CA2282951C - Electrocoagulation printing method and apparatus providing enhanced image resolution - Google Patents
Electrocoagulation printing method and apparatus providing enhanced image resolution Download PDFInfo
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- CA2282951C CA2282951C CA 2282951 CA2282951A CA2282951C CA 2282951 C CA2282951 C CA 2282951C CA 2282951 CA2282951 CA 2282951 CA 2282951 A CA2282951 A CA 2282951A CA 2282951 C CA2282951 C CA 2282951C
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- electrode active
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
- B41C1/00—Forme preparation
- B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
- B41C1/105—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by electrocoagulation, by electro-adhesion or by electro-releasing of material, e.g. a liquid from a gel
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- Duplication Or Marking (AREA)
- Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)
Abstract
An image is reproduced and transferred onto a substrate by (a) providing a positive electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, said passivated surface defining a positive electrode active surface; (b) forming on the positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink containing a coloring agent; and (c) bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive electrode active surface onto the substrate and thereby imprint the substrate with the image. Step (b) is carried out by (i) providing a series of negative electrodes each having a surface covered with a passive oxide film, the negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the 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) coating the positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance; (iii) filling the electrode gaps with the electrocoagulation printing ink; (iv) applying to the negative electrodes a bias voltage ranging from -1.5 to -2.5 volts; (v) 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 the dots of colored coagulated colloid; and (vi) removing any remaining non-coagulated colloid from the positive electrode active surface. The invention enables one to obtain an image resolution as high as 400 lines per inch, or more.
Description
ELECTROCOAGULATION PRINTING METHOD AND
APPARATUS PROVIDING ENHANCED IMAGE RESOLUTION
The present invention pertains to improvements s in the field of electrocoagulation printing. More particularly, the invention relates to an electrocoagulation printing method and apparatus providing enhanced image resolution.
~o In US Patent No. 4,895,629 of January 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, ~S 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 zo 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 2s 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 3o gas accumulation between the negative and positive electrodes.
The electrocoagulation printing ink which is injected into the gap defined between the positive and 3s 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 s 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 ~o 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.
15 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 zo 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. Alter-z5 natively, 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 3o roller and passed through the respective transfer stations for being imprinted with the differently colored images in superimposed relation.
The positive electrode which is used for 35 electrocoagulation printing must be made of an electrolytically inert metal capable of releasing trivalent ions so that upon electrical energization of the negative electrodes, dissolution of the passive oxide film on such an electrode generates trivalent ions which then initiate coagulation of the colloid. Examples of suitable electrolytically inert metals include stainless steels, aluminium and tin.
As explained in Applicant s Canadian patent No. 2,138,190 of October 13, 1998, a breakdown of passive oxide films occurs in the presence of electrolyte anions, ~o such as Cl-, Br- and I-, there being a gradual oxygen displacement from the passive film by the halide anions and a displacement of adsorbed oxygen from the metal surface by the halide anions. The velocity of passive film breakdown, once started, increases explosively in the presence of an applied electric field. There is thus formation of a soluble metal halide at the metal surface.
In other words, a local dissolution of the passive oxide film occurs at the breakdown sites, which releases metal ions into the electrolyte solution. Where a positive zo electrode made of stainless steel or aluminium is utilized in Applicant s electrocoagulation printing method, dissolution of the passive oxide film on such an electrode generates Fe3+ or A13+ ions. These trivalent ions then initiate coagulation of the colloid.
As also explained in Applicant s US Patent No. 4,895,629, the negative electrodes must be spaced from one another by a distance which is equal to or greater than the electrode gap in order to prevent the 3o negative electrodes from undergoing edge corrosion. This considerably limits the resolution of the image printed by electrocoagulation so that an image resolution of more than about 200 lines per inch cannot be obtained.
Applicant has attempted to increase the image resolution while satisfying the above minimum distance between the negative electrodes by arranging the electrodes along two closely adjacent parallel rows with the negative electrodes of one row being staggered with respect to the negative electrodes of the other row. Upon electrical energization of these electrodes, Applicant s has observed that there is a grouping between the dots of coagulated colloid formed opposite the electrode active surfaces of the energized electrodes of one row and those formed opposite the electrode active surfaces of the energized electrodes of the other row, resulting in dots ~o having an elliptical configuration rather than the desired circular configuration.
It is therefore an object of the present invention to overcome the above drawbacks and to provide ~5 an improved electrocoagulation printing method and apparatus enabling one to increase the resolution of the image printed by electrocoagulation and to obtain an image resolution as high as 400 lines per inch, or more.
zo According to one aspect of the invention, there is provided an electrocoagulation printing method comprising the steps of:
a) providing a positive electrolytically inert z5 electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, the passivated surface defining a positive electrode active surface;
3o b) forming on the positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink 35 comprising a liquid colloidal dispersion containing the electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and c) bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive s electrode active surface onto the substrate and thereby imprint the substrate with the image;
the improvement wherein step (b) i.s carried out by:
~o i) providing a series of negative electrolytically inert electrodes each having a surface covered with a passive c>x:i.de film, the negative electrodes being e~~ectri.cally insulated from one another and arranged in rect_linear ~al.ignment so that the surfaces thereof def.inc~ a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from the positive e.lectr°c:~de active :>urface by a constant predetermined gap, the negative electrodes being spaced from one another by a distance smaller than the 2o electrode gap;
ii) coating the positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefin.ic substance:
iii) filling the electrode gap with the aforesaid electrocoagulation printing ink;
iv) applying to the negative electrodes a bias so voltage ranging from -1.5 to -2.5 vol.r_s;
v) applying to selected ornes of the negative electrodes a trigger voltage sufficient to energize same and cause point-by-point selective coagulation and 3s adherence of the colloid onto the olefin-coated positive electrode active surface opposi.t.e the electrode active surfaces of the energized electrodes while the positive electrode active surface is moving, thereby forming the dots of colored, coagulated colloid; and vi) removing any remaining non-coagulated colloid from the positive electrode active surface.
According to another aspect of the invention, there is also provided an electrocoagulation printing apparatus comprising:
- a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
- means for moving the positive electrode active surface at a substantially constant speed along a predetermined path;
- means for forming on the positive electrode 2o active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing the z5 electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and - means for bringing a substrate into contact with the dots of colored, coagulated colloid to cause 3o transfer of the colored, coagulated colloid from the positive electrode active surface onto the substrate and thereby imprint the substrate with the image;
the improvement wherein the means for forming the dots of 35 colored, coagulated colloid comprise:
APPARATUS PROVIDING ENHANCED IMAGE RESOLUTION
The present invention pertains to improvements s in the field of electrocoagulation printing. More particularly, the invention relates to an electrocoagulation printing method and apparatus providing enhanced image resolution.
~o In US Patent No. 4,895,629 of January 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, ~S 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 zo 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 2s 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 3o gas accumulation between the negative and positive electrodes.
The electrocoagulation printing ink which is injected into the gap defined between the positive and 3s 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 s 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 ~o 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.
15 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 zo 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. Alter-z5 natively, 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 3o roller and passed through the respective transfer stations for being imprinted with the differently colored images in superimposed relation.
The positive electrode which is used for 35 electrocoagulation printing must be made of an electrolytically inert metal capable of releasing trivalent ions so that upon electrical energization of the negative electrodes, dissolution of the passive oxide film on such an electrode generates trivalent ions which then initiate coagulation of the colloid. Examples of suitable electrolytically inert metals include stainless steels, aluminium and tin.
As explained in Applicant s Canadian patent No. 2,138,190 of October 13, 1998, a breakdown of passive oxide films occurs in the presence of electrolyte anions, ~o such as Cl-, Br- and I-, there being a gradual oxygen displacement from the passive film by the halide anions and a displacement of adsorbed oxygen from the metal surface by the halide anions. The velocity of passive film breakdown, once started, increases explosively in the presence of an applied electric field. There is thus formation of a soluble metal halide at the metal surface.
In other words, a local dissolution of the passive oxide film occurs at the breakdown sites, which releases metal ions into the electrolyte solution. Where a positive zo electrode made of stainless steel or aluminium is utilized in Applicant s electrocoagulation printing method, dissolution of the passive oxide film on such an electrode generates Fe3+ or A13+ ions. These trivalent ions then initiate coagulation of the colloid.
As also explained in Applicant s US Patent No. 4,895,629, the negative electrodes must be spaced from one another by a distance which is equal to or greater than the electrode gap in order to prevent the 3o negative electrodes from undergoing edge corrosion. This considerably limits the resolution of the image printed by electrocoagulation so that an image resolution of more than about 200 lines per inch cannot be obtained.
