Patent Application
20140151233
This disclosure relates to a composition comprising an aqueous dispersion of an at least partially neutralized copolymer of an α-olefin and unsaturated carboxylic acid that can be electrodeposited onto a conductive substrate to form a relatively thin film. The applied coating composition can then be cured at elevated temperatures to form a crosslinked coating that helps the substrate to resist corrosion and provides an extremely durable chip resistant coating.
The coating of electrically conductive substrates by an electrodeposition process, also called an electrocoating process, is a well-known and important industrial process. Electrodeposition of primers on metal substrates is widely used many industries. In this process, a conductive article is immersed in a bath of an aqueous dispersion of film forming polymer and the article acts as an electrode in the electrodeposition process. An electric current is passed between the article and a counter-electrode in electrical contact with the coating composition until a coating is deposited on the article. In a cathodic electrocoating process, the article to be coated is the cathode and the counter-electrode is the anode. In an anodic electrocoating process, the article to be coated is the anode and the counter-electrode is the cathode.
Film forming resin compositions used in the bath of a typical cathodic electrodeposition process also are well known in the art and have been in use since the 1970's. These resins typically are made from polyepoxide resins that have been chain extended with an amine compound(s). The epoxy amine adduct is then neutralized with an acid compound to form a water soluble or water dispersible resin. These resins are blended with a crosslinking agent, usually a polyisocyanate, and dispersed in water to form a water emulsion which is usually referred to as a principal emulsion.
The principal emulsion is combined with a pigment paste, coalescent solvents, water, and other additives such as pinhole additives and anti-crater agents to form the electrocoating bath. The electrocoating bath is placed in an insulated tank containing the anode. The article to be coated is the cathode and is passed through the tank containing the electrodeposition bath. The thickness of the coating that is deposited on the article being electrocoated is a function of the bath characteristics, the electrical operating characteristics of the tank, the immersion time, and the like.
Anodic electrocoat compositions, while known, account for only a small percentage of the electrocoating industry. The first electrocoat systems were anodic but were plagued by inadequate corrosion resistance, staining of the cured film and sensitivity to the substrate. The anodic electrocoat compositions were largely replaced in the mid-1970's by cathodic electrocoatings.
Compared with cathodic electrodeposition, articles coated with known anodic electrodeposition compositions typically have poor corrosion resistance, poor chip resistance, and poor flexibility. While cathodic coatings are more widely used than anodic electrodeposition coatings, cathodic electrodeposition coatings still suffer from problems, such as having limited UV stability, poor resistance to deformation and poor resistance to chipping.
There remains a need for electrodeposition coatings that have improved UV resistance, better resistance to deformation and have improved chip resistance.
The present disclosure relates to an electrodepositable composition which is an aqueous dispersion comprising a film forming binder wherein the film forming binder consists essentially of:
i) an at least partially neutralized copolymer of an α-olefin and unsaturated carboxylic acid, which is the reaction product of a neutralizing agent with a copolymer of an α-olefin and unsaturated carboxylic acid; and
The present disclosure describes an anodic electrodepositable coating composition, articles comprising a layer of the coating composition, and a process for preparing said articles. The electrodepositable composition is an aqueous dispersion comprising a film forming binder, wherein the film forming binder consists essentially of an at least partially neutralized copolymer of α-olefin and unsaturated carboxylic acid; and a curing agent. The copolymer of α-olefin and unsaturated carboxylic acid is a copolymer that is polymerized from a monomer mixture that comprises both α-olefin such as, for example, ethylene, and α,β-unsaturated carboxylic acid monomer such as, for example, (meth)acrylic acid. The copolymer can be neutralized with an inorganic base, an organic base or a combination thereof to form the at least partially neutralized copolymer of α-olefin and unsaturated carboxylic acid. The electrodepositable compositions are particularly useful for forming a dried and cured layer of film on a conductive substrate.
As used herein, the term “(meth)acrylic” is used to denote one or both of an acrylic moiety or a methacrylic moiety. For example, the term (meth)acrylic acid means acrylic acid and/or methacrylic acid.
The term “(meth)acrylate” means one or both of an acrylate moiety or a methacrylate moiety. For example, the term methyl (meth)acrylate means methyl acrylate and/or methyl methacrylate.
As used herein, the term “aqueous dispersion” means a liquid system in which solid particles are dispersed in water. The dispersing agent for the disclosed coating composition is water, however, small amounts of volatile organic solvents may be present.
The phrases “copolymer of α-olefin and unsaturated carboxylic acid”, “acid copolymer”, and “copolymer comprising α-olefin and unsaturated carboxylic acid” are used interchangeably and mean a copolymer that is polymerized from a monomer mixture comprising at least one α-olefin monomer such as, for example, ethylene, and at least one unsaturated carboxylic acid monomer such as, for example, (meth)acrylic acid according to known copolymerization methods.
The phrase “at least partially neutralized” copolymer for the purposes of the present invention includes a continuous range of acid neutralized compositions wherein at least 30 percent of the acid groups of a copolymer comprising carboxylic acid functionality have been reacted with a base—said base being selected from an inorganic base, an organic base or a combination thereof—to form the salt of the acid copolymer. The above phrase should also be understood in the present invention to include examples wherein an excess of base is used to neutralize all or substantially all of the carboxylic acid groups of the acid copolymer.
The phrase “film forming binder” refers to the polymers and other compounds that are used to form a crosslinked network. Additives such as pigments, surfactants, flow additives, light stabilizers, fillers, etc., that do not become a part of the crosslinked network are not considered to be a part of the film forming binder.
Melt Index, as used herein, is determined in accordance with ASTM D1238 at 190° C. and 2.16 kg, and the values reported herein have units of grams/10 minutes.
The features and advantages of the present disclosure will be more readily understood, by those of ordinary skill in the art, from reading the following detailed description. It is to be appreciated that certain embodiments, which are, for clarity, described above and below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination. Also, use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the disclosure. This description should be read to include one or at least one and the singular also includes the plural unless the context specifically states otherwise.
The use of numerical values in the various ranges specified in this application, unless expressly indicated otherwise, are stated as approximations as though the minimum and maximum values within the stated ranges were both preceded by the word “about”. In this manner, slight variations above and below the stated ranges can be used to achieve substantially the same results as values within the ranges. Also, the disclosure of these ranges is intended as a continuous range including every value between the minimum and maximum values.
In the foregoing description, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art would appreciate that various modifications and changes can be made without departing from the scope of the disclosure as set forth in the claims below. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of disclosure.
In one embodiment, the electrodepositable composition is an aqueous dispersion comprising a film forming binder wherein the film forming binder consists essentially of: i) an at least partially neutralized copolymer of α-olefin and unsaturated carboxylic acid; and ii) a curing agent.
In another embodiment, the electrodepositable composition is an aqueous dispersion consisting essentially of: i) an at least partially neutralized copolymer of α-olefin and unsaturated carboxylic acid; and ii) a curing agent.
In still another embodiment, the electrodepositable composition is an aqueous dispersion comprising a film forming binder and a surfactant wherein the film forming binder consists essentially of: i) an at least partially neutralized copolymer of α-olefin and unsaturated carboxylic acid; ii) a curing agent.
In the above embodiments, the at least partially neutralized copolymer of α-olefin and unsaturated carboxylic acid is the reaction product of a neutralizing agent with a copolymer of α-olefin and unsaturated carboxylic acid.
An acid copolymer of the present invention can be polymerized from a monomer mixture comprising α-olefin and unsaturated carboxylic acid monomers. Suitable α-olefins can have the formula R(R1)C═CH2, wherein R and R1 are each independently chosen from hydrogen or an alkyl radical having in the range of from 1 to 8 carbon atoms. In some embodiments, the α-olefins can be chosen from, for example, ethylene, propylene, 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-methyl-1-hexene and a combination thereof.
The unsaturated carboxylic acid monomers can include α,β-ethylenically unsaturated carboxylic acids having in the range of from 3 to 8 carbon atoms. Suitable unsaturated carboxylic acids include, for example, acrylic acid, methacrylic acid, maleic acid, and maleic acid mono-esters (also referred to in the art as the “half-ester” of maleic acid). Other suitable carboxylic acid monomers include, for example, crotonic acid, itaconic acid, fumaric acid, haloacrylic acids such as chloroacrylic acid, citraconic acid, vinylacetic acid, pentenoic acids, alkyl (meth)acrylic acids, alkylcrotonic acids, alkenoic acids and combinations thereof.
In one embodiment, acrylic acid is the carboxylic acid monomer for use in polymerizing the copolymer comprising α-olefin and unsaturated carboxylic acid. In another embodiment, methacrylic acid is the unsaturated carboxylic acid monomer used to form the copolymer comprising α-olefin and unsaturated carboxylic acid. In a third embodiment, a combination of acrylic acid and methacrylic acid are the unsaturated carboxylic acid monomers used in polymerizing the copolymer comprising α-olefin and unsaturated carboxylic acid.
The copolymer comprising α-olefin and unsaturated carboxylic acid can be a random copolymer formed from ethylene with acrylic acid and/or methacrylic acid, and can optionally comprise one or more additional monomers. The additional monomers can include, for example, one or more of alkyl (meth)acrylates wherein the alkyl groups have from about 1 to about 8 carbon atoms; styrene or substituted styrene; (meth)acrylonitrile; vinyl acetates; vinyl ethers; and combinations thereof. The additional monomers can be used in the range of from 0 to 40 percent by weight, based on the total weight of the monomers in the copolymer comprising α-olefin and unsaturated carboxylic acid.
Examples of copolymers suitable for use include copolymers such as, for example: ethylene/(meth)acrylic acid/n-butyl(meth)acrylate; ethylene/(meth)acrylic acid/iso-butyl(meth)acrylate; ethylene/(meth)acrylic acid/methyl(meth)acrylate; ethylene/(meth)acrylic acid/ethyl(meth)acrylate; and a combination thereof.
Suitable copolymers useful in the practice of the present invention can be linear, branched, or graft copolymers. The process for producing these polymers is well-known in the art and will not be described herein. Suitable examples of the copolymers of α-olefin and unsaturated carboxylic acid are commercially available and include, for example, NUCREL® acid copolymer resins available from DuPont, Wilmington, Del.
In some embodiments, the copolymer of α-olefin and unsaturated carboxylic acid can have a carboxylic acid containing monomer content in the range of from 5 to 25 percent by weight based on the total weight of all of the monomers that make up the copolymer. The copolymer of α-olefin and unsaturated carboxylic acid can have a melt index in the range of from 10 to 1000.
In other embodiments, the melt index of the copolymer of α-olefin and unsaturated carboxylic acid is in the range of from 50 to 800, in other embodiments, the melt index is in the range of from 100 to 500, and in further embodiments, the melt index is in the range of from 200 to 450. In one embodiment, the copolymer of α-olefin and unsaturated carboxylic acid is a NUCREL® acid copolymer resin which has a melt index of about 300 and a (meth)acrylic acid monomer content of about 20 percent. In another embodiment, the copolymer of α-olefin and unsaturated carboxylic acid is a NUCREL® acid copolymer resin which has a melt index of about 400 and a (meth)acrylic acid monomer content of about 19 percent.
The acid copolymer can be present in the electrodepositable composition in the range of from 55 to 90 percent by weight, based on the total solids content. As used herein, the term “total solids” content means the total weight of all ingredients that are present in the electrodepositable composition, excluding water and other small amounts of volatile organic solvent that may be present.
In some embodiments, the acid copolymer can be present in the electrodepositable composition in the range of from 55 to 85 percent by weight, based on the total solids content.
In further embodiments, the copolymer of α-olefin and unsaturated carboxylic acid can be present in the electrodepositable composition in the range of from 60 to 80 percent by weight, based on the total solids content.
A neutralizing agent (that is, a base) is added to neutralize at least a portion of the carboxylic acid groups of the copolymer comprising α-olefin and unsaturated carboxylic acid. The neutralizing agent can be any base that is capable of reacting with an acid copolymer to form a salt of the acid. The base can be selected from the group consisting of an organic base, an inorganic base and combinations thereof. Inorganic bases include, for example, metal hydroxides such as, for example, potassium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide. Organic bases include ammonia, primary amines, secondary amines, tertiary amines, hydrazine, mono-, di-, tri- or tetra-alkylhydrazines. Combinations of any of the above listed neutralizing agents are suitable. Acid-base chemistry is well-known to one of ordinary skill in the art, and therefore the use of other bases not specifically recited herein should not be considered novel and should not be considered outside the intended scope of the present invention.
In some embodiments, the neutralizing agent is potassium hydroxide, sodium hydroxide or a combination thereof. In other embodiments, the neutralizing agent can be an amine of the formula;
N(R2)3
wherein each R2 is independently selected from the group consisting of H, CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CH2OH, CH2CH2OH, CH2CH2CH2OH, CH2CH(OH)CH3, CH(CH3)CH2OH and CH(OH)CH2CH3. In some embodiments, the neutralizing agent can be selected from the group consisting of ethanolamine, N-methylethanolamine, N-ethylethanolamine, N,N-dimethylethanolamine, dimethylamine, diethylamine, diisopropylamine, dipropylamine, trimethylamine, triethylamine and a combination thereof.
In some embodiments of the present disclosure, the neutralizing agent can be present in an amount that is theoretically capable of neutralizing greater than or equal to 30 percent of the carboxylic acid groups of the copolymer of α-olefin and unsaturated carboxylic acid.
In other embodiments of the present disclosure, the neutralizing agent can be present in an amount that is theoretically capable of neutralizing in the range of from 30 to 150 percent of the carboxylic acid groups of the copolymer of α-olefin and unsaturated carboxylic acid.
A peroxide curing agent can be added to the electrodepositable composition to provide a crosslinked coating upon curing. Suitable peroxides include organic and inorganic peroxide compounds. In one embodiment, the curing agent can be a metal peroxide such as, for example, zinc peroxide. In other embodiments, suitable metal peroxides can be selected from the group consisting of magnesium peroxide, barium peroxide, strontium peroxide, cadmium peroxide, titanium peroxide and a combination thereof.
In some embodiments, the curing agent can be present in the electrodepositable composition in the range of from 5 to 30 percent by weight based on the total solids. In other embodiments, the curing agent can be present in the electrodepositable composition in the range of from 5.5 to 20 percent by weight based on the total solids. In still other embodiments, the curing agent can be present in the electrodepositable composition in the range of from 6 to 10 percent by weight based on the total solids.
Other additives are optional and can be mixed with the electrodepositable composition, if desirable, and depending upon the effect of the additive. Optional additives can include, for example, surfactants, pigments, light stabilizers, anti-crater agents, flow aids, dispersion stabilizers and fillers.
Examples of surfactants include alkoxylated styrenated phenols, such as, for example, SYNFAC® 8334, available from Milliken Chemical Company, Spartanburg, S.C.; alkyl imidazoline surfactants such as those available from Huntsman, Woodlands, Tex.; and nonionic surfactants such as, for example, SURFYNOL® surfactants, available from Air Products, Allentown, Pa. Combinations thereof can also be used.
Examples of pigments include, for example, titanium dioxide, ferric oxide, red iron oxide, transparent red iron oxide, black iron oxide, brown iron oxide, chromium oxide green, carbon black, aluminum silicate, precipitated barium sulfate and a combination thereof. In one embodiment, the electrodepositable coating contains pigments. In another embodiment, the electrodepositable composition contains no pigments.
Light stabilizers, such as, for example, hindered amine light stabilizers can be added to the electrodepositable composition. Representative commercially available hindered amine light stabilizers can be, for example, TINUVIN® 770, 292 and 440 which are sold by Ciba-Geigy Corporation.
Flow additives include materials such as, for example, ethylene and/or propylene adducts of nonyl phenols or bisphenols.
In one embodiment, the electrodepositable composition is formed by combining water, an acid copolymer as described herein and neutralizing agent to form a mixture, which is stirred and (optionally) heated until the copolymer is dispersed. If the mixture is heated to obtain a dispersed copolymer, it can be cooled to ambient temperature and the curing agent along with any optional additives can be added. The mixture can then be further agitated and/or milled to disperse the curing agent and any optional additives. In one embodiment, the electrodepositable composition can be further diluted with water to obtain a total solids content in the range of from 10 to 25 percent by weight.
An electrodepositable composition formed in this manner typically will have particle sizes in the range of from 30 to 170 nanometers and a pH in the range of from 7 to 11.
In one embodiment, a substrate is coated via a process comprising;
A) providing a bath of an anodic electrodepositable coating composition wherein the electrodepositable coating composition is an aqueous dispersion comprising a film forming binder wherein the film forming binder consists essentially of: i) an at least partially neutralized copolymer of α-olefin and unsaturated carboxylic acid; and ii) a curing agent;
B) immersing the substrate in said anodic electrodepositable composition;
C) applying a voltage between a cathode and said substrate, which serves as an anode;
D) removing the substrate from the bath; and
E) heating the applied layer of electrodeposited composition.
Optionally, the process further comprises rinsing the substrate prior to E), heating the applied layer of electrodeposited composition. Rinsing, if included, is typically done using water or deionized water.
In one embodiment, the process includes immersing the substrate at least partially in the electrodepositable composition. In a second embodiment, the entire substrate is immersed in the electrodepositable composition.
In some embodiments, the electrodepositable composition is applied at a bath temperature in the range of from 25° C. to about 40° C., the applied voltage can range from 100 to 400 volts and the electric current can be applied in the range of from 1 second to 5 minutes. In other embodiments, the electric current can be applied in the range of from about 20 seconds to about 5 minutes.
The applied layer of electrodeposited composition can be heated at a temperature in the range of from 150° C. to 250° C. to dry and cure the applied layer of electrodeposited composition to produce a dried and crosslinked layer of film. In one embodiment, the thickness of a layer of dried and crosslinked electrodeposited composition is less than 12 microns. In other embodiments, the thickness of a layer of the dried and crosslinked electrodepositable composition is in the range of from 0.5 microns to less than 12 microns. In still further embodiments, the thickness of a layer of the dried and crosslinked electrodepositable composition is in the range of from 1 to 10 microns.
The substrate optionally can be cleaned to remove grease, dirt, or other extraneous material prior to coating with a layer of the electrodepositable composition. This is typically done by employing conventional cleaning procedures and materials. Suitable cleaning materials include for example, organic solvents such as, ketones, ethers, acetates, and a combination thereof; mild or strong alkaline cleaners, such as those commercially available and conventionally used in metal treatment processes. Examples of alkaline cleaners include the P3® line of cleaners available from Henkel, Dusseldorf, Germany. Such cleaning steps are generally followed and/or preceded by water rinse(s). Optionally, the metal surface may be rinsed with or immersed in one or more aqueous acidic solutions after cleaning and before contact with the subsequent electrodepositable composition. Examples of rinse solutions include mild or strong acidic cleaners, such as dilute nitric acid solutions, which are commercially available and conventionally used in metal treatment processes.
Useful substrates that can be coated with the electrodepositable composition include electrically conductive substrates such as, for example, metallic materials, for example ferrous metals such as iron, steel, and alloys thereof, non-ferrous metals such as aluminum, zinc, magnesium and alloys thereof, and a combination thereof. In some embodiments, the substrate is cold-rolled steel, zinc-coated steel, aluminum or magnesium. Thermoplastic and thermoset articles that are electrically conductive or that have been rendered electrically conductive by, for example, the addition of an electrically conductive coating can also be coated with the disclosed electrodepositable composition.
The coated substrates can be used as components to fabricate automotive vehicles, automobile bodies, truck bodies, buses, farm and construction equipment, truck caps and covers, commercial trailers, consumer trailers, recreational vehicles, including but not limited to, motor homes, campers, conversion vans, vans, pleasure vehicles, pleasure craft snow mobiles, all terrain vehicles, personal watercraft, motorcycles, boats, and aircraft. The substrate further includes industrial and commercial new construction and maintenance thereof; walls of commercial and residential structures, such office buildings and homes; amusement park equipment; automotive wheels; chromed automotive wheels; marine surfaces; outdoor structures, such as bridges, towers; coil coating; railroad cars; machinery; OEM tools; signage; sporting goods; and sporting equipment. The electrodeposited coatings can be produced on monofilament metal wires, multifilament metal wires, metal foils for packaging applications, and as protective coatings for metal circuits, indoor and outdoor furniture, hand tools, tool boxes and any other conductive substrate that would benefit from the corrosion resistance and durability afforded by the electrodepositable coatings described herein.
The substrate that is coated with a dried and cured layer of the electrodepositable composition can be used as is or additional layers of coating compositions can be applied. In the manufacture of consumer goods, the applied coating can be further coated with one or more of commercially available primers, primer surfacers, sealers, basecoat compositions, clearcoat compositions, glossy topcoat compositions and any combination thereof.
Unless otherwise specified, all ingredients are available from the Aldrich Chemical Company, Milwaukee, Wis.
NUCREL® acid copolymer resins are available from DuPont, Wilmington, Del.
Test Procedures
To test the methyl ethyl ketone solvent resistance, the layer of dried and cured composition on each panel was rubbed with a cloth saturated with methyl ethyl ketone 100 times and any excess methyl ethyl ketone was wiped off. The panel was visually rated from 1-10. A rating of 10 means no visible damage to the coating, 9 means 1 to 3 distinct scratches, 8 means 4 to 6 distinct scratches, 7 means 7 to 10 distinct scratches, 6 means 10 to 15 distinct scratches with slight pitting or slight loss of color, 5 means 15 to 20 distinct scratches with slight to moderate pitting or moderate loss of color, 4 means scratches start to blend into one another, 3 means only a few undamaged areas between blended scratches, 2 means no visible signs of undamaged paint, 1 means complete failure i.e., bare spots are shown.
Film Smoothness is rated visually by an application expert.
Preparation of Dispersion 1
380 parts NUCREL® 1050, 1668 parts water and 37 parts of N,N-dimethyl ethanolamine were charged into a suitable mixing vessel under agitation and a nitrogen atmosphere. The mixture was heated to 88° C. and stirred until the pellet form of the NUCREL® 1050 was totally dissolved and well dispersed in water. The mixture was cooled to about 32° C. and transferred to a plastic jar. 58 parts of zinc peroxide was added to the jar and the mixture was milled for 6 to 8 hours on a roller mill. Finally, 868 parts water was added to the dispersion.
The following examples show dispersions that lack the curing agent.
The ingredients of Portion 1 of Table 1 were charged into a suitable mixing vessel under agitation and a nitrogen atmosphere. The mixture was heated to 88° C. and stirred until the pellet form of the NUCREL® was well dispersed in water. The mixture was cooled to about 32° C. and the mixture was diluted with portion 2 of Table 1.
1NUCREL ® acid copolymer resin, with about 20% methacrylic acid and a melt index of about 300
2NUCREL ® acid copolymer resin, with about 19% methacrylic acid and a melt index of about 400.
Preparation of Cold-Rolled Steel Panels
Cold-rolled steel panels were cleaned by wiping them with methyl isobutyl ketone. The panels were then dipped into 0.125% aqueous nitric acid solution at 27° C. for 4 minutes and then dipped into 0.25% zirconyl nitrate solution at 27° C. for 4 minutes. The panels were force dried in an oven at 100° C. for 5 minutes. The panels were cooled to room temperature and used as is.
Electrodeposition Procedure
The treated cold-rolled steel panels were anodically coated in Dispersion 1 and comparative Dispersions A through E at a bath temperature of 32° C. for 2 minutes at 240 volts. Each coated panels was washed with deionized water and baked at about 198° C. for 10 minutes. The panels were then tested for film thickness and methyl ethyl ketone solvent resistance. The results of the test are given in Table 2.
The results show that a film of less than 12 microns (0.47 mils) can be deposited anodically using the electrodepositable coating composition and process as described herein. Comparative coating examples A through E do not contain a curing agent and therefore, show a very low resistance to rubbing with methyl ethyl ketone, which indicates that the film is not crosslinked. The presence of the curing agent significantly enhances the methyl ethyl ketone solvent resistance as shown in the film from dispersion 1.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/099,927 filed on Sep. 25, 2008 which is hereby incorporated by reference in its entirety.
