JPH031092Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an improvement of a baking drying furnace that bakes and dries a coating film by continuously transferring the object to be coated into the oven.
In particular, it relates to a baking drying oven for water-soluble paints such as electrodeposition paints.

[Prior art and its problems]

For example, in the case of a baking drying furnace that performs finish drying of automobile bodies etc. on which water-soluble paint has been electrodeposited, the object to be coated is transported into a tunnel furnace whose furnace body is formed into a chevron or a flat shape, and the workpiece is continuously dried. and transfer this to the normal
The coating is heated to a high temperature of about 170-180°C to react and cure it.

In this tunnel furnace, the length from the inlet to the outlet of the object to be coated is selected to be, for example, 80 to 160 m.
The area from the inlet to about 20 to 50 m is called the temperature rising zone, and the area from the temperature rising zone to the outlet is called the curing zone. This temperature rising zone is where the workpiece brought into the furnace is heated to a predetermined baking temperature (e.g. 150 to 200℃).
The curing zone is an area where the coating film of the object to be coated is cured by reaction at the baking temperature.

In the oven of such a baking drying oven, the object to be coated is heated to a high temperature as described above, and organic solvents, coating resins, curing agents, etc. are evaporated from the coating film, and harmful and malodorous substances are generated. When the concentration of these harmful malodorous substances in the furnace increases, yellowing of the coating film and poor drying occur, which impairs product quality, and at the same time causes the disadvantage that the working environment is significantly deteriorated.

Therefore, in the past, drying furnaces were used in which the exhaust gas containing harmful malodorous substances generated inside the furnace was deodorized and purified through a catalyst layer installed in the exhaust duct, and then discharged to the outside. A drying furnace has been proposed in which the high-temperature processing gas is directly circulated and convected back into the furnace and used effectively as a heating source within the furnace (Special Publications Nos. 58-175785 and 59-59).
(See No. 12946).

By the way, according to the inventor's experiments and research, the greatest amount of harmful malodorous substances evaporate from the coating film of the object to be coated occurs when the object is brought into the furnace through the inlet and reaches the prescribed baking temperature. It turned out that this was the case until the temperature was raised.

That is, Fig. 2 is a graph showing the experimental data, where the ordinate represents the exhaust gas concentration in the furnace [ppm] and the abscissa represents the length of the drying furnace body [m]. In the heating zone where materials are brought into the high-temperature furnace and heating begins, the amount of evaporation of organic solvents such as alcohol and thinner, and low-boiling substances such as amines increases rapidly, and from the heating zone to the curing zone. The amount of evaporation of high-boiling point substances such as paint resins, pigments, and hardening agents, which cause yellowing of paint films, is also gradually increasing, and the contamination of these low-boiling point substances, high-boiling point substances, and other harmful malodorous substances is increasing, especially in temperature rising zones. It was confirmed that the concentration was significantly higher.

Furthermore, when the object to be coated on which the water-soluble paint is electrodeposited is brought into the furnace and heated in the temperature rising zone, a large amount of water vapor is suddenly generated from the coating film.

Therefore, the exhaust gas, which has become extremely contaminated with humidity and harmful malodorous substances, is deodorized and purified through a catalyst layer as in the conventional method, and the treated gas is circulated and convected directly into the furnace. If a method is adopted in which the furnace is used as a heating source, a large amount of greasy substances that cause yellowing and delamination of the paint film will be generated in the furnace, and humid heated air will be supplied, causing the paint film to deteriorate. This method has serious disadvantages in that it causes fogging and poor drying, which significantly impairs product quality. This has become one of the particularly important issues that must be solved when finishing drying an automobile body on which a water-soluble paint has been electrodeposited in automobile painting, which requires very strict product quality.

On the other hand, similar to general baking and drying ovens, due to the demand for energy conservation, the exhaust gas inside the oven is not directly discharged to the outside, but is recirculated and convected within the oven as in the conventional method, and used effectively as a heating source. That was also desired.

[Purpose of the invention] Therefore, the present invention adopts a method in which all the exhaust gas in the heating zone is discharged to the outside only in the heating zone where a large amount of water vapor and harmful odor substances are generated. In the zone, the exhaust gas, which has a reduced concentration of harmful malodorous substances and low humidity, is deodorized and purified through a catalyst layer, and the treated gas is circulated and convected into the furnace again to be used effectively as a heating source inside the furnace. By adopting this, we aim to improve product quality by preventing paint film defects, especially in the baking drying oven for water-soluble paints, and at the same time, save energy by minimizing the running costs required for heating inside the oven. The aim is to also achieve the following.

[Structure of the idea]

In order to achieve this purpose, the present invention includes a heating zone that heats and raises the temperature of a coated object on which a water-soluble paint film is formed to a predetermined baking temperature, and a curing ring that reacts and cures the paint film. In the baking drying oven for water-soluble paint having a temperature increasing zone, an exhaust duct is disposed in the temperature increasing zone to discharge exhaust gas containing water vapor generated in the temperature increasing zone to the outside, and an exhaust duct is provided in the curing zone. , a hot air circulation path is formed for deodorizing and purifying the exhaust gas in the curing zone through the catalyst layer and circulating and convecting the treated gas back into the curing zone.

[Effect of invention]

According to the above configuration, the object to be coated on which a film of water-soluble paint has been formed is carried into the furnace and heated in the heating zone, and a large amount of water vapor and exhaust gas containing harmful odor substances are generated from the surface of the object. It is exhausted to the outside through an exhaust duct installed in the temperature rising zone. Therefore, the amount of water vapor and harmful malodorous substances in the heating zone is significantly reduced, thereby significantly reducing the humidity and contaminant concentration throughout the furnace, including the curing zone.

In the curing zone, the exhaust gas inside the furnace, which has low humidity and pollution concentration, is deodorized and purified through the catalyst layer, and the high-temperature treated gas is circulated and convected directly into the furnace, where it is effectively used as a heating source inside the furnace. Therefore, running costs can be significantly reduced without causing poor drying, fogging, yellowing, etc. of the coating film.

[Example] The present invention will be described below based on a specific example shown in the drawings.

FIG. 1 is a flow sheet diagram showing an example of a baking drying oven according to the present invention.

In the figure, 1 is a furnace body of a drying furnace, and includes a heating zone 4 in which a workpiece 3 to be coated, which is carried in through an inlet 2 and is continuously transferred, is heated to a predetermined baking temperature.
The water-soluble paint film formed on the surface of the object 3 from the latter part of the temperature-raising zone 4 to the outlet (not shown) is heated to a predetermined baking temperature (usually 170°C).
It has a curing zone 5 for reaction curing at 180°C).

Reference numeral 6 denotes an exhaust duct that is open-connected to the temperature rising zone 4 of the furnace body 1, and is used as a suction fan to collect exhaust gas containing a large amount of water vapor and harmful malodorous substances generated from the water-soluble paint film in the temperature rising zone 4. 7, the gas is sucked and sent to a catalyst layer 9 disposed in a reactor 8, and the treated gas is discharged to the outside after being deodorized and purified through the catalyst layer 9. Note that 10 is a burner for heating the catalyst layer 9 to its reaction temperature of 300 to 400°C, and 11 is a blower for supplying combustion air to the burner 10.

Here, the catalyst layer 9 is made of two types: a platinum group catalyst containing platinum (Pt) and/or palladium (Pd) as active species, which have extremely high oxidation activity, and copper (Cu) and cerium (Ce). It is constructed by combining a katsuparcerium-based catalyst consisting of a composite of active species.

Further, N is a hot air circulation path that circulates and convects hot air in the curing zone 5 of the furnace body 1, and distributes the exhaust gas in the curing zone 5 sucked through the return duct 13 by the circulation fan 12 into the reactor 14. The catalyst layer 15 is deodorized and purified, and the purified high-temperature processing gas is directly introduced into the furnace body 1 through a supply duct 16. The catalyst layer 15 is made of platinum, for example. family catalysts are used. Note that 17 is a burner that heats the catalyst layer 15 to a predetermined reaction temperature;
A blower 18 supplies combustion air to the burner 17.

The above is an example of the configuration of the baking drying furnace according to the present invention, and its operation will be explained next.

When the inside of the furnace body 1 reaches the predetermined baking temperature of 170 to 180°C, the object 3 to be coated, such as an automobile body, on which the water-soluble paint has been electrodeposited is brought in through the inlet 2, and is first placed in the heating zone 4. The object to be coated 3 is heated and heated to a predetermined baking temperature. At this initial stage of heating, the object to be coated 3 is rapidly heated from a temperature of around 20°C before being brought into the furnace body 1 to a high temperature of around 170 to 180°C, and water vapor and phenols are released from its surface. Large amounts of harmful and malodorous substances with hydroxyl groups, such as alcohols, are generated.

