Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a process for the prepara-
tion of hydrophilic polyolefin fibers which are readily dis-
persible in water and which can be blended with wood pulp
fibers to provide a pulp which can be made into high quality
paper using conventional papermaking techniques. More par-
ticularly, this invention relates to formation of polyolefin-
based fibers and treatment of these fibers by precipitating on
the surfaces thereof a hydrated material of submicron dimen-
sions. The presence of the hydrated material on the fiber
surface renders the fiber uniformly hydrophilic and ionic.
In recent years, a considerable amount of effort has
been expended in the development of water-dispersible, fibrous
polyolefin pulps having hydrophiLic properties. One procedure
developed for the purpose of attaining such properties is that
described in U.S. 3,743,570 to Yang et al, assigned to Crown
Zellerbach Corporation. According to this patent, polyolefin
fibers having a high surface area are treated with a hydro-
philic colloidal polymeric additive composed of a cationic
polymer such as melamine-formaldehyde and an anionic polymer
such as carboxymethyl cellulose. Another procedure developed
for the preparation of water-dispersible, hydrophilic poly-
olefin pulps has been one involving the spurting of a mixture
of the polyolefin and an additive such as a hydrophilic clay
or a hydrophilic polymer, for example, polyvinyl alcohol.
The spurting process used in these preparations is one in
which the polyolefin and the hydrophilic additive are dis-
persed in a liquid which is not a solvent for either com-
ponent at its normal boiling point, heating the resulting
dispersion at superatmospheric pressure to dissolve the
polymer and any solvent-soluble additive, and then dis-
charging the resulting composition into a zone of reduced
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temperature and pressure, usually atmospheric, to form the
fibrous product.
A deficiency of these polyolefin pulps has been that,
when they have been blended with wood pulp, the resulting
paper products have exhibited considerably less strength
than that of a paper prepared from wood pulp alone. How-
ever, some improvement in the strength of paper made from
blends of polyolefin pulps and wood pulp has been realized
by imparting an anionic character to the polyolefin pulp.
For example, in their German application No. 413,922, filed
March 22, 1974 and published October 17, 1974 as No.
2,413,922, Toray Industries, Inc. have disclosed the prep-
aration of anionic pulps by spurting mixtures of poly-
olefins and copolymers of olefinic compounds with maleic
anhydride or acrylic or methacrylic acids. Blends of these
pulps with wood pulp have provided paper with better
tensile strength than paper made without the copolymer
component.
Moreover, in Belgian Patent No. 850,721 to Hercules
Incorporated, it is disclosed that paper having further im-
proved strength properties can be prepared by forming a
spurted fibrous anionic polyolefin composition containing
carboxylic functionality, for example, a spurted fibrous
composition comprising a mixture of a polyolefin and a
carboxyl-containing anionic polymer, and then modifying this
fibrous product by intimately contacting the fibers in a
dilute aqueous solution or dispersion of a blend of a cer-
tain type of cationic, water-soluble, nitrogen-containing
polymer and a certain type of anionic, water-soluble,
nitrogen-containing polymer. The fiber modifying step re-
sults in deposition of the blend of cationic and anionic
nitrogen-containing polymers on the spurted fibers, and the
originally anionic fibers are converted into modified fib-
ers which are capable of bonding to the cellulosic fibers
of wood pulp.
Even so, paper prepared from blends of the aforemen-
tioned modified fibers and wood pulp, although exhibiting
satisfactory strength properties, has presented, in certain
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8706
instances, some difficulties associated with actual use of the paper. For
example, the immediate product from a paper-making machine is a roll of paper of
such size that the paper normally has to be cut into specified widths and rewound
in order to be placed in usable form. During the rewinding operation, the paper
is passed at high speed, normally over stationary metal guides, and the resulting
heat and friction cause embrittlement and flaking off of certain types of the
modified polyolefin fibers in the form of dust. Much of this dust is carried
along with the paper and, when the paper is used, for example, in offset printing,
the dust accumulates on the ink roll, necessitating frequent cleaning to insure
proper transfer of the ink to the printing roll.
Now it has been found that a paper having satisfactory strength proper-
ties and improved rewindability and printability can be prepared from polyolefin
fibers prepared by a process in accordance with this invention. The polyolefin
fibers are prepared by forming an aqueous suspension of spurted polyolefin
fibers, adding to said suspension, with stirring an aqueous solution of a water-
soluble ionized reagent capable of being converted into hydrated solid particles
submicron in size, said ionized reagent being selected from the group consisting
of the alkali metal and ammonium salts of rosin, modified rosins, ethylene-
acrylic acid and ethylene-methacrylic acid copolymers and mixtures thereof and
then adding to the resulting dispersion an ionic precipitant for said reagent,
thereby effecting precipitation of said hydrated solid particles uniformly onto
the surfaces of the polyolefin fibers. Thus, the fiber surfaces become essenti-
ally uniformly hydrophilic and ionic. As a consequence, the treated fibers are
hydrophilic, water-dispersible and very receptive to hydrophilic additives, such
as starch, which are ordinarily added in the papermaking process. The preferred
water-soluble ionized reagents of this invention are the alkali metal salts or
ammonium salts of rosin and modified rosins.
As an example of the process of this invention, spurted polypropylene
fibers are suspended in water by stirring and to the stirred suspension is added
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1~L48706
a dilute aqueous solution of the sodium salt of rosin. Stirring is continued
and then a dilute aqueous solution of alum is added to the fiber dispersion,
resulting in deposition of hydrated rosin-containing particles submicron in
size on the surface of the
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polypropylene fibers. The treated fibers may then be
isolated and stored in wet cake form, or the suspension
containing the fibers may be used directly in a papermaking
process.
Having generally outlined the embodiments of this
invention, the following examples illustrate various embodi-
ments thereof. All amounts and percentages are by weight
unless otherwise specified.
ExamPle A
A cationic, water-soluble, nitrogen-containing polymer
was prepared from diethylenetriamine, adipic acid and epi-
chlorohydrin. Diethylenetriamine in the amount of 0.97 mole
was added to a reaction vessel equipped with a mechanical
stirrer, a thermometer and a reflux condenser. There then
was gradually added to the reaction vessel one mole of
adipic acid with stirring. After the acid had dissolved in
the amine, the reaction mixture was heated to 170-175C. and
held at that temperature for one and one-half hours, at
which time the reaction mixture had become very viscous.
The reaction mixture then was cooled to 140C., and suffi-
cient water was added to provide the resulting polyamide
solution with a solids content of about 50%. A sample of
the polyamide isolated from this solution was found to have
a reduced specific viscosity of 0.155 deciliters per gram
when measured at a concentration of two percent in a one
molar aqueous solution of ammonium chloride. The polyamide
solution was diluted to 13.5% solids and heated to 40C.,
and epichlorohydrin was slowly added in an amount corres-
ponding to 1.32 moles per mole of secondary amine in the
polyamide. The reaction mixture then was heated at a tem-
perature between 70 and 75C. until it attained a Gardner
viscosity of E-F. Sufficient water next was added to pro-
vide a solids content of about 12.5%, and the solution was
cooled to 25C. The pH of the solution then was adjusted
to 4.7 with concentrated sulfuric acid. The final product
contained 12.5% solids and had a Gardner viscosity of B-C.
Example B
An anionic, water-soluble, nitrogen-containing polymer
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was prepared from acrylamide, acrylic acid and glyoxal. Toa reaction vessel equipped with a mechanical stirrer, a
thermometer, a reflux condenser and a nitrogen adapter was
added 890 parts of water. There then was dissolved in the
water 98 parts of acrylamide, two parts of acrylic acid and
one and one-half parts of aqueous 10% cupric sulfate. The
resulting solution was sparged with nitrogen and heated to
76C., at which point two parts of ammonium persulfate dis-
solved in six and one-half parts of water was added. The
temperature of the reaction mixture increased 21.5C. over
a period of three minutes following addition of the persul-
fate. When the temperature returned to 76C., it was main-
tained there for two hours, after which the reaction mixture
was cooled to room temperature. The resulting solution had
a Brookfield viscosity of 54 centipoises at 21C. and con-
tained less than 0.2% acrylamide based on the polymer
content.
