JPH0292670A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To always stably print by providing a spacer member for holding a gap between a recording sheet and a head body constant in a head body, and disposing to bring the member into pressure contact with the sheet. CONSTITUTION:Since a protrusion 25 for a spacer is formed on the side end of the ink discharge port 10 of a recording head body 2 and an electrostatic induction electrode 19 of the conveying support of a recording sheet 4 is energized with respect to the body 2, the sheet 5 passing the front side of the electrode 19 is always pressed to the protrusion 25 at the time of printing, and a gap between the surface of the sheet 5 of a flying ink adhering surface and the port 10 is held constant according to the height of the protrusion 25. Accordingly, since the thickness of an air layer between the ink adhering surface and the port 10 becomes constant, the intensity of an electrostatic field formed between a head side electrode 18 and an electrostatic induction electrode 19 becomes substantially constant, stable electrostatic induction force is operated at ink 3 held by an ink discharger 11 to always form an ink column of predetermined shape on the port 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording device, and particularly relates to an improvement in an inkjet recording device in which ink is caused to fly by an energy signal containing at least electrostatic energy. .

[Prior Art] In a conventional inkjet recording device that uses electrostatic energy, for example, a slit-shaped ink chamber filled with a predetermined amount of ink is formed in the head body, and a surface is formed at the ejection port of this ink chamber. An electrode array consisting of a group of electrodes arranged according to the pixel density is provided on one side of the ink ejection portion, while an electrode for electrostatic induction is provided on a portion of the ink chamber facing the ink ejection port. By applying a control signal according to the image information between each electrode and the electrostatic induction electrode, an electrostatic signal is applied to the ink facing the electrode array, and the electrostatic induction electrode is applied between the ink surface and the electrostatic induction electrode. An electrostatic type is known in which an electrostatic field corresponding to the image pattern is formed in the image pattern, and this electrostatic attraction causes ink to fly toward the recording sheet placed in front of the electrostatic induction electrode ( V
1 Kaisho 56-37163). Another example is a thermoelectrostatic type developed by the inventors of the present invention, specifically, a head main body is formed with a slit or through-hole ink chamber filled with a predetermined amount of ink, and this ink chamber is On one side of the ink ejection part facing the ink ejection port, a heat generating resistor array, etc., consisting of a group of heat generating resistors arranged according to the pixel density, is provided. An electrostatic signal applying means is provided to apply an electrostatic signal to the ink in order to apply an electrostatic field. It is already known that each unit of ink ftJIa heated by a predetermined electrostatic attractive force from an electric signal applying means is made to fly toward the recording sheet side according to an image pattern (Japanese Patent Application Laid-Open No. 162-225388). It is being

[Problems to be Solved by the Invention] In this type of inkjet recording device, the electrostatic attraction of the electrostatic field formed between the electrode array on the recording head side and the electrostatic induction electrode causes the ink ejection portion to The retained ink is raised from the ink ejection opening in a columnar manner, and the tip of the ink column contacts and adheres to the recording sheet, thereby forming a printed dot. Therefore, in order to obtain stable printed dots, a stable electrostatic attraction force is applied to the ink held in the ink ejection section, and an ink column of a substantially constant shape is always formed on the ink ejection port of the head body. It becomes necessary to always keep the distance between the recording sheet to which the ink adheres and the ink ejection opening constant, and to bring the ink column into contact with the recording sheet with a constant cross-sectional diameter.

However, in conventional devices, the recording head and the electrostatic induction electrode are positioned so that the gap between the ink ejection port and the electrostatic induction electrode is constant, so the gap between the ink ejection port and the electrostatic induction electrode is fixed. When the type of recording sheet that passes between the recording sheet and the ink discharge electrode changes, the thickness of the air layer between the recording sheet and the ink ejection orifices also changes as the thickness of the recording sheet changes. For this reason, if the J so of the recording sheet changes,
The strength of the electrostatic field formed between the head side electrode and the electrostatic induction electrode changes, and an unstable electrostatic attraction force acts on the ink held in the ink ejection part, so it always maintains a constant shape. The problem is that the ink column is not formed on the ink ejection opening of the head main body.

Furthermore, even if an ink column of a certain shape is formed on the ink ejection port, the ink may adhere to the surface of the recording sheet due to changes in the movement of the recording sheet or bending of the recording sheet in the printing section. Another problem is that the gap between the ink discharge port and the ink discharge port changes, and the ink column does not contact and adhere to the recording sheet with a constant cross-sectional diameter, making it impossible to obtain ink dots with a constant diameter on the recording sheet.

Furthermore, when assembling the device, in order to obtain ink dots of a desired diameter, it is necessary to position and fix the head body in μm units relative to the conveyed recording sheet, which poses the problem of requiring time and effort to assemble the device. It also had points.

[Means for Solving the Problems] The present inventors analyzed the problems mentioned above as follows, and came up with the present invention.

Specifically, the strength of the electrostatic field formed between two electrodes is determined by the distance between the north poles and the relative dielectric constant of the material that exists between these electrodes, and the head The strength of the electrostatic field formed between the ink discharge port of the main body and the static N induction electrode is expressed by the following equation.

I /ε1+12/ε2 C: Constant determined by shape V: Voltage applied between head side electrode and electrostatic induction electrode 11: Recording sheet thickness 12: Air layer between recording sheet and ink ejection port Thickness ε, : Relative permittivity of the recording sheet ε2 : Relative permittivity of air (-1) In this case, the relative permittivity of the recording sheet changes depending on the moisture ω contained in the sheet, but generally ε, = about 3. and
This is larger than the dielectric constant of air. Therefore, from the above formula, the thickness of the recording sheet! Compared to the case where the thickness I2 of the air layer changes, the effect on the electrostatic field strength E is greater than when The inventors have come to the conclusion that it is important to maintain a constant gap between the recording sheet surface to which ink adheres and the ink ejection port.

The present invention was made based on the above-mentioned conclusion, and
An object of the present invention is to provide an inkjet recording device that maintains a constant gap between a recording sheet and a head main body and can always perform stable printing.

In order to achieve the above object, an inkjet recording apparatus of the present invention includes a head body having an ink chamber in which an ink discharge port is formed, and an ink jet recording apparatus that is configured to have an ink jet recording apparatus that includes a head body having an ink chamber in which an ink discharge port is opened, and an ink jet recording apparatus that retains ink in the ink discharge section facing the ink discharge port of the ink chamber. and an energy applying means for applying an energy signal including at least electrostatic energy according to image information to each unit area, and a spacer member disposed on the head main body side is placed in pressure contact with the recording sheet, The present invention is characterized in that a gap regulating means is provided to maintain a constant gap between the head body and the recording sheet.

In such technical means, if the head main body of the recording head has an ink chamber and is provided with a spacer member, the design of the constituent members of the head main body and the shape of the ink chamber may be changed as appropriate. There is no problem, and the specific form of the ink discharge port of the ink chamber may be either a slit or a through hole.

Further, the spacer member of the gap regulating means may be appropriately selected in shape and forming method as long as it maintains a constant gap between the recording sheet and the recording head body. They may be formed continuously along the direction, they may be formed in the form of a large number of islands at intervals, or they may be formed only at both ends of the head body. In addition, the formation methods include forming the head body including the spacer member and then cutting it, using glass as the spacer member and forming it on the edge of the head body using a printing method, and adding a film or metal member to the head. Possible methods include adhering it to the main body. Note that in order to prevent the ink attached to the recording sheet from coming into contact with the spacer member during conveyance of the recording sheet, the spacer member is preferably formed on the upstream side of the ink ejection port in the conveyance direction of the recording sheet.

In addition, as a method for placing the spacer member in pressure contact with the recording sheet, the spacer member provided on the head body is pressed against the recording sheet appropriately, and the gap between the head body and the recording sheet is always kept constant. The configuration shape may be selected as appropriate, such as one that urges the head body against the recording sheet, or one that presses the recording sheet against the head body by urging the conveying support for the recording sheet.

Further, the energy applying means may be appropriately selected according to the type of recording head. For example, if it is a thermoelectrostatic type, it will be a combination of a thermal signal applying means and an electrostatic signal applying means. In this case, the thermal signal applying means may be a heat generating resistor array in which a plurality of heat generating resistors are arranged according to the pixel density to indirectly heat the ink, or radiation may be used as a heating source. The ink may be heated for each pixel density, or the ink itself having a predetermined wi resistivity may be heated by direct energization.On the other hand, regarding the electrostatic signal applying means, The design may be changed as appropriate as long as it uniformly generates an electrostatic attraction force sufficient to cause the unit area of ink heated by the thermal signal applying means to fly toward the recording sheet side. In addition, for electrostatic types, if the ink discharge unit can selectively fly ink unit areas corresponding to the pixel density according to image information, the ink discharge unit can fly ink according to the pixel density. The design may be changed as appropriate, such as by providing a control electrode and applying an electrostatic signal according to image information to a corresponding unit area of ink via each electrode.

