CA1093766A

CA1093766A - Casing paper having alkali resistance

Info

Publication number: CA1093766A
Application number: CA267,656A
Authority: CA
Inventors: Newlyn Jones; Alistair C. Stewart; Colin Elston
Original assignee: CH Dexter Ltd
Current assignee: CH Dexter Ltd
Priority date: 1975-12-12
Filing date: 1976-12-10
Publication date: 1981-01-20
Also published as: FI67896C; SE7613449L; DE2655594A1; BR7608327A; BE849313A; FR2334784A1; SE430906B; FI763536A; FR2334784B1; FI67896B; ZA766695B; GB1520260A; AU2049676A; AU505361B2; AR212095A1; NL7613681A; JPS5276196A

Abstract

ABSTRACT OF THE DISCLOSURE

Fibrous casing paper is treated with both viscose and polyethylene imine to provide an improvement in the alkaline wet strength while maintaining satisfactory viscose absorbency.

Description

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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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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 _ g ~a , 3'7~

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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the production of casing paper, which process comprises forming a fibrous paper web, treating the fibrous paper web with a viscose solution and subsequently regenerating the cellulose in the viscose by means of an acid, wherein the fibres of the paper web are treated with polyethylene imine.

2. A process according to Claim 1 wherein the treatment with polyethylene imine is carried out prior to, or simultaneously with, the treatment with the said viscose solution.

3. A process according to Claim 1 wherein the polyethylene imine is incorporated into the fibrous web in an amount of 0.1 to 2% by weight of the fibrous web, on a dry weight basis.

4. A process according to Claim 2, wherein the polyethylene imine is incorporated into the fibrous web in an amount of 0.1 to 2% by weight of the fibrous web, on a dry weight basis.

5. A process according to Claim 3 wherein the polyethylene imine is incorporated into the fibrous web in an amount of 0.2 to 1% by weight of the fibrous web, on a dry weight basis.

6. A process according to Claim 4 wherein the polyethylene imine is incorporated into the fibrous web in an amount of 0.2 to 1% by weight of the fibrous web, on a dry weight basis.

7. A process according to any of claims 1 to 3, wherein the polyethylene imine is included in the dilute viscose solution applied to the fibrous web.

8. A process according to any of claims 4 to 6 wherein the polyethylene imine is included in the dilute viscose solution applied to the fibrous web.

9. A process according to any of Claims 1 to 3 wherein the polyethylene imine is incorporated into the fibrous web prior to the treatment with the viscose solution.

10. A process according to any of claims 4 to 6 wherein the polyethylene imine is incorporated into the fibrous web prior to the treatment with the viscose solution.

11. A process according to any one of Claims 1 to 3, wherein the fibres of the web are also treated with a polyamide-epichlorohydrin resin.

12. A process according to any of claims 4 to 6, wherein the fibres of the web are also treated with a polyamide-epichlorohydrin resin.

13. A process according to any one of claims 1 to 3, wherein the fibres of the web are also treated with a polyamide-epichlorohydrin resin wherein the polyethylene imine is incorporated into the fibrous web prior to the treatment with the viscose solution, and wherein the polyethylene imine and the polyamide-epichlorohydrin resin are incorporated into the fibrous web during the web-forming process.

14. A process according to any one of claims 1 to 3, wherein the fibres of the web are also treated with a polyamide-epichlorohydrin resin wherein the polyethylene imine is included in the dilute viscose solution applied to the fibrous web and wherein the polyethylene imine and the polyamide-epi-chlorohydrln resin are incorporated into the fibrous web simultaneously with the viscose solution.

15. A process according to any one of claims 1 to 3, wherein the fibres of the web are also treated with a polyamide-epichlorohydrin resin and wherein the polyamide-epi-chlorohydrin resin is incorporated into the fibrous web in an amount of 0.1 to 4% by weight of the fibrous web, on a dry weight basis.

16. A process according to any one of claims 1 to 3, wherein the fibres of the web are also treated with a poly-amide-epichlorohydrin resin and wherein the polyamide-epi-chlorohydrin resin is incorporated into the fibrous web in an amount of 0.25 to 2% by weight of the fibrous web, on a dry weight basis.

17. Casing paper which comprises a fibrous web impregnated with cellulose and having incorporated therein polyethylene imine.

18. Casing paper according to Claim 17 which also has a polyamide-epichlorohydrin resin incorporated therein.

19. Casing paper whenever prepared by a process according to any one of claims 1 to 3.

20. Casing paper whenever prepared by a process according to any one of claims 4 to 6.

21. Casing material for processed meat products, being casing material manufactured from easing paper according to claim 17 or 18.