WO1988005798A1

WO1988005798A1 - Flame-retarding composition for thermoplastic polymers, and self-extinguishing polymeric products so obtained

Info

Publication number: WO1988005798A1
Application number: PCT/EP1987/000819
Authority: WO
Inventors: Luciano Scarso
Original assignee: V.A.M.P. S.R.L.
Priority date: 1987-02-02
Filing date: 1987-12-23
Publication date: 1988-08-11
Also published as: IT1203322B; IT8719225A0

Abstract

Flame-retarding composition for endowing thermoplastic polymers with self-extinguishing characteristics, comprising tetrabromophthalic anhydride and an inorganic complexing/sequestering agent having anionic exchange properties, and self-extinguishing thermoplastic polymers so obtained.

Description

"FLAME-RETARDING COMPOSITION FOR THERMOPLASTIC POLYMERS, AND SELF-EXTINGUISHING POLYMERIC PRODUCTS SO OBTAINED"

Description The present invention relates to a "flame-retarding" or "flame-proofing" composition for thermoplastic polymers and copolymers, such as polystyrene and styrenic polymers and copolymers in general, polyethylene, polypropylene, polyesters of the type polybutyleneterephthalate (PBT), as well as for blends of thermoplastic polymers with other compatible polymers.

Also an object of the present invention are the thermoplastic polymers and copolymers endowed with self-extinguishing properties by means of said flame- retarding composition.

It is known that a polymeric substance is rendered "seltf-extinguishing" or "flame-proof" or "flame- resistant" by means of the addition of special "flame- proofing" or "flame-retarding" agents, which are precisely capable of endowing the polymeric substance with the required characteristics of self- extinguishment. Such flame-proofing agents are normally constituted by halogenated organic substances, usually brominated substances, having a more or less complex structure. In some cases, such as, e.g., in polycondensat ion resins such as the unsaturated polyethers, the epoxy resins, the polyurethanes, and the like, flame-proofing agents are used, which bear functional groups, by means of which said agents are chemically bonded to the structure of the polymer, or are true intermediates which become a stable part of the structure of the same polymers, which they endow with self-extinguishing characteristics. In other cases, such as, e.g., in many thermoplastic resins, the flame-proofing agents are not provided with functional reactive groups which make it possible a chemical bond to be formed, i.e., a true combination to be accomplished with the structure of the polymer, and maintain their identity, even if they are i nt imate l y m i x ed and " i ncorpor a t ed " w i t h the mass of the same polymer.

In the thermoplastic resins, such as styrenic resins or polymers polyethylene, polypropylene, PBT and the like, the use is necessary of flame-proofing agents which combine with satisfactory flame-proofing characteristics also high characteristics of thermal stability and of resistance to hydrolysis, such as to be able to withstand, without decomposing or undergoing alterations, the high temperatures to which the thermoplastic resins or polymers which contain them are exposed, when they undergo the fabrication processes typical for thermoplastic resins, such as injection-moulding, extrusion, and the like. In fact, a breakdown, or hydrolysis, of such flame-proofing agents during the resin fabrication process would cause, on one hand, alterations to occur in the appearance and in the chemical and physical characteristics of the resin, due, e.g., to released bromine, and, on the other hand, a partial or total solubiIization of the same agent to occur, with a consequent extraction thereof from the resin, and the loss, by this latter, of its initial self-ext inguishing characteristics. Among the agents which are more commonly used as flame-proofing agents for thermoplastic resins, particularly for styrenic resins, there are, e.g., polybromodiphenyloxides (polybromodiphenylethers), in particular decabromodiphenylether and octabromodiphenylether, which precisely combine good flame-proofing characteristics with a satisfactory heat stability. But, recently, those skilled in the art realized that during the induced combustion of the polymers containing such agents, among the products formed due to the pyrolysis of po l yb r omo d i p heny l ox i d es, highly toxic substances are present, such as polybromobenzodioximes, and polybromobenzofurans, and that, hence, in case of fortuitous fires, the presence of thermoplastic polymers treated with such flame- proofing agents would create seriously hazardous conditions for people who would casually get exposed to the fumes from the fire.

A purpose of the instant invention is to provide a flame-retarding composition for thermoplastic polymers, copolymers, and polymer blends based on thermoplastic polymers, which does not generate, in case of an induced combustion of the polymer containing said composition, toxic substances of the type of polybromobenzodioximes, and/or polybromobenzofurans. flnotjier purpose of the present invention is to provide a flame-proofing composition for thermoplastic resins in general, which is capable of withstanding the processes of thermoplastic fabrication of the resins, such as moulding, injection, and the like, and wh i ch does not cause alterations in the appearance, and/or a decay to occur in the chemical, physical and mechanical characteristics, of the same resins.

A further purpose of the present invention is to provide self-extinguishing thermoplastic resins, which resins, in case of a fire, accidental overheating, induced combustion and the like, do not generate toxic substances of the type of po l y bromob en z o d i ox i me s and/or polybromobenzofurans.

These and still further purposes, and the related advantages which will be evidenced by the following disclosure in detail, are advantageously achieved by a flame-retarding composition for thermoplastic polymers, copolymers and polymer blends based on t he rmop l a s t i c polymers, such as polystyrene, impact-resistant polystyrene, acrylonitrile-butadiene-styrene resins, blends of polystyrene with potypheny leneoxide, of ABS with polycarbonates, polyethylene, polypropylene, PBT and the like, which composition, according to the present invention, comprises: (A) tetrabromophthalic anhydride;

(B) a complexing and/or sequestering substance or agent, of inorganic nature, endowed with anionic-exchange properties , const ituted by a basic carbonate¬hydrate of metals belonging to the second Group and/or to the third Group of the Periodic System. It is known that tetrabromophthalic anhydride is widely used as a flame-proofing agent in such polycondensation resins, as unsaturated polyesters , epoxy r esins, polyurethanes and the l ike, in that this product is a reactive intermediate, thanks to its anhydride functional groups, which enable it to get combined inside the polymer , and to become a stable part of its structure.

Tetrabromophthalic anhydride, when pyrolysed, does not generate undesirable, highly toxic products, such as polybromobenzodioximes and/or polybromobenzofurans (Chemosphene, Vol. 15, No. 5, 1986; pages 469-652). But it cannot be used as a flame-proofing agent in thermoplastic resins, such as the styrenic resins, polyethylene, polypropylene and the like, due to its poor heat stability during the thermoplatic fabrication processes these types of resins undergo, and to its poor resistance to hydrolysis, which would cause its solubilization, and consequent extraction from the polymer, which would thus lose its self-extinguishing properties. Furthermore, the dissolved portions of tetrabromophthalic anhydride would cause a decay in polymer dielectric properties.

Surprisingly, tetrabromophthalic anhydride, when combined or anyway associated with a complexing/ sequestering substance having anionic exchange properties according to the present finding, has shown to be advantageously useable as a flame- retarding agent in thermoplastic polymers. The thermoplastic resins endowed with self- extinguishing characteristics by means of the incorporation of a composition according to the present invention show in fact, as it is better set forth by the following Examples, very good characteristics of heat stability, combined with excellent chemical, physical, mechanical and dielectric properties. As the complexing/sequestering substance, endowed with anionic exchange properties, a synthetic product can be advantageously used, which is substantially constituted by a basic carbonate hydrate of aluminum and magnesium, having the chemical formula:

Mg_{4 .5}Al₂ (OH) ₁₃CO₃ . 3.5H₂O with a percent content by weight of Mgo of from 3β to

40%, and of Al₂O₃ of from 15 to 25%, with a molar ratio o f MgO / A l ₂ O₃ o f f rom 3 t o 6 . Also a mineral product can be used, which is available from natural sources, and has the chemical formula:

Mg₆Al₂ (OH) ₁₆CO₃ . 4H₂O In such type of products, the anionic exchange characteristics are thought to be due to the fact that

CO₃ can be replaced in the molecule, either totally, or partially, by an anion, or a more or less complex anionic group, which is hence "sequestered" and stably bonded in the molecular structure of the same product. The deriving product results to be very stable to temperature, and practically insoluble in water, oil, and so forth. Recording to the present invention, in order to obtain a satisfactory degree of self-extinguishment in the thermoplastic resin, with the same resin the following amounts are incorporated of the constituents of the flame-proofing composition, expressed as % by weight, relatively to the self-extinguishing resin: A) Tetrabromophthalic anhydride within the range of from 2 to 35%;

B) Complexing/sequestering agent within the range of from 0.01 to 2.5%, with a ratio, by weight, between the complexing agent and tetrabromophthalic anhydride comprised within the range of from 0.03 to 15 parts by weight of complexing agent per each 100 parts by weight of tetrabromophthalic anhydride.

The flame-retarding composition according to the present invention allows the simultaneous use of antimony oxide and/or of other known coadjuvants for the flame-resistance properties of the thermoplastic resin, as well as also the use of other known additives, such as stabilizers (of the type comprising barium, cadmium, zinc, calcium, sodium, lead, tin salts), antioxidants, lubricants, dyes and the like, also with known functions.

The preparation of the self-extinguishing thermoplastic resins of the present invention is accomplished by means of known and traditional processes, e.g., by blending the polymer, tetrabromophthalic anhydride and the complexing/sequesting agent, as well as the other various additives and coadjuvants, in a granulator/extruder, the self-extinguishing styrenic resin being obtained in the form of granules, for the following thermoplastic processing or fabrication steps.

As an alternative, tetrabromophthalic anhydride and the complexing/sequestering agent can be previously mixed with each other, and then added, as an already homogeneous mixture, to the polymer. Or, tetrabromophthalic anhydride and the complexing agent can be mixed with each other, and with a small amount of a polymeric thermoplastic binder, such as, e.g., a styrenic binder, a polyolephinic binder, and the like, e.g., by melt blending in the plastic state inside screw extruders according to known techniques, a concentrate ("master-batch") being so formed, which is then blended with the polymer to be made self- extinguishing, the operations of incorporation of the flame-retarding composition with the resin to be endowed with self-extinguishing characteristics being thus rendered simpler and more efficacious. The p r e s en t invention can be better evidenced and disclosed by the following examples of practical embodiment thereof, which examples are intended as being only indicative, and not limitative of the scope of protection of the same invention. Example 1 (Comparative Example) On a high-speed mixer a blend was prepared, which comprised the following constituents, expressed as % by weight relatively to the total weight of the same blend:

Impact-resistant polystyrene 64% Decabromodiphenylether 12%

Antimony oxide (Sb₂O₃) 4% Decabromodiphenylether was of the high-purity type for electronic use, Grade 102 E by ETHYL SRYTECH, with a Br content of 83%.

The index of stability of said decabromodiphenylether, intended as the temperature at which the product loses 10% of its weight, is 365^ºC. The above-said blend, perfectly uniform, was then granulated on a screw extruder, the resin being obtained in the form of granules.

The so-obtained styrenic resin was submitted to the characterization tests, with the following results being obtained: UL-94 1/8" Self-Extinguishment

Test, by Underwriter Labs, USA v-0 rating

UL-94 1/8" Test, after extraction in water for 2 hours at 100^ºC V-0 rating

Heat stability during the injection moulding (240^ºC for 3 minutes) Very good

"Izod" Resilience, kg. cm/cm 6.7 VICRT (5 kg), ^ºC 61

Example 2 (Comparative Example)

On the same mixer of Example 1, a blend was prepared, which comprised the following constituents, still expressed as % by weight relatively to the total weight of the same blend:

Impact-resistant polystyrene 64%

Tetrabromophthalic anhydride 12%

Rntimony oxide (Sb₂O₃) 4% Tetrabromophthalic anhydride was of RB 49 type by ETHYL

SAYTECH, with a Br content of 69%, and with an index of stability, intended as the temperature at which the product loses 10% of its weight, of 260^ºC.

The above-said blend was then granulated and the granular resin obtained was injection moulded at the temperature of 220^ºC. The product results so degraded, as to render meaningless the characterization tests.

Example 3

On the same mixer of Examples 1 and 2, a blend was prepared, which comprised the following constituents:

Impact-resistant polystyrene 63.5%

Tetrabromophthalic anhydride 12%

Mg_{4 .5}A l₂COH)₁₃CO₃ . 3.SH₂O complexing agent 0.5% Rntimony oxide (Sb₂O₃) 4% Tetrabromophthalic anhydride was the same as used in

Example 2, i.e., of RB 49 type by E THYL SAYTECH. The complexing agent had the following characteristics:

Mgo 34%

Al₂O₃ 19% MgO/Al₂O₃ molar ratio 4.5 Moisture 0.34%

Heavy Metals 10 ppm

Specific Surface Area 11 m /g pH Value of Aqueous Suspension 9.1

Granulometry of Particles smaller than 1 μm 95.7%

The above-said blend was granulated and the granular resin obtained was submitted to the same characterization tests as of Examples 1 and 2, with the following results being obtained:

UL-94 1/6" Self-Extinguishment V-0 rating

UL-94 1/6" Self-Extinguishment, after extraction in water V-0 rating

Heat stability during the moulding \fery good

"Izod" Resilience, kg. cm/cm 6.6 VICAT (5 kg), ^ºC 60

E ample 4 On the same mixer of Examples 1, 2 and 3, a blend was prepared, which comprised the following basic constituents:

Rcrylonitrile-Butadiene-Styrene Copolymer (AB5) 76% Tetrabromophthalic anhydride 15%

Mg_4.5Al₂ (OH) ₁₃CO₃ . 3.5H₂ O complexing agent 1%

Antimony oxide 6%

Tetrabromophthalic anhydride was the same as used in

Example 2 and 3, and the complexing agent was the same as used in Example 3.

The blend was granulated and the granular resin obtained was submitted to the same characterization tests as of Examples 1, 2 and 3, with the following results being obtained:

UL-94 1/8" Self-Extinguishment V-0 rating

UL-94 1/8" Self-Extinguishment after extraction in water V-0 rating Heat stability during the moulding Very good

"Izod" Resilience, kg. cm/cm 23

VICAT (5 kg), ^ºC 66

Example 5 On the same mixer of Examples 1 to 4, three blends I, II and III were prepared, which comprised respectively the costituents as reported in the following Table 1. Tetrabromophtalic anhydride was the same as used in Examples 2, 3 and 4, and the complexing agent was the same as used in Examples 3 and 4.

The three blends were separately granulated and the granular resins obtained were submitted to the same self-extinguishment and heat stability tests as of the preceeding Examples, the results of said tests being also reported in the following Table 1:

TABLE 1 Blend I II III

Low density polyethylene (LOPE) 91% - - Polypropylene (PP) talc filled (40% of talc) - 71,5% -

Polybutyleneterephthalate

(PBT) - - 65,5%

Tetrabromophtalic anhydride 7% 21% 11% Mg_4.5Al₂(OH)₁₃CO₃.3.5H₂O complexing agent 0,5% 0,5% 0,5%

Rntimony oxide (Sb₂O₃) 1,5% 7% 3% UL-94 1/8" Self-Extinguishment V-2 V-0 V-0

Heat stability during the moulding very very very good good good

Example 6

On the same mixer of the preceding Examples, and by the same operating modalities, a blend was prepared, which comprised the following constituents:

Acrylonitrite-Butadiene-Styrene Copolymer (ABS) 76% T e t rabr omoph t ha l i c anhydride 15% Antimony oxide 6% Barium and cadmium stearate 1% Tetrabromophthalic anhydride was the same as used in preceding Examples.

The blend was granulated and the granular resin obtained was submitted to injection moulding at the temperature of 220^ºC. The product results so degraded, as to render meaningless the characterization tests.

From Example 2, it results evident, and confirms the prior knowledge, that tetrabromophthalic anhydride cannot be used as a fire-proofing agent for the thermoplastic polymers, in the instant case for the styrenic polymers, in that it causes a strong thermal decay of impact-resistant polystyrene during the moulding; the degradation is such as not to allow the polymer to be processed according to the traditional plastics processing routes. From Examples 3, 4 and 5, it results evident that the flame-retarding composition according to the present invention makes it possible self -ext inguishing thermoplastic resins to be obtained, which are endowed with self-extinguishment properties, and physical, mechanical and processabiIity characteristics, which ar e substantially equal to those of the resins obtained by using a polybromodiphenyloxide according to the prior art, without the serious drawbacks which derive, as hereinabove reported, from the use of these 'latter flame-proofing agents, due to the toxicity of the products of their pyrolysis.

The test reported in Example 6 was carried out for the purpose of underlining to a still greater extent the surprising and fundamental effect achieved by the association of tetrabromophthalic anhydride with the complexing/sequestering agent endowed with anionic exchange properties, in the flame-retarding compositions according to the invention. From such test, it results in fact evident that the use of tetrabromophtalic anhydride involves the degradation of the product during the moulding step, even if considerable amounts of traditional stabilizers are used, such as, in the herein case, of barium and cadmium stearate, according to the prior art. To the invention, as hereinabove disclosed, technically equivalent variants can obviously be supplied, all of them being within the scope of protection of the same invention.

Claims

1. Flame-retarding composition for thermoplastic polymers, copolymers and polymer blends based on thermoplastic polymers, such as polystyrene, impact- resistant polystyrene, aery loni tri le-butadiene-styrene resins (AB5), blends of polystyrene with poIyphenyleneoxide, of ABS with polycarbonates, polyethylenepolypropylene, polyesters of the type polybutyleneterephtalate (PBT) and the like, which composition is characterized in that it comprises: (A) tetrabromophthalic anhydride;

(B) a complexing and/or sequestering agent, of inorganic nature, endowed with anionic-exchange properties, constituted by a basic carbonate hydrate of metals belonging to the second Group and/or third Group of the Periodic System.

2. Flame-retarding composition according to claim 1, characterized in that said complexing/sequestering agent is constituted by a basic carbonate hydrate of aluminum and magnesium, with a percent content by weight of MgO comprised within the range of from 30 to

40%, of Al₂O₃ comprised within the range of from 15 to 25%, and with a molar ratio of MgO/Al₂O₃ of from 3 to 6.

3. Flame-retarding composition according to claim 1, characterized in that the ratio between said complexing/sequestering agent and said tetrabromophthalic anhydride is comprised within the range of from 0.03 to 15 parts by weight of complexing agent per each 100 parts by weight of tetrabromophthalic anhydride.

4. Self-extinguishing thermoplastic polymers, comprising styrene-based polymers and copolymers, polyethylene, polypropylene, polyesters of the type polybutyleneterephtalate and polymeric blends based thereof, characterized in that they are rendered self-extinguishing by means of flame-retarding compositions according to claim 1.

5. Self-extinguishing thermoplastic polymers, copolymers and polymeric blends based thereof according to claim 4, characterized in that they comprise from 2 to 35% of tetrabromophthalic anhydride and from 0.01 to 2.5% of said complexing/sequestering substance.

6. Flame-retarding composition according to claim 1, characterized in that said complexing/sequestering substance and said tetrabromophthalic anhydride are pre-mixed with each other, and/or with a small amount of a polymeric thermoplastic binder, such as, e.g., a styrenic binder, a polyolephinic binder, and the like, e.g., such to form a pre-concentrate (a "master-batch").

7. Thermoplastic polymers comprising styrene-based polymers and copolymers, polyethylene, polypropylene, polyesters of the type polybutyleneterephtalate and polymeric blends based thereof according to claim 4, characterized in that they are rendered self-extinguishing by means of tetrabromophtalic anhydride.