FR2484082A1 - Permanent recording of remote information on paper - using facing electrodes, one carrying developer-contg. paper - Google Patents

Abstract

Process comprises applying for a period of over 0.1 microsecond a P. less than 300 volts between an electrode of small radius of curvature carrying a paper contg. a developer and a punctual electrode placed on the other side of the paper, the developer being of the type which undergoes an irreversible oxidation reaction with colour change in the surface part of the paper facing the punctual electrode. The paper pref. contains a fixing agent which absorbs the coloured cpd. produced by the oxidn. The appts. is also claimed. For remote reproduction of information comprising digital or analog information signals each determining the dot opacity of a document to be reproduced. The process and appts. are an improvement over prior art partic. w.r.t. speed and do not require high voltage and expensive paper.

Description

Method and device for permanent inscription on paper containing a developer

The invention, which results from a study entrusted to
Laboratory of Physics of Discharges (CNRS) and whose authors are MM. Daniel LE FUR and Max GOLDMAN, of this Laboratory, as well as MM. G. SAURET and Joseph
DUSSAUD, from the Technical Center of the Paper Industry,
Cartons and Celluloses, relates to a process of permanent registration on paper. It finds a particularly important application in remote reproduction devices from information consisting of digital or analog signals each determining the opacity at a point of a document to be reproduced. The inscription provides an image of the original document, constituted for example by a page of text, in the form of a mosaic of points where the original color of the paper has been more or less modified.

 Many paper registration methods are already known. Most have the disadvantage of requiring the implementation of high voltages, being slow and / or requiring an expensive paper. The present invention aims to provide a method and an improved device over those of the prior art, in particular in that the registration is fast, does not require high voltage and uses a paper of reduced price.

 For this purpose, the invention proposes, in particular, a method of permanent inscription on paper, characterized in that a potential difference of less than 300 volts is applied for a duration greater than 0.1 ps between a low-curvature electrode carrying a paper containing an oxidation-reducing developer and a substantially point-shaped electrode placed on the other side of the paper, the developer being of a type undergoing an irreversible oxidation reaction with color change in the surface portion of the paper facing the paper point electrode. The paper advantageously contains a fixative that absorbs the colored compound from the oxidation.

 The point electrode is placed as close as possible to the paper or in contact with it. However, it is generally not possible, given the embossing of the paper, to ensure absolute contact.

Experience shows that, surprisingly, it is not necessary that there be such contact for ions to move in the surface area of the paper, even under the small potential difference applied.

It appears that a corona discharge occurs and causes a chemical modification of the redox-forming compound in the superficial zone.

 The developer may be colorless before oxidation and then tinted. It can also be discolored by oxidation.

As an example of the first type, mention may be made of potassium iodide; when a plain paper impregnated by the so-called "size press" process is subjected to starchy potassium iodide solution at a current of 10 AU for 10 seconds through an electrode raised to a positive voltage of 60 volts, the tip of which has a diameter of 0.05 nrn, there is a permanent shift from white to brown-black. Indeed, there is oxidation of iodide in brown iodine according to the equation

The liberated iodine is immediately fixed by the starch contained in the paper.

As other examples of the first type of developer product, mention may be made of those listed in the table below. The first column of the table gives the name of the product, the second the type of turn.

<Tb>

<SEP> Reagent <SEP>: <SEP> Action <SEP> of <SEP> the <SEP> discharge
<tb><SEP> Gold <SEP> Chloride <SEP> .................. <SEP> purple
<tb><SEP><SEP> salts of <SEP> metals <SEP> Ti, <SEP> Mn, <SEP> Pb <SEP> ..... <SEP>: <SEP><SEP> brown <SEP > black
<tb><SEP> Paper <SEP> Iodotroped <SEP> 0 <SEP><SEP>:<SEP> blue
<tb><SEP> Paper <SEP> ioduroamidonne <SEP> at <SEP> turns
<tb>: <SEP> soil <SEP> red <SEP> o <SEP><SEP>:<SEP> blue
<tb>: <SEP> Indigo <SEP><SEP>:<SEP> discolored <SEP>: <SEP>
<tb>: <SEP><SEP> Tincture of <SEP> Guaiac <SEP>: <SEP><SEP>:<SEP><SEP> Blued
<tb>: <SEP> (Di) <SEP> tetramethyl <SEP> - <SEP> p <SEP> - <SEP> phenylene-:
<tb><SEP> diamine <SEP> ........................ <SEP> brown
<tb><SEP> Silver <SEP> sheet <SEP> ............... <SEP> blackened
<tb>: <SEP> Tetramethyldipara <SEP> - <SEP> diamino <SEP>
<tb><SEP> diphenylmethane <SEP>(<SEP> tetabase) <SEP> purple <SEP> pale
<Tb>
As an example of the second type, there may be mentioned lead sulfide, which is discolored by the discharge.

The inscription is made only if there is a contribution of electric charges per unit area in sufficient quantity. In practice, it has been found that very small currents, during very short time intervals, are sufficient for the point electrode straight sections that will generally be used. Practically, it is not desirable to descend to a cross-section of an electrode having a dimension less than 50 microns, given the limit of resolution of the eye. For electrodes having a circular end surface whose diameter is 1 μm. the order of a hundred microns, it is sufficient in most cases a current of 5 micro-amperes for a few microseconds to obtain a trace. It is however preferable, to obtain fully satisfactory results, to use durations of the order of 10 microseconds and larger currents, for example of the order of 10 microamperes. All these currents can be obtained with voltages of the order of 60 volts. In practice, the invention can always be implemented with potential differences below the threshold of
Paschen, 330 Volts.

 The invention also proposes a device for permanent inscription on paper, characterized in that it comprises a planar electrode intended to receive a sheet of paper impregnated with an oxidation-reducing developer undergoing an irreversible modification of color by oxidation, and a matrix of substantially point-like electrodes placed opposite the plane electrode, at a distance thereof slightly greater than the thickness of the paper to be treated, and means for applying to each of the point electrodes a positive potential, relative to to the plane electrode, which is less than 300 volts and which is independent of the potential difference applied to the adjacent point electrodes, during a predetermined time interval.

 The point electrodes may be constituted by the end portions of small diameter needles, of cylindrical or frustoconical shape, at least in their terminal part.

 The term "planar electrode" should be interpreted in a broad sense and as covering both the case of an electrode having a cylindrical surface and truly shaped plan. The so-called "flat" electrode will have the essential character of being continuous over the entire surface to treat paper.

 The invention will be better understood on reading the simplified description of a device which constitutes a particular embodiment thereof, given by way of non-limiting example.

 The description refers to the single figure that accompanies it and is a diagram of the device. This last can, in its general mechanical constitution, be similar to existing devices. It is therefore not necessary to describe here its constitution in detail. As a rule, it will include a housing of sufficient size to receive the sheet of paper to be treated. This can be made to the device on demand, which allows to use, in each particular case, a paper that gives after draw an appropriate shade. The apparatus may, however, also include a paper feed roll and a debtor device which, each time a registration is to be made, provides the necessary length of paper.

 In any case, the flat electrode will generally consist of a plate 10 of electrically conductive material (aluminum for example) placed horizontally. The device will comprise in practically all cases, not a point electrode, but an array of electrodes 11. This matrix may cover the entire useful surface of the paper 14, which has the advantage of having a static device, ensuring a high registration accuracy. However, it is also possible to use an electrode matrix which corresponds to only a fraction of the useful area of the paper (for example the entire width, but only a fraction of the length, which makes it possible to perform the inscription with only a few longitudinal displacements successive). This provision however has the disadvantage of slowing down the registration and require a mechanical drive device extremely accurate and therefore expensive.

 The matrix may be constituted by any conventional method. It is possible, for example, to use a coil of insulated copper wire (for example enamelled) made in one piece by impregnation or coating, and then cut in such a way that the point electrodes are then constituted by the straight sections of the wires in the plane of cutting. By performing a second cut, there is an electrical access to each electrode. Each of the electrodes is connected to an output member consisting of a switch 12, an electronic 13 voltage pulse application. The switches are for example constituted by unijunction transistors, which can transmit the currents of low intensity required. The switches 12 may be sequentially controlled, given the very short current passage times required, which facilitates control from signals arriving in series on a transmission line. It can also be provided block registration, which allows to simultaneously register several blocks sequentially in each block. As a general rule, the potential difference applied will be of the order of 60 volts.

Claims (6)

 1. Permanent registration process on paper,  characterized by applying for a longer period  less than 0,1 ijs a potential difference lower than  300 volts between a low-bending electrode carrying  a paper containing a developer and a sen electrode  if punctually placed on the other side of the paper,  the developer being of a type undergoing a reaction  irreversible oxidation with color change in  the superficial part of the paper facing  the point electrode.  2. Method according to claim 1, characterized in that a paper containing a fixa is used.  which absorbs the colored compound from the oxidation.  3. Process according to claim 1 or 2, ca  characterized in that the registration is done in steps  wise of a current of about 10.UA for about 10 us.  4. Process according to any one of the preceding claims, characterized in that between the electrodes a potential difference of  the order of 60 volts.  5. Process according to any one of the claims  previous arrangements, characterized in that  facing the low-curvature electrode, a matrix of  electrodes with substantially isolated point ends, isolated  from each other and associated with a circuit allowing  to apply to each electrode, a difference of poten  independent of the one applied to elec  adjacent point trodes.  6. Permanent registration system on  paper, characterized in that it comprises a  flat electrode for receiving a sheet of paper impregnated with a redox developer undergone  irreversible change of color by  oxidation and an electrode array substantially  placed in front of the plane electrode, at a  distance thereof slightly greater than the thickness of the paper to be treated, and means for applying to each of the point electrodes a positive potential with respect to the plane electrode, which is less than 300 volts and which is independent of the potential difference applied to adjacent point electrodes during a predetermined time interval.