JPH0635179B2 - Inkjet recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording apparatus, and more particularly, to an improvement of an inkjet recording apparatus that ejects ink by utilizing thermal energy and electrostatic energy.

[Prior Art] As a conventional inkjet recording device, a large number of ink ejection devices for sealing ink are provided with ejection ports (orifices) according to the pixel density, and a pressure pulse is appropriately applied to the ink ejection device. It is known that ink is ejected from an ejection port.

In this type, since it is necessary to secure a large volume ratio between the ejection port and the ink ejection device in order to maintain the ejection operation of the ink from the ejection port, it is difficult to miniaturize the ink ejection device. Therefore, the arrangement pitch between the ejection ports must be increased to some extent, and the recording density of the image cannot be set high, and the ink is ejected by mechanical scanning by applying a pressure pulse. Therefore, there is a problem that the recording speed is inevitably decreased.

As a means for solving such a problem, magnetic ink is arranged in the vicinity of the magnetic electrode array, an ink ejection state corresponding to the image density is formed by utilizing the ink rise due to a magnetic field, and the magnetic ink is recorded by an electrostatic field on the recording sheet. A so-called magnetic ink jet method that allows the ink to fly to the side (Japanese Patent Laid-Open No. 55-69469) or a slit-shaped ink reservoir parallel to the electrode array is filled with the ink and is opposed via a recording sheet. A so-called plane scanning ink jet method, in which ink is ejected toward a recording sheet according to an electric field pattern formed between an electrode and an electrode array, is applied (Japanese Patent Laid-Open No. 56-371).
No. 63), or by applying heat energy to the ink, the ink is rapidly heated to cause film surface boiling, and bubbles are rapidly grown in the discharge port (orifice) to increase the pressure. There is provided a so-called thermal bubble jet method (JP-A-55-161664) in which ink is ejected from an ejection port.

In each of the conventional inkjet recording methods described above,
In either case, not only the density of the recorded image can be increased, but also high-speed recording can be performed because electronic scanning is possible.

[Problems to be Solved by the Invention] However, in the case of applying the above-mentioned magnetic ink jet method, it is necessary to use a mixture of magnetic powder as the ink, so that the ink is necessarily black. As a result, it becomes difficult to overprint the ink to obtain a color image. Further, in the application of the above-mentioned plane scanning inkjet method,
Although the clogging of the ink can be improved by eliminating the need for a fine orifice, a high voltage must be applied to cause the ink to fly, so to prevent voltage leakage between adjacent and nearby electrodes. However, it is necessary to drive the electrode array in a time-division manner, which is not preferable for high-speed recording. Further, in the application of the above thermal bubble jet method, it is necessary to rapidly heat and raise the temperature of the heating element in order to cause boiling on the film surface. There is a problem that the heat-induced low antibody protective layer provided as a means is likely to be thermally deteriorated.

In order to solve such a problem, the inventors of the present application filled ink in the ink chamber of the head main body, applied thermal energy according to image information to the ink, and acted a predetermined electrostatic field on the ink surface. Then, a so-called thermal electrostatic ink jet recording apparatus has been already proposed in which the ink portion heated by the attracting force of the electrostatic field is caused to fly to the recording sheet side.

According to this type, there is no need to use a magnetic ink by a so-called magnetic ink jet method, and accordingly, not only can colorization based on overprinting of ink be easily realized, but also a so-called plane scanning ink jet method is required. Since it is not necessary to fly the ink only by the electrostatic field and the strength of the electrostatic field need not be extremely increased, voltage leakage between the vicinity of the ink can be effectively prevented. Since it is not necessary to fly the ink only by the thermal energy, the amount of the thermal energy can be suppressed to some extent, and the thermal deterioration of the ink can be effectively prevented. Therefore, high-speed and high-density recording can be performed while effectively preventing the drawbacks of the conventional methods.

By the way, in such a thermal electrostatic ink jet recording apparatus, the width dimension of the ink flight opening of the ink chamber controls the actual flying range of the ink, and the arrangement density of the recording pixels and the stable flight operation of the ink are stable. However, it is the current situation that no clear standard has yet been grasped as to how much the width dimension of the ink flight opening should be set.

[Means for Solving the Problems] The present invention has been made by paying attention to the above problems, and records the recording pixels at high density while taking advantage of the so-called thermal electrostatic inkjet method. You can, and
(EN) An ink jet recording apparatus that stabilizes the ink flying operation and maintains good recorded image quality.

