and does not require a complicated and precise mechanism.

Further, a relatively small amount of electric energy and thermal energy to be applied is sufficient, and the drive circuit and the like can be downsized.

Furthermore, since the electric field is not constantly applied, the liquid surface state of the liquid colorant can be stabilized before and after flight,
False flight can be prevented. In addition, the time until the liquid surface returns to a stable state after flight can be shortened,
The printing speed can be increased. Further, by appropriately setting the timings of the pulse for forming the electric field and the pulse applied to the heating element, it is possible to reduce the thermal energy required to fly the liquid colorant. Further, the timing of flying the liquid colorant can be accurately controlled regardless of the temperature of the liquid colorant before the heat energy is applied and the fluctuation of the ambient temperature, and the print quality can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the principle of the image recording method of the present invention, FIG. 2 is a graph showing the relationship between physical properties of ink and threshold electric field and liquid column growth time, and FIG. 3 is pulsed electric energy and heat. FIG. 4 is a time chart showing an example of energy application timing, FIG. 4 is a longitudinal sectional view of an embodiment of a recording head used in the image recording apparatus of the present invention, and FIG.
FIG. 7 is a graph showing the temperature dependence of the threshold value of the electric field and the characteristics of the ink, FIG. 7 is a perspective view of a modification of the recording head suitable for carrying out the present invention, and FIG. 8 is a longitudinal sectional view of another embodiment. 13 ... Liquid colorant, 16, 17, 18, 23 ... Heat energy applying means, 19, 21, 22 ... Electric energy applying means, E ... Electric energy, H ... Heat energy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-12858 (JP, A) JP-A-61-189950 (JP, A) JP-A-62-151348 (JP, A) Actual development Sho-61- 70039 (JP, U)

Claims (1)

[Claims] 1. A discharge part for discharging a liquid colorant, a supply path for supplying the liquid colorant to the discharge part, a heating element provided near the discharge part of the supply path, and the discharge part. Between the first electrode provided in the direction in which the liquid colorant is flown from the first electrode, and an electric field passing through the liquid surface of the liquid colorant in the ejection portion toward the first electrode. A second electrode for forming the liquid colorant, first voltage applying means for applying a pulsed voltage between the second electrode and the first electrode only when the liquid colorant is flown, Second voltage applying means for applying to the heat generating element a pulsed voltage that overlaps with a period during which the pulsed voltage is applied when the voltage is applied by the first voltage applying means; An image recording apparatus comprising: