JP3601246B2 - Non-magnetic one-component developer and image forming method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic developer and an image forming method applied to a printer, a digital and analog copier, a facsimile, and the like.
[0002]
[Prior art]
Generally, in the electrophotographic system, an organic photoconductive photoconductor (usually processed into a drum shape) in which a photosensitive layer mainly composed of various photoconductive substances and a binder resin is coated on a base such as a metal such as aluminum. An electrostatic latent image is formed by various means on the photoreceptor drum), and the electrostatic latent image is developed with a powdered developer. After transferring the powder on the material, fixing is performed by a method such as pressure and heating.
[0003]
[Problems to be solved by the invention]
In recent years, along with market demands such as personalization and space saving, there has been a tendency for miniaturization of electrophotographic devices such as copiers and printers. In order to reduce the size of these devices, it is desired to reduce the diameter of the photosensitive drum. As the photoconductor drum, an organic photoconductive photoconductor drum, in particular, a multilayer organic photoconductor is mainly used.
In general, the surface of a photoconductor drum is constantly polished vigorously by rubbing with a developer in a developing process and pressing by a cleaning member (a cleaning blade or the like) in contact with the cleaning process. The photosensitive layer is likely to be reduced in thickness over time. Since the electrical characteristics such as the surface potential of the photosensitive drum are deteriorated due to the decrease in the thickness of the photosensitive layer, there is a problem that the resulting image causes a decrease in image density. In particular, when an attempt is made to use a small-diameter photosensitive drum, the surface area of the photosensitive member is reduced, and the frequency of rubbing per surface increases, so that the above-mentioned phenomenon of thinning of the photosensitive member tends to be more apparent.
[0004]
Therefore, in a stacked organic photoconductive photoconductor drum, studies have been made to avoid the problem of film reduction of the photoconductor and to improve the printing durability of the photoconductor. For example, by adopting a polycarbonate resin as a resin constituting the surface layer of the drum photosensitive layer, the hardness and mechanical strength of the surface are increased, so that the film loss is reduced, and the printing durability tends to be improved. Therefore, if a small-diameter drum composed of polycarbonate is used as a constituent resin of the surface of the laminated organic photoconductive photosensitive drum, the above-described problem in a small-sized image forming apparatus can be solved, which is effective. It is.
[0005]
On the other hand, in these personal type small image forming apparatuses, other problems such as image defect problems such as a character dropout phenomenon and the occurrence of paper dust marks on the photoreceptor due to postcard passing become apparent. As described in JP-B-63-58354 and JP-A-62-258472, magnetic fine particles represented by magnetite (Fe ₃ O ₄ ) can be externally added to toner particles for improvement. Often done.
[0006]
However, these magnetite particles tend to adhere firmly to the photoreceptor drum having a polycarbonate resin as the surface layer, and as a result, there is a new problem that spot-like defects appear on the obtained image and contaminate the image. It was found to occur. As an effective countermeasure against this, at present, no very effective proposal has been found, and image quality satisfactory enough for practical use has not been obtained. In particular, there is no developer that satisfies the image quality in combination with a photosensitive drum having a small diameter of 50 mm or less. This has been a restriction in reducing the diameter of the photoconductor and, consequently, the size of the apparatus.
[0007]
Similarly, when magnetite particles are added to the toner, the developing roller is contaminated with magnetite because the magnetite particles adhere strongly to the surface of the developing roller in the non-magnetic one-component developing system. As a result, it is difficult to form a uniform thin layer of the developer on the developing roller, and the uniformity and quality of the image are deteriorated.
The present invention has been made in view of the above situation, and has been made in order to solve the problem. The purpose of the present invention is to make it possible to reduce the size of the device and to reduce the problem of image quality caused by the miniaturization. No, specifically, there is no decrease in image density because the film thickness of the photoconductor photosensitive layer is small, there is no occurrence of dropout of characters, and there is no paper dust trace on the photoconductor due to postcard passing etc. There is no problem with image contamination due to external additives adhering to the photoreceptor, and a developer capable of obtaining good image uniformity and quality in a non-magnetic one-component developing system and an image forming method using the same. To provide.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies with the aim of developing a developer that can obtain good image quality even with a small-diameter photosensitive drum in order to achieve such an object. As a result, even when a small-diameter photosensitive drum having a diameter of 50 mm or less is used, good results are obtained. The present inventors have found a developer capable of obtaining image quality, and have reached the present invention.
