JPH07333955A - Image recorder - Google Patents

Abstract

PURPOSE:To suppress the change of recording density caused by the accumulated heat of a heating means and to realize a recording action with excellent image quality as for an image recorder utilizing an electrostatic latent image forming action by a pyroelectric effect. CONSTITUTION:The surface of the pyroelectric layer 1 of a latent image electric charge holding medium 3 is selectively heated by a thermal head 4 according to an image signal. Then, electric charge is generated at the part to be heated of the medium 3 and an electrostatic latent image 17 is formed on the surface of the layer 1. The formed latent image 17 is developed with toner by a developing device 7. At this time, a proper bias voltage obtained based on the temperature of the head 4 detected by a temperature sensor 21 is impressed on a developing sleeve 10. Thus, potential contrast between the latent image 17 and the sleeve 10 is always adjusted within a proper range. Besides, even when the electric charge density of the latent image becomes excessive due to the accumulated heat of the heating means and the like, the increase of the recording density and the fogging of the image are prevented from occurring.

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 and the like, and more specifically, a coloring medium charged with an electrostatic latent image formed by utilizing a pyroelectric effect. The present invention relates to an image recording device that forms an image by developing the image on the recording medium and transferring and fixing the image on a recording medium.

[0002]

2. Description of the Related Art Pyroelectric materials have the property of generating an electric charge on the surface of the material by heating, and several proposals for applying such properties to image recording have been disclosed so far. That is, an electrostatic latent image is formed on the pyroelectric material by selectively heating the pyroelectric material according to image information, and the electrostatic latent image is visualized with a charged coloring medium to record an image. It is the one to try.

An image recording apparatus using a pyroelectric material was first disclosed in Bergman (USA).
n) et al. They are US Pat. No. 3,82.
4,098 and Applied Physics Letters
s), Vol. 21 (10), 1972, p.497-
On page 499, a copying machine using polyvinylidene fluoride (PVDF) as a pyroelectric material is proposed. In this apparatus, as shown in FIG. 5, the lamp light emitted from the light source 46 is transmitted through the original 45 and is applied to a plate in which the pyroelectric layer 43 and the conductor layer 44 are laminated to heat the lamp according to the image pattern. I do. Latent image charges are generated on the surface of the pyroelectric layer 43 due to the pyroelectric effect, and colored particles (toner) 47 charged with the latent image charges are charged.
A toner image is obtained by developing with. The obtained toner image is transferred to a recording paper or the like to obtain a copy of the original.

Thereafter, various methods for heating the pyroelectric material have been disclosed. For example, a system that uses a thermal head (thermal element array) as the heating means
Yamazaki et al. (JP-A-56-158350), Matsushita (JP-A-57-70677), Sakai et al. (JP-A-60-).
104965), and snelling (Snell)
ing) (JP-A-5-134506, US Pat. No. 5,185,619) and the like.
Further, a heating method using a laser beam is disclosed in Yamazaki et al. (Supra), Okuyama et al. (JP-A 1-161370), and the like.

Based on the device proposed by Snelling, FIG.
The basic configuration of a conventional image recording apparatus using a thermal element array as the heating means will be described with reference to FIG. The latent image charge holding medium 31 on which a latent image is formed is composed of a pyroelectric layer 32 and a conductor layer 33. The latent image charge holding medium 31 is heated by the thermal element array (heating needle) 34 controlled by the controller 36. The latent image charge holding medium 3
In order to obtain a large latent image charge density after cooling No. 1, it is important to neutralize the charges generated on the surface of the pyroelectric layer during heating (for the latent image formation process, see Example 1). Will be explained in detail in). Therefore, in the snelling, by providing the grounded conductor layer 35 on the surface of the heating needle 34, the electric charge generated during heating is removed.
The neutralization method is used. When the latent image charge holding medium 31 is cooled, a latent image 37 is formed on the surface of the pyroelectric layer 32. The formed latent image 37 is toner-developed by the developing device 38, then transferred to the recording medium 40 by the transfer unit 41, and the image 42 is formed on the recording paper. The transferred toner is fixed on the paper surface by a fixing device (not shown).

