US3493412A

US3493412A - Transferring xerographic toner images to a solid crystalline plasticizer coated receiving surface

Info

Publication number: US3493412A
Authority: US
Inventors: Herbert N Johnston; Nicholas D Gallagher
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1965-12-30
Filing date: 1966-01-17
Publication date: 1970-02-03
Anticipated expiration: 1987-02-03
Also published as: GB1183205A; DE1522714B2; US3488189A; US3619279A; DE1522714A1; FR1506810A

Description

United States Patent 0 U.S. Cl. 11717.5 14 Claims ABSTRACT OF THE DTSCLOSURE An imaging process wherein an electrostatic latent image is developed with a thermoplastic resin toner on an imaging surface and the toner image is transferred to an image receiving surface carrying an amount of a solid crystalline plasticizer sufficient to lower the toner fusion requirements when the toner image is fused to the receiving surface.

This invention relates in general to imaging systems, and more particularly, to improved receiving surfaces, their manufacture and use.

The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic xerographic process as taught by C. F. Carlson in U.S. Patent 2,297,691 involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting latent electrostatic image by depositing on the image a finely divided electroscopic material referred to in the art as toner. The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image. This powder may then be transferred to a receiving surface such as paper. The transferred image may subsequently be permanently afiixed to the support surface as by heat. Instead of latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a light and shadow image, one may form the latent image by directly charging the layer in image configuration. Several methods are known for applying the electroscopic particles to the latent electrostatic image to be developed. These methods include cascade development, magnetic brush development, powder cloud development and liquid development as described in U.S. Patents 2,618,552; 2,874,063; 2,221,776; and 2,891,911 respectively. The processes mentioned above together with numerous variations are well known to the art through various patents and publications and through the widespread availability and utilization of electrostatic imaging equipment.

A variety of types of finely divided electroscopic powders are disclosed in the Carlson patent. However, as the art of electrostatic copying has progressed, a variety of pigmented thermoplastic resins have evolved as the preferred toner materials when heat is employed to fuse the thermoplastic toner image to a support surface. While ordinarily capable of producing excellent quality images, these toner materials possess serious deficiencies in certain areas. When the toner is to be fused onto an inflammable surface such as paper, the toner resin should have a fusing temperature below the thermal degradation temperature of the paper. Upon heating to the discoloration temperature or flame point of some papers, resinous toners having high fusing temperatures often do not become sufficiently fluid to penetrate and adhere to the paper. The resulting powdery and incompletely fused images are easily removed by rubbing. On the other hand, toner resins having low fusing temperatures are usually tacky at ordinarily encountered ambient temperatures and form undesirable agglomerates during storage and handling. Additionally, images on copies manufactured from tacky toners have a tendancy to offset onto adjacent surfaces. Some tacky toners form smears on reusable electrophotographic imaging surfaces which are diflicult to remove. Where the toner materials smears excessively, a film of toner material builds up on the electrophotographic surface. This film has different electrical characteristics than the plate and, if hydroscopic in nature, detrimentally affects the conductivity of the electrophotographic surface when relative humidity is high. Thermoplastic resins having consistently uniform molecular weights are diflicult to manufacture. Since thermoplastic resins are usually an amorphous mixture of polymer chains having different molecular weights and normaly possess a non-uniform melting range rather than a sharp melting point, it is difiicult to accurately predict the temperature at which any given polymeric thermoplastic resin will fuse and adhere to a receiving sheet. Toners having erratic fusing temperatures and wide fusing temperature ranges require that the machines have a built-in fusing safety factor. Since the temperature in the fuser cannot be raised above the char point of the paper, this often imposes an undesirably low upper limit on the speed of the paper through the fuser. Further, the heat fusing units currently emplOyed to fuse conventional thermoplastic toners often cause the temperature of poorly ventilated rooms to reach levels which shorten machine component life and contribute to operator discomfort. It is known, as disclosed in U.S. Patent 3,130,064 to improve toner fusing at lower temperatures by employing business machine record cards treated with thermoplastic resins dissolved i organic solvents. Unlike a plasticizer, the thermoplastic resin apparently functions as a melting agent with like melting like. Although the disclosed plastic resin films may reduce toner fixing temperatures, the thermoplastic resin melting range problems described above have not 3 been obviated. Pencil and ink markings are difi'icult to apply and remove from surfaces coated with the thermoplastic resin films. Also, more complex equipment and specially designed paper making processes are required when the thermoplastic resin films are applied with inflammable, expensive and toxic organic solvents. Since most thermoplastic toner particles, receiving sheets, and developing processes are deficient in one or more of the above areas, there is a continuing need for a better system for fusing toner images.

