JPH03251856A - Picture forming method - Google Patents

Abstract

PURPOSE:To prevent the splashing of a toner and to obtain a high-density and high-resolution picture by specifying the surface-area average particle diameter, absolute value of the average surface charge density and absolute value of the average surface charge density of the unexposed part of an a-Si-based photosensitive body at its developing position. CONSTITUTION:An electrostatic latent image formed on an a-Si-based photosensitive body is developed with a developer consisting of at least a toner and a carrier. The surface-area average particle diameter of the toner is controlled to 2-8mum, the absolute value of the average surface charge density to 3-7nC/cm<2> (where nC is nanocoulomb) and the absolute value of the average surface charge density of the unexposed part of the photosensitive body at its developing position to 80-400nC/cm<2>. A high-resolution picture is obtained without splashing the toner by using such a two-component developer contg. fine particles. Since the average surface charge density at the unexposed part and the average surface density of the toner are limited, a high-quality picture excellent in resolution and picture density is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an image forming method comprising the step of developing an electrostatic latent image formed on an amorphous silicon photoreceptor with a developer consisting of at least a toner and a carrier. It is related to.

Conventionally, photoreceptors used in electrophotography include photoreceptors using inorganic semiconductors such as zinc oxide and cadmium sulfide, selenium-based photoreceptors, and photoreceptors using organic semiconductors. . Research and development of these photoreceptors has already progressed, and they have been put into practical use by being incorporated into image forming apparatuses such as copying machines and printers.

However, all of these photoreceptors have poor chemical and mechanical durability on the surface of the photosensitive layer, and are subject to decomposition, abrasion, and deterioration due to light, corona discharge, temperature and humidity, cleaning, developing operations, etc. during the repeated image formation process. The problem is that it is easy to do.

On the other hand, in the electrophotographic industry, there is a demand for improved image quality.
In particular, images with high resolution are required.

In order to meet the above-mentioned demand, there is a possibility of making the toner in the developer into fine particles. For example, research and development of fine particle toner having an average particle size of 10 μm or less is progressing. Incidentally, the smaller the toner particle size, the more strongly it adsorbs to the surface of the photoreceptor, making it difficult to clean it in a cleaning process. Therefore, fatigue deterioration of the photoreceptor is further accelerated.

Therefore, for example, Japanese Patent Application Laid-open No. 63-13054 discloses that an amorphous silicon-based photoreceptor (hereinafter simply referred to as aSi photoreceptor) is used, and the electrostatic latent image formed on the surface is An image forming method has been proposed in which image formation is performed by developing with a two-component developer containing fine particle toner. It is known that the a-5i photosensitive material is originally non-polluting and has excellent durability, corona discharge resistance, and moisture resistance.In addition, the surface of the photosensitive layer is strong, such as Vickers hardness. 100 compared to 60% selenium-based photoreceptor
0 to 1200, which makes it a highly durable photoconductor, and because cleaning can be done by bringing the cleaning member into sufficient pressure contact with the photoconductor, toner sticks to the photoconductor and deteriorates due to fatigue, so-called toner filming. However, from this point of view as well, it is considered to be advantageous compared to other photoreceptors.

However, the a-5i photoreceptor is a selenium-based photoreceptor,
The dielectric constant of the photosensitive layer is higher than that of other photoreceptors such as organic photoreceptors. For example, while the other photoreceptors have a dielectric constant of 3 to 4, the aSi photoreceptor has a dielectric constant of 10 to 13. Therefore, the ratio of the amount of charge effective for development on the photoreceptor is small, resulting in poor developability, insufficient image density, and, moreover, problems such as toner scattering when using fine particle toner. Ru.

The problems of image density and toner scattering have conventionally been considered to be closely related to the surface potential of the photoreceptor, the toner particle size, the amount of charge of the toner, etc., and their control is extremely complicated and not easy.

As a measure to improve the developability of the photoreceptor, it is possible to increase the layer thickness of the photosensitive layer, but since the manufacturing cost of the a-5i photoreceptor is high, the layer thickness of the photosensitive layer is at most 5.
The thickness is set to be 0 μm or less, and improvements in the material and layer structure are desired.

By the way, when forming an image by electrophotography, the resolution and density of the image are important factors that affect the quality of the image.The particle size of the toner is important for the resolution of the image, and the particle size of the toner is important for the image density. As mentioned above, characteristics such as the surface charge density of the photoreceptor, the particle size of the toner, and the amount of charge of the toner are important, and in particular, control of the amount of charge of the toner is important.

Conventionally, the amount of charge on toner is determined by the amount of charge q relative to the weight of the toner.
/M (q is the amount of charge and M is the weight) has been used. However, when the above-mentioned q/M is used as the amount of charge of the toner, it is difficult to control the image density because the above-mentioned characteristics have a complicated relationship, and the desired image density cannot be stably obtained. There was a problem.

Therefore, for example, Japanese Patent Laid-Open No. 1-193869 proposes a method in which the amount of charge q/S relative to the surface area S of the toner is used as the amount of charge of the toner.

This method has the advantage that the above-mentioned characteristics are simple and have a universal relationship, making it easy to manage image density.

However, the above publication describes a one-component developer containing a non-magnetic toner as a developer, and the particle size is 12.6 μm.
A toner with a relatively large particle size is used, and the technical field is different from that of the developer used in the present invention. Further, there is no particular description regarding the photoreceptor.

C0 Purpose of the Invention The purpose of the present invention is to prevent toner scattering when forming an image by applying a developer containing fine particle toner and a carrier to an amorphous silicon photoreceptor such as the above-mentioned a-5i. The object of the present invention is to provide an image forming method that can stably supply images with high density and high resolution.

20 Structure of the Invention The present invention provides an image forming method comprising a step of developing an electrostatic latent image formed on an amorphous silicon photoreceptor with a developer consisting of at least a toner and a carrier. is 2 to 8 μm, and the absolute value of the average surface charge density is 3 to 7 nC/ci (where nC is nanocoulomb, the same applies). The absolute value of the average surface charge density of the exposed area is 80 to 400 nC/c.
The present invention relates to an image forming method characterized by using wt.

