Method for coating on a substrate

Dec. 8, 1970

D. L. HOCHBERG

3,545,997

METHOD FOR COATING ON A SUBSTRATE

Filed Jan. 26, 1966

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INVENTOR.

DAVID LOUIS HOCHB&amp;R.G

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ATTORNEY

United States Patent Office

3,545,997

Patented Dec. 8, 1970

545 997

METHOD FOR COATING ON A SUBSTRATE David Louis Hochberg, New York, N.Y., assignor to Pitney-Bowes, Inc., Stamford, Conn., a corporation of Delaware

Filed Jan. 26, 1966, Ser. No. 523,054

Int. Cl. B41m 5/18; B44d 1/94,1/50

U.S. Cl. 117—17 2 Claims

ABSTRACT OF THE DISCLOSURE

This invention relates to a method of producing a thermographic transfer printing member which comprises applying thermographic ink particles to the topside of a substrate, irradiating the ink from the underside of the substrate and through the substrate, whereby a layer of ink is fused to the topside of the substrate and then transferring the fused ink layer to a receiving substrate which comprises placing the receiving substrate in contact with the fused ink layer, irradiating the ink layer from the underside of the substrate through a stencil means and through the substrate, whereby portions of the ink layer are transferred to the receiving substrate.

This invention relates to a method for preparing a thermally fusible coating on a substrate. The invention further relates to the preparation of a thermographic printing member which may be rejuvenated and resued in a continuous manner.

A thermographic printing method is disclosed in copending, commonly assigned application Ser. No. 503,218 of Gilbert Zweig, filed Oct. 23, 1965, now abandoned. That method makes use of radiation rich in infra-red and a stencil master which transmits the radiation in the image areas but not in the non-image areas. The stencil consists of a metallic coated transparent material known in the art as leafing foil. When such foils are typed upon, the metallic layer is transferred off in the areas struck by the typewriter keys to leave transparent image areas and forms a radiation-transmitting stencil.

The stencil is then placed over a heat fusible transfer carbon sheet which contains an infra-red absorbing pigment in the carbon layer. The stencil is placed against the non-carbon side, and a sheet of copy paper is placed next to the carbon side. The stencil is then irradiated with a source of rays which are rich in infra-red which fuses the carbon layer in the image areas and transfers it to the copy sheet to form an image corresponding to the stencil image.

After imaging, the transfer carbon is devoid of transfer material in the transfer area and has to be discarded and replaced by a new carbon sheet for the next printing. Thus the necessity of replacing the carbon sheet each time can be costly.

It is therefore an object of this invention to provide a thermal carbon transfer medium which may be rejuvenated and reused after each printing.

A further object is to provide a thermal transfer carbon by which the cost of thermal printing may be reduced.

Another object is to provide a method for continuously forming a thermal transfer carbon medium in a thermographic printing process.

Still another object is to prepare a coating of uniform thickness, even on slightly irregular support material.

A further object is to provide a method for coating a substrate which is transparent to infra-red with a material which is heat absorptive and thermally fusible.

These and other objects of my invention will become apparent as the description thereof proceeds.

The above objects may be achieved by the use of an endless belt coated with a thermographic carbon layer which is used in a thermographic printing operation and rejuvenated by recoating the used areas of each printing operation.

The invention may be better understood by reference to the figure which shows a cross-sectional view in elevation of the endless belt and the application of toner powder, thermographic printing and reapplication of toner.

A transparent endless belt 1 (made for example of Du Pont “Mylar” polyethylene terephthalate) is adapted to travel around rollers 1A and IB. An excess of a thermographic toner powder is deposited on belt 1 at 2. The belt with excess toner passes over infra-red lamp 3 in front of reflector 4 which fuses the toner particles and forms a layer 5 on belt 1. Excess, unfused toner is removed at 6 either by brush, vacuum means employing both, gravity, electrostatic forces, or the like.

Belt 1 with fused toner layer 5 is then equivalent to a transfer carbon sheet and is then used for thermographic printing at infra-red lamp 7 in front of reflector 8. For this purpose, a stencil 10, which has transparent image areas 11 and is non-transparent in the remaining areas, is placed between infra-red lamp 7 and belt 1. A receptor paper 12, which may be an envelope, paper sheet or the like on which the stencil image is to be made, is placed in contact with transfer layer 5 in register with stencil 10. Stencil 10 is then irradiated with brief but intense infrared radiation. The layer 5 is fused and transferred to receptor paper 12.

The fusing radiation from lamp 3 should be less intense than that of lamp 7 at the exposing station. This is done so that the layer fused on belt 1 by lamp 3 and deposited on the belt will not be so thick that lamp 7 will not be able to fuse it to effect transfer of the layer from belt 1 to receptor paper 12.

After the exposure to infra-red lamp 7, the layer on belt 1 has a vacant area as shown at 13. From this point, belt 1 again comes to the point for applying an excess amount of toner at 2A. The toner powder will be deposited on top of layer 5 except at point 13 where toner will be deposited on the vacant area and in contact with the surface of belt 1. The entire process is then repeated, fusing the toner in the vacant area 13A to form a new continuous layer 11 for thermographic printing.

