JPH0862952A - Image recorder and image recording method - Google Patents

Abstract

PURPOSE: To embody image recording excellent in the uniformity of density in an image recorder utilizing the formation of an electrostatic latent image by a pyroelectric effect. CONSTITUTION: The surface of the pyroelectric layer 1 of a latent image charge holding medium 3 is selectively heated in accordance with an image signal by a thermal head 4. A conductor layer 5 functioning as a charge neutralizing means is formed on the surface of the thermal head 4. The charge is generated on the surface of the heated pyroelectric layer 1 by the pyroelectric effect but it is instantaneously neutralized through the conductor layer 5. At such a time, AC voltage is impressed on the conductor layer 5 by a power source 21, and oscillating electric field is formed between the pyroelectric layer 1 and the conductor layer 5. Thus, the movement of the charge is promoted and charge neutralization excellent in uniformity and having high efficiency is executed. After finishing heating, the temporally stable electrostatic latent image 17 is formed and developed with toner.

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, and more particularly to an image recording apparatus applied to a printer, a fax machine, a copying machine, a display board and the like. More specifically, the present invention utilizes the pyroelectric effect. The present invention relates to an image recording apparatus that forms an image by developing an electrostatic latent image formed by using a charged colored medium.

[0002]

2. Description of the Related Art A method of recording an image by forming an electrostatic latent image using a pyroelectric material that generates electric charges on the surface of the material by heating and visualizing the electrostatic latent image with a charged colored medium is known. Some have been disclosed so far.

For example, in US Pat. No. 3,824,098, Bergman et al. Have proposed a copying machine using polyvinylidene fluoride (PVDF) as a pyroelectric material. In this apparatus, as shown in FIG. 5, the lamp light emitted from the light source 44 is transmitted through the original 43 and is applied to the plate in which the pyroelectric layer 41 and the conductor layer 42 are laminated, and according to the image pattern. Heating. A latent image charge is generated on the surface of the pyroelectric material due to the pyroelectric effect, and a toner image is obtained by developing the latent image charge with charged colored particles (toner) 45. The obtained toner image is transferred to a recording paper or the like to obtain a copy image of the original.

By the way, Bergman et al.
Physics Letters, V
ol. 21 (10), 1972, 497-499, mentioning latent image formation by opposite polarity charges.
That is, if the charge generated on the surface of the pyroelectric material is neutralized immediately after heating the pyroelectric material (or during heating),
When the pyroelectric material is returned to room temperature, an electric charge having the opposite polarity to that during heating is generated on the surface of the pyroelectric material. The latent image formed by the opposite-polarity charges thus obtained has an advantage that it can be stably held in time as compared with the charges generated during heating.
The latent image formed by such a process will be referred to as a “latent image formed by opposite polarity charges” in the present specification.

Further, Yamazaki et al., In Japanese Patent Laid-Open No. 56-158350, discloses a method of heating a pyroelectric material by laser light or a thermal head. Also in their recording method, latent image formation by reverse polarity charges generated when the pyroelectric material is cooled is used.

By the way, the above-mentioned prior arts by Burgman and Yamazaki et al. Mention the latent image formation by the opposite polarity charges, but do not disclose the specific means. Taylor, on the other hand, has been described in U.S. Pat.
In Example No. 7, there is disclosed a method of positively charge-neutralizing the surface of the pyroelectric material during heating by using a charge-neutralizing means composed of a conductive brush. In addition, Snellin (Snellin
g) discloses a method of neutralizing electric charges generated during heating by using a heating needle as a heating means and providing a grounded conductor layer on the surface of the heating needle.

