New polystyrenes get tough on ABS.

Tougher, glossier, more chemical- and heat-resistant PS grades are challenging ABS and other engineering resins with their cost and processing advantages.

Expect more from today's polystyrenes. Product improvements from all suppliers in the last two or three years have redefined these "commodity" resins' performance capabilities across the board.

The biggest news is in the high end of the product spectrum, which is now occupied by a new group of enhanced-HIPS materials that have emerged in the last couple of years (see PT, June '93, p. 25). Dubbed by some suppliers "advanced styrenic resins" or ASRs, they are defined by their novel combinations of high impact and high gloss. Still evolving, these materials are positioned to compete with low- and medium-impact, high-gloss ABS.

In the mid-range HIPS arena, there's an array of new materials that include extra-tough grades; high-flow, ignition-resistant (IRPS) products; and versions with improved chemical resistance or ESCR (environmental stress-crack resistance).

At the low end of the spectrum, general-purpose crystal PS grades with lower residual monomer to minimize odor and taste in food packaging are becoming the order of the day.

These developments are causing a reassessment of PS capabilities relative to ABS and other higher-performance styrenics. Improved PS grades are invading a new range of applications, sometimes displacing other resins and bringing advantages of lower cost, easier processing, and higher production rates.

HIPS GETS TOUGHER & GLOSSIER

In the last two years, four PS suppliers have commercialized enhanced-HIPS (ASR) grades with unprecedented combinations of high impact and high gloss. Several other suppliers have such materials in development.

A key difference between enhanced HIPS and traditional HIPS is the morphology of the rubber modifier particles. The new materials contain less rubber, about 8-9% by weight, with a particle-size range of 0.1-1.5 microns. Conventional HIPS contains 6-10% rubber in particle sizes of 1-8 microns. Whereas standard HIPS contains low-cis butadiene rubber, enhanced HIPS may contain a combination of different types of butadiene and even other rubbers.

Along with their unusual impact and gloss properties, these new HIPS challenge ABS with their improved processability. They can be run at 50 [degrees] F cooler melt temperatures, resulting in shorter cycle times and lower energy cost. And like all HIPS, there's no need for the predrying required with ABS. Moreover, coloring costs are said to be significantly less than for ABS.

Enhanced HIPS resins are priced around 70-80[cents]/lb--well above the 55-60[cents]/lb for traditional HIPS, but still 20-25[cents]/lb less than ABS. Enhanced HIPS materials were largely spared from the price hikes that affected all other PS and ABS materials in 1994. But the four suppliers that currently offer enhanced HIPS--Dow Plastics, BASF Corp., Chevron Chemical Co., and Huntsman Chemical Corp.--indicate that prices of these materials are due for an increase as early as this quarter.

Despite all these advantages, enhanced-HIPS consumption is still relatively small, but perhaps not for long. Suppliers estimate current usage at 25-30 million lb/yr, which could easily double in 1995. (For comparison, the domestic PS market is now approaching 6 billion lb/yr. But enhanced HIPS competes primarily with ABS, now about a 1-billion-lb/yr market.)

Although enhanced HIPS were originally developed to bridge the gap between the high end of traditional HIPS and the low end of ABS, suppliers now believe their materials have broader potential. Says Jay Blackburn, Chevron market-development manager, "We feel we can go after medium-impact and also high-impact ABS in applications that have long been over-engineered." Dow product group manager Steve Brorby agrees that as long as the key criteria are gloss and toughness, these materials can compete well with high-end ABS.

Enhanced HIPS is currently making an impact in extruded and thermoformed refrigerator liners and injection molded crispers, ice-maker bezels, handles, and trim parts, as well as small appliance housings and other consumer products.

INJECTION MOLDING GRADES

Commercial molding grades of enhanced HIPS currently include two from Dow, one from BASF, two from Chevron, and three from Huntsman. They all have very similar 60 [degrees] Gardner gloss ratings of 95-96%. As shown in the chart on p. 38, their impact properties also fall into a similar range (240-300 in.-lb for 1/8-in. samples).

