Technology's Edge September 2010

Flexibility for Shrink Film Capabilities

Editor's Note: The following is an excerpt from a presentation made at the K 2010 trade show in June by Dr. Daniel Wagner, BASF's product development–SBC polymers.

Launched onto the market three years ago, shrink films based on Styrolux® HS 70 have become well-established in the European sleeve market. Compared to conventional mixtures of SBC (styrene butadiene block copolymer) and PS (polystyrene), this material stands out for its very high final shrinkage of more than 70 percent.

BASF researchers have now developed even further improved Styrolux grades with an eye towards expanding the product line for this application. They have done so in response to the industry's desire for stiffer films that allow even larger, more complex objects to be shrink-labeled and the thickness of the sleeve film to be further reduced.

Individualized films

A two-component concept that –differs from Styrolux HS 70 is being implemented for the first time. With Styrolux T (T = toughness) and Styrolux S (S = stiffness), this concept offers two new Styrolux grades from which the desired property profile of the shrink film can be set when the processor blends them, and only once they are put together do they yield the film "Styrolux T/S". The combination of the two newly developed Styrolux grades now allows manufacturers themselves to adapt the film properties to their specific requirements.

High final shrinkage

Like Styrolux HS 70, Styrolux T/S films are particularly well-suited for the technology of transverse stretching (transverse direction or TD). TD films allow shapes having widely varying radii or unusual designs to be shrink-labeled by sleeve technology.

The new product formulation has succeeded in retaining the well-balanced shrinkage curve of Styrolux HS 70, along with a very high final shrinkage of more than 70 percent at 90°C [194°F]. The uniform, moderate rise of the shrinkage curve permits well-controlled shrink-labeling over a very broad processing range, whereas the high final shrinkage makes it possible to decorate even the most complex of shapes.

MD films

The new Styrolux T/S films not only are suitable for transverse stretching processes but, as so-called MD films, they also yield high-quality products. Stretching films in the extrusion direction (machine direction, or MD) as is done in band labeling technology is simpler from the standpoint of the machinery employed, and thus correspondingly cheaper. With the roll-on-shrink-on (ROSO) method the film label is wrapped around the bottle in the form of a band, fixed by glue, and then shrunk onto the bottle under the effect of heat.

When it comes to the products, the ROSO method used to be limited almost exclusively to –polypropylene (PP) and to just a few suppliers. The low shrinkage of classic PP-MD shrink films—20 percent at the maximum at temperatures up to 100°C [212°F]—restricted the use of this method to bottles with simple shapes. Due to its low shrinkage, a PP-MD film cannot tightly enough hug the contour of complex shapes that have greatly varying radii.

The new T/S shrink-film products can achieve shrinkage levels of as much as 45 percent at temperatures of up to 100°C [212°F], and even up to 65 percent at temperatures between 100 and 120°C [212 to 248 F]. The significantly higher final shrinkage of the MD Styrolux films means that it is also possible to tightly shrink-label complex shapes such as contoured bottles that have large radius differences, a realm that up until now had been the exclusive domain of TD sleeve films.

Growth potential

In view of the current global market volume of more than 3.5 million square meters and estimated annual growth rates of well over 10 percent for the coming years, shrink films are an extremely attractive segment of the packaging market for consumer goods. With the newly developed two-component product system Styrolux T and S, the company sees very good opportunities to contribute to the growth of this segment. BASF anticipates these two sleeve film components will be available in commercial quantities throughout the world in early 2011. pP