JPH01132935A - Method and apparatus for analyzing film - Google Patents

Abstract

PURPOSE:To continuously and simultaneously analyze the thickness and composition of a film, by irradiating the film with infrared rays polarized in parallel to an incident surface at a Brewster angle and calculating the composition of the film from the absorption spectrum of the reflection spectrum of infrared rays. CONSTITUTION:The film 12 formed on a steel plate 10 runs in the direction shown by an arrow A. The incident light 24 of timewise interfering infrared rays emitted from an FT-IR light source part 50 is incident to a concave mirror 52 for incident light to irradiate the film 12 formed on the steel plate 10 so that an incident angle theta substantially becomes a Brewster angle. Further, the reflected light 28 from the upper surface of the film 12 and the reflected light 30 from the under surface thereof are condensed to a concave mirror 54 for emitted light to be incident to an FT-IR detection part 56. A polarizer 58 is driven in the light path of the incident light 24 by a polarizer driving part 60 to be moved to an insert position. The drive part 60 moves the polarizer 58 by the order of the FT-IR control part 62. In such a state that the polarizer 58 is inserted in the light path, the incident light 24 becomes polarized light parallel to the incident surface.

Description

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

The present invention relates to a method and apparatus for analyzing coatings, and is particularly suitable for use in continuous online measurement of the thickness and composition of coatings formed on the surfaces of moving metal plates, steel pipes, etc. The present invention relates to a method and apparatus for analyzing a film that is formed on a suitable light-reflecting substrate and partially transmits light.

[Conventional technology]

In recent years, with the aim of improving the surface properties of steel materials, so-called floating steel products in which the surface of steel materials is coated with inorganic or organic coatings, electrical steel sheets with insulating coatings, and organic resin liquid PI have been developed.
A steel plate etc. have been developed. In this case, the main raw material of the coating material (Yuyaku in the case of porcelain, polyester or 1llV!J resin such as epoxy in the case of MQO1-811!I resin in the case of electrical steel sheet) is applied to the steel material in an aqueous solution or an organic solvent. It is common practice to melt the material and apply it, then heat it to a predetermined temperature to cause a reaction so that it adheres to the surface of the steel material and forms a strong film. At this time, auxiliary raw materials are also added to the main raw material pool to further improve the surface properties of the steel material. Therefore, it is very important to control the amount (thickness) and composition of the coated and baked film to optimum values in order to control product quality and reduce 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 elements to be measured are light elements, it is necessary to perform the measurement in a vacuum when fluorescent X-rays are used. Therefore, for example, a sample piece punched into a disk shape is placed in the sample chamber of the Fluorescence X&1 analyzer, evacuated to a high vacuum, and analyzed, resulting in a destructive inspection.The film thickness and component composition are continuously measured on the production line. This was extremely difficult. Therefore, infrared spectroscopy has conventionally been used for such objects to be measured. As a method for continuously analyzing the thickness of a film formed on a metal surface using infrared spectroscopy, as described in JP-A-60-73407 and JP-A-58-704, interference reflected light is analyzed. There is a method of dividing the spectrum into a spectrum and calculating the film thickness from the interference waveform (hereinafter referred to as interferometry), and a method of calculating the film thickness from the interference waveform of the spectrum. A method for measuring the amount of reflected light absorbed by a film (hereinafter referred to as an absorption method) has been proposed. In the former method, as shown in FIG. 3, for example, light emitted from a light source 20 is irradiated onto a dispersion probe 22, such as a diffraction grating, and incident light 24 of a specific wavelength is selected, and then, for example, the light is collected. The coating 12 formed on the steel plate 10 is irradiated with a suitable optical system 26 including a light lens. Then, interference occurs between the reflected light 28 on the upper surface of the pIA 12 and the reflected light 30 on the lower surface of the coating. At this time, while rotating the dispersion element 22 to scan the wavelength, the reflected light 28.30 is guided to the detector 34 by an appropriate optical system 32 consisting of, for example, a condensing lens, and the intensity of the reflected light is measured. As shown in the figure, an interference waveform is obtained in which the reflection intensity is continuous depending on the wavelength. Therefore, the thickness of the coating 12 is determined from the wavelengths that form the peaks and valleys of this interference waveform. On the other hand, in the latter absorption method, the film thickness of the pA 12 can be determined by irradiating light with a specific wavelength that is absorbed by the coating 12 and light with a specific wavelength that is not absorbed by the JIi 12 and measuring the reflection intensity of each. This is the way to find out. That is, as shown in FIG. 5, for example, the light emitted from the light source 20 is passed through a filter 36 made of, for example, a multilayer filter.
After selecting the light of a specific wavelength to be absorbed by the target WA 12, the beam splitter 38 divides the light into two parts, one of which is directly incident on the detector 34A, and the other is the target WA 12 formed on the steel plate 10.
After being absorbed and reflected by the detector 34B, the reflected light 39 enters the other detector 34B. Detectors 34A, 34B
After the incident light is converted into a light intensity signal,
Sent to calculation 8140. The computer 40 calculates the transmitted incident light 24 and the reflected light 39 absorbed by the coating 12.
By comparing and calculating the two light intensity signals of
This is to calculate the film thickness of 2.

[Problems to be Solved by the Invention] However, with the former interference method, although it is possible to determine the pA thickness of the coating 12, it is not possible to analyze the composition of the coating 12. On the other hand, with the latter absorption method, it is possible to analyze the content of a certain component in the coating, but the measurement accuracy is poor due to the influence of interference, and if the coating consists of a single component or The film thickness can be determined if the content of the components in the film is constant, but if the film has multiple compositions or the content of the components in the film is not constant, the refractive index (n) of the film is constant. Therefore, it is extremely difficult to determine the film thickness. That is, although there has been a method for continuously analyzing the film thickness of a film formed on a metal surface, there has been no method for simultaneously determining the component composition of the film. Therefore, in a line that manufactures steel plates etc. with various types of coatings,
It has previously been impossible to simultaneously and continuously analyze film thickness and component composition.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a film analysis method and apparatus that can continuously and simultaneously analyze the film thickness and component composition of a film. .

[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;
Reflection spectrum of the infrared light? Determine the component composition of the film from the absorption spectrum, and at the same time,
Alternatively, the above object is achieved by irradiating the coating with light that is not completely polarized before and afterward, and determining the thickness of the coating from the interference waveform of the reflection spectrum of the glare. Further, in an embodiment of the present invention, the coating is formed on a moving light-reflecting substrate, and the film thickness and component composition of the coating are almost continuously analyzed on-line. Further, an apparatus configuration suitable for carrying out the present invention is an analyzer for a coating formed on a light-reflecting substrate that partially transmits light, in which infrared light is applied to the coating substantially at Brewster's angle. A Fourier transform infrared spectrometer including a mechanism for irradiating and a mechanism for intermittently inserting a polarizer into an optical path so that the infrared light becomes parallel polarized light, and if the infrared light is polarized, It is equipped with a calculation unit that calculates the component composition of the coating from the absorption spectrum of the infrared reflection spectrum, and calculates the film thickness of the coating from the interference waveform of the infrared reflection spectrum if the infrared light is not polarized. be.

[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-J1
At an angle that satisfies (Brewster's angle), the polarized light component perpendicular to the plane of incidence is partially reflected and -part is transmitted, but the reflection of the component parallel to the plane of incidence is zero and all is transmitted. . That is, infrared light polarized parallel to the plane of incidence is irradiated onto the coating at substantially Brewster's angle, and the reflected light at Brewster's angle is used to obtain an infrared reflection spectrum. The component composition of the coating is determined from, for example, the absorption peak of the absorption spectrum. This allows the composition to be determined without being affected by background. Furthermore, at the same time or before and after, the film is irradiated with light that is not completely polarized, and the thickness of the film is determined from the reflection spectrum of the dazzling light, for example, the interference waveform of the baseline. Therefore, for example, it is possible to simultaneously analyze the component composition and film thickness of a film online using a single Fourier transform infrared spectrometer (FT-IR).

