TPU will absorb moisture in the air and become white in the air or it is the migration of additives added during processing, mainly because the slip agent is opaque, and yellowing is a characteristic of TPU.
TPU is a yellowing resin. In ISO, MDI will turn yellow under ultraviolet light. It can be seen that TPU yellowing is an attribute, so we need to delay the yellowing time of TPU. So how to prevent TPU from yellowing? There are many reasons, but the place should be shaded.
1. Avoid sunlight exposure to TPU. The TPU storage area should be cool and ventilated, and the TPU can be sealed in plastic bags and placed in a place without sunlight.
2. Spray yellow-resistant paint. There are usually two forms of paint spraying, one is spraying inside the mold and the other is spraying outside the mold. The spraying of yellow-resistant paint will form a protective layer on the surface of the TPU finished product to prevent the PU skin from contacting the atmosphere. Pollution yellowing, this form has been widely used.
3. Add anti-yellowing agent. In order to strengthen the anti-yellowing ability of TPU products, it is often necessary to add a special anti-yellowing agent to the raw materials, but the anti-yellowing agent is expensive, and we should also measure its economic benefits when using anti-yellowing agents, such as our black The body is not sensitive to yellowing, so we can use cheaper non-yellowing raw materials without added anti-yellowing agent. Since the anti-yellowing agent is a raw material additive, it is added to component A. We require stirring when mixing In order to distribute evenly and achieve anti-yellowing effect, otherwise local yellowing will occur.
4. Use a good mixing ratio. A good ratio can make the I liquid and P liquid achieve the fullest mixing reaction without incomplete reflection. When these phenomena occur, the finished product will be resistant to hydrolysis and greatly reduce the anti-yellowing ability, especially when the ratio is too high. Will accelerate the yellowing of the finished product.
5. Avoid pollution during manual operation. Many TPU products are contaminated during the finishing or salvage process, resulting in yellowing such as human sweat and organic solvents. Therefore, TPU products should pay special attention to the cleanness of the contact body and reduce the finishing process as much as possible.