Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF TREATING PAPERMAKING FABRIC
FIELD OF THE INVENTION
During the manufacture of paper, a web of paper fibers derived
from wood sources and also from recycled paper sources is typically formed
on the surface of a fabric mesh which is used to drain excess water from the
web. The drained web of fibers is then introduced into a series of rolls, some
of which are covered by continuous belts of fabric or felt. As the paper web
is fed through the rolls and between the layers of felt, pressure is applied
to
the paper web which forces water from the web.
The fabrics are composed of various types of polyester or
polyamide filaments of varying diameters or denier. The fabrics may be
woven together into a mesh or needled into a mesh base to form a batt. It
is highly desirable that these fabrics remain clean during their service
lives.
A clean fabric will facilitate proper drainage of water from the paper web.
Proper drainage of water from the paper web will allow the paper web to
attain optimum strength and allow it to be dried more easily in subsequent
paper manufacturing operations. Improved paper strength results in fewer
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paper breaks, allowing for uninterrupted machine operation and is a desired
characteristic of the final paper product.
The paper fiber web, which is carried by the forming fabric and
press fabrics, often contains undesirable contaminants. These include
materials that may come from recycled fiber sources and include: inks,
resins, hot melt and pressure sensitive adhesives, styrene butadiene,
polystyrene, vinyl acrylates, rubber, waxes, and polyethylene. These
materials are commonly known as stickies. Contaminants may also come
from natural fiber sources and include: fatty acids salts and their esters,
and
abietic acid salts and their esters. These materials are commonly known as
pitch. Finally, some contaminants are introduced during processing and
include: wet strength resins, latexes, vinyl acrylates and paper sizing
agents.
These contaminants are also known as white pitch. These materials may
contaminate the fabrics used to carry the paper web. They may coat the
fabrics, impeding drainage and uniform paper formation, or they may
completely obstruct the fabric in certain areas causing the appearance of
light spots or holes in the paper web which greatly detract from the aesthetic
and functional properties of the paper as well as causing the paper to break
more easily from that point onward.
Typically, these contaminants are removed after deposition.
Cleaning chemicals and solvents are often used, either continuously or
intermittently during the production of paper, or when the papermaking
equipment is not in production. These materials have varying degrees of
success depending on the nature of the contaminant and the cleaning
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method employed. In many cases, powerful solvents and caustic materials
are needed to remove the contaminants. These negatively impact paper mill
wastewater treatment facilities, as well as requiring more stringent
occupational health and safety precautions.
Applying cationic polymers to the surface of papermaking
fabrics prevents the accumulation of deposits. Further, anionic surfactants
as well as cationic polymers may be separately applied to a papermaking
fiber slurry or directly to papermaking surfaces to prevent contamination, as
described in Driesbach U.S. patent 5,556,510. This patent does not disclose
the method for making a stable product from a combination of cationic
polymer and anionic surfactant, the residual charge on the cationic polymer
or the nature of the hydrophilic moieties on the anionic surfactant. In
addition, it has been postulated that when cationic polymers alone are
applied to a papermaking surface that the cationic polymers adsorb onto the
papermaking surface and also attract anionic surfactants from the aqueous
component of the fiber slurry or paper web (D.T. Nguyen, TAPPI June 1998).
These methods also present problems. Applying an anionic surfactant along
with a cationic polymer, as described by Driesbach, presents stability
problems. These materials are typically incompatible and will not form a
stable mixture. This makes the application of this mixture difficult when
applied as either a single product or when the cationic polymer and anionic
surfactant are applied separately.
When only a cationic polymer is applied to a papermaking
fabric the efficacy of the polymer is dependent on the nature of the anionic
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species in the papermaking furnish. This furnish will vary and may diminish
the effectiveness of the polymer. According to generally accepted theories,
the cationic polymer should nave some cationic nature to ensure that it is
suitably attracted to the anionic surface of a papermaking fabric.
Hence, it would be beneficial for ease of application to have a
stable product with a balanced cationic charge that could be applied to a
papermaking surface, which would incorporate both a cationic polymer and
anionic surfactant with the specific properties needed to impart optimum
contaminant resistant properties to the papermaking fabric.
SUMMARY OF THE INVENTION
The present invention is premised on the realization that
cationic polymer and anionic surfactants interact to form a hydrophilic layer
on a negatively charged surface such as that found in papermaking. By
applying such a product to a papermaking surface such as a felt or forming
fabric, it is possible to impart a deposition resistance to that surface. This
deposition resistance may be achieved by continuously coating the surface
of the fabric with a liquid mixture including a cationic polymer, a non-ionic
surfactant and an anionic surfactant. The amount of the anionic surfactant
relative to the cationic polymer is such that the cationic polymer retains a
substantial portion of its positive charge, generally 10%-50%.
More preferably, the cationic polymer is a polydiallyldimethyl-
ammonium chloride and the anionic surfactant is a carboxylated linear
alcohol, although a wide variety of other polymers and surfactants can be
employed. The ability to apply a single stable product with specially selected
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anionic surfactants is a benefit in terms of ease of application and
uniformity
of the anionic surfactants which are complexed by the cationic polymer.
Without limiting the generality of this invention, it has been discovered that
anionic surfactants which contain a hydrophilic portion and, more
specifically,
a portion of the molecule which consists of ethylene oxide monomer adducts,
is particularly well suited for the purposes of the invention. Alternatively,
a
sulfo oxo moiety may be used in the surfactant to achieve similar results.
The invention will be further appreciated in light of the following
detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The Figure is a diagrammatic of a papermaking process.
DETAILED DESCRIPTION
The present invention is a method of improving the deposition
resistance of papermaking fabric. This is accomplished by applying the
composition of the present invention directly to the papermaking fabric by
spraying or with applicator rolls. The composition of the present invention
comprises a cationic polymer in combination with a non-ionic surfactant and
an anionic surfactant.
A wide of variety of cationic polymers can be used in the
present invention. In general, these cationic polymers must be water soluble
and are formed from cationic monomer units or both cationic and non-ionic
monomer units. By the term cationic, it is meant that the monomer unit
includes a group that either carries a positive charge or that has basic
properties and can be protonated under mild acidic conditions.
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Suitable polymers include cationic addition and condensation
polymers. The polymer will generally be composed partially of vinyl addition
polymers of cationic and optionally non-ionic vinyl monomers.
One preferred class is the quaternary ammonium polymers.
These quaternary ammonium polymers are generally derived from
ethylenically unsaturated monomers containing a quaternary ammonium
group or obtained by reaction between an epihalohydrin and one or more
amines such as those obtained by reaction between a polyalkylene
polyamine and epichlorohydrin or by reaction between epichlorohydrin,
dimethyl amine and either ethylenediamine or polyalkylene polyamine.
Cationic polymers are disclosed in U.S. Patent 5,368,694 the
disclosure of which is incorporated herein by reference. Generally, with all
these, the molecular weight must be such that the polymer is water soluble
or dispersible.
Other suitable cationic polymers include cationized
polyacrylamides including polyacrylamides cationized with dimethylsulfate or
methyl chloride by the Mannich reactions to varying degrees to achieve
varying degrees of cationicity, polymers derived from quaternized dimethyl
aminoethylacrylate, dicyanamide-formaldehyde condensates using one or
both of formic acid and ammonium chloride as reactants, cationic cellulose
starch compounds, carboxylated starch, xanthan gum, guar gum and
polyacrylic acid. One preferred cationic polymer is polydiallyldimethyl-
ammonium chloride.
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A wide variety of non-ionic surfactants can be used in the
present invention. These include ethoxylated fatty alcohols which are either
linear or branched and which may have a carbon chain length of anywhere
from 8 to 22 carbons. The degree of ethoxylation may vary from 3 moles to
22 moles of ethylene oxide per mole of alcohol. These would include the
Rexonic~ and Neodol~ line of linear alcohol ethoxylates. Ethoxylated
adducts of alkyl phenols as well as ethoxylated polyhydric alcohols including
sorbitols or sorbitan esters may be used. Additional non-ionic surfactants
include polyethylene oxide/polypropylene oxide block copolymers which
would include the Pluronic~ line of surfactants as well as ethoxylated
versions of fatty acids and polyethylene glycol esters of phosphates,
polyethylene glycol esters of fatty acids including esters derived from one
mole of polyethylene glycol and one or two moles of fatty acids,
tristyrylphenol ethoxylates and alkylpolyglycosides.
Generally the HLB of these surfactants will be from 7 to 18 with
a preferred range being from about 11 to13. Preferred nonionics include
Rexonic~ N23-6.5 and NeodoITM N23-6.5.
The third component of the present invention is an anionic
surfactant. Suitable anionic surfactants include water soluble or water
dispersible alkylarylsulfonates, sulfonated amines and amides, carboxylated
alcohol ethoxylates, diphenylsulfonate derivatives, lignin and lignin
derivatives, phosphate esters, soaps of process rosin, sulfates and
sulfonates of ethoxylated alkyl phenols, sulfates of ethoxylated alcohol,
sulfonates of napthalene and alkylnapthalene, polyethoxy carboxylic acid
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alcohols from the NeodoxT"" or SandopanT"" line of products, alky ether
sulfates, alkyl benzene sulfonates, alkyl sulfonates, alkyl phosphates, alkyl
sulfates, alpha olefin sulfonates, diphenyloxide disulfonates sulfosucinnates,
ethoxylated sulfosucinnates and succinamates. One preferred surfactant of
the present invention is a carboxylic acid capped ethoxylated tridecyl
alcohol.
A surfactant which incorporates a polyoxytheylene component in addition to
an anionic component is particularly suited for this invention in that it
allows
a stable product to be more easily formulated as well as conferring a
hydrophillic property to the papermaking surfaces on which it is applied in
conjunction with a cationic polymer.
Preferably, the composition comprises polydiallyldimethyl-
ammonium chloride in combination with trideceth (7) carboxylic acid and
linear alcohol ethoxylate such as Rexonic~ N23-6.5 or Neodol~ N23-6.5.
Alternatively, a secondary alkane sulfonate sodium salt based on n-paraffin
~~15 sodium (C14- C16 Alkyl Sec Sulfonate) such as Hostapur SAS 60 may be
used as the anionic surfactant.
The amount of anionic surfactant to cationic polymer should be
established so that the cationic polymer retains a significant portion of its
cationic charge. Generally from 10%-80% of its positive charge should be
maintained after the addition of the anionic surfactant.
With only the above three components, the composition will be
very acidic. The pH of the composition can be raised by the addition of water
soluble bases such as sodium or potassium hydroxide, sodium or potassium
carbonate, ammonia, organic amines such as triethanolamine,
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diethanolamine, monoethanolamine, or morpholine as well as other
compatible bases. Sufficient base can be added to establish a desired pH
of from about 3 up to about 10 depending on preference for the particular
papermaking operation.
The composition of the present invention will generally include
2% to 20% by weight cationic polymer, 2% to 40% by weight nonionic
surfactant, 0.5% to 10% anionic surfactant 0% to 5% base with the
remainder water.
One preferred formulation is as follows:
Agefloc WT 40HB (40% active) 5
Rexonic N23-6.5 (100% active) 7.4%
Sandopan DTC Acid (90% active) or
Hostapur SAS 60 (60% active) 1.1
with the remainder water. This is further diluted to obtain the desired
application or use concentration. Generally, the use concentration will be
2-10,000 ppm (actives) and, preferably, 30 to 100 ppm actives.
The Figure is a diagrammatic depiction of a press felt system
for use in the present invention. The press felt system 10 includes an upper
press felt run 12. As shown in the drawing, the paper travels in the direction
of arrow 14.
Low pressure fan shower 16 and high pressure needle
showers 18 apply the treatment agent of the present invention to the return
runs 22 of the upper and lower press felt runs. Alternately, coating rollers
can be employed. This, of course, is a diagrammatic depiction of a press felt
run and is intended merely for use in explaining the present invention.
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The present invention will be further appreciated in light of the
following detailed example.
EXAMPLE 1:
Mill Type: Linerboard
Furnish: 100% OCC
Application Location: Bottom of former before the first sheet side return
roll.
Problem: Stickies would accumulate on the forming fabric usually within 6-24
hours of having been cleaned. These stickies originated from the old
corrugated cardboard furnish that was being used. These stickies
manifested themselves as large diameter "patches" on the surface of the
wire, severely impeding the drainage of the paper slurry on the forming fabric
and decreasing sheet quality. The only way to clean them was through the
use of an aliphatic solvent cleaner. Other methods which had been tried as
traditional passivation chemistry using cationic polymers alone or traditional
cleaners either did not work or caused the deposition to occur in other places
on the machine. The cost of the program was becoming prohibitive and
required an excessive amount of solvent.
The above preferred formulation was applied to a shower just
slightly ahead of where the solvent was being applied at the rate of
100 ml/min and optimized to 60 ml/min. The deposition problem diminished
dramatically in an unexpected way such that the solvent cleaning frequency
has been reduced to only once per week rather than 2-3 times per day. This
has resulted in a solvent use reduction of 90% and a cost reduction of
approximately 10%.
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This method is a radical departure from the typical solvent
cleaning methods previously used to deal with pitch and stickies. Instead of
dissolving the pitch and stickies, this method prevents deposition. This, in
turn, reduces the use of solvents, which is desirable in itself. It also
reduces
cost and improves efficiency.
This has been a description of the present invention along with
the preferred method of practicing the present invention. However, the
invention itself should be defined by the appended claims WHEREIN WE
CLAIM:
