JPH10207193A - Image recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a record image with stable image quality despite changes in temperature and humidity without using an expensive potential sensor and to achieve miniaturization and productivity improvement by composing so as to restrict change in electrostatic-latent-image potential with changes in temperature and humidity. SOLUTION: The device has a control part 8 which controls the laser light source of an exposure unit 3. The instant a photoreceptive drum 1 is electrified to initial electrification potential, the computing circuit of the control circuit 8 computes, from light discharge characteristic data stored in a recording circuit, exposure energy in an area where light discharge characteristics based on temperature and humidity cross. The result of the computation is outputted to a laser drive circuit, and the laser drive circuit outputs a drive current to the laser light source of the exposure unit 3 according to the computed exposure energy. In this structure, it is unnecessary to control the surface potential of the photoreceptor by means of the expensive potential sensor, therefore productively improves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus, and more particularly, to an image recording apparatus in which a photosensitive member provided with an initial charging potential that changes in accordance with temperature and humidity can be used to change the potential of an electrostatic latent image even when temperature and humidity change. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus that stabilizes image quality and reduces the size of the apparatus by exposing with image signal light having exposure energy that does not vary.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image recording apparatus, a charging step for uniformly charging the surface of an image carrier, and an electrostatic latent image by exposing the charged image carrier to light based on image information. An exposure step of forming a toner image, a developing step of attaching a toner to the electrostatic latent image to form a toner image, an intermediate transfer body, or a transfer step of transferring the toner image to a transfer material such as recording paper;
Then, a recording image is formed through a fixing step of fixing the toner image transferred to the transfer material.

FIG. 12 shows a conventional color image recording apparatus, in which a function-separated type photosensitive drum 15 having a charge generating layer and a charge transport layer (hereinafter referred to as a photosensitive drum 15), and a surface of the photosensitive drum 15 are shown. A scorotron 16 for charging the photosensitive drum 15 to a predetermined charging potential, an exposure unit 17 for exposing the photosensitive drum 15 with an image signal light modulated based on image information to form an electrostatic latent image, and a surface of the photosensitive drum 15 Rotary developing device having a plurality of toner units 18a, 18b, 18c, and 18d for developing the electrostatic latent image with the corresponding color toners of black (K), yellow (Y), magenta (M), and cyan (C) 18, a transport drum 19 that transports the recording paper 20, a corotron 21 that transfers a toner image onto the recording paper 20 by applying a predetermined charge, and a photosensitive drum 15 that transports the recording paper 20 to the photosensitive drum 15. A peeling unit 22 for al peeling, fixing portion 2 for fixing the toner image transferred to the recording paper 20
3, a cleaner 24 for removing the toner remaining on the photoconductor drum 15 by the cleaning blade 24a, a static eliminator 25 for eliminating the surface of the photoconductor drum 15, and a potential for detecting the surface potential of the photoconductor drum 15 after exposure. The rotary developing device 18 has a sensor 26 and develops the electrostatic latent image formed on the photosensitive drum 15 in the order of K, Y, M, and C to form a full-color image.

It is generally known that the surface potential of the photosensitive drum 15 after exposure varies due to changes in temperature and humidity even when the exposure energy is controlled to a predetermined value. For example, as shown in FIG. 13, even if the photosensitive drum 15 is exposed with a predetermined exposure energy of 10 mJ / m ² or less, which is a normal use range, a surface potential difference of 20 to 50 V is generated due to a change in temperature and humidity. . This potential difference is
This does not cause a significant problem when performing binary recording as in a black and white image. However, when performing multi-value recording as in a color image, for example, a surface potential difference of the photoconductor, that is, an electrostatic latent image potential difference occurs. Then, since the amount of toner for developing the electrostatic latent image in the developing process varies, there is a problem that the density of the recorded image varies.

In order to eliminate such a surface potential difference, the exposure energy is controlled based on the measurement result of the potential sensor 26 to stabilize the surface potential of the photosensitive drum 15. More specifically, as for the exposure energy Pm corresponding to the image signal serving as a reference at the time of non-printing, for example, the image signal Cm of the halftone area having the image area ratio of 50% in the standard environment, the exposure energy at two points before and after the exposure energy Pm Energy P ₁ , P
₂ (P ₁ <Pm <P ₂ ), the photosensitive drum 15 is exposed, and the potential sensors 26 are used to expose the surface potentials V ₁ and V ₂ based on the exposure.
Is measured. Then, from the measured surface potentials V ₁ and V ₂ , linear interpolation based on two points of the exposure energies P ₁ and P ₂ is performed to obtain an exposure energy Pm corresponding to the photodischarge characteristics of the photosensitive drum 15. I have.

[0006]

However, according to the conventional color image recording apparatus, since an expensive potential sensor is used, the cost increases. In addition, in order to control the surface potential of the photoconductor drum faithfully with changes in temperature and humidity, it is necessary to frequently measure the surface potential of the photoconductor drum prior to image formation. There is a problem of doing.

When the diameter of the photosensitive drum is reduced in accordance with the downsizing of the color image recording apparatus, it becomes difficult to dispose a potential sensor around the photosensitive drum. There is a problem that control cannot be performed. Accordingly, an object of the present invention is to provide a small and highly productive image recording apparatus that can obtain a recorded image with stable image quality against changes in temperature and humidity without using an expensive potential sensor. is there.

[0008]

In order to achieve the above object, the present invention provides an image forming method based on an electrostatic latent image formed on an image carrier having a positive photodischarge characteristic with respect to ambient temperature and humidity. In an image recording apparatus for performing recording, the image recording apparatus has a positive charging characteristic with respect to the ambient temperature and humidity, and applies a predetermined initial potential to the image carrier before the electrostatic latent image is formed on the image carrier. A charging unit that charges the image carrier charged by the charging unit with an image signal light beam having a predetermined exposure energy to form the electrostatic latent image; and Developing means for developing the formed electrostatic latent image with toner to form a toner image; and at least two positive photodischarges corresponding to at least two initial potentials varying based on the positive charging characteristics Characteristic Setting the predetermined exposure energy at a predetermined image area ratio between an exposure energy determined from a point and an exposure energy larger by a predetermined value than that, and performing exposure based on the image signal light beam to the exposure unit. An object of the present invention is to provide an image recording apparatus provided with a control means for causing the image recording apparatus to perform the control.

In the above-described image recording apparatus, the control means preferably sets a predetermined exposure energy with a predetermined image area ratio of 50%. It is preferable that the developing unit sets the potential of the electrostatic latent image at which the toner weight of the toner image is saturated to be equal to or lower than the potential of the electrostatic latent image formed by the predetermined exposure energy. The charging means preferably charges the image carrier to a predetermined initial potential by applying a constant voltage to the image carrier in proximity to or in contact with the image carrier.

According to another aspect of the present invention, there is provided an image recording apparatus for recording an image based on an electrostatic latent image formed on an image carrier having a positive photodischarge characteristic with respect to ambient temperature and humidity. In the recording apparatus, the recording device has a positive charging characteristic with respect to the surrounding temperature and humidity, and charges the image carrier to a predetermined initial potential before the electrostatic latent image is formed on the image carrier. And an electrostatic latent image having an intensity modulation area and an area modulation area by exposing the image carrier charged by the charging means with a light beam having a predetermined exposure energy for a time corresponding to an image signal. Exposure means for forming, the developing means for developing the electrostatic latent image formed by the exposure means with toner to form a toner image,
Between the exposure energy determined from the intersection of at least two of the positive photodischarge characteristics corresponding to at least two of the initial potentials that fluctuate based on the positive charge characteristic, and an exposure energy that is larger by a predetermined value than that. An image recording apparatus comprising: a control unit that sets the predetermined exposure energy so that the exposure energy of a region that shifts from the intensity modulation region to the area modulation region enters, and causes the exposure unit to perform exposure based on the light beam. I will provide a.

In the above-described image recording apparatus, the developing means may be configured such that the potential of the electrostatic latent image at which the toner weight of the toner image is saturated is changed by the exposure energy in the area where the intensity modulation area shifts to the area modulation area. It is preferable that the potential is set to be lower than the potential of the latent image. The charging means preferably charges the image carrier to a predetermined initial potential by applying a constant voltage to the image carrier in proximity to or in contact with the image carrier.

[0012]

FIG. 1 shows an image recording apparatus according to a first embodiment, in which a function-separated photosensitive drum 1 having a charge generating layer and a charge transport layer, and a semiconductive charging electrode 2A. An electrode supporting member 2B for supporting the charging electrode 2A,
And a pressing member 2C for pressing the charging electrode 2A against the electrode support member 2B. The charging unit 2 charges the photosensitive drum 1 by bringing the charging electrode 2A into contact with the contact unit 2D, and the exposure energy corresponding to the image signal. Exposure unit 3 for emitting a laser beam, developer stirring / transporting chamber 4F partitioned by partition wall 4C, screw augers 4A, 4B for stirring toner in developer stirring / transporting chamber 4F, and developer attached to developing roll 4D Developing section 4 having scraper 4E for peeling off
A bias transfer roll 6 for transferring a toner image to a recording sheet 5 supplied to a transfer position by applying a predetermined charge, and a charge removing unit 7 for removing charge from the photosensitive drum 1
And a control unit 8 for controlling a laser light source (not shown) of the exposure unit 3.

FIG. 2 shows a photosensitive drum 1, which is formed by sequentially laminating an undercoat layer 1b, a charge generation layer 1c, and a charge transport layer 1d on a conductive support 1a.

The conductive support 1a is made of aluminum, copper,
Metal drums and sheets such as stainless steel, plastic foils and paper laminated with metal foil such as aluminum, or aluminum or other metal deposited, and conductive particles on metal or resin drums A resin layer in which is dispersed is used.

The undercoat layer 1b is provided as necessary to improve the adhesion between the conductive support 1a and the charge generation layer 1c and to prevent coating defects of the charge generation layer 1c. , Polyvinyl butyral, polyvinyl methyl ether, polyamide, thermoplastic polyester, thermoplastic resin such as phenoxy resin, casein gelatin, nitrocellulose, and thermosetting resin such as polyimide, polyethylene imine, epoxy resin, melamine resin, phenol resin, and polyurethane resin And organometallic compounds such as titanium coupling agents, zirconium coupling agents, and silane coupling agents are known. These materials can be used alone or in combination of two or more. Dissolve the above materials with a solvent if necessary,
After mixing, the mixture is diluted and applied on the conductive support 1a by spray coating or dip coating.
By drying in the temperature range of 00 to 200 ° C., the undercoat layer 1 is formed.
b is formed. The thickness is arbitrarily set in the range of 0.1 to 01 μm, but is 0.5 to 2 μm for ease of manufacture.
It is preferable that

The charge generation layer 1c is prepared by dissolving a binder resin in a solvent, dispersing a charge generation material in the solvent, applying the charge generation material on the undercoat layer 1b by spray coating or dip coating, and drying. There is a method in which a charge generation material is directly formed into a film by a vacuum evaporation method or the like. Examples of the binder resin include polyvinyl butyral, polyarylate (a polymer of bisphenol A and phthalic acid), polycarbonate resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, acrylic resin, polyacrylamide, Insulating resins such as polyamide resin, polyvinyl pyridine, cellulosic resin, urethane resin, epoxy resin casein, polyvinyl alcohol, and polyvinylpyrrolidone are exemplified. The charge generation material, azo dyes such as chlorodiane blue, anthantrone, quinone pigments such as pyrenequinone, quinocyanine pigments, perylene pigments, indigo pigments, bisbenzimidazole pigments, metal-free phthalocyanine, copper phthalocyanine, vanadyl phthalocyanine,
Examples include phthalocyanine pigments such as titanyl phthalocyanine and gallium phthalocyanine, azurenium salts, squarylium pigments, quinacridone pigments and the like. Charge generation layer 1
The thickness of c is arbitrarily set in the range of 0.01 to 5 μm, but is preferably 0.1 to 0.5 μm for ease of manufacture.

The charge transport layer 1d is formed by dissolving a binder resin in a solvent and spray-coating the solvent with a charge transport agent added thereto.
Alternatively, it is formed by coating on the charge generation layer 1c by dip coating or the like and drying. Charge transport agents include:
Polycyclic aromatic compounds such as anthracene, pyrene and phenanthrene, or compounds having a nitrogen-containing heterocyclic ring such as indole, carbazole and imidazole, pyrazoline compounds, hydrazone compounds, triphenylmethane compounds, triarylamine compounds, enamine compounds, stilbenes Compounds and the like can be used. For the binder resin, polycarbonate resin, polyester resin, methacrylic resin,
Acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, styrene-butadiene copolymer, vinylidene chloride
Acrylonitrile copolymer, vinyl chloride vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicon-alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin, poly-N-vinyl carbazole A known resin such as polysilane or the like can be used, but is not limited thereto. The thickness of the charge transport layer 1d is arbitrarily set in the range of 1 to 40 μm.
It is preferable to set it to 30 μm.

Further, in order to suppress wear of the photoreceptor drum having a reduced diameter, a toner image is formed after fine particles such as polyvinylidene fluoride are adhered to the surface of the photoreceptor drum. It has been confirmed by the present inventor that the quality and the quality of a recorded image are improved. Therefore, it is preferable that the above-mentioned fine particles be attached before the toner image is formed on the photosensitive drum.

The charging section 2 includes polyester, polyamide, polyethylene, polycarbonate,
Polyolefin, polyurethane, polyvinylidene fluoride, polyimide, PEN, PEK, PES, PPS, P
Conductive resin such as FK, PVdF, ETFE, CTFE, etc., or synthetic rubber composed of polymer materials such as silicon rubber, ethylene propylene rubber, butyl rubber, acrylic rubber, urethane rubber, nitrile rubber, and carbon black or metal powder It is possible to use one mixed with a powder of the same nature. Further, a polar rubber such as epichlorohydrin rubber, chloroprene rubber, EPDM rubber or the like, or a semiconductive inorganic material such as amorphous silicon may be formed by thin-film or thick-film deposition on an insulating substrate. However, since polar rubber and the like have high adhesiveness, it is necessary to devise a method such as coating the surface with a low-adhesion material or the like. Further, when a thin film or a thick film is deposited, the hardness is large, so that it is preferable to dispose the film in a non-contact manner with respect to the charge acceptor. Mixing amount of the conductive particles, 10 spark discharge easily occurs in the following ² Omega · cm, since it tends to cause dotted charging failure at 10 ¹¹ Omega · cm or more, 10 ³ Omega · cm to 10 ¹⁰ Omega
-It is preferable to use in the range of cm. In particular, 10 ³
In the case of Ω · cm to 10 ⁶ Ω · cm, the charging voltage applied to the charging unit can be set relatively low, and when used in an image recording apparatus having a process speed of 150 mm / sec or more, the potential fluctuation is suppressed to a small value. Can be.

Polyester, on the surface of the charging electrode 2A
Polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, polyimide, PEN, PEK, PES, PPS, PFK, P
Resin such as VdF, ETFE, CTFE, etc., or synthetic rubber composed of high polymer materials such as silicon rubber, ethylene propylene rubber, butyl rubber, acrylic rubber, urethane rubber, nitrile rubber, and conductive rubber such as carbon black and metal powder It is possible to use a mixture of powder and a dispersion of fine powder having high water repellency such as fluorine powder. Alternatively, polyvinylidene fluoride, a solid water-repellent powder such as polymethacrylate, zinc stearate, barium stearate, lead stearate, nickel stearate on the charged portion surface formed by the above-described polymer material,
Metal salts of fatty acids such as cobalt stearate, copper stearate, zinc oleate, magnesium oleate, zinc palmitate, cobalt palmitate, lead caprylate, lead caproate and lead linolenate may be applied. The particle size of the fine powder is preferably 10 μm or less, because if it exceeds 10 μm, it will enter the conductive electrode, and is particularly preferably 1 μm or less in consideration of the adhesive force between the charged electrode and the fine powder.

As a method for applying the fine powder, a sponge,
Mechanical method of rubbing using a rotating body such as a roll made of fiber, felt, rubber, nonwoven fabric, foam, brush, web, blade, paddle, gel, resin, metal, or a reciprocating brush-like member, electricity Alternatively, the particles may be adhered by a method of adhering fine particles or a combination of a mechanical method and an electric method. It is preferable to use a sponge, a felt, a nonwoven fabric, or a brush to suppress the pressure at the contact portion.

The charging electrode 2A may have any shape as long as it can contact or approach the photosensitive drum 1. The lower the pressing force on the photosensitive drum 1, the higher the effect of removing foreign matter. For this reason, a film tube is preferred.

As the charging voltage applied to the charging electrode 2A, a DC voltage or a voltage obtained by superimposing an AC voltage that is twice or more the charging start voltage on the DC voltage can be applied. When a voltage obtained by superimposing an AC voltage that is twice or more is applied, the surface energy of the charging unit and the photoconductor is increased, and the photoconductor drum may be adversely affected. For this reason, it is preferable to apply a DC voltage, and to apply a constant voltage for the purpose of canceling the potential fluctuation by a combination of a change in the temperature and humidity of the charging potential and a photodischarge characteristic of the photosensitive drum.

The electrode supporting member 2B has a peripheral surface formed of a metal such as aluminum or SUS for supplying power to the charging electrode 2A, or a conductive material formed so that the volume resistivity is equal to or less than the volume resistivity of the charging electrode 2A. Made of molecular material. Normally, the electrode support member 2B is fixed, and the charging electrode 2A is driven by the photosensitive drum 1 by sliding.
The electrode support member 2B may be rotated in synchronization with the rotation.

The pressing member 2C is pressed by a spring such as phosphor bronze or a spring or the like to such an extent that the charging electrode 2A does not float up from the electrode supporting member 2B.

FIG. 3 shows a control unit 8 for controlling the exposure unit 3. The recording circuit 9 stores data based on the photodischarge characteristics of the photosensitive drum 1, and the initial charging potential of the photosensitive drum 1 and the recording circuit 9. And a laser drive circuit for driving a laser light source of an exposure unit (not shown) based on the calculation result output from the calculation circuit 10 1
One. The exposure unit used in the present embodiment deflects a laser beam emitted based on an image signal by a polygon mirror and scans the photosensitive drum, and the beam diameter of the laser beam is 60 μm and the maximum light amount is 8
It is set to 〜１０10 mJ / m ² .

The developing section 4 is arranged such that the photosensitive drum 1 and the developing roll 4D have a gap g. The developing roll 4D is supplied with a developer in which a toner and a carrier are mixed from a developer stirring and conveying chamber 4F. Is done. The developer stirring and transporting chamber 4F is divided into two chambers by a partition wall 4C.
Screw augers 4A and 4B for stirring the developer in each chamber
Is provided. The screw augers 4A and 4B rotate in opposite directions to stir the developer. The developer stirred in this way circulates in the developer stirring and transporting chamber 4F partitioned into two chambers.

FIG. 4 shows a developing roll 4D, which comprises a cylindrical conductive base 40 and a magnetic recording layer 41 formed on the peripheral surface thereof. The magnetic recording layer 41 is formed by dispersing a ferromagnetic material in a binder resin, and has a pair of a north pole and a south pole in a circumferential direction, and a low magnetic force region or a non-magnetized region outside the pair is substantially constant. And are formed in a pattern as described above. The interval between the north and south poles is 25 μm to 250 μm,
The interval between the magnetic poles adjacent to each other across the low magnetic force region or the non-magnetized region is 300 μm or less, and the magnetic poles adjacent to each other across the low magnetic force region or the non-magnetized region have different polarities. Further, the magnetic poles adjacent to each other across the low magnetic force region or the non-magnetized region may be magnetic poles having the same polarity. In such a configuration, a thin layer of a certain amount of developer is held on the developing roll 4D by magnetization at the magnetic poles arranged at minute intervals and a low magnetic force effect, and the developing roll 4D having magnetic force rotates. Since the developer is transported, and the magnetic tumbling that is used in the transport of the developer using the magnetic roll and the developing sleeve is not used, the amount of toner to be developed is saturated, and as shown in FIG. The curve showing the relationship between the contrast potential and the weight of the developed toner tends to have a slope.
As a result, the developing characteristic is such that the developing weight is saturated in a region where the developing contrast potential is relatively low. Although the present invention uses a two-component developer, the same applies to a non-magnetic one-component developing unit.

The magnetic recording layer 41 is made of a magnet material or a magnetic recording material.
Γ-Fe known as a material_TwoO _ThreeAnd CrO_TwoEtc.
Made of magnetic material, conductive fine particles as required
Etc. can also be added. In addition, the binder resin contains
Resin that composes magnetic recording materials such as tapes, disks and cards
Polycarbonate, polyester, polyester
Urethane or the like can be used.

In the above-described image recording apparatus, the photosensitive drum 1 is charged to an initial charging potential according to temperature and humidity by contacting the charging electrode 2A of the charging unit 2 which is controlled at a constant voltage.

The resistivity of the charging electrode 2A changes based on changes in temperature and humidity, and the surface potential of the photosensitive member at 54 ms after exposure shown in FIG.
%), At the time of high temperature and high humidity of 28 ° C. and 85%, the initial charging potential (when the exposure energy = 0) of the photosensitive drum 1 increases due to the charge injection phenomenon. On the other hand,
At 0% low temperature and low humidity, the initial charging potential of the photosensitive drum 1 decreases. This charge injection phenomenon is not so noticeable in the DC bias + AC voltage discharge used in the conventional contact-type charging unit, but it has been confirmed that it appears significantly in the DC voltage discharge.

When the photosensitive drum 1 is charged to the initial charging potential, the arithmetic circuit 10 calculates the exposure energy in the area where the photo discharge characteristics intersect based on the temperature and humidity from the data of the photo discharge characteristics stored in the recording circuit 9. Is calculated. The calculation result is output to the laser drive circuit 11, and the laser drive circuit 11 outputs a drive current corresponding to the calculated exposure energy to a laser light source (not shown) of the exposure unit 3. For example, in FIG. 6, the photodischarge characteristics of the photosensitive drum 1 represented by a curve A at low temperature and low humidity, a curve B at medium temperature and medium humidity, and a curve C at high temperature and high humidity have an exposure energy of 3 to 4 m.
Intersect in the region of the J / m ^2, exposure unit 3 forms an electrostatic latent image by scanning a photosensitive drum 1 by an image signal light of the exposure energy region.

The electrostatic latent image formed on the photosensitive drum 1 is
Conveyed to the developing unit 4 based on the rotation of the photosensitive drum 1,
It is developed with the toner supplied by the developing roll 4D. The developed toner image is transferred to the recording paper 5 based on a predetermined charge applied from the bias transfer roll 6 at a transfer position, and the toner is fixed by a fixing device (not shown). The photosensitive drum 1 to which the toner image has been transferred is neutralized by the neutralization unit 7.

Normally, the image quality of a halftone image is determined by an image area ratio of 5
The evaluation is made based on the quality of the gradation at a low density portion of 0% or less. Therefore, in order to obtain a high-quality recorded image, it is necessary to stably and faithfully reproduce a low-density portion having an image area ratio of 50% or less. A low density portion having an image area ratio of 50% or less is exposed with energy.

FIG. 7 shows the energy distribution of the laser beam for exposing the photosensitive drum 1 in the position direction (main scanning direction). In the case of the line type used in an electrophotographic image recording apparatus, the laser beam is used. The exposure energy and the exposure area are modulated based on the light emission time in the main scanning direction.

FIG. 8 shows an image diagram of laser beam scanning. In the laser beam scanning, the exposure intensity is modulated (region A) and the exposure intensity is constant and only the exposure area is modulated (region A). B). In the following description, the area A is called an intensity modulation area, and the area B is called an area modulation area.

When a latent image profile of, for example, 200 lines is simulated based on the above laser beam, the results are as shown in FIGS. 9 and 10. FIG.
9 shows a latent image profile of a photoreceptor having a photodischarge characteristic having a constant initial charging potential, and FIG.
FIG. 9B shows an area modulation area. According to FIG. 9, the latent image potential difference ΔV is represented by a curve A at high temperature and high humidity and a curve C at low temperature and low humidity.
Has occurred. FIG. 10 shows a latent image profile of a photoreceptor having a photodischarge characteristic in which an initial charging potential changes in accordance with temperature and humidity. FIG.
0 (b) is an area modulation area. According to FIG. 10, the latent image potential difference ΔV is small as compared with the latent image profile of the photoreceptor whose initial charging potential has a constant photodischarge characteristic.

Here, the developing bias of the developing section is set to -380.
Considering the phenomenon in which the developing toner weight is saturated at −200 V at −200 V, in the latent image profile shown in FIG. 10, the variation in the amount of toner adhering to the electrostatic latent image during development based on the temperature and humidity changes. Since the size is reduced, fluctuations in the density and size of the developed toner image can be suppressed.
Therefore, the gradation in a low density portion having an image area ratio of 50% or less is improved.

FIG. 11 shows a tandem type color image recording apparatus according to the second embodiment.
Photoconductor drums 1K, 1 provided independently for colors
Y, 1M, and 1C, charging units 2K, 2Y, 2M, and 2C, and exposure units 3K, 3Y, 3M, and 3
C, developing units 4K, 4Y, 4M, and 4C, and a paper transport belt 14 that is stretched by a drive roll 12 and a driven roll 13 and transported in the direction of the arrow. The photoreceptor drums 1K, 1Y, 1M, and 1C are arranged such that the center positions are at intervals of 25 to 50 mm. The charging units 2K, 2Y, 2M, and 2C include a charging electrode 2A, an electrode support member 2B, and a pressing member 2C, as in the charging unit 2 shown in FIG. 1, but are not shown.

In the tandem-type color image recording apparatus, the exposure energy at which the latent image potential difference due to the change in temperature and humidity is set to be small, and the photosensitive drum 1K,
By exposing 1Y, 1M, and 1C, it is possible to provide a recorded image without image quality deterioration due to fluctuations in temperature and humidity.

Further, since it is not necessary to control the surface potential of the photosensitive member using an expensive potential sensor, the productivity is improved. Further, since the diameter of the photoconductor can be reduced, the size of the image recording unit can be reduced.

Hereinafter, a specific configuration of the image recording apparatus studied by the inventor to complete the present invention will be described in detail.

[Photoreceptor 1] A solvent consisting of the components shown in Table 1 was placed on a conductive support 1a made of a SUS pipe having a diameter of 15 mm.

After dip coating of Table 1, it was dried at 150 ° C. for 10 minutes to form a 0.9 μm-thick undercoat layer 1b, and a solvent comprising the components shown in Table 2

A dispersion obtained by dispersing Table 2 in a sand mill using glass beads having a diameter of 1 mm for 2 hours was dip-coated on the undercoat layer 1b, dried at 100 ° C. for 10 minutes, and dried to a thickness of 0.1 mm.
A solvent having a charge generation layer 1c of 2 μm and having the components shown in Table 3

Table 3 was formed by dip coating on the charge generation layer 1c and then dried at 135 ° C. for 1 hour to form a charge transport layer 1d having a thickness of 24 μm, thereby producing an electrophotographic photosensitive member.

[Charging part 2] The charging electrode 2A is electrically conductive.
Carbon black is dispersed and volume resistivity is 10 ^ThreeΩ
cm-10⁶Ω · cm, diameter 12.5mm, thickness 100
Use a conductive nylon tube of
100 parts of fluoroethylene and 5 parts of conductive carbon
The mixture was mixed and dispersed with 100 parts of a suitable mixed solvent.
To create a surface layer forming paint, and use a bell type electrostatic coating machine
Film thickness when dried using
It was applied to the charging electrode 2A so as to have a thickness of 10 μm. Electrode support
The holding member 2B is made of a SUS roll having a diameter of 10 mm.
A DC voltage of 1 kV required for charging the light body 1 is supplied to a power supply device (illustrated
Not applied). The pressing member 2C has a diameter of 5 mm.
1 mm thick phosphorus using a polyacetal resin roll
Bronze was used as the spring material.

[Exposure unit 3] Using a laser diode with an output of 5 to 10 mW, a 400
The exposure unit formed a laser spot in the main scanning direction at a resolution of dpi. The laser beam diameter was 60 μm, and the exposure intensity and the exposure area were modulated by controlling the application time width of the input voltage to the laser diode based on the image signal.

[Developing part 4] The magnetic recording layer 41 having a thickness of 50 μm is formed on the conductive substrate 40 by using γ-Fe ₂ O ₃ as the magnetic material of the magnetic recording layer 41 and polyurethane as the binder resin.
1 was formed. A magnetic recording head was used to magnetize the magnetic recording layer 41 so that the direction of magnetization was horizontal to the surface of the magnetic recording layer 41. The outer diameter of the developing roll 4D is 8 mm, the peripheral speed during driving is 320 mm / s, and the gap g between the photoreceptor 1 and the developing roll 4D is 300 μm and is held in a non-contact manner.

[Developer] As the toner, polyester (number average molecular weight: 4,300, weight average molecular weight: 9.8)
(00, glass transition point Tg: 58 ° C.) 94 wt% and carbon black 6 wt% were kneaded and pulverized to obtain colored particles having an average particle diameter of 7 μm. The average particle size is a value measured by a Coulter counter (manufactured by Coulter Inc.). Titanium oxide fine particles having an average particle diameter of 40 nm were externally added to the colored particles at a coverage of 30% of the toner surface area to obtain a black toner. The charging polarity is negative. As a carrier, a styrene-acryl copolymer (number average molecular weight: 23,000, weight average molecular weight: 9,8000, glass transition point Tg: 78)
° C) 30 wt%, carbon black (basic carbon black: pH = 8.5) 3 wt%, granular magnetite (maximum magnetization 80 emu / g, particle size 0.5 μm) 67 wt%
% Was kneaded, crushed and classified to prepare a carrier having an average particle size of 45 μm. The specific gravity of the carrier is 2.2. The average particle size is a value measured by Microtrac (manufactured by Nikkiso Co., Ltd.). The charging polarity is positive. The electric resistance value is 10 ¹² Ω
cm. The above toner and carrier were mixed to form a developer. The toner concentration TC (Tone) in the developer
r Concentration) is 15 wt%, the toner charge amount in the developer is 20 uC / g, and the developer is charged into the developer stirring and transporting chamber 4F. The toner concentration TC is calculated by the equation (1).

(Equation 1)

[Image recording conditions] ROS 400 dpi LDROS (analog line system) Process speed 160 mm / s Charging voltage Approx. -450 V (input voltage to film electrode is fixed at 1.1 kV) Developing bias DC component -380 V AC component 1kV _PP (6kHz) ・ Transfer condition BTR transfer

High temperature and high humidity conditions: 28 ° C., 85% RH; normal conditions: 22 ° C., 55% RH; low temperature, low humidity conditions: 1%
0 ° C. and 30% RH. When the installation environment of the apparatus was changed to three conditions of high temperature and high humidity, usually, low temperature and low humidity every 10,000 sheets, good images could be obtained in each environment.

[0050]

As described above, according to the color image recording apparatus of the present invention, fluctuations in the potential of the electrostatic latent image due to changes in temperature and humidity are suppressed, so that an expensive potential sensor can be used without using an expensive potential sensor. It is possible to obtain a recorded image having a stable image quality with respect to changes in temperature and humidity, and to provide high productivity with a small size.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an image recording device according to a first embodiment.

FIG. 2 is an explanatory diagram illustrating a configuration of a photosensitive drum.

FIG. 3 is an explanatory diagram illustrating a control unit of the exposure unit.

FIG. 4 is an explanatory diagram illustrating a configuration of a developing roll.

FIG. 5 is an explanatory diagram illustrating development characteristics of a development unit.

FIG. 6 is an explanatory diagram illustrating a surface potential at 54 ms after exposure of the photosensitive drum according to the first embodiment.

FIG. 7 is an explanatory diagram showing an energy distribution of an image signal light.

FIG. 8 is an image diagram showing a modulation process of an image signal light.

FIG. 9A is an explanatory diagram showing a conventional electrostatic latent image potential in an intensity modulation area. FIG. 3B is an explanatory diagram showing a potential of an electrostatic latent image in a conventional area modulation area.

FIG. 10A is an explanatory diagram illustrating an electrostatic latent image potential in an intensity modulation area according to the first embodiment. FIG. 3B is an explanatory diagram illustrating an electrostatic latent image potential of an area modulation area according to the first embodiment.

FIG. 11 is an explanatory diagram illustrating a tandem-type color image recording apparatus according to a second embodiment.

FIG. 12 is an explanatory diagram showing a conventional image recording apparatus.

FIG. 13 is an explanatory diagram showing a surface potential at 54 ms after exposure of a photosensitive drum in a conventional image recording apparatus.

[Explanation of symbols]

 1, photosensitive drum 1a, conductive support 1b, undercoat layer 1c, charge generation layer 1d, charge transport layer 2, charging section 2A, charging electrode 2B, electrode support member 2C, pressing member 3, exposure unit 4, development Unit 4A, screw auger 4B, screw auger 4C, partition wall 4D, developing roll 4E, scraper 4F, developer stirring and transporting chamber 5, recording paper 6, bias transfer roll 7, neutralizing unit 8, control unit 9, recording circuit 10, Arithmetic circuit 11, laser drive circuit 12, drive roll 13, driven roll 14, paper transport belt 15, photoconductor drum 16, scorotron 17, exposure unit 18, rotary developing units 18a, 18b, 18c, 148, toner unit 19, Transport drum 20, recording paper 21, corotron 22, peeling unit 23, fixing unit 24, cleaner 24a, Over training blade 25, a discharger 26, a potential sensor 40, the conductive substrate 41, a magnetic recording layer

Claims (7)

[Claims] 1. An image recording apparatus which performs image recording based on an electrostatic latent image formed on an image carrier having a positive photodischarge characteristic with respect to ambient temperature and humidity. A charging unit that has a positive charging characteristic for charging the image carrier to a predetermined initial potential before the electrostatic latent image is formed on the image carrier; and Exposure means for exposing the image carrier with an image signal light beam having a predetermined exposure energy to form the electrostatic latent image, and developing the electrostatic latent image formed by the exposure means with toner A developing means for forming an image; an exposure energy determined from an intersection of at least two positive photodischarge characteristics corresponding to at least two initial potentials fluctuating based on the positive charge characteristics; A control means for setting the predetermined exposure energy at a predetermined image area ratio between the exposure energy and the exposure energy, and causing the exposure means to perform exposure based on the image signal light beam. Recording device. 2. The image recording apparatus according to claim 1, wherein said control means sets said predetermined exposure energy with said predetermined image area ratio being 50%. 3. The developing device according to claim 1, wherein a potential of the electrostatic latent image at which the toner weight of the toner image is saturated is set to be equal to or lower than a potential of the electrostatic latent image formed by the predetermined exposure energy. 3. The image recording apparatus according to claim 2, comprising: 4. The image forming apparatus according to claim 1, wherein the charging unit is arranged near the image carrier.
2. The image forming apparatus according to claim 1, wherein the image carrier is charged to the predetermined initial potential by applying a constant voltage by contact.
Item. 5. An image recording apparatus for recording an image based on an electrostatic latent image formed on an image carrier having a positive photodischarge characteristic with respect to ambient temperature and humidity, comprising: A charging unit that has a positive charging characteristic for charging the image carrier to a predetermined initial potential before the electrostatic latent image is formed on the image carrier; and Exposure means for exposing the image carrier with a light beam having a predetermined exposure energy for a time corresponding to an image signal to form the electrostatic latent image having an intensity modulation area and an area modulation area, and Developing means for developing the formed electrostatic latent image with toner to form a toner image; and at least two positive photodischarges corresponding to at least two of the initial potentials varying based on the positive charging characteristics. Special The predetermined exposure energy is set so that the exposure energy of the region that shifts from the intensity modulation region to the area modulation region is between the exposure energy determined from the intersection of the exposure energy and the exposure energy larger by a predetermined value. An image recording apparatus comprising: a control unit for causing the exposure unit to perform exposure based on the light beam. 6. The electrostatic image forming apparatus according to claim 1, wherein the developing unit is configured to control the electrostatic latent image formed by exposure energy in a region where the potential of the electrostatic latent image at which the toner weight of the toner image is saturated transitions from the intensity modulation region to the area modulation region. 6. The image recording apparatus according to claim 5, wherein the image recording apparatus has a configuration set to be equal to or lower than the potential of the latent image. 7. The image forming apparatus according to claim 1, wherein the charging unit is provided near the image carrier.
6. A structure in which the image carrier is charged to the predetermined initial potential by applying a constant voltage by contact.
Item.