Electrostatic Dissipative (ESD) Materials
How to Protect Against Static Electricity Build Up

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When talking in terms of conductivity, both thermal and electrical, plastic materials are considered insulative.  Insulative materials do not allow the flow of thermal energy or conduct current through its mass quickly or at all.  Sometimes, however, we need our plastic parts to do just that, conduct current or ground a part.

To quantify electrical conductivity, we test either the surface or the volume resistivity of the plastic. Resistivity is the resistance to leakage current through the body (volume) or along the surface of an insulating material.  The values are then given in ohms (surface) or ohms-m (volume).  The higher the value, the better they are at resisting the conducting of the current or, the more insulating they are. Plastic materials without fillers, additives, etc., to improve conductivity are in the insulating range of the ≥ 1012 ohms resistivity, compared to metals in the conductive range of ≤ 106 ohms.

The Electrostatic Dissipative (ESD) protective range can be broken down into three categories and their corresponding resistivity ranges:

  • Anti-static (anti-stat) is 109 to 1012 ohms.  In this range, initial electrostatic charges are suppressed, preventing the buildup of static electricity.  In plastics, we can achieve this with additives.
  • Static dissipative is 106 to 109 ohms.  There are low or no initial charges in this range and prevent discharge to and from human contact.  It will also ground charges, but much slower than conductive grades.  In plastics, we can achieve this with metal fiber reinforcements and other conductive additives.
  • Conductive is less than 106 ohms.  In this range, there are no initial charges.  It provides a path for electrons to flow freely across the surface or through the bulk of these materials, making it easy to ground charges or move them to another conductive object.  In plastics, we can achieve this with metal fiber reinforcements and other conductive additives.

So, why do we need ESD protection and parts that offer that protection?  Static electricity.  Static electricity can build up to as much as 30,000+ volts.  Plastics or other insulative materials do not move the charge, and it remains on the surface.  Once a person comes into contact with the built-up charge, it will discharge via an arc or spark.  The discharge that occurs to that person can range from a mild to painful shock, and in extreme cases, can result in death.

Another reason that we need ESD protection is that electronic parts can be destroyed or damaged by a discharge as little as 20 volts.  Discharge that results in sparks can also be dangerous around flammable liquids, solids, or gases, such as in a hospital operating room.  In these cases, we would look to utilize plastic materials that have been specially compounded to meet any of the ESD ranges needed to protect against harm or damage.

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The Engineering Team here at Chase Plastics is ready and willing to walk you through any analysis needed to offer suitable electrostatic dissipative materials to meet your needs.  Give us a call at 844-411-2427 or send an email to engineering@chaseplastics.com to get support on any of your technical questions today!

If you have questions on the topic above or another issue to tackle, please submit your inquiry in the questions/contact form to the right.  Someone from our Technical Team will be in touch within 2 hours!

How to Achieve Cost Savings Through Specific Gravity

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When comparing two materials for an application, the true cost of a polymer is not limited to the price per pound.  As any molding or extrusion shop knows, there can be hidden costs in the complexity to run, scrap rate, tooling changes, special processing equipment, and many other factors.  One aspect to consider that is often overlooked is the specific gravity of the product(s) in question.

To get started, let’s look at the definition of specific gravity.  The dictionary defines specific gravity as the ratio of the density of a substance (in our case, plastics) to the density of a standard, usually water.  Now in the case of water, the density is roughly 1 gram/ml.  As such, when comparing a material’s ratio of density to 1 g/cm3, the specific gravity will be the same as the material’s density.  For instance, if a 30% glass-filled polypropylene homopolymer has a density of 1.13 g/cm3, then the specific gravity of that compound would be 1.13 as well (specific gravity is a unitless value).  Specific gravity is commonly seen on plastics’ datasheets, so we mention this description.  However, density and specific gravity can be used interchangeably for most intents and purposes since both represent how much plastic you get for a set volume of material.

