POLY(1,4-CYCLOHEXYLENE DIMETHYLENE TEREPHTHALATE) MOLDING COMPOSITIONS

Abstract: Disclosed is reinforced poly(1,4-cyclohexylene dimethylene terephthalate) containing 5-30 weight % of polyphenylene sulfide as a thermo-oxidative stabilizer.

Description: POLY(1,4-CYCLOHEXYLENE DIMETHYLENE TEREPHTHALATE) MOLDING COMPOSITIONS Technical Field This invention relates to reinforced poly(l,4-cyclohexylene dimethylene terephthalate) (PCT) molding compositions having improved thermo-oxidative stability. Background of the Invention Polyesters have been used as engineering plastics for mechanical parts of various machines, electrical equipment and parts of motor cars. Preferably, engineering plastics are provided with fire-proof properties, i.e., flame retardancy, in addition to well-balanced ordinary physical and chemical properties. Such properties are indispensable in thermoplastic polyesters in order to enlarge their use as engineering plastics, because they are normally used at temperatures higher than 100°C. This invention concerns the discovery of reinforced molding compositions based on PCT or high melting crystalline copolymers of PCT with improved thermo- oxidative stability. Surprisingly, the addition of polyphenylene sulfide (PPS) to reinforced (GFR) PCT by conventional melt blending will cause improvement in the thermo-oxidative stability of GFR PCT while maintaining excellent mechanical properties in the resulting formulations. These materials have high strength, stiffness, and heat resistance properties. These materials find application as a molding plastic in the electronics industry as printed circuit boards, connectors, etc. These are applications that require the material to have high strength, stiffness, heat resistance, and continuous use temperature rating. U.S. Patent 4,140,671 discloses mixtures of linear polyesters, polyphenylene sulfide powder, flame retardants, fiber glass and talc to reduce the warpage of the polyester. No indication of improved long-term oven stability is made. Further, the PPS is present in the form of a filler, rather than as a melt blend, as~in the present invention. U.S. Patent 4,689,365 discloses blends of poly(butylene terephthalate) (PBT) and pol (ethylene terephthalate) (PET) with polyphenylene sulfide of a specified melt flow, which provide materials with an improved heat deflection temperature. No disclosure of polyesters other .than PBT and PET is made. There is no indication of improved long-term oven stability in the blends. According to the examples, molding conditions were such that the PPS was also not melted (molding done below the melting point of PPS) . Other U.S. patents of interest include 4,251,429 and 4,284,549 (blends of PPS with polyarylates) and 4,267,397 (blend of PPS with a wholly aromatic liquid crystalline polyester) . Blends of polysulfones with polyesters are disclosed in U.S. Patent 3,742,087. Polysulfones are not useful in the present invention because the heat deflection temperataure is lowered. Description of the Invention According to the present invention, there are provided polyester molding compositions containing a reinforcing material and polyphenylene sulfide as a thermo-oxidative stabilizer, the polyester containing repeat units from terephthalic acid and 1,4-cyclohexane- dimethanol. More particularly, the present invention provides reinforced polyester molding compositions having improved physical properties comprising (a) a polyester having repeat units from terephthalic acid and 1,4-cyclohexane- dimethanol and having an I.V. of 0.5-1.0, and (b) 5 to 30%, based on the weight of polyester, of polyphenylene sulfide, the repeat units of ~ which consist essentially of and having a degree of polymerization of at least 50. The polyester portion of the molding compositions of the present invention is prepared by conventional polycondensation procedures well known in the art. The polyester, poly(1,4-σyclohexylene dimethylene terephthalate), contains repeat units from a dicarboxylic acid component and a glycol component. The dicarboxylic acid component, a total of 100 mol %, is at least 90 mol % terephthalic acid and the glycol component, a total of 100 mol %, is at least 90 mol % 1,4-cyclohexanedimethanol. The dicarboxylic acid component may contain up to 10 mol % of other conventional aromatic, aliphatic or alicyclic dicarboxylic acids such as isophthalic acid, naphthalenediσarboxylic acid, cyclohexane-dicarboxylic acid, succinic acid, sebacic acid, adipic acid, glutaric acid, azelaic acid and the like. The glycol component may contain up to 10 mol % of other conventional aliphatic or alicyclic glycols such as diethylene glycol, triethylene glycol, ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, and the like. The polyesters can be prepared by direct condensation of terephthalic acid with 1,4-cyσlohexane- dimethanol or ester interchange using dimethyl terephthalate. The essential components of the polyester, e.g., terephthalic acid or dimethyl terephthalate and 1,4-cyclohexanedimethanol are ~ commercially available. The polyesters and copolyesters described above should have an I.V. (inherent viscosity) of from 0.5 to 1.0. It is important in the present invention that the polyester and the PPS have melting temperatures close to each other so that the two can be melt blended without degradation of either. The melting temperature of the polyester is 295°C and the melting temperature of PPS is 285°C. In the prior art, PPS is used mostly as a filler and is not melt blended with the polyester. Thus, in applicants' invention, the blend of polyester and PPS is homogeneous. The improved polyester resin composition of this invention includes a reinforcing material. A preferred reinforcing filler is glass fibers which may be introduced into the composition as chopped glass fibers or continuous glass fiber rovings in amounts of 10-50% by weight of the composition. Other reinforcing materials such as metal fibers, graphite fibers, aramid fibers, glass beads, aluminum silicate, asbestos, mica, talc and the like may be used in combination with, or in place of the glass fibers . Substantially any of the types of glass fibers generally known and/or used in the art are useful in the present invention. Typical types are those described in British Patent No. 1,111,012, U.S. Patent No. 3,368,995 and German Auslegeschrift No. 2,042,447. Thus, the average length of useful fibers covers a wide range, for example, 1/16 to 2 inches (0.159 cm to 5 cm). The presently preferred glass fibers have an average length of 1/16 to 1/4 inch (0.159 cm to 0.64 cm). Glass filaments made of calcium- luminum-boron silicate glass, which is relatively free from sodium carbonate, are preferably used. Glass of this type is known as "E" glass; however, where the electrical properties of the reinforced polyesters are not important, other glasses can also be used, for example the glass with a low sodium carbonate content which is known as "C" glass. The diameters of the filaments can be in the range from 0.003 to 0.018 mm, but this is not critical for the present invention. In addition to the components discussed above, the blends of this invention may contain additives commonly employed with polyester resins, such as colorants, mold release agents, tougheners, nucleating agents, crystallization aids, plasticizers, ultraviolet light and heat stabilizers and the like. Materials such as Irganox 1010 stabilizer and/or eston 619 stabilizer in amounts of up to 2%, preferably 0.1-05% by weight of the composition, are preferred. Preferably, the molding compositions according to this invention include at least one conventional flame retardant such as a halogenated organic compound, an antimony compound, or the like. The blends of this invention are prepared by blending the components together by any convenient means to obtain an intimate blend. Compounding temperatures must be at least the melting point of the PCT. For example, the polyester can be mixed dry in any suitable blender or tumbler with the other components and the mixture melt-extruded. The extrudate can be chopped. If desired, the reinforcing material can be omitted initially and added after the first melt extrusion, and the resulting mixture can then be melt extruded. The product is especially suitable as an injection molding material for producing molded articles . These blends will find application in injection molded parts that require a good combination of strength, stiffness, heat resistance, and continuous ' use temperature such as required in the electronics industry. The following examples are submitted for a better understanding of the invention. A series of blends of PCT with 30% glass fiber (GFR PCT) are prepared containing 0, 5, 10, 20, and 30% PPS based on the weight of the polyester. These formulations are then melt blended by extrusion compounding using the 1.5 inch single screw extruder at 300°C. The resulting formulations are then molded into 1/8 inch tensile and flexural test bars using an injection molding machine. Mechanical properties are determined on these test bars (see Table 1) . Generally, the GFR PCT formulations containing PPS maintain excellent heat deflection temperature with only minimal loss of strength properties (tensile, flexural, Izod impact) . The flammability properties of these formulations are improved as shown by the increasing oxygen index with increasing PPS concentration. Thermo- oxidative stability is determined on these formulations by heating the tensile bars in a forced air oven at 180°C for 0-2352 hours and measuring the retained tensile strength (see Table 2) . Generally, the retained tensile strength increases as the PPS concentration increases in the GFR PCT blends, which represents improved thermo-oxidative stability. The blends contain conventional amounts of Beήzoflex S312 crystallization enhancer and Weston 619 and Irganox 1010 stabilizers Ryton P4 polyphenylene sulfide is used. TABLE 1 Effect of PPS on the Mechanical and Flammability Properties of PCT/30% Glass Fiber Reinforced Example No. PPS, % 10 20 30 Benzoflex S312 crystallization enhancer, % 5 4.64 4.29 3.57 2.86 Weston 619 stabilizer, % 0.25 0.23 0.22 0.18 0.14 Irganox 1010 stabilizer, % 0.25 0.23 0.22 0.18 0.14 Mold temperature, °C 120 120 120 120 120 % Ash 29.8 29.9 30.1 30.6 31.2 IV (before molding) , dl/g* 0.63 0.57 0.48 0.37 IV (af er molding) , dl/g* 0.68 0.63 0.57 0.47 0.31 Density 1.445 1.452 1.464 1.460 1.502 % Mold shrinkage 0.09 0.08 0.10 0.11 0.10 Rockwell Hardness R 122 121 120 122 122 L 113 113 114 115 116 M 100 101 101 102 104 10 Mil notched Izod ft-lb/in. ( Joules /meter ) @-40°C 1. 6c 1. 5c 1.4c 1.4c 1.6c (85. 4 ) ( 80 ) (74.7) (74.7 (85.4) @ 23°C 1. 6c 1.4c 1.3c 1.3c 1.6c (85.4) (74.7) (69.4) (69.4) (85.4) Unnotched Izod ft-lb/in. (Joules/meter) @-40°C 10.8c 8.2c 6.4c 5.1c 4.9c @ 23°C 10.9c 8.4c 6.0c 4.4c 4.8c Flexural strength 10 psi (kPa) 30.07 25.43 23.76 20.62 22.14 (207.3) (175) (163.8) (142) (152.6) Flexural modulus 10 psi (kPa) 12.47 12.69 12.86 13.54 14.39 (85.98) (87.5) (88.6) (93.3) (99.216) Heat deflection temperature °C @ 264 psi 259 259 261 252 260 (1820 kPa) TABLE 1 (Cont'd. ) Effect of PPS on the Mechanical and Flammability Properties of PCT/30% Glass Fiber Reinforced Example No. Tensile strength @ Break 10 3 psi 19.69 18.47 17.86 16.58 15.09 (kPa) (135.7) (127) (123) (114) (104) @ Yield 10 5 psi - - - - - (kPa) % Elongation @ Break 4 4 3 3 3 @ Yield - - - - - Oxygen index 20.0 20.2 20.7 21.6 25.2 *IV determinations corrected for % Ash cComplete breaks (Izod impact strength) TABLE 2 Effect of PPS on the Thermo-Oxidative Stability of PCT/30% Glass Fiber Mold temperature °C PPS, % Benzoflex S312 crystallization enhancer, % Weston 619 stabilizer, % Irganox 1010 stabilizer, % Tensile strength (§ break 10 psi (kPa) after exposure to 180°C air % Retained tensile strength after exposure to 180°C Air 85 84 86 94 81 82 85 87 76 76 76 86 73 73 75 85 67 65 66 73 62 61 64 72 60 65 70 82 56 58 62 69 The data on percent retained tensile strength show that, surprisingly, as the amount of PPS in the composition is increased, the percent retained tensile strength after extended exposure to 180°C air increases. With no PPS, only 50% of the tensile strength is retained after 2352 hours at 180°C. This steadily increases with increasing levels of PPS, indicating the improved thearmo- oxidative stability of the compositions of this invention. As used herein, the inherent viscosity (I.V.) is measured at 25°C using 0.50 g of polymer per 100 mL of a solvent consisting of 60% by weight phenol and 40% by weight tetrachloroethane. The tests used herein for determination of mechanical properties are described as follows: Tensile Strength ASTM D638-80 Elongation ASTM D638-80 Flexural Modulus ASTM D790-80 Flexural Strength ASTM D790-80 Rockwell Hardness Izod Impact ASTM D256-81 Heat Deflection ASTM D648-72 Temperature, °C Oxygen Index is defined as the minimum concentration of oxygen in an oxygen and nitrogen mixture that will support combustion of a material in a candle-like configuration (ASTM designation D2863-77). Unless otherwise specified, all parts, percentages, ratios, etc., are by weight. Weight of reinforcing glass fibers and nucleating agents(s) are based on total composition weight. The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the inventron.

Claims: CLAIMS 1. A reinforced polyester molding composition characterized as a melt blend of (a) a polyester having repeat units from at least 90 mol % terephthalic acid and at least 90 mol % 1,4-cyclohexanedimethanol, said polyester having a I.V. of 0.5-1.0, (b) 10-50% based on the weight of polyester of a reinforcing material, and said composition further comprising 5 to 30% based on the weight of polyester, of a polyphenylene sulfide, the repeat units of which consist essentially of and having a degree of polymerization of at least 50. A molding composition according to Claim 1 wherein said polyester consists essentially of repeat units from terephthalic acid and 1,4-cyclohexane¬ dimethanol. 3. The method of preparing a reinforced polyester molding composition characterized by melt blending a polyester having repeat units from at least 90 mol % terephthalic acid and at least 90 mol % 1,4-cyclohexanedimethanol 10-50% based on the weight of polyester of a reinforcing material, and 5-30% based on the weight of polyester of a polypropylene sulfide having repeat units consisting essentially of * \ ^. / n and having a degree of polymerization of at least 50

Inventors: MINNICK LARRY ALLEN, MINNICK, LARRY, ALLEN
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1990
Main classification: C08L67
IPC codes: C08K7, C08L67