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 particles. A protective colloid system can be present and 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 hydrophilicity 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 parti cles for electrophotographi c copying and pr cesses for thei r preparation. The present invention relates to toner parti cl for use in electrophotographic copying or electrostat 5. printing. More particularly the invention relates to su toner particles having a pimply surface. The inventi also relates to methods for the preparation of such ton particles. In electrophotographic cop ing the latent print 10. the photo-drum is developed with a toner consisting fine-grained pigmented thermoplastic particles. The mo common method of preparing a toner comprises melting thermoplastic material and mixing this with pigment, char modifiers, release agents etc. The product is then coole 15. crushed, ground and screened in an ai r stream to obtai particles with a size in the order of from 5 to 30 m . According to this method particles of very varying shap and sizes are obtained. This variation in shape and si gives rise to certain disadvantages in the copying process 20. Efforts have thus been made to find processes which gi toner materials having spherical and fai rly uniformly size pa ticles. One way of preparing a toner is to finely divid molten waxes or low molecular thermoplastic materials i 25. a spray drier. If such condi ions are used at the spra drying that a suitable particle size is obta ned directl the grinding step can hereby be eliminated. A disadvantag of the spray drying is, however that the size distributio of the powder is fairly w de. Further, it is not possibl 30. to satisfactori ly spray dry a melt of the thermoplasti materials which are usually used at so-called heat fixin by means of hot rolls or radiation. Spray dried powder are more suitable as toners intended for cold fi xing b means of pressing. Spray dried particles are advantageou 35. in that they are spheri cal and thus not of such varyin sh ' apes as ground parti cles. One method of preparing toner parti cles sui ta l for hot fi xing, whi ch method in principle i s very cheap is to disperse pigments, charge modifiers, release agents initiators etc in monomers which g ve polymers having suit able propert es for heat fi ing. The monomer is emulsif e ith a suitable colloid system in water, the temperatur is raised and by polymerization a fine, pigmented powde 5. of sperical particles is directly obtained and this powde can be dried, after washing, to give a powder suitabl for use n coping. Since the method is very simple severa attempts have been made to prepare toner particles in thi way. One process of this kind is disclosed in the Britis 10. patent application 2091435. In practical tests it has bee found that particles prepared by suspension polymerizatio have certain advantages such as the capab li y of gi in copies with good resolution. However, it has also bee found that such particles have a serious disadvantage i 15. that they have such a strong adhes on to the photo-dru that they are only very incompletely transferred to th paper. Such particles also agglomerate strongly with eac other which means that such a toner has very poor free flowing properties etc. 20. The drawbacks with the particles mentioned abov can be related to the smooth surface of the spherical par t cles prepared by normal suspens on polymeriza ion. Whe spherical particles with a smooth surface are used th adhesion to the photo-drum will be so strong that the 25. are not even completely removed at the cleaning of th photo-drum which follows the transfer step. Such remai ning toner thus leads to a rapid deter oration of the quali ty of the copies. A strong adhesion to the photo-drum i particularly serious if the toner consists of or contain 30. very fine particles, < 5 jm, since it is more difficul to remove such fine particles from the surface of th photo-drum by means of mechanical cleaning systems. According to the present invention it has been foun that spherical particles having a p mply surface do n 35. show the disadvantage of a strong adhesion to the phot drum. In several cases such particles even have lower adh sion than toner par cles Dreσared by the convention grinding process. The present invention thus relates to a toner whi compri ses ' an internally pigmented base parti cle, or ma parti cle, prepared by suspension polymeri za ion and havi a mean diameter of from 2 to 25 /urn, the surface of t particle being covered by a fine-grained polymeri zate wi 5. a mean dia eter of from 0.05 to 33% of the mean diamet of the base or main particle. Internally pigmented base parti cles here - refer parti cles prepared in a manner where the pigment is mi x with the monomer before the- polymerization and thus i 10. present more or less uniformly distributed in the finish polymerized base particle. The appli cation of the fine-grained parti cles the surface of the toner particles can be carried out i a manner which is techni cally so simple that the who 15. process from monomers to coated toner parti cles i s economi cally advantageous. The invention therefore represen a more economi cal way to make high quality toners. The size of the fine-grained particles which fo protuberances on the surface of the base or main particl 20. should be substantially smaller, than these particles. T diameter of the fine-grained parti cles should thus be maxi mum 33%, and preferably maximum 15%, of the diameter the base parti cle. The lower size limit is set by the small est size whi ch gi es the desi red effect of reduced adhesi 25. to the photo-drum. Already pimples having a size in th order of 0.005 ^m give a reduced adhesion. The fine-graine polymerizate suitably has a particle size in the rang of from 0.005 to 5 m, preferably from 0.02 to 2 jm. Another important factor is the degree of covering 30. ie how great a part of the surface of the parti cle whi c is covered by fine-grained parti cles. The closest possibl covering corresponds to about 91% of the surface of th base or main particle. However, such a high degree of cover ing is not necessary to reduce the adhesion to the photo 35. drum. It has- surpri singly been found that already a degre of covering of from 1 up to 10% gives a very strong reduc tion of the adhesion. Toner parti cles according to the invention wi th fin particles forming protuberances on the surface of the bas or main particles can be prepared in a number of different ways as described below. First will be described a process accordi g to whic fine-grained parti cles are adhered to the surface of bas 5. particles already prepared by suspens on polymerization To make the base particles monomer soluble initiator pigment and optional charge modifier and a dispersing agen for the pigment are fi rst m xed. The mi ture is emulsifie in water using a suitable colloid system. After evacua io 10. the temperature