WO2015066138A1

WO2015066138A1 - Flame retardant thermoplastic polymer compositions

Info

Publication number: WO2015066138A1
Application number: PCT/US2014/062838
Authority: WO
Inventors: Thomas Daniel Bekemeier; Mert KILINC; Christophe Paulo; David Pierre; Vincent Rerat; Gary Michael Wieber; Gerald Lawrence Witucki
Original assignee: Dow Corning Corporation
Priority date: 2013-10-29
Filing date: 2014-10-29
Publication date: 2015-05-07
Also published as: TW201527424A

Abstract

The invention provides a flame retardant thermoplastic polymer composition. The composition contains a thermoplastic organic polymer and at least one flame retardant agent. The flame retardant agent is an amino-functional silicone resin.

Description

FLAME RETARDANT THERMOPLASTIC POLYMER COMPOSITIONS

[0001] This invention relates to flame retardant agents for thermoplastic organic polymer compositions, and to flame retardant thermoplastic polymer compositions containing them. The invention is particularly applicable to polyamides, but is also useful for other thermoplastic polymers such as for example polyesters.

[0002] The invention provides a flame retardant thermoplastic polymer composition. The composition contains a thermoplastic organic polymer and at least one flame retardant agent. The flame retardant agent is an amino-functional silicone resin.

[0003] A composition is typically a mixture of at least two chemically different compounds. A thermoplastic organic polymer composition is a composition containing a thermoplastic organic polymer and, usually, other ingredients sometimes called additives. The thermoplastic organic polymer typically forms a polymeric matrix. The other ingredients or additives may contain, for example, flame retardant agent(s), filler(s), reinforcing agent, mineral powder etc.

[0004] A flame retardant agent is a compound which is able to provide flame retardant properties. Typically a flame retardant agent provides flame retardancy properties when added to a composition containing a thermoplastic organic polymer. Flame retardant properties are said to be obtained when the composition containing the flame retardant agent shows increased resistance to burning or other degradation by a flame compared to a composition which does not contain the flame retardant agent. A composition containing a flame retardant agent resists longer to a flame than the same composition but not containing the flame retardant agent. A flame-retardant composition may contain a thermoplastic polymer usually forming a matrix and one or more flame retardant agent(s).

[0005] A polysiloxane or silicone is a silicon containing compound containing repeating Si-O-Si bonds. A silane is a silicon containing compound which does not contain repeating Si-O-Si bonds. A polymer is a compound containing repeating units, typically forming one or more chains. An organic polymer is a polymer containing repeating C-C bonds. An organic polymer is sometimes defined as a polymer in which at least 50% of the atoms in the polymer backbone are carbon atoms. A thermoplastic polymer is a polymer which has thermoplastic properties. A thermoplastic polymer allows plastic deformation when it is heated.

[0006] A silicone is typically a material based on a polymer chain containing repeating Si-O-Si bonds. A silicone may comprise mono-functional (M), di- functional (D), tri-functional (T) and/or tetra-functional siloxane (Q) unit(s). The Si atom of a M unit is bonded to 1 O atom. The Si atom of a D unit is bonded to 2 O atoms. The Si atom of a T unit is bonded to 3 O atoms. The Si atom of a Q unit is bonded to 4 O atoms.

A silicone resin contains at least one T unit and/or at least one Q unit. Preferably a silicone resin contains two or more T units and/or Q units.

A M unit typically has the formula R₃S1O1/2. A D unit typically has the formula R₂Si02 2. A T unit typically has the formula RS1O₃/2. A Q unit typically has the formula S1O4/2. Each R is a substituent (also called a group) linked to the silicon atom. Where the unit contains more than one R, the Rs can be the same or can be different on one silicon atom. Furthermore the Rs can be different on different silicon atoms. R is often an organic substituent i.e. a substituent containing at least one C atom, preferably several C atoms forming C-C bonds.

[0007] The percentages by weight mentioned in the following description are, unless indicated differently, based on the weight of the total composition i.e. the composition containing the polymer and all other ingredients. The thermoplastic organic polymer can be formed of one or more polymers.

