US3420734A - Process of forming electrostatic printing paper from ionic fibrous cellulosic derivatives and paper thereof - Google Patents

Description

United States Patent 3 420 734 PROCESS OF FORMING ELECTROSTATIC PRINT- ING PAPER FROM IONIC FIBROUS CELLULOSIC DERIVATIVES AND PAPER THEREOF Nils T. Anderson, Vancouver, Wash., and William M.

Hearon, San Rafael, Calif., assignors to Crown Zellerbach Corporation, San Francisco, Calif., a corporation of Nevada No Drawing. Filed Apr. 2, 1965, Ser. No. 445,271 U.S. Cl. 162135 9 Claims Int. Cl. G03f /02 ABSTRACT OF THE DISCLOSURE In electrostatic printing, a method of dissipating electrical charges on the back of a dielectric film provided for receiving an image-defining electrostatic charge, where the charges on the back of the film are conducted through a cellulosic material having electrical conductive properties occurring by reason of ionic disassociation taking place in the cellulosic material. An electrostatic printing paper for practicing the method including a cellulosic base sheet having a fibrous structure composed of an ionic fibrous cellulosic derivative, which is the product formed by substituting ionizable groups in the reactive groups of the anhydroglucose units that form cellulose, the printing paper including a dielectric film extending over at least one face of the base sheet.

This invention relates to the manufacture of ionic cellulosic derivatives, products prepared from such derivatives, and processes for making such products.

The cellulosic derivatives of the invention have been found to be particularly suited for the manufacture of electrostatic printing products, where they may be incorporated in the means supporting an insulating or dielectric film in such products, with the derivatives then, by reason of their conductive properties, imparting needed electrical conductivity to the products.

Electrographic printing, as the term commonly is used today, refers to an electrostatic printing process, wherein an image-defining electrostatic charge is laid directly down upon an insulating or dielectric surface, using such electronic devices as a cathode ray tube, a pin matrix and pulsing corona discharge, or by means of a direct image transfer from one surface to another. A copy product such as a copy sheet used in making electrographic prints requires a layer presenting a dielectric or insulating surface for the reception of the image-defining electrostatic charge, which layer may take the form of a thin film of dielectric material. The copy product further requires support for this layer which is electrically conductive, whereby any stray electrical charges in the means supporting the film may be dissipated to enable the production of the clearest possible prints. In the usual copy product, this electrically conductive support for the dielectric film is provided by including in the copy product an electrically conductive web, such as a conductive fabric web, or a conductive paper web, which has the dielectric film applied over at least one face thereof.

While relating generally to the manufacture of ionic cellulosic materials, in a more specific sense the invention concerns novel electrically conductive webs produceable from the material, novel methods of producing such webs, improvements in electrostatic printing products featuring as a conductive supporting base therein webs containing ionic cellulosic derivatives, and novel methods for manufacturing such electrostatic printing products.

One general object of this invention is to provide an improved electrically conductive web, such as a paper ice or fabric web, where the conductive properties of the web are derived at least in part from the inclusion in the web, distributed therein or as a coating, or in any other manner, of ionic cellulosic derivatives having electrically conductive properties. An object related to the above is the provision of a printing product for electrostatic printing, that includes a dielectric film for receiving an imagedefining electrostatic charge, where the supporting base for this film is provided by such a web, and the web imparts the electrical conductivity needed in the supporting base.

The usual procedures which have been relied upon to provide necessary electrical conductivity in a Web emloyed in electrostatic printing products have comprised either coating or impregnating the web with a humectant, coating or impregnating the web with an ionizable inorganic or organic compound, coating or impregnating the web with metallic or organic electroconductors, or impregnating the web with a polyelectrolyte. With all of these procedures, additives to the web are responsible for electrical conductivity, and as a consequence, in manufacturing the web the additional step of incorporating the additive with the Web at some stage in its manufacture is required, a disadvantageous feature. A further problem experienced with prior-known practices relates to obtaining uniformity in the electrical conductance of a web. In electrostatic printing products optimum image characteristics are favored by uniform conductivity in the web which forms the supporting base, but in practice such uniformity, when additives are employed to obtain conductance, has been difiicult to obtain. Surface imperfections, variations in web thickness, variations in absorbency characteristics, and variations in the rate of application are some of the factors which render it hard to produce a consistently uniform product. Therefore, according to a preferred embodiment of the invention, the ionic cellulosic derivatives contemplated are incorporated into the web as part of the fibrous structure of the web, and by such a procedure the above-indicated ditficulties and disadvantages are eliminated or reduced materially.

