US 3884685 A
Description (OCR text may contain errors)
United States Patent Green, Jr. et al.
1451 May 20, 1975 LOW DENSITY PAPER USED IN TRANSFER ELECTROPl-IOTOGRAPHY Inventors: Charles J. Green, Jr.; George Treier; Robert H. MacClaren, all of Webster, NY.
Assignee: Xerox Corporation, Stamford,
Filed: Dec. 6, 1973 Appl. No.1 422,452
Related US. Application Data Division of Ser. No. 98,883, Dec. 16, 1970, which is a continuation-in-part of Ser. No. 50,886, June 29, 1970, abandoned.
References Cited UNITED STATES PATENTS 11/1962 Dalton 162/138 3,271,146 9/1966 Robinson 96/].4 3,293,115 12/1966 Luckon 162/138 X 3,420,734 l/1969 Anderson et al. 162/138 X 3,468,660 9/1969 Davenport et a1... 162/138 X 3,486,936 12/1969 Cahill 162/138 X 3,556,784 l/197l Robinson et al.. 96/].4 3,592,642 7/1971 Kaupp 96/l.4 3,615,403 10/1971 Cheng 162/138 3,708,288 l/l973 Lin 96/l.4 3,811,914 5/1974 Saito et al 96/l.4 X
OTHER PUBLICATIONS Casey, Pulp and Paper, vol. 3, lnterscience N.Y 1961, pp. 1552-1554, 1570, 1571, 1592, 1593.
Primary ExaminerRoland E. Martin, Jr.
 ABSTRACT A lightweight electrophotographic copy paper having' 3 Claims, No Drawings LOW DENSITY PAPER USED IN TRANSFER ELECTROPI-IOTOGRAPHY RELATED APPLICATIONS This is a division of application Ser. No. 98,883, filed Dec. 16, 1970, which is a continuation-in-part of our co-pending application, Ser. No. 50,886, filed on June 29, 1970, now abandoned.
BACKGROUND OF THE INVENTION This invention relates to an improved electrophotographic copy paper. It more particularly relates to an improved electrophotographic copy paper containing small resinous particles.
Paper has many uses in packaging, printing, preparation of containers, and the like. One of the basic shortcomings of conventional paper is its weight. Relatively high density of paper imposes a significant financial.
burden in shipping, mailing, and the like. For example, magazines, when printed on a paper which is sufficiently dense and thick to give the reader the impression of quality, generally weighs considerably more than is necessary if the minimum thickness of paper were used which would permit readability. Frequently among the thicker papers often referred to as paper board or box board, a relatively high weight is required to obtain the desired thickness and stiffness. In many instances, such as in the preparation of paper cups, conventional papers do not have a sufficient insulating value for use as hot cups unless an excessive quantity of pulp is employed.
In U.S. Pat. No. 3,293,114 to Kenaga et al., there is disclosed a product which overcomes the shortcomings of conventional paper. More specifically the aforementioned patent sets forth the preparation of a lightweight paper by incorporating a plurality of synthetic polymeric particles, having a generally spherical shape and defining a generally concentric spherical cavity, into paper fibers. The preparation includes the addition of from about 0.05 to 60 percent of the spherical polymeric particles, having a diameter of from about 0.5 to 200 microns, to a pulp slurry. The resulting paper product is characterized by its lightweight and excellent stiffness characteristics.
Another means of rendering paper lightweight is described in U.S. Pat. No. 3,210,239 issued to Eberl etal. This patent describes a bulked paper product which contains angulate fibrous fragments of foamed aminoplast resins as the bulking material. The preparation of the lightweight paper includes adding up to about 50 percent by weight of a disintegrated aminoplast resin to a pulp slurry before production of paper sheets. The paper product is characterized by a low densitycompared to paper using wood pulp alone.
In the art of electrophotography, paper is an important consumable in that it is used in all electrophotographic copiers. While the lightweight papers demonstrated in U.S. Pat. Nos. 3,293,114 and 3,210,239 obviate many of the problems presented by conventional paper, more peculiar needs exist in the use of-a lightweight paper as a medium for electrophotographic copying. Therefore, while there is a need for a lightweight paper for use in electrophotography, certain problems exist as to its physical and electrical properties with regard to use in machines. For example, if
such a paper has too high a curl it will cause jamming as its proceeds from the feederthrough the electropho tographic machine, Likewise, if the paper either has a high coefficient of friction or accumulates electrostatic charges at its surface, sheets of the paper will stick and will not properly feed into the electrophotographic machine.
It has been found that the difficulties as set forth above, exist when utilizing a paper which has been rendered lightweight by the addition of bulking substances. For example, lightweight paper containing gaseous thermoplastic resin spheres exhibits strong tendencies to curl which property causes the paper to wrap about the roll feeders of the machine and thereby jam it. In addition, the preparation of this resinous-gaseous filled-sphere paper results in the spheres being located at or upon the surface of the paper fibers. Being in such a position the polymeric spheres create a high coefficient of friction for the surface of the paper which high friction property further ultimately results in an undesirable electrostatic buildup. This gaseous filled thermoplastic resin filled lightweight paper, because of its undesirable electrostatic and frictional properties, is
essentially non-functional in friction type paper feeders which are found in conventional electrophotographic equipment. Therefore, because of the surface presence of the polymeric spheres the lightweight paper will retain such high electrostatic charges that it will misspuff in machines using photoreceptor drums; that is, the paper will stick to the photoreceptor drum and fail to exit.
The same disadvantages encountered in using lightweight paper containing thermoplastic gaseous filled resinous spheres in electrophotographic copying appear when the lightweight paper contains other materials for bulking purposes. For example, when using aminoplast thermosetting resins as a bulking material for paper, as taught in U.S. Pat. No. 3,210,239, the paper has inadequate curl, surface friction, and discoloration for use in electrophotographic copying. And further, when using natural polymeric substances such as cellulosics, cellulose derivatives, and proteins as bulking substances, the lightweight paper is found inadequate for electrophotographic purposes. The reason for the shortcomings of these types of bulking materials appears to be the same as that of the gaseous-filled synthetic resins in that the bulking substance appears at the surface of the paper thereby rendering it unusable in electrophotography.
These particular characteristics of bulked lightweight paper are so serious that when used in an electrophotographic machine malfunctions will occur as often as one sheet in ten and sometimes even more often. In addition, resulting copies are of poor quality due to a slight discoloration. While it might be expected that surface sizing would obviate the aforementioned .difficulties, the addition of conventional surface sizes having ordinary salts in a concentration of from about 1 to 5 percent are not generally found useful because the bulking substance is still left exposed at the surface and will still cause theproblems outlined above. In addition, the use of ordinary salts in surface sizings will cause increased tendency for the paper to scorch or discolor when tonerfusing is accomplished by radiant or pressure fusing.
OBJECTS OF THE lNVENTlON Therefore, it is an object of this invention to provide 1 a lightweight electrophotographic copy paper.
It is a further object of this invention to provide a lightweight electrophotographic copy paper having a surface sizing which renders the paper useful in electrophotographic machines.
Another object of this invention is to provide a lightweight clectrophotographic copy paper having excellent curl and friction characteristics for use in electrophotographic machines.
Still another object of this invention is to provide a preparation of a lightweight electrophotographic copy paper.
DESCRIPTION OF THE INVENTION These benefits and other advantages in accordance with the present invention are achieved in the preparation of an electrophotographic copy paper by incorporating into said paper a low density bulking material, and subsequent surface sizing of the lightweight paper to render it useful in electrophotographic machines. Electrophotographic copy papers in accordance with the present invention are more readily prepared by the addition of up to about percent of the low density bulking material, based upon the weight of the dry pulp, to the pulp slurry. The resulting lightweight paper is then surface sized with a composition comprising a binder, a salt, preferably in amounts from about 1 to 50 percent by weight based upon the amount of binder, and 40 to 50 percent clay based on the total coating composition, but such that the combination of salt and clay does not exceed 60 percent based on the total coating composition.
