JP2000176361A - Method of reusing uncoated coating fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the reuse rate of an uncoated coating material particles by using a circulating booth liquid containing water and a water-soluble alkanol amine and a water-soluble ether solvent having respectively boiling points of specified temperature and provided with the specified pH value and the specified water-soluble ether solvent amount ratio. SOLUTION: Uncoated coating material particles are sprayed by a spray gun 1 and the particles not collected by a buffle 3 are collected in a circulating booth liquid by a circulating booth liquid curtain 5. The circulating booth liquid curtain 5 is formed by circulating the liquid from a liquid tank 6 by a pump 7, and a particle-collected liquid is transferred to a blending tank 9 when the solid content concentration reaches a prescribed concentration and mixed therein with a replenishing high solid component aqueous coating material recovered in a recovery tank 4. The circulating booth liquid contains a water-solble alkanol amine of 100-300 deg.C boiling point and a water-soluble ether solvent of 180-300 deg.C boiling point, and pH is 8.5-12 and the water-soluble ether solvent amount is 3-10 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reusing uncoated paint particles which can be recovered by spray-coating an aqueous paint and reused for spray coating.

[0002]

2. Description of the Related Art Conventionally, in a water-based paint spray coating method using a wet coating booth, discarding uncoated paint not only results in paint loss,
Since the problem of environmental pollution will occur, the collected water obtained by collecting the unsprayed paint overspray in the circulating water in the wet coating booth is used for ultrafiltration membrane, reverse osmosis filtration membrane, etc. There is disclosed a method of recovering uncoated paint from collected water by using the same solid content concentration as that of the water-based paint for spray coating by filtering and concentrating the water to obtain a solid content concentration (for example, See JP-A-49-51324). However, in this method, an ultrafiltration device and a reverse osmosis filtration device are expensive as a concentrating means, and in addition to the low cost contained in the collected water in the process of filtering and condensing the collected water to recover the paint. Molecular acid components, amines, solvents, etc. flow out along with the separation liquid and are separated from the coating resin, and the concentrated recovered resin becomes unstable and thickens, resulting in reduced filtration efficiency and the desired aqueous solution for spray coating. There is a problem that it is difficult to concentrate to a solid content concentration as a paint.

Further, a method has been proposed in which uncoated paint particles generated when a water-based paint is spray-coated are captured by a baffle using a panel-shaped baffle by applying the principle of inertial collision, directly collected, and reused. (For example, WO 97-20
No. 614). By this method, it is possible to considerably increase the recycling rate of uncoated paint particles generated when spraying an aqueous paint, but the limit is 90 to 93% by weight,
At least 7-10% by weight will be wasted. From the viewpoint of effective use of resources and protection of the global environment, it is required to increase the reuse rate of uncoated paint particles.

Further, as a method of collecting and reusing uncoated paint particles generated when the water-based paint is spray-coated, uncoated paint particles are collected by a water curtain in a wet coating booth, and the collected paint particles are collected. A method has been proposed in which water and a high-concentration replenishing aqueous paint are mixed and used as an aqueous paint for spray coating (see JP-A-9-1014).
This method can increase the recycling rate of uncoated paint particles to nearly 100%. However, a large amount of trapped water having a low solid content is generated with respect to the amount of the spray-painted paint. A large amount of paint is required, and the treatment efficiency of uncoated paint particles for reuse is reduced. In this method, if the solid content concentration of the replenishing aqueous paint is further increased in order to reduce the amount of the replenishing aqueous paint, there is a limit since problems such as an extreme increase in the viscosity of the paint and a decrease in storage stability occur. In addition, if circulation is performed until the solid concentration of the collected water is increased to increase the solid concentration of the collected water mixed with the replenishing water-based paint, the stability of the collected water is reduced, and the collected water is trapped due to the increase in viscosity. Problems such as an increase in the load on the water collection and circulation pump are likely to occur.

Accordingly, the present inventors have been able to increase the recycling rate of uncoated paint particles to nearly 100%, increase the processing efficiency of uncoated paint particles, and furthermore, provide a water-based paint for replenishment. There is no need to raise viscosity extremely, no problems such as reduced storage stability, and problems such as reduced collected water stability and increased load on the collected water circulation pump due to increased viscosity. As a result of diligent studies to obtain a method of reusing uncoated paint particles of water-based paint, a method of directly collecting uncoated paint particles and a method of capturing uncoated paint particles by a booth liquid curtain of a specific composition The present inventors have found that the above problem can be solved by combining the above and have completed the present invention.

[0006]

That is, the present invention relates to a method of reusing an uncoated paint that has been oversprayed on an object provided in a transfer path of a sprayed water-based paint mist. And (A) capturing a large portion of the oversprayed uncoated paint by a paint capturing unit provided directly downstream of the transfer path in the transfer path and capturing the uncoated paint; (B) water, a water-soluble alkanolamine having a boiling point of 100 to 300 ° C., and a boiling point of 180 to 300 ° C.
Containing a water-soluble ether solvent, and having a pH of 8.5 to 8.5.
12. A circulation booth liquid from a liquid tank containing a booth liquid in which the amount of the water-soluble ether solvent is 3 to 10% by weight in 12,
By the circulation booth liquid curtain formed on the downstream side in the transfer path with respect to the paint catching unit, the unpainted paint not caught by the paint catching unit is collected, and the collected unpainted paint is collected. (C) circulating and collecting until a collected liquid having a predetermined solid content concentration is obtained, and (C) the paint contained in the collection tank in the above step (A) and the paint collected in the above step (B). Mixing the collected liquid having a predetermined solid content concentration and the replenishment high-solids aqueous paint, adjusting the aqueous paint for spray coating to a predetermined concentration, and spray-coating the object to be coated. And a method for reusing an uncoated paint.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention comprises the step (A),
This is a method for reusing an uncoated paint having (B) and (C), and each step will be described.

Step (A) In the step (A) in the method of the present invention, when a water-based paint is spray-coated on an object to be coated, the uncoated paint that has been oversprayed without being applied to the object is transferred to a paint mist. This is a step of directly capturing by a paint capturing section provided downstream of the article to be coated in the path, and storing the captured uncoated paint in a collection tank.

[0009] A baffle can be suitably used as the paint catching section. The baffle preferably has a structure capable of directly and efficiently collecting oversprayed uncoated paint particles. As an example of the baffle, for example, a structure in which a plurality of baffle plates are arranged so as to be able to expand and contract vertically and block an air flow containing uncoated paint particles, and are partially overlapped and connected to each other Baffles. As an example of the baffle plate, the uncoated paint particle capturing surface may be provided with a plurality of intake holes that open in a louver shape having an intake curved piece and a plurality of exhaust holes, It is preferable that the plurality of intake holes of the baffle plate located at the front and the plurality of exhaust holes of the overlapping portion of the baffle plate located at the rear face each other with their positions shifted. Since the airflow is bent and passes from the front to the rear of the baffle due to the misalignment between the intake hole and the exhaust hole, the efficiency of capturing the uncoated paint by the baffle can be improved.

In order to store the uncoated paint directly captured by the paint capturing portion such as the baffle in the recovery tank,
For example, there is a method of installing a collection tank below the paint capturing unit such as the baffle, and appropriately immersing the paint capturing unit in the recovery tank to re-dissolve and collect the paint adhered to the surface of the paint capturing unit. it can. In the collection tank, for example, the same kind of paint as the paint to be spray-painted is put, so that the paint adhered to the surface of the paint catching portion can be redissolved and collected.

By the step (A), it is usually possible to capture up to about 90 to 93% by weight of the oversprayed uncoated paint particles.

Step (B) In the step (B) in the method of the present invention, the uncoated paint particles, which are not captured in the above-mentioned step (A) and are transported together with the air flow behind the paint capturing section, are circulated by a circulation booth liquid curtain. This is a step of collecting, circulating and collecting until a collected liquid having a predetermined solid content concentration based on the collected uncoated paint is obtained.

The circulation booth liquid forming the curtain is as follows:
It contains water, a water-soluble alkanolamine having a boiling point of 100 to 300 ° C and a water-soluble ether-based solvent having a boiling point of 180 to 300 ° C, and has a pH of 8.5 to 12 and an amount of the water-soluble ether-based solvent of 3 to It is a circulating booth liquid from a liquid tank containing a 10% by weight booth liquid. In addition, in addition to the water-soluble ether-based solvent, a small amount of ether-based or alcohol-based solvents that can be partially dissolved in water is used for the purpose of defoaming (usually 1% by weight or less in the circulation booth). Can be used together.

Since the circulation booth liquid contains the water-soluble alkanolamine and the water-soluble ether-based solvent, the uncoated paint particles can be easily redissolved, and the solid concentration of the circulation booth liquid is considerably high. The stability is not impaired even if the temperature is increased, and the water-soluble alkanolamine and the water-soluble ether-based solvent are difficult to volatilize in the circulation, so that it is easy to maintain and control the amount of organic solvent and pH, and to stabilize the circulation booth liquid. It is possible to easily carry out the circulation and to reduce the volatilization of the organic solvent and the amine odor, so that these odors can be suppressed and the working environment is effectively improved. The pH of the circulation booth liquid is
8.5 to 12, preferably 9.0 to 12,
It is preferable because the stability of the circulation booth liquid is good even when the uncoated paint particles are easily redissolved and the solid content concentration becomes considerably high.

The water-soluble alkanolamine having a boiling point of 100 to 300 ° C. includes, for example, monoethanolamine, diethanolamine, triethanolamine, N,
N-dimethylaminoethanol, 2-amino-2-methyl 1-propanol, monoisopropanolamine, diisopropanolamine, N-methylethanolamine,
N-ethylethanolamine and the like can be mentioned.

Examples of the water-soluble ether solvents having a boiling point of 180 ° C. to 300 ° C. include, for example, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether,
Examples thereof include dipropylene glycol monomethyl ether and tripropylene glycol monomethyl ether.

Examples of ether solvents and alcohol solvents partially soluble in water which can be used in combination with the above water-soluble ether solvents include, for example, benzyl alcohol, 2-ethylhexyl alcohol, ethylene glycol monohexyl ether and ethylene glycol mono solvent. Examples thereof include 2-ethylhexyl ether.

The circulating booth liquid is circulated and collected until a collected liquid having a predetermined solid content concentration based on the collected uncoated paint is obtained. According to the solid content concentration of the paint contained in the tank in (A) and the solid content concentration of the replenishing high solid content aqueous paint mixed in the step (C) described later, a water paint for spray coating having a desired concentration is obtained. It can be set appropriately within a range where the load on the circulation booth liquid circulation device (pump) is not excessively applied and the stability of the circulation booth liquid in which the paint is dissolved is not impaired. The predetermined solid content concentration of the collection liquid is not particularly limited, but is usually in the range of 5 to 35% by weight, preferably 15 to 25% by weight.

According to the steps (A) and (B),
It is possible to capture almost all of the oversprayed uncoated paint particles (typically 97% or more).

Step (C) In the step (C) in the method of the present invention, the paint contained in the recovery tank in the step (A) and the predetermined solid concentration collected in the step (B) are determined. This is a step of mixing the collected liquid and the high-solids aqueous paint for replenishment, adjusting the aqueous paint for spray coating to a predetermined concentration, and spray-coating the article to be coated.

The solid concentration of the paint contained in the collection tank in the step (A), which is mixed for adjustment to the water-based paint for spray coating, is not particularly limited. From the viewpoints of recovery processing efficiency, stability of the paint in the recovery tank, and the like, it is suitable that the water-based paint for spray coating to be reused is at least equivalent, usually 30 to 60% by weight, and preferably 35 to 55% by weight. %.

The solid content concentration of the replenishment high solids aqueous paint mixed to adjust to the spray coating aqueous paint is higher than the solid content concentration of the reused spray coating aqueous paint. The solid content of the paint is
Usually 30 to 55% by weight, so 30% by weight
However, from the viewpoints of the treatment efficiency of uncoated paint, the stability of the paint, etc., the content is preferably in the range of 40 to 90% by weight, preferably 45 to 75% by weight.

The type of the aqueous paint used in the method of the present invention is not particularly limited as long as it is an aqueous paint. In the case of a baking type aqueous paint, a water-soluble amino resin, Aqueous paints using a hydrophobic amino resin or a water-dispersed block isocyanate compound can be suitably used. Among them, the water-soluble paint having a water-soluble amino resin as a curing agent is used, and the re-dissolvability of the recovered paint is high. Is preferred.

An example of the method of the present invention will be described below with reference to the drawings.

In FIG. 1, an aqueous paint for spray coating sprayed from a spray gun 1 is applied to an object 2 to be coated.
The uncoated paint particles that have not been applied move with the air flow, come into contact with the baffle 3 that is a paint capturing unit, and most of the uncoated paint particles are captured.

The air flow is formed by an exhaust fan (not shown) provided downstream of the circulation booth liquid curtain 5 in the paint mist transfer path.

Further, as an example of the baffle 3, a baffle plate 3a having a structure in which a plurality of baffle plates 3a are connected and capable of moving up and down can be cited. FIG. 2 shows an example of a cross-sectional view of the baffle 3 when the baffle 3 is cut along the same plane as the transfer direction of the paint mist.

In FIG. 1, a recovery tank 4 containing a paint as a recovery liquid is provided below the baffle 3, and a baffle plate having uncoated paint adhered to its surface is moved and immersed in the recovery tank 4. As a result, the uncoated paint is dissolved and collected in the collection tank 4. In FIG. 1, two baffles are provided, one of which is in a state of capturing unpainted paint, and the other one is immersed in the collection tank 4 and the baffle surface The uncoated paint adhered to is dissolved. When a certain amount of unpainted paint is captured by the baffle and reaches a certain amount, the baffle in the collection tank 4 is pulled up,
The baffle to which the uncoated paint has adhered is immersed in the collection tank 4, and this is repeated.

As for the movement of the baffle plate, as shown in FIG. 1, the baffle connected to the baffle plate may be immersed in the collection tank 4 at one time, or the baffle plate may be continuously rotated by rotation. You may make it immersed in the collection tank 4.

When the paint recovered in the recovery tank 4 reaches a predetermined concentration, a part of the paint may be sent to the blending tank 9, or when the concentration reaches the predetermined concentration, the recovery tank is replaced with a spare recovery tank. May be interchanged. The paint in the recovery tank having a predetermined concentration is blended in the blending tank 9.

In FIG. 1, uncoated paint particles not captured by the baffle 3 are removed together with the air flow.
From the rear part, it moves to the circulation booth liquid curtain 5 and contacts and is collected by the circulation booth liquid. The circulation booth liquid curtain 5
It is formed by circulating by a pump 7 from a liquid tank 6 containing a circulating booth liquid. The collection liquid, which is a booth liquid that has collected the uncoated paint particles, is circulated and, when the solid content concentration reaches a predetermined concentration, a predetermined amount of the collection liquid is passed through the collection liquid supply line 8 to the mixing tank. 9 and mixed with a predetermined amount of the paint of a predetermined concentration collected in the collection tank 4 and a predetermined amount of a replenishing high solids aqueous paint having a predetermined solid content concentration in the mixing tank 9,
After performing pH adjustment and filtration as necessary, the aqueous paint tank for spray coating 10 is used as the aqueous paint for spray coating.
Sent to

The aqueous paint stored in the aqueous paint tank 10 for spray coating is supplied to the spray gun 1 and spray-painted. The above steps are repeated, and the uncoated paint is collected and reused.

[0033]

The present invention will be described more specifically with reference to the following examples. Hereinafter, both “parts” and “%” are based on weight.

Example 1 125 parts of an alkyd resin solution I (Note 1) having a solid content of 60% was neutralized in an equivalent amount with diethanolamine, and stirred while gradually adding 157.5 parts of water to prepare an aqueous resin solution. 10 parts of carbon black and 10 parts of barium sulfate were added to this aqueous resin solution.
0 parts were mixed to disperse the pigment, and then 25 parts of Cymel 303 (Note 2) was mixed therein to obtain an aqueous coating material A having a solid content of 50.3%.

