Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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,
METHOD AND BORATE-MAGNESIUM SALT COMPOSITIONS FOR
ENHANCING PEROXIDE BLEACHING
The present invention relates to the discovery of synergistic blends of ingredients and
a process to enhance peroxide and oxygen and combinations of the two bleaçhing
10 processes used for the production of paper pulps and textiles. Ble~ching activity is
enh~nce~l beyond the additive effects of the individual ingredients.
15 Ble~ching of lignocellulosic materials can be divided into lignin ret~ining and lignin
removing ble~hing operations. In the case of ble~ing high yield pulps like
Groundwood, Thermo-Mechanical Pulp and Semi-Chemical pulps, the objective is to
brighten the pulp while all pulp components including lignin are retained as much as
possible. This kind of ble~hinp is lignin retAining Common lignin ret~ining
20 bleaching agents used in the industry are alk~line hydrogen peroxide and sodium
dithionite (hydrosulfite).
Hydrogen peroxide decG~ oses into oxygen and water with incleasillg pH,
telllpc~ e, heavy metal concentrations, etc. The decomposition products, radicals
25 like HO- and HOO., lead to lower yields by oxidation and degradation of lignin and
polyoses. Therefore, hydrogen peroxide is stabilized with sodium silicates and
chelating agents when mechanical pulps (high yield pulps) are bleached.
The ble~ching effect is achieved mainly by the removal of conjugated double bonds
30 (chromophores), by oxidation with hydrogen peroxide (P), or reduction with
hydrosulfite (Y). Other ble~ching chemicals more rarely used are FAS (Formamidine
Sulfinic Acid), Borohydride (NaBH4), Sulfur dioxide (SO2), Peracetic acid, and
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Peroxomonoslllf~te under strong ~Ik~lin~ conditions.
P~ edLI-lent including electrophilic reagents such as elemental chlorine, chlorine
dioxide, sodium chlorite and acid H2O2 increase the ble~ching efficiency of hydrogen
5 peroxide ble~ching
In the case of bleaching chemical pulps like kraft pulp, sulfite pulps, NSSC, NSSC-
AQ, soda, organosolv, and the like, that is to say with lignocellulosic material that has
been subjected to delignifying treatments, ble~.~hing includes further lignin red~lcing
10 (delignifying) reactions. Ble~ching of chemical pulps is performed in one or more
subsequent stages. Most common modern ble~ching sequences are CDEDED,
02CDEDED, O2DEopDEP, CDEoDEpD, CEHD, CEHDED, CEDED. (C chlorination,
E caustic extraction, H alkaline hypochlorite, D chlorine dioxide, 2 oxygen
delignification, CD chlorination substituted with chlorine dioxide, Eo pressurized
15 extraction with oxygen, Eop pressurized extraction with oxygen and peroxide and Ep
extraction with peroxide.)
In all of these ble~hing sequences, the first two stages are generally considered as the
"delignification stages". The subsequent stages are called the "final ble~ching". This
20 terminology describes the main effects that can be seen by the specific chemical
~ G~ S
While in the first two stages the most appale.ll effect is the reduction of residual
lignin, in the subsequent stages the most distinguishable effect is the increased
25 brightn~ss.
Hydrogen peroxide, oxygen, and combinations of the two ble~ching colllpounds have
been used in ble~.~hing paper pulp and textiles for a number of years. Environmental
pre~ e on chlorine based bleaching and the effect it has on effluent from the
30 m~nllf~ctllring process has accelerated the use of chlorine free ble~rhing processes to
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_,
reduce the amount of dioxins and AOX, absorbable organic halides, in the effluent
and bleached paper or textiles.
Oxygen ble~chin~ is contlucted under ~Ik~line pH conditions at elevated telllpel~ e
5 and pressure, with the process generating some peroxide ln-~i~ during the reaction.
Peroxide ble~ching is also conducted under ~Ik~line pH conditions, normally at
elevated te.llpeldlure. Oxygen stages are being enhanced with the addition of
peroxide. There is a trend in caustic extraction stages (wash out lignins) to pressurize
the stage and add oxygen or peroxide and sometimes both to enh~n~e bleaching
10 p~ Ir~ llance. Ozone ble~ching is beginning to make an impact. All ofthese
alternative methods are being installed or enh~nced in mills to allow the reduction or
elimin~tion of the dependency on chlorine based stages.
