Water absorbency, capacity and rate
Water absorbency is a measure of the amount of water absorbed by the wetted surface of paper and board materials.
Cobb test (Sized papers and paperboards)
The Cobb test determines the amount of water absorbed into the surface by a sized (non-bibulous) paper, paperboard, and corrugated fibreboard paper or paperboard sample in a set period of time, usually 60 or 180 seconds (Cobb60 or Cobb180). Water absorbency is quoted in g/m2.
The water absorbency of a material can have strong influence on printability and the setting rate of water based adhesives.
Smithers Pira is UKAS, ISO 17025 accredited for the determination of water absorption of paper and paperboard to British standard BS EN 20535 and International standard ISO 535. Testing can also be made in accordance with Tappi T441 and ASTM D3285 and with other test liquids.
Klemm method (Unsized papers and paperboards)
For unsized papers such as blotting papers and other papers having relatively high water absorbency the Klemm method for determining water absorbency is used. Test pieces are immersed to a set depth in water and the height of the water rise is measure after a set time. Smithers Pira test in accordance with BS 6504.
Cage method (Tissue paper and tissue products)
The water absorbency time and water absorbance capacity of tissue paper and tissue products is determined in accordance with DD ENV 12625-8.
Water absorbency rate
This test determines the liquid sorption rate of bibulous paper, paperboard, and paper products using gravimetric principles. A set volume of water is dropped onto the paper surface and the time for the drop to be absorbed is measured. The water absorbency rate is used as a measure of the acceptability of tissue, towelling and blotter papers in sorptive tasks.
Other test liquids such as ink, oil and milk are used to assess the comparative performance of papers for specific applications.
Smithers Pira testing is made in accordance with Tappi T432 or ASTM D5802.