US 3290251 A
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United States Patent 3,299,251 ELECTROSTATIC LATENT EMAGE DEVELOPING COMPOSITIONS CONTAINING AN ETHlER George R. Nelson, Holliston, Mass, assignor to Dennison Manufacturing Company, Framingliam, Mass, a
corporation of Nevada N0 Drawing. Filed Dec. 16, 1963, Ser. No. 330,597
7 Claims. (Cl. 25262.1)
This invention relates to electrophotography, and more particularly to improvements in the development of visible images from latent electrostatic images by the use of liquid developers.
In electrophotography, latent electrostatic images are formed on a photoconductive surface of a recording element by uniformly charging the surface thereof, as by a corona discharge device in the dark, followed by exposure to light in the desired image pattern. Such images have been heretofore developed or rendered visible by use of liquid developers comprising colored toner particles suspended in an insulating liquid. It is known that the insulating liquid should have high volume resistivity, preferably at least 10 ohm-centimeters and a low dielectric constant, preferably less than about 3.4. Suitable liquids include aromatic hydrocarbons such as benzene, toluene, zylene, etc.; aliphatic hydrocarbons such as hexane, cyclohexane, heptane, etc.; freons or halogenated hydrocarbons; silicone oils; or mixtures thereof. The suspended toner particles are electrostatically charged and develop the latent image by migration to the image surface under influence of the image charge.
To obtain a positive print by development as described above, the suspended toner particles should carry an electrostatic charge opposite to the charge present in the electrostatic latent image. Latent images currently used are negatively charged and the toner particles should carry a positive charge to obtain a positive print therefrom. Obtaining satisfactory positive charge of suspended toner particles has heretofore been largely a matter of trial and error. A number of previously prepared developers have been found to have either an inadequate positive charge on the suspended toner particles or to have a negative charge thereon. Negatively charged particles, when used with negatively charged latent images, provide a negative print wherein the discharged or background image areas are developed with color. The entire background may be developed, or the colored particles may deposit at the boundary between charged and uncharged areas providing a print condition known as ghosting. In either case, desired image areas are not developed.
It is the principal object of the present invention to provide improved liquid development of electrostatic images and improved liquid developers therefor having positively charged toner particles suspended therein.
In accordance with this invention it has been found that liquid developers having negative or inadequately positive charges on the toner particles suspended therein can be modified to provide the desired positive charge by dissolving in the liquid suspending medium a nonepoxy ether having a dielectric constant of about 8.0 or less. The solution of insulating liquid and ether together should have a dielectric constant less than about 3.4.
Any non-epoxy ether of carbon, hydrogen and oxygen, soluble in the insulating liquid in effective amount and meeting the above requirements for dielectric constant, can be used. Epoxy as used herein refers to the structure 3,296,251 Patented Dec. 6, 1966 ether; diphenyl ether; benzyl ether; benzyl-methyl ether; benzyl-ethyl ether; benzyl-butyl ether; phenyl-methyl ether; phenyl-ethyl ether; dioxane; trioxane 1,3,5; ethylene glycol dimethyl ether; diethylene glycol dimethyl ether; triethylene glycol dimethyl ether; tetraethylene glycol trimethyl ether; diethyl Cellosolve (ethylene glycol diethyl ether); dibutyl Cellosolve (ethylene glycol dibutyl ether); diethyl); Carbitol (diethylene glycol diethyl ether); dibutyl Carbitol (diethylene glycol dibutyl ether); dioxolane', 4 methyl, 2 vinyl 1,3 dioxolane; and alpha-ethyl-benzylether. The preferred ethers, other than furan have one of thefollowing generic formulas wherein each R, taken individually, is a lower aryl or lower aliphatic hydrocarbon radical, each R, taken individually, is a lower arylene or lower divalent aliphatic hydrocarbon radical, and n is Zero or a lower positive integer.
The amount of the other necessary to obtain the desired positive charge on a particular liquid toner depends upon the ether selected, the toner particles present, and the past treatment of the toner particles which influences the charge thereon. Generally, from about lto 10% by weight of the insulating liquid is the most frequently useful range. Suitable amounts of a particular ether for a particular liquid developer can be readily determined. It sufiices, for example, to prepare several samples of the liquid developer in question, adding differing amounts of a particular ether to each of these examples, developing a standard electrophotographic latent image with each of the so treated examples, and comparing the print quality to determine that amount which provides the best results. Too little ether will provide a negative print or a poor positive print. Unduly large amounts of ether reduce contrast and cause some precipitation of suspended toner particles. Between these limits, the amount of the ether is not particularly critical for useful results.
This invention can be better understood by reference to the following examples, wherein all parts are by weight unless otherwise indicated.
EXAMPLE 1 Toner concentrate Carbon Black 10 Resin 10 Odorless Mineral Spirits (OMS) 40 Developers Material (a) (b) (c) Toner Concentrate 0. 5 0. 5 0. 5 0. 5 OMS s- 100 100 Dioxane 0. 2 O. 5 l5 Electrostatic latent images negatively charged in a conventional corona device and exposed to light through an image, were immersed in each of the above developers. Example 1(a) provided a negative print wherein the toner particles were attracted to the boundary of the image areas but did not develop the areas themselves, a condition known as ghosting. Example 1(1)) provided prints almost free of ghosting, whereas Example 1(a) provided prints of excellent quality completely free of negative development. Example 1(0) is thus a preferred example. Example 1(d) provided a positive print free of ghosting but has slightly reduced contrast. Still higher amounts of dioxane resulted in increasing precipitation of toner.
