Flame-retarded, high-impact-strength styrene polymer formulations

Abstract: The impact strength of articles made from a flame-retarded formulated HIPS or ABS resin containing an impact modifier is increased by preparing the articles from a formulation obtained by forming a concentrate or masterbatch containing the flame retardant and impact modifier and blending the concentrate with HIPS or ABS resin.

Description: Field of Invention This invention relates to thermoplastic synthetic resin formulations, especially HIPS (high impact polystyrene) and ABS (acrylonitrile-butadiene-styrene) resins flame-retarded with at least one brominated organic flame retardant, as well as a method for producing the formulations. Background HIPS and ABS resins are well known rubber-modified styrenic polymers which offer excellent mechanical properties as well as good chemical resistance. To modify their properties, the polymers are typically compounded with various additives, such as impact modifiers, stabilizers, processing aids, pigments, and synergists, which may constitute up to about 50% of the formulated resins. The additives may be incorporated into the resins in various ways. For example, solid additives may be dry-blended with the resins by mixing the solids, heating to soften and homogenize the mass, and then sheeting, chopping, and pelletizing the formulation. Incorporation of the various additives is not a trivial matter, and the properties of articles made from the formulated resin can be affected by the manner in which it is done. A flame retardant, such as a halogenated organic compound, is often incorporated into a formulated HIPS or ABS resin so as to constitute as much as about 30 wt% of the formulation. Such incorporation can adversely affect the properties, other than the flammability, of the formulated resin. For example, a flame retardant having a high melting point range, such as decabromodiphenylethane or decabromodiphenyl oxide, will have a filler-type effect on the resin formulation, whereas a flame retardant having a lower melting point range will have a plasticizer effect. Because of the effect flame retardants have on articles made from such resin formulations, improvements in such formulations and formulation techniques are highly desirable and of significant commercial importance. FR-A-2 343 015 discloses to form a granulate from a flame-retardant and a thermoplastic compound to facilitate the production process using these flame-retardants. Summary of Invention It has been found that a significant net increase in the impact strength of articles prepared from a flame-retarded HIPS or ABS resin can be provided by incorporating the flame retardant via a concentrate, or masterbatch, which is a homogeneous blend comprising the flame retardant and a polymeric impact modifier and optionally also containing other additives ad/or a minor amount of HIPS or ABS resin sufficient to provide a homogeneous blend of the masterbatch components. When a flame-retarded formulation comprising (A) at least 50 wt% HIPS resin, 5-25 wt% halogenated flame retardant, 1-12 wt% polymeric impact modifier, and 0-6 wt% flame retardant synergist or (B) at least 50 wt% ABS resin, 5-30 wt% halogenated flame retardant, 8-38 wt% polymeric impact modifier, and 0-6 wt% flame retardant synergist is prepared by such a masterbatching process in which the concentrate is formed and dry blended with the HIPS or ABS resin, articles made from the formulation have enhanced IZOD impact strength as determined by ASTM D 256-88. In fact, it has surprisingly, and quite unexpectedly, been found that the IZOD impact strength of such articles is dramatically increased over that of articles prepared from comparable formulations in which the ingredients are combined without initially forming a concentrate or masterbatch of the flame retardant and impact modifier. Detailed Description The HIPS resins formulated in the practice of the invention are rubber-modified polymers or copolymers of styrenic compounds, such as styrene, α-alkylstyrenes, and the ar-halo- and ar-alkyl-substituted derivatives thereof. Although preparable in other ways, they are usually obtained by polymerizing one or more styrenic compounds in the presence of an elastomer, such as polybutadiene, or an elastomer-forming monomer, such as butadiene, to form a graft or block copolymer. When the resin component of the formulation is HIPS, it can be selected from the many resins available in commerce. Such resins include the Dow Styron® resins, for example, which are styrene/butadiene copolymers. The HIPS resin component of the formulated HIPS resin of this invention comprises at least 50 wt%, usually at least about 65 wt% of the formulation and can comprise as much as about 85 wt% of the formulation. The ABS resins formulated in the practice of the invention are the known thermoplastics which include acrylonitrile, butadiene, and styrene structural units in various chemical combinations; generally comprise a rigid styrene/acrylonitrile continuous phase in combination with a polybutadiene disperse phase; and frequently contain a graft copolymer of small amounts of