JPS63235805A - Method and apparatus for measuring thickness of film - Google Patents

Abstract

PURPOSE:To perform measurement with high accuracy, by irradiating a reference material and an object to be measured with infrared rays having a wavelength generating absorption in the org. substance on the surface of a metal base material and infrared rays having a wavelength generating no absorption and detecting the intensities of the reflected lights from both of them. CONSTITUTION:Infrared rays having a wavelength lambda1 generating absorption in the org. film 1b formed on the surface of a steel plate 1a are allowed to irradiate the steel plate 1a and the thickness of the film 1b is measured from the intensity of the reflected light thereof. Then, the infrared rays having the wavelength lambda2 and infrared rays having wavelengths lambda2, lambda3 (lambda2<lambda1<lambda3) generating no absorption are allowed to irradiate a reference material composed of the same metal as the steel plate 1a and having no film 1b on the surface thereof and an object to be measured to detect the intensities of the respective reflected lights therefrom. The intensities of the reflected lights are detected with respect to infrared rays having a wide wavelength range containing three wavelengths in the same way and, from the detection values, the thickness (t) of the film 1b is calculated using formula t=-1/2alpha.ln[1-1/A{(I02/ I2S+I03/I3S)/2-I0AX/I1S}] (wherein alpha is the absorption coefficient of a wavelength lambda, A is the value of the ratio of the quantities of the respective reflected lights of the infrared rays having a wide wavelength range and I0A-I03 and I1S-I3S are respectively the intensities of the reflected lights having respective frequencies from the object to be measured and the reference material 8).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for measuring the thickness of an organic film formed on the surface of a metal material such as steel for coating, using infrared rays, and a method used for carrying out the method. related to a device for

[Prior art]

The thickness of the organic film formed on the surface of the steel material by painting or the like must be set to an appropriate value in order to prevent deterioration of weldability and impart corrosion resistance. For this reason, conventionally, in the manufacturing process of forming an organic film on the surface of a steel material, the film thickness is measured online and the film thickness is controlled based on the measured value.

One such film thickness measurement technology uses the optical principle that the intensity of reflected infrared light of a specific wavelength changes depending on the thickness of the organic film, that is, Lambert's law. There are two wavelength methods, which use infrared rays of three wavelengths, and a three-wavelength method, which uses infrared rays of three wavelengths.

As a two-wavelength film thickness measurement technology, Sumitomo Heavy Industries Technical Report Vo
1.32 Na94 April 1984 r Infrared Paint Film Thickness Sensor" is known. this is,
When different types of steel sheets are used, there may be a difference of several tens of percent in reflectance, so in consideration of the fact that reflectance can be a major error factor in film thickness measurement, we have determined the difference in reflectance of steel sheets. The purpose is to eliminate errors in film thickness measurement caused by We created two equations expressing Lambert's law considering the attenuation rate of the intensity of reflected light,
The basic principle is to derive a film thickness calculation formula that does not include the reflectance of the steel plate by mutually dividing each side of these two formulas.

Furthermore, there is a proposal by the present applicant (Japanese Unexamined Patent Publication No. 61-68157) as a three-wavelength method for measuring film thickness. This includes infrared rays at wavelength λ4 where absorption occurs and wavelength λ2 where absorption does not occur. λ
, (however, 2λ4-λ, +λ), respectively, when the measurement target is irradiated with infrared rays, three equations representing Lambert's law are created that take into account the attenuation rate of the intensity of reflected light of each wavelength due to factors other than infrared absorption. The basic principle is to derive a film thickness calculation formula that does not include the attenuation rate using a certain approximation.

[Problem that the invention seeks to solve]

Both of the above two techniques provide techniques for minimizing errors in film thickness measurement based on differences in the attenuation rate of the intensity of reflected light due to causes other than infrared absorption. The effect of differences in reflectance on film thickness measurements is not taken into consideration.

It is important to use the wavelength at which the maximum infrared absorption occurs for film thickness measurement in order to increase accuracy. In this case, the intensity of the reflected light from within the film is small, so the film surface The intensity of the reflected light becomes relatively large,
Even when measuring the thickness of an organic film where the intensity of reflected light on the film surface is small in absolute value, the influence of surface reflectance cannot be ignored.

