JP2017059542A - Thermoplastic elastomer composition for protective member of battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic elastomer composition which is superior in flame retardancy, thermally conductivity, electrical insulation, chemical resistance (resistant against the dissolution in an electrolytic solution) and low-temperature flexibility (brittle fracture temperature), and which can be suitably used as a protective member of a battery pack.SOLUTION: A thermoplastic elastomer composition for a protective member of a battery pack comprises: 100 pts.mass of a thermoplastic resin which includes a component (a) consisting of 85-98 mass% of a hydrogen additive of a random copolymer of an aromatic vinyl compound and a conjugated diene compound and a component (b) consisting of 15-2 mass% of a polypropylene resin, provided that the total quantity of the components (a) and (b) is 100 mass%; and a component (c) consisting of 250-350 pts.mass of a magnesium hydroxide.SELECTED DRAWING: None

Description

The present invention relates to a thermoplastic elastomer composition. More specifically, the present invention relates to a thermoplastic elastomer composition that is excellent in flame retardancy, thermal conductivity, electrical insulation, chemical resistance, and low-temperature flexibility and can be suitably used as a battery pack protective member.

Conventionally, vulcanized rubber has been used as a member that is flexible and requires rubber elasticity. However, alternatives to thermoplastic elastomers are progressing due to environmental issues such as inability to recycle materials. Thermoplastic elastomer compositions using hydrogenated polystyrene-based thermoplastic elastomers such as styrene-butadiene-block copolymer (SBS) and styrene-isoprene-block copolymer (SIS) are conventionally known (for example, patents). Documents 1 to 4) that satisfy the stringent requirements of battery pack protection members have not been obtained.

A battery pack is a battery in which a plurality of unit cells are connected, and is also called an assembled battery. Secondary batteries, such as nickel cadmium batteries, nickel metal hydride batteries, and lithium ion secondary batteries, are often attached to devices as such battery packs. In recent years, battery packs have been used for devices with higher rated voltage and rated load current. In addition, the usage environment, conditions, and methods of battery packs are becoming stricter, such as rapid charging of charging specifications and space saving of specifications for storing and fixing battery packs in devices. For this reason, the battery pack protective member is also required to satisfy various required characteristics at a higher level.

There are two types of battery packs: a hard type and a soft type. In a hard battery pack, a combination of several single cells is stored in a plastic case storage case. In a soft battery pack, a combination of several single cells is covered with a shrink tube. The soft type has the advantage of saving space than the hard type. Therefore, there is a demand for a thermoplastic elastomer composition that can be used as a protective member for a soft battery pack.

In recent years, lithium ion secondary batteries have become widespread as mainstream storage batteries. Lithium ion secondary batteries are characterized by being capable of rapid charging and large current discharge compared to other storage batteries, but heat generation during charging and discharging is a problem in safety measures. Therefore, not only a lithium ion secondary battery body but also a battery pack protective member is required to have heat resistance, suppress heat generation and animal heat, and further promote heat dissipation.

Further, the protection member of the battery pack is required to be flexible and have rubber elasticity for the purpose of preventing damage to the storage battery body due to an impact at the time of dropping. In particular, lithium ion secondary battery packs have recently been actively installed in electric vehicles, hybrid vehicles, aircraft-related, various motor drive-related devices, etc., and their protective members are flexible even in low-temperature environments. Moreover, it is required not to lose rubber elasticity.

Lithium-ion secondary batteries also incorporate safety measures accessories such as temperature fuses, current fuses, and thermistors in the battery pack as countermeasures against ignition due to abnormal heating of the charger during charging and discharging and abnormal heating of the battery due to external short circuit. Although measures have been taken, flame retardancy is also required for battery pack protection members.

Further, in the lithium ion secondary battery, there is a possibility that the electrolytic solution or the like is decomposed to generate gas depending on the environment, state, and method used. The generation of gas inside the battery may lead to battery rupture or electrolyte external leakage, leading to the risk of smoke generation and ignition. For this reason, a battery pack protective member is also required to have resistance to electrolytic solution dissolution and flame retardancy.