That is, in the image forming method of the present invention, after applying a charge to a photoreceptor such as a tram-shaped or heald-shaped photoreceptor, an electrostatic latent image is formed by performing imagewise exposure using an analog method or a digital method. It includes a step of performing regular development or reversal development using a particularly two-component developer containing fine toner particles with a particle diameter of 2 to 8 μm, and enables high-resolution image formation by using the fine toner particles.

In addition, in the present invention, in order to make it possible to form a high-quality image with excellent resolution, image density, etc. without toner scattering using a two-component developer containing fine particle toner in the above-mentioned specific range, development is required. The average surface charge density σ of the non-exposed part of the photoreceptor at the position is the absolute surface charge density q/S in absolute value 3
It is defined in the range of ~7nC/cffl. That is, conventionally, the surface potential of the photoreceptor has been used as a characteristic value representing the charge of the photoreceptor, but what is directly related to development is the amount of charge on the surface of the photosensitive layer during development, and the surface potential of the photoreceptor is Even if they are the same, the amount of charge fluctuates and is not constant depending on changes in layer thickness, dielectric constant, etc. Therefore, in the present invention, the amount of charge on the surface of the photosensitive layer is defined by the average surface charge density σ in the specified range. Further, the amount of charge of the toner is defined by the average surface charge density q/S in the specific range, which has a direct relationship with the average surface charge density σ of the photoreceptor.

In this way, image quality during image formation can be easily managed, image density can be controlled with extremely high precision, and toner scattering can be prevented.

Furthermore, the surface of the a-5i photoreceptor is harder and denser than other photoreceptors, and has excellent light resistance, moisture resistance, corona ion resistance, mechanical abrasion resistance, etc. In addition, since a strong leaning operation is possible, there is no fatigue deterioration during repeated image formation many times, and the photoreceptor is highly durable.

Therefore, according to the image forming method of the present invention, high resolution, high density, and clear images can be stably obtained even during image formation many times.

The image forming method of the present invention will be specifically explained below using, for example, an analog image forming apparatus shown in FIG. 1 and a digital image forming apparatus shown in FIG.

In FIG. 1, a document 2 on a document table 1 is illuminated by light sources 3 (3a, 3a,
3b) in the direction of the arrow X, and the scanning light passes through the mirror groups 4a, 4b, 4c, 4d and the lens 5 as shown in the imaginary line, and the average surface when it reaches the development position after being charged by the charger 6 in advance. The absolute value of charge density is 80 to 400 n
a given a −-like charge so that it becomes C/cIIY
The -Si photoreceptor drum 10 is irradiated with imagewise light to form an electrostatic latent image. This electrostatic latent image is regularly developed by a magnetic brush method by a developing device 7 containing a two-component developer consisting of a magnetic carrier and a non-magnetic fine particle toner having a surface area average particle size of 2 to 8 μm, and is then developed on the photoreceptor drum 10. A toner image is formed thereon. Therefore, reference numeral 7a denotes a magnetic brush developing roll in the developing device 7, which magnetically attracts and conveys the developer in the developing device and develops it by bringing it into contact with the surface of the photoreceptor drum. The absolute value of the average surface charge density of the toner in the developer layer is 3 to 7 nc/cra
The composition of the developer, the particle size, shape, etc. of the toner and carrier are selected so that Thus, the photoreceptor drum 10
A high-density, high-resolution toner image is formed thereon, and this toner image is transferred to the transfer pole 8 onto the transfer paper that has been conveyed from the paper feed cassette 13 via the paper feed roll 14 and the registration roll 15. It is transcribed by action.

The transfer paper carrying the transferred toner is separated by the action of the separation pole 9, conveyed to a fixing device 17 by a conveyor belt 16, fixed, and discharged to a paper discharge tray 19 by a paper discharge roll 18. The surface of the photoreceptor drum 10 after the transfer is cleaned by the cleaning blade 11a of the cleaning device 11,
Stone prepared for the next statue formation.

Note that a probe 40 is set in place of the developing device 7, and the potential of the non-exposed area is picked up by the probe when it comes to the development position after charging, is read by the surface electrometer 41, and this is recorded by the recorder 42. Due to the photoreceptor surface potential■
, is measured.

Next, FIG. 2 shows a digital image forming apparatus.
Components common to those in FIG. 1 are given the same reference numerals. The image forming apparatus shown in FIG. 2 is roughly divided into a document reading section A, a writing section, and an image forming section C. In the reading section A, the document 2 on the document table 1 receives light #3 and a reflecting mirror 4a. , 4b and 4
The optical information obtained by optical scanning by the lens 5
The image is formed on the photoelectric conversion element 20 via the photoelectric conversion element 20, and converted into an electric signal. This electrical signal is processed by A in the signal processing device 21.
/D conversion and multi-value (binarization) processing are performed, and the obtained image signal is output to the writing device 22 of the writing section using an LED or a laser device or the like.

Image modulation of a semiconductor laser is usually performed by the image signal;
The obtained modulated laser beam is linearly scanned by a polygon mirror to imagewise expose the a-5i photosensitive drum 10 in the form of dots like a virtual line. The photoreceptor drum 10 is charged in advance with a charger 6 in the same way as in the case of FIG. 1, and has an average surface charge density of 80 to 400 nC/crl when measured at the development position after charging, An electrostatic latent image is formed by the imagewise exposure. This electrostatic latent image is reversely developed in a state where a DC bias 12 close to the surface potential of the photoreceptor drum is applied to the developing device 7 containing the same two-component developer as in the case of FIG. A dot-shaped toner image is formed thereon, and is transferred and fixed onto a transfer sheet fed at the same timing to form an image. Further, as in the case of FIG. 1, the surface of the photoreceptor after transfer is cleaned by a cleaning device and prepared for the next image formation.

a constituting the photoreceptor used in the image forming method of the present invention
-5i nausea photo originally has dangling bonds in the cough layer, has many localized levels, and has poor photoconductivity, so hydrogen atoms (H ), or by introducing halogen atoms (X) or the like to block the dangling bonds, desired photoconductivity is imparted.

