JPH0157904B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a developing method using an insulating magnetic developer. Conventionally, developing methods for electrophotography, electrostatic recording, etc. are broadly classified into dry developing methods and wet developing methods. The former method is further divided into a method using a two-component developer and a method using a single-component developer. Two-component developing methods include a magnetic brush method using an iron powder carrier, a cascade method using a bead carrier, a fur brush method using fur, etc., depending on the type of carrier for conveying the toner. Furthermore, the one-component development methods include the powder cloud method, in which toner particles are sprayed, and the contact development method, in which toner particles are brought into direct contact with the electrostatic latent image surface. (also referred to as toner development), jumping development method in which toner particles are not brought into direct contact with the electrostatic latent image surface, but are charged and flown toward the latent image surface by the electric field of the electrostatic latent image; magnetic conduction There is the MagneDry method, which develops by bringing a toner into contact with the electrostatic latent image surface. In the two-component development method, a mixed developer of carrier particles and toner particles is inevitably used, and as the development process normally progresses, the toner particles are consumed in a much larger amount than the carrier particles, so the mixing ratio of the two is changes, and the density of the visible image changes,
Further, they inherently have drawbacks such as deterioration of image quality due to deterioration of carrier particles that are difficult to consume due to long-term use. On the other hand, in one-component developing methods, the Magne-Dry method using magnetic toner and the contact developing method that does not use magnetic toner, the toner comes into contact with the entire surface of the surface to be developed, that is, the image area and the non-image area, indiscriminately. This has caused a problem in that toner tends to adhere even to non-image areas, resulting in so-called background fog and dirt. (This fog stain was also a drawback of two-component development.)
Further, even in the powder cloud method, it is inevitable that toner particles in a powder state adhere to non-image areas, and the method also has the disadvantage that background fog cannot be removed. Furthermore, in the so-called jumping development method, which belongs to the one-component development method, after toner is uniformly applied to a carrier such as a sheet, the toner is placed facing an electrostatic holding surface with a small gap, and an electrostatic image is transferred from the toner carrier. A method is known in which toner is attracted and adhered to a holding surface by the electric charge of an electrostatic image, thereby developing the image. (U.S. Patent No.
2839400, etc.) This method has the advantage that not only the toner is not attracted to the non-image area where there is no static charge, but also the toner and the non-image area do not come into contact, so the above-mentioned fogging is less likely to occur. . Furthermore, since carrier particles are not used, there is no variation in the mixing ratio as described above, and there is no deterioration of the carrier particles. However, in this method, an electric field is applied in advance to adhere the toner to the toner carrier sheet, but it is difficult to apply the toner uniformly and thinly, and uneven application is likely to occur. Another drawback is that when the applied toner layer faces an electrostatic image, it is difficult to release the toner uniformly to the electrostatic image. In this regard, in the developing device proposed in JP-A-54-43027 and JP-A-55-18656, which has magnetic toner, a movable toner carrier (sleeve roller), and a stationary magnet inside the carrier, A developing device in which a toner thickness regulating member made of a magnetic material is disposed close to the outer surface of the sleeve roller facing the magnetic pole of the magnet, and can uniformly and thinly apply toner on the outer surface of the sleeve roller, It can be said that it is an electrostatic image developing device that eliminates the above drawbacks and has high fidelity and stable image quality. An object of the present invention is to provide a developing method with excellent durability such as continuous use characteristics. Another object of the present invention is to provide a developing method that is stable against environmental changes such as high temperature and high