Pneumatic impact pulverizer

Abstract: The present invention provides a pneumatic impact pulverizer, a fine powder production apparatus and a process of producing toner for developing electrostatic images. According to the present invention, a pneumatic pulverizer comprises an accelerating tube for carrying and accelerating powder to be pulverized with high-pressure gas and a pulverizing chamber for pulverizing the powder to be pulverized. Herein, the back end of the accelerating tube is provided with a pulverization powder feed port for feeding powder to be pulverized to the accelerating tube, the pulverizing chamber is equipped with an impact member having an impact surface opposed to the opening plane of the outlet of the accelerating tube, the pulverizing chamber has a side wall against which the powder to be pulverized that has been pulverized with the impact member collides to further pulverize, and the closest distance from the side wall to a margin of the impact member, L₁, is shorter than the closest distance from the front wall of the pulverizing chamber opposed to the impact surface to the margin of the impact member, L₂. Thus, the pulverizer successfully prevents pulverized powder from fusing, coagulating, and getting coarser, and from causing localized abrasion of an impact surface of an impact member and of an accelerating tube. Thereby, pulverization efficiency improves. This realizes continuous stable operation and thus provides toner showing sharp distribution of particle sizes.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a pneumatic impact pulverizer using high-pressure gas in the form of a jet stream. Related Background Art In recent years, copying machines and printers have been required to offer higher image quality and precision. With this trend, required performance of toner serving as a developer has been evaluated more severely. Particles of toner become smaller. There is a demand for toner showing a sharp distribution of particle sizes; that is, a distribution of particles including no coarse particles and less very fine particles. A pneumatic impact pulverizer using high-pressure gas in the form of a jet stream carries raw powder material with a jet stream, and ejects the raw material from the outlet of an accelerating tube so that the raw material will collide against the impact surface of an impact member that is opposed to the opening plane of the outlet of the accelerating tube. This induces impact force and thereby pulverizes the raw powder material. For example, in a pneumatic impact pulverizer shown in Figure 20, an impact member 43 is opposed to an outlet 45 of an accelerating tube 46 to which a high-pressure gas feed nozzle 47 is connected. High-pressure gas supplied to the accelerating tube 46 attracts raw powder material into the accelerating tube 46 through a raw powder material feed port formed in the middle of the accelerating tube 46. Then, the raw powder material is ejected together with the high-pressure gas to collide with an impact surface of the impact member 43. The impact pulverizes the raw powder material. In the pneumatic impact pulverizer shown in Figure 20, a pulverization powder feed port 40 is formed in the middle of the accelerating tube 46. Therefore, the powder to be pulverized that has been attracted to the accelerating tube 46 rapidly changes its route towards the outlet of the accelerating tube due to a high-pressure air current ejected through a high-pressure gas supply nozzle 47 immediately after passing through the pulverization powder feed port 40. While changing the route, the powder to be pulverized is dispersed in the high-pressure air current and accelerated quickly. In this state, relatively coarse particles of the powder to be pulverized are involved in the portion of the high-pressure air current that is flowing at a lower flow velocity in the accelerating tube, because of the influence of inertial force. Relatively fine particles are involved in the portion of the high-pressure air current flow that is flowing at a higher flow velocity in the accelerating tube. Thus, the particles are not dispersed uniformly within the high-pressure air current. Therefore, the high-pressure current remains separated into a flow having higher concentration of powder to be pulverized and a flow having lower concentration of powder to be pulverized. Then, when the high-pressure air current collides with an opposed impact member together with the powder to be pulverized, the powder to be pulverized concentrates on part of the impact member. This deteriorates pulverization efficiency and degrades throughput. In the vicinity of an impact surface 41, dust concentration is likely to increase because of the presence of powder to be pulverized and pulverized powder. If the powder to be pulverized contains a resin or other material having a low fusion point, the powder to be pulverized may fuse, become coarser, and make coagulation. If the powder to be pulverized is abrasive, the impact surface of an impact member or the accelerating tube may suffer from powder abrasion. This results in frequent replacement of the impact member. There remain some problems that must be overcome to ensure continuous stable production. Japanese Patent Application Laid-Open No. 1-254266 has proposed a pulverizer in which the tip of an impact surface of an impact member has a conical shape with an apex angle of 110 to 175°. Japanese Utility Model Application Laid-Open No. 1-148740 has described a pulverizer whose impact surface is formed as an impact plate having a projection on a plane perpendicular to an extension of the center axis of an impact member. These pulverizers successfully suppresses a localized rise of dust concentration in the vicinity of the impact surface. Therefore, pulverized powder is less likely to fuse, become coarser, and make coagulation. Pulverization efficiency has improved slightly. A breakthrough is awaited. A similar pneumatic impact pulverizer is known from the document US-A-4 930 707, which pulverizer