That is, the gist of the present invention is characterized by containing at least toner particles containing a binder resin, a colorant, and a charge controlling agent, ferrite fine particles represented by the following general formula (1), and a fluidity improver. Non-magnetic one-component developer General formula (1) [(MnO) _x (FeO) _1-x ] · Fe ₂ O ₃
(Where x represents a numerical value of 0.01 to 0.3), and
An image forming method for developing an electrostatic latent image formed on a photosensitive drum having a diameter of 50 mm or less with a developer, wherein the developer is the non-magnetic one-component developer described above. Be in the way.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The image forming method of the present invention is particularly useful for a small-diameter photosensitive drum. Examples of the photosensitive drum constituting the present invention include inorganic drums such as selenium, arsenic-selenium, selenium-tellurium, and amorphous silicon, and organic drums such as diazo compounds and dyes.
[0010]
In order to reduce the size of the apparatus, a photoreceptor drum having a small diameter is desired. Usually, a diameter of 50 mm or less is adopted. If a smaller diameter is desired, a size of 40 mm or less is adopted. The adoption of is also proposed. However, as described above, with the conventional developer, the image quality deteriorates as the diameter of the photosensitive drum decreases, and although the apparatus itself can be downsized, satisfactory results cannot be obtained in terms of image quality. In that regard, according to the image forming method of the present invention, good images can be obtained with any of the small-diameter drums, and a small-sized apparatus with good performance can be realized. In addition, if the diameter is further reduced, the difference from the conventional technology is remarkably exhibited.
[0011]
Among the above-mentioned photosensitive drums, organic photosensitive drums are particularly preferable in terms of ease of manufacture, electrical and optical performance, cost, safety, and the like. Among the organic photosensitive drums, a stacked organic photoconductive photosensitive drum having a charge generation layer and a charge transport layer (surface layer) is particularly preferable. Preferably, the binder resin constituting the surface layer is a polycarbonate resin.
[0012]
On the other hand, the toner is a fine powder obtained by melting and kneading a binder resin, a colorant, a charge control agent, and other substances, pulverized, and classified, and the developer according to the present invention is composed of toner particles containing ferrite fine particles having a specific structure. It consists of adding a fluidity improver.
Among the toner constituent components, various known binder resins suitable for the toner can be used. For example, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer Copolymer, styrene-maleic acid copolymer, styrene-acrylate copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylic acid Octyl copolymer, styrene-phenyl acrylate copolymer, etc.), styrene-methacrylate copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer) Styrene-octyl methacrylate Styrene-based resins such as styrene or styrene-phenyl methacrylate copolymer), styrene-α-methyl methyl acrylate copolymer and styrene-acrylonitrile-acrylate copolymer (single polymer containing styrene or styrene-substituted product) (Coalescing or copolymer), vinyl chloride resin, rosin-modified maleic resin, phenolic resin, epoxy resin, saturated polyester resin, unsaturated polyester resin, low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone Resins, ethylene-ethyl acrylate copolymers, ethylene-vinyl acetate copolymers, xylene resins, polyvinyl butyral resins, and the like. Particularly preferred resins for use in the present invention include styrene resins, saturated or unsaturated resins. It may be mentioned ester resin and epoxy resin. Further, the above resins are not limited to being used alone, and two or more resins can be used in combination. Further, a crosslinked binder resin described in Japanese Patent Publication No. 50-23354, Japanese Patent Application Laid-Open No. 50-44836, or a non-crosslinked binder resin described in Japanese Patent Publication No. 55-6895, Japanese Patent Publication No. 63-32180, etc. A crosslinked binder resin can also be used.
[0013]
The softening point of the binder resin for toner is preferably 100 to 160 ° C. as measured by a flow tester method. If the softening point is less than 100 ° C., contamination during fixing (so-called “hot offset” phenomenon) is likely to occur, and if it exceeds 160 ° C., the fixing strength tends to deteriorate, which is not preferable. Further, the glass transition temperature of the binder resin is preferably such that the transition temperature (inflection point) measured by a differential thermal analyzer is 50 ° C. or more. When the glass transition temperature is lower than 50 ° C., thermal stability during long-term storage is poor, causing aggregation and solidification of the toner, which is problematic in use.
