For over 4,000 years, the evolution of the filter has been directly linked to the improvement of human health and life expectancy. The first great civilizations, like the ancient Egyptians, used sand and gravel as filter media to improve the taste and appearance of water. Today, filters have become an essential component to our entire way of life. They are found in countless industries, manufacturing facilities, processes, and in many cases, the end products themselves. More importantly, filters are enabling the tools and devices that are essential to defeating this invisible enemy and returning the world to some semblance of normalcy.
Since the onset of this pandemic, our society has gained a new appreciation for respirators, ventilators, and vaccines, as well as the vital role they play in saving lives and preventing future outbreaks. Like everything else in our modern industrial society, these life-saving tools all rely on specialized filter media and advanced filtration technology to function. It is obvious how filters are utilized in equipment like respirators and ventilators, but when it comes to vaccines the use of filter technology is not immediately apparent.
How are filters used for making vaccines?
A successful vaccine is the result of complex scientific processes that include the concentration of proteins and enzymes, blood plasma purification, virus and bacteria concentration and removal, as well as cell harvesting, clarification and washing. These procedures are all enabled by specialized filters and equipment.
Some common methods used in bioprocessing include membrane filtration, tangential flow filtration, centrifugation, and depth filtration. Implementing the proper filtration technology can have a positive effect on yield, product consistency, and overall efficiency of the entire operation.
What types of filters are used?
Hollow fiber filters possess excellent filtration performance and are commonly used in dialysis, water purification, reverse osmosis, separation of components from biological fluids, and cell culture devices to name a few.
Tangential flow filtration (TFF) systems are used extensively in the production of vaccines and other pharmaceutical drugs. They can be used to remove virus particles from solutions, clarify cell lysates, harvest and retain cells, and they can concentrate and desalt sample solutions ranging in volume from a few milliliters up to thousands of liters.
A HEPA (High Efficiency Particulate Air) filter works by forcing air through a fine mesh that traps harmful particles such as dust mites, pollen, pet dander, smoke, and even airborne viruses. HEPA filters are used in applications where contamination control is required, such as the manufacturing of semiconductors, disk drives, medical devices, food and pharmaceutical products, as well as in homes, vehicles, and hospitals.
How is Hapco involved in the filtration and ultrafiltration industry?
Hapco has been custom formulating adhesives, sealants, and potting compounds for some of the world’s largest filter manufacturers for over 40 years. Our materials and processing equipment are a key component to manufacturing a wide variety of specialized filters. As a preferred supplier to corporations like MilliporeSigma, Pall Life Sciences, and Koch Membranes, we take pride in our ability to provide customers with the highest quality polymers and the most reliable processing equipment available.
As we look to a post-pandemic future, our chemists are developing new formulations and processing methods to meet the needs of filter manufacturers around the world. We are currently conducting in-house testing on Filter-bond™ R-3590: a new epoxy formulation for the filtration market that is both Bisphenol-A (BPA) and nonylphenol-free.
What other Hapco products are used to manufacture filters?
The Filter-bond™ series was first developed in the 1980’s for various filtration and ultrafiltration applications. It includes formulations that do not contain aromatic amines or carcinogenic or mutagenic materials, systems that can be used to pot moist membrane material in place without foaming, and systems that are easily trimmed when used for pre-potting filters. Filter-bond™ includes a line of flexible and rigid materials to meet a wide variety of filtration applications. All Filter-bond™ products are compatible with Hapco’s MiniFIL™ and RapidFIL™ dispensing machines, which are used for potting or encapsulating various filter media.
Filters are one of mankind’s greatest achievements and a major reason our life expectancy has increased dramatically over the past 200 years. They clean the air we breathe, the water we drink, the fuel that moves us forward, and the medicine that keeps us healthy. Without them, there is simply no way to manufacture the life-saving and preventative drugs that offer us a light at the end of this tunnel.