To 766.9 parts of the above solution (76.7 parts of
polymer containing 75.2 parts, or 1.06 mole, of amide repeat
units) was added 39.1 parts of aqueous 40% gloxal (15.64
parts, or 0.255 equivalent based on amide repeat units, of
glyoxal). The pH of the resulting solution was adjusted to
9.25 by the addition of 111.3 parts of aqueous 2% sodium
hydroxide. Within approximately 20 minutes after addition
of the sodium hydroxide, the Gardner viscosity of the solu-
tion had increased from A to E. The reaction was then ter-
minated by the addition of 2777 parts of water and about two
and six-tenths parts of aqueous 40% sulfuric acid. The re-
sulting solution had a pH of 4.4 and contained 2.2% solids.
Example 1
Fifteen grams of air-dried spurted polypropylene was
placed in a one-gallon Waring blender together with 1.3
liters of demineralized water and the mixture was stirred
moderately. To the resulting suspension there was added
three percent (based on dry fiber weight) of a completely
hydrogenated rosin size (completely saponified) as an aque-
ous solution, with continued stirring, and there then was
added sufficient 10% papermakers' alum solution to reduce
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the system pH to about 4.1. The resulting dispersion then
was stirred at full blender speed for one minute, after
which it was diluted to 1.5 liters. This procedure was
repeated with another 15-gram fiber sample, and the two
preparations were combined.
In making handsheets using the treated polypropylene
fibers, 1.26 liters of the combined slurry described above
was partly dewatered by filtration and then added to 1.18
liters of a 2.5% wood pulp slurry (29.4 grams of dry fiber
consisting of 50% softwood bleached kraft and 50~ hardwood
bleached kraft) which had been beaten to 750 ml. Schopper-
Riegler freeness in a Noble and Wood cycle beater, using
neutral tap water as the aqueous phase. Forty-pound/3000
sq. ft. (basis weight) handsheets were made from this 30%
polypropylene/70% wood pulp fiber blend using Noble and Wood
handsheet equipment. The formed sheets were wet pressed and
then dried by two passes over a 240-250F. drum dryer.
Example 2
Polypropylene fibers were treated as in Example 1
except for the use of one percent (based on dry fiber
weight) of a wood rosin size which contained excess alkali
in place of the hydrogenated rosin size of Example 1. In
making handsheets using these fibers, 1.26 liters of slurry
was first stirred in the presence of 0.63 gram of a bonding
agent which was a 1:5 by weight blend of the cationic poly-
mer of Example A and the anionic polymer of Example B. The
resulting slurry was then partly dewatered before combining
with the standard wood pulp slurry as in Example 1. Hand-
sheets were made in the same manner as in Example 1.
Example 3
The procedure of Example 2 was duplicated except that
three percent wood rosin size was added instead of one
percent.
Example 4
The procedure of Example 3 was repeated with the excep-
tion that three percent hydrogenated rosin size of the type
used in Example 1 was used instead of three percent wood
rosin size.
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Handsheet properties for Examples 1 to 4 are listed in
Table I. The data for Example 1 show that adequate sheet
dry strength values were obtained. The data for Examples 2
to 4 show the increased strength values obtained by addition
of the bonding agent of Example 2, thus demonstrating that
the treated fibers are quite responsive to the bonding
agent.
Table I
Dry Strenqth Bonding
Bright- Mullen Instron MIT Agent in
Caliper ness Opacity Burst Tensile Fold Sheet
Ex. (mils) (%) (%) (PSi) (lb./in.) (%)*
1 8.3 92.0 92.0 15.7 10.6 15 0
2 7.8 90.6 91.9 17.5 11.5 29 6.0
3 8.0 90.1 90.9 19.7 12.3 33 4.5
4 7.8 90.8 91.2 20.1 12.9 33 6.1
*The % bonding agent in the sheet is based on
the amount of the polypropylene fiber component.
Results comparable to those of the above examples were ob-
tained when the alkali metal salts of partially hydrogenated
rosin, disproportionated rosin, dimerized rosin, polymerized
rosin, fumaric acid-modified rosin and ethylene-acrylic acid
copolymer were used in place of the rosin and completely
hydrogenated rosin sizes of the examples.
Example 5
The synthetic pulp used in this example was prepared
by first dissolving a 99.5:0.5 mixture of polypropylene
(IV = 1.9-2.2) and octadecyl 3-[3,5-di(tertiary butyl)-4-
hydroxyphenyl]propionate stabilizer in 98:2 hexane:water to
eight percent polymer solids at 215C. and 80 kg/cm2 pres-
sure. The resulting solution was released through a nozzle
into a region of autogenous pressure at 80C. and the pulp
(surface area = 3.6 m2/gm.: monoclinic crystallinity) that
formed was carried into an aqueous solution of poly(vinyl
alcohol). The poly(vinyl alcohol) (PVA) had a degree of
hydrolysis ~98% and a minimum viscosity, measured on a four
percent aqueous solution at 20C., of four centipoises. The
PV~ was affixed to the fiber in an amount of about one-half
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percent by deflaking the pulp suspension in the aqueous PVA
solution.
After dewatering and baling, the synthetic pulp wet mat
was transported to appropriate papermaking equipment where
5 50 dry pounds was suspended in soft water at two to two and
one-half percent consistency in a beater. To this pulp
slurry was added an aqueous solution of sodium resinate
formed by dissolving two dry pounds of N-wood rosin in aque-
ous sodium hydroxide (102 dry grams of NaOH), stirring at
10 80C. until the rosin was completely dissolved, and then
diluting to five percent rosin solids. The percent rosin
based on the synthetic pulp was four percent, calculated as
free acid. ~hen, 26 pounds of 12% aqueous alum (3.12 dry
lb., 6.24% based on the synthetic pulp) was added to the
15 beater, the final pH being 4.4. After the mixture was
stirred 10-15 minutes, the pH was increased to 7.4 by
addition of two and one-half liters of aqueous five percent
NaOH, after which 42 pounds of six percent cationic starch
B (Sta-Lok ~00, two and one-half dry pounds, five percent
20 based on the synthetic pulp) was added.
Wood pulp (50 dry pounds of Weyerhauser bleached hard-
wood kraft, WBHK, and 100 dry pounds of Rayonier bleached
softwood kraft, RBSK) was defibered in the beater containing
the treated synthetic pulp; the percent synthetic pulp was
25 25% of the total pulp furnish. The pulp blend was refined
to 286 Canadian Standard Freeness (CSF), first with a
Claflin refiner and then with a double disc refiner. After
internal addition of 0.35% of fortified free rosin emulsion
(Neuphor 100) and 1.25% alum to the dilute pulp slurry for
30 sizing, it was formed into a sheet on a conventional
Fourdrinier paper machine. A mixture of an aqueous six per-
cent cationic starch ~Cato~67) solution and an aqueous six-
tenths percent cationic wet-strength resin (Kymene~ 557)
solution was added at the size press. ~ight calendering was
35 applied before the sheet was rolled up. The following
physical test data were obtained after the paper was aged
for several weeks: basis weight = 26.2 lb./3000 ft.2;
caliper = 3.0 mils; Tappi brightness = 86.6%; Tappi
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87~6
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opacity = 71.4%; Mullen burst = 12.6 p.s.i.; tensile = 12.1
lb./l in. width; MIT fold = 92; IGT pick, W P = 108
KP-cm./sec.
Rewindability was tested on a small rewinder. The paper
was judged to run clean at 1500 ft./min. and gave a small but
acceptable amount of dust at 1850 ft./min. For comparison,
paper containing an oxidized polypropylene pulp treated in
accordance with Belgian Patent No. 850,721 rarely ran clean
at 800 ft./min. and never rewound with an acceptable amount
of dust at 1200 ft./min.
The paper which had been rewound at 150C ft./min. was
sheeted and then printed using a sheet-fed offset printing
press. Print quality was judged to be good, and no dust and
only a very small amount of lint were found on the offset
blanket. For comparison, paper prepared in the same way as
in this example except for omission of the sodium resinate-
alum treatment displayed very poor print quality and gave an
excessive amount of debris and lint on the offset blanket.
Example 6
The same synthetic pulp used in Example 5 was pretreated
with N-wood rosin size and alum, prior to use in the paper-
making operation, by first dispersing 50 dry pounds of the
PVA-containing pulp in 600 gallons deionized water and then
adding an aqueous solution of two dry pounds (four percent
based on the synthetic pulp) N-wood rosin dissolved in aque-
ous alkali as described in the previous example. This
mixture was stirred for 15 minutes and then treated with six
percent (based on the synthetic pulp) alum (three dr-y pounds
in two gallons of water). After vigorous stirring for 30
minutes, the resulting slurry (pH about 4.5) was dewatered in
large filter crocks to give a pulp mat, at about 20% solids,
which was transported to appropriate papermaking equipment.
