JPH0624867B2 - Image forming method - Google Patents

Description

The present invention relates to an image forming method in which ink is ejected to perform recording on a recording member.

"Prior Art" Various types of output devices have been developed for the purpose of outputting an image signal processed by a computer, a word processor, or the like.

Among these, the one that directly forms an image on a recording member such as a recording sheet is that the recording device itself can be downsized,
Because of its low price, it is regarded as the most suitable output device for small computers that have become widespread in recent years.

As such an output device, a wire dot system or an inkjet system is well known.

In the wire dot method, an ink ribbon coated with a pressure-sensitive wax and a recording paper are superposed, and a metal wire is struck from above to transfer the ink to perform recording.

Further, in the inkjet method, ink is contained in a sealed container, a pressure pulse is applied to the container, and the ink is ejected from an ejection port (orifice) of the container to perform recording.

[Problems to be Solved by the Invention] While these methods are effective in achieving miniaturization, they have the following problems.

First, in the wire dot method, noise is generated because the wire hits the ink ribbon. Further, in order to maintain the mechanical strength, the wire diameter cannot be made thinner than a certain value. Therefore,
It was difficult to increase the image density (the number of pixels in a unit area), and it was difficult to increase the resolution.

On the other hand, the ink jet system cannot reduce the size of the ink ejection mechanism due to its operating mechanism. Therefore, it is necessary to mechanically scan the ink ejection device in order to perform recording with a required image density. Therefore, the recording speed is reduced. Further, there is also a drawback that the ink ejection port is easily clogged due to the insoluble substance contained in the ink or the solidification of the ink itself.

The present invention has been made in view of the above points, and provides an image forming method capable of directly recording an image at a high image density on a recording member without causing problems such as ink clogging. That is the purpose.

“Means for Solving Problems” In the image forming method of the present invention, a heat-meltable ink layer having a volume resistivity of 10 ⁴ Ω · cm or less and a thickness of 10 μm or more is formed on a conductive support. Then, a recording electrode having a plurality of unit electrodes is arranged in the vicinity thereof, and a recording medium is arranged so as to face the heat-meltable ink layer with the recording electrode sandwiched therebetween, and the unit electrode and the Between the conductive support,
A voltage is selectively applied corresponding to an image signal to be recorded, the ink in the ink layer is ejected toward the recording medium, and an image is recorded on the recording medium.

[Operation] As described above, in the present invention, the ink of the heat-fusible ink layer is caused to fly by applying a voltage between the unit electrode and the conductive support. The ink is locally melted by a spark discharge phenomenon generated between the unit electrode and the conductive support, and the ink flies toward the recording member and adheres to the recording member surface in a dot shape. This dot becomes one recording pixel.

The unit electrodes are arranged in a line so that each unit electrode records one pixel. An image can be recorded on these unit electrodes by selectively applying a voltage according to an image signal and simultaneously subscanning the recording member in the direction orthogonal to the row of unit electrodes.

Here, if the thickness of the heat-meltable ink layer formed on the conductive support is selected to be 10 μm or more, it is possible to always record dots with a stable density on the recording member.

When the volume resistivity of the ink is selected to be 10 ⁴ Ω · cm or less, stable discharge is generated between the conductive support and the unit electrode, and good dots can be recorded.

[Example] (Outline of recording apparatus) Fig. 1 is a schematic configuration diagram of a recording apparatus suitable for carrying out the present invention.

In this device, a heat-meltable ink layer 2 is formed on a conductive support 1, a recording electrode 5 having a plurality of unit electrodes 3 is arranged above it, and a recording member 6 is arranged above it. It has been configured.

The conductive support 1 is biased in the direction toward the recording electrode 5 by a spring (not shown) or the like to press the outer surface of the heat-meltable ink layer 2 against the recording electrode 5.

Further, a transport roll 7 is provided on the back surface of the recording member 6 and is configured to press the recording member 6 toward the recording electrode 5 by a spring or the like (not shown). The carrying roll 7 rotates in the direction of the arrow 8 to carry the recording member 6, and performs the sub-scanning.

At the same time, the conductive support 1 is also driven to rotate in the direction of arrow 9.

On the other hand, the ink supply roll 11 is arranged on the outer surface of the heat-meltable ink layer 2 so as to be in contact with it. The ink supply roll 11 supplies and applies ink from the ink reservoir 15 so that the thickness of the heat-meltable ink layer 2 is always kept constant.

The ink supply roll 11 heats and pressurizes the surface of the heat-meltable ink layer 2 to smooth it, if necessary.

Further, the conductive support includes a discharge stabilization resistor 13 and
It is grounded via a first recording power supply 14 that applies a negative pulse.

Further, each unit electrode 3 constituting the recording electrode 5 is also grounded via a second recording power source 17 for applying a positive pulse.

The heat-meltable ink layer 2 is solid at room temperature in which carbon black, a coloring pigment, a coloring dye, and the like are dispersed in a binder such as wax and resin that dissolves and decomposes at a relatively low temperature. Further, magnetic powder is mixed in this.

Each of the conductive support 1 and the unit electrode 3 is made of a conductive metal.

In order to explain the structure of the recording electrode, a perspective view of the device of FIG. 1 is shown in FIG.

As shown in this figure, the recording electrode 5 has a structure in which a large number of needle-shaped conductors 3 (which are called unit electrodes in the present invention) are embedded in parallel in a spacer 4 made of an insulator. ing.

The tip of each unit electrode 3 is exposed in the through hole 10 provided in the spacer 4. Also, at the rear end of the unit electrode 3,
The second recording power source 17 is connected.

Returning to FIG. 1 again, it can be seen that the through hole 10 of the recording electrode 5 described in FIG. 2 is located just above the heat-meltable ink layer 2. As described later, the ink of the hot-melt ink layer 2 flies toward the recording member 6 through the through holes 10.

In this way, dots are recorded on the recording member 6.

Since the dots attached to the recording member 6 are carbon black, pigments, dyes, etc. dispersed in wax, resin, etc., they have a strong adhesive force and do not require any post-treatment such as pressurizing and heating.

(Role of Smooth Roll) When a voltage is applied between the unit electrode 3 and the conductive support 1 and the ink near the surface of the heat-meltable ink layer 2 flies, irregularities are generated in that portion.

The heat-meltable ink layer 2 rotates together with the conductive support 1 in the direction of arrow 9 in FIG. An ink replenishing roll 11 is provided in order to smooth the uneven portion again to the original shape and to keep the thickness of the heat-meltable ink layer constant.

The ink supply roll 11 transfers an appropriate amount of ink from the ink reservoir 15 to the hot-melt ink layer 2. Further, the distance between the axes of the ink supply roll 11 and the conductive support 1 is
It is controlled so that it is always constant. As a result, the thickness of the heat-meltable ink layer is maintained at a predetermined constant thickness.

The ink supply roll 11 can also smooth the surface of the heat-meltable ink layer 2 only by the pressing force.

However, if the ink supply roll 11 is heated, the smoothing process becomes easier.

As a result, stable dot recording can be performed for a long period of time.

(Role of Spacer) In the above embodiment, the unit electrode 3 and the heat-fusible ink layer 2
The distance between the outer surface and the outer surface has a great influence on the discharge starting voltage. That is, if the distance fluctuates randomly, the discharge generated between the conductive support 1 and the unit electrode 3 becomes unstable accordingly. Therefore, the heat-meltable ink layer 2 is constantly pressed against the spacer 4 to keep this distance stable.

Further, since the ink gradually diffuses during flight, it is necessary to keep the distance between the outer surface of the heat fusible ink layer 2 and the recording member 6 constant and to make the size of the recorded dots constant.

Further, if ink enters the gap between the recording member 6 and the recording electrode 5, the shape of the recorded dots will be disturbed.

Therefore, the transport roll 7 presses the recording member 6 against the spacer 5.

(Selection of Thickness of Heat Melt Ink Layer) In the present invention, the thickness of the heat melt ink layer 2 is 10 μm.
Select at least m. The following experiment was conducted to verify the effect.

In fact, a voltage 6 is applied between the unit electrode 3 and the conductive support 1.
00V-1300V, pulse width 100μsec-2ms
ec, discharge current of 1 mA to 30 mA was discharged.

At this time, the recording electrode 5 is a unit electrode 3 made of nickel or tungsten and having a diameter of 50 μm, which is 8 mm / mm.
Arrange them in parallel at the density of a book, and make them 20 μm to 100 μm thick.
m coated with a polyester film was used.
This film preferably has an electrical resistivity of 1.0 × 10 ¹⁰ Ω · cm or more.

For the heat-meltable ink layer, a carbon black (manufactured by Cabot Corporation, USA: Vulcan XC-72R) of 30% by weight and a wax (Nisishi Montan Wax 738A of Arakawa Chemical Industry Co., Ltd.) of 70% by weight were used.

Under the above conditions, the discharge current between the unit electrode 3 and the conductive support 1 is selected from 3 mA within the range of 1 mA to 10 mA, and the relationship between the thickness of the heat fusible ink layer 2 and the density of recording dots is shown. I asked.

The results are shown in FIG. From this graph, A, B, C
In either case, when the thickness of the heat-meltable ink layer is 10 μm or more, preferably 20 μm or more and 100 μm or less, high density dots with a density of 1.0 or more are recorded.

When the thickness of the heat-meltable ink layer is 100 μm or more, high-density dots are recorded, but the dot diameter increases, which may deteriorate the image quality. Therefore, the thickness of the heat-meltable ink layer is preferably 100 μm or less.

In this way, if the thickness of the heat-meltable ink layer is controlled by using the ink replenishing roll 11, stable high-density dots can be recorded. A heat-resistant film coated with a heat-meltable ink layer can also be used. It can be used like an ink donor film in known thermal transfer recording devices.
In this case, the accuracy of the ink thickness is not required to be as high as that of the ink donor film. This is also an advantage of the present invention.

In addition, this is the distance between the conductive support 1 and the unit electrode 3,
The same tendency is shown regardless of the values of other discharge energy supply control factors. It is also possible to change the dot density within a certain range by changing the control current value, which is one of the discharge energy supply control factors. Thereby, it is possible to give gradation to the recording dots.

(Electrical resistance of heat-meltable ink layer) In order to generate stable discharge for a required time and record dots having a predetermined density, the volume resistance value of the heat-meltable ink layer is set to 1 in the present invention. Select a value of 0.0 × 10 ⁴ Ω · cm or less.

That is, as a result of the above experiment, when the electric discharge between the conductive support 1 and the unit electrode 2 occurs, sufficient electric discharge current cannot be obtained unless the electric resistance between them is about 100 KΩ or less.

From this fact, the content of the carbon black blended in the heat-meltable ink layer was controlled and recording was performed with the volume resistivity of 10 ⁴ Ω · cm or less. As a result, it was found that dots with a higher density were recorded as compared with the case of using a heat-meltable ink layer having a higher resistance.

In addition, in order to record dots having a good density, it is preferable that the volume resistivity is 5.0 × 10 ³ Ω · cm or less.

(Composition of carbon black) In this case, the content of carbon black in the heat-meltable ink layer is preferably 20% by weight or more and 50% by weight or less.

To verify this, the change in dot density depending on the carbon black content was measured. The results are shown in FIG.

As shown in this graph, the carbon black content is 20
It can be seen that dots having a density of 1 or more can be recorded in the range of ˜50 weight percent.

Further, with respect to the wax in which the carbon black was dispersed in this way, the relationship between the content rate and the size of the recorded dots was measured. The result is shown in FIG.

From this graph, it is understood that when the carbon black content exceeds 50% by weight, the spread of dots becomes large. The volume resistivity of the heat-meltable ink layer when the carbon black content was 50 weight percent was about 1 Ω · cm. The volume resistivity does not change significantly even if the carbon black content is further increased. This is considered to be because when the concentration exceeds this range, the carbon blacks directly contact with each other in the hot-melt ink layer to form a three-dimensional conductive path. When the discharge current diffuses and flows in this conductive path, the dots spread.

From the above, it was demonstrated that the carbon black content is preferably 20% by weight or more and 50% by weight or less.

"Modification" The image forming method of the present invention is not limited to the above embodiments.

Almost the same recording can be performed even if the voltage applied between the unit electrodes and the conductive support has a polarity opposite to that of the embodiment.

Further, although the conductive support and the heat-meltable ink layer are formed in a concentric and cylindrical shape, any shape may be used as long as the heat-meltable ink layer can be continuously supplied, for example, an endless belt shape or a sheet shape. It doesn't matter.

Further, if the through hole provided in the spacer is circular, a circular dot can be recorded, but this may be another shape such as a square or a triangle.

[Advantages of the Invention] According to the image forming method of the present invention described above, since the heat-melting solid ink is melted and ejected by electric discharge, there is no clogging of the ink and a unit corresponding to each pixel. Since the electrodes can be arranged closely, a high-density image can be recorded with high image quality even in a small and low-priced device. In addition, the volume resistivity of the heat-meltable ink layer is 10 ⁴ Ω
・ Since it is selected to be less than cm, a sufficient discharge current can always be obtained,
Higher density dots are obtained compared to those with higher resistance. Further, since the thickness of the heat-meltable ink layer is selected to be 10 μm or more, there is an effect that stable high density dots can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a recording apparatus suitable for carrying out the image forming method of the present invention, FIG. 2 is a perspective view of a main part thereof, and FIG. 3 is a relationship between the thickness of the heat-meltable ink layer and the density of dots. 4 is a graph showing the relationship between the carbon black content of the hot-melt ink layer and the dot concentration, and FIG. 5 is a graph showing the carbon black content of the hot-melt ink layer and the dot size. It is a graph which shows a relationship. DESCRIPTION OF SYMBOLS 1 ... Conductive support, 2 ... Heat-meltable ink layer, 3 ... Unit electrode, 4 ... Spacer, 5 ... Recording electrode, 6 ... Recording member.

Claims (1)

[Claims] 1. A volume resistivity of 10 ⁴ on a conductive support.
A heat-meltable ink layer having a thickness of Ω · cm or less and a thickness of 10 μm or more is formed, a recording electrode having a plurality of unit electrodes is arranged in the vicinity thereof, and the heat-melting property is sandwiched by the recording electrodes. The recording medium is arranged so as to face the ink layer, and a voltage is selectively applied between the unit electrode and the conductive support according to an image signal to be recorded, and the ink of the ink layer is An image forming method comprising: flying a recording medium onto the recording medium to record an image on the recording medium.