In field of solvent-free laminating, high temperature retorting has been a difficult problem during last few years. While along with development of equipment, adhesives and technologies, solvent-free laminating for plastic with plastic under 121℃ retorting has gained a lot of application among flexible packaging manufacturers. What’s more, the number of factories which employ PET/AL, AL/PA and Plastic/AL for 121℃ retorting is growing.
This paper will focus on the latest development, control points during manufacturing and future trends.
1. Latest development
Retorting pouches now are divided into two types of substrates, plastic/plastic and plastic/aluminum. According to GB/T10004-2008 requirements, retorting process is classified as half-high temperature(100℃ – 121℃) and high temperature( 121℃ – 145℃) two standards. At present, solvent-free laminating has covered 121℃ and below 121℃ sterilization treatment.
Except the familiar materials PET, AL, PA, RCPP, which are used for three or four layers laminates, some other materials such as transparent aluminized films, retorting PVC appear on the market. While no large-scale manufacturing and application, those materials need more time and more test for massive usage.
At present, our adhesive WD8262A/B has successful cases applied on substrate PET/AL/PA/RCPP, which can reach 121℃ retorting. For plastic/plastic substrate PA/RCPP, our adhesive WD8166A/B has broad application and developed cases.
The hard point of solvent-free laminating, printed PET/Al is now solved by our WD8262A/B. We cooperated several equipment suppliers, tested and adjusted it for thousand times, and finally made WD8262A/B with good performance. In Hunan province, our customers have high enthusiasm on Aluminum retorting laminates, and it is more convenient for them to make the trial. For printed PET/AL/RCPP substrate, all layers are coated with WD8262A/B. For printed PET/PA/AL/RCPP, PET/PA and AL/RCPP layers are used WD8262A/B. The coating weight is around 1.8 – 2.5 g/m2, and speed is around 100m/min – 120m/min.
Kangda solvent-free products now have achieved great progress under 128℃ and keep challenging for 135℃ even 145 ℃ high temperature retorting treatment. Chemical resistance is also under research.
PERFORMANCE TEST
|
MODEL |
SUBSTRATES |
PEELING STRENGTH AFTER 121℃ RETORTING |
|
WD8166A/B |
PA/RCPP |
4-5N |
|
WD8262A/B |
AL/RCPP |
5-6N |
|
WD8268A/B |
AL/RCPP |
5-6N |
|
WD8258A/B |
AL/NY |
4-5N |
Difficulties:
The main problem to manufacture four-layer aluminum retorting pouches is to find the proper combination of different materials, including films, adhesives, ink and solvent. Especially, manufacturing fully printed PET/AL this outside layer is the most difficult. We used to face these cases that, when we took materials from customers to our laboratory and tested all elements including equipment, no faultiness was found. However, when we combined all the elements, performance of laminates was unsatisfying. Only when all technologies, equipment, materials are fully under control, the substrate can be successfully made. Other factory can make this substrate doesn’t mean anyone can achieve success too.
2. Control points during manufacture
1) Coating weight is around 1.8 – 2.5 g/m2.
2) Surrounding humidity
Room humidity is suggested to control between 40% – 70%. The water contained in air will participate the reaction of adhesive, high humidity will reduce the molecular weight of adhesive and bring some sub-reactions, influencing performance of retorting resistance.
3) Settings on laminator
According to different machines, suitable settings such as tension, pressure, mixer must be tested to find a proper application and make laminates flat.
4) Requirements for films
Good planeness, proper dyne value, shrinkage and moisture content etc. are all necessary conditions for retorting laminating.
3. Future trends
At present, application of solvent-free lamination is on flexible packaging, which has a fierce competition. On personal points, there are 3 ways for solvent-free lamination to develop.
Firstly, one model with more applications. One product can manufacture most substrates of flexible packaging manufacturer, which can save a lot of time, adhesive and increase efficiency.
Secondly, higher performance, which offers high resistance of heat and chemicals.
Lastly, safety of food. Now solvent-free lamination has more risks than solvent-base lamination as it has some restrictions on high performance products such as 135℃ retorting pouches.
Above all, solvent-free laminating is developing fast, more and more new technologies have come out. In the future, solvent-free laminating may take a large account of market for flexible packaging and other fields.
Post time: Oct-27-2021