JPH02282277A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a device capable of forming a high density dot image by reversely developing a latent image under non-contact state, which is formed by uniformly electrostatically charging a photosensitive body having a specified light decay curve and performing necessary dot exposure. CONSTITUTION:The photosensitive body 1, which has the light decay curve in such a shape that the absolute value of the derivation of the light decay curve is small when light quantity is small and it steeply increases as the light quantity increases by containing phthalocyanine in photoconductive semiconductor powder, is uniformly electrostatically charged by a corona charger 21 and dot-exposed with pulse width modulating spot light by a laser optical system 26, so that the latent image is formed. The latent image is developed under non-contact state by respective color developing devices 5A-5D. Then a digital image forming device capable of forming the high-resolution distinct latent image in which an adverse effect in forming the image in the bottom parts of the rising and falling curves of the light energy distribution of the pulse modulating spot light is cancelled by combining with the light decay characteristic of the photosensitive body and the high density color dot image by the non-contact development is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that uses a latent image formed of electrostatic charges, and more particularly to an image forming apparatus that performs reversal development on an electrostatic latent image formed by dot exposure.

[Background of the invention]

In the conventional electrophotographic method, in order to impart photosensitivity to a photoreceptor, it is first charged by a conventional method, and then imagewise exposed to form an electrostatic latent image (hereinafter simply referred to as latent image) directly on the photoreceptor. or by electrostatically transferring this latent image onto transfer paper directly or via an intermediate, developing it with a dry or wet developer, and fixing it to make it visible. forming an image.

In order to form a visible image using such electrophotography, it is necessary to form a latent image with excellent charging characteristics, dark decay characteristics, light decay characteristics, and gradation.

In particular, photoreceptors used in transfer type copying machines are required to have characteristics that do not cause fatigue and deterioration even when used repeatedly to obtain a large number of copies, and that gradation and image quality do not deteriorate.

Photoconductive semiconductors conventionally used in electrophotography include:
For example, inorganic photoconductive ion materials such as selenium, zinc oxide, 1-mium sulfide, cadmium selenide, photoconductive pigments such as phthalonanine, copper phthalocyanine, cobalt-7-lycyanine, nickel-7-talonani/etc. N
- Organic photoconductive materials such as vinylcarbazole, anthracene, and triallylamine derivatives are known, and these can be dispersed in a binder resin or used in photoreceptors with a two-layer structure consisting of a charge generation layer and a charge transport layer. can be formed.

In recent years, copying using transfer type copying machines has been gaining popularity, and there is a particular demand in the market for high-speed copying that can copy a large number of sheets in a short period of time. The reality is that there is a conflict between light decay speed and characteristics such as charging, dark decay, gradation, image quality, and fatigue deterioration, making it difficult to obtain a photoreceptor that is practically desirable.

In response to the growing demand for horizontal tonality, especially midtone rendering, beautiful color images, and good image quality, we have developed free conversion of images,
A digital image forming method that performs dot image exposure using a laser beam, etc., which allows accurate alignment of adjustment and image position, as well as image transmission and reception, has become a hot topic, and is showing signs of replacing conventional analog image forming methods. Image quality is improving to the point where it rivals that of printing.

Methods such as laser beam, LED array EL array, and liquid crystal Nyatta array are used for don't exposure, but
The current mainstream method is the laser beam method that allows high-density recording.

In dot exposure, similar to analog exposure, there are two exposure methods: a light area (positive area) exposure method in which non-image areas are exposed to erase the charge on the photoreceptor and a latent image is formed, and a dark area (positive area) exposure method in which the charge in the image area is erased. Although any of the negative section (negative section) exposure methods can be used, the negative section exposure method is the mainstream because of its stability in writing scanning, good dot reproduction, and savings in exposure time.

However, the light energy distribution of the spot light used for dot exposure in the negative exposure method approximates a normal distribution curve with the peak at the center of the spot, and the tail of the curve has ripples of light intensity due to diffraction, and has long Pull the hem. This problem becomes particularly important when a laser beam is converged to a diameter of 100 μm or less, or even 50 μm or less using a lens system. Furthermore, when pulse width modulation is used, the spot diameter becomes substantially smaller, which poses a serious problem. (The diameter here is a Gaussian approximation of the exposure distribution of 1 dot 1 ~, and the peak of the exposure amount is 1, /
Refers to the width of e. 100μm diameter is 16dot/mm
, a diameter of 50 μm corresponds to a writing density of 32 dots/mm. ) In the negative exposure method, the ripples are markedly 1. This may cause noise and fog. In addition, the negative area exposure method requires a combination of reversal development, and the polarity 1 is the same as the charged polarity of the photoreceptor.
- It is necessary to prepare a

Furthermore, it is necessary to select the photoconductive semiconductor constituting the photoreceptor with respect to its optical attenuation curve. Generally, the differential coefficient (absolute value) of the optical attenuation curve of the semiconductor is steep in a low light amount region, where rapid charge attenuation occurs, and rapidly decreases in a region where the light amount is greater than that, and the curve has a gentle tail.

