COMPTABILIZER FOR CARBON DIOXIDE-BLOWN POLYOLEFINIC FOAMS

Abstract: A method of making a polyolefinic foam composition comprising the steps of: (a) feeding a polyolefinic polymer into an extruder; (b) adding a nucleating agent to the resin feed; (c) optionally adding a permeation modifier to the resin feed; (d) plasticating the mixture in an extruder to form a polymeric melt; (e) incorporating a blowing agent of carbon dioxide and optionally one or more members selected from the group consisting of inorgnaic blowing agents, organic blowing agents, and combinations thereof; (f) incorporating at least one compatibilizing agent into said foamable composition wherein said compatibilizing agent is an oxygenated hydrocarbon that decreases the minimum pressure required to prevent prefoaming while retarding the collapse of foam due to excessive blowing agent migration; (g) uniformly mixing and cooling the foamable composition to a temperature effective for the expansion of the polyolefinic foam; and (h) extruding or ejecting the foamable composition through a die to form a polyolefinic foam.

Description: COMPTABTLIZER FOR CARBON DIOXIDE-BLOWN POLYOLEFINIC FOAMS FIELD OF THE f\'\Ε\TIQ\ > This is a coπnnuation-m part of U S Serial No 08/69-1.29S inventors \Vιlke> et al . entitled Process for Producing Low Densits lenιc Foam with Atmospheric Gases and Polvglycols or Polyglycol Ethers, filed on August S.1996 and a continuation-in-paπ of U S Serial No OS/746. S25. inventors Wilkes et al . entitled A Short Time Frame Process For Producing Extruded Closed Cell Low Density Propylene Polymer Foams, filed on November I S.1996. which 10 is a continuation-in-part of U.S Serial No OS/735, 271 , having the same inventors and title, filed on October 22. 1 96. which is a continuauon-in-paπ of U S Serial No OS/730, 177. having the same inventors and title, filed on October 15. 1 96 This invention relates, in general, to a process and a composition for manufacture of a foamed thermoplastic material More specifically, it relates to processes and e .trudable I 5 compositions for production of low-density uncrosslinked polyolefinic foams when using carbon dioxide as a blowing agent or in combination with an auxiliary organic or inorganic phvsical blowing agent by adding certain oxygenated hydrocarbons as a compatibilizing agent BACKGROUND OF THE rNVENTION 0 Low-density thermoplastic foams, particularly those having a density of less than about 150 kg/m\ are generally produced with physical blowing agents Physical blowing agents are chemical compounds which can be incorporated into the thermoplastic melt while within the extruders at high pressures, typically 10-20 MPa, and which can be contained by the polymer structure when the cooled thermoplastic/blowing agent mixture is rapidly reduced to ambient ptessui e Poholeftnic loams in particular .mcrosslmkeci pol .eth . len.- ioam .: ■ .; uiicrosslmkc poK prop . lene tonm weie πiaπut.iciurecl foi IΠ.HU .ear v. ith hal gennteo tu dro-rrbons pππ r iK chiororUiorocarbons (CFC's) as phvsical blowing agents During the I S0 s the worldwide scientific community presented sufficient evidence to link CFC * s with atmospheric ozone depletion and sought for world governments to regulate CFC's Ozone levels in the stratosphere have been shown to be significant in protecting life on the planet from the damaging effects of ultraviolet radiation from the sun Additionally , hvdrochlorofluorocarbons (HCFC's), another class of chemical compounds were also included in the regulations but on a more lengthy schedule it was established that the higher atomic weight halogen compounds other than fluorine that were responsible for this effect As a result of the regulations, it became necessary to find materials other than halo enated compounds which could function as physical blowing agents Many different approaches were taken, but generally in the direction of the use of hydrocarbons containing from two to five carbons or blends thereof Although these short-chained hydrocarbons may function as physical blowing agents to produce foams with satisfactory physical properties, these physical blowing agents are highly flammable U.S Patent -1.217.3 19 (Komoπ) discusses a process for producing polyolefiπ foams with various volatile organic compounds as the physical blowing agent U.S Patent 5.290.S22 (Rogers et al) and U.S Patent 5.225.451 (Rogers et al) discuss processes for ultra-low density foam using polymer blends U.S. Patent 5,059.376 (Pontiff) discusses a process to remove residual hydrocarbons in the attempt to produce a non-flammable polyethylene foam Carbon dioxide, alone or in combination with various other gases, has been used as a blowing agent to produce polyethylene foam U.S Patent 5.034.171 (Kiczek et al) discusses an ex t rusion process for producing a ' πucrocellular " thermoplastic foam and cue-; p lvcth. lene s possible poivmer and carbon dioxide as a possible men g s foaming agent L S Patent 5.462.974(Lee) discusses a foamable polyethylene lesin composition h.u mg a Mowing agent comprised of a blend of about 50% by weight of carbon dioxide and about 50 by weight of cither normal butane, isobutane. propane, ethane, or a mixture of any combination of these hydrocarbons. in mixture with the resin in a ratio of about one pan blowing agent to about 10 pans resin while using a zinc oxide nucleatioπ agent and a glycerol monostearate aging modifier U S Patent 5. 16.129 (Chaudhary et al ) and U S Patent 5.554.661 (Chaudhary et al ) discuss a process and composition for preparing uncrosslinked ethylenic polymer foam using a polymer of a defined melt tension with either argon, carbon dioxide, or blends thereof These patents generally state that argon and carbon dioxide, alone or in blends, can function as a physical blowing agent with ethylenic materials having a specific melt tension. U.S. Patent No. 5.1 16.SS 1 (Park et al.). U.S Patent No. 5.149.579 (Park et al.). and U.S Patent No. 5. IS0.7 1 (Park et al ) discuss a process and a composition for producing thermoformable polypropylene foam sheets from high melt strength polypropylene and refer to carbon dioxide as a potential blowing agent The patent discusses foam sheets in the range of densities above 2.5 lb/ft' (42 kg m J ) with sheet thicknesses below 0.200 inch (5 0 mm) which are defined by certain physical properties. U.S. Patent No. 5.567.742 (Park) discusses a dimensionally stable polypropylene foam with an inorganic blowing agent. While applicable to both open and closed cell foams, the discussed process with inorganic blowing agents is limited to combinations of cell sizes and densities which result in cell wall thicknesses within a specified range. When used as physical blowing agents in traditional low density polyolefinic foam processes, carbon dioxide either alone or in combination with other gases including uatet eπerail \ produce non-descπpt masses of polvmeπc material or otherwise pooi qual thermoplastic m m which collapse This lack of dimensional stability occurs because of the limned solubiluv t i these compounds within the molten thermoplastic extrudate which results in an uncontrollable high level of open cells in the foam structure as the thermoplastic/blowing agent combination exits the die- Additionally, even if the resultant thermoplastic materials which are made with carbon dioxide as the primary blowing agent have a visible foam structure, most of such foams tend to collapse quick K in time and become useless for most practical applications in less than 24 hours after manufacture Accordingly, in order to use carbon dioxide as the primary blowing agent, it is necessary to reduce the pre-foaming pressure required to make a foam at the die and subsequently either eliminate oi significantly reduce the rate of collapse normally exhibited by polyolefinic foam made with carbon dioxide, water or blends thereof OBJECTS OF THE INVENTION The first object of the present invention is to provide a means by which a simple, low cost, and reliable technique can be used to produce a low-density uncrosslinked polyolefinic foam which does not contain a chemical compound that has been shown to exhibit adverse effects on the stratospheric ozone concentration. A second object of this invention to provide a means by which a simple, low cost, and reliable technique can be used to produce a low-density uncrosslinked polyolefinic foam which does not contain flammable levels of hydrocarbon compounds. An additional object of the invention is to incorporate chemical compounds that do not ad . erseh affect human animal or plant lite >o the . tti se comp u s c.i" ;H- used w itlun.i sophisticated protection de - ices 01 elaborate control technolog . Λ further obiect of the inv ention is to produce a stable to.im structure tor w hich the physical properties will not significantly deteriorate over the course ot time An additional object of the invention is to produce a foam material that ill not advcrsel . affect the surface characteristics of other materials that the foam may be placed in intimate contact BROAD DESCRIPTION OF THE INVENTION In accordance with the aforementioned objects, this invention incorporates ovygenated hydrocarbon compounds with a structure containing multiple ether bonds, multiple hydroxyl bonds, carbo l groups, or some combination of these three chemical structure components that will function within the extruder to decrease the minimum pressure required to prevent prefoaming at the die while retarding the collapse of foam due to excessive blowing agent migration when the primary blowing agent is carbon dioxide In particular, the invention is directed to a method of making a polyolefinic foam composition comprising the steps of (a) feeding a polyolefinic polymer into an extruder (b) adding a nucleating agent to the resin feed. (c) optionally adding a permeation modifier to the resin feed, (d) plasticating the mixture in an extruder to form a polymeric melt. (e) incorporating a blowing agent of carbon dioxide and optionally one or more members selected from the group consisting