JP2928885B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method including a step of developing an electrostatic latent image formed on an amorphous silicon-based photoconductor with a developer including at least a toner and a carrier.

B. 2. Description of the Related Art Conventionally, as a photoconductor used for electrophotography, for example, a photoconductor using an inorganic semiconductor such as zinc oxide and cadmium sulfide, a selenium-based photoconductor, and a photoconductor using an organic semiconductor are known. Research and development of these photoconductors have already progressed, and these photoconductors have been put into practical use by being incorporated in image forming apparatuses such as copying machines and printers.

However, all of these photoconductors have poor chemical and mechanical durability on the surface of the photosensitive layer, and are decomposed, worn, and degraded by light, corona discharge, temperature and humidity, cleaning, developing operations, etc. during repeated image formation. There is a problem that it is easy to do.

On the other hand, in the electrophotographic industry, improvement in image quality is required, and in particular, images with high resolution are required. In response to the request, there is a fine particle toner in a developer, for example, research on a fine particle toner having an average particle diameter of 10 μm or less,
Development is underway. By the way, the smaller the particle size of the toner particles, the more strongly they adhere to the surface of the photoreceptor, and the more difficult the cleaning process is to clean. Therefore, the fatigue deterioration of the photoconductor is further accelerated.

Thus, for example, Japanese Patent Application Laid-Open No. 63-13054 discloses an amorphous silicon photoconductor (hereinafter simply referred to as an a-Si photoconductor). An image forming method has been proposed in which an image is formed by developing with a two-component developer containing a fine particle toner of 6 μm or less. The a-Si photoreceptor is originally known to be non-polluting and durable, having excellent corona discharge resistance and moisture resistance.In addition, the photosensitive layer surface is strong, for example, Vickers hardness is high. Compared with the selenium-based photoreceptor of 60, the order of magnitude is 1000 to 1200, which is an order of magnitude larger.It is a highly durable photoreceptor, and the cleaning member can be sufficiently pressed against the photoreceptor for cleaning. Therefore, so-called toner filming, which causes fatigue deterioration, does not occur, and this point is also advantageous in comparison with other photoconductors.

However, the a-Si photoconductor is a selenium-based photoconductor,
The dielectric constant of the photosensitive layer is higher than other photosensitive members such as an organic photosensitive member. For example, the permittivity of the a-Si photoreceptor is set to 10 to 13, while the permittivity of the other photoreceptor is set to 3 to 4. Accordingly, there is a problem that the ratio of the amount of charge effective for developing the photoreceptor is small, the developing property is deteriorated, a sufficient image density cannot be obtained, and toner scattering easily occurs when fine particle toner is used.

Incidentally, the problems of the image density and the toner scattering are conventionally known.
It is said that there is a close relationship with the surface potential of the photoreceptor, the toner particle size, the charge amount of the toner, and the like, and the control is extremely complicated and not easy.

As a measure for improving the developability of the photoconductor, it is conceivable to increase the layer thickness of the photosensitive layer. However, since the production cost of the a-Si photoconductor is high, the layer thickness of the photosensitive layer is at most 50.
μm or less, and improvement of the material and layer structure is desired.

By the way, when an image is formed by electrophotography, the image quality is influenced by the image resolution and the image density.For the image resolution, the particle size of the toner is important. As described above, various characteristics such as the surface charge density of the photoreceptor, the particle size of the toner, and the charge amount of the toner are important, and in particular, the control of the charge amount of the toner is important.

Conventionally, the toner charge amount is the charge amount based on the toner weight.
q / M (q is charge amount, M is weight) has been used. However, when the q / M is used as the charge amount of the toner, control of the image density is troublesome because the various characteristics have a complicated relationship, and a desired image density cannot be stably obtained. There was a problem.

Therefore, for example, JP-A-1-193869 discloses that the charge amount of the toner is q / S
Has been proposed. According to this method, there is an advantage that the above-mentioned various characteristics are in a simple and universal relationship and the management of the image density is facilitated.

However, the above publication describes a one-component developer containing a non-magnetic toner as a developer. A toner having a relatively large particle diameter of 12.6 μm is used. The fields are different. In addition, there is no particular description about the photoconductor.

C. The object of the present invention is to form an image by applying a developer containing a fine particle toner and a carrier to an amorphous silicon-based photoreceptor such as a-Si described above, without accompanying toner scattering, etc. An object of the present invention is to provide an image forming method capable of stably supplying an image having a high density and a high resolution.

D. The present invention provides an image forming method comprising the step of developing an electrostatic latent image formed on an amorphous silicon-based photoreceptor with a developer comprising at least a toner and a carrier. ８8 μm, the absolute value of the average surface charge density is | 3〜7 | nC / cm ² (where nC is nanocoulomb: the same applies hereinafter), and the absolute value of the amorphous silicon photoconductor at the developing position those of the image forming method characterized in that the nC / cm ² | the absolute value of the average surface charge density of the exposed portion | 80 to 400.

That is, the image forming method of the present invention forms an electrostatic latent image by performing image exposure by an analog system or a digital system after applying charge on a photosensitive member such as a drum or a belt,
This includes a step of performing regular development or reversal development using a two-component developer containing a fine particle toner having a surface area average particle diameter of 2 to 8 μm, and it is possible to form an image with high resolution by using a fine particle toner. And

Further, according to the present invention, it is possible to form a high-quality image having excellent resolution and image density without causing toner scattering or the like using a two-component developer containing the fine particle toner in the specific range. The average surface charge density σ of the unexposed portion of the photoconductor at the position is | 80 to 400 | nC / cm ² in absolute value, and the average surface charge density q / S of the toner is | 3 to 7 | nC in absolute value. / cm ²
Is defined in the range. That is, conventionally, the surface potential of the photoconductor has been used as a characteristic value representing the charging of the photoconductor,
What is directly related to development is the amount of charge on the surface of the photosensitive layer at the time of development. Even if the surface potential of the photosensitive layer is the same, the amount of charge fluctuates according to changes in the layer thickness, dielectric constant, and the like, and is not constant. Therefore, in the present invention, the charge amount on the photosensitive layer surface is defined by the average surface charge density σ in the specific range. Further, the charge amount of the toner is defined by the average surface charge density q / S in the specific range, which is directly related to the average surface charge density σ of the photoconductor. Thus, the image quality can be easily managed during image formation, the image density can be controlled with extremely high precision, and toner scattering can be prevented.

Furthermore, the surface of the a-Si photoreceptor is harder and more dense than other photoreceptors, and has excellent light resistance, moisture resistance, corona ion resistance, mechanical wear resistance, and the like. And,
Since a strong cleaning operation is possible, the photoreceptor does not suffer from fatigue deterioration and is highly durable when image formation is repeated many times.

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

Hereinafter, the image forming method of the present invention will be specifically described with reference to, 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 platen 1 is a light source 3 (3a,
3b) is scanned 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 indicated by imaginary lines, and reaches the developing surface after being charged by the charger 6 in advance. Irradiation is performed on the a-Si photosensitive drum 10 uniformly charged so that the absolute value of the charge density becomes | 80 to 400 | nC / cm ² , image exposure is performed, and an electrostatic latent image is formed. You. This electrostatic latent image has a magnetic carrier and a surface area average particle diameter of 2 to 8 μm.
Is normally developed by a magnetic brush method by a developing device 7 containing a two-component developer composed of
A toner image is formed on the photosensitive drum 10. So 7a
Reference numeral denotes a magnetic brush developing roll in the developing device 7, which magnetically attracts and conveys the developer D in the developing device and brings it into contact with the surface of the photosensitive drum to perform development. The absolute value of the average surface charge density of the toner in the layer is | 3 to 7 |
The composition of the developer, the particle diameter and the shape of the toner and the carrier, and the like are selected so as to be nC / cm ² . Thus, a high-density, high-resolution toner image is formed on the photosensitive drum 10, and this toner image has been transferred by the time from the paper feed cassette 13 via the paper feed roll 14 and the registration roll 15. The image is transferred onto the paper by the action of the transfer pole 8. The transfer paper carrying the transfer toner is separated by the action of the separation pole 9, conveyed to the fixing device 17 by the conveyance belt 16, fixed, and discharged to the discharge tray 19 by the 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, and is prepared for the next image formation.

A probe 40 is set in place of the developing device 7, and the potential of the non-exposed portion when the developing position is reached after charging is picked up by the probe, read by the surface voltmeter 41, and recorded by the recorder 42. , the photosensitive member surface potential V _s is measured.

Next, FIG. 2 shows a digital image forming apparatus, in which parts common to those in FIG. 1 are denoted by the same reference numerals. 2 is roughly divided into a document reading section A, a writing section B, and an image forming section C. In the reading section A,
Document 2 on platen 1 is light source 3, reflecting mirrors 4a, 4b and 4c
The optical information obtained by optical scanning is focused on the photoelectric conversion element 20 via the lens 5 and converted into an electric signal. This electric signal is subjected to A / D conversion and multi-level (binarization) processing in the signal processing device 21, and the obtained image signal is converted to LE signal.
Writing device 22 of writing section B using D or laser device
Is output to Normally, the semiconductor laser is image-modulated by the image signal, and the obtained modulated laser light is linearly scanned by a polygon mirror to perform image exposure on the a-Si photoreceptor drum 10 in the form of dots like virtual lines. On the photoreceptor drum 10, charging is performed so as to have an average surface charge density of | 80 to 400 | nC / cm ² when measured at the developing position after charging in the same manner as in FIG. And an electrostatic latent image is formed by the image exposure. This electrostatic latent image is reversely developed with a DC bias 12 close to the surface potential of the photosensitive drum applied to a developing device 7 containing the same two-component developer as in FIG. A dot-shaped toner image is formed thereon, and is transferred and fixed on transfer paper fed at a proper timing to form an image. As in the case of FIG. 1, the surface of the photoreceptor after the transfer is cleaned by a cleaning device to prepare for the next image formation.

The a-Si photosensitive layer constituting the photosensitive member used in the image forming method of the present invention originally has dangling bonds in the layer, has many localized levels, and has poor photoconductivity. Since a hydrogen atom (H) or a halogen atom (X) is introduced into the a-Si layer to block the dangling bond, desired photoconductivity is provided. Furthermore, in order to increase the dark resistance of the photoconductor and improve the charging characteristics,
It is desirable to introduce modified atoms (Y) such as carbon atoms (C), oxygen atoms (O), and nitrogen atoms (N) into the a-Si layer.

The a-Si photoreceptor according to the present invention may be a photoreceptor having a single-layered photosensitive layer provided on a substrate, or a function-separated type photoreceptor having a carrier generation layer and a carrier transport layer. May be a photosensitive member having a photosensitive layer having a laminated structure provided by laminating on a substrate. Further, in the photoreceptor having the single-layer structure or the laminated structure, a blocking layer may be provided between the substrate and the photosensitive layer to prevent carrier injection from the substrate, to improve sensitivity and chargeability, Further, a surface modification layer may be provided for the purpose of protecting the surface of the photosensitive layer. Furthermore, an intermediate layer for improving carrier injection efficiency can be provided between the carrier generation layer and the carrier transport layer of the photoconductor having the above-mentioned laminated structure.

Next, an example of the layer structure of the a-Si photosensitive member suitable for the present invention is shown in FIG. Hereinafter, the internal configuration will be described in more detail. The layer configuration shown in FIG. 3 shows an example in which the charging polarity is positive. For example, P ⁺
The a-Si photoreceptor 10 is formed by sequentially laminating a mold-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.

The P ⁺ -type carrier blocking layer 32 is heavy-doped with a Group IIIA element of the periodic table (boron, aluminum, gallium, or the like), and contains at least one modified atom (Y) such as a carbon atom, an oxygen atom, or a nitrogen atom. A-Si: C: H contained
(X) layer, a-Si: C: O: H (X) layer, a-Si: N: H (X)
Layer, a-Si: N: O: H (X) layer, a-Si: O: H (X) layer, a-
It is preferable that the layer be composed of a Si: C: N: H (X) layer, an a-Si: C: O: N: H (X) layer, and the like. The content ratio of the modifying atom (Y) is
0.5 to 40 atm% is preferred. Further, the thickness of the carrier blocking layer 32 is preferably 0.01 to 5 μm.

The carrier transport layer 33 is lightly doped with a Group IIIA element of the periodic table, and like the carrier blocking layer 32,
It is preferable that the a-Si: Y: H (X) layer contains at least one kind of modified atom (Y) such as a carbon atom, an oxygen atom, and a nitrogen atom. The modified atom (Y) content is 0.5
~ 40 atm% is preferred. Further, a boron atom may be introduced in order to improve charging ability and sensitivity. The thickness of the carrier transport layer 33 is preferably 5 to 50 μm.

The intermediate layer 34 is provided as needed in order to increase the carrier injection efficiency, and includes, for example, a-Si containing at least one modified atom (Y) such as a carbon atom, an oxygen atom, or a nitrogen atom. : Y: H (X) layer. Further, the content ratio of the modifying atom (Y) is preferably smaller than that of the carrier transport layer 33. Specifically, 0.01-20
atm% is preferred. The intermediate layer 34 is preferably lightly doped with a Group IIIA element 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 is preferably formed of an a-Si: H (X) layer light-doped with a Group IIIA element of the periodic table as necessary. Also, in order to improve the charging ability,
Boron atoms may be introduced to be intrinsic to improve the resistance and improve the carrier mobility. This carrier generation layer 35
Is preferably 5 to 50 μm.

The surface-modified layer 36 is formed by introducing a halogen atom (X) such as a hydrogen atom and / or a fluorine atom into an a-Si layer to block a dangling bond, Further, it is preferable that the layer be constituted by an a-Si: Y: H (X) layer into which a modifying atom (Y) such as a carbon atom, an oxygen atom, and a nitrogen atom is introduced. Specifically, a-Si: C: H (X) layer, a-Si: C: O: H
(X) layer, a-Si: N: H (X) layer, a-Si: O: H (X) layer,
a-Si: N: O: H (X) layer, a-Si: C: N: H (X) layer, a-S
Various configurations such as an i: C: N: O: H (X) layer can be adopted. In the surface-modified layer 36, the content ratio of the modified atoms (Y) such as carbon atoms, oxygen atoms, and nitrogen atoms is calculated assuming that the total of the silicon atoms and the modified atoms (Y) is 100 atm%. The ratio in which Y) is 40 to 90 atm% is preferable. The thickness of the surface modification layer 36 is preferably from 400 ° to 1 μm.

Also, if necessary, the carrier generation layer 35 and the surface modification layer 36
And a second intermediate layer may be provided between the first and second layers. It is preferable that the content ratio of the modifying atoms (Y) in the second intermediate layer is smaller than the surface modifying layer 36.

The thickness of the entire photosensitive layer is usually 20 to 50 in terms of manufacturing cost.
It is good to be μm.

It is preferable that a halogen atom (X) such as a hydrogen atom and / or a fluorine atom is introduced into each of the above layers constituting the a-Si photoreceptor 10. In particular, the inclusion of hydrogen atoms in the carrier generation layer 35 is important for blocking the dangling bonds and improving photoconductivity and charge retention. Specifically, the content ratio of hydrogen atoms is preferably 10 to 30 atm%. This hydrogen atom content ratio depends on the surface modified layer 36, the intermediate layer
The same applies to the carrier blocking layer 32 and the carrier transporting layer 33. In addition, as an impurity for controlling the conductivity type, besides boron, aluminum, gallium, indium, thallium, etc. in the periodic table IIIA for the purpose of p-type conversion.
Group elements can be used.

In order to block dangling bonds at the time of forming each layer constituting the a-Si photoreceptor 10, a halogen atom, for example, a fluorine atom is introduced in the form of SiF ₄ or the like instead of or together with a hydrogen atom. Si: F, a-Si: H: F, a-S
i: C: F, a-Si: C: H: F, a-Si: C: O: F, a-Si: C: O: H: F
And the like. In this case, the content ratio of fluorine atoms is preferably 0.5 to 10 atm%.

