JP2011162702A - Biaxially stretched nylon film for cold forming - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure stable formability by preventing breakage of an aluminum foil and production of pinholes or the like even during cold forming of all mold shapes and molding depths and to suppress occurrence of delamination between respective layers, in particular, between a base material layer and a barrier layer even when used in a process for sealing by heat sealing or under a high temperature condition for a long period of time, in a cold forming type packaging material for batteries containing a biaxially stretched nylon film as a main base material. <P>SOLUTION: The biaxially stretched nylon film is characterized in that both maximum values of thermal shrinkage stress in MD and TD at 170 to 210°C are ≤5.0 MPa, anisotropy is small, the tensile strength is large, and it is used as a main base material of a packaging material for cold forming, in particular, of a packaging material for battery cases of lithium ion secondary batteries or the like. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention is suitably used as a main base material for cold-forming packaging materials, in particular, battery case packaging materials such as lithium ion secondary batteries.
The present invention relates to a biaxially stretched nylon film for cold forming.

Conventionally, for example, chemical energy of lithium ion batteries, lithium ion polymer batteries, fuel cells, etc., or liquid capacitors including dielectric materials such as liquids, solid ceramics, and organic substances, solid capacitors, electrolytic capacitors such as double layer capacitors, etc. Various batteries including elements that convert to electric energy are widely used in personal computers, portable terminal devices (cell phones, PDAs, etc.), video cameras, electric vehicles, energy storage batteries, robots, satellites, and the like. As these battery outer bodies, metal cans formed by pressing metal into cylinders or rectangular parallelepiped containers, or laminates obtained by laminating plastic films, metal foils, etc. in the form of bags (Hereafter, exterior body) was used.

However, among the battery outer bodies, in the metal can type, since the outer wall of the container is rigid, it is necessary to design the hardware side according to the shape of the battery, and there is a problem that the degree of freedom of the shape is lost. . In addition, since the metal can type is thick, there is a drawback that it is difficult to dissipate heat when the battery generates heat, such as when used for a long time. On the other hand, the laminate type is easy to take out the metal terminal, easy to seal, or flexible, so it can be shaped to fit the appropriate space of the electronic device or electronic component. The shape of itself can be designed freely to some extent. Furthermore, since the thin film is excellent in heat dissipation, it is possible to prevent abnormal discharge due to heat generation. Therefore, the laminated body type is becoming mainstream as a battery exterior body because of advantages such as a reduction in size and weight, and high safety compared to a metal can type.

As a form of a lithium battery using a laminate type exterior body, a packaging material is processed into a cylindrical shape, and a metal terminal connected to each of the lithium battery main body and the positive electrode and the negative electrode is stored in a state of protruding outward. A bag type (for example, see FIG. 2 of Patent Document 1) in which the opening is thermally bonded and sealed, and a packaging material are formed into a container shape, and are connected to the lithium battery body, the positive electrode, and the negative electrode in the container. The metal terminal is housed in a state of protruding outward, covered with a flat packaging material or a packaging material molded into a container, and the four peripheral edges are thermally bonded and sealed (for example, FIG. 3) is known.

And since the molded type can store the battery body tightly (tight state) compared to the bag type, the volume energy density can be improved and the lithium battery body can be easily stored. There are advantages. Furthermore, among the molding types, the cold (room temperature) molding method has a lower risk of changes in the properties of the packaging material during molding, such as a decrease in strength properties due to heating and the occurrence of thermal shrinkage, compared to the heat molding method. Furthermore, since the molding apparatus is inexpensive, simple and highly productive, it is currently the mainstream molding method.

The physical properties and functions required for battery exteriors include advanced moisture resistance, sealing, piercing resistance, pinhole resistance, insulation, heat / cold resistance, electrolyte resistance (electrolyte resistance), Corrosion properties (resistance to hydrofluoric acid generated by electrolyte degradation and hydrolysis) are essential, and moisture resistance is an important factor. However, in the laminate type, especially the cold forming type, the aluminum foil generally used as a metal foil is excellent in formability, but there is a problem that pinholes and cracks are likely to occur due to non-uniform deformation that occurs during forming. There is room for improvement in terms of molding stability, which is deep and stable molding with a simple shape. In addition, the laminate type is composed of at least a base material layer, a barrier layer, and a sealant layer, but it has been confirmed that the adhesive strength between the respective layers affects the properties required for the battery outer package. . For example, if the adhesive strength between the barrier layer and the base material layer is insufficient, the heat shrink stress of the base material layer when the battery body is stored and sealed by heat sealing or when used for a long time at a high temperature. However, there is a problem that delamination (peeling) occurs between the barrier layer and the base material layer. In particular, the occurrence of delamination was high during heat sealing in which heat of around 200 ° C. was applied to the base material layer. When delamination occurs between the barrier layer and the base material layer, it may cause deterioration of strength characteristics such as piercing resistance and pinhole resistance among the required characteristics of the battery exterior body, which may cause water vapor to enter from the outside. . When water vapor enters the inside, there is a problem that the aluminum foil as the barrier layer is corroded by hydrofluoric acid generated by reacting with an electrolyte which is one of the components forming the battery.

As described above, various proposals have been made so far regarding the main quality problems of the battery-type outer casing of the laminate type, particularly the cold-forming type, that is, ensuring excellent cold-formability and suppressing delamination between the respective layers. Yes. As a method for ensuring excellent cold formability, for example, Patent Document 2 coats a base material layer surface with a fatty acid amide-based slipperiness-imparting component to improve slipping into a mold during molding. Methods for improvement, Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6 pay attention to the strength properties of the base material layer such as nylon film, and are different in order to suppress breakage of the aluminum foil during cold forming. A method of reinforcing an aluminum foil by using a base material having a low property and having a property such as high strength or high elongation, and further, a method focusing on the crystallinity of the base material layer as in Patent Document 7 Proposed. On the other hand, as a method for suppressing delamination, Patent Literature 8 proposes a method for limiting the hot water shrinkage of the base material layer, and Patent Literature 9 proposes a method for limiting the density of the base material layer to a certain range.

JP 2004-74419 A JP 2002-216714 A Japanese Patent No. 3567230 JP 2006-236938 A JP 2008-44209 A JP 2005-22336 A JP 2007-42469 A JP 2006-331897 A JP 2008-288117 A

However, the method of coating the surface of the base material layer with a slipperiness-imparting component has a problem in that productivity must be reduced because a coating step must be provided. In addition, the slipperiness-imparting component evaporates when the battery is vacuum degassed or sealed, and the evaporated component adheres to the processing equipment, which necessitates a cleaning operation to remove them, further reducing productivity. There was a problem to do. In addition, the method of reinforcing an aluminum foil using a high-strength or high-strength base material has no improvement on the suppression of delamination, although the moldability is improved. Furthermore, the method of limiting the hot water shrinkage rate of the base material layer to suppress delamination is not necessarily a condition of the occurrence of delamination in the heat sealing process in which heat of around 200 ° C., which is frequently generated, is applied to the base material. Was not met, and it was insufficient as an indicator for delamination. In addition, delamination occurs when the thermal shrinkage stress of the base material layer is greater than the interlayer adhesive strength, so delamination can be completely suppressed simply by limiting the amount of shrinkage in hot water. It was not always possible to do.

As a result of diligent research, the inventors of the present invention limited the heat shrinkage stress and tensile strength of the nylon film as the base material layer to a certain range. The present inventors have found that it is possible to achieve both excellent cold formability, which is a main quality problem, and suppression of delamination between the respective layers, thereby completing the present invention. That is, the present invention provides the following means.

[1] The maximum value of heat shrinkage stress at 170 to 210 ° C. is 5.0 MPa or less for both MD and TD, and four directions in a uniaxial tensile test (sample width: 15 mm, distance between chucks: 100 mm, tensile speed: 200 mm / min.) (0 ° (MD), 45 °, 90 ° (TD), 135 °) A biaxially stretched nylon film having a breaking strength of 240 MPa or more.

[2] 50% modulus in all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) in a uniaxial tensile test (sample width 15 mm, distance between chucks 100 mm, tensile speed 200 mm / min.) The biaxially stretched nylon film according to item 1, wherein the value is 120 MPa or more.

[3] In the battery case packaging material for cold forming formed by at least a base material layer, a barrier layer, and a sealant layer, the biaxially stretched nylon film described in the preceding item 1 or 2 is used as the base material layer. A battery case packaging material for cold forming.

[4] A battery case in which the cold-forming battery case packaging material according to item 3 above is used, and a concave portion is formed by overmolding or deep drawing so that the sealant layer becomes an inner surface.

[5] A battery, wherein the battery main body is housed in the concave portion of the battery case according to the item 4 and sealed.

The present invention relates to a biaxially stretched nylon film for cold forming that has a maximum thermal shrinkage stress at 170 to 210 ° C. of 5.0 MPa or less for both MD and TD, little anisotropy, and high tensile strength. By using stretched nylon film as the main base material for cold forming packaging materials, especially for battery case packaging such as lithium ion secondary batteries, it has been used for a long time in heat sealing and sealing processes and at high temperatures. Even in this case, it is possible to suppress the occurrence of delamination between the barrier layer and the base material layer, and the aluminum foil is ruptured or pinholes are generated even during cold forming with any mold shape and forming depth. It became possible to ensure stable moldability. In addition, as in the prior art, excellent moldability can be secured without coating with a slipperiness-imparting component, so that productivity is also excellent.

Process drawing of the tubular extending | stretching apparatus which manufactures the ONy film in the said embodiment.

The best mode for carrying out the present invention will be described below.
(Raw Material of Biaxially Stretched Nylon Film) The raw material of the biaxially stretched nylon film (hereinafter referred to as ONy film) of the present invention is not particularly limited as long as it is a polyamide resin. For example, nylon 6, nylon 66, nylon 11, nylon 12, nylon 610, nylon 612, nylon 6, 66, 12 copolymer, other polyamide copolymers, nylon MXD6, aramid, polyamideimide (PAI), aromatic Polyimide, polyetherimide (PEI), polymaleimidoamine (PMIA), polyaminobismaleimide (PABM), etc. are mentioned. Nylon 6 is used from the viewpoint of film physical properties such as productivity, cold formability and strength properties. Most preferred. In the nylon 6 raw material, the number average molecular weight is preferably 10,000 to 30,000, particularly preferably 22,000 to 24,000. When the number average molecular weight is less than 10,000, the impact strength and tensile strength of the obtained ONy film are insufficient. When the number average molecular weight is larger than 30000, the molecular chain is entangled excessively and excessive strain is generated by the stretching process. Therefore, breakage and puncture frequently occur during the stretching process, and stable production cannot be achieved.

(Manufacturing method of ONy film) The ONy film of the present invention has a draw ratio of 2.8 to 4.0 times for MD and TD, respectively, with respect to an unstretched raw film composed of any of the polyamide-based raw materials. It is obtained by heat-treating under a temperature condition of 180 to 220 ° C. after performing biaxial stretching under the following conditions. The draw ratio is preferably in the range of 2.8 to 4.0 times each of MD and TD, particularly preferably in the range of 3.0 to 3.4 times. When the draw ratio is less than 2.8 times, the impact strength and tensile strength of the obtained ONy film are insufficient. Further, when the ratio is 4.0 times or more, excessive molecular chain distortion occurs due to stretching, and thus breakage and puncture frequently occur during stretching and stable production cannot be achieved. Examples of the biaxial stretching method include simultaneous biaxial stretching by a tubular method or a tenter method, or sequential biaxial stretching, but simultaneous biaxial stretching by a tubular method is preferable from the viewpoint of longitudinal and lateral strength balance. By performing biaxial stretching in this manner, an ONy film having particularly improved strength properties and excellent cold formability can be obtained.

The obtained stretched film is put into a heat roll system or a tenter system, or a heat treatment facility combining them for an arbitrary time, and heat-treated at 185 to 215 ° C., particularly preferably 190 to 210 ° C. A film can be obtained. When the heat treatment temperature is higher than 215 ° C., the bowing phenomenon becomes too great and the anisotropy in the width direction increases, or the crystallinity becomes too high, resulting in a decrease in strength properties. On the other hand, when the heat treatment temperature is lower than 185 ° C., the thermal dimensional stability of the film is greatly reduced, so that the film is easily shrunk at the time of lamination, or delamination is performed in a process of heat sealing and sealing after cold forming. Is likely to occur, causing a problem in practical use.

The thickness of the ONy film is preferably 5 to 50 μm, more preferably 10 to 30 μm. When the thickness is less than 5 μm, the impact resistance of the laminate packaging material becomes low, and the cold formability becomes insufficient. On the other hand, when the thickness exceeds 50 μm, the strength for maintaining the shape is improved, but the effect for preventing breakage and improving the moldability is small, and only the volume energy density is reduced.

The uniaxial tensile strength at break and the 50% modulus value in four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) of the ONy film are determined by a uniaxial tensile test (sample width: 15 mm, distance between gauge points: 50 mm). , From a stress-strain curve obtained by a tensile speed of 200 mm / min). In this stress-strain curve, the tensile breaking strength in the four directions is preferably 240 MPa or more, and more preferably 280 MPa or more. As a result, the ONy film and aluminum foil are difficult to break during cold forming even in the case of a mold shape with a large forming depth, which is generally considered difficult to form, ensuring stable and excellent formability. I can do it. If the tensile breaking strength is less than 240 MPa in any one of the four directions, the ONy film will be easily broken during cold forming, and the forming depth that requires high tensile strength at high elongation is particularly high. When molding a large mold shape, stable moldability cannot be obtained. Furthermore, in the stress-strain curve, the 50% modulus values in the four directions are all preferably 120 MPa or more, and more preferably 150 MPa or more. Thereby, stable moldability can be ensured particularly when a mold shape having a relatively small molding depth is molded. When the 50% modulus value is less than 120 MPa or more in any one of the four directions, the ONy film easily breaks during cold forming, and stable moldability cannot be obtained.

The maximum value of the heat shrinkage stress at 170 to 210 ° C. of the ONy film is preferably 5.0 MPa or less for both MD and TD, and can maintain stable quality even during secondary processing such as heat sealing after molding. . When the maximum value of thermal shrinkage stress is greater than 5.0 MPa in either MD or TD, the thermal shrinkage stress of the base material increases, and in particular during the heat sealing in which heat of around 200 ° C. is applied to the base material layer, This is not preferable because delamination easily occurs between the base material layers.

(Configuration of Laminate Packaging Material) The laminate packaging material is configured by laminating one or two or more other base materials on at least one surface of the above-described ONy film. Specifically, as other base materials, pure aluminum foil for imparting high moisture resistance or an aluminum foil layer made of a soft material of an aluminum-iron-based alloy, and polyethylene for imparting sealability and chemical resistance, Examples thereof include a heat seal layer made of an unstretched film such as polypropylene, maleic acid-modified polypropylene, maleic acid-modified polyethylene, ethylene-acrylate copolymer, ionomer resin, and polyvinyl chloride. In general, a laminate packaging material including an aluminum foil layer is not suitable for cold forming because the aluminum foil layer is easily broken or pinholes during cold forming. However, since the laminate packaging material including the ONy film of the present invention has excellent moldability, impact resistance and pinhole resistance, the aluminum layer breaks during cold stretch molding or deep drawing. Can be suppressed.

The total thickness of the laminate base material including the ONy film is preferably 200 μm or less. When the thickness exceeds 200 μm, it becomes difficult to form the corner portion by cold forming, and a molded product having a sharp shape may not be obtained.

The thickness of the aluminum foil layer is preferably 20 to 100 μm. Thereby, it becomes possible to hold | maintain the shape of a molded article favorably, and it can prevent that oxygen, a water | moisture content, etc. penetrate | invade into a packaging material. When the thickness of the aluminum foil layer is less than 20 μm, the aluminum foil layer is likely to break during cold forming of the laminate packaging material, and pinholes and the like are likely to occur even when the laminate packaging is not broken. Or moisture may enter. On the other hand, when the thickness of the aluminum foil layer exceeds 100 μm, the effect of preventing breakage and pinhole generation during cold forming is not greatly improved, and only the total thickness is not preferable.

