JPH08220811A - Image forming method - Google Patents

Abstract

PURPOSE: To provide an image forming method using a carrier for a negative charge type developer by which the occurrence of character smear and uneven transfer is obviated over a long period a good transfer characteristic unaffected by environment is obtainable and good fixing performance is obtainable. CONSTITUTION: This image forming method consists of a stage of developing the latent image formed on a photoreceptor 5 and transfers developing toners onto a transfer material by using a developer consisting of coloring particles contg. a binder resin and coloring materials and the carrier. The transfer stage is a stage for transferring the latent image by passing the transfer material between a conductive roller 6 which is pressed to the photoreceptor 5 and is impressed with voltage and the photoreceptor 5. The radius of curvature of the photoreceptor 5 is >=35m and the carrier is the carrier for the negative charge type developer prepd. by coating the surfaces of magnetic particles with resin layers consisting of at least the magnesium compd. expressed by the formula Mg(X)n and/or the compd. obtd. by subjecting the magnesium compd. to a hydroxylation treatment and a resin. In the formula, X denotes O/CO3 /OH and (n) denotes an integer from 1 or 2.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an image forming method using a carrier for a negatively chargeable developer.

[0002]

2. Description of the Related Art Generally, an image forming method using an electrophotographic system such as a copying machine or a printer is performed by applying a uniform electrostatic charge to a photoreceptor having a photosensitive layer made of a photoconductive material.
By performing image exposure, an electrostatic latent image is formed on the surface of the photoconductor, and the electrostatic latent image is developed with a developer to form a toner image. Further, the obtained toner image is transferred to a transfer material such as paper and then fixed by heating or pressure fixing to form a copied image. That is, the charging process, the developing process, the transfer process, the fixing process, and the cleaning process are the basic processes. In particular, the charging and transfer processes are indispensable processes, and a corona discharge system is widely used because it is possible to apply a high electric field and has excellent image uniformity.

However, the corona discharge method has problems that a high voltage must be applied and it is dangerous and that ozone is generated due to discharge and is harmful. From such a background, in recent years, practical application of a contact charging method aiming at lower voltage and ozoneless has been studied, and particularly, in the transfer step, a contact transfer method using a conductive roller has been studied. . Since this roller transfer method does not use a discharge wire, it also has an advantage that transfer unevenness due to dirt on the discharge wire does not occur.

On the other hand, in the roller transfer system, it is difficult to secure a sufficient transfer electric field and the transferability is poor, the transferability is easily influenced by the developer characteristics, and the roller characteristics vary depending on the environment. There are problems such as a change, a problem that image unevenness occurs due to uneven pressing force, and a problem that toner is scattered due to electrical repulsion when the transfer member enters the roller because the transfer member is a roller. In particular, in images such as characters and lines, the toner is piled up in a mountain shape on the image portion. Therefore, when the roller is pressed, a pressure difference occurs between the central portion and both end portions of the image, and the image is easily disturbed.

Further, in recent years, multi-color or full-color image copying technology has been rapidly expanding, and the basic formation is divided into at least three basic colors such as yellow, magenta, cyan, and if necessary, black. It is done by overlapping them. Therefore, the toner layer becomes thicker in the overlapping portion, so that the transferability is deteriorated and the image disorder at the time of transfer is more remarkable.

In order to solve the above problems, for example, in order to reduce the environmental dependence of the transfer, to improve the surface characteristics of the transfer roller and to prevent the uneven transfer, as described in JP-A 1-267676, Applying a release agent on the surface of the image carrier before transfer,
As described in JP-A-2-28684, a method of applying a lubricant to the surface of an image carrier through a transfer roller is disclosed. However, when such a method is used, when the toner remaining on the image carrier is cleaned, a slip-through phenomenon occurs, which causes image stains. Further, when the image carrier is a photoconductor, it may cause uneven charging. Further, the release agent and the lubricant cannot be continuously applied over a long period of time, and transfer unevenness occurs after long-term use.

As described above, in the image forming method including the transfer process using the transfer roller, sufficient performance has not been obtained yet.

With the miniaturization of the apparatus and the miniaturization of the developing device, the improvement of the charge rising characteristics is achieved by providing a proper charge amount at a high speed in the two-component developer after the toner is replenished and while it moves to the developing nip portion. It was an important issue to have it. Conventionally, in order to improve the charge rising characteristics of a negatively chargeable developer, it has been generally performed to add a negatively chargeable CCA to the toner. However, in the case of using the small developing device as described above, this is not enough, and the distribution of the charge amount is expanded due to the increase of the weakly charged toner, and the toner scattering in the machine and the fog appearing in the image are remarkable. As a means on the carrier side for improving the charge rising characteristic, a positively charged CCA is added to the carrier as in JP-A 2-8860. Examples of positively charged CCA are disclosed in JP-A-49
-51951, JP-A-52-10141 and the like, quaternary ammonium compounds, JP-A-56-11461 and JP-A-54-158
An alkylpyridinium compound disclosed in 932;
Alkyl picolinium compounds (eg nigrosine SO
Nigrosine EX, etc.), but these CCA
Is an organic compound with high cohesive force and has poor dispersibility. Therefore, in the coating layer of the carrier, the distribution of the amount of charge is widened due to the ubiquity or release of CCA, so that the weakly charged component increases, and character dust is likely to occur due to the electric repulsive force when entering the transfer part / fixing start part. . Further, an increase in the weakly charged component causes excessive developability, and in particular, in a superposed image portion of a full-color copying machine, the phenomenon is severe, resulting in defective transfer.

In the electrophotographic image forming method, as a means for fixing a visible image with toner on recording paper, a roller which is kept at a temperature higher than the softening point of the toner and is in direct contact with the unfixed toner image on the recording paper (hereinafter referred to as fixing) Roller)),
By a roller (hereinafter referred to as a pressure roller) which has an elastic layer on its surface and comes into pressure contact with the fixing roller via the recording paper, the recording paper carrying the unfixed toner image is heated and fixed while being held and conveyed. The heat roller fixing method has been generally used more than ever before. As a unique problem in this heat roller fixing method, there is a so-called offset phenomenon, in which molten toner adheres to the fixing roller and contaminates,
As a countermeasure against this, a highly releasable coating layer made of a low surface energy material such as fluorine resin is provided on the surface of the fixing roller,
A method of reducing the adhesion between the molten toner and the fixing roller to prevent the occurrence of offset is generally used. However, since the coating layer made of these fluorine-based resins exhibits a strong negative charging property, electrostatic repulsion occurs between the two when the toner has a negative charging property, and when the unfixed image enters the fixing nip, the toner particles A new problem called so-called character dust, which is scattered around the image edge portion, is likely to occur.

Further, as the phenomenon of the character dust, when the unfixed image enters the fixing nip in the presence of the electrostatic repulsive force between the fixing roller and the toner as described above, the unfixed image is generated. Vibration is a trigger that causes the toner particles on the edge of the image to collapse, leading to character dust.
As a means for preventing character dust, it is effective to pass an unfixed image through a fixing device without giving vibration as much as possible.

Further, in response to the recent demand for high image quality, even if a noticeable image defect such as character dust does not occur, the fine line reproducibility and the output of a high-resolution image cause the edge of the image portion to disappear. Sharpness has come to be required.

[0012]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming method having a transfer step by a conductive roller to which a voltage is applied, for a long time without causing character dust. An object of the present invention is to provide an image forming method using a carrier for a negatively chargeable developer, which is capable of obtaining good transfer characteristics without unevenness and being not affected by the environment.

Further, an object of the present invention is to provide an image forming method which is excellent in transferability and does not cause character dust even in a heat roller fixing system having a structure in which a coating layer made of a fluororesin is provided on the surface of a fixing roller. To provide.

[0014]

The above object of the present invention can be achieved by the following constitution.

1. A step of developing a latent image formed on a photoreceptor with a developer composed of colored particles containing at least a binder resin and a colorant and a carrier, and transferring the developed toner to a transfer material. In the image forming method, the transfer step is a step of transferring by passing a transfer material between a conductive roller to which a voltage applied to the photoconductor is applied and the photoconductor. The radius is 35 mm or more, the carrier is a magnesium compound represented by at least the following general formula on the magnetic particles and / or a resin layer comprising a compound and a resin obtained by hydroxylating the surface of the magnesium compound, An image forming method, characterized in that the carrier is a negatively charged developer carrier.

General Formula Mg (X) n Here, X represents O / CO ₃ / OH, and n represents an integer of 1 or 2.

2. The latent image formed on the photoconductor was developed using a developer composed of colored particles containing at least a binder resin and a colorant, and a carrier, and the developed toner was transferred to an intermediate transfer material. In the step of transferring to the post-transfer material, the transfer step is a step of transferring by passing the transfer material between the conductive roller to which a voltage pressing the intermediate transfer member is applied and the intermediate transfer member. In the forming method, the radius of curvature of the intermediate transfer material is 35 mm or more, and the carrier is obtained by hydroxylating at least the magnesium compound represented by the following general formula on the magnetic particles and / or the surface of the magnesium compound. An image forming method, which is a carrier for a negatively chargeable developer formed by coating a resin layer made of a compound and a resin.

General Formula Mg (X) n Here, X represents O / CO ₃ / OH, and n represents an integer of 1 or 2.

3. Using a developer composed of a toner and a carrier containing at least a binder resin and a colorant, after the completion of the development step and the transfer step, they are pressed against each other and rotated,
In an image forming method in which a carrier is heated and fixed by a fixing device having a pair of rollers having an elastic layer coated with a fluororesin as a surface layer thereof, the carrier is at least a magnesium compound represented by the following general formula on magnetic particles and The image forming method is a carrier for a negatively chargeable developer having a coating layer made of a resin.

General Formula Mg (X) n Here, X represents O / CO ₃ / OH, and n represents an integer of 1 or 2.

The present invention will be described in detail below.

First, the carrier of the present invention will be described.

Examples of the magnetic particles used in the carrier of the present invention include iron, ferrite, magnetite and other metals such as iron, nickel, cobalt, copper and zinc, alloys containing these metals, and compounds. Among them, it is preferable to use magnetic particles having a specific gravity of 3 to 7 because the stress applied to the developer during mixing and stirring in the developing device is reduced. Furthermore, the saturation magnetization is 15-80emu
/ G, volume average particle size ["Microtrack SRA MK
-II "(measured by Nikkiso Co., Ltd.) is preferably 20 to 100 μm.

The resin used in the carrier of the present invention includes styrene resins, acrylic resins, styrene-acrylic resins, vinyl resins, ethylene resins, rosin-modified resins, polyamide resins, polyester resins, Silicone resin or the like can be used. These resins may be used in combination.

Specific examples of the magnesium compound used in the carrier of the present invention include magnesium oxide / magnesium hydroxide / magnesium carbonate, which can be obtained by hydroxylating the surface of magnesium carbonate (3 to 5). Mg
It also includes magnesium hydroxycarbonate having a composition of CO ₃ .Mg (OH) _2. (3-7) H ₂ O. Further, a compound obtained by subjecting the surface of the above magnesium compound other than magnesium carbonate to a hydroxylation treatment may be used. These compounds can be obtained by subjecting the surface of magnesium oxide, magnesium carbonate or the like to a hydroxylation treatment. Hydroxylation can be obtained by causing water vapor not containing carbon dioxide to act on the surface of magnesium oxide, magnesium carbonate or the like.

The above magnesium compound preferably has an average particle size of 1 nm to 200 nm and a BET specific surface area of 500 to 10 m ² / g. In particular, particles having an average particle diameter of 5 nm to 100 nm and a BET specific surface area of 200 to ²⁰ m ² / g are more preferable from the viewpoint of dispersibility. Average particle size less than 1 nm, BET specific surface area 500 m ²
Particles of / g or more are less likely to exhibit the spent prevention effect.
Further, particles having an average particle diameter of more than 200 nm and particles having a BET specific surface area of 10 m ² / g or less are difficult to disperse in the coating layer,
The amount of free components increases and the chargeability with the toner is likely to be impaired. Average particle size is transmission electron microscope LPA-3000 / 3100
The number average primary particle diameter measured by (Otsuka Electronics) is shown. The BET specific surface area is measured by the BET specific surface area measuring device Flow.
The value measured by Sorb 2300 (made by Shimadzu Corporation) is shown. Further, the resistance is preferably 10 ⁶ to 10 ¹⁰ Ωcm. The resistance measurement method indicates a value measured in a powder state under the condition that a constant pressure is applied. In this measurement, the volume resistivity measured in a normal temperature and normal humidity environment is shown.

Magnesium oxide can be formed by burning metallic magnesium. In this case, the particle size of magnesium oxide or the like can be adjusted by controlling various combustion conditions. The method for producing magnesium carbonate can be performed, for example, by obtaining sodium trihydrate crystals by adding sodium carbonate to an aqueous solution of a magnesium salt such as magnesium oxide while passing carbon dioxide. Furthermore, an anhydrous salt is obtained by drying and dehydrating this in a carbon dioxide stream. Further, the magnesium carbonate produced in the gas phase reaction can produce a single crystal by reacting the magnesium metal vapor in a steam atmosphere containing carbon dioxide. Magnesium hydroxide is heated by adding an alkali to an aqueous solution of magnesium oxide magnesium salt,
Obtained by applying pressure. Further, magnesium hydroxide produced by a gas phase reaction can be produced by hydroxylating metallic magnesium vapor in a steam atmosphere containing no carbon dioxide to produce a single crystal. The hydroxide-treated magnesium compound can be treated by leaving particles of magnesium oxide, magnesium carbonate and the like in an atmosphere of 50 ° C. and 80% RH for 1 hour. In this case, the mixing may be performed in a specific container, or the treatment may be performed by a fluidized bed device.

As the magnesium compound of the present invention, those having a single crystal structure obtained by a gas phase reaction are particularly preferable. The single-crystal magnesium compound obtained by the gas-phase reaction has a remarkable effect in improving the charge rising characteristics, as compared with the polycrystalline one. Further, since it has sharp corners, the spent toner is scraped off, which is effective for the anti-spent property.

The addition amount of the magnesium compound is preferably 0.5 to 70 wt% in the coating layer, more preferably 1 to 60 w.
t%. If the addition amount is less than 0.5 wt%, the effect is insufficient, and if it exceeds 70 wt%, it becomes difficult to form the coating layer, and the durability such as film peeling is deteriorated.

The method for producing the carrier of the present invention is not particularly limited, and examples thereof include a general fluidized bed type spray coating method, dipping type coating, and sintering type coating. Dry coating is preferred from the viewpoint that granulation does not occur and the productivity is improved, and the dispersion of magnesium oxide and magnesium carbonate is improved.

As the toner used in the present invention, a general toner can be used, but a toner externally added with inorganic fine particles which can improve the developing property and cleaning property by improving the fluidity is preferable.

As the above-mentioned inorganic fine particles, silica fine particles / titania fine particles whose surfaces are hydrophobized with a silane coupling agent, a titanium coupling agent or the like are preferably used from the viewpoint of the ability to impart a negative charging property and the effect of improving the fluidity. The inorganic fine particles preferably have a number average primary particle diameter of 5 to 100 nm.

As the binder resin used in the toner, a polyester resin is preferably used because it has a high capability of imparting a negative charging property. Further, in order to further improve the charge rising property, it is more preferable to add a negatively chargeable charge control agent such as a chromium-containing metal complex.

As the colorant used in the toner, for example, carbon black / nigrosine dye is used as the black toner, and CI pigment blue 15: 3 and CI pigment blue are used as the pigments required for the yellow, magenta and cyan toners. 15, CI Pigment Blue 15-6, CI
Pigment Blue 68, CI Pigment Red 48-3,
C. I. Pigment Red 122, CI Pigment Red 2
Pigments such as 12, CI Pigment Red 57-1, CI Pigment Yellow 17, CI Pigment Yellow 81, and CI Pigment Yellow 154 can be preferably used.

Next, the transfer method of the present invention will be described.

There is a step of developing the latent image formed on the photosensitive member and transferring the developing toner to a transfer material, or a step of temporarily transferring the developing toner to an intermediate transfer member and then transferring it to the transfer material. Then, in the image forming method, wherein the transfer step is a step of transferring by applying a voltage-applied conductive roller to the photosensitive member and the intermediate transfer member, the radius of curvature at the transfer portion is 35 mm.
This is a method using the above image carrier or intermediate transfer member.

