JP6207333B2 - Film thickness measuring method and film thickness measuring apparatus - Google Patents

Description

  The present invention relates to a film thickness measuring method and a film thickness measuring apparatus, and more particularly to a method and apparatus for measuring the film thickness of a multilayer coating film sandwiching a layer containing a bright material with high accuracy.

  Various paints are applied to the surfaces of industrial products such as automobiles, and interior materials and exterior materials of buildings for the purpose of protecting the materials and providing cosmetics, thereby forming coating films. In recent years, industrial products to which a multilayer coating film (multilayer film) has been applied in order to further enhance cosmetics are increasing. When forming a multilayer coating film, for example, on the surface of FRP or PP (polypropylene) serving as a base material, a base layer (concealing coating film) serving as an undercolor, a layer containing a glitter material such as aluminum flakes, and transparent A clear layer is formed in order. In industrial products with such a multilayer coating film, if the film thickness is thin, the specified performance cannot be achieved, and if the film thickness is thick, the coating droops or the coating film cracks. However, it is necessary to manage the film thickness within a certain range.

  As a method for measuring the film thickness of the coating film, for example, there are a method of measuring the position of the coating film surface with a laser displacement meter, and an optical coherence tomography method (Patent Document 1) that has been studied recently.

JP 2004-028618 A

  However, there are problems with the conventionally known film thickness measurement methods. For example, as a method of directly measuring the film thickness, the method of measuring the position of the coating film surface with a laser displacement meter measures the film thickness from the laser irradiation part as the base point. It was necessary to strictly manage the distance. This also has the disadvantage that the measurement system becomes complicated. Furthermore, in the optical coherence tomography described in Patent Document 1, since the resolution in the depth direction (thickness direction) of the film is insufficient, and a large number of optical elements are combined, the measurement system becomes complicated and large. There was a drawback.

  Furthermore, even in the optical coherence tomography described in Patent Document 1, a bright material such as a reflective metal flake is included in any coating film constituting the multilayer coating film to be measured. In addition, the interference intensity at the interface between the layers is not stable, and it is difficult to measure the correct film thickness.

  FIG. 1 is a schematic diagram for explaining problems in measuring the film thickness of a multilayer coating film using optical coherence tomography (Optical Coherence Tomography). In the figure, (A) is a cross-sectional view showing a coating film structure of a multilayer coating film, and (B) is a schematic diagram showing an interference waveform of the coating film.

  Here, for the sake of explanation, as shown in FIG. 1 (A), a base layer (FRP), a base layer (a concealing coating layer) serving as an undercolor, an aluminum base layer (bright material layer), a transparent layer A case where the film thickness is measured by the optical coherence tomography method for the structure in which the clear layer CC is sequentially laminated is taken as an example.

  A colored pigment for characterizing the hue of the coating film is contained in the undercolor base layer. In the aluminum base layer, a glittering material such as aluminum flake 101 is included in order to impart cosmetics. The description will focus on the aluminum base layer. The incident light OCT light is not reflected by the aluminum flakes 101 but reflected at the interface c between the aluminum base layer and the lower color base layer or within the lower color base layer ( I) and the case (II) reflected by the aluminum flake 101.

  In the case (I), the OCT light is multiply scattered by the titanium dioxide contained as a pigment in the lower color base layer, so that a plurality of peaks having different wave heights appear in the lower color base layer as indicated by reference numeral 102. Appears in the corresponding area. In the case (II), as the OCT light is reflected by the aluminum flakes 101 in the aluminum base layer, a peak having a high wave height appears randomly in a region corresponding to the aluminum base layer as indicated by reference numeral 103.

  When measuring the film thickness of the coating film using the optical coherence tomography, the film thickness is calculated from the intervals between the peak signals of a plurality of interference waveforms obtained by the measurement. However, when the multilayer coating film sandwiches the layer containing the glitter material, the interference waveform actually obtained by the measurement includes both cases (I) and (II) indicated by reference numerals 102 and 103. Since interference waveforms are mixed, it is difficult to specify the interface between the layers, and it is difficult to measure the correct film thickness.

  The present invention has been made to solve the above-described problems of the prior art, and its purpose is to measure the film thickness of a multilayer coating film sandwiching a layer containing a glittering material with high accuracy. The object is to provide a film thickness measuring method and apparatus capable of performing

  In order to achieve the above object, the first film thickness measurement method according to the present invention determines the film thickness of a multilayer coating film from the interval between peaks of a plurality of intensity signals of an interference waveform obtained by optical coherence tomography. A method of calculating, wherein the multilayer coating film is a coating film in which a base material layer, a base coating film layer, a glittering material layer, and a clear layer are sequentially laminated, and the pigment substance in the base coating film layer Multiple scattering of light occurs, and the multilayer coating film is irradiated with light from a light source to detect the intensity of interference light including reflected light from each layer or the interface between the layers in the multilayer coating film. An interference waveform acquisition step of acquiring an interference waveform of a plurality of intensity signals corresponding to each of the layers in the multilayer coating film or an interface between the layers, and a plurality in a predetermined region on the multilayer coating film In a place, the interference waveform acquisition step is repeatedly performed a predetermined number of times, and a plurality of the A multi-point measurement step of obtaining a interference waveform; an integration step of integrating a plurality of the interference waveforms to obtain an integrated interference waveform; and the glittering material layer and the base coating layer in the integrated interference waveform In the first interface specifying step for specifying the position of the peak of the first intensity signal corresponding to the interface with the multi-layer, either in the integrated interference waveform or in the plurality of interference waveforms before integration A second interface identifying step for identifying a position of a peak of a second intensity signal corresponding to an interface between the air layer surrounding the coating and the clear layer; and the peak position of the first intensity signal; A film thickness measurement method including a film thickness calculation step of calculating a film thickness corresponding to the sum of the film thickness of the clear layer and the film thickness of the glitter material layer from an interval from the peak position of the second intensity signal. It is.

  In order to achieve the above object, the second film thickness measurement method according to the present invention provides a film of a multilayer coating film from an interval between peaks of a plurality of intensity signals of an interference waveform obtained by optical coherence tomography. A method of calculating a thickness, wherein the multilayer coating film is a coating film in which a base material layer, a base coating film layer, a glittering material layer, and a clear layer are laminated in order, Multiple scattering of light is caused by the pigment substance, and the multilayer coating film is irradiated with light from a light source to reduce the intensity of interference light including reflected light from each layer or the interface between the layers in the multilayer coating film. An interference waveform acquisition step of detecting and acquiring an interference waveform of a plurality of intensity signals corresponding to each of the layers in the multilayer coating film or the interface between the layers; and in a predetermined region on the multilayer coating film The interference waveform acquisition step is repeatedly executed a predetermined number of times at a plurality of locations. A multi-point measurement step of obtaining the interference waveform; an integration step of integrating a plurality of the interference waveforms to obtain an integrated interference waveform; and the glitter material layer and the base coating film in the integrated interference waveform A first interface specifying step for specifying a position of a peak of a first intensity signal corresponding to an interface with a layer, and each of the plurality of intensity signals included in each of the interference waveforms before integration; Identifying the position of the peak of the third intensity signal corresponding to the interface between the clear layer and the glitter material layer by determining whether the signal has an interference intensity greater than a predetermined threshold; A third interface specifying step; a bright material layer thickness calculating step for calculating a film thickness of the bright material layer from an interval between a peak position of the first intensity signal and a peak position of the third intensity signal; The No, a film thickness measuring method.

  In order to achieve the above object, a first film thickness measuring apparatus according to the present invention is a film of a multilayer coating film, based on an interval between peaks of a plurality of intensity signals of an interference waveform obtained by optical coherence tomography. An apparatus for calculating a thickness, wherein the multilayer coating film is a coating film in which a base material layer, a base coating film layer, a bright material layer, and a clear layer are laminated in order, Multiple scattering of light is caused by the pigment material, a light source, branching means for branching light from the light source into reference light and incident light to the multilayer coating film, and reference light for adjusting the optical distance of the reference light An optical system; a reflected light optical system that causes the incident light to be incident on the multilayer coating film; and that extracts reflected light from the multilayer coating film; and the reflected light from the reflected light optical system and the reference light optics Interference means for causing interference with the reference light from the system, and interference light including the reflected light from the interference means. A detection means for outputting the intensity signal of the interference light and an analysis means for analyzing the intensity signal, the detection means reflecting each layer in the multilayer coating film or reflected light from the interface between the layers And detecting interference waveforms of a plurality of intensity signals corresponding to the respective layers in the multilayer coating film or the interface between the layers, and detecting a predetermined intensity on the multilayer coating film. The acquisition of the interference waveform is repeatedly performed a predetermined number of times at a plurality of locations in the region to acquire a plurality of the interference waveforms, and the analysis unit adds up the plurality of interference waveforms and integrates the interference waveforms. In the integrated interference waveform, the position of the peak of the first intensity signal corresponding to the interface between the glitter material layer and the base coating layer is specified, and the integrated interference waveform or the pre-integration Any one of the plurality of interference waveforms And specifying the position of the peak of the second intensity signal corresponding to the interface between the air layer around the multilayer coating and the clear layer, and the peak position of the first intensity signal and the second It is a film thickness measuring device that calculates a film thickness corresponding to the sum of the film thickness of the clear layer and the film thickness of the glitter material layer from the interval from the peak position of the intensity signal.

  In order to achieve the above object, the second film thickness measuring device according to the present invention is a film of a multilayer coating film from the interval between peaks of a plurality of intensity signals of an interference waveform obtained by an optical coherence tomography method. An apparatus for calculating a thickness, wherein the multilayer coating film is a coating film in which a base material layer, a base coating film layer, a bright material layer, and a clear layer are laminated in order, Multiple scattering of light is caused by the pigment material, a light source, branching means for branching light from the light source into reference light and incident light to the multilayer coating film, and reference light for adjusting the optical distance of the reference light An optical system; a reflected light optical system that causes the incident light to be incident on the multilayer coating film; and that extracts reflected light from the multilayer coating film; and the reflected light from the reflected light optical system and the reference light optics Interference means for causing interference with the reference light from the system, and interference light including the reflected light from the interference means. A detection means for outputting the intensity signal of the interference light and an analysis means for analyzing the intensity signal, the detection means reflecting each layer in the multilayer coating film or reflected light from the interface between the layers And detecting interference waveforms of a plurality of intensity signals corresponding to the respective layers in the multilayer coating film or the interface between the layers, and detecting a predetermined intensity on the multilayer coating film. The acquisition of the interference waveform is repeatedly performed a predetermined number of times at a plurality of locations in the region to acquire a plurality of the interference waveforms, and the analysis unit adds up the plurality of interference waveforms and integrates the interference waveforms. In the integrated interference waveform, the peak position of the first intensity signal corresponding to the interface between the glitter material layer and the base coating layer is specified and included in each of the interference waveforms before integration. That of a plurality of said intensity signals Accordingly, by determining whether or not the intensity signal has an interference intensity greater than a predetermined threshold value, the peak of the third intensity signal corresponding to the interface between the clear layer and the glittering material layer is obtained. It is a film thickness measuring device which specifies a position and calculates the film thickness of the glittering material layer from the interval between the peak position of the first intensity signal and the peak position of the third intensity signal.

  According to the present invention, the film thickness of a multilayer coating film sandwiching a layer containing a glittering material can be measured with high accuracy. In particular, in the present invention, since a plurality of interference waveforms are integrated by paying attention to the difference in the appearance frequency of peaks of the interference waveform, the coating film having a very low interference intensity (that is, not affected by the intensity of the interference waveform (that is, Even with a coating film having a low light reflection intensity, it is possible to measure the film thickness with high accuracy.

It is a schematic diagram for demonstrating the problem at the time of measuring the film thickness of a multilayer coating film using the optical coherence tomography (Optical Coherence Tomography). It is a block diagram which shows schematic structure of the film thickness measuring apparatus of the coating film used in embodiment of this invention. It is a schematic diagram explaining the example which measures with respect to the sample of a multilayer coating film using the film thickness measuring apparatus shown in FIG. 2, and analyzes a detection signal. It is a flowchart which shows the procedure of the film thickness measuring method which concerns on embodiment of this invention. It is a schematic diagram explaining the concept of the data processing performed in the film thickness measuring method which concerns on embodiment of this invention. It is a schematic diagram which shows the result of having measured the interference waveform with respect to the multilayer coating film shown in FIG. 1 with the film thickness measuring method which concerns on embodiment of this invention. It is a graph showing the correspondence of the result of the film thickness measurement which concerns on embodiment of this invention, and the film thickness measurement result by an electromagnetic film thickness meter.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, in the following description and drawings, the same reference numerals indicate the same or similar components, and thus descriptions of the same or similar components are omitted.

  In the following, first, a method for measuring the film thickness of a coating film using the optical coherence tomography method will be described, and then, as one embodiment of the present invention, the coating film configuration shown in FIG. 1 is the same. A method for measuring the film thickness of a multilayer coating film sandwiching a layer containing a glittering material as a measurement target will be described.

(1) Film thickness measurement by optical coherence tomography In the optical coherence tomography method used in the present invention, near infrared light having a high position resolution and high transparency to the coating film is used as a preferred light source for measurement light, and the light source is branched into two. When the optical distance between the two optical paths coincides while irradiating the light beam of one measurement system optical path to the coating film and using the light beam of the other reference system optical path as the reference light and controlling at least the optical distance of the reference system optical path The film thickness of the coating film is measured by measuring the interference light generated by superimposing the reflected light from the coating film and the reference light.

  In the present invention, since the light interference phenomenon is used, it is necessary to evaluate the distance that the light passes in wavelength units. In the present invention, since the light passes through different media (air, each layer in the coating film), the wavelength changes. Accordingly, in this specification, “distance” means “optical distance” in consideration of the refractive index of the medium unless otherwise specified.

(1-1) Apparatus Configuration FIG. 2 is a block diagram showing a schematic configuration of a coating film thickness measuring apparatus used in the embodiment of the present invention.

  The coating thickness measuring apparatus used in this embodiment employs OCT (Optical Coherence Tomography) using the principle of Michelson interferometer, and uses light from the light source and the light source. A first optical unit that causes interference, a second optical unit that irradiates the sample of the coating film with light and makes reflected light from the sample enter the first optical unit, and a third optical unit that controls the reference light And a light receiving and amplifying unit that receives and amplifies the interference light, and an analysis unit that records and analyzes the result of the amplification.

  More specifically, the film thickness measuring apparatus includes a light source 1, a beam splitter 2, a focusing lens 3, a cross mirror 5 with a position variable mechanism, a fixed mirror 6, a light receiving sensor 7, an amplifier 8, and a computer. 9. The beam splitter 2 branches the light generated by the light source 1 into incident light and reference light, and superimposes reflected light and reference light described later to cause interference. The focusing lens 3 focuses the incident light and irradiates the sample 4, and returns the reflected light from the sample 4 to the beam splitter 2. The cross mirror 5 with a position variable mechanism changes the optical distance of the reference light and returns the reference light to the beam splitter 2. The moving distance (physical distance) of the crossing mirror 5 with a position variable mechanism is transmitted to the computer 9 via a known interface. The fixed mirror 6 is a mirror fixed to the intersecting mirror 5 with a position variable mechanism. The light receiving sensor 7 receives the interference light. The amplifier 8 amplifies the output signal of the light receiving sensor 7. The computer 9 analyzes the amplified signal.

  In the present embodiment, the beam splitter 2 corresponds to the first optical unit, the focusing lens 3 corresponds to the second optical unit, the intersecting mirror 5 with a position variable mechanism and the fixed mirror 6 correspond to the third optical unit, The light receiving sensor 7 and the amplifier 8 correspond to a light receiving amplification unit, and the computer 9 corresponds to an analysis unit.

  As will be described later, in the present embodiment, the film thickness measuring device is realized as a portable portable measuring instrument, and performs measurement (multi-point measurement) at a plurality of locations on the surface of the multilayer coating film. A measurer moves the film thickness measuring device in small increments with respect to the sample 4, and the computer 9 controls the operation of each part of the film thickness measuring device, whereby a series of steps of film thickness measurement is executed.

(1-2) Operation of Apparatus An example of the operation of the film thickness measuring apparatus shown in FIG. 2 will be described. Here, since the operation of the apparatus is intended to be described, in order to simplify the description, the multilayer coating film of sample 4 is an example in which a layer including a glittering material is not sandwiched therebetween. explain.

  Sample 4 is a multilayer coating film (FIG. 3A) formed of, for example, three coating film layers A to C on an object D to be coated, and is placed on a predetermined table (not shown). ing. Light emitted from an SLD (Super Luminescent Diode) that is the light source 1 is branched by the beam splitter 2 into reference light that travels straight and incident light whose traveling direction has been changed. Incident light is incident on the sample 4 by the focusing lens 3, and reflected light from the sample 4 is also incident on the beam splitter 2 via the focusing lens 3. On the other hand, the crossing mirror 5 with a variable position mechanism changes the direction of the reference light while being moved, for example, from the left to the right in the direction indicated by the arrow X in FIG. 2, that is, while changing the optical distance of the reference light. Reference light is incident on the beam splitter 2. At this time, in the beam splitter 2, the reflected light from the sample 4 and the reference light from the intersecting mirror 5 with a position variable mechanism overlap each other, causing interference. The interference light thus formed is received by the light receiving sensor 7. The amplifier 8 amplifies the output of the light receiving sensor 9, and the computer 9 analyzes the output of the amplifier 8 and calculates the film thickness of the coating film by a method described later.

  The reason for moving the cross mirror 5 with the position variable mechanism, that is, the reason for scanning the position of the cross mirror 5 with the position variable mechanism is to change the optical distance of the reference light. When the beam splitter 2 overlaps the reflected light from the sample 4, the reference light interferes with the reflected light from a predetermined distance in the depth direction of the sample 4 according to the optical distance. That is, the intensity of the interference light increases when the optical distance of the reference light is equal to the optical distances of the incident light and the reflected light.

  For example, first, in the arrangement shown in FIG. 2, the distance from the beam splitter 2 to the fixed mirror 6 via the crossing mirror 5 with a position variable mechanism is set to the same distance as the distance from the beam splitter 2 to the surface of the sample 4. . Next, from this state, when the cross mirror 5 with a position variable mechanism is moved to the right by the thickness of the coating layer A which is the first layer, the reference light is reflected at the interface of the bottom surface of the coating layer A. Causes interference with light.

  Therefore, in order to measure the film thickness of the coating layer A, it is necessary to scan the entire thickness of the coating layer A even if the position of the intersecting mirror 5 with the position variable mechanism is at a minimum.

  When this film thickness measuring apparatus is realized as an inexpensive and simple portable apparatus, the apparatus is configured in combination with, for example, a TD (Time Domain) method. In the case of the TD method, the crossing mirror 5 which is a reference mirror is moved at a constant speed, and interference occurring at a position where the optical distance of the reference system optical path coincides with the optical distance of the measurement system optical path is observed. Get time-axis information. Since the reflected light is arranged along the time axis (the horizontal axis in FIG. 3B described later becomes the time axis), the number information of the coating films is obtained from the number of the obtained reflected lights. Further, distance information is obtained from time-axis information. That is, the information on the time axis is converted into the physical distance moved by the reference mirror, further converted into the optical distance, and further converted into the physical distance of the film, thereby obtaining the physical distance (film thickness) between the multilayer films. be able to. For example, if the time when the interference with the outermost surface is measured is t0 and the scanning speed is constant v, the moving distance Z of the reference mirror to the next interface measured at time t1 is Z = (t1−t0) / It can be obtained by v.

(1-3) Film thickness measuring method The film thickness measuring method of a multilayer coating film is demonstrated based on the typical measurement result obtained using the film thickness measuring apparatus shown in FIG. In the following description, a case where one part of a sample is measured will be described for the sake of simplicity. However, in the present embodiment, as described later, the film thickness measuring device is within a predetermined range on the sample. Measure reflected light at multiple locations. In order to measure a plurality of portions of the coating film linearly or planarly, the film thickness measuring apparatus is realized as a portable portable measuring instrument.

  FIG. 3 is a schematic diagram for explaining an example in which a sample of a multilayer coating film is measured using the film thickness measuring apparatus shown in FIG. 2 and a detection signal is analyzed. In the figure, (A) shows a sample of a multilayer coating film composed of coating film layers A to C, and (B) shows a profile representing the relationship between interference light intensity and optical distance.

  Since the refractive index between adjacent layers in the sample is different, when the sample is irradiated with measurement light (measurement light) from the light source 1 shown in FIG. 2, the measurement light is reflected on the upper surface of each layer of the sample and reflected light is reflected. a, b, c, d are generated.

  Each of these reflected lights interferes with and strengthens the reference light having an optical distance adjusted to cause interference, and is received by the light receiving sensor 7 to obtain the four peak signals shown in FIG. . Here, the horizontal axis of FIG. 3B represents the optical distance between the obtained interference lights, and the vertical axis represents the intensity of the received interference light. Reference numerals a to d attached to the peak signal in FIG. 3B correspond to the reflected lights a to d in FIG. As shown in FIG. 3B, among the intervals between the three peaks defined by the four peak signals a to d, the interval between the peak signals a and b is that of the film that generates the reflected lights a and b. It corresponds to the film thickness (that is, the film thickness of the coating film layer A), and the interval between the peak signals b to c corresponds to the film thickness of the film that generates the reflected lights b and c (that is, the thickness of the coating film layer B). The interval between the peak signals c to d corresponds to the film thickness (that is, the thickness of the coating film layer C) of the film that generates the reflected lights c and d.

  With reference to the relationship diagram (profile) between the intensity of interference light and the optical distance obtained in this way, the number of layers of the multi-layer coating film can be determined from the number of measured peaks (signals). The relative thickness of the layers can be seen from the spacing.

  The actual physical thickness T of each film in the multilayer coating film can be obtained by the following formulas 1 and 2.

Film thickness T = Optical distance L / Refractive index n (Formula 1)
Optical distance L = Z × n ^* (Formula 2)
Here, Z is a physical distance traveled by the cross mirror 5 with a position variable mechanism to obtain the film thickness T, n ^* is the refractive index of air, and n is the refractive index of the film. The interval between peaks shown in FIG. 3B corresponds to the optical distance of each layer. In other words, the interval between peaks is the moving distance (optical distance) of the cross mirror 5 with a position variable mechanism required to obtain a peak between adjacent peaks. In this way, the thickness of each layer of the multilayer coating can be calculated.

  Note that, as a light source used for measuring the film thickness, a wavelength of 780 nm or less (visible light) is not preferable because it may be affected by absorption and scattering due to impurities such as moisture. On the other hand, at a wavelength of 3000 nm or more, the spatial resolution of the film thickness measuring device becomes larger than the distance necessary for separating and detecting the layers of the coating film, so that the multilayer coating film cannot be analyzed accurately. In consideration of such spatial resolution and transmittance, the light source used in the present invention is near infrared light having a wavelength in the range of 780 nm to 3000 nm, preferably in the range of 1300 nm to 2000 nm.

(2) Film thickness measurement when the multilayer coating film sandwiches the layer containing the glittering material Next, based on the above-described method of measuring the film thickness by the optical coherence tomography method, the multilayer coating film becomes the glittering material. A method for measuring a film thickness in the case where a layer including the layer is interposed will be described.

  As described with reference to FIG. 1, when the multilayer coating film sandwiches the layer containing the glittering material, the OCT light that is incident light is not reflected by the aluminum flakes 101 and is not reflected by the aluminum base layer. There are both cases (I) of reflecting in the interface c with the color base layer or the lower color base layer and cases (II) of reflecting by the aluminum flakes 101. The interference waveform actually obtained by measurement is as follows. Since the interference waveforms in both cases (I) and (II) indicated by reference numerals 102 and 103 are mixed, it is difficult to specify the interface between the layers, and it is difficult to measure the correct film thickness. It was. In the present invention, by integrating the data of the interference waveform obtained by the measurement, the problem caused by mixing of the interference waveforms, that is, the problem that the interface b and the interface c could not be specified is solved. ing.

(2-1) Outline of Measurement Method FIG. 4 is a flowchart showing the procedure of the film thickness measurement method according to the embodiment of the present invention.

