JPS61172159A - Method for forming multicolor image - Google Patents

Abstract

PURPOSE:To provide for excellent recording accuracy, to reduce the size of the device and to reduce costs by so arranging that the spectral transmission factor and intensity modulation level will satisfy a specific relation. CONSTITUTION:After the overall surface of a photosensitive member 1 is charged electrostatically, a first image exposure is effected by an image exposure device 4, and the first color image, such as yellow image is formed by development with a developer 5. The overall surface is again charged electrostatically by an electrifier 2, the second image exposure is performed and developed by a developer 6 to form a second color image such as Magenta image in superposition on the first color image. The similar operations are repeated a required number of times and one or both of a pre-transfer electrifier 9 and pre-transfer exposure lamp 10 is energized at the stage in which the third development of the last operation is carried out until passage of the image. With the intensity modulation level of n and the spectral transmission factor of R, the relation of the equation is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multicolor image forming method, and particularly relates to at least charging,
The present invention relates to a multicolor image forming method in which a plurality of toner images of different colors are formed on a photoreceptor by repeating an image forming process including image exposure and toner development processes multiple times.

[Conventional technology]

As a multicolor image forming method as described above, Japanese Patent Application Laid-Open No. 56-1
Methods described in Japanese Patent Application Laid-open No. 44452, Japanese Patent Application Laid-Open No. 58-116553, and Japanese Patent Application Laid-open No. 58-116554 are known. In all of these methods, each repeated image exposure is performed by a separate device, and it is necessary to shift the subsequent image exposure position to the previous image exposure position so that it does not overlap. This is a developing method in which toner charged to the same polarity is attached to an electrostatic image whose potential is lower in the exposed area than the background potential. Therefore, for example, when a multicolor image such as a landscape painting is formed by performing intensity modulation and multivalued image exposure using a laser beam scanner, the influence of the already formed toner image is eliminated. The problem is that it is necessary to shift the spot positions of image exposure for each color so that they do not overlap with each other, resulting in a coarse spot distribution density and the ability to form only multicolor images that look rough and faded. be. There are also problems in that the recording apparatus becomes larger and more expensive, and the synchronization control of image exposure to the electrostatic photoreceptor becomes complicated because it is related to the position of the image exposure device.

[Problem that the invention seeks to solve]

The problems to be solved by the present invention will be explained in detail below.

In principle, the easiest way to obtain a multicolor image is to repeat the process of charging, multivalued image exposure, and development as many times as necessary to produce toner images of different colors on an electrostatic photoreceptor (hereinafter simply referred to as photoreceptor). ), but this is actually difficult and the complicated method described above is used. One of the main reasons for this is that the toner image previously formed on the photoreceptor blocks light removal in the next image exposure, and prevents image formation on the photoreceptor at the image overlapping area.
The state is schematically shown in FIG.

9(A), CB] show the case where toner adheres to the unexposed charge residual area and so-called regular development is performed to give a positive image in response to imagewise exposure.

CD) shows the case of so-called reversal development in which the charge of the developer, the bias voltage during development, etc. are changed, and toner adheres only to the areas where the charge of the photoreceptor has decreased due to imagewise exposure, giving a negative image in response to imagewise exposure. ing. In the figure, the position of the solid line indicates the potential V on the surface of the photoconductor, and the horizontal axis indicates the position on the photoconductor.

In the case of regular development, the charge applied to the entire surface of the photoreceptor in the first charging (Fig. 9 (A)-(1)) decreases due to image exposure, leaving unexposed areas 1b and 1d, as shown in Fig. 9. A]-(2)
) After the first development, toner T was added to 1b and 14 parts.

is deposited and an image of the first color is formed. Then the second
The second charging gives charge to the entire surface again (Fig. 9 (
A) - (4)), the second image exposure is 18, lb, l
When the electric potential is applied to the parts c, 1, and 1g, in order to form a correct color image, the potential of all the exposed parts decreases as shown in Figure 2 (A]-(5), and after development Figure 9 (A
) - Toner Tt as shown in (6), T1 + T2
The images of different colors formed by ,T, are 1b,
Even in the case of images to be formed in areas ld and If, in area 2b where an image is already formed with toner TI, if light is absorbed by the toner 77 layer, no drop in potential occurs (see Figure 9). (B)-(5)), unexposed 2
Toner T,
(Figure 9 CB)-(6)). As a result, an image of the color of toner 'r, +'r, is formed even in the portion 2b where an image of the color of toner T, should be formed.

In addition, in the case of reversal development, when the second exposure is given as shown in FIG. 9(C)-(5), the potential also decreases in the portion 18 where an image is already formed by the first development and the toner T. After the second development with toner T, Figure 9 [CD-(6)
Even when obtaining an image in which a superimposed image of Tm and T4 is to be formed, such as at part 18 of Therefore, the second toner does not adhere or only slightly adheres to T8, so it receives the eleventh second exposure and toner T8. T.

Only a single color image of T is formed in the 2g portion where a mixed color image of T is supposed to be formed.

The above characteristics apply to binary recording, but it becomes more complicated in the case of 3-value or 4-value recording. For example, Figure 10 [E]
1A shows a case where an electrostatic image obtained by image exposure at n = 3 levels is normally developed, and FIG. It is shown.

FIG. 10(E) shows the case of regular development, and [g]-(1) shows the area on the photoreceptor to which the first charge has been applied in advance.

The first image exposure with different intensities of (%Ll) is performed, and 3b
, 3d, 3a, 3c, and 3e are shown in which electrostatic images are formed. This electrostatic image is the first
After development, a toner image to which toners (E) to (2) T are attached is formed depending on the potential level. Next, a second charge (recharge) of V volts is applied to the photoreceptor, and then L
3a, 3c, 3e, 3f, to which toner T is not attached, although second image exposure with different intensities is applied to , and .
Potential attenuation occurs in the areas 3g, 3h, and 3i according to exposure, and when this is second developed using toner T6, as shown in B)-(6), 3f, 3f, which was not exposed or was exposed by % Toner T adheres to 3h. 3b has toner T attached to the tip.

In the areas 3d and 3d, the potential drop due to the second image exposure and 3d is insufficient, so that a considerable amount of toner T adheres to the area, even though it should not originally adhere to the area. For this reason, not only the color tone of the multicolor image is disturbed, but also the tonality of n=3 is lost.

Fig. 3 CF) shows the case of reversal development, and the first image exposure of 3Q, 3r, and 3m with different intensities is performed.

An electrostatic image similar to that shown in FIG. 10(E)-(1) is formed in the areas 3t and 3u, and this is caused by the first development using toner T in the areas 3q, 33.3 and 3u. Toner adheres depending on the potential level. Next, after being charged (recharged) by $2, a second image exposure is performed with different intensities as described above, but first, toner 3q, 3g, and 3 to which toner T is attached are exposed. The potential does not drop in the areas 3u and 3u because sufficient light does not pass through them. Therefore, a problem arises in that the toner T does not adhere or only slightly adheres to the regions 38.3t and 3u to which the toner T should adhere in the second development. As a result, as in the case of regular development, not only the color tone of the multicolor image is disturbed, but also the gradation expression is lost.

[Means to solve the problem]

The present invention has been proposed based on the above-mentioned circumstances, and an object of the present invention is to provide excellent recording accuracy when forming a multicolor image by image exposure based on a multivalued information signal. It is an object of the present invention to provide a multicolor image forming method that allows a device to be configured in a small size and at low cost, and has excellent color tone and gradation reproducibility.

The above purpose is to improve the image exposure light on the toner image formed on the electrostatographic photoreceptor by repeating the image forming process multiple times, which includes at least the steps of charging, intensity-modulated image exposure, and toner development. When the spectral transmittance at the main wavelength is R, it is achieved by a multicolor image forming method that satisfies the following relational expression. It means the wavelength (range) of light that has the greatest correlation.

[Effect]

As mentioned above, this problem basically lies in the blocking of light by the single layer of toner already formed on the surface of the photoreceptor during image exposure, but the layer directly below the layer formed by light scatterers such as toner There are many difficulties in directly measuring the amount of effective transmitted light that reaches the photoreceptor. As a result of repeated experiments by the present inventors, it has become clear that the reflectance of toner correlates with the effective exposure amount, that is, the effective amount of transmitted light under the above-mentioned practical conditions.

Therefore, for the transmittance of a single layer of toner used in the following description, the value of the reflectance R of a single layer of toner based on the measurement method described below is used.

Furthermore, since each toner image usually consists of one to two layers of toner particles, the reflectance R is a value measured using a sample in which toner particles are uniformly formed into almost one layer.

Sprinkle an appropriate amount of, for example, Y toner on the adhesive side of the Clavel (white microphone manufactured by Nichiban Co., Ltd.) with a medicine spoon, and smooth it with your fingers to remove the excess toner onto the desired toner attachment area on the adhesive side. will be removed from the area where it is being created. Note that the area is circular, and the diameter is set to ψ=30111 or more for convenience of measurement. Next, if necessary, after lightly wiping off the toner on the label, the desired sample is obtained by gently rubbing the label with a finger until substantially no toner sticks to the finger. The single layer of toner obtained as described above has almost the same adhesion state as the Y toner when, for example, a Y toner image is densely formed on the photoreceptor.

This sample was measured using a Hitachi spectrophotometer 330.
The spectral reflectance, for example, the reflectance RY of Y toner is measured using the following method.

Although the method of the present invention can be applied to the formation of multicolor images using a combination of toners of arbitrary colors, it can be particularly preferably used for the formation of so-called full-color images using yellow, magenta, and cyan toners. .

The exposure light used in the method of the present invention is not particularly limited during the first image exposure when there is no toner on the photoreceptor, and for the second and subsequent image exposures, the light is It is sufficient that the light has a spectral distribution maximum in a wavelength range in which each toner constituting the formed toner image exhibits a reflectance of a specific value or more. The light source is not particularly limited, but intensity-modulated monochromatic light from a laser, LED, liquid crystal shutter, or the like is preferably used, for example.

