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
  • G03G9/087—Binders for toner particles
  • G03G9/08784—Macromolecular material not specially provided for in a single one of groups G03G9/08702 - G03G9/08775
  • G03G9/08791—Macromolecular material not specially provided for in a single one of groups G03G9/08702 - G03G9/08775 characterised by the presence of specified groups or side chains
• • 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
  • G03G9/0804—Preparation methods whereby the components are brought together in a liquid dispersing medium
• • 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
  • G03G9/08702—Binders for toner particles comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08706—Polymers of alkenyl-aromatic compounds
  • G03G9/08708—Copolymers of styrene
• • 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
  • G03G9/08702—Binders for toner particles comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08726—Polymers of unsaturated acids or derivatives thereof
  • G03G9/08733—Polymers of unsaturated polycarboxylic acids
• • 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
  • G03G9/093—Encapsulated toner particles
• • 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
  • G03G9/093—Encapsulated toner particles
  • G03G9/09392—Preparation thereof

Definitions

• This invention relates to a method for the production of powder particles and the use of said particles as toner particles in the development of electrostatic or magnetic patterns or for use in direct electrostatic printing (DEP).
• 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.
• DEP direct electrostatic printing
• a stream of imagewise modulated toner particles is deposited directly onto a receiver material which can be either the final substrate or an intermediary member wherefrom the toner image is transferred on printing stock, e.g. paper.
• a receiver material which can be either the final substrate or an intermediary member wherefrom the toner image is transferred on printing stock, e.g. paper.
• DEP direct electrostatic printing
• Several embodiments of DEP are described e.g. in US-P 3,689,935, 4,743,926, 4,912,489, 5,038,322, 5,202,704, GB-P 2,108,432, DE-OS 3,411,948, published EP-A 266 960, and by Murata et al., in a paper presented at the Int. Conf. Applied Electrostatics (Bejing - China), 1993, p. 391-411.
• a latent magnetic image is formed in a magnetizable substrate by a patternwise modulated magnetic field.
• the magnetizable substrate must accept and hold the magnetic field pattern required for toner development which proceeds with magnetically attractable toner particles.
• 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 “touch-down” 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 application of mono-component magnetic and non-magnetic toner may proceed advantageously by brush or in a brush-like form.
• the toner particles may be applied as mono-component toner or may be transferred from a brush of magnetic carrier particles as disclosed in EP-A 675 417.
• the finely divided toner material forming a powder image is transferred from the image-forming substrate onto a final support sheet such as paper.
• the developer In order to get a high quality hard copy or print the developer must meet stringent requirements. It is for example important that the toner particles have a small average particle size and that the particle size distribution is narrow.
• toners with small average particle size makes it possible to achieve high resolution in the final image.
• PCT/EP 90/01027 it is taught how the reduction in average particle size of the toner particles from 11.3 ⁇ m to 4.5 ⁇ m improves the image resolution.
• a narrow particle size distribution of carrier and toner particles makes it easier to achieve a homogeneous spread of the electrical and/or magnetical properties over these particles.
• homogeneous spread is understood that each particle has the same electrical and magnetical properties regardless of its size.
• the shape of the toner particles is important for obtaining a high quality imaging system especially in fine detail (dot) printing.
• An identical shape preferably substantially spherical shape, is in favour of reproducible triboelectric charging and good toner powder flowability which results in reproducible development results.
• a smooth toner powder surface is preferred for equal charge distribution.
• the toner particles have to be sized through classification.
• the efficiency of this classification process is strongly determined by particle size. The smaller the particle size the less efficient the classification process. Toner particles with an average size of less than 5 ⁇ m and narrow size distribution are difficult to obtain and present a high production cost.
• polymer suspension a pre-formed polymer is dissolved in an appropriate organic solvent that is immiscible with water, the resulting solution is dispersed in an aqueous medium that contains a stabilizer, the organic solvent is evaporated and the resulting particles are dried.
• the "polymer suspension” process has an advantage over “emulsion polymerization” because any polymer, known for toner preparation can be used.
• the "polymer suspension” process can proceed with addition polymers as well as with polycondensation polymers, whereas the “emulsion polymerization” process is, inherently, restricted to the use of addition polymerizable monomers.
• silica particles can be used as dispersion (suspension) stabilizer as described in US P 4,833,060 and corresponding EP-A 334 095, where silica particles and a promoter are used to stabilize the suspension. After evaporation of the solvent, however, the silica particles stay adsorbed to the toner particles and thus impart hydrophilicity to the toner particles and under high humidity conditions may reduce the chargeability of the toner particles.
