The invention relates to a light tubing and method of raanu- facturing the same, composed mainly of long-fibred material and regenerated cellulose, used for encasing food products such as in the manufacture of sausages. In terms of its elastic properties, the said tubing corresponds to collagen tubing, but is superior to them in terms of its strength and heat-resistibility.

Food product casings are used in the packaging of various kinds of meat, sausage and other food products. The basic material used in the manufacturing of casing materials is cellulose (cellophane, regenerated cellulose, cellulose hydrate), cellulose derivatives, such as cellulose ether, proteins, collagens and other natural or synthetic polymer webs, films or laminates comprising combinations of these.

The properties of tubings made of collagen, as well as tu¬ bings made of cellophane, are inadequate owing to their lack of strength and their poor heat resistibility during the sausage manufacturing process. Collagen tubings, for example, split already at a temperature of 80 °C. Collagen and cellu- lose tubings are always heavier than corresponding fibre- reinforced tubings. Despite the weight of the collagen and cellulose tubing walls, the diameter values of the tubing produced vary. Due to these reasons, the productivity of sausage manufacturing is low.

Another practice is to use fibre-reinforced cellulose casings from webs manufactured from paper and/or rice paper (such as silkwood) , using mulberry, or other naturally occurring fibres such as hemp (e.g. abaca or manilla hemp), flax fib- res, or synthetic fibres (e.g. polyamide, polyester, and polyacryl nitrile fibres) , and even mixtures of the said fibres. The process of manufacturing the paper to be used in the aforementioned tubing material, such as manilla hemp

based paper has been described in US Patent Publications No. 3 433 663 and No. 3 135 613, for instance. The impediments to using the known fibre-reinforced cellulose tubings are the high price and inelasticity of the tubing resulting from their structure. Due to these reasons, the area of producta- bility of such tubing material is limited. They cannot, for instance, be used to replace collagen tubing.

A tubing produced in accordance with this invention re- presents a decisive improvement with regard to the aforemen¬ tioned shortcomings. For the realization of this improvement, -the manufacturing method used to manufacture the fibre-rein¬ forced cellulose tubing in accordance with this invention for the packaging of food products, is characterized by what is stated in patent claim 1 and on the part of the tubing by what is stated in the characteristic part of patent claim 4.

The unique advantage of this invention is the combination of properties achieved via the light structure; namely, the excellent further processing possibilities and the property of high heat resistibility facilitated by the tubing in comparison to collagen tubings coupled with the excellent strength properties, and superior elasticity of the tubing when compared to conventional fibrous cellulose tubings. This combination of properties means a wide area of applicability and provides a basis for a considerable higher productivity both in the manufacturing of the tubing as well as in the meat processing industry.

While elasticity is generally held to be an advantage of collagen tubing, the observation has been made that the lighter fibre-reinforcement in accordance with this invention results in strength almost the equivalent of the previously used heavier, fibre-reinforcement, but still elasticity which is not only of the same class as that of collagen tubing, but exceeds it. The thinness that results from the loss of weight of the largely manilla hemp-based paper, permits the viscose to better penetrate the matrix between the fibres. This in

turn leads to the formation of a strong composite material bond between the cellulose of the viscose and the manilla hemp, which provides also a smoother inner surface of the tubing. It has also been observed, that the curing process of salami packed in tubing in accordance with this invention is speeded up.

Hoselike tubings, in which the aforementioned webs are used, can be manufactured by applying methods and devices which are well known to the people in this profession. Such methods have been described in US Patent Publications No. 2 144 899, while the devices referred to are described No. 2 105 273, for instance.

In the following, while this invention is explained by refer¬ ring to examples, the said examples are not intended to limit the invention, but to present and provide grounds for the inventive idea.

Viscose manufactured in the known manner was necessary for the manufacturing of the tubing. During the manufacturing of the viscose, wood cellulose with a high -cellulose content was treated with lye in order to produce alkali cellulose. After controlled ageing of the alkali cellulose carbon di- sulphide was mixed into the compressed and shredded mass. The result of the reaction was cellulose xanthogenate which was then dissolved in lye, whereby the viscose was produced.

In order to manufacture fibre reinforced tubing, paper com- posed mainly of manilla hemp and unreeled from a roll was bent to form a tube. Next, the tube was impregnated using viscose applied from the nozzle in the aforementioned manner.

