GB2091897A - Xerographic developer - Google Patents

Abstract

A two-component developer composition comprised of a toner of a polyester resin of general formula <IMAGE> where R is a substituted or unsubstituted alkylene radical having from 2 to 12 carbon atoms, an alkylidene radical having from 1 to 12 carbon atoms, or a cycloalkylidene radical having from 3 to 12 carbon atoms; R' and R'' are substituted or unsubstituted alkylene radicals having from 2 to 12 carbon atoms, alkylene arylene radicals having from 8 to 12 carbon atoms and arylene radicals; X and X' hydrogen or alkyl radical having from 1 to 4 carbon atoms and n is a number from 0 to 4, and magnetic particles (specifically magnetite) in an amount of from about 20 percent to about 50 percent by weight, and a carrier material (particularly coated steel), which developer composition, when utilized in a xerographic apparatus, allows the production of high-quality images over a substantial period of time while simultaneously eliminating any cleaning problems and contamination of the machine components.

Description

SPECIFICATION Xerographic developer composition This invention is generally directed to new toner materials and more specifically, developing compositions comprised of a magnetic toner and carrier particles, which developers are useful for causing the development of images in electrostatographic imaging systems, particularly those systems employing magnetic brush development.

The electrophotographic process and more specifically the xerographic process is well known generally involving uniform charging of a photoconductive insulating surface which is conductive under the influence of light, thus allowing electrostatic charge formed thereon to be selectively dissipated in order to produce a latent image which is developed by a variety of pigmented toner materials specifically made for this purpose. These toner materials are electrostatically attracted to the latent image areas on the plate in porportion to the charge concentration contained thereon.Many processes are known for applying the toner or electroscopic particles to the electrostatic latent image to be developed such as for example the development method described in U.S. 3,618,552, cascade development, U.S. 2,784,063; 3,251,706; and 3,357,402, magnetic brush development, U.S. 2,221,776, powder cloud development and U.S. 3,166,432, touchdown development. The developed image can then be transfered to a suitable substrate such as paper and can be fixed by using a number of different techniques including for example, vapor fixing, heat fixing, pressure fixing or combinations thereof, as described for example in U.S. 3,539,161.

There are also known magnetic imaging systems wherein magnetic toner, which is generally a single-component toner, that is, no carrier material is employed. In these systems a latent magnetic image is formed on a magnetizable recording medium, which image can be used in duplicating processes for example by repetitive toning and transfer of the developed image. The latent magnetic image is formed by any suitable magnetization procedure whereby a magnetized layer of marking material is magnetized and such magnetization transferred imagewise to a magnetic substrate; where the magnetization pattern is applied directly to the magnetic substrate by a record head or similar device. The latent magnetic image can then be developed with a magnetic developer, usually comprised of toner particles containing a magnetic pigment, to render such images visible.The developed visible image can then be typically transferred to a receiver such as for example a sheet of paper which image is fused on the paper in order to produce a final copy or print referred to in the art as a hard copy.

There is described in U.S. 3,345,294 a developing composition containing specific ingredients including for example a resin, a major portion of which is a polyamide which has a sharp melting point within the range of from about 70"C to about 165 C. It is stated in column 4 of this patent, beginning at line 34, that, in order to reduce the tendency of the developer powder ortonerto adhere to the background of the print, a small amount of finely-divided magnetic substance is added to the powder, which substance may be magnetic iron oxide, ferrosferric oxide powder, a magnetide metal substance or an alloy.

US 3 985 665 (Sakaguchi et al) discloses a developer composition consisting of a pigment combined with a mixture of polyester and other resins.

