How can we prevent PU from turning yellow?
PU pipe can be divided into polyester type PU pipe and polyether type PU pipe according to material, PU air pressure hose, PU yarn jacket reinforcing pipe, PU industrial hose, PU steel wire stretching pipe, PU spiral pipe, PU stretching pipe, PU spring pipe, PU yarn jacket pipe, PU braided pipe, PU net pipe, PU single pipe and PU straight pipe. PU tube is the preferred pneumatic pressure hose in the pneumatic industry. The highly transparent TPU is transparent after extrusion. Even the TPU tube can be seen shining and shining. However, after a period of time (the period of time is related to the environment, the shorter the period of humidity and easy contact with the light source), it becomes opaque, which is somewhat similar to the white of rice.
The main reason for this phenomenon is that TPU absorbs moisture in the air, leading to color gradient, or the main ingredient added in the extrusion process is that the smoothing agent migrates out when the TPU hose contacts the air. Look at the characteristics of PU and TPU: "opaque, yellowing". Why? Because PU is a yellowing resin, MDI in ISO will yellowing under ultraviolet irradiation, so PU yellowing is an attribute, so we need to delay the time of PU yellowing. So how can we prevent PU from yellowing?
(1) sunlight should be avoided.
PU hose or high pressure hose (TPU), PU clip tube is no exception. All PU pipes are required to be stored in a cool and ventilated place. Plastic bags can be used to pack PU plastic hoses or transparent hoses in places without sunlight.
(2) spraying yellow paint:
Paint spraying usually has two forms, one is in-mold spraying, the other is out-of-mold spraying, butter-resistant paint spraying will form a protective layer on the surface of PU pipes, to avoid TPU fibers increase hoses or other TPU pipes contact with the atmosphere and pollution yellowing;
(3) add anti yellowing agent:
In order to enhance the anti-yellowing ability of PU tubes, a special anti-yellowing agent is often added to the raw materials, but the price of anti-yellowing agent is expensive. We should also measure its economic benefits when using anti-yellowing agent. For example, our black type is insensitive to yellowing, so we can use cheaper non-anti-yellowing material without anti-yellowing agent. Because anti-yellowing agent is a kind of raw material additive, it is added to ingredient A. When we mix, we need to mix in order to distribute evenly and achieve anti-yellowing effect. Otherwise, local yellowing will occur.
(4) use a good mixture ratio:
A good proportion can make I and P liquids reach the fullest mixing reaction without incomplete reflection. When these phenomena occur, the hydrolysis resistance and yellowing resistance of finished products will be greatly reduced, especially when ISO in the proportion is too high, the yellowing of finished products will be accelerated.
(5) avoid contamination during manual operation.
There are more PU tubes and high-pressure hoses contaminated in the finishing process, resulting in yellowing, such as human sweat and organic solvents, so PU products should pay special attention to the cleanliness of contacts, while minimizing the finishing procedures. After the extrusion of PU yarn-jacket tube (fiber-reinforced hose), clean, reorganize and roll up. The next step is to wrap each roll with plastic film, which directly protects the surface of PU tube and avoids contact with other substances, thus delaying the period of discoloration and yellowing of PU plastic hose to a large extent, and helping users prolong the service life.