KR101555528B1 - Coating machine and its ink filling method - Google Patents

Abstract

In a coating apparatus having a complicated ink supply pipe, the occurrence of a nozzle causing a discharge failure is suppressed.

A first means for applying a negative pressure, a second means for applying a low pressure, a third means for applying a high pressure, and a control means, and an opening / closing valve controlled by the control means, A plurality of switching valves are provided in the supply pipe and the pressure portion to the main tank is provided in the piping and the like,

A low pressure is applied to the tank to inject ink into the nozzle discharge tip from the tank and a high pressure is applied to the tank to discharge the stagnant air in the supply pipe and a predetermined negative pressure is added to the tank to form a " meniscus " The pressure supply source, opening / closing valve, etc. are controlled so that the pressure applied to the tank is switched from high pressure to low pressure one or more times immediately before printing.

Description

TECHNICAL FIELD [0001] The present invention relates to a coating apparatus and an ink filling method thereof,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating apparatus and an ink filling method thereof by an inkjet method which is essential for improving the operating rate of an apparatus in a large-sized coating apparatus adopting an ink-jet system.

The printing or coating apparatus employing the ink jet method develops as a small-sized printing apparatus for business use or for public use, and can be applied not only to domestic or office printing apparatuses, but also to applications in textile printing processes for industrial use, And is widely applied as a large-sized printing apparatus in an advertising medium. Among these, in recent years, an apparatus employing an ink jet method has been introduced to manufacture a color filter as a key device of a display device such as a liquid crystal television.

The application of the coating device in the production of the color filter is based on the use of a color filter base material having a fine grid-like light shielding portion (light shielding portion) called " black matrix " on the surface of a thin glass Is used as a device for ejecting (ejecting) ink to the fine divisions (pixels) formed by the lattice of the light-shielding portion.

The size of the color filter is becoming larger as the size of an image device (video device) is becoming larger and the effective area as a color filter is becoming larger and larger. This increases the price of a color filter as a member, It is required to reduce the manufacturing cost. Accordingly, there is a growing demand for a coating device for high quality, stability, and reliability that can contribute to manufacturing costs such as high-speed color filter production and machine operation rate as high as possible without stopping only at the price of the device.

As a coating apparatus capable of responding to such a demand, there is a demand for a large-sized coating apparatus capable of applying a large coating area at one time from the market demand as a production purpose of a large-sized color filter.

On the other hand, in order to improve productivity of a member produced by applying ink such as a color filter, it is necessary to ensure continuity of operation of ink ejection of the application device. As a simple method for realizing such continuous operation of the application device, there has been conventionally a method of cleaning the tip of a nozzle which wipes the tip of the nozzle directly with a moisture absorbing material (wicking material) Is repeated at an appropriate frequency.

Such a simple cleaning method of the nozzle in the related art is not a big problem in a coating apparatus having a low frequency of use because it is a small sized apparatus for home use. However, in a large apparatus used for industrial use, the frequency of use is high, And the total number of nozzles becomes large. Therefore, the amount of ink wiped is also considerable, and a large amount of moisture absorbing material for absorbing the amount of ink is needed. As a result, the space occupied by the large amount of moisture absorbing material becomes large, There is a problem in practicability in the application device of the nozzle, and it is not suitable as a method to cope with the problem of the discharge failure of the ink due to the bubble inside the nozzle.

As a method of improving defective ejection of ink from nozzles due to factors such as bubbles staying in the nozzle, in a conventional coating apparatus, a filter is provided in a flow path to a nozzle for ejecting ink And a method of performing a first filling step of the ink at a pressure lower than the pressure at which the ink passes through the filter and a second filling step at a pressure higher than the pressure passing through the filter to fill the ink.

According to the method of Patent Document 1, air is left in a place close to the orifice of the ink discharge portion due to printing failure, that is, ink filling failure, and air is mixed into the ink, There is no case in which a printing failure which occurs intermittently occurs in the discharge of the recording medium.

In addition, a recovery system (recovery system: a secondary mechanism for eliminating clogging due to adhesion of ink, etc. in a nozzle or ink channel) is generally referred to as a suction pump, a cap, A first printing operation involving at least a first preliminary ejection operation of a predetermined amount before the start of printing or after the end of printing; And a second printing operation involving a second predetermined amount of the second preliminary ejecting operation is performed based on a determination criterion to execute the second printing operation (Patent Document 2).

The method of Patent Document 2 can prevent the ink from sticking to the ink channel and can perform a special operation for maintaining a state in which normal normal ejection is possible, for example, "suction", "preliminary ejection" And the like are appropriately performed so that a long-time operation and good printing are maintained.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-114658

Patent Document 2: JP-A-2002-52740

In the method of avoiding incorporation of air or the like into the ink passage into the nozzle according to Patent Document 1, a stable operation can be expected so that there is no practical problem in a relatively small application apparatus. In the method of Patent Document 2, It is possible to expect an effect as a countermeasure focused on the problem that the flow around the nozzle orifice is stagnated.

However, in the methods of Patent Document 1 and Patent Document 2, in a coating apparatus in which the number of heads for discharging ink such as a coating apparatus for business use, that is, the number of nozzles is large, ink in the vicinity of the nozzles is stagnated It is not enough to remove the air bubbles attached to the wall of the place.

Therefore, an impact (sudden pressure rise) for ejecting ink from the nozzles is compressed by compressing the air bubbles, so that a sufficient amount of energy is absorbed and proper ejection of the ink is not performed. Adjustment and the like are required, and there is a problem that the application device can not be used immediately.

The inventors of the present invention have studied once again a charging method of ink capable of discharging ink appropriately from all the nozzles at the beginning of production in a coating apparatus having a plurality of nozzles for industrial use. (For example, 1) charging at a low pressure of about 15 to 30 kPa (hereinafter referred to as a low pressure), or filling the ink supply path by applying a single pressure to the ink supply pipe, (Hereinafter referred to as medium pressure) of about 30 to 80 kPa or 3) a single one of charging with a high pressure of about 80 to 150 kPa (hereinafter referred to as a high pressure) In the filling operation of the ink supplying apparatus, in a coating apparatus requiring a very large number of nozzles such as an industrial ink jet, It has been confirmed that it is not possible to sufficiently remove the bubbles staying in the place where the ink stagnates immediately before the nozzle.

An object of the present invention is to provide an ink filling method and apparatus for reliably discharging bubbles staying in a stagnant state of ink immediately before a nozzle in such an ink supply path.

The present invention is directed to a coating apparatus and a method of filling the ink devised in consideration of the above-described problems, and is a coating apparatus having an ink-jet head, which comprises a negative pressure applying means for applying a minus pressure, Pressure applying means and control means for applying a high pressure and a plurality of open / close valves and a diverter valve controlled by the control means to the ink tank, A method of filling an ink in a tank, comprising the steps of: applying a low pressure to the tank to fill ink from the tank to the nozzle discharge tip through the pipe line (pipeline) As a process just before printing, the application of the pressure to the tank is performed one time or more from the high pressure application to the low pressure application And controls and executes each process by control means before printing.

Further, the pressure difference between the application of the high pressure and the application of the low pressure in the step immediately before printing is set to 50 KPa or more. The upper limit of the low pressure immediately before printing is set to 30 KPa.

According to the ink filling method of the ink jet applying apparatus of the present invention, as the ink filling step, a low pressure is applied to the tank to fill the ink from the tank to the nozzle discharge tip through the pipe, It is possible to surely remove minute bubbles existing in the pipe wall or the connecting portion of the piping system and to switch the pressure application to the tank one time or more from the high pressure application to the low pressure application Minute bubbles adhering to the head nozzle or the inner wall of the nozzle are compressed by the first high pressure application and the area of contact with the inner wall of the nozzle is reduced due to the volume contraction of the bubble and the shape of the bubble becomes close to the sphere It becomes easy to flow, and from high pressure to low pressure The micro bubbles in the nozzle can be surely discharged from the nozzle by a sudden change of the pressure of the nozzle (pressure swing).

As a result, in preparation for the start of printing of the ink-jet applying device, ink filling into the piping from the ink tank to the head or discharge operation of the bubbles in the piping flow path and the nozzles of the plurality of nozzles as a whole can reliably be performed in a short time, It is possible to shorten the start-up of the apparatus or to reduce unnecessary waste of ink more than necessary in the ink charging, and it is possible to maximize the advantage of the ink-jet coating technique, thereby contributing to the improvement of the productivity.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a system configuration diagram showing the concept of a system for enabling ink filling of an ink-jet head in an ink-jet type coating apparatus according to the present invention, 2 is a block diagram of a system recess of a pressure air source for applying pressure to a main tank 4, and Fig. 3 is a process flow chart of the system. The inkjet head 1 in which nozzles (not shown in the figure) are formed controls ejection and stop of the ink from the nozzles of the inkjet head 1 by a command from the head control board 2 do. The ink jet head 1 is connected to a main tank 4 through an ink supply pipe 3 to supply ink. The main tank 4 is directly connected to the sub tank 6 through the ink replenishment pipe 5 to replenish the ink.

A vacuum pump 8 and a pressure air source 9, which are negative pressure applying means for applying a minus pressure, are connected to the main tank 4 through a plurality of three-way switching valves 7A and 7B . A supply solenoid valve 10 and a supplemental solenoid valve 11 are provided in the ink supply piping 3 and the ink supplemental piping 5, The opening and closing operation is performed. 2 is a block diagram showing the inside of a pressure air source 9 for applying pressure to the main tank 4 and includes a low pressure applying means for applying a low pressure for generating a low pressure of about 15 to 30 kPa A high pressure source 9H which is a high pressure source for generating a high pressure of about 80 to 150 KPa and a high pressure source 9H which is a high pressure applying means for applying a high pressure for generating a high pressure of about 80 to 150 KPa, Source and the high pressure are appropriately applied to the main tank 4 by the three-way switching valve 7C through the pressure regulator.

Hereinafter, the ink filling method of the present invention will be described in detail with reference to the process flow diagram of FIG. In the first step, the supply solenoid valve 10 is closed and the supplemental solenoid valve 11 is opened in the vacuum state as a process of replenishing ink to the main tank 4 from the sub tank 6, The pump 8 is started to make the main tank negative pressure by the operation of the three-way switching valve 7A. The ink is replenished from the sub tank 6 to the main tank 4 by keeping the main tank 4 in the negative pressure state. After this inflow amount reaches a proper amount, the supplemental solenoid valve 11 is set to " closed ", and the first process is terminated.

In the second step, the supply solenoid valve 10 is opened, and the low pressure source 9L of the pressure air source 9 is operated at a pressure of 15 to 30 kPa Is applied to the main tank 4 to fill the ink in the main tank 4 into the entire piping portion from the supply pipe 3 to the nozzle of the inkjet head 1.

In the third step, immediately after the completion of the second step, the high pressure source 9H of the pressure air source 9 is supplied with a pressure of about 80 to 150 kPa through the pressure regulator by the operation of the three-way switching valves 7A, 7B, Directional switch valve 7B to the main tank 4 by operating the three-way selector valve 7B to set the supply solenoid valve 10 to " close " after the high- ). Accordingly, minute bubbles stagnating in the ink supply pipe, such as the bend of the pipe from the main tank 4 to the nozzle of the ink jet head 1 and the pipe connecting portion, or scattered in the ink are discharged from the nozzle of the ink jet head 1 . The third step may be repeated.

However, in the charging method up to this stage, it is not sufficient to remove bubbles remaining immediately before the entire nozzle, particularly where the ink inside the head stagnates, in a coating apparatus having a large number of industrial nozzles. Therefore, even if a predetermined negative pressure is applied from this state to the printing operation, a nozzle in which ink is not ejected is generated.

Effective use of the device for a limited time (that is, improvement in operating rate) is a groundbreaking proposition for both the enterprise and the device developer, where the ink just before the nozzle in the ink supply path stagnates The fourth to sixth steps described below are further required to establish a method for surely removing bubbles adhering and staying on the wall surface of the supply path of the gas.

In the fourth step, the supply solenoid valve 10 is set to "open", and the ink is supplied to the ink supply pipe from the main tank 4 to the nozzle of the ink jet head 1, Directional switching valve 7B is operated again from the high-pressure source 9H of the pressure air source 9 through the pressure regulator in order to discharge the minute "bubbles" from the nozzles of the ink-jet head 1, A high pressure of about 150 kPa is applied to the main tank 4 for a few seconds, and immediately the fifth step is carried out.

At this time, if there is air bubbles adhered to the wall surface in the ink supply passage close to the nozzle, such as where the ink stagnates, the volume decreases in inverse proportion to the pressure rise due to the pressure increase, The shape of the bubble becomes closer to the shape of the sphere, so that the state of the flow becomes easy. Therefore, the pressure at this time is high, so that the change in the volume of the bubbles thus staying becomes large and the contact area with the wall surface is reduced, so that the fluidity of the bubbles becomes higher. However, if the fluidity of the bubbles is too high and the time is long, The amount of ink to be added is increased, which is undesirable.

