KR20240057305A - Method of adjusting inkjet head injection characteristics - Google Patents

Abstract

The present invention is a drop inspection device that changes a plurality of injection condition adjustment factors of the inkjet head, such as ink viscosity, meniscus pressure, driving voltage, driving waveform, and injection frequency, within the standard specification range of the inkjet head according to the required injection characteristics. Adjust the spraying characteristics of the inkjet head. Because of this, rather than spraying ink according to specifications uniformly applied to the inkjet head, the inkjet head can be used by changing the spraying conditions that satisfy the required spraying characteristics suitable for the ink material. Therefore, high-quality printing can be achieved even if the process specifications and ink materials are different.

Description

{Method of adjusting inkjet head injection characteristics}

The present invention relates to a method for adjusting inkjet head jetting characteristics.

In the printed electronics field, selection of an inkjet head suitable for process specifications and ink material is very important.

Depending on the structure, characteristics, and manufacturer, the inkjet head's specifications (printing effective area, number of nozzles, dpi, drop reference speed, print image format, reference injection frequency, reference discharge amount, driving voltage, etc.) ) are diverse.

The manufacturer provides the specifications of the inkjet head, but these are only reference materials for finding jetting conditions suitable for the ink material, so the jetting conditions suitable for the ink material must be found separately.

In order to find spraying conditions suitable for the ink material, through adjustment of spraying characteristics (drop meandering control, satellite removal, drop tail adjustment, discharge speed adjustment, discharge amount adjustment), Changes in drop discharge shape were confirmed using a drop watcher.

However, in order to accurately adjust the injection characteristics, the injection condition adjustment factors involved in the adjustment of the injection characteristics (ink viscosity, meniscus pressure, driving voltage, driving waveform, injection frequency, etc.) and the adjustment of the injection characteristics (drop It is necessary to understand the correlation between drop meandering control, satellite removal, drop tail adjustment, discharge speed adjustment, and discharge volume adjustment. There is no adjustment. Because of this, there are frequent cases where difficult-to-find injection conditions are not suitable for the ink material.

Korean published patent (10-2010-0081392)

The purpose of the present invention is to provide a method for adjusting inkjet head jetting characteristics that can solve the above-mentioned problems.

The method of adjusting the inkjet head jetting characteristics to achieve the above purpose is,

A first step in which a drop watcher checks the drop discharge shape of the piezo actuator type inkjet head to determine the required injection characteristics;

a second step in which the drop inspection device changes a plurality of jetting condition adjustment factors of the inkjet head within a standard specification range of the inkjet head according to the required jetting characteristics; and

A third step in which the drop inspection device checks the drop discharge shape of the inkjet head according to the plurality of changed injection condition adjustment factors,

The plurality of injection condition adjustment factors include ink viscosity, meniscus pressure, driving voltage, driving waveform, and injection frequency.

The present invention is a drop inspection device that changes a plurality of injection condition adjustment factors of the inkjet head, such as ink viscosity, meniscus pressure, driving voltage, driving waveform, and injection frequency, within the standard specification range of the inkjet head according to the required injection characteristics. Adjust the spraying characteristics of the inkjet head. Because of this, rather than spraying ink according to specifications uniformly applied to the inkjet head, the inkjet head can be used by changing the spraying conditions that satisfy the required spraying characteristics suitable for the ink material. Therefore, high-quality printing can be achieved even if the process specifications and ink materials are different.

The present invention determines the correlation between jetting characteristics and a plurality of jetting condition adjustment factors of an inkjet head, such as meniscus pressure, driving voltage, driving waveform, and jetting frequency, and adjusts the jetting characteristics of the inkjet head based on this. There is interaction between the plurality of injection condition adjustment factors, so the required injection characteristics cannot be satisfied by changing only one injection condition adjustment factor. Therefore, the required injection characteristics can be adjusted more precisely by considering the interaction between the plurality of injection condition adjustment factors and considering the plurality of injection condition adjustment factors in a complex manner.

