JP3205084B2 - Method and apparatus for measuring film thickness of coating material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the thickness of a coating material on an object to be measured, which is obtained by applying a coating material on a substrate such as paper or film, using infrared rays.

[0002]

2. Description of the Related Art It is conventionally known to measure the thickness of a coating material using an infrared film thickness meter. In the conventionally known seed film thickness measurement, the absorbance of only the base material is detected in advance by using 2 to 3 measurement light, and the absorbance of the coat component is obtained by subtracting the absorbance of the base material only from the absorbance measured for the object to be measured. The film thickness is detected by a calibration curve previously obtained from the obtained absorbance.

[0003]

The above conventional film thickness measuring method is based on the assumption that there is no change in the thickness of the base material, the absorbance of only the base material is determined for each wavelength, and this is used as correction data. In the case where the thickness of the material changes, the change is directly used as a measurement error of the film thickness. It is extremely difficult in production to make the film thickness of a film or the like as a substrate completely constant, and it is difficult to avoid some fluctuations. As described above, this kind of variation is directly related to the measurement error of the thickness of the coat component, and it is impossible to control the thickness of the coat component to be constant. When the base material is paper, the type of the base material (for example, the type of paper such as Kent paper, woodfree paper, and kraft paper)
The light absorption of the paper substrate depends on the type of paper and the presence or absence of the coating, since the surface condition of the paper varies depending on the paper, the penetration depth of the light into the paper varies, and the surface condition of the substrate changes by applying the coating. Will be different. The change in absorbance due to the type of paper can be eliminated to some extent by creating a calibration curve for each type of paper, but the change in absorbance that occurs on the substrate due to the coating cannot be eliminated, and the measurement error Is one of the causes.

[0004]

SUMMARY OF THE INVENTION According to the present invention, the thickness of a coating component can be accurately determined without being affected by fluctuations in the thickness of a substrate. It is a basic object of the present invention to provide a method and an apparatus for measuring the thickness of a coating material capable of substantially minimizing the effects of various types. To achieve the above object, the present invention is first has the time to measure the film thickness of the coating material of the object to be measured which were coated substrate, the wavelength lambda ₁ that has infrared absorption in both the coating material and the substrate One measuring light,
A second measuring beam having a wavelength lambda ₂ that has infrared absorption only to the substrate, the coating material by using a reference beam having no wavelength lambda ₃ or infrared absorption is small for the substrate without infrared absorption, the substrate only Absorbances A ₁₀ , A ₂₀ , and A ₃₀ are measured in advance, and a correction coefficient k is calculated by the following equation. K = (A ₁₀ −A ₃₀ ) / (A ₂₀ −A ₃₀ ) Absorbances at ₁ , λ ₂ , λ ₃ A ₁ , A ₂ ,
Measuring the A _3, and calculates the absorbance A of only the coating material from these measurements by the following _{equation, A = A 1 -A 3 -k} (A 2 -A 3) the absorbance A was determined in terms of the thickness Court Provided is a method for measuring the thickness of a coating material in which the thickness of the material is determined.

[0005] When the influence of scattering is large such as when the base material is translucent or colored, two reference wavelengths are used,
The absorbances obtained for the two reference lights are connected to form a reference level, and a correction coefficient (ratio) is determined based on the reference level. That is, the first measurement light having a wavelength λ ₁ having infrared absorption in both the coating material and the base material, the second measurement light having a wavelength λ ₂ having infrared absorption only in the base material, Using the first and second reference lights having two wavelengths λ ₃ and λ ₄ , both of which have no infrared absorption, the absorbances A ₁₀ and A of only the base material are used.
₂₀ , A ₃₀ , and A ₄₀ are measured in advance, and the correction coefficient k is calculated by the following equation. k = (A ₁₀ −A ₅₀ ) / (A ₂₀ −A ₆₀ ) where A ₅₀ = A ₃₀ + [(A ₄₀ −A ₃₀ ) / (λ ₄ −λ ₃ )] × (λ ₁ −λ ₃ ) , A ₆₀ = A ₃₀ + [(A ₄₀ −A ₃₀ ) / (λ ₄ −λ ₃ )] × (λ ₂ −λ ₃ ) Then, for the measured object, λ ₁ , λ ₂ , λ ₃ , λ ₄ The absorbances A ₁ , A ₂ , A ₃ , and A ₄ are measured, and from these measured values, the absorbance A of only the coating material is calculated according to the following equation. A = A ₁ -A ₅ -k (A ₂ -A ₆ ) Where A ₅ = A ₃ + [(A ₄ −A ₃ ) / (λ ₄ −λ ₃ )] × (λ ₁ −λ ₃ ), A ₆ = A ₃ + [(A ₄ −A ₃ ) / ( _{λ 4 -λ 3)] × (} λ 2 -λ 3) the absorbance a was determined in terms of the thickness determine the thickness of the coating material.

Further, the present invention relates to an apparatus for realizing the above-mentioned measuring method, which is an apparatus for measuring a film thickness of a coating material of an object to be measured in which a coating component is applied on a substrate such as paper or film. A light source, a first measurement light having a wavelength having infrared absorption in both the coating material and the substrate, a second measurement light having a wavelength having infrared absorption only in the substrate, and an infrared light in both the coating material and the substrate. Filter means for generating reference light having a wavelength having no absorption, detection means for detecting the absorbance of each light, and first and second measurement lights of only the base material with reference to the absorbance of the reference light only by the base material. A correction coefficient calculating means for calculating a ratio of absorbance; and a correcting means for correcting the absorbance detected for the object to be measured based on the ratio, so that a change in absorbance due to a change in the base material is corrected. To be Providing the film thickness measuring device over preparative material. Also in this case, if necessary, the reference wavelength can be set to two wavelengths and four wavelengths can be measured.

[0007]

According to the present invention, even if there is a change in the absorbance of the base material, the absorbance is corrected using the correction coefficient that is not affected by the change, so that the measurement can be performed without being affected by the absorption of the base material. And the true thickness of the coating material can be accurately measured.

[0008]

Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a schematic explanatory view of an infrared film thickness measuring device used in the present invention,
A measurement sample formed by coating the coating material 2 thereon is irradiated with infrared rays of 3 to 4 wavelengths to detect each absorbance, and the absorbance detected by the photometry unit 10 is processed and finally processed. The signal processing unit 30 for calculating the film thickness of the coating material 2 constitutes an infrared film thickness measuring device.
The photometric unit 10 has a built-in infrared light source 11. The infrared light emitted from the light source 11 is
2. Rotary interference filter 14 by first mirror 13
Is focused at a predetermined position, and infrared light having a specific wavelength only by one interference filter 15 incorporated in the rotary interference filter 14 is irradiated toward the measurement sample 3 via the second mirror 16. It has become. The reflected light from the measurement sample 3 is collected by a concave mirror 17 to an infrared detector 18 disposed at the focal point thereof, and is measured. The rotary interference filter 14 is provided with a motor 19
As shown in FIG. 2, in this embodiment, the first to third interference filters 15a, 15b, 15c
Are mounted at an angle of 120 ° with respect to the center of the disk, and each interference filter is provided with a small hole 15d for timing detection on a one-to-one basis. Each small hole 15d is connected to the timing detector 20 (see FIG. 1). By detection, it is detected which interference filter (infrared light of which wavelength) is used for photometry. As schematically shown in FIG. 3, the first interference filter 15 a only emits infrared light having a wavelength λ ₁ having infrared absorption in both the coating material 2 and the substrate 1 of the measurement sample 3, and the second interference filter 15 b Only the infrared light of wavelength λ ₂ in which only the substrate 1 has infrared absorption is applied to the third interference filter 1.
5c is adjusted so that either the coating material 2 or the base material 1 has no infrared absorption or only the base material 1 passes only infrared light having a wavelength λ ₃ having small infrared absorption.

Next, the signal processing section 30 basically constituted by a microcomputer will be described. Photometry unit 1
The detection signal of the infrared detector 18 of 0 is input to the signal separation circuit 33 via the amplifier 31 and the A / D converter 32, and according to the timing signal input from the timing detector 20, the wavelengths λ ₁ , λ ₂ and λ ₃ [hereinafter referred to as λ ₁ signal (= first measurement signal), λ ₂ signal (= second measurement signal), λ ₃ signal (= reference measurement signal)], and the following processing is executed. Is done. If the signal processing executed by the microcomputer is grasped as a functional block, it can be summarized into the following four blocks.

(I) Correction coefficient calculation circuit 34 The correction coefficient calculation circuit 34 is started by a base material correction coefficient registration key 35, and obtains a correction coefficient k relating to the absorbance of the base material in the following manner. Now, only the substrate 1, that is, the substrate 1 before coating the coating material 2 is set at the position of the measurement sample 3, and photometry is performed. The absorbances of the base material measured at the first and second measurement wavelengths λ ₁ and λ ₂ and the reference wavelength λ ₃ are defined as A ₁₀ , A ₂₀ and A ₃₀ , respectively. When the optical path length of the base material 1 a and _{t, A 10 -A 30 = (} a 1 -a 3) by Lambert-Beer's law _{t A 20 -A 30 = (a} 2 -a 3) t (a 1, a ₂ , a ₃ ; extinction coefficients at λ ₁ , λ ₂ , λ ₃ ), and if the ratio k of both equations is taken, then k = (A ₁₀ −A ₃₀ ) / (A ₂₀ −A ₃₀ ) = (A ₁ −a ₃ ) t / (a ₂ −a ₃ ) t = (a ₁ −a ₃ ) / (a ₂ −a ₃ ), and the ratio k is a value irrelevant to t. Now, the absorbances of the wavelengths λ ₁ , λ ₂ , λ ₃ measured for the measurement sample 3 in which the coating material 2 is coated on the substrate 1 are represented by A ₁ ,
When A _2, A _3, based on the A _3, the absorbance A by coating material _{2, A = (A 1 -A 3} ) - determined by (absorbance of the substrate at lambda ₁ relative to the A ₃₎ The second term cannot be determined practically. Therefore, assuming that Lambert-Beer's law can be applied to the second term, the above equation is expressed by the following equation. A = A ₁ −A ₃ −k (A ₂ −A ₃ ) From this, the absorbance A by the coating material is calculated. The experimental results described below have proved that the above assumptions are correct.

(Ii) Correction coefficient storage circuit 36 The correction coefficient k calculated by the correction coefficient calculation circuit 34
Memory. Since the correction coefficient k varies depending on the type of the base material 1, it is necessary to obtain, for each base material, for example, when the base material is paper, such as high-quality paper, kraft paper, Kent paper, and the like. Therefore, the correction coefficient storage circuit 36 stores the correction coefficient k for each type of base material.

(Iii) Absorbance calculation circuit 37 When the thickness measurement key 38 is operated, the absorbance calculation circuit 37 reads out the correction coefficient k from the correction coefficient storage circuit 36, and obtains three absorbances A obtained for the measurement sample 3. _1, a _2, from a _3, determined by the equation absorbance a of only the coating material 2 described above _{a = a 1 -A 3 -k (} a 2 -A 3).

(Iv) Thickness conversion circuit 39 A relational expression (regression equation) between the absorbance and the film thickness is obtained experimentally in advance (see FIG. 5), and the absorbance A obtained by the absorbance calculation circuit 37 is input. Then, the thickness is obtained from the above relational expression, and the value is output to the display 40 and displayed. <Experimental Example> Three types of papers having different paper qualities, that is, high quality paper, kraft paper, and Kent paper coated with polypropylene were used as measurement samples. The thickness range of the coating material was 3 to 30 g / m ² , and the measurement was performed for 7 points of different thicknesses for high quality paper, 14 points for kraft paper, and 17 points for Kent paper. Since the infrared absorption characteristics of paper and polypropylene are as shown in FIG. 4, 2360, 2510, and 2190 nm were selected as λ ₁ , λ ₂ , and λ ₃ . The correction coefficient k is high-quality paper, kraft paper, and Kent paper, respectively.
0.461, 0.454, and 0.414. For comparison, measurement was also performed by a conventional method. The wavelength is λ ₁ = 23
60 nm, λ ₂ = 2600 nm, and λ ₃ = 2190 nm were selected. The conventional method is equivalent to setting the correction coefficient k to 0.5 [A = A ₁ −0.5 (A ₂₀ + A ₃₀ )]. FIG. 5 shows the experimental results by the method of the present invention, and FIG. 6 shows the experimental results by the conventional method. In the figure, ●, ○, and □ indicate high quality paper, kraft paper, and Kent paper, respectively. The experimental results were evaluated with a variance of 2σ. The results were as shown in Table 1.

[0014]

[Table 1]

As is clear from the comparison between FIG. 5 and FIG. 6 and Table 1, according to the method of the present invention, the measurement accuracy can be greatly improved as compared with the conventional method. Of particular note is that, in the present invention, a single calibration curve can be used for fine paper, kraft paper, and Kent paper,
This is impossible with the conventional method. Therefore, according to the present invention, since it is not necessary to create a calibration curve for each type of substrate, the labor and time required for creating a calibration curve can be greatly reduced. In the above embodiment, the absorbance is measured for each wavelength. However, it is needless to say that the absorbance may be measured for each specific wave number, and then the true thickness may be calculated.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an infrared thickness measuring apparatus according to the present invention.

FIG. 2 is a front view of a rotary interference filter.

FIG. 3 is a graph showing infrared absorption characteristics of a coating material and a substrate.

FIG. 4 is a graph showing infrared absorption characteristics of paper as a base material and polypropylene as a coating material.

FIG. 5 is a graph showing experimental results of thickness measurement according to the present invention.

FIG. 6 is a graph showing an experimental result of thickness measurement by a conventional method.

[Explanation of symbols]

 Reference Signs List 10 photometry unit 11 light source 15 interference filter 17 concave mirror 18 infrared detector 30 signal processing unit 33 signal separation circuit 34 correction coefficient calculation circuit 37 absorbance calculation circuit 39 thickness calculation circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-226610 (JP, A) JP-A-61-120004 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 102

Claims (4)

(57) [Claims] When measuring the thickness of a coating material of an object to be measured having a substrate coated thereon, a wavelength λ _{1 at} which both the coating material and the substrate have infrared absorption.
A first measuring beam having the second measuring beam and the wavelength lambda ₃ or no infrared absorption is small for the substrate no infrared absorbing the coating material having a wavelength lambda ₂ that has infrared absorption only the substrate
Absorbance A ₁₀ , A of only the substrate using the reference light having
_20, and previously measured A _30, the correction coefficient k previously calculated by the following _{equation, k = (A 10 -A 30} ) / (A 20 -A 30) λ 1 for the measured object, lambda _2, lambda Absorbance at ₃ , A ₁ , A ₂ ,
Measuring the A _3, and calculates the absorbance A of only the coating material from these measurements by the following _{equation, A = A 1 -A 3 -k} (A 2 -A 3) the absorbance A was determined in terms of the thickness Court A method for measuring the thickness of a coated material in which the thickness of the material is determined. 2. When measuring the thickness of a coating material of an object to be measured having a substrate coated, a wavelength λ _{1 at} which both the coating material and the substrate have infrared absorption.
A second measurement light having a wavelength λ ₂ having infrared absorption only in the base material, and a second measurement light having two wavelengths λ ₃ and λ ₄ having no infrared absorption in both the coating material and the base material. Using the first and second reference lights, the absorbances A ₁₀ , A ₂₀ , A of only the substrate
_30, previously measured A _40, the correction coefficient k previously calculated by the following _{equation, k = (A 10 -A 50} ) / (A 20 -A 60) _{However, A 50 = A 30 + [} (A ₄₀ −A ₃₀ ) / (λ ₄ −λ ₃ )] × (λ ₁ −λ ₃ ), A ₆₀ = A ₃₀ + [(A ₄₀ −A ₃₀ ) / (λ ₄ −λ ₃ )] × (λ ₂ −λ ₃ ) Absorbance A ₁ at λ ₁ , λ ₂ , λ ₃ , λ ₄ for the DUT
A ₂ , A ₃ , and A ₄ were measured, and from these measured values, the absorbance A of only the coating material was calculated according to the following equation: A = A ₁ −A ₅ −k (A ₂ −A ₆ ) where A ₅ = A ₃ + [(A ₄ −A ₃ ) / (λ ₄ −λ ₃ )] × (λ ₁ −λ ₃ ), A ₆ = A ₃ + [(A ₄ −A ₃ ) / (λ ₄ −λ ₃₎ )] × (λ ₂ −λ ₃ ) A method for measuring the thickness of a coating material by converting the obtained absorbance A into a thickness to obtain the thickness of the coating material. 3. An apparatus for measuring the thickness of a coating material of an object to be measured in which a coating component is applied on a base material such as paper or film, wherein an infrared light source and infrared light are absorbed by both the coating material and the base material. Filter means for generating a first measurement light having a certain wavelength, a second measurement light having a wavelength having infrared absorption only in the base material, and a reference light having a wavelength having no infrared absorption in both the coating material and the base material Detecting means for detecting the absorbance of each light; correction coefficient calculating means for calculating the ratio of the absorbance of the first and second measurement lights only by the base material based on the absorbance of the reference light only by the base material; A correction means for correcting the absorbance detected for the object based on the ratio, wherein the fluctuation of the absorbance due to the fluctuation of the base material is corrected. 4. The first and second reference light beams having different wavelengths.
The coating material thickness measuring apparatus according to claim 3, wherein the ratio is determined using the absorbance of the first and second reference lights by the base material as a reference level.