Process for preparing novel composite charge control agents and novel composite charge control agents prepared by the process

Abstract

A composite charge control agent for use in electrostatic imaging comprises porous, inorganic core particles of at least 0.08 microns in diameter, impregnated with 2% to 50% by weight of one or more charge control chemicals and up to 50% by weight of one or more additional compounds such as a polymer, a wax, a dye, or other organic chemicals.

Claims

1. A process for producing a composite charge control agent wherein a porous inorganic core particle of at least approximately 0.08 microns in diameter is impregnated with 2% to 50% by weight of one or more charge control chemicals and up to 50% by weight of one or more additional compounds selected from the group consisting of: a polymer, a wax, a dye, and combinations thereof.

2. A process according to claim 1 wherein the inorganic core particle is chosen from the group consisting of: amorphous silica, alumina, titania and calcium carbonate.

3. A process according to claim 1 wherein the inorganic core particle is treated with a chemical to adjust its pH and/or hydrophobicity either before or after the coating or impregnation operation.

4. A process according to claim 1 wherein an aqueous or organic solution or dispersion is formed from a solvent, at least one charge control chemical and one or more additional components selected from the group consisting of: a polymer, a wax, a dye, and combinations thereof and the solution or dispersion is sprayed onto the inorganic core particles, and optionally, the composite particles are dried.

5. A process according to claim 1 comprising the steps of: forming an aqueous or organic solution or dispersion from at least one charge control chemical and one or more additional components selected from the group consisting of: a polymer, a wax, a dye, and combinations thereof; adding the solution or dispersion to a quantity of inorganic core particles which adsorb the solution or dispersion so as to form composite particles; and optionally, drying the composite particles.

6. A process according to claim 1 comprising the steps of: forming a dispersion of a mixture of at least one charge control chemical and one or more additional component selected from the group consisting of: a polymer, a wax, a dye, and combinations thereof in a liquid that does not dissolve some or all of the wax or polymer at room temperature; heating said dispersion to a temperature such that the polymer or wax dissolves; adding the heated dispersion to a quantity of inorganic core particles which function to absorb the heated dispersion so as to form a composition thereof; cooling the composition so as to precipitate the wax and/or polymer; and optionally, evaporating residual liquid from the composition.

7. A composite charge control agent comprising: porous inorganic core particles of at least 0.08 microns in diameter impregnated with 2% to 50% by weight of one or more charge control chemicals and up to 50% by weight of one or more additional compounds selected from the group consisting of: a polymer, a wax, a dye, and combinations thereof.

8. The composite charge control agent of claim 7, wherein said inorganic core particles are chosen from the group consisting of metal oxides, metal carbonates, and combinations thereof.

9. The composite charge control agent of claim 7, comprising: 50 to 95% of said inorganic core particles.

10. The composite charge control agent of claim 7, wherein said wax is an acid or amine functional wax.

11. The composite charge control agent of claim 7, wherein said polymer is at least one acid or amine functional polymer.

12. The composite charge control agent of claim 7, wherein the agent also includes an additional IR or UV visible dye or pigment.

13. A process according to claim 1, wherein the porous inorganic core particle is impregnated throughout with 2% to 50% by weight of one or more charge control chemicals and up to 50% by weight of one or more additional compounds selected from the group consisting of: a polymer, a wax, a dye, and combinations thereof.

14. A process according to claim 1, wherein the diameter of the porous inorganic core particle is from 0.08 microns to 5 microns.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The basic concept of the present inventive process is to first obtain an inorganic core particle whose particle size is approximately the same as that desired of the final charge control agent. That core particle is then impregnated with a composition that includes at least one charge control agent and optionally one or more additional materials selected from waxes, polymers, dyes, pigments, or specialty chemicals, depending on the composition desired of the final composite powder.