Furthermore, in order to increase the dark resistance of the photoreceptor and improve the charging characteristics, carbon atoms (C), oxygen atoms (0), and nitrogen atoms (N) are added.
It is desirable to introduce modifying atoms (Y) such as Y into the a-Si layer.

The a-8i photoreceptor according to the present invention may be a photoreceptor in which a single-layered photoreceptor layer is provided on a substrate, or it may be a functionally separated photoreceptor with a carrier generation layer and a carrier transport layer. The photoreceptor may have a photosensitive layer having a laminated structure in which the photoreceptor and the photoreceptor are laminated on a substrate. Further, in the photoreceptor having a single layer structure or a laminated structure, a blocking layer may be provided between the substrate and the photosensitive layer in order to prevent carrier injection from the substrate and improve sensitivity and charging ability. Further, a surface modification layer may be provided for the purpose of protecting the surface of the photosensitive layer. Furthermore, an intermediate layer can be provided between the carrier generation layer and the carrier transport layer of the photoreceptor having the laminated structure to improve carrier injection efficiency.

Next, FIG. 3 shows an example of the layer structure of the a-5i photosensitive layer according to the present invention. The internal configuration will be explained in more detail below. Note that the layer structure in FIG. 3 shows an example in which the charge polarity is positive; for example, AI! A drum-shaped substrate 3 consisting of , etc.
A-5i bad sensitivity photo 1o is constructed by sequentially laminating a P'' type carrier blocking layer 32, a carrier transport layer 33, an intermediate layer 34, a carrier generation layer 35, and a surface modification layer 36 on the photosensitive layer 1.

The P type carrier bronking layer 32 has the first [
a-3i heavily doped with a group IA element (boron, aluminum, potassium, etc.) and containing at least one modification atom (Y) such as a carbon atom, an oxygen atom, a nitrogen atom, etc.
:C:H(X) layer, a-5i :C:O:H(X) layer, a-5i:N:H(X) layer, a-5i: N:
○: H(X) layer, a-5i: O: H(X) layer,
a-5i:C:N:H(X) layer, aSi:C:O:N:
Preferably, it is composed of an H(X) layer or the like. The content of the modifying atoms (Y) is preferably 0.5 to 40 atm%. Further, the thickness of the Carrier Pro 7 King layer 32 is 0.
．． 01 to 5 μm is preferable.

The carrier transport layer 33 is lightly doped with a group mA element of the periodic table, and, like the carrier blocking layer 32, contains at least one type of modifying atom (Y) such as a carbon atom, an oxygen atom, or a nitrogen atom. -Si:Y:H(X) layer is preferred. The content of the modifying atoms (Y) is preferably 0.5 to 4 atm%. In addition, charging ability,
Boron atoms may be introduced to improve sensitivity. The thickness of the carrier transport layer 33 is preferably 5 to 50 μm.

The intermediate layer 34 is provided as necessary to improve the carrier injection efficiency, and is made of, for example, an a- 5i:Y:H(X) layer is preferred. Moreover, it is preferable that the content ratio of the modifying atoms (Y) is smaller than that of the carrier transport layer 33. in particular,
0.01 to 20 atm% is preferred. Also, the middle layer 34
It is preferable to lightly dope an element of Group IIA of the periodic table. The thickness of the intermediate layer 34 is preferably 0.01 to 5 μm. The intermediate layer 34 may be a laminate of two or more layers.

The carrier generation layer 35 may be formed using the periodic table No. 111A as necessary.
Preferably, the a-5i:H(X) layer is lightly doped with a group element. Furthermore, in order to improve charging ability, boron atoms may be introduced to make the material intrinsic, thereby increasing resistance and improving carrier mobility. The thickness of this carrier generation layer 35 is preferably 5 to 50 μm.

The surface modification layer 36 is an a-5i:H(X) layer formed by introducing halogen atoms (X) such as hydrogen atoms and/or fluorine atoms into the a-5i layer to block dangling bonds. Furthermore, modifying atoms such as carbon atoms, oxygen atoms, and nitrogen atoms (
It is preferable to construct the a-5i :Y:H(X) layer into which Y) is introduced.

Specifically, a-5i: C: H(X) layer, a-3
i:C:O:H(X) layer, a-5i:N:H(X
) layer, a-3i:O:H(X) layer, a-5i: N
: O: H(X) layer, a-5i: C:N: H
(X) layer, a-5i :C:N:O:H(X) layer, and various other structures can be adopted. In the surface modified layer 36, modified atoms such as carbon atoms, oxygen atoms, nitrogen atoms, etc.
Y) The content ratio is 40 to 40% when the total of silicon atoms and modified atoms (Y) is 1100 at%.
A ratio of 90 atm% is preferable. The thickness of the surface modified layer 36 is preferably 400 to 1 μm.

In addition, if necessary, a carrier generation layer 35 and a surface modification layer 3 may be added.
A second intermediate layer may be provided between the two layers.

It is preferable that the second intermediate layer has a lower content of modified atoms (Y) than the surface modified layer 36.

The thickness of the entire photosensitive layer is usually 20 to 5 mm from the viewpoint of manufacturing cost.
It is preferable to set it to 0 μm.

It is preferable that halogen atoms (X) such as hydrogen atoms and/or fluorine atoms are introduced into each of the above layers constituting the a-5i bad sensitivity photo 10. In particular, it is important to contain hydrogen atoms in the carrier generation layer 35 in order to block dangling bonds and improve photoconductivity and charge retention. Specifically, the content ratio of hydrogen atoms is 10 to 30 at
m% is preferred.

