JPH09281781A - Image recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image recording device provided with an excellent tone reproduction, in the image recording device utilizing an electrostatic latent image formed by means of a pyroelectric effect. SOLUTION: In the device, a surface of pyroelectric body layer 1 is selectively heated to the low temp. on a high density side, and to the high temp. on the highlight side, by a thermal head 4 corresponding to the image signal. The electrostatic latent image carrier 3 after completion of heating is, allowed to return to the room temp. by natural cooling. At this time, the electric charge with the polarity opposite to that of the electric charge generated at the time of heating are generated in large amount on the surface of the pyroelectric body layer 1. The formed electrostatic latent image 17 is made toner development by the developing device 7 however, the toner 18 is, after the electrostatic transfer on the recording paper 11 by the use of the transfer roller 12, fixed by the fixing device 15, and the desired image is formed on the recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus applied to a printer, a fax machine, a copying machine, etc., and in particular, it develops an electrostatic latent image formed by utilizing a pyroelectric effect by a charged coloring medium. The present invention relates to an image recording apparatus that forms an image by transferring and fixing the image on a recording medium.

[0002]

2. Description of the Related Art Several image forming methods using a pyroelectric material have been disclosed. For example, in U.S. Pat. No. 3,824,098, the inventor Bergman et al. Proposed a copying apparatus using polyvinylidene fluoride (PVDF) as a pyroelectric material. In this device, an electrostatic latent image is formed by heating the surface of the pyroelectric material with lamp light that has passed through the original, and the electrostatic latent image is developed with charged colored particles (toner) and transferred to a recording sheet to transfer the original. Was obtained.

In addition, Bergman et al. Applied Physics Letters (Applied Physics)
s Letters), Vol. 21 (10), 197
2nd year, pp. 497-499, it mentions latent image formation by opposite polarity charges. That is, immediately after heating the pyroelectric material, if the charge generated on the surface of the pyroelectric material is neutralized, when the pyroelectric material is cooled to room temperature, a charge of the opposite polarity to that at the time of heating is applied to the surface of the pyroelectric material. Occur. It is a great advantage that the latent image formed by the opposite polarity charges can be held relatively stably over time.

Further, Japanese Patent Application Laid-Open No. 56-158350 discloses a method of heating a pyroelectric material with a laser beam or a thermal head. Also in this recording method, latent image formation by reverse polarity charges generated when the pyroelectric material is cooled is used.

On the other hand, in Japanese Patent Application Laid-Open No. 5-134506 and US Pat. No. 5,185,619, Snelling shows that the amount of reverse polarity charge (latent image charge density) obtained is the charge in charge during heating. Focusing on the fact that it is equal to the sum, we propose a method to efficiently neutralize the electric charges generated during heating. That is, by using a heating needle as the heating means and providing a grounded conductor layer on the surface of the heating needle, the electric charge generated during heating is efficiently neutralized through the conductor layer.

In JP-A-60-119575, in the case of forming an electrostatic latent image by utilizing the pyroelectric effect, a developing method in which heating is performed in the same pattern as an image pattern to be recorded (referred to as normal development) ) Is disclosed. In this normal development method, when the density of the image pattern to be recorded is high, the printing energy applied to the heating means is increased to raise the temperature of the latent image charge holding medium to increase the latent image potential. As a result, a large amount of toner adheres to the print pattern with high density.

On the other hand, when the image pattern to be recorded is on the highlight side, the printing energy to the heating means is made small, the latent image charge holding medium is hardly heated, the latent image potential is not raised so much, and the adhered toner is reduced. We have performed control to obtain highlight images. Here, when the charge generated in the latent image charge holding medium and the polarity of the toner charge are opposite to each other, a small amount of toner is present in a portion heated to a high temperature and a large amount of toner is present in a portion heated to a low temperature. Because of the adhesion, the pattern opposite to the print pattern is heated. This is called a reversal development method.