The exhaust gas containing a large amount of water vapor and harmful odor substances generated in the temperature rising zone 4 is transferred to the suction fan 7.
is sucked into an exhaust duct with an intervening exhaust duct and sent to the catalyst layer 9 in the reactor 8.

Here, the catalyst layer 9 includes a platinum group catalyst that effectively promotes a dehydrogenation reaction that removes hydrogen from organic compounds having hydroxyl groups such as alcohols and phenols to form aldehydes (RCTO), and a platinum group catalyst that effectively promotes the dehydrogenation reaction that removes hydrogen from organic compounds having hydroxyl groups such as alcohols and phenols to form aldehydes (RCTO). Furthermore, it is combined with a Katsuparcerium-based catalyst that extremely effectively promotes the combustion reaction that oxidizes and decomposes carbon dioxide (CO ₂ ) and water (H ₂ O), which are harmless and odorless, through carboxylic acid (RCOOH). phenols in the exhaust gas sucked from inside the temperature rising zone 4 through the exhaust duct 6,
Harmful and malodorous substances such as alcohols are almost completely decomposed, and clean deodorized gas and water vapor with an extremely small amount of aldehyde are discharged to the outside.

As a result, the humidity and the concentration of harmful malodorous substances not only in the temperature rising zone 4 but also in the entire furnace body 1 including the curing zone 5 are significantly reduced. Direct circulation and convection through N does not cause yellowing or drying of the coating film, and product quality is greatly improved.

In addition, the exhaust gas in the curing zone 5 is sucked through the return duct 13 and the catalyst layer 1 is
If the high-temperature processing gas is circulated and convected into the furnace again through the supply duct 16 and effectively used as a heating source in the furnace, running costs can be significantly reduced.

In addition, hot air circulation path N in curing zone 5
If a catalyst layer 15 that is a combination of the platinum group catalyst and the above-mentioned Katsuparcerium catalyst is used instead of the conventionally commonly used platinum group catalyst, the coating film can be improved. Aldehydes, which cause the production of greasy substances that cause yellowing and delamination, are effectively oxidized and decomposed, further improving product quality.

[Effect of idea]

As described above, the baking drying oven for water-soluble paint according to the present invention is configured to exhaust to the outside a large amount of water vapor and exhaust gas containing harmful odor substances generated in the temperature rising zone. The humidity and contaminant concentration in the entire furnace, including not only the warm zone but also the curing zone, are significantly reduced, and poor drying of the paint film, fogging, yellowing, etc. are reliably prevented, and product quality is greatly improved. It has the excellent effect of

Moreover, if the amount of water vapor and harmful odor substances contained in the exhaust gas in the furnace is significantly reduced, the exhaust gas in the curing zone can be deodorized and purified by passing through the catalyst layer, and the treated gas can be directly sent to the furnace. There is no problem in circulating convection within the
Since the high-temperature process gas can be effectively used as a heating source in the furnace, running costs can be significantly reduced and energy can be saved.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet diagram showing an example of a baking drying oven for water-soluble paint according to the present invention, and FIG. 2 is a graph showing the state of generation of harmful malodorous substances in the drying oven. Explanation of symbols, 1...Furnace body of drying oven, 2...Inlet, 3...Object to be coated, 4...Temperature rising zone, 5...Curing zone, 6...Exhaust duct, 7...Suction fan , 8...reactor, 9...catalyst layer, 10...
...Burna.

Claims (1)

[Scope of utility model registration request] In a baking drying furnace for water-soluble paints, the oven has a heating zone for heating and raising the temperature of a coated object on which a water-soluble paint film is formed to a predetermined baking temperature, and a curing zone for reaction-curing the paint film. , an exhaust duct is disposed in the temperature increase zone to discharge exhaust gas containing water vapor generated in the temperature increase zone to the outside, and an exhaust duct is provided in the curing zone to exhaust the exhaust gas in the curing zone through a catalyst layer. A baking drying oven for water-soluble paint, characterized in that a hot air circulation path is formed for deodorizing and purifying the treated gas and circulating and convecting the treated gas back into the curing zone.