JP2012187482A - Method for treating water circulating through wet coating booth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can improve separability by floating-up of sludge.SOLUTION: The method for treating water containing a coating material and circulating through a wet coating booth includes a process of reducing the viscosity of the coating material, and placing the water circulating through the wet coating booth in the presence of a phenolic resin and an ettringite hydrate and/or a calcium silicate hydrate, thus separating the coating material from the water circulating through the wet coating booth. The ettringite hydrate and/or calcium silicate hydrate is preferably generated by adding a source including the oxide of one or more kinds of elements selected from the group composed of calcium, silicon and aluminum to the water circulating through the wet coating booth.

Description

  The present invention relates to a technique for separating paint from wet paint booth circulating water containing paint.

  Various paints are spray-painted in the painting process of the automobile industry, home appliances, metal product manufacturing industries, and the like. Industrially used paints are roughly classified into solvent-based paints and water-based paints, and each paint is used alone or in combination. Among these, the water-based paint has advantages that it is safe and hygienic because there is water as the main solvent, and there is no fear of pollution caused by the solvent, and its application range is being expanded.

  By the way, in the painting process, generally the yield of the paint sprayed on the object to be coated is not necessarily 100%. For example, in the automobile industry, it is about 60 to 80%, and 40 to 20% of the used paint is removed in the next process. It is the surplus paint that should be done. In order to collect the surplus paint, washing with water is usually performed in a wet painting booth, and the washing water is circulated.

  In this case, since the water-based paint dissolves or disperses in water and solid-liquid separation is difficult, it remains and accumulates in the circulating water of the wet paint booth, causing various problems. Therefore, conventionally, surplus paint in the circulating water has been aggregated and separated. For example, it has been proposed to add a melamine / aldehyde acid colloid solution to float the paint and separate it.

  Furthermore, in order to solve the problem that the sludge (aggregated paint) is fine and difficult to float, and the sludge is likely to accumulate in the booth and in the circulating water tank, Patent Document 1 describes that after reducing the viscosity of the paint. The addition of a phenolic resin is disclosed.

JP 2006-247456 A

  However, even in the method of Patent Document 1, since sludge is soft and easily broken, sludge redispersion cannot be sufficiently suppressed under stirring and turbulent flow. For this reason, the problem that sludge does not sufficiently float or is likely to take time to float.

  This invention is made | formed in view of the above situation, and it aims at providing the method which can improve the separability by floating of sludge more.

  The inventors of the present invention add the reduced viscosity paint to the phenolic resin and leave it in the presence of ettringite hydrate and / or calcium silicate hydrate, so that the sludge containing the paint is hardened and hardly redispersed. As a result, the present invention has been completed. Specifically, the present invention provides the following.

(1) A method of treating wet paint booth circulating water containing paint,
Reducing the viscosity of the paint, and placing the wet paint booth circulating water in the presence of a phenolic resin and ettringite hydrate and / or calcium silicate hydrate, the paint from the wet paint booth circulating water A method having a step of separating.

  (2) The ettringite hydrate and / or calcium silicate hydrate is added with a source containing an oxide of one or more elements selected from the group consisting of calcium, silicon and aluminum to the wet paint booth circulating water. The method of (1) description which produces | generates by doing.

  (3) The method according to (2), wherein the source contains incinerated ash and / or zeolite.

  (4) The method according to (3), wherein the incinerated ash includes 70 to 40% by mass of silicon dioxide, 25 to 10% of aluminum oxide, and 30 to 5% by mass of calcium oxide.

  (5) The method according to any one of (2) to (4), further including a step of adding a component containing calcium sulfate to the wet paint booth circulating water.

  (6) The method according to (5), wherein the component contains gypsum.

  (7) The method according to (5) or (6), wherein the source and the component contain, in a total amount, 70 to 40% by mass of silicon dioxide, 25 to 10% of aluminum oxide, and 30 to 5% by mass of calcium oxide.

  (8) The method according to any one of (5) to (7), wherein the source and the component are added at a mass ratio of 3: 7 to 7: 3.

  (9) The method according to any one of (2) to (8), wherein the source and the component are added in a total amount of 5% by mass to 20% by mass with respect to the solid content of the paint.

  (10) The method according to any one of (1) to (9), wherein the viscosity of the paint is decreased by adding a melamine / aldehyde acid colloid solution and / or an aluminum compound to the wet paint booth circulating water.

  According to the present invention, by adding the reduced viscosity paint to the phenolic resin and in the presence of ettringite hydrate and / or calcium silicate hydrate, the sludge containing the paint is hardened and hardly redispersed. Become. Thereby, the separability by floating of sludge can be improved more.

It is an electron micrograph of the sludge containing the coating material produced | generated by the method based on the Example of this invention. It is an electron micrograph of the sludge containing the coating material produced | generated by the method which concerns on a comparative example.

  Hereinafter, although an embodiment of the present invention is described, the present invention is not limited to this.

  Wet paint booth circulating water treatment method includes reducing the viscosity of the paint and keeping wet paint booth circulating water in the presence of phenolic resin and ettringite hydrate and / or calcium silicate hydrate. The wet paint booth has a step of separating the paint from the circulating water. As a result, the sludge containing the paint is hardened and hardly redispersed, and the separability due to the sludge floating can be further improved. Moreover, since the sludge to be separated and collected is hard and agglomerated, a low water content can be obtained.

  The reduction in the viscosity of the paint is not particularly limited, but may be performed by adding a melamine / aldehyde acid colloid solution and / or an aluminum compound to the wet paint booth circulating water. The melamine / aldehyde acid colloid solution is produced by further adding an acid to methylolmelamine obtained by reacting melamine and aldehyde. If necessary, an acid may be added to a methylol melamine further alkyl etherified.

  Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, paraacetaldehyde, and the like. Among them, formaldehyde and paraformaldehyde are preferable from the viewpoint of handling and reaction efficiency. The charging ratio of melamine and aldehyde is preferably 1 to 6 mol of aldehyde with respect to 1 mol of melamine. However, if the amount of aldehyde exceeds 2.5 mol, the amount of free aldehyde increases when the acid colloid solution is prepared. Therefore, the amount of aldehyde is preferably 2.5 mol or less.

  Methylolmelamine does not dissolve in water, but dissolves in an acid solution in a colloidal form. The alkylated methylol melamine obtained by further alkylating methylol melamine is water-soluble and becomes colloidal when an acid is added.

  A monobasic acid is suitable as the acid. Specific examples include organic acids such as formic acid, acetic acid, lactic acid, and propionic acid in addition to mineral acids such as hydrochloric acid and nitric acid. Hydrochloric acid is particularly preferable because a stable colloidal solution can be obtained. The amount of the monobasic acid, particularly hydrochloric acid, is about 0.5 to 1.5 mol, preferably 0.7 to 1.3 mol, per 1 mol of melamine.

  In the initial stage of preparing the colloidal solution, there are a lot of free aldehydes. However, after the preparation, the free aldehydes are reduced when left standing at room temperature for aging. The aging time is suitably 5 days to 3 months at room temperature and about 2 to 3 hours at 50 ° C. when heating.

  The addition amount of the melamine / aldehyde acid colloid solution varies depending on the amount of coating paint, the coating method, and the like, but the concentration of the melamine / aldehyde acid colloid solution in the washing water is 1 to 5000 mg / l, usually about 5 to 500 mg / l. The mass of the melamine / aldehyde acid colloid solution is preferably in the range of 0.1 to 300% with respect to the surplus coating amount.

  In addition, after adding a melamine aldehyde acid colloid solution to washing water, it is preferable to adjust pH of washing water to 4-10, especially 5-9. When the pH deviates from this range, it is difficult to sufficiently exert the effect of reducing the tackiness of the paint. Examples of the acid and alkali used for pH adjustment include known pH adjusters such as hydrochloric acid, nitric acid, sodium hydroxide, and ammonia.

  Examples of the aluminum compound include polyaluminum chloride, sulfuric acid band, or alumina sol.

  The addition of the melamine / aldehyde acid colloidal solution or the aluminum compound to the booth is usually preferably carried out by continuous injection according to the washing water spray amount to the coating booth, but may be carried out by intermittent injection. Further, the addition location of the melamine / aldehyde acid colloidal solution or the inorganic compound is not particularly limited, but a piping system immediately before the flushing water and the paint are in contact with each other is preferable.

  After reducing the viscosity of the paint as described above, a phenol resin is added.

Examples of the phenolic resin include a condensate of phenols such as monohydric phenol such as phenol, cresol and xylenol and an aldehyde such as formaldehyde, or a modified product thereof, and a phenolic resin before being crosslinked and cured. Specific examples include the following. The phenolic resin may be used alone or in combination of two or more.
[1] Condensate of phenol and formaldehyde [2] Condensate of cresol and formaldehyde [3] Condensate of xylenol and formaldehyde [4] Obtained by alkylating the phenolic resin of [1] to [3] above Alkyl-modified phenolic resin [5] polyvinylphenol

  The phenolic resin may be either a novolak type or a resol type. Since the phenolic resin is hardly soluble in water, it is preferably used as a solution or emulsion by dissolving or dispersing in a solvent that can be dissolved in water. Solvents used include ketones such as acetone, esters such as methyl acetate, water-soluble organic solvents such as alcohols such as methanol, alkaline aqueous solutions, amines, etc., preferably caustic soda (NaOH), caustic potash (KOH), etc. Of the alkaline agent.

  When using phenolic resin as alkaline aqueous solution, it is preferable that an alkali agent density | concentration is 1-25 mass%, and a phenolic resin density | concentration is 1-50 mass%. When the phenolic resin concentration is high, the phenolic resin may be dissolved by heating to about 70 to 80 ° C.

  The amount of phenolic resin added is 1 mg / L or more, preferably 5 mg / L or more in terms of the active ingredient amount (resin solid content) with respect to the wet paint booth circulating water, and with respect to the paint (solid content) in the circulating water. The amount of the active ingredient is 0.1% by mass or more, preferably 0.5% by mass or more. When the phenolic resin addition amount is too small, it is difficult to obtain a sufficient aggregation effect. On the other hand, even if the amount of phenolic resin added is excessive, it is difficult to obtain an improvement in the coagulation effect commensurate with it, and foaming may occur. For this reason, the addition amount of the phenolic resin to the wet paint booth circulating water is 1000 mg / L or less, particularly 5 to 200 mg / L in terms of the active ingredient amount, and is 100% by mass or less in terms of the active ingredient amount relative to the paint in the circulating water. In particular, the content is preferably 0.5 to 10% by mass.

  The more preferable range of the addition amount of the phenolic resin varies depending on the coating amount content in the circulating water and the kind of the coating, but the colloidal solution equivalent value of the circulating water after adding the phenolic resin is +0.001 meq / L or more. In particular, it is in the range of +0.005 to +0.05 meq / L so that it is +0.005 meq / L or more, +1 meq / L or less, particularly +0.5 meq / L or less. When the colloid solution equivalent value is out of the above range, it is difficult to obtain a good aggregation effect.

  The addition of the phenolic resin to the circulating water is not particularly limited, and may be performed intermittently or continuously in the circulating water system once or twice a day. Desirably, the metered dose is continuously delivered by a pump. Although the addition place of a phenol-type resin is not specifically limited, Usually, it is preferable that it is the separation tank inlet side of the return of circulating water.

  Ettringite hydrate and / or calcium silicate hydrate may be added to the wet paint booth circulating water, or these raw materials may be added to the wet paint booth circulating water and generated in water. However, the latter is preferable from the viewpoint of ease of addition and cost. The presence of ettringite hydrate and calcium silicate hydrate can be confirmed by observing a solid generated in the wet paint booth circulating water with an electron microscope.

Ettringite hydrate is 3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O, and calcium silicate hydrate is 3CaO · 2SiO ₂ · 3H ₂ O. These raw materials may contain a source containing an oxide of one or more elements selected from the group consisting of calcium, silicon and aluminum. The oxide is not particularly limited as long as it can be hydrated to form ettringite hydrate or calcium silicate hydrate, and one or more oxides of calcium, silicon and aluminum are optional. It may be eutectic at a ratio. Depending on the inorganic components in the wet paint booth circulating water, oxides of elements deficient in calcium, silicon and aluminum may be added. In addition, it is preferable that the sauce is pulverized at the point which can produce | generate ettringite hydrate and / or calcium silicate hydrate rapidly, and generally it is preferable that it is 100 mesh or less.

  Such a source is not particularly limited as long as it contains the oxide, but is preferably incinerated ash and / or zeolite. Incineration ash is ash left after incineration of waste (for example, paper sludge, coal ash, blast furnace slag), is rich in the oxides, and is advantageous in terms of cost. Further, zeolite is advantageous in that it does not contain impurities such as heavy metals or its content is small. Zeolite is preferably dried or incinerated in that it can change in contact with water and provide abundant oxides.

