JP3000920B2 - Method and apparatus for developing electrostatic latent image - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for developing an electrostatic latent image in an electrophotographic apparatus such as a copying machine or a printer or an electrostatic recording apparatus.

[0002]

2. Description of the Related Art In an electrophotographic apparatus such as a copying machine or a printer, or an electrostatic recording apparatus, an electrostatic latent image formed on a latent image holding member such as a photosensitive drum or a photosensitive belt. In the developing process of supplying a developer to the electrostatic latent image and visualizing the electrostatic latent image, a magnetic or non-magnetic one-component developer is used as a developer from the viewpoints of downsizing, cost reduction, and high reliability of the developing device. It is advantageous.

Conventionally, a one-component developer (hereinafter referred to as toner) is supplied to a latent image holding member such as a photosensitive drum holding an electrostatic latent image, and toner adheres to the electrostatic latent image on the latent image holding member. Let
Developing methods for visualizing the electrostatic latent image include a powder cloud method in which toner particles are used in a spray state, a contact developing method in which toner particles are directly contacted with the latent image surface of a photosensitive drum for development, and a method in which toner particles are charged. Development methods such as a jumping development method in which the electrostatic latent image is developed without contacting the latent image surface of the photosensitive drum with an electric field, and a magnetite method in which a conductive toner having magnetism is brought into contact with the electrostatic latent image surface and developed. Are known.

[0004] The contact developing method will be described. For example, as shown in FIG. 1, a toner application roller 2 for supplying toner and a photosensitive drum (electrostatic holding body) 3 holding an electrostatic latent image are used. A developing roller 1 having a conductive elastic layer is disposed in contact with or close to the photosensitive drum 3, and the developing roller 1, the photosensitive drum 3, and the toner applying roller 2 rotate in the directions indicated by arrows in FIG. As a result, the toner 4 is supplied to the surface of the developing roller 1 by the toner application roller 2, and the toner is arranged in a uniform thin layer by the layering blade 5. By rotating while contacting or approaching, the toner formed in a thin layer adheres to the electrostatic latent image 10 of the photosensitive drum 3 from the developing roller 1 and the latent image is visualized. . In this case, as shown by reference numeral 10 in the drawing, a predetermined voltage is usually applied to the developing roller 1 to apply a developing bias for developing the toner to the printing unit. As shown in Medium 11, a voltage is further applied to the layering blade 5 and the toner coating roller 2 in order to make the charge amount of the toner large and uniform, and the charge is directly injected into the toner. Sometimes. In the figure, reference numeral 6 denotes a transfer unit, which transfers a toner image to a recording medium 7 such as paper. Reference numeral 8 denotes a cleaning unit, which is a cleaning blade 9 for transferring the toner image to the surface of the photosensitive drum 3 after transfer. The remaining toner is removed.

Here, in the reversal development used in a printer or the like, it is necessary to charge the toner to the same polarity as the charge on the latent image carrier, and in general, when an organic photoreceptor is used as the latent image carrier. Has a negative charge potential,
The charge of the toner must also be negative, and if a positively charged photoreceptor such as an amorphous silicon photoreceptor is used, the charge potential is positive, so the charge of the toner must also be positive. In this case, since the frictional charging with the developing roller surface is greatly involved in the charging of the toner, it is necessary to control the compatibility between the toner and the developing roller by designing the materials of both the toner and the developing roller, and the compatibility between the toner and the developing roller is poor. In addition, image defects such as fogging and image memory tend to occur in the initial image, and these image defects are remarkable particularly in a high-temperature, high-humidity or low-temperature, low-humidity environment.

In this case, the occurrence of fogging due to the above-mentioned image defect becomes a noticeable defect even in a normal print pattern, and therefore, particularly severe improvement is required.
This fog is usually caused by the presence of weakly charged or oppositely charged toner, but as a countermeasure against defects due to image memory, as described above, voltage is applied to the developing blade or toner application roller to directly apply toner to the toner. It is also preferable to increase the amount of toner charge by a method such as injecting electric charge.In this way, by injecting electric charge and increasing the amount of toner charge, image memory and the occurrence of normal fog can be effectively prevented. However, in this case, if the toner charge amount is too large, the potential generated by the charge of the toner itself is added to the developing bias, and so-called high potential fog occurs.