is ra sed for polymerization and spherica base particles are obtained. The mean diameter of thes can be from 2 to 25 Jm, preferably from 3 to 15 /urn. The small polymer particles which are applied t the surface of the base particles can be prepared by emul 15. sion polymerization or microsuspensioπ polymerization i per se known manners and, if desi red, charge modifier and pigments can for example be incorporated at m crosuspen sion pol merization. It is desirable that the fine-gra ned particles ar 20. strongly anchored in the surface of the base particles Th s can be achieved by softening the base parti cles usin small amounts of softening agents or by heating. Hereb the fine-grained particles wi ll be anchored by meltin into the surface. It is suitable that the fine-gra ne 25. particles melt into the base particles to a depth corres ponding to about half the diameter of the fine-graine particle. However the depth can be varried, it is onl nessecary that the fine-grained particles are fi rmly an chored in the base particles and at the same time protrud 30. out from the surface of them. The polymer composition of the fine-grained particle may. be the same as that of the base parti cle. However it might be advantageous to choose a more high-meltin polymer type for the fine-grained particles on the surface 35. A higher melting po nt gives a smaller r sk that the fine grained particles wi ll agglomerate with each other instea of adhe r ng to the surface of the base particles at th coating process. In order to make the fine-grained particle on the surface particularly difficult to melt they ca be cross-linked to a higher degree than the base parti cl The fine-grained parti cles can be applied to surface of already formed base particles in w t or methods or according to a special technique, descri 5. below, to the surface of the monomer droplets, whi ch aft polymerization together wi th the latex parti cles wi ll f pimply parti cles. A toner can for example be prepared by bringing aqueous di spersion of the pigmented base parti cle in 10. contact with a latex of the fine-grained polymerizate wher by a protecti e colloid system is subsequently formed the aqueous dispersion and the temperature raised to ma the fine-grained particles adhere to the surface of t base particles. 15. At production according to this method the protecti colloid system whi ch has been used for the suspension pol meri zation of the base parti cles i s suitably fi rst deact vated. If, for example, certain inorgani c powder stabi li se have been used as protective colloids such as diffi cult 20. soluble phosphates these can be dissolved by acidi fyi the aqueous suspension of the base parti cles. The lat of the fine-grained parti cles is then slowly added. Here such conditions should be used that the latex wi ll n precipitate immediately on contact with the suspensi 25. of the base particles, since there is then a risk th the small particles in the latex wi ll agglomerate wi each other instead of being deposited on the surface the base parti cles. After agitation for some time the fine-grained parti 30. les wi ll have been precipitated on the surface of the ba particles. The system is then made more alkaline so th the protective colloid system wi ll be reformed. There then no risk of agglomeration of the parti cles when t dispersion is warmed to melt the fine-grained particl 35. into the surface of the base particles. Acidifi cation a washing is then carried out. In some cases the protective colloid system can kept intact when the latex of the fine-grained particl i s added. In thi s case latex parti cles and base parti cl which have opposite charges are used. This is achieved through controlling the Zeta-potent al of the particles. The chemical compos tion of the surfaces of the base partic les and the latex particles are chosen in such a way tha 5. the two types of particles have Zeta-potentials of opposit character at the used condition. This can be accomplishe by copo ly e ri zati on with functional monomer.s with charge of opposite character. The charged latex particles wil be attracted to the base particles of opposite charge an 10. thereby penetrate the colloid layer. To give the toner the correct tπ ' boelectr c charg the fine-grained particles on the surface must have a speci f c triboelectr c charge and this can be achieved by subse quently precipitat ng a charge mod fying agent on the sur 15. face of the coated particles. If the fine-grained particle are prepared by mic-rosuspension pol merization a charg modify ng agent can alternatively be mixed w th the monome already before the polymerization of the fine-grained par t cles. Finally the chemical composition of the fine-graine 20. particles can be selected in such a manner that no extr addition of charge modifying agent is requ red. Example of such particles which give a positive triboelectric charg are fine-grained particles of polyacrylonitri le or amino containing monomer. When fine-grained particles of polyviny 25. chloride, fluoro polymers etc are used a negative triboelec tric charge is obtained. The fine-grained particles can also be applied accord ing to a dry method. At application of the fine-graine particles by a dry method the base particles are fi rs 30. dr ed and charged to a m xer. To keep a un form mixtur in the powder bed t is advantageous to admix larger beads eg glass beads of 5 mm. The smaLl polymer particles whic are to cover the surface are then charged to the powde bed. The small particles can be present either as a disper 35. sion in a suitable liquid, whereby the liquid is evaporate from the powder bed, or as an already dried very fine gra neα Do der. The te.ioera re of he πowder be s -aise under continued agitation. The small particles wi ll the adhere to the surface of t e base parti cles and, at highe temperatures, at leas partly melt. into the surface the base parti cle. An alternative way of making the small polymer parti les melt into the surface of the base parti cles i s to intr 5. duce the coated base parti cles into an ai r stream whi for a short time is heated to a temperature of from 1 to 400° C, depending on the dwell time ' in the " hot zone. According to the above described methods the ba parti-ctes are fi rst prepared by suspension polymerizati 10- and these are then treated wi th a latex of the fine-grain polymerizate to give "pimply" toner particles accordi to the invention. According to another method for the preparation toner parti cles with a rough surface a special kind 15. process is used and herein a latex, ie the fine-grain polymerizate, is first prepared and the base particle are prepared by suspension polymerization in the presen of the already prepared latex. In the following thi s meth of preparation, which forms part of the present inventio 20. wi ll be described more in detai l. According to the last method spheri cal parti cl with a pimply surface, useful as toners in electrophot graphic copying and