also comprises an accelerating tube, and an impact member which is arranged opposite to an end of that tube. A lateral powder inlet is provided to introduce the powder to be pulverized into the gas stream passing through the accelerating tube. The impact member has an inclined or conical surface in opposition to the outlet of the tube in order to avoid coagulation of the powder. Since the feed port for the coarse material is arranged sideways at the accelerating tube in a certain distance from the end of the accelerating tube, the coarse material is introduced sideways into a gas stream which is already partly accelerated in the accelerating tube. This adversely affects the coarse powder distribution in the gas stream, thereby causing a wide spectrum of particle sizes gained after crushing the coarse powder particles at the impact member. Furthermore, only part of the accelerating tube is used for accelerating the particles, so that the pulverization efficiency of the known apparatus is low. It is, therefore, the object of the invention to provide a pneumatic impact pulverizer which produces a narrow spectrum of particle sizes with a high efficiency. The object is achieved with a pneumatic impact pulverizer having the features of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an outline cross section of an embodiment of a pneumatic impact pulverizer according to the present invention; Figure 2 is an enlarged view of a pulverizing chamber shown in Figure 1; Figure 3 shows an A-A' cross section of Figure 1; Figure 4 shows a B-B' cross section of Figure 1; Figure 5 shows a C-C' cross section of Figure 1; Figure 6 shows a D-D' cross section of Figure 1; Figure 7 shows an outline cross section of other embodiment of a pneumatic impact pulverizer according to the present invention; Figure 8 shows an E-E' cross section of Figure 7; Figure 9 shows an outline cross section of other embodiment of a pneumatic impact pulverizer according to the present invention; Figure 10 shows an F-F' cross section of Figure 9; Figure 11 shows an outline cross section of other embodiment of a pneumatic impact pulverizer according to the present invention; Figure 12 shows a G-G' cross section of Figure 11; Figure 13 shows an H-H' cross section of Figure 11; Figure 14 shows an outline cross section of other embodiment of a pneumatic impact pulverizer according to the present invention; Figure 15 shows an I-I' cross section of Figure 14; Figure 16 shows an outline cross section of other embodiment of a pneumatic impact pulverizer according to the present invention; Figure 17 shows a J-J' cross section of Figure 16; Figure 18 is a front view of a conical impact member having a projection in the center; Figure 19 is a plan view of a conical impact member having a projection in the center; Figure 20 shows an outline cross section of a conventional pneumatic impact pulverizer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically. Embodiment 1 Figures 1 to 6 are explanatory diagrams for an embodiment (Embodiment 1) of a pneumatic impact pulverizer according to the present invention. In Figure 1, powder to be pulverized 80, fed through a pulverization powder feed pipe 5, passes through a pulverization powder feed port 4 (throat) formed between the inner wall of an accelerating tube throat 2 of an accelerating tube 1 and the outer wall of a high-pressure gas ejection nozzle 3, then enters the accelerating tube 1. It is preferred that the center axis of the high-pressure gas ejection nozzle 3 be substantially aligned with the center axis of the accelerating tube 1. On the other hand, high-pressure gas, which is fed through high-pressure gas feed ports 6, should, preferably, pass high-pressure gas chambers 7 through multiple high-pressure gas introduction pipes 8, enter the high-pressure gas ejection nozzle 3, then expand rapidly and eject toward an accelerating tube outlet 9. At this time, an ejector effect arises in the vicinity of the accelerating tube throat 2. Owing to the ejector effect, the powder to be pulverized 80 is accompanied by gas coexistent with the powder to be pulverized 80 and is ejected from the pulverization powder feed port 4 toward the accelerating tube outlet 90. At this time, the powder to be pulverized 80 is uniformly mixed with high-pressure gas at the accelerating tube throat 2, accelerated quickly, then collided with an impact surface 16 of an impact member 10 opposed to the accelerating tube outlet 9 in the state of a uniform solid-gas mixed stream without a variation in dust concentration. Impact force occurring at the time of the collision is applied to individual particles (powder to be pulverized 80) that have been dispersed thoroughly. Thus, pulverization is performed very efficiently. The pulverized powder that has been pulverized with the impact surface 16 of the impact member 10 comes into secondary collision (or third collision) with the side wall 14 of a pulverizing chamber 12, then goes out of a pulverized powder discharge port 13 formed behind the impact member 10. Preferably, the impact surface 16 of the impact member 10 should have a conical shape as shown in Figure 1 or a conical projection as shown in Figures 21 and 22. This is because the conical shape or conical projection facilitates uniformity in dispersion of pulverized powder in the pulverizing chamber 12 and efficiency in secondary collision with the side wall 14. The structure having the pulverized powder discharge port 13 located behind the impact member enables smooth discharge of pulverized powder. Figure 2 is an enlarged view of a pulverizing chamber. In Figure 2, the closest distance L 1 from a margin 15 of an impact member 10 to a side wall 14, must be shorter than the closest distance L 2 from a front wall 17 to the margin 15 of the impact member 10. This is very important for successful suppression of powder concentration in a pulverizing chamber in the vicinity of an accelerating tube outlet 9. Since the closest distance L 1 is shorter than the closest distance L 2 , pulverized