JP2007160573A - Heat-shrinkable stretched multilayered film, packaging material using it and package - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable stretched multilayered film having high transparency, high strength and high gas barrier properties under a high humidity condition and also having excellent packaging properties. <P>SOLUTION: The heat-shrinkable stretched multilayered film is constituted by laminating a resin layer comprising a thermoplastic resin (b) at least on one side of an intermediate layer comprising a glycolic acid (co)polymer resin (a) formed from polyglycolic acid containing a repeating unit represented by the formula (1) in a ratio of 60 mass% or above and the hot water shrinkage factors in the longitudinal and lateral directions of the heat-shrinkable stretched multilayered film at a temperature of 90°C are respectively set to 20% or above. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat-shrinkable stretched multilayer film useful as a bag-shaped packaging material, a pillow packaging material, a tray packaging lid material, a freezing packaging material, a casing packaging material, and the like, and a package using the same.

  Traditionally, stretch-shrinkable multilayer films have excellent heat-sealing properties, and the packaging material shrinks by moderate heating to fit the contents and give a beautiful and beautiful appearance. It is widely used as a packaging material for foods such as fish, cheese and soup. Among these foods, raw meat contains hemoglobin, which is a pigment in the blood, and myoglobin, which is a pigment in the muscles, so that the content of raw meat is likely to oxidize and discolor. .

  In order to solve such a problem, for example, JP 2003-535733 A (Patent Document 1) includes a surface layer (a) made of a thermoplastic resin, an intermediate layer (b) made of a polyamide-based resin, and A stretch-oriented multilayer film comprising at least three surface layers (c) made of a sealable resin and having an impact energy of 1.5 Joules or more in terms of a thickness of 50 μm at −10 ° C. is disclosed in the specification. Describes a shrinkable multilayer film comprising a PET / mod-VL / Ny / EVOH / mod-VL / LLDPE resin construction.

  However, in the conventional shrinkable multilayer film as described in Patent Document 1, Ny and EVOH having oxygen gas barrier properties related to the storage stability of the contents have humidity dependency, particularly under high humidity. Since the oxygen permeability is high, it is not always sufficient in that the oxygen gas barrier property under high humidity is inferior.

On the other hand, vinylidene chloride resin (PVDC) is known as a material that has excellent oxygen gas barrier properties and does not depend on humidity. However, PVDC is easily pyrolyzed and coextruded (melted) with various resins. In this case, a combination of laminated resins becomes a problem. For example, it can be easily co-extruded in combination with a low melting point resin such as polyethylene, ethylene copolymer, and ionomer, but in combination with a high melting point resin such as PET and Ny having a melting point exceeding 200 ° C. There was a problem that processing was very difficult.
Special table 2003-535733 gazette

  The present invention has been made in view of the above-described problems of the prior art, and has high transparency, high strength, high gas barrier properties under high humidity, and excellent heat shrinkability. It aims at providing a stretchable multilayer film, and a packaging material and a package using the same.

  As a result of intensive studies to achieve the above object, the present inventors have made a resin comprising a thermoplastic resin (b) on at least one side of an intermediate layer comprising a specific glycolic acid (co) polymer resin (a). The heat-shrinkable stretched multilayer film in which the layers and the hot-water shrinkage in the longitudinal direction and the transverse direction at a temperature of 90 ° C. are each 20% or more has high transparency, high strength, and high humidity. The present invention has been completed by finding that it has gas barrier properties and excellent packaging suitability.

  That is, the heat-shrinkable stretched multilayer film of the present invention has the following general formula (1):

From the thermoplastic resin (b) to at least one surface of the intermediate layer made of glycolic acid (co) polymer resin (a) formed from polyglycolic acid containing a repeating unit represented by And a hot water shrinkage in the vertical direction and the horizontal direction at a temperature of 90 ° C. is 20% or more, respectively.

In the heat-shrinkable stretched multilayer film of the present invention, the oxygen gas permeability is preferably 50 cm ³ / m ² · day · atm or less under the conditions of a temperature of 23 ° C. and 100% RH.

  Furthermore, in the heat shrinkable stretched multilayer film of the present invention, an outer layer made of the thermoplastic resin (b), an intermediate layer made of the glycolic acid (co) polymer resin (a), and a sealant resin (c). It is preferable to provide an inner layer.

  The bag-shaped packaging material of the present invention is characterized by comprising the heat-shrinkable stretched multilayer film.

  Moreover, the pillow packaging material of this invention consists of the said heat shrinkable stretched multilayer film, It is characterized by the above-mentioned.

  Furthermore, the lid | cover material for tray packaging of this invention consists of the said heat shrinkable stretched multilayer film, It is characterized by the above-mentioned.

  Moreover, the packaging material for freezing of this invention consists of the said heat shrinkable stretched multilayer film, It is characterized by the above-mentioned.

  Furthermore, the casing packaging material of the present invention comprises the heat-shrinkable stretched multilayer film.

  The package of the present invention comprises the heat-shrinkable stretched multilayer film.

