JP2008178817A - Coating device and method of detecting bubble in coating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect air bubbles in a coating solution with high precision in a coating device. <P>SOLUTION: The coating device has a coating solution tank 1, a coating solution pump 2, a coating nozzle 3 discharging a coating solution pressure-delivered from the coating solution pump 2 onto a coating target member 12, pipes 11A to 11E and a tube 14. A pressure sensor 7 detects the pressure of the coating solution in the pipe 11C. A controller 8 detects bubbles in the coating solution according to the pressure detected with the pressure sensor 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a coating apparatus for forming a coating film with a coating liquid on a surface of a member to be coated such as a liquid crystal display or a PDP (Plasma Display Panel), and a bubble detection method in the coating apparatus.

  When a coating solution is formed on the surface of a member to be coated by a coating device such as a die coater, and the air bubbles are mixed in the coating solution, the coating conditions change, and the coating film is affected. It may cause defective products. Conventionally, as a method for detecting bubbles in the coating liquid, it is known to detect the bubbles in the coating liquid optically using laser light in addition to visual confirmation (Patent Document 1).

  However, the coating liquid generally has high viscosity, and it is difficult to detect minute bubbles with high accuracy by visual observation or an optical method.

JP 2005-144376 A

  This invention makes it a subject to detect the bubble in a coating liquid with high precision.

  A first aspect of the present invention includes a coating liquid tank that stores a coating liquid, a coating liquid pump that pumps the coating liquid in the coating liquid tank, and the coating liquid that is pumped from the coating liquid pump. A pressure sensor that detects a pressure of the coating liquid in the pipe in a coating apparatus including a coating nozzle that discharges toward the member, and a pipe that connects the coating liquid tank, the coating liquid pump, and the coating nozzle; And a controller for controlling the operation of the coating liquid pump and detecting bubbles in the coating liquid based on the pressure detected by the pressure sensor.

  Specifically, the control device determines a reference pressure value in which the pressure of the coating liquid in the pipe is determined in advance from an output of a discharge start signal that instructs the coating liquid pump to start a discharging operation when no bubbles are present. A reference time which is a time until reaching the reference pressure is stored in advance, an actual measurement time which is a time until the pressure detected by the pressure sensor from the output of the discharge start signal reaches the reference pressure value, and the reference time When the comparison and the actual measurement time exceed the reference time, it is determined that bubbles are present in the coating liquid.

  Bubbles are detected by comparing the measured time obtained by using the pressure detected by the pressure sensor with the reference time, so that a very small amount of bubbles can be detected with high accuracy compared to visual or optical methods. it can.

  More specifically, the reference pressure value rises after the discharge start signal is output to the coating liquid pump and before the pressure of the coating liquid in the pipe reaches a constant pressure when bubbles do not exist. It is the pressure value inside.

  By setting the rising pressure to the reference pressure value, both stationary bubbles and flowing bubbles can be reliably detected.

  As an alternative, the control device may apply the coating in the pipe when a predetermined reference time has elapsed from the output of a discharge start signal instructing the coating liquid pump to start a discharge operation when bubbles are not present. A reference pressure value that is the pressure of the liquid is stored in advance, and the measured pressure value that is detected by the pressure sensor when the reference time has elapsed from the output of the discharge start signal is compared with the reference pressure value. When the measured pressure value falls below the reference pressure value, it is determined that bubbles are present in the coating liquid.

  Since the bubble is detected by comparing the actually measured pressure value detected by the pressure sensor and the reference pressure value, the bubble can be detected with higher accuracy than visual or optical methods.

  Specifically, the reference time is a constant pressure when the reference time elapses after the discharge start signal is output to the coating liquid pump when bubbles do not exist. It is set to be in a rising state before reaching pressure.

  By setting the reference time in this way, both stationary bubbles and flowing bubbles can be reliably detected.

  By providing the pressure sensor in the pipe closer to the coating nozzle than the coating liquid pump, the flowing bubbles can be detected more reliably.

  According to a second aspect of the present invention, there is provided a coating liquid tank for storing a coating liquid, a coating liquid pump for pumping the coating liquid in the coating liquid tank, and the coating liquid pumped from the coating liquid pump. In a coating apparatus comprising a coating nozzle that discharges toward a member, and a pipe that connects the coating liquid tank, the coating liquid pump, and the coating nozzle, a method of detecting bubbles in the coating liquid in the pipe A pressure sensor for detecting the pressure of the coating liquid in the pipe, and from the output of a discharge start signal for instructing the coating liquid pump to start a discharge operation when there are no bubbles, the coating in the pipe A reference time, which is a time until the pressure of the liquid reaches a predetermined reference pressure value, is stored in advance, and the pressure detected by the pressure sensor from the output of the discharge start signal reaches the reference pressure value The measured time is the time, comparing the reference time, if the measured time exceeds the reference time, and judging with bubbles present in the coating liquid, to provide a bubble detection method.

  According to a third aspect of the present invention, there is provided a coating liquid tank for storing a coating liquid, a coating liquid pump for pumping the coating liquid in the coating liquid tank, and the coating liquid pumped from the coating liquid pump. In a coating apparatus comprising a coating nozzle that discharges toward a member, and a pipe that connects the coating liquid tank, the coating liquid pump, and the coating nozzle, a method of detecting bubbles in the coating liquid in the pipe A pressure sensor that detects the pressure of the coating liquid in the pipe is provided, and a reference time determined from the output of a discharge start signal that instructs the coating liquid pump to start a discharge operation when no bubbles are present. The reference pressure value, which is the pressure of the coating liquid in the pipe at the time when the discharge is performed, is stored in advance, and the pressure detected by the pressure sensor when the reference time has elapsed from the output of the discharge start signal. Compares the pressure value and the reference pressure value, when the measured pressure value is below the reference pressure value, and determines that bubbles are present in the coating liquid, to provide a bubble detection method.

  According to the present invention, since air bubbles are detected based on the pressure of the coating liquid in the pipe detected by the pressure sensor, it is possible to detect the air bubbles in the coating liquid with higher accuracy compared to visual or optical methods. .

(First embodiment)
FIG. 1 is a schematic explanatory diagram of a coating apparatus according to the present embodiment. This coating apparatus generally includes a coating liquid tank 1, a coating liquid pump 2, a coating nozzle 3, a three-way valve 4, a support base 5, a pressure release valve 6, a pressure sensor 7, and a control device 8.

  The coating liquid tank 1 stores the coating liquid and is connected to the port 4a of the three-way valve 4 through the first pipe 11A. As the coating solution, for example, a glass paste for PDP applied on a glass substrate can be used. However, the present invention is not limited to this, and an appropriate one may be selected from conventionally known various coating liquids according to the type of the member 12 to be coated.

  The coating liquid pump 2 pumps the coating liquid in the coating liquid tank 1 to the coating nozzle 3. The coating liquid pump 2 includes a cylinder 2a, a piston 2b that reciprocates while sliding inside the cylinder 2a, and a drive mechanism 2c for driving the piston 2b. As the drive mechanism 2c, a direct acting motor or a servo motor can be used. The coating liquid pump 2 is connected to the port 4b of the three-way valve 4 via the second pipe 11B.

  The application nozzle 3 is a slit nozzle having a known configuration, and the application liquid pumped from the application liquid pump 2 toward the application target member 12 such as a PDP placed on a support base 5 which is a granite surface plate. The coating film 13 is formed on the coated member 12 by running while discharging. The application nozzle 3 moves up and down by a lifting device and a driving device (not shown). The application nozzle 3 is connected to the port 4c of the three-way valve 4 via the third pipe 11C, the tube 14 that bends according to the position of the application nozzle 3, and the fourth pipe 11D.

  One end of a fifth pipe 11E for releasing pressure is branched from the middle of the pipe 11C. The other end of the fifth pipe 11E is an open end and is open to the atmosphere. The pipe 11E is provided with a pressure release valve 6 composed of a normally closed on / off type electromagnetic valve or the like.

  A pressure sensor 7 having a known configuration for detecting the pressure of the coating liquid in the piping between the coating nozzle 3 side of the piping 11C, specifically, between the portion of the piping 11C where the piping 11E branches and the coating nozzle 3. Is attached. By providing the pressure sensor 7 at a site close to the application nozzle 3 of the pipe 11C, it is possible to more reliably detect a flowing bubble to be described later.

  The control device 8 controls the operation of the entire coating apparatus including the coating liquid pump 2, the coating nozzle 3, the three-way valve 4, and the pressure release valve 6. When suctioning the coating liquid from the coating liquid tank 1 to the coating liquid pump 2, the ports 4a and 4b are communicated with each other, and the port 4c is shut off from the other ports 4a and 4b. The piston 2b is moved in the direction in which the volume increases. The coating liquid in the coating liquid tank 1 is sucked into the coating liquid pump 2 through the pipe 11A, the three-way valve 4, and the pipe 11B. When the coating liquid is pumped from the coating liquid pump 2 to the coating nozzle 3, the ports 4b and 4c are communicated with each other, and the port 4a is blocked from the other ports 4b and 4c, and is driven inside the cylinder 2a by the drive mechanism 2c. The piston 2b is moved in the direction in which the volume decreases. The coating solution is pumped from the coating solution pump 2 to the coating nozzle 3 through the piping 11B, the three-way valve 4, the fourth piping 11D, the tube 14, and the third piping 11C. The coating liquid 13 is applied by discharging the pumped coating liquid from the coating nozzle 3 toward the member to be coated 12.

  Next, the principle of bubble detection will be described.

  FIG. 2 shows a pressure curve when no bubbles are present in the pipes 11C and 11D and the tube 14 on the downstream side of the three-way valve 4 (time when the pumping operation is performed by the coating liquid pump 2 and pressure detected by the pressure sensor 7). Relationship). In FIG. 2, the amount of coating liquid discharged from the coating nozzle 3 per unit time (hereinafter simply referred to as the amount of discharge) from the coating nozzle 3 increases in the order of the pressure curves L1, L2, L3, and L4. The discharge pressure of 2 is also high. At time tdis, the controller 8 outputs a discharge start signal that instructs the coating liquid pump 2 to start the discharging operation, and the coating liquid pump 2 starts the discharging operation. Hereinafter, the time tdis at which the discharge start signal is output is referred to as “discharge start time”. As shown in FIG. 2, the pressure curves L1 to L4 rise differently depending on the discharge amount, but in any pressure curve L1 to L4, the pressure finally detected by the pressure sensor 7 becomes a constant value.

  Next, FIG. 3 shows a pressure curve when bubbles are mixed in the coating liquid in the pipe 11E between the three-way valve 4 and the pressure release valve 6. FIG. The bubbles mixed in the pipe 11E are non-flowable or stationary bubbles in that they are not discharged together with the coating liquid from the coating nozzle 3. Hereinafter, the bubbles mixed in the coating liquid in the pipe 11E are referred to as “stationary bubbles”. In FIG. 3, the pressure curve L <b> 1 ′ shows a case where stationary bubbles are not mixed. The pressure curves L2 'to L4' show a case where stationary bubbles are mixed, and the amount of stationary bubbles mixed increases in the order of the pressure curves L4 ', L3', L2 '. The discharge amount of the coating liquid per unit time from the coating nozzle 3 is the same in all the pressure curves L1 'to L4'.

