EP0291392A1 - Pulverulent substance for the lubrification of the recording medium of a magnetic printer - Google Patents

Pulverulent substance for the lubrification of the recording medium of a magnetic printer Download PDF

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Publication number
EP0291392A1
EP0291392A1 EP88401089A EP88401089A EP0291392A1 EP 0291392 A1 EP0291392 A1 EP 0291392A1 EP 88401089 A EP88401089 A EP 88401089A EP 88401089 A EP88401089 A EP 88401089A EP 0291392 A1 EP0291392 A1 EP 0291392A1
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EP
European Patent Office
Prior art keywords
particles
pulverulent
drum
recording medium
filaments
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP88401089A
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German (de)
French (fr)
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EP0291392B1 (en
Inventor
Bernard Cherbuy
Jacques Estavoyer
Daniel Kinet
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Bull SA
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Bull SA
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Publication of EP0291392A1 publication Critical patent/EP0291392A1/en
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Publication of EP0291392B1 publication Critical patent/EP0291392B1/en
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G19/00—Processes using magnetic patterns; Apparatus therefor, i.e. magnetography
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/005—Materials for treating the recording members, e.g. for cleaning, reactivating, polishing

Definitions

  • the present invention relates to a pulverulent substance for the lubrication of the recording medium of a magnetic printer.
  • the latent image thus formed is then developed, that is to say made visible, using a powdery developer which, made up of thermoplastic resin particles containing each of the magnetic particles, is only attracted by the magnetized areas of the recording medium and thus forms a powder image on the surface of this medium. After which, this powder image is transferred to the receiving sheet of paper.
  • a recording device which has a plurality of magnetic heads arranged one next to the other.
  • Each of these heads is formed of a metal core, of high magnetic permeability, on which is wound a winding, this core having, at one of its ends, a magnetic pole, called writing or recording, which is placed in contact with or near the magnetic layer, so that each time an electric current of suitable intensity is sent into this winding, this current creates, in the core, a magnetic flux which has the effect of magnetizing the portion of the magnetic layer located opposite the writing pole of the head.
  • the magnetized points thus formed by the different heads of the transducer must not only be perfectly delimited and all have substantially the same size, but they must also have practically the same magnetization intensity, in order to be able to each retain a quantity of developer particles. which remains practically constant from one point to another. To meet these requirements, it is essential that the distance between each head of the magnetic layer remains constant and less than a predetermined limit value.
  • the magnetized points formed on the magnetized layer each have, on the surface of this layer, a square section of the order of a hundred microns side and are distributed at a density such that the distance separating two neighboring magnetized points is practically equal to thirty microns
  • this limit value has been found equal to ten microns.
  • Adjusting the heads and recording media to keep this distance as constant as possible has It has always been a difficult problem to solve which could only be overcome by using complex and particularly expensive equipment. This is why, in order to avoid using such equipment, it has been practically necessary to bring the heads of the transducer into contact with the magnetic surface of the recording medium. However, bringing the heads into contact with this magnetic surface has the effect of generating, during the movement of the recording medium, overheating all the more important as the driving speed of this medium is higher.
  • These warm-ups are capable of disrupting, or even preventing, the recording of information on the support.
  • they cause the softening of the developer particles which have been deposited on the support, so that these particles cannot be transferred entirely onto the sheet of paper.
  • a resin film is formed on the magnetic layer of the support, the thickness of which increases over time, this film having the effect of constantly increasing the distance between the recording heads and the magnetic layer, and thus make the printing of the characters totally defective.
  • Electrostatic printers are known, for example, which have been described in the Japanese patent application published under No. 56.101177, in which the lubrication of the surface of the electrostatic drum is obtained by applying to this surface a strip of fabric impregnated with particles.
  • polyethylene, polytetrafluoroethylene or paraffin wax solids are known, for example, which have been described in the Japanese patent application published under No. 56.101177, in which the lubrication of the surface of the electrostatic drum is obtained by applying to this surface a strip of fabric impregnated with particles.
  • An electrophotographic reproduction machine which has been described in the Japanese patent application published under No. 57.078578 and in which the lubrication of the photoreceptive electrostatic surface is carried out by depositing on this surface a solid lubricant consisting of particles of polyethylene or of zinc stearate, this deposition being carried out either directly by bringing a strip of fabric containing these particles into contact with this surface, or by incorporating these particles of lubricant into the developer particles intended to be applied to this surface.
  • the present invention overcomes these drawbacks and provides a pulverulent substance which, when applied to the surface of the recording medium of a magnetic printer, provides suitable lubrication of this material. support, without causing an undesirable background on the printed sheet of paper.
  • the present invention relates to a pulverulent lubricating substance capable of being applied to the external surface of a recording medium of a magnetic printer, said substance consisting of particles of a pulverulent insulating material capable of reducing friction between said surface and a recording member applied against this surface, this substance being characterized in that it also contains particles of conductive carbon which are arranged around said insulating particles to form groups of lubricating particles, the mass ratio total of carbon to that of said insulating material being between 0.2 and 1.
  • the printing machine part of which has been shown diagrammatically in FIG. 1, comprises a recording medium which is constituted, in the example described, by a magnetic drum 10.
  • This magnetic drum 10 which is mounted so as to be able to rotate around a horizontal axis 11, is rotated, in the direction indicated by the arrow F, by an electric motor (not shown).
  • the recording of information on this drum is carried out by a magnetic recording member 12 which is kept applied to the external surface 13 of the drum 10 under the action of a spring 14.
  • This recording member 12 is formed, of known manner, of a set of magnetic recording heads which, placed one next to the other, are aligned parallel to the axis of rotation 11 of the drum 10.
  • Each of these heads generates, each time it is excited for a short time by an electric current, a variable magnetic field, which has the effect of creating, on the surface 13 of the drum which passes in front of the recording member 12, magnetized zones 15 practically punctual, the set of these zones constituting a latent magnetic image corresponding to a character to be printed.
  • These magnetized zones 15 then pass in front of a developer applicator device 16 which is arranged below the drum 10 and which makes it possible to apply to the surface 13 of this drum particles of a powdery developer contained in a reservoir 17.
  • This device applicator 16 will not be described here for the reason that it is of a type analogous to that which has been described in the French patent application published under No. 2,408,462.
  • Developer particles that are applied by this device on the surface 13 of the drum adhere, in principle, only to the magnetized areas of this drum, so that these areas, after passing in front of the applicator device 16, appear coated with a layer of developer, thus forming deposits 18 on the surface 13 of the drum.
  • These deposits 18 then pass in front of a retouching device 19 which has the role of eliminating the developer particles which have adhered elsewhere than to the magnetized zones 15, as well as the particles which are found in excess in these zones.
  • the developer particles which, after passing in front of the retouching device 19, remain on the drum are then transferred, almost entirely, onto a sheet of paper 20 which is applied to the surface 13 of the drum by means of a roller pressure 21.
  • the residual developer particles which, when this transfer is carried out, are still on the drum 10 are then removed by means of a felt pad 28 which, applied to the surface of the drum, is part of a cleaning device 22.
  • the magnetized zones which have passed past this cleaning device 22 then pass in front of a lubricating substance applicator device 23 which will be discussed later, then in front of an erasing device 24 which, excited by an alternating electric current, ensures, in a known manner, the erasing of the magnetized zones passing in front of it, the portions of the drum thus demagnetized by this erasing device then being able to be magnetized again when they appear before the registration body 12.
  • the powdery developer which is contained in the reservoir 17 of the printing machine shown in FIG. 1 is made up of magnetic particles coated with a thermoplastic resin which, by heating, is capable of melting and fixing on the sheet of paper 20 on which it was filed. This fusion is normally caused by a heating device (not shown) through which the sheet of paper 20 after passing between the drum 10 and the pressure roller 21.
  • the magnetic drum 10 which equips the printing machine shown in Figure 1 is of known structure.
  • This drum 10, a part of which has been shown diagrammatically in FIGS. 3 and 4, is essentially formed of a conductive cylindrical core 25, made for example of brass or mild steel, coated with a layer 26 of magnetic alloy, also conductive, consisting for example of a nickel-cobalt-phosphorus alloy containing approximately 76 to 82% of cobalt and 1 to 2% of phosphorus, this layer having a thickness of between ten and thirty microns about.
  • An intermediate conductive layer 27, intended to play the role of magnetic shunt and consisting of a metal or a magnetically soft alloy such as mild steel, can optionally be interposed between the cylindrical core 25 and the layer 26 of magnetic alloy.
  • the magnetic drum 10 thus formed is, as shown in Figure 1, electrically connected to earth, for reasons which will be indicated later.
  • the recording device 12 which is part of the printer shown in FIG. 1 will not be described in detail for the reason that its structure is similar to that which has incidentally been described in French patent No. 2,518,770. It will be recalled, however, that the magnetic heads which equip this recording member are positioned so that the ends of the writing poles of these heads are flush with a sliding face of this member.
  • the erasing device 24 is preferably mounted on an elastic device of known type (not shown) which keeps it constantly pressed against the surface 13 of the drum.
  • This lubricating substance consists of particles of an insulating, pulverulent, dry material, of known type, capable of reducing the friction exerted, during the rotation of the drum 10, by the surfaces of the recording member and of the recording device. 'erasures that are in contact with the surface of this drum.
  • This insulating, lubricating, pulverulent, dry material may consist of disulphide molybdenum or with a metal salt of saturated, unsaturated or partially substituted fatty acid.
  • this metal salt can be derived from one of the fatty acids such as caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, l stearic acid, arachidic acid, behenic acid, oenanthylic acid, pelargonic acid, undecylic acid, tridecylic acid, pentadecylic acid, margaric acid, nonadecylic acid, l tricosanic acid, undecylenic acid, oleic acid, linoleic acid, linolenic acid, oleostearic acid, arachidonic acid, petroselinic acid, vaccenic acid, gadoleic acid, l palmitolic acid, ketooleic acid, ricinoleic acid, as well as mixtures of these acids.
  • the fatty acids such as caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,
  • the most suitable metal salts belong to the group comprising barium, calcium, strontium, cadmium, magnesium, zinc, copper, lead, iron, cobalt and nickel stearates, palmitates of calcium, zinc, copper, aluminum, magnesium and cobalt, magnesium, zinc, copper, lead, manganese, iron and cobalt oleates, lead caprylate, lead caproate , calcium, zinc and cobalt linoleates and zinc and cadmium ricinoleates.
  • the insulating, lubricating, dry material can also consist of fine particles of polytetrafluoroethylene.
  • the insulating, lubricating, dry material always has a fine particle size, the size of the particles which constitute this material being in fact of the order of one micron.
  • this pulverulent material is, before being applied to the surface of the drum 10, mixed with very fine particles of conductive carbon, the size of these carbon particles being about a hundred times smaller than that of insulating material particles, that is to say of the order of 0.01 micron.
  • the quantity of pulverulent carbon which is thus added to the insulating, lubricating, pulverulent material is such that the total mass of carbon added remains between 0.2 M and 1 M, M being the mass of lubricating insulating material.
  • the pulverulent lubricating substance which must be applied to the surface of the drum can be obtained, for example, by taking, on the one hand, one hundred grams of pulverulent polytetrafluoroethylene, on the other hand, an amount of powdery conductive carbon between twenty and one hundred grams, and by carefully mixing these two products using a rapid mixer of known type.
  • the pulverulent mixture which is thus obtained consists of groups of particles of the type of those which have been represented and designated by G in FIG. 2, each of these groups being formed, as can be seen in this figure, of a single particle 30 of lubricating insulating material (for example polytetrafluoroethylene) surrounded, on its periphery, of particles 31 of conductive carbon.
  • G lubricating insulating material
  • the particles 30 and 31 have not been shown to scale for obvious reasons of clarity of the drawing.
  • the number of carbon particles 31 which surround the same particle of insulating material 30 depends on the level of carbon contained in the pulverulent lubricating substance, but, if the mixture of lubricating insulating material and of powdery conductive carbon has been carefully produced, this number remains practically constant when moving from one insulating particle to another. It should also be noted, that even in the case where the amount of carbon which is thus added is relatively small, that is to say equal to 0.2 times the mass of the lubricating insulating material, the number of carbon particles 31 which surround the same insulating particle 30 is high enough for these carbon particles, which are regularly distributed over the external surface of this insulating particle, to cover the whole of this surface.
  • the pulverulent lubricating substance which is formed from groups of particles G, the constitution of which has just been indicated in detail above, is regularly distributed over the external surface 13 of the magnetic drum 10 by means of an applicator device 23 which is produced so as to deposit, on this surface, a quantity of lubricating substance which remains between 0.02 and 0.08 milligrams per square meter of surface.
  • this applicator device comprises a reservoir 35 containing the pulverulent lubricating substance.
  • This tank 35 which is shown in Figure 3, in section along a plane perpendicular to the axis of rotation 11 of the drum 10, is placed, as can be seen in Figure 1, above this drum, between the cleaning device 22 and the erasing device 24.
  • This reservoir 35 is formed by two plates 36 and 37, one of which 36, of rectangular shape, is disposed approximately vertically, perpendicular to the cutting plane and so that its lower edge 38 is at a distance of five to ten millimeters from the surface 13 of the drum 10, and the other 37 of which, arranged perpendicular to the cutting plane, is inclined relative to the plate 36, these two plates being joined to each other by two transverse plates, only one of which is visible in FIG. 3, these four plates forming a non-deformable housing, having practically the shape of a prism whose edge is turned downwards .
  • the plate 37 is adjusted so that, on the one hand, the distance which separates its lower edge 40 from the surface 13 of the drum is substantially the same as that which separates this surface from the lower edge 38 of the plate 36 , and that, on the other hand, the spacing between these two lower edges 38 and 40 is at most equal to five millimeters.
  • the reservoir 35 has, at its lower part, a rectangular opening 41 which, located at a short distance from the surface 13 of the drum, extends over a length equal to the length of this drum, the width of this opening being very small compared to its length.
  • the applicator device which is shown in FIG. 3 further comprises a plurality of very flexible filaments 42 which each have one of their ends embedded inside a mass 43 of hardened resin, itself clamped in a stirrup 44 fixed inside the tank 35.
  • These filaments 42 have a length such that they pass through the opening 41 of the tank 35 and come, by their other end, to contact the surface 13 of the drum 10.
  • These filaments which have a diameter of about 0.1 millimeter, are made of a very flexible natural or synthetic material, which allows them, when suspended by one of their ends, to remain approximately in the vertical position or to return to it when, after being removed from this position, they are then released.
  • these filaments can be formed from animal fibers, of the horsehair type for example, carbon fibers, or even from a flexible threadlike plastic material, such as the polyamide material which is sold under the name of " nylon "(registered trademark).
  • the number N of these filaments 42 is such that the latter almost completely obstruct the opening 41 of the reservoir 35. More precisely, if we designate by ⁇ the surface of the cross section formed by this opening in the absence of filaments and by S the total cross-sectional area of these N filaments (the value of S being thus given by the expression: where d represents the diameter of each filament), the number N is such that the ratio S / ⁇ is between 0.35 and 0.8. It follows that the number N of filaments 42 which partially obstruct the opening 41 of the reservoir 35 is between two limit values N m and N M given, respectively, by the expressions:
  • the quantity of lubricating substance which is thus deposited, per unit of surface, on the surface 13 of this drum depends on the number N of filaments 42 which partially obstruct the opening 41 of the reservoir, this quantity being all the greater the lower the number N of these filaments. It was thus found that, in the case where the number of these filaments was equal to the limit value N m indicated above, the quantity of lubricating substance which was deposited, per square meter, on the surface of the drum was practically equal to 0 0.05 mg, whereas, in the case where the number of these filaments was equal to the limit value N M indicated above, the quantity of lubricating substance deposited, per square meter, on the drum was practically equal to 0.02 mg .
  • the device for applying the lubricating substance which has just been described is placed between the cleaning device 22 and the erasing device 24, that is to say say upstream of this erasing device, the particles which are thus deposited by this applicator device on the surface 13 of the drum allow this surface to be lubricated just before it passes under this erasing device 24 and under the recording device 12.
  • the lubricant applicator device comprises a chamber 59, which is situated above the surface 13 of the drum, and the lower partition of which is constituted by a small portion 61 of this surface 13, this portion being in the form of a strip comprised between two generatrices of the drum.
  • this surface portion 61 extends between a retaining element 128 which is placed in contact with the surface 13 and a squeegee 57 of which an edge 58 is applied to this surface 13, this retaining element 128 and this squeegee 57 being disposed, respectively, upstream and downstream of the surface portion 61, with respect to the direction of movement F of the surface 13 of the drum.
  • FIG. 4 also shows that the shell 51 is provided with a clearance 54 for the passage of an actuating lever 55 integral with the cartridge 50, this lever 55 being able to be moved by the operator between two limit positions, the first of which is shown in dashed lines in FIG. 4 and the second of which is shown in solid lines in this same figure.
  • the cylindrical wall of the cartridge 50 is pierced with an opening 56 which extends in a direction parallel to the pivot axis 52 of the cartridge and which is produced so that, when the actuating lever 55 is placed in its first position, this opening 56 is closed by the wall of the housing of the shell in which is this cartridge, while when the lever 55 is placed in its second position, this opening 56 arrives opposite the recess 53 of the shell 51 and allows the particles of lubricating substance contained in the cartridge 50 to exit the latter and thus fall into the chamber 59. These particles then form, in this chamber, a small reserve of particles which is constantly in contact with the surface portion 61 which was mentioned above.
  • the chamber 59 which extends essentially in a direction parallel to the axis of rotation of the drum, is closed at its two ends, by two side plates which have not been shown in the drawings for reasons of simplification.
  • an elastic bead 60 fixed near the edge 58 of the squeegee 57 and interposed between this squeegee and the cartridge 50, guarantees practically complete sealing of the chamber 59. Under these conditions, the particles which are accumulated in the chamber 59 theoretically can't get out of this room.
  • the amount of lubricant which is deposited per unit area on the drum 10 depends on the force with which this squeegee is applied to this drum. More precisely, it has been found that, when the force P exerted, per unit of length, on the edge 58 of the squeegee in contact with the drum had a value of 12.5 N / dm, the quantity of lubricant deposited by unit area was approximately 0.06 mg / m2. Likewise, when this force P had a value of 7.5 N / dm, the quantity of lubricant which was deposited per unit of area was substantially equal to 0.07 mg / m2.
  • this flexible blade can be a polyethylene terephthalate blade, the latter material, usually referred to as "Mylar” (registered trademark), having a module of elasticity practically equal to 480 dN / mm2, the free part of this blade having a width a practically equal to 8 mm and a thickness e practically equal to 0.2 mm.
  • Mylar registered trademark
  • the force P which is exerted, per unit of length, on the edge 58 of this blade, when the latter is subjected to a bending f equal to half the width a of the blade, that is to say here at 4 mm then has the value:
  • the quantity of lubricating substance deposited, per unit of area, on the drum 10 is substantially equal to 0.07 mg / m2.
  • the flexible blade can also be a stainless steel blade, having a modulus of elasticity practically equal to 25,000 dN / mm2, the free part of this blade having a width a practically equal to 8 mm and a thickness e practically equal to 0, 05 mm.
  • the quantity of lubricating substance deposited, per unit of area, on the drum 10 is substantially equal to 0.073 mg / m2.
  • the retaining element 128 which equips the device for applying the lubricating substance that has just been described is in the form of a pad made of a very flexible material such as, for example, foam rubber or a textile material.
  • the cleaning device 22 is arranged in the immediate vicinity of the lubricant applicator device, upstream thereof, and the felt pad which equips this device cleaning device is positioned so that it then acts, for this applicator device, as a retaining element 128.
  • the lubricating substance which is produced according to the invention is deposited on the surface of the drum 10 so that the quantity of substance deposited per square meter of surface remains between 0.02 mg and 0.08 mg. It was found, under these conditions, that the surface of the drum was properly lubricated and that, even in the case where the speed of movement of this surface reached 1.5 m / s, the heating caused by the friction of the organ d The recording and erasing on this surface were negligible.
  • the magnetic drum is electrically connected to earth and each of the particles of lubricating substance is coated, over its entire external surface, with a layer of conductive carbon, the electric charges that these particles could acquire as a result of friction, during their passage under the erasing device or the recording member by example, are systematically eliminated. Therefore, these lubricating particles, which are uniformly distributed over the surface of the drum, do not risk electrostatically attracting the developer particles when they pass in front of the developer applicator device 16, thus avoiding the formation, on the sheet of paper 20, of a background detrimental to good print quality.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)
  • Cleaning In Electrography (AREA)
  • Photographic Developing Apparatuses (AREA)

