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j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 1 ( 2 0 0 8 ) 401–407

journa l homepage: www.e lsev ier .com/ locate / jmatprotec

reasing characteristic of aluminum foiloated paperboard

. Nagasawaa,∗, R. Endoa, Y. Fukuzawaa, S. Uchinoa, I. Katayamab

Department of Mechanical Engineering, Nagaoka University of Technology, JapanKatayama Steel Rule Die, Co. Ltd., Japan

r t i c l e i n f o

eywords:

hear

reasing rule

ending

urface failure

a b s t r a c t

In this paper, to clarify a rule indentation effect on failure occurrence in the surface layer

of paperboard, an aluminum foil coated paperboard was experimentally scored and folded

by using a couple of creasing rules and square groove plates. The specimen was made with

a 15 �m thickness aluminum foil and a 360 g/m2 high quality white-coated paperboard by

using adhesive glue spray. The state of creased part was observed with a CCD microscope

and the relationship between the bending momentum resistance and the bending angle was

compared with that of the normal paperboard. The relationship between the indentation

depth of creasing rule and the in-plane stretching strain in the surface layer was investi-

gated by using a new measurement method, and the occurrence limit of surface failure of

aluminum foil was discussed with the tensile strength of the material. Through this work, it

was confirmed that the in-plane stretching strain in the surface layer has affected the fail-

ure limit of aluminum foil layer of the specimen. It was also concluded that the proposed

method of strain measurement on the bent surface layer was enable to discuss the failure

strength of surface layer.

rectangle channel on the counter die plate were experimen-

. Introduction

n aluminum foil coated paperboard is used in many print-ng fields such as decorative sheets and medicine cabinetsMizuguchi, 2002; Inagaki, 2000). When a cabinet is maderom paperboard and if any cracks occur at the outside ofolded parts, the mechanical strength of cabinet is weakenednd also the folded parts are inferior in decorative aspects.ince the aluminum decorated layer is normally made byhe evaporation method, it is difficult to respectively esti-

ate the deformation characteristics of the aluminum andhe paperboard layer. In order to reduce the failure occur-

ence on the surface layer of aluminum coated paperboard,n advanced creasing condition must be considered on theolding line. A few reports for in-plane elongation of paper-

∗ Corresponding author. Tel.: +81 258 47 9701; fax: +81 258 47 9701.E-mail addresses: snaga@mech.nagaokaut.ac.jp (S. Nagasawa), kata

924-0136/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.jmatprotec.2007.11.253

© 2008 Elsevier B.V. All rights reserved.

board during indentation of creaser were shown by Halladayand Ulm (1939). Actual creasing range was investigated as therelationship between the crease depth and the crease widthby Hine (1959). Nagasawa et al. (2001, 2003) reported about thefolding stiffness with respect to the indentation depth of thecreaser and also discussed with the crease deviation effecton the folding deformation characteristics. However, the rela-tionship between the elongation of aluminum surface layerand the geometrical creasing condition was not sufficientlyrevealed.

In this work, a uniaxial round-edge creaser and a deep-wide

yama@diemex.com (I. Katayama).

tally applied in order to determine the creasing property ofspecimens which were made with tA = 15 �m thickness as-roll aluminum foil and a 360 g/m2 high quality white-coated

402 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t

Table 1 – In-plane tensile properties of white paperboard

Ultimate TS �B,MD (MPa) 73.6 (71.7–75.4)Breaking strain εB,MD (%) 4.2 (4.0–4.6)Young’s modulus EMD (MPa) 1597 (758–2330)Ultimate TS �B,CD (MPa) 41.1 (39.2–43.3)

Breaking strain εB,CD (%) 6.8 (5.9–7.2)Young’s modulus ECD (MPa) 1042 (647–1581)

paperboard (WPB) by using adhesive spray. In order to dis-cuss the aluminum foil effect on the creasing characteristics,an aluminum foil attached to the white-coated paperboard(AL + WPB) was compared with the WPB in terms of the bend-ing moment resistance, the swelled inside profile and thein-plane tensile strain. Furthermore, the relationship betweenthe failure occurrence of aluminum layer and the normalizedindentation depth of the creaser was also discussed.

