JPS63248475A - Coating method - Google Patents

Abstract

PURPOSE:To uniformly coat a thick film at a high speed by carrying out coating while imparting ultrasonic vibration to a part in a paint pan in the method for coating a water-based or org. solvent-based paint on a band steel by a roll coating method. CONSTITUTION:When the pant is the water-based or org. solvent-based paint contg. a surface tension conditioner, or the solid or liq. dispersion-type paint, the paint is coated on a band steel by a roll coating method. In this case, a diaphragm 20 connected to an ultrasonic vibrator 22 is dipped in the paint 12 in the paint pan 10, and the paint 12 is coated while imparting ultrasonic vibration to the paint 12. As a result, a uniform thick film can be coated at a high speed. In addition, the sedimentation of the paint in the pan and the phase separation, namely phase splitting, can be controlled, when the solid or liq. dispersion-type paint is roll-coated.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for coating a steel strip with a water-based or organic solvent-based paint using a roll coating method, particularly a method for coating a steel strip that enables high-speed, uniform thickness coating. Regarding.

(Prior art) In general, water-based or organic paints have leveling properties,
Various additives such as surfactants and surfactants that adjust the interfacial tension of the paint, wax, etc. are mixed in to improve pigment wettability, dispersibility, and lubricity on the surface of the paint film after it is formed. In particular, in the case of paints with poor foam-breaking properties, such as high-molecular polyester paints, large amounts of interfacial tension regulators (e.g., silicone-based, low-molecular-weight acrylic, etc.) that have a defoaming effect are often added. , when roll-coating paints containing such additives, a paint-lifting roll (
Since the amount of paint lifted by the "pickup roll" (hereinafter referred to as "pickup roll") is small, it is difficult to coat thick films, and when the line speed is relatively high (e.g. approximately 50+w/w
(in or above) caused by insufficient supply of paint to the painted surface.
"Fading" may occur.

The ability of the paint to lift up with a trowel is called the pick-up ability, and paints with poor pink amplification characteristics are currently applied at low line speeds that do not cause abnormalities on the painted surface.

From the standpoint of improving the properties of the paint itself, studies are being conducted on additives that are both effective and pick-up, but additives that are effective for some paints may not necessarily be effective for other paints. The current situation is that the development of additives and the technology for their use to simultaneously improve pick-up properties have not yet been established.

By the way, on the other hand, when the paint contains relatively large and coarse particles such as metal powder or inorganic fillers, these sedimentary particles accumulate in the paint pan and are difficult to entrain into the paint film. In the case of such paints, a top-feed method is used to supply the paint from the paint container to the surface of the steel plate by sequentially flowing it down through several rolls, but this method cannot be applied to painting the back side of the steel plate. Not only is this difficult, but painting over a long period of time does not necessarily result in a uniform particle concentration. Furthermore, the method of supplying the liquid at the start of painting and at the end of painting is complicated, which is disadvantageous in terms of running costs for a painting line that is required to produce a wide variety of products with small lofts.

On the other hand, apart from the top-feed method, a coating method in which a portion of the paint in the paint pan is extracted, stirred vigorously, and then circulated can be applied to both the front and back sides of a steel plate, but it is applied to areas in the paint pan where the liquid flow rate is low. In addition to causing a build-up of coarse particles, air entrainment often creates fine air bubbles within the paint pan. Furthermore, in liquid dispersion type paints, sufficient dispersion cannot be achieved by stirring using such liquid flow.

(Problems to be Solved by the Invention) Thus, an object of the present invention is to improve the coating method itself for paints with poor pick-up properties without changing paint additives, thereby achieving high speed, uniformity, and thickness. An object of the present invention is to provide a method that enables film coating.

Furthermore, another object of the present invention is to provide an effective method for suppressing sedimentation in a paint pan and phase separation, that is, phase separation, during roll coating of a solid or liquid dispersed paint.