The content ratio of hydrogen atoms in the surface modified layer 36 and in the intermediate layer 3
4. Carrier blocking layer 32, carrier transport layer 33
The same applies to . In addition, as impurities for controlling the conductivity type, in addition to boron, aluminum, gallium, indium, thallium, etc.
I[Group A elements can be used.

In order to seal dangling bonds during the formation of each layer constituting the a-5i bad photosensitive photosensitive material 10, a halogen atom, such as a fluorine atom, is introduced in the form of 5IF4 instead of or together with a hydrogen atom. :F,,a-5
i: H+F,, a-5i: C+F.

a Si:C:H:F,, a Si:C:○:FX
A layer structure such as aSi:C:0:H:F may also be used. In this case, the content ratio of fluorine atoms is 0.5 to 1
0 atm% is preferred.

Each layer constituting the a-5i5 light body 10 can be formed using, for example, a glow discharge decomposition method, a sputtering method, an ion blating method, or a method of evaporating silicon in a state in which activated or ionized hydrogen is introduced in a hydrogen discharge tube (Unexamined Japanese Patent Publication No. 1972-
78413) or the like.

The above is an explanation for the case where the charge polarity of the a-5i nausea photo 10 is positive, but when the charging polarity of the a-3i nausea photo 10 is negative, the carrier bronking layer 32, the carrier transport layer 33 , the intermediate layer 34, the carrier generation layer 35, and the surface modification layer 36, the dopant introduced into each layer may be changed to an element of Group VA of the periodic table (phosphorus, arsenic, antimony, bismuth, etc.). Note that the carrier blocking layer 32 and the intermediate layer 34 are provided as necessary, and may be omitted.

Further, the carrier transport layer 33 and the carrier generation layer 35 may not have a separate layer structure but may have a single layer structure.

The base body 31 may be formed of either conductive or insulating material. Examples of the conductive material include metals such as stainless steel, aluminum, chromium, molybdenum, iridium, tellurium, titanium, platinum, and palladium, and alloys thereof. Insulating materials include polyester, polyethylene, polycarbonate,
Examples include films or sheets of synthetic resins such as cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and polyamide, glass, ceramics, and paper. When using an insulating material, it is preferable that its surface be electrically conductive treated. Specifically, for example, in the case of glass, it is conductive treated with indium oxide, tin oxide, etc., and in the case of synthetic resin films such as polyester films, it is treated with aluminum, silver, lead, nickel, gold, chromium, molybdenum, iridium, niobium, etc. , tantalum, vanadium, titanium, platinum, etc., can be subjected to a conductive treatment by a method such as vacuum evaporation, electron beam evaporation, or sputtering, or by laminating with the above-mentioned metals.

The shape of the conductive substrate 31 can be selected from various shapes such as a cylindrical shape, a belt shape, and a plate shape.

When forming images continuously at high speed, an endless belt shape or a cylindrical shape is preferable. The thickness of the base body 31 is not particularly limited, and is appropriately selected from the viewpoints of manufacturing, handling, mechanical strength, and the like.

The preferred a-3i photosensitive layer structure used in the present invention is as described above, and when such a layer structure is used, the photosensitive layer has a high dark resistance and a high charging ability at a normal layer thickness of 50 μm or less. , the average surface charge density during charging, which is a feature of the present invention, is 80-400 nC/cf (preferably 110-400 nC/cf).
A photoreceptor can be obtained that fully satisfies the condition of 300 n C/Cl11).

If the average surface charge density is less than 80 nC/cn (nC/cn), developability is poor, the desired amount of toner does not adhere during development, the image density is insufficient, and toner scattering is likely to occur. When the average surface charge density exceeds 400 nC/cnl, the average surface charge density is too high and the resolution during image formation decreases.Especially when a surface modified layer having the above structure is provided, the dark resistance of the photosensitive layer is 1012 to 1O13Ω-cm (normal a-5i: 108 to 109Ω-cm in H layer
), the charging ability of the a-Si photoreceptor is greatly increased,
A sufficient surface charge density of 180 to 4001 nC/crl is ensured.

Note that the average surface charge density σ(nC
/afl) is the relative dielectric constant ε of the photosensitive layer, and the vacuum dielectric constant to
(8,85X10-I4C/V-cm), layer thickness L (
μm) Surface potential Vs (volts) is measured respectively, 2:σ=
(εε./L)Vs.

The surface charge density σ(nC/c+fl
) and the surface potential V (volts) of the photoreceptor when it is charged is determined by the thickness L (μm) of the photosensitive layer and the dielectric constant εε. The surface potential applied to the photoreceptor is usually 300 to 800 V, preferably 400 V.
~600■.

Next, as the developer used in the present invention, a two-component developer is used which has excellent developer fluidity and triboelectric chargeability, and therefore also has excellent developability. As such a two-component developer, one consisting of non-magnetic fine particle toner and magnetic carrier particles is preferably used.

In order to obtain the non-magnetic fine particle toner, two colorants such as carbon blank are added to the thermoplastic or thermosetting resin described later.
0wt% or less, if necessary, a charge control agent is mixed with 5wt% or less, melted, kneaded, cooled, pulverized, classified, and further heat-treated if necessary to form insulating particles with a volume resistance of 1014Ω-cI11 or more and a surface area. The particles have an average particle diameter of 2 to 8 μm. Alternatively, a spherical toner may be obtained by polymerizing the colorant and other additives contained in a binder resin monomer while stirring.

Examples of the binder resin used in the toner include addition polymerization resins such as styrene resin, styrene-acrylic resin, styrene-butadiene resin, and acrylic resin, polyester resin, polycarbonate resin, polyamide resin, polysulfonate resin, and polyurethane resin. Examples include condensation polymerization resins and epoxy resins.

