MXPA99000879A - Closed cellular thermoplastic foams containing hfc- - Google Patents

Abstract

A thermoplastic thermoplastic resin or closed cell ethylene resin is disclosed which was produced by means of a non-flammable blowing agent substantially free of halogen substituents other than fluorine and comprising HFC-134 (1,1,2,3-tetrafluoroethane)

Description

THERMES TERMOPIAS-ICAS DE CELDA. CLOSED CONTAINING H C-134 FIELD OF THE INVENTION The present invention relates to the use of HFC-13 (1, 1,2, 2-tetrafluoroethane) in the production of thermoplastic foams.

BACKGROUND OF THE INVENTION In general, thermoplastic foams are made by mixing a volatile blowing agent with a molten thermoplastic resin under controlled conditions of temperature and pressure sufficient to form a mixture of resin blowing agent, plasticized, and maintaining the mixture in a state not foamed. Subsequently, the mixture is extruded through a suitable matrix in a zone of lower pressure at a controlled temperature to obtain a substantially closed cell structure having the desired body and shape. For satisfactory production of closed cell foam, the solubility of the blowing agent should be sufficiently high, as long as the mixture is passing through the matrix in the lower pressure expansion zone, so that the expansion processes uniformly to the state of closed cell. Otherwise, if the solubility is low, the blowing agent evaporates prematurely REF. 292 4 - and so rapidly and to such a degree before the cell walls are completely formed - that the resulting foam contains a high proportion of broken cells (voids), which adversely affects the usefulness of the foam, for example, as an insulating or structured material to support load. The solubility of the blowing agents in the resin is particularly critical when it is extruded through matrices of large cross section. This is because the flow rate of the extrusion mixture is generally fixed in conventionally used extruders and the back pressure in the lip (opening) is low. The greater the area of the matrix aperture the lower the back pressure exerted on the mixture and the greater the number of voids in the resulting foam. There are many conventional methods for producing thermoplastic foams. Siraux, et al., European Patent Application No. 0 406 206 A2 describes polystyrene foams and a method for producing them which involves a mixture of blowing agents comprising dichloromethane and one or more of a hydrochlorofluorocarbon (HCFC). A hydrofluorocarbon (HFC) and a fluorocarbon (FC), with dichloromethane comprising from 5 to 25 weight percent of the mixture. The system described has the disadvantage of using and requiring environmentally objectionable volatile chlorine-containing substances (by example, depleting ozone) as part of the composition of the blowing agent. Suh et al, Canadian Patent No. 1,086,450, relates to insulating closed-cell polystyrene foams and their preparation uses a mixture of blowing agents of high permeability and low permeability for the production of the foam. These foams are undesirable since they require high proportions of high permeability blowing agents that contain chlorine and / or are objectionable because they are flammable. ? uh, U.S. Patent No. 5,011,866, describes blowing agents comprising at least 70 weight percent of HFC-143a (1,1,1-trifluoroethane) or HFC-134a (1,1,1,2-tetrafluoroethane) for the preparation of insulating polystyrene foams that have small closed cells, low densities (from 1 to 6 pounds per cubic foot) and high dimensional stability among other properties. HFC-143a is objectionable for its flammability, and HFC-134a presents processing difficulties as indicated in U.S. Patents Nos. 5,146,896 and 5,204,169 to York. Omire et al. U.S. Patent No. 5,145,606, discloses eleven categories of blowing agent blended to form thermoplastics such as polystyrene and polyethylene. Included among the agent mixes of blown there are four comprising a tetrafluoroethane, which may be HFC-134a and / or HFC-134 (1, 1, 2, 2-tetrafluoroethane), mixed with one or more hydrochlorofluorocarbons (HCFC). Omire, however, teaches that HFC-134 and HFC-134a can not advantageously be used alone as a blowing agent for thermoplastics, and tetrafluoroethane should be used in combination with at least one blowing agent containing chlorine. Rubin et al, U.S. Patent No. 5,314,926, discloses blowing agents for polystyrene and other foamed plastics based on compounds other than isocyanurate which comprise 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). ) in combination with one or more partially halogenated hydrocarbons or alkanes, which may contain chlorine substituents or be free of chlorine. The system described has the disadvantage of requiring HFC-227ea, HGWP material higher (0.6), ie, environmentally objectionable, as part of the composition. Volcker et al, United States Patent No. ,334,337, discloses a high compressive strength foam prepared from polystyrene containing 5-16 weight percent of a blowing agent mixture containing an alcohol or ketone, carbon dioxide (C02) a C3 hydrocarbon C5 and fluorinated hydrocarbons. The technology described is advantageous since it includes at least one flammable component which is also a volatile organic compound (VOC); the use of which is regulated in many countries. Bartlett et al, U.S. Patent No. 5,182,040, discloses azeotropic and azeotropic binary compositions of HFC-134 with HFC-152a (1,1-difluoroethane), dimethyl ether (DME) and halocarbons and selected hydrocarbons useful as refrigerants, propellants in aerosol and blowing agents for polymeric foams.

