Xerographic toner composition

Abstract

 A xerographic toner composition is described which is chargeable positive relative polytetrafluorethylene (PTEE) coated carrier beads, the toner composition being a synthetic three-resin mixture of an acrylic polymer, a copolymer of styrene and an acrylic monomer, and a petrochemically derived aromatic hydrocarbon resin, with carbon black as pigment, the carbon black's content and pH providing fine adjustment of the toner's triboelectric charge.

Description

[0001] The present invention relates to a xerographic toner composition which triboelectrically interacts with carrier beads, and is thereby charged to a polarity opposite that of an electrostatic latent image which is to be toned. The.toner of the present invention is usable in the size classification claimed in European Patent 1785.

[0002] A well known xerographic process involves forming an electrostatic latent image of a DC polarity. This image is to be reproduced as a colored, visually perceptible image on a white sheet of plain paper. In order to produce such a copy, this latent image is subjected to the influence of a two-component developer mix, comprising small toner particles of dry powder which are electrostatically carried on the surface of larger carrier beads. Well known developer mechanisms include magnetic brush and cascade developers..Mechanical mixing of this toner and carrier triboelectrically produces a toner charge opposite that of the latent image. Thus, when the toner/ carrier mixture is presented to a latent electrostatic image, carried by a photoconductor, toner is left on the image to form a reverse-reading visual image. Thereafter, a relatively large portion of this toner is transferred to a sheet of plain paper. This toner is then heat- fused to the paper to form a permanent copy.

[0003] The use of mixtures of synthetic resins in toner formulations is of course well known. It is also known that such resinous material can be selected from natural resins, modified natural resins and synthetic resins. U.S. Patent 4 148 640 lists a number of such resins. U.S. Patent 3 893 935 recognizes that styrene-containing resins are useful toner resins, and a polymerized blend of about 40 to 100 % by weight of styrene, about O to 45 % by weight of a lower alkyl acrylate or methacrylate (1 to 4 carbon atoms), and about 5 to 50 % by weight of a higher alkyl acrylate or methacrylate (6 to 20 carbon atoms) is described.

[0004] In U.S. Patent 4 078 931 toner polymers are described which are prepared by ester group aminolysis of a styrene- n-butyl methacrylate copolymer with an aminoalcohol. U.S. Patent 3 933 665 also suggests use of styrene and n-butyl methacrylate in toners.

[0005] Anticaking agents have been extensively used in prior art toners so that the toner remains free-flowing both in storage and in copier use. Cab-O-Sil, a brand of colloidal pyrogenic silica powder (Carbot Corporation) is one such anticaking agent. While anticaking agents do in fact maintain the toner flowability, they have the disadvantages that the toner's charge varies from particle to particle as a surface content of this agent changes, thus giving a wide charge distribution to a mass of such toner; these agents are thought to be a catalyst for initiating clear filming of an organic photoconductor when used with carrier beads coated with polytetrafluorethylene; and these agents are thought to contribute to accumulation of a semipermanent toner film on the photoconductor. In addition, while toner has a natural tendency to be sensitive to humidity changes, in that its charge usually increases as the humidity decreases, some anticaking agents undesirably amplify, or perhaps even change the direction of this humidity responsiveness.

[0006] Natural products such as tree rosins, plant and animal materials have found widespread use in toner formulations. Their natural origin confers upon them a certain variability from season to season or from geographic location to location. Due to the complex natural product chemistry involved, it is difficult to anticipate or even understand these changes. Obviously, such variability is detrimental to the functioning of an electrophotographic toner wherein it is desirable to produce the same toner from year to year and at a variety of manufacturing locations. It would, therefore, seem desirable to formulate a toner devoid of these natural materials.

[0007] Object of the invention is a toner composition which is characterized by the absence of anticaking agents and which is relatively insensitive to humidity.

[0008] The object of the invention is achieved by a xerographic toner composition which is characterized in that it contains a three-resin mixture of 5 to 55 % by weight an acrylic polymer, 15 to 50 % by weight a copolymer of styrene and an acrylic monomer, 15 to 25 % by weight an aromatic hydrocarbon resin which includes styrene and styrene derivatives; and 5 to 20 % by weight of a coloring matter.

[0009] The invention provides a toner formulation in the form of a unique blend of three synthetic thermoplastic resins and a pigment such as carbon black. The present invention is characterized by the absence of anticaking agents per se, and by the absence of tree rosins thereby eliminating problems associated with the use of said anticaking agents and tree rosins. The resins of the present invention are selected t_Q give the proper triboelectric charge magnitude and polarity, i.e. positive, relative PTEE (polytetrafluoro ethylene) coated carrier beads, as well as a narrower charge distribution. The quantity of each resin is selected to give the dry toner powder the required cake resistance, friability and ability to fuse at a nominal operating temperature. Carrier beads exemplary of the type useful with the toner of this invention are described in U.S. Patents 3 947 217 and 4 147 834.

[0010] The synthetic three-resin blend prepared in accordance with this invention provides a functional electrophotographic toner with enhanced properties. An acrylic resin provides the required triboelectric magnitude and polarity with respect to PTEE carrier. The second resin is a petroleum based resin, more specifically a petrochemically derived aromatic hydrocarbon resin of styrene and styrene derivatives. This latter resin produces friability, and lowers the toner's fusing temperature. The third resin is a copolymer of styrene and an acrylic monomer, more specifically n-butyl methacrylate, which functions to adjust friability to a desired level. The styrene component of this copolymer makes the toner cake resistant, whereas the n-butyl methacrylate component provides compatibility, in both a chemical and mechanical mixing sense, of the styrene with the acrylic resin. The toner's pigment constituent is carbon black, whose content and pH provide a fine adjustment of the toner's triboelectric charge.

[0011] With the formulation of the present invention, problems associated with the use of anticaking agents and/or tree rosin are eliminated. More specifically, the present toner is relatively insensitive to humidity and provides better image definition with reduced background and toner usage. It also minimize clear filming of the copier's photoconductor, and minimizes toner contamination of the associated photoconductor and the interior of the copier in which the toner is used.

[0012] A most preferred toner according to the present invention consists essentially of about 36 % by weight Acryloid B-66, about 35 % by weight Piccotoner 1200, about 17 % by weight Nevex 100, and about 12 % by weight Raven 1020. More generally, and in accordance with the present invention, Acryloid B-66 may be used in the range of about 5 to 55 % by weight, Piccotoner 1200 may be used in the range about 15 to 50 % by weight, Nevex 100 may be used in the range about 15 to 25 % by weight, and Raven 1020 may be used in the range about 5 to 20 % by weight.

[0013] Ionac RP 70, a 70/30 styrene/acrylic copolymer by Ionac Chemical Co., has been used in the toner of this invention as a replacement for Piccotoner 1200.

[0014] Acryloid B-66 is a brand of acrylic polymer, in powder form, manufactured by Rohm & Haas Co. Piccotoner 1200 is a brand of thermoplastic resin which is a copolymer of styrene and n-butyl methacrylate manufactured by Pennsylvania Industrial Chemical Corporation. Nevex 100 is a brand of ^petrochemically derived aromatic hydrocarbon resin which includes styrene and styrene derivatives.

[0015] While any suitable colorant may be used to color the toner particles, Raven 1020 carbon black is preferred. Raven 1020 is a brand of carbon black manufactured by Columbian Carbon Company.

[0016] More specifically, Acryloid B-66 is a copolymer of 60 % n-butyl methacrylate and 40 % methyl methacrylate. In the toner of the present invention, this constituent may vary within the range of about 5 to 55 % by weight and preferably from 15 to 40 % by weight. The glass transition temperature of this constituent is 60 to 67°C. Its molecular size by weight is 110 to 165 nm, and by number is 50 to 80 nm.

[0017] Piccotoner 1200 is a copolymer of 67 to 73 % styrene and 27 to 33 % n-butyl methacrylate. In the toner of the present invention, this constituent may vary within the range about 15 to 50 % by weight. The glass transition temperature of this constituent is 66 to 73 °C. Its molecular size by weight is 160 to 200 nm, and by number is 50 to 70 nm.

[0018] Nevex 100, an aromatic hydrocarbon resin of styrene and styrene derivatives, cannot be defined as specifically as Acryloid B-66 and Piccotoner 1200 due to the relatively unrefined nature of its raw materials. In the toner of the present invention, this constituent may vary with the range about 15 to 25 % by weight. The glass transition temperature of this constituent is 52 to 56°C. Its molecular size by weight is 120 to 140 nm, and by number is 100 to 115 nm.

[0019] Raven 1020 is a furnace black within the specification ranges of a surface area of 85 to 95 m²/gram, dibutyl phthalate absorption of 50 to 60 cc/100 grams, and a pH of 6.0 to 9.0. This constituent may vary in the range of 5 to 20 % by weight.

