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Title:
SMOOTH-SURFACE MULTILAYER CASING FOR FOOD PRODUCTS, PERMEABLE TO WATER VAPOR AND SMOKE
Document Type and Number:
WIPO Patent Application WO/2014/104946
Kind Code:
A1
Abstract:
The present invention relates to a multilayer casing for food products, permeable to water vapor and smoke components and mostly useful as a casing for frankfurters, wieners, boiled-and-smoked, dried and raw-smoked sausages, and processed cheeses, etc. The invented casing has at least two layers comprising from 15% to 70% of a polyamide resin and from 30% to 85% of at least one water-soluble resin, selected from the group comprised of polyvinyl alcohol, copolymers of vinyl alcohol, polyvinylpyrrolidone, copolymers of vinylpyrrolidone, polyoxazoline, cellulose ether; and the water vapor transmission rate of the casing, measured according to DIN 53122 at 23°C and the relative humidity of 85%, is more than 200 g/m2day. The casing according to the present invention is characterized by improved mechanical reliability in combination with high permeability to process smoke and water vapor, and can be manufactured on high-capacity industrial equipment.

Inventors:
VERIN SERGEI VLADIMIROVICH (RU)
VELIKOV SERGEY ALEXANDROVICH (RU)
GOLYANSKIY BORIS VLADIMIROVICH (RU)
Application Number:
PCT/RU2013/001174
Publication Date:
July 03, 2014
Filing Date:
December 26, 2013
Export Citation:
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Assignee:
OBSCHESTVO S OGRANICHENNOI OTVETSTVENNOSTYU PROIZV KOMMERCHESKAYA ATLANTIS PAK F (RU)
International Classes:
A22C13/00
Domestic Patent References:
WO2004065466A12004-08-05
Foreign References:
DE10330762A12005-02-10
RU2131670C11999-06-20
RU2086580C11997-08-10
US20050244553A12005-11-03
US20060147661A12006-07-06
Attorney, Agent or Firm:
FALEEVA, Liubov Nikolaevna (72h. Lenina,Aksayski rayo, Rostovskaya obl. 3, RU)
Download PDF:
Claims:
Claims

1. A smooth-surface multilayer tubular biaxially-oriented casing for food products, the casing comprising a polyamide resin and a water-soluble resin, wherein the casing has at least two layers comprising from 15% to 70% of a polyamide resin and from 30% to 85% of at least one water-soluble resin selected from the group including polyvinyl alcohol, copolymers of vinyl alcohol, polyvinylpyrrolidone, copolymers of vinylpyrrolidone, polyoxazoline, and also cellulose ether, wherein the casing is characterized by value the water vapor transmission rate of the casing, measured according to DIN 53122 at 23°C and the relative humidity of 85%, of higher than 200 g/m2 day.

2. A smooth-surface multilayer tubular biaxially-oriented casing according to claim 1 , wherein said polyamide resin is at least one aliphatic (co)polyamide selected from the group including polyamide 46, polyamide 6, polyamide 66, copolyamide 46/6, copolyamide 6/66 or a blend thereof.

3. A smooth-surface multilayer tubular biaxially-oriented casing according to claim

1, wherein said polyvinyl alcohol has a weight-average molecular weight Mw between 10000 and 50000 and a degree of saponification of the acetate groups between 70 and 98%, preferably from 75 to 85%.

4. A smooth-surface multilayer tubular biaxially-oriented casing according to claims 1-3, wherein said casing has additional layers, the composition of which is different from said at least two layers.

5. A smooth-surface multilayer tubular biaxially-oriented casing according to claim 4, wherein at least one of said additional layers contains not less than 90% of said polyamide resin.

6. A smooth-surface multilayer tubular biaxially-oriented casing according to claim

4, wherein at least one of said additional layers is preferably made of a blend comprising from 70% to 95% of said polyamide resin and from 5% to 30% of said water-soluble resin.

7. A smooth-surface multilayer tubular biaxially-oriented casing according to claim 4, wherein at least one additional layer does not comprise polyamide.

8. A smooth-surface multilayer tubular biaxially-oriented casing according to claim 7, wherein said additional layer preferably contains at least one resin, selected from the group including water-soluble polyvinyl alcohol, insoluble copolymer vinyl alcohol, insoluble cellulose ester, block copolymer of polyamide and polyether, block copolymer of polyester and polyether, block copolymer of polyurethane and polyether or any blend thereof.

9. A smooth-surface multilayer tubular biaxially-oriented casing according to claim

I, wherein any layer may comprise at least one additive, selected from the group comprising pigments, colorants, highly dispersed fillers, plasticizers, stretching aids, additives to control adhesion of the casing to its contents, and slip agents, or any mixtures thereof.

10. A smooth-surface multilayer tubular biaxially-oriented casing according to claim 9, with the total number of layers from 2 to 7.

1 1. A smooth-surface multilayer casing for food products according to claim 10, wherein the total thickness of said casing is between 15 and 70 μηι.

12. A smooth-surface multilayer tubular biaxially-oriented casing according to claim

I I, wherein the summarized thickness of said at least two layers comprising said polyamide resin and said water-soluble resin is between 10 and 100% of the total thickness of the casing.

Description:
Smooth-surface Multilayer Casing for Food Products, Permeable to Water Vapor and

Smoke

Field of invention

The present invention relates to a multilayer casing for food products, permeable to water vapor and smoke components and useful mainly as a casing for frankfurters, wieners, small sausage, boiled-and-smoked, dried and raw-smoked sausages, and also processed cheeses, etc. Background of the Invention

Over the last decade melt-extruded films based on synthetic polymers (hereinafter referred to as resins), mostly polyamides, permeable to water vapor and smoke and used as casings for smoked sausages and frankfurters were launched on the market of packaging materials.

The application WO 02054878 published 18.07.2002 discloses films made of a blend of a block copolymer of polyamide and polyether (hereinafter referred to as polyether block amide or PEBA) with polyamides (hereinafter referred to as PA) proposed for use as vapor and smoke-permeable casings for sausages subjected to smoking. Such sausage casings comprise 15-85% of polyamide or polyamide blend, and 15-85% of PEBA. In a preferred embodiment the casing contains 50-70% of polyamide or polyamide blends, and 30-50% of PEBA.

Water vapor and smoke-permeable films produced from the same components and, additionally, polyvinyl alcohol (hereinafter referred to as PVA) are described in the patent RU 2333652 published 20.09.2008. The thermoplastic blend composition is 40-80% PA, 5-40% PVA, and 20-30% PEBA. The film can be made either single-layered or multi- layered. The preferred proportions of the blend components are as follows: 50-65%) PA, 24-26% PEBA and 15-25% PVA.

It should be noted that PEBA is an elastomer with a very low Young's modulus. Therefore, single-layer casings comprising PEBA, and multilayer casings wherein PEBA is present in all layers, are highly permeable to vapor, but show excessive elasticity. Such mechanical characteristics can cause deformations of sausages enclosed in this casing under their own weight and allow using only casings of small diameters. A smokable film made of a blend of an ether-ester block copolymer with an aliphatic polyamide comprised in a quantity from 50 to 99.9% is disclosed in the application WO 2082913 published 24.10.2002.

The high content of polyamide in these blends is caused by very low mechanical strength that is typical for films made of both applied block copolymers per se and compositions wherein they are predominant by weight fraction. Such films are not suitable for, e.g., sausage casings, which must withstand high mechanical loads associated with stuffing. In addition, such block copolymers are rather expensive, which increases the cost and price of the films comprising them.

A single-layer tubular smoke and vapor-permeable film comprising a polyamide, for instance PA 6 or PA 6/66, and 4 to 50% of hydrophilic compounds, including water soluble polymers, such as polyvinylpyrrolidone or polyvinyl alcohol, which form a highly dispersed phase with the domain linear size (thickness) of 0.1-3.0 μπι in the polyamide, is disclosed in the patent RU No.2182107 published 10.05.2002.

For imparting to such film the mechanical properties required for a sausage casing, it is produced by the triple bubble process, i.e. it is extruded in the form of the so-called primary tube (bubble), which is then heated in a hot water bath to about 70-80°C and biaxially stretched with simultaneous blowing by air and longitudinal stretching resulting in the secondary tube. The secondary tube is then subjected to thermosetting resulting in the finished (tertiary) tube. Characteristics of such casing allow preparing of smoked sausages and frankfurters encased therein, having a marked effect of smoking (smoke aroma and brown coloring), but with crust on the surface of sausage meat, that is not yet enough dense.

Another approach to increase the permeability of polymeric films based on blends of an aliphatic (co)polyamide and a water soluble synthetic organic polymer is also known from the prior art. The patent RU No.2341090 published 20.12.2008 disclosed a casing with a rough surface and a natural (matte) appearance, comprising, in addition to the aliphatic (co)polyamide(s) and a water soluble synthetic organic polymer(s), at least one organic and/or inorganic filler, which can be a carbohydrate, an organic synthetic powder, or an organic synthetic fiber with a mean length of fibers of 5-3000 μιη, or glass beads with an average size of 5-3000 μηι. Such casing can be single-layer or multilayer. Such casing has, among other characteristics, water vapor transmission rate, determined according to DIN 53122, which ranges from 50 to 1500 g/m day. The inventors explained the multifold growth of the water vapor transmission rate by the presence in the casing of the mentioned fillers.

However, adding of such fillers into a thermoplastic composition requires extra processing steps, which prolong the production cycle; meanwhile further production of casings, especially oriented ones, from such compositions is a complex engineering problem, because of excessive rigidity of mentioned compositions. Besides, the organic fillers in the blend are prone to thermal decomposition, under the conditions of extrusion of aliphatic (co)polyamides, and the decomposition products contaminate an extrusion machine and the casing itself at all manufacturing stages,. As regards to inorganic large - size particles of coarse-grained fillers, they as a rule, cause an accelerated abrasive wear of extrusion and shirring machines, and, in addition, tend to be dislodged and to fall out from the finished casing under mechanical loads. If such casing is intended to be filled with sausage meat for frankfurters on high-capacity stuffing apparatus it should be loaded into this apparatus in the form of rigid shirred "sticks". However the non-uniform thickness of mentioned filled casings hinders the manufacture of such sticks according to the known technology, e.g. as disclosed in patent RU No.2131670 published 20.06.1999. Besides, the advantages of a natural appearance is absolutely beside the point, if the casing is intended for frankfurters, which are peeled of casing and re-packed, e.g., into vacuum bags by their manufacturer.

A casing closest to the newly invented one is described in the patent RU No.2345104 published 27.01.2009. The single-layer casing disclosed therein consists of an aliphatic (co)polyamide and a water soluble synthetic organic polymer, the content of the aliphatic (co)polyamide being 40-94%, particularly preferably 60-85%, while the content of the water soluble polymer is 3-50%, particularly preferably 15-30%. That casing has a water vapor transmission rate (hereinafter referred to as WVTR) or water vapor permeability, determined in accordance with DIN 53 122, from 40 to 200 g/m 2 day, at a temperature of 23 °C and the relative humidity of 85°C. However, such permeability values are insufficient for production of boiled-and-smoked or raw-smoked sausages.

Moreover, as is shown below, the upper value of the water vapor transmission rate for the casing of this patent is achieved when the content of the water soluble polymer approximately corresponds to the upper value of the preferred range (30%), while industrial production of an oriented single-layer casing with such content of the water soluble polymer or higher is extremely difficult. It is to be expected that casings made of an aliphatic (co)polyamide and a water soluble synthetic organic polymer obeys to the common rule: the greater the content of hydrophilic component in a casing, the higher its permeability to water vapor and smoke.

However, a high-capacity industrial production of a mechanically strong single-layer casing becomes more and more difficult as the concentration of a water-soluble polymer in the casings grows, because of the growing instability of the process in the orientational stretch stage that is interrupted by rupture of the film more and more frequently. The same tendency regards of rupture frequency is typical for these single-layer casings, while they are being stuffed with the meat emulsion.

It is therefore the object of the present invention to provide a smooth-surface multilayer tubular biaxially-oriented synthetic casing for food products based on of blends of polyamides and water-soluble polymers characterized by improved permeability to smoke and vapor, i.e. the casing must have a WVTR higher than 200 g m 2 -24 h, without adding of additional coarse-grained fillers, which would enhance its permeability to smoke and vapor, but also cause problem in fabrication and processing of the casing. Such casing should also have improved mechanical characteristics at all stages of manufacture and in the finished form, i.e. both the finished casing, and its processing precursors the primary and secondary tubes must have the improved mechanical reliability.

Hereinafter in this description, the sign "%" shall mean the mass percentage of the total mass of the composition or blend, unless otherwise specified, or unless otherwise unequivocally follows from context. Also, the words with a prefix in round brackets shall denote both the term expressed by the word with that prefix, and the term expressed by the word without that prefix. For example, the word (co)polyamide means both polyamide (homopolymer) and copolyamide.

