Understanding Adhesive Failures

Adhesive bonded joints, whether made using pressure-sensitive tapes or liquid adhesives, can experience failure. Oftentimes, the comments we hear are, “It’s not sticking,” “It’s coming off,” or “It’s just not working.”

Fortunately, there is a method for understanding adhesive failures, and that knowledge can lead to an effective solution.

Types of Failure

Adhesive failure occurs when the adhesive system debonds or separates prematurely from one of the surfaces or substrates. In some cases, you want adhesive failure; particularly if you want the tape to peel cleanly away from the substrate (think of a Post-It Note).

In most cases, however, the reality is a bit more complicated. Sometimes, the adhesive selected  incapable of developing a strong bond, due to its chemistry and limited ability to wet out a surface with a lower surface energy than the adhesive can handle. Other times, there can be contamination left on the surface, preventing   the adhesive from bonding properly. Cleaning and proper surface preparation (including primers in some cases) can resolve this issue.

Environmental factors, like temperature, water, chemical contact and radiation are common culprits that can also deteriorate the adhesive bond to a substrate. Still, other times, there are migratory species in substrates.  Even the adhesive itself, such as plasticizers or other additives, can migrate to the substrate interface and disrupt the bond. Lastly, the release liners that protect a tape product can sometimes leave behind uncured silicone or fluorocarbons residue that can inhibit the formation of a good bond.

Cohesive Failure

This is the breakdown of the intermolecular forces within the adhesive itself, and its occurrences in the bulk layer of the adhesive. This breakdown can be caused by shear, tensile or cleavage forces that are acting on the bond line. Often, there are the environmental factors already listed that are acting simultaneously with these forces that exacerbate the effects and cause a failure.

Just as the name implies, mixed mode typically exhibits both adhesive and cohesive failures. This failure is not uncommon when plasticizer migration is involved, particularly after exposure to elevated temperatures.

Substrate Failure

This is not the only failure where the adhesive is not the culprit. The implication is that the strength of the adhesive bond exceeds the strength of the substrate itself. In some foam materials, you can observe this type of failure and, frankly, it is not always a bad thing.

 

Have more questions about adhesive bond failures? Call Tom Brown, Inc. today. We’re here to help!

Guide to Spooling Tape Products

What is spooling?

Spooling is a process where rolls of tape products can be spliced together and wound onto a common core, similarly to  fishing line or thread wound onto a reel. This traverse winding process allows significant footage to be wound onto a single roll without becoming excessively large and difficult to handle.

How Spooling Benefits Your Process

Spooling allows your machines to keep running longer and thereby reducing costs associated with downtime, labor and changeovers.

  • More material per spool as compared to pancake rolls
  • Fewer changeovers per shift
  • More up-time on automated equipment
  • Decreases downtime
  • Saves warehouse space
  • Quicker run-times


What Tape Products Can Be Spooled?

The more common types of tapes typically spooled are:

  • Double coated foam tapes
  • Single coated foam tapes
  • Double Coated Film Tapes
  • Nonwovens and tissue supported tapes

Specialized Spooling Services

There are some tapes that are difficult to spool, namely acrylic foam tapes (VHB type tapes) and unsupported transfer adhesives. These products are challenging because they tend to “knit” back together along the edges.

Tom Brown has the right spooler to solve this issue and successfully spool these products. A slightly wider secondary liner can be introduced just prior to application and the tape will spool beautifully.

There are some tape products that need a finger lift, or dry edge, along one side for the tape to facilitate easy release liner removal. Tom Brown has the right equipment to add a dry edge and wind a functional, attractive spool package.



Critical Spooling Parameters

It’s important to discuss the “put up” or spool configuration with your supplier to make sure the spools work as intended.

The first thing you typically discuss is the required width of the tape and the requested length of the spool. This discussion usually goes hand-in-hand with the core diameter and spool width. The most common core diameters for spooling jobs are 3” or 6”. But spool widths can vary greatly, with  6”-12” wide spool packages as the most common.

