Metal terminal adhesive film

Abstract

The present invention provides a metal terminal adhesive film that is not easily deformed even when heated to a high temperature. More specifically, the present invention pertains to a metal terminal adhesive film (10) interposed between a metal terminal (21) that is electrically connected to an electrode of a battery element and a packaging material that seals the battery element. The metal terminal adhesive film (10) comprises at least one resin layer that has a polyolefin backbone. The resin layer includes a crosslinked resin layer. The thermal shrinkage rate in the flow direction of the metal terminal adhesive film (10) is more than 0% to less than 40%.

Description

Adhesive Film for Metal Terminals

[0001] The present invention relates to an adhesive film for metal terminals.

[0002] In recent years, in packaging materials for sealing battery elements, film-shaped packaging materials have been used. For example, Patent Document 1 describes an adhesive film interposed between a metal terminal electrically connected to an electrode of a battery element and a packaging material for sealing the battery element.

[0003] Japanese Patent Application Laid-Open No. 2021-005556

[0004] When the adhesive film for sealing a battery element is heated to a high temperature, if the adhesive film is deformed, it may affect the sealing between the metal terminal and the packaging material.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive film for metal terminals that is difficult to deform even when heated to a high temperature.

[0006] In order to solve the above problems, the present invention provides an adhesive film for metal terminals interposed between a metal terminal electrically connected to an electrode of a battery element and a packaging material for sealing the battery element, wherein the adhesive film for metal terminals includes at least one resin layer having a polyolefin backbone, the resin layer includes a crosslinked resin layer, and the heat shrinkage rate of the adhesive film for metal terminals in the flow direction is more than 0% and less than 40%. The crosslinked resin layer may be formed by crosslinking a resin having a polyolefin backbone with a crosslinking agent. The crosslinked resin layer may be formed by thermally crosslinking a resin having a polyolefin backbone with triallyl isocyanurate.

[0007] According to the present invention, it is possible to provide an adhesive film for metal terminals that is difficult to deform even when heated to a high temperature.

[0008] It is a perspective view showing an example of a metal terminal to which an adhesive film is attached. It is a perspective view showing an example of a battery.

[0009] The present invention will be described below based on preferred embodiments. Unless otherwise specified herein or in the standards referenced herein, the conditions in the measurement procedure are: temperature: 25°C, pressure: 1 atmosphere, atmosphere: air. One or more of these conditions may be changed as specified herein or in the standards specified herein.

[0010] Figure 1 is a perspective view showing an example of a metal terminal with an adhesive film attached. Figure 2 is a perspective view showing an example of a battery with battery elements sealed in packaging material. These drawings are conceptual illustrations, and the dimensions and proportions of the components may differ from those of the actual components.

[0011] As shown in Figure 2, the battery 30 comprises a battery element 31 that serves as a power generation element, a packaging material 32 that seals the battery element 31, and metal terminals 21 electrically connected to the electrodes of the battery element 31. As shown in Figure 1, adhesive films 10 for metal terminals are provided on both main surfaces 21a in the thickness direction of the metal terminal 21. The adhesive films 10 for metal terminals are interposed between the metal terminal 21 and the packaging material 32.

[0012] The packaging material 32 shown in Figure 2 has a body 33 and a lid 34. The packaging material 32 is integrated by forming a sealing portion 35 on the peripheral edges of the body 33 and the lid 34. At least one of the body 33 or the lid 34 may have a concave molded portion 36 for housing the battery element 31, formed by drawing the packaging material 32. In the illustrated example, the molded portion 36 is formed only on the body 33, but the molded portion 36 may also be formed on the lid 34.

[0013] Preferably, the packaging material 32 has a sealant resin layer on at least the surfaces of the main body 33 and the lid 34 that face each other. Examples of sealant resins include resins having a polyolefin backbone, such as unmodified polypropylene resin and acid-modified polypropylene resin. The sealant resin layer of the packaging material 32 is heat-sealed to the adhesive film 10 for metal terminals.

[0014] The side surface 21b of the metal terminal 21 preferably has a cross-section such as a semicircle or polygon, and is shaped to reduce thickness. For example, the side surface 21b may have at least two surfaces between the main surfaces 21a, and the cross-section of the metal terminal 21 may be approximately hexagonal to octagonal. The end portion 21c of the metal terminal 21 is extended to the outside of the packaging material 32.