  As apparent from FIG. 3, the pressure finally detected by the pressure sensor 7 is constant regardless of the presence or absence of stationary bubbles. However, when stationary bubbles are present (pressure curves L2 ′ to L4 ′), the time T2 ′ to T4 ′ required from the discharge start time tdis until the pressure becomes constant is the time when no stationary bubbles exist (pressure curve). It is longer than the time T1 ′ required until the pressure becomes constant from the discharge start time tdis in L1 ′). Further, the larger the amount of stationary bubbles mixed, that is, the longer it takes to reach a constant pressure in the order of the pressure curves L4 ', L3', L2 '. From this, it is understood that the stationary bubbles can be automatically detected by utilizing the compressibility of the bubbles.

  FIG. 4 shows a case in which bubbles are mixed into the coating liquid in the pipe 11C, the pipe 11D, or the tube 14 between the three-way valve 4 and the coating nozzle 3 and the discharge operation by the coating liquid pump 2 is executed twice in succession. A pressure curve is shown. The bubbles mixed in the pipe 11C, the pipe 11D, or the tube 14 are bubbles having fluidity in that they can be discharged from the coating nozzle 3 together with the coating liquid. Hereinafter, the bubbles mixed in the coating liquid in the pipe 11C, the pipe 11D, or the tube 14 are referred to as “fluid bubbles”. In FIG. 4, a pressure curve L1 ″ indicates a case where bubbles are not mixed. The pressure curves L2 ″ and L3 ″ indicate a case where fluid bubbles are mixed. The pressure curve L2 ″ is the first discharge operation and the pressure curve L3 ″ is the second discharge operation. The discharge amount of the coating liquid per unit time from the coating nozzle 3 is the same in all the pressure curves L1 ″ to L3 ″.

  As apparent from FIG. 4, the pressure detected by the pressure sensor 7 is finally constant regardless of the presence or absence of flowing bubbles. However, there is no fluid bubble during the time T2 ″, T3 ″ required for the pressure to become constant from the discharge start time tdis when the fluid bubble is mixed (pressure curves L2 ″, L3 ″). In this case (pressure curve L1 ″), it is longer than the time T1 ″ required until the pressure becomes constant from the discharge start time tdis. In addition, since a certain amount of flowing bubbles is discharged together with the coating liquid from the application nozzle 3 by the first discharge operation, the second time compared with the time T2 '' required to reach a constant pressure in the first discharge operation. The time T3 ″ required to reach a constant pressure in the discharge operation is shortened. From these facts, it can be seen that, as in the case of stationary bubbles, it is possible to automatically detect the flowing bubbles using the compressibility of the bubbles.

  The absolute value (absolute pressure value) of the pressure finally reached differs depending on the discharge operation of the coating liquid pump 2 when the stationary bubbles are mixed and when the flowing bubbles are mixed. Therefore, when this absolute pressure value is referred to when detecting bubbles, it is difficult to detect both stationary bubbles and flowing bubbles with high accuracy. Therefore, in the present invention, bubbles are detected using a region in the pressure curve where the pressure is rising before reaching the absolute pressure value from the discharge start time tdis. Hereinafter, the bubble detection method will be described with reference to FIG.

  In FIG. 5, the pressure curve Lsd shows a case where neither stationary bubbles nor flowing bubbles are mixed, and the pressure curve Lb shows a case where at least one of stationary bubbles and flowing bubbles is mixed. In FIG. 5, the reference pressure value Psd is a preset pressure value. Specifically, the reference pressure value Psd is the value in the pipes 11B to 11E and the tube 14 after the discharge start signal is output to the coating liquid pump 2 (discharge start time tdis) when bubbles are not present (pressure curve Lsd). It is the pressure value during the rise before the pressure of the coating liquid reaches a constant pressure. Using the pressure sensor 7, the time from the discharge start time tdis when no bubbles are present until the pressure of the coating liquid in the pipes 11B to 11E and the tube 14 reaches the reference pressure value Psd is measured in advance. This time is stored in the control device 8 in advance as a reference time Tref.

  When the control device 8 actually performs the pressure feeding operation of the coating liquid to the coating nozzle 3 by the coating liquid pump 2, the time from the discharge start time tdis until the pressure detected by the pressure sensor 7 reaches the reference pressure value Psd. (Measurement time Tme) is measured. When the actual measurement time Tme exceeds the reference time Tref, that is, when the pressure rise is slower than when no bubbles are present, at least one of the pipes 11B to 11E and the tube 14 is applied to the coating liquid. Judge that air bubbles are mixed.

  Next, the operation of the coating apparatus of this embodiment will be described with reference to FIG. In the coating process (step S6-1), first, the coating liquid pump 2 sucks the coating liquid in the coating liquid tank 1. Next, a discharge start signal is output to the coating liquid pump 2 (step S6-2), and the coating liquid pump 2 starts a pressure feeding operation of the coating liquid. Simultaneously with the output of the discharge start signal (discharge start time tdis), the control device 8 starts time measurement and pressure measurement by the pressure sensor 7 (steps S6-3 and S6-4). Timekeeping and pressure measurement are continued until the detected pressure Pde of the pressure sensor 7 reaches the reference pressure Psd (step S6-5). When the detected pressure Pde reaches the reference pressure Psd, the control device 8 stops timing and pressure measurement (steps S6-6 and S6-7). The difference between the time when the timing is stopped and the discharge start time tdis is the actual measurement time Tme. The control device 8 compares the actual measurement time Tme with the reference time Tref (step S6-8).

  If the measured time Tme exceeds the reference time Tref in step S6-8, it is determined that a bubble (at least one of a stationary bubble and a flowing bubble) has been detected (step S6-9). In this case, since the next application process cannot be performed, an automatic air venting operation (S6-10) and idle discharge under application conditions (step S6-11) are executed. On the other hand, if the actual measurement time Tme is equal to or shorter than the reference time Tref in step S6-8, it is determined that no bubbles are detected (step S6-12), and the process proceeds to the next coating process.

  In the automatic air venting operation in step S6-10, first, the pressure feeding operation by the coating liquid pump 2 is executed with the pressure release valve 6 opened, and the static bubbles in the pipe 11D are discharged from the open end of the pipe 11D. Next, the pressure release valve 6 is returned to the closed state, the pressure feeding operation by the coating liquid pump 2 is executed, and the flowing bubbles in the pipe 11 </ b> C are discharged from the coating nozzle 3. In the idle discharge of step S6-11, the pressure feeding operation by the coating liquid pump 2 is executed without using the member 12 to be coated. Step S6-10 and step S6-11 are repeated until the actual measurement time Tme becomes equal to or less than the reference time Tref in step S6-8.

  In the coating apparatus of the present embodiment, bubbles are detected by comparing the measured time Tme obtained using the pressure detected by the pressure sensor 7 with the reference time Tref, so that it is compared with visual or optical methods. Therefore, a very small amount of bubbles can be detected with high accuracy. In addition, since the reference time Tref is determined by the reference pressure value that is a value during the pressure increase of the pressure curve when no bubbles are present, both stationary bubbles and flowing bubbles can be reliably detected.

(Second Embodiment)
The coating apparatus according to the second embodiment of the present invention is different from the first embodiment in the method of detecting bubbles performed by the control device 8.

  With reference to FIG. 7, a method of detecting bubbles in the present embodiment will be described. In FIG. 7, a pressure curve Lsd shows a case where neither stationary bubbles nor flowing bubbles are mixed, and a pressure curve Lb shows a case where at least one of stationary bubbles and flowing bubbles is mixed. In FIG. 7, the reference time Tsd is a preset time. Specifically, the reference time Tsd is the time when the reference time Tsd has elapsed after the discharge start signal is output to the coating liquid pump 2 (discharge start time tdis) when there are no bubbles (pressure curve Lsd). The pressure of the coating liquid in the pipes 11B to 11E and the tube 14 is set to be in a rising state before reaching a certain pressure. The pressure of the coating liquid in the pipes 11B to 11E and the tube 14 at the time when the reference time Tsd has elapsed from the discharge start time tdis when no bubbles are present is measured in advance using the pressure sensor 7, and this pressure is the reference pressure. The value Pref is stored in the control device 8 in advance.

  The control device 8 measures the pressure when the reference time Tsd has elapsed from the discharge start time tdis when the coating liquid pump 2 performs the operation of feeding the coating liquid to the coating nozzle 3. When the measured pressure (actually measured pressure value Pme) is lower than the reference pressure value Pref, that is, when the pressure rise is slower than when no bubbles are present, at least one of the pipes 11B to 11E and the tube 14 is used. It is determined that bubbles are mixed in one coating liquid.

  Next, the operation of the coating apparatus of this embodiment will be described with reference to FIG. In the coating process (step S8-1), first, the coating liquid pump 2 sucks the coating liquid in the coating liquid tank 1. Next, a discharge start signal is output to the coating liquid pump 2 (step S8-2), and the coating liquid pump 2 starts the pressure feeding operation of the coating liquid. Simultaneously with the output of the discharge start signal (discharge start time tdis), the control device 8 starts measuring time (step S8-3). When the elapsed time Te from the discharge start time tdis reaches the reference time Tsd (step S8-4), the control device 8 performs pressure measurement with the pressure sensor 7 (step S8-5). The pressure measured in step S8-5 is the actually measured pressure value Pme. Further, the control device 8 stops timing (step S8-6). Subsequently, the control device 8 compares the actually measured pressure value Pme with the reference pressure value Pref (step S8-7).

  If the measured pressure value Pme is lower than the reference pressure value Pref in step S8-7, it is determined that bubbles (at least one of stationary bubbles and fluid bubbles) have been detected (step S8-8). In this case, since the next application process cannot be performed, an automatic air venting operation (S8-9) and idle discharge under application conditions (step S8-10) are executed. On the other hand, if the measured pressure value Pme is greater than or equal to the reference pressure value Pref in step S8-7, it is determined that no bubbles are detected (step S8-11), and the process proceeds to the next coating process.

  In the coating apparatus of the present embodiment, bubbles are detected by comparing the measured pressure value Pme measured by the pressure sensor 7 with the reference pressure value Pref, so that a very small amount of bubbles is compared with visual or optical methods. Can be detected with high accuracy. Further, since the reference pressure value Pref is a value during the pressure increase of the pressure curve when no bubbles are present, it is possible to reliably detect both stationary bubbles and flowing bubbles.

  Other configurations and operations of the second embodiment are the same as those of the first embodiment.

The schematic diagram which shows the coating device of this invention. The typical graph which shows the relationship between the pressure and time when the bubble is not mixed in the coating liquid. The typical graph which shows the relationship between the pressure and time when a stationary bubble is mixed in the coating liquid. The typical graph which shows the relationship between the pressure and time when fluid bubbles are mixed in the coating liquid. The typical graph for demonstrating the method of the bubble detection in 1st Embodiment. The flowchart for demonstrating operation | movement of the coating device in 1st Embodiment. The typical graph for demonstrating the method of the bubble detection in 2nd Embodiment. The flowchart for demonstrating operation | movement of the coating device in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coating liquid tank 2 Coating liquid pump 2a Cylinder 2b Piston 2c Drive mechanism 3 Coating nozzle 4 Three-way valve 4a-4c Port 5 Support stand 6 Pressure release valve 7 Pressure sensor 8 Controller 11A-11E Piping 12 Coating member 13 Coating film 14 Tube Psd Standard pressure value Pref Reference pressure value Pme Actual measurement pressure value Tsd Standard time Tref Reference time Tme Actual measurement time

Claims (8)

A coating liquid tank for storing the coating liquid, a coating liquid pump for pumping the coating liquid in the coating liquid tank, and a coating nozzle for discharging the coating liquid pumped from the coating liquid pump toward a member to be coated; In the coating apparatus comprising the coating liquid tank, the coating liquid pump, and a pipe connecting the coating nozzle,
A pressure sensor for detecting the pressure of the coating liquid in the pipe;
And a control device that controls the operation of the coating liquid pump and detects air bubbles in the coating liquid based on the pressure detected by the pressure sensor. The controller is
A reference time, which is the time from when the discharge start signal is output to the coating liquid pump when the bubbles are not present until the pressure of the coating liquid in the pipe reaches a predetermined reference pressure value, is determined. Remember in advance,
When the measured time that is the time from the output of the discharge start signal to the pressure detected by the pressure sensor reaching the reference pressure value is compared with the reference time, and the measured time exceeds the reference time The coating apparatus according to claim 1, wherein it is determined that bubbles are present in the coating liquid.   The reference pressure value is a pressure value that is rising before the pressure of the coating liquid in the pipe reaches a constant pressure after outputting the discharge start signal to the coating liquid pump when bubbles do not exist. The coating apparatus according to claim 2. The controller is
A reference pressure value that is a pressure of the coating liquid in the pipe at a time when a predetermined reference time has elapsed from the output of a discharge start signal that instructs the coating liquid pump to start a discharge operation when there is no bubble. Remember in advance,
The measured pressure value, which is the pressure detected by the pressure sensor when the reference time has elapsed from the output of the discharge start signal, is compared with the reference pressure value, and the measured pressure value matches the reference pressure value. The coating apparatus according to claim 1, wherein when it falls below, it is determined that air bubbles are present in the coating liquid.   The reference time is the time before the pressure of the coating liquid in the pipe reaches a constant pressure when the reference time has elapsed after the discharge start signal is output to the coating liquid pump when bubbles do not exist. The coating apparatus according to claim 4, wherein the coating apparatus is set to be in a rising state.   6. The coating apparatus according to claim 1, wherein the pressure sensor is provided in the pipe closer to the coating nozzle than the coating liquid pump. A coating liquid tank for storing the coating liquid, a coating liquid pump for pumping the coating liquid in the coating liquid tank, and a coating nozzle for discharging the coating liquid pumped from the coating liquid pump toward a member to be coated; In a coating apparatus comprising the coating liquid tank, the coating liquid pump, and a pipe connecting the coating nozzle, a method for detecting bubbles in the coating liquid in the pipe,
A pressure sensor for detecting the pressure of the coating liquid in the pipe is provided;
A reference time, which is a time from when a discharge start signal is output to command the start of a discharge operation to the coating liquid pump when bubbles do not exist, until the pressure of the coating liquid in the pipe reaches a predetermined reference pressure value Is stored in advance,
Comparing the reference time with the actual measurement time, which is the time from the output of the discharge start signal until the pressure detected by the pressure sensor reaches the reference pressure value,
If the measured time exceeds the reference time, it is determined that bubbles are present in the coating liquid. A coating liquid tank for storing the coating liquid, a coating liquid pump for pumping the coating liquid in the coating liquid tank, and a coating nozzle for discharging the coating liquid pumped from the coating liquid pump toward a member to be coated; In a coating apparatus comprising the coating liquid tank, the coating liquid pump, and a pipe connecting the coating nozzle, a method for detecting bubbles in the coating liquid in the pipe,
A pressure sensor for detecting the pressure of the coating liquid in the pipe is provided;
A reference pressure value that is the pressure of the coating liquid in the pipe at the time when a predetermined reference time has elapsed from the output of a discharge start signal that instructs the coating liquid pump to start the discharge operation when no bubbles are present is previously stored. Remember,
Comparing the measured pressure value, which is the pressure detected by the pressure sensor when the reference time has elapsed from the output of the discharge start signal, with the reference pressure value;
When the measured pressure value falls below the reference pressure value, it is determined that bubbles are present in the coating liquid.

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