ABSTRACT
Reducing the quantity of wax in lipstick can improve the properties of the lipstick, including the glossiness, moisturizing capability, and longevity. However, lipsticks with less wax tend to break more easily. Therefore, to prevent breakage while reducing the wax content, we focused on the crystal structure of the wax gel and strain generated during the cooling and solidification processes as they are structural factors that affect fragility. Generally, if the crystals and strain are small, the structure is less easily broken. However, because the tip of the lipstick cools more rapidly from below than the root, the strain of the root against the tip increases owing to poor heat transmission. This creates large shrink holes in the root. While reheating from above can suppress the generation of shrink holes, it also causes the crystals to grow larger and the structure to become weak owing to slow cooling. Therefore, we adopted a rubber-molding technology generally used to form logos and complicated shapes as a strategy to mitigate these issues. This successfully reduced the strain generated inside the lipstick during the cooling process, as the rubber mold shrunk along with the lipstick, making it possible to quench the root. Therefore, we were able to realize a small crystal structure and low strain on the root of the lipstick. Our results demonstrate that it is possible to realize a lipstick with excellent features by reducing the quantity of wax.
