JPH06114330A - Continuous coating method of belt-shaped material - Google Patents

Abstract

PURPOSE:To form a smooth and perfect film by heating the film at low temperature just after applying a coating material and then applying the rapid heating and drying from inside the film within the limit heating rate without generating foams while air flow of low temperature lower than the film coating temperature is sprayed. CONSTITUTION:A xylene polyester coating material is applied on a hoop plate 11 by the thickness of 30 microns, and then rapid heating up to approximately 50 deg.C is applied by a far infrared ray heater 15 in a 'preheating zone'. Successively, the evaporation of a solvent is accelerated by spraying hot air by means of a hot air spraying nozzle 16 in a 'heat insulating zone'. Then the plate is transferred to a 'rapid heating zone' in which the rapid heating up to 200 deg.C is applied within the 'limit heating rate' by an induction heating coil 13 while spraying gas (20 deg.C air) of low temperature lower than the film curing temperature in a manner of forming a parallel jet on a film surface from an air flow nozzle 17, and the coating material is baked and dried. Thus, the beautiful coating can be carried out stably without generating rolling streaks or foams in the case even if a thickly coated steel plate is coated.

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 etc.) to a strip 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 for a functional material) to a running belt-like material, a "roll coating method" has been generally adopted conventionally. There is. This roll coating method is a roll coating method.
The paint supplied through a pick-up roll, a transfer roll, a metering roll, a smoothing roll, etc. of the water passes along the back-up roll or two deflectors. -Apply the material to be coated supported between the rolls with an applicator roll, and bake and dry it in a drying oven (while blowing hot air to the coating surface to evaporate the solvent) Temperature rise, paint curing,
Although it is a coating method (curing is performed), depending on the combination of the traveling direction of the material to be coated and the rotating direction of the applicator roll,
This can be roughly classified into two types, "natural coating method" and "reversing coating method".

For example, in FIG. 6, the coating material 2 passing along the backup roll 1 is coated with the paint in the paint pan 3 by means of a pickup roll 4 and an applicator roll 5. Roll roll with a typical two-roll method
The Tig method is shown, but the application is shown here.
This is an example of the "natural coating method" in which the rotating direction of the tarroll 5 is opposite to the running direction of the material 2 to be coated.

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 rotation direction of the tool 5 is the same as the running direction of the material 2 to be coated. The reference numeral 6 in the figure denotes a machine provided for adjusting the coating film thickness.
The drying furnace is a taling roll, and the reference numeral 7 is a drying furnace.

However, the roll coat, which is the mainstream painting technique,
In the Ting method, the following problems have been pointed out so far. For example, when manufacturing coated steel sheets, the steel sheet to which the paint has been continuously applied is then continuously sent to a drying oven, where the solvent (volatile components) in the coating film is evaporated and the coating film is cured. However, at this time, if the heating rate is increased to increase the productivity, surface defects due to bubbles occur. This surface defect is called “armpit”, and the evaporation of the solvent remaining inside the coating film intensifies due to rapid heating to generate bubbles, which deform the cured coating film surface and appear as bubble defects. However, the occurrence was remarkable especially in the case of thick film coating.

As a method of reducing this "armpit", a method of heating and drying under reduced pressure has been proposed (Japanese Unexamined Patent Publication No.
No. 139174), the equipment cost is too high to be applied to a continuous coating line, and a large effect commensurate with the cost cannot be expected.

On the other hand, Japanese Patent Laid-Open No. 3-77675 discloses that
Controls the heat-up heat pattern of the steel sheet coated with paint,
The steel plate temperature is kept below the crosslinking reaction initiation temperature of the paint resin and below the boiling point temperature of the solvent for 10 to 25 seconds to promote the evaporation of the solvent and prevent the bubble of the solvent which causes "armpit" from occurring. The proposal of is described. However, in this method, when the coating film thickness becomes thick, a long holding time is required for the solvent to evaporate, and improvement in productivity cannot be expected at all, and the effect of reducing the occurrence of "armpits" cannot be said to be sufficient. .

The problem of this "armpit" is not limited to the roll coating method, but it can be continuously used in cart float coaters, extruders, etc., which have been used in recent years. Needless to say, a similar problem was pointed out in painting.

In view of the above, the object of the present invention is to improve productivity because a smooth and sound coating can be stably formed without causing a coating defect such as "armpit". The purpose is to establish a continuous coating means for belt-shaped materials that has a relatively low equipment cost.

[0010]

The present inventor has obtained the following knowledge as a result of earnest studies to achieve the above object. a) In thick film coating on a continuous coating line, regardless of the coating device used, whether it is a roll coater or an extruder, after the coating is applied, the coating should be as smooth as possible. As a heating means for evaporating the solvent of the above and baking and curing the coating film, electric heating, induction heating, etc., are not the conventional methods of spraying a high temperature air stream onto the surface of the coating film to raise the temperature from the surface. By adopting the method in which the temperature is raised from the inside of the coating film by the above method, the occurrence of "armpits" at the time of bake hardening is almost eliminated.

B) Further, in order to smoothly evaporate the solvent in the coating film, "a means for spraying an air stream having a temperature lower than the curing temperature of the coating film on the coating film surface" is extremely effective,
"Means for providing a process of low-temperature heating at a temperature lower than the curing temperature of the coating film from immediately after coating the coating to drying and curing" is also effective. In particular, if the latter means is adopted, the coating film before baking and curing will be used. The flowability of the coating is improved, and the leveling effect of the surface tension causes "waviness" and "rolls" (the roll coating method causes the coating thickness to become non-uniform in the width direction). The appearance of streaks) "is also reduced, and the effect of forming a smooth coating film from this point becomes remarkable.

The present invention has been completed as a result of further studies based on the above-mentioned findings and the like. "When a thick film is coated on a continuous coating line, after coating the coating, the coating is cured on the surface of the coating. Rapid heating from the inside of the coating film within the "maximum heating rate at which armpits do not occur" while blowing a low temperature air stream below the temperature
Drying is performed, or first, the coating film is heated at a temperature lower than the coating film curing temperature immediately after the coating material is applied, and then the rapid heating / drying from the inside of the coating film is performed within the “limit heating rate”. Or, first, immediately after applying the coating material, low temperature heating of the coating film is performed at a temperature lower than the coating film curing temperature, and then the above-mentioned “ By performing rapid heating and drying from the inside of the coating film within the "limit heating rate", it is possible to stably produce a strip-shaped coating material with a smooth and sound coating film without "armpits" with good productivity. It has a major feature in "done".

Hereinafter, the present invention will be described with reference to specific examples.
It will be described in detail together with the effect.

Operation: First, the mechanism of occurrence of "armpit", which is a surface defect of the coating film generated during the baking and drying process, is considered as follows. Generally, the baking and drying process of the coating film is roughly divided into two,
One is a chemical process called "uniform drying process", and the rate of solvent drying from the surface becomes a rule. The second is
This is a physical process called "damping drying process", and the moving speed of the solvent in the coating film becomes a rule. The cause of the "armpit" is due to the second physical process. When the uniform drying process is completed and the drying process is attenuated, the coating film surface temperature rises and the surface is hardened, the residual solvent remains. If a large amount remains, they will become bubbles as the temperature rises, causing "armpits" and becoming surface defects. When the "solvent remaining in the coating film" evaporates and diffuses from the surface after the coating film surface is cured by rapid heating and drying, the bubble-like traces become surface defects.

The occurrence of this "armpit" is particularly problematic when the coating film thickness is increased. However, according to the conventional knowledge, the heating rate during baking and drying should be slowed until the coating film is cured in order to prevent it. It was considered effective to extend the time. However, it is difficult to prevent the productivity from being deteriorated by this measure because the coating efficiency is remarkably lowered.

Therefore, the present inventor has examined new means for effectively preventing the occurrence of "armpits" from various viewpoints, and in the process, it is thought that the occurrence of "armpits" is greatly affected. Occurrence of "armpits" when various conditions are changed by using various paints in order to understand the relationship between the heating rate during baking and drying, the film thickness, the conditions of the air flow that contacts the film surface, etc. We conducted the survey and confirmed the following.

That is, if the coating film thickness is less than 10 microns, the solvent inside the coating film diffuses sufficiently during the uniform drying process and evaporates from the surface. For example, the heating and drying rate is 50 ° C./s.
"Warming" does not occur even at a high speed of ec or more (refer to the relationship of curve A in Fig. 8 showing the result of investigation of the relationship between "coating thickness" and "heating rate" and "warm occurrence status"). I want to be). On the other hand, from FIG. 8, it can be seen that when the coating film thickness is 10 microns or more, “armpit” tends to occur unless the heating rate (baking and drying rate) is slowed down as much as possible.

[0017] However, the term "beautiful heat drying limit film thickness" refers to the limit film thickness at which "armpits" do not occur even when performing high-speed drying. When heating and drying from inside the paint while spraying an air flow, the "beautiful heat drying limit film thickness" improves.
A faster clean drying of thicker films is possible (see curve B in FIG. 8). In this case, especially if the heating rate is 10
The degree of improvement in "beautiful heat-drying limit film thickness" in the range of -40 ° C / sec is remarkable.

Therefore, in baking and drying the coating film, if heating is performed from the inside of the coating material while spraying a low-temperature air current onto the coating surface, "armpit" does not occur regardless of the type of coating material (for example, resin type). The "critical heating rate" can be maintained at a high value even when the coating film thickness is large (compare the curves A and B in FIG. 8), and even within this high "critical heating rate", the rapid heating is rapid. Since heating and drying can be performed, the work efficiency of sound coating is remarkably improved.Although Fig. 8 is an example of a beautiful heating and drying limit film thickness curve of a coating using xylene as a solvent, other solvents are used. Even in the case of the existing paint, a beautiful heating and drying limit film thickness curve can be easily obtained by a simple drying experiment.

However, in this case, when the air current is blown in the 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). However, it is not possible to suppress the occurrence of "armpits" because the surface is hardened immediately by blowing hot gas above the hardening temperature of the paint. Therefore, the temperature of the air stream to be sprayed is such a low temperature (80 ° C or lower, preferably about 20 ° C or lower) that the surface of the coating film does not harden immediately.
Therefore, it is better to pay attention so that the spray angle is substantially parallel to the coating film surface. And the flow velocity of the air flow to be sprayed is 50
It is about m / sec or less, preferably about 8 m / sec.

Further, the heating of the coating film by blowing the air flow is
As described above, it is desirable to use electric heating such as induction heating so that the temperature can be raised from the inside of the coating film. It is better to heat rapidly to 200 ° C or higher and dry quickly at the fastest possible rate.

The reason why the "beautiful heating and drying limit film thickness" is significantly improved by heating the coating film from the inside by electric heating such as induction heating while cooling the surface by blowing a low temperature gas is that the coating film is heated by this heating. Since the internal temperature rises, the diffusion coefficient of the solvent from the inside to the surface increases, the mass transfer coefficient on the surface increases, and since the surface is cooled by gas, curing is delayed until the end, It is thought that this is because the solvent is sufficiently dispersed and "chuckling" is less likely to occur.

On the other hand, when preheating is carried out at a low temperature (80 ° C. or lower) so that the coating film does not harden, immediately after the coating material is applied and before baking and drying (heating to 200 ° C. or higher) are carried out, During this period, volatilization of the solvent in the coating film is promoted to cause smooth solvent escape, and when preheating is not performed before baking and drying as in the conventional case, the "beautiful heat drying limit film thickness" is 10 Although it did not reach the micron level, even if the film thickness is 10 microns or more, the occurrence of "armpits" is minimized and a beautiful dry coating film can be obtained. Also has almost the same tendency as the curve B in FIG. 8). Moreover, when this low-temperature heating (preferably preheating at about 50 ° C.) is performed, the viscosity of the coating film is lowered, leveling is likely to proceed, and uneven defects such as “waviness” and “roll eyes” are eliminated. The effect is also brought.

As described above, by performing low-temperature preheating, "undulation" and "roll eyes" generated in the coating process of the coating material.
The effect of reducing surface irregularities such as is obtained, but the reason is as follows. For example, when a roll eye is schematically drawn, it is represented as "waviness" as shown in Fig. 9. This "waviness" tends to become smooth with the passage of time due to the flow and surface tension of the coating film (" Called "leveling"). Then, the analytical solution of "the time when the height difference becomes half (half-life)" when it is considered that the paint is a Newtonian fluid and the roll has a sine wave is as follows. As described above, the half-life is proportional to the viscosity, and thus the viscosity reduction of the paint is very effective for shortening the leveling time.

As shown in the survey results in FIG. 10, the influence of temperature change of the paint viscosity, which has a great influence on the reduction of rolls and the like, is that the paint temperature is about 80 ° C. or lower (preferably around 50 ° C.). When the temperature is raised to 40 to 50 ° C, the viscosity is greatly reduced and the fluidity is improved.
The leveling time will be very short). Therefore, if the coating film is heated at a low temperature immediately after the coating material is applied, "rolls" and "waviness" will quickly disappear until baking and drying in a heating furnace, resulting in a smooth coating surface. It is a translation.

[0025] FIG. 11 creates a leveling model considering the temperature dependence of the "viscosity of the coating solution", that is the result of numerical computation "leveling amount (coating minimum thickness for coating average thickness h ₀ FIG. 11 also shows that “the leveling of the coating film is almost completed within a few seconds immediately after coating with a roll coater”. It can be confirmed that "the leveling effect is significantly improved by heating the coating for a few seconds at a low temperature to reduce the viscosity of the coating material."

That is, also from FIG. 10 and FIG. 11, the coating temperature immediately after the roll coating is 40 to 40 by the rapid heating.
When the temperature was raised 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 proceeded within 4 to 5 seconds, and the coating film surface was present. Low
The leveling amount 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,
Far-infrared heating or the like, which is heated by radiant heat, is suitable as a low-temperature heating means for the coating film immediately after coating the coating material with a roll coater or the like. Considering the effect of preventing progress of leveling and "armpits", It is suitable to preheat by heating to about 50 ° C. and holding at that temperature for about 30 seconds.

As described above, from the above-mentioned several confirmation items, in the case of thick film coating in which the occurrence of "armpits" is a problem, the above-mentioned "critical heating" is applied while blowing a low-temperature air current over the surface of the coating film. Rapid heating from the inside of the coating within the "rate" or rapid heating of the coating immediately after coating the coating to accelerate evaporation of the solvent, then rapid heating from inside the coating within the "limit heating rate" If it is dried, or further, the coating film immediately after coating is heated at a low temperature to accelerate the evaporation of the solvent in the coating film, and then rapidly heated and dried within the “limit heating rate” while blowing a low temperature air flow on the surface of the coating film. 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 / drying equipment shown in FIG. 1, 0.4
A continuous smooth coating test according to the present invention was carried out on a strip steel plate having a thickness of mm.

That is, the strip steel plate 11 was continuously supplied to the roll coater to apply a xylene / polyester paint using xylene as a solvent to a thickness of 26 μm, and this was continuously applied to the drying furnace 7. Of the induction heating coil 13 while the 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 steel plate surface in the drying furnace. The coating film was rapidly heated to about 200 ° C. or above by internal heating by means of baking to dry. The heating rate at the time of rapid heating was set to the upper limit of the “limit heating rate” obtained from the curve B in FIG.

As a result, the coating film can be dried and cured with almost no occurrence of "armpit", and a beautifully coated xylene / polyester coated steel sheet having no surface defects can be stably produced 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 conducted on a 0.4 mm thick strip steel sheet. That is, the strip steel plate 11 is continuously supplied to the roll coater to apply the xylene / polyester-based paint at a thickness of 24 μm, and immediately after that, the heat insulation atmosphere cover is applied.
The coating film was rapidly heated to a low temperature of about 50 ° C. with a 14 “preheating zone”. The far-infrared heater 15 was used for heating in the "preheating zone". Next, a warm atmosphere cover
Painted steel plate running inside 14 (line speed: 120 m / m
in) is continuously sent to the "heat-retaining zone" and kept in the low-temperature heating state (about 50 ° C on average) until the subsequent "rapid heating zone (drying oven)" (low-temperature heating retention time). Was about 30 seconds in total). Here, the hot air blowing nozzle 16 is used as the heat source in the "heat retaining zone".

This "preheating zone" and "insulation zone"
Through the low-temperature heating state at 1, the viscosity of the coating film was lowered and the fluidity was increased, so that the leveling was sufficiently advanced, and at the same time, the evaporation of the solvent present in the coating film proceeded smoothly.

Subsequently, the coated steel sheet in this state is sent to the next "rapid heating zone (drying furnace)" to induce an induction heating coil.
Rapidly heats up to more than 200 ℃ by heating from 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 carried out in this way, according to this method, even if a thick coated steel sheet is coated with a high speed line speed, a beautiful coating without "roll eyes" or "sideways" is obtained. It was confirmed that it can be performed stably.

Example 3 Using the coating and drying equipment shown in FIG. 3, a continuous thick film coating test according to the present invention was carried out on a 0.4 mm thick strip steel sheet. That is, the strip steel plate 11 is continuously supplied to the roll coater to apply the xylene / polyester-based coating material at a thickness of 30 μm, and immediately after that, the heat-insulating atmosphere cover is applied.
The coating was rapidly heated to about 50 ° C. with 14 “preheat zones”. The far-infrared heater 15 was used for heating in the "preheating zone".