(Means for Solving the Problem) As a result of intensive study on the phenomenon of poor pick amplifier performance, the inventors found that although the paint on the surface of the pickup roll and the paint in the paint pan are the same paint,
It was found that it was extremely difficult to get wet. The meniscus shape of the part where the paint lifts up from the paint pan is schematically shown in FIG. On the other hand, with paints with poor pick-up properties, sinking of the meniscus is observed. That is, it can be seen that a kind of sliding phenomenon occurs between the paint on the roll surface and the paint in the paint pan, and the momentum is hardly transmitted in the rotational direction of the roll. In this case, the paint supply is not sufficient, so if you try to paint at high speed, you will not be able to get a thick film, and "scratching" will inevitably occur.

As a result of various experiments and studies, the inventors of the present invention found that this phenomenon is caused by the presence of a concentrated interfacial tension modifier in the extreme surface layer of the paint on the roll surface, that is, the presence of a concentrated layer of various additives. It was found that the pink-up property was improved by destroying the concentrated layer by applying ultrasonic vibration.

Furthermore, the present inventors have found that application of such ultrasonic vibrations not only destroys the concentrated layer as described above, but also prevents solid particles from settling in the paint pan in a coating method for a liquid or solid paint that is difficult to disperse. It was also found that this method suppresses phase separation of droplets and enables uniform dispersion of solids and fine uniform dispersion of liquids.

The gist of the present invention is to provide a method for coating a steel strip with a water-based or organic solvent-based paint using a roll coating method, which is characterized in that the coating is applied while applying ultrasonic vibrations to the paint in the paint pan. This is a method of painting steel strips.

The water-based or organic solvent-based paint to which the present invention is applied is not particularly limited, but preferred examples include paints containing interfacial tension modifiers and/or solid or liquid dispersion type paints. It will be done.

In addition, 1. The application of ultrasonic vibrations essentially prevents the formation of a concentrated layer, the settling of solid particles, and
It is only necessary to prevent phase separation, improve pick-up properties, and make the paint uniform. For example, a vibration plate may be installed in the paint in the paint pan, or vibrations may be generated from outside the container wall of the paint pan. may be given.

Note that the ultrasonic vibration may be a high frequency vibration subjected to frequency modulation at a constant speed.

Thus, according to the present invention, even when the pick-up roll speed is increased from 20 m/l1in to about 100+a/l1in, it is not only possible to ensure good pink-up properties, but also to consistently apply uniform coating.

(Operation) Next, the present invention will be further described with reference to the accompanying drawings.

FIG. 2 is a schematic explanatory diagram showing an example of a roll coating apparatus for carrying out the method according to the present invention, and FIG.
The figure is a schematic plan view of a part thereof.

FIG. 4 is a schematic explanatory diagram when another mechanism for applying ultrasonic vibration is provided.

In the example shown in FIGS. 2 and 3, four diaphragms 20 are arranged in the paint 12 in the paint pan 1O at a distance l from the pink-up roll 14 in the longitudinal direction of the pink-up roll 14. has been done. The other end of the diaphragm 20 extends outside the paint pan 10 and is attached to an ultrasonic vibrator 22.

In the example shown in FIG. 4, an ultrasonic vibrator 22 is directly attached to the outside of the container wall of the paint pan 10, and ultrasonic vibrations are applied from the outside of the container.

According to one aspect of the present invention, the concentrated layer is destroyed by ultrasonic vibration, and in this case, the method of applying ultrasonic vibration to the concentrated layer in the paint pan includes: There are various methods, but the following two methods are the most effective.

(1) As shown in Figures 2 and 3, a thin plate-shaped diaphragm with one end immersed in the paint pan and the other end protruding outside the paint pan is used. An ultrasonic vibrator is attached to the exposed part to add ultrasonic vibrations.

The part immersed in the paint pan faces the pick-up roll, and the distance l is set so that the antinode of the vibration of the standing ultrasonic wave generated in the paint is located at the concentrated layer near the roll. adjust.

