JP6960280B2 - Sheet-like object thickness measuring device and thickness measuring method - Google Patents

Description

The present invention relates to a sheet-like object thickness measuring device and a thickness measuring method.

For films, it is common practice to measure the film thickness, describe it in the physical characteristics table, and ship it. In particular, a microporous polyolefin film is used as a separator for various batteries, and if the thickness of the separator is different from the design value, defects such as not being able to fit in the battery can occur, so the accuracy is high. A method for measuring the thickness is required.
Conventionally, as a film thickness measuring device for a microporous film, for example, a contact type measuring device as described in Patent Document 1 is known.

Japanese Unexamined Patent Publication No. 2008-292374

The present inventors have focused on the fact that measuring the film thickness of a microporous film has a unique problem different from that of measuring the film thickness of a non-porous film. That is, since the microporous membrane has a large number of pores, when measuring the film thickness, the membrane is crushed by the weight of the measurement terminal itself, and the thickness of the membrane changes. Therefore, when measuring the film thickness using a plurality of devices, if there is a variation in the weight of the measurement terminal, the variation becomes a variation in the surface pressure applied to the microporous film of the terminal as it is. Further, even when the weights of the measurement terminals are made uniform, there is a problem that it is difficult to bring the contact surface of the terminal and the sample surface into parallel contact with high accuracy. As a result, it has been difficult to measure the thickness of the microporous membrane with good reproducibility.

In particular, such variation is serious for a microporous membrane for a battery separator, which requires high accuracy. Further, as a measuring method, in the conventional contact type measuring device, the separator may be damaged, so that the separator measured by the contact type cannot be shipped as a commercial product. In addition, it is difficult to guarantee all products in a sampling test in which only a part is taken out. As described above, in recent applications of separators for lithium ion power storage devices, it is required to measure the film thickness with high accuracy as the separator becomes thinner.

The present invention has been proposed in view of such conventional circumstances, and an object of the present invention is a sheet-like object that does not damage the film, reduces the variation in film thickness measurement, and has high accuracy. To provide a thickness measuring device and a thickness measuring method.

As a result of diligent studies to solve the above-mentioned problems peculiar to the microporous membrane, the present inventors adsorb and hold the microporous membrane, and the thickness of the microporous membrane is not contacted by using an optical method. By detecting with, we came up with the idea that the film thickness can be measured accurately without damaging the film, and have completed the present invention. That is, the present invention is as follows.
[1]
An optical system measuring instrument that can measure the thickness of a subject placed on a stage in a non-contact manner; and a planar adsorption stage that is placed on the stage and can hold a sheet-like object under negative pressure;
Equipped with
The optical system measuring instrument is a spectroscopic interference type optical detector, and is configured to include an optical unit.
The adsorption stage is made of a porous body, and the surface roughness of the porous body is 0.3 μm or less.
A device for measuring the thickness of a sheet-like object , wherein the sheet-like object is a microporous film.
[2]
The sheet-like object has an average pore diameter of 0.001 to 1 μm, a porosity of 25 to 95%, and a film thickness of 1 to 200 μm, and / or is a separator for a lithium ion storage device. The thickness measuring device for a sheet-like object according to [1].
[3]
The optical unit has a horizontality correction function for ensuring parallelism between the attraction stage and the optical unit, and the correction function is achieved by high-speed image processing of displacement data [1]. ] Or [2] .
[ 4 ]
The thickness measuring device according to any one of [1] to [3 ], wherein the optical system measuring instrument measures the surface roughness of the sheet-like object together with the thickness of the sheet-like object.
[ 5 ]
The thickness measuring apparatus according to any one of [1] to [4], wherein the optical unit has a resolution of 0.01 μm or less.
[ 6 ]
The following steps:
The L2 measuring step of measuring the distance L2 from the optical unit of the thickness measuring device according to any one of [1 ] to [ 5] to the sheet-like object held by a negative pressure on the suction stage; and the above. A step of obtaining the thickness of the sheet-like object from the difference (L1-L2) between the distance L1 and the distance L2 from the optical unit to the suction stage;
A method for measuring the thickness of a sheet-like object, including.
[ 7 ]
The thickness according to [6 ], wherein a positive pressure is generated between the suction stage and the sheet-like object when the sheet-like object held on the suction stage by a negative pressure is removed from the suction stage. Measuring method.

According to the present invention, the sheet-like object is adsorbed and held, and the thickness of the sheet-like object is detected in a non-contact manner by using an optical method, so that the variation in the film thickness measurement is dispersed without damaging the film. It is possible to provide a thickness measuring device and a thickness measuring method for a sheet-like object with a small amount and high accuracy.

It is a side view which shows typically the basic structure example about the thickness measuring apparatus of this embodiment. It is a plan view and a vertical sectional view which shows the basic structure example of the stage in the thickness measuring apparatus shown in FIG. It is sectional drawing which shows the part of the adsorption plate made of a porous body enlarged. It is sectional drawing which shows typically the state which holds the sheet-like object on the suction plate by a negative pressure. It is sectional drawing which shows typically the state of removing a sheet-like object from a suction plate by a positive pressure. It is a figure which shows typically the basic structure example of the optical unit about the thickness measuring apparatus shown in FIG. It is a graph which shows the repeatability of the film thickness measurement experiment performed in an Example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view schematically showing a basic configuration of the thickness measuring device of the present embodiment for measuring the film thickness of a sheet-like object.
The thickness measuring device 1 of the present embodiment is arranged on the stage 10, the optical system measuring instrument 20 capable of measuring the thickness of the subject placed on the stage 10 in a non-contact manner, and the stage 10. It is configured to include a planar suction stage (suction plate 11) capable of holding the sheet-like object S by negative pressure.
In the thickness measuring device 1 shown in FIG. 1, the optical system measuring instrument 20 includes an optical unit 21 arranged so as to face the stage 10.

<Stage>
2A and 2B are views showing a basic configuration example of a stage 10 in the thickness measuring device 1 shown in FIG. 1, where FIG. 2A is a plan view and FIG. 2B is a vertical sectional view.
The stage 10 shown in FIG. 2A has a planar suction plate 11 (suction stage) that holds the sheet-like object S by a negative pressure and a flat surface on which the suction plate 11 is arranged facing each other. A base 13 having an air passage 12 for transmitting a negative pressure for sucking and holding the subject (sheet-like object S) is provided on the sample base 16. Further, the base 13 is provided with a port 14 for connecting to an external drive device (not shown), and is connected to a vacuum generator (not shown) of the drive device through an air tube 15 attached to the port 14. Has been done. The boundary between the suction plate 11 and the base 13 is desired to be as smooth as possible.

As shown in FIG. 2B, the base 13 has a flat surface having the same planar shape as the lower surface of the suction plate 11 because the lower surface of the suction plate 11 is arranged facing each other, and the suction is held. An air passage 12 for transmitting a negative pressure for the purpose is provided. The base 13 is formed of a metal material such as stainless steel, aluminum, titanium and ceramic.
Although not shown, the drive device provided separately from the stage 10 is a sheet-like object in which the upper surface of the suction plate 11 is made a negative pressure by a vacuum generator and an air tube 15 connecting the vacuum generator and the base 13. S is sucked and held.
In order to remove the sheet-like object S from the suction plate 11 when it is no longer necessary to fix the sheet-like object S that has been sucked to the drive device, a positive position is formed between the sheet-like object S and the suction plate 11. It is also preferable to have a switch for sending air so that pressure can be applied.

In the thickness measuring device 1 of the present embodiment, the suction plate 11 is made of a porous body 17, and is a plate material having a substantially disk-shaped outer shape. The upper surface of the suction plate 11 has a flat shape, and serves as a holding surface for sucking and holding the sheet-like object S as a subject.
FIG. 3 is an enlarged cross-sectional view showing a portion of the adsorption plate 11 made of the porous body 17. In the porous body 17, small particles are sintered and fine gaps 17a are connected vertically and horizontally, so that the gaps 17a of the porous body 17 serve as air passages.
Therefore, as shown in FIG. 4, the negative pressure (so-called evacuation) transmitted from the base 13 is further transmitted to the suction plate 11, and the sheet-like object S placed on the upper surface of the suction plate 11 sucks. Be retained.

At this time, since there is a significant difference in the suction degree of the sheet-shaped object S depending on the suction pressure and the suction amount, the suction pressure when sucking the sheet-shaped object S on the suction plate 11 is controlled to a predetermined pressure. Is preferable. Further, in order to measure the thickness of the sheet-shaped object S with reproducibility and accuracy, it is preferable to keep the surface pressure for sucking the sheet-shaped object S constant. As a method for setting the surface pressure to a predetermined pressure, a method of providing a pressure reducing valve in the middle of the air tube 15 to control the pressure can be mentioned. Further, inclined suction may be performed in which the suction pressure is different in the plane of the suction plate 11. For example, the suction pressure is lowered in the central part and increased in the peripheral part. The slope of the suction pressure may be gradual or linear. Further, the suction pressure may be changed in a spiral shape. From the viewpoint of preventing the occurrence of wrinkles when the sheet-like object is placed on the suction plate 11, it is preferable to gradually suck the sheet-like object from the center to the outer periphery of the suction plate 11 or gradually from one end to the other end of the suction plate 11.

On the other hand, as shown in FIG. 5, when the sheet-like object S held on the suction plate 11 by negative pressure is removed from the suction plate 11, the suction plate 11 is directed from the lower surface to the upper surface, that is, the suction plate 11. By supplying air between the sheet-like object S and the sheet-like object S, the adsorption due to the negative pressure is released and the positive pressure is generated. As a result, the sheet-like object S can be removed without damaging or damaging it. Further, it is possible to prevent clogging of the adsorption plate 11 made of the porous body 17 due to foreign matter or the like, and the life of the adsorption plate 11 can be maintained for a long time.

Examples of such a porous body 17 include a sintered body, and specific examples thereof include ceramics, diamonds, calcium manganate, metallic chromium, ultra-high molecular weight polyethylene, and polymer sintered bodies.
Further, in order to ensure the adhesion between the adsorption plate 11 and the sheet-like object S, the surface roughness of the sintered body (adsorption plate 11) is 1 μm or less. From the viewpoint of accurately measuring a thin film of 10 μm or less, it is preferably 0.3 μm or less, and more preferably 0.2 μm or less. It is more preferably 0.1 μm or less from the viewpoint of more accurate measurement so that the thin film is not affected by the surface unevenness of the sintered body. When the surface roughness of the sintered body is 0.3 μm or less, it is possible to prevent the unevenness of the surface of the adsorption plate from being transferred to the thin film when sucked. This makes it possible to measure the film thickness with high accuracy even if the microporous film is a thin film. On the other hand, the lower limit is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.05 μm or more, from the viewpoint of preventing clogging. By setting the surface roughness of the sintered body (adsorption plate 11) within the above range, the measurement accuracy of a thickness of 10 μm or less is improved.
From the viewpoint of having such a fine surface shape, the inorganic sintered body of Yoshioka Seiko Co., Ltd. is preferable as the porous body 17 constituting the adsorption plate 11.

The "surface roughness" means so-called Ra (arithmetic mean roughness).
The surface roughness of the sintered body (adsorption plate 11) can be measured by, for example, the following method. That is, the surface roughness of the sintered body (adsorption plate 11) is measured using Handy Surf E-35A (trademark) manufactured by Tokyo Seimitsu Co., Ltd. The tip of the stylus is a 90 ° cone made of diamond, 5 μmR, and the measurement is performed with an evaluation length of 5 mm, a velocity of 0.6 mm / s, a cutoff value of 0.80 mm, and a load of 4 mN or less. The measurement is performed on the entire surface of the sintered body (adsorption plate 11) with a reference length of 5 mm, and the minimum value is measured.

<Optical unit>
FIG. 6 is a diagram schematically showing a configuration of an optical unit included in the measuring device 1 of the present embodiment.
The measurement technology of the optical unit is not particularly limited, and various forms of non-contact optical system measuring instruments can be used, but in the present embodiment, a spectroscopic interference type optical detector can be used. Is given as an example when is used. In the spectral interference method, the interference light of the reflected light and the reference light on the surface of the object of the projected laser light is separated for each wavelength by a spectroscopic unit, and then the intensity spectrum obtained from the received waveform of the light receiving element is displayed at high speed. This is a method of calculating the distance to an object by performing waveform analysis such as Fourier conversion processing.