Particularly when measuring the thickness of a thin film, it is desirable to consider the influence of surface reflectance in order to reduce relative errors.

Furthermore, both techniques are not suitable for highly accurate film thickness measurement in online measurements where variations in pass lines are likely to occur. This is because errors in film thickness measurement based on differences in the distance and inclination between the film thickness meter and the steel plate, that is, the three-dimensional positional relationship, are not taken into account.

The present invention was made in view of the above circumstances, and it takes into consideration not only the difference in the surface properties of steel materials, but also the surface reflection of the film and the relative positional relationship between the film thickness meter and the steel material, which were not considered in the above two techniques. It is an object of the present invention to provide a highly accurate film thickness measuring method and device that is free from these influences, taking into consideration the influence that differences in film thickness have on film thickness measurement.

[Means for solving problems]

The film thickness measurement method according to the present invention irradiates an infrared ray with a wavelength λ1 that causes absorption in an organic film formed on the surface of a metal base material,
In a film thickness measurement method that measures the thickness of an organic film from the intensity of the reflected light, the wavelength λ1 and the wavelength λ at which no absorption occurs
2. When infrared rays of λ0 (λ2 x λ1 x λ3) are irradiated on the reference material and the measurement target, which are made of the same metal material as the base material of the measurement target and have no organic film formed on the surface, the intensity of each reflected light is calculated. When the reference material and the measurement object are irradiated with infrared rays in a wide wavelength range including the three wavelengths, the intensity of each reflected light is detected, and based on these detected values, the thickness t of the organic film can be determined by the following formula. It is characterized by calculating.

Here, α: Absorption coefficient of organic film at wavelength λ1 A: Wavelength λ1°λ2. 1oA+Iot+L*: Value of the ratio of the light intensity of each reflected light when infrared rays are irradiated with infrared light in a wide wavelength range including λ. Intensity of each reflected light when irradiating infrared rays of λ2°λ: Ls+hs+Iss: When the reference material is irradiated with infrared rays of wavelength λ1. λ2. λ.

The intensity of each reflected light when irradiated with infrared rays of In a film thickness measuring device that measures the thickness of an organic film from the intensity of the wavelength λ1 and the wavelength λ2 where no absorption occurs. A light source that emits infrared rays including wavelengths λ3 (λ2, <λ1, <λ,) and wavelengths λ1. λ2. λ, a chopper that passes the infrared rays separately, and a chopper that allows the infrared rays to pass through as is; a first optical means that focuses the infrared rays that have passed through the chopper in the direction of the measurement target;
a reflecting plate disposed in the optical path of the infrared rays that has passed through the optical means and having a notch; and a second optical means for condensing the infrared rays that have passed through the notch and been reflected by the reflecting plate. ,
The reflector plate includes a light intensity detector that detects the intensity of infrared light focused by the optical means, and a film thickness calculator that calculates the thickness of the organic film based on the signal from the light intensity detector. is made of the same metal material as the measurement object, and an organic film is formed on the surface by allowing infrared rays directed toward the measurement object and reflected light from the measurement object to pass through its cutout, and reflecting infrared rays directed toward the measurement object. It is characterized in that it is arranged so as to direct the light toward a reference material that is not covered, and to reflect the reflected light from the reference material.

[Effect]

The wavelengths λ, , λ2 . emitted from the light source. The infrared rays containing wavelengths λ1, . After passing through the chopper separately as infrared rays of λ8 or λ, by the first optical means,
The light is focused in the direction of the measurement object, passes through the cutout of the reflector, is reflected by the measurement object, passes through the cutout again, is focused by the second optical means, and then the light intensity is It is detected by a light intensity detector and given as a signal to a film thickness calculator.

On the other hand, the infrared rays reflected by the reflector are sequentially reflected by the reference plate and the reflector, and after being focused by the second optical means,
The intensity is detected by a light intensity detector and given as a signal to a film thickness calculator.

The film thickness calculator calculates the wavelength λ1. λ8. The film thickness is determined based on a preset film thickness calculation formula from the detected signal of the intensity of each reflected light when the measurement target and reference material are irradiated with infrared rays of λ, and infrared rays in a wide wavelength range including these three wavelengths. Calculate.

[Principle of the invention]

Next, the principle of the present invention will be explained. Figure 4 shows steel plate 1
Infrared rays at a specific wavelength λ1 at which infrared absorption by the organic film 1b occurs toward the organic film-formed steel sheet 1 with an organic film 1b formed on the surface thereof, and two reference wavelengths near wavelength λ1 at which infrared absorption does not occur. λ2λ, (However, λ2〈Hakuλ
, ) is a schematic diagram showing a state in which the intensity of each reflected light is detected when infrared rays are irradiated.

FIG. 5 shows a steel plate 8 as a reference material made of the same material as the steel plate 1a with a wavelength λ8. λ2. FIG. 3 is a schematic diagram showing a state in which the intensity of each reflected light is detected when infrared rays of a wide wavelength range including infrared rays of λ are irradiated. Detected wavelength λ1
．． λ2. The infrared light intensity of λ is expressed by the following formula.

1, I=IIl, +R0...(1) rot-rg+R omission ・-(2) 1113"13+R3...(3) 11=AI+s I...(4) 1 g =
A-I is ... (5) I3 = A
-13s...(6) Here, ■. 1. ! . ! +163 "Intensity of reflected light when infrared rays with wavelengths λ1, λ2, and λ3 are irradiated to the organic film-formed steel sheet 1, respectively. However, ■., are virtual values assuming that no infrared absorption occurs, ■, 2°■. , are actually measured values.

L, It, Is: wavelength λ1 on the organic film-formed steel sheet 1, respectively
゜λ2. The intensity of each infrared ray reflected by the steel plate 1a and emitted from the organic layer 111b when irradiated with infrared rays of λ, where I is a virtual value assuming that no infrared absorption occurs.

R+, Rt, Rs: wavelength λ on the organic film-formed steel sheet 1, respectively
1°λ2. Intensity A of reflected light from the film surface when irradiating with infrared rays of wavelength λ1. I+s+Izs+I+s: Value of the ratio of the light intensity of each reflected light when irradiating infrared rays in a wide wavelength range including λ3, λ, and λ3. λ
FIG. 6 shows the intensity of reflected light when the steel plate 8 is irradiated with infrared rays of wavelength C and λ2. FIG. 3 is an explanatory diagram showing the intensity of reflected light at each wavelength when infrared rays of λ3 are irradiated.

The figure shows the wavelength on the horizontal axis and the intensity of reflected light on the vertical axis.In the figure, the vertical coordinates e, d, and c indicate the wavelength λ1. λ2. The intensity of each reflected light when irradiated with infrared light of λ is (Ls rlzs*13), and f, a, and b are e and d, respectively.

This is the foot of the perpendicular line drawn from C to the horizontal axis.

The area of the quadrilateral abcd is the integral value of the intensity of reflected light when irradiated with infrared rays in the wavelength range of λ3 to λ.

In addition, FIG. 7 shows that the organic film-formed steel sheet 1 is coated with wavelengths λ1°, λ2. λ
FIG. 3 is an explanatory diagram showing the intensity of reflected light at each wavelength when infrared rays of No. 3 are irradiated.

The figure shows the wavelength on the horizontal axis and the intensity of reflected light on the vertical axis. In the figure, the ordinates of fl, al, and bl are the wavelengths λ1, . λ meaning.

It is the intensity of the reflected light from the film surface (Rz, R3) among the intensities of each reflected light when irradiated with infrared rays of λ3, and a
/, the ordinate of cI is the wavelength λ3. Intensity of each reflected light when irradiated with infrared light of λ (■.2.■.,
), the ordinate of e' is the intensity of reflected light of 10M when the object to be measured is irradiated with infrared rays of wavelength C, and a" 1.
a is a1. This is the foot of the perpendicular line drawn from CI to the horizontal axis.

The area of quadrilateral a#b#C'd' is the integral value of the intensity of reflected light when irradiated with infrared rays in the wavelength range of λ8 to λ3, assuming that no infrared absorption occurs, and the area of quadrilateral The area of a#b#b'a' is the wavelength λ.

arI when irradiated with infrared rays in the wavelength range of ~λ
! It is the integral value of the intensity of the reflected light on the four surfaces of the quadrilateral a'
The area b'c'd' is the value obtained by subtracting the integral value of the intensity of reflected light on the surface of the organic film from the integral value of the intensity of reflected light assuming that no infrared absorption occurs.

Now, strength 1. If infrared rays with a wavelength λ1 are irradiated toward the organic film-formed steel plate 1, and all of the infrared rays are not reflected by the organic film surface and enter the film, then the infrared rays that are absorbed by the organic film and come out of the film are The intensity 11A is expressed by the following equation (7) representing Lambert's law.

1, A-I exp (-2αt) ・(7) Here, α: Absorption coefficient of the organic film for infrared rays at wavelength λ1 t: Thickness of the organic film However, the intensity ■ of the infrared rays incident on the film is the infrared absorption If it does not occur, the intensity of the light emitted to the outside of the film is equal to 11, so the above equation (7) can be modified as the following equation (7').

I+a=I+exp(-2αt)=·(7') Therefore, if the light intensity 11 and IIA can be actually measured, the film thickness t can be determined.

However, in actual film thickness measurement, since surface reflection occurs in the film, the intensity of the reflected light that is detected includes the intensity R3 of the surface reflected light.

However, the two conventional techniques do not consider the light intensity R3. This results in 11A+R1#IIA II +R1=l.

Therefore, the above equation (7') is applied.

That is, the film thickness is measured using the formula below.

11A+RI -(1+ +Rt)exp(-2c
rt) As is clearer, even if the light intensity R1 is small,
For film thickness measurements, where it is necessary to use the wavelength with the most significant infrared absorption to improve accuracy, a light intensity of 11
Since A is also small, good measurements cannot be expected if the influence of the light intensity R1 on measurements is ignored.

Therefore, in the present invention, the above equation (7') is transformed into the form of the difference between the light intensities rot and IIIA, which are equally affected by the difference in the light intensities R,.

(1++R+-(1+a+R+)) =l+ (1-e
xp(-2αt) ) ・”(8)Here 1.+R,・
■. 1. Also, La +R1=f. Because it is ^,...
(9) holds true.

However, the light intensity I. Since I cannot be measured, the wavelength λ2. Using the infrared intensity I02°IO2 of λ, it is approximated as follows.

This approximation is possible because the wavelength λa, λ is set to a value close to λ1, so that the relationship between the wavelength and the reflected light intensity can be regarded as a straight line.

R3 is also approximated as follows.

The wavelength λ2 can be approximated in this way. λ3 to λ.

This is because the relationship between the wavelength and the reflected light intensity can be regarded as a straight line.

Substituting the above approximate equation 01 and att equation into the third side of equation (9), where wavelength λ2. Since λ can be considered to be sufficiently close to the wavelength λ, it can be approximated as =10.

Therefore, the film thickness t is calculated by the following α Fun2, which gives the film thickness t by setting 0 in equation (2).

...(2) As shown in the above equation (8), the present invention is based on the virtual value of the intensity of reflected light when no infrared absorption occurs when the organic film-formed steel sheet l is irradiated with a specific wavelength λ1. By taking the difference between and the actual measured value, the organic film 1 that is equidistant to these two values is obtained.
Since the intensity R of the reflected light from the surface b is erased, 0
In calculating the film thickness using Equation 0, errors in film thickness measurement due to differences in light intensity R do not occur.

Next, the significance of OA in formula 04) will be explained.

A is based on the difference in the relative positional relationship between the film thickness gauge and the steel material (
This is a correction coefficient.

Assuming that no infrared absorption occurs by the organic film, the relative positional relationship between the film thickness measuring device 2 and the steel plate 1a and the steel plate 1
If the film thickness is measured under the same reflectance conditions as a,
Area of quadrilateral abed in Figure 6 and quadrilateral a in Figure 7
The areas of 'b'C'd' should be equal.

However, in actual film thickness measurement, especially on-line measurement, the areas of both quadrilaterals are not equal because there are differences in the film thickness measurement conditions.

These differences in measurement conditions all appear as differences in the amount of reflected light detected.

Therefore, quadrilateral a/ b I c/ a I and quadrilateral a
First, it is conceivable to use the value of the area ratio of bcd as a correction coefficient, but the area of quadrilateral a'b'c'd' cannot be actually measured.

Therefore, it is conceivable to use the area of the figure a'b'c'e'd' as a substitute. However, due to attenuation due to infrared absorption, the reflected light from the organic M1b surface and the steel plate 1
Since the detected light intensity fluctuates due to optical interference with the reflected light from a, the area of the figure a'b'C'e'd' is larger than the area of the quadrilateral a/bI CI dl. Since they are different, it is impossible to substitute them.

Therefore, the correction coefficient A is set to wavelength λ1. λ2. λ, and is defined as the value of the ratio of the light amounts of each reflected light when organic film-formed steel plate 1 and steel plate 8 are irradiated with infrared rays in a sufficiently wide wavelength range to the extent that the effects of attenuation due to absorption and interference can be ignored.

This can be determined because if there is a difference in the relative positional relationship between the film thickness measuring device 2 and the object to be measured, that difference will appear as a difference in the amount of reflected light.

Note that the amount of light reflected from the organic film-formed steel plate 1 includes the light reflected on the surface of the organic film 1b, but when the incident angle is around 10 degrees, the surface reflectance of the organic film 1b is about 2 to 3. %, the influence on the correction coefficient A can be ignored.

For example, in the case of an acrylic organic coating, the surface reflectance is about 3% when the incident angle is around 10 degrees, as shown in Figure 8, which shows the relationship between the incident angle and the surface reflectance. 8
If the amount of reflected light is 1 and the infrared absorption rate is 0.2, the original correction coefficient A will be 0.8, whereas the correction coefficient A when surface reflection is ignored. The value of is (0,03+0.97xO,8)/1=0.806, resulting in only a difference of 0.006.

In the case of an organic film, the influence of the surface reflectance on the film surface on the correction coefficient A can be ignored, so the correction coefficient A is calculated as the amount of each reflected light including the amount of reflected light on the film surface. It can be determined as the value of the ratio.

〔Example〕

The present invention will be specifically explained below based on the drawings.

FIG. 1 is a schematic diagram showing a film thickness measuring device according to the present invention. In the figure, film thickness measuring devices 1 and 2 according to the present invention are arranged above an organic film-formed steel plate 1 to be measured, which has an organic film 1b formed on the surface of a steel plate 18.

The film thickness measuring device 2 includes a light source 3 housed in a casing 12.
, a chipper 4, a concave mirror 6, a rotating reflector 7, a concave mirror 9, a light intensity detector 10, a film thickness calculator 11, and the like.

The light source 3 is installed in a light source chamber 3a formed by a casing wall and a light-shielding wall at one corner of the lower side of the casing 12 of the film thickness measuring device 2, and has wavelengths λ, which are absorbed by the organic film 1b, It emits infrared rays in a wide range of wavelengths, including wavelengths λ□, λ, where absorption does not occur.

A window hole is bored in the earthen wall of the light-shielding wall, and the light projection part of the light source is directed diagonally upward so that infrared rays pass through the window hole.

A chopper 4 made of a light shielding material is disposed in the optical path of the infrared rays that have passed through the window hole. As shown in the plan view of FIG. 2, the chopper 4 has a disk shape, and has circular holes 41, 42, 43.44 at four equally spaced positions.
3 have wavelengths C and λ2, respectively. A filter is installed to selectively pass infrared rays of λ, and the circular hole 44 is a hole.

Further, the chopper 4 is rotated by the drive of an attached motor 5. The axis of rotation is arranged such that the center of each circular hole is located in the optical path of the infrared rays. Organic film-formed steel sheet 1
When moving continuously, the rotational speed of the motor 5 is adjusted as appropriate depending on the variation in the film thickness of the object to be measured in the pass line direction, the line speed, etc.