Therefore, if we pick up the weak light at the tail of the optical energy distribution of the spot light mentioned above, perhaps due to the charge erasing effect in the sensitive low-light region of the semiconductor, the potential distribution of the latent image will gradually become flat at the edges. It becomes a broad low 1-like distribution that expands to
Toner development results in an indistinct dot image with blurred edges, and also causes fogging.

Therefore, there is a need for a photoreceptor design suitable for dot exposure.

Furthermore, the drum exposure method is extremely suitable for color image formation due to the many advantages mentioned above, but for color image formation, charging, image exposure, and development are repeated many times, and a color toner image is superimposed on a photoreceptor. There is a method for forming an image, and the door-to-door exposure method can also be used for this image forming method. In this method, if the formed latent image is subjected to contact development, the previously formed toner image will be damaged, so a non-contact development method using a one-component or two-component developer must be adopted.

In the contact development method, the developer comes into contact with the photoreceptor, and with the help of the edge effect of the electric field on the surface of the photoreceptor, the developer is attracted to the periphery of the image, supplementing the density and improving sharpness, or in non-contact development. In this case, the developer is far away from the photoreceptor, and the electric field applied to the developer tends to avoid the periphery and converge at the center of the dot, so it is not possible to expect sharpening of the periphery; There is no other choice but to do it. Therefore, it is important here as well to make the relationship between dot exposure and light attenuation curve appropriate.

In addition, in the above color image forming method, the attenuation of the surface potential may not be sufficient due to the light absorption of the previously adhered toner, resulting in a decrease in the amount of toner adhered later, a decrease in sharpness, and a decrease in color reproduction.

[Purpose of the invention]

An object of the present invention is to provide a digital image forming apparatus that forms high-density dont images by dot exposure and reversal development.

[Means to achieve a goal]

In order to achieve the object of the present invention, we focused on the light attenuation curve of the photoreceptor used in reversal development, and investigated the "rise" and "rise" of the light energy distribution of the pulse width modulated spot light in dot exposure.
The negative effect on image formation at the bottom of the "falling" curve is that the light attenuation of the charged potential on the photoreceptor is insensitive to low light amounts and hardly attenuates, but light that attenuates sharply beyond the low light amount region. By combining a photoconductive semiconductor having an attenuation curve, a dot latent image with a sharp falling edge potential of the dot latent image was obtained.

That is, the present invention is equipped with a photoconductor having a light attenuation curve in which the absolute value of the differential coefficient of the light attenuation curve of the photoconductor is small when the amount of light is low and increases steeply as the amount of light increases, and The image forming apparatus is configured to have a uniform charging process, an electrostatic latent image forming process by dot exposure, and a reversal developing process of the electrostatic latent image in the image forming process.

The optical attenuation curve of the photoconductive semiconductor has a charging potential of 1/2.
When the photosensitivity at the position where the potential is attenuated to 9/10 at the beginning of exposure is E 9/10, 1< (El/2 )/
(E9/10) Particularly preferably, a photoconductive semiconductor is selected which provides the relationship 2≦(E 1/2) / (E 9/10).

Semiconductors include single-layer semiconductors such as Se and CdS, and O
A two-layer structure consisting of a charge generation layer and a charge transport layer, which is commonly used in PCs, is known, but many photoreceptors exhibiting the above semiconductor characteristics are more commonly used in low electric fields than in high electric fields. The photosensitivity is low, and the photosensitivity decreases as the amount of light increases.

Furthermore, in a copying machine that performs normal regular development, characters,
In order to reproduce halftone highlight areas, it is desirable to have low photosensitivity characteristics in a low electric field (corresponding to low potential areas), and the photoreceptor characteristics corresponding to the present invention were not used.

Here, photosensitivity is defined as the amount of potential drop (absolute value of differential coefficient) of the photoreceptor per minute amount of light when the photoreceptor has a specific potential.

The semiconductor properties desirable for the present invention are found in special photoreceptors, such as photoreceptors in which phthalocyanine particles are dispersed and contained in a binder resin and coated as a photosensitive layer on a photoreceptor support.

Examples of photoconductive semiconductors used in the present invention include, for example, Japanese Patent Publications Nos. 48-34189, 49-4338, and 49
-17535, JP-A-47-30328, JP-A No. 47-
No. 30329, No. 50-3854, No. 3 and No. 51-2
Phthalocyanine-based photoconductive pigments described in No. 3738 and the like are used.

Specifically, it is a phthalocyanine pigment represented by the general formula (C2H,N2)cRn, where R is a hydrogen atom, Schuylium, lithium, sodium, potassium, copper, silver, beryllium, magnesium, calcium, zinc, cadmium, barium. , mercury, aluminum, nitrogen, indium, lanthanum, i-odium, zamarium, europium, cadrium, dysprosium, holmium, erbium, thulium, ytterbium, vanadium, titanium, tin, hafnium, lead, thorium, vanadium, antimony, chromium , molybdenum, uranium, manganese,
Iron, cobalt, nickel, rhodium, palladium.

osmium and platinum, n is O~2, among which metal-free phthalocyanine and alpha (α), beta (β), gamma (γ), chi (χ), pi (π) or epsilon (ε ) type copper phthalocyanine is preferred, and the average particle size is O1-0. Old μM is preferred.

Examples of the binder resin used in the photoreceptor of the present invention include styrene resin, acrylic resin, and vinyl chloride resin.
Vinyl acetate copolymer, vinyl acetate-methyl methacrylate copolymer, styrene-butadiene copolymer, vinyltoluene-butadiene copolymer, polycarbonate resin,
Polyurethane resin, phenolic resin, melamine resin, 7
Electrically insulating resins such as orchid resins or epoxy resins are used, but phenolic resins having a structural unit represented by the following general formula are preferred.

General formula R2 In the formula, R, R□ are a hydrogen atom or a methyl group, R2 is a hydrogen atom or an epoxy group, R,, R4 and R6 are a halogen atom, a hydrogen atom, a hydroxy group, a nitro group, an ano group, an amino group, Carboxy group or sulfonic acid group or salt thereof,
Alternatively, it is a saturated or unsaturated chain hydrocarbon group having 1 to 3 carbon atoms which may have a substituent.

The degree of polymerization of these resins is 2 to 10.000, preferably 2 to 100.

In addition, the phenolic resin represented by the above general formula is melamine,
Also effective are resins modified with lignin, chroman, indene, hydrocarbons, borihinyl alcohol, fatty acid amide, acetate, lactone, acetal, chlorophenol, thiophene, or styrenated phenol, or their monomers. Used (Japanese Patent Application Laid-Open No. 54-12303
No. 5, etc.).

The photoreceptor according to the present invention includes the photoconductive fine powder and resin, and if necessary, a sensitizing agent such as rose bengal, auramine, bromophenol blue, bromothymol blue, and 7-kujin, and other sensitizers. .7-1-linitro 9-fluorenone, 2,4.5゜7-tel-lanitro fluorenone in benzene, toluene, xylene,
For example, 100 parts of photoconductive powder, 1 to 1,000 parts of resin, 0.05 to IO parts of sensitizing agent, and 50 to 5,000 parts of organic solvent are mixed and dispersed in an organic solvent such as trichlorethylene, ethyl acetate, acetone, or methyl ethyl ketone. The photosensitive layer coating is applied to a metal plate such as copper, iron, nickel, aluminum or stainless steel, or to a paper or plastic film using a metal such as aluminum, gold, silver, copper nickel, or oxide. A layer containing powder of the metal or metal oxide or carbon black powder dispersed in a resin is applied to a support obtained by vapor-depositing or laminating a metal oxide such as tin, or to paper or a Plus Deck film. It is prepared by coating and drying a photosensitive layer on various conductive supports, such as a support obtained by coating, so that the film thickness after drying is 10 to 50 μm. Further, if necessary, an intermediate layer such as an organic polymer compound or a rectifying semiconductor layer may be provided.

By equipping the photoreceptor prepared as described above, a latent image forming step is carried out in which a good latent dot image is formed by dot exposure with spot light, especially dot exposure with pulse width modulated spot light, following the charging step. The present invention can be applied to both contact and non-contact development, and constitutes an image forming process incorporating a reversal development process particularly suitable for non-contact development, and an image forming apparatus comprising the process.