Hereinafter, the spectroscopic interference type optical unit 21 will be described.
The optical unit 21 mainly includes a light source 22 that emits light, a beam splitter 23 that separates the light from the light source 22 into incident light B1 and reference light B2, and an objective lens that concentrates the incident light B1 on an object. 24, a reference mirror 25 that reflects the reference light B2, a light receiving element 26 that receives the return light B1'and B2'reflected by the object and the reference mirror 25, respectively, and a plurality of mirrors for guiding light. It is configured with a lens.
Further, although not shown, it also includes a spectroscope that disperses the light (interference light B3) received by the light receiving element 26 for each wavelength, and an arithmetic processing unit that performs arithmetic processing.
As the light source, for example, a super luminescent diode (SLD) is used. As the light receiving element, for example, a charge-coupled device (CCD) is used.

In such an optical unit 21, the distance to the object is detected, for example, as follows.
(1) The light emitted from the light source 22 enters the beam splitter 23 and is split into the incident light B1 and the reference light B2 by the beam splitter.
(2) The separated incident light B1 is incident on an object (adsorption plate 11 or a non-specimen sheet-like object S), is reflected on the surface of the object, and is incident on the light receiving element 26.
(3) The separated reference light B2 is incident on the reference mirror 25, reflected on the surface of the reference mirror 25, and incident on the light receiving element.
(4) The light receiving element detects the interference light B3 between the reflected light B1'reflected on the surface of the object and the reflected light B2'reflected on the surface of the reference mirror 25. At this time, the optical unit 21 moves up and down so that the phase amplitude becomes maximum.
(5) The interference light B3 is separated for each wavelength with a spectroscope to obtain an intensity spectrum of the light, and the result is subjected to a fast Fourier transform (FFT) to obtain an optical distance to an object (L1 described later). And L2) are calculated.

As for the light spot area of such an optical unit 21, a light spot area of 4 mm × 4 mm is preferable because it has excellent angular characteristics. The resolution of the optical unit 21 is preferably 1 μm or less, more preferably 0.1 μm or less, and even more preferably 0.01 μm or less.

In order to measure the thickness of the sheet-shaped object S with reproducibility and accuracy, the adhesion between the suction plate 11 and the sheet-shaped object S and the parallelism between the suction plate 11 and the optical unit 21 are important. For that purpose, it is convenient to provide a position variable mechanism of the optical unit 21 in the XY directions (horizontal direction) and the Z direction (vertical direction) so that fine adjustment is possible. Further, since the optical unit 21 can process about 80,000 displacement data at high speed, it is preferable to have a horizontality correction function.

Then, in the measuring method using the thickness measuring device 1 of the present embodiment, the sheet-like object S to be measured is placed on the suction plate 11 on the stage 10 and sucked by the vacuum device. Then, the optical unit 21 detects the step between the suction holding surface (the surface of the suction plate 11) and the end face of the sheet-like object S, and converts the optically obtained step into the film thickness to read the film thickness.
In the present embodiment, since the thickness of the sheet-like object S is detected in a non-contact manner by using an optical method, it is preferable to measure the film thickness in a constant temperature room so as not to cause a difference between days.

Specifically, as shown in FIG. 6, first, the distance L1 from the optical unit 21 to the suction plate 11 arranged on the stage 10 is measured (L1 measurement step). Further, the distance L2 from the optical unit 21 to the sheet-like object S held on the suction plate 11 by negative pressure is measured (L2 measurement step). Then, from the obtained step (L1-L2) between the distance L1 and the distance L2, the step optically obtained is converted into the film thickness to obtain the thickness of the sheet-like object S.
In addition, L1 may be predetermined, and in this case, the first distance measurement step is unnecessary.

In the calculation process, it is preferable that the upper surface of the suction plate 11 serving as the reference surface is offset to cut a step in the hole portion of the porous body 17. Further, by scanning the minimum height (thickness) of the sheet-shaped object S, the values obtained by the conventional measuring device and measuring method can be substantially reproduced. In this way, in the present embodiment, since the minimum height of the sheet-like object S is scanned, the measured value always fluctuates (the fluctuation width is about ± 1 μm). Therefore, arithmetic processing by PLC (programmable logic controller) connection with the arithmetic processing unit is required.

