JPH0316189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrostatic coating method, and more particularly:
The present invention relates to an electrostatic coating method comprising spraying a coating material containing a prepolymer having free isocyanate groups onto a substrate using a high-speed rotating body to which a high voltage is applied to form a coating film.

PRIOR ART AND TECHNICAL PROBLEMS TO BE SOLVED Recently, a vehicle containing a prepolymer having free isocyanate groups is applied onto a substrate, and this vehicle is then treated with an agent consisting of ammonia or an amine in the vapor phase. A new coating method has been proposed, and the present applicant is also applying for a patent for this technique in Japanese Patent Application No. 180741/1983.

However, although this coating method is very superior in that it does not require virtually any thermal energy to cure the coating, it usually requires a coating formation chamber, A coating film curing room, a post-curing room, etc. are required, and the equipment itself becomes very large, resulting in a problem that the installation space becomes large and the equipment cost increases.

OBJECT OF THE INVENTION An object of the present invention is to provide an electrostatic coating method using a paint containing a prepolymer having free isocyanate groups, which can be carried out in a small installation space.

Structure of the Invention According to the present invention, a liquid paint is supplied in a thin film form along the inner peripheral surface of a high-speed rotating body to which a high voltage is applied,
In an electrostatic coating method comprising atomizing the paint from a circumferential edge of the high-speed rotating body and jetting shaping air for adjusting the atomization pattern from the outside of the high-speed rotating body, the liquid paint forming a coating film by using a coating material containing a prepolymer having free isocyanate groups as the shaping air, and using air containing ammonia or amine vapor to accelerate curing of the coating material as the shaping air; An electrostatic coating method is provided.

Preferred Embodiments of the Invention The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

With reference to FIG. 1 showing a side cross section and FIG. 2 showing a plan cross section of an apparatus and a simple wet coating booth suitable for carrying out the method of the present invention, this coating booth has a coating chamber 1 and a purification chamber 2. It consists of.

In the painting room 1, a specific paint, that is, a paint containing a prepolymer having free isocyanate groups, is applied to the article (substrate) 3 to be painted using a rotary atomization electrostatic painting system equipped with a shaping air jetting mechanism. Apply by spraying using machine 4. The substrate 3 is continuously carried into the coating room 1 while being suspended on, for example, a conveyor 5. After coating, the substrate 3 is blown with air by an airflow blowing mechanism 45 provided near the exit, and then carried outside.

The paint used in the method of the present invention is a paint containing a prepolymer having 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 those called isocyanate group-terminated prepolymers, which are reactive with isocyanate groups, such as polyester polyols, hydroxyl group-containing acrylic resins, hydroxyl group-containing vinyl resins, alkyd resins, polyamides, etc. The oligomer or polymer is reacted with a polyisocyanate, such as tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, diphenylmethane diisocyanate, and the isocyanate is bonded to the skeleton of the oligomer or polymer via a urethane bond, a urea bond, etc. things 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 It may be a mixture of multiple types of resins. In short, it should be understood that any paint can be used in the present invention as long as it contains a sufficient amount of free isocyanate groups to be cured with ammonia or amines or the like.

The concentration of free isocyanate groups is generally determined by the resin content.
A range of 10 to 500 mmol, especially 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-sag agents, rust inhibitors, 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.

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

The concentration of ammonia or amine contained in this shaping air varies depending on the paint used, but it is 50 to 50,000 ppm, especially
It is preferably in the range of 100 to 10,000 ppm.

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.

An important feature of the present invention is that the paint containing the prepolymer having free isocyanate groups is supplied in the form of a liquid film along the inner peripheral surface of the high-speed rotating body to which a high voltage is applied. Air containing ammonia or amine vapor for atomizing the paint from the circumferential edge and accelerating curing of the paint is sprayed from the outside of the high-speed rotating body as shaping air. The purpose is to form a coating film on a painted object.

In the present invention, the paint and shaping air are sprayed onto the substrate 3 using a rotary atomizing electrostatic coating machine 4.

