JPH05123627A - Drying furnace for coating - Google Patents

Abstract

PURPOSE:To enhance the smoothness of the surface of a coating film without increasing an equipment size by uniformizing heating up over the entire area of the coating film. CONSTITUTION:Radiation panels 3 which irradiate a material 2 to be coated with the radiation heat higher than the baking temp. of the material and a heating means 4 which blows the hot wind lower than the baking temp. of the material 2 to the material to be coated are provided within a body 1 of a drying furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drying oven used in the coating process of resin automobile parts and the like.

[0002]

2. Description of the Related Art Needless to say, the drying process of the coating film plays an important role in the coating process, but it is necessary to drain water after pretreatment, drain water after water polishing, or force putty or sealing material. A drying oven is also required for drying. Various types of commonly used coating drying ovens are known depending on various conditions such as installation location. For example, it can be classified into a tunnel type drying oven and a box type drying oven depending on its shape, and a radiation type drying oven and a convection type drying oven depending on the heat source. BACKGROUND ART As a coating drying oven for automobiles, a tunnel-type radiation drying oven, a convection drying oven, or a drying oven combining a radiation type and a convection type is widely used.

As shown in FIG. 4, a typical example of a drying oven in which a radiation type and a convection type are combined is provided with a hot air blowing duct 31 in the lower portion of the side wall of the drying oven main body 30, and a hot air suction duct in the upper side wall. 32 are provided. The hot air in the furnace sucked from the hot air suction duct 32 is guided to the combustion device 34 by the circulation fan 33, heated to a predetermined temperature, and then blown into the furnace again from the hot air blowing duct 31. Further, fresh air for combustion is introduced into the combustion device 34 by a fan 35. On the other hand, a radiant panel 36 is provided on the side wall of the drying oven main body 30, and the inside of the drying oven main body 30 is heated by the radiant heat emitted from the surface of the radiant panel 36 and is maintained at a predetermined temperature. There is.

While the above-mentioned convection drying method is excellent in thermal efficiency, it has a drawback that dust in the furnace adheres to the uncured coating surface to circulate the air in the furnace, which causes a coating film defect. is doing. On the contrary, the radiation drying method is inferior in thermal efficiency to the convection drying method, but is excellent in preventing the above-mentioned coating film defects. Therefore, in the conventional coating drying oven, the radiation type drying method is used in the uncured state immediately after coating, and the convection type drying method is used in the state where the coated surface is cured to some extent. That is, the inlet side zone of the drying furnace is of a radiant type and the outlet side zone is of a convective type so that the advantages of both drying methods can be utilized.

[0005]

Various coatings are also applied to resin-made automobile parts (bumpers, grilles, instrument panels, etc.) molded from polypropylene, polyurethane, ABS, etc., but they are thermosetting. When the paint is used, the paint is baked in the drying oven as in the car body.

Such a drying oven for resin-made automobile parts is basically a convection drying oven, a radiation drying oven, or a drying oven which is a combination of both, but when the object to be coated is resin. Since the heat capacity is large, the temperature of the surface of the article to be coated is less likely to rise than that of the surface of the coating film. Therefore, in order to satisfy the drying conditions over the entire coating film, it is necessary to increase the facility capacity. That is, the thermosetting coating material needs to be held and dried at a predetermined temperature or higher for a predetermined time, and for example, in the currently widely used top coating or intermediate coating, a temperature of 140 ° C. or higher for 20 minutes or longer is required. Must hold. Does not heat up to 140 ° C, or 14
If the drying conditions are insufficient such as when the temperature cannot be maintained for 20 minutes or more even though the temperature is raised to 0 ° C., so-called “baked sweetness” occurs, and the coating film performance is deteriorated.
It may cause peeling of the coating film. In addition, when drying is performed in a state where a temperature difference occurs between the surface of the coating object and the coating film surface, the fluidity of the coating film before curing becomes non-uniform, and as a result, the smoothness of the coating film surface is deteriorated. there were.

It is effective to employ a radiation type drying oven to solve the above problems, but in the radiation type drying oven, the coating film becomes overheated when the object to be coated stays in the oven. , The color of the coating may turn yellow, or it may cause pinholes or peeling of the coating film. For example, if the work remains in the furnace due to a failure of the transport device, the temperature of the coating film will rise too much, the curing speed of the coating resin will be faster than the evaporation rate of the solvent, and the balance between the two will not be achieved. When it is hardened and the solvent vapor evaporates from the inside, it breaks through the surface and escapes to the outside, so-called pinholes occur.

The present invention has been made in view of the above-mentioned problems of the prior art. Uniformity of temperature rise over the entire area of the coating film ensures smoothness of the coating film surface without enlarging the equipment. The purpose is to raise.

[0009]

Means for Solving the Problems The present invention for achieving the above object comprises a radiation panel for irradiating an object to be coated with radiant heat higher than the baking temperature of the object to be coated, in a drying furnace main body.
A drying oven for coating, comprising: heating means for blowing hot air having a temperature lower than the baking temperature of the object to be coated onto the object to be coated.

[0010]

In the present invention thus constructed, the object to be coated is heated by the radiant heat from the radiant panel provided in the drying furnace body. The radiant heat from the radiant panel absorbs energy into the inside of the coating film and is heated at once, so that the heating time is shortened and uniform heating is possible.
In parallel with the heating by the radiation panel, hot air having a temperature lower than the set temperature of the object to be coated is blown from the hot air blowing nozzle which is a heating means, so that the temperature of the coating film surface becomes low.
Therefore, when viewed as a whole coating, the width of the temperature distribution becomes smaller, and as a result, coating defects such as pinholes and deterioration of smoothness can be prevented, while the temperature distribution of the coating becomes uniform. Therefore, there is no need to remodel the equipment such as raising the set temperature or upsize the equipment.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a sectional view showing a coating drying oven according to an embodiment of the present invention, FIG. 2 is a sectional view of the coating drying oven of the same embodiment taken along the carrying direction, and FIG. 3 is a coating drying oven of the same embodiment. A coating film sectional view and a temperature distribution graph showing the temperature distribution of the coating film processed in the drying oven, and FIG. 5 is a coating film sectional view showing the temperature distribution of the coating film treated in the conventional combined radiation / convection drying oven and It is a temperature distribution graph.

The drying oven for coating of this embodiment is a drying oven main body 1.
A radiation panel 3 is provided on the side wall of the drying furnace main body 1 in the longitudinal direction thereof, and the inside of the drying furnace main body is heated by radiant heat emitted from the surface of the radiation panel to maintain a predetermined temperature.

For the radiation panel 3 according to this embodiment, for example, an infrared panel heater, especially a far infrared panel heater can be used. Infrared rays can be directly applied to the drying of thermosetting type paints, and far infrared rays (wavelength of 4 μm or more) are particularly effective for drying thermosetting type paints. Generally, the resin forming the paint has a property of absorbing well a wavelength of 4 μm or more. By absorbing such energy, the molecules of the paint become active in molecular motion,
Friction heat is generated between molecules. On the other hand, the absorption of energy causes intense collisions between molecules and progresses the volatilization of solvents etc., and at the same time, a phenomenon of connecting other molecules with each other, that is, a cross-linking reaction occurs, and when this becomes a polymer substance, Has dried and cured. When heated in a convection drying oven, the heat gradually permeates from the outside to the inside of the coating film, and not only does it take a considerable amount of time to dry, but when only the surface is initially cured, When the solvent vapor evaporates, it breaks through the surface and escapes to the outside, resulting in coating film defects such as pinholes, or the smoothness of the coating film surface is reduced due to the difference in temperature rising speed between the coating film surface and the inside. However, when far-infrared rays are irradiated, energy is absorbed even inside the coating film and heating is performed at once, so that the heating time is shortened and uniform heating is possible. As the far infrared heater, any of a far infrared tube type heater, a far infrared lamp type heater, a far infrared panel heater and the like can be adopted, but in the present embodiment, the far infrared panel heater is used. In this far infrared panel heater, a nichrome wire resistance heating element is built in a planar radiation surface, and a far infrared radiation element is applied or baked on the radiation surface of the outer surface thereof. This radiating element is mainly formed of a semiconductor titanium oxide obtained by reducing titanium oxide as a main component. The far-infrared tube type heater and the far-infrared lamp type heater all have a high heat-generating surface, so some degree (normally 350
It is necessary to provide a distance of (mm or more). However,
Since the radiation intensity weakens in inverse proportion to the square of the distance, in the present embodiment, a far infrared panel heater that can be placed close to the object to be coated and that can radiate heat uniformly is provided. It is preferable to use.

Further, by curving the surface of the far infrared panel heater and reflecting the energy radiated at an angle close to the radiation surface and causing it to radiate again at an angle almost perpendicular to the object to be coated 2, It can be said that it is preferable to radiate a large amount of energy to the object to be coated 2 in a concentrated manner.

A plurality of hot air blowing nozzles 4 for blowing hot air to the object to be coated are provided around the object 2 to be transported inside the drying furnace, while the upper part of the side wall is inside the drying furnace. A suction duct 5 for sucking hot air is provided. The hot air in the furnace sucked from the suction duct 5 is guided to the combustion device 7 by the circulation fan 6, heated to a predetermined temperature, and then blown again from the hot air blowing nozzle 4 toward the object 2 to be coated in the furnace. It Further, fresh air for combustion is introduced into the combustion device 7 by a fan 8.

In the drying furnace of this embodiment, the relationship among the above-mentioned set temperatures of the radiation panel 3, the hot air blowing nozzle 4, and the article 2 to be coated is as follows. That is, in the conventional combined radiation and convection type drying oven, baking of the object to be coated is mainly by hot air circulation, and radiant heating is supplementarily performed at the inlet of the drying oven. The set temperature of the object 2 is 140 ° C., the temperature of the radiant panel is 300 ° C., the temperature of the blown hot air is 170 ° C., the temperature of the sucked hot air is 150 ° C., and the temperature of the radiant panel and the hot air is Is higher than the set temperature of the object to be coated. On the other hand, in the case of the drying furnace of the present embodiment, the article to be coated 2 is baked only by radiant heating, and the hot air is used to prevent overheating due to radiant heating, that is, to cool the article to be coated 2. .. That is, the set temperature of the article to be coated 12 is 12
The temperature of the radiation panel 3 is 800 ° C, while the temperature is 0 ° C.
The temperature of the hot air sucked into the suction duct 5 is 115
The temperature of the hot air blown from the hot air blowing nozzle 4 is set to 110 ° C., and the hot air (110 ° C.) lower than the set temperature (120 ° C.) of the object to be coated is blown. ing.

FIG. 2 is a cross-sectional view of the coating drying furnace of this embodiment taken along the conveying direction of the article to be coated 2, showing an example of the setting positions of the radiation panel 3 and the hot air blowing nozzle 4. That is, in the illustrated embodiment, the temperature rising zone, the holding zone, and the cooling zone are set from the inlet side to the outlet side of the coating drying furnace, and only the radiation panel 3 is provided in the temperature raising zone. Radiation panel 3 in the holding zone
Both the hot air blowing nozzle and the hot air blowing nozzle are provided. Further, only the hot air blowing nozzle 4 is provided in the cooling zone. When the coating drying furnace total length is 30 minutes, the heating time, the holding zone, and the cooling zone have a passing time ratio of about 5 minutes for the heating zone, about 20 minutes for the holding zone, and about 20 minutes for the cooling zone. It is preferably about 5 minutes. The reason why the temperature rising zone on the inlet side of the coating drying furnace is only the radiation panel 3 in this way is that such a zone does not require a cooling action, and hot air is blown on the cooling zone on the outlet side of the coating drying furnace. The reason for using only the nozzle 4 is that the temperature increase due to radiant heat is omitted and only the hot air blowing nozzle 4 performs cooling.

