JP5257991B2 - Film thickness measuring method and measuring apparatus - Google Patents

Description

  The present invention relates to a film thickness measuring method and a measuring apparatus for measuring the thickness of a film formed on a base, and in particular, a film thickness measuring method capable of nondestructively measuring the thickness of an inner film in a bag structure. And a measuring apparatus.

Conventionally, as a method for measuring the thickness dimension of a coating formed on a base made of, for example, a steel material, there is a method using eddy current.
This method can measure the film thickness on the surface of the steel material, but if there is another electrode layer, etc. under the film, the lower layer affects the film thickness measurement value. When the thickness is small, there is a disadvantage that the measurement error increases.
Further, there is a problem that it is theoretically difficult to measure the thickness of the inner surface coating 51 in the portion where the measurement target surface becomes a shadow portion, for example, the in-bag structure 50 as shown in FIG. .

As a technique for solving the above-described problem, that is, a technique that can accurately measure the thickness of any of the steel outer surface coating 52 and the inner coating 51 of the in-bag structure 50, a method using ultrasonic waves is widely used. Yes.
One of the methods using this ultrasonic wave is, for example, as shown schematically in FIG. 8, an ultrasonic pulse is incident on the surface of the film 40 using an ultrasonic probe 30 and a reflected wave from the film surface is reflected. In this method, the thickness dimension of the coating 40 is obtained based on the time difference between the arrival times of the reflected wave Pr2 from the interface between Pr1 and the coating 40 and the base 45.

  However, in such a measurement method using ultrasonic waves, when the coating 40 has a thin film thickness of less than 100 μm, the reflected wave Pr1 from the surface of the coating 40 and the interface between the coating 40 and the underlayer 45 are used. There is a problem that the reflected wave Pr2 is superimposed and measurement becomes difficult.

  In addition, when the measurement target is a coating applied to the outer surface and the inner surface of the in-bag structure 50 as shown in FIG. 9 and the film thickness is as thin as about 10 μm, in the measurement method using ultrasonic waves, In principle, it was difficult to measure the film thickness.

For such a problem, in the measurement method disclosed in Patent Document 1, an ultrasonic pulse is incident from the outer surface to a structure such as a pipe having a coating on the inner surface, and is reflected at the interface between the two layers. The reflected wave and the second reflected wave reflected on the inner surface are received on the outer surface.
Then, the thickness of the coating is obtained based on the difference between the rise time of the first reflected wave and the time at which the combined wave in which the first and second reflected waves are superimposed first reaches zero amplitude.

JP 2001-227933 A

According to the measurement method disclosed in Patent Document 1, it is described that the film thickness can be measured even if the film is as thin as less than 100 μm.
However, it has been difficult to apply the case where the reflected wave is superimposed on the coating having a thickness of about 10 μm in a complicated manner.
In particular, it was difficult to nondestructively measure the thickness of the coating having a thickness of about 10 μm in the inner surface coating of the in-bag structure that becomes the shadow portion.
Therefore, the film thickness of the inner surface coating of the in-bag structure is measured by disassembling and observing a cross section, but there is a problem that dismantling body preparation costs and dismantling work are required.

  The present invention has been made under the circumstances as described above, and in a film thickness measuring method and a measuring apparatus for measuring the thickness of a film formed on a base, particularly the thickness of an inner surface film in a bag structure. It is an object of the present invention to provide a film thickness measuring method and a measuring apparatus that can measure non-destructively from the outside of the bag internal structure.

