Note: Descriptions are shown in the official language in which they were submitted.
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TREATMENTS FOR INHIBITING
DEPOSITION IN PAPERMAKING SYSTEMS
TECHNICAL FIELD
The present invention relates to compositions and methods for
inhibiting the deposition of organic contaminants in pulp and paper-
making systems.
BACKGROUND ART
The deposition of organic contaminants in the pulp and paper in-
dustry can cause both quality and efficiency problems in pulp and paper-
making systems. Some components occur naturally in wood and are re-
leased during various pulping and papermaking processes. The term
"pitch" can be used to refer to deposits composed of organic constituents
which may originate from these natural resins, their salts, as well as coat-
. ing binders, sizing agents, and defoaming chemicals which may be found
in the pulp. In addition, pitch frequently contains inorganic components
' 15 such as calcium carbonate, talc, clays, titanium and related materials.
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Stickies is a term that has been increasingly used to describe de-
posits that occur in the systems using recycled fiber. These deposits
often contain the same materials found in "pitch" deposits in addition to
adhesives, hot melts, waxes, and inks. All of the aforementioned materi-
als have many common characteristics including: hydrophobicity, de-
formability, tackiness, low surface energy, and the potential to cause
problems with deposition, quality, and efficiency in the process. Diagram
I shows the complex relationship between pitch and stickies discussed
here.
DIAGRAM I
Pitch Stickies
Natural Resins (fatty and resin acids, fatty esters, X X
insoluble salts, sterols, etc.)
Defoamers (oil, EBS, silicate, silicone oils, X X
ethoxylated compounds, etc.)
Sizing Agents (Rosin size, ASA, AKD, hydrolysis X X
products, insoluble salts, etc.)
Coating Binders (PVAC, SBR) X X
Waxes X
Inks X
Hot Melts (EVA, PVAC, etc.) X
Contact Adhesives (SBR, vinyl acrylates, X
polysisoprene, etc.)
The deposition of organic contaminants can be detrimental to the
efficiency of a pulp or paper mill causing both reduced quality and reduc-
ed operating efficiency. Organic contaminants can deposit on process
equipment in papermaking systems resulting in operational difficulties in
the systems. The deposition of organic contaminants on consistency
regulators and other instrument probes can render these components
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useless. Deposits on screens can reduce throughput and upset opera-
tion of the system. This deposition can occur not only on metal surfaces
in the system, but also on plastic and synthetic surfaces such as machine
wires, felts, foils, Uhle boxes and headbox components.
In the past stickies deposits and pitch deposits have typically
manifested themselves in different systems. This was true because mills
usually used only virgin fiber or only recycled fiber. Often very different
treatment chemicals and strategies were used to control these separate
problems.
Current trends are for increased mandatory use of recycled fiber
in all systems. This is resulting in a co-occurrence of stickies and pitch
problems in a given mill. It is desirable to find treatment chemicals and
strategies which will be highly effective at eliminating both of these prob-
lems without having to feed two or more separate chemicals. The mater-
ials of this invention have clearly shown their ability to achieve this goal.
U.S. Patent No. 4,871,424 teaches methods for controlling pitch
deposition from pulp in papermaking systems utilizing a water-soluble
polyvinyl alcohol having 50°~ to 100°~ hydrolysis. U.S. patent
No.
4,886,575 teaches a method for inhibiting the deposition and adherency
of hot melt andlor pressure sensitive adhesive materials, "stickier", on
the surfaces of repulping equipment using polyvinyl alcohol moieties that
also contain some hydrophobic groupings, these PVA moieties having 70
to 99% hydrolysis. "Pulp and Paper", by James Casey, Vol. III, 3rd Ed.,
pp. 1587-1588, teaches that gelatin has been suggested as a remedy for
pitch trouble.
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DISCLOSURE OF INVENTION
The present invention relates to compositions and methods for in-
hibiting the deposition of organic contaminants from pulp on the surfaces
of papermaking machinery in pulp and papermaking system comprising
adding to the pulp or to the surfaces of the papermaking machinery an
effective deposition inhibiting amount of a composition comprising poly-
vinyl alcohol and a high molecular weight gelatin.
Organic contaminants include constituents which occur in the pulp
(virgin, recycled or combinations thereof) having the potential to deposit
and reduce paper machine performance or paper quality. This includes
but is not limited to natural resins such as fatty acids, resin acids, their
insoluble salts, fatty esters, sterols and other organic constituents such
as ethylene bis-stearamide, waxes, sizing agents, adhesives, hot melts,
inks, defoamers, and latexes which may deposit in papermaking systems.
