JP2008215493A - Joint boots - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide joint boots for further improving bending fatigue resistance, in the joint boots molded by using acrylic rubber/polyamide-based thermoplastic elastomer composed of a polyamide resin and cross-linked acrylic rubber. <P>SOLUTION: The joint boots are composed of the polyamide resin and the cross-linked acrylic rubber, and are formed by including carbon black having an average basic particle size (an average primary particle size) of 50 nm or less by 0.2 to 3 wt.% there, and are molded by using the acrylic rubber/polyamide-based thermoplastic elastomer including the carbon black. Carbon black of an ASTM code (D-1765-91) of N220 to N660 is used as the carbon black having such an average basic particle size. These joint boots can not only sufficiently satisfy heat resistance required there even when used on the inboard side but also can largely improve the bending fatigue resistance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a joint boot. More specifically, the present invention relates to a joint boot formed using a thermoplastic elastomer having excellent heat resistance.

  Universal shafts are mounted on the engine and wheel sides of automobile drive shafts. To keep grease inside this joint, a joint boot as a joint cover is attached to cover the joint. Yes.

  Since the joint boot is provided on the drive shaft, the joint boot may be used at high speed rotation, bent, or bent and used in a cryogenic region.

In such joint boots, there are an outboard side (tire side) and an inboard side (engine side) depending on the part used, and for the outboard side, in order to further improve the recycling rate of recent automobile parts, the material of the parts However, replacement of vulcanized rubber parts with thermoplastic elastomers, specifically, conversion from chloroprene rubber to polyester thermoplastic elastomer that is recyclable, has high strength, high flexibility, and excellent moldability is progressing.
Japanese Patent Laid-Open No. 9-037802

On the other hand, the inboard side is not required to have high flexibility as compared to the outboard side, but is attached near the engine, so that higher heat resistance is required than the polyester thermoplastic elastomer. Therefore, conventionally, it has been considered difficult to replace vulcanized rubber with a thermoplastic elastomer as a material for the inboard side joint boot, and an inboard side joint boot using the thermoplastic elastomer has not been manufactured.
JP 2003-286341 A JP-A-1-306456

The applicant of the present invention is a joint boot formed using a thermoplastic elastomer, and can sufficiently satisfy the heat resistance required there even when used on the inboard side. A joint boot formed using an acrylic rubber / polyamide thermoplastic elastomer composed of a polyamide resin and a crosslinked acrylic rubber is proposed.
WO 2006/129252

  An object of the present invention is to provide a joint boot formed using an acrylic rubber / polyamide thermoplastic elastomer composed of a polyamide resin and a crosslinked acrylic rubber, and further improved in bending fatigue resistance. .

  An object of the present invention is a carbon black-containing acrylic rubber comprising a polyamide resin and a cross-linked acrylic rubber, in which 0.2 to 3% by weight of carbon black having an average basic particle size (average primary particle size) of 50 nm or less is contained. This is achieved by a joint boot formed using a polyamide-based thermoplastic elastomer.

  The joint boot according to the present invention has excellent low temperature and high temperature durability and grease resistance, and particularly excellent in high temperature durability and grease resistance at a high temperature such as 150 ° C. Even when used on the inboard side where the engine is required (engine side), it can be effectively adapted. Furthermore, by adding a small amount of carbon black having a small average primary particle diameter to the used thermoplastic elastomer, the bending fatigue resistance can be greatly improved.

  The polyamide-based thermoplastic elastomer in which the cross-linked acrylic rubber used in the present invention is dispersed is preferably one in which the rubber is dispersed in the polyamide resin by dynamically cross-linking the acrylic rubber with a cross-linking agent, more preferably polyamide. A resin and acrylic rubber that are covalently crosslinked are used.

  The polyamide resin is used in a proportion of 20 to 60% by weight, preferably 20 to 55% by weight, based on the total amount of the polyamide resin and the crosslinked acrylic rubber. If the polyamide resin is used in a higher ratio, the hardness becomes higher and the elastomeric property is lost. On the other hand, if the polyamide resin is used in a lower ratio, the thermoplasticity is lost.

