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Merryweather Foam Blog

Since 1948, we have been industry leaders in fabricating unique, foam components for customers in the medical, sound absorption, automotive, and unique packaging industries. At Merryweather Foam, we pride ourselves on our ability to combine experience, innovation, and excellent customer service. We have the knowledge, manpower & equipment to help you get the job done. Visit our website to see our fabrication portfolio as well as our capabilities.

Viscoelasticity and PSA and the Role in Flexible Foam Fabrication

Example of Viscoelastic Foam

Viscoelasticity and Pressure Sensitive Adhesive
No pun intended, but it is hard to separate the relationship between viscoelasticity and pressure sensitive adhesive (PSA). What exactly is viscoelasticity and why is it important in a PSA? Let's try to take a potentially complex issue and break it down.

What is Viscoelasticity?
Viscoelasticity is a blend of the words viscosity and elasticity.

  • Viscosity refers to the resistance a liquid has to flow, generally related to the thickness of the liquid.
  • Elasticity is the ability for a solid to return to its original shape once strain is removed.

Examples of elastic materials include viscoelastic foam, rubber bands, stress balls and bungee cords. High viscous materials are generally thick liquids or gels. Honey, motor oil, and syrups are considered high viscosity liquids. Low viscosity liquids flow easily, like water.

The Affect of Heat on Viscosity
Heat reduces viscosity which you can see in daily life. Oil loses viscosity as it heats in an engine. Maple syrup will flow easier when warmed. Gels will even lose their form when subjected to heat. This is an important fact to keep in mind when discussing the relationship between viscoelasticity and PSA. Heat has an effect on both.

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What Can Pressure Sensitive Adhesive Lamination Do For You?

When you need cushioning, you choose foam. The compressible yet resilient bubbles trapped in elastic material absorb shocks and vibration, giving it thousands of uses from packaging to upholstery. Foam comes in a wide range of materials and ranges from firm and heavy to soft and light. There's a foam to suit every application, but it does have limitations: it can be difficult to fit or install, and it may not have the desired final appearance or surface properties.

The way around these problems is to specify a pressure sensitive adhesive (PSA) lamination for your foam fabrication. 

Overview of PSA foam lamination:
"Lamination" refers to adding one or more layers to a sheet or roll of foam. There are two reasons you might do this:

  1. To create a composite of two or more materials, combining the properties of foam with a second material.
  2. To make it easier to attach foam to a surface or to other foam pieces.
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The Art of Roll Slitting

Ever bought foam weatherstripping or double-sided tape in individual lengths? Somehow it just doesn't work. You'd have to peel a backing strip off the pressure sensitive adhesive, there would be joins where you didn't want them, and you'd have all sorts of wasteful offcuts. That's why it's sold in rolls.

Rolls are a wonderful way of packing, transporting and using foam. Like bananas, they make their own outer skin, which makes them easy to move and reduces waste. And while hardware store rolls come in standard widths, here at Merryweather it's possible to get any width you want.

Like many manufacturing processes, roll slitting seems straightforward until you learn what it takes to produce consistent, high quality results. Here's your introduction to "The Art of Roll Slitting."

Why Slit?
Efficient manufacturing, whether of paper, cloth or foam, demands high volumes. To get the throughput, production lines are set up to make material in the widest possible widths. That's why rolls straight from the mill, loom or foam producer are usually at least 72" wide, sometimes much more.

Those rolls are convenient for shipping, distribution and storage, but for the end users, not so much. It depends on the application, but many want rolls that are somewhere between 1" and 6" wide. Getting to that width means slicing up the roll.

Slitting Processes
There are two ways of slitting wide rolls of material, rewind slitting and log slitting. Selecting the most appropriate depends on factors like the number of rolls needed, the type of material, and the edge quality sought.

Rewind Slitting
In the rewind process the roll is unwound and pulled through a series of blades before being, yes, rewound. Rewind slitting machines can take up a lot of room and have the problem that material is recoiled in the opposite direction to how it came off the roll. For some materials, like those with a pressure sensitive adhesive (PSA) on one side, that means another operation to re-rewind the material back into the original orientation.

Producing thin rolls with rewind slitting can be a challenge as the new roll may become unstable. At best it would have uneven edges, but worst case, it might just be scrap. The other issue is that the whole roll is slit at once, so it's not really a slit-to-order kind of process. (Yes, it is possible to rewind-slit a roll into just two parts, but why? It would make more sense to use a log slitter.)

Log Slitting
Log slitting really is like cutting a tree trunk into logs. It's done on machine that's part lathe and part circular saw. One end of the roll is mounted in a chuck and supported horizontally on long shaft threaded down the center. Moving along the bed of the machine, parallel to the roll, is what looks like a circular saw, although in this process it's actually a knife.

After loading, both the roll and the knife blade start to turn. Beginning at the end furthest from the chuck, the knife blade is pushed into the material roll, where it parts off a thinner roll of material. To cut the next roll the knife is withdrawn, moved along by a distance equal to the thickness needed, and pushed in again.

The advantages of roll slitting are that it's fast, there's next to no set up, and it provides a slit-to-order capability. If asked, it's possible to cut each roll to a different thickness.