• the stabilizing solid polymer particles consist of a copolymer of :
• the degrees of freedom in the composition of the copolymer that is used are limited by the fact that the solid copolymer particles, used as dispersion stabilizer, have to be sufficiently hydrophilic in order to be dispersable in water but must remain oleophilic enough to be attached to the oleophilic droplets for keeping them stabilized in dispersion. Moreover, the oleophilicity of the solid copolymer particles should be kept sufficiently low for preventing the stabilizing copolymer particles to become dissolved in the oleophilic droplets containing the dissolved toner-resin polymer.
• the "polymer suspension" process for making toner particles with narrow particle size distribution would find more applications when the droplets of the solution of the polymer in an organic solvent could be stabilized in an aqueous medium with a stabilizer that, when necessary can be washed away easily or that, when it is desired to fine tune surface properties of the toner paricles, can easily be modified and permanently deposited onto the surface of the toner particles.
• a method for producing dry toner particles comprising the steps of :
• said water-soluble (co)polymer comprises either carboxyl or sulphonic acid groups or both in acid or salt form.
• said water-soluble (co)polymer is a (co)polymer of at least one addition polymerizable hydrophobic monomer and at least one addition polymerizable ionic monomer.
• said ware-soluble (co)polymer comprises at least one carboxyl group in the form of an ammonium salt or in the form of the salt of a lower alkyl tertiair amine.
• water-immiscible solvent has to be understood as a solvent that is insoluble in water at 20 °C or dissolves therein at that temperature for no more than 10 g per 100 ml of water.
• water-insoluble substance has to be understood a substance that is less than 5 g soluble in water at 20 °C.
• the glass transition temperature (Tg) has always been determined according to ASTM Designation : D 3418-82.
• the softening temperature mentioned has been determined according to the well known ring and ball method.
• a dissolved water-soluble (co)polymer comprising both hydrophobic and hydrophilic moieties as dispersion-stabilizer offers the advantage that after evaporation of the organic solvent said (co)polymer can be washed away easily with water without need of chemically corrosive liquids.
• said water-soluble (co)polymer By the proper choice of said water-soluble (co)polymer it is possible to make use of a simple change in the composition of the aqueous medium to influence its behaviour, e.g. dispersion power, and to control its adherence to the dispersed droplets and afterwards desorption so that it can be easily washed away once the polymeric core particles are formed. Said change can be a change in pH or change in ion-content whereby salting out effects can be obtained. It is possible to use the stabilizing water-soluble (co)polymer as a kind of charge controlling agent when the stabilizing (co)polymer is not washed away, but is precipitated onto the formed polymer particles. By a proper choice of water-soluble stabilizing (co)polymer (e.g.
• the triboelectric chargeability of the particles can be controlled by precipitating the water-soluble stabilizing (co)polymer onto the particles.
• Very useful polycondensation polymers are (co)polyesters, comprising sulphonic acid groups or carboxyl groups.
• Non-limitative examples of very useful (co)polyesters are :
• polyesters comprising other acid moieties than terephthalic acid moieties : e.g. it is possible to use fumaric acid, sebasic acid, adipic acid etc.
• Water-soluble (co)polymers being particularly suitable stabilizers for use in the toner preparation method of the present invention are addition (co)polymers of at least one hydrophobic monomer, e.g. styrene and an alkyl(meth)acrylate that are addition-polymerized with at least one addition polymerizable ionic monomer.
• This ionic monomer, for forming the stabilizing water soluble (co)polymer according to the present invention is preferably an ethylenically unsaturated mono- or dicarboxylic acid or anhydride.
• stabilizing water-soluble (co)polymers for use according to the present invention, it is preferred to use acrylic acid, methacrylic acid and crotonic acid as ethylenically unsaturated mono-carboxylic acids.
• dicarboxylic acids when dicarboxylic acids are used in the production of stabilizing a water-soluble (co)polymer, for use according to the present invention, it is preferred to use maleic acid, fumaric acid, itaconic acid and citraconic acid as well as half-esters and half-amides of these dicarboxylic acids.
• the carboxylic acid or sulfonic acid groups, of both the polyesters and the addition (co)polymers to be used as stabilizing (co)polymer according to the present invention are transformed in a corresponding water-soluble salt group e.g. alkali metal salt or more preferably an onium salt, said onium salt being most preferably either an ammonium or a tertiair ammonium salt.
• a corresponding water-soluble salt group e.g. alkali metal salt or more preferably an onium salt, said onium salt being most preferably either an ammonium or a tertiair ammonium salt.
• the acidic (co)polymers, both polycondensation and addition (co)polymers have preferably a total acid number in the range of 50 to 500.
• total acid number is understood the quantity of base expressed in milligrams of potassium hydroxide, that is required to neutralize all acidic constituents in 1 g of sample (ref. ASTM D 664-58).
• Suitable addition (co)polymers to be used as stabilizer (co)polymers in a method according to the present invention and transformed in their ammonium salt are co(styrene/acrylic acid), co(styrene/ethylmaleate/maleic acid); co(styrene/n-butylmaleate/maleic acid), co(vinylacetate/crotonic acid), and co(vinylacetate/crotonic acid/methylmethacrylate).
• Particularly preferred stabilizer (co)polymers are copolymers of vinyl acetate and crotonic acid (90/10 by weight) having a total acid number of 50 to 300, and copolymers of styrene and maleic acid anhydride having a total acid number of 250 to 500, both said copolymers being used, at least partially, transformed into their ammonium salt form.
• the most preferred water soluble (co)polymer for use as stabilizer for a polymer suspension according to the present invention is a styrene/ammoniummaleinate copolymer, particularly the copolymer showing a 50/50 mole ratio of styrene and ammoniummaleinate.
• the concentration of stabilizer (co)polymer in the aqueous medium containing the droplets of organic polymer(s) dissolved in the organic water-immiscible solvent may vary widely but is e.g. in the range of 0.5 and 20 % by weight (w/w) on the total liquid composition, although it is preferred that the stabilizing (co)polymer is present in the range of 1 to 10 % (w/w).
• water-solulbe polymers to stabilize the small droplets of toner resin in a water immiscible solvent lays in the fact that it can stabilize the suspension of the droplets in the absence of particulate stabilizers, as e.g. cross-linked polymer particles or silica.
• particulate stabilizers as e.g. cross-linked polymer particles or silica.
• the use of water-soluble polymers as stabilizers provides more degrees of freedom in adapting the surface of the toner particles to a specific use, than the use of particulate stabilizing materials.
• the organic water-immiscible solvent for dissolving said organic toner-resin polymers should have a high volatility so that it can readily be removed from the discontinuous phase droplets by evaporation.
• solvents are e.g. chloromethane, dichloromethane, trichloromethane, ethylene chloride, ethyl acetate, etc. or mixtures thereof.
• toner-resin polymers are used that are soluble in ethyl acetate that has a boiling point of : 77.15 °C at normal atmospheric pressure and is slightly miscible with water in that it can be dissolved for 8.6 g in 100 ml of water at 20 °C.
• the toner resin is the toner resin
• the method of the present invention i.e. toner preparation by the "polymer suspension” process wherein the droplets of the solution of a polymer (toner resin) are stabilized by a water soluble (co)polymer as defined above, is particularly well suited for making toner particles comprising at least one polycondensation polymer as toner resin and showing a narrow particle size distribution without the need for further classification of the particles.
• Polycondensation polymers useful as toner resins are polyesters, polyurethanes, polyamides, polycarbonates, epoxy resins and the like.
• polyesters examples include polyesters, but are not limited to, polyesters, but are not limited to, polyesters, but are not limited to, polyesters, polystyrene, polystyrene, polystyrene, polystyrene, polystyrene, polystyrene, polystyrene, polystyrene, polystyrene, polystyrene, polystyrene, polystyrenethacrylate, polystyrenethacrylate, polystyrenethacrylate, polystylene glycol dimethacrylate, polystyrenethacrylate, polystyrenethacrylate, polystyrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-styrene-
• Polyester resins have normally an outspoken negative triboelectric chargeability and are therefore normally used for the production of triboelectrically negatively chargeable toners either alone or in the presence of a negative charge controlling agent, e.g. CCA 7 being a Cr(III) complex having the structure given on page 159 of the already mentioned book "Chemical Technology in Printing and Imaging Systems”. Polyester resins obtain a considerable negative triboelectric chargeability through the presence of free carboxyl groups or acid anhydride groups.
• a negative charge controlling agent e.g. CCA 7 being a Cr(III) complex having the structure given on page 159 of the already mentioned book "Chemical Technology in Printing and Imaging Systems”.
• polyester resins may be used in combination with a positive CCA, e.g. a black nigrosine salt or colorless quaternary ammonium salt such as cetylpyridinium chloride (see page 160 of the above mentioned book).
• a positive CCA e.g. a black nigrosine salt or colorless quaternary ammonium salt such as cetylpyridinium chloride (see page 160 of the above mentioned book).
