Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FELT TR~ATM~NT -- INORGANIC DEPOSIT
~;V ~ ON BY SPRAY TR~TM~NT
FT~T n OF THE INVENTION
The present invention relates to a method for
inhibiting the deposition of particulate materials onto
papermachine felts. More particularly, the present
5 invention relates to a novel felt conditioner and method of
use thereof to inhibit or prevent the deposition of
particulate materials onto p~re~rr-^hin~ felts in paper
grades having an incuL~.uLal ion of filter material such as
f ine or writing papermaking systems .
10 BA~ KOUNL~ OF THE lNv~-~Lll.
The manufacture of paper involves the processing of an
aqueous fiber suspension to produce a uniform dry paper
sheet. pAr~rr~k;n~ operations are always cnnr~rn~d with t~
problem of controlling deposits, particularly in the sheet
15 pressing 6tage where the paper web is passed through presses
covered with the porous press felts to extract retained
water from the web. It is; ~ to extract as much
water from the paper web prior to its entering the dryer
section since the mechanical removal of water through the
20 press felts is much more cost effective method to dry the
paper web than providing steam for dryers. Modern press
felts are no longer made of natural woolen materials, but
are made of synthetic f ibers such as nylon and polyester
blends. Among the desirable features of a press felt are
the following:
- freedom from plugging;
- resistance to matting;
- permeability for water r ~
- non-compressible base to provide void volume;
- smooth surface to avoid surface imperfections
on the paper.
J A clean felt, having fine pores which are relatively
open, is particularly desirable for effective paper
manufacture since this allows efficient removal of water
from the paper sheets without leaving l~-rks or other
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21 8~3466 -PC~lUS 95/04334
~7 R~'d PCTIPTO O 2 F~e lgg6
imperfections on the paper. ~However, ~elts in the press
section become filled or plugged with cont~min~nts and
reriuire freriuent, periodic shutdown and treatment with
caustic solutions (i.e. boil-out) or eventual replacement.
Felt plugging has become a major problem in modern
papermaking operations due to the increased use of recycled
water and increased use of recycled paper and a desire to
reduce poor size to minimize felt marking.
Contaminants which plug felts primarily include
inorganic fillers such as clays, precipitated calcium
carbonate, ground calcium carbonate, and titanium dioxides.
In addition, ionically charged, relatively high molecular
weight, water soluble polymers which are employed to enhance
retention of cellulosic fibers, fines, and inorganic
fillers, form flocculated particulate materials which can be
transferred from the surface of the sheet to the press
felts. The flocculated particles cannot pass through the
fine, porous structure of the modern press felt and become
entrapped therein.
Particles of latex coating binders such as, polyvinyl
acetate or styrene-butadiene rubber are also often found in
plugged E~ress felts. Other types of crnt~m;n~ntq can
include starches, natural wood pitch (fatty esters, fatty
and resin acids/salts) cellulosic fiber fines,
microbiological cnnti~min;ints and absorbants, such as talc or
bentonite, oil-based defoamers, sizing agents and insoluble
metal hydroxides . All of these rrnt~m; ni~nts can be present
to some degree based on a variety of factors, such as, the
paper machine system temperature, the wood f iber and water
sources, ~ime of year, grade of material produced, type and
riuantity of system additives, pulp production methods and
equipment designs and capacities. If not controlled by
aderiuate felt conditioning practices, these inorganic
fillers and agglomerated particulate substances can severely
impair the ability of the press felts to absorb water
thereby reducing production rates and shortening the useful
life of the felts.
EO S~EET
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Processes to inhibit the deposition of contaminants in
p~rPrr~-k; n~ felts are known in the art. U. S . Patent No.
4,715,931 to S~hPllh et al. discloses a process for
inhibiting aluminum hydroxide deposition in pArP~ kin~
5 systems which comprises adding to the felts a hydroxylated
carboxylic acid. The use of the carboxylic acid in
combination with surfactants, such as octyl phenol
ethoxylates, nonyl phenol ethoxylates and others listed
therein inhibit Alllminllm hydroxide deposition and associated
10 organic contaminants.
