NO134439B - - Google Patents

Abstract

Xerographic developer material.

Description

The present invention relates to a xerographic developer material containing toner particles containing finely divided toner material comprising a colorant and a thermoplastic resin, for example a vinyl or vinylidene resin with a melting point of at least 43.3°C, and a solid additive, as well as preferably a carrier for the toner particles.

The formation and development of images on the surface of photoconductive materials with electrostatic devices is well known.

The basic xerography process, as described by C. F. Carlson

in US Patent 2,297,691, the deposition of a uniform electrostatic charge on a photoconductive insulating layer involves exposing the layer to a light-shadow image to dissipate the charge in areas of the layer exposed to the light and to induce the resulting

end, latent, electrostatic image by depositing on the image a finely divided electroscopic material in the technical language called "toner". The toner will normally be attracted to the areas of the layer that have a charge, thereby forming a toher image corresponding to the latent electrostatic image. This powder image can then be transferred to a support surface, such as paper. The transferred image can then be fixed permanently to the support surface, for example with heat. Instead of forming a latent image by uniformly charging the photoconductive layer and then exposing the layer to a light-shadow image, one can form the latent image by directly charging the layer in image configuration. The powder image can be fixed to the photoconductive layer if the transfer of the powder image is to be eliminated. Other appropriate methods of fixation, such as treatment with "solvent or coating" can replace the aforementioned heat fixation.

Several methods are known for applying electroscopic particles to the latent electrostatic image to be developed. One method of development, which is described in US Patent 2,618,552, is known as "cascade" development. According to this method, a developer material comprising relatively large carrier particles, electrostatically coated with finely divided toner particles, is transported to or rolled or sprinkled over the surface carrying the electrostatic latent image. The composition of the carrier particles is chosen so that they triboelectrically charge the toner particles to the desired polarity. When the mixture sprinkles or rolls over the image-bearing surface, the toner particles are electrostatically deposited and connected to the charged portion of the latent image and are not deposited on the uncharged portions or background portions of the image. Most of the toner particles randomly deposited on the background are removed by the rolling carrier, apparently because of 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 fed back into the process. This method is very good for developing images with line patterns.

Another method for developing electrostatic images is the "magnetic brush" method described, for example, in US patent 2.87it-063. In this method, a "developer material containing toner and magnetic carrier particles" is carried by a magnet. The magnetic field of the magnet causes the magnetic carrier to be formed in a brush-like configuration. This "magnetic brush" is brought together with the surface which carries the electrostatic image,,,b,g the toner particles are drawn from the brush to the latent image by electrostatic attraction.

A further method for developing electrostatic latent images is the method with the so-called "powder cloud", which is described, for example, in US patent 2,221,776.

In this method, a developer material comprising electrically charged toner particles in a gaseous medium is passed past the surface carrying the latent electrostatic image. The toner particles are drawn by electrostatic attraction from the gas to the latent image. This method is particularly applicable for continuous toner development.

Other methods of development, for example the so-called "touchdown" development as described in US patent 3-166,432 can be used where appropriate.

Although some of the aforementioned developing methods are used commercially today, the most common commercial xerographic developing technique is that which goes by the name of "cascade" development.

A versatile office copier that uses this development method is described in US Patent 3,099,933. The cascade technique is generally carried out in a commercial apparatus by sprinkling a developer mixture over the top surface of a drum with a horizontal axis, which carries an electrostatic latent image. The preliminaries are transported from a trough or a sump to the upper part of the drum by means of a belt conveyor. The developer is sprinkled onto part of the drum's surface into the sump and then returned to the developer system to develop further electrostatically latent images. Small amounts of toner are periodically added to the developer material to compensate for toner consumed during development. This process is repeated for each copy produced by the apparatus and is usually repeated several thousand times during the lifetime of the developer.

It thus appears from the above description as well

as from other developing methods, that the toner is exposed to mechanical stress which tries to break down the particles into unwanted dust grains. Toner grains are detrimental to apparatus operation because they are very difficult to remove from imaging surfaces to be reused and also because they are prone to transfer to other parts of the apparatus and deposit on critical apparatus parts, such as optical lenses.

The formation of grains is slowed down when the toner contains a tough, high molecular weight resin, which is able to withstand the shearing and compressive forces exerted on the toner in the apparatus. Unfortunately, many high molecular weight materials cannot be used in high speed automatic apparatus because they cannot be melted quickly during a heat fixing step for the powder image. Attempts to rapidly fuse a high melting point toner using oversized high capacity heaters have been met with problems in preventing charring of the paper sheets and in adequately dissipating the heat developed by the fuser(s). In some cases, the receiving sheet has caught fire after passing through the fusing unit. In order to avoid charring or combustion, additional equipment, such as complicated and expensive cooling units, is thus necessary to properly dissipate the large amount of heat developed by the smelter. Incomplete removal of the heat developed will result in operator discomfort and damage to heat-sensitive equipment parts. Moreover, the increased pls.ss taken up by the heating and cooling units and the high operating costs of these will often outweigh the benefits obtained from the increased ha .rise. On the other hand, low molecular weight resins which heat melt easily at relatively low temperatures are usually undesirable because these materials tend to form thick films on surfaces of the photoconductor to be reused. These films tend to cause deterioration of the image and help to increase the maintenance time of the apparatus. Many low molecular weight resins decompose when subjected to melting conditions in high speed copiers. In addition, low molecular weight resins tend to form sticky images on the finished sheets which are easily soiled and often spread to adjacent sheets. Furthermore, low molecular weight resins are often very difficult or even impossible to crumble in conventional measuring devices. Furthermore, the toner material must be capable of receiving a charge of the correct polarity when brought into contact with the surface of the support materials in the cascade or "touchdown" development systems. The triboelectric properties and flow properties of many toners are adversely affected by changes in humidity. For example, the triboelectric values for some toners vary with changes in the relative humidity and this is not desirable when used in xerographic systems, especially in automatic precision machines that require toners with stable and predeterminable triboelectric values. One

other factor affecting the stability of the carrier's triboelectric

characteristic is the tendency of some toner materials to "colli-

you" on the surface of the carrier particles. When the developers are used in automatic developing machines that work according to the cascade^principle

sipped and turned over many times, the many collisions that occur between the carrier and the toner particles in the machine cause the toner particles carried on the surface of the carrier particles to be welded or otherwise forced into the surface as carrier particles. The gradual accumulation of permanently attached toner material on the surface of the carrier particles causes a change in the triboelectric value of the carrier particles and contributes directly to the deterioration of the copy quality by possible destruction of the carrier's carrying capacity for the toner material. A majority of known carriers and toners are of slip-

end art. Abrasive contact between toner particles, carriers and xerographic imaging surfaces increases the mutual destruction of these components. Exchange of the carriers and the electrostatic image carriers

End surfaces are expensive and time-consuming. Xerographic copies should have good line contrast as well as acceptable coverage of surfaces. When a method is designed to improve either the sharpness of the lines or the coverage of the surface areas, one can, however, expect a reduced quality

tet for the other property. Efforts to increase image density

the heat of depositing larger quantities of toner particles on the latent electrostatic image is usually rewarded with an undesirable increase in background deposits. Since most thermoplastic materials exhibit deficiencies in one or more of the aforementioned areas, fin-

there is a continuing need for improved toner and developer materials.

The purpose of the present invention is to produce a xerographic developer material which contains toner particles which are resistant to film formation and clumping, which can be melted at high speeds with less heat energy and which are resistant to mechanical stress during development.

This is achieved by the toner particles as solid additives

substance contains an ester of o-phthalic acid or m-phthalic acid or of 4,5-epoxy-tetrahydrophthalic acid.

For optimum operation in xerographic high-speed copiers using paper take-up belts, the toner should have a melting point range between about H3°C and about 150°C and a melt viscosity--4

site of less than about 2.0 x 10 poise up to temperatures of 232°C. Melting temperatures for the toner below 150°C are preferred

because problems with heat release and paper deterioration are avoided. The preliminaries preferably contain from about 0.02 to about

trained 20 weight percent, based on the weight of toner in the final developer material, of a solid hydrophobic metal salt of a higher fatty acid. The developer preferably contains from about 0.05 to about 4 percent by weight of the metal salt because maximum reduction of background deposition and image density is thereby achieved. Without the presence of a solid, stable hydrophobic metal salt of a higher fatty acid in the developer, very rapid deterioration of reusable imaging surfaces occurs, excessive background, reduced density of the toner image, poor transfer of the toner image, reduced lifetime of the carrier particles, increased difficulty in removing residual toner material from reusable imaging surfaces as well as reduced electrical stability. Although the initial potential on the electrostatic imaging surface can be reduced and the resistance to abrasion can be improved when the proportion of metal salt present is increased above about 10%, the unwanted background deposits are noticeably increased. If the charging voltage is reduced to compensate for the presence of metal salt beyond about 10$, the images begin to take on a "washed out" appearance. It is not decisive that the entire surface of each toner particle is covered with the metal salt, for example sufficient metal salt is present when about 10 to 16% of the toner particle's surface is covered with a metal salt. When the metal salt is dispersed instead of coated on a toner or carrier particle, relatively more metal salt is needed to keep a sufficient amount of the exposed salt on the surface of the toner particle or carrier particle. The additional amount of metal salt needed depends to a large extent on the surface area of the developer particles, and consequently on the selected particle diameter. Any suitable stable, solid hydrophobic metal salt of a fatty acid with a melting point above about 57°C can be used. Optimum results are obtained when about 0.05 to about 4 weight percent zinc stearate, based on the weight of the toner, is present on the outer surfaces of the particles of the developer material. Precoolers containing zinc stearate are preferred because the resulting mixture is characterized by excellent melting properties, high cleanability from electrostatic imaging surfaces, greater triboelectric stability, dense toner images and increased resistance to mechanical abrasion. Unexpectedly, both the risk of fire and the unnecessarily large power consumption found in known high-speed xerographic development processes are avoided, when

toners containing the aforementioned polymeric esterification product and metal salt are used.

Any suitable vinyl resin with a melting point of at least <i>t3.3°C can be used in the toners of this invention. The vinyl resin can be a homopolymer or a copolymer of two or more vinyl monomers. Typical monomer units that can be used to form vinyl polymers include: styrene, p-chlorostyrene, vinylnaphthalene, ethylenically unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like, vinyl esters such as vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate and the like, esters of alphamethylene-aliphatic mono-carbocyclic acids such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl alpha-chloroacrylate, methyl methacrylate, ethyl methacrylate lat, butyl methacrylate and the like, acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether and the like, vinyl ketones such as vinyl methyl ketone, vinylhexyl ketone, methyl isopropenyl ketone and the like, vinyl halides such as vinylidene chloride, vinylidene chlorofluoride and the like, as well as N-vinyl compounds such as N-vinyl pyrrole, N -vinylcarbazole, N-vinylindole, N-vinylpyrrolidene and the like as well as mixtures of these. Generally, suitable vinyl resins used in the toner have an average molecular weight between about 3,000 and about 500,000.