It is well known that peroxide ble~ching compounds, particularly hydrogen peroxide,
15 require stabilization to prevent the rapid breakdown into water and oxygen inducefl by
heavy metals. Iron, copper, and m~ng~n~se ions, either in process water or bound to
the bleachable material, have a catalytic effect on the breakdown of the peroxide,
especially at higher alkalinity levels. This results in a loss of peroxide and a lower
ble~ching efficiency. ChPl~ting agents, such as EDTA (ethylene~ mine tetraacetic20 acid), DTPA (diethylenetriamine pent~cetic acid), gluconic acid, glucoheptanoic
acid, tartaric acid, citric acid, polyphosphates, hydroxyalkanephosphonic acid, and
~mino~lk~nephosphQnic acids, along with their collespollding ~lkali metal salts, are
well known to prevent the breakdown of peroxide by forming complexes with the
metals, r~n~içring them harmless to the peroxide. Chelating agents have been used
25 directly in bleach liquor to stabilize the peroxide. Chelation or Q stages have also
been used recently as a low pH washing stage in paper pulp ble~hing to remove
metals from the pulp prior to peroxide, oxygen, or ozone ble~çhing
Magnesium sulfate, m~nesium chloride, and magnesium oxide have a stabilizing
30 effect on the perhydroxyl ion formed in ~Ik~line peroxide ble~ching
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H2O2 + NaOH > Na+ + OOH + H2O
Magnesium salts also retard the depolym~ri7~tion of cellulose, which causes loss in
strength, that can occur in oxygen or peroxide blç~ching stages. Alkali metal silicates
5 are also used in stabilizing peroxide bleach, but pose a significant risk in the
formation of insoluble silicate scale later in the process.
U.S. Patent No. 4,938,842 discloses a peroxide ble~çlling process employing
magnç~ium sulfate, sodium silicate and a chPl~ting agent.
U.S. Patent No. 3,716,447 discloses an ~Ik~line oxygen blç~rhing process in which a
cellulose pulp is pre-treated with m~,~n~siurn chloride.
U.S. Patent No. 4,849,053 discloses a peroxide blç~ching process in which pulp is
15 pre-treated with stabilizing chemicals including magnesium salts and chelating agents
such as EDTA.
U.S. Patent No. 4,619,663 discloses stabilizing compositions (and process) for
peroxide textile bleaches comprising metal chelating agents (such as
20 diethylçnetri~minepent~cetic acid) and sodiurn tetraborate decahydrate.
U.S. Patent No. 4,128,495 discloses ble~ching/dete1~ent compositio~c compri~ing
phthaloyl peroxide, preferably clesP~.~;Li~ by contact with a diluent such as
m~ ;ulll sulfate, and optionally contain sodium pell,o~ e. U.S. Patent No.
25 4,154,695 discloses similar compositions employing diacyl peroxides.
U.S. Patent No. 2,820,690 discloses a peroxide textile ble~ching process in which
peroxide is stabilized with orthophosphate plus m~gnesium ions and the solution is
optionally buffered with alkali metal borate.
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U.S. Patent No. 3,332,882 discloses a process for activating a peroxygen ble?~çhing
compound selected from group including m~gnesium peroxide, metal perborates et
al., the activator being a triacyl triazine.
5 U.S. Patent No. 4,086,175 discloses peroxide bleach compositions with a cyanamide
activator, m~gn~ium compound and burr~ling agent. The bleach can be a perborate.
U.S. Patent No. 3,384,533 discloses processes for bleaching cellulose pulps withoxygen in ~lk~line media, wherein the pulp is treated with a single catalyst selected
10 from a group including m~g,.~ c~l.onate and alkali metal borates.
There is a continual dçm~nrl for improved chlorine-free bleaclling compositions and
processes, particularly those which produce increased brightness in delignified pulps.
An object of this~invention is to provide improved blearhing compositions and
processes involving peroxides. Another object is to stabilize the hydrogen peroxide in
such bleaching compositions by preventing the catalytic effect of heavy metals which
20 may be present. A further object of the invention is to inc~ease the bleaching effects
of hydrogen peroxide.
