MXPA98002765A - Comptabilizer for carbon dioxide-blown polyolefinic foams - Google Patents

Abstract

Un método para fabricar una composición de espuma poliolefínica, el cual comprende los pasos de:(a) alimentar un polímero poliolefínico en un extrusor;(b) agregar un agente de nucleación a la alimentación de resina;(c) opcionalmente agregar un modificador de permeación a la alimentación de resina;(d) plastificar la mezcla en un extrusor para formar una fusión polimérica;(e) incorporar un agente de soplado de dióxido de carbono, y opcionalmente uno o más miembros seleccionados a partir del grupo que consiste en agentes de soplado inorgánicos, agentes de soplado orgánicos, y combinaciones de los mismos;(f) incorporar cuando menos un agente compatibilizante en la composición espumable, en donde el agente compatibilizante es un hidrocarburo oxigenado que disminuye la presión mínima requerida para impedir la espumación previa, mientras que retarda el colapso de la espuma debido a una emigración del agente de soplado;(g) mezclar uniformemente y enfriar la composición espumable a una temperatura efectiva para la expansión de la espuma poliolefínica;y (h) extruir o expulsar la composición espumable a través de un dado, para formar una espuma poliolefínica.

Description

COMPATIBILIZER FOR POLYOLEPHINIC FOAMS BLOWED WITH CARBON DIOXIDE FIELD OF THE INVENTION This invention relates, in general, to a process and composition for manufacturing a foamed thermoplastic material. More specifically, it relates to processes and extrudable compositions for the production of low density non-crosslinked polyolefin foams, when carbon dioxide is used as a blowing agent, or in combination with an auxiliary physical or inorganic physical blowing agent. , by the addition of certain oxygenated hydrocarbons as a compatibilizing agent. BACKGROUND OF THE INVENTION Thermoplastic low density foams, particularly those having a density less than about 150 kg / m 3, are generally produced with physical blowing agents. Physical blowing agents are chemical compounds that can be incorporated into the thermoplastic melt while they are inside the extruders at high pressures, typically from 10 to 20 MPa, and which can be contained by the polymer structure when the thermoplastic agent mixture / Chilled blowing is rapidly reduced to ambient pressure. Polyolefinic foams, in particular non-crosslinked polyethylene foam and non-crosslinked polypropylene foam, were manufactured for many years with halogenated hydrocarbons, primarily chlorofluorocarbons (CFCs) as physical blowing agents. During the 1980's, the world scientific community presented sufficient evidence to link chlorofluorocarbons with the depletion of atmospheric ozone, and sought world governments to regulate chlorofluorocarbons. It has been shown that ozone levels in the stratosphere are significant to protect life on the planet from the damaging effects of the sun's ultraviolet radiation. Additionally, hydrochlorofluorocarbons (HCFC), another class of chemical compounds, were also included in the regulations, but in a slower program. It was established that halogen compounds of higher atomic weight than fluorine were responsible for this effect. As a result of the regulations, it became necessary to find materials other than halogenated compounds, which could function as physical blowing agents. Many different approaches were taken, but in general in the direction of the use of hydrocarbons containing 2 to 5 carbon atoms, or mixtures thereof. Although these short chain hydrocarbons can function as physical blowing agents to produce foams with satisfactory physical properties, these physical blowing agents are highly flammable. United States Patent Number 4,217,319 (Komori) describes a process for the production of polyolefin foams with different volatile organic compounds as the physical blowing agent. U.S. Patent Number 5,290,822 (Rogers et al.) And U.S. Patent Number 5,225,451 (Rogers et al.) Describe processes for ultra-low density foam using polymer blends. United States Patent Number 5,059,376 (Pontiff) describes a process for removing residual hydrocarbons in an attempt to produce a non-flammable polyethylene foam. Carbon dioxide, alone or in combination with other different gases, has been used as a blowing agent to produce polyethylene foam. U.S. Patent No. 5,034,171 (Kiczek et al.) Discloses an extrusion process for producing a "microcellular" thermoplastic foam and cites polyethylene as a possible polymer, and carbon dioxide as a possible gas blowing agent inert. U.S. Patent No. 5,462,974 (Lee) discloses a foamable polyethylene resin composition having a blowing agent comprised of a mixture of about 50 weight percent carbon dioxide, and about 50 weight percent of either normal butane, isobutane, propane, ethane, or a mixture of any combination of these hydrocarbons, mixed with the resin, in a ratio of about one part blowing agent to about 10. resin parts, while using a zinc oxide nucleating agent and a glycerol monostearate aging modifier. U.S. Patent No. 5,416,129 (Chaudhary et al.) And U.S. Patent No. 5,554,661 (Chaudhary et al.) Describe a process and composition for the preparation of non-crosslinked ethylene polymer foam, using a polymer of a defined melting tension, with either argon, carbon dioxide, or mixture thereof. These patents generally report that argon and carbon dioxide, alone or in mixtures, can function as a physical blowing agent, with ethylene materials having a specific melting tension. U.S. Patent No. 5,116,881 (Park et al.), U.S. Patent No. 5,149,579 (Park et al.), And U.S. Patent No. 5,180,751 (Park et al.) Describe a process and a composition for the production of thermoformable polypropylene foam sheets from high melt strength polypropylene, and refer to carbon dioxide as a potential blowing agent. The patent discloses foam sheets in the scale of densities greater than (42 kg / m3) 2.5 lb / ft3, with sheet thicknesses less than (5.0 millimeters) 0.200 inches, which are defined by certain physical properties. U.S. Patent No. 5,567,742 (Park) discloses a dimensionally stable polypropylene foam with an inorganic blowing agent. Although applicable to both open and closed cell foams, the process discussed with inorganic blowing agents is limited to combinations of cell sizes and densities that result in cell wall thicknesses within a specified scale. When used as a physical blowing agent in traditional low density polyolefin foam processes, carbon dioxide, either alone or in combination with other gases, including water, generally produces undescribed masses of polymeric material, or otherwise low quality thermoplastic foams, which collapse. This lack of dimensional stability occurs due to the limited solubility for these compounds within the molten thermoplastic extrudate, which results in a high uncontrollable level of open cells in the foam structure, when the thermoplastic / blowing agent combination leaves the die . Additionally, even when the resulting thermoplastic materials that are made with carbon dioxide as the primary blowing agent, have a visible foam structure, most of these foams tend to collapse rapidly over time, and become useless to most of practical applications in less than 24 hours after manufacturing. In accordance with the above, in order to use carbon dioxide as the primary blowing agent, it is necessary to reduce the pressure before foaming required to make a foam in the die, and subsequently to eliminate or reduce in a significant manner the index of collapse normally exhibited by the polyolefin foam made with carbon dioxide, water, or mixture thereof. OBJECTS OF THE INVENTION The first object of the present invention is to provide a means by which a simple, low-cost, reliable technique can be used to produce a low-density, non-crosslinked polyolefin foam that does not contain a chemical compound that has demonstrated to exhibit adverse effects on stratospheric ozone concentration. A second object of this invention is to provide a means by which a simple technique can be used, low cost, and reliable, to produce a non-crosslinked low density polyolefin foam, which does not contain flammable levels of hydrocarbon compounds. A further object of the invention is to incorporate chemical compounds that do not adversely affect human, animal, or plant life, such that these compounds can be used without sophisticated protection devices or with elaborate control technology. A further object of the invention is to produce a stable foam structure for which the physical properties are not significantly deteriorated over time. A further object of the invention is to produce a foam material that does not adversely affect the surface characteristics of other materials with which the foam can be placed in intimate contact. WIDE DESCRIPTION OF THE INVENTION In accordance with the aforementioned objects, this invention incorporates oxygenated hydrocarbon compounds with a structure containing multiple ether bonds, multiple hydroxyl bonds, carbonyl groups, or some combination of these three components of chemical structure, which will work inside the extruder to decrease the minimum pressure required, in order to prevent prefoaming in the die, while delaying the collapse of the foam due to excessive migration of the blowing agent, when the primary blowing agent is dioxide of carbon. In particular, the invention relates to a method for manufacturing a polyolefin foam composition, which comprises the steps of: (a) feeding a polyolefin polymer into an extruder; (b) adding a nucleating agent to the resin feed; (c) optionally adding a permeation modifier to the resin feed; (d) plasticizing the mixture in an extruder to form a polymer melt; (e) incorporating a carbon dioxide blowing agent, 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 in the foamable composition, wherein the compatibilizing agent is an oxygenated hydrocarbon that lowers the minimum pressure required to prevent prefoaming, while delaying the collapse of the foam due to excessive migration of the agent of blowing; (g) uniformly mixing and cooling the foamable composition to an effective temperature for the expansion of the polyolefin foam; and (h) extruding or ejecting the foamable composition through a die, at a sufficiently high speed to form a polyolefin foam. The invention also relates to a foam composition made by the process described above. In traditional