TPR shoe material is generally a polymer material modified by thermoplastic elastomer SBS and other functional additives. After being processed by mixing, extrusion, injection molding and molding, the sole is made of anti-slip. It has the advantages of low temperature resistance, strong bending property, good gas permeability, low density and strong bonding strength, and its waste can be recycled. At present, TPR sole materials have been recognized by more and more manufacturers, merchants and consumers.
In order to improve the processing properties of SBS, enhance fluidity, flexibility, aging resistance, deformation resistance, flame resistance and economical, it is necessary to add various seasonings and various additives to the pure rubber to carry out blending and extrusion. Granulation can be processed into a variety of different properties.
The composition of raw materials has a great influence on the properties of the products. The various materials are described below.
1. Selection of main rubber
As the main raw material, SBS is the skeleton of the whole SBS shoe, which provides the main properties such as strength and elasticity.
The specific selection of the grade should be determined by the manufacturer’s performance requirements for the sole material, generally considering the cost, processing performance, and sole type. The SBS grades that are generally suitable for shoe materials are all oil and rubber grades. The more used are Maoming Petrochemical: 875,675; Li Changrong: 1475, 1487; Baling Petrochemical: 815; Yanshan Petrochemical: 4452; Dushanzi: 171.
2. Softening oil
Softening oil mainly plays a role in improving fluidity and reducing costs in SBS sole materials. The fluidity of SBS soles is generally measured in terms of melt flow rate (MFR). To reduce the hardness of SBS shoe pellets, it can be adjusted by adding a softening oil or a plasticizer. The commonly used softening oil is KN4006.
The addition of polystyrene to SBS improves the fluidity and hardness of the melt and improves the processability. The choice of resin should first consider the compatibility with SBS, generally follow the principle that “the solubility parameters are similar and compatible”. In order to make PS easy to enter SBS and enhance the role of PS crosslinking point, crystalline polystyrene (GPPS) and poly-α-methylstyrene with low softening point are generally used, and the amount is generally 10-20 parts.
Adding low-density polyethylene and polypropylene can improve hardness and wear resistance, and the dosage is generally not more than 10 parts. Polyvinyl chloride, ethylene-vinyl acetate copolymer and SBS have poor compatibility, can not be well dispersed, excessive delamination, but in order to improve ozone, can be used in small amounts.
Nitrile rubber and EVA can improve the adhesion between shoe and leather. Any resin that can enter PB section, such as modified rosin, can improve the fluidity and viscosity of the rubber, but tensile strength and tensile elongation. The rate and flexibility will decrease, and the dosage will be 4-10 parts. According to different uses, considering the amount of modified resin, a satisfactory modification effect can be obtained.
Fourth, the filler
The main purpose of adding fillers to pellets for TPR shoes is to reduce costs while increasing the hardness and wear resistance of the articles. Commonly used are white carbon black, calcium carbonate, talcum powder and the like. As the number of filler fractions increases, the hardness increases significantly, while the tensile strength and elongation at break decrease.
Therefore, the filler content should not be too high, and the type and amount should be selected according to the product performance and processing requirements. Usually less than 5% white carbon black, combined with calcium carbonate. The amount of calcium carbonate is determined according to the product requirements.
Five, chemical additives
Add 0.5% hard acid to the formula to achieve lubrication, compatibility, plasticization and other effects. The addition of a small amount of DCP in the formulation for cross-linking has a significant improvement in TPR tensile strength and bond strength, but it cannot exceed 0.7% of the elastomer content. The injection product may be sag in the injection flow path, at the thin junction of the product or when the injection pressure is insufficient.
Adding 1%-2 AC foaming agent to the formulation increases the expansion force of the TPR material, which can effectively overcome the sag phenomenon and the surface finish of the product is uniform. Micro-foaming can reduce the specific gravity of the shoe material, which is conducive to the cost reduction, but excessive foaming will affect the quality index such as hardness and strength of the product, and the dosage is controlled at 0.5%.
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