GB1583411A - Method of forming a toner - Google Patents

Description

(54) METHOD OF FORMING A TONER (71) We, XEROX CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of Rochester, New York 14644, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to electrophotography and more particularly to improved electrostatographic developing materials, their manufacture and use.

The formation and development of images on the surface of photoconductor materials by electrostatic means is well known. The basic xerographic process, as taught by C. F. Carlson in U.S. Patent 2,297,691, involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light-and-shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting latent electrostatic image by depositing on the image a finely-divided electroscopic material referred to in the art as "toner". The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image. This powder image may then be transferred to a support surface such as paper.The transferred image may subsequently be permanently affixed to the support surface as by heat. Instead of latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a lightand-shadow image, one may form the latent image by directly charging the layer in image configuratlon. The powder image may be fixed to the photoconductive layer if elimination of the powder image transfer step is desired. Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing steps.

Several methods are known for applying the electroscopic particles to the latent electrostatic image to be developed. One development method, as disclosed by E. N.

Wise in U.S. Patent 2,618,552, is known as "cascade" development. In this method, a developer material comprising relatively large carrier particles having finely-divided toner particles electrostatically coated thereon is conveyed to and rolled or cascaded across the electrostatic latent image bearing surface. The composition of the carrier particles is so selected as to triboelectrically charge the toner particles to the desired polarity. As the mixture cascades or rolls across the image bearing surface, the toner particles are electrostatically deposited and secured to the charged portion of the latent image and are not deposited on the uncharged or background portions of the image.Most of the toner particles accidentally deposited in the background are removed by the rolling carrier, due apparently, to the greater electrostatic attraction between the toner and the carrier than between the toner and the discharged background. The carrier and excess toner are then recycled. This technique is extremely good for the development of line copy images.

Another method of developing electrostatic images is the "magnetic brush" process as disclosed, for example, in U.S. Patent No.

2,874,063. In this method, a developer material containing toner and magnetic carrier particles are carried by a magnet. The magnetic field of the magnet causes alignment of the magnetic carrier into a brushlike configuration. This "magnetic brush" is engaged with the electrostatic imagebearing surface. and the toner particles are drawn from the brush to the latent image by electrostatic attraction.

Still another technique for developing electrostatic latent images is the "powder cloud" process as disclosed, for example, by C. F. Carlson in U.S. Patent No. 2,221,776.

In this method, a developer material comprising electrically charged toner particles in a gaseous fluid is passed adjacent the surface bearing the latent electrostatic image.

The toner particles are drawn by electrostatic attraction from the gas to the latent image. This process is particularly useful in continuous tone development.

Other development methods such as "touchdown" development, as disclosed by R. W. Gundlach In U.S. Patent No.

3,166,432, may be used where suitable.

Toners have generally been prepared by thoroughly mixing the softened resin and pigment to form a uniform dispersion as by blending these ingredients in a rubber mill or the like and then pulverizing this material to form it into small particles. Most frequently, this division of the resin pigment dispersion has been made by jet pulverization of the material. Although this technique of toner manufacture has produced some very excellent toners, it does tend to have certain shortcomings. For example, it generally produces a rather wide range of particle sizes in the toner particles.

Although the average particle size of toner made according to this technique generally ranges between 5 and 10 microns, individual particles ranging from sub micron in size to above 20 microns are not infrequently produced. Furthermore, this is a batch process which tends to be slow, expensive, noisy and dusty. In addition, this technique of toner production imposes certain limitations upon the material selected for the toner because the resin-pigment dispersion must be sufficiently friable so that it can be pulverized at an economically feasible rate of production.

The problem which arises from this requirement is that when the resin-pigment dispersion is sufficiently friable for really high speed pulverizing, it tends to form an even wider range of particle sizes during pulverization including relatively large percentages of fines. In addition, such highly friable materials are frequently subject to further pulverization or powdering when they are employed for developing in xerographic copying apparatus. All other requirements of xerographic developers or toners including the requirements that they be stable in storage, non-agglomerative, have the proper triboelectric properties for developing, form good images, do not film or soil the selenium xerographic plate and have a low melting point for heat fusing are only compounded by the additional requirements imposed by this toner forming process.