polyolefin foam extrusion processes, the granules of the thermoplastic resin are mixed with a solid phase nucleating agent, and then melted in a heated extruder, where the combination of plastic and nucleating agent is kept under a high temperature and pressure. The physical blowing agent, which generally becomes liquid inside the extruder, and which will evaporate at the melting temperatures of the die and at atmospheric pressure, is added to the pressurized melt. Within the molten extrudate, the physical blowing agent tends to act as a plasticizer to reduce the viscosity, and consequently, lowers the level of temperature necessary to maintain the hot melting condition of the blend of thermoplastic plastic material and nucleating agent. The blowing agent is mixed with the molten plastic and the nucleating agent, and the combination is subsequently cooled to an extrusion temperature suitable for foaming. Frequently a permeation modifying agent, which is usually an ester of a fatty acid having a chain of 16 to 22 carbon atoms, is also added to prevent the collapse of the resulting foam structure over time. The cooled combination is pushed through a die by the pressure gradient, and when released at atmospheric pressure, the liquid physical blowing agent evaporates and expands to form gas bubbles at the nucleation sites established by the particles of nucleating agent uniformly dispersed. When used as a physical blowing agent in traditional low density polyolefin foam processes, carbon dioxide, either alone or in combination with other gases, including water, generally produces undescribed masses of polymeric material, or thermoplastic foams from another way of low quality, they collapse. This lack of dimensional stability occurs due to the limited solubility for these compounds within the molten thermoplastic extrudate, which results in a high uncontrollable level of open cells in the foam structure, when the thermoplastic / blowing agent combination leaves the die . Additionally, even when the resulting thermoplastic materials that are made with carbon dioxide, water, or mixtures thereof, have a visible foam structure, most of these foams tend to collapse rapidly with time, and become useless to Most practical applications in less than 24 hours after manufacturing. In accordance with the foregoing, the invention relates to oxygenated hydrocarbons, particularly those having a carbon to oxygen ratio between about 0.5 and 1.0 in the thermoplastic / physical blowing agent mixture, which function to reduce the pressure before foaming required to foam the die and subsequently eliminate or significantly reduce the rate of collapse normally exhibited by the polyolefin foam made with carbon dioxide, water, or mixtures thereof. same. In the invention of the polyolefin foamable composition disclosed, granules of the thermoplastic resin are mixed with a solid phase nucleating agent, and then melted in a heated extruder, where the plastic and the nucleating agent are kept under a high temperature and pressure as in the traditional foam process. Carbon dioxide is added to the extrudate through an injection gate in the injection zone typical of the extruder. Optionally, an auxiliary blowing agent, which may be an inorganic or organic compound, can be added through the same gate or separate injection gates, than that used for carbon dioxide. Additionally, an oxygenated hydrocarbon compatibilizing agent is added to the foamable composition. The molecular weight of the oxygenated hydrocarbon generally determines the manner in which the oxygenated hydrocarbon is added. The oxygenated hydrocarbons having a molecular weight greater than about 10,000 are mixed in solid form with the granules of the polyolefin resin. Oxygenated hydrocarbons having a molecular weight less than about 10,000 are added in the same extrusion zone, either through the same injection gate, but preferably through a separate injection gate located at some angle, generally at 90 ° or 180 ° radially from the carbon dioxide injection gate. The chemical structure of the oxygenated hydrocarbon determines whether the oxygenated hydrocarbon is added as a hard component or as an aqueous solution at a specific rate scale. 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 or liquid liquefied form. Inside the molten extrudate, carbon dioxide, auxiliary blowing agents, if present, water, if present, and oxygenated hydrocarbon, all tend to act as plasticizers to reduce the viscosity of the melt, and therefore, to lowering the temperature level necessary to maintain the hot melting condition of the mixture of thermoplastic plastic material and nucleating agent. The carbon dioxide, the auxiliary blowing agents, if present, the water, if present, and the oxygenated hydrocarbon, are mixed with the molten plastic and the 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 at atmospheric pressure, the physical blowing agent (s) expands rapidly, but at a lower velocity than it would if it were not present the oxygenated hydrocarbon. The area of lowest pressure, such as atmospheric, at ambient temperatures, the thermoplastic / oxygenated hydrocarbon / physical blowing agent mixture expands to form bubbles of the physical blowing agent gas at the nucleation sites established by the particles of nucleating agent uniformly dispersed. The affinity of the oxygenated hydrocarbon for carbon dioxide and water, if present, also tends to slow down the diffusion rate of the gas molecules from the foam structure, such that the polyolefin foam does not collapse in 24 hours or less, as it would if the oxygenated hydrocarbon was not present. DETAILED DESCRIPTION OF THE INVENTION The term "polyolefin" includes polymers of linear or branched hydrocarbon molecules of 2 to 8 carbon atoms that contain a double bond in their structure, including alkenes such as ethene, propene, 1-butene, 2-butene, 1-pentene, 2-pentene, 3-pentene. Preferred polyolefin materials include polymers of ethene which are commonly known as polyethylene, and polymers of propylene which are commonly known as polypropylene. Broadly, the invention involves a composition and process for manufacturing a low density, closed cell polyolefin foam, having a density of 10 kg / m3 to 150 kg / m3, preferably 20 kg / m3 to 150 kg / m3 . The polyethylene resin that can be used in the foamable composition of the invention, can be that obtained by the polymerization of ethylene, or by the polymerization of ethylene with other aliphatic polyolefins, such as propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1-pentene, 4-methyl-1-hexene, or 5-methyl-1-hexene, alone or mixtures thereof, or with other different polymerizable monomers. Polyethylene 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 more preferably have three or four carbon atoms. The copolymers can include other monomers compatible with ethylene. Particularly preferred are medium density polyethylene, low density polyethylene, and linear low density polyethylene. These polyethylenes are described in the Kirk Othmer Encyclopedia of Chemical Technology, Third Edition Volume 16, pages 385, 420, the Modern Plastic Encyclopedia. (1986-87), pages 52-63, and the Encyclopedia of Polymer Science and Technology, volume 7, page 610, which are incorporated herein by reference. The term "polyethylene resin (or polyethylene material)", as used herein, includes not only ethylene homopolymers, but also ethylene copolymers composed of at least 50 mole percent (preferably at least 70 percent) molar) of an ethylene bond, such as a minor proportion of a monomer copolymerizable with ethylene, and mixtures of at least 50 weight percent (preferably at least 60 weight percent) of the ethylene homopolymer with another polymer. Preferred polyethylenes include non-crosslinked low density polyethylene having a density of about 910 to 920 kg / m3, and a melt flow index in the range of 0.2 to 3.8 grams per 10 minutes. In general, the ethylene polymer should have a melt index (flow) less than about 10 grams per 10 minutes. The melt index (flow) (ASTM D1238) as the nominal flow rate at 190 ° C and at 689.5 kPa is expressed as grams per 10 minutes. The polymeric propylene resin can be obtained by the polymerization of propylene, or by the polymerization of propylene with other aliphatic polyolefins, such as ethylene, l-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1 -pentene, 4-methyl-l-hexene, 5-methyl-l-hexene, and mixtures thereof, or with other different polymerizable monomers. The term "polymeric propylene resin (or polymeric propylene material)", as used herein, includes not only propylene homopolymers, but also propylene copolymers composed of at least 50 mole percent (preferably at least 70 percent molar) of a propylene unit, and a minor proportion of a monomer copolymerizable with propylene, and mixtures of at least 50 percent by weight (preferably at least 60 weight percent) of the propylene homopolymer with another polymer. Mixtures of polymeric propylene resin with one or more "polymeric modifiers", as used herein, are also permissible, to include low density polyethylene (LDPE), medium density polyethylene (PEDM), high density polyethylene (HDPE). ), linear low density polyethylene (LLDPE), polyolefin elastomers, polyolefin plastomers, saturated and unsaturated styrene-butadiene, randomly and blocks of rubber copolymers, polyamides, ethyl-ethylene acrylate (EEE), methyl-ethylene acrylate ( AME), ethylene-acrylic acid (AEA), ethylene-methacrylic acid (EEA), vinyl-ethylene alcohol (VEOH), vinyl-ethylene acetate (AVE), copolymer rubbers of propylene-ethylenediene monomer (MPED), and olefinic ionomers, such that the total propylene monomer units are in an excess of 50 weight percent. Preferred propylene polymer blends contain at least 50 weight percent "high melt strength" polypropylene, which has a loss tangent of less than or equal to 1.2 at a frequency of 1 radian / second. and at 190 ° C, a density of approximately 900 to 910 kg / m3, and a melt flow index on the scale of 2.2 to 3.8 grams per 10 minutes. In general, the propylene polymer should have a melt index (flow) of less than about 10 grams per 10 minutes. The melt index (flow) (ASTM D1238) is the nominal flow rate at 230 ° C and 298.2 kPa, and is expressed as grams per 10 minutes. A preferred high melt strength polypropylene used in the process of the invention has a branched molecular structure, which provides greater molecular entanglement. Permeation modifiers can be used in the foamable composition of the invention, particularly with low density polyethylene, to prevent collapse of the cellular structure within about as little as 10 minutes to about 8 hours after formation. Permeation modifiers are also referred to as age modifiers in some polyolefin extrusion techniques. Preferred permeation modifiers include octadecanamide and ethylenebistearamide. The most preferred permeation modifier for use in the foamable composition of the invention is octadecanamide. The nucleating agent, or the cell size control agent, can be any conventional or useful nucleating agent. The cell-size agent is preferably used in amounts of 0.1 to 2.0 percent by weight, depending on the desired cell size, and based on the weight of the polyolefin resin. Examples of cell size control agents are inorganic materials (in a small particle form), such as clay, talc, silica, and diatomaceous earth. Additional examples include organic cell size control agents that decompose or react at the temperature of heating inside the extrusion to release gas, such as a combination of an alkali metal salt of a polycarboxylic acid, such as acid tartrate of sodium, potassium acid 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, or calcium carbonate. An example is a combination of a monoalkali metal salt of a polycarboxylic acid, such as monosodium citrate or monosodium tartrate, with a carbonate or bicarbonate. Preferred cell size control agents are talc or a stoichiometric mixture of citric acid and sodium bicarbonate (the mixture having a concentration of 1 to 100 percent, wherein 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. The 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 ratio of 0.5 to 7.0 percent by weight, but preferably from 2.0 to 5.0 percent by weight, of the total extruder flow rate. One or more auxiliary physical blowing agents may also be included. Permissible auxiliary blowing agents include both organic and inorganic halogen-free blowing agents, and mixtures thereof. Inorganic halogen-free blowing agents are those that are environmentally acceptable and non-flammable. Organic blowing agents are those that are environmentally acceptable, but can be classified as flammable. If one or more auxiliary physical blowing agents are used, the preferred auxiliary blowing agents are inorganic blowing agents, which are inorganic atmospheric gases, and those other compounds that are chemically unreactive under the conditions of the extruder. 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 gates, but they can be injected together into the same injection gate of the mixing extruder. When the auxiliary blowing agent is argon, it is used at a proportion of 0.1 to 4 weight percent (but preferably at a rate of 0.1 to 4.0 weight percent) of the total extruder flow rate, such that the proportion by weight of argon to carbon dioxide does not exceed 0.9. When the auxiliary blowing agent is nitrogen, nitrogen may be used in a proportion of 0.1 to 1.5 weight percent of the total extruder flow rate, such that the weight ratio of nitrogen to carbon dioxide does not exceed 0.4. Although it is considered as a potential physical blowing agent in some prior art, in this invention, the water compound is not considered as an auxiliary blowing agent, because the use of water in conjunction with certain oxygenates, as described in the present, functionally it has not been associated in general with physical blowing agents. The term "organic blowing agents" includes partially fluorinated hydrocarbons, known as hydrofluorocarbons, hydrochlorofluorocarbons, or chlorofluorocarbons. In accordance with current federal laws, the use of all chlorofluorocarbons and hydrochlorofluorocarbons in products that can be made by this process is virtually prohibited, and consequently, their application in the process of the invention would be restricted. However, hydrochlorofluorocarbons can be used for insulation products made by this foamable composition of the invention. Preferred partially fluorinated hydrocarbon blowing agents are those which have molecules containing up to three carbon atoms, and which do not contain other halogen atoms, such as 1,1-difluoroethane (HFC-152a), 1, 1, 1 -trifluoroethane (HFC-143a), 1,1,1,1-tetrafluoroethane (HFC-134a), 1, 1, 1, 2, 2-pentafluoroethane (HFC-125) and 1, 1, 2, 3, 3-pentafluoropropane (HFC-245fa). The most preferred partially fluorinated hydrocarbon as an auxiliary blowing agent for this invention is HFC-134a. HFC-134a is used at a ratio of 0.1 to 3.0 weight percent of the total extruder flow rate, such that the weight ratio of carbon HFC-134a does not exceed about 1.0. The term "compatibilizing agent", as used herein, includes those materials that are used in conjunction with the carbon dioxide blowing agent, with a mixture of carbon dioxide and one or more auxiliary inorganic blowing agents, with a mixture of carbon dioxide and one or more auxiliary organic blowing agents, or with carbon dioxide and a mixture of organic and inorganic auxiliary blowing agents (1) to sufficiently plasticize the thermoplastic extrudate inside the extruder, in order to maintain the melting temperatures of the die sufficiently low to produce a closed cell foam structure, and (2) to have a sufficient affinity for carbon dioxide, to lower the pressure prior to foaming in the die. , with the physical blowing agent or with the blowing agent mixture. The compatibilizing agent is one or more materials selected from oxygenated hydrocarbon compounds that decrease the minimum pressure required to prevent prefoaming in the die, while retarding the collapse of the foam due to excessive migration of the blowing agent, when The physical blowing agent is carbon dioxide. Although not specifically limited by the ratio of oxygen to carbon, preferred oxygenated hydrocarbon compounds having a compatibilizing capacity for carbon dioxide in a polyolefin foamable composition, have at least one hydroxyl bond, and have a total atomic ratio of carbon oxygen between approximately 0.5 and 1.0. Some of the oxygenated hydrocarbons function as compatibilizing agents when used in a pure component form, while others have been found to only work when the agent is used in conjunction with water, for example, as in an aqueous solution. In general, oxygenated hydrocarbons wherein 50 percent or more of the oxygen atoms are bonded with carbon atoms through an ether bond, such as in a polyglycol, can generally function as a compatibilizing agent when added as a pure component. Oxygenated hydrocarbons wherein 50 percent or more of the oxygen atoms are bonded with carbon atoms at the hydroxyl group bond, such as a polyhydric alcohol, generally only function as a compatibilizing agent when supplied in a solution aqueous from 5 to 75 weight percent. Examples of subclasses of oxygenated hydrocarbons that have proven capacity to function as compatibilizing agents when added as pure components or when water in the foamable composition is included, they are polyglycol polyglycols and ethers. Polyglycols and polyglycol ethers are effective as compatibilizing agents when water is not included in the foamable composition, but in general lower densities can be achieved when water is added. The permissible polyglycols, as used herein, include those which are polymers of ethylene oxide, which may have a branched or linear molecular structure, with a molecular weight of less than about 20,000. These polyglycols with a linear structure include triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol. Polyglycols with a branched structure are generally referred to by their average molecular weight. Preferred branched polyglycols have an average molecular weight between about 200 and 20,000. The most preferred polyglycol is polyethylene glycol, with an average molecular weight of about 8,000, which is abbreviated herein as "PEG-8,000". Polyethylene glycol can be added at a rate of 0.1 to 2.0 percent by weight of the extruder flow amount. The preferred ratio is 0.5 to 1.0 weight percent of the extruder flow amount. The permissible polyglycol ethers include monoalkyl or dialkyl ethers of 1 to 8 carbon atoms of the ethylene oxide polymers, which may have a branched or linear structure, with a molecular weight less than about 10,000, preferably 200 to 5,000. These polyglycol ethers with a linear structure include tetraethylene glycol dimethyl ether, diethylene glycol dibutyl ether, and poly (ethylene glycol) dimethyl ether, as well as propylene oxide polymers, including tripropylene glycol dimethyl ether. The most preferred linear polyglycol ether is tetraethylene glycol dimethyl ether. Polyglycol ethers with a branched structure, are generally referred to as methoxyether or dimethoxyether of a polyethylene glycol, of a specific average molecular weight. The preferred branched polyglycol ethers are polyethylene glycol monomethyl ethers having an average molecular weight of between about 350 and 5,000. The most preferred branched polyglycol ether is the methoxyether of polyethylene glycol with an average molecular weight of about 5,000. The polyethylene glycol ether can be added at a rate of 0.1 to 2.0 percent by weight of the extruder flow amount. The preferred rate of addition of the polyglycol ether is 0.5 to 1.0 weight percent of the extruder flow amount. Examples of oxygenated hydrocarbon subclasses that have demonstrated ability to function as compatibilizing agents only when water is included in the foamable composition are polyethylene oxides, polyglycerols, polyhydric alcohols, and polyvinyl alcohols. Branched or linear longer chain ethylene oxide polymers are generally referred to as polyethylene oxides, which are sometimes abbreviated as OPE. The permissible polyethylene oxides in the process of the invention have a molecular weight of between about 200,000 and 1,000,000, preferably 250,000 to 350,000. The most effective means of adding a polyethylene oxide, is the inclusion in the feed of resin. Unlike polyglycols or polyglycol ethers, it has been found that polyethylene oxides only work in the composition of the invention when water is included in the composition. 