The present invention provides significant advantages for multicolor image formation in which color toner images are sequentially superimposed on a photoreceptor, but in consideration of the absorption spectrum of the colored toner, it is preferable to expose the colored toner with light of a wavelength that is less absorbed. In this respect, laser light with a longer wavelength than the visible light region is generally useful.

Lasers used for dot exposure include He-Ne, He-
A gas laser such as Cd or Ar, or a semiconductor laser such as GaA12As is used, and since the wavelength thereof is generally 700 nm or more, the photoreceptor generally requires the above-mentioned spectral sensitization treatment.

The developer used for reversal development is a two-component developer, which is versatile in the present invention, and the charged toner is a charge control agent or silica fine particles treated with an amine compound and other additives (patent application No. 6).
2-108213, 62-119482, etc.) are used.

In addition, it is normal for transfer type electronic copying machines to make copies of 10 or more sheets per minute, and the next charge starts several seconds after irradiation with the lamp to erase the residual charge.''2. A lamp can be used as an activation light for the photoreceptor, thereby erasing residual charge to prevent potential decay and fog increase, and to reduce light attenuation while maintaining the characteristics of the photoreceptor according to the present invention. Since the effect of speeding up the process can also be imparted, it is advantageous in terms of the performance, structure, and economy of the copying machine.

Table 1 shows an example of pulse width modulation in exposure.

The dot diameter in Table 1 is the laser beam diameter in which the exposure intensity decreases by up to 1/e, and the dot diameter corresponds to the scanning direction.
The lengths are shown in the main scanning direction and the sub-scanning direction, not shown in the figure. Modulation example (1).

The modulation pulses and dot patterns in (2) and (3) are shown in FIGS. 9(a), (b), and (C), respectively.

In modulation example (1), the level changes in five stages as shown in FIG. 9(a), and the pulse modulation circuit thereof can be constructed relatively easily. Modulation example (1) makes it possible to improve the reproducibility of line drawings compared to binary recording, and in particular, lines in diagonal directions can be reproduced clearly.

In modulation examples (2) and (3), the level changes in 256 steps as shown in FIGS. 9(b) and (c).

In the case of modulation example (2), for example, a multilevel digital video signal for recording is first converted into an analog signal by a D/A converter, and compared with a reference signal such as a triangular wave synchronized with the recording unit pixel, the signal is converted into a binary signal. , a pulse for modulation is obtained. Compared to modulation example (1), the circuit is a little more complicated, but an extremely high-quality image can be obtained.

Modulation example (3) can be implemented with a circuit similar to modulation example (2). In the embodiment (3), since the reference signal is synchronized with every two pixels in the main scanning direction, the resolution in the main scanning direction becomes substantially half, 3 dat/mm. In modulation example (3), the improvement in halftone reproduction is remarkable.

FIG. 1O shows the optical scanning state of the laser beam on the photoreceptor in modulation example (1).

〔Example〕

Next, the present invention will be specifically explained with reference to Examples, but the embodiments of the present invention are not limited thereto.

: Preparation of photoreceptor: Photoreceptor example 1 Epsilon (ε) type copper phthalocyanine pigment Lionol.
Blue (Ljonol Blue) ER (manufactured by Toyo Ink Co., Ltd.) Desmorhen (Desmorhen) 800 g (polyester polyol resin manufactured by Nippon Polyurethane Co., Ltd.) 2 g Hexamethylene diisocyanate 2 g Methyl edyl ketone
6g of the composition according to the above weight ratio was dispersed at room temperature for 10 minutes using an ultrasonic disperser, and then applied using a rotary coating machine onto a conductive support consisting of a 10 μm thick aluminum layer laminated onto an 80 μm thick polyester film. The coating machine was operated at 80 speeds per minute so that the film thickness after drying was 15 μm.
The coating process was performed with 0 rotations. The photosensitive layer of this photoreceptor is 160
It was heated and cured for about 2 hours in a drying mold heated to ~170°C.

The thus prepared photoconductor was measured using an Electrostatic Paper Analyzer (Electrostatic Paper Analyzer manufactured by Kawaguchi Electric Co., Ltd.).
static paper analyzer) SP
Two types of electrostatic properties were measured using 428 according to the steps shown in Method 11 and Method 2 in Table 2 below, and as a result, the electrostatic properties shown in Figures 1a and 1b were obtained.

