JPS6231988B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating film curing device, and more particularly, a coating film curing device for curing a coating film containing a prepolymer containing free isocyanate groups in an ammonia or amine atmosphere. Regarding.

Traditionally, the formation of coatings presents various problems in terms of thermal energy, pollution, and productivity. In the coating film forming method most commonly employed in industry, after a substrate article is coated, the coated article is transported into a baking oven and the coating film is baked at high temperature. This baking requires a large amount of thermal energy, and an expensive exhaust treatment system is required to remove harmful components such as solvents and paint tar generated during baking of the paint film from the exhaust gas. In addition, in the case of painting woodwork, etc., where the paint film cannot be baked at high temperatures, the paint film must be cured by air drying, which requires an extremely long time to harden, and during which time the wet paint cannot be used. Strict management is required to prevent dust from adhering to the membrane.

In recent years, a method for drying a coating film that does not require heat curing has been proposed, and Japanese Patent Publication No. 13038/1983 describes a method in which a vehicle containing a prepolymer containing free isocyanate groups is applied onto a substrate. A method for forming a dry coating is described, which consists in subsequently treating this vehicle with an agent consisting of ammonia or an amine in the vapor phase.

The present invention relates to an apparatus for carrying out the above-mentioned method, and particularly to an apparatus for efficiently carrying out the baking or curing of a coating film by the above-mentioned method continuously and in a substantially closed system.

That is, the purpose of the present invention is to eliminate the need for baking operations at high temperatures, and to cure the coating film in an extremely short time.As a result, the equipment is small and has high productivity, and the maintenance of the equipment is easy. The purpose of the present invention is to provide a coating film curing device.

Another object of the invention is to cure coatings containing free isocyanate groups with ammonia or amines.
An object of the present invention is to provide an apparatus for carrying out continuous processing in a closed system.

Still another object of the present invention is to provide an apparatus that can reduce costs by separating and recovering ammonia or amine contained in exhaust gas and reusing it.

Still another object of the present invention is to cure the paint film in an extremely short time even on articles for which it has been difficult to bake the paint film by heat, such as wood products, hydraulic equipment, and articles with extremely large heat capacity. Our goal is to provide a device that makes it possible.

According to the present invention, there is provided an apparatus for curing a coating film containing a prepolymer having free isocyanate groups by contacting the coating film with ammonia or amine in the gaseous phase, comprising: a curing chamber; A conveyance system for carrying in and transporting the coated article, a steam generation device for generating an air flow containing ammonia or amine vapor, and a steam generation device for supplying the air flow from the steam generation device to a curing chamber and for transporting the coated article. a circulation system that circulates the gas after contact to the steam generator; a mechanism that air-seals the inlet and outlet of the curing chamber to prevent leakage of ammonia or amine vapor; and the circulation system and/or air seal mechanism. There is provided a coating film curing device characterized by comprising a device for separating and recovering ammonia or amine from exhaust gas from and resupplying the ammonia or amine to the circulation system.

FIG. 1 is a plan layout diagram showing the coating film curing apparatus of the present invention together with an attached coating chamber and a post-curing chamber.

In FIG. 1, the coating film curing apparatus of the present invention generally includes a curing chamber 1, a conveyance system 2, a steam generator 3, a curing airflow circulation system 4, and a curing chamber 1.
It consists of an air seal mechanism 7 provided at the carry-in port 5 and the carry-out port 6.

In the specific example shown in FIG. 1, a coating chamber 8 is disposed upstream of the curing chamber 1, and a post-curing chamber 9 is disposed downstream of the curing chamber 1, and the conveyance system 2 is provided to pass through these. It is being

The painting room 8 contains articles (substrates) to be painted.
10 is for applying a specific paint, that is, a paint containing a prepolymer containing free isocyanate groups, and, like a normal simple painting booth, there is an entrance 11 into which the substrate 10 is brought in, and an entrance 11 through which the coated substrate is taken out. An application mechanism 13 such as a spray gun for applying the paint onto the substrate is provided on one side of the movement path of the substrate 10.
Further, on the other side, an exhaust suction duct 15 is provided via a paint mist collection mechanism 14 such as a filter, if necessary.

