The Effects of Magazine and Filler on the Flotation ...infohouse.p2ric.org/ref/27/26983.pdf · Filler on the Flotation Deinking of Newsprint ... magazine addition, they are told that

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The Effects of Magazine and Filler on the Flotation Deinking of Newsprint

M.K. LETSCHER and F.J. SUTMAN

The exact roles which magazine in- clusion and filler usage play in the flota- tion deinking of newsprint have been poorly understood. The objective of this study was to define what increases in brightness could be expected when maga- zine or filler is added to the newsprint fur- nish. Another objective was to determine whether the brightness increases were due to filler retention or to improved ink removal across the flotation cell. It was concluded that the fillers in the study did not significantly improve the flotation deinking efficiency of old newsprint. Retention of synthetic silica did improve brightness, but retention of kaolin clays did not. Addition of magazine as an ash source signijkantly reducedjlotation feed brightness and increased brightness across the flotation cell. Flotation accepts bright- ness with magazine was not significantly different from that of newsprint alone. Brightness increase across the flotation cell had a strong inverse correlation with process yield. Flotation did not selectively fractionate ash into the rejects.

INTRODUCTION Ash Loading

A common belief throughout the paper industry is that efficient flotation deinking of newsprint (ONP) requires a significant ash loading into the flotation cell. Old magazines (OMG) are currently an inexpensive source for this filler.

M.K. Letscher and

Betz Paperchem Inc. 7510 Baymeadows Way Jacksonville, FL, USA 32256

F.J. Sutman

Currently, the plans for most new newsprint flotation deinking plants in- clude incorporation of substantial quan- tities of old magazines into their furnish. However it is likely that the demand for magazines as furnish will outstrip the available supply in the future. A study by Andover International concluded that the availability of OMG could be a problem as early as 1995 [l]. Inorganic fillers may be used to supplement or replace old magazines as an ash source.

The papermakers designing new flotation deinking facilities for ONP are regularly told that they will need to main- tain an ash loading of 8-10% on an 0.d. fibre basis into the flotation cell [2,3]. If they cannot maintain this level with magazine addition, they are told that ad- ditional filler must be purchased and used.

Temanex Consulting Inc. reports “a 70:30 ratio of 0NP:magazine (pig- mented) grades is recommended, since (flotation) deinking efficiency is max- imized by the presence of about 8-10qo mineral pigment which acts as a catalyst” [4]. The 8-10% filler level is probably based upon an OMG content of 30-40% of total furnish, rather than vice-versa. In turn, an OMG content of 30-40% is exactly what is collected with post- consumer ONP in many western Europe- an countries (where flotation deinking gained its initial popularity).

Deinking Efficiency The effect of filler content on

deinking efficiency is not widely under- stood, although some studies have been performed. In 1967, Raimondo observed that the percentage of ink removed was

higher when using 100% magazine stock than when using 100% newspaper. Flo- tation was more efficient when paper with a substantial filler content was used; in particular, coated “illustrated” papers worked well. Raimondo suggested that the attachment of ink to the coating lay- er, as opposed to the fibres, made the ink more easily removable from these types of papers. He theorized that the coating, rather than the fillers themselves, leads to the improved deinking of “illustrated”

More recently, Zabala and McCool studied the deinking efficiency of a 100% newsprint furnish using “moderate dis- persion’’ in the pulper and adding a col- lector to the flotation cell. They reported that deinking efficiency (as measured by the number and area of ink particles re- moved) improved with the addition of clay to the pulper. Their work “showed that 2% clay was sufficient” to achieve the enhanced deinking effect [6].

Schriver et al. studied the effect of filler addition on newsprint deinking with fatty acid and displector deinking chemis- try. They concluded that, when using fat- ty acid chemistry, the addition of a calcined clay filler provided the best brightness increase - followed by talc and zeolite. Using displector chemistry, they again found that calcined filler clays provided the best brightness increase - followed by zeolites. Schriver et al. as- sumed that filler retention did not signifi- cantly affect brightness, but did not investigate this effect [7].

Study Objectives

paper P I .

This paper assesses the utility of fillers in ONP-flotation deinking plants.

JOURNAL OF PULP AND PAPER SCIENCE: VOL. 18 NO. 6 NOVEMBER 1992 5225

This laboratory study had three ob- jectives: - Determine whether the increases in

deinking efficiency that occur with magazine usage are due to the filler content of the magazine or due to undefined factors.

- Determine if inorganic fillers by them- selves can enhance ink removal as much as magazine usage at equal pulp ash content.

- Determine what portion of the im- provement in deinked pulp brightness with filler usage is due to improved deinking efficiency and what portion is due to filler retention.

EXPERIMENTAL Experimental Design

This experiment was designed to in- vestigate the effect of filler type and con- tent on the increase in brightness across the flotation cell. Ash addition levels of 1.8 (background ash level in the newsprint), 5, and 10% were chosen. The sources of ash used were magazine; cal- cined, water-washed filler clay and No. 1 coating kaolin clays; and a synthetic amorphous precipitated silica. The phys- ical properties of the fillers are listed in Table I. The amounts of newsprint and magazine or filler used were adjusted to keep a constant 0.d. solids level in the flo- tation cell regardless of ash level or fur- nish mix. Each treatment was replicated three times and the order of the runs was randomized.

In the experiment, brightness in- creases due to ash retention were isolat- ed. A baseline brightness curve was generated for each ash source. This curve illustrated the effect which ash retention had on the brightness of repulped stock if flotation did not occur. Additional baseline ash versus brightness data were generated at the 3 and 7% filler addition levels to improve the precision of the curve.

Furnish Six-month old overissue newsprint

(process 4-colour offset) and post- consumer magazines (heat-set offset) were obtained. Generous amounts of each fur- nish were cut into 2.5 x 2.5 cm (1 X l in.) squares. The furnish was stored un- der controlled temperature and humidi- ty conditions until used. The equilibrium moisture content of the newsprint and magazine was measured by oven drying per TAPPI Method T412. Samples of the furnish were ashed per TAPPI Method T211 at 575°C.

Repulping and Flotation Repulping of the newsprint and

magazine blends was performed using a Laboratory Repulping Apparatus. This apparatus consisted of a Waring Blender Jar and Blade Assembly that is powered by a Servodyne motor. This motor

. . TABLE I

THE PHYSICAL PROPERTIES OF FILLERS USED ..

Filler Type Particle Size Brightness (%) Calcined Clay [IO]

No. 1 Coating Clay I101

80 - 84% <2 pm

90 - 94% <2 pm

80 - 82

87.5 - 88.5 Water-washed Filler Clay [IO] 55 - 65% <2 &m 84

Synthetic Amorphous Precipitated Silica [ 111 mean = 6pm 96.0 minimum

provided a controlled rotor revolution rate. The orientation of the rotor was reversed to prevent cutting of the fibres. Flexible heating tape was wrapped around the blender jar. A constant temperature was provided via a thermocouple im- mersed in the pulp slurry and a tempera- ture controller. Pulping time was controlled with an automatic timer. Pulp- ing conditions were: 5% consistency, 49°C (120"F), 45 min, and 750 rpm. The initial pH in the pulper was adjusted to 9 with sodium hydroxide.

Six pounds per ton of 0.d. solids (0.3% by wt.) of a formulated multi- component surfactant-based flotation aid was added to the pulper prior to furnish addition. For each run, the stock from two pulper batches was combined and diluted to 1% consistency to provide enough stock to run the flotation cell.

When filler was used to provide ad- ditional ash, the newsprint was repulped as described previously. After pulping, the stock from two pulper batches was combined. A 30% by wt. aqueous slurry of the filler was added to the stock and mixed for 5 min using an American LR41D mixer and a Lightnin 316 SS high shear, dispersing impeller (R-500). The mixture was then diluted to 1 Yo consisten- cy. Flotation of the stock was done us- ing a Wemco Laboratory Flotation Machine. A 300 mL sample of the feed stock was saved for flotation feed re- tained ash and brightness measurements. The remaining stock was added to the cell and warmed to 49°C (120°F) using an im- mersion heater. Then the stock was float- ed for 5 min using full air (inlet valve 100% open) and an agitation rate of 1200 rpm. Froth rejects were skimmed using a rotating paddle and collected.