  According to the present invention, a heat-shrinkable stretched multilayer film having high transparency, high strength, high gas barrier properties under high humidity and excellent packaging properties, and a packaging material using the same It becomes possible to provide a package.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the heat shrinkable stretched multilayer film of the present invention will be described. That is, in the heat-shrinkable stretched multilayer film of the present invention, a resin layer made of a thermoplastic resin (b) described later is laminated on at least one side of an intermediate layer made of a glycolic acid (co) polymer resin (a) described later. Thus, the hot water shrinkage in the vertical direction and the horizontal direction at a temperature of 90 ° C. is 20% or more, respectively. In the present invention, an outer layer made of a thermoplastic resin (b) described later, an intermediate layer made of a glycolic acid (co) polymer resin (a) described later, and an inner layer made of a sealant resin (c) described later It is preferable to provide.

(Glycolic acid (co) polymer resin)
The glycolic acid (co) polymer resin (a) used in the present invention has the following general formula (1):

It is formed from polyglycolic acid containing the repeating unit represented by When the repeating unit represented by the general formula (1) in the polyglycolic acid is less than 60% by mass, the crystallinity inherent to the polyglycolic acid is impaired, and the heat-shrinkable multilayer film obtained Gas barrier properties and heat resistance are reduced.

  In such polyglycolic acid, as a repeating unit other than the repeating unit represented by the general formula (1), for example, at least one repeating unit selected from the group consisting of the following general formulas (2) to (6) Can be contained.

In the said General formula (2), n represents the integer of 1-10 and m represents the integer of 0-10. Moreover, in the said General formula (3), j represents the integer of 1-10. Furthermore, the general formula (4), _{R 1} and _{R 2} may be the same or different, represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, k is an integer of 2 to 10. By introducing these other repeating units at a ratio of 1% by mass or more, the melting point of the polyglycolic acid homopolymer can be lowered. And if melting | fusing point of the said polyglycolic acid is lowered | hung, processing temperature can be lowered | hung and the thermal decomposition at the time of melt processing can be reduced. Moreover, by copolymerizing in this way, the crystallization speed of polyglycolic acid can be controlled to improve processability.

  Examples of a method for synthesizing such polyglycolic acid include a method of dehydrating polycondensation of glycolic acid, a method of dealcoholating polycondensation of glycolic acid alkyl ester, and a method of ring-opening polymerization of glycolide. Among these, glycolide is subjected to ring-opening polymerization by heating to a temperature of about 120 to 250 ° C. in the presence of a small amount of a catalyst (for example, a cation catalyst such as organic carboxylate tin, tin halide, antimony halide, etc.). A method of synthesizing polyglycolic acid (ie, polyglycolide) by a method is preferred. Such ring-opening polymerization is preferably performed by a bulk polymerization method or a solution polymerization method.

  On the other hand, a copolymer of polyglycolic acid can be synthesized by copolymerizing at least one selected from the group consisting of glycolic acid, glycolic acid alkyl ester, and glycolide with a copolymer component. Examples of such copolymer components include ethylene oxalate, lactide, and lactones (for example, β-propiolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, δ-valerolactone, β-methyl-δ-valero). Lactone, ε-caprolactone), trimethylene carbonate, 1,3-dioxane and other cyclic monomers; lactic acid, 3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic acid, 6-hydroxycaproic acid and other hydroxycarboxylic acids Examples include acids or alkyl esters thereof; aliphatic diols such as ethylene glycol and 1,4-butanediol; aliphatic dicarboxylic acids such as succinic acid and adipic acid or alkyl esters thereof. These copolymerization components may be used alone or in combination of two or more.

  Of these, cyclic compounds such as lactide, caprolactone, and trimethylene carbonate; and hydroxycarboxylic acids such as lactic acid are preferable from the viewpoint that a copolymer that is easily copolymerized and excellent in physical properties is easily obtained. These copolymerization components are used in a proportion of usually 45% by mass or less, preferably 30% by mass or less, more preferably 10% by mass or less of the total amount of monomers charged. When the ratio of these copolymer components increases, the crystallinity of the polymer to be produced tends to be impaired, and the heat resistance, gas barrier properties, mechanical strength, and the like of the resulting heat-shrinkable multilayer film tend to decrease.

Such glycolic acid (co) polymer resin is superior to EVOH in terms of fragrance retention from the viewpoint of measurement with an odor sensor or measurement of the amount of L-menthol permeation, etc. It is superior to EVOH. Further, such a glycolic acid (co) polymer resin preferably has a melt viscosity of 300 to 10,000 Pa · s measured under conditions of a temperature of 270 ° C. and a shear rate of 120 sec ⁻¹ , and 400 to 8, 000 Pa · s is more preferable, and 500 to 5,000 Pa · s is particularly preferable.

  Moreover, it is preferable that it is 200 degreeC or more, and, as for melting | fusing point (Tm) of such glycolic acid (co) polymer resin, it is more preferable that it is 210 degreeC or more. For example, polyglycolic acid has a melting point of about 220 ° C., a glass transition temperature of about 38 ° C., and a crystallization temperature of about 91 ° C. However, the melting point of these glycolic acid (co) polymer resins varies depending on the molecular weight of polyglycolic acid, the copolymer component, and the like.

  In the present invention, the glycolic acid (co) polymer resin can be used alone, but within the range not impairing the object of the present invention, the glycolic acid (co) polymer resin contains an inorganic filler, and the like. A resin composition containing a thermoplastic resin, a plasticizer, or the like can be used. In addition, the glycolic acid (co) polymer resin may include a heat stabilizer, a light stabilizer, a moisture proof agent, a waterproofing agent, a water repellent, a lubricant, a release agent, a coupling agent, an oxygen absorbent, Various additives such as pigments and dyes can be contained.

