JPS6225425B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating method, and more specifically, to a coating method using a coating material containing a prepolymer having free isocyanate groups, while effectively separating and removing excess coating material from the coating exhaust gas. The present invention relates to a coating method that can perform coating.

Generally, in painting, the paint is sprayed and applied onto the substrate in a painting chamber, the exhaust from the painting chamber containing excess paint mist is brought into contact with a water film, and the excess paint mist is separated and collected in the water phase. Purifying paint exhaust. However, paint mist itself is often hydrophobic, making it difficult to collect in the aqueous phase, and it is also highly sticky, making it extremely difficult and troublesome to dispose of it even after it has been collected in the aqueous phase. be.

On the other hand, in recent years, new methods of drying paint films that do not require heat curing have been proposed, and
No. 53-13038 describes a drying process consisting of applying a vehicle containing a prepolymer containing free isocyanate groups onto a substrate and then treating this vehicle with an agent consisting of ammonia or an amine in the vapor phase. A method of forming a coating film is described.

Although such a method is excellent in that it requires virtually no thermal energy for curing the paint film, the above-mentioned problems regarding purification of paint exhaust gas still remain.

An object of the present invention is to provide a coating method using a coating material containing a prepolymer having free isocyanate groups, in which excess coating mist can be effectively and reliably separated and removed.

According to the present invention, a coating process in which a paint containing a prepolymer having free isocyanate groups is applied to a substrate, and a coating exhaust gas containing excess paint generated in the coating process is brought into contact with a curing accelerator solution. There is provided a coating method characterized by comprising a purification step of separating and removing components from the exhaust gas.

The method of the present invention will be explained in detail below based on specific examples shown in the accompanying drawings.

Referring to FIG. 1, which shows a simple wet-type coating booth for suitably carrying out the method of the present invention, the coating booth consists of a coating chamber 1 and a purification chamber 2.

In the painting room 1, a specific paint, ie, a paint containing a prepolymer containing free isocyanate groups, is sprayed onto an article (substrate) 3 to be painted using a paint gun 4. The substrate 3 is continuously carried into the coating chamber 1 while being suspended from a conveyor 5, for example, and after being coated is transferred to the next curing process (not shown).

The paint used in the method of the present invention is a paint containing a prepolymer containing free isocyanate groups, and is cured by contact with ammonia, amine, etc., which will be described in detail later. Suitable examples of such coatings are so-called isocyanate-terminated prepolymers, such as polyester polyols,
React oligomers or polymers that are reactive with isocyanate groups, such as hydroxyl group-containing acrylic resins, hydroxyl group-containing vinyl resins, alkyd resins, and polyamides, with polyisocyanates, such as tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, and diphenylmethane diisocyanate. and the isocyanate via a urethane bond, a urea bond, etc.
Those bonded to the skeleton of the oligomer or polymer are used. Of course, oligomers or polymers reactive with the above-mentioned isocyanate groups,
The polyisocyanate may be reacted in advance or may be reacted in parts in the form of a mixture, and the coating material may be a mixture of multiple types of resins. In short, in the present invention,
It should be understood that any coating may be used as long as it contains sufficient free isocyanate groups to be cured with ammonia or amines and the like.

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,
Surfactants, anti-sagging agents, rust preventive agents, etc. are blended in known mixing ratios. 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 to be coated include substrates made of ordinary steel plates or surface-treated steel plates, as well as wood products, textile products, plastic products, hydraulic equipment products, cast products with large heat capacity, etc. that are difficult to bake with heat. The latter type of substrate is particularly advantageous in that thermal baking is not necessary and the coating film is rapidly cured.

The purification chamber 2 is separated from the coating chamber 1 by a flow plate 6, and a liquid tank 7 is provided at the bottom thereof. Further, a gutter 8 is formed on the upper part of the flow plate 6, and the flow plate 6 is connected to the flow plate 6 from this gutter 8.
Excess paint mist collection liquid (hereinafter simply referred to as collection liquid) is supplied onto the top, and a liquid film 9 is formed.

