FLAME RETARDANT POLYKETONE POLYMER BLEND

Abstract: A reinforced flame retardant polyketone polymer blend comprising a polyketone polymer, a reinforcement, a flame retardant other than a zinc compound, and a comparative tracking index (CTI) improving compound selected from zinc compounds and silicon oils; and a method for improving the CTI of a reinforced flame retardant polyketone, comprising admixing the polyketone with a reinforcement, a flame retardant other than a zinc compound, and a CTI improving compound selected from zinc compounds and silicon oils.

Description: FLAME RETARDANT POLYKETONE POLYMER BLEND This invention relates to polyketone polymers. More particularly, the invention relates to a reinforced flame retardant polyketone polymer blend. Polymers of carbon monoxide and ethylenically unsaturated compounds which are commonly called poly- ketones or polyketone polymers have been known and are available for some time. High molecular weight linear alternating polyketones are of considerable interest because they exhibit a good overall set of physical properties. This class of polymers is disclosed in numerous patent documents, for example in US-A-4880865 and US-A-4818811. The linear alternating polyketones have established utility as premium thermoplastics in the production of shaped articles such as containers for food and drink and parts for the automotive industry. These articles can be produced by processing the polyketone polymer according to well known methods. Certain mechanical properties of the polyketones can be improved through blending with e.g. reinforcements or other polymers, or by the addition of additives to the material. For example, the stiffness and heat resistance of polyketones are improved by the addition of a reinforcement to the material, such as glass fibres. The rise of the electronics industry has placed a premium on the development of polymers which can be used to support electrical circuitry. The polymers so used should not be unfavourably affected by their proximity to changing electrical fields and currents nor should their intrinsic properties unfavourably affect the circuitry about which the polymer is exposed. This can be best expressed by considering a simple electrical circuit such as the emplacement of two electrical conductors supported on a polymer support which maintains them at some finite separation. A potential difference is found between the two conductors. In such a case, among other desirable features of the material, the polymer must physically retain the separation of the two conductors to avoid a short circuit. Exposing the polymer to a non-sterile environment subjects it to the deposition of any number of materials on its surface. As these materials become affixed to the surface of the polymer they cause a decrease in surface resistance. This enables a current to flow and thereby generates heat at the point about the deposition. Some areas may have considerably more deposits than others which can lead to voltage gradients which ultimately results in surface discharges . Such surface discharges produce very high temperatures at the point at which they occur and thereby erode the surface. This erosive action is called tracking. One method for comparing the susceptibility of materials to tracking is by their Comparative Tracking Index (CTI) . The CTI of a material is defined as the numerical value of the voltage which will cause failure by tracking when the number of drops of contaminant required to cause failure is equal to 50. For many of the electrical and electronic applications of polymers it is desirable to have a CTI greater than 350 V, in particular greater than 400 V. The maximum which can be measured is a CTI of 600 V. Flammability is another important consideration in applying particular polymers in electrical or electronic uses. Many polymers and polymer blends must be modified by the addition of a flame retardant to attain the desired level of resistance to flammability. For example, US-A-4761449 proposes the addition of an alkaline earth metal carbonate to polyketone to form a flame retardant blend. US-A-4885328 proposes the use of magnesium hydroxide as the flame retardant for poly- ketones. US-A-4921897 proposes the addition of zinc borate or barium borate as flame retardants for poly¬ ketones. Unfortunately, a combination of additives to a polymer does not necessarily uniformly improve the properties of the polymer. For example, neat poly¬ ketones, reinforced polyketones and flame retarded polyketones possess CTIs of 600V. This is generally