Reducing Sealing Failure
- May 10, 2012, Tom Bezigian
I had a nice talk with Dr. Barry Morris on a recent visit to DuPont's Chestnut Run facility in Wilmington, Delaware. We discussed his work on package performance and his White Paper entitled "Sure Ways to Reduce Package Failure". The paper can be found at:
http://www2.dupont.com/Packaging_Resins/en_US/assets/downloads/white_papers/Reduce_Package_Sealing_Failure_Barry_Morris_November_2010.pdf
A package has to first and foremost deliver its contents in perfect condition to the end user. It must also run well on packaging equipment, maintain functionality and appearance in the retail environment, and be cost effective. I can tell you from my days at Cryovac, leakers are the bain of a package supplier. Raw material suppliers, equipment suppliers and converters and bagmakers go to great lengths to prevent leakers, which of course result in much waste and cost to the entire value chain. According to information in Barry's White Paper, a 3% increase in leaker rate can result in a 20% package cost, so obviously it is imperative to keep leaker rates as low as possible. His paper specifically addressed three critical areas:
- Consistent seals over a wide temperature range
- An ability to seal difficult packages
- Better package performance
With regard to the first point, there are four polymer attributes that contribute to improved packaging efficiency:
- Wide seal temperature range
- Good hot tack properties
- Low heat seal initiation temperature
- Ability to seal through gussets and wrinkles
Since I was in college way-back-when, we studied ionomer resins and their superior heat seal, hot tack and chemical resistance properties. The graph below, taken from the above referenced paper with permission, shows hot tack strength versus temperature for various common polymers.
Traditional polyethylene resins are not sufficient to provide the protection needed for a wide variety of packaging applications. Newer metallocene polymers offer good strength properties, but over a narrow temperature range. According to Dr. White, zinc-based ionomer resins offer strong heat seals and hot tack strength over a wide temperature range all while offering superior chemical resistance, and the ability to seal through contaminants such as fats.
This last point always impressed me. Most polyethylenes are penetrated by corn oil within 2 days, while most acid copolymers can last 6 days and ionomers can last 11+ days, at which time the test is halted. In my own experience, I have seen ionomers withstand attack from essential oils in tea packaging for more than a year, while standard LDPE resins fail with a day. In dried powder flavored drink packaging, affectionately known as Kool-Aid in the United States, the difference is even more dramatic. I have seen powdered drink formulations flavored with natural essential oils fail immediately on the packaging machine, whereas ionomer resins last nearly indefinitely. I still use these samples in the extrusion coating classes I teach at UMASS-Lowell.
I'd like to thank Dr. Morris for his time. I welcome feedback as well as information from other sources to be included in this blog.
If you are interested in the next class I am teaching on extrusion coating, here is the link:
http://continuinged.uml.edu/plastics/extrusion_coating_technology.htm
I will be in Kuala Lampur next week for a few weeks. If I have internet access, I will blog while I am there.
NPE Follow Up
- May 01, 2012, Tom Bezigian
Now that everyone is rested and caught-up from a fantastic NPE show in Orlando, let's review what's new and exciting.
What I observed at the NPE show was: a LOT of international participation, a lot of high technology being implemented on traditional equipment, and an emphasis on waste recovery. What was missing from past shows was the abundance of live demonstrations of basic processes.
As far as international participation, I saw many many participants from overseas. While many view a trip overseas as a vacation, it is indeed work and is indeed expensive, so seeing a large number of overseas visitors to the US indicates something of a global economic recovery. On the flip side, the presence of so many foreign suppliers at the show in addition to their foreign service attachés indicates the desire for overseas competitors to enter the US market. This can be a good thing for converters and a potential threat for suppliers here in the US, especially where a reduced number of suppliers has occurred due to acquisitions and mergers. What I am seeing also is that the price to make something simple, such as a plastic bag, is so much less in certain parts of the world that those bags can be made and shipped to the US for less than what it costs to make locally.
As far as technology, everything today computer controlled, touchscreen, advanced logic and graphics, servo-controlled, high-speed, automated, robotic, with advanced software offering excellent monitoring, reporting and tracking abilities, trending, and on and on. The equipment underneath this technology hasn't changed too much, but the technology allows converters to produce better product more efficiently. What is "under-the-hood" so to speak that people don't see is the design of certain parts of the machine, such as molds and dies, is much more accurate than ever possible before due to advanced computer and software technology. Companies big and small, such as Rao Technologies, Beaumont Technologies, CompuPlast and Extrusion Dies for example, can all model and design molds and dies with much more precision than in the past. More to come on this in future blogs.
Lastly, companies such as Erema and Kronos have complete turn-key solutions to both consumer and industrial waste so as to minimize the size of the landfill stream and cost to the consumer. Sophisticated technology allows these plants to increase the IV (intrinsic viscosity) of PET (polyester) so that the recycled stream has the same physical properties as the virgin material. The same goes for polyethylene-based waste stream (minus the IV increase step).
All in all it was a great show. I decided to take a side trip to the Kennedy Space Center after the show, and ran into the same contingent of people from Spain that were at my hotel. Small world.
The 2012 NPE Show
- January 19, 2012, Tom Bezigian
I know it's old news, but I am excited that the NPE show has moved both its date and time to April in Orlando. Not that it's a boondoggle to be in Florida in April, but its nice to be warm and work on the Summer tan so early in the season.
If you haven't checked it out or registered yet, the website is: http://www.npe.org/
There is much to do and see at the show, including the annual ANTEC meeting. If you haven't signed up for that yet, here is the link to their website:
Last but not least, the UMASS-Lowell Plastics Engineering reunion will be held on Tuesday, April 3, 2012 starting at 5:30 pm at the Renaissance Orlando at Sea World. This is always a big event and a great opportunity to see old friends. Visit the department webiste for updates:
http://www.uml.edu/engineering/Plastics/
Why do I have these bubbles in my finished product?
- January 03, 2012, Tom Bezigian
As complicated as the extrusion process is, with all its nuances of equipment variations, materials, finished product requirements, ancillary equipment, etc., I have observed over the years that there are a core set of issues that affect every processor. I will touch on the subject of degradation as manifested by bubbles or voids in the finished product.
Screw & Die Design Models
- December 06, 2011, Tom Bezigian
I met with a couple of old friends this week, Dr. Natti Rao, who was visiting New York from Germany, and John Beaumont, a classmate from UMASS-Lowell. It's always great to catch up with old friends, and even better when I can do that and talk about screw and die design modeling. Wait... did I just say that?
Some Thoughts on Purging
- November 10, 2011, Tom Bezigian
A reader asked for some information on purging LDPE in his twin screw extrusion process. By and large, the screws within a twin screw extruder are “self-wiping” due to the close contact between elements and the high shear rates caused by this close contact. That being said, there are regions within the screw design that are low-shear regions which do not receive the same wiping action as the high-shear regions. These low-shear regions are thus susceptible to build-up of carbon, color concentrates, or any other additive used in the process.
Things have settled down
- November 08, 2011, Tom Bezigian
A lot has happened since my last post, including teaching many extrusion and polymer chemistry classes around the country, traveling, consulting, visiting friends and family, getting a sun tan and enjoying life in general. I’ve also made a conscious effort to turn back the hands of time, and I’ve lost 40 lbs (18 kg) over the summer. It’s great to be back into college clothes, and it’s great to be back writing. There have also been many new changes with the blog, all of which I see as very positive. Congrats to Yo and her team for continuing to operate what I view as the premier online magazine discussing paper, film and foil converting issues. They have done a great service to the industry and it is an honor to be associated with this team.
You Get What You Pay For, Part 2
- July 28, 2010, Tom Bezigian
Last issue I discussed what happens to a blown film manufacturer on a shoestring budget. It is a financial truth that if a company does not make enough money on the product it sells, then something has to give, i.e., either it will eventually go out of business, or some necessary expense must be eliminated. Let’s look at some of these and see what areas an end user can focus on when meeting with a supplier.
You Get what You Pay For, or Caveat Emptor.
- July 16, 2010, Tom Bezigian
Yup… the old adage is true. All things being equal, you get what you pay for. Since my days at Cryovac, Mobil Plastics, James River Corp, et al, and then consulting with many, many companies, I have seen the full gamut of quality in the blown film / cast film / extrusion coating and laminating / packaging / converting industries. The larger, more reputable companies offer excellent quality products and excellent service at a price commensurate with those attributes.
Techniques to Prevent/Minimize Die Lines
- April 29, 2010, Tom Bezigian
I’m sorry about the long gap between posts. I have been working as an expert witness on a very interesting and demanding case which has taken all of my time for the last two months. Now… back to die lines.
