US2917460A - Powder compositions useful as electroscopic toners - Google Patents

Description

POWDER COMPOSITIONS/USEFUL AS ELECTROSCOPI'G'TONERS fiamuel L. Solar, Binghamton, assignor to lnternational Business Machines Qorporation, New York, N.Y., a corporation of New'Y'ork N Drawing. Application June 17, 1955 Serial N0. 516,314

The present invention relates to powder compositions useful as electroscopic toners and par'ticularly' to such powder compositions as may be -usedasthe electros'copic powder ortoner in' the developmer'rt of electrostatic, electrographic or electrophotographi'c images by methods which have been known in the art. Electrophotography, or" as his sometimes termed, xerography, is-disc'losed-in Carlson Patents Nos. 2,297,691 and'2,551,582.-

in general, the electrophotographic-process comprises preparinga conducting plate with 'aEcQating of-a photoconductive chemical material which is electrically conductive only when exposed to light, charging the coated surface with an electrostatic charge, 'exposingsa'idchai'g'ed surface in any of the ways that a"'pliotog'raphic negative may be exposed, so as to permit the discharge of the electrostatic charge at all portions'of the photo-conductive material which have been exposed to light, then contacting said photo-conductive surface of the plate with an electroscopic powder or toner',.which may be of a composition according to the present invention, whereby the powder then adheres to those surface area portions only from which the charge was not bled off by exposure to light as aforesaid. The powder image thus formed depends upon the powder adhering to the charged portions of the photo-conductive material and not adhering to the uncharged or discharged portions thereof. This powder image is then transferred onto a pap'er or card or other material on which it is to be developed, this transferring operation being effected by bringing into contact withthe powder image on'the photo-conductive material surface as aforesaid, a paper, card or other material on which the image is'to be permanently afiixed, and preferably causing a relatively high tension electricalcharg'e to assist in transferring the powder onto the paper, etc. by moving the plate and the paper in face-to-face' c'ontact with each other through a zone across which thereis a high tension electrical charge. 7

The" next operation is to cause the powder image, which is very lightly adhering to the paper, to be permanently aflixed thereto. This has been done in accordance with the prior art by any one of tlir'ee principal methods: first, by physical pressure, thepowder has been forced into the interstices of the pape'ron which the image is to be permanently affixed, or in this instance, impressed. This method is not desirable'under all circumstances as the amount of pressure, required may be so great as to change the dimensions of the paper or card, so that in case of cars to be used in mechanical card handling machines, the change in dimensions may result in faulty operation of the card handling machines.

A second method for fixing the powder image is to expose the powder image produced as aforesaid to the vapor of a solvent, some small'portion of the solvent vase-r 'beiiigcaus'ed to condense on'to'the powder image,

- United States Patent 0 a 2,917,460 Pese a... Pa -H. 5

2, resultinga't leastpa'rtially dissolving. at" least one of the constituents of the electroscopi'epowder and causing the-solution thusformed to flowinto the interstices of the'paper to make a permanent record. This subject matter is disclosed to a greater extent in the application of Greaves, Serial No. 401,285, filed'December 310 1953, now Patent No. 2,726,166, issued December 6 1955.

A third way is to subject the powder image andthe paper on which it is disposed to heat su fficient tomelt at least one of the constituents of the powder or the powder as :a whole, so that the molten droplets so formed maybe absorbed in the interstices of thepaper to make apermanent image thereon. It has been found in carryingon the process with tabulator cards such as are used in standard types of ofiice machines, that the temperature required to meltthe'powder, which has heretofore been available commercially, is so high (in the order of 275 300'F.'), that the heat to which the paper or card stock is subjected causes un'due dehydration and consequent warping thereof. H a I Attempts have 'beenrnade to use various types of liquid plasticizers in conjunctionwitlitlie resin, which is a base ingredient of electroscopic toners of this kind. The result has been that the composite powder will fuse at a low enough temperature to'prevent damage tothe card or paper; but on the other hand, the use of the amounts of liquidplasticiz'e'rs'which have been necessary to etfect'thisiresiilthafs caused the powderparticles to be tacky at 'ordin'ary temperatures, so that the powder could not be handled properly-and in a"dsir ab le manner. In sbnie'instances-the use of liquid plasticizers has caused the powder to adhere physically, due to'its sticky character, to the uncharged portions of hephoto-conductive material surface. This has resultedin' the requirement for frequent cleaningof the plates,"-wliich is an undesired operating condition. 7 I p n I 4 The present invention seeks 'to overcome these several difficulties by'providing'an eleetrosebpie powder'or toner composition or range of compositioiis, such that the powder as a whole can be fused at atempe'ramre surficiently low that it will not undesi abl affctthe' paper or card stock exposed to thisteinperature as fe r said', while at the same time preventi' "t' 'rie'ss and otherundesired operation of the process H "tost'ickiriessor tackin'ess of the powder prior to it'sinteiitioiia'l exposure to heat as aforesaid. H

Summarizing the present inns-mien, it" comprises an electroscopic powder composition inc resins, preferably thermoplastic irif ch as a powder base, a coloring material t I color to the powder and to the permanent markniad upon the developmentthe'reof as aforesaid, and a material which will cause the powder as a whole to have a relatively low fusion point. This added material may be generically termed a solid organiccompou1id,-; Le. a compound which is a solid at room temperatures and which has a sharp melting point a'tsom ewhat aboveroom temperature, so that it will notbe tacky or tend to cause the composition as a wholeto be tacky or sticky at handling temperatures, while at vthe sarne time itcan be brought to or above its sharp melting point as aforesaid at a temperature sufiiciently low so that it canthen serve as a solvent for the resin and serve to render the powder as a whole fusible at a relatively low temperature. There are a number of materials which qualify under all'these requirements and which have melting points in the range of about C. to about C. and which when melted are solvents for a number of thermoplastic resins which may be used therewith and are miscible with such resins when dissolved.