In accordance with the present invention, these and other objects of the invention are
achieved by employing small but effective amounts of a peroxide bleach additive
25 composition comprising at least one alkali metal borate such as sodiurn borate in
conjunction with a m~gn~sium salt such as a halide.
These ingredients are used in proportions which are effective to produce synergistic
bleaching effects, i.e. effects which are qualitatively or qn~ntit~tively greater than
30 would be expected from the additive effects of the individual ingredients. Although
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the ranges of p~GI lions may vary with total dosage, the m~t~ri~l to be ble~rhe~l or
operation conditions, the propollions can range from about 2:8 to about 8:2.
Preferably both ingredients are added to the pulp or other material to be bleached
before the introduction of the peroxide(s).
s
Thus, the invention further encol,lpasses a ble~ching process wherein an additive
comprising at least one alkali metal borate and at least one m~n~cium salt is added to
a pulp or other material to be bleached, then adding at least one peroxide, said alkali
metal borate and said m~gnesiurn salt being present in quantities and p~ ol lions
10 effective to produce synergistic ble~hing effects.
Synergism, activitv beyond normal e~ecl~lion with blends of ingredients, has been
found with combinations of sodium borates and m~gn~cium salts, preferably chloride.
Each individual colllpollent enhances the ble~ching ability of hydrogen peroxide,
15 either through stabilization of the perhydroxyl ion or chelation of heavy metals. The
results with the mixtures are beyond e~e~ lion of the activity of the individualcomponents. Not all ratios of these active ingredients show synergism. Some ratios
of actives are merely additive and others are actually antagonistic, where performance
is subst~nti~lly below that expected.
These synergistic combinations are further enh~noed by the process of adding said
i~lules to paper pulp prior to the addition of hydrogen peroxide or of an ~lk~line
peroxide liquor where the llli~ e is in the pulp during the ble~ching process.
Improved bleach response is seen with pulp addition as compared to addition of the
25 mixture to the bleach liquor. Enhanced p~ .~ollllance is measured by increased in pulp
brightness or reductions in KAPPA number of the pulp. Activity is also better when
the mixtures are added to a pulp prior to the addition of bleach rather than addition in
a chelation or Q stage, with the intent of washing heavy metals out of the fiber prior to
bleaching. The reason for this difference appears to relate to the available m~gnesium
30 concentration during the peroxid~ ble~chin~ process. Magnesium stabilizes peroxide
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only when it is soluble.
Other objects and advantages of the invention will be ap~a~ellt from perusal of the
following detailed description, including the figure and the appended claims.
The invention will be further understood with reference to the acco,llpa~ying drawing,
wherein:
FIG. 1 is a plot illustrating the relative effects upon bri~htn~ss of bleached
pulp of various quantities and proportions of the active ingredients.
Lignocellulosic m~teri~lc such as untreated wood, wood chips and annual plants like
corn stalks, wheat straw, kenaf and the like can be used in accordance with the
invention. Especially suitable is material that has been defiberized in a mechanical,
chemical processes or a combination of mechanical and chemical processes such as20 GW, TMP, CTMP, kraft pulp, sulfite, pulp, soda pulp, NSSC, organosolv and the like.
It is the kind of m~t~ri~l in an aqueous ~u~pe~-~;on, hereinafter referred to a pulp,
which is treated in accordal~ce with the present invention with the specified additives
and subsequently in a follow on stage subjected to an oxygen and/or peroxide stage.
In addition to such pulp, the invention can be applied to any bleachable fibrous25 cellulosic m~t~r~
The present invention can be considered as providing a core process forrned of two
stages in a sequence; namely, a step of tre~tmçnt with ble~-hing additives and afollow on stage of oxygen and/or peroxide tre~tment This core sequence can be
30 systematically leplesellled as X--OX; viz, the i.x~ symbolizing the additives step and
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"OX" syrnbolizing the oxygen/peroxide step. The core sequence as defined herein can
be followed by one or more additional conventional pulp h~n~ling stages such as
washing and additional oxidation, peroxide tre~tm~nt ,teps as well as steps involving
treatment with bleaclling additives. Sirnilarly, the core sequence can be preceded by
5 one or more conventional steps such as those mentioned above.
