Expanded PTFE (ePTFE) Gasket Tapes

Expanded PTFE (ePTFE) Gasket Tape is increasingly becoming the preferred material of choice for any application requiring an on-site solution to both prevent and arrest leakages.

The material’s superior sealing properties combined with the ability to withstand both high temperatures and nearly all corrosive chemicals make it the obvious choice for engineers looking for a long term solution to sealing without worrying about the durability of the sealing material.

ePTFE Gasket Tapes are also known as the following:

1. Joint Sealant Tapes
2. Soft PTFE Tapes
3. Form-in-place Gasket Tape
4. Gore Gasket Tape
5. Expanded PTFE Sealing Tape
6. Self-adhesive Gasket Tape

The fact that there are so many different names poses a challenge to market this product – since each end user may have their own terminology and thus search online accordingly.

The versatility of ePTFE Gasket Tapes extends across multiple industries, as shown in the info-graphic below.

Expanded PTFE (ePTFE) Gasket Tape

The above photo shows the typical application of ePTFE Gasket Tape. Although this shows the joint sealant being applied around a metal flange, the tape is equally adept at sealing weaker materials such as glass or plastic. This is because the sealing effectiveness can be attained at low torques, allowing a completely air-tight seal even if the option to tighten around the medium is limited.

Find out more about the applications and installations of Expanded PTFE (ePTFE) Gasket Tape on our website

ePTFE Membranes – The Possibilities are Endless

It doesn’t require a scientist or an engineer to take a basic property of a material and extrapolate the possible areas of application.

We have spent the last one year developing ePTFE membranes, as we saw it as a key growth area within the PTFE space. As a technology, it remains obscure. Yet the demand for this product is so vast that it is no wonder that the few companies that have perfected it have been able to command the market (and by extension, the price).

To say that we have perfected ePTFE membranes would still be an overstatement. Being an SME, we have had to focus our R&D in those areas where clients have shown interest, rather than take a broader approach and simultaneously develop multiple variants. However, in our pursuit of client satisfaction, there have been consistent findings that have slowly allowed us to start tapping into the broader demand in the market. In addition to this, what we know about the property of the material gives us insights into other, perhaps less explored areas of application.

To start with, let us lay out the most fundamental property of this material:

ePTFE membranes allow gases and vapours to pass, while restricting liquids

This ability is what lays the foundation for the myriad applications (and potential applications) of ePTFE membranes. When coupled with the other properties of PTFE – such as temperature resistance, chemical inertness and dielectric strength – it is easy to see why the product is so much in demand.

1. ePTFE Membranes in Automotive Vent Applications
   
   Auto is a well traversed industry for ePTFE usage. We started our development of ePTFE membranes when we were asked to replicate an automotive vent as manufactured by Gore. The vent is a small disk of ePTFE membrane, with an adhesive backing. We were able to develop it in both virgin form and with a carbon filling.The purpose of this vent is to sit on a small opening at the back of the headlamp chamber. Any moisture that could potentially fog the headlights and/or condense within the chamber is released via the vent. However, as the vent is only permeable to gases and not liquids, water is no allowed back into the headlamp chamber, keeping it free from moisture.
   
   
2. ePTFE Membranes in PCB applications
   
   The effect of moisture on PCBs is well known. Apart from rust and corrosion, the presence of excess moisture can cause multiple short circuits, destroying the device within which the PCB is operating.ePTFE membranes are ideal in allowing any moisture built up within the PCB assembly to escape. At the same time, in the event of direct exposure to liquids, the ePTFE membrane shields the PCB, keeping it dry.
   The usefulness of this application is seen in nearly every industry where electronics are used. With mobility becoming more important, the chance of exposing a device to moisture becomes nearly unavoidable (think, dropping your smartphone into water). Having the protection of a breathable ePTFE membrane means the device is less likely to fail in such an event.
   
3. ePTFE Membranes in Cable Wrapping
   
   We have covered this in an earlier post. However, it is useful to reiterate that the high dielectric capabilities of ePTFE drive its use as a cable wrapping medium.ePTFE insulator tape can be made with tightly controlled thicknesses of as little as 0.05mm, with a uniform density, and dielectric constant. Wrapping individual conductors in ePTFE can cut interference, noise, cross-talk, and signal attenuation. In some applications, ePTFE tape helps limit phase shift to 4.3° and signal attenuation to 0.05 dB at 110 GHz.
   
4. ePTFE Membranes in Filtration
   
   Multiple applications within filtration exist for the use of ePTFE. Filtration itself requires different levels of porosity and pore size and the membrane needs to be customised accordingly.
   
   One of the most commonly known filters is used in vacuum pumps. It consists of a single ePTFE layer, moulded into a polypropylene housing (see below).
   
5. ePTFE Membranes in Desalination
   
   We believe this may be a huge growth area going forward. Desalination is an expensive process currently. An ePTFE layer could be used to allow for evaporated vapours from a salt water reservoir to pass through it and into an upper chamber. Consequently, it would prevent the condensed liquid from re-entering the salt water reservoir. In this manner, the water is separated from the salt using only solar energy. Spread over a wide enough area, this could effectively trap evaporating sea water to convert to fresh water.

We expect to continue adding to this list as more uses of ePTFE membrane become apparent. One thing we do know is that is a material of the future and that being able to modify and customise its texture and form would be a key proprietary skill going forward.

Charting ePTFE (expanded PTFE) Specifications as per Global Standards

One of the toughest things about being the first in a given field is that there is so little data available for testing against.

As the only Indian company manufacturing ePTFE (expanded PTFE) gasket tapes, we are constantly met with questions regarding how the properties of our material hold up against those of competing brands operating in Europe and the USA. However, since the material is so new, there do not exist any established testing standards locally for us to check the product.

Basic Initial Data

To counter this, we initially took up the task of importing tapes from other manufacturers and testing the tensile properties and specific gravity against the same. Initially, we were trying to answer only 2 questions:

1. How soft should our tape be?
   Since the extent to which we expand the PTFE can be adjusted, it directly impacts the specific gravity of the end product. For a like-to-like comparison, we were hoping to match this with global brands. We eventually found that the standard density of ePTFE Gasket Tapes is 0.6-0.65g/cm3
   It should also be mentioned that some clients have specifically come to us asking whether they can get the tapes even softer, as their application is such that not much force can be applied to the tape. We have obliged – getting the density down to as little as 0.3g/cm3 in some cases.

2. How strong should our tape be?
   ePTFE tape looks great coming out of the machine. It is pure white, soft to touch and very smooth. However, two tapes that look exactly the same, could give completely contrasting values when tested for tensile strength. We found that global brands offered tensile strengths in the range of 5Mpa to 10Mpa.
   Once we standardised our production process, our own tapes showed a tensile strength of 12Mpa, so we were satisfied with the result.

Looking for global standards

Although we were happy with the properties of our material, there were still gaps in our understanding. Most notably, what were the other properties we should be testing? And rather than compare between brands, should there not be a global standard that specified the values we needed to obtain?

Again, going through competitor data provided very little information on this front. Expanded PTFE is a very niche market and from our own experience of getting the product right, we know that not much information can be divulged with regards to the behaviour of the material.

We looked around for global standards and realised that although there are many ASTM standards for regular PTFE, for ePTFE there were none. A few competitors had put up data on compressibility (ASTM F 36) and creep relaxation (ASTM F 38), but these were only comparing values to “leading brands” and not referring to any standard for the values. Others simply quoted the values, but did not elaborate the specifications against which these values would hold up.

We also went through the certifications that competitor brands were providing. These included:

1. DVGW VP 403 – The German standard for checking ePTFE Tapes
2. TUV MUC-KSP-A066 – The TUV Standard for ePTFE
3. BAM – For use in Oxygen rich environments

We contacted each of these organisations and were given estimates on how much the testing would cost. However, at no point are any values discussed. These remain guarded by the certification bodies. Our worry was that if we sent our material to these bodies without adequately testing them ourselves first – there was a risk that we may have overlooked a certain property and due to this, the product may not pass, resulting in an expensive mistake.

Eventually, we came upon the one standard that dealt specifically with ePTFE Tapes and was willing to offer values for us to compare against – the AMS 3255A.

