Method and apparatus for generating foamed thermoplastic materials

Claim 3

The method of claim 1, which further includes subjecting said flowing mass of melt and entrained gas to a mixing action immediately prior to controlling the flow rate and temperature thereof for ultimate extrusion.

Claim 6

The method of claim 3, which further includes subjecting said flowing mass of melt and entrained gas to a mixing action immediately prior to controlling the flow rate and temperature thereof for ultimate extrusion.

Claim 9

The method of claim 3 or 4, wherein said gas and said flowing tubular configuration of thermoplastic are intermingled at a substantially constant pressure differential; and wherein said water is introduced into said thermoplastic mass at a substantially uniform rate of flow.

Claim 10

The method of claim 1, 2, 3 or 4, wherein a nucleating agent is added to said thermoplastic melt prior to the addition of blowing agent thereto.

Claim 11

The method of claim 3 or 4 wherein a nucleating agent is added to said thermoplastic melt prior to the addition of blowing agent thereto; and wherein said water is introduced into said thermoplastic mass at a substantially uniform rate of flow.

Claim 12

The method of claim 1, 2, 3 or 4, wherein said gas and said flowing tubular configuration of thermoplastic are intermingled at a substantially constant pressure differential; and wherein a nucleating agent is added to said thermoplastic melt prior to the addition of blowing agent thereto.

Claim 13

The method of claim 3 or 4, wherein said gas and said flowing tubular configuration of thermoplastic are intermingled at a substantially constant pressure differential; wherein said water is introduced into said thermoplastic mass at a substantially uniform rate of flow; and wherein a nucleating agent is added to said thermoplastic melt prior to the addition of blowing agent thereto.

Claim 16

The method of claim 12, wherein said water is introduced into said thermoplastic mass at a substantially uniform rate of flow.

Claim 17

The method of claim 12 or 13, wherein said thermoplastic melt with entrained water and gas is subjected to said mixing action at a substantially constant pressure.

Claim 18

The method of claim 12 or 13, wherein said gas generating substance is azodicarbonamide.

Claim 19

The method of claim 12 or 13, wherein said thermoplastic melt with entrained water and gas is subjected to said mixing action at a substantially constant pressure; and wherein said gas generating substance is azodicarbonamide.

Claim 20

The method of claim 12 or 13, wherein a nucleating agent is added to said thermoplastic melt prior to the introduction of water thereto.

Claim 21

The method of claim 12 or 13, wherein a nucleating agent is added to said thermoplastic melt prior to the introduction of water thereto; and wherein said thermoplastic melt with entrained water and gas is subjected to said mixing action at a substantially constant pressure.

Claim 22

The method of claim 12 or 13, wherein a nucleating agent is added to said thermoplastic melt prior to the introduction of water thereto; and wherein said gas generating substance is azodicarbonamide.

Claim 23

The method of claim 12 or 13, wherein a nucleating agent is added to said thermoplastic melt prior to the introduction of water thereto; wherein said thermoplastic melt with entrained water and gas is subjected to said mixing action at a substantially constant pressure; and wherein said gas generating substance is azodicarbonamide.

Claim 26

The method of claim 21, wherein said water is introduced into said thermoplastic mass at a substantially uniform rate of flow.

Claim 27

The method of claim 21, wherein gas is introduced into said thermoplastic mass subsequent to the entrainment of water therein and prior to said mixing action.

Claim 28

The method of claim 23, wherein said gas is introduced into said thermoplastic mass at a substantially constant pressure and wherein said water is introduced into said thermoplastic mass at a substantially uniform rate of flow.

Claim 29

The method of claim 21, 22, 23, or 24 wherein said thermoplastic melt with entrained water is subjected to said mixing action at a substantially constant pressure.

Claim 30

The method of claim 21, 22, 23, or 24 wherein said theromplastic mass in said extruder includes a nucleating agent entrained therein prior to the introduction of water thereto.

Claim 31

The method of claim 21, 22, 23, or 24 wherein said thermoplastic melt with entrained water is subjected to said mixing action at a substantially constant pressure; and wherein said thermoplastic mass in said extruder includes a nucleating agent entrained therein prior to the introduction of water thereto.

Claim 34

The method of claim 28, wherein said thermoplastic melt is polystyrene.

Claim 35

The method of claim 29, wherein said gas is air, nitrogen, carbon dioxide or water vapor.

Claim 36

Means for entraining gases and water as blowing agents in a thermoplastic melt to provide a foamed thermoplastic end product, comprising: extruder means for providing a flowing mass of thermoplastic melt; water injection means on said extruder means for injecting water at a substantially constant rate onto said flowing mass of thermoplastic melt to entrain a preselected amount of water therein; gas injection means downstream of said water injection means for injecting gas into said flowing thermoplastic melt with water entrained therein at a preselected injection pressure; first control means for using and maintaining a substantially constant pressure in said thermoplastic melt at the point of injection of said gas therein to maintain a substantially constant pressure differential at said point of injection of said gas; and second control means for controlling the flow rate and temperature of said flowing thermoplastic melt subsequent to the entrainment of water and gas therein and delivering said thermoplastic melt so controlled to an extrusion die to ultimately produce said foamed thermoplastic end product.

Claim 37

Means for entraining gases and water as blowing agents in a thermoplastic melt to provide a foamed thermoplastic end product, comprising: extruder means for providing a flowing mass of thermoplastic melt; water injection means on said extruder means for injecting water at a substantially constant rate onto said flowing mass of thermoplastic melt to entrain a preselected amount of water therein; gas injection means downstream of said water injection means for injecting gas into said flowing thermoplastic melt with water entrained therein at a preselected injection pressure; first control means for using and maintaining a substantially constant pressure in said thermoplastic melt at the point of injection of said gas therein to maintain a substantially constant pressure differential at said point of injection of said gas; and second control means for controlling the flow rate and temperature of said flowing thermoplastic melt subsequent to the entrainment of water and gas therein and delivering said thermoplastic melt so controlled to an extrusion die to ultimately produce said foamed thermoplastic end product.

Claim 38

The invention of claim 31, which further includes mixing means downstream of said gas injection means and said extruder means for imparting a mixing action to said thermoplastic melt with said water and gas entrained therein.

Claim 39

The invention of claim 32, wherein said mixing means comprises a static mixing device.

Claim 40

The invention of claim 22, wherein said mixing means comprises a dynamic mixing device.

Claim 41

The invention of claim 32, wherein said gas injection means is downstream of said extruder means; and wherein said first control means comprises: transducer means for sensing pressure in said thermoplastic melt at the upstream side of said gas injection means and generating a control signal representative of said pressure; variable displacement pump means intermediate said extruder means and said gas injection means for delivering said thermoplastic melt with entrained water to said gas injection means; and variable speed drive means for said pump means, responsive to said control signal from said transducer means, for providing a drive speed of said variable displacement pump means commensurate with said substantially constant pressure to be maintained at said point of injection of gas in said thermoplastic melt.

Claim 42

The invention of claim 32, which further includes second variable displacement pump means intermediate said gas injection means and said mixing means for controlling the flow rate and pressure at which said thermoplastic melt with entrained water and gas is delivered to said mixing means.

Claim 43

The invention of claim 36, wherein said second control means comprises an additional extruder means.

Claim 44

The invention of claim 32, wherein said gas injection means is downstream of said extruder means; and wherein said first control means comprises: transducer means for sensing pressure in said thermoplastic melt at the upstream side of said gas injection means and generating a control signal representative of said pressure; and variable speed drive means for said extruder means, responsive to said control signal for providing a drive speed of said extruder means commensurate with said substantially constant pressure to be maintained at said point of injection of gas in said thermoplastic melt.

Claim 45

The invention of claim 38, wherein said second control means comprises an additional extruder means.

Claim 46

The invention of claim 38 or 39 which includes variable displacement pump means intermediate said gas injection means and said mixing means for controlling the flow rate and pressure at which said thermoplastic melt with entrained water and gas is delivered to said mixing means.

Claim 47

The invention of claim 31, wherein said gas injection means is located on said extruder means; and wherein said first control means comprises: transducer means for sensing pressure in said thermoplastic melt at the downstream end of said extruder means as a measure of the stability of said pressure at said point of gas injection and generating a control signal representative of variations in said pressure; and variable speed drive means for said extruder means, responsive to said control signal for providing a drive speed of said extruder means to maintain a substantially constant pressure in said thermoplastic melt at said point of gas injection.

Claim 48

The invention of claim 41, which further includes mixing means downstream of said gas injection means and said extruder means for imparting a mixing action to said thermoplastic melt with said water and gas entrained therein.

Claim 49

The invention of claim 41, wherein said second control means further comprises mixing means for imparting a mixing action to said thermoplastic melt with said water and gas entrained therein.

Claim 50

Means for entraining gases and water as blowing agents in a thermoplastic melt to provide a foamed thermoplastic end product, comprising: extruder means for providing a flowing mass of thermoplastic melt with a preselected amount of gas generating reagent entrained therein; water injection means on said extruder means for injecting water at a substantially constant rate into said flowing mass of thermoplastic melt to entrain a preselected amount of water therein; first control means for sensing and maintaining a substantially constant pressure in said flowing thermoplastic melt downstream of said extruder means; and second control means including mixing means for imparting a mixing action to said flowing thermoplastic melt with water and gas entrained therein, controlling the flow rate and temperature thereof and delivering said thermoplastic melt to an extrusion die to ultimately produce said foamed thermoplastic end product.

Claim 51

Means for entraining gases and water as blowing agents in a thermoplastic melt to provide a foamed thermoplastic end product, comprising: extruder means for providing a flowing mass of thermoplastic melt with a preselected amount of gas generating reagent entrained therein; water injection means on said extruder means for injecting water at a substantially constant rate into said flowing mass of thermoplastic melt to entrain a preselected amount of water therein; first control means for sensing and maintaining a substantially constant pressure in said flowing thermoplastic melt downstream of said extruder means; and second control means including mixing means for imparting a mixing action to said flowing thermoplastic melt with water and gas entrained therein, controlling the flow rate and temperature thereof and delivering said thermoplastic melt to an extrusion die to ultimately produce said foamed thermoplastic end product.

Claim 52

The invention of claim 44, wherein said second control means comprises an additional extruder means.

Claim 53

Means for entraining gas as a blowing agent in a flowing mass of thermoplastic melt, comprising: body means having substantially aligned inlet and outlet ports and an enlarged central cavity connecting same defined therein for conveying a flow of thermoplastic melt therethrough; flow diverting means in said enlarged central cavity for converting a flow of thermoplastic melt from a flowing mass in said inlet port into a flowing tubular configuration over a finite distance in said cavity and back to a flowing mass in said outlet port; and injection means for impinging an annular stream of gas on said flowing tubular configuration transverse to the direction of flow thereof to entrain said gas in said thermoplastic melt.

Claim 54

Means for entraining gas as a blowing agent in a flowing mass of thermoplastic melt, comprising: body means having substantially aligned inlet and outlet ports and an enlarged central cavity connecting same defined therein for conveying a flow of thermoplastic melt therethrough; flow diverting means in said enlarged central cavity for converting a flow of thermoplastic melt from a flowing mass in said inlet port into a flowing tubular configuration over a finite distance in said cavity and back to a flowing mass in said outlet port; and injection means for impinging an annular stream of gas on said flowing tubular configuration transverse to the direction of flow thereof to entrain said gas in said thermoplastic melt.

Claim 55

The invention of claim 46, wherein said injection means comprises first and second juxtaposed body halves; annular gas port means for conveying gas under pressure defined in opposed mating surfaces of said body halves around said central cavity defined therein; and said opposed mating surfaces being sand blasted between said annular gas port means and the periphery of said central cavity adjacent said flow diverting means providing an annular bleed vent for conveying said gas under pressure from said annular gas port means to impinge upon said flowing tubular configuration of said thermoplastic melt.

Claim 58

The device of claim 48, wherein said injection means includes annular gas port means adjacent to said injection means and an annular bleed vent for conveying said gas under pressure from said annular gas port means to impinge upon said flowing tubular configuration.