FIELD: chemical industry.
SUBSTANCE: the invention presents a method and a device for extrusion of a tubular film and is dealt with the field of chemical industry, in particular with production of a tubular film by means of coextrusion of at least one thermoplastic polymeric material "A" with at least two thermoplastic polymeric materials "B" and "C", the yield factor of the melt of which is at least twice as much as that of "A". At that a material of "B" is applied on one side, and a material of "C" - on other side of a material of "A". Coextrusion is exercised using a circular lower die having at least by one inlet opening for each of the materials and a common outlet channel, ending in a circular discharge opening. One or all inlet openings are located closer to the circular lower die axis, than the discharge opening. Extruded materials in a molten state are running out to the outlet opening. Process of giving a form to each flow of each material is defined by chosen positions of the first parts of the lower die having planar or conical surfaces. The parts of the lower die are pressed one to another with alignment of their surfaces supplied with grooves to form a flow of each polymeric material so that to level the flow along the circumference of the outlet opening. At that at least the flow of a material "A" between one inlet opening and the outlet opening or between each inlet opening and the outlet opening is divided into on a series of separate flows of near the spiral form at least on a section of each channel having a space provided for a spill over between the spiral sections and separate streams with the overflow streams gradually forming one common circular flow. The point of conjunction of streams of materials "A" and "B" is taken in the same place used for conjunction of streams of materials "A" and "C" or very close to it. At that the material "A" is running outside in respect to the lower die axis directly before its conjunction with materials "B" and "C", as materials "B" and "C" at the same time are running in directions meeting each other directly before that conjunction. The invention ensures the circular alignment of a material in the spiral grooves at extrusion of a tubular film with the surface layers having a considerably higher yield factor of the melt as compared with the one of the inner layer.
EFFECT: the invention ensures the circular alignment of a material in the spiral grooves at extrusion of a tubular film with the surface layers having a considerably higher yield factor of the melt than one of the inner layer.
38 cl, 14 dwg
