JPS6251464B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a positively charged one-component insulating developer for electrophotography and a developing method using the 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. Two-component development methods inevitably use a developer mixture of carrier particles and toner particles, and as the development process progresses, the toner particles are consumed in far larger quantities than the carrier particles, so the mixing ratio of the two changes. However, 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 is applied to the entire surface of the surface to be developed.
That is, the toner comes into contact with the image area and the non-image area indiscriminately, and as a result, there is a problem in that the toner tends to adhere even to the non-image area, 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 to a holding surface by the electric charge of an electrostatic image, and developed by causing the toner to adhere to the holding surface. US Patent No.
2839400 specification, 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 with each other, so that 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 this electrostatic image developing device eliminates the above-mentioned drawbacks and has high fidelity and stable image quality. An object of the present invention is to provide a positively charged one-component insulating developer that has excellent durability such as continuous use characteristics, and a developing method using the developer. Another object of the present invention is to provide an electrostatically charged one-component insulating developer that is stable against environmental changes such as high temperature and high humidity, and a developing method using the developer. That is, an object of the present invention is to provide a one-component developer for developing an electrostatic image using the frictional charge of toner, which is a silicic acid fine powder synthesized by a wet method and dispersed at 4% by weight in water. The actual pH value is 7~
10.9 and 0.01 when sodium is converted to Na ₂ O
A positively charged one-component insulating developer for electrophotography, characterized by having silicic acid fine powder containing ~10% by weight and positively charged insulating toner particles that are positively triboelectrically charged with respect to a developer carrier. Our goal is to provide the following. Furthermore, an object of the present invention is to provide fine silicic acid powder synthesized by a wet method by arranging an electrostatic image holder that holds an electrostatic image on its surface and a developer carrier with a certain gap in a developing section. A fine silicic acid powder having a PH value of 7 to 10.9 when dispersed in water at 4% by weight and containing 0.01 to 10% by weight of sodium in terms of Na ₂ O, and the developer carrier. On the other hand, a positively charged one-component insulating developer having positively charged insulating toner particles that is positively triboelectrically charged is triboelectrically charged with the developer carrier, and a positively charged one-component insulating developer that is triboelectrically charged is formed. A developer is supported on the developer carrier to a thickness thinner than the gap, and the positively charged one-component insulating developer is transferred to the electrostatic image carrier in a developing section for development. The object of the present invention is to provide a developing method. The inventors of the present invention discovered that when copying is continued repeatedly using a conventionally known jumping developer, image density decreases and image quality deteriorates, especially in high temperature and high humidity. . 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 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 as necessary 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 triboelectric charge between 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 to form salts with higher fatty acids in order to improve their 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, fog, 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 There is no harm in avoiding it,
The reality is that charging uniformity sufficient for practical use has not yet been achieved. 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 causes variations in the amount of charge generated, resulting in development fog,
Problems such as toner scattering and carrier contamination may occur. In addition, these problems appear as a particularly noticeable development 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. Conventionally, it is known that finely powdered silica called colloidal silica (for example, Aerosil 200, R972 manufactured by Nippon Aerosil Co., Ltd.) is added to toner. 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. The inventor of the present invention has conducted extensive research with the aim of solving the various problems associated with conventional positively charged toners as described above, and producing high-quality images by being uniformly and strongly positively charged and visualizing the electrostatic charge image. As a result, it has been found that electrophotographic developers exhibiting various excellent properties can be obtained by incorporating a specific silicic acid fine powder synthesized by a wet method into the developer. Furthermore, it has been found that it is very effective to apply this developer to a developing device having a developer carrier such as 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. The non-magnetic cylinder 4b, which is a developer carrier, rotates in the developing section so as to move in the same direction as the surface of the electrostatic image carrier. A multipolar permanent magnet 9 is arranged inside the nonmagnetic cylinder 4b so as not to rotate. A positively charged one-component insulating magnetic developer 11 sent from a developer container 12 is applied onto a non-magnetic cylindrical surface, and the toner particles are positively charged by friction between the cylindrical surface and the toner particles. Furthermore, by arranging the iron doctor blade 10 close to the cylindrical surface (with an interval of 50 μm to 500 μm) and facing one magnetic pole (S pole in the figure) of the multipolar permanent magnet 9, the thickness of the toner layer can be reduced. Thin (30μ to 300μ)
