HIGH IMPACT MOLDING COMPOSITIONS

Abstract: Certain metal compounds such as antimony oxide and magnesium oxide are used to enhance the noched Izod impact resistance of molded objects made from selected polyamide copolymer compositions comprised of polyepsi­ loncaprolactam (nylon-6) or polyhexamethyleneadipamide (nylon-66) and preferably ethylene/ethyl acrylate and ethylene/acrylic acid copolymers.

Description: Background of the invention 1. Field of the invention This invention relates to the use of selected metal compounds as modifiers for preparing high impact resistant nylon-6 or nylon-66 molding compositions. 2. Brief description of the prior art It is known (U.S Patent No. 3,388,186 issued June 11, 1968 to Kray et al.) that compositions of nylon-6 containing ethylene copolymers having a minor proportion of acrylic or methacrylic acid or alkyl ester thereof as backbone and having grafted nylon-6 side chains, show higher impact resistance than nylon-6 molding compositions not containing the above graft copolymers. These compositions are prepared by reacting caprolactam in the ethylene copolymer melt. U.S. Patent No. 3,472,916 of October 14, 1969 to Anspon et al. discloses blends of 70-98% by weight nylon-6 homopolymer with correspondingly 2-30% by weight of ethylene/acrylic or methacrylic alkyl ester copolymer, having improved Izod impact resistance, compared to nylon-6 alone. The alkyl group in the alkyl ester copolymer contains 1-4 carbon atoms and the alkyl ester is from 10 to 60 percent by weight of the copolymer. The copolymer has "highly uniform distribution of the acrylic ester in the copolymer", presumably a random distribution. These blends are prepared by mixing together and subsequently co-extruding the ingredients. U.S Patent No. 3,963,799 issued June 15, 1976 to Starkweather, discloses ternary blends of polyamide, polyethylene or copolymers thereof, and a small amount of copolymer having an ethylenic backbone and nylon-6 side chains. Also, U.S. Patent No. 4,160,790 discloses synergistic improvement of nylon-6 or nylon-66 impact resistance by blending, in the melt, with minor proportions of both an ethylene/acrylic acid copolymer and an ethylene/ethyl acrylate copolymer. French Patent No. 1,386,563, of issue date December 14, 1964, relates to compositions of 50-99 percent by weight polyamide and the balance an olefin copolymer containing up to 10 mol percent of acid side chains. Journal of Polymer Science, Volume 54, Pages 388 and 389 (1961) in an article entitled "Linear Polyesters", by R.E. Wilfong, discloses a list of catalytic agents including various metal oxides suitable for use in the preparation of polyesters. None of the above references disclose the use of metal compounds to enhance the impact resistance of nylon-6 or nylon-66 polyamide compositions with both a copolymer of an olefin and an acid-containing comonomer and a copolymer of an olefin and a C₁-C₄ alkyl ester of said acid comonomer. The compositions of the present invention are useful as containers, e.g. bottles, or as film wrapping or as fibers. Summary of the invention In accordance with the present invention there is provided a melt-blended polyamide composition comprising the components: a) at least 60 percent by weight of the composition of a polyamide selected from polyhexamethyleneadipamide, polyepsiloncaprolactam and a mixture of polyhexamethyleneadipamide and polyepsiloncaprolactam, b) from 1 to 30 weight percent of an acid copolymer of an - olefin having 2 to 5 carbons, with 1 to 20 mol percent of an unsaturated carboxylic acid having 3 to 8 carbons, c) from 1 to 10 weight percent of an ester copolymer of an - olefin having 2 to 5 carbons, with 1 to 20 mol percent of an alkyl ester of an unsaturated carboxylic acid having 3 to 8 carbons and teh alkyl group having 1 to 4 carbon atoms, the weight proportions between the acid copolymer and ester copolymer being from 1 part of acid copolymer to 10 parts of ester copolymer up to 30 parts acid copolymer to 1 part ester copolymer, d) from 0.05 to 1.0 percent by weight based on the weight of the composition of antimony oxide or magnesium oxide. In preferred embodiments there is provided antimony oxide or magnesium oxide as the impact modifier in polyhexamethyleneadipamide/ethylene-ethyl acrylate/ethylene-acrylic acid copolymer compositions or polyepsiloncaprolactam/ethylene-ethyl acrylate/ethylene-acrylic acid copolymer compositions. Description of the preferred embodiments Polyamides suitable for use in the present invention are polyhexamethyleneadipamide (nylon-66), polyepsiloncaprolactam (nylon-6) or mixtures thereof, preferably possessing a number average molecular weight, as measured by membrane osmometry, of 15,000 to 40,000. Nylon-6 or nylon-66 suitable for use herein can contain a variety of terminal functionality, and preferred is that containing; a) a carboxyl group attached to both ends of the polyamide chain; b) a carboxyl