US20070045116A1

US20070045116A1 - Electrodepositable coating compositions and related methods

Info

Publication number: US20070045116A1
Application number: US11/213,174
Authority: US
Inventors: Cheng-Hung Hung; Alan Kaylo; Gregory McCollum; Noel Vanier; Michael White
Original assignee: PPG Industries Ohio Inc
Current assignee: PPG Industries Ohio Inc
Priority date: 2005-08-26
Filing date: 2005-08-26
Publication date: 2007-03-01
Also published as: WO2008054353A9; WO2008054353A3; WO2008054353A2; EP1948743A2

Abstract

An electrodepositable coating composition is provided including a resinous phase and catalyst nanoparticles dispersed in an aqueous medium, the resinous phase including (a) at least one active hydrogen-containing, ionic salt group-containing resin; and (b) at least one curing agent; and the catalyst nanoparticles for effecting cure between the resin (a) and the curing agent (b). The catalyst nanoparticles have an average BET specific surface area greater than 20 square meters per gram (m²/g). Methods of preparing and using the composition also are provided.

Description

BACKGROUND OF THE INVENTION

I. Field of the Invention
The present invention relates to cationic electrodepositable coating compositions comprising a resinous phase and certain catalyst nanoparticles dispersed in an aqueous medium, wherein the catalyst nanoparticles have a specified B.E.T. specific surface area to methods of preparing such compositions; and to methods for applying such compositions.
II. Technical Considerations
The application of a coating by electrodeposition involves depositing a film-forming composition onto the surfaces of an electrically conductive substrate under the influence of an applied electrical potential. Electrodeposition has gained prominence in the coating industry because, in comparison with non-electrophoretic coating methods, electrodeposition provides higher paint utilization, excellent corrosion resistance and low environmental contamination. Early attempts at commercial electrodeposition processes used anionic electrodeposition where the workpiece to be coated serves as the anode. However, cationic electrodeposition has become increasingly popular and today is the most prevalent method of electrodeposition.
Many cationic electrodeposition compositions in use today are based on active hydrogen-containing resins derived from a polyepoxide and a capped or blocked polyisocyanate curing agent. Typically, these cationic electrodeposition compositions also contain organotin catalysts to lower the temperature at which the blocking agent is released from blocked polyisocyanate and to activate cure of the electrodeposition composition.
Most of the common dialkyltin oxide catalysts are high melting, amorphous solid materials which must be introduced into the composition in the form of a catalyst paste prepared by dispersing the solid catalyst into a pigment wetting resin under extremely high shear conditions. Preparation of stable catalyst pastes can be very costly and time intensive. Further, it has been noted that some of the aforementioned organotin catalysts can cause a multitude of surface defects in the cured electrodeposited coating composition. For example, dibutyltin oxide dispersions can flocculate in the electrodeposition bath, resulting in oversized dibutyltin oxide agglomerates or particles which can settle in areas of the electrodeposition tank where agitation is poor. This flocculation phenomenon constitutes a loss of catalyst from the coating composition resulting in poor cure response. Moreover, the flocculate particles can settle in the uncured electrodeposited coating causing localized “hot spots” or pinholes in the surface of the cured coating. Also, electrodeposition bath stability can be adversely affected with the use of some organotin catalysts. It has been observed that soft, floating foams can form from a mixture of organotin catalyst, polyisocyanate curing agent and microscopic air bubbles.
Triorganotin compounds are known for use as catalysts in electrodepositable coating compositions comprised of an active hydrogen-containing resin and a blocked polyisocyanate curing agent. Such triorganotin compounds, however, have been observed to have poor cure response when used in conjunction with resinous components having phenolic hydroxyl groups. Moreover, some trialkyltin compounds, for example, tributyltin compounds, are known to be volatile at typical curing temperatures. Also, some trialkyltin compounds can be toxic. Further, many triorganotin compounds typically have the disadvantage of high cost.
In view of the foregoing, it would be advantageous to provide a cationic electrodepositable coating composition including a catalyst which overcomes the problems encountered with prior art compositions containing such catalysts as discussed above. Such compositions can provide improved storage stability and cure response at lower cure temperatures, without compromising cured film appearance and performance properties.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides electrodepositable coating compositions comprising a resinous phase and catalyst nanoparticles dispersed in an aqueous medium, the resinous phase comprising: (a) a active hydrogen-containing, ionic salt group-containing resin; and (b) at least one curing agent; and catalyst nanoparticles for effecting cure between the resin (a) a curing agent (b), the catalyst nanoparticles being selected from the group consisting of bismuth oxide; bismuth silicate; bismuth titanate; molybdenum oxide; molybdenum silicate; molybdenum titanate; tungsten oxide; tungsten silicate; tungsten titanate; a combination of cerium oxide, zinc oxide and silicon dioxide; a combination of cerium oxide and silicon dioxide; and combinations thereof, wherein the catalyst nanoparticles have an average B.E.T. specific surface area-greater than 20 square meters per gram (m²/g).
In another aspect, the present invention provides methods for electrocoating a conductive substrate serving as a cathode in an electrical circuit comprising the cathode and an anode, the cathode and anode being immersed in an aqueous electrocoating composition, the methods comprising passing electric current between the cathode and anode to cause deposition of the electrocoating composition onto the substrate as a substantially continuous film, the aqueous electrocoating composition comprising a resinous phase dispersed in an aqueous medium, the resinous phase comprising: (a) a active hydrogen group-containing, ionic group-containing electrodepositable resin; and (b) a curing agent, and catalyst nanoparticles for effecting cure between the resin (a) and the curing agent (b), the catalyst nanoparticles being selected from the group consisting of bismuth oxide; bismuth silicate; bismuth titanate; molybdenum oxide; molybdenum silicate; molybdenum titanate; tungsten oxide; tungsten silicate; tungsten titanate; a combination of cerium oxide, zinc oxide and silicon dioxide; a combination of cerium oxide and silicon dioxide; and combinations thereof, wherein the catalyst nanoparticles have an average B.E.T. specific surface area greater than 20 square meters per gram (m²/g).

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. In the drawings:
FIG. 1 is a flow diagram of certain embodiments of suitable methods for making catalyst nanoparticles in accordance with the present invention;
FIG. 2 is a schematic diagram of an apparatus for producing catalyst nanoparticles in accordance with certain embodiments of the present invention;
FIG. 3 is a perspective view of a plurality of quench gas injection ports in accordance with certain embodiments of the present invention;
FIG. 4 is a micrograph of a TEM image of a representative portion of the nanoparticles of Example 1 (10,000× magnification); and
FIG. 5 is a micrograph of a TEM image of a representative portion of the nanoparticles of Example 2 (210,000× magnification).