This begins to affect cost because we buy and sell plastic raw materials by the pound rather than its volume.  Specific gravity can be used to show how far a set weight of material will go in terms of how many parts it can produce.  Roughly stated, lighter materials can make more parts per bag or box of raw material used.

For instance, let’s use the even number of a proposed part with a volume of 100 cm3 where we have the option to use HDPE or acetal (POM) for the same job.  If we have a 25kg bag of HDPE with a density of 0.953 g/cm3, it will yield approximately 221 parts from that bag.  The math for this is as follows:

25kg bag = 25,000g of HDPE. At 0.953 g/cm3 that equals 26,232.9 cm3.
Since each part is only 100 cm3, you would be able to create 262 parts.

If we were to produce the part in acetal, the specific gravity would jump up to 1.41 g/cm3.  That would adjust the math to the following:

25kg bag = 25,000g of POM. At 1.41 g/cm3 that equals 17,730.4 cm3.
Since each part is only 100 cm3, you would be able to create 177 parts.

Therefore, if we made the parts from HDPE rather than POM, you would create roughly 48% more parts using one 25kg bag of material.  This equation works easily when comparing two materials of the same price, but what about when they are different or arguably more expensive?

Say you are comparing two materials, but one is 5% more expensive.  If the more expensive material has a specific gravity that is lower by 5%, then the two materials are functionally equivalent in cost per part. If the more expensive material is 10% lower in specific gravity, it is actually a cost savings per part to use the “more expensive” material per lb.

When comparing materials for a new job, it is always pertinent to compare the specific gravity for potential savings.

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The Engineering Team here at Chase Plastics is ready and willing to walk you through this analysis if needed or offer lighter materials for savings opportunities when possible.  Give us a call at 844-411-2427 or send an email to engineering@chaseplastics.com to get support on any of your technical needs today!

If you have questions on the topic above or another issue to tackle, please submit your inquiry in the questions/contact form to the right.  Someone from our Technical Team will be in touch within 2 hours!

Is My Dryer’s Desiccant Still Working?

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Let’s understand why materials need to be dried in the first place.  For thermoplastics, there are hygroscopic and non-hygroscopic resins.  Hygroscopic resins have an affinity for moisture, and it gets absorbed into the polymer chains of the material.  For hygroscopic resins (polymers that naturally absorb moisture such as Nylon, PBT, PET, ABS, and PC products), it is critical to ensure proper drying of the material prior to processing it.  In doing so, you will help prevent part failure due to hydrolysis and cosmetic defects such as splay or silver streaking.  Hydrolysis is the chemical breakdown of a compound due to the reaction caused by the presence of moisture in elevated temperatures.  This means that when a hygroscopic resin is processed with moisture, it causes the polymer chains to break, resulting in a significant decrease in mechanical properties.

Below is an example of the resin moisture capacity of 3 polymers; polyethylene (non-hygroscopic), polycarbonate (hygroscopic), and nylon (hygroscopic). Every polymer has its own capacity to absorb water, meaning some will absorb water more readily than others.

When molding hygroscopic materials, it’s recommended to use a desiccant dehumidifying style dryer to properly remove moisture from the material.  Let’s understand how a desiccant dehumidifying style dryer works:

  • It dries the air to the required dew point level
  • Heats the air to a specified temperature
  • Circulates the heated airflow within its own closed-loop system
  • Moisture migrates out of the polymer and is removed from the circulating air via desiccant bed

The desiccant bed is a cartridge type “filter” made up of moisture-absorbing desiccant beads.  An example of this would be the silica gel desiccant beads found in everyday consumer items/packaging (i.e., dry goods, shoe boxes, vitamin containers, clothing, and packaging).  The silica gel desiccant beads act as a dryer and capture unwanted moisture, preserving the product.

Now let’s review dryer maintenance and how you can tell if your desiccant beads are bad.  This is important to understand, so you aren’t molding material that still has moisture in it when processing.  As mentioned previously, processing hygroscopic materials with moisture leads to cosmetic defects and hydrolysis, which breaks the polymer chains affecting the overall mechanical properties of the material/ part.