That is, the present invention relates to a head main body having a narrow ink chamber whose ink flight openings are slits, and an ink unit area corresponding to the pixel density filled in the vicinity of the ink flight openings of the ink chambers. A thermal signal applying unit for appropriately applying a thermal signal corresponding to image information and an electrostatic field forming unit for forming a predetermined electrostatic field between the ink surface and the recording sheet are provided, and the thermal signal is applied based on the electrostatic field. The ink jet recording apparatus is configured to fly the formed ink unit area to the recording sheet side, and the width dimension of the ink flight opening is set under the condition that the pixel density is 8 dots / mm or more.
It is set to 200 μm or less.

In such a technical means, as the head body, for example, a pair of substrates that are substantially orthogonal to the recording sheet surface are opposed to each other,
A device is used in which the ink ejection opening is a slit and forms a narrow ink chamber. The width of the ink jetting opening may be set to 200 μm or less, but it is necessary to set the density of recording pixels to be sufficiently high while ensuring stable ink jetting operation. Is preferably set to 100 μm or less. In this case, when the ink jetting opening is composed of slits, the slits need not be uniform over the entire area and may be non-uniform, but the maximum width of the slits should be 200 μm or less. It is necessary to set.

Further, the heat signal applying means may be one that indirectly heats the ink by using a heat generating array in which a plurality of heat generating low antibodies are arranged according to the pixel density, or has a predetermined resistivity. The one that heats the ink itself by directly energizing it, the one that heats the ink by using a radiation beam such as a laser beam, or the one partition member of the head body is made of a suitable resin material and made of a suitable conductive material. It is possible to appropriately change the design by forming an organic resistance film in which powder is dispersed and contained, and heating the organic resistance film by applying electricity. The heat generating array and the organic resistance film may be provided at a wall portion adjacent to the ink flying surface or at a wall portion facing the ink flying surface as long as the ink portion for flying can be heated. .

Further, of the electrostatic field forming means, the conductive layer formed on the head body side may be set so that the potential of the ink surface is equal to the reference potential. Therefore, if it is provided in a part facing the ink chamber. Good. Also, the electrostatic induction electrode may be appropriately designed by changing the wiring position, shape, size, etc. as long as it is made of a conductive member, but from the viewpoint of simplifying the device configuration, recording It is desirable to use a cylindrical electrode that also serves as a supporting surface of the sheet, and intermittently rotate the cylindrical electrode so that the recording sheet can run. Further, the drive controller may be appropriately changed in design as long as it can apply an electrostatic signal that generates an electrostatic field to the extent that ink can fly.

Furthermore, the ink to be used may be appropriately selected as long as it can fly when a predetermined heat signal is applied. In this case, as a specific ink flight condition, the viscosity and surface tension of the ink are reduced to such an extent that the ink can fly due to the electrostatic field acting, and the conductivity of the ink is improved. It is necessary to be.

[Operation] According to the technical means as described above, since the width dimension of the ink flight opening is set to 200 μm or less, the substantial flight range of the ink is sufficiently narrowed, so that the size of the recording pixel is reduced. Not only can it be set to a sufficiently small value, but the ink portion in the ink ejection opening is surely heated for each pixel density by the heat energy of the heat signal applying means, and the ink temperature distribution tendency is given as a remarkable one. Minutes,
The viscosity, surface tension, conductivity, etc. of the heated ink portion surely changes to a flyable state, and the heated ink portion reliably fly toward the recording sheet by a predetermined electrostatic field.

[Embodiment] The present invention will be described in detail below based on an embodiment shown in the accompanying drawings.

In FIG. 1 and FIG. 2, the ink jet recording apparatus includes a head main body 1 having an ink chamber 2, and a heat signal applying means for applying a heat signal according to image information to the ink 3 contained in the ink chamber 2. 4 and an electrostatic field forming means 6 for forming a predetermined electrostatic field between the surface of the ink 3 and the recording sheet 5.

In this embodiment, as shown in FIG. 2, in particular, the head body 1 has a pair of insulating substrates 11 and 12 made of alumina ceramics, which are spaced apart from each other via a spacer portion 13 provided on either side of the insulating bodies 11 and 12. The narrow ink chamber 2 is secured between the substrates 11 and 12. The outlet portion of the ink chamber 2 is formed as a slit 2a having a width dimension l, specifically 200 μm or less. Further, as the ink 3 contained in the ink chamber 2, for example, an oil-based ink obtained by dissolving a dye in an oil-based solvent such as paraffin or olefin is used, and its physical properties are room temperature (eg, 20 ° C.). 40cps, 1cps when heated (eg 150 ℃)
While having a viscosity of about 30-40 dyne at room temperature
/ Cm and the bulk modulus is about 10 ¹² Ωcm. An ink supply pipe 14 is connected to the ink chamber 2 so as to communicate therewith.
An ink pump and an ink tank (both not shown) are provided in communication with each other, and the ink pump sequentially supplies the ink 3 in the ink tank to the ink chamber 2 through the ink supply pipe 14.

