Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates generally to a
method of preparing food casings from fibrous web materials.
More particularly, it relates to a new and improved method
for preparing food casings that includes a technique for im-
proving the absorption and viscose penetration characteris-
tics of hemp fiber webs used as the base materials for such
casings.
~s is known, the production of cellulosic cas-
ings for meat products, such as sausages and the like, pre-
sently involves the use of bonded fibrous webs as the base
materials. These fibrous base webs are formed into a tubu-
lar configuration and impregnated with a casing-forming cellu-
lose, namely viscose, as set forth in greater detail in U. S.
Patent No. 3,275,456. The base paper webs are comprised of
relatively strong, natural fibers such as Manila hemp, flax,
sisal and the like and usually utilize natural or man-made
resin bonding systems, such as dilute viscose or cationic
thermosetting resins in amounts that do not interfere with
the final viscose penetration operation used in converting
the bonded web into a food casing.
In recent years,increased activity has involved
investigation of fibers other than Manila hemp for the manu-
facture of the base web material as well as the use of
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different resin bonding systems and the addition of modify-
ing substances to promote improved adhesion between the
final fibrous food casing and the meat emulsion packed there-
in. This has included the use of polyvinyl alcohol resins
in place of viscose for the final web penetrating operation.
Thus, as will be appreciated, the industry has
tended to extend its outlook toward alternative materials ~
both in the base web component and in the impregnating solu- -
tion used in the casing-forming operation. These variations ~ -
have led to an industry concern regarding the need for assur-
ing uniform and rapid penetration of the impregnating material
into the fibrous base web. If the material has slow penetra-
bility, the manufacturing rate during the impregnating pro-
cess may be adversely affected or incomplete penetration
might result, producing a final fibrous casing with an unde-
sirable mottled appearance as well as a possible loss of
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strength or variation in strength throughout the extent of
the casing product.
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It is also known in the film art that a corona ~-
discharge treatment of a supporting film of man-made synthe-
tic material, such as photographic film base and the like,
will beneficially affect the surface characteristics of the
supporting structure to permit improved coating thereof with
photographic emulsions. As discussed by Brown and Swanson
in the December 1971 issue of Tappi, Volume 54 No. 14 at
pages 2012-2018, the treatment of cellulosic material by a
corona discharge results in an increase in the polarity of
the treated surface and can provide improved bonding charac-
teristics between overlapping cellulosic suraces. The im-
proved bonding is believed to be a surface effect and is pre-
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sumably due to degraded oxidized cellulose molecules gene~
rated on the surface of the material as a result of the
corona treatment. Devices for carrying out surface corona
treatment are commercially available. One such device is
disclosed in U. S. Patent No. 3,397,136.
In accordance with the present invention,it
has been found that a significant improvement can be achieved
in the absorbency and penetration characteristics of the `
porous base web material if the fibrous base web for casing
is subjected to a corona discharge treatment prior to the
casing-forming impregnation operation. Accordingly, it is
an object of the present invention to provide a new and im-
proved process for improving the absorbency of casing base
papers by the proper utilization of a corona discharge treat-
ment prior to forming the food casing.
Another object of the present invention is to
provide a new and improved process of the type described
that will effect a uniform, more rapid penetration of the >
impregnating material into a fibrous base web thereby en- ~-
abling an increase in the manufacturing rate of the base web
and increased speed in the impregnation process. At the
same time, the process assures complete penetration of the
base web material and the production of a final fibrous
casing free of undesirable mottled appearance or variation -~
in the physical characteristics thereof.
Other objects will be in part obvious and in
part pointed out more in detail hereinafter.
These and related objects are achieved in
accordance with the present invention by providing a new
and improved process or method for improving the fluid :
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penetrability of casing paper comprising the steps of pro-
viding a fibrous base web material for casing manufacture,
subjecting the fibrous base web to a corona discharge treat-
ment at an energy density/web surface level sufficient to
lower the rate of viscose penetration of the web, e.g. a
level o-f at least about 0.5 watt-min/ft2 and subsequently
converting the corona treated base web to a food casing by
impregnation thereof with a suitable casing-forming material.
The invention accordingly comprises the several
steps and the relation of one or more of such steps with
respect to each of the others and the article possessing
the features, properties, and the relation of elements,
which are exemplified in the following detailed disclosure.
