JPH01114452A - Ink jet printer - Google Patents

Abstract

PURPOSE:To achieve high-speed, high-density printing with erroneous flying of ink prevented, by providing a heater for locally heating that portion of ink filled in an ink jetting portion in the vicinity of each control electrode. CONSTITUTION:That portion of ink 3 filled in an ink jetting portion 2b facing a portion where a control electrode 4 is disposed is locally heated by a heater 7. The locally heated portion of the ink 3 has its surface tension and viscosity lowered and thus is ready to fly, while that portion of ink 3 adjucent to the control electrode disposed portion has its surface tension and viscosity not lowered and there is hard to fly. When, in this condition, an electrostatic signal (a) with a moderate energy quantity is applied between the control electrode 4 and counter electrode 5 according to image information (b), only easy-to-fly portion of ink 3 facing the electrode 4 flies to a recording sheet 6 positively by the induction force of an electrostatic field because of difference in surface tension and viscosity between the two portions of the ink.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to inkjet recording Rt? In particular, the present invention relates to an improvement in an inkjet recording device that causes ink to fly by an attractive force based on an electrostatic field.

[Prior Art] Conventionally, as this type of inkjet recording apparatus, there is a so-called slitjet recording apparatus as disclosed in, for example, Japanese Unexamined Patent Publication No. 56-37163. This forms a slit-shaped ink chamber filled with a predetermined amount of ink in the head body, and a group of R and ++ II electrodes are arranged in accordance with the pixel density at the ink ejection part facing the ink ejection port of this ink chamber. A counter electrode is provided at a portion of the ink chamber facing the ink ejection port, and an electrostatic signal is applied between each control electrode and the counter electrode of the electrode array according to image information. By doing so, an electrostatic field pattern corresponding to the image pattern is formed between the ink surface facing the electrode array and the counter electrode, and based on this electrostatic field (attractive force) The ink is made to fly toward the recording sheet side.

[Problems to be Solved by the Invention] In such an inkjet recording device, an attractive force caused by an electrostatic field is applied to the ink liquid level filled in the ink chamber, and the attraction force and the surface tension of the ink are combined. It is thought that the antagonism generates a surface wave corresponding to a certain wavelength, and the growth of this surface wave causes the corresponding ink area to rise toward the recording sheet side, but it is said that it maintains good ink retention at the ink ejection part. From this point of view, the ink supplied into the ink chamber usually has a certain degree of surface tension and viscosity at room temperature, so in order to make the ink fly in the above-mentioned inkjet recording device, each control electrode of the electrode array and It is necessary to apply an electrostatic signal with a large voltage value between the counter electrode and ensure a large attractive force due to the electrostatic field, especially when the electrode array is densely packed.
Voltage leakage is likely to occur between adjacent or nearby electrodes.

Therefore, in order to prevent this voltage leak, it is necessary to drive the electrode array in a time-division manner, which limits the ability to achieve high-speed recording.

In order to solve such problems, the inventors of the present application uniformly heat the entire area of the ink in the ink ejection part with a heating means when an electrostatic field is applied, thereby reducing the surface tension and viscosity of the ink in the ink ejection part. We have already provided a device that speeds up the growth of ink's surface waves without having to ensure a large attractive force due to an electrostatic field (Patent Application No. 1983).
-201778).

According to this type, it is not necessary to ensure a large attractive force due to the electrostatic field, so it is sufficient to apply an electrostatic signal with a relatively small voltage value to each control electrode of the electrode array, and each control electrode of the electrode array Even if the control electrodes are arranged in high density, voltage leakage between the control I electrodes can be effectively prevented.

However, in this type, since the entire area of the ink in the ink ejection section is uniformly heated, the surface tension and viscosity of the entire area of the ink inevitably change uniformly. Therefore, the ink portion adjacent to the &lJ control electrode electrode installation location is also in a state where it is easy to fly, and when an electrostatic icon corresponding to the image information is applied to the control l electrode, There is a risk that the ink portion adjacent to the placement location may also be erroneously ejected.

[Means for Solving the Problems] The present invention has been made in view of the above problems, and is based on a type in which ink is ejected by an attractive force based on an electrostatic field. An object of the present invention is to provide an inkjet recording apparatus that can realize high-speed a-density recording while effectively preventing such problems.

