Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-02-14
2002-06-11
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S134000, C525S138000, C525S141000, C525S331700, C525S332500, C524S106000
Reexamination Certificate
active
06403713
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a method for crosslinking an isoprene-isobutylene rubber (hereinafter referred to as butyl rubber), a particular ethylene-propylene-diene rubber (ethylene-propylene-diene rubber is hereinafter referred to as EPDM), i.e. an ethylene-propylene-diene rubber containing ethylidenenorbornene as an unsaturated component (this rubber is hereinafter referred to as ENB type EPDM), or a mixture of a butyl rubber and an ENB type EPDM, using an alkylphenol-formaldehyde resin and a particular triazole compound; as well as to a crosslinked rubber product obtained by the above crosslinking method.
The present invention relates further to a method for crosslinking a butyl rubber, an ENB type EPDM or a mixture of a butyl rubber and an ENB type EPDM, using an alkylphenol-formaldehyde resin, a particular triazole compound and a hydrazide compound; as well as to a crosslinked rubber product obtained by the above crosslinking method.
(2) Description of the Prior Art
Butyl rubber is a known synthetic rubber produced by copolymerization of isoprene and isobutylene, having an unsaturation degree of 0.5 to 3.0 mole %. Crosslinked butyl rubber has low gas permeability, weather resistance, electrical insulation, heat resistance, damping property, resistance to acids and alkalis, low water absorption, etc. and is in use in rubber stopper, o-ring, packing, curing bag, tank lining, coating of electric wire, hose, automobile tube, rubber vibration insulator, etc.
For crosslinking of butyl rubber, there have been known three methods, i.e. sulfur crosslinking, quinoid crosslinking and resin crosslinking.
Sulfur crosslinking is conducted using sulfur together with a crosslinking accelerator such as thiuram, thiazole or the like, and is in wide use when a butyl rubber is produced into a rubber hose, a rubber vibration insulator, a tube for bicycle or automobile, etc.
Quinoid crosslinking is conducted using quinone dioxime or benzoylquinone dioxime together with red lead or lead dioxide, and is suited for continuous crosslinking of coated electric wire in which a high crosslinking rate is required.
Resin crosslinking is conducted using an alkylphenol-formaldehyde resin together with an inorganic halogen compound (e.g. tin chloride or ferrous chloride) or a halogen-containing elastomer (e.g. chloroprene rubber or chlorosulfonated polyethylene), or using a halogenated alkylphenol-formaldehyde resin, and is suited when a butyl rubber is produced into, for example, a curing bag used in tire production. This resin crosslinking can produce a crosslinked butyl rubber of low compression set, but corrodes the mold used because a halogen compound is used in the resin crosslinking.
EPDM is a terpolymer of ethylene, propylene and a diene and, as the third component diene, there is used 1,4-hexadiene, ethylidenenorbornene or the like. In the present invention, there is used an EPDM containing ethylidenenorbornene as an unsaturated component, i.e. an ENB type EPDM.
ENB type EPDM is a known synthetic rubber superior in heat resistance, electrical insulation and weather resistance. For crosslinking of ENB type EPDM, there are known four methods, i.e. organic peroxide crosslinking, sulfur crosslinking, quinoid crosslinking and resin crosslinking.
Sulfur crosslinking, similarly to the sulfur crosslinking for butyl rubber, is conducted using sulfur together with a crosslinking accelerator such as thiuram, thiazole or the like and gives a cured product having superior weather resistance. Therefore, this sulfur crosslinking is in wide use when gaskets for automobile or construction, roofing sheets, etc. are produced.
Organic peroxide crosslinking can give a cured product of low compression set and therefore is in wide use when industrial rubber products such as packing and the like are produced.
Quinoid crosslinking is conducted using quinone dioxime or benzoylquinone dioxime together with red lead or lead dioxide. This crosslinking is introduced in books regarding rubber technology, but is in substantially no use in industrial production of an ENB type EPDM into a rubber product.
Resin crosslinking is conducted using an alkylphenol-formaldehyde resin together with an inorganic halogen compound (e.g. tin chloride or ferrous chloride) or a halogen-containing elastomer (e.g. chloroprene rubber or chlorosulfonated polyethylene), or using a halogenated alkylphenol-formaldehyde resin. However, rubber products obtained by subjecting an ENB type EPDM to this resin crosslinking using a halogen compound together, find substantially no application.
In resin crosslinking of a butyl rubber or an ENB type EPDM is conducted using an alkylphenol-formaldehyde resin, an organic or inorganic halogen compound is used together. This resin crosslinking using a halogen compound, however, corrodes the mold used and finds substantially no practical application. When a butyl rubber or an ENB type EPDM is crosslinked using an alkylphenol-formaldehyde resin alone and no halogen compound, the crosslinking rate is low.
Crosslinking of, in particular, ENB type EPDM using an alkylphenol-formaldehyde resin alone is unstable. When such crosslinking is tried for a compound containing a large amount of clay as a filler, the crosslinking proceeds very slowly or no crosslinking takes place, making it impossible to produce a crosslinked rubber product.
Butyl rubber and ENB type EPDM are compatible with each other and can be mixed at any proportions. Therefore, they can be crosslinked (co-crosslinked) using a common crosslinking agent and a cured product retaining the properties of the individual rubbers can be obtained. However, a mixture of a butyl rubber and an ENB type EPDM is crosslinked using an alkylphenol-formaldehyde resin alone and no halogen compound, the ENB type EPDM is not sufficiently crosslinked; therefore, it is impossible to obtain a rubber product having good crosslinked rubber properties.
Mixing of two different rubbers is generally conducted by those skilled in the art, in order to impart the properties of one rubber into other rubber. In this case, use of a common crosslinking agent is a common knowledge.
In crosslinking a mixture of two different rubbers using a crosslinking agent which is effective only to either one rubber, the effect of the crosslinking agent to the other rubber need be considered and the properties of the crosslinked rubber obtained are difficult to predict in many cases. Therefore, such crosslinking is hard to employ on an industrial scale.
When a mixture of a butyl rubber and an ENB type EPDM is co-crosslinked by those skilled in the art, it is generally conducted by sulfur crosslinking. This sulfur crosslinking is effective, for example, when an ENB type EPDM is mixed into a butyl rubber hose or when a butyl rubber is mixed into an ENB type EPDM-made roofing sheet to improve the adhesivity of the ENB type EPDM, and can prevent heat-softening of butyl rubber during sulfur crosslinking; however, the sulfur crosslinking is unsuitable when the crosslinked rubber is used for applications such as packing (which requires a low compression set) and the like.
Co-crosslinking of a mixture of a butyl rubber and an ENB type EPDM using a phenolic resin alone and no halogen compound has little practical applicability, because the ENB type EPDM is not crosslinked often and the cured product obtained has no intended properties.
By mixing a butyl rubber into an ENB type EPDM at an ENB type EPFM proportion of at least 50%, the properties of the butyl rubber can be imparted to the ENB type EPDM. That is, improvements are obtained in the adhesion between crosslinked and uncrosslinked rubbers, reduction in gas permeability, flow of compound during rubber molding, and tear strength at high temperatures, correspondingly to the mixing ratio of the two rubbers. This is a specific case in which the adhesivity, low gas permeability and excellent tear strength at high temperatures, possessed by the butyl rubber are imparted to the ENB type EPDM.
By mixing an ENB typ
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