• polyesters for use as binder for toner particles prepared according to the present invention are linear polycondensation products of (i) difunctional organic acids, e.g. maleic acid, fumaric acid, terephthalic acid and isophthalic acid and (ii) difunctional alcohols such as ethylene glycol, triethylene glycol, an aromatic dihydroxy compound, preferably a bisphenol such as 2,2-bis(4-hydroxyphenyl)-propane called "bisphenol A” or an alkoxylated bisphenol, e.g. propoxylated bisphenol examples of which are given in US-P 4,331,755.
• difunctional organic acids e.g. maleic acid, fumaric acid, terephthalic acid and isophthalic acid
• difunctional alcohols such as ethylene glycol, triethylene glycol, an aromatic dihydroxy compound, preferably a bisphenol such as 2,2-bis(4-hydroxyphenyl)-propane called "bisphenol A” or an alkoxylated bisphenol, e.g. propoxyl
• polyesters are a linear polyester of fumaric acid and bis-propoxylated bisphenol A, having a melt viscosity of 180 Pa.s and a glass transition temperature (Tg) of about 50 °C.
• Tg glass transition temperature
• Such a linear polyester is commercially available under the tradename ATLAC T500 (ATLAC is a registered tradename of Atlas Chemical Industries Inc. Wilmington, Del. U.S.A.).
• toners suited for fixing by infra-red radiation to control the glass transition temperature and melting point to use therefor a mixture of polyesters or of an epoxy resin and at least one polyester as disclosed in EP-A 601 235, that is incorporated by reference.
• epoxy resins are linear adducts of bisphenol compounds and epichlorhydrin as described e.g. by D. H. Solomon in the book “The Chemistry of Organic Film Formers” - John Wiley & Sons, Inc, New York (1967) p. 180-181, e.g. EPIKOTE 1004 (EPIKOTE is a registered trade mark of the Shell Chemical Co).
• toner resin in the preparation of toner particles according to the present invention also addition homo- or copolymers of olefinic or acrylic monomers or mixtures that can be dissolved in water-immiscible solvent(s) can be used as toner resin.
• polymers serving as toner-ingredient binders can be found e.g. in US P 3,933,665 and US P 4,833,060.
• Toner-resins may have inherently already a high triboelectrical chargeability.
• toner-resins that have good inherent positive triboelectrostatic chargeability are silicone resins (see the triboelectric series given in the article "Physics of Electrophotography” in PHYSICS TODAY, May 1986, p. 51.
• Highly positively triboelectrically chargeable resins other than silicones are polymers containing amino groups and such polymers in which the amino groups wholly or partly are transformed into onium groups being organic cationic groups.
• Monomers containing amino groups for preparing such resins by addition polymerization are described e.g. in US-P 4,663,265.
• the concentration of the toner-resin in the water-immiscible solvent may range from 5 to 5O % by weight, preferably the concentration ranges between 10 and 30 % by weight.
• the method according to the present invention makes it possible to produce toner particles wherein the average size of the particles (on weight base)- is between 3 ⁇ m and 10 ⁇ m.
• the particle size distribution of the toner particles, prepared according to the present invention is basically normal, with possibly a positive skewness, and the variation coefficient of the distribution (standard deviation/average particle size) is lower than 0.4, preferably lower than 0.3.
• the method according to the present invention can be used to produce colourless as well as coloured (pigmented or dyed) toner particles.
• Various addenda which are normally present in electrographic toner particles can be dissolved or dispersed in the organic solution of the toner-resin, such as a colorant selected from a wide variety of dyestuffs and pigments and charge controlling agents (CCA's).
• CCA's charge controlling agents
• ingredients, coloring agents as well as charging agents have to be selected properly so as to remain in the dispersed phase, i.e. in the polymer-containing droplets, and not to diffuse into the aqueous phase or accumulate in the interface of organic droplets and the aqueous medium. Therefore, preferred are oleophilic ingredients or ingredients that can be oleophilized or hydrophobized by e.g. reaction with organophilic coupling agents such as fluorine-containing silane compounds as described e.g. in US-P 4,973,540. Other oleophilization agents are silanes and titanates described in same US-P. Using such compounds reactive hydrophilic groups of the chosen ingredients form reactive sites whereto oleophilizing groups are attached.
• the selected ingredients are first enveloped or coated with an oleophilic substance, e.g. a wax, perfluoro acid, fatty acid or derivatives thereof.
• an oleophilic substance e.g. a wax, perfluoro acid, fatty acid or derivatives thereof.
• Said polymeric particles can be composed of the same resin as the toner resin as well as one or more different resins.
• CCA's are disclosed e.g. in US P 4,263,389 US P 4,264,702 and WO 92/18908. These CCA's are present in low concentations, ranging from 0.1 to 0.3 % by weight, preferably from 0.2 to 1.5 % by weight on the total toner weight.
