JP2000094690A - Ink jet recording head, ink jet recording method and ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ink jet recording head in which the problem of insufficient ink supply due to a bubble in an ink jet recording head can be solved without using a vacuum suction system, and ink jet recorder and recording method employing it. SOLUTION: The ink jet recording head 100 comprises openings 106 for ejecting ink 102 to an image recording material 110, ink channels 112 communicating with the ink ejection openings 106, and means 104 for ejecting ink 102 in response to an image signal wherein at least a pair of electrodes 114a, 114b are arranged on the side wall of the ink channel 112.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording head for recording an image by discharging ink, an ink jet recording method using the ink jet recording head, and an ink jet recording apparatus. The present invention relates to an ink jet recording head capable of preventing an ink jet recording head from flowing near an ink ejection port, an ink jet recording method using the ink jet recording head, and an ink jet recording apparatus.

[0002]

2. Description of the Related Art Ambient atmosphere is dissolved in ink in an ink jet recording head depending on the solubility of a gas in the ink, and exists as a dissolved gas. Therefore, when the dissolved gas is in a supersaturated state due to a change in temperature or pressure in the surrounding environment, bubbles are generated in the ink jet recording head.

The generation of bubbles has various adverse effects on the printing performance of an ink jet recording head as described below.

[0004] When air bubbles stay in the ink flow path and the size of the air bubbles becomes equal to or larger than the size of the ink flow path provided in the ink jet recording head, the ink supply becomes insufficient, and in the worst case printing becomes impossible. Fall into.

In an ink jet recording system in which ink is pressurized by a pressure generating means such as a heating element or an electrostrictive element disposed in a pressure chamber and an ink drop is ejected from an ejection port, if bubbles exist in the pressure chamber, the ink is originally The pressure to be applied to the ink may not be sufficiently transmitted to the ink in the vicinity of the discharge port due to the compression of the air bubbles, and ink discharge failure may occur.

Japanese Patent Laid-Open Nos. 62-113556 and 63-2952 disclose a means for solving the problems caused by bubbles present in the ink in the ink jet recording head.
There is a so-called vacuum suction method proposed in Japanese Patent Application Publication No. 65-65 and the like. This is to cover the entire end surface of the ink jet recording head body where the ink is exposed on each nozzle (ejection port) surface with a cap, place the inside of the cap in a negative pressure state, and suck and remove bubbles in the ink jet recording head together with the ink. .

[0007]

The vacuum suction system has the following problems (1) to (4). Since a pump mechanism for bringing the inside of the cap into a negative pressure state is required, it becomes an obstacle to miniaturization of the apparatus and leads to an increase in cost. Since a large amount of ink is sucked at the same time as air bubbles are sucked, a drain ink tank for holding the discharged ink is required, which hinders miniaturization of the apparatus.

Although it is possible to return the discharged ink to the ink jet recording head and use it again for printing, it is usually discarded because the mechanism for this is complicated, leading to an increase in printing cost. The ink is adhered to the nozzle surface after the suction is completed because the air bubbles in the ink jet recording head are sucked together with the ink by sealing with a cap. The ink adhered to the nozzle surface is wiped off by the wiper member (wiping step). However, it is known that this wiping process creates new problems. That is, a thin layer of lyophobic treatment or a thin layer of lyophilic treatment is usually provided on the nozzle surface. However, there is a problem that these treated thin layers may be worn or peeled off by wiping. In addition, there is also a problem that unnecessary substances (dust, dirty ink, etc.) may be pushed into the nozzles as a result of sliding in close contact with the nozzle surface.

When a printer which has been in a stopped state, especially a stopped state for a long time (several days or more) is started to perform a recording operation, the above-described series of steps for removing bubbles is complicated and time-consuming. However, there is a problem that the waiting time until the print is obtained becomes long. Therefore, the present invention has been made in order to solve the above technical problems, an ink jet recording head that can solve the problems caused by bubbles in the ink jet recording head without using a vacuum suction system, An object of the present invention is to provide an ink jet recording method and an ink jet recording apparatus using an ink jet recording head.

[0010]

The above object is achieved by the present invention described below. That is, a first aspect of the present invention is an inkjet apparatus comprising: an ink ejection port for ejecting ink to an image recording material; an ink flow path communicating with the ink ejection port; and an ink ejection unit for ejecting ink in accordance with an image signal. An ink jet recording head, wherein at least a pair of electrodes facing each other is disposed on a side wall of the ink flow path.

According to the first aspect of the present invention, by applying a voltage between the pair of electrodes to generate an electric field in the ink flow path, bubbles existing in the ink are subjected to dielectric polarization on the surface thereof. Of the ink, and repulsion by an electric field from the pair of electrodes prevents the ink from flowing in the flow direction. Therefore, intrusion of bubbles into the vicinity of the ink ejection port such as the pressure chamber is prevented.

According to a second aspect of the present invention, there is provided the ink jet recording head according to the first aspect of the present invention, wherein a surface of the pair of electrodes is covered with a protective layer.

According to the ink jet recording head of the second aspect of the present invention, by insulating the ink and the electrode,
The reaction between the two can be prevented, and when an ink having a relatively low electric resistance is applied, unnecessary current can be prevented from flowing through the ink.

According to a third aspect of the present invention, there is provided the ink jet recording head according to the first or second aspect of the present invention, wherein the shape of the section in the ink flow path where the pair of electrodes is disposed advances in the ink flow direction. Accordingly, the shape is such that the opening area of the ink flow path is continuously reduced.

According to the ink jet recording head of the third aspect of the present invention, the pair of electrodes are arranged on the side wall of the ink flow path having such a shape that the opening area of the ink flow path decreases continuously as the ink flows in the ink flow direction. As a result, the gap between the two electrodes becomes narrower in the ink flow direction, and the electric field generated when a voltage is applied between the two electrodes becomes weaker toward the upstream in the ink flow direction. By forming such a non-uniform electric field, the bubbles existing in the ink are more strongly affected by the repulsive force of the electric field from the pair of electrodes, and are prevented from proceeding in the ink flow direction. Intrusion of bubbles into the vicinity of the outlet is more effectively prevented.

According to a fourth aspect of the present invention, there is provided the ink jet recording head according to any one of the first to third aspects, wherein the ink jet recording head is located upstream of the pair of electrodes in the ink flow direction, It is characterized by having a bubble trap structure.

According to the ink jet recording head of the fourth aspect of the present invention, the bubbles which are repelled by the pair of electrodes and are prevented from proceeding in the ink flow direction are captured by the bubble trap structure. Therefore, the intrusion of bubbles into the vicinity of the ink discharge port such as the pressure chamber is effectively prevented for a long period of time.

According to a fifth aspect of the present invention, there is provided the ink jet recording head according to the fourth aspect of the present invention, wherein the bubble trapping structure has a shape of a private room capable of containing bubbles, and a wall contacting the ink in the private room has an ink-repellent surface. It is characterized by being processed.

According to the ink jet recording head of the fifth aspect of the present invention, the air bubbles are easily adsorbed to the wall of the private room, and the effect of capturing the air bubbles is further improved.

According to a sixth aspect of the present invention, there is provided the ink jet recording head according to the fourth or fifth aspect of the present invention, further comprising a vent hole communicating the bubble trap structure with the outside, and a valve capable of opening and closing the vent hole. It is characterized by having means.

According to the ink jet recording head of the sixth aspect of the present invention, the bubbles accumulated in the bubble trap structure can be released by opening the valve means automatically at a predetermined timing or manually. It is possible to prevent a problem that bubbles accumulated in the bubble trap structure overflow due to use of the period. Therefore, according to the configuration of the sixth aspect of the present invention, it is possible to provide an ink jet recording head which is semipermanent and free from troubles due to bubbles.

According to a seventh aspect of the present invention, there is provided the ink jet recording head according to any one of the first to sixth aspects, wherein ink is supplied to an ink flow path of the ink jet recording head, and ink is ejected in accordance with an image signal. An ink jet recording method in which ink is ejected from an ink ejection port by means for performing recording, wherein a voltage is applied between a pair of electrodes in the ink jet recording head to generate an electric field in an ink flow path. Is the way.

According to the ink jet recording method of the seventh aspect of the present invention, a voltage is applied between a pair of electrodes provided on the ink flow path side wall of the ink jet recording head to generate an electric field in the ink flow path. Bubbles present in the ink are biased by dielectric polarization on the surface of the air bubbles, receive repulsion by an electric field from a pair of electrodes, hinder the ink flow in the flow direction, and cause ink bubbles near the ink discharge ports such as pressure chambers. Air bubbles are prevented from entering the space.

An eighth aspect of the present invention is the ink jet recording method according to the seventh aspect, wherein the voltage applied to the pair of electrodes is an AC voltage and the electric field generated in the ink flow path is an AC electric field. Features.

According to the eighth aspect of the ink jet recording method of the present invention, even when an ionized component or a charged component is present in the ink, the component remains on the electrode or on the protective layer covering the electrode. There is no accumulation, and no change in the ink components.

According to a ninth aspect of the present invention, there is provided a conveying means for conveying an image recording medium, an ink jet recording head for ejecting ink to the image recording medium conveyed by the conveying means to record an image, and an ink jet recording head. An ink jet recording apparatus comprising: an image signal input unit for inputting an image signal to the head; wherein the ink jet recording head is the ink jet recording head according to any one of the first to sixth aspects of the present invention. Device.

According to the ninth aspect of the ink jet recording apparatus of the present invention, since the ink jet recording head to be used is any one of the first to sixth ink jet recording heads of the present invention, a discharge chamber such as a pressure chamber is formed. Air bubbles are prevented from entering the vicinity of the outlet, and defects such as ink ejection failure due to air bubbles are less likely to occur.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to embodiments. FIG. 1 is an enlarged cross-sectional view illustrating an operation state of a recording head 100 according to the first embodiment as an example of an inkjet recording head (hereinafter, may be abbreviated as “recording head”) of the present invention.