Each layer constituting the a-Si photoreceptor 10 is, for example, a glow discharge decomposition method, a sputtering method, an ion plating method,
A method of evaporating silicon in a state in which activated or ionized hydrogen is introduced in a hydrogen discharge tube (Japanese Patent Application Laid-Open No. 56-7841)
No. 3) or the like.

The above is a description of the case where the charging polarity of the a-Si photoconductor 10 is positive. However, when the charging polarity of the a-Si photoconductor 10 is negative, the carrier blocking layer 32 and the carrier transport layer 3
3. The dopant to be introduced into each of the intermediate layer 34, the carrier generation layer 35, and the surface-modified layer 36 may be changed to a Group VA element (such as phosphorus, arsenic, antimony, and bismuth) in the periodic table. Note that the carrier blocking layer 32 and the intermediate layer 34 are provided as needed and may be omitted.

Further, the carrier transport layer 33 and the carrier generation layer 35 may be formed into a single layer instead of being separated.

The base 31 may be formed of any of conductive and insulating materials. Examples of the conductive material include metals such as stainless steel, aluminum, chromium, molybdenum, iridium, tellurium, titanium, platinum, and palladium, and alloys thereof. Examples of the insulating material include films or sheets of synthetic resin such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and polyamide, glass, ceramic, and paper. When an insulating material is used, it is preferable that its surface is subjected to a conductive treatment. Specifically, for example, in the case of glass, conductive treatment with indium oxide, tin oxide or the like, and in the case of a synthetic resin film such as a polyester film, aluminum,
Metals such as silver, lead, nickel, gold, chromium, molybdenum, iridium, niobium, tantalum, vanadium, titanium, platinum, etc. are subjected to conductive treatment by a method such as vacuum evaporation, electron beam evaporation, sputtering, or laminated with the above metals. Can perform a conductive treatment.

The shape of the conductive substrate 31 can be selected from various forms such as a cylindrical shape, a belt shape, and a plate shape. When images are continuously formed at a high speed, an endless belt shape or a cylindrical shape is preferable. The thickness of the base 31 is not particularly limited, and is appropriately selected from the viewpoint of manufacturing, handling, mechanical strength, and the like.

The layer configuration of the preferred a-Si photoreceptor used in the present invention is as described above. In the case of such a layer configuration, the dark resistance of the photosensitive layer is high, and the layer has a high chargeability at a normal layer thickness of 50 μm or less. A photoreceptor which can sufficiently satisfy the condition of the average surface charge density during charging, which is a feature of the present invention, | 80 to 400 | nC / cm ² (preferably | 110 to 300 | nC / cm ² ) is obtained.

Here, when the average surface charge density is less than | 80 | nC / cm ² ,
The developability is poor, the desired amount of toner does not adhere during development, the density of the image is insufficient, and the toner is liable to be scattered. On the other hand, when the average surface charge density exceeds | 40 | nC / cm ² , the average surface charge density is too high, and the resolution decreases during image formation. In particular, when the surface-modified layer having the above-described structure is provided, the dark resistance of the photosensitive layer is 10 ¹² to 10 ¹³ Ω-cm (10 ^{8 to} 10 ⁸ Ω-cm for a normal a-Si: H layer).
~ 10 ⁹ Ω-cm), the charging ability of the a-Si photoreceptor is remarkably increased, and a surface charge density of | 80 to 400 | nC / cm ² is sufficiently ensured.

Incidentally, the average surface charge density σ (nC / c
m ² ) is the relative permittivity ε of the photosensitive layer and the vacuum permittivity ε ₀ (8.85 × 1
0 ^-14 C / V · cm), layer thickness L (μm), surface potential V _s (volt)
Respectively measured, wherein: sigma = obtained by calculating by _{(εε 0 / L) V s} .

The relationship between the surface charge density σ (nC / cm ² ) of the a-Si photoconductor and the surface potential V _s (volt) at the time of charging the photoconductor is as follows:
The film thickness L (μm) of the photosensitive layer and the dielectric constant εε ₀ are in a substantially proportional relationship with each other, and the surface potential applied to the photoreceptor is usually 300 to 800 V, preferably 400 to 600 V.

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

To obtain the non-magnetic fine particle toner, a coloring agent such as carbon black is added to a thermoplastic or thermosetting resin described below.
20% by weight or less, if necessary, 5% by weight or less of a charge control agent, melted, milled, cooled, pulverized, classified, and further heat-treated as necessary, with insulating particles having a volume resistance of 10 ¹⁴ Ω-cm or more,
Further, the particles have a surface area average particle diameter of 2 to 8 μm.
Further, a spherical toner may be obtained by polymerizing a binder resin in which the colorant and other additives are contained in a binder resin under stirring.

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

Among these resins, monomers for forming an addition polymerization type resin include styrenes such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, and 3,4-dichlorostyrene; ethylene, Ethylene 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 and the like 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, methacrylic acid Lauryl, methacrylic acid -
Α-methylene aliphatic monocarboxylic acid esters such as 2-ethylhexyl, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; acrylic acid or meth such as acrylonitrile, methacrylonitrile and acrylamide Acrylic acid derivatives; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; vinyl ketones such as hinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N- N-vinyl compounds such as vinyl indole and N-vinyl pyrrolidone; monoolefinic monomers such as vinyl naphthalenes; propadiene, butadiene, isoprene, chloroprene, Examples thereof include diolefin monomers such as pentadiene and hexadiene. These monomers can be used alone or in combination of two or more. Examples of the monomer for forming the condensation resin include ethylene glycol, triethylene glycol, 1,3-propylene glycol, and the like.

