An image forming apparatus

Abstract: An image forming apparatus includes a master having a conductive portion and an insulating portion which form a pattern; an applicator for applying the ink material on the master wherein deposition of the ink material onto the master is different depending on a direction of electric current flowing through the ink material; excessive ink material a remover, contactable to the ink material applied on the master by the applicator, for removing excessive ink material with a voltage applied between the master and the excessive ink material remover.

Description: The present invention relates to image forming apparatus, and to an image forming process, and makes use of a recording material whose viscosity can be changed by application of an electric current thereto, so that the recording material selectively makes contact with or is spaced from an electrode. The image forming apparatus may take the form of a printer or the like. Image forming apparatus of the above mentioned type is disclosed in EP-A-0326115 & US-A-5142306 (US Application 301,146 corresponding to Japanese Patent Application No. 70299/1988) which has been assigned to the assignee of the present application. An example of the image forming process appears in Figure 2 which is an enlarged sectional view of an image forming station. That station includes a pair of electrodes 1 and 2, a recording material 3 interposed between the electrodes 1 and 2 and having the property that its viscosity or adhesiveness changes by causing a current to flow through it, and an insulating portion 4 in the form of an image on the electrode 2. A recording material comprises an electrolytic material and a liquid dispersion medium. Examples of the liquid dispersion medium which may be used for a recording material in the present invention include polyhydroxylic alcohols and ethers thereof such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol (weight average molecular weight approximately 100-1000), ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methyl carbitol or the like. The above liquid dispersion medium may be used individually or as a mixture. The ink preferably contains 40-95%, more preferably 60-85% by weight of the liquid dispersion medium. The polyhydroxylic alcohol or ether dispersion medium may be mixed with another liquid dispersion medium. It is preferred that the recording medium should contain 10-100% by weight of the polyhydroxylic alcoholic or ether dispersion medium based on the total liquid dispersion medium. Another example of a liquid dispersion medium is water. Further examples include triethanolamine, formamide, dimethylsulfoxide, N-methyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, N-methyl-acetamide, ethylene carbonate, acetamide, succino-nitrile, dimethylsulfoxide, furfuryl alcohol, N,N-dimethylformamide and the like. These media may be used individually or in admixture one with another. The electrolytic material which is present in the recording medium is preferably one that does not produce halogen ions on electrolysis. It is further preferable that the electrolytic material should not be deposited as a result of electrolysis and should have an electric conductivity such as to permit smooth control of the adhesion of the recording medium by the applied voltage. Preferred electrolytic materials which may be used in the recording material of the present invention include, for example, LiBF₄, NaPF₆, NH₄PF₆ or CH₃COONa or the like. These materials may be used individually or in combination. In Figure 3 a voltage is applied across a recording medium by connecting one of the electrodes 1 to a positive potential and the other electrode 2 to a negative potential, so as to provide an image forming station. In Figure 4 the spacing between the electrodes 1, 2 is increased while the voltage across the electrodes is maintained. From this figure it is apparent that where the electrode 2 has been in direct contact with the recording medium 3, the medium 3 does not become deposited on the electrode 2. Thus the recording medium 3 is selectively deposited on the insulating portions 4 of the electrode 2. A pattern is formed by the recording material corresponding to the pattern provided by the electrode 2 and the insulating portions 4. In Figure 5 an opposite voltage is applied between the electrodes, that is the electrodes 2 and 1 are supplied with positive and negative polarities respectively. In Figure 6 the spacing between the electrodes is again increased while the voltage is maintained between them. In this case, the recording material 3 is separated from the electrode 1 and is deposited on the electrode 2. Figure 7 shows what happens when no voltage is applied between the electrodes, and the electrodes are moved apart from one another. Due to the viscosity or adhesive properties of the recording medium 3, the recording medium is deposited on both the electrodes 1 and 2 so that no image is formed by the recording material on either of the electrodes. When a printing apparatus is constituted using the above recording principle, a master is provided by forming a pattern of the insulating portions 4 on the electrode 2 as shown in Figure 4. When printing is effected by means of the recording material using such a master, after the step of applying the recording material it is possible to regulate the thickness of the recording material 3 on the master (the electrode 2) so as to prevent excessive amounts being applied, taking into account the dryness of the recording material and the spread of the image. In doing so, if the surface of the master is rubbed with a roller or the like after the step of Figure 4 is carried out, the recording material 3 may be displaced from the insulating portion 4 which provides the pattern, with the result that the printed image is not sharp. Patent specification EP-A-0322816 discloses a printing process which uses an ink which is substantially non-adhesive, but to which adhesive properties can be imparted when the ink is subjected to a pH change which may be induced by a current from a pH change-imparting electrode. Patent specification EP-A-0336238 and patent specification EP-A-0352796 disclose image forming methods using an ink which may be caused to transfer from one electroconductive member to another under the influence of a current between the two members, but they do not disclose or suggest the application of ink to a master and the selective removal of residual ink from non-image areas. In one aspect the invention provides an image forming apparatus having the features of claim 1 of the accompanying claims. In a second aspect the invention provides an image forming process having the features of claim 4 of the accompanying claims. Embodiments of the above process and apparatus enable excessive application of the recording material on to the master to be prevented and enable the master to provide a high quality image. How the invention may be put into effect will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A, 1B and 1C illustrate in cross-section an image forming process according to an embodiment of the present invention. Figures 2, 3, 4, 5, 6 and 7 show the respective steps of the image formation mechanism used in the present invention. Figures 8 and 9 are sectional views of image forming apparatuses according to embodiments of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figure 1A, the recording material has been applied on the electrode 2 which is a print master having a pattern and is movable in the direction indicated by an arrow, through the process steps described in conjunction with Figures 3 and 4. The recording material 3 is brought to the insulating portion 4 (pattern) by the electrode 1 in the form of a roller. At this time, the recording material on the insulating portion 4 has a large thickness, and is pressed on the pattern in the next step. Therefore, it is preferable that the thickness thereof is regulated to a predetermined level. The regulating operation is performed by a blade 5 at the right side of Figure 1A. Figure 1B shows the state provided after the recording material 3 on the insulating portion 4 is wiped by an elastic blade 5 made of a synthetic resin material. By the regulating action of the blade 5, the recording material 3 is partly spread out of the pattern of the insulating portion 4 to produce a spread 3a. If the recording material 3 is transferred onto an image receiving material such as paper from the master having the spread, the image is thickened or spread, so that the image quality is degraded. Figure 1C shows a process step for removing the excessive recording material, according to an embodiment of the present invention. An electrode roller 6 rolls on the master, by which the recording material 3b outside the insulating portion 4 is removed. The electrode roller 6 is supplied with a positive (+) voltage, similarly to Figure 4. Thereafter, an image receiving material 7 such as paper is overlaid on the master, so that the recording material on the master is transferred onto the image receiving material 7, so that the printing is effected. In the foregoing description, the blade regulates the recording material 3 on the master (Figure 1B). This is not always necessary, but the excessive recording material removing step of Figure 1C may be performed directly after the application step of Figure 1A. In place of the blade 5, a roller is usable. The process steps of Figures 1B and 1C may be repeated a plurality of times. Figures 8 and 9 are sectional views of printing machines using the process. An ink roll 22 retaining thereon the recording material in the form of ink, rotates in a direction indicated by an arrow. By the rotation, the ink is transferred to an ink retaining roll 21 (first inking means). At this time, the voltage is applied from a voltage source 25 between the ink retaining roll 21 (positive) and the master (and a master drum M). In accordance with the principle having been described in conjunction with Figures 3 and 4, the ink supplied from the roll 21 is selectively transferred to the non-conductive portion on the master (not shown), the master having the conductive portion provided by copper foil fixed on the master drum M and having the non-conductive portion made of plastic resin or the like. The imagewisely applied ink is made flush by the blade 5a in Figure 8, or by a conductive metal roller 5b in Figure 9. The excessive portion of the image ink on the master, that is, the ink extending into the conductive portion, is removed to the roller 24 by flowing current from the power source 26 between the ink retaining roll 24 (positive) (second inking means) and the master (and the master drum M) (negative). Then, the ink image thus formed is transferred onto a blanket 32 (an intermediate medium) press-contacted to the master drum M, and then is transferred onto the recording medium such as a sheet of paper through a nip formed between the blanket 32 and the pressure drum 35. The clearances between the ink retaining roll 21, the ink roll 22, the ink roll 23 and the ink retaining roll 24 are approximately 0.1 mm. Each of the ink retaining rolls 21 and 24 has a diameter of approximately 32 mm and includes a steel core coated with a conductive rubber layer having a thickness of 5 mm. Each of the ink rolls 22 and 23 is made of steel plated with platinum. The master drum M has a diameter of approximately 160 mm, and includes light alloy core coated with a conductive rubber layer having a thickness of approximately 5 mm. The voltage provided by the voltage sources 25 and 26 is approximately 30 V (DC) per 80 mm (image formation width). The blanket drum 32 has a diameter of approximately 160 mm made of light alloy and coated with a rubber layer having a thickness of approximately 5 mm. In place of the rubber layer, a blanket sheet having the equivalent thickness may be fixed on the surface of the light alloy. Using such an apparatus, the recording operation was performed at a recording speed of approximately 1000 mm/sec with the rotational speed of approximately 120 rpm. The recording material (ink) used contained: Glycerin 66 parts by weight NiBF₄ 7 parts by weight Carbon black 7 parts by weight Colloidal silicate hydride 34 parts by weight Water 22 parts by weight The ink was black. As described in the foregoing, according to the present invention, only the excessive recording material is removed from the master, and also, the amount of the recording material application to the master can also be regulated. Therefore, the image quality is improved, and it can be avoided that the drying period is undesirably made long. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

Claims: An image forming apparatus, comprising: a master movable along an endless path and having a conductive portion and an insulating portion which form a pattern; applying means for applying ink material on the master, wherein deposition of the ink material onto said master is different depending on the direction of an electric current flowing through the ink material, and wherein the potential of said applying means is retained at a value such that the ink material thereon is attracted to the master to form an image corresponding to said pattern; and excess ink material removing means, in the form of a conductive roller which can be contacted with the ink material on the master and can remove excessive ink material from areas outside the image on application of a voltage between the master and said excessive ink material removing means. Apparatus according to claim 1, wherein one and the same conductive roller functions both as said applying means and said removing means. An apparatus according to claim 1, wherein said applying means and said removing means are arranged along the direction of movement of said master. An image forming process using ink material having the property that when it is present between electrodes, deposition of the ink material onto the electrodes is different depending on the direction of electric current flowing through the ink material, said process comprising: providing a master having an insulating portion and a conductive portion which functions as one of the electrodes; applying the ink material to the master and forming an image on the master by application of a voltage between the master and the applying means for applying the ink material; and contacting excessive ink material removing means with the ink material on the master while a bias voltage is applied to the removing means so that excess ink material in areas outside the image becomes removed from the master. A process according to claim 4, wherein the applying means is maintained at a potential capable of attracting thereon the ink material. A process according to claim 5, wherein said means for effecting said applying step is a conductive roller. A process according to claim 6, wherein the conductive roller also functions to remove the excess ink material. A process according to any of claims 4 to 7, comprising the further steps of: transferring the ink material from said master to an intermediate material; and transferring the ink material from the intermediate material to a sheet material. A process according to claim 8, wherein said applying means and said removing means are arranged along the direction of movement of said master.

Inventors: KIKUCHI SHOJI, KOUMURA NOBORU, TOHYAMA NOBORU, KIKUCHI, SHOJI, KOUMURA, NOBORU, TOHYAMA, NOBORU
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: B41M1
IPC codes: B41M5, B41F35, B41F7