JPH0257351A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To obtain an image having a high resolution at a low recording voltage by forming recording ink on a layer in which its electric resistance is varied by heat in charge/noncharge state, and then attracting to record it at opposite electrodes due to the difference of charging state. CONSTITUTION:When a belt 3 is passed through an ink tank, ink droplet 11 or ink layer 11' adheres to uniformly charge resin and ink by a charger 7. The charge of a part heated by an electric eliminator 8 is removed to become an ink droplet 16, and ink droplet 17 of a part which is not heated has original charge to selectively form charge/noncharge state. Then, a lower electrode 18 is set to the same polarity as that of a resin layer, and its opposite electrode 9 is applied by a different polarity voltage. Then, + charge is concentrated at the end of the ink, and charge is pressed to the bottom of the ink. In this case, a large quantity of + charge is concentrated at the + end of the ink 17 which is not heated to operate Coulomb force thereat. When it overcomes the surface tension of the ink, it is attracted to a recording sheet side to record on the sheet. As a result, an image having high resolution is obtained at a low recording voltage.

Description

[Detailed description of the invention] [jutsui ship The present invention relates to an inkjet recording apparatus n.

f! tJJi Technique Conventionally, in inkjet recording devices, the so-called electrostatic attraction method, in which recording ink is attracted by electrostatic force from a nozzle to which minute pressure is applied and used for recording, is known, for example, from Japanese Patent Publication No. 36-13768. ing. This method has the advantage that there is almost no problem of nozzle clogging because ink droplets smaller than the nozzle diameter can be obtained from a relatively large nozzle. On the other hand, the disadvantage of this method is that the voltage that provides the electrostatic force necessary for recording is, for example, 2K.
It is high, more than V. Also, JP-A-49-6433
No. 8 discloses a method in which a bias voltage is applied between an ink supply section and a counter electrode, and a voltage proportional to the density on the recording side is superimposed. Although this method has the effect of lowering the recording voltage proportional to the density on the recording side, the bias voltage is 2KV and the recording voltage is 700μ, which is high, and considering the high density of nozzles, it requires an expensive and complicated recording voltage generation circuit. I need. Further, a method of superimposing polarization force on the electrostatic force between the nozzle and the counter electrode is proposed in Japanese Patent Publication No. 59-4310, but the bias voltage is −IKV, the recording voltage is 50
0■, which still requires switching at a high recording voltage.

Furthermore, a method of superimposing airflow and electrostatic force is also disclosed in Japanese Patent Application Laid-open No. 1983-
Although it is proposed in Japanese Patent No. 120452, the recording voltage is 2.
00v~IKV, which is still high.

Another drawback of the electrostatic attraction method is that it is difficult to increase the density of the nozzles. In order to solve this drawback, recording heads having slit-like openings have been proposed in Japanese Patent Publication No. 59-4311 and Japanese Patent Publication No. 60-59869, but when attracting ink from these slit-like openings, However, there are drawbacks such as instability of ejection due to vibration of the liquid surface and ejection of unnecessary ink due to interaction between adjacent electrodes.

Part of the present invention has been made in view of the actual situation as described in -1-, and is particularly aimed at obtaining high-resolution images with low recording voltage.

[-4sei.

In order to achieve the above object, the present invention forms a recording ink on a layer whose electrical resistance changes with heat, electrostatically charges the ink, and selectively heats the layer. Load the ink.

After making it into an uncharged state, in the electrostatic field between the electrode on the back side of the /6 and the electrodes arranged opposite to each other on the opposite side of the resin layer via the recording paper, the difference between the charged and uncharged states is generated. The feature is that ink is attracted to the counter electrode side and recorded. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a configuration diagram for explaining one embodiment of the present invention. In the figure, J is an ink tank, 2 is a recording ink, 3 is a belt, 4.5 is a roller, 6 is a doctor blade, and 7 is a A charging device, 8 a static eliminator, 9 a counter electrode, 10 a high-voltage power source, 1-1 an ink droplet, an ink tank filled with recording ink 2, and two rollers 4 and 5 as shown in the figure. Arrow A
Rotate in the direction of. These two rollers 4 and 5 cause the belt to move in the direction of arrow B, but this belt itself.

