[BACKGROUND ART] Foods, such as sausage and ham, are generally prepared by filling a film casing with a pasty meat material, and the thus-packaged meat material is heated for sterilization and cooking, before provision to the market. The casing (film) for packaging these foods is required to satisfy the following properties in the course of production and circulation of the foods.

(a) Strength and rigidity: required as basic properties for preventing a puncture due to an internal pressure increase during the filling and

heating of the pasty meat material, and preventing the breakage in resistance to an external stress applied during the handling of the food products.

(b) Thermal creep resistance: required so as to prevent the deformation in the course of heating and storage after filling with the content material.

Generally, the packaged product obtained by filling with the content material is subjected to heating in the state of being hung down, and if the product shape is remarkably deformed from a cylindrical shape due to its own weight, the merchandise appearance and value are remarkably impaired. As will be described later, this property is evaluated in terms of a hot-water creep characteristic or a hung deformation ratio as a practical evaluation term.

(c) Gas barrier property: required to prevent the deterioration of content material due to oxidation.

(d) Shirrability: In order to improve the efficiency of filling a casing with a pasty processed meat, shirring of the casing is frequently performed as a processing of folding a longer casing into a shorter form of bellows. In this instance, the shirrability is desired as a property of preventing the occurrence of pinholes, inter-layer peeling or layer breakage.

(e) Water vapor-barrier characteristic: required to prevent a moisture loss during distribution of the

sausage or ham product, as the weight loss not only results in a direct economical loss but also leads to a deterioration of meat quality.

(f) Meat adhesion: This is a property for a casing to adhere to the content meat at its inside film boundary and required to suppress the occurrence of gravy or meat juice at the boundary and prevent the spreading of rotting.

(g) Heat-shrinkability: required to prevent the occurrence of wrinkles at the product casing surface liable to give an impression of merchandise deterioration.

For the purpose of imparting (d) the heat- shrinkability and improving (a) the strength and rigidity, (b) the thermal creep resistance, etc., it has been ordinarily practiced to effect uniaxial or biaxial stretching of a casing heated to a temperature above the glass transition temperature.

It is difficult to compose a casing satisfying the above-mentioned properties with a single layer, so that a multilayer casing film having a plurality of component layers is ordinarily used.

As an example of such a trial, there has been proposed a polyamide-based multilayer casing film having an outer and an inner layer comprising principally a polyamide resin excellent in the above-mentioned (a) strength and rigidity, (b) thermal creep resistance,

(c) gas-barrier property and (d) meat adhesion, and an intermediate non-polar polyolefin layer for improving the water vapor-barrier characteristic (International Publications WO 95/13707 and WO 00/59724).

However, the above-mentioned multilayer casing films do not necessarily have a good balance among the properties of the inner and outer polyamide layers or are not satisfactory with respect to the above-mentioned properties, of e. g., (a) strength and rigidity and (b) thermal creep resistance required of a multilayer casing film due to the use of a partially aromatic polyamide (represented by a polyamide comprising component units of metaxylylene-adipamide (generally called"nylon MXD6") incorporated for the purpose of improving the stretchability of a polyamide layer (WO 95/13707), or the use of a copolymer nylon 6-66 layer (WO 00/59724).

[DISCLOSURE OF INVENTION] A principal object of the present invention is to provide a polyamide/polyolefin-based multilayer casing film satisfying the above-mentioned properties required of a multilayer casing film by utilizing nylon 6 that is the most frequently used polyamide resin to the highest degree.

The nylon 6-based multilayer casing film according to the present invention has been developed

so as to achieve the above-mentioned object, and comprises two polyamide layers of (a) an outer polyamide layer and (b) an inner polyamide layer, and (c) a non-polar polyolefin layer sandwiched between a pair of adhesive polyolefin layers disposed between the outer polyamide layer (a) and the inner polyamide layer (b), wherein 1) the outer polyamide layer (a) comprises nylon 6, 2) the inner polyamide layer comprises a (co-) polyamide, 3) the outer polyamide layer (a) has a thickness which is 1 to 4.5 times that of the inner polyamide layer (b), and 4) the non-polar polyolefin layer (c) has a thickness which is equal to or smaller than that of the outer polyamide layer (a).