Inside the recording head 100, an ink flow path 112 is formed from an ink tank (not shown) to a discharge port (ink discharge port) 106, and an ink flow is generated in the direction of arrow A. 1 (in FIG. 1, the ink flow path 112 is indicated by a reference numeral indicating only that area, but the ink flow path 112 indicates a communication hole inside the recording head 100 through which the ink 102 flows in the area. .
Hereinafter, the same applies to the case of “ink flow path”. ).

The ink flow path 112 is partitioned by a partition wall 122 on the downstream side in the direction of arrow A, and is divided into individual ink flow paths 112b provided corresponding to the respective ejection ports 106. The undivided ink flow path 112 upstream of the position where the partition wall 122 is provided is referred to as a common ink flow path 112a. In addition, the individual ink channel 11
Although the number of 2b is three in FIG. 1, it can be set as needed. The ink flow path 112
The shape of the opening (cross section perpendicular to the direction of arrow A) can be any shape such as a circle, a rectangle, and a hexagon.

A heating element 104 serving as an ink ejection means is disposed on a side wall in front of the ejection port 106 in the direction of arrow A of the individual ink flow path 112b (the periphery of the heating element 104 in the individual ink flow path 112b is called a pressure chamber 120). In some cases).
In the present embodiment, the heating element 104 is used as the ink discharge means. However, the present invention is not limited to this, and the present invention is not limited to this. Japanese Patent Application Laid-Open No. 506014, Japanese Patent Application Laid-Open No. 10-138494, and a method using a wave concentration method (Japanese Patent Application Laid-Open No. 6-115069). Can be adopted. Of these, those using the electrostatic suction method or the wave concentration method do not require a pressure chamber, so even if bubbles are generated, the problem of ejection failure due to mixing of the bubbles into the pressure chamber does not occur,
There is a possibility that air bubbles may stay in the ink flow path and hinder the supply of ink, and such a problem is solved by applying the present invention.

The ink flow path 112 in the recording head 100 is filled with the ink 102, and the ink 102, which has obtained the discharge energy (pressure) from the heating element 104, is dropped at the discharge port 106, forming an ink droplet 108, An image is recorded by landing on a recording material (image recording material) 110.

In this embodiment, the individual ink flow paths 112
b, a pair of opposing electrodes 11 at the most upstream side in the arrow A direction.
4a and 114b are provided. Electrodes 114a, 11
The shape of the individual ink flow path 112b in the section in which the ink flow path 4b is provided is such that the opening area of the ink flow path decreases continuously as it proceeds in the direction of arrow A (in the case where the shape of the opening is circular). Are in the shape of a trumpet), and the electrodes 114a, 114b
Are arranged. Accordingly, the gap between the electrodes 114a and 114b becomes narrower in the direction of arrow A.
Then, protective layers 116a and 116b are formed on the respective surfaces of the electrodes 114a and 114b. (Note that, in FIG. 1, to avoid complication of the drawing, reference numerals are given only to the electrodes and the protective layers disposed in the uppermost individual ink flow channel 112 b in the drawing, but other individual ink flow channels 112 b Are assigned the same reference numerals.)

When ink jet recording is performed using the recording head 100 of the present embodiment, the electrodes 114a, 114b
A voltage is applied between these by a predetermined power supply means, and as a result, a bubble inflow prevention electric field, which is a non-uniform electric field, is formed in the ink flow path. The bubble inflow prevention electric field in the present embodiment is:
The electric field on the downstream side (discharge port side) of the ink flow path 112 is strong and the upstream side (the common ink flow path 112a side) is weaker than the ink flow direction (the direction of arrow A in FIG. 1).

The action of the bubble inflow prevention electric field will be described with reference to FIG. 2 which is a schematic enlarged view around the electrodes 114a and 114b of the individual ink flow path 112b. FIG. 2 schematically shows a case in which the upper electrode 114a is used as a positive electrode.

Under the influence of a bubble inflow prevention electric field formed by the voltage applied between the electrodes 114a and 114b,
On the surface of the bubble 118 that has flowed into the individual ink flow channel 112b, a bias of charge occurs due to dielectric polarization, and a positive charge is applied to the positive electrode side (electrode 114a side) of the bubble 118 surface and a negative electrode side (electrode 114b side). Has a negative charge distribution. This is because the dielectric constant of the ink 102 surrounding the bubble 118 is larger than the dielectric constant of the bubble 118. As a result, bubbles 11
8 receives a repulsive force from both the electrodes 114a and 114b, and receives a force (called dielectrophoretic force) from the strong electric field side to the weak electric field side as a resultant force. Therefore, the bubble inflow prevention electric field always generates an acting force on the bubble 118 from the strong electric field side to the weak electric field side. As described above, the bubble inflow prevention electric field acts on the bubble 118, and the bubble 118 receives a force on the weak electric field side, that is, on the upstream side in the ink flow direction, and is prevented from proceeding in the ink flow direction. 1 prevents the bubbles 118 from entering the vicinity of the discharge port 106 such as between the right ends of the electrodes 114a and 114b in the individual ink flow path 112b and the discharge port 106).