Therefore, in order to prevent the occurrence of such image defects, the amount of toner charge is appropriately adjusted in order to prevent the occurrence of fog (normal fog, high-potential fog) while considering the occurrence of image memory. It is important to control the compatibility between the toner and the developing roller. In this case, the compatibility between the conventional toner and the developing roller is controlled by controlling the toner side by a method such as blending a charge control agent (CCA) in accordance with the material of the layering blade or the developing roller, etc. Control of the developing roller is performed by selecting a material based on the above-described criteria, and the compatibility between the toner and the developing roller is controlled.

[0008] However, these compatibility control methods have the following problems. In other words, the control on the developing roller side cannot be carried out by using only the triboelectric charging order as a reference. In the case of an elastic roller having conductivity, a conductive powder or a salt is added to impart conductivity, and thus the addition thereof changes the charging property. In the case of an elastic roller, selection of materials is limited in order to prevent contamination of the photoconductor. In addition, control of the toner side involves the following problems: (1) Since the effects of additives are not quantified, it takes time to develop a prescription suitable for a blade or a developing roller. -Control is limited due to problems such as CCA contamination. There are problems such as. Furthermore, in the conventional method, when the developing roller and the toner are combined, there is no method for judging the compatibility except for actually performing image output or measuring and evaluating the toner charge amount, and the compatibility is easily evaluated. There is also a problem that it is not possible.

The present invention has been made in view of the above circumstances, and it is possible to easily and surely control the compatibility between a toner and a developing roller. An object of the present invention is to provide a method and an apparatus for developing an electrostatic latent image capable of reliably preventing occurrence of potential fog and reliably reproducing a good image over a long period of time.

[0010]

Means for Solving the Problems and Embodiments of the Invention As a result of intensive studies to achieve the above object, the present inventor has developed a developing roller having a conductive layer formed on the outer periphery of a good conductive shaft. A thin layer of the developer is formed by carrying a developer for negative charging on the surface, and a voltage is applied to the developer by a charge injecting means to directly charge the image in order to prevent image memory and normal fogging. By injecting the toner, the charge amount of the toner is increased and made uniform, and the developing roller is rotated along the surface of the latent image holding member in a state of contacting or approaching the latent image holding member holding the electrostatic latent image on the surface. By doing
When a negatively charged developer is supplied to the surface of the latent image holding member to visualize the electrostatic latent image on the surface of the latent image holding member, the compatibility between the developer and the developing roller is determined. It has been found that the ionization potential can be easily and reliably controlled by evaluating the ionization potential of the developer as an index. As a result of further study, the ionization potential of the developer surface was set to 4.5 to 5.5 eV, and the By performing development by adjusting the ionization potential of the roller surface so as to be at least 0.3 eV or more higher than the ionization potential of the developer, normal image defects such as normal fogging and image memory do not occur, and development is performed. It is possible to effectively prevent overcharging of the agent and prevent image defects due to high-potential fog, thereby ensuring a good image. It found that it is possible to reliably reproduced across, and completed the present invention.

Accordingly, the present invention provides a developing roller having a conductive layer formed on the outer periphery of a good conductive shaft, carrying a developer for negative charging on the surface of the developing roller to form a thin layer of the developer.
The developer is negatively charged by applying a voltage to the developer by applying a voltage by a charge injecting unit, and the developing roller is brought into contact with or close to a latent image holding member holding an electrostatic latent image on the surface. By rotating the latent image holding member along the surface of the latent image holding member, a negatively charged developer is supplied to the surface of the latent image holding member to visualize the electrostatic latent image on the surface of the latent image holding member. In the developing method, the ionization potential on the surface of the developer is set to 4.5 to 5.5 eV, and the ionization potential on the surface of the development roller is adjusted to be at least 0.3 eV or more than the ionization potential of the developer. A method for developing an electrostatic latent image, which suppresses the transfer of electrons from the surface of the developing roller to the developer, thereby preventing the occurrence of high-potential fog due to overcharging of the developer. Subjected to.