The AMS is globally recognised as a leading authority for aerospace related materials. As such, we felt confident that their values would be stringent and thereby an effective standard to hold ourselves to.

The AMS 3255A prescribes many types of ePTFE Tape. Our basic tape falls under Class 2, Type 1, which requires the following properties to be met:

Property	Value/Result	Unit
Specific Gravity	0.4-1.2
Tensile Strength	3.44	Mpa
Tensile Strength (Fluid/Thermal Stability)	8.27	Mpa
Low Temperature Flexibility	No evidence of cracking
Liquid Sealability	No fluid leakage or loss of pressurization
Reparability	No fluid leakage or loss of pressurization

Armed with the above data and the testing procedures prescribed by the AMS 3255A, we were able to test our material in-house to confirm that the properties we were observing were as per the requirements of the standards.

In addition to this, we were also able to test the material with local certification bodies, to confirm the properties.

To the best of our knowledge, the AMS 3255A remains the only globally recognised standard to offer any values and/or testing procedures to verify the properties of ePTFE Gasket Tapes.

Expanded PTFE (ePTFE) Tapes – Properties and Installation Techniques

ePTFE Tapes are an ideal form-in-place gasket material made from 100% pure virgin PTFE that has been expanded to achieve a foamy structure.

While we have covered the applications of this earlier and also touched upon some of the variants, we would like to re-explore some of the finer aspects of the material as well as look at the installation in more detail.

ePTFE Structure

A number of variables contribute to what we would define as a suitable final product. While the nuances of the production technique are proprietary information, what we can reveal is that the end product, while seemingly uniform, can be anything but.

1. Specific Gravity
   In achieving a final product that matches the properties of other ePTFE Gasket Tapes in the market, one of the key properties explored was the density of the material. By varying the process, this parameter can be altered to produce different results. While most commercially available ePTFE Tapes have a specific gravity of 0.6-0.7, we were able to bring this down to 0.3, making the material much softer and more malleable.
   This reduction in density is not always preferred. In applications where the ePTFE is sandwiched between steel elements, you would prefer a higher specific gravity. However, in delicate applications, such as electronics and medicine, we may need to use a gasket or sealing element upon which large pressures cannot be applied as the equipment themselves are fragile. In such cases, a low density tape would be ideal as it would take the shape required with minimal pressure
2. Thickness
   Standard ePTFE tapes come in thicknesses starting from 1.5mm. However, certain applications such as cable wrapping and filtration require tapes as low as 0.1mm in thickness. While achieving was not easy, it did allow us to explore the properties of tapes under 1mm in thickness and gauge what made them so different.
   ePTFE Tapes fall somewhere between sintered PTFE tapes (made from skiving a fully sintered PTFE billet) and thread sealant tape (made from calendaring unsintered PTFE strips). As such, they imbibe the electrical properties of skived tapes, while retaining the malleable structure of thread sealant tape. Furthermore, the foamy structure allows for better thermal insulation as compared to both the other variants
3. Fillers
   Fillers are commonly used in PTFE to attain variations in final properties. We have experimented with fillers of PEEK and Carbon to reveal variations that significantly improve what the ePTFE tapes are capable of. Carbon allows us to make anti-static tapes, which are used extensively in the manufacture of co-axial cables. PEEK, meanwhile allows for vastly improved wear properties, while not violating any dielectric parameters or FDA parameters.
   In addition to this, we will be looking at fillers of glass and graphite. Each will bring its own unique alterations to the material.

Sizes available

FluoroFoam ePTFE gasket tape is an ideal solution for flange connections, container rims and any other metal to metal application requiring a compressible, chemically resistant seal.

The tape comes with one-side adhesive that aids in installation by allowing an exact placement of the gasket lining.

	Standard Spool Lengths (others on request)
Size (mm)	5m	10m	25m	50m
1.5 x 3
2 x 5
2.5 x 7
3 x 10
4 x 12
5 x 14
6 x 17
7 x 20
5 x 25
5 x 28

Installation guidelines:

Completely clean the sealing area and remove any dirt, corrosion, oil or leftover from old gasket material.

Cut one ending of the sealing tape and remove just a little of the protecting paper. Place the tape at the nearest possible position next to the bolts, starting next to a bolt hole. Fit the gasket around the entire flange circumference and across the endings as shown in figure 1.

Assembled in fragile flanges apply techniques as shown in figure 2. Skive the endings as shown in fig. 3 and overlap according to the recommended overlap length. Cut off the excess, tapering to the end, leaving a total thickness of approx. 120 %.

At least 4 progressive torque sequences with a torque wrench, in a star of 180° (fig. 1), should follow the first torque by hand.

Lastly perform a circular torque to check and ensure a tight and long-lasting seal.

Photos of typical applications:

The ePTFE Tape is allowed to overlap at the ends to ensure complete sealing.
Due to the softness of the tape, this overlap is accommodated during compression causing no variation in thickness

The one-side adhesive backing allows installation even on vertical surfaces, eliminating the need for grooves, clamps or bolting arrangements.

Metal-to-metal flange connections benefit greatly from the use of FluoroFoam ePTFE.
The ePTFE takes the exact shape of the gap between the two metal members ensuring a perfect seal with minimal effort

Form-in-place ePTFE gasket tape can effectively seal flanges on large shell-and-tube exchangers
Available in running lengths – the tape saves big on cost in areas where large, custom made gaskets would be too expensive

The versatility and texture of the material ensures that there is no shape that cannot be attained.
This adds to the effectiveness as well and reduces costs significantly compared with custom made gasket and sealing solutions

Advantages of FluoroFoam ePTFE Gasket Tape:

• Quick and simple installation: adhesive strip makes installation easier while the shape and versatility of the material means minimal cutting and sizing
• Reduced down time: standard sizes are immediately available ex-stock
• Reduced stock: a few spools of different sizes cover most applications within a plant
• No risk: the texture of FluoroFoam ensures the material accommodates the shape of the mating member, so there is no chance of the equipment getting damaged by the ePTFE
• Safe: ePTFE is chemically inert and can therefore be used even in the harshest environments without risk of reacting with the surrounding substances
• No waste: FluoroFoam comes in a spool, so no material gets wasted
• Cost effective – FluoroFoam can be used to replace custom made gaskets that are expensive and made-to-order. This is results in a huge cost saving in larger diameter pipes and vessels. 

Technical Details:

• Temperature range: – 240°C up to +260°C, for short periods up to +310°C
• Chemical resistance: resistant against all chemicals from pH 0-14 – except molten alkali metals and elemental fluorine at high temperature and pressure
• Pressure resistance: vacuum up to 200 bar
• Density: 0,65 g/cm³, +/- 0,1g/cm³ (for rectangular cross sections only)
• Aging resistance: FluoroFoam itself does not age and is UV-resistant. However, the adhesive backing may lose its effectiveness if kept unused for too long
• Colour: white (other pigments available on demand)
• Fillers: FluoroFoam can be offered in virgin and carbon filled variants
• Others: FluoroFoam is physiologically harmless. It has no smell or taste. It is neither contaminating nor toxic. It is made using FDA approved raw materials

ePTFE Applications in Cable Manufacturing

Despite extensive research into a new product, we are often introduced to applications that we had perhaps not considered and which open a whole new avenue of possibilities for the item in question.

Given the sheer versatility of ePTFE as a material for sealing, filtration, vibration dampening and corrosion protection, it came as little surprise to us to learn that its electrical properties open up applications into the cabling industry.

ePTFE vs PTFE

ePTFE or Expanded PTFE is a variation of pure or solid PTFE. The material is processed in a way that infuses air into the solid PTFE to give it a spongy, malleable texture that makes it a preferred material for sealing applications. The same texture – being comprised of 70% air, also lends itself to vastly improving electrical conductivity and dielectric strength.

We already know the properties of pure PTFE in electrical applications make it an insulator of unparalleled effectiveness. The invention of ePTFE resulted in a material that was up to ten times lighter and nearly halved the dielectric constant from 2.1 to 1.3.