The heat signal applying means 4 is composed of a heat generating array in which heat generating low antibodies 21 made of a Ta ₂ N thin film are arranged for each pixel density (for example, 8 dots / mm). Undergrace layer 22 formed on the inner surface side of insulating substrate 11
It is formed on the upper surface and is disposed so as to face the opening edge of one side surface of the ink chamber 2. Each heating resistor 21 is connected to a pair of energizing electrodes 23. A drive circuit 24 that outputs a drive signal K according to the image information signal G at a predetermined timing is connected to each of the upper air energizing electrodes 23. Incidentally, reference numeral 26
Is an insulating layer such as SiO ₂ for insulatingly covering the upper air heating resistor 21 and each current-carrying electrode 23.

Further, the electrostatic field forming means 6 is provided with a conductive layer 31 made of Cr / Au or the like laminated on the upper insulating layer 26, and is separated from the surface of the ink 3 by a predetermined distance and serves as a support surface of the recording sheet 5. A cylindrical electrode 32 for electrostatic induction that also functions as well as a conductive layer
31 and a drive controller 33 which is interposed between the cylindrical electrode 32 and applies an electrostatic signal B. In this embodiment, an image information signal G synchronized with the upper air drive signal K is input to the upper air drive controller 33, and an electrostatic signal B corresponding to the image information signal G is output from the drive controller 33. It is like this. Further, the rotation of the driving step motor (not shown) is transmitted to the upper air cylindrical electrode 32 via a driving belt (not shown), and the timing when the recording operation of the image information for one line is completed. Thus, the upper air drive motor is appropriately rotated in steps, and the cylindrical electrode 32 is rotated in steps by the recording dot pitch in the circumferential direction.

Therefore, according to the ink jet recording apparatus of this embodiment, when the image information signal G to be recorded is input to the drive circuit 24, the drive circuit 24 outputs the drive signal K to the corresponding heating resistor 21. Is applied. Then, as shown in FIG. 2, the heating resistor 21 generates heat, and the ink unit area M corresponding thereto receives the heat energy Q and is heated. In the heated ink unit area M, the viscosity and the surface tension of the ink 3 are lowered and the conductivity thereof is improved. On the other hand, when the image information signal G is input to the drive controller 33 in synchronization with the drive timing of the upper air heat signal applying means 4,
The electrostatic signal B is output from the drive controller 33, and the cylindrical electrode 32
Applied to. Then, an electrostatic field S is formed between the surface of the ink 3 facing the conductive layer 31 and the cylindrical electrode 32, and the ink unit region M heated based on this electrostatic field S is in front of the electrostatic induction electrode 32. The flying operation is performed toward the recording sheet 5 passing by the side. At this time, as shown by the phantom line in FIG. 2, when the end portion of the ink column 3a that is raised due to the upward flight operation comes into contact with the recording sheet 5, the ink 3 is attached and transferred to the recording sheet 5, and the recording sheet 5 is transferred. Ink dots D are formed on the surface of the ink.

In such a recording operation process, the width dimension 1 of the slit 2a was appropriately changed to examine the pitch interval m of the ink dots D that can be recorded in a good state.
The results shown in the figure were obtained. According to the figure, when the width dimension l of the slit 2a is 200 μm or less, the pitch interval m of the ink dots D is about 1/8 mm, and the recorded image quality is good. When the width dimension 1 of the slit 2a exceeds 200 μm, the pitch interval m of the ink dots D suddenly becomes rough. It was Considering such a result, when the width dimension l of the slit 2a is set narrow, firstly,
The temperature distribution of the ink 3 in the slit 2a is faithful to the heat generation state of the heating resistor 21, and secondly, the maximum value of the wavelength of the ink meniscus generated in the slit 2a portion is exclusively the slit 2a.
Is defined by the extremely small width dimension l of the ink dot D, and the ink dot D group is formed as a high-density one that is faithful to the heat generation pattern.

