JPS6357248A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To permit high-density and high-speed recording by a method in which a heater is provided near an opening through which ink is flown, and the ink is turned fliable by lowering the surface tension and viscosity of ink. CONSTITUTION:A heater 7 provided near a slit opening 5 is made of a heating resistor 20 of Ta-ZrO2 provided on the inner surface of other glass base plate 12. As the heating resistor 20, ones having a resistance value capable of controlling temperature of ink by a power controller, such as ceramic heater, plastic film heater, etc., having practically controllable heating width of about 1mm for example, may be cited. The ink 3 used includes conductive inks having temperature dependence characteristics by which viscosity and surface tension lower as temperature rises and adequate volume resistivity, such as oily and aqueous ones. The heater 7 may have a heating region enough to heat flying ink alone, not to heat all ink packed in an ink chamber 2.

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 of a type in which ink is caused to fly by attraction based on an electrostatic field.

[Prior Art] Conventionally, as this type of ink jet recording apparatus, there is a so-called slit jet recording apparatus as disclosed in, for example, Japanese Unexamined Patent Publication No. 56-37163. this is,
A slit-shaped ink chamber filled with a predetermined ink is formed in the head body, and an electrode array consisting of a group of electrodes arranged according to the pixel density is provided near the opening of the ink chamber. A counter electrode is provided at a portion facing the aperture surface (by applying an electrostatic signal according to image information between each electrode of the electrode array and the counter electrode, the ink surface facing the electrode array and the counter electrode are placed opposite to each other). An electrostatic field pattern corresponding to the image pattern is formed between the electrode and the electrostatic field, and the attractive force based on this electrostatic field causes ink to fly toward the recording sheet placed in front of the counter electrode. be.

[Problems to be Solved by the Invention] By the way, in the above-mentioned slit diene systems 1 to 1, in order to make ink fly, an electrostatic signal with a large voltage value is generated between each electrode of the electrode array and the counter electrode. Therefore, voltage leakage is likely to occur between adjacent or nearby electrodes, especially when the electrode array is densely packed. Therefore, in order to prevent this voltage leak, it is necessary to time-divisionally drive the electrode array, which limits the ability to achieve high-speed recording.

In order to solve this problem, the inventors analyzed the recording operation process of the above-mentioned slit jet method and considered what points should be improved to enable high-speed recording. The following results were obtained.

That is, in the Surin 1 to Jet method described above, an attractive force due to an electrostatic field is applied to the ink liquid level filled in the ink chamber, and a surface wave corresponding to a certain wavelength is generated by the competition between the attracting horn and the surface tension of the ink. It is thought that the growth of this surface wave causes the corresponding ink portion to rise toward the recording sheet side.

Analyzing this phenomenon based on electrohydrodynamic theory, we find that the wavelength of the surface wave mentioned above is λ, and the wave number is 2π/λ.
, if the growth rate of the surface wave in the direction of electrostatic field application is defined as n [assuming the growth rate to be an exponential function of e, nj (t, time)], then 1. 42 (ka) -2(ka) -A-(k'a)2
-4(ka)"・B・(k'a>+(ka)'-(
ka)2- (ργa) /u2- B-f(k) =
It has been found that the relational expression (1) holds true.

In equation (1), the following (2) or 5
) formula is used.

(k'a) 2-(ka)2+D n/μm'...-
・(2) f(k) −(εOV) / (rata
nh(ka))-ka...(3)A-(ρ-ρta
nh(ka)) / (ρtenρtanh(ka)) ・
Song・(4)B=,c+tanh(ka)/(ρ+ρt
anh (ka)) - - - - (5) However, each code used in formulas (1) to 5) is as follows.

a: Gap (μTrL) ρ between the ink liquid surface and the counter electrode
: Air density ρ: Ink density γ: Ink surface tension (dyne/cm) μ: Ink viscosity (cps) ε. : Dielectric constant of air V: Electrostatic signal voltage (V) Then, the specific parameter (a
= 250 μm, 7-40 dyne/cm, V
= 2500v) and the calculation result obtained in the 8th
It is shown in Figure (a). In the same figure, conductive ink (for example, μm30Cp) commonly used in the slit jet method is shown.
S), we find that ka < 5.5, that is, λ
>285 (μTrL) surface waves can only grow, and if the pixel density is 8 dots/mm, the surface wave wavelength λ
must be 125 (μm), and even if we consider it in half wavelength, it must be λ-250 (μm), so it is possible that unit ink areas corresponding to adjacent electrode parts cannot fly at the same time. It also makes sense theoretically.

