Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
  • H05B6/105—Induction heating apparatus, other than furnaces, for specific applications using a susceptor
  • H05B6/106—Induction heating apparatus, other than furnaces, for specific applications using a susceptor in the form of fillings
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B2206/00—Aspects relating to heating by electric, magnetic, or electromagnetic fields covered by group H05B6/00
  • H05B2206/02—Induction heating
  • H05B2206/023—Induction heating using the curie point of the material in which heating current is being generated to control the heating temperature

Definitions

• the present invention relates to methods of rapid heating of material, e.g., polymeric materials, by mixing combinations of susceptors of particular compositions in the material to be heated. More specifically, the present invention provides heating agents or susceptors that heat, under an alternating magnetic field, at a rate that is significantly faster than those heating agents that have been identified in the prior art. More specifically, the present invention provides heating agents that heat at average heating rates greater than 300°C/sec (575 °F/ sec).
• Leatherman 's process includes the application of RF from 1.2 KHz to 7 MHz, with a preferred range of 1.8 to 4.8 MHz and 3.5 to 4 MHz being a typical range.
• the mixed particles of Leatherman form a substantially greater percentage by weight than the inert resin carrier, e.g., polypropylene.
• the second plurality of particles constitutes about twice the weight of the first plurality of particles.
• the second particles constitute substantially 40 percent by weight of the bonding layer and said first particles constitute substantially 25 percent by weight of the bonding layer.
• the second particles are larger than - 200 mesh ( ⁇ 75 ⁇ m) and the first particles are less than 1.0 ⁇ m.
• leatherman teaches the use of very high coil current, i.e., 600 amps.
• leatherman teaches a maximum heating rate of 425°F/sec.
• thermoplastics that are able to heat thermoplastics faster than presently known methods.
• a method of rapid heating that is more economical than the presently known methods and that can attain rapid heating rates using standard commercial equipment.
• the present invention provides heating agents that heat, under an alternating magnetic field, at a rate that is significantly faster than those heating agents that have been identified in the prior art. More specifically, the invention provides heating agents that unexpectedly heat at average heating rates greater than 300°C/sec (575 °F/ sec).
• the shortcomings of the prior art with respect to the heating efficiencies of particulate heating agents are addressed by the present invention which comprises heating agents composed of unique mixtures of particulate matter incorporated in a resin matrix that provide exceptionally high heating rates under an applied alternating magnetic field.
• the invention relates to an agent for heating materials, e.g., thermoplastics, comprising dual susceptors.
• the dual susceptors comprise (a) at least one plurality of electrically non-conductive, ferrimagnetic susceptors and (b) at least one plurality of electrically conductive susceptors.
• the electrically non-conductive susceptors comprise micron-sized ferrimagnetic particles (e.g., magnetic oxides).
• the electrically non-conductive particles useful in the present invention comprise iron oxides, hexagonal ferrites, or magnetically soft ferrite particles.
• hexagonal ferrites include compounds that have the composition SrF, Me a -2W, Me a -2Y, and Me a - 2Z, wherein 2W is BaO:2Me a O:8Fe 2 O 3 , 2Y is 2(BaO:Me a O:3Fe 2 O 3 ), and 2Z is 3BaO:2Me a O: 12Fe2O 3 , and wherein Me a is a divalent cation.
• the magnetically soft ferrite particles have the composition lMebO:lFe 2 O 3 , where MebO is a transition metal oxide.
• Me a comprises Mg, Co, Mn or Zn and Meb comprises Ni, Co, Mn, or Zn.
• the electrically conductive susceptors used in the present invention comprise ferromagnetic particles or intrinsically conductive polymer (ICP) particles.
• the electrically conductive ferromagnetic particles useful in the present invention comprise elemental ferromagnetic particles or ferromagnetic alloys. Examples of ferromagnetic, electrically conductive particles comprise nickel, iron, and cobalt, and combinations thereof or of their alloys. Preferably the particles are ferromagnetic.
• ICPs include, but are not limited to, polyaniline (PAni), polypyrrole (PPy), polythiophene (PTh), polyethylenedioxythiophene, and poly(p-phenylene vinylene).
• the particles may be irregularly- shaped, spherically- shaped or in flake form.
• the ferrimagnetic particles have a size of from about l.O ⁇ m to about 50 ⁇ m and the ferromagnetic particles have a size of from about 5 ⁇ m to about lOO ⁇ m, more preferably, from about lO ⁇ m to about 50 ⁇ m.
