- February 01, 2002, Stanley Sacharow, Contributing Editor
Advances in closure technology are expanding the definition of “flexible.”
Over the past decade, flexible packaging has been elevated into new and more expansive markets by the introduction of a wide variety of novel package closures. No longer used solely for rigid containers, bottles, and tubes, the “flex-pack closure” has created a niche of its own for the converter and user of flexible packaging.
There are at least six techniques that can be used to create a flex-pack closure capable of both re-opening and recloseability:
- pressure-sensitive adhesives
- snap closure
- laser uses
Zippers Take Off
Introduced into the market in the late 1980s by firms such as Dole, Nestlé, and Sargento Cheese, “zippers” have rapidly evolved into a popular consumer requirement.
The zipper has become the driving force for the current rage over stand-up pouches and the increasing use of pre-made pouches over form/fill/seal operations. Improvements in application machinery, new zipper blends, and major advances in package machinery modifications have added to the zipper's increasing use.
Cost has been an additional factor. From a high of 6 cents/ft in 1985, most zippers now cost about 3 cents/ft. (These costs vary depending on package size, zipper type, and volume utilized.)
Zippers now can be applied by the converter on rollstock or separately on the packaging line on either a modified machine or a specially designed packaging machine.
Pre-made pouches also are available for a wide variety of applications. Obtaining a proper seal between the zipper and rollstock is essential on the packaging line. This must be accomplished without slowing down the entire filling line. The zipper is applied to the inside of the packaging by heat-sealing the zipper flange to the sealing layer of the base stock. Various blends of coextruded materials are used for zipper formulations, including ethylene vinyl acetate and low-density polyethylene.
Most zipper styles on packages today utilize a standard “arrowhead and receiver” design. The reclosable interlocks may come in contact with particulate matter and often clog. In order to eliminate this problem, various “clog-resistant” styles have been developed. Presto Products “140 Fresh-Lock” zipper is available designed with twin clasps that slide past each other to engage, plus a wide interior base, so the zipper locks even when particles enter the track.
New zipper styles and forms are being developed rapidly. These include powder-proof, variable alignment, peel seal, and barrier zippers. A transverse-direction zipper for overwrap applications also has been introduced by ITW Minigrip.
In the U.K., Supreme Plastics recently introduced a series of “Keyseal Zippers” that offer improved sealing properties for faster and more efficient f/f/s production. Their cross-web zippers include the latest cross-web or transverse zipper application technology. The narrow width of the profile allows more zippers per roll.
Sliders Arrive from Japan
During the mid-1990s, sliders began to appear in US supermarkets, having been previously seen in Japanese markets. Pactiv first introduced the disposable “Hefty One Zip” in 1995, followed soon by products from both Presto Products and Pliant Corp.
The first sliders were on storage bags only; the 1998 introduction by Kimberly Clark “Huggies” marked the first US commercial package using sliders. Applications soon increased rapidly — from Green Giant vegetables to Sargento cheese products.
A slider closure operates when the slider opens or closes a track by moving along it to provide a consumer seal. These tracks may be offered as track profiles on 1-in. strips on a reel. The track is unwound, and strips of film or fins at the base of the track are heat-sealed to film to be made into bags.
Sliders are added once the bags are formed. A slider package must be compatible with existing f/f/s equipment in the packaging plant. Representative horizontal f/f/s machines compatible with slider technology include Bossar, Klöckner, Bartelt, and Laudenberg.
The actual slider is composed of various LDPE blends. Recent work by Ticona and Pactiv has shown that an LDPE blend with 40% addition of COCs (cyclic olefin copolymer) improves closures' top retention by 30%. The COC addition also helps prevent track curvature significantly.
The advantages of sliders for consumer packages include easy operation, even by people with reduced motor skills, since one-handed loading is possible. In addition, sliders create a more secure press-to-close system.
Resealable closures also can be made by using a variety of PSAs.
It is important the entire package construction be considered carefully prior to the actual adhesive selection. The reseal adhesives' properties must be compatible with the product that is packaged and be able to adhere satisfactorily to the base film. There also should be good “wetout” and a steady, controlled peel.
Adhesives used for p-s applications often include both solvent- and emulsion-type acrylics; hot melts; and two-component reseal systems. Solvent acrylics are generally preferred because of their excellent resistance to various chemicals and oils. They often are applied to label stock but also may be used at the converter level on rollstock.
An alternate approach to the p-s system is a snap closure. The “Easy Snap” bag from Sig Pack consists of two rigid tracks, made of special rigid polypropylene, that span the width of the bag. When the consumer closes the bag, there is a distinctive snap feel and sound. The technology assures the consumer the bag is closed.
In a recent application for Necco Ultra Mints, the firm leases a Sig Easy Snap module from Sig Doboy that laminates the special PP track to the PP film. Using an Infinity vertical f/f/s bagger, the output is 50 bags/min. This package recently won an AmeriStar award.
Now, laser techniques have joined the ranks of zipper technology as an effective method to create such features as “easy-open,” “easy-tear,” “easy breathe,” “easy-fill,” and “easy pack.”
Laser Machinery Co. (LMI) recently developed laser system solutions to help manufacturers keep pace with converting process changes and produce “easy-tear” packages to customer specifications. Taking advantage of the relatively high absorption of polymeric materials to the CO2 laser wavelength, LMI developed “AcuTear” products such as “AcuScore” that use a well-focused laser beam to vaporize a narrow groove on the film to the precise depth needed, leaving the functional barrier layers intact and maintaining package strength. By using the proper laser beam delivery optics and web handling equipment, packaging material can be scored in the web direction at speeds as high as 1,500 fpm.
Thicker flexible materials can be processed with laser systems. For example, LMI's systems use lasers to perform intermittent, deeper scoring to depth specifications and create “easy-tear” features in materials where score lines may not be suitable. Another product, “AcuBreath,” also is capable of producing small hole sizes to precise specifications. Unlike electrostatic perforations that do not create consistent hole sizes, LMI laser perforating systems perforate material as thick as 0.008 in. accurately.
Laser capabilities are of further value to converters, providing cross-web scoring and contoured or two-dimensional score lines for more advanced reclosable applications. LMI systems for cross-web and contouring integrate beam steering, vision systems, and web speed into a single PC-based control module. Further, AcuPower™ was developed to adjust laser power on the fly. AcuPower optimizes speed and power, enables the laser to provide precisely the right amount of power for the speed, and results in very accurate and consistent cut quality for any job with no burnthrough at any point along the contour-scoring pattern.
Closures — fitments, dispensing, spouts, push-pull and snip-tops — now are appearing on the market as part of a flex-pack. Propelled by the popularity of both water and energy drinks in flex-packs, these often provide convenient access to the product.
Kapak Corp. recently developed “Smartspout” flex-pack utilizing its “Simple Squeeze” dispensing technology. There are numerous additional fitments on the market for flex-packs containing beverages. Variations include spout design, method of use, and value differences.
Reclosables is a “hot topic” in flexible packaging today. For a case history on zippered packaging, go to pffc-online.com, simply click on “Browse Back Issues,” and select July 2001. And, more information will be available at Flexcor 2002, sponsored by The Packaging Group and held March 5-7 at the Sofitel Hotel in Rosemont, IL (O'Hare). For more information call 732/636-0885; firstname.lastname@example.org.
Stanley Sacharow has been in the flexible packaging industry for more than 35 years. His company, The Packaging Group, is an organizer of targeted conferences and a consultant to the international packaging/converting industry. He is also the author of PFFC's “Package Converting” column.