Dow's AIM 4800 has a Gardner impact above 300 in.-lb at 73 F; notched Izod is 5.5 ft-lb/in. at 73 F and 1.7 ft-lb/in. at 0 [degrees] F. Doug Kunneman, senior market manager for large appliances, says the company has targeted applications such as refrigerator crisper trays and housings or covers for portable appliances and vacuum cleaners. Dow says a 60 [degrees] Gardner gloss of 98% can be achieved with AIM 4800 using a mold temperature of 150 F.

More recently, Dow introduced AIM 4810, which ASR product market manager Andy Shafer says has toughness similar to AIM 4800 but lower gloss (85% at 100 F mold temperature) and is aimed at textured parts.

BASF's ES 9524 high-gloss specialty HIPS was the first enhanced HIPS to hit the market over a decade ago. (It was manufactured by Mobil Chemical using BASF technology.) It's still used commercially in internal and external parts for refrigerator/freezer units, such as trim, kick panels, ice handles, and ice-maker bezels. It has a Gardner impact of 280 in.-lb and notched Izod of 2.3 ft-lb/in. Industry manager Gary Clemens says BASF is aiming to further improve ES 9524's toughness and heat resistance. BASF is also considering additional application-specific high-gloss HIPS grades.

Huntsman's XI 2124 high-gloss HIPS was first introduced in 1992 but has been improved recently, according to company researchers. It has a gloss rating of 95%, Gardner impact of 250 in.-lb, and notched Izod impact of 1.8 ft-lb/in.

Huntsman also offers what director of marketing development Rich Marchetti jokingly calls the "poor man's XI 2124." He describes grade 400 HIN 9100 as a HIPS made by conventional technology that offers performance somewhere between that of traditional HIPS and an enhanced HIPS. It has notched Izod impact of 1.8 ft-lb/in. and gloss of 95% when measured at a 20 [degrees] angle, which is a more demanding test than 60 [degrees] gloss measurement. The price is intermediate as well: Whereas XI 2124 sells at a 25-30% premium over conventional HIPS, grade 400 is priced about 10% higher than HIPS.

The company is the first to offer a high-gloss (90%), high-impact, ignition-resistant enhanced HIPS. Grade XR 2158 H2N is rated UL 94V-0 at 1/8 in. It has a Gardner impact of 140 in.-lb, notched Izod impact of 1.6 ft-lb/in., and tensile yield strength of 3600 psi. The material is currently priced at $1.09/lb.

While other suppliers admit there is probably a market niche for enhanced IRPS grades, they don't appear to be actively developing any.

Chevron's enhanced HIPS constitute its new Valtra family of "modified styrenic polymers." The first commercial grade, Valtra HG200, was launched in 1992 (PT, Sept. '92, p. 13) and was recently followed by higher-gloss, higher-impact HG210. Valtra HG200 has a gloss of 90%, Gardner impact of 235 in.-lb, and notched Izod impact of 3.0 ft-lb/in. HG210 features 95% gloss, Gardner impact of [is greater than] 240 in.-lb, and notched Izod of 3.3 ft-lb/in.

Chevron's Blackburn says the best fit for these materials appears to be in appliance housings and non-electrical housewares and office products, such as dispensers and bathroom accessories. Blackburn also hints that a new Valtra grade is in development for commercial introduction sometime this year. It will have increased heat resistance and ESCR, along with high gloss and high impact.

Both Fina Oil & Chemical and Novacor Chemicals have previously revealed their development efforts in this arena (PT, June '93, p. 25). Fina's experimental enhanced HIPS, grade CX 7125, is not yet commercial, according to product manager Scot Mitchell. Other grades in development include CX 8100, which has notched Izod of 4 ft-lb/in. and is intended to replace lower-impact ABS.

Steve Cummings, Novacor's leader for marketing intelligence, says his firm is continuing to develop a family of enhanced HIPS with higher gloss and impact. Initial grades, Cummings says, will compete with low-end ABS. These grades will be for injection molded packaging, micro-floppy computer diskettes, and small appliance parts.

Amoco Polymers also has enhanced-HIPS development under way, reveals polystyrene business manager Marv Sauers. Commercial introduction can be expected within two years, he says.

SHEET USES FOCUS ON ESCR

Enhanced HIPS or ASRs are the latest specialty HIPS family to tackle sheet extrusion and thermoforming of refrigerator liners. BASF's Clemens estimates that HIPS has taken over close to two-thirds of this market from more costly ABS in the last 8-10 years.

Dow's Kunneman confirms that PS has made considerable inroads in refrigerator/freezer liners at the expense of ABS. "In 1994, 75 million lb of PS went into this application, whereas just two years ago, it was only about 20 million lb. ABS is definitely under attack in the extrusion area." Dow is projecting that by the end of 1995, only two domestic appliance makers will remain with ABS.

Owing to recent environmental regulations, refrigeration has become a moving target for HIPS where ESCR is concerned. Suppliers have had to focus on developing new materials for use as a protective barrier between the coextruded outer layers and the urethane foam insulation. That's because the HCFC-141b blowing agent, which has largely replaced CFC-11, chemically attacks conventional HIPS. The newest liners are now trilayer coextrusions.

Clemens says BASF was the first to offer an alternative to ABS for refrigerator liners with its ES 7100 enhanced HIPS, a high-impact extrusion resin with excellent ESCR. In BASF's trilayer configuration, ES 7100 is used as the core of the liner. The exterior gloss cap layer is of ES 7800, a high-gloss (97%) HIPS.

For the protective layer, BASF has come up with two new HIPS grades--XB-80 and BX-0201--which offer different balances of processability and resistance to HCFC-141b.

The key to Dow's trilayer configuration is the development of XU 70012, a new proprietary styrenic/polyolefin alloy introduced in 1991 for use as the protective layer. The core layer, which comprises about two-thirds of the liner, utilizes Dow's recently commercialized grade XSS84044, an improved-ESCR HIPS. "OEM evaluations show that it is easier to process and has potential for downgauging," says Kunneman. "We still can't downgauge as low as we can with ABS, but we come close." The cap layer of the liner is made with Dow's AIM 4900 extrusion-grade ASR. In thermoformed parts it has a gloss of 80-90%, Gardner impact of 170 in.-lb at 73 F, notched Izod of 2.3 ft-lb/in. at 73 F, tensile yield strength of 3200 psi, and tensile and flex moduli of 260,000 psi.

Chevron now offers Valtra RS300, an extrusion-grade, low-gloss enhanced HIPS for coextruding refrigerator-liner substrates. It's said to have exceptional ESCR (450 hr minimum to break) and good practical toughness (notched Izod of 3.1 ft-lb/in. at 73 F) without moisture sensitivity. Also new is XG100 high-gloss HIPS with moderate impact for the cap layer. Blackburn says XG100 is also useful in two-layer coextrusions with HIPS for uses such as shower surrounds.

Sauers says Amoco has been focusing on process modifications to minimize the gel content of its extrusion-grade HIPS. The company has one new grade with smaller gel size, which reportedly facilitates downgauging.

IRPS GOES TO HIGH FLOW

New developments in IRPS are aimed primarily at tv cabinetry, by far the dominant use. Introduction of very high-flow grades is being prompted by the trend to larger cabinets and new molding techniques.

Designs for larger cabinets are typically thin-walled and can be difficult to fill with standard-flow grades of IRPS. Newer high-flow grades are also well suited to low-pressure or gas-assist injection molding, which have become more common for large parts. The high-flow products are said to provide faster cycle times and improved part appearance.

Last year, Dow launched Styron 6010, an IRPS resin with a melt-flow rate of 10.2 g/10 min. The material is said to offer a balance of flow and practical toughness that is not typical of IRPS. It has a notched Izod impact of 2.3 ft-lb/in., tensile yield strength of 3900 psi, and flexural strength of 7000 psi.

BASF's high-flow IRPS is ES 8080, which has a melt flow of 10.5 g/10 min plus a notched Izod of 1.8 ft-lb/in., tensile yield strength of 3100 psi, and flex modulus of 300,000 psi.

Huntsman's F7000 IRPS also offers a good balance of flow and physical properties. It has a melt flow of 12 g/10 min and notched Izod impact of 1.7 ft-lb/in.

Another IRPS from Huntsman is Grade 707, which is said to be about 50% tougher than conventional IRPS. It has a notched Izod impact of 3.2 ft-lb/in. Used in injection molding and deep-draw thermoforming for several years, this grade is receiving increased interest as a replacement for higher-cost ABS/PVC alloys in applications such as extra-big rear-projection tv cabinetry, bezels, and other large electronic enclosures.

Chevron is working on its first IRPS. Blackburn says, "This is a material that will have high gloss and high impact but will not compete with existing IRPS grades in the tv market. We will primarily target it for use in electrical connectors where ABS is currently used."

Dow product market manager T.J. Wainerti expects to commercially introduce early this year a HIPS grade that's now being tested by one major tv manufacturer for applications not requiring IRPS. It features very high flow of 18-25 g/10 min together with a typical HIPS UL 94HB rating. XU 70029 will replace wood in large projection tv units (52-61 in.). Wainerti says, "We're projecting that by year 2000, 25% of the tv market will be projection sets." BASF is also aiming to develop high-flow HIPS for projection tv's, notes Clemens.

A BIG FUTURE IN C&BE?

Resin suppliers expect that housings for computers and business equipment will become a major new market for both IRPS and non-IR HIPS. The reason, they say, is that a lot of these applications have been overengineered. Dow senior marketing manager Scott Sanderude says that many cost-sensitive applications are already moving from ABS and PVC/ABS to IRPS and HIPS. Non-IR HIPS is showing potential in printer housings and keyboards.

Huntsman is now offering grade 779, the first IRPS precolored for lighter-toned computers and peripheral business equipment that offers long-term color retention (2-5 yr) in an indoor environment. Previous IRPS grades showed noticeable color shift after only a matter of days, and the same occurred within weeks for FR-ABS. Physical properties of grade 779 are said to be comparable to color-stabilized FR-ABS and ABS/PVC alloys.

HIPS IN 'ENGINEERING' ROLE

Suppliers say extra-tough HIPS grades are growing in popularity, especially as replacements for more expensive engineering resins.

Huntsman's super-high-impact grade 850 has a notched Izod of 4.2 ft-lb/in. It is replacing engineering resins for injection molding and extrusion applications requiring easy processing but not chemical resistance.

Last year, Huntsman launched very-high-flow (9.0 g/10 min), extra-tough (3.5 ft-lb/in. notched Izod) grade 336 HIPS for large toys, and grade 1983 extra-tough HIPS with 4.0 notched Izod for appliances.

BASF's super-high-impact, high-heat extrusion grade, ES 5350, has been replacing PPO blends in electronics, consumer, and automotive applications. It has notched Izod impact of 3.2 ft-lb/in. and HDT of 190 F at 264 psi.

Chevron's ES 2100 "super HIPS" has about 4.0 notched Izod impact, but not high gloss. It has generated tremendous interest as an impact modifier to upgrade HIPS in place of Shell's Kraton, according to Blackburn.

EVER-CLEANER CRYSTAL PS

Almost all suppliers are moving production to g-p crystal grades with less residual monomer to reduce odor and taste. For example, technology upgrades now permit Fina to make all of its crystal PS with residual monomer under 250 ppm, rather than offering this enhancement on only certain grades. Likewise, hardware upgrades at Chevron's PS plants reportedly have brought residual monomer levels below 200 ppm.

BASF will employ new technology to produce high-heat crystal grades with very low monomer (100-150 ppm). This technology will be used in a 40-million-lb/yr expansion to be brought on stream by mid-year at Joliet, Ill.

In 1993, Huntsman started up a new line at Belpre, Ohio, to make g-p crystal PS with residual monomer levels below 200 ppm. Material produced here is chiefly used for OPS sheet.

Novacor is also focusing on low-residual extrusion grades for blending with Phillips' K-Resin in food-contact applications. Novacor was expected to commercialize grades with residuals of 100-200 ppm by the end of 1994.

HIPS Rules in Microfloppy Disks

The 3.5-in. "microfloppy" data diskette market has already seen an estimated 75% conversion from ABS to PS, with total replacement likely within the next two years, according to Huntsman and Dow executives.

An example of a special resin tailored for this market is Huntsman's grade 2184. This low-friction HIPS is formulated for high-speed molding of thin-walled diskettes. Key features include abrasion resistance, minimal flow-line appearance, and low static-charge build-up. Its higher melt flow (7.0 g/10 min vs. 3.0 for ABS) and lower processing temperatures than diskette-grade ABS resins reportedly shorten molding cycles. Dow and Fina offer similar materials, designated Styron XU 70008 MFD and CX 7138, respectively.