MXPA00010220A - Heat-shrinkable multilayer film - Google Patents

Abstract

A polyester-surfaced heat-shrinkable multilayer film exhibiting good printability and adaptability to various automatic packaging processes is provided. The film prevents the occurrence of an excessively large heat-shrinkage stress while ensuring a necessary level of heat-shrinkability. The multilayer film includes at least three layers including an outer surface layer (a) comprising a polyester resin, an intermediate layer (b) comprising a polyamide resin and an inner surface layer (c) comprising a sealable resin. The film exhibits a heat-shrinkable stress at 50°C of at most 3MPa both in longitudinal direction and in transverse direction, and a hot water shrinkability at 90°C of at least 20%. The film is suitably produced through a biaxial inflation process at relatively high stretch ratios (7, 9, 8-3c), followed by heat-treatment with steam or warm water at a relatively low temperature (10, 12, 13, 11-3e).

Description

INTERNATIONAL APPLICATION PufíiSHED UNDER THE PATENT COOPERA? ON TREATY (PCT) (51) Inleputional Patent Classification: (11) International Publication Number: WO 99/55528 B32B 27/36, 2734, B29C 55 28 Al (43) International Publlcallon Date: 4 November 1999 (04.11.99) * - *** "llifi f MULTI-LABELING MULTI-LAYER LAYER FILM TECHNICAL FIELD The present invention relates to a heat-shrinkable multi-layer film suitable for use as a heat shrinkable packaging material that includes an outer surface layer comprising a polyester resin, an intermediate layer comprising a polyamide resin and a sealable resin layer, and also relates to a process for the production of said heat shrinkable multilayer film. BACKGROUND OF THE ART To date, the preparation of a packaging material, such as a bag, from a shrink-wrapped film through a bag making machine, and filling the packaging material has been widely practiced. with a material of content either by submitting the packaging material to a packing of flow, packed in a tray, or packed in a film by means of an automatic packing machine, mainly for packaging ham, sausage or other foods. Such heat-shrinkable resin films have conventionally been provided in many cases in multi-shrinkable multilayer film forms that include various shapes or sheet structures of various resins, including a polyolefin resin (abbreviated to sometimes as "PO") excellent in terms of sealing capacity, extrusion capacity and stretch capacity, a polyamide resin (abbreviated as "PA") excellent in terms of mechanical properties, stretch properties and barrier properties gases, a ream of vinylidene chloride (abbreviated as "VdCL") or a ream of ethylene-vimlico alcohol copolymer (abbreviated as "EVOH") especially excellent in terms of its gas barrier properties, a copolymer resin of ethylene-vinyl acetate (abbreviated as "EVA"), or a modified polyolefin resin (abbreviated as "M-PO") in the sense of including a resin that is excellent in its thermal sealing capacity and adhesion, etc. Representative examples of a laminated form or structure may include: PO / PA / PO, EVA / PA / EVA, PO / PA / EVA (for example, in accordance with that disclosed in Japanese Patent Publication (JP-B) 54- 279, Japanese open patent application (JP-A) 51-92882, JP-B 61-53218, JP-A 8-23035), and also PA / EVA / VdCl / EVA / PA (for example, in accordance with disclosed in JP-A 62-2738 9) where the respective layers are mentioned from the outer surface layer to the inner surface layer in each laminated structure. In the case where said heat shrinkable multiple layer film having a sheet structure representative of PO / PA / PO, EVA / PA / EVA or PO / PA / EVA is subjected to heat sealing through a sealing bar included in a representative automatic packing mode, the PO or EVA layer that constitutes the inner surface layer exhibits a good sealing ability but the outer surface layer of PO or EVA can also adhere on the sealing bar due to thermal fusion in such a way that it is difficult to increase the thermal sealing speed and therefore the automatic packing speed. In addition, a film having a laminated structure of this type also exhibits a tendency to insufficient transparency. In addition, a film having an outer surface layer of PO may exhibit insufficient printing capacity. Most of these difficulties are not found in a heat shrinkable multilayer film having a PA / EVA / VdCl / EVA / PA film structure, but this film presents difficulties in terms of the fact that its film properties can change according to changes in environmental conditions because the surface layers of PA are rich in moisture absorption capacity. In order to solve many of the problems that relate to the foil structures of conventional heat shrinkable multilayer films, our research and development group has proposed a heat shrinkable multilayer film that includes a layer of relatively thin external surface of a polyester ream (hereinafter sometimes abbreviated representatively as "PET") that has not been used to date for the formation of sheet films by coextrusion and stretch with a ream of polyamide, and an intermediate layer of polyamide ream, which are obtained by the harmonization of the stretching capacity of the outer surface layer of PET with the stretching capacity of the intermediate layer of PA (JP-A-99621, corresponds to US-A 5336549 and EP-B 476836). Representative exemplary structures of the sheet type of the heat shrinkable multiple layer film disclosed herein include: PET / PA / PO, PET / M-PO / PO and PET / M-PO / PA / EVOH / M-PO / PO. In the heat-shrinkable multi-layer film, the outer surface layer of PET has an essentially higher thermal resistance and a higher printability than the PO layer as a typical sealable ream and also has better anti-moisture stability than the PA layer. . In addition, since the co-stretching capacity of the external surface layer of PET and the intermediate layer of PA have been harmonized, the resulting film after the biaxial stretching presents a stability of relatively good size in applying a heat treatment which causes a decrease in thermal shrink capacity, thus offering a multilayer shrink film that shows excellent performance as a shrinkable ter packaging material. As a result of our additional studies, we have found that the aforementioned multi-shrinkable PET film with multiple layers presents several problems due to its inherent thermal shrinkage capacity when used in the case of automatic packing. The problems are the following: (a) In the case of tray packing where a processed meat product is placed in a foam-type plastic tray and then wrapped with a heat-shrinkable film, followed by heat shrinking of the film with the object to provide a product packed with the film intimately fixed on the content, the tray containing the packaged product is deformed, (b) In the case of the pizza packaging, where a pizza is wrapped with a heat shrinkable film in the form of a stamp in Three sides followed by thermo shrinking to provide a packed product, the pizza is folded which decreases the value of the merchandise. (c) When a deep-stamping container or tray containing a content there is coated with a heat-shrinkable film as a cover material, followed by shrinkage of the film to provide a packaged product, the container or the tray is deformed, (d) ) When an angular product (for example, ham) is wrapped with a shrink film and subjected to boiling treatment (for example, at 90 ° C for 10 minutes) both for heat shrinking and for sterilization the angles of the product are rounded which decreases the value of the merchandise , (e) In the case of automatic packing including heat sealing through a sealing bar, a sealing failure occurs in some cases if the sealing speed is increased. In particular, defects of small holes can occur in some cases due to double sealing in the case where the sealing interval is reduced. (f) Irregular shrinkage of the film may occur during printing in some cases, whereby the resulting printed film exhibits a print deviation or a non-flat rolled state which results in difficulties in making bags and subsequently packing. PRESENTATION OF THE INVENTION Accordingly, an object of the present invention is to provide a heat-shrinkable multi-layer film with PET surface adapted for automatic packing. As a result of further studies we carried out to achieve the aforementioned object, we find that most of the above-mentioned problems (a) - (f) relate to the multi-layer shrink film with known PET surface can be attributed to its inherent thermal shrinkage but, more than the degree or magnitude of thermal shrinkage capacity, can be attributed to an excessively important tension that occurs in the film during the shrinkage, that is, an excessive thermal shrinkage effort big. We have also discovered that while a thermal or tempering treatment