Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
  • G03G9/1131—Coating methods; Structure of coatings
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
  • G03G9/1138—Non-macromolecular organic components of coatings

Definitions

• This invention relates to a method for coating carrier particles. It relates especially to a method for coating carrier particles to be used as carrier particles in multi-component developers for electrostatic imaging with magnetic brush development as well as cascade development.
• a fluidised bed of carrier particles can be created whereto the coating solution of a chemical substance in a solvent is then added. Subsequently, the solvent is evaporated.
• a fluidised bed coater referred to as the Spiracoater
• the carrier particles are mixed (dispersed) in a solution of the chemical compound or compounds that are to be applied on the surface of the carrier particles and the particles are then spray-dried. Again this method gives good coating results, but the installation required for spray drying is expensive. Moreover, in these prior-art coating methods, based on a fluidised bed or spray drying, frequently some of the carrier particles to be coated adhere during the coating process to the wall of container of the fluidised bed or spray drying apparatus, and these particles are only coated from one side.
• carrier particles are coated by forming first a loose bed of these carrier particles by mechanical means instead of by an air flow as in a fluidised bed or spray coater and then continuously adding the coating solution to that loose bed at such a rate that, at any time, said solvent is present in an amount lower than 1.25 10 -4 ml per cm 2 of surface of said carrier particles to be coated. During this whole process the carrier particles are heated to an elevated constant temperature.
• the coating has to be very homogenous over the surface of the particles to be coated.
• the carrier particles are mixed with toner particles (and with other ingredients) to form a developer.
• the carrier particles are magnetic
• the carrier particles can be coated glass beads.
• the rubbing of the carrier particles and the toner particles induces a tribo-electric charge in the toner particles and the nature of the coating on the carrier particles determines, together with the toner ingredients, the polarity of the charge on the toner particles as well as the amount of the charge.
• the coating of the surface of the carrier particles is not even and has interruptions, then problems in charging the toner particles can occur.
• it is of utmost importance to have an even, closed coating on the surface of the particles.
• the prior-art methods described may provide coated carrier particles with good properties, but the homogeneity of the coating, i.e. having the same quality coating on each carrier particle, leaves still room for improvement.
• the objects of the invention are realised by providing a method for coating carrier particles having a volume average diameter between 20 and 200 ⁇ m, for use in electrostatic developers, comprising the steps of:
• the carrier particles to be coated are brought in a stationary vessel wherein the mechanical agitation is executed with a mechanical stirrer.
• a coating mixture is formed in a vessel by adding a coating solution comprising B ml of at least one solvent to carrier particles having a volume of A ml in said vessel, said volume A and said volume B being selected such that 0.5 ⁇ A/B ⁇ 5, or 1.5 ⁇ A/B ⁇ 5, or 2.5 ⁇ A/B ⁇ 5.
• the volume B is defined as the total amount of solvent(s) of the coating in ml
• the volume A [ml] is defined as the total weight [g] of carrier particles in the vessel divided by its density [g/cm 3 ] at 293K.
• the temperature of the coating mixture in the vessel is about room temperature to prevent agglomeration of the carrier particles.
• the temperature may be in the range from 15 to 40 degrees C or from 20 to 30 degrees C. Preferably no external heat is applied at this stage.
• the coating mixture may be mechanically agitated for a predetermined period, that can be chosen; from about 1 minute to several hours depending on the properties of the carrier particles and the coating solution where the coating mixture is composed of.
• mechanical agitation are useful in the method of this invention.
• the coating mixture is agitated in a stationary vessel by means of a mechanical stirrer.
• no stirrer is present in the vessel, but the coating mixture is agitated by oscillatory vibration, e.g. the vessel is mounted on a vibrating table.
• the vessel used for implementing the method of this invention is a tube, capped on both ends and after filling the tube with carrier particles to be coated and coating solution, the tube is agitated, e.g., by rolling the tube parallel to its cylindrical axis.
• the coating mixture in the vessel which is optionally already subjected to mechanical agitation, is subjected to an evaporation process in order to remove the solvent(s), which thereafter can be recuperated, and to apply a homogeneous layer of the coating substance on the carrier particles.