The thickness of the tape, the spool width, and the machine’s capabilities are three factors that most influence how long the spool can be. The thinner the material, the more you can put on the spool. A 3” ID core can usually be wound with additional material (up to a point), but is a little harder to handle. With a 6” core, you sacrifice a little length, but the spool package is a little easier to maneuver.

For example, a 1/16” double coated foam tape can be spooled on a 7”-10” width spool with anywhere from 2,500- 4,700 ft depending on the three factors mentioned above.

By adjusting the “pitch” – the distance between the adjacent winds of tape and the “dwell” (how long the traversing head stays on the edge prior to making the next pass or layer) – you can create different types of spools:

  • Normal
  • Pineapple
  • Pancake
  • Fixed Lobing
  • Cyclic
  • Step Pack

Want to know more about spools and how they can help your process? Contact Tom Brown, Inc. today.

Silane Coupling Agents for Use with Tapes in Glass Bonding Applications

Glass is known to be a “water loving” (the technical term is hydrophilic) surface and this makes adhesive bonds, particularly with acrylic adhesive systems, susceptible to change in high humidity conditions. The good news is that a simple treatment of the glass surface with a silane coupling agent reduces this “water loving” behavior and improves the bond strength of the tape when subjected to high humidity and moisture.

What are Silane Coupling Agents?

The chemical name for the class of silane coupling agents found to be most effective as a glass pretreatment is 3-Glycidoxypropyl trimethoxysilane resin (commercially known as Dow Corning Z6040). The important thing to understand is that this class of silanes possess both organic and inorganic reactivity that allows them to “couple” organic polymers (tape) and inorganic surfaces (glass).

The trimethoxysilyl group is subject to hydrolysis (reacts with water) and that is why the pretreatment is offered in a water/isopropyl alcohol blend (like the rubbing alcohol you can buy at the local pharmacy). The alcohol helps to stabilize the liquid and the alcohol flashes off easily at room temperature and makes it easy and safe to use.

These silanol groups condense with the hydroxyl groups on the glass surface. After this condensation reaction, the coupling agent is bonded to the glass and is now reactive with the organic material (the tape). These properties allow these materials to withstand physical, chemical, weather, and thermal degradation.

Where are they used?

Silane pretreatment is essential when fabricating curtain wall and window wall systems that relay on acrylic structural glazing tapes. The added bond stability afforded by the use of the silane coupling agent reduces the risk of de-bonding in high humidity and moist conditions.

The silane pretreatment is also used in attaching muntin bars for creating simulated divided lites on residential and commercial window systems.

How to Apply Silane Coupling Agents

  1. The glass surface should be clean and dry. If it is contaminated, it should be cleaned with a 50/50 mixture of isopropyl alcohol and water using a clean, lint-free cloth.
  2. Moisten the clean, absorbent, lint-free cloth with the silane solution and wipe over the area to be bonded with the tape in one direction. Alternately, the silane solution can be sprayed onto the perimeter to be bonded and wiped with a clean cloth around the perimeter. More is NOT better! Experience shows that a thin layer (monolayer) is much more effective and gives the best performance.
  3. To get that monolayer, the primed area should be re-wiped in one direction with a new lint-free cloth after the initial application. Under normal room temperature conditions, the tape should be applied within 2 minutes so that any residual moisture can evaporate.

Final Notes

Sometimes we’re asked how a silane coupling agent works if it’s such a small concentration (less than1%) in the liquid. We remind them to think of baking muffins or biscuits at home where you use baking powder. You use a lot of flour and other ingredients but only a very small amount of baking powder because it is highly reactive. (in case you’re wondering, it works when the dry acid and base in the powder hits water and reacts to make carbon dioxide). You don’t need a lot to get a very big result.

Tom Brown, Inc. offers premixed silence coupling agents under the 3M AP115 brand in convenient 4 oz. spray bottles. Contact us today if you’d like to learn more.

A Guide to Intumescent Foam for Passive Fire Protection

Photo Courtesy of Saint Gobain

Intumescent is a big word and not familiar to many people. In simple terms, an intumescent material swells with exposure to heat. This swelling increases the volume of the material and produces a char which is a poor conductor of heat. The combination of swelling and the associated reduced heat transfer blocks fire, smoke and hot gasses.

Intumescent materials are often liquids, putties, or sealants but they can also be foams and can be applied like a tape which offers a variety of benefits.

The foam is available in 4 thicknesses- .18,.24, .34, and .51 inches (4.5, 6.0,9.0, and 13 mm) with a pressure-sensitive adhesive on one side. You remove the liner, and apply the foam tape to the surface. The product is watertight and airtight   when compressed 30% and releases no toxic gases when heated.

Photo Courtesy of Saint Gobain

Intumescent Foam Applications

Photo Courtesy of Saint Gobain

The largest use of intumescent foams is in construction applications such as joints in floors, ceilings, windows, and doors. They can also be used in HVAC applications where fire compartmentation is needed.

Intumescent foams can also be used in automotive fuel tank areas and around battery packs in electric vehicles. In aerospace applications, these foams can be used in freight compartments or other critical areas.

Intumescent foams combine passive fire protection with the ease of installation common to tape products. Want to know more about intumescent foams? Contact Tom Brown, Inc. today.

A Guide to the Use of Polyethylene in Tape Products

Polyethylene plastic is ubiquitous in our lives. The most common use is packaging for food and plastic garbage can liners. Most of us also have that “plastic sheet” somewhere in our basement or garage that we use to cover firewood, our grill, or anything else that we need to protect.

What is Polyethylene and Where Does it Come From?

Polyethylene is produced from the polymerization (controlled reaction) of ethylene monomer is the presence of catalysts to form a stable plastic. The ethylene monomer feedstock in North America comes mostly from our abundant supply of natural gas but it can also be produced from the naphtha portion of crude oil. The abundance of natural gas production in the USA has helped to stabilize the price of ethylene monomer and ultimately has kept the price for polyethylene stable as well.

Types of Polyethylene

Polyethylene is classified primarily by density, branching (think of a tree with either very different or uniform size branches), and molecular weight. These properties affect the tensile strength, ductility, hardness, and impact strength of the material.

For tape products, the most common types of polyethylene are:

  •   Low Density Polyethylene Film (LDPE)- has a density range of 0.91-0.94g/cm³ along with both short and long chain branching which translates into lower tensile strength but great ductility.
  •   Linear Low Density Polyethylene Film (LLDPE)- has a density range of 0.915-0.925 g/cm³. LLDPE has consistent short branching in the polymer structure which leads to higher tensile strength and puncture resistance.
  •   Medium Density Polyethylene Film (MDPE)-has a density range of 0.926-0.94g/cm³.  MDPE exhibits a lower degree of short and long chain branching compared to LDPE so tensile strength is significantly improved.
  •   High Density Polyethylene Film (HDPE) – has a density range of 0.941 and above. It has a very low degree of branching and offers a significant improvement in tensile strength over both LDPE and MDPE.
  •   Ultra High Molecular Weight Polyethylene Film (UHMWPE)-has a density of 0.93 and 0.935 g/cm³ but also has a molecular weight that far exceeds the others. This results in an exceptionally tough material that offers outstanding cut, wear, and chemical resistance.
  •   Coextruded Films- also called “Coex” for short. This is essentially an “alloy” in which two films such as LDPE and HDPE are extruded together offering the good stretch and conformability of the LDPE along with the  improved toughness of the HDPE.
  •   Cross-Linked Polyethylene Foam- (PEF or XLPE)- a medium to high density polyethylene that has cross-linking bonds on the structure of the polymer. This is then exposed to radiation or a chemical reactions that creates a semi-rigid

 

How is Polyethylene Used in the Tape World?