  An outline of the measurement method will be described with reference to the flowchart of FIG. First, in step S1, an interference waveform is measured at one location on the coating film, and interference waveforms having intensity peaks respectively corresponding to the interfaces a to c in the multilayer coating film are obtained. Next, in step S2, such interference waveform acquisition in step S1 is performed at a plurality of locations on the coating film, and in step S3, a plurality of interference waveforms obtained by such multipoint measurement are integrated (S3). To do. Next, in step S4, the position of the intensity peak of the interference waveform corresponding to the interface c between the glitter material layer and the base coating film layer is specified, and in step S5, the interface a between the air layer and the clear layer on the coating film surface. The position of the intensity peak of the interference waveform corresponding to is specified. Then, from the intervals between the intensity peaks respectively corresponding to the specified interface a and interface c, in step S6, the sum of the film thickness of the clear layer and the film thickness of the glittering material layer corresponding to the interface a to c is obtained. Calculate the corresponding film thickness.

  FIG. 5 is a schematic diagram for explaining the concept of data processing performed in the film thickness measuring method according to the embodiment of the present invention.

An example of the measurement result (step S1) of the interference waveform at an arbitrary point on the coating film is as shown in FIG. In the present invention, as shown in FIG. 5B, the interference waveform is measured a plurality of times (multi-point measurement) within a predetermined range (for example, 1 cm ² ) on the coating film (step S2). Accurate film thickness measurement is realized by integrating a plurality of interference waveforms obtained by the above measurement (step S3). FIG. 5C shows an example of the measurement result of multipoint measurement.

  In the graph shown in FIG. 5C, the peak position of the interference waveform is plotted on the vertical axis. That is, the vertical axis of the graph of FIG. 5C corresponds to the horizontal axis (optical distance) of the graph of FIG. 5A, and the horizontal axis of the graph of FIG. Corresponds to the number of points on the film where the measurements were made. As shown in FIG. 5 (B), when the measurer moves the portable film thickness measuring device at a constant speed and performs multipoint measurement, the horizontal axis of the graph of FIG. 5 (C) corresponds to the time axis. I can say that.

  As shown in FIG. 1 or FIG. 5B, the interface between the air layer and the transparent clear layer CC is a, the interface between the clear layer CC and the aluminum base layer is b, the aluminum base layer and the undercolor base layer are 5 represents the interface between the lower color base layer and the base material layer, and the line denoted by reference numeral 41 in FIG. 5C corresponds to the interface a, and the line denoted by reference numeral 42 corresponds to the interface b. Correspondingly, a line indicated by reference numeral 43 corresponds to the interface c. That is, if the positions of these lines 41 to 43 are specified in the graph of FIG. 5C, the film thickness of the clear layer CC and the film thickness of the aluminum base layer are individually determined from the intervals between the peaks. Can be calculated.

  Among these, as for the position of the interface a corresponding to the line 41, as long as the coating film is flat, the peak position of the interference waveform at the interface a between the air layer and the clear layer CC is constant through multipoint measurement. Thereby, the position of the interface a can be specified. Therefore, if the position of the line 43 is specified among the lines 42 and 43, the film thickness of the clear layer CC + the aluminum base layer can be calculated. If the position 42 is specified, the film thickness of the clear layer CC and the film thickness of the aluminum base layer can be calculated individually. In FIG. 5A, the peak of the interference waveform does not appear at the interface b between the clear layer CC and the aluminum base layer. The reason is that the difference in refractive index between these layers is small, and the interference of OCT light is substantially negligible.

  Referring to FIG. 5C, it can be understood that the cross-sectional structure (cross-sectional image) of the multilayer coating film is visualized. The area between the line 41 and the line 42 corresponds to the clear layer CC, and the peak position of the interference waveform is not plotted in this area. This means that there are no defects or impurities in the clear layer CC.

  A region between the line 42 and the line 43 corresponds to an aluminum base layer, and in this region, the peak positions of the interference waveform are randomly distributed. This indicates that the aluminum flakes 101 are randomly distributed in the aluminum base layer (reference numeral 103 in FIG. 1). Also, the number of plots (points) is small compared to the area below the line 43. This is because multiple scattering of OCT light occurs in the undercolor base layer described later. The concentration of aluminum flakes is also relatively low. For reference, in the present embodiment, the concentration of aluminum flakes is about 0.1 phr (Per Hundred Resin: part by weight) to about 3 phr.

  The area below the line 43 corresponds to the lower color base layer and the base material layer, and the peak positions of the interference waveform are also randomly distributed in this area. However, the number of plots (points) is large compared to the region corresponding to the aluminum base layer. These facts obtained from the measurement data indicate that the OCT light is multiply scattered by the titanium dioxide contained as a pigment in the undercolor base layer (reference numeral 102 in FIG. 1).

(2-2) Procedure for Determining Interface between Each Layer A procedure for specifying the positions of the lines 42 and 43 shown in the graph of FIG. 5C will be described. As described above, since the peak position of the interference waveform at the interface a is constant throughout the multipoint measurement, the position of the line 41 (that is, the interface a) can be specified by this.

  A mode for specifying the position of the line 43 corresponding to the interface c will be described. In the present embodiment, the position of the interface c is specified by integrating a plurality of interference waveforms obtained by multipoint measurement. If multiple scattering of OCT light occurs in the lower color base layer or the concentration of the aluminum flake 101 contained in the aluminum base layer is lower than the concentration of titanium dioxide in the lower color base layer, the aluminum flake 101 The frequency of reflection is relatively low, and the frequency of reflection by titanium dioxide is relatively high. Therefore, even if the interference intensity due to the reflection of the aluminum flake 101 is relatively higher than the interference intensity due to the titanium dioxide, the frequency of reflection by the titanium dioxide is dominant. Therefore, a plurality of interference waveforms obtained by multipoint measurement are integrated. Then, in the interference waveform after integration, reflection (I) in the lower color base layer containing titanium dioxide becomes dominant.

  FIG. 6 is a schematic diagram showing the result of measuring the interference waveform for the multilayer coating film shown in FIG. 1 by the film thickness measurement method according to the embodiment of the present invention. FIG. 6A is a schematic diagram showing a measurement result of an interference waveform at an arbitrary point on the multilayer coating film, and FIG. 6B is an interference waveform within a predetermined range on the multilayer coating film. It is a schematic diagram showing the result of having performed multipoint measurement (for example, 200 points) and integrating a plurality of obtained interference waveforms.