In this embodiment, the electrodes 114a, 114
By continuously changing the gap between b and b in the ink flow direction, a strong bubble inflow prevention electric field composed of the strong electric field side and the weak electric field side is forcibly formed.
The bubbles 118 present therein receive a stronger repulsive force due to the electric field from the electrodes 114a and 114b, and are prevented from proceeding in the ink flow direction (the direction of the arrow A in FIG. 1).
Intrusion of the bubble 118 into the vicinity of the discharge port 106 such as 0 is more effectively prevented.

When there are ionized components or charged components in the ink 102, these components receive a Coulomb force along the direction of the electric field, and the positively charged component is placed on the negative electrode side. In addition, the negatively charged component migrates to the positive electrode side (this phenomenon is called "electrophoresis"). As a result, the protective layers 116a, 116b covering the surfaces of the electrodes 114a, 114b or the electrodes 114a, 114b.
Unnecessary deposits are formed on the surface b, and at the same time, the ink components are changed. Therefore, it is desirable that the electrophoresis does not occur by setting the bubble inflow prevention electric field to an alternating electric field in which positive and negative are alternately reversed, and it is desirable that the voltage applied to the electrodes 114a and 114b is an alternating voltage. .

The frequency of the AC voltage (electric field) can be applied in the range of several Hz to several MHz. However, if the frequency is too low, the problem caused by the electrophoresis phenomenon cannot be avoided. If the frequency is too high, the power supply becomes expensive, which is not preferable. Therefore, the preferred frequency range is 10 Hz to
1 MHz, more preferably 50 Hz to 500 kHz.
z. The waveform of the AC voltage (electric field) is not particularly limited, and any waveform such as a triangular wave, a sine wave, a rectangular wave, and a sawtooth wave can be selected.

The amplitude of the AC voltage (electric field) depends on the size of the bubble, the viscosity of the ink, the relative permittivity of the ink, the flow rate of the ink,
It is determined in consideration of the size of the ink flow path, electrode shape, and the like. The repulsive force acting on the bubbles increases as the rate of change of the square of the electric field intensity (grad (E ² )) increases. The larger the amplitude of the applied voltage is, the easier the head design and the parameter design to increase (grad (E ² )) are. Therefore, the amplitude is preferably 10 V or more based on 0 V, more preferably 50 V or more. It is. On the other hand, if a too high voltage is applied, power consumption increases, and there is a possibility that a signal for controlling the ejection unit may be adversely affected. Therefore, the amplitude is 1000 V or less based on 0 V, and more preferably 300 V or less.

In this embodiment, the electrodes 114a, 1
On the surface of the protective layer 14b, as shown in FIGS.
16a and 116b are formed.
This is for preventing a reaction between the electrode 102 and the electrodes 114a and 114b, and for preventing an unnecessary current from flowing through the ink 102 when the ink 102 has a relatively low electric resistance. If the electric resistance of the ink 102 is sufficiently high and a combination of materials that does not cause a reaction even when the electrodes 114a and 114b and the ink 102 come into contact with each other in the presence of an electric field can be selected, the protection layers 116a and 1
16b is not required.

Each of the protective layers 116a and 116b can be formed as a dense layer capable of blocking the contact between the electrode and the ink, and has an electric resistance capable of securing electrical insulation between the electrode and the ink.
Further, it may be formed of a material that does not dissolve in the ink. Examples of materials having such properties include high molecular weight materials such as polyimide resin, polyester resin, polyaramid resin, polysulfone resin, silicone resin, and fluorine-containing resin; silicon oxide, silicon nitride, silicon carbide and compounds thereof;
Examples thereof include materials such as inorganic compounds such as alumina, titanium oxide, titanium nitride, and titanium carbide, and further, compounds and mixtures of these materials, and other conventionally known insulating materials. The protective layers 116a and 116b can be formed by using any of these materials as a coating material by any means.
a, 114b can be formed by coating the surface.

As a specific method of coating the protective layers 116a and 116b, a coating solution is prepared by dissolving the coating material in an appropriate solvent, and the coating solution is applied by dip coating, spray coating, roll coating, or bar coater coating. The electrode 11 is applied by a coating means such as
For example, a method of coating and drying the surfaces of the electrodes 4a and 114b, or a method of forming the above-mentioned coating material on a film and directly affixing the coating material to the surfaces of the electrodes 114a and 114b can be used. Further, it can be formed by a conventionally known thin film forming method such as a CVD method, a sputtering method, or a vacuum evaporation method, and is formed by performing a reaction treatment such as oxidation, carbonization or nitridation on the surfaces of the electrodes 114a and 114b. You can also.

