EP0549298A2

EP0549298A2 - Flame sprayed composite coating

Info

Publication number: EP0549298A2
Application number: EP92311644A
Authority: EP
Inventors: James H. Reimer
Original assignee: Plastic Flamecoat Systems Inc
Current assignee: Plastic Flamecoat Systems Inc
Priority date: 1991-12-23
Filing date: 1992-12-21
Publication date: 1993-06-30
Also published as: KR930012290A; BR9205092A; MX9207501A; TW247290B; JPH05345966A; CA2085852A1; CN1073697A; EP0549298A3

Abstract

A composite coating and method of application are provided that comprise flame spraying a layer of thermoplastic onto a substrate and thereafter flame spraying an overlying layer of another, higher melting powder such as metal onto the thermoplastic surface so as to embed unmelted particles of the higher melting powder in the thermoplastic.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to composite coatings applied by flame spraying to an underlying substrate. More particularly, the invention relates to composite flame sprayed coatings comprising an intermediate plastic layer that is flame sprayed onto a substrate, and an overlying metal, metal-containing, or ceramic layer that is flame sprayed onto the plastic layer.

2. Description of Related Art

Methods and apparatus for coating substrates, particularly metal, with a layer of thermoplastic material by means of flame spraying have previously been disclosed, for example, in United States Patent Nos. 4,632,309 and 4,934,595, and in pending United States Patent Application Ser. No. 07\760,866, filed September 16, 1991. These methods and devices enable a user to melt powdered thermoplastic resin and apply it to a substrate at coverage rates that make the process acceptable for applying protective coatings over a wide variety of uses. Such uses can include, for example, coating structural steel used in bridges or other construction, coating piping or vessels that may be subjected to corrosion, coating ship hulls to reduce the rate of barnacle formation and facilitate barnacle removal, and the like.
Methods and apparatus for applying thin metal coatings to plastic substrates have also been disclosed. Most of such methods employ means for melting, vaporizing or ionizing the metal prior to applying it to the surface of the substrate. These coating processes are normally performed under carefully controlled conditions and require high temperatures to melt or vaporize the metal.

SUMMARY OF THE INVENTION

According to the present invention, a substrate coating and method of application are disclosed that utilize an intermediate layer of flame sprayed plastic in combination with an overlying layer of flame sprayed, powdered metal, metal-containing particles or ceramic particles. Preferred substrates are metal surfaces, although other substrates can also be used within the scope of the invention. Application of the coating disclosed herein does not require melting or ionization of the metal, metal-containing or ceramic particles used to form the overlying layer.
In one form the invention provides a protective composite coating for a substrate, the coating comprising a first continuous layer of flame sprayed thermoplastic, and a second continuous overlying layer of flame sprayed powder partially embedded in the first layer, said powder having a higher melting point than the first layer, and being selected from the group consisting of metal, metal containing materials, and ceramics.
Preferably the powder is selected from the group of metal-containing materials consisting of metal alloys, metal oxides and metal nitrides. The powder may be selected from the group of metals consisting of copper, aluminium, carbide, tungsten carbide, stellite, chromium, stainless steel, nickel, titanium and alloys thereof.
The powder may comprise glass beads.
Preferably the thermoplastic is selected from the group consisting of ethylene methacrylic acid copolymer, ethylene vinyl acetate copolymer and polypropylene. The thermoplastic may be ethylene methacrylic acid copolymer.
Preferably, the substrate is selected from the group consisting of metals, metal-containing materials, ceramic materials, cellulosic materials and polymeric materials.
The first layer may have a thickness ranging from about 8mils to about 12mils. The first layer may have a thickness of about 10mils.
Preferably, the second layer has a thickness up to about the thickness of the first layer.
Preferably, the powder has an average particle size that does not exceed the thickness of the first layer.
In another form, the invention provides a method for coating a substrate comprising the steps of:
providing a first powder comprising a major portion of a thermoplastic resin;
flame spraying the first powder on to the substrate to form a substantially continuous intermediate layer of thermoplastic resin having an outwardly facing surface opposite the substrate;
providing a second powder comprising a major portion of unmelted particles of a material selected from the group consisting of powdered metals, powdered metal-containing materials, and ceramics; and
flame spraying the unmelted particles of the second powder onto the intermediate layer in such manner that a substantially continuous overlaying layer is formed which comprises unmelted particles of the second powder embedded in the outwardly facing surface of the intermediate layer.
The method may also comprise a step of cleaning the surface of the substrate.
Preferably, the first powder is flame sprayed onto the substrate at a temperature greater than the melting point of the thermoplastic resin.
Preferably, the second powder is flame sprayed onto the substrate at a temperature greater than the melting point of the thermoplastic resin, but less than the melting point of the major portion of the second powder.
Preferably, the method comprises the additional step of cooling the intermediate layer prior to applying the overlying layer.
Preferably, the method comprises the additional step of polishing the overlying layer.
Preferably, the second powder comprises an anti-foulant material.
Preferably, the second powder comprises an abrasion-resistant material.
Preferably, the second powder comprises a corrosion-resistant material.
In another form, the invention provides a composite coating for a substrate, the coating comprising a first layer of thermoplastic that is flame sprayed onto the substrate, and a second layer of powdered material that is flame sprayed onto the first layer.
Preferably, the thermoplastic is selected from the group consisting of ethylene methacrylic acid, ethylene vinyl acetate and polypropylene. The thermoplastic may be ethylene methacrylic acid.
Preferably, the powdered metal comprises a material selected from the group consisting of copper, aluminium, carbide, tungsten carbide, stellite, chromium, stainless steel, nickel, titanium, and alloys thereof. The powdered metal may comprise copper.
Preferably, the substrate is a metallic surface.
Preferably, the first layer has a thickness ranging from about 8mils to about 12mils. The thickness of the first layer may be about 10mils.
Preferably, the second layer has a thickness that is up to about the thickness of the first layer.
Preferably, the metal powder has an average particle size that does not exceed the thickness of the first layer.
In a further form, the invention provides a composite coating for a substrate, the coating comprising a first layer of thermoplastics that is flame sprayed onto the substrate, and a second layer of powder having a higher melting point than the first layer that is flame sprayed onto the first layer, said powder being selected from the group consisting of metals, metal-containing materials, and ceramics.
The invention also extends to a coating as aforesaid, in combination with a substrate.
According to a preferred embodiment of the method of the invention, powdered thermoplastic material, preferably ethylene methacrylic acid (EMAA) copolymer, is first flame sprayed onto a substrate to form an intermediate thermoplastic layer. The powder used to form the overlying layer is then heated in a flame sprayer device to a temperature greater than the melting point of the thermoplastic material comprising the intermediate layer, but lower than the melting point of the metal. The heated powder, preferably metal or a metal oxide, is then sprayed over the thermoplastic intermediate layer, causing the powder particles to embed in the surface of the thermoplastic. As the surface of the thermoplastic intermediate layer becomes fully coated with particles of the metal powder, additional metal will not adhere because the metal is not in a molten state.
The composite coatings of the invention can be specially adapted for uses such as corrosion-resistant, antifoulant or wear-resistant applications by selecting a powdered material for the overlying layer which exhibits the desired property.

BRIEF DESCRIPTION OF THE DRAWINGS

The apparatus of the invention is further described and explained in relation to the following figures of the drawings wherein:

Figure 1 is a photomicrograph of a cross-section taken through a substrate made in accordance with the present invention, wherein an aluminum substrate is coated with an intermediate layer of EMAA and an overlying layer of copper powder; and
Figure 2 is a photomicrograph of a cross-section taken through a substrate made in accordance with the present invention, wherein an aluminum substrate is coated with an intermediate layer of EMAA and an overlying layer of tungsten carbide powder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, an improved spray coating is provided that comprises an intermediate layer comprising a major portion of a thermoplastic resin, and an overlying layer that comprises a major portion of a metal, metal-containing, or ceramic powder.
The spray coating of the invention can be applied to a wide variety of substrate materials to achieve desirable surface properties and characteristics. Depending upon the particular substrate and the coating materials employed, such application can be performed in the field, at the use site, or in a plant. Exemplary substrates that can be coated in accordance with the present invention include metals, metal-containing materials, ceramic materials, cellulosic materials materials and polymeric materials, provided that such surfaces have been satisfactorily clean, brushed, or otherwise prepared as necessary to facilitate bonding of a thermoplastic intermediate layer to which an overlying layer of powdered metal, metal-containing or ceramic material can subsequently be applied. According to a preferred embodiment of the invention, the surface to be coated is prepared by sand blasting, if necessary, to an SSPC-6 specification to remove all dust and extraneous matter.
Following preparation of the substrate surface, a powdered thermoplastic material is applied to the substrate to form an intermediate surface coating preferably having a thickness ranging from about 8 to about 12 mils. According to a particularly preferred embodiment of the invention, the intermediate surface coating is flame sprayed onto the substrate as disclosed in United States Patent No. 4,934,595, or in pending United States Patent Application Ser. No. 07\760,866, filed September 16, 1991, the entire specifications of which are incorporated by reference herein.
Suitable thermoplastic resins for use in forming the intermediate layer of the coating disclosed herein include, for example, EMAA, ethylene vinyl acetate (EVA) and polypropylene, although other similarly effective resins can likewise be used within the scope of the invention. Although substrates to be coated as provided herein are preferably made of metal, substrates made of other materials can likewise be coated within the scope of the invention provided that the thermoplastic resin flame sprayed onto the substrate to form the intermediate layer will adhere to the substrate surface.
After the substrate has been coated with the intermediate layer of thermoplastic resin, an overlying layer is applied that preferably comprises a major portion of a powdered metallic material. Although a metallic material is preferred for use in forming the overlying layer of the composite coating of the invention, it will be appreciated, however, that powdered metal-containing or ceramic materials can also be applied to a substrate using the methods disclosed herein, and the use of such materials likewise falls within the scope of the present invention. Metal-containing materials can include, for example, metal oxides, metal nitrides, and the like.
A preferred metallic material for use in forming the overlying layer of the subject composite coating is powdered copper, although other metallic materials such as, for example, aluminum, carbide, tungsten carbide, stellite, chromium, stainless steel, nickel, titanium, metal oxides, metal alloys, and the like, can also be used. According to a preferred embodiment of the invention, the metallic overlying layer is applied to the thermoplastic-coated substrate in the same manner as the thermoplastic layer, except that the powdered metal is substituted for the powdered thermoplastic, and a surface preparation step is not generally required. The overlying layer can be applied either before or after the thermoplastic layer has cooled to ambient temperature. Surface preparation, usually just washing, of the thermoplastic intermediate layer should not be needed unless the plastic surface has been contaminated such as by oil or the like prior to application of the overlying layer.
The powdered metal, metal-containing or ceramic particles used to form the overlying layer are preferably heated by combustion from the flame spray gun to a temperature greater than the melting point of the thermoplastic material used to form the intermediate layer of the composite coating, but less than the temperature that will char, ignite or otherwise degrade the thermoplastic, and less than the melting point of the powder particles. When heated to such temperature, the powder particles will become partially embedded in the surface of the thermoplastic layer when propelled against it by the force of the stream emanating from the flame spray gun coupled with a softening or melting of the thermoplastic at the surface of the intermediate layer due to the relatively greater temperature of the heated powder particles. Once the surface of the intermediate layer has been substantially covered by the partially embedded heated particles of the overlying layer, further spraying will typically result in the excess powder bouncing off and accumulating below the work surface. Such excessive spraying can generally be minimized by advancing the flame spray gun to a new area as surface coverage is observed by visual monitoring.
Although the size of the thermoplastic particles used in flame spraying the intermediate layer can vary according to the type of material and substrate, the thermoplastic material, the temperature used in the flame spray gun, and the desired thickness of the intermediate layer, thermoplastic particle sizes ranging from about 40 mesh to about 120 mesh are preferred. Although the thickness of the intermediate layer of thermoplastic material will preferably range from about 8 to about 12 mils, it will be understood that the preferred thickness can vary either above or below that range, depending upon factors such as, for example, the size, geometry and material of the substrate; the intended use; the use environment; the nature and amount of abrasion likely to be experienced during use; the type, particle size and thickness of the metal powder to be applied over the thermoplastic layer; and the like.
Similarly, the size of the powder particles used in flame spraying the overlying layer can vary according to the type of material, the substrate, the intended use, the thermoplastic material, the temperature used in the flame spray gun, and the desired thickness of the overlying layer. Preferably, the average particle size will have a maximum diameter that is less than or equal to the thickness of the intermediate layer onto which the particles are sprayed. Although the thickness of the overlying layer of metallic or ceramic material will preferably range from about one to about ten mils, it will be understood that the preferred thickness can vary, depending upon factors such as the particle dimensions, the extent to which the particles are embedded in the intermediate layer, the intended use, the use environment, the amount and nature of any abrasion to which the coating will be subjected during use, and the like.
Once the overlying layer of the subject composite coating has been applied, further processing can be done, if desired, to achieve particular finishes. Thus, for example, where the overlying layer comprises copper, the resultant flame sprayed metal surface can be polished to achieve a slick, shiny surface appearance.
If the overlying surface layer of the composite coating subsequently becomes scratched or damaged, repair is usually easily accomplished by spraying additional metal, metal-containing or ceramic powder onto the remaining thermoplastic material of the intermediate layer.
The composite coatings and coating method of the invention are further described and explained in relation to the following examples, with reference to the photomicrographs of the accompanying figures.

Example 1

A test coupon of aluminum was prepared for use as a substrate by sandblasting the surface to a one to three mil anchor profile. The test coupon was then coated with an intermediate layer of PF 111 (a product designation of Plastic Flamecoat Systems, Inc. for EMAA having a melting point of about 160°F, 71°C.) by flame spraying the material onto the top surface of the aluminum to achieve a thermoplastic layer having a thickness of about ten mils. After allowing the thermoplastic-coated substrate to cool to ambient temperature, an overlying layer of powdered copper was flame sprayed onto the thermoplastic intermediate layer. The thickness of the overlying layer was about three mils, and the powdered copper was heated to a temperature of about 300°F (149°C) by the flame spray gun prior to application to the coupon. The fuel gas used in the flame spray gun was propane. A cross-sectional cut was thereafter made through the coupon, and the structure of the cross-section is shown in the accompanying photomicrograph identified as Figure 1. The substrate, intermediate and overlying layers referred to above are clearly visible in Figure 1.

Example 2

A test coupon of aluminum was prepared for use as a substrate by sandblasting the surface to a one to three mil anchor pattern. The test coupon was then coated with an intermediate layer of PF 111 by flame spraying the material onto the top surface of the aluminum to achieve a thermoplastic layer having a thickness of about ten mils. After allowing the thermoplastic-coated substrate to cool to ambient temperature, an overlying layer of powdered tungsten carbide was flame sprayed onto the thermoplastic intermediate layer. The thickness of the overlying layer was about three mils and the powdered tungsten carbide was heated to a temperature of about 300°F (149°C) by the flame spray gun prior to application to the coupon. The fuel gas used in the flame spray gun was propane. A cross-sectional cut was thereafter made through the coupon, and the structure of the cross-section is shown in the accompanying photomicrograph identified as Figure 2. The substrate, intermediate and overlying layers referred to above are clearly visible in Figure 2.
Other alterations and modifications of the invention will likewise become apparent to those of ordinary skill in the art upon reading the present disclosure, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.

Claims

A protective composite coating for a substrate, the coating comprising a first continuous layer of flame sprayed thermoplastic, and a second continuous overlying layer of flame sprayed powder partially embedded in the first layer, said powder having a higher melting point than the first layer, and being selected from the group consisting of metal, metal containing materials, and ceramics.
A composite coating according to claim 1 wherein the powder is selected from the group of metal-containing materials consisting of metal alloys, metal oxides and metal nitrides.
A composite coating according to claim 2 wherein the powder is selected from the group of metals consisting of copper, aluminium, carbide, tungsten carbide, stellite, chromium, stainless steel, nickel, titanium and alloys thereof.
A composite coating according to claim 1 wherein the powder comprises glass beads.
A composite coating according to claim 1, 2, 3 or 4, wherein the thermoplastic is selected from the group consisting of ethylene methacrylic acid copolymer, ethylene vinyl acetate copolymer and polypropylene.
A composite coating according to claim 5 wherein the thermoplastic is ethylene methacrylic acid copolymer.
A composite coating according to any of claims 1 to 6, wherein the substrate is selected from the group consisting of metals, metal-containing materials, ceramic materials, cellulosic materials and polymeric materials.
A composite coating according to any of claims 1 to 7, wherein the first layer has a thickness ranging from about eight mils to about 12 mils.
A composite coating according to claim 8, wherein the first layer has a thickness of about 10 mils.
A composite coating according to any of claims 1 to 9, wherein the second layer has a thickness up to about the thickness of the first layer.
A composite coating according to any of claims 1 to 10, wherein the powder has an average particle size that does not exceed the thickness of the first layer.
A method for coating a substrate comprising the steps of:
providing a first powder comprising a major portion of a thermoplastic resin;
flame spraying the first powder on to the substrate to form a substantially continuous intermediate layer of thermoplastic resin having an outwardly facing surface opposite the substrate;
providing a second powder comprising a major portion of unmelted particles of a material selected from the group consisting of powdered metals, powdered metal-containing materials, and ceramics; and
flame spraying the unmelted particles of the second powder onto the intermediate layer in such manner that a substantially continuous overlying layer is formed which comprises unmelted particles of the second powder embedded in the outwardly facing surface of the intermediate layer.
A method according to claim 12, further comprising an initial step of cleaning the surface of the substrate.
A method according to claim 12 or 13, wherein the first powder is flame sprayed onto the substrate at a temperature greater than the melting point of the thermoplastic resin.
A method according to claim 12, 13 or 14, wherein the second powder is flame sprayed onto the substrate at a temperature greater than the melting point of the thermoplastic resin but less than the melting point of the major portion of the second powder.
A method according to claim 12, 13, 14 or 15 comprising the additional step of cooling the intermediate layer prior to applying the overlying layer.
A method according to any of claims 12 to 16, comprising the additional step of polishing the overlying layer.
A method of any of claims 12 to 17 wherein the second powder comprises an antifoulant material.
A method of any of claims 12 to 18, wherein the second powder comprises an abrasion-resistant material.
A method of any of claims 12 to 19 wherein the second powder comprises a corrosion-resistant material.