Fun Fact: Hippocrates (460-370BC) was the first major proponent of water filtration in recorded history. He advised people to first boil, then filter water through two sewn together pieces of cloth which eventually came to be known as a Hippocrates’ Sleeve.
The term “viscosity” refers to the thickness or flowability of a liquid. Viscosity numbers range from 1 (water) to millions of centipoise (cP) or pascal seconds (Pa.s), 1cP = 0.001 Pa.s. Refer to our viscosity comparison chart here.
Urethane and epoxy resins with viscosities ranging from <100cP to 1,000cP are ideal for most generic casting applications. They de-air very well on their own and flow easily into closed molds, whether mixed and poured by hand or dispensed using meter-mixing equipment. However, there are many specialty materials, such as, Hapco’s Steralloy™, Filterbond™ and Hapflex™ resins that are formulated for highly-engineered applications, and because of their unique chemistries, they have a thicker viscosity than other products, making them a bit trickier to process.
When mixing and pouring by hand, Hapco always recommends vacuum degassing the mixed resin prior to pouring. With viscous materials, it can be helpful to add a few drops of a surfactant, such as Hapco’s
Anti-Air™ product, which reduces surface tension and allows the resin to degas more easily. However, vacuum degassing alone does not always alleviate air bubbles due to cavitation of the material as it flows through the mold. It may also be necessary to cure your parts under pressure using a pressure-pot or molding chamber, like Hapco’s unique X-Series Molding Chambers.
When using meter-mix dispensing, Hapco recommends designing a mold that fills from the bottom up. A general rule in this case is to design the mold so that the output opening(s) equals 2-4 times that of the input. In simple terms, if you have a 0.50” diameter input, your out-put should equal 1”-2” in diameter. This enables a “pressure drop,” which minimizes any back-pressure build-up caused by shooting a viscous material into a closed mold.
When dealing with complex mold geometry, it may be beneficial to use a two-step degassing process. After initially degassing the resin mix, fill the molds and place them under vacuum again for an additional few minutes. This not only helps to release trapped air caused by material cavitation, but it will also “pull” the viscous material into the cavity to ensure a complete fill, especially if your mold has thin walls or complex geometry. While degassing the molds, the material inside will not swell up as it did during the initial degassing step, however, it may continue to “boil” somewhat. Therefore, it is advisable to fabricate a small “chimney” around the top of your mold to prevent material from spilling out. You can do this easily with wax, putty, or a simple strip of packaging/duct tape wrapped around the top of the mold. After secondary degassing you may find the need to top off the molds to ensure they are filled to proper height, in which case you should be able to do so without the need for further degassing
Other suggestions for thinning higher viscosity materials are as follows: Pre-heat the resin to 80° – 110°F. It is really only necessary to pre-heat the thicker component which is typically the Part A for most materials. As a general rule, for every 10° you heat the material above room temperature, the material viscosity is cut in half. Bear in mind though, that heat will also cause the material to gel faster, thereby reducing your overall work time. In lieu of pre-heating the resin, you can pre-heat the molds instead. This will maintain work time for mixing, and still thin the resin viscosity as it flows into the warm molds. Another suggestion would be to add a small amount of solvent, such as, isopropyl alcohol or acetone into the resin mix. Solvents will cut the viscosity without impacting curing or material properties in most cases, as they will flash off quickly once the material starts its exothermic reaction.
The bottom line is that you will need to incorporate the proper equipment and techniques into your process in order accommodate using viscous materials. Water-thin materials require very little in the way of specialized equipment and they certainly make things easier. However, limiting your material offerings can also limit your opportunities for getting more of those “high-dollar” projects. My advice for expanding your business opportunities is to think “outside of the mold-box,” and have enough flexibility in your process to take on those jobs that nobody else wants!
In our previous post, we discussed the application of potting and encapsulating using urethanes and epoxies. When choosing the proper urethane or epoxy for an electrical application, there are some important considerations to keep in mind. In this article, we will discuss those considerations and how they apply to the world of urethanes and epoxies.