In the measurement using the 5P-428, a voltage of 5 KV was applied to the corotron corona discharger, the distance between the discharge wire and the sample surface was 9 mm, and the sample was positively charged. For both image exposure and erasing exposure, the sample surface was exposed to tungsten light at an angle of 2854° through an infrared transmission filter shown in FIG. 8 at an illuminance of 3 lux.

Also, the photosensitivity ratio for method 1 is (El/2)/(E 9/10)-8,0 for method 2.
(El/2)/(E 9/10)=2.7.

The above sensitivities are not subject to dark decay correction. Also, methods 1 and 2
Regarding method 1, although the amount of exposure light is larger, the photosensitivity ratio is higher. For this reason, it is easy to produce the effect of sharpening the latent image.

On the other hand, method 2 is characterized in that the spectral sensitization is substantially high and the amount of exposure light required to form a latent image is small.

That is, from FIG. 1, it can be seen that when conventional a, in which no pre-charging exposure is performed, and b, in which pre-charging exposure is performed, the latter has clearly higher sensitivity.

Further, when comparing the charging potentials, both are around 800V, and no significant difference is observed.

Photoreceptor example 2 Alpha (α) type copper phthalocyanine pigment Festogen Blue GP (manufactured by Dainippon Ink and Chemicals) 0.33g Vylon 2
00 (Saturated polyester resin manufactured by Toyobo Co., Ltd.) 2 g Methyl ethyl ketone 8 g After ultrasonically dispersing the composition with the above weight ratio at room temperature for 15 minutes, it was placed on a conductive support made of 15 μm thick aluminum laminated on an 80 μm thick polyester film. , rotary coating machine 7 per minute
00 revolutions, coating was carried out so that the film thickness after drying was 15 μm.

This photosensitive layer was dried by heating at 80° C. for about 10 minutes in a heating drying mold to prepare a photoreceptor. Using this photoreceptor, the electrostatic properties were measured using the above 5P-428 using two methods, Method 1 and Method 2 of Photoreceptor Example 1, and the processes of charging, dark decay, and light decay were compared and examined. As a result, the charging potential was 900 V and the dark decay rate was 20% in both cases.

The photosensitivity ratio for method 1 is (E 1/2)/(E 9/10) -7,0 for method 2
Then, (E 1/2)/(E 9/10) = 3.0.

Photoconductor example 3 Heta (β) type copper 7 talocyanine pigment Festogen Blue
e) GNPT (manufactured by Dainippon Ink Chemical Industries, Ltd.) 0
, 47 g2〇- Panlite (polycarbonate resin manufactured by Ryotai Kasei Co., Ltd.) 1.4 g Methylene chloride 14 g The composition according to the above weight ratio was ultrasonically dispersed at room temperature for 10 minutes, and then placed on a 100 μM thick stainless steel plate by rotation. The coater was rotated at about 800 revolutions to coat the film to a dry film thickness of 20 μm. This photosensitive layer was dried with hot air at 50°C for 10 minutes to obtain a photoreceptor.

Using this photoconductor, the electrostatic properties were measured using Method 1 and Method 2 in the same manner as Photoconductor Example 2, and the charging, dark decay, and light decay processes were compared and examined.
00V 1 dark decay rate was 22%.

In method 1, the photosensitivity ratio is (E 1/2)/(E 9/1
0) = 5.0, in method 2 (E 1/2)/(E 9
/10)=2.0.

Comparative Photoreceptor Example A sample photoreceptor was prepared by vacuum-depositing 5e-Te to a thickness of 70 μm on an aluminum substrate. The Te concentration is higher at about 30% in the upper layer, and spectral sensitization is performed to have spectral sensitivity even to infrared light.

Using this photoreceptor, electrostatic properties were measured in the same manner as Photoreceptor Example 1.

In both Methods 1 and 2, the charging potential was 950V.

The dark decay rate was 25%. Also, the photosensitivity ratio is method 1 and method 2.
(E 1/2)/(E 9/10)=0.9, and as shown in FIG. 2, the spectral sensitivity in the high potential region is higher. Moreover, no effect of activating exposure was observed.

Embodiment 1 FIG. 3 shows a color multicolor image forming/forming apparatus according to an embodiment of the present invention. Incidentally, the development by this apparatus is based on a non-contact reversal development method using a two-component developer. In the figure, 1 is a photoreceptor according to the present invention that rotates in the direction of the arrow; 2
1 is a corona charger, L is image exposure light with a wavelength of 800 nm irradiated from the semiconductor laser optical system 26, 5A, 5B, 5
C, 5D are developing devices having yellow, magenta, cyan, and black toners, 33 is a transfer electrode, 34 is a separation electrode, P
30 is a transfer paper, 30 is a pre-transfer exposure lamp, 36 is a cleaning device, 368 is a fur brush, 36b is a toner collection roller, and 36c is a scraper.