  As the polyamide resin, nylon resin, for example, nylon 3, nylon 4, nylon 6, nylon 7, nylon 8, nylon 4 2, nylon 4 6, nylon 6 6, nylon 6 9, nylon 6 10, nylon 11, nylon 12, A resin having a softening point or melting point of 160 ° C. to 280 ° C., such as nylon 666 (caprolactam-hexamethylene adipamide copolymer), a mixture, or a copolymer can be used.

  As the acrylic rubber to be covalently crosslinked, as described in Patent Documents 2 to 3, the covalent crosslinking with the polyamide resin is about 100 to 350 ° C., preferably about 150 to 300 ° C., more preferably about Since it is carried out by dynamic crosslinking under heating conditions of 180 to 280 ° C., α-olefin-alkyl (meth) acrylate copolymers having excellent heat resistance are preferably used. Also, with emphasis on oil resistance, homopolymers or copolymers of alkyl (meth) acrylates and alkoxyalkyl (meth) acrylates, copolymers of these with α-olefins, and polymer blends of these various polymers A thing etc. are also used suitably.

As the α-olefin, C ₂ -C ₁₂ α-olefin such as ethylene, propylene, butene-1, isobutylene, pentene, heptene, octene, decene, dodecene, etc. are used, preferably C ₂ -C ₄ α-olefin. Olefin is used. The alkyl (meth) acrylate, methyl acrylate, ethyl acrylate, n- butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, decyl acrylate, C ₁ -C ₁₂ alkyl groups such as dodecyl acrylate, preferably acrylates having an alkyl group of C ₁ -C _4, methyl methacrylate, ethyl methacrylate, n- butyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, C ₁ -C _12, such as dodecyl methacrylate alkyl groups, preferably methacrylate having an alkyl group of C ₁ -C ₄ is used. As the alkoxyalkyl (meth) acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, methoxybutyl acrylate, ethoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxy butyl methacrylate, an alkoxyl group having C ₁ -C ₂ such as ethoxy butyl methacrylate and alkoxyalkyl (meth) acrylate having an alkyl group of C ₂ -C ₄ is used.

  In these copolymers, a crosslinkable group-containing (meth) acrylate having a carboxyl group, a hydroxyl group, a chlorine group, an epoxy group, a diene group, an isocyanate group, an amine group, an amide group, an oxazoline group or the like is further copolymerized. Preferably, as such a crosslinkable group-containing (meth) acrylate, those generally used for acrylic rubbers mainly composed of alkyl (meth) acrylate (and alkoxyalkyl (meth) acrylate) are used as they are. .

In the case of an α-olefin-alkyl (meth) acrylate copolymer obtained by further copolymerizing such a crosslinkable group-containing (meth) acrylate, 10 to 69.9 mol% of the α-olefin and alkyl (meth) acrylate are added. Those having a composition of 29.6 to 89.5 mol% and 0.5 to 10 mol% of a crosslinkable group-containing (meth) acrylate are used. Such a copolymer is essentially non-crystalline and has a glass transition temperature Tg. Is below room temperature. An example of such an acrylic rubber copolymer is also described in Non-Patent Document 1 below. Regarding the alkoxyalkyl (meth) acrylate copolymer, the crosslinkable group-containing (meth) acrylate is 0.5 to 10 mol%, and the rest is an arbitrary copolymer composition of alkyl (meth) acrylate and alkoxyalkyl (meth) acrylate. What has is used. Furthermore, an ethylene-maleic acid monoalkyl ester copolymer or the like can also be used.
Rubber World Blue Book 393-4 (1987)

  The covalent crosslinking between the polyamide resin and the acrylic rubber copolymer is performed in the presence of a crosslinking agent according to the type of the crosslinkable group in the acrylic rubber copolymer, such as a polyol, a polyamine, a polyisocyanate, and an epoxy group-containing compound. Further, it is carried out by a dynamic crosslinking method in which the polyamide resin and the acrylic rubber copolymer are melt-mixed at the above temperature, generally by a method in which a crosslinking agent is added while masticating with a biaxial kneader. As a mixing method other than dynamic crosslinking, for example, without adding a polyamide resin, acrylic rubber is sufficiently vulcanized by either a dynamic or static method and then pulverized, and then the melting point or softening of the polyamide resin The method of mixing with a polyamide resin at the temperature more than a point is mentioned.