Another method of toner formation consists of blending a water latex of the desired toner resin with a colorant and then spray drying this combined system to the desired particle size. The spray drying step consists of atomizing the colorant-water latex blend into small droplets, mixing these with a gas, and holding the droplets in suspension in the gas until evaporation drives off the liquid in the droplets and heat and surface tension forces cause the resin particles in each droplet to coalesce encasing the colorant included in that droplet. Most frequently, spray drying utilizes air as the gas for the drying step.The gas is heated to raise the temperature of the resin particles to a point where they coalesce so that the many small particles originating in any one droplet formed during atomization come together to form a small, hard spherical toner particle which entraps any colorant initially included within the droplet. The colorant used may be either water soluble in which case it may be merely added and dissolved into the resin latex or water insoluble dye in which case it may first be placed in an aqueous suspension and then added to the resin latex. Spray dried toners are not toally satisfactory as it is difficult to completely remove all the solvent and the solvent which remains in the toner particles acts to effect triboelectric properties and contribute to blocking of the toner when in use.

It has been proposed in United Kingdom Patent 1,319,tut15 that toner be prepared directly from the monomer by polymerization of the monomer in toner sized particles containing a colorant. A method of suspension polymerization to form toner particles is disclosed in U.S. 3,634,251 of Maeda et al. The method of the British patent comprises preparing a kneaded oil phase component made up of one or more liquid resin monomers, coloring material, the polymerization initiator and a finely-divided inorganic dispersion stabilizer such as a metal powder or inorganic salt or oxide and a polar resinous additive which is soluble in a monomer. After suspension polymerization of the monomer, if required, the finelydivided dispersion stabilizer is removed by dissolution in an acid and the polymer particles are removed from the aqueous phase and dried to produce toner. However, this process is not totally successful as it requires a high ratio of inorganic stabilizer which needs to be removed or it affects the quality of the toner. Further, the removal of the inorganic stabilizer adds a process step thereby minimizing the advantage of forming a toner in one operation from the monomer. The process in any case often results in incomplete polymerization that leaves residual monomer that affects the triboelectric, blocking and fixing. properties of the toner. This incomplete polymerization of the monomer was theorized as caused by the pigment inhibiting polymerization. The Maeda et al process also entails the removal of the inorganic component and problems of incomplete polymerization.

It has also been proposed that a suspension polymerization process similar to the above referenced British patent but not making use of an inorganic stabilizer be carried out to produce an encapsulated toner.

This process is performed generally by mixing a monomer, a colorant and an initiator to form an oil soluble organic phase; dispersing this oil soluble phase in controlled size between 5 to 20 microns in a water phase, employing a suspending agent, for example polyvinyl alcohol; polymerizing, employing conventional suspension polymerization techniques; introducing a second monomer which is allowed to diffuse into the first polymer and consequently swells the polymer; introducing a water soluble initiator; and heating this reaction mixture to effect a polymerization of the second monomer and form the desired toner (see U.S.Patent No. 4,077,804), It is found that the second initiator, the water soluble initiator, generates a free radical which attacks the surface of the swollen polymer particle and promotes polymerization at the surface by reacting with monomer at the surface thereby decreasing the monomer concentration and causing the transport of monomer to the surface by diffusion. The process is found to be self terminating when the total amount of sorbed monomer has been converted to polymer at the surface, thus providing an encapsulated toner. However, while this process may be used to produce encapsulated toners, it still does not provide an acceptable method for producing toners which are not encapsulated and which may withstand the abrasion, stress and humidity variation to which toners are subject in ordinary development systems.

A method of producing small methyl methacrylate beads is disclosed in U.S.

Patent 2,701,245 to Lynn. This process uses large amounts of wetting agent, a short period of mixing to size the monomer and does not agitate during polymerization.

However, this process does not produce colored beads and the large amount of wetting agents required have impurities undesirable in toners and further have a wide range of particle size.

A Journal of Applied Polymer Science article at Volume 16, page 1867 and 1868 (1972) discloses that polymerization of small particle size polymers may be carried out after sizing by high speed stirring of a paddle stirrer. However, the article indicates that control of sizing is difficult and does not deal with the complications caused by introduction of colorant into the system.

As can be seen, there remains a need for a process of producing toners which would not involve extensive processing steps of polymer formation, colorant addition, mix ing and particle formation. There remains a need for process which would produce toner particles directly from monomer that has good triboelectric properties, abrasive resistance, blocking resistance and colorant load ing capability. Since the prior forming methods are deficient in one or more of the above areas, there is a continuing need for an improved method of formation of toners for use in electrophotographic development.

By means of the present invention it is possible to provide the following: (i) a method of producing a toner which overcomes the above noted deficiencies in processes of toner production; (ii) a toner of stable properties; (iii) a method of direct polymerization of coloured toners (iv) a method which prevents inhibition of polymerization by toner colourants; (v) a method of producing a low cost toner, and (vi) a method of coating pigment to pre vent interaction with monomer during polymerization to form toners.