[0015] Examples of materials for the metal terminal 21 are not particularly limited, but include aluminum, copper, nickel, iron, gold, platinum, or alloys containing at least one of these metals. The metal terminal 21 may have a metal plating layer or a surface treatment layer on at least a portion of its main surface 21a and side surface 21b.

[0016] The inside of the battery 30 may contain an electrolyte. Examples of batteries include secondary batteries such as lithium-ion batteries. The electrolyte of the battery may be liquid (electrolyte solution), gel, solid, etc. The electrolyte is LiPF ６ LiBF ４ , LiN (SO ２ F) ２ It may also contain fluorine compounds such as the following. The electrolyte may contain carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) as a medium.

[0017] When inserting the adhesive film 10 for metal terminals between the metal terminal 21 and the packaging material 32, for example, as shown in Figure 1, an assembled product 20 is produced in which the adhesive film 10 for metal terminals is joined from outside one side surface 21b of the metal terminal 21 to outside the other side surface 21b. On both sides of the bonded portion 11 where the adhesive film 10 for metal terminals is bonded to the metal terminal 21, the tabs 12 protrude to the outside of the metal terminal 21.

[0018] The adhesive film 10 for metal terminals is positioned with its flow direction (MD direction: Machine Direction) facing the width direction of the metal terminal 21, from one side surface 21b to the other side surface 21b. The ear portions 12 of the adhesive film 10 for metal terminals that protrude outward from the side surface 21b are formed by cutting the adhesive film 10 for metal terminals in the TD direction (Transverse Direction), which intersects the MD direction. As shown by the arrows in Figure 1, the MD direction is the direction connecting one ear portion 12 to the other ear portion 12, and the TD direction is the direction along the length direction of the metal terminal 21.

[0019] The adhesive film 10 for metal terminals comprises at least one resin layer having a polyolefin skeleton. Examples of resins having a polyolefin skeleton include unmodified polypropylene resin, acid-modified polypropylene resin, unmodified polyethylene resin, and acid-modified polyethylene resin. Here, an example of acid modification is having a carboxylic acid functional group or a carboxylic anhydride functional group. Unmodified means not having a carboxylic acid functional group or a carboxylic anhydride functional group. In this specification, when simply referred to as polypropylene resin, it means unmodified polypropylene resin.

[0020] Examples of acid-modified monomers used for acid modification of resins having a polyolefin skeleton include unsaturated carboxylic acids or unsaturated carboxylic acid anhydrides. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, and maleic acid. Examples of unsaturated carboxylic acid anhydrides are not particularly limited, but include unsaturated dicarboxylic acid anhydrides such as maleic anhydride.

[0021] The resin layer constituting the adhesive film 10 for metal terminals includes a crosslinked resin layer. The crosslinked resin layer is formed by crosslinking a resin having a polyolefin skeleton with a crosslinking agent. This makes it possible to suppress the thermal shrinkage rate of the adhesive film 10 for metal terminals.

[0022] The thermal shrinkage rate of the adhesive film 10 for metal terminals in the flow direction (MD direction) is greater than 0% and less than 40%. This makes it possible to provide an adhesive film 10 for metal terminals that is resistant to deformation even when heated to high temperatures. The thermal shrinkage rate in the flow direction is measured as the thermal shrinkage rate in the MD direction of the film alone by a suspension test described later.

[0023] The crosslinked resin layer may be crosslinked by energy ray irradiation and / or by a crosslinking aid. Examples of energy rays include at least one selected from ultraviolet rays, X-rays, gamma rays, electron beams, etc. When crosslinking with ultraviolet rays, a photopolymerization initiator may be added to the resin to facilitate the initiation of the crosslinking reaction.

[0024] While not particularly limited, compounds capable of crosslinking the resin by energy ray irradiation are preferred as crosslinking aids. Examples of such compounds include at least one selected from compounds having two or more unsaturated bonds in one molecule, such as vinyl groups, allyl groups, acryloyl groups, and methacryloyl groups. An example of an unsaturated bond is an olefinic carbon-carbon double bond.

[0025] Examples of the aforementioned crosslinking aids include, specifically, polyfunctional vinyl compounds. Examples of such polyfunctional vinyl compounds include polyfunctional (meth)acrylate compounds, polyfunctional (meth)acrylamide compounds, triallyl isocyanurate, triallyl cyanurate, and trimethyl isocyanurate. Here, (meth)acrylate is an abbreviation for acrylate and / or methacrylate, and (meth)acrylamide is an abbreviation for acrylamide and / or methacrylamide.

[0026] Examples of the polyfunctional (meth)acrylate compounds include ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and di(trimethylolpropane)tetraacrylate. Examples of the polyfunctional (meth)acrylamide compounds include N,N'-methylenebisacrylamide, polyethylene glycol bisacrylamide, and N-[tris(3-acrylamidepropoxymethyl)methyl]acrylamide.

[0027] The adhesive film 10 for metal terminals may include an acid-modified polypropylene layer and an unmodified polypropylene layer. The surface layer 10a (metal adhesive layer) on the metal terminal 21 side of the adhesive film 10 for metal terminals may be an acid-modified polypropylene layer. The surface layer 10b (outer packaging adhesive layer) on the packaging material 32 side of the adhesive film 10 for metal terminals may be an unmodified polypropylene layer.

[0028] A separate resin layer (core layer) may be laminated between the metal adhesive layer and the exterior material adhesive layer. If the core layer is omitted, the adhesive film 10 for metal terminals may have a two-layer structure consisting of the metal adhesive layer and the exterior material adhesive layer, or it may have a one-layer structure in which the same resin layer serves as both the metal adhesive layer and the exterior material adhesive layer. If a core layer is provided, the core layer may be one layer (resulting in a three-layer structure for the adhesive film 10 for metal terminals), or multiple core layers may be provided. For example, there may be two or more core layers (resulting in a four or more-layer structure for the adhesive film 10 for metal terminals), or for example, three layers (resulting in a five-layer structure for the adhesive film 10 for metal terminals).

[0029] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[0030] <Manufacturing of Adhesive Films for Metal Terminals> As shown in Table 1, adhesive films for metal terminals were manufactured with one to three layers. In the case of a single-layer structure, the composition of the resin layer is shown in the metal adhesive layer column. In Table 1, the resin types are as follows. Here, PP means polypropylene and PE means polyethylene. T is the melting peak temperature Tpm measured by differential scanning calorimeter (DSC) in accordance with JIS K7121. The melt flow rate (MFR) was measured by mass measurement in accordance with ISO 1133, with a load of 2.16 kg and a temperature of 230°C.

[0031] aPP-1: Maleic anhydride-modified random PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=140°C, MFR=7g / 10min. aPP-2: Maleic anhydride-modified block PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165°C, MFR=5g / 10min. aPP-3: Maleic anhydride-modified block PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165°C, non-flowing due to crosslinking layer. aPP-4: Maleic anhydride-modified block PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165°C, MFR=2g / 10min. aPP-5: Maleic anhydride-modified random PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=140°C, non-flowing due to the cross-linked layer. aPE-1: Maleic anhydride-modified PE (containing maleic anhydride-modified polyethylene, polyethylene, and polyethylene elastomer), T=80°C, non-flowing due to the cross-linked layer.

[0032] bPP-1: Block PP (containing polypropylene, maleic anhydride-modified polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165°C, MFR=5g / 10min. bPP-2: Block PP (containing polypropylene, maleic anhydride-modified polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165°C, non-flowing due to crosslinked layer.

[0033] rPP-1: Random PP (containing polypropylene, maleic anhydride-modified polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=140℃, MFR=7g / 10min. rPP-2: Random PP (containing polypropylene, maleic anhydride-modified polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165℃, MFR=2g / 10min.

[0034] <Film-only testing> The adhesive film for metal terminals was tested individually using the following method.

[0035] (Thermal shrinkage rate, suspension test) (1) A sample was punched out into a rectangular shape with a width (TD direction) of 10 mm and a length (MD direction) of 55 mm to obtain a test specimen. For punching out the test specimen, a device was used consisting of an SD-type lever-type sample cutting machine SDL-100 manufactured by Dumbbell Co., Ltd., fitted with a Super Straight Cutter manufactured by Dumbbell Co., Ltd. as the punching blade, and a punching backing sheet (cardboard) manufactured by Dumbbell Co., Ltd. was used. The test specimen had a first end in the length direction (MD direction) and a second end on the opposite side of the first end. A mark A was made along the width direction at a position 50 mm from the first end in the length direction, and a mark B was made along the width direction at a position 25 mm from the first end in the length direction, and the initial length of the test specimen was measured. The distance from the first end to mark A was taken as the initial length of the test specimen in the MD direction, and the length in the width direction on mark B was taken as the initial length of the test specimen in the TD direction. (2) The test specimen was fixed to a wire mesh (made of stainless steel (SUS304)) with heat-resistant tape (Maxell Corporation, No. 626050 film tape: made of polyester film (25 μm thick) and silicone adhesive layer (30 μm thick)) at a position outside of mark A (approximately 55 mm from the first end, i.e., near the second end), and the test specimen was suspended from the wire mesh. (3) The wire mesh and the test specimen suspended from the wire mesh were heated in a 190°C oven for 120 seconds, then the wire mesh and the test specimen were removed from the oven and allowed to cool naturally in a room temperature environment (25°C, 1 atm atmospheric pressure). Inside and outside the oven, the wire mesh was placed on two stainless steel (SUS304) cans placed side by side. One day after the start of natural cooling, the post-heating length of the test specimen was measured. An optical microscope (Keyence Corporation, Digital Microscope VHX-5000) equipped with a complementary metal-oxide-semiconductor (CMOS) image sensor and electronic image processing means was used to measure the initial length and the length after heating. The distance from the first end to mark A was defined as the length in the MD direction after heating, and the length in the width direction on mark B was defined as the length in the TD direction after heating. The thermal shrinkage rate in the MD and TD directions was calculated using the following formula: Thermal shrinkage rate [%] = (Initial length - Length after heating) / Initial length × 100. Measurements were performed on three samples (test pieces) for each example and comparative example, and the average value was calculated. The results are shown in the table.

[0036] (Surface Roughness) The surface roughness Ra (arithmetic mean roughness) of the target film before bonding was measured using a laser confocal microscope equipped with a white light interferometer (VK-X3100, manufactured by Keyence Corporation) according to the method specified in JIS B 0601:2013. Three samples were measured for each example and comparative example, and the average value was calculated and listed in the table.

[0037] (Storage Modulus) The storage modulus in the MD direction was measured using a tensile rheometer in a 170°C environment according to the method compliant with ISO 6721-4:1994. An RSA-G2 (manufactured by TA Instruments) was used as the test apparatus. (1) The target film was cut to a length (MD direction) of 50 mm and a width (TD direction) of approximately 5 mm. The exact width of the test piece was measured with calipers, and the exact thickness was measured with a dial gauge. The test piece was then set in the tensile rheometer with a chuck distance of 20 mm. (2) The temperature was raised at 5°C / min in an air atmosphere, and the measurement was performed in tensile mode (Transducer mode) with the setting item "Normal Force Transducer" set to "Spring", vibration frequency of 1 Hz, and Strain (amplitude of strain of the test piece) of 0.01%. A high storage modulus of elasticity at 170°C means that the film is less likely to deform even when heated to high temperatures. In one embodiment, the storage modulus of elasticity in the MD direction at 170°C of the film is preferably 1.0 × 10⁻¹⁰. ４ Pa or higher, more preferably 1.0 × 10⁻⁶ ５ It is Pa or higher.

[0038] <Assembled Product Testing> As shown in Figure 1, assembled products in which an adhesive film for metal terminals was laminated to metal terminals were subjected to the following test method.

[0039] (Thermal shrinkage rate, flat test) (1) An aluminum plate (0.4 mm thick, 44 mm x 52.5 mm) was used as the metal terminal. (2) The aluminum plate was sandwiched between two 10 mm wide target films so that the metal bonding surface was in contact with the aluminum side, and temporary bonding was performed by heat sealing at a set temperature of the top peak of the metal bonding layer (the highest melting peak temperature of the metal bonding layer) + 10°C, with a heating pressure of 0.4 MPa and a heating time of 15 seconds. (3) In the sample after temporary bonding, the dimensions of the ear portion that protruded outward from the side surface of the aluminum plate were measured using an optical microscope (Keyence Corporation, Digital Microscope VHX-5000) equipped with a CMOS image sensor and electronic image processing means. Specifically, markings were drawn at the center of the ear portion in the MD direction and TD direction, and the initial lengths in the MD direction and TD direction were measured on these marks. (4) A polytetrafluoroethylene (PTFE) sheet was placed on a stainless steel tray, and the sample after temporary bonding was placed on the PTFE sheet. The sample was then heated in a 190°C oven for 10 minutes along with the stainless steel tray and PTFE sheet. (5) The sample was removed from the oven along with the stainless steel tray and PTFE sheet, and allowed to cool naturally to room temperature (25°C). One day after the start of natural cooling, the dimensions of the ear portion were measured using the optical microscope described above. In the MD direction, the length after heating was measured on the mark as before heating, and in the TD direction, the length after heating was measured at the point where the dimension had shrunk the most. The thermal shrinkage rate for each was calculated using the following formula: Thermal shrinkage rate [%] = (initial length - length after heating) / initial length × 100 For each example and comparative example, six samples were measured, and the average values ​​were calculated and listed in the table.