[0008]

However, in the above-mentioned conventional method for controlling the image recording apparatus, as shown in FIG. 2A, due to the heat radiation characteristic of the latent image charge holding medium, the highlight side (low gradation) is obtained. On the higher density side, the temperature change is smaller with respect to the change of the printing energy. In addition, the amount of toner adhered to the surface potential (toner gamma characteristic) is also shown in FIG.
As shown in (e), since the gradation can be expressed better on the low gradation side, the gamma characteristic tends to be more nonlinear. Therefore, the number of gradation levels to be controlled is required to be higher than the gradation of substantial image density, and high-precision gradation control is required.

An object of the present invention is to solve the above problems and to provide an image recording apparatus having good gradation controllability by making the gamma characteristic linear.

[0010]

According to the present invention, a latent image charge holding medium having a pyroelectric layer, and the latent image charge holding medium are selectively heated according to an image signal to obtain the latent image charge. In an image recording apparatus provided with a heating means for forming an electrostatic latent image on a holding medium, the heating amount of the heating means is applied to print pixels having a high density of a recording image with a small printing energy, The heating amount of the heating means is set so that a large amount of printing energy is applied to a pixel whose recorded image has a low density.
An image recording device comprising: a control device for controlling the heating device; and a developing device for visualizing the electrostatic latent image formed by selectively heating by using colored particles having a polarity opposite to the polarity of the electrostatic latent image. The device is obtained.

Further, according to the present invention, there is provided an image recording apparatus characterized in that the heating means is a line type thermal head or a serial type thermal head.

Further, according to the present invention, the line type thermal head is connected to a ground potential, and a conductive layer as a charge neutralizing means is formed on the line type thermal head.
The conductive layer is a conductive layer formed by vapor deposition, and a minute amount of conductive carbon particles is added to the polymer material to obtain an image recording apparatus.

Further, according to the present invention, an image recording device characterized in that the conductive layer is a conductive film can be obtained.

Further, according to the present invention, in order to visualize the electrostatic latent image, the insulating and non-magnetic colored particles are mixed with magnetic carrier particles, and the colored particles are charged by friction between the particles so that the carrier particles are charged. By holding the developer adhered to the surface on a sleeve containing a magnet roller and bringing it into contact with the latent image charge holding medium, the developer is selectively selected according to the charge distribution on the latent image charge holding medium. An image recording apparatus is obtained which is characterized in that toner is attached.

[0015]

According to the present invention, the latent image charge-holding medium on which a latent image is formed is selectively brought into contact with or brought into contact with a charged coloring medium such as toner so that the coloring medium is selectively deposited on the surface of the pyroelectric layer. The latent image is made visible and developed (developed), and the coloring medium attached to the latent image charge holding medium is then transferred and fixed to the recording medium to form a desired image on the recording medium. Done.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. The image recording apparatus according to this embodiment includes an endless belt-shaped latent image charge holding medium 3, a thermal head 4 as a selective heating unit, a conductive layer 5 as a charge neutralizing unit, a controller 16, and a developing unit as a developing unit. It is composed of a device 7, a transfer roller 12 as a transfer means, and a fixing device 15.

As the latent image charge holding medium 3, there is used an endless belt made of two layers of a pyroelectric layer 1 (thickness: about 100 μm) and a conductor layer 2 (thickness: about 500 Å). . The materials for the pyroelectric layer 1 and the conductor layer 2 include
PVDF (polyvinylidene fluoride) and aluminum were used, respectively. The conductor layer 2 is connected to the ground potential via the conductive rubber roller 20. The thermal head 4 used in this embodiment is a line-type thermal head generally used for thermal transfer recording, in which minute heat generating elements that generate heat by Joule heat have a pitch of about 83 μm (300 dots).
/ Inch) has a structure in which the latent image charge holding medium 3 is arranged in a line in the width direction. These heating elements were selectively heated by the controller 16 according to the recorded image (image signal) 19 to selectively heat the latent image charge holding medium 3.