1 is a flowchart showing a method for adjusting inkjet head jetting characteristics according to an embodiment of the present invention.
Figure 2 is a diagram showing an example of a drop inspection device.
Figure 3 is a diagram showing various drop discharge shapes identified by the drop inspection device.
Figure 4 is a diagram showing a driving schematic diagram of a piezo actuator type inkjet head.
Figure 5 is a table showing the correlation between injection condition adjustment factors for each required injection characteristic.
Figure 6 is a diagram illustrating the adjustment of the driving voltage and driving waveform of the K company inkjet head.
Figure 7 is an image of the drop ejection shape of Company K's inkjet head, showing the ejection characteristics (scattering ink) according to ink viscosity (ink temperature) and driving voltage.
Figure 8 is an image of the drop ejection shape of Company K's inkjet head, showing the ejection characteristics (scattering ink) according to the driving voltage and driving waveform at high ink viscosity (low ink temperature).
Figure 9 is an image of the drop ejection shape of Company K's inkjet head, showing the ejection characteristics (scattering ink) according to the driving voltage and driving waveform at low ink viscosity (high ink temperature).
Figure 10 is an image of the drop discharge shape of Company K's inkjet head, showing the injection characteristics (discharge amount) according to the driving voltage and driving waveform.

Hereinafter, a method for adjusting inkjet head jetting characteristics according to an embodiment of the present invention will be described in detail.

As shown in FIG. 1, the method for adjusting inkjet head jetting characteristics according to an embodiment of the present invention is,

A first step (S11) in which a drop watcher checks the drop discharge shape of the piezo actuator type inkjet head and determines the required injection characteristics;

A second step (S12) in which the drop inspection device changes a plurality of jetting condition adjustment factors of the inkjet head within a standard specification range of the inkjet head according to the required jetting characteristics; and

It consists of a third step (S13) in which the drop inspection device checks the drop ejection shape of the inkjet head ejected according to the plurality of changed ejection condition adjustment factors.

Hereinafter, the first step (S11) will be described.

As shown in FIG. 2, a drop watcher photographs ink ejected from an inkjet head and analyzes the captured image to confirm the drop discharge shape. The drop inspection device basically consists of a camera, lighting, video analysis, and control unit, and any known drop inspection device can be used.

As shown in FIG. 3, the drop discharge shape can appear in various forms depending on injection conditions.

The drop inspection device checks the captured drop discharge shape and determines that the required injection characteristics required for the confirmed drop discharge shape to have a normal injection shape include drop meander control, removal of so-called satellite flying ink, and drop tail. Determine which of the following is adjustment, discharge speed adjustment, or discharge volume adjustment.

Hereinafter, the second step (S12) will be described.

Multiple injection condition adjustment factors

A plurality of injection condition adjustment factors of the inkjet head for changing injection conditions include ink viscosity, meniscus pressure, driving voltage, driving waveform, and injection frequency.

Ink viscosity is dependent on ink temperature. When the ink temperature is high, the ink viscosity is low, and when the ink temperature is low, the ink viscosity is high. Ink temperature is influenced by the temperature of the ink reservoir where ink is stored and the temperature of the head heater that heats the inkjet head.

Meniscus pressure is formed by controlling negative pressure inside the ink reservoir. Here, negative pressure means pressure lower than atmospheric pressure. By maintaining the inside of the ink reservoir in a vacuum and generating negative pressure inside the ink reservoir, meniscus pressure is formed in the ink inside the nozzle of the inkjet head.

As shown in FIG. 4, a piezo actuator type inkjet head ejects drops in a drop-on-demand manner. According to the drop-on-demand method, as the space in the piezo (PZT) part expands and then contracts by electrodes, ink is pushed out of the nozzle and a drop is ejected.

The size at which the space of the piezo (PZT) portion expands and then shrinks varies depending on the voltage and waveform applied to the piezo (PZT). The waveform is governed by pulse width, pulse dwell, and frequency. Therefore, the drop discharge shape can be changed depending on waveform conditions such as voltage, pulse width, pulse dwell, and frequency.

