Farm tire with tread of rubber composition containing starch/plasticizer composite

ES 2 298 685 T3

DESCRIPTION

Agricultural tire with a rubber composition tread containing a starch / plasticizer compound.

Field of the invention

This invention relates to an agricultural tire, and more specifically to an agricultural tractor drive tire, according to claim 1.

Background of the invention

Agricultural tractor drive tires are agricultural service tires that have treads intended to engage the ground, which are configured with stud projections significantly spaced from each other so that the tire tread of the tractor wheel driven can act somewhat like a gear to engage the ground and thereby propel the tractor itself across the terrain.

Such treads of the agricultural tire due to their widely spaced lugs, which catch on the ground, have a ratio of the net tread area to the gross tread dimensions (net to gross ratio expressed as a percentage of the tread area) in a range of just 15 22 percent to 22 percent compared to more conventional passenger car tires which may have a more net to gross ratio on a 50 to 85 percent scale, because it is normally desired for passenger car tires to have a significantly higher road surface and thereby a smoother ride for the vehicle itself.

It can be readily recognized that significant demands are normally made on the rubber composition of tire treads for this type of agricultural tractor driven tires.

For example, such farm tractor driven tires can be expected to be capable of propelling the tractor through the field in the midst of significantly uneven ground and crop stubble. Consequently, Such tire treads with the tread lugs significantly spaced from each other can be expected to help catch the soil to propel the tractor itself as well as to prevent mud and dirt from excessively adhering to the recessed portion of the tire. the tread surface between the protruding studs as it would be a problem if the tread were provided with studs very close to each other and consequently with a relatively narrow groove configuration such as passenger car tire treads.

A measure of such tread configuration of the agricultural tractor driven tire in its aforementioned net-gross ratio, where the gross is the overall tread footprint, including the intermediate region between the lugs and where the net represents the travel surface of the external surface of the studs themselves.

Consequently, significant considerations for this type of tire intended for agricultural service as an agricultural tractor-driven tire include adequate resistance to abrasion both for the running surface of the spaced-apart tread lugs and the surface significantly exposed intermediate between the tread studs. Since the amount on the tread lug itself is relatively small, the individual tread lugs must be of a rubber composition with significant physical properties such as, for example, stiffness, resistance to wear. cracking, tear resistance, high elongation, relatively low modulus at large elongations, and good aging resistance.

For this invention a rubber composition for such agricultural tire treads has been provided with a conjugated diene-based rubber composition containing a particular reinforcement such as a starch / plasticizer preformed complex compound of a core of starch particles. composed of an optimally minimized plasticizer and where the starch / plasticizer complex compound is further reacted with an organosilane polysulfide optimally minimized in situ within the conjugated diene-based elastomeric host.

The rubber composition additionally contains rubber-strengthening carbon black together with a coupling agent for the starch compound / plasticizer combination. It may also optionally contain precipitated silica reinforcing aggregates. The philosophy is to provide such an agricultural tire tread configuration with a sulfur vulcanized rubber composition, with improved physical properties, where the optimized starch / plasticizer complex compound provides a significant contribution.

Historically, starch has sometimes been proposed for use in elastomer formulations for various purposes in the form of a starch / plasticizer compound. Such a starch / plasticizer compound is used in conjunction with the carbon black reinforcing filler.

US-A-5,672,639 refers to a rubber composition containing a starch / plasticizer compound as

ES 2 298 685 T3 is a tread band for a tire where the plasticizer can be, for example, a poly (ethylene vinyl alcohol) and / or cellulose acetate. The ratio of starch to plasticizer can be, for example, 1/1 to 2/1.

US-A-6,273,163 and 6,458,871 relate to the preparation of a rubber composition containing a starch / plasticizer composite reinforcement together with at least one additional reinforcing filler (eg carbon black and / or silica) where a primer Organosilane polysulfide is mixed in an initial non-productive mixing phase and a second organosilane polysulfide is mixed in a subsequent productive mixing phase.

The term "phr" when used herein, and in accordance with conventional practice, refers to "parts of a respective material per 100 parts by weight of rubber or elastomer."

In describing this invention, the terms "rubber" and "elastomer", as used herein, may be used interchangeably, unless otherwise prescribed.

The term "silica", as used herein, refers to synthetic amorphous silica, particularly aggregates thereof, such as, for example, precipitated silica and fumed silica, and particularly precipitated silica.

A reference to the Tg of an elastomer refers to its glass transition temperature, which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10 ° C per minute.

Summary and practice of the invention

In accordance with this invention, an agricultural tire, preferably a tire driven by an agricultural tractor, is provided with a circumferential tread pattern composed of lugs widely spaced from each other mainly in the form of elongated bars extending substantially diagonally to across at least a part of the tread, the ratio of the width of a medium lug to the length of the lug being 1/10 to 1/3, the radial heights of the individual studs being greater than the associated tread surface of the individual stud, where said tread has a net-gross value in a range of 15 to 22, alternatively from 16 to 20 percent and where said tread band tread is of a rubber composition composed of, based on parts by weight per 100 parts by weight of rubber (phr):

(A) 100 parts by weight of at least one conjugated diene-based elastomer, (B) 25 to 120, alternatively 25 to 90, phr of an elastomer reinforcing filler composed of (1) 25 to 120, of alternatively 25 to 90 phr of a starch compound / plasticizer, or (2) 1 to 20, alternatively 5 to 10, phr of synthetic plasticizer / starch compound, and, correspondingly 5 to 119, alternatively 15 to 85 , carbon black rubber reinforcing phr;

where said starch has a softening temperature according to ASTM No. D1228 on a scale of 180 ° C to 220 ° C and where said starch / plasticizer compound has a softening temperature in a range of 110 ° C to 1701C according to ASTM No. D1228, and has a plasticizer / starch weight ratio in a range from 0.1 / 1 to 0.6 / 1, alternatively from 0.25 / 1 to 0.4 / 1; and (C) optionally a coupling agent for said starch / plasticizer compound, wherein said coupling agent has one half reactive with hydroxyl groups contained in said starch / plasticizer compound and another half interactive with said diene-based elastomer.

The sub-claims relate to preferred embodiments of the invention.

Said coupling agent may be, for example, a bis (triethoxysilylpropyl) polysulfide with an average of 2 to 4, usually preferably an average in a range of 2 to 2.6 connecting sulfur atoms in its polysulfuric bridge in a proportion of weight of said coupling agent to said plasticizer / starch in a range of 0.05 / 1 to 0.3 / 1.

