JP2885276B2 - Image recording device - Google Patents

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 facsimile, a copying machine, and the like, and more particularly, to developing an electrostatic latent image formed by utilizing a pyroelectric effect with a charged colored medium. Further, 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, Bergman et al. Propose a copying apparatus that uses polyvinylidene fluoride (PVDF) as the pyroelectric material. In this apparatus, an electrostatic latent image is formed by heating the surface of a pyroelectric material with lamp light transmitted through a document, developed by a charged colored particle (toner), and transferred to a recording paper to transfer the latent image. Was obtained.

Also, Bergman et al., Applied Physics Letters (Applied Physic).
s Letters), Vol. 21 (10), 197
2nd year, pp. 497-499, mentions the latent image formation by the opposite polarity charge. In other words, if the charge generated on the surface of the pyroelectric material is neutralized immediately after heating the pyroelectric material, 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.

Japanese Patent Application Laid-Open No. Sho 56-158350 discloses a method of heating a pyroelectric material by using a laser beam or a thermal head. Also in this recording method, latent image formation by the opposite polarity charge 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, the inventor of the present invention, Snelling, states that the amount of the opposite polarity charge (latent image charge density) obtained by heating is determined by the charge Focusing on the fact that the sum is equal to the sum, a method for efficiently neutralizing the charge generated during heating is proposed. That is, by using a heating needle as a heating means and providing a grounded conductor layer on the surface of the heating needle, charges generated during heating are efficiently neutralized through the conductor layer.

Japanese Patent Application Laid-Open No. Sho 60-119575 discloses a developing method in which an electrostatic latent image is formed by using a pyroelectric effect by heating in the same pattern as an image pattern to be recorded (referred to as regular development). ) Is disclosed. In the normal development method, when the density of an 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, thereby increasing the latent image potential. As a result, a print pattern with a large amount of toner attached and a high density is obtained.

On the other hand, when the image pattern to be recorded is on the highlight side, the printing energy to the heating means is reduced, the latent image charge holding medium is hardly heated, the latent image potential is not increased so much, and the amount of toner adhered is reduced. Control to obtain a highlight image. Here, when the polarity of the charge generated on the latent image charge holding medium and the polarity of the toner charge are opposite, a small amount of toner is applied to a portion heated to a high temperature, and a large amount of toner is applied to a portion heated to a low temperature. To adhere, heating is performed in a pattern opposite to the printing pattern. This is called a reversal development method.

[0008]

However, in the above-described conventional method of controlling an image recording apparatus, as shown in FIG. Side), the temperature change is smaller with respect to the change in printing energy on the higher density side. The toner adhesion amount (toner gamma characteristic) with respect to the surface potential is also shown in FIG.
As shown in (e), since the lower gradation side can express better gradation, the gamma characteristic tends to be more nonlinear. For this reason, a higher number of gradation steps to be controlled is required than a substantial image density gradation, and high-precision gradation control is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image recording apparatus with good tone controllability by solving the above problems and making the gamma characteristic linear.

[0010]

According to the present invention, there is provided a latent image charge holding medium having a pyroelectric layer, and the latent image charge holding medium is selectively heated in accordance with an image signal. In an image recording apparatus provided with a heating unit for forming an electrostatic latent image on a holding medium, a heating amount of the heating unit is applied to a pixel having a high density of a recorded image with a small printing energy, and The heating amount of the heating means is applied to a pixel having a low density of a recorded image so that a large printing energy is applied.
Control means for controlling the heating means; cooling means for cooling the electrostatic latent image formed by heating to form a latent image having a polarity opposite to that of heating; and a cooling means for controlling the polarity of the electrostatic latent image. An image recording apparatus comprising a developing device for developing an image using charged colored particles is obtained.

Further, according to the present invention, there is provided an image recording apparatus characterized in that the cooling means is based on natural cooling and cools to room temperature.

Further, according to the present invention, there is provided an image recording apparatus characterized in that the cooling means is a forced cooling means such as forced air cooling or heat conduction with a heat sink.

Further, according to the present invention, there is provided an image recording apparatus characterized by being cooled to room temperature by the cooling means.

Further, according to the present invention, there is provided an image recording apparatus characterized in that the developing device visualizes the image at room temperature.