DETAILED DESCRIPTION

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
The present invention provides electrodepositable coating compositions comprising a resinous phase and catalyst nanoparticles dispersed in an aqueous medium, the resinous phase comprising: (a) at least one active hydrogen-containing, ionic salt group-containing resin; (b) at least one curing agent. The catalyst nanoparticles effect or facilitate cure between the resin (a) and the curing agent (b), as described in detail below.
The catalyst nanoparticles are selected from the group consisting of bismuth oxide; bismuth silicate; bismuth titanate; molybdenum oxide; molybdenum silicate; molybdenum titanate; tungsten oxide; tungsten silicate; tungsten titanate; a combination of cerium oxide, zinc oxide and silicon dioxide; a combination of cerium oxide and silicon dioxide; and combinations thereof, such as composite particles of two or more of these compounds or combinations.
In some embodiments, the catalyst nanoparticles comprise bismuth oxide. In other embodiments, the catalyst particles comprise bismuth oxide and silica. In other embodiments, the catalyst particles comprise bismuth oxide and bismuth silicate. In other embodiments, the catalyst particles comprise bismuth oxide, bismuth silicate and silica.
In some embodiments, the catalyst nanoparticles may be a complex metal oxide comprising a homogeneous mixture, or solid state solution of two or more (up to x) metal oxides, labeled MO₁, MO₂, . . . , MO_x,
The catalyst nanoparticles have an average B.E.T. (Brunauer, Emmett, and Teller) specific surface area greater than 20 square meters per gram (m²/g), in some embodiments greater than 25 square meters per gram (m²/g), and in other embodiments greater than 30 m²/g. In some embodiments, the average BET specific surface area is less than 300 m²/g. The BET specific surface area (“SSA”) can be measured by any method well known to those skilled in the art, such as by nitrogen absorption according to ASTM D 3663-78 standard based upon the Brunauer, Emmett, and Teller method described in J. Am. Chem. Soc'y 60, 309 (1938). For example, the BET specific surface area (“SSA”) can be measured using a Gemini Model 2360 surface area analyzer (available from Micromeritics Instrument Corp. of Norcross, Ga.).
In certain embodiments, the catalyst nanoparticles have a calculated equivalent spherical diameter of less than 500 nanometers, in other embodiments less than 100 nanometers and in still other embodiments less than 50 nanometers. As will be understood by those skilled in the art, a calculated equivalent spherical diameter can be determined from the B.E.T. specific surface area according to the following equation:
Diameter (nanometers)=6000/[BET(m²/g)*ρ(grams/cm³)]
The catalyst nanoparticles can have an average primary particle size of less than 500 nanometers. In some embodiments, the catalyst nanoparticles can have an average primary particle size of less than 100 nanometers, and in other embodiments less than 50 nanometers. In some embodiments, the catalyst nanoparticles have an average primary particle size of less than 30 nanometers and in other embodiments less than 20 nanometers. The particles typically have an average primary particle size greater than 1 nm. The average primary particle size can be determined by visually examining an electron micrograph of a transmission electron microscopy (“TEM”) image, measuring the diameter of the particles in the image, and calculating the average particle size (“APS”) based on the magnification of the TEM image. One of ordinary skill in the art will understand how to prepare such a TEM image, and determine particle size based on the magnification and the Examples contained herein illustrate a suitable method for preparing a TEM image. The primary particle size of a particle refers to the smallest diameter sphere that will completely enclose the particle. As used herein, the phrase “primary particle size” refers to the size of an individual particle as opposed to an agglomeration of two or more individual particles.
It will be recognized by one skilled in the art that mixtures of one or more particles having different average particle sizes can be incorporated into the compositions in accordance with the present invention to impart the desired properties and characteristics to the compositions. For example, particles of varying particle sizes can be used in the compositions according to the present invention.
The catalyst nanoparticles can be present in the coating composition in an amount sufficient to effect cure of the coating composition at or below a temperature of 360° F. (182.2° C.). In some embodiments, catalyst nanoparticles are present in the coating composition in an amount sufficient to effect cure of the coating composition at or below a temperature of 340° F. (171.1° C.). In other embodiments, catalyst nanoparticles are present in the coating composition in an amount sufficient to effect cure of the coating composition at or below a temperature of 320° F. (160° C.). In other embodiments, catalyst nanoparticles are present in the coating composition in an amount sufficient to effect cure of the coating composition at or below a temperature of 300° F. (149° C.). One skilled in the art would understand that the cure temperature can vary based upon the amount and type of catalyst nanoparticles used.
When the film-forming composition of the present invention is in a liquid medium, the particles have an affinity for the medium of the composition sufficient to keep the particles suspended therein. The affinity of the particles for the medium is greater than the affinity of the particles for each other, thereby preventing agglomeration of the particles within the medium. This property is due to the nature of the particles themselves. The particles are also substantially free of any surface treatment. The particles used in the composition of the present invention may be added to the composition neat during the formulation thereof, and may be added at high loadings without appreciable viscosity increases, allowing for formulation of high solids coating compositions.
The shape (or morphology) of the particles can vary depending upon the specific embodiment of the present invention and its intended application. For example, generally spherical morphologies can be used, as well as particles that are cubic, platy, or acicular (elongated or fibrous). In general, the particles are substantially spherical in shape.
The catalyst nanoparticles may be prepared by various methods, including gas phase synthesis processes, such as, for example, flame pyrolysis, hot walled reactor, chemical vapor synthesis, among other methods. In certain embodiments, however, such particles are prepared by reacting together one or more organometallic and/or metal oxide precursors and any other ingredients in a fast quench plasma system. In certain embodiments, the particles may be formed in such a system by: (a) introducing materials into a plasma chamber; (b) rapidly heating the materials by means of a plasma to a selection temperature sufficient to yield a gaseous product stream; (c) passing the gaseous product stream through a restrictive convergent-divergent nozzle to effect rapid cooling and/or utilizing an alternative cooling method, such as a cool surface or quenching stream, and (d) condensing the gaseous product stream to yield ultrafine solid particles. Certain suitable fast quench plasma systems and methods for their use are described in U.S. Pat. Nos. 5,749,937, 5,935,293, and RE 37,853 E, which are incorporated herein by reference. One process of preparing particles suitable for use in certain embodiments of the coating compositions of the present invention comprises: (a) introducing one or more organometallic precursors and/or inorganic oxide precursers into one axial end of a plasma chamber; (b) rapidly heating the precurser stream by means of a plasma to a selected reaction temperature as the precurser stream flows through the plasma chamber, yielding a gaseous product stream; (c) passing the gaseous product stream through a restrictive convergent-divergent nozzle arranged coaxially within the end of the reaction chamber; and (d) subsequently cooling and slowing the velocity of the desired end product exiting from the nozzle, yielding ultrafine solid particles.
The precursor stream may be introduced to the plasma chamber as a solid, liquid, gas, or a mixture thereof. Suitable liquid reactants that may be used as part of the precursor stream include organometallics, such as, for example, cerium-2 ethylhexanoate, zinc-2 ethylhexanoate, tetraethoxysilane, molybdenum oxide bis(2,4-pentanedionate), among other materials, including mixtures thereof. Suitable solid precursors that may be used as part of the precursor stream include solid silica powder (such as silica fume, silica sand, or precipitated silica), bismuth oxide; bismuth silicate; bismuth titanate; molybdenum oxide; molybdenum silicate; molybdenum titanate; tungsten oxide; tungsten silicate; tungsten titanate; cerium acetate, cerium oxide, zinc oxide, silicon dioxide and other oxides, among other materials, including mixtures thereof. The reactant stream may be introduced to the reaction chamber as a solid, liquid, or gas, but is usually introduced as solid.
In certain embodiments, the catalyst nanoparticles are prepared by a method comprising: (a) introducing a solid precursor into a plasma chamber; (b) heating the precursor by means of a plasma to a selected reaction temperature as the precursor flows through the plasma chamber, yielding a gaseous product stream; (c) contacting the gaseous product stream with a plurality of quench streams injected into the plasma chamber through a plurality of quench gas injection ports, wherein the quench streams are injected at flow rates and injection angles that result in the impingement of the quench streams with each other within the gaseous product stream, thereby producing ultrafine solid particles; and (d) passing the ultrafine solid particles through a converging member.
Referring now to FIG. 1, there is shown a flow diagram depicting certain embodiments of suitable methods for making catalyst nanoparticles. As is apparent, in certain embodiments, at step 100, a solid precursor is introduced into a feed chamber. Then, as is apparent from FIG. 1 at step 200, in certain embodiments, the solid precursor is contacted with a carrier. The carrier may be a gas that acts to suspend the solid precursor in the gas, thereby producing a gas-stream suspension of the solid precursor. Suitable carrier gases include, but are not limited to, argon, helium, nitrogen, oxygen, air, hydrogen, or a combination thereof.
Next, in certain embodiments, the solid precursor is heated, at step 300, by means of a plasma to a selected temperature as the solid precursor flows through the plasma chamber, yielding a gaseous product stream. In certain embodiments, the temperature ranging from 2,500° to 20,000° C., such as 1,7000° to 8,000° C.
In certain embodiments, the gaseous product stream may be contacted with a reactant, such as a hydrogen-containing material, that may be injected into the plasma chamber, as indicated at step 350. The particular material used as the reactant is not limited and may include, for example, air, water vapor, hydrogen gas, ammonia, and/or hydrocarbons, depending on the desired properties of the resulting catalyst nanoparticles.
As is apparent from FIG. 1, in certain embodiments, after the gaseous product stream is produced, it is, at step 400, contacted with a plurality of quench streams that are injected into the plasma chamber through a plurality of quench stream injection ports, wherein the quench streams are injected at flow rates and injection angles that result in impingement of the quench streams with each other within the gaseous product stream. The material used in the quench streams is not limited, so long as it adequately cools the gaseous product stream to cause formation of ultrafine solid particles. Materials suitable for use in the quench streams include, but are not limited to, hydrogen gas, carbon dioxide, air, water vapor, ammonia, mono, di and polybasic alcohols, silicon-containing materials (such as hexamethyldisilazane), carboxylic acids and/or hydrocarbons.
The particular flow rates and injection angles of the various quench streams are not limited, so long as they impinge with each other within the gaseous product stream to result in the rapid cooling of the gaseous product stream to produce catalyst nanoparticles. This is different from certain fast quench plasma systems that utilize Joule-Thompson adiabatic and isentropic expansion through, for example, the use of a converging-diverging nozzle or a “virtual” converging diverging nozzle, to form ultrafine particles. In the present invention, the gaseous product stream is contacted with the quench streams to produce ultrafine solid catalyst nanoparticles before passing those particles through a converging member, such as, for example, a converging-diverging nozzle, which, inter alia, can reduce the fouling or clogging of the plasma chamber, thereby enabling the production of ultrafine solid particles from solid reactants without frequent disruptions in the production process for cleaning of the plasma system. In the present invention, the quench streams primarily cool the gaseous product stream through dilution, rather than adiabatic expansion, thereby causing a rapid quenching of the gaseous product stream and the formation of ultrafine solid particles prior to passing the particles into and through a converging member, such as a converging-diverging nozzle, as described below.
Referring again to FIG. 1, after contacting the gaseous product stream with the quench streams to cause production of ultrafine solid particles, the particles are, at step 500, passed through a converging member, wherein the plasma system is designed to minimize the fouling thereof. In certain embodiments, the converging member comprises a converging-diverging (De Laval) nozzle. In these embodiments, while the convergent-divergent nozzle may act to cool the product stream to some degree, the quench streams perform much of the cooling so that a substantial amount of ultrafine solid particles are formed upstream of the convergent-divergent nozzle. In these embodiments, the convergent-divergent nozzle may primarily act as a choke position that permits operation of the reactor at higher pressures, thereby increasing the residence time of the materials therein. The combination of quench stream dilution cooling with a convergent-divergent nozzle appears to provide a commercially viable method of producing ultrafine solid particles from solid precursors, since, for example, (i) a solid precursor can be used effectively without heating the feed material to a gaseous or liquid state before injection into the plasma, and (ii) fouling of the plasma system can be minimized, or eliminated, thereby reducing or eliminating disruptions in the production process for cleaning of the plasma system.
As shown in FIG. 1, in certain embodiments of the methods of the present invention, after the ultrafine solid particles are passed through a converging member, they are harvested at step 600. Any suitable means may be used to separate the ultrafine solid particles from the gas flow, such as, for example, a bag filter or cyclone separator.
Now referring to FIG. 2, there is depicted a schematic diagram of an apparatus for producing ultrafine solid catalyst nanoparticles in accordance with certain embodiments of the present invention. As is apparent, a plasma chamber 20 is provided that includes a solid particle feed inlet 50. Also provided is at least one carrier gas feed inlet 14, through which a carrier gas flows in the direction of arrow 30 into the plasma chamber 20. As previously indicated, the carrier gas acts to suspend the solid reactant in the gas, thereby producing a gas-stream suspension of the solid reactant which flows towards plasma 29. Numerals 23 and 25 designate cooling inlet and outlet respectively, which may be present for a double-walled plasma chamber 20. In these embodiments, coolant flow is indicated by arrows 32 and 34.
In the embodiment depicted by FIG. 2, a plasma torch 21 is provided. Torch 21 vaporizes the incoming gas-stream suspension of solid reactant within the resulting plasma 29 as the stream is delivered through the inlet of the plasma chamber 20, thereby producing a gaseous product stream. As shown in FIG. 2, the solid particles are, in certain embodiments, injected downstream of the location where the arc attaches to the annular anode 13 of the plasma generator or torch.
A plasma is a high temperature luminous gas which is at least partially (1 to 100%) ionized. A plasma is made up of gas atoms, gas ions, and electrons. A thermal plasma can be created by passing a gas through an electric arc. The electric arc will rapidly heat the gas to very high temperatures within microseconds of passing through the arc. The plasma is often luminous at temperatures above 9000 K.
A plasma can be produced with any of a variety of gases. This can give excellent control over any chemical reactions taking place in the plasma as the gas may be inert, such as argon, helium, or neon, reductive, such as hydrogen, methane, ammonia, and carbon monoxide, or oxidative, such as oxygen, nitrogen, and carbon dioxide. Air, oxygen, and/or oxygen/argon gas mixtures are often used to produce ultrafine solid particles in accordance with the present invention. In FIG. 2, the plasma gas feed inlet is depicted at 31.
As the gaseous reaction product exits the plasma 29 it proceeds towards the outlet of the plasma chamber 20. As is apparent, an additional reactant, as described earlier, can be injected into the reaction chamber prior to the injection of the quench streams. A supply inlet for the reactant is shown in FIG. 2 at 33.
As shown in FIG. 2, in certain embodiments of the present invention, the gaseous product stream is contacted with a plurality of quench streams which enter the plasma chamber 20 in the direction of arrows 41 through a plurality of quench gas injection ports 40 located along the circumference of the plasma chamber 20. As previously indicated, the particular flow rate and injection angle of the quench streams is not limited so long as they result in impingement of the quench streams 41 with each other within the gaseous reaction product stream, in some cases at or near the center of the gaseous product stream, to result in the rapid cooling of the gaseous product stream to produce ultrafine solid particles. This results in a quenching of the gaseous product stream through dilution to form ultrafine solid particles.
Referring now to FIG. 3, there is depicted a perspective view of a plurality of quench gas injection ports 40 in accordance with certain embodiments of the present invention. In this particular embodiment, six (6) quench gas injection ports are depicted, wherein each port disposed at an angle “θ” apart from each other along the circumference of the reactor chamber 20. It will be appreciated that “θ” may have the same or a different value from port to port. In certain embodiments of the present invention, at least four (4) quench gas injection ports 40 are provided, in some cases at least six (6) quench gas injection ports are present. In certain embodiments, each angle “θ” has a value of no more than 90°. In certain embodiments, the quench streams are injected into the plasma chamber normal (90° angle) to the flow of the gaseous reaction product. In certain embodiments, the quench streams are injected into the plasma chamber normal (90° angle) to the flow of the gaseous reaction product. In some cases, however, positive or negative deviations from the 90° angle by as much as 30° may be used.
In certain methods of the present invention, contacting the gaseous product stream with the quench streams results in the formation of ultrafine solid particles, which are then passed into and through a converging member. As used herein, the term “converging member” refers to a device that restricts passage of a flow therethrough, thereby controlling the residence time of the flow in the plasma chamber due to pressure differential upstream and downstream of the converging member.
In certain embodiments, the converging member comprises a convergent-divergent (De Laval) nozzle, such as that which is depicted in FIG. 2, which is coaxially positioned within the outlet of the reactor chamber 20. The converging or upstream section of the nozzle, i.e., the converging member, restricts gas passage and controls the residence time of the materials within the plasma chamber 20. It is believed that the contraction that occurs in the cross sectional size of the gaseous stream as it passes through the converging portion of nozzle 22 changes the motion of at least some of the flow from random directions, including rotational and vibrational motions, to a straight line motion parallel to the reaction chamber axis. In certain embodiments, the dimensions of the plasma chamber 20 and the material are selected to achieve sonic velocity within the restricted nozzle throat.
As the confined stream of flow enters the diverging or downstream portion of the nozzle 22, it is subjected to an ultra fast decrease in pressure as a result of a gradual increase in volume along the conical walls of the nozzle exit. By proper selection of nozzle dimensions, the plasma chamber 20 can be operated at atmospheric pressure, or slightly less than atmospheric pressure, or, in some cases, at a pressurized condition, to achieve the desired residence time, while the chamber 26 downstream of the nozzle 22 is maintained at a vacuum pressure by operation of vacuum pump 60. Following passage through nozzle 22, the ultrafine solid particles may then enter a cool down chamber 26.
As is apparent from FIG. 2, in certain embodiments of the present invention, the ultrafine solid particles may flow from cool down chamber 26 to a collection station 27 via a cooling section 45, which may comprise, for example, a jacket cooled tube. In certain embodiments, the collection station 27 comprises a bag filter or other collection means. A downstream scrubber 28 may be used if desired to condense and collect material within the flow prior to the flow entering vacuum pump 60.
In certain embodiments, the residence times for materials within the plasma chamber 20 are on the order of milliseconds. The solid precursor may be injected under pressure (such as greater than 1 to 100 atmospheres) through a small orifice to achieve sufficient velocity to penetrate and mix with the plasma. In addition, in many cases the injected stream of solid precursor is injected normal (90° angle) to the flow of the plasma gases. In some cases, positive or negative deviations from the 90° angle by as much as 30° may be desired.
The high temperature of the plasma rapidly vaporizes the solid precursor. There is a substantial difference in temperature gradients and gaseous flow patterns along the length of the plasma chamber 20. It is believed that, at the plasma arc inlet, flow is turbulent and there is a high temperature gradient; from temperatures of about 20,000 K at the axis of the chamber to about 375 K at the chamber walls. At the nozzle throat, it is believed, the flow is laminar and there is a very low temperature gradient across its restricted open area.
The plasma chamber is often constructed of water cooled stainless steel, nickel, titanium, or other suitable materials. The plasma chamber can also be constructed of ceramic materials to withstand a vigorous chemical and thermal environment.
The plasma chamber walls may be internally heated by a combination of radiation, convection and conduction. In certain embodiments, cooling of the plasma chamber walls prevents unwanted melting and/or corrosion at their surfaces. The system used to control such cooling should maintain the walls at as high a temperature as can be permitted by the selected wall material, which often is inert to the materials within the plasma chamber at the expected wall temperatures. This is true also with regard to the nozzle walls, which may be subjected to heat by convection and conduction.
The length of the plasma chamber is often determined experimentally by first using an elongated tube within which the user can locate the target threshold temperature. The plasma chamber can then be designed long enough so that precursors have sufficient residence time at the high temperature to reach an equilibrium state and complete the formation of the desired end products.
The inside diameter of the plasma chamber 20 may be determined by the fluid properties of the plasma and moving gaseous stream. It should be sufficiently great to permit necessary gaseous flow, but not so large that recirculating eddys or stagnant zones are formed along the walls of the chamber. Such detrimental flow patterns can cool the gases prematurely and precipitate unwanted products. In many cases, the inside diameter of the plasma chamber 20 is more than 100% of the plasma diameter at the inlet end of the plasma chamber.
In certain embodiments, the converging section of the nozzle has a high aspect ratio change in diameter that maintains smooth transitions to a first steep angle (such as >45°) and then to lesser angles (such as <45° degree.) leading into the nozzle throat. The purpose of the nozzle throat is often to compress the gases and achieve sonic velocities in the flow. The velocities achieved in the nozzle throat and in the downstream diverging section of the nozzle are controlled by the pressure differential between the plasma chamber and the section downstream of the diverging section of the nozzle. Negative pressure can be applied downstream or positive pressure applied upstream for this purpose. A converging-diverging nozzle of the type suitable for use in the present invention is described in U.S. Pat. No. RE37,853 at col. 9, line 65 to col. 11, line 32, the cited portion of which being incorporated by reference herein.
The methods and apparatus of the present invention, which utilize quench gas dilution cooling in combination with a converging member, such as a converging-diverging nozzle, have several benefits. First, such a combination allows for the use of sufficient residence times of solid material within the plasma system that make the use of solid reactants practical. Second, because ultrafine solid particles are formed prior to the flow reaching the converging member, fouling of the plasma chamber is reduced or, in some cases, even eliminated, since the amount of material sticking to the interior surface of the converging member is reduced or, in some cases, eliminated. Third, this combination allows for the collection of ultrafine solid particles at a single collection point, such as a filter bag, with a minimal amount of such particles being deposited within the cooling chamber or cooling section described earlier.
The catalyst nanoparticles described in detail above can be present in the electrodepositable coating composition of the present invention in an amount of at least 0.1 percent by weight of metal (bismuth, molybdenum, tungsten, cerium, and/or zinc) based on weight of total resin solids present in the electrodepositable coating composition. Also, the catalyst nanoparticles can be present in the electrodepositable coating composition of the present invention in an amount less than or equal to 5.0 percent by weight metal, often less than or equal to 3.0 percent by weight metal, and typically less than or equal to 1.0 percent by weight metal based on weight of total resin solids present in the electrodepositable coating composition. The level of catalyst nanoparticles present in the electrodepositable coating composition can range between any combination of these values, inclusive of the recited values. The catalyst is present in an amount sufficient to effect cure (as determined by a method described in detail below) of the composition at a temperature at or below 360° F. (182.2° C.).
As used herein, the term “cure” as used in connection with a composition, e.g., “composition when cured” or a “cured composition”, shall mean that any crosslinkable components of the composition are at least partially crosslinked. In certain embodiments of the present invention, the crosslink density of the crosslinkable components, i.e., the degree of crosslinking, ranges from 5% to 100% of complete crosslinking. In other embodiments, the crosslink density ranges from 35% to 85% of full crosslinking. In other embodiments, the crosslink density ranges from 50% to 85% of full crosslinking. One skilled in the art will understand that the presence and degree of crosslinking, i.e., the crosslink density, can be determined by a variety of methods, such as dynamic mechanical thermal analysis (DMTA) using a TA Instruments DMA 2980 DMTA analyzer conducted under nitrogen. This method determines the glass transition temperature and crosslink density of free films of coatings or polymers. These physical properties of a cured material are related to the structure of the crosslinked network. In an embodiment of the present invention, the sufficiency of cure is evaluated relative to the solvent resistance of the cured film. For example, solvent resistance can be measured by determining the number of double acetone rubs. For purposes of the present invention, a coating is deemed to be “cured” when the film can withstand a minimum of 100 double acetone rubs without substantial softening of the film and no removal of the film.
It should be noted herein that the catalyst is characterized in that the catalyst is substantially non-volatile at the curing temperature, that is, at temperatures at or below 360° F. (182.2° C.). By “substantially non-volatile” is meant that the catalyst does not volatilize from the film into the curing oven environment at these temperatures during the curing process.
As aforementioned, in addition to the catalyst, the electrodepositable coating composition of the present invention comprises (a) one or more active hydrogen-containing, ionic salt group-containing resins, and (b) one or more curing agents.
In some embodiments, the active hydrogen-containing, ionic salt group-containing resin is a cationic resin, for example such as is typically derived from a polyepoxide and can be prepared by reacting together a polyepoxide and a polyhydroxyl group-containing material selected from alcoholic hydroxyl group-containing materials and phenolic hydroxyl group-containing materials to chain extend or build the molecular weight of the polyepoxide. The reaction product can then be reacted with a cationic salt group former to produce the cationic resin.
A chain extended polyepoxide typically is prepared as follows: the polyepoxide and polyhydroxyl group-containing material are reacted together neat or in the presence of an inert organic solvent such as a ketone, including methyl isobutyl ketone and methyl amyl ketone, aromatics such as toluene and xylene, and glycol ethers such as the dimethyl ether of diethylene glycol. The reaction typically is conducted at a temperature of 80° C. to 160° C. for 30 to 180 minutes until an epoxy group-containing resinous reaction product is obtained.
The equivalent ratio of reactants; i.e., epoxy:polyhydroxyl group-containing material is typically from 1.00:0.50 to 1.00:2.00.
The polyepoxide typically has at least two 1,2-epoxy groups. In general the epoxide equivalent weight of the polyepoxide will range from 100 to 2000, typically from 180 to 500. The epoxy compounds may be saturated or unsaturated, cyclic or acyclic, aliphatic, alicyclic, aromatic or heterocyclic. They may contain substituents such as halogen, hydroxyl, and ether groups.
Examples of polyepoxides are those having a 1,2-epoxy equivalency greater than one and preferably two; that is, polyepoxides which have on average two epoxide groups per molecule. The preferred polyepoxides are polyglycidyl ethers of polyhydric alcohols such as cyclic polyols. Particularly preferred are polyglycidyl ethers of polyhydric phenols such as Bisphenol A. These polyepoxides can be produced by etherification of polyhydric phenols with an epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin in the presence of alkali. Besides polyhydric phenols, other cyclic polyols can be used in preparing the polyglycidyl ethers of cyclic polyols. Examples of other cyclic polyols include alicyclic polyols, particularly cycloaliphatic polyols such as 1,2-cyclohexane diol and 1,2-bis(hydroxymethyl)cyclohexane. The preferred polyepoxides have epoxide equivalent weights ranging from 180 to 2000, preferably from 186 to 1200. Epoxy group-containing acrylic polymers can also be used. These polymers typically have an epoxy equivalent weight ranging from 750 to 2000.
Examples of polyhydroxyl group-containing materials used to chain extend or increase the molecular weight of the polyepoxide (i.e., through hydroxyl-epoxy reaction) include alcoholic hydroxyl group-containing materials and phenolic hydroxyl group-containing materials. Examples of alcoholic hydroxyl group-containing materials are simple polyols such as neopentyl glycol; polyester polyols such as those described in U.S. Pat. No. 4,148,772; polyether polyols such as those described in U.S. Pat. No. 4,468,307; and urethane diols such as those described in U.S. Pat. No. 4,931,157. Examples of phenolic hydroxyl group-containing materials are polyhydric phenols such as Bisphenol A, phloroglucinol, catechol, and resorcinol. Mixtures of alcoholic hydroxyl group-containing materials and phenolic hydroxyl group-containing materials may also be used. Bisphenol A is preferred.
The resin can contain cationic salt groups, which can be incorporated into the resin molecule as follows: The resinous reaction product prepared as described above is further reacted with a cationic salt group former. By “cationic salt group former” is meant a material which is reactive with epoxy groups and which can be acidified before, during, or after reaction with the epoxy groups to form cationic salt groups. Examples of suitable materials include amines such as primary or secondary amines which can be acidified after reaction with the epoxy groups to form amine salt groups, or tertiary amines which can be acidified prior to reaction with the epoxy groups and which after reaction with the epoxy groups form quaternary ammonium salt groups. Examples of other cationic salt group formers are sulfides which can be mixed with acid prior to reaction with the epoxy groups and form ternary sulfonium salt groups upon subsequent reaction with the epoxy groups.
When amines are used as the cationic salt formers, monoamines typically are employed. Hydroxyl-containing amines are suitable, and polyamines also may be used.
Tertiary and secondary amines are used more often than primary amines because primary amines are polyfunctional with respect to epoxy groups and have a greater tendency to gel the reaction mixture. If polyamines or primary amines are used, they should be used in a substantial stoichiometric excess to the epoxy functionality in the polyepoxide so as to prevent gelation and the excess amine should be removed from the reaction mixture by vacuum stripping or other technique at the end of the reaction. The epoxy may be added to the amine to ensure excess amine.
Examples of hydroxyl-containing amines include , but are not limited to, alkanolamines, dialkanolamines, alkyl alkanolamines, and aralkyl alkanolamines containing from 1 to 18 carbon atoms, preferably 1 to 6 carbon atoms in each of the alkanol, alkyl and aryl groups. Specific examples include ethanolamine, N-methylethanolamine, diethanolamine, N-phenylethanolamine, N,N-dimethylethanolamine, N-methyidiethanolamine, 3-aminopropyldiethanolamine, and N-(2-hydroxyethyl)-piperazine.
Amines such as mono, di, and trialkylamines and mixed aryl-alkyl amines which do not contain hydroxyl groups or amines substituted with groups other than hydroxyl which do not negatively affect the reaction between the amine and the epoxy may also be used. Specific examples include ethylamine, methylethylamine, triethylamine, N-benzyldimethylamine, dicocoamine, 3-dimethylaminopropylamine, and N,N-dimethylcyclohexylamine.
Mixtures of the above mentioned amines may also be used.
The reaction of a primary and/or secondary amine with the polyepoxide takes place upon mixing of the amine and polyepoxide. The amine may be added to the polyepoxide or vice versa. The reaction can be conducted neat or in the presence of a suitable solvent such as methyl isobutyl ketone, xylene, or 1-methoxy-2-propanol. The reaction is generally exothermic and cooling may be desired. However, heating to a moderate temperature of 50 to 150° C. may be done to hasten the reaction.
The reaction product of the primary and/or secondary amine and the polyepoxide is made cationic and water dispersible by at least partial neutralization with an acid. Suitable acids include organic and inorganic acids. Non-limiting examples of suitable organic acids include formic acid, acetic acid, methanesulfonic acid, and lactic acid. Non-limiting examples of suitable inorganic acids include phosphoric acid and sulfamic acid. By “sulfamic acid” is meant sulfamic acid itself or derivatives thereof; i.e., an acid of the formula:

wherein R is hydrogen or an alkyl group having 1 to 4 carbon atoms. Sulfamic acid is preferred. Mixtures of the above mentioned acids may also be used.
The extent of neutralization of the cationic electrodepositable composition varies with the particular reaction product involved. However, sufficient acid should be used to disperse the electrodepositable composition in water. Typically, the amount of acid used provides at least 20 percent of all of the total neutralization. Excess acid may also be used beyond the amount required for 100 percent total neutralization.
In the reaction of a tertiary amine with a polyepoxide, the tertiary amine can be pre-reacted with the neutralizing acid to form the amine salt and then the amine salt reacted with the polyepoxide to form a quaternary salt group-containing resin. The reaction is conducted by mixing the amine salt with the polyepoxide in water. Typically, the water is present in an amount ranging from 1.75 to 20 percent by weight based on total reaction mixture solids.
In forming the quaternary ammonium salt group-containing resin, the reaction temperature can be varied from the lowest temperature at which the reaction will proceed, generally room temperature or slightly thereabove, to a maximum temperature of 100° C. (at atmospheric pressure). At higher pressures, higher reaction temperatures may be used. Preferably, the reaction temperature is in the range of 60 to 100° C. Solvents such as a sterically hindered ester, ether, or sterically hindered ketone may be used, but their use is not necessary.
In addition to the primary, secondary, and tertiary amines disclosed above, a portion of the amine that is reacted with the polyepoxide can be a ketimine of a polyamine, such as is described in U.S. Pat. No. 4,104,147, column 6, line 23 to column 7, line 23. The ketimine groups decompose upon dispersing the amine-epoxy resin reaction product in water. In an embodiment of the present invention, at least a portion of the active hydrogens present in the resin (a)comprise primary amine groups derived from the reaction of a ketimine-containing compound and an epoxy group-containing material such as those described above.
In addition to resins containing amine salts and quaternary ammonium salt groups, cationic resins containing ternary sulfonium groups may be used in the composition of the present invention. Examples of these resins and their method of preparation are described in U.S. Pat. Nos. 3,793,278 and 3,959,106.
Suitable active hydrogen-containing, cationic salt group-containing resins can include copolymers of one or more alkyl esters of acrylic acid or methacrylic acid optionally together with one or more other polymerizable ethylenically unsaturated monomers. Suitable alkyl esters of acrylic acid or methacrylic acid include methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethyl hexyl acrylate. Suitable other copolymerizable ethylenically unsaturated monomers include nitriles such acrylonitrile and methacrylonitrile, vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride and vinyl esters such as vinyl acetate. Acid and anhydride functional ethylenically unsaturated monomers such as acrylic acid, methacrylic acid or anhydride, itaconic acid, maleic acid or anhydride, or fumaric acid may be used. Amide functional monomers including acrylamide, methacrylamide, and N-alkyl substituted (meth)acrylamides are also suitable. Vinyl aromatic compounds such as styrene and vinyl toluene can be used so long as photodegradation resistance of the polymer and the resulting electrodeposited coating is not compromised.
Functional groups such as hydroxyl and amino groups can be incorporated into the acrylic polymer by using functional monomers such as hydroxyalkyl acrylates and methacrylates or aminoalkyl acrylates and methacrylates. Epoxide functional groups (for conversion to cationic salt groups) may be incorporated into the acrylic polymer by using functional monomers such as glycidyl acrylate and methacrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate, 2-(3,4-epoxycyclohexyl)ethyl(meth)acrylate, or allyl glycidyl ether. Alternatively, epoxide functional groups may be incorporated into the acrylic polymer by reacting carboxyl groups on the acrylic polymer with an epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin.
The acrylic polymer can be prepared by traditional free radical initiated polymerization techniques, such as solution or emulsion polymerization, as known in the art, using suitable catalysts which include organic peroxides and azo type compounds and optionally chain transfer agents such as alpha-methyl styrene dimer and tertiary dodecyl mercaptan. Additional acrylic polymers which are suitable for forming the active hydrogen-containing, cationic resin (a) which can be used in the electrodepositable compositions of the present invention include those resins described in U.S. Pat. Nos. 3,455,806 and 3,928,157.
Polyurethanes can also be used as the polymer from which the active hydrogen-containing, cationic resin can be derived. Among the polyurethanes which can be used are polymeric polyols which are prepared by reacting polyester polyols or acrylic polyols such as those mentioned above with a polyisocyanate such that the OH/NCO equivalent ratio is greater than 1:1 so that free hydroxyl groups are present in the product. Smaller polyhydric alcohols such as those disclosed above for use in the preparation of the polyester may also be used in place of or in combination with the polymeric polyols.
Additional examples of polyurethane polymers suitable for forming the active hydrogen-containing, cationic resin (a) include the polyurethane, polyurea, and poly(urethane-urea) polymers prepared by reacting polyether polyols and/or polyether polyamines with polyisocyanates. Such polyurethane polymers are described in U.S. Pat. No. 6,248,225.
Epoxide functional groups may be incorporated into the polyurethane by methods well known in the art. For example, epoxide groups can be incorporated by reacting glycidol with free isocyanate groups. Alternatively, hydroxyl groups on the polyurethane can be reacted with an epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin in the presence of alkali.
Sulfonium group-containing polyurethanes can also be made by at least partial reaction of hydroxy-functional sulfide compounds, such as thiodiglycol and thiodipropanol, which results in incorporation of sulfur into the backbone of the polymer. The sulfur-containing polymer is then reacted with a monofunctional epoxy compound in the presence of acid to form the sulfonium group. Appropriate monofunctional epoxy compounds include ethylene oxide, propylene oxide, glycidol, phenylglycidyl ether, and CARDURA® E, available from Resolution Performance Products.
Besides the above-described polyepoxide, acrylic and polyurethane polymers, the active hydrogen-containing, cationic salt group-containing polymer can be derived from a polyester. Such polyesters can be prepared in a known manner by condensation of polyhydric alcohols and polycarboxylic acids. Suitable polyhydric alcohols include, for example, ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, diethylene glycol, glycerol, trimethylol propane, and pentaerythritol. Examples of suitable polycarboxylic acids used to prepare the polyester include succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and trimellitic acid. Besides the polycarboxylic acids mentioned above, functional equivalents of the acids such as anhydrides where they exist or lower alkyl esters of the acids such as the methyl esters may be used.
The polyesters contain a portion of free hydroxyl groups (resulting from the use of excess polyhydric alcohol and/or higher polyols during preparation of the polyester) which are available for cure reactions. Epoxide functional groups may be incorporated into the polyester by reacting carboxyl groups on the polyester with an epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin.
Sulfonium salt groups can be introduced by the reaction of an epoxy group-containing polymer of the types described above with a sulfide in the presence of an acid, as described in U.S. Pat. Nos. 3,959,106 and 4,715,898. Sulfonium groups can be introduced onto the polyester backbones described using similar reaction conditions.
It should be understood that the active hydrogens associated with the cationic resin include any active hydrogens which are reactive with isocyanates at temperatures sufficient to cure the electrodepositable composition as previously discussed, i.e., at temperatures at or below 360° F. (182.2° C.). The active hydrogens typically are derived from reactive hydroxyl groups, and primary and secondary amino, including mixed groups such as hydroxyl and primary amino. In one embodiment of the present invention, at least a portion of the active hydrogens are derived from hydroxyl groups comprising phenolic hydroxyl groups. The cationic resin can have an active hydrogen content of 1 to 4 milliequivalents, typically 2 to 3 milliequivalents of active hydrogen per gram of resin solids.
The extent of cationic salt group formation should be such that when the resin is mixed with an aqueous medium and other ingredients, a stable dispersion of the electrodepositable composition will form. By “stable dispersion” is meant one that does not settle or is easily redispersible if some settling occurs. Moreover, the dispersion should be of sufficient cationic character that the dispersed resin particles will electrodeposit on a cathode when an electrical potential is set up between an anode and a cathode immersed in the aqueous dispersion.
Generally, the cationic resin in the electrodepositable composition of the present invention contains from 0.1 to 3.0, such as from 0.1 to 0.7 milliequivalents of cationic salt group per gram of resin solids. The cationic resin typically is non-gelled, having a number average molecular weight ranging from 2000 to 15,000, preferably from 5000 to 10,000. By “non-gelled” is meant that the resin is substantially free from crosslinking, and prior to cationic salt group formation, the resin has a measurable intrinsic viscosity when dissolved in a suitable solvent. In contrast, a gelled resin, having an essentially infinite molecular weight, would have an intrinsic viscosity too high to measure.
The active hydrogen-containing, cationic salt group-containing resin (a) can be present in the electrodepositable composition of the present invention in an amount ranging from 40 to 95 weight percent, typically from 50 to 75 weight percent based on weight of total resin solids present in the composition.
The electrodepositable composition of the present invention also comprises at least one curing agent, such as a polyisocyanate, polyester or carbonate. The polyisocyanate curing agent may be a fully blocked polyisocyanate with substantially no free isocyanate groups, or it may be partially blocked and reacted with the resin backbone as described in U.S. Pat. No. 3,984,299. The polyisocyanate can be an aliphatic or an aromatic polyisocyanate or a mixture of the two. Diisocyanates are preferred, although higher polyisocyanates can be used in place of or in combination with diisocyanates.
Examples of suitable aliphatic diisocyanates are straight chain aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate, norbornane diisocyanate, and 1,6-hexamethylene diisocyanate. Also, cycloaliphatic diisocyanates can be employed. Examples include isophorone diisocyanate and 4,4°-methylene-bis-(cyclohexyl isocyanate). Examples of suitable aromatic diisocyanates are p-phenylene diisocyanate, diphenylmethane-4,4′-diisocyanate and 2,4- or 2,6-toluene diisocyanate. Examples of suitable higher polyisocyanates are triphenylmethane-4,4′,4″-triisocyanate, 1,2,4-benzene triisocyanate and polymethylene polyphenyl isocyanate, and trimers of 1,6-hexamethylene diisocyanate.
Isocyanate prepolymers, for example, reaction products of polyisocyanates with polyols such as neopentyl glycol and trimethylol propane or with polymeric polyols such as polycaprolactone diols and triols (NCO/OH equivalent ratio greater than one) can also be used. A mixture of diphenylmethane-4,4′-diisocyanate and polymethylene polyphenyl isocyanate can be used.
Any suitable alcohol or polyol can be used as a blocking agent for the polyisocyanate in the electrodepositable composition of the present invention provided that the agent will deblock at the curing temperature and provided a gelled product is not formed. Any suitable aliphatic, cycloaliphatic, or aromatic alkyl alcohol may be used as a blocking agent for the polyisocyanate including, for example, lower aliphatic monoalcohols such as methanol, ethanol, and n-butanol; cycloaliphatic alcohols such as cyclohexanol; aromatic-alkyl alcohols such as phenyl carbinol and methylphenyl carbinol. Glycol ethers may also be used as blocking agents. Suitable glycol ethers include ethylene glycol butyl ether, diethylene glycol butyl ether, ethylene glycol methyl ether and propylene glycol methyl ether.
In one embodiment of the present invention, the blocking agent comprises one or more 1,3-glycols and/or 1,2-glycols. In one embodiment of the present invention, the blocking agent comprises one or more 1,2-glycols, typically one or more C₃to C₆1,2-glycols. For example, the blocking agent can be selected from at least one of 1,2-propanediol, 1,3-butanediol, 1,2-butanediol, 1,2-pentanediol and 1,2-hexanediol. It has been observed that the presence of such blocking agents facilitates dissolution or dispersion of the organotin catalyst in the resinous phase or components thereof.
Other suitable blocking agents include oximes such as methyl ethyl ketoxime, acetone oxime and cyclohexanone oxime and lactams such as epsilon-caprolactam.
In some embodiments, the curing agent comprises one or more polyester curing agents. Suitable polyester curing agents include materials having greater than one ester group per molecule. The ester groups are present in an amount sufficient to effect cross-linking at acceptable cure temperatures and cure times, for example at temperatures up to 250° C., and curing times of up to 90 minutes. It should be understood that acceptable cure temperatures and cure times will be dependent upon the substrates to be coated and their end uses.
Compounds generally suitable as the polyester curing agent are polyesters of polycarboxylic acids. Non-limiting examples include bis(2-hydroxyalkyl)esters of dicarboxylic acids, such as bis(2-hydroxybutyl) azelate and bis(2-hydroxyethyl)terephthalate; tri(2-ethylhexanoyl)trimellitate; and poly(2-hydroxyalkyl)esters of acidic half-esters prepared from a dicarboxylic acid anhydride and an alcohol, including polyhydric alcohols. The latter type is suitable to provide a polyester with a final functionality of more than 2. One suitable example includes a polyester prepared by first reacting equivalent amounts of the dicarboxylic acid anhydride (for example, succinic anhydride or phthalic anhydride) with a trihydric or tetrahydric alcohol, such as glycerol, trimethylolpropane or pentaerythritol, at temperatures below 150° C., and then reacting the acidic polyester with at least an equivalent amount of an epoxy alkane, such as 1,2-epoxy butane, ethylene oxide, or propylene oxide. The polyester curing agent (ii) can comprise an anhydride. Another suitable polyester comprises a lower 2-hydroxy-akylterminated poly-alkyleneglycol terephthalate.
In some embodiments, the polyester comprises at least one ester group per molecule in which the carbon atom adjacent to the esterified hydroxyl has a free hydroxyl group.
Also suitable is the tetrafunctional polyester prepared from the half-ester intermediate prepared by reacting trimellitic anhydride and propylene glycol (molar ratio 2:1), then reacting the intermediate with 1,2-epoxy butane and the glycidyl ester of branched monocarboxylic acids.
In some embodiments, where the active hydrogen-containing resin comprises cationic salt groups, the polyester curing agent is substantially free of acid. For purposes of the present invention, by “substantially free of acid” is meant having less than 0.2 meq/g acid. For aqueous systems, for example for cathodic electrodepositable, coating compositions, suitable polyester curing agents can include non-acidic polyesters prepared from a polycarboxylic acid anhydride, one or more glycols, alcohols, glycol mono-ethers, polyols, and/or monoepoxides. Suitable polycarboxylic anhydrides can include dicarboxylic acid anhydrides, such as succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, and pyromellitic dianhydride. Mixtures of anhydrides can be used. Suitable alcohols can include linear, cyclic or branched alcohols. The alcohols may be aliphatic, aromatic or araliphatic in nature. As used herein, the terms glycols and mono-epoxides are intended to include compounds containing not more than two alcohol groups per molecule which can be reacted with carboxylic acid or anhydride functions below the temperature of 150° C.
Suitable mono-epoxides can include glycidyl esters of branched monocarboxylic acids. Further, alkylene oxides, such as ethylene oxide or propylene oxide may be used. Suitable glycols can include, for example ethylene glycol and polyethylene glycols, propylene glycol and polypropylene glycols, and 1,6-hexanediol. Mixtures of glycols may be used.
Non-acidic polyesters can be prepared, for example, by reacting, in one or more steps, trimellitic anhydride (TMA) with glycidyl esters of branched monocarboxylic acids in a molar ratio of 1:1.5 to 1:3, if desired with the aid of an esterification catalyst such as stannous octoate or benzyl dimethyl amine, at temperatures of 50-150° C. Additionally, trimellitic anhydride can be reacted with 3 molar equivalents of a monoalcohol such as 2-ethylhexanol.
Alternatively, trimellitic anhydride (1 mol.) can be reacted first with a glycol or a glycol monoalkyl ether, such as ethylene glycol monobutyl ether in a molar ratio of 1:0.5 to 1:1, after which the product is allowed to react with 2 moles of glycidyl esters of branched monocarboxylic acids. Furthermore, the polycarboxylic acid anhydride i.e., those containing two or three carboxyl functions per molecule) or a mixture of polycarboxylic acid anhydrides can be reacted simultaneously with a glycol, such as 1,6-hexane diol and/or glycol mono-ether and monoepoxide, after which the product can be reacted with mono-epoxides, if desired. For aqueous compositions these non-acid polyesters can also be modified with polyamines such as diethylene triamine to form amide polyesters. Such “amine-modified” polyesters may be incorporated in the linear or branched amine adducts described above to form self-curing amine adduct esters.
The non-acidic polyesters of the types described above typically are soluble in organic solvents, and typically can be mixed readily with the active hydrogen-containing resin (i) previously described.
Polyesters suitable for use in an aqueous system or mixtures of such materials disperse in water typically in the presence of resins comprising cationic or anionic salt groups.
In some embodiments, the curing agent comprises one or more cyclic or acyclic carbonates. Non-limiting examples of suitable acyclic carbonates include dimethyl carbonate, diethyl carbonate, methylethyl carbonate, dipropyl carbonate, methylpropyl carbonate, and/or dibutyl carbonate. In some embodiments of the present invention, the acyclic carbonate comprises dimethyl carbonate.
The curing agent (b) is usually present in the electrodepositable composition in an amount ranging from 5 to 60 percent by weight, typically from 25 to 50 percent by weight based on total weight of resin solids.
It should be understood that the catalyst nanoparticles can be incorporated into the electrodepositable composition of the present invention by any method or means provided that the stability of the composition is not compromised. For example, the catalyst nanoparticles can be admixed with or dispersed in the reactants used to form the resin (a) during preparation of the resin (a). Also, the catalyst nanoparticles can be admixed with or dispersed in one or more of the reactants used to form the resin (a) prior to resin preparation. In addition, the catalyst nanoparticles can be admixed with or dispersed in the resin (a) either prior to or subsequent to neutralization with an acid. The catalyst nanoparticles also can be admixed with or dispersed in the at least partially blocked polyisocyanate curing agent (b) prior to combining the resin (a) and the curing agent (b). Further, the catalyst nanoparticles can be admixed with or dispersed in the admixture of the resin (a) and the curing agent (b). Alternatively, the catalyst nanoparticles can be added to any of the optional additives, solvents, or adjuvant resinous materials as described below prior to addition of the optional ingredients to the composition. Also, the catalyst nanoparticles can be directly admixed with or dispersed in the aqueous medium, prior to dispersion of the resinous phase in the aqueous medium. The catalyst nanoparticles also can be added neat to the electrodepositable composition subsequent to dispersion in the aqueous medium. Additionally, if desired, the catalyst nanoparticles can be added on-line to the electrodeposition bath in the form of an additive material. It should be understood that the catalyst can be incorporated into the electrodepositable composition by one or more of the above described methods.
The electrodepositable composition may optionally contain a coalescing solvent such as hydrocarbons, alcohols, esters, ethers and ketones. Examples of preferred coalescing solvents are alcohols, including polyols, such as isopropanol, butanol, 2-ethylhexanol, ethylene glycol and propylene glycol; ethers such as the monobutyl and monohexyl ethers of ethylene glycol; and ketones such as methyl isobutyl ketone and isophorone. The coalescing solvent is usually present in an amount up to 40 percent by weight, typically ranging from 0.05 to 25 percent by weight based on total weight of the electrodepositable composition.
The electrodepositable composition of the present invention may further contain pigments and various other optional additives such as plasticizers, surfactants, wetting agents, defoamers, and anti-cratering agents, as well as adjuvant resinous materials different from the resin (a) and the curing agent (b).
Suitable pigments include, but are not limited to, iron oxides, lead oxides, carbon black, coal dust, titanium dioxide, talc, clay, silica, and barium sulfate, as well as color pigments such as cadmium yellow, cadmium red, chromium yellow, and the like. The pigment content of the aqueous dispersion, generally expressed as the pigment to resin (or pigment to binder) ratio (P/B) is usually 0.05:1 to 1:1. In a particular embodiment, the electrodepositable coating composition of the present invention is free of lead-containing compounds.
The electrodepositable coating composition of the present invention is used in an electrodeposition process in the form of an aqueous dispersion. By “dispersion” is meant a two-phase transparent, translucent, or opaque aqueous resinous system in which the resin, pigment, and water insoluble materials are in the dispersed phase while water and water-soluble materials comprise the continuous phase. The dispersed phase can have an average particle size of less than 10 microns, and can be less than 5 microns. The aqueous dispersion can contain at least 0.05 and usually 0.05 to 50 percent by weight resin solids, depending on the particular end use of the dispersion.
The electrodepositable compositions of the present invention in the form of an aqueous dispersion have excellent storage stability, that is, upon storage at a temperature of 140° F. (60° C.) for a period of 14 days, the compositions are stable. By “stable dispersion” is meant herein that the resinous phase and the nanoparticulate catalyst remain uniformly dispersed throughout the aqueous phase of the composition. Upon storage under the conditions described above, the dispersions do not flocculate or form a hard sediment. If over time some sedimentation occurs, it can be easily re-dispersed with low shear stirring.
In the process of electrodeposition, the electrodepositable composition of the present invention in the form of an aqueous dispersion is placed in contact with an electrically conductive anode and cathode, where the substrate serves as the cathode. Upon passage of an electric current between the anode and cathode while they are in contact with the aqueous dispersion, an adherent film of the electrodepositable composition will deposit in a substantially continuous manner on the cathode. The film will contain the active hydrogen-containing resin, the blocked polyisocyanate curing agent, the catalyst, and the optional additives from the non-aqueous phase of the dispersion.
The thickness of the electrodepositable coating applied to the substrate can vary based upon such factors as the type of substrate and intended use of the substrate, i.e., the environment in which the substrate is to be placed and the nature of the contacting materials.
In yet another embodiment, the present invention is directed to a coated substrate comprising a substrate and a composition coated over the substrate, wherein the composition is selected from any of the foregoing compositions. In still another embodiment, the present invention is directed to a method of coating a substrate which comprises applying a composition over the substrate, wherein the composition is selected from any of the foregoing compositions. In another embodiment, the present invention is directed to a method for forming a cured coating on a substrate comprising applying over the substrate a coating composition, wherein the composition is selected from any of the foregoing compositions.
In another embodiment, the present invention is directed to a method of coating a substrate further comprising a step of curing the composition after application to the substrate. The components used to form the compositions in these embodiments can be selected from the components discussed above, and additional components also can be selected from those recited above.
As used herein, a composition “over a substrate” refers to a composition directly applied to at least a portion of the substrate, as well as a composition applied to any coating material which was previously applied to at least a portion of the substrate.
Electrodeposition is usually carried out at a constant voltage in the range of from 1 volt to several thousand volts, typically between 50 and 500 volts. Current density is usually between 1.0 ampere and 15 amperes per square foot (10.8 to 161.5 amperes per square meter) and tends to decrease quickly during the electrodeposition process, indicating formation of a continuous self-insulating film. Any electroconductive substrate known in the art, especially metal substrates such as steel, zinc, aluminum, copper, magnesium or the like can be coated with the electrodepositable composition of the present invention. Steel substrates are preferred. It is customary to pretreat the substrate with a phosphate conversion, usually a zinc phosphate conversion coating, followed by a rinse which seals the conversion coating.
After deposition, the coating is heated to cure the deposited composition. The heating or curing operation can be carried out at a temperature in the range of from 250 to 400° F. (121.1 to 204.4° C.), typically from 300 to 360° F. (148.8 to 182.2° C.) for a period of time ranging from 1 to 60 minutes. The thickness of the resultant film typically can range from 10 to 50 microns.
The invention will be further described by reference to the following examples. Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLES

Nanoparticle catalyst materials according to the present invention were prepared as follows:
Particles from solid precursors were prepared using a DC thermal plasma reactor system of the type described in U.S. Pat. No. RE 37,853E. The main reactor system included a DC plasma torch (Model SG-100 Plasma Spray Gun commercially available from Praxair Technology, Inc., Danbury, Conn.) operated with 60 standard liters per minute of argon carrier gas and 28 kilowatts of power delivered to the torch. Solid reactant feed compositions comprising the materials and amounts listed in Tables 1-5 were prepared and fed to the reactor at a rate of 2.5 grams per minute through a gas assistant powder feeder (Model 1264, commercially available from Praxair Technology, Inc., Danbury, Conn.) located at the plasma torch outlet. At the powder feeder, 2.6 standard liters per minute argon were used as carrier gas. Oxygen at 10 standard liters per minute was delivered through two ⅛ inch diameter nozzles located 180° apart at 0.69″ downstream of the powder injector port. Following a 9.7 inch long reactor section, a quench system was provided that included a quench gas injection port that included 6⅛ inch diameter nozzles located 60° apart radially and a 7 millimeter diameter converging-diverging nozzle located 3 inches downstream of the quench gas injection port. Quench air was injected at the quench gas injection port at a rate of 100 standard liters per minute.

Example 1

	TABLE 1


	Material	Amount

	Bismuth Trioxide¹	195 grams
	Fumed Silica²	5 grams

	¹Commercially available from Pharmacie Central de Guinea, France.
	²Commercially available from Cabot Corporation, Massachusetts; Cab-O-Sil M5 grade.

Nanoparticles having a theoretical composition of 97.5 weight percent bismuth oxide and 2.5 weight percent silica were prepared by the above method using the feed composition listed in Table 1. The measured B.E.T. specific surface area of the nanoparticles was 32 square meters per gram using the Gemini model 2360 analyzer and the calculated equivalent spherical diameter was 21 nanometers. FIG. 4 is a micrograph of a TEM image of a representative portion of the particles (10,000× magnification). The micrograph was prepared by weighing out 0.2 to 0.4 grams of the particles and adding those particles to methanol present in an amount sufficient to yield an adequate particle density on a TEM grid. The mixture was placed in a sonicater for 20 minutes and then dispersed onto a 3 millimeter TEM grid coated with a uniform carbon film using a disposable pipette. After allowing the methanol to evaporate, the grid was loaded into a specimen holder which was then inserted into a TEM instrument.

Example 2

Particles from solid precursors were prepared using the same apparatus and operating conditions identified in Example 1, except that the solid reactant feed composition comprised the materials and amounts listed in Table 2.

	TABLE 2


	Material	Amount

	Bismuth Trioxide
³	20 grams
	Silica⁴	80 grams

	³Commercially available from Sigma Aldrich Co., St Louis, Missouri, having an average particle size of 3 microns.
	⁴Commercially available under trade name WB-10 from PPG Industries, Inc., Pittsburgh, PA.

Nanoparticles having a theoretical composition of 20 weight percent bismuth oxide and 80 weight percent silica were prepared by the above method using the feed composition listed in Table 2. The measured B.E.T. specific surface area was 143 square meters per gram using the Gemini model 2360 analyzer and the calculated equivalent spherical diameter was 12 nanometers. FIG. 5 is a micrograph of a TEM image of a representative portion of the particles (210,000× magnification). The micrograph was prepared in the manner described in Example 1.

Example 3

Particles from solid precursors were prepared using the same apparatus and operating conditions identified in Example 1, except that the solid reactant feed composition comprised the materials and amounts listed in Table 3.

TABLE 3

Material Amount

Bismuth Trioxide

³ 40 grams

Silica

⁴ 60 grams
Nanoparticles having a theoretical composition of 40 weight percent bismuth oxide and 60 weight percent silica were prepared by the above method using the feed composition listed in Table 3. The measured B.E.T. specific surface area was 80 square meters per gram using the Gemini model 2360 analyzer and the calculated equivalent spherical diameter was 15 nanometers.

Example 4

Particles from solid precursors were prepared using the same apparatus and operating conditions identified in Example 1, except that the solid reactant feed composition comprised the materials and amounts listed in Table 4.

TABLE 4

Material Amount

Bismuth Trioxide

³ 60 grams

Fumed Silica ⁴ 40 grams
Nanoparticles having a theoretical composition of 60 weight percent bismuth oxide and 40 weight percent silica were prepared by the above method using the feed composition listed in Table 4. The measured B.E.T. specific surface area was 62 square meters per gram using the Gemini model 2360 analyzer and the calculated equivalent spherical diameter was 16 nanometers.

Comparative Example 5

Bismuth silicate particles from a solution process were prepared using feed composition comprised the materials and amounts listed in Table 5. A solution was prepared by adding powder of components 1, 2, and 3 to the liquid of component 4. The solution was heated to 97 degrees Celsius to increase solubility of the solid components. Component 5 was added to the solution to form bismuth silicate particles. The precipitated particles were collected by filtering from the solution and drying at room temperature.

TABLE 5


Component	Material	Amount

1	Bismuth Trioxide³	70.73 grams
2	Aminocaproic acid	81.22 grams
3	Sulfamic acid	30.03 grams
4	Deionized water	209.04 grams
5	Sodium silicate	98.46 grams

Nanoparticles having a theoretical composition of 40 mole percent bismuth oxide and 60 mole percent silica were prepared by the above method using the feed composition listed in Table 5. The measured B.E.T. specific surface area was 109 square meters per gram using the Gemini model 2360 analyzer. The resulting product was agglomerated porous material.

Coating Composition Examples 1A to 1D

Coating compositions were prepared using the components and weights (in grams) shown in Table 6. Coatings were prepared by adding components 1 to 3 to a suitable vessel under agitation with a tong press for 3 minutes.

TABLE 6


			Comparative	Comparative	Comparative
Component	Material	Sample 1A	Example 1B	Example 1C	Example 1D

1	Resin ⁵	30	30	30	30
2	MIBK	5	5	5	5
3	Example 1 catalyst	0.831
	material
	Dibutyl tin dilaurate		1.982
	Bi₂O₃ ¹			0.831
	Bismuth				6.007
	methanesulfonate⁶

⁵The resin was prepared from the following components as set forth below:

		weight
1	Epon 828^5a	817.1
2	Bisphenol A	239.0
3	MACOL 98 A MOD 1^5b	291.5
4	Methylisobutyl ketone (mibk)	70.93
5	Benzyldimethyl amine	0.92
6	Benzyldimethyl amine	2.64
7	Crosslinker^5c	1429.2
8	Ketimine^5d	98.23
9	N-methyl ethanolamine	77.68
10	Epon 828	17.1
11	MIBK	2.56
12	Deionized H₂O	33.0
13	Epon 828	17.07
14	MIBK	2.56
15	MIBK	705.52

^5aEpoxy resin available from Resolution Performance Products

^5bBisphenol ethylene oxide adduct available from BASF Corporation.

^5cThe crosslinker was prepared as follows:

		weight
1	PAPI 2940¹	1320.00
2	Methyl isobutyl ketone (mibk)	626.47
3	trimethylolpropane	134.19
4	Dibutyltindilaurate	1.00
5	Diethyleneglycol monobutyl ether	1135.61
6	MIBK	61.96
	TOTAL	3279.23

¹Isocyanate, available from Dow Chemical Co Items 1 and 2 were charged to a 4 neck round

bottom flask, fit with a stirrer, temperature measuring probe, N₂blanket and Dean-Stark

trap and heated to 80° C. Charge 3 was added and the reaction mixture exothermed to about

90° C. and was then heated to 105° C. The mixture was then held at this temperature until

the measured isocyanate equivalent is 297 ± 10. Charge 4 was then added and charges 5 and 6

were added over about 30 minutes without exceeding 110° C. The mixture was then held at

110° C. until the infrared spectrum indicated the absence of isocyanate.

^5dMIBK diketimine of diethylene triamine at 72.7% in MIBK

All weights were in grams. Items 1, 2, 3, and 4 were charged to a 4 neck round bottom

flask, fit with a stirrer, temperature measuring probe, N₂blanket and Dean-Stark trap

and heated to 130° C. Charge 5 was added and the mixture exothermed to about 150° C. The

temperature was allowed to drop to 143° C. and held at this temperature for 30 minutes.

Charge 6 was then added and the mixture was held until the epoxide equivalent weight

(based on solids) was 1087. Charges 7, 8, and 9 were added and the mixture was held at

123° C. for one hour. Charges 10 and 11 (mixed) were added and the mixture was cooled to

96-99° C. over 90 minutes. Charge 12 was added over 15 minutes with the temperature at

96-99° C. Charges 13 and 14 mixed were added, charge 15 was added. The mixture was

then held at 96-99° C. for two hours. The resin had a solids content of about 75%.

⁶Made using the material and process described in the Example 2, Canadian patent # 2362073.

The compositions of Table 6 were applied to galvanized test substrates (APR26917, ACT Laboratories, Hillsdale, Mich.) using a draw down bar (PG&T Co.). Each composition was applied to form a 5 mils (127 microns) thickness coating layer on a surface of the substrate. Panels were placed in an electrical oven for 20 minutes. Curing was tested using a double-rub method with acetone as solvent. The film is marked as cured if no penetration or significant scratch is observed after 100 times of double-rubbing. Results of the testing are set forth in Table 7. Lower curing temperature indicated better catalytic activity of the materials.

	TABLE 7


	Temperature (° F.)

	400	380	360	340	320

Example 1A	Cured	Cured	Cured	Cured	Not cured
Comparative	Cured	Cured	Cured	Cured	Not cured
Example 1B
Comparative	Not cured	Not cured	Not cured	Not cured	Not cured
Example 1C
Comparative	Cured	Cured	Not cured	Not cured	Not cured
Example 1D

As shown in Table 7 above, the coating composition of Example 1A according to the present invention successfully cured at the same temperature (340° F.) as Comparative Example 1B, which contained more than twice as much of dibutyl tin dilaurate catalyst. Also, the coating composition of Example 1A (having bismuth oxide and silica) according to the present invention successfully cured at a temperature of 340° F., whereas the coating composition of Comparative Example 1C using the same amount of bismuth trioxide¹alone did not.

Coating Composition Examples 2A to 2C

Coating compositions were prepared using the components and weights (in grams) shown in Table 8. Coatings were prepared by adding components 1 to 3 to a suitable vessel under agitation with a tong press for 3 minutes.

TABLE 8

Example Example

Component Material Example 2A 2B 2C

1 Resin ⁵ 30 30 30

2 MIBK 7 6 5

3 Example 2 catalyst 4.158

material

Example 3 catalyst 2.079

material

Example 4 catalyst 1.386

material
The compositions of Table 8 were applied to galvanized test substrates, cured and tested as above. Results are set forth in Table 9.

TABLE 9

Temperature (° F.)

400 380 360 340 320

Example 2A Cured Cured Cured Cured Not cured

Example 2B Cured Cured Cured Cured Not cured

Example 2C Cured Cured Cured Cured Not cured
The coating compositions of Examples 2A-2C according to the present invention cured at a temperature of 340° F.

Coating Composition Examples 3A to 3D

Coating compositions were prepared using the components and weights (in grams) shown in Table 10. Coatings were prepared by adding components 1 to 3 to a suitable vessel under agitation with a tong press for 3 minutes.

TABLE 10


		Example	Example	Example	Example
Component	Material	3A	3B	3C	3D

1	Resin⁵	10	10	10	10
2	MIBK	2	2	2	2
3	Example 2	0.284
	catalyst
	material
	Example 3		0.284
	catalyst
	material
	Example 4			0.284
	catalyst
	material
	Example 1				0.284
	catalyst
	material

The compositions of Table 10 were applied to galvanized test substrates, cured and tested as above. Results are set forth in Table 11.

TABLE 11

Temperature (° F.)

400 380 360 340 320

Example 3A Cured Cured Cured Cured Not cured

Example 3B Cured Cured Cured Cured Not cured

Example 3C Cured Cured Cured Cured Not cured

Example 3D Cured Cured Cured Cured Not cured
The coating compositions of Examples 3A-3D according to the present invention cured at a temperature of 340° F.

Coating Composition Examples 4A to 4D

Coating compositions were prepared using the components and weights (in grams) shown in Table 12. Coatings were prepared by adding components 1 to 3 to a suitable vessel under agitation with a tong press for 3 minutes.

TABLE 12

Example Example

Component Material Example 4A 4B 4C

1 Resin ⁵ 20 20 20

2 Example 2 catalyst 0.480

material

Example 2 catalyst 0.240

material

Example 2 catalyst 0.120

material
The compositions of Table 12 were applied to galvanized test substrates, cured and tested as above. Results are set forth in Table 13.

TABLE 13

Temperature (° F.)

400 380 360 340 320

Example 4A Cured Cured Cured Cured Not cured

Example 4B Cured Cured Cured Not cured Not cured

Example 4C Cured Cured Not cured Not cured Not cured

Coating Composition Examples 5A to 5D

Coating compositions were prepared using the components and weights (in grams) shown in Table 14. Coatings were prepared by adding components 1 and 2 to a suitable vessel under agitation with a tong press for 3 minutes.

TABLE 14


		Comparative	Comparative	Comparative	Example	Example
Component	Material	Example 5A	Example 5B	Example 5C	5D	5E

1	Resin⁵	10	20	10	10	10
2	Bismuth Trioxide⁷		0.189
	Bismuth Trioxide			0.5
	and Silica⁸
	Example 2 catalyst				0.5
	material
	Example 5 catalyst					0.113
	material

⁷Commercially available from Nanostructured and Amorphous Materials Inc., Houston, TX. having a B.E.T. specific surface area of 3.5 m²/g and a particle size of 193 nm.
⁸A mixture of 20 weight percent Bismuth trioxide from Nanostructured and Amorphous Materials and 80 weight percent precipitated silica from PPG Industries under the trade name WB-10.

The compositions of Table 14 were applied to galvanized test substrates, cured and tested as above. Results are illustrated in Table 15.

	TABLE 15


	Temperature (° F.)

	400	380	360	340	320

Comparative	Not cured	Not cured	Not cured	Not cured	Not cured
Example 5A
Comparative	Cured	Cured	Not cured	Not cured	Not cured
Example 5B
Comparative	Cured	Cured	Not cured	Not cured	Not cured
Example 5C
Example 5D	Cured	Cured	Cured	Cured	Not cured
Example 5E	Cured	Cured	Not cured	Not cured	Not cured

Both of the composition of Example 5D and the composition of Comparative Example composition 5C contained similar amounts of bismuth trioxide and silica. As shown in the above Examples, the composition of Example 5D cured at a lower temperature (340° F.) compared to the Comparative Example composition 5C (380° F.).

Electrodeposited Coatings—Example 6

Electrodeposited coatings were prepared comprising catalyst nanoparticles of Example 1 above using the components and weights (in grams) shown in Table 16.

TABLE 16


				Pigment
Component		Weight	Resin solids	Solids

1	Plasticizer⁹	76.9	26.9
2	Non-ionic surfactant¹⁰	6.8	6.8
3	Resin¹¹	1057.5	396.6
4	Deionized water	350.5
5	Propylene glycol	12.5
	monomethyl ether
6	Ethylene glycol	6.3
	monohexyl ether
7	Plasticizer¹²	49.9
8	Deionized water	200
9	W9771-1P5 pigment	239.6	47.1	74.4
	paste¹³
10	Deionized water	1800
	Total	3800	495.7	74.4

⁹The plasticizer was prepared as follows: 711 g of DER732 aliphatic

epoxy resin available from Dow Chemical Co., and 164.5 g bisphenol A

were charged to a suitably equipped 3-liter round-bottomed flask. The

mixture was heated to 130° C. and 1.65 g benzyldimethyl amine was

added. The reaction mixture was held at 135° C. until the epoxide

equivalent weight of the mixture was 1232. 78.8 g of butyl carbitol

formal available as Mazon 1651 from BASF Corporation was added and

then the mixture is cooled to 95° C. 184.7 g Jeffamine D400

polyoxypropylene diamine available from Huntsman Corp. was added and

the reaction held at 95° C. until the Gardner-Holdt viscosity of

a sample of the resin diluted 50/50 in methoxy propanol was “HJ”.

A mixture of 19.1 g Epon 828 and 3.4 g butyl Carbitol formal was added

and the mixture held until the Gardner-Holdt viscosity of a sample of

the resin diluted 50/50 in methoxy propanol was “Q-”. 988.6 g of

this resin was poured into a mixture of 1242.13 g deionized water and

30.2 g sulfamic and mixed for 30 minutes. 614.8 g deionized water was

then added and mixed well. The final aqueous dispersion had a measured

solids content of 35.8%

¹⁰MAZON 1651 butyl carbitol formal non-ionic surfactant commercially

available from BASF Corp.

¹¹The resin was prepared as follows:

		weight
1	Epon 828^5a	476.6
2	Bisphenol A	139.4
3	MACOL 98 A MOD 1^5b	170.0
4	Methylisobutyl ketone (MIBK)	41.37
5	Benzyldimethyl amine	0.54
6	Benzyldimethyl amine	1.54
7	Crosslinker^5c	833.7
8	Ketimine^5d	57.30
9	N-methyl ethanolamine	45.31
10	Epon 828	10.0
11	MIBK	1.49
12	Deionized H2O	19.3
13	Epon 828	9.96
14	MIBK	1.49
15	MIBK	99.22
16	Bi₂O₃particles of Example 1	27.15
17	sulfamic acid	61.3
18	Deionized H₂O	845.8
19	Deionized H₂O	1141
20	Deionized H₂O	980

All weights were in grams. Items 1, 2, 3, and 4 were charged to a 4

neck round bottom flask, fit with a stirrer, temperature measuring

probe, N₂blanket and Dean-Stark trap and heated to

130° C. Charge 5 was added and the mixture exotherms to

about 150° C. The temperature was allowed to drop to

143° C. and held at this temperature for 30 minutes. Charge

6 was then added and the mixture was held until the epoxide

equivalent weight (based on solids) was 1087. Charges 7, 8,

and 9 were added and the mixture is held at 123° C. for one

hour. Charges 10 and 11 (mixed) were added and the mixture is

cooled to 96-99° C. over 90 minutes. Charge 12 was added

over 15 minutes with the temperature at 96-99° C. Charges

13 and 14 mixed were added and a slurry of items 15 and 16 was

added. The mixture was then held at 96-99° C. for two

hours. 1644 g of the reaction mixture was poured into a solution

of items 17 and 18 with good stirring. The resulting dispersion was

mixed for thirty minutes and then charge 19 was added with stirring

over about 30 minutes. Charge 20 was added and mixed well. About

1000 g of water and solvent were stripped off under vacuum at

60-65° C. The resulting aqueous dispersion had a solids

content of 37.75%

¹²The plasticizer was prepared as follows:

1	MAZEEN 355 70^12a	1423.49
2	acetic acid	15.12
3	Dibutyltindilaurate	1.52
4	Toluene diisocyanate 80/20	200.50
5	acetic acid	49.32
6	deionized H2O	1623.68
7	deionized H2O	766.89

^12aAmine functional diol of amine equivalent weight 1131

available from BASF Corporation

Items 1 and 2 were charged to a 4 neck round bottom flask, fit with a

stirrer, temperature measuring probe and N₂blanket and mixed for

10 minutes. Item 3 was added and then item 4 was charged over about 1

hour allowing the reaction mixture to exotherm to a maximum temperature

of 100° C. The mixture was then held at 100° C. until the

infrared spectrum indicates the absence of isocyanate (approximately

1 hour). 1395 g of the reaction mixture was poured into a mixture of

items 5 and 6 and mixed for 1 hour. Item 7 was then added over about

1 hour and mixed for about 1 hour. The resulting aqueous solution had

a solids content of about 36%.

¹³Commercially available from PPG Industries, Inc.

The components in Table 16 were mixed as follows: Charge 2 was added under mild agitation to charge 1, and then blended with the mixture of charges 3 and 4. Charges 5, 6, and the mixture of charges 7 and 8 were sequentially added. Charge 9 was diluted with charge 10, and then added to the blend prepared above.
Phosphated cold rolled steel panels from ACT, C700/DI, were electrocoated and cured as set forth below:

TABLE 17

Film build Double Acetone

Electrocoat Conditions Cure time/temp (mils) Rubs

2 min/200volts/90° F. 25′/360° F. 0.76 >100

2 min/220volts/90° F. 25′/340° F. 0.81 >100

2 min/220volts/90° F. 25′/320° F. 0.86 10
Cure was determined by soaking a cotton cloth in acetone and rubbing the cured film with an even back and forth stroke, up to 100 times. The films were evaluated for the degree of mar. As shown in Table 17, an electrodeposited coating containing nanoparticles according to the present invention (Example 6) showed acceptable mar resistance at cure temperatures as low as 340° F. (171.1° C.).
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numeous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims

1. An electrodepositable coating composition comprising a resinous phase and catalyst nanoparticles dispersed in an aqueous medium,

the resinous phase comprising:

(a) a active hydrogen-containing, ionic salt group-containing resin; and

(b) a curing agent; and

the catalyst nanoparticles for effecting cure between the resin (a) and the curing agent (b), the catalyst nanoparticles being selected from the group consisting of bismuth oxide; bismuth silicate; bismuth titanate; molybdenum oxide; molybdenum silicate; molybdenum titanate; tungsten oxide; tungsten silicate; tungsten titanate; a combination of cerium oxide, zinc oxide and silicon dioxide; a combination of cerium oxide and silicon dioxide; and combinations thereof, wherein the catalyst nanoparticles have an average B.E.T. specific surface area greater than 20 square meters per gram (m²/g).

2. The electrodepositable coating composition according to claim 1, wherein at least a portion of the catalyst nanoparticles are dispersed in one or both of the resin (a) and the curing agent (b) prior to dispersing the resinous phase in the aqueous medium.

3. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles comprise bismuth oxide.

4. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles comprise bismuth oxide and bismuth silicate.

5. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles further comprise silica.

6. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles have an average B.E.T. specific surface area greater than 25 square meters per gram (m²/g).

7. The electrodepositable coating composition according to claim 6, wherein the catalyst nanoparticles have an average B.E.T. specific surface area greater than 30 square meters per gram (m²/g).

8. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles have an average primary particle size of less than 500 nanometers.

9. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles are present in the electrodepositable coating composition in an amount sufficient to effect cure of the electrodepositable composition at a temperature at or below 360° F. (182.2° C.).

10. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles are present in the electrodepositable coating composition in an amount sufficient to effect cure of the electrodepositable composition at a temperature at or below 340° F. (171.1° C.).

11. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles are present in the coating composition in an amount sufficient to effect cure of the coating composition at or below a temperature of 320° F. (160° C.).

12. The electrodepositable coating composition according to claim 1, wherein the catalyst nanoparticles are present in the coating composition in an amount ranging from 0.1 to 5.0 percent by weight of metal based on weight of total resin solids present in the electrodepositable coating composition.

13. The electrodepositable coating composition according to claim 1, wherein the catalyst further comprises dioctyltin oxide and/or its derivatives.

14. The electrodepositable coating composition according to claim 1, wherein the catalyst is substantially non-volatile at a temperature at or below 360° F. (182.2° C.).

15. The electrodepositable coating composition according to claim 1, wherein the resin (a) comprises active hydrogens derived from reactive hydroxyl groups and/or primary amine groups.

16. The electrodepositable coating composition according to claim 1, wherein the resin (a) compresses the reaction product of a polyepoxide and a diglycidyl ether of a polyhydric phenol.

17. The electrodepositable coating composition according to claim 1, wherein at least a portion of the active hydrogens present in the resin (a) comprise primary amine groups derived from the reaction of a ketimine-containing compound and an epoxy group-containing material.

18. The electrodepositable coating composition according to claim 1, wherein the curing agent (b) is at least partially blocked with a blocking agent.

19. The electrodepositable coating composition according to claim 1, which is free of lead-containing compounds.

20. A method for electrocoating a conductive substrate serving as a cathode in an electrical circuit comprising the cathode and an anode, the cathode and anode being immersed in an aqueous electrocoating composition,

the method comprising passing electric current between the cathode and anode to cause deposition of the electrocoating composition onto the substrate as a substantially continuous film, the aqueous electrocoating composition comprising a resinous phase and catalyst nanoparticles dispersed in an aqueous medium,

the resinous phase comprising:

(a) a active hydrogen-containing, ionic salt group-containing resin; and

(b) a curing agent; and