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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.

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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Using Rogers PORON Medical® Urethane Foams

Next time you leave wet footprints on a dry floor notice how little of your sole actually contacts the surface. It's mainly just the heel and the area in front of your toes. In most people those parts are well-padded, but diseases like diabetes reduce that cushioning, and painful ulcers can result. The solution is to increase the load-bearing area under the foot, and that's a perfect application for PORON Medical® urethane foam.

Flexible urethane foam has many uses, from mattresses and pillows to gaskets in household appliances. Most of these applications don't place great demands on how the foam performs, but medical applications are different. Whether used for wheelchair cushions, shoe inserts or wrist rests, foam for medical uses must be durable, compression set-resistant, and consistent from batch-to-batch.

Rogers PORON Medical® urethane foams are specially formulated to meet these challenging requirements. For a better understanding of their special properties this blog post addresses:

  • How Urethane Foam is Made
  • Flexible Foam Fabrication
  • Foam Properties
  • Medical Applications
  • Characteristics of PORON Medical® Foam

How Urethane Foam is Made
When a polyol, (a compound of oxygen and hydrogen atoms) is mixed with isocyanate, (a compound of oxygen, nitrogen and carbon) and water, they react immediately, producing polyurethane and carbon dioxide gas. The process is similar to baking dough into bread, with the gas creating bubbles or pores in the material as it sets. Additives like surfactants and filler materials influence hardness, pore size and distribution, and with very precise control it's possible to create foam with predictable properties and uniform small pores. In the case of PORON®, those pores are around 100 microns in size.

Making PORON® foam starts with creating a polyurethane 'froth' that gets deposited onto a moving web or belt. A gate controls the height of the froth, allowing a thin layer through to heating and then cooling stages before being coiled up on a roll for transport.

Flexible Foam Fabrication
Urethane foams like PORON Medical® foam can be fabricated several different ways. Shapes are cut from thin sheets using steel rule dies, thicker sheets are cut by waterjet cutter. Many different pressure sensitive adhesives can also easily be applied to urethane foams.

Foam Properties
Polyurethane foam is usually specified in terms of density. This is referenced in terms of the weight in pounds of a cubic foot. Denser foam supports greater loads and retains its properties better over time. However, density does not necessarily equate to firmness.

Firmness describes how much load it takes to compress a piece of foam material. The actual measurement used is Indentation Force Deflection (IFD). IFD testing, (standardized in ASTM D3574) involves placing a disk on the foam and increasing the load until a target level of compression is achieved.

The most widely quoted measure of firmness is 25% IFD, This is the load required to compress the material to 25% of it's free or unloaded height. Foam with a low IFD number is easily compressed, so feels softer than one with a higher number.

"Resilience" or surface feel describes the springiness of a foam material. In a foam pillow low resilience is desirable while people usually expect more springiness in their seat cushions. Resilience is determined by a foam's formulation and is calculated by dropping a ball onto the surface. A material causing a rebound less than 40% of the drop height is considered to have a "dead" feel.

Tensile strength, tear strength and elongation are all important performance measures. Foams that tear easily and are difficult to handle tend not to make durable support products and create considerable waste for their manufacturers. The ASTM D3574 standard provides methods for testing for tensile strength, tear strength and elongation.

Medical Applications
Foam is used in many ways in medicine, from medical device packaging to wound control. For PORON® foam the principal application is to provide support. A few of the places you might find PORON Medical® foam are:

  • Wheelchair seat cushions, where users not only need comfort over extended periods but also benefit from the increased stability contoured polyurethane foam provides.
  • Orthotic inserts, which provide relief from diabetes-induced ulcers through load spreading and impact cushioning. One study found PORON® provided superior dampening and durability to other cushioning materials, especially when bonded to a second material that resists shear forces.
  • Running injuries - a study published in the British Journal of Sports Medicine showed that polyurethane running shoe inserts provided relief from chronic running-induced injuries.
  • Bed Cushions, which prevent pressure ulcers, commonly called bed sores, by distributing pressure away from bone protrusions.
  • Prosthetic devices, where they improve comfort for amputees.
  • Slings & ankle supports, also to improve comfort.
  • Wrist Rests, to provide support
  • Head Restraints, providing cushioning to protect against vibration or impact forces.

Special Characteristics of PORON Medical® Foam
Rogers Corporation developed PORON® as an exceptionally elastic yet also highly predictable material. With an open structure porous structure it has excellent recovery characteristics and low compression set values. It has good resistance to solvents along with low outgassing, which means less odor than other foams. Being flame retardant, it's also good in situations where fire is a possibility.