• Common toner compositions are colored although colorless toner particles may be used to control e.g. the gloss and/or mechanical resistance of fixed toner images (ref. e.g. published EP-A 486 235 and EP-A 081 887).
• Typical colorants and CCA's are disclosed in "Chemical Technology in Printing and Imaging Systems” edited by J.A.G. Drake - The Royal Society of Chemistry - Thomas Graham House, Science Park, Cambridge U.K. (1993), p.154-161.
• the toner particles contain in the resinous binder a colorant which may be black or has a color of the visible spectrum, not excluding however the presence of infra-red or ultra-violet absorbing substances and substances that produce black in admixture.
• the colorant is usually an inorganic pigment which is preferably carbon black, but is likewise e.g. black iron (III) oxide.
• Inorganic coloured pigments are e.g. copper (II) oxide and chromium (III) oxide powder, milori blue, ultramarine cobaltblue and barium permanganate.
• carbon black examples include 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.).
• a magnetic or magnetizable material in finely divided state is dispersed into the organic water-immiscible solvent containing the dissolved toner-resin polymer(s).
• the coloring pigments such as carbon black as well as the magnetic pigments may be precoated with an oleophilizing substance or have been reacted therewith as is the case for a magnetic iron oxide that through free hydroxyl groups can be linked to the above discussed silane oleophilizing agents and organic isocyanates.
• Suitable substances having magnetic character or obtaining such property are e.g. magnetizable metals including iron, cobalt, nickel and various magnetizable oxides, e.g. heamatite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), CrO 2 and magnetic ferrites, e.g. these derived from zinc, cadmium, barium and manganese.
• magnetizable metals including iron, cobalt, nickel and various magnetizable oxides, e.g. heamatite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), CrO 2 and magnetic ferrites, e.g. these derived from zinc, cadmium, barium and manganese.
• various magnetic alloys e.g. permalloys and alloys of cobalt-phosphors, cobalt-nickel and the like or mixtures of these.
• organic colored black dyes may replace partially or wholly carbon black, e.g. use is made of nigrosine type dyes that at the same time have positive charge control properties (ref. the above mentioned book “Chemical Technology in Printing and Imaging systems” p. 160 and US-P 4,525,445)
• Toners for the production of color images may contain organic dyes or pigments of the group of phthalocyanine dyes, quinacridone dyes, triaryl methane dyes, sulphur dyes, acridine dyes, azo dyes and fluoresceine dyes. A review of these dyes can be found in "Organic Chemistry” by Paul Karrer, Elsevier Publishing Company, Inc. New York, U.S.A (1950).
• EP-A 384 040 EP-A 393 252, EP-A 400 706, EP-A 384 990 and EP-A 394 563.
• the colorant is preferably present therein in an amount of at least 1 % by weight with respect to the total toner composition, more preferably in an amount of 1 to 10 % by weight.
• the dispersing of the toner-resin solution in the aqueous solution of water-soluble (co)polymer-stabilizer proceeds in an agitation device to yield fine droplets of the toner-resin(s) dissolved in the water-immiscible solvent.
• Any type of high shear type agitation device such as a colloid mill containing a fast rotating rotor in small mixing interspace can be used, or the suspension can be formed by ultrasonic agitation as described in EP-A 255 716.
• the stabilizer (co)polymer is removed on separating the solids from the liquid phase, e.g. by centrifuging, and washing the solid particles with water and centrifuging and removing liquid again. This procedure is repeated until all of the stabilizer (co)polymer is washed away. Normally said procedure is repeated four times.
• a change of the pH may assist in an easier washing away of the stabilizer (co)polymer, that comprises acidic groups. For example, an increase in pH to 8 has been found advantageous, preferably by adding ammonium hydroxide or introducing NH 3 gas into the aqueous phase. Volatile basic substances can be easily removed in the drying stage.
• the polymer particles are separated and dried and may be used as such as electrostatographic or magnetographic toner having their final composition and triboelectric chargeability.
• the chargeability of the toner particles prepared according to the present invention is the same as the chargeability of toner particles (comprising the same toner resin and ingredients) made by the classical melt-kneading, crushing and classification process.
• the method according to the present invention is also very suitable to produce core particles that will be used to form core-shell toner particles.
• the method of the present invention i.e. toner preparation by the "polymer suspension” process wherein the droplets of the solution of a polymer (toner resin) are stabilized by a water soluble (co)polymer as defined above, is particularly well suited for making spherical core particles comprising at least one polycondensation polymer as toner resin. Since all stabilizer has been washed away, there is between core and shell no third polymeric substance present. Therefore it is easier to fine-tune the properties (dielectric, melting, hardness, etc) of core-shell toner particles using core particles prepared according to the present invention.
