GB2113413A - Eleotrophotographic toner - Google Patents

Abstract

A xerographic toner comprises a resinous binder having dispersed therein a crystalline plasticizer for said resin and a thermally conductive material. The thermally conductive material may serve as the only colorant. The toner is particularly well suited for use in xerographic processes and devices which provide copies at a high rate of speed or in xerographic processes and devices wherein low fusing energy is desired. A significant change in melt viscosity of resinous toner particles is achieved. Suitable resins are vinyl resins or styrene/methacrylate copolymers. The conductive material may be iron oxide and the plasticizer may be diphenylisophthalate.

Description

SPECIFICATION Electrophotographic toner This invention relates to electrophotographictoner capable of reducing the energy requirement of image fixing, that is, to the attachment of the image to a supporting substrate by means of fusion.

The art of electrophotographic toner production is rather well developed due to its extensive commercial utility. The advantage to be gained by a reduction of the amount of energy required to fuse an image produced by the xerographic process with resinous particles has long been recognized and numerous efforts have been made to achieve such reduction in energy. Traditionally, the electropho tographiccommercial process known as xerography, has utilized small particles which contain a resin compound for several purposes. First, the xerographic process utilizes small particles, desirably in the range of from 10 to 20 Rm in diameter, which carry an electrostatic charge.Electrically insulating materials, typically resinous materials, adequately provide the desired particles which readily acquire and retain for a reasonable amount of time an electrostatic charge. At the same time, the xerographic process requires a particle which can be easily fused to the supporting substrate so as to provide a permanent image that can endure handling. The industry has adopted the use of resinous material for this purpose which material is normally treated in such a manner so as to allow the resin to attach itself by fusion to the supporting substrate, usually paper. In the majority of cases, the method utilized to attach the resin particle to the supporting substrate is a thermal treatment which raises the temperature of the particle above its glass transition temperature (Tg) thereby allowing the resin to flow onto the supporting substrate and attach itself thereto.The obvious approach to the solution of this problem is to use lower melting resins, but the toner material must be shipped, stored and handled within a machine, and it has been found that low melting resins will cause many problems in these areas due to blocking phenomenon and flow characteristics.

Typical resin toners of the prior art are described in papers such as U.S. 2,788,288 to Rheinfrank et al.

U.S. 2,891,011 to Insalaco and U.S. 3,326,848 to Clemens et al.

One approach to reduce the energy required to properly fix a resin toner to a substrate may be found in U.S. 3,681,107 to Moriconi et al. It is proposed therein to provide a vinyl resin toner particle containing a solid ester of o-phthalic or m-phthalic acid and a solid metal salt of a fatty acid. According to the examples in said patent, a commercial xerographic machine containing a fuser which normally operated at 315"C could be lowered by 38"C. In U.S. 3,893,934 to Braun et al, specific additive material is combined with the vinyl resin toner particle and has found to likewise reduce the required temperature of the fuserto obtain a suitable and comparative quality fixed image. This patent suggests the use of an arylsulfonamideformaldehyde adduct.

Another approach to reducing the required temperature for fixing the toner image to a substrate by fusion is found in U.S. 3,740,334 to Jacknow et al wherein the resin toner particle contains a solid additive having a melting point between 45"C and 135"C. Combined therewith as a mixture in the toner composition is a solid, stable hydrophobic metal salt of a fatty acid uniformly mixed with the toner material and available at the external surfaces thereof.

Yet another approach to reducing the temperature at which resinous material will adhere to a substrate by fusion in the xerographic art is found in U.S.

Patents 3,488,189 to Mayer et al and 3,493,412 to Johnston et al which teach the use of a solid crystalline plasticizer availble at the image bearing surface. The crystalline plasticizer is made available such as by mixing it with a binder and applying it to the surface of an image-receiving sheet whereupon the toner particle is heated in the presence of the crystalline plasticizer.

All of the above approaches have succeeded to some degree in reducing the amount of energy required to fix a resinous toner material to a substrate. However, with the ever increasing speed of xerographic machines, there is a continuing need to reduce further the energy required to fix a resinous toner to a substrate by means of heat.

Also in the prior art of xerography and the preparation of toner materials utilized therein, a considerable body of knowledge has been developed with respect to including a magnetic component with the resinous toner particle. Several reasons have been set forth for the introduction of magnetic particles into the toner such as to provide magnetic properties or to contribute color. For example, in U.S. 3,239,465, to Rheinfrank, a magnetic component is added to a resin toner material to provide magnetic transfer of the image from one surface to the other which method is independent of atmospheric conditions, as well as to provide magnetic images. Further, it was observed that magnetic particles could be fixed by means of high frequency electromagnetic radiation and thus, Rheinfrank suggests a broad range of concentrations of magnetic material and a resin toner.Such range of resin to magnetic component can vary from 19:1 to 2:3. Since this early beginning in the addition of magnetic material to a resin toner material, numerous examples could be mentioned and among them are U.S. 3,345,294 to Cooper and U.S. 3,627,682 to Hall, Jr. et al. In the former patent, magnetic and carbon black particles are mixed together with resin material to form a toner material. In the latter patent, a mixture of different types of magnetic material are introduced together with the resinous material, each type of magnetic material both being present in the same toner particle. Other coiorants such as carbon black or dyes are also suggested for the magnetic toner.

In accordance with this invention, there is provided a toner composition comprising a thermoplastic resin material having dispersed therein a crystalline plasticizer for said resin and a thermally conductive material such as iron oxide of the type previously utilized to provide magnetic properties to toner particles. It has now been discovered that the addition of crystalline plasticizer to the thermoplastic resin in combination with a thermally conductive material will reduce melt viscosity of the resin material to a surprising degree. That is, the combination of the crystalline plasticizer with the thermally conductive material greatly reduces the melt viscosity above the Tg and thus reduces the amount of energy required to fuse the toner material to a substrate.A reduction in fusing energy requirements of up to about 50 percent of that previously required is provided in accordance with this invention. Such great reduction in fusing temperature immediately suggests both an increase in speed of xerographic machines as well as reduction in the energy required to adequately fix an image comprising resinous toner material.

In accordance with this invention, a relatively small amount of thermally conductive material is added to the resin material in combination with crystalline plasticizer. In practice, any amount of thermally conductive material which cooperates with the crystalline plasticizer to reduce the melt viscosity of the resin material, may be employed.

Thus, any suitable amount of thermally conductive material in the resin material can be effectively utilized but is usually in the range of from 5 parts to 25 parts by weight based on 100 parts by weight of the resin. Of course, greater amounts of the thermally conductive material can be utilized in the resin material, but will not significantly further reduce the melt viscosity of the resin. In many applications, the thermally conductive material may exceed 25 or even 50 parts by weight to 100 parts by weight of the resin since magnetictoners are highly desirable for many reasons other than for the purpose of reducing the melt viscosity of the resin toner material.Should reduction in melt viscosity be the sole or primary objective, an amount of thermally conductive material up to 10 parts by weight is preferred since higher amounts do not significantly further reduce the melt viscosity.

As is well known, plasticizer added to resinous material dissolves therein. However, in accordance with this invention, the addition of plasticizer which has limited solubility in the resin provides crystalline aggregates in the thermoplastic resin which aid greatly in reducing the melt viscosity of the resin at fusing temperatures but does not affect the Tg of the resin under normal conditions of handling and use.

Accordingly, sufficient plasticizer is added to the resinous thermoplastic material to provide crystalline aggregates therein which, in combination with the thermally conductive additive, provides the desired reduced melt viscosity of the resin. Typically, amounts in the range of from 5 parts to 30 parts by weight based on 100 parts by weight of resin are sufficientto produce the desired reduction in melt viscosity, while an amount in the range of from 15 parts to 25 parts by weight appears optimum.

Obviously, the plasticizer to be dispersed in the resin material is determined by the resin material. As mentioned above, the plasticizer is chosen so as to have limited solubility in the resin at normal operating, handling and storage temperature. Thus, the plastitizer should have limited solubility so that crystalline aggregates of the plasticizer reside in the resin below 75"C. At an elevated temperature, such as 75"C, the plasticizer melts and induces reduced viscosity of the resin material at its melting point.

Typical plasticizers include the diphenyl phthalates, pentaerithrital tetrabenzoate, triphenylamine derivatives, low molecular weight polycaprolactones, polyepoxies, and the like.

As noted above, the state of the art of toner manufacture is highly developed and there is known numerous thermoplastic resinous materials which can be utilized as the base for toner material in the xerographic process. The above-mentioned patents contain numerous examples of thermoplastic resins to which the crystalline plasticizer and thermally conductive components of this invention can be added. For example, any suitable vinyl resin can be employed. Typical vinyl resins include vinyl esters, vinyl ethers, vinyl ketones, vinylidene halides, nvinyl compounds and mixtures thereof. Numerous examples of these, as well as vinyl esters of alphamethylene aliphatic monocarboxylic acids are known in the art as, for example, in the U.S. Patent 3,740,334. Further, other materials are taught in U.S.

Patent 3,079.342 to Insalaco particularly pointing out advantageous styrene methacrylate ester copolymers. Typical exempiary resin materials include styrene n-butyl-methacrylate copolymer and styrene/isobutyl methacrylate copolymer, with styrene generally comprising from 50 percent to 95 percent of the copolymer on a weight basis. Because of the combination of physical properties desired in a toner material, a particularly preferred resin is a copolymer having 60 percent styrene and 40 percent n-butyl methacrylate.

The thermally conductive material is typically a metal or metal oxide finely ground and blended evenly, in small amounts, with the resin to be utilized as the toner material. Generally, the particle size of the thermally conductive material is less than 1 tFtm.

As mentioned above, iron oxide is preferred because of its dense black color and also because of the magnetic properties it can contribute to the toner material. Other suitable thermally conductive materials can be employed. Typical thermally conductive materials include iron, ferrites, copper, aluminum, nickel, steel, aluminum oxide, ceramic materials, garnet and any other non-reactive material having a thermal conductivity greater than the resin material into which it is dispersed. Mixtures of suitable thermally conductive materials may also be used.

In accordance with this invention, the melt rheology behavior of the resin is significantly changed by incorporating a thermally conductive material such as black iron oxide (Fe3O4) in place of carbon black as a colorant in the toner material. The resin containing thermally conductive material has rheological properties close to Newtonian liquids whereas the same resin containing carbon black without the thermally conductive material is non Newtonian in behavior. The melt viscosity of the toner material of this invention is significantly reduced in comparison with toner materials containing only carbon black as a colorant. Thus, when utilizing thermally conductive materials such as black oxide as a colorant, such material has the dual functions of lowering the melt viscosity, as well as acting as a colorant for the toner particles.Obviously, the thermally conductive material must not react with or degrade the resin into which it is dispersed.

Also, the thermally conductive material may be incorporated into the toner material together with a colorant such as a dye or pigment. Conventional prior art dyes and pigments are usable herein. The dye or pigment should be present in amounts effective to render the toner highly coloured so that it will form a clearly visible image on a recording member. Generally less than 20 percent by weight of pigment based on the total weight of toner may be used. Carbon black is preferred because of its availability and dense black color which it imparts to the toner composition. Thus, carbon black can be dispersed in the resin material together with the thermally conductive material such as iron oxide and crystalline plasticizer to enhance the color of the toner.

The toner compositions of the present invention may be prepared by any well known toner mixing and comminution technique. For example, the ingredients may be thoroughly mixed by blending, mixing and milling the components and thereafter micropulverizing the resulting mixture. Another well known technnique for forming toner particles is to spray dry a ball milled toner composition comprising a colorant, a resin, the crystalline plasticizer and thermally conductive material of this invention and a solvent.

The incorporation of a distinct plasticizer phase in the resin toner particle of this invention constitutes a solid reservoir which does not significently affect the Tg or the blocking temperature of the solid toner material in any negative manner. Rather, the crystalline plasticizer and thermally conductive material reduce the toner viscosity at fixing temperature as will be more particularly described below.

Generally, the quality of toner fixing to a supporting substrate at a given temperature increases with a decrease in toner melt viscosity. Accordingly, the measurement of the melt viscosity of the toner aids in the determination of the degree of flow and penetration of the toner into the surface of a receiving substrate such as paper during the heat fixing step. The expression "melt viscosity" as employed herein, is a measure of the ratio of shear stress to shear rate in poise at a given temperature.

All viscosity measurements are determined using the Rheometrics Inc. Cone and Plate Mechanical Spectrometer.

When the toner mixtures of this invention are to be employed in a cascade or magnetic brush development process, the toner should have a particle size of less than 30 cm and preferably between 4 and 20 cm for optimum results. For use in powder cloud development methods, particle diameters of slightly less than one m are preferred.

Typically, coated and uncoated carrier materials for cascade and magnetic brush development are well known in the art and are useful with the toner materials of the present invention. Such carrier materials may comprise any suitable solid material provided that the carrier particles acquire a charge having an opposite polarity to that of the toner particles when brought into close contact with the toner particles so that the toner particles adhere to and surround the carrier particles. Typical carriers include sodium chloride, ammonium chloride, alu minum potassium chloride, granular zircon, methyl methacrylate, glass, silicon dioxide, nickel, steel, iron, ferrite and the like. The carriers may be employed with or without a coating. Many of the foregoing and other typical carriers are described in U.S. Patent 2,638,416 to Walkup et al, U.S.Patent 2,618,552 to Wise, and U.S. Patent 2,930,351 to Giamo. Generally, satisfactory results are obtained when 1 part toner is used with 10 to 200 parts by weight of carrier.

If desired, the toner compositions of the present invention may be applied to an electrostatic latent image as a single component developer without the presence of carrier particles. If the toner contains magnetically attractable components, the toner may be applied to the electrostatic latent image with the aid of a magnetic applicator.

The toner compositions of the present invention may be employed to develop electrostatic latent images on any suitable electrostatic latent image bearing surface including conventional photoconductive surfaces. Well-known photoconductive materials include vitreous selenium, organic or inorganic photoconductors embedded in a nonphotoconductive matrix, organic or inorganic photoconductors embedded in a photoconductive matrix or the like.

The invention will be more fully described with reference to the attached drawings wherein: Figure 1 is a graphical representation of log melt viscosities in poises of prior art materials in relation to various temperatures.

Figure 2 is a graphical representation of log melt viscosities in poises of both prior art materials and toner compositions of this invention in relation to various temperatures.

Figure 3 is a graphical representation of log log viscosities in poises of prior art materials in relation to shear rate.

Figure 4 is a graphical representation of log log viscosities in poises of both prior art materials and compositions of this invention in relation to shear rate.

As stated above, the degree of toner fix or the quality of fixing the toner material to an image receiving substrate is generally recognized as being related to the melt viscosity of the toner. A series of viscosity measurements are shown utilizing a resin typically found in high speed xerographic commercial equipment comprising a copolymer of 60 percent styrene and 40 percent n-butylmethacrylate, by weight. In the following description, parts and percentages are by weight. To 100 parts by weight of this copolymer is added 10 parts by weight carbon black as a colorant. The melt viscosity in poises at a shear rate of 1 sec.-1 at temperatures in the range of from 150 to 250"C are measured and presented in Figure 1 as Curve A. As noted above, all viscosities reported herein are in poises.To indicate the effect of adding a crystalline plasticizer to the resin, there is added 20 parts by weight m-diphenyl isophthalate based on 100 parts by weight of the copolymer to the composition of Curve A. On examination at 30"C of the toner material thus produced the plasticizer is found to exist in aggregates dispersed through the resin. The melt viscosity of this toner is measured in the range of 150 to 250"C and is presented in Figure 1 as Curve B.

In like manner, the effect on melt viscosity of the above-described styrene/n-butyl methacrylate copolymer resin toner is determined upon addition of iron oxide. To separate samples of 100 parts by weight of the above-desribed resin there is added 10 parts and 20 parts of black iron oxide. The melt viscosity of each sample is determined and is shown in Figure 2 wherein Curve C represents the resin with 10 parts by weight of black iron oxide added and Curve D showing the results provided bythetoner material with 20 parts by weight of the iron oxide added. In the compositions of Curves C and D, the black iron oxide totally replaces the carbon black as a colorant.

Toner material is then prepared in accordance with this invention by mixing 80 parts by weight of the above-described styrene/n-butyl methacrylate copolymer with 10 parts by weight of Mapico iron oxide (commercially available from the Columbian Carbon Company) and 20 parts by weight of metadiphenyl isophthalate. The melt viscosity was determined over a temperature range of from 130 to 230"C and is shown in Figure 2 as Curve E. To another 80 parts by weight of the copolymer, there is added 20 parts by weight of Mapico iron oxide and 20 parts by weight of diphenyl isophthalate. The melt viscosity was measured over the same temper- ature range as for Curve E and the results are shown in Figure 2 as Curve F. Again, the iron oxide is the only colorant of compositions of Curves E and F.

The rheological properties of the various toner composites described above are also compared in terms of the shear rate and viscosity. The data obtained are shown in Figures 3 and 4 as log curves of melt viscosity versus shear rate for the compositions described above with respect to Figures 1 and 2. The viscosity data are determined at two different temperatures and indicated in Figures 3 and 4. The letter designations on the curves of Figures 3 and 4 refer to the same compositions having the same letter designations as the curves in Figure 1 and 2.

The above data demonstrate that replacement of carbon black with a thermally conductive material, as well as the addition of the crystalline plasticizer, significantly reduces the melt viscosity of the toner composite. For example, comparison of Curve A of Figure 1 with Curve E of Figure 2 indicates that the melt viscosity was reduced 37.5 times by the substitution of the thermally conductive material and addition of a crystalline plasticizer in the resin particles. The addition of the crystalline plasticizer and the thermally conductive material clearly has a synergistic effect in decreasing the melt viscosity of composite material.Although it is proposed herein to utilize iron oxide to replace carbon black as the colorant, it is fully understood that carbon black can be utilized together with thermally conductive materivals such as iron oxide for the purpose of enhancing the black color of the toner. The amount of carbon black is determined by the color desired as in the prior art oftonertechnology as represented by the patents referred to above.

1 part by weight of a toner of the present invention containing 100 parts by weight of a copolymer of 60 parts by weight of styrene and 40 parts by weight of n-butylmethacrylate, 10 parts by weight of black iron oxide, and 20 parts by weight of meta-diphenyl isophthalate and having an average particle size of 12 pm is mixed with 10 parts by weight of magnetically attractable carrier particles comprising steel shot particles having an average particle size of 250 ym coated with a thin coating of a terpolymer of vinyl triethoxy silane, butylmethacrylate and styrene. The resulting developer mixture is applied by a rotating cylindrical magnetic brush applicator to an electrostatic latent image on a selenium alloy photoreceptor drum to form a toner image conforming to the electrostatic latent image on the drum.The deposited toner image is then electrostatically transferred to a paper sheet and fused between internally heated rollers treated with silicon oil. Because of the significantly lower melt viscosity of this toner, the fuser rolls may be operated at a lower temperature or, alternatively, the throughput of the imaged paper sheets between the fuser rolls may be increased without adversely affecting the quality of the fixed toner image. Obviously, heat energy savings andior increased fuserthroughput may be achieved with other types of known fusing systems such as flash fusers and radiant fusers. These fusers can employ, for example, xenon flash lamps or resistive wire heating elements. Thus, it is clearly apparent that similar results may be achieved by substituting flash fusing or radiant fusing for roll fusing.

It is also to be understood that the abovedescribed methods and arrangements are simply illustrative of the application of the principles of the invention and that many modifications may be made without departing from the spirit and scope thereof.

For example, the toner compositions of this invention may be combined with dopants and additives to improve various physical properties of the toner and its performance in imaging devices. Moreover, the toner may be used with or without carrier particles.

The toner compositions of this invention may be utilized in dry or liquid development processes and various materials may be added thereto to render such compositions more effective or efficient for such purposes. Such additives and dopants are well known in the prior art and are intended to be within the scope of this invention.

Claims (10)

1. An electrophotographic toner composition comprising a resin material having dispersed therein a crystalline plasticizer for said resin and a thermally conductive material.

2. A composition of Claim 1, wherein the thermally conductive material is present in the range of from 5 to 25 parts by weight based on 100 parts of said resin.

3. A composition of Claim 1 or 2, wherein the crystalline plasticizer is present in the range of from 5 to 30 parts by weight based on 100 parts of said resin.

4. A composition of Claims 2 and 3, wherein the crystalline plasticizer is present in the range of from 15 to 25 parts by weight, and the thermally conductive material is present in the range of 5 to 25 parts by weight based on 100 parts of said resin.

5. A composition of any preceding claim, wherein the resin is a styrene and methacrylate ester copolymer.

6. A composition of any preceding claim, wheren the thermally conductive material is iron oxide.

7. A composition of Claim 6, wherein the iron oxide is also the principal colorant for the toner.

8. A composition of Claim 6, further including carbon black to enhance the color of the toner.

9. A composition of any preceding claim, wherein the crystalline plasticizer is diphenyl isophthalate.

10. A composition of any of claims 1-3, wherein the resin is a vinyl resin.