Do You Know Relative Humidity and How it Affects On Printing?
October 28, 2017
Relative Humidity and How it Affects 55 Printing
The dry months of winter always seem to set the stage for an increase in printing and print finishing problems. All of the printing paper reps I know brace themselves for an onslaught of complaints. Static, fiber cracking and coating problems are typical. But is winter really such a dry time?
We’re taught that proper Relative Humidity (RH) is a critical factor in the performance of paper. It is a proven fact that decreased RH has a negative impact on food quality. The lower the RH, the more the paper will crack. Paper works like a sponge, it absorbs moisture from the air. The more moisture content in a sheet of paper, the more pliable the fiber. With less moisture, the more brittle the fiber becomes causing it to break or crack.
You might be surprised to see that the average relative humidity going into the winter months is, well, about average. There is a 12 point drop going into October, after six months of steadily increasing relative humidity. If you go by this data, you’d think there would be fewer problems in the winter months since RH is higher, on average. April should be the worst the month for humidity problems in the pressroom and bindery, but it’s not. The reason is that this RH data is only half of the story. The other half of the story happens once you get inside the pressroom or bindery. Once inside, your temperature and RH are very different. Digital printing actually lowers the RH on top of normal environmental conditions. It’s simple once you understand the concept of relative and absolute humidity.....
Relative moistness is the proportion of incomplete water vapor weight to the immersion vapor weight at a given temperature. Consider it the measure of water vapor really exhibit noticeable all around partitioned by how much water vapor it could hold at that temperature, communicated as a rate. Supreme dampness is the mass of water vapor display in a volume of airspace, normally communicated as grams per cubic meter (g/m3). Above all, the most extreme total moistness changes with temperature. For example, at 32o Fahrenheit, a cubic meter of air can just "hold" 4.85 grams of water vapor. At 68o Fahrenheit the air can hold 17.24 grams. At 86o Fahrenheit it can hold 30.2 grams. In this manner, amid icy winter a long time there is far less water vapor per cubic meter than in summer.
Be that as it may, if the extremely imperative RH is about that year round, why are there more issues in winter? How about we utilize a situation where it's 75% RH and 32o Fahrenheit. That implies the air has .75 x 4.85 = 3.64 g/m3. (keep in mind, 4.85 is the most extreme it can hold at 32o.) Now how about we go inside where it's warmed to 68o. At 68o the air can hold 17.24 g/m3. In any case, the ecological air we are acquiring from the outside just has 3.64 g/m3. This implies our indoor RH is 3.64/17.24 = .21 or 21%. Unless the indoor air is humidified, we now have an issue with low RH. It ought to be in the area of a half. In the mid-year, the inverse is valid. We're carrying warm air with high water vapor content into a significantly colder condition. The indoor air is promptly immersed so the RH can be greatly high.
The fact of the matter is that in the event that you find that your print completing outcomes have changed for no evident reason, and there was a huge change in the climate, it's conceivable that RH is behind the change. Winter is, in fact, a dry time. In Reno, it is likewise critical to recall that with the expansion in rising, the air gets cooler and hence is less equipped for holding water vapor, so by and large the higher the elevation the less the dampness.
The hotter atmosphere in the summers of Northern Nevada enables the air to hold a larger number of grams of dampness than in the colder months. When utilizing swamp coolers in the hotter months, dampness is included once again in the air which helps the RH inside most printing offices.
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