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
  • G03G9/097—Plasticisers; Charge controlling agents
  • G03G9/09708—Inorganic compounds
  • G03G9/09725—Silicon-oxides; Silicates
• • 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
  • G03G9/087—Binders for toner particles
  • G03G9/08784—Macromolecular material not specially provided for in a single one of groups G03G9/08702 - G03G9/08775
  • G03G9/08797—Macromolecular material not specially provided for in a single one of groups G03G9/08702 - G03G9/08775 characterised by their physical properties, e.g. viscosity, solubility, melting temperature, softening temperature, glass transition temperature
• • 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
  • G03G9/097—Plasticisers; Charge controlling agents
  • G03G9/09708—Inorganic compounds

Definitions

• This invention relates to electrostatographic toners suitable for use in a electrostatic developer, be it two component or monocomponent developers.
• this invention relates to heat fixable electrostatographic colour toners suitable for use in a full colour printing system .
• an electrostatic latent image is formed by the steps of uniformly charging a photoconductive member and imagewise discharging it by an imagewise modulated photo-exposure.
• an electrostatic latent image is formed by imagewise depositing electrically charged particles, e.g. from electron beam or ionized gas onto a dielectric substrate.
• the obtained latent images are developed, i.e. converted into visible images by selectively depositing thereon light absorbing particles, called toner particles, which usually are triboelectrically charged.
• dry development the application of dry toner powder to the substrate carrying the latent electrostatic image may be carried out by different methods known as, “cascade”, “magnetic brush”, “powder cloud”, “impression” or “transfer” development also known as “touchdown” development described e.g. by Thomas L. Thourson in IEEE Transactions on Electronic Devices, Vol. ED-19, No. 4, April 1972, pp.495-511.
• the latent image is developed with a finely divided developing material or toner to form a powder image which is then transferred onto a support sheet such as paper.
• the transferred image may subsequently be permanently affixed to the substrate by heat, pressure, or a combination of heat and pressure.
• Electrophotographic processes can not only be employed to form monochrome (black) images, but also to form colour images. It is known to form full colour images by sequentially forming and developing electrostatic colour separation images with cyan, magenta, yellow and black toners respectively. In such applications high quality toners are needed.
• Quality comprises features such as uniform darkness of the image areas, background quality, clear delineation of lines, good resolution of the image and particularly for colour images correct hue, high saturation and high lightness.
• each of the colour toners should present a high degree of colour mixing.
• electro(photo)graphy in "graphical" applications, i.e. in applications where the images are used in the printing industry or are compared with images the printing industry is accustomed to, the demands on colour balance and high fidelity rendition of slight differences in hue, saturation and lightness are at their highest.
• One of the important requirements for the system is that it allows the easy fusing and intimately mixing of two or more toner layers of different colours to yield a faithful rendition of the hues present in the original.
• a way to achieve this is to use an electr(photo)graphic system that uses a heat fixing step for producing the final image.
• any colour patch in the image may be reached with as few as possible overlaying toner layers so as to avoid problems with colour mixing in thick layers, with height and/or gloss differences between high density and low density areas.
• a high colour efficiency which means a high colour density pro gram toner (pro particle) is a very desirable feature.
• High colour efficiency is achieved by employing as colourant a dye molecularly dissolved in the toner resin.
• organic colouring pigment particles is preferred in the production of colour toners.
• Generaly organic colouring pigment particles with an average particle size of about 50 nm or less, are dispersed in the binder resin. The use of such organic colouring pigment particles is preferred notwithstanding the great efforts needed to finely and evenly disperse said particles in the binder resin.
• Fine and even dispersion of the pigment is necessary not only because a bad dispersion influences negatively the quality of the toner particles as such (e.g. due to different pigment load of the individual toner particles uneven charge distribution, colour deviations within individual toner particles, uneven melt characteristics etc.), but also because it will be necessary to add more pigment to achieve the desired density (increasing the cost of the toner) or more toner particles are to be deposited one over another to give the desired colour density in the final image (raising problems as to the melt energy that has to be delivered in a heat fixing process and the problems with height and/or gloss-differences between high density and low density areas).
• hydrophilic silica particles having dyes covalently bonded to the particle surfaces through silane coupling agents and a polymer having at least one segment capable of adsorbing onto the surface of the silica particles and at least one segment capable of enhancing the dispersability of the silica particles in the toner resin.
• a simple, cost effective way to finely and evenly divide organic colouring pigment particles in toner particles without negatively influencing the properties of the toner particles e.g. hot offset properties, stability, flowability, easy cleaning of the photconductive member.
• toner particles useful for high fidelity electrostatographic colour image reproduction i.e. for full colour reproduction, yellow, magenta, cyan and black toner particles, which contain finely and evenly divided pigments (e.g. organic colouring pigment) so as to yield a high colour rendering in a heat fixing process, without presenting problems of too high a melt viscosity and lack of definition.
• a dry electrostatographic toner composition having toner particles comprising at least one organic colouring substance, at least one binder resin and at least one inorganic filler material, characterised in that
• the dispersion of organic colouring pigment particles in a toner resin is greatly facilitated and the tendency of the pigment particles for agglomeration greatly reduced when during the melt kneading step of the toner production inorganic filler materials are present.
• EP 078,077 a water fixable toner containing inorganic, water insoluble fillers is disclosed in order to have a toner that can be fixed without requiring a strictly controlled amount of water.
• inorganic filler material in the bulk of toner particles intended for use in an development process employing a heat fixing step has been disclosed in order to have silica particles at the surface of the toner particles (e.g. JP 18995/1969).
• melt viscosity at 120 °C of said resinous toner matrix containing 1 m2 surface of said filler material(s) pro gram of resin(s) is, in comparison to the melt viscosity of the same resinous toner matrix without any of said filler material(s), not raised or is raised by a factor f of at most 1.1.
• the low interaction between the inorganic filler material(s) and the binder resin(s) making up the resinous toner matrix is not only beneficial in limiting the raise of melt viscosity of the resinous matrix comprising said inorganic filler materials, but is also beneficial in enhancing the dispersability of the organic colouring pigment particles in the toner mass. It is believed, without however being bound by any theory, that the inorganic filler material has to have enough free and active surface in such a way that the organic colouring substance(s) can interact with the inorganic filler material and be dispersed troughout the toner particles together with the inorganic filler material.
• inorganic filler material is, according to the present invention to be understood any filler being composed of more than 90 % of pure inorganic material.
• Small organic alterations such as e.g. those to inhibit moisture degradation of the filler, can be incorporated, as long as the surface activity of the inorganic filler is not completely altered by said small organic alteration.
• the inorganic filler material that, according to the present invention, is incorporated in the bulk of toner particles useful for high fidelity electrostatographic colour reproduction and to be used in an electro(stato)graphic system comprising a heat fixing step, has to be colourless and transparent.
• the use of spherical, inorganic filler particles has proved to offer advantages over non spherical particles.
• spherical fumed inorganics of the metal oxide class selected from the group consisting of silica (SiO2) and alumina (Al2O3) or mixed oxides thereof are selected.
• the fumed metal oxide particles have a smooth, substantially spherical surface.
• Their specific surface area is preferably in the range of 20 to 400 m2/g, more preferably in the range of 50 to 200 m2/g.
• the specific surface area (BET surface) can be measured by a method described by Nelsen and Eggertsen in "Determination of Surface Area Adsorption measurements by continuous Flow Method", Analytical Chemistry, Vol. 30, No. 9 (1958) p. 1387-1390.
• hydrophobic or hydrophilic inorganic particles to disperse an organic colourant in the toner particles according to the present invention, on the condition that the inorganic filler particles are chemically non-reactive towards the binder resin(s) and that the melt viscosity at 120 °C of the resinous matrix containing 1 m2 surface of said inorganic filler paricles pro gram of resin(s) is, in comparison to the melt viscosity of the same resinous matrix without any of said filler material(s), not raised or at most by a factor f of 1.25
• the proportions for fumed metal oxides such as silica (SiO2) and alumina (Al2O3) incorporated in the particle composition of the toner particles are in the range of 3 to 30 % by weight.
• the toner particles used in accordance with the present invention may comprise any conventional resin binder.
• the binder resins used for producing toner particles according to the present invention may be addition polymers e.g. polystyrene or homologues, styrene/acrylic copolymers, styrene/methacrylate copolymers, styrene/acrylate/acrylonitile copolymers or mixtures thereof.
• Addition polymers suitable for the use as a binder resin in the production of toner particles according to the present invention are disclosed e.g. in BE 61.855/70, DE 2,352,604, DE 2,506,086, US-P 3,740,334.
• polyesters prepared by reacting organic carboxylic acids (di or tricarboxylic acids) with polyols (di- or triol) are the most prefered polycondensation polymers.
• the carboxylic acid may be e.g. maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, etc or mixtures thereof.
• the polyolcomponent may be ethyleneglycol, diethylene glycol, polyethylene glycol, a bisphenol such as 2,2-bis(4-hydroxyphenyl)-propane called "bisphenol A” or an alkoxylated bisphenol, a trihydroxy alcohol, etc or mixtures thereof.
• Polyesters, suitable for use in the preparation of toner particles according to the present invention are disclosed in e.g. US-P 3,590,000, US-P 3,681,106, US-P 4,525,445, US-P 4,657,837, US-P 5,153,301.
• the inorganic filler material according to the present invention can be added to yellow, magenta and cyan toners to enhance the dispersability of the organic colouring pigment particles in the toner particles.
• the colourant is a mixture of at least three organic colouring pigments (yellow, magenta and cyan) to ensure a neutral grey (black) colour
• Neutral black means that the black colour absorbs the light of the visible spectrum in an amount that is independent of the wavelenght.
• organic colouring pigment(s) e.g. a cyan dye
• the inorganic black pigment, used together with an organic colouring pigment to have a neutral black is carbon black.
• Examples of carbon black are lamp black, channel black and furnace black e.g. SPEZIALSCHWARZ IV (trade name of Degussa Frankfurt/M - Germany) and VULCAN XC 72 and CABOT REGAL 400 (trade names of Cabot Corp. High Street 125, Boston, U.S.A.).
• the colour toners may contain organic colouring pigments of the group of phthalocyanine dyes, quinacridone dyes, triaryl methane dyes, sulphur dyes, acridine dyes, azo dyes and fluoresceine dyes.
• organic colouring pigments of the group of phthalocyanine dyes, quinacridone dyes, triaryl methane dyes, sulphur dyes, acridine dyes, azo dyes and fluoresceine dyes.
• the colourant is preferably present therein in an amount of at least 0.5 % by weight with respect to the total toner composition, more preferably in an amount of 1 to 10 % by weight.
• the toner particles may contain (a) charge control agent(s).
• charge control agent(s) for example, in published German patent application (DE-OS) 3,022,333 charge control agents for yielding negatively chargeable toners are described.
• Very useful charge controlling agents for providing a net positive charge to the toner particles are described in US-P 4,525,445, more particularly BONTRON NO4 (trade name of Oriental Chemical Industries - Japan) being a nigrosine dye base neutralized with acid to form a nigrosine salt, which is used e.g.
• a charge control agent suitable for use in coloured toner particles is zinc benzoate and reference therefor is made to published European patent Application 0 463 876 decribing zinc benzoate compounds as charge controlling agents. Such charge controlling agent may be present in an amount up to 5 % by weight with respect to the toner particle composition.
• the toner powder particles according to the present invention may be prepared by mixing the above defined binder resin(s) and ingredients (i.e. organic colouring substance, inorganic filler, etc) in the melt phase, e.g. using a kneader.
• the kneaded mass has preferably a temperature in the range of 90 to 140 °C, and more preferably in the range of 105 to 120 °C.
• After cooling the solidified mass is crushed, e.g. in a hammer mill and the obtained coarse particles further broken e.g. by a jet mill to obtain sufficiently .small particles from which a desired fraction can be separated by sieving, wind classification, cyclone separation or other classifying technique.
• the actually used toner particles have preferably an average diameter between 3 and 20 ⁇ m on volume, more preferably between 5 and 10 ⁇ m when measured with a COULTER COUNTER (registered trade mark) MULTIZISER particle size analyzer operating according to the principles of electrolyt displacement in narrow aperture and marketed by COULTER ELECTRONICS Corp. Northwell Drive, Luton, Bedfordshire, LC 33, UK.
• COULTER COUNTER registered trade mark
• MULTIZISER particle size analyzer operating according to the principles of electrolyt displacement in narrow aperture and marketed by COULTER ELECTRONICS Corp. Northwell Drive, Luton, Bedfordshire, LC 33, UK.
• an electrolyte e.g. aqueous sodium chloride
• the particles passing one-by-one each displace electrolyte in the aperture producing a pulse equal the displaced volume of electrolyte.
• particle volume response is the basis for said measurement.
