EP0690355A1

EP0690355A1 - Humidity-stabilized toners and developers

Info

Publication number: EP0690355A1
Application number: EP95420140A
Authority: EP
Inventors: Peter S. Alexandrovich; Michael P. Kubisiak; John C. Wilson
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1994-06-08
Filing date: 1995-06-02
Publication date: 1996-01-03
Also published as: JPH086300A

Abstract

Electrophotographic toners and developers having polymeric binder and a charge control agent that is a mixture of a first component having the general structure:

and a second component having the general structure:

X¹ and X are each H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, or halo. R^a and R^b are each H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, or benzoylamino. M is Cr, Co, or Fe. n, n', m, and m' are each 1, 2, or 3. Each R⁺ is a cation. R¹ and R are each independently, alkyl having from 2 to 18 carbons.

Description

The invention relates to electrographic materials, particularly toners and developers. This invention more particularly relates to negative charging, humidity stabilized toners and to developers including those toners.
In electrography, image charge patterns are formed on a support and are developed by treatment with an electrographic developer containing marking particles which are attracted to the charge patterns. These particles are called toner particles or, collectively, toner. Two major types of developers, dry and liquid, are employed in the development of the charge patterns.
In electrostatography, the image charge pattern, also referred to as an electrostatic latent image, is formed on an insulative surface of an electrostatographic element by any of a variety of methods. For example, the electrostatic latent image may be formed electrophotographically, by imagewise photo-induced dissipation of the strength of portions of an electrostatic field of uniform strength previously formed on the surface of an electrophotographic element comprising a photoconductive layer and an electrically conductive substrate. Alternatively, the electrostatic latent image may be formed by direct electrical formation of an electrostatic field pattern on a surface of a dielectric material.
One well-known type of electrostatographic developer comprises a dry mixture of toner particles and carrier particles. Developers of this type are employed in cascade and magnetic brush electrostatographic development processes. The toner particles and carrier particles differ triboelectrically, such that during mixing to form the developer, the toner particles acquire a charge of one polarity and the carrier particles acquire a charge of the opposite polarity. The opposite charges cause the toner particles to cling to the carrier particles. During development, the electrostatic forces of the latent image, sometimes in combination with an additional applied field, attract the toner particles. The toner particles are pulled away from the carrier particles and become electrostatically attached, in imagewise relation, to the latent image bearing surface. The resultant toner image can then be fixed, by application of heat or other known methods, depending upon the nature of the toner image and the surface, or can be transferred to another surface and then fixed.
Toner particles often include charge control agents, which, desirably, provide high uniform net electrical charge to toner particles without reducing the adhesion of the toner to paper or other medium. Positive charging toners, incorporating positive charge control agents have been widely used. Negative charging toners, incorporating negative charge control agents, have been less common.
Many negative charging toners have shortcomings, such as moderate or high sensitivity to changes in relative humidity. Since different toners are suitable for different uses, there is a continuing need for improved negative charging toners.
US-A-3,565,805 teaches the additional of a liquid "tackifying agent" to a developer. Included amoung the listed agents are fatty acid amine surfactants.
Great Britain Patent No. 1,117,224 teaches a process for producing toner particles using a surfactant. Numerous surfactants are listed. Among these are various sulfonation products including sulfonated derivatives of fatty acid esters, such as the diamyl or dioctyl esters of sodium sulfosuccinic acid.
US-A-3,694,359 teaches toner that includes a wetting agent, such as sodium di-isooctyl-succin-1-sulfonate. Merrill and others states: "The wetting agent aids in promoting even, uniform contact between the toner and the paper support to which the toner image is ultimately fixed by heat. It is most advantageously used when fusing is accomplished through the use of infrared radiation, as it reproduces a uniform, high-density image otherwise difficult to obtain." (column 6, lines 24-30)
US-A-4,912,009 teaches that styrene-acrylic toners contaminated by surfactant used in producing the toner binder, tend to have unstable charging characteristics when subjected to changes in temperature and humidity.
US-A-4,814,250 teaches toner that includes, as a charge control agent, a mixture of dioctylsodiumsulfosuccinate and sodium benzoate.
US-A-4,624, teaches a charge-controlling and coloring agent having the general formula:

where X₁ and X₂ are H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro or halo; m, m', n, and n' are each from 1 to 3; R1 and R³ are H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, or benzoylamino; Y+ is an ammonium ion, aliphatic ammonium ion, alicyclic ammonium ion or heterocyclic ammonium ion; and M is chromium, cobalt, or iron. A negative charge control agent having the structural formula:

is marketed, by Hodagaya Chemical Co., for use in negative charging toners.
The invention, in its broader aspects, provides electrophotographic toners and developers having polymeric binder and a charge control agent that is a mixture of a first component having the general structure:

and a second component having the general structure:

X¹ and X are each H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, or halo. R^a and R^b are each H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, or benzoylamino. M is Cr, Co, or Fe. n, n', m, and m' are each 1, 2, or 3. Each R+ is a cation. R¹ and R are each independently, alkyl having from 1 to 18 carbons.
It is an advantageous effect of at least some of the embodiments of the invention that negatively charging toners can be provided which have favorable charging and humidity control characteristics.
The term "particle size" used herein, or the term "size", or "sized" as employed herein in reference to the term "particles", means the median volume weighted diameter as measured by conventional diameter measuring devices, such as a Coulter Multisizer, sold by Coulter, Inc of Hialeah, Florida. Median volume weighted diameter is the diameter of an equivalent weight spherical particle which represents the median for a sample; that is, half of the mass of the sample is composed of smaller particles, and half of the mass of the sample is composed of larger particles than the median volume weighted diameter.
The term "charge control" refers to a propensity to modify the triboelectric charging properties of the resulting toner.
The term "glass transition temperature" or "Tg" as used herein means the temperature at which a polymer changes from a glassy state to a rubbery state. This temperature (Tg) can be measured by differential thermal analysis as disclosed in "Techniques and Methods of Polymer Evaluation", Vol. 1, Marcel Dekker, Inc., New York, 1966.
The toner of the invention has a charge control agent comprising a mixture of two or three components.
The first component is has the general structure:

where X¹ and X are each selected from H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro and halo; m, m', n, and n' are each selected from integers from 1 to 3; R^a and R^b are each selected from H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, and benzoylamino; R⁺ is a cation; and M is chromium, cobalt, or iron. As discussed above, materials like these are disclosed in US-A-4,624,907. In currently preferred embodiments of the invention, the first component has the structural formula:

where R⁺ is an inorganic cation, such as NH₄⁺, Na⁺, H⁺, or a mixture thereof.
The second component of the charge control agent of the invention is a material that is both a surfactant and a charge control agent. It is presently preferred that the second component be capable of acting as an anionic surfactant in water solution. It is also presently preferred that the second component be capable of use as a negative charge control agent, independent of any other charge control agent, in a negatively charging electrophotographic toner. In a currently preferred embodiment of the invention, the second component has the general structure:

R⁺ is a cation. It is currently preferred that R be an inorganic cation. R¹ and R are each, independently, alkyl having from 2 to 18 carbons. In a particularly preferred embodiment of the invention, the second component is dioctyl sodium sulfosuccinate, which has the structural formula:

Specific examples of the second component also include:

and
In a currently preferred embodiment of the invention, the charge control agent includes an optional third component: a flow control aid. In that embodiment of the invention, the second component is a gummy solid that cannot be readily handled by conventional powder handling apparatus without the addition of the flow control aid. Examples of such flow control aids include: silica, titania, and polymeric beads. A currently preferred flow control aid is an alkali metal benzoate salt, such as sodium benzoate. As Comparative Examples F demonstrate, the flow aid does not provide a charge control function in the developer.
The charge control agent, and each component thereof, is present in the toner of the invention in an amount effective to modify, and preferably, improve the properties of the toner. It is preferred that a charge control agent improve the charging characteristics of a toner, so the toner quickly charges to a negative value having a relatively large absolute magnitude and then maintains about the same level of charge. It is also preferred that a charge control agent improve the charge uniformity of a toner composition, that is, insure that substantially all of the individual toner particles exhibit a triboelectric charge of the same sign with respect to a given carrier. (The term "bicharged" is used herein to identify a toner in which the toner particles do not all have the same polarity.) It is also preferred that toner throw-off be minimized. The term "toner throw-off" refers to the amount of toner powder thrown out of a developer mix as it is mechanically agitated, for example, within a development apparatus. Throw-off can cause unwanted background development and general contamination problems.
The first and second components are each present in a sufficient concentration to effect the charging characteristics of the toner even if the other component were not present. In a preferred embodiment of the invention, the first component has a concentration, relative to the total weight of the toner of from 0.5 to 5.0 weight percent; or, more preferably, from 1.5 to 3.5 weight percent. In that embodiment, the second component has a concentration of from 0.10 to 2.5 weight percent; or, more preferably, from 0.10 to 0.50 weight percent. The third component, when present, has a concentration of from 0.02 to 0.4 weight percent.
Both components of the charge control agent are dispersed within the toner. The first component is present in the toner in the form of fine particulate inclusions. The second charge control agent is not phase separated within the toner (at least in so far as phase separation visible in toner melted onto a glass slide under a microscope at 650 times magnification). This is an advantageous feature. It has been empirically determined that materials that cause a toner to separate into different phases can be correlated with increased clumping of the toner powder, and can also lead to irreproducible manufacture of toner.
The properties of the thermoplastic polymer binders employed as the toner matrix phase in the present invention can vary widely. Typically, and preferably, amorphous toner polymers having a glass transition temperature in the range of 50°C to 120°C or blends of substantially amorphous polymers with substantially crystalline polymers having a melting temperature in the range of 65°C to 200°C are utilized in the present invention. It is currently preferred that such polymers have a molecular weight distribution including an insoluble, very high molecular weight fraction and one or more fractions having a number average molecular weight in the range of 1000 to 500,000 and a weight average molecular weight in the range of 2 X 10³ to 2 X 10⁶. It is also currently preferred that the thermoplastic polymers used in the practice of this invention be substantially amorphous; however, as indicated above, mixtures of polymers can be employed, if desired, such as mixtures of substantially amorphous polymers with substantially crystalline polymers.
Polymers useful as binders in the toner of the invention include styrenic/acrylic copolymers. In general, preferred styrenic/acrylic copolymers have a glass transition temperature in the range of 50°C to 100°C. In a particular embodiment of the invention, the resin is a copolymer of styrene and butyl acrylate, crosslinked with divinyl benzene; produced in a suspension or emulsion polymerization process. An initiator and, optionally, a chain transfer agent are used in the synthesis. The ratio of styrene to butyl acrylate is in the range of from 90:10 to 60:40 and the divinyl benzene is used at a level of 3 weight percent or less, preferably, at a level of 0.1 to 1.0 weight percent. In a particular embodiment of the invention, the binder is a polymer disclosed in U.S. Patent Application No. 08/255,522, entitled "Particulate Polymer, Electrophotographic Toner, and Preparation Methods", filed June 8, 1994 by Sorriero and others.
An optional but preferred component of the toner of the invention is colorant: a pigment or dye. Suitable dyes and pigments are disclosed, for example, in US-A-Re-31,072 and in US-A-4,160,644; US-A-4,416,965; US-A-4,414,152; and US-a-2,229,513. One particularly useful colorant for toners to be used in black and white electrostatographic copying machines and printers is carbon black. Colorants are generally employed in the range of from 1 to 30 weight percent on a total toner powder weight basis, and preferably in the range of 2 to 15 weight percent.
The toner of the invention can also contain other additives of the type used in previous toners, including leveling agents, surfactants, stabilizers, and the like. The total quantity of such additives can vary. A present preference is to employ not more than 10 weight percent of such additives on a total toner powder composition weight basis.
Dry styrenic/acrylic copolymer toners of this invention can optionally incorporate a small quantity of low surface energy material, as described in US-A-4,517,272 and US-A-4,758,491. Optionally the toner can contain a particulate additive on its surface such as the particulate additive disclosed in US-A-5,192,637.
The charge control agent is incorporated into the toner. The two or three components of the charge control agent can each be added to the toner separately or may be combined in some manner before addition to the remaining ingredients of the toner. This should make it clear that the term "charge control agent" used herein is largely a matter of convenience. Charge control is observed when the two or three components are present in the toner. The nature of specific chemical and physical interactions among the components of the charge control agent and the other ingredients in the toner is not understood. The claimed invention is not, however, limited thereby. The components of the charge control agent of the invention can be mixed into the toner in any convenient manner, such as blending in the manner described in US-A-4,684,596 and US-A-4,394,430, with an appropriate polymeric binder material and any other desired addenda. The mixture is then ground to desired particle size to form a free-flowing powder of toner particles containing the charge agent.
A preformed mechanical blend of particulate polymer particles, charge control agent, colorants and additives can, alternatively, be roll milled or extruded at a temperature sufficient to melt blend the polymer or mixture of polymers to achieve a uniformly blended composition. The resulting material, after cooling, can be ground and classified, if desired, to achieve a desired toner powder size and size distribution. For a polymer having a T_g in the range of 50°C to 120°C, or a T_m in the range of 65°C to 200°C, a melt blending temperature in the range of 90°C to 240°C is suitable using a roll mill or extruder. Melt blending times, that is, the exposure period for melt blending at elevated temperature, are in the range of 1 to 60 minutes. After melt blending and cooling, the composition can be stored before being ground. Grinding can be carried out by any convenient procedure. For example, the solid composition can be crushed and then ground using, for example, a fluid energy or jet mill, such as described in US-A-4,089,472. Classification can be accomplished using one or two steps.
In place of melt blending or the like, the polymer can be dissolved in a solvent in which the charge control agent and other additives are also dissolved or are dispersed. The resulting solution can be spray dried to produce particulate toner powders. Limited coalescence polymer suspension procedures as disclosed in US-A-4,833,060 are particularly useful for producing small sized, uniform toner particles.
The toner particles have an average diameter between 0.1 micrometers and 100 micrometers, and desirably have an average diameter in the range of from 4 micrometers and 30 micrometers for currently used electrostatographic processes. The size of the toner particles is believed to be relatively unimportant from the standpoint of the present invention; rather the exact size and size distribution is influenced by the end use application intended. So far as is now known, the toner particles can be used in all known electrostatographic copying processes.
The developers of the invention include carrier and toner of the invention. Carriers can be conductive, non-conductive, magnetic, or non-magnetic. Carriers are particulate and can be glass beads; crystals of inorganic salts such as aluminum potassium chloride, ammonium chloride, or sodium nitrate; granules of zirconia, silicon, or silica; particles of hard resin such as poly(methyl methacrylate); and particles of elemental metal or alloy or oxide such as iron, steel, nickel, carborundum, cobalt, oxidized iron and mixtures of such materials. Examples of carriers are disclosed in US-A-3,850,663 and US-A-3,970,571. Especially useful in magnetic brush development procedures are iron particles such as porous iron, particles having oxidized surfaces, steel particles, and other "hard" and "soft" ferromagnetic materials such as gamma ferric oxides or ferrites of barium, strontium, lead, magnesium, or aluminum. Such carriers are disclosed in US-A-4,042,518; US-A-4,478,925; and US-A-4,546,060.
Carrier particles can be uncoated or can be coated with a thin layer of a film-forming resin to establish the correct triboelectric relationship and charge level with the toner employed. Examples of suitable resins are the polymers described in US-A-3,547,822; US-A-3,632,512; US-A-3,795,618 and US-A-3,898,170 and Belgian Patent No. 797,132. Other useful resins are fluorocarbons such as polytetrafluoroethylene, poly(vinylidene fluoride), mixtures of these, and copolymers of vinylidene fluoride and tetrafluoroethylene. See for example, US-A-4,545,060; US-A-4,478,925; US-A-4,076,857; and US-A-3,970,571; and US-A-4,726,994. Polymeric fluorocarbon coatings can aid the developer to meet the electrostatic force requirements mentioned above by shifting the carrier particles to a position in the triboelectric series different from that of the uncoated carrier core material to adjust the degree of triboelectric charging of both the carrier and toner particles. The polymeric fluorocarbon coatings can also reduce the frictional characteristics of the carrier particles in order to improve developer flow properties; reduce the surface hardness of the carrier particles to reduce carrier particle breakage and abrasion on the photoconductor and other components; reduce the tendency of toner particles or other materials to undesirably permanently adhere to carrier particles; and alter electrical resistance of the carrier particles.
In a preferred embodiment of the invention, the carrier is strontium ferrite coated with fluorocarbon on a 0.5 percent weight/weight basis, and treated with an aqueous solution of 4 weight percent KOH and 4 weight percent of a 2 parts by weight to 1 parts by weight mixture of Na₂S₂O₈ and Na₂S₂O₅ as disclosed in U.S. Patent Application No. 08/127,382, filed Sept. 24, 1993, by William E. Yoerger. The fluorocarbon carrier is also referred to herein as "modified Kynar".
In a particular embodiment, the developer of the invention contains from 1 to 20 percent by weight of toner of the invention and from 80 to 99 percent by weight of carrier particles. Usually, carrier particles are larger than toner particles. Conventional carrier particles have a particle size of from 5 to 1200 micrometers and are generally from 20 to 200 micrometers.
The toners of the invention are not limited to developers which have carrier and toner, and can be used, without carrier, as single component developer.
The toner and developer of the invention can be used in a variety of ways to develop electrostatic charge patterns or latent images. Such developable charge patterns can be prepared by a number of methods and are then carried by a suitable element. The charge pattern can be carried, for example, on a light sensitive photoconductive element or a non-light-sensitive dielectric surface element, such as an insulator coated conductive sheet. One suitable development technique involves cascading developer across the electrostatic charge pattern. Another technique involves applying toner particles from a magnetic brush. This technique involves the use of magnetically attractable carrier cores. After imagewise deposition of the toner particles the image can be fixed, for example, by heating the toner to cause it to fuse to the substrate carrying the toner. If desired, the unfused image can be transferred to a receiver such as a blank sheet of copy paper and then fused to form a permanent image.
The invention is further illustrated by the following Examples and Comparative Examples. Unless otherwise indicated, all starting materials were commercially obtained. In Tables 1-9, "Ex" and "Com Ex" are the Example number or Comparative Example number, respectively; "RH (%)" is percent relative humidity; "Q/m (µC/g)" is the charge to mass ratio in microCoulombs per gram of toner for the indicated procedures; "bicharged" indicates simultaneous positive and negative charging; and "T.O. (mg admix)" is throwoff in milligrams.

EXAMPLES 1a-1i, 2a-2i:

Poly(styrene-co-butyl acrylate-co-divinylbenzene) binder synthesis

An organic phase was prepared by combining divinyl benzene (1.40 grams), t-dodecanethiol (1.50 grams), azo-bis pentanenitrile (4 grams), styrene (160 grams), and butyl acrylate (40 grams). An aqueous phase was prepared by combining distilled water (400 grams), potassium dichromate ((0.10 grams), poly(n-methylaminoethanol)adipate (2 grams: as 20 grams of 10 weight/weight percent solution in distilled water), and Ludox™ brand colloidal silica marketed by E.I. du Pont de Nemours (2 grams: as 4 grams of a 50 weight/weight percent dispersion in distilled water). The organic and aqueous phases were emulsified using a high shear mixing device, a Microfluidizer™ marketed by Microfluidics Corp. of (city,state). The resulting emulsion was placed in a three necked round bottom flask equipped with a mechanical stirrer, condenser, and nitrogen inlet. The flask was placed in a constant temperature bath at 77°C for 16 hours under continuous stirring. The flask was then vented, flushed with argon and heated to 85°C for another three hours. The resulting polymer was filtered, washed, and dried.

Preparation of toner

A dry blend was prepared of 50.0 grams of the poly(styrene-co-butyl acrylate-co-divinylbenzene) binder and 3.5 grams of Regal 300™ carbon black, marketed by Cabot Corp., 1.25 grams of a material marketed as "T-77" by Hodagaya Chemical Co., of New York, New York, and 0.5 grams of Aerosol OT-B, marketed by American Cyanimid of Wayne, New Jersey. T-77 has the structural formula:

Aerosol OT-B is a mixture of 85 parts by weight of a compound having the structural formula:

and 15 parts by weight of sodium benzoate. The dry blend was added to a heated two-roll compounding mill. The roller surfaces were set to 150°C. The melt was exercised on the mill for 20 minutes, then was removed and cooled. The resulting slab was first coarse ground to 2mm size on a laboratory mill, then finely pulverized to approximately 12 micrometer size on a Trost TX jet mill. The toner thus prepared had a concentration of T-77 of 2.5 parts per hundred and a concentration of Aerosol OT-B of 1 part per hundred parts of styrene/n-butyl acrylate/divinyl-benzene binder resin. This toner was used in Examples 1a-1i.
This procedure was repeated for Examples 2a-2i, except that the amount of Aerosol OT-B was changed to 1 gram (2 parts per hundred (pph) parts of toner binder).

Preparation of developer (Modified Kynar coated carrier)

Developer was prepared for each of the toners indicated above, by substantially the following procedure. Untreated, coated carrier particles were prepared by mixing 0.5 grams of 0.3 micrometer poly(vinylidene fluoride) powder marketed by Pennwalt Corp. as Kynar 301F, and 100 grams of bare (uncoated) strontium ferrite core particles. The mixture was placed in a bottle and rolled on a roll mill for 1 hour to thoroughly disperse the polymer over the surface of the carrier. The mixture was then cured at 230°C for 2.5 hours to fuse the polymer to the surface of the particles. The volume average particle size of the carrier particles was from about 25 to 35 micrometers. Distilled water (150 ml), KOH (6 grams) and 6 grams of a mixture of 2 parts by weight of Na₂S₂O₈ and 1 part by weight of mixture of Na₂S₂O₅; were combined in a 500 ml three-neck flask. The flask was fitted with a stirrer, sealed from the ambient atmosphere, and placed in a 60°C water bath. Untreated, coated carrier (100 grams) was then added and the mixture was allowed to stir for 2 hours. The resulting liquid was then filtered off and the particles were washed with 900 ml of water, six times. The particles were collected and allowed to dry at 60°C and were then allowed to cool.
Developer was prepared by mixing toner particles prepared as described above at a weight concentration of 10% toner with the carrier particles.

Evaluation of toner charging

Toner charge was measured in microcoulombs per gram of toner (mc/g) in a "MECCA" device at the indicated relative humidities. Prior to measuring the toner charge, the developer was vigorously exercised to cause triboelectric charging by placing 4 gram samples of the developer into plastic vials, capping the vials, and placing each vial, for two minutes, on a "bottle-brush" device comprising a magnetic toning roller with a stationary shell and a magnetic core rotating at 2000 rpm. The magnetic core had 12 magnetic poles arranged around its periphery in alternating north-south fashion. After this exercise the developer samples were incubated in open topped vials, at the relative humidities indicated below, for a minimum of 16 hours.
After incubation, the toner charge level, that is, the charge to mass ratio or Q/m, was taken after 2 minutes shaking on a wrist action robot shaker operated at about 2 Hz and an overall amplitude of about 11 cm. Toner Q/m was also taken after shaking the developer for 10 minutes on the wrist action shaker, and also after 2 minutes exercising on the bottle brush. Relative humidities were maintained for these procedures at the same levels as for the respective incubations.

Toner charge level was measured for each sample by placing a 150 milligram sample of the charged developer in a MECCA apparatus and measuring the charge and mass of transferred toner in the MECCA apparatus. This involves placing the 150 milligram sample of the charged developer between electrode plates and subjecting it, simultaneously for 30 seconds, to a 60 Hz magnetic field and an electric field of about 2000 volts/cm between the plates. The toner is released from the carrier and is attracted to and collects on the plate having polarity opposite to the toner charge. The total toner charge is measured by an electrometer connected to the plate, and that value is divided by the weight of the toner on the plate to yield the charge per mass of toner (Q/m). Values are reported in Table 1 for the respective measurements under the designations: "2 min shaker Q/m", "10 min shaker Q/m", and "2 min bottle-brush Q/m".

TABLE 1

TONERS WITH 3 COMPONENT CHARGE CONTROL AGENT : T-77 and OT-B
Ex	RH (%)	2 min shaker Q/m (µC/g)	10 min shaker Q/M (µC/g)	2 min bottle-brush Q/m (µC/g)
1a	13	-10.70	--	--
1b	52	-13.49	--	--
1c	79	-11.77	--	--
1d	13	--	-10.77	--
1e	52	--	-13.87	--
1f	79	--	-15.48	--
1g	13	--	--	-11.60
1h	52	--	--	-15.55
1i	79	--	--	-17.47
2a	13	-12.45	--	--
2b	52	-14.29	--	--
2c	79	-9.46	--	--
2d	13	--	-13.46	--
2e	52	--	-15.13	--
2f	79	--	-13.67	--
2g	13	--	--	-15.64
2h	52	--	--	-16.58
2i	79	--	--	-18.41

EXAMPLES 3a-3c

The same procedures were substantially followed as described in Examples 1a-1i, except that 0.85 grams of a material marketed as Aerosol OT by American Cyanamid of Wayne, New Jersey was used in place of 1 gram of OT-B. Aerosol OT differs from Aerosol OT-B, only in that sodium benzoate is not present. The toner was evaluated only by the 2 min bottle-brush procedure at the indicated relative humidities. Results are presented in Table 2. TABLE 2

TONER WITH 2 COMPONENT CHARGE CONTROL AGENT: T-77 AND OT

Example Toner Conc (wt %) RH (%) 2 min bottle-brush Q/m (µC/g)

3a 10.26 10 -12.44

3b 10.40 56 -17.71

3c 10.47 80 -18.30

EXAMPLES 4a-4x

Toners were prepared and evaluated substantially as described in Examples 1a-1i, except on a larger scale. For each example, 100 parts of poly(styrene-co-butylacrylate-co-divinylbenzene) was melt blended with 7 pph (7 parts per hundred parts of the binder polymer) of carbon black (Black Pearls 430, marketed by Cabot Corp., along with the amounts of T-77 and Aerosol OT-B indicated in Tables 3-4. Melt blending was performed on a 30mm co-rotating twin screw extruder, L/D = 30/1, marketed by Werner-Pfleiderer of Ramsey, New Jersey. Barrel temperature was set at 250°F. The extrudate was ground into toner of approximately 12 micron volume weighted diameter on an Alpine Fluid Bed Grinder, Model 100AFG, marketed by Micron Powder Systems, Summit, New Jersey. The toners were evaluated for performance as a function of relative humidity on a modified Kynar coated carrier, as described in Examples 1a-1i. Results are reported in Table 3.

TABLE 3

TONERS WITH 3 COMPONENT CHARGE CONTROL AGENT: T-77 and OT-B
Example	T-77 (pph)	OT-B (pph)	RH (%)	2 min bottle-brush Q/m (µC/g)
4a	2.5	1.5	10	-15.5
4b	2.5	1.5	50	-13.9
4c	2.5	1.5	75	-11.3
4d	1.5	2.5	10	-23.4
4e	1.5	2.5	50	-17.5
4f	1.5	2.5	75	-11.7
4g	1.5	0.5	10	-12.0
4h	1.5	0.5	50	-13.9
4i	1.5	0.5	75	-12.3
4j	2.5	2.5	10	-26.4
4k	2.5	2.5	50	-19.3
4l	2.5	2.5	75	-13.9
4m	2.5	1.0	10	-12.1
4n	2.5	1.0	50	-13.4
4o	2.5	1.0	75	-10.2
4p	2.5	0.5	10	-9.7
4q	2.5	0.5	50	-12.6
4r	2.5	0.5	75	-12.8
4s	3.5	2.5	10	-20.0
4t	3.5	2.5	50	-15.2
4u	3.5	2.5	75	-11.7
4v	3.5	0.5	10	-8.5
4w	3.5	0.5	50	-10.6
4x	3.5	0.5	75	-11.2

COMPARATIVE EXAMPLES A1-A3

Toners were prepared and evaluated substantially as described in Examples 4a-4x, with the exception that no OT-B was added. Results are reported in Table 4. TABLE 4

TONERS WITH T-77 ONLY

Example T-77 (pph) OT-B (pph) RH (%) 2 min bottle-brush Q/m (µC/g)

A1 2.5 0 10 -10.4

A2 2.5 0 50 -15.3

A3 2.5 0 75 -18.7

EXAMPLE 5 AND COMPARATIVE EXAMPLE B

Developers were prepared as in Examples 1a-1i, except 2.5 pph of T-77 and 0, 0.15, 0.25, 0.35, and 0.50 pph of Aerosol OT-B were used. The developers were evaluated in Ektaprint 1575 copiers, marketed by Eastman Kodak Co. of Rochester, New York, which had been modified to use negative polarity developers. Tests of 35,000 copies were run: 15,000 at 50% relative humidity, 10,000 at 75% relative humidity, and 10,000 at 10% relative humidity. In Comparative Example B, with no Aerosol OT-B present, a significant and undesirable charge rise was seen at 75% relative humidity. In Example 5, with 0.15 pph OT-B some variation of charge with humidity was seen, especially at high RH. At the Aerosol OT-B level of 0.25 pph substantially stable charge was seen across the entire RH range. At the 0.35 and 0.5 pph levels of Aerosol OT-B, evidence of rising charge at 10% RH was seen.

COMPARATIVE EXAMPLES C1-C3

The same procedures were substantially followed as described in Examples 1a-1i, except that 0.15 grams of sodium benzoate was used in place of Aerosol OT-B. The toner was evaluated only by the 2 min bottle-brush procedure at the indicated relative humidities. Results are presented in Table 5. TABLE 5

TONER WITH T-77 AND SODIUM BENZOATE

Comparative Ex RH (%) 2 min bottle-brush Q/m (µC/g)

C1 10 -9.66

C2 56 -16.33

C3 80 -15.90

COMPARATIVE EXAMPLES D1-D9

The same procedures were substantially followed as described in Examples 1a-1i, except that the Aerosol OT-B was deleted. Results are presented in Table 6.

TABLE 6

TONER WITH T-77 ONLY
Comp. Ex	RH (%)	2 min shaker Q/m (µC/g)	10 min shaker Q/m (µC/g)	2 min bottle-brush Q/m (µC/g)
D1	13	-8.64	--	--
D2	52	-15.19	--	--
D3	79	-18.13	--	--
D4	13	--	-8.88	--
D5	52	--	-16.09	--
D6	79	--	-22.85	--
D7	13	--	--	-11.16
D8	52	--	--	-17.30
D9	79	--	--	-23.29

COMPARATIVE EXAMPLES E1-E3

The same procedures were substantially followed as described in Examples 1a-1i, except that the carbon black and T-77 were deleted. Aerosol OT-B was present at a level of 2pph. The toner was evaluated only by the 2 min bottle-brush procedure at the indicated relative humidities. Results are presented in Table 7. TABLE 7

TONER WITH AEROSOL OT-B ONLY

Comp Ex RH (%) 2 min bottle-brush Q/m (µC/g)

E1 10 -15.77

E2 56 -17.11

E3 80 -7.52

COMPARATIVE EXAMPLES F1-F3

The same procedures were substantially followed as described in Examples 1a-1i, except that the carbon black and T-77 were deleted and 0.10 grams of sodium benzoate was used in place of Aerosol OT-B. The toner was evaluated only by the 2 min-overnight procedure at the indicated relative humidities. Results are presented in Table 8. TABLE 8

TONER WITH SODIUM BENZOATE ONLY

Comparative Ex RH (%) 2 min bottle-brush Q/m (µC/g)

F1 10 -1.49 (bicharged)

F2 54 -3.21 (bicharged)

F3 82 -4.72 (bicharged)

COMPARATIVE EXAMPLES G1-G3, H1-H3, I1-I3, J1-J3, K1-K3

The same procedures were substantially followed as described in Examples 1a-1i, except that the carbon black and T-77 were deleted, sodium benzoate was not present, and the following charge control agent second components were used:

Preparation 1

A mixture-of 56.88 grams (0.20 mol) of dihexyl maleate, 21.85 grams (0.21 mol) of sodium bisulfite, and 21.85 grams of water was weighed into a 250 ml round bottom flask. The flask was closed and heated on a steam bath with stirring until the mixture became homogeneous (about 21 hours). The flask was cooled resulting in a very viscous, clear amorphous grease which was dissolved in toluene and heated to boiling to remove water. The mixture was then filtered and concentrated in a 90°C bath under vacuum. Yield was 69.0 grams of an amorphous waxy solid. Elemental analysis gave: C = 47.88, H = 7.20, S = 7.00, Na = 6.3. This compares to theoretical values for C₁₆H₂₉O₇SNa of C = 49.47, H =7.52, S = 8.25, Na = 5.9.

Preparation 2

A mixture of 68.49 grams (0.30 mol) of dibutyl maleate, 32.78 grams (0.315 mol) of sodium bisulfite, and 33 ml of water was combined in a closed flask. The flask was heated on a steam bath for about 17.5 hours with stirring. The reaction mixture was cooled resulting in crystallization. The crystallized product was dissolved in hot isopropanol, filtered hot, and cooled, and the resultant crystals were collected, and dried. Yield was 77.0 grams. Melting point was 81-85°C. Elemental analysis gave: C = 41.19, H = 6.37, S = 8.15, Na = 6.9. This compares to theoretical values for C₁₂H₂₁O₇NaS of C = 43.37, H =6.37, S = 9.65, Na = 6.9.

Preparation 3

A mixture of 68.87 grams (0.4 mol) of diethyl fumarate, 43.71 grams (0.42 mol) of sodium bisulfite, and 43.71 grams of water, was combined in a round bottom flask. The flask was heated on a steam bath for about 19 hours with stirring. The reaction mixture was cooled resulting in crystallization. The crystallized product was dissolved in ethanol, filtered, and cooled, and the resultant crystals were collected, washed with ether, and dried. Yield was 70.7 grams. Melting point was 135-139°C. Elemental analysis gave: C = 34.50, H = 4.77, S = 10.89, Na = 8.5. This compares to theoretical values for C₈H₁₃O₇SNa of C = 34.78, H =4.74, S = 11.61, Na = 8.3.

Toner Evaluation

Developers were prepared, as described above, using modified Kynar carrier. The toners were evaluated by the 2 min bottle-brush procedure at the indicated relative humidities. Results are presented in Table 9.

All of the second components demonstrated charge control characteristics reasonably similar to that of the Aerosol OT material, and can be predicted would provide acceptable results if used as second components in developers of the invention.

TABLE 9

TONER WITH VARIOUS SECONDARY COMPONENTS ONLY
Comparative Ex	Toner Conc (wt %)	RH (%)	2 min bottle-brush Q/m (µC/g)
G1	9.69	10	-13.92
G2	9.83	54	-23.38
G3	9.96	82	-14.78
H1	10.29	10	-14.52
H2	10.11	54	-23.03
H3	9.48	82	-17.34 (bicharged)
I1	9.03	10	-17.52
I2	10.95	54	-12.20
I3	8.06	82	-15.75 (bicharged)
J1	9.72	10	-18.92
J2	9.27	54	-17.86
J3	10.27	82	-14.71
K1	9.37	10	-14.28
K2	9.00	54	-15.21
K3	10.29	82	-4.94

COMPARATIVE EXAMPLES F4-F7, G4-G7. H4-H7

Two different developers were prepared using the toners of Examples F, G, and H.

Preparation of developers-PMMA coated carrier

Developer was prepared for each of the toners indicated above, by mixing toner particles prepared as described above at a weight concentration of 12% toner with carrier particles comprising strontium ferrite cores thinly coated (approximately 2 percent by weight) with poly(methyl methacrylate). The volume average particle size of the carrier particles was from about 25 to 35 micrometers.

Preparation of developers-modified Kynar coated carrier

Developer was prepared for each of the toners indicated above, by mixing toner particles prepared as described above at a weight concentration of 12% toner with carrier particles comprising strontium ferrite cores thinly coated (approximately 0.5 percent weight/weight) with dehydrofluorinated and oxidized fluorocarbon as disclosed in US-A-4,726,994. The volume average particle size of the carrier particles was from about 25 to 35 micrometers.

Evaluation of toner charging

The developers were evaluated by the "2 min shaker" procedure described above and were then subject to a "10 min bottle-brush" procedure differing from the above described "2 min bottle-brush" procedure, only in duration. Relative humidity was 37%.

Evaluation of throw-off

Throw-off values (T.O.) were determined by taking the 4 gram developer sample that had been bottle-brush exercised for 10 minutes, admixing in 6% more toner to provide a final toner concentration of about 18%), followed by 2 minutes more exercise on the wrist action shaker. This developer was then placed on a roll containing a rotating magnetic core, similar to a magnetic brush roll used for electrostatic development. A Plexiglas housing contained the assembly, and had a vacuum filter funnel mounted directly over the roll. The weight of toner, in milligrams, collected on a piece of filter paper after one minute of running the magnetic core at 2000 revolutions per minute was reported as the throw-off value.

Results are presented in Tables 10-11.

TABLE 10

DEVELOPER WITH PMMA CARRIER COATING AND SODIUM BENZOATE, AEROSOL OT, OR AEROSOL TR
Comp Ex	2 min shaker Q/m (µC/g)	10 min bottle-brush Q/m (µC/g)	Throw off (mg admix)
F4	-13.06	--	--
F5	--	-33.03	33.6
G4	-19.25	--	--
G5	--	-37.57	0.9
H4	-22.36	--	--
H5	--	-43.56	1.4

TABLE 11

DEVELOPER WITH MODIFIED KYNAR CARRIER COATING AND SODIUM BENZOATE, AEROSOL OT, OR AEROSOL TR
Comp Ex	2 min shaker Q/m (µC/g)	10 min bottle-brush Q/m (µC/g)	Throw off (mg admix)
F4	(bicharged)	--	--
F5	--	-24.89	75.8
G4	-5.00 (bicharged)	--	--
G5	(bicharged)	-49.33	7.4
H4	-16.07 (bicharged)	--	--
H5	--	-54.29	11.8

The comparative examples summarized in Tables 10 and 11 further demonstrate the charge control characteristics of two second component materials and the lack of charge control characteristics in the flow control aid added to Aerosol OT-B.
An advantage provided by the developer of the invention can be seen, most easily, by contrasting the Examples and Comparative Examples A and D. In the developers of those comparative examples, T-77 was present as a first component, but no second component was present. In the Examples, T-77 and Aerosol OT-B or Aerosol OT was present. The developers containing T-77 only demonstrated high charge under wet conditions and low charge under dry conditions (Comparative Examples A1-A3 and D1-D9). In developers of the invention in the Examples, this behavior was reversed (low charge under wet conditions and high charge under dry conditions) or the response of charge/mass to relative humidity was substantially eliminated depending upon the concentration of second component. Similar results were seen in both laboratory tests and actual long term use on a copier; however, the concentrations of second component needed for similar results on a copier were less than the concentrations required in laboratory tests.
If the Examples are contrasted with Comparative Examples in which first component was absent and second component was present (Comparative Examples G-K), it is also apparent that the developer of the invention has better charge control characteristics, particularly in terms of bicharging.

Claims

An electrophotographic toner comprising polymeric binder and a charge control agent comprising a mixture of a first component having the general structure:
wherein
X¹ and X are each selected from the group consisting of H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, and halo;
R^a and R^b are each selected from the group consisting of H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, and benzoylamino;
M is selected from the group consisting of Cr, Co, and Fe;
n, n', m, and m' are each 1, 2, or 3;
and R⁺ is a cation; and
a second component,
said second component being capable of use, in the absence of said first component, as a negative charge control agent,
said second component being an ionic surfactant when in water solution.
The toner of claim 1 wherein said second component is an anionic surfactant when in water solution.
The toner of claim 1 or 2 further characterized as comprising polymeric binder and a charge control agent comprising a mixture of a first component having the general structure:
wherein
X¹ and X are each selected from the group consisting of H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, and halo;
R^a and R^b are each selected from the group consisting of H, C₁-C₅ alkyl, C₁-C₅ alkoxy, nitro, halo, sulfonamido, methylsufonyl, ethylsulfonyl, acetylamino, and benzoylamino;
M is selected from the group consisting of Cr, Co, and Fe;
n, n', m, and m' are each 1, 2, or 3;
and R⁺ is a cation; and
a second component having the general structure:
wherein
R¹ and R are each independently, alkyl having from 2 to 18 carbons, and
R⁺ is a cation.
The toner of claim 1, 2, or 3 wherein R¹ and R are each alkyl having from 4 to 13 carbons.
The toner of claim 1, 2, 3 or 4 wherein R¹ and R each have the same number of carbons.
The toner of claim 1, 2, 3, 4, or 5 wherein said first component has the general structure:
The toner of claim 1, 2, 3, 4, 5, or 6 wherein each R⁺ is an inorganic cation.
The toner of claim 1, 2, 3, 4, 5, 6, or 7 wherein each R⁺ is selected from the group consisting of Na⁺, H⁺, and NH₄⁺.
The toner of claim 1, 2, 3, 4, 5, 6, 7, or 8 wherein said charge control agent further comprises a flow control aid.
The toner of claim 1, 2, 3, 4, 5, 6, 7, 8, or 9 wherein said charge control agent further comprises alkali metal benzoate salt.
An electrostatographic developer comprising the toner of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 and carrier particles.
An electrostatographic developer according to claim 11 wherein said carrier particles comprise core material coated with fluorohydrocarbon polymer or poly(methyl methacrylate).