Different requirements of the film, blow molding process is also different
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The blown film is formed by extruding the plastic into a thin tube (tube blank), and then inflating it with compressed air (gauge pressure 0.02 to 0.03 MPa), and cooling the shaped film product. The following describes the differences in specifications, processes, and blow molding methods for blown films of different needs.
The types of films produced by blow molding mainly include: HPVC, SPVC, LDPE, HDPE, PP, PS, PA, EVA, PVA, and the like.
Specification difference
1. The general specifications of blown film are: thickness 0.01~0.25mm, and the diameter is 10~5000mm.
2, the common specifications of small packaging blown film: thickness 0.01 ~ 0.25mm, folding diameter 20 ~ 40mm.
The difference between the blow molding process
1. The process flow of blown film is: material plasticizing extrusion → forming tube blank → inflation molding → cooling → traction → coiling.
2. The process of blown film that needs to be printed is: material plasticizing extrusion → forming tube blank → inflation molding → cooling → herringbone frame → nip roller → corona treatment → film guide roller → coiling.
The difference in blow molding
The blown film is generally classified into an upper blow method, a flat blow method, and a down blow method.
Up-blowing method: adopts a right-angle head, the discharge direction of the extruder is perpendicular to the extruder, and the film bubble tube is inflated and formed above the machine head. Mainly used in the production of large-size polyethylene film.
Flat Blowing Method: The horizontal machine head is used. The film bubble tube is on the same horizontal line as the center line of the machine head. It is generally used to produce small and medium-sized polyethylene and polystyrene blown film.
Blowing method: the right angle head is used, and the film bubble tube is below the head, perpendicular to the horizontal direction. This process is suitable for producing resin with small viscosity and good fluidity. Cooling must use tap water or cooling water as cooling medium, such as poly Resin such as propylene, nylon or polyvinylidene chloride.
The advantages of the upper blowing method are: the shape of the bubble tube is stable; the equipment has a small footprint; the product has a large specification and a large thickness; and the cooling process is long. The disadvantages are: high floor height is required; it is not suitable for raw materials with low viscosity; the product specification range is narrow; the right angle head is easy to decompose auxiliary machine, which is more complicated.
The advantages of the flat blowing method are: easy film introduction and convenient operation; the film thickness is relatively uniform; the inflation ratio is large and the strength is high. The disadvantages are: the equipment covers a large area; it is not suitable for the production of large-size films; it is not suitable for raw materials with low viscosity.
The advantage of the down-blowing method is that it is advantageous for film cooling; it is suitable for raw materials with small viscosity and high fluidity; and the product has good transparency. Disadvantages: not suitable for the production of thicker film; installation and construction costs; operation is not convenient.