Reject Consistency and Yield Calculations

Reject volume was measured using a graduated cylinder. The reject con- sistency was determined by filtering a measured volume of the rejected liquid through a pre-weighed qualitative filter paper and then weighing the dried pad. Total solids loss was calculated by mul- tiplying the reject consistency by the to- tal reject volume. Percent yield was calculated as follows:

solids added to the flotation cell - reject solids solids added to the

flotation cell

Pulping Brightness and Ash Content Determination

Pulp brightness was chosen as the response variable to quantify deinking performance. Brightness is most strong- ly influenced by the smallest ink particles in the sheet when these particles are present in sufficient numbers. Previous experience with image analysis had shown that the vast majority of ink particles in laboratory repulped newsprint were not visible with the naked eye ( < 50 pm) when this type of chemistry was employed. The small number of ink particles that were >50 pm were the major contributor to visible dirt in the sheet. Visible dirt or speck reduction is an important function of flotation deinking. Yet, the small num- ber of larger particles present do not characterize the majority of the popu- lation.

In previous work by the present authors, a technique which integrates the light reflectance curve over the entire visi- ble wavelength range was developed. This technique can provide more information on the aesthetic qualities of the sheet than a measurement at a single monochromatic wavelength. This measurement system is not an industry-wide method; the decision was made to present these data in a sys- tem which would be familiar to everyone.

Pulps pads were formed from 300 mL samples of the flotation feed and accepts using 15 cm qualitative, medium filtration speed filter paper in a Buchner funnel. The pads were pressed and dried according to TAPPI Method T218. TAPPI brightness of the pads was mea- sured at 457 nm using a Technidyne Brightimeter according to TAPPI Method T452. Four replicate brightness measurements were made on the top of each pad.

The amount of retained ash in each pulp pad was determined by ashing one half of the pad in a muffle furnace at 575°C per TAPPI Method T211.

Analysis Technique For each filler and magazine, the

replicate baseline brightness measure- ments were plotted against the retained ash at the 1.8, 3, 5 , 7, and 10% added ash levels. Linear regression analysis was used to fit a line to the data. The 95% confidence limits on the regression line were calculated using published proce- dures [8,9].

The mean flotation feed and accept brightness and retained ash were calcu-

5226 JOURNAL OF PULP AND PAPER SCIENCE: VOL. 18 NO. 6 NOVEMBER 1992

lated for newsprint blended with each filler and magazine at the 1.8,5, and 10% added ash levels. The 95% confidence limits on each brightness mean were cal- culated. For each filler or magazine blended with newsprint, the feed and ac- cept brightness means and their confi- dence limits were plotted on the baseline graphs at the mean retained ash level.

The flotation accepts brightness of each filler type and level was compared to the flotation accepts brightness of the control (no magazine or filler) via a one- way analysis of variance [9]. Differences between means were compared at a 0.05 level for significance.

RESULTS Data Summary

The experimental results are sum- marized in Figs. 1-5. Each graph summa- rizes the data for one ash source. The regression line and 95% confidence limits represent the relationship between filler retention and brightness without flotation deinking. This baseline brightness versus retained ash curve is important because it separates the effects of ash retention on brightness from the effects of flotation on brightness for each ash source. The mean value of each flotation feed and accepts brightness at the background, 5 , and 10% ash addition levels is plotted. These values are bracketed by their confidence inter- vals. The background data are common to all five graphs. Data are summarized (including the statistical significance of the results) in Table 11.

Ash Reduction Across Flotation Cell

Figures 1-5 show that the reduction in pulp ash content during the flotation

process is consistently very small. This is indicated by the minimal decrease in re- tained ash between the flotation feed and accepts for the different runs. All 1 1 com- binations of filler type and level showed mean ash losses across the flotation cell of < 1 % on an 0.d. stock basis. Gener- ally, the filler split evenly with the fibre. Since the flotation cell did not act as a filler fractionator, the role which filler plays in flotation deinking was ques- tioned.

