Flame retardant polymer composition

Abstract: Flame retardant polymer compositions comprise linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon and a minor quantity, relative to the polymer, of an alkaline earth metal carbonate.

Description: The present invention relates to a flame retardant polymer composition, in particular based upon a linear alternating polymer of carbon monoxide and one or more olefinically unsaturated compounds. The general class of polymers of carbon monoxide and one or more olefinically unsaturated hydrocarbons has been known for some years. More recently, the class of linear alternating polymers of carbon monoxide and unsaturated hydrocarbons, now known as polyketones, has become of greater interest, in part because of improved methods of production. Such methods are shown by EP-A-181,014 and 121,965. The resulting polymers are generally high molecular weight thermoplastic polymers having utility in the production of articles such as containers for food and drink and parts for the automotive industry or structural members for use in the construction industry. With regard to any plastic material employed in a public application, some concern must be shown for the consequences of the material catching fire and burning. Many plastics produce highly toxic gases upon combustion. The use of polyketones has advantages in this regard since only atoms of carbon, hydrogen and oxygen are present in the polymer molecule. Nevertheless, it would be of advantage to provide for flame retardant compositions of polyketone polymers for many other reasons, such as maintaining the shape of articles or structural members subjected to fire, for extended periods of time. Katz and Milewski, "Handbook of Fillers and Reinforcements for Plastics" 1978 and Troitzsch, "International Plastics Flammability Handbook" 1983 disclose that calcium carbonate shows significant flame retardancy predominantly through its diluent effect of highly filled plastics. An example of highly filled plastics containing calcium carbonate is diclosed in CA-A-1220600 wherein 150 - 600 pbw of calcium carbonate are incorporated in 60 - 100 pbw of ethylene/CO/VA copolymer. The invention relates to a flame retardant polymer composition comprising a linear alternating polymer of the formula wherein B is the moiety of an alpha-olefin of at least 3 carbon atoms polymerized through the olefinic unsaturation, x and y being integers, the ratio of y:x being no more than 0.5, and a quantity of 2% to 30% by weight, based on total composition, of magnesium or calcium carbonate as flame-retarding additive, particularly calcium carbonate. If in the above formula y is not 0, the --CO(C₂H₄)-- units and the --CO(B)-- units occur randomly throughout the polymer molecule. In the modification of the invention which employs copolymers of carbon monoxide and ethylene without the presence of a second ethylenically unsaturated hydrocarbon, the term y=0 and the ratio of y:x is also 0. When terpolymers are employed, i.e., y is greater than 0, ratios of y:x from 0.01 to 0.1 are preferred. The end groups or "caps" of the polymer chain will depend on the particular materials present during its production and whether and how the polymer has been purified. The precise nature of the end groups is of little significance with regard to the overall properties of the polymer so that the polymer is fairly represented by the polymer chain as depicted above. Suitable alpha-olefins have up to 20 carbon atoms inclusive, preferably up to 10 carbon atoms inclusive and include propylene, butene-1, octene-1 and dodecene-1. Thus, the polyketone polymers are copolymers of carbon monoxide and ethylene or terpolymers of carbon monoxide, ethylene and a second aliphatic alpha-olefin of 3 or more carbon atoms, particularly propylene. Of particular interest are those polymers of molecular weight from about 1,000 to about 200,000, particularly those of molecular weight from 10,000 to 50,000, and containing substantially equimolar quantities of carbon monoxide and olefinically unsaturated compound. Such polymers are conveniently produced by contacting the carbon monoxide and the olefinically unsaturated compound(s) under polymerization conditions in the presence of a catalytic amount of a catalyst formed from a compound of the Group VIII metals palladium, cobalt or nickel, the anion of a non-hydrohalogenic acid of a pKa less than about 6, preferably less than about 2, and a bidentate ligand of phosphorus, arsenic or antimony. Production of these polymers is illustrated, for example, in EP-A-181,014 and 121,965. The physical properties of the polymer will be determined in part by the molecular weight and by whether the polymer is a copolymer or a terpolymer. Typical melting points are from about 175 °C to about 300 °C, more typically from 210 °C to 280 °C. The calcium or magnesium carbonate is typically provided in the form of a fine powder, having a particle size, for example, of above 0.04 µm but below 100 µm. The Ca or Mg carbonate is preferably employed as such, but in alternate modifications alkaline earth metal compounds may be utilized which serve to generate Ca or Mg carbonates during processing or upon exposure of the resulting composition to heat at temperatures lower than those at which flame would result. An example of a material useful as an Ca or Mg carbonate precursor is the corresponding alkaline earth metal bicarbonate. The Ca or Mg carbonates are employed as the sole flame retarding material and alternatively are utilized with other materials such as ammonium thiosulfate, asbestos, alkali metal carbonates or bicarbonates, e.g., potassium bicarbonate or stannous or stannic oxide. The preferred compositions of the invention, however, are those wherein Ca or Mg carbonate is employed