CA1168498A - Treatment process for controlling triboelectric charge of dispersion polymerized toners - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to a process for preparing postively charged dry toner compositions by dispersion polymerization which comprises in-corporating into the monomer phase during said dispersion polymerization certain triboelectric charge control materials, as represented by the follow-ing formula:

X

wherein R1, R2, R3, and R4 are independently selected from the group consisting of alkyl radicals of from 1 to about 7 carbon atoms, and x is an anion such as halide, nitrate, or sulfate.

Description

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BACKGROUND OF THE INVENTION
This invention rel~tes generally to processes for preparing toners and more specifically to improved proeesses for preparing toners having improved properties, which toners are useful as developing compositions in electrophotographic imaging systems.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known, as detailed for example in U. S. Patent 2,297,6~ everal methods have been used in the prior art for applying the toner particles to the formed latent electr~
static image including cascade ~evelopment as described in U.S. Patent

2,618,552, magnetic brush development as described in U.S. Patent 2,874,063, powder cloud development as described in U.S. Patent 2,221,776, and touchdown development as described in U.S. Patent 3,1669432.
Toners can be prepared by numerous well known methods, one method involving thoroug~y mixing the softened resin and pigment to thereby form a uniform dispersion, as by blending these ingredients in a rubber mill or the like, and subsequently pulverizing this material in order to form it into small particles. Although this technique of toner manufacture has produced some very excellent toners it does tend to have eertain short-comings. Thus, for example, such a process gener~lly results in a toner which has a rather wide range of particle sizes that is, the toner contains resin having individual p~rticles ranging in diameter from submicron in size, to above 20 microns. Additionally, this is a batch process which tends to be eather slow, expensive, and dusty. Further, this technique of toner production imposes certain limitations upon the material selected for the toner, as the resin pigment dispersion must be sufficiently friable so that it can be pulverized at an economically feasible rate of production. One of the problems which arises from this requirement is that when the resin pigment disperison is sufficiently friable for relatively high speed pulver-izing, it tends to form an even wider range of particle sizes during pulve-rization including relatively large percentage of fines. Also, the highly friable materials are frequently subject to further polymerization or powder-ing when they are employed for developing in xerographic imaging systems.
Other requirements of xerographic developers, include the requlrements `~ 35 that they be stable in storage, non-agglomerative, have the proper tribo-;

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;' 1 1 ~g~198 electric properties for developing, do not film or soil the xerographic plate and have a low melting point for heat fusing.
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 a 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.
It has been proposed in United Kingdom Patent 1,319,815 that toner compositions be prepared directly from the monomer by polymer-ization of the monomer and toner sized particles containing a colorant, while a method of suspension polymerization to form toner particles is disclosed in U.S. 3,634,251. 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 fine-ly-divided inorganic dispersion stabilizer such as a met~l powder or inor-ganic salt or oxide, and a polar resinous additive which is soluble in the monomer. After suspension polymerization of the monomer, if required, the finely divided disperison 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 1 :~ 68498 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 Irom the monomer. The process in any case often results in incomplete polymerization that leaves residaul monomer that affects the triboelectric, blocking and fixing properties of the toner. This incomplete p~ymerization of the monomer was theorized as caused by the pigment inhibiting polymerization.
It has also been proposed that a suspension polymeri~ation pro-cess 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, employ-ing a suspending agent, for example polyvinyl alcohol; polymerizing, employ-ing conventional suspension polymerization technigues; 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. 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 - 25 of absorbed monomer has been converted to polymer at the surEace, 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 30 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 35 colored beads and the large amount of wetting agents required have im-purities undesirable in toners and further have a wide range of particle size.

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~ ~ournal of Applied Polymer Science article at Volurne 16, Page 1967 and 1968 (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.
Also more importantly, toners prepared by current procssses such as dispersion polymerization processes and suspension polymerization processes result in developers wherein the toner is charged negatively rather than positively and one important object of this invention is to prepare by a simple method a toner resin which will be charged positively. Also there remains a need for processes of preparing toners which would not involve extensive processing steps of polymer formation, colorant addition, mixing and particle formation. There also continues to be a need for pro-cesses which would result in the production of toner particles directly from monomer materials which particles will have good triboelectric properties, abrasive resistance, good blocking temperature and excellent color loading capabilities.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a process for preparing toner which overcomes the above-noted disadvantages.
A further object of the present invention is to provide a process for preparing toners which charge positively when used in a two component development system, and more specifically when used as conductive developers in reversal xerographic imaging systems.
It is a further object of this invention to provide processes for producing toner in high yields and at low cost.
Yet another object of the present invention is to provide poly-meri~ation methods for preparing toners which would charge positively relative to the carriers when used in a developer system.
These and other objects of the present invention are accomplished by providing a process for preparing positively charged dry toner composi-tions by dispersions polymerization which comprises incorporating into the monomer phase during said dispersion polymeri~ation certain tribo-I 1 6~98 electric charge control materials, as represented by the following formula:

