Smoke and water vapor permeable food casing with optimized adhesive properties, process for its production and its use

Abstract

Tubular, seamless, water vapor permeable, smokable, biaxially stretch-oriented and partially or fully heat-set food casing with at least two layers based on thermoplastic polymers, characterized in that at least one layer A, which does not form the inner layer, comprises a blend of 60 to 95 wt.% of one or more aliphatic (co)polyamides and 5 to 40 wt.% of at least one hydrophilic polymer, wherein the hydrophilic polymer is polyvinylpyrrolidone, polyvinyl alcohol or a partially saponified polyvinyl acetate, a copolymer with vinyl alcohol units, a polyalkylene glycol or a copolymer with alkylene glycol units, a polymer of N-vinylalkylamides or a homopolymer of or a copolymer with units of α,β-unsaturated carboxylic acids or α,β-unsaturated carboxylic acid amides, and that the inner layer I consists of a blend of 40 to 90 wt.% of one or more aliphatic (Co-)polyamides and 60 to 10 wt.-% of a block copolymer selected from polyether amide, polyether ester and polyether urethane, and optionally one or more additives which improve the thermoplastic processability of the blend and / or influence the properties of the casing, wherein the food casing has a water vapor permeability of 80 to 220 g / m. 2 d, measured according to DIN ISO 15106-3 at a humidity gradient of 85 to 0% and at a temperature of 23 °C.

Description

[0001] The invention relates to a tubular, seamless, water vapor-permeable, smokeable, biaxially stretch-oriented, and partially or fully heat-set food casing with at least two layers based on thermoplastic polymers. It exhibits high permeability to smoke and water vapor and specifically adjustable adhesion properties to the filling material. The food casing is suitable for use as an artificial sausage casing, particularly for air-dried, optionally smoked raw sausage, especially for salami.

[0002] Casings based on regenerated cellulose or collagen are traditionally used to produce smoked and / or dried sausages. However, the production of these casings is technically complex. Cellulose casings are generally manufactured using the viscose process. In this process, cellulose is first converted into cellulose xanthate using caustic soda and carbon disulfide (CS2). The resulting viscose solution must first mature for several days before being fed to the casing spinning machines. These machines essentially consist of a spinneret, coagulation baths, washing and preparation baths, and drying stations. In the coagulation baths, the cellulose xanthate is regenerated into cellulose. Collagen casings – also known as hide fiber casings – consist of hardened connective tissue protein. During their production, connective tissue from animal hides is first mechanically crushed and chemically digested.The resulting homogenized mass is then further processed in a dry or wet spinning process. In the wet spinning process, the collagen mass is extruded through a ring die and solidified in a coagulating precipitation bath (G. Effenberger, Wursthüllen - Kunstdarm, Holzmann-Buchverlag, Bad Wörishofen, 2nd ed.

[1991] pp. 21-27).

[0003] As an alternative to the aforementioned casings, smoke and water vapor permeable casings based on synthetic polymers were described and introduced to the market.

[0004] EP 1 380 212 A1 describes (stretched) casings made from a blend of a copolyamide (PA6 / 66, 85:15) and a crosslinked N-vinylpyrrolidone polymer ("PVPP"). In the examples of EP '212, the proportion of PVPP in the blend varies from 4 to 50%. The values ​​given for water vapor permeability range from 1000 to ≤ 2000 g / m². 224 hours, measured at 40°C and 90% relative humidity. Additionally, the weight loss for sausages after 15 days and after 2 months is given. The values ​​for a cellulose fiber casing are provided for comparison. The weight loss of the sausage in cellulose fiber casings after 15 days was significantly higher than for the copolyamide and PVPP casings.

[0005] WO 09 / 078455 A1 describes films for smoking and / or drying food consisting of a polyamide matrix with a finely dispersed hydrophilic component. The latter is, for example, a (co)polymer of N-vinylpyrrolidone, vinyl alcohol, or polyethylene glycol. The hydrophilic component is present in the polyamide matrix in the form of domains with a diameter of 0.1 to 3 µm in the film plane. The examples show biaxially stretched casings with water vapor permeability in the range of 211 to 509 g / m². 224h, measured at 30°C and 65% rH For comparison, a collagen shell (“Cutisin”) with a permeability of 1200 g / m 2 24 hours under the same conditions.

[0006] EP 3 014 996 A1 discloses a multilayer, coextruded food casing with a porous inner layer. The pores of the inner layer are created by a supercritical pore-forming agent, such as supercritical nitrogen or supercritical carbon dioxide. Other pore-forming agents are explicitly excluded. The inner layer has a porosity of 5 to 95 vol.% and comprises pores with a diameter of 0.01 to 2000 µm. A functional additive, for example a food coloring, an odorant, or a flavoring agent, such as liquid smoke, can be absorbed and stored in the pores, which can then be transferred to a food product contained in the casing upon heating. Thermoplastic polymers such as (co)polyamides, polyolefins, vinylidene chloride copolymers, (co)polyesters, vinyl copolymers (polyvinyl alcohol, ethylene / vinyl alcohol copolymers, polyvinylpyrrolidone, polystyrene, etc.) or combinations thereof are used for the inner layer.The porous inner layer can also contain hydrophilic components, such as polyesteramides or polyetheramides. These improve the water vapor permeability of the matrix polymers of the porous inner layer. The shell further comprises at least one layer that acts as a barrier to water vapor and / or oxygen, and optionally also additional functional layers.

[0007] DE 103 30 762 A1 discloses a smoke- and water vapor-permeable food casing based on aliphatic (co)polyamide and at least one other thermoplasticizable (co)polymer. The casing is impregnated with liquid smoke on the inner side facing the food. The casing can also be multilayered, with the inner layer comprising the aforementioned polymer mixture.

[0008] The subject of DE20 2004 021 408 U1 is a smokeable, tubular food casing. It is manufactured using a jet blow molding process from a mixture of polyamide, polyvinyl alcohol, and polyether-block-amide.

[0009] DE 103 39 801 A1 relates to an inherently stable shirred food casing based on a thermoplastic blend of at least one (co)polyamide and at least one hydrophilic component. The casing is generally single-layer. The hydrophilic component is preferably polyvinyl alcohol or a block copolymer with polyamide and polyether blocks.

[0010] DE 101 47 155 A1 discloses a seamless tubular food casing made of thermoplastic starch and at least one other polymer. It can also be multilayered with an inner layer made of this mixture. The other polymer is preferably a homo- or copolymer of hydroxycarboxylic acid units, a polyetherurethane, or a polyesteretherurethane. The casing carries at least one transferable colorant, aroma, and / or flavoring on its inner surface.

[0011] DE 103 02 960 A1 claims a biaxially oriented smoke-permeable casing comprising aliphatic polyamide or copolyamide and at least one water-soluble synthetic polymer and having a water vapor permeability in the range of 40 to 200 g / m 2d. The water-soluble polymer is preferably a polyvinyl alcohol, a polyalkylene glycol, a vinylpyrrolidone (co)polymer, a polymer of N-vinylalkylamides, or a (co)polymer with units of α,β-unsaturated carboxylic acids or α,β-unsaturated carboxylic acid amides. The examples show casings with a water vapor permeability in the range of 81 to 110 g / m 2 d, measured at 23°C and 85% r.h.

[0012] The water vapor permeabilities cited in the cited documents were measured under different climatic conditions and are not comparable. In EP 1 380 212 A1 and WO 09 / 078455 A2, the cellulose fiber casing and collagen casing used for comparison show that the latter is significantly superior in water vapor permeability to the polyamide-based casing claimed in each case.

[0013] A general shortcoming of the casings described above is their strong adhesion to the filling material, especially the sausage meat. This strong adhesion can be explained by the polyamides, which form the matrix in all these casings and thus determine the surface properties. The amide groups contained in polyamides are chemically analogous to the amide groups in meat protein. Both types of amide groups can form hydrogen bonds with each other, which are energetically favored and create adhesion forces at the polyamide / protein interface.

[0014] Casings based on regenerated cellulose often also exhibit high adhesion to the sausage meat. Surface modifications have long been common practice for these casings to reduce the polarity of the cellulose surface or to adapt it to the specific application. Typically, the inner surfaces of these casings are coated with a reactive hydrophobic agent that chemically bonds to the hydroxyl groups of the cellulose. Common reactive hydrophobic agents include alkyldiketenes and chromium-fatty acid complexes (see, among others, GB 887 466 A, US 3 582 364 A, and DE 34 47 026 A1).

[0015] Strong adhesion to the sausage mass is disadvantageous for the user, as it makes peeling off the casing difficult or even impossible. Very low adhesion is also undesirable; this can cause the casing to "lift" from the meat surface during sausage production, resulting in the accumulation of meat juice or mold growth in the sausage / casing space. To cover all applications for smoked and / or dried sausage products, users require a casing range with graded adhesion.

[0016] Accordingly, the task was to provide a permeable plastic casing with a specifically adjustable adhesion of the inner surface to the sausage meat filling. At the same time, the casing had to meet the technical requirements applicable to the production of smoked and / or dried sausage products, specifically burst resistance, temperature resistance, shape retention, and high smoke and water vapor permeability. Furthermore, the casing had to be cost-effective and easy to manufacture.

[0017] The problem was solved with a tubular casing comprising one or more layers based on a blend of aliphatic (co)polyamide and one or more hydrophilic polymers, and another layer arranged on the inner side of the casing based on a blend of aliphatic (co)polyamide and a block copolymer of the polyetheramide, polyetherester, or polyetherurethane type. The adhesion can be adjusted by the mixing ratio of the polymers used for the inner layer.

[0018] The invention thus relates to a seamless, tubular, water vapor permeable, smokeable, biaxially stretch-oriented and partially or fully heat-set food casing with at least two layers based on thermoplastic polymers, which is characterized in that at least one layer A, which does not form the inner layer, comprises a blend of 60 to 95 wt.% of one or more aliphatic (co)polyamides and 5 to 40 wt.% of at least one hydrophilic polymer, wherein the hydrophilic polymer is polyvinylpyrrolidone, polyvinyl alcohol or a partially saponified polyvinyl acetate, a copolymer with vinyl alcohol units, a polyalkylene glycol or a copolymer with alkylene glycol units, a polymer of N-vinylalkylamides or a homopolymer of or a copolymer with units of α,β-unsaturated carboxylic acids or α,β-unsaturated carboxylic acid amides, and that the inner layer 1 consists of a blend of 40 to 90 wt.-% of one or more aliphatic (co-)polyamides and 60 to 10 wt.% of a block copolymer selected from polyether amide, polyether ester and polyether urethane, and optionally additives which improve the thermoplastic processability of the blend and / or influence the properties of the casing, wherein the food casing has a water vapor permeability of 80 to 220 g / m. 2 d, measured according to DIN ISO 15106-3 at a humidity gradient of 85 to 0% and at a temperature of 23 °C.

[0019] Surprisingly, it was found that layers made of blends of aliphatic (co)polyamides with block copolymers of the aforementioned types form a significantly lower adhesion to the sausage mass than layers made of corresponding (co)polyamides alone.

[0020] In the context of the present invention, the term "(co)polyamide" is used as an abbreviation for "polyamide and / or copolyamide." Aliphatic copolyamides also include heterofunctional polyamides, for example, polyetheramides, polyesteramides, polyetheresteramides, and polyamideurethanes. "(Meth)acrylic acid," "(meth)acrylamide," etc., stand for "acrylic acid and / or methacrylic acid" or "acrylamide and / or methacrylamide," respectively.

[0021] Among the aliphatic (co)polyamides, poly(ε-caprolactam), also referred to as PA 6, copolyamides of ε-caprolactam and ω-laurolactam (= PA 6 / 12), copolyamides of ε-caprolactam, hexamethylenediamine, and adipic acid (= PA 6 / 66), and copolyamides of ε-caprolactam, 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine), and isophthalic acid are preferred. Copolyamides of the types PA 6 / 12 and PA6 / 66 are particularly preferred. Layer A can therefore contain not only aliphatic but also isocyclic or aromatic diamine or dicarboxylic acid units. "Isocyclic" refers here to compounds containing a saturated carbon ring (e.g., isophoronediamine).

[0022] The casing has at least one layer A made of a blend comprising 60 to 95 wt.% of one or more aliphatic (co)polyamides and 5 to 40 wt.% of one or more hydrophilic polymers. The layer preferably consists of this blend and, optionally, the additives listed below, which are present therein in minor amounts. The proportion of additive(s) is generally no more than 10 wt.%, preferably no more than 7 wt.%, in each case based on the weight of the layer.

[0023] The hydrophilic polymer is preferably a) a polyvinylpyrrolidone (PVP) or a water-soluble copolymer comprising vinylpyrrolidone units and units of at least one α,β-olefinically unsaturated monomer, b) a polyvinyl alcohol (PVAL), as obtainable by partial or complete saponification of polyvinyl acetate (PVAC), or a copolymer containing vinyl alcohol units (for example a copolymer containing units of vinyl alcohol and propen-1-ol), c) a polyalkylene glycol, in particular polyethylene glycol, polypropylene glycol or a corresponding copolymer with alkylene glycol units, in particular ethylene glycol and / or propylene glycol units, and units of other monomers, d) a polymer of N-vinylalkylamides, for example poly(N-vinylformamide), poly(N-vinylacetamide) or e) a (co-)polymer of or with units of α,β-unsaturated carboxylic acids or α,β-unsaturated carboxylic acid amides, in particular with units of (meth)acrylic acid and / or (meth)acrylamide.

[0024] Of these groups, a) is particularly preferred. A PVP with a K value (according to Fickentscher) in the range of 12 to 50 is especially preferred.

[0025] The blend may also contain additives that improve its thermoplastic processability and / or influence the properties of the casing. Properties that can be influenced include color, transparency, feel, the tendency of the casing layers to block each other, and the moisture retention capacity of the casing. Organic polyhydroxy compounds are preferably used to improve the thermoplastic processability and transparency of the casing. Particularly preferred polyhydroxy compounds are ethylene glycol, propylene glycol, glycerin, diglycerin, and pentaerythritol. Additives that influence other casing properties include polysaccharides such as starch or starch derivatives, inorganic fillers such as calcium carbonate, barium sulfate, talc, mica, etc., and color pigments.

[0026] Layer I, located on the inner casing surface and in contact with the food, consists of a blend of 40 to 90 wt.% of one or more aliphatic (co)polyamides (as already defined) and 10 to 60 wt.% of a block copolymer of the polyether amide, polyether ester, or polyether urethane type. Layer I preferably consists of this blend and, optionally, one or more of the additives listed below. This type of block copolymer is understood to be chain molecules incorporating blocks (or segments) of aliphatic polyethers. The polyether blocks, in turn, are based on aliphatic diols, preferably 1,2-ethanediol (→ polyethylene glycol), 1,2-propanediol (→ polypropylene glycol), or 1,4-butanediol (→ polytetramethylene glycol, also called poly-THF). The remaining segments are blocks of aliphatic polyamide (in the case of polyether amides) or those of semi-aromatic polyester (in the case of polyether esters).those made of aromatic or aliphatic polyurethanes (in the case of polyether urethanes). The polyether blocks are arranged along the polymer chains, alternating with the blocks of polyamide, polyester, or polyurethane, and are covalently bonded to the latter at the end.

[0027] Block-co-polyether amides of this type are commercially available under the name Pebax® (manufacturer Arkema SA). Corresponding block-co-polyether esters are marketed under the name Arnitel® (manufacturer DSM). Corresponding block-co-polyether urethanes are offered, for example, under the name Irogran® A (manufacturer Huntsman International LLC).

[0028] Particularly preferred are block-co-polyether-amides with blocks of polyethylene glycol and of poly(ε-caprolactam) or poly(ω-laurolactam) as well as block-co-polyether-esters with blocks of polyethylene glycol and of polybutylene terephthalate.

[0029] The latter blend may also contain additives that influence the thermoplastic processability and / or the properties of the casing. These include, for example, agents that reduce the tendency of the casing surfaces to block against each other, particularly polysaccharides and mineral fillers such as calcium carbonate, or dyes and / or pigments.

[0030] The total thickness of the casing wall is generally in the range of 15 to 80 µm, preferably in the range of 25 to 50 µm. The inner layer I generally has a thickness in the range of 2 to 12 µm. It generally contributes 3 to 25%, preferably 5 to 15%, to the total thickness of the casing wall. Preferably, the food casing consists of one or two layers A and the inner layer I. If two layers A are present, they preferably have a different composition.

[0031] Optionally, the casing according to the invention is colored by dyes and / or pigments added to one or more of the aforementioned blends.

[0032] The food casing according to the invention preferably has a water vapor permeability of 80 to 220 g / m 2 d, particularly preferably from 100 to 180 g / m 2 d, measured according to DIN ISO 15106-3 at a humidity gradient of 85 to 0% and a temperature of 23°C. It is also smokeable and permeable to smoke components. This means that color- and aroma-imparting substances, such as those found in gaseous or condensed smoke produced by the combustion of wood, can diffuse through the casing in practical quantities.

[0033] The casing according to the invention is manufactured according to the principle of thermoplastic coextrusion combined with a tube blowing process or a process of biaxial tube stretch orientation

[0034] The casing obtained in the blow-molded tubular film process is referred to in the context of the invention as "unstretched" tubular film. This refers to tubular films that are stretched during forming in the melt state, but not at temperatures below the crystallization temperature or below the softening temperature in the case of amorphous materials. In this process, the two or more annularly coextruded, superimposed melts are stretched by inflation in the circumferential (transverse) direction and in the longitudinal direction by means of driven squeeze rollers. Since the deformation occurs directly from the melt, the degree of orientation of the polymer chains is low and negligible. These films are referred to as unoriented films.

[0035] In biaxial stretch orientation, a tube with a relatively thick wall is first produced by coextrusion of two or more melts. This tube is only slightly or not at all inflated. This so-called primary tube is then quickly cooled. In a subsequent step, the primary tube is heated to the temperature required for biaxial stretch orientation and then stretched in the transverse and longitudinal directions by internally acting gas pressure and by means of driven squeezing rollers. This achieves a high degree of orientation of the polymer chains in both directions. Longitudinal and transverse stretch ratios are within the range generally customary in practice. They depend primarily on the type of (co)polyamide used. After biaxial stretch orientation, partial or complete heat setting is advantageously carried out. This allows the shrinkage of the casing to be adjusted to the desired value.Stretch-oriented plastic sausage casings typically exhibit a shrinkage of less than 25% in the longitudinal and transverse directions, preferably 8 to 20% in the longitudinal and transverse directions, when immersed in water at 90°C for 1 minute. For heat-setting, the casing is preferably inflated using a gas volume introduced between two pairs of squeeze rollers and passed through a channel heated with IR radiators or hot air.

[0036] The entire process is also referred to in expert circles as the “double bubble” or “triple bubble” process.

[0037] The casing produced by the tubular blow molding process preferably has a thickness of 40 to 150 µm, and the casing produced by biaxial stretch orientation preferably has a thickness of 20 to 75 µm. For use as a sausage casing, the variant produced by biaxial stretch orientation is preferred.

[0038] The casing according to the invention can then be made into sections tied on one side or section by section into so-called shirred sticks. Furthermore, it can be formed into a so-called crown casing. For this purpose, the casing is inflated, asymmetrically exposed to hot air or thermal radiation, and converted into a helical shape using a crown forming tool.

[0039] The following examples serve to illustrate the scope of the invention without limiting it. Percentages are by weight unless otherwise stated or apparent from the context.

[0040] The following starting materials were used: Aliphatic polyamides: PA1: Polyamide 6 / 66 with a relative viscosity of 4.0 (measured in 96% sulfuric acid) and a crystallite melting temperature of approximately 195°C (Ultramid® C40 L 07 from BASF SE) PA2: Polyamide 6 with a relative viscosity of 4.0 (measured in 96% sulfuric acid) and a crystallite melting temperature of approximately 220°C (Ultramid® B40 from BASF SE) Hydrophilic polymer: PVP: Powdered polyvinylpyrrolidone with a Fikentscher K value of 16-17.5 (measured in water) (Plasdone® K-17 from Ashland Inc.) Polyether block copolymers: PEA Polyether amide, composed of blocks of polyethylene glycol and poly-(ω-laurolactam) and with a crystallite melting temperature of approximately 158°C (PEBAX® MV 3000 SP 01 from Arkema SA) PEE Polyether ester, composed of blocks of polyethylene glycol and polybutylene terephthalate and with a crystallite melting temperature of approximately 185°C (Arnitel® VT 3118 from DSM Engineering Plastics BV) PA-AB Masterbatch made of quartz powder and polyamide 6, weight ratio 10:90, (Grilon® XE 3690 from Ems-Chemie AG) Example 1: Production of a compound from polyamide and polyvinylpyrrolidone

[0041] PA1 and PVP were metered into a commercially available twin-screw kneader (cylinder diameter 25 mm, L / D ratio 36, 12 barrels, feed points for granules on barrel 1 and for powder on barrel 7, with a two-hole outlet nozzle, manufacturer Coperion GmbH) in a mass ratio of 85% to 15%. At a screw speed of 200 rpm and a temperature range of 120°C to 210°C, the polyamide was melted and mixed with the PVP to form a plastic compound. The transparent strand emerging from the nozzle was cooled by immersion in a water bath and, after solidification, cut into granules using a strand chopper. The granules were dried at approximately 100°C in a circulating air dryer. The granules are referred to below as Comp. 1. Example 2: Production of a three-layer, biaxially stretched casing

[0042] The components listed in Table 1 below were fed into the three extruders of a commercially available coextrusion and tube stretching system (double-bubble system with a 3-layer coextrusion ring die). In the extruders, the components were melted, homogenized into blends, and conveyed toward the die. In the die, the melt streams were forced axially through annular channels and concentrically merged. The melt film emerging from the annular gap was formed into a primary tube with a diameter of 13 mm using a calibrator and cooled to room temperature. The primary tube was then reheated to approximately 80°C and stretched transversely and longitudinally using an air cushion. The stretch ratios were 3.30 in the transverse direction and 1.95 in the longitudinal direction.The stretched tube was passed through squeeze rollers, then subjected to a second air cushion and passed through a fixation channel equipped with IR emitters. During this process, the tube reached a surface temperature of approximately 150°C. Finally, the tube was squeezed again, cooled while lying flat, and wound up. The resulting sleeve had a diameter of 43 mm and a film thickness of 28 to 32 µm. Table 1 Extruder supplied components Proportional layer thickness [%] Designation % by weight A Comp. 1 85 10 PA2 10 PA-AB 5 B Comp. 1 100 80 C → inner layer PA2 80 10 PEA 15 PA-AB 5 Example 3

[0043] Example 2 was repeated with the difference that extruder C was fed with components according to Table 2 below. Table 2 Extruder supplied components Designation % by weight C → inner layer PA2 65 PEA 30 PA-AB 5 Example 4

[0044] Example 2 was repeated with the difference that extruder C was fed with components according to Table 3 below. Table 3 Extruder supplied components Designation % by weight C → inner layer PA2 75 PEE 20 PA-AB 5 Example 5

[0045] Example 2 was repeated with the difference that extruder C was fed with components according to Table 4 below. Table 4 Extruder supplied components Designation % by weight C → inner layer PA2 55 PEE 40 PA-AB 5 Comparative example 1 (V1)

[0046] Example 2 was repeated with the difference that extruder C was fed with components according to Table 5 below. Table 5 Extruder supplied components Designation % by weight C → inner layer PA2 65 Comp. 1 30 PA-AB 5 Comparative example 2 (V2)

[0047] Example 2 was repeated with the difference that extruder C was fed with components according to Table 6 below. Table 6 Extruder supplied components Designation % by weight C → inner layer PA2 95 PA-AB 5 Comparative Example 3 (V3) Production of a single-layer, biaxially stretched casing

[0048] The components listed in Table 6 below were fed into the extruder of an extrusion and tube stretching system (double-bubble system with a single-layer extrusion ring die). In the extruder, the components were melted, homogenized, and conveyed toward the die. In the die, the melt stream was forced axially through an annular channel. The melt film emerging from the annular gap was formed into a primary tube with a diameter of 14 mm using a calibrator and cooled to room temperature. The primary tube was then reheated to approximately 80°C and stretched in the transverse and longitudinal directions using an introduced air cushion. The stretch ratios were 3.07 in the transverse direction and 2.15 in the longitudinal direction. The subsequent steps were carried out analogously to Example 1. The resulting seamless casing had a diameter of 43 mm and a film thickness of 23 to 28 µm. Table 7 Extruder supplied components Designation % by weight A → Total shift PA2 10 Comp. 1 85 PA-AB 5

[0049] To evaluate the casings, water vapor permeability measurements were performed under laboratory conditions and an application-specific test was conducted. The latter provided information on the casings' permeability under practical conditions and on their adhesion to the contents. The contents were raw sausage (salami). The results are summarized in Table 8.

[0050] The application-specific testing proceeded as follows: Casing sections were filled with commercially available salami sausage meat at a constant filling pressure, sealed at the ends with metal clips, and weighed. The sausages were suspended in a climate chamber and subjected to fermentation, maturation, and drying using a temperature and humidity profile typical for salami. The total residence time in the climate chamber was 14 days. The weight change of each sausage was then measured. To test the adhesion of the casings to the sausage surface, the sausages were cut into slices approximately 2 cm thick. The casing sitting on the slices was severed axially. At the cutting point, the casing was lifted off and manually peeled off circumferentially. The results were scored on a scale of 1 to 10: 1 = no adhesion; casing can be removed without force, no meat sticking ... 5 = clear adhesion: casing can be removed with moderate force, little sausage meat adhesion ... 10 = very strong adhesion: peeling requires high force, tearing out larger pieces of sausage meat Table 8: Test results Example Water vapor permeability 1) [g / m 2 d] Weight loss of sausage filling NotePeeling behavior 2 142 21 3 3 175 22 1 4 118 17 4 5 138 20 2 V1 181 23 9 V2 19 6 6 V3 219 25 10 1) measured according to ISO 15106-3 at a humidity gradient of 85% to 0% relative humidity and at 23°C

[0051] The above data confirm that casings with the layer on the inside composed according to the invention exhibit only low to moderate adhesion to the salami filling. In contrast, casings with the layer on the inside composed according to the state of the art exhibit medium to high adhesion. Furthermore, the data demonstrate that the moisture permeability of the casings according to the invention is almost as high as that of casings according to the state of the art (V3).

Claims

[1] Tubular, seamless, water vapor permeable, smokeable, biaxially stretch-oriented and partially or fully thermoset food casing with at least two layers based on thermoplastic polymers, characterized bythat at least one layer A, which does not form the inner layer, comprises a blend of 60 to 95 wt. % of one or more aliphatic (co-)polyamides and 5 to 40 wt. % of at least one hydrophilic polymer, wherein the hydrophilic polymer is polyvinylpyrrolidone, polyvinyl alcohol or a partially saponified polyvinyl acetate, a copolymer with vinyl alcohol units, a polyalkylene glycol or a copolymer with alkylene glycol units, a polymer of N-vinylalkylamides or a homopolymer of or a copolymer with units of α,β-unsaturated carboxylic acids or α,β-unsaturated carboxamides, and that the inner layer I consists of a blend of 40 to 90 wt. % of one or more aliphatic (co-)polyamides and 60 to 10 wt.-% of a block copolymer selected from polyether amide, polyether ester and polyether urethane, and optionally one or more additives which improve the thermoplastic processability of the blend and / or influence the properties of the casing, wherein the food casing has a water vapor permeability of 80 to 220 g / m. 2 d, measured according to DIN ISO 15106-3 at a humidity gradient of 85 to 0% and at a temperature of 23 °C. [2] Food casing according to claim 1, characterized by that the aliphatic or isocyclic (co-)polyamide is a polyamide 6, a copolyamide of ε-caprolactam and ω-laurolactam (PA 6 / 12), a copolyamide of ε-caprolactam, hexamethylenediamine and adipic acid (PA 6 / 66) or a copolyamide of ε-caprolactam, 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine) and isophthalic acid. [3] Food casing according to claim 1 or 2, characterized bythat it consists of layer I and two layers A with different composition. [4] Food casing according to one or more of claims 1 to 3, characterized by that it has a diameter (caliber) of 28 to 90 mm, preferably 34 to 60 mm, and a wall thickness of 15 to 80 µm. [5] Food casing according to one or more of claims 1 to 4, characterized by that the inner layer I has a thickness of 2 to 12 µm. [6] Food casing according to one or more of claims 1 to 5, characterized by that it exhibits a shrinkage of less than 25% in the longitudinal and transverse directions, preferably 5 to 15% in the longitudinal and transverse directions, when immersed in 90 °C water for one minute. [7] A process for producing a food casing according to one or more of claims 1 to 6, characterized bythat it is produced by coextrusion combined with a tube blow molding process or by a process with biaxial tube stretch orientation. [8] Method according to claim 7, characterized by that the food casing is made up into sections tied on one side or into shirred sticks. [9] Use of the food casing according to one or more of claims 1 to 6 as an artificial sausage casing, in particular for air-dried, optionally smoked raw sausage, especially salami.