JPH01209148A - Ink jet recording apparatus - Google Patents

Abstract

PURPOSE:To obtain a good recorded article by keeping the height of the liquid level of ink constant regardless of the amount of the ink, by forming an opening to the side wall of an ink tank in the vicinity of the bottom part thereof and applying air pressure from the opening at the driving time of an apparatus. CONSTITUTION:The air from an air supply source flows in an air chamber 9 from an air inflow port 8 and pressure is applied to the ink in an ink storage chamber 10 from the opening 6 provided to the partition wall 11 between the ink storage chamber 10 and the air chamber 9 in the vicinity of the bottom part thereof. The ink in the ink storage chamber 10 is supplied to an ink jet head from an ink inflow port 7. At the driving time of an ink jet recording apparatus, for example, equal air pressure Pa is applied to an ink tank 4 and the ink jet head so as to be capable of stably holding the ink to an ink emitting orifice. The air pressure Pa is propagated to the opening 6 through the air chamber 9 to be applied to the ink in the ink storage chamber 10. At this time, the liquid level of the ink is formed at the position of the height 0 of the opening 6 and, even when the ink in the ink storage chamber 10 is consumed, the air flows in the ink storage chamber 10 in the amount corresponding to the consumption amount of the ink from the opening 6 to hold the liquid level of the ink at the point of the height 0.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inkjet recording apparatus that records characters, images, figures, etc. on a recording material by ejecting ink from minute openings.

BACKGROUND OF THE INVENTION FIG. 3 shows an inkjet recording apparatus described in Japanese Patent Application Laid-Open No. 125425/1983, which utilizes air flow and electrostatic force. An ink discharge port 1 is provided opposite to an air discharge port 2 through which an air flow at a constant flow rate flows out, and the ink held in the ink discharge port 1 is transferred to an electrode 3 provided in front of the air discharge port 2. The air is sucked in by the electrostatic force generated by the air flow, and is ejected from the air outlet 2 while being accelerated by the air flow.

The ink tank 4 that supplies ink to the ink discharge port 1 includes
An air supply source 5 that supplies air flow to the air outlet 2 is branched and connected to apply a constant air pressure, and the pressure of the air flowing between the ink outlet 1 and the air outlet 2 and the ink are The pressure of the ink held in the ejection port 1 is set to be almost the same, and when no signal power is applied to the electrode 3, there is no ejection, and the ink is stably held in the ink ejection port 1. It is set as follows.

Problems to be Solved by the Invention When no signal voltage is applied as in the configuration shown in Figure 3,
In an inkjet recording device in which ink is held in the ink ejection port 1 and ejected only when a signal voltage is applied, the ink ejection port 1 is The height difference H=QA between position 0 and the ink liquid level A in the ink tank 4 influences the ink ejection state. That is, when the ink liquid level A increases, the ink pressure applied to the inkjet head increases, making it easier to eject ink and increasing the amount of ink ejected, and conversely, when the ink liquid level A decreases, the ink pressure applied to the inkjet head decreases. The amount of ink ejected decreases.

Therefore, if two ink tanks 4 are used as shown in Fig. 3, the ink level A will decrease as the ink in the ink tank 4 is consumed and the amount of ink decreases, causing the ink to be ejected from the inkjet head. There is a drawback that the amount gradually decreases and the recording density on the recorded object gradually becomes thinner.

In order to compensate for these drawbacks, a method has been proposed in the past to raise and lower the ink tank 4 itself, but this requires the provision of a special up-and-down mechanism, which is a drawback in terms of the simplicity of the device. was.

The present invention eliminates the above-mentioned drawbacks and operates an inkjet recording apparatus by keeping the ink liquid level constant regardless of the amount of ink in the ink tank 4 without requiring a special up-and-down mechanism.

Means for Solving the Problems In the present invention, an opening is provided near the bottom of the side wall of an ink tank that supplies ink to an ink jet head, and air pressure is applied to the ink in the ink tank through this opening.

