Tubular casings, especially sausage casings, based on polyamide.

The invention relates to a tubular packaging film, in particular to a sausage casing for scalded and cooked sausage, based on polyamide, which has improved physical properties compared to the known polyamide hoses and can be used advantageously for packaging purposes, but especially for use as a wrinkle-free, deformation-resistant sausage casing for scalded and cooked sausages is suitable.

There are already numerous tubular films made of synthetic plastic, e.g. B. based on polyester or polyamide, become known. But especially when it comes to sausage casings, high demands are made, which relate in particular to their physiological suitability, strength and dimensional stability.

One shortcoming that tubular films made of many synthetic materials have is their reduced strength due to water absorption. In many cases, the filling material is water-based and releases moisture to the adjacent packaging film. In particular when scalding or boiling the tubular casings filled with sausage meat, when the film material comes into contact with hot water or steam, the strength of the film material disadvantageously drops sharply as a result of water absorption.

If the sausages hanging from their straps are treated with hot steam in the cooking cabinet, the sausage casing is heavily stressed by the weight of the filling compound in the lower part and expanded with insufficient shape retention of the casing material, so that a pear-shaped deformed product results from the originally cylindrical sausage .

To compensate for this undesirable effect, the thickness of the packaging film has hitherto been increased accordingly or attempts have been made to increase the film strength by means of complex process steps in the manufacture of tubes.

With these measures, however, the strength of the casing material, which is reduced at cooking or brewing temperature, can only be improved to a limited extent, so that the resistance of the casing material to a change in shape at this temperature is increased only to a small extent. If the casing material is too thick, there is also the risk that the packaging casing will become too stiff and inelastic. It can then expand only insufficiently when the filling compound is pressed in and, after the cooking or brewing process in the cooled state, does not adapt adequately to the shrunk content, so that the product obtained looks wrinkled and unsightly.

It is therefore an object of the invention to provide a tubular packaging film, in particular sausage casing for cooked and cooked sausage, based on polyamide, which can meet the high requirements with regard to the dimensional stability when treated with hot water and with regard to the wrinkle-free appearance of the heat-treated, cooled product, this Problem to be solved with little effort and simple means.

This object is achieved by the packaging film specified in claim 1. The subclaims indicate preferred embodiments of the film.

The tubular packaging film is constructed in one layer and essentially consists of a polymer mixture with two main components, namely the polyamide and the polyester portion. The polyamide is a saturated linear aliphatic polyamide with the general formula NH-CO-R which is customary for the production of tubular packaging films¹-CO-NH-R², in the R^l and R² are the same or different and - (CH₂)_n- (n = 2-7) mean, for example polyhexamethylene adipamide (R.^{l =} (CH₂)₄, R² = (CH₂)₆), or a polyamide with the general formula NH-R³-CO, where R³ equal - (CH₂)_n- (n = 2-7, in particular 4-6), preferably polycaprolactam (R.³ = (CH₂)₅), as well as statistical copolyamides, which are produced from units of these polymers and using adipic acid, azelaic acid, sebacic acid and terephthalic acid and diamines, such as hexamethylene diamine or trimethyl hexamethylene diamine. A preferred copolyamide is made from caprolactam, hexamethylene diamine and adipic acid. The polyamide portion can also be a mixture of different polyamides. Of the above-mentioned polyamides, polycaprolactam (polyamide 6) is particularly preferred. For bubble extrusion purposes, polyamides with a relative viscosity in the range from about 2.5 to 4.5, in particular 2.8 to 4.2, measured in sulfuric acid (96% / 20 ° C.) are used.

The polyester present in the polymer mixture of the shell material is a condensation product of diols with terephthalic acid and optionally additionally up to 20 mol% isophthalic acid. The diols are in particular aliphatic compounds of the formula HO- (CH₂)_n-OH (n = 2-6), such as ethylene glycol, 1,4-butylene glycol, 1,3-propylene glycol or hexamethylene glycol and alicyclic compounds such as 1,4-cyclohexanedimethanol. Polybutylene terephthalate (PBTB) is very particularly preferably used in the polymer mixture, the polymer having an average melt viscosity which is customary for film extrusion.

The added polyterephthalate or polyisophthalate can be modified to a small extent with aliphatic dicarboxylic acids.

Although the possible proportion of the polyester in the polymer mixture consisting of polyamide / polyester can be 70 to 5% by weight, it has been shown that in this range, values ​​between 50 and 25% by weight of polyester decrease the film properties entry. In particular, the extruded film tube tends to splice before and during the stretching process. This disadvantage does not occur in the other concentration range (70-50, 25-5% by weight). In particular, polyester fractions of 65 to 50 and 25 to 10% by weight in the polymer mixture are of particular advantage.

With the particularly low proportion of the polyester of 25 to 10% by weight, particularly wrinkle-free sausage casings are obtained which have good sliding properties without the addition of an antiblocking agent.

The polymer mixture can also contain other additives, such as. B. dyes, pigments and processing aids that ensure a trouble-free manufacturing process.

Silicone oils, in particular polydialkylsiloxane (alkyl = C_l-C₄), which are used in an amount of 0.05 to 1.2, in particular 0.1 to 0.6,% by weight, based on the polymer mixture of polyester and polyamide. A particularly suitable polydialkylsiloxane is polydimethylsiloxane with a viscosity of 10 to 100,000, in particular 500 to 30,000 mm²/ s (23 ° C). This addition surprisingly brings about improved sliding properties of the film during its production, without thereby disadvantageously accelerating the crystallization of the polymers before the stretching process.

The packaging film has a wall thickness between 10 and 50 _/around. It is preferably used in a biaxially oriented form. The measures known in the production of polyamide films are used for their production.

First, the individual components are mixed together. However, it is also possible to carry out the mixing process in the extrusion device. The tubular pre-film extruded by the blown film process is simultaneously biaxially stretched by being inflated and pulled away. In order to obtain a thermostable film, it is heat-set in the usual way after stretching. The film obtained has a thickness of 10 to 50, in particular 25 to 45_/around.

For packaging pasty foods, it is used in sections, in a gathered form or in a curved form as a so-called "coronary gut". The gathering is done with known gathering devices. When the pasty filling material is pressed in, the gathered hose is unloaded. When the contents are subsequently preserved under the influence of hot water, the uniform cross-section of the packaging casing is retained, and after cooling, bulging, wrinkle-free packaging is obtained. The packaging envelope thus shows both excellent resistance to deformation when exposed to hot water and sufficient elastic elasticity to be able to fit tightly on the cooled product. Surprisingly, these properties are still present even in the case of relatively large tube calibres of 90-120 mm, so that the packaging casing is also suitable as a sausage casing for particularly large and heavy sausages.

The invention is illustrated by the following example.

example

A mixture of granules of 78 parts by weight Polyamide 6 and 22 parts by weight Polybutylene terephthalate are combined with 0.3 part by weight. Polydimethylsiloxane (Visc. 1000 mm²/ s) plasticized in an extruder at approx. 240 ° C and formed into a tube with a diameter of 30 mm by a round die. The tube, which is kept amorphous by quenching with a cooling mandrel, is then immediately brought to stretching temperature by means of IR emitters, stretched in both directions with the aid of a gas cushion inside the tube, reducing the thickness and increasing the surface area, and heat-set in this state. After laying flat, the hose is laid flat with a width of 145 mm and a thickness of 36 _/to get wrapped up.

To test the resistance to deformation, a 1 cm wide strip is cut out of the hose in the transverse direction, which is loaded with the load K₁ is stretched in water at both 20 ° C and 80 ° C. The load K₁ is calculated<maths id="math0001" num=""><img file="EP0176980A2_D0001.tif" /></maths><ul id="ul0001" list-style="none"><li>p = internal pressure = 0.04 N / mm²</li><li>r = half caliber = 45 mm</li><li>d = thickness = 0.036 mm</li><li>A = cross section = 0.36 mm²</li></ul>

For the change in scope applies if<ul id="ul0002" list-style="none"><li>1₀ = Length of the test strip before stretching,</li><li>1₁ = Length after loading with K₁ at 20 ° C,</li><li>1₂ = Length after loading with K₁ at 80 ° C.<maths id="math0002" num=""><img file="EP0176980A2_D0002.tif" /></maths></li></ul>If the test strip is relieved after both expansions, the new length is 1₃ at values ​​of 0.95 · 1₁ up to 0.98 · 1₁.