Further, by appropriately changing the width dimension 1 of the slit 2a, the difference ΔP between the lower limit pressure P _min of the ink 3 with which the slit 2a is filled and the upper limit pressure P _max when the ink 3 flows out is examined. As a result, it was found that ΔP is substantially inversely proportional to the width dimension 1 of the slit 2a, and the narrower the width dimension 1 of the slit 2a is, the larger the pressure difference ΔP becomes. This is because the narrower the width dimension 1 of the slit 2a is, the stronger the capillary force due to the capillary phenomenon is. Therefore, if the pressure difference ΔP is set to be large, first, the ink is controlled when the ink supply is controlled. It is possible to set the supply pressure of the ink to a rough level to some extent, and secondly, the ink meniscus is kept stable even against disturbance. Then, the pressure difference Δ
It is desirable that P is at least about 1 cmH ₂ O. In the ink used in the experiments by the inventors of the present invention, the pressure difference ΔP is about 1 cmH ₂ O when the width dimension 1 of the slit 2a is 200 μm. Was confirmed.

The used ink 3 is an oil-based ink in which a pigment is dispersed or a dye is dissolved in an oil-based medium such as paraffin or olefin and has a viscosity of 20 to 300 c at room temperature (eg, 20 ° C.).
ps, when heated (eg 150 ℃), the viscosity decreases by about one digit, while surface tension is about 30-40dyne / cm at room temperature,
Moreover, when the same experiment as described above was conducted for the one having the physical properties of volume resistivity of about 10 ⁶ to 10 ¹³ Ωcm, the width dimension 1 of the slit 2a was 200 as similar to the above.
It has been confirmed that a high quality and high density image can be obtained if the thickness is less than or equal to μm. Further, as shown in FIG. 5, the same experiment as described above was performed for the type in which the width dimension 1 of the slit 2a changes in a wave shape according to the arrangement position of the heating resistor 21. It has also been confirmed that when the maximum width dimension of the slit 2a is 200 μm or less, a high quality and high density image can be obtained.

[Effects of the Invention] As described above, according to the inkjet recording apparatus of the present invention, the width dimension of the ink ejection opening is set to 200 μm or less on the premise of the so-called thermal electrostatic inkjet method, and Since the target flying range is restricted, the ink dot diameter can be reduced, so that not only the density of recording pixels can be increased, but also the thermal energy from the heat signal applying unit can be increased. Since the corresponding ink portion can be reliably heated by the above, the ink temperature distribution pattern can be made accurate according to the heat generation pattern, and the ink flying operation can be stabilized, thus maintaining good recorded image quality. be able to.

[Brief description of drawings]

FIG. 1 is a perspective explanatory view showing an embodiment of an ink jet recording apparatus according to the present invention, FIG. 2 is a sectional explanatory view thereof, and a third embodiment.
FIG. 4 is a graph showing the relationship between the width dimension of the slit and the pixel density of the ink dots in the inkjet recording apparatus according to the embodiment, and FIG. 4 is the width dimension of the slit and the upper limit pressure of the ink in the inkjet recording apparatus according to the embodiment. FIG. 5 is a graph showing the relationship between the lower limit pressure and the differential pressure, and FIG. 5 is an explanatory view showing a modified example of the ink jet recording apparatus according to the present invention. [Explanation of Codes] (1) ... head body, (2) ... ink chamber (2a) ... slit, (3) ... ink (4) ... thermal signal applying means, (5) ... recording sheet (6) …… Electrostatic field forming means (l) …… Slit width dimension

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Seiichi Kato 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business Office (72) Inventor Koichi Naito 2274, Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd.Ebina Business In-house (72) Inventor Kiyoshi Horie 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd. Ebina Works (56) References JP-A-59-12858 (JP, A) JP-A-62-251150 (JP, A) JP-A-63-17054 (JP, A)

Claims (1)

[Claims] 1. A head main body having a narrow ink chamber having an ink ejection opening as a slit, and an image for each ink unit region corresponding to a pixel density filled in the vicinity of the ink ejection opening of the ink chamber. A heat signal applying means for appropriately applying a heat signal corresponding to information and an electrostatic field forming means for forming a predetermined electrostatic field between the ink surface and the recording sheet are provided, and the heat signal is applied based on the electrostatic field. An ink jet recording apparatus in which an ink unit area is made to fly to the recording sheet side, and the width dimension of the ink flight opening is set to 200 μm or less under the condition that the pixel density is 8 dots / mm or more. Characteristic inkjet recording device.