And uniformly regulated. By adjusting the rotational speed of the cylinder 4b, the surface speed and preferably the internal speed of the developer layer are made to be substantially equal to or close to the speed of the electrostatic image holding surface. As the doctor blade 10, a permanent magnet may be used instead of iron 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 has f of 200~4000Hz and Vpp of 500~
3000V is fine. As described above, in this developing step, the non-magnetic cylinder 4b containing the multipolar permanent magnet 9 was used in order to stably hold the one-component magnetic developer on the developer carrier. Further, in order to form a thin and uniform developer layer, a doctor blade 10 made of a magnetic thin plate or a permanent magnet was placed close to the surface of the cylinder 4b. When a magnetic doctor blade is used 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 between the doctor blade and the developer carrier. This is advantageous in controlling the thickness of the developer layer in other parts of the developer carrier, for example, in the development part 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, there is also the effect of 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 allows them to be used easily, 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 average particle size of the magnetic powder usually used is 0.05 to 5μ,
Preferably it is 0.1 to 1μ. This magnetic powder is contained in the toner in an amount of 10 to 70% by weight, preferably 15 to 35% by weight.
It is better to include it. With this content, an appropriate magnetic moment will work in the above-mentioned development method, and
Good images can be created and the fixing properties are also excellent. As the coloring material used in the toner, conventionally known carbon black, iron black, etc. can be used, and all the conventionally known dyes as positive charge control agents are mixed with the silicic acid fine powder synthesized by the wet method used in the present invention. Can be used in combination. Various dyes include, for example, benzyldimethyl-hexadecyl ammonium chloride, decyl-trimethylammonium chloride, nigrosine base, nigrosine hydrochloride, safranin gamma and crystal violet. Various conventionally known methods can be applied to produce the silicic acid fine powder used in the present invention by a wet method. For example, the decomposition of sodium silicate with an acid can be expressed using the general reaction formula (the reaction formula is omitted below): Na ₂ O・xSiO ₂ +HCl+H ₂ O→SiO ₂・nH ₂ O+
NaCl In addition, after decomposition of sodium silicate with ammonia salts or alkali salts, and generation of alkaline earth metal silicate from sodium silicate,
A method of decomposing with an acid to produce silicic acid, a method of converting a sodium silicate solution to silicic acid using an ion exchange resin,
There are methods that use natural silicic acid or silicates. In addition to anhydrous silicon dioxide (silica), silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate can be used as the silicic acid fine powder here. The particle size is 0.01~ as the average primary particle size.
It is desirable that it be within the range of 2μ. In addition, the amount of these silicic acid fine powders applied is based on the weight of the developer.
Effective at 0.01 to 20%, particularly preferably
It has excellent stability when added at 0.1 to 3%.
A more preferred form of addition is that 0.01 to 3% by weight of the silicic acid fine powder based on the weight of the developer is attached to the surface of the toner particles. Silicic acid fine powder synthesized by a wet method can be used with the average primary particle size adjusted to a range of 0.01 to 2 μm. In the present invention, a fine silicic acid powder synthesized by a wet method is used as described above, and it exhibits an effect. Those containing SiO ₂ are particularly desirable. In addition, the wet-process silicic acid fine powder used in the present invention, which imparts stable and strong positive chargeability to the toner, is
Unlike the dry process silica conventionally used in toners, it has minute pores in its internal structure and contains many water molecules bonded to silanol groups on the surface of the pores by van der Waals forces. Unlike the water adsorbed on the surface of dry process silica, the water content in the internal structure of such fine silicic acid powder remains relatively stable even under changes in the environment. The reason why the developer containing the silicic acid fine powder synthesized by the wet method, which is a feature of the present invention, exhibits stable positive chargeability against the environment is because of the stable water content in the internal structure. Conceivable. The water contained in the internal structure of fine silicic acid powder is, for example, 2 at a temperature of 900°C.