The photoreceptor 1 is uniformly exposed to infrared light by a pre-charging exposure lamp 35, and then its surface is uniformly charged by a corona charger 21 comprising a scorotron electrode. Subsequently, image exposure light according to the recording data is irradiated from the laser optical system 26 onto the photoreceptor l. A latent image is thus formed. This latent image is developed by the developing device 5A containing the first yellow toner T1.

The photoreceptor on which the toner image has been formed is uniformly exposed again by the pre-charging exposure lamp 35, uniformly charged by the corona charger 21, and receives image exposure light according to recorded data of another color component. The formed latent image is developed by the developing device 5B containing the second magenta toner T2.

As a result, a two-color toner image is formed on the photoreceptor l using the first toner T1 and the second toner T2.

Similarly, cyan toner T3 and black toner 7
4 are developed in a superimposed manner, and a four-color toner image is formed on the photoreceptor l.

The multicolor toner image thus obtained on the photoreceptor is uniformly and negatively irradiated by a pre-transfer exposure lamp 30 as required, and then transferred to a transfer paper P by a transfer pole 33.

The transfer paper P is separated from the photoreceptor 1 by the separation pole 34 and fixed by the fixing device 31. Meanwhile, the photoreceptor 1 is cleaned by a cleaning device 36.

The fur brush 36a of the cleaning device 36 is kept out of contact with the photoreceptor 1 during image formation, and when a multicolor image is formed on the photoreceptor 1, it comes into contact with the photoreceptor 1 after the transfer, and moves in the direction of the arrow. Scrape off any remaining toner while rotating.

When the cleaning is finished, the fur brush 36a is separated from the photoreceptor 1 again. An appropriate bias is applied to the toner collection roller 36b while rotating in the direction of the arrow, and the toner T and the like are collected from the fur brush 36b. It is further scraped off with a scraper 36c.

FIG. 4 shows the laser optical system 26 in this embodiment. In the diagram, 3
7 is a semiconductor laser diode, 38 is a rotating polygon mirror, 39
is an fθ lens.

FIG. 5 is a sectional view of the developing device 5. In the figure, numeral 51 is a housing, 53 is a sleeve, and 54 is a magnetic field generating means provided in the developer conveying body, that is, the sleeve.

A magnetic roll having a south pole, 55 a layer forming member, 56 a fixing member for the member, 57 a first stirring member, and 58 a second stirring member. 59 is a sleeve cleaning member, 6
0 is a developing bias power supply, 18 is a developing area, that is, a sleeve 53
The area where the toner conveyed by is transferred to the photoreceptor under electrostatic force, T represents toner and D represents developer. In this developing device, the two stirring members 57 and 58 are screw-shaped, and rotate in the direction of the arrow in the figure to stir and transport the developer. The stirring member 57 is shaped to be conveyed toward the front of the page, and the stirring member 58 is conveyed toward the back of the page. A wall 52 is provided so that the developer does not accumulate in the intermediate area between the two, and therefore the developer is exchanged in this area in the left-right direction in the drawing.

Toner is replenished to the developing device 5 from the front side in FIG.
As a result, the toner and carrier are roughly circulated toward the front side of the page, and the toner and carrier are mixed uniformly. However, the position of toner replenishment is not particularly limited to this, and for example, a method of replenishing toner from the right side in FIG. 5 to the sleeve shaft may be used.

In this way, the developer mixture is sufficiently stirred and mixed, and is transported in the same direction as the rotational direction of the sleeve 53 by the transporting force of the sleeve 53 rotating in the direction of the arrow and the magnetic roller 54. A layer forming member 55 held by a fixing member 56 extending from the housing 52 is pressed against the surface of the sleeve 53 to regulate the amount of developer to be conveyed and form a developer layer.

Other means for forming the developer layer when carrying out the development of this embodiment include, for example, a magnetic or non-magnetic regulating plate placed at a certain distance from the sleeve, and a magnetic or non-magnetic regulating plate placed close to the sleeve. Any conventionally known device such as a magnetic roll may be used.