[0008] In one preferred embodiment of the invention, one of these polymers forming the thermoplastic organic polymer is polyamide. Preferably at least 50% by weight based on the total weight of all thermoplastic organic polymers present in the composition, is formed of polyamide. Preferably, the thermoplastic organic polymer is essentially formed of polyamide. We have found that amino- silicone resins are particularly suitable to provide flame retardant properties to polyamide. [0009] In other preferred embodiments the thermoplastic organic polymer contains polyester. In such preferred embodiments, preferably at least 50% by weight based on the total weight of thermoplastic organic polymers present in the composition, is formed of polyester. More preferably, the thermoplastic organic polymer is essentially formed of polyester.

[0010] It is believed the aminosilicone resin is incorporated within the thermoplastic matrix without reaction between the amino functions of the additive and the matrix. Preferably the thermoplastic matrix is free of reactive unsaturations that could otherwise potentially react with the aminofunctions of the flame retardant agent. It is believed that the amino functions of the flame retardant agent are only susceptible to possibly react in case the composition is exposed to flame.

[0011] A reactive unsaturation is an unsaturation able to react in contrast with an unreactive unsaturation. For example unsaturations contained in aryl groups, for example phenyl, have very few reactivity because of their aromatic character. Those unsaturations are thus considered as non reactive unsaturations. The polymer(ic) matrix used in the present invention is preferably a polymer, a copolymer or a mixture of polymers which is /are free of reactive unsaturations. If present, the unsaturations of the polymer, copolymer or mixture of polymers are preferably only non reactive unsaturations.

[0012] Preferably the thermoplastic polymer is free from polymer containing reactive unsaturations. Preferably the thermoplastic polymer is free from ABS (acrylonitrile butadiene styrene), SBS (poly(styrene-butadiene-styrene)) and/or or diene elastomer. Preferably the thermoplastic polymer is free from polyphenylene ester. Preferably the thermoplastic polymer is free of EPDM (ethylene propoylene diene rubber).

[0013] The thermoplastic polymer can be a saturated polymer, substantially free of unsaturations. The thermoplastic polymer may be PE (polyester), PA (polyamide), polyolefin like PP (polypropylene) or PE (polyethylene), PC (polycarbonate), PS (polystyrene), PET (polyethylene terephtalate), PBT (polybutylene terephtalate), PMMA (poly(methylmethacrylate)), POM (polyoxymethylene), PEEK (polyether ether ketone), PES (polyether sulfone), PPO (oly(phenylene oxide)).

The thermoplastic polymer may be a mixture of polymers or a copolymer.

[0014] Thermoplastic polyamides are widely used for many applications in which the polyamide is shaped, for example by injection moulding, blow moulding or extrusion. For example, thermoplastic polyamide compositions are frequently used for casings for electrical equipment or wiring. In such use the thermoplastic polyamide composition is required to have a certain level of fire resistance, but polyamides are not inherently flame retardant. Flame retardant polyamide compositions have been produced comprising halogen-containing flame retardant agents such as brominated polystyrene, polybromodiphenyl or polybromodiphenyl oxide. Such halogen- containing flame retardant agents may be hazardous to health and there is a need for flame retardant thermoplastic polyamide compositions which do not contain halogen- containing flame retardant agents.

[0015] CN- 102604377- A describes a flame retardant thermoplastic polyamide composition comprising 30-90% by weight thermoplastic polyamide resin, 5-40% bromine-containing flame retardant, 0.5-15% auxiliary flame retardant and 0-50% reinforcing material. The auxiliary flame retardant comprises zinc borate and organosilicone resin in weight ratio 9: 1 to 1 : 1.

[0016] JP-2004-115582-A describes preparing a flame retardant polyamide composition by kneading 80-99.9% by weight polyamide resin with 0.1-20% liquid silicone. JP-2004-115651-A describes a flame retardant polyamide composition comprising a polyamide resin containing aromatic units and a metal borate compound. JP-2003-192923-A describes a flame retardant thermoplastic resin composition comprising 20-94.9% by weight thermoplastic resin, 0.1-20% silicone compound containing a vinyl group and 5-60% reinforcement.

[0017] We have found according to the invention that certain silicone resins are particularly effective as flame retardant agents in halogen-free polyamide compositions and other thermoplastic organic polymer compositions. It is believed an amino silicone compound containing only M and D units will not provide the flame retardancy effect. At least one T and/or at least one Q unit is needed. A linear aminosilicone compound is not appropriate for the present invention.