The inkjet head itself adjusts the voltage and waveform according to the purpose of controlling jetting characteristics.

Change of multiple injection condition adjustment factors according to required injection characteristics

As shown in FIG. 5, the drop inspection device changes a plurality of jetting condition adjustment factors of the inkjet head according to the identified required jetting characteristics, and controls the inkjet head to jet ink according to the changed jetting condition adjusting factors. Changes in the plurality of injection condition adjustment factors are made within the standard specification range of the inkjet head.

If the required injection characteristic is to eliminate drop meandering, the injection condition adjustment factors are adjusted by lowering the ink viscosity, increasing the meniscus pressure, increasing the driving voltage, increasing the pulse width, and lowering the injection frequency.

If the required injection characteristic is to remove flying ink, the injection condition adjustment factors are adjusted by increasing the ink viscosity, lowering the driving voltage, reducing the pulse width, and lowering the injection frequency.

If the required injection characteristic is drop tail removal, the injection condition adjustment factors are adjusted by lowering the ink viscosity, lowering the meniscus pressure, lowering the driving voltage, reducing the pulse width, and increasing the injection frequency.

When the required jetting characteristic is jetting speed adjustment, adjust the jetting condition adjustment factors by lowering the ink viscosity, lowering the meniscus pressure, increasing the driving voltage, increasing the pulse width, and increasing the jetting frequency to accelerate the jetting speed. do. To slow down the ejection speed, the injection condition adjustment factors are adjusted by increasing the ink viscosity, increasing the meniscus pressure, lowering the driving voltage, reducing the pulse width, and lowering the injection frequency.

When the required injection characteristic is discharge volume adjustment, to increase the discharge volume, the injection condition adjustment factors are adjusted by lowering the ink viscosity, lowering the meniscus pressure, increasing the driving voltage, increasing the pulse width, and increasing the injection frequency. To reduce the discharge amount, the injection condition adjustment factors are adjusted by increasing the ink viscosity, increasing the meniscus pressure, lowering the driving voltage, reducing the pulse width, and lowering the injection frequency.

Since there is an interaction between the injection condition adjustment factors, the required injection characteristics cannot be satisfied by changing only one injection condition adjustment factor. Therefore, the plurality of injection condition adjustment factors must be changed by taking into account the interaction between the plurality of injection condition adjustment factors.

In addition, due to the influence between the standard specifications of the inkjet head and the spraying condition adjustment factor, there is a range in which the spraying condition adjustment factor can be adjusted. Therefore, the injection condition adjustment factors must be adjusted within the range.

Hereinafter, the third step (S13) will be described.

The drop inspection device checks the drop discharge shape of the inkjet head sprayed according to the changed injection condition injection condition adjustment factor to determine whether the injection shape is normal.

If the injection shape is not normal, repeat the above steps to readjust the injection characteristics.

Test example

Using a product from Company K as an inkjet head, the spraying characteristics were evaluated according to the adjustment of the spraying condition adjustment factor. Company K itself can adjust the driving voltage and driving waveform as shown in FIG. 6.

Company K’s usage standards are as follows.

· Head heater temperature/ink reservoir temperature (adjust ink viscosity): 25 to 45 ℃

· Meniscus pressure: -3 ~ -8 kPa

· Driving voltage: 80 ~ 120% (default 100%)

- VH1: 5.5 ~ 8.5 V (default ≒6.5V, K company head parameter name: 1LA, 1LB, 1RA, 1RB)

- VH2: 10.5 ~ 15.5 V (default ≒12.5V, Company K Head parameter name: 2L, 2R)

· Driving waveform (pulse width): T1 + T2 = 8 ~ 35 usec

· Injection frequency: 5 ~ 25 kHz

- T1 + T2 + delay time (dwell) = 200 msec ~ 40 usec

Referring to Figures 5 and 7, the lower the ink temperature (higher ink viscosity), the less satellite ink occurs at high driving voltages. Additionally, if the ink temperature is high and the ink viscosity falls below a certain level, spraying does not occur. In addition, at the same viscosity level, if the driving voltage is lowered, the amount of flying ink decreases, but the discharge amount and discharge speed decrease, so an appropriate driving voltage range must be determined.

