JPH01132936A - Method and apparatus for analyzing film - Google Patents

Abstract

PURPOSE:To continuously and simultaneously analyze the composition and thickness of a film, by irradiating the film with infrared rays polarized in parallel to an incident surface at a Brewster angle. CONSTITUTION:The film 12 formed on a steel plate 10 runs in the direction shown by an arrow A. The timewise interfered infrared rays emitted from an FT-IR light source part 60 are polarized in parallel to an incident surface by a polarizer 62 are subsequently set to an incident angle theta by a concave mirror 64 for incident light to irradiate the film 12. The concave mirror 64 moves in a B-direction to make the incident angle theta changeable. Further, the lights reflected by the upper and lower surfaces of the film 12 are condensed to an FT-IR light detection part 68 by a concave mirror 66 for reflected light and the concave mirror 66 is also moved in the B-direction in order to correspond to the change of the incident angle theta. Luminous intensity is converted to an electric signal by the detection part 68 to be sent to an FT-IR processing part 70 which is turn applies Fourier transform to the sent-in signal and the infrared reflection spectrum by the film 12 is calculated from the preliminarily stored reflection spectrum of a metal having film 12.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method and apparatus for analyzing a film formed on the surface of a metal such as a moving steel plate or steel pipe, which contains a substance active in the infrared region as a main component and one or more other infrared rays. A method for analyzing a film that partially transmits light, formed on a light-reflecting substrate, suitable for continuous online simultaneous measurement of the component composition and film thickness of a film containing an externally active substance. Regarding equipment.

[Conventional technology]

In recent years, with the aim of improving the surface properties of steel materials, so-called hot-roasted steel products, electrical steel sheets with insulating coatings, organic resin liquid M steel sheets, etc., have been developed in which the surface of steel materials is coated with an inorganic or organic coating. . In this case, the main raw material for the coating material (powder in the case of porcelain, organic resin such as polyester or epoxy in the case of MgO1 organic resin for electrical steel sheet) is dissolved in an aqueous solution or an organic solvent and applied. Generally, it is heated to a predetermined temperature to cause a reaction so that it adheres to the surface of the steel material and forms a robust film. At this time, in addition to the main raw materials, auxiliary raw materials are also added to further improve the surface properties of the steel material. Therefore, controlling the amount (thickness) and composition of the applied and baked film to an appropriate value is essential for product quality control.
11! This is very important because it reduces manufacturing costs. Generally, the composition and coating amount of the surface layer after plating, painting, high-temperature oxidation, etc. are analyzed by fluorescent X-ray analysis, but when the object to be measured is an organic resin or enamel, Since the element to be measured is a light element, it is necessary to perform the measurement in a vacuum when fluorescent Xa is used. Therefore, for example, a sample piece punched out in the shape of a disc is put into the sample chamber of a fluorescent Xm analyzer, evacuated to a high vacuum, and analyzed, resulting in a destructive inspection.
It was extremely difficult to continuously measure the MW-1 component composition on the production line. Conventionally, various film thickness meters have been used as continuous analysis methods that do not have such problems, but the ones that can perform continuous measurement without contact are JP-A-57-179607 and JP-A-58- 18109, Japanese Patent Laid-Open No. 58-102106, and Utility Model Application Laid-open No. 61-163915 are known. This method utilizes the fact that light of a specific wavelength is absorbed by the coating, and is a method for calculating the thickness of the coating by measuring the amount of absorption. This infrared apA thickness meter is configured as shown in FIG. 2, for example, and irradiates light of a specific wavelength that is absorbed by the coating 12 and light of a specific wavelength that is not absorbed by the target JIW 12, and the reflection intensity of each is By measuring the coating 12
Find the WJ and thickness of. Specifically, the light 22 emitted from the light source 20 is, for example, multi-W! After passing through a filter 24 consisting of an I-film filter and sorting out light of a specific wavelength that is absorbed by the coating 12, the light is split into two by a beam splitter 26. One (28, A) is directly incident on the detector 30A, and the other is ,
After being absorbed and reflected by the FT 1i12 formed on the M plate 10, the light is made to enter the other detection H30B as reflected light 28B. The light incident on the detectors 30A and 30B is each converted into a light intensity signal and then sent to the computer 32. Total! [32 is the transmitted incident light 28A and the incident light y! The thickness M of the coating 12 is calculated by comparing and calculating two light intensity signals of the reflected light 28B absorbed by A12. In principle, this filter-type infrared film thickness meter can detect the composition of a film by using multiple filters that select the wavelengths absorbed by each component, even if the film is composed of multiple components. It should be possible to analyze
In the past, there was no case where the film thickness and component composition of a coating were not simultaneously analyzed continuously on the line. The causes of this include the following problems. (2) When a film is irradiated with infrared light, in addition to the light that passes through the film and is reflected on the bottom surface of the film, there is also light that is reflected on the top surface of the film. As a result, the reflected lights interfere with each other, resulting in measurement errors, making it impossible to obtain practical measurement accuracy. ■When a film is composed of many types of components, in order to analyze its composition, it is necessary to pass the light through multiple filters and separate the light into many parts, which results in a weak light intensity. As a result, measurement accuracy decreases. ■Appropriate filters for selecting the absorption wavelength of each component cannot be easily obtained. ■In production lines where the type of coating changes frequently, filters must be replaced each time the type changes, which is impractical. In recent years, as a method to solve the above problem ■,
No. 0-73406 discloses a method for removing the influence of interference during film measurement. This method uses a device such as the one shown in FIG. The incident angle θ is varied within a predetermined range by the mirror 42, the film 44 is irradiated via the polarizer 43, and the light intensity of the light 46B transmitted through the film 44 is detected by the detector 30 via the concave mirror 48 and the reflecting mirror 50. After the detection, the thickness of the film 4111 is calculated. On the other hand, the light intensity of the light 46A reflected by the film 44 is measured by the incident angle setting photodetector 31. At this time, at the angle θ=θ0, there is no interference, so
Film 44 detected by incident angle setting photodetector 31
The intensity of the reflected light 46A becomes weaker. Therefore, by monitoring the intensity of light reflected by the film 44 with the photodetector 31 and adopting the film thickness value only when the intensity decreases, the film thickness can be continuously measured without the influence of interference.