- Toner resins containing a relatively high proportion of a styrene resin are preferred. The presence of a styrene resin is preferred because of the greater degree of image definition achieved with a given amount of additive. Also, denser images are obtained when at least about 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. Typical monomeric materials which can be copolymerized with styrene by addition polymerization thus include: p-chlorostyrene, vinylnaphthalene, ethylenically unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like, vinyl esters such as vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate and similar esters of alpha-methylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloro-

ethyl acrylate, phenyl acrylate, methyl alpha-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and the like, acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether and the like, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone and the like, vinylidene halides such as vinylidene chloride , vinylidene chlorofluoride and the like, as well as N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidene and the like and mixtures thereof. The styrene resins can also be formed by polymerization of mixtures

of two or more of these unsaturated monomeric materials with a styrene monomer. The term "addition polymerization" is intended to include known polymerization techniques, such as free radical polymerization methods, as well as anionic and cationic polymerization methods.

The vinyl resins, including resins of the styrene type, can also be mixed with one or more other resins if desired. When the vinyl resin is mixed with another resin, the added resin is preferably another vinyl resin because the resulting mixture is characterized by particularly good triboelectric stability and uniform resistance to physical deterioration. The vinyl resins used for mixing with resins of the styrene type or other vinyl resins can be produced by addition polymerization of any suitable vinyl monomer such as the aforementioned vinyl monomers. Other thermoplastic resins can also be mixed with the vinyl resins. Typical non-vinyl type thermoplastic resins include: rosin modified phenol formaldehyde resins, oil modified epoxy resins, polyurethane resins, cellulosic plastic resins, polyether resins and mixtures thereof. When the resin component of the toner contains styrene copolymerized with another unsaturated monomer or mixture of polystyrene and another resin, a styrene component of at least about 25 percent by weight, based on the total weight of the resin in the toner, is preferred because denser images are obtained and better image definition is produced with a given amount of additive.

The toner particles should have a clogging temperature of at least 43°C and a melt viscosity of less than 2.5 x 10 poise at temperatures up to 232°C. When the toner has a clogging temperature lower than 43°C, the toner particles tend to clump together during storage and during operation of the machine also to form undesirable films on the surface of reusable photo recorders, which degrades the image quality. If the melt viscosity of the toner

-4 o

is higher than 2.5 x 10 poise at temperatures above 232 C, the toner material according to the invention will not adhere sufficiently to a receiving sheet even under the melting conditions found in a normal xerography apparatus and it can be easily removed by rubbing.

To achieve maximum resistance to caking, the toner should contain from about 2 percent by weight to about 45 percent by weight of ester, based on the total weight of the toner resin.

Any suitable solid substituted or unsubstituted ester of o-phthalic acid or m-phthalic acid can be used in the toner in the developer according to the present invention. Typical solid esters of o-phthalic acid and m-phthalic acid include didecyl-4,5-epoxytetrahydrophthalate, dicyclohexyl phthalate, diphenyl phthalate, dimethyl isophthalate, diethocyethyl phthalate, triphenyl phthalate, dihydroabiethyl phthalate and the like. Esters with a melting point between 43.5°C and approximately 7955°C are preferred because toners containing these additives have greater storage stability. The maximum resistance to clumping of the toner is achieved when the toner contains from about 2 percent by weight to about 45 percent by weight, calculated on the total weight of the toner resin, of the solid ester.. As the relative amount of additive in the toner is increased above about 45 percent by weight, the mechanical strength, resistance to shrinkage and stability of the final fused toner image and deteriorate rapidly. Thus, when a toner consisting essentially of 100% ester material is used in automatic copying and duplicating machines, a lot of toner dust is generated, and the fused toner images are prone to crumble and fall off the receiving sheets when the sheets are folded. With less than about 2% additive in the toner, the toner melting and flow and triboelectric properties are essentially the same as for a toner containing no additives. If desired, mixtures of additives can be used in the toner. An increase in the relative amount of additive tends to reduce the melt viscosity of the final toner. Optimum results are obtained when the toner contains from about 2 percent by weight to about 15 percent by weight, calculated on the total weight of the toner resin, of diphenyl phthalate, the resulting toner being characterized by excellent resistance to shrinkage, high mechanical strength and improved imaging properties.

Any suitable stable, solid hydrophobic metal salt of a fatty acid with a melting point above 57°C can be used. The metal salt should be largely insoluble in water. Water-soluble metal salts lack the correct electrical properties and are adversely affected by humidity changes that usually occur in the surrounding atmosphere. However, a large part of the salts which are usually considered to be insoluble will in reality dissolve to a certain extent. In order to carry out the invention, the solubility of the salt should be vanishingly small. The salts which have the desired properties include many salts of linear saturated fatty acids, unsaturated fatty acids, partially hydrogenated fatty acids and substituted fatty acids and mixtures thereof. The metal salts can be processed in a drum or pre-milled together with the toner particles or carrier particles or be intimately dispersed in each toner or carrier particle1. This latter embodiment is, however, less advantageous than the drummed or milled mixtures, because a greater amount of metal salt is required to produce a sufficient amount of metal salt exposed on the surface of the developer particles. The metal salts are preferably mixed with toner material by mixing previously finely divided metal salt particles with previously produced finely divided toner particles in a drum. This drumming is continued until the metal salt particles are evenly distributed in the mass of toner particles. Excellent toner blends are obtained when the toner particles are drummed with metal salt particles ranging in size from about 0.5 to about 50 microns. The compositions thus prepared are preferred because the resulting treated toner exhibits very stable imaging characteristics under widely varying humidity conditions.

Typical fatty acids from which stable solid hydrophobic metal salts can be derived include: caproic acid, enanthylic acid, caprylic acid, pelargonic acid, capric acid, undecylenic acid, lauric acid, tridecic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nondecylic acid, arachiic acid, behenic acid, stillingic acid , palmitoleic acid, oleic acid, ricinolic acid, petroselinic acid, vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, licanic acid, parinaric acid, gadolinic acid, arachidonic acid, cetolenic acid and mixtures thereof. Typical stable solid metal salts of fatty acids include: zinc stearate, cadmium stearate, barium stearate, lead stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, cadmium stearate, magnesium stearate, zinc oleate, manganese oleate, iron oleate, cobalt oleate, copper oleate, lead oleate, magnesium oleate, zinc palmitate, cobalt palmitate , copper palmitate, magnesium palmitate, aluminum palmitate, calcium palmitate, lead caprylate, lead caproate, zinc linoleate, cobalt linoleate, calcium linoleate, zinc cricinoleate, cadmium-

ricinoleate and mixtures thereof.

When the solid hydrophobic metal salt of a higher fatty acid is physically mixed with or applied as a coating to toner or carrier particles, instead of being dispersed in the toner matrix, the metal salt is advantageously present in an amount of from about 0.02 to about 10 weight percent based on the weight of the toner in the final developer mixture. Optimal results are achieved with approximately 0.05

to about 4% metal salt. Although the original potential on

the electrostatic imaging surface can be reduced and the resistance to wear improved, when the amount of metal salt present is increased beyond about 10%, the unwanted background deposits are noticeably increased. If the charging voltage is reduced to compensate for the presence of metal salt beyond about 10%, the images begin to take on a "washed out" appearance. It is not essential that the entire surface of each toner particle is covered with the metal salt, for example sufficient metal salt is present when 10 to 16% of the toner particle's surface is coated with metal salt.

When the metal salt is dispersed rather than coated on a toner or carrier particle, relatively more metal salt is needed to maintain a sufficient amount of exposed salt on the surface of the toner or carrier particle. The additional amount of metal salt that is required depends to a large extent on the surface size of the particles and consequently on the diameter of the selected particles. The use of small amounts of calcium stearate as a pigment wetting agent in the zinc oxide developer powder is known and described, for example, in US Patent 3,053-688, column 5, line 41, and in Canadian Patent 633-458, column 95 line 8. The amount of calcium stearate used according to said patents to facilitate the wetting of pigments dispersed in the zinc oxide developer powder is however insufficient to produce an effective amount of exposed calcium stearate on the surface of the toner particle for the purposes underlying the present invention. When less than about 0.02 weight percent of the metal salt based on the weight of the toner is actually present on the surface of the toner particle, its triboelectricity, flow, wear, transfer, and imaging properties are substantially the same as those of a toner or carrier that does not contain a metal salt of a fatty acid. Apparently, for a given amount of metal salt based on the weight of the toner, a greater volume of salt is present on the surface of the toner or carrier when the metal salt is added to the mixture of preformed colored toner particles or carriers than when it is intimately dispersed within each toner particle or carrier. If the concentration of metal salt is increased to the point where the toner consists mostly of 100$? metal salt, the metal salt will form smooth films on the electrostatic image-bearing surface and the carrier particles used for transfer of the powder image, background removal and cleaning. US Patent 3.083.H7 describes a method for applying reactive toners containing 100? iron stearate on an electrostatic image and then transferring the developed image to a transfer sheet moistened with an alcoholic solution of gallic acid. The iron stearate reacts with the gallic acid to form a black reaction product. In addition to the problems encountered when using toner containing 1005? metal salt, electrostatic developing methods of the aforementioned type require prior liquid treatment of the receiving sheet with an accompanying increase in cost and difficulty. In addition, wrinkling, discolouration of the image and contamination will occur more often when moistened receiver sheets are used. Additional equipment to remove toxic and flammable gases may also be required.

Outstanding results have been achieved with zinc stearate. When the toner and developer particles of this invention are treated with zinc stearate, particularly in the range of from about 0.05 to about 4

weight percentage based on the total weight of toner, better flow, less background, higher image density at lower original charge voltages, and higher device speeds at lower power consumption are achieved. Drum wear is noticeably reduced.

It should be understood that the particular formulas given for the units contained in the resins according to the invention represent the main proportion of the units present, but do not exclude the presence of other monomeric units or reaction components than those indicated. For example, some commercial materials such as the polyoxyethylene ether of isopropylidenediphenol may contain traces of homologous or unreacted ethylene oxides. Any minor amount of such constituents may be present in the materials of this invention.

Any suitable pigment or dye can be used as a colorant for the toner particles. Toner colorants are well known and include, for example, carbon black, nigrosin dye, aniline blue, "Calco Oil Blue", chrome yellow, ultramarine blue, "Quinoline Yellow", methylene blue chloride. "Monastral Red". "Sudan Black BN", "Malachite Green Oxalate", lamp black, "Rose Bengal", "Monastral Red", as well as mixtures of these. The pigments or dyes should be present in the toner in a sufficient amount to make it strongly colored so that it will form a clearly visible image on a recording device. Where conventional xerographic copies of typewritten documents are desired, the toner may thus for example comprise a black pigment, such as carbon black or a black dye, such as "Amaplast Black" dye. The pigment is preferably used in an amount from about 3% by weight to about 20% by weight, calculated from the total weight of the colored toner. If the colorant used for the toner is a dye, significantly smaller amounts of colorant can be used.

The toner compositions according to the present invention can be prepared using any known technique for toner mixing and

- division. For example, the components can be thoroughly mixed by mixing and grinding the components and then micro-pulverizing the resulting mixture. Another well-known technique for forming toner particles is to spray dry a toner composition comprising a colorant, a resin and a solvent and which has been ground in a ball mill. In general, the quality of the fixed toner at a given melter temperature will decrease with increased melt viscosity of the toner. As stated above, the toner materials will not adhere sufficiently to a receiver sheet, even under the melting conditions found in a conventional xerography apparatus, if the melt viscosity of the toner is -4 o greater than about 2.5 x 10 poise at temperatures up to 232°C. The value for the toner's melt viscosity will therefore contribute to the pre-determination of the degree of flow and penetration of the toner into the recording medium, such as paper, during heat fixation. The term "melt viscosity" as used here is a measure of the ratio between the shear stress and the velocity in poise at a given temperature. All viscosity measurements were carried out with a capillary rheometer of the brand "Instron", model "TTC".

When the mixture according to the invention is to be used for cascade development, the toner should have an average particle size of less than about 30 microns and preferably between 4 and 20 microns to give optimum results. For use in "powder-cloud" development, particle diameters slightly less than 1 micron are preferred.

Suitable coated and uncoated carrier materials for cascade and magnetic brush development are known in the art. The carrier particles may be electrically conductive, insulating, magnetic or non-magnetic, provided that the carrier particles acquire a charge of an opposite polarity to the toner particles when brought into close contact with them, so that the toner particles adhere to and surround the carrier particles. When a positive reproduction of an electrostatic image is desired, the carrier particles are selected so that the toner particles receive a charge with the opposite polarity of the electrostatic latent image's charge. Alternatively, the carrier particles are selected, if an inverted reproduction of the electrostatic image is desired, so that the toner particles receive a charge with the same polarity as the electrostatic image's charge. The materials for the carrier particles are thus chosen in accordance with its triboelectric properties in relation to the electroscopic toner, so that when they are mixed or brought into contact with each other, one component of the developer will be positively charged if the second component is located below the first component in the triboelectric series and negative if the second component is located above the first component in the triboelectric series. By properly choosing materials in accordance with their triboelectric effects, the polarities of their charges when mixed are such that the electroscopic toner particles adhere to and cover the surface of the carrier particles and also adhere to the part of the electrostatic image-bearing surfaces that have a greater attraction for the toner than the carrier particles. Typical carriers include sodium chloride, ammonium chloride, aluminum potassium chloride, potassium sodium tartrate, sodium nitrate, aluminum nitrate, potassium chlorate, granular zircon, granular silicon, methyl methacrylate, glass, silicon dioxide and the like. The carriers can be used with or without a cover. Many of the aforementioned and typical carriers are described in US Patent 2,618,551, in US Patent 2,638,416

and in US Patent 2,618,552. A diameter of a fully coated carrier particle of between about 50 to about 1000 microns is preferred because the carrier particle then has sufficient density and inertia to prevent attachment to the electrostatic images during cascade development. It is undesirable for carrier particles to hang on the xerographic drum surfaces due to the formation of deep furrows in the surface during the image transfer and drum cleaning, especially when the cleaning is carried out by means of a belt cleaner, such as the belt described in US Patent 3,186,838. Also, the pressure can disappear when carrier particles hang at the xerographic imaging surfaces. Generally speaking, satisfactory results are obtained when about parts by weight of toner are used together with about 10 to about 200 parts by weight of carrier.

The toner compounds according to the present invention can be used to develop latent electrostatic images on any suitable electrostatic latent image-bearing surface including conventional photoconductive surfaces. Well-known photoconductive materials include glassy selenium, organic or inorganic photoconductors embedded in a non-photoconductive matrix, organic or inorganic photoconductors embedded in a photoconductive matrix, and the like. Representative patent documents where photoconductive materials are described include US Patent Documents 2,803-542, 2,970,906, 3-121,006 and 3-121. 007 and 3-151-982.

The following examples provide further definition, description and comparison of methods for producing the toner materials according to the present invention, and of their use for developing electrostatically latent images. Parts and percentages are given by weight unless otherwise stated.

Example I

A sample of "Xerox 813" toner particles was used as a sample. Copies of a standard test pattern were made with the toner in a modified "813 Xerox" copier. The melting temperature was set with a proportional temperature control and was controlled by means of a thermocouple placed in the center of the upper melting plate. The melting unit comprised plates mounted approximately 19 mm apart. The toner images on 20 x 33 cm copy sheets were transported through the fuser at twice the normal speed, that is, at approximately 7.5 cm per second. second. Because the motor in a standard "Xerox 813" copier stops and overheats when the machine is operated at twice the normal speed, a motor with twice the normal power had to be used. After passing through the melter again, the copy sheets were attached to a full-sided sanding drum with a diameter of approximately 12 cm. A standard "813" cleaning cloth was pressed against the copy sheet by means of a spring-loaded roller under a spring pressure of about 18 kp. By rotating the cylinder that carried the copying sheet, the entire toner image on the sheet was ground by frictional contact with the cloth. A minimal meltor temperature was found when all test letters were still legible after a grinding course of 5 revolutions with the grinding drum. "Xerox 813" carrier cards were used with the toner during the development step. The minimum fusing temperature at which intelligible copies are obtained with "8l3" tones was found to be about 321°C. Many of the copies that left the smelter had glowing parts and in some cases open flames. Micrographic examinations of the reusable imaging surface after 5000 passes revealed significant wear and degradation of the surface.