[0006]

However, in the conventional image recording apparatus as described above, variations in the temperature of the heating means and the environmental temperature change the final recording density, which deteriorates the quality of the recorded image. There was a problem. Specifically, when the temperature of the heating means rises (heat storage) or the environmental temperature inside the apparatus increases due to continuous recording, the density of the recorded image becomes excessive or the coloring medium adheres to the non-image area ( Problems such as fogging occurred.

For such heat accumulation of the heating means and environmental temperature fluctuations, a correction method by controlling the amount of heat generated by the heating means is generally used. That is, it is a method of preventing excessive heating by detecting the average temperature and the ambient temperature of the heating means with a temperature sensor and feeding them back to the control circuit of the heating means to reduce the amount of heat generation. In the conventional thermal transfer recording, such a method is often used as a heat storage correction method for the thermal head.

However, in the heat generation amount control of the heating means as described above, it is impossible to completely remove the influence of the heat accumulation of the heating means and the environmental temperature fluctuation in the image recording using the pyroelectric material. The reason will be described below with reference to specific examples.

Assuming that a thermal head is used as the heating means, it is assumed that the temperature of the thermal head as a whole has risen by 10 ° C. due to heat accumulation or environmental temperature fluctuations. When the base temperature of the thermal head rises, there are two effects on the recorded image.

The first effect is that the temperature rise in the image area becomes excessive. In other words, the amount of temperature rise in the image area is 90 ° C.
Even when set to, if the base temperature rises by 10 ° C, the actual amount of temperature rise in the image area becomes 100 ° C, resulting in an excessive increase in recording density or latent image charge retention. Problems such as thermal damage to the medium occur.

The second effect is to cause "fog" in the non-image area. That is, the non-image portion of the latent image charge holding medium should not be heated originally, but the pyroelectric layer of the non-image portion is also heated by 10 ° C. by contacting the thermal head that has accumulated heat. Since the pyroelectric material generates a latent image charge almost in proportion to the heating temperature, a latent image charge corresponding to a temperature rise of 10 ° C. is generated even in the non-image area, which causes “fog”. I will end up.

If the heat generation amount control of the above-mentioned heating means is executed, it is possible to prevent the first effect, that is, the excessive temperature rise of the image portion. However, it is impossible to prevent "fogging" that occurs in the non-image area by controlling the heat generation amount. This is because the heating value control of the heating means has no correction effect with respect to the temperature rise of the non-image portion. In the case of thermal transfer recording, the heat storage correction by controlling the heat generation amount is effective because of the characteristic peculiar to thermal transfer recording that recording (ink transfer) is not executed at a temperature below the melting point of ink. In other words, in thermal transfer recording, "fogging" does not occur even if the temperature of the non-image portion rises by about 10 ° C, so that consideration of the temperature rise of the non-image portion is generally unnecessary. On the other hand, in image recording using a pyroelectric material, a slight increase in temperature in the non-image area causes "fog", so that sufficient measures must be taken.

As described above, in an image recording apparatus using a pyroelectric material, it is extremely difficult to completely remove the influence of the heat storage of the heating means and the environmental temperature fluctuation. In particular, it has been impossible to prevent "fogging" of images by the conventional method.

The present invention has been made in view of the above-mentioned problems, and even when the average temperature of the heating means rises or the environmental temperature in the apparatus fluctuates due to continuous recording or the like, the recording density is made uniform. It is an object of the present invention to provide an image recording apparatus that maintains high image quality and can obtain high image quality.

[0015]

The image recording apparatus of the first invention of the present invention comprises a latent image charge holding medium having a pyroelectric layer, and the latent image charge holding medium selectively depending on an image signal. It comprises at least a heating means for heating to form an electrostatic latent image, and a developing means for visualizing the electrostatic latent image formed on the latent image charge holding medium by a charged coloring medium. In the image recording apparatus according to the present invention, there is provided means for detecting any one or more of the temperature of the heating means, the temperature of the latent image charge holding medium, and the internal environmental temperature of the apparatus, and the developing device according to the obtained temperature data. It is characterized by having means for controlling the amount of the coloring medium supplied from the means onto the latent image charge holding medium.

