DE2140048A1 - Thermographic printing process - Google Patents

Description

«« «« * »*.« 2 H 0048

PATENT Attorney DIPL.-ING. R. MOLLER-BDRNER PATENTANWALT DIPL-ING. HANS-H. WEY

TBERLIN-DA H LEM 33. PODBIE LS Kl ALLEE 68 SMO NCHEN 22 WIDENMAYE R STRASSE

TEL. 03Π. 762907 TELEGR. PROPINDUS. TELEX 0184 057 TEL. 0811. 225585. TELEGR. PROPINDUS TELEX 0524244

Berlin, August 5, 1971

Ing.C. Olivetti & C, S.p.A. IVEEA (Torino) / Italy

Thermographic printing process

The present invention relates to methods of printing on thermographic paper.

Various methods for printing information on sheets or webs of paper have already been developed. In the well-known electrographic process, an electrostatically charged latent image is deposited on a dielectric Paper applied and then through a liquid or solid Toner developed. The toner can then be fused to the paper using heat or steam, if necessary.

A special paper is used for "Teledeltos" printing a surface with an initial tint, usually white or light gray, and an underlayer with a contrasting one Has coloring. Printing is done by burning away portions of the surface of the paper in image form to make the contrasting to expose colored underlayer »This usually happens by applying a voltage to the paper that is high enough to cause dielectric breakdown and hence propagation to effect in the surface layer.

In U.S. Patent No. 3,255,039 an essentially similar method is described in which a paper is used, the titoer a

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Back or lower layer with contrasting color has an opaque porous coating. A pen to which a voltage is applied is used to to melt the coating in the image area to make it transparent so that the undercoat becomes visible.

In practice, these methods all have significant drawbacks and shortcomings which make their widespread use on many Areas of application have prevented. In electrographic printing, both the dielectric paper and the Toner relatively expensive, while "Teledeltos" printing the paper is both quite expensive and gives poor image quality. With these two Processes require extremely high voltages, on the order of 1000 V, for imaging on paper further restricted their use.

Another system of impactless pressure that has recently been introduced Time has been considered is electrolytic printing. According to this method, electrolysis becomes one Electrolyte solution used to create color. For example, an iodine starch reaction can be used in which Potassium iodide is electrolyzed to obtain iodine, the reacts with starch particles dispersed in the electrolyte to form color. This The system is attractive because starch and potassium iodide are inexpensive and because printing is done on ordinary paper can. However, there is a serious problem that the formed image is not permanent and fades.

Attempts have been made to achieve this by using more stable, fade-resistant colors or organic Chemicals to solve the problem of fading. A problem with this attempt is that most organic substances are not very soluble in water and do not ionize easily.

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Even if the molecule has a high charge, the ion mobility is of a large molecule under the influence of an electric field is not as large as that of an inorganic one Ions such as iodine, so that consequently a high printing speed cannot be achieved.

Another common drawback with electrolytic printing is the short-circuiting of electrodes either as a result of electrolytic metal precipitation on the electrodes or as a result the formation of a salt bridge between the electrodes.

India last few years has developed a seamless printing process that alleviates many of these difficulties. According to this method, in conjunction with a heated pen a special paper is used that develops color when heated to a temperature in the range of 70 to 120 C. That The pen is heated by applying an electric current through a heating element at the tip of the pen (usually an impulse) is sent. U.S. Patent 3,158,506 and U.S. Patent 3,51,338 describe systems of this type.

Although these systems do not require high voltages and at they use paper that is less expensive than that of the; have the required paper! for the systems described previously it is not gaining as widespread use as one would wish. This is largely due to the fact that the pen tip is for everyone printed point or each printed character a heating and cooling cycle and thus the writing speed limited to about 30 characters per second is.

The object underlying the invention is therefore in the Creation of an improved s © tBlagl © sen DriaokverffaSareiss sm see, where at the same time flies (Beseto-riLtaiig & csit ttiarBograyplaisetaeir Systems increased weriea should. . -

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To solve this problem, it is proposed according to the invention that that a conductive agent with at least a portion of a deposited on a substrate thermographic Material is connected to the electrical conductivity of at least this part of the thermographic material and that by a selected portion of the conductive material associated with the thermographic material By means of electricity being passed through, sufficient in this selected part of the thermographic material Generate heat to cause a change in color.

