Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2003-09-22
2004-06-08
Wilson, D. R. (Department: 1713)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
Reexamination Certificate
active
06746562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermo-reversible, crosslinkable elastomer capable of reversibly causing dissociation and formation of a crosslinked structure by temperature change and a composition thereof.
2. Description of the Related Art
Various investigations have previously been made on improvement of recycling property, energy saving property, processability, various properties and the like of elastomers.
In thermoplastic elastomers, physical crosslinking is utilized as compared with conventional vulcanized rubbers having a stable three-dimensional network structure in which polymeric substance and vulcanizing agent are covalent-bonded. The thermoplastic elastomers do not require complicated vulcanization/molding steps including pre-molding, and can easily be molded and processed by heat melting as thermoplastic resins. The thermoplastic elastomer is an improved product in terms of recycling property, energy saving property and processability as compared with conventional elastomers.
Typical example of such a thermoplastic elastomer conventionally known is an elastomer containing a resin component and a rubber component, in which a fine crystal resin component converts to a constraint phase (hard segment) which plays a role of crosslinking site of a three-dimensional network structure, thereby preventing plastic deformation of a rubber component (soft segment), and plastic deformation causes by softening or fusion of the resin component due to temperature elevation. Examples of such a thermoplastic elastomer containing a resin component and a rubber component include block copolymers such as styrene-butadiene block copolymer or isoprene multiblock copolymer, and resin/rubber blends of polypropylene and ethylene-propylene-diene copolymer (EPDM). Further, elastomers in which a rubber component (EPDM) in the resin/rubber blend is crosslinked with a peroxide or the like are also known.
The above-described conventional thermoplastic elastomer contains a resin component to form a constraint phase, and it is unavoidable that rubber elasticity decreases as compared with conventional vulcanized rubber. For this reason, if an elastomer that reversibly secures flowability by temperature change, i.e., an elastomer that crosslinks at room temperature, but has flowability by decrosslinking upon heating, and can reversibly conduct this conversion many times, is developed even if a resin component for forming a constraint phase is not contained, a rubber elastic body can be obtained by simple heat molding and processing without conducting complicated steps of kneading, pre-molding, vulcanization and the like that have conventionally be required, and its industrial utilization value is very high. Further, such an elastomer is very preferable in the point of recycling property.
It is known to utilize various bonding reactions as a modification method of thermoplastic resins.
For example, Japanese Patent Laid-open Application No. Hei 6-57062 proposes a composition comprising a polyolefin graft-modified with unsaturated carboxylic anhydride, and a polyhydric alcohol. It is described therein that the composition can be used by recycling. Japanese Patent Laid-open Application No. Hei 11-106578 also discloses the similar composition.
Further, Japanese Patent Laid-open Application No. Sho 60-179479 proposes an adhesive composition obtained by reacting divinyl ether with a copolymer produced by copolymerization of olefin and ethylenically unsaturated monocarboxylic acid. It is disclosed therein that adhesiveness of the adhesive composition is further improved by thermo-reversibility of crosslinking.
Japanese Patent Laid-open Application No. Hei 11-35675 proposes a resin obtained by addition reaction of a compound having alkenyl ether group and a compound having carboxyl group in the presence of a specific catalyst. It is disclosed therein that the resin has high physical properties and is excellent in recycling property.
Further, a resin utilizing reaction between isocyanate and phenol is disclosed in Angrew. Chem., 59A, 257(1947), a resin utilizing reaction between azlactone and phenol is disclosed in Macromolecules, 24, 6809(1991), and a resin utilizing reaction for forming nitroso dimer is disclosed in U.S. Pat. No. 4,168,882.
Crosslinking formation by reversible reaction in a resin polymer is known as a conventional technique, but it is in general very difficult to introduce such a crosslinked site to an elastomer. It has been also considered that poor reinforcing effect due to the low crystallinity makes it difficult to ensure sufficient strength to resist practical use, even if such a crosslinked site can be introduced. Therefore, an elastomer utilizing each reaction as mentioned above and that can practically be used is not yet known.
Further, Japanese Patent Laid-open Application No. Sho 63-69864 proposes a shape memory resin such that even if an amount of hydrogen bond (crosslinking) is decreased at a temperature higher than a glass transition temperature to deform a shape, the original shape is restored by again cooling to a temperature lower than the glass transition temperature. A resin formed by containing a large amount of hydrogen bond during curing reaction between an epoxy resin and an amine hardener is disclosed as the preferred example.
A method of utilizing hydrogen bond to prevent heat resistance or rigidity from being decreased when a compound having small molecular weight or a thermoplastic resin having large flowability is added as a flowability improver of a resin is proposed as another method. For example, Japanese Patent Laid-open Application No. Hei 5-339420 discloses a method of improving flowability and heat resistance of a thermoplastic resin by adding a compound having hydroxyl group and a compound having a group capable of hydrogen bonding with the hydroxyl group to the thermoplastic resin, and Japanese Patent Laid-open Application No. Hei 7-331002 discloses a method of improving rigidity and flowability of styrenic resin by adding a thermoplastic resin and a compound having a functional group capable of hydrogen bonding with carboxyl group to a styrenic resin having carboxyl group.
It is theoretically known that a thermoplastic elastomer is obtained by utilizing the above-mentioned hydrogen bond for the formation of crosslinking, but practically usable method is not yet known. Hydrogen bond has small bonding energy as compared with covalent bond, and hence decrosslinking tends to occurs by receiving influence of heat or the like. Elastomeric polymer forms a solid state by crosslinking, thereby developing rubber elasticity. Therefore, it is difficult to utilize hydrogen bond for crosslinking mechanism unless crosslinking state is maintained in a stable manner in use.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermo-reversible, crosslinkable elastomer capable of reversibly causing crosslinking formation and crosslinking dissociation by temperature change. More particularly, the object of the present invention is to provide a thermo-reversible, crosslinking elastomer which forms a stable crosslinked structure at room temperature, has a rubber elasticity, can sufficiently show a melt flowability at a molding temperature of general thermoplastic resins and can repeatedly reproduce crosslinking formation and crosslinking dissociation.
As a result of intensive studies on thermo-reversible, crosslinkable elastomers, it has been found that a thermo-reversible, crosslinkable elastomer having excellent recycling property and moldability is obtained by utilizing a specific reversible reaction. In other words, it has been found that, by introducing a specific reaction site in an elastomer main-chain, a thermoplastic elastomer forms a thermotropical crosslinked structure, so that crosslinking at room temperature (temperature in use) and decrosslinking-flowability at heating can repeatedly be reproduced, and that the elastomer having the reaction site extremely readily forms a crosslin
Chino Keisuke
Ikawa Masahiro
Natori Junichiro
Rader Fishman & Grauer
The Yokohama Rubber Co., LTD
Wilson D. R.
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