Further, in the image recording apparatus of the second invention of the present invention, the means for controlling the color medium supply amount is a bias voltage controller for controlling the developing bias voltage applied to the developing means. And

[0017]

The latent image charge holding medium having the pyroelectric layer is locally heated by the heating means in response to the image signal. In the heated portion of the latent image charge holding medium, the molecular orientation state in the pyroelectric layer changes, and as a result, latent image charges are generated on the surface of the pyroelectric layer.

The latent image charge holding medium on which the latent image is formed is brought into contact with or in contact with the charged coloring medium so that the coloring medium is selectively attached to the surface of the pyroelectric layer to visualize the latent image. (Development) is performed. At this time, the amount of the coloring medium supplied from the developing means is controlled so that a good recorded image can be obtained. That is, the optimum amount of the color medium supply is set based on the temperature data of any one or a plurality of the temperature of the heating unit, the temperature of the latent image charge holding medium, and the internal environment temperature obtained by the temperature detecting unit.

The amount of coloring medium supplied is controlled by the bias voltage applied to the developing means. That is, when the heat storage of the heating means is significant and the heating of the latent image charge holding medium becomes excessive, the bias voltage applied to the developing electrode of the developing means is increased in the direction of the same polarity as the latent image charge, and the latent image is formed. The potential contrast with the developing means is reduced. As the potential contrast in the developing process decreases, the amount of colored medium deposited on the latent image charge retaining medium decreases. As a result, it is possible to prevent the recording density from excessively increasing or the coloring medium from adhering to the non-image portion (image fogging).

[0020]

Embodiments of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is a diagram showing an embodiment of an image recording apparatus of the present invention. The image recording apparatus of this embodiment includes an endless belt-shaped latent image charge holding medium 3, a thermal head 4, a conductor layer 5, a temperature sensor 21, a bias voltage controller 22, a developing device 7 as a developing means, and a transfer roller 1.
2 and the fixing device 15 and the like.

As the latent image charge holding medium 3, an endless belt made of a film composed of a pyroelectric layer 1 (thickness: about 30 μm) and a conductor layer 2 (thickness: about 500 Å) was used. . PVDF and aluminum were used as materials for the pyroelectric layer and the conductor layer, respectively. The conductor layer 2 was always kept at the ground potential via the conductive 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 heating elements that generate heat by Joule heat are latent images at a pitch of about 83 μm (300 dots / inch). It has a structure in which the charge holding medium 3 is arranged in a line in the width direction. These heating elements are selectively heated by the controller 16 according to the image signal, and the latent image charge holding medium 3 is generated.
Was heated.

A conductor layer 5 is formed on the surface of the thermal head 4.
Are formed so as to cover the heat generating portion. This conductor layer 5
Is used to neutralize the charge on the surface of the pyroelectric layer during heating. In order to explain the function of the conductor layer 5, a latent image forming process in this embodiment will be described in detail with reference to FIG.

The pyroelectric layer 51 of the latent image charge holding medium has a polarization charge on the surface due to spontaneous polarization of molecules, but in the initial state, this surface charge is all neutralized (Fig. 3 (a)). That is, the floating charges existing in the air and the charges 53 supplied from the neutralizing means such as a conductive brush are attached to the surface of the pyroelectric layer 51 to be in an electrically neutralized state. Here, it is assumed that the polarization charge generated on the surface of the pyroelectric layer by the spontaneous polarization of the pyroelectric body has a positive polarity and the true charge attached to the surface of the pyroelectric layer has a negative polarity.

When the latent image charge holding medium is heated, the molecular orientation state in the pyroelectric layer changes, and the amount of polarization charge generated on the surface of the pyroelectric layer 51 decreases. Therefore, the amount of negative charges attached to the surface becomes excessive, and as a result, the surface of the pyroelectric layer is negatively charged (see FIG. 3B). At this time, if the charge neutralizing means 55 is in contact with or close to the surface of the pyroelectric layer, the excess charge generated on the surface of the pyroelectric layer 51 is removed by the charge neutralizing means, and the surface of the pyroelectric layer is again removed. It will be in a neutralized state (see FIG. 3 (c)).