In many prior art systems toner particles tend to separate from the carrier particles, which can be undesirable as the separated toner particles are then free to deposit on machine parts for example and thus contaminate the machine environment, thereby leading not only to developed images of very low resolution or no developed images whatsoever, but also to possible environmental problems. Further, because of the deposition of toner on the machine parts, it may be necessary over a period of time to replace such parts or at least to clean these parts which adds to the cost of machine maintenance.When unused toner, for example, deposits on the optical systems present in an electrophotographic machine system, a latent image corresponding to an original to be copied will not be fully formed, if formed at all, on the photoreceptor surface, thereby resulting in a final fused image of very low quality which in some instances may be unreadable depending on the amount of toner that has deposited on the optical parts of the system. Such contamination is eliminated with the toner of the present invention primarily because the toner is prevented from separating from the carrier particles as a result of the collision of the developer composition (comprised of toner and carrier particles) with the components of the electrophotographic system.It is important that the magnetic force between the toner and carrier is not too great, which force is determined by the amount of magnetic pigment present in the toner, as the electrostatic force will not be sufficient to overcome the forces between the toner and carrier and therefore the toner will not separate from the carrier when it is needed for development. Of course the electrostatic force can be increased somewhat to overcome the magnetic force present between the toner and carrier so that it will deposit on the latent image surface.

Typical suitable fusing methods that may be used to permanently fix the developed latent image to a substrate such as paper, include for example heating the toner and the developed image to cause the resins thereof to melt at least partially and become adhered to the photoconductor binder member, or copy substrate in the case of images transferred from the imaging media, followed by the application of pressure to the toner with heating such as the use of a heated roller. Solvent or solvent vapor fusing has also been used wherein the resin component of the toner is partially dissolved. The photoconductor binder member or copy substrate is typically of sufficient hardness to allow fixing solely by the application of pressure such as for example by contacting roller in an amount sufficient to calender the toner.

Along with the growth of interest in electrostatographic imaging systems there has been a need to develop new toners and developers which have certain properties so as to render the development of the images more efficient and to allow better quality of development while at the same time having no adverse effects on the photoreceptor surface.

It is an object of the present invention to provide a magnetic toner containing a magnetic material and certain resins, which toner can be mixed with a carrier to form a two-component develop.

These and other objects of the present invention are accomplished by the provision of an improved two-component developer composition comprised of a polyester resin as defined hereinafter, a magnetic component or filler, a carrier material, and as an optical ingredient a colorant or pigment, which improved developer composition when utilized in an electrophotographic apparatus, allows the production of high quality images over a substantial period of time while simultaneously eliminating any cleaning problems and contamination of the machine components since the toner particles are not deposited on said machine components due to their adherence to the carrier particles.

The polyester resins used in the developing composition of the present invention are comprised of the polymeric esterification product of a dicarboxylic acid and a diol comprising a diphenol of the following formula:

wherein R is selected from substituted and unsubstituted alkylene radicals having from about 2 to about 12 carbon atoms, alkylidene radicals having from 1 to 12 carbon atoms and cycloalkylene radicals having from 3 to 12 carbon atoms; R' and R" are selected from substituted and unsubstituted alkylene radicals having from 2 to 12 carbon atoms, alkylene arylene radicals having from 8 to 12 carbon atoms and arylene radicals; X and X' are selected from hydrogen or an alkyl radical having from 1 to 4 carbon atoms; and each n is a number from 0 (zero) to 4.Diphenols wherein R represents an alkylidene radical having from 2 to 4 carbon atoms, and R' and R" represents an alkylene radical having from 3 to 4 carbon atoms, are preferred because greater blocking resistance, increased definition of xerographic characters and more complete transfer of the toner images are achieved. Optimum results are obtained with diols in which R is a isopropylidene radical and R' and R" are selected from the group consisting of propylene and butylene radicals and n is 1 (one), as the resins formed from these diols possess higher agglomeration resistance and penetrate extremely rapidly into paper.

Typical diphenols having the foregoing general structure include: 2,2-bis(4-beta hydroxy ethoxy phenyl)-propane, 2,2-bis(4-hydroxy isopropoxy phenyl) propane, 2,2-bis(4-beta hydroxy ethoxy phenyl) pentane, 2,2-bis(4-beta hydroxy ethoxy phenyl)-butane, 2,2-bis(4-hydroxy-propoxy-phenyl )-butane, 2,2- bis(4-hydroxy-propoxy-phenyl) propane, 1,1 -bis(4-hydroxy-ethoxy-phenyl)butane, 1,1 -bis(4-hydroxy isopropoxy-phenyl) heptane, 2,2-bis(3-methyl-4-beta-hydroxy ethoxy-phenyl) propane, 1,1 -bis(4-beta hydroxy ethoxy phenyl)cyclohexane, 2,2'-bis(4-beta hydroxy ethoxy phenyl)- norbornane, 2,2'-bis(4-beta hydroxy ethoxy phenyl) norbornane, 2,2-bis(4-beta hydroxy styryl oxyphenyl) propane, the polyoxy-ethylene ether of isopropylidene diphenol in which both phenolic hydroxyl groups are oxyethylated and the average number of oxyethylene groups per mole is 2.6, the polyoxypropylene ether of 2-butylidene diphenol, in which both the phenolic hydroxyl groups are oxylkylated and the average number of oxypropylene groups per mole is 2.5; and the like.

Suitable dicarboxylic acids that may be reacted with the diols described above to form the toner resins of this invention, which acids may be substituted, unsubstituted, saturated or unsaturated, include those of the general formual: HOOCR"'n3COOH wherein R"' is a substituted or unsubstituted alkylene radical having from 1 to 12 carbon atoms, arylene radicals or alkylene arylene radicals having from 10 to 12 carbon atoms and n3 is less than 2. By 'dicarboxylic acid' is included the anhydrides of such acids where such anhydrides exist.Typical dicarboxylic acids include: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, mesaconic acid, homophthalic acid, isophthalic acid, terephthalic acid, o-phenyleneacetic-beta-propionic acid, itaconic acid, maleic acid, maleic acid anhydrides, fumaric acid, phthalic acid anhydride, traumatic acid, citraconic acid, and the like. Dicarboxylix acids having from 3 to 5 carbon atoms are preferred because the resulting toner resins containing same possess greater resistance to film formation on reusable imaging surfaces, and resist the formation of 'fines' under machine operation conditions. Optimum results are obtained with alpha unsaturated dicarboxylic acids, such as fumaric acid, maleic acid, or maleic acid anhydride, as maximum resistance to physical degradation of the toner as well as rapid melting properties are achieved. Although it is not entirely clear, it is believed that the presence of the unsaturated bonds in the alpha-unsaturated dicarboxylic acid reactants provides the resin molecules with a greater degree of toughness, without adversely affecting the fusing and comminution characteristics.

The preferred polyester material of the present invention is the reaction product of 2,2-bis(4-hydroxy isopropxy phenyl) propane and fumaric acid, as such a polyester when used as the toner resin in a developing composition results in images of very high resolution and superior quality.

Illustrative of magnetic materials or fillers that may be used in the present inventibn include for example magnetites such as Fe203, Fe3O4, Mapico black (a commerically-available material), MO-4232, a magnetite commercially available from Pfizer Pigment Company, New York, New York, and K-378, a magnetite commercially available from Northern Pigments Corporation, Toronto, Ontario Canada, and mixtures thereof. Mapico black is preferred in that the particles are black in color, of low cost, and provide excellent magnetic properties.

The amount of magnetic pigment used is of importance and in one preferred embodiment is present in an amount of 20 to 30 percent by weight, however, the amount of magnetic pigment present can range from about 15 percent to about 50 percent by weight and preferably from about 20 percent to about 30 percent based on the weight of toner. In such a situation the amount of polyester material present would range from about 50 percent to about 85 percent. When the preferred amount of magnetic pigment is present, namely 20 to 30 percent there is present 70 to 80 percent of the polyester resin. With the preferred amount of magnetic pigment few toner particles separate from the carrier particles, thus allowing for the production of images of very high quality.

As an optional ingredient there may be added to the above toner composition a colorant or pigment such as carbon black including the various forms of carbon black commercially available such as Black Pearls L, Regal 330, Vulcan carbon black, and mixtures thereof. The carbon black is usually present in an amount of from about 1 percent to about 10 percent by weight and preferably in an amount of from about 2 percent to about 5 percent by weight.

Numerous carrier materials can be employed together with the toner resin and magnetite in order to form the developing composition of the present invention providing of course that such material is capable of triboelectrically obtaining a charge of opposite polarity to that of the toner particles. Examples of carriers include potassium chloride, Rochelle salt, sodium nitrate, aluminum nitrate, potassium chlorate, granular zircon, granular silicon, methyl methacrylate, glass, steel, nickel, iron ferrites, silicon dioxide and the like.

The carriers can be used with or without a coating such coatings including fluorocarbon resins such as polyvinylidene fluoride, perfluoroalkoxy fluoride resins, polymethyl methacrylate resins and the like. Many of the typical carriers that can be used are described in U.S. 2,618,441, 2,638,552, 3,618,552, 3,591,503, 3,533,835 and 3,526,533. Also nickel berry carriers as described in U.S. 3,847,604 and 3,767,598 can be employed, these carriers being nodular carrier beads of nickel characterized by convoluted surfaces of large area. The diameter of the coating carrier particles is from about 50 to about 250 microns thus allowing the carrier to present sufficient density and inertia to avoid adherence to the electrostatic images during the development process.The preferred carrier material is a steel core coated with a polyvinylidene resin or a polymethyl methacrylate resin.

The carrier may be employed with the toner composition in any suitable combination, however, best results are obtained when there is used about 0.5 parts to about 10 parts oftonerto 100 to 200 parts by weight of carrier and preferably from about 3 parts of toner to 100 parts by weight of carrier.

The developer compositions of the present invention may be used to develop images in an electrophotographic apparatus which apparatus may contain various different photoreceptors including amorphous selenium, selenium alloys, such as selenium antimony, selenium tellurium, selenium antimony tellurium, selenium tellurium, selenium antimony tellurium, selenium arsenic, and organic photoreceptors such as polyvinyl carbazole, 4-dimethyl amino benzylidene, benzhydrazide, 2-benzylidene-amino-carbazole, 4-dimethylamino-benzylidene, 2-benzylidene-amino-carbazole, polyvinyl-carbazole, 2-nitrobenzylidene, para bromo aniline, 2,4-diphenyl quinazoline, 1,2,4-triazine, 1,5-diphenyl 3-methyl pyrazoline (2-(4'dimethylamino phenyl)-benzoxazole, 3-amino carbazole, polyvinyl-carbazole-trinitrofluoronone, charge transfer complex, phthalocyanines, layered photoreceptors and mixtures thereof.

Numerous different known methods can be utilized for preparing the toner and developers of the present invention including spray drying, jetting, and the like, however, one preferred method for preparing the toner is hot melt formation and mastication of the toner resin, and magnetite, using a Banbury rubber mill process followed by attrition to obtain toner particle sizes, of less than 25 microns on the average.

Surface additives may be added as optional ingredients to the developer of the present invention so as to assist in lubrication and of the imaging system and in particular the photoreceptor. Such materials include for example Aerosil, other silicas, metal salts of fatty acids, such as zinc stearate, mixtures thereof and the like. The Aerosil type materials function primarily as toner film reducing agent, while the stearate materials function primarily as a lubricating agent. In some instances the toner after use and a number of imaging cycles forms a small layer of film on the photoreceptor surface which in subsequent operations will adversely affect the imaging quality, since such layer adversely affects the electrical properties of the system. The Aerosil is present in an amount of from about 0.25 percent to about 0.65 percent while the stearate is present in an amount of from 0.10 percent to about 0.35 percent. Percentages outside these ranges may be useful providing they do not adversely affect the system and accomplish the objectives of the present invention.

When using the developer of the present invention in electrophotographic imaging systems, no contamination of the machine components occurred, or the contamination was so slight so as to not adversely affect the quality of the images produced. This was demonstrated by comparing the amount of toner or contamination that was deposited on a machine component when using the toner of the present invention as compared when using prior art toner, as detailed below. It was observed experimentally that significantly less toner contamination appeared on a machine component when the developer of the present invention was employed.

The toner compositions of the present invention were found to be very useful in xerographic imaging systems or magnetic imaging systems as described hereinbefore, reference Page 1 of the present application. In these systems, the toner of the present invention together with a carrier materal is employed to develop the latent electrostatic image or the magnetic latent image followed by transfer of such an image to a suitable substrate and thereafter permanently affixing the image thereto. When using the toner of the present invention in such imaging systems, images of exceptional quality were produced over substantial periods of time with very little or no unwanted toner deposition occurring on the machine parts as described in more detail hereinafter.

The invention will now be described in detail with respect to specific preferred embodiments thereof, it being understood that these examples are intended to be illustrative only and the invention is not intended to be limited to the materials, conditions, process parameters, and the like recited herein. All parts and percentages are by weight unless otherwise indicated.

Example 1 There was prepared by melt mixing followed by mechanical attrition a toner resin by mixing together 50 percent by weight of the polyester resin which is the reaction product of 2,2-bis(4-hydroxy isopropoxy phenyl) propane and fumaric acid, which polyester is commerically available from ICI Corporation, 50 percent by weight of the magnetic iron oxide commercially available as Mapico black, and as surface additives (not part of the resin blend) 0.65 percent by weight of Aerosil, and 0.35 percent by weight of zinc stearate.

Three parts by weight of the above toner resin together with 100 parts by weight of a carrier material comprised of steel coated with a polymethyl methacrylate resin were admixed together resulting in a dual-component developing composition, which when used in a xerographic imaging system employing magnetic brush development produced high quality copies of exceptional resolution. Inspection of the machine components reveals substantially no deposition of toner, or other contamination.

Example Il The procedure of Example I was repeated with the exception that there was used 75 percent by weight of the polyester resin 20 percent by weight of the magnetite Mapico black, and 5 percent by weight of the carbon black, Black Pearls L. Substantially similar results were observed when this toner resin, 3 parts by weight, were used with 100 parts by weight with the carrier material of Example I, in a xerographic imaging system employing magnetic brush development as in Example I.

Example III The procedure of Example I was repeated with the exception that there was employed in place of the Black Pearl L, 5 percent by weight of the carbon black Regal 330 and substantially similar results were obtained when this toner was used with the carrier material of Example I in the xerographic imaging device of Example I.

Example IV The procedure of Example I was repeated with the exception that there was used 70 percent by weight of the polyester resin, 20 percent by weight of Mapico black, 5 percent by weight of Black Pearls Land 5 percent by weight of Nigrosine. One part of this toner when mixed with 100 parts by weight of the carrier material of Example I resulted in a developer composition that had properties substantially similar to the composition as prepared in Example I when this material is used in a xerographic imaging device employing magnetic brush development as in Example I.

Example V The procedure of Example I was repeated with the exception that there was employed 75 percent by weight of the polyester resin, and 25 percent by weight of Mapico black with no carbon black being present.

When this developer composition, three parts by weight was mixed with 100 parts by weight of the carrier of Example 1 there was obtained exceptional prints of high quality after 7,500 imaging cycles. Additionally, it was observed that substantially no contamination occurred on the machine components as compared to substantial contamination when a developer composition comprised of 90 percent by weight, of the polyester resin of Example I, 10 percent by weight of the carbon black, Black Pearls L, and the carrier of Example I were employed.

Example Vl The procedure of Example I was repeated with the exception that there was prepared a toner and developer composition containing 72 percent by weight of the polyester resin, and 20 percent by weight of Mapico black, 6 percent by weight of the carbon black Regal 330, and 2 percent by way of a charge control agent cetyl pyridinium chloride. Substantially similar results are obtained when the developer composition of this Example is used in a xerographic imaging system.

When the toner composition of the present invention was employed as a developer, for developing images in the xerographic imaging apparatus employing magnetic brush development, commercially available from Xerox Corporation as the 3300 machine, which toner consisted of 75 percent by weight of the polyester resin of Example V, (reaction product of 2,2-bis (4-hydroxy isopropoxy phenyl) propane and fumaric acid) and, 25 percent of Mapico Black, no toner particles or dirt was observed on the corotron, after 2,500 imaging cycles; as compared to the observation of substantial amounts of "dirt" or toner particles when the same developer was employed without Mapico Black in the 3300 machine after 2,500 imaging cycles. About 25 percent of the corotron contained unwanted toner particles when no Mapico Black was used in the developer composition.

Images of very low quality, which images contained substantial areas of unwanted background deposits were obtained in the 3300 machine after 2,500 copies in view of the deposition of the toner particles on the corotron, while images of high quality with no background deposits were obtained in the 3300 machine after 2,500 copies with the developer containing Mapico Black.

Substantially similar results were observed when the above toner compositions was used in a 3300 machine with the exception that a baffle on the development housing contained substantial amounts of unwanted toner particles, about 75 percent of the baffle being covered, when no Mapico Black used, as compared to no "dirt" or toner particles on the same baffle in the 3300 machine when Mapico Black was present in the toner.

Further experiments with the above toner compositons, indicated the deposition of 60 particles per square millimeter per second on a filter device with the above developer composition containing no Mapico black, as compared to the deposition of 6 particles per square millimeter per second on the same filter device with the above developer composition containing Mapico black.

It is believed that the toner particles adhere to the carrier particles in the developer compositions of the present invention primarily because of the magnetic field that is created by the magnetic brush development system, present in many xerographic imaging systems.

Claims (9)

1. A two-com ponent developer composition of which one component comprises 20 to 50 percent by weight of magnetite, and from 50 to 80 percent by weight of a resin comprised of the polymeric esterification product of a dicarboxylic acid and a diol comprising a diphenol of the following formula:

wherein R is a substituted or unsubstituted alkylene radical having from 2 to 12 carbon atoms, an alkylene radical having from 1 to 12 carbon atoms, or a cycloalkylidene radical having from 3 to 12 carbon atoms; R' and R" are substituted or unsubstituted alkylene radicals having from 2 to 12 carbon atoms, alkylene arylene radicals having from 8 to 12 carbon atoms and arylene radicals;X and X' are hydrogen or any alkyl radical having from 1 to 4 carbon atoms; and n is a number from 0 (zero) to 4, and of which the other component is a carrier material consisting of a steel core coated with a polymethyl methacrylate resin or a polyvinylidene fluoride resin.

2. A developer composition in accordance with claim 1, wherein the magnetite is Mapico black present in an amount of from 20 to 30 percent by weight, and wherein the resin is the reaction product of 2,2-bis(4-hydroxy isopropoxy phenyl) propane and fumaric acid, and is present in an amount of from 70 to 80 percent by weight.

3. A developer composition in accordance with claim 1 or 2, wherein there is added thereto as a colorant carbon black in an amount of from 1 to 10 percent by weight.

4. A developer composition as claimed in any preceding claim, including surface additives.

5. A developer composition in accordance with claim 4, wherein the additive is a silicaceous material.

6. A developer composition in accordance with claim 4 or 5, wherein the additive is a stearate.

7. A developer composition in accordance with claims 2,3,5 and 6, including 68 percent by weight of polyester resin; 27 percent by weight of magnetite; five percent by weight of carbon black; 0.5 percent by weight of a silicaceous material, and 0.28 percent by weight of zinc stearate.

8. A developer composition in accordance with claim 7, wherein the silicaceous material is silicon dioxide.

9. A method of electrostatographic or magnetic imaging which comprises forming an electrostatic or magnetic latent image on a photoreceptor surface, developing the image with a developer composition as claimed in any preceding claim, transferring the image to a permanent substrate, and permanently affixing the image thereto by heat.