Bubble jet recording method and apparatus in which a heating element generates bubbles in a liquid flow path to project droplets

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid jet recording process and apparatus therefor, and more particularly to such process and apparatus in which a liquid recording medium is made to fly in a state of droplets.

2. Description of the Prior Art

So-called non-impact recording methods have recently attracted public attention because the noise caused by at the recording can be reduced to a negligible order. Among these, particularly important is the so-called ink jet recording method allowing high-speed recording on a plain paper without particular fixing treatment, and in this field there have been proposed various approaches including those already commercialized and those still under development.

Such ink jet recording, in which droplets of a liquid recording medium, usually called ink, are made to fly and to be deposited on a recording member to achieve recording, can be classified into several processes according to the method of generating said droplets and also to the method of controlling the direction of flight of said droplets.

A first process is disclosed for example in the U.S. Pat. No. 3,060,429 (Teletype process) in which the liquid droplets are generated by electrostatic pull, and the droplets thus generated on demand are deposited onto a recording member with or without an electric-field control on the flight direction.

More specifically said electric-field control is achieved by applying an electric field between the liquid contained in a nozzle having an orifice and an accelerating electrode thereby causing said liquid to be emitted from said orifice and to fly between x-y deflecting electrodes so arranged as to be capable of controlling the electric field according to the recording signals, and thus selectively controlling the direction of flight of droplets according to the change in the strength of the electric field to obtain deposition in desired positions.

A second process is disclosed for example in the U.S. Pat. No. 3,596,275 (Sweet process) and in the U.S. Pat. No. 3,298,030 (Lewis and Brown process) in which a flow of liquid droplets of controlled electrostatic charges is generated by continuous vibration and is made to fly between deflecting electrodes forming a uniform electric field therebetween to obtain a recording on a recording member.

More specifically, in this process, a charging electrode receiving recording signals is provided in front of and at a certain distance from the orifice of a nozzle constituting a part of a recording head equipped with a piezo vibrating element, and a pressurized liquid is supplied into said nozzle while an electric signal of a determined frequency is applied to said piezo vibrating element to cause mechanical vibration thereof, thereby causing the orifice to emit a flow of liquid droplets. As the emitted liquid is charged by electrostatic induction by the above-mentioned charging electrode, each droplet is provided with a charge corresponding to the recording signal. The droplets having thus controlled charges are subjected to deflection corresponding to the amount of said charges during the flight in a uniform electric field between the deflecting electrodes in such a manner that only those carrying recording signals are deposited onto the recording member.

A third process is disclosed for example in the U.S. Pat. No. 3,416,153 (Hertz process) in which an electric field is applied between a nozzle and an annular charging electrode to generate a mist of liquid droplets by continuous vibration. In this process the strength of the electric field applied between the nozzle and the charging electrode is modulated according to the recording signals to control the dispersion of liquid thereby obtaining a gradation in the recorded image.

A fourth process, disclosed for example in the U.S. Pat. No. 3,747,120 (Stemme process), is based on a principle fundamentally different from that used in the foregoing three processes.

In contrast to said three processes in which the recording is achieved by electrically controlling the liquid droplets emitted from the nozzle during the flight thereof and thus selectively depositing only those carrying the recording signals onto the recording member, the Stemme process is featured in generating and flying the droplets only when they are required for recording.

More specifically, in this process, electric recording signals are applied to a piezo vibrating element provided in a recording head having a liquid-emitting orifice to convert said recording signals into mechanical vibration of said piezo element according to which the liquid droplets are emitted from said orifice and deposited onto a recording member.

The foregoing four processes, though being provided with respective advantages, are however associated with drawbacks which are inevitable or have to be prevented.

The foregoing first to third process rely on electric energy for generating droplets or droplet flow of liquid recording medium, and also on an electric field for controlling the deflection of said droplets. For this reason the first process, though structurally simple, requires a high voltage for droplet generation and is not suitable for high-speed recording as a multi-orificed recording head is difficult to make.

The second process, though being suitable for high speed recording as the use of multi orificed structure in the recording head is feasible, inevitably results in a structural complexity and is further associated with other drawbacks such as requiring a precise and difficult electric control for governing the flight direction of droplets and tending to result in formation of satellite dots on the recording element.

The third process, though advantageous in achieving recording of an improved gradation by dispersing the emitted droplets, is associated with drawbacks of difficulty in controlling the state of dispersion, presence of background fog in the recorded image and being unsuitable for high-speed recording because of difficulty in preparing a multi-orificed recording head.

In comparison with the foregoing three processes the fourth process is provided with relatively important advantages such as a simpler structure, absence of a liquid recovery system as the droplets are emitted on demand from the orifice of a nozzle in contrast to the foregoing three processes wherein the droplets which do not contribute to the recording have to be recovered, and a larger freedom in selecting the materials constituting the liquid recording medium not requiring electro-conductivity in contrast to the first and second processes wherein said medium has to be conductive. On the other hand said fourth process is again associated with drawbacks such as difficulty in obtaining a small head or a multi-orificed head because the mechanical working of a head is difficult and also because a small piezo vibrating element of a desired frequency is extremely difficult to obtain, and inadequacy for high-speed recording because the emission and flight of liquid droplets have to be performed by the mechanical vibrating energy of the piezo element.

As explained in the foregoing, the conventional processes respectively have advantages and drawbacks in connection with the structure, applicability for high-speed recording, preparation of recording head, particularly of a multi-orificed head, formation of satellite dots and formation of background fog, and their use has therefore been limited to the fields in which such advantages can be exploited.

SUMMARY OF THE INVENTION

The principal object of the present invention, therefore, is to provide a liquid jet recording process and an apparatus therefor enabling the use of a simple structure, easy preparation of multiple orifices and a high-speed recording, and providing a clear image without satellite dots or background fog.

Another object of the the present invention is to provide a liquid jet recording process for recording with liquid droplets, and an apparatus therefor, comprising the steps of:

projecting a liquid from an orifice communicating with a thermal chamber by maintaining the same under pressure thereby forming a stream of said liquid directed toward a surface of a record-receiving member;

applying to the liquid contained in said thermal chamber a thermal energy generated according to electrical input signals by an electro-thermal transducer coupled to said thermal chamber in such a manner as to transmit thermal energy to the liquid contained in said thermal chamber thereby instantaneously forming bubbles in said liquid, and applying a periodical force resulting from periodical state change involving instantaneous volumic change of said bubbles to said liquid stream thereby breaking up said stream into a succession of evenly spaced uniform separate droplets; and

selectively charging and deflecting the droplets in said succession to deposit on said record-receiving member, or intercepting said droplets, thereby causing selective deposition onto said record-receiving member.

Still another object of the present invention is to provide a liquid jet recording process for recording with liquid droplets, and an apparatus therefor, comprising the steps of:

applying, each time a droplet is to be projected from an orifice communicating with a thermal chamber toward a surface of a record-receiving member, to a liquid contained in said thermal chamber, thermal energy generated in correspondence with an instantaneous value of electrical input signals by an electrothermal transducer coupled to said thermal chamber in such a manner as to transmit the thermal energy to the liquid contained in said thermal chamber thereby instantaneously forming bubbles in said liquid, and thus applying a force, fesulting from a state change involving instantaneous volumetric change of said bubbles and sufficient to cause a liquid droplet to be projected from the orifice against the surface tension of said liquid at said orifice, to the liquid present between said chamber and said orifice; and

replenishing the thermal chamber with the liquid from a reservoir therefor when said force is instantaneously attenuated after the projection of the droplet from said orifice

Still another object of the present invention is to provide a liquid jet recording process for recording with liquid droplets, and an apparatus therefor, comprising the steps of:

projecting a liquid from an orifice communicating with a thermal chamber by maintaining the same under pressure thereby forming a stream of said liquid directed toward a surface of a record-receiving member;

applying to the liquid contained in said thermal chamber thermal energy generated according to optical input signals by a photothermal transducer coupled to said thermal chamber in such a manner as to transmit the thermal energy to the liquid contained in said thermal chamber thereby instantaneously forming bubbles in said liquid. and applying a periodical force resulting from periodical state change involving instantaneous volumetric change of said bubbles to said liquid stream thereby breaking up said stream into a succession of evenly spaced uniform separate droplets; and

selectively charging and deflecting the droplets in said succession to deposit on said record-receiving member, or intercepting said droplets, thereby causing selective deposition onto said record-receiving member.