Abstract

1. L'invention concerne une substance pulvérulente pour la lubrification du support d'enregistrement d'une imprimante magnétique.2. Cette substance solide se présente sous la forme d'une poudre constituée de groupes (G) de particules, chacun de ces groupes étant formé d'une particule (30) de matière isolante lubrifiante entourée, sur sa périphérie, de particules (31) de carbone conducteur, le nombre de ces dernières particules étant suffisant pour recouvrir la totalité de la surface externe de cette particule de matière isolante lubrifiante.3. Application à la magnétographie.1. The invention relates to a powdery substance for lubricating the recording medium of a magnetic printer.2. This solid substance is in the form of a powder consisting of groups (G) of particles, each of these groups being formed of a particle (30) of lubricating insulating material surrounded, on its periphery, by particles (31) of conductive carbon, the number of these latter particles being sufficient to cover the entire external surface of this particle of insulating material lubricant.3. Application to magnetography.

Description

La présente invention concerne une substance pulvérulente pour la lubrification du support d'enregistrement d'une imprimante magnétique.The present invention relates to a pulverulent substance for the lubrication of the recording medium of a magnetic printer.

Dans les équipements modernes de traitement de l'information, on utilise de plus en plus des imprimantes rapides dans lesquelles l'impression des caractères est réalisée sans pour cela faire appel à l'impact de types d'impression en relief sur une feuille de papier réceptrice. On connaît déjà des imprimantes de ce genre, de type magnétographique, qui sont analogues à celle qui a été décrite et représentée dans le brevet français n° 2.305.764, et dans lesquelles l'impression des caractères est effectué en formant d'abord, à partir de signaux reçus provenant d'une unité de commande, une image latente magnétique sur la surface d'un support d'enregistrement magnétique ayant généralement la forme d'un tambour rotatif ou d'une courroie sans fin. D'une manière connue, cette image latente est constituée d'un ensemble de zones magnétisées de très petites dimensions, ces zones, pratiquement ponctuelles, étant habituellement désignées sous le nom de points magnétisés.In modern information processing equipment, fast printers are used more and more in which the printing of the characters is carried out without for this calling upon the impact of types of relief printing on a sheet of paper. receptor. Printers of this type are already known, of the magnetographic type, which are analogous to that which has been described and represented in French patent No. 2,305,764, and in which the printing of the characters is carried out by first forming, from signals received from a control unit, a magnetic latent image on the surface of a magnetic recording medium generally in the form of a rotating drum or an endless belt. In a known manner, this latent image consists of a set of magnetized zones of very small dimensions, these zones, practically punctual, being usually designated by the name of magnetized points.

L'image latente ainsi formée est ensuite développée, c'est-à-dire rendue visible, à l'aide d'un révélateur pulvérulent qui, constitué de particules de résine thermoplastique renfermant chacune des particules magnétiques, n'est attiré que par les zones magnétisées du support d'enregistrement et forme ainsi une image de poudre à la surface de ce support. Après quoi, cette image de poudre est transférée sur la feuille de papier réceptrice.The latent image thus formed is then developed, that is to say made visible, using a powdery developer which, made up of thermoplastic resin particles containing each of the magnetic particles, is only attracted by the magnetized areas of the recording medium and thus forms a powder image on the surface of this medium. After which, this powder image is transferred to the receiving sheet of paper.