• the electrically non-conductive particles comprise from about 10 v / o (20 w /o) to about 30 v / o (58 w / 0 ) of the heating agent.
• the electrically conductive particles comprise from about 5 v / 0 to about 15 v / 0 of the heating agent.
• the invention also relates to a welding agent comprising (a) a matrix material and (b) an agent for heating the material, wherein the agent comprises dual susceptors.
• the dual susceptors comprise (1) at least one plurality of electrically non-conductive, ferrimagnetic susceptors and (2) at least one plurality of electrically conductive, ferromagnetic susceptors.
• the matrix can be selected from any thermoplastic material or combinations of materials.
• useful matrices include, but are not limited to, polyethylene, polypropylene, polystyrene, PVC, polyacetal, acrylic (PMMA), polyamide (PA), Nylon 6, Nylon 66, polycarbonate (PC), polysulfone (PSU), polyetherimide (PEI), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), polyurethane (PU), polyphenylene oxide (PPO), polytetrafluorethylene (PTFE), or combinations thereof.
• the dual susceptors are as described above.
• the invention also relates to an article of manufacture comprising (a) a matrix material and (b) an agent for heating the material, wherein the agent comprises dual particles.
• the dual particles comprise (1) at least one plurality of electrically non-conductive, ferrimagnetic susceptors and (2) at least one plurality of electrically conductive, ferromagnetic susceptors.
• the electrically non-conductive susceptors comprise micron-sized ferrimagnetic particles and the electrically conductive susceptors comprises ferromagnetic particles or ICP particles.
• the susceptors are set forth above and further described below.
• the matrix can be selected from any polymeric or ceramic type of material or combinations of materials.
• polymeric materials include, e.g., plastics, elastomers, adhesives, coatings and natural polymers, such as rubbers.
• useful matrix materials include, but are not limited to, polyethylene, polypropylene, polystyrene, PVC, polyacetal, acrylic (PMMA), polyamide (PA), Nylon 6, Nylon 66, polycarbonate (PC), polysulfone (PSU), polyetherimide (PEI), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), polyurethane (PU), polyphenylene oxide (PPO), polytetrafluorethylene (PTFE), or combination thereof.
• the particles can be positioned on a surface of the matrix material or, alternatively, embedded in the matrix material, as necessary for the desired application.
• One of ordinary skill in the art can readily determine where the particles should be positioned.
• the invention also relates to a method of heating a material comprising
• the invention further relates to a method of rapid heating of a thermoplastic material comprising (a) providing an agent for heating the material, wherein the agent comprises (1) at least one plurality of electrically non-conductive, ferrimagnetic susceptors and (2) at least one plurality of electrically conductive ferromagnetic susceptors, in a first thermoplastic material, wherein the electrically non-conductive, ferromagnetic susceptors have a specific Curie temperature (T c ) in the first thermoplastic material, (b) applying an alternating magnetic field to the first thermoplastic material to heat the susceptors, and (c) ceasing the application of the alternating magnetic field when the susceptors reach the desired temperature.
• T c Curie temperature
• the applying comprises applying an alternating magnetic field at about 2MHz to about 30 MHz, and in preferred cases, the alternating magnetic field is applied at about 10 to about 15 MHZ.
• the method further comprises the step of providing a second thermoplastic material in contact with the first thermoplastic material before applying the alternating magnetic field.
• the method further comprises initially placing the first thermoplastic material on an uncured or partially cured thermoset material and bonding the thermoplastic material and the thermoset material while curing the thermoset material.
• the method may also include initially juxtaposing the first thermoplastic material on the thermoset material, bonding the thermoplastic to the thermoset while curing the thermoset material, and juxtaposing the bonded assembly with the second material.
• the second material is a second thermoset material with a second thermoplastic material and wherein the bonding comprises flowing and bonding the first and second thermoplastic materials while curing the thermoset material.
• the second material is a second thermoplastic material.
• the second material may have the same chemical composition as the first thermoplastic material or a different chemical composition.
• the second thermoplastic material may have the susceptors embedded therein.
• the susceptors may be embedded in adjacent surfaces of the first and second thermoplastic materials.
• the susceptors may be embedded in a surface of the first or second thermoplastic material.
• T c of the electrically non-conductive susceptors is greater than the melting temperature of the thermoplastic material, and the magnetic field is applied so that the susceptors melt the thermoplastic material. In other embodiments, T c of the susceptors is less than the melting temperature of the thermoplastic material.
• the amount of zinc in the ferrimagnetic particles can be varied as to control the Curie temperature of the particles.
