Adhesive film for metal terminals

Abstract

To provide an adhesive film for metal terminals that is resistant to deformation even when heated to high temperatures. [Solution] An adhesive film 10 for metal terminals is interposed between a metal terminal 21 electrically connected to the electrodes of a battery element and a packaging material that seals the battery element, wherein the adhesive film 10 for metal terminals comprises at least one resin layer having a polyolefin backbone, the resin layer includes a crosslinked resin layer, and the thermal shrinkage rate of the adhesive film 10 for metal terminals in the flow direction is greater than 0% and less than 40%.

Description

Technical Field

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

Background Art

[0002] In recent years, in packaging materials for sealing battery elements, film-like packaging materials have been used. Between a metal terminal electrically connected to an electrode of a battery element and the packaging material, it is sealed through an adhesive film (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the adhesive film for sealing a battery element is heated to a high temperature, if the adhesive film is deformed, there is a risk of affecting 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.

Means for Solving the Problems

[0006] 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 a resin layer having at least one polyolefin backbone, the resin layer includes a crosslinked resin layer, and the heat shrinkage rate in the flow direction of the adhesive film for metal terminals is more than 0% and less than 40%. The crosslinked resin layer may be crosslinked with a crosslinking agent to form a resin having a polyolefin skeleton. The crosslinked resin layer may be thermally crosslinked with triallyl isocyanurate to form the resin having the polyolefin skeleton. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an adhesive film for metal terminals that is resistant to deformation even when heated to high temperatures. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view showing an example of a metal terminal with an adhesive film attached. [Figure 2] This is a perspective view showing an example of a battery. [Modes for carrying out the invention]

[0009] The present invention will be described below based on preferred embodiments.

[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 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 terminals 21. The adhesive films 10 for metal terminals are interposed between the metal terminals 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 periphery 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 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 to reduce its 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 6-8-sided. The end 21c of the metal terminal 21 is extended to the outside of the packaging material 32.

[0015] The material of the metal terminal 21 is not particularly limited, but examples include aluminum, copper, nickel, iron, gold, platinum, or an alloy 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 the main surface 21a and the 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 may contain fluorine compounds such as LiPF6, LiBF4, and LiN(SO2F)2. 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, an assembled product 20 is manufactured by joining the adhesive film 10 for metal terminals from outside one side 21b of the metal terminal 21 to outside the other side 21b, as shown in Figure 1. 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 flow direction (MD direction) of the adhesive film 10 for metal terminals is set in the width direction of the metal terminal 21, from one side surface 21b of the metal terminal 21 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 in the TD 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 includes a resin layer having at least one layer of a polyolefin backbone. Examples of the resin layer having a polyolefin backbone include unmodified polypropylene resin, acid-modified polypropylene resin, unmodified polyethylene resin, acid-modified polyethylene resin, and the like. Here, examples of acid modification include having a carboxylic acid functional group or an anhydrous carboxylic acid functional group. Examples of unmodified include not having a carboxylic acid functional group or an anhydrous carboxylic acid functional group. In this specification, when simply referring to polypropylene resin, it means unmodified polypropylene resin.

[0020] Examples of the acid-modified monomer used for acid modification of the resin having a polyolefin backbone include unsaturated carboxylic acids or unsaturated carboxylic acid anhydrides. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and the like. Examples of unsaturated carboxylic acid anhydrides are not particularly limited, and include unsaturated dicarboxylic acid anhydrides such as maleic anhydride.

[0021] The resin layer of the adhesive film 10 for metal terminals includes a crosslinked resin layer. In the crosslinked resin layer, the resin having a polyolefin backbone is crosslinked. Thereby, the thermal shrinkage rate of the adhesive film 10 for metal terminals can be suppressed.

[0022] The thermal shrinkage rate of the adhesive film 10 for metal terminals in the flow direction (MD direction) exceeds 0% and is less than 40%. Thereby, an adhesive film 10 for metal terminals that is difficult to deform even when heated to a high temperature can be provided.

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

[0024] The crosslinking aid is not particularly limited, but compounds that can crosslink the resin by energy ray irradiation are preferred. For example, at least one compound selected from compounds having two or more unsaturated bonds in one molecule, such as vinyl groups, allyl groups, acryloyl groups, and methacryloyl groups, is recommended. Examples of unsaturated bonds include olefinic carbon-carbon double bonds.

[0025] Specifically, examples of the crosslinking aid include polyfunctional vinyl compounds. Examples of the 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 a metal adhesive layer and an 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 (the adhesive film 10 for metal terminals has a three-layer structure), or it may have two or more core layers (the adhesive film 10 for metal terminals has four or more layers), for example, three layers (the adhesive film 10 for metal terminals has a five-layer structure). [Examples]

[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 1 to 5 layers. In the case of a 1-layer configuration, 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 measured by differential scanning calorimeter (DSC). The melt flow rate (MFR) was measured according to ISO 1133 at 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℃, MFR=7g / 10min. aPP-2: Maleic anhydride-modified block PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165℃, MFR=5g / 10min. aPP-3: Maleic anhydride-modified block PP (contains maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165℃, non-flowing due to crosslinked layer. aPP-4: Maleic anhydride-modified block PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165℃, MFR=2g / 10min. aPP-5: Maleic anhydride-modified random PP (containing maleic anhydride-modified polypropylene, polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=140℃, non-flowing due to crosslinked layer. aPE-1: Maleic anhydride-modified PE (containing maleic anhydride-modified polyethylene, polyethylene, and polyethylene elastomer), T=80℃, non-flowing due to crosslinked layer.

[0032] bPP-1: Block PP (containing polypropylene, maleic anhydride-modified polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165℃, MFR=5g / 10min. bPP-2: Block PP (containing polypropylene, maleic anhydride-modified polypropylene, polyethylene, ethylene elastomer, and propylene elastomer), T=165℃, non-flowing due to the cross-linked 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 test> The adhesive film for metal terminals was tested individually using the following method.

[0035] (Thermal shrinkage rate, suspension test) (1) The sample was punched out to a size of 10 mm wide x 55 mm long, markings A at 50 mm from the end in the longitudinal direction and B at 25 mm from the end, and the initial length of the test piece was measured. (2) The test specimen was fixed to the wire mesh with heat-resistant tape at a position outside of mark A (approximately 55 mm from the end), and the specimen was suspended from the wire mesh. (3) After suspending in a 190°C oven for 120 seconds, the specimen was allowed to cool naturally at room temperature. After one day of natural cooling, the post-heating length of the specimen was measured. A microscope (Keyence, VHX-5000) was used for the measurement. The distance from the end to mark A was defined as the post-heating length in the MD direction, and the length in the width direction on mark B was defined as the post-heating length in the TD direction. 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, three samples were measured, and the average value was calculated and recorded in the table.

[0036] (Surface roughness) The surface roughness Ra (arithmetic mean roughness) of the target film before bonding was measured using a laser microscope (Keyence, VK-X3100) according to the method specified in JIS B 0601:2013. For each example and comparative example, three samples were measured, and the average value was calculated and recorded in the table.

[0037] (Storage modulus) The storage modulus was measured using a tensile rheometer at 170°C in accordance with ISO 6721-4:1994. An RSA-G2 (TA Instruments) was used as the test apparatus. (1) The target film was punched out to a length of 50 mm and a width 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 on a tensile rheometer with a chuck distance of 20 mm. (2) The temperature was increased at 5°C / min in an air atmosphere, and measurements were taken in Transducer mode with a Normal Force Transducer set to spring, period 1 Hz, and strain 0.01%.

[0038] <Testing of assembled products> 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] (Heat shrinkage rate, flat-lay test) (1) As metal terminals, aluminum plates (0.4 mm thick, 44 mm x 52.5 mm) were used. (2) The aluminum plate was sandwiched between two 10mm wide target films so that the metal bonding surface was in contact with the aluminum side, and temporary bonding was performed by heat sealing under the conditions of a set temperature of +10°C above the top peak of the metal bonding layer, 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 protrudes outward from the side of the aluminum plate were measured using a microscope (Keyence, VHX-5000). Specifically, markings were drawn in the center of the ear portion in both the MD and TD directions, and the initial length was measured above 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 and heated in a 190°C oven for 10 minutes. (5) After natural cooling to room temperature, the dimensions of the ear portion were measured with a microscope after one day. 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 direction 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 value was calculated and recorded in the table.

[0040] (Thickness difference, flat-lay test) For samples whose thermal shrinkage rate was measured in a flat-lay test, the thickness was measured using a thickness gauge (Mitutoyo, Thickness Gauge 547-401, measuring part φ=2mm), and the thickness difference was calculated. Thickness difference [%] = End thickness / Center thickness × 100 This thickness difference indicates that the closer the value is to 100%, the more uniform the thickness. The central thickness was measured at the intersection of the MD-direction markings and the TD-direction markings on the ear. The edge thickness was measured at the outermost position on the TD-direction markings on the ear. For each example and comparative example, six samples were measured, and the average value was calculated and recorded in the table.

[0041] (Adhesive strength) (1) After punching out the adhesive film to a size of 150mm (MD) x 10mm (TD), the metal adhesive side was folded inwards at the center in the MD direction, and a metal tab (surface-treated CuNi plate, 0.2mm thick, 40mm x 52.5mm) was sandwiched in between. (2) The sample prepared in (1) was heat-sealed using a heat sealer at a temperature of "metal adhesive layer peak top + 30°C" under conditions of 0.2 MPa and 25 seconds to bond the adhesive film to the metal tab. (3) The initial adhesive strength of the bonded material was measured. The measurement conditions were a peeling speed of 50 mm / min and 180° peeling in the MD direction. (4) The bonded samples from (2) were immersed in the electrolyte solution and stored in an 85°C oven for one week. After that, the bonded materials were removed from the electrolyte solution and washed. The electrolyte solution consisted of 1.6 mol / L of LiPF6 as the electrolyte and DMC:EMC:EC as the solvent in a volume ratio of 4:3:3, with 2000 ppm of water added. DMC stands for dimethyl carbonate, EMC stands for ethyl methyl carbonate, and EC stands for ethylene carbonate. (5) The adhesive strength of the adhesive 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 calculated and recorded in the table.

[0042] [Table 1]

[0043] [Table 2]

[0044] As shown in Table 2, the adhesive films for metal terminals of Examples 1 to 7 had a thermal shrinkage rate of less than 40% in the flow direction, which suppressed deformation of the lugs. [Explanation of Symbols]

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

Claims

1. 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 that is greater than 0% and less than 40%.

2. The adhesive film for metal terminals according to claim 1, wherein the crosslinked resin layer is formed by crosslinking the resin having the polyolefin skeleton with a crosslinking agent.

3. 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.

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