Patent Publication Number: US-3876610-A

Title: Manufacture of an electrostatic toner material

Description:
United States Patent [1 1 Timmerman et al.  
 1 1 Apr. 8, 1975 MANUFACTURE OF AN ELECTROSTATIC TONER MATERIAL [75] Inventors: Daniel Maurice Timmerman,  
 Mortsel; Jozef Leonard Van Engeland, Saint Katelijne-Waver; N051 Jozef De Volder, Edegem; August Jean Van Paesschen, Antwerp, all of Belgium [73] Assignee: Agfa-Gevaert N.V., Mortsel.  
 Belgium [22] Filed: June 29, 1973 [21] Appl. No.2 374,973  
 Related US. Application Data [63] Continuation of Ser. No. 58.176. July 24. 1970.  
 &#39; abandoned.  
 [30] Foreign Application Priority Data July 25. 1969 United Kingdom 37488/69 [52] US. Cl 260/42.2l; 8/41 R; 252/621.  
 260/33.4 R; 260/33.4 PO: 260/33.6 R;  
 [51] Int. Cl C08f 45/66; C08f 45/70; 003g 9/02 [58] Field of Search 260/4l.5 A. 41.5 R. 879. 260/880. 93.5 R. 41 A. 41 B. 41 C, 42.21,  
 [56] References Cited UNlTED STATES PATENTS 2.732.382 1/1956 Mensk 260/379 3.364.186 1/1968 Wilhelm.... 160/8072 3.502.582 4/1970 Clemens 252/62.1  
 3.511.895 4/1970 Kydonicus 260/876 3.526.533 9/1970 Jacknow 260/31.8 X 3.538.191 11/1970 Meredith 260/878 3.538.193 11/1970 Meredith 260/878 Primary E.\&#39;aminerDonald E. Czaja Assistant Examiner-H. H. Fletcher Attorney. Agent, or Firm-William .1. Daniel [57] ABSTRACT 17 Claims, No Drawings MANUFACTURE OF AN ELECTROSTATIC TONER MATERIAL This is a continuation of Ser. No. 58.176, filed July 24, 1970, and now abandoned.  
  The invention relates to the manufacture of an electrostatic toner material consisting of finely divided pigmented resinous powder.  
  It is known to convert latent electrostatic images into visible images by means of a toner consisting of minute particles of a material. usually a resin which mostly is coloured and possesses definite triboelectric properties. Depending on the electrostatic charge the resin particles are either attracted and deposited on the charged areas of the latent image, or are repelled by the charged areas and deposited on the discharged places. Such an operation is called the development of the latent electrostatic image.  
  The developer is composed of two components, the finely ground pigmented resinous toner and a relatively large granular carrier material having particle diameters of about 0.3 to 1.0 millimeter. For developing the latent image, the developing mixture is merely cascaded over the exposed plate. The carrier, e.g. glass beads, which either or not are enveloped by a resinous filmforming product, little metal spheres, etc. bear the toner as it cascades over the plate and alsocharges the toner particles to the correct polarity by frictional electrification. As a toner-laden carrier particle passes over an electrical discontinuity in the surface of the plate it is attracted to the plate on the image area.  
  Generally, the toners have been prepared by thoroughly mixing thermoplastic resins and colouring materials. The blend is then allowed to solidify by cooling and is subsequently ground to the final particle size by jet pulverization. A powdered material having a relatively irregular particle shape and size is obtained. This is a disadvantage, which results in a non-uniform triboelectric relationship between the particles and their carriers, and tends to produce a non-uniform relationship between the toner particles and the applied electrostatic field.  
  The present invention provides a method of preparing electrophotographic toner particles grown to the desired size by a special manufacturing method, namely a graft-polymerization process carried out in an organic solvent.  
  According to the invention an electrostatic toner material is provided consisting of finely divided resin particles and a colouring material, characterized thereby, that the resin particles are manufactured by polymerization of a mixture consisting of:  
  a. a solution in an inert organic solvent in a concentration of 15 to 85 by weight of at least one a,B-ethylenically unsaturated monomer, the polymers of which are insoluble in said inert organic solvent,  
  b. l to l by weight with respect to the monomer(s) present of a non-ionic polymer, which is also soluble in said inert organic solvent, and  
  c. 0.1 to by weight with respect to the monom er(s) present ofa free radical-forming polymerization initiator, said polymerization being carried out at a temperature between and 150C under continuous stirring until graft-copolymers of said monomer(s) and of said nonionic polymer are obtained, which graft-copolymers are insoluble in said inert organic solvent and have a particle size of from 1 to 10 ,u.  
  Before the beginning of the polymerization the reaction medium mainly consists of a homogeneous solution in an inert organic solvent of:  
  a non-ionic, preferably hydrophobic polymer,  
  a monomer or a mixture of monomers that can be grafted onto the non-ionic polymer, and  
  a free-radical forming polymerization initiator.  
  By heating the reaction medium the dissolved initiator decomposes under the formation of radicals. The thermally formed radicals react with the dissolved polymer either via a labile hydrogen atom or via a reactive position so as to form macroradicals. These macroradicals, dissolved in the inert organic solvent, encounter either reactive monomers or already growing polymer chains which are grafted onto the excited positions of the original polymer. In this way graft-copolymers are formed the composition of which is the following:  
  a small part (1 to l0 7c) of original polymer,  
  a large part to 99 7c) of polymer chains grafted onto the originally dissolved polymer.  
  These grafted polymer chains consist either of homogeneous chains if originally only one kind of monomer was present, or of heterogeneous chains composed according to the reactivity parameters of the various monomers present. ln addition to this graft-copolymerization, especially in an advanced stage of the polymerization process, in most cases a polymerization of the monomers present takes place simultaneously.  
  By a suited choice of the organic solvent for monomer(s), polymerization initiator and non-ionic polymer, which is a non-solvent for the graft-polymers formed, and occasionally for the non-grafted polymers of the monomer(s) present, finally a dispersion in an organic phase of small polymer particles is obtained. It is a mixture of graft-copolymer mainly being present in the outer envelope and of non-grafted(co)polymers especially being present in the nucleus. The tiny polymer spheres are agglomerates sizing meanly between 1 and 10 t.  
  If on the contrary the monomer(s) were polymerized in water according to a known emulsion polymerization technique, polymer particles would be obtained possessing a diameter that normally is comprised between 0.05 and 0.l ,u and thus would be useless for electrophotographic purposes.  
  In order to form a good toner, the tiny polymer spheres as a result of a proper choice of monomer(s) and non-ionic polymer should meet the following demands:  
  they should be of regular shape and size between 1 and 10 p. in order to yield a good image sharpness,  
  they should be sufficiently triboelectrically negative in respect of the carrier, preferably in the same order of magnitude as polystyrene is, and  
  possess good mechanical properties.  
  In contrast with the irregular, disrupted structure shown by mechanically ground toner powder, small, very regular polymer spheres are obtained by a proper choice of non-ionic polymer, monomer(s) and organic solvent and by a graft-copolymerization according to the invention, which spheres possess a diameter comprised between 1 and l0 p.. Such particles yield extremely sharp images.  
  The electrostatic as well as the mechanic demands the polymer particles should meet, directly determine the choice of the monomer(s). This monomer or these monomers, of which the resulting polymer spheres consist for 90 to 99 7: by weight, determine the insolubility of the final graft-copolymer and thus also the choice of the organic phase. This organic phase before polymerization is a solvent for the non-ionic polymer and the monomer(s) and after polymerization is a non-solvent for the graft-copolymer formed. If these conditions are taken into account. relatively non-polar organic liquids can be used as inert organic solvents such as aliphatic. cycloaliphatic or aromatic hydrocarbons, e.g. nhexane. heptane. decane, cyclohexane and white spirit, alcohols such as ethanol and long-chain alcohols, higher fatty ketones such as hexanone. and higher fatty esters. as well as mixtures thereof.  
 The non-ionic polymer should:  
  be sufficiently reactive in order to be capable of forming radical graft-copolymers with the monomers present.  
 - be non-ionic and preferably hydrophobic, and  
  be soluble in the organic phase, which has been chosen with respect to the composition of monomer(s) used.  
  If the solvent phase consists of hydrocarbons a choice can be made between poly(n-butyl methacrylate), poly(isobutyl methacrylate). low molecular weight polyhutadiene and low molecular weight polyisoprene (the high molecular weight polymers mostly are insoluble in hydrocarbons because of their branched structure polyisobutylene, copolymers of styrene and butadiene. copolymers of ethylene and vinyl acetate. copolymers of oz-olefines and N-vinylpyrrolidone. copolymers of vinyl acetate and vinyl laurate, copolymers of vinyltoluene and n-butyl acrylate or n&#39;-butyl methacrylate and polystyrene having a molecular weight beneath I000 (also because higher molecular weight polystyrene is insoluble in hydrocarbons). lf alcohols are taken the choice is more limited. Here poly-N- vinylpyrrolidone. polyethylene oxide. ethylcellulose and copolymers of ethyl acrylate and no more than 7r by weight of butadiene are satisfactory.  
  The desired electrostatic properties require that the graftcopolymer is composed in such a way that it shows in respect of the carrier a tribo-electric negativity which approximates that of polystyrene. A classification of polymers according to their triboelectric properties is given in Nature, 196 (1962) 474.  
 . lf the graft-copolymer possesses too high a triboelectric negativity in view of the carrier, the toner powder particles strongly adhere to the carrier particles during development of the electrostatic pattern and an image is obtained. which is too faintly coloured. If the triboelectric negativity is too small in respect of that of the carrier, an image is formed, which is fogged as a result of smudging of the photographic layer. As a matter of fact. a suitable combination of low triboelectrically negative and high triboelectrically negative monomers leads to the desired level.  
  The toner particles should be highly resistant against mechanical deformation and be sufficiently low melting in order to secure a good fixability. Hence. the graft-copolymer should possess a glass transition temperature of at least 40C, preferably between 40 to 50C, and a melting point between 80 and l50C. This requirement is met by an accurate ratio of hard polymer to weak polymer. The glass transition temperature and thus also the brittleness of the graft copolymer increase with growing content of monomers such as styrene, vinyltoluene and homologues, chlorostyrene,  
 methyl methacrylate. ethyl methacrylate, and propyl methacrylate. acrylonitrile, methacrylonitrile and vinyl chloride. With an increasing content of alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl methacrylate and higher methacrylates. butadiene, isobutylene, chlorobutadiene, 2-methylbutadiene, and vinylidene chloride, the toner powder will become weaker and thus tougher.  
 A combination of monomers will thus fulfil the expectations if:  
  the balance of its triboelectric negativity in respect of the carrier assures good developing properties,  
  the brittle and hard monomer components are mixed in such a ratio that they secure good mechanical properties.  
  the chosen monomer(s) in a radical initiated polymerization are sufficiently reactive in order to form graft-copolymers with the non-ionic polymer.  
  The polymerization initiator forming free radicals on heating is present in an amount comprised between 0.1 and 5 by weight based on the amount of monomer(s) present.  
