JPS62225354A - Image-recording head - Google Patents

Abstract

PURPOSE:To ensure easy selection of an ink and enable high-speed recording, by providing a thermal energy applying means constituted of a plurality of heat generating elements provided on the inner surface of one of wall members, and providing one of electric field generating electrodes of an electrical energy applying means on the inner surface of the other wall member. CONSTITUTION:An image-recording head comprises two wall members 10, 11 for supporting a liquid coloring agent 13, with a plurality of heat generating elements 16 provided on the inner surface of the wall member 11. When heat is generated by the element 16, the coloring agent 13 in the vicinity of the element 16 is caused to fly from an ejecting part 14 toward a recording member 12. In this recording head, the quantity of the liquid coloring agent 13 caused to fly can be appropriately selected by regulating the spacing between the wall members 10, 11. In addition, an electric field with appropriate intensity can be applied to the coloring agent 13 by an electric field generating electrode 19 provided on the inner surface of the wall member 10.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an image recording head that records an image on a recording member by jetting a liquid colorant such as ink.

"Prior Art" The so-called non-impact recording method is attracting attention as a method for converting image information converted into electrical signals into hard copies because it generates little noise during recording.

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

Conventionally, in the inkjet method that has been put into practical use, ink is stored in a sealed container, pressure pulses are applied to the container, and the ink is ejected from an ejection opening (orifice) of the container for recording. This method does not allow the ink ejection device to be miniaturized due to its operating mechanism, so it is necessary to mechanically scan the ink ejection device in order to print at the required image density. Therefore, this resulted in a decrease in recording speed.

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

One such method is a magnetic inkjet method, in which magnetic ink is placed near a magnetic electrode array, the ink is swelled by a magnetic field, and an ink discharge state corresponding to a pixel is formed, and the magnetic ink is ejected using an electrostatic field. This method allows high-speed recording because electronic scanning is possible, but it has the drawback that it is not easy to select the ink and it is difficult to print in color, which is an inherent characteristic of inkjet printing.

Separately, ink is placed in a slit-shaped ink reservoir parallel to the electrode array, and the ink is ejected through the recording paper according to the electric field pattern formed between the opposing electrodes and the electrode array. A method called planar inkjet method is also well known. This method eliminates the need for fine orifices to store ink and can improve ink clogging, but since the voltage applied to fly the ink is high, in order to prevent voltage leaks between adjacent and nearby electrodes, It is necessary to time-divisionally drive the electrode array, which has the disadvantage that high speed cannot be achieved.

A so-called thermal bubble jet method has also been proposed in which ink is ejected from an ejection port using thermal energy.

In this method, the ink is rapidly heated to cause film surface boiling, and the pressure increases due to the rapid formation of bubbles within the orifice, and the ink is ejected from the orifice.

However, since the temperature at which film surface boiling occurs is as high as 5 to 600°C, it has practical drawbacks such as thermal deterioration of the ink and thermal deterioration of the heating resistor protective layer provided as a heating means. had.

``Problems to be Solved by the Invention'' As mentioned above, the inkjet methods that have been developed so far have the difficulty of increasing the recording speed sufficiently, the use of special inks, and the problems with the drive. However, there are problems such as requiring a certain amount of ingenuity or causing thermal deterioration of the ink and heating means, and each method still has problems that must be solved in terms of practical use.

The present invention has been made with attention to the above points, and an object of the present invention is to provide an image head that allows easy selection of ink and enables high-speed recording.

"Means for Solving the Problems" The image recording head of the present invention arranges a liquid coloring agent, applies both electrical energy and thermal energy to the liquid coloring agent, and applies both electrical energy and thermal energy to the image recording head. The device for causing the liquid colorant to fly includes a storage means for storing the liquid colorant, a thermal energy application means for heating the liquid colorant, and an electric energy application means for applying an electric field to the liquid colorant. , the accommodation means is composed of a pair of wall members facing each other at a predetermined interval and having a discharge part for discharging the liquid colorant at -it;
The device comprises a plurality of heating elements provided on one inner surface of the wall member, and one of the electric field forming electrodes of the electric energy applying means is provided on the other inner surface of the wall member. It is.

