Shoe material formula: PVC/RB/TPR/EVA/PU system calcium carbonate selection guide!
Calcium carbonate is the mainstream filling modified powder in the shoe material industry. Reasonable selection can reduce raw material costs, while improving key indicators such as sole hardness, wear resistance, tear resistance, dimensional stability, and yellowing resistance.
The five mainstream shoe material base material formula systems of PVC, RB rubber, TPR, EVA, and PU have different requirements for the fineness, category, and addition ratio of calcium carbonate. This article summarizes the key application points of various shoe sole material powders.
RB rubber sole (sports anti slip outsole)
Rubber soles are divided into natural rubber and synthetic rubber systems. Natural rubber has excellent elasticity, but its wear resistance is weak and prone to oxidation and yellowing. The industry generally uses white carbon black as a reinforcing filler, and most formulations are combined with 800-1250 mesh modified heavy calcium for synergistic modification.
The main functions of calcium carbonate are to assist in improving wear resistance, delaying aging, improving yellowing resistance, reducing filling costs, and balancing production costs and product properties. The powder requires low impurity content and excellent dispersibility to avoid powder agglomeration and finished product powder discharge, ensuring continuous and stable mass production of rubber outsole.
PVC sole (slippers, rain boots, miner's shoes, plastic sandals)
PVC is the most mature shoe material system for calcium carbonate applications, widely used in home slippers, waterproof rain boots, sandals, and miner's shoes. Affordable products often use 400-800 mesh heavy calcium, while general formulas prioritize the use of light calcium carbonate, with a conventional addition ratio of 3% -5%.
The function of calcium carbonate is to enhance product hardness, reduce molding shrinkage, stabilize product size, optimize surface flatness, and reduce resin consumption. Light colored and white PVC products are preferred to use high whiteness and low black spot calcium carbonate to ensure a smooth surface and no white spot particles, suitable for automated assembly line production.
TPR thermoplastic rubber sole (casual shoes, children's shoes, soft slippers)
TPR combines rubber elasticity and plastic processing characteristics, supports injection molding and extrusion processes, and is made of recyclable materials. It is commonly used in children's shoes, casual soles, and soft slippers. Powder selection is divided into three levels:
1. Low end TPR products: ordinary heavy calcium, with cost control as the core;
2. Mid to high end scratch resistant TPR: Nano calcium carbonate combined with white carbon black enhances tear resistance, scratch resistance, and wear resistance;
3. Transparent TPR base material: mainly uses white carbon black and transparent powder, with only a small amount of calcium carbonate to fine tune the hardness.
Modified nano calcium carbonate can partially replace white carbon black and reduce formula costs; The powder has good dispersibility and can avoid defects such as pitting and peeling in injection molded products.
EVA foam shoe material
There are significant differences in the application of EVA system calcium carbonate, which can be divided into two directions: one-time injection sole and large foam sheet
1. EVA one-time injection lightweight midsole: The formula is mainly composed of talcum powder, with an added amount of 5% -20%. Conventional formulas rarely use calcium carbonate; Only a small amount of ultra-fine heavy calcium is added to high-density weight products to adjust their specific gravity.
2. EVA foam sheet (slipper substrate, secondary molding midsole)
Ordinary low-density foam sheet: 325-600 mesh heavy calcium, with a focus on cost advantage;
High density weighted foam sheet: 1250-2000 mesh ultra-fine heavy calcium, balancing whiteness, fineness, and surface effect of the product;
High rebound, high flatness sheet material: mainly composed of talc powder, compounded with calcium carbonate to regulate the foaming ratio.
Calcium carbonate suitable for EVA foaming requires moderate oil absorption and excellent flowability to prevent foam collapse and irregular porosity during production, ensuring a smooth foam cross-section.
PU polyurethane sole (leather shoes, workwear shoes, casual shoes)
PU sole has good rebound and resistance to repeated bending, commonly found in business leather shoes and workwear shoes. The formula generally uses 1250 mesh active ultrafine calcium carbonate and nano modified calcium powder.
The function of calcium carbonate is to regulate the softness and hardness of shoe soles, reduce foaming shrinkage deformation, improve wear and bending resistance, reduce the cost of polyol raw materials, and alleviate long-term cracking problems.
Calcium carbonate treated with surface activation has better compatibility with PU system, increased filling amount without damaging the foam structure, effectively improving the yield of finished products.