An ink-philic electrothermographic material, ie, a material whose electrical resistance changes with changes in temperature.

For example, polyethylene, polystyrene, polyimide film, etc. are used.

By applying a material that is sparse to the ink, such as Teflon, to this resin, the ink is formed into multiple independent ink droplets or an ink layer on the resin by equalizing the ink with a doctor blade. It is formed.

The situation in which ink droplets are formed on the resin will be explained with reference to FIG. 2, which is an enlarged cross-sectional view of a part of the belt.
The operation of the above embodiment will be explained with reference to similar sectional views in FIGS. 3 to 6. In the figure, numeral 3 denotes a belt made of the electrothermographic material mentioned above, numeral 12 denotes a coating film sparse with respect to the recording ink mentioned above, and the coating film 12 can be provided with holes 13 for forming recording ink droplets.

When this belt 3 is passed through an ink tank, as shown in FIG.
), the ink layer 1]-' is stamped.

Next, by the charging device 7,! To uniformly charge the M resin and ink, a corona discharge is used as a charging device. 14 is a lower electrode.

The amount of charge on the resin and ink can be freely set by appropriately selecting the corona discharge voltage, the distance between the corona wire and the resin, and the belt movement speed. Figure 3 shows a state in which the ink is charged like -, but when the ink has high conductivity, it is conceptually shown in figure (a), and when it has low conductivity, it is conceptually shown in figure (b). charged. For electrostatic attraction of ink, which will be discussed later.

It is desirable that the amount of charge in Figure 3, i.e., the surface charge density, be larger.6 However, if the surface charge density is too large, the Coulomb force acting between the equal and anti-equal charges in the figure will cause the ink to form a droplet shape. In this case, care must be taken as the droplets may collapse or move.

The uniformly charged resin and ink are selectively neutralized by the next static eliminating device 8. For example, a thermal head is used as the static eliminator, but a laser beam may also be used. 15 is a signal source.

Figure 4 shows the static elimination effect. By supplying electricity to the thermal head, the resin on the heating element of the thermal head 2 is rapidly heated. At this time, since the electrical resistance is significantly lowered, the charge in the locally heated portion is eliminated, and the ink droplet 16
However, the ink droplet 17 in the portion that is not heated retains its original charge.

This selectively charges resin-L and ink.

An uncharged state is formed.

FIG. 5 shows a situation in which ink is selectively attracted by the electrostatic field between opposing electrodes and recorded on the recording paper 9. A voltage is applied to the lower electrode 18 on the back side of the resin layer with the same polarity as that of the resin layer, and to the opposite electrode 9 side with a different polarity.

At this time, the resistance of the resin layer is large because the temperature is equal to the ambient temperature, and the ink on the resin layer and the lower electrode are in an insulated state, which is a so-called floating state.

Therefore, no charge is injected from the lower electrode 18 made of metal, and whether or not the ink is attracted by Coulomb force is determined by the difference in charge at the bottom of the ink (low conductivity) or at the bottom of the ink (high conductivity). Ru.

FIGS. 5(b) and 5(Q) schematically show the charge states of the heated ink 16 and the unheated ink 17. FIG.

At the tip of the ink, + (plus) charges are concentrated by the electrostatic field, and - (minus) charges are pushed toward the bottom of the ink.

Ink 17 that was not heated at this time has a + (plus)
Because there is a lot of charge, a large number of charges are concentrated at the tip. The charge on the tip of the ink.

When the Coulomb force acts and overcomes the surface tension of the ink, it is attracted to the recording paper and recorded on the recording paper, but since the amount of charge at the tip of the ink differs depending on whether it is heated or not, it is determined whether the ink is attracted or not.

When the conductivity is high, the ink is attracted to the flying liquid i17' (Fig. 5 (d)) from the tip of the droplet, and when the conductivity is low, it is attracted to the string-like 17'' (Fig. 5 (C)). be done.

FIG. 6 shows the relationship between temperature and electrical resistance of polyethylene as an example of Ellen 1-R thermographic material. It is undesirable to raise the temperature of the ink too high because it causes evaporation or boiling of the ink. In the present invention, it is desirable to use a material whose electrical resistance changes at a relatively low temperature, as shown in FIG.

