CA2232764A1 - Abrasion resistant graphite-containing epoxy powder coatings - Google Patents
Abrasion resistant graphite-containing epoxy powder coatings Download PDFInfo
- Publication number
- CA2232764A1 CA2232764A1 CA 2232764 CA2232764A CA2232764A1 CA 2232764 A1 CA2232764 A1 CA 2232764A1 CA 2232764 CA2232764 CA 2232764 CA 2232764 A CA2232764 A CA 2232764A CA 2232764 A1 CA2232764 A1 CA 2232764A1
- Authority
- CA
- Canada
- Prior art keywords
- composition
- coating
- epoxy resin
- pipe
- resin
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/08—Anti-corrosive paints
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
- B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
- B05D7/146—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies to metallic pipes or tubes
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Paints Or Removers (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
Abstract
A highly filled thermally conductive powder coating composition is described. The coating composition includes an epoxy resin, graphite and a mineral filler. It can be applied to a preheated pipe over a corrosion-barrier coating to provide fully cured abrasion resistant coatings at a thickness up to 100 mils.
Description
ABRASION RESISTANT GRAPHITE-CONTAINING
EPOXY POWDER COATINGS
Field of the Invention This invention relates to powder coating compositions and their use for forming protective polymer coatings on metal pipe. More particularly, this invention is directed to a thermally conductive powder coating composition comprising a highly filled epoxy resin matrix that can be applied to pre-heated metal pipes to provide a fully cured abrasion resistant polymer coating alone or in combination with a corrosion-barner undercoating.
Background and Summary of the Invention Metal pipes designed for use in subterranean environments must be protected from corrosion in order to ensure pipeline integrity, thereby preventing product leakage and the resultant environmental damage. Such corrosion protection has been typically accomplished by coating the metal pipe with a highly adherent thermosetting powder coating and use of cathodic protection on the installed pipeline.
Breaches in the coating provide focused weak points where rapid corrosion can occur.
The cathodic potential from buried anodes of more active metals or metal alloys, or from impressed negative electrical current, prevents corrosion at these sites.
In order to achieve the optimum effectiveness and minimum operational cost of such cathodic protection, damaged areas in the coating must be kept to a minimum. Although these powder coatings are quite tough and durable, mechanical damage to the coating can occur from handling, during transportation, from installation, and while in service.
Pipeline coatings are particularly susceptible to mechanical damage from abrasion when installed by the directional bore and pull-through technique. Powder coatings used as corrosion protective pipeline coatings typically contain relatively low levels of mineral fillers to assure optimum bonding to the pipe surface, and to provide suffcient flexibility for field bending of the pipe in cold climates during installation. Such corrosion-barner powder coatings are typically softer than highly filled coatings due to their lower mineral filler content, and they are more susceptible to disruption by scratching or gouging during handling or installation. Accordingly, it is becoming more of interest to apply a more highly filled polymer coating over the underlying corrosion-barner coating to protect the underlying coating from damage prior to or during installation.
The outer coatings are typically applied in a thickness at least equal to and often two or more times that of the underlying corrosion resistant coating for applications demanding greater protection. However, there are inherent difficulties in optimizing the thickness of the outer coating. Typically the inner and outer powder coating formulations are applied sequentially as part of a single coating operation. The pipe substrate is first heated to a temperature above the minimum cure temperature of the resin components but below the resin decomposition temperature. The polymer coating compositions are typically applied as a powder, preferably by electrostatic spray, to the preheated pipe. The applied powder coating compositions first melt to form a continuous polymer layer that is rapidly heated by the underlying preheated pipe to a temperature sufficient to melt and initiate polymerization and cure of the thermosetting resin component. The maximum thickness of the outer coating is linuted by the amount of latent heat in the preheated pipe and the efficiency of transfer of heat to the applied outer coating through the inner coating. It is important that the whole thickness cross-section of the outer coating is heated to sufficiently high temperature to assure complete cure of the applied outer coating. In other words, at greater coating thicknesses, it becomes more likely that some portion of the powder resin composition applied to form the important outer abrasion/impact resistant coating is not fully cured resulting in a coated pipe product having an outer coating without the requisite protective physical properties. While there can be subsequent post-cure reheat operations to complete the cure of the outer coating, such additional operations add significantly to the cost of polymer clad pipe products.
Thus, in accordance with one embodiment of the present invention there is provided a thermally conductive powder coating composition that can be applied to preheated pipes, more particularly preheated pipes also precoated with a corrosion barrier polymer composition, such as a fission bonded epoxy, to provide fizlly cured high thickness, impact-resistant outer coatings. The composition comprises a mineral filled resin matrix in particulate form that includes an epoxy resin, graphite and a mineral filler. In preferred embodiments the composition further includes an epoxy curing agent, a tertiary amine catalyst and flow control agents.
The compositions can be applied over a thermoplastic or thermosetting corrosion barrier coat in an amount sufficient to provide a fully cured protective coating having an average total thickness of greater than 20 mils, more typically about 25 to about 100 mils, and more than 40 mils in premium applications. The combination of graphite with a high level of mineral filler enables a high level of thermoconductivity resulting in an exceptionally high efficiency transfer of latent heat from the heated pipe through the underlying corrosion barrier coating to provide rapid, complete cure of the abrasion/impact resistant outer coating in full thickness cross-section. Further, in circumstances where a post-cure reheat of the coated surface is required for complete cure, for example, at high coating thicknesses, when the thermosetting polymer component has an unusually high thermoset initiation temperature, or when coating over thin-walled pipe, the graphite-containing resin composition of this invention enables more efficient heat absorption and transfer and concomitantly facilitates the reheat cure of the outer polymer coating.
In another embodiment of the present invention there is provided an improved method of forming a protective polymer coating on a metal pipe, wherein the protective polymer coating is formed by heating the pipe, applying a first resin powder coating composition to the heated pipe, and applying a second resin powder coating composition over the first coating composition. The present improvement of that method comprises the step of selecting for said second resin powder composition a resin powder coating composition of this invention comprising a mineral filled resin matrix in particulate form wherein said filled resin matrix comprises an epoxy resin, about 1 to about 10% by weight graphite, and about 40 to about 70% by weight mineral filler.
In another embodiment of this invention there is provided an improved method similar to that above except the method includes the step of reheating the coated pipe by exposing it to infra-red radiation for a predetermined time sufficient to cure the epoxy resin coating. The improvement in that reheat cure process is the selection and use of the above-described thermally conductive powder coating composition. In preferred embodiments that composition includes an epoxy resin, about 1 to about 10% by weight graphite, about 40 to about 70% by weight mineral filler, an epoxy curing agent and an effective amount of a tertiary amine catalyst. Use of that composition in the reheat process enables a reduction in the infra-red radiation exposure time for complete cure of the protective epoxy coating.
In another aspect of the present invention there is provided a method for forming a fully cured protective abrasion-resistant resin coating on a pipe wherein the coating has an average thickness of about 20 to about 100 mils. The method consists essentially of the steps of heating the pipe to a temperature above the temperature required to polymerize the resin but below the resin decomposition temperature, applying a first thermosetting polymer composition to the heated pipe to form a first corrosion protective coating layer, and applying an amount of a second thermosetting polymer composition over the first composition to form a second/outer coating layer. The second resin composition comprises the present graphite/mineral filled epoxy resin matrix in particulate form. The second resin composition is applied in an amount sufficient to provide a fully cured protective coating having an average total thickness of about 20 to about 100 mils, all without reheating the pipe.
