JPH08290111A - Production of coated metallic plate - Google Patents

Abstract

PURPOSE: To produce a coated metallic plate at a high speed by efficiently hardening a coating film. CONSTITUTION: The coated metallic plate free from the generation of cratering on the coating film is efficiently produced by coating and baking a polyester resin/melamine resin based coating material 8000-20000 in molecular weight, 20-30% in the ratio of amino resin to be blended to the total resin, <=20% in the ratio of butylated melamine resin in the amino resin and >=165 deg.C in the average b.p. of a solvent in the coating material. And the cratering is hardly generated most and the production at a high speed is enabled at the time of baking in an induction heating oven or using a temp. raising pattern by steps.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-cost coated metal plate used for automobiles, home appliances, and building materials.

[0002]

2. Description of the Related Art Conventionally, painting of home electric appliances and the like has been performed after processing and forming steel plates, but due to pollution problems and work environment problems, the amount of painted metal plates that have been painted in advance has increased. ing.

[0003]

In such a situation,
Reducing the manufacturing cost of painted metal sheets has become an important issue. In order to reduce the manufacturing cost, there are issues such as reduction of coating cost, improvement of production efficiency, and improvement of yield, but improvement of production efficiency is an important issue.

In order to improve the production efficiency, it is effective to increase the line speed (production speed), but in the conventional technique, the line speed is improved while ensuring the workability and the high quality appearance. It was difficult. That is, when the line speed was increased, cracking occurred, which is thought to be due to the volatile components in the coating film not being completely exhausted in the baking and curing process of the paint.

The present invention provides a technique that enables a coated metal plate to be produced at a high speed, and an object thereof is to efficiently perform baking (curing of a coating film).

[0006]

The present invention provides a polyester / amino resin based coating material satisfying the following (a) to (d) in order to produce a coated metal sheet at a high speed (with a high line speed). A method for producing a coated metal plate, which comprises coating, and baking and curing. (A) The molecular weight of the main resin in the paint is 8000 to 20000 (b) The mixing ratio of the amino resin is 80/20 ≧ polyester resin / amino resin ≧ 70/30 (c) The butylated melamine resin is mixed in the amino resin The ratio is 20% or less. (D) The average boiling point of the solvent in the coating material is 165 ° C. or more. Further, when baking is performed in an induction heating furnace, it is possible to particularly speed up the baking. Moreover, especially when the heat pattern for baking is stepwise heating, the speed of baking can be increased.

[0007]

The polyester / amino resin-based paint is a paint of the type in which a polyester resin is cured with an amino resin, and the polyester resin and the amino resin are essential components. The polyester resin is a resin containing more than 1 ester group in the molecule, and the amino resin is a resin having a skeleton containing an amino group such as melamine, benzoguanamine and urea. For example, methylated melamine resin and butyl resin. Examples of the resin include melamine resin and benzoguanamine resin. The coating device is not particularly limited, and a normal roll coater, curtain flow coater, or Japanese Patent Application No. 4-169.
The roller curtain coater described in No. 052 and Japanese Patent Application No. 4-289090 can be used.

As a result of intensive studies by the inventors of the coating composition which does not cause defects such as armpits during baking, the coating composition described in the present invention is suitable for high-speed baking, and a coated metal sheet can be produced with high efficiency. And completed the present invention.

If the molecular weight of the polyester resin is 8,000 or less, it is difficult to secure the processability of the coating film, and problems in performance tend to occur. Further, when the molecular weight is 20,000 or more, the high-speed baking property is poor, and when a volatile component is volatilized, an armpit is apt to occur, and the appearance of the coating film is deteriorated.

When the mixing ratio of the amino resin to the polyester resin exceeds 70/30, the appearance defect due to cracking tends to occur, and when it is less than 80/20, it becomes difficult to secure the physical properties of the coating film. Among the amino resins, the butylated melamine resin is disadvantageous in the occurrence of armpits, and when the content of the total amino resin exceeds 20%, armpits tend to occur.
It becomes difficult to manufacture painted metal sheets at high speed.

