Food casing with permeability to smoke and water vapour and with improved transparency
12568979 ยท 2026-03-10
Assignee
Inventors
Cpc classification
A22C13/0013
HUMAN NECESSITIES
International classification
Abstract
The present invention relates to a tubular, seamless, biaxially stretched, smoke-permeable and water vapour-permeable, colouristically neutral and transparent, single-layer food casing formed from a mixture including 50 to 95% by weight of aliphatic (co)polyamide, 3 to 40% by weight of at least one vinyl (co)polymer having units of N-vinyl-2-pyrrolidone and 1.5 to 7.0% by weight of at least one aliphatic diol and/or aliphatic polyol, based in each case on the weight of the mixture. The diol and/or polyol is homogeneously distributed in a matrix formed by the aliphatic (co)polyamide. The food casing is produced by an extrusion method with biaxial tube stretching and subsequent heat-setting. It is particularly suitable as synthetic sausage casing, especially for raw sausage, such as salami or mettwurst.
Claims
1. A tubular, seamless, biaxially stretched, smoke-permeable and water vapour-permeable, coloristically neutral and transparent, single-layer food casing composed of a mixture comprising at least one aliphatic (co) polyamide and at least one vinyl (co) polymer having units of N-vinyl-2-pyrrolidone, wherein the at least one aliphatic (co) polyamide is present at a fraction of 50 to 95% by weight and the at least one vinyl (co) polymer is present at a fraction of 3 to 40% by weight, based in each case on the weight of the mixture, and the mixture further comprises 1.5 to 7.0% by weight, based on the mixture weight, of at least one aliphatic diol and/or aliphatic polyol, where the diol or polyol is homogeneously distributed in a matrix of the aliphatic (co) polyamide, the food casing has a total luminous transmittance of at least 80%, determined on a casing having a thickness of 25 to 30 m in the wavelength range from 380 to 780 nm with a spectrophotometer, the food casing has a total haze of less than 10%, determined according to ASTM D 1003-6113, procedure A, without oil immersion, and the food casing does not comprise discrete domains.
2. The food casing according to claim 1, wherein the aliphatic (co) polyamide is (i) poly(-caprolactam) (PA6), (ii) a copolyamide of -caprolactam and -laurolactam (PA 6/12), (iii) a copolyamide of -caprolactam, hexamethylenediamine and adipic acid (PA6/66) or (iv) a copolyamide of -caprolactam, 3-amino-3,5,5-trimethylcyclohexylamine (isophoronediamine) and isophthalic acid.
3. The food casing according to claim 1, wherein the fraction of the aliphatic (co) polyamide is 60 to 85% by weight, based on the weight of the mixture.
4. The food casing according to claim 3, wherein the fraction of the aliphatic (co) polyamide is 70 to 80% by weight, based on the weight of the mixture.
5. The food casing according to claim 1, wherein the aliphatic diol is ethylene glycol, propane-1,2-diol, butane-1,4-diol, diethylene glycol, polyethylene glycol, polypropylene glycol (poly(propane-1,2-diol)), copolymer of ethylene glycol and propane-1,2-diol, copolymer of ethylene glycol and butane-1,4-diol, or a mixture of two or more of the foregoing compounds.
6. The food casing according to claim 5, wherein the polyethylene glycol has up to 20 ethylene glycol units.
7. The food casing according to claim 1, wherein the aliphatic polyol is a compound having three or more free hydroxyl groups.
8. The food casing according to claim 7, wherein the compound contains not more than 20 carbon atoms.
9. The food casing according to claim 7, wherein the compound is glycerol, diglycerol, 1,1,1-trimethylolpropane, 2,2-bis-hydroxymethylpropane-1,3-diol (=pentaerythritol) or a sugar alcohol selected from erythritol, sorbitol or mannitol.
10. The food casing according to claim 1, wherein the fraction of the diol and/or polyol is 1.6 to 6.0% by weight, based on the weight of the mixture.
11. The food casing according to claim 10, wherein the fraction of the diol and/or polyol is 1.7 to 5.5% by weight, based on the weight of the mixture.