BRIEF DESCRIPTION OF THE INVENTION It was discovered that 1,1,2,2-tetrafluoroethane, HFC-134, is substantially as effective as HFC-152a as a blowing agent for thermoplastic resins with greater advantages over HFC-152a to give a absence of flammability and lower permeability through thermoplastic resins. This is a surprising and unexpected result since those skilled in the art believe that HFC-134 alone and an azeotrope thereof with HFC-152a have essentially no effect on solid polystyrene. In addition, HFC-134 is superior to its isomer, HFC-134a, as a blowing agent for such foams. HFC-134 can exert lower solution pressures in the extrusion step, thus allowing the HFC-134 to be used in the equipment to manufacture conventional foams. The aforementioned discovery solves problems in this field by providing improved insulating thermoplastic foams produced with the aid of effective environmentally friendly and non-flammable blowing agents, preferably in conventional equipment. The present invention solves a further problem by providing foams suitable for use as insulating and structural elements wherein the blowing agents also exhibit acceptably low permeabilities through the thermoplastic resins; enough to improve long-term insulation values. The present invention solves these problems and provides environmentally friendly and non-flammable, effective blowing agents to produce foamed materials for packaging food and food uses, usually employing conventional equipment manufacturing equipment. In one aspect, the invention comprises a closed-cell, thermoplastic, resin-filled foam body, ie, without interconnections, produced by means of an environmentally friendly, non-flammable, low permeability polyfluorocarbon blowing agent composition comprising more than about 70 per cent. HFC-134 and it is substantially entirely free of components that they have halogen substituents other than fluorine. The present invention can be used to obtain closed cell foams having a wide range of characteristics. The foam cells typically have an average cell size of about 0.1 to about 1.5 millimeters (mm) when measured across a minimum cross-sectional body dimension. The foam body typically has a minimum cross-sectional dimension (thickness) of at least about 0.04 inch (1 mm), a cross-sectional area of at least about 2 square inches (13 square centimeters) and a density of about 0.075. at 15 pounds per cubic foot (pcf or 12 to 240 kilograms per cubic meter). Typically, the foam has a thickness of at least about 0.5 inches (1.27 cm), typically at least about 1.0 inches (2.54 cm), and usually at least about 1.5 inches (3.9 cm). The cross-sectional area of the foam body can be at least about 4 square inches (26 square centimeters), usually at least about 8 square inches (52 square centimeters) and usually at least about 16 square inches (104 centimeters) squares) . Although the density of the foam body depends on many variables, the density is typically at least 1.5 pcf (24 Kg / m3), normally at least about 3 pcf (48 Kg / m3) and usually at least about 6 pcf (96 Kg / m3). The body of the foam may be comprised of any suitable thermoplastic resin. Aungue can be used HFC-134 with a virtually unlimited resin arrangement, the thermoplastic resin is normally polystyrene; but, a polyethylene or polypropylene can also be used. Additional details regarding the composition of the foam body as well as the components / systems that are used to form the body of the foam can be found in "Modern Plastics Encyclopedia '92" Volume 68, Number "11; Chapters:" Processing Primary "," Chemical Reagents and Additives ", the description of which is incorporated herein by reference.The body of the foam is normally produced (a) by forming a substantially homogeneous molten mixture of the normally solid thermoplastic resin and an effective foaming amount of the blowing agent at a non-foaming high temperature and pressure, (b) extruding the mixture through a matrix in an expansion zone at a controlled foaming temperature and reduced pressure at an effective controlled rate to form a substantially free foam body of gaps, closed cell (c) allowing the body of the foam to cool and increase its viscosity at temperatures and pressures such that a substantially closed cell foam body having the dimensions of the cell size and density defined above at ambient temperatures and atmospheric pressures is obtained. The specific process conditions for obtaining the substantially closed cell body are understood by one skilled in the art. In one aspect, the invention comprises sheets of a closed cell foam body, of relatively low density, suitable for use as a thermoformed and starting material for producing materials for packaging food. A suitable technique for producing such foams is described in U.S. Patent No. 5,204,169; the description of which is incorporated here as a reference. Another aspect comprises a relatively thick and high density foam body suitable as insulation, for example, in the form of a panel in the construction of buildings In a further aspect the invention comprises high density closed cell insulating foams suitable for use as Structural members The insulating foam bodies of the invention are further characterized by exhibiting low permeabilities in the blowing agents, for example, low loss of the blowing agent, thereby improving the value of the thermal insulation of the foam over time as measured by its factor K. The blowing agent composition for use in this invention comprises HFC-134 only or as environmentally friendly, substantially non-flammable mixtures thereof containing less about 30 weight percent of other compatible blowing agents without halogen substituents other than fluorine. Such blowing agents usually have from 1 to 2 carbon atoms and are not classified as VOC (volatile organic compounds) photochemically reducing. That is, the blowing agent composition is substantially non-flammable, has an ozone depletion potential (ODP) of zero and a low overall halocarbon orientation (HGWP) alarm potential or "true effect". In some cases, it may be desirable to employ HFC-134 in conjunction with one or more additives or co-blowing agents selected from the group consisting of HFC-134a (1, 1, 2, 2-tetrafluoroethane, CF3CCH2F), HFC-152a ( 1,1-difluoroethane, CF2HCH3), HFC-143a (1,1,1-trifluoroethane, CF3CH3), HFC-52 (difluoromethane, CF2H2), HFC-125 (pentafluoroethane, CF3CF2H), among others. Usually, in terms of percent by weight, the amount of additive blowing agent corresponds to less than about 22, usually less than about 13, and typically substantially zero based on the total weight of the composition. of blowing agent. The blowing agent of the invention includes azeotropic and azeotropic mixtures of HFC-134 with co-blowing agents. An example of such azeotropes includes flame retardant and non-flammable mixtures of HFC-134 with HFC-152a within the range of 78 weight percent or more of HFC-134 and 22 weight percent or less of HFC-152a, and typically within the range of 87 weight percent or more of HFC-134 and 13 weight percent or less of HFC-152a. Examples of such non-flammable mixtures are also described in the references of Watanabe et al., EP 483 573 Al and Bartlett et al, mentioned above. A "effective blowing agent foaming amount" means an amount sufficient to result in a foam body having the properties described herein. Typically, an effective amount will range from about 1 to about 30 weight percent based on the total weight of the resin blowing agent composition, usually from about 2 to about 20, and typically from about 2 to about 10 percent by weight. cent in weight. The specific effective amount of the blowing agent will depend on the particular type and degree of resin that I feel used and the desired resulting properties.

A "substantially closed-voided, closed cell foam body" means a foam with a substantially uniform cell structure having more than about 50% closed cells, preferably more than 90% closed cells as measured by ASTM D2856-70. "Non flammable" means that it meets the criteria set forth in ASTM E6871-85 with the modifications listed in draft form, November, 1993, by the ASTM E27 committee or by ASTM E918; incorporated here as a reference. "Potential global alarm effect by halocarbon (HGWP) under" means a blowing agent having a HGWP value of about 0.50 or less, usually less than about 0.32 and typically less than about 0.30 as determined by the method described by DA Ficher et al, NATURE 1990, 344, P. 513; incorporated here as a reference. The cell sizes of the foam are determined by the ASTM method D2842-69, and the dimensional stability of the foam by ASTM D2126 / C758. Foam densities are determined by ASTM D1622-83. The invention was based on the discovery that contrary to the expectations of HFC-134: (1) this is superior to its HFC-134a isomer as a blowing agent for thermoplastic foams, since this and mixtures thereof exert substantially lower solution pressures (higher solubilities in the ream phase) over the range of temperatures and pressures employed in the extrusion of the compositions as foams, so that HFC-134 can be used in conventional equipment without modifications to produce closed cells substantially free of voids, (2) alone or as mixtures thereof produces high quality closed cell foams which they have desirably small cell sizes over a wide range of densities, dimensional stability and low permeability through a thermoplastic film, thereby providing long-lived insulating and structural foams; (3) is superior to HFC-143a and HFC-152a, which are recommended in the art for use in the production of insulating thermoplastic foams, since HFC-134 and mixtures thereof have lower permeability through thermoplastic films , thereby providing improved insulating characteristics, while offering the added advantage of being non-flammable; (4) If it is alone or in combination with other environmentally friendly hydrocarbon blowing agents it can be an acceptable replacement of the blowing agents used hitherto commercially for thermoplastic foams such as CFC-11, CFC-12, HCFC-22 and HCFC-142b.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 graphically depicts the solubilities in a normally solid polystyrene resin of the invention, HFC-134, compared to HFC-134a, HFC-152a and HFC-143a over a wide range of temperatures mpassing the extrusion temperatures useful in the foam production process of the invention. Figure 2 graphically depicts the interaction parameters of HFC-134, HFC-134a, HFC-152a and HFC-143a with a polystyrene over a temperature range of 20 to 220 ° C. Figures 3, 4, 5 and 6 are log-log graphs that relate the solubility of HFC-134, HFC-134a, HFC-152a and HFC-143a, respectively, as superheated steam in polystyrene resin over a temperature range of 20 to 220 ° C.

DETAILED DESCRIPTION OF THE INVENTION One aspect of the invention comprises a substantially solid, closed-cell, insulating thermoplastic foam body, wherein the cells are substantially completely filled with an agent of substantially nonflammable blowing comprising more than about 70 weight percent HFC-134, the remainder, if any, of the blowing agent comprises one or more components without halogen substituents other than fluorine, and has low HGWP values. Examples of blowing agent components suitable for use with HFC-134 include hydrofluorocarbons comprising at least one of HFC-134a, HFC-152a, HFC-32, HFC-125, azeotropic and azeotropic-like mixtures with HFCs -134, for example, as described above, among others. Other acceptable blowing agent components that can be used in conjunction with HFC-134, with or without the other components of HFC, comprise at least one of N2, C02, argon, other rare gases, among others. Hydrocarbons and other VOC compounds are desirably absent. Normally, the HFC-134 content of the blowing agent composition is at least about 78% by weight, usually at least about 87, and desirably about 100 percent. Typically, the average cell size is less than about 1.5 mm, and usually not more than about 1.2 mm. When the foam is used as an insulating body, the thickness may be between about 0.04 and about 6 inches (1 to 152 mm), and the foam density is about 0.75 to about approximately 15.0 pounds per cubic foot (12 to 240 kilograms per cubic meter). Accordingly, the foam of the present invention provides small cells, obtained using an environmentally friendly blowing agent, of low permeability, and provides long-term insulating properties to thermoplastic foam bodies while excluding the release of halocarbons which they consume. ozone and volatile organic compounds that produce smoke to the atmosphere- The polystyrene resinous component of the foam products of the invention, sometimes referred to in the art as "styrenic resin", can vary widely in chemical composition. Broadly mpassed as resins that can be employed in the present invention are the solid thermoplastic polymers of one or more polymerizable alkenylaromatic compounds. The polymer or copolymer comprises in chemically combined form at least one alkenyl aromatic compound having the general formula Ar-C (R) -CH2, in which Ar represents an aromatic hydrocarbon radical of the benzene series, typically phenyl, and wherein R usually represents hydrogen (preferably) or a methyl radical. Although any suitable alkenyl aromatic resin can be employed, examples include the solid homopolymers of styrene "," alpha-methylstyrene, o-methylstyrene, m- methylstyrene and p-methylstyrene; also the solid copolymers of two or more such alkenyl aromatic compounds, among others. The polymers may also include relatively minor proportions of other polymerizable olefinic compounds in copolymerized form., such as, for example, methyl methacrylate, acrylonitrile, methacrylic acid, acrylic acid, maleic anhydride, among others. Without wishing to be bound by any theory or explanation, it is believed that the non-styrenic monomers may contribute via their polymer sites of the oxygen and nitrogen containing portions to solvate HFC-134 (and other hydrofluorocarbon components of the blowing agent) during the step of mixing the polystyrene resin blowing agent mixtures before foaming. A desirable polystyrene resin comprises the solid homopolymer, polystyrene, because of its low cost and easy availability. Other thermoplastic resins can be foamed with the blowing agent composition based on HFC-134, including polyolefin compounds, for example, polyethylene, polypropylene, mixtures thereof, among others. The thermoplastic foam bodies of this invention are conveniently produced using conventional equipment comprising an extruder and the associated means for (1) melting the resin; (2) homogeneously mix the blowing agent composition with the melt for forming a plasticized mass at temperatures and pressures at which no foam is formed; (3) passing the plasticized mass at a rate, temperature and pressure controlled through a matrix having a desired shape, for example, a slotted die to produce rectangular pieces of foam panel having the desired thickness and surface area, an expansion zone; (4) allow the extruded foam in the expansion zone maintainable at adequate temperatures and low pressures; (5) maintaining the expansion extrudate under such temperatures and pressures for a time sufficient for the viscosity of the extrudate to increase so that the size of the cell and density of the foam remain substantially unchanged and substantially free of ruptured cells at temperature environment, for example, 25 ° C and atmospheric pressure; and (6) recovering the extruded foam body. In one aspect of the invention, the blowing agent blowing amount in the range of about 1 to about 30 percent by weight based on the total weight of the resin plus the blowing agent mixture, typically from about 2 to about about 20 weight percent, and normal weight about 2 to about 10 weight percent. At a relatively lower blowing agent concentration, the density of the resulting foam is greater. The appropriate amount of blowing agent or characteristics The resultants of the foam for any desired end use are easily determined by one skilled in the art which is reviewed and understood in the present invention. The resin is melted at a temperature of about 200 to about 235 ° C depending on the degree employed, and at pressures to which no foam is formed of about 600 psig or greater. The plasticized resin blowing agent mixture is cooled under a pressure at which no foam is formed at a temperature of about 115 to 150 ° C, usually 130 ° C, and is extruded into the expansion zone or below the ambient temperature and below the atmospheric pressure. When preparing the foams of this invention, it is often desirable to add a nucleating agent or other additive in the resin. The nucleating agents serve primarily to increase the number of cells and decrease the size of the cell in the foam, and can be used in an amount of about 0.1 to about 4 parts by weight per 100 parts by weight of the resin. Typical nucleating agents comprise at least one member selected from the group consisting of talc, mixtures of sodium bicarbonate-citric acid, calcium silicate, carbon dioxide among others. Other additives are often incorporated into the resin which include, for example, dyes, antioxidants, lubricants. stabilizers, flame retardants, among others, depending on the final use of the resin. Representative foamed products that can be made in accordance with the present invention comprise: (1) polystyrene foam sheets for the production of thermoformed, disposable packaging materials, for example, as described in U.S. Patent No. 5,204,169, of York; (2) extruded polystyrene foam boards for use as residential and industrial roofing materials and ceilings, which may be approximately 0.5 to 6 inches (1.25 to 15 cm) thick, up to 4 feet (122 cm) wide, with cross-sectional areas of 0.17 to 3 square feet (0.016 to 0.28 square meters), and up to 27 feet (813 meters) in length, with densities of approximately 1.5 to 10 pounds per cubic foot (pcf) (25 to 160 kilograms per cubic meter (kg / m3)); (3) expandable foams in the form of long plates which can be up to about 2 feet (61 cm) thick, often at least 1.5 feet (46 cm) thick , up to 4 feet (1.22 meters) wide, up to 16 feet (4.8 meters) in length, which have a cross sectional area of approximately 2 to 8 square feet (0.19 to 0.74 square meters) and a density of 6 to 15 pcf (96 to 240 kg / m3) Such foamed products are described more completed by Stochdople and Welsh in Encyclopedia of Polymer Science and Engineering, vol. 16, pages 193-205. John Wiley S Sons, 1989; incorporated here as a reference. Certain aspects of the invention are illustrated by the Figures. The accompanying figures illustrate the solubility of HFC-134 as blowing agents to produce polystyrene foam bodies, the data presented therein was obtained with the help of the well-known Flory-Huggins equation (Flory, PJ: "Principies of Polymer Chemistry "; Cornell University Press, Ithaca, NY), discussed later. Referring now to the Figures, Figure 1 is a graph of% by weight of soluble material in polystyrene resins vs. temperature, which shows that the solubility of HFC-134, compared to other HFCs, in a representative polystyrene resin (which has a vitreous transition temperature of 85 ° C and a melting point of 105 ° C) increases with the increase in temperatures, measured at the equilibrium pressures of the mixtures. Those equilibrium pressures are related to the point in the extrusion process where the blowing agent is mixed with the resin; it can not occur foaming at those pressures. Figure 1 shows that the solubility of HFC-134 and HFC-152a in the selected resin are similar throughout the temperature range, and that their solubilities are sigiificantly greater than those of HFC-134a and the HFC-l 3a. HFC-134 and FC-152a also show superior solubilities under extrusion conditions; the data demonstrating such solubility are illustrated in Figures 3, 4, 5 and 6 and are summarized below in Tables 1 and 2. Referring now to Figures 3-6, Figures 3-6 relate to the solubility of HFC-134 vapor superheated in polystyrene resin at the following selected temperatures 20 °, 60 °, 140 °, 180 ° and 220 ° C at pressures as high as approximately 3000 psia. The data presented in Figures 3-6 was determined through the use of the Flory-Huggins equation for phase equilibrium in polymer solutions. This equation uses values for the following par meters [(l) - (4)], which were obtained as follows: (i) The densities of the blowing agents in liquid state, g / cc, were derived using the standard methods , drawing a straight line through the density data in liquid state (based on experimental data from the National Institute of Standards and Technology, NIST, with equations based on the state equation of Benedict-Webb-Rubm Modified, MBWR) from -50 ° C to 50 ° C and calculating the density in liquid state as a function of temperature. The density equation (d) states that: d = AT + B, _ where A is the slope of the line, B is the constant of the line, and T the temperature (° C). The densities in liquid state are (grams / cubic centimeter, g / cm3).

Density in Liquid State Component 50 ° C 85 ° C 100 ° C 120 ° C 150 ° C HFC-134 1,214 1,104 0.994 0.888 ' HFC-134a 1,108 0.983 0.749 HFC-152a 0.819 0.655 0-572 HFC-143a 0.804 0.645 0.553 ** 0.460 Resin *** 1.056 1.051 1.041"---. 025 1.011 * 160 ° C ** 125 ° C *** Polystyrene Dylene 8G Arc, t. d. = 85 ° C, p. F. i05 ° C. (2) The densities of the superheated vapors of the blowing agents, which are tabulated below, were calculated from the known thermodynamic vapor properties data (based on experimental data from the National Institute of Standards and Technology, NIST, with equations based on the state equation of Benedict-Webb-Rubin Modified, MBWR).

Supareased Steam Densities (q / am3) Component 50 ° C 85 ° C 100 ° C 120 ° C 150 ° C HFC-134 0.04379 0.04497 0..03830 0.04867 * HFC-134a 0. 03390 0. 02975 - 0.03158 HFC-152a 0. 02495 0.02281 0.03850 ** 0.02942 HFC-143a 0.04611 0.04386 0.03204 ** 0.04349 * 160 ° C ** 125" C (3) The activity coefficients for the blowing agents that were tabulated are the following: Coe-Ticxentes of Activity Temp. ° C HFC-134 HFC-134a HFC-152a HFC-143a 50 0.877 0.6O5 0.728 0.537 85 0.447 0.273 100 0.277 0.238 120 0.218 125 150 0.112 0.174 0.133 160 0.116 These coefficients were determined by dividing the partial pressure of the experimental blowing agent by the saturated pressure at that temperature. (4) The interaction parameters, XI, were determined at four temperatures, and were presented graphically as a function of the temperature in Figure 2, by means of the following equation and constants of the equation: XI = A / T + B (where T = ° K = ° C + 273.2) Camp to AB ^ HFC-134 (< 85 ° C) 2553.95 -5.75256 HFC-134 (&85; C) 2075.829 -4.44256 HFC-143a (&85; C) 4641.477 '-11.5113 HFC-143a (> 85 ° C) 2450.138 -5.40252 HFC-152a (< 85 ° C) 1944.713 -4.51260 HFC-152a (&85; C) 2013.858 _ -4.64595 The representative XI values are: Temp. ° C HFC-134 HFC-134a HFC-152a HFC-143a 50 2.2 2.80 1.50 2.90 100 1.1 1.50 0.75 1.20 125 0.75 1.10 0.40 0.75 150 0.50 0.80 0.10 0.40 200 - . 200 -0.05 0.2Q 0.40 -0.25 Referring now to Figure 2, these data allow to calculate the limiting and superheated solubilities of the blowing agents via the Flory-Huggins equation, using the values of (l) - (4) above. Such data was graphically represented in Figures 3, 4, 5 and 6. Figures 3-6 are graphs of "% by weight" of Blowing Agent Dissolved in Res. Solution Pressure "as a function of temperature The representative solubilities of the blowing agents in the ream given at various temperatures of the extrusion process appear at atmospheric pressure (14.7 psia) are listed below in Table 1.

Table 1% in Weight of Blowing Agents Dissolved in Resin Temp. "C HFC-134 HFC-134a HFC-152a HFC-143a 200 0 .-. 5 0.08 0.05 0.15 180 0.2 0.1 0.07 0.2 140 0.3 0.15 0.1 0.3 100 0.4 0.19 0.13 0.4 60 0.5 0.2 0.08 0.5 20 0.6 * 0.16 * 0.04 0.8 Table 1 indicates that during the foam forming step for extrusion of foam production, the solubility, respectively, of HFC-134 and HFC-152a in the ream per se, differs from the amount of such material in the cells of the resulting foam, it increases progressively with the decrease in temperature at a given foaming pressure. The same trend is evident after examining the data of the Figures at the other pressures, for example, 100 psla. This effect of the solubility of the resin indicates that a more uniform, better foam will result. The solubilities of HFC-134 (and HFC-152a) in the resin are increased, i.e., that the solution pressures decrease, with the decrease in temperature during extrusion. These characteristics are advantageous for providing conditions for the formation of foam, which lead to the production of closed cells over a wide range of densities, while reducing the possibility of blown / broken cells. The data in those Figures shows that the solubility ratio HFC-134 / HFC-134a is substantially stable at a ratio of about 2/1 to the temperature range of 200 to 100 ° C during which the composition of the The resin blowing is substantially melted. The solubility ratio, however, increases at temperatures of about 60 ° C to 20 ° C, which is below the melting and glass transition temperatures of the resin. These solubilities are surprising and unexpected, and when they are transferred to the closed cell foam product, they correspond to a wide range of densities, with fewer blown / broken cells. The following Table 2 presents similar solubility data demonstrating the superiority of HFC-134 and HFC-152a over the other blowing agents at an extrusion temperature of 180 ° C, in terms of the (1) greatest limitation, is say, maximum solubilities at the extrusion temperature, (2) the lowest vapor pressures exerted by HFC 134 and 152a at a solubility of 10 weight percent on the resin, and; (3) the most favorable solubilities at 1 atmosphere of pressure at both the extrusion temperature of 180 ° C as the final resting temperature of 25CC.

Table 2 to Solubility (% Tamp. Solubility Temperature of HFC by weight Extruder Limiting Agent for 1 Atm Extruder Pressure (% by weight a HFC Load Blown ° C of HFC) 10% (ps a) Te-pp. Ext. 25 ° C HFC-134 180 81 630 0.2 0.54 HFC-134a 180 69 1000 0.11 0.16 HFC-143a 180 69 1370 0.07 0.04 HFC-152a 180 83 620 0.2 0.76 Similar results were obtained at higher and lower extrusion temperatures, e.g., 200 ° and 130 °.

Table 3 Solution Pressure of Blowing Agents in Polystyrene Resin at 140 '' C Concentrated Pressure of the Agent (% by weight Solution Blown in resin *) (psia) HFC-134 10.00 450 HFC-134a 10.00 740 HFC-143a 8.23 810 HFC-152a 6.47 340 *% in weight adjusted to reach the molar equivalence.

Employing a procedure identical to that described in detail above for "Petrothene" grade low density polyethylene from Quantum, Table 4 below presents similar solubility data demonstrating the superiority of HFC-134 over other fluorinated blowing agents at an extrusion temperature. 180 ° C, in terms of the (1) greatest limitation, that is, maximum solubilities at the extrusion temperature, (2) the lowest vapor pressures exerted at a solubility of 10 percent by weight in the ream, and; (3) the most favorable solubilities at 1 atmosphere of pressure both at the extrusion temperature of 180 ° C and the final resting temperature of 25 ° C.

Table 4 to Solubility < % Terrp. Solubility Temperature by weight of HFC a Extrusor Limiting Agent for 1 Atm of Extruder Pressure (% by weight a HFC Burst Blow of HFC ° C) 10% (ps a) Teurp. Ext. 25 ° C HFC-134 180 81 621 0.20 0.64 HFC-161 * 180 89 600 0.24 0.22 HCFC-114 ** 180 78 324 0.38 2.01 HFC-134a 180 74 828 0.14 0.22 * E1 HFC-161 is 1-fluoroethane (CFCH2-CH3). ** E1 HFCF-114 is 1, 2-d? Chloro-l, 1,2,2-tetrafluoroethane (CC1F2CC1F2).

Example 1 The following example serves to illustrate the ability to use HFC-134 to produce polystyrene insulation foam, with a uniform, thin cell structure, with a long-term insulating value, and good dimensional stability. The extruder used was designed for use with CFC-12 (CC1-FJ and was converted to a mixture of blowing agents of HCFC-142b (CFC1.CH3) / HCFC-22 (CHC1F.) 60/40% by weight. mixture HCFC-142b / HCFC-22 exhibits pressure in polystyrene solution similar to that of CFC-12 The data in example 1, reveal that HFC-134 works very similarly to the mixture HCFC-142b / HCFC-22 ( note matrix pressure, foam thickness, foam width and foam density.) With HFC-134a, the die opening had to be closed to control the process (from 1.9 mm to 1.7 mm), the which resulted in a higher operating pressure (2483 psig), it was also necessary to reduce the melting temperature of the ream (from 129 ° C to 116 ° C) to reduce premature foaming in the matrix. , foam blown with HFC-134a it was heavy (43 kg / cubic meter), had a rough surface, and did not reach the required thickness and width. Tests were conducted with the foams to produce polystyrene foam insulation using a serial, commercial extruder equipped with an experimental matrix, designed to operate at higher pressure. Diameter of the primary extruder = 120 mm. Diameter of the secondary extruder = 2-.0 mm. Polystyrene resin = Shell NX606 for general purposes, Melt index of 2.5. Nucleador = Talc of magnesium silicate.

Test 1 Test 2 Test 3 Blowing agent 22 / 142b HFC-134a HFC-134 40/60% by weight Primary extruder (rpm) 70 70"70 Primary extruder (amps) 2 26644 270 267 Extrusion rate 430 422 438 (kg / hr) Agent speed 46.5 45.8 45.1 blowing (kg / hr) Concentration of 10.82 10.86 - 10-31 blowing agent (% by weight) Concentration of 0.6 1.16 0.8 nucleator (% by weight) Extruder speed 4.9 4.9 4.9 secondary (rpm) Secondary extruder 102 122 112 (amps) Pressure of the matrix 1484 2483 1645 (psig) Melting temperature 129 116 127 (degree C) Opening of the matrix 1.9 1.7 1.9 (mm) Width of the matrix (mm) 100 100 100 Foam thickness 52 44 50 (mm) Foam width (mm) 317 249 285 Foam density 30.5 43 32.5 (kg / cubic meter) Comments Foam Foam Foam Excellent too Excellent Excellent on the rough surface of the matrix It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, * e claims as property what is contained in the following:

Claims (6)

1. A process for producing a closed cell thermoplastic polymeric foam wherein a blowing agent expands as the polymer phase solidifies, characterized in that it comprises: (a) forming a blowing agent composition comprising more than 70 weight percent of 1,1,2,2-tetrafluoroethane (HFC-134); (b) adding the blowing agent composition to a molten composition of a thermoplastic polymer resin to form a substantially homogeneous molten mixture of the thermoplastic resin and a foaming amount of the blowing agent composition at elevated, non-foaming temperature and pressure; (c) extruding the mixture through a die or otherwise forming the molten mixture in a zone at elevated temperature and pressure, foaming, and at an effective controlled rate to obtain a closed cell foam body; and (d) allowing the foam body to cool and increase its viscosity at temperature and pressure such that a substantially rigid closed cell foam is obtained.

2. The process according to claim 1, characterized in that the foam is produced with about 2 to about 10 weight percent of the blowing agent based on the total weight of the resin blowing agent composition. The process according to claim 1, characterized in that the composition of the blowing agent further comprises at least one member selected from the group consisting of HFC-134a, HFC-152a, HFC-143a, HFC-32 and HFC-125 in an amount that totals less than about 30 weight percent. 4. The process according to claim 1, characterized in that the composition of the blowing agent comprises at least 78 weight percent of HFC-134. 5. The process according to claim 1, characterized in that the composition of the blowing agent comprises at least about 87 weight percent of HFC-134. 6. The process according to claim 1, characterized in that the composition of the blowing agent consists essentially of HFC-134.