TONER PARTICLES FOR ELECTROPHOTOGRAPHIC COPYING AND PROCESSES FOR THEIR PREPARATION

Abstract: Toner particles for electrophotographic copying and electrostatic printing consist of pigmented thermoplastic base particles having the surface covered with a thermoplastic fine-grained polymerizate. The base particles are prepared by suspension polymerization and the fine-grained polymerizate originates from a latex prepared by emulsion or microsuspension polymerization. One method of preparing the toner consists of bringing an aqueous dispersion of the base particles into contact with a latex of the fine-grained polymerizate. The temperature is raised so that the fine-grained particles adhere to the surface of the base particle. A protective colloid system can be present and/or the particles can have charges of opposite character. In another method the preparation of the toner particles comprises suspension polymerization of monomer for formation of the base particles in the presence of an already prepared latex whereby the latex particles have higher hydrophility than the polymer in the base particle. The fine-grained particles can also be applied to the base particles according to a dry method.

Description: Toner particles for elec rophotographic copying and pro¬ cesses for their preparation. The present invention relates to toner particles for use in electrophotograph c copying or electrostatic 5 » printing. More particularly the invention relates to such toner particles having a pimply surface. The invention also relates to methods for the preparation of such toner particles. In electrophotographic copying the latent print on 10. the photo-drum is developed with a toner consisting of fine-grained pigmented thermoplastic particles. The most common method of preparing a toner comprises melting a thermoplastic material and mi ing this w th pigment, charge modifiers, release agents etc. The product is then cooled, τ 5. crushed, ground and screened in an air stream to obtain part cles with a size in the order of from 5 to 30 μm . Accord ng to this method particles of very varying shapes and sizes are obtained. This variation in shape and size gives rise to certain disadvantages in the copying process. 2 . Efforts have thus been made to find processes w ich give toner materials hav ng spherical and fairly uniformly sized particles. One way of preparing a toner is to finely d vide molten waxes or low molecular thermoplastic materials in 25- a spray drier. If such conditions are used at the spray drying that a suitable particle size is obtained directly the grinding step can hereby be eliminated. A disadvantage of the spray drying is, however that the size distribution of the powder is fairly wide. Further, it is not possible 30. to satisfactori ly spray dry a melt of the thermoplastic materials which are usually used at so-called heat fixing by means of hot rolls or radiation. Spray dried powders are more suitable as toners intended for cold fixing by means of pressing. Spray dried particles are advantageous 35 in that they are spherical and thus not of such varying shapes as ground particles. One method of preparing toner particles suitable for hot fixing, which method in principle is very cheap, is to disperse pigments, charge modif ers, release agents, initiators etc in monomers which give polymers having suit- able properties for heat fixing. The monomer is emulsified with a suitable colloid system in water, the temperature is raised and by polymerization a fine, pigmented powder of sperical particles is directly obtained and this powder 5. can be dried, after washing, to give a powder suitable for use in coping. Since the method is very simple several attempts have been made to prepare toner p.articles in this way. One process of this kind is disclosed in the British patent application 2091435. In practical tests it has been 10... found that particles prepared by suspension polymerization have certain advantages such as the capability of giving copies with good resolution. However, it has also been found that such particles have a serious disadvantage in that they have such a strong adhesion to the photo-drum 15. that they are only very incompletely transferred to the paper. Such particles also agglomerate strongly with each other which means that such a toner has very poor free- flowing properties etc. The drawbacks with the particles mentioned above 20. can be related to the smooth surface of the spherical par¬ ticles prepared by normal suspension polymerization. When spherical particles with a smooth surface are used the adhesion to the photo-drum will be so strong that they are not even completely removed at the cleaning of the 25. photo-drum which follows the transfer step. Such remai¬ ning toner thus lead to a rapid deterioration of the quality of the copies. A strong adhesion to the photo-drum s parti¬ cularly serious if the toner consists of or contains very fine particles, < 5 /-im, since it is more difficult to remove 30. such fine particles from the surface of the photo-drum by means of mechanical cleaning systems. According to the present invention it has been found that spherical particles having a pimply surface do not show the disadvantage of a strong adhesion to the photo- 35. drum. In several cases such particles even have lower adhe¬ sion than toner particles prepared by the conventional grinding process. The present invention thus relates to a toner which comprises an internally pigmented base particle, or main particle, prepared by suspension polymerization and having a mean diameter of from 2 to 25 /_m, the surface of the particle being covered by a fine-grained polymerizate with a mean diameter of from 0.05 to 33. of the mean diameter 5. of the base or main particle. Suitably more than 10% of the surface of the particles is covered by the fine-grained polymeri zate. Internally pigmented base particles here refer to particles prepared in a manner where the pigment is mixed 10. with the monomer before the polymerization and thus is present more or less uniformly distributed in the finished polymerized base particle. The application of the fine-grained particles on the surface of the toner particles can be carried out in 15. a manner which is technically so simple that the whole process from monomers to coated toner particles is economi¬ cally advantageous. The invention therefore represents a more economical way to make high quality toners. The size of the fine-grained particles which form 20. protuberances on the surface of the base or main particles should be substantially smaller than these particles. The diameter of the fine-grained particles should thus be ma i¬ mum 33%, and preferably maximum 15%, of the diameter of the base particle. The lower size limit is set by the small- 25. est size which gives the desired effect of reduced adhesion to the photo-drum. Already pimples having a size in the order of 0.005 /am give a reduced adhesion. The fine-grained polymerizate suitably has a particle size in the range of from 0.005 to 5 / m, preferably from 0.02 to 2 /urn . 30. Another important factor is the degree of covering, ie how great a part of the surface of the particle which is covered by fine-grained particles. The closest possible cover ng corresponds to about 91% of the surface of the base or main particle. However, such a high degree of cover- 35. ing is not necessary to reduce the adhesion to the photo- drum. It has been found that a degree of covering of 50% gives a very strong reduction of the adhesion. However, a positive effect is obtained already at a degree of cover¬ ing of 10%. The degree of covering should thus be from 10% to 91%, preferably from 20% to 91% and most preferably, from 30 to 80%. In principle it is desirable to have the fine-grained particles in a mono-layer only, but at least partly the layer may be several particles thick. 5. Toner particles according to the invention with fine particles forming protuberances on the surface of the base or main particles can be prepared in a number of different ways as described below. First will be described a process according to which 10* fine-grained particles are adhered to the surface of base particles already prepared by suspension polymerization. Herein monomers, monomer soluble initiator, pigment and optional charge modifier and a dispersing agent for the pigment are first mixed. The mixture is emulsified in water 15. using a suitable colloid system. After evacuation the tem¬ perature is raised for polymerization and spherical base particles are obtained. The mean diameter of these can be from 2 to 25 μm , preferably from 3 to 15 Jin. The small polymer particles which are applied to 20. the surface of the base particles can be prepared by emul¬ sion polymerization or microsuspension polymerization in per se known manners and, if desired, charge modifiers and pigments can for example be incorporated at microsuspen¬ sion polymerization. 