| Method of manufacturing polystyrene foam with polymer processing additives -> Monitor Keywords |
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  Method of manufacturing polystyrene foam with polymer processing additivesRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Synthetic Resins Or Natural Rubbers, Ion-exchange Polymer Or Process Of Preparing, Cellular Product Formation Prior To Or During Solid Polymer Formation In The Presence Of A Stated Ingredient Other Than Water, Ingredient Contains Only Carbon And Hydrogen Atoms, Only C And Halogen Atoms, Or Only C, H, And Halogen AtomsThe Patent Description & Claims data below is from USPTO Patent Application 20070173554. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY [0001] This invention relates to processes for forming polymeric foams, particularly to the manufacture of extruded polystyrene (XPS) foams in the absence of chlorofluorocarbon and fluorocarbon blowing agents by using one or more esters, particularly adipates, benzoates and dibenzoates, as polymer processing aids (PPA) for improving the appearance and properties of the resulting foam, and more particularly to processes for preparing extruded polystyrene foam products from polystyrene blends using carbon dioxide as a primary blowing agent. [0002] The invention relates to compositions and methods for producing extruded polystyrene (XPS) foam board suitable for insulation applications, particularly for exterior insulation finish system (EIFS) for building construction. BACKGROUND OF THE INVENTION [0003] In the traditional production of polystyrene (PS) foams using an extrusion process, it was common to utilize as blowing agents one or more halocarbons, such as methyl chloride, ethyl chloride, chlorocarbons, fluorocarbons (including HFCs) and chlorofluorocarbons (CFCs) including dichlorodifluoromethane, fluorohydrocarbons or chlorofluorohydrocarbons (which are also referred to as "soft CFCs", "HCFCs" or "HFCs"). Examples of such halocarbons include a range of CFCs such as CFC-11 (chlorotrifluoromethane), CFC-12 (dichlorodifluoromethane), and CFC-113 (1,2,2-trifluoro-1,1,2-tri-chloroethane), and hydrohalocarbons, also referred to as "soft" CFCs, HCFCs and HFCs, including HCFC-22 (chlorodifluoromethane), HCFC-123 (1,1-dichloro-2,2,2-trifluoroethane), HCFC-142b (10-chloro-1,1-difluoroethane), HFC-134a (1,1,1,2-tetrafluoroethane), HFC-152a (1,1-difluoroethane), and HCFC-141b (1,1-dichloro-1-fluoroethane. [0004] The general procedure utilized in the preparation of extruded synthetic foam bodies generally includes the steps of melting a base polymeric composition, incorporating one or more blowing agents and other additives into the polymeric melt under conditions that provide for the thorough mixing of the blowing agent and the polymer while preventing the mixture from foaming prematurely, e.g., under pressure. This mixture is then typically extruded through a single or multi-stage extrusion die to cool and reduce the pressure on the mixture, allowing the mixture to foam and produce a foamed product. As will be appreciated, the relative quantities of the polymer(s), blowing agent(s) and additives, the temperature and the manner in which the pressure is reduced will tend to affect the qualities and properties of the resulting foam product. [0005] The solubility of chlorofluorocarbons and certain alkanes in polystyrene tends to reduce the extrusion melt viscosity and improve cooling of expanded polystyrene (PS) melts. For example, the combination of pentane and a chlorofluorocarbon such as Freon 11 and 12 is partially soluble in polystyrene and has been used for generating polystyrene foams that exhibited a generally acceptable appearance and physical properties such as surface finish, cell size and distribution, orientation, shrinkage and stiffness. [0006] However, in response to the apparent contribution of such CFC compounds to the reduction of the ozone layer in Earth's stratosphere, the widespread use and accompanying atmospheric release of such compounds in applications such as aerosol propellants, refrigerants, foam-blowing agents and specialty solvents has recently been drastically reduced or eliminated by government regulation. Although certain of the "soft" CFCs such as certain hydrofluorocarbons (HFC's) including 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1-difluoroethane (HFC-152a) are thought to be much more ozone friendly and have been considered as alternative blowing agents. However, these alternative compounds are expensive, tend to be less soluble in polystyrene, tend to have higher thermal conductivity than HCFC's and may still contribute to global warming. [0007] Hydrocarbons such as pentane, hexane, cyclopentane and other homologs of this series have also been considered, but they are highly flammable and volatile, thereby raising both safety and VOC emission concerns. Carbon dioxide is an attractive candidate as a blowing agent, from both the environmental and economic standpoints. The challenges associated with successfully using CO.sub.2 as a blowing agent are, however, significant in light of the relatively low solubility, high diffusivity and poor processability of CO.sub.2 in polystyrene resins. CO.sub.2 also has an increased thermal conductivity relative to that of HCFC-142b and HFC-134a, with CO.sub.2-blown foam exhibiting about 17% and about 10% lower overall product insulation values respectively than corresponding foams produced with HCFC-142b and HFC-134a. [0008] Other previous attempts have utilized alcohols, such as ethanol, or hydrocarbon, such as cyclopentane, in conjunction with CO.sub.2 to improve the processability and enable the production of extruded polystyrene foam board having desired or target physical and thermal properties. The problems with co-blowing agents such as alcohols or hydrocarbons are their flammability, safety and the negative impact on flame performance and insulation properties of the end product. [0009] Conventional processes include polymer foam processes for making thermoformed articles wherein the blowing agent comprises a mixture of at least an atmospheric gas and at least one volatile plasticizing blowing agent. Previous attempts to mix normally liquid hydrocarbons and normally gaseous blowing agents have generally achieved only limited success and have tended to require great care in order to produce acceptable polymer foams using highly-volatile blowing agents such as carbon dioxide. SUMMARY OF THE INVENTION [0010] The objectives of the present invention include providing an improved method of making polymeric foams using one or more atmospheric gases as a blowing agent in combination with at least one ester, particularly an adipate ester, as a polymer processing aid. [0011] In an exemplary embodiment of the invention, extruded polystyrene foams are prepared from a polymeric melt, typically one that includes a high melt flow polystyrene as the primary polymeric component, an atmospheric gas such as CO.sub.2 as the primary blowing agent and at least one polymer processing aid selected from a group of esters, especially adipates having a bis(n-R) structure, wherein R is aliphatic (linear, cyclic and branched, saturated and unsaturated) or aromatic with a preferred adipate being bis(n-decanyl) adipate. [0012] In an exemplary embodiment of the invention, the polymer melt will be prepared from a major portion of one or more styrenic polymers that exhibit a high melt index, e.g., a melt index of at least about 10.0 (g/10 minutes) (as measured according to ASTM D 1238, Condition L) that is combined with no more than about 5 wt % of bis(n-decanyl) adipate as a polymer processing aid and less than about 4 wt % CO.sub.2 as a blowing agent, [0013] In an exemplary embodiment of the invention, the polymer melt will be prepared from preformed styrenic polymers or copolymers that may have been precompounded with bis(n-decanyl) adipate. Alternatively or additionally, the bis(n-decanyl) adipate can be injected directly into the polymeric melt at an intermediate position along the screw extruder path. In addition to the bis(n-decanyl) adipate, other processing aids may be incorporated in the preformed styrenic polymers or may be injected into the melt as it moves through the extruder. The blowing agent(s), such as CO.sub.2, is also injected into the polymeric melt at an intermediate portion along the screw extruder path. In any event, each of the additives and blowing agent(s) should be introduced into the polymeric melt sufficiently upstream of the extrusion die to ensure that adequate blending is achieved before the composition reaches the extrusion die. [0014] In accordance with the invention, the method of making polystyrene foam comprises mixing an atmospheric gas such as carbon dioxide, nitrogen or air and at least one a non-volatile blending agent into a polystyrene melt. The polystyrene melt may also include one or more nucleating agents such as talc, sodium bicarbonate or citric acid. The mixture of the polystyrene melt, the atmospheric gas and the blending agent are then emitted through an extrusion die, thereby reducing the pressure and allowing the blowing agent to expand and form polystyrene foam. Depending on the concentration of the blowing agent and the extrusion conditions, the resultant foam may have substantially no residual blowing agent and will exhibit acceptable foam and surface properties. DESCRIPTION OF THE DRAWINGS [0015] Example embodiments of the invention will be apparent from the more particular description of certain example embodiments of the invention provided below and as illustrated in the accompanying drawings. [0016] FIG. 1 is a schematic drawing of an exemplary extrusion apparatus useful for practicing methods according to the invention; [0017] FIG. 2 is a schematic drawing of another exemplary extrusion apparatus useful for practicing methods according to the invention; and [0018] FIG. 3 is a chart illustrating pressure measurements obtained using a variety of comparative and demonstrative compositions and methods. [0019] These drawings have been provided to assist in the understanding of the example embodiments of the invention as described in more detail below and should not be construed as unduly limiting the invention. In particular, the number, relative spacing, positioning, sizing and dimensions of the various elements illustrated in the drawings are not drawn to scale and may have been exaggerated, reduced or otherwise modified for the purpose of improved clarity. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Continue reading... Full patent description for Method of manufacturing polystyrene foam with polymer processing additives Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method of manufacturing polystyrene foam with polymer processing additives patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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