Ash Retention on Filter Pads The flotation feed filter pads had

lower ash levels than the dosage of filler applied. The retained ash level in the filter pad correlated with the particle size dis- tribution of the filler in most cases. The coating clay had the smallest particle size (90 - 94% < 2 pm) and the poorest ash retention (an average of 42% retention for all runs). Of the kaolin clays, the filler clay had the largest particle size (55 - 65% < 2 pm) and the highest ash retention (an average of 62% retention for all runs). The magazine had the highest ash reten- tion of all, averaging 78%. This may be because the magazine filler was present as microscopic coating flakes rather than discrete filler particles.

Ash retention on a medium- porosity filter paper averaged 56% for the entire experiment. Ash retention on a commercial dewatering or washing device would likely be lower. Clearly, dewater- ing or washing would be the filler- fractionating stage in a commercial operation.

Effects of OMG Addition on Deinking Efficiency

OMG addition to the furnish

without flotation clearly lowered the base- line brightness (see Fig. 1). This was an unexpected result. OMG’s high margin brightness (brightness of unprinted stock) would lead one to expect increased feed brightness with increased substitution lev- el. One plausible explanation is that higher concentrations of different inks ex- ist in the OMG furnish.

Addition of OMG significantly in- creased the brightness difference across the flotation cell. This is indicated by the wide separation of the confidence inter- vals for the mean flotation feed and ac- cept brightnesses at the 5 and 10% added ash levels. However, due to the lowering of the baseline brightness, there was no significant difference between the final brightness (flotation accepts) of the back- ground and when magazine was the filler source. OMG did not improve flotation deinking efficiency of newsprint based on flotation accepts brightness.

Effects of Silica Filler Addition on Deinking Efficiency

The addition of silica filler in- creased the baseline brightness (see Fig. 2). Filler addition at the 10% level signifi- cantly improved the final brightness over the background level. The overlap of the confidence intervals for the mean flota- tion feed and accept brightnesses clearly indicates that the improved brightness is due to filler retention - not improved deinking efficiency.

Effects of Kaolin Clay Addition on Deinking Efficiency

The kaolin clays tested (calcined, filler, and coating clay) did not signifi- cantly affect baseline brightness. The

JOURNAL OF PULP AND PAPER SCIENCE: VOL. 18 NO. 6 NOVEMBER 1992 J227

10% Added Ash

44

43 -

52 - Flotation Accepts

51 -

1' 5% Added Ash , Flotation Accepts I Background

Flotation 50 i/ Accepts

49 -

Flotation Feed

io% Added Ash Flotation Feed 47

46 - - - - -~-- . . . - - -~ .... Background

Feed 5% Added Ash --.- ~.

45 Flotation

44

43 Flotation Feed

55 - 54 - 53 -

52 - 51 -

50 -

u) 43.: u) a 48 - C c *I- I

m m .- L 46 -

45 -

Baseline Ash Content' Vs. Brightness

55.

54 - 53 - 52 -

5~

lo 49.- u) a, 4 8 -

40 I I I I I I I I I I I I 1 I i

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 1.5 8.0 8.5 3.0

% Ash Retained

Background

i T i o n Accepts 10% Added Ash - 5% Added Ash 1, Flotation Accepts

,Flotation Accepts

. ~ . .--- .~.. .~~. . . 10% Added Ash

- - ~ ~ . . ~ ~ . ~ . . . . ~ ~ . . . ~ ~ ~ . ~ ~ ~ . ~ ~ ~ - - - - - - - - . . . . . ~ -0 .

- - I

-. ---.. --..

45 ~ -Background "\5% Added Ash

U - Flotation Feed Flotation Feed

40 1 1 1 1 1 1 I I I I I I 1 1 1 ,

1.0 1.5 20 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6 0 6.5 7.0 7.5 8.0 8.5 3 0

% Ash Retained

-. ...

Fig. 1. Effect of ash from magazine on flotation deinking ef- ficiency. ciency.

Fig. 2. Effect of ash from silica on flotation deinking effi-

43 - 42 -

41 - 40 -

- Baseline Ash Content '

Vs. Brightness

I , I I I I I 1 , I I 1 1 I I I

8.0 - 7 . 5 - - \

7 0 -

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~

a''.\

Baseline Ash Content Vs. Brightness ! I l I I I I I I

41

40

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 3.0

% Ash Retained

Fig. 3. Effect of ash from calcined clay on flotation deinking efficiency. ficiency.

Fig. 4. Effect of ash from filler clay on flotation deinking ef-

55

53 54 1 C I Flotation Feed r 47 UI L 46 ..I . _-

Flotation Accepts

43

42

41

40

Flotation Feed

Vs. Brightness

I 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5 0 5.5 6.0 6.5 7 0 7.5 8.0 8.5 3 0

% Ash Retained 84 85 86 87 88 83 30 91 92 33 34 95 06 31 38 30 100

Yield (%)

Fig. 5. Effect of ash from coating clay on flotation deinking efficiency. filler sources.

5228

Fig. 6. Effect of flotation cell yield on brightness gain of all

JOURNAL OF PULP AND PAPER SCIENCE: VOL. 18 NO. 6 NOVEMBER 1992

2

slope of the ash versus brightness regres- sion line (with no flotation) remained flat

ly, one Would expect clay addition and retention to improve newsprint stock

relatively high concentration of ink par- ticles which should be removed before papermaking. One plausible explanation for the unchanging brightness levels is that the darkening effect of the ink par-

any brightening effect

significantly improved baseline brightness whereas the kaolin clays did not. This may be due to silica’s very high brightness (96 minimum) as compared to the brightness of the vari- ous clay grades (80-88).

Calcined clay (see Fig. 3) signifi- cantly increased brightness across the flo-

10% addition level. on accepts brightness y different than that

of the background data. Filler clay (see Fig. 4) significantly

increased brightness across the flotation cell a t the 5% addition level. The flota- tion accepts brightness at the 5% addi- tion level was significantly higher than that of the background. The same effects were not observed at the 10% addition level. The behaviour at the 5% addition level may be an experimental anomaly, since it was not repeated at the higher ad- dition rate.

Coating clay (see Fig. 5) signifi- cantly dropped the flotation accepts brightness at the 5% addition level. This again could be an experimental anoma- ly. The behaviour was not repeated at the loolo addition level. Addition at the 10% level significantly increased brightness across the flotation cell. The flotation ac- cepts brightness at 10% was not signfi- cantly different than the background level.

B D in all three cases (see Figs. 3-5). Normal-

brightness. Before flotation, stock has a ,

Correlation between Yield and Brightness

A strong inverse correlation be- tween yield and brightness increase across the cell was observed. Figure 6 illustrates that the brightness gain increased as the process yield decreased.

Effect of Filler Source on Frothing

The runs containing OMG consis- tently exhibited moderately stable froth in the rejects. All of the runs using filler slurries and the background control runs had very unstable froth but did produce rejects. The magazine rejects were gener- ally higher in volume, lower in consisten- cy, and higher in solids loss than the rejects of the filler or background runs.

DISCUSSION Effect of Particle Size on Flotation Efficiency

The above results indicate that fillers do not play a significant role in im- proving the flotation deinking of newsprint (as measured by brightness). The results also show that flotation did not selectively fractionate filler away from the fibre.

The kaolin clays used in the study all had median particle sizes of <2 pm [lo]. The silica filler used in the study had a mean particle size of 6 pm [ll]. Work by Mattingley states that a particle that is < 5 pm is undesirable for flotation deinking [12]. A paper by Zabala and McCool also showed that flotation deink- ing is increasingly ineffective in remov- ing particles that are < 5 pm. Small particle fractions are much more efficient- ly removed by washing [6]. A study by Marchildon et al. on the flotation deink- ing of newsprint defined all particles <SO pm as a small fraction. They indi- cated that, while flotation could remove about 50% of these particles, it was ef- fective in removing 95% of particles > 140 pm [13]. Based upon these results, and the particle size of the fillers tested in this experiment, flotation probably should not selectively remove a large frac- tion of the filler from the process.

If filler and ink particles formed larger agglomerates during the collection process, a significant removal of filler with the rejects might occur. The ex- perimental results in this study do not in- dicate this to be the case. If filler was not selectively fractionated into the froth re- jects during flotation, it is difficult to un- derstand how it could be responsible for increased ink removal. A study by Liphard et al. showed that filler removal and ink removal during flotation were not easily optimized during the same flotation step. However, filler removal could be en- hanced through the use of anionic surfac- tants [14].

