JP3069868B2 - Control method of coating thickness of cut plate - 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 for controlling a coating thickness of a cut plate, and more particularly to a method for coating a cut plate such as a metal plate cut to a predetermined length at a predetermined speed. The present invention relates to a method for controlling a coating film thickness of a cut plate suitable for controlling the thickness to a constant value.

[0002]

2. Description of the Related Art A cut sheet formed by cutting a metal sheet into a predetermined size is coated by a curtain flow coater while transporting the cut sheet as disclosed in, for example, Japanese Utility Model Application Laid-Open No. 63-144878. In general, this is done in the following manner.

The above-mentioned coating method using a curtain flow coater has a long history, and its principle is a coating method utilizing the viscosity of the coating material. The coating is performed by passing a cutting board on a conveyor so as to cross the paint in the thickness direction.

A curtain flow coater used for such a coating is provided with a head portion having a steel slit through which the coating material flows in order to continuously form a uniform thin film curtain.

[0005] When coating a cut plate with the curtain flow coater, the thickness of the coating film is determined by setting the interval between the slits, the discharge pressure of the paint, and the conveyor speed under predetermined conditions. Therefore, the control of the thickness of the coating film
The above conditions are set so as to have a predetermined thickness, and the thickness of the coating film is measured after drying.

[0006] Incidentally, steel manufacturers use a curtain flow coater to apply coatings to stainless steel sheets or the like using vinyl or other paints such as vinyl chloride. The main object of the present invention is to prevent a cut plate from being damaged during transportation to a processing maker or in a manufacturing process such as a press in the processing maker.

Therefore, the measurement of the thickness of the coating film is, for example, 4
The thickness may be about 0 μm ± 5 μm, and the accuracy is not so required. Therefore, the stainless steel plate after drying the coating film for film thickness measurement is appropriately extracted and measured with a measuring instrument such as a micrometer.

However, in recent years, painted stainless steel plates (cut plates) have been used as building materials such as wall materials and roof materials, and in particular, transparent colored painted stainless steel plates have been required.

As the paint for the transparent colored painted stainless steel plate, a fluororesin paint or the like is used.
Although the thickness is about μm, even if there is a deviation (unevenness) of about 1 μm in the thickness of the coating film, it appears as color unevenness and loses commercial value, so the film thickness deviation within one cutting board Of course, strict film thickness control is required even within a lot.

An extremely thin film (20 ± 1 μm) as described above
m) is measured by a film thickness measurement method using X-rays (JP-A-6
4-41810) are known. However, such a film thickness gauge using radiation requires safety management in accordance with legal regulations, and is therefore difficult to handle. Therefore, as a technique for measuring a thin film thickness which is safe and easy to handle, there is a method using a three-wavelength non-simultaneous photometry type infrared film thickness meter using three wavelengths in the infrared region.

As an infrared film thickness meter of the three-wavelength non-simultaneous photometry method, for example, as shown in FIG. 9, infrared light emitted from a light source 10 is transmitted through a rotary filter 12 to select a specific wavelength light. The specific wavelength light is incident on a cutting plate (metal plate) S having a coating film C, and the reflected light reflected on the surface of the cutting plate S is received by a detector 16, and a detection signal from the detector 16 is received. In some cases, the signal processing unit 18 performs processing and performs a predetermined calculation to calculate the film thickness.

In the film thickness meter, three wavelengths are selected by rotating the rotary filter 12 so as to match the optical path of the light from the light source. Therefore, the measurement at each wavelength is a non-simultaneous operation performed by sequentially switching the filters.

The principle of measurement of the infrared film thickness meter is that, when infrared rays are radiated to the surface of a coating film and transmitted therethrough, characteristic absorption inherent to the material constituting the coating film (chemical characteristics such as C—H group or O—H group). Infrared absorption spectrum related to the thickness and absorption due to stretching vibration of the bond) is obtained, and the amount of light absorption at the characteristic absorption wavelength is proportional to the thickness of the substance. Can be determined.

That is, the relationship between the amount of transmitted light and the thickness of the coating film is represented by a coating absorption coefficient α (λ) at a wavelength λ, a coating film thickness t.
Assuming that the intensity of light before passing through the coating film is I ₀ , the Lambert-Beer equation of the following equation (1) holds between the intensity of transmitted light I (λ) and the intensity of transmitted light I (λ) is measured. Then, the thickness can be obtained.

I (λ) = I ₀ exp {−α (λ) t} (1)

The three wavelengths are selectively used in order to reduce the fluctuation of the light source light intensity, the drift of the electric system or the influence of disturbance light, moisture in the air, temperature, etc., as shown in FIG. , The characteristic absorption peak wavelength (λ1), the wavelength on the high wave number side (λ2) where the characteristic absorption is small, and the wavelength on the low wave number side (λ
3) is selected, a baseline is drawn at the tail (λ2, λ3) of the characteristic absorption peak, and the film thickness is obtained from the absorption peak amount obtained by subtracting the background.

When coating with the above-mentioned curtain flow coater, the thickness measurement of the coating film is usually performed by continuously operating a film thickness meter in order to speed up the response time, and the film thickness is controlled by the detected film thickness. A method is employed in which a signal is fed back to the coating conveyor speed.

[0018]

However, the method of measuring the thickness by continuously operating the infrared film thickness meter as described above is suitable for an object to be coated having a continuous shape. Since the transfer of the plate is performed intermittently, the measurement by the film thickness meter also becomes intermittent.

Therefore, in the above-described three-wavelength non-simultaneous photometry method of the infrared film thickness meter, the infrared light is sequentially switched by filters having different transmission wavelength ranges, so that the film is calculated from the amount of light reflected on the metal surface for the predetermined three wavelengths. In order to obtain the thickness, at the end of the cutting plate S which is intermittently conveyed, the reflected light amount of one or two of the predetermined three wavelengths is reduced due to a difference between the wavelength (filter) switching timing and the conveying timing of the cutting plate. A situation that is not the value on the surface to be measured (paint film surface) will occur. As a result, the film thickness obtained by the above calculation may become an abnormal value that does not match the actual film thickness.

That is, the wavelengths λ 1, λ
2, select the [lambda] 3, and irradiating the coated film surface of each infrared light sequentially Setsuban S, to measure the reflected light intensity I _1, I _2, I _3, these light intensity I _1, I _2, I _In the case of calculating the film thickness based on (3), there is no problem if the measurement can be sequentially started from the wavelength λ1, but as shown in FIGS.
When the measurement is started from the wavelength λ3, the original calculation cannot be performed, and therefore, as shown in FIG. 8, the thickness of the coating film at the tip of the cutting plate S is calculated as an abnormal value. Become. FIG. 7 shows a state where the measurement beam diameters of the respective wavelengths are arranged in the order of measurement.

As described above, the thickness of the coating film becomes an abnormal value also at the rear end of the cutting plate S. When the measurement of the wavelengths λ1 and λ2 is completed, the rear end passes. If you do
It will be calculated as an abnormal value.

When a film thickness signal corresponding to such an abnormal film thickness value, for example, an average value, a maximum value, or a minimum value is used as a control signal for controlling the thickness of the coating film on the cutting plate S,
There has been a problem that the thickness of the coating film greatly deviates from the target film thickness.

In the case where the thickness of the coating film of the cutting plate S conveyed intermittently is continuously measured, the film thickness signal is also intermittent. A need arises to identify the signal. For the identification, a method using tracking of the cutting plate S is known, but in this method, a deviation occurs due to a cumulative error of the tracking, so that there is a problem that control is performed using a signal other than the film thickness signal to be controlled. was there.

The present invention has been made in order to solve the above-mentioned conventional problems. After coating a cutting plate at a predetermined coating speed, the three-wavelength non-simultaneous photometric infrared film thickness is transported while the cutting plate is conveyed. When measuring with a meter, it is possible to prevent the detection of abnormal film thickness values occurring at the leading and trailing ends of the cutting plate, always accurately detect the normal film thickness value, and based on the film thickness value, determine the coating film thickness. It is an object of the present invention to provide a method of controlling a coating film thickness of a cut plate, which can control a thickness of a cutting plate.

[0025]

SUMMARY OF THE INVENTION According to the present invention, a cutting plate is coated at a predetermined coating speed, the thickness of a coating film is measured while transporting the cutting plate, and the coating film speed is fed back by measuring the thickness of the coating film. A method for controlling the coating film thickness of the cutting board, which controls the thickness of the coating film by measuring the thickness of the coating film with an infrared film thickness meter of a non-simultaneous photometry method of two or more wavelengths, A mask was applied to the measurement signal output from the infrared film thickness meter over a predetermined range of the front end portion and the rear end portion of the cutting plate, and after the masking of the front end portion was released, the measurement signal output became equal to or larger than the threshold value. The object has been achieved by using a measurement signal after a lapse of a predetermined time from a time point as a control film thickness signal.

[0026]

According to the present invention, when measuring the thickness of the coating film on a cutting board using an infrared film thickness meter of a three-wavelength non-simultaneous photometry method, the thickness of the cutting board which may cause an abnormal film thickness signal is measured. Apply a mask to the measurement signal at the end, apply a threshold process to the measurement signal output after the mask is released, and wait for the signal to rise,
After that, the measurement signal sampled at the elapse of a predetermined time is used as a film thickness signal for controlling the coating film thickness, so it is possible to accurately control the film thickness of the cut plate that is intermittently conveyed and painted Becomes

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a coating film thickness control device applied to a method for controlling a coating film thickness of a cut plate according to one embodiment of the present invention. FIG. FIG. 4 is an explanatory diagram showing an operation of a mask circuit in the device.

The control device of this embodiment is provided with conveyors 20A to 20D for transporting the cutting plate S rightward in the drawing, and each of the conveyors 20A to 20D has a driving motor 22A.
To 22D are provided respectively.

A curtain flow coater 24 is provided between the conveyor 20A and the conveyor 20B so that the paint flows down from the curtain flow coater 24 into a curtain at a predetermined width, thickness and discharge pressure. Has become.

In the length direction of the conveyor 20C,
A drying furnace 26 is provided, and the cutting plate S can be transported in the drying furnace 26.

A tip detector 28 of the cutting plate S is provided above the vicinity of the conveyor 20C and the conveyor 20D, and a detection signal is sent from the tip detector 28 to the mask circuit 30.
It is possible to input to.

A pulse generator 32 is connected to the rear end roll of the conveyor 20D.
A pulse signal is input to the mask circuit 30, and an infrared film thickness meter is provided above the conveyor 20D at a position separated from the tip detector 28 by a predetermined distance.

The mask circuit 30 and the infrared film thickness meter 34
Are connected to a switch 36 so that either one of the electrical continuity can be selected by the switch 36.

The switch 36 includes a comparator 38 for comparing the input signal with a threshold value, a first data holder 40 for storing data of the first sampling, and a second data holder for storing data of the second sampling. 42,
The comparator 38, the first data holder 40, and the second
The data holding unit 42 is connected via a timer (delay circuit) 44 to enable time adjustment of data input.

The first data holder 40 and the second data holder 42 are both connected to a comparator 46 and an averager 48, and the first data holder 40 and the averager 48 operate a switch 50. Connected to a motor controller 52 for controlling the motors 22A and 22B via a switch 50.
Is switched by the comparator 46 between the first data holding unit 40 side and the averaging unit 48 side.

The comparator 46 compares the first data (film thickness signal) and the second data, which are input to the first data holding unit 40 and the second data holding unit 42 and are held, respectively. If the difference between the first data and the second data is within a predetermined range, the first data can be input to the motor controller 52 via the switch 50. If the difference is outside the range, the first data and the second data can be input. The averager 4
The data averaged in step 8 can be input to the motor controller 52 by switching the switch 50.

In this embodiment, the infrared film thickness meter 3
Reference numeral 4 denotes an infrared film thickness meter of the three-wavelength non-simultaneous photometry method shown in FIG. 9 described above. When the film thickness is measured by the infrared film thickness meter 34, the front and rear ends of the cut plate S are measured. The measurement signal output from the infrared film thickness meter 34 is masked by the mask circuit 30 over a predetermined range.

That is, as shown in FIG.
Accordingly, when the cut sheet S having a length l in which the coating film is dried is conveyed, the leading end of the cut sheet S is detected by the leading end detector 28, and the leading end and the trailing end of the cut plate S are respectively provided. Mask ranges l ₁ and l ₂ are set.

This mask range (length) is calculated by the following equation (2). The method of determining the mask range will be described later in detail.

L ₁ = l ₂ = (maximum response time at end) × (cut-plate transport speed) + α (2) (where α is a constant of 0 or more)

The mask ranges l ₁ and l ₂ are set according to the film thickness signal (measurement signal) output from the infrared film thickness meter 34.
Is performed by switching the switch 36 by the mask circuit 30.

The mask circuit 30 has a sequencer, and receives and holds data of the length 1 of the cutting plate S and the transport speed. In the mask circuit 30, the distance L1 from the tip detector 28 to the beam center of the infrared film thickness meter 34 and the mask range l ₁ and l
₂ , the tracking length L2 (= L1 +
l ₁ ) and L 3 (= L 1 + l−l ₂ ) are obtained, and these are set as counters in the mask circuit 30.

From the time when the leading end of the cutting plate S conveyed intermittently is detected by the leading end detector 28, the position of the cutting plate S is tracked by the pulse generator 32 whose pulse width changes according to the conveying speed.

When the tip of the cutting plate S has advanced by l ₁ from the beam center of the film thickness meter 34, ie, from the position shown in FIG.
The switch 36 is switched to the film thickness meter 34 when it advances by 1 so that the measured film thickness signal is input. Then, when the cutting plate S moves from the position shown in FIG. To stop the input of the film thickness signal.

As described above, a mask can be applied to the film thickness measurement signals at the front end and the rear end of the cutting plate S,
Only the film thickness signal output by the film thickness meter 34 can be input to the calculation unit 54 via the switch 36 for the cutting plate S excluding l ₁ and l ₂ after the mask is released.

The mask range (l ₁ , l ₂ ) is calculated by the equation (2) as described above. An example of how to determine the mask range will be described in detail below.

When measuring the film thickness of the moving cutting plate S, the response time at the end of the cutting plate S is (1) a delay due to the measured beam diameter and the transport speed of the cutting plate S, and (2) an infrared film. Thickness gauge 34
, (3) delay due to the rotation timing of the rotation filter, (4) delay due to the number of data averaging processing points, and (5) delay due to the sampling timing of the analog output. Hereinafter, the above (1) to
(5) will be described with a specific example.

(1) Delay due to Measurement Beam Diameter and Moving Speed of Cutting Plate S As shown in FIG.
After the measurement beam starts to be applied (state of B1), 10
The time required until it takes 0% (state of B2) is
Assuming that the transfer speed is V (m / min) and the measurement beam diameter is A (mm), the time until a predetermined response signal is output, that is, the rise delay is 60 A / V (millisecond). For example, if the measured beam diameter in the transport direction of the cutting plate S is 10 mm and the transport speed is 1
At 5 m / min, it appears as a delay of 40 milliseconds.

(2) Delay due to Time Constant of Infrared Film Thickness Meter Each wavelength (λ
The time required for the signal intensity of (1, λ2, λ3) to reach 99.99% of the signal intensity of the cutting plate S from near zero (belt conveyor surface) is obtained by the following equation (3). −τ · ln (1-0.9999) (3) Assuming that the time constant of the infrared film thickness meter is 0.5 millisecond, the required time is 4.6 from the above equation (3). Milliseconds. Also, assuming that the time for capturing a signal of one wavelength by the rotating filter is approximately 1.4 milliseconds, it is necessary to rotate the rotating filter four times before the above signal strength is reached. If the required time is 33 milliseconds, a response delay of 132 milliseconds will occur.

(3) Delay due to Rotational Timing of Rotary Filter In FIG. 4, when the rotational timing of the rotary filter does not match, for example, when the measurement beam starts to be applied to the cutting plate S in the middle of the wavelength λ1, the rotational interference filter Since the data is determined after one more rotation, the response delay of a maximum of 33 milliseconds occurs in this case.

(4) Delay due to data average processing points Delay due to each moving average processing point is (integrated points−1) × 3
It takes 3 milliseconds. Therefore, in the case of the integrated four points, the delay is 99 milliseconds. Here, the value of (integrated points-1) is based on the fact that data for the first rotation has already been obtained in the above item (2).

(5) Response delay due to sampling timing of analog output Assuming that the analog output from the data processing unit outputs a moving average value determined before that time by sampling every 20 milliseconds, a response of a maximum of 20 milliseconds Delay occurs.

As described above, the response time at the end of the cutting plate S is determined by the above-mentioned delays (1) to (5), and the total of these delays (1) to (5) is The above (2)
It can be the maximum response time at the end in the equation.

The principle of calculating the film thickness based on the measurement signal in the infrared film thickness meter 34 is as follows.

In the infrared film thickness meter of the three-wavelength non-simultaneous photometry system shown in FIG. 9 described above, three filters of the rotary filter 12 are used, and the transmission wavelength λ 1 (3490 nm),
Infrared light of λ2 (3720 nm) and λ3 (2543 nm) are sequentially irradiated to the coating film of the cutting plate S, and the intensities I ₁ , I ₂ and I ₃ of the respective reflected lights are measured.

Using the intensity of each reflected light, the following equation (4)
I ′ is calculated by the following formula, and the I ′ is substituted into the regression equation of the following equation (5) to calculate the coating film thickness t.

I ′ = I ₁ − [I ₂ − (I ₂ −I ₃ ) / 2] (4) t = C 1 · I ′ + C 2 (5) (where t is film thickness, C 1, C 2 Is the regression coefficient)

The regression equation (5) collects a large amount of data on I 'by measuring I ₁ , I ₂ , and I ₃ for a large number of samples, and is determined in advance.

The calculation based on the regression equation (5) is executed by a calculation unit (not shown), and a film thickness signal corresponding to the calculated thickness t is output to the control unit 54. The thickness of the coating is controlled.

Next, the operation of this embodiment will be described.

First, the cutting board S is conveyed at a predetermined speed by the conveyor 20A, and the curtain flow coater 24 passes the paint flowing down at a constant speed to apply the coating. Then, the cutting board S is conveyed by the conveyor 20B. Further, the coating film is dried while being conveyed in the drying furnace 26 by the conveyor 20C.

When the tip of the cutting plate S whose coating film has been dried in the drying furnace 26 is detected by the tip detector 28,
As shown in FIG. 2, the cutting plate S is moved from the position to L2.
The switch 36 is switched to the infrared film thickness meter 34 side by the mask circuit 30 at the time when the film is transported only by the mask circuit 30, and the measurement of the film thickness is started. Make sure that no signal is output.

In this case, since the mask is applied to the leading end and the trailing end of the cutting plate S over the ranges of l ₁ and l ₂ , respectively, the measurement signal output from the infrared film thickness meter 34 is As shown in FIG. 5, as shown in FIG. 8, the abnormal film thickness signal generated at the front end and the rear end of the cutting plate S is removed.

In the present embodiment, after the mask applied to the front end portion over the range l ₁ is released, the film calculated by the above equation (5) based on the measurement signal output from the infrared film thickness meter 34. A film thickness signal corresponding to the thickness is input to the comparator 38,
Threshold processing is performed on the film thickness signal.

That is, as shown in FIG. 6A, the system waits until the film thickness signal input to the comparator 38 becomes, for example, 80% or more of the expected film thickness, and thereafter, for example, has a time delay of 0.8 seconds. Thereafter, the first sampling (intensity measurement of the reflected and transmitted light performed in the order of λ1, λ2, λ3) is started, and after a lapse of 0.8 second, the second sampling is similarly started, and the first and second samplings are started. The obtained film thickness signal (data) is transferred to a first data holder 40 and a second data holder 42, respectively.
And store it.

Adjustment of data input to the first data holder 40 and the second data holder 42 is performed by a timer 44.
Done by

As described above, the first data holder 40 and the second data
The film thickness signal stored in the data holding unit 42 is
For example, the film thickness value at the time of the second sampling is smaller than that at the time of the first sampling.
%, The data (first film thickness signal) at the time of the first sampling is input from the first data holder 40 to the motor controller 52 via the switch 50, and the motor controllers 52 use the conveyors 20A and 20B. By controlling the rotation of the drive motors 22A and 22B, the speed of the cutting plate S passing under the curtain flow coater 24 is controlled to control the thickness of the coating film applied on the cutting plate S.

On the other hand, if the decrease width exceeds 10%, the first and second film thickness signals are averaged by the averager 48, and the average film thickness signal is passed through the switched switch 50. Similarly, input to the motor controller 52 and the motor 22
A, control of rotation of 22B. The switching operation of the switch 50 is performed by an input signal from the comparator 46.

As shown in FIG. 6B, when the length of the cutting plate S in the transport direction is short and the second sampling cannot be performed, only the data at the first sampling is stored in the first data holding unit 40. It is stored and the above control is performed by the first film thickness signal.

As described above in detail, according to the present embodiment, when measuring the coating film thickness of the transported cutting plate S using an infrared film thickness meter of a three-wavelength non-simultaneous photometry method, The infrared film thickness meter 34 extends over a predetermined range at the front end and the rear end of the infrared film thickness meter.
By masking the measurement signal output from
Since the abnormal film thickness signal generated at the front end portion and the rear end portion of the cutting plate S can be eliminated, the accuracy of the film thickness signal can be improved. Since the speed (coating speed) can be controlled, it is possible to control the thickness of the coating film with extremely high accuracy.

Although the present invention has been described in detail, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

For example, although the method of determining the mask range has been specifically described, the method of determining the mask range is not limited to the method described in the above embodiment.

The method of controlling the thickness of the coating film on the cutting plate S is not limited to the method of controlling the conveying speed of the conveyor, but may be the method of adjusting the flow rate of the paint from the curtain flow coater.

The wavelength in the infrared region to be used is not limited to three wavelengths, and is not particularly limited as long as it is two wavelengths or more. When the measurement is performed by a non-simultaneous photometric film thickness meter using two or more wavelengths, the same effect as the three-wavelength non-simultaneous photometric method can be expected.

[0076]

As described above, according to the present invention, a cut plate is coated at a predetermined coating speed, and the cut plate is conveyed and measured with an infrared film thickness meter of a non-simultaneous photometric method of two or more wavelengths. When controlling the thickness of the coating film by feeding back the signal corresponding to the measured film thickness, the abnormal film thickness signal caused by the leading and trailing edges of the cutting plate can be removed, so that the normal film thickness is always maintained. It is possible to accurately detect the value and control the coating film thickness based on the film thickness signal corresponding to the film thickness value.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a coating film thickness control device applied to one embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing the operation of a mask circuit.

FIG. 3 is a schematic explanatory diagram for explaining a delay due to a measurement beam diameter and a moving speed of a cutting plate.

FIG. 4 is a schematic explanatory diagram for explaining a delay due to a time constant of the infrared film thickness meter.

FIG. 5 is a schematic explanatory view showing the operation of the embodiment.

FIG. 6 is a schematic explanatory view showing the operation of the embodiment.

FIG. 7 is an explanatory diagram showing a conventional problem.

FIG. 8 is an explanatory diagram showing a conventional problem.

FIG. 9 is a schematic configuration diagram showing an infrared film thickness meter of a three-wavelength non-simultaneous photometry system.

FIG. 10 is an explanatory diagram showing the principle of an infrared film thickness meter of a three-wavelength non-simultaneous photometry method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Light source, 12 ... Rotary filter, 16 ... Detector, 18 ... Signal processing part, 20A-20D ... Conveyor, 22A-22D ... Motor, 24 ... Curtain flow coater, 26 ... Drying furnace, 28 ... Tip detector, 30 ... Mask circuit, 32 ... Pulse generator, 34 ... Infrared film thickness meter, 36,50 ... Switch, 38,46 ... Comparator, 40 ... First data holder, 42 ... Second data holder, 44 ... Timer ( Delay circuit), 48: averager, 52: motor controller, 54: control unit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-154104 (JP, A) JP-A-63-242375 (JP, A) JP-A-61-251750 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B05D 3/00 B05C 5/00 103 G05D 5/02 B05C 11/00

Claims (1)

(57) [Claims] 1. A cutting plate is coated at a predetermined coating speed, the thickness of the coating film is measured while transporting the cutting plate, and the coating speed is adjusted by feeding back the film thickness. A method for controlling the coating thickness of a cutting plate, wherein the thickness of the coating film is measured with an infrared film thickness meter of a non-simultaneous photometric method of two or more wavelengths, and the leading end and the rear end of the cutting plate are controlled. Over a predetermined range of the portion, a mask is applied to the measurement signal output from the infrared film thickness meter, and after the mask is released from the tip portion, after a predetermined time has elapsed from the time when the output measurement signal has exceeded the threshold value. A method for controlling a coating film thickness of a cutting board, wherein the measurement signal is used as a control film thickness signal.