WO2002012377A2 - Flame retardant foam from blends of vinyl aromatic and olefinic polymers - Google Patents

Abstract

Flame retardant insulating foams, and processes for their preparation, are provided. The foams include (i) a polymer blend of an alkenyl aromatic polymer such as polystyrene, and an α-olefin polymer such as polyethylene; and (ii) a flame retardant package including a halogenated alkane flame retardant, and an aromatic halogenated flame retardant, and optionally a flame retardant synergist. The flame retardant package improves the compatibility of the polymer components, and minimizes corrugation in thin foam sheets. The resulting foams are useful, for example, as thermal insulation and acoustic insulation in buildings.

Description

FLAME RETARDANT FOAM FROM BLENDS OF VINYL AROMATIC AND OLEFLNIC POLYMERS

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/223,849, filed August 8, 2000.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable.

BACKGROUND OF THE INVENTION

This invention relates to synthetic polymer foam for use as acoustic insulation, thermal insulation, and other articles.

Synthetic polymer foams are useful, for example, as insulation in building materials, vehicles, and consumer goods. There is an increased demand for improving the flame retardant properties of materials used in such products in order to make them slower to ignite and to retard flame propagation. Thermoplastic polymers can be rendered flame retardant with flame retardant additives such as halogenated organic compounds. However, the addition of flame retardants in foamed polymeric compositions is associated with a variety of problems; Such problems include difficulty in obtaining homogeneous blending of the matrix resin with the flame retardant additives, and poor foaming. In addition, the flame retardant additives tend to degrade the appearance of the resulting foam product, and can negatively affect physical properties of the foam, particularly at higher levels of the additives. Product appearance can be degraded, for example, by color changes, and unacceptable outer surface profile characteristics. The quality of the outer surface ordinarily can be preserved by utilizing a higher foam density; however, higher density foam is accompanied by an increase in raw material costs. Thus, there is a need for more efficient flame retardant systems for use with thermoplastic polymer compositions, which do not detrimentally affect foam properties.

SUMMARY OF THE INVENTION The present invention is directed to flame retardant foam made from a polymer blend and a flame retardant package in which the flame retardant package, in addition to providing beneficial

same conditions without the flame retardant package. Low density foam can be manufactured more economically than high density foam. Therefore, the foam of the invention is a flame retardant product having additional unexpected beneficial properties. Furthermore, the flame retardant package surprisingly minimizes corrugation in thin foam sheet production. Corrugation, or uncontrolled variations in foam thickness, is one of the most troublesome problems in producing thin foam sheets, which are useful, for example, in impact sound insulation.

In a first aspect, this invention is a foam of a polymeric resin composition comprising a) a polymer blend including at least one alkenyl aromatic polymer, at least one α-olefin polymer, and, optionally, a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer; and b) a compatibihzing amount of a flame retardant package including a halogenated alkane flame retardant, and an aromatic halogenated flame retardant, and optionally a flame retardant synergist. Preferred polymeric components include a combination of polystyrene, polyethylene, and an ethylene-styrene interpolymer. The foam may be utilized as an acoustic foam.

In a second aspect, this invention is a polymeric resin composition comprising at least one alkenyl aromatic polymer, at least one α-olefin polymer, an effective amount of a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer, at least one halogenated alkane flame retardant, and at least one aromatic halogenated flame retardant, and optionally a flame retardant synergist.

In a third aspect, this invention is a method of producing a flame retardant foam, and part of this aspect includes the products obtainable by that method. The method entails introducing a blowing agent into a polymeric resin composition to form a foamable gel, wherein the polymeric resin composition includes at least one alkenyl aromatic polymer, at least one α-olefin polymer, an effective amount of a compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer, at least one halogenated alkane flame retardant, and at least one aromatic halogenated flame retardant, and optionally a flame retardant synergist. The foamable gel is then expanded to form the foam. In a fourth aspect, this invention is a method for improving the processability of a foam made from a blend of alkenyl aromatic and olefinic polymers, the method comprises mixing at least one halogenated alkane flame retardant and at least one aromatic halogenated flame retardant, and optionally a flame retardant synergist with the blend. The resulting foam is useful, for example, as thermal insulation or acoustic insulation.

DETAILED DESCRIPTION OF THE INVENTION Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. Foam Composition

The fire retardant foam of the invention generally comprises (i) a polymer blend of an alkenyl aromatic polymer, and an α-olefin polymer; (ii) a flame retardant package including a halogenated alkane compound and an aromatic halogenated compound; and (iii) optionally, a flame retardant synergist. In a preferred embodiment, the foam and the polymeric resin composition employed to make the foam include the flame retardant package; and a polymer blend of polystyrene, polyethylene, and an ethylene/styrene interpolymer. The term "polymeric resin composition" is used herein to indicate a combination of a polymer blend and a flame retardant package. Alkenyl Aromatic Polymer

For purposes of this invention, the alkenyl aromatic polymer of the polymer blend is a melt- processable polymer or melt processable impact-modified polymer in the form of polymerized monovinylidene aromatic monomers as represented by the structure:

H₂C=CRAr

wherein R is hydrogen or an alkyl radical that preferably has no more than three carbon atoms and Ar is an aromatic group. R is preferably hydrogen or methyl, most preferably hydrogen. Aromatic groups Ar include phenyl and naphthyl groups. The aromatic group Ar may be substituted. Halogen (such as Cl, F, Br), alkyl (especially C₁-C₄ alkyl such as methyl, ethyl, propyl and t-butyl), C₁-C₄ haloalkyl (such as chloromethyl or chloroethyl) and alkoxyl (such as methoxyl or ethoxyl) substituents are all useful. Styrene, para- vinyl toluene, α-methyl styrene, 4-methoxy styrene, t-butyl styrene, chlorostyrene, vinyl naphthalene and the like are all useful monovinylidene aromatic monomers. Styrene is especially preferred. The alkenyl aromatic polymer may be a homopolymer of a monovinylidene aromatic monomer as described above. Polystyrene homopolymers are the most preferred alkenyl aromatic polymers. Interpolymers of two or more monovinylidene aromatic monomers are also useful.

Although not critical, the alkenyl aromatic polymer may have a high degree of syndiotactic configuration; that is, the aromatic groups are located alternately at opposite directions relative to the main chain that consists of carbon-carbon bonds. Homopolymers of monovinylidene aromatic polymers that have syndiotacticity of 75 percent r diad or greater or even 90 percent r diad or greater as measured by ¹³C NMR are useful herein.

The alkenyl aromatic polymer may also contain repeating units derived from one or more other monomers that are copolymerizable with the monovinylidene aromatic monomer. Suitable such monomers include N-phenyl maleimide; acrylamide; ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile; ethylenically unsaturated carboxylic acids and anhydrides such as acrylic acid, methacrylic acid, fumaric anhydride and maleic anhydride; esters of ethylenically unsaturated acids such as Cι-C₈ alkyl acrylates and methacrylates, for example n-butyl acrylate and methyl methacrylate; and conjugated dienes such as butadiene or isoprene. The interpolymers of these types may be random, block or graft interpolymers. Blends of interpolymers of this type with homopolymers of a monovinylidene aromatic monomer can be used. For example, styrene/C₄-C₈ alkyl acrylate interpolymers and styrene-butadiene interpolymers are particularly suitable as impact modifiers when blended into polystyrene. Such impact-modified polystyrenes are useful herein.

In addition, the alkenyl aromatic polymers include those modified with rubbers to improve their impact properties. The modification can be, for example, through blending, grafting or polymerization of a monovinylidene aromatic monomer (optionally with other monomers) in the presence of a rubber compound. Examples of such rubbers are homopolymers of C₄-C₆ conjugated dienes such as butadiene or isoprene; ethylene/propylene interpolymers; interpolymers of ethylene, propylene and a nonconjugated diene such as 1,6-hexadiene or ethylidene norbornene; C₄-Ce alkyl acrylate homopolymers or interpolymers, including interpolymers thereof with a -C₄ alkyl acrylate. The rubbers are conveniently prepared by anionic solution polymerization techniques or by free radical initiated solution, mass or suspension polymerization processes. Rubber polymers that are prepared by emulsion polymerization may be agglomerated to produce larger particles having a multimodal particle size distribution. Preferred impact modified alkenyl aromatic polymers are prepared by dissolving the rubber into the monovinylidene aromatic monomer and any comonomers and polymerizing the resulting solution, preferably while agitating the solution so as to prepare a dispersed, grafted, impact modified polymer having rubber domains containing occlusions of the matrix polymer dispersed throughout the resulting polymerized mass. In such products, polymerized monovinylidene aromatic monomer forms a continuous polymeric matrix. Additional quantities of rubber polymer may be blended into the impact modified polymer if desired.

Commercial PS (polystyrene), HIPS (high impact polystyrene), ABS (acrylonitrile- butadiene-styrene) and SAN (styrene-acrylonitrile) resins that are melt processable are particularly useful in this invention. The alkenyl aromatic polymer has a molecular weight such that it can be melt processed with a blowing agent to form a cellular foam structure. Preferably, the alkenyl aromatic polymer has a melting temperature of about 60°C to about 310°C and a melt flow rate of about 0.5 to about 50 grams per 10 minutes (American Society for Testing and Materials (ASTM) test D-1238, 200°C/5kg). A weight average molecular weight of about 60,000 to about 350,000, preferably from about 100,000 to about 300,000, is particularly suitable. In the case of an impact modified polymer, these molecular weight numbers refer to molecular weight of the matrix polymer (that is, the continuous phase polymer of a monovinylidene aromatic monomer).

The polymer blend contains, for example, from about 10 percent, preferably from about 30 percent, more preferably from about 40 percent up to about 90 percent, preferably up to about 70 percent, and more preferably up to about 60 percent by weight alkenyl aromatic polymer based on the combined weight of alkenyl aromatic polymer, α-olefin polymer, and polymeric compatibilizer. The α-Olefin Polymer

The α-olefin polymer of the polymer blend is a polymer or interpolymer containing repeated units derived by polymerizing an α-olefϊn. The α-olefin polymer contains essentially no polymerized monovinylidene aromatic monomers and no sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers. Particularly suitable α-olefins have from 2 to about 20 carbon atoms, preferably from 2 to about 8 carbon atoms, and include ethylene, propylene, 1-butene, 4-methyl-l-pentene, 1-hexene, 1-octene and the like. Preferred α-olefin polymers are homopolymers of ethylene or propylene and interpolymers of ethylene with a C -C₈ α-olefin. The α-olefin polymer may also contain, in polymerized form, one or more other non-aromatic monomers that are interpolymerizable with the α-olefin and which contain an aliphatic or cycloaliphatic group. Such monomers include, for example, vinyl acetate, acrylic acid, methacrylic acid, esters of acrylic or methacrylic acid and acid anhydrides such as maleic anhydride. The α-olefϊn polymer preferably contains at least 75 percent by weight, preferably at least 95 percent by weight, of polymerized α- olefin monomers. More preferably, the α-olefin polymer contains at least 85 percent by weight polymerized ethylene, with polymerized α-olefin monomers constituting the remainder of the polymer. In other words, the α-olefin polymer may contain polyethylene or a copolymer of ethylene and up to about 15 percent of another α-olefin.

Particularly suitable α-olefin polymers include low density polyethylene (LDPE), which term is used herein to designate polyethylene homopolymers made in a high pressure, free radical polymerization process. These LDPE polymers are characterized by having a high degree of long chain branching. LDPE useful in this invention preferably has a density of about 0.910 to 0.970 g/cc (ASTM D792) and a melt index from about 0.02 to about 100 grams per 10 minutes (g/10 min), preferably from 0.2 to about 30 grams per 10 minutes (as determined by ASTM Test Method D 1283, condition 190°C/2.16kg). The so-called linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) products are also useful herein. These polymers are homopolymers of polyethylene or copolymers thereof with one or more higher α-olefins and characterized by the near or total absence (less than 0.01/1000 carbon atoms) of long chain branching. LLDPE and HDPE are made in a low pressure process employing conventional Ziegler-Natta type catalysts, as described in US-A-4,076,698. LLDPE and HDPE are generally distinguished by the level of α-olefin comonomer that is used in their production, with LLDPE containing higher levels of comonomer and accordingly lower density. Suitable LLDPE polymers having a density of from about 0.85 to about 0.940 g/cc (ASTM D 792) and a melt index (ASTM D 1238, condition 190°C/2.16kg) of about 0.01 to about 100 grams/10 minutes. Suitable HDPE polymers have a similar melt index, but have a density of greater than about 0.940 g/cc.

Another suitable α-olefin polymer includes polypropylene. High melt strength polypropylene resins are preferred. The propylene polymer material may be comprised solely of one or more propylene homopolymers, one or more propylene copolymers, and blends of one or more of each of propylene homopolymers and copolymers; propylene homopolymers are preferred. The propylene polymer preferably has a weight average molecular weight (M_w) of at least 100,000. M_w can be measured by known procedures. Preferred propylene polymers include those that are branched or lightly cross-linked. Branching (or light cross-linking) may be obtained by those methods generally known in the art, such as chemical or irradiation branching/light cross-linking. One such resin which is prepared as a branched/lightly cross-linked polypropylene resin prior to using the polypropylene resin to prepare a finished polypropylene resin product and the method of preparing such a polypropylene resin is described in US-A-4,916,198, which is hereby incorporated by reference. Another method to prepare branched/lightly cross-linked polypropylene resin is to introduce chemical compounds into the extruder, along with a polypropylene resin and allow the branching/lightly cross-linking reaction to take place in the extruder. This method is illustrated in US-A-3,250,731 with a polyfunctional azide, US-A-4,714,716 (and published International Application WO 99/10424) with an azidofunctional silane and EP 879,844-Al with a peroxide in conjunction with a multi-vinyl functional monomer. The aforementioned U.S. patents are incorporated herein by reference. Irradiation techniques are illustrated by US-A-5,605,936 and US-A-5,883,151, which are also incorporated by reference.

Another type of α-olefin polymer are LLDPE polymers having a homogeneous distribution of the comonomer, as are described, for example, in US-A-3,645,992 to Elston and US-A-5,026,798 andUS-A-5,055,438 to Canich.

Yet another type of α-olefin polymer are substantially linear olefin polymers as described in US-A-5,272,236 and US-A-5,278,272, incorporated herein by reference. The substantially linear olefin polymer is advantageously a homopolymer of a C₂-C₂o α-olefm or, preferably, an interpolymer of ethylene with at least one C₃-C₂₀ α-olefin and/or a C₄-Cι₈ diolefin. These polymers contain a small amount of long-chain branching (that is about 0.01 to 3, preferably 0.01-1 and more preferably 0.3-1 long chain branch per 1000 carbon atoms) and typically exhibit only a single melting peak by differential scanning calorimetry. Particularly suitable substantially linear olefin polymers have a melt index (ASTMD-1238, Condition 190°C/2.16kg) of from about 0.01 to about 1000 g/10 min, and a density of from 0.85 to 0.97 g/cc, preferably 0.85 to 0.95 g/cc and especially 0.85 to 0.92 g/cc. hi addition, α-olefin polymers that have been subjected to coupling or light crosslinking treatments are useful herein, provided that they remain melt processable. Such grafting or light crosslinking techniques include silane grafting as described in US-A-4,714,716 to Park; peroxide coupling as described in US-A-4,578,431 to Shaw et al., and irradiation as described in US-A-5,736,618 to Poloso. Preferably, the treated polymer has a gel content of less than 10 percent, more preferably less than 5 percent, most preferably less than 2 percent by weight, as determined by gel permeation chromatography. Treatment of this type is of particular interest for HDPE, LLDPE or substantially linear polyethylene copolymers, as it tends to increase the melt tension and melt viscosity of those polymers to a range that improves their ability to be processed into foam in an extrusion process.

The polymer blend contains, for example, from about 10 percent, preferably from about 30 percent, more preferably from about 40 percent up to about 90 percent, preferably up to about 70 percent, and more preferably up to about 60 percent by weight of the α-olefin polymer based on the combined weight of alkenyl aromatic polymer, α-olefin polymer, and polymeric compatibilizer. Compatibilizer/Interpolymer

The polymer blend may further contain a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer. The compatibilizer can be of any type, provided that it prevents macroscopic phase separation of the polymer blend, and the polymer blend is melt processable to form a foam. Without the compatibilizer, the alkenyl aromatic polymer and the α-olefin polymer are difficult to blend and difficult to foam. The compatibilizer enhances the mixing between the polymeric components. Suitable compatibilizers include certain aliphatic α-olefin/monovinylidene aromatic interpolymers, hydrogenated or non-hydrogenated monovinylidene aromatic/conjugated diene block (including diblock and triblock) copolymers, and styrene/olefin graft copolymers. The term "interpolymer" is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes copolymers, terpolymers, etc.

Although the flame retardant package is discussed separately, the flame retardant package may also act as a compatibilizer in that it minimizes macroscopic phase separation of the polymer blend. If sufficient quantities of the flame retardant package are employed, then a polymeric compatibilizer may be unnecessary. However, polymeric compatibilizers may be advantageously employed in the present invention.

Turning to the polymeric compatibilizers listed above, examples of suitable aliphatic α- olefm monovinylidene interpolymers include the substantially random interpolymers prepared by polymerizing i) ethylene and/or one or more α-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s). The interpolymer contains, for example, in polymerized form, from about 35 to about 99 mole percent of monomer type i), about 1 to about 65 mole percent of monomer type ii), and up to 30 mole percent of monomer type iii). Preferably, the interpolymer contains from about 45-97 mole percent of monomer type i), about 3-55 mole percent of monomer type ii) and no more than 20 mole percent of monomer type iii). The interpolymer advantageously has a melt flow index (190°C/2.16kg) of about 0.1 to 50 grams per 10 minutes (g/10 min), and a molecular weight distribution which is a weight average molecular weight/number average molecular weight (M_w/M_n) of about 1.5 to about 20.

Examples of suitable α-olefins for use in an interpolymer include, for example, α-olefins containing from 3 to about 20, preferably from 3 to about 12, more preferably from 3 to about 8 carbon atoms. Particularly suitable are ethylene, propylene, butene-1, 4-methyl-l -pentene, hexene-1 or octene-1 or ethylene in combination with one or more of propylene, butene-1, 4-methyl-l- pentene, hexene-1 or octene-1. These α-olefins do not contain an aromatic, hindered aliphatic, or cycloaliphatic moieties.

Other optional polymerizable ethylenically unsaturated monomer(s) include norbornene and Ci-io alkyl or C_6-ιo aryl substituted norbornenes, with an examplary interpolymer being ethylene/styrene/norbornene. Vinyl or vinylidene aromatic monomers which can be employed to prepare the interpolymers include, for example, those represented by the following formula:

Ar I (CH₂)_n

R^l _ C = C(R2)₂ wherein R¹ is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R² is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or a phenyl group substituted with from 1 to 5 substituents selected from the group consisting of halo,

and Cι_₄-haloalkyl; and n has a value from zero to about 4, preferably from zero to 2, most preferably zero. Exemplary vinyl aromatic monomers include styrene, vinyl toluene, α-methylstyrene, t-butyl styrene, chlorostyrene, including all isomers of these compounds, and the like. Particularly suitable such monomers include styrene and lower alkyl- or halogen-substituted derivatives thereof. Preferred monomers include styrene, α-methyl styrene, the lower alkyl- (Ci - C₄) or phenyl-ring substituted derivatives of styrene, such as for example, ortho-, meta-, and para-methylstyrene, the ring halogenated styrenes, para-vinyl toluene or mixtures thereof, and the like. A more preferred aromatic vinyl monomer is styrene.

By the term "sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds", it is meant addition polymerizable vinyl or vinylidene monomers corresponding to the formula:

Aⁱ

I

R¹ — C = C(R2)₂ wherein A¹ is a sterically bulky, aliphatic or cycloaliphatic substituent of up to 20 carbons, R¹ is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R² is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; or alternatively R¹ and A¹ together form a ring system. The term "sterically bulky" means that the monomer bearing this substituent is normally incapable of addition polymerization by standard Ziegler-Natta polymerization catalysts at a rate comparable with ethylene polymerizations. Preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are monomers in which one of the carbon atoms bearing ethylenic unsaturation is tertiary or quaternary substituted. Examples of such substituents include cyclic aliphatic groups such as cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl or aryl substituted derivatives thereof, tert- butyl, norbornyl, and the like. Most preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are the various isomeric vinyl- ring substituted derivatives of cyclohexene and substituted cyclohexenes, and 5-ethylidene-2-norbornene. Especially suitable are 1-, 3-, and 4-vinylcyclohexene. Simple linear non-branched α-olefins including, for example, α-olefins containing from 3 to about 20 carbon atoms such as propylene, butene-1, 4-methyl-l -pentene, hexene-1 or octene-1 are not examples of sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds.

The substantially random interpolymers include the pseudo-random interpolymers as described in EP-A-0,416,815 by James C. Stevens et al. (equivalent to US-A-5,872,201) and

US-A-5,703,187 by Francis J. Timmers, both of which are incorporated herein by reference in their entirety. The substantially random interpolymers are conveniently made by polymerizing a mixture of polymerizable monomers in the presence of one or more metallocene or constrained geometry catalysts in combination with various cocatalysts. Preferred operating conditions for the polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from -30°C to 200°C. Polymerizations and unreacted monomer removal at temperatures above the autopolymerization temperature of the respective monomers may result in formation of some amounts of homopolymer polymerization products resulting from free radical polymerization. Examples of suitable catalysts and methods for preparing the substantially random interpolymers are disclosed in European Application No. EP-A-416,815; allowed U.S. Application Serial No. 09/302,067; EP-A-514,828; as well as US-A-5,055,438; US-A-5,057,475; US-A-5,096,867; US-A-5,064,802; US-A-5,132,380; US-A-5,189,192; US-A-5,321,106; US-A-5,347,024; US-A-5,350,723; US-A-5,374,696; US-A-5,399,635; US-A-5,470,993; US-A-5,703,187; US-A-5,721,185; US-A-5,929,154; US-A-6,013,819; and US-A-6,048,909. All of these patents and applications are fully incorporated herein by reference.

The substantially random α-olefin/ vinyl or vinylidene aromatic interpolymers can also be prepared by the methods described in IP 07/278230 employing as catalysts compounds shown by the general formula

^X \ /

R³ M

\ / \ Cp2 R2 where Cp¹ and Cp² are cyclopentadienyl groups, indenyl groups, fluorenyl groups, or substituents of these, independently of each other; R¹ and R² are hydrogen atoms, halogen atoms, hydrocarbon groups with carbon numbers of 1-12, alkoxyl groups, or aryloxyl groups, independently of each other; M is a group TV metal, preferably Zr or Hf, most preferably Zr; and R³ is an alkylene group or silanediyl group used to cross-link Cp¹ and Cp².

The substantially random α-olefin/ vinyl aromatic interpolymers can also be prepared by the methods described by John G. Bradfute et al. (W. R. Grace & Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents, Inc.) in WO 94/00500; and in Plastics Technology, p. 25 (September 1992), all of which are incorporated herein by reference in their entirety. Also suitable are the substantially random interpolymers which comprise at least one α- olefin/vinyl aromatic/vinyl aromatic/α-olefm tetrad disclosed in WO98/09999 by Francis J. Timmers et al. These interpolymers contain additional signals in their carbon- 13 NMR spectra with intensities greater than three times the peak to peak noise. These signals appear in the chemical shift range 43.70-44.25 ppm and 38.0-38.5 ppm. Specifically, major peaks are observed at 44.1, 43.9 and 38.2 ppm. A proton test NMR experiment indicates that the signals in the chemical shift region 43.70-44.25 ppm are methine carbons and the signals in the region 38.0-38.5 ppm are methylene carbons. Further preparative methods for the interpolymers used in the present invention have been described in the literature. Longo and Grassi (Makromol. Chem.. Volume 191, pages 2387 to 2396 [1990]) and D'anniello et al. (Journal of Applied Polymer Science, Volume 58, pages 1701-1706 [1995]) reported the use of a catalytic system based on methylalumoxane (MAO) and cyclopentadienyltitanium trichloride (CpTiCl₃) to prepare an ethylene-styrene copolymer. Xu and Lin (Polymer Preprints. Am. Chem. Soc. Div. Polvm. Chem.) Volume 35, pages 686, 687 [1994]) have reported copolymerization using a MgClJTiClJNdClJ Al(iBu)₃ catalyst to give random copolymers of styrene and propylene. Lu et al. (Journal of Applied Polymer Science, Volume 53, pages 1453 to 1460 [1994]) have described the copolymerization of ethylene and styrene using a TiCl4/NdCl₃/MgCl₂/Al(Et)₃ catalyst. Sernetz and Mulhaupt, (Macromol. Chem. Phvs.. V. 197, pp. 1071-1083, 1997) have described the influence of polymerization conditions on the copolymerization of styrene with ethylene using Me₂Si(Me₄Cp)(n-tert- butyl)TiCl₂/methylaluminoxane Ziegler-Natta catalysts. Copolymers of ethylene and styrene produced by bridged metallocene catalysts have been described by Arai, Toshiaki and Suzuki (Polymer Preprints. Am. Chem. Soc. Div. Polvm. Chem.) Volume 38, pages 349, 350 [1997]) and in US-A-5,652,315, issued to Mitsui Toatsu Chemicals, Inc. The manufacture of α-olefin/vinyl aromatic monomer interpolymers such as propylene/styrene and butene/styrene are described in US-A-5,244,996, issued to Mitsui Petrochemical Industries Ltd or US-A-5,652,315 also issued to Mitsui Petrochemical Industries Ltd or as disclosed in DE 197 11 339 Al to Denki Kagaku Kogyo KK._β All the above methods disclosed for preparing the interpolymer component are incorporated herein by reference. Also, although of high isotacticity and therefore not "substantially random", the random copolymers of ethylene and styrene as disclosed in Polymer Preprints Vol. 39, No. 1, March 1998 by Toru Aria et al. can also be employed as compatibilizers of the present invention. While preparing the substantially random interpolymer, an amount of atactic vinyl aromatic homopolymer may be formed due to homopolymerization of the vinyl aromatic monomer at elevated temperatures. The presence of vinyl aromatic homopolymer is in general not detrimental for the purposes of the present invention and can be tolerated. The vinyl aromatic homopolymer may be separated from the interpolymer, if desired, by extraction techniques such as selective precipitation from solution with a non solvent for either the interpolymer or the vinyl aromatic homopolymer. For the purpose of the present invention it is preferred that no more than 30 weight percent, preferably less than 20 weight percent based on the total weight of the interpolymers of atactic vinyl aromatic homopolymer is present.

Blends of an alkenyl aromatic polymer with an α-olefm polymer using an α-olefin/monovinylidene aromatic interpolymer as a compatibilizer are described in US-A-5,460,818 incorporated herein by reference. Those blends are suitable for use herein. Monovinylidene aromatic/conjugated diene block copolymers include diblock and triblock copolymers of, for example, styrene and one or more conjugated dienes such as butadiene, isoprene or norbornene. The proportion of units derived from the monovinylidene aromatic monomer is, for example, from 10 to 80 percent by weight and preferably from 30 to 60 percent by weight. These ^• advantageously have a molecular weight, as measured by viscosity against a polystyrene standard, of about 3,000 to 800,000 and preferably from 10,000 to 100,000. These block copolymers can be hydrogenated, as described in US-A-4,020,025, and the hydrogenated forms can also be used. The double bonds in the backbone of the polymer may be hydrogenated to the extent of 90 percent or more. Suitable styrene/olefin graft copolymers are also described in US-A-4,020,025 and in German Published Application 1,495,813, both incorporated herein by reference.

Preferred interpolymers are substantially random ethylene-styrene interpolymers. Such polymers maybe prepared as described, for example, in column 17, line 15 through column 20, line 3 of US-A-6,048,909 and preferably have a styrene content from about 20 to about 70 wt percent measured as described, for example, in US-A-6,048,909 to Chaudhary which is herein fully incorporated by reference. Most preferred are interpolymers such as those marketed by The Dow Chemical Company under the INDEX™ tradename. These interpolymers have a higher damping ratio than either the ethylene or the styrene components alone. A damping ratio, also called loss tangent (tg δ), is a ratio between loss modulus (viscous component of the deformation) versus storage modulus (elastic component of the deformation.) The polymer blend preferably contains from about 0.1 percent more preferably from about 2 percent, most preferably from about 3 percent, to about 50 percent, preferably to about 20 percent, more preferably to about 15 percent by weight of the compatibilizer based on the combined weight of the alkenyl aromatic polymer, α-olefin polymer, and polymeric compatibilizer. Flame Retardant Package The term "flame retardant" is used herein to indicate a flame retardant which can be any halogen-containing compound or mixture of compounds which imparts flame resistance to the foams of the present invention. "Flame retardant package" refers to at least two different types of flame retardants which may be added together or separately into a polymer blend.

The foams of the invention include a flame retardant package which functions to extinguish flames or at least slow the spread of fire in the foam. The flame retardant package includes both a halogenated alkane compound and an aromatic halogenated compound. The term "halo" or "halogenated" includes compounds containing bromine, chlorine, or fluorine, or any combination thereof. Preferably, the flame retardant is a bromine or chlorine containing compound.

In addition to providing flame retardancy to the foam, the flame retardant package has been found to enhance blending of the polymer components, and reduce the foam density. By better dispersing the components of the polymer blend, the flame retardant package also improves the ability to manufacture thin foam sheets which are often prone to corrugation in manufacturing. The flame retardant package surprisingly minimizes corrugation in thin foam sheets as observed by unaided visual inspection.

Turning to the composition of the flame retardant package, suitable aromatic halogenated flame retardants are well-known in the art and include but are not limited to hexahalodiphenyl ethers, octahalodiphenyl ethers, decahalodiphenyl ethers, decahalodiphenyl ethanes; l,2-bis(trihalophenoxy)ethanes; l,2-bis(pentahalophenoxy)ethanes; a tetrahalobisphenol-A; ethylene(N, N')-bis-tetrahalophthalimides; tetrabromobisphenol A bis (2,3-dibromopropyl ether); tetrahalophthalic anhydrides; hexahalobenzenes; halogenated indanes; halogenated phosphate esters; halogenated polystyrenes; and polymers of halogenated bisphenol-A and epichlorohydrin, and mixtures thereof. Preferred aromatic halogenated flame retardants may include one or more of tetrabromobisphenol-A (TBBA), tetrabromo bisphenol A bis (2,3-dibromopropyl ether), decabromodiphenyl ethane, brominated trimethylphenylindane, or aromatic halogenated flame retardants with similar kinetics. The halogenated alkane compound may be branched or unbranched, cyclic or acyclic.

Preferably, the halogenated alkane compound is cyclic. Suitable halogenated alkane flame retardants include and are not limited to hexahalocyclododecane; tetrabromocyclooctane; pentabromochlorocyclohexane; 1 ,2-dibromo-4-(l ,2-dibromoethyl)cyclohexane; 1,1,1,3- tetrabromononane; and mixtures thereof. Preferred halogenated alkane flame retardant compounds include hexabromocyclododecane and its isomers, pentabromochlorocyclohexane and its isomers, and l,2-dibromo-4-(l,2-dibromoethyl)cyclohexane and its isomers. Hexabromocyclododecane

(HBCD), and halogenated alkane flame retardants with similar kinetics are preferred.

In a preferred embodiment, the flame retardant package includes a combination of hexahalocyclododecane such as hexabromocyclododecane (HBCD), and tetrabromobisphenol A bis (2,3-dibromopropyl ether).

For foams, the halogen content in the final foam is typically from 0.5 wt percent to about 15 wt percent. Preferred loadings or amounts of halogenated flame retardants depend on the application, the desired level of flame retardancy, and the types of polymers in the polymer blend.

When the polymer blend includes a material having a high burning temperature, then a higher concentration of a flame retardant capable of absorbing heat over time should be employed. If the polymer blend includes components with a low burning temperature, then a lower concentration may be employed.

A compatibilizing amount of the flame retardant package is desirably added to the polymer blend. This is an amount sufficient to compatibilize the components of the polymer blend to prevent macroscopic phase separation of the components. The compatibilizing amount depends, in part, on the amount of polymeric compatibilizer present in the polymer blend. For example, if no polymeric compatibilizer is employed in the polymer blend, then the flame retardant package is added in an amount sufficient to compatibilize the alkenyl aromatic polymer and the α-olefin polymer. If a polymeric compatibilizer is employed in an amount sufficient to render the alkenyl aromatic polymer and the α-olefin polymer phases compatible or blendable, then the flame retardant package need only be added in an amount sufficient to obtain the desired flame retardancy. Even if sufficient polymeric compatibilizer is added to prevent macroscopic phase separation, the flame retardant package tends to enhance the blendability of the polymer components.

The polymeric resin compositions preferably include at least about 0.5 phr halogenated alkane flame retardant, more preferably at least about 0.8 phr, preferably up to about 8 phr, more preferably up to about 6 phr halogenated alkane flame retardant. The polymeric resin compositions preferably include at least about 0.5 phr aromatic halogenated flame retardant, more preferably at least about 0.8 phr, preferably up to about 8 phr, more preferably up to about 6 phr aromatic halogenated flame retardant. The parts are based on parts by weight per hundred parts by weight of the polymer blend.

The ratio of aromatic halogenated flame retardant to halogenated alkane flame retardant in parts by weight is preferably from about 16:1 to 1:16, more preferably from about 7.5:1 to 1:7.5, and most preferably about 5:1 to 1:5 The concentration of aromatic halogenated flame retardant is preferably at least about 0.5 parts by weight per hundred parts by weight (phr) of the α-olefin polymer component, more preferably at least 1 phr, and preferably up to 8 phr based on the weight of the α-olefin polymer component. The concentration of halogenated alkane flame retardant is preferably at least about 0.5 parts by weight per hundred parts by weight (phr) of the alkenyl aromatic polymer component, more preferably at least 1 phr, and preferably up to 8 phr based on the weight of the alkenyl aromatic polymer component. Flame Retardant Synergist

The term "flame retardant synergist" is used herein to indicate inorganic or organic compounds which enhance the effectiveness of flame retardants, especially halogenated flame retardants.

Optionally, a flame retardant synergist may be added to the polymeric resin composition along with the flame retardant. Examples of inorganic flame retardant synergists include, but are not limited to, metal oxides (for example, iron oxide, tin oxide, zinc oxide, aluminum trioxide, alumina, antimony trioxide and antimony pentoxide, bismuth oxide, molybdenum trioxide, and tungsten trioxide), zinc borate, antimony silicates, zinc stannate, zinc hydroxystannate, ferrocene and mixtures thereof. Examples of organic flame retardant synergists include, but are not limited to dicumyl (dimethyldiphenylbutane), polycumyl, halogenated paraffin, triphenylphosphate, and mixtures thereof. The flame retardant synergists may be employed in an amount from 0 phr to about

6 phr.

Other Additives

The foam of the present invention may optionally contain one or more conventional additives to the extent the additives do not interfere with the desired foam properties. Typical additives include antioxidants (such as hindered phenols (for example, IRGANOX™ 1010, trademark of and available from the Ciba Geigy Corporation), ultraviolet stabilizers, colorants, pigments, fillers, acid scavengers, and extrusion aids. In addition, a nucleating agent may optionally be added in order to control the size of foam cells. Preparation and Use of Foams

The foam structure of the invention may be prepared by conventional extrusion foaming processes. This process generally entails feeding the ingredients of the polymeric resin composition together or separately into the heated barrel of an extruder, which is maintained above the crystalline melting temperature or glass transition temperature of the constituents of the blend; heating the polymeric resin composition to form a plasticized or melt polymer material; incorporating a blowing agent into the melt polymer material to form a foamable gel; and expanding the foamable gel to form the foam product. The foamable gel may be extruded or conveyed through a die of desired shape to an area of lower pressure where the mixture expands to form a cellular foam structure. The lower pressure is preferably at an atmospheric level. Typically, the mixture is cooled to within +/-20°C of the highest crystalline melting point or glass transition temperature of the components of the polymer blend before extrusion in order to optimize physical characteristics of the foam. The polymer blend can be prepared by simple melt blending prior to introducing the polymer blend into the extruder. Alternatively, individual polymeric components can be separately charged into the extruder together with other additives to form the polymer blend as part of the foam-making process. The order of addition of the components of the polymeric resin composition is not important. It may be beneficial, however, to add low melting flame retardants to a polymer component to form a preblend prior to addition to the extruder to avoid melting the flame retardant at the extruder entrance.

Any conventional blowing agent may be used to prepare the foam of the invention. US-A-6,048,909 to Chaudhary et al. discloses a number of suitable blowing agents at column 12, lines 6-56, the teachings of which are incorporated herein by reference. Preferred blowing agents include aliphatic hydrocarbons having 1-9 carbon atoms, especially propane, n-butane and isobutane, more preferably isobutane.

The blowing agent is mixed with the molten polymeric resin composition under elevated pressure which should be greater than the prefoaming critical pressure to prevent the foam from expanding prematurely. The prefoaming critical die pressure is best determined empirically by observation of the foaming process, and may be defined as the minimum die pressure at which popping is heard at the die and the resulting foam takes on a rough surface caused by premature nucleation and expansion of the foam inside the die lip.

The range of the prefoaming critical die pressure can be estimated from a calculation based on solubility data for the blowing agent in the polymer melt as a function of temperature and pressure. For interpolation or extrapolation, the Flory-Huggins equation or the Eyring and Henry equations can be used. The Flory-Huggins theory provides an implicit relationship for solubility as a function of temperature and pressure and requires a trial and error solution procedure. The Eyring equation and Henry equation provide an explicit relationship for solubility as a function of temperature and pressure that is easier to implement. The solubility of isobutane (and other blowing agents) in low density polyethylene as a function of temperature and pressure has been experimentally determined by B.I. Chaudhary & A.I. Johns and reported in Journal of Cellular Plastics, volume 34, number 4, pages 312-328 (1998) which is herein incorporated by reference.

The prefoaming critical die pressure is best determined experimentally for formulations like those of the invention which include not only the polymer components, but also additives such as flame retardants and synergists. This is typically accomplished by preparing foams at several prefoaming die pressures and determining the effect of changes in the die pressure on the foam cell size and appearance. Below the prefoaming critical die pressure, the quality of the foam deteriorates sharply, rough skin is observed on the foam due to rupture of surface cells and typically a crackling noise is heard at the die due to rapid degassing of the blowing agent. Conversely, if the die pressure is too high, then the foam tends to nucleate significantly causing a decrease in cell size.

The foam is conveniently extruded in the form of sheet or plank material having a thickness of from about 1, preferably from about 1.5, more preferably from about 2, most preferably from about 3 mm to about 100, preferably to about 20, more preferably to about 10 mm. The desired thickness depends in part on the application. For example, as impact sound insulation in flooring, thin foam sheets less than about 10 mm thick are preferred in order to meet room height and door height restrictions.

When the foam of this invention is a thick sheet, the foam desirably has perforation channels. Perforation channels are preferably not employed when the foam is a thin sheet. Thick polymer foams may have an average thickness perpendicular to the surface perforated of at least about 25 millimeters (mm) and the polymer foam may be preferably perforated to an average depth of at least 5 mm below the surface of the polymer foam. Typically, perforation comprises puncturing the base foam. A description of how to create suitable perforation channels to accelerate release of blowing agent from the foam is provided in US-A-5,585,058, which is incorporated herein by reference. Accelerated aging of the foam to remove blowing agent may also be achieved, for example, by perforation techniques and heat aging as described in US-A-5,242,016 to Kolosowski and US-A-5,059,376 to Pontiff.

Applications for the flame resistant compositions of the present invention include articles made by various extrusion processes. Such articles may be used as acoustical insulation and/or thermal insulation, for example, in automotive and other transportation devices, building and construction, household and garden appliances, power tool and appliance and electrical supply housing, connectors, and aircraft as acoustic systems for sound absorption and insulation. Acoustic foam or acoustic insulation refers to foams useful in absorbing impact sound and/or airborne sound. The foams have properties, such as a combination of cell size and open-cell structure, which allow them to effectively serve both thermal and acoustic insulation applications. The resulting foam structure may be either closed-celled or open-celled. The open cell content will range from 0 to 100 volume percent as measured according to ASTM D2856-A. The foam advantageously has an open cell content of at least 10 volume percent, and up to 90 volume percent as measured per ASTM D 2856 Procedure A. When the foams are to be employed as thermal insulation, preferably the open-cell content of the foam is less than about 10 percent which helps to reduce the water absorption, and hence helps to maintain the thermal conductivity of the foams over a long period of time. Turning to cell size, the preferred cell size depends on the application. The foams tend to exhibit an average cell size of from about 0.1 mm, preferably from about 0.5 mm, to about 5 mm, preferably to about 3 mm, according to ASTM D3576. As discussed above regarding the flame retardant package, because the flame retardant package enhances the compatibility or blending of the polymer components, the resulting foam has an even profile with minimal corrugation upon unaided visual inspection. Preferably, the foam is corrugation-free, which means the foam sheet is flat and has a uniform thickness along its length and width. Also, as discussed previously, it is normally difficult to minimize both corrugation and foam density simultaneously. The foams of the present invention are surprisingly able to do so. The resulting foam structure typically has a density of less than about 100 kilograms per cubic meter (kg/m³), preferably less than about 40 kg/m³, more preferably less than about 30 kg/m³. Density is typically at least about 10 kg/m³.

The materials of the invention are especially suited to applications where, in addition to meeting the relevant acoustic performance standards, they must also meet any applicable fire test codes, for example office partitions, automotive decouplers, domestic appliance sound insulation, and sound proofing panels and machine enclosures. The foam is particularly well-suited for impact sound absorption, such as that found in floating floor constructions. Impact sound insulation is desirably thin. Thus, foam sheets less than about 20 mm thick are preferred. One way to measure impact sound absorption capabilities is by measuring dynamic stiffness or dynamic modulus. If the foams of the present invention are to be used in acoustic applications, then low dynamic stiffness is desirable. The dynamic modulus, and therefore the dynamic stiffness, of a foam can be reduced somewhat by mechanically stressing the foam, such as by compression. This process is referred to herein as "elastification" and will be discussed further below.

The final foam for use by the consumer, either before or after elastification as described below, preferably has a dynamic modulus of no greater than 1,500 kN/m². More preferably, the dynamic modulus is no greater than about 1,000 kN/m² even more preferably no greater than about 500 kN/m². Dynamic modulus is defined as the dynamic stiffness of the foam in N/m³, measured according EN 29052, multiplied by the thickness of the foam in meters. For foams having a thickness in the most preferred range of 3-20 mm, a dynamic modulus of 180- 1 ,500 kN/m² corresponds to a dynamic stiffness in the range of about 9-500 MN/m³. Thus, the dynamic stiffness of the foam is preferably less than about 500 MN/m³ at a thickness of 3-20 mm.

Turning to the elastification or flexibilization process, elastification tends to wrinkle the cell struts as well as cell walls so that the foam is softened and the dynamic stiffness is correspondingly reduced. The method of flexibilization is not significant. Flexibilization may be performed by any means sufficient to exert external force or pressure to one or more surfaces of the foam to compress the specimens to a percentage of their original thickness, and then releasing the applied pressure and allowing the foam to recover. Flexibilization is readily accomplished by, for example, compressing the foam by about 30 to 95 percent of its original thickness through a pair or a series of rollers or under any kind of compression system. Multiple compressions may be done in order to achieve a desired softness (as indicated by dynamic modulus). A preferred flexibilization technique involves quickly applying sufficient pressure to compress the foam from its original thickness by > 50 percent preferably > 70 percent and then releasing the applied pressure.

The flexibilization can be done at ambient temperature or at any other temperature providing the temperature does not exceed the melting temperature of the polymer. One advantage of performing the flexibilization at high temperature is to smoothen the skin of the foam, if the material exhibits some skin quality deficiency.

An example of a suitable roller system for elastification includes two banks of rollers each bounding the zone of lower pressure into which the extruded product enters in order to expand. The foam expands until it contacts the two banks of rollers. The combination of pressure from the extruding apparatus and action by the rollers moves the product toward a second roller assembly from which the foam product exits to a tensioning assembly. The tensioning assembly desirably includes moving belts, which cooperate to draw the foam body away from the second roller assembly. Once the tensioning assembly begins to act upon and advance the foam through the roller assemblies, the spacing between the roller banks may be adjusted to apply a greater or lesser amount of compressive force to the foam sheet as it advances through the roller assemblies. The composition of the polymer blend may also be appropriately modified to optimize the foam properties desired for the product's application. For example, for impact sound insulation, desired properties include sufficient softness or flexibility to absorb sound, and sufficient strength and mechanical properties to resist creep and to recover in thickness after bearing a compressive load. One suitable polymer component, polystyrene, improves mechanical properties, but tends to decrease softness. Polyethylene improves softness but may result in poorer recovery and creep performance. An ethylene/styrene interpolymer tends to provide good damping properties, but should not be added in concentrations to significantly adversely affect the strength and mechanical properties. Thus, a desirable polymer blend should balance the properties of the individual components while maintaining a uniform dispersion of the polymeric components, as a uniform dispersion enhances the foam properties.

The foregoing merely illustrates representative applications for the foam of the present invention. Skilled artisans can readily envision additional applications without departing from the scope or spirit of the present invention. EXAMPLES

The following examples illustrate, but do not in any way limit the scope of the present invention. Arabic numerals illustrate examples of the invention, and letters of the alphabet designate comparative examples. All parts and percentages are by weight unless otherwise indicated.

Melt flow or melt index measurements, and analysis of the styrene content in the ESI interpolymers may be determined, for example, as described in column 14, line 28 through column 17, line 11 of US-A-6,048,909 to Chaudhary et al, which is herein incorporated by reference. Example 1

This example describes the fonnulation and process conditions to make flame retardant thick foam sheets. The foams are prepared in commercial foaming equipment including a 2.5 inch (63.5mm) single-screw extruder, a mixer, a cooling zone, and forming die in series. The foams discussed in this Example 1 were prepared using the components listed in Table 1 where formulations 1 and 2 are examples of the present invention and the formulations labeled "comp." are comparative examples. Formulation 1 is prepared by feeding: polystyrene (PS) with a melt flow rate of 40 g/10 min. (200°C/5 kg) and weight average molecular weight (Mw) of 140,000; low density polyethylene (LDPE) with a density of 0.924 g/cm³ and a melt index of 1.85 g/10 min. (ASTM D 1238 at 190°C/2.16 kg); and a substantially random ethylene-styrene-interpolymer (ESI) (nominal styrene content = 40 wt. percent; melt index = 0.6 g/10 min. (ASTM D 1238 at 190°C/2.16 kg)) into the extruder at a weight ratio of PS/LDPE/ESI of 40/50/10, along with other formulation additives. The additives include a commercial antioxidant IRGANOX™ 1010 (tetrakis [methylene (3,5-di-tert- butyl-4-hydroxyhydrocinnamate)] methane which is a trademark and product of Ciba Geigy Corporation). The brominated cycloalkane compound hexabromocyclododecane (HBCD) is fed as powder directly into the extruder. Hexabromocyclododecane containing about 75 wt percent bromine and is available from The Albemarle Corporation under the trademark SAYTEX™ HP-900. The aromatic brominated compound bis(2,3 dibromopropyl ether) of tetrabromobisphenol- A is fed into the line through a polyethylene masterbatch containing 10 or 30 percent pure flame retardant. FR-PE-68™ is a brominated fire retardant having 68 wt percent and bromine content (tetrabromobisphenol A bis (2,3-dibromopropyl ether) 30 percent concentrate in LDPE) and is a trademark of and available from The Great Lakes Chemical Corporation. Flame retardant synergists antimony trioxide (Sb₂0₃) and chlorinated paraffin are also fed into the line through a polyethylene masterbatch. The quantity of flame retardant and other additives used in the formulation is reported in Table 1 in parts by weight per hundred parts by weight of total resin (phr).

The polymer melt is conveyed to the mixing zone of the process, where iso-butane as blowing agent is injected and mixed therein to form a foamable gel. The foamable gel is conveyed through a cooling zone at ambient temperature and then into a forming die of atmospheric pressure to expand and form the foam product. The foaming temperature is between 108°C and 110°C.

Formulation 2 and the foams for comparative samples A through F are prepared as described above except the ingredients for each formulation is as noted in Table 1 and the foaming temperature is 104°C and 110°C. When additives such as nucleator talc, and extrusion aid calcium stearate are employed, these additives are added to the extruder along with the polymer feedstock. The control foams (comparative samples A and B) are produced without flame retardants. Comparative samples C, D, and E are produced with only brominated alkane fire retardant (HBCD) and with flame retardant synergists. The addition of high levels of HBCD increases nucleation, causing cell size to drop. Comparative sample F is produced with only aromatic brominated fire retardant (tetrabromo bisphenol-A bis(2,3-dibromopropyl ether)) and with flame retardant synergists. Comparative sample F exhibits serious processing problems in that the use of high levels of tetrabromo bisphenol-A bis(2,3 -dibromopropyl ether) results in severe degradation of the polymer and product performance. If the concentration of this aromatic flame retardant is too high, then the polymeric resin composition is not foamable. The fire test results on Table 1 show that only the use of a combination of both alkane and aromatic fire retardants (as in formulations 1 and 2) results in foams able to pass the German B2 fire test according to Deutsche Industrienorm (DIN) 4201.

The results show that formulations employing a flame retardant package with both a brominated alkane compound and an aromatic brominated compound results in better overall flame resistance than formulations employing a brominated alkane compound alone or employing an aromatic brominated compound alone. Table 1

(a) : % : percent of the total polymer (b) : phr = parts per hundred parts of resin

(c) : German fire resistance test B2 according to DIN420: The foam passes the test if the flame height does not reach 15 cm.

(d): n.m. : not measured

Example 2

Example 1 is repeated with the exception that the apparatus comprises an 8 inch (200mm) extruder, a mixer, a cooling zone, and foam sheet die in series. The composition of formulations 1-3 is shown in Table 2. A control foam is produced without flame retardant and is shown for comparison. Process conditions and properties of the resulting foams are presented in Table 2. The foaming temperature is 108-110°C.

The ESI employed in this example is a commercially available substantially random ethylene styrene interpolymer with a nominal styrene content of (40 wt percent) and a melt index of 0.6 g/10 min. (according to ASTM D-1238, 190°C/2.16 kg). In the control foam without flame retardant, strong corrugation occurs which prohibits production of thin foam sheet. An 11.5 mm foam sheet is produced with the control formulation. The results in Table 2 show that the use of flame retardant, as specified in the present invention, allows production of foam sheets without corrugation. A wider range of thickness, including thin foam sheets, is also achievable.

Formulation 1 in Table 2 also shows that for a given set of parameters (such as polymer blend composition, concentration of blowing agent, concentration of nucleators, and foaming temperature) adding a two-part flame retardant package to a three-part polymer blend as described herein results in less corrugation of the foam sheet than extruding the same polymer system without the flame retardant. Table 2 also shows that, for the same parameters, use of the flame retardant package results in foams having lower density than foams having the same polymer composition without a flame retardant. This finding is unusual and beneficial because, typically, decreasing the foam density increases the corrugation. Thus, it is usually difficult to decrease foam density and to minimize corrugation simultaneously.

Table 2

^!'lb/h" means "pounds per hour"

Claims

1. A foam of a polymeric resin composition comprising: a) a polymer blend including: at least one alkenyl aromatic polymer, at least one α-olefin polymer and, optionally, a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer; and b) a compatibilizing amount of a flame retardant package including: a halogenated alkane flame retardant, an aromatic halogenated flame retardant, and optionally a flame retardant synergist.

2. The foam of claim 1 wherein the polymer blend includes the polymeric compatibilizer.

3. The foam of claim 1 or claim 2, wherein the alkenyl aromatic polymer is polystyrene; and the α-olefin polymer is polyethylene or polypropylene.

4. The foam of claim 2, wherein the polymeric compatibilizer is a copolymer of styrene and ethylene.

5. The foam of claim 2, wherein the alkenyl aromatic polymer is polystyrene; the α-olefin polymer is polyethylene or a copolymer of ethylene and up to about 15 percent of another α-olefin; and the polymeric compatibilizer is a copolymer of styrene and ethylene.

6. The foam of any of claims 1 to 5, wherein the halogenated alkane flame retardant comprises hexahalocyclododecane; tetrabromocyclooctane; pentabromochlorocyclohexane; l,2-dibromo-4-(l,2-dibromoethyl)cyclohexane; 1,1,1,3-tetrabromononane; or a combination thereof.

7. The foam of any of claims 1 to 6, wherein the aromatic halogenated flame retardant comprises one or more of hexahalodiphenyl ethers; octahalodiphenyl ethers; decahalodiphenyl ethers; decahalobiphenyl ethanes; l,2-bis(trihalophenoxy) ethanes; l,2-bis(pentahalophenoxy) ethanes; a tetrahalobisphenol-A; ethylene(N, N')-bis-tetrahalophthalimides; tetrabromobisphenol-A bis (2,3-dibromopropyl ether; tetrahalophthalic anhydrides; hexahalobenzenes; halogenated indanes; halogenated phosphate esters; halogenated polystyrenes; polymers of halogenated bisphenol-A and epichlorohydrin; or a combination thereof.

8. The foam of any of claims 1 to 7, wherein the flame retardant synergist comprises one or more of a metal oxide, halogenated paraffin, triphenylphosphate, dimethyldiphenylbutane, polycumyl, or a combination thereof.

9. The foam of any of claims 1 to 8, wherein the polymeric resin composition includes:

100 parts by weight of the polymer blend; from about 0.5 to about 8 parts by weight halogenated alkane flame retardant; from about 0.5 to about 8 parts by weight aromatic halogenated flame retardant; from 0 to about 6 parts by weight flame retardant synergist.

10. The foam of claim 1 wherein the polymer blend is free of polymeric compatiblizer.

11. The foam of any of claims 1 to 9, wherein the combined weight of the alkenyl aromatic polymer, α-olefin polymer and polymeric compatibilizer includes: about 10-90 percent by weight alkenyl aromatic polymer, about 10-90 percent by weight α-olefin polymer, and about 0.1-50 percent by weight of said polymeric compatibilizer.

12. The foam of claim 2, 9 or 11 wherein

A) the alkenyl aromatic polymer is polystyrene;

B) the α-olefin polymer is polyethylene or polypropylene; C) the polymeric compatibilizer is an ethylene/styrene interpolymer;

D) the halogenated alkane flame retardant is hexahalocyclododecane; hexabromocyclododecane; tetrabromocyclooctane; pentabromochlorocyclohexane; l,2-dibromo-4- (l,2-dibromoethyl)cyclohexane; 1,1,1,3-tetrabromononane; or a combination thereof;

E) the aromatic halogenated flame retardant is one or more of hexahalodiphenyl ethers; octahalodiphenyl ethers; decahalodiphenyl ethers; decahalodiphenyl ethanes; 1,2- bis(trihalophenoxy) ethanes; l,2-bis(pentahalophenoxy) ethanes; a tetrahalobisphenol-A; ethylene(N, N')-bis-tetrahalophthalimides; tetrabromobisphenol-A bis (2,3-dibromopropyl ether); tetrahalophthalic anhydrides; hexahalobenzenes; halogenated indanes, halogenated phosphate esters; halogenated polystyrenes; polymers of halogenated bisphenol-A and epichlorohydrin; or a combination thereof; and

F) the flame retardant synergist comprises one or more of a metal oxide, halogenated paraffin, triphenylphosphate, dimethyldiphenylbutane, polycumyl, or a combination thereof.

13. The foam of any of claims 1-9 or 12 wherein the combined weight of the alkenyl aromatic polymer, α-olefin polymer and polymeric compatibilizer includes: about 30-70 percent by weight alkenyl aromatic polymer, about 70-30 percent by weight α- olefin polymer, and about 2-20 percent by weight of said polymeric compatibilizer.

14. The foam of any of claims 1 to 13 wherein the foam is in the form of a sheet having a thickness of from about 1 to about 100 mm.

15. The foam of any of claims 1 to 13 wherein the foam is in the form of a sheet having a thickness of < 20 mm.

16. The foam of any of claims 1 to 15 wherein the foam is corrugation-free.

17. The foam of any of claims 1 to 16, wherein the foam has a density of about 10 to about 100 kg/m³.

18. The foam of any of claims 1 to 17, wherein the foam has a density of less than about 40 kg/m³.

19. The foam of any of claims 1 to 18 wherein the foam is acoustic foam.

20. The foam of claim 15 having a dynamic stiffness of less than about 500 MN/m³ at a thickness of 3-20 mm.

21. The foam of any of claims 1 to 20 having a cell size of from about 0.1 to about 5 mm.

22. A polymeric foam prepared by the process which comprises mixing a polymeric resin composition with a blowing agent to form a foamable gel, and expanding the foamable gel to form the foam, wherein the polymeric resin composition comprises: a) at least one alkenyl aromatic polymer, b) at least one α-olefin polymer, c) an effective amount of a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer, d) at least one halogenated alkane flame retardant, e) at least one aromatic halogenated flame retardant, and f) optionally a flame retardant synergist.

23. A polymeric resin composition comprising: a) at least one alkenyl aromatic polymer, b) at least one α-olefin polymer, c) an effective amount of a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer, d) at least one halogenated alkane flame retardant, e) at least one aromatic halogenated flame retardant, and f) optionally a flame retardant synergist.

24. A method of producing a flame retardant foam, the method comprising: introducing a blowing agent into a polymeric resin composition to form a foamable gel, wherein the polymeric resin composition comprises: a) at least one alkenyl aromatic polymer, b) at least one α-olefin polymer, c) an effective amount of a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer, d) at least one halogenated alkane flame retardant, e) at least one aromatic halogenated flame retardant, and f) optionally a flame retardant synergist; and expanding the foamable gel to form the foam.

25. The method of claim 24, wherein A) component a) is polystyrene;

B) component b) is polyethylene or polypropylene;

C) component c) is an ethylene/styrene interpolymer;

D) component d) is hexahalocyclododecane; tetrabromocyclooctane; pentabromochlorocyclohexane; 1 ,2-dibromo-4-(l ,2-dibromoethyl)cyclohexane; 1,1,1 ,3-tetrabromononane; or a combination thereof;

E) component e) is one or more of hexahalodiphenyl ethers; octahalodiphenyl ethers; decahalodiphenyl ethers; decahalodiphenyl ethanes; l,2-bis(trihalophenoxy) ethanes; 1,2- bis(pentahalophenoxy) ethanes; a tetrahalobisphenol-A; ethylene(N, N')-bis-tetrahalophthalimides; tetrabromobisphenol-A bis (2,3-dibromopropyl ether); tetrahalophthalic anhydrides; hexahalobenzenes; halogenated indanes; halogenated phosphate esters; halogenated polystyrenes; polymers of halogenated bisphenol-A and epichlorohydrin; or a combination thereof; and

F) component f), when present, is one or more of a metal oxide, halogenated paraffin, triphenylphosphate, dimethyldiphenylbutane, polycumyl, or a combination thereof.

26. The method of claim 24 or claim 25 wherein the polymeric resin composition includes

100 parts by weight of components a), b), and c) combined; from about 0.5 to about 8 parts by weight halogenated alkane flame retardant; from about 0.5 to about 8 parts by weight aromatic halogenated flame retardant; and from 0 to 6 parts by weight flame retardant synergist; wherein said 100 parts includes about 10-90 parts component a), about 10-90 parts component b), and about 0.1-50 parts component c).

27. The method of any of claims 24 to 26 wherein the foam has an original thickness, and the method further comprises the step of applying a compressive force to the foam to compress the foam to about 90 percent of the original thickness, and releasing the compressive force.

28. A method for improving the processability of a foam made from a blend of at least one alkenyl aromatic polymer and at least one α-olefin polymer, the method comprising mixing at least one halogenated alkane flame retardant and at least one aromatic halogenated flame retardant with the blend.

29. Use of a combination of at least one halogenated alkane flame retardant and at least one aromatic halogenated flame retardant to improve the compatibility of a blend of at least one alkenyl aromatic polymer and at least one α-olefin polymer.

30. Use as acoustical insulation of the foam of any of claims 1 to 21.

31. Use as thermal insulation of the foam of any of claims 1 to 18 or claims 20 to 21.

32. Use of the foam of any of claims 1 to 21 as impact sound insulation.