(Thermoplastic resin)
As the thermoplastic resin (b) used in the present invention, polyamide resin, polyester resin, polycarbonate resin, polystyrene resin, polyolefin resin, cyclic olefin resin, polyurethane resin, ionomer resin, biodegradable Resins can be mentioned. Among these thermoplastic resins, polyester resins, polyolefin resins, and polyamide resins are preferable from the viewpoint of excellent surface properties such as transparency, surface hardness, printability, and heat resistance.

  Examples of such polyester resins include aliphatic polyester resins and aromatic polyester resins. Such a polyester resin can be obtained, for example, by (condensation) polymerization of a dicarboxylic acid component and a diol component.

  Such a dicarboxylic acid component is not particularly limited as long as a polyester can be obtained by a normal production method. For example, terephthalic acid, isophthalic acid, adipic acid, oxalic acid, malonic acid, succinic acid, azelain Examples of the dimer acid include a dimer of an acid, sebacic acid, phthalic acid, 5-t-butylisophthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, cyclohexane dicarboxylic acid, and an unsaturated fatty acid. These dicarboxylic acid components may be used alone or in combination of two or more.

  In addition, such a diol component is not particularly limited as long as a polyester can be obtained by a normal production method. For example, ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, Examples include diethylene glycol, polyalkylene glycol, 1,4-cyclohexanedimethanol, and 2-alkyl-1,3-propanediol. These diol components may be used alone or in combination of two or more.

  Among such polyester resins, aromatic polyester resins containing an aromatic dicarboxylic acid component are preferred, terephthalic acid and isophthalic acid are used as the dicarboxylic acid component, and a diol having 10 or less carbon atoms is used as the diol component. Polyester resins obtained using these are preferred. Examples of these polyester resins include PET (polyethylene terephthalate) and PBT (polybutylene terephthalate). In addition, these polyester-type resins may be used individually by 1 type, or may mix and use 2 or more types. Further, as these polyester resins, those having an intrinsic viscosity of about 0.6 to 1.2 are preferably used.

  Examples of such polyolefin resins include ethylene homopolymers, propylene homopolymers; CLD 2-8 such as VLDPE (linear ultra-low density polyethylene) and LLDPE (linear low density polyethylene). A linear α-olefin copolymer; propylene-ethylene copolymer, propylene-ethylene-butene-1 copolymer, EVA (ethylene-vinyl acetate copolymer), EAA (ethylene-acrylic acid copolymer) , Polyolefins such as EMAA (ethylene-methacrylic acid copolymer), EMA (ethylene-methyl acrylate copolymer), EEA (ethylene-ethyl acrylate copolymer), EBA (ethylene-butyl acrylate copolymer) Examples thereof include a system copolymer. These polyolefin resins may be used alone or in combination of two or more.

  Further, examples of such polyamide resins include aliphatic polyamide polymers such as nylon 6, nylon 66, nylon 11, nylon 12, nylon 69, nylon 610; nylon 6/66, nylon 6/69, nylon 6 And aliphatic polyamide copolymers such as / 610 and nylon 6/12. Among these, nylon 6/66 and nylon 6/12 are particularly preferable in terms of moldability. These aliphatic polyamide (co) polymers may be used alone or in combination of two or more.

  Moreover, as such a polyamide-type resin, you may use the blend with aromatic polyamide which has these aliphatic polyamide (co) polymers as a main component. Such an aromatic polyamide means that at least one of diamine and dicarboxylic acid has an aromatic unit. For example, nylon 66/610 / MXD6 (here, “MXD6” is polymetaxylylene adipamide). Nylon 66/69 / 6I, Nylon 6 / 6I, Nylon 66 / 6I, Nylon 6I / 6T (where "Nylon 6I" is polyhexamethylene isophthalamide, "Nylon 6T" is polyhexamethylene terephthalamide) And the like.

(Sealant resin)
Examples of the sealant resin (c) used in the present invention include those having an appropriate seal strength in the range of 90 to 250 ° C. Examples of such a sealant resin (d) include polyethylene homopolymers or copolymers, polypropylene homopolymers or copolymers, ethylene copolymers, and ionomers. These sealant resins (d) may be used alone or in combination of two or more.

  Moreover, in this invention, it is preferable to mix and use the adhesive resin (d) in the range of 3-30 mass% to the said sealant resin (c) from an adhesive viewpoint with an adjacent resin layer.

(Heat-shrinkable stretched multilayer film)
The heat-shrinkable stretched multilayer film of the present invention is formed by laminating the above-mentioned resin layer made of the thermoplastic resin (b) on at least one side of the above-mentioned intermediate layer made of the glycolic acid (co) polymer resin (a). It is a film. And in the shrinkable multilayer film of this invention, the hot-water shrinkage | contraction rate (10 second) of the vertical direction and horizontal direction in temperature 90 degreeC needs to be 20% or more, respectively. Moreover, it is preferable that the hot-water shrinkage | contraction rate (10 second) of the vertical direction and horizontal direction in temperature 90 degreeC is 20 to 50%, respectively. When the hot water shrinkage is less than 20%, the tight fit property with the contents deteriorates. On the other hand, if it exceeds 50%, the contraction stress becomes strong and the shape of the contents tends to be deformed. The hot water shrinkage rate is a value measured by a method as described in Examples described later.

