EP0938407A1 - Systeme de traitement de polymeres aux micro-ondes - Google Patents

Systeme de traitement de polymeres aux micro-ondes

Info

Publication number
EP0938407A1
EP0938407A1 EP97945323A EP97945323A EP0938407A1 EP 0938407 A1 EP0938407 A1 EP 0938407A1 EP 97945323 A EP97945323 A EP 97945323A EP 97945323 A EP97945323 A EP 97945323A EP 0938407 A1 EP0938407 A1 EP 0938407A1
Authority
EP
European Patent Office
Prior art keywords
cavity
charge
microwave
polymer
rotatable member
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.)
Withdrawn
Application number
EP97945323A
Other languages
German (de)
English (en)
Inventor
Izak Parviz Nazarian
Ira Maroofian
Hanna Dodiuk-Kenig
Shmuel Kenig
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
HPM Stadco Inc
Original Assignee
HPM Stadco Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by HPM Stadco Inc filed Critical HPM Stadco Inc
Publication of EP0938407A1 publication Critical patent/EP0938407A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B13/00—Conditioning or physical treatment of the material to be shaped
    • B29B13/08—Conditioning or physical treatment of the material to be shaped by using wave energy or particle radiation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/72—Heating or cooling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B13/00—Conditioning or physical treatment of the material to be shaped
    • B29B13/02—Conditioning or physical treatment of the material to be shaped by heating
    • B29B13/022—Melting the material to be shaped
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/18—Feeding the material into the injection moulding apparatus, i.e. feeding the non-plastified material into the injection unit
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
    • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
    • B29C2035/0855—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using microwave
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C31/00—Handling, e.g. feeding of the material to be shaped, storage of plastics material before moulding; Automation, i.e. automated handling lines in plastics processing plants, e.g. using manipulators or robots
    • B29C31/04—Feeding of the material to be moulded, e.g. into a mould cavity
    • B29C31/06—Feeding of the material to be moulded, e.g. into a mould cavity in measured doses, e.g. by weighting

Definitions

  • the present invention relates to a polymer processing apparatus and method for melting a polymer and then transporting the melted polymer to a point of use, such as an injection mold, an extrusion die, or the like. More specifically, the present invention relates to a polymer processing apparatus and method in which microwave energy is used to accomplish melting in one chamber and transport of the melted polymer to a point of use is accomplished from another independently pressurizable chamber.
  • thermoplastic and thermosetting polymer resins are found everywhere and are used in an incredibly wide variety of applications. In spite of their widespread and divergent uses, most polymeric articles are formed using generally similar processing techniques.
  • a polymer resin is provided in a solid, pelletized form. The polymer resin pellets are initially melted or softened, and then the melted or softened material is brought into contact with an extrusion die or mold in which the polymer assumes the molded or extruded form of the intended article.
  • cycle time refers collectively to the period of time it takes to first melt a given charge of polymer resin, then to transport the molten polymer into a mold, then to allow the melt to solidify in the mold to form the molded article, and finally to open the mold and remove the molded article.
  • Faster cycle times are generally desired, because a higher output of molded articles can be produced per unit of time.
  • cycle time Another factor affecting cycle time concerns the technique which is used to transport the melted polymer from the melting chamber to the injection mold or extrusion die It would be desirable to provide an approach which accomplishes transport faster so that cycle time could be reduced It would also be desirable if such an approach required less complex, less expensive machinery so that the costs of transporting the polymer melt could be reduced
  • the present invention advantageously provides polymer processing systems and methods which use microwave energy to achieve extremely rapid, efficient melting and/or softening of polymer materials
  • microwave heating is the ability to heat polymer mate ⁇ al volumet ⁇ cally That is, heat is transferred to the material throughout its cross-section by radiation rather than by thermal conduction
  • the rate of heat transfer is not limited by the thermal conductivity of the material being heated, thus heat transfer occurs much faster Microwave melting occurs so rapidly, that significant reductions in cycle time would be achieved by the present invention
  • the use of microwave energy for melting is economically advantageous, because the system of the present invention uses energy more efficiently than conventional melting systems Heating uniformity is also improved by microwave heating
  • preferred embodiments of the present invention include separate melting and metering chambers that can be pressurized independently of each other This approach allows microwave melting to occur under a first, relatively low pressure, while molten polymer in the metering chamber can be pressurized to a second, relatively high pressure more suitable for extrusion, injection molding, or the like This greatly simplifies the structure and construction of the apparatus
  • a piston or melt pump may be used to pressurize and convey the molten polymer from the metering chamber to the cavity of the injection mold
  • a piston or melt pump to accomplish such transport, rather than screws which are more conventionally used, cycle time and machinery costs are significantly reduced
  • Preferred embodiments of the present invention involve conveying a continuous flow of polymer material through a conduit that not only serves as a passage for the polymer, but also serves as a single mode microwave cavity in which microwave energy is propagated along a path that substantially coincides with the path taken by the polymer being conveyed
  • the polymer flows through the conduit in the region where the electronic field, and hence heating efficiency, is at a maximum
  • this approach provides faster, more efficient, more flexible polymer melting capabilities
  • both polar and nonpolar polymers may be quickly and continuously melted using the approach of the present invention
  • many polymers, especially nonpolar polymers are often difficult to melt with microwaves in a reasonable amount of time in a continuous process that involves
  • the present invention relates to a method of using microwave energy to process a composition comprising at least one meltable polymer
  • a charge comprising the composition is transported into a cavity in which the charge can be irradiated with microwave energy While the charge is in the cavity, the charge is irradiated with microwave energy under conditions effective to melt the polymer
  • the melted polymer is then transported from the cavity to an independently pressu ⁇ zable metering chamber
  • the melted polymer is then transported from the metering chamber to a point of use
  • the present invention relates to an apparatus capable of using microwave energy to process a composition comprising at least one meltable polymer
  • the apparatus includes an electrically conductive housing defining a microwave processing cavity
  • a microwave energy source is operationally coupled to the cavity such that, while the charge is in the cavity, the charge can be irradiated with microwave energy under conditions effective to melt the polymer
  • a chamber is in fluid communication with the cavity such that the melted polymer can be transported from the cavity to the chamber
  • a transport mechanism is operationally coupled to the chamber in a manner such that melted polymer in the chamber can be transported to a point of use.
  • the present invention relates to a process of using microwave energy to process a composition comprising at least one meltable polymer.
  • a rotatable member is provided comprising a first cavity for holding a charge comprising a polymer resin.
  • the rotatable member is rotated to a first position such that the cavity is in communication with a supply comprising the polymer.
  • a charge comprising the polymer from the supply is delivered to the cavity.
  • the charge is irradiated with microwave energy under conditions effective to melt substantially all of the polymer, wherein said irradiating step occurs after the rotatable member is rotated away from the first position.
  • After melting the polymer at least a portion of the melted polymer is transported to a metering chamber.
  • the present invention relates to a process of using microwave energy to process a composition comprising at least one meltable polymer.
  • a rotatable member is provided, wherein the rotatable member comprises first, second, and third cavities, wherein rotation of the rotatable member causes each of the cavities to move sequentially through successive delivery, irradiating, and transport positions of a processing cycle, wherein such cycle is successively repeated by each cavity as the rotatable member rotates, and wherein the one cavity in the delivery position is capable of receiving a charge comprising the polymer, the one cavity in the irradiating position holds a charge of the composition during irradiation, and the one cavity in the transport position holds a charge comprising a substantially melted polymer resin.
  • a charge comprising a substantially unmelted polymer resin is delivered to the cavity in the delivery position.
  • the charge held in the cavity disposed in the irradiating position is irradiated with an amount of microwave energy sufficient to melt substantially all of the polymer resin of said charge.
  • At least a portion of the charge held in the cavity in the transport position is transported to a metering chamber such that said cavity is capable of receiving an additional charge comprising a polymer resin.
  • the charge from the metering chamber is injected into a mold comprising an internal volume having a shape corresponding to the article to be molded
  • the invention in another aspect, relates to an apparatus for processing a composition comprising at least one meltable polymer
  • the apparatus includes a rotatable member comprising a cavity for holding a charge of the composition
  • a microwave energy source is operationally coupled to the cavity such that the charge in the cavity can be irradiated with microwave energy under conditions effective to melt the polymer
  • a metering chamber is capable of being in fluid communication with the cavity so that the charge can be transported from the cavity to the metering chamber
  • a first transport mechanism is operationally positioned in the apparatus such that the first transport mechanism is capable of transporting the charge from the metering chamber to a point of use
  • Fig 1 is a schematic representation of a system for melting polymers according to the present invention
  • Fig 2 is a perspective schematic view of a polymer processing apparatus according to one embodiment of the present invention
  • Fig 3 is a side sectional view of the main processing unit used in the embodiment of Fig 2 in which a cavity is shown in the irradiating position
  • Fig 4 is a side sectional view of the hopper and main processing unit of the embodiment of Fig 2 in which a cavity is shown in the delivery position
  • Fig 5 is a side sectional view of the transfer cylinder, injection mechanism, and main processing unit of the embodiment of Fig 2 in which a cavity is shown m the transport position
  • Fig 6 is a side sectional view of a polymer processing apparatus according to an alternative embodiment of the present invention.
  • Fig 7 is a side sectional view of a polymer processing apparatus according to an alternative embodiment of the present invention.
  • Fig 1 is a schematic representation of a polymer processing system 10 incorporating the principles of the present invention
  • System 10 is adapted to melt a feed 12 comprising at least one polymer resin, and then deliver the molten polymer to a point of use 14, which may be the cavity of an injection mold, an extrusion die, or the like
  • a wide variety of thermosetting and thermoplastic polymer resins known to be suitable for molding or extrusion can be processed using system 10, although the use of thermoplastic materials is commonly preferred for injection molding applications
  • thermoplastic and/or thermosetting materials suitable in the practice of the present invention include polyethylene, polypropylene, polyether, polyester, a copolymer comprising butadiene and styrene, a copolymer comprising acrylonit ⁇ le, butadiene, and styrene (ABS), polyurethane, vinyl resin such as polyvinyl chloride, polyamide (such as the various polyamide resins referred to as "nylons”), epoxy resin, phenolic resin
  • relatively polar polymers such as polyvinyl chloride, polyamide, polyurethane, epoxy, polyimide, vulcanized rubber, ABS, and the like
  • relatively nonpolar polymers such as polyolefins, polyester, polystyrene, high impact polystyrene, polytetrafluoroethylene, allyl resin, styrenic resin, and the like
  • any such nonpolar polymer resin, or resins are combined with an effective amount of a microwave absorbing additive, or "sensitizer" as such materials are referred to in the art
  • such an additive will absorb microwave energy, which heats the additive Such heat is then thermally transferred to the nonpolar poly
  • the microwave absorbing additive generally may be any solid or liquid polar compound or combination of such compounds capable of absorbing and being heated by microwave energy and then thermally transferring the resultant heat energy to the polymer material to be processed
  • Such additives can be organic or inorganic Organic polar compounds may be monome ⁇ c, ohgome ⁇ c, or polymeric
  • representative classes of materials suitable for use as a microwave absorbing additive include any material known to function as an antistatic agent, carbon fibers, metal powder, color retardants of the type used in paint compositions, ultraviolet light absorbing materials commonly used in paint compositions, metal hydroxides such as Mg(OH) 2 , other inorganic salts such as CaS0 4 *H 2 0 and MgSO 4 »H 2 0, fatty acids, fatty acid esters, water, glyceryl esters, alcohols, amides, amines, hydroxylated amines such as ethanolamine, alkylene glycols, quaternary ammonium salts, low molecular weight polar polymers and
  • an appropriate amount of the microwave absorbing additive will depend upon a variety of factors such as the polymer resin being processed, the identity of the additive being used, the microwave frequency, the power output level of the microwave energy source, and the like. In selecting an appropriate amount of the microwave absorbing additive, enough of the additive should be combined with the polymer resin such that substantially complete melting, or the desired degree of softening, of the resin is achieved If too little of the microwave absorbing additive were to be used, an insufficient degree of melting or softening may occur On the other hand, if too much is used, the physical properties of the resultant polymeric article may be impaired Additionally, if too much of the additive were to be used, too much heat may be generated which might degrade or burn the polymer Generally, using 0 01 to about 20, preferably 0 01 to about 5, parts by weight of the additive per 100 parts by weight of the polymer resin would be suitable in the practice of the present invention
  • the microwave absorbing additive can be incorporated into feed 12 in any desired, convenient manner
  • the additive is a liquid
  • pellets of the polymer and liquid can be "pre-tumbled” together in order to coat the pellets with the liquid
  • the additive is a solid
  • the additive and the polymer may be compounded together to achieve a homogeneous admixture of the ingredients
  • the use of microwave energy absorbing additives to allow nonpolar polymer resins to be heated with microwave energy has been desc ⁇ bed in the art See, e g , U S Pat Nos 4,288,399, 4,360,607, 4,400,483, 4,840,758, and 5,446,270
  • System 10 generally comp ⁇ ses a first stage of operation represented by microwave cavity 16 in which feed 12 is melted using microwave energy, and a second stage of operation 22 in which the molten feed is pressurized for transport to point of use 14
  • This "multistage" approach allows microwave melting to occur at relatively low pressure, greatly simplifying the construction of microwave cavity 16 relative to a single-stage system in which microwave melting and pressu ⁇ zation for transport occur in the microwave cavity
  • Microwave cavity 16 is generally defined by walls formed from electrically conductive mate ⁇ al(s) that electrically shield the cavity, thereby substantially preventing microwaves from escaping from microwave cavity 16
  • Representative examples of such materials are well-known in the art and include corrosion-resistant metals, metal alloys, intermetallic compositions, combinations of these, and the like
  • Preferred examples of such materials include aluminum, stainless steel, copper, die-cast zinc, combinations of these, and the like
  • Microwave cavity 16 can be either a single mode microwave cavity or a multi-mode microwave cavity, as desired
  • mode refers to the specific electromagnetic field pattern that develops inside a microwave cavity The mode pattern is governed primarily by the internal geometry of the cavity and the wavelength of the electromagnetic energy which propagates within the cavity
  • a multi-mode cavity generally refers to a microwave cavity that is relatively large compared to the wavelength of microwave energy, such as, for example, a household microwave oven
  • a multi-mode microwave cavity generally contains multiple mode patterns which tend to be somewhat random The electric field strength throughout a multi-mode cavity, therefore, is typically random and difficult to control When materials are heated in a multi-mode cavity, heating uniformity can be improved by constant motion, agitation, or stirring of the material
  • a single mode microwave cavity refers to a smaller cavity that is capable of supporting only a single well-defined mode pattern which tends to be very regular and predictable When materials are heated in a single-mode cavity, good heating uniformity results without requiring constant motion, agitation, or stirring of the material being processed As compared to a multi-mode cavity, heating is significantly more uniform and easier to control in a single mode cavity
  • a single mode microwave cavity is generally more suitable for use in a continuous process (see for example the embodiments of the present invention described below in connection with Figs 6 and 7), and a multi-mold microwave cavity is generally more suitable for use in a batch process (see for example the embodiment of the present invention described below in connection with Figs 2-5)
  • Microwave cavity 16 can be provided with any suitable shape and dimensions The precise configuration of microwave cavity 16 will depend upon a variety of factors including, for example, the frequency of the microwave energy, the residence time required to accomplish melting, whether cavity 16 is intended for multimode or single mode operation, whether cavity 16 is intended for batch
  • microwave cavity 16 is cylindrical in shape and is configured to provide a single mode pattern which places the electric field parallel to the axis of the cavity The material being heated is then conveyed through the cavity in line with the axis and electric field in order to achieve the maximum heating efficiency
