EP0099921A1 - Metal silicone flame retardants for polyolefins - Google Patents

Abstract

An anti-flame composition comprises, as a percentage by weight: (A) from 60 to 98% of thermoplastics; (B) from 1 to 20% of group IIA metallic carboxylic acid salts containing from 6 to 20 carbon atoms; (C) from 1 to 20% of a silicone fluid having the average formula, $ (15,) $ in which each R is a substituted or unsubstituted organic radical, X is identical to R or to a radical selected from group of hydroxyl or alkoxyl radicals and n is an integer such that said silicone fluid has a viscosity of about 2,000 to 600,000 centipoises at 25 ° C.

Description

Metal Silicone Flame Retardants for Polyolefins

BACKGROUND OF THE INVENTION

The present invention relates to flame retardant compositions which are blends of organic polymer, certain effective low viscosity silicone polymers and a Group IIA metal carboxylate salt containing 6 to 20 carbon atoms.

Prior to the present invention, as shown by Betts et al. U.S. Patent No. 4,123,586, a mixture of silicone gum and a dibasic lead salt, such as lead phthalate, was effective as a flame retardant for cross-linked polyolefins. However, those skilled in the art know that many lead compounds are known to be toxic. It is therefore desirable to minimize the use of lead in many applications, particularly applications in the food industry where lead-containing materials can create substantial food consumption risks. It is to be noted that the present invention is also a specific improvement over the invention of MacLaury and Holub as disclosed in U.S. Patent No. 4,273,691 which is hereby incorporated by reference. In that patent, MacLaury et al. taught a range of novel flame retardant compositions and articles which were generally comprised of a polyolefin, certain metal salts of carboxylic acids as well as a broad range of silicone compositions. Within the broad class of available silicone compositions disclosed and claimed by MacLaury et al. they preferred the use of silicone gums. Silicone gums are materials of relatively high viscosity; indeed MacLaury et al. preferred the gums to have a penetration value of 400 to 4,000 or more.

It was therefore quite surprising when the present applicants discovered that improved flame retardance for thermoplastics could be achieved with relatively low viscosity silanol or trimethyl-silyl chain-stopped polydiorganosiloxane fluids, some of which silicone fluid materials are somewhat less expensive than the silicone gums preferred by MacLaury et al. Also the silanol chain-stopped, low viscosity fluids tend to disperse with greater ease thereby facilitating the preparation of flame retardant compositions as compared to the use of high viscosity gums.

It is well understood in the silicone art that although silicone gums and fluids have similar chemical constituents, nonetheless there are significant differences in physical properties among these classes of silicones. Furthermore, prior to the present invention, it would not have been obvious that such silicone fluids as will be described herein would perform significantly better, or even as well, in flame retardant applications than previously preferred silicone gums.

It is therefore an object of the present invention to provide thermoplastic compositions having a relatively greater degree of flame retardancy than heretofore available.

It is another object to provide a combination of low viscosity silicone fluid and a Group IIA metal carboxylate salt which is effective for rendering thermoplastics flame retardant.

It is another object to provide a process for rendering thermoplastics flame retardant.

These and other objects will become apparent to those skilled in the art upon consideration of the present specification and claims.

SUMMARY OF THE INVENTION

There is provided a flame retardant composition comprising by weight:

(A) 60 to 98% of thermoplastic;

(B) 1 to 20% of Group IIA metal carboxylic acid salt containing from 6 to 20 carbon atoms;

(C) 1 to 20% of a silicone fluid essentially of the average formula

wherein each R is independently a substituted or unsubstituted organic radical and which preferably is a methyl radical, X is R or a radical selected from hydroxyl or alkoxyl radicals and n is an integer such that said silicone fluid has a viscosity of approximately 2,000 to 600,000 centipoise at 25°C. DESCRIPTION OF THE INVENTION

The present invention is based on the discovery that certain carboxylic acid salts of Group IIA elements, such as magnesium stearate, can be used in combination with certain low viscosity silicone fluids to impart improved flame retardant properties to a variety of organic polymers including polyolefins, polyesters, polycarbonates, polyamides, polystyrenes etc. (hereinafter collectively referred to as "thermoplastics"). It has been found that the flame retardant properties of a variety of such organic polymers can be substantially improved as shown by oxygen index values and horizontal burning times (HBT) when the aforementioned combination of such Group IIA carboxylic acid salt and silicone fluid is incorporated in such organic polymers.

It is contemplated that the organic polymers which can be used to make the flame retardant compositions of the present invention are, for example, low density polyethylene (LDPE) having a density of 0.91 g/cm³ to 0.93 g/cm³; high density polyethylene (HDPE) having a density of 0.94 g/cm³ to 0.97 g/cm³; polypropylene having a density of about 0.91 g/cm³, polystyrene, LEXAN^R polycarbonate, and VALOX^R polyester, both manufactured by the General Electric Company, and other polymers such as polyamides, ionomers, polyurethanes, co- and terpolymers of aerylonitrile,-butadiene and styrene; as well as acrylic, polybutylene, ionomer, acetal resin, ethylene-vinyl acetate, and polymethylpentene, flexible polyvinylchloride (but not rigid PVC), and polyphenylene oxide etc. The term "low viscosity silicone fluids" includes essentially linear polydiorganosiloxanes consisting essentially of chemically combined units of the formula.

where R is a monovalent organic radical. These organic radicals will ordinarily be selected from the class consisting of C_{( 1-8)} alkyl radicals, C_{( 6-13)} aryl radicals, halogenated derivatives of such radicals, cyanoalkyl radicals, etc. In any case, the aforementioned polydiorganosiloxanes are preferably polydimethylsiloxanes which can contain from about 0.05 to 15 mole percent of methylvinylsiloxy units based upon the total moles of chemically combined diorganosiloxy units. The aforementioned polydiorganosiloxanes are preferably in the form of silanol or trimethylsilyl chainstopped siloxane fluids having an approximate viscosity of 2,000 to 600,000 centipoise at

25ºC. Of the above mentioned materials, the aryl-containing siloxanes are less preferred.

Included within the Group IIA metal carboxylic acid salts which can be utilized in the practice of the present invention are, for example, magnesium stearate, calcium stearate, barium stearate, strontium stearate. Salts of other carboxylic acids include isostearate, oleate, palmitate, myristate, lactate, undecylenic, 2-ethylhexanoate , pivaleate , hexanoate , etc. In addition to the aforementioned ingredients, the flame retardant compositions of the present invention can contain additional ingredients, such as fillers, antioxidants, and additional additives. In particular instances, ingredients such as decabromc-diphenylether, antimony oxide, processing aids and clay also can be utilized. If desired, heat activated peroxides can be employed when utilizing polyolefins as the organic polymer. Suitable reactive peroxides are disclosed in U.S. Patent Nos. 2,888,424, 3,079,370, 3,086,966 and 3,214,422. Suitable peroxide crosslinking agents include organic tertiary peroxides which decompose at a temperature above about 295ºF. and thereby provide free-radicals. The organic peroxides can be used in amounts of from about 2 to 8 parts by weight of peroxide per 100 parts of organic polymer. A preferred peroxide is dicumyl peroxide, while other peroxides such as VulCupR^R of Hercules, Inc., a mixture of para and meta α , α ,-bis (t-butylperoxy)- diisopropylbenzene, etc., can be used. Curing coagents such as triallyl cyanurate can be employed in amounts of up to about 5 parts by weight of coagent, per 100 parts of the polymer if desired. The polyolefins can be irradiated by high energy electrons, x-ray and like sources.

In the practice of the invention, the flame retardant compositions can be made by mixing together the organic polymer with the silicone fluid and the Group IIA carboxylic acid salt, hereinafter referred to as the "Group IIA salt" by means of any conventional compounding or blending apparatus, such as a Banbury mixer or on a two-roll rubber mill. Order of addition of the particular constituents does not appear to be critical, however, those skilled in the art will be able to optimize the flame retardant compositions contemplated herein without undue experimentation. Preferably, all the ingredients are formulated together except those which are sensitive to the temperatures in the range of from about 300ºF. to about 400ºF., such as heat decomposable peroxides. The ingredients are therefore at a temperature sufficient to soften and plasticize the particular organic polymer if feasible. An effective procedure, for example, would be to uniformly blend the aforementioned ingredients at a suitable temperature with the absence of the organic peroxide, then introduce the organic peroxide at a lower temperature to uniformly incorporate it into the mixture.

The proportions of the various ingredients can vary widely depending upon the particular application intended. For example, for effective flame retardance there can be employed per 100 parts of organic polymer from about 0.5 to 20 parts of the silicone fluid and 0.5 to 20 parts of the Group IIA salt. However, greater or smaller amounts can suffice in particular applications. As previously indicated, other additives may be included. Antimony oxide can be -utilized in a proportion from 1 to 10 parts, and organic halogen compounds from 5 to 30 parts, per 100 parts of the organic polymer. Reinforcing and non-reinforcing fillers also can be employed.

The flame retardant composition of the present invention can be extruded onto a conductor and in particular instances, cross- linked depending on whether organic peroxide curing agent is present. Of course, there are numerous other applications where the flame retardant compositions of the present invention may be used to great advantage. Such materials may be successfully molded, extruded or compressed etc. to form numerous useful products such as moldings, sheets, webbing, fibers and a multitude of other flame retardant plastic or polyolefin products. Thus, the flame retardant compositions of the present invention also can be utilized in such applications as applicance housings, hairdriers, TV cabinets, smoke detectors, etc., automotive interiors, fans, motors, electrical components, coffee makers, pump housings, power tools, etc. Such flame retardant compositions might also be utilized in fabrics, textiles and carpet as well as many other applications.

In order that those skilled in the art will be better able to practice the invention, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

Example 1

A mixture of 8g of a hydroxy terminated linear polydimethyl- siloxane oil having a viscosity of approximately 100 ,000 cps at 25º C and 12g of magnesium stearate (Mg Ster. ) was compounded with 180g of molten polypropylene (Hercules Pro-Fax 6523) and compression molded. The resulting plastic had a higher limiting oxygen index (LOI=27) than the Pro-Fax 6523 alone (LOI=18) . In addition, 1/8 in. x 1/2 in. x 6 in. test strips of the compounded plastic self-extinguished in a horizontal burning test. Other silicone polymers of varying chain length and viscosity such as VISCASIL^R 100M also raised the LOI of polypropylene and in some cases caused the plastic to self extinguish in the horizontal burning test.

Table I compares the oxygen index values for various formulations. In each case, the polypropylene was Hercules Pro-Fax 6523. Compounding was performed on a Brabender mixer at 400ºF and compression molded slabs were cut (1/8 in. x 6 in. x 6 in.). SE-33 is a high viscosity silicone gum available from General Electric and used for comparison in the manner of MacLaury et al.

NOTES:

The siloxane fluids (1-4) listed in Table I are essentially linear hydroxy chain-stopped polydimethylsiloxanes having varying viscosities at 25ºC, as follows:

Siloxane 1 - approximately 100,000 cps. Siloxane 2 - approximately 12,100 cps. Siloxane 3 - approximately 2,800 cps. Siloxane 4 - approximately 950 cps.

The oxygen index test method employed herein is in accordance with ASTM 2863-77. The horizontal burn test is essentially similar to ASTM D635-81. Higher oxygen index values indicated greater degrees of flame retardancy.

Example 2

The following formulations were prepared by first milling together the silicone and magnesium stearate to form a paste. This paste was then compounded into molten polypropylene (Hercules Pro-Fax 6523) using a two-roll mill at 375ºF. The relatively low viscosity of the silicone fluids gave a paste that readily mixed into the molten polyproylene. The compounded material was compression molded at 375ºF in a "picture frame" mold to form

1/8" x 6" x 6" slabs. Strips (1/8" x 1/2" x 6") cut from these slabs were utilized in a horizontal burning test and for the measurement of the limiting oxygen index.

FORMULATION

A Profax 6523

B 180g Pro-Fax 6523 and 8g silicone gum and 12g magnesium stearate

180g Pro-Fax 6523 and 8g silicone² fluid and 12g magnesium stearate

D 180g Pro-Fax 6523 and 8g VISCASIL 100M³ and 12g magnesium stearate

E 180g Pro-Fax 6523 and 8g General Electric SF-1147⁴

and 12g magnesium stearate NOTES :

1 - a polydimethylεiloxane gum having 0.2 mole percent of chemically combined methyl-vinylsiloxy units and a penetration of between 1600 and 2500.

2 - a silanol stopped polydimethylsiloxane polymer having a nominal viscosity of 90,000 - 150,000 centipoise (90-150 Pascal second).

3 - 100,000 centistoke polydimethylsiloxane fluid, trimethylsilyl stopped (i.e. M-stopped) (available from General Electric).

4 - a methyl alkyl polysiloxane fluid of 50 centistokes (General Electric). FORMULATION OXYGEN INDEX 2" HORIZONTAL BURN A 18.0 Consumed in 150 sec, flaming drips

B 24.7 self extinguished in 16-41 sec, no drips C 26.5 self extinguished in 42-69 sec, no drips D 24.1 self extinguished in 59-63 sec, no drips E consumed in 116-120 sec, flaming drips

The limiting oxygen index test was conducted according to ASTM 2863-77. The horizontal burn was conducted by igniting a 1/8" x 1/2" x 6" strip of the material clamped at one end in a horizontal position.. If the material extinguished itself during the first half inch, the time was recorded. If burning continued past the first half inch, the burning rate was timed for the next two (2) inches.

These results demonstrate that the flame retarding property of the high molecular weight silicone gums preferred by MacLaury et al. is also exhibited by relatively low viscosity silanol stopped silicone polymers and M-stopped silicone fluids which are more easily compounded into the plastic than high molecular weight gums. Example 3

The following formulations were compounded and molded as in

Example 2.

FORMULATIONS

Pro-Fax 6523 Metal Soap Silicone

A 180g 12g Mg Stearate 8g 90-150 Pascal sec. polymer¹

B 180g 18g Mg Stearate 8g 90-150 Pascal sec. polymer¹

C 180g 12g Al Tristearate 8g 90-150 Pascal sec. polymer¹

D 180g 12g Al Tristearate 8g 90-15- Pascal sec. polymer¹

E 180g 12g Mg Stearate 8g 15-30 Pascal sec. polymer²

F 180g 12g Mg Stearate 8g 2.5-3.5 Pascal sec. polymer³

G 180g 12g Sn(II)Palmitate 8g 90-150 Pascal sec. polymer¹

H 150g 10.4g Mg Stearate 6.8g gum⁴ + 8.6g Sb₂O⁵ ₃ + 24.2g Decabromodiphenyl oxide⁶ I 200g Pro-Fax PD-451 (V- grade of flame retardant polypropylene) NOTES:

1 - silanol stopped polydimethylsiloxane polymer, 90-150 Pascal sec

2 - silanol stopped polydimethylεiloxane polymer, 15-30 Pascal sec

3 - silanol stopped polydimethylsiloxane polymer, 2.5-3.5 Pascal sec

4 - polydimethylsiloxane gum having 0.2 mole percent of chemically combined methylvinylsiloxy units and a penetration between 1600 and 2500.

5 - Baker reagent

6 - available from Great Lakes Chem. Corp., DE-83R

FORMULATION OXYGEN INDEX 2" HORIZONTAL BURN

A 27.0 extinguished in 11-85 sec with flaming drips

B 24.4 extinguished in 18-44 sec, no drips

C 19.9 burned 2" in 84-93 sec, flaming drips

D 19.9 burned 2" in 77-81 sec, flaming drips

E 24.4 extinguished in 10-22 sec, no drips

F 23.9 extinguished in 28-41 sec, no drips

G - burned 2" in 106-117 sec, flaming drips

H 27.5 extinguished in 6-13 sec, no drips

I 28.2 extinguished in 6-28 sec, occasional flaming drips These flammability test results demonstrate that lower viscosity silicones used in formulations E and F work as well as the higher viscosity polymer used in A and the gum used in Example 1. The poor performance of A in this particular experiment was an exception and may have been due to heterogeneity from insufficient compounding.

Example 4

Several formulations were compounded and compression molded to discover a possible synergism between the silicone fluid/magnesium stearate combination and the conventional organo halide/antimony trioxide flame retardants.

Formulations

A) 180g Pro-Fax 6523 and 8g silicone fluid and 12g Mg stearate

B) 160g Pro-Fax 6523 and 16g silicone fluid and 24g Mg stearate

C) 180g Pro-Fax 6523 and 4g Sb ₂O₃ and 16g Decabromodiphenyl Oxide²

D) 160g Pro-Fax 6523 and 8g Sb ₂O₃ and 32g Decabromodiphenyl Oxide ₂

E) 160g Pro-Fax 6523 and 8g silicone fluid and 12g Mg stearate and 4g Sb ₂O₃ and 16g Decabromodiphenyl Oxide²

F) 200g Pro-Fax 6523

The compression molded samples were subjected to the limiting oxygen index test (ASTM D2863-77), the Underwriters Laboratories UL-94 vertical burn test, and a horizontal burn test. NOTES:

1 - a silanol stopped polydimethylsiloxane having a nominal viscosity of 90,000 - 150,000 centipoise (90-150 Pascal seconds)

2 - available from Great Lakes Chemical Co.

Formulation LOI Horizontal Burn UL-94 Vertical Burn A 25.2 extinguished in 7-10 sec, extinguished in 34-143 no drip sec, flaming drips

B 24.2 extinguished in 8-11 sec, extinguished in 60-187 no drip sec, flaming drips C 21.0 consumed with flaming extinguished in 120 drips sec, flaming drips D 22.8 extinguished in 57-78 sec, extinguished in 6-231 flaming drips sec, flaming drips E 20.5 extinguished in 3-18 sec, extinguished in 34-71 flaming drips sec, flaming drips

F 18.0 consumed flaming drips consumed These results show that only 10% by weight of the silicone fluid and stearate significantly raises the oxygen index of polypropylene and causes self-extinguishment in the horizontal burn test. However, doubling the additives to 20% of the polypropylene appears to cause no further improvement. The organobromide/antimony additives are ineffectual at these low concentrations. Combining 10% levels of each set of flame retardants (formulation E) is no improvement over A. Ex ample 5

In the following table, Pro-Fax 6523, polypropylene was combined with 6 weight percent magnesium stearate and 4 weight percent of the specified silicone. The various grades of silicones are currently available from General Electric Company. Sample B in the table is typical of the silicone flame retardants of the present invention and was the only sample which self-extinguished in the hozizontal burn test.

Sample Formulation Oxygen Index Horizontal Burn

A Polypropylene control 18 Consumed

B Viscasil 100M Silicone Fluid 24 SE, 60 sec.

C SF-1147 Methyl Alkyl Fluid - Consumed

D DF-1040 Hydride Fluid - Consumed

E SF-1188 Surfactant - Consumed

F CF-1271 Phenyl Silicone Fluid - Consumed

G FF150-10M Fluorosilicone Fluid - Consumed

Claims

CLAIMS:

Claim 1. A flame retardant composition comprising by weight:

(A) 60 to 98% of thermoplastic;

(B) 1 to 20% of Group IIA metal carboxylic acid salt containing from 6 to 20 carbon atoms;

(C) 1 to 20% a silicone fluid of the average formula.

wherein each R is independently a substituted or unsubstituted organic radical, X is R or a radical selected from hydroxyl or alkoxyl radicals and n is an integer such that said silicone fluid has a viscosity of approximately 2,000 to 600,000 centipoise at 25ºC.

Claim 2. A composition as in Claim 1 wherein said thermoplastic is high density polyethylene.

Claim 3. A composition in accordance with Claim 1, where the thermoplastic is low density polyethylene.

Claim 4. A composition in accordance with Claim 1, where the thermoplastic is polypropylene.

Claim 5. A composition in accordance with Claim 1, where the thermoplastic is polystyrene.

Claim 6. A composition in accordance with Claim 1, where the silicone fluid is a polydimethylsiloxane fluid.

Claim 7. A composition in accordance with Claim 1, where the Group IIA metal salt is magnesium stearate.

Claim 8. A composition in accordance with Claim 1, containing an effective amount of an organic peroxide.

Claim 9. A flame retardant composition in accordance with Claim 1, where the polyolefin is a acrylonitrile-butadiene-styrene terpolymer.

Claim 10. An article of manufacture comprised of a composition of Claim 1.

Claim 11. An article of manufacture comprised of a substrate and a coating of the composition of Claim 1.

Claim 12. An additive for thermoplastics effective for rendering said thermoplastics flame retardant, comprised of:

(A) 1 to 20 parts by weight of a Group IIA metal carboxylic acid salt containing from 6 to 20 carbon atoms;

(B) 1 to 20 parts by weight of a silicone fluid of the formula,

wherein each R is independently a substituted or unsubstituted organic radical, X is R or a radical selected from hydroxyl or alkoxyl radicals and n is an integer such that said silicone fluid has a viscosity of approximately 2,000 to 600,000 centipoise at 25ºC.

Claim 13. A masterbatch formulation as in Claim 12 further comprising, approximately 1 to 98 parts by weight of thermoplastics or mixture of thermoplastics, and effective for rendering additional amounts of compatible thermoplastics flame retardant.

Claim 14. A composition as in Claim 1 where the thermoplastic is selected from polycarbonate and polyphenylene oxide.

Claim 15. A composition as in Claim 1 where the thermoplastic is polymethylmethacrylate.

Claim 16. An article of manufacture as in Claim. 10 wherein said article is formed by molding, spinning, or extruding.

Claim 17. An article of manufacture as in Claim 10 wherein said article is a filament, fiber, film, webb, fabric, sheet, molded part or extruded part.

Claim 18. A process for rendering thermoplastics flame retardant comprising the steps of: adding to 60 to 98% by weight of polyolefin (i) 1 to 20% by weight of Group IIA metal carboxylic acid salt containing from 6 to 20 carbon atoms and (ii) 1 to 20% by weight of a silicone fluid of the formula.

X R₂SiO-(R₂SiO)_n---SiR₂X

wherein each R is independently a substituted or unsubstituted organic radical, X is R or a radical selected from hydroxyl or alkoxyl radicals and n is an integer such that said silicone fluid has a viscosity of approximately 2,000 to 600,000 centipoise at 25°C.