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
  • G03G9/09733—Organic compounds
  • G03G9/09758—Organic compounds comprising a heterocyclic ring

Definitions

• This invention relates to dry toner particles for use in electrostatographic printing systems.
• it relates to dry toner particles with adapted charging properties.
• electrostatography including electrography and electrophotography to form an electrostatic latent image either corresponding to the original to be copied, or corresponding to digitised data describing an electronically available image.
• an electrostatic latent image is formed by the steps of uniformly charging a photoconductive member and image-wise discharging it by an image-wise modulated photo-exposure.
• an electrostatic latent image is formed by image-wise depositing electrically charged particles, e.g. electrons or ions 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 are charged.
• charged toner particles are used in the process of Direct Electrostatic Printing (DEP), in which an image is created upon a receiving substrate by creating a flow of charged toner particles from a toner bearing surface to the image receiving substrate and image-wise modulating the flow of toner particles by means of an electronically addressable printhead structure.
• DEP Direct Electrostatic Printing
• a broad distribution of charge is characterised by (1) the presence of a relatively large amount of particles that have a charge too low for providing a sufficiently strong coulomb attraction and (2) the presence of wrong charge sign toner particles that have a charge sign opposite to the major part of the bulk of the toner particles.
• the development with such kind of developer results in an undesirable image-background fog.
• the toner particles of this invention can further incorporate any ingredient known in the art, e.g., toner resin, one or more colorants, metal oxides.
• the toner particles of this invention can be toner particles with a negative charge as well as toner particles with a positive charge.
• charge control agents for inducing or enhancing a negative chargeability are used.
• Charge control agents are well known in the art of preparation of toner particles.
• toner particles with a positive charge mainly ammonium compounds, pyridinium compounds, triphenylmethane, cationic dyes, negrosine dyes, etc. are used.
• Charge control agents for positive charging are commercially available through e.g. Ciba-Geigy of Switzerland under trade name CG 14-146, CG 16-569, BASF of Germany under trade name NEPTUNSCHWARZ X60, Orient Chemical of Japan under trade name BONTRON P51.
• toner particles with negative charge mainly metal complexes, phenylsilicates, naphthylsilicates, azo compounds, cationic polymers, modified ammonium compounds etc. are used.
• Charge control agents for negative charging are commercially available through e.g. Clariant of Germany under trade name NCS LP 2145, NCS VP 2145, COPY CHARGE NCA, Orient Chemical of Japan under trade name BONTRON E82, BONTRON S34, BONTRON S44, BONTRON F21.
• the charge control agent (CCA) can be present in any concentration known in the art, an amount between 0.5 and 5% by weight of the CCA being preferred.
• the charge limitation agent (CLA) used in toner particles of this invention is most preferably selected from meso-ionic compounds.
• Meso-ionic compounds as referred to in the present invention are a group of compounds defined by W. Baker and W.D. Ollis as "5- or 6-membered heterocyclic compounds which cannot be represented satisfactorily by any one covalent or polar structure and possesses a sextet of p-electrons in association with the atoms comprising the ring.
• the ring bears a fractional positive charge balanced by a corresponding negative charge located on a covalently attached atom or group of atoms" as described in Quart. Rev., Vol. II, p. 15 (1957) and Advances in Heterocyclic Chemistry, Vol. 19, P. 4 (1976).
• Preferred meso-ionic compounds are those represented by formula (I): wherein M represents a 5- or 6-membered heterocyclic ring composed of at least one member selected from the group consisting of a carbon atom, an oxygen atom, a sulphur atom and a selenium atom; and A - represents -O - , -S - or -N - -R, wherein R represents an alkyl group (preferably having 1 to 6 carbon atoms), a cycloalkyl group (preferably having 3 to 6 carbon atoms), an alkenyl group (preferably having 2 to 6 carbon atoms), an alkynyl group (preferably having 2 to 6 carbon atoms), an aralkyl group, an aryl group (preferably having 6 to 12 carbon atoms), or a heterocyclic group (preferably having 1 to 6 carbon atoms).
