There are many kinds of foam materials, and most thermoplastics and thermosetting plastics can be processed into foam materials. Thermoplastic foam material refers to high molecular polymer (plastic, rubber, elastic

Microporous materials with numerous bubbles inside them can also be regarded as composite materials with gas as filler. The four major molding processes of thermoplastic foam materials are described below.

1. Molding

Compression molding belongs to an earlier type of foaming process, so there is no standardized abbreviation for molding foaming. Until the emergence of polypropylene molded foam materials in recent years, it was dubbed the

"M", defined as "MPP".

In recent years, MPP has emerged, and Jihu is a kind of foamed PP created by our country. Its manufacturing process is based on the press as the key equipment for foaming, which has no essential difference from traditional molding foam in principle.

At the same time, the key difference is that the foaming agent is not a traditional AC chemical foaming agent, but supercritical CO2, so the foaming ratio can be as high as 20 times, which is very environmentally friendly. specific manufacturing

The method is to first use various processing techniques such as mixing, stretching, extrusion, etc. to make PP into sheets of different thicknesses, then cut these sheets and place them in the mold of a large press, close

chess. The upper and lower templates of the press are heated to raise the temperature of the PP sheet to near the melting point of PP, and at the same time, supercritical CO2 is injected into the mold from different directions to fully impregnate the PP sheet.

Then, the temperature of the PP sheet is lowered to a temperature suitable for foaming, the pressure of the press is quickly released, and the PP sheet is fully foamed and cooled to obtain an MPP foamed sheet.

The advantages of MPP product manufacturing and products are: impregnation in solid form; lower requirements for PP melt strength; easy control of foaming process; fine and uniform product cells; material mechanical properties

Excellent; supercritical CO2 is environmentally friendly and does not burn. But the deficiencies are also relatively clear, such as: slow impregnation; must go through the pre-processing process of making thin plates; affected by the crystallinity of polypropylene

The impact is great: the production by the press is not only discontinuous, but also has low efficiency and is difficult to large-scale industrialization; the application field is not very clear; it is a process with high manufacturing cost in foamed PP.

2. Expandable bead molding

Expandable bead molding process, that is, in an autoclave, within a certain period of time, the physical blowing agent is impregnated into the fine particles of the matrix resin by high pressure at a predetermined temperature, and then

Cool the temperature of the system to room temperature to obtain expandable beads. When using, firstly at a certain foaming temperature, use water vapor or hot air to pre-foam the expandable beads to obtain a large mung bean.

Small pre-foamed expandable beads. When preparing the product, put the pre-foamed expandable beads into the mold for heating and decompression, so that the pre-foamed expandable plastic beads are further expanded and melted.

Combined to form a predetermined shape of the foam material, which is called expandable bead molding. Due to the use of physical foaming agents, the foaming ratio is relatively large.

3. Extrusion foam molding

Add plastic and foaming agent (physical or chemical) to different positions of the extruder, press down and melt in the extruder to form a uniform solution, and then suddenly release pressure, foam, and cool at the die.

However, it is made into plates, sheets and even pipes. In the extrusion foaming process, the foaming agent must form a uniform solution with the plastic under high pressure, and instantly release the pressure at the die, foam, and cool down.

However, it is impossible to form a foamed material by means of solid phase or crystallization restraint, so the melt strength of the plastic is required to be very high, especially the melt has a strong strain hardness during the stretching process.

Therefore, foaming is more difficult.

Fourth, injection foam molding

Injection molding foam material is a relatively late development of foam material, mainly because of the contradiction between the traditional injection molding process and the necessary conditions for foaming. Today's injection molding foam materials are limited to foam times

Products with a very low rate, even foaming is not the main purpose, but only to reduce the shrinkage and shape of injection molded products, especially in the injection molding of large products such as trays and brackets.



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