JPH031091Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an improvement of a coating drying oven for baking and drying a coating film by continuously transporting an object to be coated into the oven.

[Prior art and its problems]

For example, in the case of a paint drying oven that bake-dries objects to be coated such as automobile bodies, the objects to be coated are transported into a tunnel furnace whose furnace body is formed into a mountain or flat shape and are continuously transported. , the object to be coated is usually heated to 170 to 180℃.
The coating film is cured by heating it to a relatively high temperature.

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, and the temperature rising zone extends from the inlet to approximately 20 to 50 m, and the curing zone extends from the temperature rising zone to the outlet. They are called zones. This heating zone is an area where the workpiece carried into the furnace is heated to a predetermined baking temperature (for example, 150 to 200°C), and the curing zone is an area where the workpiece brought into the furnace is heated to a predetermined baking temperature (for example, 150 to 200°C). This is the area where the coating film on the object to be coated is cured by reaction.

In the oven of such a coating 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 a significant deterioration of the working environment.

Conventionally, the exhaust gas containing harmful and malodorous substances generated in the furnace is deodorized and purified through a catalyst layer installed in the exhaust duct before being discharged to the outside.
Alternatively, the high-temperature processed gas that has been deodorized and purified is directly circulated and convected into the furnace again to effectively use it as a heating source in the furnace (Special Publication No. 58-175785).
No. 59-12946).

However, in the past, platinum group catalysts such as highly active platinum (Pt), palladium (Pd), or a composite of these, such as platinum-palladium, were most commonly used as catalysts to form the catalyst layer. According to experiments conducted by the present inventors, this platinum group catalyst can be used to carry out the so-called dehydrogenation reaction, which removes hydrogen from organic compounds with hydroxyl groups, such as phenols and alcohols, which have a unique odor and are highly toxic. Promote
These phenols, alcohols, etc. can be effectively oxidized and decomposed into aldehydes (RCHO), but this aldehyde is further converted to carboxylic acid (RCOOH), and finally harmless and odorless carbon dioxide gas (CO ₂ ) and water are produced. It was found that the ability to decompose it into (H ₂ O) was inferior.

It was also found that when the concentration of oxo compounds with aldehyde groups in the furnace increases, a large amount of greasy substances are produced that cause yellowing and delamination of the paint film.

Furthermore, the greatest amount of harmful malodorous substances evaporate from the coating film of the object to be coated occurs from the time the object is brought into the furnace until it is heated to the specified baking temperature. It has been found.

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 substances such as paint resins, curing agents, and pigments, which cause the formation of greasy substances, will gradually increase, and the contamination concentration of harmful malodorous substances such as low-boiling substances and high-boiling substances will increase, especially in temperature rising zones. was confirmed to be significantly higher.

Therefore, if the exhaust gas in this temperature rising zone is passed through a catalyst layer made of a platinum group catalyst and discharged to the outside as in the past, the exhaust gas will contain a large amount of undecomposed aldehyde, causing air pollution. In addition, when the processing gas that has passed through the catalyst layer is circulated and convected into the furnace again and used directly as a heating source in the furnace, the aldehyde becomes the causative agent and causes yellowing of the paint film, etc. This has the disadvantage that large amounts of oily substances are produced. In addition, especially in the case of automobile bodies etc. on which water-soluble paint is electrodeposited, a large amount of water vapor is generated from the coating film when heating starts in the temperature rising zone, so as mentioned above, exhaust gas in the temperature rising zone is When circulating convection through the layer and back into the furnace, there is a problem in that humid heated air is supplied into the furnace, causing coating defects.

[Purpose of invention]

Therefore, in the present invention, only in the temperature rising zone,
The system in which the exhaust gas containing harmful malodorous substances generated in the temperature rising zone is passed through the catalyst layer, deodorized and purified, and then circulated back into the furnace is stopped, and the exhaust gas is passed through the catalyst layer and completely discharged to the outside. At the same time, the catalyst layer promotes the dehydrogenation reaction of harmful malodorous substances contained in large amounts in the exhaust gas in the heating zone, effectively oxidizing and decomposing them into aldehydes, and furthermore, it The purpose of the present invention is to solve the above-mentioned conventional problems at once by forming a novel catalyst layer that can be almost completely decomposed and rendered harmless and odorless through a combustion reaction.

[Structure of the idea]

In order to achieve this purpose, the present invention includes a heating zone that heats and raises the temperature of the workpiece carried into the furnace and transferred to a predetermined baking temperature, and a reaction hardening of the coating film of the workpiece. In a painting drying furnace having a curing zone, an exhaust duct is open-connected to the temperature raising zone, and exhaust gas containing harmful malodorous substances generated in the furnace is passed through a catalyst layer, deodorized and purified, and then discharged to the outside. At the same time, the catalyst layer is a combination of a platinum group catalyst that effectively promotes the dehydrogenation reaction and two active species of copper and cerium, thereby promoting a combustion reaction that decomposes the aldehyde produced by the dehydrogenation reaction. It is characterized by a structure in which it is combined with a katsuparcerium-based catalyst that can effectively promote the process.

[Effect of invention]

According to the present invention, exhaust gas containing a large amount of harmful and malodorous substances generated in the temperature rising zone is sent through the exhaust duct to the catalyst layer consisting of a combination of a platinum group catalyst and a Katsupah cerium catalyst, and through the catalyst layer. First, a dehydrogenation reaction that relies on a highly active platinum group catalyst deprives harmful malodorous substances of hydrogen and turns them into aldehydes, which are then converted into carboxylic acids through a combustion reaction that relies on a Katsupare cerium catalyst, and then harmless and odorless carbonic acid. It is effectively oxidized and decomposed into gas and water, resulting in clean air with extremely low aldehyde content, which is then discharged to the outside.

〔Example〕

Hereinafter, the present invention will be explained based on specific embodiments shown in the drawings.

FIG. 1 is a flow sheet diagram showing an example of a coating 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.
A cue that reacts and cures the coating film formed on the surface of the object 3 from the latter part of the temperature raising zone 4 to the outlet (not shown) at a predetermined baking temperature (usually 170 to 180°C). It has a ring zone 5.

Reference numeral 6 denotes an exhaust duct which is open-connected to the temperature rising zone 4 of the furnace body 1, and exhaust gas containing harmful malodorous substances generated in the temperature rising zone 4 is sucked by a suction fan 7 and distributed into the reactor 8. The treated gas is sent to a catalyst layer 9 provided therein, 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. A commonly used platinum group catalyst is provided. Note that 17 is a burner for heating the catalyst layer 15 to a predetermined reaction temperature, and 18 is the burner 1.
This is a blower that supplies combustion air to 7.

The above is an example of the construction of a coating drying oven 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 to be coated 3 such as an automobile body is carried in through the inlet 2, and first transferred through the temperature rising zone 4 and the object to be coated is heated. 3 is 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 phenols and phenols are extracted from the coating film. A large amount of harmful malodorous substances with hydroxyl groups such as alcohols are generated (see Figure 2).

This large amount of generated exhaust gas containing harmful malodorous substances is sucked into an exhaust duct provided with a suction fan 7 and sent to a catalyst layer 9 in a reactor 8.

Here, the catalyst layer 9 includes a platinum group catalyst that effectively promotes a dehydrogenation reaction that removes hydrogen from an organic compound having a hydroxyl group and converts it into an aldehyde, and a platinum group catalyst that effectively promotes a dehydrogenation reaction that converts an organic compound having a hydroxyl group into an aldehyde. Since it is combined with a Katsupar cerium-based catalyst that extremely effectively promotes the combustion reaction of oxidative decomposition into carbon dioxide gas and water, phenols and alcohol in the exhaust gas sucked from the temperature rising zone 4 through the exhaust duct 6 are removed. etc. are almost completely decomposed, and clean deodorized gas with an extremely small amount of aldehyde is discharged to the outside.