Here, the plurality of heating elements are arranged parallel to the discharge portion of the wall member at a predetermined pitch, and when the interval between the wall members is D and the arrangement pitch of the heating elements is P,
It is preferable to select so that D<4F.

Further, it is preferable that an edge of the electric field forming electrode provided on the other inner surface of the wall member on the side of the discharge part be located away from an edge of the discharge part.

"Operation" The image recording head of the present invention applies the principle of applying electric energy and thermal energy to a liquid colorant and causing the liquid colorant in an area where both are applied to fly.

That is, it is realized, for example, in the following manner.

First, a uniform electric field is applied to the entire liquid colorant.

This alone does not cause the liquid colorant to fly. here,
Thermal energy is applied locally to this liquid colorant. As a result, the liquid colorant in the area to which this thermal energy has been applied flies.

The same thing happens even if the liquid colorant is uniformly heated to a temperature that does not cause it to fly, and then an electric field is applied locally.

Here, for example, a plurality of heating elements are arranged in an array. Then, these heating elements are kept in contact with the liquid colorant. Then, a heating element located at a position corresponding to a recording pixel is selectively caused to generate heat, and a uniform electric field is applied to the entire liquid colorant. In this way, the liquid colorant is ejected toward the recording member. One pixel can be recorded in one flight.

By repeating this process to record pixel rows in a line, and then scanning the recording member, an image can be recorded.

The image recording head of the present invention uses two wall members to hold liquid colorant. A plurality of heating elements are provided on the inner surface of the wall member.

When this heating element generates heat, liquid colorant in the vicinity of the heating element flies toward the recording member from the discharge section.

According to the recording head having such a configuration, it is possible to appropriately select the amount of liquid colorant to be ejected by adjusting the interval between the wall members.

Moreover, an electric field of appropriate strength can be applied to the liquid colorant by the electric field forming electrode provided on the other inner surface of the wall member.

"Embodiment" (Operating Principle) Here, the recording operation principle of the image recording head of the present invention will be explained in advance with reference to FIG.

First, as shown in FIG. 2a, a liquid colorant 1 is placed between a base electrode 2 and a counter electrode 3. Liquid colorant 1 includes:
For example, an ink that is liquid at room temperature and whose formulation is adjusted to provide an appropriate electrical resistance is used. Below, liquid colorant 1
The explanation will be continued by expressing simply as ink 1. Base electrode 2
and the counter electrode 3 are both simply conductive plates.

A predetermined voltage is applied between these electrodes 2.3 by a DC power supply 4. At this time, a certain electrostatic field is applied to the ink 1, and due to the electrostatic induction effect, a Coulomb force given by the product of the induced charge generated here and the electrostatic field 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 flying ink act as drag forces here. FIG. 2a shows a state in which this drag force is greater than the Coulomb force and the ink liquid level is kept horizontal.

Here, this ink 1 is locally heated. That is,
In the figure, the temperature T1 of the region S1 is made higher than the temperature TO of the other regions (FIG. 2b). As a result, the ink liquid level rises in the region S1, as shown in FIG. That is, in this region S1, the above-mentioned drag force decreases due to an increase in the temperature of the ink, and the effect of the Coulomb force locally increases. The electric field concentrates on the raised ink 1', and a strong Coulomb force acts on it. In this way, finally, as shown in FIG. 2C, a portion of the ink 1' in the region S1 grows into a columnar shape, breaks off, and flies toward the counter electrode 3.

This phenomenon can be caused even if the ink is not heated so rapidly as to bring about a phase change such as film boiling.

That is, electrical energy is applied to the ink by the electric field, and thermal energy is further applied by heating. The amounts of electrical energy and thermal energy to be applied are selected so that ink will fly only in the area where both energies are applied.

This enables practical control of the ink flying location and flying timing.

This principle could be demonstrated through the following experiment.

First, as shown in FIG. 2a, ink 1 is applied to the base electrode 2.
The voltage of the power supply 4 is gradually increased while keeping the temperature constant. When this voltage exceeds a certain voltage, ink columns 1' as shown in FIG. 2C grow randomly from the ink liquid surface toward the counter electrode 3.