Effect By taking the above-mentioned means, the height of the ink liquid surface of the ink tank that substantially acts on the inkjet head becomes the opening described above, regardless of the amount of ink in the ink tank. An inkjet recording device that is not affected by changes in the amount of ink in the tank can be realized.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional side view of an ink tank portion of an inkjet recording apparatus in an embodiment of the present invention. The configuration of the inkjet head section and air supply source is the third one.
Since it is the same as the figure, illustration is omitted. Air from the air supply source flows into the air chamber 9 through the air inlet 8, and flows into the ink storage chamber through the opening 6 near the bottom of the side wall of the ink storage chamber 10, that is, the partition wall 11 between the ink storage chamber 10 and the air chamber 9. 10
Apply pressure to the ink inside. The ink in the ink storage chamber 10 is supplied to the inkjet head from an ink outflow lower provided near the bottom of the ink storage chamber 10.

When the inkjet recording apparatus is driven, an air pressure Pa equal to 61, for example, is applied to the ink tank 4 and the inkjet head so that ink can be stably held in the ink ejection ports. This air pressure Pa is propagated to the opening 6 via the air inlet 8 and the air chamber 9, and the pressure Pa is applied to the ink in the ink storage chamber 10. At this time, an ink level is formed at the 0-height position of the opening 6, and even if the ink in the ink storage chamber 10 is consumed, air corresponding to the consumed amount flows out into the ink storage chamber 10 through the opening 6. , there is no change in the fact that the ink liquid level is maintained at the zero height point.

The opening 6 is circular so that air can easily flow out as the ink is consumed. The size of the opening 6 is appropriately determined depending on the air pressure Pa and the size of the ink storage chamber 10. The partition wall 11 is provided in order to reduce the pipe resistance loss of air pressure (
It has two thin walls.

Next, the principle of forming the ink level at the height O of the opening 6 will be explained. Assume that the ink liquid level height in the initial state is A, H = OA, the air pressure in the ink storage chamber 10 is Pa', the ink density is ρ, and the gravitational acceleration is 9.
The pressure Pa at the opening 6 is Pa = Pa' 10p pH The ink decreases and the ink level drops, and the ink level 72,
-7R becomes *-A10, and if the air pressure in the ink storage chamber 10 changes to Pl, the pressure at the opening 6 becomes Pa > Pa "10ρy), and the pressure balance collapses. When this happens, the meniscus formed in the opening 6 ruptures in an attempt to maintain the pressure balance, forming bubbles and increasing the air pressure Pa'' in the ink storage chamber 10 to a pressure of Pa. The pressure Pa at the opening 6 at that time is Pa=Pa±p9H. The value of Pa' changes depending on the ink level height A1, that is, the amount of ink in the ink storage chamber 10, and is maintained in balance with Pa acting on the height O. This means that the substantial head pressure force acting on the inkjet head is always at the height O and is independent of the ink level, which depends on the height A. Therefore, in the configuration shown in FIG. 1, the water head pressure due to the ink liquid level in the ink tank 4 acting on the inkjet head can be always set to a constant value that can be defined by the height O, and the amount of ink consumed can be set to a constant value. An inkjet recording device with constant ejection characteristics can be realized regardless of the inkjet recording device.

Next, the state of the ink in the ink tank 4 when air pressure Pa is applied to the ink tank 4 and when it is not applied will be described. Figure 2 (a) shows the air pressure Pa
is applied. Further, FIG. 2(b) shows a state in which the inkjet recording apparatus is not driven, with no air pressure being applied. In FIG. 2(a), air chamber 9
Air pressure Pa is applied to the upper part of the ink storage chamber 10, and air pressure Pa' is applied to the upper part of the ink storage chamber 10. When these air pressures are released, Pa decreases to atmospheric pressure, and accordingly, Pa' also decreases, causing an expansion of the air. As a result, as shown in FIG. 2(b), the ink storage chamber 10
The ink inside flows into the opening 6 and the air chamber 9, and the height B
A liquid level is formed at the position of . The air chamber 9 is provided to accommodate these inks, and the air inlet 8
This serves to prevent ink from leaking outside. Therefore, the volume required for the air chamber 9 must be large enough to accommodate all of these flowing inks 9, but the actual volume is the volume of the ink storage chamber 10 and the air Pressure Pa
determined by the size of Performing rough calculations rather than exact calculations, if the air volume in the upper part of the ink storage chamber 10 is V, then the volume Δ■ that this part expands by releasing the pressure of the air supply source, that is, the volume of ink The amount of inflow into the air chamber 9 is expressed as ΔV-Pa'/Po·V'. However, Po is atmospheric pressure.