(Note 1) Alkyd resin solution I: Resin solid content: acid value 45 mgKOH / g, hydroxyl value 40 mgKOH
/ G, number average molecular weight 5000. (Note 2) Cymel 303: a product of Mitsui Cytec Co., Ltd., a water-soluble low molecular weight methyl etherified melamine resin.

The water-based coating material A obtained as described above was diluted with water to obtain a water-based coating material having a solid content of 40%, which was subjected to air spray coating by the method shown in FIG. The amount of the paint applied by spray coating was 100 parts (40 parts in terms of solid content) / day.
The amount of paint applied to the object to be coated is 30 parts (12 parts in solid content)
5.per day, and 63 parts (25.2 parts in solid content) / day, which is 90% of the uncoated paint, is recovered by the baffle, and is 90% of the uncoated paint not recovered by the baffle. Three parts (2.52 parts in solid content) were dissolved and collected in the circulation booth liquid. The circulation booth liquid volume is 400 parts,
After about 32 days, the solid content of the collected liquid, which is a mixture of the circulation booth liquid and the uncoated paint, was 20%, and the collected liquid was in a good state without sedimentation or separation. After the 32nd day, 12.6 parts (2.52 parts in solid content) of a collection liquid having a solid content of 20% per day, 63 parts of the paint collected by a baffle, and an aqueous solution having a solid content of 50.3% as a replenisher paint Paint A24.4
(Solid content: 12.28 parts) and filtered to obtain an aqueous paint having a solid content of 40%. By applying this water-based paint to spray coating, a steady state was attained. Thereafter, in the steady state, coating and unpainted paint could be stably recovered. The recycling rate of the uncoated paint was 99%.

The composition of the circulation booth liquid was adjusted to pH 9 by adding diethanolamine to an aqueous solution containing 5% of diethylene glycol monobutyl ether. During the collection period, the collected liquid was uniform and had no sedimentation, separation or aggregation. It was in a state where it did not hinder reuse. 1% of the entire uncoated paint was not collected and reused, but was captured by a filter at an exhaust port (booth air outlet).

Example 2 125 parts of an alkyd resin solution II (Note 3) having a solid content of 60% was neutralized in an equivalent amount with diethanolamine, and stirred while gradually adding 155.4 parts of water to obtain a resin aqueous solution. 10 parts of carbon black and 10 parts of barium sulfate were added to this aqueous resin solution.
0 parts were mixed to disperse the pigment, and then 33 parts of Sumimar M30W (Note 4) was mixed therein to obtain a solid content of 49.6%.
Was obtained.

(Note 3) Alkyd resin solution II: Resin solid content: acid value 39 mg KOH / g, hydroxyl value 60 mg KOH
/ G, number average molecular weight 5000. (Note 4) Sumimar M30W: trade name, manufactured by Sumitomo Chemical Co., Ltd., water-soluble methyl etherified melamine resin solution, solid content 75%.

The water-based paint B obtained as described above was diluted with water, and subjected to air spray coating by a method shown in FIG. The amount of the paint applied by spray coating was 100 parts (40 parts in terms of solid content) / day.
The amount of paint applied to the object to be coated is 40 parts (16 parts in solid content)
/ Day, i.e., 54 parts (21.6 parts in solid content), which is 90% of the uncoated paint, was recovered by the baffle, and 80% of the uncoated paint not recovered by the baffle. Eight parts (1.92 parts in solid content) were dissolved and collected in the circulation booth liquid. The circulation booth liquid volume is 400 parts,
After about 31 days, the solid content of the collected liquid, which is a mixture of the circulation booth liquid and the uncoated paint, was 15%, and the collected liquid was in a good state without sedimentation, separation, or aggregation. . 31
After the day, a collected liquid having a solid content of 15% per day is 12.8.
Parts (1.92 parts in terms of solid content), 54 parts of paint recovered by baffle, and water paint B having a solid content of 49.6% as a supplement paint
33.2 parts (solid content: 16.48 parts) were mixed and filtered to obtain an aqueous paint having a solid content of 40%. By applying this water-based paint to spray coating, a steady state was achieved. Thereafter, in the steady state, stable coating and collection of uncoated paint could be performed. The recycling rate of the uncoated paint was 98%.

The composition of the circulation booth solution is such that N, N is added to an aqueous solution containing 5% of diethylene glycol monoethyl ether.
-The pH was adjusted to 9.5 by adding dimethylaminoethanol. During the collection period, the collected liquid was in a good state without sedimentation, separation, or aggregation, and did not hinder reuse. . 2% of the entire uncoated paint was not collected and reused, but was captured by a filter at an exhaust port (booth air outlet).

Comparative Example 1 A circulating booth was prepared in the same manner as in Example 1 except that the composition of the circulation booth was adjusted to pH 9 by adding diethanolamine to an aqueous solution containing 1% of diethylene glycol monobutyl ether. As a result, when the paint solid content of the collection liquid became 20%, a slight aggregate was observed in the collection liquid, and there was a problem in the stability of the collection liquid.

Comparative Example 2 Example 1 was repeated except that the composition of the circulation booth was adjusted to pH 9 by adding diethanolamine to an aqueous solution containing 4% ethylene glycol monoisopropyl ether. Was. As a result, when the paint solid content of the collected liquid became 20%, aggregates and sedimentation were observed in the collected liquid, and there was a problem in the stability of the collected liquid. The concentration of ethylene glycol monoisopropyl ether was reduced to 0.5%.

[0044]

According to the method of the present invention, it is possible to increase the recycling rate of uncoated paint particles to nearly 100%, and to increase the treatment efficiency of uncoated paint particles. A method for recycling paint particles can be provided.

Further, according to the method of the present invention, it is not necessary to extremely increase the paint viscosity of the replenishing water-based paint, and there is no problem such as a decrease in storage stability and a decrease in the stability of collected water. Also, it is possible to provide a method of reusing the uncoated paint particles of the water-based paint, which has no problems such as an increase in the load of a collecting water circulation pump due to the increase in viscosity.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of the method of the present invention.

FIG. 2 is a schematic diagram illustrating an example of a cross section of the baffle 3 when the baffle 3 illustrated in FIG. 1 is cut along the same plane as a paint mist transfer direction.

[Explanation of symbols]

 1 Spray gun 2 Coating object 3 Baffle 3a Baffle plate 4 Recovery tank 5 Circulating booth liquid curtain 6 Liquid tank 7 Pump 8 …… Collection liquid supply line 9 …… Formulation tank 10 …… Aqueous paint tank for spray coating

Claims (5)

[Claims] 1. A method of reusing an uncoated paint oversprayed on an object provided in a transfer path of a sprayed water-based paint mist, comprising: (A) On the other hand, most of the oversprayed uncoated paint is captured by a paint capturing unit that directly captures the uncoated paint provided on the downstream side in the transfer path, and the captured paint is captured by the paint capturing unit. (B) containing water, a water-soluble alkanolamine having a boiling point of 100 to 300 ° C and a water-soluble ether solvent having a boiling point of 180 to 300 ° C, and having a pH of 8.5 to 12. A circulation booth liquid from a liquid tank containing a booth liquid having an amount of the water-soluble ether-based solvent of 3 to 10% by weight, wherein the circulation booth is formed on the downstream side of a transfer path with respect to the paint catching section. By the liquid curtain, the liquid Collecting the uncoated paint that has not been collected, circulating and collecting the collected uncoated paint until the collected liquid has a predetermined solid content concentration based on the collected uncoated paint, and (C) the above-described step (A). ) Is mixed with the paint contained in the collection tank, the collected liquid having a predetermined solid concentration collected in the above step (B), and the high-solids aqueous paint for replenishment, and spray-coated with a predetermined concentration. A step of spray-coating an object to be coated after adjusting to a water-based paint. 2. The method according to claim 1, wherein the water-based paint is a water-based paint containing a water-soluble amino resin as a curing agent. 3. The method according to claim 1, wherein the solid content of the water-based paint for spray coating is in the range of 30 to 55% by weight. 4. The recycling method according to claim 1, wherein the solid concentration of the collected liquid in the step (B) is in the range of 5 to 35% by weight. 5. The recycling method according to claim 1, wherein a solid content concentration of the replenishing high solid content aqueous coating material is in a range of 40 to 90% by weight.