EP0450548A2

EP0450548A2 - Apparatus for recording by discharging a liquid

Info

Publication number: EP0450548A2
Application number: EP91105151A
Authority: EP
Inventors: Motokazu Canon Kabushiki Kaisha Kobayashi
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1990-03-31
Filing date: 1991-04-02
Publication date: 1991-10-09
Also published as: JPH03284952A; EP0450548A3

Abstract

Bubbles are generated by electrolysis in a liquid (4) such as an ink in a nozzle (1) and the liquid is discharged from the nozzle according as the bubbles grow. The amount of discharge is controlled by the voltage of and application time of current to be applied, i.e., the amount of electric energy to be applied.

Description

The present invention relates to a recording apparatus of a type in which an ink in the form of a liquid is made to adhere to a recording medium such as paper to perform recording, and to an apparatus and method for discharging a liquid used in the recording apparatus as well as to an apparatus for processing information having such a recording apparatus.
Heretofore, various types of methods for discharging a liquid have been used in recording apparatuses. Among them, a method is included in which an ink is discharged by the action of a gas generated in the ink and which is advantageous in that less noises are produced during the operation. As a representative example of this type, there has been well known a so-called bubble jet type method in which bubbles are generated in the ink and the ink is discharged according as the bubbles expand rapidly. The bubble jet type method generates bubbles in accordance with electric pulses applied to a heat generating element of an electro-thermal converting element or the like. According to this method, a recording apparatus can be obtained which have various advantages that it has a good discharge response, it can perform recording at a higher rate, it enables construction of recording heads in reduced sizes and at low costs.
Other types of discharging methods utilizing the action of a gas include a method in which an ink is discharged in accordance with generation of a plurality of gases. An example of such a method is the discharge method as described in U. S. Patent No. 3,177,800. In this method, electrodes are arranged in the ink, between which sparks are generated to gasify and ionize the ink and form a plurality of gases whose pressure causes the ink to be discharged.
The above-described two types of discharge methods include heating of the ink upon generation of bubbles. Therefore, in these methods, heat accumulation in the ink occurs, for example, when the ink is discharged continuously for performing recording in a recording apparatus. The heat accumulation changes the viscosity of the ink or otherwise deteriorates the characteristics of the ink, which causes the amount of the ink to be discharged to change according as recording proceeds. Hence, the density of recorded images varies during the recording, resulting in that image quality tends to be deteriorated.
In view of the above-described points, conventional recording apparatuses utilizing the aforementioned type of bubble jet method generally are provided with a control mechanism for controlling the temperature of a recording head, i.e., the temperature of an ink to be discharged to be within a predetermined range. However, such a mechanism is not mandatory for recording actions and the provision of it might sometime gives adverse influences on the cost, size, and other factors of the recording apparatuses.
Further, in the discharge method disclosed in the aforementioned publication, it is essentially impossible to control the size of ink droplets to be discharged. This is because the discharge of ink droplets is carried out by the very action of generation of gases by instantaneous sparking between electrodes and hence it is difficult to vary the size of the ink droplets to be discharged by controlling the time during which the gas generation action continues or the like factor.
An object of the present invention is to provide a method and apparatus for discharging a liquid which will cause no heat accumulation in a recording liquid nor deterioration of characteristics of the liquid.
Another object of the present invention is to provide a method and apparatus for discharging a liquid which can readily control the size of droplets of the liquid to be discharged.
Still further object of the present invention is to provide a recording head which can retain the density of recorded images at a constant level during recording and give rise to good image quality, and a recording apparatus having such a recording head.
Yet another object of the present invention is to provide a recording apparatus which can improve image quality without increasing the cost and size of the apparatus.
According to the first aspect of the present invention, there is provided a method for discharging a liquid, comprising the steps of:
providing a liquid to be discharged;
arranging electrodes in contact with the liquid;
applying a voltage to the liquid through the electrodes to cause electrolysis in the liquid to generate a gas; and
discharging the liquid by action of the gas generated by the electrolysis.
According to the second aspect of the present invention, there is provided an apparatus for discharging a liquid, comprising:
a plurality of nozzles for introducing a liquid for recording, the nozzles having respective walls;
a pair of electrodes provided on each of the respective walls of the nozzles in contact with the liquid; and
a driving circuit electrically connected to the electrodes, the driving circuit applying voltage to cause electrolysis in the liquid to thereby generate a gas.
According to the third aspect of the present invention, there is provided a recording apparatus having a liquid discharging apparatus and means for conveying a recording medium to a position where recording is performed by the liquid discharging apparatus, wherein the liquid discharging apparatus comprising:
a plurality of nozzles for introducing a liquid for recording, the nozzles having respective walls;
a pair of electrodes provided on each of the respective walls of the nozzles in contact with the liquid; and
a driving circuit electrically connected to said electrodes, the driving circuit applying voltage to cause electrolysis in the liquid to thereby generate a gas.
Here, the recording apparatus may be outputting means for an information processing apparatus.
The aforementioned information processing apparatus may be any one of a work station, a personal computer, a host computer, a word processor, a copying apparatus having an image reader, a facsimile, and an optical disc apparatus.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.
Figs. 1A through 1F are each a schematic cross-sectional side view showing the discharging apparatus used in the discharging method according to the present invention, showing the action of discharging a liquid.
Fig. 2 is a schematic cross-sectional side view showing the discharging apparatus according to one embodiment of the present invention used as an ink jet recording head.
Fig. 3 is a schematic perspective view showing the discharging apparatus according to one embodiment of the present invention used as an ink jet recording head.
Fig. 4 is a perspective view showing the ink jet recording apparatus to which the present invention is applied.
Fig. 5 is a schematic block diagram showing the information processing apparatus to which the present invention is applied.
Fig. 6 is a schematic block diagram showing the portable printer for the information processing apparatus to which the present invention is applied.
Hereafter, the present invention will be described in more detail by way of embodiments with reference to the accompanying drawings.

Embodiment 1

Figs. 1A through 1F are each a schematic cross-sectional side view showing the discharging apparatus for explaining the method for discharging a liquid according to the present invention, which show various supposed discharging actions with lapse of time. Hereafter, the discharging method of the present invention will be explained referring to Figs. 1A through 1F.
As shown in Fig. 1A, as soon as current at a predetermined voltage starts to be applied between electrodes 2A and 2B, electrolysis occurs at respective portions of the electrodes 2A and 2B where they contact a liquid 4 as a medium to be discharged to thereby form numerous fine bubbles. When the voltage continues to be retained many bubbles formed on the respective electrodes come to join and form a larger bubble, thus growing larger and larger. In accordance with the bubble growth, a liquid surface at an opening portion provided on a front end portion of a nozzle 1 rises, receiving an action of pushing forward and that of surface tension, and the liquid surface gradually takes a shape of droplet (cf. Figs. 1B and 1C). When the growth of bubbles has proceeded further to reach a stage where the bubbles which grow on the electrode 2A come in contact with those which grow on the electrode 2B, these bubbles come to join and altogether form a single bubble. At this timing the application of current is stopped when the size of the bubble is the maximum (cf. Fig. 1D). Thereafter, the liquid 4 in the vicinity of the opening portion which is taking a shape of droplet according as the bubble grows leaves the nozzle 1 and is flown away forward from the nozzle 1. At the same time, the surface of the liquid remaining in the nozzle 1 starts to take an action to return to the same state as before the discharging (cf. Fig. 1E), and fully restore the state before the discharging after a predetermined time (cf. Fig. 1F).
Figs. 2 and 3 are schematic cross-sectional view and schematic perspective view, respectively, of the apparatus for discharging a liquid to which the method for discharging a liquid of the present invention is applied. The apparatus for discharging a liquid according to the instant embodiment is used in a recording apparatus in which recording is performed by discharging an ink and causing the ink to adhere to a recording material or medium such as recording paper. While Figs. 2 and 3 show an apparatus for discharging a liquid having a single nozzle, generally recording apparatuses are constructed in the form of a recording head having a plurality of nozzles arranged in an array.
In Figs. 2 and 3, reference numeral 1 denotes a nozzle which is composed of an insulating resin such as silicone resin, acrylamide resin, TEFLON resin (polytetrafluoroethylene), or phenol resin. The use of the insulating resin can prevent the occurrence of chemical changes of the nozzle 1 with the ink 4 (designated by the same reference numeral as the liquid in Fig. 1) therein and hence can prevent the corrosion of the nozzle 1. However, the nozzle 1 may be constructed with a metal such as stainless steel. In this case, an electric insulating material is provided on the boundary between the electrodes 2A and 2B and the nozzle 1.
The electrodes 2A and 2B may be made of a metal such as plate of gold, platinum, or copper, a plate composed of an insulating material plated with such a metal, or an electroconductive carbon. Of these, preferred is platinum from a point of view of durability. Reference numeral 3 denotes a driving circuit, which is provided with a direct current source or an alternating current source, and establishes voltage between the electrodes 2A and 2B based on driving data transmitted from a control portion (not shown).
Reference numeral 4 denotes an ink as a medium to be discharged. The ink used in the instant embodiment is a mixture of an ink solvent as explained hereinbelow with a coloring agent as explained hereinbelow.
The ink solvent to be used is preferably the one which causes electrolysis to generate bubbles upon application of current. In the case where an ink solvent is used which generates no bubble upon application of current, an electrolyte as explained hereinbelow may be dissolved in the solvent so that bubbles can be generated. As for the ink solvent, there may be used water or various inorganic or organic solvents alone or as admixtures. There can be cited, for example, sulfuric acid, nitric acid, hydrochloric acid, N-methylacetamide, N-methylformamide, formamide, ethylene carbonate, acetamide, succinonitrile, dimethyl sulfoxide, sulfolane, glycerin, 1,2-ethanediol, (ethylene glycol), furfuryl alcohol, N,N-diemthyl-acetamide, N,N-dimethylformamide, nitrobenzene, N-methyl-pyrrolidone, 1,2-propanediol (propylene glycol), diethylene glycol, 2-ethoxyethanol, hexamethylphosphoric triamide (hexamethylphosphoric acid triamide), 2-nitropropane, nitroethane, γ-butyrolactone, propylene carbonate, triethylene glycol, 1,2,6-hexanetriol, dipropylene glycol, hexylene glycol, and the like. Needless to say, the ink solvent usable in the present invention is not limited to the aforementioned solvents.
Those substances which can be used as an electrolyte include, for example, potassium chloride, sodium chloride, sodium hydroxide, potassium hydroxide, sodium acetate, sodium phosphate, sodium hydrogen phosphate, lithium borofluoride, sodium borofluoride, sodium perchlorate, potassium perchlorate, tetrabutylammonium perchlorate, and the like.
As for the coloring agent which can be mixed with the ink solvent, there can be used a dye, pigment or colored particles. Any dyes that are generally used in the field of printing, recording or the like such as carbon black may be used in the present invention without restriction. The ink is prepared by dissolving the dye or dispersing the pigment in the aforementioned ink solvent. If desired, additives such as a viscosity increasing agent, or a viscosity decreasing agent may be added to the ink. Further, in order to adjust the voltage to be established for generating bubbles, pH of the ink may be adjusted by addition of a pH adjusting agent, a buffer or the like.
In the instant embodiment, there is used a discharging apparatus wherein the nozzle 1 is made of silicone resin, an opening portion at the tip of the nozzle has a diameter of 2 mm, the distance between a tip portion of the nozzle and an electrode is 1.5 mm, area of the electrode 2A and 2B made of platinum is 0.1 cm². The diameter and shape of the nozzle, the shape and area of the electrodes and the like may be set appropriately depending on discharge amount, kind of medium to be discharged, and the like.
Three experiments were conducted using the discharging apparatus shown in Figs. 2 and 3, and the results obtained are described hereinbelow.

Experiment 1

Using a 0.1 M aqueous sulfuric acid solution containing no coloring agent as a medium to be discharged, direct current at a voltage of 6 V was applied for 5 seconds between the electrodes 2A and 2B through the driving circuit 3 connected to the electrodes.
Current applied was about 200 mA, and the discharge amount of the medium to be recorded was about 0.15 ml.

