How Moisture Affects Corrugated Durability & Strength

October 5, 2015

Denise asks,

Do you have a graph or chart that shows how moisture in paper affects its durability and strength? For example, how much moisture does board start off with from the Corrugator? If you store a corrugated sheet in a cooler or if it sits outside in hot humid weather, how much can moisture increase in the board? Does increase amounts of moisture in board effect the durability and strength of the board?

It would be very helpful to me if I had access to a chart or graph that I could show to my customer on how humidity, moisture and temperature change effects the durability of corrugated products.

You may want to check the FBA handbook. George Maltenfort’s book Corrugated Shipping Containers: An Engineering Approach (ISBN-13: 978-0961630218) contains some excellent charts and tables on compression strength vs. moisture content. Unfortunately, this book is out of print, but if you can locate a copy it may be very useful.

Corrugated board stabilizes at 7 percent moisture at an environment of 72 degrees Fahrenheit and 50% relative humidity. Above and below these conditions board takes on and gives off moisture. Recycled and Kraft components react differently. The upper limit on moisture content is 20 percent.

There are very mobile and portable scientific instruments to measure moisture content (MC). There are many multipliers used to factor compression based on initial performance at the beginning of the life cycle/supply chain. However, generally the rule of thumb is that increases in moisture causes board to lose strength.

If anyone out there knows of a good source for George’s book please pass the information along.


C vs B Flute Starch Consumption

October 5, 2015

Ruel asks,

Here I am again with my questions regarding glue consumption comparison between C and B flute.

Is there a standard or industry accepted equivalents or conversion of glue consumption between B and C flute?

We have a customer with tolling contract with us who wants to change their box from C flute to B flute. Since our price to them is on a per MT basis, our revenue is affected because of reduced Semi Chemical Medium usage. We are evaluating the new tolling fee that we will charge, thus, we are looking all aspects that could have an impact on the cost. One of them is the glue consumption. We don’t have much data for B flute since our common products are in C flute. We have data from our short runs showing equivalent of C : B is about 1 : 1.17, or a 17 percent increase of glue consumption when shifting to B flute. I have also read articles from Harper Love citing that C to B has equivalents of 1.20. I just wanted to be sure that this value is within the typical values of the industry.

I will assume that the glue applicator roll, metering roll, and gap settings will all stay the same. That leaves the variations to the type of fluting, the shape of the flute profile and the number of flutes per foot. New flute profiles are more pointed and less rounded than before so there is less starch applied to the glue tips.

Are the pin adhesion values staying consistent between the two flutes?


Effect of moisture on corrugated sheet size

August 31, 2015

Steve asks,

I really appreciated the article on litho mounting…good stuff and thanks!

On a somewhat related topic…we are die cutting f flute for an application in which dimensional accuracy-and stability- are very critical. Particularly the body score dimensions, though all dimensions including depth are important. One of the issues we are concerned about is the effect of humidity on the growth of the finished product. We do not have environmental controls on our production floor and in summer, the humidity can get quite high, and change day to day. Conversely in winter we deal with very low levels.

We know this affects the sheet sizing…but to what degree? Is there a matrix for various board grades which may show the percent of growth in grain /cross grain direction?

What should we expect to see?   Any guidelines you can offer would be helpful!

I can address the issue of the magnitude of the changes in the finished product from changes in relative humidity. The literature reports that from zero to 80% relative humidity sheets can grow up to 1.6 percent parallel to the flutes and up to 0.7 percent perpendicular to the flutes. I believe there will be changes also in the Z direction (thickness of the sheet). There is a difference between kraft/semichemical containerboards and those with high amount of recycled content.

As the sheet takes on moisture it also becomes “soft” so depending on the die cut method, the sheets could be “squirming” around in the equipment. Do you index to one side of the sheet? Is there print image differentiation from one panel to the next?

Hazard Analysis And Critical Control Point

August 26, 2015

Nat asks,

I have a question about HAZARD ANALYSIS AND CRITICAL CONTROL POINT ( HACCP ). Do you happen to have any document to indicate that HACCP does not apply to corrugated box because the food does not have a direct contact with the box.

Can you provide any input on writing a description.

See if this language is sufficient.

Corrugated is considered for indirect food contact according to the FDA (21 CFR). Since this corrugated is a secondary package and has no substance such as an aqueous or film coating that comes in direct contact with food it does not fall within the guidelines established by HACCP.

The communication should state the description, intended use and conditions for use of the package, name and location of the manufacturer, and should be signed by an official representative of the company.

– Ralph


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