Archive for the ‘Testing and Specifications’ Category

Checking Moisture of Corrugated Sheets

January 31, 2018

Tim asks,

Recently we encountered corrugated sheets with dry liners and medium that created problems converting. Is there a way for us to test sheets for moisture content at our facility? If so, is there a listing of the ranges?

Moisture meters, or moisture analyzers, can be used to test the moisture content of corrugate sheets. There are a number of portable, hand-held models available. (Most look surprisingly like a taser) They are rather inexpensive (ranging from $50 to $600) and a modest range of testers with varying capabilities and features are available in this range. These units provide instant readings of paper moisture content and should meet your needs. If you purchase a meter/analyzer make sure it is suitable for measuring paper. Some of the least expensive models are only for wood or hard materials. Also check the accuracy rating of the device. If it has a .01% or .02% for paper it should do fine. The same devices may have a 1% – 3% accuracy for wood, but that won’t affect testing paper.

6 to 8 percent moisture is the sweet spot for corrugated paperboard. Below 6% and the risk of cracking scores will increase, perhaps significantly depending on the paper. If the moisture content goes above 8% you will start to see a decrease in compression strength. Reports indicate compression strength can decrease as much as 6.5% per every 1% of moisture over 8%.

Now, in your case (simple checking for machineability) moisture meters/analyzers should work fine. However, they are not the most accurate method for checking paperboard moisture. Should you ever need to certify board for food or pharmaceuticals you may want to find a testing facility that can provide results via the oven method.

– Ralph

Decoding Customer’s Specs

January 3, 2018

Richard asks,

I was a given a spec for an RSC with the paper spec’d as:

K7K 230g + 140g + 230g Kraft C/F.

I don’t know how to interpret this. I’ve reached out to our board suppliers, but I thought you may be able to shed some light. I’m assuming this is a standard way to spec board in some other part of the world.

The paperweight is the easiest to decode. To convert the paper weights from grams to #/MSF simply divide the values by 4.88 and round accordingly to match the closest available weight.


  • 230g = 47.13
  • 140g = 28.68

The other parts of the specification may be a code that is specific to the customers operation. The K7K probably denotes Kraft over Kraft liners and not test liner. The 7 is the caliper, 7mm or .177”. The ‘Kraft C/F’ probably denotes Kraft Corrugated Fluting.

However, that’s a lot of ‘probablies’. To be on the safe side I would try to get the customer to confirm the K7K and the C/F.

– Ralph

What the #1W?!

December 1, 2017

Steve asks,

I have a customer asking me to interpret and explain this call out “ 200E #1W”.

The 200E part is easy. It’s the #1W is a bit more ambiguous…I don’t believe it is industry standard expression. Could it be a designation for coated SBS?

Oh yes. A long history here.

# 1 could be Kemi, Coated SBS, or Coated label stock

#2 does not exist anymore or a lightly coated white top or uncoated SBS

#3 is what we refer to today as uncoated white top.

— Ralph

Hot Melt Glue Separation

December 1, 2017

Mike asks,

I have a customer that runs case make up units using a solid set hot melt. As of late we have an issue with the appearance of the seal on the bottom of the carton. When we are using light weight single ply liners the customer is not seeing fibre pull when breaking the bottom flaps apart to check for a bond. They are now considering this test to be a fail. Even though we can do a shake test and it passes. When pulling the cartons apart by hand the strength feels the same if you have fibre pull or not. When we are not seeing fibre pull what you see is the hot melt glue lines on each flap that is stuck to the paper so it looks like the glue came apart in the middle.

Anyway, is there is a tool that we can measure the bond strength on the bottom of a carton?

If glue is remaining on both flaps and is not separating from the paperboard, then the bond between the paperboard and the glue would appear to be good. If we take a lesson from the corrugator, too much glue can be as bad as too little glue. Too much and you risk shear within the glue itself. I’m not positive if the same ‘holds’ true (pun intended) in hot melt. I know too much hot melt can cause a variety of problems, but I’m not sure if shear within the glue is one of them. I’ve reached out to some of my industry contacts and I’m awaiting their input. I’ll update this post as when received.

I’m not sure if here is an official measuring device. However, I would think that if the box was to hold, say 25 pounds, you could get 25 pounds of weights at the local sporting goods store, place them in the bottom of the box and then somehow suspend the box so the full weight was on the bottom flaps. Perhaps do a few jerk tests where you would quickly lift the box with the weights in it. This would simulate the additional forces of acceleration. If it supports the weight, perhaps your customer would accept this as proof that the bond is sufficient to hold the prescribed weight. Be careful when you are testing.

Okay readers, has anyone else seen this type of separation with hot melt? Do you have any experience or suggestions to pass along?

— Ralph