When the heating is finished and the latent image charge holding medium is cooled to the initial temperature, the polarization state inside the pyroelectric layer also returns to the initial state. At this time, since the surface of the pyroelectric layer has already been separated from the charge-neutralized state, the negative charge on the surface of the pyroelectric layer becomes insufficient, and the surface of the pyroelectric layer apparently becomes positively charged. (See FIG. 3D). That is, a positive latent image is formed on the heated portion of the latent image charge holding medium after cooling.

The latent image thus formed gradually disappears due to the attachment of the floating charges existing in the air, but since such a phenomenon generally takes time, it is usually held for several hours to several tens of hours. It is possible to

The conductor layer 5 of FIG. 1 is provided as the above-mentioned charge neutralizing means. In this embodiment, a metal thin film of aluminum or chromium having a thickness of about 1000 angstrom is formed on the surface of the thermal head by vapor deposition. It is configured by doing. The material and structure of the charge neutralizing means are not limited to those shown in this embodiment,
Other materials and forms such as a thin film of a conductive organic material and a structure in which a conductive film is sandwiched between a thermal head and a pyroelectric layer can be used.

After the heating, the latent image charge holding medium was returned to room temperature by natural cooling to form a latent image 17. In addition to the natural cooling, the latent image charge holding medium 3 can be cooled by using a forced cooling means such as forced air cooling or heat conduction with a heat sink.

Latent image 1 formed on latent image charge holding medium 3
No. 7 was developed using the developing device 7. In this embodiment, 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. 10 and held in contact with the latent image charge holding medium 3 to hold the latent image charge holding medium 3
The latent image was visualized by selectively adhering toner according to the above charge distribution.

A bias voltage was applied to the sleeve 10 using a bias voltage controller 22. The bias voltage to be applied is based on the representative temperature of the thermal head 4 obtained from the temperature sensor 21 (thermistor) and the latent image 17
Control was performed so that an appropriate potential contrast was obtained between the sleeve 10 and the sleeve 10. That is, the bias voltage is set so that the toner is not attached to the non-image portion even when latent image charges are generated in the non-image portion due to the heat storage of the thermal head 4.

The latent image charge holding medium 3 which has been developed 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 surface of the recording paper 11. Electrostatically transferred to. In this example, a voltage of about +1 kV was applied to the conductive rubber roller to electrostatically transfer the toner.

The recording paper 11 to which the toner has been transferred is passed through a fixing device 15 composed of 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 form a recording medium on the recording paper 11. It was fixed.

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, etc. are not limited to the method used in the present embodiment, but are conventional. The same effect can be obtained by using other methods such as those used in the electrophotographic recording.

After the toner is transferred onto the recording paper 11, the latent image charge holding medium 3 is conveyed again to the latent image forming section (thermal head section) and the next latent image formation is executed. Prior to this,
When the untransferred toner remains on the latent image charge holding medium 3, it is removed by using a cleaner (not shown) if necessary.

Further, latent image charge 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 is easily neutralized by bringing a grounded conductive brush (not shown) or the like into contact with the surface of the pyroelectric layer 1 as needed. , The latent image charge holding medium 3 can be returned to the initial state.

As a result of performing a recording experiment under the above-mentioned apparatus configuration, it is possible to perform good recording without "fog" of an image even when continuous recording is performed and heat is accumulated in the thermal head. Was confirmed. Further, it was confirmed that even when multi-gradation recording was performed by controlling the temperature of the heating element of the thermal head, high stability of the recording density was obtained and high-quality image recording was possible.

(Embodiment 2) FIG. 2 is a diagram showing an embodiment of the present invention in the case of using a system in which a latent image forming step and a developing step are simultaneously executed. The components of the device are almost the same as those in the first embodiment, and the same reference numerals are used in the drawings.

