KR20020092462A - Method and device for treating contaminated coating compositions - Google Patents

Abstract

The present invention relates to a method of treating a liquid comprising an electrodepositable coating composition and contaminants. The method includes contacting at least a portion of the liquid with a filtration medium containing diatomaceous earth to separate at least some contaminants from the liquid.

Description

METHOD AND DEVICE FOR TREATING CONTAMINATED COATING COMPOSITIONS}

Electrodeposition is the primary method for the application of corrosion resistant primers in the automotive sector. Electrodeposition has the advantage of reducing raw material and waste disposal costs as well as providing improved paint utilization with improved corrosion resistance compared to non-mobile coating processes.

The electrodeposition process involves immersing an electrically conductive substrate in an electrocoating tank that receives a bath of an aqueous electrocoating composition, the substrate serving as a charged electrode in an electrical circuit comprising an electrode and an oppositely charged counter electrode. Sufficient current is applied between the electrodes to deposit a substantially continuous tacky film of the electrocoating composition on the surface of the electrically conductive substrate.

The electrocoated substrate is then transferred to a cleaning operation step of cleaning with an aqueous cleaning composition. Typical cleaning operation steps have several stages that may include closed loop spray and / or dip coating, described below. For example, in spray cleaning application, the electrocoated substrate exits the electrocoating tank and is transferred to the cleaning tank while spray applying an aqueous cleaning composition to the electrocoated surface of the substrate. Excess cleaning composition is drained from the substrate to the lower cleaning tank. The cleaning composition is then recycled to the spray device for subsequent spray application. In immersion cleaning application, the electrocoated substrate is transferred to an immersion tank to be immersed in the aqueous cleaning composition and subsequently transported with one or more spray cleaning applications as described above.

Recycling the coating or cleaning composition is desirable from an economic or environmental point of view. However, if the coating or cleaning composition is contaminated, the contaminants can adversely affect the quality and appearance of the electrodeposition coating. For example, contaminants can cause cratering or other unacceptable defects in the cured coating.

Accordingly, it is desirable to provide a method and apparatus for removing contaminants from an electrodeposition coating composition and / or a cleaning composition in order to provide a smooth electrodeposition coating having a good appearance.

Summary of the Invention

The present invention provides a method for treating a liquid comprising the electrodepositable coating composition and contaminants. Such methods include contacting at least some of the liquid with a filtration medium comprising diatomaceous earth to separate at least some of the contaminants from the liquid.

The invention also provides a method of treating a liquid comprising a topcoat composition and contaminants, said method comprising contacting at least a portion of said liquid with a filtration medium comprising diatomaceous earth to separate at least some contaminants from the liquid. .

The invention also provides an electrodeposition coating system comprising a coating tank containing a liquid electrodepositable coating composition and one or more cleaning tanks containing the liquid cleaning composition. The at least one coating composition and the cleaning composition further comprise contaminants and the at least one filtering device is in fluid communication with the at least one coating tank and at least one cleaning tank. The filtration device includes diatomaceous earth. Liquid from one or more of the tanks is filtered through a filtration device to remove at least some contaminants from the liquid.

The invention also provides a liquid electrocoating bath comprising (a) a dendritic material that can be deposited on a cathode to form a coating, and (b) contaminants that can form defects on the surface of the coating deposited from a liquid electrocoating bath. It provides an electrodeposition coating system comprising. The filtration medium is in fluid communication with the bath. The filtration medium includes diatomaceous earth. The liquid from the bath is filtered through a filtration medium to remove at least some contaminants from the liquid.

The invention also provides a liquid electrocoat comprising (a) a dendritic material that can be deposited on an anode or cathode to form a coating and (b) a contaminant that can form defects on the surface of the coating deposited from a liquid electrocoat bath. Provide a way to deal with swearing. The method comprises the steps of (a) removing at least some liquid from the electrocoated bath; (b) contacting at least a portion of the liquid removed from the electrocoat bath with a filtration medium comprising diatomaceous earth to remove at least some contaminants from the liquid; And (c) returning at least a portion of the filtered liquid to the bath.