The polyvinyl alcohol component of this invention can be derived
or synthesized by polymerizing vinyl acetate to form polyvinyl acetate and
alcoholysis or hydrolysis of the polyvinyl acetate to form polyvinyl alcohol.
The polyvinyl alcohol can have a percent hydrolysis from about 50% to
100% with about 70% to about 100% preferred. The term "percent hy-
drolysis" is defined as the mole ratio of the hydroxyl groups to the starting
acetate groups in the hydrolyzed polyvinyl acetate (polyvinyl alcohol)
polymer multiplied by 10. Most preferably, the polyvinyl alcohol has a
percent hydrolysis from about 85.5% to about 87%. It is further preferred
that the polyvinyl alcohol has a molecular weight from about 15,000 to
about 125,000. The polyvinyl alcohols useful in the present invention are
readily commercially available. Representative polyvinyl alcohols include
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Airvol~ 205 (MW~25,000), Airvol~ 523 (MW~78,000) and Airvol~ 540
(MW~125,000), all available under their respective tradenames from Air
Products, Inc.
5 The gelatin that is preferred for use in the synergistic composition
has a molecular weight ranging from about 100,000 to about 250,000.
Most preferably, the gelatin has a molecular weight of about 130,000. One
such gelatin is commercially available from Hormel Foods under the trade-
name Flavorset GP-4. The term "high molecular weight gelatin" is defined
as a gelatin having a molecular weight of about 100,000 or higher.
Surprisingly, it has been found that when the components are mix-
ed, in certain instances, the resulting mixtures possess a higher degree
of inhibiting organic deposition than that of the individual ingredients
comprising the mixture. Accordingly, it is possible to produce a highly
efficacious inhibitor for use in pulp and papermaking systems. Because
of the enhanced activity of the mixture, the total quantity of the deposition
inhibitor treatment may be reduced. In addition, the high degree of inhi-
bition which is provided by each of the ingredients may be exploited with-
out use of higher concentrations of each.
The composition of polyvinyl alcohol and high molecular weight
gelatin shows enhanced activity as a deposition inhibitor when employed
in a PVAlgelatin weightlweight ratio of from about 1:1 to about 10:1.
Superior synergistic effects are demonstrated when the weight/weight
ratio is about 8:1.
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The compositions of the present invention may be compatible with
other pulp and papermaking additives. These can include starches, ti-
tanium dioxide, defoamers, wet strength resins, and sizing aids.
The compositions of the present invention can be added to the
papermaking system at any stage. They may be added directly to the
pulp furnish or indirectly to the furnish through the headbox. The inven-
tive compositions may also be sprayed onto surfaces that are suffering
from deposition, such as the wire, press felts, press rolls and other
deposition-prone surfaces.
The compositions of the present invention can be added to the
papermaking system neat, as a powder, slurry or in solution; the pre-
ferred primary solvent being water but is not limited to such. When add-
ed by spraying techniques, the inventive composition is preferably diluted
with water to a satisfactory inhibitor concentration. The inventive compo-
sitions may be added specifically and only to a furnish identified as con-
taminated or may be added to blended pulps. The compositions may be
added to the stock at any point prior to the manifestation of the deposition
problem and at more than one site when more than one deposition site
occurs. Combinations of the above additive methods may also be em-
ployed by feeding either the polyvinyl alcohol or high molecular weight
gelatin separately, by way of feeding the pulp millstock, feeding to the
paper machine furnish, and spraying on the wire and the felt simultane-
ously.
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The effective amount of the composition to be added to the paper-
making system depends on a number of variables including the pH of the
system, hardness of the water, temperature of the water, additional addi-
tives, and the organic contaminant type and content of the pulp. Gener-
ally, from 0.5 parts to about 150 parts of the inventive composition per
million parts of pulp is added to the papermaking system. Preferably,
from about 2 parts to about 100 parts of the inventive composition are
added per million parts of pulp in the system.
There are several advantages associated with the present inven-
tion as compared to prior processes. These advantages include an abili-
ty to function without being greatly affected by hardness of the water in
the system; an ability to function while not adversely affecting sizing and
fines retention; an ability to function at very low dosages; reduced envi-
ronmental impact; and improved biodegradability.
Further, these compositions have proven effective against both the
pitch and stickies manifestation of organic deposition problems providing
for an effective reduction of these problems in paper mills utilizing a
variety of virgin and recycled fiber sources.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph of percent detackification at 25°C versus dosage
for various deposition control agents tested and reported in Table I
below.
