HOUSTON - Polyethylene resins made with metallocene catalyst technologies have moved into commercial and industrial applications, giving processors benefits, drawbacks and new challenges as they try to find applications to take advantage of the new resins' properties. Six processors presented papers on their experiences with metallocene linear low density PE at the Specialty Polyolefins '96 conference Sept. 25-27 in Houston. The conference was sponsored by Schotland Business Research Inc. of Skillman, N.J.
The processors primarily use metallocene LLDPE resins as coating, sealant and tie layers for a variety of laminated packages, including bags for fresh-cut produce, coffee, meats and cheeses, pet food bags, compression-rolled, oriented films used in packaging breakfast cereals, and form-fill-seal bags used in bulk and single-serving sizes for condiments and other food products.
In those applications, the metallocene resins are low-cost alternatives to ionomers and ethylene-vinyl acetate.
The materials ``offer environmental friendliness and ease of operation,'' said Stephen G. Junker, product development engineer for Tredegar Film Products' MonaxPlus Films. ``They are competitively priced with EVAs and significantly lower-priced than typical ionomer-grade sealants, Tredegar Film Products of Richmond, Va., is a unit of Tredegar Industries Inc. of Richmond. Junker works at the company's Terre Haute, Ind., facility.
``It is as though we are getting some of the sealing performance of the ionomers, but paying the price of an EVA,'' Junker added.
Junker, Will Taber, Jeffrey S. Brandenburg and Jesse Trevino each presented papers that appear to confirm forecasts made by resin producers at previous conferences that metallocene resins would improve hot tack and seal strength, while lowering costs and providing improved odor and custom oxygen transmission rates.
Their papers are among the first to provide details on applications of metallocene resins by processors.
``These metallocene resins also provide increased tear and puncture resistance compared to conventional extrusion coating grades of low density and linear low density polyethylene,'' said Taber, a product development engineer for Sealright Films, a division of Sealright Inc. Taber works at Sealright's DeSoto, Kan., facility.
``Another advantage is that ionomers and acrylic acid copolymers have the tendency to impart an increased level of odor to the material specification that can negatively affect the product packaged,'' he said.
``The metallocene extrusion coating resins have less plastic odor, thus they are considered more product friendly than ionomers and acrylic acid copolymers for specific applications,'' Taber added.
However, Taber said his company has not documented specific cases of higher output, al-though he said he feels confident that productivity gains will be proven with metallocene resins.
``We know we can run at lower temperatures, but we haven't done optimization work yet,'' he said.
Brandenburg is vice president for marketing and technical services for New England Extrusion Inc. of Turners Falls, Mass. It makes films for form-fill-seal food and medical applications.
His company experimented with blended films containing 10, 20, 30, 40 and 50 percent metallocene resins made by Exxon Chemical Co., combined with LDPE and EVA. For the experiment, New England Extrusion used two Exxon resins, a plastomer and an enhanced polyolefin, he said.
New England Extrusion found the blends had improved breath-ability, stiffness and impact strength, and could increase line speeds with the metallocene blends.
The increased speeds were a result of improved hot-tack strength and seal strength, Brandenburg said.
``We were able to get eight unique films without varying the base LDPE or EVA content. If you vary the LDPE or EVA content, you can get an whole new series of films,'' Brandenburg said.
``Wouldn't it be interesting to be able to pick individual properties that you want [in a packaging film], and get them immediately?'' he asked.
The resins' individual properties have made them valuable for one of New England Extrusion's product lines, he said.
``Metallocene resin blends have found a real home in packaging fresh-cut produce.
``You can't just package produce to keep dust out. You have to have a living, symbiotic device that lets food live in an atmosphere it likes - where it can breathe oxygen in, and carbon dioxide out,'' Brandenburg said.
Trevino, sales manager for roll stock for the XF business unit of World-Pak Corp., a subsidiary of Inteplast Corp. of Livingston, N.J., said his company has patented technology to produce a line of films made with metallocene resins.
``The patented technology is really a new recombination of film processing technologies that are well-established and have been well-reported in technical journals over the past 30 years,'' Trevino said.
``The result is a small material innovation, resulting in a big packaging revolution,'' he added.
The technology incorporates a variety of techniques to produce a coextruded, cross-laminated, isotropically oriented, high-strength film marketed under the IntePlus trade name.
By using metallocene resins in the laminated layers, World-Pak was able to reduce the thickness of the lamination layer from 15 percent to 5 percent of the coextruded film, Trevino said.
World-Pak used metallocene resins from Dow Chemical Co. of Midland, Mich., and Exxon, and what Trevino described as a precursor of metallocene resins from Mitsui Sekka Chemicals Inc. of Tokyo.
``Metallocene resins helped us achieve a reduction in gauge of between 30 and 50 percent over nonmetallocene LLDPE or LDPE films, depending on the application,'' Trevino said.
Beyond reduced gauges, Trevino said World-Pak noted increased lamination strength, improved heat sealability and hot- tack performance, increased tear resistance, increased puncture resistance and an enhanced coefficient of friction, which is necessary to keep bags from sliding off conveyors and pallets.
However, as Taber did, Trevino noted his company has several continuing challenges for metallocene resins.
``Metallocene resins have not been a total panacea for World-Pak Corp. in our search for a high-strength, high-performance film.
``There are still a few characteristics that remain a challenge,'' he said, explaining that World-Pak would like to find an interlaminar adhesion product that could be used to combine two resins, such as polypropylene and PE, in a coextruded film that would exhibit the properties of both.