It then was dispersed in soft water and to the resulting
slurry (pH 7.4) was~added 42 pounds of an aqueous six percent
solution of Sta-Lok 400 (two and one-half dry pounds, five
percent based on the synthetic thetic pulp), foliowed by 50
dry pounds of WBHK and 100 dry pounds of RBSR pulp. The
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8706
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pulp blend was refined to 348 CSF and then made into paper
as described in Example 5.
The calendered sheet gave the following test data after
natural aging: basis weight = 28.9 lb./3000 ft.2; caliper
= 3.6 mils; Tappi brightness = 86.0%; Tappi opacity = 73.0%;
Mullen burst = 13.6 p.s.i.; tensile = 13.5 lb./l in. width;
MIT fold = 110; IGT pick, W P = 66 KP-cm./sec. ~ewindability
and printability of the paper prepared in tnis example were
essentially equivalent to those of the paper of Example 5.
Example 7
Using the same synthetic pulp as that of Example 5 and
- following substantially the procedure of Example 5 except for
minor variations in amounts of materials used, the pulp was
treated with the sodium salt of a partially hydrogenated wood
rosin instead of the sodium salt of the N-wood rosin of
Example 5. In so doing, 40 dry pounds of the pulp, dispersed
in water, was treated with an aqueous solution formed by dis-
solving two and four-tenths pounds of the partially hydrogen-
ated rosin in aqueous sodium hydroxide containing 135 dry
grams of NaOH, and then diluting the solution to 12% solids.
The percent hydrogenated rosin based on the synthetic pulp
was six percent, calculated as free acid.
To the resulting dispersion was added ten pounds of 12%
aqueous alum, the pH was adjusted from 4.6 to 6.8, a six per-
cent cationic starch solution was added in the amount of 33pounds, wood pulp (40 pounds WBHK and 80 pounds RBSK) was
added, the pulp blend was refined to 335 CSF and then the
blend was made into paper as in Example 5 except to omit
addition of the wet-strength resin at the size press. After
aging, the following test data were obtained: basis weight =
29.2 lb./3000 ft.2; caliper = 3.6 mils; Tappi brightness =
87.5%; Tappi opacity = 73.8%; Mullen burst = 13.3 p.s.i.;
tensile = 14.1 lb./l in. width; MIT fold = 110; IGT pick,
W P = 78 KP-cm./sec.
In the rewindability test, the paper gave a slight
amount of fine powder on the spreader bar at 1240 and 1600
ft./min., and it was concluded that the paper could be re-
wound without difficulty at these speeds. After the rewound
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paper had been sheeted and trimmed, it was evaluated for
printability as in Example S. Print quality was judged to be
good, and only a small amount of fine debris transferred to
the offset blanket during the making of 500 impressions. It
was concluded that, in comparison to a paper which had been
prepared in the same way except for omission of the hydrogen-
ated rosin-alum treatment, the paper of this example would
provide at least five times as many impressions before print
quality became affected by offset blanket contamination.
ExamPle 8
The procedure of Example 7 was essentially repeated ex-
cept that no cationic starch was added following the hydro-
genated rosin-alum treatment. The following test data were
obtained after the paper was aged for several weeks: basis
weight = 28.5 lb./3000 ft.2; caliper = 3.4 mils; Tappi
brightness = 87.1%; Tappi opacity = 77.9%; Mullen burst =
12.8-p.s.i.; tensile = 13.4 lb./l in. width; MIT fold = 130;
IGT pick, VVP = 97 KP-cm./sec. A roll of the paper product
was rewound without difficulty at 1220 ft./min. When paper
from this roll was printed, as described in Example 5, a
noticeable amount of fine debris was transferred to the off-
set blanket. It was concluded that, in comparison to a paper
which had been prepared in the same way except for omission
of the hydrogenated rosin-alum treatment, the paper of this
example would provide four times as many impressions before
print quality became affected by offset blanket contamina-
tion. Thus, not adding cationic starch internally moderately
reduced the printability of this paper product in comparison
to the product of Example 7.