Among these resins, monomers for forming addition polymerization type resins include styrenes such as styrene, 0-methylstyrene, m-methylstyrene, p-methylstyrene, and 3,4-dichlorostyrene; ethylene, Ethylenically unsaturated monoolefins such as propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl fluoride; vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, etc. Vinyl esters; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methacrylic acid -n-octyl, dodecyl methacrylate, lauryl methacrylate, methacrylic acid-
α- such as 2-ethyl-xyl, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, etc.
Methylene aliphatic monocarboxylic acid ester; acrylic acid such as acrylonitrile, methacrylonitrile, acrylamide, or methacrylic acid 'J/L' acid ff11,
Vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; N-vinylpyrrole, N
- N-vinyl compounds such as vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone; monoolefin monomers such as vinylnaphthalenes; propadiene, butadiene, isoprene, chlorobrene, pentadiene,
Examples include diolefin monomers such as hexadiene. These monomers can be used alone or in combination of two or more. Furthermore, examples of monomers for forming the condensation type resin include ethylene glycol, triethylene glycol, 1,3-propylene glycol, and the like.

In addition, as a charge control agent, JP-A Nos. 59-88743, 59-88745, 59-79256, 5
No. 978362, No. 59-228259, No. 59-1
Negative charge control agents are described in each publication of No. 24344;
Positive charge control agents are described in the publications No. 204850 and No. 59177571, and any of these can be used.

Further, in order to prevent offset development due to toner adhesion to the fixing roller, a low molecular weight polyolefin (polypropylene, polyethylene, Wanx, etc.) may be contained in the binder resin in an amount of 0 to 5 wt%.

In addition, 0 to 3 wt% of hydrophobic silica is added to the toner for the purpose of imparting developer fluidity and other charge control properties (negative).
Can be added externally.

By the way, in order to achieve high-resolution image formation, the toner of the present invention has a surface area average particle diameter of 2 to 8 μm (
The toner particle surface has a specific surface charge density of 180 to 40 μm, preferably 3 to 7 μm).
(l n C/cn!, preferably 110-300 n
An average surface charge density of 3 to 7 nC/cfI (preferably
3-5 nC/cffl).

When the surface area average particle diameter of the toner is less than 2 μm, images tend to fog and toner scatters.
If it exceeds 8 μm, the resolution of the image will decrease. Furthermore, when the surface charge density of the toner is less than 3n C/ci,
Since toner scattering increases and image density decreases when it exceeds 7 nC/a+7, it is essential that the toner in the present invention has a particle size and surface charge density within the above ranges.

Next, methods for measuring each of the above physical properties will be explained.

(1) To obtain the surface area average particle diameter (d) of the toner, first, the volume-based particle size distribution is measured using "Coulter Counter Model TAU" manufactured by Coulter Electronics.

Next, assuming a spherical shape, the volume-based particle size distribution is converted into a surface area-based particle size distribution. From this surface area-based particle size distribution, 50% of the total surface area (integral value) of the toner
The (median) particle size giving the following is obtained, and this is taken as the surface area average particle size (d) of the toner. Here, the average surface area 5 (cffl) of the toner can be obtained by converting the particle size distribution based on the surface area.

For reference, the measurement method of the Coulter counter TAff type will be explained below with reference to FIG. This measurement method is also called the pore passage method, the electrozone method, or the Coulter method after the name of the inventor, and has conventionally been most frequently used in the measurement of toner particles. To measure using this method, first disperse and suspend the toner in an electrolyte solution, create a partition wall with pores as shown in the figure, apply a voltage to both sides of the partition wall, and then pass the suspension through the pores. The toner in the liquid also passes through, and the electrical resistance of the pores changes depending on the size of the particles, which is observed as a pulse. By measuring this pulse, a volume-based distribution can be obtained.

(2) Average surface charge density (q/S) of the toner
To measure the toner, first calculate the average charge q of the toner in nC (nanocoulombs) by using the apparatus shown in Figure 5 in the following development process.
Measure in units of. That is, the collected sample developer is magnetically attracted to the magnetic sleeve roll of the apparatus shown in FIG. AC1DC
A bias is applied, causing the toner in the developer to fly from the sleeve surface to the copper plate surface and adhere thereto. Here, by rotating the magnetic sleeve roll once, all the toner in the developer on the outer periphery is transferred to the copper plate. Since there is charged toner on the surface of the copper plate, a mirror image charge of the same amount and opposite sign is generated, so when the charged toner on the copper plate is blown off with an N2 gas injector, the mirror image charge flows into the coulomb meter. , its charge amount q (nC) is measured. Before blow-off, the weight M (g) of the toner is determined by measuring the difference in weight between the copper plate alone and the copper plate supporting the toner. Further, the specific charge amount q/M can usually be measured using a method called a blow-off method to obtain an equivalent value.

Thus, the average specific charge of the toner q/M (nC/g
)-P is measured. To calculate the average surface charge density q /S (n C/cJ) of the toner from this value, first (
The average surface area s (cf
fl) is obtained from PXM/S.

As the carrier for the two-component developer used in the present invention,
A toner that can stably impart the above-mentioned specific surface charge density to the toner is selected, and the magnetic material may be used as is, coated with a resin or the like, or mixed with a resin as a fine powder. However, it is preferably a coated carrier in which the surface of magnetic particles is coated with a resin. The magnetic material includes substances that are extremely strongly magnetized in the direction of a magnetic field, such as metals such as iron, cobalt, and nickel, ferrite, magnetite,
Alloys or compounds containing ferromagnetic elements such as iron, cobalt, and nickel, including hematite, or alloys that do not contain ferromagnetic substances but become ferromagnetic through appropriate heat treatment, such as manganese. A Heusler alloy containing manganese and copper such as copper-aluminum or manganese-copper-tin, chromium dioxide, or the like is used.

The surface area average particle diameter (d) of the carrier is 40 to 120
The resistivity of the carrier is 108 Ω to prevent charge from being injected into the carrier by the bias voltage and adhering to the image forming surface, or from leaking the bias voltage and causing the latent image charge to disappear. -cm or more, preferably 10" ohm-cm or more, and more preferably 10" ohm-cm or more.