As the ink 102, various inks such as water-based ink, oil-based ink, WAX-based hot-melt ink, and resin-based hot-melt ink can be used. This is because the dielectric constant of each ink varies depending on the frequency of the applied voltage, but is several times to 80 times the dielectric constant of a normal vacuum.
The component 18 is air, oxygen, hydrogen, nitrogen, or the like. In any case, the dielectric constant is substantially equal to the vacuum dielectric constant, and the above-described bubble inflow prevention electric field works effectively.

FIG. 3 shows a recording head 3 according to a second embodiment as another example of the ink jet recording head of the present invention.
It is an expanded sectional view showing the operation state of 00. As with the recording head 100 of the first embodiment, the ink flow path 312 includes a common ink flow path 312a on the upstream side in the direction of arrow B and an individual ink flow path 312b partitioned by a partition wall 314 on the downstream side.
Consists of In this embodiment, the electrodes 314a and 314b are provided only in a narrow area as shown in FIG.

In this embodiment, the individual ink flow path 312b
Are not linearly formed, and are not configured to make the electric field intensity non-uniform by changing the gap between the electrodes 114a and 114b as in the recording head 100 of the first embodiment. The present embodiment is an example in which a local non-uniform electric field is formed in the ink flow path 312 to generate a repulsive force on the bubble 318. In the case of the present embodiment, the bubbles 318
14a and 314b, the electric field suddenly changes (increases).
Bubbles can be prevented from flowing into 12b. According to the configuration of the present embodiment, the configuration of the ink flow path 312 is simple, and the size of the electrodes 314a and 314b can be reduced, so that the overall size can be reduced.

The structure of the members constituting the second embodiment,
The shape and material, and the operation and effects of the second embodiment are the same as those of the first embodiment except for those specific to the second embodiment described above.

FIG. 4 shows a recording head 4 according to a third embodiment as another example of the ink jet recording head of the present invention.
It is an expanded sectional view showing the operation state of 00. Recording head 4
Inside 00, an ink flow path 412 is formed to connect from an ink tank (not shown) to a discharge port (ink discharge port) 406 formed in the nozzle plate 430 so that ink flows in the direction of arrow C. Has become. This ink channel 4
Numeral 12 is partitioned by a partition wall (not shown) on the downstream side in the direction of arrow C, and a plurality of individual ink channels 412b provided corresponding to the plurality of ejection ports 406 in the depth direction of the drawing are formed. That is, the present embodiment also has a plurality of discharge ports as in the first embodiment, and when viewed from the relation with the discharge ports,
FIG. 4 is different from FIG. 1 showing the first embodiment in that the direction of the cross section of the recording head is perpendicularly different. The undivided ink flow path 412 upstream of the position where the partition wall is provided is referred to as a common ink flow path 412a.

On the side wall of the individual ink flow path 412b, a heating element 404 serving as an ink discharging means is disposed (the heating element 404 in the individual ink flow path 412b is surrounded by the pressure chamber 4).
20). The ink 402 is filled in the ink flow path 412 in the recording head 400,
The ink 402 that has obtained the discharge energy (pressure) from the nozzle 4 is dropped at the discharge port 406 and becomes an ink droplet 408.
An image is recorded by landing on a recording material (image recording material) 410.

A pair of electrodes 414a and 414b facing each other are disposed downstream of the common ink flow path 412a in the direction of arrow C. The shape of the common ink flow path 412a in the section where the electrodes 414a and 414b are provided is such that the opening area of the ink flow path decreases continuously as it proceeds in the direction of arrow C. Individual ink channel 41
Electrodes 414a and 414b are provided on the side wall 2b.
Therefore, the gap between the electrodes 414a and 414b becomes narrower in the direction of arrow C. The electrode 414
a, 414b on the respective surfaces of the protective layers 416a, 41
Although 6b is formed, the protective layers 416a and 416b are not essential, as described in the first embodiment.

In this embodiment, the electrodes 414a, 414
b, and the common ink flow path 412a
And a concave bubble reservoir 42 having a bubble trap structure at a position deviated from a main flow path of the ink 402.
4 are provided. The bubble reservoir 424 has a shape of a private room capable of storing bubbles.

When ink-jet recording is performed using the recording head 400 of the present embodiment, similar to the first embodiment,
A bubble inflow prevention electric field, which is a non-uniform electric field, is formed in the ink flow path 412. However, in the present embodiment, the bubble inflow prevention electric field is formed in the region of the common ink channel 421a.

Therefore, in the present embodiment, it is not necessary to provide the electrodes 414a and 414b for generating a bubble inflow prevention electric field for each individual ink channel 412b, and it is sufficient to provide only the common ink channel 412a. The configuration is simple. Further, the electrode 414b can also be used as a wiring connected to the heating element 404. Note that the electrodes 414a and 414b are preferably arranged near the bubble reservoir 424 so that an electric field acts on the bubble reservoir 424.