ExamPle 9
The procedure of Example 7 was substantially duplicated
except that the sodium salt of the partially hydrogenated
wood rosin was replaced with the sodium salt of the modified
rosin formed by reaction of rosin with fumaric acid and com-
posed of a mixture of rosin and the rosin-fumaric acid adduct
(about 85% of the acid groups of the modified rosin being
neutralized with sodium hydroxide). The physical properties
and the rewindability and printability of the paper product
82~o
were quite comparable to the corresponding properties of the
product of Example 7.
Example lO
The synthetic pulp used in this example was prepared in
the same way as that of Example 5 except that tetrakis-
[methylene 3-(3,5-ditertiarybutyl-4-hydroxyphenyl)propionate]-
methane was used as the stabilizer and the pulp was not
carried into an aqueous solution of poly(vinyl alcohol).
Instead, after release into a region of autogenous pressure
]0 at 80C., it was withdrawn through a water seal and then
baled and transported to appropriate papermaking equipment.
To a Hollander beater containing 300 gallons of soft water
was added eight pounds of a five percent solution of sodium
hydroxide. The pH of the resulting solution was 10, and to
]5 this solution then was added 12.5 pounds of a 20% solution
of the ammonium salt of an ethylene-acrylic acid copolymer
(20% acrylic acid, molecular weight approximately 25,000),
followed by 50 dry pounds of the synthetic pulp.
The pulp was dispersed by circulating it in the beater
for five minutes, following which the copolymer was precip-
itated in situ by the addition of 27 pounds of a five per-
cent sulfuric acid solution to the beater, this reducing the
pH to 6.2. The resulting mixture was circulated in the
beater for five minutes, after which forty-two pounds of a 25 six percent solution of cationic starch (Sta-Lok~400, five
percent based on the synthetic pulp) was added and allowed
to mix for a further five minutes, when 150 dry pounds of
cellulose wood pulp (50 pounds of Weyerhauser bleached hard-
wood kraft pulp, plus 100 pounds of Rayonier bleached soft-
wood kraft pulp) was added, together with enough soft waterto adjust the consistency to approximately five percent.
The mixture was circulated through a Claflin refiner to
reduce the Canadian Standard Freeness to S07, then diluted to
1.8% consistency and pumped once through a double disc re-
finer to reduce the Canadian Standard Freeness to 332. Afterinternal addition of 0.35%, dry basis, fortified free rosin
emulsion (Neuphor *100) precipitated in situ by 1.25% alum at
pH 5.5 for internal sizing, the dilute slurry was formed into
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a continuous web on a conventional Fourdrinier paper machine.
The web was dried by passing it over steam heated drying
cylinders, surface sized with a six percent solution of cati-
onic starch (Cato ~7), redried in the normal manner, passed
5 through three nips of a conventional calender stack, at suc-
cessive pressures of 50, 100 and 150 p.l.i., and collected on
a roll. After aging for several weeks, the paper gave the
following test results: basis weight = 31.7 lb./3000 ft.2;
caliper = 4.0 mils; Tappi brightness = 88.7%; Tappi opacity =
79.2%; Mullen burst = 13.2 p.s.i.; tensile = 14.2 lb./1 in.
width; MIT fold = 76. Rewindability and printability of the
paper prepared in this example were essentially equivalent
to those of the paper of Example 7.
ExamPle 11
Using the same synthetic pulp as that of Example 10 and
following substantially the procedure of that example except
to form in the beater, prior to the synthetic pulp addition,
a solution of the sodium salt of a partially hydrogenated
rosin (six percent hydrogenated rosin based on the synthetic
pulp) and to precipitate the hydrogenated rosin by the addi-
tion of an aqueous solution of calcium nitrate (six percent
calcium nitrate based on the synthetic pulp). The paper
product, after aging, had the following properties: basis
weight = 30.6 lb./3000 ft. ; caliper = 3.7 mils; Tappi
brightness = 87.9%; Tappi opacity = 78.8%; Mullen burst =
13.7 p.s.i.; tensile = 14.3 lb./l in. width; MIT fold = 73;
IGT pick, WP = 97 KP-cm./sec. Rewindability and printabil-
ity of the paper product were essentially equivalent to
those of the paper of Example 7.
