FI67896B - ALKALIFAST OMSLAGSPAPPER - Google Patents

Description

Ri ^ F®l ΓΒ1 (11) ADVERTISEMENT 67896 lBJ (11) UTLÄGGNIN GSSKRIFT 0/070 ^ (45) Patent granted 10 C6 1985 Patent meddelat, r .. D 21 D 3/00 // D 21 H 5 / 00, (51) Kv.lk.4 / lnt.CI. 'A 22 c l3 / 00 FINLAND — FINLAND (21) Patent application - Patencansökning 763536 (22) Application date - Ansökningsdag 08.12.76 (23) Starting date - Giltighetsdag 08.12.76 (41) Made public - Blivit offentlig 1 3.06,77

National Board of Patents and Registration Date of publication and publication. - 28.02.85

Patents and registries '' Ansökan utlagd och utl skriften publicerad (32) (33) (31) Requested privilege— Begärd priority 12.12.75 England-England (GB) 51007/75 (71) C.H. Dexter Limited, Chirnside, Duns, Berwickshire, Scotland, United Kingdom-Storbritannien (GB) (72) Newlyn Jones, Foulden, Berwickshire, Scotland,

Alistair Charles Stewart, Edinburgh, Scotland, United Kingdom-Storbritannien (GB), Colin Elston, Windsor, Connecticut, USA (7A) Forssen δ Salomaa Oy (5A) AI ka 1stust peel paper - Aikaiifast omslagspapper

The present invention relates to a process for making shell paper, especially coatings or sausage casings for finished meat products or the like, which process comprises forming a fibrous paper web, treating the fibrous paper web with a dilute viscose solution having a cellulose content of 0.5-3% by weight and then regenerating the viscose. with acid.

Peel paper is usually made from paper webs containing relatively strong, tough natural fibers such as manila hemp, sisal hemp or flax fibers. The paper web is impregnated with a dilute viscose solution obtained, for example, by diluting to a 1% cellulose content of a solution containing 7% by weight of cellulose (as cellulose xanthate) and 6% by weight of sodium hydroxy. The web impregnated with viscose is dried and the cellulose in the viscose is then regenerated by passing the web through an acid regeneration bath containing, for example, 1-8% by weight of an aqueous solution of sulfuric acid. The web is then washed free of acid and dried to obtain a paper web containing acid 2 67896 regenerated cellulose. This peel paper is then generally formed into rolls ("storage rolls").

Shells for packaging meat products, such as sausage, can be made from shell paper by cutting it into strips, which are then bent to form tubes. The tubes are impregnated 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 acid regeneration bath containing, for example, dilute sulfuric acid and optionally salts such as sodium sulfate or ammonium sulfate. The tube is then passed through one or more baths to wash away the acid or salts.

If desired, the tube may be passed through a water bath containing a plasticizer of regenerated cellulose, for example glycerin. The tubes are then dried by passing them through a heated chamber (with the tube inflated) to obtain a cellulosic tubing with a paper web inside. This pipe material can then be filled with the meat processing product under pressure. This type of process is described in detail in U.S. Patent 3,135,613.

The purpose of treating the starting paper web with a dilute viscose solution and subsequent regeneration is to provide a web with such strength and structural integrity that it can withstand the treatment with the highly alkaline viscose solution used to form the shell tubes. The amount of cellulose in the peel paper is in fact relatively low; thus, the basis weight of the shell paper (weight per unit area 2) can typically be 20 g / m, of which the proportion of cellulose 2 is 0.6 g / m, compared to the material of the shell tubes, which typically has a weight of 2 2 square meters 70-80 gm, of which 50 -60 g / m can be calculated as the proportion of cellulose. However, despite the initial viscose treatment, treatment with the highly basic viscose solution used to form the shell tubes inevitably causes a degree of softening and deterioration of the web. This sets a limit on the production speed if efforts are to be made to avoid difficulties in handling the webs and possible interruptions in production. There is thus a need in the art for shell paper with improved alkali resistance to allow higher production rates in the manufacture of shell tubes.

