Polyamide is an abbreviation for polyurethane, and is a polymer compound containing a plurality of repeating amino groups in a polymer main chain, and is obtained by chemically reacting an isocyanate with a polyol compound. Polyurethane for sole is a microporous elastomer between rubber and plastic. It is a microporous elastic structure with open pores. The diameter of the cells is 0.01-0.1mm, and the free foaming density is 0.25~0.35. (Forming density 0.3-1) It usually has 1-2mm self-skinning and has excellent resilience and great energy absorption capacity.
First, polyurethane is the ideal material for the manufacture of soles
1. Polyurethane sole has the characteristics of softness, warmth, oil resistance, flexing resistance and wear resistance. It is 6 times more wear-resistant than rubber. It can adjust its density and hardness in a wide range according to the requirements of use. It can be made into two colors (double density). The double bottom of the sole is a micro-foamed, highly wear-resistant work surface, and the inner sole is a flexible foam that is comfortable to wear.
2, very light, the specific gravity is only 0.3-0.8, much lighter than the commonly used sole material, more suitable for thick-soled shoes that require impact resistance and anti-perforation. 15% of the world's safety protective shoes (labor shoes) use polyurethane (PU) soles .
3, the mold requirements are lower, the production is convenient to invest and save (the foam pressure is small when foaming, only 0.14-0.2Mpa).
4, the molding method is simple and feasible, can not only produce the soles but also the production of shoes, (PU base and various fabrics have strong adhesion) varieties and flexible production changes, suitable for modern industrial production.
Second, the production process
1. Preparation of PU sole stock solution
The stock solution can be divided into two types: polyester type and polyether type. In the early years, the polypropylene glycol system was developed, and most of them are polyester type systems. The preparation methods are different due to their different properties.
Polyester PU sole stock preparation is mostly prepared by prepolymer method or semi-prepolymer method. Generally, it can be made into two-component or three-component. Part A consists of partial polyester, chain extender, foam stabilizer and hair. Soaking agent and other components, 40e ~ 70e mixed and static degassing derived. In the all-water foaming system, the foaming agent is water, and the amount of water in the component A must be determined, and the content thereof is generally about 0.4%. The B component is a terminal isocyanate prepolymer obtained by reacting a part of a polyester polyol with an isocyanate. The relative molecular mass of polyester is preferably 1500~2000. In the isocyanate, the ratio of pure MDI to liquefied MDI is 19B1. During the reaction, one-tenth of the inhibitor must be added to hinder the occurrence of side reactions. It can be kept at a certain temperature for 2h~3h, and the NCO% is controlled at about 19%. The C component is a catalyst (a two-component stock solution is added to the A component). The three-component system is suitable for two-color, low-hardness sports shoes and low-density sandals. When used, the A component and the C component are uniformly mixed, and then mixed with the B component. It is characterized by low viscosity and reactivity reduction, small hardness and dimensional change of the product and good molding stability. The preparation of the polyether type liquid solution is mostly carried out by a one-step method. The component A is obtained by thoroughly mixing a polyether polyol, a chain extender, a foaming agent, a catalyst and a foam stabilizer in a mixer; the component B is a modified isocyanate or a liquefied MDI. Polyester diol can impart high strength, wear resistance and strong adhesion to the upper of the sole. The polyether sole overcomes the disadvantages of poor water resistance and poor low temperature elasticity of the polyester sole, and the moldability is good. Excellent low temperature flexibility and elasticity while maintaining the physical and mechanical properties of the sole. However, under low-density conditions, the polyester sole has poor dimensional stability, while the polyether sole has good dimensional stability at the same density, but has low mechanical properties, so in a water-foaming system, it can be scaled. A method of mixing two alcohols to improve the mechanical strength and wear resistance of the article. This work has been reported in foreign countries. For example, the poly(ether 2 ester) polyol of Mipolur PE2 Polidol A [2] is a mixed polyol containing both ether and ester, and the performance of the sole material is between polyester type and polyether type. Domestic scholars have also done some work to check Liu Sheng and other domestic polyether as the main raw material to blend the characteristic amount of polyester polyol to improve, synthesize poly (ester 2 ether) foam sole material, which has excellent physical and mechanical properties. According to the GB10508289 index, the cost is 10%~15% lower than that of pure polyester PU sole material [3].
2, PU sole molding process
The PU sole has a unit sole, a full polyurethane boot shoe, a direct insolation of the upper, a hard sole and an intermediate layer of the sole, and the molding of the whole shoe and the combined sole. The sole, upper or upper of the all-polyurethane boots are made of PU. The all-polyurethane shoes made of micro-porous PU elastic, the boots are soft, the soles are wear-resistant, oil and chemical resistant, and the whole shoes are light and warm. Sex and comfort. PU soles are generally formed by low pressure casting or high pressure casting, and a few are also injection molded. The process flow is shown in Figure 1. The molding equipment is a sole casting machine. The atmospheric pressure pouring equipment for polyester PU molding is mainly composed of a casting machine, a ring or a turntable drying tunnel. In the PU sole stock solution, since the components A and B are liquid and the mixing reaction is severe, the accurate metering of the equipment and the uniformity of the mixing of the components during the molding process are two important factors directly affecting the performance of the product. For the two-color sole, it is molded by a two-color casting machine, generally using a mold with an intermediate plate, and is subjected to secondary casting and heat curing.
Third, the conditions for the production of PU soles
1. Production site: 8m wide, 20m long, about 160m2, corresponding raw materials, semi-finished products and finished goods warehouse. Because of the lighter equipment and large floor space, it can be placed on the upper floor (for installation and movement, the equipment has no land) Foot screw). If the PU sole is to be produced, there should be a painting place; if the shoe is produced, the equipment and place for sewing the upper and shaping should be added.
2. Materials: Raw materials should be kept at 0.5-1 tons, A material is 18kg per barrel, and B material is 20kg per barrel. Although the amount of C material is very small, it can be prepared for about 10kg because it is not easy to deteriorate. In addition, it is necessary to prepare 50 kg of release agent, a large bucket of cleaning agent (methylene chloride) and a number of color pastes. (Article source from Global Polyurethane Network)
3, the power is about 50kw, if the production line oven does not need electric heating, the power needs about 20kw.
4. The air compressor 壹 sleeve (gas volume 0.6m3/min, air pressure 0.6~0.8MPa, power 5.5kw) is used as the main air source and spray release agent.