It is, therefore, an object of this invention to provide a receiving surface overcoming the above-noted deficiencies.

It is another object of this invention to provide a receiving surface which reduces the quantity of heat energy necessary to fuse toner images.

It is another object of this invention to provide a receiving surface which eifectuates uniform and sharp toner fusion temperatures.

It is another object of this invention to provide a receiving surface which is receptive to ink and pencil markmgs.

It is another object of this invention to provide a receiving surface which is easily erasable.

It is another object of this invention to provide a receiving surface which allows the employment of cooler, more compact toner fusing units.

It is another object of this invention to provide a receiving surface which permits the use of higher electrophotographic imaging machine speeds.

It is another object of this invention to provide a receiving surface which allows the employment of high melting non-tacky toners.

It is another object of this invention to provide a receiving surface having physical and chemical properties superior to those of known receiving sheets.

The above objects and others are accomplished, generally speaking, by providing a receiving surface treated with a solid crystalline plasticizer which eifectuates complete thermoplastic toner fusion under heating conditions at which untreated surfaces afford only marginal or no fusion. Crystalline plasticizers, which separate from the thermoplastic resins when the plasticized resin is cooled to room temperature are used because tacky images and attendant offset problems are then avoided. It is believed that separation occurs in the form of tiny islands of crystalline plasticizer particles in a matrix of tone material. Although it is not clear, it is believed that when solid, crystalline plasticizers are heated above their melting point, they weaken the Van der Waal forces existing in the thermoplastic toner polymers and allow slippage of the long linear polymer chains thereby promoting fluidity at lower temperatures. Experiments have revealed that some liquid plasticizers provide virtually complete toner fusion under heating conditions at which untreated receiving surfaces give only marginal fusion, but the resulting image is either permanently tacky or tacky for extended periods of time. Receiving surfaces carrying tacky images plasticized with liquid plasticizers will offset toner material to adjacent surfaces and cause feathering of the images. Additionally, the non-imaged areas of receiving surfaces treated with liquid plasticizer will at room temperature actively soften and render tacky any thermoplastic image on adjacent surfaces. A solid crystalline plasticizer having a melting point greater than about 45 C. is preferred, because premature melting and activation during storage is avoided and rapid plasticizer recrystallization in toner images is promoted. To be effective, the solid plasticizer should have a melting point below the melting range of the thermoplastic toner resin. The uniform and sharp melting point characteristics of crystalline plasticizers permit the employment of cooler and more efficient fusing units in precision electrostatic imaging machines.

Outstanding results have been obtained with ethylene glycol dibenzoate (EDDB) and blends of EGDB and diphenyl phthalate (DPP). When receiving surfaces treated with EGDB are employed, the speed of existing electrophotographic copying machines have been more than doubled. Additionally, EGDB recrystallizes in seconds when cooled to room temperature. Other suitable solid plasticizers may, however, be substituted for EGDB. Typical solid, crystalline plasticizers include: ethylene glycol dibenzoate, dimethyl isophthalate (DMIP), glycerol tribenzoate, dicyclohexyl phthalate (DCHP), diphenyl phthalate, and blends thereof.