powder can efficiently come into secondary collision with the side wall. The impact member 10 should, preferably, have an impact surface including a plane that is inclined by  1 smaller than 90° (more preferably, 55 to 87.5°, or further more preferably, 60 to 85°) with respect to the longitudinal axis of the accelerating tube. The slope assists in dispersing pulverized powder uniformly and facilitates efficiency in secondary collision with the side wall 14. In a pulverizer shown in Figure 20, an impact member has an impact surface 41 or a plane standing perpendicularly to an accelerating tube 46. Compared with this pulverizer, a pulverizer having an inclined impact surface seldom causes powder to be pulverized or powder composed of a resin or an adhesive material to fuse, coagulate, or get coarser. This enables pulverization at a high dust concentration. Even when abrasive powder is to be pulverized, abrasion occurring on the inner wall of the accelerating tube or the impact surface of an impact member will not concentrate regionally. This further extends the service life of the pulverizer and realizes stable operation. The longitudinal axis of an accelerating tube 1 should, preferably, be inclined by 0 to 45° with respect to the vertical axis. Within this range, powder to be pulverized 80 will not block a pulverization powder feed port 4. When a pulverization powder feed pipe 5 has a conical member on the bottom, a small amount of powder to be pulverized or powder with poor fluidity may stagnate around the lower part of the conical member. In this case, the slope of the accelerating tube 1 should range from 0 to 20° (more preferably, 0 to 5°) with respect to the vertical axis. Thus, the powder to be pulverized will not stagnate around the lower part of the conical member but enter the accelerating tube smoothly. The side wall of a classifying chamber should, preferably, have a substantially circular or elliptic cross section as shown in Figure 5 on the C-C' line of Figure 1. This facilitates uniform pulverization and smooth discharge of pulverized powder. Figure 3 shows an A-A' cross section of Figure 1. Figure 3 helps understand the mechanism that powder to be pulverized 80 is fed to an accelerating tube 1 smoothly. The distance between a plane containing an accelerating tube outlet 9 that is perpendicular to an extension of the center axis of the accelerating tube, and an outermost circumference 15 of an impact surface 16 of an impact member 10 opposed to the accelerating tube outlet 9, L 2 , should, preferably, range from 0.2 times to 2.5 times, or more preferably, 0.4 times to 1.0 times as long as the diameter of the impact member 10. When the distance L 2 is less than 0.2 times the length of the diameter of the impact member 10, the dust concentration in the vicinity of the impact surface 16 may become abnormally high. When the distance L 2 exceeds 2.5 times the length of the diameter, impact force gets weak. This may deteriorate the quality of pulverized powder. The closest distance L 1 from the outermost circumference 15 of the impact member 10 to the side wall 14, should, preferably, range from 0.1 times to 2 times as long as the diameter of the impact member 10. When the L 1 is less than 0.1 times the length of the diameter, passage of high-pressure gas causes a great pressure loss. Pulverization efficiency may deteriorate. Pulverized powder tends to flow less smoothly. When the L 1 is 2 or larger times the length of the diameter, secondary collision of powder to be pulverized against an inner wall 14 of a pulverizing chamber becomes less effective. Consequently, pulverization efficiency deteriorates. To be more specific, the preferable length of the accelerating tube ranges from 50 to 500 mm, and the preferable diameter of the impact member 10 ranges from 30 to 300 mm. Furthermore, the impact surface 16 of the impact member 10 and the side wall 14 should, preferably, be made of ceramic in terms of durability. Figure 14 shows a B-B' cross section of Figure 1. In Figure 4, powder to be pulverized passes through a pulverization powder feed port 4. At this time, the distribution of the powder to be pulverized on a plane perpendicular to the vertical axis of the pulverization powder feed port 4 becomes more partial, as the slope of an accelerating tube 1 with respect to the vertical axis gets larger. The smaller the slope is, the distribution becomes more uniform. The most preferable slope of the accelerating tube ranges from 0 to 5°. This fact has been verified using a transparent acrylic resin accelerating tube for inner observation as the accelerating tube 1. Figure 5 shows a C-C' cross section of Figure 1. In Figure 5, pulverized powder is evacuated backward through a pulverizing chamber 12 between an impact member support 11 and a side wall 14. Figure 6 shows a D-D' cross section of Figure 1. In Figure 6, two high-pressure gas introduction pipes 8 are installed. The number of high-pressure gas introduction pipes may be one, or three or more. Embodiment 2 Figures 7 and 8 show an embodiment of a pneumatic impact pulverizer having secondary gas intakes 18 between an accelerating tube outlet 9 and a pulverization powder feed port 4. The secondary gas intakes 18 formed between the accelerating tube outlet 9 and pulverization powder feed port 4 supply gas for preventing occurrence of turbulence due to a whirl occurring in the vicinity of an inner wall of an accelerating tube and thus regulating a stream in the accelerating tube. Herein, the whirl occurs when the high-pressure gas ejected from a high-pressure gas ejection port expands and accelerates rapidly in the accelerating tube. When powder to be pulverized is accompanied by the high-pressure gas that has rapidly expanded in the accelerating tube and accelerated quickly, the secondary gas fed through the secondary gas intakes regulates a stream. This further improves acceleration performance and upgrades pulverization efficiency. As for the arrangement of secondary gas intakes, Figure 8 shows a cross