It is expressed as a weight loss rate (loss on ignition) when heated for a period of time, and this loss on ignition is 0.1 to 10% (preferably
0.3 to 6%) is particularly desirable. The silicic acid fine powder synthesized by the wet method stably and strongly positively charges the toner, but as a result of a more detailed study of the silicic acid fine powder synthesized by the wet method, it was found that the silicic acid fine powder synthesized by the wet method was submerged in water. It is clear that it is preferable to use a fine silicic acid powder whose pH value when dispersed at 4% by weight is 5 to 11 (more preferably 7 to 10.9, such as the wet silica used in the examples below). It became. This seems to be influenced by the various elements contained in the raw materials used when synthesizing the silicic acid fine powder or the processing agents used during the synthesis process, and it is preferable to mix alkaline earth metals or alkali metal elements. It is thought that it is having an effect. Experiments have shown that among these, those mixed with an appropriate amount of sodium ions have a particularly effective effect. In order to positively and stably charge the toner, it is particularly good to use silicic acid that satisfies the above PH conditions and contains an appropriate amount of sodium ions.The preferred sodium content that provides the above PH value is Na. It is 0.01 to 10% in terms of ₂ O. This is due to the interaction of sodium ions mixed into the SiO ₂ lattice near the surface of the fine silicic acid powder added to the toner, or sodium ions attached to the surface of the fine silicic acid powder, with moisture adsorbed inside or on the surface of the fine powder. This is thought to be because the toner is effective in forming stable positive charges. That is, among the silicic acid fine powders synthesized by the wet method used in the present invention, the pH of the aqueous dispersion is 7 to 7.
In particular, the sodium content in the silicic acid fine powder is 0.01 to 10% in terms of Na ₂ O (particularly, the sodium content necessary to maintain a preferable pH in water dispersion is 0.1 to 10%). It is preferable to use silicic acid fine powder containing 2.0%). Next, examples of particularly preferred silicic acid fine powders synthesized by the wet method used in the present invention will be given. Of course, this example does not limit the scope of the claims of the present invention.

[Example 1]

100 parts by weight of zinc oxide, 20 parts by weight of styrene-butadiene copolymer, 40 parts by weight of n-butyl methacrylate, 120 parts by weight of toluene, 1% by weight of rose bengal.
A mixture consisting of 4 parts by weight of methanol solution was dispersed and mixed in a ball mill for 6 hours. This was applied to a 0.05 mm thick aluminum plate using a wire bar to a dry coating thickness of 40 μm, and the solvent was evaporated with hot air to create a zinc oxide binder photoreceptor in the form of a drum. This photoreceptor was subjected to -6 KV corona discharge to uniformly charge the entire surface, and then an 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. The magnetic flux density on the sleeve surface is 700 Gauss, and the distance between the ear cutting blade and sleeve surface is 0.2 mm. This sleeve rotating magnet fixed (sleeve peripheral speed is the same as that of the drum, rotation direction is opposite) type developer was set at a distance between the photosensitive drum surface and the sleeve surface of 0.25 mm, and the sleeve was biased with 400Hz 1000V AC and -150V DC bias. was applied. A toner consisting of 100 parts by weight of Priorite S-5A (Gutsdeyer Chemicals, styrene-butadiene copolymer), 60 parts by weight of magnetite, and 3 parts by weight of nigrosine spirit was mixed with 1.0 parts by weight of wet process Silica Nipseal ER (Nippon Silica). It was developed using a positively charged one-component insulating developer containing % by weight of the powder, and then the powder image was transferred while irradiating -7 KV direct current corona from the back side of the transfer paper to obtain a copied image. Fixing was carried out using a commercially available plain paper copying machine (trade name: NP-5000, manufactured by Canon). The images obtained were clear, had high density and resolution, and had no fog. The number of durable sheets
The transfer efficiency was excellent at 30,000 sheets, and the density was high at 1.25 even under the environmental conditions of 35°C and 85%, and the transfer efficiency was good at 85%. [Comparative Example 1] A developer was prepared in the same manner as in Example 1, except that Nipsil ER was not added, and development, transfer, and development were carried out using the same device.
