Base material film for packaging film

Abstract

A base material film for forming a packaging film by being laminated with a sealant film, said base material film being composed of a stretched film comprising at least one base layer having a high-density polyethylene with a density of 0.95 g / cm3 or higher as a main component, wherein the thermal shrinkage in the stretching direction is less than 5% at 120°C, and the tensile modulus of elasticity is 2,000 MPa or higher.

Description

Base film for packaging films

[0001] The present invention relates to a base film used to form various packaging films.

[0002] Films used to form packaging bags such as pouches and gusset bags used to package daily necessities, food, etc. (so-called packaging films) are made more functional by laminating films made of different materials such as the following: - Base film: This film improves strength and serves as a printing base material, and is made of nylon, polyester, polypropylene, etc. - Barrier film: This film blocks oxygen, water vapor, light, etc., and is made of barrier resins such as EVOH (ethylene-vinyl alcohol copolymer), or synthetic resin films vapor-deposited with metals such as aluminum or inorganic materials such as its oxides. - Sealant film: This film serves to heat-seal (thermally fuse) films together, and is made of low-density polyethylene, linear low-density polyethylene, etc.

[0003] In recent years, there has been a demand for reducing the environmental impact of plastic products in general, and recycling of packaging films is also being sought. However, laminated films made of different materials as described above have the problem that they are difficult to separate and recycle. Therefore, as a means of improving recyclability, a method of using a single resin raw material has been proposed. In light of the fact that polyethylene is the most widely used packaging material, a packaging film with excellent recyclability has been developed in which both the sealant film and the base film are made of polyethylene.

[0004] However, packaging films in which both the sealant film and the base film are made of polyethylene have insufficient mechanical strength, and are therefore prone to misalignment during printing (so-called printing misalignment). Therefore, in order to prevent such misalignment, a method of using a uniaxially stretched film made of polyethylene as the base film has been proposed, as in Patent Document 1. Furthermore, a laminate in which a vapor-deposited film is provided on a base film has also been proposed to improve gas barrier properties.

[0005] JP 2019-171861 A

[0006] However, the base film of Patent Document 1 uses medium-density polyethylene as a raw material, and therefore the difference between the heat resistance temperature and the melting temperature of the sealant film is small, resulting in the disadvantage that the heat resistance of the base film is insufficient, and wrinkles occur during the heat-sealing process when making bags. In addition, although a uniaxially stretched film is used as the base film, its rigidity is not sufficient, and misalignment (i.e., printing misalignment) may occur due to stretching caused by stress in the printing process. In addition, the packaging film of Patent Document 1 has a vapor deposition layer laminated on the base film to improve barrier properties, but it is thought that thermal shrinkage of the base film due to insufficient heat resistance and cracks or fissures in the vapor deposition layer due to stretching of the base film during transportation after vapor deposition due to insufficient rigidity occur, and therefore sufficient gas barrier properties are not obtained (water vapor permeability is 1.0 g / m ２ ・day or more).

[0007] An object of the present invention is to provide a substrate film for a packaging film that not only overcomes the problems of conventional substrate films for packaging films such as those described in Patent Document 1, but also has excellent recyclability, is free from printing misalignment due to elongation during the printing process, is free from wrinkles due to heat sealing during bag production, and is capable of forming a uniform and stable vapor-deposited layer that does not develop cracks or fissures during lamination of the vapor-deposited layer or during transportation after vapor deposition.

[0008] The present invention is directed to a base film for forming a packaging film by laminating it with a sealant film, the base film having a density of 0.95 g / cm ３ The film is composed of a stretched film having at least one base layer whose main component is the above-mentioned high-density polyethylene (hereinafter referred to as specific high-density polyethylene) (i.e., 50% by mass or more of specific high-density polyethylene), and is characterized by a heat shrinkage rate in the stretching direction (longitudinal direction or width direction) at 120°C of less than 5% and a tensile modulus of elasticity of 2,000 MPa or more.

[0009] The invention described in claim 2 is characterized in that, in the invention described in claim 1, the content ratio of the specific high-density polyethylene in the base layer is 90 mass% or more.

[0010] The invention described in claim 3 is a substrate film according to claim 1 or claim 2, which has a vapor deposition layer (an inorganic vapor deposition layer, a metal vapor deposition layer, etc.) on one side thereof, and has an oxygen permeability of 1.0 cc / (m ２ The barrier substrate film for packaging films is characterized in that the film has a shelf life of 100 days or less.

[0011] The invention described in claim 4 is characterized in that a sealant film is laminated on the surface of the barrier substrate film described in claim 3 opposite to the surface having the vapor deposition layer.

[0012] The base film for packaging film (hereinafter simply referred to as base film) described in claim 1 is made of polyethylene, so that there is no need to separate the packaging film laminated with a sealant film made of polyethylene when discarding it, and therefore it has excellent recyclability. Furthermore, the base film described in claim 1 is made of specific high-density polyethylene (0.95 g / cm ３ Since the base film is made of polyethylene containing as its main component a high-density polyethylene having a density of 1000 or more (high-density polyethylene having a density of 1000 or more or more), it can be stretched at a high stretching temperature, has excellent heat resistance, and does not wrinkle when heat-sealed during bag making. It can also be stretched at a high stretching ratio, and has excellent mechanical strength and rigidity, so that printing misalignment due to elongation does not occur during the printing process. In addition, since the base film described in claim 1 has excellent heat resistance, when a vapor-deposited layer is laminated onto the base film to form a laminate film having barrier properties (barrier base film), heat shrinkage does not occur during the vapor deposition process, and a uniform vapor-deposited layer without cracks or fissures can be formed, thereby achieving good barrier properties. Furthermore, since the base film has excellent mechanical strength and rigidity, even when a vapor-deposited layer is laminated onto the base film to form a laminate film having barrier properties (barrier base film), the vapor-deposited layer does not crack or fissure during transportation, etc., thereby preventing the barrier properties from being impaired.

[0013] The substrate film described in claim 2 has a high ratio of specific high-density polyethylene in the base layer, making it highly recyclable and capable of being melted and recycled. It also effectively prevents printing misalignment due to stretching during the printing process and wrinkles due to heat sealing.

[0014] The barrier substrate film described in claim 3 is obtained by laminating a vapor deposition layer on one side of a substrate film having a high ratio of specific high-density polyethylene, thereby adjusting the oxygen permeability to an extremely low level, and therefore has good recyclability and can impart extremely high and stable barrier properties to the packaging bags after bag production.

[0015] The packaging film according to the fourth aspect of the present invention has a sealant film laminated on one of the base layers of the barrier substrate film, so that a packaging bag can be easily formed.

[0016] The base film according to the present invention is made of specific high-density polyethylene (0.95 g / cm ３ The present invention is based on a stretched film having a base layer primarily composed of high-density polyethylene (high-density polyethylene having a density of 100°C or higher), and has a heat shrinkage at 120°C and a tensile modulus (tensile modulus at room temperature) adjusted to fall within predetermined ranges. The inventors of the present invention discovered that problems with conventional polyethylene monomaterial substrate films, such as print misalignment due to elongation during the printing process, wrinkles caused by heat sealing during bag production, and the inability to achieve stable, high barrier properties after vapor deposition, are related to the density of the polyethylene raw material and the tensile modulus and heat shrinkage of the substrate film. They then discovered that specifying these physical property values ​​within predetermined ranges can eliminate the print misalignment and wrinkles and enable stable, high barrier properties to be achieved after vapor deposition. This finding led to the invention of the present invention.

[0017] The substrate film according to the present invention is made of a specific high-density polyethylene (i.e., 0.95 g / cm ３ It is necessary that the base layer is made of a polyethylene having a density of 0.95 g / cm or higher. ３If the density of the polyethylene is 0.95 g / cm or more, the crystallinity of the polyethylene is improved, and the mechanical strength and rigidity of the film can be improved by stretching the film, thereby preventing printing misalignment due to elongation during the printing process. ３ If the density is 0.95 g / cm or more, the stretching at high temperatures becomes possible, thereby improving heat resistance and suppressing the occurrence of wrinkles due to heat sealing during bag making. ３ If the content of the specific high-density polyethylene in the base layer is less than 70% by mass, the mechanical strength and heat resistance of the substrate film will be insufficient, which is undesirable. The content of the specific high-density polyethylene in the base layer is preferably 70% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0018] Also, specific high density polyethylene (i.e., 0.95 g / cm ３ The above high-density polyethylene can be obtained by a polymerization method (constant pressure method) using a Ziegler-Natta catalyst or a metallocene catalyst. The density of the specific high-density polyethylene is 0.95 g / cm. ３ There is no particular limitation as long as it is equal to or greater than 0.97 g / cm ３ This means that the density is preferably 0.97 g / cm or less. ３ If the density exceeds 0.955 g / cm, the film becomes hard and easily torn, which may make it difficult to produce a stretched film. ３ More preferably, it is 0.962 g / cm or more. ３ It is particularly preferable that the above value is satisfied.

[0019] The melting point of the specific high-density polyethylene is preferably in the range of 130 to 140°C, and more preferably 132 to 140°C. If the melting point is less than 130°C, stretching at a temperature equal to or higher than the stretching temperature (120°C) described below may not be possible, and the heat resistance of the stretched film may decrease. The "melting point" refers to the value measured in accordance with JIS K 7121:1987, and is determined by measuring the temperature at which a main endothermic peak appears using a differential scanning calorimeter (DSC).

[0020] On the other hand, the melt mass flow rate (MFR) of the specific high-density polyethylene is preferably 0.01 to 3.00 g / 10 min, more preferably 0.02 to 2.50 g / 10 min, and even more preferably 0.1 to 2.00 g / 10 min. A melt mass flow rate (MFR) of 0.01 g / 10 min or higher allows molding using a general-purpose extruder without the need for special equipment, while a melt mass flow rate of 3.00 g / 10 min or lower allows sufficient film strength to be imparted. The melt mass flow rate can be obtained by measurement in accordance with the provisions of JIS K7210:1999.

[0021] Furthermore, as described above, in order to specify the tensile modulus and heat shrinkage of a substrate film made of specific high-density polyethylene within the predetermined numerical ranges of the present invention, it is necessary to stretch an unstretched film (raw sheet) made of specific high-density polyethylene, and a method of stretching at a higher stretching temperature than usual can be preferably used. Furthermore, the stretching direction is not particularly limited, and may be the longitudinal direction (MD) or the transverse direction (TD). (Biaxial stretching in MD and TD is also possible.) The stretching ratio is also not particularly limited, but in the case of uniaxial stretching, stretching is preferably performed by approximately more than 4 to 10 times in the longitudinal direction or transverse direction, and in the case of biaxial stretching, stretching is preferably performed by approximately more than 4 to 10 times in each of the longitudinal direction and transverse direction. Stretching at the above-mentioned stretching ratios improves the mechanical strength and rigidity of the substrate film, making it possible to prevent printing misalignment due to elongation during the printing process. In the case of uniaxial stretching, if the stretching ratio is 3 times or less, non-uniform stretching may occur, and stretching spots (stretching irregularities) may occur. Conversely, if the stretching ratio exceeds 10 times, the film may break. In the case of uniaxial stretching, the stretching ratio is more preferably 6 times or more from the viewpoint of improving mechanical strength and rigidity. Furthermore, in the case of uniaxial stretching, in order to stretch at a stretching ratio of more than 4 times to 10 times, the density should be 0.95 g / cm ３ It is preferable to use a specific high density polyethylene having a density of 0.95 g / cm or more. ３If polyethylene of less than this value is used, it may be difficult to stretch the film at a draw ratio of more than 4. As a method for stretching in the longitudinal direction, a method in which the rotation speeds of take-up rolls are made different can be suitably used, and as a method for stretching in the width direction, a method in which the left and right sides of the unstretched film are gripped in a tenter and expanded in the width direction can be suitably used.

[0022] Furthermore, the stretching temperature when obtaining the above-mentioned stretched film is not particularly limited, but from the viewpoint of improving dimensional stability by heat treatment and obtaining a film with excellent heat resistance, it is preferably 120°C or higher and lower than 130°C, which is a temperature range higher than the stretching temperature of ordinary polyethylene films. If the stretching temperature is lower than 120°C, the dimensional stability by heat treatment decreases and heat resistance decreases, which is undesirable because wrinkles tend to occur when the base film is heat-sealed to form a bag, and conversely, if the stretching temperature is 130°C or higher, melt fracture occurs during film formation, which is undesirable because it reduces the yield. The stretching temperature is more preferably 125°C or higher and lower than 130°C, and particularly preferably 127°C or higher and lower than 130°C. When the stretching temperature is 125°C or higher, the density is preferably 0.95 g / cm. ３ It is preferable to use a specific high density polyethylene having a density of 0.95 g / cm or more. ３ If the temperature is less than this, it may be difficult to stretch the film at 125°C or higher.

[0023] Furthermore, when the tensile modulus (tensile modulus at room temperature) of a substrate film made of specific high-density polyethylene is specified within a predetermined numerical range according to the present invention to eliminate printing misalignment and wrinkles and to exhibit stable barrier properties after vapor deposition, the tensile modulus must be 2,000 MPa or more, more preferably 2,500 MPa or more, and particularly preferably 3,000 MPa or more. A substrate film with a tensile modulus of less than 2,000 MPa is undesirable because it is more likely to cause printing misalignment during the printing process and fails to provide stable barrier properties (barrier properties that do not deteriorate due to impact) after vapor deposition. The higher the tensile modulus of the substrate film, the better, but considering the properties of the specific high-density polyethylene, which is the main raw material, a maximum value of approximately 5,000 MPa is considered appropriate.

[0024] Furthermore, as described above, stretching improves mechanical strength and rigidity (tensile modulus), but stretching the film also increases the likelihood of thermal shrinkage, making it more susceptible to wrinkling during heat sealing during bag production. Therefore, when using a method for specifying the thermal shrinkage rate in the stretching direction at 120°C of a substrate film made of specific high-density polyethylene within the specified numerical range of the present invention to eliminate printing misalignment and wrinkling and thereby achieve stable barrier properties after vapor deposition, it is preferable that the thermal shrinkage rate in the stretching direction at 120°C be less than 5%. A substrate film with a thermal shrinkage rate in the stretching direction at 120°C of 5% or more is undesirable because it is more likely to cause wrinkling during heat sealing during bag production or because a uniform vapor deposition layer cannot be formed during vapor deposition due to thermal shrinkage, making it difficult to achieve good barrier properties. The lower the thermal shrinkage rate in the stretching direction at 120°C, the better; specifically, less than 3% is more preferable, less than 2% is even more preferable, and less than 1% is particularly preferable. A value below 0% (i.e., stretching at 120°C) is undesirable because it is more likely to cause wrinkling during heat sealing.

[0025] Furthermore, the storage modulus of the above-mentioned base film (stretched film) at 100°C is preferably 400 MPa or more, more preferably 500 MPa or more, even more preferably 600 MPa or more, and particularly preferably 700 MPa or more. If the storage modulus of the base film at 100°C is less than 400 MPa, printing misalignment is likely to occur during the printing process, which is not preferable. Note that the higher the storage modulus of the base film at 100°C, the better, but considering the properties of the specific high-density polyethylene that is the main raw material, the maximum value is thought to be around 1500 MPa.

[0026] The substrate film according to the present invention has a base layer of a single layer structure made of the above-mentioned specific high-density polyethylene. Meanwhile, a film in which a barrier resin layer (i.e., a layer made of a resin with barrier properties) is interposed between base layers made of the above-mentioned specific high-density polyethylene, or a film in which a barrier resin layer is laminated on one or both sides of a base layer made of the above-mentioned specific high-density polyethylene, is called a barrier substrate film. The barrier resin in the present invention refers to a resin that has the function of inhibiting the permeation of gases such as oxygen and water vapor. Suitable examples of such barrier resins include ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol, and derivatives thereof.

[0027] Furthermore, when a barrier resin layer is interposed between base layers made of specific high-density polyethylene, or when a barrier resin layer is laminated on one or both sides of a base layer made of specific high-density polyethylene, an adhesive layer can be provided between the barrier resin layer and the base layer made of specific high-density polyethylene. By providing such an adhesive layer, it becomes possible to more effectively prevent delamination between the barrier resin layer and the base layer made of specific high-density polyethylene. Furthermore, acid-modified polyethylene, acid-modified polypropylene, etc. can be suitably used as such an adhesive, but acid-modified polyethylene is preferred from the viewpoint of monomateriality. In the substrate film according to the present invention, when another layer such as a barrier resin layer is interposed between base layers made of specific high-density polyethylene as described above, or when another layer such as a barrier resin layer is laminated on both sides of a base layer made of specific high-density polyethylene, from the viewpoint of improving recyclability, it is preferable that the specific high-density polyethylene account for 70% by mass or more of the entire barrier substrate film, and more preferably 74% by mass or more.

[0028] In addition, as a method for manufacturing the base film, raw materials containing the above-mentioned specific high-density polyethylene are mixed in a predetermined blending ratio, and the mixture is formed into a film by melt extrusion using an extruder equipped with a T-die, thereby obtaining a raw film before stretching the base film.

[0029] In addition, in a method for producing a barrier substrate film having a barrier resin layer between two front and back base layers each made of specific high-density polyethylene, the resins to be used for the base layer, the barrier resin layer, and the adhesive layer are each prepared, and the resins for each layer are co-extruded using a multi-layer extruder equipped with a T-die to obtain a raw film of the barrier substrate film before stretching.

[0030] The thus-produced base film or raw film before stretching of the barrier base film is uniaxially stretched under the stretching conditions as described above to obtain a stretched base film or barrier base film.

[0031] Here, the thickness of the raw film before stretching is preferably 50 to 300 μm, more preferably 80 to 250 μm, and particularly preferably 100 to 200 μm. If the thickness of the raw film is 50 μm or more, it can obtain strength that can withstand the stress during stretching. Furthermore, if the thickness of the raw film is 300 μm or less, it can obtain sufficient transparency after stretching.

[0032] The thickness of the substrate film or the base layer of the barrier substrate film after stretching is preferably from 10 to 40 μm, more preferably from 15 to 35 μm, and particularly preferably from 20 to 30 μm.

[0033] The thickness of the barrier resin layer after stretching is preferably 1 to 8 μm, more preferably 2 to 6 μm, and particularly preferably 2.5 to 5.0 μm. If the thickness of the barrier resin layer after stretching is 1 μm or more, sufficient oxygen and water vapor barrier properties can be obtained as a barrier film.

[0034] Furthermore, if the thickness of the barrier resin layer after stretching is 8 μm or less, a film with excellent recyclability can be obtained.

[0035] The thickness of the adhesive layer after stretching is not particularly limited, but is preferably 0.3 to 2 μm, more preferably 0.5 to 1.5 μm.

[0036] Furthermore, the base film or barrier base film according to the present invention is used in a packaging film (i.e., a film for forming a packaging bag) by laminating a sealant film on one side thereof, and then laminating the packaging film so that the sealant film surfaces are joined together, cutting the film into a predetermined shape, and heat-sealing the periphery to form a pouch, gusset bag, two-sided bag, three-sided bag, etc. As the sealant film to be attached to the base film according to the present invention, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene, etc. can be suitably used, but from the viewpoint of improving heat-sealability, low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), which has a melting point lower than that of the base film, is preferred in order to provide a difference in melting point from the base film.

[0037] Furthermore, the substrate film according to the present invention can be used as a packaging film by laminating, if necessary, a barrier resin layer, a printed layer, a vapor-deposited layer made of a metal such as aluminum oxide, a metal oxide such as silicon dioxide, or an inorganic compound, a substrate layer made of ordinary polyethylene (low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene, high-density polyethylene, etc.) on the surface opposite to the adhesive surface of the sealant film. In addition, when a vapor-deposited layer made of a metal such as aluminum oxide, a metal oxide such as silicon dioxide, or an inorganic compound is laminated on one surface (or both surfaces) of the substrate film according to the present invention, it is preferable to provide an anchor coat layer made of a mixture of a urethane resin, a curing agent, and a silane coupling agent, etc., between the vapor-deposited layer and the substrate film in order to increase the adhesion of the vapor-deposited layer.

[0038] Furthermore, the substrate film according to the present invention can be used as a packaging film by providing a coating layer between the sealant film and the substrate film, if necessary. The coating layer is made of a barrier resin, which means a resin that has the function of suppressing the transmission of gases such as oxygen and water vapor. Suitable examples of such barrier resins include ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol, and derivatives thereof.

[0039] Furthermore, the melting point of the base film (after stretching) made of specific high-density polyethylene is preferably 135° C. or higher. When the melting point of the base film is 135° C. or higher, it is possible to increase the difference in melting point between the base film and the sealant film, and this makes it possible to suppress thermal shrinkage of the base film during heat sealing.

[0040] The substrate film according to the present invention will be described in more detail below based on examples, but the present invention is not limited to the embodiments of these examples and can be modified as appropriate within the scope of the present invention. The properties in the examples and comparative examples were evaluated as follows.

[0041] <Tensile Modulus (Tensile Modulus at Room Temperature)> Test specimens were prepared by cutting the stretched films obtained in the Examples and Comparative Examples into strips measuring 200 mm in the machine direction (MD) and 10 mm in the transverse direction (TD). According to JIS-K-7127, the test specimens were stretched in the machine direction (MD) using a tensile tester (Shimadzu Corporation, Autograph®, Model AG-5000A) under conditions of 25°C x 65% RH, a chuck distance of 80 mm, and a tension speed of 10 mm / min. The tensile modulus (MPa) was calculated as the ratio of the tensile stress within the tensile proportional limit corresponding to two points between 0 and 1% strain to the corresponding strain.

[0042] <Heat Shrinkage at 120°C> A sample of a predetermined size (12 cm x 12 cm) was cut from the stretched film produced in the Examples and Comparative Examples, and a 10 cm long, perpendicular benchmark line parallel to each side of the sample was drawn 1 cm inward from each side. The sample was placed in an oven at 120°C and heated for 10 minutes, then removed and cooled to room temperature (about 25°C). The distance between the benchmark lines in the stretching direction (i.e., MD) of the heat-treated sample was measured, and the heat shrinkage (%) was calculated from the change in the benchmark line distance in the stretching direction before and after heating using the following formula (1).

[0043] [Equation 1] Heat shrinkage rate in the stretching direction (%)=[(gauge line distance before heating−gauge line distance after heating) / gauge line distance before heating]×100 (1)

[0044] <Appearance after printing> Packaging films were produced by laminating a 100 μm-thick linear low-density polyethylene (LLDPE) sealant film onto one side of the substrate films produced in the Examples and Comparative Examples. A commercially available gravure printing ink was then printed on the side of the packaging film opposite the sealant film using a gravure printing machine equipped with a gravure roll and doctor blade under specified conditions (printing speed = 75 m / min, drying temperature = 70°C, contact pressure of the nip roll on the substrate film = 0.15 MPa). The printed surface was then visually evaluated using the following three-point scale.

[0045] ○: No printing misalignment is observed. △: Very slight printing misalignment is observed. ×: Printing misalignment is clearly observed.

[0046] <Appearance after heat sealing> Packaging films were produced by attaching (laminating) a 100 μm thick linear low-density polyethylene (LLDPE) sealant film to one side of the base film produced in the Examples and Comparative Examples. The resulting packaging films were then overlapped so that the sealant films were bonded together, and heat-sealed at a temperature of approximately 120°C using a heat sealer. The heat-sealed surface was then visually evaluated using the following four-point scale.

[0047] ◎: No wrinkles are observed. ○: Almost no wrinkles are observed. △: Slight wrinkles are observed, but there is no problem. ×: Wrinkles are clearly observed.

[0048] <Oxygen Permeability (Gas Barrier Properties)> An anchor coating agent consisting of a mixture of a urethane resin, a curing agent, and a silane coupling agent was coated on the surface of the long stretched film obtained in the Examples and Comparative Examples to form a 0.1 μm-thick anchor coating layer. A vapor-deposited layer consisting of an inorganic compound was laminated on the anchor coating layer using silicon dioxide as the vapor deposition material by vacuum vapor deposition to obtain a barrier substrate film. The obtained barrier substrate film was then cut to a predetermined size (15 cm x 15 cm) to prepare a test piece. The oxygen permeability of the test piece was measured using an oxygen permeability measuring device (MOCON OX-TRAN, manufactured by Mocon, USA) in an atmosphere of 23°C and 75% humidity in accordance with JIS K 7126B. The oxygen permeability was measured by permeating oxygen from the vapor-deposited layer side toward the substrate film side. The measured oxygen permeability was evaluated using the following two-level scale.

[0049] ○: Oxygen permeability is 1.0 cc / (m ２ ×: Oxygen permeability is 1.0 cc / (m ２ ・day)

[0050] <Water Vapor Permeability (Gas Barrier Property)> The barrier substrate film used in the above-described oxygen permeability measurement (a film obtained by coating the surface of the stretched film obtained in the Examples and Comparative Examples with an anchor coating agent and then vapor-depositing the coating) was cut to a predetermined size (15 cm x 15 cm) to prepare a test specimen. The test specimen was then measured in accordance with JIS K 7129A using a water vapor permeability measuring device (L80-4000J, manufactured by Lissie, Switzerland) in an atmosphere of 40°C and 90% humidity. The water vapor permeability was measured by allowing water vapor to permeate from the vapor-deposited layer side toward the substrate film side. The measured water vapor permeability was then evaluated according to the following two-level scale.

[0051] ○: Water vapor permeability is 1.0 g / (m ２ ×: Water vapor permeability is 1.0 g / (m ２The resin raw materials used to prepare the stretched films in the examples and comparative examples are as follows: HDPE1: High density polyethylene (density: 0.951 g / cm ３ , melting point: 133 ° C., MFR (melt flow rate measured according to a method in accordance with JIS K7210, the same applies hereinafter): 1.0 g / 10 min) HDPE2: high-density polyethylene (density: 0.960 g / cm ３ , melting point: 135 ° C, MFR: 1.0 g / 10 min, Novatec HY540 manufactured by Japan Polyethylene Co., Ltd.) MDPE: medium density polyethylene (density: 0.943 g / cm ３ Melting point: 126°C, MFR: 0.24g / 10min, Prime Polymer Co., Ltd., Hi-Zex 5100E)

[0052] [Example 1] <Preparation of base film> The above-mentioned high-density polyethylene HDPE1 (i.e., density = 0.951 g / cm ３ A specific high-density polyethylene (specified high-density polyethylene) was continuously formed into a film by melt-extrusion at 200°C using an extruder (manufactured by LABTECH) equipped with a T-die, and the long film was cooled and wound up on a take-up roll to obtain an unstretched film (raw film) having a thickness of approximately 147 μm. The unstretched film was then stretched 6.0 times in the longitudinal direction (MD) while heated to 127°C, to produce a uniaxially stretched polyethylene film (i.e., substrate film) having a thickness of approximately 24 μm.

[0053] The resulting substrate film was then used to measure the tensile modulus, heat shrinkage at 120°C, and gas barrier properties (oxygen permeability, water vapor permeability) after deposition using the methods described above. The resulting substrate film was also used to evaluate the appearance after printing and after heat sealing using the methods described above. The measurement and evaluation results for the substrate film of Example 1 are shown in Table 1, along with the properties of the substrate film.

[0054] Example 2 A uniaxially oriented polyethylene film (i.e., substrate film) of Example 2 was produced in the same manner as in Example 1, except that the resin raw material was changed to the above-mentioned high-density polyethylene HDPE2. The produced substrate film was then used to measure the tensile modulus, heat shrinkage at 120°C, and gas barrier property after vapor deposition using the methods described above, and the appearance after printing and the appearance after heat sealing were also evaluated. The measurement results and evaluation results of the substrate film of Example 2 are shown in Table 1, along with the properties of the substrate film.

[0055] [Examples 3, 4, and 5] Uniaxially stretched polyethylene films (i.e., substrate films) of Examples 3, 4, and 5 were produced in the same manner as in Example 1, except that the stretching temperature when stretching the unstretched film (raw sheet) in the longitudinal direction (MD) was changed to 125°C, 120°C, and 128°C, respectively. Using the produced substrate films, the tensile modulus, heat shrinkage at 120°C, and gas barrier property after vapor deposition were measured by the methods described above, and the appearance after printing and the appearance after heat sealing were also evaluated. The measurement results and evaluation results of the substrate films of Examples 3, 4, and 5 are shown in Table 1, along with the properties of the substrate films.

[0056] Example 6 A uniaxially stretched polyethylene film (i.e., substrate film) of Example 6 was produced in the same manner as in Example 1, except that the stretching temperature when stretching the unstretched film (raw sheet) in the longitudinal direction (MD) was changed to 125°C and the stretching ratio was changed to 4.5 times. The produced substrate film was then used to measure the tensile modulus, heat shrinkage at 120°C, and gas barrier property after vapor deposition using the methods described above, and the appearance after printing and the appearance after heat sealing were also evaluated. The measurement results and evaluation results of the substrate film of Example 6 are shown in Table 1, along with the properties of the substrate film.

[0057] Example 7 A uniaxially stretched polyethylene film (i.e., substrate film) of Example 7 was produced in the same manner as in Example 1, except that the stretch ratio when stretching the unstretched film (raw sheet) in the longitudinal direction (MD) was changed to 10 times. The produced substrate film was then used to measure the tensile modulus, heat shrinkage at 120°C, and gas barrier property after vapor deposition using the methods described above, and the appearance after printing and the appearance after heat sealing were also evaluated. The measurement results and evaluation results of the substrate film of Example 7 are shown in Table 1, along with the properties of the substrate film.

[0058] [Comparative Example 1] The resin raw material was MDPE (i.e., density = 0.943 g / cm ３ A uniaxially oriented polyethylene film (substrate film) of Comparative Example 1 was produced in the same manner as in Example 1, except that the uniaxially oriented polyethylene film (medium-density polyethylene) was changed to 120°C when the unstretched film (raw sheet) was stretched in the longitudinal direction (MD), and the stretching temperature was changed to 120°C and the stretching ratio was changed to 4 times. The produced substrate film was then measured for its tensile modulus, heat shrinkage at 120°C, and gas barrier property after vapor deposition by the methods described above, and its appearance after printing and appearance after heat sealing were also evaluated. The measurement results and evaluation results of the substrate film of Comparative Example 1 are shown in Table 1, along with the properties of the substrate film.

[0059] [Comparative Example 2] A uniaxially stretched polyethylene film (substrate film) of Comparative Example 2 was produced in the same manner as in Example 1, except that the stretching temperature when stretching the unstretched film (raw sheet) in the longitudinal direction (MD) was changed to 115°C. The produced substrate film was then used to measure the tensile modulus, heat shrinkage at 120°C, and gas barrier property after vapor deposition using the methods described above, and the appearance after printing and the appearance after heat sealing were also evaluated. The measurement results and evaluation results of the substrate film of Comparative Example 2 are shown in Table 1, along with the properties of the substrate film.

[0060] Comparative Example 3 An attempt was made to produce a uniaxially oriented polyethylene film in the same manner as in Example 1, except that the stretching temperature when stretching the unstretched film (raw sheet) in the longitudinal direction (MD) was changed to 130°C. However, because the stretching temperature was 130°C, many breaks occurred during stretching due to melting of the resin, and it was not possible to obtain an evaluable uniaxially oriented polyethylene film.

[0061] Comparative Example 4 An attempt was made to produce a uniaxially stretched polyethylene film in the same manner as in Example 1, except that the stretching ratio when stretching the unstretched film (raw sheet) in the longitudinal direction (MD) was changed to 11 times. However, because the stretching ratio was 11 times, many breaks occurred during stretching, and no uniaxially stretched polyethylene film that could be evaluated was obtained.

[0062] Comparative Example 5 An attempt was made to produce a uniaxially stretched polyethylene film in the same manner as in Example 1, except that the stretching ratio when stretching an unstretched film (raw film) in the longitudinal direction (MD) was changed to 3 times. However, because the stretching ratio was 3 times, so-called stretching unevenness occurred, and a uniform uniaxially stretched polyethylene film that could be evaluated could not be obtained.

[0063] [Comparative Example 6] An unstretched film (raw sheet) was obtained in the same manner as in Example 1, except that the thickness was adjusted to about 26 μm. The unstretched film obtained was then used to measure the tensile modulus, heat shrinkage at 120°C, and gas barrier property after vapor deposition using the methods described above, and the appearance after printing and the appearance after heat sealing were evaluated. The measurement results and evaluation results of the substrate film of Comparative Example 6 (i.e., the unstretched film) are shown in Table 1, along with the properties of the substrate film.

[0064]

[0065] From Table 1, it can be seen that the substrate films (Examples 1 to 7) that use specific high-density polyethylene as the main raw material and that satisfy the requirements of the present invention in terms of tensile modulus and heat shrinkage at 120°C do not suffer from printing misalignment, have good appearance after heat sealing, and obtain good gas barrier properties (low oxygen permeability and water vapor permeability) after vapor deposition. In contrast, in Comparative Example 1, the density was 0.95 g / cm ３It can be seen that because Comparative Example 2 uses a base film made of polyethylene less than 115°C, it cannot be stretched more than 4 times, resulting in a low tensile modulus, prone to printing misalignment, and a large heat shrinkage at 120°C, which makes it prone to wrinkling during heat sealing, and good barrier properties cannot be obtained after vapor deposition. In Comparative Example 2, the stretching temperature is as low as 115°C, which reduces dimensional stability during heat treatment and reduces heat resistance (large heat shrinkage at 120°C), making it prone to wrinkling during heat sealing and preventing good barrier properties from being obtained after vapor deposition. In Comparative Example 6, the base film is not stretched, which reduces the tensile modulus, prone to printing misalignment, and prevents good barrier properties from being obtained after vapor deposition.

[0066] The substrate film according to the present invention has the excellent effects as described above, and therefore can be suitably used as a material for packaging films for forming various packaging bags.

Claims

1. A base film for laminating with a sealant film to form a packaging film, the base film having a density of 0.95 g / cm ３ A base film for packaging films, which is composed of a stretched film consisting of at least one base layer whose main component is the above-mentioned high-density polyethylene, and which is characterized in that the thermal shrinkage rate in the stretching direction at 120°C is less than 5% and the tensile modulus of elasticity is 2,000 MPa or more.

2. The base layer has a density of 0.95 g / cm ３ 2. The base film for packaging films according to claim 1, characterized in that the content of the high density polyethylene is 90% by mass or more.

3. The substrate film according to claim 1 or 2, which has a deposition layer on one side thereof and has an oxygen permeability of 1.0 cc / (m ２ .day) or less.

4. A packaging film comprising the barrier substrate film according to claim 3 and a sealant film laminated on the surface opposite to the surface on which the vapor deposition layer is formed.

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