LOW TEMPERATURE TOUGHENED POLYAMIDE Background of the Invention Since the original development of polyamides, effort has been directed to the improvement of the ductility or toughness of these polymers in the molded configuration. Typically, one or more polymers which exist in a separate phase have been blended with polyamides to improve their properties. A significant advance in this area was made in past decades with the discovery that such polyamides can be toughened by rubbers defined by their tensile modulus, particle size, and functional or reactive sites. While previously developed polyamide compositions have provided markedly improved toughness, the retention of high toughness at exceptionally low temperatures has been difficult to attain.

Summary of the Invention The present invention provides a toughened polyamide composition which exhibits unexpectedly good toughness at low termperatures.

Specifically, the present invention provides a toughened thermoplastic composition comprising, complementally,

(a) about from 60 to 90 percent by weight of a first phase consisting essentially of at least one polyamide matrix resin of number average molecular weight of at least 5,000, and

(b) about from 5 to 30 percent by weight of a dispersed phase consisting essentially of at least one copolymer of ethylene and propylene, wherein the units in the copolymer derived from ethylene and propylene each comprise at least about 40 % by weight of the copolymer, and further comprising about from 0.1 to 3.0 weight % of groups capable of reacting with the acid or amine moieties on the polyamide, and

(c) about from 3 to 30 percent by weight of a dispersed phase consisting essentially of at least one copolymer of ethylene and propylene, wherein the units in the copolymer derived from ethylene and propylene each comprise at least about 40 % by weight, the copolymer being substantially free from reactive units, both of copolymers (b) and (c) being substantially amorphous.

Detailed Description of the Invention The compositions of the present invention are a blend of at least one polyamide and toughening copolymer. Polyamides which can be used include those which have a relative viscosity (ratio of solution and solvent viscosities in a capillary viscometer at 25°C using an 8.4% by weight solution of polymer dissolved in formic acid containing 10% by weight of water) of about 50 or more and preferably at least about 70. Such polyamides include the polymers of diamines and dicarboxylic acids or the functional equivalents of dicarboxylic acids such as dicarboxylic acid chlorides or diamides, or of amino acids or lactams, and copolymers thereof. Representative polyamides which can be used include polyhexamethylene adipamide (6,6 nylon), poly-e-caproamide (6 nylon), polyhexamethylene sebacamide (610 nylon), polyhexamethylene dodecanoamide (612 nylon) and polytetramethylene adipamide (4,6 nylon). Still other polyamides which can be used in the present invention are those described in Epstein et al., U.S. Patent 4,410,661, hereby incorporated by reference. In general, the polyamides used in the matrix should have a number average molecular weight of at least about 5,000.

The polyamide can be either crystalline or amorphous, of blends thereof. Similarly, blends of two or more chemically different polyamides can also be used. For example, blends of nylon 6 and nylon 6,6 exhibit excellent performance characteristics when combined with tougheners in accordance with the present invention, as do copolymers of the same polyamides. Nylon 4,6 may be preferred because of its excellent high temperature properties, and nylon 612 is particularly good for the preparation of toughened polyamides, since it is less moisture sensitive than many other polyamides.

The polyamide comprises about from 60 to 90 percent by weight of the polymer blend. Less than 60 weight of the polyamide generally does not provide the balance of properties required of an engineering plastic, while the toughening effect of the present compositions is not realized to an appreciable extent when significantly less than about 10 weight % of the combined tougheners is present.

The toughening, or dispersed, phase of the present blends

comprises, in combination, about from 10 to 40 percent by weight of the polymer blend. The dispersed phase comprises grafted and ungrafted copolymers, each present in the indicated minimum quantities. The copolymers are both derived from ethylene and propylene, wherein the units in the copolymer derived from ethylene and propylene each comprise at least about 40 % by weight of the total of ethylene and propylene units. While the toughening copolymers can be either random or block, random copolymers are preferred to attain the desired amorphous configuration. One of the toughening copolymers further comprises about from 0.1 to 3.0 weight % groups capable of reacting with the acid or amine moieties of the polyamide. Such reactive groups can vary widely, and can, for example, correspond to those identified in Epstein, U.S. Patent 4,174,358, hereby incorporated by reference, as elements B, C, D, and E. Of these, those reactive groups derived from maleic anhydride have been found to be particularly satisfactory.

Both of the toughening copolymers in the dispersed phase are substantially amorphous. This is indicated by the substantial absence of melting and freezing transitions as shown by conventional Differential Scanning Calorimetry (DSC) techniques. Either component of the toughening phase of the present blends can further comprise up to about 10% by weight of at least one diene monomer. Such diene monomers include unsaturated branched, straight chain and cyclic compounds having from 4 to 14 carbon atoms amd at least one additional conjugated or nonconjugated unsaturated carbon-carbon bond. Such diene monomers can be selected, for example, from hexadiene, norbornadiene, ethylidenenorbornene (ENB), dicyclopentadiene (DCPD), butadiene, isoprene, divinylbenzyl and allylstyrene, of which 1,4-hexadiene is preferred. These terpolymers, containing a diene component, are typically designated EPDM materials, as described more fully, for example, in Volume 6 of Encyclopedia of Polymer Science and Engineering, Second Edition, John Wiley & Sons, New York (1986), in the section on Ethylene- Propylene Elastomers on pages 522-564, hereby incorporated by reference. The blends of the present invention are typically prepared by physically admixing the components, so as to provide a particle size of the

toughening phase of about from 0.01 to 3 microns, and preferably at least about 0.1 microns. Conventional polymer processing equipment can be used, such as multi-screw extruders, or other conventional plasticating devices such high shear mills, so long as the applied shear is sufficient to provide the required small particle size and without significant degradation of the blend components. In the alternative, the polymer blends can be made by coprecipitation from solution, blending or by dry mixing the components together followed by melt fabrication of the mixture.