U.S. Patent No. 4,861,42g to Barnett et al discloses a
process for inhibiting white pitch deposition in felts by
treating the felts with an organic, anionic polyelectrolyte.
STTMMA~v OF ~ INVFNTION
It is an object of this invention to provide a method
of treating papermachine felts to inhibit the deposition of
particulate contaminants therein and thereby maintain
porosity of the the felt.
It is another object of this invention to eliminate or
reduce off-line felt ~.lPAn;n~ (boil-out) with damaging
caustic or acid solutions.
It is another object of this invention to provide a
method of treating papPrr--h;nP felts to inhibit the
deposition of inorganic particles derived from fillers used
in the manufacture of fine paper and/or writing paper.
It ls a further object of this invention to provide a
method to inhibit or eliminate the deposition of inorganic
particles derived from waste paper containing filler
particles .
3 0 In accordance with the present invention, there has
been provided a method for treating p~rPrr-ch;n~ felts to
, inhibit the deposition of particulate contaminants and to
maintain the porosity of the felts comprising contacting the
felts in a continuous or intermittant manner during the
paper production with an aqueous solution of a pH control
agent and a nonionic or anionic surfactant wherein the p~
control agent is added to the aqueous solution in an amount
, ,,, _ . , .. , , _,,, . ,, . . . , , , , _ _ _ _ _ _ , _ _
WO 95l29292 ~ I 8 8 4 6 6 P~ 4
sufficient to provide a pH in the range 9 to 13, and wherein
the surf actant is present in the aqueous solution in a
uullc.:..LLc~tion range 0. 01 to 5% on a weight basis.
Dl~'rATT.T..n DT..~rRTP~ ON
The present invention relates to an improved press felt
conditioning LLeai L which inhibits or prevents the
deposition of particulate substances into press felts. The
press felt conditioning Llaai Ls of the present invention
maintain felt porosity, i.e., they inhibit compaction of the
felts, reduce the loss of caliper of the felts which is
otherwise caused by wear and ~ ~:ssion and thus reduce the
frequency of off-line cleaning ~Luced.lLas. More
particularly, the present invention relates to the use of an
a~ueous 601ution of one or more water soluble nonionic or
anionic surfactants in combination with certain pH control
agents, which, when applied to papermachine press felts,
control or inhibit the deposition of particulate
contaminant6 into the press f elts .
Suitable surfactants generally include any anionic or
nonionic surfactants which are water-soluble at the use
concentration and which provide effective wetting at a pH in
the range 9 to 13 . The surf actants of the present invention
which have been found to provide unexpected efficacy when
combined with the pH control agents of the invention
include, dodecyl benzene sulfonates, lauryl ether sulfates,
sodium xylene sulfonate, linear olefin sulfonates, fatty
amine oxides, phosphate esters, and mixtures thereof. Other
suitable surfactants include, but are not limited to, octyl
phenol ethoxylates, nonyl phenol ethoxylates, dodecyl phenol
ethoxylates, primary alcohol ethoxylates, ~C~In~q~ry alcohol
ethoxylates, ethoxylated polyu,Ly~Lu~ylene glycols, dialkyl
phenol ethoxylates, polyoxyethylene sorbitan monoester, and
linear alkybenzene sulfonic acids. These are more fully
disclosed in U.S. Patent No. 4,861,429 which is incuL~oL~ted
herein in its entirety. Suitable surfactants also include
amphoteric surfactants such as fatty imidazoles and their~
carboxylated and sulfonated derivatives, fatty amidobetanes,
_
~ WO95l29292 21 884~6 r~
~atty sl~lrhos~m;~9n-betanes. While these surfactants are
cationic under acid pH conditions, they are anionic under
normal papermaking conditions.
Suitable pH control agents include, but are not limited
5 to meta-silicates, phosphates, carbonates, and the like, and
mixtures thereof. Preferred pH control agents include
sodium meta-silicate, sodium phosphate and sodium carbonate,
and is most preferably sodium meta-silicate.
