Line printer incorporating liquid ink jet recording

Abstract

Apparatus and method for printing one or more copies. Mirror-reversed, transferable liquid ink jet indicia are formed on a transfer surface and then immediately transferred to one or more webs maintained in continuous contact with the surface to form one or more copies. In forming multiple copies, the contact between the transfer surface and the webs is such as to transfer only a portion of the ink to each of the webs in turn. If the same transfer surface is used continually, means may be provided to remove any residual ink from the surface prior to the formation of succeeding liquid indicia. Alternatively, the surface may be continually changed, in which case residual ink does not present any problems.

Description

This invention relates to live printing apparatus and method, and more particularly to this type of printing incorporating liquid ink jet recording.

In the last few years electrically or mechanically controlled ink jets have been used to an ever increasing extent in different fields of recording techniques. Typical examples are the liquid jet oscillograph described by Elmqvist in U.S. Pat. No. 2,566,443, in which the tracing ink jet is subject to mechanical deflection, or Sweet's electrical control of an ink jet for the same purpose, according to Swedish Pat. No. 203,696. A plurality of different ink jet systems are utilized as electrically controlled tracing elements in terminal printers for data processing machines. Such ink jet systems are described for instance in Swedish Pat. No. 174,887, U.S. Pat. Nos. 3,298,030, 3,278,940 and 3,717,875. Finally, Hertz in Swedish Pat. Nos. 311,537, 324,669 and 347,357 describes a method which by electrical means permits intensity modulation of a tracing ink jet and which can be used inter alia for the reproduction of pictures etc. A survey on ink jet printing is given by Kamphoefner in IEEE Transations on Electron Devices Vol. ED 19, April 1972.

These and similar ink jet methods have met with great interest in recent years and this is due among other things to the speed at which they can trace in different colors on untreated paper and also to the tracing process being noiseless. However, all of these methods suffer from a serious drawback in that they do not permit simultaneous printing of an original and several copies in the way this can be realized in conventional mechanical typewriters or line printers, for instance by means of carbon paper. In many connections, inter alia juridical matters, the possibility of taking exact copies simultaneously as the original is prepared, is of the utmost importance. The above drawback has therefore long been cited as a disadvantage of ink jet techniques.

The object of the invention hereinbelow described is to provide a method that eliminates the above-mentioned drawback which as yet is typical of all ink jet recording methods. The new method as now suggested therefore is not restricted to a certain ink jet principle and can be used also for tracing liquids other than ink. For the sake of simplicity, however, the tracing head described by Hertz in Swedish Pat. Nos. 324,669 and 347,375 will be used by way of example in the following description to elucidate the function of the new method.

In principle, the new method provides that the liquid ink jet records the indicia, alphanumerical or other characters and symbols, on a transfer substrate by means of a tracing liquid which does not dry on or is absorbed by the substrate during the transfer operation. From the substrate the recording is then transferred to the paper by the paper being mechanically pressed against the transfer substrate. By selecting a suitable material as a transfer substrate and by choosing a suitable mechanical pressure and ink of adequate properties, a plurality of copies can be obtained from one and the same recording on the transfer substrate.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combination of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

Depending upon the use contemplated, the new method can be realized in different ways. Some embodiments will be described hereinbelow with reference to the accompanying drawings, in which

FIG. 1 is a side view showing the basic apparatus and principle of the method of this invention;

FIGS. 2 and 3 illustrate two different ways of cleaning the transfer surface before a new recording is applied to it; and

FIG. 4 shows an alternative method and apparatus for which cleaning is not necessary.

FIG. 1 shows an embodiment which is specifically suited for line printers which are widely used as terminal printers for data processing machines. One way of constructing such a line printer with ink jets as printing means is described by Hertz in Swedish Pat. No. 347,375 (FIG. 3) where a great many oscillating ink jets are arranged in juxtaposed relation. FIG. 1 shows a side view of such a line printing system in which the liquid jets 1 emerge from the capillary tubes 2 and are directed between the control electrodes 3 against the recording substrate which in the present instance is the slowly continuously rotating platen 4. The liquid jets are usually directed perpendicularly to the axis of the platen 4, but other directions that approach the tangent to the surface of the platen may also be suitable. This printing system can then produce alphanumerical or other characters on the surface of the continuously rotating platen 4 in the manner described in Swedish Pat. No. 347,375, but in the present instance it is important that the characters are printed in mirror-reversed fashion on the platen 4 and that the surface of the platen does not absorb the ink or the liquid deposited on it by the liquid jets.

Owing to the continuous rotation of the platen in the direction of the arrow the place on the platen surface where the characters have been printed, will be moved past the rolls 6a, 6b and 6c. Each of these rolls presses one continuous paper web 5a, 5b and 5c, respectively, at a suitable pressure against the platen 4 in such a way that the paper web will have the same speed as the surface speed of the platen 4 so that no slip will occur between the platen 4 and the paper webs. If the mechanical force between the rolls 6a to 6c is selected in a suitable manner, part of the tracing liquid is transferred to the paper webs 5a to 5c in a similar way as occurs in the well-known offset printing process. It is obvious that more than three paper webs can also be used. In contrast to an offset printing process, the tracing liquid is here impressed upon several paper webs, the mechanical pressure between the rolls 6a to 6c being preferably selected in such a way that the tracing liquid is distributed equally between the different paper webs 5a to 5c and that but an insignificant part of the tracing liquid remains on the platen when it has passed the last paper web 5c. To ensure that no tracing liquid remains on the surface of the platen 4 when it again passes the liquid jets 1 a suitable cleaning device 7, such as a roller or brush of moist and/or absorbing material, is inserted between the last paper web 5c and the liquid jets 1, which device cleans the surface of the platen while the latter rotates past the cleaning device 7.

An important advantage of the above-described line printer is that it permits production of the copies at the same time as new characters and symbols are printed by the liquid jets on the surface of the platen, whereby the transfer speed will be considerably greater when compared with other conceivable methods.

The surface of the transfer substrate, i.e., the platen 4, is an important detail of the embodiment illustrated in FIG. 1. This surface should be of such a nature that the tracing liquid is not absorbed by or spread over it by reason of the surface tension forces, but remains on the surface in the form of small droplets. Moreover, the surface should be of such a nature that not all of the tracing liquid is transferred to the paper web 5a upon contact with it, since in such a case no liquid will be left to produce the copies on the paper wevs 5b and 5c. A meterial having such surface properties for certain water-based tracing liquids is rubber cloth of the type used in the conventional offset printing process. It is also important that the rolls 6a to 6c are of such a material as to produce a suitable and approximately constant pressure along the entire interengagement surface with the platen 4. Rubber has proved to be a suitable material for this purpose.

Another important detail is the cleaning of the surface of the platen 4 after it has passed the last paper web 5c and before new characters are recorded by the liquid jets on the paper web. Because of the aforementioned desirable surface properties of the platen, it is probable that a certain proportion of the tracing liquid will be left after it has been impressed on the last paper web 5c. This may produce a disturbing background in subsequent recordings. It has already been mentioned that this cleaning can be effected by means of a suitable roller or brush 7. Alternatively, such cleaning can be accomplished as shown in FIG. 2 by means of a fine powder 8 which is blown from a nozzle 9 against the platen surface. The powder should have absorbent properties for the tracing liquid and it should be able to disengage itself from the platen surface either under its own weight, by the effect of an electric field, or by an air flow directed against the platen surface.

Another way of solving this problem is shown in FIG. 3 in which the surface of the platen 4 immediately before it passes the last paper web 5c is charged, for instance negatively, with the aid of a corona discharge 10 which is generated by the voltage source 11 on a suitable pointed means 12 directed towards the platen surface in such a way that the tracing liquid thereon is negatively charged. In this case, the surface of the platen must be formed of an insulating material applied as a thin layer to the electrically conductive, grounded platen 4. At the same time, a positive voltage is applied to the roll 6c so that an electric field is formed through the paper web 5c between the platen 4 and the roll 6c. This field will act upon the negatively charged droplets of the tracing liquid so that they will be transferred to the paper web. The roll 6c is presupposed to be electrically conductive in this case. In this manner all of the tracing liquid is transferred from the platen 4 to the last paper web 5c so that practically no tracing liquid is left on the platen surface when the liquid jet 1 again impinges upon the surface.

Cleaning of the platen 4 will be altogether unnecessary if a continuous strip of a suitable material as shown in FIG. 4 is substituted for the platen 4. In FIG. 4 a transfer substrate in the form of a strip 13 is moved from a supply reel 15 past the tracing liquid jet 1 and is then conducted with the aid of the cylinder 14 to contact the paper webs 5a to 5c, the characters recorded on the strip 13 being transferred to the paper webs in the same way as in FIG. 1. The cylinder 14 may be stationary and/or have other geometrical forms. Since the transfer substrate in this case passes the liquid jet 1 but once no cleaning of the substrate will be required.

Finally, it is obvious that record means other than paper may also be used for the webs 5a to 5c and that the number of webs is not restricted to three. Likewise, tracing liquids other than ink may be used. Moreover, this line printer can be used not only in connection with the recorder described by Hertz in Swedish Pat. No. 324,669 but with all recorders that generate the record track by means of a liquid. This particularly applied to recorders making use of liquid jets.

It will thus be seen that the objects set forth above, among those made apparent from the preceeding description, are efficiently attained and, since certain changes may be made in carrying out the above methods and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

We claim:

1. A line printer, comprising in combination

a. means to generate a controlled ink jet in a mirror-reversed form;

b. movable transfer substrate means having a thin-layered insulating surface and being adapted to receive directly on its surface said ink jet and form transferable liquid indicia thereon, the surface of said substrate means being formed of a material which does not absorb said liquid ink and over which said liquid ink does not spread through surface tension forces;

c. a plurality of movable web strips adapted for continuous, simultaneous contacting of said transfer substrate means at successive points of its movement;

d. pressure applying roll means associated with each of said webs and adapted to maintain contact between said web and said transfer substrate means with a pressure adjusted to permit the direct transfer of a portion of said liquid indicia onto each of said webs and to move said webs through engagement with said transfer substrate means, the last of said pressure applying roll means being electrically conductive;

e. means to move said transfer substrate means and said web means at the same linear speed thereby to form a right-reading copy of said indicia on each of said webs;

f. means to remove residual ink from said transfer substrate means subsequent to transfer of said liquid indicia onto the last of said web strips; and

g. means to deposit an electrical charge of one sign on said transfer substrate means just prior to its contacting the last of said webs and means to deposit an electrical charge of the opposite sign on said last of said webs thereby to serve at least in part as said means to remove residual ink from said transfer substrate means.