According to the present invention, there is provided an apparatus for developing an electrostatic latent image by the above-described developing method of the present invention, comprising: a latent image holding member capable of holding an electrostatic latent image on a surface; A developing roller having a conductive layer formed thereon and arranged to rotate along the surface of the latent image holding member in a state of contacting or approaching the surface of the latent image holding member; Charge injecting means for applying a voltage to the developer to directly inject electric charge, and carrying a developer for negative charging on the surface of the developing roller to form a thin layer of the developer. By injecting an electric charge directly into the developer by the charge injecting means to negatively charge the developer, and rotating the developing roller along the surface of the latent image holding member in this state, the latent image is formed. Supplying a negatively charged developer to the surface of the holding member to hold the latent image In the electrostatic latent image developing device for visualizing the electrostatic latent image on the surface, a developer having a surface ionization potential of 4.5 to 5.5 eV is used as the developer, and the ionization potential of the developing roller surface is adjusted to the above-described value. By adjusting the ionization potential to be at least 0.3 eV or more higher than the ionization potential of the developer surface to suppress the transfer of electrons from the development roller surface to the developer, high potential fog due to overcharging of the developer is prevented. A developing device for an electrostatic latent image, characterized in that the developing device is configured to prevent the electrostatic latent image from developing.

The ionization potential is the energy required to separate one electron from an atom or molecule in a gaseous ground state to infinity and dissociate it into a cation and a free electron. The developer and the developing roller are directly irradiated with ultraviolet light (3.5 to 6.2 eV), respectively, and the photoelectrons emitted at this time are measured and easily obtained from the threshold value of the power plot of the quantum efficiency. it can.

Hereinafter, the present invention will be described in more detail.
As described above, the method and apparatus for developing an electrostatic latent image according to the present invention, as described above, charge is directly injected into the negatively charged developer carried on the developing roller to make the developer negatively charged. When developing an electrostatic latent image, the compatibility between the charging roller and the developer is controlled by using the ionization potential of the surface of both as an index, and the ionization potential of the developer surface is adjusted to 4.5 to 5.5 eV. Wherein the ionization potential of the developing roller surface is adjusted to be at least 0.3 or more larger than the ionization potential of the developer surface.

The above-mentioned developer is a negatively chargeable developer, and usually a one-component developer is suitably used, and the ionization potential on the surface is 4.5 to 5.5 eV, preferably 5.1 to 5.5 eV. It is only required to be 4 eV, and a commercially available negatively chargeable one-component developer can be suitably used. In this case, it is practically difficult to make the ionization potential on the developer surface larger than 5.5 eV, and even if it can be initially controlled with a charge control agent or the like, it cannot be stable. On the other hand, if it is smaller than 4.5 eV, it may be difficult to properly control the charging property in the case of negative charging.

Next, the developing roller is, as described above,
A conductive layer is formed on the outer periphery of a good conductive shaft,
In this case, any shaft may be used as long as it has good electrical conductivity, but it is usually a metal core made of a metallic solid body or a metal cylindrical body hollowed inside. And the like.

The conductive layer formed on the outer periphery of the shaft may be made of various kinds of resin such as conductive powder or the like when developing the belt or drum-like latent image holding member and the developing roller in a non-contact state. It can be made of magnetic powder mixed or conductive resin, etc., and when developing in a state where the drum-shaped latent image holding member and the developing roller are in contact with each other, the development nip is relatively unnecessary. A soft elastic body is used. And as a base component of such a conductive layer, polyurethane, natural rubber, butyl rubber, nitrile rubber, polyisoprene rubber, polybutadiene rubber, silicone rubber, styrene-butadiene rubber, ethylene-propylene rubber, chloroprene rubber, acrylic rubber, And a mixture thereof, and the like. In the present invention, polyurethane or silicone rubber is particularly preferably used. In this case, the conductive layer may be a layer composed of a single layer of an elastomer or a foam material or a layer composed of a plurality of layers obtained by laminating these layers. Further, a coating film is formed on the base material layer by using a resin such as polyamide, fluororesin, acryl, urethane-modified acryl, polyurethane, polycarbonate, silicone, polyester, or polyamine, or a mixture of these with a conductive material. You may.