[0015]

According to the present invention, the latent image charge holding medium having the latent image formed thereon is selectively brought into close proximity to or in contact with a charged coloring medium such as toner, so that the coloring medium selectively contacts the surface of the pyroelectric layer. The latent image is then developed (developed), and the colored medium deposited on the latent image charge holding medium is then transferred and fixed to a recording medium, and a desired image is formed on the recording medium. Done.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The image recording apparatus according to the present 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. The fixing device 15 includes a transfer unit 12, a transfer roller 12 as a transfer unit, and a fixing unit 15.

As the latent image charge holding medium 3, an endless belt made of a two-layer film composed of a pyroelectric layer 1 (thickness of about 100 μm) and a conductive layer 2 (thickness of about 500 Å) was used. . 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 a ground potential via a 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 a minute heating element that generates heat by Joule heat has a pitch of about 83 μm (300 dots).
/ Inch), 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 in accordance with the recorded image (image signal) 19, and the latent image charge holding medium 3 was selectively heated.

A conductive layer 5 is formed on the thermal head 4 as charge neutralizing means, and is connected to a ground potential. In this embodiment mode, a thin film having a thickness of 0.1 μm is formed by evaporating aluminum or chromium, but another material such as a conductive organic material can be used.
In this embodiment mode, the conductive layer is formed by vapor deposition; however, a conductive film in which conductive carbon particles are added in a minute amount 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 interposed between the thermal head 4 and the platen roller 6. The thermal head 4 is not limited to the line type thermal head as used in the present embodiment, but may be a serial type thermal head. Charges (excess charges) are generated on the surface of the pyroelectric layer 1 of the heated latent image charge holding medium 3 by a pyroelectric effect, which is caused by a thermal head which is in close contact with the surface of the pyroelectric layer 1. 4 is instantaneously neutralized through the conductive layer 5.

Here, the relationship between the printing pattern and the heating pattern will be described. As for the heating pattern, reversal development is performed in which a highlight portion having a low density is strongly heated to a high temperature, a portion having a low density is weakly heated and kept at a low temperature, and the pattern is inverted from that of a normal thermal transfer printer or a thermal printer. FIG. 2A shows the relationship between the input energy and the maximum temperature of the thermal head heating element. The increase of the temperature decreases as the temperature increases (the differential value of the temperature tends to decrease), which is exactly the same as in 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) is linear as shown in FIG. 2B, and the pyroelectric film has a polarity that generates a negative charge upon heating. Therefore, the relationship between the input energy and the surface potential of the pyroelectric film is also as shown in FIG.

The heated latent image charge holding medium 3 was returned to room temperature by natural cooling to form a latent image 17 of opposite polarity charges. The latent image charge holding medium 3 is 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 using the developing device 7. In the present embodiment, a two-component magnetic brush development is used as a development method. That is, a sleeve containing a magnet roller 9 containing a developer 8 in which insulating and non-magnetic colored particles (toner) are mixed with magnetic carrier particles, and the toner is charged by friction between the particles and adhered to the carrier surface. 10 and brought into contact with the latent image charge holding medium 3 to selectively adhere toner in accordance with the charge distribution on the latent image charge holding medium 3 to visualize the latent image.

Here, as shown in FIG. 1, a bias potential is applied between the conductive layer 2 of the latent image charge holding medium 3 and the roller sleeve 10 of the developing device 7 to reduce the surface potential of the latent image charge holding medium 3. The shift is performed as shown in FIG. The relationship between the toner adhesion amount and the surface potential is as shown in FIG. 2 (e). From the relationship between FIG. 2 (d) and FIG. 2 (e), the relationship between the toner adhesion amount and the input energy is linear. As shown in FIG. Further, the relationship between the toner density and the image density is as shown in FIG.
The relationship between FIG. 2 (h) and FIG. 2 (h) is more linear than the relationship between (f) and FIG. 2 (g). Therefore, gradation control is easy at both low and high densities, and an image without gradation jump can be obtained.

The latent image charge holding medium 3 after development is superimposed on a recording paper 11 as a recording medium, and a toner is applied to the recording paper 11 by pressing a transfer roller 12 to which a voltage is applied from the back of the recording paper 11. It was electrostatically transferred to the surface. In the present embodiment, a voltage of about +1 kV is applied to the conductive rubber roller to perform the electrostatic transfer of the toner. The recording paper 11 to 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 temporarily melted to fix the toner on the recording paper 11. Was. The method of developing a latent image, the type of developer, the method of transferring to a recording medium, the method of fixing to a recording medium, and the like are not limited to the method used in the present embodiment. The same effect can be obtained by using other methods such as those used in photographic recording.

