DE2419278A1 - NON-COPY RECORDING MEDIUM AND METHOD OF MANUFACTURING THE SAME - Google Patents

Description

April 22, 1974

YEDA RESEARCH AND DEVELOPMENT COMPANY LTD., Rehovot, Israel

Non-copiable recording medium and method of making the same

The invention relates to a non-copyable recording medium and a method for producing the same.

Often documents with written text or drawings or the like have to be kept secret. However, it comes suggest that such documents are briefly stolen and copied. Most copier processes and copier machines use it a bright source of light. Among these copying processes, the Xerox process should be mentioned in particular.

Thus, it is an object of the present invention to provide a recording medium to create which cannot be copied with conventional copying machines using strong light sources and a method for producing such a recording medium.

This object is achieved according to the invention by a recording medium which contains a photochromic compound, which quickly becomes dark when bent with a strong light source.

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The recording medium can contain the photochromic compound or be coated with a composition which the Contains photochromic compound. The photochromic compound must rapidly become exposed when exposed to a strong light source take on dark coloring. In particular, this photochromic compound must respond to light intensities, which in conventional Photocopying machines, e.g. B. Xerox machines, so that when copying the recording medium dark so that it is impossible to recognize the recorded information against the dark background of the blackened recording medium. The recording medium according to the invention becomes completely dark or black when exposed to a strong light source and the recorded information are no longer recognizable.

A particular advantage of the invention is that the photochromic compounds return to their original state after some time Will regain color if kept in the dark during this time. The recorded information readable again.

The photochromic substance must be used immediately during exposure the strong light source and also for a period of time which is shorter than the duration of the photocopying process. Therefore, the photochromic compound should absorb particularly strongly in the wavelength range in which the wavelength of the light used for photocopying lies.

The photochromic compound can be incorporated into or applied to the recording medium in various ways will:

(a) The document can first be processed in a conventional manner, e.g. B. be made by means of a typewriter, and roof. becomes a thin coating of the photochromic compound applied from a solution or a suspension thereof.

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After the solvent or suspending agent has evaporated, the photochromic compound remains as a solid coating the recording medium. In particular, a carrier material can also be used, so that the photochromic compound adheres better to the recording medium. Plastics or the like are embossed as carrier materials. The coating can be carried out by spraying, by brushing on or by rolling on with rollers, which are wetted with the solution will happen. If desired, only part of the paper can be coated.

(b) The paper is first completely or partially coated with the photochromic compound and then is the paper prepared in this way for the production of the document by means of a typewriter or by handwriting Applying a drawing or the like. Manufactured.

(c) The photochromic material is incorporated into the paper during papermaking, e.g. B. together with the filler material or the binder.

A wide variety of photochemical compounds are suitable for the stated purpose. One can be organic as well use inorganic photochromic compounds. The following organic compounds are particularly suitable: 6'-nitro-1,3,3-tri-methylindolino-benzospiropyran and its 5-methoxy ^ derivatives, its 8'-methoxy derivatives, its 8'-bromo derivatives and its 5 ', 7'-dichloro derivatives. Further various naphthospiropyrans and derivatives are suitable of triphenylmethane. Inorganic photochromic compounds are doped zinc oxide or doped titanium dioxide suitable.

Various plastics and resins are suitable as carrier materials for the photochromic compounds in methods (a) and (b). In particular, the results are satisfactory with polystyrene, polyisobutylene, polyvinyl alcohol and

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Polyvinyl chloride achieved as well as with the corresponding copolymers. Furthermore, "Satisfactory results are obtained with Shellac and rosin.

To apply the photochromic materials, the polymer Substance and the photochromic material in a suitable volatile solvent, such as. B. benzene, chloroform bder the like. resolved and if necessary can still a suitable plasticizer, such as dibutyl phthalate, added will.

Some of the photocopying machines used use light sources, which emit essentially no light in the ultraviolet range. White paper, which is colorless photochromic Contains compounds is not effectively blackened by such light sources. It is therefore required in this If you want to modify the paper by one or both of the following methods:

(1) Use of colored paper, which is the Photocopying provides the lowest possible contrast;

(2) using photochromic compounds, which

absorb in the visible range, which stains the paper.

The invention is explained in more detail below with the aid of an example.

example

From 5 g of 6'-ifitro-1,3,3-trimethylindolino-benzospiropyran and 100 ml of benzene is made up into a solution. A second solution of 10 g of polystyrene in 100 ml of benzene is made. Equal volumes of these two solutions are mixed and dibutyl phthalate is added in such an amount that that 1 & ew .- # dibutyl phthalate in the combined solution

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are included.

The solution obtained in this way is applied by spraying or brushing and a thin coating is obtained (30-100 microns) on paper. The paper thus treated is conventionally used as a typewriter paper and a clearly legible record is obtained. After inserting this labeled paper into an Apeco photocopier machine you get a completely black copy and you can't do anything on the typewritten document recognize. The document is then stored in the dark for about 1 hour at room temperature. The The photochromic compound returns to its original color and the recording becomes legible again.

Similar results are obtained with the other photochromic compounds mentioned above.

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Claims (5)

PATENT CLAIMS 1. Non-photocopiable recording medium, . characterized by a content of a photoehromen Compound that quickly darkens when exposed to a strong light source. 2. Recording medium according to claim 1, characterized in that it consists of paper, which the photochromic Compound is incorporated or which is coated with the photochromic compound. 3. Recording medium according to one of claims 1 or 2, characterized in that the photochromic compound 6 '-B "is itro-1,3,3-trimethyl-indolino-benzospiropyran or the 5-methoxy derivative, or the S'-methoxy derivative or the 8'-bromo derivative or the 5 ', 7'-dichloro derivative thereof or an indolino-naphthospiropyran or a derivative of triphenylmethane or doped zinc oxide or doped Titanium dioxide. 4. Recording medium according to one of claims 1 to 3, characterized in that it is coated with a mass which contains a carrier material or a binder in addition to the photochromic compound. 5. Method of manufacturing the recording medium according to one of claims 1 to 4, characterized in that one containing the photochromic compound Spray, spread or roll up mass on paper or that the photochromic compound is incorporated during the manufacture of the paper. 409845/0994