The development for blow molding machine

Blow molding is a plastic process where a thermoplastic resin is heated to its forming temperature, at material melting point it is made to form a hollow tube called parison or preform. In the beverage packaging industry, blow molding process is more widely used, and many plastic bottles are produced through the technology.

The heated plastic material is placed between two femal molds that are cooled by some medium. The blow molds close on the heated parison or preform and a gas, usually air enters via an open end of the plastic prefom via a blow pin or needle. The gas is flown into the closed female mold halves, to take the shape of the internal female closed mold, to make the bottle preform blow up to bottle. The bottle mold are then separeated and the cooled, bottle is allowed to drop out and repeat.

Over 100 years ago, to blow mold hollow objects, two sheets of cellulose nitrate were clamped between two female mold halves. Steam injected to soften the material, seal female mold halves and stretch the heated sheets to form the inside shape. But the high flammability of cellulose nitrate limited the usefulness of this technology.

In the early 1930s, more suitable materials, such as cellulose acetate and polystyrene(PS) come into the world. Unfortunately, because of the high cost and poor performance, limites the process.Finally, in the early 1950s, high density polyethylene(HDPE) was devloped and now blow molding is the largest user of HDPE, which is the largest volume thermoplastic produced in the world.

Now, most thermoplastic resins are suitable for plastic bottle blowing mould. Naturally, several are the leaders. In the year of 2000, HDPE is over 57% for blow molding marketing and PET follows with 33% market. So these two plastic resins are used over 90% of the blow-molding industry. All the other thermoplastic resins such as PP, PS, PVC…all combine for other uses in the approximate 10% blow-molded industry.

Regularly, the choice of material used is on the basis of performance, cost, barrier, availability,cleanliness, processing, transparency and strength. In the rapid growing markets at present are the automotive gasoline tanks, the 55-gallon drums(both HDPE) and the 20-oz soft drink products, the pint milk bottle(both PET), and the beer market is just starting with specialty marketing.