Here, FIG. 8(b) shows the calculation results obtained by replacing some of the parameters, for example, the surface tension γ of the ink with 20 dyne/Cm in the above-mentioned equation (1). According to the same figure, 3
It is understood that in the case of conductive ink with 0 (Cps), surface waves with ka < 111, that is, λ > 141 (μTrL), can grow, and the growth rate itself also increases, and this point was taken into consideration. As a result, it has been found that it is preferable to use ink with low surface tension in order to achieve high-speed recording in the three-jet method.

By the way, in FIGS. 8(a) and (b), it was shown that the growth rate n of the surface wave is dominated by the isodirectional wave number, but
When a normal slit opening is used as an ink flying opening in an ink chamber, the influence of this slit opening cannot be ignored. In other words, if q is the opening width of Surin 1, a surface wave of λx-2g is formed in the width direction (x direction) of the slit opening, so
If the wavelength of the surface wave in the direction) is λ, then the substantial growth rate n of the surface wave corresponds to −f((π/g> +(2π/λ)2).

Now, when g=150 (μm), the actual growth rate n(
The calculation results of λ, ) are shown in FIGS. 8(a) and 8(b). In the figure, the minimum wavelength for the start of flight is approximately 900 μm for 40 dyne/cm ink, but for 20 dyne/cm ink,
/cm of ink, it would be about 160 μm.

On the other hand, since the ink flying speed is limited to a response in the vicinity of 1π/Ω, the dependence on λ is almost eliminated, but the dependence on viscosity becomes large. That is, if normal ink (surface tension γ = 40 dyne/cm
, viscosity μ = 30 cps) as 7 = 20 dyne/
cm, μm5 cps, the density of dots that can be simultaneously flown is 160:900=5.
6 times higher, and the ink flight speed is 130
It is confirmed that the speed becomes faster by 00 near 50 = 17 times. Based on this, considering the conditions for high-density, high-speed recording,
It turns out that it is sufficient to use an ink with low surface tension and low viscosity.

However, it is extremely difficult to create the above-mentioned low surface tension and low viscosity ink at room temperature, so it is difficult to increase the recording speed by driving the electrode arrays all at once in a highly dense electrode array. The current situation is that this has not actually been achieved.

[Means to Solve the Problem] The inventors of the present invention focused on the property that the surface tension and viscosity of ink depend on temperature, and developed a method for high-density, high-speed recording based on the basic structure of the so-called slit jet method. This made it possible.

That is, the present invention provides a head body having an ink chamber with an opening for ink flying, a large number of control N poles disposed in each ink unit area according to pixel density, and A counter electrode is provided facing the opening surface, and an IC electrostatic signal is applied between each control electrode and the counter electrode according to image information, and an IC electrostatic signal is formed between the ink surface and the counter electrode. The present invention is based on an inkjet recording apparatus in which ink is ejected onto the recording sheets 1 to 1 disposed on the front side of a counter electrode by an attractive force based on an electrostatic field, and a heating means is provided in the vicinity of the ink ejection opening. be.

In such technical means, the head main body may be designed by appropriately changing the design as long as it has a predetermined ink chamber, but considering manufacturing workability, two insulating substrates may be spaced apart, It is desirable that an ink chamber be secured between both members. In addition, it is preferable that the ink flying opening be slit-shaped from the viewpoint of effectively preventing ink clogging, and from the viewpoint of reliably dividing the ink unit area to be jetted according to the pixel density. From this point of view, a hole-shaped one is desirable.

