Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2003-05-23
2004-12-21
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S541000, C156S096000
Reexamination Certificate
active
06832637
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to preparation of an article of manufacture, such as a tire via application of at least one partially pre-cured component. Tires are often prepared with pre-cured, pre-shaped components such as for example, application of pre-cured tread strips to a cured carcass as in the case of re-treaded tires. Thus precured tread and cured carcass are joined together using a cushion gum followed by heating the resulting assembly at an elevated temperature to cure the cushion gum. Such pre-cured component may also be, for example, a sidewall apex. In such cases, the pre-cured component is subjected to more heat than is necessary which may be detrimental for the component. This invention is directed to the use of a partially pre-cured component to prepare a tire assembly prior to the curing of the entire components of the tire assembly.
BACKGROUND OF THE INVENTION
For preparation of a retreaded tire, a pre-cured, shaped, tread rubber strip is conventionally applied to a cured tire carcass with a thin uncured rubber layer, often referred to as a cushion gum layer, positioned between said pre-cured rubber tread strip and said cured tire carcass to form an assembly thereof. The tire assembly is then cured by heating at an elevated temperature in an enclosed autoclave. Such method of retreading tires is well known to those having skill in such art.
Similarly, pre-cured, shaped, rubber tire sidewall apexes are built into a tire assembly and the assembly cured at an elevated temperature in a suitable mold. The building of pre-cured rubber apexes into a tire assembly is also well known to those having skill in such art.
Partially pre-cured rubber components for such tread strips and tire (sidewall) apexes are not used for commercial preparation of tires because of blows, or voids, typically occurring in such tread strips, and they remain when they are subsequently subjected to the additional heating cycle to fully cure the shaped and pre-cured rubber compositions.
Such blows, or voids, are usually in a form of a multiplicity of small and large voids, usually small voids somewhat similar to a region of a closed cellular configuration, within the pre-cured rubber tread strip or apex, as the case may be, which may not be visible on the surface thereof. Apparently, cured tread strips or tread apexes, as the case may be, for use in building, and subsequently curing, a tire assembly do not normally contain such blows.
While the causes of the formation of such blows, or voids, in a partially pre-cured tread strip is not fully understood, it is important to appreciate that blows, or voids, may form, for example, due to one or more of the following three causes:
(A) Volatile ingredients may form by a degradation of one or more materials in the rubber composition which try to escape upon removal of the partially pre-cured rubber composition from the high pressure and high temperature environment of the mold in which it has been partially pre-cured.
(B) Partially pre-cured rubber compositions have a lower modulus as compared to a comparable fully cured rubber composition and therefore have less resistance to blow, or void, formation.
(C) Presence of moisture or other volatile ingredients within the rubber composition try to expand upon its removal from the high pressure and high temperature environment of the mold in which the rubber composition has been partially pre-cured.
This invention is directed to the preparation of a tire via use of partially pre-cured rubber compositions, for example tread strips and/or sidewall apexes, in the manufacture of tires, including retreaded tires in the case of partially pre-cured tread strips, in which such blows are at least minimized, and preferably essentially eliminated, and therefore intended to be at least equivalent to the use of pre-cured rubber components.
During the subsequent curing of the partially cured rubber composition, the modulus of rubber composition gradually increases with time during the curing step from the lower modulus condition of the partially cured rubber composition.
In the description of this invention, the terms “rubber” and “elastomer” if used herein, may be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term “phr” refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” may be used interchangeably unless otherwise indicated.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, an article of manufacture is prepared by:
(A) partially sulfur curing a sulfur curable rubber composition in a partially curing step to from about 10 to about 80, alternately about 50 to about 70 percent of its cured condition, particularly where said partially cured rubber composition is in a form of a rubber tread strip for retreading a cured rubber carcass or sidewall rubber insert such as an apex, within in a rigid mold at a temperature in a range of about 120° C. to about 200° C.;
(B) removing said partially cured rubber composition from said mold and allowing said partially cured rubber composition to cool to a temperature of less than 50° C.;
(C) applying said partially pre-cured rubber composition to an uncured, sulfur curable, rubber composition to form an assembly thereof;
(D) sulfur curing said assembly in a suitable container, for example an autoclave or mold, in a curing step at a temperature in a range of about 120° C. to about 200° C., and
(E) removing said sulfur cured assembly from said mold in a subsequent cooling step to allowing said cured assembly to cool to a temperature of less than 40° C.;
wherein for said partially cured rubber composition:
(1) said partially curing and cooling steps for said partially cured rubber composition are conducted in a nitrogen atmosphere to the exclusion of oxygen,
(2) said partially cured rubber composition contains from about 0.1 to about 3 phr of bis-imide selected from at least one of N,N′-m-xylylene-bis-citraconimide and N,N′-m-phenylene bismaleimide, and/or
(3) said partially cured rubber composition is immediately, preferably within about 0.5 to about 10, and more preferably within 0.5 to 5, seconds following removal from said mold, immersed in water, said water having a temperature within about 0° C. to about 20° C. to rapidly cool the partially cured rubber composition to a temperature of less than 100° C.
In one aspect of the invention, said partially cured rubber composition may be a sidewall insert and particularly a tire sidewall insert in a form of an apex.
In one aspect of the invention, said partially cured rubber composition can contain said bis-amide and said partially curing and cooling steps are conducted in a nitrogen atmosphere to the exclusion of oxygen.
In one aspect of the invention, said partially cured rubber composition can contain said bis-amide and said partially cured rubber composition is immediately, preferably within about 0.5 to about 10, and more preferably within 0.5 to 5, seconds following removal of said assembly from its mold, immersed in water, said water having a temperature within about 0° C. to about 20° C. to rapidly cool the assembly to a temperature of less than 100° C.
In one aspect of the invention, said partially cured rubber composition may be simply immediately, preferably within about 0.5 to about 10, and more preferably within 0.5 to 5, seconds following removal from said mold, immersed in water, said water having a temperature within about 0° C. to about 20° C. to rapidly cool the partially cured rubber composition to a temperature of less than 100° C.
In further practice of
Dotts Douglas Blair
Majumdar Ramendra Nath
Padovan Joseph
Tipton Marvin Wayne
Maki Steven D.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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