Furthermore, as is clear from FIG. 6, by changing the peak value and pulse width of the energizing pulse to the thermal spatula I-, the temperature of the heating element, that is, the temperature of the electrothermography material, can be controlled to increase the surface charge. By changing the density stepwise, that is, the induced ink coverage can be controlled according to the density of the recorded image.

In the above explanation, the charged polarity of the resin layer and ink and the polarity of the counter electrode were the same. Figure 7(a).

(b) shows the effect of the difference in polarity of the opposing electrodes.

Now, assume that the surface potential of the ink is +100OV.

In the case of the same polarity shown in FIG. 7(a), when a voltage of 12 KV is applied to the opposing electrode, charged and uncharged droplets face each other '? The potential difference with the FL pole is 3KV and 2KV. On the other hand, in the case of different polarity shown in FIG. 7(b), when a voltage of 3 KV is applied to the counter electrode, the potential difference between the charged and uncharged droplets and the counter electrode is 3 KV.

It becomes 2KV. In this way, the voltage of the ink flying becomes larger in the case of different polarities than in the case of the same polarity.

Furthermore, when the polarity is the same, charged droplets fly, but when the ink is in a floating state, the amount of charge in the ink is not as sensitive. becomes larger.

By the way, an electrostatic image creation method using the electrothermography material is also disclosed in Japanese Patent Publication No. 35-14722, but this method uses such an electrostatically charged material as raw wood. The device is placed in close contact with the original and irradiated with heat to obtain an electrostatic image.Since infrared rays are used as the heat source, the device is large, complex, and expensive.

No. 111'735-14722 does not disclose the concept of selectively changing the charging state of the ink (recording medium) of the electrothermographic material Saito 1- in advance.

In addition, a method of developing an electrostatic latent image formed by heat or light on an electrothermographic material or a photoconductive material using a developer was introduced in Japanese Patent Publication No. 44-95.
No. 12 and US Pat. The potential difference between the developer and the developer is used only as an auxiliary means for development, and is different from the present invention. Moreover, it is only a device that develops an electrostatic latent image, and unlike the present invention, which treats ink on a resin layer as a latent image, it cannot be directly recorded on Azusa paper, for example. Since the image is developed with one unit of electrothermographic material or photoconductive material coated on the paper, a step of transfer to plain paper is required.

As is clear from the above explanation, according to the present invention, high voltage is required for corona discharge and ink attraction, but so-called high recording voltage switching (approximately 500 V) is effective for the thermal head. The driving voltage could be lowered to about 20V. Furthermore, since ink droplets and ink layers are formed in advance, the disadvantages of conventional nozzles and slit-shaped apertures can be overcome.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining one embodiment of the present invention.
2 to 5 are detailed explanatory diagrams of the present invention, FIG. 6 is a characteristic diagram of the electrothermographic material, and FIG. 7 is an explanatory diagram of the charging state. 2... Ink, 3... Belt, 7... Charging device,
8...Static charge removal '4A position, 9...Counter electrode, 11...
Ink droplet, 15... Signal source, 16... Ink droplet that has been heated, 17... Ink droplet that has not been heated. Figure 1 Figure 4 Figure 5 Figure 2 Figure 6 Figure Temperature (Co) Figure (a) (b)

Claims (1)

[Scope of Claims] 1. Recording ink is formed on a layer whose electrical resistance changes by heat, the ink is electrostatically charged, and the layer is selectively heated to charge the ink. After the ink is brought into an uncharged state, the difference between the charged and uncharged states causes the ink to change in the electrostatic field between the electrode on the back side of the layer and the electrodes facing each other on the opposite side of the resin layer via the recording paper. An inkjet recording device characterized by attracting and recording to a counter electrode side. 2. The inkjet recording apparatus according to claim 1, wherein the charging state is changed in multiple steps by controlling the heating temperature according to the density of the image to be recorded. 3. The inkjet recording apparatus according to claim 1 or 2, wherein the polarity of the charge is the same as that of the counter electrode.