Further, as for the control electrode and the counter electrode, as long as they are designed so that an electrostatic field pattern corresponding to the image pattern can be formed on the ink surface, the design of the arrangement position and shape may be changed as appropriate. In addition, the ink used may be oil-based or water-based, as long as it has temperature-dependent characteristics such that the viscosity and surface tension decrease as the drying temperature increases, and it is a conductive ink with an appropriate volume resistivity. .

Furthermore, the heating means does not need to heat the entire ink filled in the ink chamber, and may be designed to heat only the part of the ink that is substantially in flight.
The specific amount of heating is determined as appropriate, taking into account the strength of the electrostatic field, the physical properties of the ink used, the gear between the end of the head body and the counter electrode, etc. It is desirable that the heating means be placed within a range of approximately 1 mm from the end of the head body. Regarding the specific configuration of the heating means, as long as it can heat the part of the ink that can fly, it may use a heat generating resistor or the like. You may change the design as appropriate, such as by using IT.

[Operation] According to the above-mentioned technical means, the portion of the ink filled in the ink chamber facing the ink flying opening is heated by the heating means, and at this time, the heated ink portion The surface tension and viscosity of the particles are reduced, making them easier to fly. In this state, even if a not-so-large amount of energy is applied between the control electrode and the counter electrode as an electrostatic signal according to the image information, no electrostatic signal is formed between the ink facing the control electrode and the counter electrode. Due to the attractive force of the electrostatic field, the corresponding ink portions reliably fly toward the recording sheet disposed in front of the counter electrode.

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

◎Example 1 In FIG. 1, Infusiera 1 to the recording device include a head main body 1 having a slit-shaped ink chamber 2, and an ink chamber 2.
An electrode array consisting of a large number of control electrodes 4 is arranged facing each ink unit area corresponding to the pixel density of the ink 3 filled in the ink chamber 2, and an electrode array is arranged facing the slit opening 5 of the ink chamber 2. A counter electrode 6 is provided, and a heating means 7 is provided near the slit opening 5.

In this embodiment, the head main body 1 includes a pair of glass substrates 11.12 and a slit-shaped ink chamber 2 formed between the pair of glass substrates 11.12, as shown in FIGS. 2 to 4. A spacer member (not shown) made of an insulating resin film is interposed therebetween.

In addition, the above control electric +! i4 is one of the above glass substrates 11
Specifically, a metal layer made of Cr/CLJ/Cr with a thickness of 1000A is deposited on the entire surface of the inner surface of the glass substrate 11, and a photolithography process is applied to this entire surface metal layer. By applying this process, an electrode pattern with a pixel density of, for example, 8 lines/# is formed, and Ni is placed on the electrode pattern to a thickness of about 2 μm and grown by a plating method.

This control electrode 4 is approximately 100μ from the edge of the glass substrate 11.
m, and these control electrodes 4
In order to prevent short circuits between the control electrodes 4 due to deposits as much as possible, an insulating protective layer 13 made of SiO2 or the like is formed with a thickness of about 10 μm, leaving an exposed portion of 500 μm from the edge of the glass substrate 11. It is coated with a film. Then, +350(v), O(
A first switching element 14 for switching V) is connected.

Further, the heating means 7 includes a heating resistor 20 made of Ta-7r02 provided on the inner surface of the other glass substrate 12.
Specifically, on the inner surface of the glass substrate 12, a metal layer 21 made of Aj with a thickness of approximately 5 μm is vacuum-deposited on the entire surface, and from the edge of the glass substrate 12, a metal layer 21 of about 5 μm
After removing a band-shaped region located between 0 μm by a photolithography process, the heat generating resistor 20 was deposited to a thickness of about 500 Δ by a mask sputtering method. and the heating resistor 20 located between the two separated metal layers 21 (specifically, 21a and 21b).
The resistance value is about 30Ω, and an insulating protective layer 22 made of 5i02 is entirely deposited on the heating resistor 20 and the metal layer 21 to a thickness of about 2 μm. And furthermore,
Between the separated metal layers 21a and 2Ib is a type for energizing the heating resistor 20. +! 23 are connected.

Then, one glass substrate 11 on which the control electrode 4 is formed
and the other glass substrate 12 on which the heating resistor 20 is formed are bonded to each other with a distance of about 100 μm using the above-described spacer member. After bonding both glass substrates 11.12, the ends of the head body 1 are polished to ensure parallelism of the end surfaces of both glass substrates 11.12. At this time, the control electrode 4 is connected to the head body 1
It is set at a position 50 μm from the end.

Further, the counter electrode 6 is a hole-shaped member that can be rotated in steps, and also has the function of a conveyance member for the recording sheet 8. They are placed with a gap between them. The counter electrode 6 has a voltage of -1700 (v) according to the image information.
), Q (v), a second switching element 1 that switches
5 is connected.

Furthermore, the supply pressure of the ink 3 filled into the ink chamber 2 is set so that the surface shape of the ink 3 is approximately parallel to the end of the head when no electrostatic signal is applied. Ink 3 used in this example is a dye-soluble oil-based conductive ink containing diisopropylnaphthalene as the main solvent, and has a viscosity of 35 cps at room temperature, 6 cps at 80°C,
The surface tension is 36 dyne/cm at room temperature,
The electrical resistivity is 28 dyne/cm at 80°C, 10 Ωcm at room temperature, and 107 Ωcm at 80°C.

Next, the performance of the inkjet recording apparatus according to this example will be evaluated.

Now, the temperature of the ink 3 in the slit opening 5 is about 8 by the thermocouple.
Appropriate electrostatic signal pulses are applied to the control electrode 4 array and the counter electrode 6 while adjusting the voltage applied to the heating resistor 20 (AC 50 Hz) so that the temperature is about 0°C, and at the same time the pixel density (d (dot)/#) and the upper limit of the frequency of the electrostatic signal pulse were investigated, and the results shown in the table below were obtained. The on-duty of the above pulse is 10
% (on operation time of 1 to off operation time of 9),
In addition, as Comparative Example 1, a case without heating is given, and Comparative Example 2
As an example, the case where the entire head body 1 is placed in a constant temperature bath at 80° C. and the entire ink 3 is heated is taken as an example.

Table According to the above table, it is confirmed that the example is a desirable embodiment in terms of achieving higher density and higher speed.

Furthermore, in order to analyze how the depth dimension aS of the heated region affects the flying speed of ink, the inventors of the present invention calculated the heating Assuming that the depth dimension a3 of the region is the position where the movement of the ink is blocked, calculations were performed for the case where the ink viscosity μ→0, and the results shown in FIG. 5 were obtained.

According to the same figure, setting m=a8/a (gap between the ink liquid level and the counter electrode) to 1.0 or less, preferably 0.1 or less increases the response speed in the long wavelength (short wavelength) region. It has been theoretically confirmed that this method is advantageous in terms of achieving the following. However, it has been experimentally confirmed that if aS is set smaller than necessary, the amount of movable ink itself will decrease, and the dot size to be recorded will become unnecessarily small. It is necessary to set the dimensions of a.

Incidentally, the heating resistor 20 used in this example is as follows:
If the resistance value is controlled to the extent that the ink temperature can be controlled by a known power control means, the actual heat generation width can be set to 1.
A ceramic heater, a plastic film heater, etc. can be selected as appropriate, provided that the temperature is kept to about M. Furthermore, if the heating resistor 20, which is the heating means 7, is relatively thick, a step will be formed at the slit opening 5, but the slit width should be maintained at about 50 to 200 μm at the ink flying part. If this is possible, there will be no hindrance to the ink flying operation.

