Abstract

Natural leather is widely used in fashion products and has excellent physical properties owing to its structurally dense organisation. However, this high density leads to a high weight, which has been noted as a disadvantage. A fundamental method for improving the weight of natural leather materials is to reduce the weight of the naturally derived high-density collagen fibre tissue by structurally changing it into a low-density tissue. A low-density natural leather manufacturing technology is being developed to do so by infiltrating and foaming thermally expandable materials into a natural leather processing process; however, the dyeing of the fabric after foaming is uneven and the fabric becomes hard. In this study, we developed a wet-foaming process to replace the existing dry-foaming process after dyeing. The wet-foaming process is performed during the natural leather processing process (before the dyeing process) to improve the fixation and dyeability of thermo-expandable microcapsules (TEMs). By applying TEMs to the retanning process along with lignin (a natural product-based fixing agent) and then proceeding with the TEM foaming in liquid it is possible to provide stable foaming with flexibility of the TEMs in the leather tissue and to minimise the loss to drain. Furthermore, in the subsequent dyeing process, the TEMs dyed in the foamed state show an improved dyeing levelness.