is conventionally applied to a PET film (polyester resin) as a post-biaxial stretch treatment for the removal of heat shrinkage to provide size stability, a multilayer film with a surface PET film laminated with a PA layer after biaxial stretching under appropriate conditions can be subjected to an optimal heat treatment (ie, a heat treatment capable of exercising a relatively low temperature relaxation) to effectively reduce the heat shrink stress while retains a necessary level of thermal shrinkage capacity, thus solving most of the problems presented above that are found in automatic packing. It was also found that in order to carry out a heat treatment of this type which exerts a relaxing effect at a low temperature after an inflation process as a preferable biaxial stretching process, it is extremely preferred to use steam or hot water which have a large thermal capacity as the heat treatment medium. The heat shrinkable multilayer film according to the present invention is based on the aforementioned findings and more specifically comprises at least three layers including an outer surface layer (a) comprising a polyester resin, an intermediate layer (b) ) comprising a ream of polyamide and an inner surface layer (c) comprising a sealable ream; said multilayer film having a heat shrinkage stress at 50 ° C of a maximum of 3MPa both in the longitudinal direction and in the transverse direction, and a shrinkage capacity with hot water at 90 ° C of at least 20%. According to the present invention, there is also offered a process for producing a heat shrinkable multilayer film, comprising the steps of: co-extruding at least three species of molten thermoplastic reams to form a tubular product comprising at least three layers that they include an outer surface layer (a) comprising a polyester ream, an intermediate layer (b) comprising a polyamide resin and an inner surface layer (c) comprising a sealable ream, cooling the tubular product to a temperature with water lower than the lowest temperature of the melting points of the polyester resin, the polya-ida resin and the sealable ream that constitute the layers (a), (b), (c), reheat the tubular product to a temperature that it is at most the lower temperature of the melting points of the polyester ream, polyamide ream and sealable ream constituting the layers (a), (b), (c), pulling the tubular product vertically while introducing a fluid into it. the tubular product for stretching the tubular product in a ratio of 2.5-4 times both in the vertical direction and in the circumferential direction, thus offering a biaxially stretched tubular film, bending the tubular film, again introducing a fluid into the bent tubular film to form a tubular film, heat treat the tubular film from its outer surface layer (a) with steam or hot water at a temperature of 60-98 ° C, cool the treated tubular film ter for providing a biaxially stretched film having a heat shrink stress at 50 ° C of at least 3 MPa in both the longitudinal and transverse directions, and a shrinkage in hot water at 90 ° C of at least 20% . BRIEF DESCRIPTION OF THE DRAWING Figure 1, the only figure of the drawing, is a schematic illustration of an apparatus system suitable for practicing one embodiment of the heat shrinkable multilayer film production process according to the invention. DETAILED DESCRIPTION OF THE INVENTION The heat shrinkable multilayer film according to the present invention comprises at least 3 layers including an outer surface layer (a) comprising a polyester ream, an intermediate layer (b) comprising a res polyamide and an inner surface layer (c) comprising a sealable ream. The polyester ream (PET) constituting the outer surface layer (a) may comprise either an aliphatic polyester ream or an aromatic polyester ream. More specifically, examples of dicarboxylic acids constituting the polyester ream can include: terephthalic acid, isophthalic acid, italic acid, 5-t-butyl isophthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, acid oxalic, malonic acid, succinic acid, agelaic acid, sebacic acid, and dimeric acids comprising dimers of unsaturated fatty acids. These acids can be used either individually or in combination of two or more species. Examples of diols constituting polyester res they may include: ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, diethylene glycol, polyalkylene glycol, 1,4-c-clohexan-d-methanol, 1,4-butanedium, and 2-alkyl-1,3-propanediol. These diols can be used either individually or in combination of two or more species. Among these, it is preferred to employ an aromatic polyester neighbor that includes an aromatic dicarboxylic acid component, with a polyester formed in particular being preferred. from terephthalic acid such as dicarboxylic acid and a diol having a maximum of 10 carbon atoms, such as, for example, polyethylene terephthalate or polybutylene terephthalate. It is also preferred to employ a copolyester resin formed by the replacement of a portion of Preferably at most 30 mol%, more preferably at most 15 mol%, of terephthalic acid with another dicarboxylic acid, such as isophthalic acid, or a copolyester resin between terephthalic acid and a mixture of diols, for example ethylene glycol and 1, 4-c? clohexand? ol (for example, "Kadapac PET # 9921", available from Eastomen Kodak Co.). The polyester ream may preferably be a resin having an intrinsic viscosity of about 0.6-1.2. The outer surface layer (a) may contain up to 20% by weight of a thermoplastic ream other than the res polyester, such as for example a thermoplastic elastomer represented by thermoplastic polyurethane, or a polyolefin resin modified with an acid, such as for example maleic acid, or an anhydride thereof. Examples of the polyamide (PA) ream constituting the intermediate layer (b) may include: aliphatic polyamides, such as nylon 6, nylon 66, nylon 11, nylon 12, nylon 69, nylon 610 and nylon 612; and aliphatic copolyamides such as nylon 6/66, nylon 6/69, nylon 6/610, nylon 66/610, and nylon 6/12. Among these aliphatic polyamides, nylon 6/66 and nylon 6/12 are particularly preferred, taking into account their molding capacity and ease of processing. These (co-) aliphatic polyamides can be used either individually or in a mixture of two or more species. It is also possible to employ a mixture of said (co-) aliphatic polyamide with a minor amount of an aromatic polyamide. Here, the aromatic polyamide is a polycondensation product between a day and a dicarboxylic acid, at least one of which contains at least partially an aromatic unit. An aromatic copolyamide is preferred. Examples of these may include: a copolymer of an aliphatic nylon and an aromatic polyamide including an aromatic diamine unit, such as nylon 66/610 / MXD6 (where "MXD6" represents polymethaxylene adipamide), and a copolymer of a nylon aliphatic and an aromatic polyamide including an aromatic carboxylic acid unit such as nylon 66/69/61, nylon 6/61 and nylon 6I / 6T (where "(nylon) 61" represents a polyhexamethylene isophthalamide, and "(nylon) 6T "represents a polyhexamethylene terephtamide). These polyamide reams can be used either individually or in mixtures in order to offer a melting point of preferably 160 to 210 ° C. The intermediate layer (b) may contain up to about 30% by weight of a thermoplastic ream other than the polyamide resin, such as for example a polyolefin resin modified with an acid, such as for example maleic acid, or an anhydride thereof, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ionomer resin, or a (partially) saponified villil ethylene-acetate polymer. The sealable resin constituting the inner surface layer (c) may be appropriately selected from among thermoplastic resins which include: polimeleted polyolefins by the use of a single site catalyst or metallocene catalyst (sometimes abbreviated as "SSC"), including polyethylene linear low density (abbreviated as "SSC-LLDPE") and very low density polyethylene (abbreviated as "SSC_VLDPE"); conventional types of ethylene-α-olefin copolymers, including "LLDPE" and "VLDPE" in terms of generally accepted abbreviations; copolymers of ethylene-vmilo acetate (abbreviated as "EVA"), ethylene-methacrylic acid copolymer (abbreviated as "EMAA"), ethylene-methacrylic acid-saturated aliphatic carboxylic acid copolymer, low density polyethylene, ionomopic resin (abbreviated as "(ream) 10"), ethylene-acrylic acid copolymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer (abbreviated as "EMA") and ethylene-butyl acrylate copolymer (abbreviated as "EBA") "). Said preferred class of sealable reams can be called ethylene copolymer, typically a copolymer having a greater amount (ie, more than 50% by weight) of ethylene with a minor amount (ie, less than 50% by weight, of preferably up to 30% by weight) of a copolymethyllable vinyl monomer with ethylene