That is, as shown in FIG. 1, the present invention provides a head main body 1 having an ink chamber 2 in which an ink discharge port 2a is opened.
and a large number of control electrodes 4 arranged in units of gA according to the pixel density of the ink 3 filled in the ink ejection portion 2b facing the ink ejection port 2a. An electrostatic signal according to image information is applied between each control 611 electrode 1li4 and the counter electrode 5, and an electrostatic signal is applied between the ink 3 surface and the counter electrode 5. Due to the attractive force based on the formed electrostatic field, the counter electrode 5
In the type in which the ink 3 is ejected onto the recording sheet 6 disposed on the front side of the ink discharge section 2b, the ink discharge section 2b
A heating means 7 is provided for centrally heating the ink 3 filled in the vicinity of each fl control pole 4.

In such technical means, the head body 1 may be designed by appropriately changing the design as long as it has a predetermined ink chamber 2, but considering manufacturing workability, two insulating substrates may be spaced apart. death.

It is desirable that the ink chamber 2 is secured between both members. Further, as the ink ejection port 2a, the ink 3
From the viewpoint of effectively preventing clogging, a slit-like material is preferable, and from the viewpoint of reliably dividing the ink unit area to be ejected according to the pixel density, a perforated material is desirable. .

Furthermore, regarding the control electrode 4 and the counter electrode 5, the ink 3
As long as the design is such that an electrostatic field pattern corresponding to the image pattern can be formed on the surface, the arrangement position, shape, etc. may be changed as appropriate. In addition, the ink 3 to be used may be oil-based or water-based as long as it is a conductive ink that has temperature-dependent characteristics such that the viscosity and surface tension decrease as the temperature increases and has an appropriate volume resistivity. do not have.

Furthermore, regarding the heating means 7, an appropriate heat generating part may be provided corresponding to the &lI ill electrode 4 arranged according to the pixel density, and the location thereof is the control electrode 4.
It may be on the same side as the control electrode 4, or it may be on the side opposite to the control electrode 4. In this case, the heat generating section may be a heat generating element such as a heat generating resistor, or may be appropriately selected using radiation or the like. The specific degree of heating by the heating means 7 should be determined by considering the strength of the electrostatic field, the physical properties of the ink 3 used, the gap between the end of the head body 1 and the counter electrode 4, etc. Although the selection is made as appropriate, at least the ink 3 in the ink ejection part 2b is adjusted to such an extent that the part of the ink 3 adjacent to the heat generating part is difficult to fly.
It is necessary to ensure a contrast in surface tension and viscosity. In this case, from the standpoint of heating efficiency, it is preferable not to heat the ink 3 corresponding to the locations other than the location where the control electrode 4 is disposed. There is no problem even if the ink 3 corresponding to the location other than the location is slightly heated.

[Operation] According to the technical means as described above, the ink ejection section 2b
A portion of the ink 3 filled in the ink 3 corresponding to the location where the control electrode 4 is disposed is intensively heated by the heating means 7 . At this time, the surface tension and viscosity of the ink 3 portion that has been intensively heated is reduced and the ink 3 is set in a state where it is easy to fly.
As for the part, the surface tension and viscosity are not lowered, and the part is kept in a state where it is difficult to fly. In this state, the control electrode 4
When a not-so-large electrostatic signal corresponding to the image information is applied between the ink 3 and the counter electrode 5, the contrast between the surface tension and viscosity of the ink 3 makes it easier for the ink 3 facing the control electrode 4 to fly. Only the portion of the ink 3 reliably flies toward the recording sheet 6 disposed in front of the counter electrode 5 due to the attractive force of the electrostatic field formed between the surface of the ink 3 and the counter electrode 5.

[Embodiments] Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

◎Example 1 In FIG. 2, an inkjet recording apparatus includes a head main body 1 having a slit-shaped ink chamber 2 in which an ink discharge port 2a is IJI, and an ink discharge portion 2b facing the ink discharge port 2a is filled with ink. an electrode array consisting of a large number of control electrodes 4 disposed facing each unit area according to the pixel density of the ink 3; a counter electrode 5 disposed facing the ink ejection opening 2a; It is provided with a heating means 7 that heats the ink 3 in the discharge portion 2b with a temperature distribution according to the arrangement pattern of the M m Ti electrodes.

