JP2010529281A - Electrodeposition bath containing a mixture of a boron-containing compound and chlorhexidine - Google Patents

Abstract

  In order to control the growth of microorganisms in an electrodeposition bath, an electrodeposition bath comprising a mixture of (i) at least one boron-containing compound and (ii) chlorhexidine is disclosed. Combining (i) and (ii) at low concentrations provides better microbial control than either (i) or (ii) at higher concentrations.

Description

  The present invention relates to an improved electrodeposition method. More particularly, the present invention relates to an improved electrodeposition bath comprising a mixture of at least one boron-containing compound and chlorhexidine.

  Electrodeposition as a coating method is becoming increasingly important in the coating industry. Worldwide, over 80% of all manufactured vehicles are primed by cationic electrodeposition.

  Compared to coating means other than electrophoresis, electrodeposition provides the advantages of increased paint utilization, improved corrosion protection and relatively low environmental pollution. (1) Electrodepositable coating compositions contain only very small amounts of organic solvents, and (2) downstream processes such as closed loop rinses reduce the loss of coating components to the surrounding environment during coating application. Electrodeposition generally provides an environmental advantage because it can be minimized.

  Electrodeposition methods are well known and involve immersing an electrically conductive substrate (ie, a workpiece) in a bath of an aqueous electrocoating composition. In the case of a cationic electrocoating composition, the workpiece is used as the cathode. After electrodeposition of the coating onto the workpiece, the electrocoated substrate is rinsed with an aqueous rinsing composition.

  A typical rinse operation has multiple stages that may include closed loop spraying and / or dip coating. Such rinsing methods are well known for electrocoating methods, but for the sake of clarity, closed-loop spraying methods use deionized water or reverse osmosis water to spray the surface from the substrate. Excess electrocoating material is removed. In dip coating, excess electrocoating material is removed from the substrate by immersing the substrate in a tank of deionized or reverse osmosis water. The rinse composition is recyclable and reusable. In a typical electrocoating operation, the electrodeposition bath is filtered through an ultrafilter to remove ionic contaminants, and the ultrafiltrate is used in a rinse operation.

  It is economically and environmentally desirable to recycle the coating or rinse composition. However, recycling of the aqueous coating or rinse composition can create an environment that promotes the growth of microorganisms such as algae, fungi and bacteria. Microorganisms can adversely affect the quality and appearance of the electrodeposited coating. In addition, the presence of microorganisms in the electrocoating or rinsing composition may result in the formation of sediment in the tank and process parameters such as pH, conductivity, film build, throwpower (ie , The rate of film deposition relative to the position of the anode) and stability changes can be caused. Also, “dirt” deposition of particulates and biofouling can occur, thereby adversely affecting the appearance of the applied coating and reducing system efficiency.

  In early electrodeposition methods, the “ultrafiltrate” used in the rinse step typically contained solvents, heavy metals and other organic materials that helped control the growth of the microorganisms described above. However, the reduction of volatile organic compounds (VOCs), harmful air pollutants (HAPs), and environmentally undesirable components such as heavy metals such as lead and chromium results in an outbreak of bacteria.

  Several compounds are known for controlling bacterial growth in electrodeposition baths that are free of heavy metals and have a low organic solvent content. For example, silver ions and antioxidants such as hydrogen peroxide and calcium hypochlorite are utilized. However, silver ions are expensive and can form stains in the electrodeposition bath. Oxidizing agents may oxidize the organic components of the electrodepositable composition.

  A microbicide composition comprising a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one is a coating composition free of this microbicide. May cause a rougher appearance. In addition, such microbicide compositions can contain metal salts such as magnesium nitrate and magnesium chloride, which can cause coating defects due to gas evolution at the cathode. The use of microbicides can be inconvenient and they can lose effectiveness over time. In addition, some microbicides require special handling and disposal.

  Halonitroalkanes can adversely affect the appearance of the applied coating and can contribute to the corrosion of metal parts.

  U.S. Pat. No. 4,732,905 discloses a composition used to control microbial growth in aqueous systems. US Pat. No. 6,017,431 discloses the use of sulfamic acid in an electrodeposition bath. U.S. Pat. Nos. 3,937,679, 3,959,106, 3,975,346 and 4,001,101 include quaternary The use of boric acid as a solubilizer for ion group-containing film-forming resins having onium bases such as ammonium groups and ternary sulfonium groups is disclosed. U.S. Pat. No. 4,443,569 discloses cathodic electrodeposition based on a nitrogenous base-containing binder containing a tertiary amino group, a primary and / or secondary hydroxyl group, and a metal compound. A composition is disclosed. US 2003/0033248 discloses an improved electrodeposition bath containing boric acid.

  In view of the above, there is a need for an electrodeposition bath that resists biodegradation that is free of heavy metals, has low or no VOC, while maintaining excellent coating application conditions, coating appearance and functional properties To do. It is also desirable to eliminate the need to handle toxic microbicides often used in electrodeposition baths neutralized with organic acids.

  The present invention provides an electrodeposition bath with improved microbial resistance. This improvement is due to the fact that chlorhexidine and an effective amount of a boron-containing compound selected from boric acid, boric acid equivalents and mixtures thereof can be used for the growth of microorganisms in an electrodeposition bath compared to the growth of microorganisms in the absence of said components. In the electrodeposition bath in an amount sufficient to delay The electrodeposition bath comprises an aqueous dispersion of an aqueous carrier and a film forming binder. The film-forming binder comprises an epoxyamine adduct and a blocked isocyanate.

  Unless stated otherwise or otherwise, numerical range limits or numerical parameters specified herein are approximations. Range limits used in the description and / or claims should be construed as modified by the term “about”. Slight differences above and below the stated range limits do not necessarily depart from the intended scope of operation of the present invention. The ranges provided herein are continuous and are understood to incorporate any or all of the values within the stated range limits unless the value is specifically or specifically excluded. The As such, any value within the specified range is trusted as that value is individually and specifically described herein.

  It has been found that adding a mixture of chlorhexidine and a boron-containing compound to the electrodeposition bath provides a level of microbial protection that is superior to using either compound individually at higher concentrations. Such results are unexpected and, more surprisingly, the use of boron-containing compounds and chlorhexidine in amounts effective to reduce microbial growth in the electrodeposition baths described herein can Can be achieved without loss of important process parameters such as pH and conductivity.

Suitable boron-containing compounds include those selected from boric acid, boric acid equivalents, and mixtures thereof. As used herein and in the claims, “boric acid equivalent” means any of a number of boron-containing compounds that can be hydrolyzed in an aqueous medium to form boric acid. Specific and non-limiting examples of boric acid equivalents include boron oxides such as B ₂ O ₃ , boric acid esters such as those obtained by reaction of boric acid with alcohols or phenols such as trimethyl borate, Triethyl borate, tri-n-propyl borate, tri-n-butyl borate, triphenyl borate, triisopropyl borate, tri-t-amyl borate, tri-2-cyclohexylcyclohexyl borate, triborate Examples include ethanolamine, triisopropylamine borate, and triisopropanolamine borate. In addition, amino-containing borates and tertiary amine salts of boric acid are also useful. Such boron-containing compounds include, but are not limited to, 2- (beta-dimethylaminoisopropoxy) -4,5-dimethyl-1,3,2-dioxaborolane, 2- (beta-diethylaminoethoxy) -4,4 , 6-trimethyl-1,3,2-dioxaborinane, 2- (beta-dimethylaminoethoxy) -4,4,6-trimethyl-1,3,2-dioxaborinane, 2- (beta-diisopropylaminoethoxy-1, 3,2-dioxaborinane, 2- (beta-dibutylaminoethoxy) -4-methyl-1,3,2-dioxaborinane, 2- (gamma-dimethylaminopropoxy) -1,3,6,9-tetraoxa-2- Boracycloundecane and 2- (beta-dimethylaminoethoxy) -4,4- (4-hydroxybutyl) 1,3,2-dioxaborolane.Boric acid equivalents also include metal salts of boric acid (ie, metal borate), although such metal borate is readily available in aqueous media. Suitable examples of metal borates useful in the electrodeposition bath of the present invention include, for example, calcium borate, potassium metaborate, and tetraboric acid. Potassium borates such as potassium, potassium pentaborate, potassium hexaborate, and octaborate, sodium metaborate, sodium diborate, sodium tetraborate, sodium pentaborate, sodium perborate, sodium hexaborate And sodium borate such as sodium octaborate, as well as ammonium borate are useful, as well as any boron-containing compound It is then, for example, borate bismuth and boric acid yttrium.

  Suitable boric acid equivalents can also include organic oligomeric and polymeric compounds comprising boron-containing moieties. Suitable examples are formed by reacting an active hydrogen-containing polymer, such as a hydroxy-functional acrylic polymer or polysiloxane polymer, with boric acid and / or a borate ester to form a polymer having borate ester groups. And polymeric borate esters such as

  Suitable polymers for this purpose include any of a variety of active hydrogen-containing polymers such as those selected from at least one of acrylic polymers, polyepoxide polymers, polyester polymers, polyurethane polymers, polyether polymers and silicon-based polymers. Also mentioned. “Silicon-based polymer” means a polymer comprising one or more —SiO— units in the backbone chain. Such silicon-based polymers include hybrid polymers such as those comprising organic polymer blocks having one or more —SiO— units in the backbone. Preferably, boric acid is used in the electrodeposition bath of the present invention.

  The boric acid or boric acid equivalent of the present invention is present in the electrocoating bath at a concentration ranging from greater than 0.3% to less than 2.0% of the total weight of the bath. Preferably, the boric acid or boric acid equivalent of the present invention is present in the electrocoating bath at a concentration ranging from 0.4% to 1.7% of the total weight of the bath. Most preferably, the boric acid or boric acid equivalent of the present invention is present in the electrocoating bath at a concentration ranging from 0.5% to 1.6% of the total weight of the bath.

Chlorhexidine is a known antiseptic compound. This is also known as 1,6-bis [5- (p-chlorophenyl) biguanidino] hexane and has the structural formula shown in FIG.

  Chlorhexidine is present in the electrocoating bath at a concentration of greater than 0.01% to 0.2% of the total weight of the bath. Preferably, chlorhexidine is present in the electrocoating bath at a concentration ranging from 0.02% to 0.18% of the total weight of the bath. Most preferably, chlorhexidine is present in the electrocoating bath at a concentration ranging from 0.03% to 0.16% of the total weight of the bath.

  If chlorhexidine is present at the lowest concentration, 0.01% of the total weight of the bath, the concentration of boric acid is higher than 0.5% of the total weight of the bath, more preferably 1.0% of the total weight of the bath It is desirable to maintain the above concentration.

  In another embodiment, the present invention is an electrodepositable composition comprising a film-forming resin having an ionic base and suitable for use as an electrodeposition bath comprising boric acid and chlorhexidine. An example of such a film-forming resin is an epoxy-based resin having an amine base and / or a sulfonium base.

  In a preferred embodiment, the electrodepositable composition has a pH of 7 or less. At pH higher than 7, such cationic compositions tend to adsorb carbon dioxide from the ambient atmosphere, and as a result can gradually transition to pH lower than 7 over time. Thus, compositions having a pH of 7 or less are more stable and process conditions can be more easily controlled.

  As used herein, the term “principal emulsion” refers to an aqueous emulsion of an epoxyamine adduct binder blended with an acid neutralized crosslinker to form a water soluble product. It means an electrocoating composition comprising. The binder of the electrocoating composition is generally a blend of an epoxyamine adduct and a blocked polyisocyanate crosslinker. While microbicides are potentially useful for various cathodic electrocoating resins, epoxyamine adduct resins are particularly preferred. These resins are generally disclosed in US Pat. No. 4,419,467, which is incorporated by reference.

  Preferred crosslinkers for epoxyamine adduct resins are also well known in the prior art. These are aliphatic, alicyclic, and aromatic isocyanates such as hexamethylene diisocyanate, cyclohexamethylene diisocyanate, toluene diisocyanate, and methylene diphenyl diisocyanate. These isocyanates are pre-reacted with a blocking agent such as an oxime, alcohol or caprolactam that blocks the isocyanate functionality (ie cross-linking functionality). Upon heating, the blocking agent separates, thereby providing reactive isocyanate groups and causing crosslinking. Isocyanate crosslinkers and blocking agents are well known in the prior art and are disclosed in the aforementioned U.S. Pat. No. 4,419,467.

  The cathode binder and blocked isocyanate of the epoxy amine adduct are the major resin components of the electrocoating composition and are usually present in an amount of about 30-50% by weight of the composition solids. To create an electrocoating bath, the solid is generally diluted with an aqueous medium.

  In addition to the binder resin described above, the electrocoating composition usually contains a pigment that is incorporated into the composition in the form of a pigment paste. The pigment paste is prepared by grinding or dispersing the pigment in a grinding solvent and optional ingredients such as wetting agents, surfactants and antifoam agents. Any of the pigment grinding solvents well known in the art can be used, or the novel additives described above can be used. After grinding, the particle size of the pigment should be as small as practical, and generally the particle size is about 6-8 using a Hegman powder gauge.

  Examples of the pigment that can be used in the present invention include titanium dioxide, basic lead silicate, strontium chromate, carbon black, iron oxide, and clay. These should be used judiciously because pigments with high surface area and oil absorption can have undesirable effects on the adhesion and flow of electrodeposited coatings.

  The weight ratio of pigment to binder is also important and should preferably be less than 0.5: 1, more preferably less than 0.4: 1, usually about 0.2: 1 to 0.4: 1. It has been found that higher pigment to binder weight ratios also adversely affect adhesion and flow.

  The coating composition of this invention can contain arbitrary components, such as a wetting agent, surfactant, and an antifoamer. Examples of surfactants and wetting agents include alkyl imidazolines, such as those available as “Amine C” from Ciba-Geigy Industrial Chemicals (Tarrytown, New York), from Air Products and Chemicals (Allenols, Ireland). Acetylene alcohol available as (registered trademark) 104 ”can be mentioned. These optional ingredients, when present, constitute about 0.1-20% by weight of the binder solids of the composition.

  Optionally, a plasticizer can be used to facilitate flow. Examples of useful plasticizers are hot water insoluble materials such as ethylene or propylene oxide adducts of nonylphenol or bisphenol A. The plasticizer is usually used at a concentration of about 0.1 to 15% by weight of the resin solids.

  The electrocoating composition of the present invention is an aqueous dispersion. The term “dispersion”, when used within the context of the present invention, is considered to be a two-phase translucent or opaque aqueous resin binder system in which the binder is in the dispersed phase and water is in a continuous layer. . The average particle size of the binder phase is about 0.1 to 10 microns, preferably less than 5 microns. The concentration of the binder in the aqueous medium is generally not critical, but usually the majority of the water dispersion is water. The aqueous dispersion usually contains about 3-50% by weight, preferably 5-40% by weight, of binder solids. Aqueous binder concentrates that are further diluted with water when added to the electrocoating bath generally have a range of 10-30% by weight binder solids.

  Preparation of an antimicrobial additive containing an electrocoating sample. According to Table 1, the amount of boric acid and / or chlorhexidine was added to a 49 ml sample of CORMAX® VI available from DuPont (Wilmington, Delaware). The amounts of boric acid and chlorhexidine listed in Table 1 are by weight percent based on the total weight of the sample.

To assess the antimicrobial activity of a compound, the “Challenge Inoculum” was isolated by isolating 11 unique bacteria from a contaminated electrocoating bath in 5 different automobile assemblies. Prepared. The electrocoating sample was prepared by adding 1 milliliter (ml) of the challenge inoculum to 49 ml of electrocoating sample dispersion. This bacterial inoculation resulted in bacterial numbers ranging from 1.0 × 10 ⁵ to 1.7 × 10 ⁶ CFU / ml. These challenge samples were incubated at room temperature for 30 days with agitation and sterile air agitation (air less than 0.1 liter / min). Samples were tested for the presence of bacteria by standard plate counting methods at 1 hour, 24 hours, 1 week, 2 weeks, 3 weeks and 30 days after inoculation. Trypsin soy agar (TSA) was used for the calculation of bacteria from electrocoated samples using standard spread plate technology.

  Table 1 shows the bacterial count data for the microbicides tested and control data.

N.D.−細菌は検出せず Table 1

ND-no bacteria detected

  The results in Table 1 show that electrocoating baths containing only 1.0% and 1.5% boric acid or only 0.01% or 0.1% chlorhexidine have sufficient microbial population during the test period. Indicates that control cannot be brought about. Example E containing 1.5% boric acid showed an increase in the number of microorganisms after 3 weeks before finally controlling the population. In contrast, electrocoating compositions containing greater than 0.5% boric acid and greater than 0.01% chlorhexidine showed a decrease in microbial population.

  The electrocoating bath compositions were tested to determine the effect of biocide additives on electrocoating bath conductivity and film build, respectively. The test results are shown in Table 2.

Table 2

Claims (6)

  An improved coating electrodeposition method comprising (a) (i) a film-forming binder comprising an epoxyamine adduct and (ii) an aqueous carrier having a blocked polyisocyanate crosslinker dispersed therein; (B) (1) at least one boron-containing compound selected from boric acid, boric acid equivalents or combinations thereof, and (2) 1,6-bis [5- (p-chlorophenyl) biguanidino] hexane ( An electrodeposition bath comprising the use of an aqueous electrodeposition bath comprising an effective amount (sufficient to retard microbial growth in the electrodeposition bath) and a biocide in combination with chlorhexidine) The pH of this is 7 or less.   The method of claim 1, wherein the boron-containing compound comprises borate, borate ester, boron oxide and mixtures thereof.   The method of claim 1, wherein the boron-containing compound comprises boric acid.   The electrodeposition bath of claim 1, wherein the amount of boron-containing compound is present in an amount sufficient to provide an amount of boron in the range of greater than 0.3% to less than 2.0% of the total weight of the bath.   The battery of claim 1 wherein 1,6-bis [5- (p-chlorophenyl) biguanidino] hexane is present in the bath in an amount ranging from greater than 0.01% to 0.2% of the total weight of the bath. Bathing.   An improved method of depositing a coating by electrodeposition, wherein (a) (i) a film-forming binder comprising an epoxyamine adduct and (ii) a blocked polyisocyanate crosslinker dispersed therein A carrier; (b) (1) at least one boron-containing compound selected from boric acid, boric acid equivalents or combinations thereof; (2) 1,6-bis [5- (p-chlorophenyl) biguanidino The use of an aqueous electrodeposition bath comprising an effective amount (sufficient to retard microbial growth in the electrodeposition bath) in combination with hexane (chlorhexidine); A method in which the pH of the electrodeposition bath is higher than 7.