Brentwood Plastics blog

PE Film Lead Time Factors

Posted by Joel Longstreth on Wed, Apr 24, 2019 @ 06:05 PM

The ship date for custom PE film involves much more than a first-come-first-serve queue.  An extruder who runs their backlog in this fashion or has a salesman running the backlog is not long for this world.  

ancient pyramid art

This is nothing new.  Egyptologists have determined that customers and suppliers have been at loggerheads for thousands of years. 

The primary consideration in setting up a backlog is minimizing scrap.  The scheduler's agenda is to consolidate a sequence of films made out of the same PE resin as long as possible to avoid transition scrap.  With resin cost at about 75 cents per pound, every pound of scrap is really about $ 1.00 lost factoring in labor, electricity and overhead. 

This is crucial to survival in coextrusion.  Complex 7 and 9 layer films can literally take all day to set up. 

A medium scale extrusion line puts out about 500 pounds an hour.  What would you do ?

It's best practices to have some leeway in ship dates.  We promise our orders for "week of _____ ".  A smart play is to promise a Thursday ship date.  4 out of 5 chance it will ship early or on the date.  1 in 5 chance it will be a day late and so what ?  only a day late. 

It's also best practices to have a few dummy orders in the backlog to both act as a cushion for breakdowns and allow for opportunities.  If an order comes in with a ship date 3 to 4 weeks out for a resin running today, it makes common sense to move it up in the queue to avoid setup scrap instead of running it as a stand-alone 3 weeks later.

Distant secondary considerations are width and thickness changes ( there's the central theme of avoiding scrap again ) followed by pigmentation.  Cleaning out after colors is time consuming and messy.  The line must be shut down, purged, what is called the screen pack / breaker plate must be changed.  The ordeal is followed by an expensive, frustrating waiting game while the remnants of the color clear out.  

Back in the day, we had a shrewd customer who went out of his way to pay his bills every Saturday.  A check for all invoices in the week would show up like clockwork on Monday morning.  Why ?  To tempt the film extruder to deviate from fundamental priorities.

Of course, there are a few justifiable exceptions.  Re-work of returned or defective product or doing an occasional favor for a good customer who is out of film and shut down.  

So now you know why:

Coextruded films have such extended lead times

shrink films have such a wide variation in MD / TD shrink ratios
( the order goes on the machine that needs work )

pigmented films have longer lead times

Are you wondering where is our proof that first-in-first-out doesn't work ?  That's easy.  The outfit we sold out to in 1984 ran orders in the sequence received.  It took them 3 years to declare bankruptcy.


Read More

Topics: LDPE film, poly film, polyethylene film

PE Film Make / Buy Decision

Posted by Joel Longstreth on Thu, Aug 04, 2016 @ 03:25 PM

It's cliche but true - when milk is cheap, why buy a cow ?  Peter Drucker said it is better to integrate upstream than downstream.  The case for vertical integration play involves payback analysis and other factors.  Henry Ford made his own power mainly because he was fed up with dirty intermittent power.  I can relate.

The most common fallacy of vertically integrated PE film supply is not treating it as a stand-alone P & L.  


Many companies opt to buy film even though they consume enough film to feed a grass roots film plant.
Procter and Gamble Clopay have had a symbiotic relationship for generations.  When P & G puts up a diaper operation, a Clopay embossed film plant will pop up in close proximity.  It's only one item.  

Custom flexible packaging has more moving parts.  There are good reasons to buy PE film on the outside:
1.  Lead time     Using multiple extruders increases the likelyhood of finding a line which needs work.  The New York tri-state area is the best example in the US.

2.  Painless rejection   Rejecting film which comes from an outside source does not generate the acrimony resulting from an internal rejection.  Gotta keep the prima donna pressmen happy, right ?  Finding another film source is easy.  Finding a reliable pressman is not.  If you don't reject film outright, specious claims are a time-tested means to shaving a few cents off raw matierial costs.  The extruder would rather take a discount than see the film show up on his dock.

3.  Cash flow and turns   Most bag makers do not understand the concept of borrowing to pay invoices timely.   Line of credit ?   What's that ?   It's simpler to buy from multiple sources and string out your accounts payable.  If you do hit your credit limit, buy from a different extruder.  

Buying resin is more complex.  
You have to:
forecast 90 days rolling
wait sometimes five weeks for the railcar to show up
pay bills timely
provide quarterly financial statements to the resin companies

If you're on the wrong side of the market, every penny you're off =  $ 2,000.   Film prices drop shortly after CDI comes out.  Whatever is in the silos gets devalued.  Why bother ?   It's much less risky to order film for each job.

4.  Lowest cost   Overcapacity in blown film is a time-honored tradition.  Don't just keep your supplier honest.  Constant reverse auctions give new definition to keeping a supplier honest.

One of our successful alumni - Dave Frecka, founder of Next Generation Films - is betting big on yet another expansion literally the size of two homesteads.  He's betting that his customers will not make their own film.

Flexible packaging converters see making film as much simpler than their complicated processes which involve inks, plates, solvent recovery, adhesives, people, bag and pouch making.  They visit a blown film plant, see an operator sitting down reading a book or taking a smoke break.  The operator is sitting down because he's exhausted from all hell breaking loose over the last two hours.