Then, V does not exceed the volume V of the ink storage chamber 10, and Pa' is smaller than Pa and is a nearby value, so if △■〉Pa/PO・V, the necessary conditions are satisfied. Become.

Generally, Pa is 9/7 to 0.08 to 27 cm to 0.15.
Since the value of is adopted, it is sufficient that the volume of the air chamber 9 is 10 to 20% of the volume of the ink storage chamber 10.

When air pressure is applied again, the state shown in FIG. 2(b) returns to the state shown in FIG. 2(a), and the ink level is kept constant in the operating state.

From the above explanation, when air pressure is applied, the ink liquid level that affects the inkjet head is 0 at the height of the opening 6, and when air pressure is not applied,
Air chamber 9: height B of the ink liquid level formed when the second ink flows in is the actual ink liquid level. The height B of the ink liquid level varies depending on the ink consumption status in the ink tank, so the height is not constant, and when no air pressure is applied, that is, when the inkjet recording device is not driven, the ink that acts on the inkjet head. The water head pressure is not constant. Generally, in an ink jet recording apparatus such as that shown in FIG. 3, when the ink liquid level is lower than the nozzle position when the apparatus is not driven, a more reliable apparatus can be realized in terms of preventing ink from dripping from the nozzles. Therefore, the second
It is preferable that the height B of the ink liquid level in FIG. 3B is not much higher than the height O.

The diameter of the opening 6 is 2 mm, and the air pressure Pa is 0.096.
11,-.

/d, the liquid level in the ink storage chamber 10 is 23 mm.
Even if the pressure difference was changed, the result was that the pressure difference applied to the ink outflow lower was at most ±l mm in terms of liquid level height.

Note that in the above explanation, the third inkjet head is
Although the head that utilizes an air flow and electrostatic force as shown in the figure has been described, the present invention is also applicable to various inkjet heads that use an air flow, such as Japanese Patent Laid-Open No. 51-10973.
Inkjet heads described in Japanese Patent Application Laid-open No. 8 and Japanese Patent Application Laid-open No. 167469/1984 (2) can also be used.

Effects of the Invention As described above, in the present invention, an opening is formed near the bottom of the side wall of the ink tank, and air pressure is applied from this opening when the inkjet recording device is driven. The height of the ink liquid level in the ink tank that substantially acts on the head can be kept constant regardless of the amount of ink in the ink tank.

As a result, the inkjet head can always have the same ink ejection characteristics, and good recorded matter can be obtained over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional side view of an ink tank section of an inkjet recording apparatus according to the present invention, and FIG. 2(a) is a side view of the ink tank section. (b) is a cross-sectional side view for explaining the operation of the ink tank portion of the inkjet recording apparatus according to the present invention, and FIG. 3 is a schematic diagram showing the overall configuration of a conventional inkjet recording apparatus. 4. Ink tank, 6. Opening, 7. Ink outlet, 8. Air inlet, 9. Air chamber, 10. Ink storage chamber, 11. Partition wall.

Claims (3)

[Claims] (1) An inkjet head that flies ink droplets together with an airflow, an ink tank that supplies ink to the inkjet head, and an air supply source that supplies airflow to the inkjet head and the ink tank, The tank has an opening near the bottom of the side wall,
An inkjet recording apparatus characterized in that air pressure is applied through the opening when driving the inkjet head. (2) The inkjet recording apparatus according to claim 1, further comprising a chamber communicating with the opening of the ink tank, and applying air pressure from the opening through the chamber. (3) The ink jet recording apparatus according to claim 2, wherein the capacity of the chamber is 10 to 20% of the capacity of the ink tank.