[0014]
The colorant is not particularly limited as long as it is conventionally used, and any suitable pigment or dye can be used. For example, titanium oxide, zinc white, alumina white, calcium carbonate, navy blue, iron black, carbon black, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, rhodamine dye, chrome yellow, quinacridone, benzidine yellow, rose bengal, triallyl Methane-based dyes, anthraquinone dyes, monoazo and disazo-based dyes and pigments are used alone or in an appropriate mixture according to the color of the corresponding developer. The content of the colorant may be sufficient to color the developer so that a visible image can be formed by development, and is, for example, 3 to 20 parts by weight based on 100 parts by weight of the binder resin. Is preferred.
[0015]
With respect to the charge polarity of the developer, a measure for controlling the charge depending on the composition of the binder resin to be used may be considered. However, usually, various known charge control agents are added as a component of the developer.
Examples of the charge control agent for obtaining a positively chargeable toner include various nigrosine compounds, and quaternary compounds described in JP-B-1-54694, JP-B1-54695, and JP-B1-54696. Ammonium salt compounds; triphenylmethane compounds described in JP-A-51-455, JP-B-63-57787, JP-B-2-501506, etc .; JP-A-3-119364; Examples thereof include imidazole derivatives and metal complexes of imidazoles described in JP-A-202856 and JP-A-3-217851. Among these, a positively chargeable toner containing at least one selected from a nigrosine compound, a quaternary ammonium salt compound and a triphenylmethane compound is preferable. As a method for incorporating the charge control agent into the toner, there are a method of adding the charge control agent inside the toner and a method of adding it externally. When added internally, these compounds are used in an amount of usually 0.05 to 20 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the binder resin. When externally added, the amount is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the resin. Within the above addition range, the internal addition and the external addition of the charge control agent may be performed in combination.
[0016]
In addition, as an auxiliary agent that can be internally added to the toner for the purpose of improving heat characteristics and physical characteristics, known agents can be used. For example, polyalkylene wax, paraffin wax, higher fatty acid, fatty acid amide, Metal soap and the like can be mentioned. The addition amount is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the binder resin.
As a method for producing the toner, the above components may be mixed, kneaded with a kneader or the like, cooled, pulverized, and classified.
[0017]
The developer according to the present invention is characterized by containing, independently of the toner particles (as a so-called ordinary external additive), ferrite fine particles represented by the following general formula (1) and a fluidity improver.
[0018]
General formula (1) [(MnO) _x (FeO) _1-x ] · Fe ₂ O ₃
(Where x represents a numerical value of 0.01 to 0.3)
x is preferably 0.05 to 0.3.
[0019]
The shape of the Mn-based ferrite represented by the general formula (1) is preferably octahedral. In such a case, the particles may be subjected to a de-squaring process by a known method as long as the octahedral shape is not damaged. When the particle diameter is not octahedral, for example, in the case of a spherical shape, the polishing effect of scraping paper dust marks on the photoreceptor by postcard passing is small, and in the case of a needle shape, it is easily attracted to the photoreceptor and the developing roller. There is a problem, and both are not preferable because image contamination occurs.
[0020]
Further, the average particle size is preferably from 0.1 to 1.0 μm, particularly preferably from 0.3 to 0.7. If the particle size is smaller than the above range, the particles are easily adsorbed to the photoreceptor, and if the particle size is larger, streak-like flaws are generated on the photoreceptor, and any of these causes image contamination, which is not preferable. The average particle diameter was measured as a cumulative 50% diameter by measuring the particle size distribution of 300 or more particles by scanning electron microscope observation.
[0021]
Further, the ferrite fine particles according to the present invention preferably have a saturation magnetization of 85 emu / g or less at a measurement magnetic field of 2 kOe. When the saturation magnetization is larger than the above range, aggregation of fine particles due to magnetic attraction tends to occur in the developer in continuous actual shooting or the like, and when these aggregates are developed on the photoconductor, the surface of the photoconductor and the It is not preferable because it strongly adheres to the developing roller in the magnetic one-component developing method and causes fatal image contamination. In general, the ferrite fine particles according to the present invention have a lower saturation magnetization value than magnetite (Fe ₃ O ₄ ) fine particles having the same shape and the same particle diameter, and thus, the aggregation of the particles is substantially unlikely to occur. Therefore, adsorption to the developing roller in the photosensitive member surface and the non-magnetic one-component developing method is relatively alleviated, and image contamination tends to be suppressed. A commercially available BH tracer was used for the measurement of the saturation magnetization.
[0022]
In the present invention, it is essential to add a fluidity improver in combination. If the fluidity of the toner particles is insufficient, the aggregation of the toner particles becomes intense. As a result, the aggregation of the magnetic fine particles easily occurs, and the adsorption of these aggregates to the photoreceptor is deteriorated. This phenomenon causes fatal image contamination especially in a small-diameter drum having a high frequency of surface rubbing.
[0023]
As the fluidity improver, any known fluidity improver may be used. In particular, metal oxide fine particles such as silicon oxide, titanium oxide and aluminum oxide are preferred. These metal oxides preferably have an average primary particle diameter of 5 to 100 nm and are preferably subjected to a hydrophobic treatment with various hydrophobic treatment agents. In particular, silicon oxide fine particles that have been subjected to a hydrophobic treatment with dimethyldichlorosilane, hexamethyldisilazane, a silicone compound, or the like are more preferable.
[0024]
The amount of the additive fine particles used is 0.1 to 5 parts by weight of the ferrite fine particles represented by the general formula (1) and 0.01 to 2.0 parts by weight of the fluidity improver based on 100 parts by weight of the toner particles. It is preferred that the content be contained by weight.
The average particle diameter of the toner is preferably 5 to 20 μm, and the image forming method using the present toner can be either a normal developing method when the charged electrodes of the photosensitive drum and the toner have different polarities or a reversal developing method of the same polarity. Is also applicable.
[0025]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
In the following Examples and Comparative Examples, “parts” simply means “parts by weight”.
[0026]
Example 1
Styrene resin 100 parts (monomer weight ratio: styrene / n-butyl acrylate = 82/18)
1 part Nigrosine dye charge control agent (Bontron N-04, Orient Chemical Co., Ltd.)
7 parts of carbon black (Mitsubishi Carbon Black MA100S, manufactured by Mitsubishi Chemical Corporation)
4 parts of polypropylene (NP505, manufactured by Mitsui Petrochemical Industries, Ltd.)
[0027]
The above components were mixed, kneaded, pulverized and classified to obtain a positively chargeable black toner having an average of 11 μm.
With respect to 100 parts of the toner, ferrite fine particles represented by [(MnO) _0.1 (FeO) _0.9 ] · Fe ₂ O ₃ (octahedral shape, average particle size of about 0.5 μm, saturation magnetization of 81 emu / g) and 0.3 part of hydrophobized silicon dioxide (Aerosil R972, trade name, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter: about 16 nm) were externally added using a Henschel mixer.
[0028]
Next, a real copying test was performed using a commercially available copying machine evaluation apparatus using a laminated organic photoconductor having a diameter of 30 mm as a photosensitive drum using a resin of the surface layer as a photosensitive drum using this developer. The toner for replenishment used in the actual test was of the same composition as the toner used for the developer. The actual shooting environment was performed at 25 ° C. and 50% RH.
In addition, as the actual copying method, first, 200 sheets of officially made postcards were continuously copied to confirm the transferability, and then, 9800 sheets of continuous copying were performed on normal copy paper to confirm the durability (total developer). 10,000).
[0029]
As a result, the image had good image quality with no missing images or unevenness. Also, no trace of paper dust was generated due to the postcard passing on the photoreceptor. Further, the image density after 10,000 sheets was sufficiently high, and was almost comparable to the initial state. Further, it was found that there was no problem with other image quality, and that the image had good durability. Further, no image contamination was caused by the adhesion of the toner additive. It should be noted that the state of film reduction of the photosensitive drum after actual copying of 10,000 sheets was extremely slight, and it was found that there was no practical problem.
[0030]
Comparative Example 1
Except that the ferrite fine particles used in Example 1 were replaced with magnetite fine particles (the shape and the average particle diameter were the same as the ferrite powder of Example 1 and the saturation magnetization was 91 emu / g), the same as Example 1 was carried out. A developer was prepared, and an actual image was evaluated. As a result, no omission in the image or occurrence of paper dust was observed in postcard passing, but spot-shaped image defects were observed on the image after 3000 to 4000 sheets of continuous actual shooting, and the number of defects was increased along with the actual number of images. Was found to be increasing, indicating that there was a problem in practical use. At this time, adhesion of magnetite fine particles was observed on the photoreceptor.