25. it is desirable that the fine-grained particles are strongly anchored in the surface of the base particles. This can be achieved by softening the base particles using small amounts of softening agents or by heating. Hereby the fine-grained particles will be anchored by melting 30. into the surface. It is suitable that the fine-grained particles melt into the base particles to a depth corres¬ ponding to about half the diameter of the fine-grained particle. However the depth can be varried, it is only nessecary that the fine-grained particles are firmly 35. anchored in the base particles and at the same time protrude out from the surface of them. The polymer composition of the fine-grained particles may be the same as that of the base particle. However, it might be advantageous to choose a more high-melting polymer type for the fine-grained particles on the surface. A higher melting point gives a smaller risk that the fine¬ grained particles wi ll agglomerate with each other instead of adhering to the surface of the base particles at the 5. coating process. In order to make the fine-grained particles on the surface particularly difficult to melt they, can be cross-linked to a higher degree than the base particles. The fine-grained particles can be applied in a wet method to the surface of already formed base particles TO- or according to a special technique, described below, to the surface of the monomer droplets, which after polymeriza¬ ion together with the latex particles will form pimply particles. A toner can for example be prepared by bringing an 15. aqueous dispersion of the pigmented base particle into contact with a latex of the fine-grained polymerizate where¬ by a protective colloid system is subsequently formed in the aqueous dispersion and the temperature raised to make the fine-grained particles adhere to the surface of the 20. base particles. At production according to this method the protective colloid system which has been used for the suspension poly¬ merization of the base particles is suitably fi rst deacti¬ vated. If, for example, certain inorganic powder stabi lisers 25. have been used as protective colloids such as difficultly soluble phosphates these can be dissolved by acidifying the aqueous suspension of the base particles. The latex of the f ne-grained particles is then slowly added. Hereby such conditions should be used that the latex wi ll not 30. precipitate immediately on contact with the suspension of the base particles, since there is then a risk that the small particles in the latex will agglomerate with each other instead of being deposited on the surface of the base particles. 35. After agitation for some time the fine-grained partic¬ les wi ll have been precipitated on the surface of the base particles. The system is then made more alkaline so that the protective colloid system will be reformed. There is then no risk of agglomeration of the particles when the dispersion is warmed to melt the fine-grained particles, into the surface of the base particles. Acidification and washing is then carried out. However, the protective colloid system does not have 5. to be reformed if the latex particles have a higher melting point than the base particles. When warming to a temperature at wh ch the base particles softens so much that the latex particles melt into the base particles, the latex particles are still hard and consequently the latex particles do TO. not agglomerate with each other. If the protective colloid would not be reformed a preferable degree of covering should be at least 30%. In some cases the protective colloid system can be kept intact when the latex of the fine-grained particles 15. is added. In this case latex particles and base particles which have opposite charges are used. This can be accom¬ plished by copolymerization ith functional monomers with charges of opposite character. The charged latex particles will be attracted to the base particles of opposite charge 20. and thereby penetrate the colloid layer. According to another method of preparation the protec¬ tive colloid system is dissolved after the preparation of the base particles whereupon they are washed and redis- persed. The latex of the fine-grained particles is added. 25. To bring these to precipitate on the surface of the base part cles in the absence of the protecti e colloid the base particles and the latex particles have to be provided with opposite charges. This is achieved through controlling the Zeta-potenti a I of the particles. The chemical composi- 30. tion of the surfaces of the base particles and the latex particles are chosen in such a way that the two types of particles have Zeta-potenti a Is of opposite character at the used cond tion. The required composition of the surface of the particles can be obtained by copolymeri sati on with 35. functional monomers in known manner. Also at this method of production the latex particles must have a higher melting point than the base particles to make sure that the latex particles will not agglomerate at the following heating. To give the toner the correct t ri boe leet ri c charge the fine-grained particles on the surface must have a speci¬ fic t ri boe lectri c charge and this can be achieved by subse¬ quently precip tating a charge modifying agent on the sur¬ face of the coated particles. If the fine-grained particles 5. are prepared by mi c rosuspensi on polymerization a charge modifying agent can alternat vely be mixed with the monomer already before the polymerization of the fine-grained par¬ ticles. Finally the chemical composition of the fine-grained particles can be selected in such a manner that no extra 10- addition of charge modifying agent is requi red. Examples of such particles which give a positive t ri boe lect ri c charge are fine-grained particles of polyacry loni t ri le or amino- containing monomer. When fine-grained particles of polyvinyl chloride, fluoro polymers etc are used a negative triboelec- 15. trie charge is obtained. The fine-grained particles can also be applied accord¬ ing to a dry method. At application of the fine-grained particles by a dry method the base particles are first dried and charged to a mixer. To keep a uniform mixture 20. in the powder bed it is advantageous to admix larger beads, eg glass beads of 5 mm. The small polymer particles which are to cover the surface are then charged to the powder bed. The small particles can be present either as a disper¬ sion in a suitable liquid, whereby the liquid is evaporated 25. from the powder bed, or as an already dried very fine¬ grained powder. The temperature of the powder bed is raised under continued agitation. The small particles wi ll then adhere to the surface of the base particles and, at higher temperatures, at least partly melt into the surface of 30. the base particle. An alternative way of making the small polymer partic¬ les melt into the surface of the base particles is to intro¬ duce the coated base particles into an ai r stream which for a short time is heated to a temperature of from 150 35. to 400°C, depending on the dwell ime in the hot zone. According to the above described methods the base particles are first prepared by suspension polymerization and these are then in a wet process coated by treatment with a latex of the fine-grained polyme ri zate to give "pimply" toner particles according to the invention. According to another method for the preparation of toner particles with a rough surface a special kind of process is used and herein a latex, ie the fine-grained 5. polymerizate, is first prepared and the base particles, are prepared by suspension polymerization in the presence of the already prepared latex. In the following this method of preparation, which forms part of the present invention, will be described more in detail. 10 " .. According to the method spherical particles with a pimply surface, useful as toners in electrophotographic copying and electrostatic printing, are produced by first preparing a latex, an aqueous dispersion, of finegrained polymer particles. The latex can be prepared according 15. to the emulsion polymerization technique using water soluble initiators and suitable emulsifiers or according to the technique of mi crosuspensi on polymerization whereby the monomer is first finely di-vided in water, by means of inten¬ sive emulsifying and using surfactants, and then polymerized 20. using initiators which usually are soluble in the monomer. In certain cases water soluble initiators can, however, be used in mi crosuspensi on polymerization. The latex particles shall be insoluble in the monomers and optionally other solvents and for this purpose they 25. are preferably cross-li nked. Further, the surface of the latex particles shall have a fixed hydrophi li c/hydrophobi c character. At the production of pimply particles according to the method latex is mixed with a monomer or a monomer mi x- 30. ture. Monomer soluble initiator, pigment, charge modifying agent, release agent etc can have been added to the monomer in advance. The mixing conditions, with regard to pH etc, should be selected in such a manner that the latex particles leave the aqueous phase and migrate to the monomer phase 35. or to the monomer - water - phase boundary. Additional water and a suitable colloid system is then charged. The monomer is suspended to small drops and the temperature is raised for polymerization. After polymerization a fine¬ grained pigmented powder is obtained. At investigation with a scanning electron microscope it is found that the latex particles of suitable hydrophi li c/hydrophobi c balance have migrated from the inner of the drops to the surface of the polymer particles formed at the suspension polyme- 5. rization. Hereby a pimply surface is obtained on these particles. By varying the hydrophi li c/hydrophobi c balance it is possible to control the displacing of the latex particles with regard to the surface of the formed base particles. 10. If the latex particles have a very hydrophobic charac¬ ter, for example if they have been prepared from pure styi— ene, divinyl benzene and with hydrogen pero ide as initiator, they will not at all penetrate the surface of the formed polymer particles. Such latex particles can 15. thus not be seen by studying the formed polymer particles in a scanning microscope. On the other hand, if the latex particles are too hydrophilic they can be forced out entire¬ ly from the main particle at the polymerization and after the polymerization be fsund in the aqueous phase. 20. Suitable hydrophility for the latex particles depend on the hydrophility of the main particles. The latex partic¬ les should have a higher hydrophility than the polymer of the main particles. The upper limit for the hydrophility of the latex particles is the level where the latex partic- 25. les start being pressed out from the main particles to the aqueous phase during the polymerization. The degree of hydroph lity can for example be control¬ led at the preparation of the latex particles by adding certain amounts of monomer with anionic character in a Ika- 30. line en ironment, for example ethacrylic acid, itaconic acid, styrene sulphonic acid, etc. Compounds with cationic character in acid environment can also be incorporated in the latex polymer to make the latex particles more hydro¬ philic, eg trimethylammoni ummethyI methacrylate halide. 35. However, it is not necessary to use ionised groups to achi¬ eve hydrophility. Control of hydrophility can also be ac i¬ eved by polar, non-ionised monomers, eg methyl methacrylate, acrylo nitrile, allyl alcohol, 2-dimethylaminoethyl methacr late. As polar monomers such containing amino groups or hydroxyl groups are preferred. It is also possible to use amphoteric latex which contains both acid and basic groups for obtaining a suitable hydrophility. The determining factors for the latex particles to form pimples 5. according to this method are thus that the latex particles are not soluble in the monomer or the monomers which form the main particle and that the surface of the latex partic¬ les have a more hydrophilic character than the polymer of the formed main particle. 10. Cross-linking is of course not necessary if the poly¬ mer composition of the latex particles is such that the latex particles are not soluble in the monomers without being cross-linked. An example of this is latex particles of po lyac rylon tri le, or of copolymeri zates having a high 15. acrylonitπ ' le content. Otherwise the latex particles are cross-linked to obtain insolubility. The degree of cross-linking in the latex particles is of certain importance. At a low degree of crosslinking the latex particles will swell in the monomers. The size 20. of the pimples in the finished particles will then be greater than the size of the particles in the used latex. Hereby a certain amount of latex will suffice to cover a greater part of the surface of the main particles. The swelling of the latex particles also results in that the 25. difference in hydrophility between the monomer and the latex particle will be diminished since the composition of the swelled latex particles will be more like that of the monomers. The size of the pi ples is, besides the degree of 30. swelling, also determined by the size of the particles in the latex. At a smaller size a lower part by weight of latex is required to give a determined degree of covering of the surface of the final particles. The smallest s ze of the pimples is decided both by the size the pimples 35. should have to sufficiently eli inate the attraction to the photo-drum due to van der Waal forces and by the small¬ est size which it is technically possible to prepare. With regard to van der Waal attraction this will decrease to a high extent already when the base particles, the main par icles, are removed from each other by 10 nm. If half the size of the pimples is outside the surface of the base particle it should then suffice with a diameter of 20 nm for the particles in the used latex. The largest size of 5. the pimples is a diameter corresponding to about 33% of the diameter of the spherical main particle. The .ean dia¬ meter of the particles in the latex should be from 0.05 to 33% of the mean diameter of the ma n particle, and this should be within the range of from 2 to 25 /_m. 10. The chemical composition of the latex particles form¬ ing the pi ples can be selected arbitrari ly as long as the particles are not dissolved in the monomer or monomer mixture used for formation of the main particle. As has been stated, the hydrophi li c-hydrophobi c balance must, 15. however, be considered. Further, the fact that the pimples influence the tπ ' boelectric properties of the final particle must also be considered. The pimples represent the outer contour of the toner particles. At rubbing, the type and level of the t ri boe lect ri c charge is thus determined by 20. the chemical composition of the pimples. Further it should be considered that the electrostatic charge wi ll be greater ith protuberances in the form of p ples due to the increa¬ sed surface of the powder particles. It is suitable to choose such a che ical composition 25. for the latex particles for ing the pimples that they wi ll be harder than the main polymer. Hereby deformation when the toner particles are attracted to the photo-drum is reduced and a smaller contact surface is obtained. The van der Waal forces are hereby reduced. A harder surface 30. is also an advantage when the powder is stored, since the risk of agglomeration is then reduced. Finally, the harder surface can reduce the risk of tack at contact with the hot fixing rolls. The degree of covering, which is an important factor, 35. is within the ranges previously stated. Typical degrees of covering for this method of preparation is from 20 pre¬ ferably from 40 to 80% at a mono-layer. The property of the pimply spherical particles to give a decreased adhesion to surfaces and between the particles themselves can give advantages also in other fields than electrophotographic copying. It has thus been found that they give a reduced adhesion to the screen if they are used for electrostat c printing according to the 5. "dry silk-screen" method. Such prints will thus have a stronger colouring than if spherical particles with smooth surface are used. The rough surface results, as has been mentioned, in 5-. reduced mutual attraction between the particles. A 105. powd-e-r of such particles will thus have better free-flowing properties. Owing to the low tendency to formation of powder aggregates particles with a rough surface are advantageously used also in powder coating operations, for example for coating of metal articles when the powder s sintered on. 15. Choice of material will be discussed more in detail below and when nothing else is stated this is valid indepen¬ dent of the method of preparation of the base or main particles coated with fine-grained polymerizate. As monomers, alone or in mixture, for the preparation 20. of the latex particles the following can for example be used: styrene and different der vatives of styrene, acrylic acid and methacrylic acid or esters thereof, acrylo nitrile, vinyl chloride, vinyl fluoride, vinylidene fluoride, vinyl acetate etc. To obtain cross-linking poly- 25. functional monomers can be used, eg divinyl benzene, ethy- Lene glycol diacrylate, ethyleneglycol dimethacrylate, t ri methyloIpropane triacrylate etc. The amount of cross- Linker can be varied to a high degree as long as the latex particles fulfi l the requirements on correct hydrophility 30. and- insolubility. For the preparation of the base particle, or the main particle, the same monomers, and also cross-linkers, as above can be used, but generally such a mixture is used that this particle wi ll have a lower softening point than 35. the latex particles. The preferred main monomers for both latex particles and base or main particles are styrene, acrylates and metha- crylates . As emulsifiers for the preparation of the latex particles conventional surfactants for emulsion and micro- suspension polymerization respectively are used. However, care should be taken that the emulsifier system will not to a too igh degree negatively influence the function 5. of the colloid system which is used for the preparation of the base particle or the main particle. It is also advan¬ tageous if the used emulsifiers have such a water solubility that they can be washed away from the surface of the produced pimply toner particles. 