Applicant has attempted to increase the image resolution while satisfying the above minimum distance between the negative electrodes by arranging the electrodes along two closely adjacent parallel rows with the negative electrodes of one row being staggered with respect to the negative electrodes of the other row. Upon electrical energization of these electrodes, Applicant s has observed that there is a grouping between the dots of coagulated colloid formed opposite the electrode active surfaces of the energized electrodes of one row and those formed opposite the electrode active surfaces of the energized electrodes of the other row, resulting in dots ~o having an elliptical configuration rather than the desired circular configuration.
It is therefore an object of the present invention to overcome the above drawbacks and to provide ~5 an improved electrocoagulation printing method and apparatus enabling one to increase the resolution of the image printed by electrocoagulation and to obtain an image resolution as high as 400 lines per inch, or more.
zo According to one aspect of the invention, there is provided an electrocoagulation printing method comprising the steps of:
a) providing a positive electrolytically inert z5 electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, the passivated surface defining a positive electrode active surface;
3o b) forming on the positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink 35 comprising a liquid colloidal dispersion containing the electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and c) bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive s electrode active surface onto the substrate and thereby imprint the substrate with the image;
the improvement wherein step (b) i.s carried out by:
~o i) providing a series of negative electrolytically inert electrodes each having a surface covered with a passive c>x:i.de film, the negative electrodes being e~~ectri.cally insulated from one another and arranged in rect_linear ~al.ignment so that the surfaces thereof def.inc~ a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from the positive e.lectr°c:~de active :>urface by a constant predetermined gap, the negative electrodes being spaced from one another by a distance smaller than the 2o electrode gap;
ii) coating the positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefin.ic substance:
iii) filling the electrode gap with the aforesaid electrocoagulation printing ink;
iv) applying to the negative electrodes a bias so voltage ranging from -1.5 to -2.5 vol.r_s;
v) applying to selected ornes of the negative electrodes a trigger voltage sufficient to energize same and cause point-by-point selective coagulation and 3s adherence of the colloid onto the olefin-coated positive electrode active surface opposi.t.e the electrode active surfaces of the energized electrodes while the positive electrode active surface is moving, thereby forming the dots of colored, coagulated colloid; and vi) removing any remaining non-coagulated colloid from the positive electrode active surface.
According to another aspect of the invention, there is also provided an electrocoagulation printing apparatus comprising:
- a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
- means for moving the positive electrode active surface at a substantially constant speed along a predetermined path;
- means for forming on the positive electrode 2o active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing the z5 electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and - means for bringing a substrate into contact with the dots of colored, coagulated colloid to cause 3o transfer of the colored, coagulated colloid from the positive electrode active surface onto the substrate and thereby imprint the substrate with the image;
the improvement wherein the means for forming the dots of 35 colored, coagulated colloid comprise:
- a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, the negative elec:troc~es being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative elect:rodr~ active surfaces disposed in a plane spaced from the positive electrode active surface by a constant p:rec~c:termined gap, the negative electrodes beincx spaced from one another by a ~o distance smaller than the electrode gap;
- means for coating the positive electrode active surface with an olefinic subst<~nce to form on the surface micro-droplets o.f olefi_nic substance;
- means for filling the electrode gap with the electrocoagulation pr:~nting ink;
- means for applying to the negative electrodes 2o a bias voltage ranging from -1.5 to -2.5 volts;
- means for 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 electrode while said positive electrode active surface is moving, thereby forming the dots of c:alared, ,~oagu:lated colloid;
3o and - means ior_ :removing any remaining non-coagulated colloid from the positive electrode active surface.
Applicant has found quite unexpectedly that by utilizing negative e:l.ectrolytically inert electrodes each having a surface coated with a passive oxide film and applying to these electrodes a bias voltage ranging from -1.5 to -2.5 voles, the negative electrodes can be positioned closer to one another withaut undergoing edge s corrosion, thereby permitting the distance between the electrodes to be smallex than the e=;_ectrode gap. If the bias voltage is less than 1.5 volts, the passive oxide film of each elect~zode upon being energized dissolves into the ink, resu.Lting in a release of metal. ions and ~o formation of edge corrosion. 0n the other hand, if the bias voltage is hig:~er tan -~ . 5 volts, such a voltage is sufficient to trigger the electrocoagulation of the colloid present in thc:: irk orz t~~:e anode. Thus, by operating with a bias voltage c>f --1,5 to -2.5 volts, preferably about -2 volts, and by positioning the negative electrodes ~uff~_ci.ently close to one another, an image resolution as high as 400 lines per inch, or more, can be obtained without adverse effect.
~o Preferably, the negative electrodes each have a cylindrical conf:igurati.on with a circular cross-section and a diameter :rangi ng ~-rom about: f 0 ~m to about 50 um.
Electrodes having a diameter of about 20 um are preferred. The gap which is defined between the positive z5 and negative electrodes can range from about 35 um to about 100 um, the smaller t_rle electrode gap the sharper are the dots of coagulated coll;:id produced. Where the electrode gap is of the order of 50 um, the negative electrodes are preferably spaced from one another by a :zo distance of about 30 urr; t:o about 40 ~Zm. On the other hand, when the elecarode gap is of the order of 35 ~Zm, the negative electrodes ar_e prefera~:~ 1y spaced from one another by a distanr_:e of about. ~0 Vim.
:>s Examples of suitable electrolytically inert metals from which the negative electrodes can be made include chromium, ruickel, stainless steel and titanium;
g _ stainless steel is particularly preferred. The positive electrode, on the other hand, can be made of stainless steel, aluminum or l~i.n.
Coating of the positive electrode with an olefinic substance prior to electrical energization of the negative electrodes weakens tr~.e adherence of the dots of coagulated colloid to the positive electrode and also prevents an uncontrolled corrosion of the positive to electrode. In addition, ga:~ generat:ed as a result of electrolysis upon energizing the negative electrodes is consumed by reacaion with the olefinic substance so that there is no gas a~:cumu:'~ation between the negative and positive electrodes. Applicant has found that it is no n5 longer necessary to admix a meta,~ oxide with the olefin substance; it is believed that the passive oxide film on currently available electrode contains sufficient metal oxide to act as catalyst for the desired reaction.
o Examples of suitable olefinic substances which may be used to coat the surface of the positive electrode in step (b) (ii) inc:l.ude unsaturated fatty acids such as arachidonic acid, ~~.inoleic acid, linolenic acid, oleic acid and palmitoleic acid and unsaturated vegetable oils z5 such as corn oil, linseed oil, ol.i~,re oil, peanut oil, soybean oil and sunflower oil. Oleic acid is particularly preferred. The micro-droplets formed on the surface of the positive elE=ctrode act:.ive s~.a:rf<~c:e generally have a size ranging from about 1 to about 5 um.
~o The olefin-coated positive active surface is preferably polished to increase the adherence of the micro-droplets onto the positive electrode active surface, prior to step (b) (ii.) . Eor example, use can be ~5 made of a rotating brush provided with a plurality of radially extending bristles made of riorsehair and having extremities contact:i.ng the surface of the positive electrode. The friction caused by the bristles contacting the surface upon rotation of the brush has been found to increase the adherence of the micro-droplets onto the positive electrode active surface.
Where a polychromic image is desired, steps (b) and (c) of the above electrocoagulation printing method are repeated several times to define a corresponding number of printing stages arranged at predetermined ~o locations along the aforesaid path and each using a coloring agent of different color, and to thereby produce several differently colored images of coagulated colloid which are transferred at the respective transfer positions onto the substrate in superimposed relation to provide a polychromic image. It is also possible to repeat several times steps (a), (b) and (c) to define a corresponding number of printing stages arranged in tandem relation and each using a coloring agent of different color, and to thereby produce several zo differently colored images of coagulated colloid which are transferred at respective transfer positions onto the substrate in superimposed relation to provide a polychromic image, the substrate being in the form of a continuous web which is passed through the respective Zs transfer positions for being imprinted with the colored images at the printing stages. Alternatively, the printing stages defined by repeating several times steps (a), (b) and (c) can be arranged around a single roller adapted to bring the substrate into contact with the dots 30 of colored, coagulated colloid of each printing stage and the substrate which is in the form of a continuous web is partially wrapped around the roller and passed through the respective transfer positions for being imprinted with the colored images at the printing stages. The last 35 two arrangements are described in US Patent No.
4,895,629.
When a pr.~lychromic image of high definition is desired, it is preferable to bring an endless non-extensible belt moving at substantially the same speed as the positive electrode active surface and having on one s side thereof a colloid retaining surface adapted to releasably retain dots of c~lec:trc:o:oagulated colloid, into contact with the positive electrode active surface to cause transfer of i:hne differently colored images at the respective transfer positions onto the colloid retaining ~o surface of such a belt in superimposed relation to provide a polychrom.ic _~.mage, and thereafter bring the substrate into contact with the colloid retaining surface of the belt to calase to ansfer c>- flue polychromic image from the colloid retaining surfac°e onto the substrate and ~s to thereby imprint the substrate with the polychromic image. As e:~plained in Applicant's copending Canadian patent application No. :'.,214,300 filed August 29, 199'7, by utilizing an endless non-extensible belt having a colloid retaining surface such as a.~ porous surface on zo which dots of colored, coagulated colloid can be transferred and by moving such a bElt independently of the positive electrode, from one priruting unit to another, so that the colloid retaining surface of the belt contacts the colored, c:oagalated colloid in zs sequence, it is possib7_e to sir~nif icantly improve the registration of the difft,rentiy colored images upon their trans:Eer onto th.e col:Loi~ retain~.rlg :surface of the belt, thereby providing a polychromic image of high definition which can thereafter be ~.ransferred onta the paper web or 30 other substrate. For example, ~.zs:= can be made of a belt comprising a plastic material having a porous coating of silica.
Accordingly, the present invention also ss provides, in a furthexv aspect thereof, an improved multicolor el.ectrocoagulation printing method comprising the st=eps of a) providing a positive electrolytically inert electrode having a continuous passivated surface moving at substantially constant speed al~~ng a predetermined path, the passivated surface defining a positive electrode active surface;
b) forming on the positive electrode active surface a plurality of dots of colored, coagulated ~o colloid represent,~tive of a desired image, by electrocoagulation of an electrolytically coagul.able colloid present in an electroccagu.Lation printing ink comprising a liquid coll.o:i.dal dispf~rsion containing the electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
c) bringing an endless non-extensible belt moving at substantially the same speed as the positive electrode active surface and havi.rug on one side thereof a 2o colloid retaining surface adapted to rel.easably retain dots of electrocoagulated colloid, into contact with the positive electrode active surface to cause transfer of the dots of colored, coagu7.ated colloid from the positive electrode active surface onto the colloid retaining 25 surface of the belt and to thereby imprint the colloid retaining surface with the image;
d) repeating steps (b) and (c) several times to define a corresponding n~zmber of printing stages arranged :~o at predetermined lc~~atiot~s along the path and each using a coloring agent: of dif:i=event co:l.or, to thereby produce several differently colored images of coagulated colloid which are transferred at respec.t.ive transfer positions onto the colloid retaining surface in superimposed 35 relation to provide a polychromic image; and e) bringing a substrate ~.rnto contact with the colloid retaining surface of the belt to cause transfer of the polychromi~~ image from tie colloid retaining surface onto the substrate <rnd t:o thereby imprint the s substrate with the polychromic image;
the improvement wherein step (b) is carried out as defined above.
~o According to yet anothc>.r aspect of the invention, there is provided an improved electrocoagulation printing apparatus comprising:
- a positive electrolyt:ically inert electrode having a t5 continuous passivated surface defivuing a positive electrode active surface;
- means for moving the positive electrode active surface at a substantia:Lly c~:onsi:ant speed a:1 ong a predetermined zo path;
- an endless non-exten~~ible belt raving on one side thereof a colloid retaining surface adapted to releasably retain dots of elect~rocoagulated colloid;
?5 - means for moving the belt at substantially the same speed as the positive electrode active surface;
- a plurality of printing units arranged at predetermined :~o locations along 'the path, each printing unit comprising:
- means for forming on the positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by a5 electrocoagulation of an electrol~;rtically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colioi.dal d.i.spersion containing the electrolytically coagulable colloid, a dispersion medium, a soluble electrolyte and a colori..ng ,gent, and - means for bringing the belt into contact with s the positive electrode active sur~Fc~ce at a respective transfer station to cause transfer of the dots of colored, coagulated colloid from t:hE:;; positive electrode active surface onto the colloid retain.i.ng surface of the belt and to imprint the colloid rei:aining surface with to the image, whereby to produce several differently colored images of coagulated colloid which are transferred at the respective transfer stations onto t~hue colloid retaining i5 surface in superimposed a°elat.ion t;o provide a polychromic image; and - means for bringing a substrate into contact with the colloid retaining surface of the belt to cause transfer ~o of the polychromic image from the colloid retaining surface onto the substrate and to thereby imprint the substrate with the polycr~rom~~c image;
the improvement wherein t:he means for forming the dots of 'S colored, coagulated colloid are as defined above.
The positive electrode t.ased can be in the form of a moving endless belt as desca:i.bed in Applicant's US
Patent No. 4,661,222, or in the form of a revolving .so cylinder as described in Applicant's US Patent Nos. 4,895,629 and 5,533,60:1. In the latter case, the printing stages or units are arranged around the positive cylindrical electrode. Preferably, the positive electrode active surface and the ink are maintained at a tem-perature of about 35-60°C, preferably 40°C, to increase the viscosity of the coagulated colloid in step (b) sc that the dots of colored, coagulated colloid remain coherent during th~:i.r transfer in step (c), thereby enhancing transfer of the colc_~r.ed, coagulated colloid onto the substrate or be:Lt. For example, the positive electrode active surfac~~ can be heated at the desired s temperature and the ink applied on the heated electrode surface to cause a transfer of heat therefrom to the ink.
Where the p~osit:ive cy)...indrical electrode extends vertically, stem> (b) (i.i'~ cf the above electro-~o coagulation printing method is advantageously carried out by continuously discharging the ink onto the positive electrode active surface°_ f=rcm a fluid discharge means disposed adjacent the electrode gap ~.t a predetermined height relative to the positive e~~ectrode and allowing 15 the ink to flow downwardly a~.ong t~~~ pos:itive electrode active surface, thfe ink being trous carried by the positive electrode upon rotation thereof to the electrode gap to fill same. Preferably, excess ink flowing downwardly of_f the posit::ive electrode active surface is zo collected and the collected ink is recirculated back to the fluid discharge means.
The colloid generally used is a linear colloid of high molecular caeight, that is, one having a weight 25 average molecular weight between about 10,000 and about 1,000,000, preferably between 100,000 and 600,000.
Examples of suitable colloids include natural polymers such as albumin, gelatin, casein and agar, and synthetic polymers such as pol.yac~r.yl is acid, polyacrylamide and :~o polyvinyl alcohcl. A part~i.cularly preferred colloid is an anionic copolymer of acrylamide and acrylic acid having a weight average molecular weight of about 250,000 and sold by Cyanamid Inc. under the trade mark ACCOSTRENGTH 86.
Water is preferably used as the medium f_or dispersing the colloid to provide the desired colloidal dispersion.
The in.k also contains a soluble electrolyte and a coloring agent. Preferred electrolytes include alkali metal halides and al.kal_~_ne earth met al halides, such as lithium chloride, sodium chloride, potassium chloride and s calcium chloride. Potassium ch~L.oride is particularly preferred. The coloring agent can be a dye or a pigment.
Examples of suitable dyes which may be used to color the colloid are t:he water soluble dyes available from HOECHST
such as Duasyn Acid Black for coloring in black and ~o Duasyn Acid Blue for col~:or~_ng in cyan, or those available from RIEDEL-DEHAEN such ass Anti-Halo Dye Blue T. Pina for coloring in cyan, Anti.-Halo Dye AC Magenta Extra V01 Pina for coloring in magenta and Anti-Halo Dye Oxonol Yellow N. Pina for coloring in yellow. When using a pigment as a o coloring agent, use clan roe made c,>f the pigments which are available from CABOT CORP. such as Carbon Black Monarch~
120 for coloring in black, or. those available from HOECHST such as Hostaperm Blue B2G or B3G for coloring in cyan, Permanent Rubi.ne F6B or h6B for coloring in zo magenta and Permanent Yellow DGR or DHG for coloring in yellow. A dispersing agent is added for uniformly dispersing the pigment into the .irak. Examples of suitable dispersing agents include the anionic dispersing agent sold by Boehme Filatex f.anada Inc::. l.xnder the trade mark 2s CLOSPERSE 25000.
After coagulation of the colloid, any remaining non-coagulated colloid is removed from the positive electrode active surface, for examp~_e, by scraping the :.o surface with a soft rubber squeegee, so as to fully uncover the colored, coagulated col:loi.d. Preferably, the non-coagulated colloid thus remcwed is collected and mixed with the collected ink, rind the collected non-coagulated colloid in admixture with she collected ink is .a recirculated :back to the aforesaic.~ fluid discharge means.
The optical density of trie dots of colored, coagulated colloid may be vat:~ied by varying the voltage and/or pulse duration of the pulse-modulated signals applied to the negative electrode.
After step (c), the positive electrode active surface is generally cleaned to r<emove therefrom any remaining coagulated co:Lloid. According to a preferred embodiment, the positive electrode i.s rotatable in a io predetermined. direction and any remaining coagulated colloid is removed froru tre positive electrode active surface by providing an elongated rotatable brush extending parallel to the longitudinal axis of the positive electrode, the brush beir~:g provided with a is plurality of rad:ially extending bristles made of horsehair and having extremi.t.ies contacting the positive electrode active surfa~~e, rotating the brush in a direction opposite to the direction of rotation of the positive electrode so as to cause the bristles to fractionally engage the positive electrode active surface, and directing jets of c.:Leaning liquid under pressure against the positive electrode active surface, from either side of true t:>rus~. zn such~ an embodiment, the positive electrode actW a surft~cE: and the ink are ;~s preferably maintained at a temperature of about 35-60°C
by heating the cleaning .li<~uic~i to thereby heat the positive electrode active surface upon contacting same and applying the ink an true rieat.f,,d c-electrode surface to cause a transfer of heat therefrom to the ink.
ao Preferably, the elect.rocoagulati.on printing ink contains water as the dispersing medium and the dots of differently colored, coac:tulated colloLd representative of the polychromic image are moistened between the :.5 aforementioned steps (d) and (e) so t::.hat the polychromic image is substantially complete.l.y transferred onto the substrate in step ( e: ) .
Acc;ording to another preferred embodiment, the substrate is in the form of a continuous web and step (e) is carried out by providing <~ support roller and a pressure roller extending parallel to the support roller and pressed thereagainst to form a nip through which the belt is passed, the su~:~port:. rol ~ ez and pressure roller being driven by the belt upon movement thereof, and guiding the web so as to pass througri the nip between the to pressure roller and the porous surface of the belt for imprinting the web with tie pc~lychromic image.
Preferably, the belt with the porou:~ surface thereof imprinted with the polyc;hromi.c image is guided so as to travel along a path extending in a ~:~lane intersecting the is longitudinal axis of the positive electrode at right angles, thereby exposin~~ the porous surface to permit contacting thereof. by the web. Where the longitudinal axis of the positive electrode extends vertically, the belt is preferably guided so as to travel along a zo horizontal path with the porous surface facing downwardly, the support r_ol.l.er and pressure roller having rotation axes disposed in a plane extending perpendicular to the horizontal path. Such an arrangement is described in the aforementioned Canadian appl.ic~~tion No. 2,214,300.
~5 After step (e) , t:he porous s»rface of the belt is generally cleaned to remove therefrom any remaining coagulated colloid. According to a preferred embodiment, any remaining coagulated colloid is removed from the :SO porous surface of the belt by providing at least one elong<~ted rotatable brusr~ disposed on the one side of the belt and at least one support roller extending parallel to the brush and disposed on the opposite side of the belt, the brush and support roller raving rotation axes a5 disposed in a plane extending per.penc~icular to the belt, the brush being provided with a pl!arality of radially extending bristles made of ho:r:~ehair and having extremities contacting the porous surface, rotating the brush in a direction opposite to the direction of movement of thE: belt; au as to cause the bristles to frictionally engage the porous surface while supporting the belt with the support roller, directing jets of cleaning liquid under pressure against the porous surface from either side of the brush and rf~moving the cleaning liquid with any dislodged coagulated colloid from the porous surface.
Further features and advantages of the invention will become more readily apparent from the description of preferred embodiment: as illustrated by way of examples in the accompanying drawings, in which:
Figure 1 is a fragmentary sectional view of an electrocoagulation printing apparatus according to a preferred embodiment of the invention, showing a printing head with a series of_ nectative electrodes;
zo Figure 2 is a fragmentary Longitudinal view of the printing head illustrated in c'ig. 1;
Figure 3 is a tragmentary sectional view of one .?5 of the negative electrodes i.l.lustratec:~ in fig. 1; and Figure 4 is a schematic diagram Showing how an input signal of information is processed to reproduce an image by electrocoac~ulation of a ~~:ollcoid.
so Referring first to Fig. 1, there is illustrated a positive electrode 10 in the f~7rm of a revolving cylinder and havinc a passivated surface 1? defining a positive electrode active surface-~ adapted to be coated s5 with an olefinic substance by means of a positive electrode coating device= (r?ot s~nowr.) . A device 14 is provided for discharging an e_c.ectroc.~oagulation printing ink onto the surface 12. The electrocoagulation printing ink consists of a colloidal dispersion containing an electrolytically coagi.rlable colloid, a dispersing medium, a soluble electrolyte and a coloring agent. A printing s head 16 having a series of negative electrodes 18 is used for electrocoagulating the col.loz.d contained in the ink to form on positive electrode surface 12 dots of colored, coagulated colloid representative of a desired image. As shown in Fig. 2, the printing head 16 comprises a to cylindrical electrode carrier 20 with t:he negative e_Lectrodes 18 being a Lec:tri cal l y insulated from one another and arranged in rectilinear alignment along the length of the el.ect;rode carrier 20 t~o define a plurality of corresponding negative act..i.ve surfaces 22. The is printing head 16 is positioned relative to the positive electrode 10 such that the surfaces 22 of the negative electrodes 18 are disposed in a plane which is spaced from the positive electrode surface 12 by a constant predetermined gap 29. The electrodes 18 are also spaced zo from one another by a distance smaller than the electrode gap 24 to increase image resolution. The device 14 is positioned adjacent the electrode gap 24 to fill same with the electrocoagulat~on printing ink.
?s As shown in Fig. 3, the negative electrodes 18 each have a cylindrical body 26 made of an electrolytically inert. metal and covered with a passive oxide film 28. The end surface of the electrode body 26 covered with such a film defines the aforementioned :;o negative electrode ~uc:tivE~ surface 22.
Figure 4 is a schematic diagram illustrating how the negative electrodes 18 are energized in response to an input signal of informat~_on 30 to form dots of s5 colored, coagulated colloid represenr_ative of a desired image. As shown, a bias circuit 32 is provided for applying to the negative e.lectrcldes 18 a bias voltage ranging from -1.5 to -2.5 volts. A driver circuit 34 is also used fo.r addressinG se:Lected ones of the electrodes 18 so as to apply a 'rigger voltage to the selected electrodes and energise same. :~:uch an electrical energizing causes point-by-point selective coagulation and adherence of the colloid onto the olefin-coated surface 12 of the pos~.t=ive ele:~tr.c:~de 10 opposite the electrode active surfaces 22 while the electrode 10 is rotating, thereby forming on the surface 12 a series of to corresponding dots of colored, coagulated colloid.
A bias voltage within the above range ensures that there is no dissolu'ion of the passive oxide film 28 into the ink and that there is no accidenta:L triggering t5 of the electrocoagulation. Such a bias voltage also enables the electrodes l8 to be spac:~ed from one another by a distance which is smaller than the electrode gap 24, thereby providing an image resolution as high as 400 lines per inch, or more.
zo When it is desired to reproduce a polychromic image, use is preferably made of a central processing unit (CPU) for controlling t:he dxiver circuit associated with each color pri:riting unit.
- means for coating the positive electrode active surface with an olefinic subst<~nce to form on the surface micro-droplets o.f olefi_nic substance;
- means for filling the electrode gap with the electrocoagulation pr:~nting ink;
- means for applying to the negative electrodes 2o a bias voltage ranging from -1.5 to -2.5 volts;
- means for 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 electrode while said positive electrode active surface is moving, thereby forming the dots of c:alared, ,~oagu:lated colloid;
3o and - means ior_ :removing any remaining non-coagulated colloid from the positive electrode active surface.
Applicant has found quite unexpectedly that by utilizing negative e:l.ectrolytically inert electrodes each having a surface coated with a passive oxide film and applying to these electrodes a bias voltage ranging from -1.5 to -2.5 voles, the negative electrodes can be positioned closer to one another withaut undergoing edge s corrosion, thereby permitting the distance between the electrodes to be smallex than the e=;_ectrode gap. If the bias voltage is less than 1.5 volts, the passive oxide film of each elect~zode upon being energized dissolves into the ink, resu.Lting in a release of metal. ions and ~o formation of edge corrosion. 0n the other hand, if the bias voltage is hig:~er tan -~ . 5 volts, such a voltage is sufficient to trigger the electrocoagulation of the colloid present in thc:: irk orz t~~:e anode. Thus, by operating with a bias voltage c>f --1,5 to -2.5 volts, preferably about -2 volts, and by positioning the negative electrodes ~uff~_ci.ently close to one another, an image resolution as high as 400 lines per inch, or more, can be obtained without adverse effect.
~o Preferably, the negative electrodes each have a cylindrical conf:igurati.on with a circular cross-section and a diameter :rangi ng ~-rom about: f 0 ~m to about 50 um.
Electrodes having a diameter of about 20 um are preferred. The gap which is defined between the positive z5 and negative electrodes can range from about 35 um to about 100 um, the smaller t_rle electrode gap the sharper are the dots of coagulated coll;:id produced. Where the electrode gap is of the order of 50 um, the negative electrodes are preferably spaced from one another by a :zo distance of about 30 urr; t:o about 40 ~Zm. On the other hand, when the elecarode gap is of the order of 35 ~Zm, the negative electrodes ar_e prefera~:~ 1y spaced from one another by a distanr_:e of about. ~0 Vim.
:>s Examples of suitable electrolytically inert metals from which the negative electrodes can be made include chromium, ruickel, stainless steel and titanium;
g _ stainless steel is particularly preferred. The positive electrode, on the other hand, can be made of stainless steel, aluminum or l~i.n.
Coating of the positive electrode with an olefinic substance prior to electrical energization of the negative electrodes weakens tr~.e adherence of the dots of coagulated colloid to the positive electrode and also prevents an uncontrolled corrosion of the positive to electrode. In addition, ga:~ generat:ed as a result of electrolysis upon energizing the negative electrodes is consumed by reacaion with the olefinic substance so that there is no gas a~:cumu:'~ation between the negative and positive electrodes. Applicant has found that it is no n5 longer necessary to admix a meta,~ oxide with the olefin substance; it is believed that the passive oxide film on currently available electrode contains sufficient metal oxide to act as catalyst for the desired reaction.
o Examples of suitable olefinic substances which may be used to coat the surface of the positive electrode in step (b) (ii) inc:l.ude unsaturated fatty acids such as arachidonic acid, ~~.inoleic acid, linolenic acid, oleic acid and palmitoleic acid and unsaturated vegetable oils z5 such as corn oil, linseed oil, ol.i~,re oil, peanut oil, soybean oil and sunflower oil. Oleic acid is particularly preferred. The micro-droplets formed on the surface of the positive elE=ctrode act:.ive s~.a:rf<~c:e generally have a size ranging from about 1 to about 5 um.
~o The olefin-coated positive active surface is preferably polished to increase the adherence of the micro-droplets onto the positive electrode active surface, prior to step (b) (ii.) . Eor example, use can be ~5 made of a rotating brush provided with a plurality of radially extending bristles made of riorsehair and having extremities contact:i.ng the surface of the positive electrode. The friction caused by the bristles contacting the surface upon rotation of the brush has been found to increase the adherence of the micro-droplets onto the positive electrode active surface.
Where a polychromic image is desired, steps (b) and (c) of the above electrocoagulation printing method are repeated several times to define a corresponding number of printing stages arranged at predetermined ~o locations along the aforesaid path and each using a coloring agent of different color, and to thereby produce several differently colored images of coagulated colloid which are transferred at the respective transfer positions onto the substrate in superimposed relation to provide a polychromic image. It is also possible to repeat several times steps (a), (b) and (c) to define a corresponding number of printing stages arranged in tandem relation and each using a coloring agent of different color, and to thereby produce several zo differently colored images of coagulated colloid which are transferred at respective transfer positions onto the substrate in superimposed relation to provide a polychromic image, the substrate being in the form of a continuous web which is passed through the respective Zs transfer positions for being imprinted with the colored images at the printing stages. Alternatively, the printing stages defined by repeating several times steps (a), (b) and (c) can be arranged around a single roller adapted to bring the substrate into contact with the dots 30 of colored, coagulated colloid of each printing stage and the substrate which is in the form of a continuous web is partially wrapped around the roller and passed through the respective transfer positions for being imprinted with the colored images at the printing stages. The last 35 two arrangements are described in US Patent No.
4,895,629.
When a pr.~lychromic image of high definition is desired, it is preferable to bring an endless non-extensible belt moving at substantially the same speed as the positive electrode active surface and having on one s side thereof a colloid retaining surface adapted to releasably retain dots of c~lec:trc:o:oagulated colloid, into contact with the positive electrode active surface to cause transfer of i:hne differently colored images at the respective transfer positions onto the colloid retaining ~o surface of such a belt in superimposed relation to provide a polychrom.ic _~.mage, and thereafter bring the substrate into contact with the colloid retaining surface of the belt to calase to ansfer c>- flue polychromic image from the colloid retaining surfac°e onto the substrate and ~s to thereby imprint the substrate with the polychromic image. As e:~plained in Applicant's copending Canadian patent application No. :'.,214,300 filed August 29, 199'7, by utilizing an endless non-extensible belt having a colloid retaining surface such as a.~ porous surface on zo which dots of colored, coagulated colloid can be transferred and by moving such a bElt independently of the positive electrode, from one priruting unit to another, so that the colloid retaining surface of the belt contacts the colored, c:oagalated colloid in zs sequence, it is possib7_e to sir~nif icantly improve the registration of the difft,rentiy colored images upon their trans:Eer onto th.e col:Loi~ retain~.rlg :surface of the belt, thereby providing a polychromic image of high definition which can thereafter be ~.ransferred onta the paper web or 30 other substrate. For example, ~.zs:= can be made of a belt comprising a plastic material having a porous coating of silica.
Accordingly, the present invention also ss provides, in a furthexv aspect thereof, an improved multicolor el.ectrocoagulation printing method comprising the st=eps of a) providing a positive electrolytically inert electrode having a continuous passivated surface moving at substantially constant speed al~~ng a predetermined path, the passivated surface defining a positive electrode active surface;
b) forming on the positive electrode active surface a plurality of dots of colored, coagulated ~o colloid represent,~tive of a desired image, by electrocoagulation of an electrolytically coagul.able colloid present in an electroccagu.Lation printing ink comprising a liquid coll.o:i.dal dispf~rsion containing the electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
c) bringing an endless non-extensible belt moving at substantially the same speed as the positive electrode active surface and havi.rug on one side thereof a 2o colloid retaining surface adapted to rel.easably retain dots of electrocoagulated colloid, into contact with the positive electrode active surface to cause transfer of the dots of colored, coagu7.ated colloid from the positive electrode active surface onto the colloid retaining 25 surface of the belt and to thereby imprint the colloid retaining surface with the image;
d) repeating steps (b) and (c) several times to define a corresponding n~zmber of printing stages arranged :~o at predetermined lc~~atiot~s along the path and each using a coloring agent: of dif:i=event co:l.or, to thereby produce several differently colored images of coagulated colloid which are transferred at respec.t.ive transfer positions onto the colloid retaining surface in superimposed 35 relation to provide a polychromic image; and e) bringing a substrate ~.rnto contact with the colloid retaining surface of the belt to cause transfer of the polychromi~~ image from tie colloid retaining surface onto the substrate <rnd t:o thereby imprint the s substrate with the polychromic image;
the improvement wherein step (b) is carried out as defined above.
~o According to yet anothc>.r aspect of the invention, there is provided an improved electrocoagulation printing apparatus comprising:
- a positive electrolyt:ically inert electrode having a t5 continuous passivated surface defivuing a positive electrode active surface;
- means for moving the positive electrode active surface at a substantia:Lly c~:onsi:ant speed a:1 ong a predetermined zo path;
- an endless non-exten~~ible belt raving on one side thereof a colloid retaining surface adapted to releasably retain dots of elect~rocoagulated colloid;
?5 - means for moving the belt at substantially the same speed as the positive electrode active surface;
- a plurality of printing units arranged at predetermined :~o locations along 'the path, each printing unit comprising:
- means for forming on the positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by a5 electrocoagulation of an electrol~;rtically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colioi.dal d.i.spersion containing the electrolytically coagulable colloid, a dispersion medium, a soluble electrolyte and a colori..ng ,gent, and - means for bringing the belt into contact with s the positive electrode active sur~Fc~ce at a respective transfer station to cause transfer of the dots of colored, coagulated colloid from t:hE:;; positive electrode active surface onto the colloid retain.i.ng surface of the belt and to imprint the colloid rei:aining surface with to the image, whereby to produce several differently colored images of coagulated colloid which are transferred at the respective transfer stations onto t~hue colloid retaining i5 surface in superimposed a°elat.ion t;o provide a polychromic image; and - means for bringing a substrate into contact with the colloid retaining surface of the belt to cause transfer ~o of the polychromic image from the colloid retaining surface onto the substrate and to thereby imprint the substrate with the polycr~rom~~c image;
the improvement wherein t:he means for forming the dots of 'S colored, coagulated colloid are as defined above.
The positive electrode t.ased can be in the form of a moving endless belt as desca:i.bed in Applicant's US
Patent No. 4,661,222, or in the form of a revolving .so cylinder as described in Applicant's US Patent Nos. 4,895,629 and 5,533,60:1. In the latter case, the printing stages or units are arranged around the positive cylindrical electrode. Preferably, the positive electrode active surface and the ink are maintained at a tem-perature of about 35-60°C, preferably 40°C, to increase the viscosity of the coagulated colloid in step (b) sc that the dots of colored, coagulated colloid remain coherent during th~:i.r transfer in step (c), thereby enhancing transfer of the colc_~r.ed, coagulated colloid onto the substrate or be:Lt. For example, the positive electrode active surfac~~ can be heated at the desired s temperature and the ink applied on the heated electrode surface to cause a transfer of heat therefrom to the ink.
Where the p~osit:ive cy)...indrical electrode extends vertically, stem> (b) (i.i'~ cf the above electro-~o coagulation printing method is advantageously carried out by continuously discharging the ink onto the positive electrode active surface°_ f=rcm a fluid discharge means disposed adjacent the electrode gap ~.t a predetermined height relative to the positive e~~ectrode and allowing 15 the ink to flow downwardly a~.ong t~~~ pos:itive electrode active surface, thfe ink being trous carried by the positive electrode upon rotation thereof to the electrode gap to fill same. Preferably, excess ink flowing downwardly of_f the posit::ive electrode active surface is zo collected and the collected ink is recirculated back to the fluid discharge means.
The colloid generally used is a linear colloid of high molecular caeight, that is, one having a weight 25 average molecular weight between about 10,000 and about 1,000,000, preferably between 100,000 and 600,000.
Examples of suitable colloids include natural polymers such as albumin, gelatin, casein and agar, and synthetic polymers such as pol.yac~r.yl is acid, polyacrylamide and :~o polyvinyl alcohcl. A part~i.cularly preferred colloid is an anionic copolymer of acrylamide and acrylic acid having a weight average molecular weight of about 250,000 and sold by Cyanamid Inc. under the trade mark ACCOSTRENGTH 86.
Water is preferably used as the medium f_or dispersing the colloid to provide the desired colloidal dispersion.
The in.k also contains a soluble electrolyte and a coloring agent. Preferred electrolytes include alkali metal halides and al.kal_~_ne earth met al halides, such as lithium chloride, sodium chloride, potassium chloride and s calcium chloride. Potassium ch~L.oride is particularly preferred. The coloring agent can be a dye or a pigment.
Examples of suitable dyes which may be used to color the colloid are t:he water soluble dyes available from HOECHST
such as Duasyn Acid Black for coloring in black and ~o Duasyn Acid Blue for col~:or~_ng in cyan, or those available from RIEDEL-DEHAEN such ass Anti-Halo Dye Blue T. Pina for coloring in cyan, Anti.-Halo Dye AC Magenta Extra V01 Pina for coloring in magenta and Anti-Halo Dye Oxonol Yellow N. Pina for coloring in yellow. When using a pigment as a o coloring agent, use clan roe made c,>f the pigments which are available from CABOT CORP. such as Carbon Black Monarch~
120 for coloring in black, or. those available from HOECHST such as Hostaperm Blue B2G or B3G for coloring in cyan, Permanent Rubi.ne F6B or h6B for coloring in zo magenta and Permanent Yellow DGR or DHG for coloring in yellow. A dispersing agent is added for uniformly dispersing the pigment into the .irak. Examples of suitable dispersing agents include the anionic dispersing agent sold by Boehme Filatex f.anada Inc::. l.xnder the trade mark 2s CLOSPERSE 25000.
After coagulation of the colloid, any remaining non-coagulated colloid is removed from the positive electrode active surface, for examp~_e, by scraping the :.o surface with a soft rubber squeegee, so as to fully uncover the colored, coagulated col:loi.d. Preferably, the non-coagulated colloid thus remcwed is collected and mixed with the collected ink, rind the collected non-coagulated colloid in admixture with she collected ink is .a recirculated :back to the aforesaic.~ fluid discharge means.
The optical density of trie dots of colored, coagulated colloid may be vat:~ied by varying the voltage and/or pulse duration of the pulse-modulated signals applied to the negative electrode.
After step (c), the positive electrode active surface is generally cleaned to r<emove therefrom any remaining coagulated co:Lloid. According to a preferred embodiment, the positive electrode i.s rotatable in a io predetermined. direction and any remaining coagulated colloid is removed froru tre positive electrode active surface by providing an elongated rotatable brush extending parallel to the longitudinal axis of the positive electrode, the brush beir~:g provided with a is plurality of rad:ially extending bristles made of horsehair and having extremi.t.ies contacting the positive electrode active surfa~~e, rotating the brush in a direction opposite to the direction of rotation of the positive electrode so as to cause the bristles to fractionally engage the positive electrode active surface, and directing jets of c.:Leaning liquid under pressure against the positive electrode active surface, from either side of true t:>rus~. zn such~ an embodiment, the positive electrode actW a surft~cE: and the ink are ;~s preferably maintained at a temperature of about 35-60°C
by heating the cleaning .li<~uic~i to thereby heat the positive electrode active surface upon contacting same and applying the ink an true rieat.f,,d c-electrode surface to cause a transfer of heat therefrom to the ink.
ao Preferably, the elect.rocoagulati.on printing ink contains water as the dispersing medium and the dots of differently colored, coac:tulated colloLd representative of the polychromic image are moistened between the :.5 aforementioned steps (d) and (e) so t::.hat the polychromic image is substantially complete.l.y transferred onto the substrate in step ( e: ) .
Acc;ording to another preferred embodiment, the substrate is in the form of a continuous web and step (e) is carried out by providing <~ support roller and a pressure roller extending parallel to the support roller and pressed thereagainst to form a nip through which the belt is passed, the su~:~port:. rol ~ ez and pressure roller being driven by the belt upon movement thereof, and guiding the web so as to pass througri the nip between the to pressure roller and the porous surface of the belt for imprinting the web with tie pc~lychromic image.
Preferably, the belt with the porou:~ surface thereof imprinted with the polyc;hromi.c image is guided so as to travel along a path extending in a ~:~lane intersecting the is longitudinal axis of the positive electrode at right angles, thereby exposin~~ the porous surface to permit contacting thereof. by the web. Where the longitudinal axis of the positive electrode extends vertically, the belt is preferably guided so as to travel along a zo horizontal path with the porous surface facing downwardly, the support r_ol.l.er and pressure roller having rotation axes disposed in a plane extending perpendicular to the horizontal path. Such an arrangement is described in the aforementioned Canadian appl.ic~~tion No. 2,214,300.
~5 After step (e) , t:he porous s»rface of the belt is generally cleaned to remove therefrom any remaining coagulated colloid. According to a preferred embodiment, any remaining coagulated colloid is removed from the :SO porous surface of the belt by providing at least one elong<~ted rotatable brusr~ disposed on the one side of the belt and at least one support roller extending parallel to the brush and disposed on the opposite side of the belt, the brush and support roller raving rotation axes a5 disposed in a plane extending per.penc~icular to the belt, the brush being provided with a pl!arality of radially extending bristles made of ho:r:~ehair and having extremities contacting the porous surface, rotating the brush in a direction opposite to the direction of movement of thE: belt; au as to cause the bristles to frictionally engage the porous surface while supporting the belt with the support roller, directing jets of cleaning liquid under pressure against the porous surface from either side of the brush and rf~moving the cleaning liquid with any dislodged coagulated colloid from the porous surface.
Further features and advantages of the invention will become more readily apparent from the description of preferred embodiment: as illustrated by way of examples in the accompanying drawings, in which:
Figure 1 is a fragmentary sectional view of an electrocoagulation printing apparatus according to a preferred embodiment of the invention, showing a printing head with a series of_ nectative electrodes;
zo Figure 2 is a fragmentary Longitudinal view of the printing head illustrated in c'ig. 1;
Figure 3 is a tragmentary sectional view of one .?5 of the negative electrodes i.l.lustratec:~ in fig. 1; and Figure 4 is a schematic diagram Showing how an input signal of information is processed to reproduce an image by electrocoac~ulation of a ~~:ollcoid.
so Referring first to Fig. 1, there is illustrated a positive electrode 10 in the f~7rm of a revolving cylinder and havinc a passivated surface 1? defining a positive electrode active surface-~ adapted to be coated s5 with an olefinic substance by means of a positive electrode coating device= (r?ot s~nowr.) . A device 14 is provided for discharging an e_c.ectroc.~oagulation printing ink onto the surface 12. The electrocoagulation printing ink consists of a colloidal dispersion containing an electrolytically coagi.rlable colloid, a dispersing medium, a soluble electrolyte and a coloring agent. A printing s head 16 having a series of negative electrodes 18 is used for electrocoagulating the col.loz.d contained in the ink to form on positive electrode surface 12 dots of colored, coagulated colloid representative of a desired image. As shown in Fig. 2, the printing head 16 comprises a to cylindrical electrode carrier 20 with t:he negative e_Lectrodes 18 being a Lec:tri cal l y insulated from one another and arranged in rectilinear alignment along the length of the el.ect;rode carrier 20 t~o define a plurality of corresponding negative act..i.ve surfaces 22. The is printing head 16 is positioned relative to the positive electrode 10 such that the surfaces 22 of the negative electrodes 18 are disposed in a plane which is spaced from the positive electrode surface 12 by a constant predetermined gap 29. The electrodes 18 are also spaced zo from one another by a distance smaller than the electrode gap 24 to increase image resolution. The device 14 is positioned adjacent the electrode gap 24 to fill same with the electrocoagulat~on printing ink.
