JP2024039637A - How to measure the number of particles generated from fluororesin tubes - Google Patents

Abstract

[Problem] To provide a method for measuring the number of particles that can accurately evaluate the cleanliness of the inner surface of a fluororesin tube. [Solution] A method for measuring the number of particles released into a solvent from a fluororesin tube, which includes flowing a solvent into the fluororesin tube to clean the inner surface of the fluororesin tube, filling the fluororesin tube with the solvent, leaving the fluororesin tube filled with the solvent, flowing the solvent into the fluororesin tube again, and measuring the number of particles released from the fluororesin tube into the solvent. [Selected Figure] Figure 1

Description

The present disclosure relates to a method for measuring the number of particles generated from a fluororesin tube.

Patent Document 1 describes a method for manufacturing a fluororesin tube in which a fluororesin or a resin mixture based on a fluororesin is melt-extruded and formed into a tube shape, in which clean air is flowed into the tube after or during tube formation; A method for manufacturing a particle-reduced fluororesin tube is described, which is characterized by carrying out a purging process to remove particles within the tube.

Japanese Patent Application Publication No. 2000-233435

The present disclosure aims to provide a method for measuring the number of particles that can accurately evaluate the cleanliness of the inner surface of a fluororesin tube.

According to the present disclosure, there is provided a measuring method for measuring the number of particles released into a solvent from a fluororesin tube, the inner surface of the fluororesin tube being washed by flowing a solvent into the fluororesin tube, and the Fill the fluororesin tube with the solvent, leave the fluororesin tube with the solvent filled in the fluororesin tube, flow the solvent into the fluororesin tube again, and remove the solvent from the fluororesin tube. A measurement method is provided for measuring the number of particles emitted into the air.

According to the present disclosure, it is possible to provide a method for measuring the number of particles that can accurately evaluate the cleanliness of the inner surface of a fluororesin tube.

FIG. 1 is a system diagram showing an example of an embodiment of a system used to implement the measurement method of the present disclosure.

Hereinafter, specific embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

As a method for measuring the number of particles released into a solvent from a fluororesin tube, Patent Document 1 describes a method in which ultrapure water is circulated through a specimen tube at a flow rate of 3.8 l/min, and the ultrapure water is continuously It is stated that it was measured using a particle counter. Even by using such a conventional method, it is possible to grasp the cleanliness of the inner surface of the fluororesin tube to some extent. However, when tubes that have been confirmed to have a high level of cleanliness using conventional methods are actually installed in semiconductor manufacturing equipment, unexpected particles may be found to be emitted from the fluororesin tubes into the solvent. The yield rate of semiconductor manufacturing may be lowered.

Therefore, there is a need for a method for measuring the number of particles that can accurately evaluate the cleanliness of the inner surface of a fluororesin tube before it is installed in semiconductor manufacturing equipment.

In the measurement method of the present disclosure, in order to measure the number of particles released into the solvent from the fluororesin tube, the inside of the fluororesin tube is cleaned with a solvent in advance, and the solvent is allowed to stay in the cleaned tube for a certain period of time. Then, the number of particles released from the fluororesin tube into the solvent is measured.

Since the measuring method of the present disclosure has the above-described configuration, it is possible to grasp the cleanliness of the inner surface of the tube more accurately than the conventional measuring method. Therefore, by using the measurement method of the present disclosure, it is possible to understand the level of cleanliness of two tubes, even if the two tubes have the same cleanliness when using a conventional measurement method. In addition, since the level of cleanliness can be determined before installing the tube in semiconductor manufacturing equipment, the yield rate in semiconductor manufacturing can be increased.

Next, the measurement method of the present disclosure will be explained in detail.

The measurement method of the present disclosure is a measurement method that measures the number of particles released from a fluororesin tube into a solvent. The measurement method of the present disclosure mainly includes three steps. That is, in the measurement method of the present disclosure,
By flowing a solvent into the fluororesin tube, the inner surface of the fluororesin tube is cleaned (cleaning process).
Fill the fluororesin tube with a solvent, leave the fluororesin tube with the solvent filled in the fluororesin tube (solvent retention process),
The solvent is poured into the fluororesin tube again, and the number of particles released from the fluororesin tube into the solvent is measured (measurement step).

In the cleaning step, the inner surface of the fluororesin tube is cleaned by flowing a solvent into the fluororesin tube.

In the cleaning step, the flow rate of the solvent flowing to clean the inner surface of the fluororesin tube is preferably 5 to 50 mL/min, more preferably 10 mL/min or more, and more preferably 20 mL/min or less.

In the cleaning process, the flow rate of the solvent flowed to clean the inner surface of the fluororesin tube is such that it can sufficiently clean all of the inner surface of the fluororesin tube, and the number of particles released from the inner surface of the fluororesin tube is reduced. It is preferable that the amount is sufficiently reduced.

In one embodiment of the cleaning process, the inner surface of the fluororesin tube is cleaned while measuring the number of particles released into the solvent, and a graph is drawn in which the cleaning time is plotted on the horizontal axis and the number of particles is plotted on the vertical axis. Cleaning of the inner surface of the fluororesin tube can be completed after the measured number of particles has decreased to a height corresponding to 1/3 of the peak height of the curve in the graph. Further, in one embodiment of the cleaning process, cleaning of the inner surface of the fluororesin tube is finished after the curve of the graph becomes almost flat, that is, after almost no decrease in the number of measured particles is observed. I can do it.

In the cleaning step, the flow rate of the solvent flowed to clean the inner surface of the fluororesin tube is preferably 10 to 200 times the internal volume of the fluororesin tube, more preferably 100 times or less, More preferably, the amount is 50 times or less, and still more preferably 18 times or less.

The inner surface of the fluororesin tube can be cleaned at room temperature (for example, 10 to 30°C). The temperature of the solvent supplied to the fluororesin tube may be room temperature (for example, 10 to 30°C).

Cleaning of the inner surface of the fluororesin tube can be completed by stopping the supply of the solvent into the fluororesin tube. In addition, after confirming that the number of particles emitted from the inner surface of the fluororesin tube has been sufficiently reduced by the above method, the next solvent retention step can be carried out without stopping the supply of solvent into the fluororesin tube. May be implemented. Furthermore, after cleaning the inner surface of the fluororesin tube, the next solvent retention step may be carried out after removing the solvent from inside the fluororesin tube, or the solvent may be left inside the fluororesin tube. , the following solvent retention step may be performed.

Following the washing step, a solvent retention step is performed. In the solvent retention step, the fluororesin tube is filled with a solvent, and the fluororesin tube is left to stand in a state where the fluororesin tube is filled with the solvent. In one embodiment of the solvent residence step, the flow rate of the solvent within the fluororesin tube is 0 mL/min.

The method of filling the fluororesin tube with the solvent is not particularly limited, and any method may be used as long as the fluororesin tube is filled with the solvent so that the entire inner surface of the fluororesin tube is in contact with the solvent. In one embodiment, the cleaning step is carried out by cleaning the inside surface of the fluoropolymer tube at a flow rate such that all of the interior surface of the fluoropolymer tube is exposed to the solvent, and after the cleaning is completed, the solvent is introduced into the fluoropolymer tube. The solvent retention step is carried out by stopping the supply and keeping the fluororesin tube filled with the solvent for a certain period of time.

From the viewpoint of improving measurement accuracy, the time for which the fluororesin tube filled with the solvent is left is preferably 10 minutes or more, more preferably 20 minutes or more, still more preferably 2 hours or more, and even more preferably is 4 hours or more, particularly preferably 6 hours or more, and although the upper limit is not particularly limited, it can be 24 hours or less in consideration of measurement efficiency.

The temperature at which the fluororesin tube filled with the solvent is left may be room temperature (for example, 10 to 30° C.). The temperature of the solvent retained in the fluororesin tube may be room temperature (for example, 10 to 30°C). From the viewpoint of increasing measurement accuracy, it is preferable to leave the fluororesin tube filled with the solvent without applying heat and pressure to the fluororesin tube filled with the solvent. Further, from the viewpoint of improving measurement accuracy, it is preferable to leave the fluororesin tube filled with the solvent alone without vibrating the fluororesin tube filled with the solvent.

After carrying out the solvent retention step, the solvent is flowed into the fluororesin tube again, and the number of particles released from the fluororesin tube into the solvent is measured (measurement step). Even if it is confirmed that the number of particles emitted from the fluororesin tube into the solvent has almost no longer decreased during the cleaning process, the solvent should remain in the fluororesin tube after cleaning the inner surface of the fluororesin tube. In this case, a larger number of particles may be measured than the number of particles observed at the end of the cleaning process. It has now been found that the number of particles measured in this manner more accurately reflects the cleanliness of the inner surface of the fluororesin tube than the number of particles measured using conventional methods.

In the measurement step, the flow rate of the solvent flowing to measure the number of particles released from the fluororesin tube into the solvent is preferably 10 to 500 mL/min, more preferably 100 mL/min or more, and more preferably It is 300 mL/min or less.

The number of particles can be measured at room temperature (for example, 10 to 30° C.).

A commercially available particle counter can be used to measure the number of particles. The diameter of the particles to be measured may be 50 nm or more, 30 nm or more, or 20 nm or more.

The number of particles can be calculated by, for example, ending when a decrease in the number of particles is hardly observed, and adding up the number of particles measured until the end. By determining the measurement method and integration method, it becomes possible to accurately compare the cleanliness of the inner surfaces of two or more fluororesin tubes.

In one embodiment of the measurement method,
After cleaning the particle measurement line, install the fluororesin tube to be measured upstream of the particle counter.
Clean the inner surface of the fluororesin tube by flowing the solvent into the fluororesin tube while measuring the number of particles in the solvent used to clean the inner surface of the fluororesin tube using a particle counter.
We confirmed that the number of particles in the solvent used to clean the inner surface of the fluororesin tube had hardly decreased.
Stop the supply of solvent into the fluororesin tube, leave the fluororesin tube for at least 10 minutes with the solvent filled in the fluororesin tube,
Restart the supply of the solvent into the fluororesin tube, and use a particle counter to measure the number of particles in the solvent that has passed through the fluororesin tube.

The solvents used in each step of the measurement method of the present disclosure may be the same or different, but from the viewpoint of facilitating measurement, it is preferable to use the same solvent.

The solubility parameter of the solvent is preferably 14 to 35 (MPa) ^1/2 , more preferably 16 (MPa) ^1/2 or more, still more preferably 17 (MPa) ^1/2 or more, and more preferably is 25 (MPa) ^1/2 or less, more preferably 20 (MPa) ^1/2 or less. It is presumed that the particles adhering to the inner surface of the fluororesin tube include particles derived from polymer fume generated from the molten fluororesin during the tube manufacturing process. Solvents with solubility parameters within the above ranges are difficult to dissolve particles derived from polymer fumes generated from fluororesins, so by using solvents with solubility parameters within the above ranges, the number of particles can be determined more accurately. It is assumed that it can be measured.

Examples of the solvent include n-hexane (14.9), n-heptane (15.1), diethyl ether (15.1), diisobutyl ketone (16.0), diisopropyl ketone (16.4), and ethyl amyl. Ketone (16.8), cyclohexane (16.8), butyl acetate (17.0), cyclopentane (17.8), isopropyl alcohol (18.0), ethyl acetate (18.6), acetone (20. 3), dioxane (20.5), acetaldehyde (21.1), amyl alcohol (22.3), cyclohexanol (23.3), n-propyl alcohol (24.5), ethyl alcohol (26), ethylene Examples include glycol (29.9). The numerical value in parentheses is the solubility parameter ((MPa) ^1/2 ) of the solvent.

The solubility parameters are detailed in the following literature:
Koichiro Nakanishi, “Solubility Parameter”, Heat Measurement, Japanese Society of Thermometry, Vol. 9, No. 2, pp. 61-68, 1982. For the solubility parameter of the solvent, for example, the values listed on the following website are adopted. can.
“Plastic Materials Dictionary Dissolution of Plasticizers and Solvents - Solubility Parameter Numerical Order”, [online], [Retrieved August 30, 2020], Internet <URL: https://www.plastics-material.com/% E5%8F%AF%E5%A1%91%E5%89%A4%E3%82%84%E6%BA%B6%E5%89%A4%E3%81%AE%E6%BA%B6%E8% A7%A3-%E6%BA%B6%E8%A7%A3%E5%BA%A6%E3%83%91%E3%83%A9%E3%83%A1%E3%83%BC%E3%82 %BF%E6%95%B0%E5%80%A4%E9%A0%86/>

The solvent is preferably at least one selected from the group consisting of isopropyl alcohol and ethylene glycol, and isopropyl alcohol is more preferred.

The solvent is preferably filtered using a filter before being supplied to the fluororesin tube. For example, a filter with a filtration accuracy of 30 nm or less can be used for filtration. By filtering the solvent in advance, it becomes possible to more accurately measure the number of particles having a diameter greater than the filtration accuracy.

For example, a fluororesin tube having a length of 10 cm to 100 m can be used in the measurement method of the present disclosure. The inner diameter of the fluororesin tube is, for example, 2 to 23 mm.

The tube used in the measurement method of the present disclosure is formed from a fluororesin. As the fluororesin, a fluororesin having melt processability is preferred. In this disclosure, melt processable means that the polymer can be melted and processed using conventional processing equipment such as extruders and injection molding machines. Therefore, melt-processable fluororesins usually have a melt flow rate of 0.01 to 500 g/10 minutes as measured by the measuring method described below.

The melt flow rate (MFR) of the fluororesin is preferably 0.5 to 100 g/10 minutes, more preferably 1 to 50 g/10 minutes, and still more preferably 2 to 40 g/10 minutes.

MFR is based on ASTM D-1238, using a die with a diameter of 2.1 mm and a length of 8 mm, a load of 5 kg, and any temperature within the range of approximately 230 to 400 °C, which is the general molding temperature for fluororesin. (for example, 372°C).

The melting point of the fluororesin is not particularly limited, but is preferably 100 to 324°C, more preferably 220 to 315°C. The above melting point is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is raised at a rate of 10° C./min using a differential scanning calorimeter (DSC).

Examples of the fluororesin include tetrafluoroethylene/fluoroalkyl vinyl ether copolymer, tetrafluoroethylene (TFE)/hexafluoropropylene (HFP) copolymer, TFE/ethylene copolymer [ETFE], TFE/ethylene/HFP copolymer, ethylene/chlorotrifluoroethylene (CTFE) copolymer [ECTFE], polychlorotrifluoroethylene [PCTFE], CTFE/TFE copolymer, polyvinylidene fluoride [PVdF], TFE/vinylidene fluoride ( VdF) copolymer [VT], polyvinyl fluoride [PVF], TFE/VdF/CTFE copolymer [VTC], TFE/HFP/VdF copolymer, and the like.

As the fluororesin, at least one selected from the group consisting of tetrafluoroethylene/fluoroalkyl vinyl ether copolymer and tetrafluoroethylene/hexafluoropropylene copolymer is particularly preferred.

Next, a system for implementing the measurement method of the present disclosure will be described with reference to the drawings. FIG. 1 is a system diagram showing an example of an embodiment of the system of the present disclosure. As shown in FIG. 1, a system 1 according to an embodiment of the present disclosure includes a solvent container 11, a filter 14, and a particle counter 17.

A solvent is contained in the solvent container 11 and connected to a joint 15 via a pump 12, a valve 13, and a filter 14. The joint 15 and the joint 16 are configured so that a fluororesin tube 21 to be measured can be connected thereto. The solvent in the solvent container 11 is supplied by a pump 12 to a fluororesin tube 21 connected to a fitting 15 and a fitting 16 through a filter 14 . Part or all of the solvent that has passed through the fluororesin tube 21 is introduced into the particle counter 17, and the number of particles in the solvent is measured.

In the system 1 shown in FIG. 1, a flow meter 18 is installed downstream of the particle counter 17, and the flow rate of the solvent introduced into the particle counter 17 is determined by the flow meter 18 (a flow meter equipped with a flow rate adjustment valve). is adjusted. The remaining solvent that has not been introduced into the particle counter 17 has its flow rate adjusted by a flow meter 19 (a flow meter equipped with a flow rate adjustment valve), and is discharged to the outside via the flow meter 19.

Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

<1> According to the first aspect of the present disclosure,
A measurement method for measuring the number of particles released from a fluororesin tube into a solvent, the method comprising:
cleaning the inner surface of the fluororesin tube by flowing a solvent into the fluororesin tube;
filling the fluororesin tube with the solvent; leaving the fluororesin tube with the solvent filled in the fluororesin tube;
A measurement method is provided in which the solvent is again flowed into the fluororesin tube and the number of particles released from the fluororesin tube into the solvent is measured.
<2> According to the second aspect of the present disclosure,
A measuring method according to the first aspect is provided, wherein the flow rate of the solvent that is flowed to clean the inner surface of the fluororesin tube is 10 to 50 mL/min.
<3> According to the third aspect of the present disclosure,
The inner surface of the fluororesin tube is cleaned while measuring the number of particles released into the solvent, and a graph is plotted with the cleaning time on the horizontal axis and the number of particles on the vertical axis, and the number of particles measured is There is provided a measuring method according to the first or second aspect, in which cleaning of the inner surface of the fluororesin tube is finished after the height has decreased to 1/3 of the peak height of the curve of the graph.
<4> According to the fourth aspect of the present disclosure,
There is provided a measuring method according to any one of the first to third aspects, wherein the fluororesin tube is left filled with the solvent for 4 hours or more.
<5> According to the fifth aspect of the present disclosure,
There is provided a measuring method according to any one of the first to fourth aspects, in which the solvent is passed through a filter having a filtration accuracy of 30 nm or less and then supplied into the fluororesin tube.
<6> According to the sixth aspect of the present disclosure,
There is provided a measuring method according to any one of the first to fifth aspects, wherein the solubility parameter of the solvent is 14 to 35 (MPa) ^1/2 .
<7> According to the seventh aspect of the present disclosure,
There is provided a measuring method according to any one of the first to sixth aspects, wherein the solvent is isopropyl alcohol.
<8> According to the eighth aspect of the present disclosure,
There is provided a measuring method according to any one of the first to seventh aspects, wherein the length of the fluororesin tube is 100 m or less.
<9> According to the ninth aspect of the present disclosure,
There is provided a measuring method according to any one of the first to eighth aspects, wherein the fluororesin tube has an inner diameter of 2 to 23 mm.
<10> According to the tenth aspect of the present disclosure,
The first to first fluororesin tubes are formed from at least one fluororesin selected from the group consisting of tetrafluoroethylene/fluoroalkyl vinyl ether copolymer and tetrafluoroethylene/hexafluoropropylene copolymer. A measuring method according to any one of nine aspects is provided.

Next, embodiments of the present disclosure will be described using Examples, but the present disclosure is not limited to these Examples.

In the Examples and Comparative Examples, the following tubes were used.
Tube A
A tube formed from a tetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer. Outer diameter 6.35mm, inner diameter 3.95mm. After the tube is manufactured in a clean room, the inner surface of the tube is exposed to the atmosphere outside the clean room.
Tube B
A tube formed from a tetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer. Outer diameter 6.35mm, inner diameter 3.95mm. After manufacturing the tube in a clean room, both ends of the tube are sealed with caps inside the clean room without exposing the inner surface of the tube to the atmosphere outside the clean room.
Tube C
A tube formed from a tetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer. Outer diameter 6.35mm, inner diameter 3.95mm. A tube manufactured in a clean room using manufacturing conditions different from those for tube A, and then the inner surface of the tube exposed to the atmosphere outside the clean room.

The copolymers forming tubes A to C all have the following physical properties.
Composition: Tetrafluoroethylene/perfluoro(propyl vinyl ether) = 94.5/5.5 (mass%)
MFR: 2g/10min Melting point: 303℃

Each numerical value in Examples was measured by the following method.

(composition)
Measured by ¹⁹ F-NMR method.

(Melt flow rate (MFR))
According to ASTM D1238, using a melt indexer (manufactured by Yasuda Seiki Seisakusho Co., Ltd.), the mass (g /10 minutes).

(melting point)
Using a differential scanning calorimeter (DSC), the temperature was determined as the temperature corresponding to the maximum value in the heat of fusion curve when the temperature was increased at a rate of 10° C./min.

(number of particles)
The number of particles with a diameter of 30 nm or more was measured using a particle counter (manufactured by Rion Corporation, light scattering type liquid particle detector KS-19F).

Example 1
Tube A was produced by cutting the tube into 0.5 m in a class 100 clean booth.

For the measurement, System 1 shown in FIG. 1 and commercially available high-purity isopropyl alcohol (IPA) were used. As the filter 14, an in-line filter manufactured by Kitz Microfilter (NHM series, filtration accuracy of 3 nm) was used.

It was confirmed in advance using a particle counter that the number of particles with a diameter of 30 nm or more released into the IPA from the measurement line was 10 particles/mL or less.

After connecting tube A to fittings 15 and 16 of system 1 shown in Fig. 1, inject tube A into the tube A at a flow rate of 10 mL/min to achieve the flow rate (total flow rate of IPA relative to the inner volume of the tube) listed in Table 1. The inner surface of tube A was washed by pouring IPA into the tube.

Next, the pump 12 was stopped, and the tube A was left standing for 0.5 hours with IPA filled inside the tube A.

The supply of IPA into tube A was restarted, and IPA was allowed to flow into tube A at a flow rate of 110 mL/min. A portion of the IPA that had passed through tube A was introduced into a light scattering type liquid particle detector (particle counter) at a flow rate of 10 mL/min, and the number of particles in the IPA was measured. Although the number of particles decreased to the blank level within 10 minutes, measurement was continued for 16 minutes. The number of particles was measured 15 times in total with an interval of 2 seconds between each measurement. The number of particles released from tube A into IPA (particles/cm ² ) was calculated. The results are shown in Table 1.

Examples 2-8
The number of particles released from the tube into IPA (particles/cm ² ) was calculated. The results are shown in Table 1.

Comparative examples 1 to 6
The number of particles was measured without washing the tube and without filling the tube with IPA. The type of tube, type of solvent, etc. were changed as shown in Table 1. Other conditions were the same as in Example 1, and the number of particles (particles/cm ² ) released from the tube into IPA was calculated. The results are shown in Table 1.

As shown in the results in Table 1, in Comparative Examples 1 and 4 using the conventional measurement method, it was confirmed that the same number of particles were released into the solvent from both tube A and tube B. .
On the other hand, in Example 3 using the measurement method of the present disclosure, it was confirmed that a large number of particles were released from tube A into the solvent. Furthermore, in Example 7 using the measurement method of the present disclosure, it was confirmed that fewer particles were released into the solvent from tube B than from tube A.
That is, when using the conventional measuring method, the cleanliness of the inner surfaces of tube A and tube B are evaluated to be equivalent, but when using the measuring method of the present disclosure, the cleanliness of the inner surface of tube B is evaluated to be the same as that of tube A. It can be seen that the cleanliness level is higher than that of the inner surface.
Similarly, when comparing the results of Comparative Examples 5 and 6 with the results of Examples 7 and 8, the cleanliness of the inner surfaces of tubes B and C is evaluated to be equivalent when using the conventional measurement method. , it can be seen that when the measuring method of the present disclosure is used, it can be confirmed that the cleanliness of the inner surface of tube B is higher than the cleanliness of the inner surface of tube C.
From the above results, it can be seen that the measuring method of the present disclosure provides data that can more accurately grasp the cleanliness of the inner surface of the tube than the conventional measuring method. Therefore, by using the measurement method of the present disclosure, for example, the cleanliness of the inner surface of the tube can be accurately evaluated before installing the tube in semiconductor manufacturing equipment, so that the yield in semiconductor manufacturing can be increased.

1 System 11 Solvent container 12 Pump 13 Valve 14 Filter 15, 16 Fitting 21 Fluororesin tube 17 Particle counter 18, 19 Flow meter

Claims (10)

A measurement method for measuring the number of particles released from a fluororesin tube into a solvent, the method comprising:
cleaning the inner surface of the fluororesin tube by flowing a solvent into the fluororesin tube;
filling the fluororesin tube with the solvent; leaving the fluororesin tube with the solvent filled in the fluororesin tube;
A measurement method comprising flowing the solvent again into the fluororesin tube and measuring the number of particles released from the fluororesin tube into the solvent. The measuring method according to claim 1, wherein the flow rate of the solvent flowing to clean the inner surface of the fluororesin tube is 10 to 50 mL/min. The inner surface of the fluororesin tube is cleaned while measuring the number of particles released into the solvent, and a graph is plotted with the cleaning time on the horizontal axis and the number of particles on the vertical axis, and the number of particles measured is 3. The measuring method according to claim 1, wherein the cleaning of the inner surface of the fluororesin tube is completed after the height has decreased to one-third of the peak height of the curve in the graph. 3. The measuring method according to claim 1, wherein the time for leaving the fluororesin tube filled with the solvent is 4 hours or more. The measuring method according to claim 1 or 2, wherein the solvent is supplied into the fluororesin tube after passing through a filter having a filtration accuracy of 30 nm or less. The measuring method according to claim 1 or 2, wherein the solubility parameter of the solvent is 14 to 35 (MPa) ^1/2 . The measuring method according to claim 1 or 2, wherein the solvent is isopropyl alcohol. The measuring method according to claim 1 or 2, wherein the length of the fluororesin tube is 100 m or less. The measuring method according to claim 1 or 2, wherein the fluororesin tube has an inner diameter of 2 to 23 mm. 2. The fluororesin tube is formed from at least one fluororesin selected from the group consisting of tetrafluoroethylene/fluoroalkyl vinyl ether copolymer and tetrafluoroethylene/hexafluoropropylene copolymer. The measurement method described in 2.

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