WO1998040436A1

WO1998040436A1 - Gels

Info

Publication number: WO1998040436A1
Application number: PCT/GB1998/000602
Authority: WO
Inventors: Antony Perkins; Narinder Kehal; Neil Thompson; Philip James Hammond; Rudolf Robert Bukovnik
Original assignee: Raychem Limited
Priority date: 1997-03-07
Filing date: 1998-02-25
Publication date: 1998-09-17
Also published as: GB9704709D0

Abstract

Flame-retarded gels of oil-extended triblock copolymers are made with less than 40 % (pref. 35 %, 30 %) flame retardant additive while achieving at least 25 % (pref. 45 %, 65 %) reduction in burn rate under UL-94 Horizontal Burn Test. Preferred additives, e.g. char-forming and intumescent, esp. Phosphorous-containing, can achieve self-extinction of the test sample and non-ignition of cotton wool positioned 30 cm below the test sample (this being a modification of the above Test Method).

Description

GELS

This invention relates to gel compositions comprising a block copolymer having an elastomeric mid-block between relatively hard end blocks and at least 200 (preferably at least 300) parts by weight, per 100 parts by weight of the said copolymer, of an extender liquid which extends and softens the said mid-block. The relatively hard end blocks of the copolymer are selected to undergo phase separation within the copolymer mass, thus acting as pseudo-cross-links in the gel at temperatures below the end-block softening temperature, while the gel remains fully thermoplastic at higher temperatures, as known per se. Such gels made from block copolymers having styrene (which term includes alpha-methyl styrene) end blocks are described in WO-A-8800603 (RK308), WO-A- 9005166 (RK403), WO-A-9305113 (RK451), WO-A-9323472 (RK469), and WO-A- 9418273 (RK472), the disclosures of all of which are incorporated herein by reference. Other such gels, made from block copolymers having alkyl methacrylate end blocks of potentially higher temperature performance, are described in WO-A-9700292 (RK509), the disclosure of which is incorporated herein by reference.

Although the block copolymers may be largely composed of combustible hydrocarbon, and a majority by weight of the gels may be combustible extender liquid, preferably paraffin/naphthene oil, it has been found according to the present invention that the gels may be flame-retarded to a commercially significant degree using surprisingly low levels of various flame-retardant additives.

The invention accordingly provides a flame-retardant gel composition comprising a block copolymer having an elastomeric mid-block between relatively hard end blocks, at least 200 (preferably at least 300) parts by weight, per 100 parts by weight of the said copolymer, of an extender liquid (preferably a hydrocarbon oil) which extends and softens the elastomeric mid-block (preferably substantially only the mid-block) of the said copolymer, and flame-retardant additive in an amount of not more than 40% by weight based on the combined weight of the said copolymer, extender liquid and additive, the amount of the said additive being sufficient to reduce the burning rate of a sample of the composition by at least 25%, preferably at least 45%, more preferably at least 65%, when tested in accordance with the UL-94 Horizontal Burn Test (19 April 1995 version).

The relatively hard, phase-separating end blocks of the copolymer may for example be polystyrene or poly (alpha-methyl styrene), as in the styrene-ethylene/butylene-styrene (SEBS) and styrene-ethylene/propylene-styrene (SEPS) triblock copolymers described in the first five references mentioned above, or the end blocks may be alkyl (preferably methyl) methacrylate as in the sixth reference above. The copolymers are not necessarily restricted to triblocks, and more than one kind of end block may be present, for example as in the methacrylate-styrene-alkylene-styrene-methacrylate penta-block copolymers also described in the sixth reference. The extendable mid-block will preferably be a poly alky lene, more preferably a hydrogenated poly alky lene, of relatively high molecular weight, preferably having a number average molecular weight Mn of at least 38000, preferably within the range from 38000 to 150000, more preferably 50000 to 140000, especially 60000 to 130000. The harder end blocks preferably have lower Mn, for example in the range from 30000 to 40000.

Depending on the specific gel composition and the specific flame-retardant additive selected, it has been found possible to produce gel compositions according to the present invention wherein the amount of the said additive is sufficient (a) to achieve self-extinction of the said sample when tested as aforesaid and/or (b) to avoid ignition of cotton wool positioned 30 cm below the said sample when so tested. Furthermore, the flame-retarding performance according to the present invention may be achieved in preferred cases when the amount of the flame-retardant additive is not more than 35 % , preferably not more than 30% , by weight of the composition. It is usually preferable that the amount of the flame- retardant additive is at least 5%, preferably at least 10%, more preferably at least 15%, by weight of the composition. It has very surprisingly been found that the desired levels of flame-retardancy tend to be achieved more easily as the proportion of combustible extender oil in the gel increases, contrary to the natural expectation that more oil would render the gel more combustible. Thus, the present invention may be especially useful in gels wherein the weight ratio of the extender liquid to the said polymer is within the range from 3: 1 to 30: 1, preferably 4: 1 to 15:1, especially 4:1 to 10: 1.

Suitable flame-retardant additives may be selected from known flame-retardant materials. One class of such materials, for example, comprises halogenated organic compounds, preferably in combination with a synergist such as antimony oxide. Preferably, the flame-retardant additive comprises a char-forming or intumescent material. Especially-preferred flame-retardant additives comprise phosphorus or a phosphorus compound.

In one preferred form of the gel compositions according to the present invention, the flame-retardant additive comprises inorganic phosphate, preferably ammonium polyphosphate, preferably together with a nitrogen-containing synergist therefor. Preferred synergists include organic amine phosphates, preferably melamine phosphate. These flame-retardant additives may further include polyols, preferably pentaerythritol.

In other preferred forms of the invention, the flame-redardant additive comprises organic phosphates other than the above synergists, possibly, but not necessarily, in the absence of inorganic phosphates. Preferred organic phosphates for this form of the invention include phosphate oils, for example one or more selected from tris(2- chloroethyl)phosphate (TCEP), tris(2-chloropropyl)phosphate (TCPP), trixylyl phosphate, and tributoxy ethyl phosphate.

In a further preferred form of the invention the flame-retardant additive comprises red phosphorus, the additive preferably being supplied in the form of a mixture of the phosphorus with organic polymer (preferably a phenol-formaldehyde resin), the amount of the red phosphorus preferably being up to 70%, more preferably up to 60%, by weight of the additive mixture.

Mixtures of the various additives hereinbefore described may be used. The additive materials and quantities will preferably be selected to retain physical properties of the gels within typical "gel-like" ranges, for example substantially elastic recovery after elongation up to 100% , preferably up to 200% ; tensile strength less than 1 MPa; and dynamic storage modulus G' less than 0.05MPa, as described in the aforementioned WO-A-9005166. Some classes of additive, notably the phosphate oils, when used in higher percentages may tend to reduce the elongation of the gel material below desirable levels. Lower levels of the phosphate oils together with additional amounts of one or more solid flame-retardant additives may be advantageous.

The invention includes the use of the gel compositions as a sealant between adjacent solid surfaces, many such uses of un-flame-retarded gels being known per se. The invention also includes sealant gaskets or profiles comprising a carrier member carrying coatings of the gel composition. The invention is especially relevant to gels for use in commercial or domestic environments, for example in appliances, instrumentation, communications equipment, where UL94 performance is increasingly required.

Specific embodiments of the present invention will now be described by way of example.

The weight percentages of flame retardants (based on the whole composition) indicated in the following table were stirred together with the extender oil, the copolymer and a small amount of antioxidant. After five or ten minutes, the mixtures were converted into gels using known methods and conditions by mixing for 1 hour at 220°C in a 1 litre Baker Perkins Z-blade mixer. The resulting gels with the indicated oil/copolymer weight ratio (O/R) were made for these examples either from SEPS triblock copolymer available under the Trade Mark "Septon 2006" (from Kuraray) and a paraffm/naphthene oil available under the Trade Mark "Vestan A360B" from Fina Chemicals, or from SEBS triblock copolymer available under the Trade Mark "Kraton G1654" from Shell and a paraffm/naphthene oil available under the Trade Mark "Witco 380" from Witco. In all cases, 0.5% of antioxidant (Irganox 1010 Trade Mark) was included, based on the total composition weight. The gels were pressed into 125 mm x 50 mm x 6 mm plaques. Bar samples 125 mm long, 13 mm wide, and 6 mm thick were cut from these plaques using a hot knife and were tested in accordance with the UL 94 Horizontal Burning Test (April 19, 1995) to give the indicated burmng rates in mm per minute ("SE" =Self extinguished). Also recorded was ignition (Y) or non-ignition (N) of cotton wool placed 30 cm below the test sample as a modification of this test, which does not call for the cotton wool.

In another set of Examples using Kraton G1654 SEBS triblock copolymer, the following results were similarly obtained.

Flame retardant additives in the above gel formulations

Examples 22 to 25, 32 and 33 illustrate the aforementioned point that some additives may detract from desirable gel properties to some extent. The Phosflex additives used at 30% levels in Examples 22 and 23 produced good flame-retarding performance, but reduced the elongation to break from the desirable 100+ % to less clearly "gel-like" levels of 67% and 49% respectively, while tensile strength and dynamic storage modulus remained within the desirable gel-like ranges. When the same additives were used at 10% level as in Examples 32 and 33, the elongations were over 200% and over 100% respectively, but with less flame retardancy. The 20% additive levels of Examples 24 and 25 produced good flame retardancy with expected borderline gel elongations. Thus, mixtures of the Phosflex oils with other solid flame-retardant additives may advantageously provide good flame retardancy with better gel properties, possibly with less total additive.

Claims

1. A flame-retardant gel composition comprising a block copolymer having an elastomeric mid-block between relatively hard end blocks, at least 200 (preferably at least 300) parts by weight, per 100 parts by weight of the said copolymer, of an extender liquid which extends and softens the elastomeric mid-block of the said copolymer, and flame-retardant additive in an amount of not more than 40% by weight based on the combined weight of the said copolymer, extender liquid and additive, the amount of the said additive being sufficient to reduce the burning rate of a 125 mm x 50 mm x 6 mm sample of the composition by at least 25%, preferably at least 45%, more preferably at least 65%, when tested in accordance with the UL-94 Horizontal Burn Test (19 April 1995).

2. A composition according to claim 1, wherein the amount of the said additive is sufficient (a) to achieve self-extinction of the said sample when so tested and/or (b) to avoid ignition of cotton wool positioned 30cm below the said sample when so tested.

3. A composition according to claim 1 or 2, wherein the said copolymer comprises one or more styrene-alkylene-styrene or alkylmethacrylate-alkylene- alkylmethacrylate thermoplastic elastomer triblock copolymers, the alky lene mid- block preferably having number average molecular weight Mn within the range from 38000 to 150000 and the end blocks preferably having number average molecular weight Mn within the range from 30000 to 40000.

4. A composition according to claim 3, wherein the alky lene mid-block is hydrogenated, preferably being an ethylene/propylene and/or ethylene/butylene block.

5. A composition according to any preceding claim, wherein the amount of the flame- retardant additive is not more than 35% , preferably not more than 30% , by weight of the composition.

6. A composition according to any preceding claim, wherein the amount of the flame- retardant additive is at least 5% by weight of the composition.

7. A composition according to any preceding claim, wherein the weight ratio of the extender liquid to the said copolymer is within the range from 3:1 to 30:1, preferably 4: 1 to 15:1, especially 4: 1 to 10:1.

8. A composition according to any preceding claim, wherein the flame-retardant additive comprises a halogenated organic compound, preferably in combination with antimony oxide.

9. A composition according to any preceding claim, wherein the flame-retardant additive comprises a char-forming or intumescent material.

10. A composition according to any preceding claim, wherein the flame-retardant additive comprises phosphorus or a phosphorus compound.

11. A composition according to claim 10, wherein the flame-retardant additive comprises inorganic phosphate, preferably ammonium polyphosphate, together with a nitrogen-containing synergist therefor.

12. A composition according to claim 11, wherein the synergist comprises an organic amine phosphate, preferably melamine phosphate.

13. A composition according to claim 11 or 12, wherein the flame-retardant additive further includes a polyol, preferably pentaerythritol.

14. A composition according to claim 10, wherein the flame-retardant additive comprises an organic phosphate.

15. A composition according to claim 14, wherein the organic phosphate comprises a phosphate oil, preferably one or more selected from tris(2-chloroethyl)phosphate, tris(2-chloropropyl)phosphate, trixylyl phosphate, and tributoxyethyl phosphate, optionally together with one or more solid flame-retardant additives.

16. A composition according to claim 10, wherein the flame-retardant additive comprises red phosphorus, the additive preferably being provided in the form of a mixture of the phosphorus with organic polymer (preferably a phenol-formaldehyde resin), the amount of the red phosphorus preferably being up to 70% , more preferably up to 60%, by weight of the said additive mixture.

17. A composition according to any preceding claim, wherein the extender liquid is a combustible oil, preferably a paraffin/naphthene oil.

18. Use of a gel composition according to any preceding claim as a sealant between adjacent solid surfaces.

19. A sealant gasket or profile comprising a carrier member carrying a coating of a gel composition according to any of claims 1 to 17.