According to the present invention there is provided a method of forming a toner comprising treating a pigment in order to prevent its inhibiting polymerization in a step comprising suspending the pigment in a mixture of water and a silane which can react with the pigment to prevent its inhibit ing polymerization, dispersing the thus treated pigment in a monomer, treating the monomer containing dispersed pigment in an aqueous medium to form a toner size monomer in suspension, carrying out polymerization, and recovering toner.

The treatment of carbon black by silanes according to the above method has been found to be a particularly desirable method of cladding a toner pigment for use in a toner forming system.

The toner formation method of the inven tion is carried out in one stance by the use of a styrene monomer to which is added lauroyl peroxide and Molacco (registered Trade Mark) -H carbon black that has been treated with an active silane dispersion agent such as triethoxy silane. The carbon particles are coated with the silane by sus pension of the carbon in water followed by addition of triethoxy silane ("Siliclad", Clay Adams Division of Becton Dickinson Co.).

The mixture of silane and carbon is agitated to allow the silane to form a coat on the surface of the carbon particles. The treated (cladded) carbon is dispersed in a styrene monomer with, lauroyl peroxide and sus pended in an aqueous medium as polymer ization is carried out. After polymerization is complete, for example in 6 hours, the particles are recovered and found to be suitable for use as toner materials without further processing. Typical toner particles recovered in the method of the invention are 12 microns average particle size.

Any polymeric material which may be formed by dispersion polymerization and which has a melting point within the range suitable for use as a toner may be used in the toner forming method of the present invention. Typical monomeric units which may be employed to form polymers include: styrene; p-chlorostyrene; vinyl naphthalene; ethylenically unsaturated mono-olefins such as ethylene, propylene, butylene and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide and vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate; esters of alphamethylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acry- late, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl-alpha-chloroacrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate; acrylonitrile; methacrylonitrile; acrylamide; vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether and vinyl ethyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; vinylidene halides such as vinylidene chloride and vinylidene chlorofluoride; and N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone; and mixtures thereof. Generally, suitable vinyl resins employed in the toner have a weight average molecular weight from 3,000 to 500,000.

Toner resins containing a relatively high percentage of styrene resins are typically preferred. The presence of a styrene resin is preferred because a greater degree of image definition is achieved with a given quantity of additive material. Further, denser images are obtained when at least 25 percent by weight, based on the total weight of resin in the toner, of a styrene resin is present in the toner. The styrene resin may be a homopolymer of styrene or styrene homologues or copolymers of styrene with other monomeric groups containing a single methylene group attached to a carbon atom by a double bond.Thus, typical monomeric materials which may be copolymerized with styrene by addition polymerization include: p-chlorostyrene; vinyl naphthalene; ethylenically unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like; vinyl halides such as vinyl chloride, vinyl bromide and vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate; esters of alpha-methylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acry- late, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl-alpha-chloroacrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate; acrylonitrile; methacrylonitrile; acrylamide; vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether and vinyl ethyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; vinylidene halides such as vinylidene chloride and vinylidene chlorofluoride; and N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone; and mixtures thereof. The styrene resins may also be formed by the polymerization of mixtures of two or more of these unsaturated monomeric materials with a styrene monomer. The expression "addition polymerization" is intended to include known polymerization techniques, such as radical, anionic and cationic polymerization processes.Monomer forming polystyrene and copolymers of styrene and n-butylmethacrylate have been found to be particularly suitable for the polymerization method of the invention as they result in good yields of completeLy polymerized monomer which are suitable for use as toner material as they possess good triboelectric and fusing properties.

Any suitable pigment material may be used in the method of the invention. A pigment generally should be capable of being dispersed in a polymer, be insoluble if water is used in the cladding method and give strong, clear, permanent colors when used in toner. Typical of such pigments are phthalocyanines, lithols and toluidene.Typ Ical of phthalocyanine pigments are copper phthalocyanine, mono-chlor copper phthalocyanine, hexadecachlor copper phthalocyanine, metal-free phthalocyanine, mono-chlor metal-free phthalocyanine, and hexadecachlor metal-free phthalocyanines; anthraquinone vat pigments such as: Vat yellow 6 GL CI 1127, quinone yellow 18-1, indanthrone CI 1106 and pyranthrone CI 1096; brominated pyranthrones such as: dibromopyranthrone, vat brilliant orange RK, anthrimide brown CI 1151, dibenzanthrone green CI 1101 and flavanthrone yellow CI 1118; thioindigo pigments such as: thioindigo red and pink FF; azo pigments such as: toluidine red CI 69 and hansa yellow; and metalized pigments such as: azo yellow (green gold) and permanent red.

