WO2004086008A1

WO2004086008A1 - Method for measuring pore size of porous filter material

Info

Publication number: WO2004086008A1
Application number: PCT/JP2004/003102
Authority: WO
Inventors: Tomonori Takahashi
Original assignee: Ngk Insulators Ltd.
Priority date: 2003-03-24
Filing date: 2004-03-10
Publication date: 2004-10-07
Also published as: JP2004286635A; JP3845067B2

Abstract

A method for measuring the pore size of a porous filtering material in which pressurized gas is supplied to a dry filtering material and a wet filtering material where the pores are filled with a test liquid, pressure of the pressurized gas is boosted stepwise, flow rate of gas permeating each filtering material is detected at each stage of gas pressure, and then mean pore size is determined based on a mathematical expression (MFPD=(4BϜCOSθ)/P). This method includes a step for boosting a pressure to the next gas pressure stage after holding the wet porous material under a constant pressure for (S)-30 sec when the passing time (S) of a filtrate determined by a mathematical expression (S=(X/J)×Vs/Vr) is shorter than 3 sec, or for (S)-(S×10) sec if the passing time (S) of the filtrate is equal to or longer than 3 sec, where X is the thickness (m) of the filtering material, J is the line speed (m/s) of the filtrate during actual use, Vs is the viscosity (Pas) of the test liquid, and Vr is the viscosity (Pas) of the filtrate. According to the method, mean pore size can be measured with high accuracy for a filtering material having three-dimensionally complicated pores and the quality can be evaluated while reflecting the performance of the filtering material during use.

Description

Specification

Method of measuring pore size of porous filter

The present invention provides a method for evaluating a filter related to the average pore diameter by applying a so-called bubble point method. More specifically, the present invention provides a pore size measurement method capable of evaluating a filter body related to an average pore size that is useful for practical use in a filter body in which pores of a ceramic body or the like are three-dimensionally complicated. . Background art

Evaluation of the average pore diameter of various filtration media is essential as evaluation of the basic performance, and various evaluation methods such as a bubble point method, a mercury method, and a bacterial filtration method have been conventionally performed. Above all, the bubble point method is widely used for quality control of various types of filtration media because of relatively simple measurement.

By the way, the bubble point method is described in ASTM F 316-86. However, when a filter in which each pore is filled with a test liquid is installed in a pressurized gas flow path, one of the filters becomes one. When the pressure of the pressurized gas applied to the test liquid filled in each pore of the filter on the surface exceeds the resistance due to the surface tension of the test liquid filled in each pore of the filter, The gas-liquid interface utilizes the fact that the gas-liquid interface extends to the opening of the pores of the filter to allow gas permeation. The measurement of the average pore diameter in this method is performed by: Using the assumption that the ratio of the amount of gas permeated through the body equals the ratio of the amount of permeated gas permeating through pores larger than the pore diameter corresponding to the gas pressure at each stage, with respect to the permeated gas permeating through all pores. (“ANUAL BOOK 〇 F AMER I CAN STANDARDS” vo l. 1 1.01, AMER I CAN SOC I ETY FOR TEST I NG AND MATER I AL

See S issue).

Specifically, a filter body not filled with the test liquid (hereinafter referred to as “dry filter body”) and a filter body filled with the test liquid (hereinafter referred to as “wet filter body”) are included. Each filter is placed on a holder with each end sealed, and a pressurized gas is supplied to one surface of each filter, and the pressure of the pressurized gas is increased step by step. The amount of gas passing through each filter is detected, and the ratio of the gas flow rate passing through the wet filter to the gas flow rate passing through the dry filter (wet filter Z dry filter) corresponds to the gas pressure corresponding to 1Z2. The pore diameter is regarded as the average pore diameter (MFPD), and is determined from the following equation (1).

MFPD = 4Br COS Θ / Ρ (1)

"In the above formula (1), MFPD is the average pore diameter (^ m), 0 is the contact angle (°) of the test liquid filled in the pores of the filter with the material constituting the filter, and τ is the filtration Surface tension (NZm) of the test liquid filled in the pores of the body, B is a constant number of cavities (0.715) or 1, P is the gas passing through the wet filter relative to the gas flow through the dry filter Indicates the gas pressure (MPa) at which the flow rate ratio (wet filter / dry filter) becomes 1/2. 0 may usually approximate 0 degree. "

Conventionally, as a method for evaluating the average pore diameter by this method, in each gas pressure stage, the gas pressure of the supplied gas is held until the amount of change in the gas flow rate for a certain period of time becomes a specific value or less, and then the following There is a method in which the step of increasing the pressure to the gas pressure step is repeated stepwise. According to this conventional method, a state in which the amount of change in the gas flow rate for a certain period of time is equal to or less than a specific value is regarded as a state in which the gas flow rate is saturated, and the gas pressure is maintained until the gas flow is saturated. The gas-liquid interface waits until the gas-liquid interface has sufficiently developed to the pore openings of the filter.The gas flow path of the wet filter through which the gas passes is part of the gas through the dry filter. It is based on the assumption that it is the same as the transmission path.

However, this conventional evaluation method was not always sufficient as an evaluation method for an actual product because it did not take into account the characteristics of the filter to be actually evaluated. Disclosure of the invention

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and can accurately and highly accurately measure an average pore diameter of a filter having three-dimensionally intricate pores. It is an object of the present invention to provide a method for measuring the pore size of a filter, which enables quality evaluation reflecting the performance of the filter. As a result of earnest studies to solve the above-mentioned problems, the present inventor has obtained the following knowledge regarding the point that an appropriate evaluation result could not be obtained by the conventional method.

That is, as shown in FIG. 6 (a), in the filter to be actually evaluated, the fluid to be filtered in the ordinary filtration flows in a distribution determined by the connection of the pores. On the other hand, as shown in Fig. 6 (b), when the gas is passed through the wet filter sequentially from low pressure, the gas starts to permeate preferentially to large pores, which is different from normal filtration. Follow the route. In particular, in the case of porous ceramics, the fluid flow path of the filter is formed by the combination of a plurality of pores and is three-dimensionally complicated and intricate. However, it is easy to follow the path of gas permeation of the dry filter and a path that is significantly different from ordinary filtration.

However, according to the conventional evaluation method, gas permeation of the dry filter and partial gas permeation of the wet filter with respect to the flow path of the fluid to be filtered in practical use pass through such various flow paths. Was not taken into consideration at all in that it had a significant effect on the evaluation results, and was not sufficient in terms of accuracy and delicateness, and was also sufficient in evaluating the performance of each product in actual use. It turned out to be nothing. In addition, the following findings were obtained.

(1) In the conventional evaluation method, since the change in the gas flow rate of the wet filter at a certain pressure for a certain period of time is less than a specific value, it is regarded as a so-called gas saturation state. Even when the interface is moving, it may be considered as so-called saturation of gas permeation. For this reason, the permeated gas through the long flow path is detected in a gas pressure stage after the original gas pressure stage, and this is an error factor.

(2) In the conventional evaluation method, when the gas pressure is maintained until the so-called saturation, as is clear from (1) above, the gas-liquid interface develops by stacking at each gas pressure stage. For this reason, in the conventional method, the influence on the evaluation results due to the lack of accuracy of the control equipment and measurement equipment at each gas pressure stage is accumulated and amplified, and this is a factor that further reduces the accuracy and accuracy of the evaluation results. It was.

③ In a dry filter, gas permeation depends on one path determined by the gas flow rate. The portion of the gas that enters through a certain pore always permeates through a particular path. In the measurement of wet filter media in the conventional evaluation method, the gas pressure is maintained until the so-called saturation However, when the holding time is long, the gas circulates largely, and the path through which the gas passes through the reference dry filter is different from the path through which the gas permeates through the wet filter. For this reason, in the conventional method, there is a difference in the actual evaluation target from the reference dry filter, which is a factor that further reduces the accuracy of the evaluation result.

