Sealing Guide

Sealing Guide/FSealing Guide/FAQ’AQ’ssBasic Filtration Concepts/Basic Filtration Concepts/Chemical Compatibility Chemical Compatibility

Appendix A Microporous Media Sealing Guide69

For information or to order, call 1.800.362.6276 or 516.484.3600 / fax 516.484.6129 / www.pall.com/materialsSeal

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When sealing microporous membranesor media into a plastic part, there are anumber of factors that should be takeninto consideration. These include handling,environmental, and design factors, aswell as, the integral properties of themedia and other materials.

You also need to consider how the sealis made. Will the membrane be in con-tact with the plastic part or is it actuallythe membrane’s support mesh? Are yousealing membrane to plastic or plastic toplastic? What are the thermoplastic qualitiesof the two materials? Are you sealing likeor unlike materials?

The following is a list of tips that will helpyou when handling and sealing membranes.

Handling and Environmental Factors

• When handling membranes, individualsshould wear gloves; oils on the hands canaffect membrane properties adversely.

• Static eliminators are helpful forhandling and placement of die cutmembrane and processing ofmembrane ribbons, especially for highspeed operations. The relative humidityin the membrane processing area canalso be a factor.

• Tension control is important to ensureproper tracking of roll stock membraneand membrane ribbons.

• Parts and work surfaces must be cleanand free of particulates.

• Molded parts must be free of silicone-based, mold release agents.

Design Factors

• The design of the seal area in amembrane device is a critical factor inthe integrity of the finished seal. Theseal is nearly always the weakest areain the device. It is desirable to radius allangles in contact with the membrane. Itis also preferable to have the flow in thefinished device go in the direction of theseal so that the membrane is supportedin the device when filtration occurs;filtration in the direction away from theseal can cause stress on the seal.

• Minimize excess flash around the seal area.

• Parallelism and alignment of tooling topart and fixture is critical.

• Molded parts should be designed toeliminate or minimize stressed areas.

Material Properties

• Media are available on a variety ofsupport materials. The supportdetermines many of the sealing and handling characteristics.

• For some supported membranes and composite media, the seal willactually be made between the support or composite material and theplastic part, not the membrane. It isimportant to keep this in mind whendetermining melting temperatures,dwell time, etc.

• Use the appropriate resin for thedesired process.

• Parameters for each of the sealingmethods will vary depending on boththe media properties and those of theplastic to which it is being sealed.

Sealing Methods

There are several possible sealing methods available to the designer of a plastic part orhousing containing a membrane or other microporous media:

• Adhesive sealing • Heat sealing• Mechanical sealing - Ultrasonic welding

- Insert molding - Heated dies- Radio frequency

General Sealing Information

This information is intended to serve only as a guide. Users should verify the conditions appropriate to their specific use. Information on our materials is also available oneither our industrial web site at HYPERLINK http://www.pall.com/industrial or our healthcare web site at HYPERLINK http://www.pall.com/healthmedia.

For additional information on adhesive sealing and ultrasonic welding, please visit our supplier market on-line at HYPERLINK http://www.pall.com/materials. Here you will findvarious suppliers who may be able to assist you with your sealing needs. If you would like to speak to someone for additional information please call us at 1-800-362-6276.

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For information or to order, call 1.800.362.6276 or 516.484.3600 / fax 516.484.6129 / www.pall.com/materials

Appendix A Microporous Media Sealing Guide 70

A pressure-sensitive adhesive seal uses athin layer of adhesive to seal the media tothe housing. The adhesive can beapplied in a peel-and-stick format. Checkwith a converting company for informationon configurations of membranes, adhesives,support layers, and release liners. UV setscan also be used.

When evaluating an adhesive seal, compatibility of the adhesive with thehousing, the membrane, and the intendedapplication need to be considered.Compatibility of the adhesive with themembrane and housing polymers shouldbe discussed with your adhesive supplieror media converter.

Industry standards for adhesives can becritical. Some industries have basicrequirements for the adhesive used;specifically, the electronics and medicalindustries. Most adhesive manufacturersare aware of these requirements andhave adhesives that comply with theappropriate standards or regulations. If not, check with an adhesive manufac-turer that specializes in your industry.

• Polyurethanes, epoxies, or similarchemically compatible pure polymers work well as adhesives.

• Avoid using adhesives containingsuspended solids; particulate–ladenadhesives will not penetrate the pores,causing poor adhesion and probableby-pass of particulates into thedownstream filtrate.

• Surface treatment, such as plasma or chemical treatment, may increaseadhesive wettability.

• Unfilled polymers are preferableregardless of the method used forsealing because they will wet the surfaceof the membrane better than filledpolymers, creating a stronger bond.

• Do not use cyanoacrylate when sealingSupor® membranes.

For More Information

Adhesive Sealing

Avery Dennison LoctiteSpecialty Tape Division Rocky Hill, CT USAPainesville, OH USA 860-571-5100440-358-2600 www.loctite.comwww.averydennison.com

Adhesive Sealing

Heat sealing uses a variety of heatsources and pressure to melt the housingand membrane together. Heat seals aretypically classified according to the heatsource; among these are ultrasonic welding,heated dies, and radio frequency welding.

With heat seals it is possible to form twodifferent types of bonds. If the membraneand housing materials have the properthermal characteristics, the media andhousing can be melted together to forma secure seal. Another type of bondoccurs when the housing material melts ata lower temperature than the membrane.

The molten housing plastic penetratesinto the structure of the medium, forminga seal. Many of Pall Corporation’s materi-als form this type of seal, includingPallflex® composite media.

Heat Sealing



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Ultrasonic Welding (UW)

Ultrasonic welding is based on heat,pressure and time. The heat is createdby the use of high frequency mechanicalmotion (vibrations). The high frequencyenergy travels through the material andmust be focused at the desired meltlocation. The greater the vibration thehotter the material becomes.

• A high frequency, low amplitude setting is preferred.

• For weld areas greater than 1.5"diameter, use 20 kHz; for smallerdiameters, use 40 kHz.

• Seal to an energy director rather than a wide, flat surface.

• Avoid long duration weld times at high amplitudes.

• Some single, and most multiple,ultrasonic welds may cause damage to membranes.

• Avoid secondary ultrasonic weld cycles.• Provide a smooth transition from the

seal to the membrane.• Cutting, placement and sealing of

membrane can be accomplished atone time.

• Cushion parts to dampen vibrationsthroughout the entire part.

• Care must be taken to minimizeexcess ultrasonic vibrations to maintainpore integrity. Improper use ofultrasonics can lead to damage of themicroporous membrane’s porestructure.


Ultrasonic Welding

Branson Ultrasonic Corporation Dukane CorporationDanbury, CT USA St. Charles, IL USA203-796-0334 630-584-2300www.branson-plasticsjoin.com www.dukane.com

Heat is transferred through a die underpressure directly to the materials to bejoined for the appropriate time necessaryto form an integral seal. The heated diemelts the housing or the media at thepoint of contact which, in combinationwith the applied pressure, bonds thehousing and membrane together.

• The plastic to which the microporousmembrane is being sealed should havea melting temperature similar to orlower than the membrane.

• Keep geometry of the membranesimple; round membrane couponsprovide the best results.

• To minimize plastic buildup on tooling,use lower temperatures and higherpressures for longer times.

• A high-temperature, non-stick coatingon the heat seal die is recommended.

• Adequate seal land width is important,50-125 mils is recommended.

• Transparency in the seal area is usuallyindicative of a complete seal.

• Short seal times may result in themembrane and its backing pullingapart when the seal die is removed.This is known as delamination.

• In some cases, sealing and cuttingmay be accomplished in a single step.This depends on the membrane typeand the shape of the part and must bedetermined during the design phase.

• Relationships between time,temperature, and pressure must beoptimized through experimentation.Larger coupon sizes and seal landwidths will require higher pressures.


Heated Dies

Forward Technology Industries, Inc.Minneapolis, MN USA612-559-1785www.forwardtech.com

Heated Dies

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Radio frequency (RF) uses heat, pressureand time to form a seal. The heat is gen-erated from high-energy electromagneticwaves (27-31 MHz), which excite themolecules of the materials being bonded.The excitement of the molecules createsheat which combines with pressure andtime to form an integral seal.

• RF sealing can only be used withplastics having the correct dielectricproperties, such as PVC and acrylic.

• The most common method for RFsealing of microporous membranes isto encapsulate the membrane betweentwo plastic housings.

• Longer seal times are preferred forbetter control of the sealing process.

• Avoid potential arcing, which cancause sealing failures.

Radio Frequency Sealing


Radio Frequency Sealing

CallananElk Grove, IL USA847-364-4242

Mechanical Sealing

Membranes can be sealed in place bymechanical means, such as a filter sup-port that is clamped in place using an

O-ring or gasket or by insert molding themembrane into plastic components.

Insert Molding

In this technique the media is held inplace or placed into a mold, while moltenplastic is forced into the mold, forming anintegral piece containing the membrane.Insert molding is a good choice for pro-ducing high volume/low cost compo-nents containing membranes.

• Minimal pinch force should be appliedto prevent membrane damage.

• Avoid venting hot gases through themembrane.


Insert Molding

Husky Krauss Maffel SandrettoBolton, Ontario Canada Alach, Germany Freedom, PA USA770-487-6234 www.krauss-maffel.de 724-775-4255www.huskyims.com www.sandretto.net



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Die Cutting and Slitting

LTI AtlantaSuwanee, GA USA770-418-9005www.Itiatlanta.com

Die Cutting and Slitting

If your operation includes die cutting andslitting of the media, here are a fewguidelines to help you when consideringyour process.

• Conventional steel rule, rotary andimpact dies work well with bothunsupported and supportedmembranes.

• Male/female dies can be used withmost supported and unsupportedmembranes.

• When cutting membranes, dies must bekept sharp with diametrical clearancemaintained at 0.0003" or less.

• Dies should strike through themembrane to a hard surface. The useof interleafing layers may be necessary,depending on the membrane type.

Housing Method Membrane

ABS Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Acrylic Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

EVA Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Latex Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Natural Rubber Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

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Sealing Compatibility Guide continued next page


Polycarbonate Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Polyester (PBT) Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Polyethylene Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Polypropylene Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

PVC Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

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Silicone Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Styrene Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Synthetic Rubber Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

Urethane Adhesive Sealing

Ultrasonic

Heated Dies

Radio Frequency

Mechanical Seal

Insert Molding

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References Used

Handbook of PlasticJoiningCopyright 1997Plastics Design Library

Modern PlasticsEncyclopedia 99The McGraw-HillCompanies

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Not Compatible

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Documents

Sealing Guide