The aqueous felt conditioner solutions of the present
10 invention are prepared by diluting the surfactants in water
to a final u..cell~Lc.tion in the range of 100 to 2000 ppm and
then adding the pH control agents in an amount ef f ective to
provide a pH in the range 9 to 13, preferably 10 to 12, and
most preferably 11 to 12. Alternatively, the surfactant and
pH control agent can be premixed in a ratio to give the
desired pH and surfactant uullcell~L~tion by dilution with
water . Fresh water may be used to prepare the aqueous f elt
~Le~ solution or optionally, recycled white water may
be used. The aqueous felt conditioner solution generally
contains between 30 ppm to 2000 ppm surfactant, preferably
50 ppm to 1500 ppm.
The felt conditioners of the invention may optionally
include a solubilizing agent to aid in wetting and/or one or
more chelants for facilitating use in high hardness waters.
Suitable solubilizing agents include glycols such as e.g.,
hexylene glycol or diethylene glycol, glycol ethers such as
e.g., ethylene glycol r ~ buLyl ether. Suitable chelants
are those capable of stabilizing calcium ion under high pH
conditions and include, but are not limited to,
ethylPnP~ minp tetraacetic acid tEDTA), nitrilo triacetic
acid (NTA), diethylenetriamine pentaacetic acid (DTPA), and
the like.
The present invention also relates to a method f or
inhibiting the deposition of various organic and inorganic
contaminants in a felt in a press section of the papermaking
system wherein the felt is prone to such deposition. In
accordance with the present invention, the felt conditioners
_ _ _ _ _ _, _ ~ .. . . . . . _ . _
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of the present invention are applied by metering or spraying
the press felts into the fresh water shower system,
preferable a low ~res ~IL~: 5hower. These felt conditioners
are generally applied to the sheet side of the f elts,
preferably with a fan = shower. The felt conditioners are
preferably sprayed at low pLeS27UL~::6, i.e., in the range 2 to
7 kg/cm2, preferably 3 to 5 kg/cmZ.
It is considered an important feature of the present
invention that the felt conditioners of the present
invention are applied by metering into one or more fresh
water showers which are directed onto the press felt on its
run the point where the felt no longer contacts the paper
sheet and the suction box, pref erably between the press nip
and the suction (Uhle) box which is utilized for dewatering
the felt. The application of an aqueous solution of a pH
control agent and one or more nonionic or anionic
surfactants onto press felts in this area has been found to
produce felt conditioning effectiveness which is ul.e,c~e- Led
based upon the conditioning effects of these felt
conditioners in other areas or of the individual components.
For typic21 pAr~ kin~ processes, the felt
conditioners of this invention can be sprayed or metered
intermittently during the paper making operation, typically
2 to 3 times per day, at an actives concentration of 1 to 5
percent on a weight basis. Alternatively, the felt
conditioners can be sprayed or metered continuously at an
actives concentration of 0.01% to 0.2%, preferably at an
active concentration of 0.1% on a weight basis.
The total dosage amount of aqueous felt treatment
applied to the felts is also considered an important feature
of the present invention. In general, best results have
been obtained when at least 6 liters of felt treatment is
applied per square meter of felt per minute (l/m2/min),
preferably between 6 to 10 l/m~/min.
The felt conditioners of this invention are
particularly useful for treating felts used in the
manufacture of paper grades having an incorporation of
~ W095129292 218~ C~4
f iller materials such as e . g ., f ine paper or writing paper .
These paper grades typically contain large quantities of
inorganic fillers such as clay, calcium carbonate, titanium
dioxide, and the like. The felt conditioners of this
5 invention are also effective in p~r~ k; ng systems using
th~ n;r;-l pulp (TMP) which typically has a high level
of fines which are known to plug press felts.
The following examples are provided to illustrate the
present invention in accordance with the principles of this
10 invention, but are not to be construed as limiting the
invention in any way except as indicated in the i~p-~nrl"
claims. All parts and peLct:nl dges are by weight unless
otherwise indicated.