(2) A first implementation of the inventive process is the production of novel composite charge control agents by impregnating a suitable inorganic core whose particle size is approximately that desired of the final charge control agent. This can involve use of one or more agents selected from organic chemicals, dyes, pigments or commercial charge control chemicals. In each case the particle size of the charge control agent is reduced to a size significantly smaller than the inorganic core particle size, and preferably below 1 micron. If the charge control chemical is in the form of a large particle size powder, its size can be reduced by any common dry or wet milling operation and could include use of a dispersant to maintain the milled particles in a dissociated state. The charge control agent can also be dissolved in a suitable aqueous or organic solvent.

(3) Suitable charge control agents include, but are not limited to, amino acids, basic dyes, quaternary ammonium salts, organo boron complexes, polymeric amines, metal complex dyes, acid dyes, and salicylate metal complexes. A partial list of suitable charge agents is disclosed in U.S. Pat. No. 4,362,803 and an extensive list of commercially available charge control agents is available in the reference work Toner Raw Material Handbook and Information Service published by Toner Research Services.

(4) A suitable porous core particle can be amorphous silica, alumina, titania, metal carbonates or metal silicates. The inventive process may be carried out with a broad range of particle size cores depending on the particle size of the toner or powder that the charge agent will be used in. If the particle size of the core is too small a pigment charge control agent may not be adsorbed on the core but will instead exist as separate particles. It is also not desirable to have the core similar in size to that of the toner, unless the formulated charge control agent can be broken into smaller aggregates during toner melt mixing operations. The optimum size core will vary with a particular toner, the surface area of the inorganic core and the charge level desired. In general, a particle size within the range of 0.08 and 5 microns is preferred for most toners. Air classification of the core particles can be used to produce a desired particle size or size distribution if it is not available commercially.

(5) The surface chemistry and pH of the core can also play a synergistic role in the composite charge agent. For example, inorganic cores with acidic surfaces may contribute to higher negative charging of the composite agents while basic cores may be preferred for positive charge agents. In general, higher surface area cores with larger pores will allow for adsorption of higher quantity and smaller particle size charge agents. Suitable inorganic cores in various particle size ranges are commercially available from such companies as Ineos Silica, Fuji Sylysia, Rhodia, Rhone Poulenc, PPG, J.M. Huber and Degussa. They include silicon, aluminum and titanium oxides as well as metal carbonates and silicates. It is also possible to produce precipitated inorganic oxide particles with specific compositions and particle sizes, with many such processes described in the literature.

(6) One technique for impregnating the inorganic cores is to form an aqueous or solvent based solution or dispersion of the charge control chemicals, spray the dispersion onto a fluidized suspension of the cores, and dry the composite particles by known drying techniques. This is accomplished by using such devices as fluid bed, V-cone blender, etc. A second option is to adsorb the solution or dispersion on a quantity of inorganic core particles and then dry the composite particles. The quantity of inorganic core particles is approximately the amount required to absorb all of the fluid.

(7) While the above process can provide some improvement over traditional charge control agents, it does not provide a completely adequate solution in that the charge agent may be loosely adsorbed on the inorganic core and can become dislodged during imaging processes and lead to image and hardware problems.

(8) A more preferred composite charge control agent consists of impregnating the inorganic core with a composition consisting of one or more charge control chemicals and at least one or more wax or polymer compounds. The primary function of the wax or polymer is to act as a binder for the charge control chemical. In general, any wax or polymer that is solid at room temperature and can be formed into a solution, dispersion or emulsion can be suitable for this implementation. However, to achieve the maximum benefit from the inventive process it is preferred to choose a wax or polymer binder that offers some synergetic benefit to the toner charging or other toner property. For example acidic groups on the wax or polymer can increase negative charging while basic groups can contribute to higher positive charging.

(9) The quantity of polymer or wax binder used will depend on its desired functions. If the function is simply to bind the charge control agent to the core, a minimal amount of wax or polymer may be desired. However, it is possible to use this process as a convenient method of incorporating some or all of the wax commonly used as an internal toner lubricant. The majority of current toners contain from 3% to as much as 10% or more internal wax lubricants that act as release agents for hot roll fusing systems. As the toned image contacts heated fuser rolls the wax melts and coats the rolls. However these lubricants are not usually compatible with toner polymers and they reduce shear in melt extrusion, thus making toner preparation difficult. An additional problem of toners containing melt mixed wax lubricants is that the incompatible wax may separate from the toner during milling operations. The wax particles form satellites that can adhere to toner surfaces. During the electrophotographic process these wax particles may separate from the toner and adhere to such machine components as charge rolls or photoreceptors, with resulting degradation of print image quality. Polymer/wax compatibilizers are sometimes included in a toner composition to minimize this problem but this does not provide a completely satisfactory solution. Use of wax-coated inorganic cores can be an effective method of providing uniformly distributed wax within a toner as the particles disperse much easier. Wax coated inorganic cores can also allow the use of significantly lower concentrations of wax.

(10) A number of techniques can be used to impregnate the inorganic cores with the above composition. First, the charge control agent can be dispersed in an aqueous or solvent system where the wax or polymer is dissolved, dispersed or emulsified. That composition can either be sprayed on the inorganic cores or adsorbed as already described. A second technique for forming the composite particles is to use a solvent precipitation process as described in U.S. Pat. No. 3,971,749 to Blunt. A wide variety of wax, olefin and hydrocarbon polymers can be dissolved in such heated hydrocarbon fluids as odorless mineral spirits, Magie oils, paraffin oils or other hydrocarbon fluids and when cooled the wax or polymer precipitates. Some examples of polymers suitable for this purpose are most waxes, polyethylenes, propylene, high ethylene content ethylene-vinyl acetate polymers, and hydrocarbons such as Picco 5120 (Hercules). For this implementation the preferred hydrocarbon fluid is one that is environmentally friendly, will dissolve the wax or polymer, and can easily be evaporated. The quantity of fluid used is approximately the amount required to completely wet the inorganic core. An excess of fluid could technically be used although that requires more time and effort for its evaporation. A third technique for forming the composite particles is to form an aqueous or organic solvent solution of charge control agent and polymers and either spray or adsorb the solution on the inorganic cores as already described. For this implementation a wide range of fluids are possible, including hydrocarbons, acetone, toluene, and environmentally friendly bio derived fluids. For this implementation a relatively small amount of charge dye can be used as the polymer/dye mixture is predominantly adsorbed on the surface of the inorganic core. This implementation is especially useful for preparing colored charge control agents or ones that may use solvent soluble organic chemicals such as quaternary ammonium compounds.

(11) The techniques described for forming composite charge control agents can also be used to produce more complex charge control agents. Thus, additional modifying agents may be included during any one of the above processes. For example, conductivity modifying agents, colored dyes, IR or UV-absorbing dyes or pigments can be included in the compositions to either adjust electrostatic properties or provide an additional security or identification feature.

(12) Any of the above charge control agents can be used in the same manner as traditional charge control agents. For melt mixed toners the amount of inventive charge control agent may range from 0.5 to 4% or more, depending on the charge rate, charge magnitude and charge distribution desired. The inventive composite charge control agents can be designed to have the same charge characteristics as traditional charge agents such that they are used at the same concentration. Optionally, the charge agents can be designed with lower charge magnitude such that higher concentrations are used. This can be an effective technique for achieving more uniform toner charging or incorporation of higher wax concentrations. Because the composite charge agents are less expensive to produce the higher concentration would not add to toner cost.

(13) The inventive charge control agents are not limited to use only in conventional dry toners. A variety of non-traditional processes are currently being used to produce toners. These include such techniques as suspension polymerization, aggregated emulsion, solvent milling, evaporative coalescence and others. Each of these toners must also achieve certain levels of charge magnitude, charge rate, and charge stability. Inclusion of traditional charge control agents in most of these processes has either been difficult at best so that the toner producer frequently relies on external additives to control toner charge. While this may provide an adequate technical solution for these so-called chemical toners, relatively large amounts of expensive additives are required. These additives can present difficulties in EP hardware as they frequently separate from the toner and collect on drums, charge rolls, developer rolls or cleaning blades. In addition, these ultra fine additives can become airborne during use and present possible environmental issues. The inventive composite charge control agents can be easily used in many of these processes because of the ability to control their particle size and charge properties. It is also easy to design either positive or negative charge agents as well as a broader array of colorless charge agents.

(14) The inventive charge control agents are suitable for applications in addition to toners. Electrostatic powder coating also relies on charged powders. Until recently this industry did not adequately concern itself with carefully controlling the powder charging, resulting in inefficient and wasteful spraying. The inventive composite charge agents can be especially beneficial for this process as versions can be produced at low cost and with great versatility.

(15) As can be readily seen from the previous discussion, the inventive process provides numerous benefits for the production of a wide variety of electrostatic charge control agents.

(16) First, it is very versatile as almost any dye, pigment or organic chemical capable of altering toner charge could be coated or impregnated in the core. For example, a wide variety of colored charge agents are possible. Also, both positive and negative charge control agents can be produced. The technique also provides a simple way to produce complex charge agents in that mixtures of charge chemicals and optionally conductive or modifying components can be included in the particle. The technique provides a simple method of producing charge agents with almost any desired size. The technique also provides a method of lowering the cost of charge control agents, one of the most expensive components of a toner. This benefit is based on the fact that a small amount of active charge agent chemical is contained primarily on the inorganic core, which typically has very high surface area. For example, it is possible to impregnate the inorganic core with as little as 5% of an expensive, commercially available charge agent and achieve a desired electrostatic charge. Another unforeseen benefit for the composite charge agent was the use of wax as the charge agent binding component. By proper selection of the wax, improved toner fixing and anti-offset can be achieved when compared to toners without the wax. By judicial selection of the type and quantity of wax used for these novel composite charge agents it may be possible to reduce or eliminate use of additional wax in the toner. This would provide a significant benefit in terms of toner preparation, but an even greater benefit in that it could reduce the amount of free wax particles that tend to accumulate on charge rolls and photoreceptors. This unexpected benefit is possible because the small particle size and high surface area of the inorganic cores provides a large amount of effective surface area to be coated with wax. The composite charge control agents have also been found to disperse much easier during melt mixing as compared to conventional charge agents and this can improve toner processing rates. The composite charge agents can also be safer to use. Certain charge control dyes are potentially flammable but this would be reduced when adsorbed on an inorganic core.

(17) The following examples are provided as representative techniques for forming composite charge control agents according to the present invention. They are illustrative but are not meant to define limitations of the process.

Example 1

(18) 60 g of Bontron E-84 (Orient Chemical) was dissolved in 300 ml MEK. This was added to 400 g Multifex MM (Specialty Minerals) precipitated calcium carbonate in a 600 ml beaker. The mixture was agitated in an ultrasonic bath for two minutes and placed in an oven to dry. A toner was prepared by extruding a mixture of 2% of the charge agent complex, 4% polypropylene wax, 40% magnetic iron oxide and 64% styrene acrylic resin. The extruded mixture was jet milled, classified and blended with 0.5% hydrophobic silica. It was placed in an HP 4250 laser printer and over 1000 prints were produced with quality equal or superior to OEM prints and with no deterioration in quality over that run length.

Example 2

(19) 50 g of positive charge agent P12 was dissolved in 400 ml of methanol and this was added to 450 g of Multifex MM precipitated calcium carbonate, mixed for 5 minutes in a vessel with dish-shaped heads and an anchor/paddle agitator and then dried. The product was used as a positive charge agent to produce a commercially viable Kyocera toner.

Example 3

(20) 5 g of Otsuka BS-1 resin (48.7% concentration) was dissolved in 200 ml of methanol. 25 g of positive charge agent P12 was next dissolved in the above solution. This solution was then added to 222.5 g of Multifex MM precipitated calcium carbonate and mixed 5 minutes. It was dried and used to produce a positive charge toner.

Example 4

(21) 0.5 g of Bayer Macrolex Red H dye and 4.5 g Baker Petrolite Unicid 425 were dissolved in 25 g heated odorless mineral spirits. This was added to 14 g Fuji Sylysia grade 460 silica that had been air classified to collect under 5 micron particles. The dispersion was cooled to precipitate the wax and dried to form red composite particles that could be used as charge control agents

Example 5

(22) A dispersion was prepared by media milling 30 g T-77 charge agent (Hodogaya Chemical) and 110 g odorless mineral spirits. After milling 1 hour, the dispersion was separated and washed with additional OMS and 210 g dispersion collected. 140 g of the dispersion and 20 g Unicid 425 polymer were heated to 110 C. 20 g HP 270 silica was added to the heated dispersion and the mixture cooled and dried. 30 g of the final product was formulated into a toner comprised of crosslinked polyester resin, 40% iron oxide, and 4% polyolefin wax. The toner was jet milled, classified and the triboelectric charge measured using a ferrite carrier and Vertex blow-off device. The charge at 10 seconds was 16.0 and 21.5 at 20 minutes. A control toner using 1.5% T-77 charge agent had triboelectric charge of 19 at 10 seconds and 17.6 at 20 minutes.

Example 6

(23) 30 g of an iron based commercial charge control agent was media milled with 110 g odorless mineral spirits. The milled pigment was screen separated and washed with OMS. 163 g was collected. This was separated into two fractions. 82 g of the dispersion was placed in a 400 ml beaker, along with 18 g additional OMS and 10 g Ineos HP270 silica. The mixture was heated to approximately 100 C. and cooled with moderate stirring. The modified charge control agent was dried and processed into a toner comprised of styrene-acrylic resin, 4% polyolefin wax, 40% magnetic oxide and the above charge control agent. Triboelectric charge measurements were made using a commercial device supplied by Vertex, a standard ferrite carrier and mixing for 10 seconds, 2 minutes, 5 minutes and 20 minutes. The charge at 10 seconds was 14.6 and 21.4 at 20 minutes. A control toner using 1.5% of the same iron based charge agent gave charge measurements of 14.7 at 10 seconds and 8.6 at 20 minutes. Print tests using a Hewlett Packard laser printer showed improved quality when compared with the control toner.

Example 7

(24) The second portion of pigment dispersion (82 g) from experiment 6 was combined with 18 g OMS, 10 g Ineos HP270 silica and 15 g Unicid 425 polymer (Baker Petrolite). The modified charge agent was processed as in Example 13 and used to produce a toner with the same composition as Example 13. Triboelectric charge was 25.7 at 10 seconds and 33.2 at 20 minutes. This experiment demonstrated improved charge when an acid functional wax was included in the composite charge agent composition. Print tests using a Hewlett Packard laser printer showed improved quality when compared with the control toner.

Example 8

(25) A pigment dispersion was prepared by media milling 7.5 g Ticona Topas polymer, 65 g OMS and 16 g commercial iron base charge agent. The dispersion was separated, combined with 20 g Ineos HP 270 silica and dried. The modified charge agent was used to produce a toner as in Example 13. Triboelectric charge ranged from 17.4 at 10 seconds to 18.9 at 20 minutes

Example 9

(26) A composition of 16 g Hodogaya TRH charge control agent and 130 g distilled water were media milled for 2 hours, screen separated, and washed, providing 300 g of dispersion. 32 g of Michem Lube 156 (Michelman) was then stirred into the above dispersion. 40 g of Ineos HP 260 silica was slowly added to the resulting dispersion, providing a very slight excess of liquid. The composite charge agent particles were dried and 2% incorporated in a toner composition as in Example 13. The resulting toner was tested in a Hewlett Packard printer and exhibited print quality superior to a comparative toner that had been prepared with 2% of standard TRH charge control agent.

(27) The inventor does not want to be limited to the technique of impregnating the porous particles, the type of porous particles or the size of the porous particles. Also, instead of the charge control agent above many other dyes, pigments, chemicals, or biological components could be impregnated in the porous inorganic core to provide composite particles.