section in which multiple secondary gas intakes are bored on the inner wall of the accelerating tube to form a concentric plane that is perpendicular to the center axis of the accelerating tube. The arrangement is not limited to this example. When gas pressure is concerned, gas with atmospheric pressure or gas with pressure applied can be used as gas to be fed through the secondary gas intakes. The pressure or flow rate of gas or air is adjustable according to the purpose or situation of use. Embodiment 3 Figures 9 and 10 show an embodiment of a pneumatic impact pulverizer having a ring-type secondary gas intake 19 between an accelerating tube outlet 9 and a pulverization toner feed port 4. Air with normal pressure or air or gas with pressure applied is fed to the secondary gas intake 19 via a gas introduction member 20. Figure 10 shows an F-F' cross section of Figure 9. Embodiment 4 Figures 11 to 13 are schematics showing another embodiment of a pneumatic impact pulverizer according to the present invention. In Figure 11, numerals identical to those in Figure 1 denote the same members. In a pneumatic impact pulverizer shown in Figure 11, the longitudinal slope of an accelerating tube 1 should, preferably, range from 0 to 45° (more preferably, 0 to 20°, or further more preferably, 0 to 5°) with respect to the vertical line. Powder to be pulverized 80 passes through an accelerating tube throat 4 via a pulverization powder feed port 20, and enters the accelerating tube 1. Compressed gas or compressed air is routed to the accelerating tube 1 through an opening formed between the inner wall of the throat 4 and the outer wall of the pulverization powder feed port. The powder to be pulverized 80 that has been fed to the accelerating tube 1 is accelerated instantaneously to have a high speed, then ejected from an accelerating tube outlet 9 to a pulverizing chamber 12 at a high speed. Then, the powder to be pulverized 80 collides with an impact surface 16 of an impact member 10 to pulverize. Thus, powder to be pulverized 80 is supplied from the center of a throat 4 of an accelerating tube 1, dispersed in an accelerating tube 1, and ejected uniformly from an accelerating tube outlet 9. This allows the ejected powder to efficiently collide with an impact surface 16 of an impact member 10 opposed to the outlet 9. This results in higher pulverization efficiently. When an impact surface 16 of an impact member 10 has a conical shape as shown in Figure 11 or a conical projection as shown in Figure 19, post-collision dispersion improves. Therefore, powder to be pulverized neither fuses, coagulates, nor gets coarser. This enables pulverization at a high dust concentration. When abrasive toner is to be pulverized, abrasion occurring on an inner wall of an accelerating tube or an impact surface of an impact member does not concentrate regionally. This realizes extended service life and enables stable operation. Figure 12 shows a G-G' cross section of Figure 11. Powder to be pulverized 80 is fed to an accelerating tube 1 via a pulverization powder feed nozzle 20. High-pressure gas is fed to the accelerating tube 1 via a throat 4. Figure 13 shows an H-H' cross section of Figure 11. Similarly to a pulverizer shown in Figure 1, if the longitudinal slope of an accelerating tube 1 ranges from 0 to 45°, powder to be pulverized 80 will not block a pulverization powder feed port 20 but go down to be processed. If powder to be pulverized 80 has poor fluidity, the powder tends to stagnate on the bottom of a pulverization powder feed pipe 5. When the slope of the accelerating tube 1 ranges from 0 to 20° (more preferably, 0 to 5°), the powder to be pulverized 80 will not stagnate but enter the accelerating tube 1 smoothly. Comparing a pulverizer shown in Figure 1 with another one shown in Figure 11, the pulverizer of Figure 1 offers higher pulverization efficiency. This is because powder to be pulverized 80 is excellently dispersed and fed to an accelerating tube. Embodiment 5 Figures 14 and 15 show an embodiment of a pneumatic impact pulverizer having secondary gas intakes 18 between an accelerating tube outlet 9 and a throat 4. Figure 15 shows a I-I' cross section of Figure 14. Embodiment 6 Figures 16 and 17 show an embodiment of a pneumatic impact pulverizer having a ring-type secondary gas intake 19 between an accelerating tube outlet 9 and a throat 4. Air with normal pressure or gas or air with pressure applied is fed from a gas introduction means 20 to the secondary gas intake 19. Figure 17 shows a J-J' cross section of Figure 16. Next, materials comprising toner will be described. When a heating pressure fixing unit or a heating pressure roller fixing unit is used, toner binder resins listed below are usable. Homopolymer of styrene or substitution products thereof such as polystyrene, poly-p-chlorostyrene, and polyvinyl toluene; styrene-p-chlorostyrene copolymer, styrene-vinyl toluene copolymer, styrene-vinyl naphthalene copolymer, styrene-acrylic ester copolymer, styrene-ester methacrylate copolymer, styrene-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, and other styrene copolymers; polyvinyl chloride, phenol resin, natural denaturated phenol aldehyde resin, natural resin denaturated maleic resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane resin, polyamide resin, fran resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumarone-indene resin, and petroleum resins. In a heating pressure fixing method of a pressure heating roller fixing method in which oil is hardly or never applied, an offset phenomenon or a phenomenon that part of a toner image on a toner image support member is transferred to a roller, or adhesion of toner to the toner image support member must be treated attentively. Toner that fixes with a smaller amount of thermal energy is likely to cause blocking or caking during storage or in a developing unit. These problems must also be solved. The above phenomena are caused mainly from the properties of a binder resin contained in toner. The studies of the