WO2015097060A1

WO2015097060A1 - Method for producing a foamed extruded film

Info

Publication number: WO2015097060A1
Application number: PCT/EP2014/078468
Authority: WO
Inventors: Gregory J. WARKOSKI
Original assignee: Solvay Specialty Polymers Usa, Llc
Priority date: 2013-12-23
Filing date: 2014-12-18
Publication date: 2015-07-02

Abstract

Disclosed herein is a method for preparing a microcellular foamed film including providing a combined mixture of a thermoplastic polymer resin with at least one foaming and/or nucleating agent to an extruder (140), melting the mixture (combination) in the extruder (140) and forming micropores in the molten polymer mixture while passing the mixture through a pressure drop zone of an extruder die (160) such that the film is formed by; forcing the combination rapidly through an extruder die (160) of an extruder thereby forming an extrudate and subsequently also rapidly sending the combination through a nip sizing gap (230) such that the mixture is simultaneously being foamed and squeezed between a base (first) (110) and second (120) roller forcing expansion of the molten combination to expand within a die opening gap path without completely filling the nip sizing gap or the die opening gap path with the molten mixture (combination) during forming of the foamed polymer film (210).

Description

Method for producing a foamed extruded film

Cross-reference to related applications

This application claims priority to U.S. provisional application No. 61/919958 filed on December 23^rd, 2013 and to European application No. 14168491.0 filed on May 15^th, 2014, the whole content of each of these applications being incorporated herein by reference for all purposes..

Background

Extruded industrial films are often manufactured and slit to tape size and utilized to provide enhanced products that include improved thermal, dielectric, flammability, and structural properties. For the wire and cable industry in particular, films in tape form are often wrapped around single or bundled groups of conductors (wires) within cables or themselves used as jacketing to provide these specific required properties. Reduction in the density of a solid film (from "neat" polymer) by producing a foamed film via controlling the foaming ratio (the ratio of the air or gas portion of the film compared with the solid portion of the film) often offers advantages in reducing the weight of the article produced as well as the amount of material consumed, while always providing improved dielectric properties in comparison to the solid polymer film analogue.

Generally, foams and films formed during the foaming process, have additional advantageous properties over solid (neat) polymer alternatives including improved flammability, thermal insulation, soundproofing, lighter weight, better impact resistance, electrical insulation/dielectric properties and often better optical characteristics. The properties of the foams and their film counterparts can be tailored to specific needs. Accordingly, foams and foamed films in particular are widely used in a variety of fields including not only insulating and soundproofing materials, but also cushioning and vibration-isolation light reflection plates, light diffusion plates, etc.

Foams are normally manufactured using a foaming technique in which a neat polymer resin is mechanically foamed or using a method in which a resin compound can be combined with a physical foaming agent, or possibly be combined with an inorganic nucleating agent, and/or a chemical foaming agent that is subsequently extrusion-molded to prepare a foamed film. In the foaming process, it is important to control the size, shape, and quantitative distribution of initially the cellular pores which evolve into structured foamed cells during the extrusion process and hence foaming ratio. Further, when adjusting these features, processing should enable precise adjustment of the dimensions (width and length) of foamed articles manufactured there from.

All these properties/features are generally adjusted by both modifying nature and amount of foaming ingredients (e.g. foaming agent, nucleating agent) and/or by acting on foaming process conditions, including e.g. for extrusion foaming, control of different zones' temperatures, etc.

Nevertheless, such composition and process parameters are unable to finely tune precisely the desired foaming ratio and desired specific dimensions.

In preparing microcellular foams, a technique for adjusting the foaming ratio of a foam is disclosed in, for example, Japanese Patent No. 3199951. This patent discloses a method for preparing a thermoplastic elastomer based on the fact that an increase in foaming magnitude occurs by using increased melt ductility within a range in which the strength of the walls of cells formed in accordance with a growth of air bubbles is maintained, and includes a process for measuring, as a melt ductility, a feeding rate of a composition containing a melt ductility enhancing agent, a process for measuring a foaming magnitude of the composition, and a process for selecting a composition and/or a foaming temperature for obtaining a desired foaming magnitude.

