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
  • G03G9/09—Colouring agents for toner particles
  • G03G9/0926—Colouring agents for toner particles characterised by physical or chemical properties
• • 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
  • G03G9/08793—Crosslinked polymers
• • 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
  • G03G9/08795—Macromolecular material not specially provided for in a single one of groups G03G9/08702 - G03G9/08775 characterised by their chemical properties, e.g. acidity, molecular weight, sensitivity to reactants

Definitions

• the present invention relates to toner particles comprising radiation curable compounds. It relates also to a method for producing toner images, wherein the toner images are highly resistant to wear.
• a latent image is formed that is developed by attraction of so called toner particles. Afterwards the developed latent image (toner image) is transferred to a final substrate and fused to this substrate. In DEP the so called toner particles are imagewise deposited directly on a final substrate and fused to this substrate.
• Toner particles are basically polymeric particles comprising a polymeric resin as main component and various ingredients mixed with said toner resin. Apart from colourless toners, which are used e.g. for finishing function, the toner particles comprise at least one black and/or colouring substances, e.g., coloured pigment.
• the toner particles can be present in a liquid or in a dry developer composition.
• the images are built up by application of particulate marking elements in multiple, superimposed layers onto the substrate.
• the problems associated with multiple, superimposed layers of particulate marking particles that are in one way or another fixed on a substrate are manifold, not only with respect to image quality but also with respect to image stability and with respect to mechanical issues.
• EP-A 471 894, EP-A 554 981, US 4,828,950 and US 4,885,603 it has been disclosed to apply a layer of transparent toner particles on top of the toner image to provide better resistance to physical damage.
• a capsule toner having a core comprising a polymerizable compound, a polymerization initiator and other normal toner ingredients.
• the core is surrounded by a hard shell that breaks during the fixing step.
• the polymerizable compound is polymerized, in this particular disclosure, by low energy visible light.
• toner particles comprising a radiation curable compound, characterised in that said radiation curable compound having a Tg ⁇ 35 °C.
• toner particles to be used in electrostatographic printing apparatus have preferably a quite high mechanical strength in order to be able to withstand the mechanical influences (pressure, friction, etc) in the printing apparatus before and during development, it is important to preserve the mechanical strength of the toner particles.
• the radiation curable compound to be incorporated in toner particles according to this invention, comprises an oligomeric or polymeric compound instead of only monomeric compounds.
• a monomeric compound may be present in the mixture of radiation curable compounds, as long as the mixture of radiation curable compounds (i.e. a radiation curable composition) itself has a Tg ⁇ 35 °C.
• the oligomeric or polymeric radiation curable compounds have a Tg ⁇ 35 °C, preferably the Tg is larger than 40 °C.
• the radiation curable composition or compound can be added to the toner particles in addition to a toner resin and other toner ingredients. Due to the oligomeric or polymeric nature of the radiation curable compounds these compounds can also be used as sole toner resin.
• toner particles according to the present invention can be coloured (i.e. comprise a pigment or a dye) the toner particles of the present invention are especially useful when they are intended to form a clear finish layer on top of a toner image. When the clear toner particles according to the present invention are used to provide a clear finish layer on top of the image, an image with very even gloss is obtained.
• the word “clear” means herein not giving, in a wavelength range extending from 400 to 700 nm, a visible diffuse density, said visible diffuse density being defined as less than 15 % light reduction integrated over that wavelength range.
• An "image on a substrate” is, in the context of this invention, meant to include a substrate carrying human readable or/and machine readable text, a substrate carrying figures, a substrate carrying pictures (both coloured and monochromatic) as well as a substrate carrying a combination of at least two of the above.
• a clear finish layer can be useful on any toner image, but is especially useful when it is applied on top of a toner image showing different thickness in the image are mostly toner images made up by the overlay of several layers of different types of toner particles (e.g.
• Said clear finish layer can be produced by depositing said clear toner particles by an image-wise depositing step, a non-image-wise depositing step or a counter-image-wise depositing step. It is preferred that said clear toner particles are deposited either non-image wise (i.e. in a uniform layer over the whole surface of the substrate, having toner particles or not) or counter-image-wise. Counter-image-wise means that a thicker fixed clear finish layer is present in the lower thickness areas of the image and a thinner fixed clear finish layer is present in the higher thickness areas of the image.
