paper and board grades（下）

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1、Chapter2Paperboardgradesmadeofbleachedpulp,anditsbasisweightisthesameasforwhitetoplinerboard.Boardcanbecoatedeitheronmachineoroffmachine.Typicalcoatingisasinglecoatingwithabladecoater.Coatedwhitetoplinerboardisusedfordemandingcorrugatedboardapplications,likeforcontainersthatareusedinadisplayinst

2、ores.TestlinerisproducedespeciallyinCentralEuropeandinAsia.Variousfurnishesareusedintestliner(Fig.16).Becauseofthemixedwasteused,afour-plystructureisoftenpreferredfortworeasons.First,byusingfourplies,thelinerboardpropertiescanbeoptimizedbetterthanwithatwo-plystructure.Second,sincethedrainageresi

3、stanceofthemixedwasteisveryhigh,itwouldbedifficulttodewateroneheavybaseplyonthewiresection.Bysplittingthebaseplyinto2−3plies,drainageontheformingsectionbecomesaloteasier.Figure16.Testliner.Burstandcrossmachinedirectionalcompressionstrengtharethemostimportantstrengthpropertiesforlinerboard.Bursti

4、smeasuredwithMullentester,ascompressionstrengthismeasuredbyeithertheringcrushtestorshortcolumntest(SCT,sometimesalsocalledSTFItest).Althoughtheprintingprocessforlinerboardisnotverydemanding(especiallyforbrownlinerboard),certainsmoothnessisrequired.SmoothnessismeasuredbyBendtsenorSheffieldmethod;

5、alsotheEmvecotesterisused.Thetopsidefrictioncoefficientisimportantbecausethestackedcorrugatedcontainersshouldnotslide.Thispropertyismeasuredasaslideangle.Therearevariousdesignsfortheformingsectionsofamodernlinerboardmachine.Thebasicstructureoftheboardistwoplies.Thiscanbemadewithtwofourdriniers(F

6、ig.17),afourdrinierandagapformer(Fig.18),orwithasinglegapformerequippedwithamultichannelheadbox.Separateformingofpliesisneededtoproducemottled,whitetop,andcoatedwhitetoplinerboard.Thereforethemostcommonformingsectionforthosegradesisabasefourdrinierandanon-topfourdrinierthatcanbeequippedwithatopd

7、ewateringunit.Itisalsopossiblethatthetopplyunitisagapformerorthatbothunitsaregapformers.Thesamewiresectionsareusedalsoforbrownlinerboard.Insomecases,whenmixingofthewhitewatersisnotcritical,likewithbrownlinerboardsimultaneous