Many customers have reported that high transparency TPU is transparent when it is first made, why does it become opaque after a day and look similar in color to rice after a few days? In fact, TPU has a natural defect, which is that it gradually turns yellow over time. TPU absorbs moisture from the air and turns white, or this is due to the migration of additives added during processing. The main reason is that the lubricant is opaque, and yellowing is a characteristic of TPU.

TPU is a yellowing resin, and MDI in ISO will turn yellow under UV irradiation, indicating that TPU yellowing is a property. Therefore, we need to delay the yellowing time of TPU. So how to prevent TPU from yellowing?

Method 1: Avoid

1. Choose to develop black, yellow, or dark colored products in the initial stage of developing new products. Even if these TPU products turn yellow, their appearance cannot be seen, so naturally there is no problem of yellowing.

2. Avoid direct sunlight exposure to PU. The PU storage area should be cool and ventilated, and PU can be wrapped in plastic bags and placed in a place without sunlight exposure.

3. Avoid contamination during manual operation. Many PU products are contaminated during the process of sorting or salvaging, resulting in yellowing such as human sweat and organic solvents. Therefore, PU products should pay special attention to the cleanliness of the contact body and minimize the sorting process as much as possible.

Method 2: Adding ingredients

1. Directly select TPU materials that meet UV resistance specifications.

2. Add anti yellowing agents. In order to enhance the anti yellowing ability of PU products, it is often necessary to add a specialized anti yellowing agent to the raw materials. However, anti yellowing agents are expensive, and we should also consider their economic benefits when using them. For example, our black body is not sensitive to yellowing, so we can use cheaper non anti yellowing raw materials without anti yellowing agents. As anti yellowing agents are a raw material additive added to component A, we require stirring when mixing to achieve uniform distribution and anti yellowing effect, otherwise local yellowing may occur.

3. Spray yellow resistant paint. There are usually two forms of paint spraying, one is in mold spraying and the other is out of mold spraying. The spraying of yellow resistant paint will form a protective layer on the surface of PU finished products, avoiding pollution and yellowing caused by contact between PU skin and the atmosphere. This form is currently widely used.

Method 3: Material replacement

Most TPU is aromatic TPU, which contains benzene rings and can easily absorb ultraviolet light and cause yellowing. This is the fundamental reason for the yellowing of TPU products. Therefore, people in the industry regard the anti ultraviolet, anti yellowing, anti-aging and anti ultraviolet of TPU as the same concept. Many TPU manufacturers have developed new aliphatic TPU to solve this problem. Aliphatic TPU molecules do not contain benzene rings and have good photostability, never turning yellow

Of course, aliphatic TPU also has its drawbacks today:

1. The hardness range is relatively narrow, generally between 80A-95a

2. The processing process is very meticulous and easy to process

3. Lack of transparency, can only achieve a transparency of 1-2mm. The thickened product looks a bit foggy

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