In an invisible automotive coating, TPU backing is an important part, but do you know how TPU is made? What is fundamental difference between a good TPU and a bad TPU? Why can all TPU stealth car covers be guaranteed for 5 or even 10 years? Does it clearly turn yellow after 1-2 years? Today, Hezhizhong invisible car clothing factory will tell you about it.
1. How is TPU made?
TPU is abbreviation of "thermoplastic polyurethanes" in English, and its scientific name is "thermoplastic polyurethane elastomer rubber", which can be found in Baidu's encyclopedia. Main characteristics: good recovery, good elasticity, high strength...
Invisible TPU car cover
Everyone knows about TPU invisible car cover, but how is TPU made? In fact, going back to source, TPU was originally extracted from oil, and final product was size of a grain of rice. The more transparent color, better quality! Companies with such processing and production technologies are well known, among them are Bayer Substrate from Germany and Agutek from USA.
Please note that when refining TPU, depending on technology and composition of refining, appearance and performance of TPU may vary. In invisible automotive coating industry, it is mainly divided into aliphatic and aromatic TPU. Below is an image of finished product made of TPU particles:
There are TPU particles, but we can't use them directly, we need to stretch them onto surface of film, just like turning "grains of wheat" into dough. In this link, we have technology and we have done a relatively good job. There are manufacturers such as Agutek from USA and Motan from Japan.
TPU main material from invisible TPU car covers
Knock on key, key is here. At present, invisible car clothing factory is divided into two batches: ① purchase TPU particles, and then make film by yourself (or find another factory); ② Directly purchase TPU film backing.
For well-known domestic brands such as Hezhizhong and Romantik, second option is to directly purchase aliphatic TPU substrates from Agutec in USA.
Secondly, what is difference between a good TPU and a bad TPU?
Invisible car covers come in good and bad, just like TPU! As mentioned above, in automotive invisible coating industry, quality of TPU is mainly in aliphatic and aromatic compounds. So, what is aliphatic TPU, what is aromatic TPU and what is their most significant difference?
1. Aromatic and aliphatic TPU
TPU is produced by reaction of three components: a diisocyanate, a chain extender and a polymeric diol.
①If diisocyanate component is "diphenylmethane diisocyanate (MDI)", generated TPU is aromatic (containing a benzene ring);
②If diisocyanate component is "hexamethylene diisocyanate (HDI)", resulting aliphatic TPU.
Aliphatic TPU HDI
2. A significant difference is different degree of resistance to yellowing!
The big difference between aromatic and aliphatic TPU is in "yellowing resistance" performance!
The reason aromatic TPU turns yellow easily is due to its "diphenylmethane diisocyanate (MDI)" benzene ring structure, as shown in figure below:
MDI has a methylene bridge between two phenyl groups. This methylene group is easily oxidized in an ultraviolet environment, with loss of hydrogen at methylene bridge, as shown in figure below:
The reason for yellowing of TPU stealth car cover
Quinonimine structure formed by oxidation of MDI
As a result of this chemical reaction, a conjugated system is formed between two aromatic rings, called quinoneimine. Although this oxidation reaction has little effect on physical properties of TPU, it does cause permanent yellowing of TPU.
The diisocyanate component of Aliphatic TPU is HDI, which does not contain benzene rings, has a stable structure, is not easy to oxidize, and is very resistant to yellowing!
3. Aromatic and Aliphatic TPU Yellowing Experiment
The following is a set of experimental data for aromatic TPU, anti-yellowing aromatic TPU (i.e. TPU with added UV stabilizer) and aliphatic TPU, yellowing of these three substrates under same UV light intensity Degree:
TPU anti-yellowing test
As can be seen from above figure, yellowing index of aromatic TPU and anti-yellowing aromatic TPU exceeds 40 after 1000 hours of UV exposure; aliphatic system is relatively horizontal and after 1500 hours of irradiation yellowing index is still low at 10.
Third, advantages and disadvantages of invisible car coverage!
Of course, apart from quality of TPU itself, TPU film surface production technology is also key to performance of invisible automotive coating. The surface of TPU membrane from different manufacturers varies greatly in strength, penetration resistance, heat resistance and other properties!
Of course, in addition to TPU base material, adhesive layer and coating technology are also directly related to performance of invisible automotive coating. If you want to study it closely, influencing factors include: building environment, installation site, technique, construction technology, etc.
So, you will find that even if many car owners put on so-called "TPU" invisible car cover, which seller guarantees them life, yellowing will still turn yellow after 1-2 years, and some even may' 1 year passed, reason may be that you have pasted manufacturer's own aromatic TPU, and design is still very bad!