This phenomenon has been described, for example, by J. R. Melcher (USA M.
, 1. T, published by PRESS) rFIELD, -COU
PLED 5URFACEWAVESJ (P61
- It can be interpreted as the growth phenomenon of unstable electrohydrodynamic waves described in P.66).

In other words, when the Coulomb force acting upward and the drag force acting downward perpendicular to the ink liquid surface maintain a certain balance, certain perturbations (such as deformation of the liquid surface or electric field) that occur naturally occur. (local non-uniformity), the Coulomb force is locally concentrated. Therefore, 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 an intensity insufficient for the growth of the disordered ink columns, and is applied to the ink. When the ink is heated in this state, the surface tension, viscosity, etc. of the ink in the heated area are reduced.

As a result, even in the electric field as described above, unstable surface waves are generated, and ink columns grow in that region.

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

(Embodiment of Recording Head) FIG. 1 is a longitudinal sectional view showing an embodiment of the image recording head of the present invention and its peripheral portion.

Here, a pair of wall members 10.11 are arranged with one edge thereof facing toward the recording member 12.

The recording member 12 is plain paper used for recording in general copying machines and the like.

The pair of wall members 10.11 are arranged at a predetermined interval, and the liquid colorant 13 is accommodated therebetween. The wall member 10.11 has a slit having a constant width in the direction perpendicular to the plane of the paper at one edge facing the recording member 12. In the present invention, this portion is referred to as the discharge section 14. The liquid colorant 13 forms a convex curved surface 13' in the discharge portion 14 due to its surface tension.

On the inner surface of one wall member 11, a large number of heating resistors 16 are arranged in an array in a direction perpendicular to the plane of the paper, and each of these has a common electrode 17 at one end and a lead electrode 18 at the other end. is connected. Further, a heat-resistant insulating layer 20 is formed to cover the heating resistor 16 and the electrodes 17 and 18.

Furthermore, an electric field forming electrode 19 is formed on the inner surface of the other wall member 10 over almost the entire surface thereof.

Figure 3 shows a perspective view of its main parts.

The heating resistors 16 arranged in an array have, for example, a structure similar to that of a conventional thermal head commonly used for thermal recording.

In this embodiment, a so-called edge-type thermal head is used, and it is possible to perform recording at a recording density of 8 dots) and 7 mm on thermal recording paper with a coloring temperature of about 90°C.

When recording on this thermal paper, each heating resistor receives 0.5W/
Dot power is applied for 1 m5ec.

Further, the distance between the pair of wall members 10 and 11 is 100 μm.
was selected.

Returning to FIG. 1 again, the distance β between the ejection section 14 and the recording member 12 was selected to be 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 example, the electric field forming electrode 19 was grounded, and a voltage of +1500 V was applied to the counter electrode 21. These constitute an electric energy applying means.

Furthermore, on the electrodes 17 and 18 at both ends of the heating resistor 160,
The power supply 23 was connected. These constitute a thermal energy applying means.

A control means 24 is connected to the power supplies 22 and 23 so that the application of energy is turned on and off according to the image signal of the image to be recorded. This control means 24 (well, it consists of a circuit consisting of a known shift register driver for driving a thermal head, etc.) In this embodiment, as the liquid colorant 13, about 15 parts of carbon black pigment is mixed in liquid paraffin. A percent dispersed ink was used.The volume resistivity at 20°C was 1.0 x 10' Ω-cm, and the viscosity was 30
0 cp, and the surface tension was 70 dyne/cm.

In the recording head having the above configuration, the electric field forming electrode 19
When a voltage is applied by the power source 22 between the electrode 21 and the counter electrode 21, a uniform electric field is applied to the liquid colorant 13 in the vicinity of the discharge portion 14.

In this state, current is selectively supplied to the heating resistor 16. For this example, 1 m5e at 2.5 V and 25 mA
energization was performed.

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

On the right, when the above operation was performed without applying a voltage between the electric field forming electrode 19 and the counter electrode 21, no ink flying occurred.