において In actual use, the part of the fluid to be filtered that enters through a certain pore permeates through a specific path, in the same way as when the gas of the dry filter passes. For this reason, in the conventional method, the path of the fluid to be filtered that passes through the filter in actual use and the path of the gas that passes through the wet filter are different. In this regard, there is a difference between the substantial evaluation targets. This was a factor that did not sufficiently reflect the performance of the filter body during actual use. The present inventor made further studies based on the above findings, and found that the gas pressure of the gas supplied to one surface of the filter body was changed at each gas pressure stage so that the fluid to be filtered was actually filtered. When the gas pressure is maintained at a predetermined ratio of holding time based on the time required to pass through the body and the gas pressure is shifted to the next gas pressure stage, it is possible to accurately and accurately evaluate the practically useful average pore diameter And completed the present invention. That is, the present invention provides a dry filter in a dry state, and a wet filter in which pores of the dry filter are filled with a test liquid, supplying a pressurized gas to each filter, The pressure is increased stepwise, the gas flow permeating through each filter is detected at each gas pressure step, and then the average pore diameter is calculated based on the following equation (1). If the fluid passage time (S) determined by the following formula (2) is less than 3 seconds, then (S) seconds to 30 seconds. If the fluid passage time (S) is 3 seconds or more, Is a porous filtration characterized by including a holding-pressure increasing step of holding the wet filter at a constant pressure for a holding time of (S) seconds to (SX 10) seconds and then increasing the pressure to the next gas pressure stage. The present invention provides a method for measuring the pore diameter of a body.

MFPD- (4Br COS Θ) / Ρ (1)

“In the above formula (1), MFPD is the average pore diameter (^ m), 0 is the contact angle (°) of the test liquid filled in the pores of the filter with the material constituting the filter, and a is the contact angle of the filter. The surface tension (NZm) of the test liquid filled in the pores, B is the capillary constant (0 Ί 15) or 1, P is the permeability of the wet filter to the gas flow through the dry filter. The gas pressure (MPa) at which the gas flow ratio (wet filter / dry filter) becomes 12 is shown. "

S = (X / J) XV s / V r (2)

"In the above formula (2), X is the thickness (m) of the filter in the filtration direction, J is the linear velocity (mZs) of the fluid to be filtered in practical use, and Vs is the viscosity of the test liquid ( P a · s) and Vr is the viscosity (P a · s) of the fluid to be filtered. ”

In the present invention, in the holding-pressurizing step, the ratio of the gas flow rate passing through the wet filter to the gas flow rate passing through the dry filter (wet filter Z dry filter) is 15 to 1/2. It is preferably carried out in the range, more preferably in all gas pressure stages in this range. The holding time of each gas pressure step in the range where the gas flow rate ratio is 15 to 1/2 is the average of the gas pressure steps in the range where the gas flow rate ratio is 1/5 to 12. The holding time is preferably within 10% of the soil, and more preferably the holding time in the range where the gas flow rate ratio is 1Z5 to 1Z2 is 1 second to 1 minute. Further, in the holding-pressurizing step, the pressure value for increasing the pressure from one gas pressure step to the next gas pressure step is determined by a membrane when the fluid to be filtered is permeated at the linear velocity (J) of the fluid to be filtered in practical use. It is preferable that the pressure increase value is larger than the differential pressure, and each pressure increase value from one gas pressure step to the next gas pressure step in a range where the gas flow rate ratio is 1 to 5 to 1 Z 2 is It is further preferable that the average flow rate is within 20% of the soil in the range where the gas flow rate ratio is 1Z5 to 1/2. Further, it is preferable that each boosted value in the range where the ratio of the gas flow rates is 1Z5 to 12 is 0.01 to 0.04 MPa. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory diagram schematically showing the configuration of an apparatus for implementing the evaluation method of the present invention.

FIG. 2 is a cross-sectional view schematically showing a state in which a filter is installed on a holder in one example of the evaluation method of the present invention.

FIG. 3 is a graph showing the relationship between the gas flow rate and the gas pressure detected in each filter (dry filter, wet filter). FIG. 4 is a graph showing the relationship between the average pore diameter and the gas pressure retention time obtained in each of the examples and comparative examples.

FIG. 5 is a graph showing the distribution of the average pore diameter when 22 samples were measured by the methods of Example 1 and Comparative Example 8.

Figs. 6 (a) and 6 (b) are explanatory diagrams schematically showing the presence of pores in a ceramic filter, and Fig. 6 (a) is a schematic diagram of the flow of the fluid to be filtered in practical use. Fig. 6 (b) schematically shows the gas flow in the conventional measurement method. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of an embodiment of the present invention will be specifically described for each process based on the drawings. FIG. 1 shows the flow of a measuring device that is usually used in the evaluation method of the present invention, and includes a pressurized gas supply source 11 and a pressure of a gas introduced from the pressurized gas supply source 11. Control, a pressure sensor 16 for measuring the pressure set by the relevant regulator 12, a holder 10 for installing the filter 2, and a gas flow supplied to the filter. And a flow meter 14 for measurement. FIG. 2 is a cross-sectional view showing a state where the filter body 2 is installed in the holder 10. Fig. 3 is a graph showing the relationship between the permeated gas flow rate and the gas pressure detected in each filter (dry filter and wet filter). H in the graph indicates the permeate gas of the wet filter. It indicates the gas pressure at which the flow rate is 1 Z 2 with respect to the permeate gas flow rate of the dry filter. In the average pore diameter evaluation method of the present invention, first, as shown in FIGS. 1 and 2, a dry filter body 2 in a dry state was sealed in a holder 10 using a sealing member 3. Install in the state. The seal member 3 is a combination of a polymer such as epoxy or a glaze and a packing, a ring or the like. After measuring the gas permeation amount, install the wet filter 2 in which the pores of the same dry filter 2 are filled with the test liquid with the ends thereof similarly sealed in the holder 10 and measure the gas permeation amount. I do.

The filter 2 to be evaluated in the present invention is not particularly limited except that it is a porous body. For example, the filter 2 can be applied to various filter such as filter paper, an organic resin filter, and a ceramic filter. However, the evaluation method of the present invention It can be particularly preferably applied to a filter body in which pores are complicated and complicated, and in this regard, application to a ceramics filter is preferable. Further, the present invention can also be applied to a ceramics filter in which one or more filtration membranes having different pore diameters are laminated on a porous base material. Furthermore, although a plate-shaped filter is shown in FIG. 2, a filter, such as a tube or a monolith, can be measured by preparing a holder.

In the present invention, examples of the test liquid 4 to be filled in the pores of the dry filter 2 include high-purity water, denatured alcohol, and mineral oil as described in D1129 and D1193 of ASTM F316-86. , 1,1,2-trichloro-1,2,2-toluolate, or a fluorine-based inert liquid (trade name: Florinato FC-140, a fluorine-based inert liquid manufactured by SLEM) is preferred.

In addition, examples of the fluid to be filtered that is to be filtered in actual use include water and petroleum.

Next, in the present invention, a stepwise pressurized gas is supplied to one surface of the dry filter and the wet filter, and at this time, in the measurement of the permeated gas of the wet filter, each gas pressure step is measured. If the passage time (S) of the fluid to be filtered determined by the equation (2) is less than 3 seconds, (S) seconds to 30 seconds, and if the passage time (S) of the fluid to be filtered is 3 seconds or more, (S) After holding the wet filter at a constant pressure for a holding time of S) seconds to (SX 10) seconds, the pressure is increased to the next gas pressure stage. This is because, by shortening the holding time at each gas pressure stage, the gas permeation path between the dry filter and the wet filter to be tested becomes more similar. For this reason, accurate and highly accurate evaluation is possible. The pore diameter can be measured accurately by setting the retention time to 10 times or less the passage time (S) of the fluid to be filtered. However, when (S) is shorter than 3 seconds, (S) Even if the retention time is 30 seconds or less even if the retention time exceeds 10 times, the pore size can be measured with good delicateness.

Here, (S) obtained from Expression (2) depends on the linear velocity (J) of the fluid to be filtered in practical use, but (J) is usually used when designing a filtering device using the filtering body. It is set to a known value when the filter is manufactured considering its design. In addition, (J) may be set to have a predetermined width. In that case, (S) also has a predetermined width. In such a case, the above (S) is not more than 3 seconds. ) Max A value of 3 seconds or more and (S) less than 3 seconds means that the maximum value of (S) is less than 3 seconds. Then, the upper limit of the retention time is more likely to be higher when the maximum value is closer to the maximum value of (S), and is preferably 10 times or less, and more preferably 2 times or less, the maximum value of (S). '

If the holding time is too short, the gas flow rate that should be detected in the pressurization stage is not detected, such as when the gas-liquid interface is moving in a long flow path. Will be smaller than the evaluation result. Therefore, the holding time must be longer than the value of (S). If (S) has a predetermined width, (S) here also means the maximum value. Further, if the holding time is too short, operability and responsiveness of the device will become problematic.

That is, in a preferred embodiment of the present invention, in each gas pressure stage, the retention time is longer than (S) and as short as possible therein, so that the filtration target fluid to be actually filtered is a filter. The gas pressure is maintained for a time close to the time when the gas passes through. For this reason, the path of the gas in the wet filter is similar to the path through which the fluid to be filtered respectively passes, and the evaluation can sufficiently reflect the performance of the filter in actual use. Since the fluid to be filtered and the test liquid have different viscosities due to differences in viscosity, the time required to pass through the membrane and the time required for gas pressure discharge are different. Is corrected.

