Milk is a very common food in our daily lives. But I don't know if you have noticed the packaging of milk, especially in the form of soft packaging. This article will provide a brief analysis of the soft packaging of milk, and hope to inspire friends who are ready to join the relevant industry.
Common milk soft packaging is divided into two categories: all-plastic soft bag packaging and paper-plastic composite packaging. These two categories can continue to be subdivided into several different types. We will introduce one by one.
Film knowledge: Talking about milk soft packaging
Pure PE black and white film
Pure PE black and white film is the earliest form of milk soft packaging. It is generally produced by a three-layer co-extrusion blown film process. Depending on the equipment, it is also possible to produce a five-layer or even seven-layer co-extrusion blown film structure. As the name suggests, this film is white on the outside and black on the inside. The purpose of this design is to print on the outer white background; at the same time, the inner black is used to achieve a certain light-proof effect, and the shelf life of the milk is extended. Milk is a high-value content and therefore requires a high level of packaging strength. Therefore, 1MI linearity is often used with a small amount of low-melting high pressure production, and a certain amount of metallocene is added to the heat seal layer to ensure heat sealing effect.
EVOH co-extruded black and white film
An EVOH barrier layer was added to the EVOH co-extruded black and white film relative to the pure PE black and white film. Therefore, at least five layers of co-extruded structure are required for production. In fact, many manufacturers are already using a seven-layer coextrusion structure to optimize the functional design of each layer. The choice of binder resin is a key consideration in the design of EVOH co-extruded black and white film formulations. The improper selection of the binder resin causes insufficient EVOH adhesion, delamination, and water ripple. Compared with pure PE black and white film, the barrier property of EVOH co-extruded black and white film has been greatly improved. Therefore, it is commonly used in summer and autumn, when the temperature is high, the milk is packaged.
The roof pack is named after its sloping roof shaped like a roof. This milk package has a beautiful appearance, good shelf display and easy opening. The packaging material has a simple structure and is generally PE coated cardboard. Just because the processing temperature of the PE lamination process is high, it is necessary to select the production of the coated PE with low odor. Because there is no barrier property, the roof pack is only suitable for pasteurized milk that needs to be stored refrigerated.
Tetra Pak is a rapidly growing form of milk packaging in recent years. It is a paper aluminum-plastic composite structural package invented by Tetra Pak. According to the shape, it can be subdivided into Tetra Pak, Tetra Pak, Tetra Pak, etc. Due to the expiration of Tetra Pak's patents, a large number of domestic Tetra Pak production plants have emerged in recent years. The packaging materials of Tetra Pak are processed by a multi-head co-extrusion coating process.
The first step: bonding the printed paper and the aluminum foil by LDPE lamination, and obtaining a "paper/LDPE/aluminum foil" structure;
The second step: co-extruding the Eaa/heat-sealed PE on the aluminum foil side to obtain the structure of â€œpaper/LDPE/aluminum foil/Eaa/heat-sealed PEâ€;
The third step: the outer side of the paper is coated with the outer side of the LDPE protection to obtain the final product "LDPE / paper / LDPE / aluminum foil / Eaa / heat seal PE" structure.
Since the back seal of the Tetra Pak package is a lap seal structure, special heat seals are required during the packaging process to enhance the back seal strength.
SIG Combibloc was promoted by SIG. The packaging material structure of SIG Combibloc is similar to the Tetra Pak package, so it can theoretically be produced using the same multi-head co-extrusion coating equipment. However, in general, the paper thickness of the SIG Combibloc is thicker, and the requirements for heat-sealing PE are different for the different heat-sealing methods. The heat seal of SIG Combibloc is achieved by hot air purging the hot cover, so the low temperature unsealing performance of the heat seal layer is more demanding. Therefore, the heat-sealing PE of SIG Combibloc generally requires the use of polyolefin plastomers to meet the requirements.
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