• R represents an alkyl group (preferably having 1 to 6 carbon atoms), a cycloalkyl group (preferably having 3 to
• examples of the 5-membered heterocyclic ring as represented by M include an imidazolium ring, a pyrazolium ring, an oxazolium ring, an isoxazolium ring, a thiazolium ring, an isothiazolium ring, a 1,3-dithiol ring, a 1,3,4- or 1,2,3-oxadiazolium ring, a 1,3,2-oxathiazolium ring, a 1,2,3-triazolium ring, a 1,3,4-triazolium ring, a 1,3,4-, 1,2,3- or 1,2,4-thiadiazolium ring, a 1,2,3,4-oxatriazolium ring, a 1,2,3,4-tetrazolium ring and a 1,2,3,4-thiatriazolium ring.
• Meso-ionic compounds are known for use in the fixing step of a photographic process as disclosed in European patent specification EP-A-431 568.
• Triazolium thiolate meso-ionic compounds are well known in silver halide photography and are used for increasing temperature latitude as disclosed in Japanese patent specification JP-A-60-117240, for reducing fog as disclosed in United States patent US-A-4 615 970, in preparing silver halide emulsions as disclosed in United States patent US-A-4 631 253, in bleach etching baths as disclosed in European patent specification EP-A-321 839, to prevent pressure marks as disclosed in United States patent US-A-4 624 913, and in European patent specification EP-A-554 585 for enhancing the printing properties and especially the printing endurance of a lithographic printing plate according to the DTR process.
• Preferred meso-ionic compounds for use in toner particles useful in the method of this invention correspond to the formula : wherein R 1 and R 2 each independently represents an unsubstituted or substituted alkyl group, alkenyl group, cycloalkyl group, aralkyl group, aryl group or heterocyclic group, A represents an unsubstituted or substituted alkyl group, alkenyl group, cycloalkyl group, aralkyl group, aryl group, heterocyclic group or -NR 3 R 4 and R 3 and R 4 each independently represents hydrogen, an alkyl group or aryl group and wherein R1 and R2 or R1 and A or R3 and R4 can combine with each other to form a 5- or 6-membered ring.
• the CLA is present in the toner particles for at least 0.5% by weight, more preferably for at least 1% by weight.
• Toner particles having a speed of tribo-electric charging and the stability of the charge for long printing time combined with a narrow charge distribution are very desirable in any printing system using electrostatographic means wherein dry toner particles are used as the marking material.
• toner particles with a charge distribution which is narrow i.e. the charge of the toner particles shows a distribution wherein the coefficient of variability ( ⁇ ), i.e. the ratio of the standard deviation to the average value, is equal to or lower than 0.4, preferably lower than 0.3.
• ⁇ coefficient of variability
• the charge distribution of the toner particles is measured by an apparatus sold by Dr. R. Epping PES-Laboratorium D-8056 Neufahrn, Germany under the name "q-meter”.
• negatively chargeable toner particles according to this invention further preferably comprise (1) at least one triboelectrically negatively chargeable thermoplastic resin serving as a binder having a volume resistivity of at least 10 13 ⁇ -cm, and (2) at least one resistivity lowering substance being an onium compound having a volume resistivity lower than the volume resistivity of the binder, wherein the resistivity lowering substance(s) is (are) capable of lowering the volume resistivity of the binder by a factor of at least 3.3 when present in the binder in a concentration of 5% by weight relative to the weight of the binder.
• Resistivity decreasing substances suited for use in toner particles according to the present invention are cationic, anionic or amphoteric type surfactants - see e.g.
• resistivity decreasing substances are within the following classes of compounds:
• positively chargeable toner particles according to this invention further preferably comprise (1) one or more triboelectrically positively chargeable thermoplastic resins serving as a binder having a volume resistivity of at least 10 13 ⁇ -cm, and (2) at least one substance having a volume resistivity lower than the volume resistivity of the binder, and wherein the substance(s) (2) when present in the binder in a concentration of 5% by weight lower(s) the volume resistivity of the binder by a factor of at least 3.3.
• Useful resistivity decreasing substances for use in positively chargeable toner particles of the invention are anionic compounds according to one of following general formulae: (R-COO) - M n+ (R-PO 3 ) 2- M 2n+ (R-O-SO 3 ) - M n+ (R-PO 4 ) 2- M n+ (R-S-SO 3 ) - M n+ (RH-PO 4 ) - M n+ (R-SO 3 ) - M n+ (R 2 -PO 4 ) - M n+ wherein :
• M + is a cation, e.g. an alkali metal cation, preferably Li + , and n represents valency number 1 where necessary multiplied by a whole number to satisfy charge equivalency with the negative charge of the associated anionic group.
