Molding Process of blown film
The molding process of blown film, protective film manufacturer ichuan film will take you to learn more about it:
1. Requirements for raw materials: polyethylene blown film mainly includes heavy packaging film, General packaging film and agricultural film according to the use requirements. Melt index for molecular weight of polyethylene resin (MI)The size of. If the melt index is small, its molecular weight is high and its tensile strength is also high. On the contrary, if the melt index is large, its molecular weight is low and its tensile strength is also low.2. Uniformity of head annular gap: the uniformity of head annular gap directly affects the uniformity of product thickness. It has an important influence on the quality of products. The die gap is generally 0. 6 ~ 1mmm, use steel feeler gauge to adjust the annular gap of the die to ensure uniform punishment. Temperature control: PE has good thermal stability. <300 ° C is not easy to decompose without contact with oxygen. >Contact with oxygen at 300 ℃ is easy to cause crosslinking. Polyolefin blown film generally has a higher temperature than the head temperature, and PE has good thermal stability, because Olefin is not easy to decompose, the body temperature is high, plasticization is sufficient, fluidity is good, while the head temperature is low, and the film is easy to shape. The temperature of LDPE Hopper should not be too high to prevent adhesion of granular materials. The temperature of barrel can reach 180 ℃, and the temperature of handpiece can be 10 ~ lower than that of fuselage ~ If the molding temperature is not too high or too low at 20℃, the film cannot be fully plasticized, resulting in irregular material flow and smooth expansion and stretching. This is because the tensile strength of the film is also low, and the surface gloss is poor, the transparency is reduced, and even the patterns like wood rings and unmelted crystal nuclei (Fisheye). At this time, the impact strength of the film also decreases, and the welding seam of the film is obvious in severe cases. After the belt is stable, adjust the traction ratio to make the thickness uniform. Uneven film thickness, adjusting bolts, uneven layout can be adjusted by air volume. The protective film manufacturer ichuan film is the latter to reduce the air volume of the Air ring. The air volume decreases, the local temperature increases, and the compressed air expands further to solve the uneven local thickness. However, the head temperature must be uniform. 3. Temperature: Temperature control is the key in blow molding film process and an important parameter affecting quality. The advantage of this temperature control method is that the high temperature of the material is short and it is not easy to decompose, which can reduce the number of disassembling the head and improve the production capacity of the machine (See table 1). 4. Cooling and setting: When the tube bubble is just extruded from the handpiece, the temperature is relatively high and becomes a semi-flowing state. Now the cooling capacity is insufficient, and the film is bonded to each other under the pressure of the traction roller, and the host capacity cannot be volatilized. The air supply volume around the cooling air ring shall be uniform, otherwise the film thickness shall be uneven, otherwise the film thickness shall be uneven. The distance between the wind ring and the die is 30 ~ 100mm. 5. Drafting multiple: the ratio of traction speed to extrusion linear speed forms a traction ratio, which is usually controlled at 4- 6. The traction ratio is the longitudinal drafting multiple, which is generally controlled at 2. 5- 3, this is easier to operate, and the vertical and horizontal strength of the film is similar. If the inflation ratio is too large, the inflation film will swing like a snake, and it is difficult to control the uniformity of thickness.