styrene and acrylonitrile on polybutadiene chains to bridge the rigid and elastomer phases. When the resin component of the formulation is ABS, it can be selected from the many resins available in commerce. Such resins include GE Cycolac® resins, Monsanto Lustran® resins, and Dow Magnum® resins, for example. The ABS resin component of the formulated ABS resin of this invention comprises at least about 50 wt% of the formulation and can comprise as much as about 70 wt% of the formulation. One of the additives which will be present in the formulated resin of this invention is one or more flame retardants, and halogenated flame retardants have been recommended and employed in that application. Halogenated flame retardants especially useful in the practice of this invention are selected from the group consisting of tetrahalobisphenol-A, N,N'-bis(tetrahalophthalimide), N,N'-ethylenebis(terahalophthalimide), halogenated polystyrene, and pentahalobenzyl acrylate, in all of which halo is selected from chloro and bromo, and also bis-halophenyl compounds represented by the following structural formula which are solids at ambient temperature: in which formula each X is selected independently from chlorine and bromine; m and n can be the same or different and can range from 1 to 5; Y is selected from oxygen, alkylene, -NR- (where R is selected from hydrogen and hydrocarbyl), alkylenedioxy, aryldioxy, and a chemical bond. Alkylene is preferably lower alkylene, i.e., straight chain or branched C₁-C₆, such as methylene, ethylene, isopropylene, butylene, and t-butylene ―methylene or ethylene being preferred. Hydrocarbyl includes alkylene, especially lower alkylene, but also unsaturated alkylene and aromatic groups such as phenyl and alkylphenyl or halophenyl. Alkylenedioxy includes,-e.g., methylenedioxy and 1,2-dioxyethylene, while aryldioxy includes dioxyphenyl, for example. In the preferred flame retardants, halo and X are bromo. Among the aforesaid flame retardants the bis-halophenyl compounds are preferred, and among these compounds, decabromodiphenyl oxide, decabromodiphenyl ethane, 1,2-bis(tribromophenoxy)ethane, and decabromodiphenyl amine are especially attractive. In addition to one or more halogenated flame retardants, the formulated resin of this invention optionally includes up to about 6 wt%, e.g, 2-6 wt%, of a flame retardant synergist. A number of materials, such as metal oxides (e.g., iron oxide. tin oxide, zinc oxide, aluminum trioxide, alumina, antimony tri- and pentoxide) and metal hydroxides and boron compounds (e.g., zinc borate), as well as antimony silicates and ferrocene, are known to enhance the effectiveness of flame retardants, especially halogenated flame retardants. A particularly effective and preferred synergist is antimony trioxide. The flame retardant synergist can be combined with the flame retardant and impact modifier in the concentrate or masterbatch, or the synergist can be admixed with the resin component of the formulation. In addition to flame retardant, the formulated HIPS of this invention includes one or more polymeric impact modifiers. It is well known that the addition of certain materials to an ABS or HIPS resin tends to toughen articles molded therefrom. Among these materials are styrene/butadiene/styrene triblock copolymer, styrene/isoprene/styrene triblock copolymer, styrene/butadiene diblock copolymer, polycaprolactone, and functionalized ethylene/propylene copolymers, and ― in the case of ABS resins ― poly(haloolefins). Among these impact modifiers, a styrene/butadiene/styrene triblock copolymer is especially effective in both HIPS and ABS; and it is preferred to use that block copolymer together with a halogenated polyolefin resin, such as chlorinated polyethylene, in ABS. The concentrate or masterbatch of this invention can be formed by conventional techniques such as by combining, either continuously or batchwise, the flame retardant, impact modifier, and optional additives in a stirred kettle, drum mixer, mixing tube, mechanical high-intensity mixer, kneader, or extruder whereby a homogeneous blend of the concentrate or masterbatch is obtained. It will of course be recognized that only those innocuous ingredients which do not adversely affect the IZOD impact strength of articles made from the fully formulated HIPS or ABS resin will be included in the concentrate or masterbatch. Such a determination can be made empirically by simple trial and error techniques. Accordingly, the optional additives may be selected from pigments, flame retardant synergists, thermal stabilizers, plasticizers, antistatic agents, ultraviolet stabilizers, blowing agents, fillers, reinforcing rubbers, and the like. The temperature for forming the concentrate or masterbatch of this invention is not critical, provided the temperature is low enough to avoid thermal degradation of the concentrate, yet high enough to provide a homogeneous blend of the concentrate's components. Those skilled in the art can readily determine suitable processing temperatures. After the concentrate or masterbatch is formed, it is combined with the HIPS or ABS resin to form the flame retardant resin formulation. Such a combination can be obtained by the use of a single or twin screw extruder, a high intensity mixer, or a continuous mixer. It is understood of course that, when an extruder is used, the concentrate and the resin may be combined and fed to the extruder, or the concentrate and resin may be fed to the extruder separately. The following examples are given to illustrate the invention and are not intended as a limitation thereof. Unless otherwise specified, quantities mentioned in these examples are quantities by weight. COMPARATIVE EXAMPLE A A formulated HIPS resin was prepared and tested by: (1) shaking the following ingredients together in a plastic bag for two minutes: 80.5 parts of HIPS resin (Dow Styron® 492T), 3.0 parts of styrene/butadiene/styrene block copolymer impact modifier (Kraton® D4141 of Shell Chemical Co.), 12.0 parts of decabromodiphenylethane flame retardant (Ethyl Corp.), 4.0 parts of Sb₂O₃ synergist, and 0.5 part of zinc stearate processing aid, (2) extruding the mixture on a Haake-Buchler System 40 Rheometer equipped with a twin-screw extruder head at 175-190-215-215°C and 65 rpm, cooling the extruded material in an ice bath, pelletizing the extruded material, injection molding the pellets into ⅛" (∼3.2 mm) test bars on a Battenfeld BSKM 100/40 machine at 216°C, and (3) testing the bars for IZOD impact strength according to ASTM D 256-88. The bars were found to have an IZOD impact strength of 1.4±0.1 ft-lbs/inch (∼4.8±0.3 J/cm) of notch. EXAMPLE 1 Comparative Example A was repeated except that the flame retardant, impact modifier, and processing aid were preblended in a Brabender mixer at 175°C and 66 rpm for two minutes, and the resultant blend was sheeted on a two-roll mill and chopped into small pieces in a Osterizer mixer to form a masterbatch before shaking them together with the HIPS and antimony trioxide in the paper bag. The test bars had an IZOD impact strength of 2.04±0.03 ft-lbs/inch (∼7.0±0.1 J/cm) of notch. When the example was repeated except that the temperatures of the twin screw extruder were 160-190-215-215°C, the IZOD impact strength of the test bars was 2.02±0.05 ft-lbs/inch (∼7.0±0.2 J/cm) of notch. Thus, with both extrusion conditions, masterbatching increased the impact strength of the formulation by ∼46%. COMPARATIVE EXAMPLE B A formulated ABS resin was prepared and tested by: (1) shaking the following ingredients together in a plastic bag for two minutes: 64.9 parts of ABS resin (Dow Magnum® PG-914), 13.1 parts of polychloroethylene impact modifier (Tyrin® 3611 of Dow Chemical Co.), 5.0 parts of styrene/butadiene/styrene block copolymer impact modifier (Shell Kraton® D1102), 12.5 parts of decabromodiphenylethane flame retardant (Ethyl Corp.), 4.0 parts of Sb₂O₃, synergist, and 0.5 part of dibutyltin maleate stabilizer (Thermolite® 13 of Atochem No. Am.), (2) extruding the mixture on a Haake-Buchler System 40 Rheometer equipped with a twin-screw extruder head at 210-210-220-220°C and 60 rpm, pelletizing the extruded material and drying it at 88°C for four hours, injection molding the pellets into ⅛" (∼3.2 mm) test bars on a Battenfeld BSKM 100/40 machine at 195°C, and (3) testing the bars for IZOD impact strength according to ASTM D 256-88. The bars were found to have a IZOD impact strength of 4.8±0.2 ft-lbs/inch (∼16.5±0.7 J/cm) of notch. EXAMPLE 2 A formulation comparable to that of Comparative Example B was prepared by: (1) blending 13.1 parts of polychloroethylene impact modifier (Tyrin® 3611 of Dow Chemical Co.), 5.0 parts of styrene/butadiene/styrene block copolymer impact modifier (Shell Kraton® D1102), 12.5 parts of decabromodiphenylethane flame retardant (Ethyl Corp.), 0.5 part of zinc stearate processing aid, and 1.0 part of dibutyltin maleate stabilizer (Thermolite® 13 of Atochem No. Am.) in a Brabender mixer at 175°C and 66 rpm for two minutes, sheeting the resultant blend on a two-roll mill, and chopping it into small pieces on a Glouster grinder to form a masterbatch, (2) dry-blending the masterbatch with 63.9 parts of ABS resin (Dow Magnum® PG-914) and 4.0 parts of Sb₂O₃ synergist, and (3) extruding, pelletizing, drying, molding, and testing the formulation as in Comparative Example B. The test bars had an IZOD impact strength of 9.0±0.4 ft-lbs/inch (∼31±1.4 J/cm) of notch ― an increase of ∼88% over the impact strength of Comparative Example B. EXAMPLE 3 Example 2 was repeated except that the styrene/butadiene/styrene block copolymer impact modifier was dry-blended with the masterbatch together with the ABS resin and synergist instead of being included in the masterbatch. The IZOD impact strength of the test bars was 5.8±0.2 ft-lbs/inch (∼20±0.7 J/cm) of notch. EXAMPLE 4 Example 2 was repeated except that the polychloroethylene impact modifier was dry-blended with the masterbatch together with the ABS resin and synergist instead of being included in the masterbatch. The IZOD impact strength of the test bars was 7.6±0.3 ft-lbs/inch (∼26.2±1.0 J/cm) of notch. As demonstrated in Examples 3 and 4, the improvement in impact strength is not as great when less than all of the impact modifier is included in the masterbatch.

Claims: A process for preparing a flame-retarded rubber-modified styrenic polymer formulation which comprises a halogenated flame retardant, a polymeric impact modifier, at least 50 wt% of HIPS or ABS resin, and 0-6 wt% of flame retardant synergist and which provides improved impact strength to articles made therefrom; said process comprising the steps of (a) forming a concentrate containing the halogenated flame retardant and the polymeric impact modifier and (b) blending the resultant concentrate with the HIPS or ABS resin. The process of claim 1 wherein (a) the polymeric impact modifier is selected from one or more of the group consisting of styrene/butadiene/styrene triblock copolymers, styrene/isoprene/styrene triblock copolymers, styrene/butadiene diblock copolymers, polycaprolactone, functionalized ethylene/propylene copolymers, and poly(haloolefins) and (b) the halogenated flame retardant is selected from one or more of tetrahalobisphenol-A, N,N'-bis(tetrahalophthalimide), N,N'-ethylenebis(tetrahalophthalimide), halogenated polystyrene, pentahalobenzyl acrylate, and bis-halophenyl compounds of the structural formula: in which each X is selected independently from chlorine and bromine; m and n are the same or different integers of 1-5; and Y is selected from oxygen, alkylene, -NR- (where R is hydrogen or hydrocarbyl), alkylenedioxy, aryldioxy, and a chemical bond. The process of claim 2 wherein the polymeric impact modifier comprises a styrene/butadiene/styrene triblock copolymer. The process of claim 3 wherein the flame retardant is selected from decabromodiphenyl oxide, decabromodiphenylethane, 1,2-bis(tribromophenoxy)ethane, decabromodiphenyl amine, pentabromobenzyl acrylate, and mixtures thereof. The process of claim 4 wherein the flame retardant is decabromodiphenylethane. The process of claim 3 wherein the flame retardant is N,N'-ethylenebis(tetrabromophthalimide). The process of any of the claims 1-6 wherein the formulation comprises 2-6 wt% of one or more flame retardant synergists selected from metal oxides, hydroxides, and silicates, boron compounds, and ferrocene and the process comprises (a) forming a concentrate containing the halogenated flame retardant, the flame retardant synergist, and the polymeric impact modifier and (b) blending the resultant concentrate with the HIPS or ABS resin. The process of any of the claims 1-6 wherein the formulation comprises 2-6 wt% of one or more flame retardant synergists selected from metal oxides, hydroxides, and silicates, boron compounds, and ferrocene and the process comprises (a) forming a concentrate containing the halogenated flame retardant and the polymeric impact modifier and (b) blending the resultant concentrate with the HIPS or ABS resin and flame retardant synergist. The process of any of the preceding claims wherein the formulation comprises at least 50 wt% HIPS resin, 5-25 wt% halogenated flame retardant, 1-12 wt% polymeric impact modifier, ad 0-6 wt% flame retardant synergist. The process of any of the preceding claims wherein the formulation comprises at least 50 wt% ABS resin, 5-30 wt% halogenated flame retardant, 8-38 wt% polymeric impact modifier, and 0-6 wt% flame retardant synergist.

Inventors: DOUCET DAVID KIM, JONES JANET FAYE, LANDRY SUSAN DUNCAN, PETTIGREW FRANCIS ALEXANDER, REED JON SHANNON, TORRES JAMES ELTON, DOUCET, DAVID KIM, JONES, JANET FAYE, LANDRY, SUSAN DUNCAN, PETTIGREW, FRANCIS ALEXANDER, REED, JON SHANNON, TORRES, JAMES ELTON
Applicants: ALBEMARLE CORP, ALBEMARLE CORPORATION
Application year: 1992
Main classification: C08K5
IPC codes: C08K5, C08L53, C08L51, C08J3, C08L55