There are three ways to tell a desiccant is bad in your dryer:

  • You cannot hold the desired set dew point on your dryer for the material. If it never reaches the desired dew point or doesn’t hold it for long, then it’s probably time to change the desiccant.
  • Pull the desiccant beads out and squish them between your fingers. If they are very brittle and crumble upon doing so, they’re bad and need to be replaced.
  • Take a styrofoam cup, fill it with about 1 inch of desiccant beads, and pour water on them, just enough to cover them or leave a few above the water. It’s good to know what the water temperature is before filling the cup.  If the cup and water get hot, then they’re still good.  However, if it remains cold, then it’s time to change the desiccants.  When desiccants absorb moisture, they give off heat.  You can then use a thermometer to measure the water temperature difference after the water reacts with the desiccant beads to see the change in temperature.

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The Chase Plastics team of engineers is ready to assist with any drying and process related questions you may have. Give us a call at 844-411-2427 or send an email at engineering@chaseplastics.com to get support on any of your technical needs today!

If you have questions on the topic above or have another issue to tackle, please submit your inquiry in the questions/contact form. Someone from our technical team will be in touch once it has been submitted.

Hunt for resin continues, even as supplies improve

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Frank Esposito
Plastics News
April 9, 2021

North American resin availability is improving in the wake of recent outages, but many companies throughout the supply chain still can’t get all the material they need.

In the wake of Winter Storm Uri, which hit Texas and the Gulf Coast in mid-February, many material suppliers put customers on force majeure sales limits or other types of allocation.

LyondellBasell Industries of Houston operates multiples sites making polyethylene, polypropylene and related resins and compounds in Texas. In an email to Plastics News, spokeswoman Chevalier Gray said that “nearly all of our assets, except for Corpus Christi, are back to normal operations.”

A spokesman for Wilmington, Del.-based DuPont Co. said that the firm still has force majeure limits in place for nylon, polybutylene terephthalate and several other materials. DuPont “is taking commercially reasonable steps to mitigate the effects of these shortages on its customers, but many of the upstream supply constraints persist,” he said.

“We take this matter very seriously and recognize the importance of supply reliability to meet the needs of our customers,” he added.

At Midland, Mich.-based Dow Inc., the firm “has continued to restart units and ramp rates through March and into April, as we manage a few raw material constraints and freeze damage repairs,” a spokesman said.

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Visit our new 3D Printing page

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Let our experts help you simplify and guide you through the most complex 3D printing material selection processes.

3D printing helps manufacturers reduce time and costs while increasing efficiency. Chase Plastics will help you navigate the process of additive manufacturing with the tools, resources and suppliers to help you thrive. As a stocking distributor with several options, our trusted experts simplify and guide you through the most complex 3D printing material selection processes to provide more design freedom and efficiency at your target cost.

 

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Recovery underway for resin distribution in 2020

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Frank Esposito
Plastics News
August 19, 2020

North American resin distributors have overcome many obstacles to keep their customers supplied with material during the global COVID-19 pandemic — and their work isn’t over.

“We almost have a moral obligation to provide key raw materials to our customers at a time like this,” said Vishal Goradia, senior vice president at Vinmar International of Houston. “Early on, we saw the global effect of rolling shutdowns. It was affecting a different region every month, but we kept our focus on being reliable to our customers and suppliers.”

Plastics News recently spoke with several resin distribution executives to see how they were navigating the uncharted waters of 2020. Here’s what they had to say:

The year begins…

Many executives said the year was off to a good start. Then the pandemic caused global shutdowns across almost every industry in March.

“A lot of places shut down and there were some stranded rail cars of resin,” said Ed Holland, President and CEO of M. Holland Co. in Northbrook, Ill. “The trough in May wasn’t as deep as we expected, and June and July bounced back.”

“In mid-March, everything fell off,” added Kevin Chase, president of Chase Plastic Services Inc. in Clarkston, Mich. “In automotive, all tiers were shut down until most places made automotive an essential business. We’re slowly recovering now.”

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