[0018] A halogen-free flame retardant thermoplastic organic polymer composition according to the invention comprises a thermoplastic organic polymer and is characterised in that the composition contains an amino-functional silicone resin as flame retardant agent

[0019] A flame retardant agent according to one aspect of the invention for a thermoplastic organic polymer composition is characterised in that the flame retardant agent comprises 5 to 90%, preferably 50 to 90%, by weight of an amino-functional silicone resin, from 5 to 30% by weight of an auxiliary flame retardant selected from borate salts, melamine compounds and phosphinate salts, and from 0 to 45% by weight of a mineral powder based on the weight of all flame retardant agents with the total being 100%.

[0020] The invention also includes the use of a flame retardant agent comprising an amino-functional silicone resin for improving the flame retardance of a thermoplastic organic polymer composition.

[0021] The amino group or the amino groups present in the silicone resin is or are usually present in at least one R substituent which R is linked to a silicon atom as explained above. R is preferably an amino-substituted alkyl, aryl or aralkyl substituent. For example R is an aminoalkyl substituent.

[0022] The amino-functional silicone resin may comprise siloxane units selected from M units of the formula R₃S1O1_/2, D units of the formula R2S1O2_/2 or R2S1O1_/2 OZ, T units of the formula RS1O_3/2 _, RS1O2_/2 OZ or RSiOi_/2(OZ)₂, and Q units of the formula S1O4_/2 , S1O_3/2OZ, SiC>2_/2(OZ)2, or SiOi 2(OZ)3, where each R represents an organic group bonded to silicon or an amino group bonded to silicon and Z represents hydrogen or an alkyl group. The amino groups of the silicone resin then are usually present in organic groups R which can be amino-substituted alkyl, aryl or aralkyl groups, for example aminoalkyl groups. At least some of the siloxane units of the silicone resin are T units or Q units. The amino functional silicone resin thus has the formula M_x D_yT_zQ_w in which x, y, z and w can each be 0-100% in mole percent provided that z+w is different from 0, preferably at least 1%.

[0023] The amino-substituted organic group can for example be of the formula R'- (N(R")-A')_q-N(R")-A- wherein A and A' are each independently a linear or branched alkylene, arylene or aralkylene group having 1 to 10 carbon atoms and optionally containing an ether linkage; q = 0-4; R' is hydrogen or an alkyl, hydroxyalkyl, aryl or aralkyl group having 1 to 10 carbon atoms; and each R" independently is hydrogen or an alkyl, hydroxyalkyl, aryl or aralkyl group having 1 to 10 carbon atoms. Where A and/or A' is an alkylene group, the alkylene group can for example have 1 to 6 carbon atoms. Where R' and /or R" is an alkyl group, the alkyl group can for example have 1 to 8 carbon atoms, usually 1 to 4 carbon atoms. For example, the amino-substituted organic group can contain a primary aminoalkyl group in which R' and R" are both hydrogen; q = 0 or 1; and A and A' (if present) each contain 2 to 4 carbon atoms. Examples of preferred aminoalkyl groups include:

-(CH₂)₃NH₂, -(CH₂)₄NH₂, -(CH₂)₃NH(CH₂)₂NH₂, -CH₂CH(CH₃)CH₂NH(CH₂)₂NH₂, -(CH₂)₃NHCH₂CH₂NH(CH₂)₂NH₂, -CH₂CH(CH₃)CH₂NH(CH₂)3NH₂, -CH₂NH₂, -(CH₂) NH(CH₂)₄NH₂ and -(CH₂) 0(CH₂)₂NH₂. Many of these groups contain both primary and secondary amine groups. The amino-substituted organic group can alternatively contain only a secondary amine group, for example -(CH2)3-NH-(C6Hs) or -(CH2)3NH(CH3), or a tertiary amine group, for example -(CH2)3-N-(CH₃)2

Examples of preferred aminoaryl groups include aminophenyl such as 4-aminophenyl. Examples of preferred aminoaralkyl groups include aminobenzyl groups such as - CH2C6H4-NH2 and -CH(C6H5)NH2. The amino-substituted organic group can be present in M, D and/or T siloxane units.

[0024] The amino-functional silicone resin preferably has an amine equivalent weight of 200 to 2000 g/amine nitrogen, more preferably 300 to 1000 g/ amine nitrogen. [0025] Organic groups R in the amino-functional silicone resin other than amino- substituted organic groups can for example be alkyl and/or alkenyl groups having 1 to 6 carbon atoms and/or aryl or aralkyl groups having 6 to 10 carbon atoms. Alkyl groups R bonded to silicon are preferably methyl groups but can for example be ethyl groups. Alkenyl groups are not usually present in the amino-functional silicone resin but if present can be vinyl groups.

[0026] We have found that amino-functional silicone resins containing aryl groups, for example phenyl groups, can be more effective flame retardants for polyamide compositions than amino-functional silicone resins which do not contain aryl groups. The amino-functional silicone resin may for example comprise at least 50% by weight aryl groups based on the total weight of organic groups R in the amino-functional silicone resin, more preferably at least 60% aryl groups, and may for example contain 70 or 75 up to 80% or more aryl groups, preferably phenyl groups. One preferred type of silicone resin is thus an amino-functional phenyl methyl silicone resin.

[0027] The amino-functional resin used as flame retardant agent may contain other functionalities than the amino functionalities. Preferably, the resin also contains aryl functionalities, for example phenyl functionalities. It is meant that such additional functionalities are present in the resin at positions not directly linked to the aminofunctions. Those aryl functionalities can enhance compatibility with polymeric matrix, and/or the Tg and or thermal resistance.

[0028] The amino-functional silicone resin contains T and/or Q units. It preferably contains T units of the formula RS1O_3/2 in combination with M units of the formula R₃S1O1_/2 and/or D units of the formula R₂Si022- Amino-substituted organic groups are usually present in D units. Such D units can be (methyl)aminoalkylsiloxane units, for example (methyl)aminopropylsiloxane units NH2(CH2)3(CH3)Si022, (methyl)N- methylaminopropylsiloxane units, CH3NH(CH2)3(CH3)Si022, (methyl)N- phenylaminopropylsiloxane units, C6HsNH(CH2)3(CH3)Si02/2, or (methyl)-N- benzylaminopropylsiloxane units C6H5(CH2)NH(CH2)3(CH3)Si022 · The amino- substituted groups can alternatively be present in M units. Such M units can be (dimethyl)aminoalkylsiloxy units, for example NH2(CH2)3(CH₃)2SiOi 2 or aminoalkylsiloxane T units NH2(CH2)₃SiC>3_/2. Amino groups bonded to silicon can be present in D units such as (methyl)aminosiloxane units (H3C)(NH2)SiC>2/2- Aryl groups can be present in D units such as diphenylsiloxane units or methylphenylsiloxane units and/or in T units such as phenylsiloxane T units. Aralkyl groups can be present in D units such as for example methylbenzylsiloxane units and/or in T units such as benzylsiloxane T units. Alkyl groups can be present in D units such as (methyl)aminoalkylsiloxane units as described above or in (methyl)aminoarylsiloxane or (methyl)aminobenzylsiloxane units, and optionally in methylphenylsiloxane units and/or dimethylsiloxane units, and/or in M units such as trimethylsiloxy units and/or T units such as methylsiloxane units CH₃S1O_3/2.

[0029] The amino-functional silicone resin preferably contains less than 25% by weight hydroxy and/or alkoxy groups, for example 0 to 12% or 0 to 8% by weight combined hydroxy and/or alkoxy groups. Preferably the amino-functional silicone resin is free of residual alkoxy groups. Any hydroxy and/or alkoxy groups can be present in T units for example methylmethoxysilicone units CH3(OCH3)SiC>2/2 , methylhydroxysilicone units CH₃(HO)SiC>2_/2 or phenylhydroxysilicone units C6H5(HO)SiC>2/2, or D units for example dimethylmethoxysilicone units (CH₃)2(CH₃0)SiOi 2 or in Q units for example ROS1O_3/2 where R is alkyl or H .

[0030] The amino-functional silicone resin can be a liquid or solid resin. A liquid amino-functional silicone resin can for example have a kinetic viscosity of 200 to 50,000 centiStokes at 25°C. A solid resin can be preferred for ease of incorporation into the polymer matrix, which is usually in solid form too before forming the composition.

[0031] The thermoplastic organic polymer composition in which the amino-functional silicone resin flame retardant agent is incorporated comprises a thermoplastic organic polymer and optionally one or more fillers and/or reinforcing agents. The thermoplastic organic polymer is often the major component of the thermoplastic organic polymer composition i.e. it forms at least 50% by weight of the total thermoplastic organic polymer composition. The thermoplastic organic polymer can for example be a polyamide or alternatively can be a polyester. A polyamide is often designated by the term nylon.

[0032] Suitable thermoplastic polyamides include for example polycaprolactam (nylon-6), polyhexamethyleneadipamide (nylon-6,6), polyhexamethylenesebacamide (nylon-6, 10), polytetramethyleneadipamide (nylon-4,6), poly(metaxylylyene adipamide), polyhexamethylenephthalamide, polyhexamethyleneisophthalamide, Polyricin Polyamide 11 derived from vegetable oils: polyundecanolactam (such as Rilsan (trade mark) by Arkema), polyamide 12 (polydodecanolactam such as Vestamid L (trade mark) by Evonik). Alternatively the thermoplastic polyamide can contain aromatic moieties, for example polyhexamethyleneisophtalamide (nylon 61) or polyhexamethyleneterephtalamide (nylon 6T), or can be a fully aromatic polyamide such as Kevlar (trade mark) or Nomex (trade mark) from Dupont, Teijinconex, Twaron or Technora (trade marks) from Teijin, Kermel (trade mark) from Kermel or Sepctra from Honeywell. The thermoplastic polyamide can be a copolymer such as nylon-6, 66 made from caprolactam, hexamethylenediamine and adipic acid or nylon-66,610 made from hexamethylenediamine, adipic acid and sebacic acid. The thermoplastic polyamide can be a blend of any of the above polymers to achieve more balanced set of performances.

[0033] Examples of suitable polyesters include polyethylene terephthalate and polybutylene terephthalate, and blends and copolymers thereof.

[0034] The amino-functional silicone resin flame retardant agent can for example be incorporated in the thermoplastic organic polymer composition at 10 to 50% by weight amino-functional silicone resin, preferably 15 to 50%, for example 20 to 40% by weight, based on the weight of the thermoplastic organic polymer.

[0035] Examples of reinforcing agents which can be used in the thermoplastic organic polymer composition include fibrous compounds such as glass fibres, carbon fibres, metal fibres, natural fibres or ceramic fibres. Glass fibres can for example be in the form of continuous glass fibres, glass fibres cut to staple fibre length, milled glass fibre or a nonwoven or woven glass fire fabric. A fibrous reinforcing agent can for example be present at 0 to 150% by weight based on the weight of the thermoplastic organic polymer. For example glass fibres can be present in a polyamide composition at 10 to 150% by weight based on the weight of the thermoplastic organic polymer, preferably 15-100%, particularly from 15 up to 50 or 60% by weight. For example, the glass fibres can be present at 0 to 60% by weight of the composition based on the weight of the organic polymer and the glass fibres.

[0036] Examples of fillers which can be used in the thermoplastic organic polymer composition include talc, silica, calcium carbonate, mica, kaolin, titanium oxide, carbon black, metals, ceramic powder, borosilicate and/or clays such as wollastonite. Fillers can for example be present at 0 or 5 up to 50 or 95% by weight based on the weight of the thermoplastic organic polymer.

[0037] The amino-functional silicone resin can be used as the only flame retardant in the thermoplastic organic polymer composition but is most effectively used in combination with an auxiliary flame retardant which can for example be selected from borate salts, melamine compounds and phosphinate salts. The amino-functional silicone resin preferably comprises the major proportion by weight of the total flame retardants in the thermoplastic organic polymer composition. The amino-functional resin preferably forms at least 50% by weight of the weight of all flame retardant agents present in the composition.

[0038] An example of a suitable flame retardant borate salt is zinc borate such as that sold by U.S. Borax as 'Zinc Borate 500'. Zinc borate can for example be used at 1 to 20% by weight based on the thermoplastic organic polymer.

[0039] Melamine cyanurate, a hydrogen-bonded complex of melamine and cyanuric acid, is one example of a suitable melamine compound and is available for example from BASF as 'Melapur MC 25' . Melamine cyanurate can for example be used at 1 to 20% by weight based on the thermoplastic organic polymer. Other examples of melamine compounds are melamine phosphates such as melamine polyphosphate. [0040] An example of a suitable phosphinate salt is the metal phosphinate sold by Clariant as 'Exolit PO-1230' . The metal phosphinate can for example be used at 1 to 50% by weight based on the thermoplastic organic polymer, for example 1 to 20%.