The core sequence, X--OX, should not be hlte.,.lpted by a washing cycle. Et is
p[efc.led that the order of the core sequence be X--OX; that is, the additive and pulp
followed by at least one oxidation stage (oxygen and/or peroxide). The hl,poll~lce of
10 having the additive treatment precede an OX step resides in the fact that subsequent
delignification/oxidation results are unexpectedly enhanced while ret~ining desirable
viscosity pr~,l,c.~ies.
The scope of the variations in the overall methods of treating pulp including the 2-
15 stage sequence of the invention is very wide and can be illustrated by the following
possible r~lesP~ ive sequences.
As used herein, the symbol R rel)resell~ unbleached, brown stock, A is a transition
metal removing tre~tm~nt P is any peroxide compound treatment step, O is any
20 oxygen and X--OX is the core process of the invention:
R-X-OX
R-A-X-OX
R-O-X-OX
R-A-O-X-OX
R-A-X-OX-X-OX
R-P-X-OX
R-A-P-X-OX
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g
The above is merely illustrative and is not considered limiting.
The conci~t~ncy of the pulp in the ble~ing additive lre~ n~ step can range from
0.01% to 60%, preferably from 5% to 2S%.
It is customary that a chemical base such as NaOH, MgO, or other suitable ~lk~line
material be added to the pulp in order to control the acidity at a desired pH level. Any
suitable ~lk~line material can be used to control acidity provided it does not adversely
effect the process or product. Any sequence of chemical addition of pH controlling
10 alkali and additives in the first step, including the cimnlt~neous addition, can be
carried out. The starting pH is not narrowly critical. The starting pH can be 1 to 11.
Preferably, the starting pH of the pulp for the X stage (after addition of caustic and
addition of peroxomonosulfuric acid and/or its salts) is between 7 and 11. It is to be
noted that the pH profile over the course of the X stage has been clet~rmin~od to be
lS subject to wide variation and is not narrowly critical.
Trials have shown that the X-stage tre~tm~nt (additive stage) is very little affected by
tel,lpelal~e; that is, the reaction is not very telll~ dlllre depenrlent Thus, the
ble~c~ling additive treatment step is effective at low tenlpelalllres such as S degrees C.
20 as well as at ltl~cldlures of up to 100 degrees C. Preferable tellll)~-dlules forthe
additive tre~ nt are in the range of 40 degrees C. to 70 degrees C.
Depending on telllp~ .~lure, pH and chernical charge the residence time le~luiled is
typically between 1 second up to 10 hours, frequently I minute to 2 hours, although
25 the upper time limit is not critical. Thus, for example the retention time varies as to
how long the pulp takes to pass through the conventional ble~cl-ing tower, high
intensity mixing zone or the like. Some parts of the pulp may move through rapidly;
e.g. 1/2 hour, while other parts of the pulp may take 24 hours or longer to passthrough. Accordingly, the process of the invention is not dependent on a narrow
30 range of time parameters. Uniform distribution of the additive is hll~. .ati~e to treat
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all of the fiber to obtain the best results. Addition of dilution water with the additive
prior to addition to pulp followed by high shear mixing, such as in a centrifugal stock
pump, gives the best results.
5 It is to be noted that the ble~l~hing additive stage can be applied to any kind of treated
(bleached) or untreated (e.g. brown stock) pulp. Advantageously, one or more heavy
metal and organic co.~ --in~ s elimin~ting process steps can be initially carried out
at plet~e~ ent to favorably impact the delignification efficiency of the aforesaid
stage.
Ple..~ e conditions for the X-stage can vary for this process as is conventional in pulp
operations. Typically, from atmosphere to 0.5 MPa, is suitable.
The tre~tment stage in which ble~c-hing additives are used can be dç~ign~ted by the
15 symbol "X". The new process which is the subject of this invention fea~ s a
combined application of the X stage with any other kind of oxygen and/or peroxide
stage, generally~described by the symbol (OX). The new process can be abbreviated
by "X--(OX)" whereby "(OX)" can stand for O (oxygen dçlignification), Eo, Ep, Eop,
Eoh (extraction stages reinforced with oxygen, peroxide, oxygen and peroxide as well
20 as oxygen and hypochlorite respectively), and P (peroxide stage). Although
hypochlorite has been mentioned as a possible optional stage that can be used incombination with the X--OX process of the invention after the OX stage, efforts are
being made in the industry to elimin~te the use of chlorine chemicals whenever
possible.