One of the largest uses for polyethylene film is for surface protection films. If you’ve ever purchased a new refrigerator, wash machine, or dishwasher, you most likely have had to remove “that film” from the painted metal or stainless steel. LDPE is the prevalent film used for this application along with Coex. Aside from appliances, surface protection films are used widely in electronics, building and construction applications, and in the painted metals industries. These films are mainly coated with acrylic pressure-sensitive adhesives which are “tuned” to be removable from the applied surface.

LDPE and MDPE are often used in tapes for patching, bundling, sealing, and wrapping. The conformability of the film allows intimate surface contact and enables good adhesion. A rubber-based adhesive system is commonly used for adhesion to a broad range of materials. These tapes are also used as a separator between dissimilar metals such as steel and aluminum. The tape creates an interface that prevents galvanic corrosion.

HDPE is often used for release liners. Silicone release coatings can be applied to the film and then adhesives can be coated on them allowing a tape to be produced with a tough release liner that is difficult to tear during application and removal.

UHMWPE tapes offer very low friction and can be used to protect surfaces that experience repeated contact and wear. The UHMPE absorbs shock without fracturing and can be used for hopper liners, chutes, and in high wear furniture applications. These tape are usually coated with an aggressive acrylic adhesive system that has excellent adhesion to many surfaces and can be used indoors or outdoors.

Polyethylene foam is renowned for its’ ability withstand pressure without losing its’ cushioning ability. These foam tapes are coated with either acrylic or rubber-base adhesives and can be used for mounting mirrors, POP displays, clips, signs, and as glazing tapes to seal insulated glass units into framing systems.

Want to know more about polyethylene tapes? Contact Tom Brown, Inc.

Temperature Performance of Foam Tape

Foam tapes are often gauged by a variety of physical properties; compression, compression set, density, and tensile strength. One of the important properties is temperature resistance. As foam tapes become more readily utilized throughout a large variety of industries, temperature performance becomes critical in deciding which tapes are best suited to which applications.

Engineering for Hot and Cold Applications

Though elevated temperature resistance is the most common attribute when testing foam tapes, foam tapes are also needed for cold temperature applications. Foam tapes can be used throughout cold temperature environments such as truck and trailer applications, refrigerated facilities, and construction.. These tapes must be able to be used in temperatures that may sometimes be lower than -20 degrees Fahrenheit. On the other end of the spectrum, tapes may need to be used in very high temperature environments, particularly for under the hood automotive and transportation applications. These foam products need to resist temperature cycling from cold to extremely hot and maintain their integrity and ability to seal. Some common temperature performance data for acrylic, polyurethane and polyolefin foams are listed in the table below.

Note: The temperature data is general and not specific to any one product.

 Accommodating Expansion and Contraction

Foam tapes can experience both expansion and contraction as the temperature rises and falls. Not only must foam tape be rated for specific temperature extremes, it must also be tested for intense variations within those extremes. Some foam tapes are going to be held at a consistently high or consistently lower temperature. Others need to be able to resist cycling within a temperature spectrum. The best bonding tapes accommodate the expansion and contraction of the materials that they are bonding. This is a feature that makes foam bonding tapes superior to other methods of bonding, such as mechanical fasteners or other adhesives. In this situation, the foam tape operates as a buffer, distributing stress and offering additional flexibility.

Bonding, Sealing, and More

Foam tapes are designed to bond and seal in one easy application. (many foam tapes require some type of compression but not all). When you look at these properties in conjunction with temperature resistance, the number of applications can be astonishing.

Specialty tape products are often needed whenever temperature extremes are going to be present. Foam tapes are tested to varying temperature extremes, and different tapes may be necessary depending on the application’s needs. Tom Brown, Inc. has a wide variety of foam tape products, including Saint-Gobain, 3M, Foamseal, and Adhesives Research series.

The Importance of Cell Structure in Structural Spacer Tapes

Structural spacer tapes are used alongside one or two part structural silicone sealants to ensure that glass remains bonded to the metal framing system for the life of a building. The controlled density and thickness of a spacer tape provides a highly consistent gap or channel into which the silicone sealant is applied. A diagram of a typical application is shown below:

What might not be obvious is how the cell structure in the spacer tape enables the silicone sealant to cure.