Afin d'obtenir, sur la feuille de papier, des caractères imprimés présentant une haute qualité d'impression, il est nécessaire d'enregistrer, sur la couche magnétique du support d'enregistrement, des images latentes magnétiques dont les différents points constitutifs sont très petits et très proches les uns des autres. Pour enregistrer ces images latentes, on utilise un organe d'enregistrement, appelé transducteur, qui comporte une pluralité de têtes magnétiques disposées les unes à côté des autres. Chacune de ces têtes est formée d'un noyau métallique, de haute perméabilité magnétique, sur lequel est bobiné un enroulement, ce noyau présentant, à l'une de ses extrémités, un pôle magnétique, dit d'écriture ou d'enregistrement, qui est placé au contact ou à proximité de la couche magnétique, de sorte que, chaque fois qu'un courant électrique d'intensité convenable est envoyé dans cet enroulement, ce courant crée, dans le noyau, un flux magnétique qui a pour effet de magnétiser la portion de la couche magnétique située en regard du pôle d'écriture de la tête.In order to obtain printed characters having a high print quality on the sheet of paper, it is necessary to record, on the magnetic layer of the recording medium, magnetic latent images whose different constituent points are very small and very close to each other. To record these latent images, a recording device, called a transducer, is used, which has a plurality of magnetic heads arranged one next to the other. Each of these heads is formed of a metal core, of high magnetic permeability, on which is wound a winding, this core having, at one of its ends, a magnetic pole, called writing or recording, which is placed in contact with or near the magnetic layer, so that each time an electric current of suitable intensity is sent into this winding, this current creates, in the core, a magnetic flux which has the effect of magnetizing the portion of the magnetic layer located opposite the writing pole of the head.

Les points magnétisés ainsi formés par les différentes têtes du transducteur doivent, non seulement être parfaitement délimités et avoir tous sensiblement la même taille, mais ils doivent également présenter pratiquement la même intensité d'aimantation, afin de pouvoir retenir chacun une quantité de particules de révélateur qui reste pratiquement constante d'un point à un autre. Pour satisfaire à ces exigences, il est indispensable que la distance qui sépare chaque tête de la couche magnétique reste constante et inférieure à une valeur limite prédéterminée.The magnetized points thus formed by the different heads of the transducer must not only be perfectly delimited and all have substantially the same size, but they must also have practically the same magnetization intensity, in order to be able to each retain a quantity of developer particles. which remains practically constant from one point to another. To meet these requirements, it is essential that the distance between each head of the magnetic layer remains constant and less than a predetermined limit value.

C'est ainsi, par exemple, que, dans le cas où les points magnétisés formés sur la couche magnétisée présentent chacun, sur la surface de cette couche, une section carrée de l'ordre d'une centaine de microns de côté et sont répartis à une densité telle que la distance séparant deux points magnétisés voisins est pratiquement égale à trente microns, cette valeur limite a été trouvée égale à une dizaine de microns. L'ajustement des têtes et du support d'enregistrement pour maintenir cette distance aussi constante que possible a toujours été un problème difficile à résoudre qui n'a pu être surmonté qu'en faisant appel à des équipements complexes et particulièrement coûteux. C'est pourquoi, pour éviter d'avoir recours à de tels équipements, on a été pratiquement conduit à mettre les têtes du transducteur en contact avec la surface magnétique de support d'enregistrement. Cependant, la mise en contact des têtes avec cette surface magnétique a pour effet d'engendrer, lors du déplacement du support d'enregistrement, des échauffements d'autant plus importants que la vitesse d'entraînement de ce support est plus élevée.Thus, for example, in the case where the magnetized points formed on the magnetized layer each have, on the surface of this layer, a square section of the order of a hundred microns side and are distributed at a density such that the distance separating two neighboring magnetized points is practically equal to thirty microns, this limit value has been found equal to ten microns. Adjusting the heads and recording media to keep this distance as constant as possible has It has always been a difficult problem to solve which could only be overcome by using complex and particularly expensive equipment. This is why, in order to avoid using such equipment, it has been practically necessary to bring the heads of the transducer into contact with the magnetic surface of the recording medium. However, bringing the heads into contact with this magnetic surface has the effect of generating, during the movement of the recording medium, overheating all the more important as the driving speed of this medium is higher.

Ces échauffements sont capables de perturber,voire d'empêcher, l'enregistrement des informations sur le support. En outre, il provoquent le ramollissement des particules de révélateur qui ont été déposées sur le support, de sorte que ces particules ne peuvent être transférées en totalité sur la feuille de papier. A la longue, il se forme, sur la couche magnétique du support, un film de résine dont l'épaisseur s'accroît avec le temps, ce film ayant alors pour effet d'augmenter constamment la distance entre les têtes d'enrigistrement et la couche magnétique, et de rendre ainsi l'impression des caractères totalement défectueuse.These warm-ups are capable of disrupting, or even preventing, the recording of information on the support. In addition, they cause the softening of the developer particles which have been deposited on the support, so that these particles cannot be transferred entirely onto the sheet of paper. In the long term, a resin film is formed on the magnetic layer of the support, the thickness of which increases over time, this film having the effect of constantly increasing the distance between the recording heads and the magnetic layer, and thus make the printing of the characters totally defective.

Afin de diminuer les frottements des têtes sur le support d'enregistrement et de réduire ainsi notablement les échauffements engendrés par ces frottements, on peut songer à déposer sur la couche magnétique du support d'enregistrement des particules solides de substance lubrifiante du type de celles qui ont déjà été utilisées dans l'art antérieur pour assurer la lubrification de la surface d'enregistrement de machines imprimantes électrostatiques. On connaît, par exemple, des imprimantes électrostatiques qui ont été décrites dans la demande de brevet japonaise publiée sous le N° 56.101177, dans lesquelles la lubrification de la surface du tambour électrostatique est obtenue en appliquant sur cette surface une bande de tissu imprégnée de particules solides de polyéthylène, de polytétrafluoréthylène ou de cire de paraffine.In order to reduce the friction of the heads on the recording medium and thus significantly reduce the heating generated by this friction, one can consider depositing on the magnetic layer of the recording medium solid particles of lubricating substance of the type which have already been used in the prior art to provide lubrication of the recording surface of electrostatic printing machines. Electrostatic printers are known, for example, which have been described in the Japanese patent application published under No. 56.101177, in which the lubrication of the surface of the electrostatic drum is obtained by applying to this surface a strip of fabric impregnated with particles. polyethylene, polytetrafluoroethylene or paraffin wax solids.

On connaît également une machine de reproduction électrophotographique qui a été décrite dans la demande de brevet japonaise publiée sous le N° 57.078578 et dans laquelle la lubrification de la surface électrostatique photoréceptive est réalisée en déposant sur cette surface un lubrifiant solide constitué de particules de polyéthylène ou de stéarate de zinc, ce dépôt étant effectué, soit directement en amenant au contact de cette surface une bande de tissu contenant ces particules, soit en incorporant ces particules de lubrifiant aux particules de révélateur destinées à être appliquées sur cette surface.An electrophotographic reproduction machine is also known which has been described in the Japanese patent application published under No. 57.078578 and in which the lubrication of the photoreceptive electrostatic surface is carried out by depositing on this surface a solid lubricant consisting of particles of polyethylene or of zinc stearate, this deposition being carried out either directly by bringing a strip of fabric containing these particles into contact with this surface, or by incorporating these particles of lubricant into the developer particles intended to be applied to this surface.

On a cependant observé que, en déposant sur la couche magnétique du support d'enregistrement d'une imprimante magnétique, des particules de substances lubrifiantes déjà employées pour la lubrification du support d'enregistrement d'une imprimante électrostatique, ces particules lubrifiantes,par suite du frottement qu'elles subissaient lors de leur passage sous le transducteur, se chargeaient d'électricité statique et qu'elles étaient alors capables, lors de leur passage devant le dispositif applicateur de révélateur, d'attirer les particules résineuses de révélateur contenues dans ce dispositif. De ce fait, les particules de révélateur qui étaient ainsi attirées par les particules lubrifiantes formaient, lorsqu'elles étaient ensuite transférées sur la feuille de papier, un fond indésirable qui réduisait fortement le contraste entre l'image que l'on voulait imprimer et le fond original du papier.However, it has been observed that, by depositing on the magnetic layer of the recording medium of a magnetic printer, particles of lubricating substances already used for the lubrication of the recording medium of an electrostatic printer, these lubricating particles, consequently of the friction which they underwent during their passage under the transducer, were charged with static electricity and that they were then capable, during their passage in front of the developer applicator device, of attracting the resinous particles of developer contained in this device. As a result, the developer particles which were thus attracted to the lubricating particles formed, when they were then transferred to the sheet of paper, an undesirable background which greatly reduced the contrast between the image which one wanted to print and the original background of the paper.

La présente invention remédie à ces inconvénients et propose une substance pulvérulente qui, lorsqu'elle est appliquée sur la surface du support d'enregistrement d'une imprimante magnétique, assure une lubrification convenable de ce support, sans pour cela provoquer un fond indésirable sur la feuille de papier imprimée.The present invention overcomes these drawbacks and provides a pulverulent substance which, when applied to the surface of the recording medium of a magnetic printer, provides suitable lubrication of this material. support, without causing an undesirable background on the printed sheet of paper.

Plus précisément, la présente invention concerne une substance lubrifiante pulvérulente apte à être appliquée sur la surface externe d'un support d'enregistrement d'une imprimante magnétique, ladite substance étant constituée de particules d'une matière isolante pulvérulente capable de réduire les frottements entre ladite surface et un organe d'enregistrement appliqué contre cette surface, cette substance étant caractérisée en ce qu'elle contient en outre des particules de carbone conducteur qui sont disposées autour desdites particules isolantes pour former des groupes de particules lubrifiantes, le rapport de la masse totale de carbone à celle de ladite matière isolante étant compris entre 0,2 et 1.More specifically, the present invention relates to a pulverulent lubricating substance capable of being applied to the external surface of a recording medium of a magnetic printer, said substance consisting of particles of a pulverulent insulating material capable of reducing friction between said surface and a recording member applied against this surface, this substance being characterized in that it also contains particles of conductive carbon which are arranged around said insulating particles to form groups of lubricating particles, the mass ratio total of carbon to that of said insulating material being between 0.2 and 1.

La présente invention sera mieux comprise et d'autres buts, détails et avantages de celle-ci apparaîtront mieux dans la description suivante, donnée à titre d'exemple non limitatif et en se référant aux dessins annexés sur lesquels :

  • . La figure 1 représente une machine imprimante magnétique équipée d'un dispositif permettant de déposer sur le support d'enregistrement magnétique la substance lubrifiante pulvérulente réalisée selon l'invention,
  • . La figure 2 représente des groupes de particules lubrifiantes constituant la substance lubrifiante pulvérulente de l'invention,
  • . la figure 3 est une vue en coupe montrant la constitution d'un dispositif applicateur qui, monté sur une imprimante magnétique, permet de déposer, de façon régulière, sur le support d'enregistrement de cette imprimante, la substance lubrifiante pulvérulente de l'invention, et,
  • . La figure 4 est une vue en coupe montrant la constitution d'un autre dispositif applicateur permettant de déposer, de façon régulière, sur le support d'enregistrement d'une imprimante magnétique, la substance lubrifiante pulvérulente de l'invention.
The present invention will be better understood and other objects, details and advantages thereof will appear better in the following description, given by way of nonlimiting example and with reference to the appended drawings in which:
  • . FIG. 1 represents a magnetic printing machine equipped with a device making it possible to deposit on the magnetic recording medium the pulverulent lubricating substance produced according to the invention,
  • . FIG. 2 represents groups of lubricating particles constituting the pulverulent lubricating substance of the invention,
  • . FIG. 3 is a sectional view showing the constitution of an applicator device which, mounted on a magnetic printer, makes it possible to deposit, regularly, on the recording medium of this printer, the pulverulent lubricating substance of the invention , and,
  • . Figure 4 is a sectional view showing the constitution of another applicator device for depositing, on a regular basis, on the recording medium of a magnetic printer, the pulverulent lubricant of the invention.

La machine imprimante dont une partie a été schématiquement représentée sur la figure 1 comprend un support d'enregistrement qui est constitué, dans l'exemple décrit, par un tambour magnétique 10. Ce tambour magnétique 10, qui est monté de manière à pouvoir tourner autour d'un axe horizontal 11, est entraîné en rotation, dans le sens indiqué par la flèche F, par un moteur électrique (non représenté). L'enregistrement des informations sur ce tambour est réalisé par un organe d'enregistrement magnétique 12 qui est maintenu appliqué sur la surface externe 13 du tambour 10 sous l'action d'un ressort 14. Cet organe d'enregistrement 12 est formé, de manière connue, d'un ensemble de têtes d'enregistrement magnétique qui, placées les unes à côté des autres, sont alignées parallèlement à l'axe de rotation 11 du tambour 10. Chacune de ces têtes engendre, chaque fois qu'elle est excitée pendant un court instant par un courant électrique, un champ magnétique variable, ce qui a pour effet de créer, sur la surface 13 du tambour qui défile devant l'organe d'enregistrement 12, des zones magnétisées 15 pratiquement ponctuelles, l'ensemble de ces zones constituant une image latente magnétique correspondant à un caractère à imprimer. Ces zones magnétisées 15 passent ensuite devant un dispositif applicateur de révélateur 16 qui est disposé au-­dessous du tambour 10 et qui permet d'appliquer sur la surface 13 de ce tambour des particules d'un révélateur pulvérulent contenu dans un réservoir 17. Ce dispositif appplicateur 16 ne sera pas décrit ici pour la raison qu'il est de type analogue à celui qui a été décrit dans la demande de brevet français publiée sous le N° 2.408.462. Les particules de révélateur qui sont appliquées par ce dispositif sur la surface 13 du tambour n'adhèrent, en principe, que sur les zones magnétisées de ce tambour, de sorte que ces zones, après être passées devant le dispositif applicateur 16, apparaissent revêtues d'une couche de révélateur, formant ainsi des dépôts 18 sur la surface 13 du tambour. Ces dépôts 18 passent alors devant un dispositif de retouche 19 qui a pour rôle d'éliminer les particules de révélateur qui ont adhéré ailleurs que sur les zones magnétisées 15, ainsi que les particules qui se trouvent en surnombre sur ces zones. les particules de révélateur qui, après être passées devant le dispositif de retouche 19, subsistent sur le tambour, sont ensuite transférées, en quasi totalité, sur une feuille de papier 20 qui est appliquée sur la surface 13 du tambour au moyen d'un rouleau de pression 21. Les particules résiduelles de révélateur qui, lorsque ce transfert est réalisé, se trouvent encore sur le tambour 10 sont alors enlevées au moyen d'un patin de feutre 28 qui, appliqué sur la surface du tambour, fait partie d'un dispositif de nettoyage 22. Les zones magnétisées qui ont défilé devant ce dispositif de nettoyage 22 passent ensuite devant un dispositif applicateur de substance lubrifiante 23 dont on parlera plus loin, puis devant un dispositif d'effacement 24 qui, excité par un courant électrique alternatif, assure, de manière connue, l'effacement des zones magnétisées passant devant lui, les portions du tambour ainsi démagnétisées par ce dispositif d'effacement pouvant alors être à nouveau magnétisées lorsqu'elles se représentent devant l'organe d'enregistrement 12.The printing machine, part of which has been shown diagrammatically in FIG. 1, comprises a recording medium which is constituted, in the example described, by a magnetic drum 10. This magnetic drum 10, which is mounted so as to be able to rotate around a horizontal axis 11, is rotated, in the direction indicated by the arrow F, by an electric motor (not shown). The recording of information on this drum is carried out by a magnetic recording member 12 which is kept applied to the external surface 13 of the drum 10 under the action of a spring 14. This recording member 12 is formed, of known manner, of a set of magnetic recording heads which, placed one next to the other, are aligned parallel to the axis of rotation 11 of the drum 10. Each of these heads generates, each time it is excited for a short time by an electric current, a variable magnetic field, which has the effect of creating, on the surface 13 of the drum which passes in front of the recording member 12, magnetized zones 15 practically punctual, the set of these zones constituting a latent magnetic image corresponding to a character to be printed. These magnetized zones 15 then pass in front of a developer applicator device 16 which is arranged below the drum 10 and which makes it possible to apply to the surface 13 of this drum particles of a powdery developer contained in a reservoir 17. This device applicator 16 will not be described here for the reason that it is of a type analogous to that which has been described in the French patent application published under No. 2,408,462. Developer particles that are applied by this device on the surface 13 of the drum adhere, in principle, only to the magnetized areas of this drum, so that these areas, after passing in front of the applicator device 16, appear coated with a layer of developer, thus forming deposits 18 on the surface 13 of the drum. These deposits 18 then pass in front of a retouching device 19 which has the role of eliminating the developer particles which have adhered elsewhere than to the magnetized zones 15, as well as the particles which are found in excess in these zones. the developer particles which, after passing in front of the retouching device 19, remain on the drum, are then transferred, almost entirely, onto a sheet of paper 20 which is applied to the surface 13 of the drum by means of a roller pressure 21. The residual developer particles which, when this transfer is carried out, are still on the drum 10 are then removed by means of a felt pad 28 which, applied to the surface of the drum, is part of a cleaning device 22. The magnetized zones which have passed past this cleaning device 22 then pass in front of a lubricating substance applicator device 23 which will be discussed later, then in front of an erasing device 24 which, excited by an alternating electric current, ensures, in a known manner, the erasing of the magnetized zones passing in front of it, the portions of the drum thus demagnetized by this erasing device then being able to be magnetized again when they appear before the registration body 12.

Le révélateur pulvérulent qui est contenu dans le réservoir 17 de la machine imprimante représentée sur la figure 1 est constitué de particules magnétiques enduites d'une résine thermoplastique qui, par chauffage, est capable de fondre et de se fixer sur la feuille de papier 20 sur laquelle elle a été déposée. Cette fusion est normalement provoquée par un dispositif de chauffage (non représenté) que traverse la feuille de papier 20 après son passage entre le tambour 10 et le rouleau de pression 21.The powdery developer which is contained in the reservoir 17 of the printing machine shown in FIG. 1 is made up of magnetic particles coated with a thermoplastic resin which, by heating, is capable of melting and fixing on the sheet of paper 20 on which it was filed. This fusion is normally caused by a heating device (not shown) through which the sheet of paper 20 after passing between the drum 10 and the pressure roller 21.

Le tambour magnétique 10 qui équipe la machine imprimante représentée sur la figure 1 est de structure connue. Ce tambour 10, dont une partie a été schématiquement représentée sur les figures 3 et 4, est formé, pour l'essentiel, d'une âme cylindrique conductrice 25, constituée par exemple de laiton ou d'acier doux, revêtue d'une couche 26 d'alliage magnétique, également conductrice, constituée par exemple d'un alliage nickel-cobalt-phosphore contenant environ de 76 à 82 % de cobalt et de 1 à 2 % de phosphore, cette couche ayant une épaisseur comprise entre dix et trente microns environ. Une couche conductrice intermédiaire 27, destinée à jouer le rôle de shunt magnétique et constituée d'un métal ou d'un alliage magnétiquement doux tel que l'acier doux, peut, éventuellement, être interposé entre l'âme cylindrique 25 et la couche 26 d'alliage magnétique. Le tambour magnétique 10 ainsi constitué est, comme le montre la figure 1, relié électriquement à la terre, pour des raisons qui seront indiquées plus loin.The magnetic drum 10 which equips the printing machine shown in Figure 1 is of known structure. This drum 10, a part of which has been shown diagrammatically in FIGS. 3 and 4, is essentially formed of a conductive cylindrical core 25, made for example of brass or mild steel, coated with a layer 26 of magnetic alloy, also conductive, consisting for example of a nickel-cobalt-phosphorus alloy containing approximately 76 to 82% of cobalt and 1 to 2% of phosphorus, this layer having a thickness of between ten and thirty microns about. An intermediate conductive layer 27, intended to play the role of magnetic shunt and consisting of a metal or a magnetically soft alloy such as mild steel, can optionally be interposed between the cylindrical core 25 and the layer 26 of magnetic alloy. The magnetic drum 10 thus formed is, as shown in Figure 1, electrically connected to earth, for reasons which will be indicated later.

L'organe d'enregistrement 12 qui fait partie de l'imprimante représentée sur la figure 1 ne sera pas décrit en détail pour la raison que sa structure est analogue à celle qui a été accessoirement décrite dans le brevet français N° 2.518.770. On rappellera cependant que les têtes magnétiques qui équipent cet organe d'enregistrement sont positionnées de telle sorte que les extrémités des pôles d'écriture de ces têtes viennent affleurer une face de glissement de cet organe.The recording device 12 which is part of the printer shown in FIG. 1 will not be described in detail for the reason that its structure is similar to that which has incidentally been described in French patent No. 2,518,770. It will be recalled, however, that the magnetic heads which equip this recording member are positioned so that the ends of the writing poles of these heads are flush with a sliding face of this member.

En outre, afin d'obtenir, sur la couche magnétique du tambour 10, des images latentes magnétiques capable de reproduire, sur la feuille de papier 20, des caractères imprimés de haute définition et parfaitement nets, cette face de glissement est appliquée en permanence contre la surface 13 du tambour 10, sous l'action exercée par le ressort 14. Par ailleurs, afin de permettre aux images latentes magnétiques formées par cet organe d'enregistrement d'être correctement effacées, le dispositif d'effacement 24 est, préférentiellement, monté sur un dispositif élastique de type connu (non représenté) qui le maintient constamment appuyé contre la surface 13 du tambour. Bien que les surfaces de l'organe d'enregistrement et du dispositif d'effacement qui se trouvent ainsi en contact permanent avec le tambour 10 soient relativement réduites, on comprend alors que les frottements exercés par ces surfaces lors de la rotation du tambour sont à l'origine d'échauffements qui sont d'autant plus importants que le coefficient de frottement des surfaces ainsi mises en contact est plus élevé et que la vitesse de rotation du tambour est plus grande. Si la surface 13 du tambour n'était pas correctement lubrifiée, ces échauffements pourraient atteindre une valeur telle que, non seulement l'enregistrement des images latentes sur le tambour se trouverait fortement perturbé, mais les particules de révélateur qui sont déposées sur la surface du tambour subiraient un ramollissement tel qu'elles colleraient sur cette surface et formeraient sur celle-ci une tenace pellicule d'enduit qui, très difficile à retirer, conduirait à l'arrêt immédiat du travail en cours.In addition, in order to obtain, on the magnetic layer of the drum 10, magnetic latent images capable of reproducing, on the sheet of paper 20, printed characters of high definition and perfectly sharp, this sliding face is permanently applied against the surface 13 of the drum 10, under the action exerted by the spring 14. Furthermore, in order to allow the latent magnetic images formed by this recording member to be correctly erased, the erasing device 24 is preferably mounted on an elastic device of known type (not shown) which keeps it constantly pressed against the surface 13 of the drum. Although the surfaces of the recording member and of the erasing device which are thus in permanent contact with the drum 10 are relatively reduced, it will then be understood that the friction exerted by these surfaces during the rotation of the drum is at the origin of overheating which is all the more important as the coefficient of friction of the surfaces thus brought into contact is higher and the speed of rotation of the drum is greater. If the surface 13 of the drum was not properly lubricated, this heating could reach a value such that not only the recording of the latent images on the drum would be greatly disturbed, but the particles of developer which are deposited on the surface of the drum. drum would soften such that they would stick to this surface and form on it a tenacious film of coating which, very difficult to remove, would lead to the immediate cessation of work in progress.