At this time, the applied voltage is +2 to +5 kV in absolute value.
DC is preferred.

The transfer roller comprises a cored bar made of a stainless steel rod and a resin material such as polyurethane rubber, silicone rubber, styrene-butadiene copolymer elastomer, olefinic elastomer or the like, which is a foamed type having a cell size of about 10 to 100 μm or an open-cell type. In addition, the resin material is composed of carbon black as a conductivity-imparting agent, a low-resistance inorganic substance such as metal powder, or an electrically conductive elastic portion mixed with an organic conductive agent. Single layer type,
Polyvinylidene fluoride (PVDF), polyamide 6 (nylon 6), polyamide 66 (nylon 66), polyethylene terephthalate (PET), perfluoroacrylate resin (PF) is formed on the outer peripheral surface of the single layer type elastic portion.
A), the surface coating layer made of polyester resin, etc.
There is a coating type that provides a film thickness of up to 100 μm.

The outer diameter of the transfer roller is preferably 15 to 30 mm. Further, the electric resistance between the shaft body and the outer periphery of the roller when 100 V is applied is preferably 10 ² Ω · cm to 10 ¹⁰ Ω · cm. Further, the rubber hardness is preferably 60 ° or less (JIS-K6301 Asker-C scale hardness) as measured by a rubber hardness meter.

As the photoconductor used in the present invention, a commonly used selenium photoconductor, amorphous silicon photoconductor, or OPC photoconductor can be used.

The mechanical structure of the fixing device for fixing the toner image formed by the developer of the present invention onto the recording paper is as follows.
It is preferable that both the fixing roller and the pressure roller have elastic layers on their surfaces, and it is particularly necessary that the rubber hardness of both rollers be close to each other. When the fixing roller and the pressure roller having such a structure are pressed against each other, since the elastic layers on the surfaces of both rollers exhibit the same deformation, the fixing nip formed in the pressing contact portion has a shape without a curvature, and therefore, a straight shape is obtained. This is because the recording paper does not vibrate, which is a trigger of character dust, because a proper paper passage path is secured. In this case, the hardness of both rollers is 50 ° or more and 85
It is preferably not more than °. If the hardness is less than 50 °, the amount of deformation of the elastic layer on the roller surface becomes excessive, causing a problem in the paper passing property of the recording paper. When the hardness is higher than 85 °, it becomes difficult to secure the nip width required for fixing the toner. Further, in order to achieve the present invention, it is preferable that the hardness difference between both rollers is within 15 °. When a fixing roller and a pressure roller having a hardness difference of 15 ° or more are used in combination, the curvature generated in the fixing nip portion causes vibration when the recording paper passes, leading to character dust.

The elastic layer having these hardnesses can be formed of silicone rubber, fluororubber or the like. For these hardnesses, the values measured by an Asker C hardness meter are used.

Further, according to the present invention, it is possible to provide a releasing layer made of a fluororesin having a low surface energy in order to impart a releasing property to the roller surface for the purpose of preventing offset. Specific examples of the release layer made of such a fluorine resin include polyvinylidene fluoride (PVF), polytetrafluoroethylene (PTFE), and polytetrafluoroethylene / perfluoroalkoxy vinyl ether copolymer (PFA). You can In this case, the thickness of the release layer made of a fluororesin is preferably 20 to 70 μm.

[0044]

The magnesium compound has a very strong positive charging property and can easily make the toner negatively charged when added to the carrier. Therefore, the charging characteristics are excellent, and the charge amount distribution does not change. Further, since it is a hard inorganic material, the toner spent generated in copying a large number of sheets is gradually scraped off by friction between the carriers, and stable charge rising characteristics can be obtained for a long period of time.

When the surface of the magnesium compound is subjected to hydroxylation treatment, the magnesium compound becomes an inorganic material having a low degree of hydrophobicity, so that it is affected by humidity. Especially by absorbing water under high humidity, the positive charging property is increased. Therefore, in order to prevent the change of the chargeability due to the humidity, the surface of the magnesium compound is subjected to a hydroxylation treatment in advance, whereby the change with time of water absorption can be prevented.

Further, since a certain layer is hydroxylated and has a core, it does not impair the hardness of the magnesium compound as the core component, and thus exerts a great effect in preventing toner spent.

The structure of the magnesium compound is preferably a single crystal structure obtained by a gas phase reaction. The single-crystal magnesium compound obtained by the gas phase reaction has a higher purity and a higher positive charging property than general polycrystalline magnesium compounds, and has a remarkable effect in improving the charge rising characteristics.

Further, since it is a single crystal having a small grain size, the dispersibility in the carrier shell is good.

Furthermore, when this magnesium compound is added to the carrier, the spent is drastically reduced, and it is possible to maintain good charge rising characteristics for a long period of time. This is because the single-crystal magnesium compound is a hard inorganic material and has a sharp angle, so that the spent toner is gradually scraped by friction between the carriers.

In order to prevent character dust when entering the transfer roller portion, the charge amount distribution of the developer should be made as narrow as possible to reduce the weak charge component, and the charge amount distribution should be maintained for a long time. It can be achieved by things. In order to narrow the distribution of the amount of charge, it is necessary to improve the rise of charge, and the object of the present invention can be achieved by improving the positive chargeability of the carrier.

