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

Corn Vs. Tapioca, Adapting the Formula for Corrugating

August 17, 2015

Ruel asks,

My question is regarding the types of starch. Between corn and tapioca, will one provide better bonding in the corrugator or are they both so similar that it makes no difference?

We are planning to experiment with tapioca starch because it is cheaper per ton/kilo, but I want to make sure we are not sacrificing quality for cost. Also relevant to this, do you know of a generic adhesive formulation of tapioca? We are more familiar with cornstarch and we have no experience with tapioca. Do they have different reaction to caustic soda, etc.

The best I can do to process your question is pass you along to one of the excellent associates my network of technical contacts. Roman Skuratowicz, Lead Industrial Application Specialist at Ingredion Inc. was happy to help out. See his comments below.

– Ralph

“We have experience with both tapioca and corn starch, in the US we are using corn starch almost exclusively but tapioca starch is being used extensively in Asia. There are no significant bonding differences between the two starches. Both starches have similar granule structure, gel temp, and similar amylose/amylopectin ratios, although tapioca has larger amylose molecular weight on average. The largest differences in corrugating adhesives are the critical caustic values and alkali sensitivity of tapioca starch, and this will vary by region, growing condition, or age of the root before it is processed.

Tapioca starch has a lower critical caustic level, meaning less caustic is required to swell the granule compared to corn starch. The simple adjustment here is to lower the amount of caustic in the formula, and that needs to realistically be done in the field with the tapioca starch being employed. I would recommend lowering caustic 10% relative to a corn starch formulation as a start, then adjusting caustic further based on the gel temp of the adhesive.

The bigger issue by far is the alkali sensitivity of tapioca starch, which as I indicated varies day to day, root to root, and by process conditions. We ran an audit of unmodified tapioca starch from our Thailand facility and saw variations of 400% daily over a two week period. As a result, many corrugators will use very low viscosity formulations so they can absorb potential swelling from the starch. Many in Asia and Australia have moved to hybrid systems like the Rapidbond mixer or more accurately no-carrier formulations. In No-carrier adhesives, all of the starch slurry is partially swollen to a fixed viscosity (caustic addition is varied), and then quenched with boric acid solution (rather than borax). These formulas are more tolerant to swings in alkali sensitivity. Another option to use existing high shear mixing equipment is to test the alkali sensitivity of incoming batches and adjust caustic level based on these values. For this I recommend an alkali sensitivity viscosity test rather than a settling test, as a settling test will take 24 hours to run. If you decide to follow this route I can assist with test methods, however the bulk of formulation work you will need to do yourself based on adhesive performance.”

– Roman
 

Affects of moisture in litho laminated sheets and critical moisture content

August 17, 2015

Seth asked,

I have been researching the affects of water moisture in litho laminated sheets and moisture content is critical. However, I’ve yet to find a source that discusses the acceptable range of moisture in litho. So my questions are, what is the acceptable range of moisture? Is it a based on paper weight, geographical location(humidity/temperature), dependent on the process/machine, or a combination of all the above?

Given that paper is the majority of our cost, both in a print shop and sheet/box plant, at what range should we hold our vendors accountable?

If you have been to a label printer you know how carefully they control the atmosphere before and after printing to prevent curl and laminating issues at your end. How well do you control temperature and moisture content at your facility? I have seen entire “clean” rooms at high volume plants. Is yours an ongoing operation or just intermittent?

Then there are the other questions that relate to substrate conditions, ideally 7% moisture, and the adhesive and its application.

For additional information I reached out to our network and contacted Brian Tankersly at Lewisburg Printing. Below is Brian’s insight. Thank you Brian for contributing this valuable information.

– Ralph

“Everything that you mentioned is a contributing factor. The mills manufacture paper with an application specific moisture content target as Ralph correctly mentioned. A litho supplier will measure a sheet in terms of RH (Relative Humidity) because it gives a very good indication as to the moisture content of the paper. Your printer will understand this measurement method.

I have attached our client recommendation sheet which has some related information and a good article on humidity prepared by Glatfelter. We have established an acceptable range of 35%-55% RH for litho labels specifically for double face application. This range can be expanded but it is dependent upon the litho substrate, glue type, corrugated RH, lamination equipment and the die cutting/finishing equipment. The RH is measured using a sword hygrometer typically before the sheet is printed and again post press.

Litho Substrate:

Although all paper reacts to the environment, I have found that NewPage Sterling Ultra (specifically 80#C1S) to be the most stable. The type of coating the litho printers is applying can affect this as well.

  •  A good domestic long fiber sheet is much more stable than a foreign sheet.
  • You may want to establish basis weight crossover points (price versus cost) for items exceeding 40”x 56”. In other words, use 100# stock when dealing with the larger sheets.

Glue:

  • Minimize glue application. Heavy glue can create issues downstream.
  • A secondary glue with decreased dwell time may be needed for ‘trouble jobs’ on the EM model/blanket model laminators.
  • Wisdom manufactures a good Hybrid (30% resin/ 70% dextrin) glue but most of the manufactures do a great job. Engage the vendor.

Temperature/Humidity:

  • Ideal is 50% RH. I start to get concerned when the RH of litho drops below 35%. This does not necessarily mean it will crack if it is being finished properly but it could be more prone to crack.
  • If litho exceeds 55% RH (really closer to 60%) then it has a tendency to curl. I am less concerned by this number but it is something that needs to be monitored.
  •  Note: Once the label is at your facility and unwrapped, it will immediately begin to react to your environment (harmonize) so it will take on the properties of your facility (good or bad)
  •  Options for a climate controlled room for extreme manufacturing conditions (zone humidifiers, etc)”

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