Grâce au dépôt, sur la surface 13 du tambour, d'une substance lubrifiante contenue dans le dispositif applicateur 23, ces inconvénients se trouvent éliminés. Cette substance lubrifiante est constituée de particules d'une matière isolante, pulvérulente, sèche, de type connu, capable de réduire les frottements exercés, lors de la rotation du tambour 10, par les surfaces de l'organe d'enregistrement et du dispositif d'effacement qui sont en contact avec la surface de ce tambour. Cette matière isolante, lubrifiante, pulvérulente, sèche, peut être constituée par du bisulfure de molybdène ou par un sel métallique d'acide gras saturé, non saturé ou partiellement substitué. C'est ainsi que ce sel métallique peut dériver de l'un des acides gras tels que l'acide caproïque, l'acide caprylique, l'acide caprique, l'acide laurique, l'acide myristique, l'acide palmitique, l'acide stéarique, l'acide arachidique, l'acide béhénique, l'acide oenanthylique, l'acide pélargonique, l'acide undécylique, l'acide tridécylique, l'acide pentadécylique, l'acide margarique, l'acide nonadécylique, l'acide tricosanique, l'acide undécylénique, l'acide oléique, l'acide linoléique, l'acide linolénique, l'acide oléostéarique, l'acide arachidonique, l'acide pétrosélinique, l'acide vaccénique, l'acide gadoléique, l'acide palmitolique, l'acide cétooléique, l'acide ricinoléique, ainsi que des mélanges de ces acides. Les sels métalliques qui conviennent le mieux font partie du groupe comprenant les stéarates de baryum, de calcium, de strontium, de cadmium, de magnésium, de zinc, de cuivre, de plomb, de fer, de cobalt et de nickel, les palmitates de calcium, de zinc, de cuivre, d'aluminium, de magnésium et de cobalt, les oléates de magnésium, de zinc, de cuivre, de plomb, de manganèse, de fer et de cobalt, le caprylate de plomb, le caproate de plomb, les linoléates de calcium, de zinc et de cobalt et les ricinoléates de zinc et de cadmium.By depositing, on the surface 13 of the drum, a lubricating substance contained in the applicator device 23, these drawbacks are eliminated. This lubricating substance consists of particles of an insulating, pulverulent, dry material, of known type, capable of reducing the friction exerted, during the rotation of the drum 10, by the surfaces of the recording member and of the recording device. 'erasures that are in contact with the surface of this drum. This insulating, lubricating, pulverulent, dry material may consist of disulphide molybdenum or with a metal salt of saturated, unsaturated or partially substituted fatty acid. This is how this metal salt can be derived from one of the fatty acids such as caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, l stearic acid, arachidic acid, behenic acid, oenanthylic acid, pelargonic acid, undecylic acid, tridecylic acid, pentadecylic acid, margaric acid, nonadecylic acid, l tricosanic acid, undecylenic acid, oleic acid, linoleic acid, linolenic acid, oleostearic acid, arachidonic acid, petroselinic acid, vaccenic acid, gadoleic acid, l palmitolic acid, ketooleic acid, ricinoleic acid, as well as mixtures of these acids. The most suitable metal salts belong to the group comprising barium, calcium, strontium, cadmium, magnesium, zinc, copper, lead, iron, cobalt and nickel stearates, palmitates of calcium, zinc, copper, aluminum, magnesium and cobalt, magnesium, zinc, copper, lead, manganese, iron and cobalt oleates, lead caprylate, lead caproate , calcium, zinc and cobalt linoleates and zinc and cadmium ricinoleates.

La matière isolante, lubrifiante, sèche peut également être constituée de fines particules de polytétrafluoroéthylène.The insulating, lubricating, dry material can also consist of fine particles of polytetrafluoroethylene.

Il faut maintenant signaler que la matière isolante, lubrifiante, sèche, dont la nature vient d'être précisée ci-­dessus, présente toujours une fine granulométrie, la taille des particules qui constituent cette matière étant en effet de l'ordre de un micron. En outre, selon la présente invention, cette matière pulvérulente est, avant d'être appliquée sur la surface du tambour 10, mélangée à de très fines particules de carbone conducteur, la taille de ces particules de carbone étant environ cent fois plus petite que celle des particules de matière isolante, c'est-à-dire de l'ordre de 0,01 micron. La quantité de carbone pulvérulent qui est ainsi ajoutée à la matière isolante, lubrifiante, pulvérulente est telle que la masse totale de carbone ajoutée reste comprise entre 0,2 M et 1 M, M étant la masse de matière isolante lubrifiante. C'est ainsi que la substance lubrifiante pulvérulente qui doit être appliquée sur la surface du tambour peut être obtenue, par exemple, en prenant, d'une part cent grammes de polytétrafluoroéthylène pulvérulent, d'autre part une quantité de carbone conducteur pulvérulent comprise entre vingt et cent grammes, et en mélangeant soigneusement ces deux produits à l'aide d'un mélangeur rapide de type connu. Le mélange pulvérulent que l'on obtient ainsi est constitué de groupes de particules du type de ceux qui ont été représentés et désignés par G sur la figure 2, chacun de ces groupes étant formé, comme on peut le voir sur cette figure, d'une seule particule 30 de matière isolante lubrifiante (par exemple de polytétrafluoroéthylène) entourée, sur sa périphérie, de particules 31 de carbone conducteur. Sur la figure 2, les particules 30 et 31 n'ont pas été représentées à l'échelle pour des raisons évidentes de clarté du dessin. Le nombre de particules de carbone 31 qui entourent une même particule de matière isolante 30 dépend du taux de carbone contenu dans la substance lubrifiante pulvérulente, mais, si le mélange de matière isolante lubrifiante et de carbone conducteur pulvérulent a été soigneusement réalisé, ce nombre reste pratiquement constant lorsqu'on passe d'une particule isolante 30 à une autre. Il faut également signaler, que même dans le cas où la quantité de carbone qui est ainsi ajoutée est relativement faible, c'est-à-dire égale à 0,2 fois la masse de la matière isolante lubrifiante, le nombre des particules de carbone 31 qui entourent une même particule isolante 30 est suffisamment élevé pour que ces particules de carbone, qui se trouvent régulièrement réparties sur la surface externe de cette particule isolante, recouvrent la totalité de cette surface.It should now be noted that the insulating, lubricating, dry material, the nature of which has just been specified above, always has a fine particle size, the size of the particles which constitute this material being in fact of the order of one micron. In addition, according to the present invention, this pulverulent material is, before being applied to the surface of the drum 10, mixed with very fine particles of conductive carbon, the size of these carbon particles being about a hundred times smaller than that of insulating material particles, that is to say of the order of 0.01 micron. The quantity of pulverulent carbon which is thus added to the insulating, lubricating, pulverulent material is such that the total mass of carbon added remains between 0.2 M and 1 M, M being the mass of lubricating insulating material. Thus the pulverulent lubricating substance which must be applied to the surface of the drum can be obtained, for example, by taking, on the one hand, one hundred grams of pulverulent polytetrafluoroethylene, on the other hand, an amount of powdery conductive carbon between twenty and one hundred grams, and by carefully mixing these two products using a rapid mixer of known type. The pulverulent mixture which is thus obtained consists of groups of particles of the type of those which have been represented and designated by G in FIG. 2, each of these groups being formed, as can be seen in this figure, of a single particle 30 of lubricating insulating material (for example polytetrafluoroethylene) surrounded, on its periphery, of particles 31 of conductive carbon. In FIG. 2, the particles 30 and 31 have not been shown to scale for obvious reasons of clarity of the drawing. The number of carbon particles 31 which surround the same particle of insulating material 30 depends on the level of carbon contained in the pulverulent lubricating substance, but, if the mixture of lubricating insulating material and of powdery conductive carbon has been carefully produced, this number remains practically constant when moving from one insulating particle to another. It should also be noted, that even in the case where the amount of carbon which is thus added is relatively small, that is to say equal to 0.2 times the mass of the lubricating insulating material, the number of carbon particles 31 which surround the same insulating particle 30 is high enough for these carbon particles, which are regularly distributed over the external surface of this insulating particle, to cover the whole of this surface.

La substance lubrifiante pulvérulente, qui est formée de groupes de particules G dont la constitution vient d'être indiquée en détail ci-dessus, est répartie régulièrement sur la surface externe 13 du tambour magnétique 10 au moyen d'un dispositif applicateur 23 qui est réalisé de façon à déposer, sur cette surface, une quantité de substance lubrifiante qui reste comprise entre 0,02 et 0,08 milligramme par mètre carré de surface.The pulverulent lubricating substance, which is formed from groups of particles G, the constitution of which has just been indicated in detail above, is regularly distributed over the external surface 13 of the magnetic drum 10 by means of an applicator device 23 which is produced so as to deposit, on this surface, a quantity of lubricating substance which remains between 0.02 and 0.08 milligrams per square meter of surface.

Dans une forme avantageuse de réalisation qui est illustrée sur la figure 3, ce dispositif applicateur comprend un réservoir 35 contenant la substance lubrifiante pulvérulente. Ce réservoir 35, qui est représenté sur la figure 3, en coupe suivant un plan perpendiculaire à l'axe de rotation 11 du tambour 10, est placé, comme on peut le voir sur la figure 1, au-dessus de ce tambour, entre le dispositif de nettoyage 22 et le dispositif d'effacement 24. Ce réservoir 35 est formé de deux plaques 36 et 37, dont l'une 36, de forme rectangulaire, est disposée à peu près verticalement, perpendiculairement au plan de coupe et de manière que son bord inférieur 38 se trouve à une distance de cinq à dix millimètres de la surface 13 du tambour 10, et dont l'autre 37, disposée perpendiculairement au plan de coupe, est inclinée par rapport à la plaque 36, ces deux plaques étant réunies l'une à l'autre par deux plaques transversales dont l'une seulement 39 est visible sur la figure 3, ces quatre plaques formant un boîtier indéformable, ayant pratiquement la forme d'un prisme dont l'arête est tournée vers le bas. En outre, la plaque 37 est ajustée de telle sorte que, d'une part, la distance qui sépare son bord inférieur 40 de la surface 13 du tambour est sensiblement la même que celle qui sépare cette surface du bord inférieur 38 de la plaque 36, et que, d'autre part, l'écartement entre ces deux bords inférieurs 38 et 40 est au plus égal à cinq millimètres. Dans ces conditions, le réservoir 35 présente, à sa partie inférieure, une ouverture rectangulaire 41 qui, située à une faible distance de la surface 13 du tambour, s'étend sur une longueur égale à la longueur de ce tambour, la largeur de cette ouverture étant très petite en comparaison de sa longueur.In an advantageous embodiment which is illustrated in FIG. 3, this applicator device comprises a reservoir 35 containing the pulverulent lubricating substance. This tank 35, which is shown in Figure 3, in section along a plane perpendicular to the axis of rotation 11 of the drum 10, is placed, as can be seen in Figure 1, above this drum, between the cleaning device 22 and the erasing device 24. This reservoir 35 is formed by two plates 36 and 37, one of which 36, of rectangular shape, is disposed approximately vertically, perpendicular to the cutting plane and so that its lower edge 38 is at a distance of five to ten millimeters from the surface 13 of the drum 10, and the other 37 of which, arranged perpendicular to the cutting plane, is inclined relative to the plate 36, these two plates being joined to each other by two transverse plates, only one of which is visible in FIG. 3, these four plates forming a non-deformable housing, having practically the shape of a prism whose edge is turned downwards . In addition, the plate 37 is adjusted so that, on the one hand, the distance which separates its lower edge 40 from the surface 13 of the drum is substantially the same as that which separates this surface from the lower edge 38 of the plate 36 , and that, on the other hand, the spacing between these two lower edges 38 and 40 is at most equal to five millimeters. Under these conditions, the reservoir 35 has, at its lower part, a rectangular opening 41 which, located at a short distance from the surface 13 of the drum, extends over a length equal to the length of this drum, the width of this opening being very small compared to its length.

