Note: Descriptions are shown in the official language in which they were submitted.
6~
The present invention relates to casing paper, which may
be used for the production of packaging for mea-t products such as
sausage.
Casing paper is commonly manufactured from paper webs of
relatively strong, high-tenacity natural fibres, such as abaca,
sisal or flax. The paper web is saturated with a dilute viscose
solution, for example a solution obtained by diluting a solution
containing 7% by weight of cellulose (as cellulose xanthate) and
6% by weight of sodium hydroxide to a 1~ cellulose content. The
viscose-saturated web is dried and the cellulose in the viscose
is then regenerated by passing the web through an acidic re-
generating bath containing, for example, a 1-8% aqueous sulphuric
acid solution. The web is then washed free of acid and dried to
produce a paper web impregnated with acid-regenerated cellulose.
This casing paper is then generally formed into rolls ("master
~ rolls").
; Caslngs for the packaging of processed meats, e.~. sausage,
may be manufactured from the casing paper by cutting it into
strips which are then folded to form tubes. The tubes are satu-
rated with an alkaline viscose solution, containing, for example,
7~ by weight of cellulose and 6% by weight of sodium hydroxide.
The cellulose in the viscose is then regenerated by means of an
acidic re~enerating bat~ containing, for example, dilute sul-
phuric acid and possibly such salts as sodium sulphate or
ammonium sulphate. The tube is then passed through one or more
baths in order to wash out the acid and the salts.
If desired, the tube may be passed through an aqueous
bath which contains a plasticizer, e.g. glycerine t for the re-
generated cellulose. The tube is dried by passing it through a
3a heated chamber (the tube being in an inflated state) to give a
cellulosic tubing which has embedded there~n a paper web. This
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tubing may then be stu**ed with a processed meat product under
pressure. A process o~ this type is described in detail in United
States Patent No. 3,135,613.
The purpose in treating the initial paper web with dilute
viscose solution, followed by regeneration, is to provide the web
with strength and structural integrity so that it may withstand
the treatment with the highly caustic viscose solution used in
the formation of -the casing tubes. The amount o* cellulose in
the casiny paper is, in fact, comparatively low; thus, the casing
paper may have a typical basis weight (weight per unit area) of
20 grams/m2, of which the cellulose accounts for 0.6 g/m2, com-
pared with the material of the casing tubes which may have a
typical basis weight of 70-80 g/m2, of which 50 60 gjm2 may be
accounted for by the cellulose. However, despite the initial
treatment with viscose, the treatment with the highly caustic
viscose solution used in the ~ormation of the casing tubes will
inevltably entail a certain degree of softening and weakening of
the web. This imposes a limit on the production speeds if
difficulty in handling the webs and possible breakdowns in pro~
duction are to be avoided. There is accordingly A need in the
art *or casing paper having~an improved alkali resistance in
order to permit hlgher production speeds in the manufacture of
the casing tubes.
In United States Patent 3,378,379, there is disclosed a
tubular regenerated-cellulose casing for dry sausage~ which
casing is provided with a coating comprising a cationic thermo-
setting resin bonded to the inside wall thereof. The patent
suggests that polyethylene imine may also be employed for this
coating, although this material is not, in *act, a cationic
thermosetting resin. The purpose o* the inner coating is to
; improve the adhesion o* the sausage casing to a dry sausage pro-
duct despite any shrinkage which may occur when the dry sausage
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product is processed and dried in the casing over a prolonged
period of time. It should be noted, however, that in the afore-
said process it is not the casing paper as such which is treated
with the thermosetting resin, but the tubular casing material.
In -the embodiment illustrated in U.S. Patent 3,378,379, the
cationic thermosetting resin is applied to the inner surface of
the casing tube after the application of glycerine and before the
casing is dried, in an inflated state, in a heated chamber.
Another problem recognised in U.S. Patent No. 3,378,379
is the variation in extensibility in the transverse direction
exhibited by casing paper strips cut from different parts of the
master roll. This can cause variation in the properties of the
final casing tubes, which may therefore be unsatisfactory to the
meat packager, for whom dimensional stability in the product is
of commercial importance. To meet this problern it is suggested
in the aforesaid U.S. Patent that a cationic thermosetting resin
: (e.g. a reaction product of epichlo~ohydrin and a polyamide, a
modified melamine-formaldehyde resin or a modified urea-formalde-
hyde resin) may be employed as the bonding agent in the casing
paper, instead of the ~ommonly employed acid-regenerated viscose.
: The cationic thermosetting resin is employed in an amount of at
least 0.5% by weight based upon the dry weight of the impregnated
fibrous w:eb~ The resin may be incorporated into the fibrous web
by adding the resin to the fibrous slurry prior to forming the
fibrous weh. ALternatively, the formed fibrous web may be
impregnated with the resin by passa~e through an aqueous solution
: of said resin. The said U.S~ patent also discloses the use of
the thermosetting resin in combination with~viscose which is not
regenerated with an acid; however, in the latter case the vis-
: 30 cose may be auto-regenerated by storing the web for a suffic.ient
period.
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33~76~
In United Kingdom Patent Specification 1,091,105 there is
described a process in which casing paper is produced by incor-
porating into a paper web an alkaline-curing resin such as poly-
ethylene imine or a polymeric reaction product of epichlorohydrin
and a polyamide. The use of the alkaline-curing resin in place
of the customary treatment with dilute viscose is said to result
in a casing paper which has more uniform characteristics across
its width and which results in a casing having improved burst
strengths. However, it has now been found that the casing paper
so produced has an alkali resistance which is insufficient to
permit sufficiently high production speeds for the commercial
manufacture of the casing tubes.
It is an object of the present invention to provide a
process for the production of casing paper having a good alkaline
wet strength and from which casing tubes may be produced using
high-speed com~ercial processes.
Accordingly, the present invention provides a process for
- the production of casing paper, which process comprises forming
a fibrous paper web, treating the fibrous paper web with a
~0 viscose solution and subsequently regeneratiny the cellulose in
the viscose by means of an acid, wherein the fibres of the paper
web are treated with polyethylene imine. Preferably, this treat-
ment is carried out prior to, or simultaneously with, the treat-
ment with the said viscose solution.
The present invention also provides casing paper when pre-
pared by the aforesaid process, as well as casing material
(casing tubes or skins) prepared from the said casing paper by a
process comprising the application of a caustic viscose solution
and subsequent acid regeneration.
It has been ~ound that there is~a synergistic effect be-
tween polyethylene 1mine (PEI) and the viscose, which can result
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in a marked improvement in the alkaline wet strength of casing
paper produced accordiny to the present invention, whilst the
viscose absorbency of the casing paper remains satisfactory. It
has been fo~nd that PEI, when used in the absence of any other
binding agent, provides virtually no increase in the wet strength
of the paper web. Moreover the attainment of such an improved
alkaline wet strength is particularly surprising since PEI can
be decomposed, under cer-tain conditions, by acids.
Normally, the amount of PEI added will be 0.1 to 2%, and
preferably 0.2 to 1~, by weight of the fibrous web, on a dry
weight basis.
The viscose is generally added -to the fibrous material in
amounts which are customary in the art for the production of
casing papers containing acid-regenerated viscose.
The PEI may be added to the fibres during the paper-web-
making process or may be applied to the fibrous web as made.
Conveniently, however, the PEI may be included in the dilute
viscose solution itself.
In a parkicularly preferred embodiment of the present
invention, the fibres of the paper web are also treated with a
polyamide-epichlorohydrin resin. Preferably, the fibrous web s
treated~with~both the polyethylene imine and the polyamide-
epichlorohydrin resin prior to or simultaneously with the treat-
ment with the viscose solution~ It has been found that the
alkali resistance-of casing paper prepared by this method can be
significantly higher than would be expècted from results abtained
by treatment with either of the treating agents alone.
Normally the amount of the polyamide-eplchlorohydrin resin
will be 0.1 to ~%, and preferably 0.25 to 2%, by weight of the
~ibrous web, on a dry we1ght basis~
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The fibrous webs used in making casinq paper are conven-
tionally composed of natural vegetable fibres of pure cellulose
and are preferably composed of long lightweight nonhydrated
fibres of the Musa type, particularly hemp fibres of the Manila
or abaca hemp variety. Webs made from this material are generally
soft porous papers of uniform texture and thickness and have for
some time found wide acceptance as the primary fibre component
of the fibrous base webs used in casing manufacture.
Prior to its impregnation with a caustic viscose solution
or the like in order to form the final casing material, the
casing paper may be treated in order to improve its absorbency
yet further. One preferred method is to subject at least one
side of the web to a corona discharge treatment at an energy
density of at least 0.5 Watt-min / ft2 of web surface. The usual
level will exceed 1.5 Watt-min/ft and i5 preferably 5 to 40 Watt-
min/ft . This treatment is described in B.W. Conway and J.P.
Molinari's Canadian Patent No. 1,061,631.
~; - The present invention is ]llustrated by the fol]owing
Examples.
Example 1
Handsheets were made in the laboratory using an abaca
stock. A 0.1~ solution of Polymin P (the trade mark of a poly-
ethylene imine marked by BASF, Germany) was ~dded to the sheet
mould in an amount sufficient to provide 1~ of polyethylene imine
in the resultant handsheets, on a dry weight basis. The sheets
were then ~aturated with a dilute viscose solution and then sub-
jected~to the acid-regeneration process. The sheets were then
tested~for their~wet tensile strength and alkaline wet tensile
stren~th ~ the Instron and the Scott~tensile testers respec-
tivel~. For testing -the alkaline wet tensiles, the sheets were
saturated with a 6~ caustic soda solution.
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The results are shown in Table 1 below.
Example 2
Handsheets were made in the laboratory using an abaca
stock, but no polyethylene imine was added to the mould. The
handsheets so produced were then impregnated with Polymin P and
with viscose using a laboratory sizepress, to give approximately
a 2% pickup of the Polymin P and the viscose. The said additives
were present in the saturating bath of the sizepress in the ratio
of 10 parts by weiyht dry Polymin P to 90 parts dry viscose. The
treated handsheets were then subjected to the acid regeneration
process and were subsequently tested for their wet tensile
str~ngth and alkaline wet tensile strength, as described in
Example 1.
For comparison purposes, handsheets were made that were
treated with either viscose only or Polymin P only, and these
were tested as described above.
The results~are shown in Table 1 below.
; In Table 1 the wet tensile and alkaline wet tensile
strengths are average~s of a number o test results. In the cases
of the viscose only and of Example 1 results are presented for
two different sheet weights.
T a_b 1 e
TREATMENT SHEET WEIGHT WET TENSILE ALKALINE WET TENSILE
(gsm) (gm/25 mm)- - (gm/lS mm~
..._ _
Polymin P only 24.4 60 10
Vis~ose only and 26.4 920 15
acid regeneration 27.3 950 60
Example 1 25.0 800 210
27.5 ~1070 240
30 Example 2 24.6 990 310
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Example 3
Non-viscose treated casing paper base was manufactured on
a small-scale (24 inches wide~ paper machine. The base stock was
prepared by defibering a known weight of abaca pulp at a con-
sistency of appro~imately 4%, and adding to the base stock vari-
ous quantities of additive selected from Polymin ~, Kymene 557
(the trade mark of a water~soluble epichlorohydrin-polyamide
resin marketed by Hercules Powder Company) and mixtures thereof.
The pre-treated base paper was then converted to casing
paper on a commercial continuous-process unit, the base paper
being first saturated with a viscose solution in a sizepress.
After partial drying of the base paper sheets, the viscose was
regenerated in an acid press, the sheets being subsequently
washed to remove any excess chemicals, dried and wound up. The
amount of viscose applied to the sheet in the process was approxi-
mately 2% by weight of the original sheet.
The finished casing papers were then tested for conven-
tional wet tensile strength, this being measured on strips of the
paper 25 mm wide which were saturated with water. The alkali
resistance of the casing papers was measured by recording the
tensile stren~th of wet strips, 15 mm wide, after soaking them
for 20 minutes in a 6% solution of sodium hydroxide (the results
being designated as the alkaline wet tensile strength). The
absorbency of the sheets was also measured as the time taken for
water to climb l inch up a vertical strip of the casing paper.
A high absorbency value will indicate that an undesirable sizing
effect had taken place, which would interfere with the resatur-
ating of the casing paper with viscose as effected during the
customary manufacture of caslng tubes or skins.
The results~obtained are shown in Table 2 belowO The
tensile strengths are quoted both as measured (for an average
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of seven tests for each sample) and also as corrected to a con-
stant basis weight in order to allow direct comparison of the
effects to be observed. This, of course, depends upon the
assumption that strength is directly proportional to weight,
an assumption which may not be perfectly correct, but which is
suEficiently valid for the present purposes.
Also quoted is the ratio of the wet strength initially
retained after the 20 minutes' soak in alkali. This helps in
assessing the true alkali resistance of the sheets, but should
be considered in conjunction with the actual strength figures.
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From the results given in Table 2, the following con-
clusions can be drawn.
The use of polyamide-epichlorohydrin resin with regenerated
viscose provides an increase in wet strength at an addition level
of 1%-2% by weight, but appears to have no significant ef~ect on
the alkaline wet strength.
The alkaline wet strength is increased with increasing
levels of polyethylene imine when this is employed alone in the
base sheet.
A combination of a polyamide-epichlorohydrin resin and
polyethylene imine causes an increase in wet tensile strength
similar to that obtained by pretreating the base with polyamide-
epichlorohydrin resin alone, but brings about a very marked
improvement in alkaline wet tensile strength at all levels used.
However, the addition of 0.5% to 1% polyamide-epichlorohydrin
resin in combination with 0.5% of polyethylene imine (by weight
.
of the base web, on a dry weight basis) appears to be a parti-
cularly efficient amount, based on considerations of both per-
formanc~ and addition levels.
No detrimental effect on absorbency appears to be caused
by any of the add1tions made.
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