  In principle any polymerization initiator known in the art and forming free radicals upon heating may be used.  
 such as organic peroxides, e.g. benzoyl peroxide,  
 methyl ethyl ketone peroxide, cyclohexanone peroxide, di-tert.-butyl hydroperoxide, lauroyl peroxide, capryloyl peroxide, and diacetyl peroxide, azo compounds such as azo-bis-isobutyronitrile, inorganic peroxides such as hydrogen peroxide and ammonium persulphate, dialkyl peroxide carbonates such as diisopropyl peroxide carbonate; and redox catalysts such as di tert.-butyl hydroperoxide and tetraethylenetetramine.  
  The initiators are chosen depending on their temperature of decomposition and the desired temperature of polymerization, but especially depending on the nonionic polymer chosen on which grafting will be carried out. For instance, azo-bis-isobutyronitrile, because of its insufficient reactivity cannot be used for grafting on polybutadiene, polyisoprene, copolymers of butadiene or isoprene, polyvinyl chloride and copolymers of vinylchloride. For this purpose more energetic phenyl or benzoyl radicals originating from benzoyl peroxide or cumene hydroperoxide are needed.  
  On the contrary, for a grafting by addition on double bonds such as eg on polyester of unsaturated dibasic acids (maleic acid, fumaric acid, and itacohic acid) with saturated dibasic alcohols, or such as on disproportionated polyalkyl methacrylates, the less reactive radicals originating from azo-bis-isobutyronitrile or dialkyl peroxide can be used indeed.  
  Taking into account the aforesaid one can use methyl ethyl ketone peroxide or cyclohexanone peroxide for polymerizations at temperatures between 30 and 50C, benzoyl peroxide and azo-bis-isobutyronitrile for polymerizations at temperatures between 60 and C, and di-tert.-butyl hydroperoxide for polymerizations carried out above C.  
  When the above described combination of solvent, monomer, nonionic polymer and polymerizationinitiator are heated to the decomposition temperature of the initiator with thorough stirring. the formed radicals induce the polymerization of the monomer(s)- present. Doing so, graft-copolymers of the non-ionic polymer present are formed.  
  That actually graft-copolymers are formed indeed can be shown very easily by extraction of the formed copolymers with solvents for the non-ionic polymer present at the beginning of the reaction. No pure nonionic polymer is extracted anymore. By an elemental and an infrared analysis of the extracted copolymer the grafting on the non-ionic polymer is shown clearly.  
  With certain high reactive monomers. thus in cases that the toner particles might grow too large, chaintransfer agents or polymerization retarders can be added to the graft-copolymerization medium. In this way further polymerization on the particles can be reduced or eliminated so as to obtain a dispersion of graftcopolymers of reduced molecular weight and of narrow molecular weight distribution. Suitable chain transfer agents or retarders are alkyl mercaptans, allyl compounds such as allyl alcohol and terpene derivatives such as allocimene and myrcene.  
  Separation of the polymer particles after graft-copolymerization can occur according to methods known in the art, e.g. by spray-drying. Other separation methods can be used too. e.g. an evaporation of the organic solvent. But in this case there is some danger of agglomeration of the polymer particles, which necessitates an additional fine grounding of the material.  
  Then the polymer particles have to be coloured. The pigment or dyestuff (colouring material) has to be present in the toner in an amount, which suffices for strongly colouring the toner, so that a clearly visible image is obtained. Usually the pigment is a black pigment e.g. carbon black. In cases wherein a colour copy is desired, organic pigments or dyestuffs can be used. Usually the colouring material is used in an amount comprised between 0.1 and 7t by weight with respect to the total weight of the toner mass. The best way for mixing the polymer with the colouring material chosen is ball-milling.  
  An especially effective method for accepting the colouring material consists in carrying out the graft-polymerization in the presence of dissolved dyestuff or dispersed pigment. ln that case the polymer envelops the pigment or dyestuff.  
  A most valuable method for adding the colouring material consists in building in into the graft-copolymer. For this purpose dyestuffs or colour couplers are used, which can be copolymerize by a radical mechanism via built-in unsaturated bonds. With radically polymerisable dyestuffs a coloured graft-copolymer is obtained directly, whereas with monomeric colour couplers the finally formed graft-copolymer obtains its desired colour only by a suitable treatment after polymerization.  
  By the term colour couplers chemical compounds are understood having built-in unsaturated polymerizable bonds, which chemical compounds may be coloured by a suitable chemical reaction, e.g. by an oxidative coupling or a coupling resulting in the formation of an azo dyestuff. This chemical treatment normally takes place after the polymerization reaction, so that finally coloured graft-copolymers are obtained.  
  On development of electrostatic imagesthe toner is loosely applied to the latent electrostatic image in the form of a covering layer, wherein the toner remains loosely bound by electrostatic attraction. The most usual developing method is cascade development. According to this method the electrostatic toner is mixed with a grainy carrier which may be electrically conductive or insulating The grainy carrier particles, when brought in close contact with the powdery toner particles, obtain a charge of a polarity opposed to that of the toner particles, so that the latter envelop the grainy carrier particles. If a positive reproduction of an electrostatic image is desired, the carrier is chosen in such a way that the toner particles obtain a charge with a polarity opposite to that of the electrostatic image. In order to obtain a negative copy the carrier can be chosen in such a way that the toner particles obtain a charge having the same polarity as that of the electrostatic image.  
  The carrier particles have to be large enough and in all events have to be larger than the toner particles. They have such a shape, that they roll over the imagecarrying surface. On the charged areas of the surface the toner particles are attracted and separated from the carrier particles, which due to gravity continue their rolling motion.  
  The toner particles are fixed on paper or any other support by heat or solvent fixing. As heat energy or sol- -vent is added to the toner, the toner softens, tends to become more fluid, flows together and is ineversibly attached to the paper film.  
  The manufacture of graft-copolymers according to the invention is illustrated by the following preparations.  
 preparation 1: Graft-copolymer of methyl methacrylate and polybutadiene In a reaction flask equipped with a stirrer, a reflux condenser and a nitrogen inlet 7.5 g of polybutadiene having a molecular weight of 5500 were dissolved at C in g of white spirit. To this solution were added successively 200 g of white spirit, g of methyl methacrylate,, 6 g of laurylmercaptane and 3.25 methacrylate, of benzoyl peroxide. The mixture was heated to 80C. The polymerization was exothermic and the temperature rose to 90C.  
  A few minutes after the beginning of the exothermic phase, the solution became turbid and after 10 min of polymerization a milky suspension of polymethyl methacrylate particles was obtained carrying on their surface envelopes of polybutadiene grafted thereon. The exothermic phase lasted some 10 minutes, whereupon heating was regulated in such a way, that the temperature of the suspension was maintained at 85C. After a reaction time of 16 h at this temperature a dispersion was obtained which was filtered through nylon cloth whereby a dispersion was obtained containing 27.8 g of solid matter for every 100 g of dispersion. Total yield of graft-copolymer: 130.8 g having an intrinsic viscosity measured in butanone at 25C of 0.12 dl/g. Melting point: C. Size of the graft-copolymer particles was comprised between 2 and 5 p..  
 Preparation 2: Graft-copolymer of styrene, methyl methacrylate and polybutadiene In a reaction flask 3.75 g of polybutadiene (molecular weight: 5500) were dissolved at 80C in 50 g of white spirit. To this solution were successively added 100 g of white spirit, 60 g of methyl methacrylate, 15 g of styrene and 1.625 g of benzoyl peroxide.  
  The solution was heated with stirring to 85C. As the polymerization was slightly exothermic, the temperature of the solution rose to 90C. This solution became turbid some l0 min. after the beginning of the exothermic phase, and 20 min. later a milky dispersion formed. After 30 min. of polymerization the temperature of the dispersion was maintained at 85C.  
  After 16 h of polymerization, the mixture was cooled with stirring and filtered through nylon cloth. Per 100 g of dispersion 33.4 g of solid matter was present. Total yield: 78.2 g of graft-copolymer having an intrinsic viscosity of 0.224 dl/g.  
  Melting point: 134C. Particle size: comprised between 4 and 7 ,u.  
 Preparation 3 Preparation 2 was repeated with the difference. however, that 37.5 g of styrene and 37.5 g of methyl methacrylate were allowed to react.  
  The reaction time was shortened to h 45 min. Yield: 230 g of dispersion containing 74.75 g of solid matter. Particle size between 2 and 5 u. Intrinsic viscosity: 0.23 dl/g. Melting point: 150C.  
 Preparation 4 Preparation 2 was repeated with the difference, however, that the quantity of monomer of preparation 3 was taken but that n-hexane was chosen as solvent. Yield: 224 g of dispersion containing 77.728 g of solid matter. lntrinsic viscosity: measured at 25C in tetrahydrofuran: 0.35 dl/g. Melting point: 150C. Particle size: comprised between 2 and 5 ,u..  
 Preparation 5 1n a reaction flask equipped with a stirrer. a reflux condenser and a nitrogen inlet 18.75 g of low molecular weight polybutadiene were dissolved in 750 g of nhcxane. The solution was refluxed until a homogeneous solution was obtained, while a nitrogen current was bubbled through the solution.  
  To the latter were successively added 187.5 g of methyl methacrylate, 187.5 g of styrene and 8.125 gof benzoyl peroxide. The mixture was stirred and refluxed. This polymerization is slightly exothermic and after about 1 h of refluxing the first turbidity arose. After a total reaction period of h and 30 min. a milky suspension was obtained. each 100 g part of which contained 34.5 g of solid matter. Total yield: 1 104 g of dispersion containing 381 g of graft-polymer. Intrinsic viscosity measured at 25C in tetrahydrofuran: 0.32 dl/g. Melting point: 158C. Glass transition temperature: 49C. Particle size: between 2 and 5 1..  
 Preparation 6: Graft-copolymer of styrene, acrylonitrile, methyl methacrylate and poly(n-butyl acrylate) I In a reaction flask equipped with a stirrer, a nitrogen inlet and a reflux condenser 18.75 g of poly(n-buty1 acrylate) were dissolved at room temperature in 750 g of n-hexane. To this solution were added 187 g of distilled styrene, 93.75 g of distilled acrylonitrile, 93.75 g of methyl methacrylate and 8.125 g of benzoyl peroxide.  
 With stirring and while a gentle nitrogen current was led through the solution, the latter was brought at reflux temperature. The polymerization was little exothermic. After 16 h the dispersion was cooled to 25C. In the dispersion some 20 g of agglomerate formed, which were filtrated through nylon cloth and rinsed with some n-hexane. Yield: 1141 g of dispersion containing 358.5 g of solid matter. Intrinsic viscosity of&#39;the graft-copolymer measured in tetrahydrofuran at C: 0.91 dl/g. Melting point: about 208C. Particle size: comprised between 0.5 and 2 a.  
 Preparation 7 Preparation 6 was repeated but with the following ingredients:  
 poly-(n-butyl acrylate) 37.5 g n-hexune 2.5 l styrene 187 g acrylonitrile 93.75 g methyl methacrylate 93.75 g benzoyl peroxide 18.75 g  
  The mixture was brought to reflux temperature and the reaction time amounted to 20 hours. Yield: 2051 g of dispersion containing 402 g of solid matter. Intrinsic viscosity measured at 25C in tetrahydrofuran: 0.66 dl/g. Particle size: about 1 1..  
