US3385730A - Writing medium for electrostatic printing - Google Patents

Description

y 8, 1968 E B. @QELPH 3,385,730

WRITING MEDIUM FOR ELECTROSTATIC PRINTING Filed April 1, 1964 10 \Z\ \\\\\\\\\\I\\\\\\\\ Dielectric t ng Paper Base .Sheei carzkz'zrzz'r Ammonium l2 Chloride and @{ycerinc INVENTD/Z y 'arl B. Eel D 1 United States Patent 3,385,730 WRITING MEDIUM FOR ELECTROSTATIC PRINTING Earl B. Ralph, Des Plaines, 11]., assignor to A. B. Dick Company, Niles, Ill., a corporation of Illinois Filed Apr. 1, 1964, Ser. No. 356,382 5 Claims. (Cl. 11720l) ABSTRACT OF THE DISCLOSURE The invention is addressed to an electrostatic writing medium adapted to receive a latent electrostatic image capable of subsequent development by a liquid or powdered developer and in which .the electrostatic writing medium is formed with a dielectric insulating coating on the surface of a paper base sheet which is impregnated for uniform distribution of the combination of a polyhydric alcohol and ammonium choride.

This invention relates to a writing medium for use in electrostatic dry copy processes and it relates more particularly to a coated paper on which a latent electrostatic image can be formed for subsequent development by conventional dry or liquid toners.

Writing media for dry electrostatic printing processes are generally formed of a dielectric coating on an electrically conductive base whereby the latent electrostatic image is received on the surface of the dielectric coating for retention until developed by the dry or liquid toner. It is preferred to fabricate such writing media of a dielectric coating applied onto a paper base sheet but the combination is found often times to be deficient by reason of the variations occurring in the electrical conductivity of the paper base sheet, depending somewhat upon the composition of the paper, the relative humidity conditions existing at the time of copy preparation, the previous history of the coated copy paper, and many other factors.

It is an object of this invention to produce a writing medium which is characterized by low cost and ready availability; which can be manufactured of a dielectric coating on a paper base sheet which exhibits good electrical conductivity independent of the previous history of the writing medium in storage and substantially independent of the humidity conditions existing in the ambient atmosphere at the time of copy production; which exhibits improved electrical conductivity, and which can be used to produce copy of good quality consistently, from batch to batch, with very little variation or with little sensitivity to the wide changes occurring in atmospheric conditions.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of this invention is shown in the accompanying drawing, in which:

FIG. 1 is a perspective view partially in section of a writing medium embodying the features of this invention.

In order to minimize these variables and to produce a coated paper writing medium having improved electrical conductivity in the base sheet on which the dielectric coating is formed, attempts have been made to formulate the base sheet of materials which would increase moisture retention and control independent of the humidity in the ambient atmosphere and which would impart higher electrical conductivity. In my previously issued Patent No. 3,075,859, description is made of an electrostatic writing medium in the form of a dielectric coating on a paper base sheet wherein the latter is formulated to contain a humectant or ionizable metal salt, and preferably the combination of a humectant and an ionizable metal salt "ice uniformly distributed throughout the base sheet to render the base sheet substantially insensitive to changes in humidity conditions in the ambient atmosphere and to improve the electrical conductivity of the base sheet and thereby to produce an improved writing medium for dry electrostatic printing.

It has now been found, in accordance with the practice of this invention, that the specific combination of ammonium chloride and a polyhydric alcohol which, when uniformly distributed substantially throughout the base sheet, will provide optimum characteristics in the base sheet for use as an electrostatic writing medium when provided with a suitable dielectric coating.

Best results are secured with the combination of glycerine as the polyhydric alcohol and ammonium chloride present in the ratio of 1 part by weight ammonium chloride to 2 /2 parts by weight of glycerine but the ratio can be varied within the range of 1 part by weight of ammonium chloride to 1 to 4 parts by weight of glycerine. Instead of glycerine, use can be made of other polyhydric alcohols such as ethylene glycol, dior triethylene glycol, propylene glycol, pent-a erythritol, sorbitol and the like, in corresponding amounts.

It is desirable to incorporate an amount of the mixture of glycerine and ammonium chloride into the paper base sheet suflicient to provide the desired stabilization and improved electrical conductivity but not so much as will squeeze out of the base sheet to wet .the adjacent surface of the dielectric coating, when the sheets are plied one on the other, as in a stack or when rolled, thereby to interfere with the desired dielectric properties of the coating and the ability of the coating to receive and retain good definition in the latent electrostatic image. The amount of ammonium chloride and glycerine will depend somewhat upon the basis weight of the paper, the amount of moisture left in the paper, and the conditions under which the sheet is packed or otherwise left in the roll. In practice, with a coating composition formulated in accordance with the following Example 1, it is undesirable to exceed a coating weight of 12 pounds per 3000 square feet of surface area but it is desirable to make use of an amount of at least 2 pounds per 3000 square feet of surface area. Optimum results are achieved by the application of the materials in a coating weight of 3 to 7 pounds glycerine-ammonium chloride per 3000 square feet. When calculated on percent by weight of the paper base sheet, the broad range is 0.1 to 35 percent by weight of the polyhydric alcohol and preferably 0.1 to '15 percent by weight of ammonium chloride and 0.1 to 20 percent by weight of the polyhydric alcohol.