Furthermore, from the viewpoint of developing a battery with a low environmental load, the halogenated component is also required for the protection member of the battery pack.

In addition, as “a heat conductive elastomer composition useful for a heat radiating member such as an electric or electronic component”, “from an aluminum hydroxide whose surface is coated with an organic coupling agent to an elastomer composition mainly composed of a styrene elastomer”. The thermal conductivity of the elastomer is improved by blending the thermal conductive filler made of magnesium oxide with the surface covered with inorganic and / or organic matter and magnesia clinker, which is an inactivated magnesium oxide. Has been proposed (Patent Document 5). However, the battery pack protective member, in particular, the battery pack protective member of the lithium ion secondary battery does not satisfy the strict requirements.

JP 58-133202 A JP 58-145751 A JP 59-53548 A JP 62-48757 A JP 2011-207962 A

The object of the present invention is to have flame resistance of V-0 in the UL94V0 test without using a halogen flame retardant, thermal conductivity, electrical insulation, chemical resistance (electrolytic solution solubility), and low temperature flexibility. An object of the present invention is to provide a thermoplastic elastomer composition which is excellent in (brittle fracture temperature) and can be suitably used as a protective member for battery packs, particularly soft battery packs.

As a result of diligent research, the present inventors focused on the characteristics necessary for safety measures for battery packs, and as a basic polymer material, a random copolymer of a specific aromatic vinyl compound and a conjugated diene compound was obtained. The present inventors have found that a thermoplastic elastomer composition containing a hydrogenated product and a polypropylene resin and containing magnesium hydroxide as a non-halogen flame retardant can solve the problem, and has completed the present invention.

That is, the present invention includes 85 to 98% by mass of a hydrogenated product of a random copolymer of component (a) aromatic vinyl compound and conjugated diene compound, and component (b) 15 to 2% by mass of polypropylene resin, Here, the total of the component (a) and the component (b) is 100% by mass, and 100 parts by mass of the thermoplastic resin; and component (c) 250 to 350 parts by mass of magnesium hydroxide; It is a thermoplastic elastomer composition.

According to a second aspect of the present invention, in the test of dynamic solid viscoelasticity by the tensile method measured according to JIS K7244-4: 1999, the peak temperature of the loss tangent is a single peak. The thermoplastic elastomer composition according to the first invention, which is observed in a range of 50 ° C to 0 ° C.

The third invention of the present invention further comprises 70 to 90 parts by mass of the component (d) thermally conductive filler with respect to a total of 100 parts by mass of the component (a) and the component (b). The thermoplastic elastomer composition according to the first invention or the second invention.

According to a fourth aspect of the present invention, the component (d) is at least one selected from the group consisting of magnesium oxide, magnesium silicate, magnesium carbonate, and boron nitride. The thermoplastic elastomer composition according to any one of the above.

5th invention of this invention is a protection member for battery packs which consists of a thermoplastic-elastomer composition in any one of 1st-4th invention.

The thermoplastic elastomer composition of the present invention has a flame retardancy of V-0 in the UL94V0 test without using a halogen flame retardant, and has thermal conductivity, electrical insulation, chemical resistance (electrolytic solution solubility). And low temperature flexibility (brittle fracture temperature), it can be suitably used as a protective member for battery packs, particularly soft battery packs.

About the thermoplastic elastomer composition of this invention, each component which comprises a composition, a manufacturing method, and the implementation method are demonstrated.

Component (a) Hydrogenated random copolymer of aromatic vinyl compound and conjugated diene compound (essential component)
The hydrogenated product of a random copolymer of an aromatic vinyl compound and a conjugated diene compound used as component (a) of the present invention is a substance obtained by hydrogenating a random copolymer of an aromatic vinyl compound and a conjugated diene compound.

The content of the aromatic vinyl compound in the component (a) is preferably 30% by mass or less, more preferably 15% by mass or less, from the viewpoint of obtaining a flexible molded product. Moreover, from the viewpoint of shape stability, extrusion processability, and resistance to electrolytic solution dissolution of the molded product, the content of the aromatic vinyl compound as the component (a) is preferably 5% by mass or more.

Examples of the aromatic vinyl compound include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylstyrene, N, N-diethyl-p-aminoethylstyrene, vinyl. One or two or more types can be selected from toluene, p-tert-butylstyrene, etc. Among them, styrene is preferable.

As the conjugated diene compound, for example, one or more kinds are selected from butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc., among which butadiene, isoprene, and A combination of butadiene and isoprene is preferred.

From the viewpoint of long-term thermal stability, the component (a) is preferably one in which at least 90 mol% or more of the aliphatic double bonds based on the conjugated diene compound are hydrogenated.

In the dynamic solid viscoelasticity test measured according to JIS K7244-4: 1999, the component (a) is observed as a single peak at a peak temperature of the tensile loss tangent in a range of −50 ° C. to 0 ° C. Is preferred. By using such a component (a), flame retardancy, thermal conductivity, electrical insulation, chemical resistance (electrolytic solution solubility), and low temperature flexibility (brittle fracture temperature) can be expressed in a balanced manner. it can.

The weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (hereinafter sometimes abbreviated as GPC) of the component (a) is preferably 5,000 to 1,000,000, more preferably 10,000. The value of polydispersity (Mw / Mn) is preferably 10 or less. When the mass average molecular weight and polydispersity of the component (a) are in the above ranges, the extrusion processability is good.

Commercial examples of the component (a) include “Dynalon 1320P (trade name)” (hydrogenated styrene-butadiene random copolymer, mass average molecular weight = 300,000, Mw / Mn = 1.1) manufactured by JSR Corporation. Can give.

Component (b) Polypropylene resin (essential component)
Component (b) of the present invention is, for example, a propylene homopolymer; a copolymer of propylene and a small amount of other α-olefin such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, etc. Polypropylene resin such as (block copolymer, random copolymer), and plays an important role in maintaining chemical resistance (electrolytic solution solubility). Component (b) preferably has a melting point (Tm) measured by a differential scanning calorimeter (DSC) of 120 to 167 ° C. from the viewpoint of chemical resistance (electrolytic solution solubility). Further, those having a melt mass flow rate in the range of 0.1 to 10 g / 10 min improve the dispersion of the component (a) in the composition of the present invention, improve the heat resistance of the composition, and further improve the heat resistance of the present invention. Since it has the effect of making the external appearance of the molded article obtained from a composition favorable, it is preferable.

In the present specification, the melt mass flow rate (MFR) is a value measured under conditions of 230 ° C. and a load of 21.18 N according to ASTM D-1238 unless otherwise specified. The melting point (Tm) measured with a differential scanning calorimeter (DSC) is a Diamond DSC type differential scanning calorimeter manufactured by PerkinElmer Japan Co., Ltd. The second melting curve (melting curve measured in the last heating process) measured by a program that cools to 10 ° C., holds at −10 ° C. for 5 minutes, and raises the temperature to 230 ° C. at 10 ° C./min. The peak top melting point on the higher temperature side.

The ratio of the component (a) to the component (b) is flame retardancy, thermal conductivity, electrical insulation, chemical resistance (electrolytic solution solubility), low temperature flexibility (brittle fracture temperature), and extrusion. From the viewpoint of expressing the moldability in a well-balanced manner, particularly from the viewpoints of flexibility, extrusion processability, and chemical resistance, the component (a) is 85 to 98 mass% and the component (b) is 15 to 2 mass%. Here, the sum of both is 100% by mass. Preferably they are component (a) 85.5-97.5 mass% and component (b) 14.5-2.5 mass%.

Component (c) Magnesium hydroxide (essential component)
Component (c) of the present invention is magnesium hydroxide and plays an important role in imparting flame retardancy to the composition. It also has the effect of improving the thermal conductivity of the composition. Magnesium hydroxide is suitable for imparting flame retardancy to a resin composition for battery pack protection members because it is more excellent in electrical insulation than ordinary flame retardants such as halogen flame retardants and phosphorus flame retardants. Magnesium hydroxide having various particle sizes and surface-treated products are commercially available. Any component of magnesium hydroxide may be used as the component (c) of the present invention.

The blending amount of the component (c) is 100 parts by weight of the total of the component (a) and the component (b), from the viewpoint of balance between flame retardancy and thermal conductivity, and the productivity of the composition and molded product. It is the range of 250-350 mass parts. Preferably it is 260-325 mass parts.

Component (d) Thermally conductive filler (optional component)
Thermally conductive fillers can be generally classified into those having conductivity and those having electrical insulation. There are various types of surface treatments that take into account the miscibility with the resin, and they are properly used according to the purpose. Further, the shape includes powder, fiber, scale, and the like. Among these, a thermal conductive filler having high electrical insulation is preferable as the optional component (d) of the present invention because of the characteristics required for the battery pack protection member. Moreover, the non-fibrous thing is preferable from the problem of thermal conductivity anisotropy. More preferably, it is powdery. Specifically, as the component (d), magnesium silicate, magnesium oxide, magnesium carbonate, boron nitride and the like are preferable. As the component (d), one or more of these can be preferably used.

When using the said component (d), the compounding quantity is 70-90 mass with respect to a total of 100 mass parts of a component (a) and a component (b) from a viewpoint of the balance of electrical insulation and thermal conductivity. Part is preferred. More preferably, it is 75-85 mass parts.

Component (e) Polyphenylene ether resin (optional component)
Polyphenylene ether resin is an engineering plastic with excellent heat resistance, electrical characteristics, and chemical resistance, and is known to be completely compatible with polystyrene, but on the other hand, it has poor fluidity and is difficult to mold. Therefore, it is generally used as a styrene-modified polyphenylene ether resin blended with a polystyrene resin for the purpose of improving molding processability, fluidity, and impact resistance. By adding 2 to 8 parts by mass of the above component (e) to 100 parts by mass of the total of component (a) and component (b) in the composition of the present invention, chemical resistance (electrolytic solution resistant) Solubility), in particular, resistance to dissolution in a high-temperature electrolyte can be improved. As the component (e), a polyphenylene ether resin or a styrene-modified polyphenylene ether resin may be used.

In the heat-curable elastomer composition of the present invention, inorganic fillers other than the component (c) and the component (d) can be blended as desired. In addition to the effect of improving some physical properties such as compression set of molded products, the inorganic filler has an economic advantage due to the increase in the amount. Examples of the inorganic filler include calcium carbonate, talc, mica, clay, barium sulfate, natural silicic acid, synthetic silicic acid (white carbon), titanium oxide, carbon black, and the like. The blending amount can be arbitrarily set as long as it does not contradict.

In addition to the above-described components, the thermosetting elastomer composition of the present invention may further include various anti-blocking agents, sealability improvers, rubber softeners, heat stabilizers, antioxidants, as desired. Ultraviolet absorbers, antistatic agents, lubricants, crystal nucleating agents, coloring agents, and the like can be included.

Examples of the antioxidant include 2,6-di-tert-p-butyl-p-cresol, 2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, 4,4 Examples thereof include phenolic antioxidants such as -dihydroxydiphenyl and tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, phosphite antioxidants, and thioether antioxidants. Of these, phenolic antioxidants and phosphite antioxidants are preferred.

The thermoplastic elastomer composition of the present invention can be produced by melt-kneading the above components (a) to (c) and other optional components in any order or simultaneously. The method of melt kneading is not particularly limited, and a known method can be used. For example, a single screw extruder, a twin screw extruder, a roll, a mixer, or various kneaders can be used. In the case of using a mixer or a kneader, for example, it is preferable to perform melt kneading under a discharge temperature of 170 to 240 ° C. When using a biaxial kneader, it is preferable to perform melt kneading at, for example, a screw rotational speed of 50 to 500 rpm and a kneading temperature of 170 to 240 ° C.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to this.

Examples 1-14, Comparative Examples 1-8
Using a 20 L capacity pressure kneader, a blend having a blending ratio shown in any one of Tables 1 to 3 was melt-kneaded under a discharge temperature of 175 ° C. The obtained composition was extruded into a strand shape using a twin screw extruder at a die set temperature of 210 ° C., cooled in water using a water tank, and cut to obtain cylindrical pellets. Subsequently, using the obtained pellets, using a heating press machine, after heat pressing at a temperature of 220 ° C., a preheating time of 3 minutes, and a pressing time of 3 minutes, immediately at a temperature of 30 ° C. and a pressing time of 3 minutes. Cold pressing was performed to obtain a press sheet having a thickness of 1 mm. Similarly, press sheets having thicknesses of 2 mm, 3 mm, and 6 mm were obtained. The manufacturability of the above steps was evaluated according to the following criteria. The following tests (1) to (8) were performed. The results are shown in any one of Tables 1-3.
O: Press sheets of various thicknesses could be obtained without any problem. X: There was a problem in at least any one of the above steps, such as the melt kneading in the pressure kneader was not stable due to overload, and granulation was not possible. It was.

Measuring method (1) Insulation:
According to JIS K6271 method, the 1 mm-thick press sheet obtained above was used as a sample, and the measurement was performed by the double ring method.
(Evaluation criteria) An insulation resistivity of 10 14 Ωcm or more was considered acceptable.

(2) Thermal conductivity:
“Kemtherm QTM-D3 (trade name)” manufactured by Kyoto Electronics Industry Co., Ltd. was used as a measuring device, and the 1 mm-thick press sheet obtained above was used as a sample, and JIS R2616 was used at 25 ° C. (room temperature). Measurement was carried out by the prescribed hot wire method. The direction of heat conduction is the thickness direction of the test piece.
(Evaluation criteria) 0.80 W / (m · K) or more was regarded as acceptable.

(3) Flame retardancy:
Measured according to UL94V0. The 1 mm-thick press sheet obtained above was used for the sample.
(Evaluation Criteria) Acceptance was V-0 level.

(4) Extrusion processability:
Using a 40mm single screw extruder equipped with a screw with a compression ratio (CR) of 2.7 and a tube mold with 7mm outer diameter and 1mm thickness, screw rotation 15rpm, mold outlet resin temperature The tube was subjected to extrusion molding under the conditions of 230 ° C. and a pulling rate (calculated as the ratio of the thickness dimension of the mold to the thickness of the obtained tube) 1.3. Extrusion processability and the appearance of the molded product were evaluated according to the following criteria.
Extrusion processability:
○: There is no uneven thickness, and a product with dimensions is obtained.
Δ: Discharge unevenness (surging) is slightly observed, and uneven thickness is partially generated.
X: Discharge unevenness (surging) is remarkably observed and uneven thickness is severe.
Appearance of molded product (tube):
◯: Appearance defects such as rough skin are not observed on the tube surface.
Δ: Appearance defects such as rough skin are partially observed on the tube surface.
X: Appearance defects such as remarkable skin roughness are recognized on the tube surface.

(5) Chemical resistance:
The state of the press sheet after the 1 mm thick press sheet obtained above was immersed in a lithium hexafluorophosphate aqueous solution (lithium salt concentration: 1 mol / liter) at a temperature of 80 ° C. for 2 hours was visually observed. Moreover, about the sample containing a component (e), the same test was done also on the conditions immersed at 100 degreeC for 2 hours. The evaluation criteria are as follows.
○: No change at all Δ: Sheet shape slightly changed or swollen,
X: Part of the sheet was dissolved

(6) Hardness:
Measurement was performed in accordance with JIS K6253 (after 15 seconds of HDA). The sample used was the 6 mm thick press sheet obtained above.
(Evaluation criteria) Less than 90 ° was regarded as acceptable.

(7) Dynamic solid viscoelastic properties:
In accordance with JIS K7244-4: 1999, the sample was punched out from the 2 mm thick press sheet obtained above to a size of 10 mm × 40 mm, held at −60 ° C. for 10 minutes, and heated at a rate of 4 ° C./min. It measured with the temperature program which heats up to 100 degreeC.
A: The peak of the tensile loss tangent (tan δ) is observed as a single peak at −50 ° C. to 0 ° C.
X: In cases other than the above good (◯) evaluation.

(8) Embrittlement temperature Measured according to JIS K7216-1980. The sample used was punched into the A shape from the 2 mm thick press sheet obtained above.
(Evaluation criteria) -5 ° C or lower was regarded as acceptable.

