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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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PORON: When Fire is a Possibility

Many types of foam burn rapidly. Some even drip burning material on to the surface below, helping a fire spread rapidly. However, there are foams formulated to provide high levels of fire resistance. Whenever possible these should be used near potential sources of ignition.

The fire-resistance of foam for use in appliances, enclosures and equipment is measured by testing to procedures set out in the UL94 standard. (Note: this does NOT address foam used in upholstery or building construction.) Flammability (the ease with which a material burns,) is shown by a UL94 rating, such as the UL94 V-0 indication carried by PORON® 4701-V0-M.

Foam Flammability
Anything composed of carbon and hydrogen will burn if conditions are right, and that means having oxygen and an ignition source. All foams are formed from these elements and oxygen is always present in the atmosphere, so to start a fire all that's needed is an ignition source. This could be provided by an electrical spark, such as when motors or relays produce arcing. High temperatures, as caused by friction between moving parts or electrical current flowing through wiring are others possible causes.

UL94 flammability ratings
The UL organization is an independent global testing organization dedicated to improving safety. Founded in 1894 as "Underwriters Electrical Bureau" it started out by testing noncombustible insulation material and grew to become first "Underwriters Laboratories" and now just UL.

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Introducing Spunbond Materials

Spunbond materials are a subset of what's termed non-woven fabrics. That is, they are webs of material without the interlacing of threads produced by weaving on a loom. That means the fibers are randomly oriented and not interlocked, so a bonding process or medium is needed to fix them in place.

Non-woven fabrics are everywhere. Disposable wipes, diapers and pillow covers are just a few of the many uses around the home, but they're also used in agriculture, civil engineering and automobile interiors.

Why So Popular? 
Non-woven fabrics compete with wovens in two ways. First, they can be engineered to have practically any combination of properties needed. Tensile strength, absorption, and density are just of few of the characteristics polymer chemists are able to manipulate. In contrast, woven fabrics derive their properties mainly from the characteristics of the yarns employed.

Second, non-woven production processes are much faster than weaving. While a loom might turn out three to seven meters of woven material per hour, many non-woven processes could produce several hundred meters per hour. Naturally, this has an impact on cost.

Non-woven Production Processes 
Non-woven materials may be produced either from short lengths of fiber, (known as staple fibers,) or from continuous filament. Fibers can come from many sources, both natural and man-made, but filament is generally produced from polymers such as polypropylene, polyester and nylon.

A variety of methods are used to randomly orient fibers into a web before bond them together. One issue is that staple fibers must go through some kind of chopping process first. In contrast, spunbond materials, while lacking the randomness of fiber, are made directly from the polymer.

The Spunbond Process 
Polymer is melted and extruded through very fine holes, typically measuring 15 to 35 microns diameter. These thin continuous strands are made to spin as they solidify before landing on a moving conveyor or web of supporting material. The spinning randomizes the orientation of the strand as it lands and the conveyor motion ensures it forms a mat or web of material.

A bonding process, mechanical, chemical or thermal, joins the overlapping filament coils together, creating an engineered fabric. From polymer pellets to fabric web, it's an integrated process, and so highly cost-competitive.

Types of Spunbond Materials 

  • Polypropylene. This offers low density, good chemical and water resistance, and is readily formed as a breathable material. It works well in protective bags, sheets, pockets or pouches, is a good filter medium and absorbs oil well thanks to a porous structure. Spunbond polypropylene is also used for single-use gowns in the medical field.
  • Polyester. More expensive than polypropylene, this has higher tensile strength and better heat stability. It can be dyed or printed with conventional textile industry methods. Applications include fabric softener dryer sheets, automotive carpet backing and geotextiles.
  • Nylon. Has good tensile strength and tear resistance. Can absorb water but resists attack by alkalies and weak acids. Has good heat resistance and is air permeable. It's widely used as carpet underpad reinforcement, as quilt backing, and in automotive interiors.
  • Polyethylene. Similar to polypropylene, although with generally inferior properties, this is chemical and water resistant, and has good electrical insulation characteristics. A porous structure makes it a good oil absorber.
  • Polyurethane. This is an emerging material in spunbond form. Somewhat elastic, uses are anticipated in masks, diapers, medical tape, and also disposable clothing, thanks to textile-like properties.
  • Rayon. This creates non-wovens with textile-like properties like good drape and soft feel.
  • Bicomponent fibers. These consist of one polymer molded around a second, different, polymer. This enables a combination of properties such as the ability to take a dye combined with high strength.

Emerging Applications 
Development of spunbond manufacturing processes is continuing, with new forms of material entering the market and new applications being found. Spunbond foam offers superior handling characteristics with lower weight and increased softness. Today, we are able to laminate adhesive to spunbond materials to film, foam, and other materials as well as die cut, water jet cut, slit, and kiss cut this material in a number of application settings. The cost-effective spunbond process facilitates engineering of specific performance characteristics such as strength, water and chemical resistance, and feel. New spunbond materials are emerging constantly, and improved manufacturing methods are enabling yet more applications. Already spunbond polypropylene is seen as an alternative to polyurethane foam, and other applications are sure to follow. If you are interested in learning more about Spunbond Fabrics, give us a call and we would be happy to help you learn more. 

