Manufacturing method of laminated film

Abstract

This invention provides a method for manufacturing laminated films that reduces curling when heat-sealing a substrate with a different material. [Solution] A method for manufacturing a laminated film, comprising the steps of: applying an anchor coating agent to one side of a substrate made of polyethylene terephthalate with a thickness of 5 to 30 μm and drying it at 50 to 80°C to form an anchor coating layer; and laminating a sealant with a thickness of 3 to 20 μm, made of low-density polyethylene, linear low-density polyethylene, ethylene-methacrylic acid copolymer, or ethylene-acrylic acid copolymer, wherein the substrate is a film with an orientation angle of less than 40°.

Description

Technical Field

[0001] The present invention relates to a method for producing a laminated film having heat sealability.

Background Art

[0002] Polyethylene terephthalate (PET) films are highly transparent and have stiffness, so they are used as packaging materials for foods and the like. For example, Patent Document 1 describes a packaging laminated film formed by laminating a biaxially oriented polyester film and a sealant film.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In addition to the above-described characteristics, PET films are excellent in toughness, electrical insulation, heat and cold resistance, chemical resistance, etc., so they are also widely used as industrial materials in various fields such as electricity, environment, and optics. On the PET film, layers of various materials are laminated according to the application. For example, on the PET film, a different material from PET can be heat-sealed through a sealant to form a laminate. In this case, if there is a difference in the thermal shrinkage rate between the PET and the different material, the laminate will curl due to thermal shrinkage during heat sealing, and the transportability and processability in subsequent processes will deteriorate.

[0005] Therefore, an object of the present invention is to provide a method for producing a laminated film in which curling when heat-sealing with a material different from the base material is reduced.

Means for Solving the Problems

[0006] The present invention relates to a method for manufacturing a laminated film, comprising the steps of: applying an anchor coating agent to one side of a substrate made of polyethylene terephthalate with a thickness of 5 to 30 μm and drying it at 50 to 80°C to form an anchor coating layer; and laminating a sealant with a thickness of 3 to 20 μm, made of low-density polyethylene, linear low-density polyethylene, ethylene-methacrylic acid copolymer, or ethylene-acrylic acid copolymer, on the anchor coating layer, wherein the substrate is a film with an orientation angle of less than 40°. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for manufacturing a laminated film in which curling is reduced when the substrate is heat-sealed with a material different from that of the substrate. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a cross-sectional view showing the schematic configuration of a laminated film according to an embodiment. [Figure 2] Figure 2 shows the cutting position of the PET film from the mother roll. [Figure 3] Figure 3 illustrates the height of the edge rise of the laminate after heat sealing. [Figure 4] Figure 4 is a diagram illustrating the heat sealing method in the embodiment. [Modes for carrying out the invention]

[0009] Figure 1 is a cross-sectional view showing the schematic configuration of a laminated film according to an embodiment.

[0010] The laminated film 1 comprises a base material 2 and a sealant 3 laminated on one side of the base material 2.

[0011] The base material 2 is a film made of polyethylene terephthalate (PET). It is preferable to use a biaxially oriented PET film for the base material 2. Since PET film has excellent heat resistance, cold resistance, water resistance, and electrical insulation properties, using a PET film as the base material 2 allows the laminated film 1 to be used as an industrial material in various fields.

[0012] As the base material 2, a PET film with an orientation angle of less than 40° is used. Here, the orientation angle is the angle that the slow axis makes with respect to the flow direction (MD direction) of the PET film. In biaxially oriented PET film, the molecular chains are oriented obliquely to the MD direction during stretching. Therefore, rectangular PET films cut parallel to the MD direction and the TD direction, respectively, tend to curl around an axis perpendicular to the orientation direction of the molecular chains, so the corners of the rectangular PET film are more prone to lifting due to curling compared to the sides. In this embodiment, by using a base material 2 with an orientation angle within the above range, the acute angle that the orientation direction of the molecular chains makes with respect to the MD direction can be reduced, and the direction of the curl axis (the axis perpendicular to the orientation direction of the molecular chains) can be brought closer to the MD direction or the TD direction, thereby reducing the lifting of the corners of the rectangular base material.

[0013] The thickness of the base material 2 is preferably 5 to 30 μm. If the thickness of the base material 2 is less than 5 μm, the toughness of the laminated film 1 will decrease, which is undesirable. Also, if the thickness of the base material 2 exceeds 30 μm, the thickness of the laminated film 1 will increase, which is undesirable.

[0014] Furthermore, it is preferable to apply an anchor coating agent to the surface of the substrate 2 on which the sealant 3 is laminated in order to improve the adhesion between the substrate 2 and the sealant 3. In addition, the surface of the substrate 2 on which the sealant 3 is laminated may be subjected to corona treatment, plasma treatment, or the like.

[0015] The sealant 3 is a layer that imparts heat-sealability to the laminated film 1 and is used to heat-seal dissimilar materials other than PET. Preferably, the material of the sealant 3 is one of the following: low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ethylene-methacrylic acid copolymer (EMAA), or ethylene-acrylic acid copolymer (EAA). The sealant 3 can be formed by extruding and laminating these resins onto one side of the substrate 2.

[0016] The thickness of sealant 3 is preferably 3 to 20 μm. If the thickness of sealant 3 is less than 3 μm, it is undesirable because the heat seal strength with dissimilar materials may decrease. If the thickness of sealant 3 exceeds 20 μm, it is undesirable because the thickness of the laminated film 1 becomes large.

[0017] The thickness of the laminated film 1 is preferably 8 to 50 μm. If the thickness of the laminated film 1 is within this range, it can contribute to making equipment and other devices using the laminated film 1 thinner, and the environmental burden can be reduced by reducing the amount of material used.

[0018] Here, we will describe the manufacturing method of the laminated film 1 according to the embodiment.

[0019] Figure 2 shows the cutting position of the PET film from the mother roll.

[0020] First, as the base material 2, a PET film with an orientation angle of less than 40° is prepared. The PET film serving as the base material 2 can be obtained by slitting a mother roll into a strip with a predetermined width parallel to the MD direction. However, the orientation angle of the PET film varies depending on the position in the width direction (TD direction). Therefore, the PET film used as the base material of the laminated film 1 according to the present embodiment is cut out from a portion excluding the portions of the strip-shaped regions 11a and 11b each including the edge portions 10a and 10b in the width direction of the mother roll 5 shown in FIG. 2 (for example, the strip-shaped region 12 shown in FIG. 2). Thereby, the orientation angle of the PET film used as the base material 2 can be within the above-described range.

[0021] Next, after performing a surface treatment such as corona treatment on one surface of the base material 2 as necessary, an anchor coat agent is applied. The anchor coat agent is applied to one surface of the base material 2 in the state of a coating solution dissolved in ethyl acetate. Then, the base material 2 coated with the coating solution of the anchor coat agent is heated and dried to volatilize the solvent, thereby forming an anchor coat layer. The drying temperature for volatilizing the solvent is set to 50 to 80°C. When the drying temperature is less than 50°C, it is not preferable because the solvent cannot be sufficiently volatilized. Also, this drying step is performed with a tension for conveyance applied to the base material 2. However, when the drying temperature exceeds 80°C, while the heat shrinkage force of the base material 2 increases, the heat shrinkage is suppressed by the tension applied to the base material 2. Therefore, internal stress due to heat shrinkage remains in the base material 2 cooled after the drying step. When heat is applied to the base material 2 in the step of heat-sealing a different material to the sealant 3, the shrinkage of the base material 2 increases due to the remaining internal stress, leading to an increase in the curl of the laminated film 1. Therefore, the drying of the coating solution of the anchor coat agent is performed at a temperature of 80°C or lower.

[0022] Next, a sealant 3 is laminated on one surface of the base material 2. The sealant 3 can be formed by extrusion laminating any one of thermoplastic resins such as LDPE, LLDPE, EMAA, and EAA on the base material 2.