In this embodiment, as shown in FIG. 2, the head main body 1 has a pair of insulating substrates 11 and 12 made of alumina ceramics, glass, etc. separated by a predetermined size (50 μm in this embodiment) through a spacer portion 12a. A slit-shaped ink chamber 2 is formed between the pair of insulating substrates LL12, and the ink discharge port 2a side of the ink chamber 2 is secured as an ink discharge portion 2a in which ink 3 to be discharged is held. This is how it was done. The ink 3 filled in the ink chamber 2 is a dye-soluble oil-based ink containing diisopropylnaphthalene as the main solvent, and has a viscosity of 35 cps at Tokogata and 6 cps at 80°C.
s, surface tension is 36 dyne/as at room temperature
The electrical resistivity of 28dyne/cIR1 at 80°C is 1080 at room temperature and 10701 at 80'C. Furthermore, the supply pressure of the ink 3 is set so that the surface shape of the ink 3 is approximately parallel to the end of the head body 1 when no electrostatic signal is applied.

Further, as shown in FIGS. 2 and 3, a heating resistor 20, which is a component of the heating means 7, is provided at a location corresponding to the ink discharge portion 2b on the inner surface of the one insulating substrate 11.
are arranged according to the pixel density (in this embodiment, 8 pixels/layer). In this embodiment, the heat generating resistor 20 is formed into a U-shaped band pattern using NiCr at a location corresponding to the ink ejection portion 2b of the insulating substrate 11 and near both ends in the direction of the arm. A current-carrying conductor 21 made of a Cr/Au metal heat 51i film is formed, leaving only the necessary parts. It will be placed in the specified position. and,
The entire inner surface of the insulating substrate 11 is covered with an insulating layer 22 of 5in2 that covers the heating resistor 20 and the current-carrying conductor 21.
is deposited with a thickness of about 2 μm. Further, a thermal signal applying means 23 is connected to the energizing contact 21 of the heating resistor 20.

Furthermore, a control N-pole 4 is formed on the insulating layer 22 of the insulating substrate 11 in accordance with pixel secretion. This 1I11 control electrode 4 is formed on the insulating layer 22 of the insulating substrate 11 to a thickness of 1.
A Cr layer of 0OOA, a Cu layer of 1 μm on top of that, and a 1i1 gold layer of 1000A Cr layer on top of that are vapor-deposited over the entire surface, and a photolithography process is applied to this entire metal layer to form the inner cable. A dense electrode pattern is formed. This system! The IIfj electrodes 4 are arranged at a distance of about 50° C. 1 m from the #Ii portion of the insulating substrate 11, and on these control electrodes 4, in order to prevent short circuits between the control electrodes 4 due to deposits etc. as much as possible. Insulation protection II consisting of 5102, etc., leaving an exposed part of 500 μm from the edge of the insulating substrate 11! 131 is deposited to a thickness of about 1.0 μm. A first electrostatic signal applying means 32 is connected to each of the control electrodes 4, which selectively supplies r+350 (V) and O(V) (1) pulse signals in accordance with image information.

Furthermore, the counter electrode 5 is a roll-shaped member that can be rotated in steps, and also has the function of a conveying member for the recording sheet 6. While being arranged across a gap,
This counter electrode 5 has L; T-1,700 (
A second electrostatic signal applying means 33 for switching and supplying pulse signals of V) and O(V) is connected.

Further, the thermal signal applying means 2 used in this embodiment
FIG. 4 shows a drive circuit consisting of electrostatic signal applying means 32 and 33.

In the figure, reference numeral 41 is a crystal oscillator circuit that generates a reference clock CL for the operation of the entire drive circuit, 42 is a counter that receives the reference clock CL as an input signal, and 43 is a decoder for decoding the count value signal K of the counter 42. For example, a PLA (Programmable Lo
gic Array), and outputs a counter reset signal R during one line repetition period tlcfQ in FIG. 5 to reset the counting operation of the counter 42. 44 is a transfer lock generation gate which generates a data transfer lock CL1 as shown in FIG. 5 by gating the transfer timing f+i number T1 and the reference clock C.

In this embodiment, the thermal signal applying means 23 has a switching device 45 that is turned on periodically according to the thermal timing signal TI (2m5 in this example), and when the switching element 45 is turned on, the corresponding heating resistor 20
A predetermined heating voltage (a) is applied to. The first electrostatic signal applying means 32 also includes a shift register 46 that stores the serial image data DT in accordance with the data transfer lock CL1 and outputs it as parallel data, and a shift register 46 that stores the serial image data DT in accordance with the data transfer lock CL1 and outputs it as parallel data. A latch circuit 47 that latches data from 46, a gate circuit 48 that inputs the data in this latch circuit 47 and outputs a signal according to the data based on the output enable signal T3, and It operates on and off based on the output, and the control electrode power supply voltage vb <350 (V) in this example)1 is applied to the corresponding control electrode 4.
High voltage switching element 4 that selectively applies 0 (V)
It consists of 9. Further, the second electrostatic signal applying means 33 is turned on periodically in response to the output enable signal @T3, and applies the counter electrode TI power supply voltage C(
This embodiment includes a high voltage switching element 50 that applies -1,700 (v).

Next, the operation of the inkjet recording apparatus according to this embodiment will be explained.

Now, if we focus on the printing sequence for one line, first,
The heating resistors 20 arranged in units of pixel density are heated and driven periodically according to the thermal timing signal T1 shown in FIG. At the same time, the drive signal DR shown in FIG. 5 is applied to the counter electrode 5 periodically as well as the output enable signal T3.

In such an operation process, when the heating resistor 20 is heated, only the ink unit area M corresponding to the control electrode 4 is heated to about 80° C., for example, as shown in FIGS. 2 and 3. is heated centrally. At this time, since the temperature of the ink 3 portions other than the ink unit area M remains at approximately room temperature, the temperature distribution of the ink 3 within the ink discharge section 2a is controlled by tI.
It has a contrast corresponding to the arrangement pattern of the I electrodes 4. Therefore, the surface tension and viscosity of the ink ψ position region M corresponding to the control Il electrode 4 decrease as the temperature rises,
Only this ink unit region M is set to be in a state where it is easy to fly, while the surface tension and viscosity of the ink 3 portion at locations other than the location where the control electrode 4 is arranged maintain a state where it is difficult to fly. In this state, when an electrostatic signal corresponding to the image information is applied between the control electrode 4 and the counter electrode 5, an electrostatic field pattern corresponding to the image information pattern is generated from the ink 3 surface toward the recording sheet 6 side. Due to the attractive force based on this electrostatic field pattern, only the ink unit area M corresponding to the image information is raised toward the recording sheet 6 side, resulting in a raised ink column 3a.
The leading edge of the dot (indicated by the imaginary line in FIG. 2) comes into contact with and adheres to the recording sheet 6, and a printed dot D is formed.

When evaluating the performance of this embodiment, we compared it with a type that uses uniform heating as a heating means, and it was confirmed that printing results could be obtained in which adjacent dots could be divided without time-division driving. Ta.

Furthermore, in this embodiment, the heating means 7 supplies the heating resistor 20 with a pulse current that is periodic to an electrostatic signal, so it supplies a continuous current to the heating resistor 20. Compared to the type, even when used for a long time, it is possible to effectively avoid a situation in which heat accumulates in the ink 3 more than necessary and the contrast of the temperature distribution of the ink is impaired.

Example 2 In the inkjet recording apparatus according to this example,
As shown in FIG. 6, the configuration of the heating resistor 20 constituting the heating means 7 is similar to that of the first embodiment.

In the figure, each heating resistor 20 has a pair of connecting portions 20 in a region facing the current-carrying conductors 21 arranged on both sides.
a, and a U-shaped extension 20b extending in the depth direction of the ink chamber 2 is connected to this connection m20a.

Therefore, according to the inkjet recording apparatus according to this embodiment, in addition to achieving the same functions and effects as those of the first embodiment, the temperature distribution of the ink unit region M corresponding to the control till electrode 4 in the ink ejection portion 2b can be improved. Wide V in the opposite direction! Since the ink can be made uniform over the surrounding area, the entire ink unit region M to be ejected can be set in a state where it is easy to eject, and the ejecting operation of the ink 3 can be made more stable accordingly.

Friend 1 In the inkjet recording apparatus according to this embodiment,
As shown in FIG. 7, heating means 7 different from Example 1.2.
It has a heat generating part.

That is, the heating section of the heating means 7 is connected to the ink ejecting section 2.
A heating resistor 25 is disposed integrally extending along the length direction of b, and current-carrying conductors 26 are disposed on both sides thereof,
The dimension width in the depth direction of the ink chamber 2 of the heating resistor portion 25a corresponding to the location where the control electrode 4 is disposed is set to the other portion 25b.
It is set narrower, and the heat generation Φ of the heating resistor portion 25a corresponding to the location where the control electrode 4 is disposed is made larger than that of the other portion 25b.

Therefore, according to this embodiment, the portion of the ink 3 that does not correspond to the location where the shrine IIl electrode 4 is disposed is also slightly heated by the heating resistor portion 25b having a large width, but the resistance of the heating resistor 25 changes. By adjusting as appropriate, the ink unit area M corresponding to the heating resistor portion 25a having a small width can be heated in a concentrated manner while maintaining the desired contrast, so that the same functions and effects as in each of the above embodiments can be achieved. will be played.

In this embodiment, by changing the width dimension of the heating resistor 25, the ink 3 in the ink ejection section 2b is given an appropriate ffl Iff distribution, but the present invention is not limited to this. For example, as shown in Fig. M8, the thickness of the heating resistor 25 is appropriately changed to reduce the amount of heat generated by the bulky heating resistor portion 25C compared to the thicker portion 2.
5d or more, or as shown in FIG. 9, heat generating resistors 25 having uniform width and thickness may be continuously arranged along the length direction of the ink ejection portion 2b. The thickness of the insulating layer 27 covering the heating resistor 25 is changed as appropriate, so that the thin insulating m portion 27a is thicker than the thick insulating layer portion 2.
There is a method that takes advantage of the fact that it has better heat transfer traces than 7b.

[Effects of the Invention] As explained above, according to the inkjet recording apparatus according to the present invention, by devising the heating means, each system tlL! ! The surface tension and viscosity of only the ink portion corresponding to the pole are reduced to make the ink easier to fly,
At this stage, an electrostatic field corresponding to the image pattern is applied to the ink, so the ink portion corresponding to the control electrode corresponds to the image pattern and can be reliably ejected without increasing the energy level of the electrostatic field. It becomes possible to do so. Therefore, even if the pixel density is set high and each control electrode according to the pixel density is driven all at once, it effectively prevents ink from flying erroneously and also effectively prevents voltage leakage between adjacent control electrodes. It is possible to achieve stable, high-speed, high-density thinning recording.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a schematic configuration of an inkjet recording device according to the present invention, FIG. 2 is a cross-sectional explanatory diagram showing Embodiment 1 of the inkjet recording device according to the present invention, and FIG. 3 is a direction shown in 4 is a block diagram showing the drive circuit used in the first embodiment, FIG. 5 is a timing chart showing the operation of the inkjet recording apparatus according to the first embodiment, and FIG. FIG. 7 is an explanatory diagram corresponding to FIG. 3 showing essential parts of Example 2 and Example 3 of the inkjet recording apparatus according to the present invention, and FIGS. 8 and 9 are modifications of the inkjet recording apparatus according to the present invention. Need an example? '
, Is 111i plane view. [Explanation of symbols] (1)...Head body (2)...Ink chamber (2a)...Ink discharge port (2b)...Ink discharge portion (3)...Ink (4)... ... Control electrode (5) ... Counter electrode (6) ... Recording sheet (7) ... Heating means (20, 25) ... Heating resistor (23) ... Heat signal application means ( Drive unit) Patent applicant
Fuji Xerox Co., Ltd. Representative Patent Attorney Tomohiro Nakamura (2 others) Fig. 1 20; Heating resistor 23: Heat signal application means Fig. 2 Fig. 3 Fig. 6

Claims (1)

[Claims] 1) An ink chamber (2) in which an ink discharge port (2a) is provided.
a head main body (1) having an ink discharge port (2a);
) The ink (
3), a large number of control electrodes (4) arranged corresponding to a unit area according to the pixel density, and a counter electrode (5) arranged opposite to the ink ejection port (2a). , an electrostatic signal according to the image information is applied between each control electrode (4) and the counter electrode (5), and the ink (3) surface and the counter electrode (5)
In an inkjet recording apparatus, the ink (3) is caused to fly onto a recording sheet (6) disposed in front of a counter electrode (5) by an attractive force based on an electrostatic field formed between the ink and the ink. An inkjet recording apparatus characterized in that a heating means (7) is provided for centrally heating the vicinity of each control electrode (4) of the ink (3) filled in the ejection part (2b). 2) The heating means (7) includes heating resistors (20, 25),
The inkjet recording apparatus according to claim 1, further comprising a drive section (23) that supplies heating current to the heating resistor (20, 25). 3) The inkjet recording apparatus according to claim 2, wherein the drive section (23) supplies a pulsed heating current periodically at the application timing of the electrostatic signal.