The particular binder to be used in the surface sizing composition is not critical to the electrophotographic copy paper of the instant invention. Therefore any commercially available binder products conventionally used in surface sizing compositions may be used. Typical binders include starch, starch derivatives, polyvinyl alcohol. polystyrene, and mixtures thereof. Because of its anti-scorch properties, polystyrene latex in a weight ratio of from about 40 percent or more is a particularly useful binder in the sizing of the present invention.
The particular salt to be used in combination with the binder in a ratio of from about 1 to 50 percent by weight can be any salt which in combination with the binder yields a surface sizing which imparts to the lightweight paper the properties of scorch resistance, improved conductivity, and strength retention under conditions of heating. Preferable salts within the purview of the present invention include the sulfate salts of any metal. Typical salts of this group which give exceptional results are magnesium sulfate, zinc sulfate and sodium sulfate and the hydrates thereof.
Any type of coating clay known to those skilled in the art may be used within the purview of the present invention. The only requirement relating to the clay composition is the amount present in the surface size. As mentioned above, the clay should be present in an amount of from about 40 to 50 percent by weight based on the total composition, but such that the combination of salt and clay does not exceed 60 percent by weight.
While the binder, salt and clay surface sizing of the present invention has been described with respect to the three major components, it is'well understood to one skilled in the art that many additives can be used in the binder salt composition. For example, wetting agents can be added in order to improve the application of the. surface coating.
As heretobefore mentioned, the lightweight electrophotographic copy paper of the present invention contains from up to about 10 percent of bulking material. For optimum properties for use in electrophotographic machines the paper should comprise over percent cellulose fiber to avoid roughness in the paper surface. Therefore, the lightweight paper of the instant invention preferably should contain from about 0.5 up to 5 percent bulking material.
The particular material used for bulking the paper is not critical within the purview of the present invention and may be synthetic resins of the type described in U.S. Pat. Nos. 3,293,114, 3,210,239, 3,128,478, 2,929,106, and 2,797,201. Natural bulking substances, such as foamed starch and cellulosic materials, can be used with similar results. In addition, inorganic bulking substances such as hollow glass, ceramic and metal microspheres can be used.
In the preparation of the lightweight electrophotographic copy paper of the instant invention, it is found that bulking material accumulates on the surface of one side of the paper. In this condition the coefficient of friction of that particular side of the paper is very high.
Therefore, while not a requirement in the preparation of the electrophotographic copy paper of the present invention, it is preferable to subject the side of the paper having the bulking material on its surface to a mechanical rubbing treatment with a cotton fabric material before the step of surface sizing whereby flattening, abrading, or breaking of the excess bulking material occurs at the surface of the paper. By means of the mechanical treatment of the paper those loose or protruding particles of bulking material are removed or broken thereby rendering the subsequent surface size more effective.
EMBODIMENTS OF THE INVENTION In one general embodiment of the instant invention, an aqueous pulp slurry is prepared and about 3 percent by weight, based on the dry pulp, of Saran microspheres, which are gaseous filled thermoplastic resin particles produced by the Dow Chemical Company of Midland, Michigan are added to the slurry. The pulpresin composition is then fed into a paper making machine which sequentially forms a paper sheet of the pulp fibers and applies a surface size composition comprising 12 percent sodium sulfate, 38 percent clay and 50 percent ethylated starch in an aqueous dispersed solution. There results a lightweight paper which functions properly as copy paper in electrophotographic machines and shows no indication of discoloration.
In electrophotographic machines, the novel lightweight copy paper is coordinated in the ordinary electrophotographic process of charging an electrophotographic plate, imaging the charged plate with activating radiation, developing said image with electroscopic marking particles, and transferring said image by heat or pressure fixing to the lightweight copy paper of the instant invention. The conventional electrophotographic process is fully detailed in U.S. Pat. No. 2,297,691 to C. F. Carlson.