1g, As initiator at the production of the latex particles according to emulsion polymerization technique conventional water soluble initiators can be used, eg persuIphates, hydrogen peroxide, hydroperoxides, etc. For latex according to the mi crosuspension polymerization technique conventio- 15, nal monomer soluble initiators can be used, eg dialkyl peroxi di carbonates, tert.butyl peroxi pi va late, octanoyl peroxide, lauroyl peroxide, tert.butyl perox (2eth Lhexano- ate), benzoyl peroxide, 2,2-azobi si sobutyroni t ri le, 2,2- azobi s-2,4-dimethyIva leronitri le and similar compounds. 20. ? o r ^e preparation of the base or main particles the same initiators as those for preparation of latex according to mi c rosuspensi on polymerization can be used. As protective colloid in the colloid system for the preparation of base or main particles, water soluble collo- 25, ids of the type cellulose derivatives, polyvinyl alcohol etc or powder stabilisers of the type difficultly soluble phosphates, methal hydroxides, si lica etc can be used. The powder stabilisers are preferably used together with a suitable co-stabiliser. 30, As colorants to be mixed with the monomer for the base or main particles inorganic colorants, organic color¬ ants, magnetite or carbon black are used. In certain cases it is suitable to give the pigments a surface treatment so that they will remain finely divided in the monomer 35, drops. Toner particles according to the invention will thus be colored throughout, ie the colorant is present included, and more or less uniformly distributed in the polymerice base or main particle. As has been stated it is also possible to let colorant and certain other additives be present in latex prepared according to mi c rosuspensi on polymerization processes. The toner particles of the invention can be used together with conventional carriers for developer 5. composition in known manner. The invention is further illus¬ trated in the following examples which, however, are not intended to limit the same. Parts and per cent relate to parts by weight and per cent by weight, unless otherwise stated. 10. Example 1 - 14 relate to the first described method with its different variations, where fine-grained particles are adhered to the surface of base particles. Example 15 - 21 relate to the second described method with fine-grained particles present at the preparation 15. of the base particle. Example 1. Preparation of a fine-grained polymerizate 40 g of styrene, 1.8 g of sodium dodecylsulphate and water to totally 395 g were charged to a 500 ml glass flask equip¬ ped with cooling means, agitator and a valve for evacuation 20. and introduction of nitrogen. The mixture was heated to 80°C under agitation. At 80°C 5 g, 3.5% of hydrogen peroxide were added and the same time the mixture was subjected to a nitrogen atmosphere. The polymerization was then allowed to continue for 25. 12 hours which gave a 0.11 μm 10% seed latex. 120 g of the above seed latex, 200 g of 5g/kg sodium dodecylsulpahte, 0.4 g of divinyl benzene, about 50%, 27.6 g of styrene and water to totally 395 g were charged to the same equipment as above and the same procedure was 30. then followed. In this manner a cross-linked polystyrene latex was prepared with particles of 0.16 / um and a dry content of 10%. Example 2. Preparation of a fine-grained polymerizate. 250 g of styrene, 0.8 g of neozapon Schwartz X 51 35. charge modifier (from BASF) and 2.5 g of 2,2'-azobis (2,4- di methy Iva leroni tri le) were charged to the same equipment as in Example 1. The monomer mixture was heated and the bulk polymerization allowed to continue for two hours at 85°C which resulted in a viscosity increase at 24°C from 10.5 to 13 seconds (Ford-cup, 4 mm nozzle). 198 g of bulk polymerizate, 2 g of divinyl benzene, about 50%, 7 g of 2, ' azobi s (2, -dimethyl aleroni tri le ) were emulsified with 828 g of 3g/kg sodium dodecyIsu Iphate 5. in an Ultra Turrax for some minute. The pre-e ulsi on was charged to a 2-step Manton Gaulin homogenizer, model 15 M, where a narrow drop size distribu¬ tion of 0,19 μm (determined with a Coulter Nanosizer) was obtained. The homogenized emulsion and 1 g of sodi umdodecyl- 10. sulphate were charged to a 1,5 I glass autoclave which was placed under nitrogen gas atmosphere. The emulsion was polymerized at 65°C during 12 hours. In this way a 0,19 _ιm, 19% mi crosuspensi on with charge modifier incorporated during polymerization and cross-linked with 0,5% divinyl 15. benzene was obtained. Example 3. Preparation of base particle To a solution of 2kg 0.16 molal trisodium phosphate 520 g of 1.0 molal calcium chloride solution were added under agitation and finally 150 g of a 0.2% solution of 20. sodium dodecyIbenzenesuIphonate. The now obtained mixture was di luted to 2965 g with 0.2% potassium dichromate solu¬ tion and forms the dispersion medium. 700 g of styrene, 300 g of butyl methacrylate, 80 g of carbon black "Pπ ' ntex V" (Degussa) and 3 g of neozapon 25. schwartz X 51 (BASF) were dispersed in a ball mill to give a carbon-monomer dispersion. 10 g of 2,2-azobi s (2,4-di ethyLva leroni t ri le) were dissolved in 990 g of carbon-monomer dispersion and added together with the dispersion medium (2965 g) to a reactor. 30. The mixture was put under nitrogen gas atmosphere and allo¬ wed to polymerize at a rapid heating from room temperature and further at 85°C for 1 hour under moderate agitation. The mixture was cooled to room temperature and pH adjusted to about 3 whereby 35 g of 2,2-azobi s (2,4-di methyIvaleroni - 35. trile) were added. After agitation for a couple of minutes pH was adjusted to about 9 and the mixture was recirculated through a dispersion unit "Ystral" (Bergius Trading AB) and emulsified to a suitable drop size for toner particles. The reactor was once again placed under nitrogen gas at os- 1 6 phere and polymerization continued for 18 hours at 65°C under moderate agitation. The suspension was then cooled to room temperature. A part of the polymerizate was transferred to a vessel 5. and pH adjusted to 2 which HCl and calcium phosphate which functions as protective colloid was hereby dissolved. The suspension was filtered and first washed with acidified water and then with distilled water to finally be dried at 35°C. 10. In this manner toner particles with a particle size of about 10 μm and with a charge of -12uC/g against a Hδganas carrier were obtained. Copying tests with the toner in a Mita DC 313 Z first gave good copying results but the reproducabi li ty was fairly rapidly impaired due to 15. the strong adhesion of the spherical, smooth toner particles to the photo-drum. Example 4. Coating of base particl.es with fine-grained particles. 362 g of 10% polystyrene latex prepared according 20. to Example 1, 390 g of 1.5 g/kg sodium dodecyIsulphate and 2 I of water were mixed and form the coating dispersion. 2 kg 1.5 g/kg sodium dodecyIsuIphate were charged to a reactor containing 4 kg of a suspenion prepared accor¬ ding to Example 3 and pH was then adjusted to 2 with HCl. 25. The coating dispersion was then added for 20 minutes under good agitation and then mixed for totally 1 hour before the temperature was raised to 65°C. At 65°C pH was adjusted with NH, to 8.3 and the temperature further raised to 90°C. After less than 5 minutes at 90°C the now coated toner 30. suspension was cooled to room temperature. Subsequently pH was adjusted to 2 using HCL and cal¬ cium phosphate, which functions as protective colloid, was hereby dissolved. The suspension was filtered and first washed with acidified water and then with distilled water. 