• the method further comprises the step of providing a second thermoplastic material in contact with the first thermoplastic material before applying the alternating magnetic field.
• the method further comprises initially placing the first thermoplastic material on an uncured or partially cured thermoset material and bonding the thermoplastic material and the thermoset material while curing the thermoset material.
• the method may also include initially juxtaposing the first thermoplastic material on the thermoset material, bonding the thermoplastic to the thermoset while curing the thermoset material, and juxtaposing the bonded assembly with the second material.
• the second material is a second thermoset material with a second thermoplastic material and wherein the bonding comprises flowing and bonding the first and second thermoplastic materials while curing the thermoset material.
• the second material is a second thermoplastic material.
• the second material may have the same chemical composition as the first thermoplastic material or a different chemical composition.
• the second thermoplastic material may have the susceptors embedded therein.
• the susceptors may be embedded in adjacent surfaces of the first and second thermoplastic materials.
• the susceptors may be embedded in a surface of the first or second thermoplastic material.
• T c of the susceptors is greater than the melting temperature of the thermoplastic material, and the magnetic field is applied so that the susceptors melt the first thermoplastic material.
• the invention also relates to a sealable apparatus comprising a first element having a shaped matrix and having a rim; a second element having an annular area for bonding to the rim of the first element; at least one plurality of electrically non-conductive susceptors and at least one plurality of electrically conductive susceptors disposed in the rim of the first element or in the annular area of the second element, for heating the rim or the annular area to a predetermined temperature upon application of an alternating magnetic field, for bonding the first element and the second element together.
• the susceptors are disposed in both the rim and the annular area.
• the matrix used in the sealable apparatus preferably comprises at least one thermoplastic material and can be selected from any thermoplastic material or combinations of materials.
• useful matrices include, but are not limited to, polyethylene, polypropylene, polystyrene, PVC, polyacetal, acrylic (PMMA), polyamide (PA), Nylon 6, Nylon 66, polycarbonate (PC), polysulfone (PSU), polyetherimide (PEI), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), polyurethane (PU), polyphenylene oxide (PPO), polytetrafluorethylene (PTFE), or combinations thereof.
• the particles can be positioned on a surface of the matrix material or, alternatively, embedded in the matrix material, as necessary for the desired application. One of ordinary skill in the art can readily determine where the particles should be positioned.
• Fig. 1 is a top view of a heating agent in sheet or tape form comprising a mixture of electrically non-conductive, micron-sized ferrimagnetic (e.g., ferrite) particles and electrically-conductive, micron-sized ferromagnetic particles randomly dispersed in a thermoplastic matrix.
• ferrimagnetic e.g., ferrite
• the present invention provides heating agents comprising combinations of susceptors that heat, under an alternating magnetic field, at a rate that is surprisingly faster than those heating agents that have been identified in the prior art.
• the heating agents of the present invention heat at average heating rates greater than 300°C/sec (575 °F/ sec).
• the present invention uses a combination of at least two susceptors and high frequency alternating magnetic fields to generate heat, which is used to bond or weld plastic substrates.
• the welding agent of the present invention comprises multiple susceptors embedded in a plastic, e.g., thermoplastic matrix.
• Both ferromagnetism in a ferromagnetic material and ferrimagnetism in a non-conductive ferromagnetic material disappears at the Curie temperature as thermal oscillations overcome the orientation due to exchange interaction, resulting in a random grouping of the atomic particles.
• a non-conductive ferrimagnetic material is placed in an electromagnetic field, the hysteresis losses in the material cause its temperature to rise, eventually reaching its Curie temperature.
• the material crystal lattice undergoes a dimensional change, causing a reversible loss of magnetic dipoles. Once the magnetic dipoles are lost, the ferrimagnetic properties cease, thus halting further heating.
• the rapid heating phenomenon seen in the methods and compositions of the present invention are due to the combination of the non- conductive susceptors and the second electrically conductive susceptors.
• the addition of the second susceptor type helps to focus the magnetic field on the non- conductive susceptors, enabling the temperature to continue to rise rapidly.
• important parameters in this process are the following:
• the size and shape of the ferrimagnetic Hysteresis Loop are controlled by the choice of the susceptor. For example, a magnetically hard ferrite exhibits a larger hysteresis loop than does a magnetically soft ferrite. The larger the hysteresis loop, the greater is the heat that can be generated per cycle. To take advantage of the larger hysteresis loop, the strength of the applied, alternating magnetic field must be sufficiently large to permit the loop to be completely traversed in each cycle (e.g., for the susceptor to reach magnetic saturation).