Hereinafter the mechanical reliability of the casing shall mean the probability of that a randomly selected piece of the casing equal to 33m (the casing length in the shirred stick) will withstand without rupture mechanical stress typically taking place at its filling on automatic stuffing equipment. Description of Invention

As a result of intensive studies, it was surprisingly found that the object of the present invention is achieved by a smooth-surface multilayer tubular biaxially-oriented casing for food products, comprising a polyamide resin and a water-soluble resin, such casing having at least two layers comprising from 15% to 70% of polyamide resin and from 30% to 85% of at least one water-soluble resin selected from a group including polyvinyl alcohol, copolymers of vinyl alcohol, polyvinylpyrrolidone, copolymers of vinylpyrrolidone, polyoxazoline, cellulose ether, and the water vapor transmission rate of the casing, measured according to DIN 53122 at 23°C and 85% relative humidity, is more than 200 g/m 2 day.

According to the present invention, above-mentioned polyamide resin consists of at least one individual aliphatic (co)polyamide. The polyamide resin can be represented by any thermoplastic synthetic (co)polyamide (Nylon), but in the preferred embodiments the above-mentioned resin is a thermoplastic aliphatic polyamide or copolyamide selected from the group including polyamide 46, polyamide 6, polyamide 66, copolyamide 46/6, copolyamide 6/66, or any blends thereof.

Polyamide 46 is produced commercially by, e.g., Royal DSM (Netherlands) and sold under the general trademark Stanyl®. Polyamide 6, polyamide 66, copolyamide 6/66 are supplied by, e.g., BASF SE (Germany), UBE Industries, Ltd. (Japan), and Royal DSM (Netherlands) under the trademarks Ultramid®, Nylon® and Akulon®, respectively.

The above-mentioned water-soluble resin comprises at least one water-soluble (co)polymer and, optionally, a water-soluble plasticizer.

The above-mentioned water-soluble (co)polymer is a (co)polymer with a solubility in water heated up to 80°C of at least 20 g/1.

A preferred synthetic water-soluble polymer is polyvinyl alcohol, particularly with the weight-average molecular weight Mw between 10000 and 50000, and the degree of saponification of the acetate groups between 70 and 98%, preferably from 75 to 85%.

Polyvinyl alcohol generally (as conventional in the art) means water-soluble products of complete or partial saponification of vinylacetate, which may nominally be regarded as copolymers of vinyl alcohol and vinylacetate. In the narrow, strictly chemical sense, polyvinyl alcohol is a homopolymer from residues of vinyl alcohol. Hereinafter the term polyvinyl alcohol is used in the wide sense, unless otherwise unequivocally follows from context. Polyvinyl alcohol of different grades is produced by, e.g., the companies Kuraray Co., Ltd., and Nippon Synthetic Chemical Industry Co., Ltd. (Japan) under the trademarks Mowiol® and Gohsenol®, respectively, and by the company ChangChun Petrochemical Co., Ltd. (Taiwan) under the trademarks PVA BF, PVA BP and PVA BC.

Polyvinylpyrrolidone (hereinafter referred to as PVP) and water-soluble copolymers of vinylpyrrolidone (e.g., with vinylacetate) are supplied by, e.g., BASF SE (Germany) under the trademark Kollidon®. Polyoxazolines of different molecular weights are produced and sold by Polymer Chemistry Innovations Inc. (USA) under the trademark Aquazol®.

The above-mentioned cellulose ether can be represented by, e.g., the thermoplastic methyl cellulose, supplied by Dow Chemical Co. (USA) under the trademark Methoce®.

Water-soluble resins are preferably selected in accordance with the requirements of the patent RU No.2182107, i.e. the preferred materials are those, which form a highly dispersed phase in the polyamide.

The content of the water-soluble resin in the above-mentioned at least two layers comprising the polyamide and the water-soluble resin, can vary from 30 to 85%, depending on the casing structure and intended application. Typically, the content of PVA in the proposed casing ranges within 30-50%, however, if the casing is intended for uncooked sausage products, the layer not contacting with the wet sausage meat can comprise from 50 to 85% of PVA.

The compositions of the above-mentioned at least two layers can be different, or similar, or the same. In some cases, it is preferable to have different water-soluble polymers in different layers of the casing. For instance, the use of a blend of polyamide and PVA in the outer layer of the tube, and a blend of polyamide and PVP in the inner layer of the multilayer casing contacting with the contents, can be particularly useful when high permeability and smokability in combination with enhanced adhesion of the casing to the sausage meat is needed.