Thus, the chopper 4 intermittently blocks infrared rays, allows the infrared rays to pass through the circular holes 44 either as they are, or after being reduced in intensity, and filters at wavelengths λ1... λ2. λ infrared rays are passed through each separately. The chopper 4 and the motor 5 are equipped with a rotation angle detector 1.
4 are interlocked and connected, and their outputs are input to the film thickness calculator 11.

In the optical path of the infrared rays that have passed through the chopper 4, there is disposed a concave mirror 6 whose reflecting surface faces downward so that the reflected light goes toward a window hole 16 formed in a circular shape approximately in the middle of the bottom surface of the casing 12.

Above the window hole 16, a reflection plate 7 that can be rotated horizontally and concentrically with the window hole 16 is arranged. Center angle 90″ from
The two sector shapes are cut out symmetrically with respect to the center, and the notches 7a, 7a are cut out.
The remaining two blade portions 7b formed with.

One side of 7b is plated with high reflectance, for example gold plating, to make it a reflective surface, and is arranged with the reflective surface facing upward.
For example, it is rotated intermittently by driving an attached motor 13.

The optical path of the infrared rays from the concave mirror 6 is arranged in the rotation range of the notch 7a of the rotary reflector 7, and when the notch 7a is located on the optical path, the infrared rays pass, and the transmitted light is removed from the organic film-formed steel plate 1. The reflected light also passes through the other opposing notch 7a.

A table 17 is arranged above the rotating reflector plate 7 on which a steel plate 8 made of the same metal material as the organic film-formed steel plate 1 is placed. The stand 17 is a steel plate 1 on which an organic film is formed by infrared rays from a concave mirror 6.
It is arranged horizontally so that the point of symmetry with respect to the rotating reflector 7, which is the upper light condensing point, is on the lower surface of the steel plate 8. The inclination of the concave mirror 6 is adjusted so that the angle of incidence of the reflected light on the rotating reflection plate 7 is about 10''. If so, they can be replaced with ones of the same metal material accordingly.

When the blade portion 7b of the rotary reflector 7 is located on the optical path, the infrared rays from the concave mirror 6 are reflected, and the reflected light from the steel plate 8 is also reflected from the opposite blade portion 7b.
Reflect.

In this case, the angle of incidence of the infrared rays reflected by the rotating reflector 7 and incident on the steel plate 8 is equal to the angle of incidence on the organic film-formed steel plate 1, which is about 10''.

A rotation angle detector, such as a photocoupler, is connected to the rotating reflector 7 and the motor 13, and its output is input to the film thickness calculator 11. In the optical path of the infrared rays from the rotating reflector 7, a concave mirror 9 is disposed diagonally above the rotating reflector 7 so that the infrared rays are focused toward the light intensity detector 10 with its reflecting surface facing downward. ing.

On the lower side of the casing 12, in one corner opposite to the light source 3, a light intensity detector 10 is arranged with its light receiving part facing the concave mirror 9. is equipped with a film thickness calculator ll, and a rotation angle detector 1
Based on the input signal from the chopper 4, the infrared rays passing through the chopper 4 have wavelengths λ1. λ2. λ.

A wide range of wavelengths including infrared or wavelength λ, λ2 or λ,
In addition, based on the input signal from the rotation angle detector 15, it is determined whether the infrared rays are coming from the organic film-formed steel plate 1 or the infrared rays from the steel plate 8, and the detected value of the intensity of each reflected light is determined. Based on this, the film thickness is calculated from the film thickness calculation formula 〇荀formula set in advance.

In the film thickness measuring device 2 as described above, the wavelength λ1 . λ2. The infrared rays in a wide wavelength range including λ can be filtered as is or by three filters installed in the chopper 4 to reduce the wavelength to λ.

λ2. Each chopper 4 is used as infrared light of λ3. Thereafter, the infrared rays are focused in the direction of the organic film-formed steel plate 1 by the concave mirror 6, and when the notch 7a of the rotary reflecting plate 7 is located in the optical path, the infrared rays pass through, and the blade portion 7 is placed on the optical path.
When b is located, it is reflected.