group attached to one end and an acetamide group attached to the other end of the polyamide chain; c) an amino group attached to both ends of the polyamide chain; and d) a carboxyl group attached to one end and an amino group attached to the other end of the polyamide chain. More preferred is nylon-6 or nylon-66 having a carboxyl group attached to one end and an amino group attached to the other end of the polyamide chain. Carboxylic acid-containing comonomers suitable for preparing the ethylene/carboxylic acid copolymer include those monomers selected from the group consisting of unsaturated monocarboxylic acids of 3 to 6 carbon atoms, unsaturated dicarboxylic acids of 4 to 8 carbon atoms, and mixtures thereof. Representative examples of such monomers include acrylic acid, methacrylic acid, crotonic acid, maleic acid, and fumaric acid. Preferred are acrylic acid and methacrylic acid, more preferred is acrylic acid. Ester-containing monomers suitable for preparing the ethylene/alkyl ester copolymers of the present invention are those C₁ to C₄ alkyl esters of the aforementioned carboxylic acid-containing monomers, preferably acrylic acid and methacrylic acid, or other substituted acrylic acids. Representative examples of such esters include methyl, ethyl, propyl, isopropyl, butyl, isobutyl and t-butyl esters of such acids. Preferred are methyl and ethyl acrylate and methyl and ethyl methacrylate; more preferred is ethyl acrylate and ethyl methacrylate; most preferred is ethyl acrylate. A preferred α-olefin suitable for use in the present copolymers is ethylene. Therefore, in the most preferred embodiments of the present invention, the nylon-6 or nylon-66 compositions will contain minor proportions of ethylene/acrylic acid copolymer (EAA) and ethylene/ethyl acrylate copolymer (EEA) as well as the modifier. The polyamide ingredient amounts to at least 60 percent by weight of the composition, the balance consisting essentially of EAA and EEA and an effective amount of inorganic modifier. Moreover, these preferred copolymers of ethylene each contain from 1 to 20 mol percent of the said comonomer; preferably, 3-5 mol percent, and more preferably 3-5 mol percent of acrylic acid monomer in the EAA copolymer; and preferably 5-10 mol percent of the ethyl acrylate in the EEA copolymer. The preferred copolymers are characterized by a melt index in the range of 2-20 g/10 min as measured by ASTM D-1238 employing a load of 2,160 g and a temperature of 190°C. The polyamides, nylon-6 and nylon-66, as well as the ethylene copolymers suitable for use herein, can be prepared by any conventional polymerization processes used in the art. Especially preferred compositions of the present invention generally contain 2 to 40, more preferably 12 to 30, weight percent of ethylene copolymers. There is from 1 part of acid copolymer to 10 parts of ester copolymer up to 30 parts of acid copolymer to 1 part of ester copolymer by weight. Preferably, there is from 1 to 10 weight percent of the ester copolymer, and from 1 to 30 weight percent of the acid copolymer. More preferably, there is from 10 to 30 weight percent of the acid copolymer. The composition contains at least 60 weight percent, and preferably 70 to 88 weight percent, of nylon-6, nylon-66, or mixtures thereof, having a melt index (ASTM D-1238, condition "Q", 1000 g load at 235°C) in the range of 2 to 20 g/10 minutes, and containing up to 15% by weight, based on the nylon ingredient, of nylon monomer and water-extractable oligomers, of either nylon-6 or nylon-66 type. There is from 0.05 to 1.0 weight percent, preferably 0.10 to 0.75 weight percent, and more preferably 0.2 to 0.6 weight percent of inorganic modifier. All weight percents are based on the total weight of the composition. The inorganic modifer is a metal compound described in detail below. An improvement in impact properties is experienced by the blend containing the impact modifier. Although the mechanism leading to the improvement in impact is not clear, it is clear that there is an improvement not resulting from the neutralization of the carboxylic acid groups of the acid copolymer by the metal cation of the metal compound to form an ionic copolymer in situ. This is particularly illustrated by reviewing Example 5. In Example 5, the metal cation of the metal compound, antimony oxide, does not react with the carboxylic acid groups of the acid copolymer, under the extrusion mixing conditions similar to those used to blend the high impact composition of the present invention. However, considering the art relating to the formation of ionic copolymers, such as U.S. Patent 3,264,272, the conditions necessary to neutralize the carboxylic acid groups of the acid copolymer in the composition of the present invention are not present during the blending of the composition. Therefore, even if oxides which are basic enough to theoretically react to neutralize the carboxylic groups are used in the composition of the present invention, the conditions under which the composition is blended may not be sufficient for the reaction to proceed with any significance, if at all. The improvement in impact by the addition of such metal compounds is, therefore, not dependent on the formation of an ionic copolymer. Metal compounds suitable for use as modifiers are antimony oxide and magnesium oxide. The metal compound modifier is present in the instant polyamide compositions in an effective amount, and by the term "effective amount" is meant that amount of modifier required to increase the Izod impact resistance of molded articles of the present polyamide compositions. Generally, the amount of modifier required for such an increase ranges from 0.05 to 1.0 wt.% based on the total weight of the composition. The precise amount of modifier is dependent on such factors as concentration of each of the ingredients and the mixing or extruding conditions such as temperature, shear, etc.. which can be easily determined by routine experimentation. The molding compositions of the present invention can also contain conventional additives in small quantities such as specifically up to about 0.25 percent by weight of a metal soap as mold release agent or extrusion aid, and optionally a heat stabilizer, such as a stabilizer based on copper. The present compositions can also contain plasticizers such as nylon-6 or nylon-66 water extractable oligomers, also referred to herein as "nylon" oligomers, in amounts preferably not over 15% by weight of the polyamide ingredient. They can also include colorants, such as pigments and carbon black, as well as conventional antioxidants and stabilizers. The molding compositions of the present invention are prepared by homogeneously mixing the ingredients at temperatures between 230 to 340°c, preferably 260 to 300°C, in conventional homogeneous mixing machines. By the term "homogeneously mixing" is meant a thorough intense mixing of the components under conditions where high shear stresses prevail, particularly intense kneading. Especially suitable machines for homogeneous mixing include the one-shaft or multi-shaft screw extruders, kneaders and calenders which have a plurality of pairs of rollers. The examples which follow illustrate our invention and set forth the best modes which we have contemplated for carrying out the invention. Example 1 As indicated in Table I below, various nylon-6 compositions were prepared with ethylene/ethyl acrylate ("EEA") and/or ethylene/acrylic acid ("EAA") copolymers. The EEA copolymer was that commercially available from Union Carbide has Flexible Ethylene Copolymer DPD-6169, described as having a melt index of 6 g/10 min and ethyl acrylate content of 18 weigh percent (about 5.8 mol percent). The EAA copolymer was that commercially available from Dow Chemical as DOW EAA Resin™ 455, described as having a melt index of 5.5 g/10 min and acrylic acid content of 8 weight percent (about 3.3 mol percent). The ingredients, in pellet from except for the inorganic modifier, were by blended for about 20 minutes and then mixed and extruded under shearing action by an NRM single screw extruder in the melt; and extruded as a strand which was cooled and pelleted. The extruder was maintained at an RPM of 31, contained four heating zones, all of which were at a temperature of 300°C, and the die was at a temperature of 260°C. The resulting compositions were injection molded into test bars and tested as set forth in Table I, D-1238 and D-256 indicates ASTM testing procedures. Example 2 As indicated in Table II below, various nylon-6 compositions were prepared according to the procedure set forth in the previous examples. The nylon in these examples contains amine groups on both ends of the nylon chain. Example 3 Several samples are prepared with the ingredients according to the procedure set forth in Examples 1 and 2, except that the polyamide is the condensation product of hexamethylene diamine with adipic acid. The resulting composition will be found to have Izod ft, lbs/inch (Newton meter per meter) notch of substantially higher values than such compositions not containing antimony oxide. Example 4 Following the general procedure and utilizing the apparatus described above in Example 1, two molding compositions, listed below in Table III, were prepared and injection molded. The composition contained nylon-66 polyamide in place of nylon-6. The EEA and EAA copolymers used were the same as described above in Example 1. The compositions were prepared by first dry blending the components together on a roll mill. The compositions were then extruded through the above-described NRM extruder, containing a 2-1/2″ (6.35 cm) extrusion die, which was a temperature of 243°C. The extruder zone temperatures were Z₁ = 580°F (304°C), Z₂ = 560°F (293°C), Z₃ = 530°F (277°C) and Z₄ = 500°F (260°C). (Z, being the initial zone and Z₄ being the exit zone prior to the die). The extruder was maintained at a speed of 80-82 rpm. The results are listed below in Table III. The increase in notch Izod impact strength by the incorporation of a small amount of antimony oxide into the nylon-66 polymeric composition is quite apparent. Example 5 This example is included to show that the improved impact resistance obtained by the addition of the metal compound, in particular antimony oxide, is not the result of the formation of an ionic copolymer in situ by the metal cation of the metal compound neutralized by the carboxylic acid groups of an ethylene acrylic acid copolymer. Ethylene acrylic acid copolymer (DOW EAA™ 455) was extruded through an NRM extruder, at 250°C to 260°C, with sufficient antimony oxide for 100% neutralization of the copolymer acid groups. Infrared analysis showed a complete absence of any absorption the frequencies around 1560 cm⁻¹, characteristic of carboxylate ions, it is noted that the inability of the antimony to neutralize the carboxylic acid groups is not unexpected under the blending conditions used, considering the lack of basicity of the antimony oxide. It is noted that the probability of forming an ionic copolymer in situ in the composition of the present invention is further diminished by dilution of EAA with nylon and EEA. This result indicates that improved impact properties of the polyamide composition do not result from the formation of an ionic copolymer in situ. Examples 6-10 Examples 6-10, summarized in Table IV below, are for various nylon-6 compositions. These compositions contain ethylene ethyl acrylate copolymer (EEA), Union Carbide, DPD-6169™ (see Ex. 1), and ethylene acrylic acid copolymer (EAA), DOW EAA™ 455 (see Ex. 1). Each Example includes .25% by weight of zinc stearate as a mold release agent. The ingredients were blended in an NRM 6.35 cm (2-1/2 inch) single screw extruder. The extruder operated at 85 rpm and had four temperature zones in addition to the flange and the die. The temperatures were; Zone 1 - 575°C (302°C); Zone 2 - 550°F (288°C); Zone 3 - 550°F (288°C); Zone 4 - 500°F (260°C); flange 450°F (232°C); and the die 450°F (232°C). The resulting compositions were injection molded into test bars and tested according to Melt Index ASTM Test No. D-1238 "Q", and notched Izod ASTM Test No. D-256. A review of Table IV shows that high impact properties are obtained with carboxyl or amino terminated nylon-6 using magnesium oxide as an impact modifier. The values are relatively high considering any of the preceding Comparatives. While examplary embodiments of the invention have been described, the true scope of the invention is to be determined from the following claims:

Claims: 1. A melt-blended polyamide composition comprising the components: a) at least 60 percent by weight of the composition of a polyamide selected from polyhexamethyleneadipamide, polyepsiloncaprolactam and a mixture of polyhexamethyleneadipamide and polyepsiloncaprolactam, b) from 1 to 30 weight percent of an acid copolymer of an - olefin having 2 to 5 carbons, with 1 to 20 mol percent of an unsaturated carboxylic acid having 3 to 8 carbons, c) from 1 to 10 weight percent of an ester copolymer of an - olefin having 2 to 5 carbons, with 1 to 20 mol percent of an alkyl ester of an unsaturated carboxylic acid having 3 to 8 carbons and the alkyl group having 1 to 4 carbon atoms, the weight proportions between the acid copolymer and ester copolymer being from 1 part of acid copolymer to 10 parts of ester copolymer up to 30 parts acid copolymer to 1 part ester copolymer, d) from 0.05 to 1.0 percent by weight based on the weight of the composition of antimony oxide or magnesium oxide. 2. The composition as recited in claim 1 wherein said polyamide is polyhexamethyleneadipamide. 3. The composition as recited in claim 1 wherein there is .1% to .6% antimony oxide. 4. The composition as recited in claim 1 wherein the acid copolymer is a copolymer of ethylene and a monomer selected from acrylic acid, methacrylic acid, crotonic acid, maleic acid and fumaric acid and the ester copolymer is a copolymer of ethylene and a monomer selected from methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate. 5. The composition as recited in claims 1 and 2 comprising: at least 60% by weight of the composition of polyhexamethyleneadipamide; from 1 to 30% by weight of the composition of an ethylenic acrylic acid copolymer; from 1 to 10% by weight of the composition of an ethylene/ethyl acrylate copolymer; and from 0.05% to 1.0% by weight of the composition, of a metal compound selected from antimony oxide and magnesium oxide. 6. The composition as recited in claim 1 wherein the polyamide is polyepsiloncaprolactam.

Inventors: FLOOD, PAUL WESLEY, MASON, CHARLES DRISCOLL, SCHULZE, STEPHEN ROBERT
Applicants: ALLIED CORPORATION
Application year: 1981
Main classification: C08L77
IPC codes: C08L77, C08L33, C08L23, C08K5, C08L101, C08K3