US3468254A

US3468254A - Electrostatically chargeable printing form

Info

Publication number: US3468254A
Application number: US457672A
Authority: US
Inventors: Gerhard Ritzerfeld
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-05-28
Filing date: 1965-05-21
Publication date: 1969-09-23
Anticipated expiration: 1986-09-23
Also published as: NL6504307A; BE664631A; CH433991A; DE1271126B; GB1096801A; FR1444280A; NO118380B; SE341925B

Description

Sept 23, 1969 G. RnzERFELD 3,468,254

ELECTROSTATICALLY CHRGEABLE PRINTNG FORM Filed May 2l, 1965 2 Sheets-Sheet 1 Fig.1

Inventor: 6 Qfdrd Eluibed Sept. 23, 1969 G, RITZERFELD ELEcTRosTATIcALLY CHARGEABLE PRINTING FORM Filed May 21, 1965 2 Sheets-Sheet Fig.3

Inventor:

United States Patent() 3,468,254 ELECTROSTATICALLY CHARGEABLE PRINTING FORM Gerhard Ritzerfeld, Franzensbader Strasse 21, Berlin-Grunewald, Germany Filed May 21, 1965, Ser. No. 457,672 Claims priority, application 9Germany, May 28, 1964,

U.S. Cl. lOl-401.1 4 Claims ABSTRACT OF THE DISCLOSURE An electrostatically chargeable printing form is produced by contacting an electrically conductive surface layer of a printing form blank with a surface layer of dielectric material having a melting point above ambient temperature, preferably in the vicinity of 80 C., and applying heat to selected portions of the layer of dielectric material, preferably by infrared radiation, so as to sufliciently heat the contacting surface of the selected portions of the layer of dielectric material to make the same actively adhesive and thereby to adhere the selected portions of the dielectric layer to the contacting electrically conductive surface layer, thereby forming a printing form having an operative surface consisting of the electrically conductive surface layer with the selected portions of dielectric material adhering thereto.

The present invention relates to a method and arrangement for producing electrostatically chargeable printing forms from which copies of an original may be produced. More particularly, the present invention is concerned with printing forms which are produced from originals which contain heat or infrared ray absorbing image portions and substantially heat or infrared rays permeable image-free portions, for instance, originals which are formed by typing or printing on transparent paper.

It is an object of the present invention to provide a method for producing electrostatically chargeable printing forms which can be carried out in a simple and economical manner.

It is a further object of the present invention to provide a method of producing electrostatically chargeable printing forms, whereby the difference between the heat or infrared ray absorption characteristics of image-forming and image-free portions of an original is utilized for transferring selected portions of `dielectric material, corresponding to the image to be reproduced, onto a printing form master.

It is yet a further object of the present invention to provide a composite sheet arrangement which, when eX- posed to heat radiation, will result in the formation of an electrostatically chargeable printing form.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in View, the present invention contemplates a method of producing an electrostatically chargeable printing form, comprising the steps of contacting an electrically conductive surface layer of a printing form blank with `a surface of a layer of low melting dielectric material, and applying heat to selected portions of the layer of dielectric material and to adhere the selected portions to the electrically conductive surface layer, thereby forming a printing form having `an operative surface consisting of the electrically conductive surface layer with the selected portions of dielectric material adhering thereto.

Patented Sept. 23, 1969 In accordance with a prefered embodiment, the method of producing electrostatically chargeable printing forms, in accordance with the present invention, comprises the steps of forming a stack consisting essentially of a printing form blank composed of a carrier sheet and an electrically conductive layer consisting essentially of a metal selected from the group consisting of aluminum, cadmium, zinc and silver located on one face of the carrier sheet, an original including image-forming, infrared-absorbing portions and image-free substantially infraredpermeable portions, and interposed between the original and said printing form blank a transfer sheet composed of a substantially infrared-permeable carrier sheet and an electrostatically chargeable layer of low melting point consisting essentially of a mixture of at least one hard wax and at least one easily electrostatically chargeable soft Wax and having distributed therethrough at least one pulverulent dielectric material having a melting point higher than the melting point of the mixture, the electrostatically chargeable layer being located on one face of the carrier sheet, the carrier sheet of the transfer sheet contacting the original and the electrostatically chargeable layer of the transfer sheet contacting the electrically conductive layer of the printing form blank, subjecting the thus formed stack to infrared radiation in the direction from the original towards the printing form blank so as to heat the infrared-absorbing image-forming portions of the original and corresponding portions of the electrostatically chargeable layer thereby melting the corresponding portions at least in contact with the electrically conductive layer and causing adherence of the corresponding portions of the electrostatically chargeable layer to the electrically conductive layer, allowing the corresponding portions of the electrostatically chargeable layer to cool below the melting point thereof, and separating the printing form blank with the corresponding portions of the electrostatically chargeable layer from the stack, thus forming a printing form having an operating face consisting of the electrically conductive layer with the selected electrostatically chargeable portions thereon.

It is also within the scope of the present invention to provide .a composite sheet arrangement adapted for forming an electrostatically chargeable printing form, comprising, in combination, a first sheet member consisting essentially of a non-conductive carrier sheet and an electrically conductive surface layer on one face thereof, a second sheet member consisting essentially of a substantially infrared radiation-permeable carrier sheet and a low melting layer of dielectric material on one face thereof, the low melting layer of dielectric material of the second sheet member contacting the electrically conductive surface layer of the first sheet member, and an image carrying sheet including image-forming, infrared-absorbing portions and image-free substantially infrared-permeable portions, contacting the carrier sheet of the second sheet member, whereby upon exposure of the image carrying sheet to infrared radiation the image-forming, infrared-absorbing portions and corresponding portions of the low melting layer of dielectric material will be heated so as to make corresponding portions of the layer of dielectric material in contact with the electrically conductive surface layer actively adhesive, thereby adhering the corresponding portions of the dielectric layer to the electrically conductive surface layer, thereby forming an electrostatically chargeable printing form consisting essentially of the non-conductive carrier sheet with the electrically conductive surface layer on one yface thereof and the selected portions of the layer of dielectric material adhering to the electrically conductive surface layer.

Thus, according to the present invention, the conductive surface of a printing form blank is contacted with a dielectric and electrostatically chargeable layer of .a transfer sheet, whereby the dielectric layer is formed of an easily electrostatically chareable material of relatively low melting point. Transfer of portions of the dielectric layer from the transfer sheet to the printing form blank, in accordance with the image-forming portion of an original, is then `accomplished by selectively heating the imageforming portion of the dielectric transfer layer, for instance by means of infrared radiation which first contacts the original which is to be reproduced by means of th printing form.

Preferably, the dielectric, easily electrostatically chargeable layer of the transfer sheet will be formed of a mixture of hard wax such as montan wax and/or candelilla wax on the one hand, and an electrostatically easily chargeable soft wax such as beeswax. Y

According to a preferred embodiment of the present invention, a pulverulent dielectric material which has a melting point higher than the melting point of the wax mixture is distributed through and embedded in the dielectric layer. Suitable pulverulent dielectric materials are, for instance, synthetic plastic materials such as cellulose-triesters, for instance cellulose-triacetate, and nitrocellulose, or polycarbonates, or polyesters, known to those skilled in the art, whereby, however, such pulverulent dielectric materials should be chosen which, as mentioned above, have a melting point higher than the melting point of the wax mixture.

The printing form blank to which selected portions of the dielectric transfer layer are to be adhered, preferably will consist -of a foil of synthetic material, for instance an acetate foil, having a thin metal layer, for instance an aluminum, silver, cadmium or zinc layer applied to one face thereof, for instance by vapor deposition.

The carrier sheet of the transfer sheet, which carries the easily meltable layer of dielectric material also will consist preferably of a foil of synthetic material, for instance a polyester or polycarbonate foil such as are per se well known in the art. It is also possible to replace the carrier sheets of synthetic material with` suitably thin, heat rays, particularly infrared rays-permeable, paper.

The transfer of the image from an original onto a printing form blank, in the form of selected portions of an electrostatically chargeable, dielectric transfer layer may be carried out, according to the present invention, in the following manner:

The image is formed on a support which is permeable to a high degree for heat rays, particularly infrared rays. The image itself, for instance printed or typed indicia, are formed of a material which strongly absorbs heat rays, particularly infrered rays. The transferable, dielectric layer of the transfer sheet preferably will have a low absorptivity for heat rays, so that the heat radiation contacts rst the carrier sheet of the image, preferably at the side thereof which is opposite to the face on which the image-forming indicia or the like are located, and the heat is then transferred from the heat absorbing indicia or the like to the carrier sheet of the transfer sheet and from there, passing through the dielectric transferable layer, to the conductive layer ofthe printing form blank.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with .additional objects and advantages thereof, will be best understood from the following description of specie embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic, elevational, cross sectional, exploded view of a composite sheet arrangement according to the present invention;

FIG. 2 is a schematic, cross sectional, elevational view of the sheet arrangement while the same is exposed to infrared radiation; and

FIG. 3 is a schematic, elevational, cross sectional View of the sheets of the sheet arrangement of FIG. 2, after completion of radiation of the same with infrared rays and separation of the individual sheet members.

Referring now to the drawing, and particularly to FIG. 1, the printing form blank is shown consisting of a carrier sheet 1 of paper or of a synthetic foil, and an electrically conductive layer 2 adhering to one face of carrier sheet 1 and consisting of a metal such as aluminum, silver, cadmium or zinc. The conductive layer 2 is preferably formed by vapor deposition in a thickness of about 1 micron. Foil 1 may consist for instance of a cellulosetriester, polyvinyl chloride, polyvinyl acetate, polyethylene, polyethyleneterephthalate or polystyrene.

The transfer sheet consists of a carrier sheet 3 which should be highly permeable for infrared rays and which may be formed of paper or a foil of synthetic material. Preferably so-called condenser paper, having a thickness of only about 15 microns, or a foil of polyethyleneterephthalate, also having a thickness of about 15 microns is used as carrier sheet 3.

A layer 4 which melts at a relatively low temperature, preferably at about C. is located on one face of carrier sheet 3. Layer 4 preferably will consist of a mixture of electrostatically chargeable hard and soft waxes. Certain hard waxes such as montan or candelilla wax possess the desired electrostatic chargeability, however, a layer which consists exclusively of hard waxes generally is too brittle and, in view thereof, preferably a mixture of hard and soft waxes is used for forming layer 4.

It has been found that many of the saft waxes, fats and oils which could be mixed with hard Wax in order to reduce the brittleness thereof, are not suitable for the intended purpose, because these plasticizers are incapable of retaining electric charges or only capable of retaining electric charges to a very slight degree. Thus, the electric chargeability of the hard waxes could be reduced by admixture of such unsuitable plasticizers to such an extent that the thus formed mixture would no longer be capable to serve for producing electrostatically chargeable printing forms. However, there exist several plasticizers, particularly soft waxes which are capable of retaining electric charges to a suicient degree. These soft waxes include for instance beeswax. Furthermore, a mixture of beeswax and electrostatically chargeable pulverulent materials of small particle size such as polyesters or polycarbonates may be combined with hard wax.

The hard waxes which are suitable for forming one component of a transfer layer 4 include, in addition to montan wax and candelilla wax, also chlorinated waxes, for instance those which are obtainable under the trade name Nibren Wax, and synthetic waxes, for instance various types of synthetic waxes which are commercially available from the Badischen Anilinund Soda-Fabriken, and which are marketed under the designations:

Melting point, C.

OP-wax about O-wax about 100 A-wax 10S-105 SPO-wax 92-98 E-wax 79-82 ES-wax 79-8Z S-wax 80-83 L-wax 80-8 3 V-wax 48-5 0 wax mixture preferably will be equal to between and 30% of the weight of the wax mixture.

Suitable pulverulent materials include polyvinyl chloride, polystyrene and polyethylene.

The following examples of suitable compositions of layer 4 are given as illustrative only without, however, limiting the invention to the specific details of the examples.

Example I Percent Montan wax 80 Ozocerite Example II Percent Montan wax 7() Ozocerite 27 Aerosil 3 Example III Percent Montan Wax 80 Benzophenone 17 Aerosil 3 Example IV Percent Montan wax 60 Spermaceti 37 Aerosil 3 Example V Percent Montan wax `60 Spermaceti 30 Polyvinyl chloride 10 Example VI Percent Montan Wax 60 Beeswax 40 Example VII Percent Candelilla wax 60 Ozocerite 40 Example VIII Percent Candelilla wax 60 Spermaceti 40 Furthermore, FIG. 1 illustrates a schematic cross section through an original consisting of carrier sheet 5, for instance a paper sheet, an image-forming element 6 which includes an infrared rays-absorbing material, such as a dye, for instance an earthy or mineral pigment dye or printing and typewriter inks or a heavy metal salt. A specific infrared absorbing material is: smoke or lamp black.

FIG. 2 illustrates a stack -formed of printing form blank 1, 2, transfer sheet 3, 4, and original 5, 6.

