Packaging Container Structural Design and Manufacturing - Plastic Containers (2)

Chapter 3 Blow Molding Containers

Section 1 Overview <br> First, the concept (P152)
The semi-molten tube (or parison) obtained by extrusion or injection molding is placed in a mold, then the mold is closed, compressed air is blown into the tube billet to inflate it so that it is closely attached to the wall of the mold cavity, After cooling and demolition to obtain a certain form of hollow products, a processing method.

Second, hollow blow molding classification and process characteristics

According to the different preparation of parisons, they can be divided into two categories:
Extrusion blow molding: extrusion - stretching - blow molding;
Injection blow molding: injection - stretching - blow molding

1Definition:
Pellets (or powders) of thermoplastics are plasticized through an extruder and passed through a specific die to prepare a hot-melt tubular parison, which is then blow molded.

2 Classification: (different points according to the way of discharging)

a. Direct extrusion blow molding:
It refers to a parison made by directly extruding TP through an extruder through a die. A method of forming a material container by blow molding.

Features: Simple equipment, low cost, easy implementation, low investment, quick start; but in the semi-molten parison, the extrusion process is easy to squat, resulting in significant uneven wall thickness. Suitable for producing small containers.

b. The storage cylinder type extrusion blow molding is between the extruder and the die head, and an additional storage cylinder is provided (the cross section of the storage cylinder may be circular or circular), and the extruder will continuously plasticize. The plastic melt is fed into the storage tank. After the material in the storage tank reaches a certain amount, the extruder stops running, and the plunger in the storage tank moves forward quickly, so that the melted plastic is formed by the die head. Billet.

Features: Small equipment can produce large containers to ensure the uniformity of wall thickness but the equipment is More complex, the investment is more direct, and the extrusion is large.

3 Features:

High production efficiency, uniform parison temperature, less welding seams, larger allowable range of shape, size and wall thickness for hollow containers, wide adaptability, high strength of blow molding products, simple equipment, and low investment. However, the accuracy of products is not high.

1 Definition (process)
Using a split mold to inject the parison onto the mandrel, after the parison is properly cooled (the surface of the parison is solidified, and the shape of the parison is not deformed or deformed when the mandrel is moved), the mandrel and parison are formed. It is sent to the blow mold together, the blow mold is closed, compressed air is introduced through the core rod, the parison is blown to form the desired product, and the product is removed after cooling and setting.

2 features:
The product has no seams, no post-repair, high precision of thread or bottle mouth size, no need for finishing, high output, less auxiliary equipment, high strength at the bottom of the product, less material loss, uniform wall thickness, and high production efficiency. However, the equipment investment is large, the processing production cycle is long, and the operators are highly demanded, the shape cannot be too complicated, and the container size is limited (the height of the container cannot be too high). Suitable for the production of small precision containers.

1 Definition (process)
In a specific temperature range, the parison is forced to be extended and molded, and at the same time, the macromolecules are aligned in the wall of the product and fixed, thereby greatly improving the performance of the plastic container.
A bottomed parison heated to a suitable temperature or less and placed in a mold, and the light is stretched in the axial direction by a stretching rod, and immediately blow-molded.

2 features:
Reduce waste, high production efficiency, and easy weight control. The product has high impact toughness, high rigidity, improved transparency and gloss, and good barrier and air tightness. However, high temperature control is required for stretching and equipment investment is large. Suitable for producing small containers with simple shapes.

1Definition (principle)
Using a multi-layer composite parison, a blow molding process is used to prepare a multi-layer container molding method. Through reasonable matching of various plastic layers, effective complementarity of the plastic properties of the layers is achieved, thereby overcoming certain inherent disadvantages of single-layer plastic containers.

2 Purpose: (To improve the overall performance of the product)
a. Improve the physical and mechanical properties of plastic containers;
b. Improve container performance;
c. Shading
d. Thermal insulation
e. Reduce flammability
f. Printability

Third, blow molding commonly used materials

For example, HDPE, LDPE, LLDPE, PP, PET, PVC, PS, etc., in which PE accounts for 90%, now PP, PET are used in a large number of round bottles, and the following characteristics should be considered when selecting plastic varieties: