Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-07-20
2003-10-21
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S339000, C526S341000, C526S346000, C526S335000, C525S240000, C521S140000, C521S150000
Reexamination Certificate
active
06635727
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel and useful ethylenic copolymer rubber having cross-linkable (vulcanizable) unsaturation bonds and to a production process and use thereof.
BACKGROUND OF THE INVENTION
In general, hydrocarbon compounds having two carbon-to-carbon double bonds in the molecule are called dienes, among which a variety of compounds have been known, for example, linear dienes, such as 1,3-butadiene, 1,3-pentadiene and 1,4-hexadiene; cyclic dienes such as ethylidene-2-norbornene (ENB) and dicyclopentadiene. By co-polymerizing such a diene with an &agr;-olefin, such as ethylene or propylene, an unsaturated ethylenic copolymer rubber having vulcanizable unsaturation bond(s) can be obtained.
Such an unsaturated ethylenic copolymer rubber is a polymer product susceptible of being vulcanized which is superior in the weatherability, resistance to ozone, resistance to thermal aging and so on and can be used for rubber products, such as automobile parts, electric insulating materials, architectural and constructional materials, industrial rubber materials and so on, and used widely for materials (modofiers) for blending with plastic resins, such as polypropylene, polystyrene and the like, as well.
For the unsaturated ethylenic copolymer rubber, there have hitherto been known, for example, an ethylene/propylene/5-ethylidene-2-norbornene copolymer rubber, ethylene/propylene/dicyclopentadiene copolymer rubber and ethylene/propylene/1,4-hexadiene copolymer rubber. Among them, the ethylene/propylene/5-ethylidene-2-norbornene copolymer rubber has found its wider applications due to its higher vulcanization velocity as compared with other unsaturated ethylenic copolymer rubbers.
However, a demand has been put on the conventional unsaturated ethylenic copolymer rubbers for a further improvement of the vulcanization velocity. Thus, the vulcanization velocity of an unsaturated ethylenic copolymer rubber, namely, even that of, for example, ethylene/propylene/5-ethylidene-2-norbornene copolymer rubber, is lower as compared with that of a diene rubber, such as natural rubber, styrene/butadiene rubber, isoprene rubber, butadiene rubber or nitrile rubber. Moreover, there is a problem that free and wide control of the vulcanization velocity is limited, as compared with these diene rubbers. Furthermore, there is a problem that the ability of co-vulcanization with diene rubbers is low.
While the vulcanization velocity on vulcanizing the unsaturated ethylenic copolymer rubber may be increased by increasing the vulcanization temperature or by using a large amount of vulcanizing agent, this may accompany an increase in the process cost for the vulcanization. Vulcanization at higher temperature will cause reduction of the quality of the vulcanized rubber. Use of larger amount of the vulcanizing agent will result in an increase in the possibility of occurence of blooming on the rubber surface by the vulcanizing agent, which is undesirable both in the hygienic point of view and in the appearance. It is difficult, on the contrtary, to attempt to reduce the vulcanization duration by lowering the temperature of vulcanization of the unsaturated ethylenic copolymer rubber to economize energy consumption on the vulcanization.
On the other hand, a vulcanizable copolymer rubber exhibiting higher vulcanization velocity tends, as a general nature, to reveal a poor scorch stability. This may be attributed to the fact that a copolymer rubber exhibiting higher vulcanization velocity may suffer from a premature vulcanization, since it tends to cause the vulcanization to proceed more easily during the process steps other than the vulcanization step, such as the step of storage of the rubber blend and steps before the vulcanization step, as compared with copolymer rubbers exhibiting lower vulcanization velocities. Thus, an ability of prompter vulcanization contradicts the scorch stability, so that a copolymer rubber having both these properties may difficultly be obtained. For example, when the content of 5-ethylidene-2-norbornene is increased in the ethylene/propylene/5-ethylidene-2-norbornene copolymer rubber, a higher vulcanization velocity of the resulting copolymer rubber may be attained, nevertheless, the scorch stability thereof is decreased and the easiness in handling on the working process etc. are reduced. Explaining concretely, troubles due to the increase in the rate of increase of the viscosity may tend to occur, such as a reduction of the delivery rate, an increase of the motor load and clogging of the cylinder die. When, on the contrary, the content of 5-ethylidene-2-norbornene is reduced, the resulting copolymer rubber may reveal a higher scorch stability and improved easiness in the handling, nevertheless, the through-put of the vulcanized rubber may be decreased due to the reduction of the vulcanization velocity.
In these circumstances, it has been desired to realize an ethylenic copolymer rubber which exhibits a higher vulcanization velocity and, nevertheless, is superior in the scorch stability, workability and moldability with simultaneous attainment of superior mechanical characteristics of the vulcanized product, such as the strength of the vulcanized rubber.
In the practice, demands for the properties of sealing materials for, for example, door seal, trunk seal and window seal for automobile, which constitute representative applications of EPR and EPDM, become, with the recent general trend to high performance cars with longer life, more sophisticated, whereby it has become difficult to satisfy sufficiently all the requested high grade characteristics by the conventional unsaturated ethylenic copolymer rubbers.
Sealing performances are influenced by various parameters, including cross sectional form, resistance to compressive permanent strain and flexibility of a rubber sealant. As for the cross sectional form, recent rubber sealants have complicate configurations, as having a thinner and longer lip portion, as compared with conventional ones. For a sealant to be assembled on a part element of hard top type, a structure with greater sectional area and thinner wall thickness than the prior art is requested, whereby a problem has come up to the front, in which so-called molding deformation may occur wherein an accurate cross sectional form is not attained in the vulcanization foaming process step.
As the parameter for representing the phenomenon of molding deformation, so-called “form preservability” has been used in general and, thus, a sponge rubber having a superior form preservability is requested. While attempts were proposed from of relatively old, to use two or more polyene components for improving the form preservability of EPT and EPDM {See, for example, Japanese Patent Publications Sho 44-7713 B and Sho 47-23914 B, Japanese Patent Kokais Sho 49-62582 A (corresponding to British Patent Application No. 1412519 A), Sho 49-62583 A (corresponding to U.S. Pat. No. 3,903,061), Sho 56-22338 A, Sho 58-191705 A (corresponding to U.S. Pat. No. 4,510,303) and so on}, none has reached the goal of satifying all the requested demands.
For example, in the proposed technique of using 5-ethylidene-2-norbornene (ENB) and dicyclopentadiene (DCPD) together as the polyenes for EPDM, some of the extrusion processibility, the vulcanization velocity and the mechanical strength of the resulting vulcanized rubber may not reach a sufficient value, in accordance with the selection of the balance between the contents of ENB and DCPD. In the proposed technique of using ENB and vinylnorbornene (VNB) together as the polyenes for EPDM, the balance among the extrusion processibility, the vulcanization velocity and the mechanical strength of the resulting vulcanized rubber may be improved somewhat as compared with the concurrent use of ENB and DCPD, nevertheless, no satisfactory EPDM was obtained, since the improvement is still insufficient and a shortcoming of debased aspect of production costs accompanies.
In these circumstances, it has been desired to realize an ethylenic c
Ichino Kotaro
Kawasaki Masaaki
Koda Taku
Okada Keiji
Burns Doane , Swecker, Mathis LLP
Mitsui Chemicals Inc.
Rabago R.
Wu David W.
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