WO2025093297A1

WO2025093297A1 - Flame retardant composition with improved electrical properties and hydrolysis stability

Info

Publication number: WO2025093297A1
Application number: PCT/EP2024/079185
Authority: WO
Inventors: Eva Maria Leuschner; Sebastian Hoerold; Elke Schlosser
Original assignee: Clariant International Ltd
Current assignee: Clariant International Ltd
Priority date: 2023-10-30
Filing date: 2024-10-16
Publication date: 2025-05-08
Anticipated expiration: 2026-04-30
Also published as: TW202536085A

Abstract

A flame retardant composition with improved electrical properties and hydrolysis stability, its uses for polymers, and further application in electrical and electronic parts. Particularly, the flame retardant composition comprises an alkyl phosphinic acid salt, a hydroxyapatite and a carbodiimide, along with optional components such as a nitrogen-containing synergist, a sterically hindered phenol, and a phosphorylated fatty acid ester.

Description

Flame retardant composition with improved electrical properties and hydrolysis stability

Technical Field

The present invention relates to a flame retardant composition with improved electrical properties and hydrolysis stability, the uses thereof for polymers, and a flame-retardant polymer comprising said flame retardant composition.

Background Art

To satisfy industrial flame retardancy requirements, it is typical to introduce one or more flame retardant agents into polymer material. In modern formulations, nonhalogenated flame retardant systems are often favored, due to their ability to generate low smoke density and less toxic smoke composition during combustion, alongside other environmentally favorable characteristics.

Among the nonhalogenated flame retardants, the salts of phosphinic acids (also known as phosphinates) have been established as particularly effective flame retardants, especially in thermoplastic polymer applications, as disclosed in DE-A- 2252258 and DE-A-2447727.

Notwithstanding, the requisite high concentrations of phosphinate flame retardants in thermoplastic polymers, intended to ensure satisfactory flame resistance, can inadvertently affect the stability of the flame-retardant polymer due to the reactivity of these retardants during high-temperature polymer melt processing.

To counteract this adverse effect, synergistic combinations of phosphinates with specific nitrogen-bearing compounds, most notably melamine derivatives, have been identified. These combinations have exhibited enhanced flame retardant efficacy in a diverse range of polymers, surpassing the performance of the sole use of phosphinates, as referenced in WO 2002/28953 A1 , DE 197 34 437 A1 , and DE 197 37 727 A1. US Patent 7,420,007 B2 discloses compositions of dialkylphosphinates, inclusive of a minor quantity of selected telomers, exhibiting remarkable suitability as flame retardants for polymers. Upon incorporation of the telomer-containing flame retardant into the polymer matrix, the resultant polymer undergoes merely a negligible degree of degradation.

Furthermore, WO 2014/135256 A1 discloses polyamide compositions comprising a dialkylphosphinic salt and a salt of phosphorous acid, which notably achieved improved thermal stability, reduced tendency to migration and good electrical and mechanical properties.

In light of the broad range of applications for flame-retardant polymer compositions in industrial settings, there remains an ongoing need to devise new synergistic combinations of phosphinate flame retardants and their synergist(s). Such synergistic combinations should aim to yield polymers characterized by enhanced flame retardancy, good electrical and mechanical properties, and sustained hydrolytic stability under humid conditions.

It is therefore an object of the present invention to provide novel phosphinatecontaining flame retardant composition to help obtain a flame-retardant polymer with the above-described profile of properties.

The present invention provides a flame retardant composition comprising: as component A, from 40 to 99.9 % by weight of a phosphinic acid salt of the formula (I)

wherein R¹, R² identical or different, are Ci -Ce-alkyl, linear or branched,

M is Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K and/or a protonated nitrogen base, m is from 1 to 4; as component B, from 0.1 to 30 % by weight of a hydroxyapatite; as component C, from 0 to 50% by weight of a nitrogen-containing synergist selected from a group consisting of condensation products of melamine, reaction products of melamine with phosphoric acids, and melamine cyanurate; as component D, from 0 to 10% by weight of a carbodiimide; as component E, from 0 to 10% by weight of a sterically hindered phenol; and as component F, from 0 to 50% by weight of a phosphorylated fatty acid ester; wherein the sum of the components is always 100 % by weight.

Component A usually takes up 50 to 95 % by weight of the flame retardant composition, preferably 55 to 90 % by weight.

M is preferably aluminum, calcium, titanium, zinc, tin, or zirconium, and more preferably aluminum.

R¹ and R², identical or different, are preferably methyl, ethyl, n-propyl, isopropyl, n- butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, and/or isohexyl.

A particularly preferred example of component A) is diethyl phosphinic salt of Al.

Other examples of component A) include ethylbutylphosphinic salt, dibutylphosphinic salt, ethylhexylphosphinic salt, butylhexylphosphinic salt, ethyloctylphosphinic salt, sec-butylethylphosphinic salt, (1 - ethylbutyl)butylphosphinic salt, ethyl(1 -methylpentyl)phosphinic salt, di-sec- butylphosphinic salt (di-1 -methylpropylphosphinic salt), propyl(hexyl)phosphinic salt, dihexylphosphinic salt, hexyl(nonyl)phosphinic salt, and dinonylphosphinic salt. Hydroxyapatite component B usually takes up 0.1 to 30 % by weight of the flame retardant composition, preferably 5 to 25 % by weight, and more preferably 5 to 15 % by weight.

Hydroxyapatite, at times referred to "HAp" in the art, is a naturally occurring mineral form of calcium apatite with the formula Ca₅(RO₄)3(OH), wherein the hydroxide (OH) ions may be partially replaced by fluoride, chloride, or carbonate. It is the main component of tooth enamel and bone mineral. In the context of this invention, hydroxyapatite may be synthetic or naturally derived and can be in the form of particles, whiskers, fibers, or any other suitable morphology.

When present, nitrogen-containing component C usually takes up 5 to 45 % by weight of the flame retardant composition, preferably 15 to 45 % by weight.

Preferably, component C is selected from a group of melem, melam, melamine cyanurate, melon, dimelamine pyrophosphate, melamine polyphosphate, melem polyphosphate, melam polyphosphate, melon polyphosphate and mixed poly salts thereof, and nitrogen-containing phosphates of the formula (NH4)yH3-_yPO4 or (NH4PO3)Z, where y is 1 to 3 and z is 1 to 10 000. More preferably, component C is selected from a group consisting of melamine cyanurate, melamine polyphosphate, and melem. In one particularly preferred embodiment, component C is melem.

When present, carbodiimide component D usually takes up 1 to 10 % by weight of the flame retardant composition, preferably 2 to 6 % by weight.

In the context of this disclosure, 'carbodiimide' refers to organic compounds characterized by the functional group N=C=N. Representative examples of carbodiimides include, but are not limited to, dicyclohexylcarbodiimide (DCC) and diisopropylcarbodiimide (DIC). The term 'carbodiimide' as used herein encompasses both the foundational structure as well as its various derivations and substitutions. In a preferred embodiment, component D is a polymeric carbodiimide. In the context of this disclosure, ‘polymeric carbodiimide’ denotes a polymer derived from the polymerization of monomers containing the carbodiimide functional group (N=C=N). Such polymers can be linear, branched, or crosslinked in nature.

When present, component E of a sterically hindered phenol usually takes up 1 to 10% by weight of the flame retardant composition, preferably 2 to 5 % by weight.

In the context of this disclosure, 'sterically hindered phenol' refers to a phenolic compound wherein the hydroxyl group attached to the aromatic ring is encumbered by adjacent bulky substituents, restricting its reactivity due to steric effects. These bulky substituents can include, but are not limited to, tertiary alkyl groups, halogenated alkyl groups, and other large organic moieties. Sterically hindered phenols are often employed as antioxidants due to their ability to stabilize other molecules by donating hydrogen from their hydroxyl group. The term 'sterically hindered phenol' as used herein encompasses both the foundational structure with a hindered hydroxyl group as well as its various derivatives and substitutions.

Suitable commercial products for component E include:

Irganox® 1010 from BASF, which is pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyljpropionate);

Irganox® 245 from BASF, which is ethylenebis(oxyethylene) bis(3-(5-tert-butyl-4- hydroxy-mtolyljpropionate); and

Hostanox® 03 from Clariant, which is ethylene glycol bis[3,3-bis(3-tert-butyl-4- hydroxyphenyl)butyrate.

When present, component F of a phosphorylated fatty acid ester usually takes up 5 to 45% by weight of the flame retardant composition, preferably 15 to 45 % by weight.

In the context of this disclosure, 'phosphorylated fatty acid ester' refers to a derivative of a fatty acid wherein a hydroxyl group of the fatty acid, or an alcohol derived therefrom, has been esterified with a phosphate or a derivative thereof. The resulting structure typically comprises a fatty acid moiety ester-linked to a phosphoryl group (P=O). The fatty acid portion can originate from saturated, unsaturated, or polyunsaturated fatty acids, and the phosphate moiety may be present as mono-, di-, or tri-esters, potentially further substituted or complexed with cations or organic moieties. The term 'phosphorylated fatty acid ester' as used herein encompasses both the core structure defined by the ester linkage between the fatty acid and the phosphoryl group, as well as its various derivatives, isomers, and salts.

In a preferred embodiment, the component F comprises an ester based on alkylated triphenyl phosphates and glycerol esters.

Suitable commercial products for component F include:

Lubio® FL30, complex esters based on alkylated triphenyl phosphates and glycerol esters, a phosphorylated fatty acid ester with high bio-based content based on 2- ethylhexylphosphate (CAS: 12645-31 -7); and

Lubio® FL31 , complex esters based on alkylated triphenyl phosphates and glycerol ester, a phosphorylated fatty acid ester based on phosphor acid esters with high phosphorous content.

The flame retardant composition of the present invention optionally comprises other synergists and/or stabilizers, such as sterically hindered amines and light stabilizers (e.g. Chimasorb® 944, Hostavin® products), phosphites, phosphonites and antioxidants (e.g. Sandostab® P-EPQ from Clariant) and separating agents (Licomont® products from Clariant).

Other optional additives to the flame retardant composition of the present invention include, but unlimited to, UV stabilizers, gamma-ray stabilizers, hydrolysis stabilizers, co-stabilizers for antioxidants, antistatics, emulsifiers, nucleating agents, plasticizers, processing auxiliaries, impact modifiers, and further suitable flame retardants such as aryl phosphates, phosphonates, phosphazenes, salts of hypophosphorous acid, and red phosphorus. The invention also relates to a flame-retardant polymer composition comprising a flame retardant composition as aforementioned and a thermoplastic polymer P, wherein the flame retardant composition takes up 2 to 50% by weight of the flameretardant polymer composition.

The flame-retardant polymer composition typically comprises: from 5 to 50% by weight of the flame retardant composition as aforementioned; from 50 to 98% by weight of a thermoplastic polymer P; and from 0 to 40% by weight of a reinforcer or filler R.

The flame-retardant polymer composition preferably comprises: from 5 to 30% by weight of the flame retardant composition as aforementioned; from 65 to 90% by weight of a thermoplastic polymer P; and from 5 to 40% by weight of a reinforcer or filler R.

Examples of the thermoplastic polymer P include, but unlimited to, polyesters, polyamides, thermoplastic elastomers, thermoplastic polyurethanes, thermoplastic polyester elastomers, styrenics, polyketones, polyolefins, polyacrylates, and polymer blends comprising polyamides or polyesters or other blends. Preferably, the thermoplastic polymer P comprises polyester or polyamide.

Suitable polyesters for the thermoplastic polymer component P include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), poly-1 , 4- dimethylolcyclohexane terephthalate, polyhydroxybenzoates, block polyether esters which derive from polyethers with hydroxyl end groups, and also polyesters modified with polycarbonates or MBS (Methacrylate-Butadiene-Styrene).

Suitable polyamides for the thermoplastic polymer component P may be selected from a group consisting of aliphatic polyamides, semiaromatic polyamides, aromatic polyamides, elastomeric polyamides, and mixtures thereof. In one preferred embodiment, the thermoplastic polymer component P comprises an aliphatic polyamide, wherein the aliphatic polyamide can be selected from a group consisting of nylon-2/12, nylon-4, nylon-4/6, nylon-6, nylon-6, 6, a copolymer of nylon-6 and nylon-6, 6, nylon-6/9, nylon-6/10, nylon-6/12, nylon-6/66, nylon-7, nylon-7/7, nylon- 8, nylon-8/8, nylon-9, nylon-9/9, nylon-10, nylon-10/9, nylon-10/10, nylon-11 , nylon- 12, and nylon-6, 10, and is preferably nylon-6, nylon-6, 6, or mixture thereof.

Suitable examples for reinforcer/filler component R are selected from the conventional examples in the polymer art and are preferably based on talc, mica, silicate, quartz, titanium dioxide, wollastonite, kaolin, amorphous silicas, nanoscale minerals, more preferably montmorillonites or nanoboehmite, magnesium carbonate, chalk, feldspar, barium sulfate, glass beads and/or fibrous fillers and/or reinforcers based on carbon fibers and/or glass fibers. Preference is given to mineral particulate fillers based on talc, mica, silicate, quartz, titanium dioxide, wollastonite, kaolin, amorphous silicas, magnesium carbonate, chalk, feldspar, barium sulfate and/or glass fibers. Particular preference is given to using mineral particulate fillers based on talc, wollastonite, kaolin and/or glass fibers, with further preference given to glass fibers.

The aforementioned flame-retardant polymer compositions are suitable for production of fibers, films, moldings, or other shaped articles by any desired shaping methods, especially by injection molding or extrusion. Thus produced fibers, films, moldings, or other shaped articles are particularly suitable for uses in the electrical and electronic parts due to their optimal combination of satisfactory flame retardancy, excellent electrical and mechanical properties, and hydrolytic stability under humid conditions.

The invention also relates to the use of the flame-retardant polymer compositions as aforementioned in or for plug connectors, current-bearing components in power distributors (residual current protection), circuit boards, potting compounds, plug connectors, circuit breakers, lamp housings, LED housings, capacitor housings, coil elements and ventilators, grounding contacts, plugs, in/on printed circuit boards, housings for plugs, flexible circuit boards, engine hoods or textile coatings, and especially for all kinds of cables, cable sheaths or cable insulations. Examples

Hereinafter, the present invention is described in more detail and specifically with reference to the Examples, which however are not intended to limit the present invention.

1. Components used:

Polymer Component P: polybutylene terephthalate (PBT): Ultradur® 4500 manufactured by BASF

Reinforcer Component R:

ChopVantage® HP 3610 EC 10 4.5 mm

Component A:

Aluminium salt of diethylphosphinic acid (DEPAL), Exolit® OP 1240 manufactured by Clariant

Component B:

Hydroxyapatite (anhydrous) - Cas(PO4)3(OH): having a pH of 6.8-7.5 as measured by dispersing 100g/L in water at 20°C.

Component C:

C1 : Melapur® MC 50 (melamine cyanurate) manufactured by BASF, referred to as MC

C2: Melapur® 200/70 (melamine polyphosphate = MPP) manufactured by BASF, referred to as MPP

C3: Delflam® 20 (melem) manufactured by Delamin (UK), referred to as melem

Component D:

D1 : Stabaxol® PLF from Lanxess, a polymeric carbodiimide without monomer components

D2: Lubio® AS 3 from Schafer Add itivsysteme GmbH, a polymeric carbodiimide Component E:

E1 : Irganox® 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate), from BASF, a sterically hindered phenol (CAS: 6683- 19-8)

E2: Irganox® 245 ethylenebis(oxyethylene) bis(3-(5-tert-butyl-4-hydroxy- mtolyl)propionate), from BASF, a sterically hindered phenol (CAS: 36443-68-2) E3: Hostanox® 03, Ethylene glycol bis[3,3-bis(3-tert-butyl-4- hydroxyphenyl)butyrate], from Clariant, a sterically hindered phenol (CAS: 32509- 66-3)

Component F:

F1 : Lubio® FL30, a phosphorylated fatty acid ester with high bio-based content based on 2-Ethylhexylphosphate (CAS: 12645-31 -7) having a density of 0.948 g/cm3 (20°C), a dynamic viscosity of 79 mPa*s (20°C, ASTM D7042), a kinematic viscosity of 85 mm2/s (40°C, ASTM D7042) and a solubility in water of 3.7 g/L.

F2: Lubio® FL31 , a phosphorylated fatty acid ester, complex esters based on alkylated triphenyl phosphates and glycerol ester, based on phosphor acid esters with high phosphorous content, high thermal and hydrolytic stability having a density between 1.13-1.18 g/cm3 (20°C), a kinematic viscosity between 20-50 mm2/s (40°C, ASTM D7042), a boiling point > 250-260°C, no water solubility and a melting point of -20°C.

Comparator CM

CM 1 : l3>-phosphate tricalcium (anhydrous) - Ca3(PO4)2: pH of 8-9 (100g/L 20°C) CM 2: Dicalcium Phosphate (anhydrous) - CaHPO4: pH of 6-8 (100g/L 20°C)

2. Production, processing and testing of flame-retardant polymer samples

Specific additive components were mixed with polymer pellets in the ratio specified in the tables and incorporated in a twin-screw extruder (Leistritz ZSE 27/HP-44D) at temperatures of 240 to 280°C. Homogenized polymer strands were drawn off, cooled in a water bath, and then pelletized.

After sufficient drying, the moulding compounds were processed in an injection moulding machine (Arburg 320C/KT) at melt temperatures of 260 to 280°C to give test specimens. The flame retardancy of the moulding compounds was tested by method UL94V (Underwriters Laboratories Inc. Standard of Safety, "Test for Flammability of Plastic Materials for Parts in Devices and Appliances", page 14 to page 18, Northbrook 1998). The fire classifications of UL94V are as follows:

V-0: afterflame time never longer than 10 sec, total of afterflame times for 10 flame applications not more than 50 sec, no flaming drops, no complete consumption of the specimen, afterglow time for specimens never longer than 30 sec after end of flame application

V-1 : afterflame time never longer than 30 sec after end of flame application, total of afterflame times for 10 flame applications not more than 250 sec, afterglow time for specimens never longer than 60 sec after end of flame application, other criteria as for V-0

V-2: cotton indicator ignited by flaming drops, other criteria as for V-1 not classifiable (ncl): does not comply with fire classification V-2.

The polymer samples were evaluated for fire classification by the average afterflame time obtained from 10 flame applications to 5 test specimens of 0.8 mm or 1 .6 mm.

The Comparative Tracking Index (CTI) of tested polymer samples were measured in accordance with the International Electrotechnical Commission standard IEC 60112/3.

The determination of the hydrolysis stability was conducted with a CertoClav MultiControl 2 (laboratory autoclave) from CertoClav Sterilizer GmbH. The purpose of storing the sample in an autoclave was to test the degradation of the material as a result of high temperatures and high moisture content. The test specimens were produced by injection moulding. The number of test specimens was guided by the tests required and the number of samplings envisaged, if any. Hydrolysis stability of samples was assessed in accordance with DIN EN 5 60749-33, a standardized pressure cooker test which is commonly used in the semiconductor and printed circuit boards industry. This test replicates the distinct environmental conditions of heated storage under pressure, with 100% relative humidity at 121 °C and 1 barg.

Tensile properties were determined with a Z 010 tensile tester (from Zwick) according to DIN EN ISO 527-1/-2/-3. The method was used in order to examine the tensile deformation characteristics of test specimens and to ascertain the tensile strength, tensile modulus and other features of the tensile stress/strain relationship under fixed conditions. The test specimens were freshly produced by injection moulding or subjected to subsequent PCT treatment of 3 days. The number of test specimens was guided by the tests required. For the sample preparation, the test specimens were stored at 23°C/50% relative humidity in a climate-controlled room for at least 16 h. Test specimens having high water absorption must be stored in a bag with an airtight seal at 23°C and 50% rel. humidity for at least 24 h. The test specimen was stretched along its greatest principal axis at constant speed until it broke or until the stress (force) or strain (change in length) reached a defined value; during this operation, the stress borne by the test specimen and the change in length were measured. The measurement was effected in a climate-controlled room at 23°C and 50% relative humidity.

Blooming was determined in exposing the specimen to 100% water for 14 days at 75°C in an oven. The plates were compared visually before and after exposure to water. When blooming occurred, the plates turned white and had a film that could be manually scraped off.

For comparability, all tests in the respective series, unless otherwise stated, were performed under identical conditions (temperature programs, screw geometry, injection molding parameters, etc.). All amounts are reported as % by weight and are based on the polymer molding compound including the flame retardant combination and additives. Table 1 compares flame retardancy and electrical property (i.e. CTI) and mechanical property (i.e. elongation at break) of flame-retardant PBT molding compounds that contain glass fiber, DEPAL and, optionally hydroxyapatite (anhydrate) or its comparators. 11 is an inventive Example of the present invention. R1 is a reference Example and C1 -C2 are for comparison.

Table 1

As illustrated by Example 11 , the incorporation of a small amount of hydroxyapatite demonstrated a marked enhancement in both electrical and mechanical properties of the reference flame-retardant polybutylene terephthalate (PBT) compound, while effectively preserving a desired fire-resistant property. Contrarily, by including the same amount of calcium phosphate analogues such as Ca₃(PO₄)₂ and CaHP0₄ (i.e. CM1 and CM2), Comparative Examples C1 and C2 not only failed to demonstrate a notable improvement in the electrical properties (i.e. CTI) of the reference flame-retardant PBT compound R1 , but also obtained inferior results in the UL 94 flame resistance tests compared to the reference.

Table 2 compares flame retardancy and electrical property (i.e. CTI) of flame- retardant PBT moulding compounds that contain glass fiber, DEPAL, carbodiimide, a hindered phenol compound and optionally hydroxyapatite (anhydrate). I2-I4 represent inventive Examples of the present invention. R2 is a reference/comparative Example. Table 2

As demonstrated in Table 2, it is feasible to manufacture flame-retardant PBT compounds utilizing DEPAL (A), glass fibers (R), hydroxyapatite (B) and further adding sterically hindered phenol (E) and carbodiimide (D). During the compounding process, there was no observable increase in pressure, nor was there any formation of undesired gas or odor. Notably, the incorporation of hydroxyapatite in Examples I2-I4 did not impair flame retardancy of Reference Example R2, and it led to a marked improvement in electrical properties, as indicated by an elevated comparative tracking index (CTI). Table 3 compares flame retardancy, electrical property (i.e. CTI) and mechanical property (i.e. elongation at break) of flame-retardant PBT moulding compounds that contain glass fiber, DEPAL, nitrogen-containing synergist, carbodiimide, a hindered phenol compound, and optionally hydroxyapatite. For the comparison of mechanical properties, the moulding compounds were compared in a freshly injection-moulded state. 15-17 represent inventive Examples of the present invention. R3 is a reference Example.

Table 3

As demonstrated in Table 3, it is feasible to manufacture flame-retardant PBT compounds utilizing DEPAL (A), glass fibers (R), hydroxyapatite (B) and further adding melem (C3), different types of sterically hindered phenol (E), and carbodiimide (D1 ). During the compounding process, there was no observable increase in pressure, nor was there any formation of undesired gas or odor. Notably, the incorporation of hydroxyapatite in Examples I5-I7 did not impair the superior flame retardancy of Reference Example R3, and it again led to a marked improvement in electrical properties, as indicated by an elevated comparative tracking index (CTI). Moreover, the hydroxyapatite-incorporated examples exhibited no significant degradation in mechanical properties compared to reference example R3.

Table 4 compares flame retardancy, electrical property (i.e. CTI) and mechanical property (i.e. elongation at break) of flame-retardant PBT molding compounds that contain glass fiber, DEPAL, and further additives selected from nitrogen-containing synergist, phosphorylated fatty acid ester, and hydroxyapatite. For the comparison of mechanical properties, the molding compounds were stretched in a freshly injection-molded state. 18-111 represent inventive Examples of the present invention. R4 is a reference/comparative Example.

Table 4

As demonstrated in Table 4, it is feasible to manufacture flame-retardant PBT compounds utilizing DEPAL (A), glass fibers (R), hydroxyapatite (B) and adding further additives selected from different types of nitrogen-containing synergists (C) and phosphorylated fatty acid ester (F). During the compounding process, there was no observable increase in pressure, nor was there any formation of undesired gas or odour. Notably, the incorporation of hydroxyapatite in Examples 18-111 did not impair the superior flame retardancy of Reference Example R4, and it again led to a marked improvement in electrical properties, as indicated by an elevated comparative tracking index (CTI). Moreover, the samples including both a hydroxyapatite and a phosphorylated fatty acid ester (110 and 111 ) were noted to show a better mechanical property (i.e. elongation at break) when stretched in a freshly injection-molded state.

Table 5 compares flame retardancy, electrical property (i.e. CTI) and mechanical property (i.e. elongation at break) of flame-retardant PBT molding compounds that contain glass fiber, DEPAL, and further additives selected from nitrogen-containing synergist, carbodiimide, and hydroxyapatite. For the comparison of mechanical properties, the molding compounds were first compared in a freshly injection- molded state and subsequently compared after being subjected to a pressure cooker test (“PCT”) under conditions of 121 °C, 100% relative humidity, 1 barg for 3 days. 112-116 represent inventive Examples of the present invention. R5 is a reference/comparative Example.

Table 5

As demonstrated in Table 5, it is feasible to manufacture hydrolytic-stable and flame-retardant PBT compounds utilizing DEPAL (A), glass fibers (R), hydroxyapatite (B) and adding further additives selected from different types of nitrogen-containing synergists (C), carbodiimide (D) and phosphorylated fatty acid ester (F). During the compounding process, there was no observable increase in pressure, nor was there any formation of undesired gas or odor. Notably, the incorporation of hydroxyapatite in Examples 18-111 did not impair the superior flame retardancy of Reference Example R4, and it again led to a marked improvement in electrical properties, as indicated by an elevated comparative tracking index (CTI).

Notably, the inventive samples including both a hydroxyapatite and a phosphorylated fatty acid ester F were noted to show a better mechanical property (i.e. elongation at break) before or after a PCT test at 121 °C and 1 barg for a duration of three days. No blooming issues were observed either for the inventive examples, following the exposure of various specimen to 100% water for 14 days at 75°C in an oven.

Claims

1 . A flame retardant composition comprising: as component A, from 40 to 99.9 % by weight of a phosphinic acid salt of the formula (I)

wherein

R¹, R² identical or different, are Ci -Ce-alkyl, linear or branched, M is Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K and/or a protonated nitrogen base, m is from 1 to 4; as component B, from 0.1 to 30 % by weight of a hydroxyapatite; as component C, from 0 to 50% by weight of a nitrogen-containing synergist selected from a group consisting of condensation products of melamine, reaction products of melamine with phosphoric acids, and melamine cyanurate; as component D, from 1 to 10% by weight of a carbodiimide; as component E, from 0 to 10% by weight of a sterically hindered phenol; and as component F, from 0 to 50% by weight of a phosphorylated fatty acid ester; wherein the sum of the components is always 100 % by weight.

2. A flame retardant composition as defined in claim 1 , wherein M is aluminum, calcium, titanium, zinc, tin, or zirconium.

3. A flame retardant composition as defined in claim 1 or 2, wherein component B takes up 5 to 25% by weight of the flame retardant composition.

4. A flame retardant composition as defined in any one of the preceding claims, wherein the component C takes up 5 to 45 % by weight of the flame retardant composition, and wherein the component C is selected from a group consisting of melamine cyanurate, melamine polyphosphate, and melem.

5. A flame retardant composition as defined in claim 1 , wherein the component D is a polymeric carbodiimide.

6. A flame retardant composition as defined in any one of the preceding claims, wherein the component E takes up 1 to 10 % by weight of the flame retardant composition.

7. A flame retardant composition as defined in claim 6, wherein the component E is selected from a group consisting of pentaerythritol tetrakis(3-(3, 5-di-tert- butyl-4-hydroxyphenyl)propionate), ethylenebis(oxyethylene) bis(3-(5-tert- butyl-4-hydroxy-mtolyl)propionate), and ethylene glycol bis[3,3-bis(3-tert- butyl-4-hydroxyphenyl)butyrate.

8. A flame retardant composition as defined in any one of the preceding claims, wherein the component F takes up 5 to 45 % by weight of the flame retardant composition.

9. A flame retardant composition as defined in claim 8, wherein the component F comprises an ester based on alkylated triphenyl phosphates and glycerol esters.

10. A flame-retardant polymer composition comprising a flame retardant composition as defined in any one of the preceding claims and a thermoplastic polymer P, wherein the flame retardant composition takes up 2 to 50% by weight of the flame-retardant polymer composition.

11. A flame-retardant polymer composition as defined in claim 10, comprising: from 5 to 50% by weight of the flame retardant composition as defined in any one of claims 1 -9; from 50 to 98% by weight of a thermoplastic polymer P; and from 0 to 40% by weight of a reinforcer or filler R.

12. A flame-retardant polymer composition as defined in claim 11 , wherein the thermoplastic polymer P is selected from a group of polyethylene terephthalate, polybutylene terephthalate, poly-1 ,4-dimethylolcyclohexane terephthalate, polyhydroxybenzoates, block polyether esters which derive from polyethers with hydroxyl end groups; and polyesters modified with polycarbonates or Methacrylate-Butadiene-Styrene.

13. The use of the flame-retardant polymer composition as defined in any of claims 10-12, in or for plug connectors, current-bearing components in power distributors (residual current protection), circuit boards, potting compounds, plug connectors, circuit breakers, lamp housings, LED housings, capacitor housings, coil elements and ventilators, grounding contacts, plugs, in/on printed circuit boards, housings for plugs, flexible circuit boards, engine hoods or textile coatings, and especially for all kinds of cables, cable sheaths or cable insulations.