  • a cylind ⁇ cally-shaped, single mode microwave cavity of the present invention has the so-called TM 02 o mode configuration in which a peak electric field exists at the center axis of the cavity with another peak forming an annulus about the center axis The electric fields in both peaks thus are parallel to the center axis of the cylindrical cavity
  • At least a portion and preferably substantially all of the interior surfaces of the electrically conductive walls defining microwave cavity 16 are sufficiently reflective so that at least a portion of the radiant heat energy generated during polymer melting is reflected back into microwave cavity 16 in order to promote more effective melting of the polymer res ⁇ n(s) being processed
  • the interior surfaces of the cavity walls are preferably as reflective as practical circumstances allow Although a surface cannot be too reflective from a technical perspective, there is a level of reflectivity beyond which the incremental improvement in performance offered by additional improvement in reflectivity characteristics may not justify the extra cost of attaining such improvement
  • microwave energy and reflected radiant energy provides much better melting performance than using microwave energy alone, particularly when nonpolar polymers are being processed
  • non-polar polymers may not melt upon irradiation with just microwave energy alone unless relatively large quantities of a microwave energy absorbing additive is blended with, or otherwise incorporated into, the non-polar polymer
  • many kinds of non-polar polymers can be melted with lesser quantities of such additives
  • the amount of reflected radiant energy is sufficiently great so that the presence of microwave energy absorbing additives can be avoided altogether
  • Any technique known in the art can be used to provide the interior surfaces of the microwave cavity walls with the desired level of reflective characteristics
  • the interior surfaces of electrically conductive cavity walls formed from aluminum, stainless-steel, copper, or the like can be polished in order to enhance the reflective characteristics of such surfaces
  • the interior surfaces can be coated with an intrinsically reflective material such as gold, silver, nickel, or the like
  • a surface treatment may be more desirable for materials having relatively high wall losses in the intended operating regime
  • a microwave cavity formed from aluminum provides excellent performance in high Q applications and may not require any kind of surface treatment
  • stainless steel which is stronger than aluminum and better for cavities subjected to high internal pressures, nonetheless contributes to higher wall losses than aluminum Therefore, a surface treatment involving polishing and/or applying a finish of nickel, gold, or platinum may be desirable for stainless steel cavities
  • the reflective characteristics of the interior surfaces of microwave cavity 16 can be quantitatively defined in terms of emissivity Emissivity refers to the ratio of the radiation emitted by a surface as compared to the radiation emitted by a black body at the same temperature Materials with lower emissivity are more reflective than materials with higher resistivity
  • the interior surfaces of microwave cavity 16 preferably have an emissivity of less than 0 1 , more preferably 0 05 or less
  • microwave energy for melting is supplied to microwave cavity 16 by microwave source 18 through waveguide 20
  • microwave energy refers to electromagnetic radiation characterized by a wavelength greater than radio waves but shorter than infrared radiation
  • Preferred microwaves are characterized by a wavelength of about 1 mm (about 300 GHz) to about 50 cm (about 0 6 GHz) More preferred microwaves have a wavelength such that the frequency of the microwaves is in the range from about 0 9 GHz to about 5
  • microwave source 18 may be tunable so that microwave source 18 is capable of generating a range of microwave frequencies Alternatively, microwave source 18 may be of a "universal" type that generates microwaves characterized by only a single frequency Use of a "universal" type microwave source 18 is preferred because microwave sources that generate either 2 45 GHz or 0 915 GHz microwaves, respectively, are widely available at economic prices from a number of commercial sources Microwave sources operating at 2 45 GHz are more preferred
  • Microwave source 20 should have an appropriate power output such that microwave energy source 20 is capable of radiating microwave energy at a power level sufficient to achieve melting or softening, as desired, of the polymer res ⁇ n(s) being processed
  • a suitable power output for the microwave energy source would depend upon a variety of factors including the particular microwave energy source 20 being used, the polymer resin being processed, and the like Generally, however, an available power output level in the range from about 0 5 kW to about 500 kW would be suitable in the practice of the present invention
  • the power output level of microwave energy source 18 be controllably variable over such a wide range
  • 2 45 GHz microwave sources are most commonly available with power output ranging from 500 Watts up to 6 kW, while a few manufacturers offer units with output up to 30 kW Units operating at 6 kW are preferred
  • the output waveform from microwave source 20 is directly related to its output spectrum and is an important factor when delivering microwave power to a high Q load
  • Less expensive generators utilizing power supplies commonly found in household microwave ovens have a pulsed waveform where pulse rate is equal to the power line frequency (60 Hz in the US) and an output spectral bandwidth of approximately 5 MHz
  • high performance generators utilizing switch mode power supplies have extremely low ripple, or CW, waveforms and typical output spectral bandwidths of approximately 250 kHz
  • a useful rule of thumb is to use a microwave source having a spectral bandwidth no more than half the coupling bandwidth of the load being heated
  • polyethylene being characterized by a Q factor of 4000, has a coupling bandwidth ( ⁇ f) of 613 kHz when operating at 2 45 GHz
  • ⁇ f coupling bandwidth
  • Waveguide 20 is typically a pipelike structure that may have any suitable cross-section for carrying microwaves from microwave source 18 to microwave cavity 16
  • Preferred waveguides 20 have either a square, rectangular, or circular cross-section
  • waveguide 20 is generally formed from an electrically conductive material such as a corrosion-resistant metal, a metal alloy, an lntermetalhc composition, combinations of these, and the like
  • Preferred waveguides comprise aluminum, stainless steel, and/or copper
  • Waveguide 20 may be flexible if desirable or necessary to allow for tolerance build-ups between the respective mounting positions of the applicator and microwave generator Flexible waveguide 20 can also be used where movement between mounting positions is required However, flexible waveguide 20 could be subject to fatigue failure due to repeated working of its metallic structure Caution should be exercised during the design phase to limit the amount of flexure sufficiently to prevent any portion of the metallic structure from reaching its yield point while flexing
  • microwave power delivery systems require a device which is used to match the impedance of the load to that of the waveguide and thus the microwave generator Without this the amount of microwave power coupled to the load may be partially reduced.
  • the most common form of this device is a waveguide stub tuner, but other types of devices such as irises are also used.
  • Waveguide tuners are popular for their convenience in adjusting the match while microwave power is being delivered. Tuners are available for either manual or automatic operation.
  • Manual tuners are adjusted by turning one or more stubs, or threaded rods, into the waveguide while the operator observes a power meter which monitors the amount of microwave power reflected from the load. Tuning is accomplished when reflected power is minimized.
  • Automatic tuners operate essentially the same way, except that the stubs are driven by motors and sophisticated electronics are used to monitor reflected power and adjust the stubs accordingly.
  • the tuner When power is being delivered to a high Q load, the tuner often requires adjustment if the power output from the generator changes, such as is often required for regulating processes. As the generator changes output power, its center frequency also changes by as much as 30 MHz from zero to full output (this is a characteristic of all microwave generators which utilize magnetrons). When the Q of the load is 4000 and coupling bandwidth only 600 kHz, a small change in power output can result in complete loss of coupling to the load. Similarly, a dynamic process during which the characteristic impedance is constantly changing or changes gradually over time requires constant tuner adjustments in order to maintain coupling throughout the process.
  • the isolator includes a waveguide circulator, which directs the reflected power away from the magnetron and a dummy load which absorbs and dissipates the reflected power Often these two elements exist as separate components which work together, but they are also available from some manufacturers incorporated together as a single component
  • Waveguide power couplers and meters are available as separate components which can be incorporated into the heating system, but they are also available as a feature of the isolator
  • miscellaneous waveguide components may also be desirable depending on the configuration of the equipment onto which they are to be installed These components typically include short sections of rigid waveguide with one or more elbows to direct the microwave energy around corners Almost any configuration is possible
  • Figs 2-5 show a specific configuration of one preferred embodiment of a polymer processing apparatus 30 of the present invention
  • Apparatus 30 is provided with four main components including hopper 36, main processing unit 38, transfer cylinder 40, and injection mechanism 42
  • hopper 36 main processing unit 38
  • transfer cylinder 40 transfer mechanism 42
  • injection mechanism 42 injection mechanism 42
  • the apparatus 30 of Figs 2-5 is shown as having only one each of these four components, one or more additional hoppers, main processing units, transfer cylinders, and/or injection mechanisms may also be provided in order to increase the output capacity of apparatus 20
  • Main processing unit 38 is cylind ⁇ cally shaped and is used to melt a charge comprising a polymer resin received from raw material supply 32 provided in hopper 36
  • Main processing unit 38 includes a top housing section 44, center plate section 46, and bottom housing section 48
  • Center plate section 46 is rotatable about axis of rotation 49 and thus provides main processing unit 38 with a rotatable member to facilitate delivery, melting, and transport of polymer charges to be processed
  • top and bottom housing sections 44 and 48 are fixed and do not rotate
  • Center plate section 46 includes a top axial face 51 disposed proximal to top housing section 44 and a bottom axial face 53 disposed proximal to bottom housing section 48
  • the top axial face 51 of center plate section 46 is provided with first, second, and third cavities 50, 52, and 54 which are adapted to hold respective charges of polymer resin to be processed
  • Hopper 36 and transfer cylinder 40 are disposed on the top surface 47 of top housing section 44 approximately 120 degrees apart Intermediately between hopper 36 and transfer cylinder 40, main processing unit 38 is provided with a microwave energy source As shown in Fig 1, at least a portion 21 of the microwave energy source is disposed in top housing section 24 The microwave energy source is capable of directing microwave energy at the contents of one of cavities 50, 52, or 54 when center plate section 46 is rotated to a position such that one of such cavities is disposed below the microwave energy source portion 41
  • apparatus 30 is configured with the microwave energy source portion 41 being disposed in top housing section 44, other configurations could also be used
  • the microwave energy portion 41 could be disposed in an analogous position in bottom housing section 48
  • portions of the microwave energy source could be disposed in both the top and bottom housing sections 44 and 48 in a manner such that the two portions would cooperate to irradiate the contents of an interposed cavity with microwave energy
  • at least a portion of the microwave energy source could be disposed in center plate section peripherally around each of the cavities
  • the microwave source could be completely external to apparatus 30, but operationally coupled to apparatus 30 by a suitable waveguide
  • center plate section 46 rotates
  • This processing cycle is successively repeated by each cavity 50, 52, and 54 as center plate section 46 rotates
  • the delivery position of the cycle corresponds to the position of a cavity 50 which is rotated to a position at which a charge from supply 32 can be delivered to the cavity 50
  • cavity 50 disposed directly below hopper 34 is in the delivery position
  • top housing section 44 is provided with a through aperture 55 allowing communication between hopper 36 and the cavity 50 in the delivery position
  • controlling means (not shown) is provided so that the amount and timing of charges delivered from supply 32 through the aperture 55 can be controlled by the operator
  • the kind of controlling means used is not critical, and any such means could be used in accordance with conventional practices
  • the irradiation position corresponds to the position of a cavity 52 which is rotated to a position at which the contents of the cavity 52 can be irradiated with microwave energy by the microwave energy source portion 41
  • cavity 52 disposed directly below microwave energy source portion 41 is in the delivery position
  • irradiation of the charge with microwave energy causes the polymer resin to melt
  • such melting occurs extremely rapidly and much more quickly than could be achieved using conventional melting techniques
  • the transport position corresponds to the position of a cavity 54 which is rotated to a position at which the action of transfer cylinder 40 can be used to transfer the contents of the cavity 54 to the injection mechanism 42
  • Transfer cylinder 40 is provided with housing 56 defining a cylinder bore 58
  • a piston 60 capable of reciprocating movement upward and downward in cylinder bore 58 is also provided
  • Top housing section 44 is provided with through aperture 62 coupling the internal volume of cylinder bore 58 to cavity 54 in the transport position
  • the cavity 54 in the transport position is fluidly coupled to the interior of injection mechanism 42 by passageway 64 Passageway is formed from through aperture 63 and conduct section 65 As a result, downward movement of piston 60 forces a melted charge from the transport cavity through passageway 64 and into the injection mechanism 42
  • Injection mechanism 42 includes housing 66 enclosing a metering chamber 67 for holding a metered amount of the molten charge Injection mechanism 42 is further provided with a piston 68 which is capable of reciprocating movement inside housing 66 in directions along the longitudinal axis of injection mechanism 42 Piston 68 is disposed so that movement of the piston in the direction of arrow 70 forces a molten polymer 34 through output passage 72 From output passage 72, the molten polymer can be directed to a point of use such as an extrusion die (not shown) or the internal volume of a mold (not shown), wherein the mold volume has a shape corresponding to the shape of the article to be formed
  • supply 32 comprising polymer resin to be processed is provided in hopper 36 During polymer processing, the center plate section 46 is rotated until each of cavities 50, 52, and
  • the cavity at the delivery position is capable of receiving a charge comprising the polymer resin
  • the cavity at the irradiation position holds a charge comprising solid polymer resin which is ready to be melted
  • the cavity at the transport position holds a charge of substantially melted polymer resin ready to be transported to the injection mechanism 42
  • a charge comprising a substantially unmelted polymer resin is delivered to the cavity 50 in the delivery position
  • the charge held in the cavity 52 disposed in the irradiating position is irradiated with an amount of microwave energy sufficient to melt substantially all of the polymer resin of said charge
  • at least a portion of the charge 54 held in the cavity in the transport position is transported to metering chamber 67 such that the cavity 54 is capable of receiving a successive charge comprising a polymer resin in the next step of the processing cycle
  • the charge in the metering chamber 62 may then be injected
  • the center plate section 46 rotates until the cavities 50, 52 and 54 are advanced to the next position of the processing cycle, and the delivery, irradiation, transport, and injection steps are then repeated
  • the process cycle can be repeated as many times as desired
  • Fig 6 shows an alternative embodiment of a polymer processing apparatus 100 of the present invention
  • Apparatus 100 is adapted for continuous processing of a supply 102 comprising a polymer mate ⁇ al to be melted and subsequently delivered to a point of use (not shown)
  • Apparatus 100 includes melting unit 104 and transport unit 106 operationally coupled to melting unit 104 by conduit 106 Melting is accomplished in melting unit 104, and the molten polymer is then pressurized in transport mechanism 106 for transport to the point of use
  • Melting unit 104 includes electrically conductive, cylindrical housing 112 formed from sidewall 1 14, bottom 1 16, top 1 18, and interior partition 120
  • Interior partition 120 divides housing 112 into a feed zone 122 and a melting zone 124
  • the center region of interior partition 120 is fitted with perforated plate 126 that comprises a plurality of apertures permitting feed 102 to pass from feed zone
  • interior partition 120 and perforated plate 126 are formed from an electrically conductive mate ⁇ al to provide electric shielding at the top of melting zone 124
  • a cooling jacket (not shown) may be provided on the exterior of housing 112 in order to carry away excess heat generated during melting operations
  • Feed zone 122 includes rotatable feed screw 128 operationally supported in housing 1 12 and bushing member 130, which defines the inner diameter of the feeding section Bushing member 130 preferably is formed from hardened steel Bushing member 130 is fixedly attached to housing 112 by any suitable technique including welding, riveting, bonding with an adhesive, press fitting, and the like
  • Charge 132 of supply 102 provided in hopper 134 is gravity fed into helical chamber 136 defined by interior surface 131 of bushing member 130, feed member threads 138, and center member 140
  • Rotation of feed screw 128 motivates charge 132 through perforated plate 126 and into melting zone 124
  • the feed rate can be controlled easily by adjusting the rotational speed of feed screw 128 Generally, faster rotation of feed screw 128 provides higher feed rates
  • feed screw 128 is rotated at a rate so that a substantially continuous, steady state flow of polymer mate ⁇ al through melting unit 104 can be maintained
  • Melting zone 124 includes cylind ⁇ cally shaped, single mode chamber 140 operationally coupled to microwave source 137 by waveguide 139
  • chamber 140 not only functions as a passage for polymer material to be conveyed through melting unit 104, but cavity 140 also functions as a single mode microwave cavity
  • both microwaves and the polymer material are both conveyed along a path substantially aligned with the longitudinal axis of chamber 140
  • at least a portion of the interior surfaces 141, 142, 145, and/or 147 of housing 112 that define chamber 140 are sufficiently reflective (e g , characterized by an emissivity of less than 0 1, preferably 0 05) so that not only microwaves, but also some of the radiant energy generated during melting operations, are reflected back into chamber 140 in order to enhance melting performance
  • Chamber 140 generally has a diameter that is determined by the distance between the interior surface 141 on one side of chamber 140 and the interior surface 142 on the other side of chamber 140
  • the length of chamber 140 is determined by the distance between plate 126 at the entrance to chamber 140 and plate 144 positioned at the exit from chamber 140
  • the diameter of chamber 140 as measured between the interior surface 141 on one side of melting zone 124 and the interior surface 142 on the other side of melting zone 124 is preferably equal to an integer multiple of the wavelength of the microwaves being used for processing
  • Providing chamber 140 with such a diameter helps ensure that the microwaves will resonate inside chamber 140 to achieve uniform energy distribution and efficient melting performance.
  • such diameter is 2 to 5 times, and more preferably 2 to 3 times, the wavelength of the microwaves.
  • the diameter of chamber 140 is preferably 10.75 cm.
  • chamber 140 is less critical than the diameter.
  • chamber 140 may be provided with any suitable length as desired to ensure that the polymer residence time in chamber 140 is long enough for melting to be accomplished.
  • the preferred length of chamber 140 can be determined according to the desired electric field strength within the volume of material being heated. The field strength should be high enough to effect reasonable rates of heating but should not be so high as to result in breakdown and electric discharge (arcing) inside chamber 140. To achieve this goal, preferred electric fields are on the order of about 375 kV/m for power levels on the order of 6 kW.
  • microwave transparent liner 150 is provided in chamber 140.
  • Use of microwave transparent liner 150 confines the flowing material being processed to the core region of chamber 140, where microwave energy distribution is at a maximum. Accordingly, liner 150 promotes more uniform heating, transport, and melting of such material.
  • polymer material closer to sidewall 1 14 may have a tendency to be too cool whereas polymer material in the center of chamber 140 may be too hot.
  • the resultant temperature gradient may tend to have an adverse impact upon flow characteristics through melting zone 124.
  • the polymer material could also burn or otherwise degrade.
  • Liner 150 is provided proximal to sidewall 114, but does not line all of bottom 1 16 No liner is needed proximal to such portions of bottom 1 16, because the polymer material is typically fully melted by the time the polymer material reaches that part of chamber 140
  • Liner 150 generally is formed from a microwave transparent material that not only absorbs a relatively small percentage of the microwave energy as the microwaves travel through liner 150, but also is substantially temperature resistant so that the material will not deform, melt, or otherwise degrade du ⁇ ng melting operations
  • microwave transparent means that the material has a relative complex permittivity such that less than 1%, and more preferably less than 0 01% of the microwave energy traveling through the material is absorbed when tested according to ASTM D2520-95 Complex Permittivity (Dielectric Constant) of Solid Electrical Insulating materials at Microwave Frequencies and Temperatures at 1650°C, Test Method B (1997) A wide variety of temperature resistant, microwave transparent materials suitable for forming liner
  • the thickness of the walls of liner 150 will depend upon a variety of factors including the diameter of chamber 140, the material from which liner 150 is to be formed, the power output setting of microwave source 137, the frequency of the microwave radiation generated by microwave source 137, and the like In preferred embodiments of the invention operating at 2 45 GHz and 6 kW, and in which chamber 140 has a diameter of 10 75 cm and liner 150 is formed from quartz or a low loss ceramic, forming liner 150 with a wall thickness in the range from 2 4 to 2 7 cm, preferably 2 55 to 2 65 cm, would be suitable
  • the rotational speed of feed screw 128 generally determines the pressure in chamber 140 Desirably, melting occurs in chamber 140 at a relatively low pressure that is effective to develop sufficient force to transport polymer mate ⁇ al through chamber 140 It is particularly desirable to match the flow rate of polymer material with the heating rate so that material enters chamber 140 through plate 126 at substantially the same rate that mate ⁇ al leaves chamber 140 through plate 144 If the force is too low, however, the residence time in chamber 140 may be too long and polymer materials being processed could burn or otherwise degrade On the other hand, if the pressure is too high, the polymer feed rate will be too high to achieve sufficient melting Accordingly, melting preferably is carried out in chamber 140 under a relatively low pressure in the range from about
  • melt pump 1 10 is used to accomplish such transport Melt pump 1 10 performs at least two important functions Firstly, melt pump 110 helps control the flow rate of molten material transferred to transport unit 106 Additionally, melt pump helps homogenize the molten mate ⁇ al as well Although melt pump 1 10 is preferred, other devices, such as a check valve, could also be used
  • Transport unit 106 includes cylindrical housing 152 enclosing metering chamber 154 for holding a metered amount of molten polymer Transport unit 106 is further provided with piston 156 which is capable of reciprocating movement inside housing 152 in directions along the longitudinal axis of transport unit 106 Piston 156 is disposed so that movement of piston 156 in the direction of arrow 158 forces molten polymer 160 through outlet passage 162 to a point of use Because the operation of piston 156 acts in intermittent fashion once each piston cycle to force molten polymer to the point of use, transport unit 106 incorporating piston 156 is most effectively used for injection molding applications On the other hand, if it is desired to provide molten polymer to a point of use involving an extrusion die, then a melt pump or other similar transport device can be substituted for piston 156 in order to convey a continuous supply of molten polymer to the point of use Because metering chamber 154 is separate from and independently pressu ⁇ zable relative to chamber 140, relatively high pressures suitable for injection molding or extru
  • Fig 7 shows another embodiment of a polymer processing apparatus 200 of the present invention that is generally similar to polymer processing apparatus 100 of Fig 6 (for example, all parts of Fig 7 also found in Fig 6 bear the same identification number as the corresponding parts of Fig 6 except that the identification numbers of Fig 7 also include the suffix "A") , except that apparatus 200 further includes core member 202 positioned in chamber 140 A Core member 202 extends from plate 126A to plate 144A and has a surface 204 defining an inner surface for guiding polymer material in annular fashion through chamber 140 A
  • core member 202 further optimizes the heating performance of apparatus 200 by confining flowing material to an annular region of chamber 140 A in which the energy distribution of the resonating microwaves is most uniform
  • core member 202 is made form a microwave transparent material as defined above so that the presence of core member 202 does not interfere with melting performance at all
  • chamber 140A is a TM 02 o mode cavity operating at 2 45 GHz and having an inside diameter of 10 75 cm
  • liner 150 is made from quartz and has a thickness in the range from about 2 4 to 2 7 cm core member 202 preferably may have a radius in the range from 1 8 to about 2 cm
  • liner 150 or 150A as the case may be
  • core member 202 if any
  • are independently removable so that different sized parts can be inserted into place in chamber 140 (or 140A) as needed This allows heating performance to be optimized for any kind of polymer
  • one or both of such components can be rotatable about the axis of chamber 140 (or 140 A as the case may be) to assist with material transport or mixing If both a liner and a core member are present and rotatable, such members can be adapted for co-rotation, counter-rotation, or both, as desired While this invention has been described with respect to preferred embodiments, the present invention can be further modified within the spirit and scope of this disclosure This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims

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  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
  • Injection Moulding Of Plastics Or The Like (AREA)

Abstract

Systèmes et procédés de traitement de polymères mettant en application l'énergie micro-ondes afin d'effectuer la fusion ou le ramollissement extrêmement rapide et efficace de matériaux polymères. On peut, après l'opération de fusion ou de ramollissement, comprimer le polymère fondu afin de le transférer, par exemple, dans un moule à injection ou dans une filière d'extrusion, si nécessaire. La fusion aux micro-ondes est si rapide que l'invention permettrait de limiter considérablement la durée du traitement. L'utilisation de l'énergie micro-ondes dans un processus de fusion présente, de plus, un avantage économique, étant donné que les sources d'énergie micro-ondes sont généralement moins chères et utilisent l'énergie plus efficacement que les systèmes classiques de fusion.
EP97945323A 1996-09-30 1997-09-26 Systeme de traitement de polymeres aux micro-ondes Withdrawn EP0938407A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US2707296P 1996-09-30 1996-09-30
US27072P 1996-09-30
PCT/US1997/017399 WO1998014314A1 (fr) 1996-09-30 1997-09-26 Systeme de traitement de polymeres aux micro-ondes

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CN1886507B (zh) 2003-10-27 2010-12-29 联邦科技产业研究组织 淀粉中具有增加了直链淀粉含量的水稻及水稻制品
ES2378331T3 (es) 2006-01-17 2012-04-11 Nordson Corporation Aparato y procedimiento para la fusión y la distribución de material termoplástico
US9303152B2 (en) 2006-05-31 2016-04-05 Dow Global Technologies Llc Use of microwave energy to selectively heat thermoplastic polymer systems
JP5121267B2 (ja) * 2007-03-16 2013-01-16 日本冶金工業株式会社 Ｃｒ酸化物を含有する有価金属含有副産物のマイクロ波加熱炭素還元法
US8058349B2 (en) * 2007-11-29 2011-11-15 Styron Europe Gmbh Microwave heatable monovinyl aromatic polymers
EP2216153B1 (fr) * 2009-02-05 2013-07-24 Nordson Corporation Appareil de fusion et procéde pour liquéfier une matière thermoplastique
GB2468901A (en) * 2009-03-26 2010-09-29 E2V Tech Microwave Oven
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JP2016008305A (ja) * 2014-06-26 2016-01-18 日本製紙株式会社 可塑化セルロース及びその製造方法
DE102017106331A1 (de) 2017-03-23 2018-09-27 Krones Ag Verfahren und Vorrichtung zur Herstellung von Kunststoffobjekten
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CA2266616A1 (fr) 1998-04-09
JP2001501553A (ja) 2001-02-06
AU4655297A (en) 1998-04-24
KR20000048778A (ko) 2000-07-25

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