Carbon black has been found to be a preferred colorant as it is low in cost, may be completely cladded, and provides strong black images at relatively low loading of the col orant. The carbon black may be of any of the known types such as channel black or furnace black. The furnace black is preferred as it is lower in cost. Carbon black commonly has free radical trasandquinoid structures on the surface wicharechemi- cally active sites. The amount of carbon black necessary in the toner typically is from 1 to 20 percent. A loading of from 5 to 10 percent in the toner has beenfound to be suitable for the method of the invention.

Any silane which allows the cladding of the pigments to prevent their inhibition of or reaction with the monomer during polymerization may be used in the invention such as amine silicate-organosilane copolymers. Silanes both of water emulsified and water soluble types have been found to be suitable for the cladding method. Typical of suitable organo silanes are amino silanes, methacrylate silanes, epoxide silanes, polyamino silanes, mercapto silanes, vinyl silanes, chloroalkyl silanes, and alkoxysilanes e.g. methyltrimethoxysilane, phenyltrimethoxysilane, methylphenyldimethoxysilane and diphenyldimethoxysilane; and typical of suitable silazanes is hexamethyldisilazane.

A preferred silane is triethoxy silane (Cls/ Si(C2HsO)3) marketed as "Siliclad" by the Clay Adams Division of Becton, Dickinson and Company, which gives a good polymeric coating on carbon black that prevents hydrophilic and other types of reaction.

The silane cladding agent utilized is provided in any amount which provides a covering on the pigment sufficient to prevent the pigment inhibiting the triboelectric properties of toner and sufficient to control the hydrophilic properties of the pigment. Generally, the cladding agent is used in an amount that is the minimum which will give complete coverage as this keeps the expense and time of cladding low. Typically, an amount of cladding agent from 0.05 to 10 percent by weight of the pigment may be utilized. A suitable range has been found to be 0.1 to 4 percent by weight of the pigment. A preferred range in the case of triethoxy silane is from 0.3 percent to 1 percent for complete coverage at low cost.The surface coating formed on the carbon or other pigment particles generally comprises precipitated silanes and silanes reacted with surface groups of the carbon or other pigment, such as quinoid structures.

It is generally desirable to utilize a stabilization agent other than the monomer itself in the solution. Such an agent aids in the formation of particles which will remain dispersed in the water during polymerization.

During polymerization the particles pass through tacky stages when they have a strong tendency to agglomerate. Any suitable stabilization agent may be used. Typi cal of such stabilizers are both non-ionic and ionic water soluble polymeric stabilizers such as methyl cellulose, ethyl cellulose, sodium salt of carboxyl methyl cellulose, polyacrylate acids and their salts, polyvinyl alcohol gelatins, starches, gums, alginates, zein and casein. Suitable stabilization agents are polyacrylic acid, polymethacrylic acid, polyacrylamide and polyethylene oxide.

Stabilizer agents found to be preferred for this invention are polyethylene oxide polypropylene block copolymers and polyvinyl alcohol, which give good suspension at low concentration and narrow particle range. The stabilizer is generally added in a ratio based on the amount of water. An amount of from 0.2 to 5 percent by weight stabilizer to water is suitable. An amount of from 0.2 to 1.5 percent is preferred to give good suspension at low cost and low impurity in the toner. An optimum amount for use in formation of toners is from 0.75 to 1 percent to give low materials cost and narrow size distribution. The preferred polyvinyl alcohol contains from 1 to 20 mole percent of polyvinyl acetate groups. The optimum amount of polyvinyl acetate is about 16 mole percent to give good dispersion at low concentration and narrow particle size range.The molecular weight of suitable polyvinyl alcohols is from 10,000 to 125,000 number average molecular weight.

A preferred polyvinyl alcohol is Monsanto 20-60 of about 90,000 weight average molecular weight. The preferred polyethylene oxide - polypropylene (PEO PPO) block copolymers comprise from 40 to 80 weight percent ethylene oxide. Suitable molecular weights of the (PEO-PPO) block copolymer are from 3,000 to 27,000 weight average molecular weight. A preferred range of molecular weight is from 10,000 to 15,000 weight average to give good dispersion at low concentration.

The dispersing of pigment containing monomer may be carried out in any suitable type of mixer which results in toner particles of narrow size distribution in stable suspension in less than about 3 minutes. The mixer may be of either the batch or in line type.

Suitable for the method of the invention are reed type ultrasonic mixers such as the Dispersonic - registered Trade Mark - mixers and paddle blade mixers. A preferred type mixer for the method is the rotor stator type mixer such as the Polytron in which one element is stationary and the other rotates in close tolerance therewith while the liquid is drawn through appertures in the static element. The speed of rotation is generally greater than about 3,000 r.p.m. The shear rate should be greater than 103 sec-1. An axial turbine agitator that comprises an arrangement of discs and paddles is the other preferred type of mixer. The axial tur bine mixers are found to form stable dispersions of narrow particle size distribution at speed ranges of from 200 to 3,000 r.p.m.

