Paint protection film yellowing, refers to the car PPF exposed to natural light, ultraviolet light, heat, oxygen, chemical leaching, moisture and so on under the environment, as well as improper production process led to the color of the car coat yellowing phenomenon.
Theoretically speaking, all items will undergo a certain degree of yellowing under the influence of time and external factors, which is a natural law. However, the yellowing of the car coat as a visual feeling, often due to the different acceptance of different customers, white cars are more yellow than black cars and other reasons, resulting in car owners, stores and brands can not reach a consensus on whether the car coat has yellowing, or the cause of yellowing
So how should we objectively define whether the car coat has yellowing and determine the cause according to the degree of yellowing?
At this time, we need to submit materials to a professional third-party testing organization, which will conduct specific testing and analysis according to the standard of Yellowness Index (YI).
Generally speaking, TPU masterbatch manufacturers offer a 3-5 year warranty for masterbatch yellowing, with a warranty of ΔYi≤3.0 for masterbatch yellowing, which is yellowing with an index of 2 or less. However, in reality, most of the yellowing car ppf encountered by car owners after sale are obviously discoloured, with the index reaching a level of 3 or more. Therefore, in addition to excluding the yellowing cases caused by masterbatch below level 2, we should also make specific analysis and judgement based on several factors that may lead to yellowing of car ppf
Fisrt Understanding the causes of yellowing
There are three main elements that determine whether a car coat will yellow or not: the base film, the glue and the coating. Of these, the base film is the most likely to cause yellowing.
The most likely cause of yellowing: the base material
PVC is the most likely material to cause yellowing in a very short period of time. What is PVC? You can think of it as a hard plastic, which is less stable to light and heat and can easily yellow.
However, since the paint protective film entered the market, the material has been optimized for several generations. Now, the ppf that is simply named after PVC has disappeared. Therefore, the ppf base film that is most likely to cause yellowing is mainly made of TPH.
In fact, TPH material is to add plasticizer in PVC material to change the original hard plastic into soft plastic that is relatively easy to be installed. However, its essence is still PVC, so TPH PPF is very easy to yellowing.
In addition, aromatic TPU base materials, whose structure contains benzene ring, are easy to be oxidized under the influence of ultraviolet light, resulting in irreversible yellowing. Therefore, aromatic TPU is generally used in soft foam, ship parts, building materials and other fields that do not need high yellowing resistance, and it is completely not applicable to automobile TPU base materials.
Therefore, aliphatic TPU should be selected as the correct base material of the PPF, because its structure does not contain benzene ring, and its molecular arrangement density is dozens of times that of the aromatic group, so it is not easy to be oxidized by ultraviolet radiation and is very resistant to yellowing. Aliphatic TPUs are generally used in high-end footwear, LED accessories, optical lenses, invisible car clothing and other fields that require yellowing resistance
Second possibility of yellowing: glue
The car ppf glue has strong exclusivity, so it is necessary to use glue specially developed for car paint and TPU substrate. The color of glue shall be transparent, with stable weather resistance, and not easy to react with automobile paint and TPU base film. Non directional development glue can never be used to make ppf. When it reacts with car paint and TPU base film, it is very easy to cause TPU yellowing. If it has penetrated into TPU substrate, it will produce irreversible results.
Less possibility of yellowing: coating
TPU coating refers to a layer of transparent material applied on the surface of TPU substrate to enhance the performance of the car ppf, so that the car ppff can effectively cope with the complex climate and environment in nature. In daily use of the vehicle, dirt such as dust, rain, bird excrement, iron powder and so on adhere to the film surface and penetrate into the TPU base film under the effect of time, which will make the film surface foggy and lose luster, and also present a yellowing state from the naked eye, but in fact, this situation is mostly pseudo yellowing, not directly caused by the coating.
How to deal with the yellow ppf?
For “pseudo yellowing” caused by stain adhesion:
Some turn yellow because dust and stains fall on the car body and are not cleaned in time. In view of this yellowing, a neutral detergent without abrasive can be used to deeply clean the vehicle to try to remove it. Do not polish the car clothes unnecessarily, because polishing may damage the original protective coating of the car ppf causing new problems. Pseudo yellowing is generally localized yellowing, but if dust and stains completely penetrate into the TPU base film, it may not be removed.
For yellowing caused by base material glue:
The yellowing caused by improper selection of TPU base film and glue is generally a large area yellowing, which is irreversible. It is recommended that the store and the owner negotiate to tear it off and re install it as soon as possible.
It should be emphasized here that yellowing of TPU base film, yellowing of coating, or pseudo yellowing caused by dust stains may at most lead to the consequences of film tearing and re install, but yellowing of glue is more risky, and chemical reaction between glue and car paint may damage car paint.
How to avoid ppf yellowing?
Yellowing is a natural physical phenomenon, under the action of time, it is impossible for the car ppf not to yellow at all, so here we only discuss how to control the yellowing index of the car ppf within the industry standard level 2 (slight discoloration): 1.
1. First of all, for PVC, TPH, aromatic TPU material car coat, yellowing is basically inevitable, generally within 6 months to 2 years time most of the obvious yellowing phenomenon will occur. To avoid yellowing of the base material, you need to give priority to aliphatic TPU material. Note that the yellowing speed of different brands of aliphatic TPU material is also different, here need to cast factory, coating factory according to past industry experience carefully selected substrate particles.
2. car coat glue selection has a greater exclusivity, the coating factory should choose the market has been fully tested and certified glue brands and brands, careful to use some of the glue brands without rigorous testing and market proof.
3. Good habits for car owners are also very important, it is recommended that owners wash their cars at least once every two weeks, and go to the store every six months for maintenance of the car ppf, so as to avoid as far as possible the depth of surface stains penetrate into the base film, resulting in “pseudo-yellowing” to “real yellowing”.