• the image comprises both text and e.g. full-colour pictures
• the radiation curable groups are preferably curable by UV-light.
• Very useful radiation curable polymeric compounds, in toner particles for use in the present invention are UV curable solid epoxy resins with Tg ⁇ 35 °C as disclosed in EP-A 667 381.
• solid compositions (I) are described containing
• UV curable resins for incorporation in toner particles are powders based on unsaturated polyesters and polyurethaneacrylates
• a typical example of such a polymeric UV curable system is available through Hoechts High Chem, Hoechts-Sara Pero (Mi) Italy.
• Such a system comprises a solid unsaturated polyester resin under trade name ALFTALAT VAN 1743, having a Tg ⁇ 52 °C and an urethane adduct with acrylic functional groups under trade name ADDITOL 03546, having a Tg ⁇ 47 °C.
• ALFTALAT VAN 1743 having a Tg ⁇ 52 °C
• an urethane adduct with acrylic functional groups under trade name ADDITOL 03546, having a Tg ⁇ 47 °C.
• the properties of this system have be described in European Coating Journal n° 9/95 606-608 (1995).
• non-acrylate binder systems are useful in the present invention, e.g. a powder composed of a mixture of an unsaturated polyester resin in which maleic acid or fumaric acid is incorporated and a polyurethane containing a vinylether.
• a binder system has been developed by DSM resins of the Netherlands and the properties thereof have been described in European Coating Journal n° 3/96 115-117 (1996).
• a photoinitiator is present.
• Very useful initiators are sulphonium salts as e.g. triarylsulphonium salts, triarylsulphoniumhexafluorophosphate, benzophenones, etc.
• Typical very useful photoinitiators in the context of this invention are, e.g., 2-hydroxy-2-methyl-1-phenyl-propan-1-one, compound I, a mixture of compound I and compound II and compound III :
• the initiator photoinitiator
• the pair radiation curable compound and initiator in various combinations :
• the toner particles according to the present invention may comprise the radiation curable resins (radiation curable compounds or compositions) that preferably are UV-curable resins as sole toner resin, or the radiation curable resins may be mixed with other toner resins. In that case all toner resins, known in the art are useful for the production of toner particles according to this invention.
• the resins mixed with the radiation curable resins can be polycondensation polymers (e.g. polyesters, polyamides, co(polyester/polyamides), etc), epoxy resins, addition polymers or mixtures thereof.
• the toner particles not only comprise a compound carrying a radiation curable group, but further comprise a reactive group RGA being a member selected from the group consisting of epoxy groups, aldehyde groups, hydroxyl groups, carboxyl groups, mercapto groups, amino groups and amide groups.
• the toner particles can comprise e.g. a toner resin selected from the group described in table 1 or an epoxy resin and a UV curable solid resin (composition) with Tg ⁇ 35 °C.
• Chemical structure AV HV Tg Mn Mw 1. Polyester resin of terephthalic acid, ethyleneglycol and DIANOL 22 3 31.1 62 3.6 10 2. Polyester resin of fumaric acid and DIANOL 33 17 5.2 55 4.4 12 3.
• DIANOL 22 is a trade name of AKZO CHEMIE of the Netherlands for bis-ethoxylated 2,2-bis(4-hydroxyphenyl)propane.
• DIANOL 33 is a trade name of AKZO CHEMIE of the Netherlands for bis-propoxylated 2,2-bis(4-hydroxyphenyl)propane.
• the toner particles comprise further reactive groups RGA
• a substrate comprising a reactive group RGB, being a member selected from the group consisting of epoxy groups, aldehyde groups, hydroxyl groups, carboxyl groups, mercapto groups, amino groups and amide groups and being chosen such as to form a reaction pair with said reactive groups RGA.
• RGB reactive group
• This embodiment has the advantage that the resins comprised in the fixed image can be not only radiation cured but also thermally cross-linked and chemically attached to the substrate by chemical bonds.
• the substrate comprises reactive groups RGB and the toner particles comprise not only radiation curable compounds having a Tg ⁇ 35 °C, but also reactive groups RGA
• catalysers are e.g. acids (both organic and anorganic) and tertiary amines.
• Very suitable catalysers are p-toluenesulfonic acid, trimethylamine and triethylamine.
• Toner particles according to the present invention can be prepared by any method known in the art.