Le dispositif applicateur qui est représenté sur la figure 3 comprend en outre une pluralité de filaments très souples 42 qui ont chacun l'une de leurs extrémités noyée à l'intérieur d'une masse 43 de résine durcie, elle-même serrée dans un étrier 44 fixé à l'intérieur du réservoir 35. Ces filaments 42 ont une longueur telle qu'ils passent par l'ouverture 41 du réservoir 35 et viennent, par leur autre extrémité, contacter la surface 13 du tambour 10. Ces filaments, qui ont un diamètre de l'ordre de 0,1 millimètre, sont constitués d'une matière naturelle ou synthétique très souple, ce qui leur permet, lorsqu'ils sont suspendus par l'une de leurs extrémités, de rester à peu près en position verticale ou d'y revenir lorsque, après avoir été écartés de cette position, ils sont ensuite relâchés. C'est ainsi que ces filaments peuvent être formés de fibres animales, du genre crin de cheval par exemple, de fibres de carbone, ou encore d'une matière plastique filiforme souple, telle que la matière polyamide qui est vendue sous le nom de "nylon" (marque déposée). Le nombre N de ces filaments 42 est tel que ces derniers obstruent presque complètement l'ouverture 41 du réservoir 35. Plus précisément, si on désigne par Σ la surface de la section droite formée par cette ouverture en l'absence de filaments et par S la surface de section totale de ces N filaments (la valeur de S étant ainsi donnée par l'expression :

Figure imgb0001
dans laquelle d représente le diamètre de chaque filament), le nombre N est tel que le rapport S/Σ est compris entre 0,35 et 0,8. Il en résulte que le nombre N de filaments 42 qui obstruent partiellement l'ouverture 41 du réservoir 35 est compris entre deux valeurs limites Nm et NM données, respectivement, par les expressions :
Figure imgb0002
 The applicator device which is shown in FIG. 3 further comprises a plurality of very flexible filaments 42 which each have one of their ends embedded inside a mass 43 of hardened resin, itself clamped in a stirrup 44 fixed inside the tank 35. These filaments 42 have a length such that they pass through the opening 41 of the tank 35 and come, by their other end, to contact the surface 13 of the drum 10. These filaments, which have a diameter of about 0.1 millimeter, are made of a very flexible natural or synthetic material, which allows them, when suspended by one of their ends, to remain approximately in the vertical position or to return to it when, after being removed from this position, they are then released. This is how these filaments can be formed from animal fibers, of the horsehair type for example, carbon fibers, or even from a flexible threadlike plastic material, such as the polyamide material which is sold under the name of " nylon "(registered trademark). The number N of these filaments 42 is such that the latter almost completely obstruct the opening 41 of the reservoir 35. More precisely, if we designate by Σ the surface of the cross section formed by this opening in the absence of filaments and by S the total cross-sectional area of these N filaments (the value of S being thus given by the expression:
Figure imgb0001
 where d represents the diameter of each filament), the number N is such that the ratio S / Σ is between 0.35 and 0.8. It follows that the number N of filaments 42 which partially obstruct the opening 41 of the reservoir 35 is between two limit values N m and N M given, respectively, by the expressions:
Figure imgb0002

C'est ainsi, par exemple, que, dans le cas où l'ouverture 41 a une longueur de 40 centimètres et une largeur de 4,5 mm (c'est-à-dire présente une surface de section Σ égale à 1800 mm²) et où le diamètre d de chaque filament 42 est égal à 0,1 mm, ces deux valeurs limites sont égales respectivement, à :

Figure imgb0003
Figure imgb0004
 Thus, for example, in the case where the opening 41 has a length of 40 centimeters and a width of 4.5 mm (that is to say has a cross-sectional area Σ equal to 1800 mm² ) and where the diameter d of each filament 42 is equal to 0.1 mm, these two limit values are equal respectively to:
Figure imgb0003
Figure imgb0004

On a constaté que, lorsque le nombre N des filaments 42 répondait aux conditions qui viennent d'être indiquées ci-­dessus, ces filaments empêchaient les particules de substance lubrifiante contenues dans le réservoir 35 de tomber librement sur la surface 13 du tambour, du moins tant que ce tambour n'était pas entraîné en rotation. Il faut néanmoins signaler que le nombre N de filaments qui traversent l'ouverture 41 permet à ces derniers de conserver une certaine liberté de mouvement, de sorte que, lorsque le tambour tourne, ces filaments, qui se trouvent en contact avec la surface mobile de ce tambour, sont mis en mouvement les uns par rapport aux autres et permettent alors aux particules lubrifiantes prises dans l'enchevêtrement de ces filaments de glisser le long de ceux-ci et de tomber finalement sur la surface du tambour. La quantité de substance lubrifiante qui est ainsi déposée, par unité de surface, sur la surface 13 de ce tambour dépend du nombre N de filaments 42 qui obstruent partiellement l'ouverture 41 du réservoir, cette quantité étant d'ailleurs d'autant plus grande que le nombre N de ces filaments est plus faible. On a ainsi trouvé que, dans le cas où le nombre de ces filaments était égal à la valeur limite Nm indiquée plus haut, la quantité de substance lubrifiante qui était déposée, par mètre carré, sur la surface du tambour était pratiquement égale à 0,05 mg, alors que, dans le cas où le nombre de ces filaments était égal à la valeur limite NM indiquée plus haut, la quantité de substance lubrifiante déposée, par mètre carré, sur le tambour était pratiquement égale à 0,02 mg. Reprenant l'exemple numérique donné plus haut, on a effectivement réussi, dans ce cas, avec un nombre de filaments pratiquement égal à 125.000, à déposer, sur chaque mètre carré de la surface du tambour, une quantité de substance lubrifiante pratiquement égale à 0,03 mg.It has been found that, when the number N of the filaments 42 meets the conditions which have just been indicated above, these filaments prevent the particles of lubricating substance contained in the reservoir 35 from falling freely on the surface 13 of the drum, at least as long as this drum was not rotated. It should nevertheless be noted that the number N of filaments passing through the opening 41 allows the latter to retain a certain freedom of movement, so that, when the drum rotates, these filaments, which are in contact with the movable surface of this drum, are set in motion relative to each other and then allow the lubricating particles caught in the entanglement of these filaments to slide along these and finally fall on the surface of the drum. The quantity of lubricating substance which is thus deposited, per unit of surface, on the surface 13 of this drum depends on the number N of filaments 42 which partially obstruct the opening 41 of the reservoir, this quantity being all the greater the lower the number N of these filaments. It was thus found that, in the case where the number of these filaments was equal to the limit value N m indicated above, the quantity of lubricating substance which was deposited, per square meter, on the surface of the drum was practically equal to 0 0.05 mg, whereas, in the case where the number of these filaments was equal to the limit value N M indicated above, the quantity of lubricating substance deposited, per square meter, on the drum was practically equal to 0.02 mg . Using the numerical example given above, we have effectively succeeded, in this case, with a number of filaments practically equal to 125,000, in depositing, on each square meter of the surface of the drum, an amount of lubricating substance practically equal to 0 . 03 mg.

Etant donné que, comme on l'a d'ailleurs indiqué plus haut, le dispositif applicateur de substance lubrifiante que l'on vient de décrire est placé entre le dispositif de nettoyage 22 et le dispositif d'effacement 24, c'est-à-dire en amont de ce dispositif d'effacement, les particules qui sont ainsi déposées par ce dispositif applicateur sur la surface 13 du tambour permettent à cette surface d'être lubrifiée juste avant son passage sous ce dispositif d'effacement 24 et sous l'organe d'enregistrement 12. Avec cette disposition, on a constaté que, même dans le cas où la masse de substance lubrifiante déposée, par mètre carré de surface, était faible, c'est-à-dire égale pratiquement à 0,02 mg/m², la surface du tambour se trouvait suffisamment lubrifiée pour empêcher le ramollissement des particules de révélateur déposées sur cette surface et pour éviter ainsi la formation, sur cette surface, d'une pellicule d'enduit indésirable.Since, as already indicated above, the device for applying the lubricating substance which has just been described is placed between the cleaning device 22 and the erasing device 24, that is to say say upstream of this erasing device, the particles which are thus deposited by this applicator device on the surface 13 of the drum allow this surface to be lubricated just before it passes under this erasing device 24 and under the recording device 12. With this arrangement, it has been found that, even in the case where the mass of lubricating substance deposited, per square meter of surface, was small, that is to say practically equal to 0.02 mg / m², the surface of the drum was sufficiently lubricated to prevent softening of the developer particles deposited on this surface and thus to prevent the formation, on this surface, of an undesirable coating film.

Dans une autre forme de réalisation qui est illustrée sur la figure 4, le dispositif applicateur de substance lubrifiante comprend une chambre 59, qui est située au-dessus de la surface 13 du tambour, et dont la cloison inférieure est constituée par une petite portion 61 de cette surface 13, cette portion se présentant sous la forme d'une bande comprise entre deux génératrices du tambour. Ainsi qu'on le voit sur la figure 4, cette portion de surface 61 s'étend entre un élément de retenue 128 qui est placé au contact de la surface 13 et une raclette 57 dont un bord 58 est appliqué sur cette surface 13, cet élément de retenue 128 et cette raclette 57 étant disposés, respectivement, en amont et en aval de la portion de surface 61, par rapport au sens de déplacement F de la surface 13 du tambour. La chambre 59 peut être mise en communication avec l'intérieur d'une cartouche 50, de forme cylindrique, qui, logée dans une coquille 51 fixée au-dessus de la chambre 59, peut pivoter autour de son axe 52, cette cartouche 50 contenant des particules de substance lubrifiante. La coquille 51 est pourvue, à sa partie inférieure, d'un évidement 53 établi de manière à permettre à une partie de la paroi cylindrique de la cartouche 50 de faire saillie hors de cette coquille et de servir ainsi de cloison supérieure pour la chambre 59. Il y a lieu d'indiquer ici que la cartouche 50 et la coquille 51 sont positionnées, par rapport au tambour, de telle sorte que l'axe 52 de la cartouche est parallèle à l'axe de rotation 11 de ce tambour et que la distance qui sépare cette cartouche 50 de la portion de surface 61 est très petite, comparée au diamètre de cette cartouche. Dans ces conditions, le volume de la chambre 59 est notablement inférieur à celui de la cartouche 50. La figure 4 montre encore que la coquille 51 est pourvue d'un dégagement 54 pour le passage d'un levier d'actionnement 55 solidaire de la cartouche 50, ce levier 55 pouvant être déplacé par l'opérateur entre deux positons limites, dont la première est représentée en traits mixtes sur la figure 4 et dont la seconde est représentée en traits pleins sur cette même figure. La paroi cylindrique de la cartouche 50 est percée d'un ouverture 56 qui s'étend dans une direction parallèle à l'axe de pivotement 52 de la cartouche et qui est réalisée de telle sorte que, lorsque le levier d'actionnement 55 est placé sur sa première position, cette ouverture 56 est obturée par la paroi du logement de la coquille dans lequel se trouve cette cartouche, alors que, lorsque le levier 55 est placé sur sa seconde position, cette ouverture 56 arrive en face de l'évidement 53 de la coquille 51 et permet aux particules de substance lubrifiante contenues dans la cartouche 50 de sortir de celle-ci et de tomber ainsi dans la chambre 59. Ces particules forment alors, dans cette chambre, une petite réserve de particules qui se trouve constamment en contact avec la portion de surface 61 dont on a parlé plus haut. Afin que les particules constituant cette réserve ne puissent pas s'échapper aisément de la chambre 59, la chambre 59, qui s'étend essentiellement suivant une direction parallèle à l'axe de rotation du tambour, est fermée à ses deux extrémitées, par deux plaquettes latérales qui n'ont pas été représentées sur les dessins pour des raisons de simplification. En outre, un bourrelet élastique 60, fixé près du bord 58 de la raclette 57 et interposé entre cette raclette et la cartouche 50, garantit une étanchéité pratiquement complète de la chambre 59. Dans ces conditions, les particules qui sont accumulées dans la chambre 59 ne peuvent théoriquement pas sortir de cette chambre. Toutefois, lorsque le tambour tourne autour de son axe dans le sens F, ces particules sont sollicitées à être entraînées en déplacement en direction de la raclette 57 et, si cette raclette est maintenue appliquée sur la surface du tambour avec une force d'intensité convenable dont on indiquera la valeur plus loin, un très petit nombre de particules parvient, au cours de chacune des rotations du tambour, à se glisser sous la raclette 57 et à sortir ainsi de la chambre 59. On peut indiquer ici que la quantité de substance lubrifiante qui se trouve répartie sur une portion donnée de la surface du tambour, après son passage sous le dispositif applicateur représenté sur la figure 4, est toujours très faible, la raclette 57 étant en effet réglée, comme on le verra plus loin, de telle sorte que la quantité de substance lubrifiante qui est déposée, par unité de surface, sur le tambour est de l'ordre de quelques centièmes de milligramme par mètre carré. On a constaté cependant que, pour obtenir une répartition régulière de ces particules de substance lubrifiante sur la surface du tambour, il fallait, non seulement que le bord 58 de la raclette qui se trouve en contact avec cette surface soit parfaitement rectiligne, mais encore que cette raclette forme, avec la demi-tangente T à cette surface au point de contact 58 et orientée dans le sens de déplacement du tambour, un angle t dont la valeur reste comprise entre dix et trente degrés.In another embodiment which is illustrated in Figure 4, the lubricant applicator device comprises a chamber 59, which is situated above the surface 13 of the drum, and the lower partition of which is constituted by a small portion 61 of this surface 13, this portion being in the form of a strip comprised between two generatrices of the drum. As can be seen in FIG. 4, this surface portion 61 extends between a retaining element 128 which is placed in contact with the surface 13 and a squeegee 57 of which an edge 58 is applied to this surface 13, this retaining element 128 and this squeegee 57 being disposed, respectively, upstream and downstream of the surface portion 61, with respect to the direction of movement F of the surface 13 of the drum. The chamber 59 can be placed in communication with the interior of a cartridge 50, of cylindrical shape, which, housed in a shell 51 fixed above the chamber 59, can pivot around its axis 52, this cartridge 50 containing particles of lubricating substance. The shell 51 is provided, at its lower part, with a recess 53 established so as to allow part of the cylindrical wall of the cartridge 50 to protrude out of this shell and thus to serve as an upper partition for the chamber 59 It should be noted here that the cartridge 50 and the shell 51 are positioned relative to the drum, so that the axis 52 of the cartridge is parallel to the axis of rotation 11 of this drum and that the distance which separates this cartridge 50 from the surface portion 61 is very small, compared to the diameter of this cartridge. Under these conditions, the volume of the chamber 59 is significantly less than that of the cartridge 50. FIG. 4 also shows that the shell 51 is provided with a clearance 54 for the passage of an actuating lever 55 integral with the cartridge 50, this lever 55 being able to be moved by the operator between two limit positions, the first of which is shown in dashed lines in FIG. 4 and the second of which is shown in solid lines in this same figure. The cylindrical wall of the cartridge 50 is pierced with an opening 56 which extends in a direction parallel to the pivot axis 52 of the cartridge and which is produced so that, when the actuating lever 55 is placed in its first position, this opening 56 is closed by the wall of the housing of the shell in which is this cartridge, while when the lever 55 is placed in its second position, this opening 56 arrives opposite the recess 53 of the shell 51 and allows the particles of lubricating substance contained in the cartridge 50 to exit the latter and thus fall into the chamber 59. These particles then form, in this chamber, a small reserve of particles which is constantly in contact with the surface portion 61 which was mentioned above. So that the particles constituting this reserve cannot easily escape from the chamber 59, the chamber 59, which extends essentially in a direction parallel to the axis of rotation of the drum, is closed at its two ends, by two side plates which have not been shown in the drawings for reasons of simplification. In addition, an elastic bead 60, fixed near the edge 58 of the squeegee 57 and interposed between this squeegee and the cartridge 50, guarantees practically complete sealing of the chamber 59. Under these conditions, the particles which are accumulated in the chamber 59 theoretically can't get out of this room. However, when the drum rotates about its axis in the direction F, these particles are urged to be driven in displacement in the direction of the squeegee 57 and, if this squeegee is kept applied to the surface of the drum with a force of suitable intensity. the value of which will be indicated below, a very small number of particles manages, during each rotation of the drum, to slip under the squeegee 57 and thus to leave the chamber 59. We can indicate here that the quantity of substance lubricant which is distributed over a given portion of the surface of the drum, after it has passed under the applicator device shown in FIG. 4, is always very low, the squeegee 57 being in fact adjusted, as will be seen below, so that the quantity of lubricating substance which is deposited, per unit of surface, on the drum is of the order of a few hundredths of a milligram per square meter. However, it has been found that, in order to obtain a uniform distribution of these particles of lubricating substance on the surface of the drum, it was not only necessary that the edge 58 of the squeegee which is in contact with this surface be perfectly straight, but also that this squeegee forms, with the half-tangent T to this surface at the point of contact 58 and oriented in the direction of movement of the drum, an angle t whose value remains between ten and thirty degrees.