• the solvent(s) are evaporated by mechanically agitating and simultaneously gradually heating said coating mixture to a temperature of at most 10 degrees C above the boiling point of the solvent with the lowest boiling point.
• the mechanical agitation is by means of a mechanical stirrer.
• the mechanical agitation of the carrier particles is such that it can be described by a Froude number from 0.02 to 20, or from 0.05 to 10, or from 0.1 to 5.
• agglomeration of the carrier particles can be prevented, it is advantageous to have a low Froude number, as a higher Froude number corresponds with a heavier agitation which may result in damaging of the carrier particles and/or the coating layer already formed on the carrier particles. It is observed that, despite the relatively low Froude number and the low amounts of solvent(s), the risk of having the carrier particles tending to agglomerate is quite low using the method of this invention. It is believed that this is amongst others because the coating solution is added to the carrier particles at low temperature, i.e.
• the solvent(s) in the coating mixture formed is (are) gradually removed by mechanically agitating and simultaneously gradually heating the coating mixture to a temperature of at most 10 degrees C above the boiling point of the solvent with the lowest boiling point.
• the coating mixture may be heated to a temperature of at most 5 degrees above the boiling point of the solvent with the lowest boiling point, or to a temperature of at most about the boiling point of the solvent with the lowest boiling point, or to a temperature of at most 10 degrees below the boiling point of the solvent with the lowest boiling point.
• the boiling point to be considered is the boiling point at the pressure at which the coating proceeds.
• the pressure in the vessel at which the coating proceeds is selected from 50 % of the atmospheric pressure to 200 % of the atmospheric pressure. Preferably the pressure is about atmospheric pressure.
• the gradual heating is preferably such that the temperature is gradually increased at an average rate in the range from 0.5 to 3 degrees C per minute. Preferably the heating proceeds at a rate of at most 2 degrees C per minute.
• the rate of heating and the time of heating are adapted to the properties, such as for instance boiling point(s) and vapour tension(s), of the solvent(s) used in the coating solution.
• the solvent(s) is (are) thus evaporated and recuperated.
• the gradual heating of the coating mixture can beneficially take a time from about 10 minutes to several hours, preferably the gradual heating proceeds over a time interval from about 30 minutes to two hours.
• the coated particles can optionally be post-treated in the coating vessel or in a separate vessel, preferably equipped with heating means and mechanical agitation means.
• a post-treatment may be desirable to evacuate traces of solvent, of moisture, etc.
• the post-treatment may also be desirable to harden the coating.
• the post-treatment proceeds at a temperature above 75 degrees C, preferably the post-treatment temperature is from 75 to 180 degrees C, more preferably from 100 to 150 degrees C.
• the coated particles can be agitated as well as not.
• the agitation is executed intermittently both to avoid agglomeration of the coated carrier as well as to avoid damaging of the coating layer.
• the vessel for implementing the method of the present invention is equipped with a stirrer of which the blades are essentially perpendicular (i.e. a deviation of 10 degrees is acceptable) to the bottom of the vessel.
• the vessel, wherein carrier particles are coated by the method of this invention is basically cylindrical and the walls of the cylinder are placed in a basically horizontal plane and that the shaft of the stirrer is mounted essentially parallel to the walls of the cylinder and the blades perpendicular to these walls.
• a very useful type of mixing apparatus according to the present invention is a ploughshare mixer. Such a mixer is, e.g., commercially available from Gebrüder Lödige Maschinenbau GmbH, D33050 Paderborn, Germany.
• Carrier particles coated in a method of the present invention can be used to prepare multi-component developers for use in electrostatographic methods were an electrostatic latent image has to be developed, e.g., ionography, electrophotography as well as in electrostatographic methods were toner particles are directly image-wise applied to a final image receiving substrate as in Direct Electrostatic Printing, described in e.g. European patent application EP675417.
• the carrier particles can be glass particles that have been coated in the method according to this invention, when the developer is used in magnetic brush development, the carrier particles contain magnetic material or are magnetic particles.
