Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
  • G03G9/1132—Macromolecular components of coatings
  • G03G9/1133—Macromolecular components of coatings obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/103—Glass particles
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/107—Developers with toner particles characterised by carrier particles having magnetic components
  • G03G9/1075—Structural characteristics of the carrier particles, e.g. shape or crystallographic structure
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/107—Developers with toner particles characterised by carrier particles having magnetic components
  • G03G9/1087—Specified elemental magnetic metal or alloy, e.g. alnico comprising iron, nickel, cobalt, and aluminum, or permalloy comprising iron and nickel
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
  • G03G9/1139—Inorganic components of coatings

Definitions

• An electrostatographic developer mixture comprising nodular carrier beads, the nodular beads having a number average size distribution in the range of 50 to 1,000 microns, and between about 95 and about 99.5 weight percent, based upon the developer mixture, of carrier beads relative to the finely divided toner particles electrostatically clinging to the surface of the nodular carrier beads.
• Such developer mixtures are useful in the development of latent electrostatographic images by cascade and magnetic brush development techniques.
• CARRIER MATERIAL FOR ELECTROSTATOGRAPHIC DEVELOPER This invention relates in general to imaging systems and, more particularly, to improved imaging materials.
• the formation and development of images on the surface of photoconductive materials by electrostatic means is well known.
• the basic xerographic process as taught by C. F. Carlson in U. S. Pat. No. 2,297,691 involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light, and developing the resulting latent electrostatic image by depositing on the image, a finely-divided electroscopic material referred to in theart as toner.
• the toner is attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electroscopic image.
• This powder image may then be transferred, usually electrostatically, to a support surface such as paper.
• the transferred image may subsequently be permanently affixed to the support surface by heat, or other suitable'fixing means such as solvent or overcoating treatment may be used instead.
• a toner and carrier combination In order to develop a negatively charged latent electrostatic image,.a toner and carrier combination should be selected in which the toner is triboelectrically positive in relation to the carrier. Conversely, to develop a positively charged latent electrostatic image, a toner and carrier combination in which the toner is triboelectrically negative in relation to the carrier is used.
• This triboelectric relationship between the toner and carrier depends on the relative positions of the materials in the triboelectric series. In this series materials are arranged in ascending order of ability to take ona positive charge. Each material is positive with respect to any material classified below it in the series; and negative with respect to any material above it in the series.
• the toner particles are electrostatically attracted from the carrier partially to the charged portions of the image bearing surface, whereas they are not electrostatically attracted to the uncharged or background portions of the image which they contact.
• the cascade development process has the distinct advantage that most of toner particles accidentally deposited on the background portion are removed by the rolling carrier, due apparently, to the greater electrostatic attraction between the toner and the carrier than be tween the toner and the discharged background. The carrier particles and unused toner particles are then recycled.
• the cascade development process is extremely good for the development of line copy images, and is the most widely used commercial xerographic development technique. A general purpose office copying machine incorporating this technique is described in U. S. Pat. No. 3,099,943.
• Another technique for developing electrostatic images is the magnetic brush process as disclosed, for example, in U. S. Pat. No. 2,874,063.
• a developer material containing toner and magnetic carrier particles is attracted to and is carried by a magnet.
• the magnetic field causes alignment of the magnetic carrier particles in a brush-like configuration.
• the toner particles are attracted from the carrier particles of the brush to the charged areas of the image-bearing surface, but not to the uncharged areas. Since the charged areashave an imagewise configuration, the toner material clings to the surface in imagewise configuration, thus developing the latent image.
• a photoconductor on a conductive substrate in the form of a cylindrical drum or a flexible belt which is continuously rotated through a cycle of sequential operations including charging, exposing, developing, transferring and cleaning.
• the plate is usually given a uniform positive charge by means of a corona generating device of the type disclosed by L. E. Walkup in U. S. Pat. No. 2,777,957 which is connected to a suitable source of high potential.
• the resultant latent image is then developed with toner, and the developed image is transferred to a proximate copy receiving surface such as paper, by electrostatically charging the paper to cause it to electrostatically attract the developed image.
• a proximate copy receiving surface such as paper
• electrostatically charging the paper to cause it to electrostatically attract the developed image.
• the residual powder and carrier particles are removed before the plate is reused in subsequent cycles. This is generally accomplished by imparting an opposite charge to the photoconductive surface thereby nullifying any electrostatic attraction between the surface and the particles then rubbing the surface to physically remove all the remaining particles and exposing it to light to fully discharge the surface.