[0023] In this embodiment, the laminated film 1 uses a PET film with an orientation angle of less than 40° as the base material 2, and furthermore, the drying process of the solvent during anchor coat layer formation is carried out at 50 to 80°C, thereby suppressing the thermal shrinkage of the laminated film 1. Specifically, the thermal shrinkage rate of the laminated film 1 after being stored at 100°C for 15 minutes is 0 to 0.4% in the flow direction (MD direction) of the base material 2, and 0 to 0.3% in the direction perpendicular to the flow direction of the base material 2 (TD direction). Because the thermal shrinkage rate of the laminated film 1 is reduced, shrinkage of the laminated film 1 is suppressed even when heat is applied during heat sealing of dissimilar materials, thereby suppressing curling of the laminated body when dissimilar materials are heat sealed together.

[0024] Figure 3 illustrates the height of the edge rise of the laminate after heat sealing.

[0025] In this embodiment, the laminated film 1 is cut into a 100mm x 100mm square, and a 80mm x 80mm square of a different material 4 is heat-sealed to the center of the sealant 3 of the cut laminated film 1 to create a laminate 8. When this laminate 8 is placed on a flat surface 13 with the different material 4 facing downwards, as shown in Figure 3, the rise height h of the corners (vertices) of the different material 4 from the flat surface 13 is 20mm or less. The rise height here is the maximum height among the rise heights of the four corners of the different material. When a laminate 8 is constructed by heat-sealing a different material 4 using the laminated film 1 according to this embodiment, curling is suppressed, resulting in excellent transportability and processability in the process after heat-sealing the different material 4.

[0026] As described above, according to this embodiment, a laminated film 1 can be realized in which curling is reduced when a material different from the base material 2 is heat-sealed.

[0027] Furthermore, the dissimilar material heat-sealed to the sealant 3 of the laminated film 1 is made of a different material from the base material 2 and is not particularly limited as long as it is in the form of a thin film such as a sheet, film, or foil. For example, the laminated film 1 according to this embodiment can be used to construct an electrode support for a thin-film battery, in which a metal foil such as aluminum foil or copper foil is laminated on the base material 2 via the sealant 3 by heat-sealing it as a dissimilar material. [Examples]

[0028] The following describes specific examples of how the present invention is implemented.

[0029] (Example 1) A coating solution, prepared by dissolving an anchor coating agent (A-3210 / A-3070, manufactured by Mitsui Chemicals, Inc.) in ethyl acetate, was applied to one surface of a 12 μm thick PET film (E5100, manufactured by Toyobo Co., Ltd.) using a gravure coater, and then dried in an oven to form an anchor coating layer. After drying, EMAA (AN4233C, manufactured by Mitsui Dow Polychemical Co., Ltd.) was extruded and laminated onto the anchor coating layer to a thickness of 8 μm to produce the laminated film according to Example 1. In Example 1, the PET film was cut from the center of the mother roll in the TD direction (region 12 in Figure 2), and the drying temperature in the oven was set to 50°C.

[0030] (Example 2) A laminated film according to Example 2 was prepared using the same materials and procedure as in Example 1, except that the drying temperature in the oven was set to 80°C.

[0031] (Comparative Example 1) A laminated film according to Comparative Example 1 was prepared using the same materials and procedure as in Example 1, except that the drying temperature in the oven was set to 100°C.

[0032] (Comparative Example 2) A laminated film according to Comparative Example 2 was prepared using the same materials and procedure as in Example 1, except that the PET film was cut from the furthest end in the TD direction of the mother roll (area 11a in Figure 2) and the drying temperature in the oven was set to 80°C.

[0033] Table 1 shows the cutting positions of the PET film in the examples and comparative examples, and the oven temperature during solvent drying.

[0034] [Table 1]

[0035] The thermal shrinkage rate and curl after heat sealing of the metal foil were measured using the laminated films prepared in the examples and comparative examples by the following method.

[0036] (Thermal shrinkage rate) Samples were prepared by cutting the laminated films according to the examples and comparative examples into 120 mm x 120 mm squares. These samples were stored for 15 minutes in a forced-air constant-temperature incubator (DKN402, manufactured by Yamato Scientific Co., Ltd.) set to 100°C. After the heated laminated films were cooled to room temperature, the lengths of the laminated films in the MD and TD directions were measured, and the thermal shrinkage rate was calculated from the lengths before and after heating. The thermal shrinkage rate (%) is calculated as (L - L') / L × 100, where L is the sample length before heating and L' is the sample length after heating.

[0037] (Curl height) Samples were prepared by cutting the laminated films according to the examples and comparative examples into 100 mm x 100 mm squares. An 80 mm x 80 mm square copper foil (thickness 20 μm) was placed in the center of the sealant surface of the prepared sample, and as shown in Figure 4, it was sandwiched between fluororesin sheets and placed between the upper and lower heat source plates of a sealing machine (S-500AS, manufactured by Daiichi Pack Machinery Co., Ltd.). The sealing temperature of the upper heat source plate was set to 135°C, the sealing temperature of the lower heat source plate to 85°C, and the sealing pressure to 0.3 MPa, and heat sealing was performed for 5 seconds. After the heat-sealed laminate was cooled to room temperature, the laminate was placed on a flat surface so that the copper foil was on the flat side (see Figure 3), and the height of the rise of the corner of the copper foil from the flat surface (h in Figure 3) was measured, and the measured value was used as the evaluation value of the curl height.

[0038] Table 2 shows the thermal shrinkage rate and curl height of the laminated film. In Table 2, films where both the thermal shrinkage rate and curl height are within a favorable range are rated "○", and all others are rated "×".

[0039] [Table 2]

[0040] As shown in Table 2, the laminated films according to Examples 1 and 2 had a thermal shrinkage rate in the MD direction within the range of 0 to 0.4% and a thermal shrinkage rate in the TD direction within the range of 0 to 0.3%, and a curl height of 20 mm or less, indicating that curling after heat sealing was sufficiently suppressed.

[0041] In Comparative Example 1, the laminated film was subjected to a solvent drying oven temperature of 100°C, which prevented a reduction in the MD-direction thermal shrinkage rate upon reheating (heat storage for thermal shrinkage rate measurement). As a result, the curl height after heat sealing was also higher compared to the example. In Comparative Example 2, the laminated film used a PET film cut from the outermost end in the width direction of the mother roll as the base material. As a result, the orientation angle exceeded the range of less than 40°, preventing a reduction in the MD-direction thermal shrinkage rate upon reheating (heat storage for thermal shrinkage rate measurement). As a result, the curl height after heat sealing was also higher compared to the example. [Industrial applicability]

[0042] The present invention can be used as a transparent laminated film in which various materials are heat-sealed, and can be used, for example, as an electrode support for thin-film batteries. [Explanation of symbols]

[0043] 1. Laminated film 2 Base material 3. Sealant 8 Laminate

Claims

1. The process involves applying an anchor coating agent to one side of a substrate made of polyethylene terephthalate with a thickness of 5 to 30 μm, and drying it at 50 to 80°C to form an anchor coating layer. The process involves laminating a sealant having a thickness of 3 to 20 μm on the anchor coat layer, which is made of low-density polyethylene, linear low-density polyethylene, ethylene-methacrylic acid copolymer, or ethylene-acrylic acid copolymer. A method for manufacturing a laminated film, wherein the substrate is a film having an orientation angle of less than 40°.

2. The method for manufacturing a laminated film according to claim 1, wherein the thermal shrinkage rate of the laminated film obtained by the above manufacturing method is 0 to 0.4% in the flow direction of the substrate and 0 to 0.3% in a direction perpendicular to the flow direction of the substrate.

3. A method for manufacturing a laminated film according to claim 1 or 2, wherein an 80 mm x 80 mm square metal foil is placed in the center of the sealant of the 100 mm x 100 mm square laminated film, sandwiched between fluororesin sheets, placed between the upper and lower heat source plates of a sealing machine, the sealing temperature of the upper heat source plate is 135°C, the sealing temperature of the lower heat source plate is 85°C, the sealing pressure is 0.3 MPa, and the laminate is heat-sealed for 5 seconds, and when the laminate is placed on a flat surface with the metal foil facing downwards, the height of the corners of the metal foil rising from the flat surface is 20 mm or less.

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