Nylon Compositions for Blowmolding

Polyamides that are semicrystalline are used extensively in many applications that require good solvent resistance and good properties at elevated temperatures. They are ordinarily processed by injection molding, but there are many components of automobiles and other systems wherein such parts are hollow and to manufacture these by injection molding is very difficult and expensive. Many such parts can conceivably be made by blowmolding provided the polymer system has adequate melt strength and viscosity. Unfortunately, polyamides commonly used for injection molding have number average molecular weights generally between 10000 and 25000 which is too low to make them suitable for extrusion blowmolding. It would be desirable to have a blow moldable polyamide composition made from the usual injection moldable polyamides.

For many applications polyamide compositions with improved toughness are required. The prior art describes various techniques of modifying polyamides with tougheners. Such tougheners include low modulus ethylene copolymers containing small amounts of carboxyl or anhydride functionality. Other tougheners include ethylene acid copolymers neutralized with metal cations (see Epstein U.S. Pat. No. 4,174,358 or Murch U.S. Pat. No. 3,845,163). Combinations of polyamides with such tougheners afford unique combinations that are tough and suitable for injection molding and extrusions. These combinations, however, possess lower than optimum viscosities and melt strength for use in blowmolding.

In the instant invention, the melt viscosities of such combinations of polyamides and the aforementioned toughening polymers are increased substantially by addition thereto of small amounts of an anhydride rich polymer which acts as a coupling or crosslinking agent to react preferentially with the polyamide to increase molecular weight. At the same time, such anhydride-rich polymers react with the acid groups in the toughening polymer as well, increasing its viscosity. Other coupling agents or crosslinking agents, such as diisocyanates, epoxides, melamine, etc. are prone to react preferentially with the carboxyl groups of the toughening resins instead of with the polyamide and, therefore, do not perform well for the purpose desired herein. Thus, addition of the anhydride-rich polymer makes the semicrystalline polyamide readily processible by extrusion blowmolding to make hollow, stiff parts of various shapes.

The compositions of the present invention consist essentially of:

a) 85-65 parts by weight of a semicrystalline polyamide having a number average molecular weight between 10000 and 250000;

b) 15-30 parts by weight of an ionic copolymer of at least one alpha-olefin and at least one alpha,beta-unsaturated organic carboxylic acid which is partially or completely neutralized with a metal cation; and

c) 0.1 to 3 parts by weight of an anhydride-rich copolymer containing alternating units of maleic anhydride and an alpha-olefin selected from the group consisting of styrene, ethylene, and octadecene, which copolymer contains at least 15% by weight anhydride units.

Of course, the amounts of each additive present are relative. For example, as the amount of component b) is decreased, the amount of component c) should be increased, and as more component b) is employed, the amount of c) can be decreased.

These compositions have high melt strength compared to the base polyamide. This property aids in making the compositions blow-moldable. The compositions are readily processible by extrusion blowmolding to make hollow parts, such as containers or automotive components for under-the-hood applications.

The semi-crystalline 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 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, columns 1 and 2.

The component (b) 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. More preferably, the alpha-olefin is ethylene and the acid is acrylic 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, Al, K and the like. Representative copolymers include ethylene/butylacrylate (including isobutylacrylate) /methacrylic acid (80/10/10) 70% zinc neutralized.

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

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).

The anhydride-rich copolymer used was SMA-3000, styrene-maleic anhydride copolymer by ARCO Chemical.

Number average molecular weight was determined by Waters 150.degree. C. 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, Del.

The materials were extrusion blended using a Sterling extruder equipped with a single screw or a Werner & Pfleiderer twin screw extruder. The polymer strands were 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 11/2 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 80 parts of 66 polyamide of molecular weight of about 16000 and 20 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.

One hundred parts of the composition of Control Example 1 were melt blended with 1 part of an alternating copolymer of styrene and maleic anhydride (SMA 3000). On blowmolding as described in Control Example 1, good blowmolded containers were obtained.

Table I shows the ingredients used and blow moldability results for Control Example 1 and for Example 1. In a like manner, additional Examples and Controls were carried out using the ingredients shown in Table I and Table II, with the blowmolding results shown in the Tables.