Any catalyst or initiator which is compatible with the particular monomer being used may be utilized in the method of the invention. Typical of initiators for polymerization are the peroxide and azo initiators. Among those found suitable for use in the method of the invention are azobis (2methylpropionitrile) and lauroyl peroxide which result in complete polymerization without leaving detrimental residual materials or requiring high temperatures or pressures. The initiator may be added to the monomer during dispersion of the carbon black or may be mixed in after carbon black dispersion.

It is preferred that the polymerization initiator, treated carbon black and monomer be mixed in high shear agitation to produce a stable dispersion of the carbon black in the monomer. The carbon in stable dispersion is separated into sub-micron size particles evenly distributed throughout the monomer. The mixture may be heated during dispersion. Generally, the initiator is used in the amount necessary to achieve complete polymerization without waste of the initiator. An amount of from 2 percent to 10 percent by weight initiator to monomer has been found to be suitable, A preferred range is from 2 to 5 percent by weight of initiator to monomer to give complete polymerization without waste at low cost.

The optimum amount in the instance of lauroyl peroxide with styrene monomer systems is about 2 percent as this gives complete polymerization at low cost and results in good toner properties.

Any suitable carrier may be used in the toner of the present invention to form a developer. Suitable coated and uncoated carrier materials for cascade and magnetic brush development are well known in the art. The carrier particles may be electrically conductive, insulating, magnetic or nonmagnetic provided that the carrier particles acquire a charge having an opposite polarity to that of the toner particles when brought in close contact with the toner particles so that the toner particles adhere to and surround the carrier particles. When a positive reproduction of an electrostatic image is desired, the carrier particle is selected so that the toner particles acquire a charge having a polarity opposite to that of the electrostatic latent image.Alternatively, if a reversal reproduction of the electrostatic image is desired, the carriers are selected so that the toner particles acquire a charge having the same polarity as that of the electrostatic image. Thus, the materials for the carrier particles are selected in accordance with their triboelectric properties in respect to the electroscopic toner so that when mixed or brought into mutual contact, one component of the developer is charged positively if the other component is below the first component in the triboelectric series and negatively if the other component is above the first component in the triboelectric series.

Typical carriers include sodium chloride, ammonium chloride, aluminum potassium chloride, Rochelle salt, sodium nitrate, aluminum nitrate, potassium chlorate, granular zircon, granular silicon, polymethyl methacrylate, glass, steel, nickel, iron, ferrites, ferromagnetic materials and silicon dioxide. The carriers may be employed with or without a coating. Many of the foregoing and typical carriers are described by L. E.

Walkup in U.S. Patent No. 2,618,551; L. E.

Walkup et al in U.S. Patent No. 2,638,416; E. N. Wise in U.S. Patent No. 2,618,552; R.

J. Hagenbach et al in U.S. Patent No.

3,591,503 and U.S. Patent No. 3,533,835; and B. J. Jacknow et al in U.S. Patent No.

3,526,533. Suitable carriers for use with the toners of the present invention include nickel berry, coated ferrites and methyl terpolymer coated steel. Nickel berry is a nodular nickel particle disclosed in U.S. Patent No. 3,767,568 having a pebbled surface.

Methyl terpolymer coated steel carrier is a steel core coated with a composition such as that of Example XIII of U.S. Patent No.

3,526,533. An ultimate coated carrier particle diameter of from 50 microns to 1,000 microns is suitable because the carrier particles then possess sufficient density and inertia to avoid adherence to the electrostatic images during the cascade development process. A range of from 75 to 400 microns is generally preferred to give clear, sharp images. Adherence of carrier beads to xerographic drum surfaces is undesirable because of the formation of deep scratches on the surface during the image transfer and drum cleaning steps, particularly where cleaning is accomplished by a web cleaner such as the web disclosed by W. P. Graff, Jr.

et al in U.S. Patent No. 3,186,838. Also, print deletion occurs when carrier beads adhere to electrostatographic imaging surfaces.

The following examples further define, describe, and compare methods of preparing toners of the present invention and of utllizing them in electrophotographic applications. Parts and percentages are by weight unless otherwise indicated.