◎Example 2 In FIGS. 6 and 7, unlike in Example 1, the heating means 7 includes a radiation absorbing layer 31 formed in a band shape near the slit opening 5 of the head body 1, and a radiation absorbing layer 31 formed in the vicinity of the slit opening 5 of the head body 1. layer 31
It is composed of a quartz lamp 32 that emits radiation.

In this embodiment, the head main body 1 has a pair of glass substrates 11 and 12, as in the first embodiment, and a radiation absorbing layer 31 is formed on the inner surface of one of the glass substrates 11.
A-3in2 was deposited by sputtering and patterned into a strip having a width of 150 λm and a thickness of 1000 Δ by dry etching after passing through the first lithography process.

Then, on the radiation absorbing layer 31, an insulating protective layer 33 made of 3i02 is deposited with a thickness of 2 μm by sputtering on the other side, and further on the insulating protective layer 33, the insulating protective layer 33 made of 3i02 is deposited with a thickness of 2 μm.
A similar control electrode 4 is connected to the radiation absorbing layer 31 with a thickness of 50 μm.
It is arranged so that it polymerizes to a certain degree. Furthermore, the control electrode 4 has a thickness of 500 μm (an insulating protective layer 34 made of SiO2 is deposited to a thickness of 2 μm on the control electrode 4 so as to be exposed).

Further, on the other glass substrate 12 constituting the head body 1, there is a spacer portion 12a formed by applying, for example, a heat-fusible glass gel by a screen printing method and then firing it.
00 μm thick, and due to the presence of this spacer portion 12a, there is a gap between the pair of glass substrates 11 and 12.
A slit-shaped ink chamber 2 with a width of 00 μm is secured. Then, the end of the head main body 1 is polished so that the dimension between the end of the head main body 1 and the radiation absorbing layer 31 is about 30 μm.

Further, the quartz lamp 32 is disposed near the slit opening 5 of the head body 1 on the downstream side in the feeding direction of the recording sheet 8, and is turned on at about 200 W. Note that the glass substrate 11 on which the radiation absorbing layer 31 is formed is placed on the quartz lamp 32 side.

Therefore, according to the inkjet recording apparatus according to this embodiment, when the quartz lamp 32 is lit, the quartz lamp 32 also
The irradiated light passes through the glass substrate 11 and is absorbed by the radiation absorption layer 31. Then, this radiation absorbing layer 31 generates heat, and the ink 3 located near this radiation absorbing layer 31
The part will be heated, and the same effect as in Example 1,
It is considered to be effective. In fact, when the present inventors investigated the dot density and operating frequency that can be printed simultaneously under the same conditions as in Example 1, substantially the same results as in Example 1 were obtained.

In addition, in this embodiment, a metal layer 2 is used as an electrode for supplying current to the heating resistor 20, which is required in the first embodiment.
1, the configuration of the heating means 7 to be incorporated into the head body 1 can be simplified accordingly.

Furthermore, in this embodiment, since the quartz lamp 32 is provided on the downstream side in the feeding direction of the recording sheet 8, the ink 3 that has been blown to the recording sheet 8 side by the heat from the quartz lamp 32 can be quickly fixed. becomes possible.

Note that the radiation absorbing layer 31 is not limited to that shown in the above embodiment, and may be made of Ta.

Ta-8i C, Ta-ZrO2, C, Ta-8i.