The present invention generally relates to electrodeposition processes, and more particularly to methods and apparatus for treating contaminated electrodepositable coating compositions to provide an electrocoated substrate having good smoothness and appearance.

The summary of the invention and the following detailed description will be better understood with reference to the accompanying drawings.

1 is a process diagram schematically illustrating a process according to the present invention comprising applying an electrodepositable coating composition to an electrically conductive substrate, cleaning the coated substrate, and treating the contaminated coating and / or cleaning composition to remove contaminants. to be.

FIG. 2 is a graph showing the number of craters produced on a coated substrate versus the number of times the coating composition used to make the coating was filtered through a diatomaceous earth containing filtration device.

It is to be understood that the components, reaction conditions, and amounts used in the specification and claims may all be modified by the term “about”, in addition to the operating examples or unless otherwise indicated. Also, as used herein, the term "polymer" refers to oligomers, homopolymers and copolymers. Molecular weight is an amount that can be determined from gel permeation chromatography using polystyrene as a standard, regardless of Mn or Mw.

The method and apparatus for treating the contaminated aqueous electrodepositable coating composition and / or cleaning composition of the present invention will be described with reference to a continuous automotive electrocoating and cleaning process, but those skilled in the art are not limited thereto. It will be appreciated that it may be used as a discontinuous, for example semi-continuous or indexing process, or batch process.

In FIG. 1, like reference numerals denote similar components and include the application of an electrodepositable coating composition to an electrically conductive substrate, cleaning the coated substrate, and treating contaminated coating and / or cleaning compositions. A schematic process diagram is shown. In a continuous process, the substrate is moved continuously along the assembly line.

Useful electrically conductive substrates that can be coated include metallic materials such as iron metals such as iron, steel and alloys thereof; Nonferrous metals such as aluminum, zinc, magnesium and alloys thereof; And those formed from combinations thereof. Preferably, the substrate is formed from cold rolled steel, galvanized steel, for example hot-dip galvanized steel, hot-dip galvanized or electro-zinc-iron coated steel, aluminum or magnesium.

The electrically conductive substrate is preferably used as a component for manufacturing vehicles such as automobiles, trucks and tractors, but is not limited thereto. The electrically conductive substrate may have any shape, but is preferably in the form of parts for automobile bodies such as automobile bodies (frames), hoods, doors, fenders, bumpers and / or trims. Firstly, a coating system incorporating the concept of the present invention will be discussed in the context of covering metallic vehicle bodies. Those skilled in the art will appreciate that the coating process incorporating the present invention is also useful for coating electrically conductive parts other than automobiles.

In the electrodeposition portion 12 of the process 10 of FIG. 1, the liquid electrodepositable coating composition is immersed, for example, by immersing the vehicle body 18 in a container or bath 22 containing the liquid electrodepositable coating composition 14. 14 is applied to the surface 16 of the electrically conductive vehicle body 18 in a first step 20. The liquid electrodepositable coating composition 14 may be applied to the surface 16 of the vehicle body 18 by any suitable anionic or cationic electrodeposition process known to those skilled in the art.

In the cationic electrodeposition process, the liquid electrodepositable coating composition 14 is disposed in contact with an electroconductive anode 24 and an electroconductive cathode (electroconductive surface 16 of the vehicle body 18). After contact with the liquid electrodepositable coating composition 14, when sufficient voltage is applied between the electrodes, an adhesive film 26 of the coating composition is deposited on the vehicle body 18. The conditions under which electrodeposition is carried out are generally similar to those used for electrodeposition of other coatings. The applied voltage can vary, for example from 1 volt to several thousand volts, typically from 50 to 500 volts. Current densities generally range from 0.5 to 15 Am / ft ² and tend to decrease during electrodeposition, indicating the formation of an insulating film.

Suitable electrodepositable coating compositions can be supplied as two components. For example, (1) a transparent resin feed, which may include one or more deposition materials (ionic electrodepositable resins), crosslinking materials, and any additional water dispersible, non-colored components; And (2) one or more pigments, water dispersible pulverizing resin which may be the same film forming material as in the transparent resin feed or chemically different film forming materials as described below, and optionally additives such as wetting aids or dispersing aids. The pigment paste which can be included is mentioned. The electrodeposition bath components (1) and (2) are dispersed in an aqueous medium which may comprise a mixture of coalescing solvent and water.

The electrodepositable coating composition may comprise one or more deposition materials and a crosslinker. Suitable film forming materials include epoxy functional film forming materials, polyurethane film forming materials and acrylic film forming materials. The amount of deposition material in the electrodepositable composition is generally from about 50 to about 95 weight percent based on the total weight of solids of the electrodepositable composition.

Suitable epoxy functional materials contain one or more epoxy or oxirane groups in the molecule. For example, di- or polyglycidyl ethers of polyhydric alcohols. Preferably, the epoxy functional material contains at least two epoxy groups per molecule. Useful polyglycidyl ethers of polyhydric alcohols include epihalohydrins such as epichlorohydrin and polyhydric alcohols such as dihydric alcohols in the presence of alkali condensation and hydrogen halide reaction catalysts, for example sodium or potassium hydroxide. It can be formed by reacting.

Suitable epoxy functional materials can have an epoxy equivalent weight range of about 100 to about 2000 when measured by titration with perchloric acid using methyl violet as an indicator. Useful polyepoxides are disclosed in US Pat. No. 5,820,987, US Pat. Nos. 52, 6 to 59, which are incorporated herein by reference. Examples of suitable commercially available epoxy functional materials are EPON, registered by Shell Chemical Company as epoxy functional polyglycidyl ethers of bisphenol A prepared from bisphenol A and epichlorohydrin. Trademarks) 828 and 880 epoxy resins.

Epoxy functional materials are either primary or secondary amines that can react with epoxy groups to be acidified to form amine salt groups, or 3 that can be acidified before reacting with epoxy groups to form quaternary ammonium salt groups after reacting with epoxy groups. It can react with amines that form cationic bases, such as tertiary amines. Other useful cationic salt group formers include sulfides.

Suitable acrylic functional materials include polymers derived from alkyl esters of acrylic and methacrylic acid as disclosed in US Pat. Nos. 3,455,806 and 3,928,157, which are incorporated herein by reference.

Examples of film forming resins suitable for anionic electrodeposition include reaction products or addition products of base-solubilizing carboxylic acid containing polymers such as dicarboxylic acids or anhydrides with anhydrous oils or semi-anhydrous fatty acid esters; And reaction products of fatty acid esters, unsaturated acids or anhydrides with any additional unsaturated modifiers that further react with the polyols. Also suitable are at least partially neutralized interpolymers of hydroxy-alkyl esters of unsaturated carboxylic acids, unsaturated carboxylic acids and one or more other ethylenically unsaturated monomers. Other suitable electrodepositable resins include alkyd-aminoplast vehicles, ie vehicles containing mixed esters of alkyd resins with amine-aldehyde resins or dendritic polyols. Such compositions are described in detail in US Pat. Nos. 3,749,657, column 9, lines 1 to 75, and column 10, lines 1 to 13, which are incorporated herein by reference. In addition, as the other acid functional polymers, acid functional polymers such as phosphatylated polyepoxides or phosphatylated acrylic polymers known to those skilled in the art may be used.

Useful crosslinking materials include aromatic diisocyanates such as p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate and 2,4- or 2,6-toluene diisocyanate; Aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate and 1,6-hexamethylene diisocyanate or dimers or trimers thereof; And blocked or unblocked polyisocyanates including alicyclic diisocyanates such as isophorone diisocyanate and 4,4'-methylene-bis (cyclohexyl isocyanate). Examples of suitable blocking agents for polyisocyanates include lower aliphatic alcohols such as methanol, oximes such as methyl ethyl ketoxime, and lactams such as caprolactam. The amount of crosslinking material in the electrodepositable coating composition is generally about 5 to about 50 weight percent based on the weight of the total resin solids of the electrodepositable coating composition.

Generally, the electrodepositable coating composition also includes one or more pigments that can be incorporated in the form of pastes; Water-dispersible, non-colored components such as surfactants and wetting agents; catalyst; Membrane building additives; Leveling agents; Antifoam; Microgels; pH adjusting additives; And volatiles such as water, organic solvents and low molecular weight acids (as described in US Pat. No. 5,820,987, column 9, line 13 to column 10, line 27, incorporated herein by reference).

Suitable pigments include iron oxide, strontium chromate, carbon black, pulverized coal, titanium dioxide, talc, barium sulphate, cadmium yellow, cadmium red, chromium yellow and the like. The pigment content of the dispersion is generally expressed as the pigment to resin ratio. When pigments are used, the ratio of pigment to resin is preferably about 0.02 to 1: 1. The other additives described above are generally from about 0.01 to about 10% by weight, preferably from about 0.1 to about 3% by weight, based on the weight of the resin solids in the dispersion.

Useful solvents included in the coating composition in addition to any of the components provided for other coating components include coalescing solvents such as hydrocarbons, alcohols, esters, ethers, glycol ethers, and ketones. Preferred coalescing solvents include alcohols, polyols, ethers and ketones. Non-limiting examples of suitable solvents include isopropanol, butanol, 2-ethylhexanol, isophorone, 4-methoxy-2-pentanone, ethylene glycol, propylene glycol, and monoethyl, monobutyl and monohexyl ethers of ethylene glycol Included. Generally the amount of coalescing solvent is from 0.01 to 25% by weight, preferably from 0.05 to 5% by weight, based on the total weight of the electrodepositable coating composition.

Other useful electrodepositable coating compositions are disclosed in US Pat. No. 4,891,111, US Pat. No. 4,933,056 and US Pat. No. 5,760,107, which are incorporated herein by reference.

Suitable electrodepositable compositions are preferably in the form of aqueous dispersions. As used herein, "dispersion" means a two-phase dendritic system that is transparent, translucent or opaque, where the resin is a dispersed phase and water is a continuous phase. The average particle diameter of the dendritic phase is generally less than 1.0 μm, generally less than 0.5 μm, preferably less than 0.15 μm.

The concentration of the dendritic phase in the aqueous medium is at least 1% by weight, generally 2 to 60% by weight, based on the total weight of the aqueous dispersion (electrode bath). When the electrodepositable compositions are in the form of resin concentrates, the content of these resin solids is generally 20 to 60% by weight, based on the weight of the aqueous dispersion.

The thickness of the electrodepositable coating applied to the substrate will vary depending on factors such as the type of substrate and the intended use of the substrate, namely the environment in which the substrate is placed and the nature of the contact material. Generally, the thickness of the electrodepositable coating applied to the substrate is about 5 to about 50 mu m, more preferably about 12 to about 40 mu m.

The coating composition in the bath 22 may be recycled in a conventional manner, such as in a recycling system 13 with a pump that inhibits the settling of solids of the coating composition into the bottom portion of the bath 22. In addition, the temperature of the electrodepositable coating composition may be controlled by the use of a heat exchanger 28 in fluid communication with the bath 22 by any conventional means, such as a pipe or conduit.

Before or after the operation, the electrodeposition coating in the bath 22 may be contaminated with one or more materials that may deposit and adversely affect the quality of the cured coating. Such materials are generally referred to as "contaminants". Examples of such contaminants include silicones and petroleum lubricants such as molding lubricants and mill oils.

If such contamination occurs, the coating composition must be cleaned. In other words, contaminants must be removed. In the practice of the present invention, the cleaning step of the coating composition is carried out using a filtration device 100 in fluid communication with the bath 22, for example by conduits or pipes. Filtration device 100 comprises a housing having an at least partially hollow inner chamber. Filter media, for example activated carbon, conventional planarizing agents, for example polyester leveling agents, or most preferably filter media comprising diatomaceous earth are arranged to be removable in the housing chamber. Diatomaceous earth suitable for carrying out the invention is commercially available under the name Hyflo Super Cel diatomaceous earth from Celite Corporation. Diatomaceous earth is a soft bulky solid material, typically comprising about 88% by weight of silica and as disclosed in Hawley's Condensed Chemical Dictionary at page 365 (12 ^th ED. 1993), incorporated herein by reference, Consists of the skeleton of small prehistoric aquatic plants associated with algae.