Conversely, without energizing the heating resistor 16,
As the voltage applied between the electric field forming electrode 19 and the counter electrode 210 is increased, when this voltage exceeds 3000V, the ink 13 is randomly distributed throughout the ejection section 14.
was seen flying.

(Ink flying conditions) Since the present invention applies electrical energy and thermal energy to the liquid colorant to make it fly, it is important to control the conditions for ink flying and stable control of ink flying. It is necessary to clarify the limit value (threshold value) that can be achieved.

FIG. 4 is a graph showing the results of an experiment conducted to find this threshold value.

According to the data shown in FIG. 4a, it can be seen that as the temperature of the ink increases, the value of the threshold electric field decreases.

Furthermore, according to FIG. 4, the viscosity of the ink, although drawing a curve, decreases as the temperature of the ink increases, similar to the threshold electric field described above. Similar trends are observed for surface tension (C in the same figure) and volume resistivity (D in the same figure).

Therefore, it is clear that these factors are greatly 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 effects of changes in physical property values such as the viscosity, surface tension, and electrical conductivity of the ink.

Therefore, if an electric field is applied to a level that does not cause ink to fly at room temperature, and the ink is locally heated, the ink will fly due to the cooperation between the heat and the electrostatic field, allowing pixel-like recording. It is.

Further, according to the recording head having such a configuration, the ink ejection section 14 (FIG. 1) can be brought sufficiently close to the recording member, and the amount of ink to be ejected can be adjusted by adjusting the distance between the wall members 10 and 11. can be selected appropriately.

(Position of the electric field forming electrode) Note that the edge 19' of the electric field forming electrode 19 is preferably located at a position slightly set back from the edge of the discharge part 14, as shown in FIG. In this way, a more uniform electric field can be applied to the entire ink 13 in the ejection section 14. Further, in order to form a uniform electric field, the edge 19' of the electric field forming electrode 19 is made substantially parallel to the edge of the discharge part 14, and the distance from the counter electrode 21 is constant. Needless to say.

In reality, the distance L (shown in FIG. 1) between the tip position of the ink free surface 13' and the edge 19' of the electric field forming electrode 19 varies depending on the conductivity of the ink 13 used. , preferably about 10 to 500 μm.

When a conductive ink is used, even if the above-mentioned resistance increases further, the flight of the ink is not significantly affected.

When a resistive ink (volume resistivity of 10 6 Ω·cm or more) is used, if L is set to 500 μm or more, the time required for electrostatic induction to occur cannot be ignored.

Therefore, for example, when recording is to be performed by applying a voltage for forming an electric field in a pulsed manner and at the same time passing a current in a pulsed manner to the heating resistor 16, the pulsed voltage for forming the electric field is The application time becomes long.

For these reasons, it is preferable to form the electric field forming electrode as described above.

Actually, for the image recording head shown in FIG.
1 and the electric field forming electrode 19, 2000V, 1m5
ec voltage pulse is applied to the heating resistor 16 at the same time.
When a current of 0 V and 1 m5ec was applied (the resistance value was 300Ω), a circular dot of 150 μm was recorded as in the previous example. At this time, ink 13 was made by dispersing 15% by weight of carbon black pigment in liquid paraffin, and the volume resistivity at 20°C was 1.0X.
10" Ω・cm, viscosity 300cp surface tension 3Qdy
It was ne/cm.

For comparison, when a similar operation was performed with an electric field forming electrode 19 provided on the inner surface of the wall member 10 that reached the edge of the ejection part 14, there were places where ink did not fly.
Moreover, a discharge was induced between the counter electrode 21 and the electric field forming electrode 19.

(Pitch of heating resistors) In FIG. 3, the arrangement density (array pitch) P of the heating resistors 16 provided on the wall member 11 is set to 4 dots/mm.
(250, um), 3 dat/mm (125 μm), and 12 dat/mm (83 μm), and for the other wall member 11, a Cr (chromium) layer was deposited on a glass substrate and an electric field forming electrode 19 was formed. The formed one was prepared.