The basic configuration of the image recording apparatus proposed by Snelling will be described with reference to FIG. A belt-shaped latent image charge holding medium 51 on which a latent image is formed includes a pyroelectric layer 32 and a conductor layer 53. Heating needle 54 in contact with the pyroelectric layer 52
Is controlled by the controller 56 to selectively heat the surface of the pyroelectric layer 52 according to the image signal. On the surface of the heating needle 54, a grounded conductor layer 55 is formed as a charge neutralizing means, and the charges generated on the surface of the pyroelectric layer 52 by heating are neutralized through the conductor layer 55. When the latent image charge holding medium 31 is cooled, charges of opposite polarity are generated and a latent image 57 is formed. The formed latent image 57 is toner-developed by the developing device 58, and then the transfer means 61.
An image 62 is formed by being transferred to the recording medium 60 by (in the snelling method, the transfer device also utilizes the pyroelectric effect).

[0008]

As described above, in the case of using the latent image forming method using the opposite polarity charges, in order to obtain high recording quality, the charge neutralization during latent image formation (at the time of heating) is uneven. It is important to do this uniformly. In particular, when the halftone recording is performed by controlling the heat generation amount of the heating means and changing the heating temperature of the pyroelectric layer, high uniformity in charge neutralization is required. That is, if the charge neutralization is not uniform, the latent image potential cannot be modulated according to the heating temperature, and thus halftone recording excellent in density uniformity and stability cannot be realized. Therefore, it is essential to carry out uniform charge neutralization in order to carry out high-quality halftone recording.

However, in the conventional charge neutralization method,
It was difficult to ensure sufficient uniformity for charge neutralization. For example, in the conventional example shown in FIG. 6, it is difficult to obtain a perfect contact state between the charge neutralizing means (conductive layer 55) and the pyroelectric layer 52, and it is difficult to achieve uniform charge neutralization. It was That is, it is extremely difficult to obtain complete contact over the entire surface because fine irregularities are present on the surface of the charge neutralizing means and the surface of the pyroelectric layer. Therefore, between the pyroelectric layer and the charge neutralizing means. The contact unevenness is likely to appear as it is as non-uniformity of the recording density, and it is particularly difficult to reproduce the halftone of uniform density. As a measure for improving the contact state, the surface of the charge neutralizing means and the surface of the pyroelectric layer are finished to have a surface precision having extremely high flatness and surface roughness, or both are elastically deformed by pressing with high pressure. It is possible to think of a method of making close contact by using. However, these methods pose problems such as an increase in the cost of the device and an increase in size (to increase the rigidity), which is extremely difficult in reality.

In addition to the problem of insufficient uniformity, there is a problem that it is difficult to obtain sufficient charge neutralization efficiency by the conventional charge neutralization method. That is, the charge neutralization needs to be performed within a very short time while the temperature of the pyroelectric layer is rising,
Very high efficiency is required for charge neutralization. However, in the conventional example such as the device for snelling (FIG. 6), since the charge neutralizing means is set to the ground potential, a large electric field is not formed in the charge neutralizing region, and thus high charge neutralizing efficiency can be obtained. Difficult, especially in high-speed recording, the charge neutralization ability is insufficient and sufficient recording density (latent image charge density)
Was hard to get.

Further, another problem to be solved in the conventional image recording apparatus is lack of gradation recording characteristics when performing halftone recording. That is, in the image recording apparatus using the pyroelectric material, the density gradation control can be performed in units of recording pixels by controlling the heat generation amount of the heating unit, but the upper limit temperature (curie) that the pyroelectric material can tolerate. Temperature), the number of gradations that can be realized is limited in consideration of the temperature controllability of the heating means.

For example, PVDF, which is a general polymer pyroelectric material, has a Curie temperature of about 120.degree.
If it exceeds this range, the pyroelectric characteristics are deteriorated or completely lost. Normally, the maximum temperature at which stable characteristics are obtained is 90
It is thought to be around ℃. If the heating temperature (lower limit of temperature) for recording the lowest density is set to 40 ° C., the dynamic range of the heating temperature is 90-40 = 50 (° C.). Now, assuming that halftone recording of 64 gradations is performed, the temperature control is performed by dividing the temperature range of 50 ° C. into 64. That is, a highly accurate temperature control of ± 0.4 ° C is required. However, in practice, it is very difficult to control the heating temperature with such high accuracy, and even when a thermal head, which is relatively easy to control with high accuracy, is used as the heating means, it is usually about ± 1 ° C. Control is the limit. Therefore, in this case, the actually controllable number of gradations is 50/2 = 25 gradations, and it becomes difficult to perform recording faithful to the image signal. As described above, in the conventional image recording apparatus, it is difficult to obtain sufficient gradation recording characteristics because the allowable temperature range of the pyroelectric material is narrow.

The present invention has been made in view of the above-mentioned problems, and improves the uniformity and efficiency of charge neutralization during heating and ensures a sufficient recording density even during high-speed recording. It is an object of the present invention to provide an image recording apparatus that can obtain high density uniformity and high gradation recording characteristics.

[0014]

In the image recording apparatus of the present invention, a latent image charge holding medium having a pyroelectric layer and a latent image charge holding medium are selectively heated to form an electrostatic latent image. In the image recording apparatus including at least the heating means of No. 1, a charge neutralizing means for electrically neutralizing the surface of the latent image charge holding medium during or immediately after the heating of the latent image charge holding medium is provided. It is characterized in that it is arranged so as to be in contact with or close to the latent image charge holding medium, and an AC voltage is applied to the charge neutralizing means.

Further, the image recording apparatus of the present invention is characterized in that a DC voltage is applied to the charge neutralizing means instead of the AC voltage.

Further, the image recording apparatus of the present invention is characterized in that a pulsating current voltage in which an AC voltage component and a DC voltage component are superimposed is applied to the charge neutralizing means.

Further, the image recording apparatus of the present invention has the detection means for detecting any one or plural information of the temperature inside the apparatus, the humidity inside the apparatus, the base temperature of the heating means, and obtained. It is characterized by comprising a voltage control circuit for controlling the voltage value of the DC voltage or the DC voltage component based on information.

Further, the image recording apparatus of the present invention uses an image data
Data is divided into a plurality of image data sets according to the pixel density to be recorded, and the heat generation amount control of the heating means and the control of the DC voltage or the DC voltage component are performed corresponding to each of the image data sets. By performing the electrostatic latent image forming step a plurality of times for each set of image data, recording of image data having density gradation is performed.

[0019]

The operation of the present invention will be described with reference to FIG.

The pyroelectric layer 71 of the latent image charge holding medium has a polarization charge 74 on the surface due to spontaneous polarization of molecules, but in the initial state, this surface charge is all neutralized. That is, the floating charge existing in the air and the true charge 73 supplied from the neutralizing means such as a conductive brush are attached to the surface of the pyroelectric layer to be electrically neutralized (FIG. See a)). 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,
Description will be made assuming that a state in which a negative charge true charge of the same amount as the positive charge is attached to the surface of the pyroelectric layer and is in a neutralized state is an initial state.

The latent image charge holding medium 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,
The amount of polarization charge generated on the surface of the pyroelectric layer is reduced. 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 (FIG. 7).
(B)).

The charge neutralizing means 75 is in contact with or in close proximity to the surface of the pyroelectric layer, and the excess charge generated on the surface of the pyroelectric layer is removed by the charge neutralizing means, and the surface of the pyroelectric layer is again removed. It approaches a neutralized state (see FIG. 7 (c)).

At this time, an AC voltage whose voltage changes around the OV potential as a reference is applied to the charge neutralizing means. By applying this AC voltage, an oscillating electric field in which the electric field strength periodically changes is formed between the latent image charge holding medium and the charge neutralizing means, and the latent image charge holding medium is uniformly neutralized. That is, the charge transfer from the surface of the latent image charge holding medium to the charge neutralizing means and the charge transfer from the charge neutralizing means to the latent image charge holding medium are repeated in a short cycle, resulting in a latent image charge holding medium. The surface is in a uniform neutralized state.

