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Feb 1st, 2008                                Print this article

Cast PP gaining ground: Lower initial investment offers processors advantages

By Robert Colvin

Cast polypropylene (CPP) films are steadily gaining market share in both traditional flexible packaging applications and nonpackaging applications, says John Thompson, marketing manager, business unit film and fibers, at polymer supplier Borealis (Linz, Austria).

One of the latest flat dies for CPP from EDI, the AFVI-RHM40 Contour Die on an Ultrasplit Rapid Service module, offers processors the ability to produce high-gloss CPP. K 2007 saw what equipment producer Reifenhäuser says was a world record (460 m/min) for winding cast PP 3-layer film, processed from LyondellBasell resin, including a metallocene blend in one of the skin layers, on its MIDEX rotary arm winder. Efficiency and energy savings are two features of the REItorque extruder coupled with the chillroll for coextruded CPP, from Reifenhäuser. Windmöller & Hölscher’s latest Filmex cast film line was demonstrated at its in-house exhibition during K 2007, producing CPP films that were rewound on downstream film winders at speeds up to 450 m/min. CPP film for twist-wrap applications, such as this film made from Basell resin, allows for high graphic reproduction and good metallization properties. Indonesian flexible packaging converter PT Plasindo Lestari will be using its recently delivered, 4.8m-wide CPP extrusion line from Brückner Formtec to produce up to 13,500 tonnes of film annually. Basell’s Clryell RC213M targeting CPP twist-wrap applications contains anti-block agents but still has food-contact approvals. /TD>

Thompson says CPP has evolved from a niche product to a successful film process. The trend is toward specialties. Uwe Jebsen, product sales manager, cast film lines, at equipment manufacturer Windmöller & Hölscher (Lengerich, Germany), says, “CPP film is gaining additional market share because it is an interesting complement to the BOPP film product portfolio with enhanced film properties because of the improved resins and production equipment available.”

Demand for CPP film, along with that for biaxially oriented PP (BOPP), is growing, according to Sam G. Iuliano, product manager at flat-die manufacturer Extrusion Dies Industries (EDI; Chippewa Falls, WI), but he says CPP is establishing itself in a number of markets and nibbling away at the expense of competitive materials.

Holger Emmerich from cast-film equipment maker Brückner Formtec (Siegsdorf, Germany) says he sees parallel growth of both CPP and BOPP, but CPP is showing good growth potential in specific markets. In Europe, compared to BOPP film production volume (about 850,000 tonnes/yr), CPP has about 40% of the market with 350,000 tonnes/yr. In India, on the other hand, CPP has less than 5% of the total PP film market with BOPP taking the lion’s share.

EDI’s Iuliano says markets that don’t require the balanced strength that BOPP offers are finding CPP an attractive alternative. These include flower wrap, cosmetic overwrap, decorative packaging wrap, and stationery sleeves, as well as replacing biaxially oriented polystyrene (BOPS) thin films in other markets such as the display web used in pastry boxes or envelope window films.

Emmerich says medical pouches, infusion bags, retort applications, and barrier packaging for foodstuffs are also growing areas for CPP. Paul Bullock, sales manager cast film at equipment producer Reifenhäuser Extrusion (Troisdorf, Germany), says CPP is making inroads into metallizing and laminating applications, and form-fill-seal (FFS) packaging films for snacks, twist wrap, cake, and pasta packaging as a substitute to BOPP or polyethylene (PE) laminated to BOPP. The benefit here is saving a processing step—lamination—that can be eliminated with a web that has reasonable stiffness and can still be metallized, unlike PE.

Why this is happening appears to Iuliano as a given since the investment in a CPP line is substantially less than a dedicated BOPP tenter frame. CPP also offers more flexibility in producing shorter runs of material for customers, less downtime, and easier handling. Brückner Formtec’s Emmerich says CPP production entails less energy consumption and therefore lower overall production costs.

One trend in CPP dies that has emerged, Iuliano says, is increased width. “Just a few years ago a 3.1m-wide die would be standard but now we are seeing dies up to 5.4m in length,” Iuliano says. Wider production web permits more output at slower speeds, therefore allowing a longer time on the chill roll to obtain film with high gloss and low haze levels—approaching those of tenter-frame-produced BOPP. Brückner Formtec offers lines up to 6m.

Besides the trend to wider CPP dies, EDI also sees more use of multichannel dies for 3- to 5-layer CPP film at the expense of single-channel dies with a feedblock. Although multichannel dies can be up to double the investment, they tend to produce film longer before the cleaning of lip plateout becomes necessary. The multichannel die also allows better tolerance control of the skin layers—generally a more expensive PP copolymer than the homopolymer core layer—so the processor can use less, but still achieve the gloss and clarity desired, Iuliano says.

W&H’s Jebsen says that CPP processors today indicate their main concern is improving product cost in line with better quality of multilayer films. His company has reacted to these demands by recently introducing a number of technologies such as smooth barrier screws, edge encapsulation, special air knives, and precision winding for its Filmex cast film lines.

Downgauging is another trend Steve Post, director business development Asia, at processing equipment producer Davis-Standard (Pawcatuck, CT) say he is seeing more of his customers concentrating on, particularly to produce 15-µm lamination film.

“Historically, this has been a difficult film to produce at high line speeds as it is much softer than the 20-25-µm films and doesn’t handle well in downstream processes like vacuum metalizing and extrusion lamination,” says Post.

Wherefore the change? Post points to new PPs for CPP cores that process at much lower melt-flow rate (MFR). “Traditional CPP resins have 7-12 MFR. We’ve successfully coextruded 1-3 MFR homopolmyer materials in the core with 7-10 MFR copolymers on the skins,” Post says. “The result is a much stiffer film that can be processed at high line speeds in subsequent processes.”

Post says it is a challenge to process this wide range of materials on one screw. The company recommends using a tandem or cascade extruder where the primary extruder melts the material and the secondary extruder pumps it to the die. This allows better melt temperature control, preventing excessive shear, but still breaks down the higher-molecular-weight unmelts.

Another development promoting extruding downgauged CPP, he says, is new winding technology. Since PP is subject to secondary crystallization, Davis-Standard has developed equipment that winds the necessary air into the finished roll to prevent the outer wraps of the film from crushing the internal layers. Air management is extremely critical— too much air creates ‘baggy’ areas and subsequent machine-direction and cross-direction wrinkles; too little air creates internal stress.

Andreas Goeldel, responsible for application development and technical support of film at plastics supplier LyondellBasell Industries (Frankfurt, Germany), sees among his customers two processing trends—either higher CPP speeds or lines that target volume with wider dies, in some cases up to 6m. In Asia, he says, demand for CPP is often based on the need for very high seal strength in flexible packaging, and CPP is often laminated to BOPP to provide complementary characteristics of good sealing strength and printablity with BOPP’s gauge tolerance, gloss, and clarity.

His company recently introduced a number of PP grades targeting the CPP market to solve problems found in many applications. Premiering at last year’s K 2007 was a block hetrophasic copolymer PP, Moplen EP310K, that has low stress whitening in freezer film, a condition that is traditionally encountered in conventional PP copoylmers. Also debuting was Adstif HA740J, which helps processors achieve better cost savings during processing. The grade, when included in post-production edge trim mixed with EVOH barrier resin, can be refed into one of the layers in amounts up to 15% without the danger of producing black specks and gels.

Clyrell RC213M, a resin often used on skin layers, is an alpha olefin-modified random copolymer PP targeting cast-film technology that offers clarity, gloss, and low haze. It has a low seal-initiation temperature (SIT) of 120°C. A specially designed propylene copolymer, also with low SIT, Clyrell RC1908, targets CPP for pouches, food-packaging film, and bags.

CPP processors should be on the lookout for a new generation of random copolymer PP materials from Borealis (Linz, Austria) to be launched this year. “We will offer ...glass-clear PP films from very soft to moderately stiff,” says Borealis’s Thompson.

“The main features are highest transparency, low SIT, and orange-peel-free cast films at the highest output rates.” Thompson expects downgauging to continue, driven by cost cutting and environmental concerns.

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