JPS63212804A - Film thickness measurement method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Field of Application The present invention relates to an eddy current film thickness measurement method. This invention relates to a film thickness measurement method that can measure thickness with high accuracy.

BACKGROUND TECHNOLOGY In recent years, for the purpose of improving corrosion resistance, steel plates have been coated with Zn or other plating, and then an insulating coating has been layered on top of it.
So-called various plated steel sheets are often used.

When manufacturing such a multilayer structure film for steel sheets, it is important to control the thickness of each plating film such as Zn film and insulating coating film to the required thickness from the viewpoint of various corrosion resistance requirements.
considered extremely important.

In general, methods for measuring the thickness of various films deposited on steel plates are roughly divided into two methods: the magnetic method using electromagnetic methods and the eddy current method, and film thickness measuring devices based on each principle have been put into practical use. There is.

In the former magnetic method, as shown in Figure 5a, an electromagnet (5) consisting of a magnetizing coil (3) and a yoke (4) is magnetized with alternating current, and the steel plate (1) and electromagnet (5) By detecting the magnetic flux passing through the formed magnetic circuit with a detection coil (5), the thickness of the coating film (2), which is magnetically non-magnetic, is measured.

That is, the thickness of the coating film (2) is measured by utilizing the fact that the amount of magnetic flux depends on the thickness of the non-magnetic layer such as the coating film (2).

However, in the magnetic method, in the case of the Zn-plated steel sheet mentioned above, Z
Since both the n film and the insulating coating film are non-magnetic materials, the film thickness indication is measured as (coating film + Zn film), and there is a problem that each film cannot be measured independently.

In the latter eddy current method, as shown in Figure b, when a high frequency current is applied to the coil (6), the eddy current induced in the steel plate (1) depends on the thickness of the insulator layer such as the coating film (2). In this method, the thickness of the coating film (2) is measured by detecting the change in impedance of the coil (6).

Furthermore, when applying the eddy current method to the aforementioned Zn-plated steel sheet,
Since the Zn film is a conductor, eddy currents are generated in the Zn film, and since it is a thin film of several tens of pm, eddy currents are also induced in the steel plate underlying the Zn film, and eddy currents occur in areas other than the coating thickness. It is also a function of the Zn film thickness, and it is not possible to distinguish between the coating film thickness and the Zn film thickness and measure the thickness.

Furthermore, to explain the eddy current method in detail, The penetration depth δ is δ=fi7 (m) (1).

However, ω = 2nf, f: frequency (Hz), P = lJoX stage p, = 4nxlO” (H/ml magnetic permeability in vacuum llr
: relative magnetic permeability, P: specific resistance (Ωmm).

Since the coating part is an insulator, no eddy current occurs, but Zn
Since the membrane is a conductor, eddy currents occur. The penetration depth δ in the Zn film is calculated from equation (1) as follows: δ = 43 x 10-6 (m) = 4 m, where f = 8 MHz, p = 5.9 x lO-8 (Ωm)
And so.

Therefore, even at a high frequency of about 8 MHz, if the Zn film has a thickness of several tens of pm or less, it is expected that the magnetic flux will pass through the Zn film and be affected by the steel plate under the Zn film.

As shown in Figure 7, the Zn film thickness (Tzn) is 7.9 pm.
In the case of (marked with square in Figure 7), TzH = 24.8pm,
Compared to the case of 14.6 pm, the indicated value of the eddy current method appears higher, indicating a large measurement error.

Frequency (if 0 is 8BIHz, %H = 7.9pm ~
The measurement error in the range of 24.811 m is ±5.6 pm.

To summarize the above, (1) With the magnetic method, when the metal film is a non-magnetic material, the thickness of the coating (coating thickness) is measured, and each layer cannot be measured independently.゛■ In the eddy current method, when the metal film is thin, it is also affected by the base (steel plate), so the error in coating film thickness measurement increases compared to when the metal film is thick.

That is, both the magnetic method and the eddy current method currently used have a problem in that they cannot be applied to the measurement of the thickness of a multilayer structure film such as the above-mentioned Zn-plated steel sheet.

Purpose of the Invention In view of the current situation, the object of the present invention is to provide a film thickness measuring method that can measure the thickness of each of the metal film and insulating coating film with high accuracy even when a conductive metal film and an insulating coating film are laminated on a steel plate. It is said that

Structure of the Invention This invention is based on an eddy current method in which a coil is arranged on a multi-layered film, in which a coating film is further laminated on a metal film adhered to a steel plate, and an alternating current is applied to it, and the film thickness is measured from the change in coil impedance. In the formula film thickness measurement method, each projected component value is determined in the direction of change of impedance that changes due to increase or decrease in paint film thickness, and in the direction orthogonal to this, and the film thickness is determined based on the two component values. This is a method for measuring film thickness.

-J-J-J-fiw/r%iPtronnr4. Kotit
2tt54-rpkh+, -yJAnet Obtain the impedance component (Vy) in the direction of thickness change and the component value (Vx) perpendicular to vy. (a) Measure the metal film thickness from Vx. (b) Calculate vy and Vx. The purpose is to measure the coating thickness based on the results.

There are various calculation methods for (b), but for example, the metal film thickness is determined from the projected component value in a direction perpendicular to the same frequency as the direction of change in impedance that changes due to increase or decrease in coating thickness, and the change in impedance is The coating thickness is determined by correcting the projection component value in the direction depending on the magnitude of the projection component value in the orthogonal direction, or by correcting it by multiple regression of the two-component value and the coating thickness.

(2) Further, the above-mentioned orthogonal two-component values are obtained as a plurality of parameters of the impedance change direction that changes depending on the increase or decrease of the coating film thickness at different frequencies, and the respective projected component values in the direction orthogonal to this. Alternatively, the coating thickness is further determined by mutually combining component values of different frequencies.

The following methods can be adopted.

In addition, in this invention, the components of the target two-layer film are:
An insulating coating is layered on top of a conductive metal film.

If so, any component can be used.

The coating thickness measuring method of the present invention has the advantage that the coating thickness measurement error can be highly accurate to ±2 pm, compared to the conventional eddy current method, which has a coating thickness measurement error of ±9 pm9p. - Based on the drawings <Disclosure of the invention The film thickness measuring method according to the present invention will be described in detail below based on the drawings.

Figure 1 is an eddy current coil impedance plane (complex plane) diagram, Figure 2 is a graph showing the relationship between Zn film thickness and Vx component value, and Figure 3 is a graph showing the relationship between coating film thickness and Vy component value. It is a graph showing the relationship between.

The complex number plane diagram in Figure 1 is: TzH=7.9pm, 14.6pm, 24.8pm
The coating film thickness (T) in , Opm, 15pm, 30pm
The complex impedance measurement value is shown.

Here, the origin is TzH=14.6pm and T=Opm, and the direction of coating thickness change when T2n=14.6pm is the Y-axis and the direction orthogonal to the Y-axis is the x-axis, and the Y of each measurement point is Let the projected value on the axis be vy, and the projected value on the x-axis be Vx. Note that Vx and Vy are orthogonal two-component values of the same frequency.

The vy value corresponds to the indicated value of a conventional eddy current film thickness meter, and the vertical axis in FIG. 7 corresponds to it.

Now, the correlation between Vx and the Zn film is a linear relationship as shown in FIG. This shows that the Zn film thickness can be estimated by the Vx value with an accuracy of ± lpm without depending on the coating film thickness.

On the other hand, as shown in Figure 3, the correlation between the vy value and the coating film thickness (T) shows that the error increases as the Zn film becomes thinner, so it is necessary to correct the error at the appropriate level shown below. .

(Vx value calculation)...Depends on Zn film thickness (Tzn)↓ (vy value calculation)...Depends on both coating film thickness (T) and Zn film thickness↓ Vx value Various methods can be considered for correcting the vy value accordingly.

FIG. 3 shows the results of investigating the correlation between the vy value and the coating thickness using 14 samples with Zn films of 7.6 pm to 24.8 pm and coating films of 0 to 30 pm.