DESCRIPTION OF PREFERRED EMBODIMENT
The base webs used in forming food casing are
initially produced as continuous fibrous web materials on
conventional papermaking machines using known and conventional
papermaking techniques. The fibrous webs preferably should
exhibit substantial caustic stability when using a viscose
solution as the casing-forming material in view of the high-
ly caustic nature of that solution. Frequently, the desired
caustic stability is imparted to the base web material by
treating a preformed and dried paper with a dilute (up to
about 3 percent) viscose solution followed by the steps of
drying, regenerating the cellulose, rinsing and redrying.
This initial dilute viscose treatment bonds the web and im-
parts a sufficient caustic resistance so that the web re-
tains its structural integrity during the final casing-form-
ing operation. That process is set forth in greater detail
in U. S. Patent No. 39135,613. Additionally, gelatine cross
linked with a glutaraldehyde may also be uscd.
Alkernatively, a bonding process may involve the
us0 of resins or mixtures th0reof, such as cationic thermo-
setting resins which may be used during the web forming pro~
cess through addition to the beater of the papermaking ma-
chine just prior to web formation or as a postformation treat-
ment. The resins utilized also impart to the base web sub-
stantial resistance to the highly caustic viscose solution
yet permit full penetration of the final viscose solution
during the casing manufacturing operation. As will be appre-
ciated, the resin may be incorporated into the web at the
beater, as mentioned hereinbefore, or at the headbox or other
suitable point in the manufacturing process of the web. In
this connection, resins such as the cationic epichlorohydrin-
polyamides disclosed in U. S. Patent No. 2,926,154, cationic
melamine-formaldehyde resins described in U. S. Patent No.
2,796,362 or mixtures thereof with polyacrylamide resins as
set forth in U. S. Patent No. 3,48~,256 may be employed.
The fibrous webs used in making casing are con- -
ventionally formed or composed of natural vegetable fibers
of pure cellulose and are preferably composed of long light-
weight nonhydra~ed fibers of the Musa type, particularly - :
hemp fibers of the Manila or abaca hemp variety. Webs made
from this material are generally soft porous papers of uni-
form texture and thickness and have for some time found ~-
wide acceptance as the primary fiber component of the fibrous
base webs used in casing manufacture.
In accordance with the present invention, it
has been found that an accelerated rate of viscose penetra-
tion can be achieved if the hemp base web is subjected to a
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corona discharge treatment prior to the final casing-forming
operation. It should be noted that the corona treatment
does not appear to substantially alter the strength proper-
ties of the resultant casing material but provides a suffici-
ent improvement in viscose penetration characteristics to
assure a rapid manufacturing rate during the casing-forming
operation. This improved characteristic obviates the incom-
plete penetration and undesirable mottled appearance some-
times exhibited heretofore.
As is well known, corona discharge is the partial
or incomplete breakdown of a layer of gas, such as air, lo-
cated between two electrodes upon the application of a high
output voltage across the electrodes. The corona discharge
is repeatedly initiated with each power cycle and is readily
sustained in controlled fashion. Thus, by proper control
over the high-frequency power, the diffuse glow of the corona
can be utilized as a surface treating tool. The material to
be treated is passed over a grounded linear electrode to
expose the surface of the material to the electrical dis-
charge from a spaced parallel linear electrode maintained
at a high voltage. The energy density measured in watts may
be divided by the speed of the web material being treated
to provide an indication of the treatment level.
In accordance with the present invention, the
paper is treated by passing it through a corona discharge
surface treater of the type commercially available so that
at least one surface of the paper is subjected to a corona
discharge treatment at an energy density/web surface level
of at least about 0.5 watt-min/ft2. The conventio~al opera-
ting level will usually exceed 1.5 watt-min/ft2 with the
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preferred range extending from about 5 to 40 watt-min/ft2.
As will be appreciated, the speed of the web through the
treater or dwell time within the treater may vary substan-
tially with adjustments in the power output level. Accord-
ingly, as an example, treatment levels having a value of at
least about 600 watts at a travel speed of the web of about
S0-100 feet per minute are used in most instances but either
or both may be varied to assure a level of at least 0.5
watt-min/ft2 and the desired increase in the rate of viscose
penetration. This is particularly true where the treatment
is employed prior to drying, at some other stage of the pro-
cess well prior to viscose penetration or where a long delay
may be experienced between the corona discharge treatment
and the casing-forming operation.
The test procedures presently available for the
measurement of viscose penetration are subjective since typi-
cally they require determination of an end point by a quali-
fied observer and are measured in small time increments
~seconds). According to the preferred test method, the vis-
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cose penetration is measured by visually observing a piece
of web material floated on a concentrated (about 7 percent)
viscose solution and a determination is made of the length
of time it takes for the viscose to penetrate the material.
Thus, as will be appreciated, the end point at which indivi- ~ -
dual testers might determine that full penetration has
occurred may be observed differently. As a result, in accor-
dance with the present invention, average values resulting
from about ten tests or more are used. Further, use of the
same tester for each series of viscose penetration results
will provide a basis for comparison within that test series
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even if the absolute values might differ among tests. This
is the procedure used in the present invention and it consis-
tently shows a significant increase in the rate of viscose
penetration for material subject to the corona treatment of
the present invention. While this was true regardless of
the side of the web corona treated and the side of the web
presented to the viscose solution for penetration, it was
usually the nontreated side that was placed in contact with
the viscose, thereby tending to obviate any surface ef~ect.
As mentioned, the corona treatment can take
place immediately upon forming the base web and prior to the
initial drying operation. However, in such instances, the
effect of the corona treatment is partially dissipated by
drying prior to the casing-forming operation. Additionally,
it has been surprisingly -found that improved penetration
rates will result when one side of the web is corona treated
and the untreated side is placed in contact with the viscose
solution. Of course, as will be appreciated, the shortest
possible penetration time is preferred and at times this is
achieved by applying the viscose solution to the corona
treated side of the web.
It should also be noted that the effect of coro-
na treatment tends to decay somewhat with time and therefore
the desired point of application of the corona treatment is
preferably immediately prior to casing formation. The dis-
charge certainly could be applied, as mentioned earlier,
at any stage between web formation and casing formation
where these functions are performed in line or the web is
stored under controlled conditions. However, in practice,
the casing-forming operation is usually performed at a
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remote location from the web-forming operation and also
usually requires packaging and shipping of the base web ~-
material. Accordingly, to maximize the viscose penetration
rate and avoid the aforementioned decay, corona treatment
immediately prior to viscose penetration is preferred.
In carrying out the corona discharge treatment,
commercially available high frequency spark generators may
be used. For example, good results have been obtained using
the corona discharge surface treater sold by Lepel High Fre-
quency Laboratories, Inc. under the designation "Model ST-2",
more fully described in U. S. Patent No. 3,397,136 or by
Softal Elektroniks GMbH under the designation "Model 2003-
High Frequency Unit".
In operation, the fibrous base web is delivered,
usually from a supply roll, to a treating drum or roll posi-
tioned under an electrode within a treating chamber. The
interior of the chamber is under atmospheric conditions and
the chamber simply acts as an ozone hood or shield. The
speed of the web through the corona treating zone can be
controlled and adjusted to the level of treatment and, if
desired, both sides of the web may be treated on the same
pass. Of course, slower speeds will result in higher treat-
ment levels at a constant power output. Speeds of about 10
feet per minute up to about 2000 feet per minute may be
used. However, optimum power output levels of about 1200 ~
watts at web speeds of 50-100 feet per minute have been :
used for most casing making operations.
In order that the present invention may be
more readily understood, it is further described with refer-
ence to the following specific examples which are given
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by way of illustration only and are not intended to be a
limit on the practice of the inventionO
EXAMPLE I
Base webs were formed and dried on a paper- ,
making machine using a fiber furnish comprised of 100 ;
percent Manila hemp fibers. The webs were divided into three
categories: (1) No bonding treatment; (2) Bonded with a dilute
viscose solution; and ~3) Resin bonded by a mixture of a
cationic reaction product of epichlorohydrin and a polyamide,
(Kymene 557), and a nonionic polyacrylamide ~Cyanamer P250)
by dipping the web into an aqueous solution of the resins
until the web was saturated. Excess binder solution was
then removed by blotting and the treated webs were dried at
elevated temperatures. ~s shown in the following table, webs
from the three categories were treated at different corona
power output levels using a Lepel Model ST-2. The viscose
penetration of all webs and water climb properties of se-
lected webs were measured. The water climb is defined as
the time it takes for water to climb one inch on a vertical
strip of material one inch wide using distilled water at
25C. The viscose penetration tests used a 7 percent
viscose solution with the tested samples floated on the
solution until penetration was observed. The results are
reported in the following table as an average penetration
when the corona treated side of the webs were presented to
the viscose solution for one half of the samples tested and
the untreated sides were presented to the viscose for the
other half of the samples in each category.
s~ere~ e~arK
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Basis
Weight Corona Viscose Water Climb
(lbs. p2er Treatment Penetration* (Seconds/Inch)
2880ft ~ (sec.)
Power Web
Output Speed
(watts~ ~ft/min)
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Unbonded 13.~7 0 --- 46.3 5.3 ,-
595 100 4~.5
893 100 42.2
1190 100 40.7 4.3
21~2 50 32.3 4.4
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Dilute 13.~4 0 --- 37.4 12.2
Viscose 595 100 35.3
Bonded 893 100 31.6
1190 100 32.3 10.4
2142 50 31.7 7.6
Resin 13.01 0 --- 49.1 300
Bionded 595 100 40.6
893 100 37.1
1190 lO0 36.2 22.6
2142 50 31.7 13.5 -
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* Average of Twenty Tests
As shown, despite fluctuation due to the subjective nature
of the test, the improvement in viscose penetration is
clearly evident and the improvement in the Tate o-f both
penetration and water climb corresponds directly to the
corona treatment level.
EXAMPLE II
In order to exemplify the rapid viscose pene-
tration from the untreated side of the base web, a commer-
cial grade of casing base paper made from 100 perce~t hemp
fibers and treated with gelatin cross linked with a glutaral- - ;
dehyde on the felt side was given a corona discharge treat-
ment, also on the felt side using the Lepel ST-2 corona -~
treater. The base paper was tested for viscose penetration
by presenting the untreated side of the paper to the
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viscose. A viscose penetration rate of 52.35 seconds was
observed for the control sample which received no corona
discharge treatment while the samples receiving corona
discharge treatments at power output levels of 1200 and
1800 watts and web speeds of 400 feet per minute gave vis-
cose penetration readings of 49.68 and 41.13 seconds, res-
pectively.
EXAMPLE III
As an example of the improved result achieved
by applying the corona treatment after drying the base web,
handsheets having a basis weight of about 15 pounds were
prepared from 100 percent hemp fibers. The handsheets were
subject to no bonding operation and were treated with a coro-
na discharge treatment both before and after the drying
operation to determine the effect of the corona at different
stages in the manufacturing process. The corona treatment
was applied using a Softal Model 2003 hand held unit. The -~
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power output was 175 watts and the discharge electrode was
passed over the handsheets twice with the felt side of the
sheet exposed to the corona. The viscose penetration data
(average for three handsheets in each test group) is given
below: -
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SAMPLECORONAVISCOSE PENETRATION
APPL,ICATION ~sec.)
Wire Side ~elt Side
Toward Viscose Toward Viscose
3-A No Corona 71 79
3-BBefore Drying 67 69
3-CAfter Drying 61 59
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EXAMPLE IV
As an example of base webs made from fibers
other than hemp, handsheets were prepared from a fiber fur- ,
nish consisting of 72 percent by weight of 3/4 inch, six
denier nylon ~ibers, 25 percent by weight of kraft fibers
and 3 percent by weight of polyvinyl alcohol fibers. The
sheets were bonded with an acrylic latex binder modified
with melamine formaldehyde, and dried. The resultant hand-
sheets, with a basis weight of about 12 pounds per ream,
were affixed to a bel~ traveling at 50 feet per minute
and corona treated at substantially different power output
levels. The viscose penetration results are reported below:
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PLECORONA POWERVI~OSE PENETRATION ,~ -
OUTPUT ~watts) ~sec.)
Treated Side Untreated Side
Toward Viscose Toward Viscose Average
4-A 0 21.2 19.6 20.4
4-B 160 19.8 22.2 21.0
4-C 1755 14.3 13.7 14.0 `
EXAMPLE V
A commercial grade of casing base paper made
from 100 percent hemp fibers was corona treated at two differ- `~
ent discharge levels by adjusting only the speed of travel of
the web. Prior to treatment the base paper was bonded with -
a dilute viscose solution to provide a binder add-on of about
2 percent. The webs were then tested for viscose penetration -
together with a control sample that had received no corona
discharge treatment. The corona output level was about 1800
watts. The viscose penetration results are reported below:
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SAMPLE CORONA TREATMENT VISCOSE PENETRATION .: :
PAPER SPEED (sec.)(feet/min) ;:
Treated Side Untreated Side : .
Presented Presented
to Viscose to Viscose Average
5-A Control 51.9 45.2 48.6 ., :
5-B 400 44.0 42.6 43.3
5-C 50 38.2 35.3 36.8
EXAMPLE VI ..
As an indication of the variations that may be
observed among different testers in determining the end
point of the viscose penetration test, two independent
testers conducted the same tests on identical paper sam-
ples prepared from 100 percent hemp fibers and resin bonded
as in Example I. The results are set forth below: .
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SAMPLE CORONA WEB SPEED TESTERS AVERAGE ~-
~Watts~ (ft/min)
A B
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6-A 0 -- 39.2 52.2 45.7 ~.
6-B 75 50 39.7 50.9 45.3
6-C 150 50 39.0 48.2 43.6 `
6-D 225 50 37.9 47.9 42.9
6-E 1800 50 37.4 45.1 41.3
6-F O -- 37.8 53.2 45.5
EXAMPLE VII . :
Handsheets of 100 percent hemp fibers were pre- :
pared from about 20 liters of water and 50 grams ~dry weight)
of hemp fibers to provide a fiber dispersion at a consistency ;
of about 0.5 percent. Handsheets were prepared from the
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furnish at a basis weight of about 14 pounds. To corona
treat, the handsheets were taped to the treater roll of the ,
, Lepel ST-2 unit and the roll was rotated at a speed of
l~i 50 feet per minute through six revolutions. The individual
samples were subject to the following conditions. Sample
7-A was subject to a corona discharge treatment after drying
and was then tested for viscose penetration. The corona
treatment was at a power output level of about 1800 watts.
Sample 7-B was prepared in exactly the same way as sample
7-A except that the sheet was bonded with dilute viscose ;
after the corona discharge treatment at 1800 watts and the ;;`~
viscose was regenerated, washed and dried prior to the pene- -
tration test. Samples 7-C and 7-D repeated Samples 7-A and
7-B respectively except that no corona treatment was given to
these samples. Sample 7-E was prepared by treating the dried ~``
web with viscase and drying the viscose following which the
web was corona treated prior to regeneration of the viscose.
The corona treatment power output level was 1300 watts.
Sample 7-F was prepared by treating the dried handsheet with
viscose, regenerating the viscose and redrying the web, ~ ~
following which it was subject to the corona discharge treat- "
ment at a power output of 1800 watts. The viscose penetration
was then conducted on each of the samples and the results are
reported below together with the basis weights o-f the
materials:
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SAMPLE ~ASIS VISCOSE AVERA OE
WEIGHT PENETRATION
(lbs. per (sec.)
2880-ft2) :~
_
7-~ 14.54 115.5
7-B 15.32 134.7
7-C 13.89 120.1 `
7-D 14.69 98.0
7-E 14.65 98.6
7-F 14.4 67.6
In all of the above-reported viscose penetration
tests the corona discharge was applied to the felt side of the
sheet, and the untreated side of the sheet was presented to
the viscose. The tests were conducted at room temperature
of 76.3F.
EXAMPLE VIII
A commercial grade of casing paper made from
100 percent hemp fibers and having a dilute viscose bonding
treatment was subject to corona discharge treatment at a
power output level of 1800 watts and the viscose penetration
thereof was measured. The sampleswere retested after storage
for two months and the results of both tests are reported in ~- ,
the following table:
GRADECORONA TREATMENTVISCOSE PENETRATION ~ -
Web Speed ~ft/min) (sec.)
Original Retest
, ~
8-A Control 33.6 76.95 -
8-B 400 31.0 71.05
8-C 50 27.4 45.66
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As will be apparent to persons skilled in :~
the art, various modifications, adaptations and variations
o-f the foregoing specific disclosure can be made without
departing -from the teachings of the present invention.
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