• Susceptor Loading The amount of susceptor used is controlled and optimized for the intended application. In the case of a thermoplastic weld material, the volume fraction of the susceptor phase and the thickness of the weld material play a direct role in the temperature achieved and the rate of heating within the thermoplastic polymer.
• Particle Size The particle size is controlled and optimized for the intended application.. Particle size affects heat transfer to the thermoplastic weld material.
• Particle Shape The particle shape is controlled and optimized for the intended application. Certain shapes may exhibit unique responses to the induction field, and thus optimized heating for the application. By manipulating these parameters as described herein, the inventors have found that the rate of heating can be increased substantially.
• susceptor refers to a material that interacts with a magnetic field to generate a response, e.g., eddy currents and/or hysteretic losses.
• the methods and apparatus of the present invention are based on the use of dual "susceptors" that can be used to heat a polymer matrix. The susceptors are further described below.
• the electrically non-conductive susceptors e.g., micron-sized ferrimagnetic particles 2 and the electrically conductive susceptors, e.g., micron sized ferromagnetic particles or ICP particles 3, are dispersed in the thermoplastic host matrix 1.
• the susceptors can be dispersed throughout the article that will be heated, e.g., if the article is a tape that will be used to bond two pieces of thermoplastic together.
• a portion of the article to be welded or bonded to another article or portion of the article e.g., a rim or annular area, can be manufactured to have the susceptors embedded therein.
• One of ordinary skill in the art can readily determine where the susceptors should be placed to maximize the rate of heating and sealing or welding of the articles.
• thermoplastic bond area during fusion is achieved by induction heating of the susceptor materials, e.g., particles 2 and 3 placed in the bond interface.
• susceptor materials e.g., particles 2 and 3 placed in the bond interface.
• This technology is amenable to production line manufacturing where rapid rates of production require rapid heating of composite structures. It would also be useful in rapid field repair of composite structures, for example, and is more cost effective in initial fabrication than presently known methods of repair.
• the invention relates to an agent for heating thermoplastic materials comprising dual susceptors.
• the susceptors comprise (a) at least one plurality of electrically non-conductive susceptors and (b) at least one plurality of electrically conductive susceptors.
• the methods and compositions of the present invention utilize the fact that magnetic induction heating occurs in magnetic or electrically conductive materials when they are subject to an applied alternating magnetic field.
• the present invention specifically takes advantage of the heating that occurs in the combination of susceptors described herein.
• a current-carrying body, or coil is placed near the susceptors of the present invention, the magnetic field caused by the current in the coil induces a current in the susceptors.
• heating occurs by both eddy current and hysteresis losses. It is eddy currents losses that dominate. In the nonconducting magnetic materials, heating occurs by hysteresis losses. In this later case, the amount of energy available for heating is proportional to the area of flux vs. field intensity hysteresis curve (B vs. H) and frequency of the alternating field. This mechanism exists as long as the temperature is kept below the Curie point (T c ) of the material. At the Curie point, the originally magnetic material becomes non-ferromagnetic. Thus, at its T c , heating of the magnetic material ceases. Thus, as aforesaid, it was surprisingly found that the combination of these conductive and non-conductive susceptors as described herein, produces a rapid rate of heating, e.g., greater than 300°C/sec.
• the methods of the present invention enable the user to achieve high rates of heating by selecting the appropriate combination of susceptors based upon the desired application. For example, one of ordinary skill in the art can control the rate of heating by controlling the ratios of the susceptors.
• the dual susceptors comprise electrically non-conductive susceptors and electrically conductive susceptors.
• the electrically non-conductive susceptors are preferably micron-sized ferrimagnetic particles. Examples of the electrically non-conductive particles useful in the present invention, include, but are not limited to, iron oxides, hexagonal ferrites, or magnetically soft ferrites.
• hexagonal ferrites include compounds that have the composition SrF, Me a -2W, Me a -2Y, and Me a -2Z, wherein 2W is BaO:2Me a O:8Fe 2 O 3 , 2Y is 2(BaO:Me a O:3Fe 2 O 3 ), and 2Z is 3BaO:2Me a O: 12Fe 2 O 3 , and wherein Me a is a divalent cation.
• the magnetically soft ferrite particles have the composition lMebO: lFe 2 O 3 , where MebO is a transition metal oxide.
• Me a comprises Mg, Co, Mn or Zn and Meb comprises Ni, Co, Mn, or Zn.
• the electrically non-conductive particles e.g., ferrimagnetic particles
• the electrically non- conductive particles comprises from about 10 v / o (20 w / 0 ) to about 30 v / 0 (58 w / 0 ) of the composition.
• Examples of useful hexagonal ferrites include, but are not limited to those shown in Table 1 :
• the ferromagnetic hexagonal ferrites are also known as hexagonal ferrimagnetic oxides.
• Examples of preferred ferrimagnetic hexagonal ferrites include SrF, Co-2Y and Mg-2Y.
• a range of Curie temperatures is preferred for the susceptors to be effective in bonding and other processing of a wide range of thermoplastic and thermoset composites.
• the electrically conductive susceptors useful in the present invention include ferromagnetic particles and ICP particles.
• the electrically conductive ferromagnetic particles can be elemental ferromagnetic particles or ferromagnetic alloys. Examples of electrically conductive particles comprise nickel, iron, and cobalt and combinations thereof and of their alloys.
• Preferred ferromagnetic particles have a size of from about 5 ⁇ m to about lOO ⁇ m, more preferably, from about lO ⁇ m to about 50 ⁇ m.
• ICPs are organic polymers that conduct electric currents while retaining the other typical properties commonly associated with a conventional polymer. ICPs are different from so-called "conducting polymers" that are merely a physical mixture of a non-conducting polymer with a conducting material such as metal or carbon powder. In addition to the generation of heat by hysteresis losses in the ferrimagnetic particles, eddy current losses within the electrically conductive polymer contribute additional heating to enhance the rate of heating of the heating agent. Since ICPs tend to lose their electrical conductivity at temperatures above about 200°C, heating agents utilizing ICPs are preferably used in applications in which the maximum process welding temperature is below 200°C.
• ICPs include, but are not limited to, polyaniline, polypyrrole, polythiophene, polyethylenedioxythiophene, and poly (p-phenylene vinylene) .
• the electrically conductive particles preferably have a size of from about
• the Curie temperature of the ferrimagnetic particle changes in response to changing the proportion of zinc in the particle, such as Zn/Mg-2Y and Zn/Co-2Y.
• T c may be lowered by the partial substitution of Zn ++ for the divalent ions in the strontium ferrite (SrF), Mg-2Y, and Co-2Y.
• the substitution of Zn ++ for Mg ++ and Co ++ on "a" sites in the lattice reduces the strength of a-b interactions and decreases T c .
• sufficient zinc is added to the magnetically hard hexagonal ferrite to lower its T c significantly while still retaining its hexagonal structure and hard magnetic properties.
• One of ordinary skill in the art can readily determine the amount of zinc to be added and the methods for adding it.
• Zn to Mg-2Y also reduces its Curie temperature.
• Mg-2Y was synthesized with zinc atoms substituting for half the magnesium (Formula: Mg ⁇ Zn ⁇ Ba2Fei2 ⁇ 2 2)
• the Zn/Mg-2Y ferrite exhibits a Curie temperature of 175 °C.
• the addition of zinc to Mg-2Y reduces its Curie temperature from 260 to 175°C.
• Non-conducting particles comprise magnetically soft ferrite particles having the structure lMeO: lFe 2 O 3 , where MeO is a transition metal oxide.
• Me include Ni, Co, Mn, and Zn.
• Preferred particles include, but are not limited to: (Mn,ZnO)Fe2O 3 and (Ni,ZnO)Fe 2 O 3 , also referred to as MnZn and NiZn ferrites, respectively.
• dual susceptor formulations include, but are not limited to Strontium Ferrite/Flake Nickel; Mn-Zn Ferrite/Flake 97Ni-3Al ; Mn-Zn Ferrite/Iron. Examples are shown in Table 2:
• Both the non-conductive susceptors i.e., the ferrimagnetic particles
• certain of the conducting susceptors e.g., ferromagnetic metal particles
• Tc the Tc of either the ferrimagnetic particles and/ or the ferromagnetic particles
• the matrix material preferably comprises any thermoplastic known in the art.
• polymeric materials include, e.g., plastics, elastomers, adhesives, coatings and natural polymers, such as rubbers.
• the plastics can comprise either thermoplastic or thermoset materials.
• thermoplastics (TPs) include, but are not limited to: ethenic (vinyls, polyolefins, fluorocarbons, styrenes, acrylics), polyamides, polyesters, cellulosics, acetals, polycarbonates, polyimides, and polyethers.
• thermoset materials include, but are not limited to, phenolics, unsaturated polyesters, urethanes, silicones, ureas, melamines, epoxides.
• susceptor/ polymer systems include, but are not limited to Strontium Ferrite/Flake Nickel in HDPE; Mn-Zn Ferrite/Flake 97M-3A1 in HDPE; Mn-Zn Ferrite/Iron in HDPE; Mn-Zn Ferrite/Flake Nickel in HDPE; Fe 3 O 4 /Flake Nickel in HDPE; Fe 3 O 4 /Iron in HDPE; Fe 2 O 3 /Flake Ni in HDPE; Fe2O 3 /Iron in HDPE.
• the polymers can be combined with ferrimagnetic particles such as Zn/SrF, Zn/Co-2Y, Zn/Mg-2Y and mixtures of the hexagonal ferrites, and other combinations described herein and further combined with ferromagnetic particles and determined by one of ordinary skill in the art.
• ferrimagnetic particles such as Zn/SrF, Zn/Co-2Y, Zn/Mg-2Y and mixtures of the hexagonal ferrites, and other combinations described herein and further combined with ferromagnetic particles and determined by one of ordinary skill in the art.
• One aspect of the invention relates to an agent for heating a matrix, e.g., thermoplastic materials, comprising (a) at least one plurality of electrically non- conductive particles and (b) at least one plurality of electrically conductive particles.
• the particles may be present on a surface of the matrix, or alternatively, embedded in the matrix, depending on the desired use. For example, if two surfaces of particular articles are being bonded or welded together, then it may be desirable to have the susceptor particles embedded on only the surface of the article that is to be bonded.
• the susceptors may also be dispersed in a matrix to form a welding or bonding agent and applied to the surface of one or both thermoplastic articles to be welded, sealed or bonded.
• the welding agent can be in any desirable form, e.g., tape, spray, liquid, sheet, tube or paste, depending on the desired use.
• the carrier or matrix may be melted or evaporated away.
• One of ordinary skill in the art can readily determine where the susceptors should be placed in order to maximize the efficiency and efficacy of the controlled temperature heating of the susceptors.
• thermoplastics containing the susceptors as described herein can be shaped or molded into articles by methods known in the art, e.g., by extrusion, compression molding, injecting molding or film casting.
• the article may be fabricated by a number of different methods well known in the art. These methods include but are not limited to: (a) solution casting of the article as film or sheet, (b) extrusion compounding the article directly into film, sheet or tape form, (c) extrusion compounding the components of the article into pellets followed by compression molding the pellets into sheets or other shapes suitable for the intended application, and (d) mixing the susceptor(s) and matrix in a mixer such as the Brabender Mixer (C. W. Babender; South Hackensack, NJ) or the Haake Rheomix Mixer (Haake USA; Paramus, NJ) and compression molding the mixture into sheets or other shapes suitable for the intended application.
• a mixer such as the Brabender Mixer (C. W. Babender; South Hackensack, NJ
• the matrix comprises a ceramic type of material.
• useful ceramics include single oxides (e.g., alumina, chromium oxide, zirconia, titania, magnesium oxide, silica), mixed oxides (e.g., kaolinite), carbides (e.g., vandadium carbide, tantalum carbide, tungsten carbide, titanium carbide, silicon carbide, chromium carbide, boron carbide), sulfides (e.g., molybdenum disulfide, tungsten disulfide), and nitrides (e.g., boron nitride, silicon nitride).
• single oxides e.g., alumina, chromium oxide, zirconia, titania, magnesium oxide, silica
• mixed oxides e.g., kaolinite
• carbides e.g., vandadium carbide, tantalum carbide, tungsten carbide, titanium carbide,
• the susceptors may be added to the matrix in any order.
• the non-conducting susceptors can first be added to the thermoplastic mixture and then the electrically conducting susceptors can be added. Or the susceptors can be added in reverse order. While the susceptors can be first mixed and then added to the thermoplastic matrix, it is in fact preferred to add the particles separately because it eliminates the step of mixing the particles together.
• compositions and methods of the present invention enable the use of standard coil constructions and the use of commercially available induction generators, e.g., solid state equipment from Ameritherm.
• the present invention enables the use of lower coil current and higher frequencies than the prior art.
• the coil current used in the present invention ranges from about 50 to about 150 amps.
• Certain prior art inventions utilize very high coil currents, e.g., 600 amps to get the heating rates seen in the prior art.
• the methods of the present invention unexpectedly produce rapid heating rates at lower coil currents.
• the useful frequency range is from about 2 MHz to about 30 MHz and the preferred power ranges from about 1 KW to about 7.5 KW.
• the desired temperature is higher, e.g., bonding, welding or sealing applications
• the frequency and power will be at the higher end of the range, e.g., from about 10 MHz to about 15 MHz.
• One of ordinary skill in the art can select the appropriate power and frequency depending on the susceptor and thermoplastic selected and for the desired application, i.e., heating or bonding/ welding/ sealing.
• the field generated by the induction coil influences the heating patterns of the susceptors and the field is a function of the coil geometry.
• coil design include solenoid, pancake, conical and Helmholtz. While these coil types are among those commonly used by industry, certain embodiments of invention may require specialized coils. For example, in certain embodiments solenoid coils are preferred because solenoid coil geometry produces a very strong magnetic field. In other embodiments, pancake coils are used. Pancake coils have been found to produce a non- uniform field with its maximum at the center. One of ordinary skill in the art can readily select the type of coil based on the teachings in the art and set forth herein.
• Magnetic field strength increases with increasing number of coil turns, increasing coil current and decreasing coil-work piece separation.
• the factors can be readily manipulated by one of ordinary skill in the art to select combinations of these factors to obtain the desired magnetic field strength.
• Solenoid coil geometry produces the strongest field of all the possible geometries.
• Pancake coils are most common in one-sided heating applications. Changing the coil parameters (e.g., spacing between turns or the number of turns) can change the field values, but the pattern is generally the same. Magnetic field strength increases if the coil-part separation is reduced. If the part is placed very close to the coil, one may see the heating dictated by each turn of the coil.
• the present invention has many potential applications, especially where very rapid rates of heating are required.
• One example of such a use is in high velocity production lines, where thermoplastic materials need to be sealed, welded, or bonded in a very short time period.
• the heating agents of the present invention reach 180°C within 300 msec.
• Such rapid rates of heating enables one to heat (e.g., seal, bond or weld) thermoplastic articles very quickly.
• the potential applications for the methods and compositions of the present invention are innumerable, spanning both military and commercial markets.
• thermoset-based composites examples include fabrication and repair of aircraft structures, as well as fabrication and repair of shipboard structures.
• present invention is not limited to fusion bonding of thermoset-based composites, but also could be applied to consolidation and repair of thermoplastic composites or elevated-temperature curing of thermoset adhesives, thereby reducing repair time and increasing performance.
• the commercial sector could enjoy similar benefits with respect to the fabrication and repair of composite structures. For example, this technique can be used to repair aging metal structures with composite reinforcements or new bonding techniques developed for commodity resins such as polyethylene.
• compositions and methods of the present invention are useful for any application in which it is desirable to melt the matrix material, e.g., welding, sealing and/or bonding of thermoplastic materials.
• T c of the non-electrically conductive particles is greater than the melting temperature of the thermoplastic material.
• the susceptor particles can readily be selected based upon the teachings described herein.
• the compositions and methods of the present invention may be used in the packaging industry, specifically for closure systems.
• the broad temperature range covered by the susceptors allows for use in a wide range of commercial applications, e.g., in the food packaging industry, automotive assembly lines, etc.
• induction heating may be used in the food industry to seal lids without the use of the aluminum peel-away that is commonly used in many packages.
• the advantages of replacing foil with a direct polymer seal include lower cost, improved recyclability and the ability to control the bonding conditions, including temperature, of complex seal shapes, such as a thin ring on the rim of a beverage container, or a lid on a food tray.
• This technology can also be used for sealing bags or other similar containers for foods, including prepared foods, instant foods or ingredients.
• a cup containing a food product may be sealed with a lid by inductively heating the dual susceptors uniformly distributed throughout or concentrated in a rim of the cup or in an annular area of the lid or both. Inductively heating the dual particles at the annular seal area while pressing the cup rim and lid together, for example with an induction heating horn, fuses and co-cures the plastic material of the cup and lid.
• This method can be used for any sealing application, e.g., sealing boxes or containers enclosing any type of materials. Examples of such materials include prepared foods, foodstuffs, ingredients, liquids as well as non-edible products and liquids.
• the sealing technology can be used to seal cartridges and filters of different types, e.g., water filters, oil filters, and medical devices.
• One of ordinary skill in the art can readily apply the methods of the present invention to any application that requires sealing or bonding of thermoplastics.
• the rapid rate of heating enables the manufacture of a high volume of these products in a very short time period, thus decreasing production time, reducing costs, and increasing productivity.
• Another example of a preferable use is in manufacturing aviation, auto and marine structural components: specifically, fabricated structures that comprise one polymer component welded to another polymer component.
• the methods of the present invention can be used on production lines in the automotive industry, for sealing or welding polymer components, e.g., tail lights, etc.
• susceptors and methods of using the susceptors described herein can be applied to either one or both of the components and inductively heated to weld or seal the components together. Another use is in the repair of structures that comprise one polymer component welded to another polymer component.
• the methods of induction bonding are used to weld the seams of structures made of thermoplastic materials, for use in the field, e.g., by military forces.
• One example is useful for joining polyurethane skin to itself.
• filler particles i.e., the susceptor particles of the present invention
• these particles are designed to thermally match the softening point of a variety of thermoplastic resins, into which they can be compounded.
• the present invention is further illustrated by the following Examples.
• the Examples are provided to aid in the understanding of the invention and are not construed as a limitation thereof.
• High density polyethylene (HDPE) pellets were placed in a Haake Rheomix Mixer and mixed until the pellets melted, at which time strontium ferrite particles (HM181) (particle size: 1.4 ⁇ m; Supplier: Steward Ferrite; Chattanooga, TN) and fine leaf nickel flake (diameter: 10-20 ⁇ m, thickness: 0.5 ⁇ m; Supplier: Novamet; Wycoff, NJ) were added slowly to high density polyethylene in the Rheomix mixer until the entire quantity of both susceptors have been added such that the strontium ferrite was at 36 percent by weight ( w / 0 ) of the total mix and the flake nickel was at 41 percent by weight ( w / ⁇ ) of the total mix and thorough mixing has taken place.
• strontium ferrite particles HM181
• HM181 particle size: 1.4 ⁇ m
• Supplier Steward Ferrite; Chattanooga, TN
• fine leaf nickel flake diameter: 10-20 ⁇ m, thickness:
• the mixture was then removed from the Rheomix mixer and compression molded into sheets 10 to 20 mils thick. Small sections approximately 1 x 1-in were cut from the sheet and mounted on glass slides. These samples were then placed inside a 5-turn, 2-in long, oval-shaped (2 x Vfe-in) solenoid coil and subjected to an 11.8MHz alternating magnetic field.
• the Nova Star 1M solid state 1.0 KW induction generator (Ameritherm, Inc.; Scottville, NY) was used as the power source. Coil current was approximately 80 amps.
• Ircon 06F05 IR pyrometer (Ircon, Inc.; Niles, IL) with a response time of 10ms and a temperature range of 200 to 600°F (93 °- 315 °C) was used to measure and record temperature. Because the spot size of the pyrometer slightly impinged on the coil, the true temperature and true rate of heating were higher than the measured values. A trigger was used to mark time zero when the power was turned on. The pyrometer starts measurements at 200°F. The initial ambient temperature of the samples prior to the start of heating was 70°F.
• heating rates ranging from 1050 to 1120°F/sec. were achieved.
• One of the heating curves for 20% Strontium Ferrite and 13% Flake Nickel in High Density Polyethylene is shown in Figure 2.
• the heating rates achieved by the present invention were approximately 2.5 times as great as that reported by Leatherman (United States Patent Number 4,969,968), at a significantly lower coil current (80 vs 600 amps).
• Heating agents having HDPE as the matrix or host and containing the following combinations (a), (b) or (c) were fabricated in the same manner as described in Example 1 :
• Test Conditions (Frequency: 11.8MHz, Power: 1.0 KW, Coil: 5-turn oval solenoid (2 x Vfe-in), Length: 2-in, Coil Current: 80 amps, Matrix: High Density Polyethylene (HDPE)).
• Heating agents having HDPE as the matrix and containing from 10 v / o to 30 v / 0 micron-sized, non-conducting, ferrimagnetic particles and 13 v / 0 micron- sized, electrically conducting ICP particles are fabricated into films, sheets or other shapes suitable for the intended application by the method described in Example 1.
• the said heating agents also can be fabricated by solution casting, extrusion compounding, extrusion compounding followed by compression injection molding or by a number of other methods known by those well versed in the technology.
• Both the non-conducting and conducting particles can be irregular or spherical in shape.
• These non-conducting susceptors also can be in the form of fibers or flakes.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Lining Or Joining Of Plastics Or The Like (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• General Induction Heating (AREA)
• Soft Magnetic Materials (AREA)

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• 2002
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