EXAMPLE I To 100 grams of styrene are added 5 grams of lauroyl peroxide which are mixed until dissolved. To this mixture is added 7 grams of a cladded carbon black, Molacco-H, which has been treated with triethoxy silane, Siliclad, in a 2 percent solution with water in a beaker fdr about 5 minutes to prevent interference with the polymerization. This mixture is heated with mixing in a Waring Blender to 70"C for 5 minutes to provide a good dispersion of carbon black in the monomer mix. The pigmented monomer mix is then poured into a Waring blender jar equipped with a Polytron - registered Trade ark - mixing head along with 500 cc. of a 1.25 percent polyvinyl alcohol water solution.The two phase mixture is then stirred at about 3,000 r.p.m. for about 30 seconds to produce a pigmented droplet dispersion with an average size of 12 microns.

The sized dispersion is transferred to a reactor vessel consisting of a 1,000 ml.

round bottomed flask equipped with a paddle blade stirrer. With stirring speed of 60 to 80 r.p.m. the flask is heated to 700C and controlled at that temperature by means of a constant temperature water bath.

The progress of the polymerization is followed by injecting samples at various time intervals into a gel permeation chromatograph. The rate of disappearance of both monomer and catalyst is thus determined.

After six hours, the polymerization is complete and the suspension of 12 micron sized pigmented particles is poured into three liters of cold water. The resulting diluted suspension is centrifuged 15 minutes at 1,000 r.p.m. in a bucket type centrifuge. The supernatant liquid consisting of the diluted polyvinyl alcohol is decanted, fresh water is added and the mixture is shaken for 5 minutes to disperse the particles. This washing procedure is repeated three times. After the final wash, the sedimented slurry is poured into a stainless steel tray and allowed to air dry. The resulting cake is very friable and can be broken down to individual particles by tumbling on a roll mill.

The particles have an average particle size of from 8 to 12 microns. The divided particles are utilized in a Model D processor and found to produce good images.

EXAMPLE II 100 parts monomer consisting of a 65:35 ratio of styrene and n-butyl methacrylate, 10 parts carbon black treated as in Example I, 1 part ethyl cellulose and 2 parts azobisisobutyronitrile are mixed in a Waring blender to give a well dispersed carbon black. This mixture is added to 500 parts of 0.5 percent polyvinyl alcohol solution in a Waring blender jar equipped with a Polytron mixing head. The mixture is agitated at about 3,000 r.p.m. for 30 seconds to disperse the pigmented monomer phase in the water phase. The resulting dispersion is further stabilized by the addition of sufficient 5 percent polyvinyl alcohol solution to yield a 2.6 percent concentration of polyvinyl alcohol.The stabilized dispersion is then transferred to a 1,000 ml. polymerization flask equipped with an argon purge and paddle stirrer, and heated to 650C while stirring at 60 r.p.m. After eight hours, the resulting polymer dispersion is cooled by pouring into three liters of cold water. The particles are recovered by sedimentation and consisted of uniformly black spheres with an average particle diameter of 10 microns. These particles utilized in a Model D processor produce images of good quality.

EXAMPLE III As a control, the method of Example I is repeated except that the carbon black is not treated with Siliclad. The particles formed did not exhibit good xerographic properties as they were incompletely polymerized and tacky.

EXAMPLE IV The method of Example I is repeated except that Dow Corning reactive silane DC-Z-6020 is substituted for the Siliclad.

This is found to produce toner which gave good xerographic properties.

EXAMPLE V The method of Example II runs 7 and 8 of British patent 1,319,815, which is hereby incorporated by reference, is performed utilizing Molacco-H carbon black which has been cladded in accordance with the method of Example I of the present specification in place of the No. 3 Asahi Carbon of the patent. The toner.recovered is found to be completely polymerized, exhibits good copying qualities and is not subject to blocking.

EXAMPLE VI The method of Example II is repeated except about 3 percent by weight of hexamethyldisilazane is substituted for the diethoxy silane. The toner is completely polymerized and has good triboelectric properties.

EXAMPLE VII The method of Example I is repeated except the dispersion of treated carbon black and monomer is transferred directly into the reactor vessel. The reactor vessel contains about 600 cc of a 1.5 percent by weight solution of Pluronic - registered Trade Mark - F-127 a 70/30 polyethylene oxide - polypropylene block copolymer.

The paddle is rotated at about 800 r.p.m. for 5 minutes and then slowed to about 85 r.p.m. for polymerization. The particles have a size range of from 5 to 85 microns.

'The particles develop good images when used in a Model D processor. The particles are completely polymerized.

EXAMPLE VIII The method of Example I is repeated sub stituting Monsanto 20-60 a polyvinyl alcohol of about 90,000 weight average molecular weight having about 16 mole per cent polyvinyl. acetate groups for the polyvinyl alcohol of Example I. The toner exhibits excellent xerographic properties.

EXAMPLE IX and X The method of Examples I and VII is repeated except about 2 percent methyl tnmethoxysilane is substituted for the reactive silanes of those examples. The particles are found to be completely polymerized and satisfactory in xerographic properties.

EXAMPLES XI to XHI Examples I, II and VII are repeated substituting about 1 percent by weight diphenyldimethoxy silane for the reactive silanes of Examples I, II and VII. The toners produced have good properties and are completely polymerized.

Although specific materials and conditions are set forth in the above exemplary methods in the formation of the toner of the invention, these are merely intended as illustrations of the present invention. Various other constituents and conditions such as those listed above, may be substituted for those in the Examples with similar results.

In addition to the steps used to prepare the toner of the present invention, other steps or modifications may be used if desired. In addition, other materials may be incorporated into the toner of the invention which will enhance, synergize or otherwise desirably effect the properties of these materials for their present use. For example, additives to increase resistance to moisture absorption or to effect triboelectric properties, could be added to the surface of the particles.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure.

For instance, magnetic pigments could be used in the process if it was desired that magnetic toner be produced. Further, if toner for use in developing processes other than magnetic or cascade were desired, the particle size could be regulated to be smaller such as 1 to 5 microns for use in powder cloud development processes. The toners produced by the process of Example VII could be classified to a preferred size range to give better performance in commercial copiers.

If desired, any suitable chain transfer agents or crosslinking agent may be used in the invention to modify the polymeric toner to produce particularly desired properties.

Typical of crosslinking agents for use in the invention are aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene or derivatives thereof; diethylenecarboxylate esters such as diethyleneglycol methacrylate and diethyleneglycol acrylate; any other divinyl compounds such as divinyl sulfide or divinyl sulfone compounds provided with three or more vinyl radicals; or mixtures of the foregoing compounds. Chain transfer agents act to control molecular weight by inhibiting chain growth. Typical of chain transfer agents for use in the invention are mercaptans such as laurylmercaptan, phenylmercaptan, butylmercaptan and dodceylmercaptan; or halogenated carbons such as carbon tetrachloride or carbon tetrabromide.Also, examples of materials which become effective when used in a much larger amount such as solvents for the vinyl monomer are substituted aromatic compounds such as toluene or isopropylbenzene; or substituted fatty acids such as trichloroacetic acid or tribromoacetic acid.

Also, examples of materials which can be added as a monomer to be incorporated in the resulting polymer and simultaneously effect molecular weight control are ethylenic unsaturated monoolefins with radicals such as propylene or isobutylene; and allyl compounds such as allyl benzene, allyl acetate or allylidene chloride.

WHAT WE CLAIM IS: 1. A method of forming a toner comprising treating a pigment in order to prevent its inhibiting polymerization in a step comprising suspending the pigment in a mixture of water and a silane which can react with the pigment to prevent its inhibiting polymerization, dispersing the thus-treated pigment in a monomer, treating the monomer containing dispersed pigment in an aqueous medium to form a toner size monomer in suspension, carrying out polymerization, and recovering toner.

2. A method according to claim 1, wherein a stabilization agent is present in the aqueous medium during the treatment to form the toner size monomer.

3. A method according to claim 2, wherein the stabilization agent is polyvinyl alcohol or a polyethylene oxide-propylene block copolymer.

4. A method according to any one of the preceding claims, wherein said pigment is carbon black.

5. A method according to any one of the preceding claims, wherein lauroyl peroxide is used as a polymerization initiator.

6. A method according to any one of claims 1 to 4, wherein an azo polymerization initiator is used.

7. A method according to any one of the preceding claims, wherein the toner particles recovered are 12 microns average particle size.

8. A method according to any one of the preceding claims, wherein polymerization is substantially complete.

9. A method according to claim 8, wherein polymerization is complete in 6 hours.

10. A method according to any one of the preceding claims, wherein the silane is selected from organo silanes and silazanes.

11. A method according to claim 10,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (23)

**WARNING** start of CLMS field may overlap end of DESC **. exhibits excellent xerographic properties. EXAMPLE IX and X The method of Examples I and VII is repeated except about 2 percent methyl tnmethoxysilane is substituted for the reactive silanes of those examples. The particles are found to be completely polymerized and satisfactory in xerographic properties. EXAMPLES XI to XHI Examples I, II and VII are repeated substituting about 1 percent by weight diphenyldimethoxy silane for the reactive silanes of Examples I, II and VII. The toners produced have good properties and are completely polymerized. Although specific materials and conditions are set forth in the above exemplary methods in the formation of the toner of the invention, these are merely intended as illustrations of the present invention. Various other constituents and conditions such as those listed above, may be substituted for those in the Examples with similar results. In addition to the steps used to prepare the toner of the present invention, other steps or modifications may be used if desired. In addition, other materials may be incorporated into the toner of the invention which will enhance, synergize or otherwise desirably effect the properties of these materials for their present use. For example, additives to increase resistance to moisture absorption or to effect triboelectric properties, could be added to the surface of the particles. Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. For instance, magnetic pigments could be used in the process if it was desired that magnetic toner be produced. Further, if toner for use in developing processes other than magnetic or cascade were desired, the particle size could be regulated to be smaller such as 1 to 5 microns for use in powder cloud development processes. The toners produced by the process of Example VII could be classified to a preferred size range to give better performance in commercial copiers. If desired, any suitable chain transfer agents or crosslinking agent may be used in the invention to modify the polymeric toner to produce particularly desired properties. Typical of crosslinking agents for use in the invention are aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene or derivatives thereof; diethylenecarboxylate esters such as diethyleneglycol methacrylate and diethyleneglycol acrylate; any other divinyl compounds such as divinyl sulfide or divinyl sulfone compounds provided with three or more vinyl radicals; or mixtures of the foregoing compounds. Chain transfer agents act to control molecular weight by inhibiting chain growth. Typical of chain transfer agents for use in the invention are mercaptans such as laurylmercaptan, phenylmercaptan, butylmercaptan and dodceylmercaptan; or halogenated carbons such as carbon tetrachloride or carbon tetrabromide.Also, examples of materials which become effective when used in a much larger amount such as solvents for the vinyl monomer are substituted aromatic compounds such as toluene or isopropylbenzene; or substituted fatty acids such as trichloroacetic acid or tribromoacetic acid. Also, examples of materials which can be added as a monomer to be incorporated in the resulting polymer and simultaneously effect molecular weight control are ethylenic unsaturated monoolefins with radicals such as propylene or isobutylene; and allyl compounds such as allyl benzene, allyl acetate or allylidene chloride. WHAT WE CLAIM IS:

1. A method of forming a toner comprising treating a pigment in order to prevent its inhibiting polymerization in a step comprising suspending the pigment in a mixture of water and a silane which can react with the pigment to prevent its inhibiting polymerization, dispersing the thus-treated pigment in a monomer, treating the monomer containing dispersed pigment in an aqueous medium to form a toner size monomer in suspension, carrying out polymerization, and recovering toner.

2. A method according to claim 1, wherein a stabilization agent is present in the aqueous medium during the treatment to form the toner size monomer.

3. A method according to claim 2, wherein the stabilization agent is polyvinyl alcohol or a polyethylene oxide-propylene block copolymer.

4. A method according to any one of the preceding claims, wherein said pigment is carbon black.

5. A method according to any one of the preceding claims, wherein lauroyl peroxide is used as a polymerization initiator.

6. A method according to any one of claims 1 to 4, wherein an azo polymerization initiator is used.

7. A method according to any one of the preceding claims, wherein the toner particles recovered are 12 microns average particle size.

8. A method according to any one of the preceding claims, wherein polymerization is substantially complete.

9. A method according to claim 8, wherein polymerization is complete in 6 hours.

10. A method according to any one of the preceding claims, wherein the silane is selected from organo silanes and silazanes.

11. A method according to claim 10,

wherein the organo silane is an alkoxy silane.

12. A method according to claim 11, wherein the alkoxy silane is triethoxy silane.

13. A method according to any one of the preceding claims, wherein the silane is present in said mixture in an amount to provide from 0.1 to 4 percent by weight of the pigment.

14. A method according to any one of the preceding claims, wherein the treated pigment, the monomer and a polymerization initiator are subjected to high shear mixing so as to disperse the pigment in the monomer.

15. A method according to claim 14, wherein heat is applied during said dispersing of the treated pigment in the monomer.

16. A method according to any one of the preceding claims, wherein heat is applied to start and continue the polymerization.

17. A method according to claim 1, substantially as hereinbefore described with reference to any one of Examples I, II and IV to XIII.

18. A toner whenever formed by a method according to any one of the preceding claims.

19. A toner comprising generally spherical polymer particles having uniformly dispersed throughout each polymer particle a pigment comprising pigment particles surrounded by a coating comprising a silane reacted with surface groups of the pigment to prevent the pigment inhibiting polymerization.

20. A toner according to claim 19, wherein the polymer comprises a styrene polymer.

21. A toner according to claim 19 or claim 20, wherein the pigment is carbon black.

22. A developer comprising a carrier and a toner according to any one of claims 18to21.

23. An electrostatographic imaging process comprising establishing an electrostatic latent image on a surface and contacting said surface with a toner according to any one of claims 18 to 21 or a developer according to claim 22.