[0040] (Thickness Difference, Flat Placement Test) For the samples whose heat shrinkage rate was measured in the flat placement test, the thickness was measured with a thickness gauge (manufactured by Mitutoyo Corporation, Thickness Gauge 547-401, measuring part φ = 2 mm), and the thickness difference was calculated. Thickness difference [%] = end thickness / central thickness × 100 The closer the numerical value of this thickness difference is to 100%, the more uniform the thickness is. The central thickness was measured at the intersection position of the marking line in the MD direction and the marking line in the TD direction of the ear part. The end thickness was measured at the outermost position on the marking line in the TD direction of the ear part. For each example and comparative example, six samples were measured, and the average value was obtained and described in the table. When the thickness difference and heat shrinkage rate of the measured film are small, the film can maintain a stable shape during heating, so it is easy to seal the tab and the packaging material with stable strength.

[0041] (Adhesive Strength and Electrolyte Resistance) (1) After punching out the adhesive film into a size of 150 mm (MD) × 10 mm (TD), fold it at the central part in the MD direction with the metal bonding surface facing inward, and sandwich a metal tab (surface-treated CuNi plate 0.2 mm thick, 40 mm × 52.5 mm) between them. (2) The sample prepared in (1) was heat-sealed with a heat sealer at a temperature of "metal bonding layer peak top (the highest melting peak temperature of the metal bonding layer) + 30°C" under the conditions of 0.2 MPa and 25 seconds to bond the adhesive film and the metal tab. (3) The adhesive strength of the initial adherent was measured. The measurement conditions were a peeling speed of 50 mm / min and a 180° peel in the MD direction. (4) The sample adhered in (2) was immersed in the electrolyte, stored in an oven at 85°C for one week, then the adherent was taken out from the electrolyte, washed with dimethyl carbonate, wiped off the solvent with Kimtowel (registered trademark), and immediately the measurement in (5) below was carried out. The composition of the electrolyte was 1.6 mol / L of LiPF ６ as the electrolyte, and dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): ethylene carbonate (EC) in a volume ratio of 4:3:3 as the solvent, with 2000 ppm of water added. (5) The adhesive strength of the adherent after immersion in the electrolyte was measured. The measurement conditions were the same as in (3). For each example and comparative example, four samples were measured, and the average value was obtained and described in the table.

[0042]

[0043]

[0044] As shown in Table 2, the adhesive films for metal terminals in Examples 1 to 7 had a heat shrinkage rate in the flow direction of less than 40%, and deformation of the ear portions could be suppressed.

[0045] 10... Adhesive film for metal terminal, 10a... Surface layer on the metal terminal side, 10b... Surface layer on the packaging material side, 11... Bonding portion, 12... Ear portion, 20... Assembly product, 21... Metal terminal, 21a... Main surface of the metal terminal, 21b... Side surface of the metal terminal, 21c... End portion of the metal terminal, 30... Battery, 31... Battery element, 32... Packaging material, 33... Body, 34... Lid, 35... Sealing portion, 36... Forming portion

Claims

An adhesive film for metal terminals, interposed between a metal terminal electrically connected to the electrodes of a battery element and a packaging material that seals the battery element, The aforementioned adhesive film for metal terminals comprises at least one resin layer having a polyolefin backbone, The resin layer includes a crosslinked resin layer, The adhesive film for metal terminals has a thermal shrinkage rate in the flow direction greater than 0% and less than 40%. 　 The adhesive film for metal terminals according to claim 1, wherein the crosslinked resin layer is obtained by crosslinking the resin having the polyolefin skeleton with a crosslinking agent. 　 The adhesive film for metal terminals according to claim 1, wherein the crosslinked resin layer is obtained by thermally crosslinking the resin having the polyolefin skeleton with triallyl isocyanurate.

Images