Ainsi qu'on l'a mentionné plus haut, la quantité de substance lubrifiante qui est déposée par unité de surface sur le tambour 10 dépend de la force avec laquelle cette raclette est appliquée sur ce tambour. Plus précisément, on a trouvé que, lorsque la force P s'exerçant, par unité de longueur, sur le bord 58 de la raclette en contact avec le tambour avait une valeur de 12,5 N/dm, la quantité de lubrifiant déposée par unité de surface était sensiblement égale à 0,06 mg/m². De même, lorsque cette force P avait une valeur de 7,5 N/dm, la quantité de lubrifiant qui était déposée par unité de surface était sensiblement égale à 0,07 mg/m². Enfin, lorsque cette force P avait une valeur de 2,5 N/dm, la quantité de lubrifiant qui était déposée par unité de surface était sensiblement égale à 0,08 mg/m². Dans le cas illustré par la figure 4 où la raclette 57 se présente sous la forme d'une lame flexible comprenant, d'une part une partie fixe destinée à permettre à cette lame d'être fermement attachée sur la coquille 51, d'autre part une partie libre, de longueur b, de largeur a et d'épaisseur e (cette longueur b correspondant à la longueur du bord 58 de la lame), on sait que, lorsqu'on fait subir à cette lame une flexion telle que le bord 58 de la lame se trouve déplacé d'une distance f par rapport à sa position d'origine, la force P qui s'exerce, par unité de longueur, sur ce bord 58 a pour expression :

Figure imgb0005
E représentant la valeur du module d'élasticité du matériau constituant la lame. On voit donc que si on choisit, pour réaliser cette lame, un matériau présentant des propriétés élastiques suffisantes, on pourra déterminer les valeurs de la largeur a, de l'épaisseur e et de la flexion f qu'il convient d'adopter pour obtenir une force P dont la valeur est au moins égale à 2,5 N/dm, cette force permettant, ainsi qu'on l'a indiqué plus haut, de déposer sur la surface du tambour une quantité de lubrifiant au plus égale à 0,08 mg/m².As mentioned above, the amount of lubricant which is deposited per unit area on the drum 10 depends on the force with which this squeegee is applied to this drum. More precisely, it has been found that, when the force P exerted, per unit of length, on the edge 58 of the squeegee in contact with the drum had a value of 12.5 N / dm, the quantity of lubricant deposited by unit area was approximately 0.06 mg / m². Likewise, when this force P had a value of 7.5 N / dm, the quantity of lubricant which was deposited per unit of area was substantially equal to 0.07 mg / m². Finally, when this force P had a value of 2.5 N / dm, the quantity of lubricant which was deposited per unit of surface was substantially equal to 0.08 mg / m². In the case illustrated by Figure 4 where the squeegee 57 is in the form of a flexible blade comprising, on the one hand a fixed part intended to allow this blade to be firmly attached to the shell 51, on the other apart from a free part, of length b, of width a and of thickness e (this length b corresponding to the length of the edge 58 of the blade), it is known that, when this blade is subjected to a bending such that the edge 58 of the blade is displaced by a distance f by relative to its original position, the force P which is exerted, per unit of length, on this edge 58 has the expression:
Figure imgb0005
 E representing the value of the modulus of elasticity of the material constituting the blade. We therefore see that if we choose, to make this blade, a material with sufficient elastic properties, we can determine the values of the width a, the thickness e and the bending f that should be adopted to obtain a force P whose value is at least equal to 2.5 N / dm, this force making it possible, as indicated above, to deposit on the surface of the drum an amount of lubricant at most equal to 0, 08 mg / m².

En pratique, on s'arrange pour que l'amplitude de la flexion f subie par la lame flexible soit au plus égale à la moitié de la largeur a de cette lame, cette disposition permettant à cette lame flexible, lorsque celle-ci est réalisée en l'un des matériaux habituellement choisis pour constituer des lames élastiques, de rester dans le domaine des déformations élastiques. Il faut cependant que le matériau qui est utilisé pour réaliser cette lame flexible ne présente pas une dureté trop grande afin de ne pas risquer de détériorer la surface du tambour sur laquelle cette lame est appliquée. On a trouvé que, pour que la lame flexible reste dans la limite des déformations élastiques et ne provoque aucune dégradation de l'état de surface du tambour, le matériau employé pour constituer cette lame devait présenter un module d'élasticité E au moins égal à 300 dN/mm² et une dureté Δ au plus égale à 600 Vickers. C'est ainsi, par exemple, que cette lame flexible peut être une lame de téréphtalate de polyéthylène, cette dernière matière, désignée habituellement sous le nom de "Mylar" (marque déposée), présentant un module d'élasticité pratiquement égal à 480 dN/mm², la partie libre de cette lame ayant une largeur a pratiquement égale à 8 mm et une épaisseur e pratiquement égale à 0,2 mm. La force P qui s'exerce, par unité de longueur, sur le bord 58 de cette lame, lorsque celle-ci est soumise à une flexion f égale à la moitié de la largeur a de la lame, c'est-à-dire ici à 4 mm, a alors pour valeur :

Figure imgb0006
In practice, it is arranged so that the amplitude of the flexion f undergone by the flexible blade is at most equal to half the width a of this blade, this arrangement allowing this flexible blade, when the latter is produced. in one of the materials usually chosen to constitute elastic strips, to remain in the field of elastic deformations. However, the material which is used to make this flexible blade must not have too great a hardness so as not to risk damaging the surface of the drum on which this blade is applied. It has been found that, so that the flexible blade remains within the limit of elastic deformations and does not cause any degradation of the surface condition of the drum, the material used to constitute this blade must have a modulus of elasticity E at least equal to 300 dN / mm² and a hardness Δ at most equal to 600 Vickers. Thus, for example, this flexible blade can be a polyethylene terephthalate blade, the latter material, usually referred to as "Mylar" (registered trademark), having a module of elasticity practically equal to 480 dN / mm², the free part of this blade having a width a practically equal to 8 mm and a thickness e practically equal to 0.2 mm. The force P which is exerted, per unit of length, on the edge 58 of this blade, when the latter is subjected to a bending f equal to half the width a of the blade, that is to say here at 4 mm, then has the value:
Figure imgb0006

Dans ce cas, la quantité de substance lubrifiante déposée, par unité de surface, sur le tambour 10 est sensiblement égale à 0,07 mg/m².In this case, the quantity of lubricating substance deposited, per unit of area, on the drum 10 is substantially equal to 0.07 mg / m².

La lame flexible peut aussi être une lame en acier inoxydable, présentant un module d'élasticité pratiquement égal à 25.000 dN/mm², la partie libre de cette lame ayant une largeur a pratiquement égale à 8 mm et une épaisseur e pratiquement égale à 0,05 mm. La force P qui s'exerce, par unité de longueur, sur le bord 58 de cette lame, lorsque celle-ci est soumise à une flexion f égale à la moitié de la largeur a de la lame, c'est-à-dire à 4 mm, a alors pour valeur :

Figure imgb0007
The flexible blade can also be a stainless steel blade, having a modulus of elasticity practically equal to 25,000 dN / mm², the free part of this blade having a width a practically equal to 8 mm and a thickness e practically equal to 0, 05 mm. The force P which is exerted, per unit of length, on the edge 58 of this blade, when the latter is subjected to a bending f equal to half the width a of the blade, that is to say at 4 mm, then has the value:
Figure imgb0007

Dans ce cas, la quantité de substance lubrifiante déposée, par unité de surface,sur le tambour 10 est sensiblement égale à 0,073 mg/m².In this case, the quantity of lubricating substance deposited, per unit of area, on the drum 10 is substantially equal to 0.073 mg / m².

Afin que la lame flexible ne soit pas soumise à une usure trop rapide par suite de son frottement sur la surface du tambour, il est nécessaire que la force avec laquelle cette lame est appliquée sur cette surface ne soit pas trop élevée. Des essais ont montré que, pour obtenir une usure modérée de la lame, la force P s'exerçant, par unité de longueur, sur le bord 58 de cette lame ne devrait pas dépasser, pratiquement, la valeur de 20 N/dm. Dans ces conditions, la quantité de substance lubrifiante qui se trouve déposée, par unité de surface, sur le tambour 10 ne descend pas au-dessous de 0,04 mg/m².In order that the flexible blade is not subjected to too rapid wear due to its friction on the surface of the drum, it is necessary that the force with which this blade is applied to this surface is not too high. Tests have shown that, in order to obtain moderate wear of the blade, the force P exerted, per unit of length, on the edge 58 of this blade should not practically exceed the value of 20 N / dm. Under these conditions, the quantity of lubricating substance which is deposited, per unit of area, on the drum 10 does not drop below 0.04 mg / m².

