WO2008060405A2

WO2008060405A2 - Epoxy and thermoplastic powdered thermal spray compositions

Info

Publication number: WO2008060405A2
Application number: PCT/US2007/023283
Authority: WO
Inventors: Frank N. Longo; Thomas Gardega
Original assignee: Xiom Corporation
Priority date: 2006-11-09
Filing date: 2007-11-03
Publication date: 2008-05-22
Also published as: WO2008060405A3

Abstract

A powdered thermal spray composition comprising powdered epoxy and at least one thermoplastic compound. Thermoplastic compounds include but are not limited to nylon 11, polyolefin, polypropylene, polyethylene and mixtures thereof. A surface and/or object coated by the thermal spray composition are also provided.

Description

EPOXY AND THERMOPLASTIC POWDERED THERMAL SPRAY COMPOSITIONS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application Serial No. 60/858,063 filed November 9, 2006, which is herein incorporated in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to epoxy/thermoplastic bond coat and/or topcoat compositions comprising epoxy powder and at least one thermoplastic powder having improved mechanical and chemical properties.

BACKGROUND TO THE INVENTION

Thermal spray compositions come in powder form and can be applied to a surface by thermal spraying. The term "thermal spraying" refers to process in which a coating material feedstock, thermal spray composition, is heated and propelled as individual droplets or particles onto the surface of a substrate. The coating material is heated by the applicator (e.g., a thermal spray gun) by using combustible gas, plasma flame or electric hot air to heat and melt the plastic particles into droplets, which are propelled out of the spray gun by compressed gas. When the coating material particles strike the substrate they flatten, flow and melt into adjacent particles to form a continuous film and/or an agglomeration of particles. It is this film and/or an agglomeration of particles that coats the surface and/or prepares the surface for additional coatings thereby enhancing the bond between the additional coating and the coated surface.

It is well appreciated in the art that different types of thermal spray compositions are available on the market today which can be used to coat various surfaces such as metal, paper, wood, plastic, concrete and the like. When the surface to be coated is metal, the surface and/or substrate must be primed with special primers and/or coated with a bonding material prior to thermal spraying the surface. These primers/coatings are either in liquid form or in an electrostatic powder form that once applied must be heated. One problem with liquid primers/coatings is that they contain a large amount of High Volatile Organic Compounds (HVOC) and therefore must be applied in areas having proper ventilation and are subjected to tougher OSHA requirements since VOC are involved. Another problem associated with applying a liquid primer prior to applying a powder coating of the present invention is that two different sets of equipment are necessary to complete a job since the liquid application is different than the powdered coating application. Still another problem with the application of a liquid coating is long down times may be required for the primer/coatings to properly dry. This adds additional expense and time to a coating project.

When an electrostatically applied powder coating is used as a primer, after the powder is applied external heating must be applied to cure the coating in place. This is often achieved by a heat-belt or an induction heater. As with the liquid primer, different equipment may have to be used in order to apply the electrostatic powder to the surface to be coated and the heating process used to cure the sprayed on composition may add additional time to the project. In other words, instead of the surface to be coated being thermally sprayed and cured in a single step, multiple steps, including application of the powder and heat curing the powder are required. In addition, much more coating material must be applied since a large amount of the electrostatic coating material will be lost during the application of the coatings. As a result, using electrostatically applied particles as a primer increases labor costs as well as material cost.

In addition, many of the liquid and/or emulsion primer materials available on the market today contain solvents that slowly evaporate from the applied coating. The vapors produced by the evaporating solvents may be toxic and may continue to be emitted from the applied coating long after the coating has been applied. Moreover, vapors from the evaporating solvents of the primer may cause air pockets in the coating and therefore compromise the coatings integrity. In addition, any coating that may be applied to the primer will also be compromised. In contrast, powdered thermal spray compositions do not require liquid primers and therefore do not emit solvent vapors.

Therefore, in view of the foregoing, what is needed in the market place today are powdered thermal spray compositions that can be applied to a surface in a single spraying and once applied retains the hardness, wear resistance and bond strength expected of epoxy and the density and toughness of thermoplastics. Such a thermal spray composition must also have all of the aforementioned attributes so that it can be applied on-site and does not need to be brought back to a workshop to apply a special primer and/or bonding coat. Most importantly, the bond coating does not need extended curing times at elevated temperatures for extended periods of time.

One object of the present invention is to provide a powdered thermal spray composition that can be applied to a surface in a single spraying. In other words, the present invention relates to a powdered thermal spray that can be applied to a clean, non-coated surface and results in superior bond strength.

Another object of the invention is to provide a powdered thermal spray composition that can be applied to a surface in a single spraying and retain the hardness, wear resistance and bond strength expected of epoxy as well as the density and toughness of and flexibility of the thermoplastics.

Still another object of the invention is to provide a composition that once applied to a surface provides unique bonding/alloying characteristics such that the epoxy and the thermoplastic particles makes a new alloying composition that has unexpected temperature and corrosion resistance. In addition, if heat were applied to the coated surface after the composition of the present invention is applied then the coating would become completely alloyed and can be used as a topcoat.

The present invention has the aforementioned characteristics as well as others and overcomes the shortcomings of the prior art discussed above. The present invention is further described in the sections below. SUMMARY OF THE INVENTION

The present invention relates to a powdered thermal spray composition comprising epoxy and at least one thermoplastic material. The composition can be used as either a bond coat and/or as a topcoat. The epoxy particles provide high bond adhesion to steel, fiberglass, and the like as is normally expected when fuse bond epoxy (FBE) is applied. The thermoplastic particles of the powdered coating of the present invention provide flexibility to the coatings as well as a unique structure for bonding to any thermoplastic coating applied thereto.

The present invention also relates to a powdered thermal spray composition comprising epoxy and a polyamide, preferably nylon 11 for corrosion at high temperature and epoxy with Pebax® (polyether amide) as a preferred bond coat. In addition , these composition may further contain other additives such as glow in the dark particles, antifouling particles, antimicrobial particles and the like so that once applied to a clean, non-coated surface would provide additional properties that are associated with the additive. In a preferred embodiment of the present invention which uses glow in the dark particles, clear epoxy and clear thermoplastic material, such as clear polyethylene, is used.

Still further, the present invention relates to a powdered thermal spray composition comprising epoxy and polyethylene, polypropylene, polyolefin and mixtures thereof that can be used to coat surfaces so as to repair and prepare a surface for subsequent coating materials, or as a top coat coating. As stated above, one clear advantage of the powdered thermal spray compositions of the present invention over the thermal sprays available on the market is that the thermal spray compositions of the present invention can be applied directly to clean, non-coated surfaces without additional curing/heating time and therefore reducing labor and material costs. If the coating is to be used as a topcoat, additional heat can be applied to the coated surface in order to transform the coating to a unique alloy substance having unexpected improved temperature and corrosion resistance. In addition, relatively little, if any, HVOC are present in the composition since no solvents are necessary to produce the powdered composition.

The embodiments of the present invention are further described in the Detailed Description section of this application that directly follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 shows a cross-sectional view of a surface coated with a coating of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a powdered thermal spray composition comprising epoxy and at least one thermoplastic. The powdered thermal spray composition can be produced by cladding and/or by standard simple mixing techniques. Once the composition of the present invention is applied using heat, the heat melts at least a portion of the thermoplastic particles and at least a portion of the epoxy particles in the composition of the present invention so as to form an alloy region between the thermoplastic particles and adjacent epoxy particles as it is applied to a surface to be coated. This alloy region of the applied coating has a higher melting point than the thermoplastic particles in the composition and therefore is not melted by heat transferred with the application of a topcoat. This is shown in Figure 1.

Figure 1 shows a cross section of a coating of the present invention (10) coated on a substrate (35). Epoxy particles (20) are positioned adjacent to thermoplastic particles (30) and are attached to each other by an alloy region (25) that melts at a higher melting point than the thermoplastic (30) but a lower melting point than the epoxy (20). This unique characteristic prevents delaminating of the composition when it is used as a bond coating and second coating is applied using heat. The thermal energy transferred from the top coat being applied to the bond coating upon contact is high enough to partially melt or soften/melt the thermoplastic particles of the bond coating so that the melted thermoplastic particles of the top coat becomes part of the topcoat. In other words, application of a topcoat carries enough thermal energy to melt the thermoplastic particles of the bond coat, but not enough thermal energy to melt the epoxy particles and/or the alloy region of the bond coat. This maintains the general topology of the bond coat and allows some of the thermoplastic particles of the topcoat to melt/fuse with the thermoplastic particles of the bond coat. In essence, the thermoplastic particles of the topcoat become an extension of the thermoplastic particles in the bond coat since at least part of the thermoplastic particles of the bond coat melts into and combines with the thermoplastic particles of the top coating so that the two coatings become continuous with each other.