により求めるステップとを含むことに特徴を有する。 In order to solve the above-described problem, a film thickness measuring method according to the present invention is a film thickness measuring method for measuring a film thickness of a film formed on the inner surface of a base member, and the film is formed only on the outer surface of the base member. An ultrasonic wave having a predetermined frequency band is incident on the formed sample from the outer surface side of the base member to obtain a first amplitude spectrum in the frequency band, and a film is formed on the outer surface and the inner surface of the base member. An ultrasonic wave having a predetermined frequency band from the outer surface side of the base member to the obtained sample, and obtaining a second amplitude spectrum in the frequency band; and the second amplitude with respect to the first amplitude spectrum and obtaining an amplitude spectrum ratio of the spectrum, of the predetermined frequency band, wherein the frequency at which the amplitude spectrum ratio is most falls, the film pairs to be measured The method comprising the resonant frequency f _R (Hz) that, when the film speed of sound in the film of the measurement object and C (m / s), the film thickness d (m) of the coating film,

And the step of obtaining by

  The resonance frequency is a frequency at which the sound pressure reflectivity and the sound pressure transmittance at the coating film to be measured are minimum.

According to such a measuring method, even if it is a measuring object of the structure in a bag, the film thickness of the coating on the inner surface side can be obtained without destroying it. Therefore, preparation and dismantling work of the dismantling body is unnecessary, and the cost can be reduced.
Further, since it is not necessary to separate the superimposed reflected waves, it is possible to obtain a thin film thickness of about 10 μm, which has been difficult in the past.

In addition, the standard frequency range of the ultrasonic wave incident from the outer surface side of the base member is 20 to 100 MHz, but a higher frequency can also be used in the inspection of a thinner coating.
In the case of a film thickness of about 10 μm, the resonance frequency can be obtained by entering an ultrasonic wave having a frequency band of 20 to 100 MHz.

  In order to solve the above-described problem, a film thickness measuring apparatus according to the present invention is a measuring apparatus used in the film thickness measuring method, and includes an ultrasonic wave having a predetermined frequency band from the outer surface side of the base member. The ultrasonic wave incident means for receiving the reflected wave, the reflected wave receiving means for receiving the reflected wave of the ultrasonic wave incident by the ultrasonic wave incident means, and the resonance with respect to the coating film to be measured from the reflected wave received by the reflected wave receiving means And a calculating means for calculating a frequency and calculating the film thickness of the film using the resonance frequency.

According to such a measuring apparatus, even if it is a measuring object of the structure in a bag, the film thickness of the coating on the inner surface side can be obtained without destroying it. Therefore, preparation and dismantling work of the dismantling body is unnecessary, and the cost can be reduced.
Further, since it is not necessary to separate the superimposed reflected waves, it is possible to obtain a thin film thickness of about 10 μm, which has been difficult in the past.

  According to the present invention, in the film thickness measuring method and measuring apparatus for measuring the thickness of the coating film formed on the base, the thickness of the inner coating film in the inner bag structure is non-destructively formed from the outer side of the inner bag structure. A film thickness measuring method and a measuring apparatus that can be measured can be obtained.

FIG. 1 is a block diagram schematically showing the structure of a film thickness measuring apparatus according to the present invention. FIG. 2 is a diagram for explaining the measurement principle of the film thickness measurement method according to the present invention. FIG. 3 is another diagram for explaining the measurement principle of the film thickness measurement method according to the present invention. FIG. 4 is a graph for explaining the measurement principle of the film thickness measurement method according to the present invention. FIG. 5 is another graph for explaining the measurement principle of the film thickness measurement method according to the present invention. FIG. 6 is a graph showing the results in Example 1 of the present invention. FIG. 7 is another graph showing the results in Example 1 of the present invention. FIG. 8 is a diagram for explaining a measurement method using ultrasonic waves. FIG. 9 is a diagram for explaining a measurement target of the in-bag structure.

Hereinafter, embodiments of a film thickness measuring method and a measuring apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram schematically showing the structure of a film thickness measuring apparatus according to the present invention.
The illustrated film thickness measuring apparatus 1 includes an ultrasonic probe 2 (ultrasonic incident means) for making ultrasonic waves in a predetermined frequency band (for example, 20 to 100 MHz) incident on the measurement target W, and the ultrasonic probe 2. And a casing 3 covering the whole. The ultrasonic probe 2 is supported by a support member 6 so as to be movable up and down. The position of the ultrasonic probe 2 with respect to the measurement object W can be finely adjusted by moving the dial gauge 5 connected to the side of the support member 6 and provided outside the casing 3 up and down.

In addition, a water inlet 3a is provided on the side of the casing 3, from which water is injected into the casing 3, and at least the water 4 is interposed between the ultrasonic probe 2 and the measurement object W. Made. Thus, the ultrasonic wave is transmitted to the measurement object W by interposing the water 4 (or gel substance).
The ultrasonic probe 2 is connected to a pulsar receiver 7 (reflected wave receiving means) having an ultrasonic transmission / reception function, and the oscilloscope 8 confirms the waveform of the reflected wave received by the pulsar receiver 7.
The obtained waveform signal is subjected to frequency analysis by a computer 9 as a calculation means, and a film thickness dimension is obtained by a predetermined calculation formula described later based on the measured resonance frequency.

  In this film thickness measuring apparatus 1, as shown in FIG. 2 (a), the object to be measured W is formed of a coating, that is, an outer coating 21 and an inner coating 22 on the front and back surfaces of a base material 20 made of, for example, steel. On the other hand, ultrasonic waves are incident from the outer surface coating 21 side, and the film thickness of the inner surface coating 22 is measured. That is, even if the measurement object W has an in-bag structure, ultrasonic waves are incident from the outer surface coating 21 side, and the film thickness of the inner surface coating 22 is measured nondestructively with respect to the measurement object W.

Subsequently, the measurement principle will be described.
As shown in FIG. 2B, when an ultrasonic wave is incident on the measured object W1 having the inner surface coating 22 from the outer surface coating 21 side, a reflected wave (sound at the interface between the base member 20 and the inner surface coating 22 (sound). Pressure Pr1) and a wave (sound pressure Pt1) transmitted through the inner coating 22 is obtained.
On the other hand, as shown in FIG. 2C, when only the outer surface coating 21 is formed on the base member 20, the reflected wave (sound pressure Pr2) at the interface between the base member 20 and the external environment is transmitted therethrough. Wave (sound pressure Pt2) is obtained.

Here, it can be inferred that the reflected sound pressures Pr1 and Pr2 and the transmitted sound pressures Pt1 and Pt2 are different depending on the presence or absence of the inner surface coating 22, respectively. The applicant of the present application pays attention to the difference and, as a result of earnest research, found a method for measuring the film thickness of the inner surface coating 22 therefrom.
When an ultrasonic wave is incident from the outer surface coating 21 side, as shown in FIG. 3, in the inner surface coating 22 having a film thickness d (m), the sound pressure of the incident wave is Pi, the sound pressure of the reflected wave is Pr, and the transmitted wave is transmitted. The sound pressure reflectance r ₁₂₃ and the sound pressure transmittance t ₁₂₃ can be expressed by equations (1) and (2), respectively.

である。 In the subscripts in the expressions (1) and (2), 1 corresponds to the base member 20, 2 corresponds to the inner surface coating 22, and 3 corresponds to the external environment (air). i ² = -1.
Also, ρ ₁ and c ₁ are the density and sound speed of the base member, respectively, and ρ ₃ and c ₃ are the density and sound speed of the external environment, respectively.

It is.

である。また、ρ₂を被膜の密度として、

である。

Λ is the wavelength in the film, C is the sound velocity in the film, and f is the frequency.

It is. Also, let ρ ₂ be the coating density,

It is.

The absolute values of these equations (1) and (2) are expressed by equations (3) and (4).

On the other hand, if the measured object W2 inner surface coating 22 is not shown in FIG. 2 (c), i.e., the base member 20 is external environment (e.g., air) if direct contact with, the sound pressure reflectance r ₁₃ and the sound pressure The transmittance t ₁₃ can be expressed by the equations (5) and (6), respectively.

Here, it is assumed that there are three samples S1 to S3 for the inner surface coating 22 of the measurement object W1. The impedance Z ₃ of the inner surface coating 22 of each of the samples S1 to S3 is S1: 1 MNm ⁻³ s, S2: 3MNm ⁻³ s, and S3: 10 MNm ⁻³ s, respectively. Further, it is assumed that the impedance of the base member 20 is Z ₁ = 100 MNm ⁻³ s and the impedance of the external environment is Z ₃ = 0.01 MNm ⁻³ s.
Based on the values of the equations (3) to (6) and Z _{1 to} Z ₃ , the ratio of the sound pressure reflectance of the measured object W1 to the measured object W2 | r ₁₂₃ | / | r ₁₃ | and the sound pressure transmittance When the ratio | t ₁₂₃ | / t ₁₃ is obtained, it is shown in the graphs of FIGS. 4 and 5, respectively.

As shown in the graph of FIG. 4, the value of | r ₁₂₃ | / | r ₁₃ | is d / λ = 1/4 (where λ = C / f and C is the sound velocity in the film (m / s)). Minimum when they match. On the other hand, as shown in FIG. 5, the value of | t ₁₂₃ | / t ₁₃ is maximized when d / λ = 1/4.
Therefore, the frequency at which d / λ = 1/4 at which | r ₁₂₃ | / | r ₁₃ | is minimum and | t ₁₂₃ | / t ₁₃ is maximum is the resonance frequency f _R , and this resonance frequency f _R is represented by Formula (7).

Therefore, the film thickness d of the inner surface coating 22 can be obtained from the equation (8).

Thus, according to the equation (8), the film thickness d of the inner surface coating 22 can be obtained by measuring the resonance frequency f _R.
That is, in the film thickness measuring apparatus 1, an ultrasonic wave of a predetermined frequency band (for example, 20 to 100 MHz) is incident on the measurement target W from the ultrasonic probe 2 and the reflected wave is received by the pulsar receiver 7.
The received reflected wave is subjected to frequency analysis using the computer 9 to obtain the resonance frequency f _R, and the film thickness d is obtained by executing the equation (8) using the in-film sound velocity C measured in advance. Is required.

That is, according to the measuring method and measuring apparatus of the present invention, the film thickness d of the inner surface coating 22 can be obtained without destroying the in-bag structure. Therefore, preparation and dismantling work of the dismantling body is unnecessary, and the cost can be reduced.
Further, since it is not necessary to separate the superimposed reflected waves, it is possible to obtain a thin film thickness of about 10 μm, which has been difficult in the past.

  In the above embodiment, the example of measuring the film thickness of the inner surface coating of the bag inner structure is shown, but the present invention is not limited to this. When measuring the film thickness of the outer surface coating, the in-film sound speed and resonance frequency of the outer surface coating can be obtained and substituted into the above equation (7).

  Subsequently, the film thickness measuring method and measuring apparatus according to the present invention will be further described based on examples. In this example, the effect was verified by actually conducting an experiment based on the apparatus configuration of the film thickness measuring apparatus described in the above embodiment.

[Example 1]
In Example 1, frequency characteristics were obtained for two measurement samples S4 and S5 having not only an outer surface coating but also an inner surface coating on the base member and a measurement sample S6 having only the outer surface coating (no inner coating).
The results are shown in the graphs of FIGS. In the graph of FIG. 6, the horizontal axis represents the frequency (Hz) and the vertical axis represents the amplitude spectrum. The graph of FIG. 7 shows the amplitude spectrum ratios (φ4 / φ6, φ5 / φ6) of the samples S4 and S5 with respect to the sample S6 based on the graph of FIG.

As shown in the graph of FIG. 6, in the samples S4 and S5 on which the inner surface film is formed, a characteristic in which the amplitude is greatly reduced is observed in the vicinity of 50 MHz as compared with the amplitude spectrum of the sample S6. This characteristic is also apparent from the amplitude spectrum ratio of FIG. 7, and it is clear that the sound pressure transmittance is maximized and the sound pressure reflectivity is minimized at this frequency (resonance frequency).
From this result, it was confirmed that the resonance frequencies for the samples S4 and S5 on which the inner surface film was formed were 46.4 MHz and 48.3 MHz, respectively.

[Example 2]
In Example 2, after measuring the resonance frequency f _R (Hz) for the measurement samples S7, S8, and S9, the film thickness d is obtained by cross-sectional measurement with a microscope, and the sound velocity C in the film is obtained by C = 4f _R · d. (M / s) was determined.
The measurement results are shown in Table 1.

As shown in Table 1, the average value C = 3200 m / s of the sound velocity C in the film was used for the film thickness measurement in this example (the present invention).
Next, nine measurement sites in the lower part of the door outer (samples S10, S11, S12) in the automobile body are set as measurement objects, and the ultrasonic measurement method and microscope of the present invention are applied to the inner surface coating (back side coating) of each site. And cross-sectional measurement by each were applied, and the measurement results were compared and verified.
The experimental results are shown in Table 2.

  As shown in Table 2, the measurement result by the ultrasonic measurement method of the present invention and the cross-sectional measurement result by the microscope were substantially the same results, confirming the effectiveness of the present invention.

Example 3
In Example 3, it was verified whether or not the present invention was effective for a measurement object having a film thickness of about 10 μm.

Nine measurement sites in the lower part of the rocker outer in the automobile body are set as the measurement object, and the ultrasonic measurement method of the present invention and the cross-sectional measurement by a microscope are applied to the inner surface coating (back side coating) of each site, The measurement results were compared and verified.
In Example 3, as in Example 2, the in-film sound velocity C was set to C = 3200 m / s and used for film thickness measurement.
The experimental results are shown in Table 3.

As shown in Table 3, the measurement result by the ultrasonic measurement method of the present invention and the cross-sectional measurement result by the microscope were substantially the same results, confirming the effectiveness of the present invention.
From the experimental results of the above examples, according to the present invention, it was confirmed that the thickness of the inner surface coating particularly in the bag inner structure can be measured non-destructively from the outer side of the bag inner structure.

1 Film thickness measuring device 2 Ultrasonic touch probe (ultrasonic incident means)
3 Casing 4 Water 5 Dial gauge 7 Pulsar receiver (ultrasonic transmission / reception means)
8 Oscilloscope 9 Computer (calculation means)
20 Substrate member 21 Outer coating (coating)
22 Inner coating (coating)
W Measurement object, measurement object

Claims (4)

A film thickness measuring method for measuring the film thickness of a coating formed on the inner surface of a base member,
With respect to a sample in which a film is formed only on the outer surface of the base member, an ultrasonic wave having a predetermined frequency band is incident from the outer surface side of the base member to obtain a first amplitude spectrum in the frequency band;
Injecting an ultrasonic wave having a predetermined frequency band from the outer surface side of the base member to a sample having a film formed on the outer surface and the inner surface of the base member, and obtaining a second amplitude spectrum in the frequency band;
Determining an amplitude spectrum ratio of the second amplitude spectrum to the first amplitude spectrum;
The frequency at which the amplitude spectrum ratio falls most in the predetermined frequency band is set as a resonance frequency f _R (Hz) for the film to be measured ;
When the in-film sound velocity in the film to be measured is C (m / s), the film thickness d (m) of the film is

A film thickness measuring method comprising the steps of :   2. The film thickness measuring method according to claim 1, wherein the resonance frequency is a frequency at which the sound pressure reflectance in the coating film to be measured is minimum and the sound pressure transmittance is maximum.   The film thickness measuring method according to claim 1 or 2, wherein a frequency band of an ultrasonic wave incident from an outer surface side of the base member is 20 to 100 MHz. A measuring apparatus used in the film thickness measuring method according to any one of claims 1 to 3,
An ultrasonic wave incident means for incident ultrasonic waves having a predetermined frequency band from the outer surface side of the base member;
Reflected wave receiving means for receiving a reflected wave of the ultrasonic wave incident by the ultrasonic wave incident means;
A film thickness measuring apparatus comprising: a calculating means for calculating a resonance frequency for the coating film to be measured from the reflected wave received by the reflected wave receiving means and calculating the film thickness of the coating film using the resonance frequency .

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