Polyamide-based sausage skin which can be filled manually

The present invention relates to a sausage casing based on polyamide. It is particularly intended for sausage production on a smaller scale, in which filling is not done automatically but manually. It is particularly suitable for cooked and cooked sausages.

Fiber-reinforced cellulose casings, which are manufactured according to the viscose process and have a waterproof inner coating, have the largest share in the production of cooked and cooked sausages. In second place are the sleeves made of thermoplastic materials, especially polyamide or vinylidene chloride copolymers. The internally coated, fiber-reinforced cellulose casings are much more suitable for sausage production on a manual scale than the casings made of thermoplastic materials.

Cooked and scalded sausages are scalded after filling in water or steam at about 80 ° C, occasionally also at 110 to 130 ° C. The volume of the sausage meat increases. When it cools down, it then clearly decreases again. The sausage casing must adapt to the changing volume of the sausage meat. In particular, it should contract as it cools down so that no folds occur. Because sausage with a wrinkled casing is generally regarded as "no longer fresh". In addition, the casing should have enough tension that no liquid will accumulate under it after brewing. Such a "jelly sales" between shell and sausage meat is also considered a lack of quality.

The internally coated cellulose casings mentioned are usually soaked before filling. The highly hygroscopic cellulose is saturated with water. The water absorption is generally 110 to 140% by weight. At the same time, the shell expands ("swelling") and becomes very smooth. In this state, it is filled with the sausage meat. After scalding and cooling, the sausage is dried. The shell releases most of the water it absorbs. However, due to the impermeable inner coating, practically no moisture can escape from the sausage meat. During drying, the cellulose layer contracts strongly, so that the casing tightens the cooled sausage meat. This prevents wrinkles and jelly deposits, even if the sausage meat - as is usual for manual filling - has been filled in without pressure or with only slight pressure.

In terms of their application properties, the internally coated cellulose casings are ideal for manual filling. A disadvantage of these casings, however, is the complex and expensive manufacture using the viscose process. A cellulose xanthate solution is first applied to the fiber reinforcement preformed into a tube. The cellulose xanthate is then precipitated in dilute sulfuric acid and regenerated to cellulose hydrate. After washing and drying the shell, a polymer dispersion is applied to the inside, which then results in the water-impermeable coating.

Cooking and scalded sausage casings, on the other hand, can be produced much more simply and cost-effectively by blow extrusion of thermoplastic materials. Biaxially stretched polyamide shells have gained some importance here. DE-A 28 50 182 (= GB-A 2 035 198) describes a single-layer, biaxially stretched casing made of an aliphatic polyamide, the glass transition point of which in the dry state is at least 48 ° C. and, after water absorption, drops to at least 3 ° C, preferably down to -5 ° C. Specifically disclosed are polyamide-6 (= polycaprolactam), polyamide-7, polyamide-6,6 (= polyamide from hexamethylene diamine and adipic acid) and polyamide-6,10 (= polyamide from hexamethylene diamine and sebacic acid). According to DE-A 28 50 181, the shell also contains an ionomer resin, a modified ethylene-vinyl acetate copolymer and / or a quaternary copolymer with units of ethylene, butylene, an aliphatic, ethylenically unsaturated (C.₃-C₅) Carboxylic acid and an ester of this carboxylic acid with a (C₁-C₈) Alkanol. This casing shows a reduced tendency to tear after the sausage has been cut. The polyamide sheath according to DE-A 32 27 945 (= US-A 4 560 520 and 4 601 929) should have the same advantage.

EP-A 0 065 278 discloses a single-layer or multilayer, shrinkable flat film in which the layer or at least one layer consists of polyamide. The polyamide layer contains a linear, aliphatic (co) polyamide and a partially aromatic (co) polyamide. The linear, aliphatic (co) polyamide can be partially or completely replaced by an elastomeric component, such as polybutadiene, polyurethane rubber or nitrile rubber. The film is also stretched, but not heat-set, because it should have a high shrinkability and high shrink force. These properties are brought about by the special polymer combination in the polyamide layer.

So that the finished cooked and scalded sausages lose as little weight as possible during storage, the lowest possible permeability to water or water vapor is also desirable in the case of thermoplastics. However, many polyamides can absorb up to 10% by weight of water. Pure polyamide shells are therefore less suitable. In order to compensate for this disadvantage, multilayer casings have been developed which additionally (at least) contain a layer made of a water vapor impermeable polymer. Thus, the biaxially stretched sheath according to EP-A 573 306 consists of a middle polyamide layer and an inner and an outer layer made of a water vapor-blocking polymer, for example a polyolefin. DE-A 40 17 046 also discloses a three-layer, biaxially stretched and heat-set casing. Here the outer layer consists of aliphatic polyamide and / or copolyamide, the middle layer of polyolefin and an adhesion-promoting component and the inner layer of aliphatic and / or partially aromatic (co) polyamide.

When heated to temperatures of about 80 ° C or more, such as are achieved when the sausage is scalded, the casings begin to shrink. Through this. Thermal shrinking generally reduces the circumference of the casing by 5 to 20%. The extent of the contraction also depends on the conditions during the previous heat setting. Usually, the tube shrinks up to 40% during heat setting. At the same time, the diameter of the hose becomes more uniform. When the sausage is scalded, the thermal shrink begins almost immediately. This means that the tension of the casing is greatest at the beginning of the brewing process, while the sausage meat is still expanding in this phase. This can cause the casing to expand permanently, which means that its tension in the cooled sausage is no longer sufficient. In addition, layers of oriented polyamide have only a relatively low residual elasticity.

When producing sausages on an industrial scale, this problem is solved by filling the sausage meat under high pressure. Depending on the caliber of the sausage casing, a filling pressure of 20 to 40 kPa is usual. However, this requires specially designed filling machines. In this way, a first (partially) elastic expansion of the casing is achieved. The resetting force that arises is partially reduced during brewing, as is the thermal shrinkage force. The remaining force is then usually just enough to ensure that the cover is applied tightly and without creases.

However, a high filling pressure cannot be achieved without special filling machines. Manually filled polyamide casings are therefore usually wrinkled and unattractive after brewing and cooling. Therefore, the internally coated cellulose casings described at the beginning are still used in the craft sector.

It was therefore the task of developing a casing for cooked and cooked sausages that can be produced by blow extrusion from thermoplastic materials and that also lies wrinkle-free when the meat is filled without pressure or with little pressure, i.e. by hand and without using special filling machines.

The object is achieved by a biaxially stretched and heat-set, tubular, seamless, single-layer or multilayer food casing, in which the layer or, in the case of multilayer casings, at least one of the layers contains a block copolymer with "hard", aliphatic polyamide blocks and "soft", aliphatic polyether blocks , which corresponds to one of the formulas I to III:         E_a- (NH- [CH₂]_x-CO)_m-X_a- (AO)_n-AX_a- (CO- [CH₂]_x-NH)_m-E_a     (I) wherein<dl id="dl0001" compact="compact"><dt>A</dt><dd>an alkanediyl radical of the formula -CH₂-CH₂- (= ethane-1,2-diyl), -CH₂-CH (CH₃) - (= propane-1,2-diyl) or - (CH₂)₄- (= butane-1,4-diyl),</dd><dt>X_a</dt><dd>-O- or -NH-,</dd><dt>E_a</dt><dd>H, (C₂-C₈) Alkanoyl, benzoyl or phenylacetyl, CO-N ([CH₂]_x-1-CH₃) -CO- (C₁-C₄) Alkyl, CO-N ([CH₂]_x-1-CH₃) -CO-C₆H₅ or CO-N ([CH₂]_x-1-CH₃) -CO-CH₂-C₆H₅,</dd><dt>x</dt><dd>an integer from 5 to 11,</dd><dt>m</dt><dd>an integer from 30 to 200 and</dd><dt>n</dt><dd>is an integer from 4 to 60;</dd></dl><chemistry id="chem0001" num="0001"><img file="EP0935423B1_D0001.tif" /></chemistry> wherein<dl id="dl0002" compact="compact"><dt>X_b</dt><dd>an alkanediyl radical of the formula - [CH₂]_e.g.-, where z is an integer from 4 to 10,<i>meta</i>- or <i>para</i>-Phenylene, -NH- (C₁-C₆) Alkyl-NH-, - NH-C₆H₃- (CH₃) -NH- 〉 N- [CH₂]_x-1-CH₃, - [CH₂]_e.g.-CO-N ([CH₂]_x-1-CH₃) - or -C₆H₄-CO-N ([CH₂]_x-1-CH₃) -, where C₆H₄<i>meta</i>- or <i>para</i>Represents phenylene,</dd><dt>E_b</dt><dd>-OH, -O- (C₁-C₇) Alkyl, -O-phenyl or<chemistry id="chem0002" num="0002"><img file="EP0935423B1_D0002.tif" /></chemistry> and</dd></dl> A, m and n have the meaning given above;         - [X_a- (CO- [CH₂]_x-NH)_O-YX_a- (AO)_p-A] - (III) wherein<dl id="dl0003" compact="compact"><dt>Y</dt><dd>for -CO-, -CO- [CH₂]_e.g.-CO- or -CO-C₆H₄-CO- stands, where C₆H₄<i>meta</i>- or <i>para</i>Represents -phenylene, or for -CO-N ([CH₂]_x-1-CH₃) -CO-, -CO-N ([CH₂]_x-1-CH₃) -CO- [CH₂]_e.g.-CO-N ([CH₂]_x-1-CH₃) -CO or. -CO-N ([CH₂]_x-1-CH₃) -CO-C₆H₄-CO-N ([CH₂]_x-1-CH₃) -CO-, where C₆H₄ has the meaning given</dd><dt>O</dt><dd>an integer from 10 to 150 and</dd><dt>p</dt><dd>is an integer from 4 to 100 and</dd></dl> A, X_a, x and z have the meaning given above.

The "hard" polyamide blocks in the block copolymer of formulas I to III generally have a glass transition temperature (T_G) from 20 to 80 ° C, while the "soft" polyether blocks have a T_G from -100 to -20 ° C. The running number x is preferably 5, ie the polyamide blocks are preferably polycaprolactam blocks, while A preferably represents ethane-1,2-diyl or butane-1,4-diyl, ie the polyether blocks are preferably polyethylene glycol or polybutylene glycol blocks. The block copolymer of formula III, in which the hard and soft blocks occur in an alternating sequence, generally has an average molecular weight M_w from 20,000 to 70,000.

Of the block copolymers of the formulas I and II, those with m = 40 to 100 and n = 10 to 40 are preferred. Of the block copolymers of the formula III, those with o = 10 to 60 and p = 20 to 40 are preferred.

Block copolymers of the formula I in which X_a = -NHist, and block copolymers of the formula III, in which X_a = -O- and Y = -CO- [CH₂]₄-CO- or -CO- [CH₂]₁₀-CO- is.

The block copolymers of the formulas I, II and III are known as such and are described in US Pat. No. 4,501,861.

In a special embodiment, this layer also contains at least one aliphatic and / or partially aromatic (co) polyamide, mixed with the block copolymers. Preferred (co) polyamides of this type are polyamide-6 (PA-6), PA-6 / 6.6 (= copolyamide from ε-caprolactam, hexamethylene diamine and adipic acid), PA-6/12 (= copolyamide from ε-caprolactam and ω-amino-lauric acid lactam), PA-12 (= poly (ω-amino-lauric acid lactam) and PA-6I / 6T (= copolyamide from hexamethylenediamine, isophthalic acid and terephthalic acid). The proportion of additional polymers in this layer is up to 85% by weight, based on the total weight of the layer.

The layer with the block copolymers of the formulas I, II and / or III can also be colored by the addition of inorganic or organic pigments. Finally, other additives can also be present, in particular antiblocking agents and agents which improve the processing properties.

The food casing according to the invention is produced by bladder extrusion. Appropriate processes are known per se to the person skilled in the art. In general, the polymer (mixture) is first plasticized into a homogeneous melt and then extruded through a heated ring die. In this way you get a seamless shell. The relatively thick tube obtained during the extrusion is first rapidly cooled in order to keep the polymers in the amorphous state. It is then heated to the temperature required for stretching and stretched by blow molding. The hose is expanded by the pressure of an internal gas (usually air). The stretched tube is then partially heat set, so that residual shrinkage in the range from 5 to 20% remains at 80 ° C. The stretch ratio is slightly reduced. The area ratio of the heat-set shell is generally about 6 to 10.

A casing with somewhat less favorable shrink properties and slightly reduced strength is obtained if the hose is blow-molded immediately after leaving the ring nozzle and then also (partially) heat-set. After cooling, the casings are usually laid flat and rolled up.

For special applications, for example when a shell with an increased water vapor barrier is desired, multi-layered shells are advantageous. The additional layers preferably consist of polyamides (eg PA-6) or polyolefins (eg polyethylene or polypropylene). The polyolefins can also carry adhesion-promoting functional groups. Furthermore, the additional layers of (co) polymers with units of ethylenically unsaturated monomers (e.g. Vinyl acetate, vinyl alcohol or (meth) acrylic acid), consist of vinylidene chloride or acrylonitrile copolymers, of ionomer resins or mixtures of the (co) polymers mentioned.

In the two-layer casing according to the present invention, the additional layer is preferably located on the inside. If the shell according to the invention has three layers, the outer layer preferably contains the block copolymers of the formulas I, II and / or III. The multilayer casing according to the invention normally comprises no more than 5 layers.

The multilayer casings are generally made by coextrusion. As the number of layers to be extruded increases, the coextrusion dies become more and more technically complex and expensive, which limits the number of layers. Blow molding and (partial) heat setting then follow, as already described.

The casing according to the invention shows a high degree of shrinkage under the conditions which are generally achieved when brewing cooked and scalded sausages. It has approximately "rubber-like" resetting properties. The sausages thus produced - without the use of filling machines - are plump and wrinkle-free after brewing and cooling.

In the following examples, Gt stands for parts by weight. Unless stated otherwise, percentages are percentages by weight.

example 1

:

A mixture of<dl id="dl0004" compact="compact"><dt>70 Gt</dt><dd>Polyamide 6 (the relative viscosity of a 1% solution of the polyamide in 96% sulfuric acid was 4) and</dd><dt>30th Gt</dt><dd>a block copolymer with polypropylene glycol blocks and polycaprolactam blocks (®Grilon ELX 2112 from Ems-Chemie AG), whose melting point was 209 ° C (determined by DSC = differential scanning calorimetry)</dd></dl> was plasticized in a single-screw extruder at 240 ° C. to a homogeneous melt and extruded through an annular die to a tube with a diameter of 18 mm. The tube was quickly cooled, then brought to the temperature required for stretching, stretched by blow molding and finally heat-set, the stretching ratio being reduced by 5% in the transverse direction while remaining unchanged in the longitudinal direction. The area stretch ratio was 8.7. The finished casing had a diameter of 60 mm.

Example 2

:

A mixture of<dl id="dl0005" compact="compact"><dt>50 Gt</dt><dd>Polyamide 6 (as in example 1),</dd><dt>30th Gt</dt><dd>a block copolymer of poly (butane-1,4-diol) blocks and polylaurine lactam blocks (®Pebax 5533 SN01 from Elf Atochem SA), which had a melt index of 5 g / 10 min at 235 ° C. and 1 kg load, and</dd><dt>20 Gt</dt><dd>Polyamide 6/12 (®Grilon CF6S from Ems Chemie AG), which had a melt index of 50 g / 10 min at 190 ° C and 10 kg load,</dd></dl> was - as described in Example 1 - extruded into a tube with a diameter of 19 mm, stretched and heat-set. The area stretch ratio was 8.3. The finished sausage casing again had a diameter of 60 mm.

Example 3

:

The following mixtures were provided to produce a three-layer sausage casing:<ul id="ul0001" list-style="none" compact="compact"><li>Mixture A:<dl id="dl0006" compact="compact"><dt>90 Gt</dt><dd>Polyamide 6 (as in example 1) and</dd><dt>10th Gt</dt><dd>of the block copolymer also used in Example 1;</dd></dl></li><li>Mixture B:<dl id="dl0007" compact="compact"><dt>70 Gt</dt><dd>LDPE (low density polyethylene), which had a melt index of 0.2 g / 10 min at 190 ° C. and 2.1 6 kg load (®Lupolen 2441D from BASF AG), and</dd><dt>30th Gt</dt><dd>LLDPE (linear low-density polyethylene), which has been modified with maleic anhydride to impart adhesion to polyamide and which has a melt index of 3 g / 10 min at 190 ° C. and 2.16 kg load (®Escor CTR 2000 from Exxon);</dd></dl></li><li>Mixture C:<dl id="dl0008" compact="compact"><dt>85 Gt</dt><dd>Polyamide 6 (as in example 1) and</dd><dt>15 Gt</dt><dd>amorphous polyamide 6I / 6T, which had a melt index of 90 g / 10 min at 275 ° C and 10 kg load (®Selar PA 3426 from Du Pont de Nemours Inc.).</dd></dl></li></ul>

The mixtures were plasticized in three single-screw extruders at 240 ° C. to homogeneous melts, then brought together in a three-layer ring die and coextruded into a three-layer tube with a diameter of 29 mm. The tube was then stretched and heat set as described. The transverse stretching ratio was reduced by 20% during heat setting. The area stretch ratio was then 8.7. The diameter of the finished sausage casing was 80 mm. The total wall thickness of the casing was 54 µm. The outer layer (from mixture A) had a thickness of 34 μm, the middle layer (from mixture B) had a thickness of 16 μm and the inner layer (from mixture C) had a thickness of 4 μm.

Example 4

:

Example 3 was repeated with the only change that instead of the mixture A used there, a mixture A.<dl id="dl0009" compact="compact"><dt>70 Gt</dt><dd>Polyamide 6 (as in example 1) and</dd><dt>30th Gt</dt><dd>the block copolymer according to Example 1</dd></dl> was used.

As described in Example 3, a three-layer tube with a diameter of 28 mm was coextruded, stretched and heat-set. The area stretch ratio was 9. The diameter of the finished casing was 80 mm. With a total wall thickness of the shell of 51 μm, the outer layer (from mixture A) had a thickness of 30 μm, the middle layer (from mixture B) had a thickness of 15 μm and the inner layer (from mixture C) had a thickness of 6 µm.

Example 5

:

Example 3 was repeated with the only change that instead of the mixture A used there, a mixture A.<dl id="dl0010" compact="compact"><dt>65 Gt</dt><dd>Polyamide 6 (as in example 1),</dd><dt>20 Gt</dt><dd>of the block copolymer also used in Example 2 and</dd><dt>15 Gt</dt><dd>Polyamide 6/12 (as in example 2)</dd></dl> has been used. The diameter of the finished casing was 80 mm and its area stretch ratio was 7.9. With a total wall thickness of the shell of 56 μm, the outer layer (from mixture A) had a thickness of 35 μm, the middle layer (from mixture B) had a thickness of 15 μm and the inner layer (from mixture C) had a thickness of 6 µm.

Example 6

:

Example 3 was repeated with the only change that instead of the mixture A used there, a mixture A.<dl id="dl0011" compact="compact"><dt>50 Gt</dt><dd>Polyamide 6 (as in example 19,</dd><dt>30th Gt</dt><dd>of the block copolymer also used in Example 2 and</dd><dt>20 Gt</dt><dd>Polyamide 6/12 (as in example 2)</dd></dl> was used. The diameter of the finished casing was 80 mm. The area stretch ratio was 9.0. With a total wall thickness of the shell of 52 μm, the outer layer (from mixture A) had a thickness of 32 μm, the middle layer (from mixture B) had a thickness of 14 μm and the inner layer (from mixture C) had a thickness of 6 µm.

Comparative Example 1

:

According to DE-A 28 50 182, the polyamide 6 also used in Example 1 was extruded into a tube with a diameter of 19 mm by the process specified there, which was then stretched and heat-set as described. The area stretch ratio of the finished casing was 8.3 and its diameter was 60 mm.

Comparative Example 2

:

According to DE-A 40 17 046<dl id="dl0012" compact="compact"><dt>Component A:</dt><dd>Polyamide 6 (as in example 1),</dd><dt>Mixture B:</dt><dd>identical to mixture B in example 3 and</dd><dt>Mixture C:</dt><dd>identical to mixture C in example 3</dd></dl> as described there co-extruded into a tube with a diameter of 29 mm, stretched and heat-set. The transverse stretching ratio was reduced by 20% during heat setting. The area stretch ratio of the finished casing was 7.9 and its diameter was 52 mm. With a total wall thickness of the shell of 52 μm, the outer layer (from component A) had a thickness of 31 μm, the middle layer (from mixture B) had a thickness of 13 μm and the inner layer (from mixture C) had a thickness of 8 µm.

The measured values ​​in the following table show the superiority of the casing according to the invention over those known from the prior art. The table means:<ul id="ul0002" list-style="none"><li>1) measured according to DIN 53 455 on a strip of 15 mm width, which has been soaked for 30 minutes, with a clamping length of 50 mm;</li><li>2) denotes the tensile stress which must be used in the test according to DIN 53 455 in order to stretch the strip of 15 mm width, which has been soaked for 30 minutes, with a clamping length of 50 mm and an expansion speed of 50 mm / min by 5%;</li><li>3) Percentage increase in the outer circumference of tube sections that were previously soaked for 30 minutes and then inflated until the specified internal pressure was reached;</li><li>4) after 15 minutes of storage in water at 80 ° C;</li><li>5) The envelope was exposed to air on one side with a relative humidity (rH) of 85% at 20 ° C. The water vapor permeability was measured in accordance with DIN 53 122.</li><li>6) subjective assessment of a casing soaked for 30 minutes. The numbers mean: 1: extremely soft; 2 = very soft; 3 = soft and 4 = medium.</li><li>7) The casing was filled by hand with fine-grain cooked sausage meat at a constant, low filling pressure and sealed with metal clips. The sausages were then cooked in an oven for 60 minutes at 78 ° C. and 100% rh. After cooling to 7 ° C., the appearance and consistency were assessed.<img file="EP0935423B1_D0003.tif" /></li></ul>