That is, the general formula Mg (X) n (where X is
O / CO ₃ / OH, and n is an integer of 1 or 2. The above effects can be achieved by using a carrier for a negatively chargeable developer obtained by coating a resin layer comprising a magnesium compound represented by the formula (4) and / or a compound obtained by subjecting the surface of the magnesium compound to a hydroxylation treatment and a resin. However, the reason is that the magnesium compound has a very strong positive charging property and can easily negatively charge the toner when added to the carrier. Therefore, it has excellent charge rising characteristics,
It is possible to reduce weakly charged components. Further, since it is a hard inorganic material and the single crystal magnesium compound has an acute angle, the toner spent fused on the carrier surface is scraped off, so that stable charge rising characteristics can be obtained for a long period of time.

Further, by using the magnesium compound which has been subjected to the hydroxylation treatment, it is possible to prevent the charge amount from changing due to the environment. The cause of the decrease in the amount of charge under high humidity is that the external charge added to the toner as a fluidity improver absorbs water and the charge sequence moves. In order to prevent the water absorption of the external additive under high humidity, it was achieved by making the external additive added to the toner as hydrophobic as possible, but in recent years, in order to prevent the change of the charging property due to the environment. A means of adding inorganic fine particles such as silica to the carrier is also taken. However, in the carrier as well, the inorganic fine particles absorb water over time, and even if the external additive of the toner is made hydrophobic, the charge order of the carrier moves and the chargeability changes over time. Therefore, the purpose of the present invention can be achieved by using a magnesium compound that has been subjected to a hydroxylation treatment in advance to prevent water absorption over time under high humidity.

That is, the reason why the above effect is achieved by adding the magnesium compound which has been subjected to the hydroxylation treatment to the carrier is that the magnesium hydroxide compound has been previously subjected to the hydroxylation treatment, so that the magnesium hydroxide compound is kept under high humidity. Since the water absorption does not proceed even if left standing and used, the distribution of the charge amount does not change even under high humidity, and the generation of the weakly charged component can be suppressed.

Electric resistance when 100 V is applied 10 ² Ω · cm to ^{10 10} Ω
・ When a conductive transfer roller with a size of cm is used, the transfer electric field cannot be originally applied. Therefore, when the charge amount of the toner becomes large, the transfer electric field is easily canceled by the electric charge of the toner, and the transferability deteriorates. To do. That is, the transferability changes greatly due to the change in the toner charge amount. Further, since the transfer material is pressed by the toner, it is easily affected by the moisture adsorbed by the toner, and when a hygroscopic toner is used, the transfer electric field under high humidity becomes small. That is, the transferability changes due to the environmental change. The roller itself also changes its resistance due to changes in temperature and humidity, which causes a change in transferability. In such a situation, when the radius of curvature of the transfer portion of the intermediate transfer material is 35 mm or more, the transfer time is increased, and the transfer electric field and the pressing force are made uniform, so that the transferability is improved. And especially,
By setting the diameter of the transfer roller to 10 to 100 mm, sufficient transfer performance can be obtained without causing image distortion. When the diameter is increased, the transfer time is increased and the transfer efficiency is improved. Further, since the transfer electric field is perpendicular to the transfer direction, the image distortion due to the distortion of the transfer electric field hardly occurs. However, on the other hand, since the pressing time becomes long, the image disturbance due to mechanical vibration or the like increases. The range that satisfies both of these is 10 to 100 mm.

That is, when the radius of curvature is 35 mm or less,
The transfer rate is low and transfer unevenness occurs. If the diameter of the transfer roller is 10 mm or less, a sufficient transfer time cannot be obtained, the transfer rate becomes low, and image distortion occurs. When it is 100 mm or more, the transfer time is too long, and the image is disturbed due to contact.

In order to prevent character dust when entering the fixing nip, it is necessary to narrow the distribution of the amount of charge and to eliminate particularly weakly charged toner from the developer. This is because the weakly charged toner has a low adhesion to the recording paper and easily scatters from the edge portion of the image due to the electrostatic repulsive force with the fixing roller. Therefore, it is effective to prevent the character dust by using a developer having a small charge amount distribution of weakly charged toner and maintaining the charge amount distribution for a long period of time. In order to narrow the distribution of the charge amount of the developer and reduce the amount of weakly charged toner, it is particularly important to improve the charging rise, and for that purpose, it is effective to improve the positive charging property of the carrier.

Next, as an improvement of the fixing device used in the present invention, in order to prevent the toner scattering at the image edge portion due to the vibration of the recording paper when passing through the fixing nip portion, the unfixed image is fixed to the fixing nip portion. It is required that the passage of the recording paper in the process in which the toner is fixed through the above-mentioned process has a linear configuration. In the structure of a conventional general fixing device, since the fixing roller has a structure that presses the surface of the pressure roller by a combination of a rigid fixing roller and a pressure roller whose surface layer has elasticity, a fixing nip having a curvature is formed. Therefore, when the unfixed toner image passes through the fixing nip portion, the curvature bends the recording paper and causes vibration, resulting in character dust. In contrast to such a conventional technique, the present invention proposes a fixing device characterized in that both the fixing roller and the pressure roller have an elastic layer coated with a fluororesin as a surface layer thereof. In the fixing device of the present invention, since both the fixing roller and the pressure roller have the elastic layer, both rollers are uniformly deformed in the fixing nip portion formed by the pressing of the both, and linear fixing without curvature is performed. Since the nip is formed, a straight paper path for the recording paper is secured, and vibration of the recording paper does not occur at the fixing nip, which is extremely effective in preventing character dust.

Particularly in the image formation performed by the developer and the fixing device of the present invention, the toner in the unfixed state is stably attached to the recording paper, and the fixing roller is an elastic roller and a straight nip is formed. Because of the small shape, the shear stress applied to the toner image at the fixing nip portion is small, so even if a remarkable image defect such as character dust does not occur, the toner does not collapse at the image edge portion and the image is sharp. It is possible to fix the image with extremely high image quality and excellent reproducibility of fine lines.

