Patent Application
20050145312
The invention relates to a tire component, and tire having such component, of a rubber composition which contains a combination of environmentally renewable, plant-derived, soybean oil and plant-derived starch. The starch is provided as a starch/plasticizer composite. Such tire component may be, for example, a tire tread, a tire sidewall and/or tire innerliner. A tire component such as a tread may be used for retreading tires.
Rubber compositions for tire components are sometimes prepared which contain rubber processing oils which are typically petroleum based oils such as, for example, paraffinic oils, naphthenic oils and aromatic oils which are usually a combination of such oils. The rubber processing oils are usually used to reduce the viscosity of relatively high viscosity unvulcanized rubber compositions so that they are more easily processable in conventional rubber processing equipment such as internal rubber mixers, open roll mixing, extrusion and calendar processing.
It is desired herein to provide such rubber composition for a tire component, particularly a tire component such as, for example, a tire tread, tire sidewall and/or innerliner with a combined replacement of such petroleum based oils with a plant-derived oil and a replacement of at least a portion of its carbon black reinforcement with a plant-derived reinforcement. In one aspect, it is contemplated that such tire component may be a tread which may be used for retreading tires.
Composites of plant-derived starch and suitable plasticizer, such as for example, a poly(ethylenevinyl alcohol) are sometimes used in rubber compositions for tire components, usually in conjunction with a reinforcing filler such as carbon black and/or amorphous silica such as precipitated silica.
Use of soybean oil in rubber compositions for use as tire components are described, for example, in U.S. Pat. No. 6,448,318 in which the soybean oil was reported as being composed of, or containing, about 52 weight percent linoleic acid, about 24 weight percent oleic acid, about 8 weight percent linolenic acid and about 4 weight percent stearic acid.
However, the combination of starch/plasticizer composite and soybean oil in a tire component rubber composition is considered herein to be novel and a departure from past practice.
In the description of this invention, the term “phr” where used refers to parts by weight of a material per 100 parts by weight of elastomer(s) contained in a rubber composition. The terms “elastomer” and “rubber” are used interchangeably, unless otherwise indicated. The terms “cure” and “vulcanize” are used interchangeably, unless otherwise indicated.
In accordance with this invention, a tire component is comprised of a rubber composition comprised of, based upon parts by weight per 100 parts by weight of elastomer (phr):
(A) at least one conjugated diene-based elastomer,
(B) about 3 to about 20 phr of soybean oil,
(C) about 3 to about 20 phr of starch/plasticizer composite having a starch/plasticizer weight ratio in a range of from about 0.5/1 to about 5/1,
(D) about 35 to about 80 phr of carbon black and/or silica reinforcing filler as:
(E) a coupling agent for said starch/plasticizer composite, and silica if silica is used, having a moiety reactive with hydroxyl groups (e.g. silanol groups) contained on said starch/plasticizer composite, and said silica if used, and another moiety interactive with said conjugated diene-based elastomer(s).
In practice, said tire component may be, for example, a tire tread, tire sidewall, tire innerliner, ply coat, wire coat, chafer, apex, sidewall insert and/or toe guard. For example, said tire component may be a tire tread. For example, said tire component may be a tire tread used in the retreading of pneumatic rubber tires.
In further accordance with this invention, a tire is provided having at least one component comprised of said rubber composition. In practice, such tire component may be, for example, a tire tread, tire sidewall, tire innerliner, ply coat, wire coat, chafer, apex, sidewall insert and/or toe guard. For example, said tire may have a tread comprised of said rubber composition.
In additional accordance with this invention, a pneumatic tire is provided with a retreaded carcass retreaded with a tire tread component of this invention.
A significant aspect of this invention is an observed benefit of using a combination of plant derived soybean oil and plant-derived starch in a diene-based rubber composition for a tire component in a sense of using renewable raw materials by replacing all or a significant portion of petroleum based rubber processing oil with soybean oil and by replacing a portion of silica and/or carbon black reinforcement with a starch/plasticizer composite.
Representative of diene-based elastomers are polymers and copolymers of at least one of isoprene and 1,3-butadiene monomers and copolymers of styrene with at least one of isoprene and 1,3-butadiene monomers.
Representative of such diene-based elastomers are, for example, cis 1,4-polyisoprene, cis 1,4-polybutadiene, trans 1,4-polybutadiene, styrene/butadiene polymers (organic solution polymerization derived and/or aqueous emulsion polymerization derived), vinyl polybutadiene having a vinyl content in a range of 30 to 90 percent, isoprene/butadiene polymers, styrene/isoprene polymers, styrene/isoprene/butadiene terpolymers, as well as tin or silicon coupled elastomers and as well as such elastomers modified with one or more of primary amines, secondary amines or heterocyclic amines, and as well as such elastomers modified by containing alkoxysilane groups.
