JPH02176768A - Image forming device - Google Patents

Abstract

PURPOSE:To form a high-density dot image of high picture quality by dot exposure and reversal development by providing a photosensitive body which has a specific light attenuation curve. CONSTITUTION:The photosensitive body has the light attenuation curve whose differentiation coefficient is small in absolute value when the quantity of light is small and increases abruptly as the quantity of light increases. Then a latent image forming process wherein an excellent dot latent image is formed by the dot exposure of spot light, specially, the dot exposure of pulse-width modulated spot light is incorporated following an electrostatic charging process and uniform exposure to constitute an image forming process wherein a reversal developing process is incorporated. Consequently, the sharp dot image is formed by the dot exposure and reversal development.

Description

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

[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 first 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 materials such as selenium, zinc oxide, cadmium sulfide, cadmium selenide, phthalocyanines,
Photoconductive pigments such as copper-7 thalocyanine, cobalt phthalocyanine, and nickel phthalocyanine or organic photoconductive materials such as poly-N-vinylcarbazole, anthracene, and triallylamine derivatives are known, and these are dispersed and contained in a binder resin. Alternatively, a photoreceptor having 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 a photoreceptor that is practically desirable has not been obtained because there is a conflict between the light decay rate and characteristics such as charging, dark decay, gradation, image quality, and fatigue deterioration.

On the other hand, in response to the strong demand for gradation, especially intermediate tones, 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 emerged and is showing signs of replacing traditional analog image forming methods. The image quality is improving to the point where it rivals that of printing.

Methods such as a laser beam, an LED array, an EL array, and a liquid crystal shutter array are used for dot exposure, but the laser beam method, which enables high-speed, high-density recording, is currently the mainstream.

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. (Negative part) Although any of the exposure methods can be used, the negative exposure method is the mainstream because of its stability in writing scanning, good dot reproduction, and saving exposure time.

However, with the spot light used for dot exposure in the negative exposure method, even if pulse width modulation is used, the light energy distribution approximates a normal distribution curve with a peak at the center of the spot, and the tail of the curve is due to diffraction. It has ripples of light intensity and a long hemline. This problem is especially necessary when laser light is focused to a diameter of 100 μm or less, furthermore 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 approximates the exposure distribution of one dot using Gaussian, and refers to the width where the exposure amount is 1/e of the peak.1
00μm diameter is 16dot/Imm, 50. The um diameter corresponds to a writing density of 32 dots/I. )
In the negative exposure method, the ripples become a significant noise and cause fogging. Further, the negative area exposure method requires a combination of reversal development, and requires the preparation of toner having the same polarity as the charged polarity of the photoreceptor.

Furthermore, it is necessary to select the photoconductive semiconductor constituting the photoreceptor with respect to the optical attenuation curve. In general, the differential coefficient of the optical attenuation curve of the semiconductor is large in a low light intensity region, where rapid charge attenuation occurs, and rapidly decreases in a region where the light intensity is greater than that, and the curve has a gentle tail.

Therefore, if the weak light at the tail of the optical energy distribution of the spot light mentioned above can be picked up by the semiconductor's sensitive charge erasing effect in the low light amount region, the potential distribution of the formed latent dot image will gradually become flat at the edges. This results in a broad funnel-like distribution that expands to a wide range, resulting in an indistinct dot image with blurred edges due to toner development, and also induces fogging.

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

Furthermore, the dot exposure method is extremely suitable for color image formation due to the numerous advantages mentioned above, but charging, image exposure, and development are multiplexed in color image formation, and it is also used in a method in which color toner images are superimposed on a photoreceptor. be able to. 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 photoreceptor surface electric field, the toner is attracted to the periphery of the image, supplementing the density and improving sharpness, but in the case of non-contact development, The developer is separated from the photoreceptor, and the electric field applied to the developer tends to converge at the center of the dot, avoiding the periphery, so it is not possible to expect the periphery to become sharper, but rather to sharpen the periphery of the dot itself. There is no outside. Here again, the relationship between dot exposure and light attenuation curve appears.

In addition, in the above-mentioned multicolor development, the attenuation of the surface potential may not be sufficient due to light absorption of the previously adhered toner, resulting in a decrease in the amount of toner attachment, a decrease in sharpness, and a decrease in color reproduction.

Furthermore, since a color multicolor image naturally requires repeating image exposure, development, and the various processes associated with it many times before a single image can be obtained, it takes much more time than a monochrome image, and it requires a lot of energy from the photoreceptor. Since this increases fatigue, it is necessary to take measures to shorten the drawing time and prevent fatigue of the photoreceptor, and these points are lacking in the prior art.

[Purpose of the invention]

The objects of the present invention are (1) a digital image forming apparatus that forms high-quality, high-density dot images by dot exposure and reversal development, (2) a digital image forming apparatus that performs non-contact, reversal development, and (3) a transfer method. The object of the present invention is to provide a color multicolor image forming apparatus which is capable of superimposing color toner images on a photoreceptor, in addition to a conventional color multicolor image forming apparatus using a photoreceptor, which is capable of high speed and has little fatigue on the photoreceptor.

[Means to achieve the purpose]

To achieve the object of the present invention, we focused on the optical attenuation curve of the photoreceptor used in dot exposure, and created an image of the "rise" and "fall" curve foot portions of the light energy distribution of pulse width modulated spot light in dot exposure. The photoconductor's charged potential is insensitive to light attenuation and hardly attenuates when the light amount is low, and when the light amount exceeds the low light amount range, it attenuates steeply, and light that decays quickly overall. By combining a photoconductive semiconductor having an attenuation curve and further canceling the charge by accompanying uniform exposure, a latent dot image with a sharp drop in the peripheral potential of the latent dot 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, a uniform exposure process, an electrostatic latent image forming process by dot exposure, and a reversal development process of the electrostatic latent image in the image forming process.

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

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.

These semiconductor properties are found in a photoreceptor that is dispersed and contained in a binder resin as powder particles and coated on a photoreceptor support as a photosensitive layer.

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. 50-38543 and No. 51-23
Phthalocyanine-based photoconductive pigments described in No. 738 and the like are used.

Specifically, it is a phthalocyanine pigment represented by the general formula (CaH4Nz)4Rn, where R is a hydrogen atom, Schuylium, lithium, sodium, potassium, copper, silver, beryllium, magnesium, calcium, zinc, cadmium, barium, and mercury. , aluminum, gallium, indium, lanthanum, neodymium, samarium, europium, cadrium, dysprosium, holmium, erbium, thulium, ytterbium, rutitium, titanium, tin, hafnium, lead, thorium, vanadium, antimony, chromium, molybdenum, uranium, manganese ,iron,
Cobalt, nickel, rhodium, palladium.

osmium and platinum, where n is 0 to 2, among which metal-free phthalocyanine and alpha (α), beta (β), gamma (γ), chi (χ), pi (π) or ibrosilone (ε ) type copper phthalocyanine is preferable, and those having an average particle size of 0.1 to 0801 μm are more preferable.

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,
Electrically insulating resins such as polyurethane resins, phenolic resins, melamine resins, furan resins, or epoxy resins are used, but the general formula of phenols having the structural units shown below is represented by -Sakatsu, where R and R are hydrogen atoms or methyl groups. , R1 is a hydrogen atom or an epoxy group, R8, R and R6 are a halogen atom, a hydrogen atom, a hydroxy group, a nitro group, a cyano group, an amine group, a carboxy group or a sulfonic acid group or a 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 indicated by the above-mentioned -Kakuburu is melamine,
Those modified with resins such as lignin, chroman, indene, hydrocarbons, polyvinyl alcohol, fatty acid amides, acetates, lactones, acetals, chlorophenols, thiophenes, or styrenated phenols, or their monomers can also be used effectively. It will be done. (Unexamined Japanese Patent Publication No. 54-123035, etc.)
.

The photoreceptor according to the present invention includes the photoconductive fine powder and resin, optionally a sensitizing agent such as rose bengal, auramine, bromophenol blue, bromothymol blue, and tsukujin, and other sensitizers as described in 2.4. 7-trinitro-9-fluorenone, 2.4,5° 7-titranitrofluorenone in an organic solvent such as benzene, toluene, xylene, trichloroethylene, ethyl acetate, acetone, methyl ethyl ketone, etc., for example, 100 parts of photoconductive powder,
A photosensitive layer paint is prepared by mixing and dispersing 1 to 1,000 parts of resin, 0.05 to 10 parts of sensitizer, and 50 to 5,000 parts of organic solvent.
A support obtained by vapor-depositing or laminating a metal plate such as nickel, aluminum or stainless steel, or a metal such as aluminum, gold, silver, copper-nickel, or a metal oxide such as tin oxide on a paper or plastic film, or paper or plastic. The film thickness after drying can be applied to various conductive supports, such as a support obtained by coating a film with a layer containing the metal or metal oxide powder or carbon black powder dispersed in a resin. A photosensitive layer is formed by coating and drying the film to a thickness of 10 to 50 μm. Further, an intermediate layer such as an organic polymer compound or a rectifying semiconductor layer can be provided as necessary.

In the present invention, the uniform exposure accompanied by charging includes light attenuation,
This treatment not only relieves the fatigue phenomenon of the photoreceptor that appears in dark decay, acceptance potential, residual potential, etc., but also increases the photosensitivity of the photoreceptor.

The uniform exposure is applied at least before the imagewise exposure, and may be applied after the charging step or partially superimposed in the latter half of the charging step.

As light sources for uniform exposure according to the present invention, in addition to halogen lamps and tungsten lamps, for example, fluorescent lamps and LEDs used in transfer copying machines can also be effectively used. For phthalocyanine photoreceptors, the amount of light for image exposure is usually 0.50, while the amount of light for uniform exposure used at the same time or after charging is half the amount of exposure light for the photoreceptor. (11 to 0-4 times, especially 0.
A range of 1 to 0.3 times is preferable. The light quality for the uniform exposure can be the same as the light quality for the imagewise exposure, or light in a narrow wavelength band with a higher absorption wavelength range among the absorption wavelength ranges of the photoreceptor can be used. For example, interference filters KL45.50.55.60.65.70 and 80 manufactured by Toshiba Chemical Industries, Ltd. are used for a tungsten lamp light source at 2854°.
By combining these and a colored glass filter, a narrow wavelength band corresponding to the absorption wavelength range of the photoreceptor can be extracted, and this can be used for uniform exposure.

As described above, uniform exposure may be performed at any time before image exposure.

By equipping the photoreceptor prepared as described above, a charging step, a uniform exposure, followed by a dot exposure of spot light, particularly a dot exposure of pulse width modulated spot light, can produce a latent image giving a good latent dot image. An image forming process including a reversal development process, which is applicable to both contact and non-contact development and is particularly suitable for non-contact development, and an image forming apparatus comprising the process are configured. .

The present invention provides significant advantages for multicolor image formation in which color toner images are sequentially superimposed on a photoreceptor. However, 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 by the colored toner. Generally, laser light with a longer wavelength than the visible light region is suitable.

Lasers used for dot exposure include He-Ne, He-
A gas laser such as Cd or Ar or a semiconductor laser such as GaAQAs 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 (Japanese Patent Application No. 1983).
108213, No. 62-119482, etc.) is used.

〔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 and properties of photoreceptor: Photoreceptor example 1 Epsilon (ε) type copper phthalocyanine pigment Lionol.
Blue (Lionol Blue) ER (manufactured by Toyo Ink Co., Ltd.) 1g Desmorphen (
Desmorhen) 800 (polyester polyol resin manufactured by Nippon Polyurethane Co., Ltd.) 2g hexamethylene diisocyanate 2g methyl ethyl ketone
6g of the composition according to the above weight ratio was dispersed at room temperature for 10 minutes using an ultrasonic disperser to obtain a 10μm
On a conductive support made by laminating aluminum with a thickness of 80 μm on a polyester film, a rotary coater was used to coat the coater at 800 revolutions per minute so that the film thickness after drying was 15 μm. did. The photosensitive layer of this photoreceptor was cured by heating for about 2 hours in a drying base heated to 160-170°C.

The thus prepared photoconductor was measured using an electrostatic paper analyzer (Electro
static paper analyzer) SP
Two types of electrostatic properties were measured using the 428 according to the steps shown in Method 1 and Method 2 of Clothing 1 below, and as a result, the electrostatic properties shown in Figure 1 a and b were obtained.

The conditions for the measurement using the 5P-428 were as follows: 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 image exposure and uniform 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.

The photosensitivity ratio was (E 1/2)/(E 9/10) - 8.0 for method 1 and (E 1/2)/(E 9/10) = 2.0 for method 2. The above sensitivities are without dark decay correction. Also method 2
In the following, after charging, uniform exposure is applied for a certain period of time (55 ec), and then the numerical values are shown.

Method 2 has a lower effect of sharpening the latent image than Method 1, but has the characteristics that the amount of exposure light required to form the latent image is small and the spectral sensitivity is substantially high.

Table 1 From FIG. 1, when comparing conventional a without uniform exposure and b with uniform exposure, it can be seen that the latter has clearly higher sensitivity. Further, when comparing the charging potentials, both are near goov, and no significant difference is observed.

Photoreceptor example 2 Alpha (σ) 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
The coating process was performed while rotating at 0.00 rpm so that the film thickness after drying was 15 μm.

This photosensitive layer was heat-dried at 80° C. for about 10 minutes in a heat-drying group to prepare a photoreceptor. Using this photoreceptor, the electrostatic properties were measured using the 5p-428 described above by two methods, Method 1 and Method 5 of Photoreceptor Example 1, and the processes of charging, dark decay, and light decay were compared and examined. As a result, the charging potential is 900 V and the dark decay rate is 20% in both cases, and when comparing the amount of light at the half-life of light decay, the photosensitivity ratio is (E 1/2) in method 1.
/ (E 9/10) = 7, in method 2 (E 1
/2)/(E 9/10)=2.

In the case of method 2, sensitization was approximately doubled.

Photoreceptor example 3 Beta (β) type copper phthalocyanine pigment Festogen Blue
) GNPT (manufactured by Dainippon Ink Chemical Industries, Ltd.) 0.
47 g Panlite (polycarbonate resin manufactured by Ondai 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 coated on a stainless steel plate with a thickness of 10 μm using a rotary coating machine. The coating was applied by rotating about 800 revolutions so that the film thickness after drying was 20 μm. This photosensitive layer was heated to 50'C! 10 due to hot air
After drying for a minute, a photoreceptor was obtained.

Using this photoreceptor, method 1 and method 2 are similar to photoreceptor example 2.
As a result of measuring the electrostatic properties and comparing the processes of charging, dark decay, and light decay, the charging potential of both was
0V, the dark decay rate is 22%, and the forward light sensitivity ratio is (E 1/2)/(E 9/10) = 5.0 in method 1, and (E 1/2)/(E 9/10) in method 2. 1o) = 1.4
Met.

In the case of method 2, the sensitization was approximately twice that of method 1.

Comparative Photoreceptor Example (1) 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.

Method 1.217) Each charging potential is 950V, 37
0V.

The dark decay rate was 25% and 20%. Also, the photosensitivity ratio is method 1
, Method 2 was the same, and (E 1/2)/(E 9/10) = 0.9. Follow the steps shown in Methods 1 and 2 and apply the results to the second method.
Shown in Figures c and d. As shown in FIG. 2, the effect of uniform exposure was accompanied by a decrease in the charging potential, which was not desirable.

Embodiment 1 FIG. 3 shows a color multicolor image 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; 21
is a corona charger, L is image exposure light with a wavelength of 800'mm irradiated from the semiconductor laser optical system 26, 5A, 5B, 5
G, 5D are developing devices having yellow, magenta, cyan, and black toners, 33 is a transfer electrode, 34 is a separation electrode, P
35 is a transfer paper, 35 is an activation exposure lamp, 36 is a cleaning device, 36a is a fur brush, 36b is a toner collection roller, and 36c is a scraper.

The photoreceptor l is a corona charger 2 consisting of a scorotron electrode.
1, the surface is uniformly charged. Next, a uniform exposure lamp 35 using infrared light provides uniform exposure, and then image exposure light according to the recorded data is irradiated onto the photoreceptor 1 from the laser optical system 2B. 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 charged by the corona charger 21, and is subjected to uniform exposure again by the uniform exposure lamp 35, 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 1 by the first toner T and the second toner T2.

Thereafter, the cyan toner T8 and the black toner T are developed in a similar manner, and a four-color toner image is formed on the photoreceptor l.

The multicolor toner image thus obtained on the photoreceptor is uniformly 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 J by the separation pole 34 and fixed by the fixing device 31. On the other hand, the photoreceptor l is cleaned by the cleaning device 36.

The fur brush 36a of the cleaning device 36 is kept out of contact with the photoreceptor l during image formation, and when a multicolor image is formed on the photoreceptor l, it comes into contact with the photoreceptor l 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 l 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.

This replenishment of toner to the developing device 5 is performed from the front side in FIG.
7, the toner and carrier are roughly circulated toward the front side of the paper, 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 uniformly replenishing the toner to the sleeve shaft from the right side in FIG. 5 may be used.

In this manner, the developer mixture is sufficiently stirred and mixed, and is transported in the same direction as the rotational direction of the sleeve 530 by the transporting force of the sleeve 53 and the magnetic roller 54, which rotate in the direction of the arrow. A layer forming member 55 held by a fixing member 56 which also extends 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 according to this embodiment include, for example, a magnetic or non-magnetic regulating plate placed at a certain distance from the sleeve, or a magnetic or non-magnetic regulating plate placed close to the sleeve. Any conventionally known magnetic roller may be used.

It is advantageous for the carrier and toner constituting the developer to have small particle diameters from the viewpoint of image quality 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 when the carrier has a particle size as small as that of the toner, contamination of impurities is similarly eliminated and a magnetic brush of uniform length can be formed.

The sleeve cleaning roller 59 rotates in the direction of the arrow (FIG. 5) and scrapes off the developer that has passed through the developing area 18 and consumed the toner T from the sleeve 53 as well. 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
0.2~1.0〃Coloring agent
3 to 15 tt The above composition is mixed, ground and classified to obtain a toner having an average particle size of 3 μm.

Carrier (resin coated carrier) Core: Ferrite Coating resin: styrene/acrylic (4:6) Magnetization 27emu/g Particle size: 30μm Specific gravity 5.2g/cmj Specific resistance 1013Ω・cm or more A mixture of the above 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) manufactured by Hitachi, Ltd.
330 type), and the wavelength range is from 360 to 850 nm. The wavelength of the exposure light used for uniform exposure is preferably infrared light in order to prevent the amount of transmitted light from decreasing 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 Yellow
low)G(C.

1.21090), benzidine yellow GR (C,1
, 21100), Permanent Yellow (Perm
D) IG (Hoechst product), Brilliant Carmine
Carmine) 6 B (C, 1, 15850)
, Rhodamine 6G Lake (LaKe) (C,1,45
160) Rhodamine B Lake (c, 1.45170)
, Phthalocyanine Blue Non-Crystal (Pht
halocyanine Blue non Crys
tal) (C, 1,74160), Phthalocyanine Green (C, 1,74260), Carbon Black, Fat Yellow 5G, Fat Yellow 3
G1 Fat Red G1 Fat Red HRR,
Fat Red 5B1 Fat Black B1 Zapon Fast Black B1 Zapon Fast Black B1 Zapon Fast
Glue NFL, Zapon Core = 28- -St Red BB, Zapon First Red GE
.

Zapon Fast Yellow G1 Quinacridone Red (c, +, 4650oO).

As the uniform 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-p70 manufactured by Toshiba Glass) Figure 8 shows its spectral transmittance characteristics.

The above (1) and (2) were used as activation exposure lamps.

Table 4 shows image forming conditions in the color multicolor image forming apparatus shown in FIG.

FIG. 10 shows the spectral sensitivity characteristics of the image forming body.

The exposure distribution of the laser spot diameter is approximately Gaussian, and the diameter at the level of 1/e of the exposure light amount is approximately 45 μm.

When color images were formed under the above image forming conditions, color images with good spot 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. According to image evaluation, the exposure intensity is preferably in the range of 1.5 to 4 times the half-reduced exposure light amount of the photoreceptor under uniform exposure conditions. It is considered that this condition forms a potential pattern having a small diameter and a sharp potential change.

The exposure intensity in this case is compared to the case where uniform exposure is not used.
It is about half that, indicating that effective sensitization has been achieved.

Example 2 In Example 1, the writing resolution was set to 16 dat/mm.
The conditions were the same except that the pulse width modulation of the S value was used, the exposure distribution of the laser spot diameter corresponding to the (2) pulse was approximately Gaussian, and the sub-scanning direction was 100 μm and the main scanning direction was 30 μm.

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.

The exposure intensity in this case is compared to the case where uniform exposure is not used.
It is about half that amount, indicating that effective sensitization has been achieved.

Comparative Example (1) When a color image was formed using Comparative Photoreceptor 1 under the same conditions as Example 1, the potential contrast during development was lower than in Example, and the reproduction of the spot diameter was insufficient. Further, a toner image was not stably formed on the previous toner image.

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

In this case, an even worse image was obtained than when uniform exposure was not used.

Comparative Example (2) When a color image was formed using the comparative photoreceptor 1 under the same conditions as in Example 2, the potential contrast during development was low (compared to the example). It was enough. Further, a toner image was not stably formed on the previous toner image.

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

In this case, a worse image was obtained than when uniform exposure was not used.

[Effects of the Invention] According to the present invention, a multicolor image without noise or color turbidity can be stably formed.

[Brief explanation of the drawing]

Figure 1 shows the electrostatic characteristics of the photoreceptor according to the present invention in Example 1 when the timing of uniform exposure was changed, and Figure 2 shows the Se
Electrostatic characteristics of the photoreceptor, Figure 3 is a block diagram of a color multicolor image forming apparatus to which the color multicolor image forming method of the present invention is applied, Figure 4 is a block diagram of a laser optical system, and Figure 5 is a developing device. 6 shows the spectral reflectance of toner, FIG. 7 shows the emission spectrum characteristics of a GaAffAs infrared light emitting diode, and FIG. 8 shows the spectral transmittance characteristics of a combination of a halogen lamp and an infrared transmission filter. ■... Photoreceptors 5A, 5B, 5C, 5D... Developing device 21... Corona charger 26... Laser optical system 33... Transfer electrode 34... Separation electrode 35... Activation exposure Lamp 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, in an image forming process, a uniform exposure process, an electrostatic latent image forming process by dot exposure, and a reversal development process of the electrostatic latent image. (2) The image forming apparatus according to claim 1, wherein the photoconductive semiconductor powder of the photoreceptor contains phthalocyanine. (3) Claim 1, wherein the reversal development is a non-contact reversal development.
Or the image forming apparatus according to 2. (4) The image forming apparatus according to claim 1, 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 uniform exposure step, the latent image forming step, and the reversal development step are repeated to superimpose toner images on the photoreceptor.