GB1583564A - Method of forming toner particles - Google Patents

Description

(54) A METHOD OF FORMING TONER PARTICLES (71) We, XEROX CORPORATION, a body corporate organised under the laws of the State of New York, United States of America, of Xerox Square, 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 light-and-shadow image, one may form the latent image by directly charging the layer in image configuration. 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 brush-like configuration. This "magnetic brush" is engaged with the electrostatic image-bearing surface and the toner particles are drawn from the brush to the latent image by electrostatic attraction.

Still another technique for developing elec trostatic 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 developement.

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 resinpigment 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 totally 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.

In U. S. Patent 3,391,082 to Maclay, it is proposed that toner be formed directly from an emulsion polymerization system. However, this method is not totally satisfactory since as the toner comprises agglomerates of the small latex (.03 to .25 micron) particles the total drying of the system is difficult leading to blocking problems and also voids in the particles may cause structural weakness and uneven triboelectric properties.

It has been proposed in United Kingdom Patent 1,319,815 that toner be prepared directly from the monomer by polymerization of the monomer in toner sized particles containing a colorant. 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 finelydivided 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 finely-divided 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 particles recovered contain an unacceptably great number of particles which are either larger or smaller than the size range pre ferred for electrophotographic use. Further,' the removal of the inorganic stabilizer adds a process step thereby minimizing the advan- tage 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 is theorized as caused by the pigment inhibiting polymerization. The similar type Maeda et al process, U. S.

3,634,251, 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 leave impurities very undesirable in toners and further the toner has' a wide range of particle sizes.

A Journal of Applied Polymer Science article at Volume 16, pages 1867 and 1868 (1972), discloses that pdlymeriiation 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.

A difficulty with suspension polymeriza- tion processes ig that it is difficult to form and maintain the toner particle size particles of 5 to 30 microns in large suspension poly merization equipment. To obtain particle sizes ifl the 10 microns range requires stirrer speeds in excess of 1,000 r.p.m.In view of the high stirring speeds, the deign of large reactors becomes increasing difficult as siie increases. Large high speed reactors are much more' expensive to design and operate than a normal suspension polymerization reactor that operates at the normal 75 to 100 r.p.m. stirring speed. The forming- of toner size particles at slow speeds by utilizing large amounts of suspending agents creates difficulties as set forth above as suspending agents in large amounts must be removed from the particles in order for them to operate effectively as toner particles. The conventional reactors with paddle blade stirrers when operating at high speeds produce a broad range of particle sizes.

In formation of toner by known processes such as emulsion polymerization, spray drying or attrition from bulk, the problem of elements on the surface of the particle acting in a hydrophilic manner remains. Elements such as exposed pigment reactive groups, solvent or reactive monomers may attract water molecules and contribute to blocking of the toner and changes in triboelectric properties.

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, mixing and particle formation. There remains a need for a process which would produce toner particles directly from monomer that have good triboelectric properties, abrasive resistance, blocking resistance, narrow size variation, and good colorant loading 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 toner of high resistance to blocking (ii) a method of direct polymerization of coloured toners.

(iii) a low cost method for toner produc tion.

(iv) a method for minimizing humidity sensitivity of toner.

(v) a method of toner treatment in sus pension during polymerization pro cesses to form toners.

According to the present invention there is provided a method of forming toner particles comprising dispersing a pigment in a monomer, treating the pigment containing monomer in an aqueous medium to form a toner size monomer in suspension, agitating (preferably for longer than 3 hours) the monomer during polymerization to form polymerized toner particles, treating the toner particles after polymerization with a treatment agent selected from an acrylonitrile monomer and a silane to neutralise hydrophilic groups at the surface of the toner particles to decrease humidity sensitivity of the particles, and recovering toner particles.

The invention is now described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a view of a rotor stator mixer, Figure 2 is a view of the static element of a rotor stator mixer, Figure 3 is a view of the rotating element of the mixer, and Figure 4 illustrates a base construction for a rotor stator mixer.

The toner formation method of the invention is carried out in one instance 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 silicone dispersion agent such as tricthoxy silane ("Silidad").

The carbon particles are coated with the silane by suspension of the carbon in water followed by addition of the 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.

Then, utilising a high speed and high shear mixer, the monomer is suspended in an aqueous medium and toner size particles are formed. The suspension of toner size pigmented monomer is then transferred to a reactor which is agitated by a stirrer at about 75 r.p.m. while polymerization takes place.