Alternatively said coupling agent, having an alkoxysilane moiety to react with hydroxyl groups on the starch / plasticizer compound and hydroxyl groups on silica (eg silanol groups) can be used if silica is used, and a functionality of mercapto, or fraction, for interaction with the diene-based elastomer (s). Representative of such a coupling agent is, for example, an organomercapto alkoxysilane such as, for example, mercaptopropyl triethoxysilane. Alternatively such coupling agents can be used with a mercapto functionality, or the moiety, where the mercapto functionality, or the moiety, has been blocked by a moiety that is itself labile and in which the blocked mercapto functionality is then unblocked. under the high temperature rubber vulcanization conditions to provide the reactive mercapto functionality of the rubber. Thus an appropriate organomercapto alkoxysilane such as, for example, mercaptopropyl triethoxysilane, with its mercapto group blocked by such moiety (organomercapto trialkylsilane, or mercaptopropyl triethoxysilane having a mercapto fraction blocked with a fraction that is capable of being unblocked at an elevated temperature) for which its mercapto fraction is then unblocked during the vulcanization of the rubber composition associated with an elevated temperature such as, for example, a temperature in the range of 140 ° C to 160 ° C. For example, see US-A-6,127,468, 6,204,339, 6,414,061, 6,528,673, and 6,608,125.

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Optionally, said rubber composition for said agricultural tractor driven tire tread additionally contains 2 to 20, alternatively 2 to 5 phr of at least one additional reinforcing load and / or selected non-reinforcing load of at least one of vulcanized rubber particles, short fibers, kaolin clay, mica, talc, titanium dioxide and limestone.

Optionally, said rubber composition for said agricultural tractor driven tire tread contains short fibers in an amount of 2 to 5 phr and they are selected from fibers of at least one nylon, aramid, polyester and cellulose material.

A significant aspect of the rubber composition for such an agricultural tractor driven tire tread is the use of a cooperative combination of:

(A) said compound of starch particles / plasticizer where the weight ratio of the plasticizer relative to the starch is a relatively low ratio in a range of 0.1 / 1 to 0.6 / 1, and (B) said bis (3-triethoxysilylpropyl) polysulfide in a ratio of this to said starch compound / plasticizer is in a relatively low weight ratio in a range of 0.1 / 1 to 0.5 / 1 or having said organomercapto alkoxysilane a blocked mercapto fraction that is capable of being unblocked or separated by heating at a temperature in a range of 140 ° C to 160 ° C.

As discussed below, preferably, the plasticizer is primarily composed of an ethylene vinyl alcohol polymer, although it may contain additives or be other plasticizers. The ethylene vinyl alcohol polymer can have an (average) molecular weight, for example, in the range of 11,000 to 60,000. It may have, for example, a 60/40 vinyl alcohol / ethylene mole ratio, although it is expected that such a ratio may vary slightly.

This combination of the limited relatively low ratio of plasticizer to starch in said starch / plasticizer compound together with the limited ratio of said coupling agent to said starch / plasticizer compound is here considered significant for the rubber composition of the tread of the tire driven by an agricultural tractor of this invention with its lugs significantly spaced from each other because it provides an ability to adjust the stress / pressure curve, i.e., the stiffness of the rubber, so that the rubber composition of the tread lugs is relatively stiff at low elongations as indicated by a relatively high Shore A hardness at low elongations, still having relatively low modular values ​​at relatively high elongations.

Another significant aspect of the invention is the tread pattern of the tire driven by an agricultural tractor composed of lugs spaced from one another and having a net to gross ratio in a range of 15 to 22 percent in combination. with the prescribed rubber composition containing starch / plasticizer.

It is important to present the tread in a form of a tire driven by an agricultural tractor intended to mesh with the soil to help propel the tractor through the dirt field and possibly crop stubble as a rubber gear meshing with the ground and thereby differentiate such a tread from a more conventional automobile tire tread. It is therefore important to appreciate that only relatively few tread lugs normally contact the ground at any one time, that these lugs may encounter uneven ground, stones and / or crop stubble, and that consequently individual lugs need to be able to short-term, local elongation should be able to resist tearing, cracking, and penetration of foreign objects.

Thus, in a preferred embodiment of the invention, The agricultural tire is a tire driven by an agricultural tractor with a tread having a tread surface of knobs significantly spaced from each other designed to mesh with the ground of a rubber composition composed of at least one elastomer based of conjugated diene containing a coupled in situ organosilane polysulfide dispersion of reinforcing filler as a preformed starch / plasticizer complex compound. The tread surface of the agricultural tractor driven tire itself is of a lug configuration widely spaced from one another to provide a ratio of the net tread lug surface tread to the gross dimensions of the tread (ratio between net and gross expressed in terms of percentage of the tread surface of the lugs) in a range of 15 to 20 percent. Consequently, from an operational standpoint in the field, typically a few studs actually touch or engage the ground at any one time. Consequently, such individual tread lugs are desirably capable of experiencing locally high weights and should be stiff enough to resist extensive elongation.

It is also significant to present the challenges of the tread rubber composition of the tire driven by the agricultural tractor with its lugs significantly spaced from each other to have a suitable modular profile of sufficient stiffness (Shore A Hardness) with moderate elongations and a relatively low stiffness (eg the corresponding modular value) at high elongations (eg. the tensile value at maximum elongation), in combination with good resistance to tearing and cracking, and good resistance to aging.

Consequently, the use of a preformed starch / plasticizer combination of the ratio

ES 2 298 685 T3 prescribed plasticizer in relation to starch is a significant aspect of the invention for the tread of the tire driven by an agricultural tractor in conjunction with a reaction with an organosilane of an organosilane polysulfide in situ within the host of elastomer. In practice, the use of a plasticizer, particularly a minimalization of the plasticizer, capable of reacting with the organosilane fraction of the organosilane polysulfide has different advantages. The plasticizer is intended here to allow better separation of the individual starch particles by complexation mechanisms with the amylose molecule on the outside of the starch particle. The organosilane moiety of the organosilane polysulfide is used to react with the hydroxyl groups contained in the plasticizer to thereby link the hydroxyl groups on the outside of the plasticizer to the elastomer in situ within the elastomer host. This serves here to create a plasticizer core shell around the hard starch particles. This mechanism can be used advantageously to adjust the reinforcing capabilities of the starch based filler, where the content of the plasticizer can be adjusted with the starch content to achieve a lower starch / plasticizer ratio and thereby a lower interaction of the amylose groups in the starch with the plasticizer. This allows an ability to create core shells around the starch particles to form plasticizer / starch compounds that can favor a range of stiffness (eg, a range of modulus corresponds to different elongations) for the rubber host than contains such a compound. As a consequence, it can be seen here that the stress deformation profile of interest for the rubber composition for the application of the tread actuated by the agricultural tractor can be achieved (the stiffness mentioned above at long elongations to promote better resistance tear, sufficient stiffness at moderate elongations (represented by Shore hardness) to favor less mobility of the tread block, which can also promote less penetration of foreign objects (eg crop stubble), and promote better road tractor tire performance and better ground engagement for various types of terrain).

The mobility factor of the tread block is provided in the direction of mobility of the tread blocks, or lugs, or of the tread of the agricultural tire. In this sense, it is desired that a block of tread, or block, has sufficient rigidity to promote the proper behavior of the tires, that is, the mobility of the tire tread, and that such rigidity is also considered here. assisting after contact of the block with the harvest stubble, to promote the folding of the harvest stubble, or stalks, out of the respective block, which is also in the sense of stubble resistance of a respective block. However, if the crop stubble (e.g. crop stalks) were to be found in such a way that it would not be easily folded out of a block, then the block should have good tear resistance as a property which is another form of resistance. to harvest stubble.

It is considered in this case that the starch / plasticizer compound required for this invention with plasticizer / starch ratios in the range of 0.1 / 1 to 0.6 / 1 as described above satisfies these objectives. when used with the minimum amount of organosilane from an organosilane polysulfide in the rubber composition with the starch compound / plasticizer based on the dispersion of the filler, that is, a weight ratio of the organosilane polysulfide to the starch compound / plasticizer in a range from 0.05 / 1 to 0.3 / 1.

The fraction of the collecting reagent with the surfaces of the starch compound / plasticizer, i.e., the organosilane of the organosilane polysulfide, is generally considered herein as capable of reacting with at least one or more hydroxyl groups on the surface of the preformed composition of particles of starch / plasticizer and possibly with other reactive groups on it.

In the practice of this invention, it may be desirable for the starch / plasticizer compound to be used, for example, as a loose dry powder form or a loose dry granular form. In practice, it is desired that the synthetic plasticizer itself is compatible with the starch and has a softening temperature lower than the softening temperature of the starch so as to cause the softening of the mixture of the plasticizer and the starch at a higher temperature. lower than starch alone. This phenomenon of blends of compatible polymers of different softening temperatures having a softening temperature lower than the maximum softening temperature of the individual polymer (s) in the blend is known to those skilled in the art.

For the purposes of this invention, the plasticizing effect for the starch / plasticizer compound, (meaning a softening temperature of the compound lower than the softening temperature of the starch), can be obtained by using a polymeric plasticizer such as, for example, an ethylene vinyl alcohol polymer with a softening point of less than 160 ° C. Other plasticizers and their blends are contemplated for use in this invention, provided that they have softening temperatures lower than the softening temperature of starch, and preferably lower than 160 ° C, which could be, for example, one or more copolymers and hydrolyzed copolymers selected from ethylene-vinyl acetate copolymers with a molar vinyl acetate content of 5 to 90, alternatively 20 to 70%, ethylene-glycidal acrylate copolymers and ethylene-maleic anhydride copolymers. As stated hereinbefore hydrolyzed forms of copolymers are also contemplated herein. For example, the corresponding ethylene-vinyl alcohol copolymers, and the ethylene-vinyl alcohol-acetate terpolymers may be contemplated as long as they have a softening temperature lower than that of starch and preferably lower than 160 ° C.

In general, the mixing of the starch and plasticizer involves what is considered or believed herein to be chemical and / or physical interactions between the starch and the plasticizer.

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In general, the plasticizer / starch composition can have a weight ratio of plasticizer to starch in the range 0.1 / 1 to 0.6 / 1, as long as the plasticizer / starch composition has the temperature range required softening, and preferably, is capable of being a loose dry powder or extruded granules, before being mixed with the elastomer (s).

While the synthetic plasticizer (s) may have a natural viscosity at room temperature or 23 ° C and thus be considered a liquid for the purposes of this description, the plasticizer may actually be a viscous liquid at room temperature, since it must be taken into account that many plasticizers are polymeric in nature.

Representative examples of synthetic plasticizers are, for example, ethylene vinyl alcohol polymer, cellulose acetate and diesters of dibasic organic acids, as long as these have a softening temperature sufficiently below the softening temperature of the starch with which they are present. being combined so that the starch / plasticizer compound has the required softening temperature range.

Preferably, the synthetic plasticizer is composed of at least one polymer of ethylene vinyl alcohol and cellulose acetate, and more preferably the plasticizer is primarily composed of polymer of ethylene vinyl alcohol.

For example, said ethylene vinyl alcohol polymer can be prepared by polymerizing vinyl acetate to form a polyacetate that is subsequently hydrolyzed (acid or base catalyzed) to form the ethylene vinyl alcohol polymer. Such reaction of vinyl acetate and hydrolyzing of the resulting product is well known to those skilled in the art.

For example, vinyl alcohol / ethylene copolymers (for example in a ratio of 60/40 moles) can be obtained in powder forms in different molecular weights and crystallinity such as, for example, a molecular weight of about 11700 with a size average particle size of about 11.5 microns or a molecular weight (weight average) of about 60,000 with an average particle diameter of less than 50 microns.

Various mixtures of starch and ethylene vinyl alcohol copolymers, ie the ethylene vinyl alcohol polymer, can then be prepared according to mixing procedures well known to those skilled in the art. For example, a procedure could be used according to a recitation in the Bastioli, Bellotti and Del Trediu patent publication entitled A Polymer Composition Including Destructured Starch And Ethylene Copolymer, USA-5,403,374.

Other plasticizers can be prepared, for example, and provided they meet the appropriate Tg and starch compatibility requirements, by reacting one or more appropriate organic dibasic acids with aliphatic or aromatic diol (s) in a reaction that could sometimes be called a reaction. esterification condensation. Such esterification reactions are known to those of skill in the art.

In the practice of this invention, the inorganic fillers mentioned can be, for example, selected from one or more of clay powders, kaolin, talc, short separate fibers, thermoplastic powders such as polyethylene and polypropylene particles, or other reinforcing or non-reinforcing inorganic filler.

Such additional inorganic fillers are intended to be exclusive to or not include pigments conventionally used in the combination or preparation of rubber compositions such as zinc oxide and titanium oxide.

Such additional short fibers can be, for example, of organic polymeric materials such as cellulose, aramid, nylon and polyester.

In practice, said synthetic plasticizer / starch compound may have a moisture content in a range of zero to 30, alternatively one to six percent by weight.

In practice, the starch / plasticizer compound can be used as a partial replacement for carbon black reinforcement, depending somewhat on the desired properties of the cured or vulcanized tread rubber composition.

In practice, it is generally preferred that the rubber reinforcing carbon black is used in conjunction with the starch compound in an amount of at least 5 and preferably at least 35 phr of carbon black, depending slightly on the structure of the carbon black. The structure of carbon black is often represented by its DBP (dibutylthalate) value. Reinforcing carbon blacks typically have DBP numbers in a range of 40 to 400 cc / 100 gm, and more typically in a range of 80 to 300 (ASTM D 1265). If the carbon black content is used for the purpose of supplying an elastomer composition with adequate electrical conductivity to retard or prevent the formation of appreciable static electricity, a minimal amount of carbon black in the elastomer composition could be, for example , 10 phr if a high electrically conductive carbon black is used, otherwise normally at least 25 and often at least 35 phr of carbon black is used.

If desired, and on a practical basis, it is normally preferred that the coupling agent for the compound

ES 2 298 685 T3 starch / plasticizer can be the same stockpiler as could be used for silica reinforcement, if silica reinforcement is used. Thus, it is considered in this case that the fraction of the collecting reagent with the surface of the starch compound / plasticizer is also reactive with the hydroxyl groups (eg SiOH), and / or other reactive groups, usually on the surface of the silica. . Such silica, if used, is for example a synthetic precipitated silica.

