JP6300430B2 - 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 specifically, by introducing an air layer that serves as a reference for measurement, without applying a refractive index before and after curing of the coating film in advance. The present invention relates to a method and apparatus for measuring film thickness and film thickness change.

  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, a coating method has been introduced in which a paint (photo-curing resin) that is reactively cured by irradiation with light having a specific wavelength (for example, ultraviolet irradiation) is used to cure the paint in a few seconds.

  When the photocurable resin is reactively cured by irradiation with light of a specific wavelength, the film thickness decreases. In order to maintain the function of the coating film, it is necessary to manage the state of the coating film after coating, and it is necessary to know the film thickness of the coating film. Examples of methods for measuring the film thickness of the coating film after light irradiation include a method of measuring the position of the coating film surface with a laser displacement meter, and an optical coherence tomography method using a terahertz wave that has been studied recently. (Patent Document 1). In addition, as a method for measuring the shrinkage rate of the photocurable resin, for example, there is a method of comparing the liquid specific gravity of the paint before light irradiation with the solid specific gravity after curing.

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 method using the terahertz wave described in Patent Document 1, the resolution in the depth direction (thickness direction) of the film is insufficient, and a femtosecond laser is used as the light source, or many optical elements are used. There is a disadvantage that the measurement system becomes complicated and large. In addition, since the shrinkage of the photo-curing resin varies depending on the type of photo-curing resin used, when the shrinkage is low, the film thickness of the coating film after coating (after curing) can be measured with high accuracy and in a short time. There wasn't. In addition, the refractive index before and after curing of the coating film needs to be measured in advance, which requires a separate process.

  The present invention has been made to solve the above-described problems of the prior art, and its purpose is to increase the coating film thickness without measuring the refractive index before and after curing of the coating film in advance. An object of the present invention is to provide a film thickness measuring method and apparatus capable of measuring with accuracy and in a short time.

  Another object of the present invention is to provide a film thickness measuring method and apparatus capable of measuring a change in film thickness of a coating film with high accuracy and in a short time without measuring the refractive index before and after curing of the coating film in advance. Is to provide.

  In order to achieve the above object, a film thickness measuring method according to the present invention irradiates a coating film placed in a reference air layer having a predetermined thickness with measurement light from a light source, A method of measuring the film thickness of the coating film by detecting the intensity of interference light including reflected light, wherein the measurement light from a light source is branched into reference light and incident light to the reference air layer A branching step and an optical distance of the reference light are adjusted so that the reflected light from the reference air layer interferes with the reference light, and a plurality of first intensity signals (B, D) due to the interference are detected. A first optical distance determination that determines an optical distance (BD) corresponding to the thickness of the reference air layer from a first detection step and an interval between adjacent peaks of the detected plurality of first intensity signals. Step, placing the coating film in the reference air layer, and measuring the coating film A coating-film placing step for defining a first air layer adjacent to the irradiation side of the light source, and adjusting an optical distance of the reference light so that the reflected light from the first air layer interferes with the reference light. From the second detection step of detecting a plurality of second intensity signals (B, C ′) due to the interference and the interval between adjacent peaks of the detected plurality of second intensity signals, the first A second optical distance determining step for determining an optical distance (BC ′) corresponding to a thickness of the air layer; an optical distance (BD) of the reference air layer; and an optical distance (BC ′) of the first air layer. And a first film thickness calculating step for calculating the thickness (c′d) of the coating film.

  In addition, the film thickness measuring apparatus according to the present invention irradiates the coating film placed in a reference air layer having a predetermined thickness with measurement light from a light source, and includes interference light including reflected light from the coating film. Is a device that measures the film thickness of the coating film by detecting the intensity of the light source, the measurement light from the light source, the reference light, and the incident light on the reference air layer or the coating film. Branching means for branching into the reference light, a reference light optical system for adjusting the optical distance of the reference light, the incident light incident on the reference air layer or the coating film, and further from the reference air layer or the coating film Reflected light optical system for extracting reflected light, interference means for causing reflected light from the reflected light optical system to interfere with reference light from the reference light optical system, and interference light including the reflected light from the interference means Detecting means for detecting the interference light and outputting an intensity signal of the interference light, and An analysis means for analyzing the degree signal, and for the measurement object in the first state where the coating film is not placed in the reference air layer, the detection means includes reflected light from the reference air layer and A plurality of first intensity signals (B, D) due to interference with the reference light are detected and output, and the analysis means determines the interval between adjacent peaks of the detected plurality of first intensity signals. An optical distance (BD) corresponding to the thickness of the reference air layer is determined, and the coating film is placed in the reference air layer in a second state on the measurement light irradiation side of the coating film. For the measurement object in which the adjacent first air layer is defined, the detection means has a plurality of second intensity signals (B) due to interference between the reflected light from the first air layer and the reference light. , C ′) are detected and output, and the analysis means is adjacent to the detected plurality of second intensity signals. The optical distance (BC ′) corresponding to the thickness of the first air layer is determined from the interval between the peaks, and the detecting means determines the optical distance (BD) of the reference air layer and the first air layer. From the optical distance (BC ′) of the air layer, the thickness (c′d) of the coating film is calculated.

  According to the film thickness measuring method and film thickness measuring apparatus according to the present invention, the film thickness of the coated film after light irradiation can be measured with high accuracy without measuring the refractive index before and after curing of the coated film in advance. It can be measured in a short time. By using near-infrared light as measurement light, the film thickness can be measured even for a coating film containing a pigment and having a low visible light transmittance.

  Further, according to the film thickness measuring method and the film thickness measuring apparatus according to the present invention, since the optical coherence tomography method is adopted, the number of optical elements necessary for measurement can be reduced as compared with the prior art, The device itself can be miniaturized and manufactured in a portable size. The optical coherence tomography method irradiates the measurement target layer with measurement light and does not directly contact the measurement target layer, so the film thickness can be measured even on a wet film before the coating film is cured. It becomes possible. Since the film thickness can be measured even for the wet film before curing, the film thickness reduction rate and the film thickness can also be measured by measuring the film thickness for the cured coating film after light irradiation for curing. It is possible to measure a change in film thickness after light irradiation, such as the shrinkage rate of the film thickness. Furthermore, it is possible to measure the refractive index of a substance with an unknown refractive index without directly contacting the measurement target layer.

It is a block diagram which shows schematic structure of the film thickness measuring apparatus of the photocurable resin which concerns on embodiment of this invention. It is a schematic diagram explaining the example which measures an interference light intensity | strength with respect to the sample which consists of a coating film of photocuring resin using the film thickness measuring apparatus which concerns on embodiment of this invention. It is a schematic diagram explaining the example which measures an interference light intensity with respect to the sample which uses an air layer as a standard of measurement using the film thickness measuring device concerning an embodiment of the invention, and between quartz glass It is a schematic diagram which shows the sample in which the air layer was provided. It is a schematic diagram explaining the example which measures an interference light intensity with respect to the sample which uses an air layer as a standard of measurement using the film thickness measuring device concerning an embodiment of the invention, interference light intensity and optics It is a schematic diagram which shows the profile showing the relationship with distance.

  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 present invention, near infrared light having high position resolution and high transparency to the coating film is used as a preferred light source for the measurement light, the coating film is irradiated with the light beam of one measurement system optical path branched into two from the light source, and the other Interference caused by superposition of the reflected light from the coating and the reference light that occurs when the optical distance between the two optical paths coincides while controlling the optical distance of at least the reference system optical path with the light beam in the reference system optical path as the reference light The film thickness of the coating film is measured by measuring light. In particular, in the present invention, by introducing an air layer serving as a measurement reference, the film thickness and film thickness change of the coating film are measured without measuring the refractive index before and after curing of the coating film in advance. Below, the case where a coating film is formed using photocuring resin is demonstrated as one embodiment of this invention.

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) Apparatus Configuration FIG. 1 is a block diagram showing a schematic configuration of a coating film thickness measuring apparatus according to an embodiment of the present invention.

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

  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 sample 4 is sandwiched between layers of quartz glass 10, and an air layer 11 is provided between the sample 4 and the quartz glass 10. 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.
(2) Operation of Apparatus Next, the operation of the coating film thickness measuring apparatus according to the present embodiment will be described using an example of the film thickness measuring apparatus shown in FIG.

  The sample 4 is a coating film in which a photocurable resin is applied on a glass substrate, for example, and is placed on a predetermined table (not shown). 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 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. 1, 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. 1, 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 photocurable resin layer, for example, when the refractive index of the photocurable resin is the same as the refractive index of air, the reference light is , Interference occurs with the reflected light generated at the interface of the bottom surface of the photocurable resin.