In addition to the three basic polymeric components, the present blends can also include one or more conventional additives such as stabilzers and inhibitors of oxidative, thermal, and ultraviolet light degradation; lubricants and mold release agents, colorants including dyes and pigments, fibrous and particulate fillers and reinforcements, nucleating agents, plasticizers, and the like, each used in the quantities typical in toughened polyamide compositions, as will be known to those skilled in the art.

The toughened polyamide blends of the present invention have the outstanding combination of properties found in previously available toughened nylons, and, in addition, exhibit excellent toughness at exceptionally low temperatures. While previously available toughened nylons could exhibit ductile breaks (notched Izod measurements of 12 or higher) at ambient temperatures, they typically exhibited brittle breaks (notched Izod measurements of 6 or lower) at temperatures of -40°C. By contrast, the present compositions retain ductility at these low temperatures. This behavior is particularly surprizing in view of the significant concentration of ungrafted copolymer in the toughening phase. As shown in the Examples and Comparative Examples, the ungrafted copolymer, which is more readily prepared than the grafted copolymer, appears to improve the low temperature toughness rather than depreciate those properties, as would normally be expected when replacing quantities of the grafted copolymer.

The excellent low temperature properties of the present polymer blends makes them especially useful in a wide variety of applications in which the final molded component is exposed to extended periods of low temperatures,

including sporting goods such as ski bindings, backpack components, and ice ska blade supports; automotive components such as luggage racks and door handle and cases for outdoor radio and communication equipment; as well as other applications which will be readily apparent to those skilled in the art of designin and fabricating thermoplastic articles.

The present invention is further illustrated by the following specific Examples and Control Examples, in which the test methods described in Epstein, U.S. Patent 4,174,358 were used, including the following: Flexural Modulus: ASTM T-790-58T

Tensile Strength: ASTM D-638-58T

Elongation: ASTM D-638-58T

Notched Izod Toughness: ASTM D-256-56 Parts and percentages are by weight unless otherwise indicated. In these Examples, each of polyamides used had a number average molecular weight of greater than 5000. CONTROL EXAMPLE A

A copolymer blend was prepared from 40 parts of 6,6 nylon, 40 parts of 6 nylon, and 20 parts of ethylene propylene copolymer grafted with maleic anhydride. The ethylene propylene copolymer was made up of 40 % propylene units, as indicated by infrared analysis, and had a concentration of grafted maleic anhydride units of about 0.7%.

The components of the blend were first dry mixed by tumbling, and then compounded on a twin- screw extruder. The resulting blend was injection molded into 1/8" bars and tested in the dry-as-molded (DAM) state:

The bars exhibited the following properties: Flex Modulus 236 Kpsi

Tensile Strength 6780 psi Elongation 143%

Notched Izod, 23°C. 21.9 ft-lbs/in (ductile)

Notched Izod, -30°C. 21.5 ft-lbs/in (ductile)

Notched Izod, -40°C. 9.5 ft-lbs/in (mixed ductile-brittle)

EXAMPLE1ANDCONTROLEXAMPLEB

In Example 1, the general procedure of the above Control Example was repeated, except that, instead of the 20 parts of grafted ethylene propylene copolymer, 10 parts of this component were used, and 10 parts of ungrafted amorphous EPDM rubber were included in the polymer blend. In Control Example B, 10 parts of the grafted ethylene propylene copolymer were used with 10 parts of a semi-crystalline EPDM rubber.

The components were compounded in a twin-screw extruder as before, and the resulting blends were injection molded. The flex modulus, tensile strength and elongation were all measured on 1/8" bars, while the notched izod measurements were made on 1/4" bars. The injection molded blends exhibited the following DAM properties:

EXAMPLE C

In Control Example C, the procedure of Control Example A was repeated, except that the polyamide was 80 parts of the 66 nylon. The resulting blend was molded and tested as before, using the procedure of Example 1 and Control Example B, in which the Flexural Modulus, Tensile Strength and Elongation were measured on 1/8" bars, while the Notched Izod measurements were made on 1/4" bars. The sample exhibited the following DAM properties:

Flexural Modulus 273 Kpsi Tensile Strength 7020 psi Elongation 61.2% Notched Izod, 23°C. 20.7 ft-lbs/in (ductile) Notched Izod, -20°C. 17.0 ft-lbs/in (ductile) Notched Izod, -30°C. 10.8 ft-lbs/in (mixed ductile-brittle)