The laminate wrapping material including the ONy film of the present invention is a wrapping material having a performance that can be processed by a cold (room temperature) forming method such as stretch forming or deep drawing, although the total thickness of the wrapping material is thin. Because of its high strength, it is a laminate packaging material that can be sharply molded and that prevents the aluminum foil from being broken or pinholes during molding.

As a field where the laminate packaging material including the ONy film of the present invention is used, and as an application, particularly for a packaging material for a lithium secondary battery that uses a highly corrosive electrolytic solution and extremely hates invasion of moisture and oxygen. Although most suitable, other primary batteries and secondary batteries that require weight reduction and size reduction can also be used when the battery case is lightweight and requires sharp formability. . In addition to packaging materials for batteries, it has excellent heat sealability, chemical resistance, moldability, etc., so containers for materials containing pharmaceuticals, cosmetics, photographic chemicals, and other highly corrosive organic solvents It can also be used as a packaging material.

The present invention will be specifically described below with reference to examples and comparative examples.
Example 1 (Production of biaxially stretched nylon film) After nylon 6 pellets (relative viscosity 3.48) were melt kneaded in an extruder at 255 ° C, the melt was extruded as a cylindrical film from a die, and subsequently with water. A raw film was prepared by rapid cooling. Next, as shown in FIG. 1, the raw film is inserted between a pair of low-speed nip rolls 1 and then heated by the heater 2 and the heater 3 while air is being pressed into the film. By blowing air from the ring 4, MD and TD simultaneous biaxially stretched films 5 by the tubular method were obtained. The draw ratio was 3.0 times for MD and 3.2 times for TD.
Next, this stretched film 5 was put into a heat roll type and a tenter type heat treatment facility, respectively, and heat treated at 210 ° C. to obtain an ONy film. The ONy film had a thickness of 25 μm.

(Uniaxial tensile breaking strength of ONy film, evaluation method of 50% modulus value) For the evaluation method of uniaxial tensile breaking strength of ONy film and 50% modulus value, Tensylon (RTC-1210-A) manufactured by Orientec was used. The test was carried out at a width of 15 mm, a gap between chucks of 100 mm, and a tensile speed of 200 mm / min. The ONy film 18 was measured in four directions of 0 ° C. (MD) direction / 45 ° direction / 90 ° (TD) direction / 135 ° direction after humidity conditioning for 2 hours in an environment of 23 ° C. × 50%. . Based on the obtained stress-strain curve, the breaking strength in each direction and the 50% modulus value were determined.

(Method for evaluating thermal shrinkage stress of ONy film) The thermal shrinkage stress of the ONy film was SII Nanotechnology-EXSTAR-TMA / SS6100, the sample width was 3 mm, the distance between chucks was 15 mm, and the temperature was 30 to 245 ° C (temperature increase rate: 10). (° C./min.). For the ONy film, the maximum heat shrinkage stress value observed at 170 to 210 ° C. was measured for each of MD and TD after conditioning for 2 hours in an environment of 23 ° C. × 50%.

(Cold-formability, evaluation method for occurrence of delamination) The cold-formability of the laminate packaging material including the ONy film was evaluated. Specifically, first, the obtained ONy film was used as a base material layer, an aluminum foil (AA8079-O material, thickness 32 μm), and an unstretched polypropylene film [pyrene film CT-P1128 (trade name), manufactured by Toyobo Co., Ltd., thickness 30 μm] was dry laminated (dry coating amount 4.0 g / m ² ) to obtain a laminate packaging material. In addition, Toyo Morton Co., Ltd. TM-K55 / Toyo Morton Co., Ltd. CAT-10 (mixing ratio 100/8) was used as an adhesive for dry lamination. The laminate packaging material after dry lamination was aged at 60 ° C. for 72 hours. The laminate packaging material thus obtained was conditioned at 23 ° C. × 50% for 2 hours, and then used a compression mold (38 mm × 38 mm) with a maximum load of 10 MPa from the unstretched polypropylene film side. Molding was carried out cold (room temperature), and the maximum molding depth at which defects such as pinholes and cracks did not occur was evaluated at 0.5 mm pitch. About the laminated packaging material cold-molded by the above method, the surplus portion in the vicinity of the concave portion is set to 200 ° C. × 0.2 MPa × 2 sec. The film was heat-sealed under the conditions described above, and the presence or absence of delamination between the sealed nylon / aluminum foil was visually confirmed.

Example 2 The same procedure as in Example 1 was performed except that the stretched film was placed in a heat roll and a tenter heat treatment facility and heat treated at 195 ° C.

Comparative example 1 In Example 1, it carried out similarly to Example 1 except having put the stretched film into the heat roll and the tenter type heat processing equipment, and heat-processing at 180 degreeC.

Comparative example 2 In Example 1, it carried out similarly to Example 1 except having put the stretched film into the heat roll and the tenter type heat treatment equipment, and heat-treating at 150 degreeC.

Comparative example 3 In Example 1, it carried out similarly to Example 1 except having put the stretched film into the heat roll and the tenter type heat treatment equipment, and heat-treating at 220 degreeC.

Comparative example 4 In Example 1, it carried out like Example 1 except having used the Toyobo biaxially-stretched nylon film (Harden film-N1102, 25 micrometers in thickness) as an ONy film.

Comparative example 5 In Example 1, it carried out like Example 1 except having used the biaxially stretched nylon film (emblem ON-RT, thickness 25 micrometers) made from Unitika as an ONy film.

As shown in Table 1, the maximum value of heat shrinkage stress at 170 to 210 ° C. is 5.0 MPa or less for both MD and TD, the breaking strength in all four directions in the uniaxial tensile test is 240 MPa or more, and the 50% modulus value is 120 MPa. In Example 1 and Example 2 adjusted as described above, it was possible to achieve both excellent moldability and suppression of delamination. In Example 2 in which the breaking strength was 280 MPa or more and the 50% modulus value was 150 MPa or more, the formability could be further improved while suppressing the occurrence of delamination. On the other hand, when the maximum value of the heat shrinkage stress at 170 to 210 ° C. is both MD and TD, or when either MD or TD exceeds 5.0 MPa, delamination occurs, and the fracture in any of the four directions occurs. When the strength was 240 MPa or less and the 50% modulus value was 120 MPa or less, a decrease in moldability was observed. Therefore, all of Comparative Examples 1 to 5 could not achieve both excellent moldability and suppression of delamination. As for moldability, it is preferable that the mold can be molded in a deeper shape. In Comparative Example 3, no delamination occurred, but the moldability was inferior to Examples 1 and 2.

The present invention is suitably used as a main base material for packaging materials for cold forming, particularly packaging materials for battery cases such as lithium ion secondary batteries.

1 Tubular stretcher nip roll 2 Tubular stretcher preheating heater 3 Tubular stretcher main heat heater 4 Tubular stretcher cooling air ring 5 Tubular stretcher film

Claims (5)

The maximum value of heat shrinkage stress at 170 to 210 ° C. is 5.0 MPa or less for both MD and TD, and four directions (0 ° (0 ° (sample width 15 mm, distance between chucks 100 mm, tensile speed 200 mm / min.)). MD), 45 °, 90 ° (TD), 135 °) A biaxially stretched nylon film characterized by having a breaking strength of 240 MPa or more. 50% modulus value in all four directions (0 ° (MD), 45 °, 90 ° (TD), 135 °) in a uniaxial tensile test (sample width: 15 mm, distance between chucks: 100 mm, tensile speed: 200 mm / min.) Is 120 MPa. It is the above, The biaxially stretched nylon film of Claim 1 characterized by the above-mentioned. In the battery case packaging material for cold forming formed of at least a base material layer, a barrier layer, and a sealant layer, the biaxially stretched nylon film according to claim 1 or 2 is used as the base material layer. Battery case packaging material for cold forming. A battery case in which the cold-forming battery case packaging material according to claim 3 is used, and a recessed portion is formed by over-extrusion molding or deep drawing so that the sealant layer is on the inner surface. A battery body, wherein the battery body is housed in a recessed portion of the battery case according to claim 4 and sealed.

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