WO2010091232A2

WO2010091232A2 - Flame retardant thermoplastic vulcanizates

Info

Publication number: WO2010091232A2
Application number: PCT/US2010/023293
Authority: WO
Inventors: Vanessa Fever; Charles Page
Original assignee: Polyone Corporation
Priority date: 2009-02-06
Filing date: 2010-02-05
Publication date: 2010-08-12
Also published as: DE112010000865B4; WO2010091232A3; DE112010000865T5

Abstract

A thermoplastic vulcanizate (TPV) is disclosed which uses only an essentially halogen-free flame retardant. Optionally, an expandable graphite filler is also included in the TPV compound.

Description

FLAME RETARDANT THERMOPLASTIC VULCANIZATES

CLAIM OF PRIORITY

[0001] This application claims priority from U.S. Provisional Patent

Application Serial Number 61/150,352 bearing Attorney Docket Number 12009003 and filed on February 6, 2009, which is incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention relates to thermoplastic vulcanizates, polymer compounds which exhibit elasticity while remaining thermoplastic, which are also flame retardant.

BACKGROUND OF THE INVENTION

[0003] The world of polymers has progressed rapidly to transform material science from wood and metals of the 19^th Century to the use of thermoset polymers of the mid-20^th Century to the use of thermoplastic polymers of later 20^th Century.

[0004] Thermoplastic elastomers combine the benefits of elastomeric properties of thermoset polymers, such as vulcanized rubber, with the processing properties of thermoplastic polymers.

[0005] For safety reasons in some uses, thermoplastic elastomers should be flame retardant. There is customer demand for essentially non-halogen flame retardant thermoplastic elastomers.

[0006] A particular type of thermoplastic elastomer is a thermoplastic vulcanizate (also called "TPV") in which the elastomer component is vulcanized or crosslinked.

SUMMARY OF THE INVENTION

[0007] What the art needs is a new thermoplastic vulcanizate that is flame retardant without the use of brominated flame retardants or chlorinated polyethylene flame retardants or other halogen-containing flame retardants.

The art needs a TPV compound using only essentially halogen-free flame retardant ("HFFR TPV").

[0008] "Essentially halogen-free" means that there is no intention to include any halogen moieties in any of the flame retardants or other additives to the TPV, but that one cannot control trace amounts of impurities that may exist in such ingredients. As explained below, it is believed that the TPV concentrate used in the present invention has a very small content of halogen in the commercially available but proprietary product. For that reason, the TPV compounds of the present invention are considered "low halogen," not

"essentially halogen-free."

[0009] Unfortunately, essentially halogen-free flame retardants are very sensitive to processing conditions typically experienced by TPVs. Therefore, there is little predictable to one of ordinary skill in the art in the creation of a

HFFR TPV.

[00010] The present invention solves the problem by formulating a HFFR

TPV that utilizes ammonium polyphosphate as an essentially halogen-free flame retardant.

[00011] One aspect of the invention is a thermoplastic vulcanizate compound, comprising (a) thermoplastic vulcanizate; (b) an ammonium polyphosphate-containing flame retardant; and optionally (c) plasticizer.

[00012] Another aspect of the invention is a plastic article made from the compound.

[00013] Features of the invention will become apparent with reference to the following embodiments.

EMBODIMENTS OF THE INVENTION

[00014] TPV

[00015] TPVs of the present invention are based on the use of concentrates of TPV commercially available from companies such as ExxonMobil Corporation and are then compounded with other ingredients, such as plasticizers, antioxidants, thermal stabilizers, and one or more secondary polymers.

[00016] The TPV concentrate is a blend of a continuous phase of a polyolefin such as polypropylene and a discontinuous phase of a vulcanized rubber such as crosslinked EPDM. TPV concentrates are commercially available from ExxonMobil Corporation in a number of grades marketed under the Santoprene™ brand, particularly the Santoprene™ 8000 series grades. It was reported by the manufacturer that Santoprene™ 8000 series grades have a halogen content of less than 200 parts per million. Of the Santoprene™ 8000 grades, Santoprene™ RC8001 TPV concentrate is presently preferred. Using Santoprene™ RC8001 TPV concentrate has the advantage that, as a ready- vulcanized concentrate, there is no risk of the flame retardants interfering with the vulcanization system, or of vulcanization chemicals deactivating the flame retardants.

[00017] Essentially Halogen-Free Flame Retardant

[00018] It has been found that flame retardants that contain ammonium polyphosphate are particularly suited to endure the processing conditions employed in compounding TPV.

[00019] It has been found, particularly, that Exolit AP brand flame retardants from Clariant GmbH of Germany work well in compounds of the present invention. Presently preferred is Exolit AP 766 brand flame retardant. [00020] Optional Additives

[00021] The compound of the present invention can include conventional plastics additives in an amount that is sufficient to obtain a desired processing or performance property for the compound. The amount should not be wasteful of the additive, nor detrimental to the processing or performance of the compound. Those skilled in the art of thermoplastics compounding, without undue experimentation but with reference to such treatises as Plastics Additives Database (2004) from Plastics Design Library (www.williamandrew.com), can select from many different types of additives for inclusion into the compounds of the present invention.

[00022] Non-limiting examples of optional additives include adhesion promoters; biocides (antibacterials, fungicides, and mildewcides), anti-fogging agents; anti-static agents; bonding, blowing and foaming agents; dispersants; fillers and extenders; smoke suppresants; expandable char formers; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers; processing aids; other polymers; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of them.

[00023] Any conventional plasticizer, preferably a paraffinic oil, is suitable for use the present invention.

[00024] A preferred secondary polymer for the present invention is polypropylene homopolymer or copolymer.

[00025] A preferred anti-oxidant is a tetrakismethylene antioxidant (CAS

6683-19-8).

[00026] A preferred thermal stabilizer an Irganox brand thiodipropionate compound identified as CAS 123-28-4.

[00027] An expandable graphite filler can serve as an expandable char former in formulations of the compound in those instances when the article formed from the compound should expand as it is heated. The expandable graphite filler should have an onset of expansion temperature greater than the processing temperature of the compound, but low enough and with a high enough activity to provide a suitable expansion. Suitable expansion could be as much as 300%, in an embodiment of a door seal where the gap during normal operation becomes sealed upon onset of exposure to heat or flame. Preferred expandable graphite filler products are commercially available as Nord-Min branded products from Nordmann Rassmann of Germany.

[00028] Table 1 shows the acceptable, desirable, and preferable ranges of ingredients for the HFFR-TPV of the present invention.

[00029] Processing

[00030] The preparation of compounds of the present invention is uncomplicated once the proper ingredients have been selected. The compound of the present can be made in batch or continuous operations.

[00031] Mixing in a continuous process typically occurs in an extruder that is elevated to a temperature that is sufficient to melt the polymer matrix with addition of all additives at the feed-throat, or by injection or side-feeders downstream. Extruder speeds can range from about 50 to about 500 revolutions per minute (rpm), and preferably from about 100 to about 350 rpm.

Typically, the output from the extruder is pelletized for later extrusion or molding into polymeric articles.

[00032] Mixing in a batch process typically occurs in a Banbury mixer that is also elevated to a temperature that is sufficient to melt the polymer matrix to permit homogenization of the compound components. The mixing speeds range from 60 to 1000 rpm and temperature of mixing can be ambient. Also, the output from the mixer is chopped into smaller sizes for later extrusion or molding into polymeric articles.

[00033] Subsequent extrusion or molding techniques are well known to those skilled in the art of thermoplastics polymer engineering. Without undue experimentation but with such references as "Extrusion, The Definitive Processing Guide and Handbook"; "Handbook of Molded Part Shrinkage and Warpage"; "Specialized Molding Techniques"; "Rotational Molding Technology"; and "Handbook of Mold, Tool and Die Repair Welding", all published by Plastics Design Library (www.williamandrew.com), one can make articles of any conceivable shape and appearance using compounds of the present invention.

USEFULNESS OF THE INVENTION

[00034] TPV of the present invention has an excellent versatility because of its elastomeric performance, its thermoplastic processing, its performance at higher temperatures such as at 100⁰C and above, and its durability in the presence of oils and oil-based fuels. The addition of anti-oxidant properties, thermal stabilization, and essentially halogen-free flame retardancy by those respective functional additives makes the HFFR TPV of the present invention an excellent compound for molding into plastic articles which need flame retardancy when in use in enclosed spaces of higher temperatures and possible exposure to oils and oil-based fuels. Use in motor vehicle engine compartments and industrial products requiring high temperature performance are two of many ways the compounds of the present invention can benefit people around the world. Other uses include wire and cable sheathing and insulation, electrical distribution seals and multigates, particularly in automotive or industrial applications where elevated temperatures could be expected.

EXAMPLES [00035] Table 2 shows a TPV example of the present invention and a comparative example of a thermoplastic elastomer (TPE) compound based on Styrene-Ethylene/Butylene-Styrene (SEBS) block copolymer, their formulations, sources of ingredients, and processing conditions.

[00036] Pellets of the Example and Comparative Example were molded into tensile test bars using a Demag injection molding machine, operating at 160-180⁰C temperature and medium-high pressure. [00037] Table 3 shows the experimental results.

[00038] Example 1, as compared with a SEBS-TPE of Comparative

Example A, showed excellent physical performance, especially a V-O flame test. Of note is the significant improvement of compression set at elevated temperatures, particularly at 100⁰C. When immersed in IRM903 oil, a test reference oil used to simulate most aggressive motor oils for tests such as ASTM D 2000, for 24 hours at 7O⁰C the TPV of Example 1 exhibited a change in volume of only 40%, whereas the Comparative Example A exhibited a significantly higher change in volume of 63%. Thus, the TPV compound has superior durability in the presence of a most aggressive oil. [00039] This flame retardant TPV technology allows end product manufacturers to produce flame retardant products, suitable for use at elevated temperatures and with improved resistance to oils and oil-based fuels which avoid halogens without sacrificing performance.

[00040] The invention is not limited to the above embodiments. The claims follow.

Claims

What is claimed is:

1. A thermoplastic vulcanizate compound, comprising:

(a) thermoplastic vulcanizate;

(b) an ammonium polyphosphate-containing flame retardant; and optionally

(c) plasticizer.

2. The compound of Claim 1, further comprising polypropylene as a secondary polymer.

3. The compound of Claim 1 or Claim 2, wherein the plasticizer is a paraffinic oil.

4. The compound of any of Claims 1-3, further comprising adhesion promoters; biocides; anti-fogging agents; anti-static agents; bonding, blowing and foaming agents; dispersants; fillers and extenders; fire and flame retardants and smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers; additional processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of them.

5. The compound of any of Claims 1-4, wherein the weight percents of the ingredients comprise:

6. The compound of Claim 5, wherein the weight percents of the ingredients comprise:

7. The compound of Claim 5, wherein the compound further optionally comprises from 0-30% by weight of expandable graphite filler.

8. A thermoplastic article, comprising the compound of any of Claims 1-6.