Note: Descriptions are shown in the official language in which they were submitted.
lO~l(r~;~
1 The present disclosure relates to a new a~ novel paper
construction which substantially increases the tear strength of
the sheet while maintaining the tensile strength of the sheet
within acceptable limits.
The desire for a paper construction having an increased
tear strength has arisen because of the desirability of produc-
ing a lighter sheet, that is, less weight per unit area, or a
stronger sheetof the same weight per unit area. The advantages
of a lighter sheet include but are not limited to lower shipping
costs, lower postal rates, lower raw material costs and the in-
herent weight requirement in the finished product, as well as
stronger packaging papers.
It is known in the prior art that tear and tensile
strength are related and typically as tensile strength increases
tear strength decreases. A problem inherent in some of the prior
1 art in reducing the paper weight was that if the weight was re-
jl duced the tear strength dropped to an unacceptable level. As
refining of the fibers increases tensile strength increases and
inversely, as refining energy is decreased tear strength in-
creases. Chemicals can be added to paper furnishes to increase
tensile strength; however, normally tear strength cannot be im-
proved with chemical additions. Longer fibérs normally provide
a higher tear strength than shorter fibers.
Problems that arise with an unacceptable tear strength
include tears in the wet web of a paper-making machine resulting
in machine down time and workman expense as well as exposing
workmen to hazards in rethreading the broken web. The same prob-
lems carry over to use of the finished paper sheet in a printing
press when this is the end use of the sheet.
, . . .
l(lg~073
1 A typical known grade of paper used for printing con-
sists of 50~ bleached kraft pulp and 50% groundwood pulp which
can be utilized to produce a 35 pound paper. This designation
describes the weight per 3300 square feet of the paper produced
which is approximately 52 grams per square meter. The kraft fi-
bers may be on the order of usually 2 or 3 millimeters in length,
may be 2 to S millimeters and they primarily contribute to the
tear and tensile strength of the sheet and to machine runability.
The groundwood tends to fill in voids in the sheet and contributes
to the sheet's smoothness,opacity and denseness.
In this type of construction prior art practice would
increase the tear strength by raising the percentage of kraft
and lowering the percentage of groundwood. From a practical
standpoint the kraft percentage can only be increased to a certain
point because it is more expensive and there is only so much
available. Most bleached kraft pulps have fibers with a length
of up to 2 or 3 millimeters although some fibers may be from 2 to
S millimeters in length and it is difficult to obtain such fi-
bers with any greater length.
The present invention concerns itself with the finding
that the addition of certain amounts of a hydrophilic fiber to
natural cellulosic fibers in a nonwoven paper sheet construction
produces an unusual and unexpected increase in the tear strength
of the paper sheet. Nonwoven means there is no weaving of fibers
or twisting of fibers into threads. As a matter of example the
use of the present invention enables the manufacture of a 20
pound (approximately 30 grams per square meter) paper which has a
tear strength of a prior art paper of about 35 pounds (approxi-
mately 52 grams per ~uare meter).
109iO73
1 The hydrophilic fibers of the present invention are
acrylic, polyester and aramid fibers. The hydrophilic fibers
usable in the present invention are preferably of a 1.5 to 6.0
denier, non-crimped and should preferably be long, for example
on the order of from 1/8" to 1/2" (approximately 3.2 millimeters
to 12.7 millimeters) in length. It is recognized that fibers of -
a denier less than 1.5 may be used.
The present disclosure reveals that additions of acry-
lic and polyester fibers in an amount of from a small but effec-
tive amount up to 40% of the total sheet weight produce an in-
crease in the tear strength of non-woven paper sheet. In the
case of aramid fibers the present disclosure indicates that they
should be added in an amount of from a small but effective amount
up to 20% to produce an increase in the tear strength. In the
case of additions of acrylic and polyester fibers the tear
strength increases substantially linearly up to additions of 25
¦ and at this point show a lower increase up to about a 40% addi-
I tion. In the case of the addition of aramid fibers the tear
I strength increases substantially linearly up to an aramid addi-
~l 20 tion of 20% at which point the tear strength decreases with fur-
ther additions of the aramid fibers. In the case of tensile
strength it does decrease as tear increases when any of the three
disclosed fibers are added. Test results indicate that the small
but effective amount in the case of acrylic and aramid fibers is
on the order of 0.2~ and in the case of polyester fibers is on
the order of 0.5% which amounts give a measurable increase in the
tear strength.
In comparing tear strength improvements at constant
tensile (efficiency) it has been found as a general proposition
that as the amount of hydrophilic fibers increases, a lower effi-
lU~31(~73
1 ciency in tear improvement at constant tensile values results.
It appears that a nearly linear change in tear at constant ten-
sile is obtained in the case of additions to acrylic and poly-
ester fibers when added in from a small but effective amount up
to about 10% and then a decreased change in tear at constant
tensile results in additions above 10%. The same is true in the
case of additions of aramid fibers but only up to about a 5%
addition after which a decreased rate of change in tear at con-
stant tensile results.
The definition of acrylic fibers applicable to the pre-
sent invention are those manufactured fibers in which the fiber-
forming substance is any long chain synthetic polymer composed
of about at least 85% by ~eight of acrylonitrile units. These
acrylonitrile units are usually copolymerized with materials such
as methcrylic acid and acrylic acid. Such fibers are sold, for
example, under the trademarks ACRILAN, CRESLAN, ORLON and
ZEFRAN.
The definition of polyester fibers applicable to the
present invention are those manufactured fibers in which the
fiber-forming substance is any long chain synthetic polymer com-
posed of at least 85% by weight of an ester of a substituted aro-
matic carboxylic acid, including but not restricted to substituted
terephthalate units. Typical raw materials used in the manufac-
ture of these fibers are dimethyl terephthalate, terephthalic
acid,and ethylene glycol. Such fibers are sold for example
under the trademarks DACRON, FORTREL, KODEL and TREVIRA.
The definition of aramid fibers applicable to the pre-
sent invention are those manufactured fibers in which the fiber-
forming substance is a long-chain synthetic polyamide in which at
`` B ~4~
.. . .
109~073
1 least 85~ of the amide linkages are attached directly to the two
aromatic rings. Typical raw materials used in the production of
such fibers are meta and para-phenylene diamine and iso- and
terephthaloyl chloride. These fibers are sold for example under
the trademarks of KEVLAR and NOMEX.
~ ydrophilic fibers usable under this invention are de-
fined as ones having a substantial degree of ionic character,
and thus high water dispersability. Examples of hydrophilic
groups on fiber surfaces would be the acrylic acid groups on the
acrylic fibers, or the carboxylic groups on the polyester fibers,
or the amide groups on the aramid fibers. Conversely, polyethy-
lene or polypropylene fibers have a more hydrophobic and less a
hydrophilic nature.
Other objects and a fuller understanding of this inven-
tion may be had by referring to the following description and
claims, taken in conjunction with the accompanying drawings, in
which:
Figure 1 is a graph illustrating the relationship of
tear vs. beating time for three paper compositions, namely a
control to which no acrylic fiber has been added; a kraft pulp to
which has been added 5 percent of a 3/8" ~9.6 millimeters) x 3.0
denier acrylic fiber; and a kraft pulp to which has been added 5
percent of a 1/4" (6.35 millimeters) x 3.0 denier acrylic fiber;
Figure 2 is a graph illustrating the relationship of
tensile strength vs. beating time for the same paper compositions
shown in Figure l;
Figure 3 is a graph illustrating the relationship of
tear vs. percent acrylic fibers added to kraft pulp;
Figure 4 is a graph illustrating the relationship of
tensile strength vs. percent acrylic fibers added as in Figure 3.
'' ~
--5--
1(~'31073
1 Figure 5 is a graph illustrating the relationship of
tear vs. tensile strength of the compositions illustrated in
Figures 3 and 4;
Figure 6 is a graph illustrating the relationship of
the efficiency of the acrylic fibers vs. percent acrylic fibers
added to the paper composition;
Figures 7-12 are photo micrographs taken at about 100
times magnification and illustrating various compositions that
are found in Figure 3, namely 100~ kraft; 10~ acrylic addition;
20~ acrylic addition; 30% acrylic addition; 40% acrylic addition;
and 50% acrylic addition;
Figure 13 is a graph illustrating the relationship of
varying percentages of kraft and groundwood in a paper sheet vs.
the wet web strength for a kraft-groundwood sheet and a kraft-
groundwood sheet where 5 percent of the kraft has been replaced
with acrylic fibers;
Figure 14 is a graph illustrating the relationship of
tear vs. percent polyester and aramid fibers added to a kraft
pulp;
Figure 15 is a graph illustrating the relationship of
tensile strength vs. percent polyester and aramid fibers added
to a kraft pulp as in Figure 14;
Figure 16 is a graph illustrating the relationship of
tear vs. tensile strength of the compositions given in Table XI;
Figure -17 is a graph illustrating the relationship of
tear vs. tensile strength of the compositions given in Table XII;
Figure 1~ is a graph illustrating the relationship of
the percent change in tear of the polyester and aramid fibers vs.
percent fiber added to the paper composition;
-- 6 --
I
109~073
1 Figure 19 is a graph illustrating the relationship of
the increase in tear (percent) vs. fiber cost per ton for acry-
lic,polyester and aramid fibers;
Figure 20 is a photo micrograph taken at about 120
times magnification and illustrating a 10% polyester-90% kraft
fiber composition; and
Figure 21 is a photo micrograph taken at about 120
times magnification and illustrating a 10~ aramid-90% kraft fi-
ber composition.
The teachings of the present invention are revealed in
the following test results which illustate the addition of acry-
lic, polyester and aramid fibers to cellulose fibers.
The first tests comprise the addition of two sizes of
uncrimped acrylic fibers 3/8" (9.6 millimeters) x 3.0 denier
and 1/4" (6.35 millimeters) x 3.0 denier in varying percentages
to a medium yield unbleached kraft pulp produced at the St. Regis
Paper Company plant at Jacksonville, Florida, U.S.A.
In each of the test samples were ta~en from each beater
run at 5, 10, 15, 30 and 45 minute intervals. Five sets of hand-
2g sheets (60 grams/meter2) were made from each beater run and thedata appearing in the following Tables I-V were obtained from
tests conducted on these handsheets.
3~ .
1091lr73
1 Table I
CONTROL (No Acrylic Fiber Added)
Beating Time, Minutes
_ _ _ . _
Canadian Standard
Freeness Test (CSF),
mls. 2 756 747 705 580 405
Basis weight, g/m 60.1 59.9 60.0 59.3 59.9
Burst factor 35.9 45.7 54.5 63.8 69.0
Tensile (Breaking
Length in Km) 5.98 7.13 8.20 9.09 9.61
Tear Factor 229 199 171 156 137
Table II
2-1/2~ of 3/8" (9.6 millimeters) x 3.0 DENIER ACRYLIC FIBER
(Added after Beating)
Beati'ng Time',' Minutes
-
C S F, mls. 2 752 724 691 596 430
Basis weight, g/m 61.7 59.9 65.3 60.8 62.0
Burst factor 33.4 40.5 52.2 62.6 67.7
Tensile, Km 5.81 6.69 7.92 8.72 9.38
Tear factor 255 235 215 178 163
Table III
5~ of 3/8" (9.6 millimeters) x 3.0 DENIER ACRYLIC FIBER
(Added after Bea-ting)
Beating Time, Minutes
C S F, mls. 2 734 740 715 610 465
Basis weight, g/m 57.0 61.9 62.4 60.6 61.6
Burst factor 31.4 39.5 47.8 55.2 63.7
Tensile, Km 5.48 6.15 7.22 7.97 8.86
Tear factor 262 257 230 203 194
-- 8 --
1091073
~ 1 Table IV
: 2-1/2~ of 1/4" (6.35 millimeters) x 3.0 DENIER ACRYLIC FIBER
, (Added after Beating)
i
Beating Time, Minutes
C S F, mls. 2 756 743 705 596 423
Basis weight, g/m 59.2 61.7 54.9 59.4 63.9
Burst 33.3 41.2 51.0 57.8 67.3
Tensile, Km 5.86 6.54 7.70 8.67 9.58
Tear 250 218 186 178 175
Table V
5% of 1/4" (6.35 millimeters) x 3.0 DENIER ACRYLIC FIBER
(Added after Beating)
;
Beating Time, Minutes
C S F, mls. 2 762 733 715 616 454
Basis weight, g/m 56.g 60.4 62.0 60.7 62.5
Burst 29.9 38.9 49.0 59.3 63.1
Tensile, Km 5.08 6.31 7.26 8.44 8.23
Tear 267 228 217 192 183
Table VI shows test results where a 5~ addition of a
1/4" (6.35 millimeters) x 3.0 denier acrylic fiber was made to the
pulp prior to the beater run.
Table VI
BEATER RUN CONTAINING 5% of 1/4" (6.35 millimeters x 3.0
DENIER ACRYLIC FIBER
Beating Time _ inutes
_ 15 30 45
C S F 2 743 725 659 542 206
Basis weight, g/m 62.5 61.3 64.5 61.8 59.7
Burst 33.3 43.4 54.1 58.8 64.1
Tensile 5.63 7.06 8.01 8.87 8.11
- Tear 266 214 175 169 133
~091073
1 In the test results indicated herein the Canadian
Standard Freeness (CSF) is a measure of the rate at which a di-
lute suspension of pulp may be dewatered. The units of this test
are expressed in milliliters.
The burst streng~ as expressed in the tablets is ex-
pressed as a dimensionless number. This test is a measure of the
hydrostatic pressure required to produce rupture of the material
when pressure is applied by means of a liquid at a controlled,
increasing rate to a circular area of the material under test.
The test material is initially flat and held rigidly at the cir-
cumference. During the test the sample must be free to bulge un-
der the increasing pressure. The tests herein for burst strength
were conducted under Tappi Test No. T-403 os-76 ~1976). Equiva-
lent tests are CPPA (Canadian) Test No. D.8 (January 1964); ASTM
Test No. ~ 774-67 (1971); and ISO (International Organization for
Standards) Test No. 2758-1974 (E~.
The tear resistanoe as expressed in the tables is ex-
pressed as a dimensionless number. Tear is the average force
normally in grams, to tear a single sheet of paper after the tear
has been started. The test consists of measuring the work done
when a sample of the paper is tor~ through a specified distance.
The work is ~ne partly in rupturi~g the paper along the line of
tear and partly in bending the paper as it is being torn. The
tests herein for tear strength were conducted under Tappi Test
No. T-414 ts-65 (1965). E~uivalent tests are CPPA Test No. D.9
(September 1965); ASTM Test No. D 689-62 (1944); SCAN (Scandanav-
ian) Test No. P 11:73; and ISO Test No. 1974-1974 (E).
The tensile strength as expressed in.the tables is ex-
pressed as kilometers. The tensile strength is the maximum tensile
-- 10 --
~(J91073
force per unit width that a piece of paper or board will stand
before breaking. This test is in effect the length of a paper
sample necessary to cause breaking of the sample as the sample is
held at one end. The tests herein for tensile strength were con-
ducted under Tappi Test No. T-494 os-70 (1970). Ec~uivalent tests
are CPPA Test No. D.6 (September 1961); ASTM Test No. D 828-60
(1971); SCA~ Test No. P 16:76; and ISO Test No. 1924-1976 (E).
Figure 1 is a graph constructed from the data obtained
above (Tables III and V) and illustrates that a significantly
10 higher tear strength is obtained with the addition of 5% acrylic
fibers as compared to the control which contained no acrylic fi-
ber addition. Figure 1 also affirms the general proposition that
as beating time increases, tear strength decreases.
Figure 2 is a graph similar to Figure 1 but showing
tensile strength as a function of beating time and compares 5% -
1/4" (6.35 millimeters) x 3.0 denier acrylic addition and 5% -
3/8" (9.6 millimeters) x 3.0 denier acrylic addition to a control
which contained no addition. It shows that the tensile strength
is slightly lower with the acrylic additions; however, they are
20 well within acceptable limits for the purposes of the product of
-- the present invention. Figure 2 also illustrates an increase in
tensile strength as beating time increases.
In order to determine the optimum amount of acrylic
fiber to be added to cellulosic fiber within the teachings of the
present invention a series of test handsheets were made by the
same procedure outline above with progressively larger amounts of
acrylic fiber. The uncrimped acrylic fiber used was 1/4" (6.35
millimeters) x 3.0 denier and was added to a 570 CSF (Canadian
Standard Freeness)~ bleached softwove kraft pulp, sold under the
; 1091~73
.
1 trade name of Hibrite pulp. The results of the test are indicated
below in Table VII.
Table VII
STRENGTH PROPERTIES OF ACRYLIC FILLED HANDSHEETS
3.0 Denier x 1/4" (6.35 millimeters) Uncrimped Acrylic Fi~er
Kraft Acrylic, Tensile, Tear
% ~ Km Factor
100 0 10.9 107
10 95 5 9.5 135
8.4 181
7.6 216
6.6 244
5.9 281
5.0 290
3.4 301
2.5 241
The tear and tensile results from Table VII above have
been shown in the graphs of Figures 3 and 4 and it will be noted
that tear increases and tensile decreases linearly up to a 25%
acrylic addition. Tear increases at a lower rate from 25% up to
40% acrylic addition and then shows a sharp decrease. Tear in-
creases over a control (no acrylic addition) at a rate of about
7.3~ for each 1% acrylic added up to a 25% acrylic addition.
Figure 5 is a graph constructed from the date of Table
VII showing the tear vs. tensile relationship for the acrylic fi-
ber filled sheets and for a control sheet containing no acrylic
fiber.
Table VIII has been constructed from data included in
Table VII and illustates tear improvements in acrylic filled paper
- 12 -
109~73
.
1 sheets at constant tensile strength. The percent change in tear
is calculated by taking the difference between the tear of a con-
trol sheet and the tear of an acrylic filled sheet and dividing
the difference by the tear of the control sheet. The efficiency
is then calculated by dividing the percent change by the percent
of acrylic fibers added to the paper sheet.
Table VIII
EFFICIENCY OF ACRYLIC FIBER
Tear of
Ten- Control
sile Sheet (No Tear
of Acrylic Add- of Effici-
Acry- ed) at Ten- Acry- % ency,
Acry- lic sile of Acry- lic Change ~ Change
Kraft, lic Filled lic Filled Filled in %Acrylic
% % Sheet Sheet Sheet Tear Added _
9.~ 110 135 22.7 4.5
~.4 125 181 44.8 4.5
7.6 135 216 60.0 4.0
6.6 155 244 57.4 2.9
5.9 175 281 60.6 2.4
5.0 195 290 48.7 1.6
3.4 240 301 25.4 0.6
2.5 270 241 -10.7 -0.2
% tear improvement per 1% acrylic fiber added
Figure 6 is a graph illustrating these relationships and
it will be seen that a constant efficiency is obtained up to about
10% acrylic addition and then a decreased efficiency results as
the acrylic fiber in the sheet is increased.
Figures 7-12 are photo micrographs at about 100 magni-
fication showing the handsheets from the above tests (Table VII -
Figure 3) with varying amounts of acrylic fibers added to the
bleached kraft fibers. Figures 7-12 illustrate in visual form
the interrelationship between the cellulosic fibers and the acry-
lic fibers in their matted nonwov~n condition. ~he Figures 7-12
1091073
~' 1 show respectively 0, 10, 2Q, 30, 40 and 50 percent acrylic con-
ditions. The uncrimped nature of the acrylic fibers can also
be clearly seen from these figures.
A further series of tests were conducted in a manner
similar to those tests discussed above to illustrate the effect
in what has been referred to as wet web strength with the re-
placement of 5% of the kraft portion of various kraft-groundwood
furnishes. The results of these tests are shown in the graph of
Figure 13. The groundwood portion of the furnish may be between
20 to 80~ of the total furnish. The wet web strength is common-
ly referred to by those skilled in the art and is related to
paper making machine runability. It is the work or tensile en-
ergy which the wet sheet will absorb at a given stretch, equal
to the draw (the speed differential between the wire and the
couch~ The wet web strength is attained by integrating the
; stress-strain curve up to a stretch, usually about 3 1/2%, equiv-
alent to the draw. The wet web strength values in Figure 13
were obtained at 3'% strain. Figure 13 illustrates clearly the
increase in wet web strength for various kraft-groundwood fur-
nishes when 5% of the kraft portion of the furnish was replaced
with 3/8" (9.6 millimeters)- 3.0 denier uncrimped acrylic fibers.
A test run was made at St. Regis production facilities
in Bucksport, Maine. In this run approximateIy 60 english tons
of 34 pound letterpress paper containing acrylic and a compar-
able amount of control paper from the same pulp, except, without
acrylic were made. Comparison tests indicated results similar,
or substantially the same as theaforementioned test results set
forth herein. In addition the paper was tested in a printing
operation on production printing equipment. We found the paper
containing acryiic to perform in the printing operation in a man-
_ 14 -
. i . ~ .
1091073
!
1 ner and with results comparable to and the same as the control
paper which did not contain acrylic fiber.
In order to determine the optimum amount of polyester
fiber to be added to cellulosic fiber a series of test hand
sheets were made. The polyester fiber utilized was manufactured
by DuPont and was 3/8" (9.6 millimeters) x 3.0 denier and was
' added to a 570 CSF bleached ~raft soft wood pulp. The results of
the test are indicated in Table IX.
Table IX
STRENGTH PR~PERTIES OF POLYESTER FILLED HANDSHEETS
3.0 Denier x 3/8" (9.6 millimeters) Uncrimped Polyester Fiber
Percent Tear Burst
Fiber F~c~orTensile, Km.FactorDensity, g~cc
0 113 9.73 69.9 0.698
0.2 107 9.66 74.3 0.696
0.5 115 9.60 71.6 0.685
1.0 121 9.54 69.9 0.680
2.5 140 9.23 68.1 0.646
5.0 165 8.20 55.8 0.610
10.0 225 8.00 55.6 0.557
15.0^ 303 7.29 48.9 0.497
20.0 393 6.14 40.7 0.438
25.0 375 .5.52 38.5 0.407
30.0 390 4.83 31.9 0.,374
40.0 452 3.72 24.8 0.333
50.0 332 2.45 18.4 0.277
The tear and tensile results from Table IX have been
illustrated in Figures 14 and 15 and it will be seen that tear
increases and tensile decreases linearly up to a 25% addition of
- 15 -
1091073
;
1 polyester fibers. Tear increases at a lesser rate from 25% up
to 40% polyester addition and then shows a sharp decrease. The
curve for polyester fiber additions closely approximates the
curve for addition of acrylic fibers shown in Figure 3. The poly-
ester fiber additions give tear improvements of about 11% for
each 1% of polyester fiber added.
Figure 16 is a graph constructed from the data of Table
IX showing the tear vs. tensile relationship for the polyester
fiber filled sheets and for a control sheet containing no poly-
ester fibers.
Table X has been constructed from the data included inTable IX and illustrates tear improvements in polyester filled
paper sheets at constant tensile strength. The calculations in-
volved in Table X have been arriv~ at in the same manner as ex-
plained-in the makeup of the data described above in conjunction
with Table VIII.
Table X
EFFICIENCY OF POLYESTER FIBER AT CONSTANT TENSILE
! Ten-
sile
of Tear of
Poly- Control Tear of
ester at Poly-
Poly- Filled Poly- ester Effi-
Kraft, ester, Sheet, ester Filled Change, ciency*,
% '` % Km Tens'ile Shee't % %
99.0 1.0 9.54 110 125 13.6 13.64 ''
97.5 2.5 9.23 113 140 23.9 9.56
95.0 5.0 8.20 125 190 52.0 10.40 -'-
90.0 10.0 8.00 130 208 60.0 6.00
85.0 15.0 7.29 138 245 77.5 5.17
' 80.0 20.0 6.14 166 343 106.6 5.33
j 75.0 25.0 5.52 180 375 108.3 4.33
70.0 30.0 4.83 200 408 104.0 3.47
60.0 40.0 3.72 230 452 96.5 2.41
s0.0 50.0 2.45 266 330 24.1 0.48
* % change in tear per percent of synthetic fiber added
1091073
1Figure 18 is a graph illustrating the relationship of
percentage of polyester fiber added as compared to the percent
change in tear for polyester additions over the range of 0% to
15%. It will be noted that a nearly linear change in tear is
! noted up to about 10% addition of the polyester fibers which is
quite close to that foundin the data given hereinabove for the
addition of acrylic fibers.
Figure 20 is a photo micrograph at about 120 magnifi-
cation showing a handsheet from one of the tests given herein-
above in Table IX with the amount of polyester fiber addition
being 10% and the remainder of the handsheet being made up of
90% of a 570 CSF bleached kraft softwood pulp. The uncrimped
nature of the polyester fibers can be clearly seen in Figure 20.
A still further series of test handsheets were made by
the same procedure outlined above to determine the optimum amount
of aramid fiber to be added to a cellulosic fiber. The uncrimped
aramid fiber used was 1/4" (6.35 millimeters) by 1.5 denier and
was added to a slightly beaten 570 CSF bleached kraft softwood
pulp. The results of the tests are indicated below in Table XI.
1091073
$
1 Table XI
STRENGTH PROPERTIES OF ARAMID FILLED HANDSHEETS
1 5 Denier x 1/4" (6.35 millimeters) Uncrimped Aramid Fiber
Percent Tear Tear
Fiber FactorTensile, Km. Factor Density, g/cc
0 108 9.90 73.1 0.696
0.2 117 10.07 73.1 0.686
0.5 116 9.97 72.6 0.686
1.0 124 10.24 69.2 0.676
2.5 140 9.69 68.4 0.640
5.0 164 8.71 64.1 0.606
10.0 222 7.92 57.3 0.528
15.0 254 6.86 48.7 0.467
20.0 300 5.95 38.7 0.423
25.0 260 5.08 32.6 0.380
30.0 293 4.37 28.1 0.341
40.0 183 2.85 16.2 0.282
50.0 155 1.96 10.4 0.241 ~`
The tear and tensile results from Table XI above have ;
been shown in the graphs of Figures 14 and 15 and it will be noted ~ I
that tear increases and tensile decreases linearly up to about
a 20% aramid addition. The tensile continues its linear decrease
up through a 50% addition. Above the 20% aramid addition the
I tear factor shows a sharp decrease. In the aramid fiber additions
¦ tear increased approximately 7.5% for each 1% of the fiber added
up to an addition of about 5% of thearamid fibers.
Figure 17 is a graph constructed from the data of ~able
XI showing the tear vs. tensile relationship for the aramid fiber
filled sheets and for a control sheet containing no aramid fiber.
- 18 -
;~
} 10910'73
1 Table XII has been constructed from data included in
Table XI and illustrates tear improvements in acrylic filled
paper sheets at constant tensile strength.
Table XII
EFFICIENCY OF ARAMID FIBER AT CONSTANT TENSILE
Ten-
sile Tear
of of Tear
Aramid Control of
Filled at Aramid Effi-
10 Kraft,Aramid, Sheet, Aramid Filled Change, ciency*,
% % Km._ Tensile Sheet %
99.0 1.0 10.24 101 124 33.8 22.77
97.S 2.5 9.69 106 140 32.1 12.83
95.0 5.0 ~.71 118 179 51.7 10.34
90.0 10.0 7.92 131 215 64.1 6.41
85.0 15.0 6.86 152 252 65.8 4.39
80.0 20.0 5.95 172 274 59.3 2.97
75.0 25.0 5.08 192 288 50.0 2.00
70.0 30.0 4.37 210 293 39.5 1.32
60.0 40.0 2.85 253 205 -19.0 -0.47
50.~ 50.0 1.96 284 155 -45.4 -0.91
* % change in tear per percent of synthetic fiber added
Figure 18 also shows the relationship of the percent of
aramid fiber added to a composition in relation to the percent
change in tear and this has been shown in conjunction with the
same curve for the polyester fibers. The graph of Figure 18
covers the range of 0 to 15% fiber addition and it will be noted
that a nearly linear change in tear is noted up to about a 5%
additiGn rate of the aramid fibers.
Figure 21 is a photo micrograph at 120 magnification
showing a handsheet from one of the tests illustrated in Table XI
with 10% aramid fibers added to 90% of a 570 CSF bleached kraft
softwood pulp. This photo micrograph illustrates the physical re-
lationship between the cellulose fibers and the aramid fibers in
their matted and nonwoven condition and the uncrimped nature of
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10910'73
1 the aramid fibers can also be clearly seen from this figure.
Figure 19 is an illustration in graph form which shows
the fiber cost per ton in comparison to the increase in tear. In
~A this illustration the fiber costs used were $1.10 per pound for
polyester, 58 cents per pound for acrylic, and $9.00 per pound
for aramid. In this illustration and assuming these prices it is
seen that the aramid fibers do not compare at all with the poly-
ester and acrylic fibers on a cost per ton basi and it is noted
that the acrylic fibers appear to be more economical than the
j 10 polyester fibers on a cost per ton ~asis.
j The polyester fibers give about 1.7 times tear improve-
ment over the acrylic fiber for each percent of fiber added and
tensile strength losses for the three fibers disclosed herein are
substantially equivalent, namely about 1.7% for each 1% of fiber
added.
The cellulosic fibers can be produced either by chemi-
cal or mechanical pulping processes well known in the industry.
Included in the cellulosic fibers made by the chemical pulping
pr~cess are kraft fibers, sulfite fibers, and the like. Included
in the cellulosic fibers made by the mechanical pulping processare
stone groundwood fibers, refiner groundwood fibers, thermomechani-
cal fibers, and the like.-
The cellulosic and hydrophilic fibers are entangledwithout apparent bonding therebetweenin the paper sheet and are
interrelated by the random dispersing and intermixing of the hy-
drophilic fibersin the cellulosic fibers. Preferably the cellu-
losic fibers of this invention are fibrillated whereas the hydro-
, philic fibers are not fibrillated. This is accomplished in carry-
ing out the manufacture of the nonwoven sheet by adding the non-
fibrillated hydrophilic fibers to the cellulosic stock after the
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1091073
i 1 cellulosic stock has been fibrillated in the conventional refin-
ing and/or beater operation. The mixture of the fibrillated
cellulosic fibers and the non-fibrillated hydrophilic fibers are
completely free from any extraneous bonding agents other than
the medium provided by the fibrillating of the cellulosic fibers
which would cause an entanglement of the hydrophilic fibers to
the cellulcsic fibers. Note the various hydrophilic fibers in
the tests of Tables I, II, III, etc. were~dded after beating of
the cellulosic fibers.
While we have illustrated and descrlbed a preferred
embodiment of our invention, it will be understood that this is
by way of example only and not to be construed as limiting.
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