After polymerization is complete, the particles are treated with a treatment agent such as an organosilane which renders the particle insensitive to humidity changes.

The treatment of the dispersion polymerized toner to render it less sensitive to humidity is carried out utilizing an agent as defined above which acts to cover the surface of the toner and reacts to neutralize hydrophilic groups thereon. It is theorized that polyvinyl alcohol or other stabilizer utilized during polymerization may be absorbed on the surface or in some way grafted on the surface of the toner forming hydrophilic areas. Such agents are water soluble monomers or polymers that precipitate onto toner, and which may be silanes such as amine silicate-organ osilane copolymers.

Acrylonitrile monomer also has been found to be a suitable water soluble monomer which will precipitate onto toner.

Typical of the silanes of water emulsified or water soluble types which have been found to be suitable for the treatment method are organo silanes such as amino silanes, methacrylate silanes, epoxide silanes, polyamino silanes, mercapto silanes, vinyl silanes, chloroalkyl silanes, and alkoxysilanes e.g. methyltrimethoxysilane, phenyltrimethoxysilane, methylphenyldimethoxysilane and diphenyldimethoxysilane; as well as silazanes such as hexamethyldisilazane. A preferred silane is triethoxy silane (C,8Si(C2HsO)3) marketed as "Siliclad" by the Clay Adams Division of Becton Dickinson and Company, which gives a good polymeric coating on toner that prevents the hydrophilic action of the stabilization agent which may remain on the toner. Stabilization agents when not removed or treated may cause dispersion polymerized toner to be particularly humidity sensitive.

The treating of the dispersion polymerized toner to render it less humidity sensitive may be carried out by addition of the agent to the water that the toner was suspended in during polymerization. The treatment may also be carried out by addition of the agent to water in which the toner is again suspended after recovery from the polymerization liquid. The rinsing of the material is normally carried out after polymerization is complete and it may be convenient to then add the humidity treatment agent.

The humidity treatment agent may be added in any amount that is effective to reduce humidity sensitivity without interfering with electrophotographic properties.

A suitable amount is from 1 to 5 percent of the water in which the toner is suspended.

A preferred amount is from 1 to 2 percent as this gives good results at low cost and little change in electrophotographic properties.

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 acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acyrlate, 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 Nvinyl 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 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 alpha-methylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate, 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 therçof. The styrene resins may also be formed by the polymerization of mixtures of two or more of these unsaturated mono; meric materials with a styrene monomer.

The expression "addition polymerization" is intended to include known polymerization techniques, such as radical, anionic and cationic polymerization processes. Monomers 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 monomer, be insoluble in the water if cladding is performed and in the aqueous medium of the polymerization method and give strong, clear, permanent colors when used as toner. Typical of such pigments are phthalocyanies, lithols, toluidene and inorganic pigments such as TiO2.

Carbon black has been found to be a preferred colorant as it is low in cost, may be completely cladded so as to not inhibit polymerization, and provides strong black images at relatively low loading of the colorant. The carbon black may be of any known types such as channel black or furnace black. The furnace black is preferred as it is lower in cost. The amount of carbon black necessary in the toner typically is from 1 to 20 percent.

A loading of from 5 to 1.0 percent in the toner has been found to be suitable for the method of the invention.

If desired, a reactive material which allows the cladding of the pigments to prevent their inhibition of or reaction with the monomer during its polymerization may be used in the invention. Typical of such materials are water soluble monomers that precipitate onto carbon black or other pigments such as neutralized poly-acrylic acid and silanes such as amine silicate-organosilane copolymers, the latter giving a coating comprising precipitated silanes and silanes reacted with surface groups of the pigment.

Acrylonitrile monomer has been found to be a suitable water soluble monomer which will precipitate onto carbon. The silanes of water emulsified or water soluble types have been found to be suitable for the cladding process. Typical of suitable organo silanes are amino silanes, methacrylate silanes, epoxide-silanes, polyamino silanes. mercapto sllanes, vinyl silanes, chloroalkyl-silanes, and alkoxysilanes e.g. methyltrimethoxy-silane, phenyltri-methoxysilane, ' methylphenyldi methoxysilane and diphenyldimethoxysilane; and typical of suitable silazanes is hexamethyldisilazane.A preferred silane is triethoxy silane (Ci iSi(C2H:O)3) marketed as "^Siliclad" by the Clay Adams Division of Becton, Dickinson and Company, which gives good polymeric coating on carbon black that prevents the inhibition of the polymerization method by carbon black.

