1. Introduction

Sizing of paper is employed as a treatment to hinderthe penetration of water or ink into paper. Recently,various highly converted papers have been developed andthe prevention of water penetration is very importantfunction for some of them. Many evaluation tests forpaper sizing have thus been developed as waterpenetration, absorption and surface tests [1,2]. Amongthese, the Stöckigt, Cobb and contact angle tests arerepresentative of these, respectively. The Stöckigt test isthe most popular sizing test in Japan, although it is notwidely used in other countries. The Hercules test is themost popular in American and European countries, butnot in Japan. Thus, the purpose of this study was toreexamine various tests for sizing including the above byusing internally sized paper samples containing differentdoses of sizing agent and having different basis weight.

Further, the Klemm test, which has been employed as atest for water absorptiveness of non-sized papers, wasalso conducted as a test for sizing.

2. Experimental

2.1 MaterialsThe sized paper samples were laboratory made

handsheets prepared by an internal application method.

An Examination of Various Evaluation Tests for Paper Sizing－A Proposal to Use the Klemm Test for Sizing Evaluation－

Noriyuki Tai＊1 and Tatsuo Yamauchi＊2, #

＊1 R&D Department, Arakawa Chemical Industries, LTD., 1-1-9, Tsurumi, Tsurumi-ku,Osaka 538-0053, Japan

＊2 Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan

# corresponding author＊ A part of this report was presented at 2012 Pulp &Paper Research Conference, Japan.

Abstract : This study compared various sizing evaluation tests, including the Stöckigt and Cobb tests as the mostpopular methods, by using papers of varied basis weight and varied dose of sizing agent. Many tests, including Stöckigt,Hercules, KBB and Cobb, are severely affected by basis weight. None of these except Cobb are sufficiently sensitive toevaluate light sizing, because they measure water penetration in the Z-direction and the distance is quite small. TheKlemm test, which has been used for water absorptiveness of non-sized paper, determines the absorptiveness in the X-Ydirection and is sufficiently sensitive to evaluate even light sizing as an absolute sizing degree. The interconnected porestructure of paper makes the absorptiveness in the X-Y direction equivalent to that in the Z-direction. The StandardKlemm test gives the absorptiveness height for 10 min testing and is independent of basis weight. A shorter testing timethan 10 min could be used but the absorptiveness height is too small to detect for heavy sizing. Further, the headingedge of water uptake is often vague, and thus the absorptiveness height can be replaced by the weight increase due towater absorption (absorptiveness weight) as a more accurate measure. Furthermore, the absorptiveness weight measuredby the Klemm test which was linearly proportional to basis weight could be normalized with basis weight and specimenwidth (1.5 cm), and thus was indicated as absorptiveness height. This test was proposed as an absolute evaluation forsizing degree (Klemm test for sizing evaluation) in this report because it is independent of basis weight and is sensitiveenough to measure sizing degree accurately even with light sizing.

(Received 3 December, 2012 ; Accepted 1 March, 2013)

Technical Paper

Fig. 1 Effects of basis weight and dosage of sizingagent on Stöckigt sizing degree.

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The sizing agent used in this study was a cationic rosinsize (average particle size : 0.85 µm, viscosity: 12 mPa·sat 35% concentration) from Arakawa Chemical IndustriesCo., Ltd. The pulp used for handsheet making was acommercially available bleached hardwood pulp and wasbeaten beforehand to 380 ml CSF using a Niagara beater.Aliquots of the pulp slurry were diluted with tap water toan 1.0% concentration, and then, an aqueous suspensionof the sizing agent, which was adjusted to a concentrationof 1.0%, was gradually added to the pulp slurry at dosesof 0, 0.5, and 0.8 mass % on oven dry pulp. No otheradditives, such as alum as a retention aid, were added tothe slurry to simplify the experiment. After the addition ofsizing agent, the slurry was continuously and gentlystirred at room temperature for 1 min before sheetmolding. A series of handsheets of various basis weightfrom the above furnish were made according to JISP-8222 except basis weight, wet pressure and dryingconditions. In order to avoid a change in sheet formationaccompanied variation of basis weight from 30 to120 g/m2 at the handsheet-making, the fiber consistencyduring sheet molding was kept constant and wetcombination of sheets was conducted [3]. After wetpressing at 340 kPa, the all wet handsheets were driedwith a drum dryer heated at 80oC. All paper samples wereconditioned and then were provided for the followingtests under standard condition (23oC and 50% RH). Thedensity of almost all paper samples was around0.67 g/cm3.2.2 Tests for sizingAs tests to measure the period required water to

penetrate the thickness of the paper samples, thefollowing three tests were adopted. The Stöckigt sizingtest was conducted three times according to JIS P-8122.KBB sizing degree was measured three times by using atester (Kumagai Riki Kogyo Co.,Ltd) according to J.Tappi No.13. Hercules sizing degree was measured threetimes according to TAPPI test method T-530. As tests tomeasured the water absorptiveness, Cobb waterabsorptiveness was measured twice by using a tester (W.&L.E.Gurley) according to JIS P-8140, and the Klemmabsorptiveness test was conducted three times accordingto JIS P-8141. The first four methods above are tests forwater penetration or absorptiveness in the Z-direction ofpaper, while the last method (Klemm absorptiveness test)is a test for water absorptiveness in the X-Y-direction ofpaper. The water for these tests was distilled water, andfor Klemm absorptiveness test water containing 0.1%surfactant was also employed. The surface tensions,measured using a tester (Kyowa Interface Science Co,

Ltd), of the distilled water and that containing surfactantwere 73 and 39 mN/m at 23oC, respectively.

3. Results and discussion

3.1 Effect of dose of the sizing agent on thesizing degreeThe effects of the sizing agent dose and basis weight

of paper samples on the averaged sizing degree are shownin Figs.1～5, for Stöckigt sizing, KBB sizing, Hercules

Fig. 2 Effects of basis weight and dosage of sizingagent on Hercules sizing degree.

Fig. 3 Effects of basis weight and dosage of sizingagent on KBB sizing degree.

Fig. 4 Effects of basis weight and dosage of sizingagent on Cobb sizing degree.

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sizing, Cobb water absorptiveness for 60 s contact, andKlemm absorptiveness test, respectively. The first threetests showed that a lower dosage of the agent gave littlesizing effect, i.e., water instantaneously penetrated in theZ-direction of paper which was not over 0.01 cm for 60 g/m2 paper samples. In contrast, Cobb and Klemm testsshowed nearly linear relations with the dosage i.e. thesetests can detect a decrease in water absorption even withlower dosage of the agent. That is, the first three methodsare not sufficiently sensitive to detect the sizing effect atlower dosage but the last two methods are sensitiveenough to measure the sizing degree at the lower dosage.Further, the similar relationships with the dosage for thelast two methods mean that water penetrates or isabsorbed into paper irrespective of the Z- or X-Ydirections, due to the interconnectedness of the porestructure [4].3.2 Effect of basis weight on the sizing degreeAs shown in Figs.1～3, the Stöckigt, KBB, and

Hercules sizing degrees for higher dosage of the agentincreased with increasing basis weight. In these tests theincreased basis weight means a greater thickness, andtherefore water penetration in the Z-direction requiresmore time with increasing basis weight. Cobbabsorptiveness at lower dosage of the agent also showed ahigher value with increasing basis weight. Thus, thesizing degrees measured by these tests depend on thebasis weight and are a relative evaluation for sizingdegree. In contrast, the Klemm absorptiveness isindependent of basis weight, because water is absorbed inthe X-Y direction, and thus, the Klemm absorptiveness

height could be an absolute evaluation for sizing degree.3.3 Increases in Klemm absorptiveness heightand weight during the testing (A proposal touse the Klemm test for sizing degreeevaluation)The absorptiveness height is often too small to

measure at the higher dosage, and also the heading edgeof the height is often too irregular in shape and too vagueto determine the height. Considering the practical use ofpaper, the sizing effect for various aqueous liquids,having surface tension lower than that of pure water, isimportant. As shown in Fig.6, the absorptiveness heightusing pure water at the higher dosage of the agent wasnearly zero during the testing. In contrast, the heightincreased with increasing the testing time and reached1 cm after 10 min of testing if the water containingsurfactant was employed. Further as shown in Fig.6, the

Fig. 5 Effects of basis weight and dosage of sizingagent on Klemm sizing degree.

Fig. 6 Changes of absorptiveness height and absorptiveness weight (and the height converted from the absorptivenessweight) during Klemm test by using distilled water containing a surfactant for lightly and heavily sized papers(0.5 and 1% dosage on pulp, respectively ; basis weight : 60 g/m2, Another series of paper samples differentfrom those used for Fig.1～5.) and using distilled water for heavily sized paper. Absorptiveness height : circle,Absorptiveness weight : triangle, Lightly sized paper : blue color, Heavily sized paper : green color, byusing distilled water : open symbol, by using water containing surfactant : close symbol.

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increase in absorptiveness weight during the testing usingthe water containing surfactant, which is easily andaccurately measured as a weight increase, was examinedand compared with the increase in the absorptivenessheight. The increasing behavior of the absorptivenessweight during the testing was quite similar to that of theabsorptiveness height and further followed Lucas-Washburn equation [5]. Thus, the absorptiveness weightcould substitute for the absorptiveness height, indeed, itcould be better than the height due to its measuringaccuracy. Furthermore, this accuracy could allow shortertesting time, e.g., 3 or 5 min to evaluate sizing degree.However, the absorptiveness weight increased with

increasing basis weight. It was thus further normalizedwith basis weight and width of the paper specimen to givean absolute evaluation of sizing, in order to eliminate theeffect of basis weight on the absorptiveness weight. Thenormalized absorptiveness weight became theabsorptiveness height and is indicated as the far rightvertical axis of Fig.6. For example, the Klemmabsorptiveness height for the lightly sized paper at 10 mintesting was 2.0 cm, while the height converted from theabsorptiveness weight (21 mg) was 2.3 cm. Furthermore,the absorptiveness weight could be converted to itsvolume, assuming the density to be 1.0 g/cm3 and furtherassuming that the fiber-network structure was roughlymaintained even when it was subjected to the water. Theporosity (void volume ratio) of paper in a givendimension was taken as 57% by using the density of thepaper and that of cellulosic fiber as 0.67 and 1.55 g/cm3

[4], respectively. Thus, the absorptiveness height could becalculated to be 2.7 cm from the absorptiveness weight,the porosity and cross-sectional area of paper specimen,assuming the water to be occupying all of the voidvolume. These three absorptiveness heights do not agree,but are similar to each other.

4. Conclusions

The absorptiveness height of the Klemm test can bereplaced by the weight increase due to water absorption(absorptiveness weight) as a more accurate measure.Further the converted absorptiveness height from theabsorptiveness weight is equivalent to the measuredabsorptiveness height. This test is sensitive enough tomeasure sizing degree accurately even with light sizingand can be proposed as an absolute evaluation for sizingdegree (Klemm test for sizing evaluation) of lightly sizedpaper.

Acknowledgements

The authors express their thanks to ArakawaChemical, Rengo, and Showa Products Cos. Ltd, for theirfinancial support.

References

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2. N. Nakamura,”Sizing of Paper” Kitao publishing,Osaka , p.363 (1970).

3. T. Sakaemura and T. Yamauchi, J. PackagingScience & Technology, Japan Vol.21 (6) 461 (2012).

4. T. Yamauchi and K. Murakami, Handbook ofPhysical Testing of Paper 2nd Ed. Vol Ⅱ (J.Borch etal.ED) Marcel Dekker, Inc. New York , p.267 (2002).

5. N. Tai and T. Yamauchi, Proceedings of the 79th

Pulp and Paper Research Conference, p.140 (2012).

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