considered to be superior performance. However, when polyketones, reinforcement, and flame retardant are combined the material exhibits an unsatisfactorily low CTI, for example as low as 250V. The addition of other additives such as pigments also brings some uncertainty into the overall set of physical properties that the polymer will ultimately display. Reinforced flame retarded polyketones having CTIs in the range found useful for electrical end uses would greatly contribute to the range of applications for such polymer blends. Such polyketone blends would be especially beneficial if they could obviate or reduce the need for one or more other additives such as pigments. Such materials are useful in electrical connectors and switch gears, as supporting materials and fasteners for electrical circuitry, and as insulation for wires among other applications. It has now unexpectedly been found that the CTI of reinforced flame retardant polyketone polymers can be improved by the addition of a suitable compound. Unexpectedly, useful CTI improving compounds for use in the invention are zinc compounds, which are known per se to act as flame retardant in polyketones, and that other CTI improving compounds are silicon oils. The zinc compounds are also effective pigments for the reinforced flame retardant polyketone polymers. Accordingly, the present invention relates to a reinforced flame retardant polyketone polymer blend comprising a polyketone polymer, a reinforcement, a flame retardant other than a zinc compound, and a comparative tracking index (CTI) improving compound selected from zinc compounds and silicon oils. The invention relates also to a method for improving the CTI of a reinforced flame retardant polyketone, comprising admixing the polyketone with a reinforcement, a flame retardant other than a zinc compound, and a CTI improving compound selected from zinc compounds and silicon oils. The present invention also relates to a reinforced flame retardant polyketone polymer blend having a CTI greater than 375 V, as measured by ASTM D 3638-93, preferably greater than 400 V. The terminology "reinforced flame retardant blend" is used to indicate that the blend comprises a reinforcement and a flame retardant. The blends according to the invention have in particular a flame retardancy of at least V-l, more in particular at least V-0, as measured by the UL 94 Vertical Flammability Test, using 1.6 mm specimens. For most applications it is sufficient that the blends have a flame retardancy not higher than V-0, measured by using 0.8 mm specimens. The UL 94 Vertical Flammability Test is deemed to be the test in its version valid on 1 January 1996. The blends of this invention may incorporate common polymer additives. For instance, extenders, lubricants, pigments, plasticizers and other polymeric materials can be added to the compositions to improve or otherwise alter the properties of the composition. In general, the practice of this invention involves suitably contacting sufficient quantities of the useful material to form the inventive blend. The polyketones for use in this invention, suitably as the major component, are typically linear alternating copolymers of carbon monoxide and at least one ethyleni¬ cally unsaturated compound. Thus, the polyketone polymers are typically of a linear alternating structure which means that they contain typically one molecule of carbon monoxide for each molecule of the ethylenically unsaturated compound. Ethylenically unsaturated compounds comprise suitably up to 20 carbon atoms and include compounds which consist exclusively of carbon and hydrogen and compounds which in addition comprise hetero atoms, such as unsaturated esters, ethers and amides. Unsaturated hydrocarbons are preferred. Examples of suitable ethylenically unsaturated compounds are ali¬ phatic α-olefins, such as ethene, propene, butene-1 and hexene-1, cyclic olefins such as cyclopentene, aromatic compounds, such as styrene and α-methylstyrene and vinyl esters, such as vinyl acetate and vinyl propionate. The preferred polyketone polymers are linear alternating polymers of carbon monoxide and ethene or linear alternating polymers of carbon monoxide, ethene and another ethylenically unsaturated compound of at least 3 carbon atoms, particularly an α-olefin such as propene, butene-1 or hexene-1. When the preferred polyketone polymers of carbon monoxide, ethene and another ethylenically unsaturated compound are employed, there will be within the polymer typically at least 2 units incorporating a moiety of ethene for each unit