Repulpable pressure-sensitive adhesive tapes and labels

Repulpable Pressure-sensitive Adhesive

Tapes and Labels

Haruo Sasaki,1 Tomishi Shibano2* and Masateru Yamakage1

1The Japan Packaging Institute, 10F Togeki Building, 4-1-1, Tsukiji, Chuo-ku, Tokyo,104-0045, Japan2LINTEC Corporation, 5-14-42, Nishiki-cho, Warabi-shi, Saitama, 335-0005, Japan

In recent years, Japan has been witnessing a mounting interest in the recyclingof waste paper as a way of protecting the environment. Yet the manufacture ofrecycled paper has always been subject to the problem of plastic, metal or PE-laminated paper chips mixing in. Especially the contaminants from adhesivetapes and labels (stickies) have posed a dif®cult problem for the manufacturersof recycled paper. Therefore, the development of repulpable products substitut-ing for them has long been an earnest desire for the industry. To solve thisproblem, a comprehensive investigation into the pressure-sensitive adhesive,the release agent and the base paper has been carried out, and repulpable PSApackaging tapes and labels that are well suited for the manufacture of recycledpaper have been successfully developed. O 1998 John Wiley & Sons, Ltd.

Keywords: repulpable backaging tape; repulpable label; recycled paper

INTRODUCTION

The waste paper recycling rate in Japan has been increasing from 34.0% in 1970 to 41.5%in 1980, 51.6% in 1990, 53.3% in 1995 and 53.8% in 1996.1,2 As these statistics show,recovered paper accounts today for the majority of material for paper manufacture. Thetarget the Japan Paper Association sets for the year 2000 is 56%, reflecting society’sgrowing realization of the importance of waste paper recycling.

According to PPI’s statistics of recovered paper utilization rate in major countries otherthan Japan, the figure rose from 31% in 1991 to 39% in 1996 in the U.S.A., from 50% to60% in Germany, from 60% to 70% in the U.K., from 46% to 49% in France and from32% to 35% in China. Thus, the paper recycling rate is rising in all these countries. In

* Correspondence to: T. Shibano, LINTEC Corporation, 5-14-42, Nishiki-cho, Warabi-shi, Saitama, 335-0005, Japan

PACKAGING TECHNOLOGY AND SCIENCEPackag. Technol. Sci.11, 205±215 (1998)

CCC 0894–3214/98/050205–11 $17.50 1998 John Wiley & Sons, Ltd.

Received 30 March 1998Accepted 6 April 1998

China andother Asian countrieswherethe economyis developing rapidly, the useofpaperis expectedto increaserapidly. This will surelyexerta profoundinfluence on thepulp market across the world and the role of waste paper as a material for papermanufacturewill becomeincreasinglyimportant.

Measuresto raisetheuseof wastepaperincludeimprovementsin therecoverysystem,meticulous sortingandremovalof prohibitedmaterials,public sharingof recoveryandrecycling costs,preferentialuse of recycledpaperproductsby consumers,disuseofunnecessarily high quality paper, and development of waste paper processingtechnologiesby papermakers.It is also worthy of considerationthat productswhoserecyclinghasbeendifficult shouldbesupplantedby newrecyclable types.

In the manufactureof recycledpaper,it is well known that ‘stickies’, suchas PSA(pressure-sensitiveadhesive)tapesand labelsandhotmelt adhesives,can often poseaseriousproblem.3 Thesesticky contaminantsget stuck to the felts, wires and driercylindersof papermachines,thuscausingwebbreaks,reducedproductionanddropsinpaperquality.This paperdiscussesthenewtypepressure-sensitiveadhesive (PSA)tapesand labels developedby LINTEC Corporation, which are compatible with paperrecyclingoperations.

THE JAPANESE TAPE MARKET

According to the statistical data published by the JapanAdhesive Tapes Makers’Association, Japanproduceda total of 1223million m2 of adhesive tapesin 1996.Thelargest shareof the productionwasclaimedby kraft papertapesat 483 million m2 or39.5%of thetotal.Thiswasfollowedby cloth tapesat154million m2 (12.6%)orientatedpolypropylene(OPP)tapesat153million m2 (12.5%)andcellophanetapesat126millionm2 (10.3%).

Kraft papertape,whosestructureis asshownin Figure 1 is mainly usedfor cartonsealing.This tapeis easyto usebut leastsuitablefor recyclingdue to the presenceofpolyethylene and natural rubber type PSA in it. When recycled paper is madefromcartons, thesesticky contaminantswill hinder manufactureor reducethe quality ofrecycled paper.Therefore,cartonssealedwith this tapecanpresentquiteanobstacle formakersof recycledpaper.

