Aluminium Coating Transfer Influence factors
Aluminium Coating Transfer Influence factors
(1) Influenced by testing method of peeling strength
During the actual production, peeling strength testing can find whether aluminium coating transfer happen. But there are many methods to test peeling strength, in which of the situations, we need to pay special attention to the peeling Angle, normally using 90°or 180°. The experiment results show that peeling at different Angle would cause different results.
For example:
One customer made a laminated film testing with the testing conditions as follows:
• Laminated structure: PETink/VMPET/PE(60)
• Glue: Solvent-less adhesive WR-8105/DB8105
• Proportion: Outer layer: inner layer=100:90
• Processing: Aluminium coating and gluing with adhesive volume of 1.9g/m2 and speed at 150m/min.
Test the peeling strength and record the data of testing result with Angle of 90°and 180°.
Detection Index | PETink/VMPET/PE | |||
PETink/VMPET | VMPET/PE | |||
Peel at 90° | Peel at 180° | |||
Peeling Strength （N/15mm） | Minimum Value | 1.52/1.54 | 0.73/0.94 | 5.24/3.90 |
Maximum Value | 1.70/1.66 | 0.62/1.05 | 5.56/4.33 | |
Average Value | 1.57/1. 62 | 0.82/0.82 | 5.44/4.07 | |
States of ink transfer | No transfer of ink or aluminium coating | Completely ink transfer |
| |
The above data shows that peeling at 180°is much easier to cause aluminium coating transfer than that at 90°. And generally, “T”type peeling (peeling at 90°) will be selected as the testing standard.
(2) Cause analysis
Why dose aluminium coating transfer happen? To find out the reason, we repeated an analysis sample, that is, in the OPP/ ink /VMPET/CPE laminating process, we sampled the following different interfaces for observation, and the results are as follows:
No. | Structure | Peeling Conditions | States of Aluminium Coating |
1 | OPP/Ink/MPET | After a period of aging treatment | Peeling strength ≥1N/15mm, No transfer happens |
2 | (OPP/Ink/VMPET)/CPE | Peeling testing after 3-layer aging treatment | Peeling strength＜1N/15mm, |
3 | (OPP/Ink/VMPET)/CPE | Test the peeling strength of OPP/MPET after removing the inner layer of CPE | Peeling strength≥1N/15mm, Basically, no transfer happens |
According to the testing date above, for OPP/Ink/VMPET, laminating with PE will have a pulling effect on it, which is called “stress”. If the stress between PET/PE films is greater than the adhesion between the aluminum coating layer VM and the PET substrate, then the aluminum coating will be transferred. Ensuring the stress balance of OPP/VMPETPE in all aspects can truly solve the problem of aluminum coating transfer.
Interfacial Strength | State of Transfer | Laminating Remark |
No transfer | Keep the minimum amount of adhesive, make it fully cover the film surface, and ensure no white spots and bubbles when put into machine. | |
Adhesive Strength＜Adhesive Strength | Transfer |