Experiment 2

The procedures of Experiment 1 were repeated except that a 0.5 M aqueous sodium hydroxide solution was used as the medium to be discharged.
Current applied was about 200 mA, and the discharge amount of the medium to be recorded was about 0.15 ml.

Experiment 3

As the medium to be discharged was used an ink having a composition as set forth below.

0.1 M Aqueous sodium hydroxide solution: 50 % by weight
Diethylene glycol: 48 % by weight
Carbon black: 2 % by weight

Current at a voltage of 10 V was applied to between the electrodes 2A and 2B for 10 seconds through the driving circuit 3.
Current applied then was about 200 mA, and the discharge amount of the medium to be recorded was about 0.27 ml.
As described above, the amount of bubbles generated was controlled by the amount of electricity applied to the medium to be discharged, thus making it possible to vary the discharge amount.

Embodiment 2

Fig. 4 is a schematic perspective view showing the ink jet recording apparatus to which the present invention is applied.
In Fig. 4, a discharging apparatus 10 (hereafter, referred to as "recording head") having, for example, 16 to 256 discharge portions (nozzles) is detachably mounted on a carriage 21 which is guided on a guide shaft 20, and in this state is scanned in a direction perpendicular to the direction in which recording paper 22 is conveyed. Reference numeral 23 denotes a belt conveyor for scanning the carriage 21. Reference numeral 24 denotes a conveyor roll, and reference numeral 25 denotes a platen. These convey the recording paper 22 to a desired position. Further, reference numeral 26 denotes a discharge recovering apparatus for maintaining the discharge portions in good conditions, which includes an elastic cap, an aspirator and the like.
The system of the above-described embodiment is constructed such that signal outputs for driving the recording paper conveying means, head scanning means and discharge recovering means as well as those for driving the recording head can be controlled by controlling means based on instruction put out from CPU of the main body of the ink jet recording apparatus.
As will be apparent from the foregoing description, according to the present invention, a liquid such as an ink can be discharged in accordance with growth, for example, of bubbles generated in the liquid by electrolysis. The discharge amount can be controlled under the control of the voltage and time of current to be applied to the liquid, i.e., the amount of electric energy applied.
As a result, the discharging apparatus obtained according to the present invention causes no harmful effect due to heat accompanied by discharging action, such as increase in the temperature of the liquid in the nozzle encountered, for example, when the discharging is performed continuously. In this respect, the discharging apparatus of the invention can be used as a suitable recording head for recording apparatus.
The discharging apparatus of the present invention can be constructed in a manner simpler than the conventional ones.
In this invention, even if the fine bubbles form on only one electrode of two electrodes, it is important that the height and the width of the nozzle are set as small as possible so as to leak out no fine bubbles from the nozzle and form a large bubble which may fill the nozzle.
The electrode may have a bumpy surface so as to promote an electrolysis even if the surface of the electrode is covered with numerous fine bubbles.
A gap between two electrodes at least at one portion may be smaller than the gap between two electrodes at the other portions so as to join easily each bubble of the electrodes.
In any case, in this invention, the nozzle have an electrolytic liquid or solid, and at least, the nozzle is filled with the bubble to discharge the liquid or the liquid melting from the solid, then, the remained bubble in the nozzle may be discharged by discharging means such as pressure or suction from a supply side of the liquid. Consequently, after discharging the liquid, the supplying current may be given to the electrodes continuously so as to discharge the remained bubble in the nozzle quickly. Or, the next supplying may be stopped until the remained bubble is discharged by itself.
And, in this invention, the apparatus may further comprise an electrolysis promoter such as a catalyst and/or an electrolysis promoting means such as heating means.