The process of the invention can be used repeatedly and in combination with the
ble~ching stages commonly used in order to delignify and bleach to required levels.
The two tre~tment~, step X and step (OX) should be con~lcte~1 without intermediate
washmg.
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11
It is an object of this invention to employ at least two bleAclling additives A and B in
quantities and proportions effective to produce synergistic bleAclling effects that is, to
produce h1c~eases in brightn~-cc or other measures of bleAchin~ effects which are more
than the combined expected effects of the sepa~dle additives. The optimum total
S quantities will vary with the type of pulp or other stock to be bleached, op~ l~ling
conditions, etc. but generally the total lu~lti~y will be a small but e~.;live amount in
the range of fron about 0.02 to 0.4 weight percent of the pulp. Preferably, the amount
ranges from 0.04 to 0.12 weight percent. For a given total quantity the propollions
are those which produce a synergistic bleAching effect, preferably IllAxilll;~ g said
10 effect. Such proportions of A:B can range from about 1:1 to 9:1, preferably from
about 2:8 to 8:2, and most preferably from about 3:7 to about 7:3.
Additive A is preferably an alkali metal borate such as sodium borate, with lithium
and potassium borates also being useful. Ammonium borates can be used if there are
15 no subsequent chlorine-based stages. Various borate components such as sodium
metaborate and s ~dium tetraborate, Na2B4O~; potassium pentaborate, K4B50~o, and
ammonium borate can be used.
Additive B is a soluble mAgn~sium compound, preferably a halide such as mAg~ium
20 chloride. Magnesium fluoride or bromide may also be used, as well as the sulfate,
oxide, hydroxide. carbonate, nitrate and citrate.
FX~MPLES
25 The invention is further illustrated by the following non-limiting examples.
r.AROR~TORY MFTHODS
All laboldtoly bl~aching tests were run on a softwood kraft pulp, obtained from a mill
30 in the southern United States, which had been partially bleached through an oxygen
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12
deligrufication stage followed by a chlorine dioxide stage. All samples were taken
from a single batch of pulp. Weighed pulp samples were treated with the appropliate
dosage of the synergistic bleach enh~n~çr mixtures of the base m~t~ , mixed at
high shear for good distribution, caustic (NaOH at 2.20% on 100% active basis) and
5 peroxide (H2O2 at 1.5% on 100% active basis) added, mixed at high shear again for
good distribution, sealed in a polyethylene bag, and placed in an ultrasonic bath at
COnSl;ln~ te.l.p~ re for continuous mixing throughout the ble~ching process. Tests
were run at 80 degrees C for 60 minlltes The samples were then removed from the
bath, and 3.0 g h~n~l~heets were pr~ paled from the pulp using a British sheet mold.
10 The hand sheets were pressed according to standard TAPPI methods and air dried
ov~rnight
Brightneec measurements on the fini~hçd h~n-lch~ets were determin~d on an Elrepho
2000 Datacolor system. Bri~htn~ was measured at a wavelength of 457nm and is
15 reported in all cases as % ISO bri~htness The reported brightnPss value is an average
of 5 replicates on each sheet. The entire laboratory process is quite reproducible with
the standard deviation on 6 replicates of the bleaçlling and measurement process at
0.25% ISO measured to two decimal places.
20 This labo.~lo.~ met_od has been shown to produce excellent correlation to actual
results in mill conditions with the same chemical dosages.
SYNF.l~GI~M CALCULATION
25 Samples of the combinations were tested in the following ratios of component A to
component B: 0:10, 1:9, 3:7, 5:5, 7:3, 9:1, 10:0. The total active solids content was
kept con~ at each indicated dosage (0.02% to 0.16% by weight of dry fiber) in the
TABLES.
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13
NOM~CT ~TU~F.