The operation of the multicolor image forming method of the present invention using the monochromatic light source will be explained below. In this case, the light source used is a single light source, and all reproduced color tones are distinguished by electrical signals, but it is necessary to select a light source that satisfies the conditions of the present invention in relation to toner absorption.

As mentioned above, the image exposure on the photoreceptor in the present invention is as follows:
Light from a light source is emitted based on an image signal, for example, 3
．． This is carried out using light whose intensity is modulated by the image signal to a plurality of levels such as 4 levels.

Therefore, an electrostatic image with a plurality of potential levels corresponding to the intensity of the image exposure is formed on the photoreceptor, and when this electrostatic image is developed with toner, an amount of toner corresponding to the potential of the plurality of levels is formed. Upon deposition, a toner image having multiple levels of gradation is formed.

Now, if the image exposure is performed using light whose intensity is modulated to n levels, an electrostatic image having n potential levels is formed on the photoreceptor, but the potential difference between each potential level is The maximum potential difference of the image is divided so that it has a ratio of 1 knee to the maximum potential difference, resulting in n-mata.

For example, when n = 2, binary recording is performed when image exposure is performed using light with two intensity levels i, and the potential of the electrostatic image is divided into exposed and non-exposed areas of the photoreceptor, and their The only potential difference is the potential difference between each level of the electrostatic image.

But then, for example, if n = 3 or n = 4, it is a ternary or quaternary recording in which image exposure is carried out by light having 3 or 4 intensity levels, and each level's or 2 L
It is divided into two or three parts so that the ratio is = o, 330.

By the way, in the multicolor image forming method of the present invention, as described above, toner images of different tones are formed in a superimposed manner, so that the formation of the next toner image of a different tone can be carried out through the toner image already formed on the photoreceptor. Image exposure is performed for this purpose. Therefore, as explained earlier in FIG. 9 and FIG. This causes a potential difference between the two, which should normally be at the same potential, and the toner adhesion state is different, causing the subsequent toner image to be significantly distorted.Especially in multi-value recording with three or more values. In this case, not only the color tone is disturbed but also the tonality of the multicolor image formed is lost.

Therefore, in the multicolor image forming method in which toner images of different tones are superimposed and recorded, a desirable guideline is that the potential difference of the electrostatic image caused by the lowest exposure intensity level is the area where the toner image has already been formed and the area where there is no toner image. The purpose is to ensure that the potential difference does not become smaller than the potential difference caused by the difference in the amount of transmitted light. The guideline for the multicolor image forming method described above is the formula, 7E=1-R
It is summarized in Here, R is the transmittance of a single layer of toner due to image exposure, and this is obtained by measuring the reflectance of a single layer of toner using the method described above, and as described above, this means that the reflectance is almost the same as the transmittance. It is based on. Further, 1-R is the absorption rate by a single layer of toner during imagewise exposure.

The above equation will be explained in detail with reference to FIG. 1, taking as an example the case where the intensity modulation level n=4 for image exposure.

(A), (B), and (C) in Figure 1 are diagrams showing the potential level of n; 4 when image exposure is performed through the previous toner image. In Figure 1), there is no previous toner image. It shows the potential level of n = 4 when imagewise exposed at . (see Figure 1)
The potentials of each potential level 1.2.3 are expressed as Vo, V, , and the potential difference between each level is ΔV =, IV.

Φ0.33V. In the case shown in FIG. 1), since there is no light absorption by the previous toner image, a completely undistorted four-tone toner image can be obtained by subsequent toner development. However, in the cases of (a), (b), and (c) in Figure 1, each (IR
Since there is light absorption by the previous toner image of I), (IRl), (1-R1'') (here Rs = 3A %R1
=%, ns='d), the potential difference between the advertised voltage levels decreases, and the gradation expressiveness during toner development decreases. The level voltages in each figure are Vo in Figure 1 (A),
V,,vl. Therefore, the potential difference between levels ΔV=0.27
Becomes Vo. In the present invention, consideration should be given to the light source for image exposure and the order in which toner images are formed so as to obtain at least an inter-level potential difference of 67 or more as shown in FIG. 1(b).

In this way, for example, V, which is the third level.

(Figure 1 (b)) is the second level Va (in Figure 1)
), VS (Figure 1 (C)) is higher than Va (Figure 1 (B)), which is the fourth level, and Va (Figure 1 (B)) is the third level, v!
(in Fig. 1)) and Va (in Fig. 1 E→).

To explain more generally, the level changes depending on whether or not there is previously formed toner.
The potentials corresponding to (an integer other than 1) are not reversed and the gradation is not lost, and as a result, an excellent image can be obtained. Note that image exposure when there is a toner image in advance is blocked by the toner image, so intensity modulation of the image exposure is limited, and as a result, sufficient gradation expression cannot be achieved. Therefore, the intensity modulation level of the image exposure may be adjusted in a dither circuit that converts each color electrical signal into a digital dot pattern signal.

Intensity modulation level of image exposure using the single light source n =
In order to satisfy the conditions of the present invention in case 4, the maximum spectral distribution is in a region where the reflectance of the long wavelength side reflection region of the magenta toner is 67% or more, and in the case of the toner shown in Fig. 2, it is 610 n.
It is sufficient to use one with a long wavelength of m or more. Even in this case, when forming a full color image, the image formation order is yellow, magenta, cyan or magenta, yellow,
Cyan is good.

When forming an image by scanning a photoreceptor with light of 610 nm or more, for example, a beam with a wavelength of 750 nm (L in Figure 2) oscillated by a semiconductor laser, first a yellow image is formed, and then a magenta image is exposed. Even if the yellow toner absorbs only a small amount of light on the 750 plane, the exposure of the magenta image will not be damaged, and vice versa. Further, even after the yellow and magenta images are superimposed, both toners have little absorption of 750 nm light, so that the subsequent formation of a cyan image is not inhibited, and the required full-color image can be correctly formed.

Also, cyan, magenta, and yellow toners are all 6
800. with a reflectance of 7% or more. When light around nm is used, yellow, magenta, and cyan can be superimposed in any order.

However, if the layers are preferably stacked in descending order of spectral reflectance, a preferable alcolor image can be formed.

On the other hand, when using light around 550 nm, which does not meet the conditions of the present invention, it is possible to form yellow and magenta images without any problem, but since 550 nm light is strongly absorbed by magenta toner, reversal development is not possible. For example, in the case of cyan, cyan toner does not adhere to the magenta area during cyan development, making it impossible to obtain the desired full-color image. Even when using 750 nm light, a similar problem occurs when a cyan toner image is first created. That is, it becomes difficult for magenta toner or yellow toner to adhere thereon, making it impossible to form a desired full-color image.

Next, development suitable for the method of the present invention will be described.

Development in forming multicolor colors by the method of the present invention can be carried out by either normal development or reversal development, and the development method, conditions, equipment, etc. are not particularly limited.
In order to avoid disturbing the toner image that has already been formed during development, it is preferable to use a developing method called non-contact development in which a developer layer containing toner does not come into direct contact with the surface of the photoreceptor.

FIG. 3 shows an example of a developing device suitable for performing the above-mentioned non-contact development. A magnet body having a plurality of magnetic poles in the circumferential direction; 5 is a layer thickness regulation blade that regulates the thickness of the developer layer formed on the developing sleeve n; 5 is a layer thickness regulating blade that controls the thickness of the developer layer formed on the developing sleeve ρ after development; The scraper blade that removes the toner, the stirring rotor that stirs the developer in the developer reservoir n, the toner hopper, and the toner that has a recess on the surface for replenishing the toner from the toner hopper Z to the developer reservoir n. The replenishment roller (9) applies a bias voltage, which may have a vibrational component, to the developing sleeve N via the protective resistor 31, and forms an electric field between the developing sleeve N and the photoconductor 1 to control the movement of the toner. The figure shows that the developing sleeve n and the magnet body rotate in the directions of the arrows, but even if the developing sleeve n is fixed, the magnet body n is not fixed. Alternatively, the developing sleeve ρ and the magnet body may rotate in the same direction. When the magnet body is fixed, normally, in order to make the magnetic flux density of the magnetic pole facing the photoconductor IK larger than the magnetic flux density of the other magnetic poles, the magnetization is strengthened or two of the same polarity or different polarity are added thereto. In some cases, magnetic poles are placed close to each other.

In such a developing device, the magnetic pole of the magnet device is usually 500 to 1.
It is magnetized to a magnetic flux density of 500 Gauss, and its magnetic force attracts the developer in the developer reservoir n to the surface of the developing sleeve B, and the thickness of the adsorbed developer is regulated by the layer -'thickness regulating blade. The developer layer is moved in the same direction or in the opposite direction to the direction of the rotation arrow of the photoreceptor 1, and the surface of the developing sleeve B is placed on the photoreceptor 10 in a developing area opposite to the surface of the photoreceptor 10. Develop the electrostatic image of 1,
The remaining developer is removed from the surface of the developing sleeve B by the scraper blade 5 and returned to the developer reservoir n.

1 As the developer used in the method of the present invention, a so-called one-component magnetic developer that uses only a -component non-magnetic developer or a magnetic toner containing a magnetic material can be used. A so-called two-component toner consisting of a mixture of a non-magnetic toner and a magnetic carrier can provide a toner with a clear color without the need to contain a black or brown magnetic material, and the charging of the toner can be easily controlled. Preferably, a developer is used. In particular, when magnetic carriers are used in resins such as styrene resins, vinyl resins, ethyl resins, rosin-modified resins, acrylic resins, polyamide resins, epoxy resins, and polyester resins, triiron tetroxide, r-ferric oxide, and Products containing dispersed particles of ferromagnetic or paramagnetic materials such as chromium, manganese oxide, tutrite, anganese-copper alloy, or the surfaces of these magnetic particles are coated with the resin described above. It is preferable that the insulating carrier is made of a material having a resistivity of 10 8 Ωα or more, preferably 1σ 3 Ω or more. If this resistivity is low, the developing sleeve 2
When a bias voltage is applied to the photoreceptor 2, charges are injected into the carrier particles, causing the problem that the carrier particles tend to adhere to the surface of the photoreceptor 1, and the problem that a sufficient bias voltage is not applied.