present inventors have demonstrated that when the content of a magnetic material in toner decreases, adhesion of toner to the toner support during fixing improves but occurrence of offset increases. Furthermore, blocking and caking occurs more frequently. Therefore, when a heating pressure roller fixing method in which oil is hardly applied is adopted, choice of a binder resin becomes very important. Preferable binder materials are a cross-linked styrene copolymer or cross-linked polyester. Comonomers for styrene copolymers include acrylic acid, acrylic methyl, acrylic ethyl, acrylic butyl, acrylic dodecyl, acrylic octyl, acrylic-2-ethyl hexyl, acrylic phenyl, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamid, and other monocarboxylic acids containing double bonds, and their substitution products; for example, maleic acid, maleic butyl, maleic methyl, maleic dimethyl, and other dicarboxylic-acids containing double bonds, and their substitution products; for example, vinyl chloride, vinyl acetate, vinyl benzoate, and other vinyl esters; for example, ethylene, propylene, butylene, and other ethylene olefins; for example, vinyl methyl ketone, vinyl hexylketone, and other vinyl ketones; for example, vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, and other vinyl ethers. The above vinyl monomers are used independently or in combination of two or more monomers. A cross linking agent may be a compound containing two or more double bonds in which monomers can be polymerized; such as, divinylbenzene, divinylnaphthalene, or other aromatic divinyl compound; such as, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,3 butanediol dimethacrylate, or other carboxylic ester containing two double bonds; divinyl aniline, divinyl ether, divinyl sulfide, divinyl sulfane, or other divinyl compound; or other compound containing three or more vinyl radicals. The above compounds may be used alone or in combination. When a pressure fixing method or a light heating pressure fixing method is adopted, binder resins for use in a toner fixing with pressure may be employed. The binder resins include polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethylacrylate copolymer, ethylene-vinyl acetate copolymer, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturation polyester, and paraffin. It is preferred that a charge control agent be added to or mixed in toner particles. The charge control agent optimizes control of the number of charges according to a developing system. In the present invention, the charge control agent assists in further stabilizing the balance between the distribution of particle sizes and the number of charges. The employment of the charge control agent intensifies functional separation for optimizing image quality in groups of particle sizes and enhances complementary relationships among the particle size groups. Positive charge control agents include modified products of nigrosine and fatty acid metallic salt; such as, tributyl benzyl ammonium-1-hydroxy-4-naphthosulfonium salt, tetrabutyl ammonium tetrafluoroborate, and other quaternary ammonium salts. These substances can be used independently or in combination of two or more substances. Among them, nigrosine compounds and quaternary ammonium salts are preferable. where, R 1 represents H or CH 3 , and R 2 and R 3 represent a substituted or non-substituted alkyl group (preferably, C 1 to C 4 ). Homopolymers composed of monomers each of which is provided as the above formula, or a copolymer copolymerized with styrene, acrylic ester, methyl methacrylate, or other polymerizable monomer can be employed as a positive charge control agent. Such charge control agents also serve (fully or partly) as binder resins. Effective negative charge control agents are, for example, organometal complexes and chelate compounds; such as, aluminum acetylacetonate, iron (II) acetylacetonate, and chrome or zinc 3 and 5-ditertiary butyl salicylate. Above all, metal acetylacetonate complexes and metal salicylate complexes or salts are preferable. In particular, metal salicylate complexes or salts are preferred. The above charge control agents (that do not act as binder resins) should, preferably, be used in the form of fine particles. In this case, the number-average particle size of a charge control agent should, preferably, be 4 µm or less (more preferably, 3 µm). When mixed in toner, such charge control agent should, preferably, range from 0.1 to 20 parts by weight based on 100 parts by weight of a binder resin. When magnetic toner is employed, a magnetic material to be contained in the magnetic toner includes; magnetite, gamma-iron oxide, ferrite, excess-iron ferrite, and other iron oxides; metal such as iron, cobalt, and nickel; their alloys with metal such as aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, vanadium; and their mixtures. Those magnetic materials may have an average particle size ranging from 0.1 to 1 µm, or preferably, 0.1 to 0.5 µm. The content of a magnetic material in toner should range from 60 to 110 parts by weight based on 100 parts by weight of a resin component, or preferably, 65 to 100 parts by weight based on 100 parts by weight of a resin component. A colorant employed for toner may be a widely-adopted dye and/or pigment. For example, carbon black, copper phthalocyanine, peacock blue, permanent red, lake red, rhodamine lake, Hansa yellow, permanent yellow, and bendizine yellow can be used. The content ranges from 0.1 to 20 parts by weight, or preferably, 0.5 to 20 parts by weight based on 100 parts of a binder resin. To improve transparency of OHP film on which toner images are fixed, 12 parts by weight is preferred. More preferably, the contents should range 0.5 to 9 parts by weight. Next, a process of producing toner will be described. Embodiment 9 Styrene-butylacrylate-divinyl benzene copolymer: 100 parts by weight (monomer polymerization ratio by weight: 80.0/19.0/1.0, weight-average molecular weight: Mw350,000) Magnetic iron oxide (average particle size: 0.18 µm): 100 parts by