Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-15
2003-07-08
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S231000, C524S232000, C525S332400, C525S332700, C525S343000, C525S374000
Reexamination Certificate
active
06590017
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the use of processing aids to improve the dispersion of silica reinforcing filler in rubber compounds. More particularly, the invention provides a vulcanizable elastomeric composition containing a filler-dispersing aid, and a pneumatic tire having improved snow and ice traction, wet traction, rolling resistance and hysteresis.
BACKGROUND OF THE INVENTION
When producing elastomeric compositions for use in rubber articles, such as tires, power belts, and the like, it is desirable that these elastomeric compositions are easily processable during compounding and have a high molecular weight with a controlled molecular weight distribution, glass transition temperature (T
g
) and vinyl content. It is also desirable that reinforcing fillers, such as silica and/or carbon black, be well dispersed throughout the rubber in order to improve various physical properties, such as the compound Mooney viscosity, elastic modulus, tan delta (&dgr;), and the like. Rubber articles, especially tires, produced from vulcanized elastomers exhibiting these improved properties will have reduced hysteresis, better rolling resistance, snow and ice traction, and wet traction, and improved fuel economy for vehicles equipped with such tires. Traditionally, improved dispersion of reinforcing fillers has been accomplished by lengthened mixing times. However, in commercial applications, prolonged mixing times result in decreased production and increased expense.
With the increasing use of silica as a reinforcing filler for rubber, filler dispersion in rubber stocks has become a major concern. Because polar silanol groups on the surface of silica particles tend to self-associate, reagglomeration of silica particles occurs after compounding, leading to poor silica dispersion, a high compound viscosity and a shorter scorch time. Therefore, it is desirable to improve the dispersion of silica in rubber compounds, especially when used for tire treads, to improve performance characteristics.
Previous attempts at preparing readily processable, vulcanizable silica-filled rubber stocks containing natural rubber or diene polymer and copolymer elastomers have focused on the use, during compounding, of bifunctional silica coupling agents having a moiety (e.g., a silyl group) reactive with the silica surface, and a moiety (e.g., a mercapto, amino, vinyl, epoxy or sulfur group) that binds to the elastomer. Well known examples of such silica coupling agents are mercaptosilanes and bis-(3-trialkoxysilylorgano) polysulfides, such as bis-(3-triethyoxysilylpropyl) tetrasulfide which is known commercially as Si69. With the coupling agent acting as an intermediary, the compound viscosity is reduced and the silica particles are more easily dispersed into the elastomeric matrix. However, such silica coupling agents are expensive. In addition, the reaction of the alkoxy portion of the coupling agent with the rubber can result in the release of a substantial amount of alcohol, resulting in a rubber compound containing undesirable bubbles that may form blisters or surface defects in the resulting formed rubber articles.
To address the expense and other problems related to bifunctional silica coupling agents, recent approaches to providing improved dispersion of silica in rubber compounds have been directed to reducing or replacing the use of such silica coupling agents by employing dispersing agents, such as monofunctional silica shielding agents (e.g., silica hydrophobating agents that chemically react with the surface silanol groups on the silica particles but are not reactive with the elastomer) and agents which physically shield the silanol groups, to prevent reagglomeration of the silica particles after compounding. For example, dispersing agents, such as alkyl alkoxysilanes, glycols (e.g., diethylene glycol or polyethylene glycol), fatty acid esters of hydrogenated and non-hydrogenated C
5
and C
6
sugars (e.g., sorbitan oleates, and the like), polyoxyethylene derivatives of the fatty acid esters, and fillers such as mica, talc, urea, clay, sodium sulfate, and the like, are the subjects of our, co-owned U.S. patent applications Ser. Nos. 08/893,864; 08/893,875; 08/985,859; and 09/203,438. Such silica dispersing agents can be used to replace all or part of expensive bifunctional silica coupling agents, while improving the processability of silica-filled rubber compounds by reducing the compound viscosity, increasing the scorch time, and reducing silica reagglomeration. The use of such dispersing aids includes employing an increased amount of sulfur, to replace sulfur that otherwise would have been supplied by a sulfur-containing silica coupling agent, in order to achieve a satisfactory cure of the rubber compound.
Although the above-described silica dispersing agents provide good silica dispersion in vulcanizable elastomeric compounds, there is still a need for other silica dispersing agents that can be similarly used.
SUMMARY OF THE INVENTION
The present invention provides a processing aid for improving the dispersion of silica in a sulfur-vulcanizable elastomeric composition while eliminating or reducing the use of a bifunctional silica coupling agent. In particular, the processing aid of the invention comprises one or more amide compounds, selected from the group of amide compounds having the formula
wherein R is selected from the group consisting of primary, secondary and tertiary alkyl groups having 1 to about 30 carbon atoms, alkaryl groups having about 5 to about 30 carbon atoms, and cycloaliphatic groups having about 5 to about 30 carbon atoms; R′ and R″ are the same or different from each other and are selected from the group consisting of hydrogen, C
1
to about C
30
aliphatic, and about C
5
to about C
30
cycloaliphatic; R and R′ may be linked together to form a ring structure; and R′ and R″ may be linked together to form a ring structure.
As defined herein, the amide compound suitable for use as a processing aid in the vulcanizable elastomeric compositions of the invention has a polar end that is weakly chemically reactive with the polar groups on silica particles, such as by hydrogen bonding and the like, and a non-polar end that is weakly chemically reactive with the elastomer, such as by hydrogen bonding, van der Waals forces, and the like. The terms “processing aid” and “dispersing aid” are used interchangeably herein to refer to the dispersion of reinforcing filler, especially silica, in the compositions.
Exemplary amide compounds for use as processing aids in the invention compositions include, but are not limited to, erucamide, octadecanamide, &egr;-caprolactam, N,N-diethyldodecanamide, and N,N-diethyl-m-toluamide. Mixtures of amide compounds may also be employed.
The present invention provides a vulcanizable elastomeric composition comprising an elastomer, a reinforcing filler comprising silica or a mixture thereof with carbon black, a processing aid comprising an amide compound as described above, at least one cure agent, and a sufficient amount of sulfur to achieve a satisfactory cure of the composition. The amide compound is present in an amount of about 0.1% to about 150% by weight based on the weight of the silica. Preferably, the amide compound is present in an amount of about 0.5% to about 50% by weight and, more preferably, in the amount of about 1% to about 30% by weight based on the weight of the silica.
In another embodiment, the invention provides a process for the preparation of a vulcanized elastomeric composition comprising the steps of a) mixing an elastomer with a reinforcing filler comprising silica or a mixture thereof with carbon black, a processing aid comprising an amide compound as described above, at least one cure agent, and a sufficient amount of sulfur to achieve a satisfactory cure of the composition; and b) effecting vulcanization.
The use of an amide compound as a processing aid results in a reduction of the compound Mooney viscosity to a level that is comparable to a composition employing a
Arndt Barbara
Harlan R.
Palmer Meredith
Wu David W.
LandOfFree
Processability of silica-reinforced rubber containing an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Processability of silica-reinforced rubber containing an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Processability of silica-reinforced rubber containing an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3008767