 Preparation 8: Graft-copolymer of styrene, acrylonitrile, methyl methacrylate, and the copolymer of styrene and butadiene In a reaction flask equipped with a stirrer, a nitrogen inlet and a reflux condenser 18.75 g of copolymer of styrene and butadiene containing mole of butadiene and having a molecular weight of 10,000 to 15,000 were dissolved in 750 m1 of n-hexane.  
  This solution was brought to room temperature, while the following ingredients were added: 187.5 g of distilled styrene, 93.75 g of methyl methacrylate, 9375 g of distilled acrylonitrile and 8.125 g of benzoyl peroxide. The reaction mixture was refluxed while nitrogen was bubbled through. In the beginning a clear solution 4 copolymer of styrene and butadiene (20:80 mole 7:) 18.75 g styrene 187.75 g methyl methacrylate 93.75 g acrylonitrile 93.75 g azo-bis-isobutyronitrilc 18.75 g nhexane 750 g Yield: 1065 g of dispersion containing 386.6 g of solid matter. Particle size of the graft-copolyrner: comprised between 1 and 2 p Intrinsic viscosity of the graft-copolymer measured in tetrahydrofuran at 25C: 0.96 dl/g.  
 Preparation 10 Preparation 8 was repeated but with the following ingredients:  
 copolymer of styrene and butadiene (20:80 mole /z) 18.75 g styrene 187.5 g methyl methacrylate 93.75 g acrylonitrile 93.75 g benzoyl peroxide 1.875 g n-hexane 500 g Yield: 1012 g of dispersion containing 389.62 g of solid matter. Particle size of the graft-copolymer: comprised between 1 and 2 ,u.. Intrinsic viscosity measured in tetrahydrofuran at 25C: 0.82 dl/g. Melting point:  
 Preparation 1 1: Graft-copolymer of styrene. acrylonitrile and the copolymer of styrene and butadiene In a reaction flask equipped with a stirrer. a nitrogen inlet and a reflux condenser 18.75 g of copolymer of styrene and butadiene (:80 mole 7() were dissolved in 750 ml of n-hexane. While the mixture was stirred at room temperature 281.25 g of distilled styrene. 93.75 g of distilled acrylonitrile and 8.125 g of benzoyl peroxide were added. A nitrogen current was bubbled through the solution. which was refluxed with stirring. After 16 hours of reaction a viscous milky dispersion was obtained. Yield: 1454 g of dispersion containing 399.95 g of solid matter. Particle size: comprised between 0.5 and 2 ,u.. Intrinsic viscosity measured at C in tetrahydrofuran: 1.22 dl/g. Melting point: 190C.  
 Preparation 12: Graft-copolymer of styrene. methyl acrylate and polybutadiene.  
  In a reaction flask equipped with a stirrer, a nitrogen inlet and a reflux condenser 3.57 g of polybutadiene (molecular weight: 5500) were dissolved in 150 g of nhexane. The solution obtained was refluxed until a homogeneous solution was obtained. while nitrogen was bubbled through. To this solution were added successively: 37.5 g of methyl acrylate. 37.5 g of styrene and 1.62 g of benzoyl peroxide. After min. of polymerisation the first turbidity appeared. After 20 hours of refluxing a low viscous dispersion was obtained. Yield: 210 g containing 75.6 g of solid matter. Particle size: about 2 u. Intrinsic viscosity at 25C measured in butanone: 0.27 dl/g. Melting point: about 135C. Glass transition temperature: 49C. If the same reaction was carried cut in the absence of non-ionic polymer (polybutadiene) no dispersion but a tacky residue was obtained.  
 Preparation 13: Graft-copolymer of styrene. methyl acrylate and the copolymer of styrene and butadiene.  
  In a reaction flask equipped with a stirrer. a nitrogen inlet and a reflux condenser. 5 g of low molecular copolymer of butadiene and styrene (80:20 mole 7r) were dissolved at room temperature in 400 g of n-hexane. With stirring and while a nitrogen current was bubbled through the solution. 140 g of distilled styrene, 60 g of methyl acrylate and 6 g of benzoyl peroxide were added successively.  
  This solution was refluxed and after about 1 hour the first turbidity arose. After 24 hours of reaction a viscous milky dispersion was obtained. Yield: 595 g containing 168.4 g of solid matter. Intrinsic viscosity meal sured at 25C in butanone: 0.20 dl/g. Particle size: 2  
 11.. Melting point: 126C. Glass transition temperature: 50C.  
 Preparation 14: Graft-copolymer of styrene, methyl acrylate and poly(N-vinyl-2-pyrrolidone) In a reaction flask equipped with a stirrer, a nitrogen inlet and a reflux condenser, 1 g of poly(N-vinyl-Z- pyrrolidone) was dissolved at room temperature in 200 ml of ethanol. Thereupon were added 65 g of styrene. g of methyl acrylate and I g of benzoyl peroxide.  
  The solution was stirred while a nitrogen current was allowed to bubble through and the whole was refluxed. After some 30 min. the first turbidity arose. and after 1 hour of reaction the dispersion obtained a milky appearance. After 10 hours of reaction another 0.5 g of benzoyl peroxide was added and 24 hours later the low viscous dispersion was filtered through nylon cloth. Yield: 250 g containing 100 g of solid matter. Intrinsic viscosity: in butanone measured at 25C: 0.20 dl/g. Particle size: comprised between 1 and 2 a. Melting point: 116C. Glass transition temperature: 55C.  
 Preparation 15: Graft-copolymer of styrene. methyl acrylate and po1y(N-vinylpyrrolidone) prepared in the presence of dissolved dyestuff.  