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Fig. 2 is a graph of percent detackification at 50°C versus dosage
for various deposition control agents tested and reported in Table II
below.
MODES FOR CARRYING OUT THE INVENTION
The data set forth below were developed to demonstrate the unex-
pected results occasioned by use of the present invention. The following
examples are included as being illustrations of the invention and should
not be construed as limiting the scope thereof.
Examples
Standard Tape Detackification Test
In order to establish the efficacy of the inventive composition as
deposition control agents on plastic surfaces and specifically for adhesive
contaminants of the sort found in recycled pulp, a laboratory test was de-
veloped utilizing adhesive-backed tapes as stickie coupons. The stickie
coupon can be fabricated from any type of adhesive tape that will not dis-
integrate when placed in water. For this study, tapes made from a styrene-
butadiene rubber and vinylic esters were used. Both of these potential or-
ganic contaminants are known to cause stickies problems in secondary
fiber utilization. A second coupon was fabricated from polyester film such
as MYLAR~, a product marketed by the DuPont Chemical Company. This
material was chosen because paper machine forming fabrics are frequent-
ly made of polyester which is susceptible to considerable deposition prob-
lems caused by stickies andlor pitch.
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This test involved immersing a 5.08 cm x 10.16 cm adhesive tape
and a 5.08 cm x 10.16 polyester Mylar coupon into a 600 gram solution
being tested. The solution contained in a 600 mL beaker is placed in a
water bath with agitation and heated to the desired temperature. After 30
minutes of immersion, the tape and coupon are removed from the solu-
tion and pressed to 4530 kg force for one minute. A tensile test instru-
ment (Instron) is then used to measure the force required to pull the two
apart. A reduction in the force required indicates that the "stickie" has
been detackified. The % control or detackification is calculated by the
following equation:
detackification = untreated force - treated force) x 100
untreated force
The results of this testing are presented in Tables I and II.
TABLEI
Standard Tape Detackification Test at
25C
Example No. Dosage lppm) % Detackification
1 1 78.5
2 96.7
5 99
10 100
2 1 46
2 64
5 90
10 97
3 1 67.3
2 89.1
5 91.5
10 92.1
4 1 51
70
5 94
10 95
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TABLE I (cont'd)
Standard Tape Detackification Test at 25°C
Example No. Dosage (ppm) % Detackification
5 1 71
5 2 90
5 94.1
10 96
6 1 3
2.5 21
10 5 43
10 56
25 93
50 100
100 100
7 0.1 25
0.25 29
1 54
2.5 60
5 59
10 61
81
50 86
100 89
1000 100
25 8 1 16
2.5 36
5 40
10 59
25 78
50 89
100 93
TABLE II
Standard Tape Detackification Test
at 50C
Example No. Dosa4e ,ppm) % Detackification
1 0.25 91
0.5 96.4
1 100
2 100
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TABLE II (cont'd)
Standard Tape Detackification Test
at 50C
Example No. Dosage (ppm) % Detackification
2 0.25 86
1 94
5 98
4 0.2 22.3
0.5 53.6
1 83
2 91
5 0.25 35.7
0.5 55
1 71
2 73
6 0.25 3
1 5
5 55
10 74
97
20 7 0.25 3
1 5
5 60
10 82
25 96
25 8 0.25 10
1 25
5 90
10 95
25 97
Example 1 is 8:1 w/w ratio of Airvol 540: HMW gelatin
Example 2 is 1:2 w/w ratio of Airvol 540:HMW gelatin
Example 3 is 1:1 wlw ratio of Airvol ~540:HMW gelatin
Example 4 is Airvol~ 540
Example 5 is HMW gelatin
Example 6 is Surfonic~ N-95
Example 7 is Pluronic~ F-108
Example 8 is Igepal~ RC-520
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Airvol~ 540 is polyvinyl alcohol (MW - 125,000), available from Air
Products, Inc. (85.5-87% hydrolyzed)
HMW gelatin ~ 100,000 molecular weight
Surfonic~ N-95 is a nonyl phenol ethoxylated surfactant, available from
Texaco
Pluronic~ F-108 is a block copolymer polyoxyalkylene derivative of
propylene glycol, available from BASF Wyandotte, Inc.
Igepal~ RC-520 is an alkylphenoxypoly(oxyethylene)ethanol, available
from GAF, Inc.
These results indicate that the inventive composition of 8:1 PVA/
gelatin exhibited pronounced synergistic effects while the composition in
ratios of 1:2 and 1:1 also demonstrated synergism. These results further
indicate that polyvinyl alcohol (U.S. Pat. Nos. 4,871,424 and 4,886,575)
and high molecular weight gelatin (Pulp and Paper, Vol. III, p. 1588) were
less effective at detackification than the inventive composition. The in-
ventive composition also proved more effective than the traditional pitchl
stickies control agents, Examples 6, 7 and 8.
Contact angle measurements were also performed utilizing the in-
ventive composition. The MYLAR or tape adhesive surface is clamped on
a film stage and placed inside the glass test cell. The test solution is add-
ed to the cell by carefully pouring 15 mL of the solution into the cell. The
whole test cell was then placed inside the chamber of a goniometer
(Kruss G1 ). The MYLAR or tape adhesive surface was immersed in the
solution for 30 minutes to simulate the contact time as in the standard
tape detackification test. Contact angle provides information about the
hydrophobicity of a simulated stickies surface and the change in the hy-
drophobicity as surface-active materials are adsorbed andlor desorbed at
the surface. If the contact angle of the treated solution is lower than that
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of the untreated, this indicates that the surface becomes more hydrophilic
or less stickie. The results of this testing are reported in Tables III and
IV.
TABLE III
Contact Angle Measurements
at 25C
Material Dosa4e (ppm) Surface Contact Anple
Water -- MYLAR 58
-- tape 81
P1500 2 tape 65
5 tape 47
5 MYLAR 48
Peptein 2000 2.5 MYLAR 49
Meat soluble protein 2 tape 46
Protein 2 MYLAR 46
5 MYLAR 49
5 tape 39
Gelatin (high MW} 2.5 MYLAR 37
2.5 tape 41
Airvol~ 540 2.5 MYLAR 45
2.5 tape 54
Airvol~ 540/high MW 2.5 MYLAR 32
Gelatin (8:1 )
2.5 tape 34
P1500 is a low molecular weight gelatin (MW ~ 1500-5000)
Peptein 2000 is a low molecular weight gelatin (MW X1500-5000)
Airvol~ 540 is polyvinyl alcohol, available from Air Products, Inc.
TABLE IV
Contact Angle Measurements at 50C
o Material Dosage (ppm) Surface Contact Angle
Surfonic~ N-95 5 MYLAR 48
Pluronic~ N-95 5 MYLAR 50
High M.W. gelatin 2.5 MYLAR 34
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TABLE IV Icont'dl
Contact Angle Measurements at 50°C
Material Dosage (ppm) Surface Contact An4le
Airvol~ 540 2.5 MYLAR 24
0.5 MYLAR 41
Airvol~ 540/high MW 2.5 MYLAR 20
Gelatin (8:1 )
0.5 MYLAR 25
The results presented in Tables III and IV demonstrate that the
inventive compositions exhibit a much lower contact angle than the con-
ventional pitchlstickies control agents and polyvinyl alcohol and high
molecular weight gelatin when each are employed individually. Further-
more, the low molecular weight gelatin and meat soluble protein also
proved less effective than the inventive composition.
It is well known that surface-active materials tend to form aggre-
gates at the Critical Micelle Concentration (CMC). The CMC can be esti-
mated from the break observed in the surface tension-concentration semi-
log plot. No CMC was observed for the high molecular weight gelatin for
the concentrations studied (i.e., 0.5 ppm to 100 ppm). The CMC is expect-
ed to be higher than 100 ppm. A CMC of 10 ppm was obtained for the
Airvol~ 540. The 8:1 ratio of PVA/high molecular weight gelatin exhibited
a very low CMC of 2 ppm which is indicative of a synergistic mixture.
INDUSTRIAL APPLICABILITY
The compositions of the present invention are effective at inhibiting
the deposition of organic contaminants in papermaking systems. This may
include Kraft, acid sulfite, mechanical pulp and recycled fiber systems. For
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example, deposition in the brown stock washer, screen room and decker
system in Kraft papermaking processes can be inhibited. The term "paper-
making systems" is meant to include all pulp processes. Generally, it is
thought that these compositions can be utilized to inhibit deposition on all
5 surfaces of the papermaking system from the pulp mill to the reel of the
paper machine having a pH from about 3 to 11 and under a variety of sys-
tem conditions. More specifically, the compositions effectively decrease
the deposition not only on metal surfaces but also on plastic and synthetic
surfaces such as machine wires, felts, foils, Uhle boxes, rolls and headbox
10 components.
While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and modi-
fications will be obvious to those skilled in the art. The appended claims
15 generally should be construed to cover all such obv:~~~s forms and modi-
fications which are within the scope of the present invention.