Embodiment 3

The present invention is particularly suitably useable in an ink jet recording head having heating elements that produce thermal energy as energy used for ink ejection and recording apparatus using the head. This is because, the high density of the picture element, and the high resolution of the recording are possible.
The typical structure and the operational principle are preferably the one disclosed, for example, in U.S. Patents Nos. 4,723,129 and 4,749,796 The principle is applicable to a so-called on-demand type recording system and a continuous type recording system, particularly it is suitable for the on-demand type because the principle is such that at least one driving signal is applied to an electro-thermal converting element disposed on liquid (ink) retaining sheet or ink passage, the driving signal being enough to provide such a quick temperature rise beyond a departure from nucleation boiling point, by which the thermal energy is provided by the electro-thermal converting element to produce film boiling on the heating portion of the recording head, whereby a bubble can be formed in the liquid (ink) corresponding to each of the driving signals. By the development and collapse of the bubble, the liquid (ink) is discharged through an discharge portion to produce at least one droplet. The driving signal is preferably in the form of a pulse because the development and collapse of the bubble can be effected instantaneously, and therefore, the liquid (ink) is discharged with quick response. The driving signal in the form of the pulse is preferably such as disclosed in U.S. Patent Nos. 4,463,359 and 4,345,262. In addition, the temperature increasing rate of the heating surface is preferably such as disclosed in U.S. Patent No. 4,313,124.
The structure of the recording head may be as shown in U.S. Patent Nos. 4,558,333 and 4,459,600 wherein the heating portion is disposed at a bent portion in addition to the structure of the combination of the discharging portion, liquid passage and the above-described patents. In addition, the present invention is applicable to the structure disclosed in Japanese Patent Application Laying-Open No. 123670/1984 wherein a common slit is used a the discharge portion for plural electro-thermal converting elements, and to the structure disclosed in Japanese Patent Application Laying-Open No. 138461/1984 wherein an opening for absorbing pressure wave of the thermal energy is formed corresponding to the discharge portion. This is because the present invention is effective to perform the recording operation with certainty and at high efficiency irrespective of the type of the recording head.
The present invention is effectively applicable to a so-called full-line type recording head having a length corresponding to the maximum recording width. Such a recording head may comprise a single recording head integrally formed and a plurality recording heads combined to cover the entire width.
In addition, the present invention is applicable to a serial type recording head wherein the recording head is fixed on the main assembly, to a replaceable chip type recording head which is connected electrically with the main apparatus and can be supplied with the ink by being mounted in the main assembly, or to a cartridge type recording head having an integral ink container.
The provision of the recovery means and the auxiliary means for the preliminary operation are preferred because they can further stabilize the effect of the present invention. As for such means, there are capping means for the recording head, cleaning means therefor, pressing or sucking means, preliminary heating means by the discharging electro-thermal converting element and additional heating element and means for preliminary discharge not for the recording operation, which can stabilize the recording operation.
As regards the kind and the number of the recording heads mounted, a single head corresponding to a single color ink may be equipped, or a plurality of heads corresponding, respectively, to a plurality of ink materials having different recording color or density may be equipped. The present invention is effectively applicable to an apparatus having at least one of a monochromatic mode solely with main color such as black and a multi-color mode with different color ink materials or a full-color mode by color mixture. The multi-color or full-color mode may be realized by a single recording head unit having a plurality of head formed integrally or by a combination of a plurality of recording heads.