[Problems to be solved by the invention]

However, if the conventional device shown in Fig. 3 is used as it is to measure the coating on the metal surface, the coating on the metal surface 1.
When light is irradiated onto the coating 12, as shown in FIG. It became impossible to detect only the light 46A, and it was impossible to perform measurements to eliminate the influence of interference using the conventional apparatus shown in FIG.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and includes a film analysis method and a film analysis method that can continuously and simultaneously analyze the component composition and film thickness of a film formed on a light-reflecting substrate. The purpose is to provide equipment.

[Means to solve the problem]

The present invention provides a method for analyzing a coating formed on a light-reflecting substrate that partially transmits light, including irradiating the coating with infrared light polarized parallel to the plane of incidence at substantially Brewster's angle;
The above object has been achieved by analyzing the component composition and film thickness of the coating from the absorption peak of the reflection spectrum of the infrared light. Further, in an embodiment of the present invention, the coating is formed on a traveling light-reflecting substrate, and the component composition and thickness of the coating are almost continuously analyzed on-line. Further, the present invention provides a method for analyzing a film as described above, including:
A film is irradiated with light polarized parallel to the plane of incidence at a predetermined angle of incidence, and the reflected light of the light irradiated onto the film is separated into a spectrum, so that the intensity change depending on the wavelength of the spectral waveform is minimized. Find the angle of incidence, then irradiate infrared light polarized parallel to the plane of incidence at the angle of incidence, and measure the composition and thickness of the film from the absorption peak of the reflection spectrum of the infrared light. In this way, the above objective has also been achieved. The present invention also provides an apparatus suitable for carrying out the method, which includes a polarizer that polarizes light parallel to the plane of incidence, and irradiates the coating with the light polarized by the polarizer at an incident angle within a predetermined range. a light irradiation unit, a spectrometer that receives the reflected light of the light irradiated on the coating and separates it into a spectrum, and a photodetector that outputs a signal according to the light intensity at each wavelength of the spectrum;
A signal processing unit that finds the angle of incidence that minimizes the change in each wavelength of the signal according to the light intensity, and irradiates the coating with infrared light polarized parallel to the plane of incidence at the angle of incidence, and detects the reflection from the coating. A Fourier transform infrared spectrometer including a mechanism that receives light and measures the reflection spectrum of the infrared light, and a calculation unit that measures the component composition and film thickness of the coating from the absorption peak of the magnetic infrared reflection spectrum. It is constructed by having the following.

[Effect]

The present invention uses a transparent dielectric material (refractive index n) when analyzing a film formed on a light-reflecting substrate that partially transmits light.
When a parallel ray is incident on , the angle of incidence θ is θ=tan-10
At an angle that satisfies (Brewster's angle), part of the open light component perpendicular to the plane of incidence is reflected and - part passes through, but the reflection of the component parallel to the plane of incidence is zero and all is transmitted. . That is, when the reflected light that has interfered is dispersed into a spectrum as shown in FIG. 4, so-called interference fringes appear, in which the intensity of the light is continuous depending on the wavelength. Therefore, if we change the incident angle while observing the spectrum, the interference fringes disappear at a certain angle (Brewster's angle), so the angle θ0 at which the influence of interference can be removed.
It becomes possible to find. Therefore, the coating is irradiated with infrared light polarized parallel to the plane of incidence at substantially the Brewster angle θ0, and the component composition and PIAFf of the coating are analyzed from the absorption peak of the reflection spectrum of the infrared light. This makes it possible to simultaneously and continuously analyze the component composition and film thickness of a coating formed on a light-reflecting substrate. In addition, when analyzing a coating made of a material whose composition is completely unknown, the coating is irradiated with light polarized parallel to the plane of incidence at a predetermined angle of incidence, and the reflected light is divided into spectra. Find the angle of incidence that minimizes the change in intensity due to wavelength of the spectral waveform and use it as Brewster's angle. Next,
For example, using a Fourier transform infrared spectrometer (FT-IR), irradiate infrared light polarized parallel to the plane of incidence at a found incident angle, and determine the composition of the coating from the absorption peak of the reflection spectrum of the infrared light. Measure composition and film thickness. In this case,
It becomes possible to analyze coatings whose composition is completely unknown and whose Brewster's angle is unknown. Furthermore, when FT-IR is used, a certain wavelength range can be measured simultaneously.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. This embodiment is constructed as shown in FIG.
For example, the coating 12 formed on the surface of the steel plate 10 is
The vehicle is traveling in the direction indicated by arrow A in the figure. The temporally interfered infrared light in a predetermined wavelength range emitted from the FT-IR light source section 60 is polarized by a polarizer 62 parallel to the incident plane, and then polarized by a concave mirror 64 for incident light to have an incident angle of θ. The coating 12 is irradiated with the light. Here, the concave mirror 64 has a mechanism that moves in the direction indicated by mB in FIG. 1, so that the incident angle θ can be changed. Light reflected on the upper and lower surfaces of the coating 12 (Brewster angle θG
, reflected light 28B only from the lower surface of the coating 12)
is focused on the FT-IR front light detection 68 by the concave surface fi 66 for reflected light. The reflected light concave mirror 66 also has an R tip that moves in the direction shown by arrow B in the figure, like the incident light concave surface fi64, in order to correspond to changes in the incident angle θ. The light intensity is converted into an electrical signal by the FT-IR light detection section 68 and sent to the FT-IR signal processing section 70. The FT
- The IR signal processing unit 70 performs Fourier transform on the sent signal and calculates the infrared reflection spectrum due to the coating 12 from the previously stored reflection spectrum of the metal without the coating 12. The FT-IR signal processing unit 7 calculates the infrared reflection spectrum while changing the incident angle θ, and when the incident angle θ0 is the minimum light intensity change at each wavelength in a predetermined wavelength range, the FT-IR signal processing unit 7
0 outputs an infrared reflection spectrum to the computer 72. The calculation 8172 calculates and outputs the film thickness and component composition of the target v412 from the magnitude of a predetermined absorption peak of the sent infrared reflection spectrum and a calibration curve that has been created and stored in advance using the fi quasi-sample. . Note that when the signal processing unit 70 finds the optimal incident angle θG,
Output a movement stop command to the input/reflection concave surface a641.66,
The concave mirrors 64 and 66 maintain the optimum angle of incidence θ0. Furthermore, the signal processing unit 70 monitors changes in light intensity in a predetermined wavelength range, and determines the optimum incidence by changes in the refractive index due to changes in the composition of the coating 12 and changes in the angle of the objects to be measured (steel plate 10 and wA 12). When the angle θ0 changes and interference occurs and the change in light intensity due to wavelength becomes large, a movement command is output to the concave mirrors 64 and 66 for input and reflection, and after finding the optimum angle of incidence θ0 again, analysis of the coating 12 is started. do. The film thickness and silica content of a sample in which an epoxy resin containing silica was applied to the surface of a steel plate and baked were determined according to an example. Specifically, based on a steel plate that is not coated with resin, 40
Measure the infrared reflection spectrum from 0 to 4000c1-',
Calibration curve stored in advance and 5i near 1100cn-'
Regarding the absorption peak of −0 stretching vibration, the silica content (%) was calculated from the peak area, and the C
-Film thickness (g/rn') from absorption peak area of H stretching vibration
was calculated. The optimum angle of incidence θ0 was 60 degrees. In this case, the silica content is 25% and the film thickness is 2.5 g/m' determined from the coating amount and compounding ratio of the coating solution, and the silica content is ±2% and the WA thickness is ±O, Ig/m'. m
In this example, the same FT-IR is used for setting the optimum angle of incidence for spectrum measurement and for film analysis, so the apparatus is simple. A separate spectrometer is used to set the angle of incidence, and the wavelength range for monitoring interference fringes is set in the infrared, visible,
It is also possible to have a configuration that changes depending on the ultraviolet region and film thickness. This is because as the film thickness of the coating decreases, the pitch of the interference fringes (the wavelength difference between peaks and peaks, or between valleys) increases, so the ultraviolet region with short wavelengths is suitable for monitoring interference fringes. Conversely, as the V thickness increases, the pitch of the interference fringes decreases, which is why it is suitable to monitor in the infrared region, which has a long wavelength. In addition, in this example, a Fourier transform infrared spectrometer f
Since the i(FT-IR) is used, spectra in all wavelength ranges can be measured at the same time, and the film thickness and content of each component of a film with a complex composition can be measured simultaneously and continuously at high speed. Note that the method of implementing the present invention is not limited to this, and it is also possible to use an infrared spectrometer other than the Fourier transform type.