In still a fizrther embodiment of this invention there is provided an abrasion-resistant, corrosion-inhibited pipe coated with a thermoset multilaminate epoxy coating. The outer layer of the coating is formed by application of the present highly filled, graphite-containing coating composition in powder form to a preheated pipe precoated with a corrosion-barrier coating composition resin having a mineral filler content of less than 40% by weight, optionally with graphite at 1 to 10% by weight to enhance thermoconductivity.
Detailed Description of the Invention In accordance with the present invention there is provided a highly filled, thermally conductive powder coating composition that can be cured through a thermally induced cross-linking/polymerization mechanism to provide a fully cured, protective abrasion resistant resin coating on a metal pipe. The composition is most typically applied to a preheated metal pipe precoated with a thermosetting or thermoplastic corrosion barrier coating. The present powder coating composition comprises a highly filled resin matrix that includes a thermosetting resin, graphite, and about 40 to about 70% by weight, more typically about 50 to about 60% by weight, of a mineral filler. The resin matrix can also include a resin curing agent, a tertiary amine catalyst, a flow control agent and other additives to facilitate formulation or application of the coating composition. In one embodiment of this invention an abrasion resistant, corrosion-inhibited pipe in accordance with this invention is prepared by heating the pipe to a temperature above a temperature required to melt and polymerize the resin but below the resin decomposition temperature, applying a first thermosetting resin composition to the heated metal pipe to form a first inner corrosion barrier coating, and applying the present powder coating composition over the first coating to provide a fizlly cured protective coating having an average total thickness of about 20 to about 100 mils. Total average thickness of the inner and outer coatings are more typically about 25 to about 80 mils, and more than about 40 mils to about 80 mils in premium applications.
Generally, the thermally conductive powder coating compositions of the present invention comprise a filled thermosetting resin matrix combined with a thermosetting resin, graphite, a mineral filler, a curing agent, and a tertiary amine catalyst. In one embodiment the thermosetting resin is an epoxy resin that includes a mineral filler and graphite. The epoxy resin is melt-blended with the curing agent, the catalyst, the graphite and the mineral filler to provide a melt-blended matrix having the graphite and filler uniformly dispersed and fully wetted with the epoxy resin.
Optional additives can be employed to optimize chemical and physical characteristics of the coating composition. For example, the thermosetting resin matrix can include coupling agents and flow control agents for rheology control. The melt-mix is cooled and ground to a powder to provide the present thermally conductive powder coating compositions that are useful for preparing protective polymer coatings for metal pipe.
The coating composition of this invention comprises a thermosetting resin. Preferably the thermosetting resin is an epoxy resin that is prepared from bisphenol A and an epoxide monomer, for example, epichlorohydrin. The nature of the monomer is not critical provided that the product epoxy resin has the thermally inducible cure profiles suitable for resin formulation and application to preheated pipe . surfaces. The preferred epoxy resin component of the present coating composition has an epoxide equivalent weight of about 650 to 2,300; more preferably, the epoxide equivalent weight for the epoxy resin is about 900 to about 1,400. The melting point for the epoxy resin ranges from about 75 ° to about 130 ° C;
more preferably, the melting point ranges from about 95 ° to about 120 ° C. The melt viscosity of the epoxy resin is about 40 to about 300 poise at 150°C.
The resin matrix of the present powder coating composition also includes about 1% to about 10%, more typically about 2% to about 5% by weight graphite. Either natural or synthetic forms of graphite can be included in the filled resin matrix. In one embodiment of this invention the graphite component has an average screen size of about 275 mesh to about 375 mesh. Preferably, the graphite component of the filled resin matrix is a naturally-occurring amorphous graphite having about 80% carbon content and a screen size of 99.8%-325 mesh. The graphite component is an excellent heat conductor, with a coefficient of thermal conductivity similar to that of many metals and much higher than that of the other formula components. The graphite component also imparts other unique functionality to the 1 S powder coating composition. Not only does it enable high radiant (infra-red) heat absorption and thermal conductivity, it also imparts lubricity and abrasion resistance to the coating with resultant enhanced protection of the underlying corrosion barner coating in the coated pipe products.
The present coating composition further includes about 40% to about 70% by weight mineral filler. In one preferred embodiment the matrix includes about 50% to about 60% by weight filler and the weight ratio of mineral filler to graphite is about 4:1 to about 70:1. The mineral filler provides the desired impact and abrasion resistance to the protective coating and also contributes significantly to the thermoconductivity of the present compositions that allows their use in forming thick fully cured resin coatings without tedious and expensive reheat operations.
Suitable mineral fillers include calcium carbonate, magnesium silicate, aluminum silicate, barytes (barites), wollastonite, amorphous silica, crystalline silica, feldspar, and mica. The particulate mineral filler can also be selected from synthetic fillers such as ZEEOSPHERES, from Zeelan Industries, or FIBER;FRAX from Carborundum. The particulate mineral fillers have a median screen size of about 200 to about 400 mesh;
more preferably, the particulate mineral fillers have a median screen size of about 275 to 350 mesh. In one embodiment the mineral fillers can have median particle size of _7_ about 5 to about 20 microns. Coupling agents, such as the amine functional or epoxy functional silanes well-known in the art, can be used in the present composition in amounts effective to increase the wetting ability of the melted epoxy resin so that the resin can fully coat the filler particles.
In one embodiment of the present invention the resin matrix is an epoxy resin matrix formulated to contain about 0.1% to about 1.5% by weight of a tertiary amine catalyst. Commercially available catalysts suitable for use in the present invention include, but are not limited to, imidazole, 2-methyl imidazole, 2-propyl imidazole, 2-phenyl imidazole, 2-ethyl-4-methyl imidazole, 2-methyl imidazole epoxy resin adduct, 2-propyl imidazole epoxy resin adduct, dimethyl amino methyl phenol, 2,4,6-tri(dimethyl amino methyl) phenol, 4-dimethylaminopyridine, 4-(4-methyl-piperdinyl)pyridine, benzyldimethylamine, triethylenediamine, 2-phenyl imidazole. The amine catalysts are effective to promote polyrr~rization of the epoxy resin at elevated temperatures, typically above 3 5 0 ° F ( 199 ° C) , but not at ambient temperatures.
Preferred epoxy resin matrices for the present powder coating composition further comprise about 0.5 to about 18% by weight of one or more curing agents. A wide variety of curing agents are commercially available. Typical curing agents include primary and secondary amines, aromatic amines, carboxylic acids and anhydrides. The curing agents also can include di-functional primary and secondary polyamines, phenolic-poly (hydroxy ethers), phenol-formaldehyde resins or urea-formaldehyde resins. Specific examples include, but are not limited to, dicyandiamide, low molecular weight phenol-formaldehyde condensates, and linear phenolic resins having a free phenolic hydroxyl functionality.
The thermosetting resin formulations of this invention can include other additives to complement the physical and chemical properties of the thermally conductive powder coating composition. Thus, for example, as mentioned above, one or more commercially available coupling agents can be employed to facilitate wetting of the graphite and particulate mineral filler with the epoxy resin composition.
Coupling agents, for example amino functional or epoxy functional silane coupling agents sold by Witco, can be employed, often in trace amounts, to facilitate the resin formulation. Flow control agents, such as 2 ethyl hexyl acrylate polymer or acrylate _g_ co-polymers, can be included in the coating composition neat or absorbed onto a mineral substrate to facilitate uniform coverage of the pipe with the melted resin.
