What does the increasing use of sharp, eye-catching graphics on flexible plastic packaging have in common with the need for faster production to drive down costs? Both are important and growing trends in the packaging industry, and both depend upon the properties of advanced slip agents, which are used to reduce the coefficient of friction (COF) in bi-axially oriented polypropylene (BOPP) film. Slip agents, or additives, overcome the film’s natural tackiness, enabling it to move smoothly through high-speed converting and packaging equipment.
But not all slip agents are equally effective. Traditional organic waxes such as erucamide and oleamide deliver good slip performance, but readily and continuously migrate from the film’s surface. This migration can affect the appearance and quality of packaging materials by increasing the haze level of clear film. It can also negatively affect downstream printing and vacuum metallization operations when the additive transfers from the slip-treated face to the corona-treated face during film winding and storage. The presence of a slip additive on the corona-treated face of the film can cause non-consistent coating or metallization called the “fish eye” effect.
Organic waxes also degrade under elevated temperatures and over time. The resulting decrease in slip performance can cause deformation or even tearing of BOPP film. These issues can interrupt and slow down packaging production. Another way that organic slip additives can impair throughput is by building up on the extrusion die, which requires periodic cleaning.
These drawbacks make it difficult for traditional slip additives to support the two packaging trends mentioned above: the increasing importance of strong visual impact and the continuing need to speed up production to drive down costs.
Superior Graphics Drive Consumer Choice
In the fierce competition for consumer attention, bolder, more impactful graphics are critical to making a positive first impression. The use of brilliant colors, special effects and metallics are on the rise to differentiate products – even store brands – from competitors at the point of sale.
Another factor is the popularity of smaller packages that address the snacking and on-the-go eating megatrends. However, smaller packaging calls for greater printing precision so information can fit into limited spaces.
Technologies such as high-definition flexographic printing address both of these challenges by delivering sharper images and details, enhanced color and higher overall quality.
High-definition flexo printing can benefit from the use of new silicone slip additives for BOPP film that improve the printing and metallization of flexible packaging. Unlike traditional organics, which migrate quickly through polyolefin film, these silicone polypropylene copolymers do not migrate from the treated layer to the opposite, corona-treated layer. This eliminates or minimizes interference with the surface energy of the corona-treated face. Maintaining the integrity of corona treatment – which improves adhesion between the non-porous plastic surface and inks or coatings – is critical to high-quality printing.
Another benefit of non-migrating silicone additives is their ability to preserve the clarity of transparent films. Traditional slip additives can cause hazing of the film, which affects printing precision and dilutes the intensity of colors and effects. Test results show that new silicone slip technology keeps haze in transparent BOPP film to a level below 2 percent.
Faster Processing Lowers System Costs
According to Smithers Pira, a provider of technology-based services to the packaging industry, flexible packaging is the most economical method to package, preserve and distribute food, beverages and other consumables in that it uses less energy and fewer resources than other forms of packaging.
To maintain this cost advantage in the face of volatile polymer prices and stiff competition resulting from higher capacity than the market currently requires, converters and packaging producers need new strategies. One approach is down-gauging the film. Another is the use of advanced silicone slip additives, which can accelerate throughput to drive up productivity by:
- Reducing COF to a level of 0.2-0.3 to help ensure rapid processing and avoid film rupture or deformation that causes scrap.
- Maintaining stable slip performance over time and under high-temperature conditions.
- Preventing die build-up that causes interruptions for cleaning.
- These silicone slip additives also help keep costs down through their effectiveness at very low loadings of 2 wt% to 5 wt%. Further, they are typically added only to the outer layer of the film.
How Silicone Additives Work
Traditional organic slip additives are based on unsaturated fatty acid amides. These primary amides, which have low molecular weights, migrate rapidly through polyolefin films after extrusion and appear on the surface of the film to lower the COF. These additives are also characterized by exudation – the formation of a gel-like layer that can transfer to other film surfaces, lead to haze and affect printing operations.
Unlike these organic slip additives, silicone technologies have higher molecular weights, so they move to the surface of the film more slowly. Importantly, they provide some anchoring to the resin matrix at the surface to deliver stable COF reduction, and will not cause exudation.
The newest silicone solutions are designed to deliver improved anchoring and are suitable for both BOPP and cast films used in bags, wrappers, packages and pouches. Some can be used in sequential and simultaneous BOPP processing.
The global flexible packaging market is forecast to reach $248 billion in 2020, up from $210 billion in 2015, according to Smithers Pira. This growth is being driven by demand for convenience, greater food safety, extended shelf life and lower transportation costs, among other factors. To support continued success, the industry must address two current trends – improving package aesthetics and raising productivity. The adoption of advanced silicone slip technologies to replace problematic organic waxes can make a significant contribution to the competitiveness of flexible packaging by enabling higher-quality printing and metallization, and achieving greater system cost savings.
Dow Performance Silicones