In the fifth step, after the ink is discharged by applying the high pressure in the fourth step, the low pressure source 9L of the pressure air source 9 is supplied to the main tank 4 by the operation of the three-way switching valve 7C ) Through the pressure regulator to a low pressure of about 15 to 30 kPa. As a result, the fluidity is increased through the fourth step and the bubbles adhered to the wall surface near the nozzle, such as where the ink stagnates, are discharged out of the nozzle together with the ink, and the bubbles disappear in the ink supply path near the nozzle. After the fourth step and the fifth step, the fourth step and the fifth step may be repeated as necessary.

Further, by setting the difference in pressure (differential pressure) between the fourth step and the fifth step to 50 KPa or more, preferably more than that, it is possible to more reliably remove bubbles stuck on the wall surface and so on.

If it is possible to simultaneously block all the nozzles in the fourth step, a pressure of about 80 to 150 kPa is supplied from the high-pressure source 9H of the pressure air source 9 through the pressure regulator to the main tank 4 After the application of the film for a few seconds, the film can similarly exhibit the transition state from the fourth step to the fifth step by opening the nozzle, so that it is possible to expect to discharge the bubbles staying in the vicinity of the nozzle, have.

When the second step and the third step are omitted and the fourth step and the fifth step are carried out in the second step, the third step, the fourth step, and the fifth step, the piping from the tank to the head The air bubbles that are initially present in the head suddenly flow into the inside of the head to fill the inside of the head with the filter portion or the ink stagnant. As a result, the ink flow is blocked by the air lock phenomenon, The ink can not flow smoothly, and it becomes difficult to perform the ink inflow operation for a short time. Therefore, the ink is consumed more than necessary for the inflow and replacement of the ink, so that the ink filling operation can not be performed efficiently.

In the sixth step, the vacuum pump 8 is started and the main tank 4 is supplied with a predetermined negative pressure (in this example, a variation width of 0.5 KPa around-1 KPa in this example) by the operation of the three-way switching valve 7A, All the inkjet nozzles of the inkjet head 1 form an appropriate meniscus (a vapor-liquid interface of the nozzle ejection port (liquid interface)) to become a standby state in which ink can be ejected, Is ready for operation before printing.

From this state, in accordance with the timing at which the control command (signal) is given to the head control substrate 2 from the system control means (not shown) to continuously or eject ink droplets in accordance with the control command, A normal application (printing) operation of ejecting ink from the nozzle of the head 1 can be performed.

Next, a method of confirming whether the ink filling method for the ink jet head 1 is good or not will be described in detail. This time, it was confirmed by a coating device on which an ink jet head was mounted according to the following procedure.

First, the ink ejection operation of each of the twelve inkjet heads is confirmed, and it is confirmed that the continuous ejection operation of the ink is performed without any abnormality in the single operation.

Next, in a coating apparatus equipped with an ink jet head of these 12 (four red, green and blue colors, total number of nozzles: 6144 holes), the coating apparatus was charged by a charging method which did not include the fourth and fifth steps (Hereinafter referred to as the conventional method), that is, after the filling step of the ink in which the sixth step is performed after the first step to the third step, the normal application operation is performed. As a result, it was found that 12 heads were able to confirm the continuous ejection operation of the ink in the single head. However, when the continuous ejection operation of the ink is simultaneously performed by the application device in which 12 nozzles are mounted, It was confirmed that there was a deficiency in the landing. This means that there are a considerable number of nozzles in which the bubble stays in the supply path near the nozzle.

Here, in an ink-jet head coating device of twelve heads (four colors of red, green, and blue, total number of nozzles: 6144 holes) that have confirmed the continuous ejection operation without any abnormality, The ink filling method from the first step to the sixth step was carried out, and the state of the ink continuous ejection operation from all the nozzles was confirmed by performing a normal application operation. As a result, in the method of the present invention, the droplets of all the nozzles of the twelve ink jet heads can be confirmed from the beginning.

The effect of this ink charging method was evaluated by using 72 ink jet heads (24 colors of red, green, and blue, total number of nozzles: 36864 holes) in order to confirm whether these ink charging methods were effective even when the number was increased And was confirmed by a mounted coating device. As a result, even if the number of nozzles was increased six-fold, it was confirmed that continuous ink ejection operation was possible from the beginning, and ink deficiency did not occur at all.

(Experimental Example)

As a concrete example, a comparative experiment concerning determination of the ink ejection when the ink jet head is filled with ink by the conventional method and the ink filling method according to the present invention and the apparatus is started will be described in detail.

As to the comparative experiment, the process just before confirmation of the ink ejection affinity as the condition before the test was made common as follows so that the objectivity of the result can be obtained.