The polyurethane suitably used as the base component of the conductive layer will be described. The polyurethane elastomer and the foam material may be any of those produced by various methods. For example, carbon black may be blended in a polyurethane prepolymer. Then, it can be obtained by a known method in which a conductive material is blended with a polyhydroxyl compound, and the resulting mixture is reacted with a polyisocyanate by a one-shot method.

In this case, examples of the polyhydroxyl compound include polyols used in the production of general flexible polyurethane foams and urethane elastomers, for example, polyether polyols having a polyhydroxyl group at the end, polyester polyols, and copolymers of both. In addition to polyester polyether polyols, general polyols such as polyolefin polyols such as polybutadiene polyol and polyisoprene polyol, and so-called polymer polyols obtained by polymerizing an ethylenically unsaturated monomer in a polyol can be used.

Examples of the polyisocyanate compound include polyisocyanates similarly used for producing general flexible polyurethane foams and urethane elastomers.
That is, tolylene diisocyanate (TDI), crude TD
I, 4,4-diphenylmethane diisocyanate (MD
I), crude MDI, an aliphatic polyisocyanate having 2 to 18 carbon atoms, an alicyclic polyisocyanate having 4 to 15 carbon atoms, and a mixture or a modified product of these polyisocyanates, for example, partially reacted with a polyol. A prepolymer or the like is used.

As a suitable polyisocyanate, xylylene diisocyanate can be exemplified in addition to tolylene diisocyanate.

When a silicone rubber is used as a base material, an organopolysiloxane raw rubber can be used after being crosslinked with a crosslinking agent or the like by a conventional method. In this case, the organopolysiloxane raw rubber used in the present invention may be any one as long as it is used for a silicone rubber compound for molding, but at least two alkenyl groups (eg, vinyl group, allyl group) in one molecule. Or the like). Such organopolysiloxanes include, for example, dimethylpolysiloxane having dimethylvinylsilyl groups at both ends, dimethylsiloxane / methylvinylsiloxane copolymer having dimethylvinylsilyl groups at both ends, dimethylsiloxane having methylphenylvinylsilyl groups at both ends -Methylphenylsiloxane-methylvinylsiloxane copolymer, methyl (3,3,3-trifluoropropyl) polysiloxane having a dimethylvinylsilyl group at both ends blocked.

When the conductive layer is formed of various rubber materials, a crosslinking agent and a vulcanizing agent can be added. In this case, a vulcanization aid, a vulcanization accelerator, a vulcanization acceleration aid, a vulcanization retarder, and the like can be used in both cases of organic peroxide crosslinking and sulfur crosslinking. Furthermore, peptizing agents, foaming agents, plasticizers, softeners, tackifiers, antiblocking agents, separating agents, release agents, extenders, and coloring agents that are commonly used as rubber compounding agents in addition to the above. Etc. can be added.

For example, nigrosine, triaminophenyl methane, or the like is used for the purpose of controlling the charge amount of the one-component developer carried on the surface when the conductive layer is made of polyurethane or silicone rubber as a base material, for example, when used as a developing roller. Various charge control agents such as cationic dyes, and fine powders such as silicone resin, silicone rubber, nylon, and fluoropolymer can be added. In this case, the amount of these additives is the same as that of the above-mentioned polyurethane or silicone rubber.
The charge control agent is 1 to 5 parts by weight with respect to 00 parts by weight,
The fine powder is preferably used in an amount of 1 to 10 parts by weight.

This conductive layer is usually blended with a conductive material for imparting conductivity. In this case, as the conductive material,
First, Ketjen Black EC,
Carbon black such as acetylene black, SAF, I
SAF, HAF, FEF, GPF, SRF, FT, MT
Such as carbon for rubber, carbon for color (ink) that has been subjected to oxidation treatment, pyrolytic carbon, natural graphite,
Examples include artificial graphite, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, copper, silver, germanium and other metals and metal oxides, and powders of conductive polymers such as polyaniline, polypyrrole, and polyacetylene. In addition, inorganic ionic conductive substances such as sodium perchlorate, lithium perchlorate, calcium perchlorate, and lithium chloride; further, modified aliphatic dimethyl ammonium ethosulfate, stearyl ammonium acetate, lauryl ammonium acetate, and octadecyl trimethyl ammonium perchlorate Organic ionic conductive substances such as salts and tetrabutylammonium borate can be used alone or in combination with the powder. The amount of the conductive material is appropriately adjusted depending on the type of the conductive material, but is usually 0.01 to 50 parts by weight, particularly 0.1 to 100 parts by weight based on 100 parts by weight of the base component.
It is used in the range of 1 to 30 parts by weight.