The boiling point of the solvent is also important from the viewpoint of baking, and unless the average boiling point is 165 ° C. or higher, cracking occurs and high-speed baking becomes impossible. The average boiling point refers to a value obtained by dividing the weight of each solvent by the boiling point of the solvent in the solvent used by the total weight of the solvents. There is no particular upper limit of the boiling point, but when the average boiling point exceeds 210 ° C., the solvent is remarkably retained in the coating film and the physical properties of the coating film deteriorate.
Further, when the temperature is 175 ° C. or higher, the high speed baking property is particularly excellent.
When these conditions are met, high-speed defect-free baking is possible. When a paint that satisfies the above conditions is applied and baked, no cracking occurs even when baked at high speed.

In the present invention, the meaning of high speed is not particularly limited, but the line speed is 45 m / min or more and the baking time is 60.
The target is less than a second (since the baking time is determined by the furnace length and line speed, it cannot be defined by the line speed or furnace length alone). Examples of the metal plate include a steel plate, an aluminum plate, a stainless plate, a titanium plate, and a copper plate. Of these, examples of steel sheets include cold-rolled steel sheets, hot-rolled steel sheets, galvanized steel sheets, galvannealed steel sheets, zinc-iron alloy plated steel sheets, zinc-aluminum alloy plated steel sheets, aluminized steel sheets,
Examples thereof include chrome-plated steel sheet, nickel-plated steel sheet, zinc-nickel alloy-plated steel sheet, tin-plated steel sheet and the like.

The metal plate can be subjected to a pretreatment if necessary. Examples of the pretreatment include washing with water, washing with hot water, pickling, alkaline degreasing, grinding, polishing, chromate treatment, zinc phosphate treatment, and complex oxide film treatment. These pretreatments are carried out individually or in combination. The conditions of the pretreatment for coating may be selected appropriately.

Then, if necessary, an undercoat paint can be applied onto the metal plate and cured and dried to form an undercoat film layer. As the undercoat paint, there are polyester-based, epoxy-based, urethane-based, etc., which have a required film thickness with a roll coater, curtain flow coater, roller curtain coater, electrostatic coating machine, brush, blade coater, die coater, etc. Thus, the undercoating film layer is obtained by leaving it to stand at room temperature or curing and drying in a hot air oven, an induction heating oven, a near infrared ray oven, a far infrared ray oven, an energy ray curing oven or the like. The film thickness is arbitrary,
About 1 to 30 μm, especially 3 to 12 for coated metal plates
A dry film thickness of μm is common. The drying condition may be appropriately selected according to the content of the coating material and the desired performance, but the maximum attainable plate temperature of 150 to 2 in a hot-air stove, an induction heating furnace, a near-infrared furnace, etc.
The conditions of 40 ° C. and arrival time of about 10 to 200 seconds are common.

Then, the coating material according to the present invention is applied to a metal plate,
Alternatively, it is applied on the undercoat coating film by a coating device and cured and dried. Although the film thickness is not particularly limited, it is generally 5 to 60 μm, of which 10 to 25 μm is general. The effect of the present invention is particularly remarkable when an induction heating furnace is used as the hardening and baking method. That is, even if it is cured at a high speed, the occurrence of cracks in the coating film is suppressed, and a coating film with a more beautiful appearance can be obtained.

Further, when baking, by taking a heat pattern in which the temperature is once held during the temperature rise as shown in FIG. 1, it is possible to further suppress the occurrence of armpits.
The temperature to be retained is not particularly limited, but when the temperature is 130 to 200 ° C., which is close to the boiling point of the solvent, the effect of suppressing the armpit is large.

[0017]

EXAMPLES The present invention will be described below with reference to examples.

