Analysis of the "Tunneling" Phenomenon in the Fabrication of Amino-Liquid Solvent Composite Film (Part 2)

Third, the composite aluminum film migration phenomenon

The so-called migration is the relative sliding between the aluminized layer and the printing ink layer.

The aluminized layer not only cannot tear the ink layer, but instead the printing ink layer tears off the aluminized layer. This is also a sign of low peel strength. The migration phenomenon is easy to appear in OPP/VMPET, PET/VMOPP composite structures. Its production is related to the following factors.

1.PET film itself

The PET film itself has a certain polarity, combined with the outer electrons of the aluminum atom to form an electron cloud superposition, so that the fastness between them is very good. OPP is a non-polar material, so PET and its fastness to adhesion are poor, so that it is prone to migration phenomenon when composited by PET.

2. Evaporated aluminum film process technology

When vapor-depositing aluminum film, it is necessary to use a binder to enhance the adhesion of the aluminum film to the film. When the binder is not uniform, or when an error occurs in the vapor deposition process, migration of the aluminized layer will also occur.

3. Poor adhesive quality

Poor adhesive quality, poor solvent release, glue can easily penetrate into the aluminum plating layer, destroy the aluminum plating layer, and cause migration phenomenon.

In the choice of glue, should choose a slightly larger molecular weight adhesive. When the molecular weight is too small, although the adhesive is distributed uniformly, the relative increase in the movement will also cause the migration of the aluminum plating layer.

When the glue is prepared, the amount of the curing agent is appropriately decreased, so that the cross-linking reaction between the main agent and the curing agent is reduced, the brittleness of the film can be reduced, and the flexibility and stretchability of the film can be kept, which is favorable for controlling the aluminum plating. Layer migration. When our factory uses PU-2975 type adhesive with glue solution, the coating amount is generally controlled at 2-4g/m2. In compound OPP/VMPET, the coating quantity is 2.5g/m2 to maintain the best state.

The migration phenomenon occurs when compounding OPP/VMPET, it may also be related to misoperation. If VMPET is installed in reverse, the migration phenomenon will be apparent after curing.

Therefore, if you want to reduce or eliminate the phenomenon of migration, you should start from many aspects and take a serious and responsible attitude.

Fourth, the cured product has a "black block"

In the compound BOPP/VMPET of our factory, we found that the solidified products had uneven distribution and different sizes of “black blocks”, causing serious losses.

After testing, it was found that the VMPET surface tension has reached 5.0×10-2N/m, and the transmitted light is very weak, and the aluminum plating layer is well distributed. The adhesive used is PU-2975, which also meets the quality requirements.
So we did a series of analysis. The first step is to take a VMPET, place it in an environment with a temperature of 27°C and a relative humidity of 70%, stand for 48 hours, and then dry it. The drying temperature is 50°C and the time is 12 hours. Take out the observation of the light, resulting in uneven distribution of "black blocks."

Then it took another VMPET, sprayed a layer of water vapor on the aluminized side, and dried it again. It took less than 4 hours for a “black block” to appear.

We have concluded that this failure was caused by improper preservation. In actual production, it is advisable to place VMPET, VMCPP, VMOPP and other aluminized films in a ventilated, dry, 25°C environment.

There are still many problems in the dry composite aluminum plating film, and we need to carefully summarize it in practical work.


Author: Jiangzhong Qiu

Beijing Land Meike Instrument Development Center