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
2000-07-27
2003-07-15
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S347000, C525S349000, C525S352000
Reexamination Certificate
active
06593432
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a rubber composition and a hose. More particularly, it relates to a sulfur vulcanizing system rubber composition whose base material is EPDM, and a hose formed therefrom and used, for example, in a cooling system for an automobile engine.
2. Description of the Related Art
A hose having an inner layer formed from a vulcanized rubber composition containing EPDM as a base material has often been used in a cooling system for an automobile engine, for example, with a radiator, or heater. A sulfur vulcanizing system is often used for vulcanizing such rubber composition because of its low cost and its ease of use, though a peroxide cure system can also be used for that purpose.
A combination of a vulcanization accelerator and zinc oxide as its accelerator activator is usually employed for the sulfur vulcanizing system. A thiuram or dithiocarbamate type vulcanization accelerator having a very high vulcanizing rate (ultra-accelerator) is mainly used as the vulcanization accelerator for the sulfur vulcanization of a rubber composition containing EPDM, since EPDM has a chemical structure having few unsaturated bonds.
After the vulcanization of this rubber composition, zinc oxide remains in rubber as a free zinc salt not incorporated in crosslinks. The zinc salt migrates to the surface of the vulcanized material with the blooming of the residues of the vulcanization reaction (i.e. sulfur, vulcanization accelerator, etc.). It is known that the salt dissolves even in a cold coolant.
The dissolved zinc salt reacts with phosphoric acid in the coolant to form an insoluble compound. The insoluble compound causes various problems. The compound deposited on the inner wall surface of a hose is likely to block it, and if it is deposited on the seal of the hose and a pipe connecting the hose, it is likely to cause the leakage of the coolant therethrough.
Therefore, it is necessary to take an effective measure to prevent the dissolution of any zinc salt in a coolant to avoid any such problem, as long as zinc oxide is used for sulfur vulcanization. The inventors of this invention have experimentally found that the reduction in the amount of zinc oxide to be used brings about merely a corresponding reduction in the amount of the zinc salt to be dissolved. That is not an effective measure, since in order to prevent the dissolution of any zinc salt, it is necessary to reduce the amount of zinc oxide to a level insufficient for the purpose of its addition.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to provide a sulfur vulcanizing system rubber composition comprising EPDM as a base material such that the dissolution of zinc salt into a coolant is effectively prevented without reducing the amount of zinc oxide to be used.
It is another object of this invention to provide a hose which can be used in a cooling system for an automobile engine without causing any zinc salt to dissolve in a coolant.
The inventors of this invention have found that the thiuram or dithiocarbamate type vulcanization accelerator which has hitherto been used for the sulfur vulcanization of EPDM does not act against the dissolution of a zinc salt, but even promotes it. The inventors have also found that a thiazole type vulcanization accelerator, which is a rapid-accelerator having a relatively high vulcanizing rate, acts effectively against the dissolution of any zinc salt even if it may be used in a relatively small amount. Thus, the inventors have found that the objects of this invention can be attained by the use of a combination of specific vulcanization accelerators.
According to a first aspect of this invention, therefore, there is provided a sulfur vulcanizing system rubber composition comprising an ethylene-propylene-diene terpolymer (EPDM) as a base material, a vulcanization accelerator and zinc, the composition being such that when a vulcanized sheet thereof is left to stay for 24 hours at a normal ambient temperature in a coolant (i.e. an aqueous solution containing 50% by volume of a long-life coolant) in a volume of 10 times the volume of the vulcanized sheet, the amount of zinc dissolved in the coolant is less than 1 ppm.
Any insoluble compound even if formed due to reaction of dissolved zinc and phosphoric acid in the coolant is substantially harmless if the amount of dissolved zinc is less than 1 ppm. If the vulcanized product of the rubber composition according to this invention forms any part contacting an engine coolant, it is possible to avoid any problem caused by the deposition of such insoluble compound. More specifically, if it forms the inner layer of a hose in an engine cooling system, it is possible to avoid any blocking thereof, or any leakage of the coolant through the seal between the hose and any pipe connected therewith.
A second aspect of this invention is a sulfur vulcanizing system rubber composition comprising EPDM as a base material, a vulcanization accelerator and zinc, the vulcanization accelerator being a combination of (1) at least one vulcanization accelerator A capable of controlling the dissolution of zinc to a level as defined in the first aspect when the accelerator alone is contained in an amount of at least 0.005 mol, and (2) at least one vulcanization accelerator B classified as an ultra-accelerator.
The first accelerator A is effective for controlling the dissolution of zinc. The second accelerator B gives the physical properties required of the vulcanized product of the rubber composition, including its physical property in ordinary state and its compression set. It is generally undesirable for any rubber composition to contain too large an amount of vulcanization accelerators, since the blooming of any excessive accelerators is likely to occur. The composition according to this aspect contains in addition to the first accelerator a sufficiently large amount of second, or ultra-accelerator, since the amount of the first accelerator is relatively small. Thus, the composition gives a vulcanized product having the desired physical properties without allowing any undesirable dissolution of zinc.
A third aspect of this invention is a sulfur vulcanizing system rubber composition comprising EPDM as a base material, a vulcanization accelerator and zinc, the vulcanization accelerator being a combination of at least one thiazole type vulcanization accelerator and at least one thiuram or dithiocarbamate type vulcanization accelerator. In order to control the dissolution of zinc to a level as defined in the first aspect, it is sufficient to add at least 0.005 mol of thiazole type vulcanization accelerator. Thus, the composition does not contain any excess of vulcanization accelerators, but gives a vulcanized product having the desired physical properties, and not allowing any undesirable dissolution of zinc.
A fourth aspect of this invention is a sulfur vulcanizing system rubber composition comprising EPDM, a vulcanization accelerator and zinc, the vulcanization accelerator being a combination of each of the following: a thiazole type vulcanization accelerator, a thiuram type vulcanization accelerator, and a dithiocarbamate type vulcanization accelerator. This is a particularly preferable combination of accelerators for the composition to give a vulcanized product having the desired physical properties, and not allowing any undesirable dissolution of zinc. It appears that the combination gives a greatly accelerated vulcanization reaction and produces only a small amount of reaction residues so that their blooming may not cause any undesirable dissolution of a zinc salt.
According to a fifth aspect of this invention, the rubber composition contains a total of 2.0 to 7.0 parts by weight of vulcanization accelerators per 100 parts by weight of EPDM, including 0.1 to 3.0 parts by weight of the above-mentioned accelerator A or a thiazole type accelerator serving to control the dissolution of zinc as mentioned in the first aspect. These are particularly preferable ranges of the proportions of acc
Daikai Eiichi
Ikemoto Ayumu
Senda Koji
Jacobson & Holman PLLC
Lipman Bernard
Tokai Rubber Industries Ltd.
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