Figure 1. Conventional PSA kraft paper tape

O 1998 John Wiley & Sons, Ltd. Packag.Technol.Sci.11, 205±215 (1998)

206 H. SASAKI, T. SHIBANO AND M. YAMAKAGE

Figures2 to 4 show the structures of cloth tapes,OPPtapesand cellophanetapesrespectively,madein Japan.The cloth andOPPtapesare widely usedto sealcartonswhichhaverelativelyheavycontents.Thecellophanetapeis usedasahandysealingtapefor envelopes,wrappingsandsoon in offices,storesandschools.4 Theseadhesivetapes,whichhavetheirownspecificadvantages,arebeingputto wideuse,butarefar from idealfor recycling. The recycledpapermadefrom papercontaining thesetapesis alwayssubjectto theproblemof suchcontaminantsasNR adhesive,PEor OPP,andcellophane.

Figure 2. Conventional PSA cloth tape

Figure 3. PSA OPP tape

Figure 4. PSA cellophane tape


REPULPABLE TAPES AND LABELS 207

REPULPABLE TAPES

Figure 5 showsa repulpable kraft paper tape developedby us in 1992. Unlike theconventional products,the basepaperof this tapeemploysa kraft Clupak paperthatexhibitsgoodrepulpability without containinganywet-strengthagent.Thebackreleasecoating, which doesnot usepolyethylene,consistsof silicone anda repulpablewater-soluble polymer. This special back coating provides not only repulpability andsatisfactory releaseproperties but also markability with a marking pen and non-slippability. The non-slippability provesto be effective in preventingthe collapseofcartons sealedwith this tape.The pressure-sensitiveadhesiveis a specialacrylic PSAwhich is repulpablewith slightly alkaline water.

Figure 5. Repulpable kraft paper tape (NE0101)

Table 1. Repulpable kraft tape versus conventional tape

New kraft tape `NEO 101' Conventional kraft tape

Thickness (mm) 0.12 0.12Peel adhesion (g/cm)

Stainless steel 540 310Paper board 260 270

Tensile strength (MD, kg/cm) 5.5 5.6Elongation (MD, %) 9.4 9.4Repulpable property Very good Very poorInk-receptible property (backcoating side)

Marking pen Very good Very poorBall-point pen Good Very poorPencil Very good Very poor

Non-slip property (back coatingside)

Friction angle 10° 5°Static friction coef®cient 0.24 0.02Kinetic friction coef®cient 0.13 0.02



This PSAtape,which is repulpablewith alkaline water,is alsorepulpablewith waterprovided that the mixing ratio of tape to wastepaperis 5% or less.Figure 6 showsrecycledpapershand-madefrom thenewtapeandaconventional tape,respectively.Therecycledpapermadefrom theconventionaltapehasadhesive andPE lumps, which aresticky contaminants,whereastherecycledpapermadefrom therepulpabletapedisplaysexcellentqualitywithoutstickycontaminants.Fortherepulpingtests,16gof tapewascutinto piecesof about1 cm� 1 cm and150ml of waterwasaddedto it. Then, 0.48g(3%wt. of tape)of NaOHwasaddedandthemixture thenboiled for 30 minutes.Thewaterwasthenaddedto themixtureto give a total of onelitre andwasstirredfor two minuteswith amixer(householdmixerwith modifiedrotorblades).Hand-madesheetsweremadewith equipmentasspecifiedin JISP8209.5 Table1 showsthepropertiesof therepulpablekraft tapecomparedwith thoseof theconventionalkraft tape.This repulpablekraft tapewasputonthemarketin 1992asNEO101andsincethenits saleshavedoubledeachyear.

LINTEC Corporation has also developed a relatedproduct (NEO101W),which is

Figure 6. Repulpable kraft paper tape (`NEO 101')

Figure 7. Repulpable kraft paper tape (`NEO 101 W')



repulpablewith wateronly (Figure7). Theadhesiveof this tapeis awater-solubleacrylicPSAandthe basepaperis a white bleachedkraft. Currently,this tapeis beingusedforpaperroll endsealingandsplicing at papermills.

Figure 8 shows the constitution of the recently developed repulpableheavy-dutypackaging paper tape (NEO103) whosestrengthequalsthat of cloth tape. The highstrengthis obtainedby the basic materialsthat consistof two sheetsof kraft papersandwiching filaments.Thenewtypefilamentsaresolublein water.Thebackcoatingisthesameasthat for therepulpablekraft tapedescribedabove.ThePSAis alsothesameexcept that the coating weight is heavier. While having equal repulpability, thispackaging papertapeis hardto cut in contrastto easy-to-cutcloth tapes.Table2 showsthe propertiesof this tape.