The following is given by way of illustration, but not by way of limitation, of the preparation of an electrostatic writing medium embodying the features of this invention:

EXAMPLE 1 Treating composition: Percent by weight Glycerine 25 Ammonium chloride 10 Water 62 Butanol 3 The above composition is applied to a suitable paper base sheet, preferably after coating with a dielectric material, otherwise ammonium chloride is dissolved out of the paper into the coating whereby it might be elfective to reduce the resistivity of the dielectric. If the salt is not soluble in the dielectric coating composition or if a barrier coating is employed, between the dielectric coating and the paper, then the treating composition can be applied before coating. The composition is applied in coating weights of 3 to 7 pounds of solids embodying may be formulated of such synthetic resinous materials as polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyethylene, polyacrylic acid esters, polyvinyl acetate copolymers such as polyvinyl acetate-crotonic acid copolymer, polyesters, alkyd resins, oil modified alkyd resins, shellac, microcrystalline wax, petroleum hydrocarbon resins, :butadiene-styrene copolymers, nitrocellulose, cellulose acetate, and epoxy resins.

Thus the electrostatic writing medium of this invention is illustrated in FIG. 1 wherein the numeral represents the dielectric coating on the surface of a paper base sheet 12 containing a mixture of ammonium chloride and glycerine uniformly distributed throughout the paper base sheet in the amounts described.

It will be apparent from the foregoing that I have provided a specific formulation of materials incorporated in a paper base sheet of an electrostatic writing medium for improvement of the characteristics of the paper base sheet whereby the Writing medium becomes less sensitive to variations normally occurring in the ambient atmosphere rand whereby the paper base sheet is characterized by a desirable high electrical conductivity which it retains over an extended period of time.

It will be understood that changes may be made in the details of formulation and application and in composition, without departing from .the spirit of the invention, especially as defined in the following claims.

I claim:

1. An electrostatic Writing medium on which a latent electrostatic image is formed and developed, comprising the combination of a paper base sheet and a continuous dielectric insulating coating on the paper base sheet, and a polyhydric alcohol and ammonium chloride substantially uniformly distributed throughout the paper base sheet in which the polyhydric alcohol and ammonium chloride are present in the ratio of 1 part by weight of ammonium chloride to 1 to 4 parts by weight of the polyhydric alcohol and in which the materials are present in the base sheet in an amount within the range of 2 to 12 pounds by weight of the mixture of polyhydric alcohol and ammonium chloride per 3000 square feet of surface area.

2. An electrostatic writing medium 'as claimed in claim 1 in which the polyhydric alcohol is glycerine.

3. An electrostatic writing medium on which a latent electrostatic image is formed and developed, comprising the combination of a paper base sheet and a continuous dielectric insulating coating on the paper base sheet, and :a polyhydric alcohol and ammonium chloride substantially uniformly distributed throughout the paper base sheet in which the polyhydric alcohol and ammonium chloride are present in the ratio of 1 part by Weight of ammonium chloride to 1 t0 4 parts by weight of the polyhydric alcohol and in which the materials are present in the base sheet in :an amount within the range of 3 to 7 pounds by weight of solids composed of polyhydric ralcohol and ammonium chloride per 3000 square feet of surface area..

4. An electrostatic writing medium on which a latent electrostatic image is formed and developed, comprising the combination of a paper base sheet and a continuous dielectric insulating coating on the paper base sheet, and a polyhydric alcohol and ammonium chloride substantially uniformly distributed throughout the paper base sheet in which the ammonium chloride is present in an amount within the range of 0.1 to 25 percent 'by weight of the paper base sheet and in which the polyhydric alcohol is present in an amount within the range of 0.1 to 35 percent by weight of the paper base sheet.

5. An electrostatic writing medium as claimed in claim 4 in which the ammonium chloride is present in an amount within the range of 0.1 to 15 percent by Weight of the paper Ibase sheet and in which the polyhydric alcohol is present in an amount within the range of 0. 1 to 20 percent by weight of the paper base sheet.

References Cited UNITED STATES PATENTS 2,086,544 7/1937 Dreyfus 117- 1395 2,283,558 5/1942 Kline 204-2 2,372,829 4/1945 Holst 204-2 2,651,585 9/1953 Lytlc et a1. 117-201 X 2,776,251 1/1957 Schwartz 204-2 2,983,654 5/1961 Dalton 204-2 3,011,918 12/1961 Silvernail et a1. 162-138 X 3,075,859 1/1963 Ralph et al 117-152 X 3,116,147 12/1963 Uber et a1. 162-138 X 3,142,562 7/ 1964 Blake 204-2 X 3,216,853 11/1965 Gess 117-201 WILLIAM -D. MARTIN, Primary Examiner. E. J. CABIC, Assistant Examiner.

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