Immediately thereafter, the tube was immersed in a bath of salt / sulphuric acid whilst treating the inside of the tubing also with the same salt / acid mixture which caused the viscose to coagulate and regenerate into cellulose. The tubing which for the most part was treated in a flattened

form was then directed into a water bath and then into a bath of heated glycerine. Finally, the tubing was passed through press rollers to be dried inside a drying canal where air was blown into the tubing and the tubing was then rolled up. In accordance with this invention, the weight of the paper manufactured mainly from manilla hemp was tested and found to be c. 13 g/m ² within a range of ±1 g/m ² . The weight of the paper is given as air-dry weight after keeping the paper four hours at a temperature of 25 °C with a relative air humidity of 50 % in order to attain equilibrium conditions after the removal of the test specimen from its storage packaging. It was noted that the consumption of viscose was reduced in the manufacturing of tubing reinforced with this material.

The values presented in the table are employed to compare the elasticity and burst strength properties of the Visko Light tubing in accordance with this invention, the air-dry weight of the manilla hemp paper used in it being 13 g/m ² with a tolerance of ±1 g/m ² , with the corresponding properties of collagen tubing and heavier tubings. The size of the tubing is expressed as the trade size, which is the diameter of the tubing before it is filled. It is necessary to point out that the earlier practice was to use long-fibred material whose weight varied according to the diameter.

The elasticity of the tubing is defined as the amount of stretch per unit of pressure when filled in the wet state after soaking 30 minutes in water at 20 °C. These values are computed in the following manner.

Visko Light, size 65:

Diameter of tubing, 67.7 mm at a filling pressure of 15 kPa; Diameter of tubing, 73.3 mm at a filling pressure of 50 kPa, which results in Elasticity = (73.3 - 67.7)/(50 - 15) = 0.16 mm/kPa.

The bursting strength of the tubing was determined in the aforementioned wet state and the values set out in tabular

form.

The strength and elasticity properties were determined at a temperature of c. 20 °C, immediately after removing the tubing from the water used for soaking. The tubing weight determinations were conducted in the prevailing laboratory conditions, air-dry and without raising the temperature. Oven drying was not used.

The data thus obtained confirm the excellent elasticity pro¬ perties of Visko Light tubings as compared to the heavier fibre-reinforced tubing and collagen, which up till now has been considered to offer the best combination of elasticity in relation to diameter stability. The values presented in the table indicate that Visko Light tubings are proof of the Visko Light tubings' equivalence in terms of elasticity under pressure to collagen and even superior to collagen. With respect to burst strength, the Visko Light tubings proved to be superior to collagen and only slightly weaker than a conventional tubing composed of heavier fibrous material. Due to its thinness, the amount of Visko Light tubing that can be crumpled or shirred to form a "grub" or "stick" is greater than that of previously used heavier tubing. When compared to collagen, for instance, a grub of Visko Light contains twice as much tubing as a collagen grub of equal length.

TABLE Product Size Manilla hemp Tubing Tubing Elasti- paper weight, c. weight burst strength city mm g/m ² g/m ² kPa mm/kPa

The curing process of salami was speeded up inside the Visko Light tubing. Empirically, the curing process for Lϋbeck salami when placed inside a known and heavier fibre tubing 62 mm in diameter takes three weeks, which is to say that it loses 36 % of its weight during the three weeks. When Visko Light tubing 70 mm in diameter is used, Liibeck salami takes three weeks to cure (36 % mass reduction), although the Visko Light tubing contains c. 25 % more mass. The curing condi¬ tions were the same in these two cases. Other examples based on the same size 70 mm casing resulted in a Liibeck salami which was uniformly cured and dried after only three weeks processing in Visko Light casing whilst the same product took a further week in processing to reach the same uniformity in a heavy weight fibrous casing with attendent greater product-

weight losses.

The Bendtsen test used in the paper industry was used to determine the smoothness of the inner surface of the tubing. The test gave Visko Light tubing values of c. 700-800 cm ³ /min in average while the heavier tubing used in the comparison had values exceeding 1000 cm ³ /min in average.

It is necessary to point out that in the above the invention has been described with reference to only two of its advanta¬ geous implementation. This is in no way intended to limit the invention which will be described in accordance with the scope of the inventive idea as defined by the following patent claims.