In the thickness measuring device 1 of the present embodiment, the optical unit 21 preferably measures the surface roughness of the sheet-shaped object S together with the thickness of the sheet-shaped object S. Conventionally, there has been no means for easily detecting unevenness on the order of several tens of μm to several millimeters, but according to the apparatus of this embodiment, the surface roughness of the sheet-like object S can be measured with high accuracy. As a result, foreign matter and structural disorder can be detected.

The sheet-like object S whose thickness is measured by the thickness measuring device 1 of the present embodiment is preferably a microporous film. Such a microporous film is, for example, a planar film.
In the measuring device 1 of the present embodiment, it is possible to accurately measure a sheet-like object S, which is easily deformed (easily bent) and whose thickness is easily changed by deformation due to an external force, even if it is a thin film.
Specifically, as shown in Examples described later, the R value (maximum value-minimum value) of repeated measurement was 0.6 μm in the conventional method, but 0.1 μm according to the method of the present invention. Less than can be achieved.

In the above-described embodiment, the case where the holding surface for sucking and holding the subject (sheet-like object S) in the suction plate 11 is a flat surface has been described as an example, but the thickness measuring device 1 of the present invention is limited to this. Instead, the holding surface of the suction plate 11 that sucks and holds the subject may be configured as a curved surface. Here, the "curved surface" is intended to include a free curved surface as well as a regular curved surface such as a cylindrical shape. What kind of curved surface is adopted is designed in consideration of the type of the sheet-like object S to be adsorbed, the processing for adsorbing the sheet-like object S, and the like.

For example, when the base 13 and the suction plate 11 have a cylindrical shape, the thickness measuring device 1 is arranged at the final stage of the manufacturing line of the sheet-shaped object S (for example, a separator), and the cylindrical shape is formed in the flow of the manufacturing line. A sheet-like object S is sequentially orbited on the outer peripheral surface of the suction plate 11 of the above, and the thickness is measured by the optical units 21 arranged opposite to each other. As a result, the thickness of all products can be measured, and the products that meet the standards can be shipped as they are. On the other hand, if only a part of the product is sampled and inspected, the guarantee cannot be given to the entire product. By measuring the thickness of all products in the flow of the production line, it is possible to save the trouble of separate inspections, reduce the incidence of products that do not meet the standards, and improve reliability. be able to. Moreover, by measuring in a non-contact manner, it is possible to measure without damaging the product. Further, by scanning the thickness measuring device 1 in the width direction, the film thickness distribution can be accurately monitored in real time, and useful feedback can be provided for creating the film thickness distribution in the upstream process.

The microporous membrane whose thickness is measured by the thickness measuring device 1 and the thickness measuring method of the present embodiment as described above has a pore size of 0.001 to 1 μm and a porosity of 25 to 95%. It is suitable when it is a microporous film, which is a flat film having a film thickness of 1 to 200 μm.

The microporous membrane whose thickness is measured by the thickness measuring device 1 and the thickness measuring method of the present embodiment is a microporous membrane having a thickness of 1 μm to 100 μm and a Garley air permeation resistance of 1000 sec or less. Sometimes it is especially suitable.

Since the sheet-like object S exhibiting such a pore diameter or air permeation resistance has a high porosity, it is deformed by a slight pressure, and it is difficult to detect it with high reproducibility with a conventional contact-type thickness measuring instrument. (There are major problems such as fluctuations due to thermal expansion of the Zenmai type measuring instrument and the fact that pressure is not applied vertically). According to the thickness measuring device and the measuring method of the present embodiment, it is possible to measure the film thickness of the microporous film with little variation and high accuracy.

The sheet-like object S as such a microporous membrane is, for example, a separator for a lithium ion power storage device. In the field of separators for lithium-ion power storage devices, it is strongly required to measure the film thickness with high accuracy and reproducibility with the precise battery design and thinning of the separator. By using the thickness measuring device 1 of the present embodiment, the film thickness of the sheet-like object S such as a separator can be measured with high accuracy and with good repeatability and reproducibility.

Here, the pore size of the microporous membrane can be measured by the method shown below. That is, it is known that the fluid inside the capillary follows the Knudsen flow when the mean free path of the fluid is larger than the pore size of the capillary, and follows the Poiseuille flow when it is smaller. Therefore, it is assumed that the air flow in the measurement of the permeability of the microporous membrane follows the flow of Knusen, and the flow of water in the measurement of the permeability of the microporous membrane follows the flow of Poiseuille.

