JPH01270980A - Method for applying urethane resin paint - Google Patents

Abstract

PURPOSE:To make the drying/curing characteristics and coating efficiency of a film excellent by scattering a liquid curing catalyst into paint atomizing air in a mist form and performing painting using an electrostatic painting method while said catalyst is brought into contact with atomized paint. CONSTITUTION:Urethane resin paint utilizing the reaction of polyisocyanate is applied using a curing catalyst (e.g., trimethylamine) to promote the drying and curing of the paint. At this time, the liquid curing catalyst from the paint atomizing air hose 14 from a hose 2 is dispersed in a mixer 10 to be supplied to a painting gun 1. The urethane resin paint supplied from a hose 3 is emitted while atomized in the painting gun 1 by air containing the atomized curing catalyst. Further, the static electricity obtained by a high voltage generator 19 is imparted to atomized paint particles as DC high voltage by the electrode 20 provided to the leading end of the gun 1. As a result, the paint film can be rapidly cured at room temp. and thick painting becomes possible and coating efficiency is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a coating method that provides excellent drying and curing characteristics and coating efficiency of a coating film formed during coating with a urethane resin coating.

(Prior Art) As a conventional method for applying a urethane resin paint, there is a method as shown in FIG. 3, for example.

That is, in the figure, the urethane resin paint sent from the paint supply hose 3 is atomized in the paint gun 1 by the air sent from the air supply hose 2 in the painting booth 6, and then the atomized paint 4 is It adheres to the surface of the coating 5 to form a film. The object to be coated, which has a coating film on its surface, is placed in a baking drying oven and dried for 20 to 60 minutes at 60 to 90°C.
There is a method of forming a cured film 8 on the surface of the object to be coated 5 by drying for a minute or by drying and curing by leaving it at room temperature for several hours or more than ten hours.

However, in the heat curing method, a baking drying oven 9 is required, and the coated material (for example, plastic) is sensitive to heat.
had some drawbacks that made it unusable.

On the other hand, the room-temperature curing method has drawbacks such as poor productivity because it takes a long time to cure, and dust adheres during drying, increasing the defective rate.

A method for accelerating the curing of such urethane resin paints is to expose the undried paint film to an atmosphere of vaporized amine immediately after applying the urethane resin paint, and to infiltrate the amine into the paint film to increase its catalytic action. harden rapidly by
There is a so-called steam amine infiltration method. (Tokuko 53-19
038 and Japanese Patent Publication No. 5O-2091) Another method is to atomize the urethane resin paint with vaporized amine gas,
There is a so-called steam amine catalyst spraying method in which the amine gas and the atomized paint are brought into contact with each other to rapidly cure the paint through catalytic action.

Furthermore, there is a pre-catalyst addition method in which a curing catalyst is added to the polyol in advance, a polyisocyanate curing agent is mixed therein, and the curing is accelerated by coating.

(Problem to be solved by the invention) However, the vapor amine infiltration method in which vaporized amine is brought into contact with the coating film requires a chamber to maintain an amine atmosphere, and an air curtain is provided to prevent the amine from leaking outside. A device is needed to treat the exhaust gas.

In addition, in order to penetrate the vaporized amine from the coating surface,
It has drawbacks such as limited penetration and not being suitable for thick coatings.

Furthermore, since the amine is used in a vaporized state, there is a natural limit to the types of amine that can be used.

The steam amine catalyst atomization method, in which urethane resin paint is atomized using a one-way amine, has advantages such as rapid drying and curing of the paint film and the possibility of thick film coating. equipment was required, and there were restrictions on the types of amines that could be used. In addition, because the curing reaction is too rapid, the leveling of the coating film is not sufficient, making it unsuitable for coatings that require a high level of coating, such as topcoating, which limits its use. Ta.

Further, the pre-catalyst addition method in which a catalyst is added in advance accelerates curing, but has disadvantages such as a shortened pot life, increased loss of paint, and difficulty in handling.

Therefore, an object of the present invention is to develop a new urethane for use in electrostatic coating that allows thick film coating, has an appropriate drying and curing speed, provides a high quality coating, and has excellent coating efficiency. An object of the present invention is to provide a coating method with excellent drying and curing characteristics of a coating film formed during coating with a resin-based resin coating.

(Means for Solving the Problems) Therefore, the present invention provides a method for accelerating the curing of urethane resin paints using the reaction between polyol and polyisocyanate, in which a liquid curing catalyst is dispersed in the form of a mist in the air for paint atomization. The liquid curing catalyst is dissolved in advance in an organic solvent with a high electrical resistance value as necessary to perform electrostatic coating and form The above-mentioned problems have been solved by a method for applying a urethane resin paint, which is characterized by drying and curing the applied paint film.

-ffi-wise, spray painting often has poor coating efficiency, especially when the shape of the object to be coated becomes complex, and electrostatic coating is used as a means to solve this problem. .

When using electrostatic coating, if the liquid curing catalyst is conductive, static electricity will leak and electrostatic coating cannot be performed, so it is necessary to make the liquid curing catalyst non-conductive in advance. It is appropriate to use a solvent.

(Operation) The present invention will be described below with reference to the drawings. As shown in FIG. 1, the liquid curing catalyst diluted with a non-polar solvent supplied from the curing catalyst tank is controlled in an appropriate amount by a flow rate meter 11 and a regulating valve in the coating booth 6, and is mixed with a curing catalyst supply hose 14. Sent to 10. In the mixer 10, for example, 0.5 kg/- or more, preferably 1.0 to 6 kg/- is supplied from the paint atomizing air supply hose 2.
A liquid curing catalyst (diluted with a non-polar solvent) of .degree.Okg/cxK is supplied to the coating gun 1 after being dispersed in the form of a mist in air set to an atomization pressure.

On the other hand, the urethane resin paint supplied by the paint supply hose 3 contains an atomized curing catalyst set to a paint atomization pressure of, for example, 2.0 kg/- or more, preferably 3.5 to 6.0 kg/-, in the coating gun 1. It is atomized by air and discharged in a mist form from the coating gun 1 together with the atomized curing catalyst. On the other hand, the static electricity generated by the high voltage generator 19 is applied to the atomized paint particles by a DC high voltage from an electrode 20 provided at the tip of the coating gun 1.

Note that the electrode 20 may be provided inside the gun 19 as shown in FIG. 2, or either may be used.

For example, when using an external mixing type painting gun 1 having the structure shown in FIG.
The non-polar solvent diluted liquid curing catalyst-containing air introduced into the paint nozzle 17 is compressed to a predetermined pressure as described above and blown out from the air nozzle 16 of the air cap 15.
A low pressure area occurs at the tip of the The paint supplied into the paint gun 1 from the paint supply port 18 and guided to the paint nozzle 17 is sucked by the force of the low pressure section generated as described above and is discharged from the paint nozzle 17. At this time, the drawn paint to which a high voltage is applied directly by the electrode 20 at the tip is further broken off and atomized by the force (velocity) of the subsequent high-pressure air. The atomized paint 14 adheres to the surface of the object 5 to be coated to form a coating film. The object to be coated 5 on which the coating film has been formed in this manner is transported to a post cure chamber, and is, for example, 15 to 80'
C Preferably at 20 to 50°C, more preferably at around room temperature, for a predetermined period of time. As a result, the coating film is cured.

The urethane resin paint used in the coating method of the present invention may be any urethane resin paint used in conventional heating or room temperature drying methods, steam amine infiltration methods, steam amine catalyst spraying methods, and the like.

For example, polyols consisting of acrylic polyols, alkyd polyols, polyester polyols, polyether polyols, modified products thereof, or mixtures of these polyols, and tolylene diisocyanate (TD
I>, xylylene diisocyanate (XD I)
A two-component polyurethane resin paint consisting of polyisocyanates such as inbond diisocyanate (IPDI), diphenylmethane diisocyanate (MD I), hydrogenated products thereof, hexamethylene diisocyanate, lysine diisocyanate, and mixtures thereof;
polyethylene glycol, polypropylene glycol,
There are one-component moisture-curable polyurethane resin paints typified by polyisocyanate adducts of polyalkylene glycols such as

For these urethane resin paints, paint additives such as inorganic pigments, organic pigments, organic solvents, antifoaming agents, leveling agents, color separation prevention agents, viscosity modifiers, etc. commonly used in paints,
Alternatively, modifying resins other than polyols such as cellulose acetate and vinyl chloride resin, plasticizers, etc. can all be used.

Next, in the present invention, the catalyst that can be used is limited to tertiary amines that can be vaporized at room temperature in the conventional steam amine infiltration method and steam amine catalyst spray method, whereas the catalyst that can be used is a mist containing these tertiary amines. Any liquid amine that can be used can be used. Such liquid amines are preferably tertiary amines, such as tertiary alkyl amines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, tri-n-butylamine, triisobutylamine, tri-sec-butylamine, etc. amines, aromatic amines such as dimethylaniline, diethylaniline, tribenzylamine, N
-Morpholines such as methylmorpholine and N-ethylmorpholine, triethanolamine, methylgetanolamine, dimethylethanolamine, diethylethanolamine, diethylethanolamine, dibutylethanolamine, di(2-ethylhexyl)ethanolamine, ethylgetanol Amines, alkanolamines such as triisopropanolamine and dibutylisopropanolamine, diamines and triamines such as tetramethylethylenediamine, tetramethylhenaxamethylenediamine, tetramethylpropylenediamine, and pentamethyldiethylenetriamine can be used.

