EVALUATION AND CONTROL OF COATED PAPER STIFFNESS

Transcription

1 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). EVALUATION AND CONTROL OF COATED PAPER STIFFNESS Koji Okomori Central Researh Laboratories R&D Division Nippon Paper Industries, Co., Ltd Oji, Kita-ku, Tokyo , Japan Toshiharu Enomae and Fumihiko Onabe Paper Siene Laboratory Department o Biomaterial Sienes Graduate Shool o Agriultural and Lie Sienes The University o Tokyo Yayoi, Bunkyo-ku, Tokyo , Japan ABSTRACT Stiness is an important property o paper in printing proesses. Operational problems suh as jamming during sheet ed oset printing oten stems rom poor paper stiness. In the ase o oated papers, the Young's modulus o the oating layer aets the stiness o the whole oated paper beause external layers undergo larger strain during bending ompared to the internal layers. A method to theoretially alulate the Young's modulus o a one-sided oated sheet is presented in terms o material mehanis. The aurate interpretation o Clark stiness enables us to estimate the Young's modulus o the oating layer rom Clark stiness. The aurate alulation o Young's modulus rom the Clark stiness is shown to require an impervious ilm beause basepaper, when wetted with water, swells and roughens, giving an inorret value or the Young's modulus. INTRODUCTION Emphasis has been put mainly on printability o oated paper and luid dynamis o oating olor in the ield o oating siene beause oating is aimed at high grade printing paper. Less researh has been onduted regarding oated paper physis. However, lariying its physial properties helps examine the bending and ompression deormation that oated paper undergoes in a printing press and the durability to severe printing onditions. An example o these problems is a eeding trouble on a opy mahine, optial harater reognition mahine and sheet-ed printing press. Namely, sot paper, espeially oated paper that is likely to be with poor stiness, ongests beore a destination nip. A deinite physial value, stiness is used in the general analysis o materials behavior against a bend. The deinition is Young s modulus E times seond moment o area I, that is, EI, is the stiness o a material against a bend. Then, when one says that this paper is weak, this weak or strong is not deinitive, and just subjetively sensed by people. Though this kind o weak or strong ( sensory stiness reers to this onept thereater) is onsidered to be orrelated with stiness, Kazumori et. Al 1) reported that at the same stiness EI, the higher the Young s modulus E, the harder the paper was sensed. They added, however, that examinees evidened that the riteria o sensory stiness is resistane to a snap and slow lip both due to the weight o its own, thikness and reovery property rom a bend as well as the resistane to an external bending ore. Physial values related to stiness are summarized in the ollowing manner. Clark stiness means a bending resistane in the ase that a paper strip bents due to the weight o its own. Pure bending stiness 2)) means a stiness divided by the sample width in the ase that a paper strip is bent with the same urvature along the whole span (The loser to the support, the higher the urvature in Clark stiness.). Liveliness originally indiates the 1