A still another object of the present invention is to provide a liquid jet recording process for recording with liquid droplets. and an apparatus therefor, comprising the steps of:

applying to a liquid contained in a thermal chamber, each time a droplet is to be projected from an orifice communicating with said thermal chamber toward a surface of a record-receiving member, thermal energy generated in correspondence with an instantaneous value of optical input signals by a photothermal transducer coupled to said thermal chamber in such a manner as to transmit the thermal energy to the liquid contained in said thermal chamber thereby instantaneously forming bubbles in said liquid, and thus applying a force, resulting from a state change involving instantaneous volumetric change of said bubbles and sufficient to cause the liquid droplet to be projected from the orifice against the surface tension of said liquid at said orifice, to the liquid present between said chamber and said orifice; and

replenishing the thermal chamber with the liquid from a reservoir therefor when said force is instantaneously attenuated after the projection of the droplet from said orifice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the principle of the present invention;

FIGS. 2 to 5 are schematic views showing preferred embodiments of the present invention;

FIGS. 6 and 7 are schematic views showing representative examples of recording head constituting a principal component in the present invention;

FIGS. 8(a), (b) and (c) are schematic cross-sectional views of nozzles of other preferred recording heads;

FIGS. 9(a), (b) and (c) are schematic views of a preferred embodiment of multi-orificed recording head wherein (a), (b) and (c) are a front view, a lateral view and a cross-sectional view along the line X--Y in (b), respectively;

FIGS. 10(a) and (b) are schematic views of an another preferred embodiment of multi-orificed recording head wherein (a) and (b) are a schematic perspective view and a cross-sectional view along the line X'-Y' in (a), respectively;

FIG. 11 to 14 are views of still another preferred embodiment of a multi-orificed recording head wherein

FIG. 11 is a schematic perspective view, FIG. 12 is a schematic front view, FIG. 13 is a partial cross-sectional view along the line X1--Y1 in FIG. 11 for showing the internal structure and FIG. 14 is a partial cross-sectional view along the line X2--Y2 in FIG. 13;

FIG. 15 is a chart showing the relationship between the energy transmission and the temperature difference .DELTA.T between the surface temperature of a heating element and the boiling temperature of the liquid;

FIG. 16 is a block diagram showing an example of control mechanism for use in recording with a recording head shown in FIG. 6;

FIG. 17 is a block diagram showing an example of control mechanism for use in recording with a recording head shown in FIG. 11;

FIG. 18 is a timing chart showing the buffer function of a buffer circuit shown in FIG. 17;

FIG. 19 is a timing chart showing an example of the timing of signals to be applied to the electro-thermal transducers shown in FIG. 17;

FIG. 20 is a view of an example of printing obtainable in the above-mentioned case;

FIG. 21 is a block diagram showing an another example of control mechanism for use in recording with a recording head shown in FIG. 11;

FIG. 22 is a timing chart showing the buffer function of a column buffer circuit shown in FIG. 21;

FIG. 23 is a timing chart showing an example of the timing of signals to be applied to the electro-thermal transducers in the case of FIG. 21;

FIG. 24 is a view of an example of printing obtainable in the above-mentioned case;

FIGS. 25 to 27 are schematic perspective views of still other embodiments of the recording apparatus of the present invention;

FIG. 28 is a partial perspective view of still another preferred embodiment of the recording head constituting a principal component in the present invention; and

FIG. 29 is a cross-sectional view along the line X"--Y" in FIG. 28.

DETAILED DESCRIPTION OF THE INVENTION

The liquid jet recording process of the present invention is advantageous in easily allowing high-density multi-orificed structure which permits ultra-high speed recording, providing a clear image of improved quality without satellite dots or background fog, and further allowing arbitrary control on the quantity of projected liquid as well as the dimension of droplets through the control of thermal energy to be applied per unit time. Also the apparatus embodying the above-mentioned process is characterized in an extremely simple structure easily allowing minute working and thus permitting significant size reduction of the recording head itself constituting the essential part in the apparatus, also in the case of obtaining a high-density multi-orifice structure indispensable for high-speed recording based on said simple structure and easy mechanical working, and further in the freedom of designing the orifice array structure in any desired shape in preparing a multi-orificed head permitting easy obtainment of a recording head in a form of a full-line bar.

OUTLINE OF THE INVENTION

The outline of the present invention will be explained in the following with reference to FIG. 1 which is an explanatory view showing the basic principle of the present invention.

In a nozzle 1 there is supplied a liquid 3 under a determined pressure P generated by a suitable pressurizing means such as a pump, said pressured being either enough for causing said liquid to be emitted from an orifice 2 against the surface tension of said liquid at said orifice or not enough for causing such emission. If thermal energy is applied to the liquid 3a present in a portion of a width .DELTA.l (thermal chamber portion) located in said nozzle 1 at a distance l from the orifice 2 thereof, a vigorous state change of said liquid 3a causes the liquid 3b contained in the width l of nozzle 1 to be projected partly or substantially entirely, according to the quantity of thermal energy applied, from said orifice 2 and to fly toward a record-receiving member 4 for deposition in a determined position thereon.