electrostatic printing, are produc by fi rst preparing a latex, an aqueous dispersion, of fin 25. grained polymer particles. The latex can be prepared accor ing to the emulsion polymerization technique using wat soluble initiators and suitable emulsifiers or accordi to the technique of m i c rosuspens i on polymeri zation where the monomer is fi rst finely divided in water, by mea 30. of intensive emulsifying and using surfactants, and th polymerized using initiators which usually a r e solub in the monomer. In certain cases water soluble ini tiato can, however, be used in mi c ro s uspen s i on polymeri zation. The latex particles shall be insoluble in the monome 35. and optionally other solvents and for this purDose th are preferably c ro s s- 1 i n ked . Further, the surface of t latex oarti cles shall have a fi xed hydroD i li c/hydroDhob character. At the production of pimply parti cles according the method latex is mixed with a monomer or a monomer mix¬ 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, 5. should be selected in such a manner that the latex particles Leave the aqueous phase and migrate to the monomer phase or to the monomer - water - phase boundary. Additional water and a su table colloid system is then charged. The monomer is emulsified to small drops and the temperature 10. is ra sed for pol mer zation. After poly erization a fine¬ grained pigmented powder is obtained. At investigation with a scanning electron microscope it is found that the latex particles of suitable hydrophi l c/hydrophobi c balance have migrated to the surface of the polymer particles formed 15. at the suspension polymerization. Hereby a pimply surface is obtained on these particles. By varying the hydrophi I i c/hydrophobi c balance it is possible to control the d splacing of the latex particles with regard to the surface of the formed base particles. 20. If the latex particles have a very hydrophobic charac¬ ter, for example if they have been prepared from pure styr- ene, d inyl benzene and with hydrogen peroxide as ini¬ tiator, they will not at all penetrate the surface of the formed polymer particles. Such latex particles can 25. 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 after the polyme¬ rization be found in the aqueous phase. Suitable hydrophi I i c ty for the latex particles depend 30. on the hydrophi li c ty of the main particles. The latex particles should have a higher hydrophi Ii ci ty than the polymer of the main particles. The upper limit for the hydroph licity of the latex particles s the level where the latex particles start being pressed out from the main 35. particles to the aqueous phase during the polymerization. The degree of hydrophilici y can for example be con¬ trolled at the preparat on of the latex particles by adding certain amounts of monomer with anionic character in alka line environment, for example methacrylic acid, itaconi acid, styrene sulphonic acid, etc. Compounds wi t cation character in acid envi ronment can also be incorporat in the Latex polymer to make the Latex parti cles more hydr phi lic, eg t ri met hy I ammoni umethyL methacrylate halid 5. However, it is not necessary to use ionised groups to ach eve hydrophi licity. Control of hydrophi licity can al be achieved by polar, non-ionised monomers, eg methyl meth crylate, acrylo nitri le, allyl alcohol, 2-di methy I a i noeth methacrylate, hydroxyethyl methacrylate. As polar nonionis 10. monomers such containing amino groups or hydroxyl grou are preferred. It is also possible to use amphoteri c lat which contains both acid and basic groups for obtain a suitable hydrophilicity. The determining factors f the latex particles to form pimples according to this meth 15. are thus that the latex particles are not soluble in t monomer or the monomers whi ch form the main parti cle a that the surface of the Latex parti cles have a more hydr phi li c character than the polymer of the formed main parti le. 20. Cross-Linking is of course not necessary if the pol mer composition of the Latex particles is such that t latex parti cles are not soluble in the monomers witho being cross-Linked. An example of this i s Latex parti cl of po I ya c ryL on i t ri I e , or of copo I yme ri zates having a hi 25. a c ry I on i t ri Le content. Otherwi se the Latex parti cles a cross-Linked to obtain insolubi lity. The degree of cross-linking in the latex particl is of certain i portance. At a Low degree of crosslinki the latex parti cles wi ll swell in the monomers. The si 30. of the pimples in the finished particles wi ll then greater than the size of the parti cles in the used late Hereby a certain amount of latex wi ll suffi ce to cov a greater part of the surface of the main parti cles. T swelling of the latex parti cles also results in that th 35. difference in hydroph li city between the monomer and th latex particle wi ll be diminished since the compositi of the swelled latex parti cles wi ll be more e that the monomers. The size of the pimples i s, besides the degree swelling, also determined by the size of the particles in the latex. At a smaller size a lower part by weigh of latex is required to give a determined degree of covering of the surface of the final particles. The smallest size 5. of the pimples is decided both by the size the pimples should have to sufficiently elim nate the attraction to the photo-drum due to van " der Waal forces or due to a too strong electrostatic adhesion and by the smallest size which it is technically possible to prepare. With regard 10- to van der Waal attraction this will decrease to a high extent already when the base particles, the main particles, are removed from each other by 10 nm. If half the size of the p mples is outside the surface of the base particle it should then suffice with a diameter of 20 nm for the 15. particles n the used latex. The largest size of the pimples s a diameter corresponding to about 33% of the diameter of the spherical main particle. The mean diameter of the particles in the latex should be from 0.05 to 33% of the mean diameter of the main particle, and this should b 20. within the range of from 2 to 25 / m. The chemical composition of the latex particles form ing the pimples can be selected arbitrarily as long a the particles are not dissolved in the monomer or monome mixture used for formation of the main particle. As ha 25. been stated, the hydrophi Li c-hydrophobi c balance must however, be considered. Further, the fact that the pimple influence the triboelectric properties of the final particl must also be considered. The pimples represent the oute contour of the toner particles. At rubbing, the type an 30. level of the triboelectric charge is thus determined b the chemical composition of the pimples. Further it shoul be considered that the electrostatic charge will be greate with protuberances in the form of pimples due to the increa sed surface of the powder pa rti cles .The pimples may als 35 influence the speed in charging/decharging