US20210388525A1

US20210388525A1 - System for Electrocoating Conductive Substrates

Info

Publication number: US20210388525A1
Application number: US17/285,640
Authority: US
Inventors: Brent A. Schwartz; Tammy L. Hutchinson; Dennis J. Siefer; Judith A. Bethoski; Irina G. Schwendeman; Mark L. Follet; Amy E. Harrison
Original assignee: PPG Industries Ohio Inc
Current assignee: PPG Industries Ohio Inc
Priority date: 2018-10-15
Filing date: 2019-10-14
Publication date: 2021-12-16
Also published as: EP3867424A1; KR20210072056A; WO2020081447A1; BR112021007150A2; CN113260741A; MX2021004316A

Abstract

The present invention is directed towards an electrocoating system for electrocoating a substrate (500), the system comprising a tank (100) configured to hold an electrodepositable coating composition; at least one pump (200) in fluid communication with the tank, at least one return conduit (210) connecting the tank with an inlet of the pump, at least one recirculating pipe (300) comprising a first end in fluid communication with an outlet of the pump and a second end having at least one aperture, and the at least one recirculating pipe comprising at least one external electrode (400) positioned at least partially outside of the tank. Also disclosed herein are methods of coating substrates, systems for coating a substrate, and coated substrates.

Description

FIELD OF THE INVENTION

The present invention relates to electrocoating systems for electrocoating a substrate. The present invention also relates to a system for coating substrates, methods for coating substrates, and coated substrates.

BACKGROUND INFORMATION

Electrodeposition as a coating application method involves the deposition of a film-forming composition onto a conductive substrate under the influence of an applied electrical potential. Electrodeposition has gained popularity in the coatings industry because it provides higher paint utilization, outstanding corrosion resistance, and low environmental contamination as compared with non-electrophoretic coating methods. However, some conductive substrates are more difficult to coat by electrodeposition because of a number of factors, including the shape and size of the substrate. For example, it may be difficult to coat both the internal and external surfaces of substrates having an open-pocket shape, such as a container, using conventional electrocoat systems. Therefore, an electrocoating system that is capable of coating a wide range of substrates is desired.

SUMMARY OF THE INVENTION

Disclosed herein is an electrocoating system for electrocoating a substrate, the system comprising a tank configured to hold an electrodepositable coating composition; at least one pump in fluid communication with the tank, at least one return conduit connecting the tank with an inlet of the pump, at least one recirculating pipe comprising a first end in fluid communication with an outlet of the pump and a second end having at least one aperture, and the at least one recirculating pipe comprising at least one external electrode positioned at least partially outside of the tank, wherein: the substrate has a first surface and a second surface; the pump is configured to receive the electrodepositable coating composition from the return conduit and deliver the electrodepositable coating composition into the tank through the recirculating pipe; the external electrode is configured to provide an electric charge to the electrodepositable coating composition; and the recirculating pipe is configured to extend into the interior of the tank and position the aperture of the second end to deliver at least a portion of the electrically charged electrodepositable coating composition to the first surface of the substrate.
Also disclosed herein is a method for coating a substrate comprising electrophoretically applying a coating deposited from an electrodepositable coating composition to at least a portion of the substrate using the electrocoating system of the present invention.
Further disclosed herein are substrates coated by the method of the present invention.
Still further disclosed herein is a system for coating a substrate comprising the electrocoating system of the present invention, and further comprising a pretreatment system for pretreating the substrate prior to processing the substrate in the electrocoating system; a primer system for applying a primer to the substrate prior to processing the substrate in the electrocoating system; and/or a topcoat system for applying a topcoat coating to the substrate after processing the substrate in the electrocoating system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an electrocoating system with a recirculating pipe comprising an external electrode and extending into the tank, according to the present invention.

FIG. 2 is an illustration of an electrocoating system of FIG. 1 with an insulating part extending out of the tank the length of the recirculating pipe to the pump.

FIG. 3 is an illustration of an electrocoating system of FIG. 1 without internal electrodes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an electrocoating system for electrocoating a substrate. The present specification also discloses systems for coating a substrate, methods for coating substrates, substrates coated in accordance with one or more of the methods described herein, and/or through the use of one or more the systems described herein.

Electrocoating System

As shown in FIG. 1, the present invention is directed to an electrocoating system 10 for electrocoating a substrate, the system comprising a tank 100 configured to hold an electrodepositable coating composition; at least one pump 200 in fluid communication with the tank 100, at least one return conduit 210 connecting the tank 100 to an inlet of the pump 200, at least one recirculating pipe 300 comprising a first end 310 in fluid communication with an outlet of the pump 200 and a second end 320 having at least one aperture 330, the at least one recirculating pipe 300 comprising at least one external electrode 400 positioned at least partially outside of the tank 100, wherein the substrate has a first surface and a second surface; the return conduit 210 is configured to connect the tank 100 to an inlet of the pump 200; the pump 200 is configured to receive the electrodepositable coating composition 600 from the return conduit 210 and deliver the electrodepositable coating composition 600 into the tank 100 through the recirculating pipe 300; the external electrode 400 is configured to provide an electric charge to the electrodepositable coating composition 600; and the recirculating pipe 300 is configured to extend into the interior of the tank 100 and position the aperture 330 of the second end 320 to deliver at least a portion of the electrically charged electrodepositable coating composition 600 to the first surface of the substrate.
According to the present invention, and as shown in FIGS. 1, 2, and 3, the tank 100 is configured to hold an electrodepositable coating composition. The tank 100 may comprise any material known in the art. For example, the tank 100 may comprise plastic, metal having an insulating liner such as metal having an internal plastic liner, or metal having an insulating coating. The tank 100 may comprise any geometric shape. For example, the tank 100 may be generally rectangular or generally round or spherical. The tank 100 may comprise a base portion 110 and at least one side wall 120 extending up from the base portion 110 to form a cavity within which the electrodepositable coating composition 600 may be held.
The tank 100 is also configured to contain, at least partially, a substrate 500 for electrocoating. The substrate 500 may be a grounded electrical conductor and may generally be substantially configured of a conductive substance, such as, for example, a metallic substance. The substrate 500 serves as a counter-electrode in electrical communication with the internal electrode(s) 400 (if present) and external electrode(s) 400. The substrate 500 may comprise any cross-sectional shape, or multiple cross-sectional shapes if the substrate 500 does not have a uniform cross-sectional shape. The substrate may comprise any dimensions. The substrate 500 may comprise an open-polygon cross-sectional shape, such as an open-pocket cross-sectional shape. The cross-sectional shape may comprise a generally rectangular or a generally round cross-sectional shape. The substrate may comprise a first surface 510 and a second surface 520. The first surface 510 may comprise an internal surface of the substrate 500, and the second surface 520 may comprise an external surface of the substrate 500. For example, as shown in FIGS. 1, 2, and 3, when the substrate 500 has a generally rectangular cross-sectional shape, the first surface 510 may comprise the internal surface of the substrate 500, and the second surface 520 may comprise the external surface of the substrate 500. The substrate 500 may comprise a container, such as, for example, an intermodal container. For example, the substrate 500 may have an external length of 8 feet (2.44 m), 10 feet (3.05 m), 20 feet (6.10 m), 40 feet (12.19 m), 45 feet (13.72 m) or 53 feet (16.15 m); an external width of 7 feet (2.13 m) or 8 feet (2.44 m); and an external height of 7.5 feet (2.29 m), 8.5 feet (2.59 m) or 9.5 feet (2.90 m). The substrate 500 may have a length of at least 8 feet (2.44 m), such as at least 10 feet (3.05 m), such as at least 20 feet (6.10 m), such as at least 40 feet (12.19 m), such as at least 45 feet (13.72 m) or such as at least 53 feet (16.15 m).
The first surface 510 of the substrate 500 may have a surface area that varies based on the length of the substrate 500. The first surface 510 of the substrate 500 may have a surface area of at least 285 ft²(26.48 m²), such as at least 340 ft²(31.59 m²), such as at least 600 ft²(55.74 m²), such as at least 1,145 ft²(106.37 m²), such as at least 1,275 ft²(118.45 m²), such as at least 1,490 ft²(138.43 m²). The first surface 510 of the substrate 500 may have a surface area of 285 ft²(26.48 m²) to 1,890 ft²(175.59 m²) or larger. With respect to a container, the surface area may vary depending upon the length of the substrate 500. For example, the first surface 510 of an 8 foot substrate 500 may have a surface area of 285 ft²(26.48 m²) to 400 ft²(37.16 m²), the first surface 510 of a 10 foot substrate 500 may have a surface area of 340 ft²(31.59 m²) to 460 ft²(42.74 m²), the first surface 510 of a 20 foot substrate 500 may have a surface area of 600 ft²(55.74 m²) to 795 ft²(73.86 m²), the first surface 510 of a 40 foot substrate 500 may have a surface area of 1,145 ft²(106.37 m²) to 1,460 ft²(135.64 m²), the first surface 510 of a 45 foot substrate 500 may have a surface area of 1,275 ft²(118.45 m²) to 1,620 ft²(150.50 m²), and the first surface 510 of a 53 foot substrate 500 may have a surface area of 1,490 ft²(138.43 m²) to 1,890 ft²(175.59 m²).
The second surface 520 of the substrate 500 may have a surface area that varies based on the length of the substrate 500. The second surface 520 of the substrate 500 may have a surface area of at least such as at least 330 ft²(30.66 m²), 380 ft²(35.30 m²), such as at least 675 ft²(62.71 m²), such as at least 1,250 ft²(116.13 m²), such as at least 1,390 ft²(129.14 m²), such as at least 1,630 ft²(151.43 m²). The second surface 520 of the substrate 500 may have a surface area of 330 ft²(30.66 m²) to 1,750 ft²(162.58 m²) or larger. With respect to a container, the surface area may vary depending upon the length of the substrate 500. For example, the second surface 520 of an 8 foot substrate 500 may have a surface area of 330 ft²(30.66 m²) to 440 ft²(40.88 m²), the second surface 520 of a 10 foot substrate 500 may have a surface area of 380 ft²(35.30 m²) to 520 ft²(48.31 m²), the second surface 520 of a 20 foot substrate 500 may have a surface area of 675 ft²(62.71 m²) to 865 ft²(80.36 m²), the second surface 520 of a 40 foot substrate 500 may have a surface area of 1250 ft²(116.13 m²) to 1,575 ft²(146.32 m²), the second surface 520 of a 45 foot substrate 500 may have a surface area of 1,390 ft²(129.14 m²) to 1,750 ft²(162.58 m²), and the second surface 520 of a 53 foot substrate 500 may have a surface area of 1,630 ft²(151.43 m²) to 2,030 ft²(188.59 m²).
The substrate may have a cross-sectional area of at least 40 m², such as at least 45 m², such as at least 50 m², and may be no more than 100 m², such as no more than 85 m², such as no more than 80 m². The substrate may have a cross-sectional area of 40 m²to 100 m², such as 45 m²to 85 m², such as 50 m²to 80 m². As used herein, the term “cross-sectional area” with respect to the substrate refers to the largest cross-sectional area of the substrate as measured perpendicular to the longest axis of the substrate. With respect to a container-shaped substrate, the cross-sectional area will be the width multiplied by the height.
The substrate may comprise any conductive substrate. For example, the substrate may comprise a metal, metal alloy, and/or materials that have been metallized, such as nickel-plated plastic. Additionally, substrates may comprise non-metal conductive materials including composite materials such as, for example, materials comprising carbon fibers or conductive carbon. The metal or metal alloy may comprise, for example, cold rolled steel, hot rolled steel, steel coated with zinc metal, zinc compounds or zinc alloys, such as electrogalvanized steel, hot-dipped galvanized steel, galvanealed steel, nickel-plated steel, and steel plated with zinc alloy. The substrate may comprise an aluminum alloy. Non-limiting examples of aluminum alloys include the 1XXX, 2XXX, 3XXX, 4XXX, 5XXX, 6XXX, or 7XXX series as well as clad aluminum alloys and cast aluminum alloys. The substrate may comprise a magnesium alloy. The substrate used in the present invention may also comprise other suitable non-ferrous metals such as titanium or copper, as well as alloys of these materials.
As illustrated in FIGS. 1, 2, and 3, the electrocoating system 10 also comprises a return conduit 210 that connects the tank 100 to the pump 200. The return conduit 210 is configured to recycle the electrodepositable coating composition 600 from the tank 100 to the pump 200. The return conduit 210 may comprise any combination of pipes, hoses, valves, and any other fluid conveying devices configured to perform the purposes stated herein.
As shown in FIGS. 1, 2, and 3, the pump 200 is in fluid communication with the tank 100. The pump 200 is configured to receive the electrodepositable coating composition 600 from the return conduit 210 and deliver the electrodepositable coating composition 600 into the tank 100 through a recirculating pipe 300. The recirculating pipe 300 comprises a first end 310 in fluid communication with an outlet of the pump 200 and a second end 320 having at least one aperture 330. The recirculating pipe 300 is configured to extend into the interior of the tank 100, immersed in the electrodepositable coating composition, to position the aperture(s) 320 of the second end 310 to deliver at least a portion of the electrodepositable coating composition 600 to the first surface 510 of the substrate 500. The return conduit 210, pump 200, and recirculating pipe 300 may be directly coupled to form at least one continuous and uninterrupted loop for constrained flow of the electrodepositable coating composition 600 through the return conduit 210, pump 200 and recirculating pipe 300. The pump 200 is configured to deliver the electrodepositable coating composition 600 into the tank 100 through the recirculating pipe 300 at a flow rate and pressure appropriate for electrocoating a substrate 500, as described herein. For example, but not by way of limitation, the pump may deliver the electrodepositable coating composition 600 to the tank 100 at a pressure from about 1 psi to about 50 psi, such as from about 15 psi to about 40 psi, and at a flow rate from about 0.1 liters per second to about 65.0 liters per second. The pump 200 may comprise, for example, a centrifugal pump. It is contemplated, however, that any pump 200 configured to perform the purposes stated herein may be utilized in the electrocoating system 10 of the present invention.
As shown in FIGS. 1, 2, and 3, the external electrode 400 is positioned outside of the tank 100. The external electrode 400 is configured to provide an electric charge to the electrodepositable coating composition 600 delivered by the pump 200 into the tank 100 through the recirculating pipe 300. As such, the external electrode 400 provides the electric charge to the electrodepositable coating composition 600 prior to its delivery into the tank 100 for electrocoating. The pump 200 generally delivers the electrodepositable coating composition 600 past the external electrode 400 through the recirculating pipe 300 and into the tank 100 at a flow rate appropriate for the external electrode 400 to sufficiently electrically charge the electrodepositable coating composition 600. This flow rate of the electrodepositable coating composition 600 delivered past the external electrode 400 may vary depending upon a volume of the electrodepositable coating composition 600 delivered by the pump 200 relative to the surface area of the external electrode 400. For example, it is contemplated that as a volume of the electrodepositable coating composition 600 increases, a slower flow rate of the electrodepositable coating composition 600 may be provided to increase a contact time between the electrodepositable coating composition 600 and the external electrode 400 and enable the external electrode 400 to sufficiently electrically charge the electrodepositable coating composition 600. Likewise, it is contemplated that an increase in the surface area of the external electrode 400 requires less contact time with the external electrode 400 in order to sufficiently electrically charge the electrodepositable coating composition 600. The external electrode 400 may be configured in any variety of cross-sectional shapes, such as, for example, tubular, flat plate, C-shape, fanned, or annular, and may comprise, for example, a conductive pipe or pipe section, such as a metal pipe. For example, the external electrode 400 may have an internal surface configured to contact the electrodepositable coating composition 600, and the electrocoating system 10 may be configured such that the ratio of a total combined surface area of an external surface of the external electrode(s) 400 to a surface area of the first surface 510 of the substrate 500 is from 1:7 to 1:1, such as 1:6 to 1:2, such as 1:5 to 1:3, such as about 1:4.
At least a portion of the recirculating pipe 300 comprises the external electrode, and the portion of the recirculating pipe 300 comprising the external electrode 400 is located at least partially or completely outside of the tank 100. As used herein, at least partially or completely outside of the tank 100 means that at least a portion of the external electrode 400 is present outside of the tank 100 and not immersed in the electrodepositable coating composition 600, or that the entire external electrode 400 is located outside of the tank 100 and not immersed in the electrodepositable coating composition 600. In other words, at least a portion or all of the recirculating pipe 300 that comprises the external electrode 400 is not immersed in the electrodepositable coating composition 600 held within the tank 100. Alternatively, substantially all of the recirculating pipe 300 may comprise the external electrode 400. For example, the external electrode 400 may comprise at least 50% of the recirculating pipe 300, such as at least 60%, such as at least 75%, such as at least 85%, such as at least 95%, such as 100%. The remainder of the recirculating pipe 300 may comprise a combination of non-conductive and/or conductive materials. The recirculating pipe 300 may comprise any combination of pipes, hoses, valves, and any other fluid conveying devices configured to perform the purposes stated herein.
The external electrode 400 may be contained within an insulating part 410. The insulating part 410 may prevent a user of the electrocoating system 10 from being exposed to the electric charge of the external electrode 400 when an electrical potential is applied to the electrocoating system 10. The insulating part 410 may alternatively, or in addition to, be located on the recirculating pipe 300 that extends into the tank 100. The insulating part 410 may comprise, for example, a polyvinyl chloride (PVC) pipe in which the external electrode 400 is contained. It is contemplated, however, that any insulating part 410 configured to perform the purposes stated herein may be utilized according to the electrocoating system 10 of the present invention.
Further, if the external electrode 400 comprises an anode, a membrane may be used to cover the internal surface of the external electrode 400 so as to remove acid build-up from the electrodepositable coating composition 600 during the process of electrocoating a substrate 500. For example, about 50%, such as about 75%, such as about 80%, or more of the internal surface area of an external electrode 400 may be covered by a membrane to control pH of the electrodepositable coating composition through the removal of acid generated during electrocoating. Membrane covered anodes generally are referred to in the industry as anolyte cells. An external electrode 400 that is substantially membrane-free is one that is membrane-free to an extent that any existing membrane does not interfere, to any significant degree, with the electric charging of the electrodepositable coating composition 600 by the external electrode 400. In addition, the external electrode 400 may be completely membrane-free.
The external electrode 400 may comprise, for example, a membrane-free 316 type stainless steel pipe. The entirely exposed wall of the channel of the membrane-free metal pipe external electrode 400 combined with the flow of the electrodepositable coating composition 600 through the external electrode 400 may aid in the external electrode 400 providing the electric charge substantially uniform to the electrodepositable coating composition 600 so as to promote substantially equal electric charge distribution throughout the electrodepositable coating composition 600. Substantially equal electric charge distribution throughout the electrodepositable coating composition 600 optimizes the electrocoating of the substrate 500 by providing a substantially uniform attraction of charged molecules of the electrodepositable coating composition 600 to the oppositely charged substrate 500. Further, it is contemplated that as a volume of the electrodepositable coating composition 600 delivered to the external electrode 400 by the pump 200 increases, a greater surface area of the external electrode 400 may be provided to sufficiently electrically charge the electrodepositable coating composition 600 delivered by the pump 200. Thus, it is contemplated that a minimum surface area of the external electrode 400 per unit volume of electrodepositable coating composition 600 flow may be provided to sufficiently charge the electrodepositable coating composition 600 prior to its delivery to the tank 100 for electrocoating a substrate 500. As discussed above, the surface area of the external electrode 400 may be manipulated by, for example, increasing the length of the external electrode 400 (i.e., increasing the length of the portion of the recirculating pipe 300 that comprises the external electrode 400, or, if the entire recirculating pipe 300 comprises the external electrode 400, increasing the length of the recirculating pipe 300), or changing the cross-sectional shape of the external electrode 400.
The second end 320 of the recirculating pipe 300 may comprise a nozzle which comprises the aperture 330. The nozzle may comprise any nozzle known in the art. In addition, the second end 320 of the recirculating pipe 300 may comprise a plurality of apertures 330 through which the electrodepositable coating composition 600 may pass. The recirculating pipe may also comprise a plurality of second ends 320. For example, as shown in FIGS. 1, 2, and 3, the recirculating pipe may be branched with each branch comprising a second end 320 comprising at least one aperture 330. Each second end 320 of the branched recirculating pipe 300 may be configured to deliver at least a portion of the electrodepositable coating composition 600 electrically charged by the external electrode 400 to different sections of the first surface 510 of the substrate 500.
As discussed above, the electrocoating system 10 may comprise a plurality of return conduits 210, pumps 200, and/or recirculating pipes 300. For example, the electrocoating system 10 may comprise a plurality of recirculating pipes 300 configured to deliver the electrodepositable coating composition 600 charged by the external electrode(s) 400 to different sections of the first surface 510 of the substrate 500. Each recirculating pipe 300 may be fed by a different pump 200, or a pump 200 may pump the electrodepositable coating composition 600 to multiple recirculating pipes 300. Likewise, each pump 200 may be fed by a return conduit 210, or a return conduit 210 may feed multiple pumps 200. The number of each component (i.e., return conduit 210, pump 200, recirculating pipe 300) present in the electrocoating system 10 may depend upon a variety of factors, including, for example, the length of the substrate 500, the surface area of the first surface 510 of the substrate 500, the resin solids present in the electrodepositable coating composition 600, the charge density of the electrodepositable coating composition 600, the voltage applied during electrocoating of the substrate, the shape of the substrate, among other factors. The return conduits 210, pumps 200, and/or recirculating pipes 300 may be positioned along a length of the tank 100 such that the electrodepositable coating composition 600 is deposited substantially uniform along the length of the substrate 500 to be electrocoated. For example, the return conduits 210, pumps 200, and/or recirculating pipes 300 may be positioned equidistant along a length of the tank 100. The electrodepositable coating composition 600 flowed into the tank 100 through the recirculating pipe 300 may be substantially deposited onto the first surface 510 of the substrate 500 during electrocoating. Without intending to be bound by any theory, it is believed that positioning the recirculating pipe 300 of the electrocoating system 10 inside the tank 100 to provide a flow of electrodepositable coating composition 600 charged by the external electrode 400 to the first surface 510 of the substrate 500 allows for the deposition of a more uniform coating to be applied to the first surface 510 of the substrate 500 in comparison to an electrocoating system that does not include the recirculating pipe 300 and external electrode 400.
When a power source provides an electrical current to the electrocoating system 10, the electrodepositable coating composition 600 is charged by the external electrode 400 and, if present, the internal electrode 700, and is attracted to, and deposits on, the oppositely charged substrate 500. Equal, or substantially equal, charge distribution throughout the electrically charged fluid provided by the electrocoating system 10 of the present invention enhances the electrocoating process by generally providing a substantially uniform coating thickness of the electrodepositable coating composition 500 deposited on the substrate 500.
The electrocoating system 10 optionally may further comprise at least one internal electrode 700 positioned inside the tank 100 to provide additional electric charge to the electrodepositable coating composition 600, as shown in FIGS. 1 and 2. The internal electrode 700 may comprise any suitable conductive material known in the art. For example, the internal electrode 700 may comprise a pipe electrically coupled with the power source. The internal electrode(s) 700 may be membrane-free, or substantially membrane-free, or substantially covered by a membrane. The electrocoating system 10 may comprise a plurality of internal electrodes 700, and the internal electrodes 700 may be positioned along a length of the tank 100 such that the electrodepositable coating composition 600 is deposited substantially uniform along the length of the substrate 500 to be electrocoated. For example, the internal electrode 700 may be positioned equidistant along a length of the tank 100. The electrocoating system 10 may be configured such that the ratio of a total combined surface area of the internal electrode(s) 700 to the surface area of the second surface 510 of the substrate 500 may be from 1:7 to 1:1, such as 1:6 to 1:2, such as 1:5 to 1:3, such as 1:4. In contrast to the recirculating pipe 300 comprising the external electrode 400, the internal electrode 700 does not recirculate or transport the electrodepositable coating composition 600 within the electrocoating system 10.
Without intending to be bound by any theory, it is believed that the use of the internal electrode 700 in an electrocoating system will not provide a sufficient charge to the electrodepositable coating composition 600 to enable a uniform deposition of the electrodepositable coating composition 600 over the entire surface of the substrate 500 without the recirculating pipe 300 comprising the external electrode 400 also being present. For example, the internal electrode 700 may provide a sufficient charge to the electrodepositable coating composition 600 to deposit a coating on a surface of the substrate 500 located near the internal electrode 700, such as, for example, the second surface 520 of the substrate 500, but may not provide a sufficient charge to enable deposition on other portions of the substrate, such as, for example, the first surface 510 of the substrate 500.
The electrocoating system 10 further comprises at least one power source (not shown) to provide an electrical current to the electrocoating system 10. The power source may optionally include a rectifier. The power source is electrically coupled to the external electrode(s) 400, the substrate 500, and, if present, the internal electrodes 700, with one pole of the power source coupled to the substrate, and the other pole of the power source coupled to the external electrode(s) 400 and, if present, the internal electrode(s) 700, such that the substrate serves as a counter-electrode to the external electrode 400 and, if present, internal electrode 700. For example, if the electrodepositable coating composition 600 is a cationic electrodepositable coating composition, the substrate 500 serves as the cathode and the external electrode 400 and, if present, internal electrode 700 serve as anodes, with the polarities reversed for an anionic electrodepositable coating composition. The power source provides an electric current to the electrocoating system 10 such that the external electrode 400 and, if present, internal electrode 700, provide an electric charge to the electrodepositable coating composition 600 sufficient for electrocoating purposes. For example, but not by way of limitation, the electric current provided to the power source may be, but is not limited to, about 25 volts to about 600 volts or higher. The voltage provided to the power source may vary according to a volume of the electrodepositable coating composition 600 delivered by the pump 200. For example, a higher voltage may be provided to the external electrode 400 to sufficiently charge an increased volume and/or increased flow rate of the electrodepositable coating composition 600 delivered by the pump 200. The electrocoating system 10 may also comprise any additional or other electrical circuitry desired or needed to perform the purposes stated herein.
The electrodepositable coating composition 600 may comprise any electrodepositable coating composition known in the art. As used herein, the term “electrodepositable coating composition” refers to a composition that is capable of being deposited onto an electrically conductive substrate under the influence of an applied electrical potential. For example, as mentioned above, the electrodepositable coating composition 600 may comprise a cationic or anionic electrodepositable coating composition.
The electrodepositable coating composition comprises a film-forming binder. The film-forming binder may comprise an ionic salt group-containing film-forming polymer and, optionally, a curing agent.
According to the present invention, the ionic salt group-containing film-forming polymer may comprise a cationic salt group-containing film-forming polymer. The cationic salt group-containing, film-forming polymer may be used in a cationic electrodepositable coating composition. As used herein, the term “cationic salt group-containing film-forming polymer” refers to polymers that include at least partially neutralized cationic groups, such as sulfonium groups and/or ammonium groups, that impart a positive charge to the polymer. As used herein, the term “polymer” encompasses, but is not limited to, oligomers and both homopolymers and copolymers. The cationic salt group-containing film-forming polymer may comprise active hydrogen functional groups. As used herein, the term “active hydrogen functional groups” refers to those groups that are reactive with isocyanates as determined by the Zerewitinoff test described in the JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol. 49, page 3181 (1927), and include, for example, hydroxyl groups, primary or secondary amino groups, and thiol groups. Cationic salt group-containing film-forming polymers that comprise active hydrogen functional groups may be referred to as active hydrogen-containing, cationic salt group-containing film-forming polymers.
Examples of polymers that are suitable for use as the cationic salt group-containing film-forming polymer in the present invention include, but are not limited to, alkyd polymers, acrylic polymers, polyepoxide polymers, polyamide polymers, polyurethane polymers, polyurea polymers, polyether polymers, and polyester polymers, among others.
The cationic salt groups may be incorporated into the cationic salt group-containing film-forming polymer as follows: The film-forming polymer may be reacted with a cationic salt group former. By “cationic salt group former” is meant a material which is reactive with epoxy groups present and which may be acidified before, during, or after reaction with the epoxy groups on the film-forming polymer 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.
More specific examples of suitable active hydrogen-containing, cationic salt group containing film-forming polymers include polyepoxide-amine adducts, such as the adduct of a polyglycidyl ether of a polyphenol, such as Bisphenol A, and primary and/or secondary amines, such as are described in U.S. Pat. No. 4,031,050 at col. 3, line 27 to col. 5, line 50, U.S. Pat. No. 4,452,963 at col. 5, line 58 to col. 6, line 66, and U.S. Pat. No. 6,017,432 at col. 2, line 66 to col. 6, line 26, these portions of which being incorporated herein by reference. A portion of the amine that is reacted with the polyepoxide may be a ketimine of a polyamine, as is described in U.S. Pat. No. 4,104,147 at col. 6, line 23 to col. 7, line 23, the cited portion of which being incorporated herein by reference. Also suitable are ungelled polyepoxide-polyoxyalkylenepolyamine resins, such as are described in U.S. Pat. No. 4,432,850 at col. 2, line 60 to col. 5, line 58, the cited portion of which being incorporated herein by reference. In addition, cationic acrylic resins, such as those described in U.S. Pat. No. 3,455,806 at col. 2, line 18 to col. 3, line 61 and U.S. Pat. No. 3,928,157 at col. 2, line 29 to col. 3, line 21, these portions of both of which are incorporated herein by reference, may be used.
Besides amine salt group-containing resins, the cationic salt group-containing film-forming polymer may comprise a quaternary ammonium salt group-containing resin. As used herein, a “quaternary ammonium salt group” refers to group comprising a quaternary ammonium cation of the formula NR₄ ⁺, wherein each R group is independently an alkyl or aryl group, and a counter anion. Examples of these resins are those which are formed from reacting an organic polyepoxide with a tertiary amine acid salt. Such resins are described in U.S. Pat. No. 3,962,165 at col. 2, line 3 to col. 11, line 7; U.S. Pat. No. 3,975,346 at col. 1, line 62 to col. 17, line 25 and U.S. Pat. No. 4,001,156 at col. 1, line 37 to col. 16, line 7, these portions of which being incorporated herein by reference.
Examples of other suitable cationic resins include ternary sulfonium salt group-containing resins, such as those described in U.S. Pat. No. 3,793,278 at col. 1, line 32 to col. 5, line 20, this portion of which being incorporated herein by reference. Also, cationic resins which cure via a transesterification mechanism, such as described in European Patent Application No. 12463B1 at pg. 2, line 1 to pg. 6, line 25, this portion of which being incorporated herein by reference, may also be employed.
Other suitable cationic salt group-containing film-forming polymers include those that may form photodegradation resistant electrodepositable coating compositions. Such polymers include the polymers comprising cationic amine salt groups which are derived from pendant and/or terminal amino groups that are disclosed in U.S. Patent Application Publication No. 2003/0054193 A1 at paragraphs [0064] to [0088], this portion of which being incorporated herein by reference. Also suitable are the active hydrogen-containing, cationic salt group-containing resins derived from a polyglycidyl ether of a polyhydric phenol that is essentially free of aliphatic carbon atoms to which are bonded more than one aromatic group, which are described in U.S. Patent Application Publication No. 2003/0054193 A1 at paragraphs [0096] to [0123], this portion of which being incorporated herein by reference.
The active hydrogen-containing, cationic salt group-containing film-forming polymer may be 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 such as those having the formula:
wherein R is hydrogen or an alkyl group having 1 to 4 carbon atoms. Mixtures of the above-mentioned acids also may be used in the present invention.
The extent of neutralization of the cationic salt group-containing film-forming polymer may vary with the particular polymer involved. However, sufficient acid should be used to sufficiently neutralize the cationic salt-group containing film-forming polymer such that the cationic salt-group containing film-forming polymer may be dispersed in an aqueous dispersing medium. For example, the amount of acid used may provide at least 20% of all of the total theoretical neutralization. Excess acid may also be used beyond the amount required for 100% total theoretical neutralization. For example, the amount of acid used to neutralize the cationic salt group-containing film-forming polymer may be ≥0.1% based on the total amines in the active hydrogen-containing, cationic salt group-containing film-forming polymer. Alternatively, the amount of acid used to neutralize the active hydrogen-containing, cationic salt group-containing film-forming polymer may be ≤100% based on the total amines in the active hydrogen-containing, cationic salt group-containing film-forming polymer. The total amount of acid used to neutralize the cationic salt group-containing film-forming polymer may range between any combination of values, which were recited in the preceding sentences, inclusive of the recited values. For example, the total amount of acid used to neutralize the active hydrogen-containing, cationic salt group-containing film-forming polymer may be 20%, 35%, 50%, 60%, or 80% based on the total amines in the cationic salt group-containing film-forming polymer.
The cationic salt group-containing film-forming polymer may be present in the cationic electrodepositable coating composition in an amount of at least 40% by weight, such as at least 50% by weight, such as at least 60% by weight, and may be present in the in an amount of no more than 90% by weight, such as no more than 80% by weight, such as no more than 75% by weight, based on the total weight of the resin solids of the electrodepositable coating composition. The cationic salt group-containing film-forming polymer may be present in the cationic electrodepositable coating composition in an amount of 40% to 90% by weight, such as 50% to 80% by weight, such as 60% to 75% by weight, based on the total weight of the resin solids of the electrodepositable coating composition. As used herein, the “resin solids” include the ionic salt group-containing film-forming polymer, the curing agent (if present), and any additional water-dispersible non-pigmented component(s) present in the electrodepositable coating composition.
According to the present invention, the ionic salt group containing film-forming polymer may comprise an anionic salt group containing film-forming polymer. As used herein, the term “anionic salt group containing film-forming polymer” refers to an anionic polymer comprising at least partially neutralized anionic functional groups, such as carboxylic acid and phosphoric acid groups that impart a negative charge. The anionic salt group-containing film-forming polymer may comprise active hydrogen functional groups. Anionic salt group-containing film-forming polymers that comprise active hydrogen functional groups may be referred to as active hydrogen-containing, anionic salt group-containing film-forming polymers. The anionic salt group containing film-forming polymer may be used in an anionic electrodepositable coating composition.
The anionic salt group-containing film-forming polymer may comprise base-solubilized, carboxylic acid group-containing film-forming polymers such as the reaction product or adduct of a drying oil or semi-drying fatty acid ester with a dicarboxylic acid or anhydride; and the reaction product of a fatty acid ester, unsaturated acid or anhydride and any additional unsaturated modifying materials which are further reacted with polyol. Also suitable are the at least partially neutralized interpolymers of hydroxy-alkyl esters of unsaturated carboxylic acids, unsaturated carboxylic acid and at least one other ethylenically unsaturated monomer. Still another suitable anionic electrodepositable resin comprises an alkyd-aminoplast vehicle, i.e., a vehicle containing an alkyd resin and an amine-aldehyde resin. Another suitable anionic electrodepositable resin composition comprises mixed esters of a resinous polyol. Other acid functional polymers may also be used such as phosphatized polyepoxide or phosphatized acrylic polymers. Exemplary phosphatized polyepoxides are disclosed in U.S. Patent Application Publication No. 2009-0045071 at [0004]-[0015] and U.S. patent application Ser. No. 13/232,093 at [0014]-[0040], the cited portions of which being incorporated herein by reference. Also suitable are resins comprising one or more pendent carbamate functional groups, such as those described in U.S. Pat. No. 6,165,338.
According to the present invention, the anionic salt group-containing film-forming polymer may be present in the anionic electrodepositable coating composition in an amount of at least 50% by weight, such as at least 55% by weight, such as at least 60% by weight, and may be present in an amount of no more than 90% by weight, such as no more than 80% by weight, such as no more than 75% by weight, based on the total weight of the resin solids of the electrodepositable coating composition. The anionic salt group-containing film-forming polymer may be present in the anionic electrodepositable coating composition in an amount 50% to 90%, such as 55% to 80%, such as 60% to 75%, based on the total weight of the resin solids of the electrodepositable coating composition.
According to the present invention, the electrodepositable coating composition of the present invention may further comprise a curing agent. The curing agent may be reactive with the ionic salt group-containing film-forming polymer. The curing agent comprises functional groups that react with the reactive functional groups, such as active hydrogen groups, of the ionic salt group-containing film-forming polymer to effectuate cure of the coating composition to form a coating. As used herein, the term “cure”, “cured” or similar terms, as used in connection with the electrodepositable coating compositions described herein, means that at least a portion of the components that form the electrodepositable coating composition are crosslinked to form a coating. Additionally, curing of the electrodepositable coating composition refers to subjecting said composition to curing conditions (e.g., elevated temperature) leading to the reaction of the reactive functional groups of the components of the electrodepositable coating composition, and resulting in the crosslinking of the components of the composition and formation of an at least partially cured coating. Non-limiting examples of suitable curing agents are at least partially blocked polyisocyanates, aminoplast resins and phenoplast resins, such as phenolformaldehyde condensates including allyl ether derivatives thereof.
Suitable at least partially blocked polyisocyanates include aliphatic polyisocyanates, aromatic polyisocyanates, and mixtures thereof. The curing agent may comprise an at least partially blocked aliphatic polyisocyanate. Suitable at least partially blocked aliphatic polyisocyanates include, for example, fully blocked aliphatic polyisocyanates, such as those described in U.S. Pat. No. 3,984,299 at col. 1 line 57 to col. 3 line 15, this portion of which is incorporated herein by reference, or partially blocked aliphatic polyisocyanates that are reacted with the polymer backbone, such as is described in U.S. Pat. No. 3,947,338 at col. 2 line 65 to col. 4 line 30, this portion of which is also incorporated herein by reference. By “blocked” is meant that the isocyanate groups have been reacted with a compound such that the resultant blocked isocyanate group is stable to active hydrogens at ambient temperature but reactive with active hydrogens in the film forming polymer at elevated temperatures, such as between 90° C. and 200° C. The polyisocyanate curing agent may be a fully blocked polyisocyanate with substantially no free isocyanate groups.
The polyisocyanate curing agent may comprise a diisocyanate, higher functional polyisocyanates or combinations thereof. For example, the polyisocyanate curing agent may comprise aliphatic and/or aromatic polyisocyanates. Aliphatic polyisocyanates may include (i) alkylene isocyanates, such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (“HDI”), 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, ethylidene diisocyanate, and butylidene diisocyanate, and (ii) cycloalkylene isocyanates, such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, isophorone diisocyanate, methylene bis(4-cyclohexylisocyanate) (“HMDI”), the cyclo-trimer of 1,6-hexmethylene diisocyanate (also known as the isocyanurate trimer of HDI, commercially available as Desmodur N3300 from Convestro AG), and meta-tetramethylxylylene diisocyanate (commercially available as TMXDI® from Allnex SA). Aromatic polyisocyanates may include (i) arylene isocyanates, such as m-phenylene diisocyanate, p-phenylene diisocyanate, 1,5-naphthalene diisocyanate and 1,4-naphthalene diisocyanate, and (ii) alkarylene isocyanates, such as 4,4′-diphenylene methane (“MDI”), 2,4-tolylene or 2,6-tolylene diisocyanate (“TDI”), or mixtures thereof, 4,4-toluidine diisocyanate and xylylene diisocyanate. Triisocyanates, such as triphenyl methane-4,4′,4″-triisocyanate, 1,3,5-triisocyanato benzene and 2,4,6-triisocyanato toluene, tetraisocyanates, such as 4,4′-diphenyldimethyl methane-2,2′,5,5′-tetraisocyanate, and polymerized polyisocyanates, such as tolylene diisocyanate dimers and trimers and the like, may also be used. The curing agent may comprise a blocked polyisocyanate selected from a polymeric polyisocyanate, such as polymeric HDI, polymeric MDI, polymeric isophorone diisocyanate, and the like. The curing agent may also comprise a blocked trimer of hexamethylene diisocyanate available as Desmodur N3300® from Covestro AG. Mixtures of polyisocyanate curing agents may also be used.
The polyisocyanate curing agent may be at least partially blocked with at least one blocking agent selected from a 1,2-alkane diol, for example 1,2-propanediol; a 1,3-alkane diol, for example 1,3-butanediol; a benzylic alcohol, for example, benzyl alcohol; an allylic alcohol, for example, allyl alcohol; caprolactam; a dialkylamine, for example dibutylamine; and mixtures thereof. The polyisocyanate curing agent may be at least partially blocked with at least one 1,2-alkane diol having three or more carbon atoms, for example 1,2-butanediol.
Other suitable blocking agents include aliphatic, cycloaliphatic, or aromatic alkyl monoalcohols or phenolic compounds, including, for example, lower (e.g. C₁-C₆) aliphatic alcohols, such as methanol, ethanol, and n-butanol; cycloaliphatic alcohols, such as cyclohexanol; aromatic-alkyl alcohols, such as phenyl carbinol and methylphenyl carbinol; and phenolic compounds, such as phenol itself and substituted phenols wherein the substituents do not affect coating operations, such as cresol and nitrophenol. Glycol ethers and glycol amines 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. Other suitable blocking agents include oximes, such as methyl ethyl ketoxime, acetone oxime and cyclohexanone oxime.
The curing agent may comprise an aminoplast resin. Aminoplast resins are condensation products of an aldehyde with an amino- or amido-group carrying substance. Condensation products obtained from the reaction of alcohols and an aldehyde with melamine, urea or benzoguanamine may be used. However, condensation products of other amines and amides may also be employed, for example, aldehyde condensates of triazines, diazines, triazoles, guanidines, guanamines and alkyl- and aryl-substituted derivatives of such compounds, including alkyl- and aryl-substituted ureas and alkyl- and aryl-substituted melamines. Some examples of such compounds are N,N′-dimethyl urea, benzourea, dicyandiamide, formaguanamine, acetoguanamine, ammeline, 2-chloro-4,6-diamino-1,3,5-triazine, 6-methyl-2,4-diamino-1,3,5-triazine, 3,5-diaminotriazole, triaminopyrimidine, 2-mercapto-4,6-diaminopyrimidine, 3,4,6-tris(ethylamino)-1,3,5-triazine, and the like. Suitable aldehydes include formaldehyde, acetaldehyde, crotonaldehyde, acrolein, benzaldehyde, furfural, glyoxal and the like.
The aminoplast resins may contain methylol or similar alkylol groups, and at least a portion of these alkylol groups may be etherified by a reaction with an alcohol to provide organic solvent-soluble resins. Any monohydric alcohol may be employed for this purpose, including such alcohols as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol and others, as well as benzyl alcohol and other aromatic alcohols, cyclic alcohol such as cyclohexanol, monoethers of glycols such as Cello-solves and Carbitols, and halogen-substituted or other substituted alcohols, such as 3-chloropropanol and butoxyethanol.
Non-limiting examples of commercially available aminoplast resins are those available under the trademark CYMEL® from Allnex Belgium SA/NV, such as CYMEL 1130 and 1156, and RESIMENE® from INEOS Melamines, such as RESIMENE 750 and 753. Examples of suitable aminoplast resins also include those described in U.S. Pat. No. 3,937,679 at col. 16, line 3 to col. 17, line 47, this portion of which being hereby incorporated by reference. As is disclosed in the aforementioned portion of the '679 patent, the aminoplast may be used in combination with the methylol phenol ethers.
Phenoplast resins are formed by the condensation of an aldehyde and a phenol. Suitable aldehydes include formaldehyde and acetaldehyde. Methylene-releasing and aldehyde-releasing agents, such as paraformaldehyde and hexamethylene tetramine, may also be utilized as the aldehyde agent. Various phenols may be used, such as phenol itself, a cresol, or a substituted phenol in which a hydrocarbon radical having either a straight chain, a branched chain or a cyclic structure is substituted for a hydrogen at the aromatic ring. Mixtures of phenols may also be employed. Some specific examples of suitable phenols are p-phenylphenol, p-tert-butylphenol, p-tert-amylphenol, cyclopentylphenol and unsaturated hydrocarbon-substituted phenols, such as the monobutenyl phenols containing a butenyl group in ortho, meta or para position, and where the double bond occurs in various positions in the hydrocarbon chain.
Aminoplast and phenoplast resins, as described above, are further described in U.S. Pat. No. 4,812,215 at col. 6, line 20 to col. 7, line 12, the cited portion of which being incorporated herein by reference.
The curing agent may be present in the cationic electrodepositable coating composition in an amount of at least 10% by weight, such as at least 20% by weight, such as at least 25% by weight, and may be present in an amount of no more than 60% by weight, such as no more than 50% by weight, such as no more than 40% by weight, based on the total weight of the resin solids of the electrodepositable coating composition. The curing agent may be present in the cationic electrodepositable coating composition in an amount of 10% to 60% by weight, such as 20% to 50% by weight, such as 25% to 40% by weight, based on the total weight of the resin solids of the electrodepositable coating composition.
The curing agent may be present in the anionic electrodepositable coating composition in an amount of at least 10% by weight, such as at least 20% by weight, such as at least 25% by weight, and may be present in an amount of no more than 50% by weight, such as no more than 45% by weight, such as no more than 40% by weight, based on the total weight of the resin solids of the electrodepositable coating composition. The curing agent may be present in the anionic electrodepositable coating composition in an amount of 10% to 50% by weight, such as 20% to 45% by weight, such as 25% to 40% by weight, based on the total weight of the resin solids of the electrodepositable coating composition.
The electrodepositable coating composition according to the present invention may optionally comprise one or more further components in addition to the film-forming binder described above.
According to the present invention, the electrodepositable coating composition may optionally comprise a catalyst to catalyze the reaction between the curing agent and the polymers. Examples of catalysts suitable for cationic electrodepositable coating compositions include, without limitation, organotin compounds (e.g., dibutyltin oxide and dioctyltin oxide) and salts thereof (e.g., dibutyltin diacetate); other metal oxides (e.g., oxides of cerium, zirconium and bismuth) and salts thereof (e.g., bismuth sulfamate and bismuth lactate); or a cyclic guanidine as described in U.S. Pat. No. 7,842,762 at col. 1, line 53 to col. 4, line 18 and col. 16, line 62 to col. 19, line 8, the cited portions of which being incorporated herein by reference. Examples of catalysts suitable for anionic electrodepositable coating compositions include latent acid catalysts, specific examples of which are identified in WO 2007/118024 at [0031] and include, but are not limited to, ammonium hexafluoroantimonate, quaternary salts of SbF₆(e.g., NACURE® XC-7231), t-amine salts of SbF₆(e.g., NACURE® XC-9223), Zn salts of triflic acid (e.g., NACURE® A202 and A218), quaternary salts of triflic acid (e.g., NACURE® XC-A230), and diethylamine salts of triflic acid (e.g., NACURE® A233), all commercially available from King Industries, and/or mixtures thereof. Latent acid catalysts may be formed by preparing a derivative of an acid catalyst such as para-toluenesulfonic acid (pTSA) or other sulfonic acids. For example, a well-known group of blocked acid catalysts are amine salts of aromatic sulfonic acids, such as pyridinium para-toluenesulfonate. Such sulfonate salts are less active than the free acid in promoting crosslinking. During cure, the catalysts may be activated by heating.
According to the present invention, the electrodepositable coating composition may further comprise other optional ingredients, such as a pigment composition and/or various additives including fillers, plasticizers, anti-oxidants, biocides, UV light absorbers and stabilizers, hindered amine light stabilizers, defoamers, fungicides, dispersing aids, flow control agents, surfactants, wetting agents, pH adjusters, buffering agents, or combinations thereof. Alternatively, the electrodepositable coating composition may be completely free of any of the optional ingredients, i.e., the optional ingredient is not present in the electrodepositable coating composition. The pigment composition may comprise, for example, iron oxides, lead oxides, strontium chromate, coal dust, titanium dioxide, talc, barium sulfate, as well as color pigments such as cadmium yellow, cadmium red, chromium yellow and the like. The pigment content of the pigment composition, which excludes the electrically conductive particles described above, may be expressed as the pigment-to-binder weight ratio, and may be within the range of 0.03 to 0.1, when pigment is used. The other additives mentioned above may be present in the electrodepositable coating composition in amounts of 0.01% to 3% by weight, based on total weight of the resin solids of the electrodepositable coating composition.
According to the present invention, the electrodepositable coating composition comprises an aqueous dispersion medium comprising water and/or one or more organic solvent(s). Water can for example be present in amounts of 40% to 90% by weight, such as 50% to 80% by weight, such as 60 to 75% by weight, based on total weight of the electrodepositable coating composition. Examples of suitable organic solvents include oxygenated organic solvents, such as monoalkyl ethers of ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol which contain from 1 to 10 carbon atoms in the alkyl group, such as the monoethyl and monobutyl ethers of these glycols. Examples of other at least partially water-miscible solvents include alcohols such as ethanol, isopropanol, butanol and diacetone alcohol. If used, the organic solvents may typically be present in an amount of less than 10% by weight, such as less than 5% by weight, based on total weight of the electrodepositable coating composition. The electrodepositable coating composition may in particular be provided in the form of a dispersion, such as an aqueous dispersion.
According to the present invention, the total solids content of the electrodepositable coating composition may be at least 1% by weight, such as at least 10% by weight, such as at least 20% by weight, and may be no more than 60% by weight, such as no more than 40% by weight, such as no more than 20% by weight, based on the total weight of the electrodepositable coating composition. The total solids content of the electrodepositable coating composition may be from 1% to 60% by weight, such as 10% to 40% by weight, such as 20% to 30% by weight, based on the total weight of the electrodepositable coating composition.

Method for Coating a Substrate and Coated Substrates

The present invention is also directed to a method for coating a substrate comprising electrophoretically applying a coating deposited from an electrodepositable coating composition to at least a portion of the substrate using the electrocoating system 10 described above.
The electrodepositable coating composition of the present invention may be deposited upon an electrically conductive substrate by placing the electrodepositable coating composition in contact with an electrically conductive cathode and an electrically conductive anode, with the surface to be coated being either the anode or the cathode, depending upon the type of electrodepositable coating composition being applied. Following contact with the composition, an adherent film of the electrodepositable coating composition is deposited on the substrate when a sufficient voltage is impressed between the electrodes by a power source. The applied voltage may be varied and can be, for example, as low as one volt to as high as several thousand volts, such as between 25 and 600 volts. The current density may be between 0.5 ampere and 15 amperes per square foot.
The electrodepositable coating composition that may be used in the method of the present invention may comprise any of those known in the art, including those described above. For example, the electrodepositable coating composition may comprise a cationic film-forming resin comprising sulphonium groups and/or ammonium groups, or the electrodepositable coating composition may comprise an anionic electrodepositable coating composition comprising carboxylic acid and/or phosphoric acid groups.
According to the present invention, the method may further comprise at least partially curing the electrophoretically applied coating deposited from the electrodepositable coating composition on the substrate. As discussed above, at least partially curing the electrodepositable coating composition may comprise subjecting the substrate to elevated temperature. With respect to cationic electrodepositable coating compositions, the coated substrate may be heated to a temperature ranging from, for example, 250° F. to 450° F. (121.1° C. to 232.2° C.), such as from 275° F. to 400° F. (135° C. to 204.4° C.), such as from 300° F. to 360° F. (149° C. to 180° C.). With respect to anionic electrodepositable coating compositions, the coated substrate may be heated to a temperature ranging from, for example, 200° F. to 450° F. (93° C. to 232.2° C.), such as from 275° F. to 400° F. (135° C. to 204.4° C.), such as from 300° F. to 360° F. (149° C. to 180° C.). The curing time may be dependent upon the curing temperature as well as other variables, for example, the film thickness of the electrodeposited coating, level and type of catalyst present in the composition, type of curing agent employed, and the like. For purposes of the present invention, all that is necessary is that the time be sufficient to effect cure of the coating on the substrate. For example, the curing time can range from 10 minutes to 60 minutes, such as 20 to 40 minutes. For example, the thickness of the resultant cured electrodeposited coating may range from 1 to 50 microns, such as 15 to 50 microns.
According to the present invention, the method for coating a substrate may comprise (a) electrophoretically depositing onto at least a portion of the substrate a coating deposited from an electrodepositable coating composition using the electrocoating system 10 described above and (b) heating the coated substrate to a temperature and for a time sufficient to at least partially cure the electrodeposited coating on the substrate. According to the present invention, the method may optionally further comprise (c) applying directly to the at least partially cured electrodeposited coating one or more pigment-containing coating compositions and/or one or more pigment-free coating compositions to form an additional coating layer over at least a portion of the at least partially cured electrodeposited coating, and (d) curing the additional coating layer by allowing it to set at ambient temperature or by applying a sufficient energy from an external energy source to the coated substrate of step (c) to a condition and for a time sufficient to at least partially cure the additional coating layer. Non-limiting examples of external energy sources include thermal energy and radiation such as ultraviolet, infrared or microwave.
The optional additional coating layer may comprise one or more primer layer(s) and suitable topcoat layer(s) (e.g., base coat, clear coat layer, pigmented monocoat, and color-plus-clear composite compositions). It is understood that suitable additional coating layers include any of those known in the art, and each independently may be waterborne, solventborne, in solid particulate form (i.e., a powder coating composition), or in the form of a powder slurry. The additional coating compositions may comprise a film-forming polymer, crosslinking material and, if a colored base coat or monocoat, one or more pigments. The primer layer(s) may optionally be disposed between the electrocoating layer and the topcoat layer(s). Alternatively, the topcoat layer(s) may be omitted such that the composite comprises the electrocoating layer and one or more primer layer(s).
Moreover, the topcoat layer(s) may be applied directly onto the electrodepositable coating layer. In other words, the substrate may lack a primer layer such that the composite comprises the electrocoating layer and one or more topcoat layer(s). For example, a basecoat layer may be applied directly onto at least a portion of the electrodepositable coating layer.
It will also be understood that any of the topcoat layers may be applied onto an underlying layer despite the fact that the underlying layer has not been fully cured. For example, a clearcoat layer may be applied onto a basecoat layer even though the basecoat layer has not been subjected to a curing step (wet-on-wet). Both layers may then be cured during a subsequent curing step thereby eliminating the need to cure the basecoat layer and the clearcoat layer separately.
According to the present invention, additional ingredients such as colorants and fillers may be present in the various coating compositions from which the top-coat layers result. Any suitable colorants and fillers may be used. For example, the colorant may be added to the coating in any suitable form, such as discrete particles, dispersions, solutions and/or flakes. A single colorant or a mixture of two or more colorants can be used in the coatings of the present invention. It should be noted that, in general, the colorant can be present in a layer of the multi-layer composite in any amount sufficient to impart the desired property, visual and/or color effect.
Example colorants include pigments, dyes and tints, such as those used in the paint industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. A colorant may include, for example, a finely divided solid powder that is insoluble but wettable under the conditions of use. A colorant may be organic or inorganic and may be agglomerated or non-agglomerated. Colorants may be incorporated into the coatings by grinding or simple mixing. Colorants may be incorporated by grinding into the coating by use of a grind vehicle, such as an acrylic grind vehicle, the use of which will be familiar to one skilled in the art.
Example pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigment, azo, monoazo, disazo, naphthol AS, salt type (lakes), benzimidazolone, condensation, metal complex, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketo pyrrolo pyrrole red (“DPP red BO”), titanium dioxide, carbon black, zinc oxide, antimony oxide, etc. and organic or inorganic UV opacifying pigments such as iron oxide, transparent red or yellow iron oxide, phthalocyanine blue and mixtures thereof. The terms “pigment” and “colored filler” can be used interchangeably.
Example dyes include, but are not limited to, those that are solvent and/or aqueous based such as acid dyes, azoic dyes, basic dyes, direct dyes, disperse dyes, reactive dyes, solvent dyes, sulfur dyes, mordant dyes, for example, bismuth vanadate, anthraquinone, perylene, aluminum, quinacridone, thiazole, thiazine, azo, indigoid, nitro, nitroso, oxazine, phthalocyanine, quinoline, stilbene, and triphenyl methane.
Example tints include, but are not limited to, pigments dispersed in water-based or water miscible carriers such as AQUA-CHEM 896 commercially available from Degussa, Inc., CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS commercially available from Accurate Dispersions division of Eastman Chemical, Inc.
The colorant may be in the form of a dispersion including, but not limited to, a nanoparticle dispersion. Nanoparticle dispersions can include one or more highly dispersed nanoparticle colorants and/or colorant particles that produce a desired visible color and/or opacity and/or visual effect. Nanoparticle dispersions may include colorants such as pigments or dyes having a particle size of less than 150 nm, such as less than 70 nm, or less than 30 nm. Nanoparticles may be produced by milling stock organic or inorganic pigments with grinding media having a particle size of less than 0.5 mm. Example nanoparticle dispersions and methods for making them are identified in U.S. Pat. No. 6,875,800 B2, which is incorporated herein by reference. Nanoparticle dispersions may also be produced by crystallization, precipitation, gas phase condensation, and chemical attrition (i.e., partial dissolution). In order to minimize re-agglomeration of nanoparticles within the coating, a dispersion of resin-coated nanoparticles may be used. As used herein, a “dispersion of resin-coated nanoparticles” refers to a continuous phase in which is dispersed discreet “composite microparticles” that comprise a nanoparticle and a resin coating on the nanoparticle. Example dispersions of resin-coated nanoparticles and methods for making them are identified in U.S. patent application Ser. No. 10/876,031 filed Jun. 24, 2004, which is incorporated herein by reference, and U.S. Provisional Patent Application Ser. No. 60/482,167 filed Jun. 24, 2003, which is also incorporated herein by reference.
According to the present invention, special effect compositions that may be used in one or more layers of the multi-layer coating composite include pigments and/or compositions that produce one or more appearance effects such as reflectance, pearlescence, metallic sheen, phosphorescence, fluorescence, photochromism, photosensitivity, thermochromism, goniochromism and/or color-change. Additional special effect compositions may provide other perceptible properties, such as reflectivity, opacity or texture. For example, special effect compositions may produce a color shift, such that the color of the coating changes when the coating is viewed at different angles. Example color effect compositions are identified in U.S. Pat. No. 6,894,086, incorporated herein by reference. Additional color effect compositions may include transparent coated mica and/or synthetic mica, coated silica, coated alumina, a transparent liquid crystal pigment, a liquid crystal coating, and/or any composition wherein interference results from a refractive index differential within the material and not because of the refractive index differential between the surface of the material and the air.
According to the present invention, a photosensitive composition and/or photochromic composition, which reversibly alters its color when exposed to one or more light sources, can be used in a number of layers in the multi-layer composite. Photochromic and/or photosensitive compositions can be activated by exposure to radiation of a specified wavelength. When the composition becomes excited, the molecular structure is changed, and the altered structure exhibits a new color that is different from the original color of the composition. When the exposure to radiation is removed, the photochromic and/or photosensitive composition can return to a state of rest, in which the original color of the composition returns. For example, the photochromic and/or photosensitive composition may be colorless in a non-excited state and exhibit a color in an excited state. Full color-change may appear within milliseconds to several minutes, such as from 20 seconds to 60 seconds. Example photochromic and/or photosensitive compositions include photochromic dyes.
The photosensitive composition and/or photochromic composition may be associated with and/or at least partially bound to, such as by covalent bonding, a polymer and/or polymeric materials of a polymerizable component. In contrast to some coatings in which the photosensitive composition may migrate out of the coating and crystallize into the substrate, the photosensitive composition and/or photochromic composition associated with and/or at least partially bound to a polymer and/or polymerizable component in accordance with the present invention, have minimal migration out of the coating. Example photosensitive compositions and/or photochromic compositions and methods for making them are identified in U.S. patent application Ser. No. 10/892,919 filed Jul. 16, 2004 and incorporated herein by reference.
The additional coating layers may be applied by a topcoat system. The topcoat system may comprise any equipment and/or method known in the art to apply a topcoat coating composition. For example, the topcoat system may comprise equipment to apply a powder coating composition or a liquid coating composition. For example, the topcoat system may comprise a spray gun, a brush, a roller, a tank for immersion coating, or combinations thereof. The topcoat system may optionally further comprise a spraybooth, and the spraybooth may optionally comprise a ventilation system.
As mentioned above, the coating composition may be a powder coating composition. As used herein, “powder coating composition” refers to a coating composition which is completely free of water and/or solvent. Accordingly, the powder coating composition disclosed herein is not synonymous to waterborne and/or solvent-borne coating compositions known in the art.
According to the present invention, the powder coating composition comprises (a) a film forming polymer having a reactive functional group; and (b) a curing agent that is reactive with the functional group. Examples of powder coating compositions that may be used in the present invention include the polyester-based ENVIROCRON line of powder coating compositions (commercially available from PPG Industries, Inc.) or epoxy-polyester hybrid powder coating compositions. Alternative examples of powder coating compositions that may be used in the present invention include low temperature cure thermosetting powder coating compositions comprising (a) at least one tertiary aminourea compound, at least one tertiary aminourethane compound, or mixtures thereof, and (b) at least one film-forming epoxy-containing resin and/or at least one siloxane-containing resin (such as those described in U.S. Pat. No. 7,470,752, assigned to PPG Industries, Inc. and incorporated herein by reference); curable powder coating compositions generally comprising (a) at least one tertiary aminourea compound, at least one tertiary aminourethane compound, or mixtures thereof, and (b) at least one film-forming epoxy-containing resin and/or at least one siloxane-containing resin (such as those described in U.S. Pat. No. 7,432,333, assigned to PPG Industries, Inc. and incorporated herein by reference); and those comprising a solid particulate mixture of a reactive group-containing polymer having a T_gof at least 30° C. (such as those described in U.S. Pat. No. 6,797,387, assigned to PPG Industries, Inc. and incorporated herein by reference).
Suitable film forming polymers that may be used in the powder coating composition of the present invention comprise a (poly)ester (e.g., polyester triglycidyl isocyanurate), a (poly)urethane, an isocyanurate, a (poly)urea, a (poly)epoxy, an anhydride, an acrylic, a (poly)ether, a (poly)sulfide, a (poly)amine, a (poly)amide, (poly)vinyl chloride, (poly)olefin, (poly)vinylidene fluoride, or combinations thereof.
According to the present invention, the reactive functional group of the film forming polymer of the powder coating composition comprises hydroxyl, carboxyl, isocyanate (including blocked (poly)isocyanate), primary amine, secondary amine, amide, carbamate, urea, urethane, vinyl, unsaturated ester, maleimide, fumarate, anhydride, hydroxyl alkylamide, epoxy, or combinations thereof.
Suitable curing agents (crosslinking agents) that may be used in the powder coating composition of present invention comprise an aminoplast resin, a polyisocyanate, a blocked polyisocyanate, a polyepoxide, a polyacid, a polyol, or combinations thereof.
After deposition of the powder coating composition, the coating is often heated to cure the deposited composition. The heating or curing operation is often carried out at a temperature in the range of from 150° C. to 200° C., such as from 170° C. to 190° C., for a period of time ranging from 10 to 20 minutes. According to the invention, the thickness of the resultant film is from 50 microns to 125 microns.
As mentioned above, the coating composition may be a liquid coating composition. As used herein, “liquid coating composition” refers to a coating composition which contains a portion of water and/or solvent. Accordingly, the liquid coating composition disclosed herein is synonymous to waterborne and/or solvent-borne coating compositions known in the art.
According to the present invention, the liquid coating composition may comprise, for example, (a) a film forming polymer having a reactive functional group; and (b) a curing agent that is reactive with the functional group. In other examples, the liquid coating may contain a film forming polymer that may react with oxygen in the air or coalesce into a film with the evaporation of water and/or solvents. These film-forming mechanisms may require or be accelerated by the application of heat or some type of radiation such as Ultraviolet or Infrared. Examples of liquid coating compositions that may be used in the present invention include the SPECTRACRON® line of solvent-based coating compositions, the AQUACRON® line of water-based coating compositions, and the RAYCRON® line of UV cured coatings (all commercially available from PPG Industries, Inc.).
Suitable film forming polymers that may be used in the liquid coating composition of the present invention may comprise a (poly)ester, an alkyd, a (poly)urethane, an isocyanurate, a (poly)urea, a (poly)epoxy, an anhydride, an acrylic, a (poly)ether, a (poly)sulfide, a (poly)amine, a (poly)amide, (poly)vinyl chloride, (poly)olefin, (poly)vinylidene fluoride, (poly)siloxane, or combinations thereof.
According to the present invention, the reactive functional group of the film forming polymer of the liquid coating composition may comprise hydroxyl, carboxyl, isocyanate (including blocked (poly)isocyanate), primary amine, secondary amine, amide, carbamate, urea, urethane, vinyl, unsaturated ester, maleimide, fumarate, anhydride, hydroxyl alkylamide, epoxy, or combinations thereof.
Suitable curing agents (crosslinking agents) that may be used in the liquid coating composition of the present invention may comprise an aminoplast resin, a polyisocyanate, a blocked polyisocyanate, a polyepoxide, a polyacid, a polyol, or combinations thereof.
In addition, a colorant and, if desired, various additives such as surfactants, wetting agents or catalyst can be included in the coating composition (electrodepositable, powder, or liquid). As used herein, the term “colorant” means any substance that imparts color and/or other opacity and/or other visual effect to the composition. The colorant can be added to the composition in any suitable form, such as discrete particles, dispersions, solutions and/or flakes. A single colorant or a mixture of two or more colorants can be used.
Example colorants include pigments, dyes and tints, such as those used in the paint industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. A colorant may include, for example, a finely divided solid powder that is insoluble but wettable under the conditions of use. A colorant can be organic or inorganic and can be agglomerated or non-agglomerated. Colorants can be incorporated by use of a grind vehicle, such as an acrylic grind vehicle, the use of which will be familiar to one skilled in the art.
Example pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigment, azo, monoazo, disazo, naphthol AS, salt type (lakes), benzimidazolone, condensation, metal complex, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketo pyrrolo pyrrole red (“DPPBO red”), titanium dioxide, carbon black and mixtures thereof. The terms “pigment” and “colored filler” can be used interchangeably.
Example dyes include, but are not limited to, those that are solvent and/or aqueous based such as phthalo green or blue, iron oxide, bismuth vanadate, anthraquinone, perylene, aluminum and quinacridone.
Example tints include, but are not limited to, pigments dispersed in water-based or water miscible carriers such as AQUA-CHEM 896 commercially available from Degussa, Inc., CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS commercially available from Accurate Dispersions division of Eastman Chemical, Inc.
As noted above, the colorant can be in the form of a dispersion including, but not limited to, a nanoparticle dispersion. Nanoparticle dispersions can include one or more highly dispersed nanoparticle colorants and/or colorant particles that produce a desired visible color and/or opacity and/or visual effect. Nanoparticle dispersions can include colorants such as pigments or dyes having a particle size of less than 150 nm, such as less than 70 nm, or less than 30 nm. Nanoparticles can be produced by milling stock organic or inorganic pigments with grinding media having a particle size of less than 0.5 mm. Example nanoparticle dispersions and methods for making them are identified in U.S. Pat. No. 6,875,800 B2, which is incorporated herein by reference. Nanoparticle dispersions can also be produced by crystallization, precipitation, gas phase condensation, and chemical attrition (i.e., partial dissolution). In order to minimize re-agglomeration of nanoparticles within the coating, a dispersion of resin-coated nanoparticles can be used. As used herein, a “dispersion of resin-coated nanoparticles” refers to a continuous phase in which is dispersed discreet “composite microparticles” that comprise a nanoparticle and a resin coating on the nanoparticle. Example dispersions of resin-coated nanoparticles and methods for making them are identified in U.S. Patent Application Publication No. 2005-0287348 A1, filed Jun. 24, 2004, U.S. Provisional Patent Application Ser. No. 60/482,167 filed Jun. 24, 2003, and U.S. patent application Ser. No. 11/337,062, filed Jan. 20, 2006, which is also incorporated herein by reference.
Example special effect compositions that may be used include pigments and/or compositions that produce one or more appearance effects such as reflectance, pearlescence, metallic sheen, phosphorescence, fluorescence, photochromism, photosensitivity, thermochromism, goniochromism and/or color-change. Additional special effect compositions can provide other perceptible properties, such as opacity or texture. According to the invention, special effect compositions can produce a color shift, such that the color of the coating changes when the coating is viewed at different angles. Example color effect compositions are identified in U.S. Pat. No. 6,894,086, incorporated herein by reference. Additional color effect compositions can include transparent coated mica and/or synthetic mica, coated silica, coated alumina, a transparent liquid crystal pigment, a liquid crystal coating, and/or any composition wherein interference results from a refractive index differential within the material and not because of the refractive index differential between the surface of the material and the air.
According to the invention, a photosensitive composition and/or photochromic composition, which reversibly alters its color when exposed to one or more light sources, can be used. Photochromic and/or photosensitive compositions can be activated by exposure to radiation of a specified wavelength. When the composition becomes excited, the molecular structure is changed, and the altered structure exhibits a new color that is different from the original color of the composition. When the exposure to radiation is removed, the photochromic and/or photosensitive composition can return to a state of rest, in which the original color of the composition returns. According to the invention, the photochromic and/or photosensitive composition can be colorless in a non-excited state and exhibit a color in an excited state. Full color-change can appear within milliseconds to several minutes, such as from 20 seconds to 60 seconds. Example photochromic and/or photosensitive compositions include photochromic dyes.
According to the invention, the photosensitive composition and/or photochromic composition can be associated with and/or at least partially bound to, such as by covalent bonding, a polymer and/or polymeric materials of a polymerizable component. In contrast to some coatings in which the photosensitive composition may migrate out of the coating and crystallize into the substrate, the photosensitive composition and/or photochromic composition associated with and/or at least partially bound to a polymer and/or polymerizable component in according to the invention, have minimal migration out of the coating. Example photosensitive compositions and/or photochromic compositions and methods for making them are identified in U.S. patent application Ser. No. 10/892,919, filed Jul. 16, 2004, incorporated herein by reference.
In general, the colorant can be present in the coating composition in any amount sufficient to impart the desired visual and/or color effect. The colorant may comprise from 1 to 65 weight percent, such as from 3 to 40 weight percent or 5 to 35 weight percent, with weight percent based on the total weight of the composition.
According to the present invention, the method may optionally further comprise pretreating the substrate with a pretreatment composition prior to applying the electrodepositable coating composition using the electrocoating system. As used herein, the term “pretreatment composition” refers to a composition that is capable of reacting with and chemically altering the substrate surface and binding to it to form a film that affords corrosion protection. Non-limiting examples of a pretreatment composition include zinc phosphate pretreatment compositions such as, for example, those described in U.S. Pat. Nos. 4,793,867 and 5,588,989, zirconium containing pretreatment compositions such as, for example, those described in U.S. Pat. Nos. 7,749,368 and 8,673,091, and the like. The pretreatment composition may be brought into contact with the substrate by any of a variety of known techniques, such as dipping or immersion, spraying, intermittent spraying, dipping followed by spraying, spraying followed by dipping, brushing, or roll-coating. According to the invention, the pretreatment composition when applied to the substrate may be at a temperature ranging from, for example, 40° F. to 160° F. (4.4° C. to 71.1° C.), such as 60° F. to 110° F. (15.6° C. to 43.3° C.), such as 70° F. to 90° F. (21.1° C. to 32.2° C.). For example, the pretreatment process may be carried out at ambient or room temperature. The contact time is often from 1 second to 15 minutes, such as 4 minutes to 10 minutes, such as 5 seconds to 4 minutes.
Following the contacting with the pretreatment composition, the substrate optionally may be dried in place, e.g., air dried at room temperature or be dried with hot air, for example, by using an air knife, by flashing off the water by brief exposure of the substrate to a high temperature, such as by drying the substrate in an oven at 15° C. to 100° C., such as 20° C. to 90° C., or in a heater assembly using, for example, infrared heat, such as for 10 minutes at 70° C., or by passing the substrate between squeegee rolls. The substrate surface may be partially, or in some instances, completely dried prior to any subsequent contact of the substrate surface with any water, solutions, compositions, or the like. According to the present invention, following the contacting with the pretreatment composition, the substrate (either wet or dried) optionally may be rinsed with tap water, deionized water, and/or an aqueous solution of rinsing agents in order to remove any residue and then optionally may be dried, for example air dried or dried with hot air as described in the preceding sentence. According to the present invention, such water rinses may be eliminated and the substrate (either wet or dried in place) may be contacted with subsequent treatment compositions.
The pretreatment composition may be applied to the substrate by a pretreatment system. The pretreatment system may comprise tanks for immersion, brushes, rollers, spray guns, or combinations thereof to apply the pretreatment composition to the substrate. The pretreatment system may further comprise tanks, brushes, rollers, spray guns, or combinations thereof for applying rinse compositions, such as water, to the substrate.
According to the present invention, the method may optionally further comprise priming the substrate with a priming composition prior to applying the electrodepositable coating composition using the electrocoating system. The priming composition may be used alone or in combination with the pretreatment composition or other treatments prior to applying the electrodepositable coating composition. The priming composition may comprise a metal-rich coating composition. As used herein, the term “metal-rich coating composition” refers to film-forming compositions that include an organic or inorganic binder and at least 65% by weight metal particles, based on the total solids weight of the coating composition. As used herein, the term “metal particles” refers to elemental (i.e., zerovalent) metal and metal alloy particles. As used herein, the term “particles” refers to material in the form of particulates, such as powder or dust, as well as flakes, and may be in the form of any shape, such as, for example, spherical, ellipsoidal, cubical, rod-shaped, disk-shaped, prism-shaped, and the like. The metal may comprise zinc, aluminum, or alloys thereof. The priming composition may be brought into contact with the substrate by any of a variety of known techniques, such as dipping or immersion, spraying, electrostatic spraying, intermittent spraying, dipping followed by spraying, spraying followed by dipping, brushing, or roll-coating. It is appreciated that the metal-rich primer coatings can also be applied in dry forms such as powder or films. The metal-rich primer coatings formed from the priming composition can be applied to a dry film thickness of, for example, 2.5 to 500 microns.
After application of the priming composition to the substrate, a film formed on the surface of the substrate may be dried by driving solvent out of the film by heating or by an air-drying period. Suitable drying conditions will depend on the particular priming composition and/or application, but an exemplary drying time of from about 1 to 5 minutes at a temperature of about 60 to 250° F. (15.6 to 121° C.), such as 70 to 212° F. (27 to 100° C.) may be sufficient. More than one primer coating layer may be applied if desired. Between coats, the previously applied coat may be flashed; that is, exposed to ambient conditions for a desired amount of time.
After application of the priming composition to a substrate, the applied priming composition may be cured by any means known in the art. For example, the coating may be subjected to curing conditions sufficient to cure the priming composition. For example, the coating composition may be subjected to curing conditions such as ambient conditions, as discussed above, for a period of hours or days. Alternatively, the substrate may be subjected to curing conditions such as radiation (e.g., UV radiation) or heated to a temperature and for a time sufficient to cure the priming coating.
The priming composition may be applied to the substrate by a priming system. The priming system may comprise tanks for immersion, brushes, rollers, spray guns, or combinations thereof to apply the priming composition to the substrate. The priming system may further comprise tanks, brushes, rollers, spray guns, or combinations thereof for applying rinse compositions, such as water, to the substrate.
According to the present invention, the substrate may optionally be subjected to other treatments prior to electrocoating. For example, the substrate may be rinsed, cleaned, deoxidized, cleaned and deoxidized, anodized, acid pickled, plasma treated, laser treated, or ion vapor deposition (IVD) treated. At least a portion of the surface of the substrate may be cleaned by physical and/or chemical means, such as mechanically abrading the surface and/or cleaning/degreasing the surface with commercially available alkaline or acidic cleaning agents that are well known to those skilled in the art. These optional treatments may be used on their own or in combination with a pretreatment composition and/or a priming composition.
The present invention is also directed towards a substrate coated using the electrocoating system described above. The substrate may optionally be coated using the topcoat system. Accordingly, the substrate comprises an electrocoating layer and an optional topcoat layer.
The present invention is also directed towards a substrate coated using the pretreatment system and electrocoating system, both as described above. The substrate may optionally be coated using the topcoat system. Accordingly, the substrate comprises a pretreatment layer, an electrocoating layer and an optional topcoat layer.
The present invention is also directed towards a substrate coated using the priming system and electrocoating system, both as described above. The substrate may optionally be coated using the topcoat system. Accordingly, the substrate comprises a priming layer, an electrocoating layer and an optional topcoat layer.
The present invention is also directed towards a substrate coated using the pretreatment system, priming system and electrocoating system, each as described above. The substrate may optionally be coated using the topcoat system. Accordingly, the substrate comprises a pretreatment layer, a priming layer, an electrocoating layer and an optional topcoat layer.
The present invention is also directed towards a substrate coated according to the method of the present invention.

System for Coating a Substrate

The present invention is also directed towards a system for coating a substrate comprising the electrocoating system as described above. The system for coating a substrate may optionally further comprise the pretreatment system, the priming system, the topcoat system, or any combination thereof. For example, the system for coating a substrate may comprise the pretreatment system for pretreating the substrate; the priming system for priming the substrate; the electrocoating system for electrocoating the substrate; and the topcoat system for applying a topcoat coating to the substrate. The system for coating a substrate may comprise any combination of the systems discussed above applied sequentially. For example, the system for coating a substrate may comprise the pretreatment system followed by the electrocoat system; the system for coating a substrate may comprise the pretreatment system followed by the electrocoat system followed by the topcoat system; the system for coating a substrate may comprise the priming system followed by the electrocoat system; the system for coating a substrate may comprise the priming system followed by the electrocoat system followed by the topcoat system; the system for coating a substrate may comprise the pretreatment system followed by the priming system followed by the electrocoat system; the system for coating a substrate may comprise the pretreatment system followed by the priming system followed by the electrocoat system followed by the topcoat system; or the system for coating a substrate may comprise the electrocoat system followed by the topcoat system.
For purposes of the detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers such as those expressing values, amounts, percentages, ranges, subranges and fractions may be read as if prefaced by the word “about,” even if the term does not expressly appear. 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 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. Where a closed or open-ended numerical range is described herein, all numbers, values, amounts, percentages, subranges and fractions within or encompassed by the numerical range are to be considered as being specifically included in and belonging to the original disclosure of this application as if these numbers, values, amounts, percentages, subranges and fractions had been explicitly written out in their entirety.
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 value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.
As used herein, unless indicated otherwise, a plural term can encompass its singular counterpart and vice versa, unless indicated otherwise. For example, although reference is made herein to “a” pump, “a” recirculating pipe, “a” return conduit, “an” internal electrode, and “an” external electrode, a combination (i.e., a plurality) of these components can be used. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances.
As used herein, “including,” “containing” and like terms are understood in the context of this application to be synonymous with “comprising” and are therefore open-ended and do not exclude the presence of additional undescribed or unrecited elements, materials, ingredients or method steps. As used herein, “consisting of” is understood in the context of this application to exclude the presence of any unspecified element, ingredient or method step. As used herein, “consisting essentially of” is understood in the context of this application to include the specified elements, materials, ingredients or method steps “and those that do not materially affect the basic and novel characteristic(s)” of what is being described.
As used herein, the terms “on,” “onto,” “applied on,” “applied onto,” “formed on,” “deposited on,” “deposited onto,” mean formed, overlaid, deposited, or provided on but not necessarily in contact with the surface. For example, an electrodepositable coating composition “deposited onto” a substrate does not preclude the presence of one or more other intervening coating layers of the same or different composition located between the electrodepositable coating composition and the substrate.
Whereas specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.

Aspects

In view of the foregoing, the present invention thus relates inter alia, without being limited thereto, to the following aspects:
1. An electrocoating system for electrocoating a substrate, the system comprising a tank configured to hold an electrodepositable coating composition; at least one pump in fluid communication with the tank, at least one return conduit connecting the tank with an inlet of the pump, at least one recirculating pipe comprising a first end in fluid communication with an outlet of the pump and a second end having at least one aperture, and the at least one recirculating pipe comprising at least one external electrode positioned at least partially outside of the tank, wherein:
the substrate has a first surface and a second surface;
the pump is configured to receive the electrodepositable coating composition from the return conduit and deliver the electrodepositable coating composition into the tank through the recirculating pipe;
the external electrode is configured to provide an electric charge to the electrodepositable coating composition; and
the recirculating pipe is configured to extend into the interior of the tank and position the aperture of the second end to deliver at least a portion of the electrically charged electrodepositable coating composition to the first surface of the substrate.
2. The electrocoating system according to Aspect 1, wherein the external electrode comprises at least 50% of the recirculating pipe.
3. The electrocoating system according to Aspects 1 or 2, wherein the external electrode has an internal surface configured to contact the electrodepositable coating composition, and the electrocoating system is configured such that a ratio of a total combined surface area of the external electrode based on the surface area of the external surface area of the external electrode to a surface area of the first surface of the substrate is from 1:7 to 1:1.
4. The electrocoating system according to any one of the preceding Aspects, wherein the external electrode comprises a section of the recirculating pipe located outside of the tank.
5. The electrocoating system according to any one of the preceding Aspects, wherein the second end of the recirculating pipe comprises at least one nozzle comprising the aperture.
6. The electrocoating system according to any one of the preceding Aspects, wherein the second end of the recirculating pipe is branched and comprises at least two apertures configured to deliver at least a portion of the electrodepositable coating composition charged by the external electrode to different surface sections of the first surface of the substrate.
7. The electrocoating system according to any one of the preceding Aspects, wherein the recirculating pipe comprises a plurality of apertures configured to deliver the electrodepositable coating composition charged by the external electrode to different sections of the first surface of the substrate.
8. The electrocoating system according to any one of Aspects 1-5, wherein the electrocoating system comprises a plurality of recirculating pipes configured to deliver the electrodepositable coating composition charged by the external electrode to different sections of the first surface of the substrate.
9. The electrocoating system according to Aspect 8, wherein the plurality of recirculating pipes is positioned equidistant along a length of the tank.
10. The electrocoating system according to any one of the preceding Aspects, further comprising at least one internal electrode positioned inside the tank.
11. The electrocoating system according to Aspect 10, wherein the recirculating pipe comprises a plurality of the internal electrodes positioned along a length of the tank.
12. The electrocoating system according to Aspect 11, wherein the plurality of internal electrodes is positioned equidistant along the length of the tank.
13. The electrocoating system of any of Aspects 10 to 12, wherein the electrocoating system is configured such that a ratio of a total combined surface area of the internal electrode to the surface area of the second surface of the substrate is from 1:7 to 1:1.
14. The electrocoating system according to any one of the preceding Aspects, further comprising at least one power source to provide an electrical current to the electrocoating system.
15. The electrocoating system according to Aspect 14, wherein the power source is electrically coupled to the external electrode, the internal electrode, if present, and the substrate, wherein the substrate comprises a counter-electrode to the external electrode and the internal electrode, if present.
16. The electrocoating system according to Aspect 15, wherein the electrical connection to the power source is made such that the external electrode and internal electrode, if present, comprise anodes, and the substrate comprises a cathode.
17. The electrocoating system according to any one of the preceding Aspects, wherein the tank, the return conduit, the pump and the recirculating pipe are directly coupled to form at least one continuous and uninterrupted loop configured for constrained flow of the electrodepositable coating composition through the return conduit, pump and recirculating pipe.
18. The electrocoating system according to any one of the preceding aspects, wherein the tank comprises a base portion and at least one side wall extending up from the base portion.
19. The electrocoating system according to any one of the preceding Aspects, wherein the substrate comprises an open-polygon cross-sectional shape.
20. The electrocoating system according to any one of the preceding Aspects, wherein the substrate comprises a rectangular cross-sectional shape.
21. The electrocoating system according to any one of the preceding Aspects, wherein the substrate is a container.
22. The electrocoating system according to any one of the preceding Aspects, wherein the substrate has a cross-sectional area of at least 40 m².
23. A method for coating a substrate comprising electrophoretically applying a coating deposited from an electrodepositable coating composition to at least a portion of the substrate using the electrocoating system according to any one of preceding Aspects 1 to 18.
24. The method according to Aspect 23, wherein the electrodepositable coating composition comprises a cationic film-forming resin comprising sulphonium groups.
25. The method according to any one of Aspects 23 or 24, wherein the method further comprises at least partially curing the electrodepositable coating composition.
26. The method according to any one of Aspects 23 to 25, wherein the method further comprises applying a topcoat coating composition to at least a portion of the substrate coated with the electrodepositable coating composition.
27. The method according to any one of Aspects 23 to 26, wherein the method further comprises pretreating the substrate with a pretreatment composition prior to applying the electrodepositable coating composition.
28. The method according to any of Aspects 23 to 27, wherein the method further comprises priming the substrate with a priming composition prior to applying the electrodepositable coating composition.
29. The method according to any one of Aspects 23 to 28, wherein the substrate comprises an open-polygon cross-sectional shape or a rectangular cross-sectional shape.
30. The method according to any one of Aspects 23 to 29, wherein the substrate is a container.
31. The method according to any one of Aspects 23 to 30, wherein the substrate has a cross-sectional area of at least 40 m².
32. A substrate coated by the method according to any one of preceding Aspects 23 to 31.
33. A system for coating a substrate comprising the electrocoating system according to any one of Aspects 1 to 22, and further comprising at least one of:
a pretreatment system for pretreating the substrate prior to processing the substrate in the electrocoating system;
a priming system for priming the substrate prior to processing the substrate in the electrocoating system; and/or
a topcoat system for applying a topcoat coating to the substrate after processing the substrate in the electrocoating system.
Illustrating the invention are the following examples, which, however, are not to be considered as limiting the invention to their details. Unless otherwise indicated, all parts and percentages in the following examples, as well as throughout the specification, are by weight.

Prophetic Example

In this prophetic example, an intermodal shipping container is coated using the system and method of the present invention. The intermodal shipping container has four enclosed sides (the top or roof of the container, two side walls, and an enclosed end), an opening at the opposing end which is covered by doors (which will be open during the electrodeposition process), and a floor which has rows of structural support members crossing over from the long sides of the container and is not enclosed. The structural supports are the members which are utilized to attach and support the floor of the finished container (the floor is installed after painting). The open-pocket shape of the container makes it difficult to fully coat the inside surfaces of the container during an electrodeposition process using standard technology, i.e., electrodes positioned along the inside walls of the tank. For the electrophoresis process to work effectively (coat the entire inside surface of the container), an electrical potential must be applied at a rate and voltage potential adequate to initiate and maintain the electrodeposition process.
To apply a coating deposited from the electrodepositable coating composition to all the surfaces of the container, the container must be fully immersed into an electrocoat bath large enough to fully immerse the container. For intermodal shipping containers, the electrocoat bath may exceed 80,000 gallons of electrodepositable coating composition. The container may be lifted by the four exterior, top corners by a lifting device (e.g., a hoist or crane) and positioned above the electrocoat bath. Once in the proper horizontal position, it will be lowered into the electrocoat bath with care and manipulated in the tank during the immersion process to minimize the air bubbles that may form in the container. It is anticipated that the electrodepositable coating composition may be maintained at a temperature between 80° F. and 95° F. Cooling may be required as the electrodeposition process should generate heat. In addition, anodes with membranes may be present in the bath to remove acid which is also released during the electrocoat deposition process. A proper ratio of bare anode surface area and membrane area will need to be maintained to provide proper pH control of the bath. The interior surface, and exposed external surface area of the external electrode (if the external electrode is an anode) will need to be included in this calculation.
The external electrode will be electrically charged in the same manner as a standard electrode in electrodeposition processes with the container electrically coupled to the other pole and serve as a counter-electrode. The applied DC voltage may vary from 100V to 450V. Amperage will be dependent on coating application rate, immersion time, coulombic efficiency of the specified electrodepositable coating composition, application parameters, and applied thickness. For example, anodes of 316SS may have an effective electrical capacity of approximately 5 amps per ft²of exposed anode area. For cationic electrodeposition, use of the external anode may effectively double the effective surface area of each anode. In addition, the fully charged electrodepositable coating composition that flows through the external anode and recirculating pipe may carry or drive the electrical energy to the cathode (i.e., the container) at greater distances than a static anode wherein the electrodepositable coating composition simply contacts the surface of the anode. This allows for the electrodepositable coating composition to coat the inside of the container where it is difficult to get adequate throwpower because of the limitations of standard electrocoat systems.
It will be appreciated by skilled artisans that numerous modifications and variations are possible in light of the above disclosure without departing from the broad inventive concepts described and exemplified herein. Accordingly, it is therefore to be understood that the foregoing disclosure is merely illustrative of various exemplary aspects of this application and that numerous modifications and variations can be readily made by skilled artisans which are within the spirit and scope of this application and the accompanying claims.

Claims

What is claimed is:

1. An electrocoating system for electrocoating a substrate, the system comprising a tank configured to hold an electrodepositable coating composition; at least one pump in fluid communication with the tank, at least one return conduit connecting the tank with an inlet of the pump, at least one recirculating pipe comprising a first end in fluid communication with an outlet of the pump and a second end having at least one aperture, and the at least one recirculating pipe comprising at least one external electrode positioned at least partially outside of the tank, wherein:

the substrate has a first surface and a second surface;

the pump is configured to receive the electrodepositable coating composition from the return conduit and deliver the electrodepositable coating composition into the tank through the recirculating pipe;

the external electrode is configured to provide an electric charge to the electrodepositable coating composition; and

the recirculating pipe is configured to extend into the interior of the tank and position the aperture of the second end to deliver at least a portion of the electrically charged electrodepositable coating composition to the first surface of the substrate.

2. The electrocoating system of claim 1, wherein the external electrode comprises at least 50% of the recirculating pipe.

3. The electrocoating system of claim 1, wherein the external electrode has an internal surface configured to contact the electrodepositable coating composition, and the electrocoating system is configured such that a ratio of a total combined surface area of the external electrode based on the surface area of the external surface area of the external electrode to a surface area of the first surface of the substrate is from 1:7 to 1:1.

4. The electrocoating system of claim 1, wherein the external electrode comprises a section of the recirculating pipe located outside of the tank.

5. The electrocoating system of claim 1, wherein the second end of the recirculating pipe comprises at least one nozzle comprising the aperture.

6. The electrocoating system of claim 1, wherein the second end of the recirculating pipe is branched and comprises at least two apertures configured to deliver at least a portion of the electrodepositable coating composition charged by the external electrode to different surface sections of the first surface of the substrate.

7. The electrocoating system of claim 1, wherein the recirculating pipe comprises a plurality of apertures configured to deliver the electrodepositable coating composition charged by the external electrode to different sections of the first surface of the substrate.

8. The electrocoating system of claim 1, wherein the electrocoating system comprises a plurality of recirculating pipes configured to deliver the electrodepositable coating composition charged by the external electrode to different sections of the first surface of the substrate.

9. The electrocoating system of claim 8, wherein the plurality of recirculating pipes is positioned equidistant along a length of the tank.

10. The electrocoating system of claim 1, further comprising at least one internal electrode positioned inside the tank.

11. The electrocoating system of claim 10, wherein the recirculating pipe comprises a plurality of the internal electrodes positioned along a length of the tank.

12. The electrocoating system of claim 11, wherein the plurality of internal electrodes is positioned equidistant along the length of the tank.

13. The electrocoating system of claim 10, wherein the electrocoating system is configured such that a ratio of a total combined surface area of the internal electrode to the surface area of the second surface of the substrate is from 1:7 to 1:1.

14. The electrocoating system of claim 1, further comprising at least one power source to provide an electrical current to the electrocoating system, wherein the power source is electrically coupled to the external electrode and the substrate, wherein the substrate comprises a counter-electrode to the external electrode.

15. The electrocoating system of claim 10, further comprising at least one power source to provide an electrical current to the electrocoating system, wherein the power source is electrically coupled to the external electrode, the internal electrode, and the substrate, wherein the substrate comprises a counter-electrode to the external electrode and the internal electrode.

16. The electrocoating system of claim 1, wherein the tank, the return conduit, the pump and the recirculating pipe are directly coupled to form at least one continuous and uninterrupted loop configured for constrained flow of the electrodepositable coating composition through the return conduit, pump and recirculating pipe.

17. The electrocoating system of claim 1, wherein the tank comprises a base portion and at least one side wall extending up from the base portion.

18. The electrocoating system of claim 1, wherein the substrate comprises an open-polygon cross-sectional shape.

19. The electrocoating system of claim 1, wherein the substrate comprises a rectangular cross-sectional shape.

20. The electrocoating system of claim 1, wherein the substrate is a container.

21. The electrocoating system of claim 1, wherein the substrate has a cross-sectional area of at least 40 m².

22. A method for coating a substrate comprising electrophoretically applying a coating deposited from an electrodepositable coating composition to at least a portion of the substrate using the electrocoating system of claim 1.

23. The method of claim 22, wherein the electrodepositable coating composition comprises a cationic film-forming resin comprising sulphonium groups.

24. The method of claim 22, wherein the method further comprises applying a topcoat coating composition to at least a portion of the substrate coated with the coating deposited from the electrodepositable coating composition.

25. The method of claim 22, wherein the method further comprises pretreating the substrate with a pretreatment composition prior to applying the coating deposited from the electrodepositable coating composition.

26. The method of claim 22, wherein the method further comprises priming the substrate with a priming composition prior to applying the coating deposited from the electrodepositable coating composition.

27. The method of claim 22, wherein the substrate comprises an open-polygon cross-sectional shape or a rectangular cross-sectional shape.

28. The method of claim 22, wherein the substrate is a container.

29. A substrate coated by the method of claim 22.

30. A system for coating a substrate comprising the electrocoating system of claim 1, and further comprising at least one of:

a pretreatment system for pretreating the substrate prior to processing the substrate in the electrocoating system;

a priming system for priming the substrate prior to processing the substrate in the electrocoating system; and/or

a topcoat system for applying a topcoat coating to the substrate after processing the substrate in the electrocoating system.