JP3158894B2 - How to heat the strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of heating a strip material after applying a coating material for producing a smooth and beautiful surface coating material by a continuous coating line for the strip material (such as a metal strip). It is.

[0002]

2. Description of the Related Art Generally, in a continuous coating line for a strip material such as a steel plate, a coater (for example, a roll coater) 2 for applying a paint to the strip material 1 as shown in FIG. A line configuration in which an oven (heating furnace) 3 for drying and curing the coating film and a cooling zone 4 are employed. In this line configuration, the pre-processed strip 1 is
, A continuous coating on one side or both sides is applied, and the coated strip is subsequently fed into the oven 3 and heated to dry and harden the coating. The band 1 in the oven 3 is connected to the backup roll 5 of the coater.
Pass line ro installed behind (downstream) Bun-3
The long catenary 7 is supported by the roll 6, and is designed not to come into contact with other members such as a roll until the coating film surface is dried and hardened. The coating material which has been dried and hardened by heating in the oven 3 is cooled to a normal temperature in the cooling zone 4.

[0003] However, in the coating of the band-like material by such a continuous coating line, there is a problem that "striped irregularities spaced in the width direction of the band-like material" tend to occur when the paint is applied by a coater. Has become. This is the code to apply the paint
This is particularly noticeable when a roll coater is used, and in this case, it is called a "roll-order". The suppression is mainly performed by keeping the line speed low, and the productivity is reduced. I have invited you. In addition, the defects on the coating film surface, which are problematic in the continuous coating of the belt-like material along with the above-mentioned "rolls", are caused by the volatilization of the solvent from the inside of the coating film during the heating and drying of the ribbon-coated material. There are bubble marks (called "armpits").

For this reason, for example, JP-A-63-4869 and JP-A-63-143962 disclose a roll coater which applies a coating material to a strip-shaped material.
Disclosed are measures to reduce the risk. JP 6
As shown in FIG. 12, the transfer according to Japanese Patent Application Laid-Open No. 3-4869 is applied between a pickup roll 9 for scooping paint from a paint pan 8 and an applicator roll 10.
The roll 11 is inserted and the peripheral speed is controlled to suppress the occurrence of roll eyes. Further, the one related to JP-A-63-143962,
As shown in FIG. 13, the roll coater has a structure in which a transfer roll 11 and a doctor roll 12 are arranged in addition to a pickup roll 9 and an applicator roll 10. 13 is a blade for scraping paint), whereby the backup roll 5, the applicator roll 10, the transfer roll 11, and the doctor roll 12 are all rotated in the same direction and rolled. -Prevents the occurrence of loops.

[0005] However, increasing the number of rolls constituting the coater as in these measures leads to complicated setting of operating conditions, and furthermore, the film thickness which is the most important in forming a uniform coating film. This caused a problem that it was difficult to maintain accuracy.

[0006] On the other hand, as a measure for suppressing armpits, for example, a technique disclosed in Japanese Patent Laid-Open Publication No.
The heating temperature in an oven for drying and curing the coating film applied by the painter is set to "the temperature at which the paint cross-linking reaction starts is 10 ° C.
And the boiling point of the paint (solvent) is 10 to
A method for suppressing the occurrence of wrinkles by maintaining the temperature at a temperature lower than 30 ° C. ”is known. Certainly, in this method, the heating temperature of the coating film is maintained at "a temperature lower than the boiling point by 10 to 30 DEG C.". Occurred.

That is, the paint generally has the property of exhibiting a minimum viscosity (minimum viscosity) at the temperature (approximately 60 to 80 ° C.) unique to the paint as shown in FIG.
The holding temperature in the oven disclosed in Japanese Patent Publication No. 5-50 is 50-60 from the above "temperature at which the paint viscosity is minimal (minimum)".
The temperature is as high as ° C. or more. Therefore, in the method described in Japanese Patent Application Laid-Open No. 3-77675, the coating film is dried in a state where the paint has low fluidity (high viscosity state).
Therefore, the leveling (smoothing) of the coating film does not sufficiently proceed from application to drying (leveling is achieved by the flow of the paint, and the higher the fluidity, the faster the progress). As a result, surface irregularities remain, which leads to deterioration of the properties of the coating film surface.

[0008] As described above, the measures for improving the properties of the coating surface proposed so far correspond to the roll eyes or the armpits, respectively. What is an effective means for eliminating both defects simultaneously is as follows. It wasn't. In view of the above, it is an object of the present invention to provide a method for heating a strip material in a heating zone of a continuous coating line. An object of the present invention is to provide a "method for heating a strip-shaped material after application of a coating material" for sufficiently suppressing "remaining surface irregularities" and producing a coating material having a smooth and beautiful surface texture.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventor has made intensive studies, particularly focusing on the "property of a paint exhibiting a minimum viscosity (minimum viscosity) at a specific temperature" shown in FIG. As a result, "The band material coated with the paint by the coater is heated rapidly to the above temperature (the temperature at which the paint viscosity becomes minimal), which is sufficiently higher than normal temperature and considerably lower than the boiling point of the solvent. Then, if the temperature is maintained for a while, the leveling proceeds promptly due to the low viscosity of the paint, and the evaporation of the solvent proceeds efficiently without causing cracks due to the boiling of the solvent. With rapid heating, the coating film can be cured in a short period of time without concern about the occurrence of wrinkles or the remaining of the coating film surface irregularities. "

[0010] The present invention has been made based on the above findings and the like. The present invention relates to a method for heating a strip-shaped material after a coating material is applied in a continuous coating line for a strip-shaped material (steel plate or other metal plate). As shown by the solid line in FIG. 1, first, the strip material is rapidly heated at a heating rate of 5 to 15 ° C./sec up to the minimum viscosity region of the applied coating material, and then 5 to 40% of the solvent contained in the coating material.
The heating rate is switched to low-speed heating at 0 to 2 ° C / sec until the solvent evaporates. Thereafter, the mixture is heated at a heating rate of 3 to 10 ° C / sec to the cross-linking reaction start temperature, so as to increase the number of rolls and rolls. A stable production of a coating material having suppressed smooth and beautiful surface properties. "

Here, the “minimum viscosity region of the paint” is
The "temperature range where the viscosity of the paint is minimal (temperature range up to 10 ° C. before and after the temperature at which the viscosity of the paint is lowest)” as shown in FIG. 2) and FIG. 2 are graphs comparing "minimum viscosity ranges" for several specific paints.

[0012]

As described above, when a coating material is applied to a belt-like material by a roll coater or the like, there is a problem that the surface of the coating film becomes uneven. The time it takes for the film to decay due to the leveling action of the coating

(Equation 1) (Α in the formula is a factor determined by the uneven shape of the coating film and the drying speed). As a means for promoting the leveling action, a) decrease the roll pitch, b) paint There are four ways to reduce the viscosity, c) increase the coating thickness, and d) increase the surface tension of the paint.

However, since the roll pitch generated when the operating conditions (line speed, paint initial viscosity, wet film thickness, etc.) are determined is generally determined, the aforementioned "roll pitch" is reduced. It is difficult to promote leveling by the "method", and the "coating thickness" is a value determined by the target product, and cannot be changed without permission. The “surface tension of the paint” is almost unchanged unless solidified (skinning of the coating surface) (the surface tension is almost constant as long as the coating surface is in a fluid state). The method of increasing the size cannot be practically adopted.

However, as described with reference to FIG. 14 and FIG. 2, since the paint has a property of having a minimum (minimum) viscosity in a certain heating temperature range, the temperature of the coated material is increased and the paint is temporarily heated. If the temperature is maintained, the paint forming the coating film can be kept low in viscosity, which greatly contributes to the promotion of leveling. In addition, in the heating to the above-mentioned temperature in the heating furnace (oven), as shown in FIG. 3, there is a time lapse between "the change in the temperature of the paint" and "the decrease in the film thickness due to the evaporation of the solvent component". Since the displacement occurs (the paint temperature starts to rise rapidly in the early stage of heating, but the evaporation of the solvent component progresses gradually after a certain temperature rise), the coating is rapidly heated in the early stage of the heating zone to increase the coating thickness. If the temperature of the paint reaches a minimum viscosity before the decrease proceeds, the boiling point of the paint is generally 120 ° C. or higher, and the above-mentioned “temperature at which the paint exhibits a minimum viscosity (generally 60 to 60 ° C.)
Until 70.degree. C.), the solvent does not evaporate by boiling, and as is clear from FIG. 3, the evaporation of the solvent component is extremely small.

When the temperature of the coating is 7 ° C./sec, the “initial solvent content”, “film thickness (wet film thickness)”, and “evaporation of the solvent until the paint viscosity is minimized (minimum)”. The relationship with "amount" is substantially as shown in FIG. By the way, in the actual operation, it is general that the coating thickness is in the range of several μm to several tens μm and the initial solvent content is in the range of 40 to 70 wt%.

However, the heating rate at the initial stage of the heating is 15 ° C./s.
exceeds ec, there is a risk that relatively high among the evaporation of the coating film in solvent paint viscosity occurs "popping" occurs. On the other hand, if the temperature rise rate at the initial stage of heating is less than 5 ° C./sec, the “time shift between the change in the temperature of the paint and the decrease in the thickness of the paint film” becomes smaller,
In the initial rapid heating, the heating rate needs to be 5 to 15 ° C./sec.

The coated strip which is rapidly heated to the minimum viscosity region of the paint (the temperature range up to 10 ° C. before and after the temperature at which the paint viscosity is minimum) is heated until 5 to 40% of the solvent contained in the paint evaporates. Is it maintained at that temperature (heating rate: 0 ° C / s
ec) or the heating rate is suppressed to 2 ° C./sec or less, and the evaporation of the solvent and the progress of leveling are achieved.

In this temperature range, the viscosity of the paint is minimal (minimum)
Therefore, the leveling of the coating film proceeds smoothly and promptly, and the evaporation of the solvent in the coating film proceeds smoothly and gently, so that the surface properties are not adversely affected. However, if the heating rate in this region exceeds 2 ° C./sec, the evaporation of the solvent becomes remarkable, causing a bumping state of the solvent, so that the adverse effect on the surface properties of the coating film cannot be ignored, and the evaporation of the solvent in the coating film. Before the coating is sufficiently performed, the viscosity of the coating material becomes higher than the allowable range, and the adverse effect on the surface properties of the coating film is further increased.

If the retention period in the above temperature range is "less than 5% by evaporation of the solvent contained in the coating material", the solvent will boil when the temperature rises to the next crosslinking reaction temperature, resulting in the formation of wrinkles. In addition, the leveling of the coating film does not proceed sufficiently. On the other hand, holding in this temperature range until the "evaporation amount of the solvent contained in the paint exceeds 40%" is not practical because it leads to a remarkably long heating time and a long heating furnace. Although it is impossible to confirm the amount of solvent evaporation in the actual production line,
The evaporation rate can be estimated if the top pattern, paint type, initial solvent content and film thickness are determined. This is used to preset the furnace temperature.

After the leveling has progressed, the temperature of the coated strip material kept in the minimum viscosity range of the coating material is raised again to reach the crosslinking reaction starting temperature, and the coating film is cured. In this case, since the solvent component has been sufficiently evaporated in the “minimal viscosity range of the coating material” which is lower than the boiling point, the temperature rise to the crosslinking reaction start temperature does not generate a side even if it is heated to some extent, and it is short. The crosslinking reaction initiation temperature can be reached in a time. As a result, it is possible to obtain a smooth surface of the coating film with no occurrence of rolls and in which roll eyes are eliminated. However, if the heating rate at this time is less than 3 ° C / sec, it is necessary to lengthen the heating time and lengthen the heating furnace, while if the heating rate exceeds 10 ° C / sec, the residual solvent Concerns about the occurrence of armpits due to rapid evaporation cannot be wiped out.

As described above, the present invention suppresses "bubble formation due to solvent boiling and escaping by breaking through the coating film surface" which may occur during heating and drying in the heating zone of the continuous coating line. The present invention relates to a technique for effectively promoting the flow of paint at the time, achieving smoothness of surface irregularities due to roll eyes and the like, and forming a beautifully textured coating film. The furnace temperature condition of the heating furnace (oven) may be determined empirically with the heat pattern shown by the solid line as a target (note that the broken line in FIG. 1 indicates the heat pattern conventionally used in general). Is).

However, in the actual operation, if the rapid heating at the early stage of heating (early stage of the drying process) is carried out by a method of increasing the blowing speed of hot air, the surface of the coating film tends to have wavy irregularities. The heating is performed without increasing the hot air blowing speed (the flow velocity at the surface of the coating material is set at 6 m / sec or less), “raising the gas temperature (for example, rising to 300 to 340 ° C.)” or “other heating means (for example, Induction heating) ". Then, in the low heating rate range (when the heating rate is 0
Gas temperature of 200 to 25 ° C.
The spraying speed may be set to 8 m / sec or less while keeping the temperature within the range of 0 ° C., so that the high fluidity of the coating film is maintained and the occurrence of wrinkles is prevented.

Next, the effects of the present invention will be described more specifically with reference to examples.

EXAMPLE A coating test of a strip steel plate was performed using a continuous coating line. The steel plate used for the test had a width of 1000 mm,
It was a galvanized steel sheet with a thickness of 0.5 mm. A roll coater was used to apply the paint to the steel sheet. This roll coater was composed of three rolls: a pickup roll, an applicator roll, and a backup roll. Was to be done. The oven (heating furnace) used was one in which the inside was divided into seven zones, and the length of each zone was 2 m, 3 m, 4 m, 5 in order from 1 zone.
m, 12 m, 12 m, and 12 m, so that the heating rate could be controlled for each zone. The coating test was performed as follows.

Test Example 1 A coating test was conducted using a high-molecular polyester-based paint. This coating material had the characteristic that the viscosity changed as shown in FIG. 5 according to the temperature change, and showed a minimum viscosity (minimum viscosity) at about 80 ° C. Further, the surface tension hardly changed while the paint exhibited fluidity, and was 30 dyne / cm 2.

The paint was applied to the steel sheet under the conditions of the line speed and the coating thickness shown in Table 1, and the heat pattern after the paint was applied.
As shown in FIGS. 6 and 7, there are seven patterns according to the conventional methods (A) and (B) and the methods (1), (2), (3), (4) and (5) of the present invention. Was selected.

[0026]

[Table 1]

The coated steel sheet thus obtained was examined for "the degree of the remaining rolls (the height of the unevenness on the dried coating film)" and "the degree of the occurrence of pits". 1 is also shown.

When the height of the unevenness on the dried coating film is 0.8 μm or less, it is impossible to confirm the presence of the remaining rolls with the naked eye, and this level is usually higher for highly designed steel sheets (for home appliances). Has been requested. On the other hand, in the case of products (for building materials) where slight unevenness is allowed, it is permissible to leave rolls of about 1.2 μm, and those exceeding 1.2 μm are recognized to be out of the allowable range.

The results of the evaluation of the wobble were as follows: o: no wobble was observed on the entire surface of the coating film; Δ: a portion where the coating thickness was non-uniform, although it did not occur at a portion where the coating thickness was uniform ( (In the vicinity of both ends of the steel sheet), ×: Defective product in which wrinkles were observed even in the part of uniform coating thickness.