【Effect of the invention】

As explained above, according to the present invention, the composition and thickness of a film that partially transmits light, which is formed on the surface of a light-reflecting substrate such as a metal, can be determined simultaneously online and with high accuracy. It becomes possible to analyze. Therefore, it is possible to easily optimize the operating conditions and control the quality in the production line, and it has the excellent effect of stably producing steel materials with excellent surface properties.

[Brief explanation of the drawing]

FIG. 1 shows a diagram for carrying out the coating analysis method according to the present invention.
A front view including a partial block diagram showing the configuration of an embodiment of the device, FIG. 2 is a schematic diagram for explaining the principle of film thickness measurement by the conventional absorption method, and FIG. A schematic diagram for explaining the configuration of a conventional example used for measurement,
FIG. 4 is a cross-sectional view showing the state of reflected light when light is irradiated onto a metal whose surface is coated. DESCRIPTION OF SYMBOLS 10... Steel plate, 12... Coating, 22... Incident light, 60... Fourier transform infrared spectrometer (FT-IR)
Light source section, 62... Polarizer, 64.66... Concave mirror, θ... Incident angle, θo-al! i incident angle, 68... FT-IR light detection unit, 70... FT-IR signal detection unit, 72... calculator.

Claims (4)

[Claims] (1) A method for analyzing a film formed on a light-reflecting substrate that partially transmits light, in which the film is irradiated with infrared light polarized parallel to the plane of incidence at substantially the Brilleusta angle, and the infrared light is A coating analysis method characterized by analyzing the component composition and film thickness of the coating from the absorption peak of the reflection spectrum of external light. (2) The coating according to claim 1, wherein the coating is formed on a traveling light-reflecting substrate, and the component composition and film thickness of the coating are almost continuously analyzed on-line. analysis method. (3) In a method for analyzing a coating formed on a light-reflecting substrate that partially transmits light, the coating is irradiated with light polarized parallel to the plane of incidence at an incident angle within a predetermined range; The reflected light is divided into spectra to find the angle of incidence at which the intensity change depending on the wavelength of the spectral waveform is minimized. Next, infrared light polarized parallel to the plane of incidence is irradiated at the angle of incidence. A method for analyzing a film, comprising: measuring the component composition and film thickness of the film from the absorption peak of the reflection spectrum of the infrared light. (4) An analyzer of a coating formed on a light-reflecting substrate that partially transmits light, which includes a polarizer that polarizes the light parallel to the plane of incidence, and transmits the light polarized by the polarizer within a predetermined range. a light irradiation unit that irradiates the coating at an incident angle of , a spectrometer that receives the reflected light of the irradiated light on the coating and separates it into a spectrum, and outputs a signal according to the light intensity at each wavelength of the spectrum. a photodetector that detects the light intensity, a signal processing unit that finds the angle of incidence that minimizes the change in each wavelength of the signal according to the light intensity, and a signal processing unit that irradiates the coating with infrared light polarized parallel to the plane of incidence at the angle of incidence. , a Fourier transform infrared spectrometer including a mechanism for receiving reflected light from the coating and measuring the reflection spectrum of the infrared light; and determining the composition of the coating and the coating from the absorption peak of the magnetic infrared reflection spectrum. A coating analysis device characterized by comprising: a calculation section for measuring thickness;