Views:2 Author:Site Editor Publish Time: 2021-07-19 Origin:Site
Using high-melt-strength branched EVA foam as the foaming material or main component is a direct and simple way to make EVA foam have good foaming properties. The branched PP resin has a higher melt strength than ordinary PP, which is developed and industrially produced by Montell Company in Belgium. The melt strength of the pro-faxpf-814 resin produced by the company is 9 times that of ordinary linear PP. Since then, a large number of HMSPP products have been developed and widely used in these fields by other countries and companies. The research situation of foreign EVA foam material extrusion foaming is reported. The physical foaming properties of linear EVA foam and branched EVA foam were compared. Under the same experimental conditions, the foaming characteristics of the two materials show great differences: when linear PP is foamed, even if it is quenched with water, the opening of the bubbles is still very high, and the bubbles are connected to each other, while the branched PP There is very little bubble coalescence. It can be seen that the influence of melt strength on foaming performance is very obvious. In addition to the direct use of high melt strength PP, in order to reduce costs, ordinary PP can also be blended and modified to improve the melt strength of the system. , Respectively use 10%～15%HMSPP to blend homopolymer and copolymer PP.
The material with homopolymer PP as the resin matrix has higher rigidity, but the foaming rate and toughness of the material are not as good as the copolymer PP system, which mainly depends on the higher crystallinity of homopolymer PP, which improves the foaming rate and Improved the toughness of the foamed material. The foaming effects of hp-20p, ep1755 and RA three chemical foaming agents were compared. Among them, hp-20p and ep1755 are endothermic blowing agents. Once the heating is stopped, the blowing agent will stop decomposing, and the shape of the material will be reflected as small bubbles. RA is an exothermic blowing agent, which can continue to decompose without absorbing heat, resulting in an increase in bubble diameter. As the domestic production of high melt strength PP is still blank, in order to improve the melt strength, domestic research on PP foaming mainly focuses on the chemical crosslinking of PP, with dicumyl peroxide (DCP) as the crosslinking agent , Divinylbenzene is a co-crosslinking agent. The effects of different components and process conditions on the properties of foamed EVA foam extruded profiles were studied. Through orthogonal design, it is found that AC foaming agent, crosslinking agent, nucleating agent and foaming agent PBST have a greater influence on the tensile strength of the product. Foaming agent (AC) and cross-linking agent (DCP) were used to study the influence of process conditions on the PP extrusion foaming process.
The results show that the design of the extruder head has an important influence on the foaming form of the product. If the die design of the extruder head is unreasonable, there will be pressure loss between the screw and the die, which will easily cause the melt to foam in advance, causing the melt to explode and expand after leaving the die, causing the melt to rupture. At the same time, the screw speed also has a great influence on the product quality. If the screw speed is too low, the head back pressure is low, which is likely to cause premature foaming. When the screw speed is too high, melt slip will occur, resulting in unstable melt flow and ultimately melt fracture. In terms of temperature, on the one hand, the higher the temperature, the lower the solubility of the gas in the melt, which is likely to cause early foaming; on the other hand, the higher the temperature, the lower the melt strength, which is not conducive to the formation of unit cells, so the mold temperature Should be as low as possible. At present, the foam materials used in sports equipment mainly include PU, PS, PVC and polyolefin. However, the CFCs used in the molding process of PS foam products will destroy the atmospheric ozone layer, the products will not rot, are difficult to recycle, and cause "white pollution" to the surrounding environment; polyurethane foam has harmful isocyanate residues during the foaming process, and the foamed materials cannot be recycled use.
PVC stabilizers contain heavy metal lead, and there is an urgent need to find alternatives to the above foaming materials. EVA foam has attracted much attention due to its good thermal stability and dimensional stability, as well as higher toughness, tensile strength and high-temperature impact strength. It has attracted the attention of sports equipment suppliers for its suitable surface and soft surface, biodegradability and environmental adaptability. Foamed PP has excellent heat resistance, hygiene and heat insulation. In terms of sporting goods, foamed PP is an ideal material for floating life-saving equipment. It can be used for life jackets, lifebuoy core materials, surfboards, swimming materials for seaside swimming pools, swimming pool covers, etc. Surfboards can be made of PP foam boards produced in the United States. Gymnastics blankets, wall mats, sports mats, etc. have good energy absorption properties. It has broad market prospects in the field of sports. Relevant departments should establish EVA foam foam sheet production technology projects as much as possible, speed up research and development, and create conditions for the promotion and application of foam EVA foam in my country. The rapid growth of the market scale will attract more companies, but technical barriers, especially the requirements of EVA foam materials for recycling performance, as well as scale and capital barriers, will restrict the entry of small companies with insufficient production capacity.
Although there is no product standard in the EVA foam material industry, the downstream industry's requirements for various products, especially the increasingly stringent export standards, have also formed strong constraints on EVA foam materials. Therefore, manufacturers that meet various downstream standards will be in a more advantageous position in the competition. EVA foot pads are simple in shape and are mainly produced by the production department: foam-mounted rubber strips and perforated packaging. It is mainly applied to the bottom of various electronic products, such as: small voice, computer phone, auto parts, crafts, etc. Main function: high protection shockproof and non-slip mat. EVA rubber and plastic products are a new type of environmentally friendly plastic packaging material, which has the advantages of cushioning, shock resistance, heat insulation, moisture resistance, chemical resistance, non-toxic and non-absorbent. EVA rubber and plastic products can be designed and processed, and its shockproof performance is better than traditional packaging materials such as polystyrene (foam). The main downstream industries of EVA foam materials, namely shoes, bags, toys, sporting goods, building materials, etc., are all traditionally strong industries in my country's manufacturing industry. Driven by domestic demand and further improvement in the export market, these industries are expected to maintain growth of more than 10% in the next three years. The footwear market and the luggage market are the main downstream markets for EVA foam materials. In 2010, the Chinese market consumed about 70% of EVA foam materials. In 2010, the downstream market of EVA foam materials such as toy industry, sporting goods industry, and building materials industry consumed about 25% of EVA foam materials. In China, emerging sectors such as automotive interiors and electronic accessories consume about 5% of foam materials for electric vehicles.