JP3282240B2 - Continuous coating method for strip material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous coating method for stably applying a smooth and sound coating film (including a functional material film or the like) to a band-shaped material such as a steel plate.

[0002]

2. Description of the Related Art As a means for continuously applying a coating material (including a coating solution of a functional material) to a traveling belt-like material, a "roll coating method" has been generally adopted. I have. This roll coating method is a roll coating method.
The paint supplied via a pick-up roll, a transfer roll, a metering roll, a smoothing roll, etc. of a roll passes along a backup roll or has two deflectors. -Apply to the material to be coated supported between the rolls using an applicator roll, and bake and dry in a drying furnace (in a drying furnace, hot air is blown onto the coating surface to evaporate the solvent. Heats up and cures paint,
It is a coating method.) The combination of the running direction of the material to be coated and the rotation direction of the applicator roll,
These can be broadly classified into two types, a "natural coating method" and a "reverse coating method".

For example, in FIG. 6, a paint in a paint pan 3 is applied to a workpiece 2 passing along a backup roll 1 using a pickup roll 4 and an applicator roll 5. Roll roll with typical 2 rolls
Although the TIG method is shown here, the application is shown here.
This is an example of the "natural coating method" in which the rotation direction of the roll 5 is opposite to the running direction of the workpiece 2.

On the other hand, in FIG. 7, the roll arrangement is the same as that shown in FIG.
This is an example of a "reverse coating method" in which the direction of rotation of the tool 5 is the same as the running direction of the workpiece 2. Reference numeral 6 in the drawing denotes a mirror provided for adjusting the coating film thickness.
The term "tarling roll" designates a drying oven indicated by reference numeral 7.

[0005] However, Roll Co., which is a mainstream technology of coating,
The following problems have also been pointed out in the Ting method. For example, in the case of producing coated steel sheets, the steel sheets to which paint has been continuously applied are continuously sent to a drying oven, where the solvent (volatile components) in the coating is evaporated, and the coating is cured. However, at this time, if the heating rate is increased to increase the productivity, surface defects due to bubbles occur. These surface defects are called “armpits”, in which the evaporation of the solvent remaining inside the coating film is intensified by rapid heating to produce bubbles, which deform the cured coating film surface and appear as foam-like defects. This was particularly noticeable in the case of thick film coating.

As a method of reducing this "arm", a method of heating and drying under reduced pressure has been proposed (Japanese Unexamined Patent Publication No. Hei.
No. 139174), the equipment cost is too high to be applied to a continuous coating line, which is not practical, and a great effect corresponding to the cost cannot be expected.

On the other hand, JP-A-3-77675 discloses that
Controlling the heat-up heat pattern of the steel plate coated with paint,
Keeping the temperature of the steel sheet below the temperature at which the cross-linking reaction of the coating resin starts and below the boiling point of the solvent for 10 to 25 seconds to promote the evaporation of the solvent and prevent the generation of the solvent bubbles which cause the "stick". The proposal is described. However, in this method, when the coating film thickness is large, a long holding time is required for evaporating the solvent, so that no improvement in productivity can be expected at all, and the effect of reducing the occurrence of "stick" cannot be said to be sufficient. .

[0008] The problem of "Waki" is not limited to the roll coating method, but is a problem with continuous coating with a curtain-flow coater or an extruder, which has recently been used. It goes without saying that similar problems were pointed out in painting.

[0009] In view of the above, the object of the present invention is to provide a stable and smooth coating film without causing a coating defect such as "bump" and the like. An object of the present invention is to establish a means for continuously coating a strip material with relatively low equipment costs.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have obtained the following findings. a) During thick film coating on a continuous coating line, regardless of the coating equipment used, whether it is a roll coater or an extruder, after the coating has been applied, smooth the coating as much as possible. solvent with evaporating, but that is baked to cure the coating film preferable from the productivity surface, as a heating means for this, the method of raising the temperature from the surface by blowing hot air flow on the surface of conventional such coatings If a method in which the temperature is raised from the inside of the coating film by electric heating, induction heating, or the like is adopted instead of the above method, the occurrence of "bake" during baking hardening is almost eliminated.

[0011] b) In addition, Sum the solvent in the coating film - but for evaporated's "means Ru blowing low temperature of the air flow than the coating curing temperature of the coating film surface" is the very effective,
"Means for providing a process of heating at a temperature lower than the curing temperature of the coating film immediately after application of the paint until drying and curing" is also effective. In particular, if the latter method is adopted, the coating film before baking and curing is effective. The flowability of the coating is improved, and the leveling effect due to the surface tension causes "swelling" or "rolling" (roll coating) in the coating process, which causes the coating thickness to become uneven in the width direction. Streaks appearing) are reduced, and the effect of forming a smooth coating film from this point is also remarkable.

The present invention has been completed as a result of further studies based on the above findings and the like. "When coating a coating film having a coating thickness of 10 microns or more in a continuous coating line, While spraying a low-temperature air stream at a temperature lower than the coating curing temperature on the coating surface, perform rapid heating and drying from the inside of the coating within the “limit heating rate that does not cause cracking”, or first, immediately after applying the paint Perform low-temperature heating of the coating film at a temperature lower than the coating curing temperature, and then perform rapid heating and drying from the inside of the coating film within the above “limit heating rate”. After low-temperature heating of the coating film at a temperature lower than the film curing temperature, rapid heating from the inside of the coating film within the above “limit heating rate” while blowing a low-temperature airflow below the coating film curing temperature onto the coating film surface・ By drying, there is no “armpit” etc. And a healthy productivity strip coated material with a coating film and stably major feature in the point "which is adapted to be manufactured with a slipping.

The present invention will now be described based on specific examples.
Details will be described together with the effects.

First, it is considered that the mechanism of the generation of "bump" as a coating surface defect generated in the baking and drying process is as follows. Generally, the baking and drying process of a coating film is roughly divided into two,
One is a chemical process called “constant drying process”, in which the rate of drying the solvent from the surface is governed. The second is
This is a physical process called “decay drying process”, in which the moving speed of the solvent in the coating film is governed. The cause of the "armpit" is caused by the second physical process. When the surface of the coating film is hardened by the end of the constant drying process and the attenuation drying process, the residual solvent is removed. If a large amount remains, it becomes bubbles as the temperature rises, and becomes "blow", resulting in surface defects. When the “solvent remaining inside the coating film” evaporates and becomes bubbles as it escapes from the surface after the coating film surface is hardened by rapid heating and drying, the foamy marks become surface defects.

[0014] The occurrence of "arm" is particularly problematic when the thickness of the coating film is increased. However, according to the conventional knowledge, to prevent this, the heating speed during baking and drying is reduced until the coating film hardens. Was thought to be effective. However, this measure causes a remarkable decrease in the coating efficiency, and it is difficult to prevent productivity from deteriorating.

Therefore, the present inventor has studied a novel means capable of effectively preventing the occurrence of the "armpit" from various viewpoints. Of "Waki" when various conditions were changed using various paints to understand the relationship between heating speed during baking and drying, coating thickness, and conditions of airflow in contact with the coating surface A survey was conducted to confirm the following.

That is, if the thickness of the coating is less than 10 microns, the solvent in the coating is sufficiently diffused and evaporated from the surface during the constant drying process.
Even if the speed is higher than ec, no wobble is generated (see the relationship between the curve A in FIG. 8 showing the results of investigation of the relationship between "coating thickness" and "heating rate" and "wedge occurrence status"). I want to do that). Conversely, from FIG. 8, it can be seen that when the coating film thickness is 10 microns or more, "blow" tends to occur unless the heating rate (bake drying rate) is reduced as much as possible.

However, when the film thickness at which no waki is generated even when high-speed drying is performed is referred to as the “beautiful heat drying limit film thickness”, a low temperature is applied to the film surface during baking and drying. When heating and drying from inside the paint while spraying airflow, the "Beautiful heat drying limit film thickness" is improved,
Higher speed and beautiful drying of a thicker film becomes possible (see the relationship of the curve B in FIG. 8). In this case, especially when the heating rate is 10
When it is in the range of 40 ° C / sec to 40 ° C / sec, the degree of improvement of “the beautiful film thickness by heating and drying” is remarkable.

Therefore, when baking and drying the coating film, if the inside of the coating material is heated while blowing a low-temperature air stream onto the surface of the coating film, irrespective of the type of coating material (for example, the type of resin), the temperature is reduced.
The "limit heating rate at which no glow occurs" can be maintained at a high value even when the coating film thickness is large (compare the curves A and B in FIG. 8).
Work efficiency of so performed that the rapid heating and drying healthy painted inner is remarkably improved. FIG. 8 shows an example of a beautiful heat drying limit film thickness curve of a paint using xylene as a solvent. However, even in the case of a paint using another solvent, the beautiful heat drying limit film thickness curve can be easily obtained by a simple drying experiment. Can be sought.

However, in this case, when airflow is blown in a direction perpendicular to the surface of the material to be coated, "wrinkles (surface defects)" called "wind ripples" tend to occur (especially when the coating film is thick, this phenomenon occurs). In addition, when a hot gas at a temperature higher than the curing temperature of the paint is blown, the surface is immediately cured, so that the generation of "splash" cannot be suppressed. Therefore, the temperature of the air stream to be blown should be low enough to prevent the coating film surface from hardening immediately ( less than 80 ° C, preferably about 20 ° C or less).
It is good to pay attention so that the spray angle is substantially parallel to the coating film surface. And the flow velocity of the blowing airflow is 50
m / sec or less, preferably around 8 m / sec.

The heating of the coating film by blowing an air current
As described above, it is desirable to employ electric heating such as induction heating so as to raise the temperature from the inside of the coating film. It is preferred that the material be rapidly heated to 200 ° C. or more at a speed as fast as possible and then dried rapidly.

The reason why the "beautiful heat drying limit film thickness" is greatly improved by heating the coating from the inside by electric heating such as induction heating while cooling the surface by blowing a low-temperature gas is because this heating causes As the internal temperature rises, the diffusion coefficient of the solvent from the inside to the surface increases, the mass transfer coefficient at the surface increases, and since the surface is cooled by gas, the curing is delayed until the end, so the inside of the coating film It is considered that the solvent is sufficiently dispersed and "blow" is hardly generated.

On the other hand, during the period from immediately after the application of the paint to the time of baking and drying (heating to 200 ° C. or more), preheating for heating and holding at a low temperature (80 ° C. or less) at which the coating film is not cured is performed. It is during this time evaporation of the solvent in the coating film to the facilitation Sum - occurs dissipation of's solvent, followed from the interior paint
When heating and drying are carried out , the "beautiful heating and drying limit film thickness" did not reach 10 microns when the preheating was not performed before baking and drying as in the conventional case. Even so, the generation of “bumps” is minimized and a beautiful dried coating film can be obtained (the beautiful heat drying limit film thickness curve at this time also has almost the same tendency as curve B in FIG. 8). . Therefore, in this case as well,
Regardless of the type, the "limit heating rate at which no waki is generated"
High values can be maintained even when the film thickness is large (before
Contrast curves A and B in FIG. 8).
Rapid heating and drying within the "limit heating rate"
As a result, the work efficiency of sound painting is remarkably improved. In addition, when the above-mentioned low-temperature heating (preferably, preheating at about 50 ° C.) is performed, the viscosity of the coating film is reduced and leveling easily proceeds, and unevenness defects such as “undulation” and “rolling” are eliminated. The effect is also brought.

As described above, by performing the preheating at a low temperature, "swells" and "rolls" generated in the coating process of the paint are obtained.
And the like, the effect of reducing surface irregularities can be obtained for the following reasons. For example, when a roll is schematically drawn, it is represented as "undulation" as shown in FIG. 9, and this "undulation" tends to become smooth over time due to the flow and surface tension of the coating film (""). Leveling). When the paint is a Newtonian fluid and the roll is considered to have a sine wave, the analytical solution of "time when the height difference is halved (half-life)" is as follows. As described above, since the half-life is proportional to the viscosity, it is very effective to decrease the viscosity of the coating material to shorten the leveling time.

As shown in the investigation results of FIG. 10, the effect of the temperature change of the paint viscosity, which has a great effect on the reduction of the roll and the like, is that the paint temperature is about 80 ° C. or less (preferably about 50 ° C.). When the temperature is increased to 40 to 50 ° C., the viscosity decreases greatly.
The leveling time becomes very short. Therefore, if the coating film is heated at a low temperature immediately after the application of the paint, the "rolls" and "undulations" disappear quickly between baking and drying in a heating furnace, realizing a smooth coating surface. It is done.

FIG. 11 shows a leveling model that takes into account the temperature dependency of the “viscosity of the coating liquid” and performs a numerical calculation. The result is “leveling amount (minimum paint film thickness with respect to average paint film thickness h ₀₎ . FIG. 11 also shows that “leveling of the coating film is almost completed within a few seconds immediately after application with a roll coater”. It can be confirmed that "when the coating viscosity is lowered by heating at a low temperature for a few seconds, the leveling effect is greatly improved".

That is, from FIGS. 10 and 11, the coating film temperature immediately after the roll coating is set to 40 to 40 by rapid heating.
When the temperature rose to 50 ° C., the viscosity of the coating film decreased to 1.2 to 0.15 Pa · sec, and the leveling of the coating film rapidly progressed until 4 to 5 seconds had elapsed, and was present on the coating film surface. B
The leveling amount of the circle is 0 when low temperature heating is not performed.
It can be seen that it is improved to 0.02 with respect to 1. here,
As a low-temperature heating means for the coating film immediately after the coating is applied with a roll coater or the like, far-infrared heating or the like in which heating is performed by radiant heat is preferable, and taking into account the progress of leveling and the effect of preventing "armpit", It is appropriate to preheat to a temperature of about 50 ° C. and to maintain the temperature at that temperature for about 30 seconds or less.

As described above, even in the case of a thick-film coating in which the occurrence of "stick" becomes a problem from the above-mentioned several confirmed items, the above-described "critical heating" is performed while blowing a low-temperature airflow onto the coating film surface. Rapid heating and drying from the inside of the coating within the "rate", or promote low-temperature heating of the coating immediately after application of the paint to promote evaporation of the solvent and then rapidly heat from within the coating within the "critical heating rate" Dry, or furthermore, heat the coating film immediately after application at low temperature to promote the evaporation of the solvent in the coating film, and then rapidly heat and dry it within the “critical heating rate” while blowing a low-temperature air stream on the coating film surface. It will be clear that a coating material with a smooth and sound coating can be obtained with high productivity.

Next, the present invention will be described with reference to examples.

【Example】

<Example 1> Using the coating and drying equipment shown in FIG.
A continuous smooth coating test according to the present invention was performed on a strip steel sheet having a thickness of mm.

That is, the strip steel sheet 11 is continuously supplied to the roll coater, and a xylene / polyester paint using xylene as a solvent is applied to a thickness of 26 μm, and this is continuously supplied to the drying furnace 7. In the drying furnace, a low-temperature (20 ° C.) gas (air) is blown at a flow rate of 8 m / sec from a gas jet nozzle 12 opened at a small angle toward the surface of the steel sheet, and the induction heating coil 13 is blown. The coating film was rapidly heated to about 200 ° C. or more by internal heating, and baked and dried. In addition, the heating rate at the time of rapid heating was set to the upper limit of the "limit heating rate" obtained by the curve B in FIG.