Il faut encore signaler que l'élément de retenue 128 qui équipe le dispositif applicateur de substance lubrifiante que l'on vient de décrire se présente sous la forme d'un tampon réalisé en un matériau très souple tel que, par exemple, du caoutchouc mousse ou une matière textile.It should also be noted that the retaining element 128 which equips the device for applying the lubricating substance that has just been described is in the form of a pad made of a very flexible material such as, for example, foam rubber or a textile material.

Dans un mode de réalisation plus particulièrement avantageux qui a été représenté sur la figure 4, le dispositif de nettoyage 22 est disposé à proximité immédiate du dispositif applicateur de substance lubrifiante, en amont de celui-ci, et le patin de feutre qui équipe ce dispositif de nettoyage est positionné de telle sorte qu'il joue alors, pour ce dispositif applicateur, le rôle d'élément de retenue 128.In a more particularly advantageous embodiment which has been shown in FIG. 4, the cleaning device 22 is arranged in the immediate vicinity of the lubricant applicator device, upstream thereof, and the felt pad which equips this device cleaning device is positioned so that it then acts, for this applicator device, as a retaining element 128.

Ainsi qu'on l'a indiqué plus haut, la substance lubrifiante qui est réalisée selon l'invention est déposée sur la surface du tambour 10 de telle sorte que la quantité de substance déposée par mètre carré de surface reste comprise entre 0,02 mg et 0,08 mg. On a constaté, dans ces conditions, que la surface du tambour était correctement lubrifiée et que, même dans le cas où la vitesse de déplacement de cette surface atteignait 1,5 m/s, les échauffements provoqués par les frottements de l'organe d'enregistrement et du dispositif d'effacement sur cette surface étaient négligeables.As indicated above, the lubricating substance which is produced according to the invention is deposited on the surface of the drum 10 so that the quantity of substance deposited per square meter of surface remains between 0.02 mg and 0.08 mg. It was found, under these conditions, that the surface of the drum was properly lubricated and that, even in the case where the speed of movement of this surface reached 1.5 m / s, the heating caused by the friction of the organ d The recording and erasing on this surface were negligible.

Par ailleurs, étant donné que, comme on l'a signalé plus haut, le tambour magnétique est relié électriquement à la terre et que chacune des particules de substance lubrifiante est revêtue, sur la totalité de sa surface externe, d'une couche de carbone conducteur, les charges électriques que ces particules pourraient acquérir par suite de frottements, lors de leur passage sous le dispositif d'effacement ou l'organe d'enregistrement par exemple, se trouvent systèmatiquement éliminées. De ce fait, ces particules lubrifiantes, qui sont uniformément réparties sur la surface du tambour, ne risquent pas d'attirer électrostatiquement les particules de révélateur lors de leur passage devant le dispositif applicateur de révélateur 16, évitant ainsi la formation, sur la feuille de papier 20, d'un fond préjudiciable à une bonne qualité d'impression.Furthermore, since, as mentioned above, the magnetic drum is electrically connected to earth and each of the particles of lubricating substance is coated, over its entire external surface, with a layer of conductive carbon, the electric charges that these particles could acquire as a result of friction, during their passage under the erasing device or the recording member by example, are systematically eliminated. Therefore, these lubricating particles, which are uniformly distributed over the surface of the drum, do not risk electrostatically attracting the developer particles when they pass in front of the developer applicator device 16, thus avoiding the formation, on the sheet of paper 20, of a background detrimental to good print quality.

Bien entendu, l'invention n'est nullement limitée aux modes de mise en oeuvre décrits et illustrés qui n'ont été donnés qu'à titre d'exemple. Au contraire, elle comprend tous les moyens constituant des équivalents techniques de ceux décrits et illustrés, considérés isolément ou en combinaison, et mis en oeuvre dans le cadre des revendications qui suivent.Of course, the invention is in no way limited to the embodiments described and illustrated which have been given only by way of example. On the contrary, it includes all the means constituting technical equivalents of those described and illustrated, considered in isolation or in combination, and used in the context of the claims which follow.

Claims (11)

1. Substance lubrifiante pulvérulente apte à être appliquée sur la surface externe (13) d'un support d'enregistrement (10) d'une imprimante magnétique, ladite substance étant constituée de particules (30) d'une matière isolante pulvérulente capable de réduire les frottements entre ladite surface (13) et un organe d'enregistrement (12) appliqué contre cette surface, cette substance étant caractérisée en ce qu'elle contient en outre des particules (31) de carbone conducteur qui sont disposées autour desdites particules isolantes (30) pour former des groupes de particules lubrifiantes (G), le rapport de la masse totale de carbone à celle de ladite matière isolante étant compris entre 0,2 et 1.1. A pulverulent lubricating substance capable of being applied to the external surface (13) of a recording medium (10) of a magnetic printer, said substance consisting of particles (30) of a pulverulent insulating material capable of reducing the friction between said surface (13) and a recording member (12) applied against this surface, this substance being characterized in that it also contains particles (31) of conductive carbon which are arranged around said insulating particles ( 30) to form groups of lubricating particles (G), the ratio of the total mass of carbon to that of said insulating material being between 0.2 and 1. 2. Substance lubrifiante pulvérulente selon revendication 1, caractérisée en ce que lesdites particules de carbone conducteur (31) entourent complètement chacune desdites particules isolantes (30).2. pulverulent lubricant according to claim 1, characterized in that said conductive carbon particles (31) completely surround each of said insulating particles (30). 3. Substance lubrifiante pulvérulente selon l'une quelconque des revendications 1 et 2, caractérisée en ce que la taille de chacune des particules de carbone (31) est environ cent fois plus fois plus petite que celle des particules de matière isolante (30).3. pulverulent lubricating substance according to any one of claims 1 and 2, characterized in that the size of each of the carbon particles (31) is approximately one hundred times smaller than that of the particles of insulating material (30). 4. Substance lubrifiante pulvérulente selon l'une quelconque des revendications 1 à 3, caractérisée en ce que chaque particule de matière isolante (30) a une taille de l'ordre de 1 µ m.4. pulverulent lubricating substance according to any one of claims 1 to 3, characterized in that each particle of insulating material (30) has a size of the order of 1 µ m. 5. Dispositif apte à appliquer, sur la surface externe du support d'enregistrement d'une imprimante magnétique, une substance lubrifiante pulvérulente, ce dispositif étant caractérisé en ce qu'il comprend :
- un réservoir (35) contenant ladite substance pulvérulente et présentant, à sa partie inférieure, une ouverture (41) conformée de manière à permettre à tous les points de cette surface de passer sous ladite ouverture lors de l'entraînement du support,
- et une pluralité de filaments très souples (42) passant par ladite ouverture pour venir au contact de ladite surface externe, le nombre de ces filaments étant suffisant pour provoquer une quasi-obstruction de ladite ouverture, de sorte, que cours du déplacement du support d'enregistrement, ces filaments sont mis en mouvement l'un par rapport à l'autre et permettent aux particules de lubrifiant prises dans l'enchevêtrement de ces filaments de glisser le long de ces filaments pour tomber sur ladite surface.5. Device capable of applying, to the external surface of the recording medium of a magnetic printer, a pulverulent lubricating substance, this device being characterized in that it comprises:
- a reservoir (35) containing said pulverulent substance and having, at its lower part, an opening (41) shaped so as to allow all the points of this surface to pass under said opening during the drive of the support,
- And a plurality of very flexible filaments (42) passing through said opening to come into contact with said external surface, the number of these filaments being sufficient to cause a quasi-obstruction of said opening, so that during the movement of the support recording, these filaments are moved relative to each other and allow the lubricant particles caught in the entanglement of these filaments to slide along these filaments to fall on said surface. 6. Dispositif selon revendication 5, caractérisé en ce que le nombre N de filaments (42) est compris entre deux valeurs limites Nm et NM données, respectivement, par les expressions:
Figure imgb0008
 dans lesquelles Σ représente la valeur de la surface de section de l'ouverture (41) et d représente la valeur du diamètre de chacun desdits filaments.6. Device according to claim 5, characterized in that the number N of filaments (42) is between two limit values N m and N M given, respectively, by the expressions:
Figure imgb0008
 in which Σ represents the value of the cross-sectional area of the opening (41) and d represents the value of the diameter of each of said filaments. 7. Dispositif apte à appliquer, sur la surface externe du support d'enregistrement d'une imprimante magnétique, une substance lubrifiante pulvérulente, ce dispositif étant caractérisé en ce qu'il comprend une chambre (59) contenant ladite substance pulvérulente, cette chambre étant placée au-­dessus de ladite surface externe et étant limitée, à sa partie inférieure, par une portion (61) de ladite surface externe, cette portion (61) s'étendant entre un élément de retenue (128) placé en contact avec ladite surface et une raclette (57) dont un bord (58) est appliqué sur cette surface, cet élément de retenue et cette raclette étant disposés, respectivement, en amont et en aval de ladite portion de surface (61) par rapport au sens de déplacement (F) dudit support d'enregistrement, cette raclette (57) formant, avec la demi-tangente (T) à ladite surface externe, passant par le point de contact de cette raclette avec cette surface et orientée dans ledit sens de déplacement (F), un angle (t) dont la valeur est comprise entre dix et trente degrés.7. Device capable of applying, on the external surface of the recording medium of a magnetic printer, a pulverulent lubricating substance, this device being characterized in that it comprises a chamber (59) containing said pulverulent substance, this chamber being placed above said external surface and being limited, at its lower part, by a portion (61) of said external surface, this portion (61) extending between a retaining element (128) placed in contact with said surface and an squeegee (57) with an edge (58) applied to this surface, this retaining element and this squeegee being disposed, respectively, upstream and downstream of said surface portion (61) relative to the direction of movement (F) of said recording medium, this squeegee (57) forming, with the half-tangent (T) to said external surface, passing through the point of contact of this squeegee with this surface and oriented in said direction of movement (F), angle (t) whose value is between ten and thirty degrees. 8. Dispositif selon revendication 7, caractérisé en ce que la force (P) s'exerçant, par unité de longueur, sur le bord (58) de la raclette qui est en contact avec la surface du support d'enregistrement est ajustée de manière que la quantité de substance lubrifiant qui passe sous la raclette et se trouve ainsi déposée sur cette surface reste comprise entre 0,04 et 0,08 mg/m².8. Device according to claim 7, characterized in that the force (P) exerted, per unit of length, on the edge (58) of the squeegee which is in contact with the surface of the recording medium is adjusted so that the quantity of lubricating substance which passes under the squeegee and is thus deposited on this surface remains between 0.04 and 0.08 mg / m². 9. Dispositif selon l'une quelconque des revendications 7 et 8, caractérisé en ce que la raclette (57), est constituée par une lame flexible, réalisée en un matériau présentant un module d'élasticité au moins égal à 300 dN/mm² et une dureté au plus égale à 600 Vickers.9. Device according to any one of claims 7 and 8, characterized in that the squeegee (57), consists of a flexible blade, made of a material having a modulus of elasticity at least equal to 300 dN / mm² and a hardness at most equal to 600 Vickers. 10. Machine imprimante magnétographique, caractérisée en ce qu'elle comprend un dispositif applicateur de substance lubrifiante pulvérulente selon l'une quelconque des revendications 5 à 9.10. Magnetographic printing machine, characterized in that it comprises a device for applying pulverulent lubricating substance according to any one of claims 5 to 9. 11. Machine imprimante magnétographique, caractérisée en ce que son support d'enregistrement est lubrifié à l'aide de la substance lubrifiante pulvérulente selon l'une quelconque des revendications 1 à 4.11. Magnetographic printing machine, characterized in that its recording medium is lubricated with the aid of the pulverulent lubricating substance according to any one of claims 1 to 4.
EP19880401089 1987-05-07 1988-05-04 Pulverulent substance for the lubrification of the recording medium of a magnetic printer Expired - Lifetime EP0291392B1 (en)

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FR8706510A FR2615011B1 (en) 1987-05-07 1987-05-07 POWDERY SUBSTANCE FOR LUBRICATING THE RECORDING MEDIUM OF A MAGNETIC PRINTER
FR8706510 1987-05-07

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US4831386A (en) 1989-05-16
EP0291392B1 (en) 1992-10-14
DE3875274D1 (en) 1992-11-19
FR2615011B1 (en) 1989-06-23
DE3875274T2 (en) 1993-02-25
FR2615011A1 (en) 1988-11-10

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