Turning now to the details of the present invention, the resins which may be used as a powder base for material of this kind are all in the class of thermoplastic resins. These resins, which are considered herein as ingredient (a) may be, for example, polystyrene, poly-a-rnethylstyrene, lower alkyl polyacrylates and lower all'vl polymethacrylates in which each of said lower alkyl includes alkyl radicals having from 1 to 4 carbon atoms. These resins are generally known'for use in electroscopic powders.

The second essential ingredient according to the present invention and the one in which the invention particularly resides is a solid organic compound identified as ingredient (b) herein and consisting essentially of a compound which is solid at room temperatures, which has a sharp melting point in the range of about 85 C. to about 120 C., and which when melted is a solvent for and is miscible with at least one material of ingredient (a) above. Examples of ingredient (b) with the melting point of each in degrees centigrade in parentheses immediately thereafter respectively are: acenaphthene (93.5), acetanilide o-acetoacetotoluidide 105), o-acetotoluidide (101), o-chloroacetoacetanilide (103), 2-chloro-4-nitroaniline (106), p-dibromobenzene (86.9), P,P -methylenedianiline (93), a-naphthol (95), fi-naphthol (85), Z-naphthylamine (110), m-nitroaniline (112), 4-nitrobipheny1 (97), sorbitol hexoacetate (98), and 2,4-toluenediamine (97). It will be noted that the materials hereinabove listed as examples of ingredient (b) do not fall in any one chemical classification, but rather are effective by reason of their physical characteristics, namely, their melting points respectively and the fact that when melted they are solvents for and miscible with at least one of the resins with which they may be used as illustrated more particularly in the examples which follow. It is believed that there is no chemical reaction taking place or at least none is depended upon in accordance with the present invention between ingredient (a) and ingredient (b), or any materials coming under these two classifications. On the other hand, ingredient (b), when brought to or above its melting point, must be a solvent for at least one of the materials of ingredient (a) used therewith.

The third ingredient which is a common one in accordance with conventional prior art practice in electroscopic powders or toners is a coloring material. This material may be any suitable dye, a pigment or some combination of both. In accordance with the present invention, the use of a pigment, such as carbon black, has been found to be desirable. The present invention is further not limited to reproduction of material on a black and white basis, but other colored dyes and/or pigments may be used as desired.

The invention is further illustrated by the following examples of operative combinations of the several ingredients as follows:

Example 1 Parts by weight (a) Polystyrene 20 Ethyl polyacrylate 15 (b) Acetanilide 50 (0) Carbon black 15 Example II Parts by weight (a) Polystyrene l5 Methyl polymethacrylate 45 (b) p-Dibromobenzene 30 (0) Carbon black 10 Example III Parts by weight (a) Methyl polymethacrylate 25 (b) o-Acetotoluidide 60 (c) Carbon black 14.5 Black dye 0.5

The above ingredients were blended and ground as in Example I. The powder was found operative for the purpose stated and had a fusing point of about F.

Example IV Parts by weight (a) Polystyrene 30 Methyl polymethacrylate 10 Butyl polymethacrylate 30 (b) o-Acetoacetotoluidide 20 (0) Carbon black 10 The above ingredients were blended and ground as in Example I. The powder was found operative for the purposes stated and had a fusing point of about 205 F. Example V Parts by weight (a) Poly-a-methylstyrene 30 Methyl polymethacrylate 50 (b) 4-nitrobiphenyl 18 (c) Dye 2 The above ingredients were blended and ground as in Example I. The powder was found operative for the purposes stated and had a fusing point of about 220 F. The composition of this example in the proportions given is also operative by substituting either sorbitol hexoacetate or 2-chloro-4-nitroaniline for the 4-nitrobiphenyl, constituting ingredient (b) of this example. Either of these substitutions causes substantially no change in the fusion temperature.

While there have been described herein a number of alternatives and substitutents which may be employed in compositions embodying the present invention, other a1- ternatives will occur to those skilled in the art from the teachings hereinabove set out. I do not wish to be limited, therefore, except by the scope of the appended claim, which is to be construed validly as broadly as the state of the prior art permits.

What is claimed is:

A powder composition useful as an electroscopic toner, said composition being in the form of particles of about 2-40 microns in size and each being substantially a solid solution of the following ingredients: (a) thermoplastic resin consisting essentially of polystyrene 30 parts by weight, methyl polymethacrylate, 10 parts by weight and butyl polymethacrylate 30 parts by weight, (b) a solid organic compound consisting essentially of o-acetoacetotoluidide, 20 parts by weight, and (c) a coloring material consisting essentially of carbon black, 10 parts by weight, the composition as a whole having a fusion point of about 205 F., said thermoplastic resin (a) and said solid organic compound (b) being such that these two materials together will have a melting point sumciently low as to be below the temperature at which it is possible detrimentally to affect the quality of the paper stock with which said powder composition is used as an electroscopic toner, and said two materials together being substantially non-tacky at the lower temperature at which said powder composition is applied onto a light-exposed plate coated with a photo-conductive material for developing an electrostatic image into a powder image thereon.

References Cited in the file of this patent UNITED STATES PATENTS