humidity, and low temperature and low humidity. Specifically, the present invention provides an electrostatic image holder that holds an electrostatic image on its surface, and a developer carrier that includes a magnet that holds an insulating magnetic developer on its surface, in a constant position in a developing section. The insulating magnetic developer disposed with a gap and supported on the developer carrier is a positively charged insulating developer containing at least a toner having a binder resin and magnetic powder, and a fine silica powder. A magnetic developer, in which the fine silica powder is a fine powder produced by vapor phase oxidation of a silicon halide compound, the fine silica powder is treated with a titanate coupling agent, and the fine silica powder is treated with a titanate coupling agent. A developer is supported on a developer carrier to a thickness thinner than the gap, and the positively charged magnetic material is applied under the magnetic field of a magnet included in the developer carrier while applying a bias to the developer carrier. The present invention relates to a developing method characterized in that a developer is transferred to the electrostatic image holder in a developing section to perform development. If copying is continued repeatedly using a conventionally known jumping developer, the uniformity of the developer layer carried on the developer carrier may be impaired, and streaks may appear in the circumferential direction of the carrier. Coating defects may occur, or the thickness of the supported developer layer may become extremely thick in some areas compared to the initial thickness, resulting in spot-like unevenness or serpentine coating defects. The former is observed as white streaks on the image when developed, and the latter is observed as uneven density in the form of dots or serpentine waves. Although this phenomenon hardly occurs during normal repeated copying, it may occur especially during continuous use under extremely low temperature and low humidity environmental conditions for a long period of time, which is undesirable. Also,
Even under high temperature and high humidity conditions, the thickness of the developer layer often changes and becomes thinner, which often causes an undesirable decrease in image density. As a result of repeated studies on this point, we found that one of the causes is the stability and reliability of the charge control component, and that these causes change the adhesion of developer powder onto the sleeve and the transfer of developer powder from the sleeve. I found out that it was for the purpose of More specifically, this phenomenon is caused by the occurrence of non-uniform triboelectrification in the developer layer supported on the carrier due to changes in environmental conditions. In other words, under extremely low temperature and low humidity environmental conditions, friction between the surface of the carrier and the developer generates components with extremely large triboelectric charges, and due to the mirroring force resulting from this charge, the carrier Such components with extremely large triboelectric charges tend to accumulate in the vicinity, and this affects the uniformity of developer coating in the upper layer of the developer layer and the ease of development due to continuous durability. As a phenomenon, the above-mentioned white streaks, uneven spots, and serpentine coating defects occur. Further, the decrease in the thickness of the developer layer at high temperature and high humidity also occurs due to uneven triboelectric charging between the developer and the carrier, and is due to instability in the amount of triboelectricity of the developer near the surface of the carrier. Conventionally, known charge control agents used in such dry developing toners include amino compounds, quaternary ammonium compounds, and organic dyes, particularly basic dyes and their salts, including benzyldimethyl-hexadecyl ammonium chloride, Decyl-trimethylammonium chloride, nigrosine base, nigrosine hydrochloride, safranin γ
