US3624192A - Production of foamed resins - Google Patents

Production of foamed resins Download PDF

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Publication number
US3624192A
US3624192A US726857A US3624192DA US3624192A US 3624192 A US3624192 A US 3624192A US 726857 A US726857 A US 726857A US 3624192D A US3624192D A US 3624192DA US 3624192 A US3624192 A US 3624192A
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Prior art keywords
resin
die
zone
foamed
slits
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Expired - Lifetime
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US726857A
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English (en)
Inventor
John Gerald Mccoy
William Rees Foster
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MENSANTO CHEMICALS Ltd
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MENSANTO CHEMICALS Ltd
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    • 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
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/468—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length in a plurality of parallel streams which unite during the foaming
    • 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
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/50—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying
    • B29C44/505—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying extruding the compound through a flat die
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2007/00—Flat articles, e.g. films or sheets

Definitions

  • This application relates to the extrusion of foamable thermoplastic polyvinylaromatic resins and more particularly relates to improve processes for extruding such resins to form foamed products, e.g., low-density boards. which are strong and have smooth surfaces.
  • foamed thermoplastic resins such as foamed polystyrene are useful industrial products. These products are often made by molding processes, but extrusion processes are often considered to be more convenient. However, extrusion processes present difficulties in some instances, e.g., in the production of foamed board of good quality.
  • board is used to describe flat sheet material of substantial thickness, usually at least 0.75 inch and often 1.54 inches thick, such as the sheet materials frequently used as insulating media.
  • An object of the invention is to provide novel processes for extruding foamable thermoplastic polyvinylaromatic resins.
  • Another object is to provide novel processes for preparing extruded foamed boards, particularly low-density boards, having a good surface finish.
  • the die comprises a mild steel block 1 having 82 cylindrical channels 2 extending into it from one side.
  • the channels are arranged to communicate with a rectangular network of three horizontal and I7 vertical intercommunicating slits 3.
  • Each horizontal slit thus has 16 channels associated with it, and each vertical slit has two channels.
  • the network of slits communicates with a zone defined by the profiled surfaces 6 and 7 of two mild steel plates 8 and 9.
  • each of the plates is greater (usually about l.l-l .75 times greater) than the overall length of the slit network to ensure that the foamed resin surface is always in contact with the profiled surfaces during its initial expansion.
  • the concave surfaces of the plates adjacent to the slit network are spaced apart at a distance corresponding approximately to the width of the slit network.
  • the plates 8 and 9 are cut away as shown at 10 and Il so as to minimize the area of contact with the block I and thus minimize heat transfer from the die outlet to the plates, and they have adjustable clamp mountings (not shown) by means of which they can be set at various distances from each other as desired.
  • a series of liquid-cooling channels (not shown) is drilled through each of the plates.
  • the die also has means (not shown) for attaching it to the front end of an extruder so that, when the die is in use, a foamable resin such as foamable polystyrene is fed into the network of slits and thence through the zone into the atmosphere.
  • a foamable resin such as foamable polystyrene is fed into the network of slits and thence through the zone into the atmosphere.
  • the concave surfaces of the plates are so shaped that they conform to the corresponding surfaces of the freely expanding resin without exerting a substantial compressive force thereon.
  • EXAMPLE Part A Using the die assembly described above in which the overall length of the slit network is 1.535 inches, the width of the network is 0.785 inch, the width of the individual slits is 0.025 inch, the plates are clamped so that they are 0.79 inch apart at the lips of the die orifice and 1.375 inches apart at the end of the expansion zone, and the radius of curvature of the profiled surfaces of each of the plates is 0.5 inch, extrude foamable polystyrene containing 0.25 percent by weight of silica and 10 percent by weight of butane at a pressure of 700 psi. and a temperature of C. through the die at a flow rate of 15 pounds per hour, while maintaining the temperature of the plates at 15 C. by circulating cold water through the cooling channels.
  • the product is a foamed polystyrene board having a width of 2.75 inches, a thickness of 1.625 inches, an overall average density of 1.25 pounds per cubic foot, good strength in both the transverse and longitudinal directions, and smooth top and bottom surfaces with an excellent finish.
  • Part B Repeat Part A except for extruding the foamable polystyrene through the die directly into the atmosphere instead of using the plates to define a zone.
  • the product is a foamed polystyrene board, the density of which is similar to that of the board of Part A, but the surface finish of which is inferior in that it is slightly ribbed.
  • the die used in the practice of the invention is one having an orifice from which an extruded freely expanding and foaming resin issues with a rectangular or substantially rectangular cross section.
  • the die is one which incorporates features designed to increase its resistance to resin flow, e.g., the dies described in British Pat. Nos. 1,034,120, 1,084,000, and 1,098,408 and in copending US. application Ser. No. 726,06 l, filed May 2, 1968 in the names of William R. Foster and Stanley J. Skinner and assigned to the assignee of the present application.
  • British Pat. No. 1,034,120 describes a die having extending into it at its inlet end a plurality of separate channels communicating with a number of slits arranged in the form of a network at the outlet end of the die, each slit having a row of channels associated with it.
  • British Pat. No; 1,084,000 describes a die having a plurality of obstructions transversely distributed therein so that, when a foamable resin is extruded through the die, the obstructions together offer a substantial resistance to the flow of resin.
  • British Pat. No. 1,034,120 describes a die having extending into it at its inlet end a plurality of separate channels communicating with a number of slits arranged in the form of a network at the outlet end of the die, each slit having a row of channels associated with it.
  • British Pat. No; 1,084,000 describes a die having a plurality of obstructions transversely distributed therein so that, when a foamable resin is extruded through the die, the obstructions
  • 1,098,408 describes a particularly useful type of die which comprises a plurality of channels extending into it at its inlet end and communicating with a number of slits arranged to form the meshes of a network at the outlet end of the die, each of at least the majority of the meshes having a substantially central passage leading back from the front face of the die to a point nearer the inlet end of the die (preferably to the inlet end of the die) and not communicating directly with the slits.
  • the zone-defining surfaces have a concave curved cross section that preferably conforms exactly to the corresponding surfaces of the freely expanding and foaming resin.
  • One manner in which it is possible to machine the surfaces so that they conform exactly is by using a working drawing produced from a photograph of the foaming resin extruding freely from the die orifice. Exact conformity is not essential, however, and a cross section corresponding to an arc of a circle usually provides a sufficiently good approximation. Other simple geometric shapes such as part of a parabola can also be used if desired.
  • the zone-defining surfaces are normally spaced apart by a distance equal to or slightly greater than the width of the die orifice, and from this point they diverge as the distance from the die increases, reaching their greatest distance apart where the foamed resin is completely expanded. Preferably they thereafter extend parallel to each other for a short distance. Their greatest distance apart depends of course on the overall width of the die orifice, the degree to which the foamable resin expands, and to some extent on the type of die which is used, but it is generally about 1.2-6 times the width of the die orifice. When the die incorporates features designed to increase the resistance to resin flow, the greatest distance apart of the zone-defining surfaces is usually l.24 times, particularly 1.5-3 times, the overall width of the die orifice. For example,.when the die is of the type described above and in British Pat. No. 1,098,408 particularly good results are obtained using zone-defining surfaces having a greatest distance apart corresponding to twice the overall width of the die orifice.
  • the curvature of the zone-defining surfaces is dependent on the thickness of the foamed board which it is desired to extrude, thicker boards normally requiring a larger radius of curvature for optimum results.
  • thicker boards normally requiring a larger radius of curvature for optimum results.
  • excellent results are obtained when each of the zone-defining surfaces has a section corresponding to a segment of a circle having a radius of 0.5 inch.
  • each of the second pair of surfaces can be part of an endless belt carried on rollers.
  • the belt can be driven so that the part in contact with the resin moves along with it, or it can be free to move so that it is driven by the fractional force between it and the moving resin.
  • each endless belt is attached to one of the contoured surfaces so that the belt and the-contoured surface move together when the position of the latter is adjusted.
  • each of this pair of surfaces can be constituted by a roller of relatively large diameter, or there can be a series of rollers traversed in succession by the extruding resin.
  • the polyvinylaromatic resin which is extruded in accordance with the invention is a polymer of one or more vinyl or vinylidene aromatic monomers such as styrene, a chlorostyrene, alpha-methylstyrene, m-, or p-methylstyrene, other aralkylstyrenes, etc., including interpolymers of such monomers with one or more copolymerizable ethylenicallyunsaturated monomers such as acrylonitrile, methacrylonitrile, vinyl chloride, vinyl acetate, methyl and other alkyl acrylates and methacrylates, etc.
  • vinyl or vinylidene aromatic monomers such as styrene, a chlorostyrene, alpha-methylstyrene, m-, or p-methylstyrene, other aralkylstyrenes, etc.
  • the invention is particularly applicable to polystyrene resins, such as polystyrene itself or a toughened polystyrene, i.e., a polystyrene having physically or chemically combined therewith a minor proportion, e.g., l-l5 percent by weight, of a natural or synthetic rubber, e.g., substantially linear or branched polymers of conjugated dienes, such as butadiene, isoprene,. etc., including copolymers thereof with lesser amounts of comonomers such as styrene, acrylonitrile, methyl methacrylate, etc.
  • a natural or synthetic rubber e.g., substantially linear or branched polymers of conjugated dienes, such as butadiene, isoprene,. etc., including copolymers thereof with lesser amounts of comonomers such as styrene, acrylonitrile, methyl methacrylate, etc.
  • the resin is in admixture with a blowing agent, which is preferably a normally gaseous substance but which can be a volatile liquid.
  • a blowing agent which is preferably a normally gaseous substance but which can be a volatile liquid.
  • the blowing agent is one that is normally gaseous but which, while percent, pressure before extrusion, is present in the liquid state.
  • volatile substances that can be used are lower aliphatic hydrocarbons such as ethane, propane, a butane or butene, a pentane or pentene, etc., lower alkyl halides such as methyl chloride, trichloromethane, l,2-dichlorotetrafluoroethane etc.; and inorganic gases such as carbon dioxide and nitrogen.
  • the blowing agent can also be a chemical blowing agent, e.g., a bicarbonate'such as sodium bicarbonate, ammonium bicarbonate, etc., or an organic compound that yields nitrogen on heating such as dinitrosopentamethylenediamine, barium azodicarboxylate, etc.
  • a chemical blowing agent e.g., a bicarbonate'such as sodium bicarbonate, ammonium bicarbonate, etc.
  • an organic compound that yields nitrogen on heating such as dinitrosopentamethylenediamine, barium azodicarboxylate, etc.
  • the amount of blowing agent employed is often in the range of 3-30 percent, especially 7-20 percent, based on the weight of the resin. For example, excellent results are achieved by the use of 7'l5 percent by weight of butane in conjunction with polystyrene.
  • the foamable resin preferably also contains a nucleating agent, which assists in the formation of a large number of small cells.
  • the conventional nucleating agents can be employed, e.g., finely divided inert solids such as silica or alumina, preferably in conjunction with zinc stearate, or small quantities of a substance that decomposes at the extrusion temperature to give a gas.
  • Exemplary of the latter class of nucleating agents is sodium bicarbonate, optionally used in conjunction with a weak acid such as tartaric or citric acid.
  • a small proportion of the nucleating agent e.g., up to 5 percent by weight of the resin, is usually effective.
  • the dimensions of the orifice are less than the cross section of the desired product. Expansion takes place along both dimensions of the die, but generally greater expansion takes place across the width of the die than along its length. In this way a board is produced.
  • a suitable die size an extruded product of the desired cross section can be obtained.
  • a foamed board having a width of 4 feet or more and a thickness of up to perhaps 2 inches can be produced. Generally, the thickness is at least 0.75 inch, e.g., 1.5-4 inches.
  • an increase in the dimensions of the board can be obtained by heating it, preferably by exposing it to steam or hot Water in a suitable container for a few moments. Such treatment is usually more effectively conducted after the board has been exposed to the atmosphere for a day or two.
  • the surfaces defining the zone of lower pressure are maintained at a temperature lower than the extrusion temperature.
  • Oilor water-cooling can be employed if desired, and it can be applied, e.g., through channels within the surfaces.
  • air cooling is sufficient, although the backs of the surfaces can be provided with fins in order to increase the cooling rate.
  • the surfaces of the zone lead off directly from the die orifice. It is desirable to prevent as far as possible the conduction of heat from the extruder to the cooled surfaces. This can be achieved, e.g., by the use of a thermally insulating material or by arranging for the area of contact between the surfaces and the extruder to be as small as possible.
  • Cooling of the surfaces causes a certain amount of drag" as the resin is extruded so that the viscosity of the resin in contact with the surfaces is much higher than that of the resin within the extruder, and in fact the resin flow through the zone is normally of a "plug character.
  • the temperature of the zone-defining surfaces i.e., the average temperature of the mass of metal
  • the temperature of the zone-defining surfaces depends partly on the nature of the resin and any plasticizing effect of the blowing agent, but it is usually l0l20 C. lower, preferably 60-l05 C. lower, than the extrusion temperature.
  • the zone-defining surfaces it is usually suitable for the zone-defining surfaces to be cooled to a temperature of l040 C.
  • the extrusion temperature depends to some extent on the softening point of the resin being extruded, but in general temperatures of 95-140 C., are suitable. For example, when foamable polystyrene is being extruded, the temperature is frequently 1 130 C., particularly about 120 C.
  • the pressure within the extruder is sufficient to prevent any substantial foaming of the resin until it leaves the die orifice and enters the zone of lower pressure.
  • pressures greater than 250 p.s.i., especially 250-5,000 p.s.i., can be employed.
  • the pressure is 300-1 ,000 psi.
  • the processes and die assemblies of the invention are of particular value in the production of extruded foamed material, e.g., board having a low density, e.g., 0.9-1.5 pounds per cubic foot, and a substantial thickness, i.e., at least 1 inch and, e.g., up to about 2.5 inches.
  • a broader range of density can be produced, although there is often little advantage to be gained by increasing it above 2 or 3 pounds per cubic foot.
  • the extruded resin e.g., a board has substantially flat upper and lower surfaces and slightly curved edges. These edges can be trimmed if required, but they are often sufficiently true for may purposes.
  • a process for the production of foamed thermoplastic polyvinylaromatic resins having an improved surface finish which comprises extruding a foamable thermoplastic polyvinylaromatic resin through a rectangular die orifice into a zone of lower pressure such that foaming of the resin occurs as it moves through the zone, said zone being defined by a pair of opposing concave surfaces maintained at a temperature lower than the extrusion temperature and curved so that they substantially conform to the corresponding surfaces of the freely expanding resin whereby substantially no compressive force is exerted by said opposing concave surfaces upon said freely expanding resin.
  • each of at least the majority of the meshes of the slit network has a substantially central passage leading back from the front face of the die to the inlet end of the die and not communicating directly with the slits.
  • grooves extending from the outlet end of each of a least the majorityof the passages toward the outlet of its surrounding mesh of slits are provided in the front face of the die to assist in ensuring that a strand of foamed resin extruded from each passage substantially fills the space formed by the enveloping foamed resin issuing from the surrounding mesh of slits.
  • zone-defining surfaces have a concave curved cross section that conforms exactly to the corresponding surfaces of the freely expanding resin.
  • zone-defining surfaces have a concave cross section corresponding to an arc of a circle.
  • zone-defining surfaces reach their greatest distance apart where the foamed resin is completely expanded and thereafter extend parallel to each other.

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  • Extrusion Moulding Of Plastics Or The Like (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
US726857A 1967-05-19 1968-05-06 Production of foamed resins Expired - Lifetime US3624192A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB23303/67A GB1166937A (en) 1967-05-19 1967-05-19 Improvements in or relating to The Production Of Foamed Resins

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US64554A Expired - Lifetime US3694116A (en) 1967-05-19 1970-08-17 Apparatus for the production of foamed resins

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US (2) US3624192A (en:Method)
BE (1) BE715259A (en:Method)
DE (1) DE1778541A1 (en:Method)
FR (1) FR1566936A (en:Method)
GB (1) GB1166937A (en:Method)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3713762A (en) * 1970-06-26 1973-01-30 Kasei C Co Ltd Apparatus for the extrusion molding of foamable plastics
US3888614A (en) * 1970-11-03 1975-06-10 Monsanto Chemicals Apparatus for producing a foamed resin sheet in a curved diverging expansion zone
US3897528A (en) * 1973-11-21 1975-07-29 Dow Chemical Co Method for the extrusion of thermoplastic foam
EP0083177A1 (en) * 1981-12-25 1983-07-06 Japan Styrene Paper Corporation Method for producing polystyrene resin foam
US4536357A (en) * 1983-01-28 1985-08-20 Sekisui Kaseihin Kogyo Kabushiki Kaisha Method and apparatus for preparing multi-cellular foamed board of thermoplastic resin
EP0279668A3 (en) * 1987-02-18 1989-10-11 The Dow Chemical Company Faom structure of coalesced foam strands of profiles
US6005013A (en) * 1995-08-14 1999-12-21 Massachusetts Institute Of Technology Gear throttle as a nucleation device in a continuous microcellular extrusion system
US6284810B1 (en) 1996-08-27 2001-09-04 Trexel, Inc. Method and apparatus for microcellular polymer extrusion
US6884377B1 (en) 1996-08-27 2005-04-26 Trexel, Inc. Method and apparatus for microcellular polymer extrusion
US20170100870A1 (en) * 2014-12-17 2017-04-13 Poly-Wood, Llc Extruded board with realistic appearance
EP3209478A4 (en) * 2014-10-23 2018-07-04 3M Innovative Properties Company Foaming die and method of use
US10449702B2 (en) 2014-10-23 2019-10-22 3M Innovative Properties Company Laterally-coalesced foam slab

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE757054R (fr) * 1969-10-06 1971-04-05 Monsanto Chemicals Perfectionnements aux mousses de
JPS5546858B2 (en:Method) * 1972-08-15 1980-11-26
US4480983A (en) * 1982-05-13 1984-11-06 Motorola, Inc. Collet and method for dispensing viscous materials

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CA451864A (en) * 1948-10-12 Edward Maier Robert Extrusion process and apparatus
US2537977A (en) * 1948-07-15 1951-01-16 Dow Chemical Co Method of making a shaped thermoplastic cellular product
US2644983A (en) * 1950-06-29 1953-07-14 Us Rubber Co Tube extrusion
US2687997A (en) * 1949-12-10 1954-08-31 Marchand John Felix Dialyzers
US2893877A (en) * 1958-07-02 1959-07-07 Monsanto Chemicals Method for packaging meat
US3406230A (en) * 1963-06-24 1968-10-15 Monsanto Chemicals Extrusion of resins
US3427371A (en) * 1964-12-29 1969-02-11 Monsanto Chemicals Process and apparatus for extruding foamed articles free from warping
US3431163A (en) * 1964-07-09 1969-03-04 Monsanto Chemicals Foamed aliphatic resin products having elongated cells at right angles to a surface skin and their manufacture
US3431164A (en) * 1964-06-02 1969-03-04 Monsanto Chemicals Foamed polyvinylaromatic resin products having elongated cells at right angles to a surface skin and their manufacture

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Publication number Priority date Publication date Assignee Title
US3349434A (en) * 1961-12-18 1967-10-31 Alimentaire G A S A Soc Gen Extrusion of articles with ribbed full walls
DE1230551B (de) * 1963-07-09 1966-12-15 Reifenhaeuser Kg Vorrichtung zum kontinuierlichen Strangpressen von Formkoerpern
US3466705A (en) * 1966-03-07 1969-09-16 Owens Illinois Inc Apparatus for extruding foamable plastic materials in tubular form

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA451864A (en) * 1948-10-12 Edward Maier Robert Extrusion process and apparatus
US2537977A (en) * 1948-07-15 1951-01-16 Dow Chemical Co Method of making a shaped thermoplastic cellular product
US2687997A (en) * 1949-12-10 1954-08-31 Marchand John Felix Dialyzers
US2644983A (en) * 1950-06-29 1953-07-14 Us Rubber Co Tube extrusion
US2893877A (en) * 1958-07-02 1959-07-07 Monsanto Chemicals Method for packaging meat
US3406230A (en) * 1963-06-24 1968-10-15 Monsanto Chemicals Extrusion of resins
US3431164A (en) * 1964-06-02 1969-03-04 Monsanto Chemicals Foamed polyvinylaromatic resin products having elongated cells at right angles to a surface skin and their manufacture
US3431163A (en) * 1964-07-09 1969-03-04 Monsanto Chemicals Foamed aliphatic resin products having elongated cells at right angles to a surface skin and their manufacture
US3427371A (en) * 1964-12-29 1969-02-11 Monsanto Chemicals Process and apparatus for extruding foamed articles free from warping

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3713762A (en) * 1970-06-26 1973-01-30 Kasei C Co Ltd Apparatus for the extrusion molding of foamable plastics
US3888614A (en) * 1970-11-03 1975-06-10 Monsanto Chemicals Apparatus for producing a foamed resin sheet in a curved diverging expansion zone
US3897528A (en) * 1973-11-21 1975-07-29 Dow Chemical Co Method for the extrusion of thermoplastic foam
EP0083177A1 (en) * 1981-12-25 1983-07-06 Japan Styrene Paper Corporation Method for producing polystyrene resin foam
US4536357A (en) * 1983-01-28 1985-08-20 Sekisui Kaseihin Kogyo Kabushiki Kaisha Method and apparatus for preparing multi-cellular foamed board of thermoplastic resin
EP0279668A3 (en) * 1987-02-18 1989-10-11 The Dow Chemical Company Faom structure of coalesced foam strands of profiles
US6005013A (en) * 1995-08-14 1999-12-21 Massachusetts Institute Of Technology Gear throttle as a nucleation device in a continuous microcellular extrusion system
US6284810B1 (en) 1996-08-27 2001-09-04 Trexel, Inc. Method and apparatus for microcellular polymer extrusion
US6884377B1 (en) 1996-08-27 2005-04-26 Trexel, Inc. Method and apparatus for microcellular polymer extrusion
US20050256215A1 (en) * 1996-08-27 2005-11-17 Trexel, Inc. Method and apparatus for microcellular polymer extrusion
EP3209478A4 (en) * 2014-10-23 2018-07-04 3M Innovative Properties Company Foaming die and method of use
US10449702B2 (en) 2014-10-23 2019-10-22 3M Innovative Properties Company Laterally-coalesced foam slab
US20170100870A1 (en) * 2014-12-17 2017-04-13 Poly-Wood, Llc Extruded board with realistic appearance
US10486354B2 (en) * 2014-12-17 2019-11-26 Poly-Wood, Llc Extruded board with realistic appearance
US11712831B2 (en) 2014-12-17 2023-08-01 Poly-Wood, Llc Extruded board with realistic appearance

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Publication number Publication date
US3694116A (en) 1972-09-26
BE715259A (en:Method) 1968-11-18
DE1778541A1 (de) 1971-08-05
FR1566936A (en:Method) 1969-05-09
GB1166937A (en) 1969-10-15

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