The filtration efficiency degradation of meltblown fabric has become a critical concern in the industry. Currently, meltblown fabrics with filtration efficiency below 90% face significant market challenges, while even 90-grade fabrics have become widely available. This market reality forces manufacturers to upgrade to 95 or 99-grade products to maintain competitiveness.

Many manufacturers have reported a puzzling phenomenon: freshly produced meltblown fabric may initially meet 95 or even 99-grade standards, but its filtration efficiency drops to 92, 90, or even 85 grade after just a few days of storage. This performance degradation is actually a complex systemic issue involving multiple factors including fiber diameter, fabric density, molecular polarity of PP material, and the power output (electric field intensity) of electrostatic generators.

The primary reasons for this efficiency decline in originally 95-grade fabric after storage are fundamentally related to three key elements: the quality of electret masterbatch used in production, the storage environment conditions, and the performance of electret treatment equipment. The interaction of these factors ultimately determines whether the fabric can maintain its initial high filtration performance over time.

1.Selection of Permanent Electret Masterbatch

The electret process essentially involves electrical charging treatment. While freshly electret-treated meltblown fabric may initially achieve 95+ grade filtration efficiency, the performance often deteriorates after several days of storage. This degradation primarily results from the inherent instability of the electrostatic field, where charge dissipation directly leads to reduced filtration efficiency.

Currently, three main types of electret masterbatches are commonly used in the industry: those produced using tourmaline-based methods, silica-based methods, and nitrogen-containing chemical fatty acid compounds.

Each category presents distinct advantages and limitations. The silica-based electret masterbatch demonstrates superior comprehensive performance, offering high efficiency and exceptional charge persistence that essentially achieves permanent charge storage. This type features excellent dispersibility, complete absence of odor and toxicity, and compliance with FDA certification requirements, making it the optimal choice for maintaining long-term filtration performance in meltblown fabric applications. The silica-based technology's balanced characteristics in charge stability, environmental friendliness and regulatory compliance position it as the most advantageous solution for sustainable high-efficiency filtration materials.

We are all familiar with how static electricity builds up more easily when wearing clothes in dry winter conditions, whereas in more humid seasons, this phenomenon rarely occurs due to increased atmospheric moisture.

This principle directly applies to meltblown fabric performance. Environmental humidity significantly impacts both the generation and dissipation of electrostatic charges. When exposed to humid conditions, the moisture in the air interacts with the stored charges in the meltblown material, converting them into negative ions and consequently depleting the electrostatic charge. This charge loss directly compromises the fabric's filtration efficiency. Therefore, immediate and proper packaging after production is crucial to maintain optimal performance by preventing moisture absorption and preserving the electret charge integrity. The packaging should ensure an airtight seal to protect against ambient humidity fluctuations that could otherwise degrade the material's filtration capability over time. This protective measure is particularly critical in regions with high humidity or during seasonal transitions when atmospheric moisture levels fluctuate significantly.

To prevent charge dissipation and maintain the filtration efficiency of meltblown fabric, improvements must be made to its storage environment in the following three key aspects:

(1) Monitor and Control Temperature & Humidity

It is essential to continuously monitor and regulate the temperature and humidity levels in the production facility. Appropriate equipment should be installed to ensure these parameters remain within a stable and optimal range.

(2) Prompt Packaging and Dry Storage

Immediately after production, the meltblown fabric should be properly sealed—preferably using vacuum packaging—and stored in a dry environment to prevent exposure to external moisture. This prevents rehydration and contamination, which can degrade performance.

(3) Segregate Fabric from Different Production Lines

A critical consideration is to avoid storing meltblown fabric produced from different machines together. Mixing fabrics from different production lines can lead to charge neutralization, negatively impacting their electrostatic filtration properties.

By implementing these measures, manufacturers can significantly enhance the longevity and effectiveness of meltblown fabric, ensuring it retains its high filtration efficiency over time.

3. Electret Equipment Must Use Positive Charge

(1) Why Should Electret Equipment Use Positive Charge?

Airborne particles such as dust, bacteria, and viruses predominantly carry negative charges. When meltblown fabric is positively charged, it effectively attracts and captures these negatively charged particles.

Electret equipment must utilize positive charge rather than negative charge. This is because the fabric's positive charge enhances its ability to adsorb negatively charged airborne contaminants. Additionally, when the fabric comes into contact with skin, negative charges are more readily dissipated, whereas a positive charge degrades more slowly, ensuring longer-lasting filtration efficiency.
 

(2) How to Select an Electrostatic Electret Generator?

The market offers various specifications of electrostatic electret generators, typically categorized by output voltage: 30KV, 50KV, and 120KV. So, which one should be chosen?

According to engineers specializing in electrostatic equipment, experimental results indicate that a voltage range of 15-50KV is optimal, with a discharge distance of 4-8cm. This configuration ensures effective charging while maintaining the stability and performance of the electret treatment.
 

(3) Configuration Principles for Electrostatic Electret Generators

◆ Excessively high voltage (e.g., exceeding 50KV) may damage the molecular structure of polypropylene;

◆ If the discharge distance is too close, it may cause arcing/sparking that punctures the meltblown fabric;

◆ If the discharge distance is too far, charge scattering occurs - most charges escape without being effectively embedded in the masterbatch, resulting in insufficient electrostatic field strength in the fabric.
 

Important Note:

Be aware that some equipment may be labeled as 120KV while actually delivering only about 23KV output voltage. This significant discrepancy requires careful verification during equipment selection and operation.