High-strength, high-elasticity urethane-based adhesive
The Yokohama Rubber Co., Ltd. announced that it has established a basic technology for a two-component urethane adhesive with high strength and very good elasticity. This technology will be applied to the development of adhesives for automotive body structures, an area expected to see rapid growth worldwide. It can be also applied to various industrial adhesives, including those used in electronic devices exposed to harsh heat cycles, said the company.
According to Yokohama Rubber, the automotive industry has entered into a once-a-century period of drastic change, with reduction of car body weights as the highest priority. Multi-material structures combining lightweight materials such as aluminium and carbon fibre reinforced plastic (CFRP) with steel are rapidly coming into use, especially in Europe. This trend is increasing the need for structural adhesives because bonding the various materials used in these multi-material structures is difficult to do with traditional welding. Although the epoxy-based adhesives used to date have high strength levels, their low flexible elasticity to follow movement makes their use with multiple materials difficult. For that reason, the development of adhesives that can be used in multi-material structures is being earnestly pursued in Japan, including the establishment of a national project. Yokohama Rubber has been conducting research on adhesives that possess the high strength and elasticity required for automotive structures. The research is based on the company’s urethane adhesive technology for building and automotive window frames.
Yokohama Rubber said that using the new technology, it succeeded in achieving maximum tensile strength of 20 – 40 Mpa, comparable to that of epoxy-based adhesives with high elasticity unique to urethane adhesives with maximum elongation of 200 – 500 %. These numerical values exceed the upper limit of the so-called banana curve that defines the performance range generally considered technically difficult to achieve, said the company. It also greatly improves urethane’s curability, helping overcome slow and/or imperfect curing caused by environmental conditions, such as temperature and humidity, which is considered one of the material’s weak points. The new technology realises short tack times that enable both pot life and initial adhesion to be around 2 – 5 minutes. It is also said to improve the temperature resistance, maintaining stable physical properties in a much wider range from –30 °C to 180 °C compared with conventional urethane adhesives. In addition to its good dynamic durability, this urethane adhesive demonstrates stable strength and elongation characteristics when the deviation in the mixing ratio of the two components is kept within ±20 %. Furthermore, its physical properties can be controlled by changing the mixing ratio, which makes it possible to adjust the physical properties as required by the different materials and/or bonding locations. The company said it will continue to test this new technology and aims to use it to commercialise next-generation industrial adhesives.