In particular, if the carrier adheres to the photoreceptor 1, it will adversely affect the tone of the color image.

In addition, the resistivity is calculated as follows: After the particles are placed in a container with a cross-sectional area of 0.50 crI and tapped, the resistivity on the packed particles is
A load of tkg/cit is applied, and 100OV/cl is applied between the electrode that also serves as the load body and the bottom electrode! This value is obtained by reading the current value when a voltage that generates an electric field of L is applied.

Furthermore, if the average particle diameter of the carrier is less than 5 μm, the magnetization will be too weak, and if it exceeds a leap of μm, the image will not be improved, breakdown or discharge will easily occur, and high voltage will not be able to be applied. Particle size is 5 μm or more, blade μm
The following is preferable, and if necessary, a fluidizing agent such as hydrophobic silica may be added. As the colorant for the toner, for example, copper phthalocyanine is used for cyan color, polytungstophosphoric acid is used for magenta color, and benzidine derivatives are used for yellow color. However, the toner coloring agent is not limited to the pigments described above, and dyes may also be used, and a charge control agent may be added if necessary.

Next, the average particle diameter of the toner is preferably 1 to 20 μm, and the average charge amount is 3 to 300 μC/I! , especially 5-100
μc/f! Preferably. Average particle size of toner is 1μ
When the temperature decreases below m, the distance from the carrier particles becomes K (becomes mμ
If it exceeds m, the resolution of the image will decrease.

When a developer made of a mixture of an insulating carrier and a toner as described above is used, the bias voltage applied to the developing strip IJ-n in FIG. 3 can be easily and appropriately set. In other words, by making the carrier particles insulating, it is possible to easily set a bias voltage that does not cause breakdown (and also does not cause carrier adhesion or fogging). In order to more effectively control the development movement, the toner may also contain a magnetic material such as that used in magnetic carriers to the extent that color clarity is not impaired.

The above is the structure of the developing device and developer preferably used in the method of the present invention, but the present invention is not limited thereto.
A developing device and developer as described in Japanese Patent No. 553-116554 may be used. However, preferably
This is a developing method using a two-component developer as described above, and is disclosed in Japanese Patent Application Nos. 58-57446, 58-96900 to 96903, and 58-97973 previously filed by the applicant.
It is preferable to use a developing method using a developing device and a developer as described in the specifications of No. 58-23829 and No. 58-238296.

During non-contact development using a developing agent, that is, there is no potential difference between the photoreceptor surface and the developing sleeve, the thickness of the developer layer formed on the developing sleeve is thinner than the gap between the photoreceptor surface and the developing sleeve. It is best to perform development under conditions set so that

FIG. 4 is a schematic diagram showing an example of a color image forming apparatus suitable for carrying out the method of the present invention, in which 1 has a drum-like surface having a photoconductive photoreceptor surface such as Ss, and rotates in the direction of the arrow. 2 is a charger for uniformly charging the surface of the photoreceptor 10; 4 is a charger for uniformly charging the surface of the photoreceptor;
1 is an image exposure device; 5 to 8 are developing devices in which toners of different colors such as yellow, magenta, and cyan are used as developers; 9 and 10 are multiple color toner images superimposed on the photoreceptor 1 The formed color image is transferred to the recording medium P.
11 is a transfer device; 12 is a pre-transfer charger and a pre-transfer exposure lamp provided as necessary to facilitate transfer to
is a fixing device that fixes the toner image transferred to the recording medium P;
13 is a static eliminator consisting of one or both of a static eliminator lamp and a corona discharger for static elimination; 14 is a static eliminator that contacts the surface of the photoreceptor 1 after the color image has been transferred to remove residual toner on the surface; K is a cleaning device having a cleaning blade or a fur brush that separates from the surface of the photoreceptor 10 until the developed surface reaches the surface of the photoreceptor 10 that has already been charged. In particular, for devices that are charged in a superimposed manner, it is preferable to use a scorotron corona discharger as shown in the figure, which is less affected by previous charging and can provide stable charging.

A laser beam scanner as shown in FIG. 5 is used as the image exposure device 4 in the apparatus shown in this figure, and the wavelength of the laser beam meets the conditions of the present invention in relation to the spectral reflectance of the toner used. Of course, it must be something that satisfies the needs.

The laser beam scanner shown in FIG. 5 is a mirror scanner 1 consisting of an octahedral rotating polygon mirror, which is an intensity-modulated laser beam emitted from a laser 15 such as a semiconductor laser.
7 and scans the surface of the image forming body 1 at a constant speed through the imaging f-θ lens 18 to form image exposure for each color. Note that 19 and 2 are mirrors, and 21 is a lens device that changes the diameter of the beam incident on the imaging lens 18.