The paint used in the apparatus of the present invention is a paint containing a prepolymer containing free isocyanate groups, and is cured by contact with gas phase ammonia or amine, which will be described in detail later. Suitable examples of such paints are called isocyanate group-terminated prepolymers, such as polyester polyols, polyether polyols, hydroxyl group-containing acrylic resins, hydroxyl group-containing vinyl resins, alkyd resins,
An oligomer or polymer having reactivity with isocyanate groups such as polyamide is reacted with a polyisocyanate such as tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, diphenylmethane diisocyanate, and the isocyanate is reacted with urethane bonds, urea bonds, etc. Those bonded to the skeleton of the oligomer or polymer via a bonding agent are used. Of course, the above-mentioned oligomer or polymer reactive with isocyanate groups and the polyisocyanate may be reacted in advance or partially reacted in the form of a mixture, and this coating material may be used in combination with multiple polyisocyanates. It may be a mixture of different resins. In summary, it should be understood that any coating material may be used for purposes of the present invention as long as it contains a sufficient amount of free isocyanate groups to be cured with gas phase ammonia or amine.

The concentration of free isocyanate groups is generally determined by the resin content.
A range of 10 to 500 mmol, particularly 30 to 300 mmol per 100 g is preferred.

This paint can be used as a solvent-free paint if it is a liquid with a viscosity suitable for painting, or it can be used as a solution-type paint in which the prepolymer is diluted with a solvent. Of course, this paint contains components known per se, such as pigments, plasticizers,
It is blended with surfactants, anti-sag agents, rust preventive agents, etc. in known proportions. Suitable coatings have a non-volatile concentration of 20 to 100% by weight and a kinematic viscosity (foed cup #4) of 15 to 150 seconds.

Substrates 10 to be coated include, in addition to substrates formed from ordinary steel plates or surface-treated steel plates, manufactured products whose paint film is difficult to bake due to heat, textile products, plastic products, hydraulic equipment products, and castings with a large heat capacity. Particularly in the case of the latter substrates, the significant advantages of the present invention are achieved in that no thermal baking is necessary and the coating film hardens rapidly.

As the coating mechanism 13, a spray coating mechanism such as an air spray gun, an airless spray gun, a rotary atomization type coating device, etc. is suitably used, including non-electrostatic type and electrostatic type. Of course, other coating methods such as dip coating, roller coating, flow coating, etc. may also be employed depending on the type of substrate.

The curing chamber 1 is for bringing the coated article 10' from the coating chamber 8 into contact with ammonia or amine in the gaseous phase to carry out a curing reaction of the formed coating film,
In order to enable continuous processing, an inlet 5 for carrying the coated article 10' into the room and an outlet 6 for carrying out the article after contact with ammonia or amine are provided.

The coating film curing apparatus of the present invention includes a coating chamber 1, a curing ammonia or amine steam generator 3, and a coating chamber 1, a curing ammonia or amine steam generator 3, in order to effectively perform the coating film curing process continuously and within a short time. A curing air flow circulation system 4 is provided in connection that will be explained in more detail below.

First, the curing chamber 1 has a double wall structure partitioned by a porous partition wall 16 made of punching metal or metal lath, etc., in order to uniformly and uniformly supply a curing gas (airflow) containing ammonia or amine. A curing gas is blown through the porous partition wall 16 from a gas passage 17 located outside the partition wall 16 to the painted article 10' which is located within the partition wall 16 and moves while rotating. wear.

This gas passage 17 is connected to the curing steam generator 3 via a supply duct 18. This curing steam generator is for sending ammonia or amines in a gas phase to the curing chamber. Curing vapor is generated by spraying ammonia or amine supplied from the curing agent supply device 50.

The curing chamber 1 is provided with an air exhaust duct 22 through an air exhaust port 21, and is connected to the suction side of a fan 19 via a supercleaning mechanism 23 such as a filter if necessary.

Thus, the curing steam circulation system 4 in the coating film curing apparatus of the present invention includes the air exhaust port 21 and the air exhaust duct 2.
2, fan 19, supply duct 18, gas passage 17
and a porous partition wall 16. This circulation system 4 can be provided with a curing gas heating mechanism 24 if necessary, and the temperature of the curing gas can be maintained at room temperature or about 30°C during the winter when the temperature drops. It's becoming like that.

In addition, in the curing steam supply port or in the curing chamber,
An ammonia or amine concentration detection mechanism 25 is provided, and the detection signal controls the valve 26 of the spray device 20 so that the ammonia or amine concentration in the curing chamber can always be set to a predetermined value.

In addition to primary, secondary, or tertiary monoamines, the amines used in the present invention may be polyvalent amines, such as methylamine, ethylamine, propylamine, diethylamine, triethylamine, piperidine, morpholine, Examples include one or a combination of two or more of piperazine, ethanolamine, diethanolamine, triethanolamine, cyclohexylamine, ethylenediamine, tetramethylethylenediamine, ethylenetriamine, and the like.

Ammonia or amine can be present in the form of undiluted vapor in the curing air stream, but from the viewpoint of ease of operation and economical efficiency, ammonia or amine should be present at a concentration of 50 to 50,000 ppm, especially 100 to 50,000 ppm.
It is desirable to include it in the air stream at a concentration of 10,000 ppm.

In the present invention, a sealing mechanism generally indicated by 7 is provided at the inlet 5 and the outlet 6 of the curing chamber 1 in order to prevent leakage of ammonia or amine vapor. In FIG. 1, for this purpose, a partition plate or a flap 27 is provided at the loading inlet 5 and the unloading outlet 6 to allow the passage of articles, and an intake duct having a circumferential intake port 29a connected to the intake duct 28 is provided. 29 is arranged to suck air near the inlet and outlet to completely block curing vapor from leaking out of the curing chamber.

Further, in the present invention, the exhaust gas discharged from the intake duct 28 and the exhaust gas from the exhaust duct 30 connected to the circulation system 4 described above are introduced into the separation and recovery device 31 to recover ammonia or amine, which is then transferred to the curing agent supply mechanism. 50 and reused.

The separation and recovery device 31 includes an adsorption device 51 that performs adsorption treatment using an adsorbent such as activated carbon, a desorption device 52 that performs desorption treatment using heat, acid, alkali, etc., and a purification device 53 that performs purification by distillation, extraction, etc. It is completed.

Thus, the curing apparatus of the present invention has the significant advantage that costs can be reduced by reusing expensive ammonia or amines.

The time that a coated article is in contact with ammonia or amine varies depending on the type and thickness of the paint, the concentration in the curing gas, and the temperature, but generally speaking, it is about 10 minutes.
A very short period of time, such as 20 to 300 seconds, may be sufficient.

According to the present invention, with the above-described configuration, it is possible to continuously perform the curing treatment of a coating film with ammonia or amine in a closed system without leaking harmful ammonia or amine vapor to the outside. Moreover, by supplying ammonia or amine vapor as an airflow into a substantially sealed curing chamber and circulating this airflow through a steam generator, the contact between the coating film and the vapor is uniform, uniform, and intimate. By carrying out this process, the curing reaction of the coating film is carried out effectively and within a short period of time. Also, by circulating the steam in a closed system, an economical curing process is possible while preventing loss of ammonia or amine.

In the specific example shown in FIG. 1, in the curing chamber 1,
The coated article 10'', which has been in contact with the ammonia or amine-containing curing gas, is brought into contact with an air stream in the post-curing chamber 9.

In other words, a paint film that has just come into contact with ammonia or amines is likely to be easily scratched if you rub it with your fingernail, even if the hardening process is progressing. , requires contact with air to continue curing the coating as measured by pencil hardness.

The post-curing chamber 9 has a tunnel-like shape with an inlet 32 and an outlet 33 for the coated article 10'', and inside the post-curing chamber 9, along the movement path of the coated article,
A porous partition wall 34 is provided. There is an air passage 35 through this partition wall 34, and the air introduced into the passage 35 is blown onto the coated article 10'' through the partition wall 34, thereby proceeding with the post-curing of the coating film.Air passage 35 is connected to a blower fan 37 via a supply duct 36, while the airflow after contacting the coating in the post-curing chamber is directed to an exhaust duct 38.
From there, it is circulated to the suction side of the fan 37 via the supercleaning mechanism 39 and the heating mechanism 40.

Room temperature is sufficient for post-curing air, but in order to accelerate post-curing, it is advantageous to heat the air to a temperature of about 50°C.

In this embodiment, the transport mechanism 2 is connected via a series of wheels or sprockets 41 to a painting chamber 8,
It is arranged so as to pass through the curing chamber 1 and the post-curing chamber 9 in sequence, and is moved continuously or intermittently by a drive mechanism 42. In this embodiment, the conveying mechanism 2 is an endless overhead conveyor, the articles 10 to be coated are loaded onto the conveyor at a loading position 43, and the coated products 10a are loaded onto the conveyor at an unloading position 44.
removed from the conveyor.

In the present invention, if it is acceptable to take a certain amount of time to post-cure the coating film, a method may be adopted in which the post-curing chamber 9 is omitted and the semi-cured coated article is left in the air. Further, it is also possible to separate the coating chamber 8 and provide a conveyance system only in the coating film curing device.

According to the device of the invention as described above, the following significant advantages are additionally achieved. That is, although the furnace for drying and baking the paint film in the painting equipment consumes a huge amount of thermal energy, according to the present invention, baking at a high temperature is not necessary, resulting in significant energy savings. . In addition, it is possible to cure coatings in a short time even for items for which high-temperature baking is difficult, and because the curing time is short, equipment can be small and production capacity can be significantly improved. .
Furthermore, since it is operated at or near room temperature, there is no danger of fire, and there is no need to clean tar as in conventional baking furnaces, making maintenance easy.

Furthermore, costs can be reduced by separating and recovering expensive chemicals such as ammonia or amines from exhaust gas and reusing them.

[Brief explanation of the drawing]

FIG. 1 is a plan layout showing the coating film curing apparatus of the present invention together with an attached painting room and a post-curing room, in which 1 is a curing room, 2 is a conveyance system, 3 is a steam generator,
4 is a curing airflow circulation system, 7 is a sealing mechanism, 8 is a coating chamber, 9 is a post-curing chamber, 10, 10', 10'' is a coated article (substrate), 10a is a coated product, 13 is a coating mechanism, 16 is a porous partition wall, 17 is a gas passage, 1
8 is a supply duct, 19 is a fan, 20 is a spray device, 21 is an exhaust port, 22 is an exhaust duct, 28 is an intake duct, 29 is an intake duct having a circumferential intake port 29a, and 31 is a separation and recovery device. .

Claims (1)

[Scope of Claims] 1. An apparatus for curing a coating film containing a prepolymer having free isocyanate groups by contacting the coating film with gaseous ammonia or amine, comprising: a curing chamber; and the curing chamber. a conveyance system for carrying in and carrying out coated articles, a steam generation device for generating an air flow containing ammonia or amine vapor, and a system for supplying the air flow from the steam generation device to a curing chamber and for carrying out coated articles. a circulation system that circulates the gas after contact with the steam generator, a mechanism that air-seals the inlet and outlet of the curing chamber to prevent leakage of ammonia or amine vapor, and the circulation system and/or air seal. A coating film curing device comprising a device for separating and recovering ammonia or amine from exhaust gas from the mechanism and resupplying the same to the circulation system.