TPU car clothing film: material and performance analysis of invisible car clothing

Invisible car clothing is actually mainly composed of three parts, namely coating, TPU base film and installation adhesive. These three parts bear different tasks. The main function of the coating is to brighten the car paint, resist oil stains, resist scratches, and self-repair; and the adhesive layer, as the name suggests, is mainly used to provide stickiness to adhere the car film to the car paint. The TPU base film still plays a core role in protecting car paint. TPU base film can account for up to 70% of the cost of invisible car clothing, so it can be said to be the soul of the invisible car clothing product.

The coating is a "film" in direct contact with the air, a special polymer made of TPU, designed to enhance the performance of the invisible car clothing. The functions of the coating include anti-fouling, chemical resistance, weather resistance, scratch resistance, UV protection, hydrophobic self-cleaning, scratch repair, etc. Among them, the scratch repair function attracts the most attention. The molecules of the coating have a tight structure and have a certain degree of fluidity even after they have been cured. This allows the coating to gradually return to its original state after being disturbed, leaving no traces. This is the principle of automatic repair of invisible car clothing. That's why it's not afraid of scratches.

As long as the integrity of the car coating is ensured, the coating can, in principle, be repaired indefinitely. However, if the scratches and scratches are serious and have destroyed the transparent nano-coating of the invisible car clothing, it will be difficult to repair and heal automatically.

According to different types of solvents, the installation glue for car clothing is divided into water-based and oil-based pressure-sensitive adhesives. Oil-based ones are generally called solvent-based; according to different types of polymers, they are divided into acrylic pressure-sensitive adhesives and polyurethane pressure-sensitive adhesives. Many people in the industry will When it comes to single-component and two-component pressure-sensitive adhesives, generally speaking, one-component pressure-sensitive adhesive is acrylic type, and two-component (AB glue) is polyurethane type.

The commonly used type is solvent-based acrylic pressure-sensitive adhesive, because it not only has excellent UV resistance and aging resistance, but also maintains stable bonding, good solvent resistance and excellent chemical resistance in both high and low temperature ranges. sex.

In terms of preventing car paint from aging, car clothing mainly plays two roles. One is to act as a "golden bell" to isolate the car paint from the external environment, thereby avoiding corrosion from various acidic substances and pollutants; the other is to act as sun protection clothing. TPU has strong aging resistance, coupled with UV polymerization The chemical coating can block ultraviolet rays and prevent the car paint from yellowing and aging.

Good anti-fouling properties will make it difficult for corrosive substances to corrode the car clothing, and the service life of the car clothing will be greatly extended. Invisible car clothing manufacturers often enhance the anti-fouling properties of invisible car clothing by adding hydrophobic agents and anti-fouling additives, increasing the cross-linking density of TPU substrates and coatings, etc.

The invisibility effect of car clothing is usually measured by haze. In layman's terms, we can understand the concept of haze as the ability to scatter light. The greater the haze, the stronger the light scattering ability, which means that the transparency of the film decreases, and the human eye will be less able to see the car paint, and the presence of invisible car clothing will increase. Haze is a percentage. Usually we use a haze meter to detect the haze of the car film. According to the "Automotive Paint Protection Film" industry standard issued by the Ministry of Industry and Information Technology, the haze of glossy car coating films should be no more than 1%. This standard is even higher than the standard of no more than 2% for aviation plexiglass, which requires the production of The raw materials and manufacturing process of the car clothing film must also meet certain standards.

The first factor that affects haze is the selection of TPU raw materials. This is one of the reasons why we have always emphasized that polycaprolactone-type aliphatic TPU must be used for car clothing films. At the same time, during the production process of TPU, antioxidants, light stabilizers and other additives are added to modify the TPU, which will also affect the transparency of the TPU.

Secondly, there is the production process. Different production processes directly affect the stability of the TPU film, and because TPU is difficult to plasticize uniformly and the film is elastic, the process control accuracy is very high.

Third, whether the surface of the car film is flat and smooth, whether there are scratches and defects, and whether it is contaminated, will all affect the haze. In addition, the increase in the thickness of the car clothing film indicates an increase in light absorption and light scattering, so the haze will also increase.

In fact, all invisible car covers will turn yellow, but the length of time is different. Fundamentally, this is determined by the structure of the clothing material itself. In addition, external light, heat, and oxygen will accelerate the oxidation process of materials. At the same time, yellowing is also related to the additives added to the material, the presence of moisture, impurities, and the processing and production processes. Various chemical or mechanical impurities mixed in during the production and processing will reduce the stability of the material and cause yellowing.

