JP2598509B2 - Continuous drying and baking method for strip coating film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for drying and baking a coating film on a surface of a strip such as a steel plate, and more particularly to a method for eliminating a non-uniform pattern of a coating film occurring during drying and baking by hot air. It is about.

<Prior art> Conventionally, a method of manufacturing a coated product of a steel sheet is to apply a predetermined coating liquid to a running steel sheet surface by an appropriate coating method such as dipping, spraying, or a roll coater, and then apply the coating solution to a predetermined furnace. A continuous method of putting, drying and baking is adopted.

However, after such continuous application, the dried and baked coating film may have an uneven pattern and impair the appearance of the product.

Therefore, as a method of obtaining a uniform coating, there is Japanese Patent Publication No. 52-31892.
Japanese Patent Application Laid-Open No. 59-32978 discloses a method for controlling the roll rolling force and the amount of adhesion to the surface of a plate to be coated so that a coating unevenness recovery phenomenon occurs in a coating method using a normal rotation type roll. A method is disclosed in which the liquid properties are limited, a saucer is installed below each roll, and the coating liquid is supplied to all rolls.

In recent years, a so-called high-speed processing method has been implemented to increase productivity. Techniques corresponding to this are the above-mentioned references, but these techniques focus on the coating method, and do not consider drying and baking methods.

On the other hand, as for drying and baking,
Although there is a method of simultaneously controlling the baking state of the coating film on the front and back surfaces, there is no description about the uniformity of the coating film.

That is, even if uniform coating is performed at the time of coating, if a non-uniform pattern occurs in the drying and baking process, the product value is reduced, which is very uneconomical.

<Problems to be Solved by the Invention> The present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a method for continuously drying and baking a coating liquid applied to a strip surface uniformly. It is the purpose.

<Means for Solving the Problems> The present invention provides a method in which the coating liquid applied to the front and back surfaces of a strip is continuously dried and baked by blowing hot air in a hot blast stove, where the hot air velocity is at a location of Xm / sec. The strip is run, and when the distance from the hot air discharge port to the strip surface at this time is Ycm, Y is kept at 5 or more and Y is kept at (0.7X-9) or more according to the hot air velocity X, and The temperature rise rate from room temperature to 150 ° C is 4-30 ° C / se.
A continuous drying and baking method for strip coating films, characterized in that the coating liquid is phosphate-based,
One or more chromate salts, or a mixed aqueous solution of one or more phosphate salts or chromate salts and an organic resin, or a water-soluble organic resin, a water-soluble emulsion resin, etc. it can.

<Operation> In the present invention, when the coating plate is run at a location where the hot air velocity is Xm / sec and the distance from the hot air discharge port to the strip surface is Ycm, Y is 5 or more, that is, the running of the coating plate. The position is more than 5cm away from the hot air outlet and Y
It must satisfy 0.7X-9.

If the above conditions are not satisfied, a wind ripple is generated on the coating film on the surface of the coating plate, and the appearance of the coating film is deteriorated.

That is, if the velocity of the hot air at the traveling position of the coating plate increases, wind ripples are generated on the coating film, and if the film is dried and baked in this state, the appearance of the coating film becomes poor. For this reason, it is necessary to perform drying and baking without generating a wind ripple. Therefore, Y is limited to (0.7X-9) or more.

On the other hand, when the traveling position of the application plate is less than 5 cm from the discharge port, the application plate vibrates due to wind pressure and contacts the hot air discharge nozzle or hot air chamber, causing flaws on the application plate surface and deteriorating not only appearance but also corrosion resistance It was limited to 5cm or more.

The distance from the discharge port can be adjusted by controlling the tension in the furnace of the passing plate material.

The shape of the hot air discharge port for obtaining the above conditions may be any shape. What is important is the hot air velocity at the traveling position of the coating plate and the distance from the hot air discharge port, and the temperature rise rate from room temperature to 150 ° C at the steel sheet surface temperature is 4 to 3
0 ° C / sec.

If the heating rate is lower than 4 ° C./sec, the time required for drying and baking becomes longer. Alternatively, it is uneconomical because the furnace length for drying and baking needs to be increased.

On the other hand, if the heating rate is higher than 30 ° C./sec, boiling will occur on the surface of the coating film and powder of the coating film will be generated on the coating film surface, deteriorating the product characteristics.

For this reason, when drying and baking the coated plate, the temperature of the steel plate surface is increased from room temperature to 150 ° C at a rate of 4 to 30 ° C / sec.
Need to be controlled.

There are many factors for controlling the temperature rise rate in the actual line, such as the thickness, width, and speed of the passing material, coating composition, hot air temperature, hot air speed, and the distance of the passing material from the hot air outlet. It cannot be a constant expression. Therefore, a surface thermometer is designed at the end of the drying zone in the furnace (at the end of the catenary), and various factors are controlled so that the temperature of the steel sheet surface becomes 150 ° C.

For example, if the passing speed is doubled, the surface temperature of
The temperature of the hot air, the speed of the hot air, the distance of the sheet passing material from the discharge port, and the like are changed in order to make the temperature 0 ° C. For this reason, the rate of temperature rise from room temperature to 150 ° C. of the steel sheet surface is doubled.

When the surface temperature of the steel sheet reaches 150 ° C., the coating liquid dries. At a temperature higher than 150 ° C., the appearance of the coating film is not affected by the heating rate, the hot air velocity, or the distance from the discharge port.

The coating liquid used in the present invention may be a mixture of one or more of a phosphate or a chromate, or one or more of a phosphate or a chromate and an organic resin. Examples include a mixed aqueous solution, a water-soluble organic resin, and a water-soluble emulsion resin.

Examples of the phosphate system in the present invention include zinc, aluminum, calcium, and magnesium phosphates, or phosphates such as zinc, aluminum, calcium, and the like.
Divalent or trivalent oxides and hydroxides such as magnesium,
Carbonate dissolved or titanium oxide,
Colloidal silica, colloidal alumina, boric acid, etc. are added alone or in combination of two or more.

Next, the chromic acid type is a dichromate such as zinc, calcium, or magnesium, or a solution obtained by dissolving a divalent oxide, hydroxide, or carbonate such as zinc, calcium, or magnesium in chromic anhydride, or Titanium oxide,
One or two or more of colloidal silica, colloidal alumina, boric acid, an organic reducing agent and the like are added.

Further, as the organic resin mixed with the phosphate type or the chromate type, water-soluble or emulsion-type acrylic resins and copolymers thereof, vinyl acetate resins and copolymers thereof, butadiene-styrene copolymers, alkyds One or more of resins, phenolic resins, epoxy resins, melamine resins, and modified products thereof can be used.

Moreover, you may apply only an organic resin. Next, examples will be described.

<Example> Example 1 A material equivalent to JIS S60 with a thickness of 0.50mm and a width of 1025mm (Si: 0.1wt
%, C: 0.030 wt%), after degreasing, applying the following coating solution by a dipping method, and drying and baking in a hot air oven under the following conditions.

Coating solution A 30% magnesium dichromate solution 130 parts by weight Acrylic resin emulsion (resin solid content: 50%) 30 parts by weight Ethylene glycol 10 parts by weight Boric acid 10 parts by weight Drying and baking conditions Hot air temperature Drying oven 500 ° C Baking oven 400 ℃ Hot air speed 5-40m / sec (where the coating plate runs) Distance between the coating plate and the hot air discharge port 3-30cm The heating speed was changed to 150 ° C by changing the passing speed in the furnace. .

The results are shown in FIG. In the figure, the mark ○ indicates that a good and uniform coating appearance was obtained, the mark も の indicates that some wind ripples were observed, and the mark × indicates that the wind ripples were clearly recognized and the coating appearance was poor.

From this, it can be seen that good film appearance can be obtained with Y0.7X-9.

Also Indicates the occurrence of flaws.

This indicates that when the distance between the application plate and the hot air discharge port is less than 5 cm, the application plate vibrates due to the wind pressure, comes into contact with the hot air chamber, and a flaw is generated on the surface of the application plate.

Furthermore, the rate of temperature rise up to 150 ° C at a steel sheet surface temperature of 30 ° C / se
When the value was more than c, powder wiping (boiled on the film surface when the film was rapidly dried and the film was finely cracked) occurred on the film surface.

Example 2 A material equivalent to JIS S60 having a thickness of 0.5 mm and a width of 1025 mm (Si: 0.1 wt.
%, C: 0.030 wt%), and the following coating liquids B to E were applied respectively, placed in a place with a hot air velocity of 20 m / sec, and dried and baked. At this time, the distance from the hot air discharge port of the coating plate was 10 cm, and the rate of temperature rise from room temperature to 150 ° C. was 18 ° C./sec.

Coating Solution B 30% Magnesium Phosphate Solution 100 parts by weight Chromic Anhydride 30 parts by weight Aluminum Nitrate 30 parts by weight Coating Solution C 30% Calcium Dichromate Solution 130 parts by weight Ethylene Glycol 10 parts by weight Coating Solution D Acrylic / Styrene Resin emulsion (resin solid content: 5
0%) Coating solution E 30% magnesium dichromate solution 130 parts by weight 30% first magnesium phosphate solution 30 parts by weight Ethylene glycol 10 parts by weight Acrylic / styrene resin emulsion (resin solid content: 5
0%) 30 parts by weight Boric acid 10 parts by weight Each of the obtained coating films was uniform and had a good appearance.

Comparative Example 1 Under the conditions of Example 2, the distance from the hot air discharge port was set to 5 cm by changing the tension at the time of sheet passing. The velocity of the hot air hitting the coating plate at this time was 28 m / sec. The rate of temperature rise of the coated plate from room temperature to 150 ° C. was 26 ° C./sec.

All of the obtained dried coating films had a wind ripple and had an appearance that did not become a commercial product.

Example 3 JIS S 9 equivalent material (Si: 3.2 wt%, C: 0.005 wt%, sheet thickness
After degreasing a steel sheet (0.5 mm), the following coating solution was applied, placed in a hot air velocity of 5 m / sec, dried and baked. At this time, the distance from the hot air discharge port of the coating plate was 20 cm. The rate of temperature rise from room temperature to 150 ° C. was 13 ° C./sec.

Treatment solution F Alkyd / melamine-based water-soluble resin The obtained coating film was uniform and had a good appearance.

Example 4 In the conditions of Example 3, the distance from the hot air discharge port was set to 5 cm by changing the tension at the time of sheet passing. The speed of the hot air hitting the coating plate at this time was 19 m / sec. The rate of temperature rise from room temperature to 150 ° C. was 11 ° C./sec.

 The obtained coating film was uniform and had a good appearance.

Comparative Example 2 The hot air velocity hitting the coating plate of Example 4 was 25 m / sec. The heating rate was 16 ° C./sec.

Although the obtained coating film was almost uniform, a pattern due to slight wind ripples was observed.

<Effects of the Invention> As described above, according to the present invention, by controlling the hot air velocity at which the plate temperature of the coating plate hits the coating plate up to 150 ° C and the distance between the coating plate and the hot air discharge port, the coating plate is always uniform. Dry and baked coatings having a good appearance can be obtained stably.

[Brief description of the drawings]

FIG. 1 shows the effect of the velocity of the hot air at the place where the coating plate runs and the distance from the hot air discharge port on the uniformity of the coating film.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuo Shimada 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. Chome (without address) Inside the Mizushima Works of Kawasaki Steel Corporation (56) References JP-A-60-257878 (JP, A) JP-A-61-287477 (JP, A)

Claims (2)

(57) [Claims] When the coating liquid applied to the front and back surfaces of the strip is continuously dried and baked by blowing hot air in a hot blast furnace, the strip is moved to a place where the hot air velocity is Xm / sec. Assuming that the distance from the hot air discharge port to the strip surface is Ycm, Y is 5 or more, Y is maintained at (0.7X-9) or more according to the hot air velocity X, and the surface temperature of the strip is 150 ° C. from room temperature. 4 ~ 30 ℃ / se
A method for continuously drying and baking a strip coating film, wherein the method is controlled to c. 2. A coating solution comprising one or more of phosphate or chromate, or a mixed aqueous solution of one or more of phosphate or chromate and an organic resin, or The continuous drying and baking method for a strip coating film according to claim 1, wherein the method is a water-soluble organic resin or a water-soluble emulsion resin.