• the (polymeric) stabilizing agent is hydrophilic and the core polymer hydrophobic.
• the stabilizer is not totaly washed away, a core with ambiguous surface properties is obtained : on the spots of the core surface still covered with stabilizer the surface is hydrophilic and the other spots of the surface are hydrophobic. This ambiguity in surface properties diminishes the compatibilty with and bonding strength of a shell polymer to said core.
• Another approach, for using the particles produced according to the present invention as “core”-particles in “core-shell”-particles, is to convert the stabilizer and/or precipitate the stabilizer totaly onto said the core particle and thus forming particles with unambiguous surface properties (the surface totaly covered with stabilizer). These particles can be used as such or as new core particles for further formation of core-shell particles.
• the water-soluble stabilizing (co)polymer is precipitated on to the particles, produced by the method according to this invention, by chemical reaction, e.g. acidification of the aqueous medium, the water-soluble (co)polymer adhering to the dispersed polymer particles can be transformed into a water-insoluble species that precipitates on the particles and gives dried toner particles with different properties than when the water-soluble stabilizing (co)polymer is washed away.
• Such can be done easily by acidifying (changing the pH of) an ammonium carboxylate containing (co)polymer in which the ammonium ion on acidification is replaced by hydrogen so that poorly ionizable -COOH groups giving rise to negative triboelectric chargeability are formed.
• Onium ions other than ammonium undergo a similar transformation. In the case above a combination of conversion and precipitation is used.
• a selection of water-soluble (co)polymers containing onium groups in the polymer backbone may be used to form on alkalinization (on changing the pH) poorly water-soluble polymers having amino-groups that may stand in equilibrium with a certian amount of hydroxyl (HO - ) groups and give rise to positive triboelectric chargeability.
• the same water-soluble stabilizing polymers as described hereinbefore can be used.
• the method according to the present invention is, as indicated above, also well suited to form particles with a clean surface with unambiguous surface properties.
• the water-soluble stabilizer (co)polymer can be washed away (leaving "naked” core particles), and a shell of another polymer, with e.g. a more hydrophobic character and better triboelectric chargeability, can be precipitated onto the "naked" core particles.
• homopolymer or copolymers may be used, e.g. any vinylic or acrylic homo- or copolymer that is soluble in aqueous alkaline medium, e.g. as ammonium salt, but becomes insoluble by dropping the pH.
• These polymers are in principle equivalent to the water-soluble stabilizing (co)polymers, described above, and are chosen, not so much on the basis of stabilizing action, but on the basis of properties directly relating to the qualities of toner resins.
• the polymer composition of said layer has a glass transition value (Tg value) larger than 50 °C, and a softening temperature lower than 170 °C, preferably in the range of 120 to 140 °C enabling relatively easily fusing e.g. with radiant heat or contact with hot roller of said composition.
• Tg value glass transition value
• the Tg is lower than the indicated value conglomeration of the toner particles and caking (sticking together) may take place resulting in inferior developing results.
• a too high softening temperature will give rise to insufficiently fixed (adherent) toner images.
• Addition copolymers of the following list A can be used advantageously for obtaining a hydrophobic shell material with indicated Tg and softening temperature controlled by molecular weight.
• the molecular weight of said polymers is directly proportional to the viscosity obtained therewith in aqueous ammonia medium. Useful results are obtained with polymer that in 10 % by weight solutions in aqueous ammonia medium have a viscosity at 20 °C in the range of 25 to 150 cP.
• Total acid numbers of said polymers are preferably in the range of 50 to 500, and their melting range comprising their softening temperature is preferably from 110 to 170 °C.
• an unmodified addition copolymer of styrene/maleic acid and a partial ester thereof, e.g. mono-ethyl- or n-butyl ester is used.
• the amount of maleic acid determines the balance between solubility in alkali and the hydrophobicity.
• Such addition copolymer exhibits enough solubility in alkaline aqueous solution thereof which solution is mixed with the initially obtained toner-resin containing particles (core particles) and the addition copolymer is precipitated thereon as a shell by acidifying the solution.
• An analogous technique is described in US-P 4,904,562. In ammoniacal aqueous medium the maleic acid units form with ammonia (NH 3 ) and likewise with primary amines (R-NH 2 ) through imidization a ring-closed ureido structure (-CO-NH-CO-).
• a (co)polymer that becomes soluble in alkaline aqueous medium and insoluble in aqueous acidic medium, to form a shell on the "naked" core particles
• a (co)polymer may be used (e.g. containing amino groups) that becomes soluble in acidic medium and precipitates in alkaline medium.
