To showcase the enormous potential of SML’s extrusion lines, the films for mono-material stand-up pouches from PE were manufactured and laminated live at SML’s Innovation Days, from 9 to 10 October 2024. A state-of-the art cast film line with integrated MDO unit and a high-performance FlexPack coating and lamination line were in operation.

Mono-material-PE structures have proven to be a forward-looking solution when it comes to replacing BOPET in flexible packaging. SML’s all-PE solution combines full recyclability with maximum film performance.
 

The pouches produced during the Innovation Days had the following structure:
 

The production of all of the films for the pouches and the lamination process took place exclusively on SML extrusion lines.

Ultra-thin MDO-PE film from SML cast film lines

SML’s latest cast film lines are fitted with an MDO unit, that was especially designed to manufacture easy-to-recycle mono-material films. The 17 µm MDO-PE film for the pouch surface showed a five-layer structure and a layer distribution of 20/10/40/10/20 %. It consisted of 47% MDPE, 36% HDPE, 16% LLDPE and 1% additives – and featured the following properties:

Mechanical properties:
Machine direction MD:          > 1400 MPa (up to 1850 MPa)          
Transverse direction TD:      > 1200 MPa (up to 1500 MPa)
 

Heat resistance:
Shrinkage 120 °C/30sec, machine direction:        4 – 10 %
Shrinkage 120 °C/30sec, transverse direction:    0 – 2 %
 

Optical properties:
Gloss 45 °:       70 – 85 %
Haze:                 < 5 %
 

As can be seen from this table, the 17 µm film offers excellent optical attributes. Its high stiffness guarantees a good machinability for further processing on printing and packaging machines. 

Conventional CPE sealant film 

For the stability of the pouches, a 65 µm CPE sealant film was manufactured in a conventional cast process on the same line. Generally, CPE film produced on cast film lines from SML is characterised by its low gauge tolerance, high transparency and good sealing properties (with a low sealing initial temperature – SIT).

Laminating MDO-PE and CPE film

The 17 µm MDO-PE film and the 65 µm CPE sealant film were further-processed and laminated on a state-of-the-art FlexPack coating and laminating line. The reverse printed MDO-PE film required a very small amount of primer to improve adhesion. However, to bond the two films with their different properties, only PE was used in the extrusion process, without any other adhesives. In this way the mono-material properties of all substrates were kept, optimum recyclability is guaranteed.

Optional barrier layers for extended functionalities

To extend the functionalities of the pouch, there are three different ways to integrate oxygen barriers such as EVOH/PVOH in its structure:

• in the structure of the MDO-PE film
• in the structure of the CPE film
• as an additional layer in the PE extrusion lamination layer – PE /tie/EVOH/tie/PE

Regardless of which option is used for the integration of a barrier function, the final result is always a recyclable mono-material PE structure.

Close cooperation with Dow

For the development of the mono-material PE structure of the pouches, SML closely co-operated with the raw material manufacturer Dow. With a wide range of PE-based granulates, Dow offers customised solutions for the diverse requirements of the packaging industry. “The collaboration between Dow and SML allows us to demonstrate our broad toolbox of products that incorporate design for recyclability for packaging with our next-generation AFFINITY™ sealant and our ELITE™ and INNATE™ performance resins, enable the circular economy with REVOLOOP™ post-consumer recycled grades, and support efficient line productivity thanks to DOWLEX™ polyethelene resins and ATTANE™ ultra-low-density polyethylene (ULDPE) copolymers,” said Laurent Ziche, marketing manager at Dow. The combination of SML's advanced extrusion technology and Dow’s material expertise makes it possible to realise sustainable and high-performance packaging that meets the growing demands for environmental compatibility and functionality.

Redlham, 08.10.2024