Therefore, not only inside the heating zone 4 but also inside the furnace body 1
Since the concentration of harmful malodorous substances throughout the furnace is significantly reduced compared to the conventional method, in the curing zone 5, the exhaust gas inside the furnace is transferred to the return duct 1 as before.
3 through the catalyst layer 15, and the catalyst layer 15
Even if a hot air circulation path N is formed in which the high-temperature processing gas that has been deodorized and purified is circulated and convected into the furnace through the supply duct 16, the amount of undecomposed aldehyde in the processing gas is extremely small compared to the conventional method. Since the amount of oily substances that cause yellowing and delamination of the coating film is significantly reduced, product quality is not impaired.

In addition, especially in the case of a drying oven that bake-dries a coated object on which a film of water-soluble paint has been formed, a large amount of water vapor is generated from the surface of the coated object 3 in the temperature rising zone 4. Since the water vapor is discharged to the outside through the exhaust duct 6, there is no fear that the water vapor generated in the furnace will cause paint film defects, as was the case in the past.

Furthermore, since the aldehyde concentration in the exhaust gas discharged to the outside through the exhaust duct 6 is extremely low, there is no risk of causing air pollution.

In addition, in the present invention, since the harmful malodorous substances generated in large quantities in the temperature rising zone 4 can be discharged to the outside through the exhaust duct 6, the catalyst layer 15 interposed in the hot air circulation path N can be replaced with the conventional one. It may be formed using only platinum group catalysts used in
If this structure is made of a combination of a platinum group catalyst and a Katsupar cerium catalyst, similar to the catalyst layer 9 installed in the exhaust duct 6, the amount of produced greasy substances can be further reduced. .

In addition, in the embodiment, a case has been described in which the exhaust gas in the temperature rising zone 4 is deodorized and purified by the catalyst layer 9 and then discharged to the outside as it is. Send it to the Erofinchi Yube of the container, and
The heat may be effectively radiated from the fins of the furnace, used as a heating source for the air in the furnace, and then discharged to the outside to effectively utilize the waste heat.

[Effect of idea]

As described above, according to the present invention, the exhaust gas containing extremely large amounts of harmful and malodorous substances generated in the heating zone is discharged to the outside through the exhaust duct, and the concentration of harmful and malodorous substances throughout the furnace is significantly reduced. This has the excellent effect of preventing yellowing and poor drying of the paint film, and significantly improving product quality compared to conventional methods.

In addition, especially when applied to a drying oven for final drying of electrodeposition coatings, a large amount of water vapor generated in the temperature rising zone is also discharged outside the oven, thereby improving the quality of the coating film.

Furthermore, the exhaust duct that discharges the exhaust gas containing a large amount of harmful and malodorous substances generated in the temperature rising zone is equipped with a catalyst layer consisting of a combination of a platinum group catalyst and a Katsupahcerium catalyst. In the catalyst layer, the harmful malodorous substances in the exhaust gas are first stripped of hydrogen through a dehydrogenation reaction dependent on a highly active platinum group catalyst and become aldehydes, which are then converted into aldehydes through a combustion reaction dependent on a Katsupare cerium catalyst. The carboxylic acid is finally effectively oxidized and decomposed into harmless and odorless carbon dioxide gas and water, creating clean air with extremely low aldehyde content before being discharged to the outside, so there are concerns about air pollution. It has various excellent effects such as:

[Brief explanation of the drawing]

FIG. 1 is a flow sheet diagram showing an example of a coating drying oven 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] For coating, it has a heating zone in which the object to be coated, which is carried into a furnace and is continuously transferred, is heated to a predetermined baking temperature, and a curing zone in which the coating film on the object to be coated is cured by reaction. In the drying furnace, an exhaust duct for passing exhaust gas containing harmful malodorous substances generated in the furnace through a catalyst layer, deodorizing and purifying it, and then discharging it to the outside is connected to the heating zone, and the catalyst layer is made of a platinum group metal. A coating drying oven characterized in that it is configured to combine a Katsupar cerium based catalyst and a Katsupar cerium based catalyst which is a composite of two types of active species, copper and cerium.