IL42090A - Photocopying prevention - Google Patents

Description

PHOTOCOPYING PREVENTION '"· PHOTOCOPYING .PREVENTION ,, . : The present invention relates to a novel recording medium adapted to prevent and render impossible tlie unauthorized . e-■ production of documents by means of photocopying machines using a' bright light source, such as Xerox and the like. According to a further aspect, there is provided a recording medium which makes ( impossible the reproduction of documents by such reproducing machines, yet provides for the restoration of the document to its original legible state after a certain period of time. ■.

Certain documents carrying information in the form of typed •or written' words, drawings or the like are classified, and' it is not permitted to have these copied. Document's are marked as such, but it is sometimes difficult to prevent their removal for a short time and their photocopying. Most of the machines u'Sed for -ifeh&s purpose make use of a .bright light source. Amongst these there may be mentioned the various Xerox machines and the like.

■ . According to the present invention the recording medium contains or is coated with a photochromic compound which becomes darkr-colored immediately upon being irradiated by means of a strong light course, of the type used in such photocopying machines, thus making it practically impossible to distinguish the information on the document against the thus darkened background. Thus there is obtained a completely dark photocopy, and-none of the original' information on this sheet can be distinguished. The photochromic ' compound reverts after some time in the dark to its original shade and the information on the paper becomes legible again.

It is one of the requirements that the photochromic substance becomes dark immediately upon irradiation with the bright light source, and in any event within a period Of time which is shorter, than that which is used for effecting the photocopying process.

The photochromic compound can be applied in a number of wa¾|. onto the sheet which is to be- rendered impossible to photocopy: a. The document is produced in a conventional manner, and after this there is applied to it a thin coating 'of the photochromic compound in solution, which upon evaporation of the solvent leaves behind the desired coating of the photochromic compound, generally in a suitable carrier. The carrier is a suitable plastic or any other convenient' material . The coating is best applied by spraying or by brushing on. If desired the coating may be applied to only part of the paper. b. The paper is coated, wholly or in part, and then the information is applied in a conventional manner, as by means of a type- ' writer, hand-writing , drawing or. the like. c. ' The photochromic material is incorporated into -the paper, for example, with the filler or binder, during the manufacture process.

A wide choice of photochromic compounds is available for the above purpose. Both organic as well as inorganic compounds may be used. Amongst the organic compounds which were found to be especially suitable there may be mentioned: 6 ' -nitro-1 ,3 ,3-tri-methylindolino-benzospiropyran , its 5-methoxy-, 8'-methoxy-, 8'-bromo- and its 5 ' , 7 ' -dichloro-derivatives , as also certain naphtho spiropyrans. Amongst suitable inorganic photochromic compounds .there may be mentioned doped zinc oxide or titanium dioxide.

·.·· , Various plastics may be used as carriers for the photochromic compound in the methods of application mentioned above under (a) and (b) . Amongst these there were obtained satisfactory results with polystyrene, polyisobutylene and polyvinylchloride , as well as with corresponding copolymers'.

The polymeric substance and the photochromic material are dissolved in a suitable volatile solvent, such as for example Some of the common photocopying machines use light sources which have essentially no output in the ultraviolet region. White paper containing colorless photochromic compounds will not be effectively darkened by such light sources. It is then necessary to modify the paper in one of two ways, or by a combination of the two: the use of colored paper which gives minimum contrast on photocopying, pink paper is effective in this respect; the use of photochromic compounds which absorb in the visible spectrum, the paper thus again being colored.

Example A solution was prepared containing 5 g of 6'-nitro-l ,3,3-trimethylin-dolino-benzospi opyran in 100 ml benzene. A second solution was prepared containing 10 g polystyrene in 100 ml benzene. Equal volumes of these solutions were mixed, and there was added di butyl phthal ate so as to obtain a concentration of 1% by weight of this compound in the combined solution.

The thus obtained solution was applied by brushing or by spraying so as to obtain a thin coating (30 - 100 microns) on paper. The thus treated paper was used in the conventional manner for typewriting and a clear record was obtained. Upon introduction into an Apeco photocopying machine, a completely black copy was obtained, and nothing of the typewritten record was discernible. Upon being maintained in a dark place at room temperature for about one hour, the photochromic compound reverted to its original color, and the typewritten record became legible again.

Similar results were obtained with the other derivatives mentioned above.

It is clear that the above example is by way of illustration only, and that many modifications in the nature of the compounds, the manner of application, and the other details may be resorted to without departing from the scope and spirit of the present invention. 42090/3

Claims (9)

1. A recording medium for the prevention of unauthorized photocopying by means of photocopying machines utilizing a strong light source, comprising a sheet of paper coated with a composition containing a photochromic compound adapted to rapidly become dark when illuminated by a strong light.

2. A recording medium according to Claim 1, wherein the coating is applied by brushing or spraying.

3. A recording medium according to Claim 1, wherein the photochromic compound 1s Incorporated during the process of manufacture of the paper.

4. A recording medium according to any of Claims 1 to 3, wherein the paper 1s colored with a color which gives minimal contrast on photocopying.

5. A recording medium according to any of Claims 1 to 4, wherein the photochromic compound absorbs also in the visible range of light,

6. A recording medium according to any of Claims 1 to 3, wherein the photochromic compound is 6'-n1tro-l ,3,3-trimethylindolino-benzospiropyran , Its 5-methoxy, 8'-methoxy, 8'-bromo, or 5' 7' d1chloroder1vati ve , various indolino naphthospiropyrans , or a doped zinc oxide or titanium dioxide.

7. A recording medium for preventing unauthorized photocopying thereof, sub stantially as hereinbefore described and with reference to the examples.

8. A method of preventing the unauthorized photocopying of documents, which comprises preparing such documents on a recording mediumuas claimed in any of Claims 1 to 7. 42090/3

9. Method for the prevention of unauthorized photocopying of documents , substantial ly as hereinbefore described and wi th reference to the examples . YEDA RESEARCH AND DEVELOPMENT COMPANY LTD.