• the method of this invention can be used to coat composite carriers, which are carriers wherein a magnetic pigment is incorporated in a matrix, this matrix being e.g.
• metal oxides as any magnetisable material can be used.
• metals and metal derivatives of metals can typically be selected from the group of Ca, Cr, Mn, Fe, Co, Ni, Cu, and Zn or mixtures thereof.
• the method according to the present invention can be used for any type of coating, it can be used to coat polymers on the particles, when e.g., addition polymers comprising styrene moieties, acrylic moieties, etc., addition polymers, e.g., polyesters, polyamides, polyimides etc., polymers comprising fluor containing moieties, silicon containing polymers, etc., are solved in (a) suitable solvent(s).
• the method can as well be used to coat particles with mixtures of polymers.
• the method of this invention can also be used to coat reactive mixtures on the particles, e.g. silicone polymers together with functional organosilanes as disclosed in United States patent US4,977,054.
• the method of this invention is very well suited for coating particles with a solution comprising chemical compounds that are selected from the group consisting of a monomeric polyfunctional organosilane, an oligomeric polyfunctional organosilane, a product of the hydrolysis of a polyfunctional organosilane, a reaction product of a polyfunctional organosilane and a organosilane containing a hetero-atom, and a reaction product of polyfunctional organosilane and an alkoxide.
• These compounds have been disclosed as carrier coatings in International patent application WO98/53372, International patent application WO98/52992, and European patent application EP1004942, all of them are hereby incorporated by reference.
• Polyfunctional organosilanes for use in the present invention comprise at least 2, preferably 3 Si-atoms coupled to 1 to 3 hydrolysable groups and/or a group that can be cross-linked by polycondensation.
• the latter groups are preferably alkoxy-, acyloxy or hydroxygroups.
• the Si-atoms are preferably coupled by a Si-C bond to an organic group, e.g., to a linear or branched C1 to C10 alkylgroup, to a C5 to C10 cycloalkylgroup, to an aromatic group or combinations thereof.
• Polyfunctional organosilanes useful to prepare a coating according to this invention correspond to formula (III), (IV) and (V) (R 5 ) 4-i Si[(CH 2 ) p Si(OR 6 ) a (R 7 ) 3-a ] i wherein
• Typical examples of polyfunctional organo silane useful in this invention are : Si[(CH 2 ) 2 Si(OH)(CH 3 ) 2 ] 4 H 3 C Si[(CH 2 ) 2 Si(OH)(CH 3 ) 2 ] 3 H 6 C 5 Si[(CH 2 ) 2 Si(OH)(CH 3 ) 2 ] 3 Si[(CH 2 ) 3 Si(OH)(CH 3 ) 2 ] 4 cyclo- ⁇ OSiCH 3 [(CH 2 ) 2 Si(OH)(CH 3 ) 2 ] ⁇ 4 cyclo- ⁇ OSiCH 3 [(CH 2 ) 2 Si(O CH 3 )(CH 3 ) 2 ] ⁇ 4 cyclo- ⁇ OSiCH 3 [(CH 2 ) 2 Si(O CH 3 ) 2 CH 3 ] ⁇ 4 cyclo- ⁇ OSiCH 3 [(CH 2 ) 2 Si(O CH 3 ) 2 CH 3 ] ⁇ 4 cyclo- ⁇ OSiCH 3 [(CH 2 ) 2 Si(O C 2 H 5
• Organosilanes containing a hetero-atom Organosilanes containing a hetero-atom
• the organosilanes containing an hetero-atom for use in a carrier coating according to this invention consist of at least one silicon atom carrying an hydrolysable group and/or a group that can be cross-linked by polycondensation and at least one organic rest group, bound to the silicon atom by a carbon atom, wherein the rest group contains an hetero atom and can be an alkyl, cycloalkyl or aryl group.
• the silicon atom carrying an hydrolysable group and/or a group that can be cross-linked by polycondensation can be -SiOR, wherein R can be H, an alkyl, cycloalkyl or aryl group. Preferably H or an alkyl group or -SiOH.