A conductive layer 5 as a charge neutralizing means is formed on the thermal head 4 and is connected to the ground potential. In the present embodiment, a thin film of 0.1 μm is formed by depositing aluminum or chromium, but other materials such as a conductive organic material can be used.
Although the conductive layer is formed by vapor deposition in this embodiment mode, a conductive film in which a minute amount of conductive carbon particles is added to a polymer material and conductivity is imparted may be used. In this case, the latent image charge holding medium 3 and the conductive film are sandwiched between the thermal head 4 and the platen roller 6. The thermal head 4 is not limited to the line type thermal head used in the present embodiment, and a serial type thermal head can be used. Electric charges (excess electric charges) are generated on the surface of the pyroelectric layer 1 of the heated latent image charge holding medium 3 due to the pyroelectric effect, which is a thermal head that is in close contact with the surface of the pyroelectric layer 1. 4 is immediately neutralized through the conductive layer 5.

Now, the relationship between the print pattern and the heating pattern will be described. As for the heating pattern, the highlight portion having a low density is strongly heated to a high temperature, and the portion having a low density is weakly heated to remain at a low temperature, and the reversal development is performed so as to be a pattern reverse to that of a normal thermal transfer printer or a thermal printer. The relationship between the input energy and the maximum temperature of the thermal head heating element is shown in FIG. The increase in temperature decreases as the temperature rises (the differential value of temperature tends to decrease), which is exactly the same as the conventional example. The temperature on the pyroelectric film also shows the same tendency as in FIG.

On the other hand, the relationship between the temperature and the surface potential of the pyroelectric film (pyroelectric effect) has the linearity shown in FIG. 2 (b), and the pyroelectric film has a polarity in which a negative charge is generated by heating. Therefore, the relationship between the input energy and the surface potential of the pyroelectric film is also as shown in FIG.

After the heating, the latent image charge holding medium 3 was returned to room temperature by natural cooling to form a latent image 17 by charges of opposite polarity. The latent image charge holding medium 3 can be cooled by natural cooling, forced air cooling, heat conduction with a heat sink, or the like.
It is also possible to use forced cooling means. The latent image 17 formed on the latent image charge holding medium 3 is developed by the developing device 7. In this embodiment, the two-component magnetic brush development is used as the developing method. That is, insulating and non-magnetic colored particles (toner) are mixed with magnetic carrier particles, the toner is charged by friction between the particles, and the developer 8 in a state of being adhered to the carrier surface is covered with a magnet roller 9. The latent image was visualized by holding it on No. 10 and bringing it into contact with the latent image charge holding medium 3 to selectively attach toner according to the charge distribution on the latent image charge holding medium 3.

Here, as shown in FIG. 1, a bias potential is applied between the conductor layer 2 of the latent image charge holding medium 3 and the roller sleeve 10 of the developing device 7 so that the surface potential of the latent image charge holding medium 3 is changed. The shift is performed as shown in FIG. The relationship between the toner adhesion amount and the surface potential is as shown in FIG. 2E. From the relationship between FIG. 2D and FIG. 2E, the relationship between the toner adhesion amount and the input energy is linear. It becomes like FIG.2 (f) close to. Furthermore, the relationship between the image density and the toner adhesion amount is as shown in FIG.
From the relationship between (f) and FIG. 2 (g), the relationship becomes more linear as shown in FIG. 2 (h). Therefore, gradation control is easy at both low and high densities, and an image without gradation jump can be obtained.

After the development, the latent image charge holding medium 3 is superposed on the recording paper 11 which is a recording medium, and the transfer roller 12 to which a voltage is applied is pressed from the rear surface of the recording paper 11 to apply toner to the recording paper 11. Electrostatically transferred to the surface. In this embodiment, a voltage of about +1 kV is applied to the conductive rubber roller to electrostatically transfer the toner. The recording paper 11 on which the toner has been transferred is passed through a fixing device 15 including a heat roller 13 and a pressure roller 14 so that the toner on the surface of the recording paper 11 is once melted to fix it to the recording paper 11. It was The method of developing the latent image, the type of developer, the method of transferring to the recording medium, the method of fixing to the recording medium, etc. are not limited to the method used in the present embodiment, and the conventional electronic Similar effects can be obtained by using other methods such as those used for photographic recording.