The latent image charge holding medium 3 is heated by the thermal head 4 pressed against the conductor layer 2 side of the latent image charge holding medium 3.
Went by. In this embodiment, the developing device 7 is arranged so as to face the thermal head 4, and the latent image is developed simultaneously with the heating of the latent image charge holding medium 3. In this case, the complicated latent image forming process described in the first embodiment is not necessary. That is, in the heated portion of the latent image charge holding medium 3,
A change in the molecular orientation state occurs in the pyroelectric layer, and the amount of polarization charge generated on the surface of the pyroelectric layer decreases. Therefore, the amount of true charges attached to the surface becomes excessive (see FIG. 3B). When a coloring medium charged with the opposite polarity is brought into contact with or in proximity to this excess charge, the coloring medium adheres to the surface of the pyroelectric layer and development is performed. In this example, a positively charged toner was used as the coloring medium. The structure of the developing device is the same as that shown in the first embodiment.

Also in this case, the bias voltage is applied to the sleeve 10 of the developing device 7 by using the bias voltage controller 22. Temperature sensor 2 that detects the heat storage temperature of the thermal head
1, the latent image 17 and the sleeve 10 based on the temperature information obtained from the temperature sensor 21a that detects the internal environment temperature and the temperature sensor 21b that detects the latent image charge holding medium temperature.
The bias voltage was controlled so that an appropriate potential contrast could be obtained during the period.

For each of the subsequent recording processes such as development, transfer, fixing, etc., a desired recorded image 19 can be obtained on the recording paper 11 by using the same system as shown in the first embodiment. .

Although the present invention has been described in detail with reference to the examples, the present invention is not limited to these examples. For example, although all the line type thermal heads are used as the heating means in the above embodiments, it is possible to use any heating means such as a serial type thermal head, a lamp heating using a laser beam or an optical shutter, a flash heating and the like. is there.

Further, in the above embodiment, the latent image charge holding medium has a belt shape, but the same effect can be obtained by using another shape such as a drum shape or a flat plate shape.

Further, in the above embodiment, the recording medium is all paper, but it is clear that the present invention is effective for various other recording media. Further, it is not always necessary to transfer and fix the coloring medium to the recording medium, and by temporarily holding the coloring medium on the recording medium, it is possible to apply it to a device such as a display board that temporarily displays information. .

Further, in the above embodiment, 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.

Further, in the above embodiments, the method of applying the bias voltage to the developing means was used as the method for controlling the supply amount of the coloring medium, but it is also possible to use a method other than this. For example, the supply amount of the coloring medium can be controlled by controlling the rotation speed of the developing sleeve, controlling the charge amount of the coloring medium, or the like.

[0048]

According to the present invention, even when heat is accumulated in the heating means or the environmental temperature fluctuates due to continuous recording, the recording density is kept constant and the "fog" of the image is prevented, and high image quality is obtained. Can be recorded.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining another embodiment of the present invention.

FIG. 3 is a diagram for explaining a latent image forming process.

FIG. 4 is a diagram for explaining a configuration of an image recording device according to a conventional technique.

FIG. 5 is a diagram for explaining the basic configuration of an image recording device according to a conventional technique using lamp light heating.

[Explanation of symbols]

 1 Pyroelectric Layer 2 Conductive Layer 3 Latent Image Charge Retaining Medium 4 Thermal Head 5 Conductive Layer 7 Developer 8 Developer 11 Recording Paper 12 Transfer Roller 15 Fixer 21 Temperature Sensor 22 Bias Voltage Controller

Claims (2)

[Claims] 1. A latent image charge holding medium having a pyroelectric layer, heating means for selectively heating the latent image charge holding medium according to an image signal to form an electrostatic latent image, and the latent image charge holding medium. An image recording apparatus comprising at least a developing means for visualizing an electrostatic latent image formed on an image charge holding medium with a charged coloring medium, the temperature of the heating means, the latent image charge holding medium Of the coloring medium amount supplied to the latent image charge holding medium from the developing unit according to the obtained temperature data. An image recording apparatus comprising means for controlling. 2. The image recording apparatus according to claim 1, wherein the means for controlling the supply amount of the coloring medium is a bias voltage controller for controlling the developing bias voltage applied to the developing means.