• Suitable copolymers containing amino groups in their backbone structure are listed in the already mentioned Table 1.
• the precipitation of the polymers, cited above, on the core particles, according to the present invention can easily change the chargeability of the core particle by the choice of the amount of acidic groups comprised in the polymer that is precipitated on the "naked" core particles, prepared according to the present invention.
• the initially obtained "naked” particles serving as core particles contain as toner-resin a polymer having free acid groups (e.g. non-esterified acid groups of a polyester) and said core particles are allowed to react in dispersed state at their surface with free amino groups of a dissolved shell-forming polymer which may be a copolymer containing amino groups as presented in the already mentioned Table 1.
• reaction amine salt groups are formed that may improve positive triboelectric chargeability of the toner particles.
• the initially obtained core particles contain as toner-resin a polymer having free amino groups and said core particles are allowed to react in dispersed state at their surface with a dissolved shell-forming polymer or (co)polymer having free acid groups.
• the initially obtained core particles contain as toner-resin a polymer having free amino groups, and/or hydroxyl groups, that may be phenolate groups.
• Suited amino group-containing polymers are those listed in Table 1. Suitable hydroxyl group-containing polymers are slightly saponified polyvinylacetate and polyesters having unreacted hydroxyl or phenolate groups.
• Said core polymers after having been freed from their organic solvent are allowed to react in dispersed state in aqueous medium at their surface with at least one water-soluble polymer containing reactive halogen, e.g. water-soluble (co)polymers including copolymerized vinylbenzyl chloride or ⁇ -chloroethyl acrylate as described e.g. in US-P 3,708,289.
• Liquid toner developers in which coatings of toner particles are linked chemically to core particles are described in US-P 4,663,265 whereto reference is made for exemplifying chemical reactions useful for chemically linking core and shell polymers in toner particles of the present invention.
• the thickness of the shell of precipitated or chemically reacted polymer may range from 20 nm to 1000 nm, but is preferably between 50 and 250 nm.
• composition of the surface of the triboelectric partner e.g.carrier particles
• the kind of resin(s) contained in the toner particles and or forming their surface together with the colorant(s) and optional charge controlling agent(s) determine the net charge sign and charge height acquired by the toner particles.
• Triboelectric chargeability of toner-carrier pairs can be properly determined using the triboelectric series given in the periodical PHYSICS TODAY/May 1986, p. 51.
• Carrier particles suitable for use in cascade or magnetic brush development are described e.g. in GB-B 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 50 to 300 ⁇ m.
• the carrier particles possess sufficient density and inertia to avoid adherence to the electrostatic charge images during the development process.
• the carrier particles can be mixed with the toner particles in various ratios, best results being obtained when about 1 part by weight of toner is mixed with about 10 to 200 parts of carrier.
• the shape of the carrier particles, their surface coating and their density determines their flow properties. Easily flowing carrier particles with spherical shape can be prepared according to a process described in GB-B 1,174,571.
• Very suitable carrier particles are describe in e.g. US-P 4,879,198 and US-P 5,336,580.
• the carrier particles have preferably an electric resistivity between 10 7 and 10 14 ohm.cm, and this resistivity is adjusted by the choice of the type and thickness of the polymer coating of the carrier particles.
• the present invention is not limited to the production of two-component toners but is directed as well to the production of triboelectrically chargable mono-component toners applied without carrier particles.
• a 10 % aqueous solution of co(styrene-maleic acid) (50/50 mole ratio) being for the larger part in ammonium salt form (pH 6) and having at 20 °C a viscosity of 120 mPa.s. From this solution 1400 g are added to 8600 g of distilled water is brought with acetic acid to pH 4.5. The diluted mixture has at 20 °C a viscosity of 5.6 mPa.s. That solution is called solution A and contains the dispersion stabilizer for the emulsion droplets of solution B.
• ATLAC T500 (ATLAC is a registered trade name of Atlas Chemical Industries Inc. Wilmington, Del. U.S.A. for a linear polyester of fumaric acid and propoxylated bisphenol A) was stirred into 8000 g of ethyl acetate at room temperature. The introduction of said polyester into the ethyl acetate proceeded in very small portions at the time. The viscosity of the obtained solution, being solution B, was 5 mPa.s at 20 °C.
• the predispersion C is completed in a bottle moved on a roller-table for 45 minutes.
• a first part of 0.5 liter of the predispersion C was brought into a supply vessel, and pumped therefrom into the mixing chamber of a COBAL MILL MS12 (tradename for a high shear mixing apparatus sold by Fryma Maschinen AG, Rheinfelden, Germany).