• This toner particles can be prepared by melt kneading the toner ingredients (e.g. toner resin, charge control agent, pigment, etc) and said radiation curable compounds. After the melt kneading the mixture is cooled and the solidified mass is pulverized and milled and the resulting particles classified. Also the "emulsion polymerisation” and “polymer emulsion” techniques for toner preparation can be used to prepare toner particles according to this invention.
• emulsion polymerization a water-immiscible polymerizable liquid is sheared to form small droplets emulsified in an aqueous solution, and the polymerization of the monomer droplets takes place in the presence of an emulsifying agent; such a technique is described e.g. in US P 2,932,629, US P 4,148,741, US P 4,314,932 and EP-A 255 716.
• Toner particles useful in this invention can have an average volume diameter between 1 and 50 ⁇ m, preferably between 3 and 20 ⁇ m. When the toner particles are intended for use in colour imaging, it is preferred that the volume average diameter is between 3 and 10 ⁇ m, most preferred between 3 and 8 ⁇ m.
• the particle size distribution of said toner particles can be of any type.
• Gaussian or normal particle size distribution either by number or volume, with a coefficient of variability (standard deviation divided by the average) ( ⁇ ) smaller than 0.5, more preferably of 0.3.
• Toner particles useful in this invention, can comprise any normal toner ingredient e.g. charge control agents, pigments both coloured and black, anorganic fillers, anti-slip agents, waxes, etc.
• charge control agents, pigments and other additives useful in toner particles, to be used in a toner composition according to the present invention can be found in e.g. EP-A 601 235.
• the toner particles can be used as mono-component developers, both as a magnetic and as a non-magnetic mono-component developer.
• the toner particles can be use din a multi-component developer wherein both magnetic carrier particles and toner particles are present.
• the toner particles can be negatively charged as well as positively charged.
• the present invention also includes a method for forming a toner image on a substrate comprising the steps of :
• the radiation curing can proceed on line, e.g, in the fusing station itself of an electrostatographic apparatus or in a station immediately adjacent to said fusing station.
• the radiation curing can proceed off-line in a separate apparatus wherein the fused layer of toner particles is heated again and irradiated with curing rays. It is important that the radiation (UV-) curing proceeds on the molten toner particles and while the toner receiving layer has some fluidity.
• said radiation curing proceeds at a temperature that preferably is at most 150 °, most preferably at most 120 °C. Therefore it is preferred to use toner particles, comprising a radiation curable compound having a Tg ⁇ 35 °C, that have a meltviscosity at 120 °C between 50 and 2000 Pas, preferably between 100 and 1000 Pas.
• meltviscosities mentioned herein are measured in a RHEOMETRICS dynamic rheometer, RVEM-200 (One Possumtown Road, Piscataway, NJ 08854 USA).
• 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 fluidity of the toner receiving layer at the temperatures mentioned above can be increased by incorporating waxes or "heat solvents” also called “thermal solvents” or “thermosolvents”in the toner receiving layer on the substrate.
• heat solvent in this invention is meant a non-hydrolysable organic material which is in solid state at temperatures below 50 °C but becomes on heating above that temperature a plasticizer for the binder of the layer wherein they are incorporated.
• plasticizer for the binder of the layer wherein they are incorporated.
• Useful for that purpose are a polyethylene glycol having a mean molecular weight in the range of 1,500 to 20,000 described in US-P 3,347,675.
• Said toner receiving layer may further comprise a binding agent or mixture of binding agents, also stabilizers, toning agents, antistatic agents, spacing particles (both polymeric or anorganic).
• the toner receiving layer may contain other additives such as free fatty acids, antistatic agents, e.g. non-ionic antistatic agents including a fluorocarbon group as e.g. in F 3 C(CF 2 ) 6 CONH(CH 2 CH 2 O)-H, ultraviolet light absorbing compounds, white light reflecting and/or ultraviolet radiation reflecting pigments, and/or optical brightening agents.
• Said step of depositing said clear toner particles can be an image-wise depositing step, a non-image-wise depositing step or a counter-image-wise depositing step, as described above.
• a step of depositing clear toner particles on the image is included, it is within the scope of this invention, although all toner particles may comprise a radiation curable resin, sufficient that only said clear toner particle comprise a radiation curable resin with Tg ⁇ 35 °C.