• Typical electrostatographic cleaning devices include the web type cleaning apparatus as disclosed, for example, by W. P. Graff, Jr., et al. in U. S. Pat. No. 3,186,838.
• the Graff, Jr., et al., patent removal of the residual toner and carrier particles from the plate is effected by rubbing a web of fibrous material against the imaging surface.
• These inexpensive and disposable webs of fibrous material are gradually advanced in pressure and rubbing or wiping contact with the imaging surface to present a clean surface to the plate whereby substantially complete removal of the residual powder and carrier particles from the plate is effected.
• smooth-surfaced carrier beads which are spherical in shape.
• Spherical particles accept relatively uniform surface charge and are relatively uniform in their attraction of toner particles. This results in more uniform toner deposition and consequently more uniform final copies.
• the spherical carrier beads are more frictionless and are less likely to cause scratching of the imaging surface.
• costly procedures are required.
• the size, shape, physical characteristics and chemical composition of the carrier particles influence the quality of the developed image and the ability of the carrier to retain its original properties for long periods of use.
• the present invention is based upon the discovery that nodular carrier beads characterized by a pebbled surface with recurring recesses and protrusions giving the particles a relatively large external surface area provide excellent developer compositions for electrostatographic use.
• Such nodular carrier beads have high surface-to-mass ratio as compared with substantially smooth-surfaced carrier beads of the same mass.
• Nodular carrier particles present a plurality of small spherical surfaces with recesses defining pockets for toner particles.
• nodular carrier of this invention Carriers with wide ranges of density and triboelectric values can be obtained because the nodular beads can be prepared by agglomeration of widely differing and customized formulations of particulate mixtures.
• Nodular beads used in accordance with this invention not only have greater surface-to-mass ratio to hold more toner beads (as compared to spherical carrier particles), but also tend less to grind the toner particles and each other to fines during development use.
• the impact is mostly absorber on the outer surface of the beads and the toner material, most of which is in the pockets defined by the recesses between the surface protrusions essentially escapes impaction.
• This capacity of the nodular beads to reduce impactive damage to either the beads themselves or the toner material results in much greater developer life than has heretofore been achieved.
• the nodular carrier beads are three-dimensional solids approximately 50 1,000 microns in size, of roughly cuboidal, rounded, irregular or spheroidal shape, and with surface irregularities formed by numerous nodules and recesses. Though the beads may have randomly spaced voids or a slight degree of porosity, they should have predominantly solid cores. Preferred carrier beads have generally rounded nodules and are generally spheroidal in shape thus giving an appearance reminiscent of a raspberry or cluster of grapes.
• the carrier beads of the present invention can be prepared by any of several processes. For example,
• small particles can be agglomerated by known granulating or pelletizing procedures, preferably in the presence of a binder, and, if desired, depending on the binder, the agglomerates can then be heated to give them hardness and strength.
• One generally useful method involves mixing a particulate carrier material with a binder and charging the mixture to an inclined rotary mixing plate over which is sprayed a liquid which has the effect of wetting the particles. As the mixing plate rotates, the agglomerates continue to grow. The largest agglomerates come to the surface and roll off at the ascending side of the lower edge of the mixing plate. The smaller agglomerates remain on the rotary plate until they are big enough.
• the size range of the resultant agglomerates can be adjusted to within close tolerances.
• the green agglomerated particles can then be subjected to firing, fusing or sintering treatment to produce a hard compacted nodular bead of the aforementioned description.
• the particles which are agglomerated to form the nodular carrier beads of this invention may be spherical or non-spherical particulate materials. In the event that they are nonspherical, after the agglomeration step, it may be desired to spheroidize the particles, as by heating, to cause surface forces to draw the particles into a spherical shape.
• the constitution of the carrier is not a critical part of this invention, the criteria for selection being the same as are applicable in the case of conventional carrier materials.
• the carrier must be capable of inducing a triboelectriccharge on the toner particles, in order to attract and carry the toner particles to the latent image.
• the triboelectric relationship of the toner and carrier must be such that an acceptable development of the latent electrostatic image is produced, i.e., a dense image with low background development.
• a material which has a relatively high triboelectric relationship with the toner produces low-density images with clean background because of the inability of the electrostatic image to attract sufficient toner particles from a carrier.
• a carrier material with low triboelectric relationship to the toner will develop very low-contrast electrostatic patterns but would also produce high background density. In order to obtain a practical developer, carrier materials not falling into these extreme patterns should be avoided. In use, the average triboelectric relationship decreases with time because of cumulative physical damage to the carrier.
• the carrier material must be one which iscapable of forming beads which do not tend to cake, bridge or agglomerate during handling and storage. Adherence of carrier particles to reusable electrostatic imaging surfaces causes the formation of undesirable scratches on these surfaces during image transfer and surface cleaning steps.
• the carrier composition must be such that it is capable of resisting the deteriorating forces normally attendant continuous development processes which require the recycling of carrier particles by bucket conveyors partially submerged in the developer supply such as disclosed in U. S. Pat. No. 3,099,943.
• the carrier is to be used in a magnetic brush development process, it must also be magnetic.
• the ideal carrier material for this invention is one which exhibits a proper triboelectric relationship with the toner, is capable of being formed into nodular particles of uniform size within close tolerances, and has a high degree of resistance to physical image and impaction which can impair this critical relationship.
• any material which satisfies the foregoing requirements can be used to prepare the carrier beads of this invention.
• metals such as steel, copper, nickel, aluminum, brass and the like, and refractory materials such as carbides, nitrides, ceramics or glasses can be advantageously employed.
• the ceramic or glass material can be prepared from a wide variety of magnetic or non-magnetic refractory oxides as is well known in the art, including silica, alumina, lithium oxide, berylium oxide, magnesium oxide, calcium oxide, zinc oxide, strontium oxide, cadmium oxide, barium oxide, lead oxide, magnesium oxide, iron oxide, cobalt oxide, nickel oxide, iron oxide, and the like. Representative compositions which are useful in accordance with the present invention are disclosed in U. S. Pat.
• the selected material is particulated or comminuted by conventional grinding, milling, spray-drying or spray-cooling techniques to the desired size-distribution range which is generally between 1 and microns, but is preferably in the more restricted range of 5 to 40 microns.
• the resultant particles if they are irregularly shaped, can be spheroidized before being agglomerated by introducing them into a high velocity stream of a hot gas such as can be produced by a plasma generator. The melted particles are spheroidized due to internal forces and then quenched in a cold liquid such as water to solidify them.
• the particulate carrier material can be agglomerated to produce the aforementioned nodular carrier beads.
• a convenient method for accomplishing this result involves using conventional granulating equipment to roll particulate material with a liquid and a binder on an inclined rotary mixing plate.
• Other types of granulating devices e.g., drum and pan granulators, which impart a tumbling action to the particles, such as those disclosed in U. S. Pat. No. 3,192,290 may also be used.
• the rotating mixing plate method of forming the nodular beads by feeding the finely-divided carrier material on to a disc at a constant rate while selectively wetting the incoming feed, causes the rolling particles to come into intimate contact with each other.
• the size and quality of the agglomerates are functions of many variables in the operation of the rotary mixing plate, several of which are set forth below:
• Rate of feed of the carrier material to the plate It is important that the rate of feed and wetting be maintained, once the correct settings are obtained, to insure that the product has a uniform size distribution within a narrow range.
• the agglomeration effect is dependent upon the presence of liquid which gives the particulate carrier material balling properties.
• the agglomerated particles do not have a sufficiently high level of strength to be used in electrostatographic development processes without either a binder material being added during agglomeration or a hardening treatment after agglomeration.
• the agglomerates are very frangible and certainly not suitable for electrostatographic development purposes.
• Binders which can be used to impart great strength to the agglomerates are well known in the art.
• a suitable binder is sodium silicate.
• Other materials which can be used for this purpose include synthetic resins such as epoxy or acrylic resins, waxes, polyvinyl alcohol, dextrin, esters of saturated fatty acids, natural and synthetic adhesives and the like.
• Other material which act as lubricants or plasticizers for the binders may be additionally incorporated into the feed material to aid in the agglomeration process.
• the binder is a material such as epoxy resin which is self hardening, it is not absolutely essential that the agglomerates be subjected to a hardening after-treatment.
• binders such as sodium silicate and waxes, which in themselves do not provide the necessary strength to the carrier particles for direct use in electrostatographic development processes.
• the aftertreatment generally involves subjecting the green carrier agglomerates to high temperature conditions, generally in temperature range which effects the fusing or sintering of the carrier material and a chemical change in the binder used therefor.
• Heating is conveniently accomplished by admixing the green carrier agglomerates with a flowing hot gas such as can be produced in a combustion furnace, a plasma generator or an electric furnace.
• a flowing hot gas such as can be produced in a combustion furnace, a plasma generator or an electric furnace.
• the temperature of the hardening treatment will in the first instance depend upon the nature of the carrier material. Since refractory materials are generally employed and the heat treatment is most effective when the carrier material softens to some extent during the treatment, the temperature will be at least 1000F. Most usually it will be in the range of 2,000 to 2,700 E, but the temperature can be varied to take into account the residence time of the green carrier agglomerates in the hot flowing gases.
• the hardening post-treatment is of importance in another respect. Under the influence of heat, the agglomerated carrier particles begin to soften and, due to internal forces, they become rounded. Thus, the heat treatment not only adds strength to the agglomerates but also smoothes out large irregularities in the surfaces of the agglomerated carrier particles.
• nodular carrier heads Another way of producing nodular carrier heads is by precipitation of asalt, a metal, or a metal oxide from solution. Under controlled conditions the individual particles of the resultant precipitate are in the form of a cluster of smaller particles of generally botryoidal structure.
• One method of forming nodular particles in this manner is disclosed in Proceedings Thirteenth Annular Meeting, Metal Powder Association, Apr. 30 to May 1, 1957, in an article entitled Production and Characteristics of Chemically Precipitated Nickel Powder by K. O. Cockburn, R. J. Loree and J. B. Haworth. The authors produce nickel powder by reacting an ammoniacal nickel ammonium sulfate solution with hydrogen at elevated temperature and pressure to effect direct reduction of the nickel sulfate to elemental nickel powder.
• the individual particles of the powder are in the form of grape-like clusters formed of numerous sub-particles agglomerated together.
• Such nodular particles are generally spheroidal in shape, with an average size in the range of 30 to 200 microns, have greater than 99 percent purity, and are eminently suitable for use in the present invention, especially for developers to be used in magnetic brush development processes.
• the nodular carrier beads used in the present invention can be over-coated, if desired, by conventional rolling, spraying or dipping techniques to impart triboelectric properties, strength and/or lubricity thereto.
• Coating materials are generally film forming polymeric materials such as homopolymers and copolymers of vinyl monomers such as styrene, acrylic acid esters, methacrylic acid esters, vinyl chloride, vinylidene chloride, fluoroethylene, vinyl acetate, polyamides, polyesters, and the like.
• the thickness of the coating is not critical so long as it is not so thick as to completely fill in the recesses of the nodular carrier thereby rendering the carrier surface substantially smooth. Coatings less than about 10 p. thick are generally useful, although thicker coatings can be applied to large carrier beads, e.g., those having at least one measurement greater than about 250 u.
• the carrier agglomerates produced by the present invention are surprisingly useful when combined with conventional toner materials as electrostatographic developer compositions. They are capable of giving images of high resolution with low background noise as compared with the standard smooth-surfaced carrier particles. They are much less sensitive to lower toner concentrations and much less subject to impaction with toner than the smooth-surfaced carrier particles heretofore conventionally used in standard electrostatographic development processes.
• any toner material of any color can be used with the carrier agglomerates of the present invention.
• Such toner materials are well known and fully disclosed in the literature. See for example U. S. Pat. Nos. 3,502,582; 3,345,294; 3,391,082; 2,753,308; 3,079,342; 2,659,670; 3,326,848; 3,338,991 and 3,272,644.
• the proportion of carrier and tone materials in the developer compositions of the present invention is not as critical as with previously known carrier materials in view of the reduced sensitivity of the instant carrier materials to toner composition.
• the developer composition should contain 0.5 to 2 percent of toner.
• the toner concentration decreases from its original level.
• the density of the reproduced image shows only a slight decrease even after as much as 30 percent of the toner has been depleted.
• EXAMPLE 1 A 14 inch Dravo pelletizer equipped with a onequarter horsepower variable drive motor and three square blades measuring 3 inches X 3 inches X onesixteenth inch arranged in the oclock, 12 oclock and 3 oclock positions was used to pelletize various powdered materials.
• the pelletizing procedure was as follows. The pelletizing disc was set at an angle of 52 and driven at the rate of 53 rpm. The metal powders were fed to the disc at the rate of 15 to pounds per hour. A binder solution was introduced at a specified rate over the disc so that the powder became wetted thereby. After sufficient binder had been introduced, the wetted powder was retained on the moving disc until the desired pelletization had occurred.
• iron and nickel powders were pelletized with sodium silicate; a terpolymer of styrene, n-butyl acrylate and poly(vinyl butyral); and poly(vinyl chloride).
• the sodium silicate was in the form of a 40 Baume solution.
• the terpolymer binder was prepared by diluting a 30 percent solids solution of the terpolymer in toluene with methyl ethyl ketone to a 10 percent solids content.
• the PVC solution consisted of 10 percent solids (3 parts of polyvinyl chloride and 1 part of Luxol fast blue dye) in 9 parts of methyl ethyl ketone and 1 part of methanol.
• the pellets were dried, and in the case of those formed with sodium silicate binder the Pellets were further sintered at high temperature. After drying and sintering the pellets were then classified and their density determined. The properties of the resultant pellets are shown in the following table.
• Example 2 Each of the nodular .carrier materials produced in Example l was used to develop latent electrostatic images on a flat plate xerographic apparatus.
• the nodular carrier material was mixed with a carbon black pigmented toner consisting of a styrene-n-butyl methacrylate copolymer blended with poly(vinyl butyral) in a ratio of 200 parts of carrier to 1 part of toner.
• the resultant developed images were of good quality.
• EXAMPLE 3 developing unit to develop an imaged selenium photoconductor. Copies were made with two passes through the magnetic brush at 22 ips brush speed and 20 ips photoreceptor speed.
• An electrostatographic developer mixture comprising nodular carrier beads each having a generally spherical shape and a surface characterized by a plurality of small generally rounded nodular particles separated by recesses, said beads having an average size distribution in the range of 50 to 1,000 microns, and between about and at least about 99.5 weight percent, based on the weight of the developer mixture, of said carrier beads relative to said finely-divided toner particles electrostatically clinging to said surface of said carrier beads.
• An electrostatographic developer mixture comprising carrier beads and finely divided toner particles electrostatically clinging to the surface of said beads, each said bead comprising an irregular surfaced generally spherical three dimensional solid, the irregular surface characterized by a plurality of raised generally spheroidally shaped nodular particles separated by recesses forming the junctions between adjacent ones of said nodular particles, said recesses providing traps for accumulations of said toner particles, thereby increasing the toner carrying capacity of said bead.
• An electrostatographic developer mixture comprising nodular carrier beads each having a generally spherical shape and a surface characterized by a plurality of small generally rounded nodular particles separated by recesses, said beads having an average size distribution in the range of 50 to 1,000 microns, and at least about 0.5 weight percent, based on the weight of the developer mixture, of finely divided toner particles electrostatically clinging to the surface of the carrier beads.
• An electrostatographic developer mixture comprising nodular carrier beads each having a generally spherical shape and a surface characterized by a plurality of small generally rounded nodular particles, said beads having an average size distribution in the range of 50 to 1,000 microns and between about 0.5 and at least about 2.2 weight percent, based on the weight of the developer mixture, of finely divided toner particles electrostatically clinging to the surface of the carrier beads.

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• Physics & Mathematics (AREA)
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• Spectroscopy & Molecular Physics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Metallurgy (AREA)
• Inorganic Chemistry (AREA)
• Developing Agents For Electrophotography (AREA)

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Citations (8)

• 1971
  • 1971-06-10 US US00151995A patent/US3767578A/en not_active Expired - Lifetime
• 1972
  • 1972-03-30 CA CA138,596A patent/CA986351A/en not_active Expired
  • 1972-04-13 DE DE2217933A patent/DE2217933C3/de not_active Expired
  • 1972-05-16 CH CH724972A patent/CH546969A/de not_active IP Right Cessation
  • 1972-05-16 JP JP4851472A patent/JPS5340092B1/ja active Pending
  • 1972-05-30 AR AR242257A patent/AR198052A1/es active
  • 1972-05-31 AT AT470572A patent/AT322978B/de active
  • 1972-06-06 SE SE7207389A patent/SE377199B/xx unknown
  • 1972-06-06 BE BE784452A patent/BE784452A/xx unknown
  • 1972-06-08 IT IT25403/72A patent/IT959791B/it active
  • 1972-06-08 FR FR7220690A patent/FR2141300A5/fr not_active Expired
  • 1972-06-08 GB GB2675372A patent/GB1397445A/en not_active Expired
  • 1972-06-08 ES ES403664A patent/ES403664A1/es not_active Expired
  • 1972-06-09 AU AU43308/72A patent/AU461667B2/en not_active Expired
  • 1972-06-09 NL NL7207839.A patent/NL160097C/xx not_active IP Right Cessation
  • 1972-06-09 BR BR3718/72A patent/BR7203718D0/pt unknown
  • 1972-06-09 ZA ZA723959A patent/ZA723959B/xx unknown

Patent Citations (8)

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