Rogers Corporation makes three types of PORON Medical® foam, plus a related product, DermaBak®, a skin care material designed for use in the backings of wound dressings. PORON Medical® is available as:

  • PORON Medical® Urethane - Firm
    This is an open cell material made in densities from 15 to 20 pounds with 25% IFD in the range 6 – 25 psi. Its formulation makes it suitable for applications where energy absorbency is needed.
  • PORON Medical® Urethane - Slow Recovery
    Formulated for low resilience, which means a very slow rebound after compression, this is ideal for creating a custom fit after compression. Density is 15 pounds and the material comes in four grades of firmness with 25% IFD numbers ranging from 0.3 – 22 psi.
  • PORON® Medical® Urethane – Soft
    Available in 15 and 20 pound formulations with 25% IFD ranging from 4 - 14 psi, this versatile material is suitable for most cushioning applications.

Superior Performance
Depending on formulation and pore size, most open cell foam provides some degree of cushioning. However, low compression set resistance and poor durability render them inadequate for many medical applications. PORON Medical® foam is specially formulated to have a uniform structure of very small pores along with excellent compression set resistance. That results in predictable, and durable performance, making them the preferred choice when injury or disability necessitates cushioning. Whether the need is for a stable wheelchair seat or a long-lasting, pressure-relieving shoe insert, PORON Medical® foam should be a first choice. Have questions or would you like to schedule a call to discuss more? Please contact us today! 

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Twisting the Knife: Complex Shapes from Horizontal Contour Cutting

Horizontal contour cutting is a fast way to cut complex shapes without tooling delays.

The continuous or circulating horizontal bandknife machine slices the largest blocks of foam into thin layers or sheets. Add the ability to rotate the bandknife and the machine becomes a horizontal contour cutter, able to produce complex foam shapes quickly and efficiently.

Operating Principles
The horizontal contour cutting machine looks like a giant upturned "U" bridging a large flat table. An unbroken band of hardened steel runs through this "U", enclosed completely except for the horizontal length above and parallel to the table. This band moves continuously in one direction, with teeth along the cutting edge slicing effortlessly through large foam blocks clamped in place on the table.

Unlike the horizontal bandknife, the contour cutter has three axes of motion. The upturned "U" frame can move forwards and backwards, the band can move up and down, and the angle of the teeth can be changed by applying a twist. By synchronizing the movements of these three axes, the machine can cut angles, curves and even tight radii and sharp corners.

CAD to Part Program
A computer controls the motion, following a program developed from a CAD file of the part. Producing this program usually takes just minutes, although nesting, (adding other parts to the cutting program to minimize how much material gets thrown away) can add more time. A contour cutting machine needs no part-specific tooling, which helps gets the design into production faster and saves money. It's often possible to have pieces coming off the cutter within just a few hours of receiving the CAD file.

Precision Steel Cutting Blade
The band itself is just 0.7mm (0.030") thick and less than 4mm (0.15") deep so it's easily twisted and little material gets wasted. Twelve to fourteen teeth per inch cut smoothly, letting the machine advance the blade at up to15m/minute (49'/min) without deforming the material.

Why Horizontal Cutting?
The choice between horizontal and vertical contour cutting depends on which is the most economical way of getting the shape out of the block. Sometimes the vertical cutter is more appropriate. The horizontal machine is often used for the first cutting operation, followed by cutting in the other plane.

Benefits of Horizontal Contour Cutting

  • Cut complex shapes from large blocks.
  • Smooth edges with no steps or jagged edges in curved surfaces.
  • Tight radii and even sharp corners.
  • Good accuracy and repeatability (little piece-to-piece variation.)
  • No tooling, so no up-front costs or extended lead times.

Merryweather Capabilities
Merryweather's horizontal contour cutter handles polyethylene, polyurethane, EPE, EPS and convoluted foam in blocks as large as 2.3m (90") by 2.3m (90") by 1.3m (51") and densities up to 10 pounds. Programming direct from CAD means the machine is as suitable for producing one-offs as high volume orders.

Flexible and Accurate
The horizontal contour cutter is a three axis bandknife machine able to produce complex foam shapes quickly and efficiently. With no tooling it's suitable for cutting even one-off shapes and precise motion control leaves smooth, step-free edges. Learn more by contacting us with your questions.

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Polyester Polyurethane Foam or Polyether? Know the Difference

There's much to consider when buying flexible polyurethane foam. Density, tensile strength and Indentation Load Deflection are all important, but before looking at those there's a more important property to consider: which type of foam will work best in the application? 

There are two types to choose between: polyester polyurethane foam, and polyether polyurethane foam. Put side-by-side they're virtually indistinguishable, yet the differences in their properties could have a big impact on how your foam-based product performs. This blog post explains the differences and addresses why one might work better than the other.