• resistivity decreasing substances for use in positively charged toner particles of this invention are nonionic antistatic polyether type compounds, e.g. according to the following general formula : R 1 --[-O--(CH 2 ) n -] m --R 2 wherein each of R 1 and R 2 (same or different) represents hydrogen or an organic group, e.g. an alkyl group, m is a positive integer of at least 20, and n is a positive integer of at least 2.
• the toner particles of this invention are well suited for use in any electrostatographic printing system, and thus the invention encompasses the use of toner particles according to this invention in electrostatographic printing systems, e.g. in electrophotographic printing systems, ionographic printing systems and direct electrostatic printing systems.
• the toner particles of this invention are especially suitable for use in DEP devices, (devices for direct electrostatic printing), wherein electrostatic printing on an image receiving substrate is performed by creating a flow of toner particles from a toner bearing surface to the image receiving substrate and by image-wise modulating the flow of toner particles by means of an electronically addressable printhead structure.
• DEP devices wherein charged toner particles are transferred to the surface of a charged toner conveyor, it is observed that the charge to mass ratio of the charged toner particles present upon the charged toner conveyor (CTC) has the tendency to increase as the printing time increases.
• CTC charge to mass ratio of the charged toner particles present upon the charged toner conveyor
• the reason for this is that not all charged toner particles that pass under the printing apertures are used in the printing so that some of them are carried back to the place where the surface of the CTC is loaded with fresh toner, so that the friction between the toner particles on the surface of the CTC and the fresh toner particles can increase the charge on the toner particles. This is especially so when the surface of the CTC is loaded with charged toner particles from a magnetic brush carrying magnetic carrier particles and non-magnetic toner particles. The reason for this is that the carrier hairs of the magnetic brush further contact the charged toner particles present upon the surface of the charged toner conveyor, increasing their charge to mass ratio, unless they are consumed for image formation and are propelled through the printing apertures. So, if image parts of low or no image density frequently occur in an image, then the charged toner particles are brought in contact with the carrier hairs of the magnetic brush, multiple times before they are consumed, leading to enhanced charge to mass ratio and resulting lowered image density.
• toner particles according to this invention in a method for direct electrostatic printing comprising the steps of
• a magnetic brush is preferably used carrying magnetic carrier particles and non-magnetic toner particles.
• the carrier particles are of the carrier particles.
• a macroscopic "soft" ferrite carrier consisting of a MgZn-ferrite with average particle size 50 ⁇ m, a magnetisation at saturation of 36 Tm3/kg (29 emu/g) was provided with a 1 ⁇ m thick acrylic coating. The material showed virtually no remanence.
• the toner used for the experiment had the following composition : 97 parts of a co-polyester resin of fumaric acid and bispropoxylated bisphenol A, having an acid value of 18 and volume resistivity of 5.1 x 10 16 ohm.cm, melt-blended for 30 minutes at 110°C in a laboratory kneader with 3 parts of Cu-phthalocyanine pigment (Colour Index PB 15:3).
• a resistivity decreasing substance having the formula (CH 3 ) 3 N + C 16 H 33 Br - was added in a quantity of 0.5% with respect to the binder, as described in International patent specification WO-A-94/027192.
• the solidified mass was pulverised and milled using an ALPINE Fliessbettarnastrahlmühle type 100AFG (trade name) device and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (trade name).
• the average particle size was measured by Coulter Counter model Multisizer (trade name), and was found to be 6.3 ⁇ m by number and 8.2 ⁇ m by volume.
• the toner particles were mixed with 0.5% of hydrophobia colloidal silica particles (BET-value 130 m 2 /g) and hydrophobic colloidal titanium oxide particles.
• the second comparative toner was equal to comparative toner 1 (CT1) except for the addition of 3% by weight of a charge control agent (CCA), COPY CHARGE NCA, (trade name of Clariant) to the bulk of the particles.
• CCA charge control agent
• COPY CHARGE NCA trade name of Clariant
• the third comparative toner was equal to comparative toner 1 (CT1) except for the addition of 2% by weight of a charge limitation agent (CLA), with formula to the bulk of the toner particles.
