WO2006029734A1 - Tubular casing with structured outer layer and use thereof as a foodstuff casing - Google Patents

Abstract

The invention relates to a tubular casing for the permanent and crease-free covering of pasty or liquid goods, in particular foodstuff. Due to the structuring of its outer layer, said tubular casing has an improved machinability and a pleasant, natural appearance and haptics.

Description

Tubular shell with a structured outer layer and its use as a food casing

The present invention relates to a tubular casing for the permanent and wrinkle-free Umhül¬ treatment of pasty or liquid goods, in particular food, which has a structuring of the outer shell improved machinability and also has a pleasantly natural look and feel.

Seamless plastic covers are often used for wrapping pasty or liquid goods for manufacturing and / or packaging purposes. Typical applications are the use of such casings for the production and / or packaging of scalded and cooked sausages, melted cheese, soups or high-fat pastes. Depending on the product to be produced or packaged, however, extensive specific requirements must be met in order to meet the practical applications.

For example, in sausage production, these performance requirements include: good barrier properties, temperature resistance (sterilization temperature> 100 ° C), good adhesion to the product, good clip strength, good tear propagation resistance on hot storage, sufficient shrinkage, high strength, dimensional stability, bounce, good peelability ¬ hold, easy peelability, good hot and cold cutting behavior, good miscibility especially cold and Heißippippbarkeit, ease of assembly, especially Raffbarkeit, good Einfarbbarkeit and ink coverage, good printability and safe ink adhesion, no harm according to food law (EU directives, Federal Institute for Risk Assessment BfR, Food and Drug Administration FDA), ecological safety of the materials used.

The previously known in the market multilayer, biaxially stretched, seamless shells are tailored specifically for the production and / or packaging of meat products, especially sausages, and meet more or less pronounced the above-mentioned application-technical requirements.

From Savic, Z .: Sausage Casings, VICTUS food industry supplies, Vienna, Austria, p. 245-300 it is known that many hose covers meet many of the above requirements.

European application EP-A-0 107 854 describes a tubular, 5-layered laminate consisting of an inner layer of thermoplastic resin, a middle layer of vinylidene chloride copolymer (PVDC), an outer layer of olefin resin and two adhesive layers between the main layers. The shell contains halogenated as a component PVDC, whose use is ecologically questionable and therefore less and less accepted today.

DE-A-40 01 612 discloses a tubular, 3-layer coextruded, biaxially stretched sheath having an inner and outer layer of polyamide or a polyamide-containing polymer blend and an oxygen-barrier middle layer of aromatic polyamide or copolyamide.

In DE-A-43 39 337 a 5-layer tubular casing for packaging and wrapping of pasty foods is described. This tubular casing, in particular sausage casing, based on polyamide is characterized in that it consists of an inner and an outer layer of the same polyamide material consisting of at least one aliphatic polyamide and / or at least one aliphatic copolyamide and / or at least one partially aromatic polyamide and / or at least of a partially aromatic copolyamide, a middle polyolefin layer and two of the same material adhesion promoter layers is constructed. The proportion of partially aromatic polyamide and / or copolyamide is 5 to 60%, in particular 10 to 50%, based on the total weight of the polymer mixture of partly aromatic and aliphatic polyamides and copolyamides.

From EP-A-0 879 560 an at least 4-layer, biaxially stretched food casing with two oxygen barrier layers is known. In this case, the oxygen barrier effect is essentially brought about by a layer not containing EVOH and an outer layer containing polyamide with aromatic fractions

WO 03/073862 A2 describes a single-layer or multi-layer food casing made of a thermoplastic mixture containing at least one aliphatic polyamide and / or copolyamide, at least one inorganic and / or organic filler and optionally at least one glycol and / or polyglycol Comprising aliphatic and / or partially aromatic copolyamide. This shell requires special extruders and it is extremely difficult to control the mixing of the described components in such a way that a homogeneous or rather inhomogeneous mixture is produced as required.

The tubular sheaths described here with regard to the prior art have deficits in individual points in relation to the requirement profile described above. In particular, the sheaths known in the market show deficiencies in terms of the characteristics of good barrier properties, good machine and application properties, in particular machinability, mechanical properties, appealing natural look and feel through a permanently structured outer layer. An envelope that fulfills these characteristics is not yet known. However, customers increasingly demand a visually and haptically appealing product for industrial use, which has extraordinarily good machinability through problem-free industrial processability on automatic machines such as, for example, filling machines, cutting machines, packaging systems, conveyor systems and packaging systems.