In the present embodiment, the electrodes 414a, 414
The bubble 418, which has been prevented from proceeding in the direction of arrow C due to the repulsive force due to the electric field from b, is captured by the bubble pool 424 having a bubble trap structure with the help of the buoyancy of the bubble 418 itself. Therefore, the bubble 418 does not stay in the ink flow path 412, and the intrusion of the bubble 418 into the vicinity of the discharge port 406 such as the pressure chamber 420 can be effectively prevented for a long period of time.

In a print head having a plurality of discharge ports, discharge of ink from a certain ink discharge port causes a pressure fluctuation in the print head, causing the meniscus of another discharge port to vibrate. It is known that ejection is hindered. To suppress this phenomenon, it is known that it is effective to absorb the pressure fluctuation by arranging bubbles in the ink chamber. This embodiment has the effect of preventing ink supply failure due to air bubbles, and can absorb pressure fluctuations in the print head by leaving air bubbles in the print head.

In the present embodiment, as shown in FIG. 5, when a certain amount of bubbles 518 trapped in the bubble trap 524 having a bubble trapping structure accumulates, the valve means 528 is evacuated to release the bubbles. Through the air pocket 524
It is also a preferred embodiment to provide a vent tube 526 that communicates with the air. By opening the valve means 528 automatically at a predetermined timing or manually, the air bubble accumulation 524 is formed.
The bubbles 518 accumulated in the bubble reservoir 524 can be vented, and problems such as the bubbles 518 accumulated in the bubble reservoir 524 overflowing due to long-term use can be prevented. Therefore, by providing the bleeding pipe 526 communicating with the bubble reservoir 524, it is possible to semipermanently provide an ink jet recording head free from trouble due to bubbles.

As the bubble trap structure, a bubble pool 4
It is preferable that a wall surface in contact with the ink 402 in the inside 24 is subjected to an ink-repellent treatment. With this configuration, the bubble 41
8 is easily adsorbed on the wall surface, and the effect of capturing the bubbles 418 is improved. In this ink-repellent treatment, the surface may be coated with a material having a contact angle with the ink 402 of 70 ° or more, preferably 100 ° or more. Generally, a fluororesin-based material is known as a material having ink repellency. For example, any of the following materials can be appropriately selected.

Polytetrafluoroethylene (PTF)
E), specifically, polyflon TFE (manufactured by Daikin Industries, Ltd.) or Teflon TFE (manufactured by Du Pont);
Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), specifically, Neoflon P
FA (manufactured by Daikin Industries, Ltd.) and Teflon PFA (D
uPont); tetrafluoroethylene-hexafluoropropylene copolymer (FEP), specifically, Neoflon FEP (manufactured by Daikin Industries, Ltd.) and Teflon FE
P (manufactured by Du Pont); tetrafluoroethylene-
Hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPE), specifically, Neoflon EPA (manufactured by Daikin Industries, Ltd.) and Teflon EPE (manufactured by Mitsui DuPont Fluorochemicals); tetrafluoroethylene-ethylene copolymer (ETFE) Specifically, Aflon COP (made by Asahi Glass Co., Ltd.) and Tefzel (Du Pont
Porochlorotrifluoroethylene (PCTF)
E), specifically, Neoflon CTFE (manufactured by Daikin Industries, Ltd.) and Kel-F (manufactured by 3M); chlorotrifluoroethylene-ethylene copolymer (ECTFE), specifically, Halar (manufactured by Ausimont NV). ); Polyvinylidene fluoride (PVdF), specifically KF polymer (manufactured by Kureha Chemical Industry Co., Ltd.); polyvinyl fluoride (PVF), specifically Tedlar (Du Pont)
And the like). Recently, a perfluorofluororesin having a cyclic structure in the main chain; specifically, Cytop (manufactured by Asahi Glass Co., Ltd.) or Teflon AF (Du Po
nt). Furthermore, other resins containing a fluorine atom, for example, a fluorinated epoxy resin,
Examples include fluorinated polyimide resins, fluorinated polyamide resins, fluorinated acrylic resins, fluorinated polyurethane resins, fluorinated siloxane resins, and modified resins thereof. On the other hand, a water-repellent agent containing silicon atoms or a silicon-based resin may be used.

The bubble trap structure is not limited to a concave room structure such as the bubble pool 424 shown in FIG. For example,
As shown in a bubble pool 524 shown in FIG.
The structure in which the portion 624a communicating with the second part 624a is narrow and the inside 624b is wide is an advantageous shape because it has an effect that the air bubbles 618 that have been once captured are less likely to flow again.

In the bubble trap structure, it is necessary to provide a bubble pool 424 so that the opening faces a horizontal plane (ground) in order to effectively use the action of buoyancy of the bubble 418 itself. Therefore, in FIG. 4, since the ink droplets 408 are ejected in the right direction parallel to the horizontal plane, the bubble reservoir 424 is opened downward as it is. But,
When this is reversed upside down and the ink droplet 408 is ejected leftward and parallel to the horizontal plane, the common ink flow path 412a
It is necessary to provide a bubble pool at a location on the side wall opposite to the location where the bubble pool 424 is provided in FIG. Considering from such a viewpoint, for example, as shown in FIG. 7, if the recording head 700 according to the present embodiment discharges the ink droplets 708 obliquely downward to the right with respect to the horizontal plane, the shape shown in FIG. 724
It is preferable that the openings face the horizontal plane (the ground).

Therefore, the shape and arrangement of the air bubble reservoirs 424, 624, and 724 as the air bubble trap structure are determined by the inclination of the recording heads 400, 600, and 700 with respect to the horizontal plane.
What is necessary is just to determine suitably according to the shape of the ink flow path 412,612,712.

The structure of the members constituting the third embodiment,
The shape and material, and the operation and effects of the third embodiment are the same as those of the first embodiment, except for those specific to the third embodiment described above.

Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above-described embodiment. For example, the shape and position of the electrode, the application of a voltage, etc. Methods other than those described in the above embodiments can be applied. Further, the present invention is not limited by the ejection means described in the above embodiment.

Further, in the above-described embodiment, the ink discharge ports and the ink discharge direction are all rightward, but the ink jet recording head of the present invention may be in any direction, such as downward, upward, leftward, or intermediate therebetween. May be facing.

The ink jet recording head of the present invention having the above-described structure is a so-called conventional ink jet recording apparatus, that is, a conveying means for conveying an image recording medium, and an ink jet recording medium which is conveyed by the conveying means. It is suitably used in an ink jet recording apparatus comprising: an ink jet recording head for recording an image by discharging ink; and image signal input means for inputting an image signal to the ink jet recording head. In the ink jet recording apparatus using the ink jet recording head of the present invention, the intrusion of bubbles into the vicinity of the discharge port such as the pressure chamber of the ink jet recording head is prevented, and the troubles such as defective ink discharge due to the bubbles hardly occur.

[0066]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples. (Example 1) A printing test was performed by incorporating the ink jet recording head of the present invention into an ink jet recording apparatus of an experimental machine. The ink jet recording head used in the present embodiment has a structure like the recording head 400 shown in FIG. 4, and has a substrate 1 (a member constituting a side wall of the ink flow path 412, on which the heating element 404 is formed). Member on the side with
And the substrate 2 (a member that constitutes the side wall of the ink flow path 412 and is a member on the side where the bubble reservoir (bubble trapping structure) 424 is formed), and the nozzle plate 430. The nozzle plate 430 is made of a nickel plate having a thickness of 50 μm, and has a discharge port 406 having a diameter of 30 μm formed by laser processing. The array density of the ejection ports 406 in the direction perpendicular to the paper surface is 400 nozzles per inch,
Is 160 nozzles.

The substrate 1 and the substrate 2 are made of crystalline Si. On the surface of the substrate 1, a heating element 404, an electric wiring for driving the heating element 404, and the like are formed for each individual ink flow path 412b, and a protection layer 416b is formed on a portion facing the common ink flow path 412a. 414 whose surface is coated with
b is formed. The substrate 2 is provided with a plurality of individual ink flow paths 412 b communicating with the common ink flow path 412 a and a plurality of grooves serving as pressure chambers 420 corresponding to the heating elements 404 formed on the substrate 1. Each part of the substrate 1 and the substrate 2 is adhered so that the ink flow path 412 is not closed,
Sealing is performed so that the ink 402 does not leak outside from a portion other than the ejection port 406.

The electrodes 414a and 414b are formed of a thin film of aluminum, and are formed singly over the ink flowing direction of the recording head 400 (the direction of arrow C). The closest distance between the electrodes 414a and 414b is 25 μm, and the angle between both electrodes is 30 °. Protective layer 416a,
416b was formed by coating a polyimide resin. On the wall surface in contact with the ink 402 in the bubble reservoir (bubble trap structure) 424, CYTOP (manufactured by Asahi Glass Co., Ltd.)
Is coated and treated with ink repellency.

As the ink 402, black ink for an inkjet printer Jet Wind 300C manufactured by Fuji Xerox Co., Ltd. was used. After confirming that there was no abnormality in the printing condition at room temperature of 22 ° C., the environmental temperature was raised to 40 ° C. overnight. After leaving the solution to be in a state where dissolved gas was easily precipitated, image printing was performed without returning the environmental conditions, and the printing state was confirmed. At this time, at the same time when the power of the apparatus is turned on, the electrodes 414a and 414b for forming a bubble inflow prevention electric field have a frequency of 200 Hz and 0V.
A sine-wave AC voltage having an amplitude of 50 V with respect to
Image printing was performed after air bubbles existing in the pressure chamber 420 were discharged in a predetermined idle discharge process. As a result, no printing failure occurred during the printing test of the continuous 20 sheets.

(Comparative Example 1) For comparison, a printing test was performed under the same conditions as in Example 1 using a commercially available ink jet recording apparatus incorporating a conventional ink jet recording head. And dot failure occurred. It was confirmed that the missing dots were the result of air bubbles generated inside the head blocking the ink flow path and obstructing the ink supply, and that the defective dots were caused by bubbles entering the pressure chamber (near the heating element). Was done.

[0071]

As described above, according to the present invention, problems caused by bubbles generated in the ink jet recording head can be solved without using a vacuum suction system. Therefore, according to the present invention, a step such as vacuum suction which has been conventionally performed to remove air bubbles is not required, so that the time required until the start of printing, which was conventionally required, can be greatly reduced, and the ink that is discarded can be eliminated. The disadvantages of using the vacuum suction method, such as a significant reduction in the amount of slag, can be eliminated.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view illustrating an operation state of an inkjet recording head according to a first embodiment.

FIG. 2 is a schematic enlarged view around an electrode of the ink jet recording head of FIG. 1 for explaining the action of a bubble inflow prevention electric field.

FIG. 3 is an enlarged cross-sectional view illustrating an operation state of an inkjet recording head according to a second embodiment.

FIG. 4 is an enlarged sectional view illustrating an operation state of an ink jet recording head according to a third embodiment.

FIG. 5 is an enlarged cross-sectional view illustrating an operation state of an ink jet recording head which is a modification of the third embodiment.

FIG. 6 is an enlarged cross-sectional view illustrating an operation state of an ink jet recording head according to another modification of the third embodiment.

FIG. 7 is an enlarged cross-sectional view illustrating an operation state of an ink jet recording head which is still another modified example of the third embodiment.

[Description of References] 100, 300, 400, 500, 600, 700: Recording Head (Inkjet Recording Head) 102, 302, 402: Ink 104, 304, 404: Heating Element 106, 306, 406: Discharge Port (Ink Discharge) Outlets) 108, 308, 408: Ink droplets 110, 310, 410: Recording material (image recording material) 112, 312, 412, 612, 712: Ink channels 112a, 312a, 412a, 612a, 712a:
Common ink channel 112b, 312b, 412b, 612b, 712b:
Individual ink flow paths 114a, 114b, 314a, 314b, 414a,
414b: electrode 116, 316, 416: protective layer 118, 318, 418, 518, 618, 718: bubble 120, 320, 420: pressure chamber 122, 322: partition 424, 524, 624, 724: bubble pool (bubble trap Structure) 526: Vent tube 528: Valve means

Continuing on the front page (72) Inventor Yasufumi Suwabe 430 Green Tech Nakai, Nakai-cho, Ashigara-kami, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Yuji Suemitsu 430 Green Tech Nakai, Nakai-cho Sakai-Kamigun, Kanagawa Prefecture Fuji Xerox Co., Ltd. 2C057 AF80 AG12 AG29 AG46 AG78 AG90 AG92 AG93 AM03 AM18 BA05 BA13

Claims (9)

[Claims] 1. An ink jet recording head comprising: an ink discharge port for discharging ink onto an image recording material; an ink flow path communicating with the ink discharge port; and ink discharge means for discharging ink in response to an image signal. An ink jet recording head, wherein at least a pair of electrodes facing each other is disposed on a side wall of an ink flow path. 2. The ink jet recording head according to claim 1, wherein a protective layer is coated on a surface of the pair of electrodes. 3. An ink flow path in which a pair of electrodes is disposed has a shape such that the opening area of the ink flow path decreases continuously as the flow proceeds in the ink flow direction. The ink jet recording head according to claim 1 or 2, wherein 4. The ink jet printer according to claim 1, wherein a bubble trap structure is provided upstream of the pair of electrodes in the ink flow direction and on a side wall of the ink flow path. The inkjet recording head according to the above. 5. The ink jet recording head according to claim 4, wherein the bubble trap structure has a shape of a private room capable of containing bubbles, and a wall surface of the private room that contacts the ink is subjected to an ink repellent treatment. . 6. The ink jet recording head according to claim 4, further comprising a vent hole communicating the bubble trap structure with the outside, and a valve means capable of opening and closing the vent hole. 7. An ink jet recording head according to claim 1, wherein ink is supplied to an ink flow path of the ink jet recording head, and the ink is ejected by an ink ejection means in accordance with an image signal. An ink jet recording method for performing recording by discharging ink from a discharge port, wherein a voltage is applied between a pair of electrodes in the ink jet recording head to generate an electric field in an ink flow path. 8. The ink jet recording method according to claim 7, wherein the voltage applied to the pair of electrodes is an AC voltage, and the electric field generated in the ink flow path is an AC electric field. 9. A transport unit for transporting an image recording medium, an inkjet recording head for recording an image by discharging ink onto the image recording medium transported by the transport unit, and an image signal to the inkjet recording head. 7. An ink jet recording apparatus comprising: an image signal input unit for inputting, wherein the ink jet recording head is the ink jet recording head according to any one of claims 1 to 6.