  In a reaction flask equipped with a stirrer, a nitrogen inlet and a reflux condenser 3.0 g of low molecular poly(N-vinylpyrrolidone) were dissolved in 200 ml of ethanol. With stirring a gentle nitrogen current was bubbled through the solution, while successively 65 g of styrene. 35 g of methyl acrylate, l g of benzoyl peroxide and 1 g of CI. Solvent Yellow 42 were added at room temperature.  
  The mixture was refluxed. At the beginning a bright orangeyellow solution was obtained which gradually became turbid by polymerization. After 24 hours a yellow polymer dispersion was obtained. The largest part of the graft-copolymer particles sized about 3 u. The polymer particles were separated by centrifugation. finely ground in the presence of water by means of a mixer and filtrated on filter paper. After drying at 40C under 2-3 mm of Hg and in the presence of sodium hydroxide pellets, 90 g of polymer were obtained in the form of a fine yellow powder.  
 Preparation 16: Graft-copolymer of styrene. methyl acrylate and copolymer of butadiene and ethyl acrylate In a reaction flask equipped with a stirrer. a nitrogen inlet and a reflux condenser 2.5 g of copolymer of butadiene and ethyl acrylate (20 7t by weight ofbutadiene) were dissolved in ml of ethanol. To the homogeneous solution obtained 65 g of styrene, 35 g of methyl acrylate. 1 g of benzoyl peroxide and 130 ml of ethanol were added successively while a gentle nitrogen current was bubbled through.  
  The solution was refluxed and after about 1 hour of polymerization a first turbidity appeared. After 24 hours a viscous milky dispersion was obtained of which each part of 100 g contained 34 g of solid matter.  
  Yield: 90 g. Intrinsic viscosity measured in tetrahydrofuran at 25C: 0.36 dl/g. Glass transition temperature: 38C. Particle size: 1 to 2 u.  
 Preparation 17: Graft-copolymer with incorporated colour coupler Graft-copolymer of styrene. methyl acrylate, phenyl-3-methacryloyl-amino-4-(2&#39;- ethoxycarbonylphenylene)-azo-5-pyrazolone and copolymer of butadiene and ethyl acrylate.  
  Preparation 16 was repeated with the difference however, that the following reagents were used:  
 styrene 60 g methyl acrylate 40 g copolymer of butadiene and ethyl acrylate mole 7: of ethyl acrylate) 3 g benzoyl peroxide 1 g l-phenyl-3-methacryloylamino- 4-( 2-ethoxycarbonyl-phenylene) azo-S-pyrazolone 3 ethanol 300 ml After 24 h of reaction 400 ml of orange-yellow dispersion were obtained containing 48 g of graftcopolymer.  
 Preparation 18: Graft-copolymer with incorporated colour coupler monomer Graft-copolymer of styrene, methyl acrylate. lphenyl-3-methacryloyl-amino-5-pyrazolone and copolymer of butadiene and ethyl acrylate.  
  In a reaction flask equipped with a stirrer, a reflux condenser and a nitrogen inlet, 3 g of copolymer of butadiene and ethyl acrylate (80 7: by weight of ethyl acrylate) were dissolved in 330 ml of ethanol. To the solution obtained were successively added at room temperature 65 g of styrene. 35 g of methyl acrylate. g of l-phenyl-3-methacryloylamino-5-pyrazolone and l g of benzoyl peroxide.  
  The solution was refluxed with stirring. After 90 min. the reaction medium became turbid. After 24 h of polymerisation a bright yellow dispersion was obtained.  
  The incorporated colour coupler was coloured by diazotation. For this purpose the dispersion was cooled to room temperature. whereupon 5 g of pdiethylaminophenylene diazonium fluoroborate were added. The colour of the dispersion turned pink. After having added 35 ml of 2 N ammonium hydroxide a purplish red polymer dispersion was obtained, from which after filtration and repeated washing with ethanol. and after drying under vacuum in the presence of sodium hydroxide 68 g of purplish red powder were separated.  
 Preparation 19: Graft-copolymer of styrene, methyl acrylate and poly(ethylene oxide) In a reaction flask equipped with a stirrer, a reflux condenser and a nitrogen inlet g of poly(ethylene oxide) having a molecular weight of 600,000 was dissolved in 200 ml of ethanol. The mixture was refluxed and to the clear solution obtained 65.0 g of styrene, 35.0 g of methyl acrylate and 1.0 g of benzoyl peroxide were added. While a gentle nitrogen current was bubbled through the solution, refluxing was continued. After l hour of polymerization a first precipitate appeared and after 24 hours a milky dispersion was obtained. Yield: 260 g containing 93.6 g of solid matter. Particle size: l-3 a.  
  By spray-drying a white, free-flowing powder was separated. Glass transition temperature: 55C. Melting zone: around 134C.  
 Preparation Graft-Copolymer with incorporated colour coupler Graft-copolymer of styrene, methyl acrylate. l- (2 &#39;,2&#39;,2 &#39;-trifluoroethyl )-3-methacrylo ylamino-4- (2&#34;ethoxycarbonylphenylene)-azo-5-pyrazolene poly(N-vinylpyrrolidone).  
  Preparation 15 was repeated but the following reagents were used:  
 and  
 styrene 65 g methyl acrylate 35 g low molecular poly(N-vinylpyrrolidone) 3 g benzoyl peroxide l g l-(2&#39;.2&#39;.2&#39;-trifluoroethyl)-3-methacryloyl amino-44 2 &#39;-cthoxyearbonylphenylene )-azo-5- pyrazolone l g methanol 200 ml After 21 h of reaction and dilution with ethanol a yellow dispersion was obtained. Yield: 360 ml containing 76.6 g of polymer. Particle size: I to 6p. Melting point: 125C.  
 Example 1 To 200 ml of a dispersion of graft-copolymer particles of styrene and methyl methacrylate on polybutadiene obtained according to preparation 4, a dispersion of 6 g of Spezialschwarz IV in 55 ml of n-hexane was added. (Spezialschwarz IV is a trade mark for carbon black sold by Deutsche Goldund Silberscheideanstalt, Frankfurt a/Main, Germany). This mixture was ground for 15 hours in a ball-mill in order to disperse the carbon black as finely as possible. Then the mixture is spray-dried.  
  The dry black toner powder was then mixed with glass bends having a diameter between 600 to 800 p, in a ratio of l g of toner to g of glass beads. After positively charging a selenium drum and image-wise exposing to an original, the developing mixture obtained was run in cascade over the electrostatically formed latent image. On the selenium drum a black toner image was obtained having good image density and possessing practically no toner deposition on the non-image areas. By transfer on a paper support and subsequent fixation of the powder image, a good copy was obtained.  
 Example 2 A litre of a dispersion of graft-copolymer particles of styrene and methyl methacrylate on polybutadiene in n-hexane, prepared as described in preparation 5 was mixed with 750 ml of a 2 solution of Ceres black (trade mark of Farbenfabriken Bayer AG Leverkusen, W. Germany. for a black pigment) in cyclohexane. After spry-drying a dark toner powder was obtained, which was mixed with glass beads sizing between 600 and 800 p. in a ratio of l g of toner to 100 g of glass beads.  
 After positive charging of a selenium drum, image-- wise exposure and development with the developing mixture thus obtained, a sharp positive image appeared showing little toner deposition on the non-image areas. This image could be transferred to a paper support and fixed thereon.  
 Example 3 A dispersion in n-hexane of graft-copolymer particles of styrene and acylonitrile on a copolymer of styrene and butadiene, prepared as described in preparation 1 l. was dried to the air by evaporation. After 63 hours 1 g of the dry white powder obtainend was mixed with 100 g of glass beads sizing 600 to 800 t. This mixture was used as developer for a positively charged and image wise exposed selenium drum. An extremely sharp white powder image appeared on the selenium layer. This powder image could be transferred to a black paper support and fixed thereon. The image obtained was very sharp and showed no deposition of developer on the non-image areas.  
 Example 4 2 litres of the dispersion in ethanol of the graftcopolymer of styrene and mthyl acrylate on poly(N- vinylpyrrolidone) prepared as described in preparation 14, were spray-dried. The dry fine polymer powder having a fixing temperature of ll6C was then further treated as a toner by mixing with glass beads as described in example 3. A same good result was obtained.  
 Example 5 1 litre of the dispersion in ethanol of preparation 16, containing graft-copolymer particles of styrene and methyl acrylate on the copolymer of butadiene and ethyl acrylate was mixed with 100 ml of 10 solution by weight of polyvinylbutyral in ethanol. To this mixture 4 g of Spezialschwarz IV of example 1 and 400 ml of ethanol were added. This mixture was thoroughly mixed and finely ground for 2 hours by ball-milling. whereupon the dispersion was spray-dried. The obtained fine black powder was mixed with glass beads in Example 6 The graft-eopolymer with incorporated colour coupler monomer of styrene, methyl acrylate and lphenyl-3-methacryloylamino-5-pyrazolone on the copolymer of butadiene and ethyl acrylate. prepared as described in preparation 18, which after having coupled with a diazonium compound was obtained as a fine red toner. was mixed with glass beads in a ratio of l to lOO. By means of this developing mixture a positive red image of an electrostatic latent image was obtained. Fixing of this image could occur by subjecting the image for 5 see. to trichloroethylene vapours.  
 Example 7 The graft-copolymer of example 6 was spray-dried before coupling with the diazonium compounds. The free flowing colourless fine powder was mixed with glass beads in a ratio of l to lOO and used as a developing mixture on a positively charged and image-wise exposed selenium drum. As transfer paper a paper was used containing p-diethylaminobenzene diazonium tetrafluoroborate. This diazonium compound can be incorporated into the chemical wood pulp during the paper preparation, or can be applied as an after-layer mixed with a suitable film-forming polymer on a paper support. The colourless image transferred from the selenium drum was fixed to a red image in ammonia vapours and simultaneously fixed in trichloroethylene vapours.  
 Example 8 The dispersion of the graft-copolymer, prepared as described in preparation and coloured yellow by carrying out the polymerization in the presence of a yellow dye, was spray-dried. From the yellow powder obtained 1 g was mixed with 100 g of glass beads. Onto the selenium drum a sharp positive yellow image was obtained which after its transfer to paper was fixed by heat. The fixing point was approximately 128C.  
 Example 9 The dispersion in methanol of the graft-copolymer with incorporated colour coupler monomer prepared as described in preparation was spray-dried. After having been ground finely, the yellow powder was mixed with glass beads in a proportion of l to 100 by weight and used as developing mixture for a positively charged and image-wise exposed selenium drum. A sharp yellow powder image was formed, which was transferred to a paper support and fixed thereon at 126C.  
 Example 10 The free flowing powder of the graft-copolymer of styrene and methyl acrylate on poly(ethylene oxide) prepared as described in preparation l9 was mixed If the white powder was mixed in a l 7: proportion with other carrier particles, e.g. with spherical iron particles sizing approximately between 300 and 400 11., the developing powder obtained could be applied for the development of a negatively charged and image-wise exposed zinc oxide layer. A sharp positive image was obtained.  
 Example 1 l To 50 ml of dispersion of the graft-copolymer prepared as described in preparation l0 were added 950ml of n-hexane.  
  This diluted dispersion could be used as a electrophoretic liquid developer as follows.  
  A positively charged selenium or zinc oxide layer was developed after image-wise exposure by pouring the diluted dispersion over the photoconductor. lmmediately a positive white image appeared on the photoconductive layer. After evaporating the n-hexane. the image could be transferred from the drum to a paper support according to a known method.  
  If development occurred on a negatively charged zinc oxide layer, a reversed image was obtained (positive/negative process).  
 Example 12 A graft-copolymer incorporating a colour coupler. e.g. the graftcopolymer of preparation l9, was prepared by a polymerization under suited circumstances and in the presence of zinc oxide, which was previously sensitized with a blue dye. After the graft-copolymerization, dispersed particles of about 5-l0 micron were left possessing semi-conductive properties and in addition thereto being spectrally sensitive in a narrow region.  
  This procedure is repeated three times in separate vessels. each time with a suitable colour coupler and a suitable sensitizer for the zinc oxide.  
  The dispersions prepared in this way were mixed in equal quantities and coated onto a support, either without additional binding agent or with a separate polymer. in order to make the particles adhere to the support.  
  The mixed dispersion was coated in such a way, that only a monolayer of photosensitive little spheres was obtained:  
  After drying, the layer was charged in the dark, exposed either in contact or episcopically, and developed with an electrophoretic developer containing dispersed particles of the colour reactant in an electrically insulating liquid, e.g. a petroleum naphtha. Optionally an after-treatment in a suitable solvent is necessary, in order to make the selectively deposited colour reactant react with the colour coupler.  
  The image-resulting herefrom had the nature of a screen, interrupted by non-coloured lines (between the little spheres), and is conform to the original as far as colour rendering is concerned.  
 We claim:  
  1. Process for manufacturing electrostatic toner material comprising finely divided polymer particles by the steps comprising a. dissolving in an inert organic solvent (1) about llO% by dry weight of a graft-polymerizable nonionic polymer soluble therein and (2) about 99-90% by dry weight of at least one solventsoluble a,B-ethylenically unsaturated monomer the l homopolymer of which is insoluble in said solvent, said monomer being capable of undergoing radicalinitiated graft polymerization with said non-ionic polymer. and (3) about 0.l-5% by weight of said monomer of a free radicalforming polymerization catalyst capable of initiating said graft polymerization, said monomer being present in said solvent in a concentration of about -85% by weight and in an amount sufficient to form a graft-copolymer which comprises at least about 90-99% by weight of graft polymerized ethylenically unsaturated monomer and about l-l07r of said non-ionic polymer and is insoluble in said organic solvent.  
 b. effecting said graft-polymerization by heating said solution to about -1 50C with continuous stirring whereby said graft copolymer is produced as a dispersion in said solvent of solid particles having a size of about l-lOp. and a generally regular spherical shape. and I c. recovering said particles from said solvent in discrete. free-flowing form.  
  2. Process according to claim 1 wherein the monomer is styrene and the non-ionic polymer is polybutadiene.  
  3. Process according to claim I wherein the monomers arc styrene and acrylonitrile. and the non-ionic polymer is the copolymer of butadiene and styrene.  
  4. Process according to claim 1 wherein the monomers are styrene and methyl acrylate and the non-ionic polymer is taken from the group consisting of poly(N- vinylpyrrolidone). the copolymer of butadiene and ethyl acrylate. and poly(ethylene oxide.  
  5. Process according to claim 1 wherein the graftcopolymerization is carried out in the presence of coloring material so that uniformly colored. finely divided resin particles are obtained in which the coloring material is enveloped within said polymer.  
  6. Process according to claim &#39;1 wherein one of the alJi-cthylenically unsaturated monomers is an afi-ethylenically unsaturated. copolymerizable monomer dye. n  
  7. Process according to claim 6 wherein the a.,B-cthylenically unsaturated copolymerizable monomer dye is l-(2.2.2&#39;-trifluoromethyl)-3-methacryloylamino-4- (2&#34;-ethoxycarbonylphenyl)-azo-5-pyrazolone.  
  8. Process according to claim 1 wherein one of the afi-ethylenically unsaturated monomers is an a,,B-ethylenically unsaturated. copolymerizable color coupler, so that graft-copolymers are formed which through diazotation become uniformly colored.  
  9. Process according to claim 8 wherein the a,B-ethylenically unsaturated, copolymerizable color coupler is l-phenyl-3-methacryloylamino-5-pyrazolone and ethyl acrylate.  
  10. Process of claim 1 wherein the polymer particles obtained by polymerization step (c) are mixed with inert pigment particles in the amount of about 0. l20% by weight of the toner material.  
  11. Process for developing electrostatic images which comprises contacting said image with an electrostatic toner material prepared as in claim 1.  
  l2. Electrostatic toner material comprising finely divided spherical polymer particles having substantially regular spherical shape and a size of about ll0p., said polymer particles consisting essentially of a nucleus consisting mainly of a polymer of at least one ethylenically unsaturated monomer surrounded by an outer envelope consisting mainly of a graft-copolymer of said polymer of at least one a,B-ethylenically unsaturated monomer grafted onto a non-ionic polymer, said nonionic polymer comprising about and said grafted polymer about 99-90% by weight of said graftcopolymer. said graft-copolymer having a glass transition temperature of at least about 40C and -a melting point between about 80C and about C.  
  13. The toner material of claim 12 wherein said graftcopolymer has a triboelectric negativity approximately equal to polystyrene.  
  14. The material of claim 12 wherein colorant material is mixed with said polymer particles.  
  IS. The material of claim 14 wherein said colorant material comprises pigment particles.  
  16. The material of claim 14 wherein said colorant material comprises pigment particles or a dyestuff homogeneously distributed throughout the entirety of said polymer particles.  
  17. The material of claim-12 wherein the a.,B-ethylenically unsaturated monomer includes a monomer which is dye or a colorcoupling agent. =1: