Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2001-08-23
2003-04-22
Mayekar, Kishor (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S483000, C204S508000, C204S623000, C101SDIG029
Reexamination Certificate
active
06551481
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to improvements in the field of electrocoagulation printing. More particularly, the invention relates to an electrocoagulation printing method and apparatus providing color juxtaposition.
In U.S. Pat. No. 4,895,629 of Jan. 23, 1990, Applicant has described a high-speed electrocoagulation printing method and apparatus in which use is made of a positive electrode in the form of a revolving cylinder having a passivated surface onto which dots of colored, coagulated colloid representative of an image are produced. These dots of colored, coagulated colloid are thereafter contacted with a substrate such as paper to cause transfer of the colored, coagulated colloid onto the substrate and thereby imprint the substrate with the image. As explained in this patent, the positive electrode is coated with a dispersion containing an olefinic substance and a metal oxide prior to electrical energization of the negative electrodes in order to weaken the adherence of the dots of coagulated colloid to the positive electrode and also to prevent an uncontrolled corrosion of the positive electrode. In addition, gas generated as a result of electrolysis upon energizing the negative electrodes is consumed by reaction with the olefinic substance so that there is no gas accumulation between the negative and positive electrodes.
The electrocoagulation printing ink which is injected into the gap defined between the positive and negative electrodes consists essentially of a liquid colloidal dispersion containing an electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent. Where the coloring agent used is a pigment, a dispersing agent is added for uniformly dispersing the pigment into the ink. After coagulation of the colloid, any remaining non-coagulated colloid is removed from the surface of the positive electrode, for example, by scraping the surface with a soft rubber squeegee, so as to fully uncover the colored, coagulated colloid which is thereafter transferred onto the substrate. The surface of the positive electrode is thereafter cleaned by means of a plurality of rotating brushes and a cleaning liquid to remove any residual coagulated colloid adhered to the surface of the positive electrode.
When a polychromic image is desired, the negative and positive electrodes, the positive electrode coating device, ink injector, rubber squeegee and positive electrode cleaning device are arranged to define a printing unit and several printing units each using a coloring agent of different color are disposed in tandem relation to produce several differently colored images of coagulated colloid which are transferred at respective transfer stations onto the substrate in superimposed relation to provide the desired polychromic image. Alternatively, the printing units can be arranged around a single roller adapted to bring the substrate into contact with the dots of colored, coagulated colloid produced by each printing unit, and the substrate which is in the form of a continuous web is partially wrapped around the roller and passed through the respective transfer stations for being imprinted with the differently colored images in superimposed relation.
A polychromic image can also be formed by providing a single positive electrode in the form of a revolving cylinder, arranging the negative electrodes, the positive electrode coating device, ink injector, rubber squeegee and positive electrode cleaning device to define a printing unit and disposing several printing units each using a coloring agent of different color around the positive cylindrical electrode to produce several differently colored images of coagulated colloid which are transferred at respective transfer stations from the positive electrode surface onto the substrate in superimposed relation to provide the desired polychromic image. The substrate which is in the form of a continuous web is partially wrapped around the positive electrode and passed through the respective transfer stations for being imprinted with the differently colored images in superimposed relation. This arrangement is described in Applicant's U.S. Pat. No. 5,538,601 of Jul. 23, 1996.
Since each printing unit of the above multicolor printing apparatus requires a positive electrode coating device and cleaning device, such an apparatus is not only cumbersome but also very costly. Moreover, since the differently colored images of coagulated colloid are transferred at respective transfer stations onto the substrate in superimposed relation, and there are thus several transfer stations, it is difficult to provide a polychromic image in which the differently colored images are perfectly superimposed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the above drawbacks and to provide an improved multicolor electrocoagulation printing method and apparatus of reduced cost and cumbersomeness, capable of providing a polychromic image of high definition.
According to one aspect of the invention, there is provided a multicolor electrocoagulation printing method comprising the steps of:
a) providing a positive electrolytically inert electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, the passivated surface defining a positive electrode active surface;
b) coating the positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
c) forming on the olefin-coated positive electrode active surface a plurality of colored pixels representative of a desired polychromic image, each pixel comprising juxtaposed dots of differently colored, coagulated colloid; and
d) bringing a substrate into contact with the colored pixels to cause transfer of the colored pixels from the positive electrode active surface onto the substrate and thereby imprint the substrate with the polychromic image.
Step (c) of the method according to the invention is carried out by:
i) providing a series of negative electrolytically inert electrodes each having a cylindrical configuration with a predetermined cross-sectional dimension and an end surface covered with a passive oxide film, the negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the end surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from the positive electrode active surface by a constant predetermined gap, the negative electrodes being spaced from one another by a distance smaller than the electrode gap;
ii) filling the electrode gap with an eletrocoagulation printing ink comprising a liquid colloidal dispersion containing an electrolytically coagulated colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
iii) applying to the negative electrodes a pulsed bias voltage ranging from −1.5 to −40 volts and having a pulse duration of 15 nanoseconds to 6 microseconds, the bias voltage applied being inversely and non-linearly proportional to the pulse duration;
iv) applying to selected ones of the negative electrodes a trigger voltage sufficient to energize same and cause point-by-point selective coagulation and adherence of the colloid onto the olefin-coated positive electrode active surface opposite the electrode active surfaces of the energized electrodes while the positive electrode active surface is moving, thereby forming dots of colored, coagulated colloid;
v) removing any remaining non-coagulated colloid from the positive electrode active surface; and
vi) repeating steps (i) through (v) several times to define a corresponding number of printing stages arranged at predetermined locations along the aforesaid path and each using a coloring agent of different color to produce dots of differently colored, coagulated colloid, the distance between the negative electrodes of each printing stage being at least three times the cross-sectional dimension of each n
Castegnier Adrien
Castegnier Guy
Elcorsy Technology Inc.
Mayekar Kishor
LandOfFree
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