Example II

A control toner mixture was prepared which contained about 7.5 parts by weight of a copolymer of about 65 parts by weight styrene and 35 parts by weight butyl methacrylate, about 1.5 parts by weight polyethylene wax and about 1 part by weight carbon black ("Neo Spectra Mark II"). . This wax was available under the trademark "Tenite 812A" from Eastman Kodak and was a dry solid mass with a melting point in the range of about 104.5°C to about 110°C. After melting and initial mixing, the mixture was fed to a rubber mill and ground thoroughly so that a uniformly dispersed mixture of wax in the thermoplastic resin mass was obtained. The resulting mixture was cooled with liquid nitrogen and then finely divided in a "Szegvari" grater to produce toner particles having an average particle size of from about 10 to about 20 microns. Cooling to below room temperature was necessary to avoid film formation of the toner material on the shredder's parts. About 1 part by weight of the toner was mixed with about 99 parts by weight of a coated carrier consisting of glass beads coated with an ethyl cellulose and having an average diameter of about 600 microns. The resulting developer was used to make 8,000 copies in an "813 Xerox" copier. The copies, especially the copies produced at the end of the test, were characterized by very low image density and a strong background. An examination of the xerographic drum after the completion of the test revealed a heavy toner film on the surface of the drum.

Example III

A toner mixture was prepared which contained approximately 10 parts by weight of carbon black ("Neo Spectra Mark III"), approximately 85 parts by weight of a copolymer of 65 parts by weight of styrene and approximately 35 parts by weight of n-butyl methacrylate, and 5 parts by weight of dicyclohexyl phthalate. This phthalate has a melting point of approximately 60°C. After melting and initial mixing, the mixture was ground in a rubber mill so that a uniformly dispersed mixture of carbon black was produced in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer to yield toner particles with an average particle size of about 10 to 15 microns. The toner had a melt viscosity of about 0.5 x 10 poise at about 141°C and a clogging temperature of about 57°C. About 1 part by weight of the pulverized toner particles was mixed with about 0.01 part by weight of zinc stearate particles having a particle size of from about 5 to about 40 microns and about 99 parts by weight of "Xerox 813" carrier grains and used as developer as set forth in Example I. Under substantially identical conditions test conditions, it was found that the original drive motor could be used and that the minimum fuser temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was approximately 300°C. This was a reduction of approximately 21°C from the melter temperature required in Example I. No embers were observed on copies exiting the melter. Micrographic studies of the reusable imaging surface after 5,000 copies revealed less wear and degradation of the surface than in Example I.

Example IV

A toner mixture was prepared containing about 10 parts by weight of carbon black ("Super Oarbobar"), about 80 parts by weight of a copolymer of 65 parts by weight of styrene and 35 parts by weight of n-butyl methacrylate and about 10 parts by weight of diphenyl phthalate. This phthalate had a melting point of approximately 69°C. After melting and initial mixing, the mixture was fed to a rubber mill and ground thoroughly so that a uniformly dispersed mixture of carbon black in the thermoplastic resin mass was obtained. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of from about 6 to about 12 microns. This toner had a melt viscosity of about 0.5 x 10 poise at 135°C and a clogging temperature of about 52°C. About 1.5 parts by weight of the pulverized toner particles were mixed with about 0.01 part by weight of zinc stearate particles having a particle size between about 5 to about 40 microns and about 99 parts by weight of "Xerox 813" carrier grains and used as developer as set forth in Example I. Under given identical test conditions, it was found that the original drive motor could be used and that the minimum fuser temperature at which legible copies could be obtained after a grinding course of 5 revolutions with the grinding drum was approximately 285°C. This is a reduction of approximately 36°C from the melter temperature required in Example I. No embers were observed on copies exiting the melter. Micrographic examinations of the reusable imaging surface after 5,000 copies revealed less wear and degradation than the surface of Example I.

Example V

A toner mixture was prepared containing about 10 parts by weight of "Sudan Black BN" dye, about 80 parts by weight of a copolymer of about 65 parts by weight of styrene and about 35 parts by weight of n-butyl methacrylate and about 10 parts by weight of dihydroabiethyl phthalate. This phthalate has a melting point of approximately 70.5°C. After melting and initial mixing, the mixture was fed to a rubber mill and ground thoroughly so that a uniformly dispersed mixture of carbon black was produced in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the toner particles formed had an average particle size of from about 10 to about 15 microns. This toner had a melt viscosity of about 0.5 x 10 ^ poise at about 135°C and a clogging temperature of about 52°C. About 1 part by weight of the pulverized toner particles was mixed with about 0.05 part by weight of zinc oleate having a particle size in the range of 0.5 to 35 microns and about 99 parts by weight of "813 Xerox" carrier grains and used as developer as set forth in Example I. given identical test conditions, it was found that the original drive motor could be used and that the minimum fuser temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was approximately 288°C. This was a reduction of 33°C from the melter temperature required in Example I. No embers were observed on the copies as they exited the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less wear and degradation of the surface than in Example I.

Example VI

A toner mixture was prepared which contained about 10 parts by weight of carbon black, about 75 parts by weight of a copolymer of about 80 parts by weight of styrene and about 20 parts by weight of isobutyl methacrylate and about 15 parts by weight of dicyclohexyl phthalate. After melting and initial mixing, the mixture was fed to a rubber mill and ground thoroughly so as to produce a uniformly dispersed mixture of the dye in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of from about 6 to about 9 microns. This toner had a melt viscosity. of about 0.5 x 10 _ ji poise at about 135°C and a plugging temperature of about 54.5°C. As in all examples, the clogging temperature was determined by initially heating the toner particles in an air circulation oven at approximately 55°C for a period of 24 hours and then stepwise increasing the temperature by 5-5°C every 24 hours. The clogging temperature is the temperature at which a gentle crushing action with a spatula is necessary to remove clumping and return the toner to its original finely divided form. About 2 parts by weight of the powdered toner particles were mixed with 0.015 parts by weight of zinc stearate particles ranging in size from 5 to about 40 microns and about 99 parts by weight of "813 Xerox" carrier grains and used in place of the developer as set forth in Example I. Under substantially identical test conditions, it was found that the original drive motor could be used and that the minimum melting temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was approximately 282°C. This was a reduction of 39°C in relation to the melter temperature which was necessary in Example I. No embers were observed on the copies as when they came out of the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less wear and degradation of the surface than in Example I.

Example VII

A toner mixture was prepared which contained about 10 parts by weight of carbon black, about 75 parts by weight of a copolymer of about 80 parts by weight of styrene and about 20 parts by weight of isobutyl methacrylate and about 15 parts by weight of dimethyl isophthalate. After melting and initial mixing, the mixture was fed to a rubber mill and ground thoroughly so that a uniformly dispersed mixture of the pigment and the phthalate in the thermoplastic resin mass was obtained. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of from 6 to about 9 microns. This

-4

toner had an emslet viscosity of about 0.5 x 10 poise at about 138°C and a clogging temperature of about 54.5°C. About 1 part by weight of the powdered toner particles was mixed

together with about 0.01 parts by weight of zinc stearate particles ranging in size from about 0.5 to about 30 microns, and about 99 parts by weight of "813 Xerox" carrier grains and used as developer as set forth in Example I. Under substantially identical tests - conditions, it was found that the original drive motor could be used and that the minimum fuser temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding cylinder was approximately 293°C. This was a reduction of 28°C from the melter temperature required in Example I. No embers were observed on the copies as they exited the melter. Micrographic examinations of the imaging surface after 5000 copies revealed less wear and degradation of the surface than in Example I.

Example VIII

A toner mixture was prepared which contained about 10 parts by weight of carbon black, about 65 parts by weight of a copolymer of about 90 parts by weight of polystyrene and about 10 parts by weight of isobutyl methacrylate and about 25 parts by weight of dicyclohexyl phthalate. After melting and initial mixing, the mixture was fed to a ball mill and ground thoroughly so that a uniformly dispersed mixture of carbon black and phthalate was produced in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of from about 10 to about 15

-4 microns. This toner had a melt viscosity of about 0.5 x 10 poise at about 121°C and a clogging temperature of about 43.5°C. About 1 part by weight of the pulverized toner particles was mixed with about 1 part by weight of zinc oleate having a particle size of from about 0.5 to about 25 microns, and about 99 parts by weight of "813 Xerox" carrier grains and used as developer as set forth in Example I. Under largely identical test conditions, it was found that the original drive motor could be used and that the minimum melter temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was approximately 260 C. This was a reduction of 6l°C in relation to the melter temperature which was required in Example I. No embers were observed on the copies as they emerged from the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less wear and degradation of the surface than in Example

Example IX

A toner mixture was prepared which contained about 10 parts by weight carbon black ("Neo Spectra Mark III"), about 65 parts by weight polystyrene and 25 parts by weight diphenyl phthalate. After melting and initial mixing, the mixture was ground in a rubber mill so that a uniformly dispersed mixture of carbon black was produced in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of from about 10 to about 15 microns. The toner had a melt viscosity of about -4 o

trained 0.5 x 10 poise at about 124°C and a plugging temperature of about 46°C. About 1 part by weight of the pulverized toner particles was mixed with about 0.01 part by weight of zinc stearate particles having a particle size of from about 5 to about 40 microns and about 99 parts by weight of "Xerox 8l3" carrier grains and used as developer as indicated in Example I Under largely identical test conditions, it was found that the original drive motor could be used and that the minimum fuser temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was approximately 266°C. This was a reduction of approximately 55°C from the melt temperature required in Example I. No embers were observed on the copies as they exited the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less wear and degradation of the imaging surface than in Example I.

Example X

A toner mixture was prepared which contained about 10 parts by weight of carbon black (Super Carbobar), about 70 parts by weight of polymethyl methacrylate and 20 parts by weight of dihydroabicythyl phthalate. After melting and initial mixing, the mixture was ground in a rubber mill so that a uniformly dispersed mixture of carbon black was produced in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of from about 6 to about 12 microns. The toner had a melt viscosity of

-4 o

about 0.5 x 10 <-4> poise at about 129»5 C and a plugging temperature of about 49°C. About 1 part by weight of the powdered toner particles was mixed with about 0.01 part by weight of lead linoleate particles having a particle size of from about 3 to about

trained to 35 microns and approximately 99 parts by weight of "Xerox 8l3" carrier grain and used as developer as indicated in Example I. Under substantially identical test conditions, it was found that the original drive motor could be used and that the minimum fusing temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was about 277°C. This was a reduction of approximately 44°C from the melter temperature required in Example I. No embers were observed on the copies as they exited the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less assembly and degradation of the imaging surface than in Example I.

Example XI

A toner mixture was prepared which contained about 10 parts by weight of carbon black, about 75 parts by weight of a copolymer of 90 parts by weight of styrene and about 10 parts by weight of vinylidene chloride, and

.15 parts by weight . diphenyl phthalate. After melting and initial mixing, the mixture was ground in a rubber mill so that a uniformly dispersed mixture of carbon black was formed in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the resulting toner particles had an average particle size of from about 5 to about 12 microns. The toner had a melt viscosity of about 0.5 x 10 poise at about 135°C and a clogging temperature of about 52°C. About 1 part by weight of the pulverized toner particles was mixed with about 0.01 part by weight of zinc stearate particles having a particle size of from about 5 to about 40 microns and about 99 parts by weight of uncoated glass beads and used as developer as set forth in Example I. Under substantially identical test conditions it was found that the original drive motor could be used and that the minimum fuser temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was approximately 296°C. This was a reduction of approximately 25°C

in relation to the melter temperature required in Example I. No embers were observed on the copies as they came out of the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less wear and degradation of the surface than in Example I.

Example XII

A toner mixture was prepared which contained about 10 parts by weight carbon black ("Neo Spectra Mark III"), about 80 parts by weight of a copolymer of 70 parts by weight styrene and 30 parts by weight vinyl acetate and 10 parts by weight dicyclohexyl phthalate. After melting and initial mixing, the mixture was ground in a rubber mill so that a uniformly dispersed mixture of carbon black was produced in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of from about 10 to about 15 microns. The toner had a melt viscosity of about 0.5 x 10 _i| poise at about 138 QC and a plugging temperature of about. 5735°C. About 1 part by weight of the pulverized toner particles was mixed with about 0.01 part by weight of zinc stearate particles having a particle size of from about 5 to about 40 microns and about 99 parts by weight of coated carrier grains and used as developer as set forth in Example I. Under substantially identical test- conditions, it was found that the original drive motor could be used and that the minimum fuser temperature at which legible copies were obtained after a grinding course of 5 revolutions with the grinding drum was approximately 293°C. This was a reduction of approximately 28°C from the melter temperature required in Example I. No embers were observed on the copies as they exited the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less wear and degradation of the surface than in Example I.

Example XIII

A toner mixture was prepared which contained approximately 10 parts by weight of carbon black, approximately 70 parts by weight of a copolymer of 80 parts by weight of styrene and 20 parts by weight of acrylonitrile and 20 parts by weight of dicyclohexyl phthalate. This phthalate had a melting point of approximately 60°C. After melting and initial mixing, the mixture was ground in a rubber mill so that a uniformly dispersed mixture of carbon black was produced in the thermoplastic resin mass. The resulting mixture was cooled and then comminuted in a jet pulverizer so that the formed toner particles had an average particle size of about 5 to about 14 microns. The toner had a melt viscosity of about 0.5 x 10 ^ poise at about 126.5°C

and a plugging temperature of about 49°C. About 1 part by weight of the powdered toner particles was mixed with about 0.05 part by weight of cobalt palmitate particles having a particle size

from about 5 to about 40 microns, as well as 99 parts by weight of uncoated glass carrier grains and used as developer as indicated in Example I. Under largely identical test conditions, it was found that the original drive motor could be used and that the minimum melter temperature at which legible copies were obtained after a grinding course in 5 revolutions of the sanding drum was about 2 70°C. This was a reduction of approximately 50°C from the melter temperature required in Example I. No embers were observed on the copies as they exited the melter. Micrographic examinations of the reusable imaging surface after 5000 copies revealed less wear and degradation of the surface than, for example, I.

Example XIV

A control sample containing a portion of colored preformed toner particles of the type described in Example III having an average particle size of about 10 to about 15 microns was mixed with about 99 parts by weight of coated glass beads having an average particle size of about 250 microns and then sprinkled over the image-bearing drum surface. The developed image was then transferred electrostatically to a sheet of paper to which it was fused with heat. The remaining powder was removed from the electrostatic imaging surface using a cleaning cloth of the type described in US Patent 3,186,838. After the copying process was repeated 25-000 times, the copies and the electrostatic image-bearing surface were examined for quality and wear respectively. The copies had sharp line contrast and minimal background deposition. However, an examination of the imaging surface revealed the effects of significant wear.

Example XV

About 0.01 part by weight of zinc stearate having a particle size ranging from about 5 microns to about 40 microns was carefully stirred into one part by weight of colored pre-made toner particles of the type described in Example XIV. The resulting developer mixture was cooled and then ground thoroughly in a "Szegvari" grater for about 10 minutes. The development in Example XV was repeated with a new drum and with the aforementioned ground mixture instead of the toner indicated in Example XIV at a relative humidity of about 50% at 21°C and at a relative humidity of 80% at 26.5° C. Copies made with the latter sample had higher density in fully covered areas than copies made with the control sample. Moreover, micrographic examinations of the image-bearing surface revealed less wear than in Example XIV. Considerably less torque was required to drive the drum when . the stearate additive was used and a lower voltage was necessary to transfer the toner images to a receiver sheet.

Claims (9)

1. Xerographic developer material containing toner particles containing finely divided toner material comprising a colorant and a thermoplastic resin, for example a vinyl or vinylidene resin with a melting point of at least 43.3°C, and a solid additive, as well as preferably a carrier for the toner particles, characterized in that the toner particles as solid additive contain an ester of o-phthalic acid or m-phthalic acid or of 4,5-epoxy-tetrahydrophthalic acid. 2. Developer material in accordance with claim 1, characterized in that the finely divided toner material has a clogging temperature of at least 43.0°C and a melt viscosity -4 o which is less than 2.5 x 10 poise at temperatures up to 232°C. 3. Developer material in accordance with claim 1 or 2, characterized in that the ester has a melting point between 43.5°C and 79.5°C. 4. Developer material in accordance with one of claims 1-3, characterized in that the finely divided toner particles contain from 2 to 45% by weight of ester, calculated by the weight of the thermoplastic resin. 5. Developer material in accordance with one of claims 1-4, characterized in that the solid ester is diphenyl phthalate. 6. Developer material in accordance with one of claims 1-5, characterized in that the ester is dihydroabiethyl phthalate. 7. Developer material in accordance with one of claims 1-6, characterized in that the ester is dicyclohexyl phthalate. 8. Developer material in accordance with one of claims 1-7, characterized in that the ester is triphenyl phthalate. 9. Developer material in accordance with one of claims 1-8, characterized in that the finely divided toner material contains at least 25% by weight of a styrene resin, calculated from the total weight of the thermoplastic resin in the toner.