In theory making blown film is a simple, continuous process.  If it was really difficult and complex, there would not be over 27,000 known blown film shops on the planet. The truth is making blown film is an art despite what equipment manufacturers proffer as "turn-key" lines.  There is a learning curve. 

Let's look at how seemed to be a good idea at the time that led to a salvage play.

The same schedulers who won't schedule a print job until the plates and film are both present hate to wait for film.  The reason the printer has to wait is that a properly run film backlog prioritizes minimal scrap. When the backlog is set up on a first-in-first-out basis or disrupted by the printing plant manager who succumbs to an ultimatum from the cutomer who has threatened to cancel ( sticking the converter with the cost of the film and plates ), excessive transition scrap is the result.   Scrap factors which are not captured in the in the justification for going vertical are transition scrap, internally rejected film, startup and shutdown scrap.  The boffins pick up on the higher than projected cost of goods sold first.  Until the day of accounting reckoning arrives, it's a myopic free-for-all.  Everybody feels good about percieved free film, controlling their destiny and not getting ripped off by their film supplier.

Of course, there are many successful vertically integrated operations.  If the end product has ample gross margin, allocation of the cost burden is moot.  I'm not making this up - many lucrative operations have an internal transfer cost of a penny over resin.   

A blown film operation is capital intensive with inherent high operating leverage.  It makes or loses money incrementally on either side of break-even.  When volume falls short of the break-even, the "prisoner's dilemma" follows.  Running at a loss is better than shutting the line down.  The penultimate desperate phase is scrambling for cheap work to maintain cash flow.  Over the years, I have been to many industrial funerals known as auctions.    We get notifications of liquidations every 6 weeks or so.  We hear from leasing companies who ask if we are interested in lines they have "carved out" of a converting operation.  When the line was first up and running, there was a party atmosphere - " whooopee !  free film !  on demand ! "

So if you are contemplating making your own film either financed or with a few extra millions of extra cash, our advice is to be sure you have:

1.  sales to feed the fixed cost beast
2.  lots working capital and a line of credit
3.  a strong plant manager
4.  commitment to a 24 / 7 operation

Read More

Topics: LDPE film, PEfilm

PE film tin canning

Posted by Joel Longstreth on Fri, Feb 14, 2014 @ 04:13 PM

polyethylene film tin canning
"Tin canning" describes the longitudinal ridges which often appear in low density LDPE polyethylene film - usually blown PE film.
For many applications of PE film, tin canning does not matter.  Heat shrink film is one example.  The ridges smooth out when the film shrinks.  Same goes for industrial box liners.  Not so for film which gets printed, laminated or coated.  These demanding processes require a perfectly smooth " lay flat" film.  Any film with a slight indication of tin canning ( usually by the pressman who taps at points across the roll looking for a slight marshmallow like surface ) gets rejected before it gets put on the press, laminator or coater.
Of course only the blown film manufacturers care about the causes of tin canning.  Customers just want flat PE film.  Here are some factors which can contribute to tin canning:
resin selection
a no slip / antiblock only film with a high COF will not "settle" after being wound up
thinner films will get stretched more on the way to the winder, exacerbating any imperfections in gauge profile
treated films with their higher surface energy tug at the interfaces of the layers on the roll
wider webs have more area across the web
While the main culprit is excessive winding tension which stretches the film and does not trap microscopic pockets of air in the roll, you might have to live with occasional tin canning if you call out a no slip, wide, treated PE film.
Read More

Topics: LDPE film, PE film tin canning, blown film extruder, tin canning

Clear Polyethylene Film

Posted by Joel Longstreth on Fri, Jun 07, 2013 @ 03:52 PM


20140128 130126

The not subjective definition of LDPE film clarity is ASTM D 1003 which measures haze.  Haze is a measure of how much light gets through plastic film measured in percent.  There is an inverse correlation between the haze number and clarity of plastic film.  The lower the number, the more light gets through.

While a low haze film allows the consumer to see the product at point-of-sale, the amount of attention paid to the difference between a few points of haze is overdone.  Many PE film extruders tout their runway versions of clear film as the only film the discerning customer will pick up. Seriously ? 

What is often overlooked is the difference between haze and what is known as contact clarity.  In the above pic, note how the film appears clearer where it is in contact with the image underneath.

Someday I would like to meet the mystery shopper who does not buy bread, nuts and bolts, candy, carrots, paper towels or bottled water because the haze is 12 instead of 6.

Read More

Topics: LDPE film, clear PE film, polyethylene film, PE film haze

Plastic Film Thickness Variation

Posted by Joel Longstreth on Tue, May 22, 2012 @ 12:25 PM

While plastic film made by the blown film process can be controlled closely, there are limitations imposed by the interdependent factors of the process and plastic resin selection.