When the infrared rays that have passed through the notch 7a and are irradiated onto the organic film 1b pass through the rotary reflecting plate 7, the other notch 7a facing the notch 7a is located on the optical path of the infrared rays, so that the infrared rays irradiated onto the organic film 1b pass through the notch 7a. The light intensity of the infrared light that is focused by the second concave mirror 9 is detected by the light intensity detector 10, and this detected value is sent as a signal to the film thickness calculator 1.
1 is given.

On the other hand, the infrared rays reflected by the blade part 7b of the rotating reflector 7 are irradiated onto the steel plate 8, and the reflected light is reflected by the other blade part 7 facing the blade part 7b when reflected by the rotary reflector 7.
b is located on the optical path of the reflected light, this blade portion 7b
It is reflected again at .

The reflected infrared rays are projected onto the second concave mirror 9, and the intensity of the infrared rays condensed by this is detected by the light intensity detector 10, and this detected value is used as a signal by the film thickness calculator 11. given to.

The film thickness calculator 11 has the film thickness calculation formula α set in advance, and the respective input signals ■ . An
I. t+Ios and each input when the infrared steel plate 8 is irradiated (i No. 11!+ I tsr I ss
and the wavelength λ1. λ2. Calculated from the input signal when the organic film-formed steel plate 1 is irradiated with infrared rays in a wide wavelength range including λ, and the input signal when the steel plate 8 is irradiated with the infrared rays.
The value A of these ratios and the preset organic film 1
Based on the wavelength λ of b and the absorption coefficient α for infrared rays,
The film thickness is calculated.

9 and 10 are graphs showing the relationship between the inclination of the organic film-formed steel sheet 1 with respect to the film thickness measuring device 2 and the absorbance calculated from the detected value of the light intensity detector 10 when variously changed. Ah, FIG. 9 shows the case without correction using the correction coefficient A, and FIG. 10 shows the case with the correction.

As is clear from both figures, the error in film thickness measurement can be reduced by calculating the film thickness t by correcting it using the correction coefficient A according to the present invention.

11 and 12 are graphs showing the relationship between film thickness and absorbance when using the film thickness measuring method according to the present invention and when using the conventional technique, respectively. According to the present invention, approximately ±
Although the film thickness error is only 0.15 .mu.m, it can be seen that the conventional technique causes an error of approximately .+-.0.35 .mu.m.

Note that this comparative experiment used 3.4 μ- as the specific wavelength, 3.2 μts and 3.6 μ- infrared rays as the reference wavelength, and used Pb5e as the light intensity detector 10, so in determining the correction coefficient A. , a light amount in the wavelength range of 1.5μ11 to 4.3μ−, which is the total sensitive wavelength of the light intensity detector 10, was used.

Furthermore, 10° was used as the incident and exit angle with respect to the organic film 1b. As mentioned above, this is due to the fact that the reflectance on the surface of the organic film 1b at this angle is as small as a few percent, and the deviation of the optical axis due to the difference in the relative positional relationship between the film thickness measuring device 2 and the organic film-formed steel plate 1. This is because the smaller the angle of incidence, the smaller is the angle of incidence.

As described above, in this example, the organic film 1b on the steel plate la is used as the base material.
Although the present invention is not limited to this, it goes without saying that it can also be used to measure the thickness of an organic film formed on the surface of a metal base material in general.

In addition, in this embodiment, when determining the correction coefficient A, the wavelength λ1. λ8. Although the amount of infrared light in a wavelength range that includes λ is used, it is also possible to use the amount of infrared light in a wavelength range that does not include these three wavelengths.

〔effect〕

As described above, the present invention provides a virtual value and an actual value of the light intensity when it is assumed that the error in film thickness measurement due to the difference in reflectance on the surface of the organic film 1b is not caused by infrared absorption in the reflected light of the specific wavelength λ1. By taking the difference between According to the invention, highly accurate film thickness measurement is possible.