The polymerization time of a system containing "Siliclad" treated carbon black is about the same as the polymerization time of one not containing carbon black.

The cladding agent when utilized is provided in any amount which provides a covering of the pigment sufficient to prevent the pigment inhibiting complete polymerization to form the toner. 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.

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 polymerization of the present method are azobis-(2-methylpropionitrile) 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.

The initiator may be added to the monomer during dispersion of the carbon black or may be mixed in after the 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 with 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.By proper selection of materials in accordance with their triboelectric effects, the polarities of their charge when mixed are such that the electroscopic toner particles adhere to and are coated on the surfaces of carrier particles and also adhere to that portion of the electrostatic image bearing surfaces having a greater attraction for the toner than do the carrier particles. 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 adherences 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.

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 and not agglomerate. During polymerization, the particles pass through tacky stages when there is a tendency to agglomerate. Any suitable stabilization agent may be used.

Typical of such stabilizers are both nonionic 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 gelatines, starchs, 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 2(w60 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 size particles in stable suspension. 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) and paddle 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 apertures in the static element. The shear rate should be greater than 103 sec- An axial turbine agitator that comprises an arrangement of discs and paddles is the other preferred type of mixer. The axial turbine mixers are found to form stable dispersions of narrow particle size distribution at speed ranges of from 200 to 3,000 r.p.m.

The drawings illustrate a preferred type of rotor stator mixer. The mixer comprises a static element 22 as shown in Figure 2.

The static element comprises raised elements 15 separated by slots having a bottom 12.

The static element is mounted on base 21 supported by mounting element 24. Gaskets such as 23 are used in mounting of the element. Figure 3 illustrates the rotating element 31 of the mixer. The rotating element has blades 34 which correspond in height to the depth of the slots in the static element. The rotor is provided with a base 32 having an indented portion for attachment to suitable drive means, not shown, such as a high speed blender. Figure 1 illustrates the rotor and static element assembled to the mixing unit 11. The rotor is in close clearance with the static element and rotates around center 14. Figure 4 illustrates attachment means fo rthe mixer wherein a collar 42 is placed over base 24 of static element 22. The static element is secured with nut 43, keyed washer 44 and rubber shim 45.

The indented portions of the rotor allow better flow of the material being treated.

The shear applied by the sizing mixer is the amount which results in narrow size range distribution. The preferred rotor stator mixer applies a high shear mixing of greater than 103 sec-l for from 10 seconds to 2 minutes to achieve a size range of from 2 to 30 microns with about 95 percent between 5 and 20 microns. The volume average particle size is from 12 to 13 microns.

The time of high shear mixing in part varies with the viscosity of the aqueous medium in which the pigmented monomer is suspended. Generally, the stabilization agent changes the viscosity of the aqueous suspension medium. A suitable viscosity range generally is from 1 to 100 centipoises (cps). The preferred viscosity of the aqueous suspension medium is from 1 to 10 centipoises (cps) to give low cost and rapid mixing. An optimum range is from 1 to 3 cps to give a stable dispersion of monomer with short mixing time, low cost and little impurity in the toner.

The rotor stator high speed high shear mixer is capable of producing narrow toner particle ranges. The size range of particles is affected by the viscosity of the aqueous solution, viscosity of the monomer and ratio of monomer to aqueous suspending medium.

A suitable mixture is when the pigment containing monomer forms from 0.2 to 40 percent of the total volume of the monomer and water mixture. The size range produced may suitably be from 2 to 30 microns. However, for best toner performance, it is preferred that the range of particles be from 5 to 20 microns.

The following examples further define, describe, and compare methods of preparing toners of the present invention and of utilizing them in electrophotographic applications.

Parts and percentages are by weight unless otherwise indicated.

