PEER-REVIEWED STICKIES Full characterization of stickies in a mill: the need for a complementary approach

ANGELES BLANCO, RUBEN MIRANDA, CARLOS NEGRO, CONCEPCION GARCÍA-SUAREZ, MARTA GARCÍA-PROL, AND ALVARO SANCHEZ

ABSTRACT: To ensure machine runnability, trouble-free converting, and high quality products, stickies must be removed during stock preparation of recycled . However, the stickies removal effi- ciency along the process is not easy to assess since there are many different types of stickies that have to be considered in a mill stickies audit. Total stickies, macro-stickies, micro-stickies, and secondary stickies are quantified by different methods. Macro-stickies allow us to monitor the removal efficiency of the process while micro-stickies and sec- ondary stickies predict the deposition potential of the pulp under different conditions. Micro-stickies pre- dict calcium-soap deposits and secondary stickies predict the destabilization of the dissolved and colloidal material. Cationic demand only predicts a certain type of stickies. Therefore, an integrated approach for the full characterization of stickies throughout the process is necessary. Application: The full characterization of stickies along the process allows papermakers to identify contaminants and to improve stickies control in the mills.

raphic are bulk grades coming contaminant material with the classification and definition of stickies, Gwith a quality spectrum ranging furnish (hot melts, contact adhesives, many different classifications have from newsprint to super calendered coating binders, starches, binders, been described in previous studies. (SC) and lightweight coated (LWC).The etc.) [2]. Stickies deposits are usually First, stickies were classified as macro- recovered paper content varies accord- formed by a mixture of acrylates, eth- stickies and micro-stickies according ing to end product requirements, and ylene vinyl acetate, polyvinyl acetate, to their size.Then micro-stickies, stick- only white paper recycled grades are polyacrylates, styrene rubber, etc. ies that pass through 150 µm, 100 µm, used. Since these papers are produced [3–5].These contaminants tend to be or even 80 µm slotted screens, were on high-speed paper machines, hydrophobic, tacky, low-surface ener- further classified.According to Doshi runnability is a key factor both in the gy,soft, and deformable materials. et al, the following approximate classi- itself and in converting The presence of stickies in recy- fication can be considered [8]: operations. On the other hand, the low cled fibers can cause runnability prob- • Suspended stickies: 20 µm to 100 µm added value of paper means operating lems, increasing machine downtime • Dispersed stickies: 1 µm to 25 µm economics also have a high priority.To caused by breaks and associated clean • Colloidal stickies: 5 µm to 0.01 µm ensure trouble-free economic convert- ups.They also: • Dissolved stickies: < 0.01 µm. ing and high quality printing products, • decrease wire and felt lifetimes; But this classification by size is not all contaminants have to be removed • reduce product quality due to pick- enough. It is also necessary to consider from the stock. One of the main prob- ing, which leads to hole and spot for- the source of stickies generation.Stickies lems during stock preparation of recy- mation and poor appearance; that carry over from the repulping cled pulp is stickies removal. • reduce efficiency of converting and process are termed native or primary Stickies are considered, in general, printing; and stickies. Stickies that precipitate out of organic contaminants causing major • limit levels of fiber substitution. the pulp due to changes in pH,tempera- problems in mills using recovered In summary, stickies contribute ture, or the chemical environment [9] paper as a raw material [1]. Sources of negatively to mill productivity since are termed potential or secondary stick- stickies are natural furnish (wood they increase mill downtime, lower ies. Secondary stickies are much more ), process chemicals used in the product quality and increase chemical complex because they result from phys- plant (coating formulations, sizing and maintenance costs [6,7]. ical or chemical changes which occur all agents, wet-end additives, etc.) and in- Since there is a lack of an accepted along the paper manufacturing process. VOL. 6: NO. 1 TAPPI JOURNAL 19 STICKIES

Because stickies are so diverse,there but the correlation between the amount ing process. The recycled paper is is no universal set of solutions to reduce of stickies material in the furnish and the pulped in a high consistency batch their effects.The industry is focused on cleanliness of the paper is not always ob- pulper.The pulp is extracted through a practical aspects of stickies, e.g., pre- vious.Great effort has been taken to eval- perforated plate,as a first separation of vention, removal, and dissimulation. uate the effects of process variables on and coarse contaminants. Sta- There are four common approaches in stickies concentration and to study stick- ples and other heavy contaminants are the mill to stickies control: ies removal,control,and adsorption onto removed by high-density cleaning, a 1) prevent the release of stickies the fiber material.The effects of white four-stage hole screening (1.2 mm), from the raw material (e.g., controlling water recirculation and deposition of and a set of 0.25 mm slot screens.The pulping and disperging time, pH, and stickies are more difficult to analyze be- pulp then goes through the pre-flota- consistency), cause re-agglomeration of dissolved and tion unit (six primary and two sec- 2) remove stickies during stock colloidal material can occur. ondary cells), the forward cleaners, preparation (e.g., screening, cleaning, Properties of stickies can be meas- and the fine slot screens (0.15 mm) be- flotation), ured in different ways, often varying fore thickening in a disk filter and a 3) minimize the negative effects on with the laboratory sample preparation screw press. Remaining contaminants paper appearance (e.g.,dispersion),and technique and analytical method used. are broken down into sub-visible par- 4) prevent deposit formation in the Macro-stickies analysis techniques have ticles in the disperger.If necessary the paper machine (e.g., detackifiers, talc, been standardized; however this is not pulp can be bleached before post- fixatives, barrier chemicals). so for micro-stickies measurements flotation in a unit of 4+1 cells. Finally This set of solutions allows paper [12].The challenge is to quantify stick- the pulp is thickened by means of a mills to live with stickies, but the only ies evolution along a process and im- disk filter and screw press and stored, definitive solution is to remove them prove stickies control without a suitable ready to be sent to the paper machine. from the process. method for monitoring stickies. This As shown in Fig. 1, nine sample Parameters affecting stickies re- concern has increased in recent years points have been selected to carry out moval efficiency can be divided into due to the lower quality of the available the mill stickies audit.The first sample three main classes: furnish parameters, recovered paper, which increases the point was the outlet of the hole screen design parameters, and operating pa- amount of contaminants in the recov- because of the variability of the stick- rameters. Furnish parameters can be ered paper.Another issue involves envi- ies level before this stage, depending considered to comprise of pH,tempera- ronmental concerns, which are moving on the raw material quality, but inde- ture,fluid viscosity,fiber properties,and the industry toward closed water cir- pendent of the process. contaminant characteristics.The design cuits, thus further stimulating the accu- Water flows are counter current to of stock preparation systems for graph- mulation of contaminants. Finally, there the pulp flow.Fresh water enters the sys- ic paper grades nowadays is very simi- are the needs of the mill to be more tem at the paper machine.Water flows lar, and the removal efficiency depends competitive by increasing productivity back from the paper machine through mainly on process optimization based and reducing costs. loop 2 and,finally,through loop 1. on mill operator experience. Removal This paper presents an integrated can be facilitated under certain condi- approach for full stickies characteriza- METHODS tions: fine slots with a gentle surface, tion along a line of a newsprint Total stickies low rotor tip speeds, low stock consis- paper mill.Total stickies, macro-stickies, Total stickies content was measured by tencies, low hole or slot velocities, uni- micro-stickies, and secondary stickies solvent extraction with dichloromethane. form flow through the screen baskets, are quantified and their implications for The pulp samples were dried at 105ºC low shear and pressure forces, low tur- the process are discussed. without any pre-treatment. Extraction of bulence, etc. [10]. A compromise be- 10 g of pulp was performed in a Soxhlet tween capacity and efficiency must be MILL DESCRIPTION according to TAPPI T 204 cm-97 “Solvent established due to the combined effect PM61 of Holmen Paper Madrid pro- extractives of wood and pulp.”After the of these parameters. An overview of duces 500 tons/day of newsprint from a extraction the solvent was recovered and contaminant removal efficiency for dif- mixture of recovered old newsprint evaporated using a rotary evaporator,in a ferent processes has been published by (ONP),old magazines (OMG),and office pre-weighed vessel.The residue obtained Moss [11]. paper (OP) with an average composition after solvent evaporation was entirely Often the investment in stock prepa- of 6:3:1.About 1%–3% of the furnish is dried in an oven at 105ºC and, finally, it ration cannot be adequately justified considered to be undesirable material. was weighed. In accordance with the through machine productivity.The paper Figure 1 shows a simplified standard, all experiments were carried quality improvements can be recognized, schematic arrangement of the deink- out in duplicate. 20 TAPPI JOURNAL JANUARY 2007 STICKIES

Micro-stickies and secondary stickies Micro-stickies, in theory,range in size from 5 to 150 ␮m. How- ever they are very difficult to isolate selectively from the stick- ies smaller than 5 ␮m.Therefore we have considered in this group all the stickies smaller than 150 ␮m.The UCM deposi- tion rotor,without destabilization of the dissolved and colloidal material,was used to determine the micro-stickies content (13). Potential stickies or secondary stickies are formed when detrimental substances,smaller than 150 ␮m,agglomerate and become tacky after being destabilized by their interaction with polymers,by a sudden change of pH or conductivity,by shear forces,etc.Quantification was carried out using the UCM dep- osition rotor with the addition of polyethyleneimine (PEI), as a destabilization agent.The amount of added PEI was the the- oretical dosage needed to reach the zero current potential of the sample, determined with a Mütek PCD 03 particle charge detector used in conjunction with an automatic titrator. The first 15 L,which passed through the Somerville exper- iment,were collected to determine micro-stickies and second- ary stickies.The consistency was around 0.2% in all cases.These waters were filtered through a dynamic drainage jar (DDJ) with a 250 µm wire to remove the fiber fraction without removing the stickies. In both cases, 1.8 L were used for the deposition tests.Deposition experiments were carried out at 50ºC for 1 h. The sticky material collected in the internal and external stain- less steel film collectors were quantified by image analysis using 1. Flow diagram and sampling points along the DIP 2 the stickies measurement program developed by PIRA and deinking line. UCM.The results obtained in these methods are the percentage Macro-stickies or primary stickies of covered area by deposits collected on stainless steel films Macro-stickies were considered as solid and tacky contami- [14].All experiments were carried out in triplicate. nants larger than 150 ␮m (this was the available Somerville Since not all micro-stickies and secondary stickies pass slot screen at the mill).Contaminants were screened from the through the Somerville slots with the first 15 L,and since some pulp following the TAPPI T 275 sp-98.The pulp, at a consis- dissolved and colloidal material may destabilize and stick to- tency of less than a 1% (w/w), was introduced into the gether during collection and dilution of the samples,some pre- Somerville vibrating screen. For each experiment the neces- liminary studies were carried out to quantify this effect.It was sary amount of pulp suspension, equivalent to 75 g of dry proved that 70% of micro-stickies and secondary stickies were pulp, was screened.The total screening time was 20 min.All collected in this way with an average error below 10%. experiments were carried out in triplicate. Contaminants remaining on the surface of the screen RESULTS were washed with pressurized water and collected.The Solvent extraction contaminant suspension was then filtered in a Rapid- Extraction with dichloromethane of the full pulp was car- Köthen through a black filter.After dewatering a coated ried out to determine all types of extractable stickies pres- paper (supplied by Voith) was pressed on the black filter. ent in the sample, independent of their size. Figure 2 Both papers were dried with vacuum for 10 min.Then the shows the average results obtained from two replicates.The was removed and the stickies appeared as average error in measurements was 10%. white specks on the black filter.After washing, stickies Initially the extractible content is 11 g/kg dry pulp.This were dried again with a siliconated paper on them.After value is reduced along the deinking line to 2 g/kg dry pulp, that, the remaining non-sticky material on the black filter which means a total removal efficiency of more than 82%. was painted with a black pen and, finally, stickies were Fifty percent of this material is removed in the first loop, quantified by image analysis in a dot-counter,according to mainly in the flotation unit (31% of the total), while only INGEDE Method 4 99-12 “Analysis of macro stickies in 32% is removed in the second loop,mainly during flotation deinked pulp (DIP)” for analysis of macro-stickies in and thickening. The high efficiency removal of deinked pulp. dichloromethane extractives achieved along the process is VOL. 6: NO. 1 TAPPI JOURNAL 21 STICKIES