U.S. Patent No. 3,678,896 discloses a tubular dry sausage casing of regenerated cellulose provided with a coating comprising a cationic thermoset bonded to its inner wall. The patent suggests that polyethyleneimine can also be used for this coating, although this material is not in fact a cationic thermosetting plastic. The purpose of the inner coating is to improve the adhesion of the sausage casing to the dry sausage product, despite the possible shrinkage that can occur when the dry sausage product is handled and dried in the casing for longer periods of time. It should be noted, however, that in the above-mentioned process, the peel paper as such is not treated with thermosetting plastic, but with a tubular peel material. In the embodiment described in U.S. Patent 3,378,379, the cationic thermosetting plastic is added to the inner surface of the shell tube after the addition of glycerin and before the shell is dried in an inflated state in a heated chamber.

Another problem known in U.S. Patent 3,378,379 is the variation in the transverse direction indicated by the strips of peel paper cut from different parts of the storage roll. This may cause variations in the properties of the final shell tubes, which may therefore be unsatisfactory for the meat packer, for whom the dimensional stability of the product is commercially important. To overcome this problem, the aforementioned U.S. patent suggests that a cationic thermoplastic (e.g., a reaction product of epichlorohydrin and polyamide, a modified melamine-formaldehyde resin, or a modified urea-formaldehyde resin) can be used as a binder for acid-regenerated viscose commonly used in peel paper. The cationic thermoplastic resin is used in at least 0.5% of the dry weight of the impregnated fibrous web. The resin can be applied to the fibrous web by adding the resin to the fibrous slurry prior to forming the fibrous web. Alternatively, the formed fibrous web can be impregnated with the resin by passing it through an aqueous solution of said resin. Said U.S. patent also discloses the use of thermosetting plastic in connection with a viscose which has not been regenerated with acid, in which case, however, the viscose can be auto-regenerated by storing the web for a sufficient time.

British Patent 1,091,105 describes a process in which peel paper is made by introducing an alkali curable resin such as polyethyleneimine or a polymeric reaction product of epichlorohydrin and polyamide 4,678,96 into the paper web. The use of an alkali-curable resin instead of the conventional dilute viscose treatment is said to result in a peel paper which has more uniform width properties and results in improved puncture resistance. However, it has now been found that the alkali resistance of the shell paper thus produced is insufficient to allow sufficiently high production rates for the commercial manufacture of shell tubes.

It is an object of the present invention to provide a process for making a peel paper having good alkaline wet strength and from which peel tubes can be made using rapid commercial processes.

Accordingly, the present invention provides a process for making a kraft paper comprising forming a fibrous paper web, treating the fibrous paper web with a viscose solution and then regenerating the viscous cellulose with an acid, characterized in that the paper web fibers are treated with polyethyleneimine. This treatment is preferably carried out before or simultaneously with said viscous solution.

The term "shell paper" is used herein to mean a fibrous paper-like material that has not yet been treated with a highly alkaline viscose solution. It can be shown from the prior art that highly alkaline (or caustic) viscose solutions (commonly used to make the final food coating material) are clearly distinguishable from similar dilute viscose solutions used to impart strength and structural integrity to the paper web.

The present invention also provides a peel paper made by the above process, as well as a peel material (shell tubes or films) made from said peel paper by a process comprising utilization of a basic viscose solution followed by acid regeneration.

It has been found that there is a synergistic effect between polyethyleneimine (PEI) and viscose, which can result in a significant improvement in the alkaline wet strength of the peel paper made in accordance with the present invention, while maintaining the satisfactory viscosity absorbency of the peel paper. It has been found that when PEI is used in the absence of any other binder, it does not actually provide any increase in the wet strength of the paper web. Moreover, achieving such improved alkaline wet strength is particularly surprising, since PEI may, under certain conditions, degrade under the influence of acids.

The amount of PEI normally added is 0.1-2.0%, preferably 0.2-1.0% of the dry weight of the dry matter.

Viscose is generally added to the fibrous material in amounts conventional in the art of making peel papers containing acid-regenerated viscose.

PEI can be added to the fibers during the papermaking process or it can be added to the finished fibrous web. However, PEI can be conveniently added to the dilute viscose solution itself.

In a particularly preferred embodiment of the present invention, the fibers of the paper web are also treated with a polyamide-epichlorohydrin resin.

Preferably, the fibrous web is treated with both polyethyleneimine and polyamide-epichlorohydrin resin prior to or simultaneously with the viscose solution. It has been found that the alkali resistance of the peel paper produced by this method can be considerably higher than would be expected from the results obtained by treatment with either substance alone.

Normally the amount of polyamine-epichlorohydrin resin is 0.1-4.0% and preferably 0.25-2.0% of the dry weight of the fibrous web.

The fibrous webs used in the production of peel paper usually consist of vegetable fibers of pure cellulose and preferably of long, light non-hydrated type banana-type fibers, especially hemp fibers belonging to the manila or manilla hemp range. Webs made from this material are generally soft, porous papers with a uniform fabric structure and thickness that have long been widely accepted as the main fiber component of fibrous webs used in the manufacture of shells.

6 67896

Prior to impregnation with an alkaline viscose solution or the like to form the final peel material, the peel paper may be treated to further improve its absorbency. One preferred method is to apply at least one side of the web to a corona discharge treatment having an energy density of at least 1.6 W-min per square meter of web area. The normal level exceeds 5 VJ-min / m * - and is preferably 16-133 W-min / m. This treatment is described in B.W. Conway and J.P. Molinari's U.S. Patent Application 636,082, filed Nov. 28, 2007.

The present invention is illustrated by the following examples. Example 1 Hand sheets were made in a laboratory using manila hemp pulp. An amount of 0.1% Polymin P solution (trade name of polyethyleneimine marketed by BASF) was added to the sheet mold in an amount sufficient to provide a 1% polyethyleneimine content by dry weight on the resulting hand sheets. The sheets were then impregnated with a dilute viscose solution and subjected to an acid regeneration process. The sheets were then tested for wet tensile strength and alkali wet strength with an Instron and a Scott tensile strength device. To test the alkali wet tensile strength, the sheets were impregnated with 6% alkaline soda solution. The results are shown in Table 1 below.

Example 2 Hand sheets were made in the laboratory using manila hemp pulp, but polyethyleneimine was not added to the sheet mold. The hand sheets thus prepared were impregnated with Polymin P and viscose using a laboratory sizing press, causing approximately 2% Polymin P and viscose to migrate into the sheets. Said additives were present in the impregnation basin of the size press in a proportion of 10 parts by weight of Polymin P per 90 parts of viscose. The treated sheets were subjected to an acid regeneration process and then tested for wet tensile strength and alkali wet tensile strength as shown in Example 1.

67896

For comparison, hand sheets were prepared which were treated with either viscose alone or Polymin P alone and these sheets were treated as above.

The results are shown in Table 1 below.

In Table 1, wet tensile strengths and alkali wet tensile strengths are averages from a set of test results. In cases »where viscose alone was used and in Example 1, the results are shown for two different sheet weights.

TABLE 1 Handling Sheet weight Wet tensile strength Alkali wet tensile strength 2 (g / m) (25 mm strips) (15 mm strips) (g / m2) (g / m2)

Polymin P 24.A 60 10 alone

Viscose 26.4 920 15 alone and acid regeneration 27.3 950 60

Example 1 25.0 800 210

Example 1 27.5 1070 240

Example 2 24.6 990 310

Example 3

Viscose-untreated peel paper was made on a miniature paper machine (width 61 cm). The base stock was prepared by defibering a known weight of manila hemp pulp to a consistency of approximately 4% and adding varying amounts of additives selected from Polymin P, Kymene 557 (trade name of water-soluble epichlorohydrin-polyamide resin marketed by Hercules Powder Company) and mixtures thereof.

8 67896

The pretreated base paper was then converted to peel paper in a commercial continuous manufacturing unit, with the base paper first impregnated with a viscous solution in a size press. After partial drying of the base paper sheets, the viscose was regenerated in an acid press, after which the sheets were washed to remove excess chemicals, dried and rolled. The amount of viscose added to the sheet material in the process was approximately 2% by weight of the original sheet material.

The final peel papers were then tested for normal wet strength, measured from 25 mm wide strips impregnated with water. The alkali resistance of peel papers was measured by recording the tensile strength of 15 mm wide wet strips after soaking for 20 minutes in 6% sodium trioxide hydroxide solution (results refer to alkali wet tensile strength). The absorbency of the sheets was also measured during the time required to climb water to a height of 2.5 cm along a vertical strip of wrapping paper. The high absorbency value indicates that an undesirable sizing effect has occurred, which could interfere with the resaturation of the peel paper with viscous during the normal manufacture of the peel tubes or films.

The results obtained are shown in Table 2 below. Tensile strengths are given both measured (as an average of seven experiments per sample) and corrected to allow a direct comparison of the effects observed on a constant basis weight. This, of course, depends on the assumption that the strength is directly proportional to the weight, which is sufficiently correct for this purpose, although it may not be a completely correct assumption.

The relationship between the initial wet strength and the wet strength retained after 20 minutes of alkali immersion is also given. This helps to assess the actual alkali resistance of the sheets, although it should be considered in the context of the actual strength values.

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The following conclusions can be drawn from the results given in Table 2.

The use of a polyamide-epichlorohydrin resin with regenerated viscose provides an increase in wet strength at an addition level of 1-2% by weight, but does not appear to have a significant effect on alkali wet strength.

Alkali wet strength increases as the level of polyethyleneimine increases when this substance is used alone in the base sheet.

The combination of polyamide-epichlorohydrin resin and polyethyleneimine causes a similar increase in wet tensile strength as when treating the base with polyamide-epichlorohydrin resin alone, but brings a very significant improvement in alkaline wet tensile strength at all levels used. However, an addition of 0.5-1% polyamide-epichlorohydrin resin in combination with 0.5% polyethyleneimine (by dry weight of the base web) appears to be a particularly effective amount based on consideration of both the effect and the levels of addition.

None of the additions made had a detrimental effect on the absorption capacity.

Claims (8)

1. A method of making wrapping paper, in particular for the manufacture of cms, or scrapers, for prepared meat products or the like, in which a paper web of fibrous material is formed, treats the fibrous web with a diluted viscous solution whose cellulose content is 0.5-3 v. -% and then the cellulose in the viscose regenerates with an acid, characterized in that the paper web fibers are treated with polyethyleneimine. Process according to claim 1, characterized in that the treatment with polyethyleneimine is carried out before or simultaneously with the treatment with said viscous solution. Method according to claim 1 or 2, characterized in that the polyethyleneimine is incorporated into the fibrous web in an amount of 0.1 to 2% of the dry weight of the fibrous web. Method according to claim 3, characterized in that the polyethyleneimine is incorporated into the fibrous web in an amount of 0.2 to 1% of the dry weight of the fibrous web. Process according to any one of claims 1-4, characterized in that the polyethyleneimine is incorporated into a dilute solution as the pulp fiber web. Process according to any one of claims 1-4, characterized in that the polyethyleneimine is incorporated into the fibrous web before treatment with the viscous solution. Process according to any one of claims 1-6, characterized in that the fibers of the fibrous web are also treated with polyamide epichlorohydrin resin. Process according to claims 6 and 7, characterized in that the polyethyleneimine and the polyamide epichlorohydrin resin are incorporated into the fiber web during the web forming process.