When the heating is completed 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 neutralizing means, 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. 7 (d)). That is, a positive latent image is formed on the heated portion of the latent image charge holding medium after cooling. The latent image formed in this way is gradually disappeared due to the attachment of the floating charges existing in the air, but such a phenomenon generally takes time, and is usually held for several hours to several tens of hours.

The latent image charge holding medium on which a latent image is formed is visualized (developed) by a charged coloring medium, and transferred and fixed to a recording medium such as recording paper as necessary to record an image. Is done.

Although an AC voltage is applied to the charge neutralizing means in the above description, the charge neutralizing efficiency can be improved by applying a DC voltage to the charge neutralizing means. That is, it is possible to remove excess charges efficiently by applying a DC voltage that exerts an attractive force on the excess charges generated on the surface of the pyroelectric layer.

By applying a DC voltage or a pulsating voltage in which a DC voltage component and an AC voltage component are superimposed to each other, it is possible to change the reference potential at the time of charge neutralization. That is, even if the heating temperature is constant, it is possible to shift the obtained latent image potential by increasing or decreasing the applied DC voltage component. Therefore, when the latent image potential changes due to factors such as environmental temperature fluctuations and the temperature rise of the heating means due to heat accumulation, by adjusting the magnitude of the DC voltage component, the latent image potential can always be kept constant. Becomes

Further, the gradation recording characteristics can be improved by utilizing the property that the latent image potential (recording density) can be shifted as a whole by controlling the DC voltage component as described above. That is, when performing the halftone recording, the image data is divided into a plurality of groups according to the pixel density, and the recording is performed a plurality of times for each group. At this time, a DC voltage component corresponding to each image data loop is applied to the charge neutralizing means. That is, when recording a low-density image data loop, the DC voltage component is set low, and conversely, when recording a high-density image data loop, the DC voltage component is set high. For each group, the heating temperature is the entire range from the lowest temperature to the highest temperature determined from the ambient temperature, the Curie temperature of the pyroelectric material, and the like. By using the halftone recording method as described above, multi-tone recording can be performed, and smooth halftone recording can be executed.

[0029]

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

(Embodiment 1) FIG. 1 is a diagram showing an embodiment of the present invention in the case where an AC voltage is applied to the charge neutralizing means. The image recording apparatus of this embodiment includes an endless belt-shaped latent image charge holding medium 3, a thermal head 4 as a heating unit, a conductor layer 5 as a charge neutralizing unit, a power source 21,
It is composed of a developing device 7, a transfer roller 12, and a fixing device 15.

The latent image charge holding medium 3 is a belt made of an endless film consisting of a pyroelectric layer 1 (thickness: about 100 μm) and a conductor layer 2 (thickness: about 0.1 μm). I was there.
The materials for the pyroelectric layer and the conductor layer are PVDF, respectively.
And aluminum were used. 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.

On the surface of the thermal head 4, a conductor layer 5 as a charge neutralizing means is formed so as to cover the heat generating portion. In this embodiment, the thickness of the thermal head surface is about 0.
A metal thin film of 1 μm of aluminum or chromium was formed by vapor deposition, and this was used as a conductor layer. For the conductor layer formed on the surface of the thermal head, it is possible to use other materials such as a conductive organic material in addition to the metal thin film used in this embodiment. Further, it may be in a laminated state such as forming an insulative body layer under the conductor layer on the surface. Further, in this embodiment, the conductive layer 5 formed on the thermal head was used as the charge neutralizing means, but the form of the charge neutralizing means is not limited to this. For example, a conductive film sandwiched between the heating means and the latent image charge holding medium can be used as the charge neutralization means.

