Lightweight and Comfortable Sole Systems

Lightweight and Comfortable Sole Systems Feet are the most important part of the human skeleton, bearing the body's weight throughout life and therefore constantly under stress. During walking, running and standing, feet are expected to support body weight and withstand forces generated by ground contact. The efficient performance of these functions is made possible by the feet's complex, robust, flexible structure capable of absorbing energy. Foot comfort is connected to the contact pressure created between the sole and the ground. High pressure values at the ground-foot interface can obstruct blood flow, cause pain, or lead to various pathological disorders. To improve foot comfort, materials that reduce contact pressure in high-risk areas during load bearing must be used on the sole, and polyurethane systems are the most frequently encountered materials in this context. When selecting shoes, beyond style and fashion compliance, weight, softness, comfort and durability are also considered. Polyurethane sole systems are frequently preferred in shoe sole and slipper applications because they can be easily formulated according to desired properties. In shoe sole and slipper systems, pressing the product with lower weight is achieved through low mold density properties. However, low-density products generally require more open cells compared to high-density products, which causes problems in the dimensional stability of the product after final application and shows lower performance in strength tests compared to high-density products. In this article, we will see how new generation systems developed by Kobe Polyurethane allow achieving high strength and comfort values even from low-density products. For the dimensional stability problem that poses a risk in low-density products, we provide a solution with our newly developed Kobester polyester product. Through the new polyester system, the desired saturation level has been achieved in soft products. These newly developed system combinations provide comfort, lightness and high impact resistance while ensuring durability and long-term usability. The reaction profiles of these new systems are the same as those of standard sportswear and slipper systems, while shorter mold opening time provides ease in achieving maximum production capacity efficiency. Through the use of appropriate paints and mold release agents, excellent surface performance is demonstrated even at low mold temperatures.  

Kobe Polyurethane Sole Systems

In the Kobecat 120-Kobester LB1732-Kobenat Z002 system developed for low-density and low-hardness sportswear sole production, hardness values of 50-60 ShA can be molded with mold density varying by model at 320-420 kg/m³.   [caption id="attachment_141359" align="aligncenter"] Figure 1. Kobe Polyurethane Sole System[/caption] In slipper and sole systems, mechanical tests are performed to examine material behavior. The most important of these tests are flex resistance and tensile tests. In the developed sole system, both flex resistance and tensile tests yield better results compared to standard products. In the Kobecat 120 / Kobester LB1732 / Kobenat Z002 system developed for sportswear soles, flex properties exceeding 150,000 cycles at 0°C are demonstrated in tests conducted under more stringent conditions. In the tensile test, maximum load-bearing capacity and elongation percentage at rupture were determined. [caption id="attachment_141360" align="aligncenter"] Figure 2. Flex Test[/caption] The work performed consists of three stages. First, laboratory synthesis and application work together with design; in the second stage, test castings with the low-pressure machine within the company and their testing; and in the final stage, customer trials and testing of products resulting from customer production trials. The results of these triple verification tests are presented in the table below. [caption id="attachment_141361" align="aligncenter"] Table 1[/caption]

Kobe Polyurethane Slipper System

In the Kobecat 118-Kobester LB1732-Kobenat X001 system developed for low-density and low-hardness slipper sole production, hardness values of 55-65 ShA can be molded with mold density varying by model at 220-250 kg/m³. [caption id="attachment_141362" align="aligncenter"] Figure 3. Kobe Polyurethane Slipper System[/caption] Although flex resistance expectations are low in slipper systems, the developed Kobecat 118 / Kobester LB1732 / Kobenat X001 system demonstrates flex properties exceeding 40,000 cycles. Competing products tested under the same conditions show values between 10,000-30,000. [caption id="attachment_141364" align="aligncenter"] Table 2[/caption]     Gülhan Sarıgöl R&D Engineer Kobe Polyurethane