US3473923A - Reproduction process including transfer and redevelopment of electrostatically formed images - Google Patents

Description

U5. Cl. 96--l.4 Claims ABSTRACT OF THE DISCLOSURE A reproduction process is described wherein an electrostatic image is developed with a pulverized solid material. The material is hard and non-sticky in its normal state but melts in the range of from 70 to 170 C. to form a metastable liquid. The metastable liquid is transferred under the effect of heat to a receiving sheet, and the receiving sheet is developed with a developer powder.

This invention relates to a process for producing reproductions, and more particularly to a process for producing a number of reproductions on ordinary paper. The object is to provide a cheap and simple reproduction process without the necessity of incorporating chemicals in a receiving sheet, of using a darkroom and of using any liquid, so that the reproduction process is a dry system.

In accordance with the present invention, there is provided a reproduction process comprising (1) exposing an electrophotographic sheet (intermediate sheet) coated with a photoconductive layer to radiation to form an electrostatic image pattern, (2) developing the electrostatic image pattern with powder of a transferable and charge accepting material to form images, which have a tendency to form a metastable liquid when its melt is cooled, on the electrophotographic sheet in areas corresponding to the electrostatic image pattern, (3) transferring a part of the image of transferable and charge accepting material onto a receiving sheet, such as ordinary paper and film, and then (4) subjecting the transferred image to powder development and fixation. The thus reproduced image is so stable that discoloration and deterioration in quality, such as is encountered with the ordinary reproducing materials of silver salt, does not occur.

The transfer can be carried out several, or even 10, 20 or more times, that is, a number of reproductions can be obtained from one intermediate.

It is possible to extend the spectral sensitivity of the intermediate sheet to be used in the present invention over almost the entire visible range by the dye sensitization of the photoconductive layer. That is to say, according to the process of the present invention, copies can be obtained from any colored original without the disadvantage that there is sensitivity only for the black and purple shade as in the heat sensitive paper.

According to the process of this invention, it is possible to perform the whole reproduction process in a dry system, and further the resolving power of the present process is superior to 8. copying process in which an original image is formed, for example, by drawing, typewriting,

m States Patent 0 "ice or by other methods, on the surface of a sheet having a layer of transferable material having the tendency to form a metastable liquid when its melt is cooled on its back surface, and the transferable material corresponding to the image part is transferred onto a receiving paper by heat and powder-developed.

This invention is described in detail below.

As the intermediate sheet to be used in the process according to the present invention, there may be mentioned paper, film and metal plates having a photoconductive layer. As the most well known photoconductive materials, there may be mentioned selenium, zinc oxide, and organic semi-conductors, such as anthracene, violanthrone, phthalocyanine, Crystal Violet, polyvinyl-carbazol and the like. The intermediate sheet is electrostatically charged and exposed imagewise, in a conventional electrostatic photographic process. The sheet is then powerdeveloped with a powder developer having a component described hereinafter in detail.

The powder developer which develops the intermediate sheet mentioned above must have two properties described below.

(a) Good transferability.1t should be selected from such transferable materials that are non-adhesive at room temperature but become adhesive after melting at a temperature in the range of from C. to C., and have a high super-cooling property. That is to say the material is retained in a metastable liquid phase at room temperature for several minutes after being melted and cooled. As typical examples of such transferable material, there may be mentioned those shown in the following table (see Belgian patent specifications No. 631,304 and 644,- 239). This property is required for the transfer from the intermediate as described hereinafter.

(b) Good triboelectric charge acceptance.Namely, for powder-development of the charged image formed on the intermediate sheet by the exposure corresponding to the image, it should have a suitable triboelectric property above a given value.

To determine powder developers having said two properties mentioned above, materials having a good Supercooling property have been selected'and ground to pass a screen of 170 mesh (screen diameter 88 microns) and their triboelectric properties have been determined. The results are shown in the following table.

The values in the third column of this table are the relative coordinates in triboelectric series determined based on the two standard materials. The material of larger value is charged positive and suitable for the development of the intermediate (for example, a sheet coated with zinc oxide) to prepare a negatively charged electrostatic latent image. To the contrary, the material of smaller value is suitable for the development of the intermediate (for example, a sheet vacuum-evaporated with selenium) to prepare a positive charged electrostatic latent image.

For the triboelectric charge acceptance shown in the fourth column of the table, the absolute value of charge quantity per gram of powder passed through a screen of 170 mesh (diameter 88 microns) more than .4 microcoulomb is shown as A, that from 1 or 3 microcoulombs as B, that of about 1 microcoulomb as C and that less than 1 microcoulomb as D.

3 In practice, the charge quantity over 3 microcoulombs is preferable, whereas that of about 1 microcoulomb is sufficiently available.

Coordinate Tribo in electribotric eleccharge M.P. tric accept- TransferableMaterial C.) series ance Benzoic acid 122 1l0130 A Benztriazo1e- 100 110-130 D Sodium tartarate 140 D Potassium tartarate 110 D p-Dimethylamino-benzaldehyde 108 A Benzoin 134 105 A Grape Sugar 146 105 D 1-phenyl-3-pyrazolidine 121 105 A Sorbitol 92-97 100 D 95 95 B 92 66 A 135 66 A 134 66 A 115 66 B 82 48 D 132 45 D a e h 1h dro uinone... 124-1 .f1'tu ..Y --E 119-120 28 B o,p-Toluene sulione amide (mixtur 105-110 25 C 2,4-dihydroxybenzo-phenone 147 0 A B-Naphthol 128 0 0 Maleic anhydride 53 0 D The powder developer to be used in the process according to the present invention and having the two properties mentioned above is granulated to a grain size of 0.1-100 microns in diameter to use. It may be mixed with an infrared absorbing substance. The amount of infrared absorbing substance mixed may be less than 0.1 part by weight per part by weight of transferable and charge acceptable material. As an infrared ray-absorbing mater al may be used a finely divided inorganic or organic plgment. Typical examples thereof are carbon black, 1101'1 oxides, chrome green, ultramarine blue, cobalt blue and indigo.

The powder developer for developing an exposed intermediate sheet may be prepared by the following procedure. One part by weight of a transferable and charge accepting material is thoroughly mixed with 0-0.1 part by weight of a finely divided infrared ray-absorbing material and heated. When the transferable and charge accepting material is melted, the molten mixture is further blended sufiiciently and cooled to normal temperature. The molten mixture, after being solidified completely, is finely pulverized by suitable means and then granulated to a grain size of 0.1-100 microns in diameter. A mixture of a powder developer used in the conventional electrophotography (called toner) and finely divided transferable and charge accepting material may be used as the powder developer for developing an exposed intermediate of the present invention.

The intermediate sheet mentioned above is exposed and powder-developed with the powder developer made of the transferable and charge accepting material to form the mirror image of an original. After the mirror image of an original is formed on the intermediate sheet by the powder developer, the intermediate sheet is heated by suitable means to raise the temperature to the melting point of the transferable and charge accepting material and then cooled to room temperature, thereby to fix the powder image of the original on the intermediate sheet. The coated side of the thus processed intermediate sheet is placed upon a receiving sheet, such as paper, film, glass or cloth and heated. The heating is carried out by holding them between two hot plates or by the use of infrared rays. Or, the surface of the intermediate sheet is heated by infrared ray irradiation, followed by placing thereon a receiving sheet, and pressing them together.

Then a part of the image portion of the intermediate sheet is transferred to a receiving sheet. In the case of employing the infrared ray heating, an infrared ray-absorbing material is preferably added to the transferable and charge accepting material.

