Base material film for packaging film

Abstract

Disclosed is a base material film (F) for forming a packaging film by being laminated with a sealant film. The base material film (F) is composed of a stretched film which comprises at least one base layer (LP1, LP2) that is mainly composed of a high-density polyethylene having a density of 0.95 g / cm3 or more. The base material film (F) has a storage elastic modulus at 100°C of 400 MPa or more, and a thermal shrinkage rate in the stretching direction at 120°C of less than 5%.

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 a drawback in that they are prone to misalignment during printing (so-called printing misalignment) due to insufficient mechanical strength. Therefore, in order to prevent such misalignment, a method has been proposed in which a uniaxially stretched film made of polyethylene is used as the base film, as in Patent Document 1.

[0005] JP 2019-171860 A

[0006] However, the packaging film of Patent Document 1 uses medium-density polyethylene as the raw material for the base film, and therefore the difference between the heat-resistant temperature and the melting temperature of the sealant film is small, resulting in insufficient heat resistance of the base film, which causes wrinkles during the heat-sealing process during bag production. In addition, although a uniaxially oriented film is used as the base film, its rigidity is not sufficient, and positional deviation (i.e., printing deviation) may occur due to elongation caused by stress during the printing process.

[0007] An object of the present invention is to provide a base film for packaging films that not only overcomes the problems of conventional base 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, and is free from wrinkles due to heat sealing during bag production.

[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 having a storage modulus at 100°C of 400 MPa or more and a heat shrinkage rate in the stretching direction (longitudinal or transverse direction) at 120°C of less than 5%.

[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 characterized in that, in the invention described in claim 1 or claim 2, a barrier layer made of a barrier resin is provided between two base layers, one on the front and one on the back, made of the specific high-density polyethylene.

[0011] The invention described in claim 4 is characterized in that, in the invention described in claim 3, the barrier resin contains an ethylene-vinyl alcohol copolymer as a main component.

[0012] The invention described in claim 5 is characterized in that a vapor deposition layer is provided on one side of the substrate film described in claim 1 or claim 2.

[0013] The sixth aspect of the present invention is characterized in that a coating layer is provided on one side of the substrate film according to the first or second aspect.

[0014] A seventh aspect of the present invention is a packaging film comprising the barrier substrate film according to the third aspect, and a sealant film laminated on one of the base layers.

[0015] 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 Because it is made of polyethylene whose main component is high-density polyethylene having a density of 1000 or more, it can be stretched at a high stretch ratio, has excellent mechanical strength and rigidity, does not cause print misalignment due to stretching during the printing process, and can be stretched at a high stretching temperature, has excellent heat resistance, and does not wrinkle when heat-sealed during bag production.

[0016] 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.

[0017] The barrier substrate film described in claim 3 has a barrier layer made of a barrier resin between two base layers, one on the front and one on the back, made of specific high-density polyethylene, and therefore has excellent recyclability and can effectively prevent printing misalignment due to elongation in the printing process and the occurrence of wrinkles due to heat sealing, as well as imparting high barrier properties (properties that inhibit the permeation of gases such as oxygen and water vapor) to the packaging bag after bag production.

[0018] The barrier substrate film according to claim 4 contains a barrier resin mainly composed of an ethylene-vinyl alcohol copolymer, and therefore can impart very high barrier properties to the packaging bag after bag formation without affecting good recyclability.

[0019] The barrier substrate film according to claim 5 has a vapor-deposited layer on one side of the substrate film, and therefore can impart extremely high barrier properties to the packaging bag after it is made without affecting its good recyclability.

[0020] The barrier substrate film according to claim 6 has various coating layers on one side of the substrate film, so that various barrier properties can be imparted to the packaging bag after the bag is made.

[0021] The packaging film according to the seventh 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.

[0022] FIG. 2 is an explanatory diagram (vertical cross-sectional view) showing the layer structure of a barrier substrate film.

[0023] The base film according to the present invention is made of specific high-density polyethylene (0.95 g / cm ３The stretched film is composed of a base layer primarily composed of high-density polyethylene having a density of 100°C or higher, and the storage modulus at 100°C and the heat shrinkage at 120°C are adjusted to fall within predetermined ranges. That is, the inventors of the present invention discovered that problems with conventional polyethylene-based mono-material substrate films, such as print misalignment due to elongation in the printing process and the occurrence of wrinkles due to heat sealing during bag production, are related to the density of the polyethylene raw material and the storage modulus and heat shrinkage of the substrate film, and discovered that print misalignment and the occurrence of wrinkles can be eliminated by simultaneously specifying these physical property values ​​within predetermined ranges, which led to the invention of the present invention.

[0024] The substrate film according to the present invention is made of a specific high-density polyethylene (i.e., a polyethylene having a density of 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. ３ If 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 film can be stretched at a high temperature, 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 more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0025] In addition, specific high density polyethylene (i.e., density of 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.

[0026] 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).

[0027] 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.

[0028] Furthermore, as described above, in order to simultaneously specify the storage 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 approximately 4 to 10 times in the longitudinal direction or transverse direction, and in the case of biaxial stretching, stretching is preferably approximately 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. ３ If 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.

[0029] 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 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.

[0030] The above-mentioned base film (stretched film) must have a storage modulus at 100°C of 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.

[0031] Furthermore, as described above, stretching improves mechanical strength and rigidity (storage modulus), but stretching the film also increases the likelihood of thermal shrinkage, making it more likely to wrinkle due to heat sealing during bag formation. Therefore, it is preferable that the base film (stretched film) has a heat shrinkage rate in the stretching direction at 120°C of less than 5%. If the heat shrinkage rate of the base film in the stretching direction at 120°C is 5% or more, it is undesirable because it is more likely to wrinkle due to heat sealing during bag formation. The lower the heat shrinkage rate in the stretching direction at 120°C, the better; specifically, it is more preferably less than 3%, even more preferably less than 2%, and particularly preferably less than 1%. A heat shrinkage rate below 0% (i.e., stretching at 120°C) is undesirable because it is more likely to wrinkle due to heat sealing.

[0032] The substrate film according to the present invention comprises 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 barrier resin) 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.

[0033] 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, the specific high-density polyethylene preferably accounts for 70% by mass or more of the entire barrier substrate film, and more preferably 74% by mass or more.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 as a barrier film can be obtained. If the thickness of the barrier resin layer after stretching is 8 μm or less, a film with excellent recyclability can be obtained.

[0040] 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.

[0041] 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.

[0042] In addition, 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 or a metal oxide such as silicon dioxide, 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] <Storage Modulus at 100°C> The stretched films prepared in the Examples and Comparative Examples were cut into specimens measuring 50 mm length x 4 mm width to prepare test pieces. Using a viscoelasticity measuring device (TA Instruments' "DMA-Q800"), the test pieces were attached to a sample holder, and the storage modulus (MPa) was measured at a temperature range of room temperature (approximately 25°C) to 135°C at a heating rate of 3°C / min under the following conditions: frequency: 1 Hz, load: 0.2 N, measurement mode: tensile mode.

[0047] <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).

[0048] [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)

[0049] <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 four-point scale.

[0050] ◎: No printing misalignment is observed. ○: Almost no printing misalignment is observed. △: Slight printing misalignment is observed. ×: Printing misalignment is clearly observed.

[0051] <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.

[0052] ◎: No wrinkles are observed. ○: Almost no wrinkles are observed. △: Slight wrinkles are observed, but there is no problem. ×: Wrinkles are clearly observed.

[0053] The 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)

[0054] [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.

[0055] The storage modulus at 100°C and the heat shrinkage at 120°C were measured using the prepared base film by the methods described above. The appearance after printing and the appearance after heat sealing were also evaluated using the prepared base film by the methods described above. The measurement results and evaluation results of the base film of Example 1 are shown in Table 1, along with the properties of the base film.

[0056] [Example 2] The resin raw material was the above-mentioned high-density polyethylene HDPE2 (i.e., density = 0.960 g / cm ３ 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 uniaxially oriented polyethylene film used was changed to a specific high-density polyethylene (specified high-density polyethylene). The storage modulus at 100°C and the heat shrinkage at 120°C were measured using the produced substrate film by 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 Example 2 are shown in Table 1, along with the properties of the substrate film.

[0057] [Examples 3, 4, 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. The storage modulus at 100°C and the heat shrinkage at 120°C were measured using the produced substrate films by 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 films of Examples 3, 4, and 5 are shown in Table 1, along with the properties of the substrate films.

[0058] 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 storage modulus at 100°C and the heat shrinkage at 120°C were measured using the produced substrate film by 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 Example 6 are shown in Table 1, along with the properties of the substrate film.

[0059] 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 storage modulus at 100°C and the heat shrinkage at 120°C were measured using the produced substrate film by 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 Example 7 are shown in Table 1, along with the properties of the substrate film.

[0060] [Example 8] Using a multilayer extruder (manufactured by LABTECH) equipped with a T-die, the following resins a to f were melt-extruded (extrusion temperature: 200°C) in layers to be continuously molded into a film, and the long film was taken up while being cooled on a take-up roll to obtain an unstretched film (laminated film) having a thickness of about 157 μm and a five-layer structure as shown in FIG. 1 . The unstretched film was then stretched 6.0 times in the longitudinal direction (MD) while heated to 127°C to produce the uniaxially stretched polyethylene film (i.e., barrier substrate film) of Example 8 having a total thickness of about 25 μm. Note that the first base layer (L) consisting of HDPE1 in the obtained barrier substrate film Ｐ１ ), a first adhesive layer (L ａ１ ), a barrier resin layer (L Ｂ ), a second adhesive layer (L ａ２), a second base layer (L Ｐ２ The thicknesses of the barrier substrate films were 9.3 μm, 1.5 μm, 3.3 μm, 1.5 μm, and 9.3 μm, respectively (the proportion of the specific high-density polyethylene in the entire barrier substrate film was therefore 74.7 mass %). a. HDPE1: High-density polyethylene (density: 0.951 g / cm ３ , melting point: 133°C, MFR: 1.0 g / 10 min) b. Acid-modified polyethylene: (density: 0.91 g / cm ３ c. Ethylene-vinyl alcohol copolymer: (density: 1.19 g / cm 3, melting point: 120°C, MFR: 2.3 g / 10 min, manufactured by Mitsui Chemicals, Inc., Admer NF587) ３ , melting point: 183°C, MFR: 1.6 g / 10 min, ethylene content: 32 mol%, Kuraray Co., Ltd. EVAL F171B) d. Acid-modified polyethylene: (density: 0.91 g / cm ３ , melting point: 120 ° C., MFR: 2.3 g / 10 min, Admer NF587 manufactured by Mitsui Chemicals, Inc.) e. HDPE1: high-density polyethylene (density: 0.951 g / cm ３ , melting point: 133°C, MFR: 1.0 g / 10 min) The storage modulus at 100°C and the heat shrinkage at 120°C were measured using the prepared barrier substrate film by the methods described above. The prepared substrate film was also used to evaluate the appearance after printing and the appearance after heat sealing by the methods described above. The measurement results and evaluation results of the substrate film of Example 8 are shown in Table 1, along with the properties of the substrate film.

[0061] [Comparative Example 1] The resin raw material was MDPE (i.e., density = 0.943 g / cm ３A 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) used was changed, the stretching temperature when stretching the unstretched film (raw sheet) in the longitudinal direction (MD) was changed to 120°C, and the stretching ratio was changed to 4 times. The storage modulus at 100°C and the heat shrinkage at 120°C were measured using the produced substrate film by 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 1 are shown in Table 1, along with the properties of the substrate film.

[0062] [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 storage modulus at 100°C and the heat shrinkage at 120°C of the produced substrate film were measured by 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 2 are shown in Table 1, along with the properties of the substrate film.

[0063] 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.

[0064] 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.

[0065] Comparative Example 5 A uniaxially stretched polyethylene film (substrate film) was produced in the same manner as in Example 1, except that the stretching ratio when stretching the unstretched film (raw film) in the longitudinal direction (MD) was changed to 3 times. However, because the stretching ratio was 3 times, the obtained uniaxially stretched polyethylene film had a significant degree of stretching unevenness, and a uniaxially stretched polyethylene film that could not be evaluated was not obtained.

[0066] [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 storage modulus at 100°C and the heat shrinkage at 120°C of the obtained unstretched film were measured by 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 base film of Comparative Example 6 (i.e., the unstretched film) are shown in Table 1, along with the properties of the base film.

[0067]

[0068] From Table 1, it can be seen that when bags are made using base films and barrier base films (Examples 1 to 8) that use specific high-density polyethylene as the main raw material and that have a storage modulus at 100°C and a heat shrinkage rate at 120°C that satisfy the requirements of the present invention, printing misalignment does not occur and the appearance after heat sealing is good. In contrast, in Comparative Example 1, the density was 0.95 g / cm ３ It can be seen that because a base film made of polyethylene of less than 100°C is used, it cannot be stretched more than 4 times, resulting in a low storage modulus at 100°C, prone to printing misalignment, and a large heat shrinkage at 120°C, making it prone to wrinkling during heat sealing. In Comparative Example 2, the stretching temperature is as low as 115°C, which reduces dimensional stability during heat treatment and reduces heat resistance (leading to a large heat shrinkage at 120°C), making it prone to wrinkling during heat sealing. In Comparative Example 6, the base film is not stretched, so the storage modulus at 100°C is low, making it prone to printing misalignment.

[0069] 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.

[0070] F Barrier base film L Ｐ１ First base layer L made of specific high density polyethylene ａ１ First adhesive layer L Ｂ Barrier resin layer L ａ２ Second adhesive layer L Ｐ２ A second base layer made of specific high density polyethylene

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 The base film for packaging films is composed of a stretched film consisting of at least one base layer whose main component is the above-mentioned high-density polyethylene, and is characterized in that it has a storage modulus of 400 MPa or more at 100°C and a heat shrinkage rate in the stretching direction at 120°C of less than 5%.

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. A barrier substrate film for packaging films, comprising a barrier layer made of a barrier resin between the two front and back base layers as described in claim 1 or 2.

4. The barrier substrate film for packaging films according to claim 3, characterized in that the barrier resin is comprised primarily of an ethylene-vinyl alcohol copolymer.

5. A barrier substrate film for packaging films, comprising the substrate film according to claim 1 or 2, and a vapor deposition layer provided on one side thereof.

6. A barrier substrate film for packaging films, comprising the substrate film according to claim 1 or 2, and a coating layer provided on one side thereof.

7. A packaging film comprising the barrier substrate film according to claim 3 and a sealant film laminated on one of the base layers.

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