2. Extractives content evolution along the DIP2 line. 3. Macro-stickies evolution along the DIP2 line. in agreement with the reference liter- modern deinking mills varies from 200 tions to determine if the calcium-soap ature [4, 15]. to 400 mm2/kg.In a study carried out in deposits that are not removed during Macro-stickies 16 North American deinking ONP/OMG pre-flotation are removed at a later stage. The results of macro-stickies measure- mills, the average stickies removal was Calcium-soap micro-stickies were re- ment along the deinking line,DIP 2,as 64.5% with upper quartile at 82%.Aver- moved before post-flotation (Fig. 5). deposited area and as number of age DIP stickies concentration was In the outlet of both the fine slot macro-stickies are shown in Fig. 3. 1310 mm2/kg,with an upper quartile at screen of low consistency and disk filter Results show that 90% of total 1700 mm2/kg in coarse screen accepts. 2,the increase of micro-stickies is small- macro-stickies,expressed as area,are re- Reference data shows that deinking sys- er.This could be due to the effect of di- moved in the deinking line at the mill, tems with 0.15 mm or less slot size in lution waters.Micro-stickies accumulate which corresponds to 60% of the total the primary stage had an average stick- in the process water and, in conse- number of stickies (always referred to ies removal efficiency of 75% while all quence, dilution waters may be an im- the first point sampled). If hole pre- the other systems had stickies removal portant source of contaminants [18].On screening is considered, the total re- efficiencies of around 55%–60% [17]. the other hand,residual chemicals pres- moval efficiency would be about Micro-stickies and ent in process water may also produce 94%–95%. Stickies are mainly removed secondary stickies deposits under certain conditions. in loop 1.At the end of loop 1, macro- The measurements of small and second- If we consider the measurements of stickies level was about 200 mm2/kg, ary stickies are summarized in Fig. 4. secondary stickies, it is observed that and this level increases at the end of The quantity of micro-stickies in- the trend followed by micro-stickies loop 2 when the pulp is diluted with creased in three points along the deink- and secondary stickies is different.As water coming from the paper machine. ing line:accepts of medium consistency was expected, the deposits obtained As was expected, fine screens were the slot screens,accepts of low consistency destabilizing the potential stickies are most efficient units (82% of reduction fine screening,and accepts of disk filter higher,because in this case both micro- from the inlet to the outlet), but they 2.The case of the slot screen of medium stickies and secondary stickies are only remove 36% of total macro-stickies consistency outlet is the most impor- measured. Only the outlet of the slot in this case,because the rest had already tant increase as micro-stickies are four screen at medium consistency presents been removed by this stage. times higher than in the inlet. Micro- a different behavior.When PEI is added The comparison of these data with stickies may be produced by a shock of the increase of micro-stickies after the reference data shows that this mill has a calcium.The soap added to the pulp be- soap addition,when the pulp is diluted, high removal efficiency. It has been re- fore the screening process may react is not observed.It may be that the poly- ported that in Europe over 80% and with the calcium present in the dilution mer covers the tacky material forming even up to 99% of stickies can be re- water, forming sticky calcium-soap non-tacky aggregates. moved [16].This performance is due in micro-stickies. It is important to notice Pre-flotation removes 70% of micro- great part to significant advances in fine that these micro-stickies (calcium-soap) stickies, including calcium-soap agglom- screening, centrifugal cleaning, and are removed by flotation. erates, and 20% of potential stickies. flotation technologies during the last 20 The carryover of soap was further Cleaners remove 50% of micro-stickies years.The final average stickies area in studied under different process condi- but, logically, they do not remove dis- 22 TAPPI JOURNAL JANUARY 2007 STICKIES

4. Micro-stickies and secondary stickies deposition 5. Monitoring micro-stickies to monitor the carry over along the DIP2 line. of soap. solved and colloidal material.Fine screens increase micro-stick- ies and secondary stickies. Post-flotation does not remove micro-stickies in this case. Finally, the level of secondary stick- ies increases considerably when the pulp is diluted with water from the paper machine. Screening increases the level of stickies because the shear forces break down part of the bigger stickies that are being re- moved, increasing the amount of smaller stickies. Filtration steps also increase the level of micro-stickies.Since micro-stick- ies mainly stay in the fiber fraction, they can be released in these steps.This effect is the result of fiber thickening,and it is enhanced by the dilution of rejects at each stage with back- water.The overall effect is a wash out of micro-stickies from the rejects. On the other hand, a temperature difference be- tween the pulp and the dilution water may also favor the desta- 6. Comparison of different methods to quantify the bilization of dissolved and colloidal material. different types of stickies. Comparison of methods Figure 6 shows the comparison of the results obtained unit in the reduction of both small micro-stickies and extrac- from the different methods used to quantify the different tives.Also, the fine slot screens are not effective for removing types of stickies indicating the sample consistency.The re- micro-stickies or extractives.According to Delagoutte et al., moval efficiency of macro-stickies and dichloromethane ex- micro-stickies constitute the principal stickies species involved tractives does not present a good correlation between them, in the drying section deposit phenomenon,and the separation probably due to the different sizes of stickies measured in techniques, screening and cleaning are not able to remove each case. Johansson et al. also observed this with the same micro-stickies.The only solution is to turn to physical or chem- size definition of macro-stickies [4].There are two main dif- ical treatments,such as flotation or dissolved air flotation used ferences between the two data:the efficiency in the fine slot as water clarification systems [15]. screens and in the pre-flotation. In the reduction of macro- Comparing the efficiency of the different stages in re- stickies, the most individually efficient unit is the fine slot ducing secondary stickies and solvent extractions, the trend screen, while for dichloromethane-extractives content it is is very similar with only a difference in the disk filter 2.This the pre-flotation.The importance of flotation to remove may be due to the type of contaminants coming from the dichloromethane-extractives has already been considered by paper machine.According to Johansson et al.and Delagoutte Delagoutte et al. [15]. Finally,the fine slot screens do not re- et al. the contribution of dissolved and colloidal fractions to duce the dichloromethane extractives content. the extractives content is relatively low.Approximately 10% If we compare the efficiency of the different stages in re- of the whole deposit potential comes from the colloidal ducing extractives content and micro-stickies, although there stickies, but in Delagoutte’s work the size limit is 1 µm [4, is not a good correlation between them, the same major ten- 15].In the experiments we have conducted,extractives were dencies are achieved.The pre-flotation is the most efficient carried out from the full pulp.Secondary stickies were meas- VOL. 6: NO. 1 TAPPI JOURNAL 23 STICKIES ured as micro-stickies and potential tential problem of stickies along the tial, measured with the UCM deposi- stickies after filtration of the pulp process. Macro-stickies measurements tion rotor, is important to study the through a 150 µm slot screen. are necessary to monitor the stickies re- carry over of soap along the process. Finally, the cationic demand of the moval efficiency at the different stages; supernatant of the pulp samples was however they do not predict deposit PRECAUTIONARY SAFETY also measured as a reference. It is ob- problems. Cationic demand only pre- STATEMENT served that cationic demand is not dicts a certain type of potential stickies. Dichloromethane used in solvent ex- enough to predict stickies deposits in The proposed integrated approach tractions is harmful if swallowed or in- the process except when at the end of consists of measuring macro-stickies, haled and also by skin contact. It is a loop 2 where it follows the same trend micro-stickies, and secondary stickies. possible carcinogen and mutagen in hu- as secondary stickies. Secondary stickies could be, in princi- mans. Safety gloves and glasses in com- ple, predicted by deposition studies bination with mechanical ventilation CONCLUSIONS after destabilizing the dissolved and col- are required. An integrated approach for full stickies loidal material or by extraction meas- characterization is needed to carry out urements and cationic demand data. ACKNOWLEDGEMENTS a sticky audit in a mill.Traditional meas- Micro-stickies cannot be predicted The authors thank their colleagues at urements like macro-stickies and by extraction measurements in this Holmen Paper Madrid for their sup- cationic demands do not assess the po- case. Micro-stickies deposition poten- port, especially Alvaro Tascón and Luis

improve the stickies control in the mills by use of a INSIGHTS FROM THE AUTHORS complementary approach in stickies analysis meth- Stickies are still one of the remaining issues in the use ods. Influence of each process step on stickies con- of recovered paper for paper manufacturing and have tent can help to increase the knowledge of how the an important effect on mill competitiveness. Our systems run and average values of stickies can be study demonstrates the need of a complementary ap- helpful as benchmarking data to compare efficiency proach for solving problems associated to stickies in of the process steps in different mills. Furthermore, papermaking. Every research institute and some mills mills may learn good practices to minimize forma- have developed stickies test methods but each tion of micro-stickies and secondary stickies. method, considered separately, cannot predict all the The next step is to complete other surveys in complex phenomenology associated to stickies. which conditions in the paper mill are different, e.g. The most difficult task was coordinating the work of different final product. Also, a detailed study of some all people involved in the research. Working together process stages can be of great interest for studying with a mill implies also a high degree of coordination process conditions affecting stickies and their opti- and cooperation. The main discovery of this research mization for a better stickies removal. was the need of a complementary approach for a complete characterization and understanding of the evolution of stickies along a deinking line. The use of Blanco and Negro are professors at Universidad Complutense de Madrid (UCM), Department of Chemical only one test method, separately, does not cover the Engineering; Miranda, García-Suarez, and García-Prol are whole problematic of stickies. PhD students at UCM. Sanchez is control and development The full characterization of stickies along the manager, Holmen Paper Madrid; email Blanco at ablan- process allows mills to identify contaminants and to [email protected].

