JPH03213347A - Ink jet recording device - Google Patents

Abstract

PURPOSE:To stabilize flying of ink by a method wherein a charge adhered to a recording material with the progress of printing operation is removed by a potential stabilizing means. CONSTITUTION:In printing operation, a drive pulse responding to picture information is applied on a heat generating resistor 31 to heat a corresponding ink unit region. An electrostatic control pulse synchronized with an applying timing for the drive pulse is applied on an electrode 52 for electrostatic induction to form an electrostatic field between an electrode 51 on the head side and the electrode 52 for electrostatic induction. Through formation of the electrostatic field, ink 2 held throughout the overall length of a slitform ink delivery part 16 is flied at each ink unit region responding to a recording picture. In this case, since a potential stabilizing means 6 is arranged in a state to make contact with a recording sheet 4, a charge adhered to the recording sheet 4 with the progress of printing flows through the recording sheet 4 to the potential stabilizing means 6. As a result, the surface potential of the recording sheet 4 is kept at the same potential as that of the electrode 52 for electrostatic induction, and an electrostatic field to electrostatically suck the ink 2 is stabilized. This constitution prevents worsening of printing quality due to electrification of a recording material, and enables provision of an excellent recording picture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an inkjet recording device, and particularly relates to an improvement of an inkjet recording device that causes ink to fly using an energy signal containing electrostatic energy.

[Prior Art] The inkjet recording method, in which a recorded image is formed by flying small droplets of ink onto a recording medium such as a recording sheet, is classified into several types depending on the form of energy application to eject and fly the ink. One of these methods is the so-called electrostatic suction inkjet recording method, which uses electrostatic energy to eject ink.

The basic operating principle of this electrostatic attraction method is that an electrostatic field is formed between the ink and the recording medium placed at a predetermined gap, thereby generating an induced charge on the surface of the ink, and The ink is attracted toward the recording medium by using the electrostatic attraction force that acts on the charged ink unit area under the .

As a specific device for carrying out this electrostatic suction type inkjet recording method, for example, a slit-shaped ink ejection opening communicating with an ink chamber is formed by a pair of substrates facing each other, and a surface facing the ink ejection opening is formed. An electrode array consisting of a group of electrodes arranged according to the pixel density is provided on one side of the ink ejection port, and an electrode for electrostatic induction is provided at a portion facing the ink ejection port. A so-called electric field control type device is known in which a control signal according to image information is applied between the electrode and the electrostatic induction electrode (Japanese Patent Laid-Open No. 56-67163). In this electric field control type device, by forming an electrostatic field according to the image pattern between the ink discharge part holding ink and the electrostatic induction electrode, the electrostatic induction electrode is placed in front of the electrostatic induction electrode. Ink can be selectively ejected from predetermined portions of the slit-shaped ink ejection ports toward the printed recording sheet.

Another example of an electrostatic suction type device is a thermal control type that controls the flight of ink using thermal energy applied to the ink. Specifically, similar to the electric field control type described above, a slit-like Forms an ink ejection port,
A heating resistor array consisting of a group of heating resistors arranged according to the pixel density is provided on one side of the ink jetting portion facing the ink jetting port, while an electrostatic field such as that directed from the ink jetting portion toward the recording sheet side is provided. A method is known in which an electrostatic energy applying means is provided for applying electrostatic energy to the ink to form the ink (Japanese Unexamined Patent Publication No. 62-225388).

In this thermal control type device, the ink viscosity of the ink unit area is reduced by applying thermal energy according to image information to the ink unit area using the heating resistor array, and the electrostatic energy marking means 1i10 is used to reduce the ink viscosity of the ink unit area. By applying a predetermined electrostatic attraction force to a unit area of low-viscosity ink, it is possible to cause the ink held in the ink ejection section to fly toward the recording sheet according to the image pattern.

1 Problem to be Solved by the Invention 1 By the way, in such an electrostatic suction type inkjet recording method, as mentioned above, the ink sucked toward the recording medium is charged, so that the ink on the recording sheet, etc. A recording medium whose ink adhering surface is a resistive layer (when printing is performed, the recording medium becomes electrically charged).

This is particularly noticeable in electrostatic control type or thermal control type devices having slit-shaped ink ejection ports as shown in the above-mentioned conventional example. In other words, in the above two methods, the ink that is electrostatically attracted does not fly as small droplets and adhere to the recording medium, but the ink that rises from the ink ejection port due to electrostatic suction extends into a string shape, and this string-like An ink dot is formed when the leading edge of the ink adheres to the recording medium. Therefore, when an ink dot is formed, a current flows into the recording medium through the string-like ink, and the recording medium becomes electrically charged.

In addition, in such an electrostatic suction method, the gap between the electrostatic induction electrode placed on the back side of the recording medium and the ink ejection port is set to an extremely small value, so the gap between the electrostatic induction electrode Leakage is likely to occur between the electrode and the head side electrode, and as a means to effectively prevent this leakage, a method has been adopted in which the electrostatic induction electrode is coated with a high resistance layer or a dielectric layer. However, in this case, charges tend to accumulate on the recording medium, and the recording medium comes to have a high surface potential.

In this way, in the electrostatic suction method, as the surface potential of the recording medium changes as the printing operation progresses, the strength of the electrostatic field formed between the recording medium and the ink changes, causing the static electricity that attracts the ink to change. The strength and directionality of the electric attraction become unstable. As a result, variations occur in the amount of ink sucked and in the suction direction, and the diameter and adhesion position of the ink dots formed on the recording medium are not stable, resulting in a problem that print quality deteriorates.

The present invention has been made in view of the above-mentioned problems, and its purpose is to prevent deterioration of print quality caused by charging of a recording medium and to obtain a good recorded image by electrostatic attraction. An object of the present invention is to provide an inkjet recording device based on the above-mentioned method.

[Means for Solving the Problems] In order to achieve the above object, an inkjet recording device of the present invention includes a head main body having an ink chamber having an ink ejection port, and an ink ejection portion facing the ink ejection port. An energy signal including at least electrostatic energy according to image information is applied to each unit area of ink held in the area.
and a potential stabilizing means that is arranged in contact with the recording body that receives the ink flying from the ink ejection opening and stabilizes the surface potential of the ink receiving surface of the recording body. It is.

In such technical means, as long as the head main body has an ink chamber with an ink ejection port, the structure or shape may be changed as appropriate.
The ink ejection opening may be appropriately selected such as a slit shape including a plurality of recording pixels or a nozzle shape for each recording pixel.

Further, the structure of the energy applying means may be modified as appropriate as long as it attracts ink to the recording medium using at least electrostatic energy, that is, electrostatic attraction based on an electrostatic field. For example, a thermal control type that combines a thermal energy inlet means and an electrostatic energy application means, or an electric field control type that uses only electrostatic energy can be applied. However, in the electric field control type, ink flight is controlled only by electrostatic attraction, so compared to the thermal control type, a higher voltage is applied between the electrostatic induction electrode located on the back side of the recording medium and the head body side. It is necessary to apply the voltage between the electrodes, which tends to cause leakage between these electrodes, and also increases the amount of charge on the recording medium during the printing operation.

Therefore, considering both the prevention of leakage occurring between the electrodes and the prevention of charging of the recording medium, which is the purpose of the present invention, the thermal control type structure requires a smaller voltage value to be applied between the electrodes than the electric field control type. It is preferable to adopt

Furthermore, the thermal energy application means in the thermal control type applies ink to each recording pixel according to the image information.
As long as it can be heated, its configuration can be changed as appropriate.

Further, the recording medium may be a final recording image carrier to which the ink is fixed, such as a recording sheet, or
It may also be an intermediate transfer member that once receives ink and then transfers it to a recording sheet.

Further, the potential stabilizing means may be any device that comes into contact with the recording medium and stabilizes its surface potential at a substantially constant level so that the strength of the electrostatic field formed by the electrostatic energy applying means does not fluctuate. , for example, a conductive brush or a conductive roll connected to a constant voltage power supply or grounded. However, at the ink adhesion position,
Because the electrostatic induction electrode and the recording medium are in contact with each other via a dielectric layer or insulating layer for leak prevention, the surface potential of the recording medium has a large potential difference with respect to the potential of the electrostatic induction electrode. This may cause dielectric breakdown of the dielectric layer or insulating layer used to prevent leakage. Therefore, it is preferable that the surface potential of the recording medium is between the electrostatic induction electrode, the potential, and the path.

In order to effectively demonstrate the function of this potential stabilizing means, it is necessary to increase It is necessary to accurately determine the distance between the ink adhesion position and the contact position of the potential stabilizing means. The positioning of this potential stabilizing means will be explained in detail in the embodiments of the present invention described later.

[Effect 1 The above configuration works as follows.

Charges attached to the recording sheet during printing flow into the potential stabilizing means through the surface of the recording sheet, so that the surface potential of the recording medium is always maintained at a substantially constant value. As a result, the strength and directionality of the electrostatic field that electrostatically attracts ink to the recording medium do not change as the printing operation progresses.

[Example] Hereinafter, an inkjet recording apparatus of the present invention will be described in detail based on the accompanying drawings.

◎Embodiment In this embodiment, the present invention is applied to an inkjet recording device that employs a heat-controlled electrostatic suction method, and as shown in FIGS. 1 and 2, a slit-shaped ink jet A head body 1 having an outlet 15 and an ink chamber 17, a thermal energy applying means 3 for applying thermal energy to the ink 2 held in the ink discharge part 16 of the head body 1, the ink discharge part 16, and a recording sheet 4. The electrostatic energy applying means 5 is configured to form a predetermined electrostatic field between the ink discharge port and the electric potential stabilizing means 6, which is placed in contact with the recording sheet 4 being conveyed while facing the ink ejection opening.

First, the head body 1 is made of glass and has a thickness of about 3I.
It is composed of an insulating substrate 11 made of nIr1 and a heating resistor substrate 12 about 1 m thick made of alumina ceramics on which a glaze layer (3102) about 60 μm thick is laminated to ensure flatness and heat storage.

A recess 14 with a depth of about 1 m is formed on the wall surface of the insulating substrate 11 by sandblasting, while a recess 14 with a depth of about 500 μm is formed along the outer periphery of the heating resistor substrate 12 except for the tip side. U-shaped spacers (not shown) made of polyester film are provided, and these insulating substrates 1
1 and the heating resistor substrate 12 are bonded together via the spacer, and the slit-shaped ink discharge port 15 and the ink discharge portion 1 are bonded to each other through the spacer.
6, and an ink chamber 17 continuous thereto.

On the other hand, the thermal energy applying means 3 is formed by depositing a film by a reactive sputtering method and by a photolithography method, and from a Ta, N thin film of approximately 300 large gates for each pixel density (for example, 8 to 1, imtn). It is composed of a heating element array formed by arranging heating resistors 31, and each heating resistor 3
1 is disposed facing the opening edge of one side of the ink ejection portion 16, and each heating resistor 31 is coated with about 50 N1-Cr.
A pair of current-carrying electrodes 32 are connected to the electrodes 32, which are formed by sequentially and continuously uniformly depositing Au of about 1 .mu.m by photolithography. Then, each of the above-mentioned current-carrying electrodes 3
A switching element 33 that opens and closes in response to an image control signal is connected between the two. Incidentally, reference numeral 34 is a S having a thickness of approximately 2 μm, which is formed by high-frequency sputtering and insulatingly covers the heating resistor 31 and each current-carrying electrode 32.
An insulating layer 35 such as iO2 is a power source for supplying current to each heating resistor 31.

Further, the electrostatic energy applying means 5 applies approximately 500 pieces of Cr and about 500 pieces of Cu on the insulating layer 34 (not shown in FIGS. 1 and 2).
The head side electrode 51 is formed by sequentially depositing about 10,000 layers of Cr and about 500 layers of Cr, and the ink ejection port 15.
A roll-shaped electrostatic induction electrode 5 disposed appropriately in front of
2, and an electrostatic induction power supply 53 that is interposed between the head side electrode 51 and the electrostatic induction electrode 52 and forms an electrostatic field directed from the ink ejection part 16 toward the electrostatic induction electrode 52 side. There is. The electrostatic induction electrode 52 also functions as a transport support for the recording sheet 4, and its outer peripheral surface is designed to prevent leakage between it and the head-side electrode 51.
It is coated with a dielectric layer 54 made of polyurethane resin having a relative permittivity of 3.01 and a thickness of about 50 am. Note that the head side electrode 51 is grounded.

Furthermore, the potential stabilizing means 6 is a conductive brush with conductive carbon fibers or flocked conductive brushes, and is applied to the recording sheet 4 on the upstream side of the recording sheet conveyance direction from the printing position so as not to smudge the recorded image after printing. Contact is placed. The conductive brush 6 is connected to the electrostatic induction power source 52, and maintains the surface potential of the recording sheet 4 at the same potential as the electrostatic induction power source 52.

Further, the ink 2 accommodated in the ink chamber 17 and the ink discharge section 16 has a viscosity of 150 CP at chamber m (20° C.).
S, surface tension 3 &dyne/Cm, volume resistivity 2
×1011Ωctn, viscosity 5CPS and surface tension 20dl/ne/CI when heated (150℃)! , a conductive oil-based ink with a volume resistivity of 1×10 8 Ωcm was used.

In the inkjet recording apparatus of this embodiment configured as described above, the printing operation is performed as follows. That is, a driving pulse corresponding to the image information is applied to the heating resistor 31 to heat the corresponding ink unit area, and an electrostatic control pulse synchronized with the application timing of the driving pulse is applied to the electrostatic induction electrode 52. By forming an electrostatic field between the head-side electrode 51 and the electrostatic induction electrode 52, the ink 2 held over the entire length of the slit-shaped ink ejection section 16 is divided into ink unit areas corresponding to recording pixels. It is carried out by flying.

At this time, according to this embodiment, since the potential stabilizing means 6 is disposed in contact with the recording sheets 1 to 4, the electric charge attached to the recording sheet 4 during printing is transferred to the potential stabilizing means 6 through the recording sheet 4. flows into. As a result, the surface potential of the recording sheet 4 is maintained at the same potential as the electrostatic induction electrode 52, making it possible to stabilize the electrostatic field that electrostatically attracts the ink 2.

By the way, in the above configuration, since the charges attached to the recording sheet 4 due to printing flow into the potential stabilizing means 6 through the recording sheet 4, the surface potential of the recording sheet 4 changes from the potential state after ink adhesion to the potential state before ink adhesion. The time required to return to normal is determined by the distance between the printing position on the recording sheet and the contact position of the potential stabilizing means 6 (symbol a in FIG. 2).
. This is considered to be closely related to the distance of the potential stabilizing means (hereinafter referred to as the arrangement distance of the potential stabilizing means) and the electrical resistance of the recording sheet 4 through which the charges move.

Therefore, in order to further stabilize the printing operation in the inkjet recording apparatus having the above-described configuration, the inventor of the present application conducted experiments on the relationship between the contact position of the potential stabilizing means 6 with respect to various recording sheets and the quality of printing. , and discussed the results.

In this experiment, four types of recording sheets shown below were used, and the quality of printing was observed when the distance between the ink adhesion position and the contact position of the potential stabilizing means 6 was varied for each recording sheet.

Recording sheet A: Plain paper for electrophotography (Fuji Xerox FX-L paper) moisture content 4.5% B: Plain paper for electrophotography (Fuji Xerox "X-1 paper) moisture content 5.0% C: Recording sheet A Application of quaternary ammonium salt aqueous solution to D = Application of quaternary ammonium salt aqueous solution to recording sheet B First, prior to the printing experiment, for each of the above recording sheets,
Changes in the surface potential of the recording sheet when a charge was applied were measured over time, and based on this, the difference in the difficulty of charge transfer was quantified.

Specifically, as shown in FIG.
A conductive layer 71 with a thickness of 50 μm and a dielectric constant ε=
A dielectric layer 72 made of polyurethane (No. 3) is provided, and the recording sheet 4 is stacked thereon. On the surface of the recording sheet 4, electrodes 73 for applying electric charge and electrodes 74 for discharging electric charge are provided at intervals p. While the electrode 74 and the conductive layer 71 were grounded, a voltage V rising in a stepwise manner was applied to the electrode 73 by a power source 75. Then, assuming that the end of the electrode 73 is X=Q, the position x=x, however,
p≦1/2), the surface potential V (X,
DEL 360, etc.).

At this time, the measured surface potential V (X, , ↑) after a sufficient time t2 has elapsed since the step voltage V was applied, is expressed as v (xp, t2)=v・(x p / fl >
It can be said that

Therefore, if v(x,,t) is half the value when 1=12, that is, the time when V(xi),t)=V・(Xp/J2)/2 is set to 11, then =Xp2/ 11 [CIIt/SeC].

This value 2 (hereinafter referred to as charge diffusion constant) is a constant specific to the recording sheet that indicates the difficulty of transferring the applied charges. can be evaluated.

When the charge diffusion constants of four types of recording sheets used in the experiment were measured using the method described above, the following values were obtained.

A: /C2=0. I Ecrj/sec ]B
: 2= 1-0 [ci/sec]C: tc2
= 4.0 [ci/sec] D: 2 = 10.0
[cIi/sec]Next, printing was performed using these recording sheets, and during printing, the arrangement distance a of the potential stabilizing means 6 and the printing time interval (hereinafter referred to as printing speed>
1° and observe the printing results for each, and for each combination of printing data, nizu=/a2
(hereinafter described as evaluation formula) was calculated.

A table summarizing the experimental results is shown on the next page.

Table 1 The printing results are evaluated based on the following classifications.

◎: The diameter and position of the ink dot are within ±5% over 3000 lines ○: The diameter and position of the ink dot are within ±10% over 3000 lines Δ: Either the diameter or position of the ink dot is within 300
Within ±10% across the 0 line According to the experimental results, it was found that, common to all recording sheets, there is a tendency that good printing is performed when the arrangement distance a of the potential stabilizing means 6 is short, and It has been found that under conditions of slow printing speed, good printing can be achieved even if the distance a of the potential stabilizing means 6 is set long. This is thought to be because it takes a predetermined time for the charges attached to the recording sheet 4 due to printing to flow along the surface of the recording sheet and into the potential stabilizing means 6. Therefore, if the charge transfer in the previous printing is completed before the next printing, the ink 2
The electrostatic field that attracts electrostatically has the same strength at all times during printing, resulting in good printing.

Regardless of the installation distance a of the potential stabilizing means 6 or the printing speed 1j, under printing conditions in which the total value of the evaluation formula is 0.4 or more, the diameter of the ink dots formed on the recording sheet is Good results were obtained regarding both the formation position and the formation position.

Therefore, when designing the inkjet recording apparatus of this embodiment, the installation distance of the potential stabilizing means 6, the printing speed, and the recording sheet 4 should be determined so that 2・t・/a2≧0.4. , it is possible to always obtain good recorded images.

◎Second Embodiment In the first embodiment described above, the ink 2 ejected from the ink ejection openings 15 of the head body 1 was directly attached to the recording sheet 4 for printing, but in this embodiment, the ejected ink 2 is temporarily attached to a roll-shaped intermediate transfer body 8,
A configuration is adopted in which this ink is transferred to the recording sheet 4.

The intermediate transfer body 8 also has the function of an electrostatic induction electrode, and an insulating layer 82 of polyurethane resin is spray coated on the outer peripheral surface of a roll-shaped electrostatic induction electrode 81 by approximately 100 mL.
It is formed with a film thickness of 0.00 μm, and is further covered with a polyurethane resin layer with a thickness of 5 μm in which tin oxide fine powder with a particle size of 0.5 μm is dispersed. Note that reference numeral 83 is a transfer roll for transferring ink dots attached to the intermediate transfer body 8 onto the recording sheet 4.

In this embodiment, the potential stabilizing means 6 is an aluminum electrode roll that comes into contact with the outer circumferential surface of the intermediate transfer body 8 and is driven by the rotation of this, and this electrode roll is similar to the first embodiment. It is maintained at the same potential as the electrostatic induction electrode 81.

Next, the results of printing experiments in this example will be reported. As in the first embodiment, the experiment was conducted by varying the distance a of the potential stabilizing means 6 and the printing speed tJ. The charge diffusion constant of 2 on the outer peripheral surface of the intermediate transfer body 8 was measured and calculated using the method described in the first embodiment, and was found to be 2-40.

The results are shown on the next page.

Table 2 In the results of this experiment, almost the same tendency as in the first example appeared, and it was found that good printing was performed when the value of the evaluation formula was 0.4 or more.

For this reason, the present invention is not limited to the type of recording medium to which flying ink adheres, such as those that print directly on the recording sheet 4 or those that print via the intermediate transfer body 8, but the following formula can be used. It was confirmed that by selecting the arrangement distance a of the potential stabilizing means 6 or the printing speed tj so as to satisfy t・/a2≧0.4, it was possible to obtain a good recorded image without any disturbance. .

[Effects of the Invention] As explained above, according to the inkjet recording device of the present invention, the electric charge attached to the recording medium during the printing operation can be removed by the potential stabilizing means, and the electrostatic field that electrostatically attracts the ink can be removed. Since it is possible to prevent the ink from fluctuating due to the charging of the recording medium, the flying of ink is stabilized and it is possible to produce a good recorded image by 1q.

[Brief explanation of drawings]

FIG. 1 is a cutaway perspective view schematically showing a first embodiment of the in-plane weight recording device of the present invention, FIG. 2 is a sectional view taken along line II in FIG. 1, and FIG. FIG. 4 is an explanatory diagram showing a measuring method, and is a sectional view showing a second embodiment of the present invention. [Explanation of symbols] 1: Head body 2: Ink 3 Thermal energy applying means 4: Recording sheet (recording body) 5: Electrostatic energy applying means 6: Potential stabilizing means 8: Intermediate transfer body (recording body) 15: Ink Ejection port 16: Ink ejection part 17: Ink chamber

Claims (1)

[Claims] An energy signal including at least electrostatic energy according to image information is transmitted to a head body having an ink chamber in which an ink discharge port is opened, and to each unit area of ink held in the ink discharge portion facing the ink discharge port. The present invention is characterized by comprising: an energy applying means for applying energy; and a potential stabilizing means, which is arranged in contact with the recording body that receives the ink flying from the ink ejection opening, and stabilizes the surface potential of the ink receiving surface of the recording body. Inkjet recording head.