Any suitable receiving surface may be treated with the plasticizer material of this invention. For example, the surface of sheets, Webs, planks, or even massive objects may be coated or impregnated with the solid plasticizer of this invention. The receiving surface may be composed of any suitable organic material, inorganic material, or mixtures thereof. If the receiving surface contains a thermoplastic resin, it may be desirable to select a plasticizer which does not plasticize and distort the receiving surface. Conversely, distortion of the receiving surface may be deliberately induced to achieve a desired decorative effect.

The plasticizer composition may be applied to the receiving surface by any conventional method such as spraying, electrostatic deposition, dipping, fluidized bed coating, brushing, or roll coating. Further, the plasticizer may be added to the receiving surface in any suitable manner prior to, during, or subsequent to the manufacture of the receiving surface. For example, the plasticizer may be ap plied alone or in combination with other materials as a powder, dispersion, solution, vapor, emulsion, or melt to paper during or after the paper-making process. Optimum results have been obtained when the plasticizer is applied admixed with a binder because the problem of dust contamination is eliminated. Any suitable binder may be employed to immovably attach the solid plasticizer to the receiving surface. Typical binders include: acetylated starch, styrene-butadiene latex, carboxy-methyl cellulose, polyvinyl pyrrolidone, acrylic latex, polyvinyl acetate, polyvinyl alcohol, soy proteins, casein, hydroxyethylated starch and mixtures thereof. Any of the conventional additives such as antioxidants, emulsifiers, brightners, solvents, surfactants, suspending agents, antifoam agents, coloring agents and fillers may be employed with the binder. Binders comprising acetylated starch, styrene-butadiene copolymers, polyvinyl pyrrolidone, casein, polyvinyl alcohol and mixtures thereof are preferred because they are very stable in conventional high-speed paper coating apparatus. Surprisingly, tone images formed on re ceiving surfaces treated with a binder and plasticizer mixture are more dense than toner images formed on untreated receiving surfaces. Additionally, paper sheets treated with a binder and plasticizer mixture lie flatter after toner fusing than untreated paper. It is preferred that the binder content remains below about 40 percent, based on the Weight of the plasticizer, as this provides much more efficient fusing apparently because more plasticizer is available at the surface where the toner is to be fused to the receiving member.

Paper sheets or webs are normally employed as the receiving surface in most conventional electrostatic imaging processes. The paper may comprise organic and/or inorganic fibers such as cellulose, modified cellulose, polymeric resin, glass, and asbestos fibers. The plasticizer may be added to paper at any stage of the paper-making process. Surface coatings containing at least about 0.4 pound of plasticizer per ream (500 17 in. x 22 in. sheets, 1300 square feet) will markedly reduce toner fusion power requirements although smaller amounts may also have some effect. When the plasticizer material is incorporated into the paper prior to sheet formation, e.g., in the beater, or subsequent to web formation, e.g., by impregnation, pro

portionately more plasticizer is necessary in order to maintain a sufficient quantity of plasticizer at the surface of the paper sheet. Excellent results are obtained when from about 0.5 to about 1.5 pounds of plasticizer per 1300 square feet is applied to receiving surfaces as a surface coating.

Electroscopic toner compositions are well known to those skilled in the art. Among the patents describing such compositions are US. 2,618,551 to Walkup, US. 2,618,552 to Wise, U.S. 2,638,415 to Walkup and Wise, US. 2,659,670 to Copley, and US. 2,788,288 to Rheinfrank and Jones. These toners generally have an average particle diameter between 1 and 30 microns. Clearly, the

TONER FUSION EFFECTS OBTAINED ON PAPER T [PLASTICIZER COMPOSITIONS, PAR

doctoring with a reverse rotating No. 4 wire-wound rod and finally dried by heated air. The electrostatically imaged sheets are passed at selected speeds under a quartz filament infra-red heater unit operated with a fixed power input. For comparative evaluations, a power index value is assigned to the fusing conditions employed. The power index value is computed as follows:

Power index, watts/(in./sec.)

Power input, (watts) Transport speed, (in/sec.)

Tack and the quantity of powder rub off of the fused images onto cotton are also compared.