IMAG0153 resized 600

To understand the physics of the blown film process, think soap bubble blown vertically.  When the bubble starts out, the wall is thick and stable.  When it gets larger, the wall is thinner and starts shaking.  The relationship between the bubble size and the circular die, or aperture that the melt exits from, is a key factor called blow up ratio or BUR for short.  Gauge profile is easiest to control at low blowup ratios.  Problem: PE film made with a low blowup ratio can be weak and exhibit the dreaded straight line tear which results from too much orientation in the machine ( MD ) direction.  While the textbook happy spot is a blowup ratio of 2:1 ( bubble diameter = twice die diameter ), this is not always possible in the real world.  If scheduling realities dictate a higher blowup ratio, the operator must use tricks of the trade to achieve a flat, even plastic film.

The other component is resin selection.  Resins with higher viscosities or lower melt index, or "MI" for short, lend themselves to an even thickness profile. 

Of course, in the real world not every plastic film can be made from a very low preferably "fractional melt index" resin at a low blowup ratio.  Ironically the least critical blown film application - shrink film - is made with low melt index, low blowup ratio.  Anymore blown film plant managers are chefs who manage what winemakers call cuvees, or blends, of resins.

PE film with excessive variation is maddening when heat sealing and laminating.  "Baggy film" is a perennial complaint which will bounce a roll of film a country mile without hesitation.

There is a fundamental difference between point-to-point thickness variation and what is known in the converting industry as Yield or area derived from a specific weight.  Here are PE film conversion factors in both English and Metric units:

A good starting point for agreeing on thickness variation is the Flexible Packaging Association spec B 11.  Sorry, we can't link to it.  You have to buy a copy.

Over the years the capital equipment manufacturers have endeavored to make blown film lines which guarantee + - tight tolerances with non-adjustable features which take the operator variable out of the equation.  For now these luxury store bought turnkey lines are too rich for our blood. 

We can't help believe blown film is still an art and the operator should take responsibility for his workmanship. It is our tradition that every roll we make has the operator's ( or should we say artists ?) name on it.

Read More

Topics: blown film, pe film, LDPE film, blown film extrusion, plastic film properties, plastic film

Thicker plastic film is not always better

Posted by Joel Longstreth on Fri, Feb 17, 2012 @ 12:14 PM

The shortest route to a good sustainability scorecard is source reduction.

New resins get the job done using less wall thickness in packaging applications.  There is a definite trend towards using less, albeit slowly. 

So what is holding back adoption of thinner packaging even after the efficacy of a thinner package has been proven through drop tests and shipping tests ?

Based on my own observations and experience, it is usually one of two fear factors:

Consumer will percieve the product as being cheaped out if the packaging is thinner.  Marketing assumes this is the case without focus grouping or test marketing.  For example, a very green manufacturer of organic granola who hates plastic got cold feet about using a thinner sealant layer.  When you get down to brass tacks, it's not worth taking a chance at point of sale. 

It's also not worth taking the chance that the packaging will fail during shipment.  Seriously, what is your motivation to sponsor using less packaging if it fails ?  If it fails you get blamed and lose your job. 

We recently reduced the thickness of a frozen food bag to 3.5 mils from 5 mils.  When we asked them why they were being so conservative and not cutting the gauge to 2.5 mils, they said they were happy enough and were not interested in further reductions due to the aforementioned fear factors.

If a resin is a bad actor at 3 mils it will not work at 5 mils either.  If the right resin is matched to the application, less is needed.  It's that simple.  Many of these resins cost more per pound than a general purpose resin.  If the extruder cannot pass along the cost to the end user, what is the incentive to inventory the upmarket resin ?

Sadly, the custom of selling film by the pound impedes progress.  Even after showing the math on how much less the unit cost would be through more expensive thinner film, buyers often do not agree because they are inured to price per pound.  Most extruders live and die by pounds shipped, so there is not much motivation to push downgauging or lightweighting.

All parties would benefit from a more expensive plastic film per pound offset by gauge reduction.

Here is a link to make the calculating easy:


Read More

Topics: LDPE film, poly film, PE film packaging

PE films - Why is PE film so inconsistent ?

Posted by Joel Longstreth on Mon, Dec 12, 2011 @ 02:06 PM

dreamstime xs 20504791 resized 600                                        Polyethylene blown film does not have to be inconsistent. 

If your low priced PE film is inconsistent within the same lot, your blown film supplier probably has used off-grade resins to save money on their major cost: PE resin.  The thinking is "the customer won't know the difference."  You do know the difference because the film doesn't seal or shrink like it did 2 hours ago after you readjusted the packaging machine settings for the third time today.  You could deal with it if the film was just consistent within the same pallet.  

Shrink film is a favorite dumping ground for extruders.  Just about any PE resin will shrink, so it's tempting to blend in repro and literally floorsweep.

Problem:  If you are buying printed film, laminations or bags, you are at least one step removed from the film supplier.  You have no way of knowing if you are getting film from the same source every time.  Even if the film does come from the same source, there is a good chance their extruder has switched resins to lower cost.

You don't have to live like this.  When you get sick of it, give us a chance to prove continuity of supply in blown film is available.

Read More

Topics: pe film, plastic sheet film, LDPE film, poly film, polyethylene films

Plastics in-depth and insights


Plastic Blogs

Subscribe by Email

Most Popular Posts

Browse by Tag