PU Shoe Material Needs To Improve Performance

Under the condition of keeping the physical properties of polyurethane shoe material well, reducing the density of molded products, improving the skid resistance (especially in wet or ice covered conditions), and reducing the cost, this is the problem of polyurethane shoe materials to be improved, and it is also the demand of the market.

In addition, improving resilience is also very important.

1, reduce density and reduce density to reduce cost, and then compete with low density EVA and some PVC traditional non polyurethane shoes.

PU shoe material must meet the following requirements: 1) the size is stable, that is, shoe material does not shrink and not twist; 2) easy to process, that is, material mixing is better than tolerance, fluidity is good, product release time is short, and adhesion is good.

The density of microcellular polyurethane shoe material will be reduced, and the pore size distribution and pore structure of foam will change.

When the density of microcellular polyurethane molding products is lower than 400kg/m3, we should avoid shrinkage and other adverse effects due to too high porosity.

Reducing the density of PU material requires increasing the modulus of polymer to maintain the load capacity of molded foam.

When developing low density microcellular polyurethane foam, the equilibrium relationship between formula parameters and material structure, properties and processing characteristics should be fully understood accurately. Sometimes some additives, such as openers, surfactants, coupling agents, foam stabilizers, hardness modifiers and fillers, should be used in the formulation so as to obtain ideal bubble structure materials.

2. The foaming agents used in the all water foaming polyurethane foam are mostly chlorofluorocarbons, such as CFCS. Although these foaming agents can make the surface of the products form their own crust, they will improve the wearability and appearance of the products, but they will destroy the ozone layer and will not be conducive to the protection of the ecological environment.

The use of CFCs blowing agents has been strictly restricted internationally.

According to reports, the federal government of the United States as early as 1994 has issued laws to restrict the use of CFCs in non essential places, including footwear industry.

As people pay more and more attention to environmental problems, the footwear industry is facing new choices. It is necessary to develop new pollution-free foaming agents instead of CFCs.

The new foaming sole water is used as foaming agent, and has the same properties as the foamed microporous polyurethane sole with chlorofluorocarbons, and the processing equipment and technology have little change.

In the PU foam, the reaction of the water foaming system includes the reaction of polyols with isocyanates and the reaction of isocyanates with water. The two steps are almost simultaneous. Each step directly affects the foam formation process and the structure of the foam. Only when the reaction between urea and carbamate reaches a certain equilibrium state, can a stable PU foam structure be formed.

The former mainly produces soft segments of polymers, while the latter generates hard segments of polymers.

Under low density, the obturator rate of the cell is high, but the strength of the supporting cell is not enough, and the product is easy to contract.

Although there is no dense layer on the surface of the water blown sole, its antiwear properties are comparable to those produced by the foamed chlorofluorocarbons.

At present, the world's manufacturers of chemical additives have begun to provide users with new environmental protection products.

For example, Germany Gauss mitt chemical company has developed various auxiliaries for water foaming microcellular polyurethane, including reducing the roughness of water foaming microcellular polyurethane and increasing the softness of water foaming microcellular polyurethane.

The biggest drawback of waterborne polyurethane self foam is low elasticity and poor dimensional stability, but the elasticity can be improved by controlling the content of carbamate groups in polyurethane.

The method is: by calculating and adjusting the formula, pferring the polyol part with high molecular weight in the A component to the B component, instead of polyoxypropylene glycol in the B component, the ideal elastic material can be obtained.

In addition, by adjusting the mixing ratio of A and B components, the processing conditions such as foam forming kinetics can be controlled, and the linear shrinkage rate can be controlled within the moderate range of 0.5%~1.0%.

3. There are many factors that affect the skid resistance of polyurethane shoe materials, which are mainly manifested in the following three aspects: 1) the design of sole, sole structure and style.

The structure and pattern of sole determine the contact surface and force direction of people under different gestures such as walking or running.

2) the type of contact surface and its roughness and various environmental factors.

3) the type of shoe sole material.

4. Photodegradation and discoloration of polyurethane elastomers. Alicyclic PU elastomers are not easily discolored by ultraviolet (UV) radiation, but alicyclic isocyanate PU elastomers are more prone to photodegradation than aromatic PU elastomers.

The photodegradation of alicyclic isocyanate PU elastomers increased with the increase of hard segment mass fraction. The higher the hard segment mass fraction, the more brittle it became after 100h UV radiation.

Aromatic isocyanate PU elastomers are colored by UV radiation, but they exhibit better mechanical properties and resistance than alicyclic isocyanate PU elastomers.