How to choose ULPA sealant according to working conditions?

The sealant does not occupy a large position in the filter, but it determines one thing: the air can only pass through the filter material and cannot slip between the filter material and the frame.

If the colloid is wrongly selected, or does not cooperate well with the filter material and outer frame, the problem may not be visible in the short term. After running for a period of time, the glue seams will crack, degumm, or release pollutants, and it will be troublesome to check again. Therefore, the choice of glue is not 'just match any one that can stick', but should be determined according to the working conditions and material system. For specific leakage troubleshooting ideas, please refer to the relevant instructions for inspection after reverse installation.

First clarify the role of colloids in ULPA

The filter material of ULPA has a folded structure and needs to be continuously sealed with the outer frame. The function of the edge sealing glue is to fix the edge of the filter material to the frame and seal the ends of the pleats to prevent unfiltered air from entering the clean side from the edge.

This bonded interface has to withstand more than just static loads. When the air flows through the filter material during operation, it will exert force on the pleats, and the pressure will also fluctuate when the system starts and stops and the air volume changes. The colloid is required to maintain bond strength and seal continuity under such dynamic conditions.

The colloid must also be 'clean'. In semiconductor, pharmaceutical or precision optics projects, volatiles released from colloids can affect the process. Even if particle leakage detection is qualified, colloidal outgassing may become a source of contamination. For specific outgassing verification methods, please refer to the relevant instructions on low outgassing.

Select by temperature

Temperature is a fundamental variable affecting colloid selection. Different colloidal formulas have their own applicable temperature ranges. Regular operating temperature, short-term peak temperature and heating and cooling rates need to be provided to the supplier.

If the project is operated at higher temperatures for a long time, ordinary colloids may accelerate aging. If there is a hot and cold cycle, the expansion coefficients of the colloid, the filter material, and the outer frame are different, and stress may occur at the interface. These factors should be considered together when selecting glue. involving HEPA/ULPA air filters should be written into the technical agreement. The selection and temperature resistance conditions of

Select according to humidity and chemical medium

A high-humidity environment may affect the curing state and long-term bonding performance of the colloid. Some colloids may swell, become soft, or have a reduced bonding strength after absorbing moisture.

If the gas stream may be exposed to acidic, alkaline gases or organic solvents, the chemical resistance of the colloid must be checked item by item. Different systems such as polyurethane, epoxy, and silicone have different chemical resistances. You cannot just look at the words 'corrosion resistance'.

Cleaners and disinfectants are also variables. Pharmaceutical projects often use chlorine-containing disinfectants, hydrogen peroxide or alcohol-based cleaners, and the effects of these media on colloids need to be confirmed. For specific material selection methods, please refer to the instructions related to the comparison of glass fiber and PTFE filter materials.

Select according to volatile matter and gas release requirements

For projects that are sensitive to outgassing, colloids are one of the key control objects.

Define the target of concern—total organic carbon, specific siloxanes, or other compounds. Different targets correspond to different detection methods and limits. The colloid supplier should provide corresponding material data or test reports.

The colloid, filter media, gasket and frame are evaluated together as a single piece of material. Merely measuring the colloid itself does not mean that the entire product meets the gas release requirements. During sample verification, the entire unit should be tested according to the proposed supply configuration. For specific verification procedures, please refer to the relevant instructions of ULPA low outgassing verification.

Compatibility with filter media and frames

The colloid must be bonded to the filter material and outer frame at the same time. The filter material may be fiberglass or PTFE, and the outer frame may be aluminum alloy or stainless steel. Different combinations have different bonding properties.

When selecting glue, you should confirm: the wettability of the colloid to the filter material, the bonding strength after curing, the adhesion to the metal frame, and whether interface aging will occur after long-term operation. If the filter material or outer frame has surface treatment (such as anodization, passivation), the compatibility with the colloid must also be confirmed. For specific frame material selection, please refer to the relevant instructions on the comparison between aluminum alloy and stainless steel.

Compatibility cannot be judged by data sheets alone. Some combinations perform normally in short-term testing, only to experience degumming after long-term operation. Verification of prototypes under actual working conditions is more reliable than just looking at material certificates.

Validation and change management

After the glue selection is determined, verification and change management are steps to ensure long-term consistency.

Sample verification. Make samples according to the proposed supply configuration and test them under actual working conditions or simulated working conditions. Check bond condition, seal integrity and outgassing levels.

First item confirmed. When mass production begins, the first piece is inspected to confirm that it is consistent with the sample.

Change assessment. When there are changes to the colloid supplier, formulation or curing process, re-evaluate the impact on sealing, strength and outgassing. It cannot be assumed that 'the material name is the same' means the performance is the same. For specific procedures, please refer to the instructions related to filter material batch changes.

Regular spot checks. For long-term supply projects, the status and integrity of the glue joints can be randomly inspected at an agreed period. involving ULPA ultra high efficiency filter or HEPA high-efficiency filters are the same. The selection and verification requirements for

Project judgment example

After a semiconductor equipment project replaced the ULPA filter element, it was found that trace amounts of organic matter contamination occurred downstream after running for a period of time. The particle leakage test is qualified and the pressure difference is also normal.

The investigation revealed that the source of the contamination was the edge-sealing glue—the original plan used conventional colloid and was not screened for the low outgassing requirements of the process. The colloid releases trace amounts of volatiles at operating temperatures, which are not significant but have an impact on the process.

Treatment method: Switch to a low-gas-releasing colloid solution, redo the entire gas release test and on-site leak detection to confirm that contamination no longer occurs.

The key to this case is: the selection of sealants should not only look at bonding and sealing, but also the requirements for colloids under working conditions. involving The logic is the same when selecting HEPA/ULPA air filters .

Selection and Acceptance Checklist

About Aili Industrial’s sealant configuration package

The selection of sealant is essentially a matter of checking the filter material, outer frame, working conditions and pollution control requirements together. If this information is clarified during the planning stage, subsequent changes and verification will be much smoother.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For projects with special working conditions, temperature, humidity, chemical media and gas release requirements can be combined to assist in checking the colloid type and entire material configuration. When the filter is matched with equipment such as FFU and EFU, the compatibility of the colloid with the filter material and outer frame can also be evaluated together during the planning stage.

Provide contact media, temperature range, cleaning method and outgassing requirements when enquiring, which will help confirm the appropriate sealant solution. The specific selection is subject to the technical documents and test results confirmed by the project.