In the above examples, the physical property data were
obtained in accordance with standard test procedures. They
are as follows: caliper, Tappi 411; brightness, Tappi 452;
opacity, Tappi 425; Mullen burst, Tappi 403; MIT fold, Tappi
511; and IGT pick, Tappi 499. The dry tensile strength was
determined on an Instron tensile tester using a one-inch
wide strip and a constant rate of elongation.
As is apparent from the examples, any rosin, modified
rosin, ethylene-acrylic acid copolymer or ethylene-methacrylic
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acid copolymer in the form of its alkali metal or ammonium
salt may be used as the water-soluble ionized reagent capable
of being converted into hydrated solid particles submicron
in size in accordance with the process of this invention.
Mixtures of these alkali metal and ammonium salts may also
be used. Ordinarily, these salts are formed by complete or
substantially complete neutralization of the corresponding
acidic materials. Sodium hydroxide is the preferred base
used in preparation of the salts, although potassium, lithium
and ammonium hydroxides may also be used. The amount of
alkali metal or ammonium salt may be varied from about one
to about 10% by weight, based on the amount of polyolefin
fibers, but preferably is in the range of from about two to
about six percent, more preferably from about three to about
five percent. Both wood and gum rosins, and also tall oil
rosin, may be used as sources of the rosin and modified
rosins. The ethylene-acrylic acid and ethylene-methacrylic
acid copolymers useful in accordance with this invention are
those copolymers having a melt index of from about 50 to
about 600, preferably from about 300 to about 400, and con-
taining from about 10 to about 40%, preferably from about 15
to about 30%, by weight of acrylic acid- or methacrylic acid-
derived units.
In those examples wherein the water-soluble ionized re-
agent is an alkali metal salt of rosin or a modified rosin,
the ionic precipitant ordinarily used was papermakers' alum,
namely, hydrated aluminum sulfate (usually 14 to 18 molecules
of water of hydration). The amount of alum generally is
about 0.75 to about 1.5 times the weight of the rosin or mod-
ified rosin salt. However, it also is possible to use water-
soluble calcium and magnesium salts, such as the nitrates,
bromides and chlorides, blends of alum and sulfuric acid and
sulfuric acid alone. Any of these ionic precipitants may
also be used with the alkali metal and ammonium salts of the
ethylene-acrylic acid and ethylene-methacrylic acid copoly-
mers. However, the preferred precipitant for the copolymer
salts is sulfuric acid.
As shown in Table I, the addition of a bonding agent
~ ~8'706
improved the strength values of the paper products. Such
bonding agents are disclosed in the Belgian patent, No.
850,721, to Hercules Incorporated mentioned earlier. In
general, the addition of a cationic wet strength resin in the
preparation of paper using the hydrophilic polyolefin fibers
of this invention provides improved strength properties to
the paper, particularly in the case wherein the water-soluble
ionized reagent is an alkali metal or ammonium salt of an
ethylene-acrylic acid or ethylene-methacrylic acid copolymer.
In that case, the Mullen burst and tensile strength proper-
ties may be increased by as much as 10 to 50~ by inclusion of
a cationic wet strength resin, which is conveniently added in
the form of an aqueous solution to the beater containing the
treated polyolefin fibers, the amount of said resin added
L5 usually being from about two to about eight percent, prefer-
ably from about four to about six percent, by weight, based
on the amount of polyolefin fibers. Typical wet strength
resins are those cationic polymers disclosed by the afore-
mentioned Belgian patent, which polymers may generally be
classified as the reaction products of epichlorohydrin and a
polymer containing secondary or tertiary amine groups, or
both.
The polyolefin fibers shown in the examples are spurted
polypropylene fibers. However, the process of this invention
is applicable to spurted fibers prepared not only from poly-
propylene, but also from polyethylene, copolymers of ethylene
and propylene, copolymers of propylene and other l-olefins
such as l-butene, 4-methyl-pentene-1 and l-hexene, and mix-
tures of any of these polymers.
The process of this invention makes possible the prep-
aration of improved paper products from blends of wood pulp
(generally 70-90% of the blend) and polyolefin pulps (gener-
ally 10-30% of the blend). The treated polyolefin fibers are
receptive to added bonding agents such as starch, and the
paper products based on these treated fibers have improved
brightness, opacity and printability, as well as very accept-
able rewindability.