That is, since the thinner Zn film appears higher as an indicator, the error increases. As a method of suppressing the error, (A) Only thin 2m films (small Vx values) are determined by the magnitude of the Vx value, and depending on the magnitude of Vx, Vx<vxth Vy' = Vy-CVx・...(2) (C: constant,
Vxth: threshold value of Vx) Correct as Vx≧vxth vy' = Vy.

(B) There is a method of determining T by multiple regression of the values of Vx and Vy and the coating thickness (T). For example, the following regression formula can be considered.

T=Co+aVx+bVy+cVx2 +dVy2+e
VxVy...' (3) In the above explanation, Vx, Vy
are orthogonal two-component values at the same frequency, but the directions that change depending on the coating thickness at different frequencies are Vyl and V, respectively.
y2, V3'l, the component orthogonal to Vy2 is Vxl,
As Vx2, four parameters (VXI, Vy2
, Vyx, V3F2) to determine the coating film thickness.

Also (Vxl, Vy2) or (Vy2, Vy
It is also possible to determine the coating film thickness by x).

Example As shown in the laminated structure shown in Fig. 6, Zn of various thicknesses is applied to the steel plate (1).
A film (7) is formed, and an insulating coating film (8) made of pigment, etc. is formed.
The film thickness of each film was measured using a commercially available eddy current film thickness measuring device.

In the measuring method according to the present invention, V
The above-mentioned method (A) and method (B) were used to correct the y value.

The actual measurement of each film thickness was carried out by determining the weight of the coating film from the difference in weight between the steel plate on which the coating film was formed and the steel plate from which the coating film was removed, and then determining the thickness from the coated area and specific gravity.

Furthermore, the measurement frequency in the conventional method and the method of the present invention was 8 MHz, and the specific resistance value was p=5.9×10 −8 (Ωm).

The film thickness measurement error with the conventional method was ±9 pm, but with the measurement method of the present invention, the error was ±2.4 pm with the correction method (A).
It can be seen that the error is significantly reduced to ±2 pm with the correction of method (B).

[Brief explanation of the drawing]

Figure 1 is an eddy current coil impedance plane (complex plane) diagram, Figure 2 is a graph showing the relationship between Zn film thickness and Vx component value, and Figure 3 is a graph showing the relationship between coating film thickness and vy component value. It is a graph showing the relationship between. FIG. 4 is a graph showing the relationship between actual measured values and measured values. FIG. 5A is a schematic explanatory diagram of an apparatus showing a magnetic film thickness measuring method, and FIG. 5B is a schematic explanatory diagram of an apparatus showing an eddy current film thickness measuring method. Figure 6 shows Zn
It is a cross-sectional explanatory view of a plated steel plate. FIG. 7 is a graph showing the relationship between the coating film thickness and the value indicated by the device using a conventional eddy current film thickness measuring device. 1... Steel plate, 2... Paint film, 3... Magnetizing coil, 4
... Yoke, 5... Electromagnet, 6... Coil, 7... Zml tip 8... Insulating coating. Patent applicant: Sumitomo Metal Industries, Ltd. Figure 1 Figure 2 Zn film thickness (TZn: μrR) Figure 3 Figure M4 Actual measurement (μm) Figure 5 Figure 6 Section 7 Coating film thickness (μm)

Claims (1)

[Scope of Claims] 1 Eddy current in which a coil is arranged on a multi-layered film in which a coating film is further laminated on a metal film adhered to a steel plate, an alternating current is applied, and the film thickness is measured from changes in coil impedance. In the formula film thickness measurement method, each projected component value is determined in the direction of change of impedance that changes due to increase or decrease in paint film thickness, and in the direction orthogonal to this, and the film thickness is determined based on the two component values. Film thickness measurement method. 2 Determine the metal film thickness from the projected component value in the direction orthogonal to the direction of change of impedance that changes due to increase or decrease in the coating film thickness, and calculate the projected component value in the direction of impedance change and the projected component value in the direction orthogonal to this. 2. The film thickness measuring method according to claim 1, wherein the film thickness is determined by correcting the film thickness. 3. The film according to claim 1, wherein the orthogonal two-component values are projection component values in a direction of change in impedance that changes due to increase or decrease in coating film thickness at different frequencies and in a direction orthogonal thereto. Thickness measurement method.