US 3761413 A
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United States Patent 3,761,413 XEROGRAPHIC TONER COMPOSITION, Lauren L. Hulse, Saratoga, Calif., assignor to Memorex Corporation No Drawing. Filed Nov. 1, 1971, Ser. No. 194,697 Int. Cl. G03g 9/02 US. Cl. 252-621 3 Claims ABSTRACT OF THE DISCLOSURE A xerographic toner composition consisting essentially of finely divided resin particles produced by copolymeriz ing a mixture of methylmethacrylate, styrene and n-butylmethacrylate having a colorant intimately dispersed in the resin particles and a minor amount in the range about 0.2 to 1.0 percent by weight based on the weight of the resin particles of a polymer or copolymer of fluorocarbons containing two or three carbon atoms per molecule.
BACKGROUND OF THE INVENTION surface and fusing the toner particles on that surface,
cleaning the photoconductive surface to remove residual toner particles; the cycle is then repeated.
The photoconductive surface is commonly the exterior surface of a drum which is driven at uniform speed so that each point on the drum surface moves through the entire machine cycle over and over. The cleaning step of the cycle is commonly carried out by moving a fibrous web such as cotton cloth across a portion of the drum surface in a direction opposite to that of the drum rotation.
In connection with a study of the causes of machine malfunction, an ammeter was connected in series with the main drive motor for the drum, and the ammeter readings were recorded during continuous operation of the machine. It was observed that periodic rapid increases in the current pull of the drive motor occurred during operation. For example, a drive motor having a normal current pull of 0.50 amperes would show sudden increases in current pull of as much as 0.06 amperes. A study of the increases in current pull as related to machine operation indicated that current pull increases up to about 0.03 amperes does not appear to correlate with any malfunction of the machine but that where current pull increases are above 0.03 amperes and especially when they are above 0.04 amperes, the image surface paper becomes overheated in the fusion step of the cycle, and fires commonly occur at that point. It is believed that sudden increases in the current pull indicates suddenly increased frictional resistance to drum rotation experienced at the cleaning step of the cycle and that this is accompanied by decreased drum speed, increased residence of the image surface in the fuser, overheating of the paper and frequently fires in the fuser.
It has been found that when the toner composition described herein is used, sudden increases in current pull of as much as 0.04 amperes are rare and that prolonged operation of the machine is possible without malfunctions due to overheating.
3,761,413 Patented Sept. 25, 1973 DETAILED DESCRIPTION OF THE INVENTION The toner composition of the present invention is a mixture of resinous particles having a colorant uniformly dispersed in the particle and a small amount of finely divided polytetrafluoroethylene or of finely divided copolymer of tetrafluoroethylene and hexafluoropropylene.
The resin is prepared by copolymerizing a mixture of two parts by weight of n-butylrnethacrylate, 1.8 to 2.2 parts by weight of styrene and 0.8 to 1.2 parts by weight of methylmethacrylate. The resin is predominantly a terpolymer having a molecular weight in the range about 50,000 to 75,000 and a melt index range of 8 to 20. Molecular weight range and melt index range are controlled by adjusting the amount of polymerization initiator and the temperature employed in the polymerization step.
As determined by the Kofler Hot Bench Test, the resins are free flowing at 60 to 70 C., begin to exhibit tack at about to C. and melt at to 105 C.
A representative preparation of the toner of the present invention is described in the following example.
Example 504 grams of deionized Water, 33.8 grams of water solution of sodium phosphate having a 7.39% by weight content of sodium phosphate and 17.1 grams of a water solution of calcium chloride having a 20.3% by weight content of calcium chloride were placed in a 3L round bottom flask equipped with a mechanical stirrer, a thermometer, a condenser and an inlet for nitrogen gas. Nitrogen was bubbled through the mixture in the flask while heating it to 90 C. A mixture of 8.13 grams benzoyl peroxide, 0.04 gram of dioctyl sodium succinate (aerosol OT sold by American Cyanamid Co.), 120 grams styrene, 120 grams n-butylmethacrylate and 60 grams of methylmethacrylate was introduced into the flask. The contents of the flask were blanketed with nitrogen, mechanically stirred and held at 90 C. for four hours and at C. for one hour. When the contents had been at 90 C. for 1.5 hours, 0.15 g. of powdered calcium carbonate was added to the contents of the flask. The contents of the flask were cooled, passed through a filter and the polymer filter cake was washed with water and then dried in a vacuum oven at 104 F.
The polymer product weighed 201.2 g. and had a melt index 8.8 (ASTM D-123865T). The polymer was subjected to the Kofler Hot Bench Test and showed free flow 62 C., tack 90 C., melt 105 C.
The polymer product was then melted and 45 grams of finely divided carbon black (Regal 400-R supplied by Cabot Corp.) were intimately mixed with the molten polymer. The resulting mixture was cooled until it solidified and then jet pulverized to produce particles having an average maximum dimnesion in the range 10 to 20 microns.
Finely divided copolymer of approximately equimolar amounts of tetrafluoroethylene and hexafiuoropropylene having an estimated average maximum dimension about 0.7 micron was mixed with the polymer-carbon black particles in amount to produce a mixture having a polyfluorocarbon content of 0.5% by weight. The resulting mixture was then charged to a Twinshell blender which was run for a 15-minute blending period to produce the finished toner composition.
A number of preparations of toner were made generally following the procedure of the above example. The proportions of the monomers charged to the polymerization reaction were varied and the results indicated that the proportions must be held within the ranges two parts by weight n-butuylmethacrylate, 1.8 to 2.2 parts by weight styrene and 0.8 to 1.2 parts by weight methylmethacrylate if uniform satisfactory resin properties were to be obtained.
The polyfluorocarbon content of the toner composition was varied over a considerable range. At least 0.2% by weight of polytetrafiuoroethylene or copolymer of tetrafluoroethylenehexafiuoropropylene is required to make significant improvement, increasing polyfluorocarbon content above 1% by weight does not result in increased improvement and about 0.5 by weight appears optimum.
Polytetrafluoroethylene is commercially available in fine powder form. The powder particles are small, well below 15 microns. The commercial material, e.g., Teflon (duPont) is satisfactory for use in the toner composition. Copolymers of tetrafluoroethylene and hexafluoropylene are also available commercially. The copolymer of approximately equal molar amounts of tetrafiuoroethylene and hexafiuoropropylene employed in the above example is sold by Liquid Nitrogen Processing Corp. as TL-120FEP in the form of a powder having an average particle size about 0.7 micron; it is a preferred polyfluorocarbon for use in the toner compositions of the invention. Polyfluorocarbon preparation and properties are shown in Encyclopedia of Chemical Technology, Kirk-Othrner, Interscience Encyclopedia, Inc., N.Y., 1953, at vol. 11, pg. 689 et seq.
Carbon black is the preferred colorant but other colorants in the form of pigments or dyes may be employed. Such other colorants are well known in the art as illustrated, for example, in U.S. Pat. 3,577,345.
In addition to improving the reliability of machine operation, the toner of the present invention is unusually resistant to thermal agglomeration and exhibits remark ably strong adherence to the image surface.
Resistance to agglomeration was measured by placing toner samples in aluminum dishes and exposing them to varyin oven temperatures for 18 hour periods.
Samples of the toner produced pursuant to the above example showed essentially no agglomeration at 130 F. while a widely used commercial toner showed 50% agglomeration at 125 F. and was fused to a cake at 130 F.
The toner of the present invention can be stored in any ordinary storage facility and in any climate without experiencing agglomeration loss.
The toner of the present invention exhibits superior fix or adhesion to the image surface after fusion. This property of a toner is tested by applying pieces of transparent adhesive tape to selected areas of the image surface, peeling the tape from the image surface and then applying the tape to a blank white piece of paper. Colorant adhering to the adhesive tape is readily detected against the blank white surface. The fix of the toner of the present invention was compared with that of commercial toners using Norton Bear-Rite Mending Tape No. 335 as the transparent tape. Identical images were produced using the toner of the present invention and three commercial toners. All images were at a nominal 1.0 optical density and were produced in a Xerox 660 type machine. Transparent tape was applied and removed from the upper left, center and lower right areas of each image and the removed tape strips were placed against blank white paper for comparison. No colorant adhered to the tape strips when the toner of the present invention was employed. Colorant adhered to the tape strips with all three of the compared commercial toners in varying amounts ranging from scattered spots to heavy deposits which defined some of the text of the image.
1. A xerographic toner composition consisting essentially of:
(a) a major proportion of 10 to 20 micron particles of a polymer having a molecular weight in the range 50,000 to 75,000, said polymer being a terpolymer of 2 parts by weight n-butylmethacrylate, 1.8 to 2.2 parts by weight styrene and 0.8 to 1.2 parts by weight methylmethacrylate;
(b) from 0.2% to 1% by weight based on the terpolymer of a finely divided fluorocarbon selected from the group consisting of polytetrafluoroethylene, polyhexafluoropropylene and copolymers of tetrafiuoroethylene and hexafluoropropylene; and
(c) a colorant selected from the group consisting of dyes and pigments in amount sufiicient to color the resin.
2. A xerographic toner composition as defined in claim 1 in which the fluorocarbon polymer is polytetrafiuoroethylene.
3. A xerographic toner composition as defined in claim 1 in which the fluorocarbon polymer is a copolymer of tetrafiuoroethylene and hexofluoropropylene.
References Cited UNITED STATES PATENTS 3,502,582 3/1970 Clemens et al. 252-62.1
NORMAN G. TORCHIN, Primary Examiner J. P. BRAMMER, Assistant Examiner U.S. Cl. X.R. 1l717.5; 260-900