Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C19/00—Other disintegrating devices or methods
  • B02C19/06—Jet mills
  • B02C19/068—Jet mills of the fluidised-bed type
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/0802—Preparation methods
  • G03G9/0808—Preparation methods by dry mixing the toner components in solid or softened state

Definitions

• the invention relates to a method for producing a spherical grain shape in toners.
• Toner is a fine-grained, electrically chargeable powder that is used in electrophotography to develop latent charge images. They consist essentially of a mixture of natural and / or synthetic resins with a low melting point and dyes soluble or dispersible in the resins, as well as additives for influencing their physical properties, e.g. B. Their sense of charge, their adhesiveness to the recording material, their tendency to agglomerate, etc. The aim is a free-flowing powder which causes little mechanical wear on the electrophotographic recording elements, which is resistant to a deterioration in its physical properties and which quickly and completely from the recording material to one Image receiving material can be transferred. It has been shown that these requirements can best be met if the toners have a spherical grain shape.
• the cooled and pre-broken mass of toner is mixed in a fine mill, e.g. B. a ball mill, crushed to the desired grain size, and the toner particles are then subjected to a heat treatment, wherein the resin serving as a binder is melted, so that the toner particles can take on a spherical shape by the surface tension which is then effective.
• a fine mill e.g. B. a ball mill
• the toner particles are then subjected to a heat treatment, wherein the resin serving as a binder is melted, so that the toner particles can take on a spherical shape by the surface tension which is then effective.
• the hot air used must have a temperature of about 500 ° C, which means that the toner particles easily stick together to form inseparable agglomerates, that melt deposits form on the walls of apparatus and lines and that undesired chemical transformations occur the toner components occur.
• the object of the invention is therefore to provide a method for producing a spherical grain shape in fine-grained toners, in which the toner particles in solid form, i. H. below their melting temperature or without the use of solvents, and can be treated in a fluidized material bed with considerably less energy expenditure than the known methods, and which at the same time sharply delimits the particle size range of the toner particles into the finest particle sizes.
• toner particles permanently plastically deform even at temperatures below the melting temperature of their constituents if they are allowed to collide with a certain kinetic energy. Due to the energy released in the event of a collision, the toner particles are briefly plasticized at their point of impact, causing deformation, but not sticking together, but also no comminution. To a certain extent, this is a forging process, with one of the two colliding toner particles each being regarded as a hammer for the other.
• each toner particle finally has the shape of a polyhedron closely approximating the sphere.
• the abrasion that may form, as well as the very fine fractions below, for example, 5 ⁇ m, which would have an adverse effect on the flow behavior of the finished toner, are separated from the deformed toner particles by a subsequent centrifugal force screening.
• the described method can already be carried out at normal room temperature, it can be advantageous if the toner particles are heated to a temperature which is somewhat below the melting temperature of their constituents.
• a further advantage of the method according to the invention has been found that surface-active substances can be applied to the toner particles at the same time as they are deformed by the mutual impact and friction stress .
• the surface-active substances are either embedded in the toner mass after thermal melting of the already spherical toner particles, but this is only possible with thermally insensitive substances, or they are mixed on the surface of the toner part Chen brought and held there by adhesive forces alone, so that they can easily be rubbed off by mechanical effects when the toner is used as intended later and thus deteriorate the toner quality.
• a fluid bed counter jet mill known per se is proposed, as has been described, for example, in the journal "Aufaufungs-Technik", 1982, No. 5, pp. 236-242.
• Such a mill consists essentially of a cylindrical grinding chamber with a vertical axis, in the lower area of which evenly distributed nozzles open for the introduction of the opposing gas jets, and in the upper area a centrifugal sifter in the form of a counter-centrifugal force from the visible air from the outside rotating basket sifter with internal flow.
• the only resource here is the gas introduced through the nozzles, which not only serves to generate the impact and friction stress, but also to transport the goods to the classifier, and there as classifying air.
• the number and size of the nozzles, the direction of the nozzle axes and the operating pressure and temperature of the gas supplied to the nozzles allow the intensity of the gas jets directed against one another to be varied simply and within wide limits, so that an optimal adjustment to the product to be treated is easily possible .
• the grain size up to which all fine particles are to be separated is determined by the choice of the speed of the basket sifter. It applies that the higher the speed is selected, the smaller the grain size, and vice versa.
• the process steps of producing the spherical grain shape, applying surface-active substances and separating the very fine fraction can be carried out in one work step with such a fluidized bed counter-jet mill, so that the procedure is very simple.

Landscapes

• Engineering & Computer Science (AREA)
• Food Science & Technology (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Developing Agents For Electrophotography (AREA)
• Glanulating (AREA)
• Disintegrating Or Milling (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

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Citations (5)

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• 1985
  • 1985-03-23 DE DE3510610A patent/DE3510610C2/de not_active Expired
• 1986
  • 1986-02-14 EP EP86101877A patent/EP0197264B1/fr not_active Expired
  • 1986-02-14 AT AT86101877T patent/ATE39580T1/de active
  • 1986-03-24 JP JP61064290A patent/JPH0614193B2/ja not_active Expired - Lifetime
  • 1986-03-24 US US06/843,447 patent/US4762765A/en not_active Expired - Fee Related

Patent Citations (5)

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