2. Experimental

2.1. Preparation of specimens

When a failure crack occurs on the aluminum foil layer, sincethe in-plane elongation of the surface layer seems to exceedthe breaking limit of the aluminum foil, it is required to eval-uate the in-plane tensile strain in the surface layer of thespecified paperboard. Hence, the square lattice of 0.5 mm wasprinted on the specimens of 360 g/m2 high quality white-coated paperboard (WPB) with the line width of 0.1 mm inorder to estimate a normal strain on the surface of the WPB.The specimens were made with a 15 �m thickness of alu-minum foil and the lattice printed WPB by using an adhesivespray. Here, the aluminum foil was made from the 1N30-H18(JIS: Japan Industrial Standard -H4160), while the polyesteradhesive 3M #55 was sprayed once onto the surface of theWPB with a distance of 200 mm. After mounting the aluminumfoil on the glued paperboard, all the specimens (AL + WPB)were slowly pressed by a thick rubber plate with a pressure of100 Pa.

The WPBs were rectangular in shape and had thicknesstP = 0.37 (0.36–0.38) mm, length 60 mm and width 40 mm. Theresults of tensile testing for MD (grain direction) and CD (cross

machine direction) of the WPB are shown in Table 1. The ten-sile testing results of specified aluminum foil were as follows:Ultimate TS �B = 161 (158–168) MPa, Breaking strain εB = 1.5(1.2–1.8)%, Young’s modulus E = 11.7 (9.1–13.5) GPa. Where, the

Fig. 1 – Schematic of scoring, bending test and geometrical paramdevice of bending test.

e c h n o l o g y 2 0 1 ( 2 0 0 8 ) 401–407

tensile testing was carried out under the following condi-tions: the feed velocity: 1 mm/min, the room temperature:291 (288–293) K, the room humidity: 36.5 (34–40)%, the sam-ple numbers: five pieces, the width of specimen: 15 mm, thespecimen length: 60 mm (chuck distance: 35 mm). The thick-ness of specimens composed of aluminum foil and WPB wast = 0.390–0.395 mm.

The authors reported about a creasing test for 350 g/m2

waste white-coated paperboard by using a narrow width chan-nel (Nagasawa et al., 2003; Endo et al., 2007). Compared withthis waste paperboard, the specified WPB has roughly twicehigher tensile strength εB, similar stiffness (Young’s modulus)E, 1–2% larger breaking strain �B and 24% thinner thickness tP.These differences are discussed in the following sections.

2.2. Experimental methods

Fig. 1(a) illustrates the geometrical relationship among acreaser (creasing rule), a scored specimen (AL + WPB or WPB)and a channel die, while Fig. 1(b) defines the creaser direc-tion angle �. Since the creased part is altered mechanically byfolding itself, we call the initial state as the score (the initialcrease) for identifying the initial one and the altered one. Thescore is produced by the creaser indentation, where the rubberfixtures were not considered in this case.

Dimensions of the creaser and the channel die were asfollows: the thickness of creaser b = 1.2 mm, the tip radius ofcreaser r = 0.6 mm, the effective length of creaser = 40 mm, thechannel width W = 2 mm. The depth of channel die d was con-sidered as d > t. The value of W was empirically chosen asW ≈ b + 2t, while the ratio b/t ≈ 3 was considered to be largerthan the ratio b/t = 1.6 used in the past work (Nagasawa et al.,2003; Endo et al., 2007).

In this work, when the crease line is transverse perpendic-ular to MD, the creaser direction angle is defined as � = 90◦,while when the crease line is parallel to MD, the angle isdefined as � = 0◦. The nominal shear strain � = 2h/W was var-ied from 0.0 to 1.0, in order to investigate the effect of creaserindentation depth on the creasing characteristics such as thebending moment resistance, the swelled inside profile of thespecimen and the failure mode of the surface layer. Here, h isthe indented depth (height) of creaser onto the surface of thespecimen.

