CA2201472A1 - Non-linear styrenic polymer-based foams - Google Patents

Abstract

Disclosed is a process for preparing a low density closed-cell polymer foam comprising a plurality of closed-cells having an average cell size of at least about 0.08 millimeter characterized in that the process comprises the steps of heat plastifying an expandable or foamable monovinyl aromatic polymer formulation comprising a non-linear monovinyl aromatic polymer composition and an environmentally acceptable blowing agent; and reducing the pressure on the mixture to form a foam. A stable monovinyl aromatic polymer foam prepared from a non-linear styrenic polymer composition and environmentally acceptable blowing agents is also disclosed.

Description

~ 2 ~ ~ ~ 7 ~
WO 96/11970 PCTJ~JS95/13362 NON-LINEAR STYRENIC POLYMER-BASED FOAMS
The present invention relates to monovinyl aromatic polymer foams. More particularly, this invention relates to non-linear monovinyl aromatic polymer-based foams.
Monovinyl aromatic-based resins, such as, for example, styrene-based resins, are5 well-known and widely employed in transformation processes into molded and/or extruded articles. In these processes, styrene-based resins having lower meltflow rate (such as from 0.5 9/10 minutes to 5 9/10 minutes) are usually preferred. The physical properties of such monovinyl aromatic polymers, also known as styrenic polymers, generally improve as the molecular weight increases. The processability of such monovinyl aromatic polymers, however, 10 generally decreases as the molecular weight increases. Accordingly, the choice of a monovinyl aromatic polymer having sufficient properties usually involves a compromise between physical property requirements and processing requirements.
One approach to improve the processability of monovinyl aromatic polymers has been the addition of processing aids, such as plasticizers. It is known that the addition of 15 plasticizers to polymer resins reduces the viscosity and increases the processability while decreasing the physical strength thereof. A problem frequently encountered with the use of such plasticizers is that they also reduce certain properties of such polymers.
Another approach has been the use of specific copolymerizable monomers in the polymerization process. Suitable copolymerizable monomers include polyfunctional monomers 20 such di-, tri- or tetraf un*ional monomers, such as, for example divinyl benzene, di(meth)acrylates, tri(meth)acrylates, and allylic compounds copolymerizable with the monovinyl aromatic monomer(s).
It also is common pra*ice to improve the physical properties of styrenic polymers by modifying the styrenic polymer matrix with toughening agents such as rubbers. However, the addition of toughening agents is known to affect the processability of styrenic polymers adversely.
Japanese PatentApplication 61-87713 describes a process of producing randomly branched styrenic polymers having molecular weights above 540,000 and improved physical properties, such as mechanical strength, as well as good processability. The styrenic polymers 30 described contain a substantial level of residual toluene (approximately 6 percent). It is believed that this styrenic polymer has a high melt flow rate due to the presence of volatile components. Likewise, adverse effe*s on the Vicat heat distortion temperature and melt strength properties of this polymer would be expected. The process comprises the use of one or more organic peroxides, such as alkylperoxy-alkylfumarates.
Styrenic polymers are known to be useful in a large variety of applications. Forexample, thermoplastic foams such as styrene polymer foams which are widely used in the fields of constru*ion, civil engineering and thermal insulation. The styrene polymer foam suitable for such applications desirably has relatively small cells and dimensional stability.

Wo 96/11970 ~, 2 ~ ~ ~ 7 ~ PCT/US95/13362 These foams are the so-called extruded foams. 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 used as a base for further decorative material.
Extruded foams and their manufacture are discussed in U.S. Patent Nos.

2,409,910; 2,515,250; 2,669,751; 2,848,428; 2,928,130; 3,121,130; 3,121,911; 3,770,688;

3,815,674; 3,960,792; 3,966,381; 4,085,073; 4,146,563; 4,229,396; 4,312,910; 4,421,866;

4,438,224; 4,454,086 and 4,486,550. For a considerable period of time, styrene polymer foams have been extruded employing a variety of organic blowing agents, such as chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's), and otherfully halogenated 10 hyd rocarbons as wel I as mixtu res thereof. An alternative blowing ag ent system uti I izing carbon dioxide and an alkane is set forth in U.S. Patent Nos. 4,344,710 and 4,424,287.
Due to increased environmental concerns about ozone depletion, greenhouse effects and air quality in general, large efforts are being made to replace CFC's and other fully halogenated hydrocarbons currently used as blowing agents in the foam industry with 15 environmentally more acceptable blowing agents.
Further, it would be highly desirable to provide a process for preparing a low density aromatic polymer foam from a non-linear monovinyl aromatic polymer using an environmentally more acceptable blowing agent.
In one aspect, the present invention is a process for preparing a low density 20 closed-cell polymer foam comprising a plurality of closed cells having an average cell size of at least about 0.08 millimeter (mm), the process comprising the steps of heat plastifying an expandable or foamable non-linear monovinyl aromatic polymer composition useful in this invention and an environmentally acceptable blowing agent; and reducing the pressure on the mixture to form a foam. Advantageously, the foam of the invention can be produced using 25 only C2 as a blowing agent.
Yet in another aspect, the present invention is a stable monovinyl aromatic polymer foam having a plurality of closed cells having an average cell size of at least about 0.08 mm and containing an environmentally acceptable blowing agent prepared by extruding the non-linear monovinyl aromatic polymer composition of the present invention using30 environmentally acceptable blowing agents.
For purposes of the present invention, environmentally more acceptable blowing agents is meant to include inorganic blowing agents, such as C2~ alone or in combination with other blowing agents, such as lower alcohols, ethers, HCFC's or HFC's.
Particularly surprising advantages of using the non-linear styrenic polymer 35 composition useful in the present invention in a process to prepare foam include: reduced pressure drop across the extrusion line; lower foam density by increasing the blowing agent efficiency; and maintenance of good mechanical and heat resistance properties of the foam. In addition, such compositions are especially advantageous in that they permit the preparation of Wo 96/11970 ~ , 7 ~ PCTIUS95/13362 such articles using blowing agent mixture(s) that are less stable and have a shorter half-life than those chlorofluorocarbons previously used without excessive shrinkage during the manufacture thereof and/or during the storage thereof in fresh foam. That is, the resulting foamed articles have (in fresh foam form) relatively good dimensional stability at ambient temperatures (for example, 21C (70F)); typically shrinking to no less than about 80 (preferably no less than about 90) percent of their initial foamed volume under such manufacturing and/or storage condition.
The non-linear polymers of the present invention have a molecular weight of from 75,000 to 500,000 and are derived from at least 50 weight percent of a monovinyl 10 aromatic monomer, optionally with one or more additional comonomers. They comprise a polymer matrix of at least one monovinyl aromatic monomer and, optionally, one or more additional comonomers. The term "non-linear polymer" as used herein means a polymer containing monomer units having at least 1 and up to 4 branching points. The weight average molecular weight of branches emanating from the said branching points will generally be at 15 least 1,000, preferably 5,000 or higher. The structure of such non-linear polymers can be a comb-type form wherein the said monomer units have 3 branching points, a star-type form wherein the said monomer units have from 2 to 4 branching points, or a dendritic structure wherein the branches themselves have branched units attached to them as long as there are no more than 4 branches per monomeric unit.
The higher temperature of polymerization, at least after the initial polymerization phase, of the polymers of the present invention, as compared with those of the Japanese reference referred to above results in branching chain length somewhat lower than in the said reference (i.e., lower than 300,000) which is believed to result in the improved melt strength of the polymers of the invention.
Representative monovinyl aromatic monomers include styrene; alkyl-substituted styrenes such as c~-alkylstyrenes (for example, -methylstyrene and a-ethylstyrene); ring--substituted styrenes (for example,2,4-dimethyl-styrene; o-ethylstyrene, t-butylstyrene, vinyltoluene and particularly p-vinyltoluene; ring-substituted halostyrenes such as chlorostyrene and 2,4-dichlorostyrene; styrene substituted with both a halo and alkyl group, 30 such as 2-chloro-4-methylstyrene; vinyl anthracene, and mixtures thereof. In general, the polymer matrix is preferably derived from styrene or a combination of styrene and ~-methylstyrene. Styrene is the most preferred monovinyl aromatic monomer.
In general, the non-linear monovinyl aromatic polymer will advantageously comprise from 50 to 100, preferably from 65 to 100, more preferably from 75 to 100, weight 35 percent of the monovinyl aromatic monomer(s), based on the total weight of the monomers.
Other comonomers can optionally be employed in combination with the monovinyl aromatic monomer(s). Representative of such other comonomers are the polyvinyl aromatic monomers; the conjugated dienes such as butadiene and isoprene; the ct,l3-o WO 96/11970 = PCT/US95/13362 ethylenically unsaturated carboxylic acids and Cl-C8 esters, preferably Cl-C4 esters, thereof such as acrylic acid, methacrylic acid, methylacrylate, methyl methacrylate, ethylacrylate, ethylmethacrylate, n-butylacrylate, n-butylmethacrylate and 2-ethylhexylacrylate; the ethylenically unsaturated amides such as acrylamide and methacrylamide; vinylidene chloride 5 and vinylidene bromide; vinyl esters such as vinyl acetate; and maleimides such as N-phenyl maleimide. If employed, these comonomers will generally be employed in amounts less than 40, more generally less than 35, weight percent based on the total weight of the monomers employed in preparing the non-linear monovinyl aromatic polymer.
The non-linear character of the polymers of the present invention is introduced 10 by the use of one or more specific initiators in the polymerization process. Suitable initiators include copolymerizable organic peroxide initiators. Represenldli~e copolymerizable organic peroxide initiators useful in the present invention include acrylic acid derivatives containing a peroxide unit, such as a percarbonate, perester, perketal, or a hydroperoxide. The copolymerizable functionality could be derived from any vinylic species that is capable of 15 copolymerization with the monovinyl aromatic monomer employed.
Representative copolymerizable organic peroxide initiators include alkylperoxy-alkylfumarates, such as, for example, t-butylperoxy-methylfumarate, t-butylperoxy-ethylfumarate, t-butylperoxy-n-propylfumarate, t-butylperoxy-isopropylfumarate, t-butylperoxy-n-butylfumarate, t-butylperoxy-t-butylfumarate, t-butylperoxy-sec-20 butylfumarate, t-butylperoxy-n-hexylfumarate, t-butylperoxy-n-octylfumarate, t-butylperoxy--2-ethylhexylfumarate, t-butylperoxy-phenylfumarate, t-butylperoxy-m-toluylfumarate, t-butylperoxy-cyclohexylfumarate, t-amylperoxy-n-propylfumarate, t-amylperoxy-isopropyl-fumarate, t-amylperoxy-n-butylfumarate, t-amylperoxy-t-butylfumarate, t-amylperoxy-n--octylfumarate, t-amylperoxy-2-ethylhexylfumarate, t-hexylperoxy-ethylfumarate, t-hexyl-25 peroxy-n-propylfumarate, t-hexylperoxy-isopropylfumarate, t-hexylperoxy-n-butylfumarate, t-hexylperoxy-t-butylfumarate, t-hexylperoxy-cyclohexylfumarate, t-hexylperoxy-2--ethylhexylfumarate, t-hexylperoxy-phenylfumarate, cumylperoxy-ethylfumarate, cumylperoxy-isopropylfumarate, cumylperoxy-n-butylfumarate, cumylperoxy-t-butylfumarate, cumylperoxy-2-ethylhexylfumarate, cumylperoxy-m-toluylfumarate, and cumylperoxy-30 cyclohexylfumarate. Preferredinitiatorsaret-butylperoxy-isopropylfumarate,t-butylperoxy-n--butylfumarate, t-butylperoxy-sec-butylfumarate, t-butylperoxy-t-butylfumarate, t-butylperoxy-ethylfumarate, t-butylperoxy-n-hexylfumarate, t-butylperoxy-phenylfumarate, with t-butylperoxy-n-butylfumarate and t-butylperoxy-t-butylfumarate being especially preferred.
The copolymerizable organic peroxide initiators are typically employed in amounts of from 0.001 to 2.0, preferably from 0.001 to 0.5, most preferably from 0.002 to 0.3, weight percent, based on the total weight of the monomers.

WO 96/11970 ~ 7 2 PCTIUS95/13362 The monovinyl aromatic polymer compositions of the present invention can be prepared by any of the several polymerization methods known to those skilled in the art including, for example anionic, cationic or free radical, which is preferred, polymerization. The monovinyl aromatic polymers can be prepared by well-known methods including, for example, mass, emulsion, suspension and mass suspension methods. In general, continuous methods are r employed for polymerizing the monovinyl aromatic monomer(s). Mass polymerization is the most preferred polymerization process for use in the present invention. Typically, mass polymerization re5ults in a mixture of non-linear and linear polymers.
In this invention, the proportion of linear to non-linear polymers is not 10 particularly critical as long as the melt strength specifications of the polymer are met. The proportion of linear to non-linear polymers depends on the type, amount and number of additions of initiatorto the polymerization mixture as well as on the number and molecular weight of the branches of the non-linear polymer. If the non-linear polymer has a high number of high molecular weight branches (e.g. Mw of up to 50,000), then relatively lower amounts of 15 the non-linear polymer are required to achieve the desired melt strength specification. If, on the other hand, the molecular weight of both the non-linear polymer and its branches are relatively low (e.g., both Mw of less than 50,000), a higher proportion of the non-linear polymer will be required. In the case where the molecular weight of both the non-linear polymer and its branches are relatively high, as low as 5 percent by weight will be sufficient to 20 achieve the desired mélt strength.
The non-linear monovinyl aromatic polymer compositions useful in the present invention advantageously have a weight average molecular weight (Mw) between 75,000 and 500,000, preferably between 100,000 and 400,000, more preferably between 120,000 and 380,000. The molecular weight distribution (Mw/Mn (number average molecular weight)) of 25 the non-linear monovinyl aromatic polymer composition useful in the present invention is advantageously of from 1.1 to 5, pl eferdbly 1.5 to 4, and most preferably 1.8 to 4. The compositions useful in the present invention advantageously exhibit improved melt strength properties while essentially maintaining other important physical properties such as rigidity and toughness, and, in the case of clear matrix polymers, transparency and processability.
30 Typically, the non-linear monovinyl aromatic polymer composition useful in the present invention exhibits melt strength properties in the range between 0.5 9 at 1 90C to 10.0 9 at 230C, preferably from 1.5 g at 1 90C to 8.0 g at 230C, and most preferably from 1.6 g at 1 90C
to 6.0 g at 230C.
The non-linear monovinyl aromatic polymer compositions useful in the present 35 invention advantageously have a Vicat heat distortion temperature of at least 60C, preferably between 70C and 1 1 0C. It has been found that the non-linear monovinyl aromatic polymer compositions useful in the present invention, at a given melt and Vicat heat distortion temperature exhibits a melt strength of at least 20, preferably at least 30, more preferably at ~ 2 ~ ~ ~ 7 ~ - O

least 50 percent higher than linear monovinyl aromatic polymer compositions of same melt flow rate at a given Vicat heat distortion temperature.
In a pref~rred embodiment, the preparation of non-linear styrenic thermoplastic polymer resin compositions in accordance with the present invention is preferably carried out 5 by feeding monovinyl aromatic monomer, advantageously in the presence of suitable amounts of an organic liquid reaction diluent, such as, for example, ethyl benzene, and in the presence of other optional additives, such as mineral oils, chain transfer agents and rubber, into a first, out of three, stirred tube-type reactor having 3 reaction zones. The 3 reactors are assembled in a series and each have 3 reaction zones with independent temperature control. The 10 polymerization mixture is then initially heated up to at least 90C for at least one hour to initiate the polymerization and then to at least 140C for at least four hours. The copolymerizable organic peroxide initiator is then added to the polymerization mixture at any desired stage of the polymerization process. Typically, the initiator is added in the first reaction zone of any reactor, preferably of the first reactor. Typically, the polymerization is started at 15 100C and within the first reaction zone of the reactor, then the temperature is increased in order to maintain an approximately constant polymerization rate. Usually, the temperature in the third reaction zone of the third reactor reaches 180C.
The polymerization mixture leaving the reactor is passed through a heater at a temperature in excess of 200C and then subjected to vacuum. At this point, unreacted 20 monomers and diluents are evaporated and condensed in a condenser to be recycled to the feed in the first reaction zone. The polymer melt is then extruded and granulated.
The number, length, as well as molecular weight of the branches of non-linear polymers are readily determined by well-known kinetics calculations, based on the monomer composition, initiator reactivity, and/or process conditions. Such calculations are well known, 25 for example from Principles of Poly.,.eri~dlion, 2nd edition, John Wiley and sons, New York, 1981 .
The aforementioned polymer compositions are particularly well suited for the preparation of closed-cell monovinyl aromatic polymer foamed articles of relatively low density. For purposes of the present invention, the term " low density" is meant to include foam densities of from 16 kg/m3 (1 pound per cubic foot (pcf)) to 80 kg/m3 (5 pcf). Especially preferred foam densities are from 24 kg/m3 (1.5 pcf) to 64 kg/m3 (4 pcf) having relatively small or fine cell size and having relatively large cross-sectional area(s) (for example, cross-sectional areas of at least abou~ 50 cmZ (8 square inches, (in2)) and a minimum cross-sectional dimension of at least 0.6 cm (0.25 inches), preferably of 1.25 cm (0.5 inches).
As has been noted, a preferred feature of the present invention is the use as the blowing agent herein of a blowing system which consists essentially of a carbon dioxide blowing agent. Optionally, the blowing agent can be an admixture of carbon dioxide with other blowing agents, such as lower alcohols, that is, C1-C6 alcohols, preferably a C1-C4 alcohol.

~ 7 ~

, Representative lower alcohols include, for example, methanol, ethanol, isopropanol, propanol, butanol, pentanol, hexanol, and isomers thereof, with ethanol being especially preferred.
Optionally, the blowing agent system may be comprised of a carbon dioxide blowing agent in - an admixture with ethers, such as dimethylether, diethylether, methylethylether, methyl 5 acetate, ethyl acetate, with dimethylether being especially preferred. Optionally, the blowing agent system may be comprised of a carbon dioxide blowing agent in an admixture with HCFC's or hydrofluorocarbons (HFC's), such as, for example 1-chloro-1,1-difluoroethane (HCFC-142b), difluoroethane (HFC-152a) or 1,1,1,2-tetrafluoroethane (HFC-134a).
In one embodiment of the present invention, the blowing agent system may be 10 comprised of a carbon dioxide blowing agent in an admixture with C1-C6 hydrocarbons, such as, methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane and hexane, with n-butane, isobutane, n-pentane and isopentane being especially preferred. Yet in another embodiment of the present invention, the blowing agent system may be comprised of a carbon dioxide blowing agent in an admixture with ethanol and isopentane. It is 15 surprising that these particular blowing agent systems work as well as they do in the manufacture of low density monovinyl aromatic polymer foams.
In the pr eparation of styrenic thermoplastic polymer foams in accordance with the present invention, it is most conveniently done in a manner generally as shown and described in U.S. Patent No. 2,669,751, wherein the blowing agent is injected into a heat-20 -plastified polymer stream within an extruder. From the extruder the heat-plastified gel i5 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. ~rom the mixer, the gel 25 passes through coolers such as are described in U.S. Patent No. 2,669,751 and from the coolers to a die which extrudes a generally rectangular board. A generally similar extrusion system and a preferred extrusion system is shown in U.S. Patent No. 3,966,381.
Generally, the blowing agent mixture is pumped into the heat-plastified alkenyl aromatic resin and admixed therewith prior to expansion to form foam. The blowing agent 30 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. Patent Nos. 3,751,377 35 and 3,817,669.
In the preparation of foams in accordance with the present invention, it is often desirable to add a nucleating agent to reduce the cell size. Talc, magnesium oxide, calcium-silicate and calcium stearate, are suitable nucleating agents which reduce cell size. Various WO 96/11970 ~ PCT/US9S/13362 other additives may be utilized such as, for example, plasticizers or lubricants such as mineral oil, butyl stearate or dioctyl phthalate; fire retardant chemicals; stabilizers, including antioxidants (for example, alkylated phenols such as di-tert-butyl-p-cresol or phosphites such as trisnonyl phenyl phosphite); mold release agents, for example, zinc stearate; pigments and 5 extrusion aids all of which are commonly used in foam preparation.
The foams prepared in the present invention can be used in numerous applications. Particularly, the foams of the present invention are suitable for use in the fields of construction, civil engineering and thermal insulation in general, as well as flotation (buoyancy) billets and for decorative purposes including floral/craft billets.
The following examples are given to illustrate the invention and should not be interpreted as limiting it in any way. Unless stated otherwise, all parts and percentages are given by weight.
The following test methods were employed to determine the physical properties of both the monovinyl aromatic polymer resin and the foam prepared thererlvl".
15 Melt Flow Rate The melt flow rate (MFR) is measured using a Zwick MFR Measurement Apparatus, Model 4105, according to the test procedure ASTM D-1238-86 at 200C and 5 kilograms (kg) load.
Melt Strenqth Melt strength measurements are made using an extrusion plastometer as described in ASTM D-1 Z38 at the temperatures given in the examples. A heated cylinder is filled with the polymer sample at a constant temperature with one end of the cylinder restricted with a small die (8 mm long) with an orifice having a diameter of 2.1 mm.
A constant load of 5 kg or a constant speed of the traverse (preferably of 10 25 mm/minutes) is applied to force the polymer through the orifice of the die after a predetermined heating time has elapsed. The extrudate passes vertically downward under a first pulley, then passes vertically upward over a second pulley and then passes horizontally to a wind-up drum. In the present invention, unless otherwise indicated, this wind-up drum is rotated at 100 revolutions per minute (rpm). Each pulley is of black anodized aluminum alloy, 30 has a nominal diameter of 31.75 mm (1.25 inches) measured at the center of a 120 V-groove, and is 2.9 mm (0.114 inches) thick. Both pulleys have a precision instrument bearing and are statically balanced.
The strain on the first pulley is measured via a strain cell having a capacity of 60 grams or less. Typically, the most sensitive range of 0-10 grams is used for accuracy purposes.
35 The strain cell is calibrated using analytical weights. The first pulley is mounted on a force lever which is adj ustable to permit increasing the force applied to the strain cell by factors of up to 8 times the applied force. The wind-up drum is aluminum and has a diameter of 50.8 mm (2.0 inches) and is about 76.2 mm (3 inches) wide. The drum is equipped with a means for adjusting WO96/11970 ~ ~ 0 ~1 4 7 ~ PCT/US95/13362 the speed over a range of from 0 to 2,000 rpm. The force at a given rate of rotation is a measure of the melt strength of the material.
Molecular Weiqht The weight average molecular weight (Mw) and number average molecular 5 weight (Mn) for the polymers are determined by the gel permeation chromatographic techniques described by ASTM test method D-3536 (polystyrene standard) and e,~ ,sed without correction for the differences between polymers and polystyrene standards.
Densitv The density of the foams is measured according to test method ASTM D-1622.
10 Cell Size The cell size of the foams is measured according to test method ASTM D-3576.
Compressive Strenqth The compressive strength of the foams is measured according to test method ASTM D-1621.
15 Thermal Dimensional Stability The dimensional stability of the foams is measured according to test method DIN-18164, tests WD and W, and according to test method ASTM C-578.
Examples 1-2 Closed-cell styrene homopolymer foams were prepared from non-linear 20 polystyrene (Resin 1) according to the process of the present invention, utilizing a 2 inch (5.08 cm) diameter extruder which feeds a rotary mixer. The rotary mixer discharge was passed through heat exchangers. The discharge from the heat exchangers was, in turn, passed through a plurality of interfacial surface generators or static mixers. The discharge from the static mixers was passed to a slot die. Foam was discharged from the slot die at a rate of about 25 60 kg/h (130 pounds per hour). The monomeric compositions and respective properties of Resin I are setforth in Table 1. The resin type and the respective blowing agent(s) proportions as well as the properties of each foam sample are set forth in Table ll.
Comparative Examples A-B
Foam samples (Comparative Example A-B) were prepared following the 30 procedure of Example 1, except that linear polystyrene (Resin ll) was employed instead of non-linear polystyrene. The monomeric compositions and respective properties of Resin ll are set forth in Table 1. The resin type and the respective blowing agent(s) proportions as well as the properties of each foam sample are set forth in Table ll.
Examples 3-4 Closed-cell styrene homopolymer foams were prepared with varying amounts and types of blowing agent(s) in accordance with the present invention using the same procedure and type of equipment as described in Example 1, except for using Resin lll as the non-linear polystyrene and for using an 8 inch (20.3 cm) diameter extruder. The monomeric g .

WO96/11970 ~a 2 0 ~ ~ 7 ~ PCT/US95113362 compositions and respective properties of Resin lll are set forth in Table 1. The resin type and the respective blowing agent(s) proportions as well as the properties of each foam sample are set forth in Table ll.
Comparative Examples C-D
Foam samples (Comparative Example C-D) were prepared following the procedure of Example 3, except that linear polystyrene (Resin IV) was employed instead of non-linear polystyrene. The monomeric compositions and respective properties of Resin IV are set forth in Table 1. The resin type and the respective blowing agent(s) proportions as well as the properties of each foam sample are set forth in Table ll.
As readily apparent from Table ll, the non-linear polystyrene (Examples 1, 2, 3 and 4) is easily processed in the foaming process, particularly at a much lower pressure. Specifically, although Resins lll (Examples 3 and 4) and IV (Comparative Example C and D) have similar melt flow rates, Resin lll is processable at a much lower pressure. The closed-cell foams of Examples 1-4 exhibit lower foam density than the foams of Comparative Examples A-D. Also, the foams 15 f the present invention exhibit improved mechanical properties as well as the thermal dimensional stability over the foams made from linear polystyrene.
Examples 5-8 Closed-cell polystyrene copolymer foams were prepared with varying amounts and types of blowing agent(s) in accordance with the present invention using the same 20 procedure and type of equipment as described in Example 1 and 3. Resin V was employed for Examples 5 and 6 and Resin Vl was employed for Examples 7 and 8. The monomeric compositions and respective properties of each resin are set forth in Table 1. The resin type and the respective blowing agent(s) proportions as well as the properties of each foam sample are set forth in Table lll.
25 Comparative Examples E-F
Foam samples (Comparative Example E-F) were prepared following the procedure of Example 5, except that linear polystyrene (Resin Vll) was employed instead of non-linear polystyrene. The monomeric compositions and respective properties of Resin Vll are set forth in Table 1. The resin type and the respective blowing agent(s) proportions as well as the 30 properties of each foam sample are set forth in Table lll.
As readily apparent from Table lll, the non-linear polystyrene copolymer resins (Examples 5-8) were processed with a slightly lower pressure than the linear polystyrene copolymer resins (Comparative Examples E and F). Further, the foams of the present invention exhibited low density, larger cell size, improved mechanical properties and dimensional 35 stabil;ty Examples 9-13 Closed-cell styrene copolymer foams were prepared in accordance with the present invention using the same procedure and type of equipment as described in Example 1, WO 96/11970 ~ 4 7 ~ PCTIUS95/13362 except for using Resin Vlll as the non-linear polystyrene and for using an 1-1/2 inch (3.1 cm) screw-type extruder with a slit die. The blowing agents were composed of carbon dioxide and a low ozone depieting gas, such as HCFC 142b or HFC 1 52a. The monomeric compositions and respective properties of Resin are set forth in Table 1. The resin type and the respective blowing 5 agent(s) proportions are setforth in Table IV.
Comparative Examples G-K
Foam samples (Comparative Examples G-K) were prepared following the procedure of Example 9, except that linear polystyrene (Resin IX) was employed instead of non-linear polystyrene. The monomeric compositions and respective properties of Resin IX are set 10 forth in Table 1. The resin type and the respective blowing agent(s) proportions as well as the properties of each foam sample are set forth in Table IV.
As readily apparent from the data shown in Table IV, with the use of non-linear polystyrene resins, according to the present invention, the foaming temperature can be increased as a result of the higher melt strengths characteristics of these non-linear polymers.
15 Consequently, the blowing agent efficiency is improved significantly allowing for production of low density foams.

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Ex. or Comp. Ex. 1 Ex. A* 2 Ex. B*

Resin Type I II* I II*
HBCD (a), pph 2.5 0 2.5 0 Additives (c)~ pph 0.5 0.5 0.5 0.5 CO2, pph (b) 5.0 4.4 4.0 4.0 Ethanol, pph 0 0 2.0 2.0 Pentane, pph 0 0 0 0 Foaming Temp., C 128 128 130 128 Pressure Drop, bar 96 189 36 130 Board Thickness, mm 25 25 25 25 Density, Kg/m3 44.3 48.7 35.6 41.8 Cell Size vertical, mm 0.32 0.43 0.41 0.24 Vertical Compressive 377 455 394 Strength, kPa Extrusion Compressive 225 369 140 --Strength, KPa Horizontal Compressive 215 318 188 --Strength kPa Dimensional Stability DIN 18164 - WD, % 1.1 1.0 1.6 --DIN 18164 - W Thickness, X 0.0 0.0 0.3 --DIN 18164 - W Length, % 0.0 -0.2 0.8 --DIN 18164 - W Width, %-0.1 -0.4 -0.2 --ASTM C-578 - thickness, % 0.1 -0.2 1.0 --ASTM C-578 - length~ % 0.1 -0.1 1.5 --ASTM C-578 - width, % -0.2 -0.1 -0.2 --22Q ~ ~ ? 2 Table II (Cont.) Ex.Comp. Ex. Comp.
Ex. or Comp. Ex. 3 Ex. C* 4 Ex. D*

Resin Type III IV* III IV*
HBCD (a), pph 2.5 2.5 2.5 2.5 Additives (c), pph 0.5 0.5 0.5 0.5 C02~ pph (b) 4.0 4.0 4.0 4.0 Ethanol, pph 1.5 1.5 0 0 Pentane, pph 0 0 1.6 2.0 Foaming Temp., C 128 117 117 109 Pressure Drop, bar 67 76 62 72 Board Thickness, mm 50 50 70 90 Density, Kg/m3 36.2 38.8 34.8 39.4 Cell Size vertical, mm 0.35 0.41 0.29 0.31 Vertical Compressive 338 347 348 621 Strength, kPa Extrusion Compressive 253 279 192 169 Strength, kPa ~orizontal Compressive 161 199 152 152 Strength kPa Dimensional Stability DIN 18164 - WD, % 2.0 2.6 2.1 2.5 DIN 18164 - W Thickness, % 0.0 -0.1 0.3 0.1 DIN 18164 - W Length, % -1.1 -1.3 -1.6 -3.4 DIN 18164 - W Width, %-1.5 -1.4 -1.3 -0.9 ASTM C-578 - thickness, % 0.1 -0.1 0.4 -0.1 ASTM C-578 - length, % -0.9 -1.1 -0.7 -1.4 ASTM C-578 - width, % -1.1 -1.1 -0.4 -0.5 22~72 W O 96/11970 PCTrUS95113362 Table III

Ex. or Comp. Ex. Ex. 5 Ex 6 Comp. Ex.

5 Resin type V V VII*
HBCD (a), pph (b) 2.5 2.5 2.5 Additives (c)~ pph 0.5 0.5 0.5 COz, pph 4.6 4.7 4.7 Ethanol, pph 1.0 0 1.0 Pentane, pph 0 2.0 0 Foaming Temp., C 112 117 117 Pressure Drop, bar 69 50 79 Board Thickness, mm 50 50 50 Density, kg/m3 35.9 33 7 34.6 Cell size vertical, mm 0.43 0.23 0.35 Vertical Compressive Strength, 272 321 249 kPa Extrusion Compressive Strength~279 237 261 kPa ~orizontal Compressive 148 149 133 Strength, kPa Dimensional Stability DIN 18164 - WD (d), % 5.4 6.6 4.7 DIN 18164 - W thickness, % 0 0.6 DIN 18164 - W length, %-1.8 -1.7 -1.0 DIN 18164 - W width, Z -2.8 -2.2 -2.9 ASTM C-578 - thickness, % 0.1 0.5 0 ASTM C-578 - length, Z -1.3 -0.7 -0.9 ASTM C-578 - width, % -1.6 -0.6 -1.6 .

W 096/11970 a ~ Q ~ ~ 7 2 PCTrUS95113362 Table III (Cont.) Ex. or Comp. Ex. Comp. Ex. Ex. 7 Ex. 8 Resin type VII* VI VI
HBCD (a), pph (b) 2.5 2.5 2.5 Additives (c), pph 0.5 0.5 0.5 CO2, pph 4.9 5.0 5.0 Ethanol~ pph 0 0 2.0 Pentane, pph 2.0 0 0 Foaming Temp., C 116 122 119 Pressure Drop, bar 47 78 34 Board Thickness, mm 50 25 25 Density, kg/m3 33.8 41.0 34.5 Cell size vertical, mm0.19 0.28 0.34 Vertical Compressive Strength,393 424 481 kPa Extrusion Compressive Strength, 237 350 153 kPa Horizontal Compressive 142 201 169 Strength, kPa Dimensional Stability DIN 18164 - WD (d), ~ 19.9 3.3 4.4 DIN 18164 - W thickness, % -0.3 -0.4 ~0.1 DIN 18164 - W length, % -1.4 -0.2 0.5 DIN 18164 - W width, % -1.8 -0.2 -0.1 ASTM C-578 - thickness, % -0.3 -0.1 -0.1 ASTM C-578 - length, Z -0.9 -0.1 1.4 ASTM C-578 - width, %-0.1 -0.1 -0.2 ~ q ~ 7 2 Wo 96/11970 PCT/US95/13362 X P~--I --I I CO ~~7 1 _~ H
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2~ 7 ~ 0 1. A process for preparing a low density closed-cell polymer foam comprising a plurality of closed cells having an average cell size of at least about 0.08 millimeter characterized in that the process comprises the steps of heat-plastifying an expandable or 5 foamable monovinyl aromatic polymer formulation comprising a non-linear monovinyl aromatic polymer composition and an environmentally acceptable blowing agent; and reducing the pressure on the mixture to form a foam.
2. Process according to Claim 1 characterized in that the non-linear monovinyl aromatic polymer composition comprises an at least three-point branched polystyrene.
3. Process according to Claim 1 characterized in that the blowing agent is solely carbon dioxide.
4. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dioxide and lower alcohols.
5. Process according to Claim 4 characterized in that the blowing agent is a 15 mixture of carbon dioxide and ethanol.
6. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dioxide and C1-C6 hydrocarbons.
7. Process according to Claim 6 characterized in that the blowing agent is a mixture of carbon dioxide and pentane.
8. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dioxide and a blowing agent of HCFC's and HFC's.

9. Process according to Claim 8 characterized in that the blowing agent is a mixture of carbon dioxide and HCFC-142b.

10. Process according to Claim 8 characterized in that the blowing agent is a 25 mixture of carbon dioxide and HCFC-1 52a.

11. Process according to Claim 1 characterized in that the blowing agent is dimethyl ether.

12. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dio~cide and dimethyl ether.

13. A stable monovinyl aromatic polymer foam having a plurality of closed cells having an average cell size of at least 0.08 mm and a density between 16 kg/m3 and 80 kg/m3 prepared by extruding the non-linear monovinyl aromatic polymer composition using environmentally acceptable blowing agents.

Claims (13)

1. A process for preparing a low density closed-cell polymer foam comprising a plurality of closed cells having an average cell size of at least about 0.08 millimeter characterized in that the process comprises the steps of heat-plastifying an expandable or foamable monovinyl aromatic polymer formulation comprising a non-linear monovinyl aromatic polymer composition and an environmentally acceptable blowing agent; and reducing the pressure on the mixture to form a foam.

2. Process according to Claim 1 characterized in that the non-linear monovinyl aromatic polymer composition comprises an at least three-point branched polystyrene.

3. Process according to Claim 1 characterized in that the blowing agent is solely carbon dioxide.

4. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dioxide and lower alcohols.

5. Process according to Claim 4 characterized in that the blowing agent is a mixture of carbon dioxide and ethanol.

6. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dioxide and C1-C6 hydrocarbons.

7. Process according to Claim 6 characterized in that the blowing agent is a mixture of carbon dioxide and pentane.

8. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dioxide and a blowing agent of HCFC's and HFC's.

9. Process according to Claim 8 characterized in that the blowing agent is a mixture of carbon dioxide and HCFC-142b.

10. Process according to Claim 8 characterized in that the blowing agent is a mixture of carbon dioxide and HCFC-152a.

11. Process according to Claim 1 characterized in that the blowing agent is dimethyl ether.

12. Process according to Claim 1 characterized in that the blowing agent is a mixture of carbon dioxide and dimethyl ether,

13. A stable monovinyl aromatic polymer foam having a plurality of closed cells having an average cell size of at least 0.08 mm and a density between 16 kg/m3 and 80 kg/m3 prepared by extruding the non-linear monovinyl aromatic polymer composition using environmentally acceptable blowing agents.