That is, the excess paint mist is introduced into the purification chamber 2 through the lower opening 10 while coming into contact with the liquid film 9. The collected liquid forming the liquid film 9 is stored in a liquid tank 7 and pumped to the pump 1.
1 and piping 12 to the gutter 8 for circulation.

Further, a spray nozzle 13 is provided in the purification chamber 2, through which a portion of the collection liquid is sprayed, and the surplus paint mist and the collection liquid are brought into contact here as well. An eliminator 14 is provided above the nozzle 13, where gas-liquid separation is performed, and purified air is discharged into the outside air via an exhaust passage 15 by a fan 15'.

An important feature of the present invention is that a paint containing a prepolymer having free isocyanate groups is used as the paint, a curing accelerator solution is used as the collection liquid, and the collection liquid is separated from the exhaust gas containing excess paint mist. The purpose is to bring the liquid into contact. That is, by bringing the excess paint mist into gas-liquid contact with the curing accelerator solution, the curing of the excess paint proceeds rapidly, and as a result, the adhesiveness of the paint is lost, and the collected paint is transferred to the liquid tank 7. A significant advantage is achieved in that it is easier to dispose of it if it settles to the bottom. Furthermore,
Since the paint itself is easily compatible with the curing accelerator solution, its collection is carried out effectively and quickly. ) method can be carried out even more effectively.

The curing accelerator used in the present invention varies depending on the type of paint used, but in general, ammonia, amines, alcohols, and phenols can be used, and from the viewpoint that it can be used in the form of an aqueous solution, ammonia, Amines are preferably used.

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

Further, the concentration of the curing accelerator in the collecting liquid used is sufficient to be on the order of several percent at most, and it is most suitable for practical use to use it in the form of an aqueous solution. This concentration control can be achieved by, for example, installing a PH meter 16 in the liquid tank 7 and replenishing the hardening accelerator solution from the pipe 17 as appropriate in response to pH changes.

As described above, according to the coating method of the present invention, it is possible to effectively and easily separate and remove surplus paint mist, but in the present invention, it is not necessary to provide the coating chamber 1 and the purification chamber 2 adjacent to each other. Instead, they can be provided separately depending on the space and the like. In this case, exhaust air from the painting room may be introduced into a purification room separated by a duct or the like.

In addition, in the embodiment shown in the attached drawings, the contact between the surplus paint mist and the collection liquid is controlled through the liquid film 9 and the nozzle 13.
However, the method is not limited to this method, and a bench-type painting booth such as that described in Japanese Patent Publication No. 55-6427,
Liquid contact type as described in Publication No. 54-38040, other Japanese Patent Application Laid-open No. 88670/1983, Japanese Utility Model Publication No. 1987-
It can also be applied to any type of painting booth as described in Publication No. 84554 and the like.

Further, in the embodiment shown in FIG. 1, it is also possible to provide a recovery mechanism for a curing accelerator such as an amine in the exhaust passage 15 and reuse the recovered amine or the like as a collection liquid.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view schematically showing a simple wet-type coating booth in which the method of the present invention can be suitably carried out. 1 is a painting room, 2 is a purification room, 3 is a base, 4 is a paint gun, 6 is a flow plate, 7 is a liquid tank, 8 is a gutter,
9 is a liquid film, 13 is a spray nozzle, 14 is an eliminator, and 16 is a PH meter.

Claims (1)

[Scope of Claims] 1. A coating process in which a paint containing a prepolymer having free isocyanate groups is applied to a substrate, and a coating exhaust gas containing excess paint generated in the coating process is brought into contact with a curing accelerator solution to remove the excess paint. A painting method comprising a purification step of separating and removing paint from the exhaust gas. 2. The coating method according to claim 1, wherein the curing accelerator solution is an ammonia or amine aqueous solution.