• the pump was desactivated and the rotor activated to make 1200 rpm for 15 s.
• the remaining part of the predispersion C was brought into the supply vessel.
• the pump was reactivated at a pumping rate of 760 ml/min and the rotor of the mixing chamber kept rotating. Once the supply vessel became empty the pump was desactivated but the rotor in the mixing chamber kept stirring for still 15 sec.
• the organic solvent, viz. the ethyl acetate, of the obtained emulsion droplets was evaporated at 50 °C under reduced pressure (about 50 kPa), while blowing air over the emulsion at that pressure to take away the solvent vapour. After about 8 hours the evaporation was completed and a dispersion of stabilized solid polymer particles in water was obtained. At this moment it is possible to measure average particle size and size distribution.
• the dispersion of particles was divided in recipients for fitting in a SORVALL RC2B (tradename of DUPONT - USA) sedimentation centrifuge and was centrifuged at 2000 rpm for 20 min. The supernatant fluid was decanted, and the sediment was washed with water. The supernatant liquid was flushed away with water. Thereupon, 100 ml of demineralized water were added and the suspension agitated with stirring rod. The sediment was then dispersed again in water an placed in an ultrasonic bath for 15 min, centrifuged at 4000 rpm, decanted and the sediment washed again with water. This procedure was repeated 3 times.
• MUNTERS LK (tradename of AB CALL Munters Torkan - Sweden) air stream dryer operating with air at 40 °C.
• the dry paste was introduced into a J + K mill (IKA UNIVERSALMUHLE M20, tradename), 0.5 % by weight of hydrophobic silica with BET surface of 260 m 2 /g (AEROSIL R812, tradename of Degussa, Germany) and sieved over a sieve of 40 ⁇ m hole diameter, giving toner particles 1 (TP1.)
• the toner charge after triboelectric contact with a coated ferrite carrier particles having a diameter of about 55 ⁇ m was measured with a commercial q/m-meter.
• the triboelectric charging was carried out with a toner concentration of 3 % on the total toner-carrier mixture.
• the result of said charge measurement expressed in ⁇ C/g is given Table 2 hereinafter.
• This charge was compared to the charge of toner particles with the same toner resin and ingredients as TP1, but prepared by a classical melt-kneeding method (TP2). From these values it can be seen that the chargeability of the two toners is equivalent and that thus the polymeric stabilizer is totaly washed away in a fairly simple washing step.
• the stabilizer was not washed away, but precipitated onto the particles by introducing after step 5 an acidifying step and then drying the particles, giving particles TP3.
• the particles size and the chargeability was measured as explained above and are mentioned in table 2. It is clear that by simply precipitating the stabilizing (co)polymer onto the particles the surface properties can largely be changed.
• SMA3000 (is a registered trademark of ATOCHEM North America. Inc) resin being a copolymer of styrene and maleic anhydride containing styrene units in a proportion of 3 with respect to maleic anhydride units in the number of 1, having a melting range of 115 to 130 °C, acid number 280 and viscosity at 30 °C of 15 % aqueous solution of 26 mPa.s, were brought into 1 liter of demineralized water. During continuous stirring 10 g of a 25 % aqueous ammonia solution were added. The mixture was brought to a temperature of 70 °C to obtain complete dissolution whereupon it was cooled down again to room temperature (20 °C).
• the dispersion of particles was divided in recipients for fitting in a SORVALL RC2B (tradename of DUPONT - USA) sedimentation centrifuge and was centrifuged at 5000 rpm for 20 min. The supernatant fluid was decanted, and the sediment was washed with water. The supernatant liquid was flushed away with water. Thereupon, 100 ml of demineralized water were added and the suspension agitated with stirring rod. The sediment was then dispersed again in water an placed in an ultrasonic bath for 15 min, centrifuged at 5000 rpm, decanted and the sediment washed again with water. This procedure was repeated 3 times.
• MUNTERS LK (tradename of AB CALL Munters Torkan - Sweden) air stream dryer operating with air at 40 °C.
• the dry paste was introduced into a J + K mill (IKA UNIVERSALMUHLE M20, tradename) for 20 sec treating the particles and mixing with 0.5 % hydrophobic silica with BET surface of 260 m 2 /g (AEROSIL R812, tradename of Degussa, Germany) to improve the flow of the dried toner powder, which after passing a wind sifter was sieved over a sieve of 40 ⁇ m hole diameter (TP4).
• a J + K mill IKA UNIVERSALMUHLE M20, tradename
• AEROSIL R812 tradename of Degussa, Germany

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