Figure9 showsarepulpablelight-duty packagingpapertape(NEO105)developedasaproductthat canreplacecellophanetape.The basepaperis a wood-freepaperandthebackreleasecoatingis aspecialsilicone. Thereleasepropertyof thesiliconeis controlledsoasto ensuresmoothoperationwith a tapedispenser.Thetapesurfaceallowsmarkingby amarkingpen,ball-point penor pencil.Theadhesiveis aspecial acrylic PSAthatcanlose adhesivenesswhen dispersedinto small, less tacky particlesthroughagitation inalkaline water.Repulpability is slightly lower thanthepackagingtapeintroducedabove,but is adequatefor practicalapplications.Though it doesnot havethe transparencyof

Figure 8. Repulpable heavy duty packaging paper tape (`NEO 103')

Table 2. Repulpable heavy-duty packaging tape versus cloth tape

New paper tape `NEO 103' Conventional cloth tape

Thickness (mm) 0.21±0.28 0.34Peel adhesion (g/cm)

Stainless steel 560 350J. Dow ball tack (No.) 30 >32Holding power >70 000 6 000(section 25� 25 mm2, 1 kg loadat 40°C)Tensile strength (MD, kg/cm) 6.8 7.1Repulpable property Very good Very poor



cellophanetape, this packaging tape is suitablefor sealingenvelopesand wrappings(Table3).

Following the development of these three types of repulpable PSA tapes, thedevelopmentof repulpabletapesthat canreplaceOPPtapesis now beingundertaken.

Figure 9. Repulpable light duty packaging paper tape (`NEO 105')

Figure 10. Conventional release paper for label

Table 3. Repulpable light-duty packaging tape versus cellophane tape

New paper tape`NEO 105'

Conventionalcellophane tape

Thickness (mm) 0.080 0.048Peel adhesion (g/cm)

Stainless steel 500 280J. Dow ball tack (No.) 8 19Holding power 1 500 26 000(section 24� 25 mm2, 1 kg load at 40°C)Tensile strength (MD, kg/cm) 5.7 3.5Repulpable property Good Very poorInk-receptible property

Marking pen Very good Very goodBall-point pen Good GoodPencil Very good Very poor



JAPANESE LABEL MARKET

Japan’sproduction of PSAlabelsin 1996was942milli onm2. Of thisfigure,paperlabelsaccountedfor 775milli onm2 (82.3%)andfilm labels167million m2 (17.7%).6 By papertype,about70%wasoccupied by wood-freepaperandcast-coatedpaper,andabout30%by coatedpaper,thermalpaperandothers.Theadhesivesused,whichareeither acrylicorrubber types, were predominantlyacrylic.7 ThesePSAs are not repulpable and thusbecomesticky contaminantsin papermanufacture. Also, as shown in Figure 10, thereleaselinersmainly usedin Japanareglassinepaperor PEcoatedpapercoatedwith alayer of silicone.Thesetwo typesarebeingusedin different applications accordingto

Figure 11. Repulpable PSA paper label

Table 4. Repulpable label versus conventional label

New label cast-coatedpaper face stock

Conventional labelcast-coated paper

face stock

Repulpable property Very good Very poorPeel adhesion (g/cm) 1 700 1 700

Stainless steelJ. Dow ball tack (No.) 6 6Holding power (s) >70 000 >70 000

Non-creep Non-creepLiner release force(g/5 cm) 9 10Adhensive bleeding* (into neutralized paper) Good GoodDie-cutability Good Good

* Test condition: 40°C, 95% RH, 7 days.



their advantagesanddisadvantages. It is to be noted,however,that the glassinetype isrepulpableandthereforerecyclablewhile thePEcoatedtypeis not repulpablebecauseofpolyethylene.