After the toner is transferred to the recording paper 11, the latent image charge holding medium 3 is conveyed again to the thermal head 4 to execute the next latent image formation. Prior to this, when the untransferred toner remains on the latent image charge holding medium 3, the cleaner 22 is used to remove the toner if necessary. Further, latent image charges may remain on the latent image charge holding medium 3 after the toner is transferred. In this case, the latent image charge on the surface of the pyroelectric layer 1 can be easily neutralized by bringing a grounded conductive brush (not shown) or the like into contact with the surface of the pyroelectric layer 1 as necessary. Then, the latent image charge holding medium 3 can be returned to the initial state.

As a result of carrying out the gradation recording experiment under the above-mentioned apparatus structure, it is possible to perform the excellent gradation recording in which the OD density is linear from the highlight (low density) side to the high density side. Was confirmed.

The present invention is not limited to this embodiment. For example, in the above-described embodiment, the latent image charge holding medium 3 has a belt shape or a drum shape, but the same effect can be obtained by using another shape such as a flat plate shape. . Although all recording media are paper, it is obvious that the present invention is effective for various recording media. Further, it is not always necessary to transfer or fix the coloring medium to the recording medium, and a device for temporarily displaying information such as a display plate by temporarily holding the coloring medium on the latent image charge holding medium 3 or the recording medium. It can also be applied to. Further, although the coloring medium is all colored particles (powder toner), other forms of coloring medium such as liquid toner and liquid ink may be used.

[0027]

According to the present invention, the relationship between the input energy and the image density can be made almost linear by combining the gamma characteristic of the toner and the temperature characteristic with respect to the input energy in reverse. As a result, gradation controllability can be improved, and good printing with excellent density reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an image recording apparatus according to an embodiment of the present invention.

FIG. 2A is a diagram for explaining a relationship between input energy and temperature, FIG. 2B is a diagram for explaining a relationship between pyroelectric film temperature and surface potential, and FIG. 2C is a diagram. It is a diagram for explaining the relationship between the input energy and the surface potential,
(D) is a diagram for explaining the relationship between the input energy and the surface potential when a bias is applied, (e) is a diagram for explaining the relationship between the surface potential and the toner adhesion amount, and (f) is a diagram. It is a figure for demonstrating the relationship between input energy and toner adhesion amount, (g) is a figure for demonstrating the relationship between toner adhesion amount and image density, (h) is input energy and image density. It is a figure for explaining a relation.

[Explanation of symbols]

 1 Pyroelectric Layer 2 Conductive Layer 3 Latent Image Charge Retaining Medium 4 Thermal Head 5 Conductive Layer 6 Platen Roller 7 Developer 8 Developer 9 Magnet Roller 10 Sleeve 11 Recording Paper 12 Transfer Roller 15 Fixer 16 Controller 17 Latent Image 18 Toner 19 Recorded image 20 Conductive rubber roller 21 Untransferred toner 22 Cleaner 23 Collected toner

Claims (5)

[Claims] 1. A latent image charge holding medium having a pyroelectric layer,
An image recording apparatus comprising: a heating unit for selectively heating the latent image charge holding medium according to an image signal to form an electrostatic latent image on the latent image charge holding medium. The heating amount is applied to the pixels having a high density of the recorded image so that the printing energy is small, and the heating amount of the heating means is applied to the pixels having a low density of the recording image to have a large printing energy. An image recording apparatus comprising: a control unit that controls the unit; and a developing unit that visualizes by using colored particles that are oppositely charged to the polarity of the electrostatic latent image formed by selective heating. 2. The image recording apparatus according to claim 1, wherein the heating means is a line type thermal head or a serial type thermal head. 3. The line type thermal head is connected to a ground potential, a conductive layer as a charge neutralizing means is formed on the line type thermal head, and the conductive layer is a conductive layer formed by vapor deposition. 3. The image recording apparatus according to claim 2, wherein a minute amount of conductive carbon particles is added to the polymer material. 4. The image recording apparatus according to claim 3, wherein the conductive layer is a conductive film. 5. The visualization of the electrostatic latent image is performed by mixing insulating and non-magnetic colored particles with magnetic carrier particles, charging the colored particles by friction between the particles, and adhering to the carrier surface. The developer is held on a sleeve containing a magnet roller and brought into contact with the latent image charge holding medium to selectively attach toner according to the charge distribution on the latent image charge holding medium. The image recording apparatus according to claim 1, wherein