JPS61291069A - Electrostatic coating method - Google Patents

Abstract

PURPOSE:To dispense with equipment such as a film curing chamber, in a coating method using a paint containing a prepolymer having a free isocyanate group, by using air containing a specific curing promoter as shaving air. CONSTITUTION:A painting booth is equipped with a painting chamber and a purifying chamber and a paint containing a prepolymer having a free isocyanate group is sprayed and applied to an article 3 to be painted by a rotary atomizing type electrostatic applicator 4 equipped with a shaving air jet mechanism. At this time, if a paint film is formed to the article 3 while air containing ammonia or amine vapor for promoting the curing of the paint is injected from the outside of a high speed rotor as the shaving air 61, a curing chamber is dispensed with and painting is performed in a small installation space.

Description

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

Prior Art and Technical Problems to be Solved In recent years, Brevo 1 having a free incyanate group has been developed.
A new coating method has been proposed in which a vehicle containing 1 mer is applied onto a substrate and this vehicle is then treated with an agent consisting of ammonia or amine in the vapor phase, and the present applicant has also filed a patent application. Patent applications for this technology are currently pending, such as No. 58-180741.

However, although this method of coating is very superior in that it requires virtually no thermal energy to cure the coating, it usually requires A forming room, a coating film curing room, a post-curing room, etc. are required, and the equipment itself becomes very bulky, resulting in a problem that the installation space becomes large and the equipment cost increases.

The object of the invention, that is, the object of the present invention, is to provide a coating method using a coating material containing a prepolymer having free incyanate groups,
To provide an electrostatic coating method that can be carried out in a small IK space.

Structure of the Invention According to the present invention, a liquid paint is supplied in a thin film along the inner peripheral surface of a high-speed rotating body to which a high voltage is applied.1-1 The paint is atomized from a circumferential edge of the high-speed rotating body. In the electrostatic coating method, which comprises spraying shaving air for adjusting the atomization pattern from the outside of the high-speed rotating body, the liquid paint is a paint containing a prepolymer having free isocyanate groups, and There is provided an electrostatic coating method characterized in that a coating film is formed using air containing vapor of ammonia or amine for accelerating curing of the coating material as the shaving air.

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

Refer to FIG. 1 showing a side cross-section of an apparatus and a simple wet-type coating booth suitable for carrying out the method of the present invention, and FIG. 2 showing a plan cross-section (7). It consists of a purification chamber 2.

In the painting room 1, a specific paint, that is, a paint containing a prepolymer having free incyanate groups, is applied to the article (substrate) B to be painted using a rotary atomizing electrostatic paint machine equipped with a shaving air jetting mechanism. Apply by spraying according to step 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 so-called incyanate group-terminated prepolymers, which are reactive with incyanate groups such as polyester polyols, hydroxyl group-containing acrylic resins, hydroxyl group-containing vinyl resins, alkyd resins, polyamides, etc. An oligomer or polymer having the following is reacted with a polyisocyanate, for example, 1) diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, or diphenylmethane diisocyanate, and the incyanate is combined with a urethane bond,
Those bonded to the skeleton of the oligomer or polymer via E7 such as a urea bond are used. Of course, the polyisocyanate may be reacted in advance with the above-mentioned oligomer or monomer reactive with isocyanate groups, or it may be partially reacted in the form of a mixture. Also, this paint may be a mixture of multiple types of resins. In summary, it should be understood that any paint can be used in the present invention as long as it contains a sufficient amount of free incyanate groups to be cured with ammonia or amines or the like.

The concentration of free incyanate groups is generally 1002
It is preferably in the range of 10 to 500 mmol, particularly 30 to 300 mmol.

If this paint is a liquid with a viscosity suitable for painting,
It can be used as a solvent-free paint or as a solution-based paint by diluting the prepolymer somewhat with a solvent. Of course, this paint contains known paint ingredients,
For example, pigments, plasticizers, surfactants, anti-sagging agents, rust preventive agents, etc. are blended in known mixing ratios. Suitable paints are those with non-volatile concentrations in the range of 20 to 100 parts by weight and kinematic viscosity (Ford Cup #4) in the range of 15 to 150 seconds.

Suitable amines for use in the present invention include -class, secondary, or tertiary monoamines, as well as polyvalent amines, such as methylamine, ethylamine, propylamine, diethylamine, etc. , triethylamine, piperidine, morpholine, piperazine, ethanolamine, jetanolamine, triethanolamine, dimethylethanolamine, cyclohexylamine, ethylenediamine, tetramethylethylenediamine,
Examples include ethylenetriamine, etc., or a combination of two or more thereof.

The concentration of ammonia or amine contained in this shaving air varies depending on the paint used, but it is 50 to 50.0 [30P7) m.

In particular, it is preferable that the content be in the range of 1 [111 to 1 [], 000 ppm.

Substrates to be painted (7) In addition to substrates made of ordinary steel plates or surface-treated steel plates, there are also wood products, textile products, plastic products, hydraulic equipment products, and products with large heat capacity that are difficult to bake away. For example, cast products, etc., especially in the case of the latter substrate, there is no need for baking by heat,
(No. 7 is also very advantageous in that the coating film cannot be cured quickly.

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 a high-speed rotating body to which a high voltage is applied]7
, atomizing the paint from the circumferential edge of the high-speed rotating body;
Further, air containing ammonia or amine vapor for accelerating curing of the paint is blown out from the outside of the high-speed rotating body as waping air to form a paint film on the object to be coated.

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

This electrostatic coating machine 4 has a housing 50 and a high-speed rotating body ( That is, an air motor 52 is housed in a housing 50, and a high-speed rotating body 51 is fixed to the tip of a rotating shaft 53 of the air motor 52 by a fastening means such as a nut 54. ing.

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

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

A paint supply pipe 30 is connected to the broken housing 50, and a predetermined paint is supplied from this paint supply pipe 60.
The paint is supplied into the high-speed rotating body 51 through the paint supply vibe 56.

That is, the paint supplied from the paint supply pipe 60 is supplied in the form of a thin film along the inner circumferential surface 57 of the high-speed rotating body 51 to which a high voltage is applied, and further along the circumferential edge 5B of the high-speed rotating body 51. The liquid is atomized and applied onto the substrate 6.

Furthermore, in this electrostatic atomizer 4, a large number of jet ports 59 for shaving air, that is, air for adjusting the atomization pattern, are arranged in an annular manner on the side of the nozzing 50 where the rotating body is attached. The predetermined air supplied from the pipe 31 is directed from the jet port 59 through the annular air channel (-60) in the housing 50 to the shaving air 61 for adjusting the atomization pattern in a circumferential direction toward the base 6. 1- It is squirted.

In the present invention, by using air containing ammonia or amine vapor in the shaving air, the atomization pattern is simultaneously adjusted and the paint containing a prepolymer having free incyanate groups is formed on the substrate 3. This eliminates the need for a special curing chamber for curing the coating film formed on the substrate 6, and eliminates the need to increase the size of the equipment itself. Space advantageous! F is also advantageous in terms of equipment costs.

Returning again to FIGS. 1 and 2, the shaving air sprayed from the electrostatic sprayer 4 is regulated to a predetermined pressure from the compressed air supply source 62 via the regulator 66 and the shaving air supply pipe 61. However, in the present invention, since air containing ammonia or amine vapor is used as shaving air, a mixing mechanism 34 is provided in the middle of this supply path to mix ammonia or amine vapor into the air. It is being

That is, the mixing mechanism 34 has ammonia or amine pumped from the ammonia or amine storage tank 35.
A spray is supplied through a nozzle 66 and mixed with air.

The air containing the ammonia or amine vapor formed by smelting is supplied to the electrostatic atomizer 4 through a shaving air supply pipe 61 via a filter 67 provided within the mixing mechanism 64 .

In this case, Kd in the middle of the shaving air supply pipe 31,
An ammonia or amine art detector 68 is provided, and a pulp 69 controls the amount of ammonia or amine supplied to the nozzle 66 in response to a signal from the detector 38, thereby controlling the amount of ammonia or amine in the shaving air. Concentration is controlled.

Further, the paint containing the prepolymer having free incyanate groups is supplied to the electrostatic coating machine 4 from a compressed air supply source 3.
The paint pressure feeding tank 40 and the paint supply pipe 60 are all passed through E7 through E7.

The above-mentioned paint and shaving air are supplied through automatic control valves 41 and 42 from 1 to 0 as appropriate.
-OFF Controlled.

In a simple wet-type painting booth where 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. In addition, a gutter 8 is formed on the upper part of the flow plate 6, and from this gutter 8, excess paint mist collecting liquid (hereinafter referred to as the collecting liquid) is collected onto the flow plate 6. Normally, water is used. , oil may be used), and a liquid film 9 is formed.

In other words, the excess paint mist comes into contact with the liquid film 9 (which is introduced into the purification chamber 2 one by one through the lower opening 10 and is atomized as it passes through the lower opening 10, and is brought into contact with the collected liquid).
Collected into the collection liquid. The collected liquid forming the liquid film 9 is stored in the liquid tank 7 and sent to the gutter 8 again via the pump 11 and piping 12.
It is supplied to the government and allocated for cyclical use.

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 14 is provided above the collision plate 13,
Gas-liquid separation is also carried out here, and the purified air is discharged into the outside air by the fan 16 via the exhaust passage 15 17 .

In addition, if necessary, a purification mechanism (not shown) consisting of activated carbon, catalyst, etc., for purifying organic solvents, ammonia, amines, etc. contained in the exhaust gas from the exhaust passage 15, may be installed. -But it's okay.

In the purification chamber 2, excess paint and exhaust gas containing ammonia or amines are collected in the collection liquid at contact 1 with 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 transferred to an airflow spraying mechanism 4
5 to further accelerate the curing of the coating film.

This airflow blowing mechanism 45 is installed near the outlet side of the coating chamber 1, and blowers 46 and 47 blow circulating airflows in opposite directions onto the substrate 3, so that the coating film is evenly cured. It is said that it will be carried out in In addition to the function of accelerating the hardening of the paint film as described above, the airflow blowing mechanism 45 also has the effect of preventing harmful ammonia or chlorine from being discharged outside the painting chamber 1. That is, the air flow formed by the mechanism 45 acts as an air curtain, blocks the ammonia or amine mist, and blows off the ammonia or amine attached to the substrate 6 to the outside of the coating room 1. The effect of preventing them from leaking is achieved.

Thus, according to the present invention, it is possible to form and cure a coating film without providing a special operating room such as a curing room, and it is possible to perform coating in a small installation space, which is extremely advantageous in terms of equipment cost. In addition, in this example, harmful ammonia or amines can be easily discharged outside the painting area, which can be said to be extremely desirable in terms of environmental protection.

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

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

In the above-described embodiment of the present invention, the paint is supplied using the compressed supply source 62, but of course, any other supply device known per se such as a gear pump or a plunger pump may also be used. The supply of fresh shaving air is also shown in the accompanying drawings.1. The present invention is not limited to the embodiment described above, and various means can be adopted as long as it is possible to supply air containing ammonia or amine vapor at a predetermined concentration for one month.

[Brief explanation of the drawing]

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; FIG. 2 is a sectional plan view of the coating booth of FIG. 1; and FIG. , a side sectional view of the rotary atomizing electrostatic atomizer used in the painting booth of FIG. 1, FIG. 4, 11, and a front view of the electrostatic atomizer of FIG. 3. 1 painting room, 2 purification chamber, 3 base, 4 rotary atomizing electrostatic coating machine, 60 paint supply pipes, 61 shaving air supply pipe, 32 compressed air supply source, 34 mixing mechanism, 3
5 ammonia or amine storage tank, 40 paint pressure feeding tank, 51 high speed rotating body, 57 inner peripheral surface, 58 circumferential edge, 59 shaving air outlet, 61 shaving air.

Claims (1)

[Claims] (1) Supplying liquid paint in a thin film along the inner peripheral surface of a high-speed rotating body to which a high voltage is applied, atomizing the paint from the circumferential edge of the high-speed rotating body, and An electrostatic coating method comprising ejecting shaving air for adjusting the atomization pattern from the outside of the container, wherein a paint containing a prepolymer having free isocyanate groups is used as the liquid paint, and the paint is used as the shaving air. An electrostatic coating method characterized by forming a coating film using air containing ammonia or amine vapor to accelerate curing.