Furthermore, when the present invention is applied to online measurement in an organic film coating line for copper strips, the film thickness can be controlled with high precision to a desired value by feeding the measured value as a signal to the film thickness control circuit. The present invention has significant effects, such as being able to produce high-quality organic film-forming metal materials without causing welding defects, rolling defects, etc., and improving yields.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a film thickness measuring device according to the present invention, and FIG.
The figure is an enlarged view of the chopper in FIG. 1, FIG. 3 is an enlarged plan view of the rotary reflecting plate 7 in FIG. 1, FIGS. 4 to 8 are detailed explanatory views of the present invention, and FIG. 9. FIG. 10 is a graph showing the effect of correction by correction coefficient A.
FIG. 11 is a graph showing the relationship between film thickness and absorbance when using the measuring method according to the present invention, and FIG. 12 is a graph showing the relationship between film thickness and absorbance when using the conventional method. 1a...Mesh plate 1b...Organic film 2...Film thickness measuring device 4...Chopper 7...Rotating reflection plate 10...
Light intensity detector 11...Film thickness calculation lid frame Applicant
Sumitomo Metal Industries Co., Ltd. Representative Patent Attorney Kono
Noboru Answer 1 Illustration Z Enro 7 Lobe 3 Calculation 4 Figure N5 Figure Tanto'4q Zusen 8 Figure"2 -1 0 1 2 (Associate) @1≧L-
11 Koisasan q Zuko 10 Diagram Thickness (μ-) Mushroom Diagram Ambiguous (71 Sosan 12 Diagram

Claims (1)

[Claims] 1. A film thickness measuring method in which an organic film formed on the surface of a metal base material is irradiated with infrared rays having a wavelength λ_1 at which absorption occurs, and the thickness of the organic film is measured from the intensity of the reflected light, The wavelength λ_1 and the wavelengths λ_2 and λ_3 at which no absorption occurs
Intensity of reflected light when infrared rays of (λ_2, <λ_1, <λ_3) are irradiated on the reference material and the measurement target, which are made of the same metal material as the base material of the measurement target and have no organic film formed on the surface. Detect the intensity of each reflected light when the reference material and the measurement target are irradiated with infrared rays in a wide wavelength range including the three wavelengths, and based on these detected values, calculate the film thickness of the organic film using the following formula. A film thickness measuring method characterized by calculating t. t=-(1/2α)ln{1-1/A(I_0_2/I
_2_3+I_0_3/I_3_5/2-I_0_A/
I_1_5)} Here, α: Absorption coefficient of the organic film for wavelength λ_1 A: Ratio of the amount of each reflected light when the measurement object and reference material are irradiated with infrared rays in a wide wavelength range including wavelengths λ_1, λ_2, and λ_3. Values I_0_A, I_0_2, I_0_3: Intensities of each reflected light when the measuring object is irradiated with infrared rays of wavelengths λ_1, λ_2, λ_3 I_1_3, I_2_3, I_3_5: Reference material has wavelength λ
Intensity 2 of each reflected light when irradiating with infrared rays of _1, λ_2, and λ_3, irradiating infrared rays with a wavelength λ_1 that causes absorption in the organic film formed on the surface of the metal base material, and determining the organic film from the intensity of the reflected light. In a film thickness measuring device that measures the thickness of
It is equipped with a light source that emits infrared rays including (λ_2<λ_1<λ_3), a filter that passes infrared rays of wavelengths λ_1, λ_2, and λ_3 separately, and a chopper that passes the infrared rays as they are, and measures the infrared rays that have passed through the chopper. a first optical means for condensing light in the target direction; a reflection plate disposed in the optical path of the infrared rays passing through the first optical means and having a notch; a second optical means for condensing the infrared rays reflected by the plate; a light intensity detector for detecting the light intensity of the infrared rays condensed by the optical means; and a signal from the light intensity detector to detect the organic and a film thickness calculator for calculating the thickness of the film, and the reflecting plate allows infrared rays directed toward the measurement object and reflected light from the measurement object to pass through its notch, and also reflects infrared rays directed toward the measurement object. A film thickness measurement characterized in that the light is directed toward a reference material made of the same metal material as the measurement target and on which no organic film is formed, and is arranged to reflect the reflected light from the reference material. Device.