12. The food casing according to claim 1, wherein the at least one vinyl (co) polymer having units of N-vinyl-2-pyrrolidone is polyvinylpyrrolidone, a copolymer composed of or having units of N-vinyl-2-pyrrolidone and one or more vinyl esters, a copolymer composed of or having units of N-vinyl-2-pyrrolidone and one or more esters or amides of ,-unsaturated carboxylic acids, or a copolymer composed of units of N-vinyl-2-pyrrolidone and N-vinylimidazole.
13. The food casing according to claim 12, wherein the copolymer composed of or having units of N-vinyl-2-pyrrolidone and one or more vinyl esters is vinyl acetate, and the copolymer composed of or having units of N-vinyl-2-pyrrolidone and one or more esters or amides of ,-unsaturated carboxylic acids comprises methyl ester as the ester and acrylamide as the amide.
14. The food casing according to claim 1, wherein the fraction of the vinyl (co) polymer having units of N-vinylpyrrolidone is 8 to 25% by weight.
15. The food casing according to claim 14, wherein the fraction of the vinyl (co) polymer having units of N-vinylpyrrolidone is 10 to 20% by weight.
16. The food casing according to claim 1, wherein the food casing is partially heat-set and exhibits a residual shrinkage of less than 20% in longitudinal and transverse directions, measured after immersion and storage of the food casing for one minute in water having a temperature of 90 C.
17. The food casing according to claim 1, wherein the food casing has a wall thickness of 10 to 50 m.
18. The food casing according to claim 17, wherein the food casing has a wall thickness of 15 to 40 m.
19. The food casing according to claim 1, wherein the food casing has a diameter of 12 to 60 mm.
20. The food casing according to claim 19, wherein the food casing has a diameter of 15 to 50 mm.
21. The food casing according to claim 1, wherein the food casing has a water vapour permeability of 200 to 500 g/m.sup.2 d, determined based on single-sided exposure of a sample of the food casing to air of 85% relative humidity at a temperature of 23 C.
22. The food casing according to claim 21, wherein the food casing has a water vapour permeability of 250 to 400 g/m.sup.2 d, determined based on single-sided exposure of the sample of the food casing to air of 85% relative humidity at the temperature of 23 C.
23. The food casing according to claim 1, wherein the total luminous transmittance of the food casing is at least 85%, determined on the casing having a thickness of 25 to 30 m in the wavelength range from 380 to 780 nm for the spectrophotometer.
24. The food casing according to claim 1, wherein the total luminous transmittance of the food casing is at least 90%, determined on the casing having a thickness of 25 to 30 m in the wavelength range from 380 to 780 nm for the spectrophotometer.
25. A method for producing a food casing according to claim 1 comprising melt compounding the mixture of the aliphatic (co) polyamide, the at least one vinyl (co) polymer having units of N-vinyl-2-pyrrolidone and the at least one aliphatic diol and/or aliphatic polyol to convert the mixture into a homogeneous melt, extruding the homogeneous melt and processing the extrudate into pellets, remelting the pellets and extruding the remelted pellet to produce a primary tube having a relatively high wall thickness, cooling the primary tube rapidly to obtain polymers in an amorphous, heating the cooled primary tube to a temperature necessary for biaxial stretching, and stretching the heated primary tube in longitudinal and transverse directions by a gas pressure acting from inside, where the stretching is an area stretch ratio in the range from 1:6 to 1:12.
26. The method for producing the food casing according to claim 25, wherein the area stretch ratio is in the range from 1:8 to 1:10.
27. A raw sausage comprising a food casing as claimed in claim 1.
28. The raw sausage according to claim 27, wherein the raw sausage is a smoked raw sausage.
Description
DETAILED DESCRIPTION OF ADVANTAGEOUS INVENTIVE EMBODIMENTS
(1) The food casing of the invention for a thickness of 25 to 30 m has a light transmissibility [total transmittance .sub.t] in the wavelength range from 380 to 780 nm of at least 80%, preferably at least 85%, more preferably at least 90%, more particularly at least 92%, especially at least 94%, determined according to DIN EN ISO 13468-2:2006 with a spectrophotometer.
(2) The food casing of the invention for a thickness of 25 to 30 m has, generally, a total haze of less than 15%, preferably less than 10%, determined according to ASTM D 1003-13, Procedure A (measurement without oil immersion).
(3) The total transmittance is measured according to DIN EN ISO 13468-2:2006 with a spectrophotometer having a stabilized light source, a monochromator, a measuring beam and a reference beam (.fwdarw.two-beam instrument), an integrating sphere (Ulbricht sphere) and a photodetector.
(4) During the measurement the ratio () of the photodetector signals I.sub.sam() (sample) to I.sub.ref() (reference beam) for the set wavelength is indicated:
()=I.sub.sam()/I.sub.ref()
(5) The following readings are taken: .sub.1() without sample over the entrance port of the integrating sphere .sub.2() with sample over the entrance port of the integrating sphere
(6) The readings are taken for the 380 nm to 780 nm spectral range in steps of 5 nm. For each wavelength, the total spectral transmittance .sub.1() is given by:
.sub.1()=.sub.2()/.sub.1()(formula 1)
(7) The total transmittance for the entire wavelength range .sub.t in % is computed as follows:
(8)
(9) The term (co)polyamide is used in connection with the present invention as an abbreviated designation for Polyimide and/or copolyimide. The term copolyimide here also includes polyamides having three or more different monomer units. Preferred among the aliphatic (co)polyamides are poly(-caprolactam), also referred to as PA 6, copolyamides of -caprolactam and -laurolactam (=PA 6/12), copolyamides of -caprolactam, hexamethylenediamine and adipic acid (=PA6/66) and also copolyamides of -caprolactam, 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine) and isophthalic acid. The copolyamides are also reckoned to include heterofunctional polyamides, more particularly polyetheramides, polyesteramides, polyetheresteramides and polyamidurethanes. Of these polymers, preference is given to those with a block-like distribution of the various functionalities, i.e. block copolymers. Particularly preferred block copolymers are poly(ether-block-amides).
(10) The fraction of the aliphatic (co)polyamide is generally 50 to 95% by weight, preferably 60 to 85% by weight, more preferably 70 to 80% by weight, based in each case on the total weight of the mixture.
(11) The term vinyl (co)polymer having vinylpyrrolidone units is used in connection with the present invention as an abbreviated designation for homopolymers or copolymers which are formed by polymerization of ,-unsaturated aliphatic monomers wherein one monomer unit is always N-vinyl-2-pyrrolidone. Preference here is given to a) polyvinylpyrrolidone (homopolymer of N-vinyl-2-pyrrolidone) b) copolymers of N-vinyl-2-pyrrolidone and one or more vinyl esters, especially vinyl acetate c) copolymers of N-vinyl-2-pyrrolidone and one or more esters or amides of ,-unsaturated carboxylic acids, especially methyl acrylate and acrylamide d) copolymers of N-vinyl-2-pyrrolidone and N-vinylimidazole Particularly preferred among these groups are a) and d).
(12) The fraction of this or these component(s) in the mixture is generally 3 to 40% by weight, preferably 8 to 25% by weight, more preferably 10 to 20% by weight. The term diol represents an aliphatic compound having two free hydroxyl groups, examples being ethylene glycol, 1,2-propanediol, 1,4-butanediol, diethylene glycol, polyethylene glycol, poly(1,2-propanediol) (=polypropylene glycol) and copolymers of ethylene glycol and 1,2-propanediol or of ethylene glycol and 1,4-butanediol. Preferred among these are polyethylene glycol and also copolymers of ethylene glycol and 1,2-propanediol.
(13) The term polyol represents an aliphatic compound having three or more free hydroxyl groups, examples being glycerol, diglycerol, 1,1,1-trimethylolpropane, 2,2-bishydroxymethyl-1,3-propanediol (pentaerythritol), and also sugar alcohols such as erythritol, sorbitol and mannitol.
(14) Preferred among these is glycerol. General preference is given to diols and polyols having 2 to 20 carbon atoms, more particularly those having 2 to 12 carbon atoms. The fraction of the at least one diol and/or polyol is generally 1.5 to 7.0% by weight, preferably 1.6 to 6% by weight, more preferably 1.7 to 5.5% by weight, based in each case on the total weight of the mixture.
(15) In the mixture there may also, optionally, be relatively small fractions of further polymers, examples being semi-aromatic (co)polyamides and (co)polymers composed of or having units of ,-unsaturated carboxylic acids or ,-unsaturated carboxamides, more particularly having units of (meth)acrylic acid and/or (meth)acrylamide.
(16) The fraction of optional further polymers in the mixture is generally 0 to 20% by weight, preferably 1 to 15% by weight, more preferably 2 to 10% by weight, based on the total weight of the thermoplastic mixture.
(17) The mixture optionally further comprises additives which are soluble, liquid or solid at room temperature and which further influence the properties of the casing. In this way it is possible to tailor, for example, the blocking tendency, the tactile qualities, the moisture storage capacity or the peeling behaviour. Examples of additives contemplated include polysaccharides and finely divided inorganic fillers, more particularly antiblocking pigments and colour pigments, and also plastifying and compounding auxiliaries such as mono-, di- and triesters of glycerol with carboxylic acids, formamide, acetamide, N,N-dimethylformamide, N,N-dimethylacetamide, and also customary plastics stabilizers.
(18) The fraction of any other additives present is generally 0 to 10% by weight, preferably 0.5 to 8% by weight, more preferably 1 to 5% by weight, based on the total weight of the mixture.
(19) Another subject of the invention is a method for producing the food casing of the invention. Production takes place generally by extrusion methods, which are known per se to the skilled person.
(20) First of all the mixture for extrusion is produced by melt compounding in an apparatus suitable for this purpose, preferably in a twin-screw extruder with attached pelletizing die, air cooling section and pelletizer. The pellets obtained in this way are melted again in a further extruder and then processed to give a tubular casing.
(21) After the melting in the further extruder, the mixture is again homogenized and plastified. The melt is then extruded through an annular die. This forms a primary tube having a relatively high wall thickness. The primary tube is then rapidly cooled in order to freeze in the amorphous state of the polymers. It is thereafter then heated again to the temperature required for stretching, for example to about 80 C. The tube is then stretched in longitudinal and transverse directions, preferably carried out in one operation. The longitudinal stretching is typically performed by means of two pairs of squeeze rolls, with increasing drive speed; the transverse stretching is accomplished by a gas pressure which acts from inside on the walls of the tube. The area stretch ratio (being the product of longitudinal stretch ratio and transverse stretch ratio) is generally about 6 to 18, preferably about 8 to 11.
(22) After stretching has taken place, the tube is preferably also heat-set. This allows the desired shrinkage properties to be established with precision. The heat-setting leaves a residual shrinkage of generally less than 20% in longitudinal and transverse directions, measured on a sample immersed in water of 90 C. for 1 min. Finally, the tube is cooled, collapsed to a flat state and wound up.
(23) In one particular embodiment, the tube is subsequently wreathed. For this purpose the tube is inflated, heated on one side (generally without contact, by radiant heat) and then curved in the heated state, so that it takes on a ring or spiral shape. Methods and apparatus for wreathing are common knowledge to the skilled person and are also described in the patent literature.
EXAMPLES
(24) The examples below serve for illustration, but have no limiting character on the scope of the invention. Percentages are weight percentages, unless indicated otherwise or apparent from the context. Starting Materials Used were as Follows:
Aliphatic Polyamides (PA): PA1: polyamide 6/66 having a relative viscosity of 3.4 (measured in 96% sulfuric acid) and a crystallite melting temperature of 192 C. (measured by DSC) PA2: copolyamide of -caprolactam, 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine) and isophthalic acid, having a melt volume flow rate (MVR) of 5 cm.sup.3/10 min (measured at 235 C. under a load of 2.16 kg) and a crystallite melting point of 212 C. Vinyl (co)polymers having vinylpyrrolidone units (vinylpyrrolidone (co)polymers): VP1: polyvinylpyrrolidone having a K value of 25 and an average molecular weight M.sub.w of 34 000 daltons VP2 copolymer of N-vinyl-2-pyrrolidone and vinyl acetate (ratio 60:40) having a K value of 30-50 and a molecular weight M.sub.w of 51 000 daltons Prior-Art Water-Soluble Polymer: WP1 polyvinyl alcohol having a molecular weight M.sub.w of 11 000 Da and a degree of hydrolysis of 88% Diol or polyol: Diol polyethylene glycol (PEG) having an average molar mass of 400 Polyol glycerol 96%, purity according to DAB (German pharmacopeia) Parameters Used in Characterizing the Casings Haze measured according to ASTM D 1003 with a hazemeter in the wavelength range 400-700 nm (without oil immersion 4 total haze) (Byk-Gardner, model HAZE-GARD PLUS) .sub.t=total luminous transmittance, measured according to DIN EN ISO 13468-2:2006 on films 26 to 30 m thick in the wavelength range 380 to 780 nm with a spectrophotometer with integrating sphere attachment 150 nm (Agilent, model CARY 5000) WTR=water vapour permeability, measured according to DIN 53122 with single-sided exposure of samples to air of 85% relative humidity and at 23 C. [g/m.sup.2.Math.d]
Examples 1 to 5: Production of Compounds Composed of Aliphatic Copolyamide, Vinylpyrrolidone (Co)Polymer and Diol or Polyol (Inventive)
(25) A twin-screw extruder (manufacturer: Coperion, screw diameter: 25 mm) with single-hole exit die was charged sequentially via three discrete metering apparatuses with the components listed in table 1. The ratio of the metering rates [mass per unit time] to one another corresponded to the percentage values indicated in the table. The extruder was conditioned to 180 C. at the polyamide feed point. In the subsequent barrel zones, the temperature conditioning was raised gradually to a maximum of 230 C. The screw speed was about 200 rpm. In this way the polyamide was melted and plastified to form a homogeneous mixture with the pulverulent vinylpyrrolidone (co)polymer and also the diol or polyol. The mixture emerged from the extruder via the pelletizing die, as a water-clear, uniform extrudate. For cooling, the extrudate was passed through a water bath and then comminuted into granular pellets by means of a strand pelletizer. The pellets were dried in a forced-air drier at about 100 C.
(26) TABLE-US-00001 TABLE 1 Components of the Compounds in Examples 1 to 5 Aliphatic Vinylpyrrolidone Example polyamide (co)polymer Diol or polyol 1 PA1 VP1 Diol 77.3% by weight 21% by weight 1.7% by weight 2 PA2 VP1 Diol 77.3% by weight 21% by weight 1.7% by weight 3 PA1 VP1 Polyol 73.8% by weight 21% by weight 5.2% by weight 4 PA1 VP2 Diol 77.3% by weight 21% by weight 1.7% by weight 5 PA1 VP2 Polyol 75.5% by weight 21% by weight 2.7% by weight
Comparative Example C1: Replication of WO02/078455 A1, Example 1 (Closest Prior Art)
(27) Initial Remarks
(28) Example 3 of WO '455 states that a mixture of the components PA6.66 [=PA6/66] (90% by weight, ULTRAMID C35, BASF) [the figure stated was 94% by weightthis is evidently a typographical error] and polyvinylpyrrolidone (10% by weight, POVIDEN [grade not specified], BASF) was introduced into an extruder and melted. The melt is said then (directly) to be extruded through an annular die and shaped to form a primary tube. Not set out are the type of extruder used and the manner in which said components were supplied to the extruder. In the extrusion technology field, mixtures are commonly understood to be dryblends, produced by simple mechanical premixing of the components at room temperature. Dryblends can be supplied to an extruder in general by a simple method, as by means of a mounted hopper, for example.
(29) Accordingly, first 90% by weight of pellet-form PA1 [PA6/66] and 10% by weight of pulverulent VP1 [polyvinylpyrrolidone] were placed into a mixing drum, where they underwent intense circulation for around 30 minutes. The resulting powder-pellet mixture was supplied via a customary feed hopper to a single-screw extruder, which was conditioned to a temperature profile rising from 160 C. to 235 C. It was immediately apparent that the mixture was not taken up uniformly and in the specified proportions by the extruder. The polyvinylpyrrolidone particles underwent settling through between the substantially larger PA6/66 granular pellets, and so the fraction of polyvinylpyrrolidone in the extruder to start with was substantially higher than the mixture proportion. As a result of the absorption of ambient moisture by the hygroscopic polyvinylpyrrolidone particles, moreover, there was agglomeration and sticking of powder particles on the base of the hopper and, ultimately, the extruder opening became clogged. It was necessary to switch to the compounding of the components by means of a twin-screw extruder, which provides for separate feeding and metering of the components.
Comparative Example C1a Replication of WO 02/078455 A1, Example 1 (Amended Method)
(30) 90% by weight of PA1 [pellet-form PA6/66] and 10% by weight of VP1 [pulverulent polyvinylpyrrolidone] were compounded by means of a twin-screw extruder under the same conditions as described for examples 1 to 5. In contrast to those examples, the material emerging from the pelletizing die of the extruder this time was a markedly hazy extrudate.
Comparative Example C2: Production of a Compound as in Examples 1 to 5, without Addition of Diol or Polyol
(31) A further compound was produced from 89% by weight of PA1 and 21% by weight of VP1, under the same conditions as described for examples 1 to 5.
Comparative Example C3: Replication of DE 103 02 960 A1, Example 1 (Closest Prior Art)
(32) In a stirred tank with liquid jacket heating and close-clearance stirrer, 75% by weight of WP1 were introduced at room temperature. With stirring at around 1000/min, first 15% by weight of diol and then 7.5% by weight of polyol and also 2.5% by weight of water were added. The contents of the tank were heated to 100 to 110 C., stirred at this temperature for 15 min, and cooled again with further stirring to 30 to 40 C. A metering apparatus was used to meter the resultant powder into a heated twin-screw extruder (properties as described under examples 1 to 5). The screw speed was 250/min, and the heaters were set to temperatures of 120 C. (feed point) downstream rising to 180 C. (die). The emerging extrudate was cooled on an air cooling section and then comminuted into granular pellets using a strand pelletizer.
Comparative Examples C4 to C9: Production of Compounds as in Example 1, with Additions of Diol and/or Polyol of Below 1.5 and, Respectively, Above 7.0% by Weight (not Inventive)
(33) Further compounds were produced from the components set out in table 2, using a twin-screw extruder, under the same conditions as described for examples 1 to 5.
(34) TABLE-US-00002 TABLE 2 Components of the compounds of examples C4 to C9 Example Aliphatic Vinylpyrrolidone No. polyamide (co)polymer Diol Polyol C4 PA1 VP1 1.0% by weight 78.0% by weight 21% by weight C5 PA1 VP1 8.0% by weight 71.0% by weight 21% by weight C6 PA1 VP1 8.0% by weight 71.0% by weight 21% by weight C7 PA1 VP1 2.8% by weight 5.2% by weight 71.0% by weight 21% by weight C8 PA1 VP1 3.5% by weight 6.5% by weight 69.0% by weight 21% by weight C9 PA1 VP1 4.5% by weight 7.0% by weight 67.5% by weight 21% by weight
Examples 6 to 10 Production of Biaxially Stretched Tube Casings
(35) The pellets obtained according to examples 1 to 5 were supplied (without further additions) via a feed hopper to the single-screw extruder of a standard commercial extrusion and tube stretching unit (double-bubble unit with mono-annular die). In the extruder the pellets were melted and the melt was plastified and conveyed in the direction of the die. In the die the melt flow was pressed axially through distribution channels which opened out in an annular gap. The melt film emerging from the gap was shaped by means of a calibrator into a primary tube 13 mm in diameter and at the same time was cooled to room temperature. The primary tube was then heated to around 80 C. again and stretched in transverse and longitudinal directions by means of an inserted air cushion. The stretch ratios were about 3.30 in transverse direction and about 1.95 in longitudinal direction. The stretched tube was passed through squeeze rolls, then subjected to a second air cushion and passed through a setting tunnel equipped with IR lamps. The tube here reached a surface temperature of around 150 C. Finally, the tube was squeezed off again, cooled in the collapsed state, and wound up. The resulting casing had a diameter of 43 mm and a film thickness in the 26 to 30 m range.
(36) The test results for the casings are set out in table 3.
(37) TABLE-US-00003 TABLE 3 Data of the inventive casings Film thickness Example Pellets used for (averaged over WTR Haze .sub.t No. production periphery) [m] [g/m.sup.2 d] [%] [%] 6 as in example 1 26 320 8.2 87.6 7 as in example 2 30 370 7.0 92.1 8 as in example 3 28 360 2.9 94.5 9 as in example 4 29 260 9.1 85.0 10 as in example 5 28 280 9.4 82.7
Comparative Example C10: Casing as in WO 02/078455 A1, Example 3 (Amended Production Method)
(38) The pellets obtained as in example C1a were supplied (without further additions) to the extruder of the extrusion and tube stretching unit described in examples 6 to 10, and were processed under the same conditions to give a biaxially stretched casing.
Comparative Example C11: Casing Analogous to Examples 6 and 8, without Diol or Polyol
(39) The compound produced as in example C2 was supplied (without further additions) to the extruder of the extrusion and tube stretching unit described in examples 6 to 10, and was processed under the same conditions to give a biaxially stretched casing.
Comparative Example C12: Casing as Per DE 103 02 960 A1, Example 2
(40) The pellets of example C3 were premixed with pellet-form PA1 in a ratio of 30 to 70 parts by weight. The mixture was supplied to the extruder described in examples 6 to 10, plastified therein to form a homogeneous melt, and processed under the stated conditions likewise to give a biaxially stretched tube casing.
Comparative Examples C13 to C18: Casings Analogous to Examples 6 and 8, with Fractions of Diol and/or Polyol of Less than 1.5 or More than 7.0% by Weight
(41) The pellets of examples C4 to C9 were supplied (without further additions) to the extruder of the extrusion and tube stretching unit described in examples 6 to 10, and were processed under the same conditions to give biaxially stretched casings.
(42) TABLE-US-00004 TABLE 4 Data of the casings from comparative examples C10 to C18 Film thickness Example Pellets used for (averaged over WTR Total haze .sub.t No. production periphery) [m] [g/m.sup.2 d] [%] [%] C10 as in example C1a 26 170 16.3 76.4 C11 as in example C2 27 310 18.1 73.1 C12 30% by weight as in 25 90 28.5 47.5 example C3 70% by weight PA1 C13 as in example C4 26 310 11.8 78.0 C14 as in example C5 24 330 14.5 79.8 C15 as in example C6 25 370 13.2 78.3 C16 as in example C7 26 340 13.8 77.5 C17 as in example C8 24 370 17.6 72.1 C18 as in example C9 25 380 22.1 61.4
(43) Relative to the casings according to inventive Examples 6 to 10, the casings of Comparative examples C10 to C12 showed significantly higher values for haze and lower values for transmittance. This demonstrates the superiority of the casings of the invention in terms of transparency (and hence also low opalescence) relative to the prior art. The comparison of the haze values and of the transmittance values of the casing of comparative example C11 with those of inventive Examples 6 and 8 (all three of which contained the same copolyamide and a 21% by weight fraction of PVP) directly showed the haze-reducing effect of the diol or polyol in the casing of the invention. Examples C13 to C18 show that fractions of diol and/or polyol outside the range from 1.5% by weight to 7.0% by weight lead again to a significant increase in the haze value and to a drop in the transparency value relative to the casings of the invention.