Note that the specific resistance of the carrier (or toner) is
, after tapping in a container with a cross-sectional area of 5 ctA, a load of 1 kg/ctl was applied on the packed particles, and a voltage of 102 to 105 v/c1 was applied between the load and the bottom electrode.
It is determined by applying a voltage that causes electrolysis, reading the current value flowing at that time, and performing a predetermined calculation. At this time, the thickness of the carrier (or toner) particle layer is about one layer.

In addition, the carrier used in the present invention has a spherical shape in order to improve the fluidity of the developer, improve the triboelectric charging property between the carrier and the toner, and make it difficult for blocking to occur between carrier particles or between the carrier and the toner. It is preferable that the

In order to obtain such a spherical carrier, for example, in the case of a resin-coated carrier, for example, styrene-acrylic resin is coated with styrene-acrylic resin in a thickness of 0.1 to 2 μm (0.5 to 5 tnt based on the weight of the carrier) on magnetic particles that have been previously formed into a spherical shape. %), and in the case of a resin-dispersed carrier, the dispersed particles made by dispersing 30 to 70-t% of magnetic fine powder in a resin may be heat-treated to make them spherical, or Spherical particles may be directly produced by spray drying.

The two-component developer is a mixture of the carrier and toner in a weight ratio of (98 to 85): (2 to 15), and if necessary, hydrophobic silica in an amount of 0.1 to 3% by weight based on the toner; A fluidizing agent such as colloidal silica and silicone varnish, and a cleaning aid such as a fatty acid metal salt and a fluorine-based surfactant may be added.

(3) Here, the surface area average particle diameter (
d) is measured by a light scattering method using a Microtrunk Particle Size Monitor Model 7981-X3 (manufactured by Lees & Northra, Inc.). In this light scattering method, the "Mie" or "Matxwell" electromagnetic equation is applied to the light scattering phenomenon of spherical particles, and the measurement is performed using the apparatus shown in FIG. 6 based on the measurement principle.

Figure 6 shows an outline of the measurement principle. He-Ne: When a light beam from a gas laser hits a sample cell, the light is scattered by particles in the sample cell. When this scattered light is focused by the lens 1, a Franhofer diffraction image appears on the focal plane of the lens.

In reality, since there are many particles in the laser beam, a superposition of diffraction images of individual particles will appear.

The light intensity distribution of the diffraction image depends on the particle diameter if the wavelength of the light hitting the particles is constant. Therefore, if the intensity distribution of this light is measured by some method, it can be easily replaced with the particle size distribution of the sample.

The detailed structure of the image forming method of the present invention is as described above. Among them, the surface charge density σ(nC
/cffl) and toner surface charge density q/5 (nC/
c+fl) is shown in absolute value. If a positively charged photoreceptor is used, the sign of the surface charge density σ of the photoreceptor is positive, and the sign of the toner is negative when regular development is performed using the analog image forming apparatus shown in Figure 1. In the case of reversal development using the digital image forming apparatus shown in FIG. 2, it is considered positive.

Further, if it is a negatively charged photoreceptor, a sign opposite to the above is given.

E. EXAMPLES The present invention will be specifically explained by examples below, but the embodiments of the present invention are not limited thereto.

(Example 1) The a-5i photoreceptor of this example is a positively charging photoreceptor manufactured by a known glow discharge method, and has the layer structure shown in FIG. 3, and the specific structure of each layer is as follows. It is.

(1) Base 31 A drum-shaped aluminum base with a diameter of 108 mm (2)
Blocking layer 32 (P” type) P with a thickness of 1 μm
a-5i of type ゛: C: H layer, carbon atom concentration (C) -10 atm% (however, silicon atom concentration 1:S
i) carbon atom concentration [C] = 100 atm%).

(3) Carrier transport layer 33 Boron-doped a-5i with a thickness of 15 μm: C:
It is an H layer, and the carbon atom concentration (C) is 10 atm%.

(4) Intermediate layer 34 Boron-doped a-5i with a thickness of 0.5 μm: C:
It is an H layer, and the carbon atom concentration (C) is 5 atm%.

(5) Carrier generation layer 35 A boron dope a-Si:H layer with a thickness of 15 μm.

(6) Surface modified layer 36 is an a-5i:C:O:H layer with a thickness of 0.3 μm, and has a carbon atom concentration [C) = 55 atm% and an oxygen atom concentration [0]-1 atm% (however, Silicon atom concentration (S
i) Ten carbon atom concentration [C] + oxygen atom concentration CO) =
1100at%).

Next, the developer used in this example is as follows.

(1) Preparation of toner After thoroughly mixing the above materials in a ball mill for 5 hours,
The mixture was kneaded using two rolls at 170°C. Next, after being left to cool naturally, it was coarsely pulverized with a Cantermill, further pulverized with a fine pulverizer using a jet stream, and then classified with an air classifier while changing the classification conditions to obtain a surface area average particle size of 1.3 μm. ~9.5
Seven types of toners with different particle sizes in the μm range were obtained, and these toners were tested No. 1 to No. 7 (see Table 1 below).
And so. In addition, for the next test No. 8 to No. 13, toner for the previous test No. 4 (particle size 5.5μ) was used.
Separate and take out 8 parts of toner from m) and further test Nos.
Eight portions of toner (particle size: 6.8 μm) were separated and taken out to prepare a total of 21 types of toner.

(2) Preparation of carrier Dissolve 5 parts by weight of styrene-methacrylate (4:6) copolymer resin in 1 oz of toluene, mix with 100 g of ferrite particles with a surface area average particle size of 73 μm, and spray dry the mixture using a spray drying method. The film thickness after drying is 1μ.
A coated carrier coated with a resin was prepared so as to have a thickness of m, and this was divided into 21 pieces for the preparation of a developer later.

(3) Preparation of developer, test No. 1 to No. 7 with different particle sizes
Hydrophobic silica (Aerosil R-805) was added to the toner based on the correspondence data of silica amount and toner particle size shown in FIG. 9, and the average surface charge density of the toner was -4 , 0nC/ct6, 1.0 to 7.1% by weight of toner was added and mixed, and test No.
, No. 1 to No. 7, seven types of developers were prepared.

Next, test No. with the same particle size <5.5 μm,
Toners for Nos. 8 to No. 13 are all 1. Iht
% of silica is added, and the toner concentration is 1.0 to 1.0 so that when subjected to development, the surface charge density is in the 8 stages shown in Table 1 below.
Six types of developers, Test No. 8 to No. 13, were prepared by mixing the developer with the above-mentioned divided carrier while changing the amount to a range of 10-t%.

In addition, when preparing the developers of Tests No. 8 to No. 13, the relationship between toner concentration and toner surface charge density was measured in advance using a modified copying machine described later, and the obtained data was used. (FIG. 7) was used to prepare a developer exhibiting a desired toner charge density.

Next, the toners of Test No. 14 to No. 21 were all made to have a particle size of 6.8 μm, 0.91 wt% of silica was added, and the average surface charge density of the toner was -4, Toner 5.2 to be 0nC/crR
Eight types of developers, No. 14 to No. 21, were prepared by mixing wt% and t%.

A photographic test of this example was conducted as follows using the 21 types of developers prepared as described above.

An analog copying machine (see Figure 1) equipped with a charger, a contact magnetic brush developer, an electrostatic transfer device, and a blade cleaning device: Ll-Bix 5070 (manufactured by Konica ■), and the a-5i photoreceptor described above. Using a modified machine equipped with a drum, 21 types of live-action tests (including comparative tests) were conducted as shown in Table 1.

The environmental conditions during the test were room temperature and room temperature (temperature 20°C).
1 (relative humidity 60%), and in each test, image formation was performed continuously for 30 minutes, and based on the image evaluation method described later,
The density and resolution of the obtained images were evaluated, and the presence or absence of toner scattering was also evaluated, and the results are shown in Table 1.

When conducting a test using the developer of Test No. 14 to No. 21, the surface of the photoreceptor must be adjusted so that the surface charge density of the photoreceptor becomes the value of the eight levels of test No. 14 to No. 21 in Table 1. Image formation was performed by changing the potential in eight steps in the range of 180 volts to 1150 volts.

In addition, in order to perform the test of Nα14 to N0.21,
The relationship between the surface potential of the photoreceptor and the surface charge density of the photoreceptor was measured in advance using the modified machine, and the obtained data (
The test was carried out by applying a desired surface charge density to the photoreceptor using the photoreceptor (FIG. 8).

By the way, in order to measure the surface charge density of the photoreceptor, the first
As will be explained with reference to the figure, before image formation for each test, the developing device 7 is pulled out and a probe 40 is set in its place. The surface potential of the photoreceptor is determined by amplifying it, reading it with a surface electrometer 41, and recording it with a recorder 42.

was measured. After the test, pull out the photoreceptor drum and
Cut out a small piece, measure the film thickness L (μm) of the photosensitive layer,
Then, the capacitance C of the photosensitive layer was measured using a coulomb meter to give CL/ε. The specific inductivity was calculated from Here, the vacuum dielectric constant ε. is known. The above data is calculated using the formula σ=(
εε. /L)V.

The surface charge density σ of the photoreceptor was determined for each test.

Regarding the surface area average particle size of the toner and carrier, each particle size was measured based on the method described above when preparing the developer, and the average charge density of the toner was measured for each test after the development after image formation. The sample was collected and measured based on the measurement method described above.

Image evaluation method: (1) Image density A manuscript with a reflection density of 1.3 was copied, and the reflection density of the copied image was measured using a "Sakura Densitometer" (manufactured by Konica Corp.). In the evaluation, when the reflection density was 1.0 or more, it was rated "OJ", when it was 0.8 to 1.0, it was rated "Δ", and when it was less than 0.8, it was rated "x".

(2) Resolution In accordance with JIS Z4916, the number of evenly spaced lines per anus as a blade is 4.0, 5.0, 6.
Using a chart with 3 lines, 8.0 lines, 10.0 lines, 12.5 lines, and 16.0 lines, the copied image was visually judged, and the brightness at which the lines could be distinguished was displayed as the resolution.

(Visually observe the inside of the 3-toner scattering copying machine and the copied image. If there is almost no toner scattering and the image is in good condition, it is marked as "OJ." If there is some toner scattering, but it is at a practical level, it is marked as "△."
, Cases in which a large amount of toner scattering was observed and were problematic in practical use were marked as "×".

Table 1 (blank below) From Table 1, it can be seen that in the test according to the present invention, all characteristics such as image density, resolution, and toner scattering were excellent, but in the comparative test, at least one of the above characteristics was excellent. It is understood that it is bad and has no practical use. In particular, the following is clear from the above.

d=2 to 8 μm is a practical level, and 3 to 7 μm is good.

q/S -3~-7n C/CT1 is at practical level -3~-5nC/cIIN is good.

a = +80 to +400 n C/cell is a practical level.

+110~+300 n C/c++! is good.

(Example 2) The a-5i photosensitive drum of Example 1 was equipped with a three-color reader of blue, red, and black, a semiconductor laser writing device, a charger, a blue, red,
Digital electrophotographic copying machine (see Figure 2) equipped with three black contact-type reversal magnetic brush developing devices (modified non-contact type) and a blade cleaning device: U-Bix
Using a modified machine equipped with DC8010 (manufactured by Konica ■), using the following 21 types of developer as the developer,
Tests (including comparative tests) as shown in Table 2 were conducted.

In this embodiment, the reading device is used only for black images, a BK image signal is output to the writing device every rotation of the photoreceptor drum, only the black developing device is operated, and a DC bias of 150 to 1050 volts is applied. Image formation was performed on the bottom using a reversal development method. The developer used in this test was one in which the toner becomes positively charged due to friction with the carrier.