  Furthermore, the thickness of the heat-shrinkable stretched multilayer film of the present invention is preferably in the range of 20 to 150 μm. If the thickness of the film is less than the lower limit, the strength and gas barrier properties tend to be unsatisfactory. On the other hand, when the upper limit is exceeded, the internal pressure in inflation stretching during film production becomes high and film formation becomes difficult, and there is a tendency for economic disadvantages such as an increase in the amount of discarded packaging materials.

In the heat-shrinkable stretched multilayer film of the present invention, the resin layer made of the thermoplastic resin (b) is laminated on at least one surface of the intermediate layer made of the glycolic acid (co) polymer resin (a). An outer layer made of the thermoplastic resin (b) described above, an intermediate layer made of the glycolic acid (co) polymer resin (a), and an inner layer made of the sealant resin (d) described above. It is preferable to provide. Furthermore, from the viewpoint of adhesion between the layers of the above layers, an adhesive layer made of an adhesive resin (d) may be provided in addition to the above layers. Here, the example of the lamination | stacking aspect of the heat shrinkable stretched multilayer film of this invention is shown. However, these are merely examples, and the present invention is not limited to these.
1: (a) / (d) / (b),
2: (b) / (d) / (a) / (c),
3: (b) / (e) / (a) / (e) / (c),
4: (b) / (e) / (b) / (e) / (a) / (e) / (c).

  As the thickness of the intermediate layer made of such glycolic acid (co) polymer resin (a), the thickness of the intermediate layer is preferably 1 to 20 μm, and more preferably 1 to 10 μm. When the thickness of the intermediate layer is less than the lower limit, the function of high gas barrier property tends to be not obtained, and control of the film thickness during extrusion and film formation tends to be difficult. On the other hand, if the upper limit is exceeded, the rigidity of the resulting film tends to increase excessively, and the amount of packaging materials discarded tends to be economically disadvantageous.

  Moreover, as thickness of the outer layer which consists of such a thermoplastic resin (b), it is preferable that the thickness of a resin layer is 1-20 micrometers, and it is more preferable that it is 1-10 micrometers. If the thickness of the outer layer is less than the lower limit, the strength of the package tends to be insufficient. On the other hand, when the upper limit is exceeded, the film is too hard and the stretchability tends to deteriorate.

  Furthermore, as thickness of the inner layer which consists of such sealant resin (c), it is preferable that the thickness of an inner layer is 10-120 micrometers, and it is more preferable that it is 10-80 micrometers. When the thickness of the inner layer is less than the lower limit, sufficient seal strength tends to be not obtained. On the other hand, when the upper limit is exceeded, the strength of the package is insufficient and the transparency of the film tends to deteriorate.

  Moreover, as thickness of the adhesive bond layer which consists of such adhesive resin (d), it is preferable that the thickness of an adhesive bond layer is 1-10 micrometers, and it is more preferable that it is 1-5 micrometers. When the thickness of the adhesive layer is less than the lower limit, sufficient adhesive force tends not to be obtained. On the other hand, even if the upper limit is exceeded, no further improvement in adhesive strength can be expected, and there is a tendency for economic disadvantages such as an increase in the amount of packaging material discarded.

  Furthermore, when the resin layer comprising the thermoplastic resin (b) is provided as described above, the thickness of the resin layer is preferably 1 to 20 μm, and preferably 1 to 10 μm. It is more preferable that If the thickness of the resin layer is less than the lower limit, the strength of the package tends to be insufficient. On the other hand, when the upper limit is exceeded, the film is too hard and the stretchability tends to deteriorate.

In such a heat-shrinkable stretched multilayer film, the oxygen gas permeability is preferably 50 cm ³ / m ² · day · atm or less at a temperature of 23 ° C. and 100% RH, and preferably 30 cm ³ / m ^2. More preferably, it is not more than day · atm, more preferably not more than 20 cm ³ / m ² · day · atm. When the oxygen gas permeability exceeds the above upper limit, when food such as raw meat whose contents are easily oxidized is packaged, deterioration such as loss of redness tends to occur when the package is stored.

Further, in such a heat-shrinkable stretched multilayer film, the moisture permeability (WVTR) is preferably 20 g / m ² · day or less from the viewpoint of reduction. If the water vapor transmission rate (WVTR) exceeds 20 g / m ² · day, moisture in the contents of the package is likely to permeate and evaporate, and the taste amount that is the mass of the package tends not to be maintained.

  Furthermore, in such a heat-shrinkable stretched multilayer film, the haze value (cloudiness value) is preferably 10% or less, more preferably 8% or less, and particularly preferably 5% or less. If the haze value exceeds the upper limit, the shape, hue, etc. of the contents of the package tend to be unable to be visually judged.

  Moreover, it is desirable that such a heat-shrinkable stretched multilayer film has sufficient strength. For example, if the contents are boned meat, etc., the film will be pierced by a hard, sharp projection, and a hole will be opened. ) May open. Examples of methods for evaluating the strength include methods such as a piercing strength test, a gelboflex test (twist test, temperature condition: 5 ° C.), and a hexagonal rotational strength test described in the examples described later. .

The heat-shrinkable stretched multilayer film as described above can be suitably used as a bag-shaped packaging material, a pillow packaging material, a tray packaging lid material, a frozen packaging material, a casing packaging material, and the like. In addition, since such a heat-shrinkable stretched multilayer film is excellent in gas barrier properties, for example, in the case of vacuum packaging, in the case of gas pack packaging in which a gas such as nitrogen, carbon dioxide, oxygen, etc. is enclosed, an oxygen scavenger is enclosed. As in the case of packaging, the present invention can be suitably applied to a packaging technique that provides a gas composition or partial pressure condition different from the environment outside the package.
Furthermore, such a heat-shrinkable stretched multilayer film can be used for packaging articles such as foods that contain components that are susceptible to oxidative degradation or transpiration. Such heat-shrinkable stretched multilayer film is a food containing hemoglobin or myoglobin that easily undergoes oxidative discoloration, or derivatives thereof, such as beef, pork, horse meat, mutton, chicken, salmon, whale meat, fish meat. It can be particularly suitably used as a packaging material for processed meat products belonging to raw meats such as (fish and fish containing blood and red fish), sausages and hams. Further, such a heat-shrinkable stretched multilayer film can also be suitably used as a packaging material for dairy products such as butter and cheese containing carotenoid pigments that are likely to cause oxidative discoloration as well as heme pigments. Can be suitably used as a packaging material for salads, side dishes, vegetables, fruits, cereals and processed products thereof that have been subjected to various cooking treatments.

  In addition, the packaging body provided with such a heat-shrinkable stretched multilayer film is subjected to various conditions such as a room temperature condition of 10 to 40 ° C, a chilled or refrigerated condition of -1 to 10 ° C, and a freezing condition of -60 to -1 ° C. It can be stored or distributed.

(Method for producing heat-shrinkable stretched multilayer film)
Next, a method for producing the heat-shrinkable stretched multilayer film of the present invention will be described. The heat-shrinkable stretched multilayer film of the present invention forms a tubular body by coextruding at least two molten resins into a tubular shape,
The tubular body is water-cooled to below the melting point of the resin, and then the tubular body is reheated to a temperature equal to or higher than the melting point of the resin. A biaxially stretched film by stretching 2.5 to 4 times in the longitudinal direction and the lateral direction (circumferential direction of the tubular body) while being drawn in the flow direction),
Next, the biaxially stretched film is folded, and then heat treated with steam or hot water at 60 to 95 ° C. from the outer surface side of the biaxially stretched film while putting a fluid into the biaxially stretched film, and the heat treatment At the same time, by 10% to 35% relaxation (relaxation) in the vertical and horizontal directions,
Can be manufactured.

  In the present invention, from the viewpoint of realizing improvement of various properties required for a packaging film, the stretching ratio is 2.5 to 4 times in the longitudinal direction and the transverse direction (each direction of MD / TD). Preferably there is. When the draw ratio is less than 2.5, the heat shrinkability of the film necessary after heat treatment cannot be obtained, and the uneven thickness of the film also becomes large, so that packaging suitability tends to be difficult to obtain.

  Moreover, in this invention, it is preferable that the heat processing temperature which is relaxation heat treatment conditions is the range of 60-95 degreeC. When the heat treatment temperature is less than 60 ° C., relaxation during the heat treatment tends to be difficult, and when it exceeds 95 ° C., bubbles tend to meander and become unstable. Furthermore, in the present invention, the relaxation rate is preferably in the range of 5 to 35%. If the relaxation rate is less than 5%, the film tends to shrink spontaneously at room temperature, and the dimensional stability such as width unevenness tends to deteriorate. On the other hand, if it exceeds 35%, the bubble after relaxation becomes unstable, There is a tendency to cause unevenness and make stable production impossible.

  In general, the highly stretched film is not subjected to high relaxation heat treatment. The reason is that it is considered that a high relaxation heat treatment that works in the direction of reducing the rigidity and strength of the film obtained by stretching is not desirable. However, in the present invention, it has been found that a high-strength film can be obtained even by performing a high stretch-high relaxation heat treatment. Although the reason for this is not necessarily clear, the present inventors speculate as follows. That is, the crystal part and the amorphous part of the film constituent molecules are molecularly oriented by stretching, and tensile strength and the like are improved. In this state, the elongation at break of the film tends to decrease, but since the orientation of the amorphous part is relaxed while maintaining the crystal orientation by high relaxation heat treatment, the elongation at break is maintained while maintaining the film strength such as tensile strength. The present inventors speculate that this is improved. The present inventors infer that the physical properties of the film, that is, puncture strength, drop impact strength, pinhole resistance, and the like can be sufficiently achieved by the effect of relaxation of the amorphous part.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example. The resins used in Examples and Comparative Examples are shown together with their abbreviations in Table 1. Moreover, the manufacturing conditions of the heat-shrinkable stretched multilayer film in Examples and Comparative Examples are summarized in Tables 2 and 3.

Example 1
First, in order from the outer side to the inner side and the thickness shown in the parenthesis in the lamination mode, PGA (3 [mu] m) / M-PE (1.5 [mu] m) / VLDPE (40 [mu] m) is used for each resin with a plurality of extruders. Melt extrusion was performed, and the melted resin was introduced into an annular die, where it was melt-bonded so as to have the above-described layer configuration, and co-extrusion processing was performed. The molten annular body having a temperature of 250 ° C. flowing out from the die outlet was cooled to 10 to 25 ° C. in a water bath to obtain an annular body having a flat width of about 180 mm. Next, the obtained flat annular body is heated while passing warm water of about 90 ° C., and then converted into a bubble-shaped tubular body in the longitudinal direction (MD) by the inflation method while cooling with a 15 ° C. to 20 ° C. air ring. Simultaneous biaxial stretching was performed at a stretching ratio of 2.9 times in the transverse direction (TD). Next, the obtained biaxially stretched film is introduced into a cylindrical heat treatment tube to form a bubble-shaped film, and relaxed by 5% in the machine direction (MD) and 10% in the transverse direction (TD) at a heat treatment relaxation temperature of 90 ° C. Relaxed heat treatment was performed for about 2 seconds to obtain a biaxially stretched film (heat-shrinkable stretched multilayer film). The folding width of the obtained heat-shrinkable stretched multilayer film was about 450 mm and the thickness was 44.5 μm.

(Examples 2-3, Comparative Examples 1-4)
A biaxially stretched film (heat-shrinkable stretched multilayer film) was obtained in the same manner as in Example 1 except that the film production conditions were changed as shown in Tables 2 and 3, respectively. In addition, in the manufacturing conditions of the film of Comparative Example 3, PVDC was thermally decomposed during the coextrusion process, and a biaxially stretched film (heat shrinkable stretched multilayer film) could not be obtained. Moreover, in the manufacturing conditions of the film of Comparative Example 4, bubble rupture occurred during biaxial stretching, and a biaxially stretched film (heat-shrinkable stretched multilayer film) could not be obtained.

  The folding widths of the obtained heat-shrinkable stretched multilayer films were about 450 mm (Examples 2 to 4), about 450 mm (Comparative Example 1), and about 416 mm (Comparative Example 2), respectively. Moreover, the thickness of the obtained heat-shrinkable stretched multilayer film was 50 μm (Example 2), 38 μm (Examples 3 and 4), 38.5 μm (Comparative Example 1), and 60 μm (Comparative Example 2), respectively. .

<Evaluation of properties of heat-shrinkable stretched multilayer film>
(I) Evaluation Method Various properties of the heat-shrinkable multilayer film were evaluated or measured by the following method.

(1) Hot water shrinkage The hot drawing shrinkage film for deep drawing obtained was marked at a distance of 10 cm in the machine direction (longitudinal direction, MD) and in the direction perpendicular to the machine direction (lateral direction, TD). The film sample was immersed in hot water adjusted to 90 ° C. for 10 seconds, then taken out and immediately cooled with water at room temperature. Thereafter, the marked distance was measured, and the ratio of the decrease from 10 cm to the original length of 10 cm was displayed as a percentage. One sample was tested five times, and the average value in each of the vertical and horizontal directions was displayed as the hot water shrinkage.

(2) Transparency (haze value)
Based on the method described in JIS K-7105, the haze (haze;%) of the film sample was measured using a haze meter NDH-Σ80 manufactured by Nippon Denshoku Industries Co., Ltd. as a measuring device. The haze value means that the smaller the value, the better the transparency, and the larger the value, the worse the transparency.

(3) Film strength (breaking strength test)
Using a TENSILON RTC-1210 type (manufactured by Orientec) as a measuring device, a strip-shaped film sample having a width of 10 mm and a length of 50 mm was stretched at a temperature of 23 ° C. at a crosshead speed of 200 mm / min, and the film sample was broken. The stress at the time was measured.

(4) Gas barrier properties (i) Oxygen permeability According to JIS K-7126, oxytolan (OX-TRAN 2/20) manufactured by Modern Control Co., Ltd. is used under conditions of a temperature of 10 ° C. and / or 23 ° C. and 100% RH. And measured.
(Ii) Moisture permeability (WVTR)
Based on the method described in JIS Z-0208, the measurement was performed by the cup method under the conditions of a temperature of 40 ° C. and a humidity of 90% RH.

(5) Pinhole resistance Gelboflex tester no. 902 was used to conduct a torsion test (film sample size: 60 mmφ × 300 mm, test speed 40 cycles / min, twist angle: 440 ° C.) under a temperature condition of 5 ° C. Sampling was performed every 100 times up to 100 to 1000 times, and the presence or absence of pinholes was visually observed. The number of twists in which pinhole generation was recognized was used as an index of pinhole resistance. That is, it can be judged that the larger this value, the better the pinhole resistance.

(6) Melt hole resistance After fixing a film sample on an embroidery frame having a diameter of 15 cm and applying 1 g of lard to the center of the film sample, 70 ° C, 75 ° C, 80 ° C, 85 ° C, 90 ° C, Dry heat treatment was performed at 95 ° C. and 100 ° C. for 5 minutes. The film sample treated under each temperature condition was visually observed for the presence of a melt hole in the center of the sample. The temperature at which melt holes occurred was used as an index of resistance to melt holes. That is, it can be judged that the higher the temperature, the better the melt hole resistance.