More specifically the liquid 3a present in said thermal chamber portion .DELTA.l, when subjected to thermal energy, causes an instantaneous state change of forming bubbles at a side thereof receiving said thermal energy, and the liquid 3b present in the width l is partly or substantially entirely projected from the orifice 2 by means of the force resulting from said state change. Upon termination of supply of thermal energy or upon immediate replenishment of liquid of an amount emitted, the bubbles formed in the liquid 3a are instantaneously reduced in size and vanish or contract to a negligible dimension.

The liquid of an amount corresponding to the emitted amount is replenished into the nozzle 1 by volumetric contraction of bubbles or by a forced pressure.

The dimension of droplets 5 projected from the orifice 2 depends on the quantity of thermal energy applied, width .DELTA.l of the portion 3a subjected to the thermal energy in the nozzle 1, internal diameter d of nozzle 1, distance l from the orifice 2 to the position of action of said thermal energy, pressure P of the liquid, and specific heat, thermal conductivity and thermal expansion coefficient of the liquid. It is therefore easily possible to control the dimension of the droplets 5 by changing one or two of these factors and thus to obtain a desired diameter of droplet or spot on the record-receiving member 4. Particularly a change in distance l, namely in the position of action of thermal energy during the recording allows arbitrary control of the size of droplets 5 projected from the orifice 2 without altering the quantity of thermal energy applied per unit time, thereby allowing easy obtainment an image with gradation.

According to the present invention, the thermal energy to be applied to the liquid 3a present in the thermal chamber portion .DELTA.l of the nozzle 1 may either be continuous in time or be intermittent pulsewise.

In case of pulsewise application it is extremely easy to control the size of droplets and the number thereof generated per unit time through suitable selection of the frequency, amplitude and width of pulses.

Also in case of energy application discontinuous in time, the thermal energy to be applied may be modulated with the information to be recorded. Namely by applying thermal energy pulsewise according to the recording information signals it is rendered possible to cause all the droplets 5 emitted from the orifice 2 to carry recording information and thus to achieve recording by depositing all such droplets onto the record-receiving member 4.

On the other hand, in case of discontinuous energy application without modulation by the recording information, the thermal energy is preferably applied repeatedly with a certain determined frequency.

The frequency in such case is suitable selected in consideration of the species and physical properties of the liquid to be employed, shape of nozzle, liquid volume contained in the nozzle, liquid supply speed into the nozzle, diameter of orifice, recording speed etc., and is generally selected within a range from 0.1 to 1000 KHz, preferably from 1 to 1000 KHz and most preferably from 2 to 500 KHz.

The pressure applied to the liquid 3 in this case may be selected either at a value causing emission of liquid 3 from the orifice 2 even in the absence of effect of said thermal energy, or at a value not causing such emission if without said thermal energy. In either case it is possible to cause projection of a succession of droplets of a desired diameter at a desired frequency by repeated volumetric changes resulting from bubble formation of the liquid 3a in the thermal chamber portion .DELTA.l under the effect of thermal energy or by a vibration resulting from repeated volumetric changes in thus formed bubbles.

The liquid droplets projected in the above-explained manner are subjected to control by electrostatic charge, electric field or air flow according to the recording information to achieve recording.

In case of thermal energy application that is continuous in time, the size of droplets and the number thereof generated per unit time are, as confirmed by the present inventors, principally determined by the amount of thermal energy applied per unit time, pressure P applied to the liquid present in the nozzle 1, specific heat, thermal expansion coefficient and thermal conductivity of said liquid and the energy required for causing the droplet to be projected from the orifice 2. It is therefore possible to control said size and number of droplets by controlling, among the above-mentioned factors, the amount of thermal energy per unit time and/or the pressure P.

In the present invention the thermal energy applied to the liquid 3 is generated by supplying a thermal transducer with a suitable energy. Said energy may be in any form as long as it is convertible to thermal energy, but preferably is in the form of electric energy in consideration of easy of supply, transmission and control, or in the form of energy from a laser in consideration of the advantages such as a high converting efficiency, possibility of concentating a high energy into a small target area, potential for miniaturization and ease of supply, transmission and control.

