According to Adhesives Age magazine, 25% of all consumer goods today are marketed in flexible packaging, in a continuing shift away from traditional folding cartons, boxes and fiberboard cases and trays. In fact, the flexible packaging market is the only packaging segment still exhibiting rapid growth, outpacing the annual growth rate of other types of rigid packaging. The Flexible Packaging Association forecasts a 4% to 5% growth rate through this year.
A variety of market, consumer and regulatory factors are driving the demand for flexible packaging. New packaging trends in snack food, fresh-cut produce and baking-mix packaging, as well as the rapidly growing use of pouches for many food products, all contribute to the growth of the flexible packaging market.
Flexible packaging often requires the use of laminates of two or more films bonded together to achieve desired properties such as moisture and oxygen barrier protection, heat sealability, and printability. Bonding is usually accomplished by thermal or chemical means with either solvent-based or water-based adhesives. Solvent-based adhesives, however, can be problematic for food packaging applications because they can impart unwanted flavors and odors to the contents. When used in manufacturing, they also produce Volitile Organic Compounds (VOC’s), When emitted into the atmosphere, VOC’s create atmospheric pollution and pose a threat to the health of employees who are exposed to the fumes.
Early attempts to eliminate VOCs focused on waterborne polyurethane dispersions and acrylic emulsion-based laminating adhesives, with urethanes reserved for higher-performing laminates and acrylics used for less demanding applications. Since then, adhesive manufacturers have responded to the increasing demands of converters by developing numerous generations of flexible packaging products, each offering improvements over their predecessors in terms of processing, performance and regulatory compliance. While earlier generations are still used for non-food applications, later generations have largely replaced them in today’s food packaging laminates.
First generation single-component solventless laminating adhesives are high in viscosity, yielding good green bond strengths but requiring high application temperatures, typically 80ºC to 90ºC. Their disadvantages, however, include the need for water-misting equipment to facilitate the adhesive reaction, poor appearance in the lamination and inconsistent cure rates.
Second generation adhesives consist of two reactive components, both lower in viscosity than a first-generation system. These adhesives have the advantage of a consistent and rapid cure rate. Their limitations, however, are low initial bond strengths and the presence of moderate to high residual isocyanate monomer in the laminate.
Third-generation laminating adhesives were developed to address the limitations of their predecessors by having a consistent cure rate, low residual monomer and increased initial bond strengths. Typically based on moderate-viscosity polyurethane polymers, they require only 50ºC to 70ºC application temperatures and have low residual isocyanate monomer content that virtually eliminates regulatory and safety issues.
Fourth-generation solventless laminating adhesives offer continued improvement, further lowering the isocyanate-monomer content and viscosity without extending cure times. LPS Industries makes extensive use of fourth-generation VOC-free adhesives for all its flexible packaging options.