selected from the group consisting of α-olefms having from 3 to 8 carbon atoms and unsaturated carboxylic acids and more saturated carboxylic acid esters having up to 8 carbon atoms. carbon, including acrylic acid, methacrylic acid, acrylic esters, methacrylate esters, and vmyl acetate, or an acid modified product of the ethylene copolymer (preferably modified with up to 3% by weight of a more saturated carboxylic acid). It is also possible to use a thermoplastic resin, such as a ream thermoplastic like polypropylene resin, polyester ream or aliphatic nylon. The sealable resin may preferably have a melting point of at most 150 ° C, most preferably at most 135 ° C. It is also possible to employ a mixture that includes at least one kind of said sealable ream within a quantity that does not affect the transparency of the resulting film or a product sealed therewith. Among the above, preferred examples of such sealable reams constituting the inner surface layer (c) may include: SSC-LLDPE, SSC-VLDPE, LLDPE, VLDPE, EVA, EMAA, ethylene-methacrylic acid-saturated aliphatic carboxylic acid copolymer , and reams of 10. A particularly preferred class of SSC-type polyolefins may include those obtained by the use of a limiting geometry catalyst (a type of metallocene catalyst developed by the Dow Chemical Company). The limiting geometry catalyst can provide ethylene-α-olefin copolymers which can be classified as substantially linear polyethylene resin having from about 0.01 to 3, preferably from about 0.01 to about 1, more preferably from about 0.05 to about 1. long chain branch (s) per 1000 carbon atoms. Since the long chain branches have each about 6 or more carbon atoms selectively introduced into their molecular structure, the ethylene-α-olefin copolymer can exhibit excellent physical properties and good formability or processing ability, one example of these copolymers is the copolymer commercially available from Dow Chemical Company ba or the commercial name of "AFFINITY" or "ELITE" (including 1-octane as á-olefma). Other examples of polyethylene reams that are obtained by the use of a metallocene catalyst may include the polyethylene reams available from Exxon Co. under the tradename "EXACT". A metallocene-catalyzed polyolefin of this type (SSC-polyolefin) can preferably have a dispersion factor defined by a ratio (Mw / Mn) between a weight-average molecular weight (Mw) and a number-average molecular weight (Mn) less than three, more preferably from 1.9 to 2.2. The heat shrinkable multilayer film according to the present invention includes the aforementioned outer surface layer (a) comprising a polyester resin, the intermediate layer (b) comprising a polyamide resin, and an inner surface layer ( c) comprising a sealable resin, such as its layers of indispensable components, but may also include a layer intermediate intermediate other than the intermediate layer (b) comprising a polyamide ream for the purpose, for example, of providing the multi-layer film with improved functionality or processability. Examples of an optional intermediate layer of this type may include the optional intermediate layers presented below. An intermediate gas barrier layer (d), particularly an oxygen barrier layer, comprising a gas barrier layer, such as for example: EVEOH; aromatic polyamides including an aromatic diamine unit, such as for example polymethacrylic adipamide (nylon MXD6); and amorphous aromatic polyamides including an aromatic carboxylic acid unit, such as for example polyoxymethylene terephthalamide isophthalamide (nylon 6I / 6T) which is a copolymer of isophthalic acid, terephthalic acid and hexamethylenediamine. Another type of preferable intermediate layer may comprise a copolymer of ethylene and at least one monomer species containing an oxygen atom in its molecule. Specific examples may include: EVA, EMAA, ethylene-methacrylic acid-saturated aliphatic carboxylic acid copolymer, EMA, EAA, EBA and resin of 10. In addition, a metallocene-catalyzed polyolefin layer having a density of less than 0.900 g / cm3 It has a good stretching orientation characteristic and can be preferably inserted as an optional intermediate layer to provide a multilayer film having a high thermal shrink capacity. One or more adhesive layers can be inserted as an optional intermediate layer, as desired, for example, in hydrocarbon, fatty acid lubricants, fatty acid amide lubricants, ester lubricant and metal soaps. The lubricants can be in liquid or solid state. Specific examples of hydrocarbon lubricants may include: liquid paraffin, natural paraffin, polyethylene wax and microcrystalline wax. Lubricants of fatty acids may include stearic acid and lauric acid. Fatty acid amide lubricants may include: stearic acid amide, palmitic acid amide, N-oleyl-palmitic acid amide, erucic acid amide, arachidic acid amide, oleic acid amide, methylene-bis-stearoyl amide , and ethylene-bis-stearoyl amide. Ester lubricants may include butyl stearate, hardened castor oil, ethylene glycol monostearate, and stearic monoglyceride. Metal soaps can be derived from fatty acids having from 12 to 30 carbon atoms and can include representative zinc stearate and calcium stearate. Among these, the lubricants of fatty acid amides and calcium metal soaps may be preferred because of the good compatibility they have with a thermoplastic ream, particularly a polyolefin resin. Specifically preferred examples of lubricants can include behenic acid amide, oleic acid amide and erucic acid amide. These lubricants can preferably be added in the form of a master batch.

Said masterbatch containing, for example, from 5 to 20% by weight of a lubricant, can preferably be added in an amount sufficient to provide the concentration of 0.05 to 2% by weight of the lubricant in a ream layer in question. The antistatic agent may preferably be a surfactant, which may be any of ammonium surfactants, cationic surfactants, non-ionic surfactants, amphoteric surfactants and mixtures thereof. The unsightly agent can be added preferably in a proportion of 0.05 to 2% by weight, more preferably 0.1% by weight of a layer of beef to which it is added. In the aforementioned layer structure, it is also possible to add an inorganic lubricant (antiblocking agent) or an anti-clouding agent. The inorganic lubricant may include known inorganic fillers to be added to the reams forming films for the purpose of preventing adhesion of the films therebetween, such as talc, earth, diatomaceous, silica, zeolite, calcium carbonate and alummosilicate. Spherical fillers can be desired. Among these, silica and aluminosilicate are preferred because of their good dispersibility. Said inorganic lubricant is added in the form of a master batch. The anti-cloudy agent is added in order to avoid worsening of the ability to see the content of such moisture (for example "meat") due to the fixation of the small drops of water on an internal surface of a packaging film in the case of a tray packing, etc, and a known anti-clouding agent can be employed. Said anti-clouding agent can be kneaded in a film or applied on a surface. The anti-clouding agent is generally added on the inner surface layer but can be added on the outer surface layer for the purpose of being transferred into the inner surface layer when a tubular film is split along its split portion in a single film and then rolled around a roll. A heat shrinkable multilayer film can be preferably formed by laminating the aforementioned layers, followed by stretching in a final multilayer film form having a total thickness of 3 to 120 μm, particularly 10 to 90 μm. More specifically, a film subjected to shrinkage with heat drying as in a tray packing, pizza packing, covering formation, etc., can preferably have a relatively small thickness of a maximum of 50 μm, and a film subjected to shrinkage with moist heating as in the case of boil shrinkage or in queuing water may preferably have a relatively large thickness of at least 35 μm. More specifically, it is preferred that the outer surface layer (a) comprising a polyester ream have a thickness of 0.5 to 10 μm, particularly 1 to 5 μm, it is preferred that the intermediate layer (b) comprising a resin of polyamide having a thickness of 3 to 50 μm, particularly of 5 to 30 μm, and it is preferred that the inner surface layer (e) comprising a sealable ream has a thickness of 8 to 80 μm, particularly of 10 to 60 μm. In order to provide the multi-layer film with an appropriately harmonized biaxial stretching capacity, it is preferred that the layer (a) has a thickness less than the thickness of the layer (b), more specifically a thickness representing 3 a 70%, particularly from 6 to 50% of the thickness of the layer (b). The optionally placed gas barrier layer (d) can have a thickness of, for example, 1 to 30 μm, preferably 2 to 15 μm. Below 1 