EXAMPLE 2 Toner concentrate Carbon Black l Resin l0 OMS 6 Developers Material (a) (b) (0) Toner Concentrate 0. 0. 5 0. 5 0.5 0. 5 OMS 100 100 100 100 100 Diethyl Ce1losolve 7. 5 Dibutyl Cellosolve... 10.0 Diethyl Carbitol 5.0 a. Dibutyl Carbitol 9. 0
Example 2(a) again provided negative prints which were rendered positive, by the addition of the various ethers indicated in Examples 2(b) through 2(e). While the amounts of ether stated are preferred, greater or lesser amounts can be used.
EXAMPLE 3 Material (a) Carbon Black 0.2 0.2 Resin OMS Dioxane Each of the above formulations provided positive prints and was prepared by dispersing the carbon black in the melted resin, cooling and ball-milling, followed by suspension in the OMS in which the ether was dissolved.
EXAMPLE 4 The base developer provided a negative print. Addition of any of the ethers specified to the OMS of the 'base developer provided good quality positive prints. The developers were prepared as stated in Example 3.
In each of the preceding examples, the resin used was an alkyd resin, Aroplaz 1279-P1 of the Archer Daniels Company, a resin found to provide negatively charged toner particles. OMS is a mixture of paraffin hydrocarbons obtained from the American Mineral Spirits 4 Company having a distillation range from 352 to 390 F. and a flash point of 125 C.
EXAMPLE 5 A commercially available liquid developer, Electrophotographic Toner EHS obtained from the Cabot Corporation, was found to provide a negative print with a negatively charged latent image when 0.5 parts of the commercial developer were further diluted with 75 parts OMS. Addition of 10 parts dioxane provided positive prints of good quality.
In copending application, Serial No. 326,245, filed November 26, 1963, liquid developers are disclosed wherein the toner particles are liquid droplets suspended in the insulating liquid. The following emulsion developer of this type was found to give a negative print with a negatively-charged latent electrostatic image.
EXAMPLE 6 External phase Lube Oil 564 30 Aluminum Dresinate 731 .01
Internal phase Ethanol 32 Dye:
Orasol Black BV 2 Spirit Soluble Fast Brown BE 2 0.5 part of the internal phase were emulsified in the external phase with two minutes mechanical mixing in a Hamilton-Beach mixer. 400 parts additional OMS was then added with hand stirring. The resulting developer gave negative prints with a negatively charged latent image. Dilution of the concentrated emulsion with a solution of 3150 parts OMS and 50 parts dioxane, in place of the 400 parts OMS, provided good quality positive prints.
Lube Oil 564 and the Aluminum Dresinate are dispersant aids as more fully disclosed and claimed in my copending application Ser. No. 343,142, filed February 6, 1964. They may be omitted if the emulsion is used before substantial separation occurs. Lube Oil 564 is a copolyrner of laurylmethacrylate-diethylaminoethyl-methacrylate obtained from the E. I. du Pont de Nemours and Company. Dresinate 731 is the sodium salt of poly-rosin acid obtained from Hercules Chemical Co.
The latent images employed in the foregoing examples comprised paper coated with particles of photoconductive zinc oxide and a sensitizing dye suspended in a thermoplastic resin. The coating was charged by a corona device at 6 kv. negative potential and discharged with light through an image.
It should be understood that the foregoing description is for the purpose of illustration only and that the invention includes all modifications falling within the scope of the appended claims.
1. For developing an electrostatic image, a liquid developer consisting'essentially of an insulating liquid having suspended therein finely-divided toner particles with an average size less than about 40 microns, said developer being characterized by having dissolved in said insulating liquid as charge modifier and in an amount sufiicient to provide a positive charge on said toner particles and not more than about 15% by weight of said insulating liquid, an organic ether selected from the group consisting of furan, 4 methyl, 2 vinyl 1,3-dioxolane, and ethers having one of the following structures:
wherein each R, taken individually, is a phenyl, benzyl, or lower alkyl radica-l, each R, taken individually, is a phenylene, benzylene or lower alkylene divalent radical, and n is zero or a lower positive integer, said ether having a dielectric constant less than about 8.0, said solution of liquid and ether having a dielectric constant less than about 3.4 said toner particles in said insulating liquid, absent said ether, having inadequate positive charge to develop a positive print from a negatively charged image.
2. A liquid developer according to claim 1, wherein said ether is selected from the group consisting of furane; dibutyl ether; diamyl ether; diphenyl ether; benzyl ether; benzyl-methyl ether; benzyl-ethy-l ether; benzyl-butyl ether; phenyl-methyl ether; phenyl-ethyl ether; dioxane; trioxane 1,3,5; ethylene glycol dimethyl ether; diethylene glycol dimethyl ether; triethylene glycol dimethyl ether; tetraethylene glycol trimethyl ether; ethylene glycol diethyl ether; ethylene glycol dibutyl ether; diethylene glycol diethyl ether; diethylene glycol dibutyl ether; dioxolane; 4 methyl, 2 vinyl 1,3-dioxolane; and alpha-ethyl-benzyl-ether. l
3. A liquid developer according to claim 1 wherein said ether is dioxane.
4. A liquid developer according to claim 1 wherein said ether is dibutyl ether.
5. A liquid developer according to claim 1 wherein said ether is ethylene glycol dimethyl ether.
6. A liquid developer according to claim 1 wherein said ether is diphenyl ether.
7. A liquid developer according to claim 1 wherein said ether is 'benzyl methyl ether.
References Cited by the Examiner UNITED STATES PATENTS 2,213,006 8/1940 Johnson 106-26 2,877,133 3/1959 Mayer 25262.1 2,892,794 6/1959 Insalaco 252-62.1
OTHER REFERENCES Fieser and Fieser, Organic Chemistry, 3d ed., Reinhold, pp. 137-138 (1956).
SAMUEL H. BLECH, Primary Examiner.
JULIUS GREENWALD, Examiner. J. D. WELSH, Assistant Examiner.