In some embodiments, above-mentioned layers can comprise up to 10% of other resins, such as insoluble cellulose ester, block-copolymer of polyamide and polyether, block-copolymer of polyester and polyether, block-copolymer of polyurethane and polyether, polyethylene, ethylene/vinylacetate copolymer, and polysiloxane. The above block copolymers can be added, if modification of the elastic properties and transparency of the film is required. Small quantities (up to ~ 2%) of polyethylene, a copolymer of ethylene and vinylacetate, or polysiloxane can be added, e.g., into the meat contact layer, to modify adhesion of the casing to the sausage meat.

Besides the above layers, the casing under the present invention may have at least one additional layer comprising not less than 90% of polyamide resin.

Above multilayer casing can also comprise at least another additional layer preferably made of a blend comprising from 70% to 95% of a polyamide resin and from 5% to 30% of a water soluble resin, instead of, or together with the above additional layer comprising not less than 90% of polyamide resin. Presence in the casing of an additional layer(s) made of a neat polyamide resin and/or a blend of a polyamide resin with a reduced quantity of (at most 30%) a water-soluble resin is sometimes advantageous for improvement of the mechanical properties of the casing, particularly the casing intended for boiled-and-smoked sausages of large diameter. Such a layer (layers) should be preferably made sufficiently thin to not affect the overall vapor permeability of the casing.

Instead of, or together with the above additional layers, the invented casing can comprise layers totally free of (co)polyamides, but comprising such (co)polymers as soluble polyvinyl alcohol, insoluble copolymer of vinyl alcohol (e.g., a copolymer of ethylene and vinyl alcohol - EVOH), insoluble cellulose ester, block-copolymer of polyamide and polyether, block-copolymer of polyester and polyether, block-copolymer of polyurethane and polyether, or any blend of the above (co)polymers. In particular, the invented casing may have a layer or layers made of elastomeric PEBA or PEBA blends with a water-soluble (co)polymer, such as PVA or PVP, of various qualitative compositions. Due to the extremely high moisture-absorbing ability of its components, such layer is particularly useful as the outer layer of the casing for frankfurters and sausages subjected to smoking by dipping into or spraying with liquid smoke.

Such materials as the compositions, where PVA, PVP or PEBA predominate quantitatively, are unsuitable as raw materials for production of an oriented single-layer film, because of insufficient mechanical strength and high moisture sensitivity; besides, such films are unfit for casings comprising food products - for the same reason. Nevertheless, it was unexpectedly found, that such materials and compositions can be successfully used as separate layers of multilayer structures.

Block copolymers of polyamide and polyether are manufactured and sold by, e.g., Arkema S.A. (France) under the general trademark Pebax®.

Block copolymers of polyester and polyether are manufactured and sold by E.I. du Pont de Nemours and Co. (USA) under the trademark Hytrel® and by Royal DSM under the trademark Arnitel®.

Thermoplastic polyurethanes with polyether blocks are manufactured and sold by, e.g., Lubrizol Corp. (USA) under the trademark Estane®.

Above-mentioned at least two layers comprising a polyamide resin and a water-soluble resin can be adjacent or separated by other layers.

The total number of layers in the casing is preferably from 2 to 7. Each layer may additionally comprise at least one additive selected from the group comprising pigments, colorants, highly dispersed fillers, plasticizers, stretching aids, additives for adhesion control of the casing to its contents, and slip agents, or any mixtures thereof.

The above-mentioned plasticizer can be represented by at least one substance selected from the group comprising polyols, polyglycols, polyol esters, N-substituted or unsubstituted aliphatic carboxylic acid amides, and substituted or unsubstituted aliphatic sulfamides.

The total thickness of the casing is preferably from 15 to 70 μιη, i.e. the thickness of the multilayer casing is comparable with that of a single-layer casing. The summarized thickness of the layers comprising polyamide and a water-soluble resin preferably ranges from 10 to 100% of the total thickness of the casing.

As a result of the performed studies it was found that unlike the prior art single-layer films based on blends of (co)polyamide with water-soluble polymers, the multilayer tubular biaxially-oriented casing according to the present invention provides improved smoke and vapor permeability with a WVTR higher than 200 g/m day, while being free of any coarse-grained fillers normally used to achieve a rough surface and to enhance the water vapor transmission rate, such as, e.g., starch or cellulose. Moreover, none of the layers in the invented casing comprise the blend of (co)polyamide, PEBA and PVA in accordance with the patent RU No.2333652 published 20.09.2008, which is characterized by combination of high water vapor transmission rate and smokability with more or less satisfactory mechanical properties. Being used for production of smoked sausages and frankfurters, such casing provides encased sausage with formation of characteristic dense brown crust on its surface and development of marked smoke flavor.

It was also ascertained that a high-capacity production of permeable casings with increased content of a water-soluble polymer became possible only after its reorientation from single-layer casings to multilayer ones with the comparable thickness.

Being both dry and wet the invented casing is characterized by an improved mechanical reliability; this improvement is manifested in significant reduction of its rupture frequency during its stuffing, as compared with its single-layer analogues. In addition, due to the improvement of the mechanical properties of the primary and secondary tubes, it became possible to manufacture the casing on high-capacity equipment on a commercial scale.

It was also found that as the level of polyvinyl alcohol in the layers contacting the contents grows, the adhesion of the casing to the sausage meat decreases, which facilitates removal of the casing off the frankfurters and sausages with the use of automatic peeling machines (or peelers).

The preferred method of manufacture of the casing according to the invention is so called triple-bubble technique.

Typically, the casing according to the present invention is manufactured using extrusion equipment (machines) with several extruders and one multilayer extrusion head, but when the compositions of several layers are the same, one extruder supplying corresponding zones of the multilayer head with the extrudate, can be used for their formation.

The manufactured casing can be used as is or can be cut along one edge or both edges of the flattened tube to make, respectively, a half-tube or two long flat films. The casing can be made straight, curved or ring-shaped, and also can be converted into a shirred stick.

The casing according to the present invention can be used for preparing sausages, frankfurters, pates and cheeses, preferably those which are to be subjected to smoking and/or drying treatment. The suitable smoking techniques can comprise operations of their treatment with natural smoke produced by smoldering hardwood, or with atomized or sprayed liquid smoke. Besides, sausages incased in the invented casings can be smoked by their dipping into the liquid smoke solution, with subsequent thermal processing.

Following description demonstrates some possible embodiments of the present invention. The shown examples have only illustrative character and they unconditionally do not cover the total scope and spirit of the present invention, disclosed by its claims. Embodiments of the invention.

Embodiments of the invention.

Test methods.

1. Evaluation of the water vapor transmission rate

The evaluation is carried out in accordance with DIN 53122 at 23°C and the relative humidity of 85%.

2. Evaluation of smoking effects

The evaluation is performed by 10 experts, who individually assesses the smoking effects (the flavor and crust color) achieved on samples of frankfurters enclosed in different casings under the same smoking conditions, on the scale where «10» corresponds to the effect achieved for frankfurters in the commercially produced NOJAX® cellulose casing supplied by Viskase ' Co. (Darien, Illinois, USA), with the same diameter and thickness as the tested casings, while «0» corresponds to the effect achieved with the use of a casing comprised of PA 6/66 only, with subsequent calculation of the mean value.

3. Evaluation of the weight loss fraction in the process of cooking of frankfurters Weight loss in the production of frankfurters occurs primarily at the stage of smoking / roasting / drying (65-75°C, total time about 50 minutes) due to pervaporation of the water through vapor-permeable casings. Thus, this parameter characterizes the ability of a casing to transmit water vapor under the actual conditions of the sausage product cooking process.

Weight loss (kg) is calculated as the difference between the weight of a string of frankfurters after stuffing and the weight of the same string after final cooking. Weight loss fraction is the ratio of the weight loss to the weight of the string of frankfurters after stuffing, expressed as a percentage.

4. Evaluation of the casing's mechanical reliability

In the process of filling, on a standard stuffing equipment, of a certain quantity of casing, determined by its length L (m), but not less than 500 (m), the calculated value is the average number of breaks (N) per one shirred stick comprising 33 (m) of casing. The casing's reliability R(%) is calculated by the following formula:

33N

R = 100 (1 — ) List of designations and materials used

PVA - trademark Mowiol 5-88®, manufacturer: Kuraray Co., Ltd., Japan;

PA 6/66 - trademark Ultramid C33®, manufacturer: BASF SE, Germany;

PA 6 - trademark Ultramid B33L®, manufacturer: BASF SE, Germany;

PEBA - trademark Pebax®3000 MV, manufacturer: Arkema S.A., (France).

Example 1

A. Preparation of the water-soluble material

PVA (as per definition) was first mixed with 14% of glycerol in a mixer for dry and highly viscous materials, then passed through a twin-screw extruder with a vacuum degassing zone to produce plasticized PVA in the form of cream-colored or yellowish pellets. B. Making of the casing

The hoppers of two extruders operating at the same rate within a single two-layer extrusion machine are being loaded with a blend of 35% of the PVA pellets made in accordance with Section A of this example, and 65% of PA 6/66 pellets for melting and mixing in the extruder. Then the melts are fed into the two-layer head, where the molten two-layer extrudate was formed. After that it was extruded through the ring-shaped die as a tubular film precursor, which was quenched with cold water to temperature 13-15°C resulting in a solidified primary tube with an average thickness of 128 μιη and an average diameter of 7.5 mm. A system of rollers transports the flattened primary tube to the action zone of a flat-wall infrared emitter, where it is heated to the temperature about 80°C, and then passes to the stretching zone. In this zone, the primary tube is subjected to longitudinal and transversal stretching with factors of 2.7 and 3.6, respectively, by means of introduced into the tube compressed air with a positive pressure of about 2 atm, and pair two active nip rollers, which kept this air from leakage and rotated with differing speeds. Next the resulting biaxially stretched tube as a weakly blown bubble is transferred to the action zone of a tubular infrared emitter, where it is heated to 150°C and held at this temperature for 5 seconds. At this stage of annealing or thermosetting, the casing is geometrically relaxed simultaneously with shrinkage of 15% in the longitudinal direction and of 23% in the transversal direction. As a result, a two-layer tubular casing is made with a diameter of 21-22 mm and an average thickness of 20 μηι, suitable for use as a casing for frankfurters which is wound on reels at a speed of ~300 m/min.

Manufacture of 5000 length meters of casing was trouble-free.

The casing is shirred to make stable sticks, as described in the patent RU No.2131670 (published 20.06.1999), and used for production of Molochniye frankfurters. Hereinafter the Molochniye frankfurters are made with the use of a meat emulsion prepared according to the Russian State Standard (hereinafter referred to as GOST) No52196-2003. The manufacturing process for such frankfurters includes high-rate stuffing by use of apparatus "Handtmann", cooking and smoking.

The WVTR of the casing, its behavior during stuffing, and the properties of the end product are shown in Table 3.

Example 2

The hoppers of three extruders operating at the same rate within a three-layer extrusion machine are loaded with the following blends: - Extruder A, which forms the layer adjacent to the inner surface of the tube - 45% of the same PVA pellets as those of Example 1 (section A) and 55% of PA 6 pellets,

- Extruder (B), which forms the intermediate (core) layer - 40% of the same PVA pellets as those of Example 1 (section A) and 60% of PA 6/66 pellets,

- Extruder C, which forms the layer adjacent to the outer surface of the tube - 40% of the same PVA pellets as those of Example 1 (section A) and 60% of PA 6/66 pellets, which are then melted and mixed in these three extruders. After that the melts are fed to the three-layer head, where the molten three-layer extrudate is formed and extruded through an annular die as the primary tube. Then a tubular film comprising three layers of equal thickness is made according to the technique described in Example 1.

Manufacture of 5000 length meters of such tubular casing was practically trouble-free. The casing was also shirred into stable sticks and used to make Molochniye frankfurters.

The WVTR of the casing, its behavior during stuffing, and the properties of the end product are shown in Table 3.

Example 3

The hoppers of three extruders operating at different rates within a three-layer extrusion machine are loaded with three compositions shown in Table 1.

Table 1

Share of the extruder in

Extruder the total production rate Composition

of the machine, %

A 20 Pebax® 3000 MV pellets

45% of the same PVA pellets as those of

B 40 Example 1 (section A) and 55% of PA 6/66 pellets

40% of the same PVA pellets as those of

C 40 Example 1 (section A) and 60% of PA 6/66 pellets Then, according to the technique described in Example 1, a tubular film is made, wherein its three layers with thicknesses proportional to the production rates of the corresponding extruders are sequentially located in the direction from the inner surface of the tube to its outer surface, and the layers' compositions are the same as those in Extruders A to C, respectively.

Manufacture of 5000 length meters of such tubular casing was practically trouble-free.

The casing is also shirred into stable sticks and used to make Molochniye frankfurters.

The WVTR of the casing, its behavior during stuffing, and the properties of the end product are shown in Table 3.

Example 4

The hoppers of the three extruders, which form the layers according to Example 3, are loaded with the following 3 compositions, shown in Table 2. Table 2

Then the casing are made in accordance with Example 3, with the exception that first the primary tube with the thickness of 153 μιη and the diameter of 15.3 mm is extruded as the basis for subsequent preparation of the finished tubular film with the thickness of 24 μηι and the diameter of 45 mm. Manufacture of 5000 length meters of such tubular casing was practically trouble-free.

Casing in the form of rolls was used to produce «Cervelat» raw-smoked sausage, the meat emulsion for which was made according to GOST 16290-86. The sausage stuffed into the casing was subjected to aging at relative humidity 90% and temperature of 4°C during 6 days to allow meat emulsion to get ripened, cold smoking at 20-22°C for 2 days, and drying for 7 days at a temperature of 13-15°C and relative humidity not more than 82%), and more drying during 20-23 days at 10-12°C and air relative humidity not more than 76%.

The WVTR of the casing, its behavior during stuffing, and the properties of the end product are shown in Table 3.

Comparative Example 1

The same polymeric composition as that of Example 1 (Section B) is loaded into the hopper of the single-layer extrusion machine (manufactured by Ankele Kunststoffmaschinenbau GbR, Germany) with the nominal capacity equal to the total production rate of the three extruders in Example 1, melted and mixed in the extruder, then fed to the single-layer head for extrusion through an annular die, as the primary tube. Then it is attempted to make a single-layer tubular film according to the technique described in Example 1 and at the same production rate. The attempts to manufacture a single-layer tubular film failed, because of repeated breaks of the tubular film at the stage of orientation stretching.

Then the production rate of the extruder and, consequently, of the entire line is reduced thrice. Still, even after that the manufacture of a single-layer tubular film is accompanied by its frequent breaks. Having spent the same quantity of raw materials as that of Example 1 , we succeeded in manufacturing only about 500 length meters of such tubular film.

The casing is also shirred into stable sticks and used to make Molochniye frankfurters.

The WVTR of the casing, its behavior during stuffing, and the properties of the end product are shown in Table 3. Comparative Example 2

A single-layer tubular film is made in accordance with Comparative Example 1 at the same production rate, with the exception that the hopper of the single-layer extrusion machine is loaded with 40% of PVA pellets made as described in Section A of Example 1 , and 60% of PA 6/66 pellets. Because of repeated breaks of the tubular film at the stage of orientation stretching, no casing is manufactured. For this reason, its properties are not shown in Table 3.

Analysis of Comparative Examples 1 and 2 shows that a single-layer permeable casing with a content of a water-soluble resin higher than 30% is either impossible to be made at all, or possible to be made only at a production rate and with losses of raw materials and work time unacceptable for commercial-scale production.

Comparative Example 3

A single-layer tubular film is made in accordance with Comparative Example 1 at the same production rate, with the exception that the hopper of the single-layer extrusion machine is loaded with 25% of PVA pellets made in accordance with Section A of Example 1, and 75% of PA 6/66 pellets.

Manufacture of 5000 length meters of this tubular casing proceeded satisfactorily. Due to infrequent breaks at the stage of stretching, the amount of raw materials consumed is about 5% greater than that of Example 1.

The casing is also shirred into stable sticks and used to make Molochniye frankfurters.

The WVTR of the casing, its behavior during stuffing, and the properties of the end product are shown in Table 3. Comparative Example 4

A single-layer tubular film is made according to Comparative Example 1, with the exception that the hopper of the single-layer extrusion machine is loaded with 100% of PA 6/66 pellets.

The casing is also shirred into stable sticks and used to make Molochniye frankfurters. The WVTR of the casing, its behavior during stuffing, and the properties of the end product are shown in Table 3.

Comparative Example 5

The NOJAX® cellulose casing with the diameter of 22 mm and in the form of shirred sticks is used to manufacture the same Molochniye frankfurters as those of Example 1.

Comparative Example 6 The "Fibrose" fiber-reinforced cellulose casing with the diameter 22 mm and in the form of a roll is used to manufacture «Cervelat» raw-smoked sausages according to the technique described in Example 4.

Table 3

Stuffing Crust Share in

Example, WVTR, Smoke

(mechanical color and weight loss, No. g/m day flavor

reliability) density %

Without breaks

1 205 5.9 4.7 9.5

(-100%)

Without breaks

2 225 8.2 6.9 1 1.3

(-100%)

Without breaks

3 256 8.5 7.4 12.1

(=100%)

Without breaks

4 520 8.9 9.5 8.8

(=100%)

Comparative Frequent breaks

198 5.9 3.9 9.0 1 (=21%)

Comparative

No sample obtained

2

Comparative Almost without

150 3.5 1.2 7.3 3 breaks (=80%)

Comparative Without breaks

85 0 0 5.1 4 (=100%)

Comparative Without breaks

724 10 10 13.5 5 (=100%)

Comparative Without breaks

550 10 10 9.0 6 (=100%) The data shown in the Table confirm the conclusion that the object of the present invention has been successfully achieved.