μm, the oxygen barrier improving effect can be limited and above 30 μm, extrusion of the layer and stretching and processing of the multilayer film can be complicated. The adhesive ream layer can be placed in several layers, each having a thickness in the range of 0.5 to 5 μm. The heat shrinkable multiple layer film can be formed by first forming a film not yet expected by co-extrusion through several extruders, and then said film can be stretched biaxially through a known process, such as for example the tensioning process. The stretch ratio may preferably be 2.5 to 4 times in both the longitudinal and transverse directions. The heat shrinkable multilayer film formed in this way can also be laminated with another resin layer in accordance with a known lamination process. The heat-shrinkable multilayer film can preferably be formed by inflation according to the process of the present invention. A preferred embodiment is described with reference to Figure 1, the only figure of the drawing. Several extruders 1 (only one shown) are provided corresponding to the number of laminated resin species, and the respective resins of the extruders are co-extruded through an annular die 2 to form a tubular product 3 that includes at least three layers of an outer surface layer (a) comprising a polyester ream, an intermediate layer (b) comprising a polyamide ream, and an inner surface layer (c) comprising a sealed resin. The tubular product three then pulled vertically downward in a water bath 4 and collected by pinch rollers 5 while cooling to a temperature below the lower temperature of the melting points of the main reams constituting the respective ream layers (ie, the polyester ream, the polyamide resin and the sealable resin), preferably at a temperature of 40 ° C or less. The tubular film 3A collected in this way, while optionally introducing an opening aid such as soybean oil as desired, is introduced in a bath 6 of running water for example at a temperature of 80-95 ° C, which is at most the lower temperature of the melting points of the main reams constituting the respective layers, and the tubular film heated in this way 3b is pulled upwards to form a tubular film bubble 3C with flowing air introduced between pairs of pinch rollers 7 and 8, whereby the tubular film 3C is biaxially stretched simultaneously in a preferred ratio of 2.5 to 4 times, more preferably 2.8 to 4 times, in each of the vertical direction or machine direction (MD) and transverse direction or lateral direction (TD) while the 3C film is cooled with cold air at a temperature of 10-20 ° C coming from a cooling air circuit 9. The film biaxially stretched in this 3d form is bent once or placed flat and then pulled down to again form a tubular film bubble 3e with fluid air introduced between pairs of pinch rollers 10 and 11. The bubble of the tubular film 3e is kept inside a treatment tube 12 where steam is blown from blowholes 13 (or where hot water is sprayed from spray holes) against the tubular film 3e to heat-treat the tubular film 3e after biaxial stretching at 60-98 ° C, preferably 60-80 ° C, for about 1-20 seconds, preferably for about 1.5-10 seconds, thus allowing the tubular film to relax by 2-25%, preferably 5-15%, in each direction vertical (MD) and the transverse direction (TD). A tubular film 3E after heat treatment corresponds to a heat-shrinkable multilayer film according to the present invention and is wound onto a pick-up roller 14. The heat-shrinkable multilayered film thus obtained according to the present invention is provided with a thermal shrinkage reduced to 50 ° C of a maximum of 3MPa, preferably a maximum of 2.5 MPa in each direction of the machine (MD) and the transverse direction (TD), while maintaining an adequate level of shrinkage capacity in water hot at 90 ° C of at least 20%, preferably at least 25%, especially at least 30%, in at least one direction, preferably in each of the MD and TD directions, thus having good performances in the automatic packing. A film that has a shrinkage capacity with water hot at 90 ° C of at least 20%, preferably at least 25%, and especially at least 30%, can be tightly adjusted on almost all types of materials contained to provide well packaged products. Such shrinkage capacity levels with hot water correspond to a shrinkage capacity by application of dry heat at 120 ° C of at least 15%, particularly 20% or more, thus presenting a pleasant packing effect of the materials contained in a Automatic packing process that includes a step of dry shrinkage packing. In addition, due to a moderately reduced heat shrink effort of at most 3 MPa, preferably 2.5 MPa or less, the heat shrinkable multilayer film according to the present invention exhibits excellent adaptability or suitability to a baler machine and excellent thermal sealability , can effectively prevent the deformation of the contents and the container, such as a tray or a deep stamping container, thus allowing a high-speed production of automatically packaged products that have an excellent appearance. In addition, a maximum heat shrinkage stress at the actual heat shrinkage temperature for packing should preferably be set at a maximum of 4 MPa, more preferably as maximum at 3.5 MPa. In order to perform such low heat shrinkage effort while maintaining a sufficiently high hot water shrinkage capacity, it is particularly preferred to ensure a relatively high stretch ratio of 2.5 to 4 times, especially 2.8 to 4 times in each of the MD / TD directions, and then perform a heat treatment at a temperature within a range of 60 to 98 ° C, particularly 60 to 80 ° C, with steam or hot water having a thermal capacity. In a lower stretch ratio, it becomes difficult to ensure a necessary level of heat shrink capacity after the heat treatment, and the film has a large local fluctuation in its thickness, thus being able to present a suitable correspondence with an automatic packing machine . On the other hand, in the case where a medium having a small thermal capacity such as for example heated air is used or a lower temperature of heated air is used or a temperature lower than 60 ° C is adopted in the heat treatment after biaxial stretching, it becomes difficult to obtain the objective effect of sufficiently reducing the heat shrinkage effort. In the process of producing the heat shrinkable multiple layer film described above in accordance with the present invention, the multilayer film before or after stretching may be exposed to actinic radiation. By exposure to actinic radiation, the multilayer film can have improved thermal resistance and improved mechanical strength. Due to a moderate cross-linking effect, exposure to actinic radiation can have an effect of providing improved film-forming ability by stretching and improved thermal resistance. In the present invention, known actinic radiations such as α-rays, β-rays, electron rays, β rays, or X-rays can be used. In order to provide an adequate level of crosslinking effect, electronic rays and rays are preferred, and electronic rays are especially preferred taking into account the ease of handling and the high processing capacity for the production of the layer film. multiple The conditions for the aforementioned exposure to actinic radiation can be set appropriately according to their purpose, as for example according to the required level of crosslinking. For example, it is preferred to conduct exposure to electron beams at an accelerating voltage within a range of 150 to 500 kilovolts to provide an absorbed dose of 10-200kGy (kilo-gray) or by exposure to lightning and a dose of radiation. 0.05 to 3 kGy / hour in order to provide an absorbed dose of 10-200 kGy. By exposure to actinic radiation, such as, for example, electron beams, it is also possible to offer improved adhesion to the meat, ie, adhesion to a processed meat product, for example ham or sausage from layer (c), thus avoiding the generation of ugo stagnated between the film and the content, thus improving the appearance of the packaged product and maintaining the quality of the content. For a similar purpose, it is also possible to expose the inner surface layer (c) to corona discharge. The corona discharge treatment can be effected by the use of a corona discharger equipped with a high frequency energy supply comprising a high frequency oscillator and a high voltage transformer, by applying a film on a treatment roller coated with silicone, and exposing the film to corona discharge by applying AC power of a maximum of 4kW with a maximum voltage of 18 kilo-volts and a frequency of 5-120 kHz in the form of an alternating wave, preferably a sine wave , between the discharge electrode and the treatment roller, thus providing the treated film surface with a reduced surface tension of at most 36 dina / cm2, more preferably at most 34 dma / cm2.

EXAMPLES The present invention will now be described more specifically on the basis of examples and comparative examples. It will be noted, however, that the scope of the present invention is not restricted to such examples. Some physical properties described here are based on measured values in accordance with the following methods. < Methods of measuring physical properties > 1. Shrink capacity in hot water A sample film in which marks are indicated at a distance between them of 10 cm in each of a machine direction (MD) and a transverse direction (TD) perpendicular to the direction of The machine is immersed for 10 seconds in hot water adjusted to 90 ° C and then removed from there, followed by an immediate rapid cooling in water at room temperature. Then, the distance between the marks is measured and indicates a decrease in the distance as a percentage of the original distance of 10 cm. Five sample films of each product film are subjected to the aforementioned measurement, and the average value of the percentage decrease is indicated in each of the MD and TD directions. 2. Dry thermal shrinkage A three-mm-thick corrugated board is placed in a frame, and a Geer kiln is placed ("Model MOG-600", available at K.K. Robert) and heated to a prescribed temperature. In the oven, a sample film is placed in which marks are indicated at a distance between them of 10 cm in each of the directions MD and TD. In this case, the door of the oven is closed immediately after the placement of the sample film in such a way that the period of opening of the door is restricted within a period of 3 minutes. After closing the door, the sample film is left to stand for 30 seconds in the Geer oven and then renew for natural cooling. Subsequently, the distance between the marks in the sample film is measured, and a decrease in distance is indicated as a percentage of the original distance of 10 cm. 5 samples of each film are subjected to the measurement before mentioned, and the average value of the percentage decrease is indicated in each of the MD and TD addresses. 3. Heat Shrinkage Effort A sample film strip of 150 mm length and 15 mm width taken at its MD and TD directions, respectively, is cut from a multi-layer film product, and fitted with a 100 mm fastener opening in a universal tester ("Model 5565"), available from Instron Co.) placed in a thermostat container ("Series 3119" , available from Instron Co.) maintained at a temperature of 23 ° C, followed by an increase in temperature at the rate of .tlc.ctti --- i-t.itai-. 2 ° C / mm. in the container with thermostat. In the following examples and comparative examples, the stress values of thermal shrinkage that vary with the increase in temperature are indicated and are measured at a temperature of a range of 40 ° C and 50 ° C in the course of the increase in temperature. < And film production companies > The following are examples and comparative examples for the production of heat shrinkable multiple layer films. The reams used in the following production examples are shown inclusively in Table 1 together with their abbreviations. Example 1 By using an apparatus having an arrangement as illustrated roughly in Figure 1, a tubular laminate having a laminar structure from the outer layer to the inner layer of PET (2J / M-PE (1.5 J / NY-1 (7) / VEO (5J / M-PE (1.5J / VL-2 (24) with thickness ratios of the respective layers indicated in parentheses was co-extruded by extruding the respective resins through of several extruders 1 (only one is shown), respectively, and by introducing the melt reams to an annular die 2 to merge the respective layers in the order described above: The melted tubular laminate 3 extruded through the die 2 was rapidly cooled to 10-18 ° C in a 4-well bath to form a 3a flat tubular product. Then, the flat tubular product 3a was passed through a hot water bath 6 at a temperature of 92 ° C and formed into a bubble-like tubular film 3c which was then biaxially stretched in ratios of 3.1 times in MD direction and 3.2 times in the TD direction by the inflation process while it was cooling with cooling air at a temperature of 15-20 ° C coming from an air circuit 9. Afterwards, the biaxially stretched 3d film was guided in a tube of 2 meter long heat treatment 12 to form a bubble tube 3e which was then thermally treated for 2 seconds with steam at a temperature of 70 ° C blown from steam blow holes 13, while allowing a Relaxation of 5% in the MD direction and 5% in the TD direction, thus offering a biaxially stretched film (multiple layer heat shrink film) 3f. The biaxially stretched film obtained in this way had a width in the flat state of 362 mm and a thickness of 41 μm. Lamina type structure and film production conditions (biaxial stretching), etc. of the biaxially stretched film obtained in this way are shown inclusively in table 2 together with the biaxially stretched film production structure and conditions obtained in other examples and comparative examples.

Examples 2-21 and Comparative Examples 1-12 Several biaxially stretched films were prepared in a manner similar to Example 1 except that the sheet structures and the film production conditions (biaxial stretch) were respectively changed in accordance with that illustrated in the table. 2, and the relaxation and heat treatment conditions were respectively changed as shown in Table 3. Each of the biaxially stretched films obtained in the previous examples and comparative examples was subjected to the aforementioned measurement of physical properties and tests of performance evaluation described below. The results appear in Tables 3-7 presented below. < Performance evaluation tests > 1. Boiling test A sample tubular film was obtained in the manner described above and heat sealed in two directions, ie MD and TD directions, and a rupture portion was cut in order to provide a bag with a length of 350 mm (in the TD direction of the film) and a width of 150 mm (in the MD direction). Ham was inserted in the form of a rectangular parallelepiped as contained in the bag and sealed with vacuum at a space percentage of 15% (i.e., a circumferential length of the bag film being 115% of the content), followed by 10 minutes of thermal sterilization in a hot water bath at a temperature of 90 ° C. The appearance of the packaged product was then evaluated in accordance with the following standard. A: The shape of the ham after the thermal sterilization did not substantially change form, and the film was tightly adjusted on the ham. No breakage of the bag film after the heat treatment was observed. B: The corners of the ham, after the thermal sterilization were relatively deformed which decreases the value of the merchandise. Cl: The corners of the ham after the thermal sterilization disappeared due to round deformation decreasing the value of the merchandise. C2: A tight enough adjustment was not achieved due to insufficient shrinkage and some wrinkles were present in the packaging film. 2. Possibility of printing The printing was carried out on a surface (on the side of the external surface) of a sample film by using a flexographic printer (available from SMB Co.) under the following conditions: Ink: RESINO INK WHITE (white resin ink) (10 kg) containing 15% hardener.

Rubber plate: two rubber plates were fixed on a cylinder with a diameter of 380 mm at a pitch of 190 mm. Heater temperature: 21 ° C at the station, and 50 ° C at the bridge. Speed: 70 m / min. The evaluation was carried out in accordance with the following standard: A: no substantial shrinkage was observed after printing (< 3%) and no print deviation was observed. The film after the printer could be wrapped in a smooth roll and then used to form bags without problem. B: Shrinkage after printing was Ü3% and D5%, but no print deviation was observed. The film, after printing, could be wrapped in a substantially smooth roll and could be used to form bags later. C: Shrinkage after printing was greater than 5%, and print deviation was caused which resulted in wrinkles in the film. After printing, the film was rolled into a roll, which however was not smooth, thus causing difficulty forming bags later. 3. Packing performance with film Each sample film was used as a cover film for film packaging together with a film of commercially available multiple layers ("FA-1", available in Kureha Kagaku K.K.) as a base film. A paper board was placed on a base film and slices of bacon were placed there to be packed with film with a sample film heated to a temperature of 130 ° C by a film packing machine. A: The film that forms the packaged product did not present substantially wrinkles, and no warps were observed nor in the marginal portion where the sliced bacon is not found. B: The packaged product film was substantially free of wrinkles, but a marginal portion where the sliced bacon was not present was slightly bent towards the lid film side presenting a warping portion of a height of less than 1 cm from a horizontal base where the packaged product was placed. Cl: The packaged product film had substantially no wrinkles but a marginal portion where the bacon was not sliced had a noticeable bulge towards the lid film side, thus providing a lesser appearance to the packaged product. The marginal portion had a camber height that exceeded 1 cm in relation to a horizontal base in which the packaged product was placed. C2: The packed product film presented wrinkles, thus creating a negative appearance for the packaged product which seriously damages the value of the merchandise. 4. Flow packing performance The flow packing performance was evaluated by using a horizontal flow packing machine ("NW406", available in Ohmori Kikai K.K.). A sample film was provided as a 380 mm wide film formed by cutting edge portions on both lateral sides of a tubular film as obtained in a production sample. The sample film was subjected to flow pack formation at the conditions of a central seal temperature of 180 ° C, a top seal upper seal temperature of 100 ° C, and a lower seal lower seal temperature. 140 ° C to provide 170 mm wide and 300 mm long flow packing bags. In a flow pack bag, a cylindrical ham of 300 mm in circumference and 200 mm in length was inserted and packed with vacuum, followed by 10 minutes of boiling in hot water at a temperature of 90 ° C. A: A sealing bar was aligned with portions to be sealed from superimposed films, and bag making was performed stably with a film speed of 30 m / min while causing little shrinkage along the sealed section.

B: A deviation between a position of a sealing bar and a sealing portion of superimposed films was observed. As a result, stable processing of bags at a film speed of 30 m / min due to shrinkage along the sealed portion could not be carried out while bagging was possible at a film speed of 10 m. / sec. 5. Packing performance on tray A tubular film breaking portion as obtained in a production example was cut to form a 450 mm wide flat film. Trays made of polystyrene, each with raw meat, were subjected to packing by gas replacement at a rate of 35 trays / minute while blowing a mixture of 80% by volume of carbon dioxide and 20% by volume of oxygen as the replacement gas through the use of a flow packing machine ("Delta 2000", available from Dapack Co.). The packaging was carried out at a space rate of 20% in relation to the tray. Then, the packing was introduced into a shrink tunnel (available from Meurer Co.) for shrinkage while blowing air at a temperature of 170 ° C for 6 seconds. A: No deformation of the tray was observed after passing through the shrink tunnel, so that a packaged product showing an appearance was obtained nice. B: Some tray formation was observed after passage through the shrink tunnel. Cl: A noticeable tray deformation was observed after passage through the shrink tunnel, thus providing a packaged product that has a problematic appearance. C2: The film could not be adjusted on the tray due to insufficient shrinkage, thus providing a packaged product with appearance problems. 6. Performance of pizza packaging A tubular film in accordance with that obtained in a production example was cut along its line of rupture to form a flat film 750 mm wide. The flat film was used for gas replacement of a non-cooked pizza in the form of 300 mm in diameter and 10 mm in height and was placed on a polystyrene foam plate at a speed of 35 pizza / min while blowing gas carbonate by the use of a flow packing machine ("Delta 2000", available from Dapack Co.). The resulting packaging bag had sizes of 380 mm in length and 360 in width. The packing bags were passed through a shrink tunnel (available from Meurer Co.) for shrinkage while blowing air at a temperature of 200 ° C. A: The packaged pizza after it passes through the tunnel Shrinkage did not present warping, thus having a good appearance. B: The packaged pizza after passing through the shrink tunnel presented warping, seriously damaging the value of the merchandise. 7. Cap Performance (Adaptability as Tray Cap Material) A tubular film obtained in the production example was cut along its line of rupture to form a flat film 840 mm wide. The flat film was used as a cover film to cover trays each having a sheet-like structure from the inner side to the outer side of polyethylene (20 μm) / adhesive resin / VEO (ethylene-vinyl acetate copolymer saponified ) (7 μm) / adhesive resin / polystyrene foam (300 μm) and sizes 225 mm (length) x 155 mm (width) x 40 mm (height), in such a way that the flat film covered with its inner side the top polyethylene (inner) side surface of each tray by using a tray machine ("INPACK NEMA 4", available from Ross Co.) under the conditions of a seal temperature of 110 ° C and a speed of 20 trays (packages) / min. The packed trays obtained in this way were evaluated in accordance with the following standard A: The product that remained for a day after the packed, no softening of the lid film or tray formation was observed so the package presented a pleasant appearance. C: In the product one day after packing, no softening of the film was observed, but the tray was deformed which decreases the value of the merchandise. Table 1: Resins and additives Abbrevia-resin / additive * manufacturer (trade name) Ny-1 nylon copolymer 6/66 Mitsubishi Engineering Plástic K.K. (NOVAMID 2340A1) Ny-2 nylon copolymer 6/66 Ube Kosan K.K. (UBE NYLON 5034B) Ny-3 nylon copolymer 6/12 Toray K.K. (AMILAN CM 6541X3) Nylon copolymer 66/610 EMS K.K. / MXD / 6 (MILTIPOLYAMID BM18SBH) PET copolyester from terephtha- Kanebo K.K. ethylene lactide * 1 (BELBET IGF-8L) PET-2 copolyester terephtha Eastman Kodak Co. ethylene coating * 2 (KODAPAK PET 9921) EVOH ethylene copolymer Kurary K.K. saponified-acetate (EVAL EPG156B) vinyl VL-1 ethylene copolymer- Sumitomo Kagaku K.K. butene-1 (SMIKASEN CN2011) (d = 0.905 g / cm3) VL-2 ethylene copolymer- Sumitomo Kagaku K.K. Hexene (SMIKASEN CS3009) (d = 0.908 g / cm3) VL-3 ethylene copolymer- DSM octene (TEAMEX 1000F) (d = 0.902 g / cm3) SVL-1 ethylene copolymer- Dow Chemical Co. octene * 3 (AFFINITY PL1845) (d = 0.910 g / cm3) SVL-2 ethylene copolymer- Dow Chemical Co. octene * 3 (AFFINITY PF1140) (d = 0.895 g / cm3) SLL ethylene copolymer- Dow Chemical Co. octene * 3 (ELITE 5400) (d = 0.916 g / cm3) M-PE very low polyethylene Mitsui Kagaku K.K. Modified density * 4 (ADMER SF730) Thermoplastic polyurethane TPU- Kuraray K.K. tico * 5 (KURAMILON U1195E) LUB-1 master lot of lubriNippon Pigment K.K. sing * 6 (NIPPISUN COLOUR MB60) LUB-2 lubricant master batch Sumitomo Kagaku K.K. sing * 7 (SMIASEN A-26) AF anti-cloudy additive Riken Vitarnin K.K. * 8 (KP-410) Abbreviation melting point Remarks ** crystal (c 'C) Ny-1 195 T | rel = 4.5 EVOH 160 MFR = 6.5 g / 10 min. VL-1 107 MFR = 4.0 g / 10 min. VL-2 119 MFR = 3.0 g / 10 min. VL-3 124 MFR = 3.0 g / 10 min. SVL-1 106 MFR = 3.5 g / 10 min. SVL-2 94 MFR = 1.6 g / 10 min. SLL 122 MFR = 1.2 g / 10 min. M-PE MFR = 2.7 g / 10 min. TPU LUB-1 -LUB-2 MFR = 2.0 g / 10 min. AF * l: The acid is unat mixture of: 12% molar of isophthalic acid Y 88% molar of terephthalic acid. * 2: Copolyester between terephthalic acid and ethylene glycol diols and 1,4-cyclohexanedimethanol. * 3: Polymerized in the presence of metallocene catalyst. * 4: Modified with an unsaturated carboxylic acid. * 5: Nitrogen content = 4.1%, d (density) = 1.21 g / cm3. * 6: Polyethylene terephthalate (base resin) containing 2. 