REATED WITH PLASTICIZERS TS BY WEIGHT] Polyvinyl Power Styrenepyrrolidone, index, butadiene solids Acetylated watts/ Grind 1 Latex (Iggy (K-BO) starch (in./sec.) Toner Fusion Results 500 Fuses, no rub off, non-tacky. 250 Very poor fusing, powdery rub ofi. 133 Good fusing, no rub off, slightly tacky; 133 Do. 125 Good fusing, no rub off, non-tacky. 115 Do. 299 (DMIP) 276 Do. VIII 80 (EGDBL. 130 Do. IX 80 (EGDB) 225 Do.

1 Prepared by diluting ball mill grinds oi the following compositions (parts by weight) with the indicated additives:

Ethylene glycol Dicyclohexyl phthalate Diphenyl phthalate dibenzoate (E GDB) Dimethyl isophthalate (DCHP) grind (DPP) grind grind (DMIP) grind Plasticizer 150 150 150 150 Sodium salt of processed rosin (Dresinate X) 1 1 1 1 Polyvinyl pyrrolldone (PVP Type K-). 2 2 2 2 Water 7 147 277 146 plasticizer treated receiving surface should be used with In the following Examples X-XXXIX, sheets treated those thermoplastic resin toners which will be plasticized by the specific plasticizer employed in the receiving surface. Selection of compatible combinations of solid crystalline plasticizer ad thermoplastic resin toner will be obvious to those skilled in the art. Blends of two or more plasticizers may be used to broaden the toner spectrum of the receiving surface. Typical thermoplastic resins include: acrylic resins, methacrylic resins, cellulose acetate, cellulose nitrate, polystyrene, polyethylene, polypropylene, polycarbonate, modified phenolformaldehyde resins and mixtures thereof.

The following examples further define, describe and compare exemplary methods of preparing the receiving surfaces of the present invention and of utilizing them as substrates for electrostatic latent images. Parts and percentages are by weight unless otherwise indicated.

In the following, Examples LIX are carried out with a toner comprising a styrene and n-butylmethacrylate copolymer, polyvinyl butyral, and carbon black prepared by the method disclosed by M. A. Insalaco in Example I of US. Patent 3,079,342. The treated receiving sheets carry a surface coating of a plasticizer mixture applied as an aqueous dispersion by means of a smooth metal reverse roll in a Dietzco-Dixon Pilot Coater followed by with the compositions in Table A are compared with untreated sheets. Different quantities of treatment material per ream and various transport speeds are employed to demonstrate how these two factors affect fusing energy requirements. The power index required to obtain equivalent fusion with untreated paper is determined by comparing the rub off from a treated sheet with a standardized rub off series obtained with untreated sheets. The images on untreated and treated sheets are deemed equivalent when the quantity of rub off from each is identical. The toner material is rubbed off by drawing a two-inch square cloth (Crockmeter Square, Test Fabrics, Inc.) weighted with a 500 gram balance weight across and along an 11 inch length of the imaged sheet. The percentage reduction in power input required to obtain equivalent fusion was calculated according to the following formula:

Power index required to obtain equivalent fusion with untreated paper TABLE A.-PLASTICIZER COMPOSITIONS, PARTS BY WEIGHT Hydroxy- Sodium ethyl salt of derivative processed of corn Polyvinyl Styrene- Ethylene Polyvinyl rosin starch cohol butadiene glycol pyrrolidone (Dresinate (Penford Elvauol latex Treatment system dibenzoate (K-30) X Gum 280) 72-60 Water (D ow 636) 840. 0 11. 2 265. 0 840. 0 11. 2 304. 0 840. 0 11. 2 304. O 840. 0 11. 2 304. 0 840. 0 11. 2