  As shown in FIG. 6A, the measurement result shows that the OCT light, which is incident light, is not reflected by the aluminum flakes 101, but at the interface c between the aluminum base layer and the lower color base layer or in the lower color base layer. The interference waveforms of both the case (I) that reflects and the case (II) that reflects by the aluminum flake 101 are mixed. The interference waveform indicated by symbol (I) in FIG. 6A is an interference waveform corresponding to case (I) in FIG. 1, and the interference waveform indicated by symbol (II) is equivalent to case (II) in FIG. It is an interference waveform.

  Here, as described with reference to FIG. 5C, when multipoint measurement is performed, in the region corresponding to the aluminum base layer, the number of plots is plotted in the region corresponding to the undercolor base layer. Less than the number of. On the other hand, in the region corresponding to the undercolor base layer, the number of plots is larger than the number of plots in the region corresponding to the aluminum base layer due to the influence of multiple scattering of the OCT light. That is, when multiple scattering of OCT light occurs in the lower color base layer, or when the concentration of aluminum flakes is relatively low at 0.9 phr, the frequency of reflection by aluminum flakes in the aluminum base layer is low. Low, meaning that the frequency of reflection by titanium dioxide in the undercolor base layer is high.

  Therefore, when focusing on such a frequency difference and referring to the integration result of the interference waveform shown in FIG. 6 (B), the reflection (I) in the undercolor base layer having a high frequency is dominant. It can be said that the intensity peak of the interference waveform after integration indicated by reference numeral 51 in the drawing corresponds to the reflection in case (I), that is, the interface c between the aluminum base layer and the undercolor base layer. Therefore, the position of the intensity peak indicated by the reference numeral 51 corresponds to the position of the line 43 (that is, the interface c).

  Thereby, since the position of the line 41 has already been specified, the interface a is determined from the interval between the position of the interference peak of the interface a corresponding to the line 41 and the position of the interference peak of the interface c corresponding to the line 43. The film thickness of the clear layer CC + aluminum base layer corresponding to between the interfaces c can be calculated.

  FIG. 7 is a graph showing a correspondence relationship between the film thickness measurement result and the film thickness measurement result obtained by the electromagnetic film thickness meter according to the embodiment of the present invention. In the graph, the measured value of the film thickness obtained by the present invention is plotted on the vertical axis of the graph, and the measured value of the film thickness obtained by the electromagnetic film thickness meter is plotted on the horizontal axis of the graph.

  As shown in the graph of FIG. 7, the result of the film thickness measurement according to the present invention shows a very good correspondence with the result of the film thickness measurement by the electromagnetic film thickness meter. Therefore, it was shown that the film thickness measurement method according to the present invention is a highly accurate measurement method that can replace the film thickness measurement by the electromagnetic film thickness meter.

  Thus, according to the present invention, the film thickness of the multilayer coating film sandwiching the layer containing the glittering material can be measured with high accuracy. In particular, in the present invention, since a plurality of interference waveforms are integrated by paying attention to the difference in the appearance frequency of peaks of the interference waveform, the coating film having a very low interference intensity (that is, not affected by the intensity of the interference waveform (that is, Even with a coating film having a low light reflection intensity, it is possible to measure the film thickness with high accuracy.

  As mentioned above, although this invention was demonstrated by specific embodiment, this invention is not limited to above-described embodiment. The film thickness measuring apparatus shown in FIG. 2 and the above-described embodiment are merely examples, and those skilled in the art can make various changes and substitutions within the scope of the technical idea of the present invention.

  For example, in addition to specifying the position of the line 43 corresponding to the interface c described above, the position of the line 42 corresponding to the interface b can be specified. In this aspect, the interference waveform of case (II) reflected by the aluminum flakes is extracted by statistically processing the frequency distribution of the peak of the interference waveform due to the reflection of the aluminum flakes.

  When the film thickness of the coating film is measured using the optical coherence tomography method, light interferes with the difference in refractive index from the air on the coating film surface, and the interference waveform on the coating film surface has the strongest interference waveform. As a result of observation by the inventors of the present invention for various multilayer coating films, it was found that the interference intensity at the interface between the coating films was less than 0.4, assuming that the interference intensity on the coating film surface was 1. Considering the fact that the reflection intensity of light by the aluminum flake 101, which is a bright material, is relatively stronger than the interference intensity at the interface between the coating films, the reflection by the aluminum flake 101, that is, the case (II) in FIG. As a threshold value in statistical processing when extracting a corresponding interference waveform, the interference intensity can be set to about 0.5 to 1.5, for example.

Based on the threshold condition that the interference intensity is about 0.5 to 1.5, the interference waveform is selected for each interference waveform obtained by multipoint measurement, and a plurality of peaks of the selected interference waveform are selected. The position of the interface b (the position of the line 42) is specified based on the position of . In this case, since all the positions of the three interfaces a to c are specified, the film thickness of the clear layer CC and the film thickness of the aluminum base layer can be calculated individually.

  Here, in the above embodiment, the position of the interface c is specified by integrating a plurality of interference waveforms obtained by multipoint measurement. However, a plurality of interference waveforms at a plurality of measurement points are integrated. Before each measurement at one point, an interference waveform (reflection by the aluminum flake 101) corresponding to case (II) in FIG. 1 is extracted in advance by statistical processing using a threshold, and the measurement point After subtracting this extracted interference waveform from the interference waveform obtained for one point in advance, a plurality of interference waveforms for a plurality of measurement points may be integrated. Thereby, the interference waveform corresponding to case (I) in FIG. 1 becomes more dominant, and the position of the interface c can be specified more strictly.

  In the above embodiment, the position of the interface a corresponding to the line 41 is calculated from the peak position of the integrated interference waveform after multipoint measurement, but the position of the interface a is arbitrary on the coating film. It may be calculated from the peak position of the interference waveform at one point. As long as the coating film is flat, the peak position of the interference waveform at the interface a between the air layer and the clear layer CC is constant.