A heat-resistant metal thin film such as Cr S i O or Ta CS i 02, or a polymer resin film in which carbon black or the like is dispersed may also be used. Further, in the above embodiment, the control type II4 and the radiation absorbing layer 31 are arranged in an overlapping manner, but the invention is not necessarily limited to this. However, in order to effectively prevent the electrostatic field contrast acting on the ink 3 from being flattened by the conductive ink, it is desirable to arrange the control N pole 4 close to the end of the head body 1. Furthermore, when the control electrode and the radiation absorption layer are arranged in an overlapping manner as in the above embodiment, the insulation protection layer 33 may undergo dielectric breakdown due to internal polarization within the radiation absorption layer 31 that occurs when a signal is applied to the control electrode 4. It is preferable that the radiation absorbing layer 31 has a large electrical resistivity, from the viewpoint of preventing such a situation and making the electric field profile generated in the ink 3 uniform. Furthermore, regarding the radiation absorption layer 31,
Considering the need to set the ink heating area close to the electrostatic field acting area and the ease of manufacturing the head body 1, the radiation absorbing layer 31 is formed on the glass substrate 11 on the side where the control electrode 4 is formed. However, it is not necessarily limited to this, and it may be formed on the glass substrate 12 on the side opposite to the glass substrate 11 on which the control electrode 4 is formed. In addition, if the black ink directly absorbs radiation and causes a temperature rise even in areas where there is no radiation absorption layer, a radiation shielding layer made of a reflective layer such as aluminum is provided at an appropriate position.
It is necessary to shield unnecessary radiation.

[Effects of the Invention] As explained above, according to the inkjeler 1 to recording device according to the present invention, a heating means is provided near the ink flying opening, and the heating means reduces the surface tension and viscosity of the ink. At this stage, an electrostatic field pattern corresponding to the image pattern is applied to the ink, so that the ink can be moved easily without using a high voltage electrostatic signal. Even if the pixel density is set high and each control electrode is driven simultaneously according to the pixel density, there is almost no risk of voltage leakage between adjacent control electrodes, making it possible to perform high-density, high-speed recording. It can be realized.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing Embodiment 1 of an ink jet recording apparatus according to the present invention, FIG. 2 is a sectional view showing a specific structure around the head body in Embodiment 1, and FIGS.
The figure is a view in the direction of arrows viewed from the ■ and ■ directions in Figure 2, Figure 5 is a graph showing the relationship between the growth rate of surface waves and the wave number using the heating area as a parameter, and Figure 6 is a graph showing the relationship between the growth rate of surface waves and the wave number using the heating area as a parameter. A cross-sectional explanatory diagram of a main part showing Example 2 of such an inkjet recording device,
Figure 7 is a view from the direction of arrow V in Figure 6, and Figure 8 (a
) (b) is a graph showing the results of an analysis of the ink flight process based on electrohydrodynamic theory for inks with different surface tensions. On the other hand, it is a graph diagram showing the result of analyzing the ink flying operation process based on electrohydrodynamic theory while considering the slit opening. [Explanation of symbols (1)...Head body (2)...Ink chamber (3)
... Ink (4) ... Control electrode (5) ...
Slit opening (opening for ink flying) (6)...Counter electrode (7)...Heating means (8)...Recording sheet (
20)... Heat generating resistor (31)... Radiation absorption layer (
Radiation absorbing member) (32)...Quartz lamp (radiation generating member) Patent applicant Fuji Xerox Co., Ltd. Representative Patent attorney Tomohiro Nakamura (2 others) Figure 8 (a) Figure 8 (b) ) a Fig. 9 (a) Input, y () 1m) Fig. 9 (b) Input y (J-1m)

Claims (1)

[Scope of Claims] 1) A head main body having an ink chamber with an opening for ink flying, a large number of control electrodes arranged facing each ink unit area according to pixel density, and An electrostatic signal corresponding to image information is applied between each control electrode and the counter electrode, and an electrostatic signal is formed between the ink surface and the counter electrode. An inkjet recording device that causes ink to fly onto a recording sheet placed in front of a counter electrode by an attractive force based on an electrostatic field, characterized in that a heating means is provided near the ink flying opening. Inkjet recording device. 2) The inkjet recording apparatus according to claim 1, wherein the ink flying opening is constituted by a slit. 3) The inkjet recording apparatus according to claim 1, wherein the heating means is constituted by a heating resistor. 4) The inkjet recording apparatus according to claim 3, wherein the width dimension of the heating resistor along the depth direction of the ink flying opening is set to 1 mm or less. 5) The heating means comprises a radiation absorbing member formed in a band shape near the ink flying opening, and a radiation generating means for irradiating the radiation absorbing member with radiation. The inkjet recording device according to item 1.