US 3090755 A
Description (OCR text may contain errors)
3,090,755 XERGGRAPHIC PROCESS TONER AND METHOD OF PRODUCING SAME Andrew Erchak, Bernardsvilie, and John C. Van Dyk, Morris Plains, N.J., assignors to International Business Machines Corporation, New York, N .Y., a corporation of New York No Drawing. Filed Dec. 31, 1958, Ser. No. 784,039 6 Claims. (Cl. 252-621) This disclosure deals with a xerographic toner which consists of shellac and carbon black in the form of particles enclosed partially or wholly in a thin rubber or equivalent coating. The requirements which led to the development of this toner are set forth briefly as follows.
A xerographic toner in addition to having the necessary features of functioning in an xerographic process and producing good quality prints must comprise two good characteristics. The first of these is that it should not soil the selenium plate used in such a process after a few hours of automatic machine operation, necessitating solvent cleaning. The tendency of a toner to adhere to the plate and resist mechanical removal in time results in the deterioration of print quality. A satisfactory toner then in this respect must perform as good, if not better than those presently commercially available.
The second, and a very important feature is that the degree of fix of the toner to the paper by heating be such that the toner cannot be easily rubbed off. Although no standard tests to establish the degree of fix have as yet been established, a simple test sometimes made is that of simply rubbing a clean white handkerchief, for example, across a page of heat fixed xerographically printed paper under firm pressure. If a smudge appears on the handkerchief the fix is not suflicient, and if not, it is. In brief, the degree of fix obtained should be comparatively as good as that obtained with a solvent fixed toner.
All presently commercially available toners fall to pass the above smudge test.
The shellac toners of this invention have a degree of fix superior to that of prior toners. In addition, their tendency to film on the selenium plate while at a faster rate than higher melting toners, is still adequate to make them commercially feasible.
It is known, of course, that shellac as a toner for this process is in itself not novel, but the subsequent treatment thereof in accordance with the disclosure herein produces novel toners.
The novel subject matter of this application comprises a toner for developing a xerographic image comprising a sufficiently low melting finely divided resin, of which shellac is an example, pigmented for example with carbon black, characterized in that the resin particles are encased, either wholly or in part, in a thin coating of a higher melting coating compound such as rubber, polyvinyl acetate, polystyrene, styrene butadiene or an acrylic. This application also includes methods of making these toners. These toners greatly reduce filming of the image plate used in xerographic processes and retain good fixing properties.
In view of the foregoing an important object of this invention is to provide new xerographic toners which do not smudge, smear or film the image plate on repeated use thereof, thus improving the process whether it comprises hand or machine operation.
Another object of this invention is to provide toners of this kind which are basically composed of a sufl'iciently low melting, non-tacky material facilitating firm fixing thereof by heat, so that the image reproduced on the printed paper will not smudge easily.
3,990,755 Patented May 21, 1963 Another object of the invention is to provide improved toners of this type which give strongly colored images with excellent resolution and good contrast and appearance.
Another object of this invention is to provide novel methods of producing the novel toners herein disclosed.
Other objects of the invention will be pointed out in the following description and claims, which disclose, by Way of example, the principle of the invention and the best mode which has been contemplated, of applying that principle.
The important feature of this invention comprises the encasement, either wholly or in part, of pigmented low melting resins in powder form with a low filming coating. As a specific embodiment of this invention, the resin is desirably shellac, subdivided into particles of micronic size, and impregnated with any one of the various pigments which are known in the art of xerography, comprising for example the commonly used carbon black. The pigmented powdered particles are then encased in a low filming material, of which rubber has been found to be highly effective. The final product is processed to agglomerated particles, and is then ready for dusting or otherwise applying to the plate or drum containing an electrostatic image to be developed and fixed.
As one detailed example of a toner in accordance with this invention, shellac is milled and blended on a two-roll heated rubber mill with from 2 to 20% carbon black to provide the pigmented resin which is the basis by way of example, for subsequent processing in accordance with this invention. For a large scale operation a Banbury mixer is desirable. The pigmented resin is further processed to reduce its particle size to less than 25 microns. At this stage the toner would be suitable for use in fixing the electrostatic image of the xerographic process, but it Would film the plate badly.
Further in accordance with 'the invention, rubber is added to the mix in the form of a solvent solution and the two are stirred vigorously to effect complete blending as well as complete or partial coating of the individual pigmented resin particles with the rubber. A suitable rubber solution for the purpose is a 2% solution of pure rubber in benzene which is further diluted, as will be explained below, before blending with the pigmented resin. The blending and mixing step can continue for ten minutes to one-half hour. The mixture is then filtered and allowed to dry. !If any large lumps of the resultant product occur the mixture is reground to produce a final product in the proper degree of fineness.
A more specific example of this procedure comprises diluting cc. of a 2% solution of rubber in benzene by admixture with an additional cc. of benzene in a stainless steel beaker equipped with an agitator. A suitable commercial 2% benzene rubber solution, for example, is presently available from Mallinckrodt Company. While the diluted solution of rubber is being vigorously agitated in the beaker, 100 grams of the pigmented resin is added. A suitable toner is 90 parts of a finely powdered shellac commercially obtainable for example from Gillespie, Rogers & Pyatt, and known as PO #2 Lemon Shellac. This shellac has a melting point of between 158" F. to 176 F. In this example 10 parts of carbon black, commercially available as Neo Spectra Mark 11, is used, but a very wide range of suitable carbon blacks are available in the art.