2 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). speed at whih a textile reovers rom ertain urvature. Naito et al. 4) applied this to paper and deined the liveliness o paper to be an inverse o reovery time squared so that this immediate reovery property would be onneted with stiness. Liveliness and Clark stiness may be more suitable to analyze paper behavior on a o-set press eeding sheets with sution pads beause how ast the paper sheet reovers ater it bents due to the weight o its own and the moment o inertia o the paper is relatively important. Table 1 lists some physial values regarding stiness inluding those mentioned above. Table 1. Terminology related to stiness Physial value Equation Conept Stiness S, EI Resistane to a bend Clark stiness (Handling stiness) Flexing resistane Pure bending stiness Liveliness 1 Sensory stiness Young s modulus L 100, EI ET bw, 12W LW 100, EI b EI b t 2 E, σ ε Seond moment o area I, bt Bending moment M, 12 EI r Resistane to a bend due to the weight o its own Stiness divided by sample width Stiness divided by sample width when bent with the same urvature along the whole span Inverse o squared time o reovery rom ertain urvature Stiness subjetively estimated by people longitudinal elasti modulus Integral o squared distane rom neutral axis Fore times distane where, L is overhung length (m); W basis weight (g/m 2 ); t time (s). T is thikness; b is sample width; σ is stress; ε strain; r radius o urvature. There has been a lot o researh regarding stiness o unoated paper, but ew regarding that o oated paper. Naito et al. 5) measured stiness o oated paper in several methods and ompared them as well as unoated paper, then onluded that pure bending stiness is more orrelated to sensory stiness than Clark stiness. Nagai et al. 6) alulated the Young s modulus o the oating layer o two-sided oated paper rom Gurley stiness, but it an not be applied to one-sided oated paper whih are regularly produed on a laboratory sale. Basepaper property dominates most mehanial properties o the whole oated paper. However, partiularly with regard to stiness in a bending mode, a oating layer has onsiderable eets 7)8). This is beause the strain the outlying oated layer undergoes is muh larger than that the inner basepaper layer does. However, beause the relative density o dry oating is about twie as large as that o basepaper, Clark stiness dereases with inreasing oat weight even i Young s modulus o the two layers were equal. Considering that oated paper a omposite material onsisting o the two layers, that is, oating and basepaper, this work aims at the estimation o how muh the oating layer ontributes to the total stiness o the oated paper. For this purpose, we assumed that determination o Young s modulus o a oating layer would be the best approah, beause it is independent o the oat weight and thikness, but is dependent only on the olor ormulation and oating struture. In the beginning, theoretial and empirial methods were established to determine Young s modulus o a oating layer. Then, eets o starh and plasti pigment ormulation on Young s modulus o the oating layer were examined. Finally, double oating with olors having dierent olor ormulations was evaluated 2

3 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). in view o improvement o stiness o the oated paper. THEORY It is assumed that oated paper is a omposite material having two parallel layers o uniorm and homogeneous substane glued together. Nagai et al. 6) showed the equation to alulate Young s modulus o the oating layers or two-sided oated paper, assuming the same oat weight on the two sides. However, it is usually diiult to oat a sheet to meet this requirement on a laboratory sale. Thereore, another equation or one-sided oated paper or it was led as mentioned below. The total stiness R a is the average Young s modulus E a times seond moment o area I a o the whole oated paper (See Figure 1.). R E I E bt a = a a = a 12, (1) where T and b are oated paper thikness and width, respetively. Seond moment o area o the oated layer I, its Young s modulus E, seond moment o area o the basepaper layer I and its Young s modulus E give the equation (2). Ra = E I + E I (2) Then, the reerene axis (y-axis) is taken at the bottom o the ross setion to determine the oordinate o the neutral axis N-N, where no strain ours. The bending stress develops only in z-axis and the integration o the stress with regard to y 0- axis (y-n) is 0. Consequently, equation () is obtained. E y da + E y da =, () where A and A are area o the basepaper and the oating layer, respetively. Substituting y 0 =y-n into equation () leads equation (4). ( ) + ( ) = 0 (4) E y N da E y N da I this is solved with regard to N, Equation (5) is obtained. E E yda + E yda N = = E da + E da 2 2 E h + E( 2hh + h ) =, 2E h + 2E h h 0 ybdy + E E bh h + h h + E bh ybdy (5) where h and h are thikness o the basepaper and oating layer, respetively. Equation (2) and (5) give Young s modulus o the oating layer E as shown in equation (6). Thereore, E an be alulated i one measures stiness o oated paper R a.

