Blister Resistance

The ability of a coated paper to resist the formation of a blister during the heatset drying of heatset ink. A blister is an oval-shaped bubble protruding from both sides of the paper web. Blistering is caused by moisture trapped in paper evaporating rapidly under the increased temperature of heatset drying. As the vapor expands, it may not be able to escape through the surface of the paper if the paper coating is of low porosity, in which case it bursts the paper's internal structure apart. In order for a coated paper to possess high blister resistance, it must have a lower moisture content than usual, and it must have adequate porosity and internal bond strength. As a paper's basis weight increases, so does its tendency to blister, as heavier paper will possess more moisture. Coated one side paper does not tend to blister. (See also Blister.)

Tests to measure a paper's blister resistance involve conditioning a coated paper to a particular relative humidity, then immersing the paper in a hot oil bath. The temperature of the bath can be altered to determine the temperature at which blistering will occur. Another test involves covering a coated paper with a thick lacquer (to simulate the heavy ink coverage which is one of the causes of blistering). The paper is run through an oven for a set period of time, and the paper is examined for blistering. Varying the time spent in the oven and the oven temperature help to gauge the specific blister resistance of the paper. (See also Fiber Puffing.)

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