The present invention also provides a process for producing a nylon 6-based multilayer casing film, comprising the steps of: providing a co-extruded and cooled tabular product having a laminar structure including (a) another polyamide layer comprising nylon 6, (b) an inner polyamide layer comprising a (co-) polyamide, and (c) a non-polar polyolefin layer sandwiched between a pair of adhesive polyolefin layers and having a thickness equal to or smaller than that of the outer

polyamide layer (a), the outer polyamide layer (a) having a thickness which is 1 to 4.5 times that of the inner polyamide layer (b), re-heating the tubular product through a warm water bath within at most 5 seconds, inflating the tubular product while externally heating the tubular product to biaxially stretch the tubular product, and heat-treating the inflated tubular product from its outer polyamide layer (a) to anneal the inflated tubular product.

Some history and details as to how we have arrived at the present invention as a result of study for achieving the above object, will now be briefly described.

Nylon 6 is a representative of general- purpose aliphatic polyamides, and it is well known that a film thereof is excellent in (a) strength and rigidity, (b) thermal creep-resistance and (f) meat adhesion and also has (c) good gas-barrier characteristic. However, in the case of providing a nylon 6/polyolefin laminate film by lamination with a non-polar polyolefin layer for also imparting (e) the water-vapor barrier characteristic, it has been considered very difficult to co-stretch the nylon 6/polyolefin laminate film. A first reason therefor is that the inter-layer adhesion between these two

layers is poor, so that an effective stretching thereof becomes difficult due to frequent occurrence of peeling between these layers. However, this difficult has been already solved, e. g., by inserting an adhesive polyolefin layer modified by introduction of acidic group between the two layers (WO 95/13707 and WO 00/59724). A second and more essential reason is that nylon 6 has a considerably high melting point (e. g., 225 °C) compared with polyolefins (typically having melting points of ca. 110-170 °C) and a noticeable crystallizability. Accordingly, it has been extremely difficult to find out a condition for effective co-stretching of a nylon 6/polyolefin laminate film while suppressing crystallization harmful to the stretching. Accordingly, the above- mentioned WO 95/13707 has proposed to solve the problem by incorporating a partially aromatic polyamide (polyamide or nylon MXD6). The partially aromatic polyamide has a better gas-barrier property than nylon 6 and therefore well functions also for providing an improvement in (c) gas-barrier property.

However, the partially aromatic polyamide is a special polyamide resin, and the inclusion thereof not only is uneconomical but also is liable to impair (a) the strength and rigidity that is the greatest characteristic of nylon 6. Further, the partially aromatic polyamide is liable to be affected by the

moisture, and can fail to well exhibit its characteristic gas-barrier property if it is used in a large amount in the inner polyamide layer contacting the pasty content material. Accordingly, based on a premise of using an identical polyamide composition for both the outer polyamide layer and the inner polyamide layer, WO 95/13707 has adopted a large thickness ratio of 4.6: 1 (in Examples), but this is not necessarily desirable particularly in view of a balance of mechanical properties which is principally governed by the outer polyamide layer and the inner polyamide layer. (For example, the film is liable to be curled, so that the operation of filling with the pasty content material becomes difficult. More specifically, for example, the clipping for tight sealing of the casing film ends after the filling becomes difficult.) On the other hand, WO 00/59724 has solved the difficulty of co-stretching of a nylon 6/polyolefin laminate film by a combination of one layer of nylon 6 and a thicker layer of another polyamide. This can solve several of the above-mentioned problems accompanying the use of a partially aromatic polyamide, but this modification functions to lower (a) the strength and rigidity and (b) the thermal property which are characteristic of nylon 6 and also inevitably results in an inferior performance in

respect of (c) the gas-barrier property compared with a structure principally comprising a nylon 6 layer.

In contrast thereto, as a result of our study, it has been found possible to solve the difficulty of co-stretching of a nylon 6/polyolefin laminate film by using a nylon 6/polyolefin laminate film including an outer polyamide layer comprising nylon 6 as a principal polyamide layer and having a thickness equal to or larger than that of the polyolefin layer and subjecting the nylon 6/polyolefin laminate film once co-extruded and cooled to a sequence of heating to a stretching temperature within an extremely short period (e. g., dipping in a warm bath at 70-80 °C within 5 seconds) and stretching immediately thereafter, thus affording appropriate co- stretching conditions. Based on the knowledge, we have arrived at the present invention. As a result, the multilayer casing film of the present invention enjoying the benefits of the nylon 6-based polyamide/polyolefin multilayer film to the maximum, has been obtained.

[DESCRIPTION OF THE PREFERRED EMBODIMENTS] According to a basic layer structure, the multilayer casing film of the present invention comprises two polyamide layers of (a) an outer polyamide layer and (b) an inner polyamide layer, and

(c) a non-polar polyolefin layer sandwiched between a pair of adhesive polyolefin layers disposed between the two polyamide layers (a) and (b).

The outer polyamide layer (a) comprises nylon 6 which is particularly excellent in strength, rigidity, thermal creep resistance and meat adhesion, and also retains a good gas-barrier characteristic.

The melting point thereof is generally on the order of 220-230 °C. It is preferred that the outer polyamide layer consists essentially of nylon 6 alone (i. e., except for optional additives, such as a lubricating agent and a nucleating agent), but another resin can be co-used within an extent of not exerting adverse effects thereby, more specifically in an amount of at most ca. 10 wt. %, preferably up to ca. 5 wt. %. Representative examples of such another resin may include other polyamide resins constituting the inner polyamide layer (b) described below.

The inner polyamide layer (b) comprises a (co-) polyamide, i. e., a polyamide homopolymer or copolymer, and most preferably comprises nylon 6 similarly as the outer polyamide layer (a), but it is also possible to use nylon 6-66, nylon 6-69, nylon 61 (polyhexamethylene isophthalamide), etc., in addition to nylon 6. It is preferred that the melting point is at least 180 °C, more preferably at least 200 °C. In addition to the (co-) polyamide, it is possible to mix

at most 30 wt. %, preferably up to 10 wt. %, of another resin. Representative examples of such another resins are other polyamides, examples of which may include: nylon 66, nylon 69, nylon 612, nylon MXD6, nylon 61 (polyhexamethylene isophthalamide), nylon 6T (polyhexamethylene terephthalamide), nylon 66-6I, nylon 6-69, nylon 66-610-MXD6, and nylon 6I-6T.

In the present invention, so as to most effectively enjoy the properties of nylon 6 constituting the outer layer, the outer polyamide layer (a) has a thickness which is 1-4.5 times, preferably more than 1 and at most 4.0 times, further preferably 1.2-3.0 times, that of the inner polyamide layer (b). That is, the outer polyamide layer (a) requiring utmost degrees of mechanical strength, rigidity and thermal creep resistance, has a thickness which is equal to or larger than that of the inner polyamide layer (b). However, if the thickness of the outer polyamide layer (a) exceeds 4.5 times the thickness of the inner polyamide layer (b), the product multilayer casing film is liable to curl at the time of filling with a pasty content material, thus causing difficulties, such as difficulty in clipping for tight sealing of casing ends.

Particularly, in the case of effecting warm water heating prior to the heat-stretching, the crystallization of the outer polyamide layer (a) is

promoted by moisture absorption, whereby the stretching is obstructed due to an excessively large expansion force at the time of heat stretching.

A non-polar polyolefin layer (c) sandwiched between a pair of adhesive polyolefin layers is disposed between the above-mentioned two polyamide layers (a) and (b). The non-polar polyolefin layer (c) is disposed to ensure a water vapor-barrier characteristic of the product multilayer casing film, but the thickness thereof is suppressed to at most the thickness of the outer polyamide layer (a). The lower limit of the thickness may preferably be at least 30 %, particularly at least 50 %, of the outer polyamide layer (a), from the viewpoint of a required water vapor-barrier characteristic.

The non-polar polyolefin resin constituting the non-polar polyolefin layer (c) may be a polyolefin homopolymer or copolymer. The melting point may be at least 80 °C, preferably 110 °C or higher. Specific examples thereof may include : ethylene-a-olefin copolymers, such as VLDPE (very low-density polyethylene), and LLDPE (linear low-density polyethylene); and polypropylene resins, such as PP (polypropylene), PP-Et (propylene-ethylene copolymer), and PP-Et-But (propylene-ethylene-butene copolymer).

In case where LLDPE, PP or PP copolymer having a relatively excellent heat resistance is used as the

non-polar polyolefin resin constituting the non-polar polyolefin layer (c), the product multilayer casing film tends to have an improved thermal creep resistance.

It is possible to color (c) the non-polar polyolefin layer (c) by blending a colorant to the non-polar polyolefin resin. This embodiment is preferred in order to alleviate thermal deterioration of the colorant than the embodiment of coloring the polyamide layer (a) or (b), and is preferred in order to alleviate the lowering in extrudability than the embodiment of coloring the adjacent adhesive polyolefin layers.

The non-polar polyolefin layer (c) is sandwiched between a pair of adhesive polyolefin layers and then disposed between the above-mentioned polyamide layers (a) and (b). The adhesive polyolefin layers are effective in ensuring the intimate adhesion of the non-polar polyolefin layer (c) which is inherently poor in adhesiveness, to the adjacent layers, particularly the polyamide layer (a) or (b), thereby preventing the inter-layer peeling during the stretching step or the shirring step, and also in improving the pin-hole resistance of the product multilayer casing film. However, such an adhesive polyolefin layer has a rather low cohesion strength, and a thick layer thereof makes it difficult to

increase the strength because of cohesion breakage of the adhesive polyolefin layer per se. It may be possibly conceived of to provide a single adhesive polyolefin layer having a water vapor-barrier characteristic by mixing an adhesive polyolefin resin and a non-polar polyolefin resin and disposing the adhesive polyolefin layer between the polyamide layers (a) and (b). In this case, however, the adhesive effect intended by the adhesive polyolefin layer is lowered, so that it is difficult to attain the desired properties. Accordingly, it is preferred to functionally separate the adhesive polyolefin layer and the non-polar polyolefin layer (c), and dispose the non-polar polyolefin layer in a form of being sandwiched with a pair of the adhesive polyolefin layers between the polyamide layers (a) and (b).

The adhesive polyolefin resin constituting the adhesive polyolefin layers may comprise at least one species of adhesive polyolefin resin, selected from acid-modified ethylene-a-olefin copolymers and acid-modified polypropylene-based resins, inclusive of, e. g., acid-graft-modification products of VLDPE, LLDPE, PP, PP-Et and PP-Et-But.

According to a most preferred embodiment, the multilayer casing film of the present invention is caused to have a 5-layered structure comprising the above-mentioned outer polyamide layer (a) and inner

polyamide layer (b), and the non-polar polyolefin layer (c) sandwiched with a pair of the adhesive polyolefin layers disposed between the polyamide layers (a) and (b). As a result, it is possible to attain a multilayer casing film having a good harmony among the above-mentioned properties (a)- (f) required of a multilayer casing film for a pasty content material. It is however possible to insert an additional layer, as desired, in order to strengthen a part of the above-mentioned properties, or for another purpose.

For example, it is possible to insert an intermediate layer of EVOH (ethylene-vinyl acetate copolymer saponification product), nylon MXD6, etc., in order to strengthen the gas-barrier property.

Further, it is a most preferred form of the multilayer casing film according to the present invention that the outer polyamide layer (a) constitutes the outermost layer of the multilayer casing film, but the outer polyamide layer (a) can be subjected to a printing treatment or provided with a matte-finish layer as the outermost layer. Such an outermost matte-finish layer may also be preferably formed as a polyamide resin-based layer. In case where the matte-finish layer comprises nylon 6, the thickness thereof is included as a part of the outer polyamide layer (a) thickness. For the purpose of

matting, an inorganic material or organic material in the form of fine particles of at most 20 urn in diameter may be added, and specific examples thereof may include fine particles of silicon oxide compounds, such as silica, talc and mica, and volcanic expanded particles (so-called"shirasu balloon"in Japanese) as inorganic materials. Specific examples of organic materials may include fine particles of thermoplastic resins, such as VLDPE, LLDPE, LDPE, EVA, EEA, EAA, EMA, EMAA, MMA, and MAA.

Further, it is also possible to add an inorganic or/and organic material as a lubricating agent or a nucleating agent to the polyamide layer (a) or/and the polyamide layer (b) in order to improve the processability of the product multilayer casing film.

The multilayer casing film of the present invention may preferably be formed as a multilayer casing film having a total thickness (as a single sheet) of 15-120 urn, more preferably 25-80 urn.

For the respective layer thicknesses, the layer (a) may have a thickness of 7-80 urn, preferably 10-40 urn ; and the layer (b) may have a thickness of 2 - 18 µm, preferably 3-12 urn. The non-polar polyolefin layer (c) may have a thickness of 7-25 pm, preferably 12-20 urn. Each adhesive polyolefin layer may have a thickness of ca. 0.5-5 urn. The gas-barrier layer may be disposed as desired

depending on the desired level of gas-barrier property in a thickness for satisfying the desire as a lower limit. The upper limit may be determined depending on the stretchability. In view of these factors, the gas-barrier layer may generally have a thickness of ca. 1-20 urn, preferably ca. 2-10 pm.