The thermally conductive powder coating composition of the present invention is prepared by dry blending the epoxy resin, the mineral filler, the graphite, the curing agent, and the catalyst to provide a dry-mixed powder composition which is then transferred via a hopper into an extruder for melt-blending to disperse the solid components and wet the mineral filler and graphite with melted epoxy resin.
The extruder can be any extruder commonly used in the art such as a single screw extruder or a twin-screw extruder. It is important that the melt-blended matrix be processed through the extruder at a rate/temperature selected to limit the polymerization of the epoxy resin while the melted matrix is in the extruder. The melted resin blend is extruded through a die, through a chilled roller, and cooled on a cooling belt in a flat continuous solid matrix sheet. The solid matrix is then chipped to provide a granulated composition which is then ground into a powder and size classified to provide a thermally conductive powder coating composition having an median or average particle size of about 30 microns to about 100 microns, more typically about 40 to about 70 microns.
The thermally conductive powder composition according to the present invention is applied to a metal pipe, most typically over a preapplied thermoplastic or thermosetting resin corrosion barrier coating, to provide a protective polymer coating.
The protective powder coating composition may be applied by any of the methods commonly known in the art. For example, a metal pipe can be heated and thereafter immersed in a fluidized bed of the powder coating composition, or the powder coating composition can be electrostatically applied to the heated metal pipe. In that later method, the thermally conductive powder composition is applied to the metal pipe as the pipe is advanced through a series of powder spray stations. The pipe is typically rotated about its longitudinal axis to ensure that the entire exterior of the pipe is uniformly coated with the coating composition.
Prior to application of the inner corrosion barrier coating the metal pipe is washed to remove soils, lubricants, or other contaminants. The pipe is then advanced to a blast-cleaning station where it is abrasively cleaned. For example, the pipe can be subjected to grit blasting to provide a surface profile for optimum adhesion of the applied resin. The pipe is then advanced to a heating station where it is heated to a pre-determined temperature that is above the temperature needed to cure the thermally conductive powder coating composition but below the temperature at which the powder coating composition decomposes. The method of heating is not critical.
The pipe can be heated in a furnace, with an induction coil or a forced air heater. The pipe is heated to a temperature of about 3 50 ° F to about 5 50 ° F ( 199 ° C to about 3 24 ° C), more preferably about 400 ° F to about 5 00 °
F (204 ° C to about 260 ° C).
In one preferred embodiment the hot metal pipe is grounded and advanced to a spray station where a first epoxy powder coating composition (a corrosion barrier coat) is electrostatically applied to the hot pipe to provide an inner coating having a thickness of about 8 to about 15 mils. The epoxy powder composition may be applied by one or more spray heads. Preferably the pipe is continually rotated along its longitudinal axis to ensure that the electrostatic application of the powdered resin provides a uniform coating of the resin composition to provide a corrosion barrier. The heated pipe retains sufficient residual thermal energy to melt and polymerize the applied powdered resin to provide a cured epoxy resin coating.
A second epoxy coating is applied immediately after application of the first coating. Typically the pipe is advanced to a second spray station where a second epoxy resin coating composition is applied over the first epoxy coating composition.
Use of two separate spray stations allows the over-spray from each electrostatic spraying operation to be separately recovered and recycled.
The second powder coating composition comprises a mineral filled resin matrix in particulate form. The resin matrix comprises an epoxy resin and about 1% to about 10% by weight graphite, and about 40% to about 70% by weight mineral filler. The metal pipe, already coated with an inner corrosion barrier coating, retains sufficient thermal energy to melt and fully cure the after-applied outer coating composition without necessity of re-heating the coated metal pipe, even when it is applied at a rate sui~icient to provide total average coating thicknesses of about 20 to about 100 mils, more typically about 25 to about 80 mils (or about 45 to about 80 mils in certain premium applications). Typically the ratio of the thickness of the outer coating to the thickness of the inner coating is generally greater than 1:1, more typically greater than 2:1. Application of a second epoxy resin coating composition over a first epoxy coating composition on a hot metal pipe according to the present invention provides a fully cured protective polymer coating that is heterogeneous in thickness cross-section.
Following application of the present thermally conductive powder coating composition, the coating is allowed to cure for about 1 to about 10 minutes, more preferably 2 to about 5 minutes before the pipe is advanced to a cooling station where the coated pipe is typically either quenched/cooled with water or ambient air.
In another embodiment of the present invention, a protective polymer coating is formed on a metal pipe. Typically a first epoxy resin powder is applied to a hot pipe to provide a corrosion-resistant coating, and thereafter a second highly filled powder coating composition is applied over the first/inner coating. Preferably the second resin powder coating composition is a mineral filled epoxy resin matrix in particulate form. The resin matrix comprises an epoxy resin, about 1 to about 10% by weight graphite, and about 40 to about 70% by weight mineral filler. In a preferred embodiment, the second powder coating composition is applied in an amount sufficient to provide a fizlly cured protective polymer coating having an average total thickness of about 20 to about 100 mils without re-heating the coated pipe. In one embodiment the average total thickness of the protective polymer coating is about 25 to about 80 mils.
In yet another embodiment of this invention there is provided an improvement in a process where a protective polymer coating is applied to a metal pipe by heating the pipe, applying a first epoxy resin powder coating to the surface of the heated metal pipe, applying a second thermosetting resin over the first coating composition and re-heating the pipe to fully cure the resin coatings by exposing the pipe to infra-red radiation for a predetermined time sufficient to cure the epoxy resin coating. By selecting the second resin powder coating as a thermally conductive powder coating composition comprising a mineral filled resin matrix in particulate form that includes an epoxy resin, about 1 to about 10% by weight graphite, and about 40%
to about 70% by weight mineral filler, the coated pipe can be exposed to infra-red radiation for a time less than the pre-determined time and still provide a fizlly cured protective epoxy coating on the pipe.
Protective coatings on metal pipe in accordance with this invention are evaluated for imperfections such as holidays, or discontinuities in the protective coating. Highly charged electrical probes trail the exterior surface of the pipe. If the underlying metal pipe is exposed through a holiday or imperfection in the polymer coating, the probe provides an electronic signal and indicates the location of the imperfection. If a holiday or discontinuity is detected, the imperfection in the protective coating is typically repaired using a 2-component epoxy patch/glue or application of the powder coating components with localized heating.
The following non-limiting examples are provided to illustrate thermally conductive powder coating compositions of the present invention. The ingredients listed in Examples 1 and 2 are compounded in a mixer to uniformly disperse the solid components of the powder composition. The dry mixed components are fed into an extruder to provide a melt-blended matrix that is forced through a die and then cooled on a chilled roller and cooling belt to provide a solid resin matrix composition in the form of a continuous sheet. The solid sheet-shaped resin matrix is chopped into granules and then ground to provide the powder coating composition.
ExamJ~le 1 Weight Percent Epoxy resin 34.01 Phenolic hardener 6.43 Amine catalyst 0.16 Flow control agent 1.00 Mica 5.12 Barium sulfate 51.21 Graphite 2.05 Total 100 Example 2 Weieht Percent Epoxy resin 45.02 Phenolic hardener 6.43 Dicyandiamide 0.53 Catalyst 0.25 Flow control agent 1.00 Quartz silica 42.50 Mica 4.50 Gra~ 2.00 hite , Total 100 Example 3 Weisht Percent Epoxy resin 3 8.60 Dicyandiamide 0.90 Amine catalyst 0.15 Flow control agent 1.00 Wollastonite 57.3 5 Graphite 2.00 Total 100 The protective polymer coating prepared using the formulation listed in Example 3 was evaluated for its impact and abrasion resistance. The coating exhibited excellent resistance to impingement from a concrete mixture containing either iron ore or crushed stone. Ring samples were cut from the coated pipe and the ring samples were evaluated for low temperature elongation, cathodic disbonding, hot water adhesion. The results of the tests are tabulated in Table 1.