EXAMPLE I To about 100 grams of styrene are added about 5 grams of lauroyl peroxide which are mixed until dissolved. To this mixture is added about 7 grams of a cladded carbon black, Molacco-H, which has been treated with triethoxy silanc Siliclad, in about a 2 percent solution with water in a stirred beaker for about 5 minutes to prevent interference with the polymerization. This mixture is heated with mixing in a Waring Blender to about 70"C for about 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 rotorstator mixing head along with 500 c.c. of an about 1.25 percent polyvinyl alcohol water solution.The two phase mixture is then stirred at about 4,500 r.p.m. for 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 from 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 litres 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. During the final wash a 1 percent by weight solution of triethoxy silane with water was used as the wash solution. 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 11 100 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 were mixed in a Waring Blender to give a well dispersed carbon black. This mixture was added to 500 parts of 0.5 percent polyvinyl alcohol solution in a Waring Blender jar equipped with a Polytron mixing head. The mixture was agitated at 4,500 rp.m. for 30 seconds to disperse the pigmented monomer phase in the water phase. The resulting dispersion was 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 was then transferred to a 1,000 ml. polymerization flask equipped with an argon purge and paddle stirrer, and heated to 65"C while stirring at 60 r.p.m. After eight hours, the resulting polymer dispersion was cooled by pouring into three liters of cold water. The particles were recovered by sedimentation and consisted of uniformly black spheres with an average particle diameter of 10 microns.

The particles are placed in 3 litres of a 1 percent solution of triethoxy silane with water and shaken for 5 minutes. These particles utilized in a Model D processor produce images of good quality.

EXAMPLE 111 The method of Example I is repeated except that TiO2 is substituted for carbon black and is not treated with Siliclad. The toner is treated with Siliclad. The particles formed exhibit good xerographic properties and are completely polymerized. The particles are operable in a xerographic repro duction process utilizing a Model D copier and have a size between 5 and 15 microns.

EXAMPLE IV The method of Example I is repeated except that Dow Corning reactive silane DC Z-6020 is substituted for the triethoxy silane in both instances. This is found to produce toner which has 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. 35 Asahi Carbon of the patent. The toner recovered is treated with triithoxy silane and is found to exhibit improved copying qualities and is not subject to humidity sensitivity.

EXAMPLE Vl The method of Example I was performed except that an ultrasonic mixer (Biosonic Transducer) is substituted for the rotor stator (Polytron) (Registered Trade Mark) mixer.

The particles that result have a particle range of about 95 percent between 5 and 100 microns. The particles are operable as toner when utilized in a Model D processor.

EXAMPLE Vll The method of Example I is performed with particle sizing taking place by high speed stirring of the paddle blade stirrer at about 1,000 r.p.m. for about 15 minutes.

The paddle stirrer is then slowed to about 75 r.p.m. for completion of polymerization.

The particles recovered have a size range of 95 percent between 5 and 100 microns and are operable as toner.

EXAMPLE Vlll The method of Example I is performed utilizing acrylonitrile monomer in an amount of about 1.7 percent with water as the cladding agent and toner treatment material.

The toner produced is of good quality.

EXAMPLE IX The method of Example I is repeated substituting as the stabilization agent Monsanto 20-60 a polyvinyl alcohol of about 90,000 weight average molecular weight and about 16 mole percent polyvinyl acetate groups. The toner recovered is of good quality.

EXAMPLE X The method of Example I is repeated except a 70/30 polyethylene oxide-poly- propylene block copolymer of from 10,000 to 15,000 number weight MW (Pluronic (Registered Trade Mark) F-127) is substituted for polyvinyl alcohol as the stabilization agent. The toner is of good quality.

EXAMPLE XI The method of Example I is repeated except a 40/60 polyethylene oxide-poly- propylene block copolymer of from 10,000 to 15,000 number average molecular weight (Tetronic 1504) is substituted for the polyvinyl alcohol stabilizer. The toner is of good quality.

EXAMPLE Xll The method of Example I is repeated except about 2.5 percent by weight acrylonitrile monomer is substituted in both instances for the triethoxy silane. The toner has good triboelectric properties, is not subject to blocking and is completely polymerized.

EXAMPLE Xlll The method of Example II is repeated except about 3 percent by weight of hexamethyldisilazane is substituted in both instances for the diethoxy silane. The toner is completely polymerized and has good triboelectric properties. The particles exhibit stable triboelectric properties at varying humidities.

EXAMPLE XIV 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 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. The particles are not humidity sensitive.

EXAMPLE XV As a control, the method of Example I is repeated without treatment with triethoxy silane during rinsing. The toffer displaces a greater triboelectric variation when humidity changes from 15 percent to 85 percent than does the toner of Example I.