It is important to appreciate that the starch compound could be used as a total replacement for carbon black, ie instead of carbon black for the tractor tread rubber composition. However, it is considered in this case that the starch compound is normally to be used in combination with carbon black normally as a partial replacement for carbon black, for the sulfur vulcanizable tractor tread rubber composition.

It is important to appreciate that although starch can be used in combination with the starch / plasticizer compound, they are not considered equal alternatives here. Thus, while starch may sometimes be considered suitable as a reinforcement for the elastomer composition with the coupling agent, the starch / plasticizer compound itself may be considered more desirable for some applications, even when used without a coupling agent.

If silica is used as reinforcement together with carbon black, the weight ratio of silica to carbon black is preferably a weight ratio in the range of 0.1 / 1 to 10/1, that is at least 0, 1/1, alternatively at least 0.9 / 1, optionally at least 3/1 and sometimes at least 10/1.

The weight ratio of said silica coupling agent to the starch / plasticizer compound and silica, if silica is used, can, for example, be in a range from 0.01 / 1 to 0.2 / 1 or even up to 0 , 4/1, while the weight ratio of the organosilane polysulfide to the starch compound / plasticizer is in the mentioned range of 0.05 / 1 to 0.3 / 1, and alternatively in a range of 0.11 / 1 at 0.23 / 1.

Starch is named as a compound of amylose units and / or amylopectin units. Starch is normally composed of a combination of amylose and amylopectin units in a ratio of 25/75. A slightly broader range of amylose to amylopectin unit ratios are cited herein to provide a starch for the starch compound that interacts with the plasticizer somewhat differently. For example, it is considered in this case that the suitable ratios can be from 20180 to 100/0, although the most suitable range is considered to be 15/85 to 35/63.

Starch can normally be obtained from plants of natural origin, as mentioned above. The starch / plasticizer composition may be present in various granular forms such as fibrils, spheres, or macromolecules, which may, in one aspect, depend somewhat on the ratio of amylose to amylopectin in the starch as well as the plasticizer content in the compound.

The relative importance of such forms of starch is the difference in their strength associated with the associated morphology of the filler. The morphology of the filler primarily determines the final form of the starch compound within the elastomer composition. Furthermore, the severity of mixing conditions such as high shear and high temperature can allow optimization of the final filler morphology. Thus, the starch compound, after mixing, may be in a form of one or more of those described above.

It is important to appreciate that starch itself is hydrophilic in nature, which means that it has a strong tendency to bind or absorb water. Thus, the moisture content for the starch and / or the starch compound has previously been discussed here. This is considered an important or desirable feature in the practice of this invention because water can also act somewhat as a plasticizer with the starch and can sometimes be associated with the plasticizer itself for the starch compound such as polyvinyl alcohol and acetate. cellulose, or another plasticizer that has similar functions, such as polyvinyl alcohol and / or cellulose acetate esters or any plasticizer that can lower the melting point of starch.

Various grades of starch / plasticizer composition can be developed for use with various elastomer compositions and treatment conditions.

As noted above, starch typically has a softening point in the range 180 ° C to 220 ° C, depending in part on the ratio of amylose to amylopectin units, as well as other factors, and thus , it does not soften easily when the rubber is mixed in a conventional way, for example, at a temperature in a range of 140 ° C to 165 ° C. Consequently, after the rubber is mixed, the starch remains in a granular solid form, although it may become somewhat elongated under higher shear forces generated while the rubber is being mixed with its compounding ingredients. Thus, starch remains largely incompatible with rubber and is normally present in the rubber composition in individual domains.

However, it is now considered here that supplying starch in the form of a starch starch compound and a plasticizer is particularly beneficial if such a composition is supplied with a softening temperature in the range of 110 ° C to 160 ° C.

Plasticizers can normally be combined with the starch such as, for example, by appropriate physical mixing processes, particularly mixing processes that provide adequate shear force.

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The combination of starch and, for example, polyvinyl alcohol or cellulose acetate, is referred to herein as a "compound". Although the exact mechanism may not be understood, it is believed that the combination is not a simple mixture but is a result of physical and / or chemical interactions. The interactions are believed to lead to a configuration where the starch molecules interact via amylose with the vinyl alcohol, for example the plasticizer molecule to form complexes, perhaps involving chain entanglement. The large individual amylose molecules are believed to be interconnected at different points by the molecule with the individual amylopectin molecules as a result of hydrogen bonding (which could otherwise also be in the nature of hydrophilic interactions).

This is considered beneficial here, because by varying the content and / or proportions of the natural and synthetic components of the starch combination it is believed that it is possible to alter the balance between the hydrophobic and hydrophilic interactions between the starch components and the plasticizer to allowing, for example, the charge of a starch compound to vary in shape from spherical particles to fibrils.

In particular, it is considered in this case that adding a polyvinyl alcohol to the starch to form a starch compound, particularly when the polyvinyl alcohol has a softening temperature in a range of 90 ° C to 130 ° C, can be beneficial in providing a resulting starch / plasticizer compound with a softening temperature in a range of 110 ° C to 160 ° C, and thus supplying a starch compound to mix well with a rubber composition during its mixing phase at a temperature, for example, in a range of 110 ° C to 165 ° C or 170 ° C.

Historically, the more homogeneous the dispersion of the rubber compound components in the rubber, the better the resulting vulcanized properties of that rubber. In this case, it is considered that it is a particular characteristic of this invention that the starch compound is mixed with the rubber composition under high shear conditions and at a temperature in a range of 140 ° C to 165 ° C, so as to obtain a very good dispersion in the rubber mixture obtained. This is considered important here because after mixing the elastomer composition containing the starch compound / plasticizer at a temperature to reach the melting point temperature of the compound, the starch compound will contribute to the development of high shear forces which is considered beneficial for the dispersion of the ingredient within the rubber composition. Above the melting point of the starch compound, for example around 150 ° C, it will melt and maximize its reaction with the coupling agent.

In one aspect, such a rubber composition can be supplied vulcanized with sulfur. Sulfur vulcanization is carried out in a conventional manner, that is, by polymerizing under conditions of elevated temperature and pressure for a suitable period of time.

In the practice of this invention, as noted above, the rubber composition is comprised of at least one diene or rubber-based elastomer. Thus, the elastomer is considered to be a sulfur vulcanizable elastomer. The diene-based elastomer can be selected from at least one of isoprene homopolymers and

1,3-butadiene and copolymers of isoprene and / or 1,3-butadiene with an aromatic vinyl compound selected from at least one of styrene and alpha-methylstyrene. Accordingly, such elastomer, or rubber, may be selected, for example, from at least one of cis 1,4-polyisoprene rubber (natural and / or synthetic, and preferably natural rubber), 3,4-polyisoprene rubber, rubbers styrene / butadiene copolymer rubbers, isoprene / butadiene copolymer rubbers, styrene / isoprene copolymer rubbers, styrene / isoprene / butadiene terpolymer rubbers, cis-

1.4- polybutadiene and polybutadiene rubber with a medium or high level of vinyl with a 1,2-vinyl content in a range of 15 to 85 percent and butadiene / acrylonitrile copolymers prepared by emulsion polymerization. Such a medium or high vinyl polybutadiene rubber may be more simply referred to in this case as high vinyl polybutadiene.