That is, it becomes the heat for causing the imaging color change in the thermographic material by use of a printhead that has mutually spaced electrodes that carry current through part of the thermographic Send a coating that is made more conductive by passing through a film of a conductive Saline solution is moistened. The conductive salt solution can be applied to the thermographic coating in liquid form, combined with the thermographic fabrics to form a conductive thermographic coating for printing in the dry state or mixed with the thermographic materials in liquid form and on ordinary paper be applied distributed in the movement path of the write head.

Further details and advantages of the invention are based on some exemplary embodiments shown in the drawing described in more detail below. Show it:

Pigs i a printing system according to a first embodiment (3rd invention,

Fig. 2 shows a printing system according to a second embodiment of the invention j

Fig. 3 of an operating system according to a third embodiment aer Srf iEadnaiag ηηύ

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Figure h shows the underside of a print head according to the invention.

Pig. 1 shows a printing system according to an embodiment of FIG Invention, in which the carrier paper 11 with a thermographic Material 13 is coated. To see in the therraography Coating 13 to produce an image with the aid of the method according to the invention, the coating 13 is initially, for example with Using a distributor 17, moistened with a conductive saline solution. The Sohreibkopf 19, the two separated from each other Arranged electrodes 21 has is moved along the surface of the thermographic coating 13 by following the path of movement of the manifold 17, while the ends of the electrodes with the part moistened by the conductive salt solution 15 of the coating 13 are in light contact.

The one for the color-forming thermpchemical reaction in the thermographic Coating 13 required heat is generated by a part of the two electrodes 21 bridging Saline 15 a current is sent through it. The energy requirement for this process is less than 1 mW / sec per printed dot. A voltage V of 50 V on 3 electrodes 21, which can be separated by 0.0508 mm, generates a current of about 20 mA and is sufficient to start printing to effect in a fraction of a millisecond.

In contrast to the electrolytic process, where a charge is used (Q = I χ T, where I = current intensity nnu T = time) ₉ , the present printing process is different from that with the aid of the passage of a current (IR χ T, where R = Resistance) depending on the heat generated. Now, since the strength and duration of the current in the solution the amount of heat generated determine!, The Elektrodeiazwischenraufflg are the conductivity of the Löswag _9, the applied voltage and duration of the applied Sp & mramg regulated or changeable ,, are the versotoiedemartigstea KoraMisationen

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possible, being for a particular application to obtain the desired thickness characteristics is selected a suitable one can be.

The particular type of release paper sheet is not critical at all. Heat developable coatings are on onion peel paper, Banknote paper, electrographic paper and "Electrofax" carrier paper have been produced. For the thermographic A wide variety of materials can be used and suitable examples are disclosed in U.S. Patent 3,451,336 and U.S. Patent No. 3,451,336 GB-PS 953 150 described. The one manufactured by "3M Company" and paper commercially available under the trademark "Thermofax" can also be used. However is the printing speed, i.e. the performance, depends on the thermographic materials. A higher speed can be achieved with thermographic materials that less Require energy supply to trigger the color-forming reaction and thus change their color at a lower temperature.

The distributor for the conductive salt solution can be similar to that described in a 15 »Ap ^ 7- ■. It is of course also possible to moisten the thermographic coating 13 with the conductive solution 15 ^ by means of other methods, and the distributor 17 is only shown as an example of a relatively simple method. The conductive salt solution 15 may, for example, an aqueous solution of salt of an alkali or alkaline earth metal such as CaCl ₂₉ KCl, KI, KBr, bone, NaCl, NaI, NaBr or Na ₀ SO. be. Since the conductivity of the solution is beneficial in the process and usually increases with concentration, a higher concentration results in a higher printing speed. A salt at an appropriate concentration can be selected for a specific application. When applying a 50 V DC voltage to two 0.0508 am of each other

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Separately arranged electrodes were used when using a 10 ^ strength KBr solution to moisten the coating 13 in just 200 microseconds and when using a 20% NaCl solution for moistening the coating 13 in 250 microseconds scored good points.

The electrode wires 21 of the print head 19 can be arranged separated from each other at a distance of 0.0506 mm, and, while they are printing, brought into light contact with the surface of the paper. The electrode wires 21 can be made of a platinum-iridium alloy. Tungsten carbide, chrome, nickel or iron wires can also be used be used. If a larger point is to be printed, the distance between the electrodes can be changed be enlarged.