Having described the invention above, the following examples are given to more fully illustrate specific embodiments thereof. The examples are given for illustrative purposes only and are not intended to be limiting on the scope of the invention. In the examples all parts are by weight unless otherwisespecified.
EXAMPLE I An electrophotographic copy paper according to the present invention is prepared by the following technique:
A surface sizing is prepared by adding 100 parts by weightof Penford Gum 280, an ethylated starch manufactured by the Penick and Ford Company of Cedar Rapids, Iowa, 50 parts by weight Vino] 125, a polyvinyl alcohol manufactured by the Air Reduction Chemical and Carbide Co. of New York, New York, and 18 parts sodium sulfate to 1500 parts of water. A 220 parts by weight pre-dispersed clay solution, made with Nuclay, manufactured by Freeport Kaolin Co. of New York, New York, which was prepared by adding enough clay to water to obtain a 60 percent solids mixture, is then added to the coating composition.
A slurry is prepared by adding 1000 lbs. of dry softwood kraft fiber, manufactured by the St. Regis Paper Company of New York, New York, 500 lbs. of hardwood kraft fiber manufactured by the International Pulp Sales Co. of New York to 50,000 gallons of water in a hydrapulper. The fiber is refined to a 350 Canadian Standard Freeness in a Jordan. Thereafter 90 lbs. of Experimental Resin CX 705 8-,] which are gaseous resinous spheres manufactured by the Dow Chemical Company of Midland, Michigan, are added to the slurry. The slurry is diluted to 0.5 1 percent by weight of fiber and then fed into the head box ofa Fourdrinier paper machine. The resulting paper passes through the dryers and at the size press the above prepared sizing composition is applied to the paper. The sized sheet is then dried and very lightly calendcred.
The resulting surface sized lightweight electrophotographic copy paper is cut to fit a Xerox 720 machine. A stack of 200 sheets are then placed in a Xerox 720 machine and set to copy a standard pattern 200 times. There is no jamming of the machine and all 200 copies are of excellent quality demonstrating no discoloration.
EXAMPLE ll A urea-formaldehyde foam (0.8 lb/cubic foot, l5O micron cell diameter) manufactured by the DuPont Corporation of Wilmington, Delaware is pulverized in an Abbe mill with a one-sixteenth inch screen plate. Discrete amounts of the disintegrated foam are then blended with a slurry of 1000 lbs. of dry softwood kraft fiber, 500 lbs. of hardwood kraft fiber, and 5,000 gallons of water, the slurry being prepared in the same manner as Example I. A total of about 2 percent by weight of the disintegrated thermo-setting resin material is added to the slurry. The slurry is then diluted to about 1 percent by weight of fiber and a sized sheet prepared in the same manner as Example I using the same sizing composition. The resulting lightweight paper is tested in a Xerox 720 machine in the same manner as Example I with the same advantageous results.
While the invention has been described in terms of preferred embodiments, it is to be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.
What is claimed is:
l. A method of electrophotographically copying comprising:
a. charging an electrophotographic plate;
b. exposing the charged electrophotographic plate to activating radiation to create an electrostatic image;
0. developing the resulting electrostatic image with electroscopic marking particles; and
d. transferring said developed image to an electrophotographic copy paper comprising paper making fibers having incorporated therein a low density bulking material in a proportion of up to about l0 percent by weight of the paper making fibers, and a surface size on said bulked paper having a composition comprising binder material, a metallic sulfate salt which imparts conductivity to the paper, in an amount of from about 1 to 50 percent by weight based on said binder, and clay in an amount of from about 40 to 50 percent of the total composition, the combination of salt and clay not exceeding 60 percent of the total composition.
2. The method of claim 1 wherein the transfer step takes place'by heat fixing.
3. The method of claim 1 wherein the transfer step