Multiplex image reproducing apparatus

Abstract

A method of reproducing multiplex images wherein an electrostatic image is formed on an image retainer by using a common electrostatic image forming device, the electrostatic image formed on the image retainer is developed, the steps of the above are repeated to superpose a plurality of toner images on the image retainer, and the toner images is transferred on a recording paper by one step. The developings other than the first time developing are carried out in such a manner that the surface of a developer layer on a developer feeding carrier does not contact with the surface of the toner image on the image retainer.

Description

1.000 practise practice the method of the present invention, it is preferable to use the image retainer having a highly insulating layer as the image retainer. Once the developer is trapped by the image retainer, generally speaking, it is remarkably difficult to remove, because not only the van der Waals' force but also the image forming force acts, to cause troubles such as the fog and the reduction in the transfer ratio. These phenomena can be prevented by suitably charging the image retainer in the same polarity as that of the charges of the toners. However, the ordinary magnetic image retainer constructed of a conductive base and a magnetic layer has such a low insulating property that it is difficult to charge. Despite of this fact, this ordinary image retainer can be charged by forming an insulating layer on the surface of the magnetic layer. By using the image retainer having the insulating layer on the surface of the magnetic member, the unnecessary trap of the toners can be prevented to enhance the transfer efficiency, and a charger is placed in front of the magnetic image writing operation to effect the charging operation so that the fog can be prevented. Moreover, the insulating layer is also effective for protecting the magnetic layer and for preventing the toner filming. If this toner filming occurs, there arises no practical problem if it takes place on the insulating layer. Moreover, the magnetic layer may also act as the conductive base if it is conductive. In case the thickness of the insulating layer is excessive, it drops the density and magnetization of the magnetic image recorded. Therefore, that thickness is preferred to be no more than 50 μm or, preferably, no more than 10 μm.

Incidentally, FIG. 42 shows an embodiment of the reproducing apparatus which uses an image retainer having the insulating layer, but the pre-writing charger 2 and the charge eliminating means 13 can be omitted in case an image retainer having no insulating layer is used.

In the embodiment of FIG. 42, the writing operation of the magnetic image is conducted by the reproducing method of parallel magnetization type using a ring head. However, a perpendicular magnetization type method can be likewise used as the magnetically writing means. In this case, the magnet 32 is fixed, and its opposed magnetic poles are made different from the magnetizing direction by the writing operation so that the toners may be reluctant to jump to the non-image portion but liable to jump to the image portion. In this case, it is needless to say that the magnetizing direction and the magnetization facilitating direction of the magnetic layer should be aligned.

On the other hand, the magnetic erasing head 63' and the magnetic recording head 63 may be disposed in front of, in front of and at the back of, or at the back of the pre-writing charger as shown in FIGS. 42 and 43.

The image reproducing process using the reproducing apparatus according to the method of the present invention will be described in the following with reference to FIGS. 44 to 46.

In the embodiment of FIG. 44, by the reproducing apparatus of FIG. 42: (1) the surface of the image retainer 61 has its charges eliminated by the image eliminating means 13 and cleaned by the cleaning means 14; and the initial state, in which the surface of the image retainer 61' is charged to a suitable potential e (in which the broken lines indicate the presence of the charges) in the same polarity as that of the toners, is established by the pre-writing charger 2 so as to prevent the fog.

