JP2930210B2 - Control method of coating film quality in continuous coated steel plate manufacturing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of continuously applying a paint on a steel sheet and performing drying and baking, in order to maintain a constant film thickness and color tone of the finished coated steel sheet. The present invention relates to a technique for generally controlling the quality of a coating film based on signals from a meter, a film thickness meter, and a colorimeter.

[Conventional technology]

Conventionally, as a technique of applying a paint on a steel sheet and drying and baking it, Japanese Patent Application Laid-Open No. 57-102265 is disclosed. The color of the coated steel sheet is not constant due to changes in the steel sheet, the pigment in the paint, and the baking temperature, which may result in rejected products.

Also, as in JP-A-61-230767, in the technique of averaging the sampling values and controlling the same coating amount by the average value, the finished film thickness changes due to a change in the solvent dilution ratio. It is difficult to say that this is an effective means because the same change factors as in the technique of Japanese Patent Application Laid-Open No. 57-102265 can be considered.

[Problems to be solved by the invention]

Considering that the quality of the coated steel sheet is not only the film thickness but also the color difference as a major control factor, the present invention uses a colorimeter (for example, “Coating Engineering” vo1.2
3. No. 6 (1988)) to obtain coated steel sheets of excellent quality and high yield by changing the control target of coating amount and baking temperature.

[Means for solving the problem]

The present invention relates to a method for controlling the quality of a coating film in a continuous coated steel sheet manufacturing apparatus, which comprises a coating step of applying a paint to a running strip surface and a drying and baking step. In the above, the film thickness is controlled by a film thickness meter that measures the coating film thickness from the weight of the supplied paint, and the sheet temperature is controlled by a sheet thermometer disposed on the exit side of the drying and baking furnace. A color difference signal (ΔE, ΔL) is detected by a side color meter installed on the side, and when the color difference ΔL falls outside the upper and lower control limits according to the color difference signal, the control target value of the film thickness is changed and When the value is exceeded, the control target value of the baking temperature is changed according to the magnitude of the measured value of the film thickness and the target value and the magnitude of the measured value of the sheet temperature and the upper and lower control limit value.

 The operation based on the color difference signal is as follows.

(1) Color difference ΔL between standard and sample Now, assuming that tw is a setting signal to the system (coating amount) that controls the film thickness, the following operation is performed using the minimum value ΔLmin and the maximum value ΔLmax of ΔL as the upper and lower control limits. I do.

(A) Increase tw when ΔL <ΔLmin (b) Decrease tw when ΔL> ΔLmax (2) Color difference ΔE The upper limit of ΔE is ΔEmax, and when ΔE> ΔEmax, the coating film thickness td and sheet temperature T The temperature setting signal To of the system performing the printing is determined according to the criteria shown in Table 1 according to the measured value.

In Table 1, td: large means that the film thickness is larger than the target. Td: small means that the film thickness is smaller than the target. T: large means T> Tmax T: medium means Tmin ≦ T ≦ Tmax T: small Indicates T <Tmin. Here, Tmax and Tmin are upper and lower control limit values of the sheet temperature, respectively.

[Action]

The color is evaluated by tristimulus values, X, Y, and Z. JIS (Z872
The definition defined in 2) is as follows: X = ∫P (λ) (λ) ρ (λ) dλ / ∫P (λ) (λ) d (λ) (1) Y = ∫P (λ) (λ ) Ρ (λ) dλ / ∫P (λ) (λ) d (λ) (2) X = ∫P (λ) (λ) ρ (λ) dλ / ∫P (λ) (λ) d (λ (3) where P (λ): energy distribution of the light source (here, the value of the C light source is used) (λ), (λ), (λ): color matching function (here, the value of the 2 ゜ field of view is Used) ρ (λ): reflectance of the measurement object. P (λ), (λ), (λ), (λ) are JI
Since all the values described in S are used, X, Y, and Z can be calculated by measuring the reflectance ρ (λ) of the object. ρ (λ) may be obtained for each fixed wavelength by spectrally dividing the ratio of the reflected light to the incident light. However, it is easy to measure the absolute reflectance because of the influence of the incident angle and the difficulty in completely measuring the reflected light. is not. Therefore, the measurement is often performed with reference to a standard reflector having a known reflectance. As the reference standard reflector, a solidified BaSO ₄ powder is used internationally, and the value of Grum et al. Is often used.

Since it is difficult to strictly manage the color using the absolute values of X, Y, and Z, a color difference ΔE obtained by numerically processing X, Y, and Z is used for color management.

For example, the color difference of a hunter that is often used practically will be described.

Hunter's color difference The color difference ΔE is obtained by calculating differences ΔL, Δa, and Δb from the standard sample,
It is determined by the following equation.

In the present invention, the upper and lower limits of ΔL are determined and the film thickness control system is adjusted. On the other hand, when ΔE exceeds the limit, the control target temperature of the baking temperature is raised or lowered in accordance with the standard according to the film thickness and the drying furnace outlet temperature level. I do.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the method of the present invention. The strip 1 is coated with a paint by a coating device 2 and is heated and dried in an oven 3.

The coating device supplies the paint to the pickup roll 7 from the paint tank 5 by the paint pump 6, and the pickup roll 7 applies the paint to the surface of the strip 1 via the applicator roll 8. The thickness of the coating film is adjusted by an adjusting device 28 for adjusting the contact pressure of the applicator roll 8 of the pickup roll 7.

The oven 3 is provided with a hot-air nozzle 4 for blowing hot air supplied from a hot-air inlet pipe 26.

The paint application meter 11 is attached to the paint tank 5. This is a gravimetric method, and the change in weight is taken out as an integral value.
The amount of application is primarily controlled by the pressing pressure of the pickup roll 7 and the number of rotations of the pickup roll.

Next, the baking thermometer 13 is attached to the outlet side of the oven 3. In order to make the plate temperature detected by the plate thermometer 13 coincide with the target plate temperature, the temperature of the hot air blown into the final zone of the oven 3 is changed. This control is performed by changing the set point of the hot air temperature controller 22.

The present invention is not limited to the primary control of the coating amount and the plate temperature, but is to control the film pressure and the color difference, which are the final targets of the coated steel plate, within certain values. Dry film thickness meter
Attach 14 and meter 15 after cooling.

The output signal of the film thickness meter 14 and the output signal of the colorimeter 15 pass through a separately installed comparison circuit 25 and a coating controller 21 and a hot air temperature controller.
These are output as setting signals for the 22 cascade control systems.

 FIGS. 2 and 3 show the output of a colorimeter for ΔL 1 when the film thickness changes and (2) when the baking temperature changes for one paint applied to the steel sheet.

In this case, upper and lower limits to be managed are set, and the target value is changed with respect to the upper and lower limits, for example, as follows.

(B) If ΔL decreases, the setting signal for the system that controls the film thickness is increased.

(B) If ΔE becomes high, the setting signal for the system that performs the printing temperature is raised.

Here, (a) and (b) show an example of a simple control standard. Further, the characteristics of the film thickness and the printing temperature with respect to ΔL and ΔE are examined, and the control standard as shown in Table 1 is created. You may change the settings accordingly.

As a result, there is no change in the coating color due to the coating film thickness and the baking temperature, and a good quality product is obtained.

〔The invention's effect〕

According to the method of the present invention, the target values of the film thickness and the baking temperature are raised and lowered according to the color difference signal, and the final coating film quality of the strip is controlled, so that a strip having a uniform color tone can be obtained. .

[Brief description of the drawings]

FIG. 1 is an overall flow sheet of an embodiment of the present invention, FIG. 2 is a grab showing a relationship between a film thickness and a color difference signal ΔL, and FIG.
5 is a graph showing a relationship between a printing temperature and a color difference ΔE. DESCRIPTION OF SYMBOLS 1 ... Strip board 2 ... Coating device 3 ... Oven 4 ... Hot air nozzle 5 ... Paint tank 6 ... Paint pump 7 ... Pickup roll 8 ... Applicator roll 11 ... Coating amount meter 12 ... Hot air Thermometer 13 Plate thermometer 14 Film thickness meter 15 Colorimeter 21 Coating amount controller 22 Hot air temperature controller 23 Color difference controller 24 Film thickness controller 25 Comparison circuit 26 Hot air inlet pipe 27 Adjustment valve 28 Pickup roll adjustment machine

Claims (1)

(57) [Claims] In a method for producing a coated strip comprising a coating step of applying a paint to the surface of a running strip and a step of drying and baking it, a film thickness meter for measuring the coating thickness from the weight of the supplied paint. The film thickness is controlled, the sheet temperature is controlled by a sheet thermometer arranged on the exit side of the drying / baking furnace, and the color difference ΔL, ΔE is detected by a colorimeter installed downstream of the drying / baking step, and the color difference is detected. When ΔL is outside the upper and lower limits, the control target value of the film thickness is changed, and when the color difference ΔE exceeds the upper limit value, the magnitude of the measured value of the film thickness and the target value, and the measured value of the sheet temperature and the upper and lower control values. A method for controlling the quality of a coating film in a continuously coated steel sheet manufacturing apparatus, wherein a control target value of a baking temperature is changed according to a magnitude of a limit value.