The heat to bring about the change in color in the thermo

2 graphic overlay 13 is made with the help of IR heating of the conductive saline solution is generated between the electrodes 21. Because the salt used to generate heat is a Is electrolyte, it may be that electrolysis also contributes to a small extent to the printing process, in particular when the electrolytic products react with thermographic substances and thereby Color form. Since the electrodes 21 per se are not heated during the printing process, the printing speed is not limited by the need for a cool down cycle for the printhead so they can be quite high can.

It is not necessary to moisten the coating 13 with 3 conductive saline solution ± 5. The coating 13 only needs to <OCE conductive solution 15 are zn moistened sufficiently beb iie Leitfäiaigkeit <äes moistened part as far ZK ®2 "ß ©! AeBij" that ias Brweiseii aöglicfa _o It has proven ρ is © Sicea the paper aaeli this BeiirraoüseB in substantial tr © els © m amffräSalto

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According to one shown in Fig. 2 of the accompanying drawings second embodiment of the invention can be the method use according to the invention for printing on ordinary paper. According to this embodiment, the distributor 17 distributes on the Surface of the paper 11 is a mixture 15 of the thermographic chemical preparation and a conductive material such as Salt in water. The pens 21 of the print head 19 are then with the moistened part of the paper 11 in contact brought and print in the same way as described above with reference to the embodiment according to Fig.l.

The therraographic used in solution 15 according to FIG Material can be that in the aforementioned GB-PS 953 150 or in U.S. Patent 3,451,338. The solution can to increase their conductivity a salt or a conductive one Polymer of any kind can be added. One conductive approach that has been shown to be effective is as follows:

Composition 1

Calcium resinate (5.23fc> Ca) 44 g

Cobalt naphthenate (6% Co) 8g

Polyvinyl alcohol - 88% hydrolysed with a viscosity of 35-45 cp in 4% water solution at 20 C as determined by the Hoeppler falling ball method - in 7% aqueous Solution 143 g

Ditertiary nonionic surfactant

Acetylene glycol type with a melting point of 37 C and a boiling point of 260 ° C (manufactured by "Air Reduction Co," New York, N.Y. under the trademark "Surfynol 104») 0.3g Conductive "Calgon" polymer 26l (trade name) 50 g Water 100 g

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Composition 2

1,3-trimethyl-6 ⁸ -chloro-8 'Metlioxyindolia-

benzospiropyran 33 g

(or l ^^ - trimethyl-S'-methoxyindoline benzospiropyran)

Polyvinyl alcohol (as in the composition l)? 8 g Surfynol 104 (as in Composition 1) 0.15 g

Water 80 g

Compositions 1 and 2 are separated in ball mills

ground in order to produce suspensions with a partial

to obtain the size before the two compositions

be mixed together to spread on the paper Ii will.

In Composition 1, the 50 grams of conductive Calgon polymer be exchanged for 50 g NaCl = In this case, polyvinyl alcohol can be replaced by a binding agent that is compatible with the salt be replaced. Hydroxyethyl cellulose and sodium carboxymethyl cellulose have proven to be useful for this purpose.

The water content of the composition can be varied at will to meet the flow requirements of the manifold 17.

It is also possible to incorporate the salt or the conductive polymer with the thermographic material into the coating 13, as illustrated in FIG on the paper 11 to be printed, whereby the transfer of swiseheH over electrodes 21 de, s print head 19 auroti over thermograph! see coating 13 takes place »

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Those discussed above with reference to the embodiment according to FIG Compositions are also suitable for use as the conductive thermographic coating of Figure 3. In this case the solution is coated with the aid of normal coating processes, for example by a stripping or applied by other standard methods. When using salt, which is the preferred material, a humectant must be used in place of the conductive Calgon polymer how glycerin can be incorporated to prevent the crystallization of the salt and in the coating to provide a moisture content. The amount of glycerin added must be about 40 percent by weight of the salt be. Therefore, when using 50 g of salt 20 g glycerine incorporated. In addition, a binding agent compatible with the salt must be used, otherwise the Binder can precipitate out of solution in the course of the coating process.

Since the coating is in a dry state and is less conductive than a saline solution, it is used for the Higher voltage is preferred for printing. Good results have been achieved by applying 220-320 V DC voltage for about 100 microseconds on two Elektro.den 21 that were in contact with the thermographic coating 13.

An additional advantage of the printing process after the The invention is that there is no corrosion or scale formation on the electrodes. In addition, the pressure electrodes without affecting the print resolution remain on the paper surface.

Good results have been achieved with all three of the embodiments described above.

In commercially available machines, a thermograph! Sehes printing usually xn same way as in electro-

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graphic printing carried out, in which characters are formed by selected printing points of a 5x7 dot matrix. When printing characters of this type, using the method according to the invention, it is possible to use a print head as shown in Fig. K of the drawing. In this print head, the underside of which is illustrated in FIG. K , seven pairs of electrodes 23 are arranged in a row and enclosed in a rigid carrier material 25 which can be made, for example, of ceramic material or of a plastic such as "Teflon" (trade name). The ends of the electrodes 23 can cut off flush with the surface of the carrier material 25. The electrodes 23 of each electrode pair can be arranged at a distance of 0.0508 mm from one another, wherein each electrode pair can be arranged at a distance of 0.127 mm from the adjacent pairs.

Printing is done with a printhead of this type by moving the printhead over the surface of the paper or another substrate to be printed either in the embodiments of the invention according to Fig.i and 2 of the drawing behind the distributor 17 or, in the embodiment according to FIG. 3 of the drawing, via a drawing any selected portion of the surface of the thermographic coating. The electrodes 23 receive voltage surges from a voltage source as needed to print the correct points in the 5x7 die shape.

It is also possible to have one across the width of the paper To use a sufficient series of pairs of electrodes to print the characters of a complete line at the same time.

A complete description of a printhead corresponding to the printhead of Figure k of the drawings which can be used for printing in accordance with the method of the invention is contained in the aforementioned U.S. patent application Ser.No. 28 565. 209 809/1110

Claims ;

Claims (1)

Claims 1. Thermographic printing process, characterized in that that a conductive agent (15) with at least part of one applied to a layer support (II) thermographic material (13) is connected to the electrical conductivity of at least this part of the to multiply thermographic material, and that by a selected part of the with the thermographic Material associated conductive means is passed through it to in this selected part "The thermographic material has enough heat to cause it of a change in color. 2. The method according to claim 1, characterized in that when connecting a conductive agent with at least a part of a thermographic material applied to a layer support a part of a thermographic coating (13) on a layer support (II) moistened with an electrically conductive liquid (15) will. 3. The method according to claim 2, characterized in that when passing current through a selected portion of the thermographic material a portion of the with the conductive liquid (15) moistened thermographic Material (13) touched by a pair of electrodes (21) arranged separately from one another and that on the electrodes a voltage is applied. k. Method according to claim 1, characterized in that when connecting a conductive agent (15) to at least part of a thermographic material (± 3) applied to a layer carrier (li), a mixture (15) of thermographic material and electrically conductive material is applied to the Layer support (II) is applied. -13- 2 0 3 8 0 9/1110 ^{= 13} ~ 2U0048 5. The method according to claim 4, characterized in that when applying a mixture of thermographic! Material and electrically conductive material on the support of the support (il) with a uniform Coating (13) made of a mixture of thermographic Material and conductive material is coated. 6. The method according to claim 4, characterized in that when applying a mixture of thermographic material and electrically conductive material to the substrate the mixture is distributed in liquid form on selected parts of the support (II). 7. Method of printing on a substrate with a Coating that reacts chemically when heated so that it changes its color, characterized in that on the Coating (13) applied electrically conductive liquid (15) and then through part of the conductive liquid current is passed through the moistened coating, to get enough warmth in the part of the moistened coating to produce a change in color. 8. The method according to claim 7 »characterized in that when a current is passed through part of the applied conductive liquid, the liquid is raised touches both sides of the part by a pair of electrodes (2t) and that a voltage is applied to the electrodes will. 9. A method for printing on a receiving medium, characterized in that a on the receiving medium (13) Mixture of heat-reactive, color-forming Material and electrically conductive material applied and that by part of the mixture applied Current is passed through to generate sufficient heat in the part to cause a change in color. 2 0 9 8 0 9/1110 BATH ORIGINAL 2U0048 10. A method for printing on paper with a coating of a mixture of conductive material and material which reacts chemically when heated so that it changes its color, characterized in that the coating touches by two electrodes (21) arranged separately from one another and that A voltage is applied to the electrodes, which are arranged separately from one another, in order to generate a current in the ψ part of the coating lying between the electrodes, which generates enough heat in it to cause a change in color. Hou./Di -22,741 BAD ORIGINAL 209809/1110