?s As shown in Fig. 3, the negative electrodes 18 each have a cylindrical body 26 made of an electrolytically inert. metal and covered with a passive oxide film 28. The end surface of the electrode body 26 covered with such a film defines the aforementioned :;o negative electrode ~uc:tivE~ surface 22.
Figure 4 is a schematic diagram illustrating how the negative electrodes 18 are energized in response to an input signal of informat~_on 30 to form dots of s5 colored, coagulated colloid represenr_ative of a desired image. As shown, a bias circuit 32 is provided for applying to the negative e.lectrcldes 18 a bias voltage ranging from -1.5 to -2.5 volts. A driver circuit 34 is also used fo.r addressinG se:Lected ones of the electrodes 18 so as to apply a 'rigger voltage to the selected electrodes and energise same. :~:uch an electrical energizing causes point-by-point selective coagulation and adherence of the colloid onto the olefin-coated surface 12 of the pos~.t=ive ele:~tr.c:~de 10 opposite the electrode active surfaces 22 while the electrode 10 is rotating, thereby forming on the surface 12 a series of to corresponding dots of colored, coagulated colloid.
A bias voltage within the above range ensures that there is no dissolu'ion of the passive oxide film 28 into the ink and that there is no accidenta:L triggering t5 of the electrocoagulation. Such a bias voltage also enables the electrodes l8 to be spac:~ed from one another by a distance which is smaller than the electrode gap 24, thereby providing an image resolution as high as 400 lines per inch, or more.
zo When it is desired to reproduce a polychromic image, use is preferably made of a central processing unit (CPU) for controlling t:he dxiver circuit associated with each color pri:riting unit.
Claims (42)
1. In an 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, said passivated surface defining a positive electrode active surface;
b) forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and c) bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive electrode active surface onto said substrate and thereby imprint said substrate with said image;
the improvement wherein step (b) is carried out by:
i) providing a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
ii) coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
iii) filling the electrode gap with said electrocoagulation printing ink;
iv) applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volt;
v) applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid; and vi) removing any remaining non-coagulated colloid from said positive electrode active surface.
a) providing a positive electrolytically inert electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, said passivated surface defining a positive electrode active surface;
b) forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and c) bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive electrode active surface onto said substrate and thereby imprint said substrate with said image;
the improvement wherein step (b) is carried out by:
i) providing a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
ii) coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
iii) filling the electrode gap with said electrocoagulation printing ink;
iv) applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volt;
v) applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid; and vi) removing any remaining non-coagulated colloid from said positive electrode active surface.
2. A method as claimed in claim 1, wherein a bias voltage of about -2 volts is applied to said negative electrodes.
3. A method as claimed in claim 1, wherein said negative electrodes each have a cylindrical configuration with a circular cross-section and a diameter ranging from about 20 to about 50 µm.
4. A method as claimed in claim 3, wherein said negative electrodes each have a diameter of about 20 µm.
5. A method as claimed in claim 3, wherein said electrode gap ranges from about 35 to about 100 µm.
6. A method as claimed in claim 5, wherein said electrode gap is about 50 µm and wherein said negative electrodes are spaced from one another by a distance of about 30 to 40 µm.
7. A method as claimed in claim 5, wherein said electrode gap is about 35 µm and wherein said negative electrodes are spaced from one another by a distance of about 20 µm.
8. A method as claimed in claim 1, wherein said negative electrodes are formed of an electrolytically inert metal selected from the group consisting of chromium, nickel, stainless steel and titanium.
9. A method as claimed in claim 8, wherein said electrolytically inert metal comprises stainless steel.
10. A method as claimed in claim 1, wherein steps (b) and (c) are repeated several times to define a corresponding number of printing stages arranged at predetermined locations along said path and each using a coloring agent of different color, to thereby produce several differently colored images of coagulated colloid which are transferred at respective transfer positions onto said substrate in superimposed relation to provide a polychromic image.
11. A method as claimed in claim 10, wherein said positive electrode is a cylindrical electrode having a central longitudinal axis and rotating at substantially constant speed about said longitudinal axis, and wherein said printing stages are arranged around said positive cylindrical electrode.
12. In 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, said passivated surface defining a positive electrode active surface;
b) forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electro coagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
c) bridging an endless non-extensible belt moving at substantially the same speed as said positive electrode active surface and having on one side thereof a colloid retaining surface adapted to releasably retain dots of electrocoagulated colloid, into contact with said positive electrode active surface to cause transfer of the dots of colored, coagulated colloid from the positive electrode active surface onto the and colloid retaining surface of said belt and to thereby imprint said colloid retaining surface with the image;
d) repeating steps (b) and (c) several times to define a corresponding number of printing stages arranged at predetermined locations along said path and each using a coloring agent of different color, to thereby produce several differently colored images of coagulated colloid which are transferred at respective transfer positions onto said colloid retaining surface in superimposed relation to provide a polychromic image; and e) bringing a substrate into contact with the colloid retaining surface of said belt to cause transfer of the polychromic image from said colloid retaining surface onto said substrate and to thereby imprint said substrate with said polychromic image;
the improvement wherein step (b) is carried out by:
i) providing a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
ii) coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
iii) filling the electrode gap with said electrocoagulation printing ink;
iv) applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volts;
v) applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid; and vi) removing any remaining non-coagulated colloid from said positive electrode active surface.
a) providing a positive electrolytically inert electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, said passivated surface defining a positive electrode active surface;
b) forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electro coagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
c) bridging an endless non-extensible belt moving at substantially the same speed as said positive electrode active surface and having on one side thereof a colloid retaining surface adapted to releasably retain dots of electrocoagulated colloid, into contact with said positive electrode active surface to cause transfer of the dots of colored, coagulated colloid from the positive electrode active surface onto the and colloid retaining surface of said belt and to thereby imprint said colloid retaining surface with the image;
d) repeating steps (b) and (c) several times to define a corresponding number of printing stages arranged at predetermined locations along said path and each using a coloring agent of different color, to thereby produce several differently colored images of coagulated colloid which are transferred at respective transfer positions onto said colloid retaining surface in superimposed relation to provide a polychromic image; and e) bringing a substrate into contact with the colloid retaining surface of said belt to cause transfer of the polychromic image from said colloid retaining surface onto said substrate and to thereby imprint said substrate with said polychromic image;
the improvement wherein step (b) is carried out by:
i) providing a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
ii) coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
iii) filling the electrode gap with said electrocoagulation printing ink;
iv) applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volts;
v) applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid; and vi) removing any remaining non-coagulated colloid from said positive electrode active surface.
13. A method as claimed in claim 12, wherein a bias voltage of about -2 volts is applied to said negative electrodes.
14. A method as claimed in claim 12, wherein the negative electrodes each have a cylindrical configuration with a circular cross-section and a diameter ranging from about 20 to about 50 µm.
15. A method as claimed in claim 14, wherein said negative electrode each have a diameter of about 20 µm.
16. A method as claimed in claim 14, wherein said electrode gap ranges from about 35 to about 100 µm.
17. A method as claimed in claim 16, wherein said electrode gap is about 50 µm and wherein said negative electrodes are spaced from one another by a distance of about 30 to 40 µm.
18. A method as claimed in claim 16, wherein said electrode gap is about 35 µm and wherein said negative electrodes are spaced from one another by a distance of about 20 µm.
19. A method as claimed in claim 12, wherein said negative electrodes are formed of an electrolytically inert metal selected from the group consisting of chromium, nickel, stainless steel and titanium.
20. A method as claimed in claim 19, wherein said electrolytically inert metal comprises stainless steel.
21. A method as claimed in claim 12, wherein said positive electrode is a cylindrical electrode having a central longitudinal axis and rotating at substantially constant speed about said longitudinal axis, and wherein said printing stages are arranged around said positive cylindrical electrode.
22. In an electrocoagulation printing apparatus comprising:
- a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
- means for moving said positive electrode active surfaces at a substantially constant speed along a predetermined path;
- means for forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and - means for bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive electrode active surface onto said substrate and thereby imprint said substrate with said image;
the improvement wherein said means for forming said dots of colored, coagulated colloid comprise:
- a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another arid and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
- means for coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
- means for filling the electrode gap with said electrocoagulation printing ink;
- means for applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volts;
means for applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid;
and - means for removing any remaining non-coagulated colloid from said positive electrode active surface.