After scoring the specimens under the feed velocityV = 1 mm/min, the bending moment resistance of creaseM Nm/m was measured with respect to the rotation angle� = 0–90◦ by using the bending test machine as shown in

eters. (a) Scored profile; (b) creaser direction angle; (c)

j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 1 ( 2 0 0 8 ) 401–407 403

Fig. 2 – Schematic of surface strain measurement and folding test. (a) Strain measurement on coated surface of paperboard;( fter c

FattAtoamtoftittr2rcf

Fww

b) complete bending by rubber rollers; (c) sectional profile a

ig. 1(c) (Nagasawa et al., 2001). The scored part was foldedt its right angle and at the same time the outer surface ofhe specimen was observed using a CCD microscope in ordero investigate the distance of the opened crack Da mm forL + WPB. For estimating the surface elongation of the WPB,

he engineering strain ε = s2/s1 − 1 was used. Here, s1 is theriginal (initial) lattice distance, while s2 is the lattice distancefter being deformed as shown in Fig. 2(a). Through the experi-ent result, as the aluminum surface crack occurred at � < 90◦,

he strain ε was calculated at � = 90◦. At the same time, theccurrence frequency of aluminum foil breaking was countedor the five pieces by varying the nominal shear strain �. Sincehe surface strain of WPB seems to be related to the swellednside profile of WPB, the thickness of swelled inside Dsi andhe height of swelled inside Hs were observed with the foldingest as shown in Fig. 2(b and c), by varying the �. The foldingollers were made by a hard rubber, and their diameter was

0 mm. The pressing force of 14.8 N was applied to the foldingollers previously. By passing through the folding rollers, therease of specimen was crushed and the crushed hinge wasormed in � = 180◦.

ig. 3 – Relationship between bending moment resistance and roith respect to WPB; (b) creased in parallel to grain direction withith respect to AL + WPB; (d) creased in parallel to grain direction

reased.

3. Results and discussion

3.1. Response of bending moment resistance

Fig. 3(a and b) illustrate examples of the bending momentresistance M Nm/m at the creased line without any aluminumfoil, and Fig. 3(c and d) illustrate examples of the bendingmoment resistance M Nm/m at the creased line with respectto the specimens of AL + WPB. A local maximum bendingmoment resistance Mmax was found at a certain angle � largerthan 20◦ and less than 80◦ for the AL + WPB, while the Mmax forthe WPB specimen was found at a certain angle � larger than20◦ and less than 60◦.

For � > 0.4, the moment response M–� with the AL + WPBwas similar to that of the WPB specimen, except for the rota-tion angle of Mmax, defined here as the peak angle �P. The Mmax

was reduced by increasing the �, and the peak point disap-peared for � > 0.8. The relationship between the Mmax and the� was shown in Fig. 4(a), and the corresponded peak angle �P

was shown in Fig. 4(b). Fig. 4(c) shows the initial gradient of

tation angle. (a) Creased in transverse to grain directionrespect to WPB; (c) creased in transverse to grain directionwith respect to AL + WPB.

404 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 1 ( 2 0 0 8 ) 401–407

Fig. 4 – Effect of nominal shear strain on bending characteristics with respect to scoring direction and aluminium foil effect.) effe

(a) Maximum bending moment resistance; (b) peak angle; (c

the bending moment resistance with the rotation angle (thecrease rigidity) Gi = ∂M/∂� which was linearly approximated for� = 1–8◦. Here, the Gio is a value of Gi measured at � = 90◦, � = 0.0.

For the anisotropic properties of white-coated paperboards,it is known that the difference of Mmax for � = 0◦, 90◦ becomesdisappeared with the increase in � (Nagasawa et al., 2003). Inthat paper, the difference of Mmax with crease direction disap-peared for � > 0.5 and the difference of Gi with crease directiondisappeared for � > 1.0. These tendencies are almost the sameas the results of the WPB specimens, despite that the former(Nagasawa et al., 2003) has b/tP ≈ 1.6 and the latter (this work)has b/tP ≈ 3.2.

From Fig. 4(a–c), the following features are found: (1) theMmax of AL + WPB is 10–25% larger than that of WPB, when� < 0.2; (2) the Mmax of AL + WPB is almost same as that of WPBfor � > 0.4; (3) the peak angle �P of AL + WPB is smaller thanthat of WPB for � < 0.7. The difference angle of �P between theAL + WPB and the WPB is decreased with the increase in �; (4)when � > 0.6, the initial gradient Gi is apt to be independentto the aluminum foil attachment. The difference of Gi/Gio wasless than ±5% for � = 0.6–1.0.

