Toner with two crosslinked polyesters

Abstract: A process for preparing low fix temperature toner resin mixture comprising melt blending a resin mixture comprised of a first polyester resin with a low gloss value, and a second polyester resin with a high gloss value, to form a toner resin mixture having an intermediate gloss value.

Description: The present invention is generally directed to processes for the preparation of toner resins and toners. Toner utilized in development in the electrographic process is generally prepared by mixing and dispersing a colorant and a charge enhancing additive into a thermoplastic binder resin, followed by micropulverization. As the thermoplastic binder resin, numerous polymers are known, including polystyrenes, styrene-acrylic resins, styrene-methacrylic resins, polyesters, epoxy resins, acrylics, urethanes and copolymers thereof. As the colorant, carbon black, magnetite and various colored pigments may be selected, and as the charge enhancing additive, alkyl pyridinium halides, distearyl dimethyl ammonium methyl sulfate, metallic alkyl salicylates, and the like are known. To fix the toner to a support medium, such as a sheet of paper or a transparency, hot roll fixing is commonly used. In this method, the support medium carrying a toner image is transported between a heated fuser roll and a pressure roll, with the image face contacting the fuser roll or belt. Upon contact with the heated fuser roll or belt, the toner melts and adheres to the support medium, forming a fixed image. Such a fixing system is very advantageous in heat transfer efficiency and is especially suited for high speed electrophotographic processes. Fixing performance of the toner can be characterized as a function of temperature. The lowest temperature at which the toner adheres to the support medium is called the Cold Offset Temperature (COT), and the maximum temperature at which the toner does not adhere to the fuser roll is called the Hot Offset Temperature (HOT). When the fuser temperature exceeds HOT, some of the molten toner adheres to the fuser roll during fixing and is transferred to subsequent substrates containing developed images, resulting for example in blurred or extraneous images This undesirable phenomenon is called offsetting. Between the COT and HOT of the toner, is the Minimum Fix Temperature (MFT) which is the minimum temperature at which acceptable adhesion of the toner to the support medium occurs, as determined by, for example, a creasing test. The difference between MFT and HOT is called the Fusing Latitude, and the temperature range therebetween is referred to'the fusing range. The hot roll or belt fixing system and a number of toners used therein, however, exhibit several problems. First, the binder resins in the toners can require a relatively high temperature in order to be affixed to the support medium. This may result in high power consumption. Low vinyl type binder resins such as styrene-acrylic resins may have an additional problem known as vinyl offset. Vinyl offset occurs when a sheet of paper or transparency with a fixed toner image comes in contact for a period of time with, for example, a polyvinyl chloride (PVC) surface containing a plasticizer used in making the vinyl material flexible such as, for example, in vinyl notebook binder covers, and the fixed image adheres to the PVC surface. Another problem, particularly for highlight and process color applications is the inability to readily form images which have variable or operator selectable gloss properties, for example, images having colored regions with high gloss levels and black regions, for example text regions, with low or intermediate gloss levels. US-A-4 863 824 discloses a process to produce a low-fix temperature toner resin by mixing two non-linear polyesters having specific amount of chloroform insolubles. It is an object of the present invention to provide simple and economical processes for the preparation of toners with many of the advantages illustrated herein. Accordingly, the present invention provides a process, method of imaging and low melt toner as defined in the appending claims. The present invention will be described further, by way of examples, with reference to the accompanying drawings, in which:- Figure 1 illustrates the effect of crosslinked gel content levels in toner resin blends on the gloss properties measured in Gardner Gloss Units of the fixed toner images measured at 0.74 toner mass per unit area of the present invention; Figure 2 illustrates the effect of crosslinked gel content levels in toner resin blends on the gloss properties measured in Gardner Gloss Units of the fixed toner images measured at 1.05 toner mass per unit area of the present invention; and Figure 3 is a partial schematic cross-sectional view of an extrusion apparatus suitable for the processes of the present invention. The present invention provides a process for fabricating low fix temperature toner resins by non-reactive melt mixing in any melt mixing device, batch or continuous, but preferably continuous such as, for example, an extruder wherein a first partially crosslinked polyester base resin with a low gloss value is melt mixed with a second polyester resin with a high gloss value, under high shear conditions, to form a toner resin mixture having an intermediate gloss value, and wherein the first polyester resin is present in an amount of from 20 to 80 weight percent of the resin mixture and contains of from 20 to 40 