On the surface of the pyroelectric layer 1 of the heated latent image charge holding medium 3, electric charges (excess electric charges described in the section of action) are generated by the pyroelectric effect. Be harmonized. Here, an AC voltage was applied to the conductor layer 5 by the AC power supply 21. In the present specification, the AC voltage means a voltage whose voltage changes periodically with OV as a reference. In this embodiment, the amplitude is 1.5 kV and the frequency is 1.
An alternating voltage whose voltage changes sinusoidally at 00 Hz was applied to the conductor layer 5. Thereby, charge transfer between the surface of the pyroelectric layer 1 and the conductor layer 5 was promoted, and high-speed and uniform charge neutralization was performed.

The frequency and amplitude of the applied AC voltage are
In the case of the device configuration as in this embodiment, each of 50 to 50
It is desirable that the frequency is 500 Hz and 1 kV or higher. However, the optimum frequency and amplitude values are not necessarily limited to the above ranges because they depend on the material and surface shape of the charge neutralizing means and the latent image charge holding medium. The same effect can be obtained by using a waveform other than a sine wave, such as a triangular wave or a rectangular wave, as the waveform of the applied AC voltage.

After the heating, the latent image charge holding medium was returned to the greenhouse by natural cooling to form a latent image 17 with an opposite polarity charge. In this embodiment, the temperature rise amount on the surface of the pyroelectric layer 1 is set to 4
When the temperature was 0 ° C., a latent image potential of about 900V was obtained.

Latent image 1 formed on latent image charge holding medium 3
No. 7 was developed using the developing device 7. In this embodiment, a two-component magnetic brush development was used as a development method. In other words, the magnetic particles are mixed with the magnetic particles that are absolutely insulative and non-magnetic, and the toner is charged by the friction between the particles, and the developer 8 adhered to the surface of the carrier particles is enclosed in the magnet roller 9. The toner is held on the formed sleeve 10 and brought 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,
The latent image was visualized.

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 of about 1 kV is applied is pressed from the rear surface of the recording paper 11 to record toner. It was electrostatically transferred to the surface of the paper 11.

By passing the recording paper 11 to which the toner has been transferred through a fixing device 15 composed of a heat roller 13 and a pressure roller 14, the toner on the surface of the recording paper 11 is once melted and fixed on the recording paper 11.

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 this embodiment, and 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 to 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. If the latent image charge remains,
If necessary, a neutralization means (not shown) such as a conductive brush grounded is brought into contact with the surface of the pyroelectric layer 1 to neutralize the latent image charge on the surface of the pyroelectric layer 1. If the toner and the latent image charge remaining after the transfer are small, a cleaner and a discharging unit are not always necessary.

As a result of performing a recording experiment under the above-mentioned apparatus configuration, an OD value of about 1.6 was obtained on plain paper having low smoothness.
It was confirmed that it is possible to perform high-density recording having the maximum image density of 1 and halftone recording having high density uniformity (OD value variation of about ± 0.05).

As a comparative experiment, a recording experiment was conducted with the conductor layer 5 grounded without applying an AC voltage to the charge neutralizing means (conductor layer 5). As a result, it was confirmed that the dispersion of the OD value at the time of recording the halftone was extremely deteriorated to an average of about ± 0.6, and the maximum recording density was also decreased to about 1.4.

As is apparent from the above comparative experiments, the present invention in which an AC voltage is applied to the charge neutralizing means can improve the efficiency and uniformity of charge neutralization at the same time.
Enables high quality image recording.

(Embodiment 2) FIG. 2 is a diagram showing an embodiment in which a DC voltage is applied to the charge neutralizing means. Except that the DC power source 22 is connected to the charge neutralizing means, the device configuration is almost the same as that of the first embodiment, and the same reference numerals are used in the drawings.

When the latent image charge holding medium 3 is heated by the thermal head 4, the heated latent image charge holding medium 3 is heated.
Electric charges are generated on the surface of the pyroelectric layer 1 due to the pyroelectric effect, which is neutralized through the electric conductor layer 5 which is a charge neutralizing means. In this embodiment, the power source 22 is applied to the conductor layer 5 so that
Charge generated by applying a DC voltage of 300 V (negative polarity)
The efficiency of charge neutralization was improved by applying a strong suction force to the.

As a result of carrying out a recording experiment under the above-mentioned apparatus configuration, an OD value of about 1.6 was obtained on plain paper having low smoothness.
It was confirmed that high density recording with the maximum recording density of 1 is possible.

As described in the first embodiment, when the charge neutralizing means (conductor layer 5) is grounded, the recording density is about 1.4, and a DC voltage is applied to the charge neutralizing means. It was confirmed that the above-mentioned effect is effective in improving the charge neutralization efficiency (image density).

(Embodiment 3) FIG. 3 shows an embodiment in which a pulsating voltage is applied to the charge neutralizing means and the direct current voltage component is controlled by the temperature of the heating means and the environmental temperature in the apparatus. It is the figure which showed.

The image recording apparatus of this embodiment comprises an endless belt-shaped latent image charge holding medium 3, a thermal head 4 as a heating means, a conductive layer 5 as a charge neutralizing means, and a temperature sensor 2.
3, 24, voltage control circuit 30, developing device 7, transfer roller 1
2 and the fixing device 15 and the like.

Electric charges are generated on the surface of the pyroelectric layer 1 heated by the thermal head 4 due to the pyroelectric effect, but these are neutralized through the conductive layer 5. The voltage control circuit 30 applied to the conductive layer 5 a pulsating current voltage in which an AC voltage component and a DC voltage component were superimposed. In this embodiment, the AC voltage component has an amplitude of 1.5 kV and a frequency of 100 Hz. In addition, the voltage value of the DC voltage component is based on the temperature information measured by the temperature sensor 23 that detects the storage temperature of the thermal head 4 and the temperature sensor 24 that detects the environmental temperature inside the device, and the voltage control circuit. 30 was used to vary between -200 and + 200V.

The voltage control circuit 30 includes an A / D converter 25,
25 ', arithmetic unit (CPU) 26, D / A converter 27,
It is composed of a voltage amplifier (DC power supply) 28 and an AC power supply 29. The arithmetic unit 26 compares the temperatures detected by the temperature sensor 23 and the temperature sensor 24, and calculates the optimum DC voltage component value to be applied to the conductive layer 5 based on the data of the higher temperature. . In this way, by controlling the DC voltage component according to the heat storage temperature of the thermal head 4 and the environmental temperature inside the apparatus, the latent image potential obtained was controlled to be always constant.

For example, when the temperature of the thermal head 4 is raised by 10 ° C. due to heat storage, and the DC voltage component is not superimposed, the surface potential of the pyroelectric layer 1 is 10 as a whole.
The temperature shifts by a heating amount of ℃ (about 220 V in this embodiment). Therefore, there arise problems that the image density is unnecessarily increased, and toner adhesion (fog) easily occurs on the non-image portion. Therefore, the DC voltage component of the pulsating current voltage applied to the charge neutralizing means has a polarity opposite to that of the latent image, and the magnitude of the DC voltage component is set to a value that cancels out the increase in the surface potential generated by heat storage. By doing so, the shift of the surface potential can be prevented and the latent image potential can be always kept constant.

The latent image charge holding medium 3 forms a latent image 17 by charges of opposite polarity as it cools after being heated. For each of the subsequent recording processes such as development, transfer, fixing, etc., the desired recording image 19 can be obtained on the recording paper 11 by using the same method as that shown in the first embodiment.

As a result of executing the recording experiment under the above-mentioned apparatus configuration, even when the temperature of the thermal head 4 is increased by 8 ° C. due to heat storage by continuous recording of 10 sheets,
It was confirmed that the density of the recorded image did not fluctuate, and good image recording could be performed without fogging on the non-image area.