EXAMPLE XVIXVII The method of Examples I and XIV is repeated except about 2 percent methyltrimethoxysilane is substituted in each instance for the reactive silane of Examples I and XIV. The particles in each instance are found to be completely polymerized, satis factory in xerographic properties and are not sensitive.

EXAMPLES XVIII--XIX The methods of Examples I and II arc repeated substituting in each instance about 1 percent by weight diphenyldimethoxy silane for the reactive silanes of Examples I and II. The toners produced have good properties and are completely polymerized.

The particles have a size range of about 95 percent between 5 and 20 microns and good humidity stability.

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 or magnetic particles could be used in the method 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.

Further the sizing may be performed as a through-put or in line process rather than the batch process illustrated. Additionally while the treatment for humidity sensitivity control is illustrated utilizing dispersion polymerized toner, it is possible to similarly treat toner formed by the conventional attrition processes or by emulsion polymerization processes.

The basic method steps used in the present invention are the subject of our co-pending application 32193/77 (Serial No. 1,580,411) which describes and claims a method of forming a toner comprising treating a pigment in order to prevent its inhibiting polymerization by suspending the pigment in a mixture of water and a silane which can react with the pigment, dispersing the 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 the toner.

WHAT WE CLAIM IS:- 1. A method of forming toner particles comprising dispersing a pigment in a monomer, treating the pigment containing monomer in an aqueous medium to form a toner size monomer in suspension, agitating the monomer during polymerization to form polymerized toner particles, treating the toner particles after polymerization with a treatment agent selected from an acrylonitrile monomer and a silane to neutralize hydrophilic groups at the surface of the toner particles to decrease humidity sensitivity of the particles, and recovering toner particles.

2. A method according to Claim 1 wherein the pigment is carbon black.

3. A method according to Claim 1 or 2 wherein the monomer comprises styrene.

4. A method according to any one of Claims 1 to 3 wherein the agitation is carried out for longer than 3 hours.

5. A method according to any one of Claims 1 to 4 wherein the toner particles range in size from 5 to 20 microns.

6. A method according to any one of Claims 1 to 5 wherein the pigment containing monomer forms 0.2 to 40 percent of the total volume of the monomer and water mixture.

7. A method according to any one of Claims 1 to 6 wherein an initiator is present during the pigment dispersion in the monomer.

8. A method according to Claim 7 wherein the initiator is lauroyl peroxide.

9. A method according to any one of Claims 1 to 8 wherein an effective amount of stabilizer is present during the treatment to form the toner size monomer.

10. A method according to Claim 9 wherein the stabilizer is polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polymethacrylic acid or polyacrylamide.

11. A method according to claim 10, wherein the stabilizer is present in an amount of from 0.75 to 1 percent by weight of the aqueous medium.

12. A method according to any one of claims 1 to 11, wherein the toner size monomer is formed by mixing the pigment and monomer at greater than 103 sec~l shear rate.

13. A method according to claim 12, wherein the shear mixing is carried out for from 10 seconds to 2 minutes.

14. A method according to any one of claims 1 to 13, wherein the particles are spherical.

15. A method according to any one of claims 1 to 14, wherein the treatment agent comprises an acrylonitrile monomer.

16. A method according to any one of

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

Claims (36)

**WARNING** start of CLMS field may overlap end of DESC **. factory in xerographic properties and are not sensitive. EXAMPLES XVIII--XIX The methods of Examples I and II arc repeated substituting in each instance about 1 percent by weight diphenyldimethoxy silane for the reactive silanes of Examples I and II. The toners produced have good properties and are completely polymerized. The particles have a size range of about 95 percent between 5 and 20 microns and good humidity stability. 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 or magnetic particles could be used in the method 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. Further the sizing may be performed as a through-put or in line process rather than the batch process illustrated. Additionally while the treatment for humidity sensitivity control is illustrated utilizing dispersion polymerized toner, it is possible to similarly treat toner formed by the conventional attrition processes or by emulsion polymerization processes. The basic method steps used in the present invention are the subject of our co-pending application 32193/77 (Serial No. 1,580,411) which describes and claims a method of forming a toner comprising treating a pigment in order to prevent its inhibiting polymerization by suspending the pigment in a mixture of water and a silane which can react with the pigment, dispersing the 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 the toner. WHAT WE CLAIM IS:-

1. A method of forming toner particles comprising dispersing a pigment in a monomer, treating the pigment containing monomer in an aqueous medium to form a toner size monomer in suspension, agitating the monomer during polymerization to form polymerized toner particles, treating the toner particles after polymerization with a treatment agent selected from an acrylonitrile monomer and a silane to neutralize hydrophilic groups at the surface of the toner particles to decrease humidity sensitivity of the particles, and recovering toner particles.