Therefore, in order to measure the film thickness of the photo-curing resin layer, it is necessary to scan the entire thickness of the photo-curing resin layer even if the position of the intersecting mirror 5 with the position variable mechanism is the minimum.
(3) Information obtained from measurement of interference light Light reflection occurs in a portion where the refractive index changes discontinuously. That is, the reflected light from the sample is information reflecting a change in the refractive index in the sample. The major causes of refractive index change in the coating film are “difference in refractive index between coating films (between layers)” and “including coating film with a size corresponding to λ / 2 with respect to light source wavelength λ” Products (mainly pigments), phase separation structures, etc.

  Among these, the refractive index change due to the refractive index difference between the layers is considered that the thickness of each layer of the coating film is substantially constant, so the position in the depth direction of the coating film is substantially constant. This feature makes it possible to distinguish whether the change in refractive index is due to the difference in refractive index between layers or due to the presence of inclusions.

FIG. 2 is a schematic diagram for explaining an example in which measurement is performed on a sample made of a coating film of a photo-curing resin by using the film thickness measurement device according to the embodiment of the present invention, and a detection signal is analyzed. FIG. 2 (A) shows a sample of a coating film composed of a glass plate and a surface photocurable resin layer. FIG. 2B shows a profile representing the relationship between the interference light intensity and the optical distance. For example, the following relationship exists in the peak pattern shown by the profile in FIG. 2B as an example, and can be used for calculation of the film thickness and refractive index of the coating film.
Number of peaks The peak of the interference light intensity, that is, the place where the strongest interference light is generated is the place where the change in the refractive index is the largest, the interface where the refractive index of the coating film changes, and the coating film and the surroundings. Means the interface. For example, when a sample placed in a natural environment (in the air) includes a material and a multilayer coating film of N layers on the material, the difference in refractive index between the air and the surface layer of the multilayer coating film, and the material In consideration of the difference in refractive index between the lowermost layer and the lowermost layer of the multilayer coating film, the number of interfaces surrounding the multilayer coating film where the refractive index changes is N + 1. That is, the number of interfaces where the refractive index changes is one more than the number of layers of the multilayer coating film having different refractive indexes. Thereby, it can be seen from the number of peaks corresponding to the interface how many layers the multilayer coating film is composed of.
-Distance between peaks The distance between peaks is the optical distance, and is determined by the thickness and refractive index of the film. Therefore, the film thickness of each layer can be obtained from the distance between the peaks. As will be described in detail in the embodiments to be described later, in the present invention, by introducing an air layer as a measurement reference, the optical distance between peaks without measuring the refractive index before and after curing of the coating film in advance. Thus, the film thickness of the coating film can be measured. By obtaining the optical distance of the air layer from the optical distance between the peaks both before and after curing of the coating film, it is possible to measure both the film thickness and the refractive index before and after curing of the coating film.
-Peak height and peak pattern From the ratio of peak height, the state of each interface and layer can be known, and the internal structure of the coating film can be known from the peak pattern.
(4) Film thickness measuring method Next, the film thickness measuring method of photocuring resin based on the typical measurement result obtained using the film thickness measuring apparatus which concerns on this Embodiment is demonstrated. First, a method for obtaining the relative optical distance of the photocurable resin from the distance between peaks will be described. Next, a method for measuring the film thickness by introducing an air layer as a measurement reference without measuring the refractive index before and after the curing of the photocurable resin in advance will be described.

  FIG. 2 (A) shows a sample of a coating film composed of a glass plate and a surface photocurable resin layer. 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. 1, the measurement light is reflected on the upper surface of each layer of the sample, and reflected light is reflected. produces α, β, γ.

  Each of these reflected lights interferes with and strengthens the reference light having an optical distance adjusted so that interference occurs, and is received by the light receiving sensor 7 to obtain the three peak signals shown in FIG. . Here, the horizontal axis of FIG. 2B represents the optical distance between the obtained interference lights, and the vertical axis represents the intensity of the received interference light. Reference numerals α to γ attached to the peak signal in FIG. 2B correspond to the reflected lights α to γ in FIG. As shown in FIG. 2B, among the intervals between the two peaks defined by the three peak signals α to γ, the interval between the peak signals α to β is that of the film that generates the reflected light α and β. This corresponds to the film thickness (that is, the film thickness of the photo-curing resin), and the interval between the peak signals β to γ corresponds to the film thickness (that is, the thickness of the glass plate) of the film that generates the reflected light β and γ.

A specific procedure for obtaining the interval between the peaks will be described. First, the sample 4 is irradiated with the measurement light for measuring the film thickness from the light source 1 and corresponds to the reflected light α reflected from the interface of the surface layer of the photocurable resin. 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 (maximum). The position of the position changing mechanism with crossing mirror 5 at this time the P _alpha. Next, the position of the cross mirror 5 with a position variable mechanism is moved, and the cross mirror 5 with a position variable mechanism is at a position where the intensity of the interference light corresponding to the reflected light β reflected from the interface of the bottom surface of the photocurable resin reaches a peak. Adjust the position. The position of the intersecting mirror 5 with the position variable mechanism at this time is P _β . The information on the positions P _α and P _β corresponds to the positions of the peak signals α and β in the profile shown in FIG.

  With reference to the relationship diagram (profile) between the intensity of interference light and the optical distance obtained in this way, the relative thickness (optical distance) of these layers can be found from the interval between peaks. 3 and 4 are schematic diagrams illustrating an example in which the interference light intensity is measured for a sample using an air layer as a measurement reference, using the film thickness measurement device according to the embodiment of the present invention. is there. FIG. 3 shows the sample 4 in which the air layer 11 is provided between the quartz glass 10 and FIG. 4 shows a profile representing the relationship between the interference light intensity and the optical distance. In the following description, when expressing the thickness of a layer, the lower case letter of the alphabet means the physical distance, and the upper case letter of the alphabet means the optical distance.

  First, as shown in FIG. 3I, the air layer 11 is formed by stacking two quartz glasses 10 in a state where the coating film sample 4 is removed. When the interface on the surface layer side of the air layer 11 is b and the interface on the bottom surface side is d, the thickness of the air layer 11 is expressed as bd in the physical distance and BD in the optical distance. The air layer 11 is irradiated with measurement light for film thickness measurement from the light source 1 to measure the optical distance BD of the air layer 11. As shown in the profile of FIG. 4I, the peak A corresponds to the peak of the interference light intensity at the interface a, and the peak B corresponds to the peak of the interference light intensity at the interface b. Similarly, the peak D corresponds to the interface d, and the peak E corresponds to the interface e. That is, the measured value BD corresponds to the optical distance between peak B and peak D shown in FIG.

  Next, as shown in FIG. 3 (ii), a photocuring resin sample 4 to be measured for film thickness is inserted into the air layer 11. When the interface on the surface layer side of the sample 4 is c ′, the thickness of the air layer 11 ′ in this state is represented as BC ′ in the optical distance. The air layer 11 ′ is irradiated with measurement light for measuring the film thickness from the light source 1 to measure the optical distance BC ′ of the air layer 11 ′. This measured value BC ′ corresponds to the optical distance between peak B and peak C ′ shown in FIG.

  Next, as shown in FIG. 3 (iii), a curing light source (not shown) that irradiates light for curing (for example, ultraviolet rays) is irradiated on the sample 4 in a wet state for a predetermined time. Then, the photo-curing resin is cured. The film thickness of the sample 4 ′ after light irradiation is reduced by curing. When the interface on the surface layer side of the sample 4 ′ after curing is c ″, the thickness of the air layer 11 ″ in this state is represented by BC ″ in terms of optical distance. The air layer 11 ″ is irradiated with measurement light for film thickness measurement from the light source 1 to measure the optical distance BC ″ of the air layer 11 ″. The measured value BC ″ corresponds to the optical distance between the peak B and the peak C ″ shown in FIG. 4 (iii).

  From the above measurement, the optical distance BD of the air layer 11, the optical distance BC ′ of the air layer 11 ′, and the optical distance BC ″ of the air layer 11 ″ were obtained. Using these three measured values for the optical distance of the air layer, for the photocured resin sample to be measured, the wet film thickness before curing, the CURE film thickness after curing, the curing shrinkage rate, the refractive index of the wet film, And all of the refractive index of the CURE film can be obtained by calculation.

First, the thickness bd (physical distance) of the air layer 11 as a measurement reference is obtained. If the refractive index of air is n ^* , then n ^* = 1.

Thus, the optical distance becomes the physical distance as it is. The wet film thickness c′d shown in FIG.

And can be represented by measured values BD and BC ′ of the optical distance without using the value of the refractive index. The CURE film thickness c ″ d shown in FIG.

And can be represented by the measured values BD and BC ″ of the optical distance without using the refractive index value. The shrinkage ratio of the film thickness before and after curing of the photo-curing resin is

And can be represented by the measured values BD and BC ″ of the optical distance without using the refractive index value.

The refractive indices of the wet film and the CURE film themselves can also be expressed by measured values BD and BC ″ of the optical distance. Refractive index _{n w} of the wet film,

Can be expressed as, the refractive index _{n c} of the CURE film,

It can be expressed as. Here, since the optical distance C′D ′ corresponds to the optical distance between the peak C ′ and the peak D ′ shown in FIG. 4 (ii), the peak of the interference light intensity at the interface c ′ shown in FIG. 3 (ii). And the peak of the interference light intensity at the interface d, and the optical distance between these peaks is obtained. Similarly, the optical distance C ″ D ″ corresponds to the optical distance between the peak C ″ and the peak D ″ shown in FIG. 4 (iii), and therefore at the interface c ″ shown in FIG. 3 (iii). The peak of the interference light intensity and the peak of the interference light intensity at the interface d are measured, and the optical distance between these peaks is obtained.

  As described above, when three measured values relating to the optical distance of the air layer are used, the wet film thickness before curing, the CURE film thickness after curing, the curing shrinkage rate, and the wet are measured for the photocured resin sample to be measured. All of the refractive index of the film and the refractive index of the CURE film can be obtained by calculation. According to the method of the present invention, since the refractive indexes of the WET film and the CURE film are not required for the measurement of the film thickness, it is not necessary to consider the error due to the refractive index measurement, and the work process can be simplified. Can do.

The spatial resolution ΔT in the depth direction (thickness direction) of the film obtained by this film thickness measuring device is determined by the nature of the incident light, and increases as the wavelength width Δλ of the light source is wider and the wavelength λ _{0 of} the light source is shorter. To do. The spatial resolution ΔT can be obtained by the following equation 1.

ΔT = 2ln (2 / π × (λ ₀ ² / Δλ)) (Formula 1)
Here, λ ₀ is the center wavelength of the incident light, and Δλ is the spectral width of the incident light. ln means a natural logarithm.

  Therefore, for example, when an infrared LED having a center wavelength of 1310 nm and a spectral width of about 90 nm is used as the light source of the film thickness device according to the present embodiment, the resolution ΔT is 8.4 μm. The resolution ΔT improves as the wavelength increases with a shorter wavelength. In the case of assuming a multilayer coating film for an automobile outer plate, the thickness of each layer is usually about 10 to 15 μm or more. Thus, it can be seen that an infrared LED with a wavelength of 1310 nm and a spectral width of about 90 nm can provide sufficient resolution for measuring coatings for automotive skin applications. If it is necessary to make the coating film of each layer thin and highly functional in the future in order to save the process in automobile manufacturing, in order to resolve the lack of resolution, the light source is based on the relationship shown in Equation 1. And the resolution of the measuring device may be further increased.

  Conversely, the wavelength can be specified. For example, when an infrared LED having a resolution ΔT of about 15 μm and a spectral width of 90 nm is used, it can be seen that the necessary observation wavelength is about 1.7 μm according to Equation 1 above. When an infrared LED having the same resolution ΔT of about 15 μm and a spectral width of 120 nm is used, it can be seen that the necessary observation wavelength is about 2.0 μm according to Equation 1 above.

  Further, 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, near infrared rays having a wavelength in the range of 780 nm to 3000 nm, preferably in the range of 1300 nm to 2000 nm are used as the light source in the present invention.

  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. 1 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 the description using FIGS. 2 to 4 described above, the case of measuring one place of the sample has been described. However, the film thickness measuring apparatus measures the reflected light from a plurality of places to measure the two-dimensional coating film. Alternatively, three-dimensional information can be obtained. When measuring multiple points of a coating film linearly or planarly, the device can be moved to a portable measuring instrument, or fixed to another movable mounting table, and the workpiece can be moved. By doing so, various aspects of measurement can be realized.

  Since it is sufficient for the optical distance of the measurement system and the optical distance of the reference system to coincide with each other in order to obtain interference light, the beam splitter 2, the focusing lens 3, the crossing mirror 5, and the fixed mirror 6 in the apparatus shown in FIG. The arrangement 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.

  Furthermore, this film thickness measuring apparatus can be realized as an inexpensive and simple portable apparatus in combination with 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. 2B is the time axis), information on the number of coating films is obtained from the number of reflected lights obtained. 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.

  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 intersecting mirror 5 with the position variable mechanism is continuously scanned in the thickness direction of the photo-curing resin layer to be measured, and the intensity of the interference light and the intersection with the position variable mechanism are 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.

  Moreover, although the said embodiment demonstrated the case where the coating film which is a measuring object was formed with the photocurable resin, the raw material of a coating film is not limited to a photocurable resin, It hardens | cures by the normal drying process of a coating material. It may be a paint. The light for curing is not limited to ultraviolet light (UV), but may be light having a specific wavelength that can cure the photo-curing resin. Further, instead of the photo-curing resin, a resin that is cured by an electron beam may be used. In this case, an electron beam source that emits an electron beam having a specific energy may be used as the curing electron beam. .

  Moreover, in the said embodiment, although the glass plate was used for the board | substrate and the light for hardening was irradiated to the photocurable resin through the glass plate from the downward direction of the sample 4 as shown in FIG. The mode of incident light is not limited to this. Instead of the glass plate, it may be a coating film constituting an outer plate for automobiles. In this case, the photo-curing resin located on the surface layer is from the surface layer side of the photo-curing resin (that is, the sample shown in FIG. 3). The light for curing may be irradiated from above (4).

  In the above embodiment, an air layer is used as a measurement reference. However, the reference layer may be a layer that can transmit measurement light and has a known refractive index. For example, the gas layer is not limited to an air layer, and may be another gas layer having a known refractive index, or may be a liquid layer having a known refractive index as long as the photocured resin to be measured is not water-soluble.

The present invention will be described more specifically with reference to the following examples.
<1> Measurement of optical distance of air layer A quartz glass plate was prepared, and two glass plates were placed on both ends to form a support column. Further, a quartz glass plate was placed thereon so as to produce an air layer having a uniform thickness. Next, the optical distance BD of this air layer was measured using the film thickness measuring apparatus of the present invention shown in FIG.
<2> Preparation of WET film Next, the lid of the quartz glass plate is opened, the UV curable material is applied onto the lowermost quartz glass, the lid is closed, and the upper and lower layers of the WET film are sandwiched between the quartz glass plates. And an air layer. As a UV curable material, a paint containing an alkylphenone photopolymerization initiator manufactured by BASF was prepared. Specifically, a paint prepared by adding 3% by mass of DAROCUR (registered trademark) 1173 to trimethylolpropane triacrylate (TMPTA) was prepared and used.
<3> Measurement of Optical Distance of Each Layer Next, using the film thickness measuring apparatus of the present invention shown in FIG. 1, measurement light was incident from above and the optical distances BC ′ and C′D ′ of each layer were measured.
<4> Calculation of film thickness of WET film From the optical distance BD of the air layer measured in <1> and the optical distance BC ′ of the air layer measured in <3>, c′d = BD−BC ′, The film thickness (physical distance) c′d = 139.4 μm of the WET film was obtained. Further, from this physical distance with respect to the WET film and the optical distance C′D ′ of the WET film measured in <3>, the refractive index n _W = 1 of the WET film from C′D ′ / c′d. .432 was obtained.
<5> Curing treatment of WET coating film Next, the WET coating film was irradiated with light for curing to cure the coating film. For curing the coating film, SUPERCURE-203S manufactured by Mitsunaga Electric Co., Ltd. equipped with a 200 W mercury xenon lamp as a light source for curing was used. The curing light irradiation conditions were such that the distance between the sample and the mercury xenon lamp was 20 mm, and the curing light was irradiated for 10 seconds at an irradiation output of about 180 mW.
<6> Measurement of optical distance of each layer and calculation of film thickness of CURE film Using the film thickness measuring apparatus of the present invention shown in FIG. The optical distances BC ″ and C ″ D ″ were measured. From the measured optical distance BC ″ of the air layer and the optical distance of the air layer measured in <1>, the film thickness (physical distance) c ″ of the CURE film from c ″ d = BD−BC ″. d = 119.2 μm was obtained. Further, from this physical distance with respect to the CURE film and the optical distance C ″ D ″ of the CURE film measured in <6>, the refraction of the CURE film is obtained from C ″ D ″ / c ″ d. The rate n _C = 1.487 was obtained.
<7> Calculation of Shrinkage and Shrinkage Ratio From c′d = 139.4 μm and c ″ d = 119.2 μm calculated in <4> and <6>, coating film from c′d−c ″ d A shrinkage amount of 20.2 μm was obtained. Moreover, the contraction rate of the coating film = 14.5% was obtained from (c′d−c ″ d) / c′d.

DESCRIPTION OF SYMBOLS 1 Light source 2 Beam splitter 3 Focusing lens 4 Coating film sample 5 Crossing mirror with a position variable mechanism 6 Fixed mirror 7 Light receiving sensor 8 Amplifier 9 Computer 10 Quartz glass 11 Air layer

Claims (13)

By irradiating measurement light from a light source on a coating film containing a pigment placed in a reference air layer having a predetermined thickness, and detecting the intensity of interference light including reflection light from the coating film, A method for measuring the film thickness of the coating film,
A branching step for branching measurement light from a light source into reference light and incident light to the reference air layer;
A first detection step of adjusting the optical distance of the reference light, causing the reflected light from the reference air layer to interfere with the reference light, and detecting a plurality of first intensity signals due to the interference;
A first optical distance determining step for determining an optical distance corresponding to a thickness of the reference air layer from an interval between adjacent peaks of the detected plurality of first intensity signals;
A coating film placing step for placing the coating film in the reference air layer, and defining a first air layer adjacent to the measurement light irradiation side of the coating film;
A second detection step of adjusting the optical distance of the reference light to dry the reflected light from the first air layer and the reference light, and detecting a plurality of second intensity signals due to the interference;
A second optical distance determining step for determining an optical distance corresponding to a thickness of the first air layer from an interval between adjacent peaks of the plurality of detected second intensity signals;
A first film thickness calculating step for calculating the thickness of the coating film from the optical distance of the reference air layer and the optical distance of the first air layer;
The film thickness measuring method, wherein the coating film is an ultraviolet curable resin or an electron beam curable resin, and the light from the light source is near infrared light within a wavelength range of 1300 nm to 2000 nm. Adjusting the optical distance of the reference light, causing the reflected light from the coating film to interfere with the reference light, and detecting a plurality of third intensity signals due to the interference;
A third optical distance determining step for determining an optical distance corresponding to the thickness of the coating film from an interval between adjacent peaks of the detected plurality of third intensity signals;
A first refractive index calculation step of calculating a refractive index of the coating film from the optical distance of the reference air layer, the optical distance of the first air layer, and the optical distance of the coating film; The film thickness measuring method according to claim 1. Curing step of curing the coating film and defining a second air layer adjacent to the measurement light irradiation side of the coating film after curing;
A fourth detection step of adjusting the optical distance of the reference light to cause the reflected light from the second air layer to interfere with the reference light, and detecting a plurality of fourth intensity signals due to the interference;
A fourth optical distance determining step for determining an optical distance corresponding to a thickness of the second air layer from an interval between adjacent peaks of the detected plurality of fourth intensity signals;
3. A second film thickness calculating step of calculating a thickness of the coating film after curing from the optical distance of the reference air layer and the optical distance of the second air layer. The film thickness measuring method described in 1. A fifth detection step of adjusting the optical distance of the reference light, causing the reflected light from the cured coating film to interfere with the reference light, and detecting a plurality of fifth intensity signals due to the interference;
A fifth optical distance determining step for determining an optical distance corresponding to the thickness of the coating film after curing from an interval between adjacent peaks of the plurality of detected fifth intensity signals;
Second refractive index calculation for calculating the refractive index of the coating film after curing from the optical distance of the reference air layer, the optical distance of the second air layer, and the optical distance of the coating film after curing. The film thickness measuring method according to claim 3, further comprising a step.   A curing shrinkage rate calculating step for calculating a shrinkage rate before and after curing of the coating film from the optical distance of the reference air layer, the optical distance of the first air layer, and the optical distance of the second air layer. The film thickness measuring method according to claim 3, further comprising: The first detection step comprises:
An intensity signal of the first interference light due to the interference between the first reflected light reflected from the first interface on the surface layer side of the reference air layer and the reference light;
Detecting a second reflected light reflected from the second interface on the bottom side of the reference air layer and an intensity signal of the second interference light due to interference between the reference light and
Said first optical distance determining step comprises:
From the difference between the optical distance of the reference light when the intensity signal of the first interference light is a maximum and the optical distance of the reference light when the intensity signal of the second interference light is a maximum, The film thickness measurement method according to claim 1, which is a step of determining the optical distance corresponding to a thickness of a reference air layer.   The film thickness measuring method according to claim 1, wherein the light source is either an LED or an SLD. By irradiating measurement light from a light source on a coating film containing a pigment placed in a reference air layer having a predetermined thickness, and detecting the intensity of interference light including reflection light from the coating film, An apparatus for measuring the film thickness of the coating film,
A light source;
Branching means for branching the measurement light from the light source into reference light and light incident on the reference air layer or the coating film;
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 reference air layer or the coating film, and for extracting reflected light from the reference air layer or the coating film;
An interference stage for causing the reflected light from the reflected light optical system to interfere with the 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,
For the measurement object in the first state where the coating film is not placed in the reference air layer,
The detection means detects and outputs a plurality of first intensity signals due to interference between reflected light from the reference air layer and the reference light, and the analysis means detects the plurality of first intensity signals detected. Determining the optical distance corresponding to the thickness of the reference air layer from the spacing between adjacent peaks of
For the measurement object in which the first air layer adjacent to the measurement light irradiation side of the coating film in the second state where the coating film is placed in a reference air layer is defined,
The detecting means detects and outputs a plurality of second intensity signals due to interference between the reflected light from the first air layer and the reference light, and the analyzing means detects the plurality of detected second second signals. Determining the optical distance corresponding to the thickness of the first air layer from the spacing between adjacent peaks of the intensity signal;
The detection means calculates the thickness of the coating film from the optical distance of the reference air layer and the optical distance of the first air layer,
The film thickness measuring device, wherein the coating film is an ultraviolet curable resin or an electron beam curable resin, and the light from the light source is near infrared light within a wavelength range of 1300 nm to 2000 nm. For the measurement object in the second state,
The detection means detects and outputs a plurality of third intensity signals due to interference between reflected light from the coating film and the reference light, and the analysis means detects the plurality of detected third intensity signals. From the interval between adjacent peaks, determine the optical distance corresponding to the thickness of the coating film,
The detection means, and the optical length of the reference air layer, and the optical distance of the first air layer, and an optical distance of the coating film to calculate the refractive index of the coating film, according to claim 8 Film thickness measuring device. Furthermore, it further comprises a curing means for curing the coating film, and is in a third state where the coating film is cured by the curing means, a second state adjacent to the measurement light irradiation side of the cured coating film. For a measurement object with a defined air layer,
The detection means detects and outputs a plurality of fourth intensity signals due to interference between the reflected light from the second air layer and the reference light, and the analysis means detects the plurality of the fourth intensity signals detected. Determining the optical distance corresponding to the thickness of the second air layer from the spacing between adjacent peaks of the intensity signal;
The film thickness measurement according to claim 8 or 9 , wherein the detection means calculates a thickness of the coating film after curing from an optical distance of the reference air layer and an optical distance of the second air layer. apparatus. For the measurement object in the third state,
The detection means detects and outputs a plurality of fifth intensity signals due to interference between the reflected light from the coating film after curing and the reference light, and the analysis means detects the plurality of fifth lights detected. From the distance between adjacent peaks of the intensity signal, determine the optical distance corresponding to the thickness of the coating after curing,
The detection means calculates the refractive index of the coating film after curing from the optical distance of the reference air layer, the optical distance of the second air layer, and the optical distance of the coating film after curing. The film thickness measuring apparatus according to claim 10 . The detection means calculates the shrinkage rate before and after curing of the coating film from the optical distance of the reference air layer, the optical distance of the first air layer, and the optical distance of the second air layer. The film thickness measuring apparatus according to claim 10 . The film thickness measuring apparatus according to claim 8 , wherein the light source is either an LED or an SLD.