METHOD FOR THE PREPARATION OF STYRENE POLYMER FOAM AND FOAM PREPARED THEREBY

Abstract: Styrene polymer foam that is more environmentally acceptable, capable of making foam insulation over a wide range of densities, decorative and does not require the modification of existing equipment for high pressure operation is prepared using a mixed blowing agent of carbon dioxide plus ethyl chloride and optionally a fluorocarbon to provide a foam having primary cells and secondary cells defined by the struts and walls. The method of preparation involves heat-plastifying the styrene polymer and adding to the heat-plastified polymer a mixed blowing agent of carbon dioxide, ethyl chloride and optionally a fluorocarbon under a pressure sufficiently high to prevent foaming; reducing the temperature of the mixture and reducing the pressure of the mixture as it is extruded to form the foamed product.

Description: METHOD FOR THE PREPARATION OF STYRENE POLYMER FOAM AND FOAM PREPARED THEREBY This invention relates generally to extruded styrene polymer foams. More particularly it relates to the use of a mixed blowing agent of carbon dioxide plus ethyl chloride and optionally certain specific fluoro- carbons. The variety of styrene polymer foams contem¬ plated within the scope of this invention are the so-called "extruded foams". Such extruded foams have a fairly uniform cell size when compared to the so-called "molded bead foams". One of the larger applications for extruded styrene polymer foams is in the field of thermal insu¬ lation. Styrene polymer foam that is suitable for thermal insulation desirably has relatively small cells and good dimensional stability. It is also desirable <®_ that the insulating value of the foam be maintained for as long a period as possible. Extruded foams are also employed in the so-called decorative field wherein a foam plank may be cut into a "decorative foam" and be used as is or else used as a base for further decorative material. Par¬ ticularly desirable stable styrene polymer foam can often be obtained by employing the method set forth in U.S. Patent No. 3,960,792 to M. Naka ura. For many years, styrene polymer foams have been extruded employing methyl chloride alone as the blowing agent or a mixture of methyl chloride with chlorofluorocarbons. Generally the products of these processes must be aged for a period of time to permit the methyl chloride to leave the cells and air to enter by an appropriate diffusion process through the cell walls. Also, in foams employing methyl chloride as ' the total blowing agent or as a partial blowing agent, the period of aging for thicker extruded boards and planks can present an inconvenient warehousing problem. Also, due to the undesirable physical characteristics of methyl chloride, caution and good ventilation are utilized when such foams are stored or cut to shape. Styrene polymer foam has been prepared using ethyl chloride as a significant component of the blowing agent. Such foam preparation is set forth in U.S. Patents 4,393,016 and 4,451,417. An alternative blowing agent system utilizing carbon dioxide and an alkane is set forth in U.S. Patents 4,344,710 and 4,424,287. It would be desirable if there were available an improved process for the preparation of alkenyl aromatic polymer foam which used blowing agents that are more environmentally acceptable than methyl chloride; which are capable of making insulating foam over a wide range of densities as well as decorative foam; and which could be used on existing equipment without modification to very high pressure operation. These benefits and other advantages in accor¬ dance with the present invention are achieved in a process for the preparation of an extruded alkenyl aromatic thermoplastic resinous elongated foam body, the body defining a plurality of closed nonintercon- necting gas-containing cells therein, the steps of the method including (1) heat-plastifying an alkenyl aro¬ matic synthetic resinous material; (2) adding to the heat plastified synthetic resinous, material a volatile fluid foaming agent to provide a foaming agent resinous polymer mixture under a pressure sufficiently high that foaming is prevented; (3) mixing the fluid foaming agent with the plastified resin to-form a blowable resinous mixture; (4) reducing the temperature of the mixture to a temperature such that when pressure is removed therefrom, a foam of desirable quality is obtained; (5) reducing the pressure on the mixture to thereby cause the mixture to form a foam of desired quality: characterized by employing- a blowing agent mixture of from 3-45 weight percent of carbon dioxide, from 5-97 weight percent ethyl chloride and from 0-90 weight percent of a member selected from the group consisting of dichlorodifluoromethane, l-chloro-1,1- difluoroethane and mixtures thereof, the blowing agent mixture being utilized at a level of 3-18 parts by weight per 100 parts by weight of resinous material. Also contemplated within the scope of the present invention is a synthetic resinous thermoplastic foam prepared in accordance with the hereinbefore described method wherein an alkenyl aromatic thermo- plastic synthetic resinous elongate foam body having a machine direction and a transverse direction, the body defining a plurality of closed noninterconnecting gas-containing cells therein, with the further limita¬ tion that the cells contain at least residual vaporized blowing agent hereinbefore described. By the term "alkenyl aromatic synthetic resin" is meant a solid polymer of one or more polymer- izable alkenyl aromatic compounds. The polymer or copolymer comprises in chemically combined form, at least 75 percent by weight of, at least one alkenyl aromatic compound having the general formula R Ar-C=CH- wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halo-hydrocarbon radical of the benzene series, and R is hydrogen or the methyl radical. Examples of such alkenyl aromatic resins are the solid homopolymer of styrene, a-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ar-ethylstyrene, ar-vinylxylene, ar-chlorostyrene or ar-bromostyrene; the solid copolymers of two or more of such alkenyl aromatic compounds with minor amounts of other readily polymerizable olefinic compounds such as methylmethacryl- ate, acrylonitrile, maleic anhydride, citraconic anhy¬ dride, itaconic anhydride, acrylic acid, rubber rein¬ forced (either natural or synthetic) styrene polymers, etc. Blowing agents useful in the practice of the present invention of commercial purity are generally satisfactory. In the practice of the present inven¬ tion, carbon dioxide is generally employed in the proportions of from 3-45 weight percent of total blowing agent whereas ethyl chloride is employed at a level of 5-97 weight percent, preferably at a level of 19-97 weight percent, and the dichlorodifluoromethane or 1,1,1-chlorodifluoroethane is employed from 0-90 weight percent of the total weight of the total blowing agent component. In the preparation of foams particularly suitable for thermal insulation, carbon dioxide is employed at a level of from 3-25 weight percent of the total blowing agent whereas ethyl chloride is employed at a level of 5-60 weight percent, preferably at a level of 20-60 weight percent, and the chlorofluoro- carbons are employed at a level of 30-90 weight percent. The dichlorodifluoromethane or chlorodifluoroethane, or a mixture of each, may be utilized. In the event that it is desired to prepare foam particularly suitable for decorative applications, that is, a large cell foam that is readily cut and machined to desired configur¬ ations, carbon dioxide is employed at a level of from 3-45 weight percent, ethyl chloride at a level of from 60-97 weight percent and the chlorofluorocarbon component from 0-25 weight percent. The blowing agent mixture may be supplied to the alkenyl aromatic resin in any conventional manner. For example, a mixture of the desired composition of blowing agent may be directly injected into a heat plastifying and mixing apparatus such as an extruder, and the components of the mixture may be separately injected into the heat-plastified resin. Alternatively alkenyl aromatic resinous particles may be treated in a pressure vessel and the blowing agent mixture impregnated into the particles at ambient or elevated temperature. Generally, the preparation of alkenyl aromatic resinous polymer foams in accordance with the present invention is conveniently done in a manner generally shown and described in U.S. Patent 2,669,751, wherein the volatile fluid foaming agent is injected into a heat-plastified polymer stream within an extruder. From the extruder the heat-plastified gel is passed into a mixer, the mixer being a rotary mixer wherein a studded rotor is enclosed within a housing which has a studded internal surface which intermeshes with the studs on the rotor. The heat-plastified gel from the extruder is fed into the inlet end of the mixer and discharged from the outlet end, the flow being in a generally axial direction. From the mixer, the gel passes through coolers such as are described in U.S Patent 2,669,751 and from the coolers to a die which extrudes a generally rectangular board. A suitable extrusion system is shown in U.S. 3,966,381. In the preparation of foams in accordance with the present invention, it is often desirable to add a nucleating agent to reduce the primary cell size. Talc, calcium silicate, indigo, and the like are suit¬ able agents which reduce primary cell size. Various other additives may be utilized, such as fire retardant chemicals, stabilizers and the like. In the preparation of foams in accordance with the present invention, the blowing agent may be added to the resin in any convenient manner. Generally the blowing agent mixture is pumped into heat plasti- fied alkenyl aromatic resin and admixed therewith prior to extrusion to form foam. The blowing agents may be admixed and pumped as a combination stream into the heat plastified resin, or they may be supplied as separate streams. Adequate mixing of the blowing agents into the heat plastified resin is required in order to obtain a product of desirable uniformity. Such mixing may be accomplished by a variety of means including rotary mixers such as extruders, so-called static mixers or interfacial surface generators, such as are utilized in U.S. Patents 3,751,377 and 3,817,669. Examples of the invention and Comparative Examples are given below. It should be noted that the Comparative Examples are not prior art. Further, the Examples are illustrative only, and should not be construed as limiting the invention. The following abbreviations are employed in the examples that follow: Chlorid pel pounds per cubic fool KICI l-Lh l e nun in111 imeters FC-12 Dichlo odi 1 luorυmeLhane Vert Vertical or thickness, FC-1421. 1,1, l-Chlυio i I Inoroeth ne compression sLrengLli ll ii z Horizontal or width, °C Cent i rade compression strength lϊxt 1-xtru i.on υr longitudinal Fahreuhei I i reel ion pit I pounds per square inch Kll Relative Humidity III inch ll.s pounds I III square inches ,t 2 Square feet pph parts per hundred hr hour (c) Comparative Example BTU Uri t i h Theruia I Uni I CO, Carbon Dioxide Example 1 A styrene polymer foam was prepared utilizing a 2-1/2 inch diameter extruder which fed a rotary mixer generally of the configuration disclosed in U.S. Patent 2,669,751. The rotary mixer discharge was passed through three heat exchangers of the variety shown in U.S. Patent 3,014,702. The discharge from the heat exchangers was in turn passed through a plurality of interfacial surface generators or static mixers of the type shown in U.S. Patent 3,583,678. The discharge from the static mixers was passed to a slot die. Foam was discharged from the slot die at a rate of 200 pounds per hour. Three experimental foams were prepared; one in accordance with the present invention. The results are set forth in Table I. TABLE I EFFECT OF BLOWING AGENT TYPE ON SKIN QUALITY AND COMPRESSI E STRENGTH Pressure Density Surface Fresh Coinpressive Strength (psi) Blowing Agent (psi) (pc ) Quality Vert Horiz Ext 6.8 pph C0 2 (c) 1800 4.03 5 158.5 97.6 69.8 4.0 pph CO (40%) 6.0 pph EtCl (60%) 1000 2.14 1 44.2 26.5 23.5 11.3 pph EtCl (ci 320 2.29 1 12.6 23.3 14.2 _% The skin quality is a measure of surface smoothness. The sample is visually assigned a value between 1 and 5 according to surface smoothness, one being the smoothest. (c) Comparative Example. The foregoing table shows that the addition of C0 2 to EtCl reduces the density at about equivalent number of moles of blowing agent and increases the compressive strength considerably even at lower foam density. The resultant foam obtained with the mixture of carbon dioxide and ethyl chloride was a large cell foam suitable for decorative processes. Example 2 The general procedure of Example 1 was repeated with the exception that a foam suitable for insulation was obtained. Extrudates were also made for comparative purposes. The results are set forth in Table II. TABLE II EFFECT OF BLOWING AGENT... TYPE ON SURFACE QUALITY" Die Cell Cross- _•-_•._ Pressure Size Density section Surface Fresh 5 yr Blowing Agent (psi) (nun) (pcf) (in ) Quali y k-factor k-factor 6.8 pph C0 2 (c ^ 1800 0.12 4.03 6.33 5 0.212 0.279 5.5 pph CO / . . 5.5 pph FC-12 1 } 1275 0.10 4.24 6.34 4 0.191 0.224 3.9 pph CO / (30%) 4.6 pph FC-l42b/ (35%) 4.6 pph EtCl (35%) 975 0.43 2.15 8.75 1 0.208 0.212 _ Λ.«_ Typical additive levels include 1.5 pph FR-651P (monochloropentabromo cyclohexane), 0.15 pph barium stearate, and 0.03 pph irøgnesium oxide. Typically the foaming temperature varies between 106°C and 125°C. _. * __•_ The sample is visually assigned a value between 1 and 5 according to surface smoothness one being the best and 5 the worst. Fresh k-factor (thermal conductivity) is measured at a mean temperature of 75°F using a direct reading heat flow meter apparatus according to ASTM C518. The 5 year k-factor is a calculated value from a computerized mathematical model. The units on k-factor are BTU-in/hr. °F. ft . (c) Comparative Example. Table II shows that much larger cell size can be obtained by using carbon dioxide and 1,1,1-chlorodi- fluoroethane as mixed blowing agent and that the larger the cell size, the lower the density and the larger the cross-section. The smoothness of the foam skin is important for many insulation applications. When carbon dioxide is used in combination with several other blowing agents, the die pressure is reduced. Adding dichlorodifluoromethane improved the skin quality slightly and addition of ethyl chloride to carbon dioxide and dichlorodifluoromethane as mixed blowing agent improved the skin quality considerably as shown in Table II. Example 3 The general procedure of Example 1 was repeated to form a variety of compositions. The results are set forth in Table III. ' TABLE III EFFECT OF BLOWING AGENT TYPE ON COMPRESSIVE STRENGTH AND DIMENSIONAL STABILITY ** Dimen ional Change Thick- Cell Coinpressive.Strength (psi) Ambient Aging after 7 days of exp ness Blowing Densi y Si2e Time to 167°F (inches) Agent ( pcf) (mm) Vert lloriz Ext _ . J_ . __ . Y_i__ ________ _____■____ ______ 1 5.3 pph EtCl/, 8.0 pph FC-12 ICJ 2.08 0.27 15.2 19.9 52.7 20 4.8 2.9 -0. 1-1/2 5.3 pph EtCl/. . 8.0 pph FC-12 ICJ 2.03 0.25 19.1 18.2 35.9 20 3.2 2.2 1. 5.3 pph EtCl/, . 8.0 p ppphh FFCC--1122 lC ' 2.22 0.22 40.2 26.5 28.0 10 0.7 H1.4 0. 30 -0.2 1.6 2. 2 2.19 0.32 19.1 23.8 34.6 20 4.3 1.0 1. 1.1 1.5 pph CO / 3.5 pph EtCl/ 7.5 ppii FC-12 1.91 0.32 17.3 21.8 30.9 20 0.6 1.9 0. 0.9 1.5 pplt CO / 2.5 pph EtCl/ 7.5 pph FC-12 2.21 0.26 30.7 22.0 39.2 20 0.6 1.8 0. TABLE III (continued) Foaming temperature ranges between 115°C and 126°C; Die pressure ranges between 450 psi and 570 psi; Barium stearate = 0.15-0.2 pph; Magnesium oxide = 0.01-0.04 pph; FR-651P = 1.7-2.0 pph; Talc = 0-0.15 pph; Indigo = 0-0.07 pph. The Federal Specification, HH1-524C, allows less than 2% dimensional change in any direction after exposing foa samples ' for 7 days at 167°F dry or at 158°F/97% RII. (c) Comparative Exampl e . Table III shows that addition of carbon dioxide to ethyl chloride and dichlorodifluoromethane mixed blowing agent improved the dimensional stability at elevated temperatures which was quite an unexpected result because of its fast permeation rate through polystyrene. Example 4 The general procedure of Example 1 was repeated with styrene/acrylic acid copolymers (SAA), polystyrene (PS) and PS/SAA blends. A foam suitable for insulation was obtained. Foam was discharged from the slot die at a rate of about 250 pounds per hour. The PS had a Mw (weight-average molecular weight) of about 200,000 and the SAA was three (3) percent by total weight acrylic acid with a Mw of about 160,000, unless otherwise noted. The results are set forth in Table IV. TAUI. IV £.H__T UF IH-SIN ΪYI'E UN COHI'KKtiS I STKKNIV-II AND UIHI_NSIϋNAI. STABILITY INSULATION HOΛKI)" Tula I !.-!!!_'!!___!!_! __!.;.!*___. { l U I owing Cell _f__!i * ? __y u "_ _:___:"- FC-12 KtCl O AgυuL li s in l ) _ιι_ily Size Aging (Juyti) ______!__.__ i^ __(_i(ljU! _l'S__ £ ___ . _:.2 _ .__°_ _1>L'!_- _L.'!_i _l!E_._ {_ > _>!!_ ϊy_ » _;_ (|i-C) (mm) l'riur tu Teat .»{ ■ ¥_•£_. !!_(■:'!_• !._•_. . __:r£ !!_!£-_■ _•_:_ 7.U A.U 1.3 i2. a SAA 2.23 U.35 21 58. 20. 'J 2b. I -0.50 0.50 U.JO (-7%) (_2%) (11%) U.O 5.5 i.a 15.3 SAA 2.A9 . U.3U 21 7U.7 2*1.3 2a.6 -U.90 U.AU 0.110 (52%) (36%) (12%) a.u 2.5 u.a 11.3 BAA 2.13 U.J5 21 A7.3 25.6 26.6 -0.20 U.3U U.AU (71%) (22%) (7%) 6.0 5.5 u.a 12.3 SA 2.29 U.A2 21 A3. 31.2 .10.3 -0.70 U.AU U.AU (A'J%) (A5%) (6%) fa.lt 5.5 u.a 12.3 1/2 rS/SAA 2.03 O.AI 21 A1.5 22.2 22. -U.5U U.2U U.5U (A.%) (A5%) (6 ) 7.U A.U 1.3 12.3 2/1 * " t'S/SAA 2.1'J 0.39 5A.3 21.7 22. A -0.60 U.AU 0.60 (57%) (32%) (11%) 7.U A.U 1.3 12.3 SAA 2.23 U.AU 21 55.1 23.1 33. B -0.50 0.<JU 0.30 (5/%) (.12%) ( 11%) 7.U A.U 1.3 1 .3 l*S 2.U5 U.39 2) AI.7 22. «J 25.7 -0.10 o./o u./o (57%) (32%) (11%) a.u 5.5 i.a 15.3 2.21 U.37 A3. 21.1 31.2 i.oo i.y 0.60 (52%) C»6%) (12%) a.u 2.5 u.a 11.3 I'S 2.U2 U.A1 21 35. A 30.2 1.2 u . AU i.o o . ao (71%) (22%) (7%) TAIILK IV (coiαinti-il) EFFECT OF RES IN TYI'E ON COHI'UESS I VE STKENϋTH ANII DIMEN IONAL STAIilLITΫ OF INSULATION UOAUII Uluwiiig 'Ceil ϋftϋE . 'Jyyg •.._ i:__l._*- FC-12 EtCl C Ag-nl Res i II Ueutiily Si_e Aging (days) *__!»!_?*___;_! j_*_; _!_.t'_£*ϊ_ϊ_.!_ .il____.i _'L_: *!_.___!__ ' _._._!!•_ _!___._ _l>___> ______ _'y__._ _!!_£_-.- !___._ ?li2E_l_..'_£SLi!-B _!_ • £_. !.'2_!._: _•___.. V_:€_ i!_* * ' ! __ _- l 6.U 5.5 u.a 12.3 PS 2.26 0.39 21 3A.a 27.5 33.0 -O.AO I.A . LU (A9%) (A5%) (6%) a.o 5.5 u.a IA.3 PS l.'JB 0.37 21 35.5 IB.O 2A.6 -0.70 1.7 0.50 6.U 2.5 i.a IU.3 I'S 2.15 0.39 21 A6.A 2B.6 2A.I -0.20 0.10 0.60 (5B%) (_A%) (IB%) a.u 2.5 i.a 12.3 PS 1.95 0.39 21 A0.3 2A.3 31.5 0.03 O.'JO 0.20 (65%) (20%) (15%) 6.0 5.5 i.a 13.3 I'S 2.05 0.3A 21 AI.6 25.0 26.1 -0.7 O.'JO 0.10 (A5%) ( l%) (IA%) Foaming t mp ra I lire between IOU u O ami I33° ; Hie pressure ranges between 650 si uιι<l BOO (>_i; Calcium slearale - 0.05 ppli; Magnesium uxiile = 0.05 ppli; Copper plilli locy n ne i lie = 0.03 ppli; FH-6511' - O.H |i|>lι. "'Weight ratio of I'S/SAA I percent liy tula) weight, acryli aciil with a Mw ul aliuiii 1110,000. uιιi|i rul ive Example. Table IV shows foam having dimensional stabil¬ ity at an elevated temperature and elevated humidity when utilizing a mixed blowing agent of carbon dioxide, ethyl chloride and dichlorodifluoromethane. Example 5 The general procedure of Example 1 was again repeated with a PS having a Mw of about 200,000. Foam was discharged from the slot die at a rate of about 250 pounds per hour. The results are set forth in Table V. TAUI.E V EFFECT OF III.UWIN- AUENT COHI' SITIUN ON Clt I Sl'NESS OF OECOUATIVE UI I.I.ETS" Total Cell FC-12 ElCI CO., Ulowing Agent I'ulymer Density Size Aging (days) _-___L'__:5_:___: t__ i " _*_t._I. tl'jil _:__5L_____' !_':__ (.•_'.••_ -L'L'hl (u|i|;) _(_!!__ _.._,{l!_!!!_ ..... T i": _.(_!___i_ (mm) __-_i ___£__ ■ Ex Ton Center _'. _l 1iiia 0 9.0 1.0 10.0 CS 1.97 2.36 12.5 IA.3 21.1 10.0 9.3 10.1 (90%) (10%) 0 9.0 1.5 10.5 I'S 1.82 I.AA 20. IA.I 13.5 10.1 9.8 10.0 (at%) (IA%) 0 a.o 1.0 9.0 I'S 2.15 1.B6 17. ιa.2 17.9 10.6 10.A 11.(1 ( an) (11%) 1.0 a.o 1.0 10.0 I'S i.ai i.ao 17. ιa.3 17.8 to.a 10.6 to.a (10%) (ao%) (l«%) Fuamiug lcmperatiir- between I08"C and H7°Cj Uie pressure ranges between 270 psi and A50 psi; Calcium stearate = 0.05 ppli; Magnesium oxide = 0.05 ppli; FK-ύSIP ranges between 0.6A ppli and 1.37 ppli. Crispuess Test - The laboratory crispuess test involves a free steel ring and an IusIron , tensile testing machine. The small ring is forced into a sample of decorative billet at a rale of 5 iu/iuiu for a total of 0.3 in. The force-peuelration is recorded on a strip chart run at 20-30 in/min. The force is read from the chart al a penetration of 0.1 in. The steel ring has an 0.75" outside diameter and an 0.670" inside diameter. The axial length is not critical but should he at least 0.5". The acceptable machinab 1ity is obtained if the crispuess is between 8.0-11.0. > («> c oiiipar l ive Example . Table V shows that the use of a C0 2 /EtCl mixture results in a low density, large cell foam suit¬ able for decorative purposes. Example 6 The general procedure of Example 1 was repeated to obtain a foam suitable for insulation. The results are set forth in Table VI. Table VI shows that a small cell, low density insulating foam having good dimensional stability can be obtained when utilizing a mixed blowing agent of carbon dioxide, ethyl chloride and dichlorodifluoro¬ methane in selected amounts. TABLE VI EFFECT O' BLOWING AGENT ON DIMENSIONAL STABILITY * Dimensional Change (%) Total Cell FC- 12 EtCl CO Blowing Agent Density Size Aging Prior at 158°F/ Ambi ent [.11 " " (pph) (pph) (ppfi) (____h) (pcf) (nun) to Testing (Days) Vert Iloriz Ext 8.9 2.4 0.7 12.0 2.29 0.29 1 0.2 0.3 0.7 (74%) (20%) (6%) 10.4 1 .2 0.4 12.0 2.64 0.25 -0.2 -0.3 0.5 (87%) ( 10%) (3%) 1 1 . 3 1 .3 0.4 13.0 2.56 0.22 0.00 -0.1 0.7 (87%) ( 10%) (3%) 13.0 1 .5 0.5 15.0 2.43 0.15 -0.9 0.2 0.3 (87%) ( 10%) (3%) Foaming Temperature ranges from about 115°C to about 128°C; Die pressure ranges from about 600 psi to about 900 psi; Barium stearate = 0.15 pph; Copper phthalocyanine blue = 0.03 pph; Tetrasodiunipyrophosphate = 0.06 pph; llexabromocyclododecane = 1.6 pph. " " TEST CONDITfONS: 48 hours followed by 24 hours at ambient conditions before remeasuring dimensions. (c) Compa ati e Example.

Claims: WHAT WE CLAIM IS; 1. A process for the preparation of an extruded alkenyl aromatic thermoplastic resinous elongated foam body, the body defining a plurality of closed noninterconnecting gas-containing primary cells therein, the steps of the method including (1) heat-plastifying an alkenyl aromatic synthetic resinous material; (2) adding to the heat-plastified synthetic resinous material a volatile fluid foaming agent to provide a foaming agent resinous polymer mixture under a pressure suf¬ ficiently high that foaming is prevented; (3) mixing the fluid foaming agent with the plastified resin to form a blowable resinous mixture; (4) reducing the temperature of the mixture to a temperature such that when pressure is removed therefrom, a foam of desirable quality is obtained; (5) reducing the pressure on the mixture to thereby cause the mixture to form a foam of desired quality: characterized by employing a blowing agent mixture of from 3-45 weight percent of carbon dioxide, from 5-97 weight percent ethyl chloride and from 0-90 weight percent of a fluorocarbon member selected from the group consisting of dichlorodi¬ fluoromethane, l-chloro-l,l-difluoroethane and mixtures thereof, the blowing agent mixture being utilized at a level of 3-18 parts per 100 parts of resinous material. 2. The process of Claim 1 employing in the blowing agent mixture from 3-25 weight percent of carbon dioxide. 3. The process of Claim 1 wherein the blowing agent mixture includes from 5-60 weight percent of ethyl chloride. 4. The process of Claim 1 employing in the blowing agent mixture from 30-90 weight percent of the fluorocarbon member. 5. The process of Claim 1 employing in the blowing agent mixture from 0-30 weight percent of fluoro¬ carbon member. 6. The process of Claim 1 wherein the blowing agent mixture includes 3-25 weight percent carbon dioxide, 20-60 weight percent ethyl chloride and 30-90 weight per¬ cent of fluorocarbon member. 7. The process of Claim 1 employing as a blowing agent mixture 3-45 weight percent carbon dioxide, 60-90 weight percent ethyl chloride and from 0-25 weight percent fluorocarbon member. 8. A foam prepared in accordance with any one of Claims 1-7 and having a crispness in the range from 8.0-11.0. 9. A foam prepared in accordance with any one of Claims 1-7 and having a density in the range from 1 to 5 pcf and a smoothness less than 4. 10. A foam prepared in accordance with any one of Claims 1-7 and having less than 2 percent dimensional change in any direction after exposure for 7 days at 158°F and 97 percent relative humidity.

Inventors: KENNEDY JOHN M, SUH KYUNG W, KENNEDY, JOHN, M., SUH, KYUNG, W.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C08J9
IPC codes: B29C47, B29K25, B29K105, C08J9