FIELD OF THE INVENTION

The present invention generally relates to flame retardant styrene polymer compositions that have improved impact strength. The compositions additionally have flexural modulus and heat deflection properties similar to styrene polymer compositions not containing flame retardants.

BACKGROUND

Heretofore, whenever flame retardants were added to various thermoplastic polymers such as styrene resins, various physical properties were affected such as reduced impact strength. This is due to the fact that while imparting flame retardancy, the flame retar- dant causes embrittlement when added to produce the desired flame retardancy.

European Patent Applications 262,615 and 87/05615 to Haaf and Abolins, respectively, relate to flame retardant polyphenylene ether compositions and more specifically to compositions of a polyphenylene ether resin and a high impact polystyrene in which a post brominated polystyrene oligomer or polymer and antimony oxide are used in combination to impart better flame resistance, impact strength, and mold flow. IPO International Bureau 88/03542 relates to modified polyphenylene ether resins having improved flow properties and, in particular, it relates to modified polyphenylene ether resins incorporating a brominated al enyl aromatic resin, a diester of tetrabromophthalic acid, and a flame retardant enhancer such as antimony trioxide. Flame retardant polystyrenes have various applications in injection molded products such as television cabinets, television racks, business machine

housings, table-top and lap-top computers, smoke detec¬ tor housings and modular furniture including hospital furniture.

The compositions of the present invention are also useful especially for making other molded articles such as medical disposal boxes for the receipt, storage, and eventual disposal of contaminated medical products; for electrical boxes and connectors, electrical materi¬ als, and the like. While the impact properties of flame retardant polystyrene may be acceptable when the flame retardant is decabromodiphenyloxide without the use of a com- patibilizer, in a preferred embodiment of the inven¬ tion, the flame retardant excludes this composition and its analogs. These brominated diphenyl oxides may pyrolize to form furans which are potentially hazardous and environmentally toxic. Thus, it is preferred to use a flame retardant package of the present invention such as brominated polystyrene and to utilize the co - patibilizing agent to improve the impact properties.

SUMMARY OF THE INVENTION

Generally, when flame retardancy is imparted to styrene polymeric resins, impact strength is reduced due to the fact that the polymeric resins become embrit¬ tled. In the present invention the impact strength of the flame retardant polymer is further augmented by incorporating therein a compatibilizing agent comprising a block copolymer.

Thus, the present invention relates to a flame retardant package which comprises a flame retardant, a flame retardant synergist and an compatibilizing agent. In a preferred embodiment, the flame retardant is a brominated styrene polymer such as brominated polys¬ tyrene. The compatibilizing agent is a styrene butadi¬ ene block copolymer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises four com¬ ponents: a styrene polymeric resin, a flame retardant synergist, a flame retardant, and a compatibilizing agent or property enhancer.

Alternatively, this invention can be en¬ visioned as a two component system comprising the styrene polymer and a flame retardant package where the package comprises the flame retardant, the flame retar¬ dant synergist and the compatibilizing agent. Similar¬ ly, the blend compositions of the present invention can be blended in a one part or two part process. In the one part process, all of the ingredients are mixed in the same step although they may be etered at various points of the mastication process. In the two part process, two or more ingredients may be premixed such as the flame retardant package.

The styrene polymeric resins having utility in this invention comprises high impact polystyrene (HIPS) , polystyrene, poly-α-methylstyrene, polyvinyl naphtha¬ lene, styrene-acrylonitrile copolymer, styrene maleic anhydride copolymer, EPDM modified styrene acrylonitrile copolymer, styrene-acrylic copolymer, acrylonitrile- styrene-acrylic terpolymer, polystyrene-polyphenylene oxide blend, or acrylonitrile-butadiene-styrene graft copolymer. Of these, the preferred is high impact polystyrene. High impact polystyrene is understood in the art as a thermoplastic resin product from styrene monomer along with elastomers such as polybutadiene which are introduced into the polystyrene matrix.