Starch/plasticizer composites have been suggested for use in elastomer compositions for various purposes, including tires. For example, see U.S. Pat. Nos. 5,672,639. Various other U.S. patents, for example, U.S. Pat. Nos. 5,403,923; 5,374,671; 5,258,430 and 4,900,361 disclose preparation and use of various starch materials. Typically, starch may be composed of about 25 percent amylose and about 75 percent amylopectin. The Condensed Chemical Dictionary, Ninth Edition (1977)), revised by G. G. Hawley, published by Van Nostrand Reinhold Company, Page 813). Starch can be, reportedly, a reserve polysaccharide in plants such as, for example, corn, potatoes, rice and wheat as typical commercial sources.
Preferably said starch is comprised of amylose units and amylopectin units in a ratio of about 15/85 to about 35/65 and has a softening point according to ASTM No. D1228 in a range of about 180° C. to about 220° C. and where said starch/plasticizer composite has a softening point, reduced from said starch alone, in a range of about 110° C. to about 170° C. according to ASTM No. D1228 which is considered herein to be necessary or desirable to provide the starch/plasticizer composite softening point to approach of to be within the temperature region used for the mixing of the rubber composition itself.
For the starch/plasticizer composite, in general, starch to plasticizer weight ratio is in a range of about 0.5/1 to about 5/1, alternatively about 1/1 to about 5/1, so long as the starch/plasticizer composition has the required softening point range, and preferably, is capable of being a free flowing, dry powder or extruded pellets, before it is mixed with the elastomer(s).
For the purposes of this invention, the plasticizer effect for the starch/plasticizer composite, (meaning a softening point of the composite being lower than the softening point of the starch), can be obtained, for example, through use of a polymeric plasticizer such as, for example, poly(ethylenevinyl alcohol) with a softening point of less than 160° C. Other plasticizers, and their mixtures, may be used, provided that they have softening points of less than the softening point of the starch, and preferably less than 160° C., which might be, for example, one or more copolymers and hydrolyzed copolymers thereof selected from ethylene-vinyl acetate copolymers having a vinyl acetate molar content of from about 5 to about 90, alternatively about 20 to about 70, percent, ethylene-glycidal acrylate copolymers and ethylene-maleic anhydride copolymers. As hereinbefore stated, hydrolysed forms of copolymers are also contemplated.
Representative examples of synthetic plasticizers are, for example, poly(ethylenevinyl alcohol), cellulose acetate and diesters of dibasic organic acids, so long as they have a softening point sufficiently below the softening point of the starch with which they are being combined so that the starch/plasticizer composite has the required softening point range.
Preferably, the synthetic plasticizer is comprised of at least one of poly(ethylenevinyl alcohol) and cellulose acetate.
In practice, various coupling agents may be used to aid in coupling the starch/plasticizer composite, and amorphous, preferably precipitated, silica if used to the associated diene-based elastomer(s). Representative coupling agents are those used as coupling agents for precipitated silica. Representative of such coupling agents are, for example, although not intended to be limiting, are bis(3-trialkoxysilylalkyl) polysulfices, particularly bis(3-triethoxysilylpropyl) polysulfides having an average of from about 2 to about 4 connecting sulfur atoms in its polysulfidic bridge. Preferably, such coupling agent has only a minor average of only from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge where a reduced sulfur content is desired in the rubber composition, or a more liberal average of from about 3.4 to about 3.8 connecting sulfur atoms in its polysulfidic bridge.
Various synthetic, amorphous silicas may be used, preferably precipitated silicas. Such precipitated silicas include, for example, and not intended to be limiting, various HiSil™ silicas from PPG Industries, various Zeosil™ silicas from Rhodia, various VN™ silicas from Degussa and various Hubersil™ silicas from J. M. Huber.
It is readily understood by those having skill in the art that the rubber composition of the tread rubber would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, curing aids, such as sulfur, activators, retarders and accelerators, processing additives, such as oils, resins including tackifying resins, silicas, and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants, peptizing agents and reinforcing materials such as, for example, carbon black. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur vulcanized material (rubbers), the additives mentioned above are selected and commonly used in conventional amounts.
The presence and relative amounts of the above additives are not considered to be an aspect of the present invention which is more primarily directed to use of a combination of soybean oil and starch/plasticizer composite in a diene-based rubber composition suitable for a tire component.
The tires can be built, shaped, molded and cured by various methods which will be readily apparent to those having skill in such art.
The following Examples are provided to more fully describe the invention. The parts and percentages are by weight unless otherwise indicated.
Rubber samples are prepared by blending various oils with a diene-based rubber composition and are referenced herein as Samples A through E, with Sample A being a Control Sample.
The Samples were composed of a blend of cis 1,4-polyisoprene natural rubber and styrene/butadiene rubber.