  Further, in the film thickness measuring apparatus shown in FIG. 2, it is sufficient that the optical distance of the measuring system and the optical distance of the reference system coincide with each other in order to obtain interference light. The lens 3, the crossing mirror 5, and the fixed mirror 6 can be relatively freely arranged. That is, the arrangement of these constituent elements may be any arrangement that matches the optical path lengths of the two optical systems. Further, the optical system itself may be realized as various systems in which, for example, a half mirror or a total reflection mirror is arranged.

  Moreover, in said embodiment, the structure which controls the optical distance of a reference beam is made into the crossing mirror 5 with a position variable mechanism in which a linear reciprocation is possible. That is, the moving mechanism of the crossing mirror 5 is a linear motion mechanism. However, for example, a rotating mechanism capable of stable position scanning is realized by fixing the crossing mirror on the rotating disk, connecting the rotating disk and the motor shaft, and rotating the motor at a constant speed. The optical distance of light may be controlled. The position of the crossing mirror 5 with a position variable mechanism can be controlled by, for example, a stepping motor, and highly accurate position control is possible. A servo motor may be used in place of the stepping motor. In this case, position control with higher accuracy is possible compared to the case of using the stepping motor.

  In the above-described embodiment, an SLD (Super Luminescent Diode) is used as a measurement light source. However, in addition to the SLD, various lights that do not require coherency such as an LED (Light Emitting Diode) can be used. .

  As the light receiving sensor, a photomultiplier tube, a photodiode, or the like can be used. An amplification method for amplifying the output of the light receiving sensor is not particularly defined, but a lock-in amplifier can be used to increase accuracy.

  In the above embodiment, when the position of the cross mirror 5 with a position variable mechanism is adjusted to a position where the intensity of the interference light reaches a peak, the position of the cross mirror 5 with a position variable mechanism is acquired and transmitted to the computer 9. However, the position of the cross mirror 5 with the position variable mechanism is continuously scanned in the thickness direction of the multilayer coating film to be measured, and the intensity of the interference light and the cross with the position variable mechanism are crossed. When the set of the moving distance (physical distance) of the mirror 5 is transmitted to the computer 9 as needed, and after the scan is completed, the computer 9 analyzes the set data and the intensity of the interference light reaches a peak. The position of the crossing mirror 5 with the position variable mechanism may be determined.

DESCRIPTION OF SYMBOLS 1 Light source 2 Beam splitter 3 Focusing lens 4 Sample of multilayer coating 5 Crossing mirror with position variable mechanism 6 Fixed mirror 7 Light receiving sensor 8 Amplifier 9 Computer

Claims (20)