The ink used was one in which carbon particles were dispersed in liquid paraffin at 20°C.
The material used had a volume resistivity of 1X10'Ω'cm, a viscosity of 200 cp, and a surface tension of 30 dyne/cm. Furthermore, wall members 10, 11 having a spacing D (FIG. 3) selected to be 1.1 times, 2 times, 4 times, and 6 times the arrangement pitch P of the heating resistors 16 were prepared.

Each heating resistor 16 has l wa t t/do t (
7) Apply 1m5ec of power to the discharge part 14 and the counter electrode 2.
1 and a voltage of 2000V1m5ec was applied between the counter electrode 21 and the electric field forming electrode 19. The results are shown in Table 1.

Arrangement pitch of heat-generating group antibodies; P Distance between wall portions; D Here, in the part marked *, the ink 13 overflowed near the heat-generating resistor 16 and adhered to the recording member.

In addition, in the part marked with **, one heat generation of one heating resistor 16 causes the ink 13 in the vicinity to flow into the ejection part 14.
The dots were dispersed in a direction perpendicular to the longitudinal direction of the recording member 12, and two or more dots were recorded on the recording member 12.

That is, if the interval between the wall members exceeds four times the arrangement pitch P of the heating resistors 16, the ink will not fly as a single dot.

This is because the ink is incompressible, so it forms a surface wave shape with a certain wavelength determined by the balance between the electrostatic field and surface tension, and the ink column splits to correspond to this surface wave shape. it is conceivable that.

Also, if the spacing between the wall members is too narrow, the heating resistor 16
The ink 13 expands due to the heat generated by the ink, and the ink overflows from the ejection portion solely due to the force of this thermal expansion.

From the above, it is preferable to select D/P to be 1/2 or more, more preferably 1 or more and 4 or less.

"Variation" The present invention is not limited to the above embodiments.

The shape, arrangement, etc. of the heating resistors provided on the inner surface of the wall member may be changed as appropriate. In this case, the configurations conventionally used in various thermal heads can be used as they are.

Furthermore, the material and shape of the electric field forming electrode provided on the inner surface of the wall member may be changed in various ways.

"Effects of the Invention" According to the image recording head of the present invention described above, the temperature is such that the ink, the heating resistor, etc. do not undergo significant thermal deterioration;
An electric field that does not cause leakage between the electrodes causes the ink to fly, allowing high-speed, high-density recording to be performed.

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

Also, the electrical energy and thermal energy that should be applied.

A relatively small amount is required, and it is possible to downsize the drive circuit and the like.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the image recording head of the present invention, FIG. 2 is a schematic diagram explaining the recording principle of the present invention, FIG. 3 is a perspective view of the main part thereof, and FIG. 4 is a threshold value of the electric field. The temperature dependence of
A graph showing the characteristics of ink. l0111...Wall member, 13...Liquid colorant, 14...Expectation part, 16...Heating element, 19...Electric field formation electrode.

Claims (1)

[Scope of Claims] 1. A liquid coloring agent is arranged, and both electrical energy and thermal energy are applied thereto, and the liquid coloring agent in a region where both of the energies are applied is made to fly, It has a storage means for storing the liquid colorant, a thermal energy application means for heating the liquid colorant, and an electric energy application means for applying an electric field to the liquid colorant, and the storage means are arranged opposite to each other at a predetermined interval. and a pair of wall members each having a discharge portion formed on one edge for discharging the liquid colorant,
The thermal energy applying means includes a plurality of heating elements provided on one inner surface of the wall member, and one of the electric field forming electrodes of the electric energy applying means is provided on the other inner surface of the wall member. An image recording head characterized by: 2. The plurality of heating elements are arranged parallel to the discharge portion of the wall member at a predetermined pitch, and the distance between the wall members is set to D.
and when the arrangement pitch of the heating elements is P, D<
The image recording head according to claim 1, wherein the image recording head is selected to have 4P. 3. A patent claim characterized in that an edge of the electric field forming electrode provided on the other inner surface of the wall member on the side of the discharge part is located away from an edge of the discharge part. The image recording head according to the range 1 or 2.