For Control Sample A, a petroleum based rubber processing oil was used for the rubber composition as well as carbon black reinforcement.
Samples B, C and E contained soybean oil replace the petroleum based processing oil (other than processing oil contained in the oil extended styrene/butadiene rubber).
Samples B, C and E also contained a starch/plasticizer composite to replace a portion of the carbon black.
For Samples B and C, both soybean oil and starch/plasticizer composite are added in one or more of the non-productive mixing stages.
Samples B and C differ only in that for Sample C, the starch/plasticizer composite is mixed in the second non-productive mixing stage instead of the first non-productive mixing stage.
Sample D is similar to Sample C except no starch/plasticizer is used.
Sample E is similar to Sample C except that no soybean oil is used.
For this Example, the first, non-productive mixing step (without sulfur curative) is conducted in an internal rubber mixer for about 3 minutes to a temperature of about 170° C. The sequentially subsequent second non-productive mixing step (also without the sulfur curative) is conducted in an internal rubber mixer for about 2.5 minutes to a temperature of about 165° C.
The sequentially subsequent productive mixing step (with the sulfur curative) is conducted in an internal rubber mixer for about 1.5 minutes to a temperature of about 116° C. The rubber composition is cooled to below 40° C. between each of the non-productive mixing steps and between the second non-productive mixing step and the productive mixing step.
Ingredients for the Sample preparation are illustrated in the following Table 1.
1Natural cis 1,4-polyisoprene rubber
2Aqueous emulsion polymerization prepared styrene/butadiene elastomer containing about 23.5 weight percent styrene obtained as Plioflex ® 1502
3Aqueous emulsion polymerization prepared styrene/butadiene elastomer containing about 23.5 weight percent styrene obtained as Plioflex ® 1712
3AOil contained in the above Plioflex ® 1712 rubber.
4N220 rubber reinforcing carbon black, an ASTM designation
5Composite of starch and poly(ethylene vinyl alcohol) plasticizer obtained as Mater-Bi 1128RR ™ from the Novamont Company
6Rubber processing oil as 130A ™ from the Valaro Company
7Soybean oil (food grade) from the Archer Daniels Midland Company
8Composite of a bis(3-triethoxysilylpropyl) polysulfide having an average in a range of from 2 to 2.6 connecting sulfur groups in its polysulfidic bridge
9Sulfenamide type
The following Table 2 illustrates cure behavior and various physical properties of the Samples. The aged Samples were cured Samples (160° C. for about 74 minutes) aged for 3 days in a hot air oven at 90° C.
1Data obtained according to Automated Testing System instrument by the Instron Corporation which performs multiple tests in one operation. Such instrument may determine, for example, ultimate tensile, ultimate elongation, modulii, etc. Data reported in the Table is generated by running the ring tensile test station which is an
2Data obtained according to DIN 53516 abrasion resistance test procedure using a Zwick drum abrasion unit, model 6102 with 10 Newtons force. The DIN abrasion results are reported as relative values, in terms of percentages, compared to a control rubber composition. Such DIN abrasion testing is well known to those having skill in
3The fabric backed sample tear strength test is intended to provide a measure of tear strength, or resistance to tear, for a fabric backed rubber sample cured at a temperature of 160° C. for 79 minutes. Samples of size 0.5 × 1 × 6 inches (1.27 × 2.54 × 15.24 cm) are cut along each of its 15.2 cm long edges
4The crack growth test is measure of crack growth during dynamic continuous flexing without relaxation of the sample. The test is sometimes referred to as a DeMattia (Pierced Groove Flex Test). The crack growth of the sample is measured in inches per minute and converted to minutes per millimeter (min/mm) for this Example. The test
From Table 2 it is seen that Sample B which used the combination of soybean oil and starch/plasticizer composite, exhibited similar physical properties compared to those of Control Sample A (which did not contain soybean oil or starch/plasticizer composite).
From Table 2 it is seen that Sample C, used the same combination of soybean oil and starch/plasticizer composite as Sample B, but where the starch/plasticizer composite was added in the second non-productive mixing stage. Again, Sample B exhibited similar physical properties, including aged physical properties, as such properties of Control Sample A.
From Table 2, it is also seen that Sample D, which is the same as Sample C, but without the starch/plasticizer composite, exhibited lower rebound properties compared to those of Control Sample A. For a tread rubber composition, a high rebound property is usually desirable where reduced rolling resistance is desired.
From Table 2 it is further seen that Sample E, which is the same as Sample C but without the soybean oil, that the elongation was lower. For a tread rubber composition, maintained elongation properties is usually desirable where damage resistance is desired.
Therefore, it is concluded that the combination of the starch/plasticizer composite and soybean oil provided the best match of the physical properties to the Control Sample A.
While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.