• Suitable milling and air classification may be obtained when employing a combination apparatus such as the Alpine Fliessbeth-Gegenstrahlmühle (A.F.G.) type 100 as milling means and the Alpine Turboplex Windsichter (A.T.P.) type 50 G.C as air classification means, available from Alpine Process Technology, Ltd., Rivington Road, Whitehouse, Industrial Estate, Runcorn, Cheshire, UK.
• A.F.G. Alpine Fliessbeth-Gegenstrahlmühle
• A.T.P. Alpine Turboplex Windsichter
• Another useful apparatus for said purpose is the Alpine Multiplex Zick-Zack reformer also available from the last mentioned company.
• the toner particles according to the present invention may also be prepared by a "polymer suspension” process.
• the resin is dissolved in a water immiscible solvent with low boiling point and the pigment and the inorganic filler are dispersed in that solution.
• the resulting solution/dispersion is dispersed in an aqueous medium that contains a stabilizer, the organic solvent is evaporated and and the resulting particles are dried.
• suspension stabilizer it is possible to use e.g. silica particles, water soluble organic protective colloids (e.g. polyvinylalcohol), surface active agents, etc.
• spacing particles may be added externally to said toner particles.
• Said spacing particles may be embedded in the surface of the toner particles or protruding therefrom or may be externally mixed with the toner particles, i.e. are used in admixture with the bulk of toner particles after the toner particles are produced.
• These flow improving additives are preferably extremely finely divided inorganic or organic materials the primary (i.e. non-clustered) particle size of which is less than 50 nm; essentially the same inorganic materials as those used in the preparation step of the toner particles are preferred, but the particles are preferentially hydrophobic.
• Silica particles that have been made hydrophobic by treatment with organic fluorine compounds for use in combination with toner particles are described in published EP-A 467439.
• the proportions for fumed metal oxides such as silica (SiO2) and alumina (Al2O3) to be admixed externally to the toner particles, prepared according to the present invention are in the range of 0.1 to 10 % by weight in respect to the toner particles.
• Fumed silica particles are commercially available under the tradenames AEROSIL and CAB-O-Sil being trade names of Degussa, Franfurt/M Germany and Cabot Corp. Oxides Division, Boston, Mass., U.S.A. respectively.
• AEROSIL R972 (tradename) is used which is a fumed hydrophobic silica having a specific surface area of 110 m2/g. The specific surface area can be measured by a method described by Nelsen and Eggertsen in "Determination of Surface Area Adsorption measurements by continuous Flow Method", Analytical Chemistry, Vol. 30, No. 9 (1958) p. 1387-1390.
• a metal soap e.g. zinc stearate, as described in the United Kingdom Patent Specification No. 1,379,252, wherein also reference is made to the use of fluor containing polymer particles of sub-micron size as flow improving agents, may be present in the developer composition comprising the toner particles according to the present invention.
• the powder toner particles according to the present invention may be used as mono-component developer, i.e. in the absense of carrier particles but are preferably used in a two-component system comprising carrier particles.
• toner particles When used in admixture with carrier particles, 2 to 10 % by weight of toner particles is present in the whole developer composition. Proper mixing with the carrier particles may be obtained in a tumble mixer.
• Suitable carrier particles for use in cascade or magnetic brush development are described e.g. in United Kingdom Patent Specification 1,438,110.
• the carrier particles may be on the basis of ferromagnetic material e.g. steel, nickel, iron beads, ferrites and the like or mixtures thereof.
• the ferromagnetic particles may be coated with a resinous envelope or are present in a resin binder mass as described e.g. in US-P 4,600,675.
• the average particle size of the carrier particles is preferably in the range of 20 to 300 ⁇ m and more preferably in the range of 30 to 100 ⁇ m.
• iron carrier beads of a diameter in the range of 50 to 200 ⁇ m coated with a thin skin of iron oxide are used.
• Carrier particles with spherical shape can be prepared according to a process described in United Kingdom Patent Specification 1,174,571.
• a RHEOMETRICS dynamic rheometer RVEM-200 (One Possumtown Road, Piscataway, NJ 08854 USA) is used.
• the viscosity measurement is carried out at a sample temperature of 120 °C.
• the sample having a weight of 0.75 g is applied in the measuring gap (about 1.5 mm) between two parallel plates of 20 mm diameter one of which is oscillating about its vertical axis at 100 rad/sec and amplitude of 10 ⁇ 3 radians.