Other conductive materials include electron acceptors capable of forming charge transfer complexes, such as tetracyanoethylene and its derivatives, tetracyanoquinodimethane and its derivatives, benzoquinone and its derivatives, chloranil and its derivatives, Anthraquinone and its derivatives, anthracene and its derivatives, dichlorodicyanobenzoquinone and its derivatives, ferrocene and its derivatives, phthalocyanine and its derivatives, and the like can be used alone, or two or more can be used in combination. Among these, tetracyanoquinodimethane and tetracyanoethylene are particularly preferably used. The amount of the electron accepting substance capable of forming the charge transfer complex is preferably 0.001 to 20 parts by weight, particularly preferably 0.01 to 1 part by weight, based on 100 parts by weight of the polymer substance.

[0027]

On the other hand, in the present invention, when the development is performed by negatively charging the developer, there is no particular limitation. It is preferable to use a conductive conductive material or an organic ionic conductive material. The reason is that the conductive powder itself has a property of easily emitting electrons, and therefore has a low ionization potential of itself, and therefore, when it is blended, the ionization potential as a base resin tends to be low. This is because the object of the present invention may not be sufficiently achieved. In this case, in the case of blending the conductive powder, not only the case where the conductivity is controlled thereby, but also the case where carbon or the like is blended for coloring. In addition, as long as the ionization potential can be adjusted to a predetermined value, the addition of the conductive powder itself may be used. The preferable resistance value in the case of negative charging is 10 ⁵ to 10 ¹⁰ Ωcm.

[0029]

The hardness of the conductive layer is not limited, but particularly when the development is carried out in contact with the latent image holding member,
It is preferably set to 60 ° or less, particularly 25 to 55 ° on the JIS-A scale. In this case, if the hardness exceeds 60 °, the contact area with a latent image holding member such as a photosensitive drum becomes small, and good development may not be performed. Conversely, if the hardness is too low, the compression set becomes large. If the developing roller is deformed or decentered for some reason, uneven image density occurs. For this reason, even when the hardness of the conductive layer is set to a low hardness, it is preferable to reduce the compression set as much as possible, specifically, it is preferable to set the compression set to 20% or less.

The surface roughness of the conductive layer, that is, the surface roughness of the developing roller is not particularly limited.
10-point average roughness of 15 μm Rz or less, especially 1 to 10 μm
It is preferably Rz. When the surface roughness exceeds 15 μmRz, the thickness of the toner layer of the one-component developer (toner) and the uniformity of charging may be impaired. However, when the surface roughness is 15 μmRz or less, the adhesion of the toner can be improved. In addition to this, it is possible to more reliably prevent image deterioration due to roller wear during long-term use.

According to the developing method and the developing apparatus of the present invention, a charge is directly injected into a negatively charged developer carried on a developing roller to charge the developer negatively, and the electrostatic latent image is developed with the developer. In this case, the ionization potential of the surface of the developing roller is set to 4.5 to 5.5 eV.
The development is performed so as to be at least 0.3 eV or more. In this case, the adjustment of the ionization potential of the developing roller surface can be performed by selecting a material for forming the conductive layer and blending additives such as the conductive material, the lubricant, and the surfactant. And
The developing method and the developing device according to the present invention prevent normal fog and image memory from occurring by directly injecting charge into the developer to increase and uniform the charge amount of the developer, and adjust the ionization potential. Thus, the occurrence of high-potential fog can be reliably prevented, and a good image can be reliably reproduced over a long period of time.

The ionization potential was measured by preparing a sheet-like sample of the conductive layer as described above.
This is directly irradiated with ultraviolet light (3.5 to 6.2 eV), the photoelectrons emitted at this time are measured, and it can be easily obtained from the threshold value of the power plot of the quantum efficiency.
In this case, as a measuring device, AC-1 manufactured by Riken Keiki Co., Ltd.
A commercially available surface analyzer such as M can be used.

Here, the above-described high-potential fog which is prevented from occurring by the present invention will be described. High-potential fog is a phenomenon in which, as shown in FIG. 2, a normal image fog is a phenomenon in which a sand-like image appears in a portion which is originally a white image due to a weakly charged or oppositely charged toner. Is a phenomenon in which a band-like or streak-like image appears at a high density in a portion which is originally a white image due to an excessively high charge amount. The generation mechanism will be described with reference to FIG. 3. In the case of reversal development using negatively charged toner, as shown in FIG. The developing bias is located in the middle of the black background portion, which is the low potential portion where the attenuated portion is attenuated, whereby good development is performed. The developing baisu has a potential on the surface of the developing roller, but charged toner is present in a developing portion of the developing roller that is in contact with the photoreceptor. Therefore, the potential generated by the charge of the toner itself is further applied to the developing bias. The actual developing bias is obtained by adding a voltage generated by charging of the toner itself to a voltage applied by the power supply. In this case, if the toner charge amount becomes too high, as shown in FIG. 3B, the potential generated due to the toner becomes large, so that the actual developing bias exceeds the potential of the high potential white background portion. In some cases. Then, toner adheres also to a white background portion and development occurs, and a fog image defect occurs in an obtained image, which is high-potential fog.

Therefore, in order to prevent the occurrence of normal fogging and image memory, it is effective to inject electric charge directly into the toner to increase the charge amount of the toner to some extent.
In this case, it is necessary to appropriately suppress the charge amount of the toner in order to prevent the occurrence of the high-potential fog. As in the present invention, the ionization potential on the surface of the negatively chargeable toner is set to 4.
By adjusting the ionization potential of the developing roller surface to at least 0.3 eV or more than the above-mentioned toner surface, the electric charge is directly injected into the toner to increase the charge amount of the toner. When preventing the occurrence of normal fogging and image memory, the charge amount of the toner can be reliably adjusted so that the developing bias does not exceed the potential of the high-potential white background portion, and the occurrence of high-potential fog can also be reliably prevented. Things. That is, as described above, the ionization potential adjusted in the present invention is the energy required to separate one electron from an atom or molecule in the ground state to infinity and dissociate it into a cation and a free electron. Therefore, when developing with negatively charged developer, by setting the ionization potential on the surface of the developing roller high, electrons are transferred from the surface of the developing roller to the developer having a low ionization potential carried on the surface of the developing roller. This makes it difficult for the developer to move, thereby preventing the developer from being negatively charged to an excessively high potential, and allowing the developer to be negatively charged within an optimal potential range by injecting the charge, thereby reliably generating high-potential fog. Can be prevented.

The developing method and the developing apparatus of the present invention
A developer is carried on the surface of a developing roller formed by forming a conductive layer on the outer periphery of a good conductive shaft to form a thin layer of the developer, and a charge is directly injected into the developer to remove the developing roller. By rotating along the surface of the latent image holding member in a state of contacting or approaching the latent image holding member holding the electrostatic latent image on the surface, supplying a developer to the surface of the latent image holding member The electrostatic latent image on the surface of the latent image holding member is visualized. Specifically, development can be performed by the mechanism shown in FIG. In this case, in FIG. 1, the developing is performed in a state where the developing roller 1 and the latent image holding member 3 are in contact with each other, but the developing is performed in a non-contact state where the developing roller 1 and the latent image holding member 3 are close to each other. In FIG. 1, a drum-shaped latent image holding member is used as the latent image holding member 3, but a latent image holding member having another shape such as a belt shape may be used. Further, in FIG. 1, a power supply 11 for applying a voltage to the layering blade 5 and the toner applying roller 2 is provided as a means for injecting electric charge into the developer. However, the present invention is not limited to this. When a toner stirring blade 12 is provided as in the apparatus shown in FIG. 4 instead of the roller 2, a voltage may be applied to this blade, and further a voltage may be applied to the toner storage case. A known method can be adopted.