However, the above-mentioned technique is limited to the case in which only water (H₂0) is used as a foaming agent. That is, this technique cannot be applied to the case in which a polymer resin having no miscibility to water is extrusion-molded. In order to obtain a desired foaming

magnitude, it is necessary to repeatedly perform a foaming magnitude adjustment several times by measuring a melt ductility of the composition while varying the contents of constituent elements in the composition. For this reason, the process for obtaining a desired foaming magnitude is circuitous and often quite complex. Furthermore, it is necessary to use a separate melt ductility measuring device. In addition, there is an associated degradation in production efficiency. It is also difficult to finely adjust the foaming temperature, and to maintain a desired processing temperature.

Moreover, it is difficult if not impossible to prevent the extruded product emerging from the extrusion die from providing an expanded and

uncontrolled foamed section prior to being cooled. Thus, this technique has many problems.

Japanese Patent Unexamined Publication No. 1997-057822 discloses a technique for detecting a frictional force generated between a foaming die and a resin foamed in the foaming die, and controlling a feeding rate of the resin, to prevent an extruded product from being surged due to a frictional force between an extrusion die and the extruded product, and thus, to prepare a foamed product having an uniform foaming ratio and a high dimension accuracy. However, although this technique can prepare foam having a relatively uniform foaming ratio because it can provide a uniform frictional force, there is a problem in that the foaming ratio cannot be finely controlled.

Regarding physical density adjustment of foams, Korean Patent Unexamined Publication No. 1999-0063440 discloses a technique for preparing a foamed thermoplastic resin sheet (films are often sheets that have been slit to a proper width) having a large thickness and a high foaming magnitude. In accordance with this technique, an extrusion die is used which includes a foaming zone and a cooling zone. The extrusion die also includes a pressure reducing chamber which can maintain a desired pressure reduction degree by a seal member, in order to achieve additional foaming, and thus to obtain a foam having a high foaming ratio. In accordance with this technique, the spacing between a pair of walls defining the pressure reducing chamber is adjusted. Thus, it is possible to prevent air or gas bubbles from being grown in a width direction of the sheet or in a direction perpendicular to a thickness direction of the sheet, and thus to prepare a foamed

thermoplastic resin sheet having a large thickness and a high foaming magnitude. However this process requires a more gentle or gradual temperature profile due to heat conduction as the foaming zone and cooling zone are in direct contact with each other. For this reason, the density of the foam is reduced (more gas or air is trapped), so that the foam may easily vary in cross- sectional shape during a subsequent pultrusion process. For the adjustment of the wall spacing of the pressure reducing chamber, a separate driving unit is needed and thus separate capital equipment costs are added. As a result, the preparation process becomes complex. Furthermore, there is degradation in the physical properties of the extruded product due to the (often unde sired) additional foaming. None of the previously described processes or techniques and equipment provide for a foamed film preparation technique capable of controlling not only the foaming ratio but also the width and thickness of the film to ensure the resultant post molten mixed extrudate composition is forming a filmed product with the desired density and stable, cross-sectional shape.

As a consequence the method of the present invention relates to preparing a foamed polymer film and an extrusion process for the same, which results in preparing foamed films that exhibit exceptional dimensional and foam density uniformity.

Summary of the Invention

A first embodiment of the present invention is a method comprising :

(i) melting in an extruder having a die a polymer foamable composition

comprising a polymer, a foaming agent and, optionally a nucleating agent, so as to obtain a molten composition;

(ii) allowing for drawing the molten composition through said die, so as to form molten extrudate;

(iii) passing the molten extrudate through a die opening gap path comprised between said die and a nip sizing gap, where the molten extrudate is expanding to its final foamed form, without over or under filling said die opening gap path, so as to obtain a fully expanded extrudate;

and;

(iv) passing said expanded extrudate through said nip sizing gap, allowing the expanded extrudate to exist within the nip sizing gap thereby completely filling without over or under filling the nip sizing gap during solidifying of the fully expanded extrudate, hence forming a solid foamed polymer film extrudate.

A second embodiment for forming a solid foamed polymer film extrudate from a polymer foamable composition comprising a polymer, a foaming agent and, optionally a nucleating agent is a method comprising using a roller system and an extruder having an extruder die, wherein the roller system further comprises a base roller, a second roller, and a third roller arranged in a vertical stack arrangement and wherein a nip sizing gap is existing between the base roller and the second roller, wherein the roller system and extruder are arranged providing a die opening gap path existing between the extruder die and the nip sizing gap along which a molten polymer exits the extruder die and enters and expands and begins foaming, forming a foamed molten polymer extrudate prior to entering into the nip sizing gap such that the time the foamed molten extrudate exists in the die opening gap path prior to entering the nip sizing gap is being controlled by the speed of the roller system, so as to enable cooling and forming said solid foamed polymer film extrudate.

According to the techniques mentioned above, a solid foamed polymer film extrudate can be obtained which possess very precise foaming ratio and finely tuned dimensions.

The speed of molten polymer flowing through the extruder die and subsequently the foamed molten extrudate flowing through the die opening gap path and the nip sizing gap is generally controlled by the relational speed of the rollers of the roller system. It is in particular possible that the speed is controlled by controlling speed of all rollers, or by controlling speed of the second and third rollers.

The rate of controlled speed advantageously ensures that the molten composition is reducing or eliminating development of a bank of molten composition within the die opening gap path or the nip sizing gap during forming of the foamed polymer film extrudate.

Achieving the desired film thickeness is advantageously achieved by controlling the distance between the die opening gap path and said nip sizing gap.

The foamed polymer film extrudate generally possesses a uniform microcellular foamed closed cell structure, wherein the foamed closed cells are advantageously equal to or no greater than 150 microns in size, preferably equal to or no greater than 100 microns in size, more preferably equal to or no greater than 50 microns in size.

Yet another embodiment of the invention is an article of manufacture comprising a foamed polymer film extrudate, said film comprising foamed closed cells that are advantageously equal to or no greater than 150 microns in size, preferably equal to or no greater than 100 microns in size, more preferably equal to or no greater than 50 microns in size.

Detailed Description of the Invention

In the method of the first embodiment, use can be made of a roller system comprising a base roller, a second roller, and a third roller arranged in a vertical stack arrangement for drawing said molten extrudate. In this method, the speed of molten extrudate exiting said die, the speed of passing said molten extrudate through said die opening gap path and the speed of passing said fully expanded extrudate through nip sizing gap are all the same, so that there is no accumulation of molten extrudate or fully expanded extrudate in any of die opening gap path and nip sizing gap.

Said speed can be controlled by the relational speed of the rollers of the roller system. It is in particular possible that the speed is controlled by controlling speed of all rollers, or by controlling speed of the second and third rollers.

In the method of the invention, use is made of a polymer foamable composition comprising a polymer, a foaming agent and optionally, a nucleating agent.

Among the polymers which can be used in the methods of the invention, mention can be notably made of polycarbonates, aromatic polyetherketone polymers, aromatic sulfone polymers, semi-aromatic polyamides, aromatic thermoplastic polyetherimides, aromatic polyphenylene polymers, and mixtures thereof.

With regard to the nature of the foaming agent, use can be made of physical foaming agents and/or chemical foaming agents. Physical foaming agents generally refer to those compounds that are in the gaseous state in the foaming conditions (generally high temperature and pressure) because of their physical properties. Any conventional physical blowing agent can be used such as inert gases, e.g. C0₂, nitrogen, argon; hydrocarbons, such as propane, butane, pentane, hexane; aliphatic alcohols, such as methanol, ethanol, propanol, isopropanol, butanol; aliphatic ketones, such as acetone, methyl ethyl ketone ; aliphatic esters, such as methyl and ethyl acetate ; fluorinated hydrocarbons, such as 1,1 ,1,2-tetrafluoroethane (HFC 134a) and difluoroethane (HFC 152a); and mixtures thereof.

Chemical foaming agents generally refer to those compounds which decompose or react under the influence of heat in foaming conditions, to generate a foaming gas.

Suitable chemical foaming agents include notably simple salts such as ammonium or sodium bicarbonate, nitrogen evolving foaming agents ; notably aromatic, aliphatic-aromatic and aliphatic azo and diazo compounds, such as azodicarbonamide and sulphonhydrazides, such as benzene sulphonhydrazide and oxy-bis(benzenesulphonhydrazide), tetrazoles, including those described notably in U.S. patent Nos. 3,442,829, 3,873,477, 4,142,029 and 4,774,266, and in particular 5-phenyltetrazole. The chemical foaming agents can optionally be mixed with suitable activators, such as for example amines and amides, urea, sulphonhydrazides (which may also act as secondary foaming agent), etc.

It is generally known that chemical foaming agents may be present in powder form, concentrates or masterbatches in the form of pellets. Said pelletized foaming agent masterbatches can be made with a thermoplastic carrier material such as notably olefmic polymers, polystyrene polymers and others.

Suitable nucleating agents that may be used in the present invention include, but are not limited to, metallic oxides such as titanium dioxide, magnesium oxide, silicon oxide, clays, talc, silicates, silica, aluminates, barites, titanates, borates, nitrides, notably boron nitride, and even some finely divided, unreactive metals, carbon-based materials (such as diamonds, carbon black, nanotubes and graphenes) or combinations including at least one of the foregoing agents. In alternative embodiments, silicon and any crosslinked organic material that is rigid and insoluble at the processing temperature may also function as nucleating agents.

In alternative embodiments, polymer foamable composition used in the method of the invention may include additional fillers. This includes fibrous fillers such as aramid fibers, carbon fibers, glass fibers, mineral fibers, or combinations including at least one of the foregoing fibers. Some nano-fillers and nano -reinforcements can also be used as nucleating agents. These include such materials as nano-silicates, nano-clays, carbon nanofibers and carbon nanotubes as well as graphenes and multi-layered graphitic nano-platelets.

Brief Description of the Drawings

FIG. 1 is a process schematic view of the conventional (Prior Art)

"3-stack" system normally employed for extruding solid films carrying out a general extruding process for preparation of a normally solid polymer film with a large pool or "bank" of the molten (mixture) combination utilizing primarily a die sizing gap.

FIG. 2 is a similar process schematic view illustrating the "3-stack" system which is the subject of the present disclosure in that the process is extruding foamed polymer film using both the nip sizing gap and/or a die opening gap path together with the extruder and extrusion die arrangement and generally using higher speed base and second rollers than for those shown in Fig.1.

Detailed Description Referring to the drawings, and specifically Figure 1 , the extruding and foaming process is carried out through an extruder [140] with a hopper, [150] through which the polymer (without any blowing and/or nucleating agents) is added, and appropriate feeding means (not shown) through which all other ingredients of the foamable composition are introduced, an extrusion die [160], through which the molten composition flows and a conventional processing unit consisting of a "3-stack" arrangement [110, 120, and 130] of three rollers, where the base roller [110] is aligned in a parallel arrangement and in the order shown and given, to achieve an advancing direction of the molten extrudate using the inversely rotating (with respect to each other) second and third rollers [120 and 130]. In this conventional arrangement [100], semi- so lid and eventually solid polymer film [190] is formed from the initially molten pool or "bank" [185] of polymer which exists at the exit of the extruder [140] through the extruder die [160] and is eventually squeezed through a die sizing gap [180]. The solid film eventually reaches the take-up spool [170]. Normally, the speed of the second [120] and third [130] rollers dictates the physical attributes associated with the thickness of the film as these rollers are "carrying" the cooling extrudate toward its final destination.

Referring now specifically to Figure 2, the extruding and foaming process is carried out through an identical extruder [140] and hopper [150], and feeding means arrangement through which the ingredients of the polymer foamable composition are added as described above, an extrusion die [160] through which the molten composition flows and a processing unit consisting of a "3-stack" arrangement [110, 120, and 130] of the same three rollers, where the base roller [110] is aligned in a parallel arrangement and in the order shown and given, to achieve an advancing direction of the molten extrudate product using the inversely rotating (with respect to each other) second and third rollers [120 and 130]. In this arrangement [200], a molten and eventually foamed solid polymer film [210] is formed quickly as it exits the extruder [140] and extruder die [160] utilizing both the die opening gap path [220] section that is a gap situated between the extruder die [160] and the nip sizing gap [230] section which is the distance between the base roller [110] and the second roller [120] and that begins at a point where the foamed film has been fully expanded to a specified (by the user) dimension and density. Indeed, the thickness of the molten extrudate at the end of the die path is the same as the nip sizing gap: in other terms, the nip sizing gap is not compressing/nor creating a build-up of material, because of a volume of molten extrudate exceeding the said nip sizing gap.

The foamed film eventually reaches the take-up spool [170]. In this case, it is the speed of primarily the base roller [110] as well as the speed of the second roller (and to a varied extent the third roller) that assists with both the proper foaming (density) as well as the thickness and dimensional stability of the finished foamed film product [210] as these rollers ensure that no "bank" or pool of molten cooling extrudate accumulates or exists during the process. In this process, as the molten polymer extrudate exits the die, it expands fully in the distance between the die opening gap path and the nip sizing gap thereby also allowing the film to achieve its proper dimension and density as well as preventing crushing or physical distortion of the cellular structure of the foamed film or tape. Thus, foamed films having a desired shape can be manufactured.

The molten extrudate feeds through the die opening gap path [220] after emerging from the extruder die [160] in a high-temperature state, and is exposed to atmospheric pressure at a this high-temperature state before being sufficiently cooled. For this reason, the extruded product is "post-foamed" in that it utilizes an internal foaming pressure. The method for preparing a uniform microcellular foamed (in this case closed cell structures that are less than 50 microns in size) polymer film and an extrusion process for the same requires mixing a (mostly high temperature) thermoplastic polymer resin that is plasticized in an extruder with at least one foaming and/or nucleating agent(s), melting the mixture and forming micro-pores in the melted or molten mixture composition as the compositional mixture flows through a pressure drop and temperature controlled zone of an extruder and into the extrusion die. The molten composition forms micropores while cooling as the extrudate and the cellular structure of the foam begins forming immediately as what becomes a compositional mixture extrudate exits the extrusion die.

The extruded product expands not only in the direction of the extrusion stream (along the length) but also in an axial direction that is mostly

perpendicular to the extrusion direction (along the width of the film as it is exiting the extruder die). The result is that the foaming ratio - and thus the density of the foam varies with the lapse of time, composition of the polymer system (including the foaming and nucleating agent concentrations and fillers ) as well as the speed of the base [110] and second rollers [120]. Additionally, the process can be further controlled by changing the distance between the die opening gap path and the nip sizing gap thereby also allowing the film to achieve its proper dimension and density and still preventing crushing or physical distortion of the cellular structure of the foamed film or tape. The parameters described must be carefully monitored and controlled to ensure reducing or eliminating any inconsistencies involving density or thickness. Prepared foamed films or tapes will not have the desired foaming ratio, and often have a very nonuniform cross-sectional shape if these process conditions are not utilized and properly controlled.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

The invention will now be described in more details with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

Raw materials

A talc concentrate containing 30 % w/w of talc

Udel^®P-1700NT sulfone polymer commercially available from Solvay Specialty Polymers USA, LLC, having a melt flow rate according to ASTM D 1238 of 7.0g/10min as measured at 343°C and 2.16 kg weight.

5 -phenyl tetrazole chemical blowing agent

Polypropylene polymer

Working example

The Udel^®P-1700NT sulfone polymer was compounded with talc so as to obtain a weight amount of being 0.8 % relative to the total weight of the polymer foamable composition. Compounding into pellets was performed on a

Berstorff 25 mm twin screw extruder having an L/D ratio of 40:1 and eight barrel sections, of which sections 2-8 are equipped with heating and cooling. The base polymer pellets and the talc were first tumble-blended for twenty minutes and then the mix was fed to the throat of the extruder. The extruder was set at a barrel temperature of 330° for barrel sections 2-8. The die temperature was set at 340°C and a screw speed of 200 rpm was used along with a throughput rate of 25 lb/hr. Vacuum venting of the melt was performed at barrel section 7. The extrudate from the extruder was cooled in a water trough and then pelletized. The pellets produced from the formulation were dried at temperatures between 110 and 150°C for 8 hours. The compounded pellets were then fed to a foaming set up, along with pellets containing the polypropylene polymer and the 5-phenyl tetrazol wherein the feed ratios were adjusted to achieve that the percentage by weight of the Udel^®P-1700NT sulfone polymer was 95.87 %, the percentage by weight of talc was 0.80 %, the percentage by weight of the 5-phenyl tetrazol was 1.00 %, and the percentage by weight of the polypropylene was 2.33 %, all the percentage by weight were relative to the total weight of the polymer foamable composition. The foaming setup consisted of a ¾ inch diameter Brabender single screw extruder with 4 heating/cooling zones and with an L/D ratio of 30: 1 , fitted with an extruder die. The molten composition was drawn through the extruder die so as to form the molten polymer extrudate. The extrudate exited the extruder die at a cross-sectional area that was about 25 % that of the cross sectional area achieved when the fully foamed film forming extrudate reached the nip sizing gap. In this manner, the foamed film reached the desired, properly dimensioned thickness and width as well as providing homogenous closed cell structural integrity.

Claims

C L A I M S

1. A method comprising :

(i) melting in an extruder having a die a polymer foamable composition

(iii) passing the molten extrudate through a die opening gap path comprised between said die and a nip sizing gap, where the molten extrudate is expanding to its final foamed form, without over or under filling said die opening gap path, so as to obtain a fully expanded extrudate; and;

(iv) passing said fully expanded extrudate through said nip sizing gap, allowing the expanded extrudate to exist within the nip sizing gap thereby completely filling without over or under filling the nip sizing gap during solidifying of the fully expanded extrudate, hence forming a solid foamed polymer film extrudate.

2. The method of claim 1, wherein use is made of a roller system comprising a base roller, a second roller, and a third roller arranged in a vertical stack arrangement for drawing said molten extrudate.

3. The method of claim 2, wherein the speed of molten extrudate exiting said die, the speed of passing said molten extrudate through said die opening gap path and the speed of passing said fully expanded extrudate through nip sizing gap are all the same, so that there is no accumulation of molten extrudate or fully expanded extrudate in any of die opening gap path and nip sizing gap.

4. The method of claim 3, wherein said speed is controlled by the relational speed of the rollers of the roller system.

5. The method of claim 1, wherein said polymer is selected from the group consisting of polycarbonates, aromatic polyetherketone polymers, aromatic sulfone polymers, semi-aromatic polyamides, aromatic thermoplastic polyetherimides, aromatic polyphenylene polymers, and mixtures thereof.

6. The method of claim 1, wherein said foaming agent is selected from physical foaming agents, chemical foaming agents and mixtures theretrom.

7. The method of claim 6, wherein said foaming agent is a physical foaming agent selected from the group consisting of C02, nitrogen, argon; hydrocarbons, such as propane, butane, pentane, hexane; aliphatic alcohols, such as methanol, ethanol, propanol, isopropanol, butanol; aliphatic ketones, such as acetone, methyl ethyl ketone ; aliphatic esters, such as methyl and ethyl acetate ; fluorinated hydrocarbons, such as 1,1,1,2-tetrafluoroethane (HFC 134a) and difluoroethane (HFC 152a) ; and mixtures thereof.

8. The method of claim 6, wherein said foaming agent is a chemical foaming agents elected from the group consisting of inorganic carbonates and organic nitrogen evolving foaming compounds selected from the group consisting of aromatic, aliphatic-aromatic and aliphatic azo and diazo compounds, such as azodicarbonamide and sulphonhydrazides, such as benzene sulphonhydrazide and oxy-bis(benzenesulphonhydrazide), tetrazoles, and in particular 5-phenyltetrazole.

9. The method of claim 1, wherein the foamable polymer composition comprises a nucleating agent selected from the group consisting of metallic oxides such as titanium dioxide, magnesium oxide, silicon oxide, clays, talc, silicates, silica, aluminates, barites, titanates, borates, nitrides, notably boron nitride, and even some finely divided, unreactive metals, carbon-based materials (such as diamonds, carbon black, nanotubes and graphenes) or combinations including at least one of the foregoing agents.

10. A method for forming a solid foamed polymer film extrudate from a polymer foamable composition comprising a polymer, a foaming agent and, optionally a nucleating agent, said method comprising using a roller system and an extruder having an extruder die, wherein the roller system further comprises a base roller, a second roller, and a third roller arranged in a vertical stack arrangement and wherein a nip sizing gap is existing between the base roller and the second roller, wherein the roller system and extruder are arranged providing a die opening gap path existing between the extruder die and the nip sizing gap along which a molten polymer exits the extruder die and enters and expands and begins foaming, forming a foamed molten polymer extrudate prior to entering into the nip sizing gap such that the time the foamed molten extrudate exists in the die opening gap path prior to entering the nip sizing gap is being controlled by the speed of the roller system, so as to enable cooling and forming said solid foamed polymer film extrudate.

11. An article of manufacture comprising a foamed polymer film extrudate, said film comprising foamed closed cell structured film with structural cells that are equal to or no greater than 150 microns in size.

12. The article of claim 11, wherein said foamed polymer film extrudate is substantially uniform in both dimensions and density along its width, length and thickness.