5% by weight of silica. * 7: Polyethylene (base resin) containing 4% aluminosilicate and 2% elution acid amide. * 8: Very low density linear polyethylene (base resin) containing 8% by weight of a mixture of diglyceryl laurate / ethylene oxide ether of higher alcohol (4.5 / 3.5). ** Orel = relative viscosity,? Lnt = intrinsic viscosity, MFR = melt flow rate. Table 2: Film structure and film formation conditions Ex. and Ex. Laminated layers (thickness) Comp. 1st 2nd 3rd 4th 4th 5th (μm) (μm) (μm) (μm) (μm) (μm) Ex. 1-3 PET + M-PE Ny-1 EVOH M-PE VL-2 + Ex. comp.1 LUB-1 * 1 LUB-2 * 3 (2) (1.5) (7) (5) (1.5) (24) Ex. 4-11 PET + M-PE Ny-1 EVOH M-PE VL-1 + Ex. comp.2-3 LUB-1 * 2 LUB-2 * 3 (1.5) (1.5) (8) (5) (1.5) (19) Ex. 12-15 PET + M-PE Ny-1 EVOH M-PE VL-2 Ex. Comp.4-5 LUB-1 * 1 + AF * 4 (1) (1) (5) (3) (1) (13) Ex. 16 PET + M-PE Ny-1 EVOH M-PE VL-2 LUB-1 * 1 + AF * 4 (1.5) (1) (7) (4) (1) (16) Ex. 17 PET + M-PE Ny-l + Ny-3 EVOH M-PE VL-1 + Ex. Comp .6 LUB-1 * 1 (50 + 50%) LUB-2 * 3 (1.5) (1.5) (8) (5) (1.5) (19) Ex. 18 PET + M-PE Ny-l + Ny-4 EVOH M-PE VL-2 + Ex. Comp .7 LUB-1 * 1 (70 + 30%) LUB-2 * 3 (2) (1.5) (7) (5) (1.5) (22) Ex. 19 PET + M-PE Ny-1 M-PE VL-1 + - Ex. Comp .8 LUB-1 * 1 LUB-2 * 3 (3) (2) (15) (2) (42) Ex 20 PET + M-PE Ny-1 M-PE SLL - LUB-1 * 1 (4) (2) (25) (2) (25) - Ex. 21 PET + M-PE Ny-1 EVOH M- PE SLL LUB-1 * 1 (4) (1.5) (20) (3) (1.5) (50) Ex. 22 PET-2 M-PE Ny-2 EVOH M-PE VL-3 + LUB-2 * 3 (2) (1.5) (8) (5) (1.5) (21) Ex. comp.9-11 PET + M-PE Ny-2 M-PE VL-1 + - LUB-1 * 1 LUB-2 * 3 (4) (3) (17) (3) (27) Ex. comp.11-12 PET + M-PE Ny-1 EVOH M-PE VL-1 + LUB-1 * 1 LUB-2 * 3 (4) (2) (12) (16) (2) (19) condition and film formation Ex and thickness Temp. of wide relation of Eg total heating of comp film. (μm) flat stretch (° C) MD TD (nm) E; jj. 1-3 41 92 3.1 3.2 362 Ex. comp.1 Ex. 4-11 36.5 92 2.9 3.1 362 Ex. comp.2-3 Ex. 12-15 24 92 2.9 3.1 515 Ex. comp.4-5 Ex. 16 30.5 92 2.9 3.1 515 Ex. 17 36.5 92 3.0 2.9 515 Ex. Comp .6 Ex. 18 39 87 3.0 3.4 515 Ex. Comp .7 Ex. 19 64 92 2.9 3.1 362 Ex. Comp .8 Ex. 20 58 92 2.9 3.1 362 Ex. 21 80 92 2.6 2.9 412 Ex. 22 39 92 3.1 3.2 335 Ex. comp 54 92 2.3 2.5 515 9-11 Ex. comp 45 92 2.3 2.5 515 11-12 * 1: PET: LUB- 1 = 98: 2 (weight) * 2: PET: TPU: LUB-1 88: 10: 2 (weight) * 3: VL-1: LUB -2 = 97 3 (weight), VL-2: L UB-2 = 97: 3, o), VL-3: LUB-2 = 97: 3 (weight) * 4: VL-2: AF = 90: 10 (weight) Table 3: Thermal treatment conditions and performance evaluation (1) Eg ex.2.2 ex. comp 1 Temperature of 70 80 70 NT * treatment (° C) Reliability rate 5/5 5/5 10/10 - (%) MD / TD Effort of 40 ° C 1.2 / 0 3 0.5 / 0 2 0.3 / 0 3 2.6 / 3 .3 termoencogi50 ° C 2.3 / 2 0 1.8 / 0 7 0.9 / 1. 1 3.3 / 3. 1 (MPa) Capacity of enco- 32/35 27/32 27/33 33/36 hot water (%) MD / TD 90 ° C Capacity 120 ° C 20/22 17/19 16/18 22/24 shrinkage 160 ° C 25/27 20/22 20/22 28/30 with dry heating (%) MD / TD Flow pack AAAB Boiling test AAA Cl Printing capacity Packaging with pel- AAA Cluster E .4 ex.5 ex.6 Treatment temperature (° C) 70 70 70 Relaxation rate (%) MD / TD 5/5 5/10 10 / 10 Heat shrink effort - 40 ° C 2.1 / 1.4 1.0 / 0.2 1.0 / 0.6 (MPa) 50 ° C 2.7 / 2.6 1.8 / 1.1 1.5 / 1.5 Shrink capacity at 28/33 28/32 27/31 Hot water (%) MD / TD 90 ° C Shrink capacity- 120 ° C 21/33 20/21 17/18 to heating at 160 ° C 25/26 24/23 21/22 dry (%) MD / TD Flow packed AAA Boiling test A A A Print capacity A A A Packed with film A A A * NT = untreated Table 4: Thermal treatment conditions and performance evaluation (2) Ex 7 Ex 8 Ex 9 Ex 10 Temperature of 70 70 60 80 CC treatment) Relaxation rate 10/15 15/15 5/10 5/10 (%) MD / TD Effort of 40 ° C 0.6 / 0.1 0.8 / 0. .3 1.4 / 1.1 0.7 / 0.2 termoencogi50 ° C 1.2 / 0.7 1.1 / 1. , 1 2.1 / 2.2 2.0 / 0.5 ment (MPa) Encope capacity- 27/31 25/32 30/33 27/33 hot water (%) MD / TD 90 ° C capacity 120 ° C - / - - / - - / - - / - shrinkage 160 ° C - / - - / - - / - - / - with dry heating (%) 1 YID / TD Flow packing AAAAAAA Boiling test AAAAAAA Print capacity AAAAAAAA with movie- - - - -c eg. 11 Example or example comp .2 comp .3 Treatment temperature CC) 90 N.T * 70 Relaxation rate (%) MD / TD 5/10 - 0/0 Heat shrink effort - 40 ° C 0.7 / 0.3 2.7 / 3.9 2.5 / 3.0 (MPa) 50 ° C 2.2 / 0.7 3.2 / 4.7 3.1 / 4.7 Shrink capacity at 25/26 31/36 30/34 Hot water (%) MD / TD 90 ° C Shrink capacity - 120 ° C - / - 23/24 27/22 to heating at 160 ° C - / - 28/29 26/27 dry (%) MD / TD ABB flow packing Boiling test A Cl B Print capacity A C B Packed with film _ Cl B * NT = not treated Table 5: Thermal treatment conditions and performance evaluation (3) Ex. 12 Ex. 13 Ex. 14 Ex. fifteen Temperature 70 70 65 60 treatment (° C) Relaxation rate 5/5 10/10 5/5 5/10 (%) MD / TD Effort of 40 ° C 1.2 / 1.5 1.1 / 0.6 1.3 / 0.6 1.9 / 1.3 heat shrink-50 ° C 2.0 / 2.6 1.8 / 1.3 2.5 / 1.8 2.4 / 1.9 cubic meter (MPa) Enco31 / 34 capacity 28/31 37/36 33/33 hot water (%) MD / TD 90 ° C capacity 120 ° C capacity 22/25 17/20 20/23 23/22 shrinkage 160 ° C 26 / 29 21/23 25/28 26/26 with dry heating (%) MD / TD Flow pack AAAA Packed bag AAA Print capacity AAB CAUTION Filled with AA-film Cap AAAA Pizza packed AAAA Ex.16 Example Example comp .4 comp .5 Treatment temperature (° C) 70 NT * 60 Relaxation rate (%) MD / TD 10/10 5/5 Thermal shrinkage effort - 40 ° C 0.6 / 0.2 3.0 / 4.4 2.9 / 2.5 (MPa) 50 ° C 1.3 / 0.7 3.4 / 5.0 3.4 / 3.2 Shrink capacity in 28/32 32/35 33/35 hot water (%) MD / TD 90 ° C Shrink capacity - 120 ° C 14/19 24/27 22/25 to heating at 160 ° C 20/23 30/33 26/29 dry (%) MD / TD ABA flow packing Packing in tray A Cl B Capacity of ACB printing Packed with film - -Tapa ACC Pizza packing ACC * NT = untreated Table 6: Conditions of thermal treatment and performance evaluation (4) Ex.17 Ex. comp.6 Ex.18 Ex. comp.7 Temperature of 70 NT * 70 NT * CC treatment) Relaxation rate 5/5 - 5/5 (%) MD / TD Effort of 40 ° C 1.4 / 0.4 2.3 / 2.2 1.5 / 0.9 3.1 / 3.0 termoencogi- 50 ° C 2.7 / 1.6 3.3 / 3.1 2.7 / 2.0 3.4 / 3.5 (MPa) Capacity of enco- 36/39 39/42 39/40 42/43 hot water (%) MD / TD 90 ° C Packed flow A B A B Boiling test A B A B Packing in tray A B A B Printing capacity C A C tion Ex.19 Example Ex.20 Comp .8 Treatment temperature CC) 70 N.T. * 70 Relaxation rate (%) MD / TD 5/15 - 5/15 Heat shrink effort - 40 ° C 0.2 / 0.2 1.7 / 2.7 0.8 / 0.2 (MPa) 50 ° C 0.6 / 0.5 3.1 / 3.9 0.7 / 1.2 Shrink capacity in 26/22 29/32 24/26 hot water (%) MD / TD 90 ° C Flow packing - Boiling test ABA Packing in tray - - - Printing capacity AC Á * NT = untreated Table 7 : Thermal treatment conditions and performance evaluation (5) Ex.21 Ex.22 example Comp. 9 comp. 10 Temperature 70 70 70 N. T. * CC treatment) Relaxation rate 10/10 5/5 10/10 (%) MD / TD Effort of 40 ° C 0.1 / 0.2 1.4 / 1.3 0.1 / 0.2 1.4 / 2.5 Heat shrinkage 50 ° C 0.3 / 0.5 2.1 / 2.6 0.4 / 0.5 2.6 / 3.4 (MPa) Capacity of enco22 / 25 28 / 34 18/19 25/26 hot water (%) MD / TD 90 ° C Boil test A C2 Packed in tray C2 Print capacity AA Filled with film - C2 - Example Example comp .11 comp .1 Treatment temperature (° C) 70 70 Relaxation rate (%) MD / TD 10/10 - Heat shrink effort - 40 ° C 0.1 / 0.2 0.8 / 2.0 (MPa) 50 ° C 0.4 / 0.6 3.2 / 3.8 Capacity shrinkage on 17/18 24/26 Hot water (%) MD / TD 90 ° C Boil test C2 Packed on tray C2 Printing capacity A Packed with C2 film * NT = untreated INDUSTRIAL EXPLOITATION As described above, the present invention offers a heat shrinkable multi-layer film that prevents excessively large thermal shrinkage effort from occurring while ensuring a necessary level of heat shrink capacity, thus exhibiting excellent adaptability to several automatic packing processes and also a good printing capacity.