In case of using electric energy the above mentioned transducer is an electrothermal transducer which is provided, either in direct contact or via a material of a high thermal conductivity, on the internal or external wall of the thermal chamber portion .DELTA.l of the nozzle 1 in such a manner that the liquid 3a can be effectively subjected to the thermal energy generated by said electrothermal transducer provided at least in a portion of the internal or external wall of said thermal chamber portion.

In case of using laser energy, the above-mentioned transducer may be the liquid 3 itself or may be another element provided on said nozzle 1.

For example a liquid 3 containing a material generating heat upon absorption of laser energy directly absorbs the laser energy to cause a state change by the resulting heat, thereby causing the projection of droplets from the nozzle 1. Also for example, a layer generating heat upon absorption of laser energy, if provided on the external surface of nozzle 1, transmits the heat generated by the laser energy through the nozzle 1 to the liquid 3, thereby causing a state change therein and thus projecting droplets from the nozzle 1.

The record-receiving member 4 adapted for use in the present invention can be any material ordinarily used in the technical field of the present invention.

Examples of such record-receiving member are paper, plastic sheet, metal sheet and laminated materials thereof, but particularly preferred is paper in consideration of recording properties, cost and handling. Such paper can be, for example, ordinary paper, pure paper, light-weight coated paper, coated paper, art paper etc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now there will given a detailed explanation on the preferred embodiments of the present invention, while making reference to the attached drawings.

Referring to FIG. 2 showing in a schematic view an embodiment suitable for droplet on-demand recording utilizing electric energy as the source of thermal energy, the recording head 6 is provided, at a fixed position on the nozzle 7, with an electrothermal transducer 8 such as a so-called thermal head encircling the thermal chamber portion The nozzle 7 is supplied with a liquid recording medium 11 from a liquid reservoir 9 under a determined pressure through a pump 10 if necessary.

A valve 12 is provided to control the flow rate of liquid 11 or to block the flow thereof to the nozzle 7.

In the embodiment of FIG. 2 the electrothermal transducer 8 is provided at a determined distance from the front end of nozzle 7 and in intimate contact with the external wall thereof, and said contact can be made more effective by interposing a material of a high thermal conductivity therebetween or by preparing the nozzle itself with a material of a high thermal conductivity.

Though in said embodiment the electrothermal transducer 8 is fixedly mounted on the nozzle 7, it is also possible to suitably control the size of droplets of liquid 11 projected from the nozzle 7 by rendering said transducer displaceable on the nozzle 7 or by providing additional electrothermal transducers in other positions.

The recording in the embodiment shown in FIG. 2 is achieved by supplying recording information signals to a signal processing means 14 and to convert said signals into pulse signals, and applying thus obtained pulse signals to the electrothermal transducer 8

Upon receipt of said pulse signals corresponding to said recording information signals, the electro-thermal transducer 8 instantaneously generates heat which is applied to the liquid 11 present in the thermal chamber portion coupled with said transducer 8. Under the effect of thermal energy the liquid 11 instantaneously undergoes a state change which causes the liquid 11 to be projected from an orifice 15 of the nozzle 7 in the form of droplets 13 and to be deposited on a record-receiving member 16.

The size of droplets 13 projected from said orifice 15 depends on the diameter of orifice 15, quantity of liquid present in the nozzle 7 and in front of the position of electrothermal transducer 8, physical properties of the liquid 11 and the magnitude of electric pulse signals.

Upon projection of droplets 13 from the orifice 15 of nozzle 7, the nozzle 7 is replenished, from the reservoir 9, with the liquid of an amount corresponding to the projected amount In this case the time required for said replenishment has to be shorter than the interval between succeeding electric pulses.

After a part of substantially all of the liquid present from the position of electrothermal transducer 8 to the front end of nozzle 7 is emitted therefrom by a state change in said thermal chamber portion upon transmission of thermal energy from said transducer 8 to the liquid 11, and simultaneously with the instantaneous replenishment of liquid from the reservoir 9 through a pipe, the area in the vicinity of said electrothermal transducer 8 proceeds to resume the original thermal stationary state until a next electrical pulse signal is applied to the transducer 8.

In case the recording head 6 is composed of a single head as shown in FIG. 2, a scanning for recording can be achieved by selecting the displacing direction of the recording head 6 orthogonal to that of record-receiving member 16 in the plane thereof, and in this manner it is rendered possible to achieve recording on the entire surface of the record-receiving member 16. Further the recording speed can be increased by the use of multi-orificed structure in the recording head 6 as will be explained later, and the displacement of recording head 6 during the recording can be eliminated by the use of full-line bar structure in which a number of nozzles are arranged in a l