It is an object of the present invention to develop a tubular casing which has the mentioned profile of requirements, in particular with regard to excellent machinability and application properties, in particular a very good mechanical strength and good barrier properties.

It has now surprisingly been found that this object is achieved by a tubular casing comprising an outer layer A consisting of a main component either of an aliphatic homopolyamide or an aliphatic copolyamide or a blend of aliphatic homo- and copolyamide or a blend of aliphatic homo- or copolyamide and a partially aromatic polyamide, wherein said outer layer A has been mechanically treated with an abrasive material.

The tubular casings according to the invention are preferably seamless and biaxially stretched; they are preferably obtained by coextrusion.

The structure of the tubular casing preferably has a total thickness of 5 to 150 .mu.m, more preferably 25 to 80 .mu.m with diameters of the individual layers of 0.5 to 75 .mu.m.

The tubular casings according to the invention are single-layered, preferably multi-layered, preferably at least three-layer, particularly preferably five-layer tubular casings.

In a particularly preferred embodiment, the tubular casing according to the invention has the following sequence of layers:

Layer A: outer layer, preferably with the possibility of printing Layer B: second outer layer (between outer layer and middle layer)

Layer C: middle layer

Layer D: Second inner layer between inner layer and middle layer

Layer E: inner layer with contact to the product

Optionally, one or more layers except the outer layer A, which is mechanically treated, may be omitted or added. - A -

The outer layer A consists of the main component either of an aliphatic homopolyamide or an aliphatic copolyamide or a blend of aliphatic homo- and copolyamide or a blend of aliphatic homo- or copolyamide and a partially aromatic polyamide. Suitable aliphatic homo- and copolyamides are those polyamides, as described in general terms in Kunststoffhandbuch Part 3/4 "Polyamides" page 22 ff, Carl Hanser Verlag Munich Vienna 1998. The aliphatic polyamide is a homopolyamide of aliphatic primary diamines and aliphatic dicarboxylic acids or a homopolymer of ω-amino-carboxylic acids or their lactams. The aliphatic copolyamide contains the same units and is, for. Example, a polymer based on one or more aliphatic diamines and one or more dicarboxylic acids and / or one or different ω-aminocarboxylic acids or their lactams. The aliphatic primary diamines contain in particular 4 to 8 C atoms. Suitable diamines are tetra-, penta-, hexa- and octamethylenediamine, particularly preferred is hexamethylenediamine. The aliphatic dicarboxylic acids contain in particular 4 to 12 C atoms. Examples of suitable dicarboxylic acids are adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid. The ω-aminocarboxylic acid or its lactams contain 6 to 12 C atoms. An example of ω-aminocarboxylic acids is 11-aminoundecanoic acid. Examples of lactams are ε-caprolactam and ω-laurolactam. Particularly preferred aliphatic polyamides are polycaprolactam (PA 6) and polyhexamethylene adipamide (PA66). A particularly preferred aliphatic copolyamide is PA 6/66, which consists of caprolactam, hexamethylenediamine and adipic acid units. Partially aromatic polyamides are described in Kunststoffhandbuch Part 3/4 "Polyamides" page 803 ff Carl Hanser Verlag Munich Vienna 1998.

In the partially aromatic polyamides and copolyamides, either the diamine units predominantly or exclusively form the aromatic units, while the dicarboxylic acid units are predominantly or exclusively aliphatic in nature, or the diamine units are predominantly or exclusively aliphatic in nature, while the Dicarbonsäureienheiten über¬ predominantly or exclusively the aromatic Form units. Examples of the first embodiment are partly aromatic polyamides or copolyamides in which the aromatic diamine units consist of m-xylylenediamine and phenylenediamine. The aliphatic dicarboxylic acid units of this embodiment usually contain from 4 to 10 carbon atoms, such as e.g. Adipic acid, sebacic acid and azelaic acid.