It is advantageous for the carrier and toner constituting the developer to have small particle sizes from the viewpoint of image resolution and gradation reproducibility. For example, even when the carrier in the developer layer has a small particle size of 40 μm or less, by using means such as the layer forming member 55 described above, impurities and agglomerates in the developer can be automatically removed and a uniform length can be obtained. A magnetic brush can be formed. Furthermore, even if the carrier has a particle size as small as that of the toner, contamination of impurities is similarly eliminated and a magnetic plan of uniform length can be formed.

The sleeve cleaning roller 59 rotates in the direction of the arrow.
(FIG. 5) The developer that has passed through the development area 18 and consumed the toner T is scraped off from the sleeve 53. Therefore, the amount of toner T conveyed to the development area can be kept constant, and the development conditions are stabilized.

Next, the composition of the developer used in the developing method of this embodiment will be described.

(Developer formulation) Tonapolystyrene 45 parts by weight Polymethyl methacrylate 44 //Charge control agent
02~l, Qtt coloring agent
3 to 15 tt The above composition is mixed, ground, crushed and classified to obtain a toner having an average particle size of 3 μm.

Carrier (resin coated carrier) core diferrite Coating resin: styrene/acrylic (4:6) Magnetization 27emu/g Particle size: 30μ edition Specific gravity 5.2g/c river 3 Specific resistance 1013Ω・cm or more A mixture of the upper and lower compositions was used as a developer.

FIG. 6 shows data on the spectral characteristics of the toner.The spectral characteristics of the toner were determined by pasting double-sided tape with good transparency on one side of a blank sheet of paper to create an adhesive surface.

The toner is evenly rubbed onto this adhesive surface and the spectral reflectance is measured. This is corrected by the spectral reflectance when there is no toner to obtain the spectral reflectance of toner. still,
For this measurement, a spectrophotometer (HITACHI) was used.
330 type), and the wavelength range is from 360 to 850 nm. The wavelength of the exposure light used in the pre-charging exposure and image exposure is preferably infrared light in order to prevent a reduction in the amount of transmitted light due to absorption of light by the toner on the photoreceptor.

In order to provide the toner with such spectral characteristics, the following colorant may be used.

Benzidine Ye
low)G(C.

1.21.090), benzidine yellow GR (c,
+, 21100), permanent house Cl − (Pe
DHG (Hoechst product), Brilliant Carmine (Brillia)
nt Carmine) 6 B (C, 1, 15850
), Rhodamine 6G Lake (LaKe) (C,1,4
5160) Rhodamine B Lev (C, 1,451,70)
, Phthalocyanine Blue Non-Crystal (Pbt)
halocyanine Blue non Crys
tal) (C, T, 74160), Phthalocyanine Green (C, 1,74260), Carbon Black, 7
Atsuto (Fa) Yellow 5G1 Fatsuto Yellow 3
G, Fat Red G, Fat Red HRR, Fat 1/Tudo 5B.

Fatt Black HB, Zapon First (Zap
onFast) Black RE, Zapon-Fast
Bra/Li B1 Zapon Firth 1 Blue HF L
1 Zapon Firth i...Red BB, Zapon First Red GE.

Zapon Fast Yellow G, Quinacridone Red (c, 1.465000).

As the pre-charging exposure lamp 35, various light sources that emit infrared light or a white light source covered with an infrared transmission filter can be used.

In this example, (1) GaAQAs infrared light emitting diode (LN172 manufactured by Matsushita Electric Industrial Co., Ltd.) The spectral distribution shown in FIG. 7 shows its emission spectrum characteristics.

(2) Combination of halogen lamp and infrared transmission filter (IR-D70 manufactured by Toshiba Glass) Figure 8 shows its spectral transmittance characteristics.

The above (1) and (2) were used as the pre-transfer exposure lamp.

Table 3 shows image forming conditions in the color multicolor image forming apparatus shown in FIG.

Table 3 The exposure distribution of the laser spot diameter is approximately Gaussian, and the exposure distribution is 1. The diameter at the /e level is about 45 μm and I.

When color images were formed under the above image forming conditions, color images with good spont diameter reproduction could be stably formed.

Particularly in the area where the toner images were superimposed, the toner image was stably formed on top of the previous toner image. Also, according to image evaluation, the exposure intensity is 1.5 of the half-decreased exposure light amount of the photoreceptor.
A range of ~4 times is preferred. It is considered that this condition forms a potential pattern having a small diameter and a sharp potential change.

In addition, the surface potential was measured at the developing section under the same conditions as method (1) and method (2) described in Photoreceptor Example 1, with and without exposure before charging, using the exposure intensity as a parameter, and the data for Photoreceptor Example 1 was obtained. Potential characteristics similar to those in FIG. 1 were obtained.

Example 2 In Example 1, the writing resolution was set to 6 dots/mm.
Five-value pulse width modulation was used, and the exposure distribution of the laser spot diameter corresponding to one pulse was approximately Gaussian, and the conditions were the same except that it was changed to 100 μm in the sub-scan direction and 30 μm in the main scan direction.

When color images were formed under the above image forming conditions, it was possible to stably form color images with good reproduction of spot diameters corresponding to pulse width modulation.

Particularly in the area where the toner images were superimposed, a toner image was stably formed on top of the previous toner image.

According to image evaluation, the exposure intensity is preferably in the range of 1.5 to 4 times the half-decreased exposure light amount of the photoreceptor. It is considered that this condition forms a potential pattern having a small diameter and a sharp potential change.

Example 3 An experiment was conducted with the same configuration as in Example 1 except that photoreceptor examples (1 to 3) and each method (1 to 2) were used, and the resulting color samples were evaluated for impression carbonization (E 1./ 2)/(E 9/10), the better the image was obtained. In particular, it was preferable that the above value was 3 or more. Also, better images were obtained using method (1).

Comparative Example (1) When a color image was formed using Comparative Photoreceptor 1 under the same conditions as Example 1, the reproduction of the diameter was insufficient compared to that of Example. Also, there is a stable 1-ner image on the previous 1-ner image.
No image was formed.

This is probably because a stable potential pattern was not formed due to the shielding effect of the previous toner image or variations depending on the amount of adhesion.

When the exposure intensity was weak, the toner image formation was insufficient, and when the exposure intensity was strong, the dot diameter became thicker and the resolution decreased.

Comparative Example (2) Color image formation was performed using the comparative photoreceptor (1) under the same conditions as in Example 2, but the reproduction of the spot diameter corresponding to pulse width modulation was insufficient compared to the example. . Further, no toner image was stably formed on the previous toner image.

This may be because a stable potential pattern was not formed due to the shielding effect of the previous toner image or due to variations depending on the amount of adhesion.

When the exposure intensity was weak, the image formation was insufficient, and when the exposure intensity was strong, the diameter became thicker, and a decrease in the force was observed.

〔Effect of the invention〕

According to the present invention, a multicolor image without noise or color turbidity can be stably formed.

[Brief explanation of drawings]

Figure 1 shows the electrostatic characteristics of the photoreceptor according to the present invention with and without pre-charging exposure, Figure 2 shows the electrostatic characteristics of the Se photoreceptor, and Section 3 shows the application of the color multicolor image forming method of the present invention. Fig. 4 is a block diagram of the non-norr multicolor image forming apparatus, Fig. 4 is a block diagram of the laser optical system, Fig. 5 is a cross-sectional view of the developing device, Fig. 6 is a diagram showing the 1-nor spectral reflectance characteristics, Fig. 7 Figure 1 shows the emission spectrum characteristics of a GaAQAs infrared light emitting diode, and Figure 8 shows the spectral transmittance characteristics of a combination of a GaAQAs lamp and an infrared transmission filter. In addition, Fig. 9 (a,), (+)), and (c) are diagrams showing examples of pulse width modulation, and Fig. 1O is a diagram showing the scanning state of Zaheem on the photoreceptor. Yes 3,■...Photoreceptor 5A, 5B, 5C, 5D...Developing device 21
...Corona charger 26...Laser optical system 33.
...Transfer electrode 34...Separation electrode 35...Pre-charging exposure rung 36...Cleaning device T,, T2...Toner

Claims (5)

[Claims] (1) Equipped with a photoconductor having a light attenuation curve in which the absolute value of the differential coefficient of the photoconductor's light attenuation curve is small when the amount of light is low and increases steeply as the amount of light increases, and the photoconductor is uniformly charged. An image forming apparatus having an electrostatic latent image forming step by dot exposure and a reversal development step of the electrostatic latent image in an image forming step. (2) The image forming apparatus according to claim 1, wherein the photoconductive semiconductor powder of the photoreceptor contains phthalocyanine. (3) The image forming apparatus according to claim 1 or 2, wherein the reversal development is non-contact development. (4) The image forming apparatus according to any one of claims 1 to 3, wherein the dot exposure is dot exposure using pulse width modulation. (5) The image forming apparatus according to any one of claims 1 to 4, wherein the charging step, the latent image forming step, and the reversal development step are repeated to superimpose toner images on the photoreceptor.