The average particle size of the thermoplastic particles used in the composition of the present invention range from about -200 μm to (+) 44 μm mesh, preferably from about - 100 μm to about (+) 44 μm mesh and more preferably -75 μm to about (+) 44 μm mesh. The average size of the epoxy particles used in the composition of the present invention ranges from about - 200μm to about (+) 44μm., preferred range being about 100 μm to about (+) 44 μm mesh. Although these are sizes of thermoplastic particles and epoxy particle that can be used particles outside of these exemplified ranges are also considered to fall within the scope of the present invention.

The average melting point of the epoxy used in the present composition is about 300 degree F and the average melting point of a thermoplastic particle used is about 200 degree F. The alloy/new substance created by the melting of epoxy and thermoplastic particles has an operating surface temperature well above 300 degrees F, suggesting that it has unique and unexpected properties, which allow it to operate at such high temperatures. The thermal energy that is transferred to the surface of the epoxy/thermoplastic composition of the present invention when used as a bond coat is high enough to melt the thermoplastic particles on the surface of the bond coat so that the melt into/with the thermoplastic of the topcoat being applied to make one continuous/intertwined top coating. This unique characteristic thoroughly bonds the topcoat to the bond coat. As a result, the powdered thermoplastic composition of the present invention once applied to a surface by heat forms an extremely ridged bond keyed and melted together into a bond coat that can be partially re-melted when a second coating is applied using heat. The coating produced from the composition of the present invention possesses very high tensile and shear strength. In addition, the alloy region created between the epoxy particles and the thermoplastic particles melts at a lower temperature than the epoxy particles and a higher temperature than the thermoplastic particles, de-lamination of the coating upon heating does not occur since the heat applied is not high enough to melt the alloy region thereby securing the integrity of the coating.

On embodiment of the present invention is directed to a thermally sprayable polymer coating composition comprising at least one thermoplastic material selected from the group consisting of polyamides, polyolefins and mixtures thereof wherein the polyolefins are selected from the group consisting of polypropylene, polyethylene, ethylene acrylic acid (EAA), ethylene malacrylic acid (EMAA), and mixtures therefore and the polyamide is selected from the group consisting of nylon-11 , nylon-12, nylon,- 33, nylon-6, nylon-66, and mixtures thereof.

The thermal spray composition of the present invention produces a thermal spray coating that retains the hardness, wear resistance and bond strength expected of epoxy and also takes on the density and toughness of nylon 11 and/or the coating/filler characteristics of polyethylene. In addition, these unique properties allow for a thick application of the thermal spray composition without cracking.

In a preferred embodiment of the present invention, the thermal spray coating comprising up to about 50% thermoplastic material (e.g., nylon 11 ) by weight of the composition, preferably up to about 40% thermoplastic material (e.g., nylon 11 ) by weight of the composition and more preferably up to about 35% thermoplastic material (e.g., nylon 11 ) by weight of the composition. Other weight percentages of thermoplastic material can also be used to make the composition of the present invention and are envisioned to be part of the present invention providing that the mass of the thermoplastic materials used is no more than 60% by volume when used as a fuse-bond coating. If used as a topcoat, the percentage by mass and the volume of the thermoplastic particles, e.g., nylon 11 , would vary according to the environment in which the coated surface will be exposed.

The powdered thermal spray composition of the present invention can be applied to a surface in a thickness of up to about .020 thick and possesses the attributes of Fuse Bonded Epoxy (FBE). Conventional FBE requires post heating, i.e. induction-heating coils, to effect melting after the powder has been applied electrostatically. The composition of the present invention, however, has the same benefits of FBE, can be applied on-site with minimum pre-heat, and can be applied thicker than liquid and/or electrostatically applied powdered materials without cracking. In other words, the composition of the present invention does not require post heating to effect melting after the powdered coating has been applied and as a result can be applied quicker and less expensive than existing electrostatically epoxy containing powders.

Still another embodiment of the present invention is directed to a composition comprising epoxy and nylon 11 components that can be used for potable water and food handling areas/containers. The non-toxic epoxy components that can be used in the composition of the present invention include, but are not limited to, those selected from the group consisting of Corvel ® 101160 Jersey Cream, Corvel ® 10-1161 White [3], Corvel® 10-2026[4], Corvel® Red, Corvel® Red Brown, Corvel® Dark Blue, Corvel® Blue [1], Corvel® Blue [2], Corvel® Gray [1], [2], and [3] all available from Rhom and HAAS POWDER COATINGS, Reading PA, diglycidyl ether bisphenol A type, epoxy resins of the diglycidyl bisphenol F type, epoxy resins of a type where the backbone is formed by vinyl copolymerication and the epoxy group is present and available for further reaction; epoxy compounds containing one or more oxirane groups and 15 to 80 carbon atoms, epoxy compounds consisting of esters of epoxidized fatty acids having 14 to 22 carbon atoms, such as epoxidized cottonseed oil, epoxidized linseed oil, epoxidized olive oil, epoxidized coconut oil, methyl epoxystearate, butyl epoxystearate, tridecyl epoxystearate, butyl epoxymyristate, butyl epoxypalmitate, oxtyl epoxytallate, and mixtures thereof. It is understood that these non-toxic epoxy compounds can be used alone or in combination with other non-toxic epoxy compounds not listed.

The epoxy used to produce the powder coating composition of the present invention can be selected based on the surface to be coated, the final use of the surface to be coated and the conditions in which the surface to be coated will be subjected to once the coating is applied. The same is true for the thermoplastic material used in the coating composition of the present invention.

Since the powdered thermal sprays of the present invention grip deep into the imperfections of the surface to which it is applied, increasing the imperfections of the surface to which it is applied enhances the adhesion of the thermal spray coating. One way to increase these imperfections of a surface is to first degrease the surface followed by grit blasting. Degreasing makes the imperfections already on the surface more available for bonding by removing greasy deposits from these imperfections as well as eliminating any adverse chemicals that might interfere with the chemical bonding of the thermal spray of the invention. The grit blasting, on the other hand, increases the imperfections of the surface to be treated allowing the thermal spray to adhere deep into the imperfections of the surface. Grit blasting at 0.3 Mpa (40 psi) using fine steel and/or alumina grit (0.2 to 0.5 mm) is recommended. In the alternative any other sort of surface roughing can be used.

The epoxy based thermal spray compositions of the present invention are designed to replace the currently available fuse bond epoxy applied electrostatically and then heated using induction, as well as two component liquid epoxies, liquid urethanes and other liquid primers currently used to treat surfaces for subsequent application of a functional coating. In other words, the powered thermal spray epoxy based compositions of the present invention can be used to coat clean, non-coated surfaces (surfaces without primer) in which it will be used as the main coating or, in the alternative, can be used as a base coat for subsequent applications of functional top coatings that would normally not adhere to the surface without a primer.

When the composition of the present invention is to be used as a functional coating (i.e. topcoat), it can be heated using induction heating in situ to convert the entire applied coating to the alloyed/new substance produced when applied. That is the thermoplastic and epoxy materials not already converted to an alloy/new substance discussed above is completely converted to the alloy. This new topcoat provides superior temperature and corrosion resistance. For example, the alloy/new substance has been found to withstand temperature in excess of 550 ⁰F.

As with the other embodiments of the present invention described above, degreasing the surface and grit blasting the surface to increase the available imperfections in the surface enhances the adhesion of the thermal spray. In addition, the surface can be heated to about 100⁰F to about 200⁰F and the temperature of the substrate held at the preheated temperature while indexing so as to effectively cause plastic stream melting (i.e. wetting the surface) on impact. If the object to be coated is small enough, the complete object can be heated prior and during coating. If a large surface is being coated, only the portion of the surface being coated at any given time needs to heated. Electric, hot air or flame sources can be used to pre-heat and maintain the temperature of the surface to be coated, although this is not essential for all compositions being applied. In another embodiment of the present invention, the nylon 11 of the thermal spray composition described above is replaced with at least one polyolefin component selected form the group consisting of polypropylene, polyethylene, polypropylene, poly ether amides, Pebax®, mixtures thereof and the like. This composition can be used as a bond coat that is applied to a surface prior to the application of a second composition. For example, the epoxy/ nylon -11 bond coat can be applied to a surface first and then an anti-fouling composition comprising a thermoplastic can be applied directly on top of the epoxy/polyethylene coat. For the reasons stated above, the epoxy/polyethylene bond coat will form a secure bond with the bond coat. For non-polyamide topcoats the preferred bond coat is epoxy/co-polyether amide (e.g. Pebax®), since co-melting occurs and stronger linkage between the topcoat and the bond coat result. The bond coat composition provides a coating that provides the characteristics of an epoxy compound as described above with the "gel-coating" characteristics of the thermoplastic. This composition is ideally used as a bond coat for anti-fouling coatings since gel-coat is often used as the final coating of fiberglass boats.

The epoxy/polyethylene bond coat can be applied by thermal spraying the surface and/or object on-site only minutes before the application of the second composition. In other words, no drying time is necessary for the bond coat and the topcoat can be applied to the bond coat immediately after application of the fuse bond coating. The present invention is also directed to an object coated with either the epoxy/ thermoplastic coating alone or an object coated with an epoxy/thermoplastic coating and then with a second composition. One specific embodiment is directed to an object coated with the epoxy/nylon-11 bond coat of the present invention and an antifouling and/or anti-microbial coating thereafter. Still another embodiment of the invention is directed to an object coated with the epoxy/Pebax® bond coat of the present invention and a non-polyamide topcoat. Still another embodiment of the present invention comprises a clear epoxy/clear thermoplastic composition containing at least one phosphorescent particle so as to make the object and/or surfaces "glow in the dark."

Various types of thermal spray guns can be used to apply the thermal sprays of the present invention. Thermal spray guns typically use mixtures of oxygen-fuel gas, air-fuel gas, air-liquid fuel, oxygen-liquid fuel, and plasma and/or electric hot air as a heat medium to melt and propel the individual droplets to a prepared substrate. Thermal spray devices fall within general classification of equipment: (1 ) wire combustion, (2) powder combustion, (3) plasma-powder, (4) high velocity oxygen-fuel gas-powder, (5) high velocity oxygen-fuel gas-wire, (6) high velocity air-liquid fuel-powder, (7) high velocity oxygen-liquid fuel-powder, (8) detonation gun powder, and (9) water cannon plasma. In general, thermal spray devices use wire combustion, powder combustion, plasma combustion or electric arc combustion.

In the wire combustion process a combustion heat source is initiated and feed stock material in wire or rod form is driven into the heat medium where a compressed air stream concentrates the heat source about the axially fed feed stock whereby it is melted atomized and propelled to the substrate for deposition of the coating.

In the powder combustion process a combustion heat source is initiated and feed stock material in powder form is introduced axially or tangentially to the propagated flame. The feedstock powder material is delivered by means of a powder feeder or gun mounted hopper.

In the plasma powder system a heat source is generated by passing an inert gas between the gap formed by an electrode and nozzle that are at an electrical potential. A high voltage, high frequency, low amperage arc is struck which bridges the gap between the electrode and nozzle. This small amperage arc partially ionizes the inert gas and generates a conductive path for the low voltage, high amperage potential to complete a circuit. The inert gas is thereby totally disassociated expands and exits the nozzle bore at high velocity. During the recombination of the disassociated gas heat is generated which is used to melt the feedstock material powder injected into the plasma flame tangentially. The velocity of the flame propels the feedstock material powder onto a substrate.

Although any of the above thermal spray processes can technically be used to apply the thermal compositions of the present invention, a powder combustion thermal spray process is preferred. In particular, a powder combustion thermal spray process using the thermal spray system described in co-pending United States Patent Application No.10/909,115 that is incorporated herein in its entirety by reference is most preferred. The thermal spray compositions of the present invention can be produced using standard blending techniques including cladding. Cladding, a well-known process, involves agglomerating two or more powder materials together using a binder so that they do not separate during spraying. The compositions of the present invention can also be produced using simple mechanical mixing.

While the above description contains many specifics, these specifics should not be construed as limitations of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other embodiments within the scope and spirit of the invention as defined by the claims appended hereto.

Claims

What is claimed is:

1. A thermally sprayable polymer coating composition comprising:

(i) epoxy; and

(ii) at least one thermoplastic material.

2. The thermally sprayable polymer coating composition of claim 1 , wherein said at least one thermoplastic material is selected from the group consisting of polyamides, polyolefins and mixtures thereof.

3. The thermally sprayable polymer coating composition of claim 1 wherein the epoxy is a non-toxic epoxy compound.

4. The thermally sprayable polymer coating composition of claim 3 wherein said non-toxic epoxy is selected from the group consisting of, diglycidyl ether bisphenol A type, epoxy resins of the diglycidyl bisphenol F type, epoxy resins of a type where the backbone is formed by vinyl copolymerication and the epoxy group is present and available for further reaction; epoxy compounds containing one or more oxirane groups and 15 to 80 carbon atoms, esters of epoxidized fatty acids having 14 to 22 carbon atoms, epoxidized cottonseed oil, epoxidized linseed oil, epoxidized olive oil, epoxidized coconut oil, methyl epoxystearate, butyl epoxystearate, tridecyl epoxystearate, butyl epoxymyristate, butyl epoxypalmitate, oxtyl epoxytallate, and mixtures thereof.

5. The thermally sprayable polymer coating composition of claim 1 wherein said thermoplastic composition has an average particle diameter size of about (-) 200 μm to about (+) 44 μm.

6. The thermally sprayable polymer coating composition of claim 5 wherein said thermoplastic composition has an average particle diameter size of about (-) 100 μm to about (+) 44 μm.

7. The thermally sprayable polymer coating composition of claim 6 wherein said thermoplastic composition has an average particle diameter size of about (-) 75 μm to about (+) 44 μm.

8. The thermally sprayable polymer coating composition of claim 1 wherein said average size of said epoxy particles ranges from about (-) 200 μm to about (+) 44μm.

9. The thermally sprayable polymer coating composition of claim 1 , wherein said composition comprises up to about 60% thermoplastic material by weight of the composition.

10. The thermally sprayable polymer coating composition of claim 9 wherein said composition comprises up to about 50% thermoplastic material by weight of the composition.

11. The thermally sprayable polymer coating composition of claim 9 wherein said composition comprises up to about 35% thermoplastic material by weight of the composition.

12. The thermally sprayable polymer coating composition of claim 4 wherein said composition comprises up to about 40% epoxy by weight of the composition.

13. The thermally sprayable coating composition of Claim 1 , wherein the composition is in a powdered particulate form.

14. The thermally sprayable polymer coating composition of claim 1 further comprising at least one component selected from the group consisting of glow in the dark particles, antifouling particles, antimicrobial particles filler particles, pigments, preservatives, fibers and mixture thereof.

15. The thermally sprayable polymer coating composition of claim 13 wherein said antifouling particles are selected from the group consisting of cuprous oxide, cupric oxide, copper powder, oxine copper, organocopper compounds, organonickel compounds, zinc sulfate, zinc oxide and zinc pyrithione, other organozinc compounds and mixtures thereof.

16. The thermally sprayable coating composition of Claim 2 wherein the polyolefins are selected from the group consisting of polypropylene, polyethylene, ethylene acrylic acid (EAA), ethylene malacrylic acid (EMAA), and mixtures therefore and the polyamide is selected from the group consisting of nylon-11 , nylon-12, nylon,- 33, nylon-6, nylon-66, and mixtures thereof.

17. A thermally sprayed film formed from the coating composition of claim 1.

18. A structure coated with said thermally sprayed film of claim 17.

19. A method of coating a surface with a thermally sprayed polymer composition comprising applying said thermally sprayable polymer composition of claim 1 to a surface to produce a surface wherein at least a portion of said surface is coated with said thermally sprayable polymer composition.

20. The method of claim 19 further comprising the application of a top coat on said coated surface, said top coat being thermally sprayed on at least a portion of said coated to produce a surface having a first coating and a top

coating.