The pigmented toner introduced into the beaker was first prepared by thoroughly mixing and blending the shellac and the carbon black. When the contents of the beaker has been agitated to effect thorough blending of the constituents, the mixture is filtered on a Biichner funnel, and then air dried, for example for three days or less it forced heat is used. The filtered and dried prod- A uct' not unusually will contain some lumps, requiring its V The introduction of the acetone results in the precipitation of the rubber onto the toner particles, The final mix is then treated as before, that is, filtered, air dried and reground to produce the finished product.
A further method of compounding the toner consists in adding the coating ingredient, for example the rub ber, either in solution in a volatile solvent or in an emulsion to the shellac and carbon black on a two-roll mill. The mixture is then milled to thoroughly blend it and as before jet ground; The resulting product is an improved and useful toner which, however, does not exhibit 'quite as good non-filming properties as the toners prepared by the other methods herein described.
By these procedures and any modifications thereof which would be readily apparent to those skilled in the art, the toner resin is first pigmented with a suitable pigment and the pigmented particles are then completely or partially encased in a less tacky or a higher melting material.
With regard to the toner particle coating material, when using rubber, it is preferred that pure latex solutions be employed. In addition, however, the coating material may comprise water emulsions as suggested above of such materials as polyvinyl acetate, polystyrene, styrene butadiene, acrylics, nylon, polyethylene, polyvinyl chloride, and other materials suitable for the purpose.
Those skilled in this art will readily recognize that there are known equivalents of the basic toner ingredients, namelyshellac, and these are contemplated as within the idea of this invention to provide high melting, less tacky coatings for these toners after they have been pigmented.
An important improvement in the xerographic processing art results from the use of the toners of this invention, namely that this toner does not foul or film the image plate readily, adapting it particularly for use in automatic xerographic reproducing equipment with a minimum of plate or drum cleaning. In addition, advantage results from its excellent fixing qualities at suitably low temperatures. 'Finally, these toners give sharp, strongly colored prints with excellent resolution.
It is believed that the decrease in filming or 'fouling of the plates is the result of the encasement of the toner in a less tacky coating, such as the rubber coating.
While there have been described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device and its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.
What is claimed is:
1. A xerographic toner consisting essentially of particles of an average size of less than 25 microns of shellac pigmented with between about 2% and 20% pigment, said particles coated with a non-filming material having a higher melting point than said resin and selected from the group consisting of rubber, polyvinyl acetate, polystyrene, polyethylene, polyvinyl chloride, nylon, acrylic plastics and styrene butadiene synthetic rubber.
2. An improved xerographic toner comprising finely divided powder particles of an average size of less than 25 microns and consisting essentially of finely divided particles of shellac which are pigmented with between about 2% and 20% pigment, the pigmented shellac particles being overcoated with material selected from the group consisting of rubber, polyvinyl acetate, acrylic plastics, nylon, polystyrene, polyethylene, polyvinyl chloride, and styrene butadiene synthetic rubber.
3. An improved xerographic toner comprising finely divided powder particles of an average size of less than 25 microns and consisting essentially of finely divided particles of shellac which are pigmented with between about 2% and 20% pigment, the pigmented shellac particles being overcoated with rubber.
4 The method of making a xerographic toner comprising the steps of blending and comminuting finely divided particles of shellac with from between about 2% and about 20% of pigment to form pigmented particles, blending the pigmented particles with a liquid containing rubber for overcoating said pigmented particles,'extracting the solids from the resulting mixture, air drying said solids, and grinding the air dried product to particles of an average size of less than 25 microns.
5. The method of making a xerographic toner com prising the steps of blending and comminuting finely divided particles of shellac with from between about 2% and about 20% of pigment to form pigmented particles, blending the pigmented particles with a liquid containing a material selected from the group consisting of rubber, polyvinyl acetate, polystyrene, polyethylene, polyvinyl chloride, nylon, acrylic plastics, and styrene butadiene synthetic rubber for overcoating said pigmented particles, extracting the solids from the resulting mixture, air drying said solids, and grinding the air dried product to particles of an average size of less than 25 microns.
6. A xerographic toner consisting essentially of particles of an average size of less than 25 microns of shellac having a melting point of between about 158 F. to 176 F. which are'pigmented with between about 2% and about 20% of a pigment and overcoated with a material selected from the group consisting of rubber, polyvinyl acetate, polystyrene, polyethylene, polyvinyl chloride, nylon, acrylic plastics and styrene butadiene synthetic rubber.
References Cited in the file of this patent UNITED STATES PATENTS Re. 20,029 Fischer July 7, 1936 2,009,435 Coolidge et a1. July 30, 1935 2,618,551 Walkup Nov. 18, 1952 2,724,659 Jobbins Nov. 22, 1955 2,899,335 Straughan Aug. 11, 1959 2,940,934 Carlson June 14, 1960 FOREIGN PATENTS 564,712 Canada Oct. 14, 1958