According to the coating drying oven of the present embodiment having the above-mentioned structure, the object 2 to be coated is heated by the radiation heat from the radiation panel 3 provided on the side wall of the drying oven body 1. When far infrared rays are radiated from this radiation panel, energy is absorbed even inside the coating film and heating is performed at once, so that the heating time is shortened and uniform heating is possible. Since the hot air blowing nozzle 4 blows hot air at a temperature lower than the set temperature of the object to be coated in parallel with the heating by the radiation panel, the coating film surface temperature becomes low.

This state will be described with reference to FIGS. 3 and 5. FIG. 3 shows the temperature distribution of the coating film when treated in the drying oven of this example, while FIG. 5 shows the temperature distribution of the coating film when treated in the conventional combined radiation and convection drying oven. In the figure, “10” indicates a resin material, “11” indicates a base coating film made of a primer or the like, “12” indicates a color base coating film, and “13” indicates a clear coating film. According to the conventional combined radiation and convection drying oven, the radiant heat 14 causes the clear coating film 13 to the color base coating film 12, as shown in FIG.
Although each coating film is heated through the base coating film 11 to generate a slight temperature gradient, the hot air 15 by the convection method is set higher than the set temperature of the coating film, so that the hot air 15 is directly blown onto the coating film. The resulting clear coating 13 has the highest temperature rise, and as a result, the temperature gradient toward the inside of the coating is further promoted. On the other hand, when treated in the drying furnace of this embodiment, the radiant heat 14 causes the clear coating film 1 as shown in FIG.
3 through the color base coating film 12 and the base coating film 11 to raise the temperature of each coating film, and a slight temperature gradient is generated, but the clear coating film 13 having the highest temperature has a hot air temperature lower than the set temperature of the coating film. Since 16 is sprayed, the temperature of the clear coating film 13 drops. Therefore, the width of the temperature distribution is reduced when viewed as a whole coating film, and as a result, coating film defects such as pinholes and deterioration of smoothness can be prevented.
There is no need to modify the equipment or increase the size of the equipment, such as raising the set temperature by making the temperature distribution of the coating film uniform.

The present invention is not limited to the above-mentioned embodiments and can be modified in various ways.

[0021]

As described above, according to the present invention, a radiation panel for irradiating an object to be coated with radiant heat higher than the baking temperature of the object to be coated in the drying furnace body, and the object to be coated. Since the heating means for blowing hot air lower than the baking temperature onto the article to be coated is provided, the temperature distribution of the coating film becomes uniform, and the smoothness of the coating film surface can be improved without increasing the size of equipment.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a coating drying oven according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the coating / drying furnace of the same embodiment taken along the carrying direction.

FIG. 3 is a coating film cross-sectional view and a temperature distribution graph showing a temperature distribution of a coating film treated in the coating drying oven of the same example.

FIG. 4 is a vertical cross-sectional view showing a conventional combined radiation / convection type drying oven.

FIG. 5 is a cross-sectional view and a temperature distribution graph showing a temperature distribution of a coating film processed in a conventional combined radiation / convection drying oven.

[Explanation of symbols]

1 ... Drying oven main body, 2 ... Coating object, 3
... Radiation panel, 4 ... Hot air blowing nozzle (heating means), 5 ... Suction duct (heating means), 6 ... Circulation fan (heating means), 7 ... Combustion device (heating means)

Claims (1)

[Claims] 1. A radiant panel for irradiating an object to be coated with radiant heat higher than a baking temperature of the object to be coated, in a drying furnace body,
And a heating unit for blowing hot air having a temperature lower than the baking temperature of the object to be coated onto the object to be coated.