Further, as the charge control agent, JP-A-59-88743,
9-88745, 59-79256, 59-78362, 59-22
Nos. 8259 and 59-124344 each have a negative charge control agent,
Also, JP-A-51-9456, JP-A-59-204851, JP-A-59-2048.
Nos. 50 and 59-177571 describe positive charge control agents, and any of them can be used.

Further, for the purpose of preventing offset development due to adhesion of the toner to the fixing roller, a low molecular weight polyolefin (polypropylene, polyethylene, wax, or the like) can be contained in an amount of 0 to 5% by weight based on the binder resin.

Also, hydrophobic silica is added to the toner in an amount of 0 to 3 wt% for the purpose of imparting fluidity and other charge controllability (negative) of the developer.
Can be added externally.

By the way, the toner of the present invention has a surface area average particle diameter of 2 to 8 μm during production in order to achieve image formation with high resolution.
(Preferably 3 to 7 μm) and a specific surface charge density | 80 to 400 |
C / cm ² , preferably | 110 to 300 | Average surface charge density at which particularly excellent developability is exhibited in combination with nC / cm ³ | 3 to 7 | nC / c
m ² (preferably | 3 to 5 | nC / cm ² ).

When the surface area average particle diameter of the toner is less than 2 μm, the image is easily fogged and the toner is scattered. When it exceeds 8 μm, the resolution of the image is reduced. Also,
When the surface charge density of the toner is less than | 3 | nC / cm ³ , toner scattering increases. When the surface charge density exceeds | 7 | nC / cm ³ , the image density decreases. It is essential that the particle diameter and the surface charge density are within the range.

 Next, methods for measuring the above-described physical properties will be described.

(1) In order to obtain the surface area average particle diameter (d) of the toner, first, the particle diameter distribution on a volume basis is measured with a “Coulter counter TAII type” manufactured by Coulter Electronics.
Next, the volume-based particle size distribution is converted into a surface area-based particle size distribution assuming a spherical shape. From this particle size distribution based on the surface area, a (median) particle size that gives 50% of the total surface area (integral value) of the toner is obtained, and this is defined as a surface area average particle size (d) of the toner. Here, the average surface area S (cm ² ) of the toner is obtained by converting the particle size distribution based on the surface area.

For reference, the measurement method of the Coulter Counter TAII will be described below with reference to FIG. This measuring method is also called a small hole passing method, an electrozone method or a Coulter method from the name of the inventor, and has been most frequently used in the measurement of toner particles. To measure by this method, first, the toner is dispersed and suspended in the electrolyte solution, a partition having a pore is formed as shown in the figure, and the suspension is passed through the pore while applying a voltage to both sides thereof. The toner in the liquid also passes through, and the electric resistance of the pores changes according to the size of the particles, and is observed as a pulse. By measuring this pulse, a volume-based distribution is obtained.

(2) In order to measure the average surface charge density (q / S) of the toner, first, the average charge amount q of the toner is measured in units of nC (nano coulomb) by the following developing process using the apparatus of FIG. I do. That is, the collected sample developer is magnetically attracted to the magne sleeve roll of the apparatus shown in FIG. A copper plate is arranged close to the magne sleeve roll, and AC and DC biases are applied between the copper plate and the magne sleeve roll, so that the toner in the developer flies from the sleeve surface to the copper plate surface and adheres. Let it. Here, by rotating the magne sleeve roll once, all the toner in the developer on the outer periphery thereof is transferred to the copper plate. Because the copper plate surface charged toner is present, since this and mirror image charge of the same amount and opposite sign is generated, the charged toner on the copper plate when you blow-off with N ₂ gas injectors, image charge within coulomb meter Flow and its charge q (nC) is measured. Before the blow-off, the difference between the weight of the copper plate alone and the weight of the copper plate carrying the toner is measured, and the weight M (g) of the toner is measured. In addition, the specific charge amount q / M can usually be obtained even when measured by a method called a blow-off method.

Thus, the average specific charge q / M (nC / g) of the toner =
P is measured. From this value, the average surface charge density of the toner
q / S (nC / cm ² ) is determined from P × M / S using the average surface area S (cm ² ) of the toner previously obtained by the measurement method (1).

As the carrier of the two-component developer used in the present invention, those capable of stably imparting the specific surface charge density to the toner are selected, and when the magnetic material is used as it is, a resin or the like is coated on the surface. When used as such, there may be cases where the powder is mixed with a resin as fine powder, but a coated carrier in which the surface of magnetic particles is coated with a resin is preferred. As the magnetic material, a substance which is extremely strongly magnetized in the direction by a magnetic field, for example, iron,
Alloys or compounds containing ferromagnetic elements such as metals such as cobalt, nickel, ferrite, magnetite, hematite, etc., iron, cobalt, nickel, etc. An alloy that exhibits ferromagnetism, for example, a Heusler alloy containing manganese and copper, such as manganese-copper-aluminum or manganese-copper-tin, or chromium dioxide is used.