The image-forming portions 6 of the original are heated by infrared rays emanating from radiator 7. The rays penetrate through infrared-permeable carrier sheet 5 of the original so that a thermal image is formed corresponding to the image-forming portions 6 of the original, and the thermal energy thereof is carried by convection through carrier sheet 3 of transfer sheet 3, 4 to the transferable layer 4 of the transfer sheet. The thermal energy corresponding to image-forming portions 6 suffices to melt the corresponding portions of layer 4. This will cause the molten portions of layer 4, which in FIG. 3 are indicated by reference numeral 4b, to adhere to electrically conductive layer 2 of printing form blank 1, 2.

Upon allowing the stack to cool below the melting point of layer 4, and separating of the sheet members of the stack into printing form, transfer sheet and original, it will be found that the initially molten portions of transfer layer 4 will separate from carrier sheet 3 of the transfer layer and will adhere to electrically conductive layer 2 of the printing form blank, thereby converting the printing form blank into a printing form.

Portions 4a of transfer layer 4 which correspond to the image-free portions of original 5, 6 and which have not been exposed to such heat, will be retained on carrier sheet 3 of the transfer sheet and will form thereon a negative of image 6.

The image-forming portions 4b which now adhere to the electrically conductive layer 2 of the printing form are electrostatically chargeable.

In order to keep the heat requirement of this thermographic copying process as small as possible, it is desirable to keep layer 4 as thin as possible. On the other hand, the potential of the electric charge of a dielectric layer having a thickness of less than l0 microns drops considerably and, consequently, the most desirable thickness of layer 4 is about l0 microns.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt is for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of the invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of producing an electrostatically chargeable printing form, comprising the steps of forming a stack consisting essentially of a printing form blank composed of a carrier sheet and an electrically conductive layer located on one face of said carrier sheet, an original including image-forming, infrared-absorbing portions and image-free substantially infrared-permeable portions, and interposed between said original and said printing form blank a transfer sheet composed of a substantially infrared-permeable carrier sheet and an electrostatically chargeable layer having a melting point above ambient temperature consisting essentially of a mixture of at least one hard wax and at least one easily electrostatically chargeable soft wax and having distributed therethrough between 10 and 30% of the weight of said mixture of at least one pulverulent dielectric material having a particle size of up to 30l microns and having a melting point higher than the melting point of said mixture, said electrostatically chargeable layer being located on one face of said carrier sheet, said carrier sheet of said transfer sheet contacting said original and said electrostatically charegable layer of said transfer sheet contacting said electrically conductive layer of said printing form blank; subjecting the thus formed stack to infrared radiation in the direction from said original towards said printing form blank so as to heat said infraredabsorbing image-forming portions of said original and corresponding portions of said electrostatically charageable layer to at least the melting point of the latter thereby melting said corresponding portions at least in contact with said electrically conductive layer and causing adherence of said corresponding portions of said electrostatically charageable layer to said electrically conductive layer; allowing said corresponding portions of said electrostatically chargeable layer to cool below the melting point thereof; and separating said printing form blank with said corresponding portions of said electrostatically chargeable layer from said stack, thus forming a printing form having an operating face consisting of said electrically conductive layer with said selected electrostatically chargeable portions thereon.

2. A method as defined in claim 1, wherein the melting point of said electrostatically chargeable layer of said transfer sheet is in the vicinity of about C.

3. A composite sheet arrangement adapted for use in forming an electrostatically chargeable printing form, comprising, in combination, a first sheet member consisting essentially of a non-conductive carrier sheet and an electrically conductive surface layer consisting essentially of a metal selected from the group consisting of aluminum, cadmium, zinc and silver on one face thereof; a second sheet member consisting essentially of a substantially infrared radiation-permeable carrier sheet and a layer of dielectric material having a melting point above ambient temperature on one face thereof, said layer 4of dielectric material of said second sheet member contacting said electrically conductive surface layer of said rst sheet member and consisting essentially Of a mixture of between about 60 and 80% by weight of at least one hard wax and between about 40 and 20% by weight of at least one easily electrostatically chargeable soft wax and having distributed therethrough in an amount equal to between about 10 and 30% of the weight of said mixture at least one pulverulent dielectric material hav- UNITED STATES PATENTS 2,297,691 10/1942 Carlson lOl-149.4 XR 2,357,809 12/1944 CarlSOn. 3,120,611 2/1964 Lind. 3,122,997 3/1964 Raczynski et al. lOl-149.2

EDGAR S. BURR, Primary Examiner U.S. Cl. X.R.

lOl-426; 1l7-36.l