Referring to Figures 5 and 8, flying ink can be reduced by adjusting the driving waveform (pulse width) within a certain range of driving voltage. If the drive waveform (pulse width) is reduced, the discharge amount and discharge speed decrease, and conversely, if the drive waveform (pulse width) is increased, the discharge amount and discharge speed increase.

Comparing Figures 8 and 9, it can be seen that when the ink viscosity (ink temperature) changes, the appropriate driving voltage and driving waveform change, and it can be confirmed that there is a mutual influence between the injection condition adjustment factors.

Referring to Figures 5 and 10, as the driving voltage increases, the discharge amount and discharge speed increase, and conversely, as the driving voltage decreases, the discharge amount and discharge speed slow down. The discharge amount and discharge speed are proportional. By changing the drive waveform (pulse width), the discharge amount and discharge speed can be adjusted, and the effect of reducing flying ink appears within a certain range.

Claims (6)

A first step in which a drop watcher checks the drop discharge shape of the piezo actuator type inkjet head to determine the required injection characteristics;
a second step in which the drop inspection device changes a plurality of jetting condition adjustment factors of the inkjet head within a standard specification range of the inkjet head according to the required jetting characteristics; and
A third step in which the drop inspection device checks the drop discharge shape of the inkjet head according to the plurality of changed injection condition adjustment factors,
A method of adjusting inkjet head jetting characteristics, wherein the plurality of jetting condition adjustment factors are ink viscosity, meniscus pressure, driving voltage, driving waveform, and jetting frequency. According to paragraph 1,
If the required injection characteristic is drop meander removal,
A method of adjusting the jetting characteristics of an inkjet head, characterized in that the jetting condition adjustment factors are adjusted by lowering the ink viscosity, increasing the meniscus pressure, increasing the driving voltage, increasing the pulse width, and lowering the jetting frequency. According to paragraph 1,
If the required spraying characteristic is removal of flying ink,
A method of adjusting the jetting characteristics of an inkjet head, characterized in that the jetting condition adjustment factors are adjusted by increasing the ink viscosity, lowering the driving voltage, reducing the pulse width, and lowering the jetting frequency. According to paragraph 1,
If the required injection characteristic is drop tail removal,
A method of adjusting the injection characteristics of an inkjet head, characterized in that the injection condition adjustment factors are adjusted by lowering the ink viscosity, lowering the meniscus pressure, lowering the driving voltage, reducing the pulse width, and increasing the injection frequency. According to paragraph 1,
If the required injection characteristic is discharge speed adjustment,
To accelerate the ejection speed, the injection condition adjustment factors are adjusted by lowering the ink viscosity, lowering the meniscus pressure, increasing the driving voltage, increasing the pulse width, and increasing the injection frequency,
In order to slow down the discharge speed, inkjet head injection characteristics are adjusted by adjusting the injection condition adjustment factors by increasing the ink viscosity, increasing the meniscus pressure, lowering the driving voltage, reducing the pulse width, and lowering the injection frequency. method. According to paragraph 1,
If the required injection characteristic is discharge volume adjustment,
To increase the discharge amount, the injection condition adjustment factors are adjusted by lowering the ink viscosity, lowering the meniscus pressure, increasing the driving voltage, increasing the pulse width, and increasing the injection frequency,
In order to reduce the discharge amount, an inkjet head injection characteristic adjustment method characterized by adjusting the injection condition adjustment factors by increasing the ink viscosity, increasing the meniscus pressure, lowering the driving voltage, reducing the pulse width, and lowering the injection frequency. .