Foam Stability The use of OMG in the furnish

consistently contributed to foam stabili- ty. The use of fillers by themselves did not. The physical form of the filler in the repulped OMG may be different than in a filler that is simply added to a slurry. The microscopic coating flakes in OMG could possibly contribute to stability

whereas discrete pigment particles would not.

If filler content does not encourage foam stability, a component in the OMG other than the fillers may cause the beneficial effect. There are many other components of coating colour other than filler. Table 111 lists some of the more common ingredients in coating formula- tions [15]. The nature and quantity of la- tex and starch binders in coatings make them likely candidates to be foam builders and stabilizers. However, identification of the possible foam stabilizing compo- nent(s) and how they function was be- yond the scope of this study.

Other Benefits of Magazine Magazine usage in an ONP-to-

newsprint deinking operation has other substantial benefits which must not be overlooked. Virgin newsprint typically has a low percentage of long fibre in the sheet network (due to the very high mechanical pulp content). Recycling de- grades the few long fibres present, damaging tensile strength. Old magazines (No. 5 grade LWC) typically will have at least 50% bleached kraft fibre as basestock furnish. The inclusion of OMG in the furnish can give a valuable boost to web tensile strength where required.

Flotation Chemistry There are many different systems

of deinking chemistry and equipment available. We have not attempted to ex- trapolate these findings to all systems. The flotation aid used in this study is a multi-component formulation of synthet- ic surfactants. It is designed to aid in the separation of ink particles from fibres in the pulper and enhance their subsequent attachment to air bubbles in the flotation cell. The chemistry employed is similar to displector chemistry but provides stronger collecting than dispersing properties. Traditionally, displectors are alkoxylat- ed fatty acid derivatives. They are designed to add dispersing properties to the collecting properties of fatty acid. Our experience is that to expect one chemical formulation to both disperse and collect is a compromise situation.

The flotation aid used in this ex- periment differs from fatty acids in that an ONP/OMG pulper may be run at a pH of 9 with excellent results. A pH of 9 provides adequate fibre swelling for ink

JOURNAL OF PULP AND PAPER SCIENCE: VOL. 18 NO. 6 NOVEMBER 1992 J229

removal and defiberizing. The pH levels of 10-10.5 commonly employed with other chemistries are not required. At these pH levels, peroxide bleach liquor (peroxide, silicate, and chelant) must be added to minimize mechanical fibre yel- lowing. Repulping at pH 9 avoids fibre yellowing and the addition of bleach li- quor is not necessary. Bleaching chemi- cals are saved until after ink removal, where they effectively increase brightness. The use of synthetic surfactants also eliminates the requirement for calcium chloride (as a soap insolubilizer).

CONCLUSIONS Retention of kaolin clay fillers did

not significantly improve the brightness of the ONP stock. None of the kaolin clay fillers consistently improved flotation ac- cepts brightness. Retention of the synthet- ic silica filer did significantly improve the brightness of the ONP stock. A signifi- cant increase in flotation accepts bright- ness with silica filler at the 10% addition level was due to filler retention, not im- proved deinking efficiency.

Addition of OMG to the ONP stock significantly reduced flotation feed brightness. The brightness increase across the cell significantly improved with in- creasing OMG use. Flotation accepts brightnesses with OMGIONP were not significantly higher than those obtained with ONP alone. Based on flotation ac- cepts brightness, OMG addition did not improve deinking efficiency. OMG usage does have other significant benefits such as stabilizing foam and improving strength. None of the individual fillers stabilized foam.

Independent of filler source, brightness increase across the flotation cell had a strong inverse correlation with process yield. The flotation cell did not selectively fractionate ash into the rejects. The ash level from the flotation feed to accepts dropped only slightly. The major ftfer loss from the pulp was caused by drainage of the water from the fibres through filter paper.

ACKNOWLEDGEMENTS The authors wish to thank Betz

Paper Chem, Inc. for its support of this work. We also thank J.M. Huber Corp. and Englehard Corp. for contributing

REFERENCES 1. “Paper Industry Demand For Old Maga-

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5230 JOURNAL OF PULP AND PAPER SCIENCE VOL. 18 NO. 6 NOVEMBER 1992