- a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
- means for moving said positive electrode active surfaces at a substantially constant speed along a predetermined path;
- means for forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent; and - means for bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive electrode active surface onto said substrate and thereby imprint said substrate with said image;
the improvement wherein said means for forming said dots of colored, coagulated colloid comprise:
- a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another arid and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
- means for coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
- means for filling the electrode gap with said electrocoagulation printing ink;
- means for applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volts;
means for applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid;
and - means for removing any remaining non-coagulated colloid from said positive electrode active surface.
23. An apparatus as claimed in claim 22, wherein said negative electrodes each havr a cylindrical configuration with a circular cross-section and a diameter ranging from about 20 to about 50 µm.
24. An apparatus as claimed in claim 23, wherein said negative electrodes each have a diameter of about 20 µm.
25. An apparatus as claimed in claim 23, wherein said electrode gap ranges from about 35 to about 100 µm.
26. An apparatus as claimed in claim 25, wherein said electrode chap is about 50 µm and wherein said negative electrodes are spaced from one another by a distance of about 30 to 40 um.
27. An apparatus as claimed in claim 25, wherein said electrode gap is about 35 µm and wherein said negative electrodes are spaced from one another by a distance of about 20 µm.
28. An apparatus as claimed in claim 22, wherein said negative electrodes are formed of an electrolytically inert metal selected from the group consisting of chromium, nickel, stainless steel and titanium.
29. An apparatus as claimed in claim 28, wherein said electrolytically inert metal comprises stainless steel.
30. An apparatus as claimed in claim 22, wherein said means for applying said trigger voltage to selected ones of said negative electrodes comprises driver circuit means for addressing selected ones of said negative electrodes so as to apply said trigger voltage to the selected negative electrodes.
31. An apparatus as claimed in claim 22, wherein said means for forming said dots of colored, coagulated colloid and said means for bringing said substance into contact with said dots of colored, coagulated colloid are arranged to define a printing unit, and wherein there are several printing units positioned at predetermined locations along said path and each using a coloring agent of different color for producing several differently colored images of coagulated colloid which are transferred at respective transfer stations onto said substrate in superimposed relation to provide a polychromic image.
32. An apparatus as claimed in claim 31, wherein said positive electrode axis a cylindrical electrode having a central longitudinal axis and wherein said means for moving said positive electrode active surface includes means for rotating said positive cylindrical electrode about said longitudinal axis, and wherein said printing units being arranged around said positive cylindrical electrode.
33. In a multicolor electrocoagulation printing apparatus comprising:
- a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
- means for moving said positive electrode active surface at a substantially constant speed along a predetermined path;
- an endless non-extensible belt having on one side thereof a colloid retaining surface adapted to releasably retain dots of electrocoagulated colloid;
- means for moving said belt at substantially the same speed as said positive electrode active surface;
- a plurality of printing units arranged at predetermined locations along said path, each printing unit comprising:
- means for forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulated of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersion medium, a soluble electrolyte ana a coloring agent, and - means for bringing said belt into contact with said positive electrode active surface at a respective transfer station to cause transfer of the dots of colored, coagulated colloid from the positive electrode active surface onto the colloid retaining surface of said belt and to imprint said colloid retaining surface with the image, whereby to produce several differently colored images of coagulated colloid which are transferred at said respective transfer stations onto said colloid retaining surface in superimposed relation to provide a polychromic image; and - means for bringing a substrate into contact with the colloid retaining surface of said beat to cause transfer of the polychromic image from said colloid retaining surface onto said substrate and to thereby imprint said substrate with said polychromic image;
the improvement wherein said means for forming said dots of colored, coagulated colloid comprise:
- a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
- means for coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
- means for filling the electrode gap with said electrocoagulation printing ink;
- means for applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volts;
means for applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid;
and - means for removing any remaining non-coagulated colloid from said positive electrode active surface.
- a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
- means for moving said positive electrode active surface at a substantially constant speed along a predetermined path;
- an endless non-extensible belt having on one side thereof a colloid retaining surface adapted to releasably retain dots of electrocoagulated colloid;
- means for moving said belt at substantially the same speed as said positive electrode active surface;
- a plurality of printing units arranged at predetermined locations along said path, each printing unit comprising:
- means for forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulated of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersion medium, a soluble electrolyte ana a coloring agent, and - means for bringing said belt into contact with said positive electrode active surface at a respective transfer station to cause transfer of the dots of colored, coagulated colloid from the positive electrode active surface onto the colloid retaining surface of said belt and to imprint said colloid retaining surface with the image, whereby to produce several differently colored images of coagulated colloid which are transferred at said respective transfer stations onto said colloid retaining surface in superimposed relation to provide a polychromic image; and - means for bringing a substrate into contact with the colloid retaining surface of said beat to cause transfer of the polychromic image from said colloid retaining surface onto said substrate and to thereby imprint said substrate with said polychromic image;
the improvement wherein said means for forming said dots of colored, coagulated colloid comprise:
- a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
- means for coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
- means for filling the electrode gap with said electrocoagulation printing ink;
- means for applying to said negative electrodes a bias voltage ranging from -1.5 to -2.5 volts;
means for applying to selected ones of said 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 said energized electrodes while said positive electrode active surface is moving, thereby forming said dots of colored, coagulated colloid;
and - means for removing any remaining non-coagulated colloid from said positive electrode active surface.
34. An apparatus as claimed in claim 33, wherein said negative electrodes each have a cylindrical configuration with a circular cross-section and a diameter ranging from about 20 to about 50 µm.
35. An apparatus as claimed in claim 34, wherein said negative electrodes each have a diameter of about 20 µm.
36. An apparatus as claimed in claim 34, wherein said electrode gap ranges from about 35 to about 100 µm.
37. An apparatus as claimed in claim 36, wherein said electrode gap is about 50 µm and wherein said negative electrodes are spaced from one another by a distance of about 30 to 40 µm.
38. An apparatus as claimed in claim 36, wherein said electrode gap is about 35 µm and wherein said negative electrodes are spaced from one another by a distance of about 20 µm.
39. An apparatus as claimed in claim 33, wherein said negative electrodes are formed of an electrolytically inert metal selected from the group consisting of chromium, nickel, stainless steel and titanium.
40. An apparatus as claimed in claim 39, wherein said electrolytically inert metal comprises stainless steel.
41. An apparatus as claimed in claim 33, wherein said means for applying said trigger voltage to selected ones of said negative electrodes comprises driver circuit means for addressing selected ones of said negative electrodes so as to apply said trigger voltage to the selected negative electrodes.
42. An apparatus as claimed in claim 33, wherein said positive electrode is a cylindrical electrode having a central longitudinal axis and wherein said means for moving said positive electrode active surface includes means for rotating said positive cylindrical electrode about said longitudinal axis, said printing units being arranged around said positive cylindrical electrode.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2282951 CA2282951C (en) | 1999-09-15 | 1999-09-15 | Electrocoagulation printing method and apparatus providing enhanced image resolution |
| US09/430,020 US6210553B1 (en) | 1999-09-15 | 1999-10-29 | Electrocoagulation printing method and apparatus providing enhanced image resolution |
| EP00120007A EP1084829B1 (en) | 1999-09-15 | 2000-09-14 | Electrocoagulation printing method and apparatus providing enhanced image resolution |
| DE2000603988 DE60003988T2 (en) | 1999-09-15 | 2000-09-14 | Electrocoagulation printing method and device for generating increased image resolution |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2282951 CA2282951C (en) | 1999-09-15 | 1999-09-15 | Electrocoagulation printing method and apparatus providing enhanced image resolution |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2282951A1 CA2282951A1 (en) | 2001-03-15 |
| CA2282951C true CA2282951C (en) | 2004-02-24 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2282951 Expired - Fee Related CA2282951C (en) | 1999-09-15 | 1999-09-15 | Electrocoagulation printing method and apparatus providing enhanced image resolution |
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| Country | Link |
|---|---|
| CA (1) | CA2282951C (en) |
| DE (1) | DE60003988T2 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2379746A1 (en) * | 2002-03-28 | 2003-09-28 | Elcorsy Technology Inc. | Electrocoagulation printing method providing an image having enhanced optical density |
-
1999
- 1999-09-15 CA CA 2282951 patent/CA2282951C/en not_active Expired - Fee Related
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2000
- 2000-09-14 DE DE2000603988 patent/DE60003988T2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DE60003988D1 (en) | 2003-08-28 |
| DE60003988T2 (en) | 2004-04-22 |
| CA2282951A1 (en) | 2001-03-15 |
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