In addition to the aromatic diamine units and the aliphatic dicarboxylic acid units, aliphatic diamine units and aromatic dicarboxylic acid units may also be present in amounts of up to 5 mol% each. A particularly preferred embodiment consists of m-xylylenediamine and adipic acid units. This polyamide (PA-MXD6) is eg from the company Mitsubishi Gas Chemical Company Inc. under the name MX-Nylon. Examples of this second embodiment are partially aromatic polyamides and copolyamides in which the aliphatic diamines usually contain 4 to 8 carbon atoms. Among the aromatic dicarboxylic acids, in particular isophthalic acid and terephthalic acid are to be emphasized. In addition to the aliphatic diamine units and the aromatic dicarboxylic acid units, it is also possible for aromatic diamine units and aliphatic dicarboxylic acid units to be present in amounts of up to 5 mol% each.

A particularly preferred embodiment consists of units of hexa-methylenediamine, isophthalic acid and terephthalic acid. This polyamide (PA6I / 6T) is z. B. sold by the company. DuPont De Nemours under the name Selar PA. The addition of partly aromatic polyamide PA6I / 6T is preferably carried out in amounts of between 2 and 40% by weight per layer, in particular between 5 and 20% by weight. The addition of partially aromatic polyamide PA-MXD6 is preferably carried out in amounts between 5 and 40 wt .-% per layer, in particular between 10 and 30 wt .-%. In addition, layer A may include additives such as lubricants, antiblocking agents, nucleating agents, fillers and color pigments or a mixture of these.

Preferably, the layer A can be printed with and without abrasive pretreatment.

The second outer layer B present in the above-described five-layered embodiment consists, for example, of an approximately completely hydrolyzed ethylene-vinyl acetate copolymer (EVOH) having an ethylene content of 25 to 53% by weight, preferably of 29 to 38% by weight. The layer thickness is usually between 2 and 30 μm, in a preferred embodiment between 2 and 8 μm, particularly preferably between 3 and 6 μm. Optionally, layer B may consist of the polymers and additives mentioned in the description of layer A or layer D, but may also have a different composition than layer A or be omitted altogether.

The middle layer C present in the five-layer embodiment described above consists for example of the polymers and additives mentioned in the description of layer A, but optionally has a composition other than layer A or may optionally be of polyolefin homopolymer or copolymer or a blend of these a melting point of the lowest melting component of at least 110 ⁰ C. If desired, layer C can also consist of the polymers and additives mentioned in the description of layer B, but if appropriate have a composition other than layer B or be omitted altogether. The second inner layer D located between the middle layer C and the inner layer E, which is present in the five-layer embodiment described above, is, for example, an adhesion-promoting layer. This consists preferably of modified polyolefins. These are modified homopolymers and copolymers of ethylene or propylene and optionally further linear α-olefins having 3 to 8 C atoms, the monomers from the group of α, β-unsaturated dicarboxylic acids, such as maleic acid, fumaric acid, Itaconic acid or its Säure¬ anhydrides, acid esters, acid amides or Säureimide grafted included. Also suitable are ionomeric copolymers of ethylene and propylene and optionally of further linear α-olefins containing 3 to 8 C atoms with α, β-unsaturated carboxylic acids, such as acrylic acid, methacrylic acid and / or their metal salts and / or their alkyl esters or corresponding graft - Polymers of said monomers to polymers or partially saponified ethylene-vinyl ester copolymers, which are optionally graft-polymerized with a monomer of said acids. The layer thicknesses are usually between 1 and 30 μm and in a preferred embodiment between 1 and 6 μm. Optionally, layer D may consist of the polymers and additives mentioned in the description of layer A or B, but if appropriate have a composition other than layer A or B.

The inner layer E present in the above-described five-layered embodiment consists for example of the main component of the polymers and additives mentioned in the description of layer A, but optionally has a different composition than layer A. In addition, the layer may also contain other substances, preferably color pigments. keep ent. The preferred layer thickness of the layer E is less than 10 μm.

The tubular casing according to the invention can furthermore optionally contain a layer of natural fibers with a fiber length in the range of 5 to 10,000 μm and / or a natural fiber mixture of different fiber types and / or fiber lengths.

To improve the processing behavior and the opening behavior of the inner layer E and / or the outer layer A additives may be added. In particular antiblocking and slip additives have proven to be suitable. These antiblock additives are based e.g. based on silica.

To reduce the influence of light on the product, individual layers of UV absorbers can be added. Inorganic pigments, in particular zinc, titanium, iron and silicon oxides, have proven useful here. In a preferred embodiment, the inorganic ultrafine pigment is introduced into the composite by means of a masterbatch whose carrier material is compatible with the base material of the layer. The amount of pigment is usually at 0.1 to 5 wt .-%, preferably 0.5 to 2.5 wt .-% based on the total weight of the tubular casing.

The mechanical treatment of the outer layer can be carried out with the aid of compressed air and an abrasive blasting medium.

The necessary for structuring the outer layer blasting with air pressure and a suitable blasting agent is well known (product brochure of Friedrich Goldmann GmbH & Co. KG, 68229 Mannheim).

Suitable abrasives are a wide variety of materials that must be adapted to the material of the layer A in order to achieve the desired effect. For this purpose, in general, materials which are capable of mechanically changing the outer layer of the hose are suitable. As a blasting agent in this case a mixture of noble corundum and / or electric corundum and / or special steel corundum and / or glass beads and / or glass bead and / or nutshell granules and / or corncob and / or plastic granules and / or cast steel blasting round and / or cast steel abrasive edged and / or cast steel abrasive round stainless and / or steel wire grain cylindrical and / or steel wire grain rounded and / or steel wire grain cylindrical rust resistant and / or steel wire grain rounded rust resistant and / or or hard cast blasting abrasive round and / or hard cast blasting abrasive edged and / or malleable shot blasting abrasive and / or light metal blasting and / or non-ferrous metals. The blasting agents differ in shape, size, particle distribution and hardness and can be used as required.

For a particularly good machinability, a fine grain size of the blasting material, preferably special steel corundum, in the range between 0.05 .mu.m to 500000 .mu.m is suitable. Particularly suitable is a range between 5 .mu.m to 5000 .mu.m, in particular a range between 50 .mu.m to 25 .mu.m. The jet duration and the jet pressure depend on the type of plastic hose and the take-off speed and must be set individually. However, it has been shown that with increasing withdrawal speed of the internal pressure and the jet pressure must be increased.

In addition, other blasting agents are suitable, which permanently deform the surface by means of suitable technology. These include sodium bicarbonate ("baking powder") based powders such as, for example, "Armex Blast Media" from the manufacturer "Brotherton Specialty Products Limited", which is sold in the industry for cleaning work, and the material has a density of about 2 , 16 g / cm ³ and can be used in various size distributions By means of suitable blasting technology, intentionally desired effects can be achieved even with inherently soft materials, up to the removal of outer layers. By choosing the nozzles and the rotational and translational velocities, a desired repeating structure of the outer layer can be incorporated.

The tubular casing according to the invention usually has a free shrinkage in at least one orientation direction measured in a water bath at 100 ^° C. after 15 minutes between 1 and 35%, in particular between 2 and 20%.

The invention furthermore relates to a process for the production of the tubular casing according to the invention with improved machinability comprising the step of forming the outer layer A of a preferably at least three-layer, more preferably five-layer tubular casing having an outer layer A consisting of an aliphatic homopolyamide or an aliphatic copolyamide as main component or a blend of aliphatic homo- and copolyamide or a blend of aliphatic homo- or copolyamide and a partially aromatic polyamide is mechanically treated with an abrasive material.

The production of the tubular casing according to the invention is preferably carried out by an extrusion process. The fibrous, granular or powdered raw material is compressed in an extruder, melted, homogenized and discharged through a nozzle and formed into a seamless tube. The exiting primary tube is cooled by air or water cooling and then simultaneously biaxially stretched. A particularly suitable method is the simultaneous biaxial stretching by means of double-bubble technology, in which the stretching of the primary bubble takes place via an adjacent internal pressure. For selective adjustment of the shrinkage properties, the shell can then be subjected to a heat treatment.

The tubular casing according to the invention is preferably biaxially stretched with a degree of planar stretching of 4 to 10 and more preferably of 6 to 10, since in this flatness degree the fiber orientations cause a particularly high tear propagation resistance with very positive peeling behavior. In addition, a particularly good printability is made possible at these flatness levels, as well as an excellent bumpiness and cylindricity of the finished sausage achieved.

The mechanical treatment of the outer layer of the tube can be integrated in the abovementioned process sequence, or can be carried out separately after the production of the tube. For the mechanical treatment of the outer layer A, the sand blasting method is preferably used, which allows both discontinuously (sections) and continuously (rolls) to treat the goods. From an economic point of view, continuous operation is preferred, it being possible to machine both flattened and inflated goods. It was surprising in this type of treatment that the mechanically treated outer layer was still present even after brewing at high temperatures. Surprisingly, by a suitable choice of the jet parameters (blasting medium, grain size, pressure, air flow, nozzle head and the like), the somewhat soft inflated product could be treated without any problems and over the entire surface without any defects. In this context, it has proven particularly advantageous that a homogeneous or inhomogeneous structure of the outer layer could be created via the beam parameters. By means of a suitable process management, the mechanical damage to the outer layer of the hose could be kept low at the same time. It was also surprising that the external friction of the plastic hose was positively changed by the abrasive treatment of the outer layer. External friction always occurs when two different substances or active surfaces are in contact and a relative movement is or will be generated. The external types of friction, the static friction and the sliding friction, which are particularly relevant for the machinability of filling machines, have also been positively changed. The static friction (friction) F _H depends on the normal force F _N and on the adhesion friction coefficient μ _H , but independent of the size of the contact surface. The coefficient of static friction μ _H is determined by Columbus' law through the roughness and the types of substances of the rubbing surfaces. In the case of stiction, there is no relative movement between the friction partners plastic / steel or plastic / plastic. The sliding friction (kinetic friction) F _GL depends on the normal force F _N and on the coefficient of sliding friction μ < _3L and is always smaller than the static friction F _H. It depends on the relative speed of the rubbing surfaces (plastic / steel or plastic / plastic). During automatic filling, the sausage meat is inserted into the sausage casing and closed with the help of a metal clip. The holding force for filling the hose is applied by the so-called casing brake, a ring consisting primarily of plastic. Due to the filling pressure applied when filling the hose, the hose is pressed against the casing brake and braked depending on the size of the friction coefficients. Since this process is a discontinuous process, static friction prevails during start-up and sliding friction during filling. If the static friction is significantly greater than the sliding friction, it can lead to Kali¬ berschwankungen by different frictional forces during automatic filling of the hose. The lower the static friction deviates from the sliding friction, the closer the process tolerances can be maintained. This is of utmost importance for the industrial use of the sausage casing. As a measure of the quantitative assessment of these relationships, the ratio between slip and static friction coefficient can be used. This variable represents the difference between the two types of rubbing and approaches 1 for equal values. With the help of this ratio, an improved assessment of start-up processes in discontinuous process management, such as in Filling machines, be made. This ensures favorable process control in narrow tolerance ranges, the closer this ratio approaches the value 1.

This could be confirmed by assessing the cylindricity and the caliber constancy. The caliber constancy is of decisive importance for the dimensional accuracy of the finished sausages. To assess the caliber constancy, the standard deviation σ can be used, which is a measure of the scattering. The standard deviation of a given data set is defined as the square root of the variance, ie the arithmetic mean of all quadratic deviations of the data from its arithmetic mean:

With: σ the standard deviation μ the expected value

N the scope of the record

Xi the feature values at the zth element of the population

The expected value is the recommended filling caliber (EFK), which corresponds to the mean value for a statistically validated data volume.

The cylindricity is important for the dimensional stability of the finished sausage and is determined by the caliber difference between the sausage diameter top, middle and bottom. To evaluate the cylindricity, the standard deviation σ can also be used.

For both the cylindricity and the caliber constancy a connection between the sliding and static friction ratio could be discovered. The more this ratio deviates from the value 1, the worse the tolerances. For a particularly good manufacturing tolerance, the ratio should approach the value 1.

For the tubular casings according to the invention, a very good value between 0.9 and 1 could be established.

Surprisingly, it was additionally shown that the haptic and optical properties of the shell produced resembled those of a natural fiber intestine with and without a barrier layer in a more economical production. By a suitable choice of process control in the mechanical Treatment, preferably sandblasting, the barrier properties of the hose could be maintained.

However, it is also conceivable to reduce the barrier properties by the targeted choice of the process parameters. An oxygen barrier, when stored, is known to prevent premature graying of the meat facing the inside of the casing. The water vapor barrier behin¬ in storage known to the induced by evaporation of water from the product weight loss of the merchandise, on the one hand reduces the proceeds of the product and on the other hand can lead to wrinkled unsightly products due to volume shrinkage.

Another object of the invention is the use of the tubular casing according to the invention as a wrapper for pasty or liquid products. The use of a seamless tubular casing according to the invention is preferred. The particular advantage of a seamless tubular casing is that a continuous, spiral-shaped peeling of the sausage is possible without being restricted by defects such as, for example, a connecting seam. In addition, the visual and haptic impression, the barrier properties and the mechanical integrity in the production of sausage, for example, the seamless tubular casing is excellent without being affected by a seam. Preferably, the tubular casing according to the invention is used for packaging of sausages, pet food, cheese, dough or soups.

The object of the invention will be explained in more detail with reference to the following examples.

Examples

Comparative Example 1

A multi-layer seamless tubular casing consisting of 3 layers

Layer A: 100% PA6 / 66 (Ultramid C35F from BASF) with a layer thickness of 8 μm. Layer B: -

Layer e: 90% PA6 / 66 (Ultramid C35F from BASF) + 10% color masterbatch brown with one

Layer thickness of 15 microns.

Layer D: -

Layer E: 93% PA 6 (Durethan B40F Fa. Bayer) and 7% antiblocking agent with a layer thickness of 7 μm.

was formed on three single-screw extruders via a ring nozzle to a primary tube. The tube was rapidly cooled, then heated to the minimum temperature required for stretching, strongly biaxially stretched by means of internal compressed air, and then thermofused in another heating zone. The tube could be adjusted by the thermal oxidation in its mechanical properties and had an average wall thickness of 30 microns.

Comparative Example 2

A multi-layer seamless tubular casing consisting of the following 5 layers:

Layer A: 88% PA6 / 66 (viscosity = 195, melting point 196 ⁰ C) + 10% color masterbatch microns black with a layer thickness of the 22nd Layer B: 100% EVOH (32 mol% ethylene, MFI = I, 6 g / 10 min) with a layer thickness of

3 μm.

Layer C: 100% PA6 (viscosity number = 225) with a layer thickness of 12 μm. Layer D: 100% adhesion promoter (anhydrite-modified polyolefin based on LLDPE, melting point = 120 ° C., MFI = 1.65 g / 10 min) with a layer thickness of 4 μm. Layer E: 97% PA6 (viscosity number = 225) + 3% antiblock masterbatch with a layer thickness of 8 μm.

was plasticized and homogenized on 5 single-screw extruders and separated by means of a 5-layer

Coextrusion nozzle in tube form transferred. The tube was rapidly cooled, then heated to the minimum temperature required for stretching, biaxially stretched by means of compressed air acting internally and then thermofused in another heating zone. The hose could be adjusted by the heat setting in its mechanical properties and had an average wall thickness of 49 microns.

example 1

A multi-layer seamless tubular casing consisting of 3 layers

Layer A: 100% PA6 / 66 (Ultramid C35F from BASF) with a layer thickness of 8 μm (outer layer treated) Layer B: Layer e: 90% PA6 / 66 (Ultramid C35F from BASF) + 10% color masterbatch brown with one

Layer thickness of 15 microns. Layer D: -

Layer E: 93% PA 6 (Durethan B40F Fa. Bayer) and 7% antiblocking agent with a layer thickness of 7 μm.

was formed on three single-screw extruders via a ring nozzle to a primary tube. The tube was cooled rapidly, then heated to the minimum temperature required for stretching, strongly biaxially stretched by means of internal compressed air and then heat-set in another heating zone. The tube could be adjusted via the heat setting in its mecha¬ African properties and had an average wall thickness of 30 microns. The layer A was sandblasted with special steel corundum with a size of about 150Dm to 250Qm.

Example 2

A multi-layer seamless tubular casing consisting of the following 5 layers:

Layer A: 88% PA6 / 66 (viscosity number = 195, melting point 196 ° C) + 10% color masterbatch black with a layer thickness of 22 μm (outer layer treated).

Layer B: 100% EVOH (32 mol% ethylene, MFI = 1, 6 g / 10 min) with a layer thickness of 3 μm.

Layer C: 100% PA6 (viscosity number = 225) with a layer thickness of 12 μm.

Layer D: 100% adhesion promoter (anhydrite-modified polyolefin based on LLDPE, melting point = 120 ° C., MFI = 1.6 g / 10 min) with a layer thickness of 4 μm.

Layer E: 97% PA6 (viscosity number = 225) + 3% antiblock masterbatch with a layer thickness of 8 μm. was plasticized and homogenized on 5 single-screw extruders and converted into a tube by means of a 5-layer coextrusion die. The tube was rapidly cooled, then heated to the minimum temperature required for stretching, biaxially stretched with the aid of internally acting compressed air and then heat-set in a further heating zone. The tube could be adjusted by the heat-setting in its mechanical properties and had an average wall thickness of 49 microns. The layer A was sandblasted with special steel corundum with a size of about 150 .mu.m to 25 .mu.m.

Example 3

A multi-layer seamless tubular casing consisting of the following 5 layers:

Layer A: 88% PA6 / 66 (viscosity number = 195, melting point = 196 ° C) + 2% cellulose fibers

(Hardwood cellulose with 0L = 23 μm and 0D = 17 μm) + 10% color masterbatch red with a layer thickness of 22 μm. Layer B: 100% EVOH (32 mol% ethylene, MFI = I, 6 g / 10 min) with a layer thickness of

3 μm. Layer C: 100% PA6 (viscosity number = 225) with a layer thickness of 12 μm.

Layer D: 100% adhesion promoter (anhydrite-modified polyolefin based on LLDPE, melting point = 120 ° C., MFI = 1, 6 g / 10 min) with a layer thickness of 4 μm. Layer E: 97% PA6 (viscosity number = 225) + 3% antiblock masterbatch with a layer thickness of 8 μm.

was plasticized and homogenized on 5 single-screw extruders and converted into a tube by means of a 5-layer coextrusion die. The tube was rapidly cooled, then heated to the minimum temperature required for stretching, biaxially stretched with the aid of internally acting compressed air and then heat-set in a further heating zone. The tube could be adjusted by the heat-setting in its mechanical properties and had an average wall thickness of 49 microns. The layer A was sandblasted with special steel corundum with a size of about 100 .mu.m to 350 .mu.m.

Reference Example 1

It concerns the product plastic casing Walsroder "K smok" with 3 layers and a total layer thickness of 30 μm of the company CaseTech GmbH & Co. KG. Reference Example 2

It concerns the product plastic casing Walsroder "K plus" with 5 layers and a total layer thickness of 49 μm of the company CaseTech GmbH & Co. KG.

Test criteria:

Sheath sections were watered for 30 minutes, then filled with finely granulated boiled sausage meat at constant filling pressure and sealed at the ends with metal clips. Then the sausages were hung, treated in a brewing cupboard with smoke generator for 30 minutes with fumed water vapor at 75 ⁰ C, then cooked for 60 minutes with steam at 80 ⁰ C without smoke. The sausages were cooled in the air to room temperature and then stored in a refrigerator at about 6 ⁰ C. Table 1 shows the result evaluation. Assessment by a butcher: 1 = very good, 2 = good, 3 = satisfactory, 4 = sufficient, 5 = poor, 6 = very poor

Table 1

The relevant properties of the multilayer seamless tubular casing described below were determined as follows:

Stiction: The static friction (friction) F _H depends on the normal force F _N and on the coefficient of static friction μ _H , on the other hand independent of the size of the contact surface. The static friction coefficient μ _H is determined by Columbus' law through the roughness and the types of substances of the rubbing surfaces. In the case of stiction, there is no relative movement between the friction partners plastic / steel or plastic / plastic. The static friction coefficient is determined in accordance with DIN 53375.

Sliding friction: The sliding friction (movement friction) F _GL depends on the normal force F _N and on the sliding friction coefficient μo _L and is always smaller than the static friction F _H. It depends on the relative speed of the rubbing surfaces (plastic / steel or plastic / plastic). The determination of the sliding friction takes place according to DIN 53375. Ratio μπr to μH: The ratio between slip and static friction coefficient lies between O and 1. This variable represents the difference between the two types of friction and approaches the value 1 for equal values of both friction mechanisms. With the aid of this ratio, an improved assessment of startup processes in discontinuous process management, such as, for example, in filling machines, can be carried out. This ensures favorable process control in narrow tolerance ranges the closer this ratio approaches the value of 1.

Caliber constancy: Caliber consistency is critical to the dimensional accuracy of finished sausages. To assess the caliber constancy, the standard deviation σ is used, which is a measure of the scattering. The standard deviation of a given data set is defined as the square root of the variance, ie the arithmetic mean of all squared deviations of the data from their arithmetic mean:

With: σ the standard deviation μ the expected value N the extent of the data set x, the feature values at the zth element of the population

The expected value is the recommended filling caliber (EFK), which corresponds to the mean value for a statistically saved data quantity. The scope of the data set during testing was 100 sausages per tested caliber.

Cylindricity: The cylindricity is important for the dimensional accuracy of the finished sausage and is determined by the caliber difference between the sausage diameter above, middle and below. To assess the cylindricity, the standard deviation σ is also used.

Water vapor permeability: according to ASTM F1249-01 at a temperature of 23 ⁰ C and a relative humidity of 85%. The value indicates the amount of water vapor in grams, which passes through a 1 m ² area of the casing to be tested for one day (24 hours) under the specified test conditions. Oxygen permeability: The determination of O2Du according to DIN 53380 Part 3 at a temperature of 23 ⁰ C and a relative humidity of 75%. The value indicates the volume of oxygen in milliliters which, at an oxygen partial pressure of 1 bar, passes through a 1 m ² surface of the casing to be tested for one day (24 hours) under the given test conditions.

Weight loss: The casings to be tested are filled to the brim with a commercially available filling machine with test material susceptible to oxidation (test sausage based on cooked sausage), closed on both sides by a clip. After weighing the sausages obtained, they are stored in a refrigerated storage room at <4 ° C. After 20 days, the sausages are weighed again, with the percentage weight loss being the ratio of the difference in weight before and after storage to weight before storage (school grade principle).

Peeling properties: it was evaluated how easily the casing could be peeled off after cutting and how good the peeling behavior (for example change of direction when peeling) was (school grade principle).

Natural look: subjective judgment about the visual impression, such as semi-gloss appearance and natural structured outer layer of finished sausages (school grade principle)

Natural feel: subjective judgment about the haptic impression as firm grip and natural surface of the sausages (school note principle)

Preliminary behavior: objective judgment on the number and length of cracks caused by hot cutting (core temperature of the sausage meat approx. 4O ⁰ C) (school grade principle)

Maschinengängigkeit: Objective judgment on the flow behavior on general processing machines such as filling machines, cutting machines, lamination machines and packaging machines. (School note principle)

Characteristics of the Weapons: objective judgment on the squeezing characteristics (school grade principle)

Claims

claims: 1. tubular casing comprising an outer layer A consisting of a main component of either an aliphatic homopolyamide or an aliphatic copolyamide or a blend of aliphatic homo- and copolyamide or a blend of aliphatic homo- or copolyamide and a partly aromatic polyamide, said outer layer A with an abrasive material was treated mechanically. 2. tubular casing according to claim 1, characterized in that it comprises at least three layers. A tubular casing according to claim 2, characterized in that it comprises: a) an outer layer A containing as the main component a polyamide or a mixture of several polyamides, b) optionally a layer B which has an oxygen barrier character, c) if appropriate, a core layer C which contains as main component a polyamide or a mixture of several polyamides, d) one, opposite the adjacent layer C or B or A and the adjacent one Layer E contains adhesion-promoting layer D, and e) an inner layer E containing as main component a polyamide or a mixture of several polyamides. 4. tubular casing according to one of claims 1 to 3, characterized in that it additionally comprises a layer of natural fibers having a fiber length in the range of 5 to 10,000 microns and / or a natural fiber mixture of different fiber types and / or fiber lengths auf¬. 5. tubular casing according to one of claims 1 to 4, characterized in that it is seamless. 6. tubular casing according to one of claims 1 to 5, characterized in that the total thickness of 5-150 microns. 7. tubular casing according to one of claims 1 to 6, characterized in that the mechanical treatment of the outer layer by means of compressed air and an abrasive ;, --._, ^ - StMnriütel. 8. A process for the production of the tubular casing according to one of claims 1 to 7 5 comprising the step that the outer layer A of a tubular casing consisting of either an aliphatic homopolyamide or an aliphatic copolyamide or a blend of aliphatic homo- and copolyamide or a consisting of Haupt¬ as a Haupt¬ Blend of aliphatic homo- or copolyamide and a partially aromatic polyamide is mechanically treated with an abrasive material. 10. The method according to claim 8, characterized in that the abrasive material is special steel corundum with a grain size in the range between 0.05 microns to 500000 microns. 10. The method according to claim 8, characterized in that the abrasive material is a powder based on sodium bicarbonate. 11. Use of the tubular casing according to one of claims 1 to 7 as a wrapping material for pasty and liquid products. 12. Use according to claim 11, characterized in that the pasty filling is sausage meat.