This electrostatic coating machine 4 is shown in the third section showing its side sectional view.
Referring to FIG. 4, which shows a front view and a front view, the device is comprised of a housing 50 and a high-speed rotating body (cup) 51 that is rotatably mounted on the housing 50 at high speed.

That is, the air motor 52 is located inside the housing 50.
A high-speed rotating body 51 is fixed to the tip of a rotating shaft 53 of this air motor 52 by a fastening means such as a nut 54.

The housing 50 is also attached to an electrically insulating support rod 55.

Although not shown in the electrostatic coating machine 4, a high voltage from a predetermined high voltage generator is applied to a high-speed rotating body 51 via a cable (not shown).

Further, a paint supply pipe 30 is connected to the housing 50, and a predetermined paint supplied from the paint supply pipe 30 is supplied into the high speed rotating body 51 through a paint supply pipe 56.

That is, the paint supplied from the paint supply pipe 30 is
Inner peripheral surface 57 of high-speed rotating body 51 to which high voltage is applied
is supplied in a thin film along the high speed rotating body 5.
1 is atomized from the circumferential edge 58 and applied onto the substrate 3.

Furthermore, in this electrostatic atomizer 4, a large number of jet ports 59 for shaping air, that is, air for adjusting the atomization pattern, are arranged in an annular manner on the side of the housing 50 where the rotating body is attached. Predetermined air supplied from the air supply pipe 31 is passed through the annular air chamber 60 in the housing 50 from the jet port 59 toward the base 3 in a circumferential shape for adjusting the atomization pattern. It is ejected as air 61.

In the present invention, by using air containing ammonia or amine vapor as shaping air, the atomization pattern can be adjusted simultaneously.
This is to accelerate the curing of a paint film containing a prepolymer having free isocyanate groups formed on the substrate 3, and thereby is a special method for curing the paint film formed on the substrate 3. This eliminates the need for a curing chamber, prevents the equipment itself from becoming larger, and is advantageous in terms of installation space and equipment costs.

Returning to Figures 1 and 2 again, the electrostatic coating machine 4
The shaping air jetted from the compressed air supply source 32 is adjusted to a predetermined pressure and supplied through the regulator 33 and the shaping air supply pipe 31, but in the present invention, the shaping air is Since air containing ammonia or amine vapor is used, a mixing mechanism 34 is provided along the supply path to mix the ammonia or amine vapor into the air.

That is, ammonia or amine, which is pumped from an ammonia or amine storage tank 35, is supplied to the mixing mechanism 34 by spraying through a nozzle 36 and mixed with air. The air containing the ammonia or amine vapor thus formed is supplied to the electrostatic atomizer 4 through the shaping air supply pipe 31 via a filter 37 provided in the mixing mechanism 34 .

In this case, an ammonia or amine concentration detector 38 is installed in the middle of the shaping air supply pipe 31.
A valve 39 controls the amount of ammonia or amine supplied to the nozzle 36 in response to a signal from the detector 38, thereby controlling the concentration of ammonia or amine in the shaping air.

The paint containing the prepolymer having free isocyanate groups is also supplied to the electrostatic coating machine 4 via a compressed air supply 32 through a paint pumping tank 40 and a paint supply pipe 30 .

The supply of the paint and shaping air described above is controlled to be turned on and off as appropriate via automatic control valves 41 and 42, respectively.

Further, in a simple wet type painting booth in which painting work is performed, the purification chamber 2 is separated from the painting chamber 1 by a flow plate 6, and a liquid tank 7 is provided at the bottom of the cleaning chamber 2. Furthermore, a gutter 8 is formed in the upper part of the flow plate 6, and from this gutter 8, an excess paint mist collecting liquid (hereinafter simply referred to as the collecting liquid) is collected onto the flow plate 6. ) is supplied and the 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, and is collected by gas-liquid contact with the collection liquid that is atomized when passing through the lower opening 10. Collected in the liquid. liquid film 9
The collected liquid forming the
The water is then supplied to the gutter 8 again via the piping 12 and used for circulation.