weight percent crosslinked gel content and has a gloss value of from 5 to 10 gloss units, and the second polyester resin is present in an amount of from 80 to 20 weight percent of the resin mixture and contains from 5 to 15 weight percent crosslinked gel content and has a gloss value of from 20 to 30 gloss units, and wherein the resulting melt blended toner resin mixture has an intermediate gloss value of 10 to 25 gloss units. The term "non-reactive" as used herein means substantially no increase in gel content or no increase resin molecular weight is observed during the melt mixing or blending of the polyester resins and toner components, while small amounts of gel breakdown and minor decreases in molecular weight as a result of the high shear melt mixing step, may be observed. In an embodiment, the first polyester resin is present in an amount of from 20 to 80 weight percent of the resin mixture and contains of from 20 to 40 weight percent crosslinked gel content and has a gloss value of from 5 to 10 gloss units, and the second polyester resin is present in an amount of from 80 to 20 weight percent of the resin mixture and contains from 0 to 15 weight percent crosslinked gel content and has a gloss value of from 20 to 75 gloss units, and wherein the resulting melt blended toner resin mixture has an intermediate gloss value of 10 to 70 gloss units. Toner resins prepared by a process related to the present invention are disclosed in detail in the aforementioned US-A-5,227,460. Low fix temperature toner resins are formulated in embodiments by a melt mixing process comprising: melt mixing under high shear, at a temperature of about 70 to about 160°C, a base polyester resin containing a partially crosslinked polyester fraction, and a second polyester resin which contains a partially crosslinked polyester fraction, or preferrably the second polyester resin contains essentially only linear unsaturated and uncrosslinked resin with molecular weight properties which are different from the base polyester resin mixture, thereby forming a polymer melt; and thereafter cooling, crushing, grinding, and classifying the toner composition into suitably sized toner particles. In a preferred embodiment, a low fix temperature toner resin mixture is formulated by a process comprising preblending a first polyester base resin containing from about 20 to about 35 weight percent of crosslinked gel, a second polyester resin containing from 0 to about 15 weight percent of crosslinked gel, and optional toner additives, such as carbon black, colored pigments and charge additives; feeding the mixture to an extruder; gently heating the mixture at a temperature above the glass transition temperature of the base resin component and the second resin component, for example, above about 70 °C but below a temperature above which the the unsaturated polyester component begins to undergo thermally induced crosslinking or degradation reactions, such as above about 200 °C, to obtain a melt mixture of the first and second polyester resins and to further disperse the optional additives therein while avoiding significant thermal degradation or crosslinking; keeping the melt mixture in the extruder for a sufficient residence time for example, 10 seconds to about 10 minutes, at a given temperature such that the required amount of mixing and dispersion is achieved; providing sufficiently high shear during the melt mixing thereby keeping any crosslinked gel particles originally present in the mixture small in size and well distributed in the polymer melt; optionally devolatilizing the melt to remove any effluent volatiles; and pumping the cross-linked resin melt mixture through a die to a pelletizer. The weight ratio of the first polyester to the second polyester, in embodiments, is from about 1:3 to about 3:1 depending upon the gloss and fusing properties desired. The resulting solidified toner mixture can then be pulverized and classified to obtain particles of desirable size and distribution. The solidified toner can be directly reextruded as a solid mass or subsequent to pulverization and classification into particles. The pigmented toner composition that results from dispersive melt mixing or blending in the present process invention contains resin which is comprised of mixtures of crosslinked or gel portions or mixtures of crosslinked and linear portions. The crosslinked portions comprise very high molecular weight densely crosslinked microgel particles having average diameter less than about 0.1 micron and are insoluble in substantially most any solvent, including tetrahydrofuran, toluene, and the like solvents, and macrogel particles having average diameter greater than about 0.1 micron. The linear portion comprises lower molecular weight resin molecules which are soluble in various solvents such as, for example, tetrahydrofuran, toluene and the like. The high molecular weight highly crosslinked gel particles are preferrably substantially uniformly distributed within the linear or uncrosslinked resin portions upon completion of the melt blending. In the process of the present invention, the fabrication of gloss controllable resin and toner compositions thereof may be carried out in a melt mixing device such as an extruder described in US-A-4,894,308. Generally, any high shear, temperature controllable melt mixing device suitable for processing polymer melts may be employed, provided that the objectives of the present invention are achieved. Examples of continuous melt mixing devices include single screw extruders or twin screw extruders, continuous internal mixers, gear extruders, disc extruders and roll mill extruders. Examples of batch internal melt mixing devices include Banbury mixers, Brabender mixers, and Haake mixers. One suitable type of extruder is the fully intermeshing co-rotating twin screw extruder such as, for example, the ZSK series of twin screw extruders available from Werner & Pfleiderer Corporation, Ramsey, New Jersey, U.S.A. For example, a small ZSK-40 twin screw extruder has a screw diameter of 40 millimeters and a length-to-diameter (UD) ratio of 52.5. The extruder can melt the base resin, disperse optional toner additives and colorants into the uncrosslinked or partially crosslinked resins, optionally devolatilize the melt to remove any effluent volatiles if needed, and pump the melt through a die such as, for example, a strand die to a pelletizer. With reference to Figure 1, there is shown the effect of crosslinked gel content levels in toner resin blends on the gloss properties measured in Gardner Gloss Units (GGU) of fixed toner images measured at 0.74 toner mass per unit area (milligrams per square centimeter) at 370°F (188°C). Composition "A" is a toner comprised of an unblended 7 percent by weight gel containing crosslinked polyester which has a relatively high gloss value of about 22 GGU. Composition "B" is a toner comprised of an unblended 30 percent by weight gel containing crosslinked polyester which has a relatively low gloss value of about 7 GGU. Composition "C" is a toner comprised of a 2:1 weight ratio of the 30 percent by weight gel containing crosslinked polyester and 7 percent by weight gel containing crosslinked polyester and a total gel content of about 14 weight percent. This blended toner has an intermediate gloss value of about 14 GGU and which gloss is approximately midway between the unblended toner compositions "A" and "B". Composition "D" is a toner comprised of a 1:2 weight ratio of the 30 percent by weight gel containing crosslinked polyester and 7 percent by weight gel containing crosslinked polyester, respectively, with a total gel content of about 9 percent by weight. This blended toner has a gloss value of about 20 GGU, and is also an intermediate gloss value between the unblended toner compositions "A" and "B". With further reference to Figure 2, there is shown another example of the effect of crosslinked gel content levels in toner resin blends on the gloss properties measured in Gardner Gloss Units of fixed toner images measured at 1.05 toner mass per unit area at 370°F (188°C). Composition "A" is a toner comprised of an unblended 7 percent by weight gel containing crosslinked polyester which has a relatively high gloss value of about 28 GGU. Composition "B" is a toner comprised of an unblended 30 percent by weight gel containing crosslinked polyester which has a relatively low gloss value of about 8 GGU. Composition "C" is a toner comprised of a 2:1 weight ratio of the 30 percent by weight gel containing crosslinked polyester and 7 percent by weight gel containing crosslinked polyester, respectively, and a total gel content of about 14 weight percent. This toner has an intermediate gloss value of about 16 GGU and is an intermediate gloss value between the unblended toner compositions "A" and "B". Composition "D" is a toner comprised of a 1:2 weight ratio of the 30 percent by weight gel containing crosslinked polyester and 7 percent by weight gel containing crosslinked polyester, respectively, and a total gel content of about 8 weight percent, and which toner has an intermediate gloss value of about 25, which is intermediate between the unblended toner compositions "A" and "B". For a better understanding of the present invention, a typical extrusion apparatus suitable for the process of the present invention is illustrated in Figure 3. Figure 3 shows a twin screw extrusion device 1 containing a drive motor 2, a gear reducer 3, a drive belt 4, an extruder barrel 5, a screw 6, a screw channel 7, an upstream supply port or hopper 8, a downstream supply port 9, a downstream devolatilizer 10, a heater 11, a thermocouple 12, a die or head pressure generator 13, and a pelletizer 14. The barrel 5 consists of modular barrel sections, each separately heated with heater 11 and temperature controlled by thermocouple 12. With modular barrel sections, it is possible to locate feed ports and devolatilizing ports at required locations, and to provide segregated temperature control along the screw channel 7. The screw 6 is also modular, enabling the screw to be configured with modular screw elements and kneading elements having the appropriate lengths, pitch angles, and the like, in such a way as to provide optimum conveying, mixing, reaction, devolatilizing and pumping conditions. In operation, the components to be non-reactively blended and extruded, for example, the base resin and the second polyester resin component, enter the extrusion apparatus from the first upstream supply port 8 and/or second downstream supply port 9. The base resin and the second polyester resin component, usually in the form of solid pellets, chips, granules, or other forms can be fed to the first upstream supply port 8 and optionally to second downstream supply port 9 by starve feeding, gravity feeding, volumetric feeding, loss-in-weight feeding, or other known feeding methods. Heating takes place from two sources: (1) external barrel heating from heaters 11, and (2) internal heating from viscous dissipation and shear within the polymer melt itself. The rotational speed of the extruder screw preferably ranges from about 50 to about 500 revolutions per minute. If needed, volatiles may be removed through downstream devolatilizer 10 by applying a vacuum. At the end of screw channel 7, the cross-linked resin is pumped in molten form through die 13, such as for example a strand die, to pelletizer 14 such as, for example, a water bath pelletizer, underwater granulator, etc. With further reference to Figure 3, the rotational speed of the screw 6 can be of any suitable value provided that the objectives of the present invention are achieved. Generally, the rotational speed of screw 6 is from about 50 revolutions per minute to about 500 revolutions per minute. The barrel temperature, which is controlled by thermocouples 12 and generated in part by heaters 11, is from about 70°C to about 160°C, and preferrably from about 90 to about 110°C. The temperature range for mixing the base resin and second polyester resin mixture and optional additives in the upstream barrel zones is from about the melting temperature of the base resin to below the cross-linking onset temperature, and preferably within about 40°C of the melting temperature of the base resin. For example, for an unsaturated polyester base resin the temperature is preferably about 90°C to about 130°C. The die or head pressure generator 13 generates pressure from about 50 pounds per square inch to about 500 pounds per square inch. In one embodiment, the screw is allowed to rotate at about 100 revolutions per minute, the temperature along barrel 5 is maintained at about 70°C in the first barrel section and 160°C further downstream, and the die pressure is about 50 pounds per square inch. When melt mixing in a batch internal melt mixing device, the residence time is preferably in the range of about 10 seconds to about 10 minutes. The rotational speed of a rotor in the device is preferably about 10 to about 500 revolutions per minute. Thus, in a process of the present invention, a base resin and a second polyester resin in admixture with optional toner additives, are fed to a melt mixing apparatus and non-reactive melt mixing is carried out at low to moderate temperatures and specified above and at high shear to produce a resin blend which enables the preparation of low fix temperature toners with good fusing latitude and low vinyl offset properties, and intermediate gloss properties as illustrated herein. The base resin used in the process of this invention is a polymer, preferably a linear polymer such as a linear unsaturated polyester. In preferred embodiments, the base resin has a degree of unsaturation of about 0.1 to about 65 mole percent, preferably about 1 to about 50 mole percent. In a preferred embodiment, the linear unsaturated polyester base resin is characterized by number-average molecular weight (M n ) as measured by gel permeation chromatography (GPC) in the range typically from 1,000 to about 20,000, and preferably from about 2,000 to about 5,000, weight average molecular weight (M w ) in the range typically from 2,000 to about 40,000, and preferably from about 4,000 to about 15,000. The molecular weight distribution (M w /M n ) is in the range typically from about 1.5 to about 6, and preferably from about 2 to about 4. The onset glass transition temperature (T g ) for the base resin as measured by differential scanning calorimetry (DSC) is in the range typically from 50°C to about 70°C, and preferably from about 51°C to about 60°C. Melt viscosity as measured with a mechanical viscometer at 10 radians per second is from about 5,000 to about 200,000 poise, and preferably from about 10,000 to about 100,000 poise, at 100°C and drops sharply with increasing temperature to from about 100 to about 5,000 poise, and preferably from about 250 to about 2,000 poise, as temperature rises from 100°C to 130°C. Linear unsaturated polyesters used as the base resin are, in embodiments, low molecular weight condensation polymers which may be formed by the step-wise reactions between both saturated and unsaturated diacids, diesters or anhydrides and dihydric alcohols such as glycols or diols. The resulting unsaturated polyesters are reactive, that is cross-linkable, in two respects: (i) unsaturation sites (double bonds) along the polyester backbone chain; and (ii) functional groups such as carboxyl, hydroxy, and the like, groups amenable to acid-base or condensation reactions. Typical unsaturated polyesters useful for this invention are prepared by melt polycondensation or other polymerization processes using diacids, diesters and/or anhydrides and diols. Suitable diacids and anhydrides include but are not limited to saturated diacids and/or anhydrides such as, for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic add, isophthalic acid, terephthalic acid, hexachloroendomethylene tetrahydrophthalic acid, phthalic anhydride, chlorendic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, endomethylene tetrahydrophthalic anhydride, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, and the like, diesters derived therefrom and mixtures thereof; and unsaturated diacids and/or anhydrides such as, for example, maleic acid, fumaric acid, chloromaleic acid, itaconic acid, citraconic acid, mesaconic acid, maleic anhydride, diesters thereof, and the like, and mixtures thereof. Suitable diols include, but are not limited to, for example, propylene glycol, ethylene glycol, diethylene glycol, neopentyl glycol, dipropylene glycol, dibromoneopentyl glycol, propoxylated bisphenol-A, ethoxylated bisphenol-A, 2,2,4-trimethylpentane-1,3-diol, tetrabromo bisphenol dipropoxy ether, 1,4-butanediol, 1,3 butanediol, and the like, and mixtures thereof, soluble in highly dissolving solvents such as, for example, tetrahydrofuran, toluene, and the like. Preferred linear unsaturated polyester base resins are prepared from diacids, diesters and/or anhydrides such as, for example maleic anhydride, fumaric acid, and the like and mixtures thereof, and diols such as, for example, propoxylated bisphenol-A, propylene glycol,1,3 butanediol, and the like, and mixtures thereof. A particularly preferred polyester is poly(propoxylated bisphenol A fumarate). Substantially any suitable unsaturated polyester can be used in the process of the invention, including unsaturated polyesters known for use in toner resins and including unsaturated polyesters whose properties previously made them undesirable or unsuitable for use as toner resins but which adverse properties are eliminated or reduced by introducing a crosslinked gel component therein and thereafter forming a melt mixture with a second polyester resin component as illustrated herein. Other suitable unsaturated polyester compounds are disclosed in "UNSATURATED POLYESTERS: STRUCTURE AND PROPERTIES", by Herman V. Boenig, p. 17, Elsevier Publishing Co., New York, (1964), and the aforementioned commonly owned US-A-5,227,460. Any appropriate initiation technique for cross-linking may be used to introduce the crosslinked content into the base resin or into the second polyester resin prior to melt mixing the base resin and the second resin to prepare the toner compositions of the present invention. Crosslinking techniques and processes suitable for preparing partially crosslinked resin mixtures for use in the present invention are described in commonly assigned US-A-4,894,308 and copending application USSN 08/393,606. Free radical initiators such as, for example, organic peroxides or azo compounds are preferred for this process. Suitable organic peroxides include diacyl peroxides such as, for example, decanoyl peroxide, lauroyl peroxide and benzoyl peroxide, ketone peroxides such as cyclohexanone peroxide and methyl ethyl ketone, alkyl peroxyesters such as, for example, t-butyl peroxy neodecanoate. Suitable azo compounds include 2,2'-azobis(isobutyronitrile), and other similar known compounds. Minor amounts, of less than about 10 weight percent of the resin content, of a diluent resin may be employed to provide improved compatibility, hot melt flowability, and the like properties. For example, useful diluent resins include resins or waxes without olefinic double bonds, carboxylic acids or hydroxyl groups, other functional groups which are not readily abstracted by free radical species under the conditions of the present process, such as methyl terpolymer, a polyvinylidine fluoride, a polymethyl methacrylate, hydrogenated poly(styrene-butadiene), polystyrene methacrylate, polyvinyl chloride, a wax component with a weight average molecular weight from about 1,000 to about 6,000, and mixtures thereof, for example, mixtures of from 2 to 4 diluent resin or wax components. The crosslinked portions of the partially crosslinked resin component can be of very high molecular weight microgel particles with high density crosslinking as measured by gel content and which are not soluble in substantially any solvents such as, for example, tetrahydrofuran, toluene, and the like. The microgel particles are highly crosslinked polymers with a short cross-link interpolymeric separation distances. The linear portions of the partially crosslinked resin component or components have number average molecular weight (M n ), weight average molecular weight (M w ), molecular weight distribution (M w /M n ), onset glass transition temperature (T g ) and melt viscosity substantially the same as the base resin without crosslinked gel content. In embodiments, the partially crosslinked unsaturated polyester base resin when melt blended with a second unsaturated polyester enables the preparation of toners with minimum fix temperatures in the range of about 100°C to about 200°C, preferably about 100°C to about 160°C, more preferably about 110° to about 150°C. Also, these low fix temperature toners have fusing latitudes ranging from about 10°C to about 120°C and preferably more than about 20°C and more preferably more than about 30°C. Processes of the invention can produce toner resins and thus toners with minimized or substantially no vinyl offset. The melt mixed resin blends of the present invention have the important rheological property of allowing a toner prepared therefrom to show low fix temperature and high offset temperature. The low fix temperature is believed to be a function of the molecular weight and the molecular weight distribution of the linear portion, and is not believed to be significantly affected by the amount of microgel or degree of cross-linking in the resin. In addition to rendering a unique rheological property to the toner resin not attainable in conventional crosslinking processes for preparing toner resins, the melt mixing processes of the present invention have several other important advantages. By choosing the type and molecular weight properties of the base resin, the minimum fix temperature can be easily manipulated The hot offset temperature can also be easily manipulated by controlling the gel content in the partially crosslinked resin which can be in turn be regulated by the amount of free radical initiator, and vinyl monomer used in preparing the starting crosslinked resin materials. Thus, it is possible to produce a series of resin blends and thus toners with operator selectable gloss properties. The blended resins are generally present in the toner in an amount of from about 40 to about 98 percent by weight, and more preferably from about 70 to about 98 percent by weight, although they may be present in greater or lesser amounts, provided that the objectives of the invention are achieved. For example, toner resin produced by the process of the invention can be subsequently melt blended or otherwise mixed with a colorant, charge carrier additives, surfactants, emulsifiers, pigment dispersants, flow additives, and the like. The resultant product can then be pulverized by known methods such as milling to form toner particles. The toner particles preferably have an average volume particle diameter of about 5 to about 25, more preferably about 5 to about 15 microns. Various suitable colorants can be employed in toners of the invention, including suitable colored pigments, dyes, and mixtures thereof including carbon black, such as Regal 330® carbon black (Cabot), Acetylene Black, Lamp Black, Aniline Black, Chrome Yellow, Zinc Yellow, Chrome Orange, Cadmium Red, Hostaperm Pink, Rhodamine Lake B, Brilliant Carmine, Heliogen Blue, Hostaperm, Hostaperm Green, titanium dioxide, cobalt, nickel, iron powder, Sicopur 4068 FF, and iron oxides such as Mapico Black (Columbia), mixtures thereof and the like. The colorant, preferably carbon black; cyan, magenta and/or yellow colorant, is incorporated in an amount sufficient to impart the desired color to the toner. In general, pigment or dye is employed in an amount ranging from about 2 to about 60 percent by weight, and preferably from about 2 to about 7 percent by weight for color toner and about 3 to about 50 percent by weight for black toner. Various known suitable effective positive or negative charge enhancing additives can be selected for incorporation into the toner compositions produced by the present invention, preferably in an amount of about 0.1 to about 10, more preferably about 1 to about 3, percent by weight Examples include zinc stearate and quaternary ammonium compounds inclusive of alkyl pyridinium halides; alkyl pyridinium compounds, reference US-A-4,298,672; organic sulfate and sulfonate compositions, reference US-A-4,338,390; cetyl pyridinium tetrafluoroborates; distearyl dimethyl ammonium methyl sulfate; aluminum salt complexes such as Bontron E84™ or E88™ (Hodogaya Chemical); and the like. Additionally, other internal and/or external additives may be added in known amounts for their known functions. The resulting toner particles optionally can be formulated into a developer composition by mixing with carrier particles. Illustrative examples of carrier particles that can be selected for mixing with the toner composition prepared in accordance with the present invention include those particles that are capable of triboelectrically obtaining a charge of opposite polarity to that of the toner particles. Accordingly, in one embodiment the carrier particles may be selected so as to be of a negative polarity in order that the toner particles which are positively charged will adhere to and surround the carrier particles. Illustrative examples of such carrier particles include granular zircon, granular silicon, glass, steel, nickel, iron ferrites, silicon dioxide, and the like. Additionally, there can be selected as carrier particles nickel berry carriers as disclosed in US-A-3,847,604, comprised of nodular carrier beads of nickel, characterized by surfaces of reoccurring recesses and protrusions thereby providing particles with a relatively large external area. Other carriers are disclosed in US-A-4,937,166 and 4,935,326. The selected carrier particles can be used with or without a coating, the coating generally being comprised of fluoropolymers, such as polyvinylidene fluoride resins, terpolymers of styrene, methyl methacrylate, a silane, such as triethoxy silane, tetrafluoroethylenes, other known coatings and the like. The diameter of the carrier particles is generally from about 50 microns to about 1,000 microns, preferably about 200 microns, thus allowing these particles to possess sufficient density and inertia to avoid adherence to the electrostatic images during the development process. The carrier particles can be mixed with the toner particles in various suitable combinations. Best results are obtained when about 1 part carrier to about 10 parts to about 200 parts by weight of toner are mixed. Toners produced by the process of the invention can be used in known electrostatographic imaging methods, although the fusing energy requirements of some of those methods can be reduced in view of the advantageous fusing properties of the subject toners as discussed herein. Thus, for example the toners or developers can be charged, for example, triboelectrically, and applied to an oppositely charged latent image on an imaging member such as a photoreceptor or ionographic receiver. The resultant toner image can then be transferred, either directly or via an intermediate transport member, to a support such as paper or a transparency sheet. The toner image can then be fused to the support by application of heat and/or pressure, for example with a heated fuser roll at a temperature lower than 200°C, preferably lower than 150°C. The invention will further be illustrated in the following, non-limiting examples, it being understood that these examples are intended to be illustrative only and that the invention is not intended to be limited to the materials, conditions, process parameters and the like recited herein. Parts and percentages are by weight unless otherwise indicated. EXAMPLE I Preparation of a 7 Weight Percent Gel Content Resin . A 7 weight percent partially crosslinked polyester was prepared by mixing 0.5% by weight benzoyl peroxide with 99.5% by weight of an unsaturated polyester resin HETRON 3091T, available from Ashland Chemical Company as follows. The dry mixture was tumble blended at room temperature for about 30 minutes to ensure proper mixing before crosslinking by reactive extrusion. The processing conditions were as follows: Extruder (Model GSK-40) with a barrel temperature profile of 40/40/180/180/180/180/180/180/180/150/150°C; Screw Speed: 300 rpm; and Feed Rate: 300 lb/hr. The partially crosslinked resin obtained had a melt index of 9.1g/10 min measured at 117°C, using 2.16 kg weight and a gel content of 7 weight percent as measured by GPC and filtration methods. TONER A: Preparation of a 7 Weight Percent Gel Content Toner. A toner was prepared by tumble blending for 30 minutes at room temperature a mixture of 95% weight percent of the above resin containing about 7 weight percent partially crosslinked polyester with about 5 weight percent Regal® 330 carbon black. The dry mixture was then melt mixed in an extruder as follows: Extruder (Model GSK-40) with a barrel temperature profile of 90/90/90/90/90/90/90/90/90/90/90/110°C; screw speed: 240 rpm; feed rate: 200 lb/hr; and water injection: 3 weight percent. The resultant toner was evaluated for fusing performance and image gloss in accordance with the general procedures disclosed in the aforementioned commonly owned U.S. Patent No. 5,376,494. The image gloss was 28 Gardner Gloss Unit at 370°F and at 1.05 developed toner mass per unit area (TMA, in milligrams per square centimeter). This toner provided a fuser a roll life of only 16,200 prints prepared on, for example, a Xerox Corporation Model 5090 machine. EXAMPLE II Preparation of a 30 Weight Percent Gel Content Resin . A 30 weight percent partially crosslinked polyester was prepared by mixing 1.0% by weight benzoyl peroxide with 99.0% by weight of an unsaturated polyester resin, Hetron 3091T available from Ashland Chemical Company as follows. The dry mixture was tumble blended at room temperature for about 30 minutes to ensure proper mixing before crosslinking. The processing conditions were as follows: Extruder (Model GSK-40) with a barrel temperature profile of 40/40/170/170/170/170/170/170/170/150/150 °C; screw speed of 300 rpm; and feed rate of 300 lb/hr. The partially crosslinked resin obtained had a melt index of 6.3g/10 min measured at 117 °C, using 16.6 kg weight, and a gel content of 30 weight percent. TONER B: Preparation of a 30 Weight Percent Gel Content Toner. A toner was prepared with the above partially crosslinked 30 weight percent gel content resin by tumble blending for 30 minutes at room temperature a mixture of 95% weight percent of the above 30 weight percent partially crosslinked polyester resin and 5 weight percent Regal® 330 carbon black. The dry mixture was then melt mixed in an extruder as follows: Extruder (Model ZSK-40) with a barrel temperature profile of 120/120/120/90/90/90/90/90/90/90/90/110°C; screw speed of 240 rpm; feed rate of 200 lb/hr; and water injection of 3 weight percent The resultant toner was evaluated for fusing performance and image gloss. The image gloss was 8.3 Gardner Gloss Units at 370°F and at 1.05 TMA. This toner provided a fuser a roll life of greater than 81,000 prints, at which time the test was terminated. EXAMPLE III TONER C: Preparation of Intermediate Image Gloss Toner by Blending Low and High Gel Content Resins. A toner with intermediate gloss properties was prepared as follows. A mixture of 63 percent by weight of high gel content HETRON 3091T resin from Example II and 32 percent by weight of low gel content HETRON 3091T resin from Example I were tumbled blended with 5 weight percent Regal® 330 carbon black for 30 minutes. The mixture was then melt mixed in an extruder at the following conditions: Extruder (Model GSK-28) with a barrel temperature profile: 120/115/115/115/115°C; screw speed: 250 rpm; and feed rate: 6 lb/hr. The resultant toner with a gel content of about 14 weight percent was evaluated for fusing performance and had a image gloss of about 17 Gardner Gloss units at 370°F and at 1.05 TMA. This gloss is approximately intermediate between the 8.3 and the 28 of the toners mixtures formed in Example I and II, respectively. Thus, is possible to readily obtain a large number of toners with intermediate gloss values by properly blending various ratios of two different resins or toners which have different crosslinking levels and different gloss levels. EXAMPLE IV TONER D: Preparation of Intermediate Image Gloss Toner by Blending Low and High Gel Content Resins . A toner with intermediate gloss properties was prepared as follows. A mixture of 32 percent by weight of high gel content HETRON 3091T resin from Example II and 63 percent by weight of low gel content HETRON 3091T resin from Example I were tumbled blended with 5 weight percent Regal 330® carbon black for 30 minutes. The mixture was then melt mixed in an extruder at the following conditions: Extruder (Model GSK-28) with a barrel temperature profile: 120/115/115/115/115°C; screw speed: 250 rpm; and feed rate: 6 lb/hr. The resultant toner with a gel content of about 8 weight percent was evaluated for fusing performance and had a image gloss of about 25 Gardner Gloss units at 370°F and at 1.05 TMA. The gloss is an intermediate value between the 8.3 and the 28 of the toners mixtures formed in Example I and II, respectively. The toners prepared in Example I to IV had a minimum fix temperature of about 330°F (170°C) and did not show any hot offset initially a temperatures up to 415°F(213°C), the highest temperature before permanent damage to the fuser rubber will occur. However, the fusing latitude of over 85 °F (41°C)decreases with time, the rate of which depends upon the degree of stress applied to the rolls. Roll failure occurs when hot offset occurs at the operating temperatures of about 360 °F (182°C). The gel content, gloss, minimum fix temperature (MFT), hot offset temperature (HOT), and fusing latitude (FL) results for the toners prepared in Examples I - IV are summarized in Table 1. Toner Sample Linear Content Wt. % Gel Content Wt. % Garder Gloss Units MFT °C HOT °C FL °C Toner A 93 7 28 168 >213 >45 Toner B 70 30 8.3 172 >213 >41 Toner C 86 14 17 170 >213 >43 Toner D 92 8 25 170 >213 >43 EXAMPLE V Preparation of Toner with Image Gloss of from about 40 to about 70 Gardner Gloss Units. An unsaturated polyester resin, RESAPOL HT available from Rasana Co. (Brazil), M w =15,600 and M n =6,800, having a similar structure but with a higher molecular weight compared to commercially available SPAR-II (available from Goodyear Co., M w =13,200, M n =6,400), was crosslinked to about a 36.5 weight percent gel content and formulated substantially in accordance with resin and toner of Example II with the exception that the pigment used was PV Fast Blue at 3.3 weight percent rather than carbon black. A series of toners were then prepared by melt blending this crosslinked resin component with varying amounts of the starting uncrosslinked polyester resin and pigment such that the final gel levels of the resulting toners were 3, 5, 7, and 9 weight percent, respectively. A toner containing zero (0%) weight percent crosslinked polyester was also prepared and exhibited the highest gloss value in the series. The observed image gloss at 188°C (370°F) and respective gel content of the toners are listed in the accompanying Table 2. The developed images were fused as in the preceding examples or by employing a fusing system and monoamino functional silicone release agent as disclosed in the aforementioned copending USSN 08/314,759 and 08/315,006. The resulting high gloss color images had pictorial color qualities. 36.5% gel Crosslinked RESAPOL HT RESAPOL HT Gel Level in Toner (Wt %) Image Gloss at 188°C 0% 96.7% 0 73 8.2 88.5 3% 66 13.7 83.0 5% 62 19.2 77.5 7% 61 24.7 72.0 9% 58

Claims: A process for preparing a low fix temperature toner mixture, comprising the step of preparing the tuner resin by melt blending a resin mixture comprising a first polyester resin with a low gloss value and a second polyester resin with a high gloss value, wherein the first polyester resin is present in an amount of from 20 to 80 wt.% of the resin mixture and contains of from 20 to 40 wt.% crosslinked gel content and has a gloss value of from 5 to 10 gloss units, the second polyester resin is present in an amount of from 80 to 20 wt% of the resin mixture and contains from 5 to 15 wt.% crosslinked gel content and has a gloss value of from 20 to 30 gloss units wherein the resulting melt blended toner mixture has an intermediate gloss value of 10 to 25 wherein substantially no increase in gel content nor an increase in resin molecular weight is observed during the melt blending. The process as claimed in claim 1, wherein the second polyester resin contains of from 85 to 95 wt.% uncrosslinked or linear unsaturated polyester resin. The process as claimed in any of claims 1 or 2, wherein the weight ratio of the first polyester to the second polyester is from 1:3 to 3:1. The process as claimed in any of claims 1 to 3, further comprising adding to the melt blending resin mixture, in an amount of 0.1 to 50 wt.% based on the weight of the resins, at least one member selected from the group consisting of a colorant, a charge control additive, a surfactant, an emulsifier, a wax, optional additives and a pigment dispersant. The process as claimed in claim 4, further comprising providing water injection into the extruder at a downstream location to achieve a lower temperature and a higher shear stress condition with respect to the melt mixture. The process as claimed in claim 1, further comprising preblending a mixture of at least two polyester resins, and optionally an unreactive resin or wax, feeding the mixture to an extruder, heating the mixture at a temperature of from 70°C to 120°C to melt the resin mixture and to further disperse the resin or wax, retaining the melt mixture in the extruder for a sufficient residence time of from 1 to 10 minutes, providing sufficiently high shear during the mixing thereby keeping crosslinked gel particles small in size and well distributed in the melt, and pumping the resulting resin melt through a dye to a pelletizer.

Inventors: CHOW SHE C, CHOW, SHE C.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1996
Main classification: G03G9
IPC codes: G03G15, G03G9