4 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). E = R a h N 2 E y N h + h N 2 y h N dy dy = Ra E ( h N ) E N ( h + h N ) ( h N ) (6) Clark stiness has been known as a standard method to measure stiness o paper or textile or a long period. Following is how to alulate Young s modulus o a oating layer rom it. First, Clark stiness is deined this way. A long paper strip is nipped at one end and supported upright. As the nip rotates, the strip lops suddenly rom the bend side to another at ertain nip angle. The angles where this ours on both the sides are measured. The overhung part is extended until the dierene o the angles reahed 90 degrees. The satisatory overhung length L ubed divided by 100 is a Clark stiness. In Clark s publiation 9) and JIS(Japan Industrial Standard) 10), L is measured in m, but in mm in Tappi test methods 11). The reason why the ubed length is used is expressed in equation (7), as Oda et. al 12) showed. L EI ET = 100 bw 12W (7) Aording to their work, the overhung length L(m), Young's modulus E(dyne/m 2 ), thikness T(m), basis weight W(g/m 2 ) empirially satisies the equation where the two terms are equal (not only proportional) in the ondition that those variables are expressed in the speiied units above. Theoretially, as Takadera et al. 1) showed, this ation is represented by an equation o a beam with one end ixed, equation (8), 2 d θ = q sin θ 2 (8) dq (Boundary ondition: q=0 at θ=α and q=k= b( W 10 EI 4 ) G L at θ=β (9) where, q, θ, α, β is a distane rom the ree end, an angle rom the downward vertial diretion at q, an angle at the ree end and an angle o the nip at the ixed end, respetively. I the nip angle is even on the right and let sides, β is equal to 225 degrees. All the other variables are equal to that o equation (7). They alulated that a paper strip lops at this angle at a ondition, Κ=2.71. Κ is orrespondent to a kind o orreted overhung length whih has no unit and is independent o Young's modulus and thikness o the material. Pratially, sine basis weight ats as a load to bend a paper strip, it must be multiplied by the gravitational onstant G. Thus, equation (10) is obtained regarding Clark stiness by substituting K=2.71 into equation (9). L ET = GW 10 4 ( ), L EI ET = = (10) 20 bw 12W In the irst equation o equation (10), every unit is equal to that o equation (7). To adjust every variable to the gs system o units, basis weight was orreted as W 10-4 (g/m 2 ). In addition, G=981(m/s 2 ). In the seond equation, the units, basis weight in g/m 2, length and thikness in m and Young's modulus in dyne/m 2, an be used. Atually, drat and the vibration o the paper strip may prompt it to lop earlier than it would otherwise. Thus, a little shorter L may be measured than the true L. 4

5 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). Leading a general empirial equation is very diiult beause the oeiient varies depending on the method in whih Young's modulus and thikness are measured, as Oda et al. disussed. In our preliminary experiment to hek i this equation is right, polyethylenetelephthalate (PET) ilm having uniorm thikness was subjeted to Young's modulus alulation beause thikness o paper varies depending on the measurement method. Table 2 shows that Young's modulus alulated based on theoretial equation (10) ame lose to the dynami Young's modulus measured by the ultrasound veloity method, but is about twie as large as that in the reerene. In ontrast, Young's modulus alulated based on the empirial equation (both the sides assumed to be equal in equation (7)) was onsiderably larger than the dynami Young's modulus. In this work, equation (10) is used R a (=EI). Then, equations (4) and (5) are used to alulate Young's modulus o a oating layer. Table 2. Young's Modulus o Polyethylenetelephthalate (PET) ilm Method and equation Clark L EI 100 = bw Clark L EI 20 = bw Ultrasound veloity Reerene * (Bending mode at 2 ) Modulus, GPa Chemistry handbook, Applied Chemistry Vol. 2, Materials, Japan Chemistry Soiety ed., Maruzen, Tokyo, p1124(1986) EXPERIMENTAL Table shows the oating olor ormulation used. Calium arbonate (Brilliant-15, Shiraishi Industry), Starh (Ae-A, Oji ornstarh), SB-latex (TO-15, Mitsui Toatu Chemials) and Dispersant (Aron T-40, Toa Gosei Chemials) were used. Basestok was ommerial wood-ree ine paper (25 s Stökigt sizing degree and 64 g/m 2 basis weight) and impervious polyethylenetelephthalate (PET) ilm 100 µm thik to apply oating uniormly. Hereater this basepaper and PET ilm will be reerred-to as just basepaper and baseilm, respetively. Coating was applied manually with wire bars, #6, 10 and 16, Kumagai Riki Kogyo, then dried at an atmospheri temperature. Those were onditioned at 20 C and 65 % relative humidity or more than 24 hours (Hereater onditioning reers to this ondition.) and subjeted to measurements. Table. Formulation o oating olor Constituent parts Calium arbonate 100 SB-latex 10 Starh 5 Sodium polyarylate 0.8 Solids ontent = 50% In the experiment to examine eets o water absorption to the basepaper, distilled water was applied with a wire bar #10 to about 10 g/m 2, then dried at an atmospheri temperature. Pure Bending stiness was measured ater samples were onditioned. Coated paper and oated ilm were ut into a 5 mm 5 mm square with one edge ut sharply at 45 degrees to be observed. The speimen was adhered on a speimen stub or SEM with two-sided ondutive tape, then platinum-oated or 00 s in an ion spatter, E-100, Hitahi and observed on a ield emission type mirosope, S-4000, Hitahi. To prepare a oated ilm with rough oating/ilm interae, baseilm was hot-pressed at 200 C or one minute 5

6 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). together with a sandpaper sheet, Telon board, iron board sandwihed in this order outward on either side, as illustrated in Figure 2. The baseilm hot-pressed without a sandpaper sheet was ompared to it beause the hot-press hanged Young's modulus o baseilm a little. These baseilm sheets were oated with the olor o Table and dried at an atmospheri temperature. Clark stiness was measured aording to JIS P 814. The sample width was 0 mm. The results were rounded to three orders o a signiiant igure. Pure bending tester has a harateristi that a paper strip is bent with the same urvature along the whole span. This tester measures early stiness at the beginning o a bend and average stiness. In this work, only early stiness is plotted in every igure. Coated produts were ut basially to a 100 mm 100 mm square ater onditioning. The sample was set on a tester with a span o 50 mm in Mahine diretion in the ase o paper and a width o 100 mm. The tester used was pure bending tester JTC-1, Nihon Seiki. Young's modulus o a oating layer was alulated aording to equations (5) and (6) rom Clark stiness and aording to the equation, S PB = ET /12 rom pure bending stiness. Young's modulus o a oating layer was examined by hanging olors ormulation. Binder mixture was prepared only with starh and SB-latex. The mixture ratio was ive sorts; starh:sb-latex = 0:15, :12, 5:10, 7:8 and 10:5. Those were applied on baseilm, then dried at an atmospheri temperature. Clark stiness o the oated ilm was measured ater onditioning. Calium arbonate o the olor o Table was all replaed with plasti pigment(pp) here. The PP used was polystyrene emulsion P-2 and P-4, Mitsui Chemials, with harateristis listed in Table 4. The olor was prepared to be 27 to % solids and applied on baseilm then dried at an atmospheri temperature. Clark stiness was measured ater onditioning. Table 4. Resin onstants o plasti pigments Plasti pigment P-2 P-4 Appearane Milky-white Milky-white Major Ingredient Styrene Styrene Struture Dense (not hollow) Dense(not hollow) Involatile ingredients, % PH Visosity, ps Partile diameter, µm Baseilm was used to make uniorm oatings. Two kinds o olors shown in Table 5 were used. First, olor SF was applied manually with a wire bar #16 and dried at an atmospheri temperature. Then, olor SC was oated additionally on it in the same way ater the irst layer was well dried. Another kind o sample oated in the reversed order o the two olors was also prepared. Pure bending stiness was measured. Table 5. Formulation o oating olor or double oating Color type SF(Starh-ree) SC(Starh-ontaining) Calium arbonate SB-latex Starh 0 5 Sodium polyarylate unit: parts Solids ontent = 50% To estimate a general range o Young s modulus o basepaper, several wood-ree and wood-ontaining basepapers were used. RESULTS AND DISCUSSION 6

7 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). Figure shows Clark stiness and pure bending stiness o the oated ilm and pure bending stiness o the oated paper. Clark stiness has a dimension o stiness divided by the weight o its own. Consequently, it dereases as oat weight inreases beause Young's modulus o the oating layer is low or its high relative density. The data sattered beause it is diiult to apply oating uniormly by hand and the results depended on whether the thik side was nipped or the thin side. Pure bending stiness inreased additionally by the amount o stiness that the oating layer shared with inreasing oat weight. Figure 4 shows Young's modulus o the oating layer alulated rom the three kinds o stiness in Figure. Young's modulus o the oating layer on the ilm was about 0.7 GPa rom Clark stiness and 0.5 GPa rom pure bending stiness. These data sattered to some extent or the same reason as beore - nonuniorm thikness, but did not depend on the oat weight. On the other hand, the oat weight dependene was ound with the oating on paper. Some o them resulted in negative values below about 17 g/m 2 oat weight. This apparently stems rom that Young's modulus was misalulated. The possible reasons or this are: (1) inreased thikness and dereased Young's modulus due to water absorption, (2) moisture ontent hange even in the same atmosphere due to water absorption, () Pore-illing near basepaper surae with a oating and a roughened oating/basepaper interae due to dehydration rom a wet oating, (4) Changes in oating omposition and strutures during onsolidation proesses and the dierene in Young's modulus rom a oating on ilm. I reason (4) is true, this is speial to paper and the evaluation o a oating on ilm is not appliable to the paper ase. However, reasons (1) to () are true, oating on paper is not appropriate to evaluation o Young's modulus o a oating layer. From here, those possible reasons were examined. Table 6 shows hanges in physial properties o basepaper that absorbed distilled water. Water absorption swelled the basepaper by 6 % in thikness. The basis weight was inreased 2 % beause o the hysteresis via high moisture ontent (wetting). Then, Young's modulus was redued by 4 %. This suggests that Young's modulus o unwetted basepaper annot be used as an alternative Young's modulus o the basepaper layer, thus misalulating Young's modulus. Table 6. Changes in sheet properties o wood-ree paper by water appliation No water appl. Ater water appl. Average (Std. dev.) Average (Std. dev.) Thikness, µm 80.2 (0.5) 85.0 (0.8) Basis weight, g/m (0.6) 65.6 (0.5) Pure bending stiness, g m 1.22 (0.06) 0.95 (0.1) Young's Modulus, Gpa 2.77 (0.12) 1.82 (0.24) Figure 5 shows pure bending stiness o the oated ilm with a rough or smooth oating/ilm interae. Stiness o the oated ilm with a smooth interae was larger than that or a rough interae. This means that the smoother the interae, the larger the oated sheet stiness, thus implying that Young's modulus o a oating layer would be misalulated i the oating was applied on basepaper due to roughening 14). Sanning Eletron Mirographs, Piture 1 and 2, are ross setions o the oated paper and the oated ilm, respetively. It is revealed that the oating illed the surae pores o the basepaper and that the interae is rough, while the oating/ilm interae is very smooth and the thikness is onstant. This exempliied that this dierene was one o the reasons why the alulated results o Young's modulus were dierent between paper and ilm in Figure 4. Figure 6 shows Young's modulus o the blend ilm made on baseilm only rom starh and SB-latex. With inreased starh ratio, the blend ilm Young's modulus inreased remarkably. The ratio % orresponds to the binder omposition o the olor used in Figure 4. The Young's modulus o the blend ilm then was 0.60 GPa, being 7

8 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). lose to the average o Young's modulus (0.66 GPa) o the oating layer o Figure 4. Figure 7 shows Young's modulus o the oating layer ontaining only plasti pigment(pp) in plae o alium arbonate as a untion o ormulated parts o starh (The total binder parts was 15). Remarkable starh eets on Young s modulus were ound with the two PPs irrespetive o the partile diameter (0.2 µm and 0.50 µm). Some data o Young's modulus was alulated as negative values, presumably beause the nonuniorm oating (thik parts loally present) misled the thikness to a larger value than the average. The larger the partile diameter o PP, the higher the Young's modulus. It is probably beause the small partile made the struture tighter during onsolidation. Young's modulus o the oating ontaining only alium arbonate as pigment is also plotted rom Figure 4. Young's modulus o the oating in the ase o the smaller PP was lose to that in the ase o alium arbonate. However, PP is expeted to make Clark stiness (stiness against the weight o its own) o the whole oated paper larger than mineral pigments even i Young's modulus o the oating layer is on the similar level beause PP is lighter. Figure 8 shows Young s modulus o basepaper. Ash ontents o wood-ree A(WF-A) is higher than wood-ree B(WF-B). Generally, Young s modulus o base paper are between 0.5 and.5 GPa and depends on pulp ormulation, pulp reeness, iber orientation, size press and so on. As shown on beore, the ase o oating layer, Young s modulus is between 0.1 and 2.0 GPa depends on binder ormulation, binder ontents, pigment paking and so on. As a measures to improve oated paper stiness, external oating o high Young's modulus ontaining a higher ratio o starh was tried. Figure 9 shows pure bending stiness o the oated ilm versus the total oat weight. The oated ilm with the starh-rih (SR) oating external exhibited higher stiness than internal. This suggests that external oating o a olor ontaining onstituents to be sti ats to improve the stiness o the whole oated paper. Pratially, too muh ormulation o starh to the external oating should redue the pik strength. Consequently, are must be taken in deiding the right ormulation ratio o starh to maintain other properties. CONCLUSIONS 1. The equation was led to alulate Young's modulus o a oating layer rom stiness and thikness both o a one-sided oated sheet and only basesheet (paper or ilm). Then, Clark stiness was interpreted theoretially and aurately, then the method by whih Young's modulus o a oating layer was alulated rom Clark stiness was established. 2. Young's modulus o the oating layer on paper was ound to be misalulated. It is beause thikness (due to swelling) and basis weight (due to hysteresis) inreased ater oating and those values o unwetted basepaper were not appliable to alulation. Thereore, impervious ilm must be used.. Young's modulus o the blend ilm made rom starh and SB-latex inreased with inreased starh ratio. Starh helps improve Young's modulus o a oating layer. Plasti pigment o the smaller partile diameter made the oating Young's modulus higher, but was lose to that o alium arbonate. However, light PP ould improve stiness against the weight o its own. 4. External deposit o starh-rih (sti) oating improved stiness o the whole oated ilm. 5. Young s modulus o base paper is between 0.5 and.5 GPa and depends on pulp ormulation, pulp reeness, iber orientation, size press and so on. The ase o oating layer, Young s modulus is between 0.1 and 2.0 GPa depends on binder ormulation, binder ontents, pigment paking and so on. 6. Partiularly with regard to stiness in a bending mode, a oating layer has onsiderable eets. This is beause the strain the outlying oated layer undergoes is muh larger than that the inner basepaper layer does. Literature 1) KAZUMORI, K., NAITO, T., USUDA, M. and KADOYA, T., Relation between handle and bending properties o paper, Japan Tappi J., 5(8): 47(1981) 2) FELEERS, C. and CARLESSON, L., Measuring the pure bending properties o paper, Tappi J., 62(8): (1979) ) NAITO, T., USUDA, M., KADOYA, T. and KATO, M., Liveliness o Paper, I. Method o measurement, Japan Tappi J., 7(4): 5(198) 4) NAITO, T., and ABE, T., The pure bending properties o paper, 1991 International Paper Physis Conerene 8

9 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). Proeedings, 59(1991) 5) NAITO, T., IIDA, K. and ABE, T., The 55th Pulp and Paper Researh Conerene Proeedings, 40(1988) 6) NAGAI, T. and MATSUDA, N., Eet o oating layer on oated paper stiness, The 51st Pulp and Paper Researh Conerene Proeedings, 44(1984) 7) OKOMORI, K., ENOMAE, T. and ONABE, F., Evaluation and ontrol o oated paper stiness, Japan Tappi J., 51(4): 59(1997) 8) OKOMORI, K., ENOMAE, T. and ONABE, F., Evaluation and ontrol o oated paper stiness, Tappi Advaned oating Fundamentals Symposium Proeedings: P121-12(1999) 9) CLARK, J. D A., "Determining the rigidity, stiness and sotness o paper", Paper Trade Journal, 100(1): 41(195) 10) Tappi Test Method T451m-84, Flexural properties o paper(clark Stiness) 11) JIS P Testing method or stiness o paper by selbending 12) ODA, M. KADOYA, T., USUDA, M. and KIMURA, M., Stiness o paper (1), Subjetive judgement and Clark s Stiness measurements, Japan Tappi J., (): 5(1979) 1) TAKADERA, M., NAKAI, H., OHIRA, S. and SHINOHARA, A., "Priniple o measuring abri stiness by Clark method (II)", Sen-i Gakkai Preprints 1990(G), The Soiety o Fiber Siene and Tehnology, Japan, S-92(1990) 14) LEPOUTRE, P. and SILVEIRA, G., "Examination o ross-setions o blade- and roll-oated LWC paper", Journal o Pulp and Paper Siene, 17(5): J (1991) 9

10 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). y y 0 b h +h h N z Coating layer h h T N 0 Basepaper x Fig. 1. Shemati ross setion o oated paper or alulating seond moment o area. Hot-press Hot-press Iron board Telon board Sand paper PET ilm Sand paper Telon board Iron board Fig. 2. Order o sheets in hot-press to make a rough 10

11 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999) Clark stiness, 1/100 m Coated ilm Coated paper Coated ilm Pure bending stiness, g m Coat weight, g/m Fig. Clark stiness and pure-bending stiness o oated paper and ilm as a untion o oat weight. Young's modulus, GPa Clark, on ilm Pure bending, on ilm Pure bending, on paper Coat weight, g/m 2 Fig. 4 Calulated Young's modulus o oating on paper or ilm as a untion o oat weight. 11

12 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). 4 Pure bending stiness, g m Hot-pressed with sand paper Hot-pressed without sand paper Coat weight, g/m 2 Fig. 5 Inluene o interae shape on relationship between basis weight o oated ilm and pure bending stiness. 2.5 Young's modulus o blend ilm, GPa Starh ratio, % Fig. 6 Stah eet on modulus o latex/starh blend ilm 12

13 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). 1.5 Young's Modulus o oating, GPa Small PP Calium Carobnate Large PP Starh added, parts Fig. 7 Starh and plasti pigment(pp) eet on oating modulus. Young's modulus, GPa Clark Pure Bending WF: Wood ree WC: Wood Containing 0.0 WF-A (MD) WF-B (MD) WC-A (MD) WC-B (MD) WC-B (CD) Rough WC (MD) Rough WC (CD) Fig.8 Young's Modulus o Basepaper 1

14 Proeedings o Tappi advaned oating undamentals symposium, Tappi press, Atlanta, USA, (1999). 4.0 Pure bending stiness, g m SF(under)+SC(top) SC(under)+SF(top) Coat weight, g/m 2 Fig.9 Eet o double-oating order o starh-ontaining(sc) and starh-ree(sf) olors on pure bending stiness o oated ilm. Piture 1. Cross setion o oated paper Piture 2. Cross setion o oated ilm. 14