[0041] The invention thus includes a halogen-free flame retardant agent for a thermoplastic organic polymer composition, characterised in that the flame retardant agent comprises 50 to 90% by weight of an amino-functional silicone resin, from 5 to 30% by weight of an auxiliary flame retardant selected from borate salts, melamine compounds and phosphinate salts, and from 0 to 45% by weight of a mineral powder, all based on the weight of total of all flame retardant agents. The mineral powder can for example be talc. The flame retardant agent may contain an intumescent additive such as for example ammonium polyphosphate. No halogen containing compound is added.

[0042] The flame retardant agent is thus halogen- free, that is it contains less than 1 % by weight halogen and preferably has no measurable halogen content. Similarly the thermoplastic organic polymer composition is halogen-free in the sense that it contains less than 1% by weight halogen. In one preferred embodiment the composition is phosphorus free, although in other embodiments a phosphorus compound can be present for a particular purpose, for example a melamine phosphate or metal phosphinate as auxiliary flame retardant or ammonium polyphosphate as an intumescent additive.

[0043] The thermoplastic organic polymer composition can be shaped by moulding, for example by injection moulding, extrusion or blow moulding, to form a variety of products such as casings, containers, profiles or fibres. The amino-functional silicone resin, or a flame retardant agent comprising the amino-functional silicone resin, can conveniently be incorporated in the thermoplastic organic polymer composition by extrusion, for example in a twin screw extruder. If the amino-functional silicone resin is a liquid, the twin screw extruder may be equipped with a liquid injection line for the silicone compounds and also a side feeder for feeding the thermoplastic organic polymer and any powder form co-additives such as an auxiliary flame retardant or mineral powder. The thermoplastic organic polymer and co-additives may be physically mixed before introduction to the side feeder. It may be convenient to premix the thermoplastic organic polymer with any fibrous reinforcing agent such as glass fibres before mixing with other ingredients. If the amino-functional silicone resin is a solid, all components of the thermoplastic organic polymer composition may be physically mixed before introduction to the extruder. The amino-functional silicone resin, or a flame retardant agent comprising the amino-functional silicone resin, can alternatively be incorporated in the thermoplastic organic polymer composition in an internal mixer such as a Brabender Plastograph (Trade Mark) mixer equipped with roller blades, or a Banbury mixer, or on a roll mill. When forming injection moulded articles from the thermoplastic organic polymer composition, the amino-functional silicone resin, or a flame retardant agent comprising the amino- functional silicone resin, can be incorporated in the thermoplastic organic polymer composition by extrusion as described above and the extrudate can be pelletized and then moulded in an injection moulding machine.

[0044] Polyamide compositions, particularly compositions based on nylon-6 or nylon- 6, 6, are widely used for casings for electrical and electronic products and wiring and are required to be flame retardant because of the risk of fire started by an electrical fault. The main benchmark test for compositions for such casings is the UL-94 test of Underwriters Laboratories Inc., particularly the Vertical Burning Test. In this test a total of 5 specimens each of length 125mm and width 13mm and of thickness 0.7mm or 1.5 mm or 3.0mm are tested per thickness. Each specimen is mounted with long axis vertical and supported such that its lower end is 10 mm above a Bunsen burner. A blue 20 mm high flame is applied to the center of the lower edge of the specimen for 10 seconds and removed. If burning ceases within 30 seconds, the flame is reapplied for an additional 10 seconds. If the specimen drips, particles are allowed to fall onto a layer of dry absorbent surgical cotton placed 300 mm below.

[0045] The requirements for a UL94 rating of V-0 are that the specimens must not burn with flaming combustion for more than 10 s after application of the test flame. The total flaming combustion time must not exceed 50 s for the 5 flame applications. The burning and glowing time after the second flame application must not exceed 30 s. The specimens must not burn with flaming or glowing combustion up to the holding clamp and must not drip flaming particles that ignite the dry absorbent surgical cotton located 300 mm below. The requirements for a UL94 rating of V- 1 are that the specimens must not burn with flaming combustion for more than 30 s after application of the test flame. The total flaming combustion time must not exceed 250 s for the 5 flame applications. The burning and glowing time after the second flame application must not exceed 60 s. The specimens must not burn with flaming or glowing combustion up to the holding clamp and must not drip flaming particles that ignite the dry absorbent surgical cotton located 300 mm below. The halogen-free and phosphorus-free flame retardant polyamide compositions of the present invention are capable of achieving a UL94 rating of V-l for specimens of thickness 1.5mm.

[0046] The invention is illustrated by the following Examples, in which parts and percentages are by weight.

Examples 1 to 18

[0047] Polyamide compositions were prepared from the following materials in the proportions shown in Table 1 below

PA-6 nylon-6

GF glass fibre

ASR 1 amino-functional silicone resin comprising NH2(CH₂)3(CH₃)Si022 D units, diphenylsiloxane D units, phenylsiloxane T units and trimethylsiloxy M units, having an alkoxy content of less than 0.5%, an amine hydrogen equivalent weight of 500 g/mole amine nitrogen, a phenyl content of 64.6% and a viscosity of 3750 centiStokes at 25°C

ASR2 amino-functional silicone resin comprising NH2(CH2)3(CH3)SiC>2/2 D units, phenylsiloxane T units, diphenylsiloxane D units, trimethylsiloxy M units and dimethylsiloxy D units, having an alkoxy content of 4%, an amine hydrogen equivalent weight of 890 g/ mole amine nitrogen , a phenyl content of 70.0% and a viscosity of 5000 centiStokes at 25°C ASR3 amino-functional silicone resin comprising NH2(CH2)3(CH3)SiC>2/2 D units, phenylsiloxane T units and trimethylsiloxy M units, having a viscosity of 2000 centiStokes at 25°C

Talc talc from Imifabi sold as HTP Ultra 5 talc

ZB US Borax Zinc Borate 500

MC MC 25 melamine cyanurate

Table 1

[0048] All compositions were made starting from a masterbatch containing 70% PA-6 and 30% glass fibres, sold by Albis Plastics, as Altech ® PA6 A 2030/109 GF30. The Altech polyamide masterbatch was dried at 100°C for 6 hours in an desiccant hot air blowing dryer. The dried polyamide was mixed physically with the solid additives zinc borate, talc and melamine cyanurate (if used). The solid additives mixed with polyamide were fed to the main inlet of a Brabender co-rotating twin screw extruder of screw diameter D 20mm and L/D 40 equipped with a liquid injection head and when the polymer came out of the die, amino-functional silicone resin was started to be injected. The amino-functional silicone resin was heated at 68°C to lower its viscosity and was pumped through a metal piping line kept at 62°C to the injection head in the extruder. The total throughput to the extruder was 1.6 kg/h. The extruder temperature profile was 260-245-240-240-240°C from hopper to the die section. The screw speed was 180 rpm.

[0049] The flame retardant polyamide composition extruded was passed through a water bath for cooling and then pelletized. Pelletized material was injected moulded into rectangular bars of dimensions 135 mm x 12.5 mm x 1.5 mm for UL-94 testing. Prior to injection moulding, the polymer pellets were dried again to avoid any degradation due to moisture present in the pellets. The sample bars were tested according to the UL-94 Vertical Burning Test as described above. The results are shown in Table 2 below.

Table 2

[0050] It can be seen that all the products of Examples 1 to 18 passed the UL-94 Vertical Burning Test with a rating of V- 1.

Comparative Example CI

[0051] The 30 wt.% glass filled nylon-6 polyamide was extruded and injection moulded into sample bars as described above. The sample bars failed the UL-94 Vertical Burning Test, burning totally up to the holding clamp and ignite the dry absorbent surgical cotton located 300 mm below.

Comparative Example C2

[0052] The 30 wt.% glass filled nylon-6 polyamide was blended with talc and extruded with a methoxy-terminated dimethyl, methoxyphenyl siloxane phenyl silsesquioxane resin to form a composition comprising 56% nylon-6, 24% glass fibre, 16% silsesquioxane resin and 4% talc. The composition was pelletized and injection moulded into sample bars as described above. The sample bars failed the UL-94 Vertical Burning Test, burning totally up to the holding clamp and ignite the dry absorbent surgical cotton located 300 mm below.

[0053] Comparison of Comparative Example C2 with the Examples of the invention indicates that the presence of amino groups in the silicone resin is essential for effective flame retardancy of the polyamide.

Comparative Example C3

[0054] The 30 wt.% glass filled nylon-6 polyamide was blended with talc, melamine cyanurate and zinc borate and extruded with a mixture of aminopropyltriethoxysilane and a diphenyl methylphenyl silicone resin to form a composition comprising 47.25% nylon-6, 20.25% glass fibre, 15% aminopropyltriethoxysilane, 7.5% diphenyl methylphenyl silicone resin, 4% talc, 5% melamine cyanurate and 1% zinc borate. The composition was pelletized and injection moulded into sample bars as described above. The sample bars failed the UL-94 Vertical Burning Test, burning totally up to the holding clamp and ignite the dry absorbent surgical cotton located 300 mm below.

[0055] Comparison of Comparative Example C3 with the Examples of the invention such as Examples 9, 17 and 18 indicates that the presence of amino groups in the silicone resin is essential for effective flame retardancy of the polyamide, and that a mixture of an aminosilicone and a phenyl silicone resin is not effective as a flame retardant for polyamide.

Claims

1. A halogen-free flame retardant thermoplastic polymer composition comprising a thermoplastic organic polymer, characterised in that the composition contains an amino-functional silicone resin as flame retardant agent.

2. A halogen-free flame retardant thermoplastic polymer composition according to Claim 1, characterised in that the composition contains from 10 to 50% by weight, based on the weight of thermoplastic organic polymer, of the amino- functional silicone resin.

3. A halogen- free flame retardant thermoplastic polymer composition according to Claim 1 or Claim 2 characterised in that the amino-functional silicone resin contains aryl groups.

4. A halogen-free flame retardant thermoplastic polymer composition according to Claim 3 characterised in that the silicone resin is an amino-functional phenyl methyl silicone resin.

5. A halogen- free flame retardant thermoplastic polymer composition according to Claim 3 or Claim 4 characterised in that at least 50% by weight of the organic groups bonded to the silicon atoms of the silicone resin are aryl groups.

6. A halogen-free flame retardant thermoplastic polymer composition according to any of Claims 1 to 5 characterised in that the amino-functional silicone resin contains T units.

7. A halogen-free flame retardant thermoplastic polymer composition according to any of Claims 1 to 6 characterised in that the amine equivalent weight of the amino-functional silicone resin is from 300 to 1000 grams per mole amine nitrogen.

8. A halogen-free flame retardant thermoplastic polymer composition according to any of Claims 1 to 7 characterised in that the amino-functional silicone resin is present at 20 to 40% by weight based on the weight of thermoplastic organic polymer.

9. A halogen-free flame retardant thermoplastic polymer composition according to any of Claims 1 to 8 characterised in that the composition contains 10 to 50% by weight glass fibres based on the weight of thermoplastic organic polymer.

10. A halogen- free flame retardant thermoplastic polymer composition according to any of Claims 1 to 9 characterised in that the amino-functional silicone resin forms 50 to 100% of the total flame retardant agent(s) present(s) in the thermoplastic polymer composition.

11. A halogen- free flame retardant thermoplastic polymer composition according to any of Claims 1 to 10 characterised in that the thermoplastic organic polymer is a polyamide.

12. A halogen- free flame retardant thermoplastic polymer composition according to any of Claims 1 to 10 characterised in that the thermoplastic organic polymer is a polyester.

13. A halogen-free flame retardant agent for a thermoplastic organic polymer composition, characterised in that the flame retardant agent comprises 5 to 90% by weight of an amino-functional silicone resin, from 5 to 30% by weight, of an auxiliary flame retardant selected from borate salts, melamine compounds and phosphinate salts, and from 0 to 45% by weight of a mineral powder all based on the weight of the total of flame retardant agents.

14. A halogen-free flame retardant agent according to Claim 13, characterised in that the auxiliary flame retardant comprises zinc borate.

15. A halogen- free flame retardant agent according to Claim 13 or Claim 14, characterised in that the auxiliary flame retardant comprises melamine cyanurate.

16. A halogen- free flame retardant agent according to any of Claims 13 to 15, characterised in that the auxiliary flame retardant comprises melamine polyphosphate.

17. A halogen-free flame retardant agent according to any of Claims 13 to 16, characterised in that the auxiliary flame retardant comprises a metal phosphinate.

18. Use of a flame retardant agent comprising an amino-functional silicone resin for improving the flame retardancy of a thermoplastic organic polymer composition. A process for improving the flame retardancy of a thermoplastic organic polymer composition wherein an aminofunctional silicone resin is incorporated in the thermoplastic organic polymer composition as flame retardant.