Further, a collision plate 13 is provided in the purification chamber 2, and the collected liquid is separated from the airflow by collision here. An eliminator 1 is placed above the collision plate 13.
4, gas-liquid separation is also carried out here, and the purified air is discharged into the outside air by a fan 16 via an exhaust passage 15.

If necessary, a purification mechanism (not shown) made of activated carbon, a catalyst, etc., for purifying organic solvents, ammonia, amines, etc. contained in the exhaust gas from the exhaust passage 15 may be attached. Also good.

In the purification chamber 2, exhaust gas containing excess paint and ammonia or amine comes into contact with the collection liquid and is collected in the collection liquid. In this case, since ammonia or amines are usually easily water-soluble, when water is used as a collection liquid, ammonia or amines are easily collected and environmental pollution is effectively prevented. Furthermore, since ammonia or amine is collected along with the excess paint, the excess paint collected in the collection liquid rapidly hardens, causing the paint to lose its tackiness and the collected paint to be removed. It will be appreciated that a significant advantage is also achieved in that if the liquid settles to the bottom of the bath 7, its disposal becomes easier.

The substrate 3 on which a predetermined coating film has been formed is subjected to air blowing by an air blowing mechanism 45 to further accelerate the curing of the coating film.

This airflow blowing mechanism 45 is provided near the exit side of the coating chamber 1, and blowers 46 and 47 blow circulating airflows in opposite directions onto the substrate 3, thereby uniformly curing the coating film. It is becoming more and more common to do so. This airflow blowing mechanism 45 has the effect of preventing harmful ammonia or amine from being discharged outside the coating room 1, in addition to the function of accelerating the hardening of the coating film as described above. That is, the air flow formed by the mechanism 45 acts as an air curtain to block the ammonia or amine mist, and also blows off the ammonia or amine adhering to the substrate 3, thereby preventing it from leaking outside the coating room 1. The effect of preventing this is achieved.

Thus, according to the present invention, it is possible to form and cure a coating film without providing a special operation area such as a curing room, and coating can be carried out in a small installation space, which is extremely advantageous in terms of equipment costs. Become. Further, in this example, it is possible to easily prevent harmful ammonia or amine from being discharged outside the coating area, which is extremely desirable in terms of environmental conservation.

The method of the present invention is particularly advantageously applied when painting is carried out on a small scale.

The method of the present invention also has the advantage that it can be carried out using an existing paint booth.

Note that in the above-described embodiment of the present invention, the paint is supplied using the compressed supply source 32;
Of course, any other supply device known per se such as a gear pump or a plunger pump can be used to supply the shaping air, and the supply of shaping air is not limited to the embodiment shown in the attached drawings. Insofar as it is possible to prepare and supply air containing a given concentration of vapor,
Various means can be employed.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of an apparatus and a simple wet coating booth suitable for carrying out the method of the present invention;
2 is a plan sectional view of the painting booth shown in FIG. 1, FIG. 3 is a side sectional view of the rotary atomizing electrostatic atomizer used in the painting booth shown in FIG.
The front view of the electrostatic coating machine shown in FIG. 1 is a painting chamber, 2 is a purification chamber, 3 is a substrate, 4 is a rotary atomizing electrostatic coating machine, 30 is a paint supply pipe, 31 is a shaping air supply pipe, 32 is a compressed air supply source, and 34 is a mixing mechanism, 35 is an ammonia or amine storage tank, 40 is a paint pressure feeding tank, 51 is a high-speed rotating body, 57 is an inner peripheral surface, 58 is a circumferential edge,
59 is a shaping air outlet, and 61 is a shaping air outlet.

Claims (1)

[Claims] 1. Supplying a liquid paint in a thin film along the inner peripheral surface of a high-speed rotating body to which a high voltage is applied, and atomizing the paint from a circumferential edge of the high-speed rotating body; An electrostatic coating method comprising jetting shaping air for atomization pattern adjustment from the outside of the high-speed rotating body, wherein a paint containing a prepolymer having free isocyanate groups is used as the liquid paint; An electrostatic coating method characterized in that a coating film is formed using air containing ammonia or amine vapor for accelerating curing of the coating material as shaping air.