of the particle because their small radius of curvature compared to th radius of the base article. The degree of covering, is an important factor an we have found that already a covering of from 1 up to 10 has a posi tive effect. The property of the pimply spheri cal parti cles give a decreased adhesion to surfaces and between the pa ticles themselves can give advantages also in other fiel 5. than electrophotographic copying. It has thus been fou that they give a reduced adhesion to the screen if th are used -for el trostatic printing according to the "d si Ik-screen" method. Such prints wi ll thus have a strong colouring than if spherical particles with smooth surfa 10. are used. The rough surface results, as has been mentione in a reduced mutual attraction between the parti cles. powder of such particles wi ll thus have better free-flowi properties. Owing to the Low tendency to formation of powd 15. aggregates particles with a rough surface are advantageous used also in powder coating operations, for example f coating of metal articles when the powder is sintered on. Choice of material wi ll be discussed more in deta below and when nothing else is stated this is valid indepe 20. dent of the method of preparation of the base or main pa ticles coated with fine-grained polymerizate. As monomers, alone or in mixture, for the preparati of the latex particles the following can for example used: styrene and different derivatives of styrene, acryl 25. acid and methacrylic acid or esters thereof, acrylo nitri l vinyl chloride, vinyl fluoride, vinylidene fluoride, vin acetate etc. To obtain c ross- I i nki ng po Lyfunct i ona I monome can be used, eg divinyl benzene, ethylene glycol diacrylat ethy leneg I yco I d i metha c ryI ate, t ri methyIo Lpropane tri 30. crylate etc. The amount of cross-Linker can be varied a high degree as Long as the Latex particles fulfi l t requi rements on correct hydrophi lity and insolubi lity. For the preparation of the base particle, or t main particle, the same monomers, and also cross-linker 35. as above can be used, but generally such a mixture is us that this particle wi ll have a lower softening point th the latex particles. The preferred main monomers for both latex parti cl and base or main particles are styrene, acrylates and meth 12 cryIa s . As emulsifiers for the preparation of the latex pa ticles conventional surfactants for emulsion and micr suspension polymerizat on respectively are used. Howeve 5__ care should be taken that the emulsifier system will n to a too high degree negatively influence the ' functi of the colloid system which is used for the preparati of the base particle or the main particle. It is also adva tageous if the used emulsifiers have such a water solubili tQ. that they can be washed away from the surface of the pr duced pimply toner particles. As initiator at the production of the latex particl according to emulsion polymerizat on technique convention water soluble initiators can be used, eg persulphate 15. hydrogen peroxide, hydroperox des, etc. For latex accordi to the m crosuspens on polymer zat on technique conventi nal monomer soluble initiators can be used, eg dialk peroxid carbonates, tert. utyl peroxipivalate, octano peroxide, lauroyl peroxide, tert.butyl peroxy 2ethyIhexan 20. ate), benzoyl peroxide, 2,2-azob sisobutyron tri le, 2, azob s-2,4-d methylvaleron tri le and similar compound For the preparation of the base or main particles the sa initiators as those for preparation of latex accordi to microsuspens on polymer zat on can be used. 25. As protective colloid in the colloid system for t preparation of base or main particles, water soluble coll ids of the type cellulose derivatives, polyvinyl alcoh etc or powder stabilisers of the type difficultly solub phosphates, etalhydroxides, silica etc can be used. T 30. powder stabilisers are preferably used together with suitable co-stabil ser. As colorants to be mixed with the monomer for t base or main particles inorganic colorants, organic colo ants, magnetite or carbon black are used. In certain cas 35. it is suitable to give the pigments a surface treatme so that they will remain finely divided in the monom drops. Toner particles according to the invention wi thus be colored throughout, ie the colorant is prese polymeri ce base or main parti cle. As has been stated i s also possible to let colorant and certain other additiv be present in latex prepared according to m i c ros u spens i polymerization processes. 5. The toner particles of the invention can be us together with conventional carriers for developer compos tion in known manner. The invention is further i llustrat in the following examples which, however, are not intend to Limit the same. Parts and per cent relate to parts 10. weight and per cent by weight, unless otherwise stated. Example 1 - 11 relate to the fi rst described meth with its different variations, where fine-grained particl are adhered to the surface of base particles. Example 12 - 16 relate to the second described meth 15. with fine-grained particles present at the oreparati of the base particle. Exam le 1. Preparation of a fine-grained polymerizat Emulsion polymerization. 40 g of styrene, 1.8 g of sodium dodecylsulpha 20. and water to totally 395 g were charged to a 500 ml gla flask equipped with cooling means, agitator and a val for evacuation and introduction of nitrogen. The mi xtu was heated to 80°C under agitation. At 80°C 5 g, 3.5% hydrogen peroxide was added and the same time the mi xtu 25. was subjected to a nitrogen atmosphere. The polymerization was then allowed to continue f 12 hours which gave a 0.11 ^um 10% seed latex. 120. g of the above seed Latex, 200 g of 5g/kg sodi dode cy L s u I pa h t e , 0.4 g of divinyl benzene, about 50%, 27 30. 9 o styrene and water to totally 395 g were charged the same equipment as above and the same procedure w then followed. In thi s manner a cross-linked polystyre latex was prepared with parti cles of 0.16 /jm and a d content of 10%. 35. Example 2. Preparation of a fine-grained polymeri zat i crosuspenion polymeri zation. 250 g of styrene, 0.8 g of neozapon schwartz X charge modi fier (from BASF ) and 2.5 g of 2,2 '-azobi s (2, d i met h I va I e ron i t r i I e ) were charged to the same equipme as in Example 1. The monomer mixture was heated and th bulk polymerization allowed to continue for two hours a 85°C which resulted in a viscosity increase at 24°C fro 10.5 to 13 seconds (Ford-cup, 4 mm nozzle). 