JPH01285355A - Ink jet recorder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an inkjet recording apparatus, and more particularly to a means for improving the bubble removal function and ink ejection performance of an inkjet head of an inkjet recording apparatus.

[Conventional technology]

The recording methods of inkjet recording devices include continuous injection type,
It can be classified into three types: impulse type (on-demand type) and electrostatic attraction type.

The continuous jet type records by selectively depositing predetermined ink droplets by electrically deflecting continuously ejected ink. The problem is that the configuration is complicated because it requires several devices.

In addition, although the structure of the electrostatic suction type is relatively simple, special care is required when handling it because it requires high voltage.Furthermore, there are many restrictions on the physical properties of the ink, such as conductivity, and the frequency The problem is that the responsiveness is poor.

However, the on-demand type ejects ink droplets only when necessary using the pressure of an ejection energy generating element such as a piezoelectric element, and has a very simple structure that does not require any extra equipment and is easy to handle. It also has excellent frequency response and is thought to be the most popular type of recording device.

By the way, in order to realize a full-color printer using the above-mentioned inkjet recording method, it is necessary to realize not only high resolution but also faithful halftone expression.

There are two ways to express halftones: a digital method such as a dither method, and an analog method that changes the recording dot size.In digital halftone expression methods, resolution is required to increase the number of gradations. Therefore, as a halftone expression method, there are greater expectations for analog expression methods in which the recording density is controlled by changing the recording dot size.

In an on-demand head, the recording dot size can be easily and accurately controlled by changing the voltage and pulse width applied to a conversion element such as a piezoelectric element.

[Problem that the invention seeks to solve]

However, with conventional on-demand type inkjet beds, when ink is continuously ejected, microbubbles are trapped inside the head after a certain period of time has elapsed, and printing in this state results in bubble-entrained ejection, resulting in the amount of ink ejected. There has been a problem in that the direction and ejection direction are not constant, and in some cases, ejection becomes impossible, resulting in deterioration of image quality.

Such printing defects due to bubble entrainment and ejection do not occur when deaerated ink from which dissolved air is removed are used, but they occur due to continuous ejection when ordinary ink that has not been deaerated is used.

In other words, when continuous ejection is performed using normal ink that has not been degassed, air dissolved in the ink is generated as microbubbles due to cavitation, etc., and these bubbles continue to grow, making ejection unstable. Eventually, air is taken in from the tip of the head, resulting in the phenomenon of printing defects due to bubble entrapment and ejection.

Note that since the degassing effect of degassing ink generally lasts for only several hours in an open system, it is not practical to use degassing ink to deal with the printing defects.

Therefore, when using an inkjet recording device for boat fishing, when bubbles are trapped and ejected, a pressurization system or a pressure reduction system pump is activated to discharge the ink from the bubbles trapping area, thereby changing the properties of the ink. A recovery device is provided separately.

However, in conventional inkjet recording devices, even if this type of recovery device is used, it is extremely difficult to remove air bubbles trapped within the head because the head itself has a minute and precise structure. In fact, it was not possible to eliminate bubble entrainment and discharge.

[Means for solving problems]

The present invention was developed in view of the problems of the prior art described above, and it is possible to easily remove air bubbles in the head, improve the stability of ink ejection, and form dots with excellent gradation. The purpose of the present invention is to provide an inkjet recording device that can

The present invention provides an inkjet recording apparatus equipped with a pump for removing air bubbles such as a recovery device, in which a heater is provided at least in a part of the vicinity of the inkjet head, and when the pump is activated, immediately before or after the pump is activated, the heater is used to remove the inkjet head and the inkjet head. The above object is achieved by an inkjet recording apparatus configured to heat at least a portion of ink within an inkjet head.

〔Example〕

The present invention will be specifically described below with reference to the drawings.

FIG. 1 is a schematic vertical sectional view showing the main parts of an inkjet recording apparatus according to an embodiment of the present invention.

In FIG. 1, an inkjet head 10 has a plurality of straight nozzles (or ink flow paths) 1 formed in a predetermined arrangement, and a cylindrical piezoelectric element, for example, on the outer periphery near the tip (exit) of each nozzle 1. 2 is attached, and the part of the nozzle 1 surrounded by the piezoelectric element 2 forms an ejection energy action chamber.

When an electric signal is supplied from the drive unit 7 to the piezoelectric element 2, the volume of the ink pressurizing chamber 3 in the twizzle 1 including the ejection energy application chamber decreases or increases due to contraction or expansion of the piezoelectric element 2. Therefore, ink droplets 5 are ejected from the orifice 4.

The inkjet head 10 generally has a plurality of ink ejecting means each including the nozzle 1 and the piezoelectric element 2 as described above, and the rear end of each nozzle 1 communicates with the sub-ink tank 15.

A filter 6 is attached to the rear end of each nozzle l to prevent dust and air bubbles in the ink from entering the nozzle l. This filter 6 not only functions to prevent dust and air bubbles from entering, but also serves as a fluid resistance element that balances fluid resistance with the orifice 4 on the tip side.

In FIG. 1, the number 20 indicates a recovery device which is also a bubble removal means.

This recovery device 20 is installed opposite the ink ejection opening (orifice) 4 of the inkjet head 10, and only when necessary is a cap 8 placed on the front surface of the head where the orifice 4 is located.
The ink in the head 10 can be suctioned and discharged through the recovery system tube 9 by a vacuum (suction) pump 11.

The sub-ink tank 15 is connected to the inkjet head 10.
Ink is sequentially supplied to the sub-ink tank 15 from the main ink tank 17 through the ink supply tube 16.

