ANTEC spotlights new materials and processes.

The SPE's Annual Technical Conference, held recently in New Orleans, offered both an exhibition and a technical program that required an unprecedented three volumes to bind the 3500-page proceedings. Presented here are just a few highlights of the meeting: details on a new "microlayer" molding technology; first processing specifics on new-generation polyolefin copolymer film resins; a new on-line quality inspection method for extruded profiles; novel nylon/fluoroelastomer thermoplastic alloy; high-heat acrylic copolymers; and a new moisture analyzer.

MICROLAYER MOLDING

In three papers at the conference, Dow Plastics of Midland, Mich., divulged more details about its patented microlayer injection molding technology, which the company refers to as Lamellar Injection Molding or LIM. As we reported last month (p. 40), the process (which Dow is offering to license) produces molded parts from multiple resins in distinct microlayers-some as small as 0.1 microns thick. Dow has molded samples with up 2000 layers, but more typically, the number would range between 50 and 500.

This "lamellar," or layered, morphology contrasts with conventional alloy/blend dispersions or the "skin-and-core" structure of coinjected parts. Far from random, the microlayer arrangements are controllable and repeatable from shot to shot, says Mark Barger, research project leader and a co-inventor of the technology.

As an offshoot of Dow's work in microlayer coextrusion, the molding process employs a feedblock to combine the original flows from a dual-barrel injection machine into a three-layer feed stream. A five-layer stream would result from the addition of a third material, such as an adhesive tie layer for incompatible resins.

From the feedblock, the melt runs through tailor-made "layer multipliers." Within these modules, a set of channels repeatedly divides prior feedstreams and then recombines them into new streams consisting of more numerous, but thinner, layers. Dow says these lamellae remain distinct during the injection process and even "fold over" each other within the mold, creating parts with more layers than the multipliers alone would bring about.

So far, Dow has performed microlayer molding on a 700-ton Battenfeld coinjection press in its lab. A wide range of dual-cylinder equipment, however, can accommodate the new process. "You don't need topshelf process control," says Barger. "You just need to be able to inject the materials simultaneously." In fact, Dow says existing presses can be upgraded for microlayer injection. Barger also describes the technology as "tolerant" of different gate designs and locations.

The process can also combine a variety of dissimilar polymers as long as the viscosities stay within a factor of three and the melt temperatures are close, according to Barger. "You need to maintain coextrusion guidelines," he says. Combining different resins in a layered structure can enhance a number of properties, such as gas barrier, dimensional stability, heat resistance, and optical clarity. For example, PC/PBT microlayer parts microlayer parts have 40-50 [degrees] F higher heat-distortion resistance due to the inherent support offered by the new process's planar interfaces co-inventor Walter Schrenk explains. AT the same time, co-continuous lamellae in this blend improve ESCR by limiting solvent diffusion and blunting craze growth, according to a paper by Barger.

In another example, a microlayer structure of 10% EVOH with 90% HDPE reduced oxygen permeability by a factor of 300 compared with blends of the two or HDPE alone, Barger says. Polystyrene and nylon can be coinjected to yield clarity equal to PET plus better barrier properties. Microlayer injection allows molders to take advantage of multiple resins' properties without the expense of compounding, and novel properties can be obtained by combinations of low-cost and engineering resins.

For licensing information, contact commercial development manager George Mignon in Midland at [phone]. (CIRCLE 37)

NEW FILM RESINS

New experimental work from Dow Plastics examines the processing and film properties of novel olefinic copolymers produced by the company's new Insite Constrained Geometry Catalyst Technology (CGCT). With their narrow molecular-weight distributions, these materials promise superior physical properties--especially clarity, toughness and strength--compared with conventional film resins. The work supported Dow's claim that the new resins offer these property enhancements at no sacrifice in processability.

Dow researchers M.S. Edmondson and S.E. Pirtle investigated the blown film processability of a 1.0 MI, 0.908 g/cc octene-based CGCT copolymer. Dow used standard extrusion equipment--including a 2.5-in., 24:1 Egan extruder with 60-hp drive and a modified LLDPE screw with double mixing section as well as a 24-in. spiral die and dual-lip air ring.

With film thickness at 1 mil and melt temperature and nip height held constant, the CGCT copolymer ran better than one of Dow's commercial 1.0 MI Attane ULDPE grades, the researchers reported. The ULDPE required a screw speed of 94.1 rpm to achieve the same output rate as the CGCT resin at 88.8 rpm. At the same output rate, the CGCT copolymer also produced lower pressure at the die and screen pack than the ULDPE.

Also, the authors correlated the CGCT resin's film properties with three typical processing variables-blow-up ratio, output rate, and die gap. By optimizing tbe three variables, they made blown film with haze levels as low as 2.4%. Indeed, the authors claimed that blown films made from CGCT resin on conventional lines can attain the clarity of cast films. The authors additionally optimized film strength by choosing amongst processing conditions. CD tear, for instance, increased with increasing die gap and decreasing BUR. In a related study that did vary film thickness, the only departure from conventional property expectations showed up as haze levels improving with increasing thickness.

Meanwhile, Mobil Chemical Co. of Edison, N.J., discussed optimal processing parameters for its relatively new "Super Strength" hexene-based LLDPE and introduced new grades to the year-old resin family. According to product development manager Vincent Crotty, the new grades will bring Super-strength to markets once held exclusively by octene-copolymer LLDPE. Mobil claims its Super Strength offers 50% greater impact and 30% greater tear strength than other LLDPEs.

One new grade, NTX-108, targets applications in laminations and heavyduty shipping sacks that were previously closed to hexene resins. This new grade contains an additive package with a proprietary acid neutralizer in place of conventional stearates. In the past, stearates used to neutralize any catalyst residues would sometimes bloom to the film surface, interfering with adhesion. Crotty says only that the new acid-neutralizing additive is a naturally occurring substance not normally used in film.

Another grade, NTX-107, is designed to permit a narrow die gap and facilitate downgauging. According to Crotty, the proprietary processing aid in this grade permits processors to produce film at narrow die gaps with physical properties equivalent to, or slightly better than, those obtained from Super Strength at wider gaps.

Mobil also reported that it had successfully run Super Strength LLDPE on an HDPE line--one from Alpine American of Natick, Mass. Crotty said the trial ran a small film line up to its throughput limit, and the film suffered no loss of physical properties compared with film made on an LLDPE line. Only minor modifications to the HDPE equipment were required so it would conform to LLDPE's dissimilar blow-up ratio and bubble shape. (CIRCLE 38)

PROFILES IN QUALITY

For profile extrusion with a hightech quality check, a new approach to continuous machine-vision surface inspection of extruded profiles was outlined in a paper by W. Michaeli and M. Behrens of the IKV, Germany's Plastics Processing Institute.

Rather than simply deploying camera-based machine vision to identify defects through contrast changes, the IKV bases its system on the intersection of a laser beam with the profile surface. The camera then records defect-induced distortions of that beam. What's most noteworthy about this method is that the images of the distorted laser beam can be correlated to individual defect types-such as bubbles, foreign bodies, pimples, or sink marks. The system, then, fosters not just defect detection, but precise classification through the singular nature of the beam distortions associated with a given defect type.

The IKV designed its system for scanning profiles up to 3.1-in. wide at 0.02-in. intervals. With high-resolution CCD arrays--a type of video camera--the systems's measuring resolution could push below 40 microns (1.6 mils).

Unfortunately, the image-processing power needed to turn the light intersection patterns into meaningftil defect information does present a hurdle. To accomplish the data-crunching tasks, the IKV had to link several computers into a parallel-processing array. Given these computing requirements, Behrens estimates that the price of assembling one of these new inspection systems would fall in the $50,000-70,000 range. (CIRCLE 39)

PUMP, DON'T EXTRUDE 

A gear pump may have a place on a PVC calendering line, according to a paper by Dr. R. Stehr and P. Andersen of Switzerland's Maag AG (sold here by Maag Pump Systems, Matthews, N.C.). In commercial application that has run for over a year, a Maag customer has used a gear pump in place of the single-screw discharge extruder normally set up in a "cascade" arrangement with a continuous mixer. Beyond cost reduction and space savings, the gear pump can lead to quicker start-ups and energy savings, the authors claim. CIRCLE 40)

NYLON-BASED FLUOROELASTOMER

A new nylon-based thermoplastic fluoroelastomer that has been under development for several years will be introduced in the third quarter for test marketing by 3M Specialty Fluoropolymers Dept., St. Paul, Minn.

3M first released information on this alloy three years ago, but the material has undergone significant changes since then (see PT, May '90, p. 11). Initially, it was described as having the fluoroelastomer as the continuous phase. However, processability requirements dictated changing this to the current composition, in which nylon makes up the continuous matrix, and the fluoroelastomer serves as the dispersed phase.

S. Nam, research specialist, says the fluorinated TPE utilizes a proprietary compatibilization technology that exploits reactive end-group sites on both resins. The alloy utilizes 3M's Fluorel elastomer and nylon 6. The material is designed primarily for injection molding of high-performance, precision automotive under-hood components.

The new alloy, which has not yet been given a commercial trade name, offers a continuous-use temperature range up to 300 F and a brittle point of -40 F. It has a specific gravity of 1.57, Shore D hardness of 44, ultimate elongation of 300%, and tensile strength of 1800 psi. 3M declined to reveal pricing, although it's expected to be sold as a premium material. CIRCLE 41)

HIGH-HEAT ACRYLIC

A new amorphous acrylic copolymer that is said to span the long-term, high-temperature performance gap between polymethyl methacrylate (PMMA) and polycarbonate has been introduced by ICI Acrylics Inc., Compton, Calif.

Jason Shen, R&D manager for acrylic products, says this new class "HHA" (high-heat acrylic) copolymer is composed of methyl methacrylate (MMA) and maleimide. The glass-transition temperature ranges from 248 to 293 F, compared with 230 F for typical PMMA. However, Shen says HHA has similar processing characteristics and is miscible with PMMA. It also is fully compatible with conventional acrylic impact modifiers. HHA's density, dimensional stability, optical properties, and chemical resistance are comparable to those of PMMA, though HHA displays superior abrasion resistance, according to Shen. He says HHA is premium priced."

Typical properties of HHA include tensile strength of 9800 psi, flexural strength of 17,000 psi, light transmittance of 92%, haze index of 0.5%, and yellowness index of 0.4%. Primary applications for HHA will include industrial and automotive lighting. (CIRCLE 42)

NEW MOISTURE ANALYZER

A new moisture analyzer designed to provide measurements of moisture levels in hygroscopic polymers such as nylon, PET and acrylic was introduced by Kayeness Inc., a Dynisco Co. unit located in Morgantown, Pa.

This Aquascan unit employs a nondestructive dielectric-capacitance technology, which is unlike typical "loss-of-weight" heating methods used to determine moisture content. The user drops resin samples into a sensor box that contains a dielectric grid and ports for nitrogen or descicated-air purging. The sensor box is linked to a personal computer with dedicated DOS- or Windows-based software, which provides database capabilities and readout display. Base price is $8500. CIRCLE 43)

New LLDPE for Large-Part Molding

Quantum Chemical Corp.'s USI Division has introduced a new linear lowdensity polyethylene called Petrothene GA 568-000 for large part injection molding.

GA568-000 has a density of 0.925 g/cu cm, a melt index (g/10 min) of 35 and a brittleness temperature of 18 F. It is FDA approved, meeting the requirements of 21CFR 177.1520. Applications include housewares, trash cans and other consumer products.

A spokesman for Quantum says the introduction of GA 568-000 rounds out the company's line of injection molding LLDPE grades with a melt index range from 5 to 135 g/10 min.

(CIRCLE 125)