5_ 198 g of bulk polymerizate, 2 g of divinyl benzene about 50%, 7 g of 2,2'azobis(2,4-dimethylvalerom " trile ' were emulsified with 828 g of 3g/kg sodium dodecylsuLphat in an Ultra Turrax for some minute. The pre-emulsioπ was charged to a 2-step Manton Gauli 10. homogenizer, model 15 M, where a narrow drop size dis tribution of 0,19 m (determined with a Coulter Nanosizer was obtained. The homogenized emulsion and 1 g of sodiumdo decyIsuLphate were charged to a 1,5 L glass autoclave whic was placed under nitrogen gas atmosphere. The emulsio 5_ was polymerized at 65°C during 12 hours. In this way 0,19 Jm, 19% microsuspension with charge modifier incor porated during polymerization and cross-linked with 0,5 divinyl benzene was obtained. Examp Le 3. Preparation of base particle 20. To a solution of 2kg 0.16 molal trisodium phosphat 520 g of 1.0 molal calcium chloride solution was adde under agitation and finally 150 g of a 0.2% solution o sodium dodecyLbenzenesulphonate . The now obtained mixtur was diluted to 2965 g with 0.2% potassium dichromate solu 5. tion and forms the dispersion medium. 700 g of styrene, 300 g of buthyl methacrylate, 8 g of carbon black "Printex V" (Degussa) and 3 g of neozapo schwartz X 51 (BASF) were dispersed in a ball mill to giv a carbon- onomer dispersion. 30. 10 g of 2,2-azobi s (2, 4-di methyIva Leroni tπ " le) wa dissolved in 990 g of carbon-monomer dispersion and add together with the dispersion medium (2965 g) to a reacto The mixture was put under nitrogen gas atmosphere and all wed to polymerize at a rapid heating from room temperatu 35_ and further at 85°C for 1 hour under moderate agitatio The mixture was cooled to room temperature and pH adjust to about 3 whereby 35 g of 2,2-azob s ( ,4-di methyIva leron trile) was added. After agitation for a couple of inut pH was adjusted to about 9 and the mixture was recirculat through a dispersion unit "Ystral" (Bergius Trading A and emulsified to a sui table drop size for toner parti cle The reactor was once again placed under nitrogen gas atmo phere and polymerization continued for 18 hours at 65 5. under moderate agitation. The suspension was then cool to room temperature. A part of the polymeriza e was transferred to a vess and pH adjusted to 2 with HCl and calcium phosphate whi functions as protective colloid was hereby dissolved. T 10. suspension was fi ltered and fi rst washed with acidifi water and then with disti lled, water to finally be dri at 35°C. In this manner toner particles with a parti cle si of about 10 μm and with a charge of -12uC/g against 15. Hδganas carrier were obtained. Copying tests with the ton in a Mita DC 313 Z fi rst gave good copying results b the rep roducab i I i ty was fai rly rapidly impai red due t the strong adhesion of the spheri cal, smooth toner particl to the photo-drum. 20. Example 4. Coating of base particles with fine-grain particles. 70 g of 10% polystyrene Latex prepared accordi to Example 1, 390 g of 1.5 g/kg sodium dode cy I s u L phat and 2 I of water was mixed and form the coating dispersion. 25. 2 kg 1.5 g/kg sodium dodecyL su Iphate were charge to a reactor containing 4 kg of a suspenion prepared acco ding to Example 3 and pH was then adjusted to 2 with HCl The coating dispersion was then added for 20 minutes unde good agitation and then mi xed for totally 1 hour befor 30. the temperature was raised to 65°C. At 65°C pH was adjuste with NH-, to 8.3 and the temperature further raised to 90°C After less than 5 minutes at 90°C the now coated tone suspension was cooled to room temperature. Subsequently pH was adjusted to 2 using HCL and ca I 35. cium phosphate, whi ch functions as protective colloid was hereby dissolved. The suspension was fi ltered and fi rs washed wi th acidified water and th n with di sti l led water A sample was doped with 0.05% neozapan Schwartz X 5 ' , case on the amount of polymer, by slurrying the f itercake i water after the washing and mixing with a 1% methanol solu¬ tion of the charge modifier and filtration was then carried out again. Investigation with a scanning electron icroscope 5. showed that the polystyrene particles had been adsorbed 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 used was so that about 10% of the surface of the base particles was covered by 10. fine-grained particles. In this manner toner particles with a "pimply" surface were obtained and they gave a charge of -14 uC/g against a Hδganas carrier. Copying tests with a Mita DC 313Z did from the beginning give very good copies and the reproducability was stiLL good after 30000 cop es. 15. A particularly good background and clean copies were noted. The photo-drum was only covered by small amounts of toner which could be removed easily. ExampIe 5. Coating of base particles with fine-grained particles. 20. Base particles were prepared in the same manner as in Example 3 and coated in the same manner as in Example 4 but with 40 g of 19% polystyrene latex prepared in accor dance with Example 2. Microscopy showed that the particles had been adsorbe 25. and melted into the base particles to about half thei volume and the degree of surface coating was also her in the order of 10%. In this manner pimply toner particle were obtained where the "pimples" contained a charge modi fier which gave a charge of -17 uC/g. As the toner of Examp 30. le 4 this toner also had excellent copying properties. Example 6. The process of Example 4 was repeated with the differ ence that the amount of latex was lowered to 35 g. icroscopy showed a Lower degree of covering, abou 35. 5%. Despite this toner particles obtained better copyin properties than toner particles according to Example 3. Examp I 7 ■ The process of Example 4 was repeated with th differens that the amount of latex was Lowered to 7 g This covering corresponds about 1 % of the surface b despite the low covering a positive effect compared example 3 was noted. Example 8. Preparation of base particle suspension. 5. The process of example 3 was repeated with the diffe ence that in connection with the addition of 35 g of 2 -azobi s- ( ,4di meth L va Ie roni t ri Ie) at pH 3, 8 g of dimethy ami noethyImetacryLate were also added. In this way a suspe sion of base particles was prepared with a Zeta-potent i 10. changing from positive to negative with increasing pH a higher pH value than for the suspension in Example 3. Example 9. Preparation of a base particle suspension. ' The process of Example 3 was repeated with the dif erence that after emulsifying to suitable drop size f 15. toner particles 11 g of t ri methyIami noet yLmethac ryIa bromide were added. In this way a suspension of base parti les was prepared, with a Zeta-potential changing from pos tive to negative at a higher pH than for the suspensio of Example 3 and 8. 20. Example 10. Preparation of a fine-grained polymerizat 1 g of 2-suIfoethyImethac ryIate was added to an aut clave together with 309 g of water and pH was adjust to about 4 with NH,, and 0,4 g of 1mM CuSO. solution a -> 4 80 g of styrene were added. The mixture was heated to 80° 25. At 80°C 10 g of 3,5% H ?°? as added at the same time the mixture was put under nitrogen gas atmosphere. T polymerization was then allowed to continue for 12 hour which resulted in a 0,14 /-im, 20% latex which was free fr surfactants. 30. 