Subsequently, the coated steel sheet running in the heat-retaining atmosphere cover 14 is continuously sent to the "heat-retaining zone", and hot air is blown to the subsequent "rapid heating zone (drying furnace)". The blowing of hot air from the nozzle 16 accelerated the evaporation of the solvent (about 30 seconds) without curing the surface of the coating film.

This "preheating zone" and "insulation zone"
Through the low-temperature heating state at 1, the viscosity of the coating film was lowered and the fluidity was increased, so that the leveling was sufficiently advanced, and at the same time, the evaporation of the solvent present in the coating film proceeded smoothly.

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 to bake and dry the coating material. In this "rapid heating zone", an induction heating coil 13 is used as a heat source to perform internal heating, and in order to complete the evaporation of the solvent remaining inside while suppressing the hardening of the coating film surface, the air flow nozzle 17 is used. Rapid heating was performed within the "critical heating rate" while blowing a low temperature gas (20 ° C. air in this example).

FIG. 4 shows the heat pattern immediately after the coating of the above coating material to the outlet of the rapid heating zone (drying furnace). The heating method applied to each heating zone is a "low-temperature electric heating method" to promote the progress of leveling in the preheating zone, and a "hot air method" to accelerate the evaporation of the solvent in the heat insulating zone. "Blowing method" is a rapid heating zone, in order to accelerate evaporation while suppressing hardening of the coating surface, heating from inside the coating such as induction heating, electric resistance heating, infrared heating can be performed while blowing a low temperature gas. It can be said that the "electric heating method" is preferable.

By the way, the higher the velocity of the air stream blown by the rapid heating zone, the higher 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 5 m / sec), and when the parallel jet exceeds 50 m / sec (8 m / sec on the surface), wrinkle-like surface scratches occur on the coating surface. Therefore, in this embodiment, the air flow guide plates 18 and 19 are provided so that the air flow to be blown is parallel to the coating film surface. In this case, it is more effective to blow the air stream from the side direction of the coated steel sheet, as schematically shown in FIG.

By applying the continuous coating method according to the present invention to the continuous coating test carried out in this manner, even if a thick coated steel sheet is coated by a high speed line speed, "roll eyes" and "sideways" are applied. It was confirmed that a beautiful coating that does not generate "can be performed stably.

Table 1 shows "conventional method (method of baking and drying in a drying furnace following the line as it is after coating of coating material)" and "method of the present invention according to this embodiment" as confirmed by experiments. “Compatible conditions for producing beautifully painted steel sheets” are compared and shown. The "coating thickness" is the value after baking and drying, and the "heating rate" is the heating rate in the rapid heating zone.

[0043]

[0044]

[Summary of Effects] 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. , The industrially useful effect is brought about.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of an example of coating / drying equipment used in the examples for carrying out another method according to the present invention.

FIG. 3 is an explanatory view of an example of coating / drying equipment used in the examples for carrying out another method according to the present invention.

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

FIG. 5 is an explanatory diagram related to a preferable air flow blowing unit.

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

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

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

FIG. 9 is an explanatory diagram of a roll eye.

FIG. 10 is a graph showing a change in viscosity of a coating material with temperature.

FIG. 11 is a graph showing changes over time in the coating film leveling amount by numerical calculation.

[Explanation of symbols]

 1 Backup Roll 2 Painted Material 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 Insulated Atmosphere Cover 15 Far infrared heater 12 Insulated atmosphere cover 16 Hot air blowing nozzle 17 Air flow nozzle 18 Guide plate 19 Guide plate

Claims (3)

[Claims] 1. In thick film coating in a continuous coating line, after coating the coating material, the coating film surface is sprayed with a low temperature air flow below the curing temperature of the coating film within a "critical heating rate at which armpits do not occur". A continuous coating method for strip-shaped materials, characterized by rapid heating and drying from inside the film. 2. In thick film coating on a continuous coating line, first, immediately after coating the coating material, low temperature heating of the coating film is carried out at a temperature lower than the coating film curing temperature, and then "limit heating rate at which armpits do not occur". A continuous coating method for strip-shaped materials, characterized by rapid heating and drying from inside the coating film. 3. In thick film coating in a continuous coating line, first, immediately after coating the coating material, low temperature heating of the coating film is carried out at a temperature lower than the coating film curing temperature, and subsequently, on the coating film surface is less than the coating film curing temperature. A continuous coating method for strips, characterized by rapidly heating and drying from the inside of the coating film within a "critical heating rate that does not cause armpits" while spraying a low temperature air stream.