(1) Preparation of toner 400 d of toluene was put into the separable flask in step 21, and the air in the flask was replaced with nitrogen. Thereafter, the toluene in the flask was heated to reflux. Next, 132 g of styrene and n-butyl acrylate were placed in the flask.
1-48 g of benzoyl peroxide and 0.5 g of benzoyl peroxide were added, and the first stage polymerization reaction was carried out under reflux for 12 hours to produce a high molecular weight polymer component.

After 12 hours, styrene 18 was added to the flask.
A second stage polymerization reaction was carried out by dropping a mixture of 4 g of n-butyl acrylate, 56 g of monoacryloyloxyethyl succinate, 80 g of monoacryloyloxyethyl succinate, and 8 g of hendiyl peroxide over 2 hours.

After the dropwise addition of the mixture was completed, the second stage polymerization reaction was continued at reflux temperature for an additional hour to produce a low molecular weight polymer component. Then, add 8g of zinc oxide to the flask.
was added and stirred for 1 hour.

Thereafter, the solvent toluene was distilled off under reduced pressure to obtain a resin that was a reaction product of a polymer having a carboxyl group in its side chain and zinc oxide. 100 parts of this resin and 10 parts of carbon black (manufactured by Cabot, trade name "Mogal LJ")
and 3 parts of nigrosine dye, and after cooling, coarsely pulverized, further finely pulverized with a jet mill, and further classified with an air classifier to obtain a surface area particle size within the range of 1.3 to 9.5 μm, as described in the second section below. Eight types of toners having different particle sizes shown in the table were prepared and used for tests Nα1 to Nα8.

On the other hand, as a carrier for preparing a developer, a surface area average particle size of 4
A spherical iron powder carrier of 0 μm was prepared and divided into 21 parts to be used for preparing a test developer. The toners of Tests No. 1- No. 8 were all combined with the carrier so that the average surface charge density of the toners was +
4.1nC/c+fl mixed to give tesl-
Eight types of developers No. 1 to No. 8 were prepared.

Next, among the eight types of toner, the surface area average particle diameter was 5.4.
From the μm toner (Test No. 5 toner), 7 parts of toner were further separated and tested) No. 8 to Nα1
When these seven portions of separated toner are subjected to development, the toner content is varied so that the seven levels of surface charge density shown in Table 2 are obtained, and the toner content is varied and mixed with the aforementioned divided carrier to form eight types of separated toner. Developers were prepared, and these were used as developers for test Nα8 to series 14.

Also, among the eight types of toners, the surface area average particle size was 6.7.
From the μm toner (toner of test Nα6), two portions of toner were further separated and taken out for test Nos. 15 to No. 021. This one portion of toner has an average surface charge density of +4.1n C/c with the iron powder carrier.
Test Nα15 to N021 mixed so that lr
A developer was obtained.

The 21 types of developers thus prepared and the DC801
0 modified machine, 21 types of tests were conducted according to the test order shown in Table 2, based on the same test method, test conditions, measurement method, and evaluation method as in Example 1, and the results were summarized in the second example.
Shown in the table.

Incidentally, images were formed by using the developers of Test No. 15 to No. 21 and changing the surface potential of the second photoreceptor in the range of 180 volts to 1150 volts.

(Left below) From Table 2, it can be seen that in the test according to the present invention, the characteristics such as image density, resolution, and toner scattering were all above the practical level, whereas in the comparative test, at least one of the above characteristics was poor. It is understood that this is not practical.

9. Effects of the Invention As is clear from the above explanation, the image forming method of the present invention uses a developer containing fine particle toner, uses a highly durable a-5i bad-sensitizing light, and is effective in forming an image. The surface charge density of the toner and photoconductor, which have a close relationship with each other, is selected within the optimal range, making it possible to form images with high density and high resolution, while also reducing fatigue during repeated image formation over a long period of time. Effects such as extremely little deterioration and toner scattering are achieved.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing each side of an analog and digital copying machine according to the present invention, FIG. 3 is a sectional view showing the layer structure of an a-Si photoreceptor suitable for the present invention, and FIG. 4 is an explanatory diagram of an apparatus for measuring the particle size of toner, Figure 5 is an explanatory diagram of a method for measuring the surface charge density of toner (blow-off method), and Figure 6 is an explanatory diagram of an apparatus for measuring the particle diameter of carrier. , FIG. 7 shows test No. 8 to No. 13 in Example 1.
Figure 8 shows the relationship between the toner content (ivt%) in the developer and the surface charge density of the toner in Example 1. FIG. 9 is a diagram showing the relationship between the toner particle size and the amount of silica added when preparing the developer in Test Nos. 1 to N017 of Example 1. In addition, in the symbols shown in the drawings, 2...... Original 3... Light source 6... Charger 7... ...Developer 8...Transfer device 10...Photoreceptor 11...Cleaning device 12...
......DC bias 17...Fixer 20...Photoelectric conversion device 21...Image processing device 22... ...Laser writing device 31...
...Base 32 ...Blocking layer 33 ...
...Carrier transport layer 34...Intermediate layer 35...Carrier generation layer 36...
. . . Protective layer 40 . . . Probe 41 . . . Surface electrometer 42 . . . Recorder.

Claims (1)

[Claims] 1. In an image forming method comprising a step of developing an electrostatic latent image formed on an amorphous silicon photoreceptor with a developer consisting of at least a toner and a carrier, the surface area average particle diameter of the toner is 2 to 8 μm, the average surface The absolute value of the charge density is |3 to 7|nC/cm^2 (where nC is nanocoulomb; the same applies hereinafter), and the average of the non-exposed area at the development position of the amorphous silicon photoreceptor. The absolute value of the surface charge density is |80-400|nC/
An image forming method characterized in that the image forming method is cm^2.