weight Nigrosine: 2 parts by weight Low molecular weight ethylene-propylene copolymer: 4 parts by weight The above materials are prepared and mixed using a Henschel mixer (FM-75 manufactured by Mitsui Miike Chemical Industries, Co., Ltd.), then kneaded using a biaxial kneader (PCM-30 manufactured by Ikegai Iron Works, Co., Ltd.). Then, the kneaded mixture is cooled, then coarsely pulverized to have a diameter of 1 mm or less using a hammer mill. This results in coarsely-pulverized powder for producing toner. The resulting coarsely-pulverized powder for toner is classified and pulverized using a fine powder production apparatus (hereafter, fine power production system A) made up of a pneumatic classifier and a pneumatic impact pulverizer shown in Figure 1. In the pneumatic impact pulverizer, an accelerating tube is inclined in the longitudinal direction by about 0° (substantially, resting vertically) with respect to the vertical line. An employed impact member has an impact surface that is shaped like a cone having an apex angle of 160° and an outer diameter of 100 mm. The closest distance from the plane of an accelerating tube outlet that is perpendicular to the center axis of the accelerating tube to the outermost circumference of the impact surface of the impact member opposed to the accelerating tube outlet, L 2 , is 50 mm. A pulverizing chamber has a cylindrical shape of 150 mm in inner diameter. Therefore, the closest distance L 1 is 25 mm. A table-type quantitative feeder is used to measure out coarse powder at a rate of 35.4 kg/H. Then, an injector feeder is used to feed the powder to the pneumatic classifier via a raw material feeder and a feed pipe. The classified coarse powder is routed to a coarse powder discharge hopper, then evacuated to a pneumatic impact pulverizer through a pulverization powder feed pipe. Then, the classified coarse powder is pulverized using compressed air that is compressed with pressure of 6.0 kg/cm 2 (G) or 6.0 Nm 3 /min. Then, the pulverized powder is mixed with coarse powder fed from the raw material feeder, fed back to the pneumatic classifier, then pulverized in a looped state. The classified fine powder is scavenged by while accompanied by suction air originating from a discharge fan. This resulted in a finely pulverized-and-classified product showing sharp distribution of particle sizes of 8.4 µm in weight-average diameter. The finely pulverized-and-classified product is classified using a dispersion separator DS5UR (Japan Pneumatic Industries, Co., Ltd.). This classification eliminates very fine particles that are smaller than a specified particle size. A product thus classified to permit high yield turned out to be excellent toner. Various methods are conceivable to measure the distribution of particle sizes of a finely pulverized-and-classified product or toner. In this process, a Coulter counter was used. A Coulter counter TA-11 (Coulter Inc.) was used as a measuring instrument. An interface (Japan Scientific Machinery Manufacturing Co., Ltd.) for outputting a number distribution or a volume distribution and a personal computer CX-1 (Canon Inc.) were connected. 1-% NaCl solution was prepared as electrolyte by using first class sodium chloride. A measuring procedure will be described. First, 0.1 to 5 ml of a surface-active agent as a dispersant, preferably, alkylbenzene sulfonium salt was added to 100 to 150 ml of the above electrolyte solution. Then, 2 to 20 mg of a test sample was added. The electrolyte with the sample suspended was dispersed for about one to three minutes using an ultrasonic dispersing device. Using the Colter counter TA-11 whose aperture was set to 100 µ, the numbers of reference particles of 2 to 40 µ in diameter were counted to produce a distribution of particle sizes. Based on the measured values, a weight-average particle diameter and a volume-average particle diameter were calculated. Embodiment 10 Coarsely-pulverized toner powder identical to that used in Embodiment 9 was employed. In the fine powder production system A of the same type as that used in Embodiment 9, the slope of an accelerating tube was set to 15°, and a coarse powder feed rate, to 33.6 kg/H. This pulverization provided a finely pulverized-and-classified product showing sharp distribution of particle sizes of 8.6 µm in weight-average diameter. Embodiment 11 Coarsely-pulverized toner power identical to that used in Embodiment 9 was employed. In the fine powder production system A of the same type as that used in Embodiment 9, a distance from an impact surface was set to 100 mm, and a coarse powder feed rate, to 32.6 kg/H. This pulverization provided a finely pulverized-and-classified product showing sharp distribution of particle sizes of 8.5 µm in weight-average diameter. Embodiment 12 Coarsely-pulverized toner powder and the fine powder production system A identical to those used in Embodiment 9 were employed. A distance from an impact surface was set to 30 mm, and a coarse toner powder feed rate, to 30.3 kg/H. This pulverization provided a finely pulverized-and-classified product showing sharp distribution of particle sizes of 8.4 µm in weight-average diameter. Embodiment 13 Coarsely-pulverized toner powder and the fine powder production system A indentical to those used in Embodiment 9 were employed. A distance from an impact surface was set to 22 mm, and a coarse toner powder feed rate, to 22.5 kg/H. This pulverization provided a finely pulverized-and-classified product having a weight-average diameter of 8.4 µm. Embodiment 14 Coarsely-pulverized toner powder and the fine powder production system A indentical to those used in Embodiment 9 were employed. A cylindrical pulverizing chamber had an inner diameter of 120 mm. A coarse powder feed rate was set to 22.5 kg/H. This pulverization provided a finely pulverized-and-classified product having a weight-average diameter of 8.4 µm. Embodiment 14a Coarsely-pulverized toner powder and the fine powder production system A identical to those used in Embodiment 9 were employed. A