[0037]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 100 parts of polytetramethylene ether glycol (OH value = 56) (parts by weight, the same applies hereinafter) were mixed with 1.0 part of sodium perchlorate, and
The mixture was stirred while controlling the temperature at 4 ° C., and then 4,4′-diphenylmethane diisocyanate (NCO% = 33.6) was added to 1
3.48 parts were added and stirred and mixed. Next, this reaction mixture was poured into a mold heated to 90 ° C. in advance, and a curing reaction was performed at 90 ° C. for 12 hours to obtain a roller having a conductive layer formed on the outer periphery of a metallic shaft. The surface of the obtained roller was polished to adjust the surface to a JIS 10-point average roughness of 5 μmRz to obtain a developing roller.

On the other hand, a sheet sample similar to the conductive layer of the developing roller was prepared, and the ionization potential was measured using the obtained sheet sample.
V.

The above-mentioned roller is mounted on the developing unit shown in FIG. 4 as a developing roller 1, and a negatively chargeable toner (ionization potential of 5.1 eV) for a laser beam printer 4029 manufactured by IBM Corporation is used as a toner to perform reversal development. When an image was formed and the image was evaluated, a good image was obtained without any image defects such as fog and density unevenness. Here, the developing unit shown in FIG. 4 is different from the toner applying roller 2 in FIG.
Is the same as the unit in FIG. 1 except that
The other parts are denoted by the same reference numerals as in FIG. 1 and their description is omitted. In the drawing, Bias1 indicates that a developing bias is applied to develop the toner on the printing unit, and Bias2 indicates that a voltage is applied to the blade 5 in order to increase the amount of toner charge and obtain uniform charge. The photosensitive drum 3 was a negative charging photosensitive drum.

Next, the developing unit alone was taken out, the developing roller was rotated several times while applying a voltage of -500 V as Bias2 to the blade 5, and a developing bias of -400V during normal development was applied as Bias1. The surface potential of the developing roller which appeared at this time was measured using a surface potentiometer, and was -520 V. In this case, the potential of the white background on the photosensitive drum surface is -60.
Since the voltage was set to 0 V, it was confirmed that the surface potential of the developing roller during printing was lower than the potential of the white background portion of the photosensitive drum.

Comparative Example 1 Glycerin was added with propylene oxide and ethylene oxide to give a molecular weight of 500
Polyether polyol (OH value 33) 100 with 0
Parts, 1.0 part of 1,4-butanediol, 1.5 parts of a silicone surfactant, and 0.1 part of nickel acetylacetonate.
5 parts, 0.01 parts of dibutyltin dilaurate and 2.0 parts of acetylene black are added, premixed using a mixer, and then kneaded with a paint roll to uniformly disperse acetylene black to prepare a polyol composition. did.

The polyol composition was stirred under reduced pressure to remove bubbles, and then urethane-modified MDI (NCO% = 2
3) was added and stirred for 2 minutes.
And heated for 2 hours to form a conductive layer on the outer periphery of the metallic shaft to obtain a roller. The surface of the obtained roller is polished and the surface is JIS 10-point average roughness 5
The developing roller was adjusted to μmRz.

On the other hand, a sheet sample similar to the conductive layer of the developing roller was prepared, and the ionization potential was measured using the obtained sheet sample.
V.

When an image test was carried out using this roller in the same manner as in Example 1, high potential fogging, in which toner was developed on a white background along the image printing direction, occurred, resulting in an image defect. Further, as in Example 1, the developing unit was taken out, and the surface potential of the developing roller when a developing bias was applied under the same conditions was measured.
V, which is higher than the potential of the white background of the photosensitive drum, and it was recognized that image fogging was caused.

Example 2 Glycerin was added with propylene oxide and ethylene oxide to give a molecular weight of 500
Polyether polyol (OH value 33) 100 with 0
Part, urethane-modified MDI (NCO% = 23) 25
, 2.5 parts of 1,4-butanediol, 0.01 part of dibutyltin laurate and 0.25 part of a quaternary ammonium salt were stirred and mixed. Next, the shaft is arranged, and 110
Pour the reaction mixture into a mold heated to
A curing reaction was performed at 110 ° C. for 2 hours to obtain a roller. The surface of the obtained roller is polished to adjust the average roughness to 5 μm Rz, and then the roller is immersed in a solution of 5 parts of a fluoroolefin / vinyl ether copolymer fluororesin dissolved in toluene, pulled up, and heated and dried. Then, a surface treatment was performed, and this was used as a developing roller.