Slitting Capabilities
The log slitter at Merryweather can handle rolls up to 20" diameter, and the ballscrew-driven knife has a positional accuracy of +/- 0.003" (0.076mm). That makes it capable of producing very thin, large diameter rolls, sometimes referred to as "pancake" rolls. The minimum core diameter, (the tube at the center of every roll,) is just 1" and the widest roll that can be slit is 90".

Edge Quality
It's difficult to slit rolls so they have a good, clean appearance from the side or end. Knife quality and condition are critical, and so too is the speed of cut. The tightness of the roll also has a bearing on edge quality.

When the blade is dull it tends to compress the material and produce an uneven edge. (The same happens if the roll is loosely wound.) To avoid this, Merryweather use automatic knife sharpening on their slitter. Conversely , when the blade is too sharp it can produce so-called, "angle hair" whiskers of material at the edges.

The speed at which the knife penetrates the material is important too. Move in too fast and the material compresses, move too slowly, and heat build sup in the knife, potentially damaging low melting point materials like foam. The Merryweather roll slitter knife is hydraulically driven for a smooth, well-controlled cut. Depending on the material being cut, water or a lubricating material might be sprayed on to the knife to help it work more easily.

Attention to Detail
For material that's sold in roll for, like foam weatherstripping, or foam coated on one or both sides with a PSA, roll slitting is an essential process. Both the rewind and log slitting process can deliver good results, when done with care on quality machinery. There is after all, an art to roll slitting!

Have questions? We're here to help! Please get in touch with us regarding your next project and we will be happy to answer your questions! 

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3M Select Converter Status - Why It Matters

Since 1948, the hardworking and passionate team at Merryweather Foam, Inc. has committed itself to becoming an industry leader in the world of manufacturing unique foam components for customers all over the world. We're incredibly appreciative of our dedicated customers, many of whom have been with us since the beginning. We're not a business that is willing to just rest on its laurels, however, which is why we're always taking steps to continually improve and eliminate waste in our manufacturing processes.

This is a large part of the reason why we're always working hard to achieve new quality certifications that allow us to prove that Merryweather Foam has earned its place as one of the most trusted manufacturers working today. One of those is 3M Select Converter Status, which means a number of important things for both our company and for our customers.

What is 3M Select Converter Status?
3M Select Converter status is a quality certification awarded by 3M Converter Solutions. 3M Converter Solutions is a global engagement platform targeting markets like electronics assembly, appliance assembly and beyond. They're a company that has pledged to act with uncompromising honesty and integrity in all of their interactions with customers, to always satisfy the needs of their users with innovative and superior solutions and to respect the social and physical environments around the world. Given that pedigree, it's easy to see why Select Converter status is both such a sought-after qualification and one that the company is very selective when it comes to awarding with their partners.

In order to achieve 3M Select Converter status, we completed a range of product-specific training sessions. That, coupled with the large volume of 3M produced materials that the company is responsible for handling each year, allowed us to become a trusted name in terms of our manufacturing processes, our engineering quality and the knowledge of our sales personnel.

What 3M Select Converter Status Means for Our Customers
For our valued customers, working with a 3M Select Converter like Merryweather Foam brings with it a host of different benefits that can't be ignored. These include but are not limited to things like:

  • Access to 3M-certified Specialists and Support Services
  • Competitive Pricing
  • Access to the Latest Solutions that 3M has to Offer and More

The Dependable Solution You Can Trust
At Merryweather Foam, we understand that every application represents a unique circumstance that requires a unique material solution. As a 3M Select Converter, this puts our sales team in the perfect position to connect you with the right specialists and technical support operators, both in-house and directly at 3M. This level of support in turn is able to give you all of the specific answers that you need and who can recommend the perfect product and materials options out of the thousands that are released by 3M each year.

3M Pressure Sensitive Adhesive & Industrial Adhesive
As 3M Select Converters, our unique relationship with 3M puts us in a better position to provide our customers with the specific items they need for any application when they need them the most. Case in point: 3M currently makes some of the highest quality UL Certified Adhesive and pressure sensitive available on the market today.

Adhesives in general are routinely taking the place of traditional bonding techniques, due in large part to the significant advancements that companies like 3M are making. Pressure sensitive and industrial adhesives are so customizable to the application that not only can they be die cut, but they're also strong enough to remove the need for a weld of any type.

As 3M Select Converters, we're specialists in these types of pressure sensitive and industrial adhesives. You get the benefit of not only purchasing the highest quality solution from 3M, but also having it converted to fit your needs by Merryweather Foam. This is the type of versatility that you just won't find anywhere else.

Unbeatable Prices
This in turn allows us to pass the savings onto you, as a way to give back for all the support you've given us throughout our history. You get all of the materials and other items that you need when you need them the most and Merryweather gets the comfort that comes only with knowing that we were able to help you carry your project through to completion and to excel beyond your wildest dreams.

Let us Help
Please get in touch with us! We would love to help you on your next project--big or small. 