In this case, the pore diameter d (μm) and the bending rate τ (dimensionless) are the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)) and the water permeation rate constant R _liq (m ³ /). (M ² · sec · Pa)), air molecular rate ν (m / sec), water viscosity η (Pa · sec), standard pressure Ps (= 101325 Pa), pore ratio ε (%), film thickness L ( From μm), it can be obtained by using the following equation.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶
τ = (d × (ε/100) × ν / (3L × Ps × R _gas )) ^1/2
Here, R _gas is obtained from the air permeability (sec) by using the following equation.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ^-4 ) × (0.01276 × 101325))

Further, R _liq is obtained from the water permeability (cm ³ / (cm ² · sec · Pa)) by using the following equation.
Rlik = water permeability / 100
The water permeability is calculated as follows. A microporous membrane soaked in alcohol in advance is set in a stainless steel liquid-permeable cell having a diameter of 41 mm, the alcohol in the membrane is washed with water, and then water is permeated with a differential pressure of about 50,000 Pa for 120 seconds. The water permeation amount per unit time, unit pressure, and unit area was calculated from the water ^{permeation amount (cm 3) after the elapse, and this was taken as the water permeability.}
Further, ν is derived from the gas constant R (= 8.314), the absolute temperature T (K), the pi, and the average molecular weight M of air (= 2.896 × 10 ^-2 kg / mol) using the following equation. Desired.
ν = ((8R × T) / (π × M)) ^1/2

Further, the number of holes B (pieces / μm ² ) can be obtained from the following equation.
B = 4 × (ε/100) / (π × d ² × τ)
The porosity (%) is a value measured by cutting a 10 cm × 10 cm square sample from a microporous membrane, determining its volume (cm ³ ) and mass (g), and the membrane density (g / g /). It is a value calculated from cm ^{3) using the following equation.} In the case of the polyethylene film, the film density was calculated to be constant at 0.95 by the following formula.
Porosity = (volume-mass / membrane density) / volume x 100

Although the embodiments of the present invention have been described above, the present invention is not limited to this, and can be appropriately changed without departing from the spirit of the invention.

Hereinafter, Examples and Comparative Examples performed for confirming the effect of the present invention will be described.
WI-5000 manufactured by KEYENCE CORPORATION was used as the thickness measuring device of the example. An inorganic sintered body manufactured by Yoshioka Seiko Co., Ltd. was used as the adsorption plate. With this device (WI-5000), the displacement amount information of the above (1) to (5) can be simultaneously collected at a total of 80,000 points with a resolution of 15 × 15 μm pitch in an area of 4 × 4 mm.
As a sheet-like object, a separator for a lithium ion power storage device made of a polyolefin flat film was used as the sample film.

In addition, as a comparative example, as a conventional contact-type film thickness measuring device, a film thickness measuring system that combines an LKG laser displacement meter manufactured by KEYENCE Co., Ltd. and a dial gauge type world-class film thickness meter manufactured by Toyo Seiki Co., Ltd. used.

Using the film thickness measuring devices of Examples and Comparative Examples, the degree of crushing (film thickness) of the film when the fixed points of the sample film were continuously measured at 30 points was measured.
In the examples, a significant difference was observed in the degree of adsorption of the sample membrane depending on the suction pressure and the suction amount. In the vacuum pump used in this example, the adsorption condition of the 6 μm thick film was good, and the flicker of the film thickness was small. However, on the other hand, the end face of the 25 μm thick film was warped. Therefore, it is necessary to optimize the suction conditions.
On the reference surface of the adsorption plate, a step in the pore portion of the porous body was cut by an offset function. Since the minimum height was scanned, the measured value constantly fluctuated, but the fluctuation range was about ± 1 μm.
The reproducibility of the film thickness measurement experiment is shown in Table 1 and FIG.

As shown in the graphs shown in Table 1 and FIG. 7, no crushing of the film occurred in the examples, while crushing (decrease) of the film thickness of about 0.6 μm (about 4%) was confirmed in the comparative example.
Further, the R value (maximum value-minimum value) of the repeated measurement was 0.6 μm in the comparative example, but could be less than 0.1 μm in the example.
By adopting the "minimum height" of the film in the non-contact measurement of the system of this example, the measured value of the film thickness and the value of the feeler gauge inspection report in the conventional system could be roughly reproduced.

Next, the fixed points of Samples 1 to 3 having different compositions, thicknesses, porosities, and air permeability were continuously measured 30 times using the measuring device (Example) of the present application and the conventional measuring device (Comparative Example). The fluctuation value (variation) of the time was measured.
Here, as sample 1, a polyolefin flat film similar to the sample film in the above experimental example was used. As Sample 2, a polyethylene microthick film was used. As Sample 3, a polyethylene non-woven fabric was used.

The porosity was measured by the above method.
The air permeability was measured as follows. That is, the air permeability was defined as the air permeability resistance measured by GB2 ™, a Garley type air permeability meter manufactured by Toyo Seiki Co., Ltd., in accordance with JIS P-8117.

For Samples 1 to 3, the film thickness measurement was repeated 30 times using the measuring device (Example) and the conventional measuring device (Comparative Example) of the present application, and the fluctuation value (maximum value-minimum value) was evaluated. .. The results are shown in Table 2 together with the thickness, porosity and air permeability of each sample.

As is clear from Table 2, when the conventional measuring device was used (comparative example), it was 0.6 to 2.2 μm, but when the measuring device of the present application was used (example), it was 0.0 μm. there were.
When the sample 1 was measured without suction, the in-plane variation was 0.3 μm, and it was presumed that the gap between the sample and the sample table was uneven.

From the above results, according to the present invention, by adsorbing and holding the microporous membrane and measuring the thickness of the microporous membrane in a non-contact manner using an optical method, there is little variation and high accuracy. It was confirmed that the film thickness of the microporous membrane can be measured.

According to the present invention, the thickness of a sheet-like object, particularly a microporous film, can be measured more accurately. In particular, when the method of the present invention is used for measuring the thickness of the microporous film for a battery separator, defects such as not entering the battery can can be reduced, which is industrially useful.

1 Thickness measuring device 10 Stage 11 Adsorption plate (adsorption stage)
12 Air passage 13 Base 14 Port 15 Air tube 16 Sample base 17 Porous body 17a Gap 20 Optical system measuring instrument 21 Optical unit 22 Light source 23 Beam splitter 24 Objective lens 25 Reference mirror B1 Incident light B2 Reference light B1', B2' Return light B3 Interference light S Sheet-like object

Claims (7)

An optical system measuring instrument that can measure the thickness of a subject placed on a stage in a non-contact manner; and a planar adsorption stage that is placed on the stage and can hold a sheet-like object under negative pressure;
Equipped with
The optical system measuring instrument, Ri optical detector der spectral interference type, is configured to include an optical unit,
The adsorption stage is made of a porous body, and the surface roughness of the porous body is 0.3 μm or less.
A device for measuring the thickness of a sheet-like object , wherein the sheet-like object is a microporous film. The sheet-like object has an average pore diameter of 0.001 to 1 μm, a porosity of 25 to 95%, and a film thickness of 1 to 200 μm, and / or is a separator for a lithium ion storage device. The thickness measuring device for a sheet-like object according to claim 1. The optical unit has a horizontality correction function for ensuring parallelism between the attraction stage and the optical unit, and the correction function is achieved by high-speed image processing of displacement data. The thickness measuring apparatus according to 1 or 2. The thickness measuring device according to any one of claims 1 to 3 , wherein the optical system measuring instrument measures the surface roughness of the sheet-like object together with the thickness of the sheet-like object. The thickness measuring apparatus according to any one of claims 1 to 4, wherein the optical unit has a resolution of 0.01 μm or less. The following steps:
The L2 measuring step of measuring the distance L2 from the optical unit of the thickness measuring device according to any one of claims 1 to 5 to the sheet-shaped object held by a negative pressure on the suction stage; and the above. A step of obtaining the thickness of the sheet-like object from the difference (L1-L2) between the distance L1 and the distance L2 from the optical unit to the suction stage;
A method for measuring the thickness of a sheet-like object, including. The thickness according to claim 6 , wherein a positive pressure is generated between the suction stage and the sheet-like object when the sheet-like object held on the suction stage by a negative pressure is removed from the suction stage. Measuring method.

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