After the toner is transferred to the recording paper 11, the latent image charge holding medium 3 is again conveyed to the thermal head 4, and the next latent image is formed. Prior to this, if untransferred toner remains on the latent image charge holding medium 3, removal using a cleaner 22 is performed as necessary. Further, the latent image charges may remain on the latent image charge holding medium 3 after the transfer of the toner. In this case, if necessary, a grounded conductive brush (not shown) or the like is brought into contact with the surface of the pyroelectric layer 1 to easily neutralize the latent image charges on the surface of the pyroelectric layer 1. To return the latent image charge holding medium 3 to the initial state.

As a result of executing a gradation recording experiment under the above-described apparatus configuration, it is possible to perform favorable gradation recording with a linear OD density from the highlight (low density) side to the high density side. Was confirmed.

The present invention is not limited only to the present embodiment. For example, in the above-described embodiment, the latent image charge holding medium 3 is formed in 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 the recording medium is entirely paper, it is clear that the present invention is effective for various other recording media. Further, the transfer and fixing of the coloring medium to the recording medium are not always necessary, 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. Application to is also possible. Further, the coloring medium is all colored particles (powder toner), but 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 nearly linear by combining the gamma characteristic of the toner and the characteristic of the temperature with respect to the input energy in reverse. Thereby, gradation controllability can be improved, and good printing with excellent density reproducibility can be obtained.

[Brief description of the drawings]

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

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. It is a diagram for explaining the relationship between input energy and surface potential,
(D) is a diagram for explaining the relationship between the input energy and the surface potential at the time of bias application, (e) is a diagram for explaining the relationship between the surface potential and the amount of adhered toner, and (f) is a diagram for FIG. 7 is a diagram for explaining the relationship between the input energy and the toner adhesion amount, FIG. 9G is a diagram for explaining the relationship between the toner adhesion amount and the image density, and FIG. It is a figure for explaining a relation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 pyroelectric layer 2 conductive layer 3 latent image charge holding medium 4 thermal head 5 conductive layer 6 platen roller 7 developing device 8 developer 9 magnet roller 10 sleeve 11 recording paper 12 transfer roller 15 fixing device 16 controller 17 latent image 18 Toner 19 Recorded image 20 Conductive rubber roller 21 Untransferred toner 22 Cleaner 23 Collected toner

Claims (9)

(57) [Claims] 1. A latent image charge holding medium having a pyroelectric layer,
A heating unit for selectively heating the latent image charge holding medium in accordance with an image signal and forming an electrostatic latent image on the latent image charge holding medium; The heating amount is applied such that a small amount of printing energy is applied to a pixel having a high density of a recorded image, and the heating amount of the heating unit is applied a large amount of printing energy to a pixel having a low density of the recorded image. Control means for controlling the means, cooling the electrostatic latent image formed by heating, cooling means for forming a latent image having a polarity opposite to that of heating, and charged opposite to the polarity of the electrostatic latent image An image recording apparatus, comprising: a developing device for developing an image using colored particles. 2. The image recording apparatus according to claim 1, wherein said cooling means is based on natural cooling, and cools down to room temperature. 3. An image recording apparatus according to claim 1, wherein said cooling means is a forced cooling means such as forced air cooling or heat conduction with a heat sink. 4. The image recording apparatus according to claim 1, wherein the cooling is performed to room temperature by the cooling unit. 5. The image recording apparatus according to claim 4, wherein said developing device visualizes the image at a room temperature. 6. The image recording apparatus according to claim 1, wherein said heating means is a line-type thermal head or a serial-type thermal head. 7. The line type thermal head is connected to a ground potential, a conductive layer is formed on the line type thermal head as a charge neutralizing means, and the conductive layer is a conductive layer formed by vapor deposition. 7. The image recording apparatus according to claim 6, wherein a minute amount of conductive carbon particles is added to the polymer material. 8. The image recording apparatus according to claim 7, wherein said conductive layer is a conductive film. 9. The visualization of the electrostatic latent image may be performed by mixing insulating and non-magnetic colored particles with magnetic carrier particles, charging the colored particles by friction between the particles, and attaching the particles to the surface of the carrier. The developer is held on a sleeve enclosing a magnet roller and is brought into contact with the latent image charge holding medium, thereby selectively adhering toner according to the charge distribution on the latent image charge holding medium. The image recording apparatus according to any one of claims 1 to 8, wherein the image recording apparatus comprises: