EP1937455A2 - Dispositif et procede pour le moulage evolue de mousse structuree - Google Patents

Dispositif et procede pour le moulage evolue de mousse structuree

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Publication number
EP1937455A2
EP1937455A2 EP06820982A EP06820982A EP1937455A2 EP 1937455 A2 EP1937455 A2 EP 1937455A2 EP 06820982 A EP06820982 A EP 06820982A EP 06820982 A EP06820982 A EP 06820982A EP 1937455 A2 EP1937455 A2 EP 1937455A2
Authority
EP
European Patent Office
Prior art keywords
accumulator
gas
advancing
extruder
polymer
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Withdrawn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
EP06820982A
Other languages
German (de)
English (en)
Inventor
Chul B Park
Xiang Xu
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.)
Individual
Original Assignee
Individual
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Filing date
Publication date
Priority claimed from CA 2517995 external-priority patent/CA2517995A1/fr
Application filed by Individual filed Critical Individual
Publication of EP1937455A2 publication Critical patent/EP1937455A2/fr
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/38—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length
    • B29C44/42—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length using pressure difference, e.g. by injection or by vacuum
    • B29C44/421—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length using pressure difference, e.g. by injection or by vacuum by plastizising the material into a shot cavity and injecting using a plunger
    • 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
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/3442—Mixing, kneading or conveying the foamable material
    • 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
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/3469—Cell or pore nucleation

Definitions

  • the present invention i elates to polymeric foam processing in general, and more specifically to systems and methods for manufacturing structural foams via injection molding.
  • Structural foams are plastic foams manufactured using conventional preplasticating- type injection-molding machines, where a physical blowing agent (PBA) and/or a chemical blowing agent (CBA) is employed to produce a cellular (foam) structure during processing.
  • PBA physical blowing agent
  • CBA chemical blowing agent
  • the structural foam molding technology was initially invented by Angeli Jr. ct al. (US Patents 3,268,636 (1966) and 3,436,446 (1969)), and further improvements were made to it (US Patent 39SS403 (1976)).
  • low-pressure preplasticating-typc structural roam molding machines arc most commonly used, because the required molding system for producing large products is small with low pressure in the cavity.
  • the cell number density (or cell density) of structural foams is typically less than 10 3 ceIIs/cm 3 ', the cell size is greater than 1 mm, and the cell-size distribution is very non -uniform.
  • Stnictural foams also have very poor surface quality, very low void fraction, and poor mechanical properties (due Io the large gas pockets). The processing conditions and the product quality are very inconsistent, too. Development work has been broadly practiced to improve the cellular structure, surface quality, and process consistency in the structural foam molded products.
  • Patent 4,548,776 issued in 1985 to J. Holdredge.
  • a valve-like mixing nozzle assembly including a rotating mixing turbine, mounted in the flow path of the plastic material can be selectively operated to control the flow of plastic material into an injection mold and thereby to improve the cellular structure of molded foams.
  • High-pressure structural foam molding has been developed and widely practiced to improve the surface quality of structural foams by using an expandable mold.
  • a typical high-pressure process a foarrtable polymer melt is injected into the mold cavity with a full shot; the melt is then subjected to high packing pressure to compress the cells formed during mold filling; after a solid skin is formed, the overall mold volume is expanded; then with the compression released, foaming of the core materials fills out the mold.
  • a good example is US Patent 3,801, 686 issued in 1974 to W. T. Kyritsis et al.
  • Another variation of this process is that instead of moving the mold, one or more movable cores that initially occupy part of the mold cavity can be used to provide a necessary foaming space.
  • This variation is known to be good for thick-walled parts.
  • An example of this variation is British Patent 1.194,191.
  • the high-pressure process can produce the finishes superior to those of the low-pressure one, but compared to the high cost, it can only provide a partial improvement in surface appearance by compression of the foams formed in the solid skin.
  • parts geometry is limited due to the requirements of moving mold, and the molding system should be larger because of the high pressure in the mold,
  • Gas counter-pressure foam molding was developed purely as the swirl-free molding technique, and has received a considerable amount of attention.
  • the concept behind counter-pressure is to utilize a gas pressurized mold, which, through controlled venting allows the foam expansion stages of the cycle to occur after a smooth surface has been formed.
  • Numerous development efforts starting as early as the mid-seventies have advanced the gas counter-pressure molding technology. Examples include U.S. Patent 4,255,368 issued in 1981 to O. Olabisj, and U.S. Patent 4,952,365 issued in 1990 to T, Shibuya ct al
  • thermoplastic melt containing a blowing agent is first injected into a gas-pressurized mold cavity in a full shot, then releasing the gas pressure, and thereafter enlarging the volume in the molded cavity by movement of a mold wall.
  • a thermoplastic melt containing a blowing agent is first injected into a gas-pressurized mold cavity in a full shot, then releasing the gas pressure, and thereafter enlarging the volume in the molded cavity by movement of a mold wall.
  • Examples include, U.S. Patent 4,096,218 issued in 1978 to A, Yasuikc et al., U.S. Patent 4,133,858 issued in 1979 to A. Hayakawa et al.. and U.S. Patent 4,783,292 issued in 1988 to R. K. Rogers.
  • Hcndry a process to provide a predetermined skin thickness of an injection foam molded part was developed by first injecting solid pjastic resin into a mold and then injecting a foamed plastic resin like in co-injection molding but with one extrusion barrel.
  • microcellular foams can be produced by inducing a thermodynamic instability through a rapid pressure drop, e.g., higher than 0.9 GPa/s in the nucleation device of an extrusion system.
  • a microcellular injection-molded article having an average cell size of less than about 60 microns can be produced using a polymeric material, a nucleating agent in an amount between about 2.5 and about 7 weight percent, and a blowing agent amount less than 1.5 weight percent by inducing a pressure drop rate less than 1.0 GPa/s in the solution of blowing agent and polymeric material.
  • microcellular and supermicrocellular foamed materials having cell densities in the range of about 10 9 to 10 15 cells per cubic centimeter of the material with the average cell size being at least less than 2.0 microns can be produced by inducing a thermodynamic instability to the plastic material saturated with a sufficient amount of supercritical fluids.
  • microcellular polymeric materials can be produced using a very low blowing agent level (less than 0.08% by weight) via injection molding based on the reciprocating-typc injection molding system.
  • microcellular foams can be produced by controlling pressure drop rate and shear rate via a nucleator that is upstream to the pressurized mold and extrusion system with a reciprocating screw.
  • Microcellular foams have also been produced using expandable hollow microspheres.
  • U.S. Patent 5,665,785 issued in 1995 to T. R. McCIelian, it was claimed that microcellular foams can be produced by adding expandable thermoplastic hollow microspheres containing a volatile material in an injection molding process.
  • U.S. Patent 6,638,984 issued in 2003 to D. S. Soane et al., it was claimed mat microcellular foams can be made upon heating the thermo-expandable microspheres which are characterized by having a polymeric wall surrounding one or more pockets or particles of blowing agent or propellant within the microsphere.
  • Microcellular molded foams have also been made by other methods.
  • M. Shimbo ct al. (Foams'99, pp. 132-137, 1999)
  • microcellular injection molding was demonstrated based on a preplasticating-type system on a small scale.
  • this art does not teach how to stabilize the barrel pressure in order Io better disperse the gas in the polymer melt.
  • the present invention is directed to improving the process consistency while simplifying the required system modification based on the widely-practiced preplasticating-type structural foam molding system. It is our purpose to propose an inexpensive method to effectively improve the uniformity of cellular structure, the surface quality, and the consistency of production process based on a prcplast ⁇ cating-typc structural foam molding system.
  • This invention is a processing technology based on the modification of the conventional low-pressure preplastic ⁇ ting-type structural foam molding system. Thjs invention can be applied easily by retrofitting the existing low-pressure structural foam molding machines with slight modification.
  • Our advanced low-pressure structural foam molding technology is characterized by a design that facilitates the uniform dispersion/dissolution of gas in the polymer melt during the structural foam molding process, thereby mini-raizing the chance of creating large undissolved gas pockets.
  • an additional accumulator i.e., a hydraulic piston, a spring-loaded piston, an expandable tube, or some instrument of this nature
  • a gear pump between the extrusion barrel and the shut-off valve (before the main accumulator) to completely decouple the gas dissolution operation from the injection and molding operations.
  • This invention would ensure that the pressure in the extrusion barrel can be relatively well maintained and that consistent gas dosing can be attained to achieve a uniform polymer/gas mixture regardless of the pressure fluctuations caused by the injection and molding operations.
  • the cost of manufacturing the parts in structural foam molding is significantly reduced by using our invention. Because ⁇ the void fraction ts increased by 10 ⁇ 20%, the expensive plastic material will be used less, and therefore, the material cost will be reduced accordingly. Since the plastic material cost of structural foam molding is typically about 50% of the total cost, the total cost will be reduced by 5 ⁇ 10% from the reduced amount of plastic material. In addition, the cost for CBA will also be significantly reduced. It should be noted that this cost reduction is accompanied with the enhanced properties of structural foams.
  • Another major benefit of the present invention is the consistency of the product quality and the manufacturing (processing) conditions due to the consistent gas dosing realized by the art provided in this invention.
  • Figure 1 shows a schematic illustration of system configuration Option 1.
  • Figure 2 shows a schematic illustration of system configuration Option 2.
  • Figure 3 shows a schematic illustration of system configuration Option 3.
  • Figure 4 shows a schematic illustration of system configuration Option 4.
  • Figure 5 shows a schematic illustration of system configuration Option 5.
  • Figure 6 shows a schematic illustration of system configuration Option 6.
  • Figure 7 shows a schematic illustration of system configuration Option 1
  • Figure 8 shows a schematic illustration of system configuration Option 8.
  • Figure 9 shows a schematic illustration of system configuration Option 9
  • Figure 10 shows a schematic illustration of system configuration Option 10.
  • Figure 11 shows a schematic illustration of system configuration Option 11.
  • Figure 12 shows a schematic illustration of system configuration Option 12.
  • Figure 13 shows the cell density of HDPE structural foams produced from this invention at various talc sizes, talc contents, and N 2 contents
  • the injected gas typically N 2
  • the solubility limit locally or globally. It is because of the overdosed gas content and/or the pressure fluctuations during each cycle, that the injected gas cannot completely dissolve into the polymer matrix during processing.
  • shut-off valve is typically used between the plasticating extrusion barrel and the accumulator to prevent the reverse flow from the accumulator to the extrusion barrel.
  • this shut-off valve cannot completely decouple the functions of the extrusion barrel and the accumulator. Since the valve needs to be shut off during the injection period, the rotation of the plasticating screw needs to be stopped; otherwise, the material supplied from the extrusion barrel will go nowhere and the system pressure may exceed the safety limit., which is both dangerous and potentially damaging.
  • the manufactured structural foams typically have uncontrallably formed numerous large gas pockets, especially along the weld lines, which governs the maximum achievable void fraction of the final foam products.
  • the void fraction of structural foam determines the materials saving, and therefore, it is desirable to maximize the achievable void fraction.
  • the achievable void fraction is in the range of 0.08 to 0.20 and is typically determined by the geometry of the products (i.e., a low void fraction for complicated geometry and a high value for simple geometry) and the shot size.
  • means for allowing the flow of the polymer melt to continue which means pieferably comprise a positive displacement pump, such as a gear pump, combined with an additional accumulator (i.e., a hydraulic accumulator;, a spring-loaded piston, an expandable tube, or some instrument of this nature), be attached between the extrusion barrel and the shut-off valve (before the main accumulator).
  • a positive displacement pump such as a gear pump
  • an additional accumulator i.e., a hydraulic accumulator;, a spring-loaded piston, an expandable tube, or some instrument of this nature
  • the plasticating screw is still rotating and the generated polymer/gas mixture is accumulated m the newly added accumulator
  • the temporarily stored polymer/gas mixture in the new accumulator is moved to the main accumulator to be injected in the next cycle
  • Our invention would ensure that the pressure in the extrusion ban el can be relatively well maintained to be constant, and that consistent gas dosing can be attained to achieve a uniform polymer/gas mixture regardless of the pressure fluctuations in the main accumulator caused by the injection and molding operations.
  • a uniform polymer/gas mixture with a constant gas-to- ⁇ olymcr weight ratio in which the gas has been completely (or Substantially) dissolved provides the basis for producing a uniform and fine-celled foam structure unlike the existing structural foam molding technologies
  • Use of a gear pump is preferred because it entails a very important benefit of controlling the pressure in the extrusion barrel and thereby maintaining a consistent polymer-to-gas weight ratio.
  • the pressure in the extrusion barrel will be relatively well maintained due to the positive displacement nature of the gear pump for the viscous polymer melts. Since the gas flow rate is a sensitive function of the barrel pressure, a constant gas flow rate can be obtained by having a constant pressure in the extrusion barrel as mentioned above.
  • the flow rate of polymer/gas mixture can be controlled by varying the rotational speed of the gear pump. Therefore, by independently controlling both the flow rates of gas and polymer/gas mixture, the polymer flow rate can also be controlled, and thereby a consistent polymer-to-gas weight ratio can be easily achieved. As a result, the uniform state of polymer/gas mixtures can be easily accomplished.
  • the application of a gear pump confers this veiy unique advantage, which may not be achieved with a shut-off or non-returnable check valve.
  • this accumulator can be hydraultcally driven so that a constant melt pressure can be maintained.
  • a piston loaded with a spring can also be used as an accumulator. Tn the case of using a spring-loaded piston, the pressure will increase over time as the melt/gas mixture is accumulated in the accumulator because the force of spring (and thereby the melt pressure) is proportional to the displacement of the piston.
  • An expandable tube can also function the same as a spring-loaded piston. Although the pressure of the accumulated melt increases, the gear pump will prevent the pressure increase in the barrel corresponding to this pressure increase in the accumulator.
  • shut- off valve or a non-returnable check valve
  • an additional accumulator needs to be installed before the shut-off valve (or non- returnable check valve).
  • This accumulator stores the formed polymer/gas mixture during the injection operation. If a hydrauli cally driven constant-pressure cylinder is used, the gas amount can be relatively easily adjusted accordingly because of the constant accumulator pressure (and thereby the constant barrel pressure). So in the case of using no gear pump, use of a hydraulically driven accumulator is strongly recommended. If a spring-loaded piston or an expandable tube is used as the accumulator instead of a hydraulic one, the accumulator pressure will be increased over time (as described above). Since there is no gear pump between the extrusion barrel and the additional accumulator, the barrel pressure will also be increased over time. For a small shot-sized product (i.e., with a short injection time), this may not affect the consistency in the final product significantly.
  • the filial product may have non-uniform cell structures. But because of the additionally attached accumulator and the continuous rotation of the screw, the dispersion, of gas in the polymer melt is still better than that in the currently practiced structural foam molding technology, and consequently, lhe eel] structure is better than that of the current structural foams.
  • complete dissolution of the injected gas may be performed by maintaining a "sufficiently high pressure" in both the extrusion barrel and the accumulators.
  • a "sufficiently high, pressure” indicates that the melt pressure is much higher than the solubility pressure for the given amount of gas injected into the polymer melt.
  • dissolution of the injected gas in the polymer melt is facilitated.
  • maintaining a "sufficiently high pressure" after complete dissolution of gas indicates mat the formation of a second phase in the polymer melt is prevented during the accumulation, stage.
  • solubility pressure for the appropriate gas content that can produce a fine-celled structure is relatively low (e.g., 140 psi ⁇ 1 ,400 psi for 0.1 % ⁇ 1.0% N 2 in HDPE) compared to the pressure capacity of any existing low-pressure prepiasticating- Lype structural foam molding machines (-3,000 psi), a "sufficiently high pressure" can be easily maintained in the retrofitted low-pressure structural foam molding machines.
  • a low pressure can also be chosen during the practice of our invention in the extrusion barrel and/or the accumulators to mechanically disperse the injected gas in the polymer melt as described in US Patent 4,548,776.
  • the pressure in the accumulator can be chosen to be lower than the solubility pressure during some period of time.
  • the extrusion barrel pressure may be below the solubility pressure so that the injected gas bubbles can be mechanically dispersed by the mixing actions of the mixing elements on the screw (and optionally the static mixers) instead of completely dissolving the gas into the polymer matrix.
  • the injected gas (especially Nj with a low solubility) may not be dissolved completely in the polymer melt because of the low solubility of ga$ and/or the short residence time. Then the dispersed second-phased gas pockets will be most likely the nuclei of the cellular structure in the molded foams regardless of the added nucleating agent. Because of the consistency in the gas content in the polymer using the additional accumulator and the gear pump, the cellular structure will be uniform.
  • the cell-nuclei density will be governed by the distributed nucleating agent.
  • any commonly used nucleating agents such as talc, CaCO 3 , or a small amount of second phase polymer in blend
  • these nucleating agents can he added and distributed in the polymer matrix to produce a fine-cell structure.
  • a reasonably high cell density of 10 ⁇ 10 cells/cm 3 can be easily achieved from any conventionaj extrusion foam processing (CP. Park, Chap 8, Polyojef ⁇ n Foam, in: Polymeric Foams and Foam Technology, 2nd Ed , D.
  • this cell density is easily obtained in extrusion because a uniform concentration of gas in the polymer can be relatively easily obtained in extrusion through the constantly maintained barrel pressure From this, we could theoretically conclude that a similar cell density of 10 4 - 10 7 cells/cm 3 should be obtained from, the structural foam molding as long as the gas dissolves in the polymer matrix uniformly.
  • talc or CaCo 3 has already been used in the existing structural foam molding technology and that heterogeneous nuclcation will occur once there is gas uniformly dissolved in the polymer.
  • the added nucleating agents cannot play the same role that they play in extrusion foaming.
  • the undissolvcd pockets typically govern cell nuclcation and a very low cell density in the range of 10 1 ⁇ 10 3 cells/cm 3 (typically with a large cell size above ⁇ mra) is obtained even though talc is added.
  • this newtechnology i.e., by dissolving the blowing agent uniformly through the attached gear pump and additional accumulator, we can produce foams with cell densities that match those of extruded foams. This means that the cell nucleation mechanism in the new technology is almost the same as that observed in conventional extrusion foaming.
  • CBA chemical blowing agent
  • any high molecular-wcight blowing agents siich as HCs, RFCs, HCFCs, and FCs, can also be used with a proper amount ofnucleating agent.
  • the present invention may also be used to produce fine-celled wood fiber/plastic composite structural foams. In this case, both wood fiber and void can be used Io decrease the expensive plastic cost. Unlike in extrusion, lhe volatile generated from the wood fibers are liquified under pressure in the mold and only the added blowing agent contributes to the void fraction. The volatiles/extractions generated from the wood fibers will play as a nucleating agent together with any added nucleating agent.
  • the present invention is better than the currently practiced CBA based foam injection molding of wood fiber composites (A.IC. Blcdzki and O. Faruk, Blowing Agents and Foam Processing, Stuttgart, Germany, May 10-1 1 , 2005).
  • the polymer/WF composite should be heated to a high temperature and a significant amount of volatilcs will be generated as described in US Patent 6,936,200.
  • the present invention of making the injected N 2 be better dispersed atid play a proper role as the blowing agent can avoid the need to overheat the materials and therefore the generated volatilcs will be much less, indicating better wood fiber composite foams.
  • the extrusion barrel (1) melts and moves the polymer forward through the rotation of its plasticating screw (2).
  • the gaseous blowing agent originally contained in a gas cylinder (3) is pressurized first and then mctered by a gas pump (4) while being consistently injected into the extrusion barrel (1) through a gas injection port (5), which is mounted on the extrusion barrel (1).
  • the gas initially mixes with the polymer melt and forms a second phase; it gradually dissolves into the polymer melt through the rotating motion of the screw (2).
  • the screws (2) may have optionally some mixing sections to enhance the mixing and dissolution of gas m the polymer melt. The art of using mixing section of the screw is well known.
  • a gear pump (7) as discussed earlier, the pressure in the extrusion barrel (1) can be relatively well maintained because of the positive displacement nature of flue gear pump (7).
  • shut-off valve or a non-returnable check valve
  • the mixture is then charged into the main accumulator (10) to accumulate a desirable shot size.
  • a sufficiently high back pressure can be applied to the mixture using a hydraulic system (1 1).
  • the mixture is ready to be injected into the mold (12).
  • the shut-off valve (9) is closed; a hydraulic pressure is applied on the piston of the hydraulic system (11) for injection.
  • the nozzle shut-off valve (13) mounted between, the accumulator (10) and the mold (12) is opened; the foamablc mixture is forced into the mold cavity through the runner and the gate, and foaming occurs simultaneously.
  • the main shut-off valve (9) is closed. But the plasticatmg screw (2) in the extrusion barrel (1) is continuously rotating at the same speed and the gas is also continuously injected into the melt.
  • the gear pump (7) is running at the same speed.
  • This continuously formed polymer/gas mixture is now accumulated in the secondary accumulator (15) driven by hydraulic system (16) during injection (or moid filling).
  • the nozzle shut-off valve (13) is closed and the main shut-off valve (9) is opened.
  • the main accumulator (10) start to receive the polymer/gas mixture from the gear pump (7).
  • the secondary accumulator (15) starts to discharge the stored polymer/gas mixture to the main accumulator (10) as well. This can be done by setting up a slightly higher pressure in the secondary accumulator (15). The higher pressure in the secondary accumulator (15) will not affect the barrel pressure much because of the gear pump (7).
  • the molded part (14) is cooled, it is ejected out to empty the mold and to be ready for the next cycle.
  • FIG 2 shows another configuration. This system is exactly the same as that of Option 1 (shown in Figure 1) except for the restraining mechanism of the secondary accumulator (15). Instead of using a hydraulic system that is operated under a constant pressure, a spring-loaded piston (or an expandable rube) (24) is used as the secondary accumulator. The exact same operation is used as in the case of Option 1 and the only difference is the pressure in the secondary accumulator (15). But the pressure changes in the secondary accumulator (15) could not affect the barrel pressure significantly because of the gear pump (7).
  • a spring-loaded piston or an expandable rube
  • FIG 3 shows a variation of Option I (shown in Figure 1 )
  • Option 1 shows a variation of Option I (shown in Figure 1 )
  • the only difference from Option 1 is that there is no gear pump used between the cxtaision barrel (1) and the secondary accumulator ( 1). instead, a non-returnable check valve (6) can be optionally used.
  • the constant pressure-driven hydraulic piston (16) will make the pressure in the barrel (1) relatively constant during injection. But there would be slight: pressure fluctuations due to the pressure difference in the accumulators.
  • FIG 4 shows a variation of Option 2 (shown in Figure 2).
  • Option 2 shows a variation of Option 2 (shown in Figure 2).
  • the only difference from Option 2 is that there is no gear pump used between the extrusion barrel (1) and the secondary accumulator (15). Instead, a non-returnable check valve (16) can. be optionally used.
  • a spring-loaded piston (or an expandable tube) (24) is used for the secondary accumulator (15), the accumulator pressure will increase as the accumulated amount increases. If the shot size is small and therefore the injection time is short, the changes of the gas content jn the polymer melt due to the increase in the pressure of secondary accumulator (15) (and thereby due to the increase m the barrel pressure) may not be large.
  • Figure 5 shows another variation of Option 1.
  • the differences arc tbatno secondary accumulator is added and a non-returnable check valve (S) is used between the main accumulator (10) and the gear pump (7) instead of a shut-off valve.
  • S non-returnable check valve
  • the non- returnable check valve (8) allows the melt flow only in one direction, i.e., from the gear pump (7)to the main accumulator (10), but not in the opposite direction, a continuous screw rotation with a constant barrel pressure can be realized. This will simplify the modification to the existing system.
  • the gear pump (7) may be broken down easily.
  • a lower injection pressure in the accumulator (10) may have to be used.
  • the shot-size control will be more difficult.
  • Figure 6 shows a variation pf Option 3. The difference is that a non-returnable check valve (8) is used between the secondary accumulator (15) and the main accumulator (10) instead of a shut-off valve. Due to the one-way flow feature of the non-returnable check valve (8), i t will be relatively easier to realize a continuous screw rotation without strict timing control of valve operations during injection and molding operations.
  • Figuie 7 shows another system configuration. Instead of utilizing two different accumulators after the gear pump, as shown in the other options, two compatible accumulators (10 and 18) and molding units (12 and 20) are attached after the gear pump (7) so that each accumulator-molding unit can be alternating.
  • the other shut-off valve (17) attached to the other accumulator (18) is closed Once lie required amount of material is stored in the accumulator (10), the shut-off valve (9) is ;loscd and at the same time, the other shut-off valve (17) is opened to accumulate the lowing polymer/gas mixture to the other accumulator (18) During this accumulation process in the other accumulator, injection (or mold filling) is performed in the first nolding system.
  • the first nozzle shut-off valve (13) is opened and the foamablc )olymer/gas mixture stored in accumulator (10) is injected into the mold (12) under high >ressure in the hydraulic system (11).
  • the nozzle shut-off 'alve (13) is closed and the accumulator (10) is ready to receive the polymer/gas mixture.
  • the molded part (14) is cooled, it is ejected out.
  • the other shut-off valve (17) is closed nd the first shut-off valve (9) is opened simultaneously.
  • the other lozzlc shut-off vcilve (21) is opened and the injection and molding operations aie onducted in the other molding system.
  • This alternating accumulation, and injection, will c continued.
  • the amount of polymer/gas mixture can be controlled by the rotational ..pee ⁇ oase ⁇ on rne snot sizes ot these two molding systems and the required cooling times.
  • more than two accumulators and molding units can be used.
  • Figure 8 shows another variation of Option 7. The difference is that a bypass accumulator will be additionally used for the r ⁇ ulti-moldmg system.
  • a gear pump and a bypass accumulator are used to facilitate the achievement of a continuous rotation of plasticating screw and a consistent gas dosing.
  • Figure 9 shows another variation of Option 7.
  • the difference is no gear pump is added between the extrusion barrel (1) and the main accumulators (10 and IS). Tnstcad, an accumulator is attached. In this case, a continuous rotation of plasticating screw and a consistent gas dosing can be still realized through close control of the shut-off valves (9 and 17).
  • the modification for retrofitting to the existing system is simplified using this option.
  • Figure 10 shows a variation of Option 1 for a multi-accumulator and single-mold system that has a single large cavity or multiple cavities in the mold.
  • both the accumulators (10 and 18) and the mold cavities can be filled in sequence, and continuous rotation of the plasticating screw and consistent gas dosing can be easily achieved.
  • injection may need to be done by multi accumulators in sequence.
  • the gear pump (7) With the gear pump (7), the pressure m tbe barrel (1) will be maintained easily.
  • Figure 11 shows a variation of Option 10 for a multi-accumulator and single-mold system that has a single large cavity or multiple cavities in the mold.
  • a bypass accumulator will be additionally used for the multi-molding system.
  • a gear pump and a bypass accumulator are used to facilitate the achievement of a continuous rotation of plasticating screw and a consistent gas dosing.
  • injection can be done by multi accumulators simultaneously or in sequence. Even in. the case of simultaneous injection, the accumulators can be filled in sequence, and the secondary accumulator (hydraulic piston, spring-loaded piston, or expandable tube) (23) is helpful to accommodate the melt during injection so that a continuous rotation of extruder screw and a consistent gas dosin g can be realized.
  • Figure 12 shows a variation of Option 10. The difference is that no gear pump is added between tbe extrusion barrel (1) and line accumulators (10 and 18). Instead, an accumulator is attached. In this case, a continuous rotation of plasti eating sci evv and a consistent gas dosing can be still realized through close control of the shut-off valves (9 and 17). The modification for retrofitting to the existing system is simplified using this option.
  • HDPE H5534, Equistar Chemical
  • Talc and N 2 were used as the nucleating agent and blowing agent, respectively, in the critical experiments.
  • a total of 21 sets of experiments were conducted while varying the talc size, talc content, and N 2 content as shown in Table 1.
  • talc size two kinds of talc (0.8 microns and 2.5 microtis) were used The talc content was varied from 0.1 % to 1.0% whereas the N 2 content was varied from 0.1% to 0,5% (at relatively low levels in consideration of the low solubility of N 2 ).
  • the void fraction was varied by controlling the shot size of the polymer/gas mixture in the main accumulator for the fixed volume of mold cavity.
  • various void fractions in the range of 10% ⁇ 60% were successfully achieved without Formation of any large gas pockets or a non-uniform cell structure unlike the existing structural foams.
  • the cell size was greater with afi increase in the void fraction by using a reduced shot size, a very uniform cellular structure was achieved. This indicates that a very high void fraction up to 60% can be obtained from this tec nhology without forming any large gas pockets or a non-uniform cell structure. Therefore, even for a high void fraction, the rate of scrapping/recycling the defective structural-foam products due to the formation of large gas pockets will be completely removed using the present technology.

Abstract

Technologie évoluée de moulage de mousse structurée permettant d'améliorer la dispersion de l'agent gonflant dans la matrice polymère, ce qui permet d'améliorer l'état existant de la technique bien connue reposant sur une technologie de moulage de mousse structurée dont le fondement est la machine de moulage par injection du type à préplastification (en arrangement appelé « piggy-bag »). La mise en place d'un système de maintien du flux en fusion de matrice polymère, de préférence par le biais d'un accumulateur additionnel et d'une pompe à engrenages, permet de stabiliser les conditions de traitement pour disperser le gaz le gaz injecté de façon plus uniforme dans la matrice polymère. Une telle technologie permet de réduire la taille de cellule des mousses structurées, d'uniformiser la structure de cellule, d'augmenter la partie de vide (c'est-à-dire d'accentuer les économies de matériau), de réduire le tourbillon de surface et de réduire aussi le contraste de ligne de soudure.
EP06820982A 2005-09-02 2006-08-30 Dispositif et procede pour le moulage evolue de mousse structuree Withdrawn EP1937455A2 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
CA 2517995 CA2517995A1 (fr) 2005-09-02 2005-09-02 Dispositif et methode de moulage perfectionne de mousse structuree
US11/219,309 US20070052124A1 (en) 2005-09-02 2005-09-02 Apparatus and method for advanced structural foam molding
PCT/IB2006/003364 WO2007026257A2 (fr) 2005-09-02 2006-08-30 Dispositif et procede pour le moulage evolue de mousse structuree

Publications (1)

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EP1937455A2 true EP1937455A2 (fr) 2008-07-02

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WO2020061535A1 (fr) * 2018-09-21 2020-03-26 Nike, Inc. Système et procédé de moulage

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US5968429A (en) * 1997-03-20 1999-10-19 Eastman Chemical Company Apparatus and method for molding of polyester articles directly from a melt
US6322347B1 (en) * 1999-04-02 2001-11-27 Trexel, Inc. Methods for manufacturing foam material including systems with pressure restriction element

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CN110253824A (zh) * 2019-05-31 2019-09-20 界首市旭升塑胶制品有限公司 一种塑胶鞋吹气发泡注射机

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