and crystal violet are used. Nigrosine base and nigrosine hydrochloride are often used as positive charge control agents. These are usually added to a thermoplastic resin, heated and melted and dispersed, and then finely ground to adjust the particle size to an appropriate particle size before use. However, these dyes used as charge control agents have complex structures, inconsistent properties, and poor stability. Further, decomposition or deterioration occurs due to decomposition during thermal kneading, mechanical impact, friction, changes in temperature and humidity conditions, etc., resulting in a phenomenon in which charge controllability is deteriorated. Therefore, when a toner containing these dyes as a charge control agent is used for development in a copying machine, the dye decomposes or changes in quality as the number of copies increases, causing deterioration of the toner during durability. Furthermore, since it is extremely difficult to uniformly disperse these dyes as charge control agents in thermoplastic resins, this has the fatal drawback of causing a difference in the amount of triboelectrification between the toner particles obtained by pulverization. have. For this reason, various methods have been used to more uniformly disperse these dyes into resins. For example, basic nigrosine dyes are used by forming salts with higher fatty acids to improve compatibility with thermoplastic resins, but unreacted fatty acids or salt dispersion products are often exposed on the toner surface. This contaminates the carrier or toner carrier, causing a decrease in toner fluidity, fogging, and a decrease in image density. Alternatively, in order to improve the dispersion of these dyes into the resin, a method has been adopted in which the dye powder and the resin powder are mechanically pulverized and mixed beforehand and then hot melt-kneaded, but the inherent poor dispersion is The reality is that this cannot be avoided, and that sufficient uniformity of charge has not yet been obtained for practical use. In addition, many charge control dyes are hydrophilic,
Due to poor dispersion in these resins, the dye is exposed on the toner surface when it is crushed after melt-kneading. When these toners are used under high humidity conditions, they have the disadvantage that good quality images cannot be obtained because these dyes are hydrophilic. In this way, when a conventional dye with charge control properties is used in a toner, there is a possibility that the dye may be present on the surface of the toner particles, between the toner particles, between the toner and the carrier, or between the toner and the toner carrier such as a sleeve. This will cause variations in the amount of charge generated, leading to development fog,
Problems such as toner scattering and carrier contamination may occur. Furthermore, these phenomena become particularly noticeable when a large number of copies are made, resulting in a result that is practically unsuitable for copying machines. Furthermore, under high humidity conditions, the toner image transfer efficiency is significantly reduced, making it unusable. Furthermore, when the toner is stored for a long period of time even at room temperature and humidity, the toner often aggregates and becomes unusable due to the instability of the charge control dye used. The inventor of the present invention solved the various problems associated with the conventional chargeable toner as described above, and as a result of intensive research aimed at providing a high-quality image by being strongly charged uniformly and visualizing the electrostatic charge image, An electrophotographic image displaying a fine silica powder produced by vapor phase oxidation of a silicon halide compound, which exhibits various excellent properties when the fine silica powder is treated with a titanate coupling agent and is incorporated into an insulating magnetic developer. It was discovered that a developer for use in Furthermore, it has been found that it is very effective to apply this developer to a developing device having a sleeve roller. The developing process used in the present invention will be explained. FIG. 1 shows a cross-sectional view of one embodiment of the developing process used in the present invention. In the figure, the electrostatic image holder 1 moves in the direction of the arrow. Non-magnetic cylinder 2 which is a developer carrier
rotates in the same direction as the surface of the electrostatic image holder in the developing section. A multipolar permanent magnet 3 is arranged inside the nonmagnetic cylinder 2 so as not to rotate.
The one-component insulating magnetic developer 6 sent from the developer container 4 is applied onto the non-magnetic cylindrical surface, and the friction between the cylindrical surface and the toner particles causes the toner particles to have a polarity opposite to that of the electrostatic image charge. Gives a charge. Furthermore, an iron doctor blade 5 is placed close to the cylindrical surface (at intervals).
50μ to 500μ), and is arranged to face one magnetic pole (in the figure, the S pole) of the multipolar permanent magnet 3, thereby regulating the thickness of the toner layer to be thin (30μ to 300μ) and uniform. By adjusting the rotation speed of the cylinder 2, the surface speed and preferably the internal speed of the developer layer are substantially equal to the speed of the electrostatic image holding surface.