Although two areas of toner application are shown in the figure, this is for illustration. There is actually only one tone applicator since belt 1 is continuous and is recycled.

Belt speeds have been varied from between one-half and four feet per second using 200 watt/inch infra-red lamps but can be increased by use of more powerful lamps.

Belt 1 may be made part of a thermographic printing machine and it will be obvious that the necessary means for moving belt 1 and for turning the infra-red lamps on at the proper times for applying the toner powder, and feeding stencils and receptor paper may all be provided as well known in the art to provide a continuous method.

The toner powder used is a thermographic type, i.e. it is readily fusible under heat. Suitable toners are made by mixing a pigment which absorbs infra-red in a molten wax, allowing the wax to harden, and pulverizing the wax and classifying it into a finely divided powder. As suitable waxes for pebble milling, Castorwax (Baker Castor Oil Co.) was one such wax. The wax melting point must not be too high since this would lead to damaging of the stencil before fusion of the powder occurs.

Suitable pigments are those whtich absorb appreciable amounts of infra-red radiation, such as carbon black and black magnetizable iron oxide.

3,545,997

The amount of pigment can vary from about 5% up to the maximum capable of dispersion in the wax, up to 50% or more. Generally, 20% is quite satisfactory for good image density and low smearing tendency. Smearing of copy images is worsened by employing lower melting waxes and/or by increasing the pigment concentration.

Low melting waxes can be used if they are hard waxes and can be milled in the solid state. They should have a melting point above about 71° C. Some suitable waxes are described in the subsequent specific examples of toner preparation.

In addition, a fusible toner can be made from readily available resinous materials such as shellac and the like, in the same manner.

The following examples describe the preparation of suitable thermographic toner compositions.

EXAMPLE I grams of Castorwax (Baker Castor Oil Co.) having a melting point of 85° C. were placed in a beaker and heated with agitation until molten. Then 20 grams of Regal SRF carbon black (Cabot Corp.) and 1 gram of Armour PE 200 antistatic agent were blended into the wax while still molten until a more or less uniform mixture was obtained. The blend of wax and carbon black was then poured on a flat surface and allowed to solidify at ambient temperature. The resulting solid mass was then placed in a micro pulverizer for about 15-30 sec., after which it was placed in a half-filled pebble mill and milled overnight (about 18 hours) until finely pulverized and 7.5 percent of the starting weight passed through a 400 mesh (75 micron opening) sieve. The resulting —75 micron toner power had a fusion temperature of 85° C. (Fisher-Johns).

EXAMPLE II

In the same manner as described in Example I, 60 grams of Candelilla wax (Ross Wax Co.) were combined with 40 grams of finely divided carbon black (Regal SRF, Cabot Corp.). 2.4 percent of the finely divided powder passed through a 400 mesh sieve and had a fusion point of 71° C. (Fisher-Johns). This amount was useful as a thermographic toner.

EXAMPLE III

A thermographic toner powder was produced in the same manner described in Example I from 50 grams of Castorwax (Baker Castor Oil Co.) and 50 grams IRN 350 magnetic iron oxide (William and Co.) which had a melting point of 85° C. (Fisher-Johns). 4.8 percent passed through a 400 mesh sieve and this amount was useful as a thermographic toner.

EXAMPLE IV

A thermographic toner powder was prepared as in Example I, from 80 grams of Petrolite WB-8 wax (Bareco Wax Co.) and 20 grams Vulcan 3 finely divided carbon (Cabot Corp.). The amount of product passing through a 125 mesh sieve was useful as a thermographic toner powder and had a melting point 84° C. (Fisher-Johns).

EXAMPLE V

Petronauba D wax (Bareco Wax Co.) and Regal SRF finely divided carbon were combined as in Example IV, with similar results in obtaining a thermographic toner powder.

EXAMPLE VI

Cerathane Polymer 63 (Bareco Wax Co.) was substituted in Example V and the thermographic toner powder obtained had a melting point of 82° C. (Fisher-Iohns).

In the same manner as described above, any substrate which is somewhat transparent to infra-red can be coated. Thus even paper as well as numerous types of plastic sheet materials may be coated. It is only necessary that the granular or powdered material be heat absorptive and that the web material be transmissive of infra-red radiation and have a deformation temperature well above the fusion temperature of the coating material. This can be readily accomplished by mixing carbon black with the fusible material. The method may therefore be used to produce a coated web by continuously depositing a heat absorptive granular or powdery material on the surface of the web and heating from below with infra-red to fuse a layer of the material on the surface of the web. The coating thickness is quite uniform because the heat of fusion propagates through the fusible layer of particles for a given distance regardless of the thickness of the layer of excess fusible particles.

Moreover, although I have described application of thermographic toner to the belt as a powder, the thermographic toner could be fused onto the belt by having a solid mass of toner in contact with the surface of the belt, and passing radiation from the opposite side of the belt and through the belt to fuse the toner.

While I have disclosed certain specific embodiments of my invention, this is only for the purpose of illustration. It will be understood that various changes and modification may be made without departing from the spirit of the disclosure or the scope of the appended claims.