1) The cleaning liquid (organic solvent such as PMA) in the head is discharged.

2) The ink jet head is filled with ink according to each method to be compared.

3) Cleaning: Wiping around the nozzle by non-woven fabric.

4) Flushing: ink ejection from all nozzles.

5) Test printing (check for lack of ink)

Likewise, the process after the test is also performed,

1) Forced discharge of total ink from main tank to nozzle

And 2) charging the cleaning liquid (charging from the main tank to the nozzle).

(Experimental result of the conventional method)

The ink ejection result from the nozzle after the ink filling by the conventional method will be described below. The supply solenoid valve and the supplemental solenoid valve 11 are closed together and the vacuum pump 8 is started to apply negative pressure to the main tank 4 by the operation of the three-way selector valve 7A The first step of supplying an appropriate amount of ink from the sub tank 6 to the main tank 4 is terminated and the supplemental solenoid valve 11 is set to the "closed" state by making the supplemental solenoid valve 11 "open" Respectively.

A low pressure of 15 to 30 kPa is supplied from the low pressure source 9L of the pressure air source 9 through the pressure regulator to the main tank 4 by the operation of the three-way switching valves 7A, 7B, And the supply solenoid valve is opened so as to fill the nozzles of the ink jet head 1 from the main tank 4 through the ink supply pipe. As a result, the air in the supply pipe is discharged, and finally the ink is discharged from the nozzle.

Subsequently, as a third step, a high pressure of 140 kPa is applied from the high pressure source 9H of the pressure air source 9 through the pressure regulator to the main tank 4 by the operation of the three-way switching valve 7C, The supply solenoid valve 10 is closed and the main tank is opened to the atmosphere by the operation of the three-way switching valve 7B. In this way, the ink was charged by discharging and removing the staying bubbles simultaneously with the discharge of the ink. As a result, at low pressure, fine bubbles in the supply piping that have not been discharged are discharged.

Thereafter, as the fourth step, the supply solenoid valve 10 is opened, the vacuum pump 8 is started, and the negative pressure is applied to the main tank 4 by the operation of the three-way switching valve 7A (In this example, a variation width of 0.5 KPa around-1 KPa) was applied to complete the sixth process in which all the inkjet nozzles of the inkjet head 1 produced an appropriate meniscus.

And a coating operation (test printing) in which ink is ejected from an inkjet nozzle of a coating device.

As a result of counting the number of ink droplets landed on a glass substrate for a color filter by this coating operation, it was found that the number of nozzles (referred to as nozzle defects) 29 of them.

(Table 1)

Red green blue Number of nozzles 12288 12288 12288 Number of nozzle defects 20 22 29 Discharge rate (%) 99.84 99.82 99.76

(Experimental result of the method of the present invention)

The results of the ink filling method for the ink jet head 1 of the present invention will be described below.

The supply solenoid valve and the supplemental solenoid valve 11 are closed together as the first step and the vacuum pump 8 is started to operate the main tank 4 , And the supplemental solenoid valve 11 is opened so as to supply ink from the sub tank 6 to the main tank 4. [

A low pressure of 15 to 30 kPa is supplied from the low-pressure source 9L of the pressure air source 9 to the main tank 4 through the pressure regulator by the operation of the three-way switching valves 7A, 7B, And the ink is filled in the nozzle of the inkjet head 1 from the main tank 4 via the ink supply pipe with the supply solenoid valve being opened.

Subsequently, as a third step, a high pressure of 140 kPa is applied from the high pressure source 9H of the pressure air source 9 through the pressure regulator to the main tank 4 by the operation of the three-way switching valve 7C, The supply solenoid valve 10 is closed, and the main tank is opened to the atmosphere by the operation of the three-way switching valve 7B. As a result, the ink was charged by discharging and removing the staying bubbles simultaneously with the discharge of the ink.

Thereafter, as the fourth step, the supply solenoid valve 10 is opened and the pressure of the pressure source 9 is increased from the high pressure source 9H of the pressure air source 9 through the pressure regulator to 140 kPa To the main tank 4 for several seconds.

Immediately thereafter, as a fifth step, a low pressure of 15 to 30 kPa is supplied from the low-pressure source 9L of the pressure air source 9 through the pressure regulator to the main tank 4 for several seconds Respectively.

As in the case of Comparative Example 1, as a sixth step, a predetermined negative pressure (in this example, about 0.5 kPa in the present embodiment, about 0.5 kPa in this example) is applied from the vacuum pump 8 to the main tank 4 by the operation of the three- And the sixth step in which all of the ink jet nozzles of the ink-jet head 1 make an appropriate meniscus is terminated.