In the present invention, in the gas pressure stage where the ratio of the gas flow rate permeating the wet filter to the gas flow permeating the dry filter (wet filter dry filter) is 1/5 to 1/2, It is preferable to set such a holding time, and it is more preferable to set the holding time as described above in all the gas pressure stages in this range. This is because the average particle size is determined when the gas flow rate ratio is 1 Z2, so accurate control should be performed near this point, especially from the point where the gas flow rate in the wet filter starts to increase. Is preferred. Therefore, the gas pressure holding time in each gas pressure stage may be set to a range outside the above setting up to the gas pressure stage where the ratio of the gas flow rates is 1 to 5.

In addition, in the gas pressure stage in which the ratio of the gas flow rates is in the range of 1/5 to 1/2, the gas pressure holding time in each gas pressure stage should be as small as possible in order to perform accurate and precise evaluation. It is preferable to make them even. Specifically, the holding time at each gas pressure stage in the range where the ratio of the gas flow rate is 1/5 to 1/2 is set (the wet filter Z and the dry filter) in the range where the ratio is 1/5 to 1/2. It is preferable that the average gas pressure holding time in the entire gas pressure stage be within 10% of soil.

In the present invention, the pressure increase value from one gas pressure stage to the next gas pressure stage is larger than the Sarian differential pressure when the fluid to be filtered is permeated at the linear velocity (J) in practical use. Closer is preferred. Preferably, the pressure is 1 to 10 times the transmembrane pressure. If the pressure increase value is too small, the gas-liquid interface does not move within the holding time, and if it is too large, the resolution of the pore diameter is lost. When there is a range in the transmembrane pressure, it is preferable that the transmembrane pressure is larger than the maximum transmembrane pressure.

Further, for the same reason as described above, the pressure increase value is controlled as described above at the gas pressure stage in the range where the gas flow rate ratio is 1/5 to 1/2, and further at all gas pressure stages in this range. Is preferred.

In addition, in the present invention, in each gas pressure stage in a range where the gas flow rate ratio is 1Z5 to 1/2, in order to perform accurate and precise evaluation, the respective boosted values should be as evenly as possible. Is preferred.

Specifically, it is preferable that each boosted value in this range be within ± 20% of the average boosted value in all gas pressure stages in this range. Further, the range in which the pressure holding time and the pressure increase width are managed is preferably from a lower pressure stage when the pore size distribution is wide. In addition, in the present invention, when the pressure increase value with respect to the previous gas pressure stage in each gas pressure stage, and each gas pressure holding time in each gas pressure stage are as described above, accurate and high accuracy can be obtained, An evaluation reflecting actual performance can be performed, but the average pore diameter is 0.05 to 2 microns, the thickness is 10 to 300 microns, If the flow rate of the filtration fluid is 11 O mZ days, and if the filter body is made of ceramics, considering the performance of the measuring device, the pressure increase value of each gas pressure step with respect to the previous gas pressure step is set to 0.01. The gas pressure holding time in each gas pressure step can be selected from the range of 1 second to 1 minute. When measuring the dry filter, the pressure increase should be longer than the operation time of the device and the holding time longer than the response time. Good.

Further, the pressurized gas used in the present invention is preferably, for example, an inert gas such as air, argon, or nitrogen, and is difficult to dissolve in a test liquid, taking into account evaluation conditions, detection means, cost, and the like. What is necessary is just to select suitably.

Next, in the present invention, the permeated gas flow rate of each filter body is detected at each gas pressure stage, and the average pore diameter is determined based on equation (1). As shown in Fig. 3, in a dry filter, the gas flow rate detected increases almost in proportion to the pressure increase of the pressurized gas because there is no pressurized gas in the pores. Medium and solid lines). On the other hand, in a wet filter, the test fluid to be pressed by the pressurized gas is present in the pores, and until the pressure of the pressurized gas overcomes the resistive force due to the surface tension of the test liquid, the gas is released. One-liquid interface does not move. Therefore, in the initial stage of pressurization, even if the pressure of the pressurized gas increases, no permeated gas is detected, and when the pressure of the pressurized gas reaches a certain pressure, the flow rate of the permeated gas starts to increase, In the figure, the gas flow overlaps with the permeated gas flow rate-gas pressure line in the dry filter (shown by the dotted line in the figure). Then, the permeated gas flow rate detected at each gas pressure from the time when the permeated gas flow rate starts to increase to the time when the permeated gas flow rate in the dry filter finally overlaps with the straight line of the gas pressure is determined by a series of gas passages. It changes depending on the pore size distribution of the pores. The gas pressure H at which the flow rate of the permeated gas in the wet filter is 1 to 2 with respect to the flow rate of the permeate gas in the dry filter is determined. / 2), and the pore diameter corresponding to the gas pressure H is defined as the average pore diameter based on the equation (1).

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. In each of the examples and comparative examples, the filter body was evaluated using the following sample, test liquid, and fluid to be filtered.

(Sample)

A disk-shaped alumina substrate with an average pore diameter of about 10 // m, a diameter of 30 mm, and a thickness of 3 mm, an alumina intermediate layer with an average pore diameter of about l ^ mu and a thickness of 200 im, and an average A 15 m-thick titania filtration layer composed of isotropic particles of titania having a particle diameter of 0.5 μm was formed into a film, and the ceramic filter was fired in this order.

(Fluid to be filtered as a standard for evaluation) Be filtered fluid water (viscosity: 1 X 10- ⁶ ms), the practical conditions of water purification etc. is 1 one 5 m / day, membranes differential pressure at that time becomes 0. 0026- 0. 0128MP a . A suitable boosting width is 0.0128 MPa or more.

(Test fluid)

Florina one Bok ^{^{(viscosity: 2. 2X 10- 6 m 2 /}} s, the surface tension: 16 dyn eZc m) was used. Accordingly, the passage time (S) of the fluid to be filtered obtained from the equation (2) is 0.6-2.9 seconds. The preferred holding time is 30 seconds or less.

(Examples 1 to 6, Comparative Examples;! To 4)

A sample not filled with the test liquid (dry filter) was placed in a holder of a pore size evaluation device with its end sealed with a glaze and an O-ring, with a titania layer on the pressurized gas supply side. Next, pressurized air was supplied to the pressurized gas supply side. The pressure was increased by 0.017-0.02 IMP a every 30 seconds, and the gas flow rate was measured. Next, the sample was immersed in the test liquid, and the pores in the sample were completely filled with the test liquid. Next, a sample (wet filter) completely filled with the test liquid was placed in a holder of a pore diameter evaluation apparatus with its ends similarly sealed.

Then, pressurized air was supplied to the pressurized gas supply side. At this time, in Examples 1 to 6, the gas pressure was maintained at each gas pressure level for 1 second, 2 seconds, 4 to 16 seconds, 9 to 11 seconds, 18 to 22 seconds, 25 to 30 seconds, In Comparative Examples 1-4, the gas pressure was maintained at each gas pressure stage for 55-65 seconds, 290-310 seconds, 470-490 seconds, 590-610 seconds, and 0.017-0.02 IMP a each. The pressure was increased and the gas flow was measured. From the gas pressure at which the gas flow rate of the wet filter was equal to the gas flow rate of the dry filter, the average pore diameter of each sample was determined based on equation (1).

(Evaluation)

As shown in FIG. 4, the shorter the retention time, the smaller the measurement result of the average pore diameter. If the retention time is longer than S, even if the connection path of the pore through which a part of the fluid to be filtered permeates in practical use is long, the gas permeates through the path even in a wet filter, and is evaluated. If the retention time is closer to S, an excessively long path through which the gas that permeates the dry filter and the part of the fluid to be filtered in practical use cannot permeate is less likely to be included in the evaluation, resulting in an accurate evaluation. . (Examples 7-28, Comparative Examples 5-26)

In the gas permeation measurement of the wet filter of the same filtration membrane sample as in Example 1, the gas pressure of the supplied air was maintained as saturated when the change in the permeated gas flow rate became 12 mLZ minutes or less in 30 seconds, and was maintained until that time. Thereafter, the average pore diameter of 22 different samples was determined in the same manner as in Example 1 except that the pressure was increased to the next gas pressure step, and Comparative Examples 5 to 26 were obtained. The pressure corresponding to the average pore was 0.35 MPa, and the gas permeation amount of the dry filter was about 1000 OmL / min. Example 16 The average pore diameter of 22 different samples was determined assuming that the gas pressure holding time in the gas permeation measurement of the wet filter of Example 16 was 911 seconds, and this was set as Example 7-28.

(Evaluation)

As shown in FIG. 5, in Examples 6 to 27 of the present invention, the average pore diameter was in the range of 0.13 to 0.15Π1 (standard deviation 007). On the other hand, in Comparative Example 6-27, in which the gas pressure is maintained until the so-called gas saturation state is reached, and then the pressure is increased, the holding time at each gas pressure stage varies from 30 seconds to 20 minutes, and the average pore diameter Varied from 0.16 to 0.21 m (standard deviation: 0.011), and the average pore diameter was larger than the retention time of about 10 minutes shown in Fig. 4. Industrial applicability

As described above, according to the present invention, it is possible to accurately and accurately evaluate the average pore diameter of a filter having three-dimensionally intricate pores, and furthermore, to perform filtration during actual use. It is possible to provide a method for evaluating a filtration body capable of quality evaluation reflecting the performance of the body.

Claims

The scope of the claims

1. For a dry filter in a dry state, and a wet filter in which pores of the dry filter are filled with a test liquid, pressurized gas is supplied to each filter, and the pressure of the pressurized gas is gradually increased. Pressurized, and at each gas pressure stage, detect the gas flow through each said filter,

Next, there is provided a method for measuring the pore size of a porous filtration body for obtaining an average pore size based on the following formula (1),

(S) seconds to 30 seconds when the passage time (S) of the fluid to be filtered obtained by the following formula (2) is less than 3 seconds, and (S) when the passage time (S) of the fluid to be filtered is 3 seconds or more. ) Seconds to (SX 10) seconds, holding the wet filter at a constant pressure, and then increasing the pressure to the next gas pressure stage. Measuring method.

MFPD- (4B COS ZP (1)

“In the above formula (1), MFPD is the average pore diameter (zm), 0 is the contact angle (°) of the test liquid filled in the pores of the filter with the material constituting the filter, and r is the fineness of the filter. The surface tension (N / m) of the test liquid filled in the holes, B is a fixed number of cavities (0.715) or 1, P is the gas permeating the wet filter relative to the gas flow permeating the dry filter. Indicates the gas pressure (MPa) at which the flow ratio (wet filter / dry filter) is 1Z2. "

S = (X I) XVs / Vr (2)

“In the above formula (2), X is the thickness (m) of the filter in the filtration direction, J is the linear velocity of the fluid to be filtered (m / s) in practical use, and V s is the test liquid. And Vr is the viscosity of the fluid to be filtered (P a · s). ”

2. The holding and pressurizing step is performed in a range where the ratio of the gas flow rate passing through the wet filter to the gas flow rate passing through the dry filter (wet filter Z dry filter) is 1/5 to 1 Z 2. 2. The method for measuring the pore size of a porous filter according to claim 1.

3. The porous filtration according to claim 2, wherein the holding and pressurizing step is performed in a total gas pressure stage in which a ratio of the gas flow rate (wet filter / dry filter) is 1 to 5 to 1/2. A method for measuring the pore size of a body.

4. Maintain each gas pressure step within the range of the gas flow rate ratio of 1/5 to 1/2. The porosity according to any one of claims 1 to 3, wherein the holding time is within 10% of the average holding time of the gas pressure step in a range where the ratio of the gas flow rate is 1/5 to LZ2. A method for measuring the pore size of a filtered material.

5. The method for measuring the pore size of a porous filter according to claim 4, wherein each retention time in a range where the ratio of the gas flow rates is 1Z5 to 1/2 is 1 second to 1 minute.

6. The membrane when the fluid to be filtered is permeated at the linear velocity (J) of the fluid to be filtered in practical use at the linear pressure (J) of the fluid to be filtered in the holding and boosting step. The method for measuring the pore size of a porous filtration body according to any one of claims 1 to 5, wherein the pressure increase value is larger than the differential pressure.

7. Each pressure increase value from one gas pressure stage to the next gas pressure stage in a range where the ratio of the gas flow rate is 1 to 5: LZ2 is 1 Z 5 to 1 7. The method for measuring the pore size of a porous filtration body according to claim 6, wherein the soil is within 20% of the average pressurization value in the range of Z2.

8. The pore diameter measurement of the porous filter according to claim 7, wherein each pressure increase value in a range where the ratio of the gas flow rates is 1 Z 5 to 1/2 is 0.01 to 0.04 MPa. Method.