TPU is mainly divided into aromatic TPU and aliphatic TPU. The structure of aromatic TPU contains benzene rings, which are easily oxidized by ultraviolet rays and produce irreversible yellowing. Therefore, aromatic TPU is generally used in soft foam, ship parts, and building materials. This type of field does not require high resistance to yellowing. The structure of aliphatic TPU does not contain benzene rings, and the molecular arrangement density is dozens of times that of aromatic TPU. It is not easily oxidized by ultraviolet rays and is very resistant to yellowing. It is generally used in high-end shoes and clothing, LED accessories, optical lenses, and invisible car clothing. In areas where yellowing resistance is required, aliphatic TPU must be selected as the base material for car clothing. At the same time, aliphatic TPU used in car clothing has special requirements for additives such as UV stabilizers and antioxidants. Only proprietary brands of aliphatic TPU can truly resist aging and yellowing.

The elastic modulus represents the ease of elastic deformation of a material under a certain stress. The greater the elastic modulus, the more difficult it is to deform. This is reflected in the car film, which means the lower the elongation. The elastic modulus is numerically equal to the stress in a unidirectional stress state divided by the strain in that direction.

The elastic modulus of TPU materials has a wide range, between 10 and 100Mpa. The softer the TPU, the lower the elastic modulus. The car clothing film product is relatively soft. Although it is easy to stretch, during construction, earthworm lines or glue flowers are prone to appear in places with large curvatures and corners when flushing water, and it is even easy to flake. side. The harder the TPU, the higher the elastic modulus and the higher the hardness. The car clothing film product is relatively hard and difficult to stretch during construction. Especially in the winter in the north, the product does not show soft elasticity and it is difficult to construct without the assistance of steam.

There are many factors that affect the elastic modulus. Because TPU car clothing film is a composite film, which is composed of TPU substrate, coating, and glue, so these three have an impact on the elastic modulus of the car clothing film. Among them, the TPU base material has a greater impact on the elastic modulus of the car clothing film due to its large proportion.

First of all, in practical applications, the most suitable range of hardness of TPU particles is 90~95A (A Rockwell hardness).

Second, the formula composition, manufacturer and process conditions of TPU particles will also affect the elastic modulus.

Third, the external temperature also affects the elastic modulus. The higher the temperature, the tensile strength and elastic modulus will change. This is why hot air is used when applying film in northern winter.

Finally, there is a certain interaction between the TPU base material, coating, and glue, so the affinity and matching between the three will affect the elastic modulus of the car clothing film. At this time, it is a test of the TPU car clothing film manufacturer's It's time to control the elastic modulus stability.

First, in terms of protection, the thicker the film, the higher the protective performance. Secondly, in terms of construction difficulty, the thicker the car clothing film, the more laborious it is to stretch it, and the construction performance will be correspondingly worse, which will also test the skill of the film applicator. Third, in terms of use, due to the increase in thickness, the stiffness of the car clothing film increases accordingly. As time goes by, the corners are more likely to warp and deglue, which puts higher requirements on the installation glue of the car clothing film. . Therefore, the increase in thickness places higher requirements on the physical properties of the TPU base film, which requires a balance of stretchability, ductility, toughness and other aspects of performance.

Common car film thickness reference: (1mil=1/1000inch=0.0254mm. Mil, one thousandth of an inch)

The 6.5mil car clothing film has a slightly thin film thickness and average protective performance. It is an entry-level economical product and covers a wider range of car models;

7.5mil car film is currently the mainstream model in the market. It has been proven that its protective performance and construction performance are relatively balanced, and the price is relatively moderate;

Car wrap films with a thickness of 8 mil or above are thicker, have stronger protective properties, are relatively more expensive, and require high construction technology. At the same time, they also have higher requirements for the matching of the base film and glue, such as improper material selection. There may be a risk of edge warping later on.

TPU made from polycaprolactone polyol has excellent resilience, abrasion resistance, weather resistance, hydrolysis resistance and low temperature flexibility.

Polyester TPU has excellent mechanical properties, wear resistance, tear resistance, chemical corrosion resistance, high temperature resistance, easy processing, etc., but has poor hydrolysis resistance. Polyester is easily attacked by water molecules and breaks. The acid generated by hydrolysis can further catalyze the hydrolysis of polyester.

Polyether TPU has excellent low-temperature flexibility, hydrolysis resistance, mold resistance, UV resistance, etc. The product feels good, but the peel strength and breaking strength are relatively poor, and it also undergoes thermo-oxidative degradation, which means it is easy to be exposed to high temperatures. oxidative decomposition under circumstances.

From the production side, experienced casting plants and coating plants will now choose polycaprolactone aliphatic TPU particles. However, due to the relatively low price of polyester TPU, some manufacturers will use polyester TPU in order to reduce costs. TPU.