• the present invention also includes an apparatus for forming toner images on a substrate comprising :
• toner particles comprising a UV-curable resin and thus the means for radiation curing the toner particles comprise are means for UV-curing ( UV-light emitters as e.g. UV lamps).
• UV-light emitters as e.g. UV lamps.
• said means for fusing said toner images emit infrared radiation (are infra-red radiators) and said means for UV curing (e.g. one or more UV emitting lamps as, e.g. high pressure mercury lamps) are installed immediately after said fusing means so that the UV curing proceed on the still molten toner image.
• a combination of infra-red radiators (the means for fusing the toner particles) and UV emitting lamps (the means for radiation curing) in a single station (a fixing/curing station), so that the fusing and the radiation curing proceed simultaneously, is also a desirable design feature of an apparatus according to this invention.
• the apparatus according to the present invention can comprise if so desired, more than one fixing/curing station.
• the UV emitting means are preferably UV radiators with a capacity (an intensity) between 20 W/cm and 150 W/cm.
• the means for image-wise depositing toner particles can, in apparatus according to this invention, be direct electrostatic printing means (DEP), wherein charged toner particles are attracted to the substrate by an electrical field and the toner flow modulated by a printhead structure comprising printing apertures and control electrodes.
• Said means for image-wise depositing toner particles can also be toner depositing means wherein first a latent image is formed.
• said means for image-wise depositing toner particles comprise :
• Said latent image may be a magnetic latent image that is developed by magnetic toner particles (magnetography) or, preferably, an electrostatic latent image.
• an electrostatic latent image is preferably an electrophotographic latent image and the means for producing a latent image are in this invention preferably light emitting means, e.g., light emitting diodes or lasers and said latent image bearing member comprises preferably a photoconductor.
• the solidified mass was pulverized and milled using an ALPINE Fliessbettarnastrahlmühle type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (tradename).
• the average particle size of the separated toner was measured by Coulter Counter model Multisizer (tradename) was found to be 8.0 ⁇ m by volume.
• the toner particles were mixed with 0.5 % of hydrophobic colloidal silica particles (BET-value 130 m 2 /g).
• the preparation of the Yellow toner was repeated, but instead of 2 parts SICOECHTGELB PY13, 2 parts of CABOT REGAL 400 (carbon black, trade name of the Cabot Corp. High Street 125, Boston, U.S.A.) were used.
• the four toners, Y, M, C and K had a meltviscosity at 120 ° C of 250 Pas (measured as described above at a frequency of 16 Hz.
• the solidified mass was pulverized and milled using an ALPINE Fliessbettarnastrahlmühle type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (tradename).
• the average particle size of the separated toner was measured by Coulter Counter model Multisizer (tradename) was found to be 8.0 ⁇ m by volume.
• the clear toner CT had a meltviscosity at 120 °C of 195 Pas.
• the toner particles were mixed with 0.3 % of hydrophobic colloidal silica particles (BET-value 130 m 2 /g).
• Each of the above prepared toners were used to form carrier-toner developers by mixing said mixture of toner particles and colloidal silica in a 4 % ratio with silicone-coated Cu-Zn ferrite carrier particles having an average diameter of 55 ⁇ m.
• Full colour toner images were produced using a commercial CHROMAPRESS (a trade name of Agfa-Gevaert NV, Mortsel, Belgium). The images were covered with a layer of clear toner such that 0.9 mg/cm 2 clear toner was present. The fusing took place with radiant heat (a IR-lamp) at 120 °C and the fused tone layer was immediately, without cooling irradiated with a UV-lamp for 0.5 sec with a high pressure mercury lamp and intensity of 80 W/cm. A second image without UV-curing was also produced. The resistance of both images against solvents was tested by rubbing the image 10 consecutive times with a cloth soaked with MEK (methylethyleketone). The UV-cured image, whereas the non-cured image disappeared after rubbing once.
• CHROMAPRESS a trade name of Agfa-Gevaert NV, Mortsel, Belgium.
• the UV-cured image showed an even high gloss of more than 90 % when measured under an angle of 60 ° with a gloss measuring device (MINOLTA MULTI-GLOSS 268, trade name of Minolta, Osaka, Japan).

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Cited By (11)

Citations (7)

• 1997
  • 1997-06-27 EP EP19970201977 patent/EP0821281B1/de not_active Expired - Lifetime

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