If the transmission speed of ultrasonic waves in the paint is C (n+/s) and the ultrasonic frequency is f (c/s), then 12 = n/2
It is better to choose xc/f (where the number is an integer).

The thickness of the diaphragm is several 11 to several 1 mm thick, and the length, width, and folding position are determined depending on the frequency to be used and the material of the diaphragm. A plurality of diaphragms are added in a row along the roll axis according to the length of the roll.

(2) As shown in FIG. 4, an ultrasonic vibrator is attached to the outside of the container wall of the paint pan, and ultrasonic vibrations are radiated into the paint inside the pan.

In this case, a plurality of ultrasonic transducers are attached depending on the size of the paint pan container. In addition, the distance l between the mounting position (bottom of the paint pan) and the pickup roll is such that the antinode of the vibration of the ultrasonic standing wave generated in the paint is the position of the concentrated layer near the roll. Adjust so that the

l' is selected in exactly the same way as l shown in case (1) above.

In addition, the frequency of ultrasonic waves is generally 15KfLz to 50KH.
Use a range of 2. Below 15KHz, the vibration sound enters the audible range and the noise is loud; on the other hand, above 50KHz,
This is because it is difficult to manufacture a vibrator with a large output.

The frequency to be added does not need to be constant; in particular, in order to be able to agitate the entire paint pan without forming standing waves in the paint pan, it is necessary to vary the frequency above and below a constant frequency. It is preferable to add ultrasonic vibrations that have been subjected to frequency modulation.

Next, the present invention is also effective in preventing sedimentation and accumulation of solid particles, etc. For example, as shown in FIG. An ultrasonic vibrator is attached to the edge of the board outside the paint pan to add high-frequency vibration. The high-frequency vibration propagates through the diaphragm and is radiated toward the paint in the paint pan to agitate the paint and suppress settling of solid particles in the paint and phase separation of droplets.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 In this example, using the roll coating equipment shown in Figs. 2 and 3, a high-molecular polyester paint was diluted with thinner to a Ford cup viscosity (Na4) of 80 tJ'.
A painting experiment was conducted on the color line.

The coating base material is electrogalvanized steel plate (width 1500mm)
.

After applying zinc phosphate chemical conversion treatment to the film (thickness = 0.5+++m), epoxy-polyester primer coating (8μm)
I used the one that had been treated with

The color line roll has a pickup roll width of 200 mm.
(1wm, diameter 300m11., applicator roll width 2000+a+w, diameter 300ff111, rubber hardness 40 degrees.

The size of the paint pan is 2300m+m wide and 80km long.
, the depth was 15h+m.

Four diaphragms with a width of 400IIl11 were installed in parallel. The material was stainless steel, the plate thickness was 3 mm, and the internal length of the paint pan was 700 mm. The number of diaphragms was four, and the distance between the diaphragms and the roll was 40 IIll.

The frequency used is 18) [Hz, and the ultrasonic output is 400W/
There was only one roll.The roll peripheral speed ratio is line speed/applicator roll/pickup roll=1/1.270.4
was held constant.

The results are summarized in Table 1, but without ultrasonic vibration, 1
While it was difficult to coat with a thickness of 0μ or more, applying vibration made it possible to coat a thick film at high speed.

Table 1 Example 2 In this example, a solid particle dispersed paint was used, and the effect of ultrasonic vibration on preventing sedimentation of solid particles was evaluated.

First, in order to investigate the agitation situation inside the paint pan, the average particle size was 3.
When a chromate aqueous solution containing 20-t% barium sulfate with a μm1 specific gravity of 4.5 is placed in a paint pan and is not stirred,
Changes in liquid concentration over time were measured in the case of circulating flow agitation and in the case of ultrasonic application.

The application of ultrasonic vibration was performed using the same roll coating device as in Example 1, but in this example, the diaphragm had a width of 5.
I installed four of 0 Rin's in parallel.