Thereafter, it was confirmed by an application operation (test printing) in which ink was ejected from the inkjet nozzle of the application device. As a result, as shown in Table 2, the number of " nozzle defects " decreased to 0 or 1.

(Table 2)

Red green blue Number of nozzles 12288 12288 12288 Number of nozzle defects 0 One 0 Discharge rate (%) 100 99.99 100

From the results of this comparison experiment, it can be confirmed that the conventional ink filling method does not sufficiently remove bubbles staying in the ink supply path for all the nozzles, and has a great effect on the ink filling method of the present invention.

As for the difference in the results, in the present invention, by applying a high pressure to the main tank 4 to reduce the volume of the bubbles in the fourth step, the contact area with the wall surface is reduced, It is deformed close to a spherical shape so that it is easy to move. Then, by applying a low pressure to the main tank 4 in the fifth step without leaving a gap therebetween, the air bubbles close to the spherical shape are increased in volume as they are made to move more easily, It can be thought that it is discharged.

As a result, reliable ink ejection operation can be performed continuously, and ink can be appropriately ejected from all the nozzles from the start of use of the application device, thereby making it possible to contribute to production activity in a short time.

As described above, according to the present invention, in the ink filling step, a low pressure is applied to the main tank to fill the ink from the tank to the nozzle discharge tip portion through the pipe line, and then the high pressure is applied to the tank at least once, The pressure applied to the tank is changed from the high pressure to the low pressure one or more times immediately before the ink jet head 1 is caused to make an appropriate meniscus on all the ink jet nozzles, And the control of the opening / closing / switching valve and the like can remarkably reduce the nozzle dislodgement, and as a result, the ink jet head having a plurality of nozzles as in the industrial ink jet dispenser can perform coating without nozzle defects , The inherent characteristics of inkjet application Improving the quality of Lin coated products, it can contribute significantly to the cost of the product down.

INDUSTRIAL APPLICABILITY The present invention can be applied to a large-sized apparatus such as a coating apparatus comprising a plurality of ink jet heads among coating apparatuses by an ink-jet method.

1 is a system configuration diagram of a coating device.

2 is a block diagram of a low-pressure, high-pressure pressure source.

3 is a process flow chart of the system of the application device.

Description of the Related Art [0002]

1: inkjet head 2; Head control substrate

4: Main tank 8: Vacuum pump

9: Pressure air source

Claims (6)

A main tank in which ink is filled and an ink-jet head for discharging ink are connected through an ink supply pipe (ink supply pipe) As a method, It is possible to switch the pressure applied to the main tank to a high pressure which is a minus pressure, a low pressure having an upper limit of 30 KPa or a pressure of at least 50 KPa higher than the low pressure by using a switching valve provided in the ink supply pipe , When the ink is filled into the ink jet head from the main tank, Maintaining the pressure applied to the main tank at the low pressure for a predetermined period of time; And switching from the low pressure to the high pressure to maintain the high pressure state, When ink is ejected from the inkjet head after the ink is filled in the inkjet head, Maintaining the pressure applied to the main tank at the high pressure state for a predetermined period of time; And a step of switching from the high pressure to the low pressure to maintain the low pressure state, And thereafter switching the pressure applied to the main tank from the low pressure to the negative pressure to maintain the negative pressure so as to bring the ink into an atmospheric state in which ink can be discharged Wherein the ink is applied to the ink-jet head. 1. A coating apparatus having an ink jet head, wherein a main tank for filling ink and an ink jet head for discharging ink are connected via an ink supply pipe, Pressure applying means for applying a low pressure of 30 KPa to the main tank, High pressure applying means for applying a high pressure to the main tank at a pressure of at least 50 KPa higher than the low pressure, A switching valve provided in the ink supply pipe for switching the pressure applied to the main tank to a negative pressure, Respectively, Wherein when the ink is charged from the main tank to the ink tank, the pressure applied to the main tank is maintained at the low pressure state, and then the high pressure state is maintained by switching from the low pressure to the high pressure, Wherein when the ink is ejected from the inkjet head after the ink is filled in the inkjet head, the pressure applied to the main tank is maintained at the high pressure for a predetermined period of time and then is switched from the high pressure to the low pressure, And thereafter the pressure applied to the main tank is switched from the low pressure to the negative pressure to maintain the negative pressure so that the ink is discharged into the waiting state . delete delete delete delete

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