REPULPABLE LABELS

Figure 11 showsthe repulpablePSA paperlabel developedin 1996. It containsthreebasicmaterials,namely,wood-freepaper,cast-coated paperandcoatedpaper.ThePSAisa new acrylic type that is mainly dispersedto becomenon-adhesivein weak alkaline

Table 5. Laboratory repulpable test (hand-made recycled paper)

Sample* labelcontent (%)

NaOH(%)

Testequipment

Testcondition New label

Conventionallabel

Case 1 100 3 Modi®edhousehold

mixer

30 min boilingat 80°C±90°C

Very good Very poor(`Stickies')

;Disintegrate 2

min;

Hand sheetCase 2 100 3 Modi®ed

householdmixer

Boiling 30 minat 80°C±90°C

;Disintegrate 2

minVery good Very poor

;Add

aluminiumsulphate(pH = 5)

;Hand sheet

Case 3 50 0.8 : Disintegrate 20min

Good Very poor

10 0.8 : ;Hand sheet Good Very poor

Case 4 20 0 : : Very poor Very poor10 0 : : Good Very poor

Case 5 10 0 JIS standarddisintegrator

: Good Very poor

* Sample: label�wood-free paper.



aqueoussolutionandpartly dissolvedin it. As well astheglassinetypereleaseliner, theclay coated and water-solubleclear coated releaseliners, have been developedassubstitutesfor the PEcoatedtype; they exhibit high-dimensionalstability.

Table4 showsthepropertiesof thedevelopedrepulpablelabel.In peeladhesion,tackand holding power, this product does not show any marked difference from theconventional label. It is alsoequivalentto the conventionallabel in liner releaseforce,label die-cuttabilityandadhesivebleeding.The repulpabilityof the developed product,however, is goodin contrastto the conventionallabel.

Table5 showstheresultsof repulpabilitytestsconductedata laboratory.In case1,16gof PSA label wasaddedwith 150ml of waterand thenwith 0.48g(3% wt.) of NaOHbeforebeingsubjectedto 30 minutesof boiling. Then,themixturewasaddedwith waterto a total of 1 l andwasstirredfor two minuteswith a dedicatedmixer. Themixturewasthen formed into a hand-madesheet,which wascheckedfor the presenceof adhesivelumps or stickiness.In case2, the stirredsample of case1 wasaddedwith aluminumsulphateto a pH level of 5 beforethehand-madesheetwasproduced. In case3, additionof NaOH was reducedfrom 3% to 0.8%, and no boiling was carriedout. Testswereconductedat wood-freepaperto PSAlabelmixing ratiosof 5 to 5 and9 to 1. In case4,tests were conductedwith water only without adding NaOH. In case5, a standarddisintegrator JISP8209wasusedinsteadof a mixer. The mixing ratio of thePSAlabelwas10%,andthesamplewasdisintegratedwith wateronly for 20minutesat3 000r.p.m.

Table 6. Pilot-plant repulpable test (July 1995)

Test 1. Waste paper/repulpable label = 70/30 Weight 310 kgNaOH 0.8% (pH = 11.4)5.34% Pulp

5 min at 340 rpm23°C

Aluminium 650 mm widthsulphate 6.5 m/min speed

;No stickies, goodperformance recycledpaper

Test 2. Waste paper/repulpable label = 90/10 Weight 250 kgNaOH 0% (pH = 7.9)4.2% Pulp

No stickies, good performance recycled paper



Table6 showsthe testresultsusinga 5 m3 pulper.Both the recycledpapersobtainedusingthe two testconditionswereof goodquality.

From theseresults,it wasfound that the new productis repulpablein alkaline waterevenat 100%contentandit is repulpablein waterprovidedthat themixing ratio is 10%or less.Underordinaryrecyclingconditions, thelabelscomprisenomorethan2 or 3%ofthe pulp. It is also to be notedthat de-inking andflotation shouldfurther improve thequality of recycledpaper.This newlabel is well suitedto useon wrappings,envelopes,magazines,cartons,sheetsandroll products,andbusinessletter forms.

CONCLUSIONS

Theuseof repulpablePSAtapesandlabelsin Japanis still limited, butat thecurrentrateof growth,it will not belong beforetheserepulpabletapesandlabelsclaim a largeshareof the market.The new repulpablelabel developed in 1997 is repulpableusingwater,evenonly at 100%labelcontent.This productwill surelycontributeto theproductionofhigh-qualityrecycledpaper.

REFERENCES

1. Monthly Paper and Pulp Statistics.Research& StatisticsDepartment,Minister’s SecretariatofM.I.T.I.

2. JapanExportsand ImportsMonthly.Ministry of Finance.3. Suzuki,T. Technologyon Adhesion& Sealing(Japan)39 (4), 23 (1995).4. Handbook of PSA Tape, ed. T. Shibano and Y. Urahama.JapanAdhesive Tapes Maker’s

Association,(1995).5. JISP8209:Methodof PreparingHandsheetsfor Pulptesting.JapaneseIndustrialStandard.6. LabelShinbunApril 1 (1997).7. Shibano,T. Paper,Film & Foil ConverteckJapanOctober46 (1993).



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Repulpable pressure-sensitive adhesive tapes and labels