(II) Evaluation result About each heat-shrinkable stretched multilayer film obtained in Examples 1 to 4 and Comparative Examples 1 and 2, various properties of the heat-shrinkable stretched multilayer film were evaluated or measured by the above methods. Table 4 shows the obtained results.

  As is clear from the results shown in Table 4, it was confirmed that the heat-shrinkable multilayer film for deep drawing of the present invention has high transparency, high strength, and high gas barrier properties under high humidity. .

<Evaluation of packaging suitability of pouch packaging materials (pouch packaging suitability)>
(I) Production of packaging body Using the heat-shrinkable stretched multilayer film obtained in Examples 1 and 3, pouch-shaped bags (12 cm × 12 cm) are prepared, and each is filled with beef leg meat and packaged. The pouch packaging (Examples 5 and 6) was obtained by shrinking in hot water at 80 ° C. for 10 seconds. Also, comparative pouch packagings (Comparative Examples 5 and 6) were obtained in the same manner as described above except that the heat-shrinkable stretched multilayer films obtained in Comparative Examples 1 and 2 were used. The oxygen gas permeability at temperatures of 10 ° C. and 23 ° C. of each heat-shrinkable stretched multilayer film used in Examples 5 and 6 and Comparative Examples 5 and 6 was measured by the method described above. The results obtained are shown in Table 5.

(II) Evaluation of Package Each obtained pouch package was stored for 30 days, 45 days, and 60 days under conditions of 1-2 ° C. and 100% RH, and the color tone after opening was evaluated. That is, after opening the pouch package, the contents were cut out from the surface with a thickness of 1 cm, and the surface of the contents was used as a specimen, and a color difference meter SE2000 manufactured by Nippon Denshoku Industries Co., Ltd. was used. Redness) was measured. The results obtained are shown in Table 5. In addition, it can be said that redness is so strong that a value is high, and a discoloration degree is small.

  As is apparent from the results shown in Table 5, it was confirmed that the heat-shrinkable stretched multilayer film of the present invention did not cause discoloration that would cause a practical problem even when stored for a long time under high humidity conditions. It was. Therefore, it was confirmed that the heat-shrinkable stretched multilayer film of the present invention has excellent pouch packaging suitability.

<Evaluation of packaging suitability of bag-shaped packaging materials (bag packaging suitability)>
(I) Production of packaging body The heat-shrinkable stretched multilayer film obtained in Examples 1 to 3 was processed into a bag (bag) having a width of 300 mm and a length of 500 mm using a Kureha Chemical (BM48) bag making machine. did. And after filling each bag with about 1 kg of cow prickly block meat, vacuum packaging using a Multivac AGW type vacuum packaging machine, and then shrinking in hot water for 10 seconds at 80 ° C. Examples 7 to 9) were obtained. These test samples were kept in a state where water adhered without wiping off the water adhering at the time of hot water shrinkage. Further, a comparative bag package (Comparative Example 7) was obtained in the same manner as described above except that the heat-shrinkable stretched multilayer film obtained in Comparative Example 1 was used.

(II) Evaluation of packaging body Each obtained bag packaging body was preserved for 60 days under conditions of 1 to 2 ° C and 100% RH, and the color tone after opening was evaluated. That is, after opening the bag package, the a value (redness) in the Lab value was measured by the method described above. The results obtained are shown in Table 6.

  As is apparent from the results shown in Table 6, it was confirmed that when the heat-shrinkable stretched multilayer film of the present invention was used, no discoloration that would cause a practical problem even when stored for a long time under high humidity conditions was confirmed. It was. Therefore, it was confirmed that the heat-shrinkable stretched multilayer film of the present invention has excellent bag packaging suitability.

<Evaluation of packaging suitability of pillow packaging material>
First, using the heat-shrinkable stretched multilayer film obtained in Example 3, 150 g of commercially available sliced roast ham and an oxygen scavenger (Mitsubishi Gas Chemical, SS-100) were encapsulated. Next, using a horizontal pillow packaging machine (manufactured by Ibaraki Seiki Co., Ltd., CFP-3000N) under the conditions of a seal temperature of 120 ° C. and a shrinker temperature of 135 ° C. (hot air), a foamed PS tray (length 220 mm × width 120 mm × depth 20 mm) ) Was put in a horizontal pillow packaging to obtain a tray-in pillow packaging (Example 10). The obtained tray in pillow package (Example 10) was excellent in both transparency and film tension. The obtained tray-in pillow package was stored for 30 days under conditions of temperature 5 ° C. and 1000 lux fluorescent lamp irradiation, and then the oxygen concentration in the package was measured (gas chromatographic analysis). The oxygen concentration in the package was 0.0%, and it was confirmed that the oxygen-free state was well maintained. Furthermore, no discoloration of sliced ham was observed in the package after storage for 30 days.

  Therefore, it was confirmed that the heat-shrinkable stretched multilayer film of the invention has excellent pillow packaging suitability.

<Evaluation of packaging suitability of tray packaging materials>
Using the heat-shrinkable stretched multilayer film obtained in Example 3 as a cover material, a barrier tray (length 195 mm × width 145 mm × depth 30 mm) using EVOH as a gas barrier layer as a tray, and 200 g of sliced beef as contents Using a case ready machine (manufactured by Mondini, CV / VG-S type SE2671T) as a packaging machine, sealing conditions of 120 ° C. × 3 seconds, gas (O ₂ / CO ₂ = 80/20 vol%) replacement for 4 seconds A lid (lid) was processed under the conditions to obtain a tray package (Example 11). The obtained tray package (Example 11) was excellent in both transparency and film tension, and had a beautiful appearance. Further, when the obtained tray package was stored at 5 ° C. for 5 days, no meat discoloration or significant bacterial growth was observed (the number of general bacteria before storage: 10 ⁴ / g → general bacteria after 5 days) Number: 10 ⁵ / g, number of coliforms before storage: <10 / g → number of coliforms after 5 days: <10 / g). The number of general bacteria was determined by counting the number of colonies generated after 30 ° C. × 72 hours by a pour plate method using a normal agar medium, and the number of coliforms was 37 ° C. × 24 hours using a dezoxycholate medium. This was determined by counting the number of colonies generated after the culture.

  Therefore, it was confirmed that the heat-shrinkable stretched multilayer film of the invention has excellent tray packaging suitability.

<Evaluation of packaging suitability of freezing packaging materials>
The heat-shrinkable stretched multilayer film obtained in Example 3 was processed into a three-side sealed pouch (bag) having a width of 200 mm and a length of 300 mm by hand-made bag. Then, after filling the pouch with about 200 g of frozen bigeye tuna sac, vacuum packaging was performed using a Multivac AGW-type vacuum packaging device to obtain a frozen packaging (Example 12). Further, a comparative refrigeration package (Comparative Example 8) was obtained in the same manner as above except that the heat-shrinkable stretched multilayer film obtained in Comparative Example 2 was used. Twenty of each of the refrigeration packages thus obtained (Example 12 and Comparative Example 8) were packed in a foamed polystyrene box together with dry ice, and transported back and forth between about 200 km one way. After arrival, the occurrence of broken bags in the packaging was examined. As a result, the number of broken bags was 0 (0%) in the freezing packaging (Example 12), and the comparative freezing packaging (Comparative Example 8). There were 8 broken bags (40%). Therefore, it was confirmed that the heat-shrinkable stretched multilayer film of the invention has excellent freezing packaging suitability.

<Evaluation of packaging suitability of casing packaging materials>
(I) Production of packaging body The heat-shrinkable stretched multilayer film obtained in Examples 1 to 3 was processed into a casing having a folding width of 60 mm by hand-made bag. And after fastening one side of each casing with a clip, it filled with 250 g of liver sausage paste meat, and boiled for 60 minutes at the temperature of 80 degreeC, and obtained the packaging body for Examples (Examples 13-15). Further, a comparative casing packaging (Comparative Example 9) was obtained in the same manner as described above except that the heat-shrinkable stretched multilayer film obtained in Comparative Example 1 was used.

(II) Evaluation of packaging body Each obtained packaging body for casing was stored for 30 days under the conditions of irradiation at 5 ° C, 100% RH, and 1000 lux fluorescent lamp, and the color tone after opening was evaluated. That is, after opening the bag package, the a value (redness) in the Lab value was measured by the method described above. The results obtained are shown in Table 7.

  As is apparent from the results shown in Table 7, it was confirmed that the heat-shrinkable stretched multilayer film of the present invention did not cause discoloration that would cause a practical problem even when stored for a long time under high humidity conditions. It was. Therefore, it was confirmed that the heat-shrinkable stretched multilayer film of the present invention has excellent casing packaging properties.

  As described above, according to the present invention, a heat-shrinkable stretched multilayer film having high transparency, high strength, high gas barrier properties under high humidity, and excellent packaging suitability, and It becomes possible to provide a packaging material and a package using this.

Therefore, the heat-shrinkable stretched multilayer film of the present invention, and a packaging material and package using the same are useful as technologies relating to bag-shaped packaging, pillow packaging, tray packaging, freezing packaging, casing packaging, and the like.

Claims (9)

The following general formula (1):
From the thermoplastic resin (b) to at least one surface of the intermediate layer made of glycolic acid (co) polymer resin (a) formed from polyglycolic acid containing a repeating unit represented by A heat-shrinkable stretched multilayer film characterized in that the hot-water shrinkage in the longitudinal direction and the transverse direction at a temperature of 90 ° C. is 20% or more. ^2. The heat-shrinkable stretched multilayer film according to claim 1, wherein the oxygen gas permeability is 50 cm ³ / m ² · day · atm or less under conditions of a temperature of 23 ° C. and 100% RH.   The outer layer made of the thermoplastic resin (b), the intermediate layer made of the glycolic acid (co) polymer resin (a), and the inner layer made of a sealant resin (c), 2. A heat-shrinkable stretched multilayer film according to 2.   A bag-shaped packaging material comprising the heat-shrinkable stretched multilayer film according to any one of claims 1 to 3.   A pillow packaging material comprising the heat-shrinkable stretched multilayer film according to any one of claims 1 to 3.   A cover for tray packaging, comprising the heat-shrinkable stretched multilayer film according to any one of claims 1 to 3.   A refrigeration packaging material comprising the heat-shrinkable stretched multilayer film according to any one of claims 1 to 3.   A casing packaging material comprising the heat-shrinkable stretched multilayer film according to any one of claims 1 to 3.   A package comprising the heat-shrinkable stretched multilayer film according to any one of claims 1 to 3.