When fixing was carried out, the image density was as low as 0.63, and only an unclear image with a lot of fogging was obtained. 35
Under environmental conditions of 85% °C and 85%, the density was extremely low at 0.32, making the image impractical. [Example 2] AC polyethylene AC-392 (manufactured by Allied chon)
Polyethylene oxide) 100 parts by weight Solvent Black 3 5 parts by weight EPT-1000 (Magnetite manufactured by Toda Kogyo)
60 parts by weight Toner powder was prepared from the above materials, and 1% by weight of Carplex #1120 was mixed with the toner to prepare a developer. This developer was developed and transferred in the same manner as in Example 1, and then fixed under pressure using a pressure roller to obtain an image. Images 1, 2, and 3 were clear with no fog. Further, a continuous durability test was conducted using this developer, and the images after 10,000 copies were almost the same as the initial image. [Example 3] Polymist A-12 (polyethylene, Allied Chemical Co., Ltd.) 100 parts by weight Solvent Black 3 5 parts by weight Imusil-A108 (wet process silica, Illinois Minerals Co.) 15 parts by weight EPT-1000 (Magnetite manufactured by Toda Kogyo)
60 parts by weight After mixing the above ingredients well in a blender, approx.
The mixture is kneaded with two rolls heated to 150°C, cooled, and coarsely pulverized with a cutter mill, then pulverized with a pulverizer using a jet air stream, and further classified with an air classifier to obtain particles with an average particle size of 13μ. A developer was obtained. This developer was developed and transferred in the same manner as in Example 1, and then fixed under pressure using a pressure roller to obtain an image.
The image density was high at 1.30, and the image was clear with no fog. After 10,000 sheets of durability, the image is
The value was 1.20, which was almost the same as the initial value, and the image was excellent in terms of fog and resolution.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of a developing process applicable to the present invention. 1... Electrostatic image holder, 4... Nonmagnetic cylinder, 10
...Doctor blade, 11...Insulating developer.

Claims (1)

[Scope of Claims] 1. A one-component developer that develops an electrostatic image using the frictional charge of toner, which is a fine silicic acid powder synthesized by a wet method, when dispersed at 4% by weight in water. A positively charged insulating toner having a pH value of 7 to 10.9 and containing 0.01 to 10% by weight of sodium in terms of Na ₂ O, which is positively triboelectrically charged with respect to a silicic acid fine powder and a developer carrier. A positively charged one-component insulating developer for electrophotography, characterized by having particles. 2. The developer according to claim 1, wherein the positively charged insulating toner particles are positively charged insulating magnetic toner particles containing magnetic powder. 3 An electrostatic image holder that holds an electrostatic image on its surface and a developer carrier are arranged with a certain gap in a developing section, and silicic acid fine powder synthesized by a wet method is immersed in water. PH value when dispersed by weight% is 7~
10.9 and 0.01 when sodium is converted to Na ₂ O
A positively charged one-component insulating developer having silicic acid fine powder containing ~10% by weight and positively charged insulating toner particles that are positively triboelectrically charged with respect to the developer carrier is used on the developer carrier. A triboelectrically charged, positively charged one-component insulating developer is supported on the developer carrier to a thickness thinner than the gap, and the positively charged one-component insulating developer is transferred to the developing section. A developing method comprising transferring the electrostatic image to the electrostatic image holder and developing the image. 4. The developing method according to claim 3, wherein the positively charged insulating toner particles are positively charged insulating magnetic toner particles containing magnetic powder. 5. The developing method according to claim 3 or 4, wherein the developer carrier is a sleeve containing a magnet.