• the hetero atoms can be N, P, S, F, Cl, Br, O, B and Al, but are more preferably N or F.
• Typical useful nitrogen containing alkoxysilanes are : H 2 N-(CH 2 ) 3 Si(OCH 3 ) 3 H 2 N-(CH 2 ) 3 Si(OC 2 H 5 ) 3 H 2 N-(CH 2 ) 2 -HN-(CH 2 ) 3 Si(OCH 3 ) 3 H 2 N-(CH 2 ) 2 -HN-(CH 2 ) 3 Si(OCH 3 ) 2 CH 3 C6H5-HN-(CH 2 ) 3 Si(OCH 3 ) 3 C6H5-HN-(CH 2 ) 3 Si(OC 2 H 5 ) 3 H 2 N-(CH 2 ) 2 -HN-(CH 2 ) 2 -HN-(CH 2 ) 3 Si(OCH 3 ) 3 H 2 N-(CH 2 ) 2 -HN-(CH 2 ) 2 -HN-(CH 2 ) 3 Si(OCH 3 ) 3 H 2 N-(CH 2 ) 2 -HN-(
• Typical useful fluor containing alkoxysilanes are : F 3 C-(CH 2 ) 2 SiR' 3-x (OR) x F 3 C-(CF 2 ) 7 -(CH 2 ) 2 SiR' 3-x (OR) x (F 3 C) 2 CF-O-(CH 2 ) 3 SiR' 3-x (OR) x (3-F 3 C-C 6 H 4 )-SiR' 3-x (OR) x (3-F 3 C-C 6 H 4 ) 2 -Si(OR) 2 wherein 1 ⁇ x ⁇ 3, R, R' equal or different are alkyl, cycloalkyl or aryl, preferably R and R' are either methyl or ethyl.
• the alkoxide for use in a coating according to this invention corresponds preferably to formula (II): M 1 (OR 1 ) y Wherein
• Preferred alkoxides are : Si(OC 2 H 5 ) 4 , B(OC 2 H 5 ) 3, Al(O-i-C 3 H 7 ) 3 and Zr(O-i-C 3 H 7 ) 4 . It is highly preferred to use Si(OC 2 H 5 ) 4 as alkoxide in a polycondensation network on the carrier particles of this invention.
• any low boiling solvent capable of dissolving the coating chemicals can be used. Since it is preferred in the method of this invention to use coating chemicals as disclosed in WO98/53372, WO98/52992, and EP1004942, it is preferred to use lower aliphatic alcohols as solvent.
• the coating chemicals are:
• the components of the coating solution (for coating 1,000 g of Cu-Zn-Ferrite carrier particles with a density of 5.1 g/cm 3 ) and the relative amounts both in weight and in volume are given in the table 1 immediately below.
• the solution was pre-reacted at room temperature for one hour under gentle stirring. Then the solution was further diluted by adding 27.3g of isopropanol, and 0.155g of a Nitrogen containing charge controller (H 2 N-(CH 2 ) 2 - HN-(CH 2 ) 2 -HN-(CH 2 ) 3 Si(OCH 3 ) 3 ). From this solution above an amount of 313 g was prepared as final coating solution for 7,500 g of carrier particles. 7,500g of Cu-Zn-Ferrite carrier particles were stirred in a vessel and kept at a constant temperature of 80 degrees C. The solution above was added to the carrier at a rate of 14 g/min over 22 minutes. Then the temperature of the carrier particles was raised to 140 degrees C for post-treating, particularly hardening, the coating on the carrier.
• a Nitrogen containing charge controller H 2 N-(CH 2 ) 2 - HN-(CH 2 ) 2 -HN-(CH 2 ) 3 Si(OCH 3
• Invention example 2 is executed using the same procedure as in Invention example 1 except for the presence of 0.155g nitrogen containing charge controller added to the solution after the addition of the isopropanol.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Developing Agents For Electrophotography (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

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Citations (4)

• 2001
  • 2001-04-11 EP EP01201338A patent/EP1146398A3/de not_active Withdrawn

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