TEST PROCEDURE TOTAL THICKNESS RESULTS
(mils) Elongation 4-point, -30C' 68-75 1.9/PD
Elongation 4-point, 0 C' 66-76 1.7/PD
Elongation 4-point, RT' 68-77 2.5 /PD
Elongation 4-point, RT' 36-38 4.9/PD
Impact ASTM G14 68-75 160 in.-Ibs Adhesion CAN/CSA-2245.2068-75 1 Rating CDT ASTM G95 68-75 0 mm disbondment Hardness ASTM D 25832 nr 40 Gouge TISI Gouge Test335 24 kg Gouge TISI Gouge Test350 26 kg 1. Four Point Bend Test at the specified temperature 2. Test performed using a Barcol Impressor Model # GYZJ934-1 produced by the Barber Colman Co. and sold by Paul Gardner Associates 3. TISI Gouge Test Four Point Bend Test: The degree of bending that the coated metal pipe having a pipe diameter "PD" can withstand without the protective polymer cracking or disbonding from the pipe is measured on a Four Point Bender. A strap cut from a coated metal pipe having a thickness "t" including the polymer coating is supported on top of two parallel pins that are spaced a distance "d" from each other. Two additional pins are placed on top of the metal strap at a distance greater than "d" from each other so that the two pins under the strap are centered between fhe two pins on top of the metal strap when viewed vertically. The two pins on top of the strap are rigidly held in place. The two pins under the metal strap are mounted on a movable block that moves in a vertical direction and forces the strap to bend. After the strap is bent, it is released from the apparatus and the angle "A" that the strap remains bent from linear is measured. The angle °/PD that a pipe having a pipe diameter of "PD" can be bent without the protective polymer cracking or disbonding is determined by the equation:
_At °/PD - d Technical Inspection Services. Inc. Gouge Test: The abrasion resistance of the protective polymer coating prepared using the formula listed in Example 2 was evaluate by moving a weighted gouge along the longitudinal direction of the coated pipe at a rate of 10 inches per minute. The amount of force, determined by the weight on the gouge, required to expose the bare metal pipe as discerned using a holiday detector is listed in Table 1.
EPOXY POWDER COATINGS
Field of the Invention This invention relates to powder coating compositions and their use for forming protective polymer coatings on metal pipe. More particularly, this invention is directed to a thermally conductive powder coating composition comprising a highly filled epoxy resin matrix that can be applied to pre-heated metal pipes to provide a fully cured abrasion resistant polymer coating alone or in combination with a corrosion-barner undercoating.
Background and Summary of the Invention Metal pipes designed for use in subterranean environments must be protected from corrosion in order to ensure pipeline integrity, thereby preventing product leakage and the resultant environmental damage. Such corrosion protection has been typically accomplished by coating the metal pipe with a highly adherent thermosetting powder coating and use of cathodic protection on the installed pipeline.
Breaches in the coating provide focused weak points where rapid corrosion can occur.
The cathodic potential from buried anodes of more active metals or metal alloys, or from impressed negative electrical current, prevents corrosion at these sites.
In order to achieve the optimum effectiveness and minimum operational cost of such cathodic protection, damaged areas in the coating must be kept to a minimum. Although these powder coatings are quite tough and durable, mechanical damage to the coating can occur from handling, during transportation, from installation, and while in service.
Pipeline coatings are particularly susceptible to mechanical damage from abrasion when installed by the directional bore and pull-through technique. Powder coatings used as corrosion protective pipeline coatings typically contain relatively low levels of mineral fillers to assure optimum bonding to the pipe surface, and to provide suffcient flexibility for field bending of the pipe in cold climates during installation. Such corrosion-barner powder coatings are typically softer than highly filled coatings due to their lower mineral filler content, and they are more susceptible to disruption by scratching or gouging during handling or installation. Accordingly, it is becoming more of interest to apply a more highly filled polymer coating over the underlying corrosion-barner coating to protect the underlying coating from damage prior to or during installation.
The outer coatings are typically applied in a thickness at least equal to and often two or more times that of the underlying corrosion resistant coating for applications demanding greater protection. However, there are inherent difficulties in optimizing the thickness of the outer coating. Typically the inner and outer powder coating formulations are applied sequentially as part of a single coating operation. The pipe substrate is first heated to a temperature above the minimum cure temperature of the resin components but below the resin decomposition temperature. The polymer coating compositions are typically applied as a powder, preferably by electrostatic spray, to the preheated pipe. The applied powder coating compositions first melt to form a continuous polymer layer that is rapidly heated by the underlying preheated pipe to a temperature sufficient to melt and initiate polymerization and cure of the thermosetting resin component. The maximum thickness of the outer coating is linuted by the amount of latent heat in the preheated pipe and the efficiency of transfer of heat to the applied outer coating through the inner coating. It is important that the whole thickness cross-section of the outer coating is heated to sufficiently high temperature to assure complete cure of the applied outer coating. In other words, at greater coating thicknesses, it becomes more likely that some portion of the powder resin composition applied to form the important outer abrasion/impact resistant coating is not fully cured resulting in a coated pipe product having an outer coating without the requisite protective physical properties. While there can be subsequent post-cure reheat operations to complete the cure of the outer coating, such additional operations add significantly to the cost of polymer clad pipe products.
Thus, in accordance with one embodiment of the present invention there is provided a thermally conductive powder coating composition that can be applied to preheated pipes, more particularly preheated pipes also precoated with a corrosion barrier polymer composition, such as a fission bonded epoxy, to provide fizlly cured high thickness, impact-resistant outer coatings. The composition comprises a mineral filled resin matrix in particulate form that includes an epoxy resin, graphite and a mineral filler. In preferred embodiments the composition further includes an epoxy curing agent, a tertiary amine catalyst and flow control agents.
The compositions can be applied over a thermoplastic or thermosetting corrosion barrier coat in an amount sufficient to provide a fully cured protective coating having an average total thickness of greater than 20 mils, more typically about 25 to about 100 mils, and more than 40 mils in premium applications. The combination of graphite with a high level of mineral filler enables a high level of thermoconductivity resulting in an exceptionally high efficiency transfer of latent heat from the heated pipe through the underlying corrosion barrier coating to provide rapid, complete cure of the abrasion/impact resistant outer coating in full thickness cross-section. Further, in circumstances where a post-cure reheat of the coated surface is required for complete cure, for example, at high coating thicknesses, when the thermosetting polymer component has an unusually high thermoset initiation temperature, or when coating over thin-walled pipe, the graphite-containing resin composition of this invention enables more efficient heat absorption and transfer and concomitantly facilitates the reheat cure of the outer polymer coating.
In another embodiment of the present invention there is provided an improved method of forming a protective polymer coating on a metal pipe, wherein the protective polymer coating is formed by heating the pipe, applying a first resin powder coating composition to the heated pipe, and applying a second resin powder coating composition over the first coating composition. The present improvement of that method comprises the step of selecting for said second resin powder composition a resin powder coating composition of this invention comprising a mineral filled resin matrix in particulate form wherein said filled resin matrix comprises an epoxy resin, about 1 to about 10% by weight graphite, and about 40 to about 70% by weight mineral filler.
