Note: Descriptions are shown in the official language in which they were submitted.
Back~round of the Inventio~
Extansible (compacted) paper produced, for example,
in accordance with the apparatus and process disclosed in U.S.
Patent No. 2,624,245 has certain well recognized advantages and
commercial uses. Such paper is subjected, while in a partlally
moistened condition, to compressive compactior. in the direction
of web movament tmachine direction or ~D) between a pressure
nip, thus compacting and forcing the fibers together to produce
an inherent stretchabilit~ without creping. Compacted paper
has improved tensile energy absorption (TEA) burst and tear
characteristics which are highly desirable for such end uses
as the manufacture of paper sacks. However, extensible paper
has reduced tensile strength and stiffness, tne diminution of
the latter characteristic increasing the difficulty of convert-
ing this paper into sacks.
It is the purpose of the present invention to improve
the tensile strength and stiffness of compacted paper without
sacrificing tear strength and additionally, to produce a ràdical
improvement in TEA and burst strengths. The method by which
these objectives are achieved is by the selective im.pregnation
of starch as an external sizing,
.~.J' .~7";~
lO~S~i
parti-~ularly in a manner whic'.l will not destroy the exten-
sible na~ure of the paper,
External sizing of non-extensible paper is well
known and has generally been used to improve the printing
qualities of higher grade papers by applying to one or
both sides a coating of starch, clay9 polyvinyl alcohol
or the like. In a pap~r entitled "On Machine Surface
Sizing Trials With Acid Mcdified Wheat Flour" Vol. 53
No. 8 August 1970/Tappi, it was noted that the sizing of
Kraft paper by applying thereto an a~id modified wheat
flour or a hypochlorite - oxidized starch has the effect
of increasing burst, tensile and stretch strengths~ U,S.
Paten~ No~ 3,362,869~to Welch discloses the application
o a starch coating to one side of a moist compacted paper
prior to drying of the paper in order to provide glazing
thereof. It is the teaching of this patent that ordinary
glazing of compacted paper by reintroducing sufficient
moisture for this purpose into the web after compacting
would destroy much o the extensible nature of the web and
its attendant advantages. Therefore, in order to avoid
undue wetting of the webg a coating of starch is applied
to one surface of a still moist web after compacting and
immediately prior to a drying roll~ which inhibit3 increas-
ing the moisture content of the web while the starch adhes
ively bonds the web to the drying roll and when the web is
held under pressure against the roll9 results in glazing
of the starch coated side of the web.
It is the purpose of the present invention to
treat a compacted paper web with a starch solution in a
particular way which overcomes or disregards the adverse
ef.ect upon the compac~ed web caused by introducing moisture
thereto. 1~4~55~
In accordance with the present invention,
an apparatus is provided for treating a paper web to
improve its tensile strength, TEA, burst strength and stiffness
consistin~ essentially of in combination and in series a
compactor for compressively compacting said web, means for
receiving said compacted web from said compactor and feeding
said web to a starch impregnating means for impregnating both
sides thereof witn a solution containing starch, said starch
impregnating means including at least two counter-
rotating rollers defining a pressure nip therebetween,
nozzle means for feeding said starch solution to said web
as it enters said nip, means for transporting said web into
said nip wherein said solution is forced under pressure
to impregnate said web witn 1 to 10% by weight of said starch
based on weight of said web, and means for drying said web
a~ter the impregnation of said starch solution.
The apparatus preferably includes drying meansdisposed ahead of said compactor to adjust the moisture
content of saia web to 20 to 50% prior to tne web entering
said compactor.
In accordance with another Draf~rred ~rbodiment,
the apparatus includes drying means interposed between
the compactor and said counter-rotating rollers to adjust
the moisture content of said web after compacting to 1
~o 15% by weight.
In another embodiment of the present invention,
the apparatus includes drying means disposed after the
starch impregnating means for adjusting the moisture
content of said web after impregnation of said starch
solution to a moisture content of 5 to 10% by weight. The
apparatus may also include means for recovering and reusing
Al
S~ii6
excess starch solution from the starch impregnating means.
The compactor may consist of an elastomeric belt and
rotary cylinder compactor unit.
Further aspects and objectives of the invention
will be seen by examination of the following detailed
specification, including specific examples, and accompany~
ing drawings in which:
Fig. 1 is a schematic representation of a com
pactor for producing extensible paper~
Fig~ 2 is a schematic representation of dryer
sections which receive the compacted web after processing
by the apparatus of Fig~ 1 and a size press intermediate
said dryer sections for applying a solution of starch into
the web; and
Figo 3 is a schematic illustration of an alternate
form of the invention wherein the compacted web is fed
.,~ .
~ 5 5~
directly to a ~ize press and ~herefrom to a dryer section,
and;
Figs. 4-9 illustrate grap~ically the effects of
varying percentages of starch vis a vis different ~trength
factors 9 compacted and uncomp~cted paper~
Referrin~ now ~o the drawing3 Fig~ 1 illustrates
generalLy ~ c.mpactor 10 for producing an uncreped exter.si
ble paper web 11. The apparatu3 10 in~ludes a looped
elastomeric traveling belt 1~ and a rotar~ cylinder 13
having a smooth (chrome plated) outer surf~ce for rPceiving
the web 11 thereon. A plurality of guide rolls 14, 15, 16
and 17 are po~i~ioned with-n the loop of the belt 129 guide
roll 14 operating to squeeze the belt 12 against the cylino
der 13 at a press nip N wherein the belt 12 is temporarily
reduced in thickness as it travels therethrough~ A section
of the guide rolls 15 is spaced from the first guide roll
14 and urges a portion 12a of the belt against the cylinder
13 at the off-running side o~ the nip N9 and web guide
means 18, 19 feed the web onto the cylinder 13 for move-
ment through the nip N. The apparatus 10 is shown located
in a paper machine between the second and third dryer sec-
tions. A dryer roll shown fragmentarily at 20 indicates
the last roll of the ae~ond dryer section and the roll 33
(also shown fragmentarily) indicates the first roll of the
third dryer section 30. The web is conveyed from the
dryer roll 20 beneath the paper roll 19 and over an ex-
pander (paper guide) roll 183 and then into the nip N. The
web 11 is brought into contact with the surfa~-e of the
chrome plated roll 13 before it enters the nip N. The web
11 is then held agains~ the surace of the roll 13 for an
appreciable angular distance by the belt portion 12a a~d
lV4;~55d~
the ~eb is then separa.ed ~rom both the belt 12 and the
surface of the roll 13 and trained around a paper guide
roll 22 and over another expander guide roll 23 and onto
the dryer roll 33~
The web 11 coming off the dryer drum 20 has the
optim~m amount of moisture required for the compacting
trea~ment. This optimum may vary between 20 to 50 percent
moisture as the web 11 enters the ~pparatus 10~
As previously indicated, the roll 13 has a smooth
surface, preferably chrome plated~ The roll 13 is mounted
on bearings 13a for rotation and is driven by a suitable
source of power, such as a motor indicated diagrammatically
at M. In fact, thelmotor M is the driving power for the
entire device 10. In this way, the roll 13 drives the belt
12 primarily through pre3sure engagement at the nip N so
that tension in the belt 12 is reduced at the nip N~ As
will be appreciated, some power is required to drive the
belt ~2 around the various guide rolls, such as the rolls
14, 15, 16 and 17 and the point at which the belt 12 is
driven (which in this case is at the nip N? is a point at
which tension in the belt is reduced. Since the belt is
elastomeric in character there is a slight reduction in
the stretching of the belt resulting from the reduction
in tension and this ~auses the belt 12 to compress the web
11 longitudinally of its direction of travel as the web ll
passes through the nip, and immediately thereafter~ The
smooth surface of the roll 13 is conducive to relative
sliding bet~een the web 11 and the roll 13~ The web 11
which is held in close frictionaL contact with the belt
is thus compacted in the machine direction (MD) without
creping, A lubricant shower 25 is provided just beneath
Sf~
the web 11 at the oncoming side of the nip N, Preferably
the lubricant shower 25 is a silicone shower but other re-
lease agents are suitable which applies a relatively small
amount of liquid, ln the fonm of a film~ to the surface of
the roll 13.
The roll 13 is heatedg as shown here diagram~a-
tically, by a suitable source of steam S fed axially into
the roll 13 in the manner in which steam is fed into the
usual paper machine dryer dr~m. The steam maintains a rel-
atively high temperature about 212 and up to 350 F, at
,the surface of the roll 13 so as to create a very thin
steam film or cushion between the web 11 and the drum 130
This steam cushion assists in permitting relative sliding
between the web 11 and the drum 13 (which is essential to
permit the web to be compacted by the belt) and tends to
soften some of the ingredients of certain types of paper~
The apparatus thus far described is well known
and forms no part of the present invention beyond illus~
trating the production of compacted paper which is sub~
sequently treated according to the invention~ The remain-
der of this specification will be devoted to specific as-
pects of the treating of compacted pape~in-accordance:'w~th
the teachings and discoveries afforded by the invention~
After leaving the compacting apparatus 10 9 the
web 11 will pass through the dryer section 30 which in
cludes conventional drying rolls,31 - 36, the web 11 first
passing over drying roll 33 thence to roll 34 etc. as shown~
Felt dryer belts 37 and 38 are arranged upon guide rolls 39
and in contact with the respective dryer rolls 31 - 36 to
assure the intimate engagement between the web 11 and the
respective dryer rolls~
SS6
After leaving the compactor 10, the moisture
contained in the web is approximately 35 to 45% moisture
by weight. After passing through dryer section 309 the
moisture content of the web 11 will be approximately 1 to
15 percent of ~hoisture by weight,
Reference numeral 4û indicates a size press ar-
rangement for treating the dried compacted web 11 in accord-
a~ce with the present invention. Web 11 first passes over
guide rolls 41, 42 and therefrom proceeds between a nip
formed by two counter~rotating size press rolls 43 and 44O
Nozzles 46, 47 control the starch metering valves 48, 49
in conduit 50, 51 which permit a metered quanity of a
starch solution 52 to flow into the nip between size press
rolls 43, 44, Edge catch pans 53 collect the excess starch
solution at each end of the nip~, The starch solution is
supplied from a starch solution supply tank 54 having there-
in an agitator 56, starch in solution being drawn from the
tank 54 through conduit 57 to the pump 58 which supplies
metering valves 48 and 49. A starch return pump 60 ser-
viced by line 61 from catch pans 53 returns the starch
solution via line 62 to the supply tank 54~,
During the passage of web 11 between the nip of
press roll 43 and 44, a solution of starch is applied under
pressure to both sides of the web in accordance wit4 vary-
ing percentages indicated below by way of specific examples.
The passage of the web 11 `~hrough the starch solùtion and
between the rolls,43, 44 will be sufficient and will be so
regulated as to the speed of application and the ~trength
of the starch solution to permit and to cause impregnation
of starch into both surfaces of the web 11 in accordance
with a predetermined amount~ The weight of starch impreg-
.. . . ... ...... . .. ..
_
1~ 3~ ~ ~
nated and deposited in the ~7eb will be from 1 percent tolO percent by weight to the total weight of the web after
drying in order to achieve good results 9 wi~h optimums of
different strength characteristics being obtained by im-
pregnating starch in accordance with the percentage shown
in Figs~ 49~ During this process ~he moisture content of
the web will increase from the 1 to 15 percent ~-alue at
the outlet of the dryer section 30 to a value of 35 to 45
percent.
Following the appli~ation and impregnation of
starch into both sections of the web 11 ~he web passes
around guide roll 64 and thence into the second dryer
section 66. ~ryer section 66 contains a plurality of
dryer rollers 67,689 69, 709 etc. about which pass dryer
felts 71~ 72 guided by rolls 73, The dryer section 66
is similar in all respects to the dryer section 30 and the
web 11 passing th~rethrough will los~ thP moisture imparted
by the size press existing from the dryer section 66 with
moisture content o~ approximately 5 to 10 percent by weight.
F~gure 3 discloses an alternate embodiment of the
invention wherein the same reference numerals have been
used for si~ilar parts as shown in Fig. 2~ In accordance
with the embodiment of Fig. 39 the web 11 proceeds directly
from the compactor 10 without first going through dryer
section 30. As a ~onsequence9 the w~b 11 contains ap~
proximately 30 to 40 percent moisture by weight prior to
passing between t~e size press rolls 439 44. It will be
appreciated that since the web 11 co~tains this amount of
mois.ure3 lesser amounts ol the starch solution will be
caused to impregnate the web, however9 a sufficient amount
of starch in solution will impregnate the web to provide
104;~55~i
significant and beneficial results in regard to increasing
tensile, burst and TE~ characteristics9 and may be expected
to be in the order o~ approximately 50 percent of the im-
provement achieved with the configuration of Fig. 2, After
passing through the size pre.s 40~ the web 11 feeds into
the dryer section 66 which redllce~ th2 moisture content of
the web to a moisture level of 5 to 10 percent by weight.
The advantage of the arr3ngement sk.own in section 3 is the
use of a single dryer sectlon to receive the web fro~ the
size press, although the mcisture content of a web will
ordinarilly require a larger dryer section to reduce the
moisture content to acceptable levels~
It should be noted that with respect to both ar~
rangements, Figs. 2 and 3, it should be possible to obtain
glazing of the paper web 11 by feeding the web down~tream
of the size press 40 around a single dryer roll provided
that the starch solution when applied in the press 40
provides sufficient bonding of the web to the cylinder.
Inr.,order to achieve glazing9 a pressure contact.with the
drying cylinder, as shown for example in United States
Patent No~ 3,362,869~ The difference between the presse~
arrangement and that shown in Patent NoO 3~36298699 referred
to above in describing the background of the present in~
vention, is that the starch applied in the said United
States Patent is a surface coating -used to achieve adhesive
bonding between the web and the dryer roLl9 whereas in the
present in*ention the web becomes ~mpregnated with starch
on both sides to ~chieve the subseq~ent additional improve~
ments of radically increased tensile~ burst and T~A stren~ths~
Such additional effects are made possible by the use of the
size press, which includes the size press rolls for forcing
the starch solution .into both web surfaces,
.
~()4;~55~
Having described the apparatus of the invention
we will now set for~h several examples illustrating the
particular constituents used in carrying out the invention
and the measured results~ Example NoO 1
EXAMPLE_l
~URNISH of unbleached 30% Softwood
unbleached 70% Hardwood
UN~EFI~ED = (i2 Sec~ W)
STARCH - ~acid modified corn starch)
.. . . . .
STARCH (% Add~?
o% 2.8%5.7%
Tensile ~lbs,/in.~
: MD 6.0 14~021.0
CD 5O5 80810.6
Elong, (%)
MD 9.1 8018,5
CD 1.3 2032~8
TEA (ftolbs~/ft~ )
MD 4.17 7.95 14,12
CD 0.62 1,66 2,60
TEAR (~ms~
MD 54~8 630666,8
CD 61~6 76~588,8
Burs~ si) 5~4 17.723.7
Stif~ness (Tabor Unit~
MD .40 0~98 1~19
CD o48 1~01 1,13
~.
- 1 2 -
104;~S~
EXAMPLE 2
URNISH of unbleached 30~/~ Softwood
unbleached 70% Hardwood
REFINED (14 Sec. Williams Freeness)
STARCH Unmodified Potato Starch
STARCH %
0% 1.3% 3,0% 507% 10,7%
Tens ~ bs./in~ 7.912.8 14.0 15,1 1505
Stretch % 8.5 7.2 7.1 7.2 701
TE~ ~ - 8.2 8.9 809
Stiffness Tabor ~,56 - 1.02 1.15 1.20 1033
Tear (gms)
MD 69~783.1 88.8 88.1 84.6
CD 88.4100~4 103,2 101.6 lOloC
Burst ~psi) 8.716.6 17.7 19.3 25.8
EXAMPLE 3
URNISH o unbleached 30% Softwood
unbleached 70% Hardwood
REFINED (40 Sec. Williams Freeness)
STARCH (Acid Modified Corn Starch)
STARCH ~% Add,)
0% 1.4% 3.8% 5~7%
Tensile (lbs~/in ~
MD 140621.7 26.3 2906
CD 9.010.1 12.4 12.6
~ 2
l~k'~;~556
EXAMPLE 3 (con't)
O% 1,4%3,8% 5.7%
Elon~, (%)
MD 10.4 g.7 10.9 8,6
CD 2,4 3.4 3.5 3O9
TEA ~ft.lbs./ft.2)
MD 1207 16,621,1 27.2
CD L.97 2,803,87 4~42
Tear (~ms)
- MD 78.7 75~2 73.9 68~5
CD 97.6 1~1.1121,4 90D9
Burst (psi) 18~8 28,6 30.8 35~6
.,
Stiffness (Tabor Uni~
MD .65 1.16 1.20 1~73
CD .85 .~9 1.01 1.31
~ . . ..
From the above examples, it is apparent that ~wo
factors strongly influenced the results. These were (1)
the degree of refining applied and (2) the amount or type
of starch added, Corn starch promoted greater improvements
in tensile strength and stiffness than potato starch under
identical conditions. These were the properties it was
desired to improve for better converting characteristics.
Moreover, it was concluded that although tear strength on
compacted paper was generally reduced by increased refining
and increased starch levels, the effect at freeness levels
usually associated with sack production may not be great
enough to offset the other advant~ges of si2ing~ Generally
~ 3
5~
at between 3 and ~% added potato starch, properties levelled
out, showing no ~ar~ed changes beyond this additive level.
Contrasted to this with added corn starch, tren~s in
properties continued beyord this point~ No tackiness or
brittleness was apparent in any of the samples tested up
to about 8%. Above this, however~ some brittleness was
observed.
In keeping with the principles of the present in-
vention, it is suggested that sli~htly converted (plas-
ticized) starch should be s~perior to highly converted starches,
particularly at high percentage levels of starch impreg-
nation. Such plasticized starch should be highly compato
ible with the extensible qualities of compacted paper.
This is not, however, in any way to suggest that the use
of unconverted starch is undesirable, since the examples
disclosed herein were made using starch in the highly converted
form.
~ eferring to Fig~ 4, a diminution of tear occurs on
compacted paper with increasing starch content at 525 C~Fo
(23,7 Schopper Riegler)O This work was done with an acid
modified corn starch (Eclipse N) manufactured by AoE~ Staley4
With a lower level of refining9 i.e~ 9 at 730 CoFo tl4~3
Schopper Riegler), tear strength is markedly increased with
increased starch levels~ At some i~ermediate level of re~
fining then, one would expect to see small effects~ That
this is true can be seen in the more extensive work done
on potato starch (see Fig, 5), where the effect of increased
starch on tear is in fact rather small, The tear appears
to approach some fixed value which is probably dependent
on pulp ~ariables~
Tear strength of unrefined paper increases with
10~55~;
starch addition bec~use of greater Eiber bonding which re-
sults in greater forces required to pull fibers loose dur-
ing tearing, On refined stock used in thîs study it is
believed that optimum bonding for tear development has
already been achieved by refining, so that additional
bonding caused by the-~tarch leads to ir.creased shear failo
ure of the fibers and reduced tear. The CD ~Cross Direc~
tion, as opposad to Machire Direction9 MD3 tear reuslts
which are in all cases considerably better for compacted
than for uncompacted papers can be explained by the fact
that in CD tear, the failure must propagate across com-
pacted fibers9 and that compacted fibers with their lower
modulus and higher elongation are more difficult to shear
than uncompacted fibers. The initial increase in CD tear
as starch is increased results from greater bonding and
more difficulty in rupturing these bondsO Further in-
creases in starch level however, leads to i~creased fiber
modulus or stiffness, as well as further increases in
bonding, which favors fiber shear failure and reduced tear.
As is normal for extensible paper9 W tear was some-
what lower than the CD vlaues. The refined stoc~ lost
tear strength on adding starch as previously discussed ( see
Fig. 6).
Now to direct attention to properties improved hy
the addition of starch, that is 9 tcnsile~ stiffness and
TEA, on Fig~ 7 are shown MD tensile results for potato and
corn starch at different levels~ Two different refining
levels were explored in each instance~ Note that where~
as tensile gains for potato starch occur during the first
3% addition~ increased tensile with corn starch continues
to higher additive levels~ Also it may be observed that
16- 10~ 56
the addition of 3% starc~ to compacted paper brings the
tensile up to the level of the untreated (uncompacted)
sample~ This may be understood by recalling that the
molecular structure of corn starch9 having a more linear
orientation than potato starchg creates a fil~ with higher
tensile strength~
The use of corn starch ~t high levels ~5%~ doubled
stiffness of compacted sheets9 approaching the untreated
(uncompacted) control. Or. Figo 8 can be seen the results
for potato starch al-so3 where gains are not as dramatic9
particularly at the interm~diate refining levels normal to
sack paper production. At 3% potato starch addition9 the
maximum benefit appears t~ have been achieved 9 an approxi~
mately 40% increase in stiffness.
Another property increased by starch addition is the
work to break in the machine direction ~TEA) largely co~-
tributed to by the increased tensile (see Fig. 9). While
a 30% increase is evident with corn starch, only a~out
half this ~an be obtained with the same level of potato
starch~ The usual five to seven fold MD TEA increase over
uncompacted paper is evident9 whether starch treated or not~
No significant differences in burst strength occurred
between compacted and non-compacted sheets with increased
size addition. About 30% to 40% increase at the 3% level
were obtained in either instance~ This i3 expected since
CD tensile and TEA properties which affect burst, are not
markedly changed during the compaction process. The re-
sults of the burst test are thus dependent on the starch
level~
~ 6
It will be understood that the foregoing description
has been of specific embodiments of the invention and i8
therefore representative, In order to understand the scope
of the invention9 reference should b~ ~ade to the appended
claims.
~7