How Structural Silicone Sealants Cure

One part silicone sealants are formulated with all the ingredients needed to reach a cured state (paste phase to rubber  phase). The curing process is initiated by a reaction with moisture in the air. One part systems are low cost and easy to use and apply.

Two part sealants separate the reactive portion or catalyst from the base adhesive formula and then join them together via a mixing and pumping process. Two part systems lend themselves to higher volume, higher speed operations where quick handling and cure time are needed in an assembly operation.

Both one and two part sealants outgas and do generate small amounts of VOCs (volatile organic compounds); even the low VOC grades.

Spacer Tape Cell Structure and Sealant Curing

Closed cell foams consist of a series of unbroken chambers or cells which resemble small inflated balloons in a compact configuration. Closed cell foams are very strong durable materials but they don’t permit the passage of air or moisture through the foam matrix.

Open cell foams by contrast have cell walls that are broken with air filling the spaces in between. This series of “broken cells” create a pathway for the movement of air, moisture, and VOCs.

Examining the chart below tells the story of why cell structure is so critical.

High WVTR values like those seen above allow moisture to reach the one part system to facilitate curing and simultaneously provide a pathway for the escape of VOCs from the bond area.

Structural spacer tapes and silicone sealants are made to work hand in hand. Each truly enables the other and when done correctly, long lasting, reliable, structural silicone glazed facades will result. Want to know more about structural spacer tapes? Call Tom Brown, Inc. for samples or a quote.

Understanding Different Foam Tape Core Materials

Foam bonding tapes feature a variety of core materials and it can be a bit bewildering as to why.


The most common types of foam core chemistries are:

  •    Acrylic
  •    Polyurethane
  •    Polyethylene

The foam core performs several vital functions within the bond area:

  •    It distributes loads over a large area enhancing energy absorption
  •    Improves stress relaxation
  •    Compensates for substrate mismatch and lack of planarity
  •    Enhances conformability

Each core chemistry offers a unique set of properties making it suitable for certain applications. The best way to visualize this is by observing the stress strain curves of each type:

(Photo Courtesy of Saint Gobain )

Advantages and Applications for Core Chemistries

(Photo Courtesy of Saint Gobain )

Want to learn more about how foam bonding tapes can provide multiple benefits over traditional mechanical fasteners and liquid adhesives? Contact Tom Brown, Inc. today.

Glazing Tapes- A Primer

The term “glazing tape” is frequently used throughout the residential and commercial window industry and it can mean very different types of products to different users.

If you’re in the curtain wall or window wall segment, the “glazing tape” you refer to would be a “structural glazing tape”. This type of tape uses a high strength, monolithic, foamed acrylic adhesive system that can bond an insulated glass unit into a metal framing system. The acrylic foam is very viscoelastic and gives high elongation properties allowing it to effectively handle the varying loads of wind and weather.

If you are a commercial glazier or fabricator making or installing storefronts, low rise office buildings, and schools, the “glazing tape” you refer to might also be called a “spacer tape” or “structural glazing spacer”. This tape relies upon a semi-rigid, open cell polyurethane foam core that allows air and moisture to reach the structural silicone sealant that is the primary system bonding the glass unit in place. The open cell structure allows the silicone to cure and reach maximum bond strength. This is an example where tape and sealant work hand in hand to deliver the best of both worlds.

If you’re a manufacturer of residential windows, the “glazing tape” you use will likely be made from a polyethylene (PE) or polyvinyl chloride (PVC) core that has been coated with an acrylic or rubber –based adhesive system. These are lower density materials that are easier to compress to form a seal for the window. They are more economical than the commercial type products and are well suited to the sizes and loads common to residential windows.

So as you can see, “glazing tape” is a rather broad term that covers many different yet high performing products. Want to learn more about all of these products from 3M, Saint Gobain, and Adhesives Research? Contact Tom Brown, Inc. for samples and to have your questions answered.