Fig. 5 shows representative sectional views (CCD micro-scope) of the WPB specimens creased part which were foldedwith � = 90◦ at the right angle. When the � is relatively small,since the delamination of inner layer is little, the hinge bulgebecomes small as shown in Fig. 5(a and b). When the � isnot sufficient (� < 0.3) especially for the inner delamination,the outer surface layer at the crease line is apt to be brokenby folding the specimen. When the � > 0.4, the swelled pro-

file of hinge becomes large and the inner delamination is welldone as shown in Fig. 5(c and d). The swelled profile and theinner delamination are supposed to contribute to reduce theMmax and the tensile stress in the outer surface layer. Namely,

ct of nominal shear strain on crease rigidity.

the crease line is changed so as to extrude the delaminatedlayer and to reduce the bending rigidity with the increasein �.

3.2. Surface elongation and surface failure tendency

The failure occurrence of aluminum foil was counted as thefrequency p for all the specimens of AL + WPB and the dis-tance of opened crack Da was measured as shown in Fig. 6(aand b). The measurement was carried out at the right angle(� = 90◦). From Fig. 6(a and b), a critical shear strain was found atwhich the surface crack was increased remarkably for a certaintransition region: � = 0.2–0.4. In order to discuss the breakingstress in the aluminum foil layer, the surface tensile strainof WPB specimen was estimated by using the printed latticeelongation as shown in Fig. 2(a). For identifying the elonga-tion of surface layer, the printed lattice distance of 0.5 mmwas empirically sufficient as shown in Fig. 5. Since the printedlattice pitch is required to detect the elongation on the bentsurface of crease, the outer arc length of crease part must belonger than the printed lattice pitch. The radius of the creaseouter surface � was empirically 1.2tP–2tP, assuming that themeasured arc length is in the right angle (90◦), (�/2)� ≈ 2tP–3tP

should be covered by the multiple lattices.Fig. 6(c) shows the relationship between the surface tensile

strain of WPB and the nominal shear strain. It is confirmedthat the surface strain ε is decreased with increase in �, and thestrain for � = 0◦ is apt to be smaller than that for � = 90◦. Sincethe ratio of tensile strength � /� is 0.55 and the ratio of

B,CD B,MD

Young’s modulus ECD/EMD is 0.65, these anisotropic propertiesseem to contribute to make the difference of ε with respectto the crease direction. In the case of � = 90◦, as � = 0.3 was thecritical condition for the breaking point, ε ≈ 0.07 was the corre-

j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 1 ( 2 0 0 8 ) 401–407 405

Fig. 5 – Sectional views of creased part at the right angle with respect to WPB. (a) � = 0.0, � = 90◦; (b) � = 0.3, � = 90◦; (c) � = 0.4,� = 90◦; (d) � = 0.6, � = 90◦.

sssε

ttan

Fc

ponded critical strain. In the case of � = 0◦, the correspondedtrain was ε ≈ 0.1. On the other hand, the breaking strain of thepecified aluminum foil was 0.015. Hence, the measured strainfrom the printed lattice should be furthermore verified, but

he strain ε can be used for knowing the correlation betweenhe aluminum foil breaking and the creasing conditions suchs �, W, b and t. This gap is supposed to be caused from theext two points:

ig. 6 – Effect of nominal shear strain on surface breaking of alumrack on aluminum foil; (b) breaking frequency of aluminum foil;

(1) As there was an adhesive layer between the aluminum foiland the WPB, the measured ε was not equal to the strainof aluminum foil itself.

(2) As the measured ε was for the WPB without tensile sus-

tained aluminum foil, it was shown as a large value.

By considering many actual conditions, the surface strainmeasured by the printing lattice is supposed to be useful for

inum foil layer with AL + WPB. (a) Distance of opened(c) in-plane tensile strain of WPB surface layer.

406 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 1 ( 2 0 0 8 ) 401–407

Fig. 7 – Effect of nominal shear strain on sectional profile of creased part with complete folding. (a) Height of swelled inside

Acknowledgement

part Hs; (b) thickness of swelled inside part Dsi.

estimating the critical condition of the aluminum foil failure,although the parameter � is quite simple and usable. As thenominal shear strain does not describe the inside state of worksheet, the surface strain should be observed if the work sheetis made by unknown laminated materials. When � > 0.5, sincethe measured strain was ε = 0.05–0.08 and the breaking strainof εB was 0.04–0.07, we can see that they are almost equalto each other. So that, the printed lattice method enables toexplain the reason why the outer surface of WPB is sustainedwithout any cracks for � > 0.5. If the fine lattice is directlyprinted on the aluminum foil, the estimation of critical failurecondition would be performed.

When the waste white-coated paperboard was used formaking the AL + WPB specimens (Endo et al., 2007), whereW = 1.5 mm, b = 0.71 mm and tP = 0.46 mm, the Mmax wasalmost similar to Fig. 4(a) for � > 0.4. However, the critical nom-inal shear strain was relatively large (� = 0.4–0.6), comparedwith Fig. 6(b). Therefore, by increasing the ratio b/t from 1.6 to3.2, the critical nominal shear strain is apt to be increased.

3.3. Sectional profile of crease and surface failure

As a certain kind of cabinet is completely folded, the swelledprofile of hinge at � = 180◦ was investigated with respect toFig. 2(c). When the creaser indentation was not sufficient forthe inner delamination, the aluminum foil layer of crease wasapt to be broken by folding the specimen near to the rightangle. After passing through the right angle, the surface wasalmost kept in sustained state when � > 0.5, � = 0◦. Since thein-plane tensile stress of aluminum foil is characterized withthe geometrical bending deformation of WPB, the geometricalfeatures seem to be related to the crease profile. The thicknessof swelled inside Dsi and the height of swelled inside Hs areshown in Fig. 7.

The height Hs was apt to be reduced by attaching the alu-minum foil, the thickness Dsi showed a complicated crossingtendency for the aluminum foil attachment. By seeing the Hs, aconstant gradient started at a certain nominal shear strain andthis point was almost corresponded to the critical failure con-dition of aluminum foil for folding in � = 180◦: the critical value

� ≈ 0.4 for � = 90◦ and � ≈ 0.5 for � = 0◦. Namely, it is found thatthe variation of Hs has a possibility to characterize the criticalfailure condition of the surface layer of the specimen. Both Hs

and Dsi were remarkably changed for � = 0–0.3 and the differ-

ence of Hs, Dsi for the crease direction was obvious. Since thevariation of them is based on the inner delamination, it is con-firmed that the anisotropic features of WPB are well describedby showing Hs and Dsi.

4. Concluding remarks

The crease characteristic of an aluminum foil (1N30-H18)attached with a glue on a paperboard (a high quality white-coated, 360 g/m2) was investigated by varying the nominalshear strain �, using a deep-wide channel die counter plate.The results obtained were as follows:

(1) Mechanical properties of crease folding such as themaximum bending moment resistance Mmax, the initialgradient Gi (bending stiffness), the peak position angle�P, the thickness of swelled inside Dsi and the height ofswelled inside Hs were characterized by the nominal shearstrain � (calculated by the ratio of indentation depth ofcreaser and the channel width) for both the aluminum foilattached paperboard and its non-attached paperboard.

(2) The failure of aluminum foil surface layer depends on thein-plane elongation of the paperboard surface layer.

(3) The correlation between the occurrence frequency of thealuminum foil failure and the � was revealed. There is acritical nominal shear strain at which the in-plane break-ing of aluminum foil remarkably occurs.

(4) The occurrence frequency of the aluminum foil failuredepends on the crease direction angle � with respect tothe grain direction of the paperboard. The critical nomi-nal shear strain of the specified material was roughly 0.3for � = 90◦, while it was roughly 0.4 for � = 0◦, where therotation angle � of crease was the right angle.

(5) The printed lattice of 0.5 mm pitch on the paperboard wasproposed to analyze the in-plane elongation of the paper-board surface layer during the folding process.

This work was supported by Nagaoka University of Tech-nology, Research and Development Center Project of GrantNumber 16R.

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