Claims (1)

1. CLAIMS A heat shrinkable multilayer film, comprising at least three layers including an outer surface layer (a) comprising a polyester resin, an intermediate layer (b) comprising a polyamide resin, and an inner surface layer (c) comprising a sealable resin; said multilayer film presents a thermal shrinkage stress at a temperature of 50 ° C of a maximum of 3 MPa in both the longitudinal and transverse directions, and a shrinkage capacity in hot water at a temperature of 90 ° C. at least 20% A heat-shrinkable multi-layer film according to claim 1, wherein the outer surface layer (a) has a thickness less than the intermediate layer (b). A heat-shrinkable multilayer film according to claim 1, further including an intermediate layer (d) comprising a gas barrier resin between the outer surface layer (a) and the inner surface layer (O. multiple layer heat shrinkable film according to claim 1, wherein the resin The polyester of the outer surface layer (a) comprises a polyester between terephthalic acid and a diol having a maximum of 10 carbon atoms. A heat-shrinkable multilayer film according to claim 1, wherein the polyester resin of the outer surface layer (a) comprises a copolyester between ethylene glycol and a dicarboxylic acid mixture comprising a larger amount of terephthalic acid and a lower amount of isophthalic acid. A heat-shrinkable multilayer film according to claim 1, wherein the polyester resin of the outer surface layer (a) comprises a copolyester between the terephthalic acid and a mixture of diols comprising a major amount of ethylene glycol and a minor amount of 1,4-cyclohexanedimethanol. A heat-shrinkable multilayer film according to claim 1, wherein the polyamide resin of the intermediate layer (b) comprises an aliphatic copolyamide. A heat-shrinkable multi-layer film according to claim 1, wherein the sealable resin of the inner surface layer (c) comprises an ethylene copolymer or a product modified with acid of the ethylene copolymer. 9. A heat-shrinkable multilayer film according to claim 8, wherein the ethylene copolymer comprises a copolymer of a larger amount of ethylene with a minor amount of a vinyl monomer selected from the group consisting of alpha-olefins, unsaturated carboxylic acids , and more saturated esters of carboxylic acids. 10. A heat-shrinkable multilayer film according to claim 1, wherein the sealable resin comprises a ream selected from the group consisting of linear low density polyethylene catalyzed by metallocene, linear low density polyethylene, linear low density polyethylene. , ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid-saturated carboxylic acid copolymer, and ionomer resins. 11. A heat shrinkable multilayer film according to claim 3, wherein the gas barrier resin comprises a copolymer of saponified ethylene-vinyl acetate. 12. A heat shrinkable multilayer film according to claim 1, which includes in addition an intermediate layer comprising a copolymer of ethylene with a vinyl monomer containing oxygen between the outer surface layer (a) and the inner surface layer (c). 13. A heat-shrinkable multi-layer film according to claim 1, further having a shrink capacity with application of dry heat at a temperature of 120 ° C of at least 15%. 14. A heat shrinkable multiple layer film according to claim 1, which also has a pattern printed on the outer surface layer (a). 15. A process for the production of a heat-shrinkable multilayer film, comprising the steps of: co-extruding at least three species of melted thermoplastic resins to form a tubular product comprising at least three layers including a surface layer external (a) comprising a polyester resin, an intermediate layer (b) comprising a polyamide resin and an inner surface layer (c) comprising a sealable resin, cooling the tubular product with water to a temperature below the lower temperature of the points of fusing the polyester resin, polyamide resin and sealable resin constituting the layers (a), (b) and (c), reheating the tubular product to a temperature that is at most the lowest temperature of the melting points of the polyester resin, polyamide resin and sealable resin constituting layers (a), (b) and (c), vertically pulling the tubular product while introducing a fluid into the tubular product to stretch the tubular product in a ratio of 2.5 4 times both in a vertical direction and in a circumferential direction, thus providing a biaxially stretched tubular film, bending the tubular film, again introducing a fluid into the bent tubular film to form a tubular film, heat treating the tubular film from of its outer surface layer (a) with steam or with hot water at a temperature of 60-98 ° C, and cooling the thermally treated tubular film to provide a biaxially stretched particle that presents a heat shrinkage stress at a temperature of 50 ° C of at least three MPa both in the longitudinal direction and in the direction transverse, and that presents a capacity of shrinking in hot water at a temperature of 90 ° C of at least 20%. 16. A blown plastic container containing a multilayer film according to any of claims 1-14. 17. A packaged product, comprising a multilayer film according to any of claims 1-14, and a content material packaged with the multilayer film in a heat shrunk state. 18. A packaged product according to claim 17, having a pattern printed on the outer surface layer (a). 19. A packaged product according to claim 17, wherein the multilayer film has been heat shrunk with hot water. 20. A packaged product according to claim 17, wherein the multilayer film has been heat shrunk with hot gas. 21. A packaged product according to claim 17, wherein the contained material has been packed with film by coating the contained material placed on a base film with the multilayer film, and by the heat sealing the multilayer film on the base film in a marginal portion of the multilayer film and the base film where the contained material is not found. 22. A packaged product according to claim 17, wherein the contained material has been packaged by flow by inserting the material contained in a flow packing material formed by the multilayer film and by heat sealing marginal portions of the film of multiple layers on each other. 23. A packaged product according to claim 17, wherein the contained material has been packaged in a tray by wrapping the contained material in a tray with the multilayer film, and by thermal shrinkage of the multilayer film. . 4. A packaged product according to claim 17, wherein the contained material has been packed in a tray by placing the material contained in a resin tray having a peripheral marginal portion where the contained material is not found, by means of the coating of a material contained with the film of multiple layers, and by heat sealing the multilayer film on the marginal portion of the resinous tray. A packaged product according to claim 17, wherein the material contained is food. A packaged product according to claim 25, wherein the food is meat. A packaged product according to claim 25, wherein the food is pizza.