Click Image to Enlarge
In the past two years, a new player has quietly emerged among North American suppliers of metallocene-catalyzed polyolefins. AtoFina Petrochemicals in Houston has brought out metallocene medium-density polyethylene (mMDPE) film and blow molding grades, as well as a family of metallocene PP (mPP) homopolymers and copolymers for film and injection molding. Based on the company’s own catalyst technology, these Finacene resins boast improved mechanical, optical, and barrier properties, as well as excellent processability.
The mMDPE resins are produced in Bayport, Texas, in a 460-million-lb/yr, Phillips-type slurry-loop reactor—one of the largest of its kind in the world. Two grades for blown film and extrusion blow molding are now commercially available. Both are hexene copolymers with a density of 0.934 g/cc and MI of 0.9. The mPP homo- and copolymers, approaching 20 in total, are made in a 100-million-lb/yr liquid propylene multi-loop reactor at LaPorte, Texas.
PE for clear, stiff film
Launched in early 2001, the company’s first mMDPE is Finacene M 3410 EP for blown film. Compared with other mPE resins, it reportedly brings a unique combination of excellent processability, good compatibility with LDPE and LLDPE, high stiffness, and excellent optical properties (9% haze and 60 gloss rating at 45°).
In 1-mil film produced on an LLDPE extrusion line, M 3410 EP has 35% higher slow-puncture strength and 60% higher tear strength than conventional MDPE, according to marketing manager Rob Maes. Applications include tissue and towel overwrap and high-clarity shrink film.
The new material has also found use as a 20-30% blend component for downgauging LDPE monolayer films. A 70/30 blend of LDPE and M 3410 EP at 1.1-mil gauge compares favorably with 1.4 mils of a 0.8-MI liner-grade LDPE. The thinner film has higher stiffness and tensile strength, reduced blocking, and good optics.
Finacene M 3410 EP can also be used as a substitute for LDPE to add bubble stability to LLDPE-rich monolayer films. M 3410 EP provides all the processing benefits afforded by LDPE but with much less deterioration of LLDPE’s mechanical properties, explains Maes. An 80/20 blend of 1-MI LLDPE and M 3410 EP yields less gauge variation than an 80/20 LLDPE/LDPE blend at equivalent output rate, he notes. What’s more, the M 3410 EP blend has better tear strength, higher stiffness and tensile strength, enhanced slow puncture strength, and less blocking.
|Properties of Financene mPP Vs. Conventional PP Homopolymers & Random Copolymers|
2% RCO mPP
4% RCO mPP
|Tensile Str., psi|
|Secant Modl, psi|
|MVTR g/100 sq in./24 hr|
Melting Point, F
A 70/30 blend of LDPE and M 3410 EP can be used to downgauge clarity shrink film while increasing shrink-retention force by 20% compared with a traditional 70/30 LDPE/LLDPE mix. Such a blend also offers enhanced stiffness and tensile strength, higher tear strength, and better creep resistance. Adding M 3410 EP to LDPE shrink film also prevents burn-through in the shrink tunnel, according to Maes. In coextruded structures, blending M 3410 EP into the core layer produces a high-clarity film with good stiffness for downgauging.
M 3410 E is also being used as a majority component (up to 90%) to downgauge tissue and towel overwrap. According to Maes, it offers increased stiffness and tensile strength, excellent bubble stability, low gels, high gloss, and good contact clarity. Stiffness and MD tear strength can be tailored for specific applications by blending with Finathene 6410, a 0.961-g/cc, 1.2-MI, medium-molecular-weight, high-clarity homopolymer HDPE.
|Coextruded mLLDPE/mMDPE Clarity Filma vs. OPP (1-Mil Films)|
Dart Impact, g
MD Tear, g
TD Tear, g
|aA/B/A, 25/50/25%. A=95% mLLDPE (1.0 MI, 0.918 g/cc) + 5% LDPE (0.8 MI, 0.924 g/cc). B=100% Finacene M 3410 EP.|
In coextruded film for flexible specialty packaging, M 3410 E provides excellent clarity, low seal-initiation temperature, and good seal strength, stiffness, tensile strength, and toughness. The accompanying table shows how a 1-mil coextruded clarity film with an mMDPE core layer compares favorably with 1.1-mil OPP film.
MDPE for glossy bottles
Finacene BM359 SG, the new mMDPE extrusion blow molding grade, is touted for its exceptional gloss, flexibility (for squeeze bottles), and processability (high output without melt fracture). Its gloss outshines that of previous glossy HDPE resins by 50% to 100%, according to marketing manager Allan Potter. In fact, this hexene copolymer boasts surface gloss comparable to glossy PP (60 to 90 gloss rating at 50°) and is suited to packaging of personal-care products like shampoos, sun creams, body lotions, and cosmetics. BM350 SG is reportedly also glossier than other MDPEs and does not need any blending to obtain the right squeezability.
BM359 SG offers excellent processability in monolayer uses for flexible high-gloss bottles and in coextrusions with an inner layer of stiffer HDPE, says Potter. BM359 SG also sports high ESCR (>1000 hr).
mPP for film & molding
AtoFina now offers a family of isotactic mPP homopolymers and random copolymers for cast film, heat-seal layers, and injection molding. Homopolymers range in MFR from 3 to 40 g/10 min and melting point from 302 to 312 F. Random copolymers range from 7 to 30 MFR and 237 to 297 F melting point.
For cast film, AtoFina offers mPP homopolymers and copolymers with excellent clarity and moisture barrier. They are aimed at higher-end food and non-food packaging. Marketing manager Joe Schardl cites improved processability and higher line speeds due to reduced draw resonance compared with other PP homopolymers and random copolymers. The table on p. 30 shows that Finacene mPPs have comparable or better tensile strength relative to non-metallocene PPs, plus improved stiffness, clarity, and MVTR.
For sealant layers, the company particularly recommends its higher-ethylene-content mPP random copolymers. They can be used in clear and opaque multi-layer BOPP films for snack-food packaging and the like. According to Schardl, Finacene materials have much lower extractables, seal-initiation temperatures as low as 212 F, and excellent hot tack.
For injection molding, AtoFina offers clear homopolymers and random copolymers. They have scored commercial success in containers and housings for office equipment.
“These are premium materials, so we are going after higher-value end-uses where they are successful on a cost/performance basis,” says Schardl. Applications involve replacing standard PP and other clear polymers like PS, ABS, and acrylics. “Finacene’s clarity is very comparable with such materials, and its processability is excellent,” says Schardl.