[0031]
Comparative Example 2
A developer was prepared exactly in the same manner as in Example 1 except that the hydrophobized silicon dioxide fine particles used in Example 1 were not added, and a real-photo evaluation was performed.
As a result, image contamination and image quality deterioration due to the adhesion of the magnetic powder to the photoreceptor and the developing roller began to occur on about 5,000 sheets.
[0032]
Example 2
Example 1 was repeated except that a modification of a commercial copying machine using a laminated organic photoconductor having a diameter of 24 mm in which the resin of the surface layer of the photoreceptor drum was a polycarbonate resin was used as an apparatus for evaluating a real image. The evaluation was performed in the same manner as in Example 1.
As a result, there was no omission or unevenness in the image, and no generation of paper dust marks due to postcard passing on the photoreceptor was observed. Further, it was found that the image density after 10000 sheets was sufficiently high and the image had good durability. Further, no image contamination and no deterioration in image quality due to the adhesion of the toner additive to the photosensitive drum and the developing roller occurred.
[0033]
Example 3
In the toner composition of Example 1, a toner was prepared in the same manner as in Example 1 except that the nigrosine dye charge control agent was changed to a quaternary ammonium salt compound (trade name: Bontron P51, Orient Chemical Co., Ltd.). A live-action evaluation was performed.
As a result, in each of the copying machines, there was no omission or unevenness in the image, and no generation of paper dust marks due to postcard passing on the photoreceptor was observed. Further, it was found that the image density after 10000 sheets was sufficiently high and the image had good durability. Further, no image contamination and no deterioration in image quality due to the adhesion of the toner additive to the photosensitive drum and the developing roller occurred.
[0034]
Example 4
In the toner composition of Example 1, a toner was prepared in the same manner as in Example 1 except that the nigrosine dye charge controlling agent was changed to a triphenylmethane compound (COPY BLUE, manufactured by Hoechst), and a real-photo evaluation was performed. went.
As a result, in each of the copying machines, there was no omission or unevenness in the image, and no generation of paper dust marks due to postcard passing on the photoreceptor was observed. Further, it was found that the image density after 10000 sheets was sufficiently high and the image had good durability. Further, no image contamination and no deterioration in image quality due to the adhesion of the toner additive to the photosensitive drum and the developing roller occurred.
[0035]
【The invention's effect】
According to the present invention, it is possible to reduce the size and space of the apparatus without restrictions due to image quality. In particular, the problem that is likely to occur when the diameter of the photosensitive drum is reduced can be easily improved. Specifically, the photosensitive drum has the following effects, and thus has a great industrial value.
1. 1. No reduction in image density 2. No occurrence of missing image 3. There is no trace of paper dust due to postcard passing. 4. No image contamination due to external additives adhering to the photoreceptor No image non-uniformity and quality deterioration due to external additives adhering to the developing roller

Claims (7)

A non-magnetic one-component developer containing at least a toner particle containing a binder resin, a colorant and a charge control agent, ferrite fine particles represented by the following general formula (1), and a fluidity improver.
General formula (1) [(MnO) _x (FeO) _1-x ] · Fe ₂ O ₃
(Where x represents a numerical value of 0.01 to 0.3) The non-magnetic one-component developer according to claim 1, wherein the ferrite fine particles have an octahedral shape. The non-magnetic one-component developer according to claim 1, wherein the ferrite fine particles have an average particle diameter of 0.1 to 1.0 μm. 4. The non-magnetic one-component developer according to claim 1, wherein the ferrite fine particles have a saturation magnetization of 85 emu / g or less in a measurement magnetic field of 2 kOersted. 5. The non-magnetic one-component developer according to claim 1, wherein the charge control agent comprises at least one selected from a quaternary ammonium salt compound, a nigrosine compound and a triphenylmethane compound. Agent. 6. An image forming method for developing an electrostatic latent image formed on a photosensitive drum having a diameter of 50 mm or less with a developer, wherein the developer is a non-magnetic one-component developing device according to claim 1. An image forming method, which is an agent. 7. The image forming method according to claim 6, wherein the diameter of the photosensitive drum is 40 mm or less.