35. A sample was doped with 0.05% neozapan schwartz X 51, based on the amount of polymer, by slurrying the filtercake in water after the washing and mixing with a 1% methanol solu¬ tion of the charge modifier and filtration was then carried on the surface of the base particles screen the effect of the charge modifier in the base particle. Investigation with a scanning electron microscope showed that the polystyrene particles had been adsorbed 5. by the base particles and, due to the heat treatment, been melted into the base particles to about half their volume. The amount of polystyrene latex was adjusted so that about 50% of the surface of the base particles was covered by fine-grained particles. In this manner toner particles 10. with a "pimply" surface were obtained and they gave a charge of -14 uC/g against a Hδganas carrier. Copying tests with a ita DC 313Z did from the beginning give very good copies and the reproducabi I i ty was sti ll good after 30000 copies. A particularly good background and clean copies were noted. 15. The photo-drum was only covered by small amounts of toner which could be removed easi ly. Examp le 5. Coating of base particles w th fine-grained particles. Base particles were prepared in the same manner as 20. in Example 3 and coated in the same manner as in Example 4 but with 218 g of 19% polystyrene latex prepared in accor¬ dance with Example 2. icroscopy showed that the particles had been adsorbed and melted into the base particles to about half their 25. volume and the degree of surface coating was also here in the order of 50%. In this manner pimply toner particles were obtained where the "pimples" contained a charge modi¬ fier which gave a charge of -17 uC/g. As the toner of Example 4 this toner also had excellent copying properties. 30. Exam le 6. The process of Example 4 was repeated with the differ¬ ence that the amount of latex was lowered to 228 g. Microscopy showed a lower degree of covering, about 30 to 35%. Despite this toner particles obtained better 35. copying properties than toner particles according to Example 3. Examp le 7. Preparation of base particle suspension. The process of example 3 was repeated with the differ¬ ence that in connection with the addition of 35 g of 2,2 -azobi s- (2, di methyIva leroni t ri le) at pH 3, 8 g of dimethyl- aminoethyImetacrylate were also added. In this way a suspen¬ sion of base particles was prepared with a Zeta-potenti a I changing from positive to negative with increasing pH at a higher pH value than for the suspension in Example 3. Example 8. Preparation of a base particle suspension. The process of Example 3 was repeated with the diff¬ erence that after emulsifying to suitable drop size for toner particles 11 g of trimethylaminoethylmethacrylate 10, bromide were added. In this way a suspension of base partic¬ les was prepared, with a Zeta-potenti a I changing from posi¬ tive to negati e at a higher pH than for the suspensions of Example 3 and 7. Examp le 9. Preparation of a fine-grained polymerizate. 15 100 g of styrene, 2 g of sodi umdodecylsuIphate and 397,5 g of water buffered to pH 9 (NH,+r.H,) and 0,5 g of 1 mMCuSO, solution were added to a reactor. The mixture was heated to 80°C. At 80°C 0,9 g of 50% metylethyIketone- peroxide were added at the same time as the mixture was 20, put under nitrogen gas atmosphere. The poly erization was then allowed to continue for 12 hours, which resulted in a 0,1 μm 20% latex. 100 g of the above prepared seed latex, 1,6 g of sodiumdodecylsulphate, 0,5 g of 1 mM CuSO, solution and 25 317,5 g of water buffered to pH 9 and 80 g of styrene were added to an autoclave. The mixture was heated to 80°C. At 80°C 0,7 g of 50% methylethylketoneperoxide were added at the same time as the mixture was put under nitrogen gas atmosphere. The polymerization was then allowed to 30. continue for 12 hours, which resulted in a 0,17 μm 20% latex . 100 g of the last prepared latex, 1,6 g of sodiumdode¬ cylsulphate, 0,5 g of 1 mM CuSO, solution and 317,5 g of water buffered to pH 9 and 65 g of styrene were added to 35 an autoclave. The mixture was heated to 80°C. At 80°C 0,6 g of 50% methylethylketoneperoxide were added at the same time as the mixture was put under nitrogen gas atmosphere. The polymerization was then allowed to continue for 12 hours, which resulted in a coating latex with 0,27 μm particles and 20% dry content. Example 10. Preparation of a fine-grained polymerizate. 1 g of 2-sulfoethyImethacrylate was added to an auto¬ clave together with 309 g of water and pH was adjusted 5. to about 4 with NH,, and 0,4 g of 1mM CuSO, solution and 80 g of styrene were added. The mixture was heated to 80°C. At 80°C 10 g of 3,5% H 2 0p were added at the same time as the mixture was put under nitrogen gas atmosphere. The polymerization was then allowed to continue for 12 hours, 10. which resulted in a 0,14 yum, 20% latex which was free from surfactants . 40,6 g of the above prepared latex, 200 g of water and 0,4 g of 1 mM CuSO, solution were added to an autoclave equipped with two dropping funnels. To one dorpping funnel 15. 72 g of styrene were added and to the other dropping funnel 76 g of water and 1 g of 2-suIfoethyImethacrylate, for which pH was adjusted to about 4 (NH,), were added. The autoclave was heated to 80°C. At 80°C .10 g of 3,5% H 2 0 2 were added at the same time as the whole system was put 20. under nitrogen gas atmosphere. The content of both the dropping funnels were added during about 3 hours. The poly¬ merization was then allowed to continue for 12 hours. In this manner a surfactant free coating latex was prepared with particles of 0,26 μm and a dry content of 20%. 25. Examp le 11. Coating of base particles with latex. 150 g of 20% coating latex prepared according to example 9, 90 g of 5 g/kg sodi umdodecyIsuIphate and 1260 g of water were mixed and form the coating dispersion. To an autoclave with 4 kg of suspension of base par- 30. tides, prepared according to Example 3, 480 g of 5 g/kg sodi umdodecy Isulphate and 3520 g of water were added. pH was adjusted to 2 and then the coating dispersion was added during 20 minutes under good agitation. The mixture was allowed to stand under agitation for about 1 hour before 35. the temperature was raised to 83°C. After less than 5 minu¬ tes at 83°C and pH 2 the thus coated toner suspension was cooled to room temperature. The suspension was filtered and washed with water. The sample was then doped with 0,05% neozopanschwarts x51 (BASF) by slurrying the filtercake in water and mixing it with a 1% methanol solution of the doping media and filtrating once again. Finally the sample was dried at 35°C. In this manner toner particles with a pimply surface 5. were obtained, and they gave a ( charge of -16 jC/g against a Hδgana's carrier. The toner was tested in a Mita DC 313 Z and gave good copying properties. The example illustrates coating of base particles with latex, when the calcium phosphate colloid was dissolved 10. (pH2). Thus, it was possible to heat the mixture to obtain adhesion between base and latex particles, without agglo¬ meration, even when the protective colloid was not rebuilt by raising the pH, when the latex particles were harder than the base particles. 15. Example 1 . Coating of base particles with latex. 150 g of 20% coating latex prepared according to Example 10, 90 g of 5 g/kg sodi umdodecyIsu Iphate and 1260 g of water were mixed and constitute the coating dispersion. To an autoclave containing 4 kg suspension of base 20. particles, prepared according to Example 7, 480 g of 5 g/kg sodi umsuIphate and 3520 g water were added. The coating dispersion was added during 20 minutes at good agitation, without preceding adjustment of pH and thus the protective colloid was not dissolved. The mixture was. allowed to stand 25. under agitation for an hour before the temperature was raised to 90°C. After a minute or so at 90°C the coated toner suspension was cooled to room temperature. The suspen¬ sion was acidified to pH 2 and filtrated and washed with water. The sample was doped in the same manner as in Exam- 30. pie 11 and in this way pimply toner particles with good copying qualities were obtained. The example illustrates coating of base particles with latex, when the protecti e colloid was present. Thus it was possible to bring together latex- and base particles 35. and heat the mixture to obtain adhesion between base- and latex particles, in spite of the presence of protective colloid consis ing of precipitated calcium phosphate. In another test the method according to this test was repeated, ith the difference that the base particles were prepared according to Example 8. The test showed that the same result was obta ned i rrespective of the base par¬ ticles being prepared according to Example 7 or 8. When both the tests were repeated with the difference that the 5. Latex was prepared according to Example 9, the latex agglo¬ merated in the water phase when the temperature was raised and thus no markedly pimply toner par icles were obtained. The same thing happened when the test was repeated with base particles prepared according to Example 3 and latex 10. prepared according to Example 9. Also when the test was repeated with base particles prepared according to Example 3 and latex prepared according to Example 10, no ramaining coating was obtained after the drying. Thus it was possible to coat base particles with latex also in the presence 15. of active protective colloid, when as well base particles as latex particles were copo lyme ri zed with small amounts of functional monomeres but of opposite charge character. Examp le 13. Coating of base particles with latex. 4 kg of suspension of base particles, prepared accor- 20. ding to Example 3, were acidified to pH 2 and filtered and washed with water. The fi lter cake was suspended in 7 kg of water and pH was adjusted to 1. Then 125 g of coa¬ ting latex, prepared according to Example 10 and di luted to 1250 g was added. The mixture was then heated to slight- 25. ly more than 80°C and was then cooled to room temperature. The suspension was fi ltered and doped in the same manner as in Example 11. In this way pimply toner particles with excellent copying qualities were obtained. Examp le 14. Coating of base particles with latex. 30. The method in Example 13 was repeated, with 4 kg of base particles, prepared according to Example 8. This time it was possible to carry out the coating at a higher pH than 1. It was possible to choose a pH up to about 5, but the test was made at pH 2. In this way pimply toner 35. particles were obtained which also had good copying quali¬ ties. Example 13 and 14 i llustrated surfactant free coating of washed base particles with latex prepared according to Example 10, by controlling the Z-potential of the base particles. At a higher pH the Z-potential of the base par¬ ticles was negative, which brought about that no or very few sulfonated latex particles were adsorbed on the surface of the base part cles. When pH was lowered, the Z-potential 5. of the base particles became positive, which resulted in latex particles migrating to the base particles. The mixture could then be heated to obtain adhesion between base- and latex particles. Even if the sample was not heated, there was a certain adhesion between the particles. This was 10. particularly true for particles as in Example 14. By copolymeri zati on with functional monomers, as dimethylaminoethylmethacrylate and tr methylami noethyl-methacrylate bromide, it was possible to influence the Z-potential of for example the base partic- 15. les, at a given pH. In this manner it was possible to per¬ form the coating operation at a higher pH in Example 14 than in Example 13. Example 15. Preparation of anionic latex. 110 g of styrene, 0.33 g of sodiumdodecyl sulphate 20. and water to a total of 1067 g were charged to a 1.5 I glass reactor with a double jacketing and equipped with agitator and valve for evacuation and introduction of nitro¬ gen gas. The mixture was heated to 80°C under rapid agita¬ tion. At 80°C 33 g of a 1% potassium persulphate solution 25. was added and at the same time the mixture was subjected to nitrogen gas atmosphere. The polymerization was allowed to continue for 12 hours and resulted in a 0.28 μm 8% seed latex . 300 g of the above seed latex. 0.30 g of sodium dode- 30. cylsulphate and water to a total of 1060 g were charged to the same equipment as above, but in this case a dropping funnel was also connected. 100 g monomer was charged to the funnel. Depending on the desired composition of the final latex vary ng amounts of methacrylic acid, divinyl 35. benzene ( about 50%) and styrene were charged. In this exam¬ ple 1.8 g of methacrylic acid, 24 g of about 50% divinyl benzene and 74.2 g of styrene were charged and this is presumed to give a polystyrene latex cross-linked with 9.7% divinyl benzene (100%) and which also contains 1.5% methacr* lic acid. The mixture in the glass reactor was heated to 80°C under moderate agitation. At 80°C 40 g of a 1% potassium persulphate solution was added and at the same time the 5. mixtures in the reactor and in the funnel were subjected to nitrogen gas atmosphere. The monomer mixture was then allowed to drop down into the reactor for about 3 hours. The polymerization was then allowed to continue for 12 hours which gave an 0.48 jm 9% latex which is presumed 10. to have the above stated composition. Examp le 16. Preparation of toner particles with pimply surface. To a solution of 2 kg of 0,16 molal trisodium phos¬ phate 520 g of 1.0 molal calcium chloride solution were 15. added under agitation and finally 150 g of 0.2% sodium dodecy Ibenzene sulfonate were added. The now obtained mixture was diluted to 2965 g with 0.2% potassium dichro- mate solution and forms the dispersion medium.. 700 g of styrene, 300 g of butyI . methac rylate, 80 g of carbon black 20. "Printex v" (Degussa), 3 g of charge modifier "Neozapon Schwartz X51" (BASF) and 3.5 g of azobisisobutyronitrile and 50 g of polyethylene wax, as release agent, were dis¬ persed under controlled temperature in a ball mill. During the process the temperature was allowed to slowly reach 25. 105°C. 1 kg of fairly warm carbon-monomer dispersion was charged to an autoclave containing 555 g of 9% latex pre¬ pared according to Example 15 and water to a total of 1 kg. During slow agitation HCl added until the latex had been absorbed by the monomer phase. This was established 30. by simple microscope investigation. The mixture was then made alkaline (pH about 9) by NH, and 35 g of 2,2azobi s (2,4- dimethylvaleronitπ ' le) were added. After agitation for a couple of minutes the dispersing medium (2965 g as above) was added. The agitation in the reactor was intensified 35. so that satisfactory agitation was obtained and the mixture was recirculated through a dispersing unit "Ystral" (Bergius Trading AB) and was hereby emulsified to a suitable size for toner particles. The reactor was put under nitrogen gas atmosphere and polymer zation was allowed to continue for 18 hours at 65°C under moderate agitation. Th,e suspen¬ sion was then cooled to room temperature, pH was adjusted to 2 with HCl and calcium phosphate, which functions as protective colloid, was hereby dissolved. The suspension 5. was filtered and washed first with acidified water and then with clean water and finally dried at 35°C. Investiga¬ tion with scanning electron microscope showed that the cross-linked polystyrene latex particles with 1.5% methacry¬ lic acid had been oriented towards the phase boundary 10.., su-rface of the toner particles so that about half the volume of' the latex particles protruded out from the surface. Copying tests in a Mita DC 313Z with a Hδganas carrier gave excellent copying properties and the reproducabi Ii ty was still good after 30000 copies. 15. Example 17. This exemple shows how the position of the latex particles in the phase boundary surface of the toner partic¬ les can be controlled at the production of pimply particles. Four latexes with varying contents of methacrylic 20. acid, 0.5%, 1%, 2% and 2.6%, and a constant amount of divi¬ nyl benzene 9.7% were prepared according to Example 15. In the same manner as in Example 16, 5% of the above described latexes (calculated as dry latex) were in turn added to 1 kg of the warm carbon-monomer dispersion which 23.. was then emulsified and polymerized in accordance with the procedure described in Example 16. In this manner four different types of toner with varying roughness were obtained. Investigations with scanning electron microscope showed that: JO. 1) Toner particles in the case wherein latex with 0.5% methacrylic acid had been absorbed had an almost smooth sui— face. 2) Toner particles with 1% methacrylic acid latex had an uneven surface but only a minor part of the diameter of 35. the latex particles protruded above the phase boundary surface of the toner particles. 3) Toner particles with latex containing 2% methacrylic acid had an uneven surface and the latex particles were well visible above the phase boundary surface. It was estimated that a little more than half the diameter pro¬ truded out from the phase boundary surface. 4) Toner particles with latex containing 2.6% methacrylic acid also had well visible latex particles in the surface 5. but the latex was found to be even more protrusive than before. In all cases the unevenesses were fairly uniformly distributed over the surface of the toner particles. Copying tests in a Mita DC 313Z with HδganSs carrier gave excellent 10. copying results above all with toner types with latex con¬ taining a higher part of methacrylic acid. Example 18. This example shows how it is possible to control the size and degree of covering of pimples on the toner 15. particles. A latex with 2.6% methacrylic acid and 5% divinyl benzene (calculated as 100%) was prepared according to Example 15 but the amount of seed latex and the amount of totally added monomer was adjusted so that a 0.-3 μm 20. latex was obtained. In the same -manner as in Example 16, 2 and 3.2% respectively of latex (calculated as dry) was absorbed by carbon-monomer dispersion which was emulsified and polymerized in accordance with Example 16. This resulted first of all in an increased degree of covering (part of 25. surface covered by latex in relation to total smooth toner surface without absorption of latex) with increased amount of absorbed latex. The case with absorption of 3.2% latex gave a better degree of covering than any of the cases in Examples 16 and 17. This is probably not only due to 30. the absorption of a more fine-grained latex (0.3 μm compared with 0.5 μm in Examples 16 and 17) but also because the latex has a lower degree of cross-linking, which leads to an increased swelling of the latex particles in this example. It was also found that the pimples in this example 35. have a diameter of about 0.4 μm which means that the mass of the latex particles has increased to a corresponding extent. A third test in connection with this was the absorp¬ tion of 5% of 0.5 μm latex (calculated as dry) with 2.6% methacrylic acid and 5% divinyl benzene or, in other words, the same size and amount as in Examples 16 and 17 but with a lower degree of cross-1i nki ng. The result of this was that so much of the latex was oriented towards the surfaces of the toner particles that the basic shape of these were 5. changed from spherical to buckly and thus to increased surface for the oriented latex. Copying tests with toner with 3.2% absorbed latex according to the above gave, as the earlier examples, good copying results. Example 19. Preparation of amphoteric latex. 10. To the same equipment as in Example 15 1.5 g of "Quer- ton 16CI29" (KenoGard), 1.5 g of 1mM CuSO, and water to a total of 1032 g were added. To the connected funnel 150 g of styrene charged. The mixture in the glass reactor was heated to 80°C under moderate agitation. At 80°C 18 15. g of 3.5% H O added and at the same time the mixtures in the reactor and the dropping funnel were placed under nitrogen gas atmosphere. The monomer was added to the reactor during about half an hour. After additionally 2 hours 1.5 g of Querton 16CI29 charged and the reactor again 20. placed under nitrogen gas atmosphere. The polymerization was then allowed to continue for 10 hours which resulted in a 0.13 μm 11% seed latex. 150 g of a seed latex, 3.3 g of Querton 16CI29, 1.5 g of 1mM CuSO, and water to a total of 1082 g were charged 25. to the same equipme_nt as above. To the dropping funnel 103.5 g of monomer charged. Depending on the desired compo¬ sition of the final latex varying amounts of (2-dimethyl- aminoethyI)-methylacrylate (DMAEMA), methacrylic acid, divinyl benzene (about 50%) and styrene were charged. 30. In this Example 4.71 g of DMAEMA, 0.51 g methacrylic acid, 12 g of about 50% divinyl benzene and 86.28 g of styrene were charged and presumed to give a polystyrene latex, cross-linked with 5% divinyl benzene (100%) and which also contains 3.9% DMAEMA and 0.4% methacrylic acid. 35. pH of the mixture in the reactor was adjusted to 2 with HCl and heated to 80°C under moderate agitation. At 80°C 15 g of 3.5% H 2 0 2 added and the mixtures in the reactor and the funnel were at the same time subjected to nitrogen gas atmosphere. The monomer mixture was then allowed to drop down into the reactor for about 3 hours. The polymerization was then allowed to continue for 12 hours and this resulted in a 0.2 μm 9% latex which is presu¬ med to have the above stated composition. 5. Example 20. Preparation of toner particles with "pimply" surface using amphoteric latex. In the same manner as in Example 16 3.5% of amphoteric latex (calculated as dry) prepared according to example 19 were absorbed in the warm monoinei—carbon dispersion, 10. but the absorption took place in alkaline envi ronment with NH,/Na0H. After the absorption pH was adjusted to about 9 and the mixture emulsified and polymerized in accordance with Examp le 16. Investigation with a scanning elect r.on microscope 15. showed that the latex particles of 0.2 μm had been oriented towards the surface. The basic shape of the toner particles had also been changed from smooth spherical to buckly « spherical. In the same manner as in Example 19 additionally 20. two latexes were prepared which had the same dry contents calculated in moles of amine and carboxyl c acid groups but the ratio was changed from 5:1 to- 1 :1 and 1 :5 respec¬ tively of amine carboxylic acid. In the same manner as above two additional types of toner particles were pre- 25. pared using these new latexes. Investigation in microscope showed that also for the two later types the 0.2 μm latex particles had been oriented towards the surface. However, in these cases the basic shape of the toner particles was still smooth but 30. part of the diameter of the latex particles protruded out from the phase boundary surface. In this manner particles suitable for copying of electrostatic printing were prepared. Examp le 21. Orientation of cationic latex. 35. In the same manner as in Example 19 cationic cross- linked latex was prepared based on 2-t π " methy lammoni ummeth- acrylate bromide (TMAEMA) with the difference that TMAEMA was charged to the reactor and only divinyl benzene and styrene were charged to the dropping funnel. In the same manner two 0.2 μm polystyrene latexes cross-linked with 5% divinyl benzene (100%) and containing 0.5 and 4.1% TMAEMA respectively were prepared. In the same manner as in Example 16 3.5% of these cationic latexes (calculated as dry ) were 5. absorbed to the warm carbon-monomer dispersion and the latexes were adsorbed using NH,/Na0H. pH was adjusted to about 9 and the mixtures emulsified and polymerized as in Example 16. Hereby two different types of toner particles were obtained. Investigation with scanning electron micro- 10 ~ .„ sco.pe. showed that the Latex particles had been oriented in varying degrees to the surface depending on the TMAEMA- content of the latex. In the case with 0.5% TMAEMA in the latex the latex had not been oriented towards the surface. In the case 15. with 4.1% TMAEMA in the latex the latex particles had to a large extent agglomerated outside the toner particles and thus migrated to the aqueous phase. This shows that also for Latex containing TMAEMA it is possible to control the orientation of the Latex after it has been absorbed 20. in the carbonmonomer dispersion. Example 22-24 relate to the application of fine-grained particles according to a dry method. Example 22. Preparation of a fine-grained polymerizate. The process of Example 2 was repeated with the diffe- 25. rence that divinyl benzene and sodium dodecyIsu Iphate were excluded. The organic phase was instead emulsiefied with 828 g of 3 g/kg ammonium laurate. In this way a 0,2jm micro- suspension containing charge modifier was obtained. Example 23. Coating of base particles with f ne-grained 30. particles in a dry process. 4 kg of suspension of base particles, prepared accor¬ ding to Example 3, were acidified, filtered and washed with water. The filter cake was finally dried at 35°C. The m crosuspensi on, prepared according to Example 22, 35. was precipitated by adding acid and airdried in thin Layers spread on glass sheets at 30°C. 1 kg of dry base particles and 40 g of dry fine-grained part cles, obtained from the dried mi c rosuspensi on, were charged together with polyethy- len granules, about 4 mm in size, to a powder mixer and mixed for 1 hour. The temerature of the powder bed was then raised during continued agitat on to 55°C and held there for 30 minutes in order to adhere the fine-grained particles to the base particles. inally the temperature 5. was raised for a short period to about 70°C in order to partly melt the fine particles into the surface of the base particles, where upon the powder bed was cooled to room temperature. The coated base particles was then sepa¬ rated from the granules by sieving. 10. In some cases the toner particles were mixed with aerαsil R972 to support good powder and tri boelectri ca L properties. In this way toner particles with good copying proper¬ ties were obtained. 15. Example 24. Coating of base particles with fine-grained particles. 4 kg of suspens on of base par icles, prepared accor¬ ding to Example 3 were acidified, fi ltered and washed with water. The filter cake was finally dried at 35°C. 1 kg 20. of dry base particles was charged together with polyethylen granules about 4 mm in size to a powder mixer. Vacuum was applied to the mixer and the jacket temperature was adjusted to 30°C. The microsuspension from Example 22 was added on portions of 10 ml. About 50 ml/min. were added and the 25. addition of dispers on was stopped after 200 ml, which was equal to 40 g of dry fine-grained particles. The mixer was operated until the mixture became dry, whereupon the vacuum pumping was interrupted and the temperature was increased during continued agitation to 55°C and after 30. that to 70°C in the same manner as in Example 23. The particles were then prepared in the same manner as in Example 23. In this way toner particles with good copying charac¬ teristics were obtained. 35.

Claims: C l a i ms 1. Toner f-or electrophotographic copying or electro¬ static printing, characterized in that it comprises an internally pigmented thermoplastic base or main particle 5. prepared by suspension pol merization and having a mean diameter within the range of from 2 to 25 μm , the surface of the base particle being covered by a fine-grained thermo¬ plastic polymerizate prepared by emulsion- or microsuspen- sion polymerization and having a mean diameter of from 10. 0.05 to 33 per cent of the mean diameter of the base partic¬ le and whereby 10 to 91 per cent of the surface of the base particle is covered by the fine-grained polymerizate. 2. Toner according to claim 1, characterized in that from 20 to 91 per cent of the surface of the base particle 15. is covered by the fine-grained polymerizate. 3. Toner according to claim 1 and 2, characterized in that the mean diameter of the fine-grained polymerizate is from 0.2 to 15 per cent of the mean diameter of the base particle. 20. 4. Toner according to claim 1 or 2, characterized in that from 30 to 80 per cent of the surface of the base particle is covered by the fine-grained polymerizate. 5. Toner according to any of the preceding claims, characterized in that also the fine-grained polymerizate 25. s internally pigmented. * 6. Toner according to any of the preceding claims, characterized in that the melting point of the fine-grained particles is >10°C higher than that of the base particles. 7. Toner according to any of the preceding claim-s, 30. characterized in that the fine-grained particles have been prepared by mi crosuspensi on polymerization and contain a charge modifying agent. 8. A method for the preparation of a toner for electrophotographic copying or electrostatic printing accor- 35. ding to claim 1, characterized in that an aqueous dispersion of an internally pigmented thermoplastic base particle prepared by suspension polymerization and having a mean diameter within the range of from 2 to 25 μm is brought into contact with a latex of a fine-grained thermoplastic polymerizate having a mean diameter of from 0.05 to 33 per cent of the mean diameter of the base particle where¬ after the temperature is raised so that the fine-grained particles adhere to the surface of the base particles to 5 « a degree of covering of 10-91%. 9. A method according to claim 8, characterized in that the fine-grained particles adhere to the surface of the base particles to a degree of covering of 20 - 91%. 10. A method according to claim 8 och 9, characterized 10. n that the aqueous dispersion of the pigmented base par¬ ticle contains polymerization serum from the polymerization of the base particle, which serum contains a protecti e colloid system . 11. A method according to claim 8 och 9, characterized 15. n that an aqueous dispersion of the pigmented base particle is brought into contact with a latex of the fine-grained polymerizate whereafter a protecti e colloid system is formed in the aqueous dispersion and the temperature is raised so that the fine-grained particles adhere to the 20. surface of the base particles. 12. A method according to claim 10, characterized in that the protective colloid system is deactivated before the adding of the latex of the fine-grained polymerizate, whereafter the protective colloid system is reformed and 25. the temperature is raised. 13. A method according to claim 10, characterized in that latex of the fine-grained polymerizate having func¬ tional groups of opposite charge than the base particles is added whereby the latex particles are attracted to the 30. base particles and thereby penetrating the colloid layer. 14. A method according to clai 10, characterized in that the protective colloid system is dissolved before adding of the latex of the fine-grained polymerizate, and that the latex particles have a higher melting point than 35. the base particles. 15. A method according to claim 10, characterized in that the protective colloid system is dissolved and removed from the base particles, that the base particles are redispersed, whereafter the latex of the fine-grained polymerizate is added, whereby latex particles are used having a higher melting point than the base particles and a charge of opposite character of the base particles. 16. A method for the preparation of a toner for elec- 5. trophotographic copying or electrostatic printing according to claim 1 or 2, characterized in that a internally pig¬ mented termoplastic base particle having a mean diameter within the range of from 2 to 25 μm is prepared by suspen¬ sion polymerization of a monomer or a monomer mixture in 10.. the. presence of a latex of a fine-grained thermoplas ic PO-Lymerizate having a mean diameter of from 0,05 to 33 per cent of the mean diameter of the base particle, the particles of the latex being pigmented and substantial insoluble in the monomer and said latex particles having 15. a higher degree of hydrophility than the polymer material in the main particles formed at the suspension polymeriza¬ tion. 17. A method according to claim 16, characterized in that the latex polymer material originates from a monomer 20. mixture which for control of hydrophility contains a monomer with anionic character in alkaline environment. 18. A method according to claim 16, characterized in that the latex polymer material originates from a monomer mixture which for control of hydrophility contains a monomer 25. with cationic character in acid environment. 19. A method according to claim 18, characterized in that the latex polymer material originates from a monomer mixture which for control of hydrophility contains a monomer with an amino group. 30. 20. A method according to claim 17, characterized n that the latex polymer material originates from a monomer mixture which for control of hydrophility contains a monomer with hydroxyl group. 21. A method according to any of claims 16 to 20, 35. characterized in that the latex particles are cross-1i nked . 22. A method for the preparation of a toner for elec¬ trophotographic copying or electrostatic printing according to claim 1 or 2, characterized in that a dry internally pigmented thermoplastic base particle prepared by suspension polymerization and having a mean diameter within the range of from 2 to 25 μm , is mixed with fine-grained thermoplastic particles ha ing a mean diameter of from 0.05 to 33 per cent of the mean diameter of the base particles in an amount 5. sufficient to cover 10, preferably 20, to 91 per cent of the surface of the base particle, whereafter the temperature is raised so that the fine-grained particles adhere to the surface, whereby the fine-grained particles have a higher melting point than the base particles. 10.

Inventors: HEDVALL BERTIL, MATTSON GUNNAR, PORRVIK STEN, SUNDSTROEM GOERAN, HEDVALL, BERTIL, MATTSON, GUNNAR, PORRVIK, STEN, SUNDSTROEM, GOERAN
Applicants: CASCO NOBEL AB
Application year: 1986
Main classification: G03G9
IPC codes: G03G9