Next, after the residual magneticism m has been demagnetized by the demagnetizing head 63' (shown at (3)), that surface is subjected to a first writing operation by the recording head 63 to retain a magnetic image M₁ (shown at 4)) which is firstly developed by the developing means 5 to obtain a first image T₁ (shown at (5)). Moreover, the image retainer 1 enters its second rotation in the reproducing apparatus of FIG. 42 so that it is demagnetized by the erasing head 63' (shown at (6)) and is subjected to a second writing operation by the recording head 63 (shown at (7)). The magnetic image M₂ thus formed is secondly developed by the developing means 6 to provide a second image T₂ (shown at (8)). Then, third and fourth demagnetizing, writing operations and developments are likewise repeated so that a color image having its color toner images superposed is retained on the image retainer 61. The resultant color image is made liable to be transferred by the pre-transfer charger 9 in the reproducing apparatus of FIG. 42 so that it is fixed on the recording member P by the fixing means 12 after it has been transferred to the recording member P by the transfer means 11. In the reproducing apparatus of FIG. 43, on the other hand, that color image is fixed directly on the image retainer 61' by the fixing means 12. In the reproducing apparatus of FIG. 42, moreover, the surface of the image retainer 61 having the color image transferred thereto has its charges eliminated by the charge eliminating means 13 and is cleared of the residual toners by the cleaning means 14 until the one cycle of the color image reproduction is ended by further eliminating the charges, if necessary. In case the reproducing apparatus of FIG. 43 is used, too, the image retaining process is not changed except for the shape of the image retainer 61'.

FIG. 45 shows a process which is simplified by omitting the uniformly charging step from the process of FIG. 44. FIG. 46 shows a process which is difference from that of FIG. 44 in that the charger 2 is operated to effect the uniform charging operation before each writing step. However, their basic operations are all common.

Incidentally, reference letters T₁ and T₂ indicate the toners of different colors, which are trapped by the image retainer 61 or 61'.

By conducting the developments under the non-contact jumping developing conditions, according to the method of the present invention, the developing means other than that conducting the development of each time can be easily held in an inoperative state, even if the developer layer is not removed from the developing sleeve 31, by disconnecting the developing sleeve 31 from the power supply 39 into a floating state, by grounding the same to the earth, or by positively applying a d.c. bias voltage having a polarity opposite to that of the charges of the toners to the developing sleeve 31. Of these means, it is preferable that the developing means are held inoperative by applying the bias voltage having a polarity opposite to that of the toners.

Next, the embodiments of FIGS. 44 to 46, which are practised by the reproducing apparatus of FIG. 42, will be described in more detail in the following in connection with Examples 29 to 31.

The reproducing apparatus shown in FIG. 42 was used. The image retainer 61 was prepared by forming a Co alloy having a thickness of 10 μm on an aluminum base by the electron beam heating operation and by forming the insulating layer having a thickness of 5 μm on the surface of the Co alloy and which had a circumference speed of 180 mm/sec. The surface of the image retainer 61 thus prepared was charged to +50 V by the pre-writing charger 2 using the scorotron corona discharger and was demagnetized by means of the magnetic erasing head which had its leading end spaced at a distance of about 30 μm from the surface of the image retainer 61. Next, a first image writing operation was conducted in a distribution density of 10 spots/mm by means of the recording head 63 which had a similar spacing. As a result, a first magnetic image was retained on the image retainer 61. This magnetic image was firstly developed by the developing means 6 shown in FIG. 3. This developing means 6 uses the developer, which was composed of: a carrier having 50 wt. % of magnetite dispersed contained in a resin and having an average particle diameter of 30 μm, a magnetization of 30 emu/g and a resistivity of 10¹4 Ω cm or more; and a positive magnetic toner prepared by adding 25 wt. % of magnetite, 10 wt. % of copper phthalocyanine as the cyan pigment and an electrification controlling agent to a styreneacryl resin and having an average particle diameter of 10 μm, under the condition that the ratio of the toner to the carrier was 10 wt. %. Moreover, there were resorted to the non-contact jumping developing conditions under which: the developing sleeve 31 had an external diameter of 30 mm and a number of revolutions of 100 r.p.m.; the magnet 32 and its N and S magnetic poles having a magnetic flux density of 500 gausses and had a number of revolutions of 1,000 r.p.m.; the developer layer in the developing region had a thickness of 0.7 mm; the gap between the developing sleeve 31 and the image retainer 1 was 0.8 mm; and a bias voltage having a d.c. voltage component of -50 V and an a.c. voltage component of 1.5 kHz and 1,000 V was applied to the developing sleeve 31. In the following Examples, the a.c. component has a sine wave, and its exemplified values are effective ones.

The surface of the image retainer 61 having been subjected to the first development was subjected again to an erasure by the same magnetic erasing head 63' without operating the pre-transfer charger 9, the charge eliminating means 13 and 13, the cleaning means 14 and the pre-writing charger 2, and a second writing operation was conducted in the same spot density but with the spot position being shifted from that of the first writing operation by means of the recording head 63. Next, a second development was conducted by the developing means 6 which was under the same conditions as those of the developing means 5 except that it used as its toner a toner prepared by adding polytungstophosphate as the Magenta magenta pigment in place of the cyan pigment. Likewise, a demagnetization and a third writing operation were conducted. A third development was then conducted by the developing means 7 which was under the same conditions as those of the developing means 5 except that it used as its toner a toner prepared by adding a bendizine derivative as the yellow pigment. Moreover, demagnetization and a fourth writing operation were conducted. A fourth development was conducted by the developing means 8 which was under the same conditions as those of the developing 5 except that it used a toner prepared by adding Carbon Black carbon black as the black pigment. The color image thus retained on the image retainer 61 was transferred to and fixed on the recording member P, as has been described with reference to FIG. 42. Moreover, the surface of the image retainer 61 having the color image transferred thereto had its charged eliminated by the charge eliminating means 13 and was cleared of the residual toners by the cleaning means 14.

The reproduced image thus obtained had little color toner mixing and was a remarkably clear color image.

Incidentally, in the present Example, the spot position of a subsequent writing operation may be overlapped upon that of a previous writing operation. In the writing and developing operations, moreover, the recording current of the recording head 3, and the voltage value, frequency and time selecting period of the d.c. or a.c. component of the voltage to be applied to the developing sleeve may be so changed as to adjust the developed densities of the respective colors. If the writing spot positions are superposed, the color mixing becomes liable to occur to invite color vagueness but not to drop the resolution. In this case, moreover, especially the sequence of the colors to be developed is important. By adjusting the developing densities of the respective colors in the aforementioned manner, on the other hand, it is possible to attain a color image which has its tones changed.

EXAMPLE 30

The same reproducing apparatus as that of the Example 29 was used. The color image reproduction was conducted under the same conditions as those of the Example 29 except: that a magnetic image was for a background potential of 0 V by a first writing operation without any of the charging operation of the Example 29 by the pre-writing charger 2 before the first writing operation, after the charge elimination for demagnetization by the charge eliminating means 13; that a superposed voltage composed of a d.c. voltage of -50 V and an a.c. voltage of 3 kHz and 2,000 V was applied as the bias voltage before development to the developing sleeve 31; and that charge elimination and demagnetization were effected by the charge eliminating means 13 before second and later writing operations so that a magnetic image was retained for the background potential of 0 V even during the second and later writing operations.

The reproduced image which is excellent in clearness like that of the Example 29 was thus obtained.

EXAMPLE 31

The color image reproduction was conducted by the use of the same reproducing apparatus as that of the Example 29 and under the same conditions as those of the Example 29 except: that a charging operation is conducted to +300 V before a first writing operation by the pre-writing charger 2 so that a magnetic image was retained for the background potential of +300 V by the first writing operation after it had been demagnetized; that a superposed voltage composed of a d.c. voltage of +300 V and an a.c. voltage of 2 kHz and 1 KV was applied as the bias before the development to the developing sleeve 31; and that the pre-writing charger 2 was used before the demagnetization and the second and later writing operations. The reproduced image obtained was a color image which was excellent in cleaness like that of the Example 29.

According to the Examples of the present invention, there can be attained an excellent effect that the tone or the like of the color image can be easily changed thanks to the use of the image retaining means having its image retainability and toner image formability separated so that a color image having excellent clearness and a high tone can be reproduced while stabilizing the reproduction.

Incidentally, the present invention can be applied not only to an image retainer having a belt or sheet shape, but also to an image retainer such as electrofax paper, which is placed on a base so that the color image formed thereon by the toners is fixed without being transferred. In this case, the sequence of superposing the color toner images has to be taken into consideration, but the transfer means, the cleaning means and so on can be omitted. It is true, but the the charge eliminating means can be omitted, too, in case the toners are transferred with a predetermined polarity and a charge quantity. On the other hand, the transfer should not be limited to the corona type but may be exemplified by the bias roller type, the adhesion type, the direct pressure type or other means using an intermediate transfer member, and the fixture is not limited to the heat roller type.

In the foregoing embodiments of the present invention, moreover, the magnetic recording head is used as the writing means, but another means may be likewise used if the magnetic image is to be retained on the magnetic layer. More specifically, the present invention can be applied to the method, in which the magnetic image is retained by heating imagewise a demagnetized magnetic layer, while passing through a unidorm magnetic field, by the heating means such as a laser and by cooling the heated magnetic layer in a magnetic field.

Although the foregoing description has been directed only to the reproduction of the color image, furthermore, the method of the present invention can also be applied to the superposition of an image of identical colors. In addition, the electrophotographic image and the magnetic image can be reproduced in combination if an electrophotogtaphic photosensitive layer is provided on the magnetic layer.

Claims

1. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for forming an electrostatic image on said image retainer, means for developing the electrostatic image formed on the image retainer to form a toner image, an oscillating electric field applied between the image retainer and a developer feeding carrier to develop said electrostatic images, means for superposing a plurality of toner images on the image retainer, and means for transferring the toner images onto a recording paper in one step.

2. The apparatus for reproducing multiplex images according to claim 1 wherein the surface of a developer layer on a developer feeding carrier does not contact with the surface of the toner image on the image retainer.

3. The apparatus for reproducing multiplex images according to claim 2 comprising means for superposing at least one portion of a spot distribution exposure of the preceding image exposure and at least one portion of a spot distribution exposure of the following image exposure.

4. The apparatus for reproducing multiplex images according to claim 3 wherein the spots of the preceding image exposure and the following image exposure are varied in size.

5. In an apparatus for reproducing multiplex images comprising an electrostatic image formed on an image retainer, means for developing the electrostatic image formed on the image retainer by using a developer consisting of a plurality of components, means for superposing a plurality of toner images on the image retainer, the improvement characterized in that said developing means operates under a condition mentioned below:

0.2≦V_AC /(d·f)

[(V_AC /d)-1500]/f≦1.0

where V_AC is an amplitude (V) of AC component of developed bias, f is a frequency (Hz), and d is a gap (mm) between the image retainer and a developer feeding carrier for a feeding developer.

6. The apparatus for reproducing multiplex images according to claim 5 wherein the gap between the image retainer and the developer feeding carrier is larger than the thickness of the developer layer formed on the developer feeding carrier during developing.

7. The apparatus for reproducing multiplex images according to claim 5 comprising multiplex images formed by using developers in order from the developer having a smaller absolute value of mean charge quantity.

8. The apparatus for reproducing multiplex images according to claim 3 comprising multiplex images formed by reducing successively the amplitude of the AC component of electrical field applied between the image retainer and the developer feeding carrier during development.

9. The apparatus for reproducing multiplex images according to claim 5 comprising multiplex images formed by increasing successively the frequency of the AC component of electric field applied between the image retainer and the developer feeding carrier during development.

10. In an apparatus for reproducing multiplex images comprising an electrostatic image formed on an image retainer, means for developing the electrostatic image formed on the image retainer by using a one-component developer, and means for superposing a plurality of toner images on the image retainer, the improvement characterized in that said developing means operates under the following condition:

0.2≦V_AC /(d·f)≦1.6

where V_AC is an amplitude (V) of AC component of developing bias, f is a frequency (Hz), and d is a gap (mm) between the image retainer and a developer feeding carrier for a feeding developer.

11. The apparatus for reproducing multiplex images according to claim 10 wherein the gap between the image retainer and the developer feeding carrier is larger than the thickness of a developer layer formed on the developer feeding carrier during development.

12. The apparatus for reproducing multiplex images according to claim 10 comprising multiplex images formed by using developers in order from the developer having a smaller absolute value of mean charge quantity.

13. The apparatus for reproducing multiplex images according to claim 10 comprising multiplex images formed by reducing successively the amplitude of the AC component of electric field applied between the image retainer and the developer feeding carrier during development.

14. The apparatus for reproducing multiplex images according to claim 10 comprising multiplex images formed by increasing successively the frequency of the AC component of electric field applied between the image retainer and the developer feeding carrier during development.

15. The apparatus for reproducing multiplex images according to claim 10 wherein the electrostatic image retaining member of the image retainer consists of a photosensitive member.

16. The apparatus for reproducing multiplex images according to claim 2 wherein the electrostatic image retaining member of the image retainer consists of a dielectric member.

17. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for forming an electrostatic image on said image retainer, means for superposing a plurality of toner images on the image retainer, transfer means for transferring the toner images on a recording paper by one step, and means for developing the electrostatic image formed on the image retainer to form a toner image wherein the surface of a developer layer on a developer feeding carrier does no contact with the surface of the toner image on the toner retainer other than during the first time development.

18. In an apparatus for reproducing multiplex images comprising an electrostatic image formed on an image retainer, means for developing the electrostatic image formed on the image retainer by using a developer consisting of a plurality of components, and means for superposing a plurality of toner images on the image retainer, the improvement characterized in that said developing means operates under a condition mentioned below:

0.2≦V_AC /(d·f)

[(V_AC /d)-1500]/f≦1.0

where V_AC is an amplitude (V) of AC component of developing bias, f is a frequency (Hz), and d is a gap (mm) between the image retainer and a developer feeding carrier for feeding developer; the gap between the image retainer and the developer feeding carrier is larger than the thickness of a developer layer formed on the developer feeding carrier during development; multiplex images formed by reducing successively the amplitude of AC component of electric field applied between the image retainer and the developer feeding carrier during development, and multiplex images formed by increasing successively the frequency of AC component of electric field applied between the image retainer and the developer feeding carrier during development.

19. In an apparatus for reproducing multiplex images comprising an electrostatic image formed on an image retainer, means for developing the electrostatic image formed on the image retainer by using a one-component developer, and means for superposing a plurality of toner images on the image retainer, the improvement characterized in that said developing means operates under a condition mentioned below:

0.2≦V_AC /(d·f)≦1.6

where V_AC is an amplitude (V) of AC component of developing bias, f is a frequency (Hz), and d is a gap (mm) between the image retainer and a developer feeding carrier for feeding developer; the gap between the image retainer and the developer feeding carrier is larger than the thickness of a developer layer formed on the developer feeding carrier during development; multiplex images formed by reducing successively the amplitude of AC component of electric field applied between the image retainer and the developer feeding carrier during development; and multiplex images formed by increasing successively the frequency of AC component of electric field applied between the image retainer and the developer feeding carrier during development.

20. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for forming an electrostatic image on said image retainer, means for developing the electrostatic image formed on the image retainer to form a toner image, means for eliminating residual electric charges, means for superposing a plurality of toner images on the image retainer, and transfer means for transferring the toner images on a recording paper by one step.

21. The apparatus for reproducing multiplex images according to claim 2 comprising a two-component developer having a toner and an insulating carrier.

22. The apparatus for reproducing multiplex images according to claim 2 comprising a one-component developer consisting of an insulating toner.

23. The apparatus for reproducing multiplex images according to claim 2 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer, in that order, laminated on an electroconductive supporting member, and means for forming an electrostatic image by primary charging, secondary charging, image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of the electrostatic images substantially to zero.

24. The apparatus for reproducing multiplex images according to claim 2 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer laminated on an electroconductive supporting member, in that order, means for forming the electrostatic image of a first toner image by primary charging, secondary charging and sequential image exposure, said primary charging dropping a potential of the electrostatic images substantially to zero, and means for forming the electrostatic image of a second toner image by primary charging, secondary charging, and sequential image exposure, said primary charging dropping a potential of the electrostatic images substantially to zero.

25. The method of reproducing multiplex images according to claim 2 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer laminated on an electroconductive supporting member, in that order, means for forming the electrostatic image of a first toner image by primary charging, secondary charging, image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of the electrostatic images substantially to zero, and means for forming the electrostatic image of a second toner image by primary charging, secondary charging, image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of the electrostatic images substantially to zero.

26. The apparatus for reproducing multiplex images according to claim 2 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer, in that order, laminated on an electroconductive supporting member, and means for forming the electrostatic image of a toner image by uniform primary charging on said photosensitive image retainer in the first developing, uniform secondary charging in a plurality reversed to said primary charging and sequential image exposure, said primary charging dropping a potential of the electrostatic images substantially to zero.

27. In a color image forming apparatus comprising an image retainer, means for forming a color image on said image retainer, transfer means for transferring on a transfer member the color image formed on said image retainer by said color image forming means, and fixing means for fixing on said transfer member the color image transferred on said transfer member by said transfer means, the improvement characterized in that said color image forming means comprises only one latent image forming means, and a plurality of developing means for visualizing a latent image formed on said image retainer by said latent image forming means, said one latent image forming means being used repeatedly in one cycle of a reproduced image forming step.

28. The color image forming apparatus according to claim 27, wherein said latent image forming means comprises means for applying an electric charge, a light source, a deflector for deflecting a light irradiated from the light source, and a scanning optical system arranged between said light source and said image retainer.

29. The color image forming apparatus according to claim 28 wherein said electric charge applying means

comprises a primary charger and a secondary charger.

30. The color image forming apparatus according to claim 28 wherein said light source in said scanning optical system is a laser light source.

31. The color image forming apparatus according to claim 30 wherein said deflector in said scanning optical system is a rotary polygon mirror.

32. The color image forming apparatus according to claim 27, wherein said developing means is arranged in the vicinity of said image retainer in non-contact fashion.

33. The color image forming apparatus according to claim 27 wherein an alternating electric field is applied between said image retainer and said developing means.

34. The color image forming apparatus according to claim 27 comprising electrical charge eliminating means for eliminating a residual electric charge on said image retainer each time at which said latent image forming means is used, said charge eliminating means being arranged in the vicinity of said transfer means.

35. The apparatus for reproducing multiplex images according to claim 17 consisting of a single means for forming an electrostatic image on said image retainer, and at least two of said means for

developing said electrostatic image formed on the image.36. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for charging said image retainer, means for forming an electrostatic image on said image retainer, means for developing the electrostatic image formed on the image retainer to form a toner image, an oscillating electric field applied between the image retainer and a developer feeding carrier to develop said electrostatic images, means for superposing a plurality of toner images on the image retainer, means for transferring the toner image onto a recording paper in one step, and

means for superposing at least one portion of a dot exposure of the preceding image exposure and at least one portion of a dot exposure of the following image exposure wherein the surface of a developer layer on a developer feeding carrier does not contact the surface of the toner image

on the image retainer.37. The apparatus for reproducing multiplex images according to claim 36 wherein each multiplex image is developed by repeated use of said means for developing in which an amplitude of an AC component of electric field applied between said image retainer and a developer feeding carrier for feeding developer is reduced with each of said repeated use of said means for

developing.8. The apparatus of claim 36 wherein the electrostatic image retaining member of the image retainer consists of a dielectric member.39. The apparatus of claim 36 wherein said developer layer comprises a one-component developer consisting of an insulating toner.40. The apparatus for reproducing multiplex images according to claim 36 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer, in that order, laminated on an electroconductive supporting member, and means for forming an electrostatic image by primary charging, secondary charging, image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of the electrostatic

images substantially to zero. 41. The apparatus for reproducing multiplex images according to claim 36 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer laminated on an electroconductive supporting member, in that order, means for forming the electrostatic image of a first toner image by primary charging, secondary charging and sequential image exposure, said primary charging dropping a potential of the electrostatic images substantially to zero, and means for forming the electrostatic image of a second toner image by primary charging, secondary charging, and sequential image exposure, said primary charging dropping a potential of the electrostatic image substantially to zero.42. The apparatus for reproducing multiplex images according to claim 36 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer laminated on an electroconductive supporting member, in that order, means for forming the electrostatic image of a first toner image by primary charging, secondary charging, image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of the electrostatic images substantially to zero, and means for forming the electrostatic image of a second toner image by primary charging, secondary charging, image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of

the electrostatic images substantially to zero.43. The apparatus for reproducing multiplex images according to claim 36 wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer, in that order, laminated on an electroconductive supporting member, and means for forming the electrostatic image of a toner image by uniform primary charging on said photosensitive image retainer in the first developing, uniform secondary charging in a plurality reversed to said primary charging and sequential image exposure, said primary charging dropping a potential of the electrostatic images substantially to

zero.44. The apparatus of claim 36 wherein said dot exposure of the preceding image exposure and said dot exposure of the following image exposure are varied in size.45. The apparatus of claim 36 wherein said developer layer comprises a two-component developer having a toner and an insulating carrier, said insulating carrier having a resistivity of at least 10⁸ Ω-cm when a voltage for generating an electric field of 1,000 V/cm is

applied.46. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for forming an electrostatic image on said image retainer, means for superposing a plurality of toner images on the image retainer, transfer means for transferring the toner images to a recording paper in one step, and means for developing the electrostatic image formed on the image retainer to form a toner image wherein, in the formation of each multiplex image, the surface of a developer layer on a developer feeding carrier does not contact the surface of the toner image on the image retainer other than during the development of the first toner image, wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer, in that order, laminated on an electroconductive supporting member, and said electrostatic image forming means comprises a primary charging means, a secondary charging means which exposes said image retainer to an image light simultaneously with the secondary charging and sequential uniform exposure means, said primary charging means dropping a potential of the electrostatic images substantially to zero.47. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for forming an electrostatic image on said image retainer, means for superposing a plurality of toner images on the image retainer, transfer means for transferring the toner images to a recording paper in one step, and means for developing the electrostatic image formed on the image retainer to form a toner image wherein the surface of a developer layer on a developer feeding carrier does not contact the surface of the toner image on the image retainer other than during the first development wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer laminated on an electroconductive supporting member, in that order, and said electrostatic image forming means comprises a primary charging means, a secondary charging means and sequential image exposure means, said primary charging means dropping a potential of the electrostatic images

substantially to zero.48. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for forming an electrostatic image on said image retainer, means for superposing a plurality of toner images on the image retainer, transfer means for transferring the toner images to a recording paper in one step, and means for developing the electrostatic image formed on the image retainer to form a toner image wherein the surface of a developer layer on a developer feeding carrier does not contact the surface of the toner image on the image retainer other than during the first development wherein the image retainer consists of a photosensitive image retainer having a photoconductive photosensitive layer and a transparent insulating layer laminated on an electroconductive supporting member, in that order, means for forming the electrostatic image of a first toner image by primary charging, secondary charging, and image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of the electrostatic images substantially to zero, and means for forming the electrostatic image of a second toner image by primary charging, secondary charging, and image exposure simultaneous with the secondary charging and sequential uniform exposure, said primary charging dropping a potential of

the electrostatic images substantially to zero.49. An apparatus for reproducing multiplex images comprising an image retainer having thereon an electrostatic image retaining layer, means for forming an electrostatic image on said image retainer, means for superposing a plurality of toner images on the image retainer, transfer means for transferring the toner images onto a recording paper in one step, and means for developing the electrostatic image formed on the image retainer to form a toner image wherein, in the formation of each multiplex image the surface of a developer layer on a developer feeding carrier does not contact the surface of the toner image on the image retainer other than during the development of the first toner image, wherein said developer comprises a two-component developer having a toner and an insulating carrier, said insulating carrier having a resistivity of at least 10⁸ Ω-cm when a voltage for generating an electric field of 1,000 V/cm is applied, means for generating an oscillating field between said image retainer and said developer feeding carrier.