The transferable and charge accepting material is thus transferred to a receiving sheet. If the powder development is carried out just after the transfer, the power neveloper is adhered only to the portion of the receiving sheet coated with the transferable and charge accepting material due to the adhesivity of this material, whereby to form an image.

As the powder developer used for developing a receiving sheet there may be employed any fine powder having a suitable grain size to be adhered to a molten transferable and charge accepting material. The powder developer may be prepared by dispersing in a thermoplastic resin. such as a phenol-formaldehyde resin, a molten mixture of chlorinated naphthalene and polystyrene or a copolymer of vinyl chloride and vinyl acetate, a carbonaceous material, such as carbon black or asphalt powder, an inorganic pigment, such as basic lead carbonate, zinc oxide. titanium dioxide, antimony trioxide, iron oxides, cadmium sulphide, basic chromate, molybdenum orange, cadmium yellow, chrome green, ultramarine blue, or organic pigments, such as benzidine yellow, indigo and alizarin. and granulating the thus prepared dispersion by a suitable method into granules having a diameter of from 0.1 to 50 microns. A toner used for conventional electrophotography is used in the present method. The color of such developers should be selected in accordance with the color of the receiving sheet.

When the material is heated or treated with the vapor of an organic solvent such as trichloroethylene, Freon (registered trademark of E. I. du Pont de Nemours & Co.. Delaware, USA.) acetone, chloroform and benzene after the development, a visible image, which is not affected by light, moisture and being stored permanently, can be obtained.

A powder developer, the surface of which is treated with surfactant, and the mixture of a powder developer and a powder of a solid surfactant, which is described and claimed in the specification .of our co-pending application No. 529,901 can be used in the process of the present invention. Surfactants used as wetting agents are suitable for this purpose, and examples thereof are alkylsulfosuccinates, alkyl benzene sulfonates, alkyl esters of sorbitan. long-chain hydrocarbon quaternary ammonium salts, and alkyl esters of polyoxyethylene sorbitan.

The amount of surfactant used can be selected in any amount corresponding to the kind of surface active agent, and, in general, it is suitable in an amount of about 10 10 and more especially 10 -10 molecules per cm! surface of powder developer.

Such powder developer has a strong adhesion to the transferable and charge accepting material so that the contrast of image of copy may be emphasized.

The transfer of a transferable material to a receiving sheet from an intermediate sheet can be carried out several times.

Thus, many sheets of copies can be obtained on the receiving sheet.

. The following examples further illustrate the present invention.

Example I A plate for the electrophotography, which is colorsensitived and coated with zinc oxide, is charged and exposed in a common manner and then powder-developed with the powder developer prepared by the procedure described hereinafter for the development of the intermediate sheet.

Twenty grams of benzoic acid is blended well with l g. of carbon black and heated at C. to melt the blend. After stirring the mixture well in the form of a melt, it is cooled to room temperature to solidify and is granulated into less than 400 mesh to yield the powder developer for the development of the intermediate sheet. The charge and exposed intermediate sheet is powder-developed, heated by the radiation of infrared rays and the image is fixed to yield an intermediate original image.

Then a receiving sheet was placed upon the image surface of the intermediate sheet, and heated by a heater or by irradiating infrared rays from the back of the intermediate sheet, so as to melt a part of the transferable material and to transfer it to the receiving sheet.

The receiving sheet is powder-developed with a toner, which is prepared by milling 80 parts of polystyrene, parts of phenol-formaldehyde resin and 10 parts of carbon black on a hot roll and grinding the resulting homogeneous mixture to an average particle size of -25 and fixed in the vapor of trichloroethylene.

By repeating the procedure, a great many copies can be obtained from an intermediate sheet.

Example 2 An aluminum original plate for electrophotography, which is vacuum-vaporized with amorphous selenium, is charged in a common manner, exposed and powder-developed with the powder developer for the development of the intermediate sheet, said developer being prepared by the method described hereinafter, to obtain an intermediate.