Accordingly, another object of the invention is to provide an improved electrically conductive Web, where the conductance in the web is the result of properties of the fibrous material forming the structure of the web, rather than the result of additives applied to the web structure or coated thereon.

More specifically, an object is to provide a web as described, wherein ionic fibrous cellulosic derivatives form at least a portion of the fibrous structure of the web, which derivatives, by reason of their ionic nature and through disassociation, render the web electrically conductive.

Yet another object is to provide a novel electrostatic printing sheet, featuring a dielectric or insulating film and as a support and providing a conductive base therefor a base web with ionic fibrous cellulosic derivatives forming at least a part of the fibrous structure of the web.

It has been discovered according to this invention that a number of different types of cellulosic derivatives with ionic characteristics may be employed as the fibrous material, including both cationic and anionic derivatives. Representative of the former class of derivatives are such materials which ionize in the presence of water and release positively charged cations as cellulose phosphates (formed by esterifying the hydroxyl groups in the anhydroglucose units forming cellulose), oxidized cellulose (where carboxyl groups replace the primary hydroxyl groups of the anhydroglucose units), sulfoethyl cellulose, and low substituted carboxymethyl cellulose. Illustrative of the latter group of derivatives are such materials as aminoethyl cellulose, diethylaminoethyl cellulose, and guanidoethyl cellulose, which materials, in the presence of Water, ionize and release negatively charged anions. When such materials are incorporated in a web as part of the fibrous structure of the web, it is ionic disassociation occurring in the polymer forming the cellulosic fiber in the web which renders the web electrically conductive, as opposed to disassociation of additive substances distributed in cellulosic fibers.

With electrically conductive webs perpared from cellulosic derivatives as contemplated herein, uniform electrical conductance results, so that when the webs are coated with dielectric films to make electrostatic printing products, they provide a uniformly electrically conductive base in the final products. Such a uniformly conductive base has resulted in good prints being obtained through electrograp hic printing methods with surface resistivities ranging up to 1.5)( ohms per square (even up to l.0 10 ohms per square in some applications). Heretofore, and with presently known electrographic printing processes, it has generally been considered that satisfactory image resolution was only obtainable with a resistivity in the base sheet of a printing paper of not more than IX 10 ohms per square. Thus, a further feature and object of the invention is to provide an improved electrostatic printing product, more specifically, a printing paper, which, because of superior homogeneity in the electrical conductance in a base web therein makes possible the production of satisfactory image resolution with higher surface resistivities in the base web than heretofore believed practicable.

According to a specific and preferred embodiment of the invention, a cellulosic derivative comprising phosphorylated cellulose is selected as the ionic fibrous cellulosic derivative forming the fibrous structure in the web, and the derivative itself is prepared in a unique manner whereby a high degree of phosphorylation is produceable in the derivative. According to the invention, a phosphorylated cellulosic derivative may be prepared containing up to about 18% by weight combined phosphorus. An electrostatic printing product such as a printing paper having such a phosphorylated cellulose forming the fibrous structure in the base sheet of the paper, containing from to 20% combined phosphorus, has been found to be particularly well suited for producing electrostatic prints at relatively low humidity conditions. A copy sheet producing satisfactory prints at a relative humidity of 20% or more is satisfactory for many uses. With printing papers having a base sheet made of a phosphorylated cellulose containing combined phosphorus in the range indicated, satisfactory image resolution may be obtained at a 15% relative humidity, which is, of course, a desirable factor as it reduces the extent of control required over humidity conditions.

A further feature and object of the invention is to provide an improved process for making ionic fibrous cellulosic derivatives from cellulose, which makes possible the manufacture of derivatives containing a high proportion of combined phosphorus, the process being characterized by control of temperature conditions and the use of a limited amount of water, whereby a high degree of phosphorylation of the cellulose is obtained without degradation of the cellulose.

Various other features and advantages of the invention will become apparent from reading the following description, such description including certain specific examples, inserted primarily for purposes of illustrating the invention, and not being intended as indicating the entire range of conditions and procedures under which the invention may be carried out.

As indicated above, this invention contemplates the manufacture of a web which may be used as a base sheet in an electrostatic printing product having ionic fibrous cellulosic derivatives forming at least a portion of the fibrous structure of the web. The ionic forms may be cationic or anionic. With the cationic derivatives, upon ionization in the persence of water, positively charged cations are released, and the choice of cation may be varied depending upon the properties desired in the web. The particular cation selected for a specific application depends to some extent on the level of surface resistivity desired. It is well known that the hydrogen cation possesses the greatest equivalent conductance, and that among the group of monovalent cations equivalent ionic conductance increases in the order: lithium, sodium, silver, ammonium, potassium, hydrogen. Providing the degree of ionization is not changed by the choice of cation, the l0lWSt surface resistivity is expected from a paper made from fibrous cationic cellulosic derivatives incorporating the hydorgen ion. In most cases the degree of ionization is a function of the cationic form, so this also should be considered in the selection of the cation. Other considerations also are important since it has been observed that when, for example, an aluminum ion is incorporated with a cellulose phosphate, a somewhat fluffy sheet that may be undesirable in some instances results, whereas the use of the ammonium ion results in a dense, more acceptable sheet for printing purposes.

With anionic cellulosic derivatives which ionize to release negatively charged anions (aminoethyl cellulose, diethylaminoethyl cellulose, etc.) again, the particular ion incorporated in the derivative may be selected from the group of mono-, di-, or polyvalent anions such as chloride, bromide, iodide, nitrate, hydroxyl, acetate, sulfate and the like, with the particular selection made depending upon the desired surface resistivity and the specific type of paper properties desired. It is well known that the equivalent ionic conductance for anions increases in the order: acetate, nitrate, chloride, hydroxyl; and providing the degree of ionization is independent of the anion, the lowest surface resistivity is expected from paper made with fibrous anionic cellulose derivatives incorporating the hydroxyl ion.

The surface resistivity of paper made from fibrous ionic cellulosic derivatives is approximately inversely related to the number of ionizable groups in the derivative. For example, it has been observed that the surface resistivity of webs made from cellulose ammonium phosphate decreases by about one-half when the degree of substitution of phosphate groups in the derivative is doubled. Using present day printing processes, and in the process of making electrostatic prints from a copy sheet comprising a dielectric film supported on an electrically conductive paper base sheet, as already indicated, a resistivity of not more than 1X10 ohms per square usually is required for satisfactory image resolution to be obtained. This range may be extended upwardly to about 1.5 l0 ohms per square with paper or other webs made of fibrous ionic cellulosic derivatives because of the uniform electrical conductance produceable therein.

It has been found that any cellulose-containing materials may be utilized in preparing the ionic cellulosic derivatives contemplated in this invention. Illustrative of such materials, but not being limited thereto, are papermaking pulps, ground wood or cotton linters, rayon and the like.

The following example illustrates the preparation of an ionic fibrous cellulosic derivative from cellulose, through phosphorylating the cellulose, using as a reaction medium a mixture of concentrated phosphoric acid and a weak organic nitrogenous base.

Example I An air dry bleached sulfite pulp was immersed for 5 minutes in a solution consisting of 68 parts urea and 32 parts orthophosphoric acid (containing by weight acid and the remainder water) with such solution maintained at C. As will be noted, the impregnating solution contained only a small amount of water. The acid and urea solution had a melting point of about 85 C. and 110 C. temperature at which it was maintained was well below that temperature where foaming occurs in the solution with loss of chemical (with such acid and urea solution, foaming becomes a factor at about 125 C.). After such'immersion, the pulp was removed from the solution and pressed to reduce the amount of solution retained in the fibrous cellulosi-c mass. The fibrous mass can retain up to about 10 times its weight on an air dry basis of the solution, and with relatively heavy pressures, this retention can be reduced to where the weight of retained solution about equals the weight of the air dry material. In the example, after pressing, retained solution equaled about 3 times the weight of the air dry material.

The cellulosic mass with retained solution was then cured, to bring about esterification of the hydroxyl groups in the anhydroglucose units of the polymer forming the cellulose, by placing it in a convection oven at 180 C. Different curing times, ranging from 3 to 15 minutes, were employed. After curing, the cellulosic material was washed until the washing gave no test for phosphate. Paper hand sheets were then prepared of the cellulosic product obtained from a fiber-distilled water slurry, and using :a British sheet machine. These hand sheets were then pressed between blotters and air dried 18 hours, at 50% relative humidity, and at temperatures of 73 F. The hand sheets were conditioned in air at the same relative humidity and temperature, for 24 hours before surface resistivity was determined. Surface resistivity was measured using a. Heathkit vacuum tube volt-ohmmeter, having a probe including two parallel plates placed the same distance apart as the contacting length of the plates.

