The plastic window and door market is uneven, with sealing strips bucking the trend.
In past applications, plastic doors and windows have been significantly affected by low-performance and poor-quality sealing materials, resulting in numerous quality issues and damage to the merchant's reputation. Particularly in building projects, the problems range from hardening and embrittlement, loss of elasticity and sealing function, to stickiness and oil leakage, rendering them unusable and polluting the doors and windows, affecting their appearance.
This phenomenon is attributed to companies neglecting the introduction and development of window accessories while improving the grade and performance of plastic doors and windows, leading to the development of sealing materials lagging far behind that of plastic doors and windows. Encouragingly, high-quality window accessories, especially sealing materials, are gaining acceptance and gradually entering the window market.
Material Status of Plastic Window Sealing Strips
Currently, sealing strips used abroad mainly include nitrile rubber, ethylene propylene diene monomer (EPDM) rubber, thermoplastic elastomer (TPE), polyurethane elastomer (P), and silicone rubber, with EPDM rubber, known for its excellent aging resistance, having a usage rate exceeding 60%.
Analysis of the Current Status of Plastic Window Sealing Material Development in China
In recent years, in the domestic window sealing material market, sealing strips made of plasticized polyvinyl chloride (PVC) account for over 90% of the market share, while modified high-polymer PVC and thermoplastic elastomer sealing strips recommended by relevant industry departments have extremely low market share, mostly concentrated in the areas surrounding Beijing.
EPDM rubber material was developed in China in the 1960s by the Beijing Chemical Industry Research Institute, but its application and development in windows was only put on the agenda in the mid-1990s, and was researched and developed in 2000 by the Capital Aerospace Machinery Company Rubber and Plastics Products Factory. In the latter half of the same year, it passed the acceptance inspection by relevant experts from the Ministry of Construction and is currently in mass production, but is only used by some high-end window manufacturers in China.
Domestic EPDM rubber sealing strips are about 40% cheaper than similar foreign products, but their development remains slow. This is because many users have not realized that the proportion of sealing strips in the total cost of window manufacturing is relatively small; they only consider cost savings and not the overall benefits of using high-priced, high-quality sealing materials.
Sealing Strip Cross-Section Design and Mold Making Process Status
Domestic plastic window sealing strips, due to their late development, initially had simple cross-sectional shapes, limited to the "K"-shaped strips used for glass pressure strip sealing, the large spoon strips used for window frame (sash) sealing, and the small "O" strips used for screen sashes. In contrast, foreign sealing strips, developing alongside plastic windows, have reached a level of series production and large-scale production. The design of each product's cross-section meets the requirements of its function, and the matching with the corresponding profiles is almost perfect.
Reports show that in recent years, with the introduction of foreign window manufacturing technologies, the cross-sectional shapes and varieties of domestic sealing strips have also changed significantly. However, due to the backwardness of domestic mold-making technology, and the insufficient attention given by domestic counterparts to sealing materials as window accessories, the resulting products, while close in shape to the design, have some functional defects. Examples include large gaps in mating parts and the failure to meet requirements for the amount of compression and overlap, leading to inevitable quality issues during use. In addition to the above factors, this phenomenon is also significantly affected by the raw materials used, such as the processability and expansion rate of the materials.
EPDM rubber is a sealing material with excellent comprehensive performance. Not only are its physical properties excellent, but its processing properties are also very good, and its coefficient of expansion is very small. Sealing strips made of this material are almost identical to the design requirements, which is a major reason for the rapid development of EPDM rubber in recent years.
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