From the interval between peaks of a plurality of intensity signals of the interference waveform obtained by the optical coherence tomography method,
The multilayer coating film is a coating film in which a base material layer, a base coating film layer, a glittering material layer, and a clear layer are sequentially laminated, and multiple scattering of light occurs due to the pigment substance in the base coating film layer. ,
The multilayer coating film is irradiated with light from a light source to detect the intensity of interference light including reflected light from each layer in the multilayer coating film or an interface between the layers, and the multilayer coating film Obtaining an interference waveform of a plurality of intensity signals corresponding to each of the layers or the interface between the layers; and
In a plurality of locations in a predetermined region on the multilayer coating film, the interference waveform acquisition step is repeatedly performed a predetermined number of times to obtain a plurality of interference waveforms, and
An integration step of integrating a plurality of interference waveforms to obtain an integrated interference waveform;
A first interface specifying step for specifying a position of a peak of a first intensity signal corresponding to an interface between the glitter material layer and the base coating film layer in the integrated interference waveform;
The peak position of the second intensity signal corresponding to the interface between the air layer around the multilayer coating film and the clear layer in either the integrated interference waveform or the plurality of interference waveforms before integration. A second interface identification step that identifies
A film for calculating a film thickness corresponding to the sum of the film thickness of the clear layer and the film thickness of the glittering material layer from the interval between the peak position of the first intensity signal and the peak position of the second intensity signal A method for measuring a film thickness, comprising a thickness calculating step.   The film thickness measuring method according to claim 1, wherein an interference intensity caused by the glitter material contained in the glitter material layer is higher than an interference intensity caused by the pigment substance.   The film thickness measuring method according to claim 2, wherein the bright material is metal flakes and the pigment substance is titanium dioxide. From the interval between peaks of a plurality of intensity signals of the interference waveform obtained by the optical coherence tomography method,
The multilayer coating film is a coating film in which a base material layer, a base coating film layer, a glittering material layer, and a clear layer are sequentially laminated, and multiple scattering of light occurs due to the pigment substance in the base coating film layer. ,
The multilayer coating film is irradiated with light from a light source to detect the intensity of interference light including reflected light from each layer in the multilayer coating film or an interface between the layers, and the multilayer coating film Obtaining an interference waveform of a plurality of intensity signals corresponding to each of the layers or the interface between the layers; and
In a plurality of locations in a predetermined region on the multilayer coating film, the interference waveform acquisition step is repeatedly performed a predetermined number of times to obtain a plurality of interference waveforms, and
An integration step of integrating a plurality of interference waveforms to obtain an integrated interference waveform;
A first interface specifying step for specifying a position of a peak of a first intensity signal corresponding to an interface between the glitter material layer and the base coating film layer in the integrated interference waveform;
For each of a plurality of said intensity signals included in each of the interference waveform before integration, the intensity signal is determined whether or not having an interference intensity in a range of a predetermined threshold, the interference intensity in the range A third interface specifying step for specifying a position of a peak of a third intensity signal corresponding to the interface between the clear layer and the glitter material layer based on the plurality of intensity signals determined to have :
Wherein the distance between the peak position of the peak position of the first intensity signal third intensity signals, viewed contains a luminous material layer thickness calculating step of calculating the film thickness of the luminous material layer,
The film thickness measuring method , wherein the threshold value is 0.5 or more and 1.5 or less when the magnitude of the intensity signal of the interference waveform on the surface of the multilayer coating film is 1.0 . The peak position of the second intensity signal corresponding to the interface between the air layer around the multilayer coating film and the clear layer in either the integrated interference waveform or the plurality of interference waveforms before integration. A second interface identification step that identifies
A clear layer thickness calculation step for calculating a thickness of the clear layer from an interval between a peak position of the second intensity signal and a peak position of the third intensity signal;
The film thickness measuring method according to claim 4, further comprising:   The film thickness measurement method according to claim 4, wherein an interference intensity caused by the glitter material contained in the glitter material layer is higher than an interference intensity caused by the pigment substance.   The film thickness measuring method according to claim 6, wherein the glitter material is a metal flake, and the pigment substance is titanium dioxide.   The film thickness measuring method according to claim 1 or 4, wherein the light from the light source is near infrared light within a wavelength range of 780 nm to 3000 nm.   The film thickness measuring method according to claim 1 or 4, wherein the light from the light source is near-infrared light within a wavelength range of 1300 nm to 2000 nm.   The film thickness measuring method according to claim 1 or 4, wherein the light source is either an LED or an SLD. An apparatus for calculating the thickness of a multilayer coating film from the interval between peaks of a plurality of intensity signals of an interference waveform obtained by optical coherence tomography,
The multilayer coating film is a coating film in which a base material layer, a base coating film layer, a glittering material layer, and a clear layer are sequentially laminated, and multiple scattering of light occurs due to the pigment substance in the base coating film layer. ,
A light source;
Branching means for branching light from the light source into reference light and incident light to the multilayer coating;
A reference light optical system for adjusting an optical distance of the reference light;
A reflected light optical system for causing the incident light to enter the multilayer coating film, and for extracting reflected light from the multilayer coating film;
Interference means for causing reflected light from the reflected light optical system to interfere with reference light from the reference light optical system;
Detecting means for detecting interference light including the reflected light from the interference means and outputting an intensity signal of the interference light;
Analyzing means for analyzing the intensity signal,
The detection means is
Detecting the intensity of interference light including reflected light from the interface between each layer or interlayer in the multilayer coating, a plurality of layers corresponding to the interface between each layer or the interlayer in the multilayer coating Obtain the interference waveform of the intensity signal,
In a plurality of locations in a predetermined region on the multilayer coating film, repeatedly obtaining the interference waveform a predetermined number of times to obtain a plurality of interference waveforms,
The analysis means is
Accumulating a plurality of interference waveforms to obtain an accumulated interference waveform,
In the integrated interference waveform, the peak position of the first intensity signal corresponding to the interface between the glitter material layer and the base coating layer is specified,
The peak position of the second intensity signal corresponding to the interface between the air layer around the multilayer coating film and the clear layer in either the integrated interference waveform or the plurality of interference waveforms before integration. Identify
From the interval between the peak position of the first intensity signal and the peak position of the second intensity signal, a film thickness corresponding to the sum of the film thickness of the clear layer and the film thickness of the glittering material layer is calculated. Film thickness measuring device. The film thickness measuring apparatus according to claim 11 , wherein an interference intensity caused by the glitter material contained in the glitter material layer is higher than an interference intensity caused by the pigment substance. The film thickness measuring device according to claim 12 , wherein the glitter material is metal flakes and the pigment substance is titanium dioxide. An apparatus for calculating the thickness of a multilayer coating film from the interval between peaks of a plurality of intensity signals of an interference waveform obtained by optical coherence tomography,
The multilayer coating film is a coating film in which a base material layer, a base coating film layer, a glittering material layer, and a clear layer are sequentially laminated, and multiple scattering of light occurs due to the pigment substance in the base coating film layer. ,
A light source;
Branching means for branching light from the light source into reference light and incident light to the multilayer coating;
A reference light optical system for adjusting an optical distance of the reference light;
A reflected light optical system for causing the incident light to enter the multilayer coating film, and for extracting reflected light from the multilayer coating film;
Interference means for causing reflected light from the reflected light optical system to interfere with reference light from the reference light optical system;
Detecting means for detecting interference light including the reflected light from the interference means and outputting an intensity signal of the interference light;
Analyzing means for analyzing the intensity signal,
The detection means is
Detecting the intensity of interference light including reflected light from the interface between each layer or interlayer in the multilayer coating, a plurality of layers corresponding to the interface between each layer or the interlayer in the multilayer coating Obtain the interference waveform of the intensity signal,
In a plurality of locations in a predetermined region on the multilayer coating film, repeatedly obtaining the interference waveform a predetermined number of times to obtain a plurality of interference waveforms,
The analysis means is
Accumulating a plurality of interference waveforms to obtain an accumulated interference waveform,
In the integrated interference waveform, the peak position of the first intensity signal corresponding to the interface between the glitter material layer and the base coating layer is specified,
For each of a plurality of said intensity signals included in each of the interference waveform before integration, the intensity signal is determined whether or not having an interference intensity in a range of a predetermined threshold, the interference intensity in the range Based on the plurality of intensity signals determined to have a position of the peak of the third intensity signal corresponding to the interface between the clear layer and the glitter material layer,
From the interval between the peak position of the first intensity signal and the peak position of the third intensity signal, the film thickness of the glitter material layer is calculated ,
Wherein when the magnitude of the intensity signal of the interference waveform in the multilayer coating film surface was 1.0, the threshold is Ru der 0.5 to 1.5, the film thickness measuring device. The analyzing means further comprises:
The peak position of the second intensity signal corresponding to the interface between the air layer around the multilayer coating film and the clear layer in either the integrated interference waveform or the plurality of interference waveforms before integration. Identify
The film thickness measurement apparatus according to claim 14 , wherein the film thickness of the clear layer is calculated from an interval between a peak position of the second intensity signal and a peak position of the third intensity signal. The film thickness measuring apparatus according to claim 14 , wherein an interference intensity caused by the glitter material included in the glitter material layer is higher than an interference intensity caused by the pigment substance. The film thickness measuring device according to claim 16 , wherein the glitter material is metal flakes and the pigment substance is titanium dioxide. The film thickness measuring device according to claim 11 or 14 , wherein the light from the light source is near infrared light within a wavelength range of 780 nm to 3000 nm. The film thickness measuring apparatus according to claim 11 or 14 , wherein the light from the light source is near infrared light within a wavelength range of 1300 nm to 2000 nm. The film thickness measuring device according to claim 11 or 14 , wherein the light source is either an LED or an SLD.