Or at a speed close to that. Instead of iron, a permanent magnet may be used as the doctor blade 5 to form opposing magnetic poles. Further, an alternating current bias may be applied between the developer carrier and the electrostatic image holding surface in the developing section. This AC bias should be 200 to 4000Hz and Vpp 500 to 3000V. As described above, in this developing step, the non-magnetic cylinder 2 containing the multipolar permanent magnet 3 was used in order to stably hold the one-component magnetic developer on the developer carrier. In addition, in order to form a thin and uniform developer layer, a doctor blade 5 made of a magnetic thin plate or a permanent magnet was placed close to the surface of the cylinder 2. Using a magnetic doctor blade in this way,
Opposing magnetic poles are formed between the magnetic poles of the permanent magnet contained in the developer carrier, and the toner particle chains are forced to stand up between the doctor blade and the developer carrier, and other parts on the developer carrier This is advantageous, for example, in controlling the thickness of the developer layer in the development area facing the electrostatic image surface. Further, by imparting such forced movement to the developer, the developer layer becomes more uniform, thereby achieving a thin and uniform toner layer formation that could not be achieved with a non-magnetic doctor blade. Moreover, since the gap between the doctor blade and the sleeve can be set wide, it is also effective in preventing the destruction and aggregation of toner particles. When the toner particles are transferred in the developing area, they are transferred to the electrostatic image side due to the attraction action of the electrostatic image or the action of an alternating current bias. As the binder resin for toner used in the developing method of the present invention, various material resins conventionally known as toner binder resins for electrophotography are used. For example, styrene copolymers such as polystyrene, polystyrene/butadiene copolymer, styrene/acrylic copolymer, ethylene copolymers such as polyethylene, polyethylene vinyl acetate copolymer, polyethylene vinyl alcohol copolymer, and phenolic copolymers. These include resins, epoxy resins, allyl phthalate resins, polyamide resins, polyester resins, maleic acid resins, and the like. Furthermore, there are no particular restrictions on the manufacturing method of any of the resins. This is because conventionally, resins produced by emulsion polymerization or the like tend to contain impurities and are difficult to use, but the present invention makes them easier to use, and the range of resin selection is greatly expanded. This is also a great effect of the present invention. The magnetic powder to be contained in the toner includes ferromagnetic elements and alloys and compounds containing them.
There are conventionally known magnetic materials such as alloys and compounds of iron such as magnetite, hematite, and ferrite, cobalt, nickel, and manganese, and other ferromagnetic alloys. The size of the magnetic powder that is usually used is preferably an average particle size of 0.05 to 5 μm, preferably 0.1 to 1 μm. This magnetic powder is preferably contained in the toner in an amount of 10 to 70% by weight, preferably 15 to 35% by weight. With this content, an appropriate magnetic moment is activated in the above-mentioned developing method, a good image can be created, and the fixing property is also excellent. As the coloring material used in the toner, conventionally known carbon black, iron black, etc. can be used, and all conventionally known dyes as positive charge control agents can be used in combination with the treated silica fine powder used in the present invention. I can do that. Various dyes include, for example, benzyldimethyl-hexadecyl ammonium chloride, decyl-trimethylammonium chloride, nigrosine base, nigrosine hydrochloride, safranin gamma and crystal violet. The silica fine powder produced by vapor phase oxidation of a silicon halide compound referred to herein is preferably what is called dry process silica or fumed silica, which is produced by a conventionally known technique. For example, this method utilizes a thermal decomposition oxidation reaction of silicon tetrachloride gas in an oxyhydrogen flame, and the basic reaction formula is as follows. SiCl ₄ +2H ₂ +O ₂ →SiO ₂ +4HCl Also, in this manufacturing process, for example, by using other metal halide compounds such as aluminum chloride or titanium chloride together with silicon halide, a composite fine powder of silica and other metal oxides can be produced. It is also possible to obtain a body, and it includes these as well. Its particle size is 0.001~2μ as the average primary particle size.
It is desirable that it be within the range of, particularly preferably,
It is preferable to use silica fine powder within the range of 0.002 to 0.2μ. Commercial products of silica fine powder produced by vapor phase oxidation of silicon halogen compounds include, for example,
There are product names such as the following. AEROSIL 130 (Japan Aerosil) 200 300 380 TT600 MOX80 MOX170 COK84 Ca-O-SiL M-5 (CABOT Co.) MS-7 MS-75 HS-5 EH-5 Wacker HDK N20 V15 (WACKER-CHEMIE GMBH) ) N20E T30 T40 D-C Fine Silica (Dow Corning Co.) Fransol (Fransil Co.) Examples of adding these fine silica powders to toner have been known. However, such substances do not necessarily have sufficient stability, and addition of such silica to toners requiring positive charge controllability changes the chargeability, making them unsuitable. It has been found that it is effective to incorporate such fine silica powder treated with a titanate coupling agent into a developer and use it in the developing method of the present invention. More specifically, it is particularly desirable to use the treated silica fine powder in a state in which it is attached to the surface of toner particles consisting of at least a binder resin and a colorant. A proposal to use a titanate coupling agent in toner is given in JP-A No. 55-26519, 55-
There are methods described in specifications such as No. 28019 and No. 56-51755, but these are basically proposals for the purpose of improving the dispersibility and affinity of the magnetic material for the resin in magnetic toner, and it is true that the dispersibility is improved. However, in this method, the titanate coupling agent does not affect the charging characteristics of the developer in any way.
This is different from the technical content and idea of the present invention. The titanate coupling agent used in the present invention is an organic titanium compound that can react with or adsorb the hydroxyl group on the surface of the fine silica powder or adsorbed water to form a film on the surface of the fine silica powder, and includes, for example,

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[Table] These may be used alone or in a mixed system of two or more. The method of treating the fine silica powder with a titanate coupling agent is that the titanium coupling agent used in the present invention easily reacts chemically with the chemically or physically bound water present on the surface of the fine silica powder. Since it is coated, either a dry method or a wet method can be adopted, and a wide range of treatment methods are used. For example, fine silica powder and an appropriate amount of titanium-based coupling agent are put into a mixer such as a Henschel mixer or a ball mill and mixed dry, or the titanium-based coupling agent is dissolved in an appropriate solvent and then silica fine powder is mixed. Various methods are used, such as adding the body, mixing, and removing the solvent. The amount of the titanate coupling agent to be treated with respect to the silica fine powder is 0.01 to 20% by weight (preferably 0.1 to 10% by weight). In addition to the titanate coupling agents mentioned above, it is also preferable to use a known silane coupling agent in combination. In addition, the applied amount of these treated silica fine powders exhibits an effect when the amount is 0.01 to 20% based on the weight of the developer, and particularly when it is added in an amount of 0.1 to 3%, it has excellent stability. Shows positive chargeability. Regarding the preferred form of addition, it is preferable that 0.01 to 3% by weight of treated silica fine powder based on the weight of the developer be attached to the surface of the toner particles. The developing method of the present invention configured in this way is as follows:
Since the developer used contains the above-mentioned silica fine powder as a charge control component, the amount of triboelectric charge imparted to the developer layer supported on the developer carrier is made uniform, and durability at ultra-low temperature and low humidity is achieved. Only the excess charge that tends to occur in the developer leaks through the silica fine powder to an appropriate saturation value, resulting in the formation of a stable developer layer. At high temperatures and high humidity, it is easy to maintain the amount of triboelectric charge necessary to provide a stable coating state, and no decrease in concentration occurs. Another feature is that it is easy to form a stable developer layer, so there is no development fog or scattering of the latent image around the edges, which could not be solved satisfactorily in the past, and high image density can be obtained. Good tone reproducibility. The basic structure and features of the present invention have been described above, and the method of the present invention will be specifically explained below based on Examples. However, this does not in any way limit the embodiments of the present invention. Parts in the examples are parts by weight. Example 1 Styrene-butadiene copolymer (70:30)
100 parts magnetite 60 parts nigrosine 4 parts After mixing the above materials well in a blender, 150 parts
The mixture was kneaded using two rolls heated to ℃. The kneaded product was left to cool naturally and then coarsely ground using a cutter mill. Next, the powder was pulverized using a pulverizer using a jet air flow, and further classified using an air classifier to obtain a fine powder (toner) having a particle size of 5 to 20 μm. Next, silica fine powder Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.) was placed in a closed Henschel mixer heated to 70°C, and diluted with alcohol so that the amount of titanium coupling agent was 2.0% by weight relative to the silica. The solution was stirred at high speed while adding the isopropyl triisostearoyl titanate dropwise. The obtained fine powder was dried at 120°C. The treated silica fine powder is 0.6% of the above fine powder.
A developer was prepared by adding weight percentages and mixing with a Henschel mixer. Next, the OPC photoreceptor was subjected to corona discharge of -6 KV to uniformly charge the entire surface, and then the original image was irradiated to form an electrostatic latent image. The developer carrier was a stainless steel cylindrical sleeve with an outer diameter of 50 mm. Sleeve surface magnetic flux density 700 Gauss,
The distance between the ear cutting blade sleeve surfaces is 0.2 mm.
This sleeve rotating magnet fixed (sleeve circumferential speed is the same as that of the drum, rotation direction is opposite) type developing device is installed with a distance between the photosensitive drum surface and the sleeve surface of 0.25.
mm, and an alternating current of 400 Hz, 1000 V, and a direct current bias of -150 V were applied to the sleeve. It was developed using the developer described above, and then the powder image was transferred while irradiating the back side of the transfer paper with a DC corona of -7 KV to obtain a copy image. Fixing was carried out using a commercially available plain paper copying machine (trade name: NP-5000, manufactured by Canon). The resulting transferred image has a density of 1.40
A good image with high resolution was obtained, with no fogging at all and no toner scattering around the image. At this time, the weight per unit area of the toner layer coated on the sleeve is 1.5×10 ^-3 (g/
^cm2 ). Transfer images were continuously created using the above developer and durability was examined, and the transferred images after 100,000 sheets were also completely dull compared to the initial images. Next, when the environmental conditions were set to 35℃ and 85%, the image density was 1.30, which was almost the same value as normal temperature and humidity, and clear images were obtained without fogging or scattering, and the durability was almost 100,000 sheets. There was no change. At this time, the weight per unit area of the toner layer is
It was 1.43×10 ^-3 (g/cm ² ). Then 10℃, 10%
When the transferred image was obtained at a low temperature and low humidity, the image density was as high as 1.43, and solid black was developed extremely smoothly.
The transferred image was excellent, with no scattering or hollow spots. Although durability was achieved under these environmental conditions, continuous
Even though copies were made intermittently, the density fluctuation was ±0.1 up to 100,000 sheets, which was sufficient for practical use, and no white streaks or unevenness occurred. At this time, there was almost no change in the weight per unit area of the toner layer. Comparative Example 1 A developer was obtained, developed, and transferred in the same manner as in Example 1, except that Aerosil 200 was not treated with the isopropyl triisostearoyl titanate used in Example 1, but an inverted image was obtained. It was only. Examples 2 to 7 In place of the isopropyl triisostearoyl titanate used in Example 1, isopropyl diisostearoyl tamil phenyl titanate (Example 2) and isopropyl tridodecylbenzenesulfonyl titanate were used as titanate coupling agents, respectively. (Example 3) and isopropyl tri(dioctyl phosphate) titanate (Example 4), and isopropyl 4-aminobenzenesulfonyl di(dodecylbenzenesulfonyl) titanate (Example 5) and isopropyl tri(N-ethylamino- Example 1 was carried out in the same manner as in Example 1, except that ethylamino) titanate (Example 6) and isostearoylmethacryloxyacetate titanate (Example 7) were used, and excellent results were obtained in both cases.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of a developing process applicable to the present invention. DESCRIPTION OF SYMBOLS 1... Electrostatic image holder, 2... Non-magnetic cylinder, 5... Doctor blade, 6... Insulating developer.

Claims (1)

[Scope of Claims] 1. An electrostatic image holder that holds an electrostatic image on its surface and a developer carrier containing a magnet that holds an insulating magnetic developer on its surface are arranged at a constant interval in a developing section. The insulating magnetic developer supported on the developer carrier is a positively charged insulating magnetic developer containing at least a toner having a binder resin and magnetic powder, and silica fine powder. The fine silica powder is a fine powder produced by vapor phase oxidation of a silicon halide compound, the fine silica powder is treated with a titanate coupling agent, and the fine silica powder is treated with a titanate coupling agent, and the fine silica powder is a positively charged insulating magnetic developer. The positively charged magnetic developer is supported on a developer carrier to a thickness thinner than the gap, and is applied under a magnetic field of a magnet included in the developer carrier while applying a bias to the developer carrier. A developing method comprising transferring and developing the electrostatic image holder onto the electrostatic image holder in a developing section.