Furthermore, in the foregoing embodiment,the ink has been liquid. It may, however, be an ink material solidified at room temperature or below and liquefied at room temperature. Since in the ink jet recording system, the ink is controlled within the temperature not less than 30°C and not more than 70°C to stabilize the viscosity of the ink to provide the stabilized discharging, in usual recording apparatus of this type, the ink is such that it is liquid within the temperature range when the recording signal is applied. In addition, the temperature rise due to the thermal energy is positively prevented by consuming it for the state change of the ink from the solid state to the liquid state, or the ink material is solidified when it is left is used to prevent the evaporation of the ink. In either of the cases, the application of the recording signal producing thermal energy, the ink may be liquefied, and the liquefied ink may be discharged. The ink may start to be solidified at the time when it reaches the recording material. The present invention is applicable to such an ink material as is liquefied by the application of the thermal energy. Such an ink material may be retained as a liquid or solid material on through holes or recesses formed in a porous sheet as disclosed in Japanese Patent Application Laying-Open No. 56847/1979 and Japanese Patent Application Laying-Open No. 71260/1985. The sheet is faced to the electro-thermal converting elements. The most effective one for the ink materials described above is the film boiling system.
The ink jet recording apparatus may be used as an output means of various types of information processing apparatus such as a work station, personal or host computer, a word processor, a copying apparatus combined with an image reader, a facsimile machine having functions for transmitting and receiving information, or an optical disc apparatus for recording and/or reproducing information into and/or from an optical disc. These apparatus requires means for outputting processed information in the form of hand copy.
Fig. 5 schematically illustrates one embodiment of a utilizing apparatus in accordance with the present invention to which the ink jet recording system shown in Fig. 4 is equipped as an output means for outputting processed information.
In Fig. 5, reference numeral 10000 schematically denotes a utilizing apparatus which can be a work station, a personal or host computer, a word processor, a copying machine, a facsimile machine or an optical disc apparatus. Reference numeral 11000 denotes the ink jet recording apparatus (IJRA) shown in Fig. 4. The ink jet recording apparatus (IJRA) 11000 receives processed information from the utilizing apparatus 10000 and provides a print output as hand copy under the control of the utilizing apparatus 10000.
Fig. 6 schematically illustrates another embodiment of a portable printer in accordance with the present invention to which a utilizing apparatus such as a work station, a personal or host computer, a word processor, a copying machine, a facsimile machine or an optical disc apparatus can be coupled.
In Fig. 6, reference numeral 10001 schematically denotes such a utilizing apparatus. Reference numeral 12000 schematically denotes a portable printer having the ink jet recording apparatus (IJRA) 11000 shown in Fig. 4 is incorporated thereinto and interface circuits 13000 and 14000 receiving information processed by the utilizing apparatus 11001 and various controlling data for controlling the ink jet recording apparatus 11000, including hand shake and interruption control from the utilizing apparatus 11001. Such control per se is realized by conventional printer control technology.
The invention has been described in detail with respect to embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the invention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention.
Bubbles are generated by electrolysis in a liquid (4) such as an ink in a nozzle (1) and the liquid is discharged from the nozzle according as the bubbles grow. The amount of discharge is controlled by the voltage of and application time of current to be applied, i.e., the amount of electric energy to be applied.

Claims

A method for discharging a liquid, characterized by comprising the steps of:
providing a liquid to be discharged;
arranging electrodes in contact with said liquid;
applying a voltage to said liquid through said electrodes to cause electrolysis in said liquid to generate a gas; and
discharging said liquid by action of said gas generated by said electrolysis.
An apparatus for discharging a liquid, characterized by comprising:
a plurality of nozzles for introducing a liquid for recording, said nozzles having respective walls;
a pair of electrodes provided on each of said respective walls of said nozzles in contact with said liquid; and
a driving circuit electrically connected to said electrodes, said driving circuit applying voltage to cause electrolysis in said liquid to thereby generate a gas.
A recording apparatus having a liquid discharging apparatus and means for conveying a recording medium to a position where recording is performed by the liquid discharging apparatus, wherein said liquid discharging apparatus characterized by comprising:
a plurality of nozzles for introducing a liquid for recording, said nozzles having respective walls;
a pair of electrodes provided on each of said respective walls of said nozzles in contact with said liquid; and
a driving circuit electrically connected to said electrodes, said driving circuit applying voltage to cause electrolysis in said liquid to thereby generate a gas.
An information processing apparatus provided with a recording apparatus as outputting means for outputting information, the recording apparatus having a liquid discharging apparatus and means for conveying a recording medium to a position where recording is performed by the liquid discharging apparatus, wherein said liquid discharging apparatus characterized by comprising:
a plurality of nozzles for introducing a liquid for recording, said nozzles having respective walls;
a pair of electrodes provided on each of said respective walls of said nozzles in contact with said liquid; and
a driving circuit electrically connected to said electrodes, said driving circuit applying voltage to cause electrolysis in said liquid to thereby generate a gas.