[0020] The method of manufacturing the toner of this invention is not critical, and a number of such methods will be apparent to those skilled in the art. In an exemplary method the three resins and the carbon black are dry blended at room temperature for about 20 minutes, the dry blend is then melt-mixed by a mixing extruder. The cool, extruded material is then ground to a desired particle size. If necessary, particles which are too fine can thereafter be removed using an air classifier.

[0021] In testing the toner of the present invention, it was placed in the magnetic brush developer of a commercially available IBM Series III copier/duplicator model 10. This copier includes the photoconductor defined in U.S. Patent 4 150 987. This copier also used the aforementioned PTEE coated carrier particles. In this copier, the photoconductor is uniformly charged to about -850 volt: At the copier's illumination station the photoconductor's charge is reduced to about -150 volts in the "white" areas which are not to be toned, whereas the "black" areas retain about a -800 volt charge. As this -800 volt latent electrostatic image passes through the magnetic brush developer, toner of the present invention is deposited on this "black" area to form a reverse-reading image The developer's magnetic brush roller carried a development electrode bias voltage of about -350 volts. The toner's median by weight particle size, after developer mix break-in, was between 9 microns and 12 microns, with between 11 % and 20 % by weight being smaller than 5 microns. This toner produced copies having 0.9 optical density with a toner concentration of 0.9 % in the developer mix.

[0022] It was found that the toner of the present invention was relatively insensitive to humidity changes, exhibited a narrow range of charge distribution, and minimized clear filming or toner filming of the photoconductor.

[0023] Humidity dependence of the toner comprising this invention was compared to that of the commercially-available toner used in IBM's Series III model 10 copier. The following table summarizes the results of this at 10 and 80 % relative humidity. The copies produced were typed line copy, having about 4 % of the page covered with toner characters. The optical density of these copies was in the range about 1.0 to 1.1. The term "background" is the difference, expressed in percent, between the light reflectance measured off a sheet of white paper before copying, and the light reflectance measured off this same sheet in its white area, after copying.

[0024] The toner concentration of the previous toner had to be lowered by 20 % at low humidity in order to maintain a reasonably constant optical density. This lower toner concentration for equivalent density indicates that the charge of the toner had dropped.

[0025] This lower-charged toner could not be well controlled by the copier, as indicated by the high background, the increased amount of toner used per copy, and the increased amount of toner which had to be cleaned off the photoconductor by the copiers's cleaning station.

[0026] The toner of this invention, on the other hand, showed no change in concentration at low humidity. The background rose only moderately, while the usage remained the same, and the cleaning load increased only slightly.

[0027] These data indicate the toner of the present invention to be significantly less sensitive to humidity than the previous toner.

[0028] While the invention has been particularly described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. Xerographic toner composition, characterized in that it contains a three-resin mixture of 5 to 55 % by weight an acrylic polymer, 15 to 50 % by weight a copolymer of styrene and an acrylic monomer, 15 to 25 % by weight an aromatic hydrocarbon resin which includes styrene and styrene derivatives; and 5 to 20 % by weight of a coloring matter.

2. Xerographic toner composition of claim 1 characterized in that it contains a three-resin mixture of 36 % by weight an acrylic polymer, 35 % by weight a copolymer of styrene and an acrylic monomer, 17 % by weight an aromatic hydrocarbon resin which includes styrene and styrene derivatives, and 12 % by weight of a coloring material.

3. Xerographic toner composition of claims 1 and 2 characterized in that the acrylic polymer is a copolymer of 60 % n-butyl methacrylate and 40 % methyl methacrylate; the copolymer is 67 to 73 % styrene and 27 to 33 % n-butyl methacrylate; the aromatic hydrocarbon resin includes styrene and styrene derivatives; and the coloring material is carbon black.

4. Xerographic toner composition of claims 1 to 3 characterized in that the glass transition temperature of the acrylic polymer is 60 to 67 °C and its molecular size by weight is 110 to 165 nm, and by number 50 to 80 nm; and the glass transition temperature of the copolymer is 66 to 73°C and its molecular size by weight is 160 to 200 nm, and by number 50 to 70 nm; and the glass transition temperature of the hydrocarbon resin is 52 to 56°C and its molecular size by weight is 120 to 140 nm, and by number 100 to 115 nm.