The following table summarizes the surface resistivities found for the sheets produced, and also shows the percent by weight of combined phosphorus present in the cellulose ammonium phosphate making up the sheets.

TABLE I Curing conditions Phosphorus Con- Surface resistivity tent, percent by at 50% relative Run Time (min.) weight humidity, ohms per squareXlO a 3 1, 000 b 3. 72 100 c 11. 68 19 d 17. 49 5 Paper sheets prepared as in Example I may be coated with a dielectric or insulating film, with the production of copy sheets for electrostatic printing processes, as illustrated in the following example.

Example II A cellulose ammonium phosphate was prepared from sulfite pulp as in Example I. A relatively short curing time was employed (somewhat less than 3 minutes), and paper sheets prepared from the derivative using the procedure of Example I exhibited a surface resistivity of 1.5 X 10 ohms per square at 50% relativehumidity. The paper sheets were supercalendered 10 times at 4,000 p.s.i., and a dielectric coating comprising a styrene-butadiene polymer (about 80% styrene) was applied over one face of the paper sheets using a spread of approximately 5 pounds of polymer per 3,000 square feet of paper. The polymer, when applied, was dispersed in a 50% toluene, 50% methylethyl ketone solvent, as a 20% solution. Air drying of the sheets yielded electrostatic printing papers or copy sheets, with essentially the same resistivity measured over the uncoated faces of the sheets.

Such papers were electrographically printed, using a Printapix cathode ray print out system, whereby imagedefining electrostatic charges were deposited on the dielectric films forming one set of sides of the copy sheets. The copy sheets were then developed, by dusting the surfaces of the films in the sheets with a developer substance, comprising a toner having an electrostatic charge opposite to that of the charge on the sheets, and then permanently setting the toner on the surfaces of the copy sheets by applying heat. Printed images were formed which exhibited good line resolution and had a minimum of background.

All of the paper sheets prepared as in Example I, when processed to form printing paper, and printed as above described, exhibited similar goo-d line resolution and clarity.

The lphosphorylated cellulosic derivative prepared in Example I comprises a monoammonium phosphate, and such a derivative yields paper of high brightness and good density, the derivative being the one preferred for the manufacture of electrostatic printing papers as contemplated herein. Other ionic forms of the cellulosic derivative may be employed in manufacturing electrically conductive paper, and electrostatic copy sheets from such paper. The following example illustrates the influence of different ionic groups on the electrical conductivity of paper made from a phosphate derivative of cellulose.

Example HI A cellulose ammonium phosphate was prepared and made into paper sheets as in Example I. By determining the percent by weight of combined phosphorus in the derivative, based on the dry weight of the originally used cellulose, the degree of substitution of ionic groups for hydroxyl groups in the anhydroglucose unit forming the cellulose polymer was determined. With each of such units containing three hydroxyl groups that may be phosphorylated, the maximum degree of substitution (expressed as D.S.) to be expected is 3. The derivative prepared, in its ammonium ion form, was used in the making of paper sheets as in Example I. The derivative was also treated to change the ion form of the derivative to one containing hydrogen, copper and aluminum ions, respectively, by dispersing quantities of the derivative in aqueous solutions of 10% hydrochloric acid, 10% cupric acetate, and 10% aluminum sulfate, respectively, to effect a replacement of the ammonium ion in the derivative with hydrogen, copper and aluminum ions. The cellulosic material resulting, having different ionic forms, was then washed and made into paper sheets as described in Example I. The following table illustrates for each of the ionic forms prepared the degree of substitution calculated therefor, and the surface resistivity obtained in sheets prepared from the derivative in each of its forms.

Example IV The anhydrolglucose units that form the cellulose polymer each contain a primary hydroxyl group, which may be oxidized to yield a carboxyl group. Such oxidized cellulose is commercially available, and constitutes another form of ionic fibrous cellulosic derivative that may be employed in making the copy sheets of this invention. Such oxidized cellulose, in an ionic form containing sodium and hydrogen ions, respectively, when used in preparing paper sheets as in Example I, yielded electrically conductive sheets as indicated in Table III below. In the case of oxidized cellulose, the maximum degree of substitution to be expected is 1, for the reason that each anhydroglucose unit in cellulose has but one primary hydroxyl group susceptible to oxidation.