TONER FUSION PROPERTIES OBTAINED WITH PAPERS TREATED WITH PLASIIGIZERS Power index required to obtain Power equivalent Reduction Treatment Treatment settings Transport Corresponding fusion with in power system level, used speed, fewer index, untreated input, Examples applied lbsiream watts in./seo. watts, in./sec. paper percent 864 1. 7 508 508 864 1. 4 617 617 O 864 1. 1 783 783 0 864 1. 7 508 718 29. 0 (2) 864 1. 4 617 718 14. 1 (2) 864 1.1 783 1, 438 45. 6 (1) 864 1. 7 508 718 29. 0 (1) 864 1. 4 617 957 35. 6 (1) 864 1. 1 783 957 18. 2 (1) 864 1. 7 508 664 21. 3 (1) 864 1. 4 617 7 14.1 (1) 864 1. 1 783 1, 149 31. 9 (3) 864 1. 7 508 718 29. 0 (3) 864 1. 4 617 862 28. 5 (3) 864 1. 1 783 1,438 45. 6 (3) 864 1. 7 508 640 20. 1 (3) 864 1. 4 617 957 35. 6 (3) 864 1. 1 783 1, 149 31. 9 (3) 864 1. 7 508 783 35. 2 (3) 864 1. 4 617 957 35. 6 (3) 864 1.1 783 1,149 31. 9 (3) 864 1.7 508 862 41. 1 (3) 864 1. 4 617 862 28. 5 (3) 864 1. 1 783 1, 438 45. 6 (4) 864 1. 7 508 783 35. 2 (4) 864 1. 4 617 957 35. 6 (4) 864 1. 1 7 1, 438 45. 6 (5) 864 1. 7 508 862 41. 1 (5) 864 1. 4 617 957 35. 6 XXXIX (5) 864 1. 1 783 1, 438 45. 6

1 See table A.

EXAMPLE XXXX Paper sheet are treated with ethyl phthalyl ethyl glycolate, a liquid plasticizer, by dipping the sheets into a methyl alcohol solution containing about 10 percent by Weight of the plasticizer. After the alcohol solvent is driven off, an electrostatically deposited styrene copolymer toner image is transferred to the treated sheet. The sheet is then heated on the back side with a bar type heater for 5 seconds at 125 C. The toner image is completely fused under these heating conditions. With untreated paper, the same heating conditions provide only marginal fusion of the toner image. However, upon aging, the paper treated with the liquid plasticizer is found to offset toner to adjacent sheets and cause feathering of ink images.

EXAMPLE XXXXI Paper sheets are treated with cresyl diphenyl phosphate, a liquid plasticizer, by dipping the sheets into a methyl alcohol solution containing about 9 percent by weight of the plasticizer. After the alcohol solvent is driven off, an electrostatically deposited styrene copolymer toner image is transferred to the treated sheet. The sheet is then heated on a back side with a bar type heater for 5 seconds at 125 C. The toner image is completely fused under these heating conditions. With untreated paper under these same heating conditions, only marginal fusion of the toner image is obtained. However, upon aging, the paper treated with the liquid plasticizer is found to offset toner to adjacent sheets and cause feathering of ink images.

EXAMPLE XXXXII Paper treated with a plasticizer composition containing about 1080 parts EGDB, 14.4 parts polyvinyl pyrrolidone (Ii-), 340 parts butadiene-styrene latex, 0.14 part brightner (Calcofiuor White CBP), 5 parts ammonum hydroxide (28%), 7.2 parts polymerized sodium salt of an alkyl naphthalene sulfonic acid (Daxad 11) and 1083 parts water is imaged with a styrene copolymer toner in a Xerox 813 electrophotographic copier ma chine (similar to the machine described in U.S. Patent 3,099,943) at a 12. copies per minute speed. This speed is twice the normal speed of the Xerox 813 copier. The

toner image is fused and non-tacky. No toner fix whatever is obtained with standard office bond paper run in the same machine at the same speed.

EXAMPLE XXXXIII A rosin-modified phenol-formaldehyde resin toner pre pared in the manner disclosed in Example I of U.S. Patent 2,753,308 is imaged onto a paper sheet treated with the EGDB composition of Example V above. Upon heating between two parallel heating plates, spaced one inch apart, the toner fuses more rapidly on the treated paper than on untreated paper under substantially identical heating conditions.

EXAMPLE XXXXIV A styrene-methyl methacrylate copolymer toner is imaged onto a paper sheet treated with the EGDB composition of Example VIII above. Upon heating between two parallel heater plates, spaced one inch apart, the toner fuses more rapidly on the treated paper than on untreated paper under substantially identical heating conditions.

Although specific materials and conditions are set forth in the foregoing examples, these are merely intended as illustrations of the present invention. Various other suitable thermoplastic resin toners, receiving surfaces, plasticizers, binders, and coating processes such as those listed above may be substituted for those in the examples with similar results. Other materials may also be added to the base, plasticizer, binder or toner to sensitize, synergize or otherwise improve the fusing properties or other desirable properties of the system.

Other modifictaions of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. An imaging process comprising the steps of contacting an electrostatic latent image on an imaging surface with fusible, finely-divided toner particles comprising a thermoplastic resin whereby said particles are attracted to and held on said imaging surfaces in conformanee to said electrostatic latent image, transferring the toner image to an image receiving surface, said image receiving surface carrying thereon a solid crystalline plasticizer for said toner resin when said resin and said plasticizer are fused together, said plasticizer having a melting point below the melting range of said thermoplastic resin toner and being present in an amount sufficient to reduce the toner fusion requirements, and heat fusing said toner image and said plasticizer therewith to said receiving surface.

2. The process of claim 1 wherein said image receiving surface is substantially free of material plasticizable by said solid crystalline plasticizer.

3. An imaging process according to claim 1 wherein at least about 0.4 pound per 1300 square feet of said solid crystalline plasticizer is applied at said image receiving surface.

4. An imaging process acording to claim 1 wherein said image receiving surface comprises paper.

5. An imaging process according to claim 1 wherein said solid crystalline plasticizer is immovably attached to said image receiving surface by means of a suitable binder.

6. An imaging process according to claim 5 wherein said binder composition comprises a binder selected from the group consisting of polyvinyl pyrrolidone, styrenebutadiene copolymer, acetylated starch, casein, polyvinyl alcohol, and mixtures thereof.

7. An imaging process according to claim 1 wherein said solid crystalline plasticizer is ethylene glycol dibenzoate.

8. An imaging process according to claim 7 wherein said ethylene glycol dibenzoate is blended with diphenyl phthalate.

9. An imaging process according to claim 1 wherein said solid crystalline plasticizer is dimethyl isophthalate.

10. An imaging process according to claim 1 further including cooling said heat fused toner image below the recrystallization point of said plasticizer.

11. An imaging process according to claim 1 wherein said heat fusing is carried out at a temperature below the normal melting temperature range of said toner.

12. An imaging process according to claim 1 wherein said solid crystalline plasticizer is immovably attached to said image receiving member by less than about 40 percent by weight of said binder, based on the weight of said plasticizer.

13. An imaging process according to claim 1 Wherein said solid crystalline plasticizer is available at said image receiving surface as a loose powder.

14. An imaging process comprising the steps of con tacting an electrostatic latent image on an imaging surface with fusible, finely-divided toner particles comprising a thermoplastic resin whereby said particles are attracted to and held on said imaging surface in conformance to said electrostatic latent image, transferring the toner image to an image receiving surface, said image receiving surface carrying thereon a solid crystalline plasticizer for said toner resin when said resin and said plasticizer are fused together, said plasticizer having a melting point of at least about C. and below the melting range of said thermoplastic resin toner and being present in an amount sufficient to reduce the toner fusion requirements, and heat fusing said toner image and said plasticizer therewith to said receiving surface.

Mellan, Ibert, Industrial Pla-sticizers, 1963, pp. 153, 154, 180 and 181.

WILLIAM D. MARTIN, Primary Examiner E. J. CABIC, Assistant Examiner U.S.Cl.X.R. 961.4; 1l776, 156, 2603l.6, 31.8