In another embodiment of this invention there is provided an improved method similar to that above except the method includes the step of reheating the coated pipe by exposing it to infra-red radiation for a predetermined time sufficient to cure the epoxy resin coating. The improvement in that reheat cure process is the selection and use of the above-described thermally conductive powder coating composition. In preferred embodiments that composition includes an epoxy resin, about 1 to about 10% by weight graphite, about 40 to about 70% by weight mineral filler, an epoxy curing agent and an effective amount of a tertiary amine catalyst. Use of that composition in the reheat process enables a reduction in the infra-red radiation exposure time for complete cure of the protective epoxy coating.
In another aspect of the present invention there is provided a method for forming a fully cured protective abrasion-resistant resin coating on a pipe wherein the coating has an average thickness of about 20 to about 100 mils. The method consists essentially of the steps of heating the pipe to a temperature above the temperature required to polymerize the resin but below the resin decomposition temperature, applying a first thermosetting polymer composition to the heated pipe to form a first corrosion protective coating layer, and applying an amount of a second thermosetting polymer composition over the first composition to form a second/outer coating layer. The second resin composition comprises the present graphite/mineral filled epoxy resin matrix in particulate form. The second resin composition is applied in an amount sufficient to provide a fully cured protective coating having an average total thickness of about 20 to about 100 mils, all without reheating the pipe.
In still a fizrther embodiment of this invention there is provided an abrasion-resistant, corrosion-inhibited pipe coated with a thermoset multilaminate epoxy coating. The outer layer of the coating is formed by application of the present highly filled, graphite-containing coating composition in powder form to a preheated pipe precoated with a corrosion-barrier coating composition resin having a mineral filler content of less than 40% by weight, optionally with graphite at 1 to 10% by weight to enhance thermoconductivity.
Detailed Description of the Invention In accordance with the present invention there is provided a highly filled, thermally conductive powder coating composition that can be cured through a thermally induced cross-linking/polymerization mechanism to provide a fully cured, protective abrasion resistant resin coating on a metal pipe. The composition is most typically applied to a preheated metal pipe precoated with a thermosetting or thermoplastic corrosion barrier coating. The present powder coating composition comprises a highly filled resin matrix that includes a thermosetting resin, graphite, and about 40 to about 70% by weight, more typically about 50 to about 60% by weight, of a mineral filler. The resin matrix can also include a resin curing agent, a tertiary amine catalyst, a flow control agent and other additives to facilitate formulation or application of the coating composition. In one embodiment of this invention an abrasion resistant, corrosion-inhibited pipe in accordance with this invention is prepared by heating the pipe to a temperature above a temperature required to melt and polymerize the resin but below the resin decomposition temperature, applying a first thermosetting resin composition to the heated metal pipe to form a first inner corrosion barrier coating, and applying the present powder coating composition over the first coating to provide a fizlly cured protective coating having an average total thickness of about 20 to about 100 mils. Total average thickness of the inner and outer coatings are more typically about 25 to about 80 mils, and more than about 40 mils to about 80 mils in premium applications.
Generally, the thermally conductive powder coating compositions of the present invention comprise a filled thermosetting resin matrix combined with a thermosetting resin, graphite, a mineral filler, a curing agent, and a tertiary amine catalyst. In one embodiment the thermosetting resin is an epoxy resin that includes a mineral filler and graphite. The epoxy resin is melt-blended with the curing agent, the catalyst, the graphite and the mineral filler to provide a melt-blended matrix having the graphite and filler uniformly dispersed and fully wetted with the epoxy resin.
Optional additives can be employed to optimize chemical and physical characteristics of the coating composition. For example, the thermosetting resin matrix can include coupling agents and flow control agents for rheology control. The melt-mix is cooled and ground to a powder to provide the present thermally conductive powder coating compositions that are useful for preparing protective polymer coatings for metal pipe.
The coating composition of this invention comprises a thermosetting resin. Preferably the thermosetting resin is an epoxy resin that is prepared from bisphenol A and an epoxide monomer, for example, epichlorohydrin. The nature of the monomer is not critical provided that the product epoxy resin has the thermally inducible cure profiles suitable for resin formulation and application to preheated pipe . surfaces. The preferred epoxy resin component of the present coating composition has an epoxide equivalent weight of about 650 to 2,300; more preferably, the epoxide equivalent weight for the epoxy resin is about 900 to about 1,400. The melting point for the epoxy resin ranges from about 75 ° to about 130 ° C;
more preferably, the melting point ranges from about 95 ° to about 120 ° C. The melt viscosity of the epoxy resin is about 40 to about 300 poise at 150°C.
The resin matrix of the present powder coating composition also includes about 1% to about 10%, more typically about 2% to about 5% by weight graphite. Either natural or synthetic forms of graphite can be included in the filled resin matrix. In one embodiment of this invention the graphite component has an average screen size of about 275 mesh to about 375 mesh. Preferably, the graphite component of the filled resin matrix is a naturally-occurring amorphous graphite having about 80% carbon content and a screen size of 99.8%-325 mesh. The graphite component is an excellent heat conductor, with a coefficient of thermal conductivity similar to that of many metals and much higher than that of the other formula components. The graphite component also imparts other unique functionality to the 1 S powder coating composition. Not only does it enable high radiant (infra-red) heat absorption and thermal conductivity, it also imparts lubricity and abrasion resistance to the coating with resultant enhanced protection of the underlying corrosion barner coating in the coated pipe products.
The present coating composition further includes about 40% to about 70% by weight mineral filler. In one preferred embodiment the matrix includes about 50% to about 60% by weight filler and the weight ratio of mineral filler to graphite is about 4:1 to about 70:1. The mineral filler provides the desired impact and abrasion resistance to the protective coating and also contributes significantly to the thermoconductivity of the present compositions that allows their use in forming thick fully cured resin coatings without tedious and expensive reheat operations.
Suitable mineral fillers include calcium carbonate, magnesium silicate, aluminum silicate, barytes (barites), wollastonite, amorphous silica, crystalline silica, feldspar, and mica. The particulate mineral filler can also be selected from synthetic fillers such as ZEEOSPHERES, from Zeelan Industries, or FIBER;FRAX from Carborundum. The particulate mineral fillers have a median screen size of about 200 to about 400 mesh;
more preferably, the particulate mineral fillers have a median screen size of about 275 to 350 mesh. In one embodiment the mineral fillers can have median particle size of _7_ about 5 to about 20 microns. Coupling agents, such as the amine functional or epoxy functional silanes well-known in the art, can be used in the present composition in amounts effective to increase the wetting ability of the melted epoxy resin so that the resin can fully coat the filler particles.
In one embodiment of the present invention the resin matrix is an epoxy resin matrix formulated to contain about 0.1% to about 1.5% by weight of a tertiary amine catalyst. Commercially available catalysts suitable for use in the present invention include, but are not limited to, imidazole, 2-methyl imidazole, 2-propyl imidazole, 2-phenyl imidazole, 2-ethyl-4-methyl imidazole, 2-methyl imidazole epoxy resin adduct, 2-propyl imidazole epoxy resin adduct, dimethyl amino methyl phenol, 2,4,6-tri(dimethyl amino methyl) phenol, 4-dimethylaminopyridine, 4-(4-methyl-piperdinyl)pyridine, benzyldimethylamine, triethylenediamine, 2-phenyl imidazole. The amine catalysts are effective to promote polyrr~rization of the epoxy resin at elevated temperatures, typically above 3 5 0 ° F ( 199 ° C) , but not at ambient temperatures.