The multilayer casing film may preferably be formed to have a lay-flat width of 50-600 mm, particularly 100 mm or larger so as to be suitable for providing a sausage casing subjected to hung-down heating.

The multilayer casing film of the present invention may preferably be formed through a process wherein a plurality of extruders are provided corresponding to a necessary number of starting resin species (equal to or less than a number of laminated layers since some layers can be formed of a common starting resin (mixture)) and the respective resins from the extruder are co-extruded through an annular die to form a tubular sheet before stretching (called a"parison"), which is then biaxially stretched by inflation into a casing film. The stretching ratio may preferably be ca. 2-4 times in each of vertical or machine direction (MD) and transverse or lateral direction (TD) so as to ensure a hot water- shrinkability at 90 °C of a least 5 %, particularly 10 % or higher, and also ensue a strength of nylon 6

constituting the layer (a) (and (b)). More specifically, the parison co-extruded through the annular die is cooled down to a temperature which is below the melting points of the respective layer resins by applying water onto the outer surface of the parison, and then moved to an orientation region where the parison is re-heated to a temperature allowing the stretching. In this instance, it is important that the re-heating is performed quickly (e. g., passing the parison through a warm water bath at 70-80 °C within 5 sec., preferably ca. 2-3 sec.) so as not to promote the crystallization of nylon 6. Then, the pre-heated parison is pulled vertically (e. g., upwards) to form a bubble of tubular film with fluid air introduced into the bubble between pinch rollers, whereby the tubular film is biaxially stretched simultaneously at a ratio of 2-4 times in each of the machine direction (MD) and the transverse direction (TD), while subjecting the tubular film to auxiliary heating with warm air at 80-100 °C blown through an air ring toward the circumference of the tubular film. The thus-biaxially stretched tubular film is then subjected to an annealing treatment at a temperature of 60-100 °C so as to cause a relaxation of 0-10 % in each of MD and TD, thereby proving a tubular biaxially stretched multilayer casing film according to the present invention. Incidentally, in

order to provide a good thermal creep resistance (e. g., a hot water creep of at most 25 %, preferably at most 20 %, in MD and a smaller hot water creep than in MD of at most 20 %, preferably at most 15 %, in TD according to a hot water creep test described hereinafter), it is preferred to effect the annealing at a temperature exceeding 90 °C so as to cause a relaxation ratio of below 5 %. Such an annealing condition has been difficult to adopt for a polyamide- based multilayer casing film comprising copolymer nylon as a principal layer component, because it causes a size change of the multilayer casing film after the production and before the filling with a content material.

The above-mentioned casing film production process may be performed by using an inflation apparatus system similar to the one disclosed in WO 01/98081 except for temperature conditions around the inflation step mentioned above.

The heating methods for the stretching and annealing are not limited to those described above.

For example, the heating may be effected by infrared ray heater, or with hot air or steam.

[Examples] Hereinbelow, the present invention will be described more specifically based on Examples and Comparative Examples.

The following measurements were applied to resins used and resultant multilayer casing films in Examples and Comparative Examples, and the above- mentioned properties of the multilayer casing film of the present invention are also based on the results of the measurement.

(1) Melting point (Tm) of resin (DSC) Ca. 10 mg of a measurement sample is accurately weighed and heated at a temperature-raising rate of 20 °C/min by means of differential scanning calorimeter ("DSC7", made by Perkin-Elmer Corp.) to obtain a heat-absorption peak on which a peaktop temperature is determined as a melting point. In the case of plural peaks, a principal peak is taken, and the peaktop temperature thereof is measured as a resin melting point (Tm).

(2) Hot-water creep A sample strip (having a length (MD) x a width (TD) = 150 mm x 20 mm) and a sample strip (having a length (TD) x a width (MD) = 150 mm x 20 mm) are cut out from a sample multilayer casing film by slitting and are respectively marked with a distance in a lengthwise direction for 100 mm. Each sample strip is hung down with a weight attached to its lower end so as to apply a stress of 1 kg. f/mm2 and then dipped for 10 sec. in hot water at 80 °C to measure an elongated length. The elongated length is then

expressed in percentage (%) with respect to the original length (=100 mm). The above measurement is performed 5 times for each sample multilayer casing film, and averages of 5 measured values for the respective directions are expressed in a style of, e. g., 20/15 (MD/TD) (%), indicating hot water creeps of 20 % in MD and 15 % in TD.