The composition of the rubber is preferably at least two diene-based rubbers.

In one aspect, a styrene / butadiene emulsion polymerization (E-SBR) with a relatively conventional styrene content of 20 to 30 percent styrene or, for some applications, an E-SBR with a styrene content could be used. medium to relatively high, that is, a combined styrene content of 30 to 45 percent.

The relatively high styrene content of 30 to 45 for E-SBR may be considered helpful in increasing the traction or skid resistance of the tire tread. The presence of the E-SBR itself is considered beneficial to improve the processability of the unvulcanized elastomer composition blend, especially compared to a use of a ready-made solution polymerization SBR (S-SBR).

By E-SBR prepared by emulsion polymerization it is meant that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. The content of combined styrene can vary, for example, from 5 to 50 percent.

Styrene / butadiene / acrylonitrile copolymer rubbers prepared by emulsion polymerization (E-SBAR) containing 2 to 50 percent by weight of acrylonitrile bound in the terpolymer are also contemplated as diene-based rubbers for use herein. invention.

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The prepared SBR polymerization solution (S-SBR) typically has a styrene content in a range of 5 to 50, preferably 9 to 36 percent. Its proportion of butadiene can have a vinyl content in the range of 10 to 50 percent. The S-SBR can be conveniently prepared, for example, by catalyzing organic lithium in the presence of an organic hydrocarbon solvent.

One objective of the use of S-SBR is to increase the rolling resistance of the tires, since it should tend to promote a lower hysteresis for the tire tread compositions.

3,4-polyisoprene rubber (3,4-PI) is considered beneficial in increasing tire traction when used in a tire tread composition.

3,4-PI and the use thereof is described in more detail in US-A-5,087,668.

Cis-1,4-polybutadiene (BR) rubber is considered beneficial in improving resistance to tire tread wear or tread wear.

Said BR can be prepared, for example, by polymerization in organic solution of 1,3-butadiene.

BR can be conveniently characterized, for example, as having at least 90 percent cis-1,4 content.

Natural rubber cis-1,4-polyisoprene and cis-1,4-polyisoprene are known to those skilled in the rubber art.

Commonly employed silica pigments used in rubber compounding applications can be used as silica in this invention, including fumed and precipitated silica pigments (silica), although precipitated silicas are preferred.

The silica pigments preferably employed in this invention are precipitated silicas such as, for example, those obtained by acidification of a soluble silicate, e.g. eg, sodium silicate.

Such silicas can be characterized, for example, by having a BET surface area, measured using nitrogen gas, preferably in the range of 40 to 600, and more usually in the range of 50 to 300 square meters per gram. The BET method of surface area measurement is described in Journal of the American Chemical Society, volume 60, page 304 (1930).

Silica can also normally be characterized by having a dibutylphthalate (DBP) absorption value in a range of 50 to 400, and more typically 100 to 300 cm.³/ 100 g.

Various commercially available silicas may be considered for use in this invention such as, for example only herein, and without limitation, commercially available silicas from PPG Industries under the Hi-Sil trademark registered with designations 210, 243, etc; Silicas available from Rhone-Poulenc, with, for example, Zeosil 1165 MP and silicas available from Degussa AG with, for example, designations VN2 and VN3, as well as other grades of silica, particularly precipitated silicas, which can be used for reinforcement elastomer.

Those skilled in the art will readily understand that the rubber composition would be composed by methods generally known in the rubber compounding art, such as mixing the various ingredients of sulfur vulcanizable rubbers with various commonly used additive materials such as, for example, vulcanization aids, such as sulfur, activators, retarders and accelerators, treatment additives, such as oils, resins including binder resins, silicas, and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants, peptizing products, and reinforcing materials such as, for example, carbon black. As those skilled in the art know, depending on the intended use of vulcanizable sulfur and sulfur vulcanized material (rubbers), the aforementioned additives are commonly selected and used in conventional amounts.

Typical amounts of binder resins comprise 0.5 to 10 phr. Typical amounts of processing aids comprise 1 to 50 phr. Such processing aids can include, for example, aromatic, naphthenic and / or paraffinic treatment oils. Typical amounts of antioxidants comprise 1 to 5 phr. Representative antioxidants can be, for example, diphenyl-p-phenylenediamine. Typical amounts of antiozonants comprise 1 to 5 phr. Typical amounts of fatty acids that can include stearic acid comprise 0.5 to 3 phr. Typical amounts of zinc oxide comprise 1 to 10 phr. Typical amounts of waxes comprise 1 to 5 phr. Microcrystalline waxes are often used. Typical amounts of peptizers comprise 0.1 to 1 phr.

Vulcanization is conducted in the presence of a sulfuric vulcanizing agent. Examples of suitable sulfuric vulcanizing agents include elemental sulfur (free sulfur) or sulfur donating vulcanizing agents, for example an amine disulfide, polymeric polysulfide or olefin adducts of sulfur. Preferably the sulfuric vulcanizing agent is elemental sulfur. As those skilled in the art know, sulfuric vulcanizing agents are used in an amount ranging from 0.5 to 4 phr.

Accelerators are used to control the time and / or temperature required for vulcanization and to me

ES 2 298 685 T3 improve the properties of the vulcanizate. In one embodiment, a single acceleration system, i.e. primary accelerator, can be used. Conventionally and preferably a primary accelerator (s) is used in total amounts ranging from 0.5 to 4. In another embodiment combinations of a primary and secondary accelerator could be used using the secondary accelerator in smaller amounts (0.05 to 3 phr) to activate and improve the properties of the vulcanizate. In addition, time-delayed accelerators can be used which are not influenced by normal treatment temperatures but produce satisfactory polymerization at common vulcanization temperatures. Vulcanization retarders can also be used. Suitable types of accelerators that can be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates, and xanthates. Preferably the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator is preferably a guanidine, a dithiocarbamate or a thiuram compound.

The mixing of the rubber composition is normally done in at least two phases, that is, at least one non-productive phase followed by a productive mixing phase. The final vulcanizing agents are normally mixed in the final phase which is conventionally called the "productive" mixing phase, where the mixing normally occurs at a temperature, or final temperature, lower than the temperature (s) of mixing of the preceding non-productive mixing phase. The rubber, starch compound, and fillers such as carbon black and optional silica and coupler, and / or fillers that are not carbon black or silica, are mixed in one or more non-productive mixing stages.

The invention can be better understood with reference to the following examples where parts and percentages are indicated by weight unless otherwise indicated.

Example I

A rubber composition comprised of the starch compound / plasticizer, the elastomer and resin combination is prepared and identified herein as Sample.

The rubber compositions were prepared in an internal rubber mixer using different mixing phases, that is, a non-productive mixing phase, in which the ingredients except the sulfuric vulcanizing agent and the vulcanization accelerator are mixed for approximately six minutes at a temperature of 160 ° C, removed from the mixer, layered outside and allowed to cool below 40 ° C.

The resulting rubber composition is then mixed in a productive mixing phase in an internal rubber mixer where the sulfur vulcanizing agent and accelerator are added for two minutes at a temperature of 120 ° C.

The rubber composition of the mix in the non-productive and productive sequential mixing stages is well known to those skilled in the art.

The formulations for control samples A and B and for samples C and D are shown in Table 1 below.

TABLE 1

<td></td><td>Control</td><td>Control</td><td></td><td></td>

<td>Material</td><td>Sample</td><td>Sample</td><td>Sample</td><td>Sample D</td>

<td>Non-productive mixing scale (at 160 ° C)</td><td>TO</td><td>B</td><td>C</td><td></td>

<td>Natural rubber¹</td><td> 50</td><td> 50</td><td> 50</td><td> 5</td>

<td>Styrene Butadiene Rubber ''</td><td> 50</td><td> 50</td><td> 50</td><td> 50</td>

<td>Carbon Black (N220)⁴</td><td> 65</td><td> 58</td><td> 58</td><td> 63</td>

<td>Starch / Plasticizer A³</td><td> 0</td><td> 6</td><td> 0</td><td> 0</td>

<td>Starch / plasticizer B °</td><td> 0</td><td> 0</td><td> 6</td><td> 0</td>

<td>Aromatic rubber treatment oil ''</td><td> 13,5</td><td> 13,5</td><td> 10,0</td><td> 11,5</td>

<td>Zinc oxide</td><td> 4</td><td> 3</td><td> 3</td><td> 3</td>

<td>Fatty acid</td><td> 2</td><td> 2</td><td> 2</td><td> 2</td>

<td>Resin (s)^to</td><td> 1</td><td> 3</td><td> 3</td><td> 3</td>

<td>Antioxidant ™</td><td> 4</td><td> 3</td><td> 4,3</td><td> 4,3</td>

<td>bis- (3-triethoxysilylpropyl) tetrasulfide</td><td> 0</td><td> 2,75</td><td> 1,5</td><td> 1,65</td>

<td colspan="5">Productive mixing stage (up to 120 °)</td>

<td>Sulfur</td><td> 1,8</td><td> 1,1</td><td> 1</td><td> 1,05</td>

<td>Throttle (s)</td><td> 1,65</td><td> 1,65</td><td> 1,75</td><td> 1,75</td>

<td colspan="5">¹ Cis -1,4-polyisoprene natural rubber</td>

ES 2 298 685 T3 ^ Styrene / butadiene copolymer elastomer, emulsion polymerization prepared containing approximately 23.5 percent styrene obtained as SBR 1721 from the Enichem Company ³Styrene / butadiene copolymer elastomer, emulsion polymerization prepared containing about 23.5 percent styrene and about 37.5 parts by weight per 100 parts by weight of the diluent oil elastomer obtained as Carifiex S5820 from Shell Company ⁴N-220 carbon black, an ASTM designation.

^sComposed of starch and ethylene vinyl alcohol polymer plasticizer) in a weight ratio of the plasticizer in relation to the starch of 0.6 / 1 with a softening temperature according to ASTM No. D1228 of about 142 ° C; where the starch is composed of amylose units and amylopectin units in a 1/3 weight ratio and a moisture content of 5 weight percent obtained as Mater Bi 1128R from the Novamont-Montedison Company⁶Composed of starch and ethylene vinyl alcohol polymer plasticizer in a weight ratio of plasticizer in relation to starch of 0.38 / 1 with a softening temperature according to ASTM No. D1228 of about 132 ° C; where the starch is composed of amylose units and amylopectin units in a 1/3 weight ratio and a moisture content of approximately 5 weight percent obtained as Mater Bi 1128R from the Novamont-Montedison Company⁷The high aromatic type ⁸Primarily stearic acid ⁹Resins as an alkyl phenol formaldehyde binder resin such as SP1068 from the Schenectady Company, as an aliphatic and aromatic resin such as Struktol 40MS from Schill &amp; Seilacher and as a heat reactive hydrocarbon resin such as NECIRES SF21 0 from the Nevcin Company ¹⁰Of the mixed type of aryl-p-phenylenediamines ¹¹A coupler as a 50% active compound composed of an organosilane tetrasulfide and carbon black in a 50/50 weight ratio available as X50S material from Degussa AG. Organosilane polysulfide is technically understood to be a combination or mixture where the average polysulfide bridge contains 3.5 to 4 connecting sulfide atoms, although the mixture may contain such polysulfides with a range of 2 to 8 sulfide atoms. Connection.

¹²N-tert.-butyl-2-benzothiazyl sulfenamide and diphenylguanidine in the case of samples A and B and dicyclohexylamino-benzothiacyl and dibenzothiazyl disulfide in the case of samples C and D.

ES 2 298 685 T3

Various physical properties for the rubber samples in Table 1 are provided in Table 2 below. TABLE 2

<td rowspan="3"></td><td colspan="4">Samples</td>

<td>Control</td><td>Control</td><td></td><td></td>

<td>Sample A</td><td>Sample B</td><td>Sample C</td><td>Sample D</td>

<td>Starch compound A</td><td> 0</td><td> 6</td><td> 0</td><td> 0</td>

<td>Starch compound B</td><td> 0</td><td> 0</td><td> 6</td><td> 0</td>

<td>Coupling Agent Compound (Carbon Black Coupling Agent)</td><td> 0</td><td> 2,75</td><td> 1,50</td><td> 1,65</td>

<td colspan="3">Strain under stress. Dolimerization 74 minutes at 160 ° C</td><td colspan="2" rowspan="2"></td>

<td colspan="3"></td>

<td>Modulus (ring) 300%</td><td> 7,7</td><td> 6,9</td><td> 5,4</td><td> 5,4</td>

<td>Maximum tensile strength (MPa)</td><td> 17,2</td><td> 15,9</td><td> 16,4</td><td> 16,0</td>

<td>Maximum elongation (%)</td><td> 563</td><td> 597</td><td> 692</td><td> 667</td>

<td>Energy¹ specific strength (MPa)</td><td> 36,5</td><td> 37</td><td> 43</td><td> 40,1</td>

<td>Scratch resistance^z resistance test at 100 ° C</td><td colspan="4" rowspan="2"></td>

<td></td>

<td>Adhesion of the skin itself (N / MN)</td><td> 30</td><td> 37</td><td> 44</td><td> 40</td>

<td>Shore A hardness (23 ° C)</td><td> 60,2</td><td> 55,7</td><td> 55,4</td><td> 54,6</td>

<td colspan="5">Deformation under stresses Dor aging. Dolimerization 74 minutes at 160 ° C:</td>

<td colspan="5">aging for 3 days in air at 90 ° C</td>

<td>Modulus (ring) 300% (MPa)</td><td> 10,5</td><td> 8,8</td><td> 6,8</td><td> 8,0</td>

<td>Maximum tensile strength (MPa)</td><td> 14</td><td> 14,6</td><td> 15</td><td> 15,8</td>

<td>Maximum elongation (%)</td><td> 403</td><td> 447</td><td> 569</td><td> 530</td>

<td>Energy¹ specific tear (MPa)</td><td> 23</td><td> 29</td><td> 36,3</td><td> 35,9</td>

<td>Shore A hardness (23 ° C) 64.2</td><td> 58,8</td><td> 58,10</td><td> 59,1</td><td></td>

<td>Deformation under stresses Dor aging</td><td colspan="4">or. Dolimerization 74 minutes at 160 ° C:</td>

<td colspan="5">aging for 14 days in air at 60 ° C</td>

<td>Modulus (ring) 300% (MPa)</td><td> 9,4</td><td> 8,1</td><td> 6,5</td><td> 6,8</td>

<td>Maximum tensile strength (MPa)</td><td> 16,2</td><td> 15,6</td><td> 16,10</td><td> 16,2</td>

<td>Maximum extension (%)</td><td> 493</td><td> 545</td><td> 644</td><td> 612</td>

<td>Specific energy of tearing¹ (MPa)</td><td> 31</td><td> 34</td><td> 41</td><td> 39</td>

<td>Scratch resistance^z. resistance test at 100 ° C</td><td colspan="4" rowspan="2"></td>

<td></td>

<td>Adhesion of the skin itself (N / MN)</td><td> 36</td><td> 45,7</td><td> 42</td><td></td>

<td>Shore A hardness (23 °)</td><td> 63,60</td><td> 59,10</td><td> 58,7</td><td> 57,4</td>

ES 2 298 685 T3

Since specific tear energy is determined by the area under the stress-strain curve until failure.

²The tear resistance test was done to determine the interfacial adhesion of a rubber composition (Sample) to it. Interfacial adhesion was determined by polymerizing one rubber composition sample against another rubber composition from the same sample with a Mylar film (with a cut window in the Mylar film) placed between the rubber compositions. Tear strength was determined by dragging one polymerized rubber composition out of the other at a right angle with the two extremities being thereby spaced 180 ° apart from each other using an Instron machine. The polymerized contact area was formed by placing a Mylar sheet, with a cut window in the Mylar sheet, between the rubber compositions during polymerization through the window in the Mylar film, which allowed the two Materials will come into contact with each other during polymerization. Tear resistance is sometimes referred to as skin adhesion.

The results provided in Table 2 for sample C, which contained starch / plasticizer compound B with the low plasticizer / starch ratio of 0.38 / 1 and the low coupling agent / compound ratio, are considered here remarkable. .

In particular, sample C, compared to control sample A, (without the starch / plasticizer compound), achieved a significant combination of (A) relatively high maximum elongation of 692 percent (versus 563 percent for sample A), (B) relatively low tensile strength of 16.4 MPa (versus 17.2 MPa for sample A), (C) relatively high tear energy of 43 MPa (versus 36.5 MPa for sample A ), (D) Relatively high skin adhesion of 44 N / MM (versus 30 N / MM for sample A), and (E) acceptable Shore A hardness (55.1) (versus 62 for sample A).

The ratio of the combination of relatively low stiffness to high elongation, indicated by maximum elongation and tear energy, is also considered significant here for this type of tractor driven wheel tire tread.

These results are even more remarkable when the aging of the Samples is considered, where the properties of Sample C showed comparatively a significantly less change, that is, for the 14-day aging test:

(A) a reduction in maximum elongation of only about 7 percent for Sample C versus a reduction of about 12 percent for Control Sample A, (B) an increase in maximum tensile strength of only approximately 2 percent for Sample C versus an increase of approximately 6 percent for Control Sample A, (C) a reduction in tear energy of approximately 5 percent for Sample C versus a reduction of approximately 15 percent for Control Sample A, and (D) an increase in tear strength of approximately 4 percent for Sample C versus a reduction of approximately 13 percent for Control Sample A.

The importance of the aging phenomenon is readily apparent, because it is desired that the tire tread of the tractor driven wheel maintains substantially significant physical properties for an acceptable period of working time.

ES 2 298 685 T3

A comparatively similar relationship can also be seen between Sample C (using the starch / plasticizer compound of a low plasticizer / starch ratio) and Sample B (using the starch / plasticizer compound of the significantly higher plasticizer / starch ratio). starch), at least in terms of tear energy in the aging experience, the results seen here for Sample C being significantly higher than those for Sample B.

The comparative differences observed above between Sample C and Control Sample A, particularly after aging of the respective samples, are here considered significant for a tractor tire tread with its lugs significantly spaced from each other and the intended operation. to mesh with the ground.

Example II

These experiments were done to examine the effect of the ratio of the coupling agent, i.e. the polysulfide organosilane to the starch / plasticizer compound B, i.e. the starch / plasticizer compound with the lower plasticizer / starch ratio of 0.28 /1.

The formulations are shown in the following Table 3 with the ingredients and mixing process indicated previously described in Example I.

The samples are identified as Control Sample E and Samples F and G. Sample G is similar to Sample C of Example I.

(Table goes to next page)

ES 2 298 685 T3

TABLE 3

<td></td><td colspan="3">Control</td>

<td>Material</td><td>Sample E</td><td>Sample F</td><td>Sample G</td>

<td colspan="4">First non-drug mixing phase (at 160 ° C)</td>

<td>Natural rubber'</td><td> 50</td><td> 50</td><td> 50</td>

<td>Styrene / Butadiene Rubber ^¿</td><td> 2</td><td> 20</td><td> 20</td>

<td>Styrene / Butadiene Rubber ^J</td><td> 41,25</td><td> 41,25</td><td> 41,25</td>

<td>Carbon Black (N220)⁴</td><td> 62,5</td><td> 57,5</td><td> 57,5</td>

<td>Starch / Plasticizer B^s</td><td> 0</td><td> 6</td><td> 6</td>

<td>Aromatic rubber treatment oil⁷</td><td> 10</td><td> 10</td><td> 10</td>

<td>zinc oxide</td><td> 3</td><td> 3</td><td> 3</td>

<td>Fatty acid⁸</td><td> 2</td><td> 2</td><td> 2</td>

<td>Resin (s)^to</td><td> 1</td><td> 3</td><td> 3</td>

<td>Antioxidant^{1 or}</td><td> 3,3</td><td> 3,3</td><td> 3,3</td>

<td>Bis-CS-triethoxysilylpropiOtetrasulfide¹¹</td><td> 0</td><td> 2,75</td><td> 1,5</td>

<td colspan="4">Productive mixing phase (at 120 ° C)</td>

<td>Sulfur</td><td> 1,0</td><td> 1,0</td><td> 1,0</td>

<td>Accelerators)¹⁷</td><td> 1,65</td><td> 1,65</td><td> 1,75</td>

<td colspan="4">'' Natural cis-1,4-polyisoprene rubber² Styrene / butadiene copolymer elastomer, prepared emulsion polymerization, containing approximately 23.5% styrene obtained as SBR 1721 from Enichem³ Styrene / butadiene copolymer elastomer, emulsion prepared by polymerization, containing approximately 23.5% styrene and containing 37.5 parts by weight per 100 parts by weight of elastomer of a diluent oil obtained as Cariflex S5820 from the Shell company⁴ N-220 carbon black, an ASTM designation⁵ A compound of starch and ethylene vinyl alcohol polymer plasticizer in a weight ratio of plasticizer to starch of 0.38 / 1 with a softening temperature according to ASTM No. D1228 of about 132 ° C; where the starch is composed of amylose units and amylopectin units in a proportion by weight of 1/3 and a moisture content of 5% by weight obtained as Mater Bi 1128R from the Novamont-Montedison company⁷ The low aromatic type⁸ Primarily stearic acid⁹ Resins as an alkyl phenol formaldehyde novolac tackifying resin such as SP1068 from Schenectadi, as an aliphatic and aromatic hydrocarbon resin such as Struktol 40MS from Schill &amp; Seilacher and as a heat reactive hydrocarbon resin such as NECIRES SF210 from the company Nevcin¹⁰Aryl-p-phenylenediamine mixing type</td>

ES 2 298 685 T3 ^Ί111η coupler as a 50% active compound composed of an organosilane tetrasulfide and carbon black in a 50/50 ratio by weight available as X50S material from Degussa AG. Organosilane polysulfide is technically understood as a compound or mixture where the middle polysulfide bridge contains 3.5 to 4 connecting sulfide atoms, although the mixture may contain polysulfides of this type with a range of 2 to 8 sulfide atoms of Connection.

¹²N-tert.-butyl-2-benzothiazyl sulfenamide and diphenyl guanidine

Various physical properties of the rubber samples in Table 3 are indicated in Table 4 below.

TABLE 4

<td rowspan="3"></td><td colspan="3">Samples</td>

<td colspan="2">Control</td><td></td>

<td>Sample E</td><td>Sample F</td><td>Sample G</td>

<td>Starch compound B</td><td> 0</td><td> 6</td><td> 6</td>

<td>Coupling Agent Compound (Carbon Black Coupling Agent)</td><td> 2,5</td><td> 2,5</td><td> 1,5</td>

<td colspan="4">Strain under stress (23 ° C). Dolimerization 74 minutes at 160 ° C</td>

<td>100% modulus (ring) (MPa)</td><td> 1,3</td><td> 1,2</td><td> 1,2</td>

<td>300% modulus (ring) (MPa)</td><td> 6,4</td><td> 5,9</td><td> 5,5</td>

<td>Maximum tensile strength (MPa)</td><td> 16,9</td><td> 16,1</td><td> 16,3</td>

<td>Maximum elongation (%)</td><td> 628</td><td> 648</td><td> 664</td>

<td>Shore A hardness (23 ° C)</td><td> 56,1</td><td> 56,7</td><td> 55,1</td>

<td>Zwick rebound (23 ° C)</td><td> 36,6</td><td> 36,6</td><td> 37,1</td>

<td>Zwick rebound (100 ° C)</td><td> 49,6</td><td> 48,6</td><td> 48,8</td>

<td>Tear resistance, 100 ° C strength test</td><td></td><td></td><td></td>

<td>Adhesion of the skin itself (N / MM)</td><td> 39,1</td><td> 41,9</td><td> 41,3</td>

<td colspan="4">Aged spreading properties (23 ° C). Dolimerization 74 minutes at 160 ° C</td>

<td colspan="4">Aged 3 days in air at 90 ° C</td>

<td>100% modulus (ring) (MPa)</td><td> 1,7</td><td> 1,7</td><td> 1,6</td>

<td>300% modulus (ring) (MPa)</td><td> 7,9</td><td> 7,3</td><td> 6,9</td>

<td>Maximum tensile strength (MPa)</td><td> 15,3</td><td> 14,7</td><td> 14,6</td>

<td>Maximum elongation (%)</td><td> 557</td><td> 583</td><td> 603</td>

<td>Shore A hardness (23 ° C)</td><td> 62</td><td> 60,5</td><td> 60,1</td>

<td colspan="4">Aged extension properties (23 ° C) Dolimerization 74 minutes at 160 ° C Aged</td>

<td colspan="4">14 days in air at 60 ° C</td>

<td>100% modulus (ring) (MPa)</td><td> 1,7</td><td> 1,6</td><td> 1,5</td>

<td>300% modulus (ring) (MPa)</td><td> 7,9</td><td> 7,2</td><td> 6,8</td>

ES 2 298 685 T3

<td>Maximum tensile strength (MPa)</td><td> 16,4</td><td> 16,3</td><td> 15,4</td>

<td>Maximum elongation (%)</td><td> 574</td><td> 607</td><td> 602</td>

<td>Shore A hardness (23 ° C)</td><td> 62,3</td><td> 59,4</td><td> 61,1</td>

<td colspan="4">Resistance to detachment. resistance test at 100 ° C</td>

<td>Skin property adhesion (N / MM)</td><td> 33,4</td><td> 30,2</td><td> 37,1</td>

In Table 4 it can be seen that the level of the coupling agent was adjusted in samples F and G to provide rubber compositions with an unaged hardness Shore A (23 ° C) similar to the control sample E with a Shore value. A of 56.1. For example, sample F exhibited a Shore A value of 56.7 which was similar to that of control sample E and sample G exhibited a Shore A value of 55.1, which is slightly lower than that of control sample E. .

Consequently, insofar as the hardness of this rubber is concerned, the Shore A hardnesses for samples F and G were similar to the control sample E.

However, it can be easily seen that modular values ​​of less than 300 percent were obtained for samples F (value of 59 MPa) and G (value of 55 MPa), compared to control sample E (value of 64 MPa). It is recognized that 300 percent of the modulus represents stress at 300 percent elongation.

It should be noted that lower values ​​of the modulus of 300 percent were observed for the samples while significantly higher maximum elongations were obtained for sample F (value of 648 percent) and sample G (value of 664 percent) compared to control sample E (628 percent value), combined with a maximum stress comparable to failure.

This indicates that significant stiffness (Shore A hardness values) can be obtained for the samples while having adequate maximum tensile strengths at relatively high maximum elongations.

This is considered here important for tires driven by an agricultural tractor that have knobs significantly spaced from each other with the application intended to bite into the ground because the stiffness of the knob provides stability to the behavior of the tire and transmission of force (moment) to the earth, softness of the block to dissipate the energy of the tear and resistance to break under locally high deformations, that is to say, elongations.

References cited in description

This list of references cited by the applicant was compiled exclusively for the information of the reader and is not part of the European patent document. It has been made with the greatest diligence; However, the EPO does not assume any responsibility for eventual errors or omissions.

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