So while many high-performance cables use solid PTFE (by way of paste extruding PTFE tube on to a conductive core), wrapping the core in ePTFE offers added possibilities in cabling.

ePTFE Tapes in Cabling

ePTFE insulator tape can be made with tightly controlled thicknesses of as little as 0.05mm, with a uniform density, and dielectric constant. Wrapping individual conductors in ePTFE can cut interference, noise, cross-talk, and signal attenuation. In some applications, ePTFE tape helps limit phase shift to 4.3° and signal attenuation to 0.05 dB at 110 GHz.

High-dielectric ePTFE insulation can be up to 50% thinner than other materials.

At higher voltages, corona discharge also becomes a concern. We have modified PTFE for better performance in wires carrying 5 kV and higher voltages. Corona-resistant (CR) PTFE eliminates the microscopic voids between conductor and insulation that can be corona- discharge initiation sites, especially in high-altitude, military, and space applications.

Shielding is the furthest from the cable’s neutral axis, so it sees the greatest flexure stress. Cutting shield-to-conductor and shield-to-jacket friction deters heat generation and keeps stress off the shield.

Placing ePTFE binders on either side of the shield (with coefficients of friction as low as 0.02) lets each conductor slide past its neighbours and the outer shield with ease, making the cable as a whole more flexible in rotation and torque, and eliminating internal abrasion. Designers who know a cable will not lose strength over time through abrasion can tighten the design envelope and still extend cable life.

Any cable jacket must protect the shields and conductors from the environment and lend extra tensile and flexural strength. Like conductor insulators, jacket layers should be thin, resist tears, withstand fluid attack, and have high tensile strength.

Many applications use durable polyurethane (PU) jackets. For environments that require low particulation, polyvinylchloride (PVC) may be a better choice.

Jackets can also be made of ePTFE for additional insulation and resistance to chemical attack. If the cable assembly slides through other machine parts, abrasion-resistant ePTFE is a good choice for extending cable life.

The advancements in ePTFE manufacture allow for uniformly thick tapes in running lengths of over 1000 meters. This opens up a world of possibilities for cable manufacture that is only now being harnessed around the world.

Expanded PTFE (ePTFE) Joint Sealant – A miracle product with varied applications

Starting 2015, Poly Fluoro Ltd. will be among the few companies globally, with the capability to manufacture expanded PTFE (ePTFE).

While the uses of ePTFE are numerous, it falls upon a select few manufacturers to produce this material. As we have covered in an earlier article, the production of ePTFE is as diverse as its applications. Some of the variants that exist include:

1. Mono-axially stretched ePTFE tape
2. Bi-axially stretched ePTFE tape and sheet
3. ePTFE membranes
4. ePTFE tubes and rods
5. ePTFE gland packing

Each of these products comes with unique production methods and specific nuances. However, the most commonly used variant at this point is the mono-axially stretched ePTFE tape.

 

ePTFE tape – also referred to as ePTFE joint sealant or PTFE Gasket Tape, is widely used for creating a sealing joint between pipes and other mating metal parts. Specifically, as a chemically inert material, this tape finds application in chemical plants, biotech plants and oil and gas pipelines. In fact, any pipe-lining application, where two pipes are connected using flanges, would benefit from using ePTFE tape, as the pliable nature of the material ensures that no gaps are left unfilled.

The tape has a soft texture and is easily compressed. Typically, the compression set of the tape is one of the parameters that define the material. The tape needs to be soft enough to compress under minimal load and ensure that it decompresses just enough to guarantee a complete sealing. At the same time, the tape needs to have adequate tensile and compressive strengths to allow for heavy loads to work upon it, without fatigue. In addition to its excellent chemical resistance, ePTFE tape also has a high temperature resistance, which allows it to be employed in applications involving high temperature fluid transfer.

ePTFE tape comes in 2 variants: adhesive and non-adhesive. The application of the adhesive is not highly complicated, but for on-site convenience, it is preferred as else the installation of the tape is difficult.

The application of the tape is very simple. As the visual below shows, the tape is laid along the flange and allowed to overlap at the ends. The soft texture of the tape means that at the point of overlap, the tape does not bulge once compressed, by simply compressed further to make a uniform seal.

ePTFE joint sealant tape is among the most sought after materials for all sealing applications.

Visit our website for more details