In order to obtain a multicolor image using this apparatus, the surface of the photoreceptor 10 is fully charged by the charger 2, first image exposure is applied by the image exposure device 4, and the first image is developed by the developer 5.
For example, an image of a yellow color is formed and printed. Charger 2
After the second image exposure, the entire surface is charged again by the developer 6.
An image of a second color, for example magenta, is formed superimposed on the image of the first color. Thereafter, the same process is repeated as many times as necessary, and one or both of the pre-transfer charger 9 and the pre-transfer exposure lamp 10 or Both are activated, and the color image is transferred by the transfer device 11 to the recording medium P that is fed in synchronization with the 10 rotations of the photoreceptor, and the transferred multicolor image is fixed to the recording medium P by the fixing device 12, and the color image is The surface of the photoreceptor 10 onto which the
3, and is cleaned by the cleaning device 14 to return to the initial state, thereby completing one cycle of color image recording.

FIG. 6 shows another example of a multicolor image forming apparatus different from the above-mentioned apparatus.

The difference between the recording apparatus of FIG. 6 and the recording apparatus of FIG. 4 is that the drum-shaped photoreceptor 1 has a structure in which a transparent insulating surface layer 1c is further provided on the surface of the photosensitive layer 1b similar to that of FIG. In some respects, in place of the charger 20 in FIG. 4, a primary charger 32 consisting of a combination of an exposure lamp and a corona discharger (in the case of a photoreceptor capable of charge injection, the exposure lamp may be omitted).

) and a secondary charger consisting of a corona discharger, and other aspects are the same as in the recording apparatus of FIG.

Therefore, the same functional parts as in FIG. 1 are designated by the same reference numerals. It is preferable to use a scorotron corona discharger as shown in the figure for the negative charger 32 and the secondary charger.

As the light source for image exposure, a laser beam scanner is used as in the case of FIG.

In this recording device, the surface of the photoreceptor 10 from which static electricity has been removed is irradiated with the exposure lamp of the primary charger 32 (as mentioned earlier, there are cases where irradiation with the exposure lamp is not required). When the photoreceptor 1 is charged with an electric device, the surface and inner surface of the photoconductive photosensitive layer 1b and the transparent insulating surface layer IC are charged as shown in FIG. 7A. When a corona discharge is performed between the secondary chargers on the charged surface of the photoreceptor 10, since the photoconductive photosensitive layer 1b is insulating, only the charge on the surface of the transparent insulating surface layer 1c is reduced. The charge on the photoreceptor 1 changes as shown in FIG. 7B. When imagewise exposure is applied to the surface of this secondarily charged photoreceptor 1, the surface charge of the photoconductive photosensitive layer 1b in the exposed area PH decreases, and the original charge remains in the non-exposed area DA.
The charge on the photoreceptor 1 changes as shown in FIG. 7C. FIG. 8 shows the changes in the surface potential of the photoreceptor 1 during this period, and the potentials in states A, B, and C in FIG. 8 are as shown in FIG. 7A, respectively.

This corresponds to the charged states of B and C. In other words, the potential of the exposed area PH where imagewise exposure is incident is the surface potential shown by C(PH) in FIG. 8, while the potential of the unexposed area DA where imagewise exposure is not incident is as shown in Almost the same surface potential as B
(DA), an electrostatic image with a surface potential indicated by C(PH) was formed by imagewise exposure with respect to this background potential. This electrostatic image can be developed by Coulomb attraction using a developer that charges the exposed area PR to the opposite polarity to that of the latent image, as in a normal electrophotographic copying machine. Note that 1a is a conductive substrate made of aluminum or the like.

Of course, imagewise exposure may be performed in step 5 so that the unexposed areas become electrostatic images, and the unexposed areas may be developed.

The present invention using the above-mentioned apparatus will be explained in detail below.

[Example 1] Using the apparatus shown in FIG. 4, developing units 5 to 7 were filled with yellow, magenta, and cyan toners having the spectral absorption shown in FIG. 2, respectively, and a full-color image forming test was conducted.

The photoreceptor used was one having an S photosensitive layer, and its circumferential speed was 180 m/see.
750 nm wavelength with intensity modulation on the charged surface
The first exposure was carried out at a density of 16 spots/fi using a laser beam scanner shown in FIG. 5 using a semiconductor laser.

The maximum exposure intensity was set to half the exposure amount (1 to 3 times the exposure amount required to reduce the potential of the photoreceptor to 3 AVC) in order to sufficiently reduce the potential of the photoreceptor.

As a result, the potential of the exposed part of the photoreceptor 1 is +350 V, +200 V, and +30 V with respect to the background part potential of +500 V.
A four-level electrostatic image of V was formed. This electrostatic image is
First reversal development was carried out using a developing device 5 as shown in the figure.

The developing device 5 contains 7 g of magnetite dispersed in a resin with an average particle size of I μm and a magnetization of 3Q emu.
, a carrier with a resistivity of 1OI4Ωα or more, and styrene.
A developer consisting of a positively charged non-magnetic toner having an average particle size of 10 tin, which is made by adding 15 parts by weight of a quinaphthalone pigment to 100 parts by weight of the toner as a yellow pigment to an acrylic resin and other charge control agents, is used in the developer. The toner ratio was 20 wt %. Also, the outer diameter of the developing sleeve O is 3011I111, and its rotation speed is 1100 rpm.