3:7 at 0.02% means in this ~1iccuccion that a total of 0.02% active solids (excludes
waters of hydration) are used to treat the pulp, and components A and B are combined
5 in a ratio of 3 parts of A to 7 parts of B. The brightnPss gains provided by co~llponellt
A alone (10:0) and col.lponellt B alone (0:10) at 0.02% active solids are used as
rer..cllce points to determine if synergism between actives is genuine.
Gain(actual) - Flopollional Gain(Coll.polle.,l A) - Proportional Gain(Col~,pol1elll B) =
10 Di~.ellce from Expected.
Gain(actual) - 30% Gain(Component A) - 70% Gain(Coll.ponelll B)= Diffèrence fromExpected.
15 If the difference from expected was positive, the synergism between actives was
considered genuine and the performance better than expected. If the di~lellce was
zero, the performance was merely additive. If the dirrelellce was a negative number,
there was antagonism bclweell the actives and pclro~lnance was worse than expected.
20 Table I sets forth the p~l)ollions of sodium borate (A) and m~.~P~ l chloride (B)
employed in ~lcces-si /e trials at various dosage levels. Each propol lion ratio is
leci~ted a numbered example, with letters ~ccignPd to each dosage level for that
pro~llional ratio. The measured brightne~cs gains for these examples are also
pre3ellted in Table I. Table II prcsellls the results of calculations to ~et~rmine the
25 brightness difference which each example leple3ellts in co~..p~ison to the expected
additive effects of the sodiurn borate and m~)esiu~ chloride.
14 2168Z9O
TABLE, 1
.
C D 8 ~ C D R
~1~ ~ O~lp. Il.lp. Il.lp. 118~ ~rlp.Il-l~h ~hll~ ~l~hb Ibl~h a~ 11~1~ RdJh
N~ Iblb 0.~12S ~.04S h~ O.~S ~d. O.llS ~ o l-S Ikl. O I~S Ad. OD~S Ad. 01~45 A~L a~ 0 I~S
0 12S
IblO ~.~ 70~ n 70 ~ 71.7 1.4 IA 4.1 1~ 44J
S~b:U~ ~ ~.7 aJ aJ a.~ 70~ 41 I.~ 1.7 ~.4
Sd~ ~ ~ ~:7 ~19J 69J 7~4 n.2 71.2 2 ~ W ~- 4~ 4J
4 50~ ~b:~ 5 ~,~ 70~ 71J 71.4 71.1 1~ 3.~ 4. 4~ 4J
5 s~ ~ ~P~ 7~ 70~ 71.5 n~ n.- I ~.4 4.~ ~.7
So~ 4~ aA aA a.~ .2 1.7 1.7 I.~ 11 2~
7 s~ ~b~ l~o a.l 69.~ .4 .5 l.l 2.7 1.
TABLE II
A C D tl A O C D
11~1~ 1~_ ~ hh~l a~ ~1 a~- ~ ~.d_l ~ ~d~l 1~ Dilt. tr_ * W. t~ S Dltt. t~ S DUt. t~ S Dltt. t~o
Y~ 0 02S hL ~ 121~ 102% ~L 0.04s ~L o~S ~ 0.12S ~kL 0.16S
Qoll~
QlO 0 0 0 0 0 OS OS OS OS OS
~ 1:7 ~IA -IS .2 ~IA ~I.I IUS -~65 -~lS ~49S -24S
SD~ 7 ~ ,Q4 ~o.2~.4 0,5IWS ~I~S ~4S '- 4 S 12S
4 Sd~ ~p, 5:5 ~.~ Q4 ~,~ 2 I.l l~3S 14S 4 S OS 34S
Sdl~ 7,3~.7 ~.4 I.~ 3.113 S l~S ~IS l-~S 123S
50~ ~ :1 0.5 -I.l 4.- 0 0.43 .3S~3~S ~31S 24S S
~ U~ ~Q,~ o o o o o OS OS OS OS OS
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While the present invention has been set forth in terms of specific embodiments
thereof, it will be understood in view of the instant disclosure, that n~ ous
variations upon the invention are now enabled to those skilled in the art, whichvariations yet reside within the scope of the present te?ching Accordingly, the
5 invention is to be broadly construed and limited only by the scope and spirit of the
claims now appended thereto.
