Plastic Injection Molding Machine
The one major advantage of the direct blow molding method is ability to mold multilayer. The multilayer molding is to create and mold multilayer at once by using various plastic resins; thus, this molding method gives
additional values to the products.
The plastic has various functions depending on the kinds. The plastic resins commonly used for the direct blow molding are HDPE (high density polyethylene), LDPE（low density polyethylene), PP (polypropylene) that are
inexpensive and easy-to-use type; yet, their weakness sides are easily oxidized and less glossy finish. Making up for their weaknesses, the high function plastic resin such as EVOH (ethylene-vinyl alcohol copolymer) and
PA (polyamide) that high antioxidant and glossy finish type are used for the multilayer molding. Unfortunately, those high functional type plastics are also high in their price; therefore, molding product only using
those types of plastic rises a unit cost per product. Comparing to the commonly used plastics, a molding difficulty only using high functional plastics is higher and unsuitable for molding at all. So, the multilayer
molding is developed; as for this molding style, high functioning plastics are used for minimum amount and the commonly used plastics are used for the rest.
The multilayer molding machines extrude layered parison. The direct molding machines are usually equipped with one extruder; the machines capable of the multilayer molding have more than one extruder depending on the required number of plastics resins. Various plastics resins are flowing into the Head unit via each extruder to become one multilayered parison. Once multilayered parison is extruded, it goes same molding manner as single-layer molding machines.