Furthermore, as long as the electrostatic induction electrode, which is one element of the electrostatic energy application means, is made of a conductive material, the design of the arrangement position, shape, size, etc. may be changed as appropriate, but the device configuration From the point of view of simplifying the
It is desirable to run the recording sheet by intermittently rotating the cylindrical electrode which also serves as the supporting direction of the recording sheet. Further, since the electrostatic induction electrode is usually disposed at a position facing the ink ejection opening of the head body, it is preferable to perform a treatment on the outer circumferential surface to suppress spark discharge with the head body side electrode. For example, resins such as Teflon, polyester, polyurethane, polycarbonate, polyimide, etc.
By providing an insulating layer made of rubber such as plain rubber, or by dispersing carbon black or tin oxide fine particles in these resins or rubber materials, the volume resistivity can be increased to 109.
One example is to provide a high-resistance layer such that the resistance is 0 CAR or less, but from the viewpoint of preventing charging of the outer circumferential surface of the electrode due to contact with a recording sheet, it is preferable to provide a high-resistance layer.

[Function] According to the inkjet recording device configured as described above, the head body is provided with a spacer member that maintains a constant gap between the recording sheet and the head body, and this spacer member is always placed in pressure contact with the recording sheet. Therefore, the gap between the recording sheet surface where the flying ink flows and the ink ejection opening of the head main body is always kept constant depending on the height of the spacer member.

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

1 and 2, the present invention is applied to a thermoelectrostatic type inkjet recording device, and shows a head body 2 having a slit-like space 1 and ink held in the ink chamber of the head body 2. a thermal energy applying means 4 for applying thermal energy to the ink 3 and the recording sheet 5;
and an electrostatic energy applying means 6 for forming a predetermined electrostatic field between them.

First, as shown in FIGS. 2 and 3, the head body 2 is made of an insulating substrate 7 made of glass with a thickness of about 3#l1lI, and a thick aluminum ceramics on which an 8102 layer 34 of about 60 μm is formed. It is composed of an insulating M board 8 with a length of about 1M, and on the wall of the insulating board 7 on the upper side,
As shown in Figure 2, a depth of about 1a was created using the sandblasting method.
The lower insulating substrate 8 has a recess 9 formed therein.
has a thickness of approximately 50 μI along its outer periphery, excluding the tip side.
A ]-shaped spacer (not shown) made of a polyester film of 1 is provided, and these insulating substrates 7 and 8 are adhered via the spacer to form an ink ejecting section 11 and an ink holding section 12. A slit-like space 1 is secured in which the

Near the ink ejection port 10 at the tip of the insulating substrate 7, there is a third
As shown by the shaded area in the figure, the ink ejection ports 10 to 100
~200μm distance A''c^sa 100~300μ7
A spacer protrusion 25 of 71L is formed along the entire length of the ink ejection port 10, and the spacer protrusion 25
A tapered portion is provided on the side surface opposite to the ink ejection opening 10 so that the recording sheet 5 can be conveyed smoothly. The spacer protrusion 25 is the spacer protrusion 25
After forming the insulating substrate 7 including the insulating substrate 7, unnecessary portions are removed using a dicing saw.

The head main body 2 configured as described above is fixed to a head holder 25, and is positioned and fixed to the apparatus main body via the head holder 25.

On the other hand, the thermal energy applying means 4 is formed by depositing a film by a reactive sputtering method and by a photolithographic etching method, and from a Ta, N thin film having a thickness of about 300 pixels for every pixel density (for example, 8 dots [/rtm]). heating resistor 13
Each heating resistor 13 is arranged facing the front edge of one side of the sulin 1-shaped space 1, and each heating resistor 13 has a Ni- A pair of current-carrying electrodes 14 are connected to the electrodes 14, which are formed by sequentially and continuously uniformly depositing approximately 500 Cr and approximately 1 .mu.m AU by photolithography. A switching element 15 that opens and closes in response to an image control signal is connected between each of the current-carrying electrodes 14. Reference numeral 16 denotes an insulating layer of SiO2 or the like having a thickness of approximately 2 μm formed by high-frequency sputtering to insulate and cover the heating resistor 13 and each of the current-carrying electrodes 14, and 11 a power supply for energizing each of the heating resistors 13. , is.

Further, the electrostatic energy applying means 6 is shown in FIGS. 2 and 3.
As shown in the figure, on the insulating layer 16, approximately SOO of Cr and C
A head-side electrode 18 formed by sequentially depositing about 10,000 U and about 500 Cr, a roll-shaped electrostatic induction electrode 19 placed appropriately away from the three ink surfaces, and a head-side electrode. 18 and an electrostatic induction power source 20 that is interposed between the electrostatic induction electrode 19 and forms an electrostatic field from the ink 3 surface toward the electrostatic induction electrode 19 side.

Note that the head side electrode 1B is grounded.

The electrostatic induction electrode 19 also functions as a transport support for the recording sheet 5, and uses a roll-shaped aluminum electrode as a core material, and has a volume resistivity of 1X1 on its outer peripheral surface.
08Ω1, rubber hardness 50° chloropropylene rubber 3
The first rocking body 22 made of an insulating material can be rotated via a conductive bearing 23 in order to apply an arbitrary voltage by the electrostatic induction power source 20. The rotational driving force is applied from one end in the axial direction (not shown). The first rocking body 22 is rotatably fixed to the main body of the apparatus by means of a bin member 26 together with the second rocking body 24 in consideration of paper jam removal and maintenance.
The free end of the bottle member 2 has a retaining ring 28a at one end.
8, the bin member 2
8 is a spring member 2 consisting of a coil spring in a compressed state.
1 is interposed. A claw-like protrusion 29 is formed at the tip of the second rocking body 24, while a locking member 30 is rotatably provided on the device body, and a biasing spring 32 pushes against the stopper wall of the device body. By engaging the protrusion 29 with the locking member 30, the second rocking body 24 is prevented from returning due to the elastic force of the spring member 21, and conversely, the second rocking body 24 is held by the second rocking body 22. The electrostatic induction electrode 19 is continuously pressed against the head body 2 with a linear pressure of 20 to 401 Jr/m by the elastic force of the spring member 21. Incidentally, reference numeral 31 denotes a cleaning member, which comes into contact with the electrostatic induction electrode 19 when the electrostatic induction electrode 19 is pressed, and cleans the outer circumferential surface of the electrostatic induction electrode 19.

The ink contained in the slit-like space has a viscosity of 150. CP, S exhibits the values of surface tension 36 dyne/3, volume resistivity 2 x 10'' Ω1, and conductivity that decreases to the values of viscosity 5 cps, surface tension 20 dyne, 'α, and volume resistivity 1 x 1080 α when heated (150 ° C). oil-based ink is used.

Therefore, according to the inkjet recording apparatus according to this embodiment, 0, 2iJ -0 according to the information of the image to be recorded.
, 6iJ is applied to the heating resistor 13 of the energy applying means 4, the heating resistor 13 generates heat, and the corresponding ink unit area receives thermal energy and is heated. Then, in this heated ink 3 unit region, the viscosity and surface tension of the ink 3 decrease and its electrical conductivity improves. On the other hand, in synchronization with the driving timing of the thermal energy applying means 4, V is applied to 2,0, 0.
．． When an electrostatic 1lIIJ control pulse of 6+1 SeC is applied to the electrostatic induction electrode 19 of the electrostatic energy application means 6, an electrostatic field is formed between the ink 3 surface and the electrostatic induction electrode 19, and this electrostatic field Based on this, the heated ink 3 unit region flies toward the electrostatic induction electrode 19, and ink dots 30 are formed on the surface of the recording sheet 5 located on the front side of the electrostatic induction electrode 19.

At this time, in this inkjet recording apparatus, a spacer protrusion 25 is provided at the side end of the ink discharge port 10 of the recording head main body 2, and an electrostatic induction electrode 19, which is a conveying support for the recording sheet 5, is provided. Since the head body 2 is energized, during printing, the recording sheet 5 passing in front of the electrostatic induction electrode 19 is always pressed against the spacer protrusion 25, and the flying ink adheres to the surface. The gap between the surface of a certain recording sheet 5 and the ink ejection port 10 is maintained constant according to the height of the spacer protrusion 25.

Therefore, since the thickness of the air layer between the ink adhesion surface and the ink ejection port 10 is constant, the strength of the electrostatic field formed between the head side N pole 18 and the electrostatic induction electrode 19 is approximately constant. Therefore, a stable electrostatic attraction force acts on the ink 3 held in the ink ejection portion 11, and an ink column having a substantially constant shape is always formed on the ink ejection port 10.

On the other hand, the spacer meeting protrusions 25 prevent the recording sheet 5 from becoming loose in the printing section, and the surface of the recording sheet 5 and the ink ejection ports 10 are always kept constant regardless of changes in the thickness of the recording sheet 5. Since the ink column is held in the gap, the tip of the ink column raised in a substantially constant shape on the ink ejection port 10 always contacts and adheres to the recording sheet 5 with a constant cross-sectional diameter, and an ink dot with a constant diameter is formed on the recording sheet 5. is formed.

On the other hand, as a comparative example, a recording device between the above-mentioned embodiment and the track was constructed in which a head body without a spacer protrusion was positioned and fixed with respect to the rotating shaft of an electrostatic induction electrode whose shaft was fixed. The printing properties of the recording sheet were tested by conveying it in close contact with the electrostatic induction electrode.

In the recording device of this comparative example, fluctuations in the gap between the electrostatic induction electrode and the ink ejection port caused by the eccentricity of the rotation axis of the electrostatic induction electrode cause periodic changes in the diameter of the ink dots formed on the recording sheet. As a result, a stable recorded image could not be obtained because density unevenness and printing defects continued to occur in the recorded image.

This confirmed the effectiveness of providing the spacer protrusion on the head body of the inkjet recording apparatus in this example.

[Effects of the Invention] As described above, according to the inkjet recording apparatus according to any one of claims 1 to 4, the air layer between the recording sheet surface, which is the surface to which flying ink is attached, and the ink ejection port is reduced. It is possible to maintain a constant thickness, and by keeping the strength of the electrostatic field formed between the head-side electric cylinder and the electrostatic induction electrode approximately constant, the ink held in the ink ejection part can be By applying a stable electrostatic attraction force, it is possible to always form an ink column having a substantially constant shape on the ink ejection port.

In addition, since the spacer member is in pressure contact with the surface of the recording sheet in the vicinity of the ink ejection orifice, it is possible to prevent the recording sheet from becoming loose in the printing area, and the surface of the recording sheet is always kept on the surface of the recording sheet regardless of changes in the thickness of the recording sheet. Since the ink discharge port and the ink discharge port are maintained at a constant gap, the ink column formed on the ink discharge port always contacts and adheres to the recording sheet with a constant cross-sectional diameter, forming an ink dot of a constant diameter on the recording sheet. Is possible.

Furthermore, the gap between the recording sheet surface and the ink ejection ports is automatically maintained constant by pressing the recording sheet and the spacer member, which facilitates positioning of the head main body when assembling the apparatus.

Further, according to the inkjet recording apparatus according to the second aspect, since the ink that has come into contact with and adhered to the recording sheet does not come into contact with the spacer member provided on the head main body, it is possible to obtain a good image without deterioration.

In addition, in claim 3, i&! According to the inkjet recording device described above, the surface of the recording sheet facing the ink ejection ports does not bend in the length direction of the ink ejection ports, and
Constant ink dots are always formed on the surface of the recording sheet over its entire length.

Further, according to the inkjet recording apparatus described in claim 4, the electrostatic induction electrode, which is an element of the electrostatic energy applying means disposed at a position facing the ink ejection opening of the head main body, is insulated. It is possible to effectively suppress the occurrence of spark discharge between the two electrodes by shielding it from the head-side electrode with the outer peripheral member equipped with a layer or high-resistance layer, so it is possible to effectively suppress the occurrence of spark discharge between the two electrodes. Therefore, it is possible to effectively prevent ink scattering and heat damage to the head body.

In particular, when a high-resistance layer is provided on the outer peripheral member of the electrostatic induction electrode, even if the outer peripheral member is temporarily charged due to contact with a recording sheet, the charged charge is removed through the high-resistance layer. can do.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of an inkjet recording apparatus according to the present invention, and FIG. 2 is a perspective view of a main part of the inkjet recording apparatus according to the first embodiment, a part of which is a perspective view. FIG. 3 is a sectional view of a main part showing the operating state of the inkjet recording apparatus according to the first embodiment, and FIG. 4 is a perspective view showing the vicinity of the ink discharge ports of the head body of the inkjet recording apparatus according to the first embodiment. [Description of symbols] 1 slit-like space 3: ink 5: recording sheet 7.8: insulating substrate 13: heating resistor 19: electrostatic induction electrode 22: first oscillator 25; spacer protrusion

Claims (1)

[Scope of Claims] 1) A head body having an ink chamber with an ink discharge port, and image information for each unit area of ink held in the ink discharge portion facing the ink discharge port of the ink chamber. In the inkjet recording apparatus, the spacer member disposed on the head body side is placed in pressure contact with the recording sheet, and the head body and the recording sheet are connected to each other. An inkjet recording apparatus characterized by being provided with a gap regulating means for maintaining a constant gap. 2) The inkjet recording apparatus according to claim 1, wherein the spacer member is provided upstream of the ink ejection port in the recording sheet conveyance direction. 3) Claim 1 or 2, wherein the spacer member is provided along substantially the entire length of the ink discharge port in the longitudinal direction.
The inkjet recording device described above. 4) The surface of the electrostatic induction electrode, which constitutes a part of the energy application means and is disposed at a position facing the ink ejection port of the head body, is coated with an insulating layer or a height resistance layer. The inkjet recording apparatus according to claim 1.