The magnetic flux density of the N and S magnetic poles of magnet n is 1000 Gauss, the rotation speed is 1000 rpm, and the thickness of the developer layer in the development area is 0.
．． 7, the gap between the developing sleeve n and the photoreceptor 1 is 0.8 m,
Developing sleeve n has +450V17) DC voltage and 1.5
KHz.

The non-contact development conditions were such that a superimposed voltage of 1000 V of AC voltage was applied.

While developing device 5 is developing the electrostatic image, developing devices 6 and 7 are
(Same structure as the developing device shown in FIG. 3) was kept in a non-developing state. This can be done by disconnecting the developing sleeve n from the power source (9) and leaving it in a floating state, or by grounding it, or by actively applying a DC bias to the developing sleeve n with a polarity opposite to that of the photoreceptor 1, that is, the opposite polarity to the toner charging. This is achieved by applying a voltage, and it is particularly preferable to apply a DC bias voltage. Although the developing units 6 and 7 are also assumed to perform development under non-contact development conditions like the developing unit 5, it is more preferable to remove the developer layer on the developing sleeve n or to separate the developing sleeve from the photoreceptor. This developing device 6K'' uses a developer in which the toner in the developing device 5 is changed to an azo reiki pigment as a magenta pigment instead of a yellow pigment. A developer with a different composition was used.

Of course, color toners containing other pigments or dyes may also be used.

A pre-transfer exposure rung 1O is applied to the surface of the photoreceptor 1 that has been subjected to the first development (this may be omitted).
On the other hand, without operating the static eliminator 13 and the cleaning device 14, the charger 2 was used again at +500V during the second rotation.
After performing the second charging, the spot positions were overlapped again using the same laser beam scanner, and a second image exposure was performed with the same spot density.

At this time, the reflectance of the laser beam with respect to the yellow toner image, which was the first layer, was 85%.

Next, a second development of the magenta toner was performed using the developing device 6. Next, after recharging, a third image exposure was carried out, and at this time, the reflectance of the laser beam to the stacked layer of the yellow toner image and the magenta toner image was 72%.
Met. The third development of the cyan toner using the developing device 7 was repeated in the same manner.

For each of the above-mentioned developments, the amplitude and frequency of the DC bias component and AC component of the voltage applied to the developing sleeve 22 are adjusted appropriately according to changes in the surface potential of the photoreceptor 10, development characteristics, color reproducibility, etc. The development density of each color can be adjusted by changing the selection door opening of the time selection conversion described in the specification of No. 58-145031.

After the third development is performed and a three-color image is formed on the photoreceptor 1, it is easily transferred by the pre-transfer charger 9 and the pre-transfer exposure lamp 10, and transferred to the recording material by the transfer device 11. The image was transferred to the computer and fixed by the fixing device 12. The photoreceptor l on which the color image has been transferred is neutralized by the static eliminator 13, residual toner is removed from the surface by contact with the cleaning blade or fur brush of the cleaning device 14, and the surface on which the color image has been formed is removed by the cleaning device 14. 14, one cycle of multicolor image formation was completely completed.

The color image recorded in the above manner had a high density of spot pixels, a finely expressed pattern, and excellent color tone and gradation.

The color mixture according to this embodiment is subtractive color mixture. On the other hand, additive color mixing is known in which the spot position is shifted for each color. When using this method, extremely high writing position accuracy is required and it is difficult to achieve high density, but this method is also effective when used for additive color mixture. In this case, even if the writing position accuracy is insufficient and a subtractive color mixture part occurs during additive color mixture where spots of some colors overlap, or if the spot is intentionally mixed between subtractive color mixture and additive color mixture in order to increase the density. Since the toner images have the advantage of being overlapped even if a certain condition is created, good color balance can be maintained.

[Example 2] The recording apparatus shown in FIG. 6 was used. The photoreceptor 1 has a transparent insulating layer with a thickness of mμm on a long-wavelength sensitized CdS photoreceptor layer with a thickness of μm, and its circumferential speed is 180 m/s.
It was set as ee. While uniformly exposing the photoreceptor using an IK-order exposure lamp, 51C-order charging was performed using a DC scorotron corona discharger so that the surface potential reached +1500 V. Next, a secondary charger consisting of a scorotron corona discharger with an AC component has a surface potential of the photoreceptor 10 of -100.
It was charged to V. A wavelength of 800 nm is applied to this charged surface.
imagewise exposed from a semiconductor laser beam having m, +500
V, +300 V.