A Little Chemistry
A polyester is a compound made up from multiple esters, linked in various chains. An ester starts out as carboxylic acid, which consists of carbon, oxygen and hydrogen. Adding an "alcohol," which in the chemical sense means a hydrocarbon compound like ethyl, replaces the hydrogen atom with a carbon-hydrogen compound. The result is a longer chain where the carbon and oxygen form a strong bond.

Ethers are only slightly different. Still a hydrocarbon, the oxygen forms two bonds to hydrocarbon compounds. One of the consequences is that ethers tend to be hydrolytically stable, or put more simply, don't break down in the presence of water. This is one of the major differences between the two types of foam.

Properties of Polyether Foam
Foams made with ethers hold up well in wet conditions. They are generally soft and flexible, due in part to relatively large pores. They are also easier to make and so less expensive than polyester foam. That's one reason polyether outsells polyester.

Polyester Foam Properties
Pound for pound, polyester foam is stronger than polyether and more rigid and supportive. Resistant to attack by many corrosive gases, it accepts additives providing fire-retardant properties and can also be formulated with electrostatic discharge (ESD) characteristics. (This type of foam is typically recognizable by its pink color.) Polyester polyurethane foam pieces can be welded together and it can be flame laminated, (where heat produces slight melting on one surface, letting it bond to another material.)

Two disadvantages against polyester are that it is:

  • Hygroscopic, meaning it deteriorates in damp conditions.
  • More expensive to produce than polyether.

Which to Use:
In general, polyether polyurethane foam is the material to use when cushioning is important, and especially if it might get wet. (Fabric-covered seats on a boat are a good example.) However, if the foam will be stretched or pulled, (as might happen when upholstering furniture,) or will be used for support and protection, (like in a transit case,) then polyester foam is the better choice. If the application is protection of electronic components then ESD protection should be considered, making polyester the only choice.

Consider the Application
Choosing polyurethane foam involves more than just looking at density; it's important to select the right type of foam for the application. Polyether polyurethane foam is generally softer, less expensive, and doesn't degrade when wet. However, if ESD protection or support are important, choose polyester polyurethane foam. Need more help? Give us a call and we can help you compare materials for your application. 

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All About Foam Convolution

Foam Convoluting is a process through which the surface of a piece of foam is customized to fit the requirements of a particular application. If a piece of foam in a hospital bed, for example, a unique pattern can be designed to allow for both levels of full body support and long-lasting comfort when compared to other options.

The Benefits of Foam Convolution
Foam Convoluting is a maximum yield process. Customizations to the foam are made specifically to provide the highest possible value given what a piece of foam will eventually be used for. If you use foam convolution to design a new piece of bedding, for example, the foam is customized in a way that will allow for things like:

  • Enhanced levels of air circulation.
  • Maximum support.
  • Increased comfort while still maintaining the desired level of support, and more.

It is for these reasons that flexible foam fabrication is often used across a wide range of industries, including in both bedding and healthcare, to create things like:

  • Acoustic applications, like use as sound treatment for a recording studio, thanks to their sound absorption properties.
  • Privacy panels that are more durable, more attractive and more versatile than concrete alternatives.
  • Office applications like ergonomic furniture, which creates a more comfortable environment for employees to maintain productive without sacrificing their health or stamina.
  • Insulation designed to eliminate drafts in a building, thus keeping cool air in during the summer and warm air in during the winter, increasing the energy efficiency of the whole building and decreasing utility bills at the same time.

Foam convolution is also often used in applications like sound management, acoustic treatment and similar products in an audio recording or other entertainment environment. Depending on the pattern being used, foam convolution can absorb mid and low range sound frequencies much better than alternative options.

The Materials Used in Foam Convolution
During this process, foam can be custom fabricated in one of four ways depending on the intended goal:

  • By pattern
  • By the total size of the pattern being worked with
  • By the depth of each intended cut that will be made
  • The spacing between multiple patterns that all come together to form a single piece.

In addition to the foam itself, a number of important materials are used during the foam convolution process. A specially designed divider is often used to slice a larger piece of foam down the middle, while at the same time also creating the specific pattern that will be present on the final product. A series of rollers move a piece of foam across the divider, allowing for the process to be largely automated after all of the initial design work has taken place.

By and large, foam convolution is one of the single best ways to achieve the results that you're after for a particular application. The products of foam convolution play an important role in the lives of millions of people on a daily basis - from acoustical engineers to patients in hospitals to people just trying to get a good night's sleep - and the process in general is something definitely worth celebrating. Questions about Foam Convoluting or other machine processes? Give us a call--we're happy to help!

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