The surface area average particle size (d) of the carrier is 40 to 120 μm.
m, and the resistivity of the carrier is 10 to prevent the carrier from being attached to the image forming surface due to the bias voltage and causing the carrier to adhere to the image forming surface, and the bias voltage from leaking to eliminate the latent image charge. ⁸ Ω-cm or more, preferably 1 Ω-cm
0 ¹³ Ω-cm or more insulative, more preferably 10 ¹⁴ Ω
-Cm or more is preferred.

Note that the specific resistance of the carrier (or toner)
After tapping in a container having a cross-sectional area of 0.5 cm ² , a load of 1 kg / cm ³ is applied on the packed particles, and an electrolysis of 10 ² to 10 ⁵ V / cm is applied between the load and the bottom electrode. It is determined by applying the generated voltage, 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 1 mm.

Further, the carrier used in the present invention has a spherical shape in order to improve the fluidity of the developer and to improve the triboelectric charging property between the carrier and the toner, and to prevent blocking between carrier particles or between the carrier and the toner. It is preferred that the In order to obtain such a spheroidized carrier, for example, in the case of a resin-coated carrier, for example, a styrene-acrylic resin is added to a preformed spherical magnetic particle.
It may be coated on a thin layer having a thickness of 0.1 to 2 µm (0.5 to 5 wt% based on the weight of the carrier). In the case of a resin-dispersed carrier, a magnetic fine powder is dispersed in a resin of 30 to 70 wt%. The particles may be heat-treated to form spheres, or spherical particles may be directly produced by spray drying.

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

(3) Here, the surface area average particle diameter of the carrier (d)
Is the Microtrack Particle Size Monitor 7981
It is measured by a light scattering method using -X ³ type (manufactured by Leeds and Northrup). In this light scattering method,
This is an application of the “me” or “Maxwell” electromagnetic equation to the light scattering phenomenon of spherical particles, and is measured using the apparatus shown in FIG. 6 according to the measurement principle.

FIG. 6 shows an outline of the measurement principle. When a light beam emitted from a He-Ne: gas laser is applied to a sample cell, light is scattered by particles in the sample cell. When this scattered light is condensed by the lens 1, a diffraction image of the Frannhofer appears on the focal plane of the lens. Actually, since a large number of particles are present in the laser beam, superposition of diffraction images by individual particles appears. The intensity distribution of the light in the diffraction image depends on the particle diameter if the wavelength of the light hitting the particles is constant. Therefore, if the light intensity distribution is measured by any method, it can be easily exchanged for the particle size distribution of the sample.

The detailed configuration of the image forming method of the present invention is as described above. Among them, the surface charge density σ (nC / c
m ²⁾ and the toner on the surface charge density ^{q / S (nC / cm 2} ) is shown in absolute values. 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 the image is normally developed using the analog image forming apparatus shown in FIG. The result is positive when reversal development is performed using the digital image forming apparatus shown in FIG. or,
If the photoreceptor is a negatively charged photoreceptor, the opposite sign is given.

E. EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but embodiments of the present invention are not limited thereto.

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

(1) Substrate 31 Drum-shaped aluminum substrate having a diameter of 108 mmφ (2) Blocking layer 32 (P ⁺ type) A P ⁺ type a-Si: C: H layer having a thickness of 1 μm, and a carbon atom concentration [C ] = 10 atm% (however, silicon atom concentration [Si] + carbon atom concentration [C] = 100 atm%).

(3) Carrier transport layer 33 is a boron-doped a-Si: C: H layer having a thickness of 15 μm,
The carbon atom concentration [C] is set to 10 atm%.

(4) Intermediate layer 34 A boron-doped a-Si: C: H layer having a thickness of 0.5 μm,
The carbon atom concentration [C] is set to 5 atm%.

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

(6) Surface modification layer 36 This is an a-Si: C: O: H layer having a thickness of 0.3 μm, and has a carbon atom concentration [C] = 55 atm% and an oxygen atom concentration [O] = 1 atm% (however, silicon Atomic concentration [Si] + carbon atomic concentration [C] + oxygen atomic concentration [O] = 100 atm%).

Next, the developers used in the present embodiment are as follows.

(1) Preparation of toner The above materials were sufficiently mixed for 5 hours by a ball mill, and then kneaded with two rolls at 170 ° C. Then, after natural cooling, coarsely pulverized by a cutter mill, further pulverized by a fine pulverizer using a jet stream, and then classified by an air classifier while changing the classification conditions, the surface area average particle size 1.3μm ~ 9.5 Seven types of toners having different particle diameters in the range of μm were obtained, and these toners were designated as Test Nos. 1 to 7 (Table 1 described later). For the next test No. 8 to No. 13, 8 parts of the toner were separated and taken out from the toner for the previous test No. 4 (particle diameter 5.5 μm), and further used for the test Nos. 14 to 21. Previous test No.5
8 toners (particle size: 6.8 μm) were separated and taken out to prepare a total of 21 toners.

(2) Preparation of carrier 5 parts by weight of a styrene-methacrylate (4: 6) copolymer resin was dissolved in 100 ml of toluene, and the resulting solution was added with a surface area average particle size of 7 parts.
A mixture of 100 g of 3 μm ferrite particles is spray-dried by a spray-drying method to prepare a coated carrier resin-coated so that the film thickness after drying becomes 1 μm.
This was divided into 21 parts for the subsequent preparation of the developer.

(3) Preparation of developer First, hydrophobic toner (Aerosil R-805) was added to the toners of Test Nos. 1 to 7 having different particle diameters based on the correspondence data between the silica amount and the toner particle diameter shown in FIG. ) And 1.0 to 7.1% by weight of the divided carrier such that the average surface charge density of the toner is −4.0 nC / cm ^2.
By adding and mixing, seven types of developers of Test Nos. 1 to 7 were prepared.

Next, Test No. 8 to No.
Toner 13 was added with 1.0% by weight of silica for each toner, and changed to a toner concentration of 1.0 to 10% by weight so that when subjected to development, the surface charge density in the eight stages shown in Table 1 below was obtained. Test No. 8 to No. 13 by mixing with the split carrier
Were prepared.

In preparing the developers of Test Nos. 8 to 13, the relationship between the toner concentration and the toner surface charge density was measured in advance by using a modified copying machine described later, and the obtained data was obtained. Using (FIG. 7), a developer exhibiting a desired toner charge density was prepared.

Next, all of the toners of Test Nos. 14 to 21 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 -4.0 nC / cm ^{2 with} respect to the divided carrier.
No. 14 to No. 21 by adding and mixing 5.2 wt% of toner so that
Were prepared.

Using the 21 kinds of developers prepared as described above, the actual shooting test of this example was performed as follows.

The above-mentioned a-Si photosensitive material was applied to a U-Bix5070 (manufactured by Konica Corporation) copying machine of an analog system (see FIG. 1) equipped with a charger, a contact type magnetic brush developing device, an electrostatic transfer device, and a blade cleaning device. Using a modified machine equipped with a body drum,
We performed 21 types of live-action tests (including comparison tests) shown in the table.

The environmental conditions during the test were room temperature and normal humidity (temperature 20 ° C,
(Relative humidity: 60%) In each test, images were formed continuously for 30 minutes, and the density and resolution of the obtained images were evaluated based on the image evaluation method described later. The results were evaluated and the results are shown in Table 1.

When the test is performed using the developers of Test Nos. 14 to 21, the surface charge density of the photoreceptor is not higher than that of Test No. 1 in Table 1.
The surface potential of the photoreceptor is set to 18 so that the values of 8 steps from 4 to No. 21 are obtained.
Image formation was performed in eight steps in the range of 0 volts to 1150 volts.

In order to perform the tests of No. 14 to No. 21, the relationship between the surface potential of the photoconductor and the surface charge density of the photoconductor was previously measured using the remodeled machine, and the obtained data ( 8th
The test was performed by giving a desired surface charge density of the photoreceptor using FIG.

By the way, the surface charge density of the photoreceptor will be described with reference to FIG. 1. In each test, the developing unit 7 is pulled out before the image formation, the probe 40 is set instead, and after the charging, The potential of the non-exposed portion at the developing position is pigged up by the probe, read by a surface voltmeter 41, and recorded by a recorder 42, whereby the photoconductor surface potential is
V _s was measured. After the test, the photoconductor drum is pulled out, a small piece is cut out, the thickness L (μm) of the photoconductor layer is measured, and the capacitance C of the photoconductor layer is measured by a coulomb meter, and the ratio is derived from CL / ε _0. The rate was determined. Here, the vacuum induction ε ₀ is known. The above data is calculated using the above formula σ =
Was determined (εε ₀ / L) surface charge density of the photoconductor for each test was introduced into V _s sigma.

In addition, the surface area average particle diameter of the toner and the carrier is measured based on the above-described method at the time of preparing the developer, and the average charge density of the toner is determined for each test by developing after image formation. The agent was sampled and measured based on the measurement method described above.

Image Evaluation Method: (1) Image Density A document having 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 Corporation). The evaluation was “「 ”when the reflection density was 1.0 or more,“ △ ”when the reflection density was 0.8 to 1.0, and“ × ”when the reflection density was less than 0.8.

(2) Resolution Based on JIS Z4916, 4.0, 5.0, 6.3, 8.0, 10.0, 1
Using a chart provided with 2.5 lines and 16.0 lines, the copied image was visually determined, and a grade in which lines could be distinguished was displayed as the resolution.

(3) Toner scattering The inside of the copying machine and the copied image are visually observed, and “○” indicates that toner scattering is hardly observed and is good, “△” indicates that toner scattering is slightly observed but is at a practical level, and “ト ナ ー” indicates toner. A case where there was a lot of scattering and there was a problem in practice was marked as "x".

From Table 1, it can be seen that in the test according to the present invention, the characteristics such as image density, resolution, toner scattering, etc. are all excellent, but in the comparative test, at least one of the above-mentioned characteristics is poor and is not practical. Is understood. In particular, in the above, the following is clear.

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

q / S = -3 to -7 nC / cm ² is a practical level.

-3 to -5 nC / cm ² is good.

σ = +80 to +400 nC / cm ² is a practical level.

+110 to +300 nC / cm ³ is good.

(Example 2) The a-Si photosensitive drum of Example 1 was replaced with a blue, red, and black three-color reader, a semiconductor laser writer, a charger, blue, red,
U-Bix DC8010, a digital type electrophotographic copying machine equipped with three black magnetic brush developing units for contact reversal development (remodeled from non-contact type) and a blade cleaning device.
Tests as shown in Table 2 (including comparative tests) were carried out using a modified machine mounted on (manufactured by Konica Corporation) and using the following 21 types of developers as developers.

