2021 is a year of rapid transformation in the automotive industry, with rapid penetration of electrification, steady advancement of intelligence, and a promising future of networked and shared services. With a deeper understanding of user interaction experience, the intelligent cockpit as an entry point for human-computer interaction is increasingly being valued by automotive manufacturers. The traditional 8-inch small screen can no longer meet users' expectations for smart cars. In order to better communicate with users, the screens on cars are becoming larger and larger, and curved screens are also beginning to be integrated into smart cabins. Various screens such as central control, instrument panel, entertainment, and head up display provide safe and reliable information flow and interaction windows for passengers inside the car, which cannot be separated from the continuous progress of optical bonding materials.
The traditional bottom coating treatment requires brushing on the cleaned and dried substrate, followed by drying, and then curing and bonding with silicone rubber material under high-temperature conditions in the mold. This kind of process is complex, and the precision of the product is also low. At the same time, the primer usually contains organic solvent components, which can pollute the environment and also pose a risk of skin sensitization to users. Stir
Taking our common car central control screen as an example, it actually has a very multi-layered functional layer composition. In terms of composition, the cover layer, touch layer, and display layer are common three-layer structures. The cover plate and touch panel are often referred to as touch panels, and the optical bonding between the touch panel and the display module is commonly referred to as full bonding. Before full bonding, the display screen and protective cover plate are only fixed around with glue, commonly known as frame bonding. Frame pasting creates an air gap between the cover plate and the display screen, which not only affects the display effect due to light refraction and reflection at the interface, but also further affects the interactive experience due to environmental substances such as dust and moisture.
For car displays with high reliability requirements, the benefits of full fit are obvious: the intervention of optical fit layer significantly improves the screen display effect; Effective bonding and filling reduce the impact of external forces, light, heat, moisture, dust, and other factors on the screen and the touch effect, allowing drivers and passengers to obtain driving information with peace of mind, while also reducing the risk of screen breakage in the event of accidents.
The traditional bottom coating treatment requires brushing on the cleaned and dried substrate, followed by drying, and then curing and bonding with silicone rubber material under high-temperature conditions in the mold. This kind of process is complex, and the precision of the product is also low. At the same time, the primer usually contains organic solvent components, which can pollute the environment and also pose a risk of skin sensitization to users. Stir
In theory, any sheet or liquid material that can be made into transparent adhesive (OCA) or liquid material (LOCA) can be fully bonded, but after the market's ups and downs, the main fully bonded materials on the market are acrylic acid and silicone. Acrylic related materials have a dominant position in the fully bonded market of consumer electronics, while fully bonded silicone materials have been favored by many car screen manufacturers, which depends on the application requirements and material structural performance.
Compared to consumer electronics, automobiles have a longer lifespan and undergo more stringent environmental testing requirements. During parking and driving, cars may encounter extreme cold temperatures as low as -40 ℃ and high temperatures as high as 70 ℃ under scorching sun exposure. During operation, they also have to withstand various adverse factors such as vibration, instantaneous impact, UV light, moisture, heat, etc. from the external environment. Some fully bonded materials used in consumer electronics may experience molecular chain breakage and rearrangement during long-term photothermal aging, leading to color reaction (mainly yellowing) and a certain degree of decline in mechanical properties, which affects the fully bonded bonding effect. In addition, acrylic optical water-based adhesive may also have problems such as high curing shrinkage and curing in shaded areas during the curing process.
The molecular structure of organic silicon
Organic silicon materials have Si-O bonds as the main chain and organic functional groups on the side. The longer bond length and larger bond angle of Si-O bonds can bring low glass transition temperature, and even some special specifications of organic silicon can maintain elasticity at -100 ℃. The Si-O bond has high energy, can withstand high temperatures of 180 ℃ for a long time, and is not easily decomposed by ultraviolet light and ozone. Organic silicon has better thermal stability, radiation resistance, and weather resistance than other polymer materials, and its service life in natural environments can reach several decades. The advantages of these structural properties provide a solid theoretical basis for the use of organosilicon as a fully adhesive material for vehicles.
The traditional bottom coating treatment requires brushing on the cleaned and dried substrate, followed by drying, and then curing and bonding with silicone rubber material under high-temperature conditions in the mold. This kind of process is complex, and the precision of the product is also low. At the same time, the primer usually contains organic solvent components, which can pollute the environment and also pose a risk of skin sensitization to users. Stir
The weather resistance of organic silicon provides it with the foundation to become a highly reliable product. The realization of high performance and high efficiency further tests the understanding of organic silicon substrates by organic silicon engineers, the innovation of formula components, and the balance of performance control.
Before 2010, silicone optical water gel was used in vehicle mounted full bonding. It was mainly a two-component addition molded silicone gel, which was thermally cured. After curing, the cone penetration was more than 60 (9.38g cone unit: 1/10 mm). Because it was like jelly after curing, it was commonly called jelly gel. At this time, due to the low strength of the OCR body and the adhesive force mostly below 0.2Mpa, it needs to be reinforced with RTVs around it, which itself mainly serves as optical filling. Due to its low intrinsic modulus, it can effectively absorb stress. The OCR bonding process during this period is relatively complex.
With the rapid development of in car screens in recent years, higher requirements have been put forward for efficiency, performance, and reliability. How should silicone R&D engineers solve this problem? For efficiency, faster curing speed means higher efficiency, and faster catalytic efficiency requires catalysts with higher catalytic activity. A highly active catalyst not only brings faster curing speed, but also shortens the pot life of the thermosetting adhesive, posing a great challenge to the process.
At this point, a UV delayed catalytic scheme came into the view of German Wacker chemical engineers: OCR was mixed and UV photoactivated catalysts were used. UV light activated pre catalytic pot life can theoretically be infinitely long, and UV activation can efficiently catalyze addition reactions when needed for catalysis. This can not only solve the problem of pot life, but also greatly shorten the curing time after bonding ® The UV series products were born and have gradually become one of the mainstream in the car fitting market.
The traditional bottom coating treatment requires brushing on the cleaned and dried substrate, followed by drying, and then curing and bonding with silicone rubber material under high-temperature conditions in the mold. This kind of process is complex, and the precision of the product is also low. At the same time, the primer usually contains organic solvent components, which can pollute the environment and also pose a risk of skin sensitization to users. Stir
Recently, Germany's Wacker Chemical has launched a new single component organic silicon OCR LUMISIL ® 202K FLEX UV. This product not only maintains the high curing speed of UV cured OCR, but also comprehensively improves performance, making it particularly suitable for the adhesive requirements of curved screens:
Pulling force greater than 6kgf/cm ², increased by 200% compared to the first generation thermosetting product
The range of adhesive substrates has been expanded, from glass and polarizers to common automotive screen substrates such as PC and PMMA. For designs using plastic cover plates, curved surfaces, or irregular shapes, effective adhesion to the substrate can enhance the reliability of the product in the later stage, avoiding problems such as cracking and poor bubbles caused by adhesion issues during the environmental testing process of the screen in the later stage
High elasticity: Generally speaking, the strength of the body is improved, and many products come at the cost of increasing crosslinking density, sacrificing product elasticity or elongation at break. LUMISIL ® 202 1 K FLEX UV not only enhances adhesive strength and body strength, but also maintains high elasticity, with a product elongation at break of nearly 1000%
Latest single component silicone water gel LUMISIL ® 202 1KFLEXUV has both strength and toughness, and excellent adhesion, which can meet the large deformation of the screen during cold and hot impact processes and effectively control stress distribution. These properties can effectively complement the diverse selection of car screen materials and personalized design of the structure.