40,6 g of the above prepared latex, 200 g of wat and 0,4 g of 1 mM CuSO, solution were added to an autocla equipped with two dropping funnels. To one dropping funn 72 g of styrene was added and to the other dropping funn 76 g of water and 1 g of 2-suIfoethyL etha cryI ate, f 35. which pH was adjusted to about 4 (NH,), were added. T autoclave was heated to 80°C. At 80°C 10 g of 3,5% H 2 was added at the same time as the whole system was p under nitrogen gas atmosphere. The content of oo t dropping funnels were added during about 3 hours. Tπe pol meriza ion was then allowed to continue for 12 hours. I this manner a surfactant free coating latex was prepare with particles of 0, 6 μm and a dry content of 20%. Example 11. Coating of base particles with Latex. 5. 6 g of 20% coating Latex prepared according t Example 10, 90 g of 5 g/kg sodi umdodecyIsulphate and 1260 of water were mixed and constitute the coating dispersion This amount of coating dispersion corresponds about 5 surface covering of the base particles. 10. To an autoclave containing 4 kg suspension of bas particles, prepared according to Example 8, 480 g of 5 g/k sodi umsuLphate and 3520 g water were added. The coatin dispersion was added during 20 minutes at good agitation without preceding ad ustment of pH and thus the protectiv 15. colloid was not dissolved. The mixture was allowed to stan under agitation for an hour before the temperature wa raised to 90°C . After a minute or so at 90°C the coate toner suspension was cooled to room temperature. The suspen sion was acidified to pH 2 and filtrated and washed wit 20. water. The sample was doped in the same manner as in Exam ple 4 and in this way pimply toner particles with goo copying qualities were obtained. The example illustrates coating of base particle with latex, when the protective colloid was present. Thu 25. it was possible to bring together Latex- and base particle and heat the mixture to obtain adhesion between base- an Latex particles, in spite of the presence of protectiv colloid consisting of precipitated calcium phosphate. In another test the method according to this tes 30. was repeated, with the difference that the base particle were prepared according to Example 9. The test showed tha the same result was obtained irrespective of the base par ticles being prepared accord ng to Example 8 or 9.- Whe both the tests were repeated with the difference that th 35. latex was prepared according to Example 1, the latex agglo merated in the water phase when the temperature was rai e and thus no markedly pimply toner particles were obtained The same tπ ng happened en the test was repeated wi base particles prepared according to Example 3 and late prepared according to Example 1. Also when the test w repeated wi th base parti cles prepared according to Exampl e and latex prepared according to Example 10, no ramaini coating was obtained after the drying. Thus it was possib 5. to coat base particles with latex also in the presen of active protective colloid, when as well base particl as latex parti cles were copo I yme ri zed with small amoun of functional monomeres but of opposite charge character. Example 12. Preparation of anioni c latex. 10. 110 g of styrene, 0.33 g of sodi umdode cy I sulpha and water to a total of 1067 g were charged to a 1.5 glass reactor with a double jacketing and equipped wi agitator and valve for evacuation and introduction of nitr gen gas. The ixture was heated to 80°C under rapid agit 15. tion. At 80°C 33 g of a 1% potassium persulphate soluti was added and at the same time the mixture was subject to nitrogen gas atmosphere. The polymerization was allow to continue for 12 hours and resulted in a 0.28 μ m 8% se latex. 20. 300 g of the above seed latex. 0.30 g of sodium dod cylsulphate and- water to a total of 1060 g were charg to the same' equipment as above, but in this case a droppi funnel was also connected. 100 g monomer was charged the funnel. Depending on the desired composition of t 25. final latex varying amounts of methacryli c acid, divin benzene (about 50%) and styrene were charged. In thi s exa ple 1.8 g of methacryli c acid, 24 g of about 50% divin benzene and 74.2 g of styrene were charged and this i presumed to give a polystyrene Latex cross-Lin ed wi 30. 9.7% divinyl benzene ( 100%) and which also contains 1. methacrylic acid. The mixture in the glass reactor was heated to 80° under moderate agitation. At 80°C 40 g of a 1% potassi persulphate solution was added and at the same time th 35. mi xtures in the reactor and in the funnel were subject to nitrogen gas atmosphere. The monomer mi xture was th allowed to drop down into the reactor for about 3 hours The polymeri zation was then allowed to continue for 1 hours which gave an 0.48 μm 9% latex whi ch i s presume to have the above stated composition. Example 13. Preparation of toner particles with pimpl surfa e. To a solution of 2 kg of 0,16 molal trisodium phos 5. phate 520 g of 1.0 molal calcium chloride solution wa added under agitation and finally 150 g of 0.2% sodiu dodecylbenzene sulfonate was added. The now obtained mix ture was diluted to 2965 g with 0.2% potassium dichro mate solution and forms the dispersion medium. 10. 700 g of styrene, 300 g of butyl methacrylate, 8 g of carbon black "Printex v" (Degussa), 3 g of charg modifier "Neozapon Schwartz X51" (BASF) and 3.5 g of azo bisisobutyronitrile and 50 g of polyethylene wax, as releas agent, were dispersed under controlled temperature in 15. ball mill. During the process the temperature was allowe to slowly reach 105°C. 1 kg of fairly warm carbon-monome dispersion was charged to an autoclave containing 100 of 9% Latex prepared according to Example 12 and wate to a total of 1 kg. During slow agitation HCl was adde 20. until the Latex had been absorbed by the monomer phase This was established by simple m croscope investigation The mixture was then made alkaline (pH about 9) by NH and 35 g of 2,2azobi (2,4-dimethylvaleronitrile) were added After agitation for a couple of minutes the dispersin 25. medium (2965 g as above) was added. The agitation in th reactor was intensified so that satisfactory agitatio was obtained and the mixture was recirculated through dispersing unit "Ystral" (Bergius Trading AB) and was hereb emulsified to a suitable size for toner particles. Th 30. reactor was put under nitrogen gas atmosphere and polymeri zation was allowed to continue for 18 hours at 65°C unde moderate agitation. The suspension was then cooled to roo temperature, pH was adjusted to 2 with HCl and calciu phosphate, which functions as protective colloid, was hereb 35. dissolved. The suspension was filtered and washed fi rs with acidified water and then with clean water and finall dried at 35°C. Investigation with scanning electron micro scope showed that the cross-linked polystyrene latex parti les with 1.5% methacrylic acid had been oriented towar the phase boundary surface of the toner particles so th about half the volume of the latex , parti cles protrud out from the surface. Copying tests in a Mita DC 313Z with a Hόganas carri 5. gave excellent copying properties and the rep roducab i I i was sti ll good after 30000 copies. Example 14. Thi s example shows how the position of the lat parti cles in the phase boundary surface of the toner parti 10. les can be controlled at the production of pimply parti cle Four latexes with varying contents of methacryli acid, 0.5%, 1%, 2% and 2.6%, and a constant amount of divi nyl benzene 9.7% were prepared according to Example 12. In the same manner as in Example 13, 0,5% of t 15. above described latexes (calculated as dry latex ) we in turn added to 1 kg of the warm carbon-monomer di spersi which was then emulsified and polymerized in accordan wi th the procedure described in Example 13. In thi s mann four different types of toner with varying roughness we 20. obtained. Investigations with scanning electron mi crosco showed t hat : 1 ) Toner parti cles in 'the case wherein latex with 0.5 methacrylic acid had been absorbed had an almost smooth sur face. 25. 2) Toner particles with 1% methacrylic acid Latex had a uneven surface but only a minor part of the diameter o the latex particles protruded above the phase boundar surface of the toner particles. 3) Toner parti cles with Latex containing 2% methacryli 30. acid had an uneven surface and the Latex parti cles wer well vi sible above the phase boundary surface. It wa estimated that a Little more than half the diameter pro truded out from the phase boundary surface. 4 ) Toner parti cles with latex containing 2.6% methacryli 35. acid also had well vi sible latex parti cles in the surfac but the latex was found to be even more protrusive tha before . In all cases the unevenesses were fai rly uniforml distributed over the surface of the toner parti cles. Copyin tests in a Mita DC 313Z with Hδganas carrier gave excellent copying results above all with toner types with latex con¬ taining a higher part of methacryli acid. Example 15. Preparation of amphoteric latex. 5. To the same equipment as in Example 12 1.5 g of "Quei— 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 10. g of 3.5% H-,0 ? added and at the same time the m xtures in the reactor and the dropping funnel were placed under n trogen gas atmosphere. The monomer was added to the reac¬ tor during about half an hour. After additionally 2 hours 1.5 g of Querton 16CI29 charged and the reactor again placed 15. under n trogen 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 16CL29, 1.5 g of 1mM CuSO, and water to a total of 1082 g were charged 20. to the same equipment as above. To the dropping funnel 103.5 g of monome-r charged. Depending on the desired compo¬ sition of the final Latex varying amounts of (2-dimethyl- am noethyl) -meth Lacr Late (DMAEMA), methacrylic acid, divinyl benzene (about 50%) and styrene were charged. 25. 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. 30. The pH of the mixture in the reactor was ad usted to 2 with HCL and heated to 80°C under moderate agitation. At 80°C 15 g of 3.5% H- j O- added and the mixtures in the reactor and the funnel were at the same time subjecte to nitrogen gas atmosphere. The monomer mixture was the 35, allowed to drop down into the reactor for about 3 hours. The polymerization was then allowed to continue for 1 ours and th s resulted in a 0.2 μ™ 9 % latex which is presu med to have the above stated composition. Example 16. Preparation of toner particles with "pimply surface using amphoteri c latex. In the same manner as in Example 13 0,3% of amphoter latex (calculated as dry) prepared according to examp 15 were absorbed in the warm monomer-carbon dispersio 5. but the absorption took place in alkaline environment wi NH,/NaOH. After the absorption pH was adjusted to abo 9 and the mixture emulsified and polymerized in accordan with Example 16. Investigation with a scanning electron mi crosco 10. showed that the latex particles of 0.2 μm had been orient towards the surface. In the same manner as in Example 15 addi tional two latexes were prepared whi ch had the same dry conten calculated in moles of amine and carboxyLi c acid grou 15. but the ratio was changed from 5:1 to 1 :1 and 1 :5 respe tively of a ine and carboxyLi c - acid. In the same mann as above two additional types of toner particles were pr pared using these new latexes. Investigation in microscope showed that also f 20. the two later types the 0.2 μm Latex particles had be oriented towards the surface. In these cases the bas shape of the toner particles was sti ll smooth but pa of the diameter of the latex parti cles protruded out fr the phase boundary surface. 25. In this manner particles suitable for copying electrostati c printing were prepared. Example 17-19 relate to the application of fine-grai ed particles according to a dry method. Example 17. Preparation of a fine-grained polymeri zate. 30. The process of Example 2 was repeated with the diff rence that divinyl benzene and sodium dodecyL suI phat e we excluded. The organic phase was instead emulsiefied i 828 g of 3 g/kg ammonium laurate. In this way a 0,2/um micr suspension containing charge modifier was obtained. 35. Example 18. Coating of base particles with fine-grain particles in a dry process. 4 kg of suspension of base parti cles, prepared acco ding to Example 3, were acidi fied, fi ltered and wash with water. The fi lter cake was finally dried at 35 ° The microsuspension, prepared accord ng to Example 17, was precipitated by adding acid and airdried in thin layers spread on glass sheets at 30°C. 1 kg of dry base particles and 4 g of dry fine-grained particles, obtained from the 5. dr ed microsuspension, 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 agitation to 55°C and held there for 30 minutes in order to adhere the fine-grained 10. particles to the base particles. Finally the temperature 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 15. rated from the granules by sieving. In some cases the toner particles were mixed with aerosil R972 to support good powder and t riboe lect ri ca L properties. In this way toner particles with good copying proper 20. ties were obtained. Example 19. Coating of base particles with f ne-graine particles. 4 kg of suspension of base particles, prepared accor ding to Example 3 were acidified, filtered and washed wit 25. water. The filter cake was finally dried at 35°C. 1 k of dry base particles was charged together with polyethyle granules about 4 mm in size to a powder mixer. Vacuum wa applied to the mixer and the acket temperature was adjuste to 30°C. The microsuspension from Example 17 was adde 30. on portions of 2 ml. About 5 ml/rain, were added and th addition of dispersion was stopped after 20 ml, which wa equal to 4 g of dry fine-grained particles. The mixer wa operated until the mixture became dry, whereupon the vacuu pumping was interrupted and the temperature was increase 35. during continued agitation to 55°C and after that to 70° in the same manner as in Example 18. The particles were then prepared in the same manne as i n Examp le 18. In this way toner particles with good copying charac teristics were obtained.