cylindrical pulverizing chamber had an inner diameter of 120 mm. A coarse powder feed rate was set to 32.6 kg/H. This pulverization provided a finely pulverized-and-classified product having a weight-average diameter of 8.6 µm. Embodiment 15 Coarsely-pulverized toner powder and the fine powder production system A identical to those used in Embodiment 9 were employed. A cylindrical pulverizing chamber had an inner diameter of 220 mm. A coarse powder feed rate is set to 28.6 kg/H. This pulverization provided a finely pulverized-and-classified product having a weight-average diameter of 8.5 µm. Embodiment 16 Coarsely-pulverized toner powder and the fine powder production system A identical to those used in Embodiment 9 were employed. An impact surface had an outer diameter of 100 mm and a conical projection with an apex angle 55° as shown in Figures 18 and 19. A distance from the impact surface L 2 , was set to 50 mm, and a coarse powder feed rate, to 35.4 kg/H. This pulverization provided a finely pulverized-and-classified product showing sharp distribution of particle sizes of 8.4 µm in weight-average diameter. Embodiment 17 Coarsely-pulverized toner powder identical to that used in Embodiment 9 was employed. A fine powder production apparatus made up of a pneumatic classifier and a pneumatic impact pulverizer shown in Figure 11 (hereafter, fine powder production system B) was used to perform classification and pulverization. The slope of an accelerating tube was 0°. An impact member had an impact surface having a conical shape with an apex angle of 160° and a cylindrical shape of 100 mm in outer diameter. A distance from the impact surface, L 2 , was set to 50 mm. A pulverizing chamber had a cylindrical shape of 150 mm in inner diameter. The closest distance, L 1 , was 25 mm. A table-type quantitative feeder was used to measure coarsely-pulverized toner powder at a rate of 26.5 kg/H. An injection feeder was used to feed the coarsely-pulverized toner powder with compressed air that was compressed with pressure of 6.0 kg/cm 2 (G) or 6.0 Nm 3 /min. Then, pulverization was carried out in a looped state. This resulted in a finely pulverized and classified product having a weight-average diameter of 8.6 µm. Comparative example 1 A pulverizer shown in Figure 20 was used as a pneumatic impact pulverizer together with a pneumatic classifier. In a classifying and pulverizing system (hereafter, fine powder production system C) coarsely-pulverized powder identical to that prepared in Embodiment 9 was employed, and high-pressure gas was fed to the pneumatic impact pulverizer by injecting compressed air at a rate of 6.0 kg/cm 2 (G) or 6.0 Nm 3 /min. Then, classification and pulverization were carried out at a throughput of 16.4 kg/H. The weight-average diameter of particles in a finely pulverized-and-classified product was 8.4 µm. Content of very fine and coarse powder was high, and the distribution of particle sizes was broad. Smoothness in feeding coarse powder to an accelerating tube and uniformity in dispersing the coarse powder in the accelerating tube were worse than those in Embodiment 9. Comparative example 2 A classifying and pulverizing system (hereafter, fine powder production system D) identical to that in Comparative example 1 was employed, except that, the impact surface had a conical shape with an apex angle of 160°. Coarsely-pulverized powder identical to that prepared in Embodiment 9 was classified and pulverized at a throughput of 20.4 kg/H. The resulting finely pulverized-and-classified product had a weight-average particle size of 8.5 µm. The distribution of particle sizes was broader than that in Embodiment 9. The conditions for production and results of Embodiments 9 to 17 and Comparative examples 1 and 2 are listed below. Data No. Fine powder production system Slope of an accelerating tube Structure of an impact surface Distance from the impact surface E9 A 0 Cone with an apex angle of 160°, on a cylinder of 100 mm in diameter 50 E10 A 15 ditto 50 E11 A 0 ditto 100 E12 A 0 ditto 30 E13 A 0 ditto 220 E14 A 0 ditto 50 E15 A 0 Cone with an apex angle of 160°, on a cylinder of 150 mm in diameter 50 E16 A 0 Conical projection with an apex angle of 160° on a cylinder of 100 mm in diameter 50 E17 B 0 Conical shape with an apex angle of 160° on a cylinder of 100 mm in diameter 50 C1 C - Plane of a cylinder 50 C2 D - Cone with an apex angle of 160°, on a cylinder of 100 mm in diameter 50 DATA-No. Structure of a pulverizing chamber Throughput Weight-average diameter Pulverization efficiency ratio E9 Cylinder of 150 mm in diameter 35.4 8.4 1.74 E10 ditto 33.6 8.6 1.65 E11 ditto 32.6 8.5 1.60 E12 ditto 30.3 8.4 1.49 E13 ditto 22.5 8.4 1.10 E14 Cylinder of 120 mm in diameter 32.6 8.6 1.59 E15 Cylinder of 220 mm in diameter 28.6 8.5 1.40 E16 Cylinder of 150 mm in diameter 35.4 8.4 1.74 E17 ditto 26.5 8.6 1.30 C1 Box-like shape 16.4 8.4 0.80 C2 ditto 20.4 8.5 1.0 * E stands for Embodiment, and C, for Comparative example. Compared with comparative examples that represent a toner production process in which toner is pulverized according to a conventional process, the embodiments of the toner production processes using the present invention provide higher pulverization efficiency rates ranging from 1.1 to 1.74 with a weight-average diameter of a finely-pulverized product ranging from 8.4 to 8.6 µm. The distributions of particle sizes in the embodiments include smaller amounts of coarse and very fine powder that those in the comparative examples. The above table demonstrates that the toner production process using the present invention is superb. A pneumatic impact pulverizer of the present invention pulverizes powder to be pulverized more efficiently than a conventional pneumatic impact pulverizer does. Furthermore, the pneumatic impact pulverizer of the present invention prevents the powder to be pulverized from fusing, coagulating, and getting coarser, and has an advantage of inhibiting the powder to be pulverized from abrading an impact member or an accelerating tube.

Claims: A pneumatic impact pulverizer comprising an accelerating tube (1) for carrying and accelerating powder to be pulverized with high pressure gas, a pulverizing chamber (12) for pulverizing powder to be pulverized, said pulverizing chamber (12) being equipped with an impact member (10) having an impact surface (16) opposed to the opening plane of the outlet (9) of said accelerating tube (1), said pulverizing chamber (12) having a side wall (14) against which powder that has been pulverized at said impact member (10) collides to further pulverize, wherein a distance (L 1 ) between said side wall (14) and a margin (15) of said impact member (10) is shorter than a distance (L 2 ) between a front wall (17) of said pulverizing chamber (12) opposed to said impact surface (16) and said margin (15) of said impact member (10), characterized in that the back end of said accelerating tube (1) opposite said pulverizing chamber (12) is provided with a pulverization powder feed port (4) and a high pressure gas ejection nozzle (3), and that said pulverization powder feed port (4) and said high pressure gas ejection nozzle (3) are concentrically arranged. A pneumatic impact pulverizer according to claim 1, wherein said accelerating tube (1) is inclined so that the longitudinal slope ranges from 0 to 45° with respect to the vertical line. A pneumatic impact pulverizer according to claim 2, wherein said accelerating tube (1) is inclined so that the longitudinal slope ranges from 0 to 20° with respect to the vertical line. A pneumatic impact pulverizer according to claim 3, wherein said accelerating tube (1) is inclined so that the longitudinal slope ranges from 0 to 5° with respect to the vertical line. A pneumatic impact pulverizer according to any one of claims 1 to 4, wherein said impact member (10) has a projection in the center of said impact surface (16). A pneumatic impact pulverizer according to any one of claims 1 to 5, wherein said impact surface (16) of said impact member (10) has an inclined plane having a slope  1 smaller than 90° with respect to the longitudinal axis of said accelerating tube (1). A pneumatic impact pulverizer according to any one of claims 1 to 6, wherein the tip of said high pressure gas ejection nozzle (3) is located in the vicinity of an accelerating tube throat (2). A pneumatic impact pulverizer according to any one of claims 1 to 7, wherein said pulverizing chamber (12) has a pulverized powder discharge port (11) for discharging the powder to be pulverized that has been pulverized on its back wall opposed to the plane of said accelerating tube outlet. A pneumatic impact pulverizer according to any one of claims 1 to 8, wherein the high pressure gas ejection nozzle (3) is coaxially arranged with the accelerating tube (1). A pneumatic impact pulverizer according to any one of the preceeding claims 1 to 9, wherein said pulverization powder feed port (4) surrounds said high pressure gas ejection nozzle (3). A pneumatic impact pulverizer according to any one of claims 1 to 9, wherein said high pressure gas ejection nozzle (3) surrounds said pulverization powder feed port (4).

Inventors: KANDA HITOSHI, MITSUMURA SATOSHI, MIYANO KAZUYUKI, OMATA KAZUHIKO, TAKAICHI MOMOSUKE, KANDA, HITOSHI, MITSUMURA, SATOSHI, MIYANO, KAZUYUKI, OMATA, KAZUHIKO, TAKAICHI, MOMOSUKE, KANDA, HITOSHI, C/O CANON KABUSHIKI KAISHA, MITSUMURA, SATOSHI, C/O CANON KABUSHIKI KAISHA, MIYANO, KAZUYUKI, C/O CANON KABUSHIKI KAISHA, Omata, Kazuhiko, c/o Canon Kabushiki Kaisha, Takaichi, Momosuke, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: B02C19
IPC codes: B01F13, B02C23, B01F5, B02C19