Thermoshrinkable polyester film and preparation method thereof

Abstract

The invention discloses a thermoshrinkable polyester film and a preparation method thereof. The preparation method comprises steps as follows: various polyester raw materials subjected to dust removal respectively enter storage bins, are respectively metered by an agravic weigher according to the proportion, simultaneously enter an inlet of a double screw extruder, are subjected to melt extrusion by a sandwich layer double screw extruder and two surface layer double screw extruders, and form a casting piece through a three-layer co-extrusion die head; the casting piece is respectively subjected to longitudinal stretching and lateral stretching, wherein the longitudinal stretching comprises a preheating zone, a stretching zone, a thermal setting zone and a cooling zone, and the thermal setting zone of the lateral stretching is more than 15m long; and the casting piece is subjected to traction rolling to obtain the thermoshrinkable polyester film. By adopting the proportioning mode of directly feeding after accurate metering by people, the instantaneous addition error range of various materials is at most 1%; and the material is biaxially stretched, so that the produced film has the advantages of greatly higher density, strength and uniformity, lower longitudinal shrinkage and lateral low-temperature shrinkage, and especially higher ductility and thermoshrinkable uniformity.

Description

technical field [0001] The invention relates to the technical field of heat-shrinkable polyester films, and also relates to a preparation method of heat-shrinkable polyester films. Background technique [0002] Heat shrinkable film is widely used due to its ability to shrink when heated at a predetermined temperature, such as: labeling bottles, packaging batteries, packaging containers and other products. Commonly used heat shrinkable films are made of polyvinyl chloride (PVC), polystyrene (OPS) or polyester (PET). [0003] Since heat shrinkable films made of PVC and OPS are relatively poor in terms of shrinkage and printing and dyeing properties, especially when incinerated, they will emit toxic pollutants, which do not conform to the development direction of green industry, and have been gradually banned. PET heat shrinkable film has attracted people's attention because of its excellent heat resistance, chemical resistance, shrinkage and printing and dyeing properties. It...

AI Technical Summary

Problems solved by technology

However, during the long-term research and experiment process of the heat-shrinkable polyester film, the inventors found that this traditional mixing method, due to the differences in the density, particle size, and particle shape of different raw materials in the polyester raw materials, would be mixed in the mixer. Chromatographic phenomena will occur during the process of evenly sending the air to the buffer silo, the process of falling gravity from the buffer silo, or the process of boiling forward in the pre-crystallizer and falling gravity in the drying tower, which will cause the raw materials to separate again and lead to uniform mixing. The property is greatly reduced, which directly affects the uniformity of the film

And especially when the proportion of a certain ingredient in the proportioning ingredients is small (less than 10%), it is more difficult to achieve the purpose of uniform mixing by means of agitator mixing

[0005] Since the heat-shrinkable polyester film requires a large transverse shrinkage rate, the current domestic and foreign heat-shrinkable polyester film production lines all adopt the unidirectional stretching process, that is, generally only transverse stretching is adopted, including preheating, stretching, heat setting and Cooling, where the length of heat setting is generally less than 9 meters, the speed of the production line is low, generally <60m / min, because only unidirectional stretching is performed, it is difficult to effectively control the performance of the product in the unstretched direction, which will lead to uneven shrinkage

Moreover, the current heat-shrinkable polyester film generally still has a certain shrinkage rate at low temperatures. Generally, it is treated at a constant temperature at 40°C for 24 hours, and the shrinkage rate in the main shrinkage direction is ≥ 1%, which leads to the shrinkage rate of the heat-shrinkable polyester film during storage and transportation. , due to shrinkage, the heat-shrinkable polyester film will appear curled and uneven before use, which will affect the use and even affect the quality of use

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