Humidity in the Paper Industry
Paper in General
The ancestor of the pulp paper manufacturing process that is used today is considered to be developed by a Chinese named Tsai-Lun during the early 2nd Century.
Paper and similar products like cardboard are made from cellulose fiber that comes from various sources (wood, rags, and grasses). The cellulose fiber is extracted with either chemical or mechanical plumping or a mix of both. After the wet fibers have undergone various treatments it is ready for pressing and drying.
Today’s highly sophisticated printing, drawing, or packing machines process this thin and sensitive material at an incredible speed. That’s why it is essential for a continuous process to adjust these high performance machines to the individual characteristics of the paper type used. Deviation of the paper properties must be avoided at any cost.
Because of that, a constant environment and a well-conditioned paper fiber are crucial!
That’s where humidity and temperature measurement plays an important role.
Why the Need to Measure Humidity?
Controlling humidity in the paper industry is essential for many factors. An incorrect level of %ERH in the paper will have the following effects on product and process:
Static Electricity
From time to time printers experience difficulties due to static electricity phenomena (paper sheets stick together etc.). This happens mostly when both paper and the ambient air are too dry.
Dimensional Changes
Vegetable fibers are highly hygroscopic and therefore absorb and desorb humidity resulting in a swelling or shrinking of paper fibers. At approx. 50%ERH, a humidity change of ±10%RH results in a length change of typically 0.1 – 0.2% of the paper. Such a humidity variation would give a 1 to 2mm variation on a 1 x 1m sheet of paper and therefore inaccurate printing results (poor positioning of paper).
Dust
The too dry paper generates dust that will lead to a layer of dust which then affects the printing quality.
Deformation
Deformation occurs if too much moisture is exchanged with the surrounding atmosphere through the edges of the stack or roll. This un-even distribution of moisture will eventually lead to rippled paper.
Ink Drying Time
High values of %ERH as well as low temperature result in longer drying times after printing which will slow down the following processes.
Best Humidity Level
Paper with a humidity level between 50-60%ERH is most suitable to work with. The ambient air should not defer more than ±8-10%RH from that level.
What Solution Can Rotronic Offer?
In 1967 , ROTRONIC was among the first producers of humidity and temperature devices specially designed for the paper industry. The heart of the latest humidity measurement equipment comes with the Rotronic capacitive foil sensor: HygroMer IN-1.
The AirChip3000 is the brains.
AirChip3000 Advantages:
- Relative humidity, temperature, and dew point outputs
- Can store 2’000 points
Rotronic Products:
Humidity and Temperature Probes:
- HC2-HS Series -40…85°C, 0…100%rh, 4mm x 18mm, ±0.8%rh and ±0.1K
- BFC-UART plate probe -40…85°C, 0…100%rh, l: 278mm w: 150mm h: 85mm ±0.8%rh and ±0.1K
Transmitter:
- HF5 series For interchangeable probes, Various analog and digital outputs, Display, All psychrometric calculations available…
- HF8 series For 2 interchangeable probes, Various analog and digital outputs, Display, Relay outputs All psychrometric calculations available…
Handheld instrument:
- HP22 For interchangeable probes, Dew point, and other psychrometric calculations, Display
- S1 Handheld with integrated sword probe designed for paper stacks. 5…99.9%rh, ±1.5%rh, and ±0.3K
- GTS Handheld with integrated sword probe designed for paper and cardboard stacks. 0…100%rh, ±1.5%rh, and ±0.3K
Customer Benefits:
Accuracy:
Choosing Rotronic gives you the best accuracy on the market. Precise humidity measurements enable the printing unit to work always on its maximum possible performance.
Communication:
Networking with Rotronic is an easy affair! With all of the different communication methods, from conventional analog output signals to RS-485, Wireless, or Ethernet RJ45, Rotronic can provide the needed interface to your printing, drawing, or packing machine.
Long Term Stability:
With long-term stability of under 1%rh per year (depending on the environment), Rotronic offers the possibility to “plug & play”: install the device and leave it. We would recommend frequent spot checks in-between calibrations.
Calibration:
To calibrate humidity measurement devices, we can provide an SCS certificate or factory calibration certificate if this is required. We can also supply a humidity and temperature generator, the HG2-S as well as unsaturated salts for on-site calibration.
Source: Rotronic