[0059]

EXAMPLES The present invention will be described below, but the present invention is not limited to these examples. In addition, "part" represents a weight part below.

[Toner] Polyester resin 100 parts Polypropylene 5 parts Azo-based chromium metal complex (charge control agent) 3 parts The following colorants are added to the above components, and kneading, kneading meat, crushing and classification are performed to obtain a volume average particle size. A powder having a diameter of 8 μm was obtained. Further, 100 parts of this powder and 2.0 parts of hydrophobic silica fine particles (number average primary particle diameter 16 nm) were mixed with a Henschel mixer to obtain a toner A.

Colorant Yellow toner; Yellow pigment (CI Pigment Yellow 17) 8 parts Magenta toner; Magenta pigment (CI Pigment Red 122) 8 parts Cyan toner; Blue pigment (CI Pigment Blue 15-3) 4 parts Black toner; Carbon Black 10 parts [Production of carrier] Specific gravity 5.0, volume average particle size 50 μm, 1000
The saturation magnetization is 25 when an Oersted external magnetic field is applied.
On the surface of emu / g Cu-Zn ferrite particles, MMA / St
A copolymer having a composition of 6/4 was prepared as follows so that the average film thickness of the coating layer was 2.0 μm.

Carrier additive No. Type Average particle size BET specific surface area Addition amount (nm) (m ² / g) (wt%) C-1 MgO 13 158 10 C-2 MgCO ₃ 13 149 10 C-3 Mg ( OH) ₂ 48 33 30 C-4 Hydroxylation treatment MgO 113 14 30 C-5 Hydroxylation treatment MgCO ₃ 183 11 20 HC-1 --- --HC-2 Nigrosine SO (Positively charged CCA) 302 5 3 HC-3 R-972 (hydrophobic silica) 6 120 50 * Average particle size indicates number average primary particle size All the magnesium compounds used in C-1 to C-5 have a single crystal structure.

[Preparation of developer] 460 g of each of the above carriers
And 40 g of toner are tested with a V-type mixer at 30 ° C; 80
The mixture was mixed for 20 minutes in a% RH environment to prepare a developer for a live-action test.

[Evaluation of Transfer Performance by Actual Machine] Kon manufactured by Konica Corporation
The transfer part of the ica 9028 is made by forming a core material made of a stainless steel rod and a resin material such as polyurethane rubber and silicone rubber on the outer periphery of the foam type with a cell size of 50 μm, and carbon black as a conductivity-imparting agent on the resin material. The method was modified to use a transfer roller composed of an elastic part mixed with the organic conductive material. The transfer roller is always in pressure contact with the photosensitive drum when developing a single-color image, and is retracted and kept at a separate position when developing a color image.
Pressed only during transfer. The applied voltage is +3 to + 4kVDC,
A transfer roller of the type that cleans the roller surface with a blade is used and modified as shown in Fig. 1.
As shown in FIG. 2, modification was performed using an intermediate transfer member. Using the modified machine, a 30,000-sheet live-copy test was conducted and the following evaluation items were examined under an environment of 30 ° C and 80% RH.

The order of development is yellow, magenta, cyan, and black.

In FIG. 1, reference numerals 1 to 4 represent developing units, and 1
Developing unit uses yellow developer, 2 developing unit uses magenta developing agent, 3 developing unit uses cyan developing agent, 4 developing unit uses black developing agent .
The photosensitive drum 5 is charged by the band electrode 8 to expose the exposed portion.
After being exposed by 11, the image is first developed by the developing device 1. After this, the photosensitive drum 5 is charged again by the strip electrode 8, exposed by the exposure unit 11, and then developed by the second developing device. Further, the photosensitive drum 5 is charged by the band electrode 8, exposed by the exposure unit 11, and developed by the developing unit 3. Further, the strip electrode 8
The photosensitive drum 5 is charged by the
Develop with the developing device. During the above steps, the transfer roller 6 is at a position retracted from the photoconductor drum 5 and is not in contact with the photoconductor. After a color image of four colors is formed on the photosensitive drum 5 by the above steps, the transfer roller 6 is brought into pressure contact with the photosensitive drum 5, and an image support such as paper conveyed from the paper feeding unit 9 between them. And then transfer. After the transfer, the photosensitive drum 5 is cleaned by the cleaning unit 7. The method shown in FIG. 1 is called a batch transfer method.

In FIG. 2, first, the photosensitive drum 5 is charged by the belt electrode 8, then exposed by the exposure unit 11, and then developed by using the yellow developer in the first developing unit. The image developed on the photosensitive drum is transferred to the intermediate transfer member 10. After that, the photosensitive drum 5 is cleaned by the cleaning unit 7. Next, the photosensitive drum 5 is charged by the strip electrode 8 and exposed by the exposure unit 11, and then developed by the magenta developer by the second developing device. Then, the image developed on the photosensitive drum 5 is transferred to the intermediate transfer member 10, and then the photosensitive drum 5 is cleaned by the cleaning unit 7. Next, the photosensitive drum 5 is charged by the strip electrode 8 and exposed by the exposure unit 11, and then development is performed with the cyan developer by the developing device 3. Then, the image developed on the photosensitive drum 5 is transferred to the intermediate transfer member 10, and then the photosensitive drum 5 is cleaned by the cleaning unit 7. Next, the photosensitive drum 5 is charged by the belt electrode 8 and exposed by the exposure unit 11, and then development is performed with the black developer by the developing device 4 (4). Then, the image developed on the photosensitive drum 5 is transferred to the intermediate transfer member 10, and then the photosensitive drum 5 is cleaned by the cleaning unit 7. As a result, a color image composed of four colors is formed on the intermediate transfer member 10. The transfer roller 6 is retracted from the intermediate transfer member while this image is formed. After the color image is formed on the intermediate transfer body 6, the transfer roller 6 is brought into pressure contact with the intermediate transfer body 6, and the image support such as paper transported from the paper feeding unit 9 is transported between them to transfer the image. Figure 2
The method described in 1. is referred to as an intermediate transfer body method.

The color image formed on the image support such as paper in FIG. 1 or 2 is fixed on the image support by using a heat roll fixing device.

[Evaluation Items] (1) Transferability 20 mm × 50 mm on the photoconductor at the initial stage and after copying 30,000 sheets.
The patch was developed and transferred, and the transfer rate when the weight of the toner attached to the transfer paper is W and the weight of the toner W ′ remaining on the photoconductor after the transfer is W ′ was determined in the following manner.

Transfer rate (%) = (weight of toner on transfer paper) / (weight of developed toner) = W ′ / (W + W ′) × 100 Incidentally, the evaluation of transfer rate is expected to be disadvantageous to transfer. The overlapping color blue was evaluated.

(2) Distribution of charge amount Initially and after copying 30,000 sheets, ES manufactured by HOSOKAWA MICRON
PART ANALYZER Model: EST-1 was used to measure under the following conditions and the resulting number% distribution curve was cut with scissors to measure the weight, and the weight of the toner with q / d distribution of -0.5femt C / μm or less It was evaluated by the percentage of the total weight.

PULSE DURATION ； 3sec Interval ； 4sec Gas Pressure ； 0.3kg / cm ² Measured Flow Rate ； 300ml / min Rotation Speed ； 200rpm Measured Toner Count ； 2000 or more (3) Character dust 200μm interval, width 200μm 1cm length line 5 sheets of the chart were copied, and the dust situation in that portion was observed and classified into the following 4 ranks for judgment.

A: No dust around the line is observed when magnified 20 times with a microscope. B: Not visible by visual inspection, but dust around the line is observed when observed with a microscope 20 times. Observed D: Dust is so intense that it is difficult to distinguish between lines.

The evaluation of character dust was carried out on three colors of superimposing colors blue, green and red, which are most likely to cause excessive developability when copying a full-color image and are disadvantageous in transferability.

The evaluation results are shown below.

(1) In case of batch transfer process (FIG. 1) Carrier No. Transfer rate (%) Initial change of 30,000 sheets Example-1 C-1 97.0 96.5-0.5 Example-2 C-2 98.4 98.5 + 0.1 Example-3 C-3 98.9 98.9 ± 0 Example-4 C-4 99.0 98.8-0.2 Comparative Example-1 HC-1 74.3 49.1-25.2 Comparative Example-2 HC-2 96.5 58.3-38.2 Comparative Example-3 HC-3 87.8 50.4 −37.4 Carrier No q / d ≦ −0.5femt C or less (%) Character dust initial 30000 sheets Change amount Blue Green Red Example-1 C-1 0.9 0.8 −0.1 AAA Example-2 C-2 0.7 0.6 − 0.1 AAA Example-3 C-3 0.8 0.8 ± 0 AAA Example-4 C-4 1.0 0.8 -0.2 AAA Comparative Example-1 HC-1 22.1 60.2 38.1 DDD Comparative Example-2 HC-2 1.3 56.4 54.2 CCC Comparative Example -3 HC-3 5.0 60.0 55.0 CCC (2) In case of process using intermediate transfer body (Fig. 2) Carrier No. Transfer rate (%) Initial 30000 sheets Change amount Example-1 C-1 98.0 97.2 0.8 Example-2 C-2 98.4 98.5 + 0.1 Example-3 C-3 98.3 98.9 + 0.5 Example-4 C-4 99.0 99.0 ± 0 Comparative Example-1 HC-1 74.3 49.4-24.9 Comparative Example-2 HC -2 96.5 57.2 -39.3 Comparative example -3 HC-3 86.2 50.4 -35.8 Carrier No q / d ≤ -0.5femt C or less (%) Initial character dust 30000 sheets Change amount Blue Green Red Example-1 C-1 1.0 1.0 ± 0 AAA Example-2 C-2 0.8 0.9 +0.1 AAA Example-3 C-3 1.0 0.9 -0.1 AAA Example-4 C-4 0.6 0.6 ± 0 AAA Comparative Example-1 HC-1 29.2 61.3 32.1 DDD Comparative Example-2 HC-2 1.3 59.6 58.3 CCD Comparative Example-3 HC-3 3.7 60.0 56.3 DDD As is clear from the above results, the embodiment of the present invention has a longer transfer unevenness than the comparative example. It is possible to obtain good transfer characteristics that are not affected by the environment.

[Evaluation of Actual Fixing Performance] Konica Copier U-
Bix 3035 is modified to the following structure and at 20 ℃; 55% RH environment
A test shot of 30,000 copies was performed and the following evaluation items were examined.

(1) Charging section → Discharge polarity was changed from negative to positive, and the potential of the photoconductor in the image area was adjusted to 750V and the potential of the photoconductor in the non-image area was adjusted to 50V. (2) Transfer area → Discharge The polarity was changed from minus to plus (3) Development unit → Development bias was changed to −150 V (4) Fixing unit → Fixing device 1 having the structure shown in FIG. 3 and fixing device 2 having the structure shown in FIG. , Each was evaluated.

The fixing device 1 will be described with reference to FIG.

A halogen heater lamp 19 is built in the center, and a hollow aluminum roller 12 having a diameter of 30 mm is provided on the surface with a rubber hardness of 80 ° by an Asker C hardness meter and a thickness of 1 mm L.
A fixing roller having a TV rubber layer 13 and a PFA tube layer 14 having a thickness of 50 μm, and a hollow aluminum roller having a diameter of 30 mm
A fixing device 1 in which a pressure roller having an LTV rubber layer 16 having a rubber hardness of 80 ° by an Asker C hardness meter and a PFA tube layer 17 having a thickness of 50 μm is pressed against the surface of 15. The cleaning roller 18 is in contact with the fixing roller.

The fixing device 2 will be described with reference to FIG.

A halogen heater lamp 19 is built in the center of the hollow aluminum roller 12 having a diameter of 30 mm.
A fixing roller having a PFA tube layer 14 of 50 μm,
The fixing device 2 is formed by pressing a pressure roller having an LTV rubber layer 16 having a rubber hardness of 80 ° by an Asker C hardness meter on the surface of a hollow aluminum roller 15 having a diameter of 30 mm.
The cleaning roller 18 is in contact with the fixing roller.

[Evaluation Items] (1) Charge amount distribution: The charge amount distribution was evaluated in the same manner as in the case of the actual evaluation of the transfer performance. (2) Character dust: In the same manner as in the case of the actual evaluation of the transfer performance. The results of evaluating the character dust are shown below.

Carrier No q / d ≦ −0.5femt C or less (%) Character dust initial 30000 sheets Change amount Fixing device 1 Fixing device 2 Example-1 C-1 1.0 0.9 -0.1 AB Example-2 C-2 0.6 0.5-0.1 AB Example-3 C-3 0.8 0.8 ± 0 AB Example-4 C-4 1.0 0.8-0.2 AB Example-5 C-5 1.1 0.7-0.4 AB Comparative Example-1 HC-1 23.1 61.2 38.1 CD Comparative Example-2 HC-2 1.2 55.4 54.2 BC Comparative Example-3 HC-3 5.0 60.0 55.0 BC As can be understood from the above results, the developer of the present invention shows a sharp charge distribution over a long period of time, Therefore, the generation of the weakly charged toner was controlled, and the generation of character dust was not observed in the image formation by the developer and the fixing device according to the embodiment of the present invention.

[0085]

The image forming method using the carrier for the negatively chargeable developer according to the present invention is an image forming method having a transfer step by means of a conductive roller to which a voltage is applied. In addition, it is possible to obtain good transfer characteristics that are free from unevenness of transfer and are not affected by the environment, and further, even in a fixing device having a coating layer made of a fluorine-based resin on the surface layer of the fixing roller, no character dust occurs.

[Brief description of drawings]

FIG. 1 is a sectional view of a photosensitive drum.

FIG. 2 is a sectional view of an intermediate transfer body (transfer drum).

FIG. 3 is a sectional view of the fixing device 1.

FIG. 4 is a sectional view of the fixing device 2.

[Explanation of symbols]

 1 1st developing device 2 2nd developing device 3 3rd developing device 4 4th developing device 5 Photosensitive drum 6 Transfer roller 7 Cleaning unit 8 Belt electrode 9 Paper feeding unit 10 Transfer drum (intermediate transfer member)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Kobayashi 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Inventor Yoshiki Nishimori 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company

Claims (3)

[Claims] 1. A latent image formed on a photoreceptor is developed with a developer comprising colored particles containing a binder resin and a colorant, and a carrier, and the developed toner is used as a transfer material. In the image forming method, the transfer step is a step of transferring by passing a transfer material between a conductive roller to which a voltage applied to the photoconductor is applied and the photoconductor. The photoreceptor has a radius of curvature of 35 mm or more, and the carrier is composed of a resin and a compound obtained by subjecting at least a magnesium compound represented by the following general formula on the magnetic particles and / or a surface of the magnesium compound to a hydroxylation treatment. An image forming method, which is a carrier for a negatively chargeable developer, which is formed by coating a resin layer. Here the general formula Mg (X) n, X represents a O / CO ₃ / OH, n is an integer of 1 or 2. 2. A latent image formed on a photoconductor is developed using a developer consisting of colored particles containing a binder resin and a colorant and a carrier, and the developed toner is intermediately transferred. In the step of transferring to the transfer material after transfer to the material, the transfer step transfers by transferring the transfer material between the conductive roller to which a voltage applied to the intermediate transfer body is applied and the intermediate transfer body. In the image forming method, which is a step, the intermediate transfer material has a radius of curvature of 35 mm or more, and the carrier has at least a magnesium compound represented by the following general formula on the magnetic particles and / or a surface of the magnesium compound is subjected to a hydroxylation treatment. A resin layer comprising a compound and a resin obtained by
An image forming method, characterized in that the carrier is a negatively charged developer carrier. Here the general formula Mg (X) n, X represents a O / CO ₃ / OH, n is an integer of 1 or 2. 3. A developer comprising a toner containing a binder resin and a colorant and a carrier is used, and after the development step and the transfer step are finished, they are pressed against each other and rotated, and a fluorine-based surface layer is formed. In an image forming method in which a fixing device comprising a pair of rollers having an elastic layer coated with a resin is used for heat fixing, the carrier comprises a coating layer comprising at least a magnesium compound represented by the following general formula and a resin on the magnetic particles. An image forming method, which is a carrier for a negatively chargeable developer having the same. Here the general formula Mg (X) n, X represents a O / CO ₃ / OH, n is an integer of 1 or 2.