A part of the surface of the obtained roller is cut off,
It was 5.4V when the ionization potential was measured. Further, when image evaluation was performed in the same manner as in Example 1,
A good image without any image defects such as fog and density unevenness was obtained.

[0048]

[0049]

[0050]

[0051]

According to the method and apparatus for developing an electrostatic latent image of the present invention, by directly injecting electric charge into the toner to increase and uniform the charge amount of the toner, ordinary fog, image memory, etc. Can be prevented, and the compatibility between the toner and the developing roller can be controlled easily and surely to prevent the occurrence of high-potential fog. It can be reliably reproduced over a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of the developing device of the present invention.

FIG. 2 is a reference diagram illustrating an example of an image in which high-potential fog has occurred and an example of an image in which normal fog has occurred.

3A and 3B are graphs showing a relationship between a developing bias and a photoconductor potential, wherein FIG. 3A is a graph showing a state when a normal image is obtained, and FIG. 3B is a graph showing a state when high potential fog occurs. It is.

FIG. 4 is a schematic view showing another example of the developing device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Development roller 2 Toner application roller 3 Photosensitive drum (latent image holding body) 4 Toner (one-component developer) 5 Layered blade 6 Transfer unit 7 Recording medium 8 Cleaning unit 9 Cleaning blade 10 Developing bias applying unit 11 Charge injecting unit 12 Toner Stirring blade

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-233479 (JP, A) JP-A-3-233478 (JP, A) JP-A-3-233477 (JP, A) JP-A-4- 191752 (JP, A) JP-A-59-90857 (JP, A) JP-A-3-187732 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08 G03G 9 / 08

Claims (3)

(57) [Claims] A developing roller having a conductive layer formed on the outer periphery of a good conductive shaft carries a negatively charged developer on the surface thereof to form a thin layer of the developer. The developer is negatively charged by applying an electric charge to the developer and directly injecting the charge into the developer, and the developing roller is brought into contact with or in proximity to a latent image holding member having an electrostatic latent image on the surface thereof. By rotating along the surface of the image carrier, a developing method of supplying a negatively charged developer to the surface of the latent image carrier to visualize an electrostatic latent image on the surface of the latent image carrier, The ionization potential of the developer surface is 4.5 to 5.
5 eV, and adjusting the ionization potential of the developing roller surface to be at least 0.3 eV or more larger than the ionization potential of the developer, thereby suppressing the movement of electrons from the developing roller surface to the developer. A method for developing an electrostatic latent image, wherein occurrence of high potential fog due to overcharging of a developer is prevented. 2. The electrostatic latent image developing method according to claim 1, wherein the conductive layer constituting the developing roller does not contain conductive powder. 3. A latent image holding member capable of holding an electrostatic latent image on a surface thereof, and a conductive layer formed on an outer periphery of a good conductive shaft,
A voltage is applied to a developing roller disposed so as to rotate along the surface of the latent image holding member in a state of contacting or approaching the surface of the latent image holding member, and a developer carried on the developing roller. And a charge injecting means for directly injecting the electric charge, and carrying a negatively charged developer on the surface of the developing roller to form a thin layer of the developer. The developer is negatively charged by directly injecting charge by means, and the developing roller is rotated along the surface of the latent image holding member in this state, whereby the surface of the latent image holding member is negatively charged. The developing device of the electrostatic latent image, which supplies the developed developer to visualize the electrostatic latent image on the surface of the latent image holding member, wherein the developer has a surface ionization potential of 4.
5 to 5.5 eV is used, and the ionization potential of the developing roller surface is adjusted to be at least 0.3 eV or more higher than the ionization potential of the developer surface, so that electrons from the developing roller surface to the developer are adjusted. An electrostatic latent image developing device, wherein the generation of high potential fog due to overcharging of the developer is prevented by suppressing the movement of the developer.