As a result, it is possible to dry and harden the coating film in a state where there is almost no "spitting", and it is possible to stably produce a beautiful coated xylene / polyester steel sheet having no surface defects at a high speed line speed. confirmed.

Example 2 Using the coating and drying equipment shown in FIG. 2, a continuous thick film coating test according to the present invention was performed on a 0.4 mm thick steel strip. That is, a strip steel sheet 11 is continuously supplied to a roll coater, and a xylene / polyester paint is applied to a thickness of 24 μm.
The coating film was rapidly heated to a low temperature of about 50 ° C. in the “preheating zone” of No. 14. The heating in the "preheating zone" was performed by a far infrared heater-15. Next, the warm atmosphere cover
Painted steel plate running inside 14 (line speed: 120m / m
in) is continuously sent to the “heat insulation zone” and kept in a low-temperature heating state (about 50 ° C. on average) until the next “rapid heating zone (drying furnace)” (low-temperature heating holding time) Was about 30 seconds in total). Here, a hot-air blowing nozzle 16 was employed as a heat source in the "warming zone".

The "preheating zone" and the "insulation zone"
Through the heating at low temperature, the viscosity of the coating film decreased and the fluidity increased, so that the leveling was sufficiently advanced and at the same time, the evaporation of the solvent existing inside the coating film smoothly progressed.

Subsequently, the coated steel sheet in this state is sent to the next "rapid heating zone (drying furnace)" and the induction heating coil
Rapid heating to about 200 ℃ or more by heating from the inside by 13 (heating rate is 20.0 ℃ / se within the limit heating rate
c), the coating film was baked and dried.

Now, according to the continuous coating test conducted as described above, according to this method, a beautiful coating which does not generate "roll eyes" or "sides" even when coating a thick coated steel sheet at a high speed line speed is obtained. It was confirmed that it could be performed stably.

Example 3 Using the coating / drying equipment shown in FIG. 3, a continuous thick film coating test according to the present invention was performed on a 0.4 mm thick steel strip. That is, a strip steel sheet 11 is continuously supplied to a roll coater, a xylene / polyester-based paint is applied to a thickness of 30 μm, and immediately after that, a heat insulating atmosphere cover is applied.
The coating film was rapidly heated to about 50 ° C. in the “preheating zone” of No. 14. The heating in the "preheating zone" was performed by a far infrared heater 15.

Subsequently, the coated steel sheet traveling in the heat insulating atmosphere cover 14 is continuously sent to a "heat insulating zone", and hot air is blown to the subsequent "rapid heating zone (drying furnace)". Evaporation of the solvent was accelerated (about 30 seconds) without hardening the surface of the coating film by hot air blowing by the nozzle 16.

The "preheating zone" and the "insulation zone"
Through the heating at low temperature, the viscosity of the coating film decreased and the fluidity increased, so that the leveling was sufficiently advanced and at the same time, the evaporation of the solvent existing inside the coating film smoothly progressed.

Subsequently, the coated steel sheet in this state was sent to the next “rapid heating zone (drying furnace)” and heated to 200 ° C. or higher, and the paint was baked and dried. In this "rapid heating zone", an induction heating coil 13 is used as a heat source to perform internal heating, and to suppress evaporation of a solvent remaining inside while suppressing the hardening of the coating film surface. Rapid heating was performed within the “critical heating rate” while blowing a low-temperature gas (air at 20 ° C. in this example).

FIG. 4 shows a heat pattern from immediately after the application of the paint to the outlet of the rapid heating zone (drying oven). The heating method applied to each heating zone is a "low-temperature electric heating method" in the preheating zone to promote the progress of leveling, and a "hot air" in the heat retaining zone to promote the evaporation of the solvent. In the "spraying method", in the rapid heating zone, heating from the inside of the coating such as induction heating, electric resistance heating and infrared heating can be performed while blowing a low-temperature gas in order to promote evaporation while suppressing the curing of the coating surface. It can be said that the “electric heating method” is preferable.

