Definition and Basic Characteristics:
A ULPA panel filter (Ultra Low Penetration Air Filter) is an air purification device that employs a rigid flat panel structure design to achieve extreme filtration efficiency for ultrafine particulate matter in the air. According to the international standard ISO 29463 (formerly EN 1822), a ULPA filter is formally defined as an air filter that, under specified test conditions, achieves a filtration efficiency of not less than 99.9995% for the Most Penetrating Particle Size (MPPS). The panel structure specifically refers to a rigid, flat panel module formed by folding or laying the filter media without partitions. This structure typically results in a smaller volume, higher structural strength, and better airflow uniformity compared to traditional partitioned filters at the same efficiency level.
Panel-type ULPA filters are the core terminal equipment for maintaining air cleanliness in modern ultra-clean environments (such as ISO Class 1-3 cleanrooms, advanced biosafety laboratories, and precision semiconductor manufacturing workshops). Their performance far surpasses that of HEPA filters (efficiency ≥99.97% for 0.3-micron particles), primarily targeting viral carriers, nano-sized aerosols, metallic fumes, and extremely fine chemical contaminants in the 0.1-0.2 micron particle size range, forming a key physical barrier for achieving “molecular-level” air cleanliness.
Core Structure and Materials Engineering
The exceptional performance of panel-type ULPA filters stems from their precisely designed structural system and rigorously selected materials.
- Filter Media
The core of the filtration system is ultra-fine glass fiber filter paper. The fiber diameter is typically controlled between 0.3-1.2 microns, and a thin filter layer with a complex three-dimensional network structure is formed through special wet or dry processes. The preparation of the filter media requires precise control of fiber diameter distribution, porosity, and surface treatment processes. Filtration technology company Trenntech, at its materials laboratory in Frankfurt, is developing a gradient filter media that blends traditional glass fibers with finer nanofibers (<0.1 micrometers in diameter) using a combination of electrospinning and meltblown technologies. The aim is to improve interception efficiency while ensuring extremely low airflow resistance.
Structural Design
The essence of the “panel” design lies in its rigid, folded structure without separators. The filter media is folded into deep, uniform corrugations using precision pleating equipment. The depth and spacing (pitch) of the pleats are optimized through fluid dynamics simulations to maximize the filtration area and achieve the lowest possible face velocity within a limited volume. The edges of the folded filter element are sealed and encapsulated with polyurethane, hot melt adhesive, or silicone, forming a rigid, monolithic flat plate without internal supports. This structure avoids the risk of metal ion release that can occur with aluminum separators in traditional separator filters, and it is also more robust and less prone to deformation or damage during handling or installation.
3. Frame and Sealing System
To ensure no bypass leakage after installation, panel-type ULPA filters typically use anodized aluminum or galvanized steel sheets for the frame, combining strength and corrosion resistance. The sealing system is the last critical line of defense for performance assurance, generally employing polyurethane foam strips or solid silicone gaskets. During installation, the sealing material deforms under pressure, ensuring an airtight seal between the filter and the mounting frame.
III. Performance Testing, Certification, and Application Areas
The performance of panel-type ULPA filters must be verified through standardized and rigorous testing. Mainstream testing follows ISO 29463, using dioctyl phthalate (DOP) or similar polydisperse aerosols as the challenge material, and employing a laser particle counter to scan the entire filter surface (including the filter element and frame seals), measuring its penetration rate near the MPPS. Only filters with an overall penetration rate not exceeding 0.0005% (i.e., efficiency ≥ 99.9995%) can be certified as ULPA grade.
Its primary applications are in fields with extremely high air cleanliness requirements:
- Semiconductor and flat panel display manufacturing: Preventing nanoscale particles from causing chip defects during critical processes such as photolithography and etching.
- Biopharmaceutical and aseptic filling: Ensuring a sterile environment and removing bacterial and viral carriers in vaccine and biological agent production.
- High-level biosafety laboratories (BSL-3/4): Preventing the leakage of dangerous pathogens and ensuring the safety of personnel and the environment.
- Precision optics and aerospace manufacturing: Eliminating ultrafine contaminants in the air that may affect product performance.
The ULPA panel filter represents the pinnacle of current deep air filtration technology. It integrates materials science, fluid mechanics, and precision manufacturing, and through engineered design, stably and reliably implements multiple microscopic physical capture mechanisms on a macroscopic scale, constructing an invisible yet crucial ultra-clean barrier for modern high-tech industries.