of inorganic blowing agents, organic blowing agents, and combinations thereof. (0 incorporating at least one compatibilizing agent mio said foamable composition wherein said compatibilizing agent is an oxygenated hydiocarbon that decreases the minimum pressure required to prevent prefoaming while retarding the collapse of foam due to excessive blowing agent migration. (g) uniformly mixing and cooling the foamable composition to a temperature effective oi the expansion of the polyolefinic foam, and (h) extruding or ejecting the foamable composition through a die at a sufficiently high rate to form a polyolefinic foam. The invention is also directed to a foam composition made by the above-described process In traditional polyolefinic foam extrusion processes, pellets of the thermoplastic resin are blended with a solid phase nucleating agent and then melted in a heated extruder where the plastic and nucleating agent combination are held under high temperature and pressure The physical blowing agent which generally liquefies within the extruder and which will vaporize at die melt temperatures and atmospheric pressure is added to the pressurized melted material Within the molten extrudate, the physical blowing agent tends to act as a plasticizer to reduce the viscosity and thus lowers the level of temperature necessary to maintain the hot melt condition of the mixture of thermoplastic plastic material and nucleating agent. The blowing agent is mixed with the melted plastic and nucleating agent and the combination is subsequently cooled to an extrusion temperature suitable for foaming. A permeation modifier agent which is usually an ester of a atty acid having a chain of 1 -22 carbon atoms is often also added to prevent the collapse of the resulting foam structure over time. The cooled combination is pushed through a die by the pressure sradient and w hen released to atmospheric pressur e, the liquified physical blowing agent vaporizes and expands to form bubbles of gas at the nucleating sites established In the uniformly dispersed nucleating agent panicles When used as physical blowing agents in traditional low density polyolefinic foam processes, carbon dioxide either alone or in combination with other gases including water, generally produces non-descript masses of polymeric material or otherwise poor quality thermoplastic foams which collapse. This lack of dimensional stability occurs because of the limited solubility for these compounds within the molten thermoplastic extrudate which results in an uncontrollable high level of open cells in the foam structure as the thermoplastic/blowing agent combination exits the die Additionally, even if the resultant thermoplastic materials which are made with carbon dioxide, water, or blends thereof do have a visible foam structure, most of such foams tend to collapse quickly in time and become useless for most practical applications in less than 24 hours after manufacture. Accordingly, the invention is directed to oxygenated hydrocarbons, particularly those that have a carbon to oxygen ratio between about 0.5 and I 0 in the thermoplastic/physical blowing agent blend to function to reduce the pre-foaming pressure required to make a foam at the die and subsequently either eliminate or significantly reduce the rate of collapse normally exhibited by polyolefinic foam made with carbon dioxide, water or blends thereof In the disclosed polyolefinic foamable composition invention, pellets of the thermoplastic resin are mixed with a solid phase nucleating agent and then melted in a heated extruder where the plastic and nucleating agent are held under high temperature and pressure as in the traditional foam process. Carbon dioxide is added to the extrudate through an injection port at the typical extruder injection zone. AJI auxiliary blowing agent, which may be an inorganic or organic compound, mav optionalK be added through the same ot separate miectioii ι ~s ,is that us d t i carbon dioxide Additionally, an oxygenated hydrocarbon compatibilizing agent is adced to the foamable composition The molecular weight of the oxygenated hvdrocarbon generaii - determines the manner in which the oxygenated hydrocarbon is added Oxygenated hydrocarbons which hav e a molecular weight above about 10.000 are mixed in solid form with the pellets cf polvolefin iesm Oxygenated hydrocarbons which have a molecular weight below about 10.000 are added in the same extrusion zone either through the same injection poπ but preferably through a separate injection port located at some angle, generally 90° or 1 SO" radially from the carbon dioxide injection poπ The chemical structure of oxygenated hydrocarbon determines whether the oxygenated hydrocarbon is added as a pure component or as an aqueous solution in a specific concentration range If the oxygenated hydrocarbon is to be added as a pure component, its melting point at normal atmospheric pressure determines whether the oxygenated hydrocarbon is injected in liquid ot heated liquified form Within the molten extrudate. the carbon dioxide, auxiliary blowing agents, if present, water. if present, and the oxygenated hydrocarbon all tend to act as plasticizers to reduce the melt viscosity and thus lower the level of temperature necessary to maintain the hot melt condition of the mixture of thermoplastic plastic material and nucleating agent The carbon dioxide, auxiliary blowing agents, if present, water, if present, and the oxygenated hydrocarbon are mixed with the melted plastic and nucleating agent and the combination is subsequently cooled to an extrusion temperature suitable for foaming. The cooled combination is pushed through a die by the pressure gradient and when released to atmospheric pressure, the physical blowing agent(s) expand rapidly but at a rate lower than would if the oxygenated hydrocarbon were not present. In the area of lower pressure such as the atmosphere at ambient temperatures, the thermoplastic oxvgenatcd hvdrocarboivphvsical blowing agent blend expands to form bubbles of the pln sical blow ing agent t tas at the nucleating sites established by the uniformly dispersed nucleating agent panicles The affinity of the oxygenated hydrocarbon for the carbon dioxide and the water, if present, also tends to slow the diffusion rate of the gas molecules from the foam structure so that the polyolefinic foam does not collapse in 24 hours or less as it would if the oxygenated hydrocarbon were not present DETAILED DESCRIPTION OF THE INVENTION The term polyolefinic is meant to include polymers of linear or branched C : to C, hydrocarbon molecules that contain one double bond in its structure, including alkenes such as ethene, propene. l -butene, 2-butene, l -pentene. 2-pentene. 3-pentene Preferred polyolefinic materials include polymers of ethene which are commonly known as polyethylene and polymers of propene which are commonly known as polypropylene. Broadly, the invention involves a composition and process for making a closed-cell low density polyolefinic foam having a density of 10 kg/nv' to 150 kg/m . preferably 20 kg/πv 1 to 150 kg m'. The polyethylenic resin that can be used in the foamable composition invention can be those obtained by polymerizing ethylene. or polymerizing ethylene with other aliphatic polyolefins. such as propylene, l-butene. l-pentene, 3-methyl- I-butene. 4-methyl- l-pentene 4-methyt- I-hexene. or 5-methyl- l-hexene alone or mixtures thereof, or with various other polymerizable monomers. Polyethylenic resins include homopolymers of ethylene and copolymers of ethylene and other ethylenically-unsaturated monomers having from three to about eight carbon atoms, propylene, butenes, pentenes, hexenes, and the like. These comonomers preferably have from three to about six carbon atoms, and most preferably have three or four carbon atoms The co|v . :ιu .'- can include other monomers compatible with ethylene Particularly prefeπed are medium dersi; . pol .eun ieπe low density polyethylene, and linear low polyethylene Such polycthylenes su described in the Kit k Othmer Encyclopedia of Chemical Technolpgv. Third Ed . Vol 10. pages 3S5. 420. the Modern Plastic Encyclopedia. ( I S6-S7). pages 52-63. and the Encyclopedia of Polvmer Science and Technology. Vol. 7, page 610, which are incorporated herein by reference The term "polyethylenic resin (or material)", as used herein, is meant to include not only homopolyπiers of ethylene. but also ethylene copolymers composed both of at least 50 mole percent (preferably at least 70 mole percent) of a ethylene unit and a minor proportion of a monomer copoiymerizable with ethylene, and blends of at least 50% percent by weight (preferably at least 60 percent by weight) of the ethylene homopolymer with another polymer. Preferred polyethylenes include uncrosslinked. low-density polyethylene having a density of about 910 to 920 kg m' and a melt flow index in the range of 0.2 to 3 S g per 10 minutes In general, the ethylene polymer should have a melt (flow) index of less than about 10 grams per 10 minutes. The melt (flow) index (ASTM DI23S) as the nominal flow rate at 1 0*C and 6S9 5 kPa. and is expressed as grams per 10 minutes The propylene polymeric resin can be obtained by polymerizing propylene. or polymerizing propylene with other aliphatic polyolefins. such as. ethylene. l-butene. l-pentene. 3-methyl- l -butene, 4-methyl- l-pentene, 4-methyl- l-hexeπe. 5-methyl- l-hexene and mixtures thereof, or with various other polymerizable monomers. The term "propylene polymeric resin (or material)", as used herein, is meant to include not only homopolymers of propylene, but also propylene copolymers composed of both at least 50 mole percent (preferably at least 70 mole percent) of a propy lene unit and a mine-- piopoition of a monomer copoiymerizable with propv lene and blend > or at least 50 percent In w eight i pretera K at least 60 percent by weight) of the propylene homopolvmer with anothei potvmer Also permissible are blends of propylene polvmeπc resin with one or more "polymeric modifiers", as used herein to include low density polyethylene (LDPE). medium deπsii . polyethylene (NOPE), high density polyethylene (HDPE). linear low density polyethylene (LDPE). polyolefin elastomers, polyolefin plastomers. saturated and unsaturated styrene-butadiene random and block copolvmer rubbers, polyamides. ethylene ethyl acrylate (EEA), ethylene methyl acrylate (EiVlA). ethylene acrylic acid (EAA). ethylene methacrylic acid (EMAA). ethylene vinyl alcohol (EVOH). ethylene vinyl acetate (EVA), ethylene propylene diene monomer copolymer (EPDN.) rubbers, and olefinic ioπomers, such that the total propylene monomer units are in excess of 50 weight percent. Preferred propylene polymer blends contain at least 50 percent by weight of "'high melt strength" polypropylene which has a loss tangent less than or equal to 1 2 at I radian/sec frequency and I90°C. a density of about 900 to 910 kg/m'. and a melt flow index in the range of 2.2 to 3.S g per 10 minutes In general, the propylene polymer should have a melt (flow) index of less than about 10 grams per 10 minutes The melt (flow) index (ASTM D 123S) is the nominal flow rate at 230 β C and 298.2 kPa. and is expressed as grams per 10 minutes. A preferred high melt strength polypropylene used in the invention process has a branched molecular structure, providing increased molecular entanglement. Permeation modifiers may be used in the foamable composition of the invention, particularly with low density polyethylene to prevent collapse of the cellular structure within about I I as little as ten minutes to up to about eight hours after formation Permeation modiltci .. ai e ai> called aging modifiers in some polyolefinic extrusion art r'refci i ed permeation moditiei s include octadecanamide and ethvlene-bis-stearamide The most preferred permeation modifier For use in the foamable composition invention is octadecanamide The nucleating agent, or cell size control agent can be any conventional oι useful nucleating agent(s). The cell size agent is preferably used in amounts of 0 1 to 2 0 weight percent, depending upon the desired cell size and based upon the weight of the polyolefinic resin Examples of the cell size control agents are inorganic materials (in small paniculate form), such as clay. talc, silica, and diatomaceous earth. Additional examples include organic cell size-controllinc agents which decompose or react at the heating temperature within the extrude to evolve gas, such as a combination of an alkali metal salt of a polycarboxylic acid, such as sodium hydrogen taπrate, potassium hydrogen succinate. sodium citrate, potassium, citrate, or sodium oxalate (or a polycarboxylic acid such as citric acid) with a carbonate or bicarbonate, such as sodium carbonate, sodium bicarbonate, potassium carbonate, potassium carbonate, or calcium carbonate A combination of a monoalkali metal salt of a polycarboxylic acid, such as monosodium citrate or monosodium tartrate. with a carbonate or bicarbonate is an example. Preferred cell size control agents are talc or a stoichiometric mixture of citric acid and sodium bicarbonate (the mixture having a I to 100 percent concentration where the carrier is a suitable polymer such as low density polyethylene or polypropylene). Mixtures of cell size control agents can be used. The physical blowing agent for this invention includes carbon dioxide as the primary blowing agent. Primary blowing agent in this context means that at least 50 mole percent of the total blowing agent is carbon dioxide. The carbon dioxide blowing agent can be used at a rate of 0.5 to 7 0 weight percent, but preferabl . 2 0 to 5 0 weight percent, of the total extrude: llow rate One oι more auxiliary physical blowing agents may also be included Permissible auxih.ir. blow ing agents include both organic and inorganic halogen-free blowing agents and mixtures thereof The inorganic, halogen-free blowing agents are those which are environmentally acceptable and nonflammable The organic blowing agents are those which are environmentally acceptable, but which may be classified as flammable If one or more auxiliary physical blowing agents are used, the preferred auxiliary 1 blowing agents are inorganic blowing agents which are inorganic atmospheric gases and those other compounds which are chemically non-reactive at the extruder conditions. Examples of the preferred auxiliary inorganic blowing agents include argon, nitrogen, neon, helium, krypton, nitrous oxide, and sulfur hexafluoride. The most preferred auxiliary inorganic blowing agent is argon When one or more auxiliary blowing agents are used with carbon dioxide, they are preferably injected individually into separate injection ports, but they can be injected together into the same injection port of the mixing extruder. When the auxiliary blowing agent is argon, it is used at a rate of 0 I to 4 weight percent (but preferably at a rate of 0.1 to 4.0 weight percent) of the total extruder flow rate so that the weight ratio of argon-to-carbon dioxide does not exceed 0 9. When the auxiliary blowing agent is nitrogen, nitrogen can be used at a rate of 0.1 to 1.5 weight percent of the total extruder flow rate so that the weight ratio of nitrogen-to-carbon dioxide does not exceed 0.4. Although considered as a potential physical blowing agent in some prior art. the compound of water is not considered in this invention as a auxiliary blowing agent because the use of water in conjunction with certain oxygenated compounds as described herein has functionality not generally associated with physical blowing agents. The term oiganic blow ing agent > include partial , tluoπnaicd h . ar c.r. s know n a . MFCs ' . HCFCs or CFCs " L dei curi eni Federal law tne u>e of . ruialK ail C ~C - aπti HCI L s arc prohibited in products w hich might be made bv this process and. thus their application in the process invention would be restricted However. HCFCs can be used foi insulation products made by this foamable composition invention The preferred partially fluoridated hydrocarbon blowing agents are those which have molecules which contain up to three carbon atoms and which do not contain any other halogen atoms, such as, 1, 1-difluoroethane (HFC- I 52a). I . l . l -tπfluoroethane (HFC-I 43a), 1. 1. 1.2- tetrafluoroethane (HFC- I 34a). 1.1.1.2.2-peπtafluoroethane (HFC- 125) and 1. 1.2.3.3- pentafluoropropane (HFC-245fa) The most preferred paπialiy fluoπnated hydrocarbon as an auxiliary blowing agent for this invention is HFC- 134a HFC- 134a is used at a rate of 0 1 to 3 0 weight percent of the total extruder flow rate so that the weight ratio of HFC- 134a-to- carbon does not exceed about 1.0 The term ' compatibilizing agent", as used herein, is meant to include those materials that are used in conjunction with either carbon dioxide blowing agent, a blend of carbon dioxide and one or more auxiliary inorganic blowing agents, a blend of caroon dioxide and one or more auxiliary organic blowing agents, or carbon dioxide and a blend of auxiliary organic and inorganic blowing agents ( I ) to sufficiently plasticize the thermoplastic extrudate within the extruder so as to maintain die melt temperatures sufficiently low to produce a closed cell foam structure, and (2) which will have sufficient affinity for the carbon dioxide to lower the pre-foaming pressure at the die with the physical blowing agent or blowing agent blend The compatibilizing agent is one or more materials selected from oxygenated hvdrocarbon compounds that will decrease the minimum pi ssuie lequired to prev ent prefoa'.uπg at the die while retarding the collapse of foam due to excessne blow ing agent migration hen the primary pln sical blowing agent is carbon dioxide Although not speciticalK limited b. the ratio, preferred oxygenated hydrocarbon compounds that having compatibilizing capability for carbon dioxide in a polyolefinic foamable composition have at least one hydro \y I bond and have an overall oxygen-to-carbon atomic ratio between about 0 5 and I 0 Some of the oxygenated hydrocarbons function as compatibilizing agents when used in pure component form, while others only have been found to work when the agent is used in conjunction with water, for example, as in an aqueous solution In general, oxygenated hydrocarbons where 50% or more of the oxygen atoms are linked to carbon atoms by ether bonding such as in a polyglycol can generally function as a compatibilizing agent when added as a pure component Oxygenated hydrocarbons where 50% or more of the oxygen atoms are linked to carbon atoms in hydroxyl group bonding such as in a polyhydπc alcohol generally only function as a compatibilizing agent when supplied in an aqueous solution of 5 to 75 percent by weight Examples of the subclasses of oxygenated hydrocarbons that have demonstrated ability to function as compatibilizing agents when added as pure components or when water is included in the foamable composition are the polyglycols and polyglycol ethers The polyglycol and polyglycol ethers are effective as compatibilizing agents when water is not included in the foamable composition, but lower densities can generally be reached when water is added Permissible polyglycols as used herein includes those that are polymers of ethylene oxide, which may have either a branched or linear molecular structure with a molecular weight of less than about 20000 Those polyglycols with a linear structure include tπethylene glycol, tetraeth lene givcol. pentaethvlene glycol. he.xaethvleiie glycol The polyglycols w ith a branched structure aie generally referred to by their average molecular weight Preterred pranchect poK l . i have an averace molecular weight between about 200 and 20000 The most preferred polyglycol is polyethylene glycol with an average molecular weight of about SOOO. which is abbreviated here-in as "PEG-S0OO" The polyethylene glycol can be added at a rate of 0 I to 2 0 weight percent of the extruder flow rate. The preferred rate is 0.5 to 1.0 weight percent of the extruder flow rate Permissible polyglycol ethers include C, - C, monoalkyl or dialkyl ethers of those polymers of ethylene oxide, which may have either a branched or linear structure wiih a molecular weight of less than about 10000, preferably 200 to 5000 Those polyglycol ethers with a linear structure include tetraethylene glycol dimethyl ether, diethylene glycol dibutyl ether, and poly(ethylene glycol) dimethyl ether, as well as polymers of propylene oxide including tripropylene glycol dimethyl ether. The most preferred linear polyglycol ether is tetraethylene glycol dimethyl ether The polyglycol ethers with a branched structure are generally referred as the methoxy ether or dimethoxy ether of a polyethylene glycol of a specific average molecular weight The preferred branched polyglycol ethers are monomethyl ethers of polyethylene glycol that have an average molecular weight between about 350 and 5000 The most preferred branched polyglycol ether is methoxy ether of polyethylene glycol with an average molecular weight of about 5000. The polyethylene glycol ether can be added at a rate of 0.1 to 2.0 weight percent of the extruder flow rate. The preferred rate of polyglycol ether addition is 0.5 to 1.0 weight percent of the extruder flow rate. Examples of the subclasses of oxygenated hydrocarbon that have demonstrated ability to function as compatibilizing agents only when water is included in the foamable composition are polvethvlene oxides, polyglycerols. polyhvdπc alcohols and pol . - in .l alcohol.- Longer chain branched oι linear polvmers ot etln lene OM.O ai e l et ' eued to as polyethylene oxides which is sometime abbreviated to I'EO The pol .cth . ler.e oxide* permissible in the invention process have a molecular weight between about 200.000 and 1.000.000. preferably 250.000 to 350.000 The most effective means of addition of a polyethylene oxide is inclusion in the resin feed Unlike the polyglycols or polyglycol ethers, the polyethylene oxides have been found only to function in the invention composition when watei is included in the composition The water can be added in the manner used for physical blowing agents The most preferred polyethylene oxide for use in the invention has an average molecular weight of about 300.000 The polethylene oxide can be added at a rate of 0 I to 2 0 weight percent of the extruder flow rate The preferred rate of polyglycol ether addition is 0.3 to 0 7 weight percent of the extruder flow rate Polymers of glycerol are generally referred to as polyglycerols Polygiycerols typically have a linear structure The shoner chain polymers consisting of about I S or less monomeric units should actually be classified as oligoglycerols Unlike the polyglycol or polyglycol ethers, but similar to the polyethylene oxides, the oligoglycerols or polyglycerols have been found to function as a compatibilizing agent when water is included in the extruded foamable composition The preferred oligoglycerols have an average molecular weight less than S00 The most effective means of addition of the oligoglycerol is in an aqueous solution The most effective concentration range of the aqueous solution is 25 to 75 weight percent of the oligoglycerol. The most preferred concentration is 33 to 50 percent by weight of the oligoglycerol. The preferred amount of compatibilizing agent solution is 0.2 to 1.0 weight percent of the total extruder flow rate The most preferred oligoglycerol contains 50 weight percent or more triglycerol (4 S-dioxa- 1.2.6. 10. 1 I -undecanepentol) and has an average moleculai weight ; about 2 'i Polv hvdπc alcohols ai e gei'eralK considered to be those oxygenated mdiocaroon molecules that have oxygen atoms bonded to carbon atoms m a given molecule onlv In two oi mot hydroxyl groups The glycols are the common name given to a specific subclass ot poly . dπc ^ alcohols which have only two hydroxyl groups The permissible polyhydπc alcohols also include fully hydroxylated linear molecules like glycerol, the erythπiols, the arabitols. the xy tols. the adonitols. the sorbitols. the mannitols. the iditols. the allitols. the talitols. and perseitol Preferred polyhydric alcohols further include non-linear compounds like pentaerythπtol. and the mositols Other polyhydric alcohols that are not fully hydroxylated, but have a carbon/oxygen ratio that is approximately unity like rhamnitol, and epifucitol are also permissible in the invention The polyhydric alcohols have generally been found to function in the extruded foamable composition invention as compatibilizing agents only when water ts present The preferred polyhvdnc alcohols have three to eight carbon atoms The most effective means of addition of the polyhydric alcohols is in an aqueous solution having a concentration range of 10 to 60 percent by weight of the polyhydric alcohol The most preferred concentration is 50 percent by weight of the polyhydric alcohol The preferred amount of compatibilizing agent used is 0 2 to 1 0 weight percent of the total extruder, flow rate The most preferred polyhydric alcohol is d-sorbitol (a stereoisomer of 1.2.3.4.5.6-hexanehexol) Polyvinyl alcohols are a specific example of a longer chain poly hydroxylated polymers and are sometimes abbreviated to PVOH. Many of the commercially available polyvinyl alcohols have a linear structure and a molecular weight less than about 200.000. The preferred polyvinyl alcohols have a molecular weight between about 13.000 and 150.000 The most effective means of IS addition of a polwinvl alcohol is inclusion in the resin Like the polvlndπc alcohols, the nolvvmv! alcohols have been found only to function in the inv ention composition w hen water is included in the composition The water can be addedin the manner used for physical blow ing agents The most preferred polyvinyl alcohol for the inv ention process has an average molecular weicht of in the range of about 13.000 to 23.000 The polyvinyl alcohol can be added at a rate of 004 to 2 0 weight percent of the extruder flow rate The preferred rate of polyglycol ether addition is 0 3 to 0 7 weight percent of the extruder flow rate. Other specific classes of oxygenated hydrocarbons which may be used as compatibilizing agents include carbohydrates which are soluble or dispersible in water including those aldoses. ketoses. monosaccharides. disaccharides, trisaccharides, oligosaccharides. and the polysacchaπdes For low density polyethylene (LDPE) foamable compositions, the most preferred compatibilizing agent for use with a physical blowing agent which is primarily carbon dioxide is an aqueous solution of an oligoglycerol of average molecular weight of about 240 and which contains at least 50 percent triglycerol The most effective usage rate is 4S to 52 weight percent concentration aqueous solution of the added at 0.55 to 0.65% of the total extruder flow rate For propylene polymer foamable compositions made with high melt strength polypropylene, the most preferred compatibilizing agent for use with a physical blowing agent which is primarily carbon dioxide is an aqueous solution of a d-sorbitol. The most effective usage rate is4S to 52 weight percent concentration aqueous solution of the added at 0.55 to 0.65% of the total extruder flow rate. Other additives, such as. coloring agents, fire retardants. antioxidants. and plasticizers, as normally known in the art can also be included in the foamable composition Besides the potyolefins. the oxygenated hydrocarpons are cxpecter. to function ι :ι a foamable composition with other polvπieπc svsiems know n κι the an 10 be capaoie 01 pioducmg foams w ith carbon dioxide blowing agent Such other s tems include but are not limited to polystyrene foam, polycarbonate foam, and polymethylmethacrylate foam Generally, the foamable composition can be made into a foam comprising the steps of (a) feeding a polyolefinic polymer into an extruder. (b) adding a nucleating agent to the resin feed, (c) optionally adding a permeation modifier to the resin feed. (d) plasticating the mixture in an extruder to form a polymeric melt. (e) incorporating a blowing agent of carbon dioxide and optionally one or more members selected from the group consisting of inorganic blowing agents, organic blowing agents, and combinations thereof, (0 incorporating at least one compatibilizing agent into said foamable composition wherein said compatibilizing agent is an oxygenated hydrocarbon that decreases the minimum pressure required to prevent prefoaming while retarding the collapse of foam due to excessive blowing agent migration, (g) uniformly mixing and cooling the foamable composition to a temperature effective for the expansion of the polyolefinic foam; and (h) extruding or ejecting the foamable composition through a die at a sufficient high rate to form a polyolefinic foam. The invention is also directed to a foam composition made by the above- described process. In particular, the foamable invention composition has equivalent utility in both a continuous process and an intermitieπt proces> The foamable composition with the compatibilizing a«_enι can be used in an extrusion process operated on ? continuous o sis using a conv ention.!' extruder svstem The continuous process for poKolefuuc foam> can produce foam of am tlιιcknes> The intermittent process is generally used for large cross-section polvolef ic foams with thicknes.s greater than about 25 mm The two processes have similar extrusion conditions but differ slightly tn preferred composition The foamable invention composition also has utility in producing foams from those polyolefinic resins that are generally regarded as being foamable in the art by a conventional foam extrusion process Low-Density Polyethylene (LDPE) and High Melt Strength Polypropylene are the preferred embodiment of such resins The two resins have significantly different melting temperatures and thus different compatibilizing agents have been found to be more effective with polypropylene than polyethylene and other different compatibilizing agent have been found to be more effective with polyethylene than with polypropylene Finally, some of the applications for such thermoplastic polyolefinic cellular bodies require specific density ranges for attainment of prescribed physical property specifications The use of carbon dioxide in combination with ceπain auxiliary blowing agents has been found to be more effective than carbon dioxide in combination with other blowing agents for producing a polyethylene foam within a specific foam density range Accordingly, preferred embodiments include ( I ) Low Density Polyethylene (LDPE) Foam made in a Continuous Process. (2) Low Density Polyethylene (LDPE) Foam made in an Intermittent Process in the range of 10 kg/m' to about 73 kg m 3 , (3) Low Density Polyethylene (LDPE) Foam made in an Intermittent Process in the range of 73 kg/m 3 to about 150 kg m 3 . (4) Hieli Melt Strength (HMS) Pol y propylene Foam made m a Continuous Process. ι ς ) High Mel; Stren th (HMS) Polypropylene Foam made in an Intermittent Process in the range of 10 kg in ' to about 50 kg/m 1 LDPE FOAM in a CONTINUOUS PROCESS Pellets of Low-density Polyethylene resin with density in the range of 910-920 kg/m' and a Melt Flow Index in the range of l .S-2.2 g 10 min (AST Condition P) are co-fed into an extruder hoppei with 0.01 to 0 05 weight percent pellets of a 20% active ingredient crystalline silica concentrate which is also based in a low-density polyethylenic material which has a Melt Flow Index that is preferably in the same range as the resin of the polyethylene pellets Pellets of commercial grade octadecanamide are added at a rate of about 1.0 to 1.25 weight percent of the total pellet feed The pellet blend is melted in the 48: 1 L:D single screw extruder and compressed by the screw to a pressure of about 1.25 MPa. The screw is mechanically driven to rotate at a rate of 30-50 revolutions per minute depending upon the desired extruder output rate Through one injection poπ which is located approximately 16 diameter lengths downstream of the extruder pellet feed throat, carbon dioxide which has been pressurized to 17.5 MPa is regulated through a control valve for delivery at about 5 to 6% of the total extruder flow rate. Through a separate injection port that is located 90" radially from the port used for carbon dioxide. l . l , 1.2-tetrafluoroethane as an auxiliary blowing agent is pumped to pressure of about 17 MPa and is subsequently regulated into the extruder at a rate of 2 to 3% of the total extruder flow rate. Through another separate injection port that is located I SO" radially from the port used for carbon dioxide, a 50% by weight aqueous solution of oligoglycerol with an average molecular weight of about 239 is pumped to a pressure of about 17 MPa and is 71 subsequent! , regulated into the extmder at A rate of about ιl of the total ex;r....e; rlov rate Immediately dow nstream of the iniection poπ me extrude- scr w ,s e uirwed ιt:ι a mixing section containing at least four sciew -diameiei lengths of multiple nιghlv -r-:ched segmented flights The physical blowing agent and the oligoglv cerol/ water solution are mixed in the pressurized melted material in the mixing zone The barrel temperatures of the four or more extruder zones of the single screw extmder subsequent to the injection zone are decreased in increments to deliver an extrusion melt temperature in the range of 105 °- 1 1 5"C to the head of the extruder at a pressure of 9 3 to 10 0 MPa if an optional gear pump is present or 15 to 17 MPa if there is no gear pump The pressuπzed melt is delivered to an annular foam die with an exit angle of 40-50" and die lands with a converging angle of 3" to 5° The cooled polyethylene/carbon dioxide/oligoglycerol/water combination extrudes through the die to atmospheric pressure and most of the physical blowing agent expands rapidly to form bubbles at the nucleating sues established by the nucleating agent particles Example I details the preferred embodiment of the invention for LDPE in the continuous process Example 2 shows what happens when the compatibilizing agent is remov ed Example 3 shows the results of an alternative compatibilizing agent with LDPE tn a continuous process PROCESS for LARGE CROSS-SECTION LDPE FOAM in DENSITY RANGE OF 10 kg m 3 to ABOUT 73 kg m 3 Pellets of Low-density Polyethylene resin with density m the range of 910-920 kg/m 1 and a Melt Flow Index in the range of t S-2.2 g 10 mm (ASTM Condition P)are co-fed into an extruder hopper with 5-6 weight percent pellets of a 20% active ingredient crystalline silica concentrate w hich is also based in a low -densit y polveihv lenic material w hicn has a Melt Plow Index mat is preferably in the same range as the resin of the polv cihv lene pellet.- Pellet > ot commercial grace octadecanamide are added at a rate of about I 0 to 1 25 w eight percent of the total pellet iced . he pellet blend is melted in the 32 I L D single screw extruder and compressed bv the screw to a pressure of about 12 5 MPa Through one injection poπ which is located approximate! v 16 diameter length downstream of the extruder pellet feed throat, carbon dioxide which has been pressurized to I 75 MPa is regulated through a control valve for delivery at about 2 to 4% of the total extruder flow rate Through a separate injection port that is located 90° radially from the poπ used for carbon dioxide. 1. 1.1.2-tetrafIuoroethane which has been separately pressuπzed to 17 5 MPa is regulated through a separate control valve for delivery- at about 2 to 4% of the total extrudei flow rate Through a third injection poπ that is located 270" radially from the poπ used for carbon dioxide, an 50 percent by weight aqueous solution of an oligoglycerol of average molecular weight of 239 and containing at least 50% tngiyceroi is pumped to a pressure of about 17 5 MPa is regulated into the extruder at a rate of about 0 6% of the total extruder flow rate Immediately downstream of the injection port, the extruder screw is equipped with a mixing section containing at least four screw-diameter lengths of multiple highly-pitched segmented flights The carbon dioxide. 1.1. 1 ,2-tetrafluoroethane. and aqueous oligoglycerol solution are mixed into the pressurized melted material in the mixing zone The molten extrudate is compressed in the final stages of the extruder to 14. 1 to 14.5 MPa and is subsequently fed through a heated pipe into a secondary extruder. The secondary extruder is any one that has been specifically designed to accept molten polymer feeds and should have a flighted screw length equivalent to at least 24 of its screw diameters with equivalence to 32 diameters being the preterred length The ratio of the screw diameter of the secondary extruder to the screw diametei of the fu st extrudet should preterablv be in the 1.25 to I 4 range The preferred screw design for optimal melt cooling has four parallel (lights radially spaced by 90° with cross-cut segment with a length about '/, of the screw diameter missing from each flight with a repeat length equivalent to four screw diameters In the secondary extruder, the extruder barrel temperatures are maintained to deliver a melt temperature in the range of 90° to 1 15 ° with 10S°C as the ideal melt temperature The pressure at the head of the extruder should be maintained at 9.3 to 1 1 .3 MPa if an optional gear pump is present or will be about 17.5 to 1 .5 MPa if there is no gear pump The cooled pressurized molten mixture of polyethylene, carbon dioxide, 1.1 , 1.2-tetrafluoroethane. and aqueous oligoglycerol solution is pumped through a pipe through into a hydraulic-pressurized piston chamber which is set to maintain a melt pressure of about 12.4 MPa The various zones of the chamber are externally cooled by forced convection air to the range of 99 β to l05 β C The specific details of the piston process are discussed in U.S. Patent 4.323.52S. In summary, as the volume of the molten mixture fills the piston chamber, the piston plunger wall moves. When the piston moves a predefined distance, a switch actuates the drive system and the gate system for the cylinder. For the current discussed process, the drive mechanism is set to move the plunger at a predefined speed so as to dispel the material through the radial die at a rate of about 2350 kg/hr. The discharged material expands rapidly in all three directions as it leaves the die, but is captured on a conveyor table equipped to move the expanded mass sufficiently to clear the die and to control the expansion of the material in the thickness and machine directions. The resulting foam block in left in the table long enough for the next adv ance of the plunge: The ό2"i block ι> placed upon additional cooling racks and allow ed to cool sufficiently for handling tv r.cailv mumιe> Example 4 details the preferred embodiment of the invention for the lntermitte-: process that can produce large cross section polyethylene foam s INTERMITTENT PROCESS for LARGE CROSS-SECTION LDPE FOAM in DENSITY RANGE OF 10 kg/m 3 to ABOUT 73 kg m 3 Pellets of Low-density Polyethylene resin with density in the range of 9 i 0-920 kg m' and a Melt Flow Index in the range of I .S-2.2 g/ 10 m (ASTM Condition P)are co-fed into an extruder hopper with 5-6 weight percent pellets of a 20% active ingredient crystalline silica concentrate which is also based in a low-density polyethylenic material which has a Melt Flow Index that is preferably in the same range as the resin of the polyethylene pellets Pellets of commercial grade octadecanamide are added at a rate of about 1 .0 to 1.25 weight percent of the totai pellet feed The pellet blend is melted in the 32 I L:D single screw extruder and compressed by the screw to a pressure of about 1 25 MPa Through one injection poπ which is located approximately 16 diameter length downstream of the extruder pellet feed throat, carbon dioxide which has been pressurized to 1.75 MPa is regulated through a control valve for delivery at about 2 to 4% of the total extruder flow rate Through a separate injection port that is located 90" radially from the poπ used for carbon dioxide, argon which has been separately pressurized to 17.5 MPa is regulated through a separate control valve for delivery at about 2 to 4% of the total extruder flow rate. Through a third injection port that is located 270" radially from the port used for carbon dioxide, an 50 percent by weight aqueous solution of an oligoglycerol of average molecular weight of 239 and containing at least 50% triglycerol is pumped to a pressure of about 17.5 MPa is regulated into the extruder at a rate of about 0 6% of the total extruder flow rate Immediately downstream of the iniection port the extrudei sciew ι> equipped w ith a mixing section containing at least four screw -diameter lengths of multiple highly -pitched segmented flights The carbon dioxide, argon, and oligoglycerol solution are mixed into the piessurized melted material in the mixing zone The molten exmidate is compressed in the final stages of the e.xtnidei to 14 I to 14.5 MPa and is subsequently fed through a heated pipe into a secondary extruder The secondary extaider is any one that has been specifically designed to accept molten polymer feeds and should have a flighted screw length equivalent to at least 24 of its screw diameters with equivalence to 32 diameters being the preferred length. The ratio of the screw diameter of the secondary extruder to the screw diameter of the first extruder should preferably be in the 1.25 to 1.4 range. The preferred screw design for optimal melt cooling has four parallel flights radially spaced by 90° with cross-cut segment with a length about { l. of the screw diameter missi g from each flight with a repeat length equivalent to four screw diameters In the secondary extruder, the extruder barrel temperatures are maintained to deliver a melt temperature in the range of 90° to 1 15 ° with I 0S°C as the ideal melt temperature The pressure at the head of the extruder should be maintained at 9.3 to 1 1 3 MPa if an optional gear pump is present or will be about 17.5 to 19.5 MPa if there is no gear pump The cooled pressurized molten mixture of polyethylene, carbon dioxide. 1.1.1.2-tetrafluoroethaπe, and aqueous oligoglycerol solution is pumped through a pipe through into a hydraulic-pressurized piston chamber which is set to maintain a melt pressure of about 12.4 MPa The various zones of the chamber are externally cooled by forced convection air to the range of 99" to I05°C. The specific details of the piston piocess aie discussed m I S Patent 32 " >. _1S In summary , as the volume of the molten mixture fills the piston cnam ei the piston plunge w all moves When the piston moves a predefined distance, a sw itch actuates the driv sv tem and the gate system for the cylinder For the current discussed process, the drive mechanism is set to move the plunger at a predefined speed so as to dispel the material through the radial die at a l ate of about 2350 kg/hr The discharged material expands rapidly in all three directions as it leaves tnc die. but is captured on a conveyor table equipped to move the expanded mass sufficiently to clear the die and to control the expansion of the material in the thickness and machine directions The resulting foam block in left in the table long enough for the next advance of the plunger The foam block is placed upon additional cooling racks and allowed to cool sufficiently for handling, typically 15 minutes Example 3 details the preferred embodiment of the invention for the intermittent process that can produce large cross section polyethylene foam in the density range of 73 kg m 3 to 100 kg m 3 Example 4 provides a description of an alternative composition that produced large cross- section foam with tetraethylene glycol dimethyl ether, carbon dioxide, and argon Example 5 shows the results when the polyglycol ether was removed from the process under the conditions of Example 4 HMS POLYPROPYLENE FOAM in a CONTINUOUS PROCESS Pellets of high melt strength polypropylene resin having a density in the range of 900 to 10 kg m 3 and a Melt Flow Index in the range of 2.0 to 4.0 g 10 min (ASTM Condition L) are co-fed into an extruder hopper with 0.5 to 2.0 weight percent pellets of a nominal 20 percent active ingredient crystalline silica concentrate which is based in a low-density polyethylene. The pellet 2S blend is melted in the 4S I L D single screw extruder and compressed bv the s : w to a pressure of about 1 25 MPa The screw is mechanicall y driven to rotate at a rate of 30- 50 rev ..:;ιons pei minute depending upon the desired extruder output rate Through one injection poπ w hich is located approximately 16 diameter lengths downstream of the extmder pellet feed thro. 1 .;, carbon dioxide which has been pressurized to 1 7 5 MPa is regulated through a control v alv e for delivery at about 5 to 6% of the total extruder flow rate. Through another separate injection poπ that is located I SO" radially from the port used for carbon dioxide, a 50% by weight aqueous solution of d-sorbitol with an average molecular weight of about 239 is pumped to a pressure of about 17 MPa and is subsequently regulated into the extruder at a rate of about 0.6% of the total extruder flow rate Immediately downstream of the injection port, the extruder screw is equipped with a mixing section containing at least four screw-diameter lengths of multiple highly-pitched segmented flights. The physical blowing agent and the d-sorbiiol/water solution are mixed in the pressurized melted material in the mixing zone. The barrel temperatures of the four or more extruder zones of the single scre extruder subsequent to the injection zone are decreased in increments to deliver an extrusion melt temperature in the range of 105°- ! 15°C to the head of the extruder at a pressure of 9.3 to 10.0 MPa if an optional gear pump is present or 15 to 17 MPa if there is no gear pump The pressurized melt is delivered to an annular foam die with an exit angle of 40-50° and die lands with a converging angle of 3 ° to 5 °. The cooled polyethylene/carbon dioxide/oligoglycerol/water combination extrudes through the die to atmospheric pressure and most of the physical blowing agent expands rapidly to form bubbles at the nucleating sites established by the nucleating agent particles. Example 6 details the preferred embodiment of the invention for the continuous process HMS POLYPROPYLENE FOAM in a INTERMITTENT PROCESS for LARGE CROSS- SECTION FOAM in DENSITY RANGE OF 10 kg/m 3 to ABOUT 73 kg/m ; Pellets of high melt strength polypropylene resin having a density in the range of 900 iv 910 kg m 3 and a Melt Flow Index in the range of 2.0 to 4.0 g/10 min (ASTM Condition L) are co-fed into an extmder hopper with 0.5 to 2.0 weight percent pellets of a nominal 20 percent active ingredient crystalline silica concentrate which is based in a low-density polyethylene. The pellet blend is melted in a 32: 1 L:D (i.e., Iength:diameter) single screw extruder, and is compressed by the screw to a pressure of about 1.25 MPa Through one injection poπ, which is located approximately 16 diameter lengths downstream of the extruder pellet feed throat, carbon dioxide which has been pressurized to 17.5 MPa is regulated through a control valve for delivery at about 3 to 6 percent of the total extruder flow rate, depending upon the target density. An aqueous solution containing 50 weight percent of d-sorbitol is pressurized and regulated into the extruder at a rate of about 0.6% percent of the total extruder flow rate through a separate injection poπ which is located either 90" or I S0° radially from the port used for carbon dioxide. Immediately downstream of the injection port, the extruder screw is equipped tvith a mixing section containing at least four screw-diameter lengths of multiple, highly-pitched. segmented flights. The carbon dioxide, water, and the d-sorbitol are mixed into the pressurized melted material in the mixing zone. The molten extrudate is compressed in the final stages of the extruder to 14.1 to 14.5 MPa and, subsequently, is fed through a heated pipe into a secondary extruder. The secondary extruder is any one which has been specifically designed to accept molten polymer feeds It should hav e a flighted screw length equiv alent to at leas: 2 of us screw diameters, with equivalence to 32 diameters being the prefeπ ed length The ratio of the screw diameter of the secondary- extruder to the screw diameter of the first extruder preferably should be greater than I 25 The preferred screw design for optimal melt cooling has four parallel flights radially spaced by 90". with a cross-cut segment with a length of about one-third of the screw diameter missing from each flight and with a repeat length equivalent to four screw diameters In the secondary extruder, the extruder barrel temperatures are maintained to deliver a melt temperature in the range of 150°C to I 70°C, with the ideal melt temperature depending upon the propylene polymer blend employed The pressure at the head of the extruder should be maintained at 9 3 to 1 1 3 MPa if an optional gear pump is present, or it will be at about 1 7 5 to 1 5 MPa if there is no gear pump present The cooled, pressurized molten mixture of propylene polymer, carbon dioxide, water, and d-sorbitol is pumped through a pipe into a hydrauiically-pressurized piston chamber which is set to maintain a melt pressure of about 12 4 NfPa The various zones of the chamber are externally cooled by forced convection air to the range of 160° to I 65*C The specific details of the piston process are discussed in U S Patent No 4.323.52S In summary, as the volume of the molten mixture fills the piston chamber, the piston plunger moves When the piston plunger moves a predefined distance, a switch actuates both the drive system and the gate system for the cylinder For the invention process, the drive mechanism is set to move the plunger at a predefined speed, so as to dispel the material through the radial die at a rate of about 7000 g/hr. The discharged material expands rapidly in all three directions as it leaves the die. but is captured on a conveyor table equipped to move the expanded mass sufficiently both to clear the die and to control the expansion ot the material in the tπickness a d maclv . directions 1 h. lesultant roam block is left in the table long enough toi tne next adv nce o: tlie : • -MILIC, The to.itii block is placed upon additional cooling racks and allowed to cool sufficiently to r -andling tv icallv for 15 minutes to one hour The following examples are provided for illustrative purposes oπlv and the inv ention described herein should not be considered limited thereto EXAMPLE I This example embodies LDPE foam made in a continuous process using a foamable composition that contains an oligoglycerol of average molecular weight of aoout 239 as the compatibilizing agent Pellets of Wesilake Polyethylene 606 are co-fed with 1 0 weight percent of pellets of Witco Kemamide (octadecanamide) and 0 OS weight percent of pellets o Schulman F20V crystalline silica into a modified 32 I L D Berlyn 2 5-ιπch (64 mm) single-screw extruder operating with a screw speed of 42-46 rpm Commercial-grade 99 S% purity carbon dioxide which has been pressuπzed is injected at a pressure of about 13 I MPa at a rate of I 9 kg hr E I DuPont de Nemours Formacel Z-4 ( l . l . I .2-tetrafluoroethane) which has been pressurized is injected at a pressure of about 13 I MPa at a rate of I 04 kg hr through a separate injection poπ 90" radially from the port used for carbon dioxide An 33.3% by weight aqueous solution of Hexagon Enterprises Hexapol G-3 (an oligoglycerol having an average molecular weight of about 239 and a typical triglycerol content of about 51%) which has been prepared from city water is pressurized and injected at a pressure of about 1 .1 MPa at a rate of about 0.27 kg hr through a separate injection port 180" radially from the port used for carbon dioxide The multi-component polymer mixture is J l subsequently pressuπzed to 1 7 1 MPa at the extmder discharge an transfer through a heated pipe to a second iar_.er 3 5-mch (S 1 ) mm) single sciew cooling extrudei 1 lie mixtui e is cooied in the coolmt s extruder to a melt temperature of S9°C and subsequently pressurized to 12 2 MI'a at the extmder discharge The extmder head pressure is regulated by a Normag 2200 gear pump system The pressurized molten polymer mixture is delivered through an annular die equipped w ith 3-ιnch (76 mm) diameter die lips. The die gap is closed sufficiently to generate a die entry pressure of about 9.7 MPa. The extruder output is about 37 kg hr The hot foam is drawn over a water-cooled hollow-tube mandrel and the outside surface is cooled by forced convection air from a poπable multi-holed ring. The draw rate is controlled by an S-configuration pull roll The foam sheet is subsequently collected at a downstream winder Samples of the foam sheet are weighed and the sheet thickness is measured immediately. Samples taken fresh from the winder have a thickness of 1.93 mm and a density of 45 kg/m 3 . Two days later, the same sample of foam has a thickness of 2.02 mm and a density of 43 Kg/m 3 EXAMPLE 2 This example illustrates the compatibilizing effect of the oligoglycerol/water mixture by a temporary deletion from the extrudable composition. During a trial run using the formulation of Example I. the supply canister of Hexapol G-3/water mixture ran empty. Almost immediately after the mixture flow stopped, the polymeric material coming through the die lips became an open cell structure with gas randomly exiting the molten mass and the extruder pressures began fluctuating wildly. When the flow of the Hexapol G-3/water mixture was restored, the extrusion line quickly returned to stable operating conditions, and produced foam equivalent to that made immediately before the process upset EXAMPLE .< This example is sunilai to Examples I but uses a solution of 40 weight percent d- sorbitol in city water as the compatibilizing agent The sorbitol solution is injected at the same rate as that used for the Hexapol G-3 of Example 1 and other component rates are kept the same In this case, samples taken fresh from the winder have a thickness of I 6S mm and a density of 54 kg/πι ! The samples exhibit thinner caliper within the hour after production but returns the next day to the original density. EXAMPLE 4 This example embodies thick cross section LDPE foam made in a intermittent process using a foamable composition that contains an oligoglycerol of average molecular weight of about 239 as the compatibilizing agent Pellets of Westlake Polyethylene 606 are co-fed with 1 4 weight percent of pellets of Akzo Nobel Armoslip I S (octadecanamide) and about 0 OS weight percent of pellets of Schulman F20V crystalline silica into a 4S I L:D Wilmington 3-inch (76 mm) single-screw extmder operating with a screw speed of 36-37 rpm. Commercial-grade 99.8% purity carbon dioxide which has been pressurized is injected at a pressure of about 13 I MPa at a rate of 0.6S kg/hr. E.I. DuPont de Nemours Formacel Z-4 (1.1.1.2-tetrafluoroethane) which has been pressurized is injected at a pressure of about 13. MPa at a rate of 1.22 kg hr through a separate injection port 90° radially from the port used for carbon dioxide. A 50 weight percent aqueous solution of Hexagon Enterprises Hexapol G-3 which has been prepared from city water is pressurized and injected at a pressure of about 13.1 MPa at a rate of about 0.27 kg hr through a separate iniection poπ I SO" radially from the port used for carbon dioxide The rv.ulti-compoiieiu mixtuie is cooled in the extmder to a melt temperature of I 07"C and subsequently pies.un-.ed to 1 9 MPa at the extruder discharge The extmder head pressure is regulated bv a \ormag 2200 gear pump system The melt pump increases the pressuie of the melt to I S 3 MPa for delivery into the cooled hydraulically pressurized piston chamber When the till of the material mov es the piston to a predefined distance, a switch actuates the drive system and the gate system for the cylinder to dispel the material through the radial die at a rate of about 533S kg/hr Samples of the resulting foam block have a fresh density of 30 9 kg/m 3 EXAMPLE 5 In this example, the Example 4 compatibilizing agent of 50 weight percent aqueous solution of the oligoglycerol is replaced by a 7.5 weight percent aqueous solution of .Air Products Airvol 103. a polyvinyl alcohol that has an average molecular weight between about 13.000 and 23.000 Problems with the pumping system for the aqueous polyvinyl alcohol solution delay its introduction into the extmder Prior to the injection of the solution, the extmder is operating with the other components at concentrations similar to that of the Example 4 formulation sans the oligoglycerol solution and producing non-descript masses of polymer at the die Upon stabilization of the aqueous polyvinyl alcohol solution flow rate at about 0.23 kg/hr. a foam begins forming which has a fresh density of 3 1.2 kg m 3 - EXAMPLE 6 This example embodies thick cross section LDPE foam made with an intermittent process in the higher density range than that of example 4 This foamable composition also contains an oligoglycerol of average molecular weight of about 239 as the compatibilizing agent, but the auxiliary blowing agent is changed from 1. 1 , 1 ,2-tetrafluorocthane to 99.99S% purity commercial grade argon. Pellets of Wesilake Polyethylene 606 and mixed with Schulman F20V crystalline talc- concentrate based in low density polyethylene are heated in a modified 32: 1 L:D Berlvn 2.5-inch (63.5 mm) single-screw extmder operating with a screw speed of 3S-42 rpm. Commercial-grade 99.8% purity carbon dioxide which has been pressurized is injected at a pressure of about 13. 1 MPa at a rate of .91 kg/hr. Commercial-grade 99.99S% purity argon which has been pressurized is also injected through a separate injection port at a rate of .91 kg/hr. A 50 weight percent aqueous solution of Hexagon Enterprises Hexapol G-3 which has been prepared from city water is pressurized and injected at a pressure of about 13.1 MPa at a rate of about 0.27 kg/hr through a separate injection port 90° radially from the port used for carbon dioxide. The five-component mixture is subsequently pressurized to 14.3 MPa at the extmder discharge an transfer through a heated pipe to a second larger 3.5-inch (S9 mm) single screw cooling extmder. The mixture is cooled in the cooling extmder to a melt temperature of about I07 * C at 4.1 MPa. The secondary extmder head pressure is regulated by a Normag 2200 gear pump system. The melt pump increases the pressure of the melt to I S 3 MPa for delivery into the cooled hydraulically pressurized piston chamber. When the fill of the material moves the piston to a predefined distance, a switch actuates the drive system and the gate system for the cylinder to dispel the material through the radial die at a rate of about 2 50 kg/hr. Samples of the resulting foam block have a fresh density of 79.S kg/m 5 . EXAMPLE 7 This example embodies HMS polypropylene foam made in a continuous process using a foamable composition that contains an oligoglycerol of average molecular weight of about 239 as the compatibilizing agent Pellets of Montell PFS 1 Polypropylene are co-fed with aboui O.OS weight percent of pellets of Schulman F20V crystalline silica into a modified 32. 1 L D Berlyn 2. -inch (64 mm) single-screw extmder operating with a screw speed of 5S-62 rpm Commercial- grade 99. S% purity carbon dioxide which has been pressurized is injected at a pressure of about 19.3 MPa at a rate of 1.6 kg/hr. A 50 percent by weight aqueous solution of Hexagon Enterprises Hexapol G-3 which has been prepared from city water is pressurized and injected at a pressure of about 19.3 MPa at a rate of about 0. IS kg hr through a separate injection poπ 1 S0° radially from the port used for carbon dioxide. The multi-component polymer mixture is subsequently pressurized to 15.9 MPa at the extruder discharge an transfer through a heated pipe to a second larger 3.5-inch (89 mm) single screw cooling extmder. The mixture is cooled in the cooling extmder to a melt temperature of 143°C and subsequently pressurized to 6.9 MPa at the extmder discharge. The extmder head pressure is regulated by a Normag 2200 gear pump system. The pressurized molten polymer mixture is delivered through an annular die equipped with 3-inch (76 mm) diameter die lips. The die gap is closed sufficiently to generate a die entry pressure of about 8.7 MPa. The extruder output is about 1 kg/hr. The hot foam is drawn over a water-cooled hollow-tube mandrel and the outside surface is cooled by forced convection air from a portable multi-holed ring. The draw rate is controlled by an S-configuration pull roll. The foam sheet is subsequently collected at a downstream winder. Samples of the foam sheet are weighed and the sheet thickness is measured immediately Samples taken fresh from the winder hav e a thickness of 0 9 mm and a densit y 1 69 kg/m " ' EXAMPLE S This example embodies thick cross section HMS polypropylene foam made in a intermittent process using a foamable composition that contains d-sorbitol as the compatibilizing agent. Pellets of Montell PFS I4 Polypropylene are co-fed with about O.OS weight percent of pellets of Techmer T- 1901 Talc concentrate Schulman into a 4S 1 L.D Wilmington 3-inch (76 mm) single-screw extmder operating with a screw speed of 36-37 rpm. Commercial-grade 99 S% purity carbon dioxide which has been pressurized is injected at a pressure of about 13. 1 MPa at a rate of 1.13 kg/hr. A 50 weight percent aqueous solution of SPI Polyols Crystalline Sorbitol 712 which has been prepared from city water is pressurized and injected at a pressure of about 1 I MPa at a rate of about 0.27 kg/hr through a separate injection port ISO 0 radially from the poπ used for carbon dioxide. The multi-component mixture is cooled in the extmder to a melt temperature of I07°C and subsequently pressurized to 15.. MPa at the extmder discharge. The extmder head pressure is regulated by a Normag 2200 gear pump system. The melt pump increases the pressure of the melt to IS.3 MPa for delivery into the cooled hydraulically pressurized piston chamber When the fill of the material moves the piston to a predefined distance, a switch actuates the drive system and the gate system for the cylinder to dispel the material through the radial die at a rate of about 7800 kg/hr. Samples of the resulting foam block have a fresh density of 25.6 kg/m 3 . EXAMPLE 9 The following table shows alternativ e compatibilizing agerr.s for HMS polypropy lene foam made in a intermittent process and the efiecuve lower density limit using a .sole blowing ageni of carbon dioxide The lower density is the point w here additional blow ing agent results m increased density due to matrix collapse

Claims: What is claimed is 1 A method of making a polyolefinic foam composition comprising the sιep> 01 (a feeding a polyolefinic polymer into an extrudei . (b) adding a nucleating agent to the resin feed. (c) optionally adding a permeation modifier to the resin feed, (d) plasticating the mixture in an extmder to form a polymeric melt, (e) incorporating a blowing agent of carbon dioxide and optionally one or more members selected from the group consisting of inorganic blowing agents, organic blowing agents, and combinations thereof. (f) incorporating at least one compatibilizing agent into said foamable composition wherein said compatibilizing agent is an oxygenated hydrocarbon that decreases the minimum pressure required to prevent prefoaming while retarding the collapse of foam due to excessive blowing agent migration; (g) uniformly mixing and cooling the foamable composition to a temperature effective for the expansion of the polyolefinic foam; and (h) extruding or ejecting the foamable composition through a die to form a polyolefinic foam, wherein said foam has a density of between 10 kg/m 3 to 150 kg/m 3 2. The method of making a foam composition of claim I . wherein said polyolefinic foam is a polypropylene foam 3. The method of making a foam composition of claim 2. wherein said compatibilizing agent is a polyglycol 4. The method of making a foam composition of claim 3, wherein said polyglycol is a branched or linear polymer of ethylene oxide having a molecular weight of between about 200 and 20000. 5. The method of making a foam composition of claim 4, wherein said polyglycol is a branched or linear polymer of ethylene oxide hav ing a molecular w igh; f about SOOO 6 The method of making a foam composition of claim 2. wherein said compatibilizing agent is a polyglycol ether 7 The method of making a foam composition of claim 6, wherein said polyglycol ether is a C, to C, monoalkvl or dialkyl ether of ethylene oxide having a branched or linear structure and a molecular weight of less than about 10000. 8. The method of making a foam composition of claim 7. wherein said polyglycol ether is monomethyl ether of ethylene oxide having a branched stmcture and a molecular weight of about 5000. 9. The method of making a foam composition of claim 2, wherein said compatibilizing agent is a polyethylene oxide and wherein water is included in the foamable composition 10. The method of making a foam composition of claim 9, wherein said polyethylene oxide has a molecular weight of about 200.000 to 1.000.000. I I . The method of making a foam composition of claim 2. wherein said compatibilizing agent is a polyglycerol and wherein water is included in the foamable composition. 12. The method of making a foam composition of claim 1 1 , wherein said polyglycerol is an oligoglycerol having a molecular weight of less than about 800. 1 . The method of making a foam composition of claim 12, wherein said oligoglycerol is in an aqueous solution and comprises 50% or more triglycerol and has an average molecular weight of about 240. 14. The method of making a foam composition of claim 2. wherein said compatibilizing agent is a polyhydric alcohol and wherein watei is included in the foam composition 15 The method of making a foam composition of claim 14. w herein saiα polvhvclπc alcohol has three to eight carbon atoms 16 The method of making a foam composition of claim 15. wherein said polyhydric alcohol is selected from the group consisting of glycerol. erythritol. arabitol, xylitol. adonitol. sorbitol. mannitol. iditol, allitol. talitol. perseitol. peπtaerythritol. inositol. rhamnitol. and epifucitol 17 The method of making a foam composition of claim 16, wherein said polyhydric alcohol is d-sorbitol IS. The method of making a foam composition of claim 2, wherein said compatibilizing agent is a polyvinyl alcohol and wherein water is included in the foam composition 19. The method of making a foam composition of claim 2. wherein said polyvinyl alcohol has a molecular weight of less than about 200.000. 20. The method of making a foam composition of claim I . wherein said polyolefinic foam is polyethylene 21. The method of making a foam composition of claim 20. wherein said compatibilizing agent is a polyglycol. 22. The method of making a foam composition of claim 21, wherein said polyglycol is a branched or linear polymer of ethylene oxide having a molecular weight of between about 200 and 20000. 23. The method of making a foam composition of claim 22, wherein said polyglycol is a branched or linear polymer of ethylene oxide hav ing a molecular weight of about SO. ' " 1 24 The method of making a foam composition of claim 20. w herein said compatibilizing agent is a polyglycol ether 25 The method of making a foam composition of claim 24, wherein said polyglycol ether is a C, to C t monoalkyi or dialkyl ether of ethylene oxide having a branched or linear stmcture and a molecular weight of less than about 10000 26. The method of making a foam composition of claim 25. wherein said compatibilizing agent is a polyethylene oxide and wherein water is included in the foamable composition 27. The method of making a foam composition of claim 26. wherein said polyethylene oxide has a molecular weight of about 200.000 to 1.000.000. 2S. The method of making a foam composition of claim 20. wherein said compatibilizing agent is a polyglycerol and wherein water is included in the foamable composition 29. The method of making a foam composition of claim 2S, wherein said polyglycerol is an oligoglycerol having a molecular weight of less than about S00 30. The method of making a foam composition of claim 29. wherein said oligoglycerol is in an aqueous solution and comprises 50 % or more triglycerol 31. The method of making a foam composition of claim 20, wherein said compatibilizing agent is a polyhydric alcohol and wherein water is included in the foam composition. 32. The method of making a foam composition of claim 1. wherein said polyhydric alcohol has three to eight carbon atoms. 33 The method of making a foam composition of claim 32. where::-, said polv hvdπ.- alcohol is selected from the group consisting of glycerol. erythπto ' . arabuol xvlitol adonitol, sorbitol, mannitol. iditol. allitol. talitol. perseitol. peniaeryiπruol. mositol rhamnitol. and epifucitol 34. The method of making a foam composition of claim 33. wherein said polyhydric alcohol is d-sorbitol. 35. The method of making a foam composition of claim 20, wherein said compatibilizing agent is a polyvinyl alcohol and wherein water is included in the foam composition 36. The method of making a foam composition of claim 35. wherein said polyvinyl alcohol has a molecular weight of less than about 200,000 37. The method of making a foam composition of claim 2, wherein said compatibilizing agent is a carbohydrate soluble or disperable in water. 38. The method of claim 37, wherein said carboyhydrate is aldose. ketose. m ' onosaccharide. disaccharide. trisaccharide. oligosaccharide or polysaccharide 39. The method of making a foam composition of claim 20, wherein said compatibilizing agent is a carbohydrate soluble or disperable in water. 40. The method of claim 39, wherein said carbohydrate is aldose. ketose. monosaccharide. disaccharide. trisaccharide. oligosaccharide or polysaccharide.

Inventors: BLY KIM A, DUNBAR HARRIS A, UHL EUGENE R, WILKES GARY R, ZWYNENBURG JAMES L, BLY, KIM, A., DUNBAR, HARRIS, A., UHL, EUGENE, R., WILKES, GARY, R., ZWYNENBURG, JAMES, L.
Applicants: TENNECO PROTECTIVE PACKAGING I, TENNECO PROTECTIVE PACKAGING INC.
Application year: 1997
Main classification: B29C44
IPC codes: B29C47, C08J9