By the way, the higher the speed of the airflow blown by the rapid heating zone, the larger the mass transfer coefficient of the coating film surface and the faster the drying of the coating film, but the collision speed from the vertical direction is 30 m / sec (surface When the parallel jet exceeds 50 m / sec (8 m / sec on the surface), wrinkled surface flaws occur on the coating film surface. Therefore, in the present embodiment, the airflow guide plates 18 and 19 are provided so that the airflow to be blown is parallel to the coating film surface. In this case, as schematically shown in FIG. 5, it is more effective to blow the air current from the side of the coated steel sheet.

By applying the continuous coating method according to the present invention to the continuous coating test conducted as described above, even if a thick coated steel sheet is coated at a high speed line speed, the "rolled eyes" and "sides" are obtained. It was confirmed that beautiful painting free of "" can be stably performed.

Table 1 shows "conventional method (method of baking and drying in a drying furnace following the line as it is after application of paint)" and "method of the present invention according to this example", which were confirmed by experiments. "Compatible conditions under which beautifully painted steel sheets can be manufactured." The "coating thickness" is a value after baking and drying, and the "heating rate" is a heating rate in a rapid heating zone.

[0043]

[0044]

As described above, according to the present invention, a beautiful coating material having a smooth and sound coating film can be stably manufactured with high productivity by a relatively simple method. Thus, an industrially useful effect is provided.

[Brief description of the drawings]

FIG. 1 shows a coating method according to an embodiment for carrying out the method of the present invention.
It is explanatory drawing of a drying equipment example.

FIG. 2 is an explanatory diagram of an example of a coating / drying facility used in an embodiment to implement another method according to the present invention.

FIG. 3 is an explanatory view of an example of a coating / drying facility used in an embodiment to carry out a further alternative method according to the present invention.

FIG. 4 is a heat pattern in a heating and drying process in an embodiment using the equipment of FIG. 3;

FIG. 5 is an explanatory diagram relating to a preferred airflow blowing means.

FIG. 6 is an explanatory diagram of a natural coating method using a roll coater.

FIG. 7 is an explanatory diagram of a reverse coating method using a roll coater.

FIG. 8 is a graph showing the effect of airflow blowing on a high-speed beautiful dry limit film thickness.

FIG. 9 is an explanatory diagram of roll eyes.

FIG. 10 is a graph showing a change in viscosity of a paint according to a temperature.

FIG. 11 is a graph showing a time change of a coating film leveling amount by a numerical calculation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Backup roll 2 Material to be coated 3 Paint pan 4 Pickup roll 5 Applicator roll 6 Metering roll 7 Drying furnace 11 Strip steel plate 12 Gas jet nozzle 13 Induction heating coil 14 Heat insulation atmosphere cover 15 Far-infrared heater 12 Warm atmosphere cover 16 Hot air blowing nozzle 17 Air flow nozzle 18 Guide plate 19 Guide plate

Claims (3)

(57) [Claims] 1. The coating thickness of a continuous coating line is 10 microns.
When applying a thick film of Ron or more, after applying the paint, quickly heat and dry the inside of the paint film within the "limit heating rate at which no fire occurs" while blowing a low-temperature air flow below the paint film curing temperature on the paint film surface A continuous coating method for a strip-shaped material. 2. The coating thickness of the continuous coating line is 10 μm.
In the case of thick film coating of more than RON , first heat the coating at low temperature at a temperature lower than the coating curing temperature immediately after application of the coating, and then rapidly from the inside of the coating within the “limit heating rate that does not generate cracks” A continuous coating method for a strip material, comprising heating and drying. 3. A coating thickness of 10 μm in a continuous coating line.
In thick film coating of Ron or more , first, immediately after application of the coating, carry out low-temperature heating of the coating at a temperature lower than the coating curing temperature, and then blow a low-temperature airflow below the coating curing temperature to the coating surface A continuous coating method for a band-shaped material, wherein rapid heating and drying from the inside of a coating film is performed within a "limit heating rate at which no waking occurs".