Nylon Compositions for Blowmolding

The polyamide matrix resin of the compositions of this invention is well known in the art and embraces those semi-crystalline resins having a molecular weight of between about 10000 and 25000 and commonly referred to as nylons. Suitable polyamides include those described in U.S. Pat. Nos. 2,071,250; 2,071,251, 2,130,523; 2,130,948; 2,241,322, 2,312,966; 2,512,606; and 3,393,210. The polyamide resin can be produced by condensation of equimolar amounts of a saturated dicarboxylic acid containing from 4 to 12 carbon atoms with a diamine, in which the diamine contains from 4 to 14 carbon atoms. Excess diamine can be employed to provide an excess of amine end groups over carboxyl end groups in the polyamide. Examples of polyamides include polyhexamethylene adipamide (66 nylon), polyhexamethylene azelaamide (69 nylon), polyhexamethylene sebacamide (610 nylon), and polyhexamethylene dodecanoamide (612 nylon); the polyamide produced by ring opening of lactams, i.e., polycaprolactam, polylauric lactam; poly-11-aminoundecanoic acid, and bis(paraaminocyclohexyl) methane dodecanoamide. It is also possible to use in this invention polyamides prepared by the copolymerization of two of the above polymers or terpolymerization of the above polymers or their components; e.g., an adipic, isophthalic acid hexamethylene diamine copolymer. Preferably the polyamides are linear with a melting point in excess of 200.degree. C. By "semicrystalline" is meant that the polyamide has a distinct melting point with a measurable heat of fusion, as described in U.S. Pat. No. 4,410,661 in Columns 1 and 2.

The ionic copolymer is made of recurring units of at least one alpha-olefin and at least one alpha, beta-unsaturated carboxylic acid, in which the acid moiety is at least partially ionized with metal ions. The alpha-olefin is preferably of 2-6 carbon atoms and the acid is preferably of 3-6 carbon atoms. Preferably the alpha-olefin is ethylene and the acid isacrylic or methacrylic acid. Other polymerizable comonomers can be present, such as acrylates or methacrylates. The metal ion can be monovalent, divalent or trivalent, as for example Na, Zn, A1, K and the like. Representative copolymers include ethylene/isobutylacrylate/methacrylic acid (80/10/10) 70% zinc neutralized.

When unmodified polyethylene is used, an anhydride modified polyethylene (modified with 1% maleic anhydride) is used as a compatibilizer. The polyethylene used can be high or low density. The functionalized polyethylene can be a polyethylene that contains up to 10% carboxylic acid or anhydride functionality. These are described in Epstein U.S. Pat. No. 4,174,358. The ratio of polyethylene to functionalized polyethylene is preferably 1:1 to 2:1 by weight.

Small amounts of an anhydride-rich polymer comprise the third additive component. This component can be an alternating polymer of styrene and maleic anhydride (e.g., SMA 3000 sold by ARCO Chemical), an alternating polymer of ethylene and maleic anhydride (e.g., ethylene-maleic anhydride polymer EMA-31 manufactured by Monsanto Chemical Company), or a higher alpha-olefin/maleic anhydride polymer (e.g., Octadecene-maleic anhydride polymer PA-18 made by Gulf Oil Company). By alternating is meant that the units substantially alternate between comonomers.

The fibrillar fluoropolymer resin is preferably a non-melt-fabricable tetrafluoroethylene polymer. The tetrafluoroethylene polymers are made by the dispersion polymerization process, in which the polymer particles formed remain dispersed in the reaction mix during the polymerization. The particles are coagulated and dried. The particles fibrillate while being physically mixed into the composition of the invention.

The fibrillatable PTFE is a well known material in the art and readily available as a commercial product. The commercially available fibrillatable PTFE is in the form of an aqueous dispersion prepared by the emulsion polymerization or in the form of a powder obtained by separation of the resin from the aqueous dispersion followed by drying. The aqueous dispersion of the fibrillatable PTFE contains usually several tens of %, say, up to 60% of the PTFE particles having a diameter of about 0.2 .mu.m while the powdery products are agglomerates of these particles of about 0.5 mm average diameter The PTFE particles of either form can be readily converted into fibrils when the particles are subjected to mechanical shearing forces.

Several of the examples of the commercially available fibrillatable PTFE are as follows: Teflon 6J (a product by Mitsui Fluorochemical Co.), Teflon 6JC (a product by the same company), Polyflon F-103 (a product of Daikin Kogyo Co.) and Polyflon F-201 (a product by the same company) as the examples of the powdery products and Teflon 30-J (a product by Mitsui Fluorochemical Co.) and Polyflons D-1 and D-2 (products by Diakin Kogyo Co.) as the examples of the aqueous dispersion products.

It has unexpectedly been discovered that if the amounts of additive ingredients are such that certain low shear/high shear viscosity ratios are obtained, good blowmolding resins are produced. For example, when the viscosity is measured at a shear rate of 3.5 per second and at a shear rate of 588 per second, it was found that if the ratio of low shear viscosity to high shear viscosity was greater than about 5 or 6 or so, the compositions could be extrusion blowmolded.

The ingredients used to make the compositions of the invention may be combined by tumble blending the components and feeding the blend to the extruder of the blowmolding equipment. It is preferable, however, that the anhydride-rich copolymer be dispersed uniformly and it has been found that melt blending the ingredients, by using such equipment as a melt extruder (e.g., single screw extruders or twin screw extruders) is preferred. The blended product is pelletized (i.e., the extruded strand is cut), dried and used for subsequent blowmolding purposes using an extrusion blowmolding machine (e.g., made by Rocheleau Inc., Hayssen Inc., etc.) and fabricated into hollow articles such as containers.

The examples set forth below were carried out using as the polyamide a 66 polyamide "Zytel" (16,000-20,000 number average molecular weight) made from adipic acid and hexamethylene diamine. The ionomeric polyolefin additive was a 70% zinc neutralized ethylene-methacrylic acid (90/10) copolymer ("Surlyn" 9520).

Anhydride-Rich Copolymers used were: SMA-3000, Styrene-Maleic anhydride copolymer by ARCO Chemical

PA-18, Octadecene-Maleic anhydride copolymers made by Gulf Oil Co. (Chemicals Div.)

The fluoropolymer used was Teflon fluoropolymer 6C or 60 sold by the Du Pont Company.

Number average molecular weight was determined by Waters 150C gel permeation chromatography equipment at 110.degree. C. with meta-cresol as a solvent.

Melt viscosity was measured on a melt capillary rheometer made by Kayeness Test Instrument. Melt flow was measured using a melt index apparatus made by F. F. Sloan Corporation, Wilmington, DE.

The materials were extrusion blended using a Sterling extruder equipped with a single screw or a Werner & Pfleiderer twin screw extruder and the polymer strands cut into pellets, dried and used to blow mold one-quart containers using a Rocheleau extrusion blowmolding machine.

The appropriate mixture of materials were blended and melt extruded using an extruder equipped with a 2 inch screw and the polymer melt made into strands and cut into small pellets.

The pellets then were fed into a blowmolding machine which was equipped with a 1 1/2 inch diameter screw and a mold to make a bottle with a volume of 1 quart. The extruder temperatures were kept at about 270.degree. C. The vertically extruded tube of the melt (parison) was qualitatively judged for its strength by stopping the extrusion and the molten parison allowed to stand and support its own weight, before pinching and blowing to make the container. If the parison does not have adequate strength, the parison breaks off easily and the melt falls down without being able to blow and make the container. If it has good strength, the molten tube (parison) supports itself without breaking and lends itself to blowing to make the container.

Using 90 parts of 66 polyamide and 10 parts ionomeric copolymer, the extruded melt did not have enough strength to support itself, broke off and fell down rapidly. No containers could be blowmolded.

Adding 0.5 parts anhydride-rich copolymer to the mixture of Control Example 1 did help, but not enough to make a satisfactory container.

The composition of Control Example 2 (88.5 parts polyamide and 10 parts ionomeric copolymer and 0.5 anhydride-rich copolymer)was melt blended with 1 part of fluoropolymer Teflon 6C. On blowmolding as described above, good blowmolded containers were obtained.

Table I shows the ingredients used and blowmoldability results for Control Examples 1 and 2 amd for Example 1.

In a like manner, additional Examples and Controls were carried out using the ingredients shown in Table I with the blowmolding results shown in the Table.