An electrostatic image showing four levels of potential, +100 V and -100 V, was formed. This electrostatic image is transferred to a developing sleeve n using a developing device 5 loaded with negatively charged yellow toner with a DC component of +5.
Development was performed while applying an alternating current voltage of 1.5 KHz and 1000 V, including 0 V. Other developing conditions were the same as in Example 1. The pre-transfer exposure lamp 10 is applied to the surface of the photoreceptor 10 where the first development has been performed (this may be omitted), while the static eliminator 13 and the cleaning device 14 are not applied during the 102nd rotation of the photoreceptor. Charging was performed again using the primary charger 32 and the secondary charger, and a second image exposure was performed. At this time, the reflectance of the laser beam to the yellow toner layer was 85%. Next, a second development was performed using the developing device 6 loaded with negatively charged magenta toner. The developing conditions were the same as those for the first time. Next, a third charging and imagewise exposure were performed, and at this time, the reflectance of the laser beam to the superimposed layer of one layer of yellow toner and one layer of magenta toner was 72%. Next, development is performed using the developing device 7 loaded with negatively charged cyan toner to obtain a three-color toner layer in which three color toner layers are superimposed, and this is applied to the recording medium P in the same manner as in Example 1. After transferring and fixing, a full-color multicolored image was obtained. This multicolor color had excellent color tone and gradation as in Example 1.

The present invention can also be applied to belt-shaped or sheet-shaped image forming bodies, or to those in which the image forming body is attached to a substrate such as electrofax paper, and the image forming body is It is also possible to fix the color image formed by the toner without transferring it. In addition to corona transfer, the transfer may be bias roller transfer, adhesive transfer, or pressure transfer via an intermediate transfer member. Of course, fixing is not limited to heat roller fixing.

In the above description, the overlapping of the three color toners of yellow, magenta, and cyan has been described, but further overlapping of the black toner gives a tighter color image, resulting in a preferable image quality.

Therefore, it is desirable to superimpose the yellow, magenta, and cyan toner images using, for example, an image exposure light source having a wavelength of around 800 nm, and then superimpose the black toner image.

Note that if the black toner has sufficient transmittance to light of the above wavelength, the order of overlapping may be selected arbitrarily, but basically the transmittance to the wavelength of the image exposure light is selected. It is preferable to superimpose them in ascending order, and it is preferable that the black toner image be formed as the final image.

The method shown in Embodiment 2 of the present invention has the great advantage of being able to reverse the polarity of the potentials in the image area and non-image area by balancing the strengths of -order charging and secondary charge; Of course, it is also possible to develop by using the same polarity and changing the developing bias conditions. It goes without saying that the NP method and KIP method can also be applied to the method of the present invention.

[Effects of the Invention] As explained above, according to the multicolor image forming method of the present invention, the recording accuracy is excellent, the device can be made small and low cost, and the multicolor image formation method during multivalue recording can be made Effects such as excellent reproducibility of color tone and gradation are achieved.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the potential levels of a four-gradation electrostatic image in the present invention, Figure 2 is a glass showing the spectral reflectance of each color toner and the spectral distribution of the laser beam used in the example, and Figure 3 is a diagram showing the spectral distribution of the laser beam. 4 and 6 are cross-sectional views of the main parts of the multicolor image forming apparatus. FIG. 5 is a schematic cross-sectional view of the laser beam scanner. Figures 9 and 1 showing the electrostatic image forming process in a color image forming apparatus
FIG. 0 is a schematic diagram illustrating the toner superposition process. DESCRIPTION OF SYMBOLS 1... Photoreceptor 2... Charger 4... Image exposure device 5-7... Developing device 9... Pre-rolling charger lO... Pre-transfer exposure lamp 11... Transfer device 12... Fixing device 13... Static eliminator
14...Cleaning device 15...Laser
16... Acousto-optic modulator 17... Mirror scanner 18... Imaging f-theta lens 19, 20
... Mirror 21 ... Lens device η ... Developing sleeve Ru ... Magnet body ... Layer thickness regulating blade δ ... Scraper blade A ... Stirring rotor
! ...Developer reservoir 4...Toner hopper 4.
...Toner replenishment roller (capital)...Power supply 3
1...Protective resistor 32...-Nth charger Ah...
Secondary charger applicant: Konishiroku Photo Industry Co., Ltd. Figure 1 (A) (!ri (8)
(3) Figure 2 21y Figure 5 Rays. Figure 6 A B C 1α

Claims (5)

[Claims] (1) Multiple toner images of different colors are formed in a superimposed manner on an electrostatographic photoreceptor by repeating an image forming process including at least charging, intensity-modulated image exposure, and toner development several times. In the color image forming method, the intensity modulation level at the time of the image exposure is defined as n, and the spectral transmittance at the main wavelength of the image exposure light with respect to the toner image already formed on the electrostatographic photoreceptor at the time of the image exposure is R. A multicolor image forming method characterized by satisfying the following relational expression. Formula 1/(n-1)≧1-R (2) The multicolor image forming method according to claim 1, wherein the intensity level n is an integer of 3 or more. (3) The multicolor image forming method according to claim 1, wherein each of the plurality of toner images is a toner image made of yellow, magenta, and cyan toners. (4) The multicolor image forming method according to any one of claims 1 to 3, wherein the plurality of toner images are formed in the order of yellow, magenta, and cyan, or each color toner image of yellow, cyan, and magenta. . (5) The multicolor image forming method according to claim 1, wherein the toner development is performed by a non-contact development method.