r le 1
This example d: ~Lates the effectiveness of the felt
conditioning treatments of the present invention for
maintaining the porosity of felts in the press section of a
paper making machine which manufactured printing grade
paper. The paper machine in this example used 100% kraft
20 pulp furnish. The furnish contained a relatively high
dosage amount of clay as filler. Before contacting the
paper, the u~ c~ of the paper machine felts is measured
by passing the felt over a vacuum box to remove excessive
water. The vacuum readings which are n~c~cs~ry to draw air
25 through the felts are representative of the o~ ess of the
paper machine felts. Typical vacuum readings for a clean
felt are normally about 12 inches of Hg. Vacuum readings of
greater than 16 inches Hg generally indicate that caustic
~le~nin~ of the felts is n~cPc~ry. An aqueous felt
30 conditioning solution was prepared containing 4 . 5% sodium
meta-silicate, 14.5% of a mixture of anionic surfactants
(sodium dodecyl hC~n7~n~ sulfonic acid and lauryl ether
sulfate), 6% chelant (EDTA) and 4% wetting agent (diethylene
glycol). The felt conditioner was metered into a spray bar
35 prior to the first Uhle box at a pressure of 2-4 kg/cm2 and
a water flow of 40 liters/min.
~ n~;tinn~: Prior to the Treatment Progr~m
.
~66
W095/29292 21 88 r ~ Q43~4
-- 8 --
Prior to treatment with the present ~elt conditioners,
the paper machine was shut down, on average, every two to
three days for caustic batch cleaning of the felt for clay
removal. The average production 1055 per shut down for
5 caustic ~-lPAni n~ was 12 tons.
rnn~itil~n~ t~er IL eaI, ,~ ProrrAm
The initial trial period was 20 days during which three
shut downs were required for caustic cleaning. Two of the
shut downs were as a direct result of the interruption of
10 the spray application of the felt conditioners of the
invention. An 18 day period was realized without any shut
downs with continuous spray application of the present felt
conditioners . Uhle box vacuums r~ ; nPd below 16 inches Hg
tllluuyll~u~ the 18 day period. All other paper machine and
15 sheet standards r~ ; nPd constant .
Scanpro testing involves detPrm;n;nq the water content
of the felts in grams H20/m2 of felt. A higher meaæure of
water content in the felt is indicative of higher felt
porosity. In addition, the Scanpro testing is a measure of
20 the uniformity of water content across the entire cross-
section of the felt. It is considered important that press
felts have a uniform water content profile across the felt.
Scanpro testing was conducted on the treated felts and were
compared to previous results of other untreated felts and
25 indicated that the treated felts had not only a higher water
content, i.e., a significant porosity illl~LU~.C -nt over the
previous untreated felts, but also indicated a more uniform
water content profile across the felt than the previous
untreated felts. At the time the felt was changed, the felt o was reported to be in good condition .
r le 2
This example ~~ LLaLes the effectiveness of the felt
conditioning solutions of the present invention for~
maintaining felt porosity of press felts in paper r~-h;nP~:
35 used to manufacture directory grade paper. The furnish
comprised 40% stone YL~UIId~ Jod pulp, 50% th~ ' An;~A1
WO 9~/29292 2 1 8 8 4 6 6 r~
pulp (TMP) and 10% Kraft pulp. Paper additives include talc
and starch.
The ~Lucedur ~ in Example 1 was repeated in this
example .
5 Conditions Prior t~ Treatment ProqrAm
This paper machine experienced downtime, on average,
437 hours per year for caustic washing of the felts to
remove fines, thus requiring the cu..~, Lion of about 10,000
kg per year of caustic chemicals. At an average production
10 rate of 125 tons per day (TPD~, this amount of downtime
results in considerable loss of production. In addition to
downtime production losses, approximately 250 tons per year
(TPY) of production loss was attributable to irregular
moisture profiles across the felts. High pressure showers
15 (8 to 12 kg/cm2) were required for felt cl~An;n~ ~o remove
fines. The average felt life for the previous 13 felts was
3 6 . 5 days .
~nrliti~nc After Treatment Proqram
Treatment of the pAr~ hin~ felts with the
20 conditioning agents of this invention resulted in a complete
elimination of llncrh~dllled downtime for caustic cleaning.
The caustic rleAning of the felts at the second press
section was reduced 50% . The vacuum box readings r~ ; n~
constant throughout the entire trial period, and Scanpro
25 results indicated uniform water content prof iles resulting
in no lost paper production. The pressure of the high
pressure showers was reduced to 8 kg/cm2. The felt life was
increased to 57 days.
J ` ` ~