• the measurement signals which are expressed in poise (P) the sample is allowed to attain thermal equilibrium for 10 minutes.
• the meltviscosity increase factor (f) was determined by measuring the melt viscosity of the pure resinous matrix according to test I, which gives the value of ⁇ r in P.
• the meltviscosity of the resinous matrix to which is added 10 % w/w of inorganic filler material is measured according to test I, yielding a value for ⁇ f in P.
• the meltviscosity factor f is determined by BET is the specific surface of the inorganic filler material particles, measured by a method described by Nelsen and Eggertsen in "Determination of Surface Area Adsorption measurements by continuous Flow Method", Analytical Chemistry, Vol. 30, No. 9 (1958) p. 1387-1390 and expressed in m2/g.
• the formula above normalizes the meltviscosity increase factor f to the addition of such an amount of inorganic filler material that the resinous matrix contains 1 m2 of filler surface pro 1 g of resinous matrix.
• the material to be tested is heated to 200° C for 15 minutes and diluted with toner resin so as to obtain a final pigment concentration of 1 % w/w in respect to the toner/resin mixture.
• a drop is placed on a dust- and fatfree microscopic glass plate.
• the microscopic glass plate and the molten sample are allowed to equilibrate at 150° C.
• an aluminium foil, 15 ⁇ m thick is applied at two sides of the drop and the drop is drawn to a layer of 15 ⁇ m thick by sliding a sharp knife over the aluminium spacer guides.
• the sample is observed by a microscope with magnification 100 x or 200 x and photographed. Visual comparison of photographs makes it possible to assess the relative degree of dispersion of the pigment.
• a predefined amount of the sample to be tested (0.5 g for toner particles, 0.2 g for masterbatch) is brought into 75 ml dichloromethane and ultrasonically stirred for 30 minutes. After cooling to room temperature the mixture, which is a dispersion of the pigment in dichloromethane, is brought to exactly 100 ml. After further dilution ( 5 times for toner, 20 times for masterbatch) the absorption of the solution/dispersion is measured in a double beam spectrophotometer. The measurement proceeds with the wavelength of maximal absorption of the pigment under investigation.
• the dispersion in dichloromethane absorbs more or less light.
• the density of the dichloromethane dispersion is taken as a measure for the degree of dispersion. The higher the density the better the dispersion.
• meltviscosity increase factor (f) measured according to test II, for different inorganic filler materials and two different resinous matrices (RESIN A and RESIN B)is presented together with the degree of dispersion of HELIOGEN BLAU (see table 1) measured according to test IV and expressed as absorbance at 640 nm.
• RESIN A 77 parts by weight, 20 parts by weight of Al2O3C (ALUMINIUMOXIDE C, a tradename of Degussa AG, Frankfurt, Germany for hydrophilic aluminiumoxide with BET surface of 100 m2/g) and 3 parts by weight of Heliogen Blau (table 1) are intimately mixed together, melt kneaded, crushed and classified to give toner particles with average particle size of 8.5 ⁇ m based on volume.
• cyan toners as in example 2 were prepared, with varying concentrations of aluminiumoxide C (examples 3 to 7).
• the resulting toners were evaluated according to test IV. The results are shown in table 5.
• Toner particles were produced by intimatly mixing 85 % w/w of RESIN A, 5 % w/w of Sicoechtgelb (table 1), 10 % w/w of aluminium oxide C, melt kneading the mixture, cooling, crushing and classifying to obtain toner particles with average particle size of 8.30 ⁇ m based on volume.
• Toner particles were produced by intimatly mixing 84.75 % w/w of RESIN A, 2.25 % w/w of Hostaperm Rosa E (table 1), 2.75 % w/w of Permanent Carmine FBB02 (table 1), 10 % w/w of aluminium oxide C, melt kneading the mixture, cooling, crushing and classifying to obtain toner particles with average particle size of 8.35 ⁇ m.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Developing Agents For Electrophotography (AREA)

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Citations (3)

• 1993
  • 1993-06-09 EP EP19930201647 patent/EP0628883B1/de not_active Expired - Lifetime
  • 1993-06-09 DE DE1993600454 patent/DE69300454T2/de not_active Expired - Fee Related
• 1994
  • 1994-06-06 JP JP6148687A patent/JPH07104505A/ja active Pending

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