Although not intended to be limiting, diatomaceous earth filtration media may be supported on a support such as, for example, a wire or metal mesh screen in a housing. Contaminated coating, such as conventional filter paper or conventional filtration cloth, such as polypropylene filtration cloth or 10 μm filtration cloth commercially available from American Felt & Filter Co. It is possible to prevent the filtration material from moving out of the housing during filtration of the composition. The content of diatomaceous earth in the filtration device 100 is less than about 1% by weight, more preferably less than about 0.1% by weight, even more preferably from about 0.01% to about 0.1, based on the total weight of the bath coating composition to be cleaned. Weight percent.

In the practice of the present invention, when the coating composition in the bath 22 is contaminated with contaminants that adversely affect the quality of the deposited coating, at least some of the contaminated coating composition is removed from the electrodeposition bath 22 by, for example, a pump. And, for example, contact with a flow through the diatomaceous earth filtration medium in the filtration device 100 to remove at least some of the contaminants from the coating composition. This filtered coating composition can then be reintroduced into the bath 22 by conventional means such as conduits or pipes. After a selected period of time determined by the type of contaminant and the degree of contamination, the diatomaceous earth filtration medium in the filtration device 100 can be removed and replaced with fresh diatomaceous earth. For example, but not by way of limitation, the filtration material is about 1 to about 100 turnsover, preferably about 1 to about 50 turns, more preferably about 1 to about 25 turns, even more preferably about It may be replaced after 1 to about 10 revolutions. As discussed in more detail in the Examples below, "rotating" refers to the number of times a volume of material is pumped, filtered and reintroduced from the bath 22 equivalent to the total starting volume of the coating composition in the bath 22. do. During this cleaning operation, part of the coating composition from the electrodeposition bath 22 is removed, preferably constantly removed, filtered and recycled to the coating composition remaining in the electrodeposition bath 22.

In addition, the electrodepositable coating composition from the bath is in fluid communication with a conventional ultrafiltration system 30 to remove soluble impurities (ultrafiltration 32) and the filtered material is recycled to the electrodeposition bath 22. In the ultrafiltration system 30, the coating composition flows through a membrane that is permeable to small particles (eg, less than about 1,000 Mw), such as water, and salts. A portion of the "permeate" 32, ie, the coating composition, passing through the membrane can be used for further cleaning operations, and a portion of the permeate, for example about 20% by weight, can be discarded. A "non-permeable" portion of the coating composition is directed back to the bath 22, for example, through one or more conduits or pipes.

During normal operating conditions where the electrocoating composition is not contaminated, the coating composition may be bypassed to allow the coating composition to simply flow through the ultrafiltration device 30 and back to the bath 22. For example, separation valves 102 and 104 or any other conventional means may be used to separate filtration device 100 from the flow of coating composition from bath 22. When the coating material passes through the filtration device 100, the separation valves 102 and 104 can be opened and the coating or blocking the throttling valve or bypass valve 105 of the main line is closed or pressed. At least a portion of the composition may be flowed through filtration device 100.

In addition, after cleaning the first electrical coating as described below, the second electrodepositable coating may be applied to the surface of the dried electrical coating. The second electrodepositable coating may be applied in a similar manner as described above to deposit the first electrodepositable coating.

The second electrodepositable coating may be the same or different than the first electrodepositable coating. For example, individual components (eg, deposition materials) of the second electrodepositable coating may be altered or the amount of each component may be varied as the case may be. Suitable components of the second electrodepositable coating include materials described above as being suitable for the first electrodepositable coating. Preferably, the first electrodepositable coating comprises an epoxy functional film forming material and a polyisocyanate crosslinking material to provide corrosion resistance, and the second electrodepositable coating is acrylic or polyurethane, preferably polyurethane, film forming material and poly. Isocyanate crosslinking materials are included to provide chip impact resistance to stones and road debris, and to UV light, which can cause photolysis and loss of adhesion of the coating to the substrate.

The electrocoated car body 34 is transferred from the electrocoated bath 22 and then exposed to air to drain excess of the electrodeposited coating composition from the interior cavity and surface 18 of the car body. The electrically covered vehicle body 34 is then transferred to a cleaning process 35 to remove excess electrodepositable coating from the vehicle body 34. The cleaning process may optionally include one or more spraying and / or immersion cleaning processes. Preferably, the electroformed vehicle body 34 is transferred to a spray cleaning tank 36 to spray apply a first cleaning composition 38 to the coated surface 40 of the electrocoated vehicle body 34. . Excess spray composition is drained to the wash tank 36 below to be recycled by the recirculation system 110 and subsequent spray recoating. When the cleaning composition is contaminated in a manner similar to that described above for treating the electrodepositable coating composition, the filtration apparatus 100 of the present invention containing the diatomaceous earth filtration medium to remove contaminants from the cleaning composition is treated with the recirculation system 110. Fluid communication is possible.

Since the cleaning composition is typically recycled, it may comprise a small amount of the electrodepositable coating composition as described above.

After the spray cleaning step, an immersion cleaning step may be performed in which the electrocoated vehicle body 34 is transferred to the cleaning immersion tank 42 and immersed in the aqueous cleaning composition 44 contained therein. The electrocoated car body 34 is then transferred out of the cleaning dip tank 42 and the excess cleaning composition is drained back into the tank for reuse. The aqueous cleaning composition 44 used for the immersion cleaning may have the same or different components as the first cleaning composition 38 described above, but preferably has the same components as the first cleaning composition 38.

After the immersion cleaning step, one or more spray applications, transferring the electrocoated car body 34 to subsequent spray cleaning tanks 46, 48 and spray applying the aqueous cleaning composition 50, 52 as described above. A cleaning step can be performed. The drainage period of each cleaning step is preferably at least 1 minute so that no standing water is present in the final cleaning composition. During the drainage period, the temperature is preferably from about 10 ° C to about 40 ° C.

The invention will be further described with reference to the following examples. The following examples are intended to illustrate the invention and are not intended to limit the invention thereto. Unless otherwise indicated, all parts and percentages in this specification and the examples below are based on weight.

Example 1

This example illustrates the use of diatomaceous earth to filter the contaminated electrodepositable polyurethane coating composition.

Filter housings or cells were made from 1 inch diameter cylindrical PVC (polyvinylchloride) pipe unions (available from Plotkin Brothers Supply Co. Inc., Pittsburgh, PA). . If the outer ring of the union is not clamped, a passage into the cavity is provided, the bottom portion of which has a capacity to accommodate about 10 cm 3 of diatomaceous earth filter media filter media.

A stainless steel screen (stainless steel wire, 15 mesh, with a diameter of about 0.024 inch) was transferred to a 10 μm filtration cloth (American Felt & Filter Co., Newburgh, NY). (So ~ Clean) 10 μm filter bags) were placed in the filter cell to hold 2.18 g of diatomaceous earth filter media.

Masterflex metering pumps (available as models 7518-12 L / S available at Cole-Parmer Instrument Co., Vernon Hills, Ill.) And Tygon LFL piping The contaminated electrocoating composition was pumped from 2 liters of bath to the filter medium in the cell, ie diatomaceous earth, and returned to the electrocoating bath, with the turnover rate varied from 8 to 18 minutes per revolution. The term " turnover rate " means the time taken to pump 2 liters of bath (i.e., volume of starting material in the bath) all through the filter cell out of the bath and back into the bath. Since the pump draws both contaminated and previously filtered material out of the bath, it is expected that a large number of revolutions will be required to remove contaminants from the bath.

As an example of the rotational calculation, the speed setting of the metering pump was set to 1.6 and 112.6 g of the coating composition was pumped from the bath into the beaker for 30 seconds. It took 9.8 minutes to pump 2200 g of the total amount of electrocoating composition through the system. Pumping and circulating the 2200 g for 40 minutes means that 4.1 revolutions have occurred (40 / 9.8). Since the electric coating bath contained 12% of the solids and the bath density was about 1.0 g / cm 3, the weight (g) of the bath was considered to be a volume (cm 3).

The contaminated electrocoating composition was a contaminated ED-8100 coating composition (cationic polyurethane electrocoating composition available from PPG Industries, Pittsburgh, Pennsylvania) during the operation of the electrocoating system. Metallic test panels (phosphorylated cold rolled steel panels, commercially available from ACT Laboratories, Inc., ILL Laboratories, Inc., product number APR10739 (A)) were electrocoated and conventionally coated. After baking in a manner (baking at 350 ° F. for 20 minutes) to form a dry film of about 1.4 mils (35 μm) thick, the tested ED-8100 was fabricated in an area of 4 inches by 6 inches in the coated panel. Some 505 "craters" are so contaminated. Craters are paint defects with circular depressions, often accompanied by rises in edges at the periphery of the depressions. The size of the craters can vary, but in this case, they have a diameter of about 1 to 2 mm.

A filter cell containing 2200 grams of contaminated ED-8100 coating composition containing 2.18 grams of diatomaceous earth (Hiflo Super-Cell Diatomaceous Earth, commercially available from Celite Corporation) (0.1% by weight of the material in the electric coating bath) as described above. Circulated through. After 60 revolutions, the craters per 4 inch by 6 inch area of the coated test panel were originally reduced from number 505 to 140. The first part of diatomaceous earth was removed and replaced with 2.2 g of a second fresh diatomaceous earth. After another 17 revolutions, there were 49 craters per 4 inch by 6 inch area of the coated test panel. The second part of diatomaceous earth was removed and replaced with 2.2 g of diatomaceous earth of the third part. After another eight revolutions, only one crater was present for the 4 inch by 6 inch area of the coated test panel. Even new, uncontaminated electrocoated baths can often have membrane defects, so the baths were considered decontaminated. Figure 2 summarizes the results of removing contaminants in the electrocoated bath by filtration through diatomaceous earth.

To confirm the presence of contaminants, test panels coated with samples of contaminated ED-8100 and uncontaminated ED-8100 coating compositions were used with a Time of Flight Secondary Ion Spectroscopy (TOF-SIMS). The analysis was carried out. In this technique, it is known that when a TOF-SIMS ion beam is probed into polydimethylsiloxane, secondary ions are removed at a ratio of mass to charge of 281, 221 and 207. The peak of the TOF-SIMS spectrum with this charge to mass ratio is evidence of the presence of polydimethylsiloxane (silicon). Each of the electrocoated compositions was deposited on a test panel as described above at a thickness of about 1.4 mils (35 μm) and baked at about 200 ° F. for 5 to 10 minutes to form a crater without risk of degrading or significantly losing contaminants. I was. The following electrocoating compositions were analyzed: A) a new uncontaminated ED-8100 coating composition, B) the above contaminated (uncleaned) ED-8100 coating composition and C) DC-200 polydimethylsiloxane (Dow Corning New ED-8100 coating composition with Mn of 9000 deliberately contaminated with 1 ppb of Corporation (Dow Corning Corporation.) In Bath A, the TOF-SIMS spectrum peaks at a ratio of mass to charge of 281, 221 or 207. In baths B and C, distinct peaks were observed at mass-to-charge ratios 281, 221 and 207. The peaks indicated that silicon was present at approximately the same intensity in the TOF-SIMS spectra of B and C. Thus, it can be concluded from the result of the TOF-SIMS test that the sample (B) is contaminated with polydimethylsiloxane or silicone.

Example 2

In a further test of the ability of diatomaceous earth to remove contaminants (eg, silicon contaminants) from an electrocoat bath, the new ED-8100 coating composition was subjected to Dow Corning Antifoam 1500 antifoam (silicone containing antifoam). Intentionally contaminated with 0.1% by weight. The phosphorylated steel test panel was electrocoated with the contaminated coating composition as described above and baked at 350 ° F. for 20 minutes as described above to form a dry coating of about 1.4 mils (35 μm) thick, followed by A number of craters were formed on the panels, indicating that more than 100 craters were generated per test panel. 1960 g of the coating composition was pumped and recycled through a cell similar to the above except that a PVC union designed with a 2 inch diameter PVC pipe was used. The filter cavity was filled with 23.1 g of diatomaceous earth and the bath material was recycled through the filter. After fifteen revolutions, the similarly coated and baked panels were essentially free of craters and contained only defects that occurred temporarily in a typical non-contaminated electric coating bath.

It will be apparent to those skilled in the art that changes to the embodiments of the invention described above are possible without departing from the concept of the invention. Therefore, it is to be understood that the invention is not limited to the specific embodiments disclosed and that modifications within the spirit and scope of the invention as defined in the appended claims also fall within the invention.

Claims (21)

A method of treating a liquid comprising an electrodepositable coating composition and contaminants, (a) contacting at least a portion of the liquid with a filtration medium comprising diatomaceous earth to separate at least some contaminants from the liquid. The method of claim 1, And wherein the coating composition comprises a dendritic material. The method of claim 1, A process wherein liquid is used as a coating in an electrodeposition coating process. The method of claim 1, Wherein the liquid is an electrodepositable coating composition located in a coating tank. The method of claim 4, wherein The treatment method wherein the coating composition is water-based. The method of claim 1, Wherein the liquid is a cleaning composition located in the cleaning tank. The method of claim 6, The treatment method in which the cleaning composition is aqueous. The method of claim 1, Liquid is present in the container, and (b) removing the liquid from the container before contacting the liquid with the filtration medium; And (c) contacting the liquid with a filtration medium and then re-adding the filtered liquid to the container. The method of claim 1, And wherein the amount of diatomaceous earth is less than about 1 weight percent of the weight of the liquid in the vessel. The method of claim 1, And wherein the amount of diatomaceous earth is less than about 0.1 weight percent of the weight of the liquid in the vessel. A method of treating a liquid comprising a topcoat composition and a contaminant, (a) contacting at least a portion of the liquid with a filtration medium comprising diatomaceous earth to separate at least some contaminants from the liquid. A coating tank containing the liquid electrodepositable coating composition; One or more cleaning tanks containing the liquid cleaning composition; And At least one filtration device in fluid communication with at least one of said cladding and cleaning tanks, At least one of the coating composition and the cleaning composition further comprises a contaminant, The filtration device comprises diatomaceous earth, Liquid from one or more of the tanks is filtered through a filtration device to remove at least some contaminants from the liquid. Electrodeposition coating system. The method of claim 12, Electrodeposition coating system, which is an automotive coating system. The method of claim 12, Electrodeposition coating system selected from the group consisting of continuous, indexing semi-continuous and batch electrodeposition coating systems. The method of claim 12, An electrodeposition coating system wherein the coating composition comprises a dendritic material. The method of claim 12, Electrodeposition coating system wherein the coating composition is water-based. The method of claim 12, Electrodeposition coating system wherein the liquid is an aqueous coating composition and the container is a coating tank. The method of claim 12, An electrodeposition coating system wherein the liquid is an aqueous cleaning composition and the container is a cleaning tank. a liquid electrocoating bath comprising (a) a dendritic material that adheres to a substrate to form a coating and (b) contaminants that can form defects on the surface of the coating deposited from the liquid electrocoating bath; And A filtration medium in fluid communication with the bath, The filtration medium comprises diatomaceous earth, The liquid from the bath is filtered through a filtration medium to remove at least some contaminants from the liquid. Electrodeposition coating system. A method of treating a liquid electrocoating bath comprising a dendritic material capable of being deposited on a substrate to form a coating and contaminants capable of forming defects on the surface of the coating deposited from the liquid electrocoating bath, the method comprising: (a) removing at least a portion of the liquid from the liquid electrocoat bath; (b) contacting at least a portion of the liquid removed from the electrocoat bath with a filtration medium comprising diatomaceous earth to remove at least some contaminants from the liquid; And (c) returning at least a portion of the filtered liquid to the bath Treatment method. A method of treating a liquid comprising an electrodepositable coating composition and contaminants, (a) contacting at least a portion of the liquid with a filtration medium selected from the group consisting of activated carbon, planarizer and diatomaceous earth to separate at least some contaminants from the liquid.