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 polyethylene oxide can be added at a ratio of 0.1 to 2.0 percent by weight of the extruder flow amount. The preferred rate of addition of the polyglycol ether is from 0.3 to 0.7 weight percent of the extruder flow amount. The glycerol polymers are generally referred to as polyglycerols. The polyglycerols typically have a linear structure. The shorter chain polymers, which consist of about 18 or fewer monomer units, must actually be classified as oligoglycerols. Unlike polyglycol or polyglycol ethers, but in a manner similar to polyethylene oxides, it has been found that oligoglycerols or polyglycerols function as a compatibilizing agent when water is included in the extruded foamable composition. The preferred oligoglycerols have an average molecular weight of less than 800. The most effective addition means of the oligoglycerol is in an aqueous solution. The most effective ratio scale of the aqueous solution is 25 to 75 weight percent of the oligoglycerol. The most preferred proportion is 33 to 50 weight percent of the oligoglycerol. The preferred amount of the compatibilizing agent solution is 0.2 to 1.0 weight percent of the total flow rate of the extruder. The most preferred oligoglycerol contains 50 weight percent or more of triglycerol (4,8-dioxa-1,2,6,10,1-undecanopentol), and has an average molecular weight of about 240. Polyhydric alcohols are considered in general, like oxygenated hydrocarbon molecules that have oxygen atoms bonded to the carbon atoms in a given molecule, only through two or more hydroxyl groups. Glycols are the common name given to a specific subclass of polyhydric alcohols having only two hydroxyl groups. Permissible polyhydric alcohols also include fully hydroxylated linear molecules such as glycerol, erythritol, arabitols, xylitol, adonitols, sorbitol, mannitol, iditole, allyl, talitol, and perseitol. Preferred polyhydric alcohols also include non-linear compounds such as pentaerythritol, and inositol. Other polyhydric alcohols that are not completely hydroxylated, but have a ratio of carbon to oxygen that is about one unit, such as ramnitol and epifucitol, are also permissible in the invention. In general, it was discovered that polyhydric alcohols function in the extruded foamable composition of the invention as compatibilizing agents only when water is present. Preferred polyhydric alcohols have from 3 to 8 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 weight percent 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-hexanohexol). Polyvinyl alcohols are a specific example of a longer chain polyhydroxy polymer, and are sometimes abbreviated as ALPV. Many of the commercially available polyvinyl alcohols have a linear structure and a molecular weight less than about 200,000. Preferred polyvinyl alcohols have a molecular weight of between about 13,000 and 150,000. The most effective means of adding a polyvinyl alcohol is the inclusion in the feed of resin. Like polyhydric alcohols, it has been found that polyvinyl alcohols only work in the composition of the invention when water is included in the composition. Water can be added in the manner used for physical blowing agents. The most preferred polyvinyl alcohol for the process of the invention has an average molecular weight on the scale of about 13,000 to 23,000. Polyvinyl alcohol can be added in a ratio of 0.04 to 2.0 percent by weight of the extruder flow rate. The preferred rate of addition of polyglycol ether is from 0.3 to 0.7 weight percent of the extruder flow amount. Other specific classes of oxygenated hydrocarbons that can be used as compatibilizing agents include carbohydrates that are soluble or dispersible in water, including aldoses, ketoses, monosaccharides, disaccharides, trisaccharides, oligosaccharides, and polysaccharides. For foamable low density polyethylene (LDPE) compositions, the most preferred compatibilizing agent for use with a physical blowing agent that is primarily carbon dioxide, is an aqueous solution of an oligoglycerol with an average molecular weight of about 240, and containing at least 50 percent triglycerol. The most effective use ratio is an aqueous solution at a ratio of 48 to 52 percent by weight of the addition of 0.55 to 0.65 percent of the total extruder flow rate. For foamable propylene polymer compositions made of high melt strength polypropylene, the most preferred compatibilizing agent for use with a physical blowing agent that is primarily carbon dioxide, is an aqueous solution of a d-sorbitol. The most effective use ratio is an aqueous solution at a ratio of 48 to 52 percent by weight of the addition of 0.55 to 0.65 percent of the total extruder flow rate. Other additives, such as coloring agents, fire retardants, antioxidants, and plasticizers, as are commonly known in the art, can also be included in the foamable composition. In addition to the polyolefins, oxygenated hydrocarbons are expected to function in a foamable composition with other polymer systems known in the art as capable of producing foams with the carbon dioxide blowing agent. These other systems include, but not limited to, polystyrene foam, polycarbonate foam, and polymethyl methacrylate foam. In general, the foamable composition can be formed into a foam comprising the steps of: (a) feeding a polyolefin polymer into an extruder; (b) adding a nucleating agent to the resin feed; (c) optionally adding a permeation modifier to the resin feed; (d) plasticizing the mixture in an extruder to form a polymer melt; (e) incorporating a carbon dioxide blowing agent, 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 in the foamable composition, wherein the compatibilizing agent is an oxygenated hydrocarbon that lowers the minimum pressure required to prevent prefoaming, while delaying the collapse of the foam due to excessive migration of the agent of blowing; (g) uniformly mixing and cooling the foamable composition to an effective temperature for the expansion of the polyolefin foam; and (h) extruding or ejecting the foamable composition through a die, at a sufficiently high speed to form a polyolefin foam. The invention also relates to a foam composition made by the process described above. In particular, the composition of the foamable invention has an equivalent utility in both a continuous process and an intermittent process. The foamable composition with the compatibilizing agent can be used in an extrusion process operated on a continuous basis using a conventional extruder system. The continuous process for polyolefin foams can produce foam of any thickness. The intermittent process is generally used for polyolefmic foams of a large cross section, with a thickness greater than about 25 millimeters. The two processes have similar extrusion conditions, but differ slightly in the preferred composition. The foamable composition of the invention is also useful in the production of foams from polyolefin resins which are generally considered foamable in the known art, by a conventional foam extrusion process. The preferred embodiment of these resins are low density polyethylene (LDPE) and polypropylene with high melt strength. The two resins have significantly different melting temperatures, and therefore, it has been found that different compatibilizing agents are more effective with polypropylene than with polyethylene, and it has been found that other different compatibilizing agents are more effective with polyethylene than with polyethylene. Polypropylene. Finally, some of the applications of these thermoplastic polyolefin cell bodies require specific density ranges to obtain the specifications of prescribed physical properties. It has been found that the use of carbon dioxide in combination with certain auxiliary blowing agents, than carbon dioxide in combination with other blowing agents, is more effective in producing a polyethylene foam within a specific foam density range. . In accordance with the above, the preferred embodiments include: (1) low density polyethylene foam (LDPE) made in a continuous process, (2) low density polyethylene foam (LDPE) made in an intermittent process, on the scale from 10 kg / m3 to approximately 73 kg / m3, (3) low density polyethylene foam (LDPE) made in an intermittent process, on a scale of 73 kg / m3 to approximately 150 kg / m3, (4) foam polypropylene of high resistance to fusion (ARF) made in a continuous process, (5) foam of polypropylene of high resistance to fusion (ARF) made in an intermittent process, in the scale of 10 kg / m3 to approximately 50 kg / m3. LOW DENSITY POLYETHYLENE FOAM IN A CONTINUOUS PROCESS Low density polyethylene resin pellets are co-fed, with a density in the range of 910 to 920 kg / m3, and a melt flow index in the range of 1.8 to 2.2 grams / 10 minutes (ASTM, Condition P), in an extruder hopper, with 0.01 to 0.05 weight percent granules of a crystalline silica concentrate with 20 percent active ingredient, which is also based on a low density polyethylene material that has a melt flow index that is preferably on the same scale as the resin of the polyethylene granules. Commercial-grade octadecanamide granules are added at a ratio of about 1.0 to 1.25 weight percent of the total granule feed. The mixture of granules is melted in the single screw extruder at 48: 1, L: D, and is compressed by the screw to a pressure of approximately 1.25 MPa. The screw is driven mechanically to rotate at a speed of 30 to 50 revolutions per minute depending on the desired output speed of the extruder. Through an injection gate that is located at approximately 16 lengths of diameter downstream of the granule feed throat of the extruder, the carbon dioxide that has been pressurized to 17.5 MPa is regulated through a control valve to deliver approximately 5 to 6 percent of the total extruder flow rate. Through a separate injection gate, which is located at 90 ° radially from the gate used for carbon dioxide, 1, 1, 1, 2 -tetrafluoroethane is pumped as an auxiliary blowing agent, at a pressure of about 17. MPa, and subsequently regulated inwardly of the extruder at a rate of 2 to 3 percent of the total flow rate of the extruder. Through another separate injection gate which is located 180 ° radially from the gate used for carbon dioxide, a 50 weight percent aqueous solution of oligoglycerol, with an average molecular weight of about 239, is pumped to a pressure of about 17 MPa, and subsequently regulated into the extruder at a rate of about 0.6 percent in the total extruder flow rate. Immediately downstream of the injection gate, the screw of the extruder is equipped with a mixing section containing at least four diameter lengths of the multiple segmented blade blades of high separation. The physical blowing agent and the oligoglycerol / water solution are mixed in the pressurized melt in the mixing zone. The barrel temperatures of the four or more zones of the single screw extruder, subsequent to the injection zone, are decreased in increments to provide an extrusion melting temperature in the range of 105 ° C to 115 ° C at Extruder head, 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 fusion is provided to an annular foam die, with an exit angle of 40 ° to 50 °, and the die lands at a convergence angle of 3o to 5o. The cooled polyethylene / carbon dioxide / oligoglycerol / water combination is extruded through the die at atmospheric pressure, and most of the physical blowing agent rapidly expands to form bubbles at the nucleation sites established by the agent particles. of nucleation. Example 1 details the preferred embodiment of the invention for low density polyethylene in the continuous process. Example 2 shows what happens when the compatibilizing agent is removed. Example 3 shows the results of an alternative compatibilizing agent with low density polyethylene in a continuous process. INTERMITTENT PROCESS FOR LOW DENSITY POLYETHYLENE FOAM OF A LARGE CROSS SECTION, ON A DENSITY SCALE OF 10 kg / m3 TO APPROXIMATELY 73 kg / m3. Low density polyethylene resin granules are co-fed, with a density on the scale of 910 to 920 kg / m3, and a melt flow index in the range of 1.8 to 2.2 grams / 10 minutes (ASTM Condition P), in an extruder hopper, with 5 to 6 weight percent granules of a crystalline silica concentrate with 20 percent active ingredient, which is also based on a low density polyethylene material having a flow index of fusion that is preferably on the same scale as the resin of the polyethylene granules. Commercial grade octadecanamide granules are added at a rate of about 1.0 to 1.25 weight percent of the total granule feed. The mixture of granules ee melts in the single screw extruder at 32: 1, L: D, and is compressed by the screw at a pressure of approximately 12.5 MPa. Through an injection gate that is located at approximately 16 lengths of the diameter downstream of the granule feed throat of the extruder, the carbon dioxide that has been pressurized at 1.75 MPa is regulated through a control valve, to provide about 2 to 4 percent of the total flow rate of the extruder. Through a separate injection gate, which is located at 90 ° radially from the gate used for carbon dioxide, 1,1,1,2-tetrafluoroethane, which has been pressurized separately at 17.5 MPa, is regulated through of a separate control valve, to provide approximately 2 to 4 percent of the total flow rate of the extruder. Through a third injection gate, which is located 270 ° radially from the gate used for carbon dioxide, a 50 weight percent aqueous solution of an oligoglycerol of average molecular weight 239 is pumped, and contains at least 50 percent triglycerol, at a pressure of approximately 17.5 MPa, in the extruder, at a rate of about 0.6 percent of the total extruder flow rate. Immediately downstream of the injection gate, the screw of the extruder is equipped with a mixing section containing at least four diameter lengths of the multiple segmented blade blades of high separation. Carbon dioxide, 1,1,1,2-tetrafluoroethane and the aqueous solution of oligoglycerol are mixed in the pressurized melt 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 fed through a heated tube into a secondary extruder. The secondary extruder is any that has been specifically designed to accept molten polymer feeds, and must have a blade screw length equivalent to at least 24 of its screw diameters, with the preferred length being equivalent to 32 diameters. The ratio of the screw diameter of the secondary extruder to the screw diameter of the first extruder should preferably be in the range of 1.25 to 1.4. The preferred screw design for optimum melting cooling has four parallel blades radially spaced 90 ° apart, with a cross-sectional segment with a length of about 1/3 of the diameter of the screw of each blade missing, with a repeated equivalent length to 4 screw diameters. In a secondary extruder, the barrel temperatures of the extruder are maintained, to provide a melting temperature in the range of 90 ° C to 115 ° C, with 108 ° C being the ideal melting temperature. The pressure at the extruder head should be maintained from 9.3 to 11.3 MPa, if an optional gear pump is present, or it will be approximately 17.5 to 19.5 MPa if there is no gear pump. The cooled pressurized molten mixture of polyethylene, carbon dioxide, 1,1,1-tetrafluoroethane, and aqueous solution of oligoglycerol, is pumped through a tube into a pressurized hydraulic piston chamber, which is set to maintain a fusion pressure of approximately 12.4 MPa. The different areas of the chamber are cooled externally by forced convection air to the scale of 99 ° C to 105 ° C. The specific details of the piston process are described in United States Patent Number 4, 323,528. In summary, as the volume of the molten mixture fills the piston chamber, the wall of the piston piston moves. When the piston moves to a predefined distance, a switch operates the impulse system and the gate system for the cylinder. For the present described process, the pulse mechanism is set to move the plunger at a predefined speed, to dose the material through the radial die, at a speed of approximately 2,350 kg / hour. The discharged material expands rapidly in all three directions as it leaves the die, but is captured on a conveyor board equipped to move the expanded mass enough to release the die, and to control the expansion of the material in the thickness and in the address of the machine. The resulting foam block to the left of the board is long enough for the next advance of the plunger. The foam block is placed on additional cooling grids, and allowed to cool sufficiently for handling, typically 15 minutes. Example 4 details the preferred embodiment of the invention for the intermittent process, which can produce a polyethylene foam of large cross section. INTERMITTENT PROCESS FOR LOW DENSITY POLYETHYLENE FOAM OF A LARGE CROSS SECTION ON THE DENSITY SCALE OF 20 kg / m3 APPROXIMATELY 73 kg / m3. Low density polyethylene resin pellets are co-fed, with a density on the scale of 910 to 920 kg / m3 and a melt flow index in the range of 1.8 to 2.2 grams / 10 minutes (ASTM Condition P) in an extruder hopper, with 5 to 6 weight percent granules of a crystalline silica concentrate with 20 percent active ingredient, which is also based on a low density polyethylene material having a melt flow index which is preferably on the same scale as the resin of the polyethylene granules. Commercial-grade octadecanamide granules are added at a ratio of about 1.0 to 1.25 weight percent of the total granule feed. The mixture of granules is melted in the single screw extruder at 32: 1 L: D, and compressed by the screw at a pressure of approximately 1.25 MPa. Through an injection gate, which is located at approximately 16 lengths of the diameter downstream of the granule feed throat of the extruder, the carbon dioxide that has been pressurized to 1.75 MPa is regulated through a control valve , to deliver approximately 2 to 4 percent of the total flow rate of the extruder. Through a separate injection gate that is located 90 ° radially from the gate used for carbon dioxide, argon, which has been pressurized separately at 17.5 MPa, is regulated through a separate control valve to provide about 2 to 4 percent of the total extruder flow rate. Through a third injection gate, which is located 270 ° radially from the gate used for carbon dioxide, a 50 weight percent aqueous solution of an oligoglycerol, with an average molecular weight of 239, is pumped, and containing at least 50 percent of triglycerol, at a pressure of approximately 17.5 MPa, into the extruder, at a rate of about 0.6 percent of the total extruder flow rate. Immediately downstream of the injection gate, the screw of the extruder is equipped with a mixing section containing at least four lengths of the screw diameter of multiple segmented blades of high separation. The carbon dioxide, the argon, and the oligoglycerol solution are mixed in the pressurized molten 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 fed through a heated tube into a secondary extruder. The secondary extruder is any that has been specifically designed to accept molten polymer feeds, and must have a blade screw length equivalent to at least 24 of its screw diameters, with the preferred length being the equivalent of 32 diameters. The ratio of the screw diameter of the secondary extruder to the screw diameter of the first extruder should preferably be in the range of 1.25 to 1.4. The preferred screw design for optimum fusion cooling has four parallel blades radially spaced 90 ° apart, with a cross-sectional segment with a length of about 1/3 the diameter of the screw of each blade missing, with a repeated equivalent length to 4 screw diameters. In the secondary extruder, barrel temperatures of the extruder are maintained, to provide a melting temperature in the range of 90 ° C to 115 ° C, with 108 ° C being the ideal melting temperature. The pressure in the extruder head should be maintained from 9.3 to 11.3 MPa, if an optional gear pump is present, or it will be approximately 17.5 to 19.5 MPa if there is no gear pump. The cooled pressurized molten mixture of polyethylene, carbon dioxide, 1,1,1-tetrafluoroethane, and aqueous solution of oligoglycerol, is pumped through a tube into a pressurized hydraulic piston chamber, which is set to maintain a fusion pressure of approximately 12.4 MPa. The different areas of the chamber are cooled externally by forced convection air, up to the scale of 99 ° C to 105 ° C. The specific details of the piston process are described in U.S. Patent Number 4,323,528. In summary, as the volume of the molten mixture fills the piston chamber, the wall of the piston piston moves. When the piston moves to a predefined distance, a switch operates the impulse system and the gate system for the cylinder. For the present described process, the pulse mechanism is set to move the plunger at a predefined speed, to dose the material through the radial die, at a speed of approximately 2,350 kg / hour. The discharged material expands rapidly in all three directions as it leaves the die, but is captured on a conveyor board equipped to move the expanded mass enough to release the die, and to control the expansion of the material in the thickness and in the address of the machine. The resulting foam block to the left of the table is long enough for the next advance of the plunger. The foam block is placed on additional cooling grids, and allowed to cool sufficiently for handling, typically 15 minutes. Example 3 details the preferred embodiment of the invention for the intermittent process, which can produce polyethylene foam of a large cross section, in the density scale of 73 kg / m3 to 100 kg / m3. 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. HIGH-RESISTANCE POLYPROPYLENE FOAM IN A CONTINUOUS PROCESS High-resistance polypropylene resin granules are co-fed to the fusion, which has a density on the scale of 900 to 910 kg / m3, and a melt flow index on the scale of 2.0 to 4.0 grams / 10 minutes (ASTM, Condition L), in an extruder hopper, with 0.5 to 2.0 weight percent granules of a crystalline silica concentrate with the nominal 20 percent active ingredient, which is based on a low density polyethylene. The mixture of granules is melted in the single screw extruder at 48: 1, L: D, and compressed by the screw at a pressure of approximately 1.25 MPa. The screw is mechanically driven to rotate at a speed of 30 to 50 revolutions per minute, depending on the desired output speed of the extruder. The carbon dioxide that has been pressurized to 17.5 MPa through a control valve is regulated through an injection damper, which is located approximately 16 lengths of the diameter downstream of the granule feed throat of the extruder. , to provide approximately 5 to 6 percent of the total flow rate of the extruder. Through another separate injection gate, which is located 180 ° radially from the gate used for carbon dioxide, a 50 weight percent aqueous solution of d-sorbitol with an average molecular weight of about 239 is pumped, at a pressure of about 17 MPa, and subsequently regulated into the extruder at a rate of about 0.6 percent of the total flow concentration of the extruder. Immediately downstream of the injection gate, the screw of the extruder is equipped with a mixing section containing at least four diameter lengths of the highly segmented multiple segmented blade screw. The physical blowing agent and the d-sorbitol / water solution are mixed in the pressurized melt in the mixing zone. The barrel temperatures of the four or more zones of the single screw extruder subsequent to the injection zone are decreased in increments to provide an extrusion melting temperature in the range of 105 ° C to 115 ° C at the head of the extruder, at a pressure of 9.3 to 10.0 MPa, if an optional gear pump is present, or from 15 to 17 MPa if there is no gear pump. The pressurized fusion is provided to an annular foam die, with an exit angle of 40 ° to 50 °, and the die lands at a convergence angle of 3o to 5o. The cooled polyethylene / carbon dioxide / oligoglycerol / water combination is extruded through the die at atmospheric pressure, and most of the physical blowing agent rapidly expands to form bubbles at the nucleation sites established by the agent particles. of nucleation. Example 6 details the preferred embodiment of the invention for the continuous process. POLYPROPYLENE FOAM OF HIGH STRENGTH TO FUSION IN AN INTERMITTENT PROCESS FOR LARGE CROSS SECTION FOAM ON A DENSITY SCALE OF 10 kg / m3 NEAR 73 kg / m3.

Granules of high melt strength polypropylene resin are co-fed, having a density on the scale of 900 to 910 kg / m3, and a melt flow index on the scale of 2.0 to 4.0 grams / 10 minutes (ASTM Condition L), to an extruder hopper, with 0.5 to 2.0 weight percent granules of a crystalline silica concentrate with the nominal 20 percent active ingredient, which is based on a low density polyethylene. The mixture of granules is melted in a single screw extruder at 32: 1 L: D (ie, length: diameter), and compressed by the screw at a pressure of approximately 1.25 MPa. The carbon dioxide that has been pressurized to 17.5 MPa through a control valve is regulated through an injection gate, which is located approximately 16 lengths of the diameter downstream of the extruder granule feed throat. to deliver approximately 3 to 6 percent of the total extruder flow rate, depending on 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 flow rate of the extruder, through a separate injection gate. which is located either 90 ° or 180 ° radially from the gate used for carbon dioxide. Immediately downstream of the injection gate, the screw of the extruder is equipped with a mixing section containing at least four lengths of the diameter of the screw, of multiple segmented blades of high separation. Carbon dioxide, water, and d-sorbitol are mixed in the pressurized molten 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 fed through a heated tube to a secondary extruder. The secondary extruder is any that has been specifically designed to accept molten polymer feeds. It must have a blade screw length equivalent to at least 24 of its screw diameters, with the preferred length being equivalent to 32 diameters. The ratio of the screw diameter of the secondary extruder to the screw diameter of the first extruder should preferably be greater than 1.25. The preferred screw design for optimal melting cooling has four parallel blades radially spaced 90 ° apart, with a cross-sectional segment with a length of approximately one third of the diameter of the screw missing, of each blade, and with a length repeated equivalent to four diameters of the screw. In the secondary extruder, the barrel temperatures of the extruder are maintained to deliver a melting temperature in the range of 150 ° C to 170 ° C, the ideal melting temperature of the propylene polymer mixture employed being dependent. The pressure at the extruder head should be maintained from 9.3 to 11.3 MPa, if an optional gear pump is present, or it will be approximately 17.5 to 19.5 MPa if no gear pump is present. The cooled pressurized molten mixture of propylene polymer, carbon dioxide, water, and d-sorbitol, is pumped through a tube, into a hydraulically pressurized piston chamber, which is set to maintain a melting pressure of about 12.4 MPa. The different areas of the chamber are cooled externally by forced convection air, up to the scale of 160 ° C to 165 ° C. The specific details of the piston process are described in U.S. Patent Number 4,323,528. In summary, as the molten mixture fills the piston chamber, the piston piston moves. When the piston piston moves to a predefined distance, a switch operates the impulse system and the gate system for the cylinder. For the process described, the pulse mechanism is set to move the plunger at a predefined speed, to dose the material through the radial die, at a speed of approximately 7,000 kg / hour. The discharged material expands rapidly in all three directions as it leaves the die, but is captured on a conveyor board equipped to move the expanded mass enough to release the die, and to control the expansion of the material in the thickness and in the address of the machine. The resulting foam block is left on the board enough for the next advance of the plunger. The foam block is placed on additional cooling grids, and allowed to cool sufficiently for handling, typically for 15 minutes to 1 hour. The following Examples are provided for illustrative purposes only, and the invention described herein should not be considered limited thereto. EXAMPLE 1 This example incorporates low density polyethylene foam made in a continuous process, using a foamable composition containing an oligoglycerol with an average molecular weight of about 239, as the compatibilizing agent. Westlake 606 polyethylene granules are co-fed, with 1.0 percent by weight of Witco Kemamide granules (octadecanamide), and 0.08 percent of Schulman F20V crystalline silica granules, to a 2.5-screw single-screw extruder. inches (64 millimeters) Berlyn at 32: 1 L: D, modified, operating at a screw speed of 42 to 46 rpm. Carbon dioxide with a commercial grade of 99.8 percent purity is injected, which has been pressurized, at a pressure of approximately 13.1 MPa, at a rate of 1.9 kg / hour. Formacel Z-4 (1,1,1,2-tetrafluoroethane) is injected from E.I. DuPont de Nemours, which has been pressurized, at a pressure of approximately 13.1 MPa, at a rate of 1.04 kg / hour through a separate injection gate at 90 ° radially from the gate used for carbon dioxide. An aqueous solution at 33.3 weight percent of Hexapol G-3 from Hexagon Enterprises (an oligoglycerol having an average molecular weight of about 239, and a typical triglycerol content of about 51 percent), which has been prepared from of city water, is pressurized and injected at a pressure of approximately 13.1 MPa, at a rate of approximately 0.27 kg / hour, through a separate injection gate at 180 ° radially from the gate used for carbon dioxide. The multi-component polymer mixture is subsequently pressurized to 17.1 MPa, at the extruder discharge, and transferred through a heated tube to a second, larger 3.5-inch (89 mm) single-screw cooling extruder. The mixture is cooled in the cooling extruder to a melting temperature of 89 ° C and subsequently pressurized to 12.2 MPa at the extruder discharge. The pressure of the extruder head is regulated by a Normag 2,200 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 closes sufficiently to generate an inlet pressure to the die of approximately 9.7 MPa. The extruder outlet is at approximately 37 kg / hour. The hot foam is directed over a hollow tube mandrel cooled by water, and the outer surface is cooled by forced convection air from a portable multi-orifice ring. The extraction speed is controlled by an extraction roller in the S configuration. The foam sheet is subsequently collected in a downstream winder. Samples of the foam sheet are weighed, and the thickness of the sheet is immediately measured. The samples just taken from the coiler, have a thickness of 1.93 millimeters, and a density of 45 kg / m3. Two days later, the same foam sample has a thickness of 2.02 millimeters, and a density of 43 kg / m3. EXAMPLE 2 This Example illustrates the compatibilization effect of the oligoglycerol / water mixture, by a temporary suppression of the extrudable composition. During a test run using the formulation of Example 1, the supply can of the Hexapol G-3 / water mixture is passed empty. Almost immediately after the mixing flow was stopped, the polymeric material coming through the die lips became an open cell structure, random gas exiting the melt, and extruder pressures began to fluctuate. wildly. When the flow of the Hexapol G-3 / water mixture was restored, the extrusion line quickly returned to stable operating conditions, and produced a foam equivalent to that made immediately before the process was altered. EXAMPLE 3 This example is similar to Example 1, but uses a solution of 40 weight percent d-sorbitol in tap water as the compatibilizing agent. The sorbitol solution is injected at the same speed as that used for the Hexapol G-3 of Example 1, and the speeds of the other components remain the same. In this case, the samples taken from the winding machine have a thickness of 1.68 millimeters, and a density of 54 kg / m3. The samples exhibit a thinner caliber within one hour after production, but return the next day to the original density. EXAMPLE 4 This example incorporates thick cross section low density polyethylene foam, made in an intermittent process, using a foamable composition containing an oligoglycerol with an average molecular weight of about 239, as the compatibilizing agent. Westlake 606 polyethylene granules are co-fed, with 1.4 weight percent Akzo Nobel Armoslip 18 (octadecanamide) granules and about 0.08 weight percent Schulman F20V crystalline silica granules, to a single screw extruder Wilmington from 3 inches (76 mm) to 48: 1 L: D, operating with a screw speed of 36 to 37 rpm. Carbon dioxide with a commercial grade of 99.8 percent purity is injected, which has been pressurized, at a pressure of approximately 13.1 MPa, at a rate of 0.68 kg / hour. Formacel Z-4 from E.I. is injected. DuPont de Nemours (1, 1, 1, 2-tetrafluoroethane) which has been pressurized, at a pressure of approximately 13.1 MPa, at a rate of 1.22 kg / hour, through a separate injection gate at 90 ° radially from the gate used for carbon dioxide. A 50 percent by weight aqueous solution of Hexapol G-3 from Hexagon Enterprises, which has been prepared from city water, is pressurized and injected at a pressure of approximately 13.1 MPa, at a rate of approximately 0.27 kg / hour, through an injection gate separated 180 ° radially from the gate used for carbon dioxide. The multi-component mixture is cooled in the extruder to a melting temperature of 107 ° C, and subsequently pressurized to 15.9 MPa at the extruder discharge. The pressure of the extruder head is regulated by a Normag 2,200 gear pump system. The fusion pump increases the melt pressure to 18.3 MPa, to be delivered to the hydraulically pressurized, cooled piston chamber. When the filling of the material moves the piston to a predefined distance, a switch operates the impulse system and the gate system so that the cylinder doses the material through the radial die, at a speed of approximately 5,338 kg / hour. The samples of the resulting foam block have a fresh density of 30.9 kg / m3. EXAMPLE 5 In this example, the 50 percent by weight oligoglycerol aqueous solution compatibilizing agent of Example 4 is replaced by a 7.5 weight percent aqueous solution of Air Products Airvol 103, a polyvinyl alcohol having a molecular weight average of between approximately 13,000 and 23,000. Problems with the pumping system for the aqueous polyvinyl alcohol solution delay its introduction into the extruder. Prior to injection of the solution, the extruder is operating with the other components in concentrations similar to those of the formulation of Example 4, without the oligoglycerol solution, and producing undescribed masses of polymer in the die. Upon stabilization of the flow rate of the polyvinyl alcohol aqueous solution at about 0.23 kg / hour, a foam having a fresh density of 31.2 kg / m3 begins to be formed. EXAMPLE 6 This example incorporates low density polyethylene foam of a thick cross section, made with an intermittent process in the higher density scale than that of Example 4. This foamable composition also contains an oligoglycerol with an average molecular weight of about 239. as the compatibilizing agent, but the auxiliary blowing agent is changed from 1, 1, 1, 2-tetra-fluoroethane to commercial grade argon with a purity of 99.998 percent. The Westlake 606 polyethylene granules are mixed with the Schulman F20V crystalline talc concentrate based on low density polyethylene, and heated in a 2.5 inch (63.5 millimeter) Berlyn single screw extruder to 32: 1, L: D, modified, operating with a screw speed of 38 to 42 rpm. Carbon dioxide with a commercial grade of 99.8 percent purity is injected, which has been pressurized, at a pressure of approximately 13.1 MPa, at a rate of 0.91 kg / hour. Argon is also injected with a purity of 99.998 percent, commercial grade, which has been pressurized, through a separate injection gate, at a speed of 0.91 kg / hour. A 50 percent by weight aqueous solution of Hexapol G-3 from Hexagon Enterprises, which has been prepared from city water, is pressurized and injected at a pressure of approximately 13.1 MPa, at a rate of approximately 0.27 kg / hour, through a separate injection gate at 90 ° radially from the gate used for carbon dioxide. The five component mixture is subsequently pressurized to 14.3 MPa at the extruder discharge, and transferred through a heated tube to a second larger single screw cooling extruder., 3.5 inches (89 mm). The mixture is cooled in the cooling extruder to a melting temperature of about 107 ° C, at 4.1 MPa. The pressure of the head of the secondary extruder is regulated by a Normag 2,200 gear pump system. The fusion pump increases the melt pressure to 18.3 MPa, to provide the piston chamber hydraulically pressurized and cooled. When the filling of the material moves the piston to a predefined distance, a switch activates the impulse system and the gate system so that the cylinder doses the material through the radial die, at a speed of approximately 2,350 kg / hour. The samples of the resulting foam block have a fresh density of 79.8 kg / m3. EXAMPLE 7 This example incorporates polyethylene foam of high melt strength, made in a continuous process, using a foamable composition containing an oligoglycerol with an average molecular weight of about 239, as the compatibilizing agent. Montell PF814 polypropylene granules are co-fed, with approximately 0.08 weight percent Schulman F20V crystalline silica granules, to a Berlyn, 2.5-inch (64 mm) single-screw extruder, at 32: 1 L: D, modified, which operates with a screw speed of 58 to 62 rpm. Carbon dioxide with a commercial grade of 99.8 percent purity is injected, which has been pressurized, at a pressure of approximately 19.3 MPa at a rate of 1.6 kg / hour. A 50 percent by weight aqueous solution of Hexapol G-3 from Hexagon Enterprises, which has been prepared from city water, is pressurized and injected at a pressure of approximately 19.3 MPa, at a rate of approximately 0.18 kg / hour. through a separate injection gate at 180 ° C radially from the gate used for carbon dioxide. The multi-component polymer mixture is subsequently pressurized to 15.9 MPa at the extruder discharge, and transferred through a heated tube to a second, larger 3.5-inch (89 millimeter) single-screw cooling extruder. The mixture is cooled in the quench extruder to a melt temperature of 143 ° C, and subsequently pressurized to 6.9 MPa, at the extruder discharge. The pressure of the extruder head is regulated by a Normag 2,200 gear pump system. The pressurized molten polymer mixture is provided through an annular die equipped with thin lips 3 inches (76 millimeters) in diameter. The die gap closes sufficiently to generate an inlet pressure to the die of approximately 8.7 MPa. The output of the extruder is about 41 kg / hour. The hot foam is directed over a hollow tube mandrel cooled by water, and the outer surface is cooled by forced convection air from a portable multi-orifice ring. The extraction speed is controlled by an extraction roller having an S configuration. The foam sheet is subsequently collected in a downstream winding machine. Samples of the foam sheet are weighed, and the thickness of the sheet is immediately measured. The samples taken from the winding machine have a thickness of 0.99 millimeters, and a density of 69 kg / m3. EXAMPLE 8 This example incorporates thick cross-section, high melt strength polypropylene foam made in an intermittent process using a foamable composition containing d-sorbitol as the compatibilizing agent. Montell PF814 polypropylene granules are co-fed with approximately 0.08 weight percent talcum powder concentrate Techmer T-1901, Schulman, in a Wilmington single-screw extruder from 3 inches (76 mm) to 48: 1 L: D, operating with a screw speed of 36 to 37 rpm. Carbon dioxide is injected with a purity of 99.8 percent, commercial grade, which has been pressurized, at a pressure of approximately 13.1 MPa, at a speed of 1.13 kg / hour. A 50 percent by weight aqueous solution of SPI Poiyols Crystalline Sorbitol 712 which has been prepared from tap water, is pressurized and injected at a pressure of approximately 13.1 MPa, at a rate of approximately 0.27 kg / hour, through of a separate injection gate at 180 ° radially from the gate used for carbon dioxide. The multi-component mixture is cooled in the extruder, at a melting temperature of 107 ° C, and subsequently pressurized to 15.9 MPa at the extruder discharge. The pressure of the extruder head is regulated by a Normag 2,200 gear pump system. The fusion pump increases the fusion pressure to 18.3 MPa, to be delivered to the piston chamber hydraulically pressurized and cooled. When the filling of the material moves the piston to a predefined distance, a switch activates the impulse system and the gate system so that the cylinder doses the material through the radial die, at a speed of approximately 7,800 kg / hour. The samples of the resulting foam block have a fresh density of 25.6 kg / m3. EXAMPLE 9 The following table shows the alternative compatibilizing agents for the high melt strength polypropylene foam made in an intermittent process, and the lowest effective density limit using a single carbon dioxide blowing agent. The lowest density is the point where the additional blowing agent results in a higher density due to the collapse of the matrix.

Claims (40)

1. NOVELTY OF THE INVENTION Having described the foregoing invention, it is considered as a novelty, and therefore, property is claimed as contained in the following: CLAIMS 1. A method for manufacturing a polyolefin foam composition, which comprises the steps of: (a) feeding a polyolefin polymer in an extruder; (b) adding a nucleating agent to the resin feed; (c) optionally adding a permeation modifier to the resin feed; (d) plasticizing the mixture in an extruder to form a polymer melt; (e) incorporating a carbon dioxide blowing agent, 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 in the foamable composition, wherein the compatibilizing agent is an oxygenated hydrocarbon which lowers the minimum pressure required to prevent prefoaming, while retarding foam collapse due to excessive migration of the agent of blowing; (g) uniformly mixing and cooling the foamable composition to an effective temperature for the expansion of the polyolefin foam; and (h) extruding or ejecting the foamable composition through a die, to form a polyolefin foam, wherein this foam has a density of between 10 kg / m3 to 150 kg / m3.
2. 2. The method for manufacturing a foam composition according to claim 1, characterized in that the polyolefin foam is a polypropylene foam.
3. 3. The method for manufacturing a foam composition according to claim 2, characterized in that the compatibilizing agent is a polyglycol.
4. 4. The method for manufacturing a foam composition according to claim 3, characterized in that the polyglycol is a branched or linear polymer of ethylene oxide having a molecular weight of between about 200 and 20,000.
5. 5. The method for manufacturing a foam composition according to claim 4, characterized in that the polyglycol is a branched or linear polymer of ethylene oxide, having a molecular weight of about 8,000.
6. 6. The method for manufacturing a foam composition according to claim 2, characterized in that the compatibilizing agent is a polyglycol ether.
7. 7. The method for producing a foam composition according to claim 6, characterized in that the polyglycol ether is a monoalkyl or dialkyl ether of 1 to 8 carbon atoms of ethylene oxide having a branched or linear structure, and a molecular weight less than about 10,000.
8. The method for manufacturing a foam composition according to claim 7, characterized in that the polyglycol ether is ethylene oxide monomethyl ether having a branched structure, and a molecular weight of about 5,000.
9. 9. The method for manufacturing a foam composition according to claim 2, characterized in that the compatibilizing agent is a polyethylene oxide, and wherein water is included in the foamable composition.
10. The method for manufacturing a foam composition according to claim 9, characterized in that the polyethylene oxide has a molecular weight of about 200,000 to 1,000,000.
11. 11. The method for manufacturing a foam composition according to claim 2, characterized in that the compatibilizing agent is a polyglycerol, and wherein water is included in the foamable composition.
12. 12. The method for manufacturing a foam composition in accordance with that claimed in the claim 11, characterized in that the polyglycerol is an oligoglycerol having a molecular weight of less than about 800.
13. 13. The method for manufacturing a foam composition in accordance with the claim claimed in the claim. 12, characterized in that the oligoglycerol is an aqueous solution, and comprises 50 percent or more of triglycerol, and has an average molecular weight of about 240.
14. 14. The method for manufacturing a foam composition in accordance with the claim claimed in the claim. 2, characterized in that the compatibilizing agent is a polyhydric alcohol, and wherein water is included in the foam composition.
15. 15. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 14, characterized in that the polyhydric alcohol has from 3 to 8 carbon atoms.
16. 16. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 15, characterized in that the polyhydric alcohol is selected from the group consisting of glycerol, erythritol, arabitol, xylitol, adonitol, sorbitol, mannitol, iditol, alitol, talitol, perseitol, pentaerythritol, inositol, ramnitol, and epifucitol.
17. 17. The method for manufacturing a foam composition according to claim 16, characterized in that the polyhydric alcohol is d-sorbitol.
18. 18. The method for manufacturing a foam composition according to claim 2, characterized in that the compatibilizing agent is a polyvinyl alcohol, and wherein water is included in the foam composition.
19. 19. The method for manufacturing a foam composition according to claim 2, characterized in that the polyvinyl alcohol has a molecular weight less than about 200,000.
20. 20. The method for manufacturing a foam composition according to claim 1, characterized in that the polyolefin foam is polyethylene.
21. 21. The method for manufacturing a foam composition in accordance with that claimed in the claim 20, characterized in that the compatibilizing agent is a polyglycol.
22. 22. The method for manufacturing a foam composition in accordance with that claimed in the claim 21, characterized in that the polyglycol is a branched or linear polymer of ethylene oxide having a molecular weight of between about 200 and 20,000.
23. 23. The method for manufacturing a foam composition according to claim 22, characterized in that the polyglycol is a branched or linear polymer of ethylene oxide, having a molecular weight of about 8,000.
24. 24. The method for manufacturing a foam composition according to claim 20, characterized in that the compatibilizing agent is a polyglycol ether.
25. 25. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 24, characterized in that the polyglycol ether is a monoalkyl or dialkyl ether of 1 to 8 carbon atoms of ethylene oxide, having a branched or linear structure, and a molecular weight of less than about 10,000.
26. 26. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 25, characterized in that the compatibilizing agent is a polyethylene oxide, and wherein water is included in the foamable composition.
27. 27. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 26, characterized in that the polyethylene oxide has a molecular weight of about 200,000 to 1,000,000.
28. 28. The method for manufacturing a foam composition according to claim 20, characterized in that the compatibilizing agent is a polyglycerol, and wherein water is included in the foamable composition.
29. 29. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 28, characterized in that the polyglycerol is an oligoglycerol having a molecular weight of less than about 800.
30. 30. The method for manufacturing a foam composition in accordance with the claim of claim 29., characterized in that the oligoglycerol is an aqueous solution, and comprises 50 percent or more of triglycerol.
31. 31. The method for manufacturing a foam composition according to claim 20, characterized in that the compatibilizing agent is a polyhydric alcohol, and wherein water is included in the foam composition.
32. 32. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 31, characterized in that the polyhydric alcohol has from 3 to 8 carbon atoms.
33. 33. The method for manufacturing a foam composition in accordance with the claim claimed in the claim 32, characterized in that the polyhydric alcohol is selected from the group consisting of glycerol, erythritol, arabitol, xylitol, adonitol, sorbitol, mannitol, iditol, alitol, talitol, perseitol, pentaerythritol, inositol, ramnitol, and epifucitol.
34. 34. The method for manufacturing a foam composition according to claim 33, characterized in that the polyhydric alcohol is d-sorbitol.
35. 35. The method for manufacturing a foam composition according to claim 20, characterized in that the compatibilizing agent is a polyvinyl alcohol, and wherein water is included in the foam composition.
36. 36. The method for manufacturing a foam composition according to claim 35, characterized in that the polyvinyl alcohol has a molecular weight of less than about 200,000.
37. 37. The method for manufacturing a foam composition according to claim 2, characterized in that the compatibilizing agent is a carbohydrate soluble or dispersible in water.
38. 38. The method according to claim 37, characterized in that the carbohydrate is aldose, ketose, monosaccharide, disaccharide, trisaccharide, oligosaccharide, or polysaccharide.
39. 39. The method for manufacturing a foam composition according to claim 20, characterized in that the compatibilizing agent is a carbohydrate soluble or dispersible in water.
40. 40. The method according to claim 39, characterized in that the carbohydrate is aldose, ketose, monosaccharide, disaccharide, trisaccharide, oligosaccharide, or polysaccharide. SUMMARY OF THE INVENTION A method for manufacturing a polyolefin foam composition, which comprises the steps of: (a) feeding a polyolefin polymer into an extruder; (b) adding a nucleating agent to the resin feed; (c) optionally adding a permeation modifier to the resin feed; (d) plasticizing the mixture in an extruder to form a polymer melt; (e) incorporating a carbon dioxide blowing agent, 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 in the foamable composition, wherein the compatibilizing agent is an oxygenated hydrocarbon that lowers the minimum pressure required to prevent prefoaming, while delaying the collapse of the foam due to excessive migration of the agent of blowing; (g) uniformly mixing and cooling the foamable composition to an effective temperature for the expansion of the polyolefin foam; and (h) extruding or expelling the foamable composition through a die, to form a polyolefin foam. * * * * *