As is clear from the results shown in Table 1,
According to the method of the present invention, the height of the concavities and convexities attributable to the rolls finally remaining on the surface of the dried coating film is reduced by 50% or more in comparison with the conventional method. It can be seen that a heat pattern having a long maintenance time near the temperature at which the viscosity is exhibited has a remarkable improvement effect. In addition, it can be seen that the method of the present invention can completely suppress the generation of wedge even at a line speed at which a significant defect occurs in the conventional method.

Example 2 A coating test was conducted using a general polyester paint. This coating material had the characteristic that the viscosity changed as shown in FIG. 8 according to the temperature change, and exhibited a minimum viscosity (minimum viscosity) at around 60 ° C. Further, the surface tension hardly changed while the paint exhibited fluidity, and was 30 dyne / cm 2.

The coating of the paint on the steel plate was performed under the conditions of the line speed and the coating thickness shown in Table 2, and the heat pattern after the coating was applied.
As shown in FIGS. 9 and 10, six patterns were selected by the conventional methods (A) and (B) and the methods (1), (2), (3) and (4) of the present invention.

[0033]

[Table 2]

The coated steel sheet thus obtained was examined for "the degree of the remaining roll (the height of the unevenness on the dry coating film)" and "the degree of the occurrence of wrinkles". 2 is also shown. In addition, the evaluation results regarding the remaining roll number and the armpit were the same as in the case of Test Example 1. Table 2
Indicate the same tendency as in the case of Test Example 1, and it can be confirmed that the method of the present invention has a remarkable effect on suppressing defects caused by rolls and patches.

[0035]

[Summary of Effects] As described above, according to the present invention, a sound and beautiful coating is performed in a continuous coating line of a strip material.
Industrially very useful effects are brought about, such as the ability to stably produce materials with high efficiency.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram comparing the heat pattern of a material to which a paint is applied by the method of the present invention and the conventional method.

FIG. 2 is a graph showing the relationship between paint viscosity and temperature of various paints.

FIG. 3 is an explanatory diagram showing a change in coating film temperature and a change in film thickness in a heating zone.

FIG. 4 “Initial solvent content”, “film thickness (wet film thickness)”, and “amount of solvent evaporated until paint viscosity is minimized” in coating film
6 is a graph showing a relationship with the graph.

FIG. 5 is a graph showing the temperature dependence of the viscosity of the paint used in Test Example 1.

FIG. 6 is an explanatory diagram showing a heat pattern in an oven in Test Example 1.

FIG. 7 is an explanatory view showing a heat pattern in an oven in Test Example 1.

FIG. 8 is a graph showing the temperature dependence of the paint viscosity used in Test Example 2.

FIG. 9 is an explanatory diagram showing a heat pattern in an oven in Test Example 2.

FIG. 10 is an explanatory view showing a heat pattern in an oven in Test Example 2.

FIG. 11 is a schematic explanatory view of a continuous coating line for a strip material.

FIG. 12 is an explanatory diagram relating to an example of a conventional roll eye reduction measure.

FIG. 13 is an explanatory diagram relating to another example of the conventional roll eye reduction measure.

FIG. 14 is an explanatory diagram relating to temperature dependence of paint viscosity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strip material 2 Coat 3 Oven (heating furnace) 4 Cooling zone 5 Backup roll 6 Pass line roll 7 Catenary 8 Paint pan 9 Pickup roll 10 Application roll 11 Transfer roll 12 Doctor roll 13 Blade

Claims (1)

(57) [Claims] When heating a strip after applying a coating in a continuous coating line of the strip, the strip is first heated at a rate of 5 to 15 ° C./sec up to a minimum viscosity range of the applied coating. After rapid heating, 5-40% of solvent contained in paint
A method for heating a strip-shaped material, wherein the heating is switched to a low-speed heating at a heating rate of 0 to 2 ° C./sec until evaporating, and thereafter heating is performed at a heating rate of 3 to 10 ° C./sec to a crosslinking reaction starting temperature.