【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, a coating 12 formed on a steel plate 10) runs in the direction indicated by arrow A in FIG. Incident light 24 of temporally interfered infrared light emitted from the FT-IR light source section 50 is incident on a concave mirror 52 for incident light, and the incident angle θ is made to substantially become Brewster's angle. , the coating 12 formed on the steel plate 10 is irradiated. The reflected light 28 from the upper surface of the coating 12 and the reflected light 30 from the lower surface are collected by the concave surface th 154 for output light, and the FT
- The light is incident on the IR detection section 56. In the optical path of the incident light 24, a polarizer 58 is driven by a polarizer drive unit 60 to an insertion position (broken line) or 'i
It is moved to the Am position (solid line). This polarizer drive unit 60
moves the finger rest section 62 of the FT-IRffilJ control section 62 and the polarizer 58. In state B (broken line) in which the optical photon 58 is inserted into the optical path, the incident light 24 becomes polarized light parallel to the plane of incidence. In the figure, 40 is a computer. The operation of the embodiment will be explained below with reference to FIG. When inputting the start of measurement into the calculator 40, the calculator 40 selects F.
T-IR9, IJ Ogoribe 62, cumulative number of repeated measurements,
A measurement start command is sent along with measurement conditions such as wavelength resolution. When the measurement is started, first, in order to move the polarizer 58 to the position shown by the solid line and retreat, the FT-IR control unit 62 instructs the polarizer drive unit 60 to move the polarizer 58 to the position shown by the solid line. Output. @The photon drive unit 60 moves the polarizer 58 to the position indicated by the solid line according to the command (step 1
10). When the movement of the polarizer 58 is completed, the FT-IR control unit 62 outputs a light emission command to the FT-IR light source unit 50, and the infrared light source and interferometer ( (not shown) to emit temporally interfered infrared light (step 112). The emitted light is irradiated onto the coating 12 at a Brewster angle θ via a concave mirror 52 for incident light. Since the incident light 24 at this time passes through the polarizer 58 and is not polarized, it is reflected by the upper and lower surfaces of the coating 12, causing an interference phenomenon. The reflected light 30 on the lower surface of the pA 12 and the reflected light 28 on the upper surface of the coating work 2 are transmitted to the FT-IR through a concave mirror 54 for output light.
The light reaches the detection unit 56 and the light intensity is detected (step 1
14). The light intensity detected by the FT-IR detection unit 56 is
This FT-IR controller 6
2, Fourier transform is performed to obtain an infrared reflection spectrum (step 116). When integrating multiple times to improve measurement accuracy, use FT-I.
The interferometer of the R light source section 50 is driven many times, and the light intensity detected and sent by the FT-IR detection section 56 is Fourier transformed in the FT-IR control section 62, and its infrared reflection spectrum is accumulated and stored. After the integration is completed, the infrared reflection spectrum stored in the FT-IR control unit 62 is sent to the computer 40. calculator 4
0 searches for the wavelengths that are the peaks and troughs of the interference waveform of the baseline in the infrared absorption spectrum where the absorption peak due to the M12 to be sent and the interference waveform overlap, and calculates the film thickness from that wavelength (step 118). For example, assuming that the peak wavelength is A1, the wavelength that is the first peak from that peak is A2, the incident angle is θ, and the refractive index of the coating is n, the film thickness t of the coating can be calculated using the following equation. t=n ・A1・A2 /j2 n'sin'#lA+ A2))...
(1) Alternatively, a method may be used in which the measured interference waveform is matched with the interference waveform obtained by theoretical calculation, and the closest film thickness t is determined. When the film thickness measurement is completed, the FT-IR control unit 6 moves the polarizer 58 to the position indicated by the broken line and inserts it into the optical path.
2 outputs a command to the polarizer drive unit 6o to move the polarizer 58 to the position indicated by the broken line. In accordance with the command, the polarizer drive unit 60 moves the polarizer 58 to the position indicated by the broken line and inserts it into the optical path (step 12).
0). Thereafter, in the same way as when measuring the film thickness, infrared light is emitted (Step 122), light intensity is detected (Step 124), and an infrared reflection spectrum is obtained by Fourier transformation and sent to the computer 40 (Step 126). At this time, the incident light 24 is polarized parallel to the plane of incidence,
Also, since the incident angle θ is Brewster's angle, the coating 12
No light 28 is reflected from the top surface, and only light 30 is reflected from the bottom surface of the coating 12. Therefore, no interference phenomenon occurs, and an infrared reflection spectrum with a flat baseline without interference waveforms can be obtained. Therefore, it is possible to improve the accuracy when determining the film components from the infrared absorption peak. The computer 40 determines the component composition of the coating 12 from, for example, the absorption peak area of the infrared reflection spectrum without interference waveforms and a previously stored calibration curve (step 128). The above is considered as one cycle of measurement, and the target Jl! on the steel plate 10!
The film thickness and component composition of 12 are almost 3! l! Continuously repeat measurements. 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 using the method of the present invention.
When compared with standard values determined from the coating amount and compounding ratio of the coating liquid, the results shown in Table 1 below were obtained. Table 1 In addition, in the method of the present invention, an infrared spectrum of 400 to 4000 CI-' is measured based on a steel plate not coated with resin,
The peak area of the absorption peak of the Si -0 stretching vibration near 1100 (111') is determined, and the silica content is determined from the peak area. In this example, a Fourier transform infrared spectrometer U (F
Since T-IR) is used, spectra in all wavelength ranges can be measured simultaneously, and the thickness and content of each component of a coating with a complex composition can be measured simultaneously and continuously at high speed. In addition,
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, it is possible to continuously and simultaneously analyze the film thickness and component composition of a partially light-transmitting film formed on a light-reflecting substrate such as a metal on-line. It becomes possible. 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 when carrying out the coating analysis method according to the present invention.
FIG. 2 is a flowchart for explaining the operation of the embodiment, and FIG. 3 is a diagram showing the conventional method for measuring film thickness by interferometry. A schematic diagram for explaining the principle; FIG. 4 is a diagram showing an example of an interference waveform obtained by the interferometry method; FIG. 5 is a schematic diagram for explaining the principle of film thickness measurement by the conventional absorption method. It is a diagram. DESCRIPTION OF SYMBOLS 10... Steel plate, 12... Coating, 24... Incident light, 40... Computer, 50... Fourier transform infrared spectrometer (FT-IR)
Light source section, 52.54... Concave mirror, θ... Incident angle, 56... FT-IR detection section, 58... Polarizer, 60... Polarizer drive section, 62-FT-IR$ I[1゜

Claims (3)

[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 Determine the component composition of the coating from the absorption spectrum of the reflection spectrum of external light, irradiate the coating with light that is not completely polarized at the same time or before and after, and determine the thickness of the coating from the interference waveform of the reflection spectrum of the light. A coating analysis method characterized by determining the (2) The coating according to claim 1, wherein the coating is formed on a traveling light-reflecting substrate, and the film thickness and component composition of the coating are almost continuously analyzed on-line. analysis method. (3) An analyzer for a coating formed on a light-reflecting substrate that partially transmits light, including a mechanism for irradiating the coating with infrared light substantially at the Brilleusta angle, and a mechanism for irradiating the coating with infrared light substantially at the Brieuster angle, and a mechanism for irradiating the coating with infrared light in parallel. A Fourier transform infrared spectrometer that includes a mechanism that intermittently inserts a polarizer into the optical path to obtain polarized light, and if the infrared light is polarized, the composition of the coating can be determined from the absorption spectrum of the infrared reflection spectrum. An arithmetic unit that calculates the film thickness of the film from the interference waveform of the infrared reflection spectrum when the infrared light is not polarized.