In modern science and technology, as well as in various aspects of daily life, the issue of connections is ubiquitous. Traditional methods of connection such as riveting, welding, threaded connections, nails, and sewing have been used for a long time. However, the recent development of adhesive technology presents a unique approach. Particularly in the era of polymers, the rapid growth of the air filter industry has highlighted the distinct role of adhesives. These adhesives offer irreplaceable advantages over traditional connection and sealing methods, representing a more scientific, practical, and effective new process that addresses critical production challenges. Adhesives have become indispensable in the air filter industry.
1. Application of Adhesives in Frame Assembly - Bonding of Paperboard/Filter Material/Metal A prime example of such filters is the flat-panel filter depicted in Figure 1, along with box-type filters. Paperboard, filter materials, and metal wires often belong to flexible materials, making traditional connection methods challenging. Adhesives make these processes effortless. Emulsion-type adhesives are commonly used in these processes, and if feasible, hot-melt adhesives can also be employed. The curing process for emulsion-type adhesives is typically water-based evaporation, which is influenced by temperature and humidity, requiring precise environmental conditions. Some manufacturers use solvent-based adhesives, which are comparatively easier to implement. However, environmental regulations have led to a shift towards solvent-free adhesives. As Huey Huey Lo from the Joint Chemical Laboratory of the Industrial Technology Research Institute in Taiwan states, the adhesive industry's trend can be summarized as "low release, high performance."
2. Application of Adhesives in Bag Filters In bag filters, the sealing of needle-punched gaps and temporary bonding before screw assembly both showcase the unique functions of adhesives. Hot-melt adhesives are often used for sealing needle-punched gaps, while water-based evaporative adhesives or environmentally friendly solvent-based adhesives are used for temporary bonding before screw assembly.
3. Application of Adhesives in Air Filters - Pleating When using paper-based filter materials, maintaining sufficient dust holding capacity (service life) and low resistance requires the filter paper area to be many times larger than the windward area of the filter. This necessitates the separation of folded filter paper layers. Adhesives once again play a crucial role in this aspect. Before the 1970s, white cardboard and aluminum foil were commonly used as separators. In 1975, Sofilta company started using latex-coated threads as separators. With technological advancements, hot-melt adhesive was gradually employed in the 1990s to fix pleat spacing, ensuring a specific distance between each layer of filter paper. Hot-melt adhesive can be adjusted to various specifications, such as temperature resistance and flame resistance, producing filters with excellent performance. It is primarily used in manufacturing pleated filters, non-partitioned filters, and some small household filters. Its characteristics include odorlessness, high-temperature resistance, rapid bonding, non-sticky texture, uniform dripping, and resistance to absorption by filter paper.
4. Application of Adhesives in Air Filters - Edge Sealing, End Sealing, and Pleat Spacing Chemically reactive adhesives are mainly used in this context. Epoxy resin adhesives were commonly used before, but with the introduction and development of polyurethane adhesive technology, epoxy resin's brittleness and poor impact resistance led to its gradual replacement by polyurethane. It is mainly used in manufacturing pleated filters, partitioned filters, non-partitioned filters, cartridge filters, and small household filters. Some companies also use hot-melt adhesives for edge sealing and pleat spacing in certain products, such as small household filters and cartridge filters. Specialized adhesives like epoxy, silicone, heterocyclic polymer, and inorganic adhesives are used for filters with specific requirements, such as high-temperature resistance.
5. Application of Adhesives in Air Filters - Bonding of Gaskets and Sealing Strips After the initial fabrication of air filters, the installation of sealing strips or gaskets requires adhesive bonding. The choice of adhesive depends on the required strength. Chemical reactive adhesives such as solvent-based adhesives and instant adhesives are chosen for higher strength requirements, while pressure-sensitive adhesives are used for weaker connections. As the filter industry advances, mature polyurethane integral foaming sealing strips have been developed, customizable in terms of color, foam density, and flame resistance. Additionally, liquid gasket adhesives are employed in non-partitioned filters to replace traditional sealing strips for effective sealing. The liquid gasket seal is a cutting-edge and reliable ceiling device for achieving large-area vertical laminar flow. It offers better sealing performance than commonly used mechanical compression devices, making it a widely adopted method internationally. The sealant in the groove is a non-Newtonian fluid, possessing characteristics like non-volatility, oil resistance, acid and alkali resistance, non-toxicity, and non-odor, as well as good flame resistance, stability, and dielectric properties.
6. Application of Adhesives in Air Filters - Adhesives for Chemical Filters Various materials can be used as adsorption materials for chemical filters, including activated carbon, alumina, zeolite (molecular sieves), silica gel, ion exchange resins, and more. However, activated carbon (including impregnated carbon), alumina (PIA), and zeolite are the popular choices. Regardless of the material used, chemical filters share a common trait – adsorption capacity. Therefore, the chosen adhesive must be environmentally friendly and should ideally not compromise adsorption performance. Adhesives can also be used to bind various particle-like adsorption materials into blocks or adhere them to certain materials. For instance, a certain amount of activated carbon particles can be fixed between two layers of non-woven fabric using adhesive, enriching the variety of chemical filter types. This represents a positive trend in the development of chemical filters.
