Printing of dairy packaging materials - milk film

Milk film

Nowadays, in some medium-sized dairy products, milk film is the most widely used packaging material, and at the same time, it often causes problems.

First of all, the heat sealability of the milk film will appear some instability. The main reasons are the blow ratio and the traction ratio. The blow ratio and draw ratio are too large and unbalanced. It should be noted that the two should not exceed 2 in general, especially Traction ratio. Sometimes, in order to increase the output, the supplier greatly accelerates the pulling speed, resulting in excessive longitudinal stretching. The product performance tends to biaxially stretch the film, resulting in decreased heat sealability.

The production of dew point line should be controlled higher, so that the inflation and traction in the melting point of the plastic as possible, to reduce the molecular stretch orientation due to inflation and traction, and the stretching orientation can only be in the plastic high elasticity In the following, the orientation of the plastic molecules occurs under the stretching in the molten state, so that the heat-sealing performance is degraded.

Secondly, for the co-extruded compound milk film after hot-filled high-temperature cooking sterilization (100 °C, 30min), the size of the bag shrinks vertically and horizontally, which is basically not the problem of raw materials but the operation problem, milk film under normal circumstances It is blown, and in its production, the blow is a horizontal mechanical stretching, and the pulling is a longitudinal stretching. When the wind cooling on the wind ring is under the vertical and horizontal tensile force, it is easy to make Some molecules are oriented in the direction of the external force. The molecular orientation can only be in Tg-

The polymer of Tf is subjected to a high elasticity state, and since such oriented molecules are not heat-set, they thermally contract.

Film storage conditions to be met

In general, the film is best used within one week after the completion of the blowing process. It must be stored for a long time. It must also be stored in a dry, cool and ventilated warehouse. The maximum length cannot exceed 3 months. Before long-term stacking, the film must be used. After the dyne liquid test, it can be used only after passing the test, otherwise it will cause losses.

For the milk film fade is a very troublesome problem, to completely solve the milk film fade, it will have some impact on the production costs, to completely solve the milk film fade only the surface printing into India, the ink is not on the surface also Don't worry, there are three ways:

One is the composite film structure outside the BOPP / printing / PE, this structure requires special filling equipment, the cost is also high, each bag to reach 0.10 yuan / only;

The second structure is PE/printing/PE. This type of structure can also be filled with ordinary filling equipment, but the cost is still relatively high. Each bag must be 0.08 yuan/approximately.

The third method is flow PE/printing/PE, that is, after the original milk film is printed, an additional process is to transfer a thin layer of transparent thin film on the printing surface.

Its advantages are:

1. The ink layer is protected by laminating film, no discoloration, and blemishes, and the brightness of the ink is very good due to the high transparency of the lamination film;

2. Due to the film's isolation from the contamination of the milk with toxic substances such as ink and residual solvents, the odor and sanitation are eliminated;

3, due to lamination, some of the original film on the trachoma is also covered, the leakage rate is almost zero. Its only drawback is that its cost is increased by 1,500 yuan per ton compared to ordinary films, but it is only increased by 0.005 yuan in the cost per bag. Compared with the former two structures, its advantage is still more obvious.