The material was stainless steel, the plate thickness was 51nlI+, and the length inside the paint pan was 800mm. The number of diaphragms was four, and the distance between the diaphragms and the roll was 40 LIIm.

The frequency used is the center frequency is 18KH2 frequency modulation width ±1
, 8 KHz, modulation rate of 0.36 KHz/ms, and ultrasonic output of 400-/l groups.

For stirring by liquid flow, use the same device, 10012/vl
The liquid was drawn out from the bottom of the paint pan at a rate of 1.5 in, and then jetted out from a plurality of nozzles provided on both sides of the paint pan in the longitudinal direction.

The base material used for painting was a cold-rolled steel plate (plate width 1500n+m,
After alkali degreasing, the concentration on the above-mentioned steel plate was evaluated using a reverse roll coater and the relative intensity ratio of S/Cr was evaluated using fluorescent X-ray analysis.

The results are summarized in Table 2. FIG. 5 summarizes these data in a graph.

Table 2 In the results shown in Table 2, the larger the relative intensity ratio, the B
This indicates that there is a large amount of aSO4, and these results almost match the time-dependent changes in the Ba5On concentration in the paint pan liquid shown in FIG. Furthermore, the coated surface was found to be normal with ultrasonic agitation, and no bubbles were observed, confirming a good agitation effect.

Although the stirring effect of the ultrasonic diaphragm was good, the temperature of the coating liquid increased significantly, so in the line coating experiment, water cooling was performed through a copper tube.

Example 3 In this example, a liquid dispersion paint was used to evaluate the effect of ultrasonic vibration on phase separation of droplets.

Paints made of a three-component system of high molecular weight polyester/melamine/epoxy have poor compatibility, and after stirring with a desper, are allowed to stand for several days to undergo complete phase separation. In the case of such droplet-dispersed paints, the diameter of the dispersed droplets is large (e.g.
(several tens of micrometers or more), coating film defects called "dents" occur on the painted steel plate.

Therefore, in this example, a coating test was conducted in the same manner as in Example 2 using the above solvent-based paint. After the start of painting, changes in phase separation over time were recorded along with coating defects.

The results are summarized in Table 3.

Table 3 Note: Two paint pans have phase separation and dents.

The results in Table 3 also show that it is impossible to form fine droplets of poorly soluble resin by simple agitation using liquid flow, and that ultrasonic agitation is effective in obtaining droplet dispersion to the extent that it does not cause coating defects. I understand that there is something.

(Effects of the invention) As described in detail above, the present invention has a simple structure of applying ultrasonic vibration, but it not only enables high-speed thick film coating, which has been a problem in the past, but also enables solid/liquid dispersion. It has great practical benefits, such as making it possible to apply uniform coatings over time, even with mold paints, and its significance is great.

[Brief explanation of drawings]

FIG. 1 is a schematic illustration of the meniscus shape of the part where paint is lifted from the paint pan; FIG. 2 is a schematic illustration of the apparatus for carrying out the method according to the invention; FIG. A partially omitted plan view of the device; FIG. 4 is a schematic explanatory diagram of another device; and FIG. 5 is a graph collectively showing data of the example.

Claims (5)

[Claims] (1) A method of applying water-based or organic solvent-based paint to a steel strip using a roll coating method, which is characterized by applying ultrasonic vibration to the paint in the paint pan.
How to paint steel strips. (2) The method according to claim 1, wherein the water-based or organic solvent-based paint contains an interfacial tension modifier. (3) Claim 1 or 2, wherein the water-based or organic solvent-based paint is a solid or liquid dispersion type paint.
The method described in section. (4) The method according to any one of claims 1 to 3, wherein a diaphragm connected to an ultrasonic vibrator is immersed in the paint in the paint pan to apply ultrasonic vibration to the paint. . (5) The method according to any one of claims 1 to 3, in which an ultrasonic vibrator is provided outside the container wall of the paint pan.