Claims: C l a i s 1. Toner for electrophotographi c copying or electro stati c printing, characterized in that i t compri ses a internally pigmented thermoplastic base or main parti cl 5. prepared by suspension polymeri zation and having a mea diameter within the range of from 2 to 25 /-im, the surfac of the base parti cle being covered by a fine-grained poly merizate prepared by emulsion- or mi crosuspension poly merization and having a mean diameter of from 0.05 to 33 pe 10. cent of the mean diameter of the base parti cle and whereb from 1 up to 10 per cent of the surface of the base parti cl is covered by the fine-grained polymerizate. 2. Toner according to claim 1, characterized in tha the mean diameter of the fine-grained polymerizate is fro 15. 0.2 to 15 per cent of the mean diameter of the bas parti cle. 3. Toner according to any of the preceding claims characterized in that also the fine-grained polymeri zat is intern'alLy pigmented. 20. 4. Toner according to any of the preceding claims characterized in that the melting point of the fine-graine parti cles is >10°C higher than that of the base parti cles. 5. Toner according to any of the preceding claims characterized in that -the fine-grained par i cles have bee 25. prepared by microsuspension polymerization and contai a charge modifying agent. 6. A method for the preparation of a toner fo electrophotographi c copying o r electrostati c printing accor ding to claim 1, characterized in that an aqueous di spersio 30. of an internally pigmented thermoplasti c base parti cl prepared by suspension polymerization and having a mea diameter within the range of from 2 to 25 μm is brough into contact wi th a Latex of a fine-grained polymeri zat having a mean diameter of from 0.05 to 33 per cent of th 35. mean diameter of the base parti cle whereafter the tempera ture is rai sed so that the fine-grained parti cles adher to the surface of the base parti cles to a degree o^ coverin of from 1 up to 10%. 7. A method according to claim 6, characteri zed in that the aqueous dispersion of the pigmented b ' ase par¬ ticle contains polymerization serum from the polymerization of the base particle, which serum contains a protective colloid system. 5. 8. A method according to claim 6, character zed in that an aqueous dispersion of the pigmented base particle is brought into contact with a latex of the fine-grained polymerizate whereafter a . protective colloid system is formed n the aqueous dispersion and the temperature is 10. raised so that the fine-grained particles adhere to the surface of the base particles. 9. A method according to cla m 7, characterized in that the protective collo d system is deactivated before the adding of the latex of the fine-grained polymerizate, 15. whereafter the protective colloid system is reformed and the temperature is ra sed. 10. A method according to claim 7, characterized in that latex of the fine-grained polymerizate having func¬ tional groups of opposite charge than the base particles 20. is added whereby the latex particles are attracted to the base particles and thereby penetrating the colloid layer. 11. A method for the preparation of a toner for elec¬ trophotograph c copying or electrostatic printing according to claim 1, characte ized in that an internally pigmented 25. termoplastic base particle having a mean diameter within the range of from 2 to 25 μm is prepared by suspension polymerization of a monomer or a monomer mixture in the presence of a Latex of a fine-grained polymerizate having a mean diameter of from 0,05 to 33 per cent of the mean 30. diameter of the base particle, the particles of the latex being substantial insoluble in the monomer and said latex p,articles having a higher degree of hydrophilicity tha the polymer material in the main particles formed at th suspension polymerizat on. 35. 12. A method according to claim 11, characterize in that the latex polymer material originates from a monome mixture hich for control of hydrophilicity contains monomer with anionic character in alkaline environment. 13. A method according to claim 11, characterize in that the Latex polymer material originates from a monom mixture whi ch for control of hydrophi licity contains monomer with cationic character in acid envi ronment. 14. A method according to claim 11, characteri z 5. in that the latex polymer material originates from a monom mixture which for control of hydrophi li city contains monomer with an amino group. 15. A method according to claim 11, characteri z in that the Latex polymer material originates from a monom 10. mixture which for control of hydrophi licity contains monomer with hydroxyl group. 16. A method according to any of claims 11 to 1 characterized in that the latex particles are cross-linked 17. A method for the preparation of a toner for ele 15. trophotographi c copying or electrostatic printing accordi to claim 1, characterized in that a dry internally pigment thermoplasti c base parti cle prepared by suspension pol merization and having a mean diameter within the ran of from 2 to 25 /JΓΠ, is mixed with fine-grained plasti 20. particles having a mean diameter of from 0.05 to 33 p cent of the mean diameter of the base particles in an amoun sufficient to cover from 1 up to 10% per cent of the surfac of the base particle, whereafter the temperature i s rai se so that the fine-grained parti cles adhere to the surface 25. whereby the fine-grained parti cles have a higher meltin point than the base parti cles.

Inventors: HEDVALL BERTIL, MATTSON GUNNAR, NILSSON STURE, PORRVIK STEN, SUNDSTRAEM GOERAN, HEDVALL, BERTIL, MATTSON, GUNNAR, NILSSON, STURE, PORRVIK, STEN, SUNDSTRAEM, GOERAN
Applicants: CASCO NOBEL AB
Application year: 1987
Main classification: G03G9
IPC codes: C08J3, G03G9