The continuous production facility for coated metal plates carried out by the present invention is as follows. After the metal plate is pretreated, the primer coating is applied with a roll coater and baked in an induction heating furnace. Then, a top coat paint is applied with a roller curtain coater and baked in an induction heating furnace. Then, it is cooled with water and the coil is wound up. The length of the induction heating furnace for baking the top coat is 40 m.

As a pretreatment, a coating type chromate treatment (Z
M1300AN, manufactured by Nihon Parkerizing Co., Ltd.,
Polyester resin type P185 as a primer paint
(Manufactured by Nippon Paint Co., Ltd.) was applied to give a dry film thickness of 5 μm and baked at an ultimate plate temperature of 220 ° C. for 40 seconds.

Table 1 shows the contents and line speeds of the top coating materials used. Melamine resin was used as a crosslinking agent.
Drying these paints with a roller curtain coater 1
It was painted to a thickness of 8 μm and baked in an induction heating furnace. The heat pattern of the induction heating furnace was two types, that is, a monotonous temperature increase and a stepwise temperature increase, and the holding temperature in the case of stepwise heating was 150 ° C. The ultimate plate temperature was 230 ° C. In the monotonous temperature increase, the plate temperature after coating was increased almost linearly to 230 ° C.

Regarding the appearance after coating and the state of baking, the appearance of the coating film after baking was visually observed to determine the smoothness of the coating film and the presence or absence of cracking. Further, a T-bending process test was performed at 20 ° C., and the presence or absence of cracks in the coating film in the bent portion was visually observed. The results of these evaluations are also shown in Table 1.

The blending ratio of the polyester resin and the melamine resin is shown by the weight ratio of each resin. In addition, the compounding ratio of the butylated melamine resin is the weight ratio of the butylated melamine resin to the total melamine resin weight.
Displayed in.

In each of the examples, the workability of the coated steel sheet and the smoothness of the coating film were good, and no cracking was observed.

In No. 3 of the comparative example, since the blending amount of the melamine resin with respect to the polyester resin was larger than that of the present invention, the film was found to be cracked.

In Comparative Example No. 6, the polyester resin molecular weight in the coating material was as high as 22000, so the smoothness of the coating film was slightly inferior and cracking occurred.

No. 7 of the comparative example had a low molecular weight of 7,000, so that the processability of the coating film could not be ensured.

In No. 9 of the comparative example, the weight of the butylated melamine resin in the total weight of the melamine resin was as high as 25%, so that the coating film was cracked.

Comparing Example Nos. 12 and 13, at a line speed of 110 m / min, the average boiling point of the solvent in the paint was 165.
In the case of ℃, there was a difference in the occurrence of cracks in the coating film depending on the baking heat pattern. That is, no cracking was observed in stepwise heating, and the coating film was slightly cracked in the monotonous temperature rise, and it is understood that the cracking is less likely to occur in stepwise heating.

Comparing Example Nos. 13 and 14 with each other,
At 14 where the average boiling point of the solvent is as high as 175 ° C., no cracking occurs even with a monotonous temperature rise, and the higher the average boiling point of the solvent,
You can see that armpits are less likely to occur.

[0030]

[Table 1]

[0031]

As described above, according to the present invention,
It is possible to efficiently manufacture a coated metal plate having good workability without causing armpits.

[Brief description of drawings]

FIG. 1 is a diagram showing a heat pattern for baking, which is an embodiment of the present invention.

Claims (3)

[Claims] 1. A method for producing a coated metal sheet, which comprises coating a polyester / amino resin-based coating material satisfying the following (a) to (d) and baking and curing the coating. (A) The molecular weight of the main resin in the paint is 8000 to 20000 (b) The mixing ratio of the amino resin is 80/20 ≧ polyester resin / amino resin ≧ 70/30 (c) The butylated melamine resin is mixed in the amino resin 20% or less (d) The average boiling point of the solvent in the paint is 165 ° C or more 2. The method for producing a coated metal sheet according to claim 1, wherein the baking is performed in an induction heating furnace. 3. The method for producing a coated metal sheet according to claim 1, wherein the heating pattern for baking is stepwise heating.