Flame-retarded reinforced polycarbonate compositions

Abstract

A reinforced polycarbonate composition, comprising polycarbonate, a reinforcing agent and a mixture of flame retardants comprising (A) a phosphate compound, (B) a polymeric phosphonate, and (C) a siloxane, wherein the composition is essentially PTFE-free.

Description

[0001] Flame-retarded reinforced polycarbonate compositions

[0002] Background of the invention

[0003] Polycarbonate (PC) is a transparent polymer possessing high impact strength which finds utility in a wide variety of applications such as laboratory safety shields, safety helmets, automotive parts, housings and covers (e.g., food and beverage containers) , manifolds, electrical and electronic components. Reinforced polycarbonates are available in the marketplace, e.g., with glass fibers (GF) . We use the notation PC / GFX(for example, PC / GF20) to indicate a polycarbonate filled with glass fibers and the concentration of the reinforcing agent, e.g., 20% by weight.

[0004] Plastics in commercial use contain flame retardants to reduce their flammability, and polycarbonate is no exception. The flammability characteristics of plastic materials are frequently measured according to a method specified by Underwriter Laboratories standard UL 94, where an open flame is applied to the lowermost edge of a vertically mounted test specimen made of the tested polymer formulation. The specimens used in the UL 94 test method vary in thickness (typical thicknesses are ~3.2 mm, ~1.6 mm, <1.0 mm, e.g., ~0.8 mm, ~0.6 mm, 0.5 mm and ~0.4 mm) . During the test, various features of the flammability of the test specimens are recorded (such as duration of flaming time and dripping behavior, i.e., whether cotton is ignited by drips from a test specimen) . Then, according to the classification requirements, the tested polymer formulation earns either V-0, V-l or V-2 at the measured thickness of the test specimen. Polymer formulation assigned with the V-0 rating is the less flammable. In the UL 94 burning test, the thinner the specimens are, the longer the burning time. That is, the thinner the test specimen, the more difficult for the specimen to pass the UL 94 flammability test. The major types of flame retardants added to plastics include brominated compounds, phosphorous compounds, nitrogen compounds and inorganic hydrated minerals. Silicon-based flame retardants such as those developed by Dow Corning are also known, but they are used less frequently. It is not uncommon that combinations of flame retardants of different classes are used to reduce the flammability of plastics in an effective manner. For example, glass-reinforced polycarbonates that were flame retarded with a combination consisting of phosphorus and silicon compounds were shown to possess good fire-retardant properties, reaching the UL 94 V-0 classification (see US 2012 / 0129990 in the name of Mitsubishi Engineering-Plastics Corporation and US 2021 / 0292549, Example 7 in the name of Sabie Global Technologies) . However, the goal was achieved owing to the presence of an anti-dripping agent in the PC / GFXcomposition. Although an anti-dripping agent is used in a small amount, usually up to 0.5% by weight based on the total weight of the PC / GFx composition, it has a strong influence on the results of the UL 94 flammability test. The reason is that polycarbonate shows strong melt dripping during combustion and therefore an anti-dripping agent is considered indispensable, especially if thin products are needed.

[0005] The most widely used anti-dripping agent is polytetrafluoroethylene (PTFE) . Indeed, PTFE was also tested in the studies reported in US 2012 / 0129990 and US 2021 / 0292549. Recently, the safety of fluorinated compounds, which are known as "forever chemicals" due to their high chemical stability and environmental persistence, is subjected to reevaluation (see for example https : / / ww .rti.org / impact / repl acing- tf e- substances- in-product ) . Because countries may restrict or ban the use of PTFE, there exists a need in developing thin products made of PC / GFXcompositions that can gain the

[0006] UL 94 V-0 rating even without the addition of PTFE. The invention

[0007] Experimental results reported below show that the flammability of a reinforced polycarbonate, e.g., glass-reinforced polycarbonate, could be reduced effectively by the addition of a ternary mixture consisting of a phosphate compound, polymeric phosphonate, and siloxane, to gain UL 94 V-0 classification in the absence of an anti-dripping agent, namely, a PTFE-free composition. The objective was achieved even for thin reinforced polycarbonate test specimens, i.e., of thickness of less than 0.7 mm, at a reasonable concentration of the added flame retardants, for example at <18 wt . % loading, enabling an acceptable balance between mechanical and flammability properties of the reinforced polycarbonate.

[0008] Accordingly, the invention is primarily directed to a reinforced polycarbonate composition, comprising polycarbonate, a reinforcing agent and a mixture of flame retardants comprising :

[0009] (A) a phosphate compound, e.g., a phosphate ester;

[0010] (B) a polymeric phosphonate; and

[0011] (C) a siloxane wherein the composition is substantially PTFE-free.

[0012] The composition of the invention comprises not less than 50%, e.g., from 50 to 75%, for example, from 60 to 70% by weight, polycarbonate, based on the total weight of the composition. In its most general form, polycarbonate is characterized by a repeat unit of formula (1) :

[0013] -O-R-O-C (0) - (1) where R is the divalent aromatic radical corresponding to the dihydroxy aromatic compound employed in the polymerization reaction with the carbonate precursor. The polymerization reaction (e.g., where the carbonate precursor is phosgene) is well known. Relevant details concerning the synthetic methods can be found, for example, in US 2011 / 0098386 and references incorporated therein. Polymerization / copolymerization products of bisphenol monomers of the formula (2) : (2) where the phenyl rings are optionally substituted with alkyl groups and L is a bridging group (e.g., -CH2-, -C (Aik1) (Aik2)-, where Aik1'2is C1-C3 alkyl groups, -SO2- or an optionally substituted ring system (e.g., cyclohexane, with the two phenyl rings connected to the same carbon ring) ) . The hydroxy groups on both Ph rings are usually linked at the para position.

[0014] The monomer bisphenol A, where the linker group is -C (083)2-: is of commercial importance. Thus, the polycarbonate used in the invention comprises a repeat unit corresponding to bisphenol A, as shown by formula (la) : or a copolymer derived from bisphenol A and other dihydroxy aromatic compounds (such as resorcinol, alkyl-substituted resorcinol, halogenated resorcinol, N-phenyl phenolphthalein bisphenol (known as PPPBP) and 1 , 1-bis ( 4-hydroxyphenyl ) -3,3,5- trimethylcyclohexane (known as TMC bisphenol) , or aromatic ester monomers, namely, isophthalates and terephthalates.

[0015] Polycarbonate is generally a linear polymer, but branched grades are also available on the marketplace. The invention pertains to all polycarbonate grades, namely, linear and branched. The synthesis of the latter type is described in US 2021 / 0292549 (supra) . Commercial polycarbonate grades which are especially suitable for use in the invention have a melt flow rate in the range from 2 to 30 grams / 10 minutes, measured according to ISO 1133, such as Makrolon® produced by Covestro or LEXAN™ produced by SABIC. More preferred are polycarbonate grades with a melt flow rate in the range from 2 to 10 grams / 10 minutes, e.g., 2 to 5 grams / 10 minutes, either linear or branched .

[0016] The copolymerization products of dihydroxy aromatic compounds and siloxane, namely, poly (carbonate-co-siloxane) , polycarbonate blends and alloys, are usually not part of the invention .

[0017] A reinforcing agent added to polycarbonate to increase strength properties, e.g., stiffness, is often in the form of fibers, e.g., chopped fibers. One important type of reinforcing agent consists of glass fibers, which are sometimes pre-coated by manufacturers with a suitable coupling agent to improve adhesion to the polymer in question. The major constituents of glass fibers applied for reinforcing polycarbonates are alumino-borosilicates ; such type of glass is known as E-glass. The glass fibers are in the form of filaments with a diameter in the range from Ip to 30p and are applied in the form of chopped strands with a length in the range from 0.5 to 10 mm, e.g., from 1 to 7 mm. The concentration of the glass fibers is usually from 10 to 40% e.g., from 15 to 35%, for example, from 15 to 25% or from 25 to 35% by weight, based on the total weight of the polycarbonate composition. Preferred compositions of the invention are therefore designated PC / GF10-40 and PC / GF15-35, such as PC / GF20. Other types of fibers used to reinforce polycarbonate include carbon and aramid fibers. Secondary nonfiber fillers worthy of mention are glass microspheres and minerals such as talc, mica, and clay; however, the composition of the invention is usually devoid of such fillers .

[0018] Turning now to the mixture of flame retardants, it consists of three components:

[0019] (A) a phosphate compound;

[0020] (B) a polymeric phosphonate; and

[0021] (C) a siloxane which are usually added at a total concentration of 12 to 18% by weight based on the total weight of the composition, e.g., from 13 to 17%, for example, from 14 to 16%, namely ~15%. Preferably, the total concentration of the phosphorus- containing compounds is greater than the concentration of the siloxane, i.e., the mixture is proportioned such that the weight ratio (A+B) :C is in the range from 5:1 to 1:1, for example, from 3:1 to 3:2, and usually around 2:1.

[0022] In its most general form, a phosphate flame retardant for use as component (A) is characterized by a functional group wherein a phosphorus atom is bonded to four oxygen atoms by three single bonds and one double bond. One subclass of phosphate flame retardants consists of (optionally halogenated) aliphatic phosphate esters. Another subclass consists of non-halogenated aromatic phosphate esters, which include triphenyl phosphate and aryl bisphosphates and their oligomers of formula (3) : wherein each Ar is independently aryl, e.g., phenyl, or arylalkyl (e.g., mono or dimethylated aryl, such as xylenyl) , and X is a bridging group comprising one or two phenyl rings, and n has an average value of from about 1.0 to about 7.0.

[0023] A few examples of aryl phosphate esters (bisphosphates) are depicted below; all are commercially available, mostly in a powdered, pelletized, or flaked form:

[0024] Resorcinol bis (diphenyl phosphate) of formula (3a) , with n in the range from 1 to 7, is available, for example, as Fyrolflex®

[0025] RDP from ICL IP:

[0026] Bisphenol A bis (diphenyl phosphate) of formula (3b) , with n=l-2, is available as CR-741 from Daihachi Chemical Industry Co. Ltd and as ADK STAB FP-600 from Adeka:

[0027] Resorcinol bis (dixylenyl phosphate) of formula (3c) with n=l, is available as PX-200 from Daihachi :

[0028] Biphenol bis (diphenyl phosphate) of formula (3d) is available as ADX STAB FP-900L from Adeka:

[0029] Hydroquinone bis (diphenyl phosphate) of formula (3e) , with 1.0<n<1.05, e.g., n=1.02, is available as Fyroflex Sol-DP® from ICL-IP:

[0030]

[0031] Aryl phosphate esters, for example, the hydroquinone-type aromatic phosphate and oligophosphate of Formula (3e) can be prepared by methods described in EP 672717, US 5,457,221, and EP 2089402, for example, by reaction of hydroquinone and POCI3, followed by reaction of the intermediate formed with phenol; or by reaction of hydroquinone with diphenyl chlorophosphate in the presence of a catalytically effective amount of MgC12.

[0032] The concentration of aryl phosphate esters of formula (3) in the reinforced polycarbonate composition of the invention may vary from 1 to 13 wt.%, e.g., from 5 to 12 wt.%, for example, from 7 to 11 wt.%. The hydroquinone bis (diphenyl phosphate) of formula (3e) was shown to perform well alongside the polymeric phosphonate and the siloxane in the PTFE-free reinforced polycarbonate compositions of the invention.

[0033] In its most general form, a polymeric phosphorate for use as component (B) is characterized by a functional group wherein the phosphorus atom is bonded to three oxygen atoms (by two single bonds and one double bond) . Poly (phosphonate ) or phosphonate oligomers for use in the invention are described, for example, in US 10,724,154 in the name of FRX Polymers, Inc., and are represented by formula (4) : wherein -O-X-O- is a structural unit derived from a dihydroxy aryl ring such as, but not limited to, resorcinol, hydroquinone and bisphenol (e.g., bisphenol A, bisphenol F, 4 , 4 ’ -biphenol , phenolphthalein, 4, 4' -sulfonyldiphenol, or combinations of these; R is a Ci-io alkyl (especially C1-5 alkyl, most preferably methyl) , C2-10 alkenyl, C2-10 alkynyl, C5-10 cycloalkyl or C6-20 aryl; and n is an integer from 1 to about 100, preferably from 1 to about 75, preferably from 2 to about 50. The group -O-X-O- is preferably derived from bisphenol A.

[0034] For example, formula (4) is reduced to formula (4a) when the structural unit -O-Ar-O- corresponds to bisphenol A and R is methyl, showing the preferred poly (phosphonate ) for use in the invention :

[0035] Polymeric phosphonate of Formula (4a) is available from FRX

[0036] Polymers, Inc. under the tradename Nofia® HM1100, in the form of pellets.

[0037] It should be noted that polymeric phosphonates are not limited to homopolymers of formula (4a) . Copolymers that include the repeat unit of formula (4a) , for example, poly (phosphonate-co- carbonate) , namely, bisphenol A based poly (phosphonate-co- carbonate) , can also be used. The weight average molecular weight of the poly (phosphonate ) , i.e., the homopolymers, e.g., of Formula (4a) , is from 10,000 to about 100,000 g / mole. The phosphorous content of the phosphonate homopolymers is >7.0 wt.%, >9.0 wt.%, e.g., from 10.0 to 11.0 wt.%, and their glass transition temperature lies in the range from 100 to 120°C, e.g., from 100 to 110°C.

[0038] The weight average molecular weight of the poly (phosphonate- co-carbonate) , e.g., the bisphenol based poly (phosphonate-co- carbonate) , is from 30,000 to 80,000 g / mole. The phosphorous content of the poly (phosphonate-co-carbonate) is from 2.0 to 7.0 wt.%, and its glass transition temperature lies in the range from 120 to 135 °C.

[0039] The phosphorous content of phosphonate oligomers, e.g., terminated with -OH end groups, is from 9.0 to 11.0 wt.%, and their glass transition temperature lies in the range from 60 to 95 °C.

[0040] Synthetic methods to produce polymeric phosphonates can be found in old patents such as US 2, 682,522 and US 4,331, 614 and relatively recent patents such as US 6,861,499, US 7,560,525, US 7,816,486 and US 9,527,984 and the many references mentioned in these relatively new patents.

[0041] The concentration of polymeric phosphonates of formula (4) in the reinforced polycarbonate composition of the invention may vary from 1 to 7 wt.%, e.g., from 2 to 5 wt.%, for example, from 2 to 4 wt.%.

[0042] Component (C) of the mixture of flame retardants is a silicone- based powder, usually polydimethylsiloxane powder, as described in US 2012 / 0129990 and US 2021 / 0292549, e.g., a powder of polydimethylsiloxane with methacrylate or methyl methacrylate functionality (collectively indicated (methyl ) methacrylate ) ) . For example, silicone powder obtained by pulverizing linear polydimethylsiloxane (40-60% by weight) supported on 40-60% by weight silica; a silicone powder obtained by pulverizing (40— 60% by weight) polydimethylsiloxane having a (methyl ) methacrylate group supported on 40-60% by weight silica; see also CAS number 68083-18-1 [dimethyl, methylvinyl siloxane, dimethylvinyl-terminated] and CAS number 300852-60-2 [dimethyl siloxane, hydroxy-terminated, hydrolysis products with silica and 3- ( trimethoxysilyl ) propyl methacrylate] .

[0043] Suitable silicone (polydimethylsiloxane) powders are available from Dow Corning under the trade name DC4-7081. The concentration of the siloxane powder in the composition of the invention is from 1 to 8 wt.%, e.g., from 3 to 7 wt . % .

[0044] In addition to polydimethylsiloxane, other types of siloxanes may be considered, including polymethylhydrosiloxane, polymethylphenylsiloxane and poly ( etherimide-co-siloxane ) , available under the tradename Siltem™ from Sabie.

[0045] Apart from polycarbonate, the reinforcing agent and the flame retardants, the composition of this invention may further contain conventional additives, such as UV stabilizers (e.g., benzotriazole derivative) , processing aids, antioxidants (e.g., hindered phenol type) and the like. The total concentration of these auxiliary additives is typically not more than 3% by weight.

[0046] The glass-reinforced polycarbonate composition of the invention is substantially anti-dripping / PTFE-f ree . By "substantially PTFE-free" is meant that the concentration of PTFE in the composition is below the acceptable amount needed to induce an anti-dripping effect; e.g., <0.3%, <0.2%, <0.1%, <0.05%, for example, from 0 to 0.1% (by weight relative to the total weight of the composition) . Most preferably, the compositions of the invention are totally devoid of antidripping agents such as PTFE.

[0047] Preferred PTFE-free glass-reinforced polycarbonate compositions of the invention comprise: from 50 (or 60) to 70% by weight polycarbonate, e.g., from 63 to 69%; from 15 to 35% by weight glass fibers, e.g., from 15 to 25%; from 5 to 10% by weight hydroquinone bis (diphenyl phosphate) of formula (3e) , e.g., from 6 to 9%; from 1 to 5% by weight poly (phosphonate ) of formula (4a) , e.g., from 2 to 4%; and from 1 to 8% by weight siloxane with methacrylate functionality, e.g., from 3 to 7%.

[0048] The PTFE-free glass-reinforced polycarbonate composition, when in the form of a test specimen having thickness (D) D<1.6 mm, e.g., D<1.0 mm, e.g., D<0.7 mm, such as D=0.5 mm, achieves UL 94 V-0 flammability test rating.

[0049] The compounding of the polycarbonate compositions of the invention may be accomplished in different ways, e.g., by melt-blending. For example, the ingredients (flame retardants in the form of powders or pellets; polycarbonate usually as pelletized polycarbonate) can be fed separately into a compounding equipment, such as a co-rotating twin-screw extruder. Alternatively, some or all of the ingredients of the composition may be premixed together, that is, they can be dry blended using suitable mixing machines, such as a Henschel mixer, and the resulting premix may then be charged to the compounding device. Glass fibers are usually added downstream through a lateral feeder. Process parameters such as barrel temperature , melt temperature and screw speed are described in more detail in the examples that follow . The molten composition exits the extruder, the extrudate can be quenched in a water bath, and pelleti zed . The pellets thus obtained are suitable for feed to an article shaping process such as inj ection molding, extrusion molding, compression molding, etc .

[0050] Articles that can be produced from the polycarbonate formulations of the invention include products found in home appliances , lighting, automotive & transportation, electrical devices , construction, electronics , IT and communication, medical & healthcare devices . Such articles constitute another aspect of the invention .

[0051] Examples

[0052] The materials used for preparing the polycarbonate formulations are tabulated in Table 1 :

[0053] Table 1

[0054] Flammability test

[0055] The flammability test was carried out according to the Underwriters-Laboratories standard UL 94, applying the vertical burn on 1.6mm, 1.0mm or 0.5mm thick test specimens. Mechanical properties

[0056] The Notched Izod impact test was carried out according to ASTM D256 using an Instron Ceast 9050 pendulum impact system. Tensile properties were determined according to ASTM D638 using a Zwick Z-010 material testing machine (type 2 dumbbells were used, with a speed test of 5 mm / min) .

[0057] Thermal properties

[0058] Heat distortion temperature (abbreviated HDT; this is the temperature at which a polymer sample deforms under a specific load) was measured according to ASTM D-648 with a load of 1820 MPa and a heating rate of 120°C / hour. The instrument was HDT / VICAT -Instron HV3S.

[0059] Rheological properties

[0060] The melt flow index was measured according to ASTM D 1238 at 300 °C, 1.2 kg. The instrument was MI3-Gottf ert . Example 1 (comparative) and 2 (invention)

[0061] PTFE-free flame retarded reinforced polycarbonate composition

[0062] To prepare the compositions, polycarbonate (Makrolon ® 3227 pellets) and the additives (as powders and pellets) were fed into a twin-screw co-rotating extruder ZSK-18-ML (Coperion) with L / D=40 through its main feeding port. The glass fibers were added downstream, via Feeder no. 3 to the seventh zone of the barrel through a lateral feeder. The operating parameters of the extruder were as follows: Barrel temperature (from the feed end to discharge end) : 50°C, 235°C, 275°C, 280°C, 280°C, 280°C, 280°C, 280°C, 290°C, die - 290°C; Screw rotation speed: 700 rpm; feeding rate: 8 kg / hour. The strands produced were pelletized in a pelletizer SP-50-Pure (Coperion) . The resultant pellets were dried in a circulating air oven at 120°C for 3 hours. The dried pellets were injection molded into test specimens using Allrounder 320C 500-170 Golden Edition (Arburg) under the conditions tabulated below:

[0063] Table 2 Specimens of 1.6 mm and <1.0 mm thickness were prepared. The test specimens were conditioned for one week at 23 °C and were then subjected to several tests to determine their properties. The compositions tested and the results are set out in Table 3.

[0064] Table 3

[0065] The results set out in Table 3 indicate that glass-reinforced polycarbonate can achieve UL 94 V-0 rating even in the absence of an anti-dripping agent, over a wide range of thicknesses, including at thicknesses <1.0 mm, i.e., down to 0.5 mm, with the aid of a combination consisting aromatic phosphate ester (hydroquinone bis (diphenyl phosphate) , polymeric phosphonate and siloxane (dimethyl siloxane bearing methacrylate functionality) .

Claims

Claims :1 ) A reinforced polycarbonate composition, comprising polycarbonate , a reinforcing agent and a mixture of flame retardants comprising :(A) a phosphate compound;(B ) a polymeric phosphonate ; and( C ) a siloxane wherein the composition is essentially PTFE- free .2 ) The reinforced polycarbonate composition according to claim 1 , comprising polycarbonate at a concentration not less than 50% by weight based on the total weight of the composition, wherein the polycarbonate contains a repeat unit corresponding to bisphenol A.3 ) The reinforced polycarbonate composition according to any one of the preceding claims , comprising glass fibers as the reinforcing agent , at a concentration of 10 to 40% by weight based on the total weight of the composition .4 ) The composition according to any one of the preceding claims , wherein the total concentration of the flame retardants (A) , (B) and ( C ) is from 12 to 18 % by weight based on the total weight of the composition, and the total concentration of the phosphorus-containing compounds (A) and (B ) is greater than the concentration of the siloxane ( C ) .5 ) The composition according to any one of the preceding claims , wherein the phosphate compound (A) is selected from the group consisting of non-halogenated aromatic phosphate esters and their oligomers of formula ( 3 ) :wherein each Ar is independently aryl or alkylated phenyl, X is a bridging group comprising one or two phenyl rings, and n has an average value of from about 1.0 to about 7.0.6) A composition according to claim 5, wherein the aromatic phosphate ester of formula (3) is hydroquinone bis (diphenyl phosphate) of formula (3e) :7) The composition according to any one of the preceding claims, wherein the polymeric phosphonate (B) is represented by formula ( 4 ) :(4)wherein -O-X-O- is a structural unit derived from a dihydroxy aryl selected from resorcinol, hydroquinone and bisphenol, R is a Ci-io alkyl and n is an integer from 1 to 100.8) The composition according to claim 7, wherein the polymeric phosphonate comprises a structural unit -O-X-O- derived from bisphenol A.9) The composition according to claim 8, wherein the polymeric phosphonate comprises a poly (phosphonate ) of formula (4a) :10) The composition according to any one of the preceding claims, wherein the siloxane is a powder polydimethylsiloxane with (methyl ) methacrylate functionality.11) The PTFE-free glass-reinforced polycarbonate composition according to any one of the preceding claims, comprising from 50 to 70% by weight polycarbonate and from 15 to 35% by weight glass fibers; and(A) from 5 to 10% by weight hydroquinone bis (diphenyl phosphate) of formula (3e) ;(B) from 1 to 5% by weight poly (phosphonate ) of formula (4a) ; and(C) from 1 to 8% by weight siloxane with methacrylate functionality .12) The PTFE-free glass-reinforced polycarbonate composition according to claim 11, comprising from 60 to 70% by weight polycarbonate and from 15 to 25% by weight glass fibers; and(A) from 6 to 9% by weight hydroquinone bis (diphenyl phosphate) of formula ( 3e ) ;(B) from 2 to 4% by weight poly (phosphonate ) of formula (4a) ; and(C) from 3 to 7% by weight siloxane with methacrylate functionality .13) The PTFE-free glass-reinforced polycarbonate composition according to any one of the preceding claims, wherein, when in the form of a test specimen having thickness (D) with D<0.7 mm, it achieves UL 94 V-0 flammability test rating.14) An article shaped from the reinforced polycarbonate composition according to any one of the preceding claims.

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