ASTM_D_3285_-_93_1999.pdf

Designation:D 3285 93(Reapproved 1999)An Amrican National StandardStandard Test Method forWater Absorptiveness of Nonbibulous Paper andPaperboard(Cobb Test)1This standard is issued under the fixed designation D 3285;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of the quan-tity of water absorbed in a specified time by nonbibulous paperand paperboard with a minimum thickness of 0.1 mm.This testmethod is generally applicable to sized paper and paperboard,but is not recommended as a sizing test for writing papers.Thetest method is based upon studies by Cobb and Loew,Cobb,and other investigators(1,2,3,4).21.2 This standard does not purport to address all of thesafety problems,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:D 585 Practice for Sampling and Accepting a Single Lot ofPaper,Paperboard,Fiberboard,and Related Products3D 685 Practice for Conditioning Paper and Paper Productsfor Testing3D 824 Test Method for Rate of Absorption of Water byBibulous Papers33.Significance and Use3.1 Water absorptiveness is a function of various character-istics of paper or board,including sizing,porosity,and fibercomposition.3.2 This test method is useful in comparing various sheetsor nonbibulous(not highly absorbent)paper or paperboard asto the relative rate of penetration of aqueous solutions,such asadhesives or coatings.It will indicate to some degree thesurface and internal sizing.This test method is not intended asa water-resistance test,nor to measure the resistance to minutequantities of a liquid,such as from a writing pen.4.Apparatus4.1 Water Absorption Apparatus,to permit one side of thespecimen to be wetted uniformly at the moment the soakingperiod begins,and to allow controlled rapid removal of thewater from the specimen at the end of the test period.Thespecimen holder as shown in Fig.1 comprises a metal ring witha machined lower face,11.28 6 0.02-cm inside diameter(corresponding to a cross-sectional area of 100 cm2),2.5 cmhigh and about 0.6 cm thick,clamped to a flat base plate about15 by 15 cm with a metal cross bar 17 by 2.5 by 0.6 cm and twowing nuts on a pair of studs.The cross bar has a hole at one endand a slot at the other to facilitate assembly and use.On thebase plate is a rubber mat,larger than the outside dimensionsof the ring,on which the specimen is clamped.NOTE1The metal parts should preferably be of brass or othercorrosion-resistant material.NOTE2Several versions of the water absorption apparatus are nowavailable.Although the basic procedure for performing the test is notchanged,the clamping mechanism is.This may affect the time required toremove the specimen from the apparatus.4.2 Metal Roller,solid brass having a smooth face 20 cmwide and weighing 10.0 6 0.5 kg.4.3 Timer,stopwatch or electric timer reading in seconds.4.4 Graduated Cylinder,100 mL.4.5 Balance,with an accuracy of 0.01 g,or better.5.Reagents and Materials5.1 Water,distilled or deionized.5.2 Blotting Paper,a quantity of sheets of standard blottingpaper,200 mm2(8 in.2),weighing 250 6 10 g/m2oven-dry,0.495 to 0.521 mm(0.0195 to 0.0205 in.)thick,and having arate of absorbency of 25 s or less when tested with 1.0 mL ofwater in accordance with Test Method D 824.The blotter musthave a capillary rise of 50 to 100 mm of water(mean of MDand CM)when measured by the Klemm Test(see annex).6.Test Specimens6.1 Obtain a sample of the paper in accordance withPractice D 585.From each test unit,cut specimens to a sizeslightly greater than the outside dimensions of the ring of theapparatus(that is,squares 125 by 125 mm).The test piecesshould be free of folds,wrinkles,or other blemishes not1This test method is under the jurisdiction of ASTM Committee D-6 on Paperand Paper Products and is the direct responsibility of Subcommittee D06.92 on TestMethods.Current edition approved Sept.15,1993.Published November 1993.Originallypublished as D 3285 73.Last previous edition D 3285 92.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3Annual Book of ASTM Standards,Vol 15.09.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United Smonly inherent in the paper.For hard-sized papers(ab-sorbing less than 100 g of water/m2)use 10 specimens per testunit.For soft-sized papers(absorbing more than 100 g/m2)use20 specimens.7.Conditioning7.1 Condition the specimens in accordance with PracticeD 685.Test under the standard conditions specified therein.8.Procedure8.1 Weigh each specimen to