Affects of moisture in litho laminated sheets and critical moisture content

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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One Response to “Affects of moisture in litho laminated sheets and critical moisture content”

  1. hanif Says:

    Hi,
    I have a question related to one my customer who is faces edge curling on C1S 80# (118gsm) after printing. But sheet is flat before printing, once paper is printed sheet get curled on edge.

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