Raw materials used Component (a):
(A1) Hydrogenated product (HSBR) “Dynalon 1320P (trade name)” of random copolymer of aromatic vinyl compound and conjugated diene compound of JSR Corporation, styrene content 10 mass%, weight average molecular weight 300,000 In the dynamic fixed viscoelastic property test measured according to JIS K7244-4: 1999, a peak of tensile loss tangent is observed as a single peak around -25 ° C.

Comparative component (a ′):
(A'1) Polyolefin elastomer resin (ethylene octene-1 random copolymer) “Engage 8150 (trade name)” by DuPont Dow Elastomer Japan.

Component (b):
(B1) Polypropylene resin (PP) “FW4BT (trade name)” manufactured by Nippon Polypro Co., Ltd., melting point 139 ° C., melt mass flow rate 6.5 g / 10 min.

Comparative component (b ′):
(B'1) Asahi Kasei Chemicals Corporation high density polyethylene resin (HDPE) "Suntech B470 (trade name)".

Component (c):
(C1) Synthetic magnesium hydroxide “Magsees S-6 (trade name)” manufactured by Kamishima Chemical Co., Ltd., an average particle size of 1.0 μm, and the particle surface was treated with a silane compound and a fatty acid.
(C2) Natural magnesium hydroxide “EP3-A (trade name)” of Kamishima Chemical Co., Ltd., average particle size of 7.1 μm.

Comparative component (c ′):
(C′1) Aluminum hydroxide “H42M (trade name)” from Showa Denko Co., Ltd., average particle size 1.0 μm, particle surface treated with silane compound and fatty acid.

Component (d):
(D1) Magnesium silicate (Mg ₃ Si ₄ O ₁₀ (OH) ₂ ) “Talc P-4 (trade name)” manufactured by Nippon Talc Co., Ltd., average particle size: 4.5 μm.
(D2) Magnesium oxide “Starmag SL-WR (trade name)” manufactured by Kamishima Chemical Co., Ltd.
(D3) Magnesium carbonate “MSPS (trade name)” manufactured by Kamishima Chemical Co., Ltd.
(D4) Boron nitride “SGB (trade name)” of Denki Kagaku Kogyo Co., Ltd.

Ingredient (e):
(E1) Styrene-modified polyphenylene ether resin (PPO) “Zylon X9102 (trade name)” manufactured by Asahi Kasei Chemicals Corporation.

As shown in Table 1 or 2, the composition of the present invention has a well-balanced expression of flame retardancy, thermal conductivity, electrical insulation, chemical resistance, low temperature flexibility, manufacturability, and extrusion processability. Therefore, it can be suitably used as a protective member for battery packs. On the other hand, as shown in Table 3, the comparative example is inferior to at least one of flame retardancy, thermal conductivity, electrical insulation, chemical resistance, low temperature flexibility, manufacturability, and extrusion processability. The battery pack cannot be used as a protective member.

Claims (5)

Component (a) includes 85 to 98% by mass of a hydrogenated random copolymer of an aromatic vinyl compound and a conjugated diene compound, and component (b) 15 to 2% by mass of polypropylene resin, wherein component (a) A thermoplastic elastomer composition for a protective member of a battery pack, comprising: 100 parts by mass of a thermoplastic resin, and 100% by mass of component (b); and component (c) 250 to 350 parts by mass of magnesium hydroxide.
When the component (a) is a dynamic solid viscoelastic property test by a tensile method measured according to JIS K7244-4: 1999, the peak temperature of loss tangent is observed as a single peak in the range of −50 ° C. to 0 ° C. 2. The thermoplastic elastomer composition according to claim 1, wherein
Furthermore, 70-90 mass parts of component (d) heat conductive filler is included with respect to a total of 100 mass parts of component (a) and component (b), The heat of Claim 1 or 2 characterized by the above-mentioned. Plastic elastomer composition.
The thermoplastic elastomer according to any one of claims 1 to 3, wherein the component (d) is at least one selected from the group consisting of magnesium oxide, magnesium silicate, magnesium carbonate, and boron nitride. Composition.
The protection member for battery packs which consists of a thermoplastic elastomer composition of any one of Claims 1-4.