Printing Method And Apparatus Using Conductive Fusible Ink

Abstract

The invention provides a method of and an apparatus for electrically printing an outline on paper. For this an ink support of greater transverse than superficial conductivity has one surface covered with a solid and fusible conductive ink. Pairs of points defining the desired outline are selected on the support. One point of each selected pair is connected to one pole of a current source and the point of each selected pair is connected to the opposite pole of the source thus causing current to flow between the points of each selected pair. The ink melts along the current paths and the molten ink is picked up by the paper, previously placed in contact with the support, thus printing the outline defined by the selected pairs of points. The apparatus comprises an endless tape; inking means for applying conductive ink to one side of the tape; a printing head providing a plurality of localized contacts with the tape; a selector which selects, under the action of control signals defining the outline, a number of pairs of contacts and connects these pairs to an electric current source; and drive and guide means for the tape and the paper.

Description

FIELD OF THE INVENTION

This invention relates to printing.

BACKGROUND OF THE INVENTION

There are various known printing methods which make use of the electrical conductivity of conductive substances that are solid at ambient temperature and which melt when heated. Reference may for instance be made to the offset printing method described in French Patent Specification No 1,460,959, in which the offset plate is prepared by electrical means from a special, so called electrographic, sheet which is covered with a layer of a conductive substance. This sheet is applied against the offset plate and is subjected to a pin-point electric arc to cause a localized heating action thus causing the conductive substance to be transferred on to the offset plate along the outline described by the pin-point arc. The conductive substance is however not ink but an oleophilic substance and the outline that is produced in this manner on the offset plate must subsequently be inked in the usual way and transferred on to paper. Even if the outline made on the offset plate by the oleophilic substance were visible, the manner of producing this outline could not be assimilated to a printing method; it is only one stage in such a method.

In U.S. Pat. No. 3,113,511 there is described a method which involves a support covered with a layer of conductive resin which in turn is covered with a protective film. According to this method, a pin-point electric arc is moved along the line to be reproduced. This arc perforates the protective film and melts the layer of resin locally and the molten resin is transferred at least partly on to the support. When the protective film and the resin, which together form a stencil, are separated from the support, the latter is found to bear an outline formed by the resin that was heated and melted by the arc. Since it is lamp black which renders the resin conductive, the outline is visible but it is only a copy of the stencil and its production can not be regarded as being a method of printing.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method of electrically printing an outline with a conductive ink, which comprises spreading in the hot state on a support, having at least a plurality of points distributed over its area of an electrical conductivity greater in the direction of its thickness (transverse conductivity) than in the direction of its surface (surface conductivity), a layer of conductive ink which is solid at ambient temperature and which is fusible when heated; cooling the ink until it solidifies; placing said layer of ink, when solid, in contact with an impression support having a surface capable of picking up the ink when molten; selecting among said plurality of points a number of pairs each of which defines a line forming a portion of the outline to be printed; and connecting one point of each selected pair to one pole of an electric current source and the other point of each selected pair to the opposite pole of said source to cause electric current to flow in the layer of ink along the rectilinear paths extending between the points of said selected pairs, the intensity of the current being such as to heat and melt the ink in said paths for the impression support to pick up this molten ink and to become covered with a set of rectilinear lines reproducing, in broken line manner, the desired outline.

With this method it is therefore possible to produce by electrical means an outline which is made by a true ink on a sheet of paper.

The invention also provides apparatus for electrically printing an outline with a conductive ink, which comprises an ink support consisting of an endless tape having at least a plurality of points distributed over its area with an electrical conductivity greater in the direction of its thickness than in the direction of its surface; inking means which are adapted to hold a supply of solid and fusible conductive ink and which include means for keeping at least part of said supply in a molten state and means for depositing on the tape an even layer of said ink; printing means including a backing member and a printing head which are placed on opposite sides of the tape, said head having a plurality of electrodes which are electrically insulated from each other and whose tips are distributed in one surface of the head, said surface being adapted to come into operative contact with the tape and form a plurality of localized electrical contacts between the tape and the head; a first drive and guide system for successively moving the tape through the inking means and through the printing means; a second drive and guide system for feeding an impression support between the tape and the backing member of said printing means and for placing said impression support in contact with the layer of ink on the tape; a selection circuit for selecting among the electrodes in the printing head a number of pairs whose tips define in the operative surface of the head a set of lines each of which constituted one portion of the outline to be printed, and for connecting to one pole of an electric current source one electrode of each selected pair and to the opposite pole of said source the other electrode of each selected pair, such connections being maintained for a sufficient length of time to allow the solid ink along the lines defined by the selected pairs to liquefy by fusion; and means for pressing the printing head and the backing member against each other whereby the impression support may be pressed for a sufficient length of time against the layer of ink on the tape to effect transfer and for keeping the printing head and the backing member away from each other for the remainder of the time.

DESCRIPTION OF THE DRAWING

In the accompanying diagrammatic drawings:

FIG. 1 is a sectional view of various elements which illustrate the printing method according the invention;

FIG. 2 is a plan view along line II--II of FIG. 1;

FIGS. 3 and 4 show printed outlines illustrating the method;

FIG. 5 is a partly sectional view showing one embodiment of the printing apparatus according to the invention; and

FIG. 6 shows a detail of FIG. 5 on an enlarged scale.

SPECIFIC DESCRIPTION

A solid ink is formed by a waxy mass acting as a vehicle, i.e., as a binder, for one or more coloring substances and one or more pigments. Various auxiliary products are also added to this mixture, in particular stabilizing agents for stabilizing pigment dispersion, thickening agents for establishing the viscosity of the ink when preparing the mixture in the liquid state, and an agent for increasing the depth of color in the final product. The binder consists of a mixture of refined natural wax (e.g. carnauba wax, ozokerite, "microwachs" and paraffin), of modified natural wax (e.g. "montanwachs"), and of synthetic wax (for instance based on polyethylene or on polyvinylic ether); this mixture has added thereto plasticizing agents that are either specific to each wax or chosen in dependence on the overall mixture (e.g. paraffin oil, vaseline and dioctylphthalate). The coloring substances are basic coloring substances (e.g. triphenylmethanes, triarylmethanes and phenazines) which are treated with an acid agent (e.g. saturated or unsaturated fatty acids and acid waxes) to produce complexes that are soluble in the vehicle. The pigment is a dark pigment, generally lamp black. The dispersion stabilizing agents are anti-friction greases (e.g. zinc stearate and magnesium oleate), or glycerine esters (e.g. monostearate, monomyristinate and dioleate), or free base oleates or stearates (e.g. triethanolamine, diethanolamine and morpholine). As for the thickening agents, these generally consist of polyethylene or aluminum stearate.

A conductive ink must contain, besides the usual ingredients listed above, a conduction agent. In the ink used with the present invention, the conduction agent consists of microscopic particles which contain or are made of a good electricity conducting material and which are dispersed in the binder mass in the same way as the other constituents. The concentration of conduction particles is so chosen that the product, once hardened by cooling, should have appreciable electric conductivity.

By way of suitable electricity conducting material for the particles, zinc and copper may be used. These metals are comminuted into microscopic fragments to form the above particles, these being incorporated in the mixture at some stage or other of its preparation. To produce a conductive ink which is black, graphite can be used to advantage for the conductive material. In this case, some modification should be made to the composition of the binder, the basic ingredient becoming a synthetic wax instead of a natural wax. This involves also making changes as regards the choice and concentration of the plasticiziers so as partly to cancel out the increase in the point of liquifaction brought about by the change in basic ingredient.

The preferred way of carrying out the method according to the invention consists in heating a conductive ink of the kind just described and in spreading a thin layer of the ink over the surface of a support of insulating material having a plurality of zones having high electric conductivity, so that the support has a conductivity which is high when a potential difference is applied across its thickness but is low when this potential difference is applied across its surface. Such a support can for instance consist of a sheet 1 of insulating material through which extends a plurality of very fine electric conductors 2. The conductor tips 3 that are located to the side 4 of the sheet over which is applied a layer of ink 5 are made flush with the surface. The layer of ink is applied hot in the liquid state and the ink is then allowed to cool. When the ink has become solid, a sheet 7 is pressed on to the layer 5 with a clamp 6. The sheet 7, which acts as an impression support or a printing medium and which may for instance be made of ordinary paper, must be both electrically insulating and able to pick up the ink when the latter is in a molten state.

Among the conductors are selected those pairs whose tips form the ends of the constituent lines of the pattern or outline to be printed, one conductor in each selected pair being connected to one pole of an electric current source and the other conductor in each selected pair being connected to the opposite pole of the current source so that with each selected pair there may be formed an electric circuit of which one portion is made up by the ink lying between the tips of the two conductors forming the pair. It has been supposed in FIG. 1 that one of the selected pairs consists of conductors 2b and 2c; these conductors are respectively connected by lines 8b and 8c to the positive and negative poles of an electric source (not shown). An electric circuit is thus formed which includes that part of the layer of conductive ink lying between the tips 3b and 3c of these conductors. An electric current comes to flow along the straight path 9 between the tips 3b and 3c of the selected conductors 2b and 2c. The voltage of the source is so chosen that this current gives off, as a result of a Joule effect within the ink along path 9, sufficient heat energy for the temperature of this ink to reach its melting point. Any ink thus liquefied (melted) is picked up by the paper 7 whereas the unliquefied (nonmolten) ink is not. Thus, upon being removed from the support, the paper 7 takes with it the rectilinear mark of an ink line, which mark is the image of the rectilinear path 9 between the tips of the selected pair of conductors. Each selected pair of conductors thus causes a rectilinear line to appear on the paper 7 and the resulting rectilinear lines together produce an impression in "broken line" form of the outline defined by all of the selected pairs. The impression is said to be in "broken line" form because the outline is made up of a succession of lines 17 but these lines are not necessarily separated from each other by intervals 16 as is the case with the outline visible in FIG. 3: they may be in contacting relationship and be joined together by angles 17, as shown in FIG. 4.

The support when constituted as described imposes a rigid pattern to any outline it can print. This rigidity of this pattern is due to the fact that the conductors 2 necessarily are in predetermined locations in the sheet of insulating material 1. As a result the broken line outline that can be printed is limited to a set of lines oriented in two orthogonal directions and possibly of lines oriented at 45.degree. to the first (i.e. diagonally of the square grid marked out by the tips 3). This is shown in FIG. 2 where the square grid marked out by the conductor tips 3 is clearly apparent: any lines making up a printed outline can only be oriented along the orthogonal directions 10, 10' and 11, 11' and possibly along the orthogonal directions 12, 12' and 13, 13' which are inclined by 45.degree. in relation to the first pair of orthogonal directions.

As for the printing apparatus for carrying out the above method, one embodiment is illustrated in FIGS. 5 and 6. It comprises an ink support consisting of an endless tape 20 which is driven in the direction of arrow 22 by a first drive mechanism, 21, along a closed loop path defined by rollers 23 to 29, which form a first guide system. The tape 20 passes through inking means 30 which comprises a supply of ink 31 kept in a molten state by a heating resistance 32 fed by a source of electric current 33. The ink supply 31 is contained in a receptacle 34 and the rollers 23 and 24 are so located as to compel the tape to become immersed in the molten ink 31. Upon issuing from the receptacle 34, a doctor blade 35 scrapes off any ink adhering to the surface 36 of the tape 20 on the inside of the closed loop, and a resilient spatula 37 evens out the layer of ink 38 adhering to the surface 39 of the tape of the outside of the closed loop. The tape 20 then passes through printing means 40 which comprise a backing member 41 and a printing head 42 respectively placed on the outside and on the inside of the tape 20.

A second drive mechanism, 43, and a second guide system, consisting of rollers 44 to 49, serve to move in the direction of the arrow 50 an impression support consisting of a strip of paper 51 and cause it to pass between the backing member 41 and the printing head 42 while applying it against the inked surface 38 of the tape 20. As long as they are in contact with each other, the ink support, formed by the tape 20, and the impression support, formed by the tape 51, or paper strip, must move in synchronism. That is why the second drive mechanism 43 acts simultaneously on the roller 49 which belongs to the second guide system (for the paper strip 51) and on the roller 27 which belongs to the first guide system (for the tape 20). The printing means 40 are shown in greater detail in FIG. 6. In this Figure are again to be seen the backing member 41, the paper strip 51, which forms the impression support, the tape 20, which forms the ink support, and the layer of solid conductive ink 38 coating the latter. The "transverse" conductivity of this ink support is due here to the presence of a plurality of small conductor elements 52 which are embedded in the synthetic material 53 of the tape 20 and which are transversely oriented to the tape, i.e., at right angles to its plane, so as to provide a multitude of electrical connections between its opposite surfaces. These conductor elements thus play a similar role to that of the conductors 2a-2e visible in FIG. 1. The noninked surface 36 of the tape 20 comes into contact with the upper surface 54 of the impression head 42. This surface 54 is fitted with electrodes 55 which provide a plurality of substantially pin-point contacts between the tape and the printing head, and it constitutes the operative surface of the latter.

The printing apparatus moreover comprises a selection circuit 56 to which each of the electrodes 55 is individually connected by an electric line formed by one of the strands of a multistrand conductor 57. This selection circuit is of any suitable type capable of selecting among the electrodes 55 a certain number of pairs, e.g., the pairs 55b, 55c; 55c, 55d; 55f, 55g, and of connecting one electrode of each pair, e.g., the electrode 55c that is common to the pairs 55b, 55 c and 55c, 55d and the electrode 55g in the pair 55f, 55g, to one pole, e.g., the positive pole, of a current source 58 and of connecting the other electrodes, i.e., in the selected example, the electrodes 55b, 55d and 55f, to the other pole, to wit the negative pole of this current source. Selection is effected in such a way that the rectilinear paths 59 along which electric current will flow inside the layer of conductive ink 38 trace out the selected outline and this selection is governed by control signals, e.g., binary signals, fed to the selection circuit by a control line 60.

Whereas the tape 38 is preferably moved in a steady continuous manner through the inking means 30, it is required to move in a discontinuous manner through the printing means 40, so that the rectilinear paths 59 may have current flowing therealong while it is stationary in relation to the printing head 42. That is why in the first guide system two of the rollers, 28 and 25, are movably mounted and are attached to springs 73 and 74, respectively, these rollers acting as tensioning rollers to enable a pair of take-up loops 61 and 62 to vary their length to compensate for any difference between the instantaneous speeds of the tape at the printing means 40 and at the inking means 30. The selection circuit 56 and the second drive mechanism 43 are of course synchronized, this being diagrammatically illustrated by a synchronization line 63.

The illustrated printing apparatus operates as follows: the tape 20 as it travels steadily and continuously through the inking means 30 becomes covered on both sides with a layer of ink. The layer 38 on the surface of the tape on the outside of the closed loop formed thereby is smoothed by the resilient spatula 37 and the other layer of ink covering the tape surface on the inside of the closed loop is scraped off by the doctor blade 35. As it proceeds towards the roller 24, the layer of ink 38 cools and solidifies. The tape thus inked comes into contact with the strip of paper 51 and both travel through the printing means 40 at the same time. While travelling through the printing means 40 the movement of the tape 20, which is synchronized with that of the strip 51 by virtue of the connection between the rollers 27 and 49, is stepped: during the forward movement of each step the selection circuit 56 effects among the electrodes 55 in the printing head 42 the selections that are required for the next printing operation, which selections are governed by the signals fed to the circuit 56 by the control line 60, and during the following stationary portion of the step, the selection circuit connects the selected electrodes to the source 58. The synchronization of these various operations is ensured by the synchronization line 63. The current flowing along the rectilinear paths 59 which come to be located in the layer of ink 38 between the tips of the various transverse conductor elements that are in contact with the selected electrodes causes the ink in these paths to melt. The paper strip 51 picks up this molten ink and thus becomes covered with corresponding ink lines (see for instance the ink lines 64 and 65), leaving indentations in the layer of ink 38 on tape 20 as it issues from the inking means (see for example the indents 66 and 67).

Since a good electrical contact must be maintained between the printing head 42 and the tape 20 and since a good physical contact must also be maintained between the layer of ink 38 and the impression support (paper strip) 51, the backing member 41 and the printing head 42 are here subjected to the action of compression springs 68 and 69 tending to press them resiliently towards one another. The pressure exerted by these spring must of course be released when the tape 20 and the strip 51 are driven forward. The springs 68 and 69 are therefore mounted on movable bearing members 70 and 71 which are subjected to the action of a clamping and releasing mechanism diagrammatically illustrated by the block 72.

The above-described printing apparatus is only one possible form of embodiment and various modifications may be made. For instance, the impression support, instead of being a strip of paper moving in the same direction as the tape 20, could consist of a sheet of paper in which case the tape 20 comes into contact with the latter along the space to be occupied by a line of print on the sheet. It is preferred then for the printing head 42 and the backing member 41 to be of a size such that they can print a full line of alphanumerical characters all at once, and for the two drive and guide systems to be so designed that the tape 20 and the sheet of paper will move at right angles to each other and to an extent such that, after the printing of a line on the sheet, the tape 20 will move in the direction of arrow 22 by a distance sufficient for a virgin or regenerated portion of tape to lie between the head 42 and the member 41, and the sheet of paper will move at right angles to the arrow 22 by a distance such as to bring the space to be occupied by the next line of print opposite the tape 20. This variant would thus give line by line printing.

In another variant, the printing head 42 is of a size such as to correspond to one character and is made to move along the tape 20 in a stepped or discontinuous manner to cause it successively to occupy the several character-receiving locations comprised by one line of print on a sheet. This variant thus leads to a character-by-character printing in the manner of a typewriter fitted with a swivelling printing head.

In a third variant, the tape 20 and the printing head 42 have a width such that they will cover an entire sheet. The printing apparatus can thus become a full-scale printshop printing machine able to print page by page. In this case, the paper would be made to move past the printing head 42 in the form either of successive, individual, sheets or in the form of a continuous band having a width corresponding to the width or length of the sheets to be printed, with the band moving either parallel to the tape, as in FIG. 1, or at right angles thereto, as just described in connection with the first variant.

Instead of imparting to the tape 20 two different forms of forward displacement, i.e., a steady, continuous, movement through the inking means 30 and a stepped, discontinuous, movement through the printing means 40, it would also be possible to impart thereto, and to the impression support 51, a single, continuous, forward movement and to arrange for the printing head 42 and for the backing member 41 to accompany the tape for the length of time needed to carry out a printing operation.

Claims

We claim:

1. A method of printing with an electrically conductive fusible ink on a printing medium, comprising the steps of:

forming a solid layer of said conductive ink on a first surface of an ink support having a second surface parallel thereto, said ink support being formed with a plurality of narrow electrically conductive zones uniformly arranged to extend transversely in closely spaced side-by-side relationship between said first and second surfaces of the ink support, said zones being electrically insulated from one another in the support;

placing said printing medium in contact with said ink layer;

placing an array of electric conductors in the vicinity of said ink layer;

arranging the electric conductors of said array so that one end thereof comes into contact with said second surface of the ink support for electrical connection of the conductors with said conductive zones; and

connecting selected pairs of said conductors to a current source in accordance with printing signals, so as to produce a flow of electric current within said ink layer along selected paths extending between the conductors of the pairs to cause localized heating and melting of the ink and transfer thereof from the layer to said printing medium in accordance with printing patterns corresponding to said signals.

2. The method defined in claim 1 wherein said ink support is a continuous strip, further comprising the step of advancing said strip past said array so that successive portions of said strip come into contact with the electric conductors of said array.

3. The method defined in claim 1 wherein said printing medium is a continuous strip, further comprising displacing said printing medium relative to said array so that successive portions of said strip contact said ink layer in the region of said array.

4. An apparatus for printing with an electrically conductive fusible ink on a printing medium, comprising:

an ink support having two parallel surfaces whereof a first surface is covered with a solid layer of said conductive ink, said ink support having a plurality of narrow electrically conductive zones uniformly arranged to extend transversely in closely spaced side-by-side relationship between said first and second surfaces of the ink support, said zones being electrically insulated from one another in the support;

a printing head having an array of electric conductors for selectively providing different printing patterns;

selection circuit means associated with the printing head for receiving control signals from a data source and for connecting selected pairs of said conductors to a current source in accordance with said control signals;

a backing member facing said array of conductors;

means for urging said printing head against said backing member with said ink support and said printing medium arranged therebetween;

first drive and guide means for placing said ink support with said ink layer facing said backing member and with said second surface thereof adjacent to said printing head for contact thereof with the conductors of said array; and

second drive and guide means for placing said printing medium between said backing member and said ink layer for contact of the medium with said layer, the electric conductors of said array extending side-by-side with one end thereof connected to said selection circuit means while their other end terminates at the surface of the printing head, so as to allow contact of the conductors of said array with said second surface of the ink support for electrical connection of said conductors with said conductive zones and thereby with said conductive ink layer on said first surface of the ink support, thereby providing current flow between the conductors of each said selected pair via the respective conductive zones in contact therewith and along selected paths extending within said conductive ink layer, to cause local heating and melting of the ink thereof by current flow along said selected paths in the layer.

5. The apparatus defined in claim 4 wherein said printing medium is a continuous strip and said second drive means includes means for advancing said strip between said backing member and said ink layer.

6. The apparatus defined in claim 4 wherein said ink support is a continuous strip and said first drive and guide means includes means for advancing said second support between said array and said backing member.