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An Overview of Die Cutting and Its Benefits

Die cutting is a dynamic process involving the creation of just about any shape from the material of your choice. We've been fabricating unique components made of foam for a range of industries since 1948, and we love what we do.

Die cutting offers a range of benefits and possibilities for your business. We use a highly effective form of die cutting called flatbed die cutting, which has advantages over other methods like rotary die cutting.

How Die Cutting Works
Die cutting uses steel rule dies to cut the desired shaped with a high degree of precision and accuracy. Mechanical or hydraulic pressure is then used almost like a cookie cutter to press into the material and create the desired shape. One type of die cutting called rotary die cutting (also referred to as gasket style cutting) involves unwinding material and putting it into a hydraulic press. An engraved steel cylinder die is then used to cut the desired shapes.

Both rotary and flatbed style die cutting allow for cutting either completely through the material or just to the release liner; this is referred to as a butt-cut or kiss-cut. Both methods also allow for consistent component creation to very accurate tolerances as well as the creative freedom to make just about any shape and size.

Flatbed Die Cutting
Flatbed die cutting, the process we use, can stamp out specific shapes of foam using steel rule dies and hydraulic pressure. It has a range of features and benefits that make it perfect for cutting foam materials to just about any shape and size you need:

The Process
The cutting die is a strip of thin steel almost like a tape measure and is referred to as a steel rule die. This flexible strip is bent to the precise shape that will be cut and then fixed in place within a slot. Once assembled, the die is then mounted into the press face down. The foam is positioned beneath the die assembly and pressed down. The pressure of the press forces the steel edge through the material and produces the desired shape with a high degree of accuracy. Cut depth is completely controllable so that the pieces can either stay within the sheet or be cut completely free.

The Benefits of Flatbed Die Cutting:

Flexibility and Creativity
Our high quality foam materials lend themselves to being cut using the flatbed process with flexible design possibilities. For us, it is a superior process over rotary die cutting or any other die cutting process (including laser or waterjet). A range of materials including any type of foam can be effectively cut using the flatbed method.

Lower Cost
Flatbed cutting is also affordable. Even if the needed component volumes are relatively low, flatbed cutting can keep expenses low because the dies in this process are less expensive than those used in rotary die cutting.

No Curving or Bowing of Thick Materials
Flatbed processes use a direct vertical cut, allowing for a tighter tolerance thicker materials like higher volumes of foam. By contrast, rotary tooling can cause curving of the material edge in thicker cuts.

Complex Shapes are Possible
In addition to design flexibility and affordability, a range of complex shapes are possible with flatbed die cutting. Complicated two-dimensional shapes are much easier to create with flatbed cutting than other methods like rotary die cutting.

Accurate and Repeatable
The steel rule die helps to ensure that the identical shape can be cut over and over again as needed.

Fast and Efficient
Nesting allows for the combining of multiple dies on one base to cut numerous parts simultaneously. Parts generation using a press is extremely fast and efficient. Ready to learn more? Give us a call and we'll discuss all the ways custom foam die cutting can work for your business.

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Case Study: How Open Cell Foam is Used to Help Measure Brain Waves

open cell medical foam

Problem: Leaking Fluids & Uncomfortable Caps

A leading provider in the healthcare sector was in need of a solution to prevent saline testing fluids from leaking from skull caps worn by EEG testing patients. Also, patients complained of discomfort from the testing electrodes because they would scratch the bare skin of the patient's scalp. EEG testing normally lasts between 30 and 60 minutes and the test is crucial in measuring brain activity so it was imperative for our customer to find a solution quickly.

Solution: Open Cell Polyurethane Foam

We've been designing and manufacturing unique foam components for our customers for nearly 70 years. Our engineering team worked with the customer to utilize open cell polyurethane foam to prevent the saline solution from escaping and running down the patient's head. This solution increased the conductivity at the point where the electrodes connected to the skull, which improves the overall quality of the EEG testing results. To solve the problem of the uncomfortable test cap, we decided to laminate felt on one side of the open cell foam to a soft fiber material that surrounded the electrode so that when it expanded with saline, it would also act like a pad on the patient’s head. That way, it would help to protect the bare skin from the bare metal electrodes. 

Success: Open Cell Foam in EEG Testing

Today, this technique is used in EEG tests in hospitals around the world. By improving the ease of testing and keeping the saline in place, the open cell foam has improved conductivity at the point of connection and increased received data rate by about 30 percent.

Summary Benefits of Open Cell Foam in this Study:

  • Increased conductivity & improved EEG testing quality data rates by almost 30%
  • Allows for better holding of testing liquids and prevents liquids from dripping on the patient during testing 
  • Affordable and cost effective design allows for single patient use
  • Improves patient comfort and satisfaction level during testing

Product Specifications:

Product Name:  Medical Foam Valve Caps for EEG Testing
Description: Fiber and Foam Laminated Components
Capabilities Applied:
  • Primary: Die Cutting & Adhesive Lamination 
  • Secondary: Packaging to Customer Specifications
Tightest Tolerances: ± .030”
Material Used: Open Cell Polyurethane Foam, Soft Fiber Material, and Acrylic Adhesive
Industry of Use: Medical Industry
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