• CLA charge limitation agent
• the first invention toner was equal to comparative toner 1 (CT1) except for the addition of 2% by weight of a charge control agent (CCA), COPY CHARGE NCA, (trade name of Clariant) and the addition of 0.25% by weight of a charge limitation agent (CLA), with formula to the bulk of the toner particles.
• CCA charge control agent
• CLA charge limitation agent
• the second invention toner was equal to the first one except for the addition of 0.5% by weight of the same charge limitation agent (CLA).
• CLA charge limitation agent
• the third invention toner was equal to the first one except for the addition of 1% by weight of the same charge limitation agent (CLA).
• the fourth invention toner was equal to the first one except for the addition of 2% by weight of the same charge limitation agent (CLA).
• the fifth invention toner was equal to the fourth one except for the toner resin, instead of 97 parts of a co-polyester resin of fumaric acid and bispropoxylated bisphenol A, AG23, was used.
• the sixth invention toner was equal to the fourth one except for the toner resin, instead of 97 parts of a co-polyester resin of fumaric acid and bispropoxylated bisphenol A, AGII was used.
• An electrostatographic developer was prepared by mixing the mixture of toner particles and colloidal silica in a 5% ratio (wt/wt) with silicon coated carrier particles.
• the developers were used in a DEP device as described hereinbelow for testing the charging properties of the toner particles.
• a printhead structure was made from a polyimide film of 50 ⁇ m thickness, double sided coated with a 5 ⁇ m thick copper film.
• the printhead structure had two rows of printing apertures.
• Each of the control electrodes was connected over 2 M ⁇ resistors to a HV 507 (trade name) high voltage switching IC, commercially available through Supertex, USA, that was powered from a high voltage power amplifier.
• the printing apertures were rectangular shaped with dimensions of 360 by 120 ⁇ m.
• the dimension of the central part of the rectangular shaped copper control electrodes was 500 by 260 ⁇ m.
• the apertures were spaced so to obtain a resolution of 33 dots/cm (85 dpi).
• a common shield electrode was arranged around the aperture zone leaving a free polyimide zone of 1620 ⁇ m.
• the printhead structure was fabricated in the following way. First of all the control and shield electrode pattern was etched by conventional copper etching techniques. The apertures were made by a step and repeat focused excimer laser making use of the control electrode patterns as focusing aid. After excimer burning the printhead structure was cleaned by a short isotropic plasma etching cleaning. Finally a thin coating of PLASTIK70, commercially available from Griffin Chemie, was applied over the control electrode side of the printhead structure.
• the charged toner conveyer (CTC) The charged toner conveyer (CTC)
• the CTC was a cylinder with a sleeve made of aluminium, coated with TEFLON (trade name of Du Pont, Wilmington, USA) with a surface roughness of 0.3 ⁇ m (Ra-value) and a diameter of 30 mm.
• toner particles were propelled to this conveyer from a stationary core / rotating sleeve type magnetic brush comprising two mixing rods and one metering roller. One rod was used to transport the developer through the unit, the other one to mix toner with developer.
• the magnetic brush was constituted of the so called magnetic roller, which in this case contained inside the roller assembly a stationary magnetic core, having three magnetic poles with an open position (no magnetic poles present) to enable used developer to fall off from the magnetic roller (open position was one quarter of the perimeter and located at the position opposite to the CTC.
• the magnetic brush was connected to a DC power supply of +140 V.
• the surface of the charged toner conveyor was positioned at 750 ⁇ m from the surface of the magnetic brush, and the surface of the charged toner conveyor was connected to an AC power supply with a sinusoidally oscillating field of 1800 V (peak to peak) at a frequency of 3.0 kHz with +100 V DC-offset.
• the surface of the charged toner conveyor was set via PU spacers means at 260 ⁇ m from the printhead structure.
• the shield electrode was connected to a DC power supply (DC5) of +100 V.
• the control electrodes were connected to a (image-wise selected) DC power source of 0 or +280 V.
• the back electrode was placed at 1000 ⁇ m from the back side of the printhead structure and was connected to a DC power supply of +1250 V.
• the receiving substrate was moved at a linear speed of 3 m/min, the linear speed of the charged toner conveyor was 6 m/min, and the linear speed of the magnetic brush was 30 m/min.

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Citations (5)

• 2000
  • 2000-10-04 EP EP00308725A patent/EP1093028A1/fr not_active Withdrawn

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