In the present embodiment, the reading device is a black image only,
The BK image signal is output to the writing device for each rotation of the photosensitive drum, and only the black developing device is operated.
Image formation was performed by a reversal development method under application of a C bias.
The developer used in this test was one in which the toner became positively charged by friction with the carrier.

(1) Preparation of Toner 400 ml of toluene was placed in a 2-liter separable flask, 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, 48 g of n-butyl acrylate and 0.5 g of benzoyl peroxide were placed in the flask, 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 184 was added to the flask.
g, 56 g of n-butyl acrylate, 80 g of monoacryloyloxyethyl succinate and 8 g of benzoyl peroxide were added dropwise over 2 hours to carry out the second stage polymerization reaction.

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

Thereafter, toluene as a solvent was distilled off under reduced pressure to obtain a resin as a reaction product of a polymer having a carboxyl group in a side chain and zinc oxide. 100 parts of this resin, 10 parts of carbon black (manufactured by Cabot Corp., trade name "Mogal L") and 3 parts of nigrosine dye are kneaded, and after cooling, coarsely pulverized,
Further, it is finely pulverized by a jet mill and further classified by an air classifier to produce eight kinds of toners having different particle diameters as shown in Table 2 below in the range of 1.3 to 9.5 μm in surface area particle diameter, and tested.
No.1 to No.8.

On the other hand, as a carrier for developer preparation,
A 40 μm spherical iron powder carrier was prepared, and divided into 21 parts to be used for preparation of a test developer. The test
All of the toners of Nos. 1 to 8 were combined with the carrier and mixed so that the average surface charge density of the toner was +4.1 nC / cm ^2, and the toners of Test Nos. 1 to 8 were tested. Different types of developers were prepared.

Next, among the eight toners, the surface area average particle size was 5.4.
From the μm toner (toner of test No. 5), 7 parts of toner were further separated and taken out for test No. 8 to No. 14. When this 7 part of separated toner was subjected to development, The toner content was changed so that the surface charge density became 7 levels, and mixed with the split carrier to prepare 8 types of developers, which were used as the developers of Test Nos. 8 to 14 .

Further, among the above eight kinds of toners, the surface area average particle diameter is 6.7.
Test further with μm toner (Test No. 6 toner)
Seven portions of the toner for No. 15 to No. 21 were separated and taken out. These seven parts of the toner were mixed with the iron powder carrier so that the toner average surface charge density became +4.1 nC / cm ² , thereby obtaining developers of Test Nos. 15 to 21.

Using the thus prepared 21 kinds of developer and the modified machine of DC8010, according to the test order of Table 2, 21 kinds of tests based on the same test method, test conditions, measuring method and evaluation method as in Example 1. And the results are shown in Table 2.

When a test is performed using the developers of Test Nos. 15 to 21 described above, the photosensitive members are exposed so that the surface charge density of the photoreceptor becomes seven stages of Test Nos. 15 to 21 in Table 2. Imaging was performed by changing the surface potential of the body in seven steps from 180 volts to 1150 volts.

Table 2 shows that in the test according to the present invention, the characteristics such as image density, resolution, and toner scattering are all at or above the level of practical use, whereas in the comparative test, at least one of the characteristics is defective, and It is understood that there is no sex.

F. Advantageous Effects of the Invention As is clear from the above description, according to the image forming method of the present invention, the use of the developer containing the fine particle toner, the use of the highly durable a-Si photoreceptor, and the mutual Since the surface charge density of the closely related toner and photoreceptor is selected in the optimal range, high density, high resolution image formation is realized, and fatigue deterioration and deterioration during repeated image formation over a long period of time are realized. Effects such as extremely small toner scattering are exhibited.

[Brief description of the drawings]

1 and 2 are schematic diagrams showing examples of analog and digital copiers according to the present invention, FIG. 3 is a cross-sectional view showing a layer structure of an a-Si photosensitive member suitable for the present invention, FIG. Is an explanatory view of an apparatus for measuring the particle diameter of the toner, FIG. 5 is an explanatory view of a method for measuring the surface charge density of the toner (blow-off method), and FIG. 6 is an explanatory view of an apparatus for measuring the particle diameter of the carrier. FIG. 7 is a diagram showing the relationship between the toner content (wt%) in the developer and the surface charge density of the toner in Test Nos. 8 to 13 in Example 1. FIG. FIG. 9 is a diagram showing the relationship between the surface potential and the surface charge density of the photoconductor in Test Nos. 14 to 21. FIG. 9 is a diagram showing the toner particle size during developer preparation in Test Nos. 1 to 7 in Example 1. FIG. 4 is a diagram showing the relationship between the amount of silica and the amount of silica added. In the reference numerals shown in the drawings, 2... Original 3... Light source 6... Charging device 7... Developing device 8... Transfer device 10. Device 20 Photoelectric conversion device 21 Image processing device 22 Laser writing device 31 Substrate 32 Blocking layer 33 Carrier transport layer 34 Intermediate layer 35 Carrier generation layer 36 Protective layer 40 Probe 41 Surface electrometer 42 Recorder.

Continuation of the front page (72) Inventor Nobuaki Kobayashi 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Inside (58) Fields investigated (Int.Cl. ⁶ , DB name) G03G 9/08 G03G 13/08 G03G 5 / 08

Claims (1)

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