As a comparative experiment, the same continuous recording experiment was conducted without controlling the DC voltage component. As a result, the image density increases according to the heat of the thermal head 4, and the OD value of the first image and the tenth image is 0.
A density difference of 3 occurred. At the same time, the amount of fogging on the non-image area increases, and in the 10th image, the OD appears on the non-image area.
Fog with a value of about 0.4 (OD value of recording paper was about 0.2) occurred.

As is apparent from the results of such comparative experiments, the present invention in which the DC voltage component applied to the charge neutralizing means is controlled according to the base temperature of the heating means is the basis of the heating means.
Since it is possible to perform recording with a constant density even when the temperature changes, it is possible to perform image recording without density unevenness and stable continuous recording.

In this embodiment, the direct current voltage component is controlled as a method for compensating the heat storage of the heating means, but such a control method can also be used for compensation for the temperature inside the apparatus. Further, since the humidity inside the apparatus also affects the charging characteristics and transfer characteristics of the toner, it is also effective to control the DC voltage component in accordance with the humidity inside the apparatus in order to eliminate these effects. Furthermore, the density of the recorded image can be easily adjusted by allowing the user of the apparatus to arbitrarily adjust the magnitude of the DC voltage component.

Further, in the present embodiment, the case where the pulsating voltage is applied to the charge neutralizing means is described, but even when only the DC voltage is applied, the image density adjustment similar to the above is executed by controlling the voltage value. It is possible to

[0060]

[Embodiment 4] FIG. 4 is a diagram showing an embodiment in which multi-gradation recording is executed by combining the heat generation amount control of the heating means and the control of the DC voltage applied to the charge neutralization means. is there.

The magnitude of the DC voltage applied to the charge neutralizing means (conductive layer 5) is determined by the controller 1 of the thermal head 4.
6'is the same as that of the second embodiment except that it has a voltage control circuit 31 for changing it in conjunction therewith, and the same reference numerals are used in the drawings.

In the present embodiment, the image data is divided into a plurality of groups according to the densities, and the magnitude of the DC voltage applied to the charge neutralizing means is changed stepwise in accordance with the density, whereby the gradation recording characteristics are improved. It is possible to improve. Hereinafter, the recording procedure will be described with reference to FIG. 8 by exemplifying the case where the DC voltage is changed in two steps and the gradation control in 64 steps is executed.

First, the image data is divided into two groups according to the density. That is, it is divided into an image data group having a density of 1 to 32 gradations and an image data group having a density of 33 to 64 gradations.

Next, the voltage control circuit 31 obtains the concentration of the first stage when the heating element is heated to the lower limit temperature (40 ° C.) and the 32nd stage when the heating element is heated to the upper limit temperature (90 ° C.). A DC voltage V ₁ is applied to the conductor layer 5 which is a charge neutralizing means so that the concentration can be obtained. Then, only the image data of the low density group is sent from the controller 16 ', and recording is performed on the recording paper by each process of latent image formation, development and transfer (low density area in FIG. 8).

Next, the DC voltage is changed to V ₂ so that the 33rd step density is obtained when the heating element is heated to the lower limit temperature and the 64th step density is obtained when the heating element is heated to the upper limit temperature. To do. Then, recording is performed on the image data of the high density group, and the image is superposed on the image previously formed on the recording paper (high density area in FIG. 8).

As described above, the image data is divided into a plurality of groups according to the densities, and a DC voltage corresponding to each of the groups is applied to the charge neutralizing means, while an image is formed by a plurality of recordings, so that a substantial image is formed. The dynamic range of temperature can be expanded, and halftone recording with a large number of gradations can be executed. In the above example, since the temperature range of 50 ° C. is divided into 32 parts, the required temperature control accuracy is ± 0.8 ° C. In other words, compared with the case where no grouping is performed, the required temperature accuracy is 1 /
It becomes possible to set to 2, and stable gradation control becomes easy.

If the number of groups is increased and the recording is executed while changing the DC voltage of the charge neutralizing means in multiple steps, it is possible to further improve the gradation recording characteristics.

Although the recording method as shown in this embodiment is disadvantageous in terms of recording speed, it is an extremely advantageous method for recording when high image quality is required.

The recording procedure is not limited to the procedure shown in this embodiment. For example, depending on the heating method or the charge neutralization method, it is possible to perform only the latent image forming step in plural times and to perform the developing and transferring steps only once.

Further, in the present embodiment, only the DC voltage is applied to the charge neutralizing means, but the same effect can be obtained by applying the pulsating current voltage and performing the recording while changing the DC voltage component in multiple steps. Obtainable.

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 or the latent image charge holding medium, it is possible to temporarily display information on the display plate or the like. It can also be applied to display devices.

In the above embodiments, 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.

[0076]

According to the present invention, by applying an AC voltage, a DC voltage, or a pulsating voltage to the charge neutralizing means, the efficiency and uniformity of charge neutralization in the latent image forming process are greatly improved. It becomes possible. This enables halftone reproduction and high-speed recording with excellent density uniformity.

Further, according to the present invention, the reference potential of the latent image can be controlled by controlling the magnitude of the DC voltage component or the DC voltage component of the pulsating current voltage applied to the charge neutralizing means. As a result, it becomes possible to easily and highly accurately compensate for changes in the image density due to environmental temperature fluctuations and heat storage of the heating means.

Further, according to the present invention, by controlling the DC voltage applied to the charge neutralizing means in multiple stages, it is possible to stably perform multi-gradation recording, and to obtain a smooth halftone recorded image. Obtainable.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment in which an AC voltage is applied to a charge neutralizing means.

FIG. 2 is a diagram for explaining an embodiment in which a DC voltage is applied to the charge neutralizing means.

FIG. 3 is a diagram for explaining an example in which a voltage to be applied is controlled based on temperature information.

FIG. 4 is a diagram for explaining an example in which halftone recording is performed by controlling the amount of heat generated by a heating unit and controlling the voltage applied to a charge neutralizing unit.

FIG. 5 is a diagram for explaining the principle of a conventional copying apparatus using lamp heating.

FIG. 6 is a diagram for explaining a configuration of an image recording apparatus according to a conventional technique using a grounded charge neutralizing means.

FIG. 7 is a diagram for explaining a latent image forming process.

FIG. 8 is a diagram for explaining a gradation control method by controlling a DC voltage applied to a charge neutralizing means.

[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

Claims (6)

[Claims] 1. A latent image charge holding medium having a pyroelectric layer,
An image recording apparatus comprising at least a heating means for selectively heating the latent image charge holding medium to form an electrostatic latent image, wherein the latent image charge holding medium is heated during or immediately after the heating. A charge neutralizing means for electrically neutralizing the surface of the latent image charge holding medium is arranged so as to be in contact with or close to the latent image charge holding medium, and a voltage is applied to the charge neutralizing means to charge the medium. An image recording apparatus having improved uniformity or efficiency of sum. 2. The image recording apparatus according to claim 1, wherein an AC voltage is applied to the charge neutralizing means. 3. The image recording apparatus according to claim 1, wherein a DC voltage is applied to the charge neutralizing means. 4. The image recording apparatus according to claim 1, wherein a pulsating voltage in which an AC voltage component and a DC voltage component are superposed is applied to the charge neutralizing means. 5. The temperature of the apparatus, the humidity in the apparatus, and the heating means base.
And a voltage control circuit for controlling the voltage value of the DC voltage or the DC voltage component based on the obtained information. The image recording apparatus according to claim 3, wherein the image recording apparatus comprises: 6. An image recording method for recording an image using the image recording apparatus according to claim 3, wherein a plurality of image data are recorded according to a pixel density at which the image data should be recorded. The image data is divided into sets, and the amount of heat generated by the heating means is controlled and the DC voltage or the DC voltage component is controlled corresponding to each of the image data sets. An image recording apparatus characterized in that image data having a density gradation is recorded by performing a plurality of times for each set.