TABLE III Surface resistivity, ohms per Derivative Ionic form D.S. square at 59% relative humidity Oxidized cellulose Na+ 0.67 140 Do H+ 0.67 125 The following example illustrates an anionic cellulosic derivative employable to make electrically conductive paper, and electrostatic copy sheets with such paper forming the base sheet therein.

Example V An aminoethyl cellulose 'was prepared from cellulose, such as sulfite pulp, and ethyleneimine, according to the method of Soifer and Carpenter Textile Research Journal, volume 24, page 847 (1954). With aminoethyl cellulose, the hydrogen atoms of the three hydroxyl groups in the glucose residue units in cellulose are replaced by ethyleneimine and the maximum degree of substitution to be expected, therefore, is 3. Aminoethyl cellulose, due to its amino group, has a capability of forming amine salts which, in the presence of water, undergoes disassociation with the liberation of anions, as for example, the hydroxyl ion. A derivative so prepared having a hydroxyl ionic form, and a degree of substitution of 2.5, was made into hand sheets as described in Example I. These hand sheets had a surface resistivity at 50% relative humidity of 20 10 ohms per square.

Electrostatic printing papers or copy sheets may be prepared from the paper sheets made in accordance with Examples III, IV and V by coating faces of the paper sheets with an insulating or dielectric film as described in Example II. Paper sheets prepared from cellulose phosphate in an aluminum ion form tended to exhibit undesirable fiufliness, but after coating with an insulating film, all sheets were usable in an electrostatic printing process and had requisite electrical conductivity.

As discussed above, cellulose ammonium phosphate, when prepared to contain a high percentage of combined phosphorus, produces paper sheets that, when made into copy sheets, may be emloyed to produce prints at relatively low humidity conditions with good prints obtained. In obtaining a relatively high percentage of combined phosphorus in a phosphorylated cellulose product, as contemplated by this invention, the amount of water present in the solution in which the cellulose is initially immersed is limited to not more than about by Weight of the solution. The solution itself comprises a weak organic nitrogenous base (and exemplary of these are such materials as urea and thiourea which donate the ammonium ions, such weak base resulting in a pH in the solution within the range of about 5 to 8 whereby degradation of the cellulose is inhibited), and a phosphoric compound such as orthophosphoric acid. The solution itself should have a melting point which is below about 150 C., preferably below about 125 C., whereby during the immersion step, temperatures may be maintained at a low enough level to inhibit degradation of the cellulosic material. In 'a treating solution comprising urea and orthophosphoric acid, the proportions of acid in the treating solution ranges from to 80% by weight of the solution, with the proportion of urea comprising essentially the remainder, and thus also ranging from 20% to 80%. With the preparation done as outlined above, a phosphorylated cellulosic product may be obtained containing from 15% to 20% combined phosphorus, and such a product is usable in making electrostatic printing copy sheets where humidity conditions as low as about 15% relative humidity.

Example VI An ionic fibrous cellulosic derivative was prepared as in Example I, and subjected to a 15 minute curing time, to produce a derivative containing 17.49% combined phosphorus. The derivative was rnade into paper sheets as described in Example I, and these sheets conditioned at the relative humidities indicated in the table below (at temperatures ranging from 72 F. to 77 F.) for 24 hours. The sheets were then tested for surface resistivity, with results obtained as summarized in Table IV.

TAB LE IV Surface restivity, ohms per squareXlOt Run 50% relative 20% relative 15% relative humidity humidity humidity Example VII A cellulose ammonium phosphate was Prepared from cellulose, as in Example I, and subjected to a curing time of approximately 10 minutes at 180 C. This yielded a derivative which, when made into a paper sheet, evidenced a surface resistivity at 50% relative humidity of 22x10 ohms per square. Oxidized cellulose of the type described in Example IV, had a surface resistivity of 140x10 ohms per square, at 50% relative humidity. The following table sets forth the surface resistivities of blends of these derivatives with ordinary sulfite pulp.

TAB LE V Surface Amount of resistivity at derivitive 50% relative in blend, humidity, percent ohms per squareXlO Run Derivative a Oxidized cellulose b Cellglose ammonium phosphate. 0. o

Papers prepared from these blends were coated with a dielectric material as set forth in Example II, and electrostatic prints made with the copy sheets so produced exhibited good line resolution.

While an air convection oven may be used in curing the ionic fibrous derivatives, in some instances infrared heating may be preferable, as this enables relatively high temperatures to be used without the danger of surface scorching.

Example VIII Heavy blotter-type hand sheets prepared from bleached sulfite pulp were immersed in an esterifying bath of the composition indicated in Example I, maintained at a temperature of C. to C., for a period of about 5 minutes. The sheets were then removed from the bath, and pressed to retain about 300% by weight of the esterifying solution. The sheets were then cured in an infrared oven, macerated, and washed until the washings gave no test for phosphate. The following table indicates the surface resistivities obtained for the various sheets, with such sheets cured at the temperatures and for the lengths of time indicated.

TABLE VI Curing conditions Surface resistivity at 50% relative Run humidity, ohms Temperature, C. Time, min. per squareXlO All of such sheets, when prepared into copy sheets for electrostatic printing, produced good electrostatic prints. If desired, the impregnation and curing steps may be combined, as illustrated by the following example.

Example IX Bleached sulfite pulp was thoroughly immersed in a phosphorylating mixture of the type described in Example I, with such mixture in different runs maintained at the temperatures set forth in the following table, and with the immersion in different runs continued for periods of time as indicated in the table. The pulp in the various runs was then removed from the treating solution, washed and made into paper sheets, and surface resistivities then determined.

TABLE VII Curing Conditions Surface Phosphorus resistivity at Run content, 50% relative Tempera- Time, percent by humidity, ture, 0. min. Weight ohms per squareXlO It will be apparent from the above that there is contemplated by this invention a novel form of electrostatic printing product, where the support for the dielectric film in the product comprises a web which is electrically conductive by reason of ionic disassociation of the fibers making up the structure of the web. The conductance of the web need not be the result of properties of any additive added to the pulp which forms the web. An additive may, on occasion, be mixed with the pulp to produce certain characteristics if desired, however, with the invention the required conductivity in the base web is produceable without employing such additives. As a consequence, manufacturing procedures may be simplified, and truly uniform electrical conductivity in the base web of an electrostatic printing product is obtainable. This latter characteristic is believed to be a factor in making possible the use of papers in copy sheets with higher resistivities than normally thought usable if satisfactory prints are to be obtained.

Various types of cellulosic derivatives may be employed to provide the fibrous structure in the web, including cationic and anionic forms. Webs produced from different types of derivatives are subject to some variation, and in a particular manufacture the type of derivative which is used is dictated by the characteristics desired in the final product.

In producing cellulose ammonium phosphates, a preferred form of derivative, various procedures are employable. The curing times employed preferably lie within the range of /2 to 20 minutes, and temperatures are used ranging between 150 C. to 240 C. As indicated in the various examples, the length of curing time, and the curing temperature selected, will affect the amount of phosphorylation which takes place. By proper selection of reaction conditions, a derivative containing a high degree of phosphorylation is produceable suitable for making copy sheets for electrostatic printing usable at low relative humidities.

Although it is preferred to employ the ionic fibrous cellulosic derivatives as part of the stock mixture from which cellulosic webs are formed, these fibrous derivatives may be applied to a web made from unmodified cellulose as a coating or impregnating solution or mixture in a suitable solvent or diluent such as water to render the web more electrically conductive. Such a coating or impregnating material may be applied either to the side of the web upon which the dielectric film is subsequently applied, or to the side opposite that to which the dielectric film is subsequently applied, or to both sides of the web thereby to form at least a portion of the fibrous structure of the web. Similarly, such coating or impregnating material may be applied to cellulosic webs made at least in part of ionic fibrous cellulosic derivatives to impart additional electrical conductivity thereto.

While various examples have been included herein for the purpose of fully illustrating the invention, it should be obvious that the invention is capable of substantial variation. It is desired to cover all modifications and variations as would be apparent to one skilled in the art, and that come within the scope of the appended claims. It is claimed and desired to secure by Letters Patent: 1. In the manufacture of a printing paper, the process comprising preparing from fibrous cellulosic material an ionic fibrous cellulosic derivative which disassociates in the presence of water with the helease of charged ions, said derivative being the product formed by substituting ionizable groups in the reatcive groups of the anhydroglucose units that form cellulose, preparing a web from the cellulosic derivative with such derivative forming the fibrous structure of the web, and applying a dielectric film over at least one face of said web with the film then having an electrically conductive backing by reason of the ionic nature of the fibrous structure forming the web.

2. In the manufacture of an electrostatic printing product, the process comprising collecting a mass of fibrous cellulosic material, immersing such mass in a phosphoric solution comprising phosphoric esterifying medium and a weak organic nitrogenous base, with such solution having a melting point below about C. and containing not more than about 15% by weight water, recovering the mass from such solution with the mass impregnated with solution, curing the impregnated mass by heating the same at temperatures ranging from about C. to 240 C. for a period of time ranging from /2 to 20 minutes, washing the resulting mass to produce an ionic fibrous cellulosic derivative, preparing a cellulosic web from the cellulosic derivative with the derivative forming the fibrous structure of the web, and applying a dielectric film over one face of said web. 3. In the manufacture of an electrostatic printing product, the process comprising collecting a mass of fibers cellulosic material, impregnating the mass with a liquid phosphoric esterifying medium, curing the impregnated mass to form an ionic fibrous cellulosic derivative of the cellulosic material through heating the impregnated mass at elevated temperatures, said derivative being the product formed by substituting ionizable phosphate groups in the reactive groups of the anhydroglucose units that form cellulose, Washing the cellulosic deriavtive, preparing a cellulosic web from the cellulosic derivative with the deriavtive forming the fibrous structure of the web, and applying a dielectric film over one face of said web. 4. The process of claim 3, wherein the impregnation and 1 1 curing steps are carried on conjointly by immersing the mass in a heated liquid esterifying medium.

5. An electrostatic printing paper comprising a base Web having a fibrous fabric composed at least in part of an ionic fibrous cellulosic derivative, said deriavtive being the product formed by substituting ionizable groups in the reactive groups of the anhydroglucose units that form cellulose,

the cellulosic deriavtive making up the base web operating by the ionic nature thereof to impart electrical conductivity to the base web and the amount of such deriavtive in said web being sufficient to produce a resistivity of not more than 1.5 ohms per square at a relative humidity of 50%, and

a dielectric film joined to and extending over at least one face of the base web.

6. An electrostatic printing paper comprising a cellulosic base sheet having a fibrous structure composed of an ionic fibrous cellulosic derivative, said deriavtive being the product formed by substituting ionizable phosphate groups in the reactive groups of the anhydroglucose units that form cellulose,

said cellulosic derivative in said base sheet containing from 15% to by weight phosphorous, combined in the cellulosic derivative as phosphorylated cellulose, and

a dielectric film joined to the base sheet extending over at least one face of the sheet.

7. An electrostatic printing paper comprising a cellulosic web which includes an ionic fibrous cellulosic derivative, said derivative being the product formed by substituting ionizable groups in the reactive groups of the anhydroglucose units that form cellulose, said web having a layer of dielectric material extending over at least one face thereof, and the web providing a conductive backing for the layer of dielectric material by reason of the inclusion of the cellulosic derivative.

8. In electrostatic printing, wherein an image-defining electrostatic charge is laid down upon one face of a dielectric film, the method of dissipating electrical charges on the back ofsuch film by conducting such charges through a fibrous cellulosic derivative which forms a web provided over the back of such film, such web having electrically conductive properties through ionic dissassociation taking place in the cellulosic derivative, said derivative being the product formed by substituting ionizable groups in the reactive groups of the anhydroglucose units that form cellulose.

9. An electrostatic printing paper comprising a cellulosic web which includes an ionic fibrous cellulosic derivative selected from the group consisting of phosphorylated cellulose, oxidized cellulose, sulfoethyl cellulose, carboxymethyl cellulose, and aminoethyl cellulose, and a layer of dielectric material extending over at least one face of said web, the derivative operating by the ionic nature thereof to impart electrical conductivity to the web, the amount of such derivative in the web being sufficient to produce a resistivity of not more than 1.5 1O ohms per square at a relative humidity of References Cited UNITED STATES PATENTS 2,357,962 9/1944 Leemann 162138 2,482,755 9/1949 Ford et a1. 8116.2 2,987,433 6/1961 Ward 162157 3,161,505 12/1964 Tomanek 961.5

FOREIGN PATENTS 1,057,440 5/ 1959 Germany.

OTHER REFERENCES Phosphorylation of Cotton With Inorganic Phos phates, American Dyestuff Reporter, vol. 53, No. 10, pp. 23-25, May 11, 1964 (copy in 8120).

S. LEON BASHORE, Primary Examiner.

US. Cl. X.R.