  The incinerated ash preferably contains 70 to 40% by mass of silicon dioxide, 25 to 10% of aluminum oxide, and 30 to 5% by mass of calcium oxide. Thereby, ettringite hydrate or calcium silicate hydrate is easily produced. Zeolite generally contains only about 3% by mass of calcium oxide, and the deficiency is preferably compensated with gypsum or the like to be described later. However, depending on the inorganic component in the wet paint booth circulating water, the oxide may not be included in the above ratio.

  Moreover, it is preferable that the method of this invention has the process of further adding the component containing a calcium sulfate to wet coating booth circulating water. Thereby, the production | generation of the ettringite hydrate which uses calcium sulfate as a component is promoted more. However, in the case where sulfates and calcium salts are sufficiently present in the wet paint booth circulating water, it is not always necessary to add the above components. In addition, it is preferable that the said component is also pulverized like the sauce.

  Such a component is not particularly limited as long as it contains the above calcium sulfate and can be hydrated, but preferably contains gypsum. Since gypsum is insoluble in water, it is advantageous in that the increase in salt concentration in booth water is small. The gypsum is not particularly limited, and may be any gypsum such as anhydrous gypsum and hemihydrate gypsum. Gypsum is also preferred in that it produces calcium oxide when contacted with water.

  When the above components are too small, the formation of ettringite hydrate is hardly promoted sufficiently, and when the sauce is too small, not only calcium silicate hydrate but also ettringite hydrate is hardly formed. . For this reason, it is preferable that a sauce and the said component are added by the mass ratio of 3: 7-7: 3, More preferably, it is 4: 6-6: 4. Thereby, the production of ettringite hydrate and calcium silicate hydrate is improved in a well-balanced manner. However, the ratio of the source and the above components may be appropriately changed according to the inorganic components in the wet paint booth circulating water.

  If the source and the above components are too small relative to the solid content of the paint, it is difficult to obtain sufficient curing of the sludge, but it is uneconomical even if it is excessive. Therefore, the source and the above components are preferably added in a total amount of 5% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less, based on the solid content of the paint.

  The location where the ettringite hydrate and / or calcium silicate hydrate is present is not particularly limited, but may usually be a pipe before a floating separation apparatus described later or a circulating water tank. The former is preferable from the viewpoint of efficient sludge separation in the flotation separation apparatus, and the latter is preferable from the viewpoint of efficiently separating and collecting such sludge because the re-dispersed sludge tends to accumulate. The addition of the source and the above components is not particularly limited, and may be performed intermittently or continuously in the circulating water system once or twice a day. In addition, the sauce and the above components may be added at different times or locations, or may be mixed and added.

  Thereafter, the paint (sludge) is levitated and separated from water using a levitating separator. The flotation separation device may be a general pressurized flotation device. The separated and recovered sludge is subjected to incineration and landfill treatment after gravity dewatering or after dewatering by a normal method.

  The above-described method of the present invention is useful in the treatment of wet paint booth circulating water containing water-based paint, wet paint booth circulating water containing solvent-based paint, and wet paint booth circulating water containing water-based paint and solvent-based paint.

  The melamine / aldehyde acid colloid solution and the phenolic resin were used as solutions as follows.

  Methylolated melamine 0.05 mol obtained by reacting 2 mol of formaldehyde with 1 mol of melamine was added to 100 ml of 1.35% by mass hydrochloric acid aqueous solution and aged (hereinafter abbreviated as “M / F”). ).

  10 g of caustic soda and 150 g of pure water were placed in a beaker, heated to 70 ° C., and 40 g of novolac-type phenolic resin (manufactured by Gunei Chemical Co., Ltd.) “Resitop PSM 4324” was added and dissolved by stirring. .

  As the source, itaya-zeolite (manufactured by Sieglite) having a powder of 100 mesh or less was used. As the above component, anhydrous gypsum powder was used, and both were mixed at a mass ratio of 1: 1.

  In the comparative example, instead of the source and the above components, the conventionally known flocculant, Agent A: Cationic polymer “Glyfix DC302” (manufactured by Kurita Kogyo Co., Ltd.), and Agent B: Inorganic flocculant “Seviolite Miracle PV80 (Omi Mining Co., Ltd.) was used.

<Test example>
Using a test device with a retained water volume of 50 L, the circulating water volume was 100 L / min. The paint was sprayed for 20 minutes at a rate of 10 g / min. The drug is a melamine / aldehyde acid colloid solution, a solid sulfuric acid band (manufactured by Sumitomo Chemical Co., Ltd.), a phenolic resin, and a mixed powder of the source and the above components (flocculating agent in the comparative example) in the amounts shown in Table 1 Added. Then, the sludge is transferred to a cylinder containing 1 liter of water (distance 30 cm from the bottom of the cylinder to the water surface), and after 50 times of up and down shaking, the ratio of sludge rising to the total sludge and the sludge ascent rate are obtained. It was. In addition, the sludge that floated was collected and placed on a filter cloth for 1 hour, and then its water content was measured. The results are shown in Table 1. In addition, the quantity of the chemical | medical agent in Table 1 is the quantity with respect to the solid content of a coating material. The sludge ascent rate was calculated based on the time taken for almost all sludge in the water to rise to the surface.

[Water-based paint]
Top coating: “GWP-600” (manufactured by Nippon Paint)
Intermediate coating: “AR-2300” (manufactured by Nippon Paint)
[Solvent paint]
Clear paint: “OG173” (manufactured by Nippon Paint)

  As shown in Table 1, the comparative examples are the examples except that the mixed powder of the source and the above components is not used, or the melamine / aldehyde acid colloid solution or the sulfuric acid band and the phenol resin are not used. Is equivalent to And the Example had larger floating amount and speed | rate of sludge, and the moisture content was lower than any comparative example using the same coating material. Only by using all of the melamine / aldehyde acid colloidal solution or sulfuric acid band, the phenolic resin, the mixed powder of the source and the above components, the effect of improving the sludge flying height and speed, and reducing the water content Was found to be obtained. Table 2 also shows that the combination of the melamine / aldehyde acid colloidal solution or the sulfuric acid band and the phenolic resin produces the above-mentioned effects peculiar to the mixed powder of the source and the above components.

  Further, the floating sludge collected in Example 1 and Comparative Example 1 was observed with a scanning electron microscope according to a conventional method. The results are shown in FIGS. FIG. 1 (Example, magnification 2500 times) shows ettringite crystals that look like needles and calcium silicate crystals that look like thin plates, whereas FIG. 2 (Comparative example, magnification 1000 times) shows such crystals. Is not confirmed. As a result, ettringite hydrate and calcium silicate hydrate were present in the sludge of the example, but not present in the sludge of the comparative example. And the presence of calcium silicate hydrate.

Claims (10)

A method for treating circulating water in a wet paint booth containing paint,
Reducing the viscosity of the paint, and placing the wet paint booth circulating water in the presence of a phenolic resin and ettringite hydrate and / or calcium silicate hydrate, the paint from the wet paint booth circulating water A method having a step of separating.   The ettringite hydrate and / or calcium silicate hydrate is obtained by adding a source containing an oxide of one or more elements selected from the group consisting of calcium, silicon and aluminum to the wet paint booth circulating water. The method of claim 1 to generate.   The method of claim 2, wherein the source comprises incinerated ash and / or zeolite.   The method according to claim 3, wherein the incinerated ash contains 70 to 40% by mass of silicon dioxide, 25 to 10% of aluminum oxide, and 30 to 5% by mass of calcium oxide.   The method according to any one of claims 2 to 4, further comprising a step of further adding a component containing calcium sulfate to the wet paint booth circulating water.   The method of claim 5, wherein the component comprises gypsum.   The method according to claim 5 or 6, wherein the source and the component contain, in a total amount, 70 to 40% by mass of silicon dioxide, 25 to 10% of aluminum oxide, and 30 to 5% by mass of calcium oxide.   The method according to claim 5, wherein the source and the component are added in a mass ratio of 3: 7 to 7: 3.   The method according to any one of claims 2 to 8, wherein the source and the component are added in a total amount of 5% by mass or more and 20% by mass or less based on the solid content of the paint.   The method according to any one of claims 1 to 9, wherein the viscosity of the paint is reduced by adding a melamine / aldehyde acid colloid solution and / or an aluminum compound to the wet paint booth circulating water.