2. A method according to Claim 1 wherein the pigment is carbon black.

3. A method according to Claim 1 or 2 wherein the monomer comprises styrene.

4. A method according to any one of Claims 1 to 3 wherein the agitation is carried out for longer than 3 hours.

5. A method according to any one of Claims 1 to 4 wherein the toner particles range in size from 5 to 20 microns.

6. A method according to any one of Claims 1 to 5 wherein the pigment containing monomer forms 0.2 to 40 percent of the total volume of the monomer and water mixture.

7. A method according to any one of Claims 1 to 6 wherein an initiator is present during the pigment dispersion in the monomer.

8. A method according to Claim 7 wherein the initiator is lauroyl peroxide.

9. A method according to any one of Claims 1 to 8 wherein an effective amount of stabilizer is present during the treatment to form the toner size monomer.

10. A method according to Claim 9 wherein the stabilizer is polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polymethacrylic acid or polyacrylamide.

11. A method according to claim 10, wherein the stabilizer is present in an amount of from 0.75 to 1 percent by weight of the aqueous medium.

12. A method according to any one of claims 1 to 11, wherein the toner size monomer is formed by mixing the pigment and monomer at greater than 103 sec~l shear rate.

13. A method according to claim 12, wherein the shear mixing is carried out for from 10 seconds to 2 minutes.

14. A method according to any one of claims 1 to 13, wherein the particles are spherical.

15. A method according to any one of claims 1 to 14, wherein the treatment agent comprises an acrylonitrile monomer.

16. A method according to any one of

claims 1 to 14, wherein the treatment agent comprises a silane.

17. A method according to claim 16, wherein the silane is an organo silane or a silazane.

18. A method according to claim 17, wherein the silane is an alkoxysilane.

19. A method according to claim 18, wherein the silane is triethoxy silane.

20. A method according to any one of claims 1 to 19, wherein the treatment is carried out during agitation of the toner in water.

21. A method according to any one of claims 1 to 19, wherein the toner is treated to reduce humidity sensitivity by suspending the toner in a solution of water and said treatment agent.

22. A method according to claim 21, wherein said treatment agent is present in an amount of from 1 to 5 percent by weight of the agent/water system.

23. A method according to claim 22, wherein the agent is present in an amount of from 1 to 2 percent by weight of the agent/water system.

24. A method according to any one of claims 1 to 23, wherein the treatment is carried out prior to recovery of the toner from the polymerization liquid.

25. A method according to any one of claims 1 to 23, wherein the treatment is carried out during rinsing of the toner after polymerization.

26. A method of forming toner particles substantially as hereinbefore described with reference to the accompanying drawings.

27. A method of forming toner particles substantially as hereinbefore described with reference to any of Examples I to XIV or XVI to XIX.

28. A toner whenever made by a method according to any one of claims 1 to 27.

29. A toner of low humidity sensitivity comprising a generally spherical polymer particle having dispersed therein a pigment and having a coating thereon of the reaction product of an acrylonitrile monomer or a silane and hydrophilic groups at the surface to decrease the humidity sensitivity of the particle.

30. A toner according to claim 29, wherein the pigment comprises pigment particles, each surrounded by a coating comprising precipitated silanes and silanes reacted with surface groups of the pigment.

31. A toner according to claim 29, wherein the pigment comprises pigment particles, each surrounded by a polyacrylonitrile coating.

32. A toner according to any one of claims 29 to 31, wherein the polymer comprises a styrene polymer.

33. A toner according to any one of carbon black.

34. A toner of low humidity sensitivity substantially as hereinbefore described with claims 29 to 32, wherein the pigment is reference to any of Examples I to XIV or XVI to XIX.

35. A developer comprising a carrier and a toner according to any one of claims 28 to 34.

36. An electrostatographic imaging process comprising establishing an electrostatic latent image on a surface and contacting the surface with an electrostatographic material comprising a toner according to any one of claims 28 to 34 or a developer according to claim 35.