Blanco García-Prol García-Suarez Miranda Negro Sanchez

24 TAPPI JOURNAL JANUARY 2007 STICKIES

Rodriguez.We also acknowledge the fi- Errigo, L., TAPPI J. 80(4): 63(1997). M.C., et al., European pat. 0922475 (Feb. 11, 1998). nancial support of the project PROLI- 6. Blanco, A., Negro, C., Monte, C., et PAPEL-CM S-0505/AMB/0100 and the al., Prog. 11(2): 14. Blanco, A., Monte, M.C., Otero D., research grant of R. Miranda from the 26(2002). et al., Pulp Paper Can. 101(9): Autonomic Community of Madrid. TJ 7. Doshi, M.R., Recent Advances in 40(2000). Paper Recycling–Stickies, Doshi & 15. Delagoutte, T., Brun, J., and Gal- Recieved: July 9, 2004 Associates, Appleton, Wisconsin, land, G., New Technological Devel- Accepted: October 1, 2006 USA, 2002. opments in Paper Recycling, IPE- 8. Doshi, M., Blanco, A., Negro, C., et CTP-PTS, Valencia, Spain, 2003, p. LITERATURE CITED al., Prog. Paper Recycling 13(1): 25. 1. Blanco, A., Negro, C., and Tijero, J., 44(2003). 16. Heiss, O.U., Kemper, M., Wiese, Paper Recycling: An Introduction to 9. Doshi, M., Prog. Paper Recycling H. et al., TAPPI J. 83(3): 73(2000). Problems and Their Solutions, Euro- 13(3): 4(2004). 17. Doshi, M.R., Prog. Paper Recy- pean Communities, Belgium, 1998. 10. Rienecker, R., and Bergfeld, D., cling 12(4): 31(2003). 2. Haynes, R.D., Prog. Paper Recy- 54th Appita annual conference pro- 18. Garver, T.M., Xie, T., and Boegh, cling 12(2): 19(2003). ceedings, vol. 2, pp 449-458, Aus- K.H., TAPPI J. 80(8): 163(1997). 3. Wilhelm, D.K., Makris, S.P., and tralia, 2000. Banerjee, S., TAPPI J. 82(12): 11. Moss, C.S., TAPPI J. 80(4): 63(1999). 69(1997). This paper is also published on 4. Johansson, H., Wikman, B., Lind- 12. Doshi, M.R., Blanco, A., Negro, www.tappi.org ström, E., et al., Prog. Paper Recy- C., et al., Prog. Paper Recycling 12(4): and summarized in the January cling 12(2): 4(2003). 35(2003). issue of Paper360º magazine. 5. Hsu, N.N.C., Schroeck, J.J., and 13. Blanco, A., García, J., Monte,

CORRECTION An error appeared in the paper “Calculations relating to web buckling resulting from roller misalignment,” by James K. Good and Joseph A. Beisel, which ran in the December 2006 TAPPI JOURNAL (Vol. 5, No. 11). Figure 5 was missing from the published paper and not referenced in the relevant paragraph on p. 12. The figure and corrected paragraph are as follows:

VERIFICATION OF crometer. The down- TROUGH MODEL stream rollers sit upon Expression (14) provides a model for an adjustable table of a predicting the occurrence of former lathe bed so troughs.A set of experiments were that the web span conducted to test the validity of the length (a) is easily ma- displacement form (1), the shear and nipulated. Tests were tension stiffening assumptions,and to run for polyester, verify that the web orthotrophy was newsprint, and spun- included satisfactorily. In these ex- bond polypropylene periments a downstream roller was nonwoven webs.Table I misaligned until a trough was pro- shows the properties of duced. Figure 5 shows the experi- these webs. In these mental setup.The web is traveling 5. Experimental setup. tests web tension and from left to right in this picture and span length were set. ␪ the horizontal span is the test span. constant web edge position and web The misalignment ( j) was slowly in- Note the troughs in the web. Also, tension is measured.The downstream creased until troughs were pro- note the absence of troughs at the roller is mounted upon a yoke, as duced.The span length would then ␪ web edges (y = 0,b). Before entering shown.The rotation ( j) of the yoke is be set to a new value and the experi- the test span, a web guide maintains precisely adjusted using an end mi- ment was repeated.

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