R4 - N - R2 ~ X
~ R3 J
wherein Rl, R2, R3, and R4 are independently selected from the ~oup consisting of alkyl radicals of from 1 to about 7 carbon atoms, and x is an anion such as halide, nitrate, or sulfate. Preferably X is halide such as chloride, bromide, iodi~e or fluoride~
~xamples of alkyl radicals include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and the like.
Illustrative examples of the triboelectric charge control ma-terials include tetrabutyl ammonium chloride, tetrabutyl ammonium bromide, tetrabutyl ammonium iodide, tetrabutyl ammonium nitrate, tetrapentyl lS ammonium chloride, tetrapentyl ammonium bromide, tetrapentyl ammonium iodide, tetrapentyl ammonium nitrate, tetrahexyl ammonium chloride, tetrahexyl ammonium bromide, tetrahexyl ammonium iodide, tetrahexyl ammonium nitrate, tetraheptyl ammonium c~oride, tetraheptyl ammonium bromide, tetraheptyl ammonium iodide, tetraheptyl ammonium nitrate, 2~ mixtures of any of the above, and the like.
The triboelectric control materials are present in amounts of from about 0.05 percent to about 5 percent, and preferably from about 0.1 percent to about 1.0 percent, by weight of the toner resin.
Examples of resins to which is added the triboelectric control 25 materials of the present invention include 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. Monomeric units which may be employed to form polymers include: styrene, ~chlorostyrene; ethyl-enically unsaturated mono-olefins such as butylene, and the like; vinyl 30 esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate and the like; esters of alphamethylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloro-ethyl acrylate, phenyl acry-late, methyl-alpha-chloroacrylate, methyl methacrylate, ethyl methacrylate, 35 butyl methacrylate and the like; vinyl ethers such as vinyl isobutyl ether, and the like; vinyl ketones such as vinyl hexyl ketone, and the like; vinylidenehalides and N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, 1 ~6~98 and the like; and mixtures thereof. Generally, suitable vinyl resins em-ployed have a weight average molecular weight between about 3,000 to about 500,000 Pigments useful for coloring the toner resin include various 5 carbon blacks and commercially available dyes, and magnetites and mix-tures thereof. The pigment or dye should be present in sufficient quantity so as to render the toner resin highly colored. Preferably the pigment or dye is present in amounts of from about 3 percent to about 75 percent by weight based on the total weight of toner.
Any suitable carrier material can be employed as with the treated toner of the present invention as long as such particles are capable of triboelectrically obtaining a charge of opposite polarity to that of the toner particles which in the present invention in one embodiment would be a negative polarity to that of the toner particles which are positively 15 charged so that the toner particles will adhere to and surround the carrier particles. Thus the carriers can be selected so that the toner particles acquire a charge of positive polarity and include materials such as glass, steel, nickel, iron ferrites, silicon dioxide, and the like. Carrier materials may be used with or without a coating such coatings including fluorocarbons 20 such as polyvinylidene fluoride and the like. Also nickel berry carriers as described in U.S. Patent 3,847,604 can be employed, these carriers being ,:
modular carrier beads of nickel characterized by surfaces of reoccuring recesses and protrusions providing particles with a relatively large external area. The diameter of the coated carrier particles from about 50 to about 25 1,000 microns thus allowing the carrier to possess sufficient density and inertia to aovid adherence to the electrostatic images during the devel-opment process. The carrier may be employed with the toner composition in any suitable combination, however, best results are obtained when about 1 part per toner is used and about 10 to about 200 parts by weight of carrier.
30 The diameter of the toner particles range from about 5 microns to about 30 microns.
Developer compositions of the present invention may be used to develop electrostatic latent images on any suitable electrostatic surface capable of retaining charge including conventional photoconductors. However, 35 the developers of the present invention are best utilized in systems wherein the negative charge resides on the photoreceptor and this usually occurs -~ ~ 68~

with organic photoreceptors. Illustrative examples of such photoreceptors include polyvinyl carbazole, 3-dimethyl amino benzylidene, benzhydrazide, 2-benzylidene-amino carbazole9 polyvinyl carbazole, 2-nitro benzylidene-~bromo aniline, 2,4-diphenyl quinozoline, 172,4-triazine, 1,5-diphenyl-3-methyl pyrazoline, 3-amino carbazole, pol~7vinyl carbazole-trinitrofluorenone, charge transfer complexes, phthalocyanines and mixtures thereof, layered photoresponsive devices such as those containing generating and transport layers, overcoated photoresponsive devices and the like.
The colorant can be dispersed in the monomer by admixing the colorant with the monomer under intensive agitation as obtained, -for example, in a high speed, high shear mixer such as a Waring Blender equipped with a Polytron high shear head, a homogenizing mixer or the like, capable of a speed of from about 1000 to 3000 rpm. The amount of colorant added can range from about 3 to about 7S Yveight percent based on the weight of the monomer. Preferably, prior to dispersion of the colorant in the monomer, dispersing aids can be added to the monomer such as surfactants, dispersants and the like to assist in effecting a u niform dispersion. It has been found that increasing the viscosity of the monomer prior to addition of the colorant is an effective means of stabilizing the colorant dispersion.
Suitable oil soluble surfactants can be employed to aid the dispersion of colorant. Generally, from about 0.25 to about 3 weight percent surfactant based on the weight of monomer is sufficient. Stabilization of the colorant dispersion can be obtained by increasing the viscosity ~f the monomer-colorant dispersion through addition of a polymer soluble in the monomer. Generally, the most conveniently employed is the polymer corresponding to the monomer employed; however, other suitable polymers which are soluble in the monomer can also be employed. Stabilization can be effected by addition of from about 1 to about 20 weight percent polymer based on the weight of the monomer. A uniform dispersion of the colroant in the monomer can be effected bycontinuous high speed mixing for from about 10-20 minutes although longer or shorter periods can be employed depending upon the particular mixer employed. Once the colorant/monomer dispersion is ob-tained, the triboelectric control agent can be added. Generally, from 0.5 to 5.0 percent by weight of monomer is sufficient.
Once the colorant/monomer/charge control agent dispersion is obtained, a polymerization initiator can be admixed therewith just prior `I 3 ~

to commencement of polymerization. Most conveniently, the polymerization initiator can be dissolved in a portion of monomer and the resulting solution can be blended with the colorant/monomer dispersion. Illustrative poly-merization initiators which can be suitably employed are azobisisobutyronitrile (AIBN), benzoyl peroxide, lauroyl peroxide, and the like. Generally, from about 0.5 to about 10.0 weight percent initiator based on the weight of monomer is sufficient.
ln addition to the preparation of a readily polymerizable organic phase, the dispersion polymerization process of the present invention employs an aqueous phase containing a suspending agent. The aqueous phase can be prepared by dissolving a suspending agent in water with continuous agi-tation. Suitable water soluble suspending agents are, for example, water soluble polymers such as polyvinyl alcohol, polyethylene oxide"nethyl cellulose, hydroxyethyl cellulose, cyanoethyl cellulose and the like. Generally,from about .2 to about 10 weight percnet suspending agent based on the weight of water has been found sufficient to effect a dispersion of the organic phase when said phase is admixed with the aqueous phase. Above about 10 weight percent, the resulting viscosity of the aqueous phase would generally be too high to enable the obtainment of the desired particle size.
Preferably, 0.5 to about 4 weight percent suspending agent is employed.
In addition to the organic suspending agent, there can also be added water insoluble particulates, such as carbon black, silicon dioxide ~luminum oxide, magnetite or organic materials, to provide additional droplet stabilization and final toner flowability behavior. These particles, typically in the size range from 0.1 um to .4 um and in amounts from .01 to 1.0 weight percent based upon the weight of water, have been found sufficient.
After preparation of the aqueous phase, the aqueous phase can be charged to a reaction vessel and stirred at high speeds of from about 1000 to about 8000 rpm, while the organie phase is added thereto. Under these conditions, the orgnaic phase is rapidly and uniformly dispersed within the aqueous phase as a plurality of particles having an average particle size ranging from 1 to about 100 microns. Generally, sufficient orgnaic phase is added to the aqueous phase to effect a volumetric ratio of organic phase to aqueous phase ranging from about 0.05:1 to about 0.4:1, and pre-ferably ranging from about 0.1:1 to about 0.2:1.

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~ :~ 68~98 Upon completion of the addition and dispersion of the organic phase in the aqueous phase, the speed of agitation can be reduced to about 80 to 300 rpm. Polymeri~ation can be rapidly effected at a polymeri~ation temperature o~ about 3~ C to about 95 C. Under these polymeri~zation - 5 conditions, the reaction will be complete within from about 1 to 7 hours.
~Iigher or lower temperatures can be employed depending upon the par-ticular polymerization initiator employed.
When using wltreated carbon black as the colorant, initiation of polymerization sometimes becomes complicated because of the ability of the carbon black to trap the free radicals generated. AIB~, however, has been found to be an effective initiator even with carbon black.
Upon completion of the polymerization, the polymerized particles can be recovered by cooling the reaction vessel to room temperature while stirring continuously to prevent agglomeration. Thereafter, the reaction medium can be thoroughly washed with water to remove the suspending agent and the particles can be recovered by filtration and drying.
The following examples are being supplied to further define the species of the present invention, it being noted that these examples are intended to illustrate and not limit the scope of the present invention.
Parts and percentages are by weight unless otherwise indicated.
EXAM PLE I
As controls there was prepared by disperison polymerization, at a temperature of 75 C toner materials by subjecting to polymerization after mixing 86 grams of the monomer styrene n-butyl methacrylate, 95 percent styrene, 5 percent n-butyl methacrylate, containing thereon 14 grams of grafted carbon black. This resulted in an oil phase containing 100 grams of the above monomer mix to which was added, 7.74 grams of lauroyl peroxide, 9 percent by weight. The aqueous phase was comprised of 500 milliliters of water, 0.2 grams of carbon black, 0.5 grams of polyvinyl alcohol, and 0.05 grams of potassium iodide.
The second control contained no potassium iodide.
EXAM PLE II
Two toners were prepared by dispersion polymerization. The first toner contained an oil phase of 86 grams of the monomer material 35 styrene n-butyl methacrylate (95/5),14 grams of grafted carbon black, 7.74 grams of lauroyl peroxide, and 0.5 grams of tetraheptyl ammonium ~J68~9~

chloride. The oil phase was comprised of 500 grams of water, 0.2 grams of carbon black, 0.5 grams of polyvinyl alcohol, and 0.05 grams of potassium iodide.
The second toner was comprised of the same ingredients as 5 above with the exception that the oil phase contained û.23 grams of tetra-butyl ammonium nitrate, instead of the tetraheptyl ammonium chloride, and the aqueous phase contained 0.1 grams of potassium iodide, instead of 0.05 grams of potassium iodide.
Three parts per weight of the above toners, and 100 parts per 10 weight of 0.35 percent per fluoroalkoxy fluoropolymer, commercially availablefrom E.I. DuPont, coated on a Hoeganaes steel carrier were placed in a glass jar, and roll mixed at a linear speed of 90 feet per minute, for the period of time indicated. The triboelectric charge in microcoulombs per gram (~t'c/gm) was measured by blowing off the toners from the carrier 15 in a Faraday cage.
60 min 180 min 300 min 24 hrs Toner Controll +10 +5 +1 -6 Toner Control 2 +9 +2 +2 -7 Toner I (Ex. II) +6 ~3 +3 ~2 Toner II (Ex II) +10 -~10 +12 +25 As the above examples establish both control toners 1 and 2, although exhibiting positive triboelectric behavior for short time periods, they ultimately reverted to a negative tribo charge at longer times. It 25 is a requirement of the toner of the present applieation that the triboelectric charge remain positive through 24 hours of testing. For toners 1 and II
which contain the added triboelectric charge control agents, the tribo remains positive during the entire 24 hours of the test. Therefore, the use of charge control agents, as exemplified in toner Examples I and Il, 30 when dispersed in the monomer phase, can be successfully used to control the triboelectric behavior of the resulting toner.
Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are in-tended to be included within the scope of this invention.

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Claims (5)

WHAT IS CLAIMED IS:

1. A process for preparing positively charged dry toner materials by disperison polymerization, which comprises incorporating into the monomer phase during said dispersion polymerization of a toner resin, a triboelectric charge control material of the following formula wherein R1, R2, R3, and R4 are independently selected from the group consisting of alkyl radicals of from 1 to about 7 carbon atoms, and X is an anion selected from halide, nitrate, and sulfate.

2. A process in accordance with Claim 1 wherein the triboelectric charge control material is present in an amount of from about 0.05 percent to about 5 percent.

3. A process in accordance with Claim 1 wherein the X anion is chloride, and the toner resin is a copolymer of styrene/n-butylmethacrylate.

4. A process in accordance with Claim 1 wherein the triboelectric charge control material is tetra butyl ammonium chloride, tetrabutyl ammon-ium bromide, tetrabutyl ammonium iodide, tetrabutyl ammonium nitrate, tetrapentyl ammonium chloride, tetrapentyl ammonium bromide, tetrapentyl ammonium iodide, tetrapentyl ammonium nitrate, tetrahexyl ammonium chloride, tetrahexyl ammonium bromide, tetrahexyl ammonium iodide, tetrahexyl ammonium nitrate, tetraheptyl ammonium chloride, tetraheptyl ammonium bromide, tetraheptyl ammonium iodide, tetraheptyl ammonium nitrate, and mixtures thereof.

5. An improved process for preparing positively charged dry toner materials by dispersion polymerization, the improvement comprising the preparation of a readily polymerizable organic phase (1) by admixing the monomer material styrene/n-butylmethacrylate with a polymerization initiator dissolved therein, and a colorant, and from about 0.05 percent to about 5 percent by weight of the triboelectric charge control material tetraheptyl ammonium chloride, (2) admixing said polymerizable organic phase with an aqueous phase prepared by dissolving a suspending agent in water, effecting polymerization at a temperature of from about 30°C to about 95°C, and subsequently recovering the polymerized particles.