  The acrylic rubber / polyamide thermoplastic elastomer thus obtained is obtained by, for example, immersing its press film (thickness: about 0.2 mm) in an organic solvent such as dichloromethane, toluene, tetrahydrofuran and the like for 48 hours. % Or more, preferably 30% or more has a crosslinking density such that it is not extracted. Further, in this acrylic rubber / polyamide thermoplastic elastomer, a commonly used plasticizer or filler such as phthalate ester, phosphate ester, carbon black, silica or the like can be added and used.

  Such an acrylic rubber / polyamide thermoplastic elastomer can be produced by the method described above. In addition, a commercially available product such as the Zeotherm series manufactured by ZEON CHEMICALS can be used as it is for the same type in which only covalent crosslinking between acrylic rubber and polyamide is not performed.

  In general, thermoplastic elastomers used for molding joint boots are thermoplastic and are supposed to be recycled. Recycled materials have a different thermal history from virgin materials (new materials), so white to light-colored materials may have slightly different product colors, especially when recycled materials are mixed with virgin materials to form products. There is a problem that the difference in color tone is emphasized as a mottled pattern. For this reason, the thermoplastic elastomer is usually colored black, and the color change due to the recycled material is usually suppressed.

  In order to color the thermoplastic elastomer black, a black pigment, generally carbon black, is used, but the present inventors have added the amount of black carbon black for coloring and the average basic particle size (average primary particle size). It was found that the durability of the joint boot formed from the size varies greatly depending on the size.

  That is, a carbon black-containing acrylic rubber / polyamide thermoplastic elastomer comprising a polyamide resin and a cross-linked acrylic rubber and containing 0.2 to 3% by weight of carbon black having an average basic particle size (average primary particle size) of 50 nm or less. When 0.2 to 3% by weight, preferably 0.5 to 2.5% by weight of carbon black is added and incorporated, the bending fatigue resistance is greatly improved, while the added amount of carbon black is used in a proportion outside this range. This effect is not seen.

  The addition of carbon black is performed by adding a predetermined amount at the stage of preparation of biaxial kneading when the rubber is dispersed in the polyamide resin by dynamically crosslinking acrylic rubber using a biaxial kneader or the like. . When a mixing method other than dynamic crosslinking is used, a predetermined amount of carbon black is added in a state of either a crosslinked acrylic rubber, a polyamide resin, or a mixture thereof.

  Carbon black can be classified by the average primary particle size (measured with a transmission electron microscope), which is the average basic particle size. When carbon black having a larger value is used, the bending fatigue resistance can be improved. Therefore, carbon black of 50 nm or less, preferably about 20 to 50 nm is used. More specifically, ASTM code (D-1765-91) is N220 to N660 (type names ISAF-HM, same-LM, same-HS, CF, HAF-LS-SC, HAF-LS, HAF, same- HS, same-VHS, XCF, FEF-LS, FEF, same-HS, GPF-LS, same-HS, GPF, etc.), preferably N330-N550 (type name HAF, same-HS, same-VHS, XCF, FEF-LS, FEF, etc.) are used. Even if the particle size is too small, the desired effect of improving bending fatigue resistance cannot be obtained. This is because the carbon black with a smaller particle size has a stronger tendency to aggregate, and the dispersion state of the carbon black in the thermoplastic elastomer is better. It is thought that there is not.

  Various additives other than carbon black, for example, an antioxidant, a stabilizer, a tackifier, a release agent, a pigment, a flame retardant, and the like can be added to the composition of the present invention. Furthermore, in order to improve strength and rigidity, a particulate reinforcing component, short fibers, and the like can be added.

  The composition is prepared by mixing using a known mixing method such as a twin screw extruder, blender, Henschel mixer, single screw extruder, roll, Banbury mixer, kneader and the like. In addition, examples of the molding method of the joint boot include blow molding, injection molding, compression molding, extrusion molding, and the like. Preferably, blow molding is used because of low anisotropy in material physical properties. It is appropriately performed in a state where the material is plasticized by heating at 280 ° C. for about 1 to 10 minutes.

  Next, the present invention will be described with reference to examples.

Examples 1-4, Comparative Examples 1-4
Covalent bonding between extrusion grade 6 nylon (Ube Industries UBE nylon 1030B) and ultra-cold resistant acrylic rubber obtained by solution polymerization method with n-butyl acrylate and 2-methoxyethyl acrylate as main components The carbon black-containing acrylic rubber / polyamide thermoplastic elastomer pellets produced by dynamically crosslinking with a biaxial kneader so as to crosslink, and adding a predetermined amount of carbon black at the stage of biaxial kneading are prepared. After drying at 100 ° C. for 5 hours, it was plasticized by heating to 260 ° C. for 3 minutes using an injection molding machine to form a sheet having a thickness of 2 mm.

  A test piece of 80 × 20 mm was cut out from the molded sheet with the resin flow direction as the longitudinal direction, and the bending fatigue resistance was measured. The measurement was performed in accordance with JIS K6260 (Demach flex crack test method for vulcanized rubber and thermoplastic rubber), changing the maximum grip distance to 50 mm and the grip movement distance to 40 mm for the test piece. did. The evaluation of the bending fatigue resistance was measured as the number of bendings until the occurrence of a crack. As a boot material, bending fatigue resistance of 2 million times or more is required.

The results obtained are shown in the following table. In addition, the addition amount of carbon black (CB) has shown the weight% in the total amount with a thermoplastic elastomer.
table
Example CB type CB addition amount (%) Number of flexing times until cracking (× 10 ⁴ times)
Example 1 N330 1.0> 200
〃 2 N330 2.0> 200
３ 3 N550 1.0> 200
４ 4 N550 2.0> 200
Comparative Example 1 N110 1.0 150
〃 2 N550 0.1 140
３ 3 N550 5.0 90
４ 4 N990 1.0 130

  From the above results, bending fatigue resistance suitable for boot materials could be obtained by defining the type (average primary particle size) and amount of carbon black added to acrylic rubber / polyamide thermoplastic elastomer. .

Claims (9)

  A carbon black-containing acrylic rubber / polyamide-based thermoplastic elastomer consisting of polyamide resin and cross-linked acrylic rubber, containing 0.2 to 3% by weight of carbon black with an average basic particle size (average primary particle size) of 50 nm or less. Joint boots molded by   The joint boot according to claim 1, wherein the polyamide resin is an acrylic rubber / polyamide thermoplastic elastomer that occupies 20 to 60% by weight of the total amount of the polyamide resin and the crosslinked acrylic rubber.   The joint boot according to claim 1, wherein the acrylic rubber / polyamide thermoplastic elastomer is obtained by dispersing rubber in a polyamide resin by dynamically crosslinking the acrylic rubber.   The joint boot according to claim 3, wherein the acrylic rubber is an α-olefin-alkyl (meth) acrylate-crosslinkable group-containing (meth) acrylate copolymer.   2. The joint boot according to claim 1, wherein the acrylic rubber / polyamide thermoplastic elastomer is obtained by covalently crosslinking polyamide resin and acrylic rubber.   The joint boot according to claim 5, wherein the acrylic rubber is an α-olefin-alkyl (meth) acrylate-crosslinkable group-containing (meth) acrylate copolymer.   The joint boot of claim 6, wherein the covalent crosslinking is performed by dynamic crosslinking at about 100-350 ° C.   The joint boot according to claim 1, wherein the carbon black having an average basic particle diameter (average primary particle diameter) of 50 nm or less is carbon black having ASTM code (D-1765-91) of N220 to N660.   The joint boot according to claim 1, which is used on an inboard side (engine side).