Preparation Process
DATE：2022/2/17 8:47:34 / READ： / SOURCE：This station
Preparation Process
(1) Extrude PP into the extruder. After a certain temperature and time, under the action of the rotating shear force of the screw, the pellets are melted and metered and then quantitatively fed into the filter. The extrusion temperature can be adjusted at 230-280℃, but on the premise that the material can be uniformly plasticized, the temperature control should be lower, and the material degradation caused by the high temperature and the long heating time of the material should be avoided as much as possible.
(2) Filtration of PP fresh material, edge material, recycled material, remanufactured material, recycled material, etc. all contain impure impurities, infusible materials, etc. These infusibles must be filtered out with a filter screen and cannot enter the die and mix into the thick sheet. The filter should be properly selected. Although the mesh size is too high and the mesh is too fine, although it is good for the extrusion of thick sheets, it will increase the frequency of replacing the filter and increase the consumption of raw materials; if the mesh is too large, the impurities will not be filtered cleanly, and will be mixed into the thick sheet. It will cause the membrane to be broken by transverse pulling. Generally, a slightly higher mesh should be selected, and the filter should be replaced every 7 to 10 times.
(3) The casting material of the die head enters the die head after filtration, and the die head is divided into two types: the flat film method T-shaped and the tubular film method round. To produce different products, it is necessary to use a single-layer die or a multi-layer co-extrusion die respectively, and adjust the distribution through the "black box" material channel above the die head, so that different materials flow out from the lip according to different layered flow channels, so that the The slabs can be layered differently as desired. Through the transformation of "black box" and die head, single-layer, two-layer, three-layer, five-layer and seven-layer co-extruded composite thick sheets can be produced. Die head and lip can be adjusted manually or automatically according to the thickness distribution feedback information of thick sheets and products, so as to make uniform thick sheets.
(4) Quench forming isotactic PP is a crystalline polymer with a maximum crystallization temperature of 90°C. The molten material is extruded from the lip and flows to the surface of the rotating quench forming roller through a gap of several millimeters. Under the co-cooling of a cold surface, a water bath (or air), the material up to 250°C is quenched to room temperature to form a thick, almost transparent amorphous sheet with very small crystallites. The quality of the thick sheet is the key to film formation. The film rupture phenomenon often occurs in the transverse stretching process, and the main reason for the film rupture is the poor quality of the thick sheet. The ideal thick sheet should have the characteristics of flat surface, uniform thickness, straight edge, no bubbles, no impurities and "fish eyes", and almost transparent. A good thick sheet has strong adaptability to the stretching process, high film forming rate and good product quality.
Author：admin