as substantially the sole material used to impart flame retardancy to the polyketone composition. The Ca or Mg carbonate is employed in quantities from 2% by weight to 30% by weight, based on total composition, quantities from 5% by weight to 15% by weight being preferred. The flame retardant compositions are produced by mixing the Ca or Mg carbonate throughout the polyketone polymer. The method of forming the composition is not critical so long as the method results in a uniform mixture of Ca or Mg carbonate throughout at least the outer layer of the polyketone polymer. In a preparation of a composition useful in the form in which it is produced, only the outermost portion of the composition need be provided with Ca or Mg carbonate. However, in most applications, a flame retardant composition is produced which is then processed further and in such applications the production of a substantially uniform mixture of polyketone polymer and Ca or Mg carbonate is preferred. In one modification, the compositions are produced by dry blending the components in particulate form and converting to a substantially uniform composition by application of heat and pressure. Alternatively, the compositions are produced by heating the polyketone polymer until molten and the Ca or Mg carbonate or precursor thereof is mixed throughout the polymer by use of a high-shear mixer or extruder. The polymer composition, in addition to polymer and Ca or Mg carbonate, may incorporate other conventional additives which do not detract from the flame retardant character of the composition. Examples of such additives are plasticizers, mould release agents and antioxidants which are added by blending or other conventional methods together with or separately from the Ca or Mg carbonate. The flame retardant compositions are processed by injection moulding, pressure forming or other conventional methods. They are characterized by properties of flexibility and strength in addition to flame retardancy and are useful in a variety of applications, particularly where exposure to elevated temperature is likely to be encountered. The compositions have particular utility in the production of containers for the food and drink industry, particularly those likely to be subjected to elevated temperatures such as the trays used in conjunction with frozen dinners. The compositions are also useful in the production of parts for the automotive industry, particularly those parts located within the engine compartment where high temperatures are encountered or those parts which encounter heat as during the baking of painted surfaces. The compositions of the invention are further illustrated by the following Examples. EXAMPLE 1 A. A first terpolymer of carbon monoxide, ethylene and propylene was prepared in the presence of a catalyst formed from palladium acetate, trifluoroacetic acid and 1,3-bis(diphenylphosphino)propane. The polymer had a melting point of 219 °C and a limiting viscosity number (LVN) of 1.60 measured at 60 °C in m-cresol. A second terpolymer of carbon monoxide, ethylene and propylene was prepared in the presence of a catalyst formed from palladium acetate, trifluoroacetic acid and 1,3-bis[di(2-methoxyphenyl)phosphino]propane. The second terpolymer had a melting point of 221 °C and a LVN of 1.83 measured at 60 °C in m-cresol. B. The first terpolymer was blended with different weight percents of calcium carbonate by use of a twin-screw extruder to produce nibs. The second terpolymer was also extruded to produce nibs for comparison purposes as a control without the addition of calcium carbonate. The nibs were injection moulded into test bars of approximately 12 cm by 1.25 cm by 0.32 cm dimensions. The test bars were then sliced lengthwise into 3 equal strips and the edges were smoothed off. These strips were tested for flame retardancy. Standard test method ASTM D2863-77 was used to evaluate the burning behaviour of the different blend compositions. 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 strip. 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. The LOI values determined for three different blends of the first terpolymer and calcium carbonate are given in Table I together with the LOI of the terpolymer without added calcium carbonate used as a control sample. One can see from the LOI values in Table I that a greater percentage of oxygen was required in an oxygen-nitrogen atmosphere to initiate and support a flame on the samples containing calcium carbonate in comparison to the control sample without calcium carbonate. The flame retardancy of the blend compositions is improved for the samples containing calcium carbonate. Sample % Weight Calcium Carbonate LOI Control none 18.5 - 19 1 5 23 - 23.5 2 10 25.5 - 26 3 25 27 - 27.5 EXAMPLE 2 A blend of a linear alternating carbon monoxide/ethylene copolymer and magnesium carbonate is produced by a procedure similar to that of Example 1. It shows good flame retarding properties.

Claims: Flame retardant polymer composition comprising a linear alternating polymer of the formula wherein B is the moiety of an alpha-olefin of at least 3 carbon atoms polymerized through the olefinic unsaturation, x and y being integers, the ratio of y:x being no more than 0.5, and a quantity of 2% to 30% by weight, based on total composition, of magnesium or calcium carbonate as flame-retarding additive. Polymer composition as claimed in claim 1, characterized in that the alpha-olefin is propene and the ratio of y:x is 0.01 to 0.2. Polymer composition as claimed in claim 1 or 2, characterized in that the quantity of carbonate is from 5% to 15% by weight, based on total composition.

Inventors: LUTZ ROBERT GARDINER, LUTZ, ROBERT GARDINER
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: C08K3
IPC codes: C08K3, C08L73