Alternatively, a selenium vacuum-evaporated plate coated with the powder developer may be contacted with other paper or film, corona discharged in their contact to transfer electrostatically thepowder developer on the selenium plate onto said paper or film and used as an intermediate sheet.

For the preparation of the developer for the development of the intermediate sheet, g. of 2,4-dihydroxybenzophenone is blended with 1 g. of carbon black and heated at 147 C. to melt the blend. The mixture in the form of a melt is stirred well, cooled to room temperature to solidify and then granulated to less than 400 mesh.

The transfer, development and fixation of the intermediate image were carried out similarly to Example 1.

Example 3 An intermediate sheet is prepared with the materials and procedure as described in Example 1 and developed with the powder developer prepared as in Example 1 by heating 20 g. of powdered 1-phenyl3-pyrazolidone and 1 g. of carbon black at 125 C. to melt. The transferable and charge accepting material adhered corresponding to the image area of original is then transferred onto a receiving sheet.

Ten grams of toner obtained by milling parts of polystyrene, 10 parts of phenol-formaldehyde resin and 10 parts of carbon black on a hot roll and grinding the resulting homogeneous mixture to an average particle size of 15-25 is added to a solution of 1 ml. of 30% aqueous solution of sodium diisooctyl sulfosuccinate (isoocty1=2- ethylhexyl) in ml. of water, stirred well to disperse, dried in vacuum and comminuted again into a particle size of less than 88 to yield the powder developer for the development of the image receiving sheet.

When the transmission density, after fixing, is determined on using the image receiving sheet as a film base, there may be observed the fOllowing difference between the density on developing with a powder developer not treated with surfactant that has been described in Exampie 1 and that on developing with a powder developer which has been treated with said surfactant.

6 (Image density) (Fog density) Powder developer without treatment 0.17 Powder developer with treatment of surfactant 1.07

From the result mentioned above, it has been found 5 that the use of powder developer, surface-treated with surfactant, elevates greatly the density after development.

Example 4 A paper 100 thick undercoated with polyvinyl alcohol is coated with a solution of polybutyl methacrylate resin in toluene so that the dried thickness may be 10 After drying the layer, a metallic type which is charged with a direct current voltage of l,000 v. is pressed onto the surface to form an electrostatic latent image, which is then developed with the same powder developer for the development of the intermediate sheet as described in Example 1. Good copies can be obtained by the same procedure as described in Example 1.

What is claimed is: 20 1. A process for producing a reproduction comprising the steps of:

(1) forming an electrostatic image pattern on a photoconductive surface,

(2) developing the image formed with pulverized solid material, said material being hard and non-sticky in normal state, melting at a temperature in the range of from 70 to C., and having a tendency to form a metastable liquid when the melt is cooled,

(3) transferring said solid material to a receiving sheet under the effect of heat,

(4) developing said receiving sheet with a developing powder while the transferred solid material contained thereon is in an adhesive state, and

(5) fixing said sheet.

2. A process as claimed in claim 1, in which said developing powder used in step (4) has been treated with a surfactant.

3. A process as claimed in claim 1, in which said developing powder used in step (4) has been mixed with a fine solid surfactant.

4. A process as claimed in claim 1, in which the development of said receiving sheet is accomplished just after the transfer and before the solid material has returned to its non-adhesive state.

5. A process as claimed in claim 1, in which said adhesive state is the result of heating said receiving sheet having the transferred solid material thereon to a temperature above the melting point of said solid material.

50 References Cited UNITED STATES PATENTS 2,297,691 10/1942 Carlson 961 3,260,612 7/1966 Dulmage et al. l1725 3,265,522 8/1966 Games 11725 3,360,367 12/1967 Stricklin 96-1 3,362,380 1/1968 Anderson et al 118-620 3,377,286 4/1968 Stricklin 252-62.1

GEORGE F. LESMES, Primary Examiner JOHN C. COOPER, Assistant Examiner US. Cl. X.R.