(3) Hot-water shrinkability A sample film on which marks are indicated at a distance therebetween of 10 cm in each of a machine direction (MD) and a transverse direction (TD) perpendicular to the machine direction, is dipped for 10 sec. in hot water adjusted at 90 °C and then taken out therefrom, followed by immediate quenching within water at room temperature. Thereafter, the distance between the marks is measured and a decrease in distance is indicated in percentage of the original distance 10 cm. Five sample films from each product film are subjected to the above measurement, and the average value of percentage decrease is indicated in each of the MD and TD in a style of, e. g., 12/15 (MD/TD)(%).

(4) Gas-barrier property An oxygen gas transmission rate through a sample film is measured by using an oxygen gas transmission meter ("MOCON OXTRAN Model-100", made by Modern Controls Co.) in an atmosphere of 30 °C/100 %

RH and indicated in a unit of (cm3/m2.day.atm).

(5) Water vapor-barrier characteristic (WVTR) A water vapor-transmission rate (WVTR) through a sample film is measured by using a water vapor transmission meter ("MOCON PERMATRAN Model- 3/31", made by Modern Controles Co.) in an atmosphere of 40 °C/90 % RH and indicated in a unit of (g/mZ. day) (6) Meat packing test A sample casing is filled with 2.3 kg of pasty sausage meat in a length of ca. 43-44 cm between clips so as to achieve an overfilling of 110 %, and after being clipped at upper and lower ends, the filled casing is heat-treated for 120 min. in a smoke chamber at 80 °C, immediately followed by cooling with water for 10 min. and standing for 1 day in a form of being hung in a refrigerator at 5 °C.

The thus-treated sausage-filled casing is evaluated with respect to the following items.

(6a) Thermal creep resistance (Hanging deformation) With respect to a sausage-filled casing sample treated in the above-described manner, a deformation (%) defined as follows is calculated.

A deformation (%) = [(a eircumferential length at a point 5 cm above the lower clip)- (a circumferential length at a point 5 cm below the upper clip)] x 100/ (the circumferential length at the point 5 cm above the lower clip). A

deformation (%) of at most 7 % is a level of deformation which cannot be substantially recognized by observation with eyes.

(6b) Weight loss A sausage-filled casing sample after the above treatment is left to stand for one month in an environment of 23 °C/50 % RH, and the weight loss (%) of the filling sausage is measured are evaluated according to the following standard.

A: The sausage weight loss is below 2 % in one month B: The sausage weight loss is 2 % or more in one month.

(7) Shirrability The shirrability of a casing film is evaluated based on the easiness of shirring (a processing for conversion into a form of bellows for facilitating the filling with a pasty content material) according to the following standard.

A: A casing is flexible and effectively shirrable, resulting in no recognizable inter-layer peeling or pinholes after the shirring.

B: A casing is shirrable, not resulting in inter- layer peeling or pinholes but being curled so that the tight sealing by clipping becomes difficult.

C: A casing is too hard to be sufficiently folded.

(8) Stretchability

A casing film is formed through a process under conditions described in an Example or Comparative Example below, and a state of inflation bubble formation is observed with eyes and evaluated according to the following standard.

A: An inflation bubble somewhat pitches up and down, but can be stably formed.

B: An inflation bubble vigorously pitches up and down, or cannot be formed due to insufficient stretching.

(Examples and Comparative Examples) In each Example or Comparative Example, a plurality of resins selected so as to provide a layer structure shown in any one of Tables 1-3 appearing hereinafter (indicated in the order of lst., 2nd.,... from the inside to the outside) with resins indicated by abbreviated symbols, of which the meanings are described hereinafter, were extruded and formed into a casing film, thereby obtaining various multilayer casing films.

More specifically, the respective resins for providing a multilayer casing film were extruded through separate extruders and introduced into an annular die to be co-extruded into a parison having a laminated structure. The parison was then cooled by showered cool water and formed into a tubular form corresponding to a lay-flat width in a range of 19-

74 mm. The resultant parison was caused to pass through a warm water bath at 70-80 °C in 2 to 3 sec., and biaxially stretched simultaneously in 2.0 to 3.0 times in a machine direction (MD) and 2.5 to 3.8 times in a transverse direction (TD) by inflation, followed by annealing at a temperature in a range of 60-100 °C for causing relaxation of 0-10 % in MD and 0-10 % in TD. The resultant biaxially stretched tubular casing film had a lay-flat width in a range of 50-210 mm and a thickness in a range of 35-50 urn.

The abbreviation symbols used in Tables 1-3 for indicating the used resins respectively have the following meanings.

<Polyamide (co) polymers> (inner layer and outer layer) Ny 6.1: nylon 6;"AMILAN CM-1021XF", made by Toray K. K.; (Tm = 225 °C) Ny 6.2: nylon 6;"NOVAMID 1020", made by Mitsubishi Engineering Plastic K. K.; (Tm = 224 °C) Ny 6.3: nylon 6;"NOVAMID 1020A", made by Mitsubishi Engineering Plastic K. K.; (Tm = 224 °C).

Ny 6.4: nylon 6 ;"NOVAMID 1020J", made by Mitsubishi Engineering Plastic K. K.; (Tm = 224 °C).

Ny 6.66: nylon 6-66,"AMILAN CM-6041XF", made by Toray K. K.; (Tm = 195 °C) Ny 6.12: nylon 6-12,"AMILAN CM-6541X3", made by Toray K. K; (Tm = 133 °C).

(Note) :"*"used in"Ny 6.1*","Ny 6.3*", etc.

indicates that it contains 5 wt. % of a lubricant master batch ("PEM-7Y 1442", made by Sumika Color K. k.; a mixture of polyethyl acrylate base polymer with 6 wt. % of CaCo3).

<Polyolefin resin> (intermediate layer) VLDPE. 1 : VLDPE ;"MORETEC VO 398CN", made by Idemitsu Sekiyu Kagaku K. K.; (Tm = 122 °C) LLDPE. 1 : LLDPE;"MORETEC 0238 CN", made by Idemitsu Sekiyu Kagaku K. K.; (Tm = 122 °C) LLDPE. 2; LLDPE;"MORETEC 0248CN", made by Idemitsu Sekiyu Kagaku K. K.; (Tm = 123 °C) LLDPE. 3; LLDPE;"MORETEC 0258CN", made by Idemitsu Sekiyu Kagaku K. K.; (Tm = 122 °C) PP-Et. l : PP-Et copolymer;"SUN AROMER PC741R", made by Montel SKD Sunrise Co.; (Tm = 133 °C).

PP-Et. 2: PP-ET copolymer,"SUN AROMER PF 631S", made by Montel SKD Sunrise Co.; (Tm = 142 °C) <Gas-barrier resin> (intermediate layer) EVOH: EVOH;"EVAL EP-G156B", made by Kuraray K. K; (Tm = 158 °C) <Adhesive polyolefin resin> m-VL. 1 : acid-modified VLDPE;"ADMER NF587", made by Mitsui Kagaku K. K.; (Tm = 123 °C). m-PP. 1 : acid modified PP;"MODIC AP P504V" ; made by Mitsubishi Kagaku K. K.; (Tm = 140 °C) m-VL. 2: acid modified VLDPE;"MODIC AP OF102", made by Mitsubishi Kagaku K. K.; (Tm = 120 °C).

m-VL. 3: acid-modified VLDPE;"ADMER SF 730", made by Mitsui Kagaku K. K.; (Tm = 118 °C). m-PP. 2: acid-modified PP;"MODIC AP P505", made by Mitsubishi Kagaku K. K.; (Tm = 138 °C) m-PP. 3: acid-modified PP:"ADTEX ER333F-2", made by Nippon Polyolefin K. K; (Tm = 134 °C) m-PP. 4: acid-modified PP;"ADMER QF551", made by Mitsui Kagaku K. K. (Tm = 135 °C).

Table 1 Example 1 Example 2 Example 3 Example 4 Layer structure 1st. Layer Ny6.3* (8) Ny6.3* (8) Ny6.3* (8) Ny6.3* (8) (IN) 2nd. Layer m-PP.4(1.75) m-PP.3(1.75) m-VL.3 (1.75) m-PP.4 (1.75) 3rd. Layer PP-Et.1 (15) PP-Et.1 (15) PP-Et.1 (15) PP-Et.1 (15) 4th. Layer m-PP.4 (1.75) m-PP.3 *(1.75) m-VL.3 (1.75) m-PP.4 (1.75) 5th. Layer Ny6.3 (22) Ny6.3 (22) Ny6.3 (22) Ny6.3 (15) Ny6-66+silica 6th. Layer - - - (OUT) 10 wt.% (5) Evaluation items Stretchability A A A A Hot water creep 10/10 21/7 21/8 13/12 (%) Hot water shirnk 13/11 15/16 14/14 13/13 (%) O2TR(cm3/ 220 220 220 250 m2#day#atm) WVTR (g/ 18 18 18 16 m2#day) Hanging deformation 4 6 6 5 (%) Weight loss A A A A Shirrability A A A A Process conditioins Stretch (times) 2.6/3.1 2.6/3.1 2.6/3.1 2.6/3.1 Anneal temp. 95°C 92°C 91°C 96°C Relaxation (%) 1/0 4/0 4/0 1/0 Numeral in ( ) represents a thicknes sin µm. Numerals separated by "/" (slush) represent<BR> values measured inMD and TD, respectively.<BR> <P>"*" in e. g. "Ny6. 3" represents that Ny6.3 contains 5 wt. % of lubricant maste rbatch.

Table 2 Example 5 Example 6 Example 7 Example 8 Layer structure 1st. Layer Ny6.2* (8) Ny6.4* (5) Ny6.3* (5) Ny6-66* (8) (IN) 2nd. Layer m-VL.1 (1.75) m-VL.1 (1.75) m-PP.4 (1.75) m-PP.4 (1.75) 3rd. Layer LLDPE.1 (15) LLDPE.1 (18) PP-Et (17) PP-Et (15) 4th. Layer m-VL.1 (1.75) m-VL.1 (1.75) m-PP.4 (1.75) m-PP.4 (1.75) 5th. Layer Ny6.2 (22) Ny6.3 (20) EVOH (4.5) Ny6.3 (22) (OUT) 6th. Layer - - Nh6.3 (18) - Evaluation items Stretchability A A A A Hot water creep 23/11 16/14 16/13 23/18 (%) Hot water shrink 14/14 13/13 15/14 15/16 (%) O2TR (cm3/ 260 240 80 280 m2#day#atm) WVTR (g/ 24 22 20 18 m2#day) Hanging deformation 7 5 6 - (%) Weight loss A A A - Shirrability A B A - Process conditions Stretch (times) 2.6/3.1 2.9/2.9 2.8/3.2 2.6/3.1 Anneal temp. 91°C 97°C 95°C 95°C Relaxation (%) 6/6 1/0 2/0 1/0 Table 3 Comp. Ex.1 Comp. Ex. 2 Comp. Ex. 3 Comp. Ex. 4 Layer structure 1st. Layer Nh6.1* (5) Ny6.3* (5) Nh6.1 (5) Nh6.1* (8) (IN) 2nd. Layer m-VL.1 (1.75) m-PP.4 (1.75) m-VL.1 (1.75) m-VL.1 (1.75) 3rd. Layer VLDPE.1 (20) LLDPE.3 (20) VLDPE.1 (18) PP-Et.2 (25) 4th. Layer m-VL.1 (1.75) m-PP.4 (1.75) m-VL.1 (1.75) m-VL.1 (1.75) 5th. Layer Ny6-66 (20) Ny6.3 (25) EVOH (4.5) Ny6.3 (20) (OUT) 6th. Layer - - Ny6-66 (18) Evaluation items Stretchability A B A B Hot water creep 38/21 - 36/27 - (%) Hot water shrink 20/19 - 20/18 - (%) O2TR (cm3/ 350 - 100 - m2#day#atm) WVTR 9g/ 28 - 23 - m2#day) Hanging deformation 23 - 13 - (%) Weight loss A - A - Shirrability A - A - Process conditions Stretch (times) 2.5/3.1 - 2.8/3.2 - Anneal temp. 81°C - 81°C - Relaxation (%) 6/7 - 5/9 -

[INDUSTRIAL APPLICABILITY] As described above, according to the present invention, there is provided a polyamide/polyolefin- based multilayer casing film formed by stretching and utilizing the properties of a nylon 6-polyamide layer suitable as a casing material for a pasty content material to the higher degree by disposing a relatively thin polyolefin layer via adhesive polyolefin layers between a relatively thick outer layer and a relatively narrow inner layer respectively of nylon 6-based polyamide. The casing film is particularly suited as a casing material for pasty meat products, such as sausage and ham but is also suitable as a casing of an analogous products using a pasty material, such as cheese.