Preferred epoxy resin matrices for the present powder coating composition further comprise about 0.5 to about 18% by weight of one or more curing agents. A wide variety of curing agents are commercially available. Typical curing agents include primary and secondary amines, aromatic amines, carboxylic acids and anhydrides. The curing agents also can include di-functional primary and secondary polyamines, phenolic-poly (hydroxy ethers), phenol-formaldehyde resins or urea-formaldehyde resins. Specific examples include, but are not limited to, dicyandiamide, low molecular weight phenol-formaldehyde condensates, and linear phenolic resins having a free phenolic hydroxyl functionality.
The thermosetting resin formulations of this invention can include other additives to complement the physical and chemical properties of the thermally conductive powder coating composition. Thus, for example, as mentioned above, one or more commercially available coupling agents can be employed to facilitate wetting of the graphite and particulate mineral filler with the epoxy resin composition.
Coupling agents, for example amino functional or epoxy functional silane coupling agents sold by Witco, can be employed, often in trace amounts, to facilitate the resin formulation. Flow control agents, such as 2 ethyl hexyl acrylate polymer or acrylate _g_ co-polymers, can be included in the coating composition neat or absorbed onto a mineral substrate to facilitate uniform coverage of the pipe with the melted resin.
The thermally conductive powder coating composition of the present invention is prepared by dry blending the epoxy resin, the mineral filler, the graphite, the curing agent, and the catalyst to provide a dry-mixed powder composition which is then transferred via a hopper into an extruder for melt-blending to disperse the solid components and wet the mineral filler and graphite with melted epoxy resin.
The extruder can be any extruder commonly used in the art such as a single screw extruder or a twin-screw extruder. It is important that the melt-blended matrix be processed through the extruder at a rate/temperature selected to limit the polymerization of the epoxy resin while the melted matrix is in the extruder. The melted resin blend is extruded through a die, through a chilled roller, and cooled on a cooling belt in a flat continuous solid matrix sheet. The solid matrix is then chipped to provide a granulated composition which is then ground into a powder and size classified to provide a thermally conductive powder coating composition having an median or average particle size of about 30 microns to about 100 microns, more typically about 40 to about 70 microns.
The thermally conductive powder composition according to the present invention is applied to a metal pipe, most typically over a preapplied thermoplastic or thermosetting resin corrosion barrier coating, to provide a protective polymer coating.
The protective powder coating composition may be applied by any of the methods commonly known in the art. For example, a metal pipe can be heated and thereafter immersed in a fluidized bed of the powder coating composition, or the powder coating composition can be electrostatically applied to the heated metal pipe. In that later method, the thermally conductive powder composition is applied to the metal pipe as the pipe is advanced through a series of powder spray stations. The pipe is typically rotated about its longitudinal axis to ensure that the entire exterior of the pipe is uniformly coated with the coating composition.
Prior to application of the inner corrosion barrier coating the metal pipe is washed to remove soils, lubricants, or other contaminants. The pipe is then advanced to a blast-cleaning station where it is abrasively cleaned. For example, the pipe can be subjected to grit blasting to provide a surface profile for optimum adhesion of the applied resin. The pipe is then advanced to a heating station where it is heated to a pre-determined temperature that is above the temperature needed to cure the thermally conductive powder coating composition but below the temperature at which the powder coating composition decomposes. The method of heating is not critical.
The pipe can be heated in a furnace, with an induction coil or a forced air heater. The pipe is heated to a temperature of about 3 50 ° F to about 5 50 ° F ( 199 ° C to about 3 24 ° C), more preferably about 400 ° F to about 5 00 °
F (204 ° C to about 260 ° C).
In one preferred embodiment the hot metal pipe is grounded and advanced to a spray station where a first epoxy powder coating composition (a corrosion barrier coat) is electrostatically applied to the hot pipe to provide an inner coating having a thickness of about 8 to about 15 mils. The epoxy powder composition may be applied by one or more spray heads. Preferably the pipe is continually rotated along its longitudinal axis to ensure that the electrostatic application of the powdered resin provides a uniform coating of the resin composition to provide a corrosion barrier. The heated pipe retains sufficient residual thermal energy to melt and polymerize the applied powdered resin to provide a cured epoxy resin coating.
A second epoxy coating is applied immediately after application of the first coating. Typically the pipe is advanced to a second spray station where a second epoxy resin coating composition is applied over the first epoxy coating composition.
Use of two separate spray stations allows the over-spray from each electrostatic spraying operation to be separately recovered and recycled.
The second powder coating composition comprises a mineral filled resin matrix in particulate form. The resin matrix comprises an epoxy resin and about 1% to about 10% by weight graphite, and about 40% to about 70% by weight mineral filler. The metal pipe, already coated with an inner corrosion barrier coating, retains sufficient thermal energy to melt and fully cure the after-applied outer coating composition without necessity of re-heating the coated metal pipe, even when it is applied at a rate sui~icient to provide total average coating thicknesses of about 20 to about 100 mils, more typically about 25 to about 80 mils (or about 45 to about 80 mils in certain premium applications). Typically the ratio of the thickness of the outer coating to the thickness of the inner coating is generally greater than 1:1, more typically greater than 2:1. Application of a second epoxy resin coating composition over a first epoxy coating composition on a hot metal pipe according to the present invention provides a fully cured protective polymer coating that is heterogeneous in thickness cross-section.
Following application of the present thermally conductive powder coating composition, the coating is allowed to cure for about 1 to about 10 minutes, more preferably 2 to about 5 minutes before the pipe is advanced to a cooling station where the coated pipe is typically either quenched/cooled with water or ambient air.
In another embodiment of the present invention, a protective polymer coating is formed on a metal pipe. Typically a first epoxy resin powder is applied to a hot pipe to provide a corrosion-resistant coating, and thereafter a second highly filled powder coating composition is applied over the first/inner coating. Preferably the second resin powder coating composition is a mineral filled epoxy resin matrix in particulate form. The resin matrix comprises an epoxy resin, about 1 to about 10% by weight graphite, and about 40 to about 70% by weight mineral filler. In a preferred embodiment, the second powder coating composition is applied in an amount sufficient to provide a fizlly cured protective polymer coating having an average total thickness of about 20 to about 100 mils without re-heating the coated pipe. In one embodiment the average total thickness of the protective polymer coating is about 25 to about 80 mils.
In yet another embodiment of this invention there is provided an improvement in a process where a protective polymer coating is applied to a metal pipe by heating the pipe, applying a first epoxy resin powder coating to the surface of the heated metal pipe, applying a second thermosetting resin over the first coating composition and re-heating the pipe to fully cure the resin coatings by exposing the pipe to infra-red radiation for a predetermined time sufficient to cure the epoxy resin coating. By selecting the second resin powder coating as a thermally conductive powder coating composition comprising a mineral filled resin matrix in particulate form that includes an epoxy resin, about 1 to about 10% by weight graphite, and about 40%
to about 70% by weight mineral filler, the coated pipe can be exposed to infra-red radiation for a time less than the pre-determined time and still provide a fizlly cured protective epoxy coating on the pipe.
Protective coatings on metal pipe in accordance with this invention are evaluated for imperfections such as holidays, or discontinuities in the protective coating. Highly charged electrical probes trail the exterior surface of the pipe. If the underlying metal pipe is exposed through a holiday or imperfection in the polymer coating, the probe provides an electronic signal and indicates the location of the imperfection. If a holiday or discontinuity is detected, the imperfection in the protective coating is typically repaired using a 2-component epoxy patch/glue or application of the powder coating components with localized heating.
The following non-limiting examples are provided to illustrate thermally conductive powder coating compositions of the present invention. The ingredients listed in Examples 1 and 2 are compounded in a mixer to uniformly disperse the solid components of the powder composition. The dry mixed components are fed into an extruder to provide a melt-blended matrix that is forced through a die and then cooled on a chilled roller and cooling belt to provide a solid resin matrix composition in the form of a continuous sheet. The solid sheet-shaped resin matrix is chopped into granules and then ground to provide the powder coating composition.
ExamJ~le 1 Weight Percent Epoxy resin 34.01 Phenolic hardener 6.43 Amine catalyst 0.16 Flow control agent 1.00 Mica 5.12 Barium sulfate 51.21 Graphite 2.05 Total 100 Example 2 Weieht Percent Epoxy resin 45.02 Phenolic hardener 6.43 Dicyandiamide 0.53 Catalyst 0.25 Flow control agent 1.00 Quartz silica 42.50 Mica 4.50 Gra~ 2.00 hite , Total 100 Example 3 Weisht Percent Epoxy resin 3 8.60 Dicyandiamide 0.90 Amine catalyst 0.15 Flow control agent 1.00 Wollastonite 57.3 5 Graphite 2.00 Total 100 The protective polymer coating prepared using the formulation listed in Example 3 was evaluated for its impact and abrasion resistance. The coating exhibited excellent resistance to impingement from a concrete mixture containing either iron ore or crushed stone. Ring samples were cut from the coated pipe and the ring samples were evaluated for low temperature elongation, cathodic disbonding, hot water adhesion. The results of the tests are tabulated in Table 1.
TEST PROCEDURE TOTAL THICKNESS RESULTS
(mils) Elongation 4-point, -30C' 68-75 1.9/PD
Elongation 4-point, 0 C' 66-76 1.7/PD
Elongation 4-point, RT' 68-77 2.5 /PD
Elongation 4-point, RT' 36-38 4.9/PD
Impact ASTM G14 68-75 160 in.-Ibs Adhesion CAN/CSA-2245.2068-75 1 Rating CDT ASTM G95 68-75 0 mm disbondment Hardness ASTM D 25832 nr 40 Gouge TISI Gouge Test335 24 kg Gouge TISI Gouge Test350 26 kg 1. Four Point Bend Test at the specified temperature 2. Test performed using a Barcol Impressor Model # GYZJ934-1 produced by the Barber Colman Co. and sold by Paul Gardner Associates 3. TISI Gouge Test Four Point Bend Test: The degree of bending that the coated metal pipe having a pipe diameter "PD" can withstand without the protective polymer cracking or disbonding from the pipe is measured on a Four Point Bender. A strap cut from a coated metal pipe having a thickness "t" including the polymer coating is supported on top of two parallel pins that are spaced a distance "d" from each other. Two additional pins are placed on top of the metal strap at a distance greater than "d" from each other so that the two pins under the strap are centered between fhe two pins on top of the metal strap when viewed vertically. The two pins on top of the strap are rigidly held in place. The two pins under the metal strap are mounted on a movable block that moves in a vertical direction and forces the strap to bend. After the strap is bent, it is released from the apparatus and the angle "A" that the strap remains bent from linear is measured. The angle °/PD that a pipe having a pipe diameter of "PD" can be bent without the protective polymer cracking or disbonding is determined by the equation:
_At °/PD - d Technical Inspection Services. Inc. Gouge Test: The abrasion resistance of the protective polymer coating prepared using the formula listed in Example 2 was evaluate by moving a weighted gouge along the longitudinal direction of the coated pipe at a rate of 10 inches per minute. The amount of force, determined by the weight on the gouge, required to expose the bare metal pipe as discerned using a holiday detector is listed in Table 1.
Claims (24)
1. A thermally conductive powder coating composition, said composition comprising a mineral filled resin matrix in particulate form, said filled resin matrix comprising an epoxy resin, about 1% to about 10% by weight graphite, and about 40% to about 70% by weight mineral filler.
2. The composition of claim 1 wherein the mineral filler comprises a particulate mineral filler selected from a group consisting of calcium carbonate, magnesium silicate, aluminum silicate, wollastonite, baryte, amorphous silica, quartz, feldspar, and mica.
3. The composition of claim 1 wherein the weight ratio of mineral filler to graphite is about 4:1 to about 70:1.
4. The composition of claim 1 wherein the epoxy resin, graphite and mineral filler are melt-blended to form the filled resin matrix.
5. The composition of claim 1 having an average particle size of about 30 microns to about 100 microns.
6. The composition of claim 1 wherein the filled resin matrix further comprises an epoxy resin curing agent.
7. The composition of claim 6 wherein the filled resin matrix further comprises an effective amount of a tertiary amine catalyst.
8. A thermally conductive powder coating composition, said composition comprising a mineral filled resin matrix in particulate form, said filled resin matrix comprising an epoxy resin, about 1 to about 10% by weight graphite, about 40 to about 70% by weight particulate mineral filler, about 0.5 to about 18% by weight curing agent, and about 0.1 to about 1.5% by weight tertiary amine catalyst.
9. In a method of forming a protective polymer coating on a metal pipe by a process comprising the steps of heating the pipe, applying a first epoxy resin powder coating composition to the heated pipe, and applying a second epoxy resin powder coating composition over the first epoxy coating composition, the improvement comprising the step of selecting said second epoxy resin powder coating composition comprising a mineral filled resin matrix in particulate form, said filled resin matrix comprising an epoxy resin, about 1% to about 10% by weight graphite and about 40 to about 70% by weight mineral filler.
10. The improvement of claim 9 wherein the mineral filler component of the second epoxy resin composition comprises a particulate mineral filler selected from the group consisting of calcium carbonate, magnesium silicate, aluminum silicate, wollastonite, baryte, amorphous silica, quartz, feldspar, and mica.
11. The improved method of claim 9 wherein the second epoxy resin powder coating composition further comprises a curing agent.
12. The improved method of claim 11 wherein the second epoxy resin powder coating composition further comprises an effective amount of a tertiary amine catalyst.
13. The improved method of claim 9 further comprising the step of applying the second epoxy resin powder coating in an amount sufficient to provide a fully cured protective polymer coating having an average total thickness of about 20 to about 100 mils without re-heating the coated pipe.
14. The improved method of claim 12 further comprising the step of applying the second epoxy resin powder coating in an amount sufficient to provide a fully cured protective polymer coating having an average total thickness of about 20 to about 100 mils without re-heating the coated pipe.
15. The improved method of claim 12 further comprising the step of applying the second epoxy resin powder coating in an amount sufficient to provide a fully cured protective polymer coating having an average total thickness of about 25 to about 80 mils without re-heating the coated pipe.
16. In a method of forming a protective polymer coating on a metal pipe by heating the pipe, applying a first epoxy resin powder coating composition to the surface of the heated pipe and applying a second epoxy powder coating composition over the first coating composition and re-heating the coated pipe by exposing it to infra-red radiation for a pre-determined time sufficient to complete cure of the epoxy resin coating, the improvement comprising the steps of selecting for said second epoxy resin powder coating composition a thermally conductive powder coating composition comprising a mineral filled resin matrix in particulate form, said filled resin matrix comprising an epoxy resin, about 1% to about 10% by weight graphite, about 40% to about 70% by weight mineral filler, an epoxy curing agent, and an effective amount of a tertiary amine catalyst, and reducing the infra-red radiation exposure time to an amount less than the amount of the pre-determined time to provide a fully cured protective epoxy coating on the pipe.
17. The improved method of claim 16 wherein the cured epoxy coating has an average total thickness of about 20 mils to about 100 mils.
18. A method for forming a fully cured protective abrasion resistant resin coating on a pipe wherein said coating has an average thickness of about 20 to about 100 mils, said process consisting essentially of the steps of heating the pipe to a temperature above the temperature required to polymerize the resin but below the resin decomposition temperature, applying a first thermosetting resin composition to said heated pipe to form a first coating layer, and applying an amount of a second resin composition over said first coating layer to form a second coating layer wherein said second resin composition comprises a mineral filled resin matrix in particulate form, said filled resin matrix comprising an epoxy resin, about 1% to about 10% by weight graphite, about 40%
to about 70% by weight mineral filler, an epoxy resin curing agent, and a tertiary amine catalyst, the amount of said second resin composition being sufficient to provide a fully cured protective coating having an average total thickness of about 20 to about 100 mils.
to about 70% by weight mineral filler, an epoxy resin curing agent, and a tertiary amine catalyst, the amount of said second resin composition being sufficient to provide a fully cured protective coating having an average total thickness of about 20 to about 100 mils.
19. The method of claim 18 wherein the first thermosetting resin composition includes graphite in an amount effective to increase its thermal conductivity.
20. The method of claim 18 wherein in the second resin composition the weight ratio of mineral filler to graphite is about 4:1 to about 70:1.
21. An abrasion-resistant, corrosion-inhibited pipe coated with thermoset multilaminate polymer coating, said coating comprising an inner thermoset epoxy resin composition having a mineral filler content less than 40% by weight of the composition and an outer thermoset epoxy resin coating composition containing about 40 to about 70% by weight mineral filler and about 1% to about 10% by weight graphite.
22. The pipe of claim 21 wherein the average thickness of the multilaminate coating is about 20 to about 100 mils.
23. The pipe of claim 21 wherein the ratio of the thickness of the outer coating composition to the inner coating composition is greater than 1:1.
24. The method of claim 21 wherein the inner thermoset epoxy resin composition includes graphite in an amount effective to increase its thermal conductivity.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US4229798A | 1998-03-13 | 1998-03-13 | |
| US09/042,297 | 1998-03-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2232764A1 true CA2232764A1 (en) | 1999-09-13 |
Family
ID=21921110
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2232764 Abandoned CA2232764A1 (en) | 1998-03-13 | 1998-03-19 | Abrasion resistant graphite-containing epoxy powder coatings |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2232764A1 (en) |
| WO (1) | WO1999046344A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007095730A1 (en) * | 2006-02-23 | 2007-08-30 | Clausi Robert N | Highly filled composite materials |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9821999D0 (en) * | 1998-10-08 | 1998-12-02 | Pasley Andrew | Structural bracket |
| DE10318836A1 (en) * | 2003-04-25 | 2004-11-11 | Voith Paper Patent Gmbh | Process for coating a cylindrical body |
| CN104774534A (en) * | 2015-04-23 | 2015-07-15 | 苏州劲元油压机械有限公司 | Corrosion-resistant paint for hydraulic oil tanks and preparation method thereof |
| CA2986221A1 (en) * | 2015-05-20 | 2016-11-24 | 3M Innovative Properties Company | High temperature stable, one-part, curable thermoset compositions |
| CN107987566B (en) * | 2017-12-12 | 2020-03-27 | 自贡格灵新材料科技有限公司 | Colored antistatic anticorrosive paint and use method thereof |
| CN115322654A (en) * | 2022-09-23 | 2022-11-11 | 枣庄市新达节能技术开发有限责任公司 | Nano heat-conducting ceramic wear-resistant and corrosion-resistant coating and preparation method thereof |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5737387B2 (en) * | 1974-04-19 | 1982-08-09 | ||
| JPS59210932A (en) * | 1983-05-17 | 1984-11-29 | Toshiba Chem Corp | Sealing resin composition |
| JPH05140478A (en) * | 1991-11-19 | 1993-06-08 | Tokyo Daiyamondo Kogu Seisakusho:Kk | Lubricating coating material |
| US5212245A (en) * | 1992-03-04 | 1993-05-18 | Ppg Industries, Inc. | Thermosetting powder coating compositions containing flow modifiers |
| AU5303596A (en) * | 1995-03-08 | 1996-10-08 | Ronald R Savin | Graphite-containing compositions |
-
1998
- 1998-03-19 CA CA 2232764 patent/CA2232764A1/en not_active Abandoned
-
1999
- 1999-03-11 WO PCT/US1999/005328 patent/WO1999046344A1/en active Application Filing
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007095730A1 (en) * | 2006-02-23 | 2007-08-30 | Clausi Robert N | Highly filled composite materials |
Also Published As
| Publication number | Publication date |
|---|---|
| WO1999046344A1 (en) | 1999-09-16 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA2206481C (en) | Cathodic disbondment resistant epoxy powder coating composition and reinforcing steel bar coated therewith | |
| US20070293614A1 (en) | Powder coating composition for pipe coating | |
| CA2074329C (en) | Powder coating composition containing a resin, a curing agent and zinc | |
| US5684066A (en) | Protective coatings having enhanced properties | |
| CA1082835A (en) | Epoxy resin powder including ethylene-vinyl acetate copolymer | |
| US20110152408A1 (en) | Coating compositions and processes for making the same | |
| JP2007313475A (en) | Multilayer coating film formation process and article coated with the multilayer coating film | |
| TW200521200A (en) | Curable alkanolamine containing epoxy powder coating composition | |
| US20040211678A1 (en) | Cathodic corrosion protection powder coating composition and method | |
| CN111117436A (en) | Zinc-rich base powder super-anticorrosion paint | |
| CA2232764A1 (en) | Abrasion resistant graphite-containing epoxy powder coatings | |
| US1873945A (en) | Materials coated with lacquers, lacquers, and a process of producing coatings | |
| JP2009220328A (en) | Polyolefin-coated steel material | |
| EP0800629A1 (en) | Coal tar enamel-coated steel pipe and process for same | |
| JP4733874B2 (en) | Polyolefin coated steel | |
| JPS5929154A (en) | Steel material coated with double layer epoxy and steel product | |
| US20210309881A1 (en) | Low application temperature powder coating | |
| JPS6336305B2 (en) | ||
| CA1093909A (en) | Metal substrate coated with mixture of epoxy resin and imidazoline derivative | |
| CN111454640A (en) | Pipeline anticorrosion epoxy powder coating containing hydroxyphenyl ketone compounds | |
| JP2021101005A (en) | Epoxy resin powder coating and method for inhibiting thermal discoloration of coating film | |
| CA3127761A1 (en) | Powder coating composition | |
| CA2287106A1 (en) | Coating composition | |
| JP5547364B2 (en) | Epoxy powder coating composition for steel and coated steel | |
| JP2657384B2 (en) | Epoxy resin powder coating composition for electrostatic coating |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |