JPH0698757B2 - Inkjet recording method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording method, and more particularly, to an improvement in the inkjet recording method necessary for maintaining good recorded image quality.

[Prior Art] As a conventional inkjet recording method, a large number of ink ejection devices for sealing ink are provided with ejection ports (orifices) corresponding 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 of 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 lowered.

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. So-called magnetic ink jet recording method (Jpn. Pat. Appln. KOKAI Publication No. 55-
69469) or ink is filled in an ink reservoir on a slit parallel to the electrode array, and the ink is applied to the recording sheet side according to an electric field pattern formed between the electrode and the electrode array facing each other through the recording sheet. So-called flat ink jet recording method (Japanese Patent Laid-Open No. 56-37163), or thermal energy is applied to the ink to rapidly heat the ink to cause boiling of the film surface, and thus the inside of the ejection port (orifice). In addition, there is provided a so-called bubble jet recording method (Japanese Patent Laid-Open No. 55-161664) in which ink is ejected from an ejection port due to a pressure increase caused by rapid growth of bubbles.

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 above magnetic ink jet recording method, it is necessary to use a mixture of magnetic powder as the ink, so that the ink inevitably becomes black, There is a problem that it is difficult to overprint ink to obtain a color image. Further, in the above-mentioned flat ink jet recording method, it is possible to improve the clogging of the ink by the amount that a fine orifice is not necessary, but since a high voltage must be applied in order to fly the ink, In order to prevent the voltage leakage between the neighboring electrodes, the arrangement pitch of the electrodes cannot be narrowed more than necessary, which is not preferable for achieving high density. Furthermore, in the above thermal valve jet recording method,
It is necessary to rapidly heat and heat the heating element in order to cause film surface boiling, which causes thermal deterioration of the ink and thermal deterioration of the heating resistor protective layer provided as a heating means. It has the problem of becoming easier.

In order to solve such a problem, the inventors of the present application apply thermal energy corresponding to image information consisting of a binary signal to the recording ink, and at the same time, the ink portion heated based on a predetermined electrostatic field is applied. A so-called thermal electrostatic ink jet recording method in which the recording sheet is made to fly is already proposed.

According to this type, there is no need to use a magnetic ink by a so-called magnetic ink jet recording method, and accordingly,
Coloring based on overprinting of ink can be easily realized, and it is not necessary to fly the ink only by the electrostatic field as in the so-called flat ink jet recording method, and it is necessary to extremely increase the strength of the electrostatic field. As much as there is no ink, it is possible to effectively prevent voltage leakage between ink
Further, since it is not necessary to fly the ink only by the thermal energy as in the so-called valve jet recording method, the thermal energy amount 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 inkjet recording method, in order to form an ink dot in a pixel density unit on a recording sheet, a means for heating ink according to the pixel density is provided, and the heated ink portion is attached to the recording sheet However, if the image information to be recorded is such that adjacent ink dot groups are formed, the adjacent ink unit areas are heated at the same time and both ink unit areas are heated. A situation arises in which the recording sheets must be flown at the same time.

Under such a circumstance, if the pixel density is set to be somewhat high, the ink unit area corresponding to the pixel density is narrowed, so that the ink ridge start-up action affects the ink unit areas. Not only will the diameter of the ink dots that adhere to the side fluctuate, but in extreme cases, the ink dots that should be recorded will drop out,
This causes a problem of impairing the quality of recorded images.

[Means for Solving Problems] In order to solve such a problem, the inventors of the present application have uniform and stable diameter dimensions of ink dots in an isolated state where ink dots to be recorded do not exist in adjacent portions. The present invention has been devised, paying attention to the fact that it has been achieved, that reproduces a recorded image with a uniform dot diameter.

That is, the present invention is premised on a so-called thermal electrostatic ink jet recording method that enables high-speed and high-density recording, and is provided in an ink containing portion having slit-like ink ejection openings formed between parallel flat plates. After the ink is filled, each ink unit area corresponding to the pixel density in the ink containing portion is heated to the extent that bubbles are not generated in correspondence with the image information, and an electrostatic field formed between the ink surface and the recording sheet. On the basis of the above, when the heated ink unit areas are caused to fly to the recording sheet side, the heating drive timings of at least the adjacent ink unit areas are made unmatched.

In such technical means, the head main body for supplying ink may be appropriately modified in design as long as it has an ink containing portion having slit-shaped ink flying openings formed between parallel flat plates. . As a means for applying heat energy to the ink, the ink may be indirectly heated by using a heating element array in which a plurality of heating resistors are arranged according to the pixel density. Needless to say, the ink may be heated for each pixel density by using as a heating source, or the ink having a predetermined resistivity may be directly energized to be heated. Further, in the type using the heating element array, the position of the heating resistor may be an edge portion adjacent to the ink flight surface or may be an edge portion adjacent to the ink flight surface as long as the ink can be heated in a predetermined area. It may be a wall.

Further, between the ink surface and the recording sheet, an electrostatic field having a strength sufficient to cause the heated ink to fly to the recording sheet side may be uniformly applied, and a means for forming this electrostatic field. However, the design may be changed as appropriate.

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

Furthermore, the number of divisions of the heating drive timing of each heating unit according to the pixel density may be appropriately selected,
If the number of divisions is set too large, the recording speed itself will decrease. Therefore, it is necessary to set the number of divisions in consideration of the harmony between the variation amount of the ink dot diameter and the recording speed. Also, regarding the specific means for separately driving each heating means, the driving timing of each heating means may be appropriately switched by the switching member, or the driving timing of the heating means may be appropriately shifted and set by the timer means. The design may be changed as appropriate.

[Operation] According to the technical means as described above, since the thermal energy corresponding to the image information is not simultaneously applied between the adjacent ink unit areas, the ink unit areas to which the thermal energy is applied are isolated. In this state, the flying operation is performed toward the recording sheet side. For this reason, the ink rising activation operations do not affect each other between the adjacent ink unit areas.

[Embodiment] An embodiment of an apparatus for realizing the inkjet recording method according to the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, the ink jet recording apparatus includes a head main body 1 having a slit-shaped space portion 2 as an ink storage portion in which an ink flight opening is a slit, and a pixel density for ink 3 stored in the slit-shaped space portion 2. A plurality of heating means 4 for applying thermal energy in units, an electrostatic field forming means 6 for forming a predetermined electrostatic field between the surface of the ink 3 and the recording sheet 5, and drive control for driving each heating means 4 in a time division manner. And means 7.

In this embodiment, as shown in FIG. 2, the head body 1 is made of a pair of insulating substrates such as alumina ceramics.
The spacers 11 (12) are spaced apart from each other to secure a slit-shaped space 2 of about 100 μm between the insulating substrates 11 and 12. The ink 3 accommodated in the slit-shaped space 2 is, for example, one in which a pigment is dispersed or a dye is dissolved in an oily solvent such as paraffin or olefin, and the physical property thereof is that the viscosity is 20 to 20 at room temperature. 300 cps, when heated (eg 200
The viscosity decreased by one digit or more, and the volume resistivity was about 10 ⁷ Ωcm.

The heating means 4 is a heating resistor depending on the pixel density.
Each heating resistor 21 is made of, for example, Ta ₂ N, and is arranged so as to face one side opening edge of the slit-shaped space portion 2, and A pair of energizing electrodes 22 are connected to each heating resistor 21. Further, an AND gate 23 as a switching element that is opened / closed in response to an image control signal from the drive control means 7 is connected to each energizing electrode 22. Reference numeral 24 indicates the heating resistor 21 and each energizing electrode 22 having a thickness of, for example, 2 μm.
insulating layer made of SiO ₂ or the like to the insulating coating of about m, 25 is a current-carrying power to the heating resistors 21.

Further, the electrostatic field forming means 6 is provided on the insulating layer 24 and has a thickness of, for example, about 1000 Å Cr (chrome) / Cu (copper) /
A conductive layer 31 made of a metal layer of Cr, a roll-shaped electrostatic induction electrode 32 which is arranged at a predetermined distance from the ink 3 surface and also functions as a support surface of the recording sheet 5, and a conductive layer 31.
And an electrostatic induction power source 33 which is interposed between the electrostatic induction electrodes 32 and forms an electrostatic field from the surface of the ink 3 toward the electrostatic induction electrode 32 side.

Furthermore, in this embodiment, the heating resistor 21 group includes four blocks B ₁ (21a- _1, 21a-2, ...
21a-i), B ₂ (21b-1, 21b-2 ... 21b-i) B ₃ (21c-1, 21c-2
... 21c-i) and B ₄ (21d-1, 21d-2 ... 21d-i). Then, the drive control means 7 temporarily stores the image information G for one line and outputs the image information G group in parallel in synchronization with a predetermined clock timing CL to output each AND gate as a switching element. 23 is composed of a shift register 41 input to one input end, and a changeover switch 42 having four normally open contacts a to d and sequentially closing the contacts a to d at a predetermined timing,
The other input end of each AND gate 23 group is connected to each contact a to d of the changeover switch 42 corresponding to each block B ₁ to B ₄ of the heating resistor 21.

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

In FIG. 3, when the image information G group consisting of binary signals for one line is set in the shift register 41, each image information G is synchronized with the predetermined clock signal CL.
It is output from 41 and input to one input terminal of each AND gate 23. At this point, the contacts a to d of the changeover switch 42 are sequentially switched to drive the drive control signal M (specifically Ma to Ma) at the timing shown in FIGS. 4 (a) to (d). Md), and the electrostatic induction power supply 33 to the electrostatic induction power supply 32 at the timing shown in FIG.
When the applied pulse signal N is applied to the block B, the recording operation of the image information G is performed for each block B.

More specifically, first, when the contact a of the changeover switch 42 becomes conductive, the drive control signal Ma is input to the corresponding AND gate 23a group, and only in the range of this AND gate 23a group. The image information G passes and the heating resistor 21a group in the block B ₁ appropriately generates heat according to the image information G. On the other hand, when a predetermined applied pulse signal N is applied to the electrostatic induction electrode 32, a predetermined electrostatic field S is formed between the surface of the ink 3 and the recording sheet 5, and as shown by the solid line in FIG. The ink unit area Ia corresponding to the heat-generating resistor 21a that has generated heat is heated, the viscosity and surface tension of the ink unit area Ia are reduced, and the conductivity thereof is improved, and the ink unit area Ia is based on the electrostatic field S. As a result, the ink dots Da are formed by flying toward the recording sheet 5 side and contacting the ends of the raised ink columns 3a with the surface of the recording sheet 5. Next, when the contact b of the changeover switch 42 becomes conductive, the drive control signal Mb is input to the corresponding AND gate 23b group, and the image information G passes only in the range of the AND gate 23a group. The heating resistor 21b group in the block B ₂ appropriately generates heat according to the image information G. And
When the predetermined electrostatic field S is formed by the predetermined applied pulse signal N, as shown by the dotted line in FIG. 5, the ink unit area Ib corresponding to the heat generating resistor 21b that has generated heat is heated and the electrostatic field S is generated. Based on the above, the ink dots Db are formed by flying toward the recording sheet 5 and contacting the end of the raised ink column 3b with the surface of the recording sheet 5. Thereafter, the contact c of the changeover switch 42, when d is sequentially conductive, respectively the corresponding AND gate 23c, the drive control signal to 23d group Mc, Md are inputted, respectively block B _3, the heat generating resistor 21c of B in _4, 21d While the group appropriately generates heat in accordance with the image information G, as shown by the one-dot chain line and two-dot chain line in FIG.
The ink unit areas Ic and Id corresponding to 1d are heated and fly to the recording sheet 5 side based on a predetermined electrostatic field S, and the end portions of the raised ink columns 3c and 3d come into contact with the recording sheet 5 surface. Ink dots Dc and Dd are formed.

In such a recording process, each unit ink area Ia to Id receives a certain amount of heat energy Q according to the image information G as shown in FIG. Since the operation can be performed, the rising speed of the ink 3 and the like do not vary depending on the adjacent unit ink areas, and the diameters of the ink dots Da to Dd formed on the recording sheet 5 are substantially uniform.

Then, when a series of recording operations for each block B is completed, the recording process of the image information for one line is completed, and at this stage, the image information G in the shift register 41 is updated and recorded. The sheet 5 is fed by one step, and the process shifts to the recording cycle of the image information for the next line.

Further, in order to verify the above-mentioned recording results, the inventors of the present invention have set the heating time of each heating resistor 21 to 0.5 ms, its applied power to 0.5 W, and the applied pulse to form the electrostatic field S to 1000
When a recording experiment was performed at (V) / 300 μm, 0.5 ms, the diameter of each ink dot D was 150 μm on average, and the standard deviation was 13
was μm. At this time, when the heating resistors 21 are simultaneously driven to heat, the diameter of each ink dot D is 170
It is confirmed that the recording operation is more stable and the diameter of the ink dot D is more uniform than the conventional one, considering that the standard deviation is 30 μm in μm, and there is a recording defect of about 10%. it can.

A similar experiment was conducted with the number of blocks of the heat generating unit 21 in the example being two, and it was confirmed that the diameter of each ink dot D was 150 μm on average and the standard deviation was 15 μm.

[Effects of the Invention] As described above, according to the inkjet recording method of the present invention, the ink unit that is at least adjacent to the ink filled in the slit-shaped ink accommodating portion is premised on the thermal electrostatic inkjet recording method. The heating drive timings of the areas are made non-coincident so that the ink flying operation according to the image information can be stably performed irrespective of the adjacent ink unit area, so that the recording operation is surely performed even if the pixel density is increased to some extent. Can be done, and
The diameter of the ink dots to be printed can be made uniform, and the quality of the printed image can be kept good.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of an apparatus for realizing an ink jet recording method according to the present invention, FIG. 2 is a perspective explanatory view showing a configuration of a head main body used in the embodiment, and FIG. FIG. 4 is an explanatory view showing a concrete example of drive control means used in the example, FIG. 4 is a timing chart showing operation timings of a series of recording operation processes in the present invention, and FIG. 5 is an explanation showing a series of recording operation processes in the present invention. It is a figure. [Explanation of Codes] (Ia, Ib, Ic, Id) ... Ink Unit Area (1) ... Head Body, (2) ... Slit Space (3) ... Ink, (4) ... Heating Means (5) ...... Recording sheet, (6) ...... Electrostatic field forming means (7) ...... Drive control means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nanaho 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business Office (72) Inventor Kiyoshi Horie 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business In-house (56) Bibliography Showa 61-70039 (JP, U)

Claims (1)

[Claims] 1. After filling an ink containing portion having slit-shaped ink flight openings formed between parallel flat plates with ink, each ink unit area corresponding to the pixel density in the ink containing portion corresponds to image information. Then, the ink is heated to such an extent that bubbles are not generated, and at the time of flying the heated ink unit area to the recording sheet side based on the electrostatic field formed between the ink surface and the recording sheet, at least the adjacent ink unit area An inkjet recording method characterized in that heating driving timings are not matched.