incorporating a moiety of the other ethylenically unsaturated compound(s) . Preferably, there will be from 10 units to 100 units incorporating a moiety of ethene for each unit incorporating a moiety of the other ethylenically unsaturated compound(s) . The polymer chain of preferred polyketone polymers is therefore represented by the repeating formula -i CO (-CH 2 -CH 2 -—]x-[CO—(-G)H- y where G is the moiety of the ethylenically unsaturated compound of at least 3 carbon atoms polymerized through the ethylenic unsaturation and the ratio of y.x is typically no more than 0.5. When linear alternating polymers of carbon monoxide and ethene are employed in the compositions of the invention, there will be no second ethylenically unsaturated compound present and the polymers are represented by the above formula wherein y is zero. When y is other than zero the —C CH2—H2-7- units and the —CO-G- units are found randomly throughout the polymer chain, and preferred ratios of y:x are from 0.01 to 0.1. The precise nature of the end groups does not appear to influence the properties of the polymer to any considerable extent so that the polymers are fairly represented by the formula for the polymer chains as depicted above. The polyketone polymers of number average molecular weight from 1000 to 200,000, particularly those of number average molecular weight from 20,000 to 90,000 as determined by gel permeation chromatography are of particular interest. The physical properties of the polymer will depend in part upon the molecular weight, whether the polymer is based on a single or on a plurality of ethylenically unsaturated compounds and on the nature and the proportion of the ethylenically unsaturated compounds. Typical melting points for the polymers are from 175 °C to 300 °C, more typically from 210 °C to 270 °C, as determined by differential scanning calorimetry. The polymers have typically a limiting viscosity number (LVN) , measured in m-cresol at 60 °C in a standard capillary viscosity measuring device, from 0.5 dl/g to 10 dl/g, more typically from 0.8 dl/g to 4 dl/g. Preferred methods for the production of the polyketone polymers are known from US-A-4808699 and US-A-4868282. US-A-4808699 teaches the production of polyketone polymers by contacting ethene and carbon monoxide in the presence of a catalyst comprising a Group VII metal compound, an anion of a nonhydrohalogenic acid with a pKa less than 6 and a bidentate phosphorus, arsenic or antimony ligand. US-A-4868282 teaches the production of polyketone polymers by contacting carbon monoxide and ethene in the presence of one or more hydrocarbons having an ethylenically unsaturated group with a similar catalyst. The blends of this invention incorporate a reinforcement, typically in a minor quantity. Suitable reinforcements are inorganic materials and include particulate fillers, such as mica and talc, and fibrous reinforcement, such as glass fibres and wollastonite. Glass fibre reinforcement is preferred. The term "glass" is employed within its conventional meaning to indicate that class of complex metal silicates which are commonly referred to as glasses. Although the addition of rare earth metal oxides or transition metal oxides to metal silicates on occasion will produce a glass of exotic properties, the glass from which the glass fibre of the invention is produced is typically the more common alkali metal silicate glass, particularly a borosilicate glass. Fibres produced of such glass are conventional and are commercially available from a large number of sources. The fibres are useful as reinforcements for polymeric products and are commercially used as such. Short, chopped glass fibres with a circular cross section are preferred. For example, fibres ranging in diameter from 5.1 to 20.3 μm (2xl0 -4 to 8xl0 -4 inch) and lengths of at least 1.5 mm, especially from 2.54-12.7 mm (0.1 to 0.5 inch), can be used with good results. The glass fibres are preferably obtained from the manufacturer with a surface treatment compatible with the polyketone polymer, such as a polyurethane sizing. The reinforcement, in particular glass fibre, is present in the blends of this invention in quantities comprising between 5 and 40 wt%, based on total weight of the blend. It is preferred that the range be between 7 and 30 wt%, between 11 and 25 wt% being most preferred. Various flame retardants may be used in this invention, typically in a minor quantity. Examples are halogenated flame retardants, such as decabromodiphenyl- oxide and bis (1, 2, 3 , 4, 7, 7-hexachloro-2-norborneno) - [a, e] -cyclooctane, antimony trioxide, alkaline earth metal hydroxides and alkaline earth metal carbonates, cf . for example US-A-4921897, US-A-4885328 and US-A-4761449. Some of these flame retardants may be combined to form synergistic mixtures, for example halogenated flame retardants with antimony trioxide. By alkaline earth metal hydroxide or carbonate, which represents a preferred class of flame retardants, is meant a hydroxide or carbonate of a metal of group IIA of the Periodic Table of Elements. While hydroxides of beryllium, magnesium, calcium, strontium, and barium are suitable, the preferred alkaline earth metal hydroxide component is magnesium hydroxide. Most preferred is magnesium hydroxide. Preferred alkaline earth metal carbonates are calcium carbonate and partially hydrated magnesium calcium carbonate. Most preferred is partially hydrated magnesium calcium carbonate. The quantity of the flame retardant compound is suitably selected between 10 and 70 %w, more suitably between 20 and 55 %w, in particular between 25 and 40 %w, based on the weight of the blend. The CTI improving compound may be selected from zinc compounds and silicon oils. The zinc compound is preferably a compound of zinc borate or zinc oxide. Zinc borate is most preferred. The typical composition of zinc borate is pZnO-qB2θ3, wherein p/q is the molar ratio of ZnO to B2O3, and is usually available in the hydrated form. A preferred zinc borate has the formula 2ZnO-3B2O3 • 3-4^0, in particular 2ZnO-3B2θ3 -3.3-3.7H2O. A preferred zinc borate preparation is commercially available 2ZnO-3B2O3 • 3.5H2O. As set out hereinafter, it may be advantageous to employ a substantially anhydrous zinc borate. The term "substantially anhydrous" expresses that the quantity of water present therein calculated as molar ratio of H2O to ZnO is typically less than 1, more typically less than 0.5. Very suitable anhydrous zinc borate is of the formula 2ZnO-3B 0 3 . Useful silicon oils can be described as comprising chains of polydihydrocarbylsiloxanes, of which the various hydrocarbyl groups may be the same or different. The chains are typically linear. The hydrocarbyl groups have in particular up to 8 carbon atoms. They are preferably alkyl groups, in particular methyl groups. It may be advantageous to employ a combination of methyl or ethyl groups, in particular methyl groups, with aryl groups, such as phenyl groups, or with alkyl groups having 3 or more carbon atoms. The hydrocarbyl groups may carry halogen atoms. Examples are polydimethyl¬ siloxane, poly[dimethylsiloxane-co- (methyl) (phenyl) - siloxane)] , typically containing 85-95 %-mole (C^^SiO repeating units and 5-15 %-mole (CH3) (CgH5)SiO repeating units, poly[ (methyl) (3,3,3-trifluoropropyl) siloxane) ] , and poly[dimethylsiloxane-co- (methyl) (3, 3 ,3-trifluoro¬ propyl) siloxane) ] , typically containing up to 10 %-mole (CH3)2SiO repeating units and at least 90 %-mole (CH 3 ) (CF3-CH 2 -CH 2 ) SiO repeating units. Polydimethyl¬ siloxane is preferred. Very usefully, the silicon oil, in particular polydimethylsiloxane, has a viscosity at 25 °C in the range of 1,000-300,000 mm 2 /s, preferably in the range of 5,000-100,000 mm 2 /s. Silicon oils or other components of the blends of this invention may be applied in the form of a masterbatch. The masterbatch may be based on a polyketone polymer but it is also possible to have the masterbatch based on another polymer, such as a polyamide or polyethene. The quantity of the silicon oil or such another component in the masterbatch is frequently in the range of 10-90 %w, based on the weight of the master¬ batch, typically in the range of 30-70 %w on the same basis . When a CTI improving compound is combined with a flame retardant, in particular an alkaline earth metal hydroxide, it may occur that there is a small decrease in the level of the flame retardancy of the blend. This is more in particular the case when a hydrated zinc borate is used as the CTI improving compound. It has unexpectedly been found that the decrease in flame retardancy is smaller or not noticeable at all when as the CTI improving compound a silicon oil or a sub¬ stantially anhydrous zinc borate is used. Therefore there is a preference for using a silicon oil or a substantially anhydrous zinc borate as the CTI improving compound. Blends comprising a polyketone polymer and a substantially anhydrous zinc borate are novel. Therefore, the present invention also relates to such blends per se. Such blends can be used as a starting material for the production of the reinforced flame retardant blends according to this invention. The quantity of the CTI improving compound present in the blends of this invention may be selected within wide ranges . The CTI improving compound is frequently applied in a minor quantity. Typically the quantity of the CTI improving compound is selected between 0.2 and 30 %w, based on the weight of the blend. When the CTI improving compound is a zinc compound, there is particular preference to have it present in a quantity between 3 and 15 %w, relative to the weight of the blend, however, substantially anhydrous zinc borate is preferably used in a quantity of between 0.2 and 10 %w, more preferably between 0.5 and 5 %w. When the CTI improving compound is a silicone oil, there is preference to have it present in a quantity between 0.2 and 5 %w, in particular between 0.5 and 3 %w, relative to the weight of the blend. The blends of this invention are produced by mixing the various materials with the polyketone polymer. The method by which this achieved is not critical to this invention. Good dispersion of the flame retardant generally contributes to good flame retardancy and CTI performance. In one blending procedure, the components are dry blended in particulate form and converted to a substantially uniform composition, e.g., by extrusion. Alternatively, the polyketone polymer is heated until molten and the other components are mixed throughout the polymer by use of, e.g., a high-shear mixer or extruder. Reinforced flame retardant polyketone polymer blends have frequently a pronounced colour. It has also been found that the use of a zinc compound in the present blends provides a thorough and even light colour which is highly desired for some applications. Thus, for certain uses this blend eliminates the need for additional pigment. Additionally, due to the light colour of the blend, a broader range of pigmented colours is achievable with these blends. The inventive blends can be processed by conventional methods such as extrusion and injection moulding into various articles of manufacture such as electrical connectors and switch gears, as supporting materials and fasteners for electrical circuitry, and as insulation for wires among other applications. The invention is further illustrated by the following examples. Example 1 (Polyketone Formation) A linear terpolymer of carbon monoxide, ethylene, and propylene was produced in the presence of a catalyst composition formed from palladium acetate, the anion of trifluoroacetic acid and 1, 3-bis (diphenylphosphino) - propane. The melting point of the terpolymer was 220 °C and it had a limiting viscosity number (LVN) of 1.1 measured at 60 °C in m-cresol. Example 2 Blends were prepared of the terpolymer of Example 1, "OCF 408BC" (trademark) chopped glass commercially available from Owens-Corning, Inc, "MAGΝIFIΝ H10" (trademark) magnesium hydroxide from Martinswerk GmbH, "FIREBRAKE ZB" (trademark) zinc borate (2ZnO-3B 2 0 3 -3.5H 2 0) from US Borax, Inc., and "MYVAPLEX 600" (trademark) glycerol monostearate processing aid commercially available from Eastman Chemical Co. The blends were prepared as shown in Table 1 by blending on a 25 mm twin screw extruder operating at a melt processing temperature of between about 250 and 270 °C. Sample A is comparative (not according to this invention) . The blends were injection moulded into 3.2 mm (1/8 in) tensile and flexural bars in an injection moulding machine. Extruded strand was used for the assessment of flame retardancy in terms of limiting oxygen index (LOI) . Example 3 (CTI) The CTI of each blend of example 2 was measured according to ASTM D 3638-93. CTI values are reported in Table 1 below. This example illustrates the substantial improvement in the CTI of blends made according to this invention (having both a zinc borate and alkaline earth metal hydroxide or carbonate) relative to blends without the zinc borate. Example 4 (Flame Testing) Standard test method ASTM D 2863-77 was used to evaluate the burning behaviour of the blends of example 2. This test measures the minimum concentration of oxygen in an oxygen-nitrogen atmosphere that is necessary to initiate and support a flame for 180 seconds on a test specimen. The result of the test is expressed as the percentage of oxygen in the oxygen-nitrogen atmosphere and is called the Limiting Oxygen Index (LOI) of the composition. LOIs are reported in Table 1 below. Each of the blends is seen to display good flame retardancy, as evidenced by LOI > 28%. Example 5 (Physical Testing) Impact, flexural, and tensile properties of the blends of example 2 are shown below in Table 2. This example shows that the advantages of the invention were achieved without significant loss of mechanical properties. Table 1. Flammability and Tracking Resistance Sample* Concentration Flame LOI CTI Zinc Borate (%wt) Retardant** (% 02) (V) A 0 H10 >40 375 B 4 H10 35 575 C 7 H10 34 >600 D 10 H10 35 >600 *A11 samples contain: 15 wt% "OCF 408BC" chopped glass fibres 25 wt% magnesium hydroxide 0.5 wt% "MYVAPLEX 600" glycerol monostearate 1 wt% tricalcium phosphate as a melt stabilizer **H10 = "MAGNIFIN H10" magnesium hydroxide Table 2. Mechanical Properties Sample Tensile Elongation Tensile Flexural Flexural Notched Izod Strength at Break Modulus Modulus Strength Impact Strength MPa (kpsi) % GPa (kpsi) GPa (kpsi) MPa (kpsi) J/m (ft-lb/in) A 63 (9.2) 4.3 5.4 (790) 4.7 (675) 109 (15.8) 64 (1.2) B 66 (9.6) 3.9 6.0 (875) 5.1 (740) 113 (16.4) 69 (1.3) C 64 (9.3) 3.7 6.2 (900) 5.2 (750) 110 (15.9) 64 (1.2) D 64 (9.3) 3.4 6.8 (980) 5.7 (825) 112 (16.2) 64 (1.2) I Example 6 A linear terpolymer of carbon monoxide, ethene and propene was produced by polymerizing the monomers in the presence of a catalyst formed from palladium acetate, the anion of trifluoroacetic acid and 1, 3-bis [bis (2-methoxy¬ phenyl)phosphino]propane. The melting point of the polymer was 220 °C and the LVN was 1.1 dl/g, as measured in m-cresol at 60 °C. Examples 7-10 (Example 7 for comparison) Blends were prepared of the terpolymer of Example 6 using as the blend components "OCF 429 YZ" chopped glass commercially available from Owens-Corning, Inc, "MAGNIFIN H5" (trademark) magnesium hydroxide from Martinswerk GmbH, zinc borate (2ZnO-3B2O3 • 3.5H2O) (FIREBRAKE 290 (trademark), ex Borax Consolidated Ltd.) and polydimethylsiloxane (MB 50-011 silicone oil masterbatch (50 %w with 50 %w polyamide-6) , ex Dow Corning) . The blends, shown in Table 3, were prepared by blending in a twin screw extruder operating at a melt temperature of about 250 °C. CTI values were determined using ASTM D 3638-93 and the flame retardancy was tested by the UL 94 Vertical Flammability Test (1.6 mm specimens) . The test results were as indicated in Table 3. Table 3 Example 7 *) 8 9 10 Composition (%w) : Polymer 60 58 55 58 Glass fibre 15 15 15 15 Magnesium hydroxide 25 25 25 25 Zinc borate - 2 5 - Polysiloxane - - - i b) Properties: UL 94 test c ) V-0 V-l V-l V-0 CTI (V) 225 300 500 425 a ) for comparison b) i.e. 2 %w masterbatch c ) at 1.6 mm

Claims: C A I M S 1. A reinforced flame retardant polyketone polymer blend comprising a polyketone polymer, a reinforcement, a flame retardant other than a zinc compound, and a comparative tracking index (CTI) improving compound selected from zinc compounds and silicon oils. 2. A blend as claimed in claim 1, characterized in that it comprises as the reinforcement a glass fibre and as the flame retardant an alkali metal hydroxide or carbonate. 3. A blend as claimed in claim 1 or 2, characterized in that it comprises as the polyketone a linear alternating copolymer of carbon monoxide and an ethylenically unsaturated compound. 4. A blend as claimed in claim 3, characterized in that the copolymer is a copolymer of carbon monoxide and ethene or a copolymer of carbon monoxide, ethene and another ethylenically unsaturated compound of at least 3 carbon atoms, such as propene, butene-1 or hexene-1. 5. A blend as claimed in any of claims 1-4, characterized in that it comprises 5-40 %w reinforcement, 20-55 %w flame retardant compound and 0.2-30 %w of the CTI improving compound. 6. A reinforced flame retardant polyketone polymer blend, characterized in that it has a CTI greater than 375 V, as measured by ASTM D 3638-93. 7. A blend as claimed in claim 6, characterized in that it has a CTI greater than 400 V, as measured by ASTM D 3638-93. 8. A blend as claimed in claim 6 or 7, characterized in that it has a flame retardancy of at least V-l, preferably at least V-0, as measured by the UL 94 Vertical Flammability Test, using 1.6 mm specimens. 9. A blend comprising a polyketone polymer and a substantially anhydrous zinc borate. 10. A method for improving the CTI of a reinforced flame retardant polyketone, comprising admixing the polyketone with a reinforcement, a flame retardant other than a zinc compound, and a CTI improving compound selected from zinc compounds and silicon oils.

Inventors: GINGRICH RANDALL POWER, KORMELINK HENDRIK GEERT-JAN, LONDA MICHELLE, GINGRICH, RANDALL, POWER, KORMELINK, HENDRIK, GEERT-JAN, LONDA, MICHELLE
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1996
Main classification: C08K3
IPC codes: C08G67, C08K3, C08K7, C08L73, C08L83