- The type of organic solvent for diluting the liquid curing catalyst used in the strength wood invention may be any non-polar organic solvent, but it is preferable from the viewpoint of drying properties that it scatters during atomization and does not remain on the coating film, and that the boiling point is 150°C. The following are preferred, and triol, quidylole, hexane, penzole, butyl acetate, etc. are preferred. On the other hand, although the dilution concentration varies depending on the type of catalytic amine used, it is generally appropriate to range from 1 to 40% amine amount/to diluting solvent, and preferably from 5 to 20%. If the amine concentration is less than 1%, the amount of diluting solvent used will be large, resulting in a large economic loss; if it is more than 40%, the conductivity will be high and the electrostatic effect may disappear. Furthermore, in the coating method of the present invention, the mixing ratio of the above-mentioned urethane resin paint and liquid curing catalyst during application is 100:0.1 to 1 by weight when the liquid curing catalyst is 100% effective.
00:50, preferably 100:0.5 to 100:30. If the catalyst amount is less than 100:0.1, the curing acceleration by the curing catalyst is insufficient;
If the amount of catalyst is greater than 0, the flowability of the paint will be poor, resulting in a citron-like finish.

The mixing ratio of the urethane resin paint and air during application is 1:100 to 1:600 by volume, preferably 1:225 to 1:375. If the air volume is less than 1:100, the atomization of the urethane resin paint will be poor, resulting in poor skin. If the air volume is more than 1:600, a large amount of atomized paint particles will bounce off, resulting in poor paint adhesion. The rate may go down.

On the other hand, the applied voltage used for electrostatic painting is within the range normally used, but specifically, the DC voltage is -40 kV.
~140kv is preferred.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Two-component polyurethane resin paint Bebon #10TH White (manufactured by Shinto Paint Co., Ltd.) was sent to the paint supply port after the coating viscosity was adjusted to 15 seconds/25°C. Meanwhile, dimethylethanolamine was added as a curing catalyst at a concentration of 10% ( Using a liquid diluted amine diluted with triol so that the amine was diluted with triol so that the amine was dispersed, the air in which the amine was dispersed was supplied from the air supply port as atomizing air, and a model 85 (manufactured by Binx Japan) was used as a painting gun. The paint was atomized using amine-containing air and electrostatically applied.

Paint exposure pressure 4.0 glare/-1 Paint discharge amount 350cc/mi
n, amine feeding amount (as 100% dimethylethanolamine amount) 2% heavy mold area vs. discharged paint amount, applied voltage -60
It was kv.

200 x 300 m/m polished steel plate (degreased by conventional method) and 200 m/mφ x 300 m/m as objects to be coated.
A polished steel plate pipe (degreased by a conventional method) having a length x plate thickness of 0.8 m/m was used.

A coating film with a thickness of 25μ was obtained, and a good cured film was obtained by post-curing at 30°C for 10 minutes.For pipes, the surface was 20μ and the back was 12μ.
A coating film with good μ was obtained.

Examples 2 to 5 Coating films were formed in the same manner as in Example 1, except that the diluted amine concentration and feed amine amount (relative to paint discharge amount) used are shown in Table 1. All had good curability and throwing power.

Comparative Example 1 A coating film was formed in the same manner as in Example 1 except that no DC voltage was applied. The curing properties were good, but the throwing power was poor, 25 μm on the front surface and 0 μm on the back surface.

Comparative Examples 2 to 4 Coating films were formed in the same manner as in Example 1, except that the diluted amine concentration used and the amount of amine fed (amount of paint discharged) are shown in Table 1. In all cases, the coating film had poor curability, poor throwing power, or both.

(Effects of the Invention) As described above, according to the method of the present invention, quick curing can be performed at room temperature, thick film coating is possible, and the throwing power is excellent, so an amine chamber or an amine vaporization device is not required, and various types of The curing catalyst can be used, and the coating efficiency is high, so the cost is low and coating can be performed with good productivity.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the painting process according to the present invention, Fig. 3 is a schematic diagram showing the painting process according to the conventional method, and Fig. 4 is a schematic diagram showing the painting process according to the present invention.
The figure is a sectional view showing the structure of one example of the coating that can be used in the present invention. 1... Paint gun, 2... Paint atomizing air supply hose, 3... Paint supply hose, 4... Atomizing paint, 5...
・Object to be coated, 6... Paint booth, 8... Cured coating film, 1
0... Mixer, 11... Flow meter, 12... Diluted curing catalyst tank, 13... Bost cure chamber, 14... Diluted curing catalyst supply port, 19... High pressure generator, 20... ··electrode. Patent applicant Nissan Motor Co., Ltd. Shinto Paint Co., Ltd.

Claims (1)

[Claims] In a method of accelerating the drying and curing of urethane resin paints that utilize the reaction of polyisocyanate using a curing catalyst after painting, a liquid curing catalyst is dispersed in the form of a mist in the paint atomizing air to atomize the paint. A method for applying a urethane resin paint, characterized in that when applying the paint while bringing the paint and a curing catalyst into contact with each other at approximately the same time, the method is applied using an electrostatic coating method, and the formed paint film is dried and cured. .