However, in the embodiment structure shown in FIG. 1, a heater 12 as a heating means is arranged near the tip (orifice 4) of each nozzle 1, and a heater 12 as a heating means is also arranged near the filter 6 at the rear end of each nozzle 1. A heater 13 is arranged.

In this embodiment, the heaters 12 and 13 are both turned on and start heating the ink at the same time as the vacuum pump 11 starts ink suction, and around the time when ink suction ends (when it ends and its (including immediately before and after).

Next, the operation of the inkjet recording apparatus described above will be explained.

When there are air bubbles in the ink in the head 10, the vacuum pump 11 starts suctioning the ink in the head 10, and at the same time, the heater 12 near the tip of the nozzle 1 and the heater 13 near the filter at the rear end of the nozzle 1 are turned on. Turn it on and heat the ink around it.

When the vacuum pump 11 finishes ink suction, the heaters 12 and 13 are turned off to stop heating the ink.

This heating operation heats only the ink in areas with high fluid resistance, such as the vicinity of the orifice 4 at the tip of the nozzle l and the filter 6 at the rear end of the nozzle, and the viscosity of the ink decreases, reducing fluid resistance. This makes it easier for ink to flow from the sub-ink tank 15 into the nozzle 1.

At the same time, the air bubbles existing in the nozzle 1 are discharged to the outside of the head 10 through the tip orifice 4.

In this way, since the ink in the areas where it is difficult to flow and bubbles are difficult to remove at room temperature is heated to make it flow more easily, it has become possible to easily and reliably remove the ink bubbles in the head 10.

The sucked amount of ink is replenished from the main ink tank 17 to the sub-ink tank 15 through the supply tube 16.

The amount of energy (heat amount) given to each heater 12, 13 must be within a range that increases the ink temperature near the orifice 4 and the filter 6, but does not increase the temperature of the entire sub-ink tank 15.

The reason for this is that if the overall temperature of the ink rises and the viscosity of the ink decreases too much, the balance between the ink and the spatula 10 will be disrupted, resulting in a significant loss of ejection stability, resulting in the inclusion of bubbles and gradation irregularities. This is because it may occur.

If the heaters 12 and 13 are turned on only during the recovery operation as described above, the ink that has risen in temperature will be sucked by the pump and discharged to the outside, so that the overall temperature of the ink in the sub-ink tank 15 will decrease. will never rise.

The heaters 12 and 13 can be placed in any other position as long as it is close to a location in the head 10 where it is difficult to remove air bubbles.

In particular, providing the heater 12.13 in areas with high fluid resistance, such as the tapered orifice 4 and the filter 6 at the rear end of the nozzle l, as in the above embodiment, is difficult to remove once air bubbles adhere to these areas. This was extremely effective in facilitating the removal of air bubbles.

In addition, it was also effective to provide a heater near parts with complicated shapes or parts with poor ink wettability to heat the ink in these parts.

Next, the results of three test examples implementing the present invention and a comparative example using the prior art will be explained.

Test example 1: Using the recording device explained in Fig. 1, driving frequency 3KH.
At z, a drive pulse with a drive pulse voltage of 30 to 8V is applied to the piezoelectric blocker 2 to eject ink droplets from the head 10 (orifice 4). It was confirmed that it was excellent.

After that, when it was continuously discharged for 3 hours, a phenomenon that bubbles were taken in occurred, but the bubble removal means (recovery device)
20, the heaters 12 and 13 were turned on for 2 seconds just before pump operation to remove air bubbles, and the original good discharge state was restored again.

After that, it was possible to discharge continuously for about 3 hours.

Test Example 2: Using the same recording device as in Test Example 1, heaters 12 and 13 were turned on for 5 seconds at the same time as the pump was activated.
Again, good recovery properties were exhibited, and stable ink ejection could be maintained.

Test Example 3: Even when the same recording device as in Test Example 1 was used and the heaters 12 and 13 were turned on for 5 seconds immediately after the pump stopped, good recovery was still achieved and stable ink ejection was maintained. I was able to do it.

Comparative example (conventional example) l: Using the recording device shown in Fig. 1, heater '1' was used during recovery operation.
2. Pump suction was performed with 13 turned off.

As a result, the viscosity of the ink was high and the fluid resistance at the filter 6 and orifice 4 was large, so the flow rate of the ink was low and the air bubbles that were mixed in the head 10 (nozzle 1) could not be removed. .

As a result, the ejection of the head 10 became unstable, and the quality of the recorded image was poor.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a heater is provided in at least a part of the vicinity of the inkjet head, and when the recovery pump is activated, immediately before or after the recovery pump is activated, the heater is used to control the inkjet head and the ink in the inkjet head. By heating at least a portion of the ink during the recovery operation, the fluid resistance of the ink can be reduced and air bubbles can be easily removed, resulting in excellent recovery performance and ejection stability. An inkjet recording device is provided.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing main parts of a recording head and a recovery device of an inkjet recording apparatus according to an embodiment of the present invention. 1--------- Nozzle (flow path), 2------
・−・Piezoelectric element. 4------------- Orifice (ink ejection port), 10.--1111---Ink jet head, 1
1...----Pump, 12.13--...
-Seventy one tar, 15-・-・・-・-Sub ink tank,
20・-・-・-Recovery device. Agent Patent Attorney Yasutake Ooto

Claims (1)

[Claims] (1) In an inkjet recording device equipped with an inkjet head that guides ink into an ink pressurizing chamber and ejects ink droplets, and a pump that removes air bubbles within the inkjet head, a heater is provided at least in a portion near the inkjet head. . An inkjet recording apparatus configured to heat the inkjet head and at least a portion of the ink in the inkjet head by the heater when the pump is activated, or immediately before or after the operation.