Here some examples of electrical applications using urethanes and epoxies:
The 3 most commonly sought after resins for electrical applications can be classified as electrically conductive, electrically insulative, and statically dissipative.
Electrically conductive materials have a low electric resistance and electrons flow easily across the surface or bulk of the material. Charges go to ground or to another conductive object that the material contacts. These materials have a surface resistivity less than 1 x10^5 Ohm/sq or a volume resistivity less than 1 x 10^4 Ohm-cm. Electrically conductive resins are typically filled with metallic or conductive particles.
Electrically insulative materials prevent or limit the flow of electrons across their surface or through their volume. Insulative materials are difficult to ground and have a high electrical resistance. Static charges remain in place on these materials for a very long time. These materials are defined as having a surface resistivity of at least 1 x 10^12 Ohm/sq or a volume resistivity of at least 1 x 10^11 Ohm-cm.
Statically dissipative materials have a surface resistivity equal to or greater than 1 x 10^5 Ohm/sq but less than 1 x 10^12 W/sq. They have a volume resistivity equal to or greater than 1 x 10^4 Ohm-cm but less than 1 x 10^11 Ohm-cm. For these materials, the charges flow to ground more slowly and in a somewhat more controlled manner than with conductive materials.
Q. What is the difference between vacuum degassing and pressurizing?
A. Vacuum de-gassing expands the air trapped during mixing or pouring, causing the bubbles to grow, rise to the surface, and in most cases, release. After a period of time the amount of trapped air decreases. The material’s viscosity and surface tension will determine how easily the air will escape. Certain materials appear to bubble indefinitely until the vacuum pump is turned off. In order to maximize the vacuum’s potential for air removal, the pump must be capable of pulling 29.6 inHg.
When placed under pressure, any air bubbles entrapped from the mixing and pouring process shrink to the point where they are no longer visible. Pressure ranging from 60-80 psi significantly reduces the chances of visible air bubbles. For pressure to be effective, the liquid thermoset material must remain under pressure until it has reached its gel time, otherwise the bubbles may expand once the pressure is relieved.
A. One method really isn’t preferred over the other. Whether you choose to use vacuum or pressure depends on the application, your capabilities, and budget. In fact, we often recommend vacuum degassing your product after hand mixing, pouring into the mold, and then using pressure to make sure all parts of the mold are filled. When using dispensing equipment, there is no air introduced during mixing. That doesn’t mean air cannot be introduced while shooting into your mold, especially one with many thin walls, sharp corners, or intricate details.
If you find yourself in a situation where you absolutely need a bubble free part (e.g., using a plaster mold or a large quantity of expensive material) it’s best to play it safe and employ both methods. If neither option is in your budget and you need a void free surface, we recommend using low viscosity materials, mixing slowly and thoroughly, and brushing a thin coat onto the mold or pattern’s surface. Using a hair dryer while brushing the thin coat will help to ease surface tension and reduce bubbles.
Potting consists of immersing the part or assembly in a liquid resin, and then curing it. Although often confused for each other, potting is different from encapsulation in that it retains the shell that is used to contain the thermoset resin while it’s curing.
Encapsulation involves building a mold or frame around an object, e.g., wires, filling the space between the frame and the object with a thermosetting material such as Di-Pak™, waiting for the resin to cure, and then removing the frame.
These processes are commonly employed to protect semiconductor components from moisture and mechanical damage. They are also used in high voltage products to allow live parts to be placed much closer together, so that the product can be smaller. They keep dirt and conductive contaminants such as impure water out of sensitive areas and serve as structural reinforcement, protecting sonar transducers and other deep submergence items from collapsing under extreme pressure. Potting with black or opaque epoxies and polyurethanes can be used to discourage reverse engineering of proprietary products such as printed circuit modules.
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