Molding, properties and application of polypropylene foam

Molding, properties and application of polypropylene foam

A plastic foam is used as a basic component to fill a large number of bubbles by physical or chemical means to obtain a foam. Compared with pure plastic, it has a series of characteristics such as low density, high specific strength, strong energy absorption capacity and good sound insulation performance. It has been widely used in transportation, military, aerospace, daily necessities, etc. Various cushions, cushions, mattresses, comb cores, thermal insulation materials, packaging materials, anti-collision and shockproof materials, decorative materials and building materials. As people's understanding of foam plastics deepens, new varieties will be continuously developed and their application range will be further expanded.
In recent years, the development of foam plastics has been rapid. In the United States, Japan, Europe and other countries and regions, both production and variety are increasing rapidly. The foams which have been industrially produced include polystyrene (PS), polyvinyl chloride (PVC), polyurethane (PUR), ABS, phenolic, urea-formaldehyde, epoxy resin, polycarbonate (PC) and the like. Polypropylene (PP) has good performance and low price. PP foam can be made by physical or chemical foaming. Since JSP first developed PP foam in 1982, JSP, BASF and GEFINEX are available worldwide. Many of the company's factories are producing PP foam, and the annual sales have reached hundreds of thousands of tons.
1 Forming of polypropylene foam plastic According to the source of foaming power in foam plastic foam molding, it can be generally divided into three types: mechanical foaming, physical foaming and chemical foaming. Mechanical foaming is by means of mechanical strong agitation, and the gas is uniformly mixed into the resin to form bubbles. Physical foaming is the formation of a large number of bubbles by means of a change in the physical state of the blowing agent in the resin. Chemical foaming is a process in which a chemical is changed by a blowing agent to generate a gas to foam the resin. Most of the PP foaming is chemical foaming, and the foaming agents used are azodicarbonamide, diisopropyl azodicarboxylate, etc., and nitrogen can also be used as a physical foaming agent for physical foaming.
The foaming process of foam can generally be divided into two stages: firstly, a large number of uniform and fine bubble nuclei are formed in a plastic melt or liquid, and then expanded into a desired bubble structure, and finally the solidification stereotypes the bubble structure. Fix it and get the foam.
Commonly used molding methods for PP foams include extrusion, injection molding, and compression molding.
Extrusion molding is one of the main methods of foam molding processing. Generally, foamed products such as profiled materials, plates, pipes, diaphragms, and cable insulation layers are extruded. Two kinds of foaming methods, physical foaming or chemical foaming, can be used in the extrusion molding process. Physical foaming mainly uses some fluorocarbons and their mixtures, as well as other low-boiling liquids. In addition, the physical foaming method of directly injecting gas is also applied in the extrusion molding process of PP foam. The process parameters affecting the extrusion foaming mainly include: extrusion pressure, extrusion temperature, residence time of the material in the extruder, axial pressure of the die, and the like. In general, as the extrusion pressure increases, the cell size decreases and the number of cells increases; high quality foams are only available in a narrow temperature range. The higher the melt temperature, the lower the polymer melt strength, and the foaming pressure within the bubble may exceed the surface tension of the foam to cause the foam to rupture. It must be optimized according to the specific polymer system to determine a suitable foaming temperature. Extending the residence time of the material in the extruder increases the number of bubbles.
Injection foam molding is a one-step molding method, which simplifies the manufacturing process of foamed plastic products. It is characterized by high output and good quality, and is especially suitable for products with complicated shapes and high dimensional accuracy requirements. There are three main factors affecting the quality of injection molded foam products: material formulation, molding equipment and process conditions. After the material formulation and molding equipment are determined, the main factor determining the performance of the product is the process conditions. Pressure, temperature and time are the most important process conditions. Whether the dissolved gas in the polymer melt can be freed to form bubbles, and whether the bubbles formed in the melt can be stabilized are closely related to the melt pressure because the pressure of the melt directly affects the gas in the melt. Solubility. As the external pressure of the melt increases, the solubility of the gas in the melt increases, the amount of supersaturated gas in the melt decreases, and the radius of the bubble decreases. The change in pressure is very sensitive to the effects of bubble growth or collapse in the melt, and it is very effective to adjust the foaming process by controlling the pressure. The physical state of the polymer is a function of temperature. Determining the appropriate temperature is very important for foam molding. The main temperature-related process parameters are barrel temperature and mold temperature. In general, increasing the outlet temperature of the melt is conducive to the growth of bubbles, but if the temperature of the melt is too high, it will not only cause degradation of the polymer, but also cause a drop in melt viscosity. In general, the melt temperature is high, the bubble diameter is increased, and the number of bubbles is reduced. The expansion ratio of the product generally decreases with the decrease of the mold temperature. Increasing the mold temperature can improve the flow condition of the melt in the mold, and can also improve the surface quality of the product and increase the expansion ratio of the product. However, the time for cooling and setting will be prolonged, which is not conducive to improving labor productivity. The injection rate has a great influence on the cell uniformity, foaming ratio and surface quality of the foamed product. The high-speed filling of the polymer melt can obtain cells of uniform size, and the injection rate can significantly increase the expansion ratio of the product.
PP foam can also be molded by a molding process, and the foam molding process can be divided into a one-step process and a two-step process. The one-step foaming process is completed in one time. After the materials are mixed by the ingredients, the blank is molded, and then heated and pressure-foamed to obtain a foamed plastic product. The basic procedure of the two-step method is similar to the one-step method. After one foaming, a part of the foaming agent is decomposed to partially foam the material, and then cooled, and the second foaming is performed under normal pressure.

Women Short Pants:we have two styles for ur choies,the main fabric is made of 100%Lyocell and 100viscose,if u have other design,please also send to us.we will according to ur requirements to do well.there are simple design but fabric is very soft and comfortable,if u wear it,it will cool ,anyother requirements,please also tell us ,we will try our best to do well.