JP2008007671A - Packing, and sealed type battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a packing, that is utilized for an insulating gasket of a sealed type secondary battery etc. and is excellent in sealing property, liquid leakage resistance, and heat cycle resistance, comprises a resin composition having a proper softness and compression reversibility, and excellent in heat resistance and chemical resistance (electrolyte resistance), and to provide a sealed type battery almost freed from such a problem as liquid leakage and lowering of caulking stress by using the packing as an insulating gasket. <P>SOLUTION: The packing comprises a resin composition produced by dynamic vulcanization of a mixture of a crystalline polypropylene and an ethylene propylene rubber, and especially, is formed by crosslinking the resin composition, and the sealed type battery uses the packing as an insulating gasket. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a packing suitably used as an insulating gasket for sealing a battery in a sealed battery. The present invention further relates to a sealed battery using the packing.

  Batteries used in mobile phones and other portable electronic devices are required to increase capacity, reduce weight, and be compact in order to improve the performance of portable electronic devices. A chargeable / dischargeable sealed secondary battery has been developed.

  Such a sealed secondary battery accommodates a power generation element composed of a positive electrode plate, a negative electrode plate, a separator, and an electrolyte solution in a cylindrical or rectangular battery case, and uses a sealing body to caulk the opening of the battery case. It is a battery sealed by.

  In such a sealing type secondary battery sealing portion (between the opening of the battery case and the sealing body), in order to fix the sealing body and maintain the sealing performance between the battery case and the sealing body. Insulating gaskets (packings) are used. This packing seals the electrolyte in the battery case and prevents its leakage, and therefore requires excellent sealing properties. Therefore, it has an excellent chemical resistance (electrolytic solution resistance) and liquid leakage resistance. High compression recovery (compression elastic modulus) is required. Furthermore, the property (short-term heat resistance) that melting and deformation do not occur due to instantaneous heating at the time of manufacture (for example, heating at about 300 to 400 ° C. for about 1 second in the process of laser welding the metal case of the battery) It is desired to have a property (heat cycle resistance) such that deterioration such as a reduction in caulking force does not occur even when the electronic device is repeatedly exposed to a high temperature due to heat generation.

  Currently, as a packing material for a sealed secondary battery, a polyolefin resin such as polyethylene or polypropylene, a tetrafluoroethylene / perfluoroalkoxy ether copolymer (hereinafter referred to as PFA), or the like is used. However, polyolefin resins such as polypropylene have low heat resistance and are hard, so they lack elasticity and have low sealing performance, and a pretreatment step is required to apply a thin butyl rubber dissolved in xylene to ensure sealing performance. There are problems in terms of work environment and manufacturing cost.

  On the other hand, PFA is moderately flexible and therefore excellent in hermeticity, high in heat resistance and compression recovery, and has excellent characteristics, but is expensive.

  In JP 2001-126684 A (Patent Document 1), as a material for packing of a sealed secondary battery, ethylene polypropylene elastomer, styrene elastomer, olefin elastomer, ethylene propylene rubber, butyl rubber, styrene butadiene rubber, Elastomers such as fluorine rubber, mixed materials of polyolefin resin and olefin rubber, or fluorine rubber have also been proposed.

  However, if these materials are also excellent in hardness and strength, they lack elasticity and have poor sealing properties. Conversely, those that have excellent elasticity have insufficient hardness and strength and ensure sealing properties. It is difficult to do so, and does not fully satisfy the above requirements.

Further, JP-A-2005-310669 (Patent Document 2) includes polyolefin resins, polyolefin elastomers, polyethylene terephthalate resins, polyester elastomers, polyphenylene sulfide resins, polyarylate resins, polyamide resins, polyamide elastomers, fluororesins and fluoroelastomers. A packing for a sealed secondary battery made of a material obtained by radiation-crosslinking a selected resin and having a residual elastic modulus of 4% or more is disclosed (claims 1 to 3). This packing is excellent in leakage resistance and safety, and has an excellent characteristic that it can maintain its shape even when the battery is abnormal due to overcharging, but now it has better short-term heat resistance and heat resistance. There is a demand for materials having cycleability.
JP 2001-126684 A JP-A-2005-310569

  The present invention solves the above-mentioned problems of the prior art, and is a packing used for applications requiring chemical resistance and heat resistance, such as an insulating gasket and an electrolytic capacitor of a sealed secondary battery, It consists of a resin composition with moderate flexibility, compression recovery, excellent heat resistance and chemical resistance (electrolytic solution resistance), and is excellent in hermeticity, leakage resistance, short-term heat resistance, and heat cycle resistance. It is an object to provide a packing. It is another object of the present invention to provide a sealed battery characterized by using this packing and having little problems such as liquid leakage and reduction in caulking force.

  As a result of diligent research, the present inventor achieves the above problems by forming a packing using a resin composition obtained by dynamically vulcanizing a mixture containing a crystalline polyolefin resin and ethylene propylene rubber. And the present invention was completed. The present inventor has found that when the packing is formed from a material obtained by crosslinking the resin composition, more excellent sealing properties, leakage resistance, short-term heat resistance, heat cycle resistance, and the like can be obtained.

  That is, the present invention provides a packing characterized by being formed of a resin composition obtained by dynamic vulcanization of a mixture containing a crystalline polyolefin resin and ethylene propylene rubber (claim 1).

  Examples of the crystalline polyolefin resin include polyethylene resin and polypropylene resin, but polypropylene resin is preferable from the viewpoint of heat resistance and cost. Claim 2 corresponds to this preferable mode. As the polypropylene resin, random type (atactic) polypropylene is preferable in order to facilitate crosslinking when performing radiation crosslinking described later. Further, a polyethylene copolymer may be used as the polypropylene resin.

  As an ethylene propylene rubber, what consists of a copolymer (EPM) of ethylene and propylene is illustrated preferably. Furthermore, an ethylene / propylene / diene terpolymer (EPDM) in which a slight diene component is added to EPM and an unsaturated bond is introduced can also be used.

  In the present specification, dynamic vulcanization is a vulcanization process of a mixture of crystalline polyolefin resin and ethylene propylene rubber, and the ethylene propylene rubber is subjected to high shear conditions in the presence of crystalline polyolefin resin particles. Means a process that is vulcanized. The average particle size of the particles used at this time is preferably 10 μm or less.

  Dynamic vulcanization is carried out in an apparatus such as a kneading roll machine, a Banbury mixer, a continuous mixer, a kneader or a twin screw extruder, such as a mixed extruder, at temperatures above the curing temperature of ethylene propylene rubber. This can be done by mixing rubber and crystalline polyolefin resin. In the dynamically vulcanized mixture, the ethylene propylene rubber is sufficiently cured, but this mixture can be molded by extrusion, injection molding, compression molding or the like.

  In order to make the molding process easier, a plasticizer may be added. However, many plasticizers are easily dissolved in an electrolytic solution, and therefore, it is necessary to consider the problem of reducing the resistance to electrolytic solution. .

  In addition to the above components, the resin composition forming the packing of the present invention includes glass fiber, carbon fiber, calcium carbonate, talc, silica, alumina, aluminum hydroxide and the like for the purpose of adjusting the rigidity. One type or two or more types of inorganic fillers may be added. Further, as long as the effects of the present invention are not impaired, other components such as organic reinforcing materials, heat-resistant agents, stabilizers represented by copper compounds and hindered phenol compounds, antioxidants, photoprotective agents, weather resistance, etc. An agent, a light stabilizer and the like can be added.

  The resin composition forming the packing of the present invention is preferably further chemically or radiation-crosslinked (Claim 3). By further cross-linking the resin composition, chemical resistance (electrolytic solution resistance) is improved, and heat resistance including short-term heat resistance is improved, so that it does not melt even when exposed to high temperatures. Therefore, it is more preferable to configure the packing.

  Examples of the cross-linking method include chemical cross-linking using a cross-linking agent and radiation cross-linking using an electron beam or other radiation. A method of crosslinking using an electron beam or other radiation is preferable because problems such as generation of burrs are less likely to occur, and the degree of crosslinking can be easily controlled. Examples of radiation include γ rays in addition to electron beams.

  The radiation dose required for crosslinking varies and is not limited depending on the type of crosslinked resin, that is, molecular weight, component ratio, etc., presence / absence or type of crosslinking aid, presence / absence or type of filler, and the like. However, as will be described later, it is preferable to irradiate an amount necessary for the dynamic viscoelasticity at 300 ° C. after crosslinking to be 1 MPa or more. The specific range of the degree of crosslinking can be easily determined by, for example, a preliminary experiment in which the radiation dose is changed.

  The resin composition thus obtained is a material having moderate flexibility, compression recovery, excellent heat resistance, chemical resistance (electrolytic solution resistance), and short-term heat resistance that can sufficiently meet recent demands. And heat cycle resistance. Therefore, when used as an insulating gasket for a sealed secondary battery or an electrolytic capacitor, it exhibits excellent sealing properties and leakage resistance, and has high durability even when used repeatedly at high temperatures.

  Further, the chemical composition or the radiation-crosslinked resin composition preferably has a compressive modulus at a compressibility of 20% of 2% or more (claim 4). By setting the compression elastic modulus to 2% or more, the effect of preventing liquid leakage due to heat cycle is enhanced. If it is 4% or more, the effect of preventing liquid leakage due to heat cycle is further increased, which is more preferable.

Here, the compression modulus means that a test piece having a thickness t ₀ before compression is compressed to a thickness t ₁ and left in an environment of 100 ° C. for 2 days, then the compressed state is released, and the thickness t ₂ after release. Is a value calculated by the formula: {(t ₂ −t ₁ ) / t ₁ } × 100. The compression rate is a value calculated by the expression {(t ₀ −t ₁ ) / t ₀ } × 100.

  The compression modulus varies depending on the molecular weight and mixing ratio of each component in the mixture of the crystalline polyolefin resin and ethylene propylene rubber to be dynamically vulcanized. In the present invention, the molecular weight and mixing ratio of each component are not particularly limited, but it is preferably adjusted so that the compression modulus at a compression rate of 20% is 2% or more.

  The compression modulus further varies depending on the presence or absence of crosslinking or the degree of crosslinking, the particle size of the crystalline polyolefin resin, and other components added to the mixture as necessary, for example, a high heat resistant resin or a plasticizer. Therefore, the compression elastic modulus can be made 2% or more also by adjusting these. Specifically, use of a crystalline polyolefin resin having a small particle diameter, addition of a high heat resistance resin, addition of a plasticizer, and the like can be mentioned.

  Further, the chemically crosslinked or radiation crosslinked resin composition preferably has a storage elastic modulus (dynamic viscoelastic modulus) at 300 ° C. after crosslinking of 1 MPa or more (Claim 5). The storage elastic modulus varies depending on the molecular weight and ratio of the components forming the mixture, the degree of crosslinking, the presence / absence or type of filler, and the like. By adjusting these, it is possible to obtain a storage elastic modulus of 1 MPa or more. it can.

  By setting the storage elastic modulus at 300 ° C. after crosslinking to 1 MPa or more, the hermeticity at high temperature becomes more excellent.

  In addition to the above packing, the present invention provides a sealed battery using the packing as an insulating gasket, that is, a bottomed battery case having an open top, a positive electrode plate, a negative electrode plate housed in the battery case, and A sealing device characterized by having an electrolyte solution, a separator disposed between the positive electrode plate and the negative electrode plate, and a sealing body that seals the opening of the battery case, and is sealed by the packing. A battery (claim 6) is provided.

  Examples of the sealed battery include secondary batteries such as a nickel cadmium storage battery and a lithium ion battery. These contain a positive electrode plate, a negative electrode plate, an electrolytic solution and a separator in a bottomed battery case having an open top, and the opening of the battery case is sealed with a sealing member. An insulating gasket is disposed between the sealing body and the opening of the battery case, or between the sealing body and the external connection terminal when an external connection terminal is installed on the sealing body, and is sealed. Is. The sealed battery of the present invention is characterized by using the packing of the present invention for the sealing.

  As described above, this packing is made of a resin composition having appropriate flexibility, compression recovery, and excellent heat resistance and chemical resistance (electrolytic solution resistance). In addition, there is no problem such as high temperature and durability against heat cycle, and even if repeated use at high temperature, the decrease in caulking force is small.

  In addition, about the material which comprises a positive electrode plate, a negative electrode plate, electrolyte solution, and a separator, and the structure of a battery, the same thing as a conventionally well-known sealed battery, for example, the sealed secondary battery of patent document 2, is used. The manufacturing method is the same as that of a conventionally known sealed battery.

  The packing of the present invention is made of a resin composition having moderate flexibility, compression recovery property, excellent heat resistance and chemical resistance (electrolytic solution resistance), and has hermeticity, leakage resistance, and heat cycle resistance. Excellent and low price. Furthermore, the sealed battery according to the present invention characterized by using this packing has no problems such as liquid leakage, has high durability at high temperatures and heat cycles, and can be used repeatedly at high temperatures. It has excellent characteristics such as a small decrease in caulking force. In particular, when a resin composition obtained by further crosslinking such as chemical crosslinking or radiation crosslinking is used for this resin composition, these effects are great and excellent short-term heat resistance can be obtained.

  Next, the best mode for carrying out the present invention will be described with reference to examples. In addition, this invention is not limited to the Example described here, As long as the meaning of this invention is not impaired, the change to another form is also possible.

  Three types of dynamically vulcanized polypropylene / ethylene propylene rubber (in the table, “PEL041”, “PEL042”, “PEL043” respectively) are added to 100 parts by weight of a phenol-based antioxidant (Irganox 1010, Ciba 1 part by weight manufactured by the company, trade name) was mixed to obtain resin compositions of Examples 1 to 3.

  Similarly, 100 parts by weight of the above-mentioned three types of dynamically vulcanized polypropylene / ethylene propylene rubber, 1 part by weight of a phenolic antioxidant (Irganox 1010, Ciba, trade name), and a crosslinking agent: tri 5 parts by weight of allyl isocyanurate (represented as “TAIC” in the table) was mixed to obtain resin compositions of Examples 4 to 6.

  Melt indexes (in the table, “MI”) of the obtained resin compositions of Examples 1 to 6, polypropylene resin (Novatech MH-4) (Comparative Example 1), and PFA (Neofuron AP-230) (Comparative Example 2) Is expressed in accordance with ASTM D-1238-98 (Test conditions: Examples 1 to 6 and Comparative Example 1 are 190 ° C. × 2.16 kg, Comparative Example 2 is 300 ° C. × 2. 16 kg).

  The resin compositions of Examples 1 to 6 and Comparative Examples 1 to 2 were molded into a predetermined shape. With respect to the molded articles of Examples 1 to 6, the specimens irradiated with an electron beam (2000 keV) with a predetermined dose (12 MRad and 24 MRad) were used as test specimens and measured according to the following items. Moreover, about the molded product of Examples 1-3 and Comparative Examples 1-2, the same measurement was performed by using the thing which has not irradiated with the electron beam as a test body. Table 1 shows the compounding prescription and the measurement results of each measurement item before electron beam irradiation. Table 2 shows the measurement results of each measurement item after irradiation with a predetermined amount of electron beam.

  [Storage elastic modulus] Based on ASTM D4065-95, the elastic modulus was measured at a rate of temperature increase of 10 ° C / min using a viscoelasticity measuring device DVA-200 (manufactured by IT Measurement & Control Co., Ltd.). In addition, the measurement was performed about each test body before electron beam irradiation and after 24 MRad irradiation (measurement temperature: 30 degreeC, 300 degreeC).

[Compressive elastic modulus]: Compressed at a compression rate of 20% (thickness: t ₁ ), left in an environment of 100 ° C. for 2 days, then released from the compressed state, and measured the thickness t ₂ after release. Calculated by the formula: {(t ₂ -t ₁ ) / t ₁ } × 100. The measurement was performed on each specimen before electron beam irradiation and after 24 MRad irradiation.

  [Gel fraction] Measured by a xylene dissolution method in accordance with JIS C 3005. In addition, the measurement was performed about each test body after electron beam irradiation of predetermined amount (12MRad, 24MRad).

  [High temperature tensile test]: Based on JIS K 7113-1995, tensile strength, elongation, and 100% modulus (in the table, expressed as “100% M”) were measured at a tensile speed of 50 mm / min (measurement temperature). : 230 ° C.). In addition, the measurement was performed about each test body after electron beam irradiation of predetermined amount (12MRad, 24MRad).

  [Heat cycle resistance]: 10 cycles of (−40 ° C., 6 hours) + (+ 100 ° C., 6 hours) are performed, and the presence or absence of abnormality in the specimen is observed. The measurement was performed on each specimen before electron beam irradiation and after irradiation with a predetermined amount (12 MRad, 24 MRad).

なお、各表において、（＊１）については、溶融、変形したため、測定しなかった。また、（＊２）は、伸びが１００％に達しなかったため、測定しなかった。

In each table, (* 1) was not measured because it melted and deformed. Further, (* 2) was not measured because the elongation did not reach 100%.

  The packings of the present invention in Examples 1 to 6 have a compression elastic modulus of 2% or more. In particular, the packings of Examples 4 to 6 to which a crosslinking agent was added and subjected to radiation crosslinking exhibited a compression elastic modulus equivalent to or higher than that when PFA was used (Comparative Example 2), and were excellent in compression recovery. It is clear from the results in Table 1.

Among the packings of Examples 1 to 6, it is shown that the packings of Examples 3 to 6 having a gel fraction exceeding 60% do not melt and deform even when heated at 230 ° C. and have excellent short-term heat resistance. ing. In particular, the packings of Examples 4 to 6, in which the crosslinking density (gel fraction) is increased by adding a crosslinking agent, are excellent in short-term heat resistance and exhibit excellent high-temperature elongation.

Claims (6)

  A packing comprising a resin composition obtained by dynamically vulcanizing a mixture containing a crystalline polyolefin resin and ethylene propylene rubber.   The packing according to claim 1, wherein the crystalline polyolefin resin is a polypropylene resin.   The packing according to claim 1 or 2, wherein the resin composition is further chemically or radiation-crosslinked.   4. The packing according to claim 3, wherein the compressive modulus at 20% compressibility of the chemically or radiation-crosslinked resin composition is 2% or more.   The packing according to claim 3 or 4, wherein the storage elastic modulus at 300 ° C of the chemically or radiation-crosslinked resin composition is 1 MPa or more. Bottomed battery case with an open top,
A positive electrode plate, a negative electrode plate and an electrolyte solution housed in the battery case,
A separator disposed between the positive electrode plate and the negative electrode plate, and
A sealing body for sealing the opening of the battery case;
A sealed battery sealed with the packing according to any one of claims 1 to 5.