Polystyrene homopolymers, polystyrene copoly- mers, or terpolymers or graft copolymers and blends thereof are preferred. The above-noted styrene polymer- ic resins are generally commercially available and have a weight average molecular weight of from about 100,000

to about 1,000,000 and preferably from about 200,000 to about 300,000.

The amount of the various flame retardants which are utilized are generally dictated by a desirable UL (Underwriters Laboratories, Inc.) 94 flammability rating. The UL 94 test is a vertical burning test. A material having a V-0 rating allows only minimal burning and no flaming drip of a standard bar of specified thickness. The V-l rating allows longer burn times than the V-0, but not flaming drip. The V-2 rating allows the same burn time as the V-l and also allows flaming drip. The fail rating is given any material not meeting the V-0, V-l, or V-2 criteria. The choice of the variously rated flame-retardant polystyrene resins depends upon the end use.

Compositions having UL9 ratings from V-0 to V-2 may be useful depending on the application. It may be preferable to achieve the V-0 rating for certain ap¬ plications. The styrene polymeric resins of the present invention contain a flame retardant synergist comprising antimony oxide or sodium antimonate. Its main function is to promote the flame retardancy properties of the flame retardant. The synergist is employed in effective amounts to improve the flame retardancy within the styrenic resin. Generally, an effective amount of synergist is from about 1 to about 8 parts, preferably from about 3 to about 7 parts and most preferably from about 4 to about 6 parts by weight per 100 parts by weight of the resin components.

Various flame retardants comprising hal-^ena- ted organic compounds are utilized in association with the antimony component. Examples of suitable halo- genated organic compounds include brominated dipen- taerithritol, tetrabromobisphenol A, ethylene-bistetra- bromophthalimide, ethylenebisdibromonorbornane-dicarbox- imide, tetrabromobisphenol A-bis(2,3-dibromopropyl

ether) , octabromodiphenyl oxide, hexabromocyclododec- ane, hexabromodiphenoxy ethane, decabromodiphenoxy ethane, decabromodiphenyloxide, tetradecabromodiphenoxy benzene, brominated polystyrene, tetradecabromodiphenyl- oxide, poly-dibromophenylene oxide, phenoxy terminated bisphenol A carbonate oligomers containing from about 50 to about 60 percent bromine, brominated epoxy resins containing from about 30 to about 60 percent bromine, and mixtures thereof. Brominated organic compounds which are especially preferred comprise brominated polystyrene, hexabromocyclododecane, ethylene-bistetra- bromophthalimide and ethylene dibromonorbornane-dicar- boximide.

In a preferred embodiment of the invention, the flame retardant excludes brominated diphenyl oxides such as octabromodiphenyl oxide, decabromodiphenyl oxide, tetradecabromodiphenyl oxide, poly-dibro aphenyl- ene oxide and the like. The flame retardant is thus preferably brominated polystyrene such as a high olecu- lar weight and low molecular weight brominated polysty¬ rene. The high molecular weight brominated polystyrene is generally understood to have a molecular weight of from about 100,000 to about 400,000, while the low molecular weight brominated polystyrene is generally understood to have a molecular weight of from about 1,000 to about 20,000. At the present time those brominated polystyrenes having a molecular weight between 20,000 and 100,000 could fall into either category and therefore should be understood to be encompassed in the present invention.

Also incorporated into the styrene resin is a compatibilizing agent which functions to improve the impact properties of the blend. Further, this com¬ patibilizing agent could be termed a property enhancer. The compatibilizing agent is preferably a copolymer of styrene and butadiene or isoprene. This copolymer is preferably a block copolymer having a diblock, triblock.

multi-block or a star radial composition. The block copolymer is a styrene-butadiene copolymer having generally a butadiene content of from about 20 percent to about 80 percent and a styrene content of from about 80 percent to about 20 percent. Preferably the buta¬ diene is from 35 to 65 percent, most preferably it is from 40 to 60 percent with the styrene comprising the remainder.

The compatibilizers are commercially available having various styrene-butadiene levels. Available from Shell Oil Co. is a material having about 75 percent butadiene and about 25 percent styrene under the name Kraton® D. Other impact modifiers include partially hydrogenated styrene butadiene or isoprene block copoly- mers (for example, Kraton® G) and functionalized block copolymers (for example, raton® GF 1901) . Both Fina and Firestone market a 50 percent butadiene and 50 percent styrene under the name Finaprene® and Stereon®, respectively. Phillips Petroleum markets a material having about 25 percent butadiene and 75 percent styrene under the name K-resin. The intermediate block copolym¬ er employed in this invention has a butadiene-styrene content of about 50:50 and gave unexpected results. The terms diblock, triblock, multiblock or star radial copolymers are understood in the art as is illustrated in the Encyclopedia of Polymer Science and Engineering. Volume 2, 1985, pp. 325-326, published by John Wiley & Sons, New York, incorporated herein by reference. In particular, the multiblock copolymers are understood to have an A _je -B- _a 'A _jj -B^A _jj -B, _^ type of structure. Stereon is an example of such a product. Further, this product has a desirable ratio of styrene to butadiene in the range of around 40/60 and a desirable weight average molecular weight of from about 50,000 to 100,000, and more par- ticularly 75,000 to 95,000. The amount of compat¬ ibilizing agent generally ranges from about 1 to about 18 and preferably from about 4 to about 15 and most

preferably from about 6 to about 12 for every 100 parts by weight of the styrene resin.

While obtaining a polymer composition meeting UL 94 V-0 criteria, the polymer composition also has an acceptable impact strength. Typically, the compatibil¬ izing agent imparts a notched Izod impact strength improvement of at least about 10 percent, preferably about 20 percent, and most preferably >30 percent over a comparable flame retardant polymer composition not containing the compatibilizing agent.

These compositions have improved Gardner and Izod impact values and similar heat deflection and flexural modulus values. The latter are unexpected because normal addition of traditional impact modifiers such as styrene-butadiene rubbers or ethylene-propylene rubbers reduces heat deflection and flexural modulus significantly. In the present invention, those values remain unexpectedly high. In particular, the composi¬ tions have superior heat deflection properties. All of these improvements are believed to indicate an improved morphological compatibility of the various components of this system, the mechanics of which are not fully understood.

The composition of this invention can also contain various traditional additives in conventional amounts. For example, various fillers and pigments can be added such as talc, calcium carbonate, bentonite, wollastonite, clay, silica, magnesium carbonate, dolo¬ mite, glass fibers, carbon black, titanium dioxide and other pigments, and the like. The amounts of said fillers generally range from about l to about 40 and desirably from about 1 to about 30 for every 100 parts by weight of the styrene resin. Various antioxidants, blowing agents, light stabilizers, lubricants, proces- sing aids, and the like, well known to the art and to the literature, can also be utilized when desired generally in small amounts as up to about 5 parts by

weight for every 100 parts by weight of the polystyrene- based polymer.

The composition of the present invention is prepared in a processing device, such as an extruder, for example, a twin-screw or a single-screw extruder, an intensive mixer, a continuous mixer, a Buss kneader, or the like. As previously discussed, the composition can be compounded in a one step process or a two step process in which a premix is formed. Customarily, the processing device should be operated at a temperature sufficient to melt the styrene resin polymer which naturally will vary with molecular weight. On the other hand, the temperature should not exceed the degradation temperature of any of the components. Usually, tempera- tures of from about 250°F to about 500°F can be util¬ ized, with from about 400°F to about 450°F being pre¬ ferred. The torque parameters of the processing device should be fairly sufficient to masticate the styrene resin and generally has from moderate to high torque. Shear rates vary from 300 to 5,000 sec-1, and preferably from 3,000 to 4,500 sec-1. Typically, all of the various components forming the flame retardant styrene resin composition of the present invention are added together to the processing device wherein they are mixed and blended to obtain said composition. Alternatively, a master batch of flame retardant and compatibilizing agent and optionally the flame retardant synergist are premixed to give a master batch and a portion of the master batch is then added to the styrene resin (and respectively, if necessary, the flame retardant syner¬ gist) to form the composition of this invention.

Generally, for every 100 parts by weight of styrene resin there is employed from about 1 to about 8 parts flame retardant synergist, from about 10 to about 25 parts flame retardant and from about 1 to about 18 parts compatibilizing agent. Preferably, for every 100 parts by weight of styrene resin, there is employed from

about 3 to about 7 parts flame retardant synergist, from about 14 to about 22 parts flame retardant and from about 4 to about 15 parts of compatibilizing agent. Most preferably, for every 100 parts by weight of styrene resin, there is employed from about 4 to about 6 parts flame retardant synergist, from about 16 to about 20 parts flame retardant, and from about 6 to about 12 parts of compatibilizing agent.

EXAMPLES

The following tables illustrate the prepara¬ tion and evaluation of flame retardant compositions of the present invention. Various HIPS resins are utilized in the following tables. The HIPS resins employed are not only from different manufacturers, but also have different styrene-butadiene content. The flame retar¬ dant is a brominated polystyrene of either a high molecular weight (Mw«300,000) identified as Pyro-Chek® 68PB or a low molecular weight (Mw«3000) identified as Pyro-Chek® LM. Both are available from The Ferro Corpo¬ ration. The compatibilizing agents are identified in the tables. One such preferred composition is a styrene-butadiene-styrene block copolymer having a weight average molecular weight of «85,000 with the name Stereon® 840A, available from The Firestone Tire & Rubber Company.

The compounding of the flame-retardant styrene resin compositions described herein was carried out in a standard counter-rotating twin-screw extruder (34mm American Leistritz) . The starting material was intro¬ duced into the extruder in the indicated amounts through a funnel; compounding was continuous with the screws being operated at 100 rp and the temperature being maintained at or below 460°F. The flame retardant polystyrene resin was extruded through a two-hole die into a water bath, then air-dried and chopped into pellets about 1/8" long and 3/16" in diameter. The

compositions were also processed where indicated in a Banbury mixer at a temperature of 250°-320°F and a shear rate of 200 to 5,000.

The pellets were then processed in a Van Dorn injection older having a 6-ounce shot capacity and a

110-ton clamping capacity. Various configuration specimens were molded to carry-out the tests described in Tables I through IX.

The physical properties described in the following examples are obtained in accordance with ASTM or UL standard test procedures as identified below: PROPERTY TEST PROCEDURE

Tensile Strength ASTM D-638

Elongation ASTM D-638 Flexural Modulus (tangent) ASTM D-790

Izod Impact (Notched) ASTM D-256

(Method A)

Izod Impact (Unnotched) ASTM D-256

Gardner Impact ASTM D-3029 Heat Deflection Temperature ASTM D-648

Flame Resistance UL 94

TABLE I

COMPOSITION; 1 2 3 4 5

HIPS RESIN (ASAHI V-O) 100 81 79.5 76.5 73.5

Pyrocheck LM (Ferro) 15 15 15 15

Sb-O, (Thermoguard S, M & T) 4 4 4 4

Stereon 840A (Firestone) 1.5 4.5 7.5

PHYSICAL PROPERTIES!

Elongation at Break (%)

Flexural Modulus, Kpsi

Izod Impact, Notched (ft-lb/in)

Izod Impact, Unnotched (ft-lb/in)

Gardner Impact (in-lb)

Heat Deflection Temp, at 264 psi, C

UL-94 1/8"

1/16"

1/32"

EXAMPLE 1: USE OF STEREON 840A TO IMPROVE IMPACT WHILE SUBSTANTIALLY MAINTAINING HDT AND FLEXURAL MODULUS

COMPOSITION;

HIPS RESIN (Huntsman 840) 78 76.5 73.5 Pyrocheck LM (Ferro) 15 15 15 Sb-O, (Thermoguard S, M & T) 4 4 4 Stereon 840A (Firestone) 3.0 4.5 7.5

PHYSICAL PROPERTIES;

Flexural Modulus, Kpsi

Izod Impact, Notched (ft-lb/in)

Izod Impact, Unnotched (ft-lb/in)

Gardner Impact (in-lb)

Heat Deflection Temp, at 264 psi, C

UL-94 1/8"

1/16"

1/32"

EXAMPLE 2: USE OF STEREON 840A TO IMPROVE IMPACT WHILE SUBSTANTIALLY MAINTAINING HDT AND FLEXUP MODULUS

TABLE III

COMPOSITION;

HIPS RESIN (Huntsman 840) 81 77.25 73.5 Pyrocheck 68 PB (Ferro) 15 15 15 Sb_0_ (Thermoguard S, M & T) 4 4 4 Stereon 840A (Firestone) 3.75 7.5

PHYSICAL PROPERTIES;

Flexural Modulus, Kpsi

Izod Impact, Notched (ft-lb/in)

Izod Impact, Unnotched (ft-lb/in)

Gardner Impact (in-lb)

Heat Deflection Temp, at 264 psi, C

UL-94 1/8"

1/16"

1/32"

EXAMPLE 3: USE OF STEREON 840A TO IMPROVE IMPACT WHILE SUBSTANTIALLY MAINTAINING HDT AND FLEXURAL MODULUS

COMPOSITION;

HIPS RESIN (Dow 475U)

Pyrocheck 68 PB (Ferro)

Sb,0, (Ther oguard S, M fi T)

Talc (Jet Fill 100, Steetley)

Kraton D-1101 (Shell)

HIPS Resin (Dow 492U)

PHYSICAL PROPERTIES;

Elongation, Break (%)

Flexural Modulus, Kpsi

Izod T-mpact, Notched (ft-lb/in)

Izod Impact, Unnotched (ft-lb/in)

Gardner Impact (in-lb)

Heat Deflection Temp, at 264 psi, C

EXAMPLE 4: USE OF KRATON D-1101 TO IMPROVE IMPACT OF FILLED SYSTEMS WHILE MAINTAINING HDT

TABLE V

COMPOSITION;

HIPS RESIN (Huntβman 840) Talc (Cantal 45-90, Cantal) Sb,0, (Thermoguard S, M & T) Pyrocheck 68 PB (Ferro) Kraton D-1101 (Shell) Stereon 840A (Firestone) 7.5 K Resin KR-01 (Phillips) 7.5

PHYSICAL PROPERTIES;

Elongation, Break (%) Flexural Modulus, Kpsi Izod Impact, Notched (ft-lb/in) Izod Impact, Unnotched (ft-lb/in) Gardner Impact (in-lb) Heat Deflection Temp, at 264 psi, UL-94 1/16" 1/32"

EXAMPLE 5: USE OF THREE TYPES OF BLOCK COPOLYMERS TO IMPROVE IMPACT PROPERTIES WHILE MAINTAINING HDT AND MODULUS PROPERTIES

TABLE VI

COMPOSITION;

HIPS RESIN (Huntsman 840)

Pyrocheck LM (Ferro)

Sb ₂ θ, (Thermoguard S, M & T)

Stereon 840A (Firestone)

Talc (Cantal 45-90 Cantal)

Talc (Select-A-Sorb, R.T. Vanderbilt) 10.0

PHYSICAL PROPERTIES;

Elongation, Break (%) 22.0 34.0 28 27

Flexural Modulus, Kpsi 431 295 308 296

Izod Impact, Notched (ft-lb/in) 0.5 1.9 1.4 1.2

Izod Impact, Unnotched (ft-lb/in) 2.2 5.8 4.8 4.5

Gardner Impact (in-lb) 3 16 15 14

Heat Deflection Temp, at 264 psi, C 90 88 87 87

UL-94 1/32" V-O V-0 V-0 V-O

EXAMPLE 6; USE OF INEXPENSIVE FILLER (TALC) WHILE MAINTAINING KEY PHYSICAL PROPERTIES OF FLAME RETARDANT HIPS COMPOSITIONS CONTAINING BLOCK COPOLYMER

TABLE VII

COMPOSITION; B.M. T.S.

HIPS RESIN (Huntsman 840) 81.0 81.0 Pyrocheck 68 PB (Ferro) 15.0 15.0 Sb_0_ (Thermoguard S, M & T) 4.0 4.0 Stereon 840A (Fireβtone)

PHYSICAL PROPERTIES;

Elongation, Break (%)

Flexural Modulus, Kpsi

Izod Impact, Notched (ft-lb/in)

Izod Impact, Unnotched (ft-lb/in)

Gardner Impact (in-lb)

Heat Deflection Temp, at 254 psi, C

UL-94 1/32" V-O V-0

EXAMPLE 7; EFFECT OF PROCESSING ON IMPACT PROPERTIES OF FLAME RETARDANT HIPS COMPOSITIONS (T.S. ~- Twin Screw Extruder & B.M. ^~~ Banbury Mixer)

TABLE VIII

COMPOSITION; 1 2

HIPS RESIN (Huntsman 840) 81.0 81.0 Sb-O, (Thermoguard S, M & T) 4.0 4.0 Stereon 840A (Firestone) 7.5 7.5 Pyrochek 68 PB (Ferro) 15.0 Pyrocheck LM (Ferro) 15.0

PHYSICAL PROPERTIES;

Tensile Strength

Flexural Moduluβ, Kpsi

Izod Impact, Notched (ft-lb/in)

Izod Impact, Unnotched (ft-lb/in)

Gardner Impact (in-lb)

EXAMPLE 8: EFFECT OF BLOCK COPOLYMER IN FLAME RETARDANT HIPS COMPOSITIONS (PYROCHECK 68 PB VS. LM)

TABLE IX

COMPOSITION;

HIPS RESIN (Huntsman 840) 81.0 76.0 76.0 76.0 76.0 76.0

Pyrocheck 68 PB (Ferro) 15.0 15.2* 15.2* 15.2* 15.2* 15.2*

Sb_0_ (Thermoguard S, M & T) 4.0 4.0 4.0 4.0 4.0 4.0

Kraton G-1651 (Shell) 4.8* 3.6*

Kraton G-1901 F (Shell) 1.2* 4.8*

KR-03 (Phillips) 4.8* 4.8*

CR-10 Peroxide concentrate, Polyvel) 0.05

PHYSICAL PROPERTIES;

Flexural Modulus, Kpsi

Izod Impact, Notched (ft-lb/in)

Izod Impact, Unnotched (ft-lb/in)

Gardner Impact (in-lb)

Heat Deflection Temp, at 264 psi,

UL-94 1/8"

1/16"

1/32"

EXAMPLE 9: EFFECT OF MISCELLANEOUS COMPATIBILIZERS IN FLAME RETARDANT HIPS COMPOSITIONS (*Pre-mixed together in a Banbury Mixer).

Table I illustrates a significant improvement in elongation and impact values with the addition of the compatibilizing agent while maintaining heat deflection temperatures and flexural modulus and, of course, achieving the desired flame retardancy through the use of a low molecular weight brominated polystyrene.

Table II illustrates a similar effect with a different high impact polystyrene resin and also through the use of the low molecular weight brominated poly- styrene.

Table III illustrates the effect with the same resin used in Table II, but with the high molecular weight brominated polystyrene flame retardant.

Table IV illustrates two additional resins and an additional compatibilizing agent. These samples further illustrate similar performance characteristics even in the presence of filler.

Table . shows three separate block copolymers as compatibilizing agents used in comparable resin systems. This data illustrates that Stereon® 840A is a preferred compatibilizing agent to improve impact properties.

In Table VI, the use of Stereon 840A is illustrated as improving impact properties and maintain- ing heat deflection, even in the presence of fillers, such as talc.

Table VII illustrates the effect of processing equipment on the present invention showing the improve¬ ments in impact properties for systems blended in both Banbury mixers and twin screw extruders. It is noted that the data set forth in this Table was collected from four different studies designed to show the significance of processing conditions on the present invention.

Table VIII illustrates the use of two differ- ent flame retardants in the same resin system.

Table IX illustrates the effect of various compatibilizing agents used in a pre-mix with the flame

retardant. It also illustrates the use of a peroxide to further improve impact properties.

While in accordance with the Patent Statutes, the best mode and preferred embodiment has been set forth, the scope of the invention is not limited there¬ to, but rather by the scope of the attached claims.