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All About Pressure Sensitive Adhesive

Foam is a fantastic cushioning material, used in industries from automotive to medical for providing comfort and protection. It's not the easiest material to work with though. Cutting accurate, high-quality shapes takes specialized equipment and more than a little skill, while securing it in place can be even more of a challenge. Conventional fasteners can pull through, especially with low density foams, and adhesives applied as a bead tend to run into the open cells, reducing flexibility rather than bonding to adjacent material--many times, the psa is used as a temporary fastener until a mechanical fastener can be put in place.

In many cases the solution is to laminate an adhesive onto the foam. Merryweather offers an adhesive lamination service which makes foam fabrications easier to handle and put in-place. Adhesives come in many forms; the type that works best with foam is known as "Pressure Sensitive Adhesive" (PSA). These come in many forms with the most popular being two sided (also known in the industry as double coated adhesive) with a carrier membrane (typically a paper, film, foil or cloth) or a transfer adhesive which peels directly off the release liner when it is removed to adhere the foam to the substrate. Double coated adhesives add stability to the foam so that it cannot be stretched out of shape. They can also be used to prevent plasticizer migration. Since transfer tapes do not have a carrier, the adhesive is extensible and more conformable, and sometimes at a cost savings.

Specifying a PSA lamination is a good first step towards simplifying foam assembly, but it's not enough. Adhesives have many different properties and the relative importance of each depends on the application. A deeper understanding of PSA's helps with selecting the best adhesive for any given application.

What is a PSA?
Some adhesives need a chemical reaction to create a bond, others use heat or exposure to UV light. In the case of a PSA the activation method is pressure. Bringing adhesive-coated surfaces together with just light pressure is enough to create a bond. (In chemical terms, the adhesive "wets" the surface, allowing a bond to form.) Increasing the pressure doesn't automatically increase the strength of the bond, although it may do so if it increases the area "wetted" by the adhesive.

Tack, Peel and Shear: The Key Adhesive Properties
Tack indicates the initial bond strength. In the lab it's usually measured by the "loop" test. A loop of adhesive-coated tape is briefly brought into contact with a surface. The force needed to separate tape and surface is the tack strength.

A high tack number shows a bond forms quickly. This can be a problem if it might be necessary to separate and reposition two surfaces, which is why "Post-It" notes have low tack. Conversely, shipping labels are secured with a high tack adhesive, which is why repositioning them is never a good idea!

As a measure of the force needed to separate two adhesive-bonded surfaces, peel indicates bond strength. It's determined by pulling the two surfaces in opposing directions, but only after the bond has had time to build strength.

Shear is measured by applying a force parallel to the bonded surfaces. It's really an indicator of bond durability.

Specification sheets for adhesives typically list all three of these parameters, usually with a note about the test procedures followed. Most often, these are ASTM standards, although Pressure Sensitive Tape Council (PSTC) testing methods are sometimes used. However, since both temperature and humidity are factors in the bond, both organizations standardize temperature and humidity during testing.

PSA Types
PSA's consist of an adhesive, mixed with an elastomeric base material and a tackifier. The tackifier, as the word suggests, increases the initial tack, while the adhesive creates the actual bond, (which may take time to build.) Forming the foundation of the PSA, the elastomer provides properties like flexibility and temperature range.

Three elastomer chemistries are used in PSA's: rubber, acrylate and silicone. Rubber is the least expensive and provides good peel and shear strength plus a high level of flexibility. Rubber-based adhesives tend to yellow over time and lack strength at elevated temperatures.

Acrylates Acrylics stand up well to UV and solvent attack and will work over a temperature range of -45 to 121 degrees Celsius (C). Their downsides are poor creep resistance and a higher price.They also require a 72 hour dwell time to build up to their full bond strength.

More expensive still, silicone-based PSA's have a broader temperature range, (-73 to 260 degrees C,) and good resistance to chemical and solvent attack.

PSA Selection
While relative importance depends on what the application needs, these points should always be considered:

  • Need for repositioning or removal – this would indicate use of a low-tack PSA.
  • Lowest temperature expected – PSA's can lose flexibility at low temperatures.
  • Highest temperature expected – elevated temperatures reduce shear strength.
  • Humidity – moisture-laden atmospheres will significantly reduce the bond strength achieved.
  • Vibration – especially if combined with high temperatures, as this can lead to premature shear failure.
  • Presence of chemicals and/or solvents – these will attack many PSA's, especially those using rubber elastomers.
  • Substrates being bonded together are very important in determining the type of PSA needed

Typical Applications and Benefits

Applying PSA to cut foam shapes simplifies assembly operations and results in higher quality products. An appropriate level of tack lets workers position foam pieces before securing them in place. Fasteners are eliminated, saving money as well as space in stores and at assembly. Perhaps most importantly, with the right PSA for the application, foam pieces will stay in place for the life of the product, avoiding warranty problems and improving quality. Whether the application is automotive interior trim, under-hood sound deadening or cushioning, acoustic control, packaging, transit cases, medical or something else, pre-laminating a PSA onto foam results in a better product.

Pick up the Phone

PSA's come in many different forms and matching properties to the application is essential. Start that discussion today by calling or emailing a product specialist at Merryweather Foam.

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