Tire with tread reinforced by silica

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a tire having a rubber tread reinforced with silica. On the one hand, the tread comprises a specific multi-component rubber blend reinforced by a fixed amount of silica or a combination of silica and carbon black.

【0002】

[Conventional technology]

Pneumatic rubber tires are rubber treads that can be a blend of various rubbers, typically reinforced with carbon black and are conventionally manufactured.

【0003】

On the one hand, rubbers are evaluated, selected and blended for the purpose of achieving the desired balance of tire tread properties and especially tire tread properties, mainly rolling resistance, traction and wear resistance.

【0004】

Sulfur-cured rubber containing a substantial amount of reinforced filler is utilized for a variety of applications that utilize rubber, including applications such as tires and especially tire treads. Carbon black is commonly used for such purposes and usually provides or enhances good physical properties for sulfur-cured rubber. Granular silica is also sometimes used for such purposes, especially when silica is used in combination with a coupling agent. In some cases, a combination of silica and carbon black is used as a reinforced filler for various rubber products, including tire treads.

【0005】

[Problems to be Solved by the Invention]

It is important to understand that, by convention, carbon black is considered to be a more effective reinforcing filler for rubber tires than silica if silica is used without a coupling agent.

【0006】

In fact, at least in comparison to carbon black, if silica is used without a coupling agent, silica particles and rubber elastomer to make silica a reinforced rubber filler for most purposes, including tire treads. Tends to lack or at least inadequate physical and / or chemical bonds with. Although various treatments and procedures have been devised to overcome such drawbacks, compounds capable of reacting with both silica surfaces and rubber elastomer molecules, ie compounds generally known as coupling agents or couplers in such technical fields. Is often used. For example, such coupling agents can be premixed or prereacted with silica particles, or added to the rubber mixture during the rubber / silica processing or mixing step. If the coupling agent and silica are added separately to the rubber mixture during the rubber / silica mixing or processing steps, the coupling agent is then considered to compound with silica in situ.

【0007】

In particular, such coupling agents are components or moieties that can react with silica surfaces (silanes) and rubbers, especially sulfur vulcanized rubbers containing carbon-carbon double bonds or unsaturateds. Consists of. In this way, the coupling agent acts as a connecting bridge between the silica and the rubber, thereby enhancing the rubber-reinforced surface of the silica.

【0008】

On one side, the coupling agent silane apparently forms a bond to the silica surface, perhaps through hydrolysis, and the rubber active ingredient of the coupling agent combines with the rubber itself. Usually the rubber-reactive component of the coupling agent is temperature sensitive, and during the final and higher temperature sulfur vulcanization steps following the rubber / silica / coupling agent mixing step, and therefore the coupling agent silane. The groups tend to combine with silica and then with rubber. However, due in part to the typical thermal sensitivity of the coupling agent, some compounding or bonding is due to the rubber-coupling agent during the early rubber / silica / coupling agent mixing stage prior to the vulcanization stage. It can occur between the reactive component and the rubber.

【0009】

The rubber-reactive group component of the coupling agent can be one or more groups such as, for example, mercapto, amino, vinyl, epoxy, and sulfur groups, preferably sulfur or mercapto moieties and even more preferably sulfur. ..

【0010】

Many coupling agents, such as silane coupling agents containing polysulfide components or structures, such as bis- (3-triethoxysilylpropyl) tetrasulfide, have been taught for use in the combination of silica and rubber.

【0011】

For silica-reinforced tire treads, US Pat. No. 5,066,721 discloses the use of solution-polymerized SBR for tire treads containing 50 parts of silica in Comparative Test Example 1 in Table 3 (column 15). .. Table 4 (column 17) exemplifies tire manufacturing. EPO application No. 501227-A also discloses the use of SBR produced by silica-enhanced solution polymerization, and SBR produced by solution polymerization is selected over SBR produced by emulsion polymerization. U.S. Pat. No. 4,519,430 comprises a solution or emulsified polymerized SBR and optionally polybutadiene rubber and / or polyisoprene rubber with a mixture of silica and carbon black, which is required as the main component of the silica / carbon black reinforced filler. Disclosure of silica-rich tire treads.

【0012】

Other US patents relating to silica and silica-reinforced tire treads include US Pat. Nos. 3,451,458, 3,664,403, 3,768,537, 3,884,285, 3,938,574, 4,482,663, 4,590,052, 5,089,554 and the United Kingdom 1,424,503.

【0013】

[Means for solving problems]

According to the present invention, based on 100 parts by weight of rubber (A) (i) Styrene / butadiene copolymer rubber produced by emulsion polymerization containing about 30-about 45% styrene about 10-about 80 phr, preferably about 15-about 60 phr (ii) Isoprene / butadiene copolymer rubber containing about 30 to about 70% by weight, preferably about 40 to about 60% by weight of isoprene / butadiene copolymer rubber about 10 to about 60 phr, preferably about 35 to about 50 phr. (iii) Sith 1,4-polybutadiene rubber about 15 to about 30 phr, and (iv) Sith 1,4-polyisoprene natural rubber A diene-based elastomer containing about 0 to about 15 phr, preferably about 5 to about 15 phr. (B) Granular silica about 50 to about 110 phr, preferably about 60 to about 85 phr (C) At least one silica coupling having a silane moiety reactive with silicon dioxide and a sulfur moiety reactive with the elastomer and having a weight ratio of silica to about 7/1 to about 15/1. Agent, as well (D) Carbon black about 0 to about 50 phr (however, if carbon black is used, the weight ratio of silica to carbon black is at least 1/1, preferably at least 4/1, and if carbon black is used. If so, the total amount of silica and carbon black is about 60 to about 120 phr, preferably about 70 to about 90 phr.) Pneumatic tires are provided with a tread vulcanized with sulfur comprising.

【0014】

In one aspect of the present invention, based on 100 parts by weight of rubber (A) (i) Styrene / butadiene copolymer rubber produced by emulsion polymerization containing about 30-about 45% styrene about 15-about 60 phr, preferably about 15-about 35 phr (ii) Isoprene / butadiene copolymer rubber containing about 30 to about 70% by weight, preferably about 40 to about 60% by weight of isoprene / about 50 phr (iii) Sith 1,4-polybutadiene rubber about 15 to about 30 phr, and (iv) Sith 1,4-Polyisoprene Natural rubber A diene-based elastomer containing about 5 to about 15 phr. (B) Granular silica about 50 to about 85 phr, preferably about 60 to about 85 phr (C) At least one silica coupling having a silane moiety reactive with silicon dioxide and a sulfur moiety reactive with the elastomer and having a weight ratio of silica to about 7/1 to about 15/1. Agent (D) Carbon black about 0 to about 50 phr (however, if carbon black is used, the weight ratio of silica to carbon black is at least 1/1, preferably at least 4/1 and at least 10 / for some applications. 1 and if carbon black is used, the total amount of silica and carbon black is about 60-about 120 phr, preferably about 70-about 90 phr.) Pneumatic tires are provided with a tread vulcanized with sulfur comprising.

【0015】

The term "phr" used and commonly used herein means "the number of copies of each material per 100 parts by weight of rubber".

【0016】

A four-component rubber blend is an important feature of the invention designed to enhance the properties of tire treads that contain a substantial amount of silica reinforcement.

【0017】

On the one hand, emulsion-polymerized styrene / butadiene (E-SBR) is required to have a medium to relatively high styrene content. Such SBR is referred to herein as E-SBR. A relatively high styrene content for E-SBR is believed to be beneficial for increasing traction or skid resistance for tire treads. The presence of SBR itself produced by emulsion polymerization is believed to be beneficial in enhancing the processability of the uncured elastomer composition mixture, especially as compared to the use of SBR produced by solution polymerization.

【0018】

SBR produced by emulsion polymerization means that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in the art in such technical fields.

【0019】

Isoprene / Butadiene Copolymer Rubbers (IBRs) reduce tire rolling resistance, as evidenced by evidence that their cured samples exhibit adequately lower hysteresis, as evidenced by their elastic repulsion values. It is considered to be beneficial for this.

【0020】

IBR is useful, for example, in solution polymerization of isoprene and 1,3-butadiene under suitable polymerization conditions to achieve the desired Tg range of about -20 ° C to about -50 ° C in its uncured state. Can be manufactured. Tg stands for glass transition temperature and can be conveniently determined by a differential scanning calorimetry at a heating rate of 10 ° C / min.

【0021】

Sith 1,4-polybutadiene rubber (BR) is considered to be beneficial for increasing the wear resistance of tire treads or tread wear resistance.

【0022】

Such BR can be produced, for example, by organic solution polymerization of 1,3-butadiene.

【0023】

BR can customarily be characterized by having a cis 1,4-content of at least 90%.

【0024】

Sith 1,4-polyisoprene natural rubber is well known to those skilled in the art of rubber technology.

【0025】

Thus, in the practice of the present invention, a well-proportioned four- or three-component reliance on silica fortifiers for the strengthening effect of silica for rubber blending and then on silica coupling agents. A rubber blend is provided.

【0026】

On the other side, when such a sulfur vulcanized rubber tread also contains carbon black, the weight ratio of silica to carbon black is at least about 1.5 / 1, preferably at least about 4/1, and some At least 10/1 for the use of.

【0027】

The commonly used siliceous pigments used in rubber compounding applications can be used as the silica of the present invention. The siliceous pigment includes a thermal decomposition method and a precipitated silicic acid pigment (silica), but precipitated silica is preferable.

【0028】

The siliceous pigment preferably employed in the present invention is precipitated silica, such as those obtained by acidification of soluble silicates such as sodium silicate.

【0029】

The siliceous pigment (silica) should have an extreme particle size ranging from, for example, 50 to 10,000 angstroms, preferably 50 to 400 angstroms. The BET surface area of the pigment measured using nitrogen gas is preferably from about 100 to about 200, more preferably from about 120 to about 180 m.²/ g. The BET method for measuring surface area is described in the Journal of American Chemical Society, Vol. 60, p. 304 (1930).

【0030】

Silica also typically has a dibutyl phthalate (DBP) absorption value in the range of about 200 to about 400, typically about 250 to about 300.

【0031】

Silica can be expected to have an extreme particle size measured by an electron microscope, for example in the range of about 0.01 to 0.05 microns, but silica particles may be smaller in size.

【0032】

Although it is often taught that the "projected" area of silica before and after mixing with rubber is suitable for characterizing various silicas, electron microscopic quantification of the projected area of silica is for sample preparation. Such characterization is inadequate or unreliable unless proper sample preparation is planned, as it is considered highly dependent. The adjustment variables include the size of the sample container and the mixing energy, and are required to be transparent in all details.

【0033】

Various commercially available silicas, eg, silicas commercially available from PPG Industries under the Hi-Sil trademarks such as 210, 243, etc., for illustration purposes only and not limited to, loans under the names Z1165MP and Z165GR. -Silica available from Rhone-Poulec, silica available from Degussa AG under the names VN2 and VN3, etc. may be considered for use in the present invention. Lonepourec Z1165MP silica is the preferred silica and is characterized by having a BET surface area of about 160-170 and a DBP value of about 250-290 and a substantially spherical shape as reported.

【0034】

The rubber composition of the tread rubber contains, for example, various sulfur vulcanizable component rubbers, for example, curing aids such as sulfur, activators, retarders and accelerators, processing additives such as oil, and adhesive resins. Resins, silica, and various commonly used such as plasticizers, fillers, pigments, fatty acids, zinc dioxide, waxes, antioxidants and ozone crack inhibitors, vulcanizers and fortifiers such as carbon black. It is readily understood by those skilled in the art that they will be compounded by methods generally known in the art of rubber compounding, such as mixing with the additive materials to be added. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur vulcanized material (rubber), the above additives are usually selected and in conventional amounts. Used for.

【0035】

If used, the typical addition of carbon black for the purposes of the present invention is described herein. If used, the amount of adhesive resin constitutes about 0.5 to about 10 phr, usually about 1 to about 5 phr. A typical amount of processing aid constitutes about 1 to about 50 phr. Such processing aids include, for example, aromatic, naphthenic, and / or paraffinic processing oils. Typical amounts of antioxidants make up about 1 to about 5 phr. Typical antioxidants are, for example, diphenyl-p-phenylenediamine and, for example, Vanderbilt Rubber. It can be something else as disclosed on pages 344-346 of the Handbook (1978). A typical amount of ozone crack inhibitor constitutes about 1-5 phr. A typical amount of fatty acid that can contain stearic acid if used constitutes about 0.5 to about 3 phr. A typical amount of zinc dioxide constitutes about 2 to about 5 phr. A typical amount of wax constitutes about 1 to about 5 phr. Microcrystalline wax is often used. A typical amount of deafening agent constitutes about 0.1 to about 1 phr. Typical deafeners can be, for example, pentachlorothiophenol and dibenzamide diphenyl disulfide.

【0036】

Vulcanization is carried out in the presence of a sulfur vulcanizing agent. Examples of suitable sulfur vulcanizers include elemental sulfur (free sulfur) or sulfur-imparting vulcanizers such as amine disulfides, high molecular weight polysulfides, or sulfur olefin adducts. Preferably, the sulfur vulcanizer is elemental sulfur. As known to those skilled in the art, sulfur vulcanizers are used in amounts ranging from about 0.5 to about 4 phr, or in some environments up to about 8 phr, from about 1.5 to about 2.5. Range Sometimes a range of 2 to 2.5 is preferred.

【0037】

Accelerators are used to control the time and / or temperature required for vulcanization and to improve the properties of the vulcanized product. Delayers are also used for vulcanization rates. In one embodiment, a single accelerator system, i.e. the primary accelerator, can be used. Conventionally and preferably, the primary accelerator is used in a total amount in the range of about 0.5 to about 4, preferably about 0.8 to about 1.5. In other embodiments, a combination of primary and / or secondary accelerators can be used, the secondary accelerator in an amount of about 0.05 to about 3 phr, eg, to activate and improve the properties of the vulcanized product. Can be used. The combination of these accelerators is expected to produce a synergistic effect on the final properties and is somewhat better than that produced by the use of either accelerator alone. In addition, it is delayed, which is unaffected at normal processing temperatures but produces satisfactory curing at normal vulcanization temperatures. action) Accelerators 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 xanthans. Preferably the primary accelerator is sulfenamide. If a secondary accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound. The presence and relative amounts of sulfur vulcanizers and accelerators are not considered to be one aspect of the invention with respect to the use of silica as a strengthening filler in combination with coupling agents.

【0038】

The presence and relative amounts of the above additives are not considered an aspect of the invention with respect to the utilization of a particular blend of rubber in the tire tread in combination with silica and silica coupling agents.

【0039】

Tires can be made, shaped, molded and cured by a variety of methods readily apparent to those skilled in the art.

【0040】

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

【0041】

[Example I]

The four-component rubber composition (blended rubber) is E-SBR and isoprene / butadiene copolymer rubber (IBR) with a relatively high styrene content, cis 1,4-polybutadiene rubber (BR) and cis 1,4-polyisoprene natural rubber ( Manufactured in a blend with NR) and referred to herein as Sample X.

【0042】

The rubber composition of Sample X was prepared by mixing the components in several stages, namely, three non-curing stages (without curing agent) and a curing developing stage (for curing agent). The resulting composition was then cured under elevated temperature and pressure conditions.

【0043】

For the uncured and undeveloped mixing step, 38% by weight of each component is added to the primary uncured and undeveloped mixing step for about 4 minutes, excluding the accelerator and sulfur curing agent that are mixed (added) in the final cured and undeveloped mixing step. Mix to a temperature of 180 ° C; mix (add) about 38% by weight of the ingredients to a temperature of about 170 ° C for about 2.5 to 3 minutes in the secondary curing undeveloped mixing step, and add about 24 to 25% by weight of the ingredients. In the tertiary curing undeveloped mixing step, it was mixed (added) to a temperature of about 160 ° C. for about 3 minutes. All done in a Banbury rubber mixer. The rubber composition (mixture) produced in the Banbury mixer was then mixed with a curing agent or accelerator and sulfur to a temperature of about 120 ° C. for about 3 minutes. The rubber was then vulcanized for about 18 minutes at a temperature of about 150 ° C.

【0044】

The rubber composition consisted of the components shown in Table 1. Table 2 illustrates the properties of the cured rubber composition.

【0045】

[table 1]

<img file="JPH071908A_D0001.tif" />1) SBR produced by emulsion polymerization with a styrene content of approximately 41% in the form available as 1721 from Huels AG Company. 2) Isoprene / butadiene copolymer rubber with isoprene content of about 50% and Tg of about -43 ° C available from Goodyear Tire and Rubber Company 3) Sith 1,4-polybutadiene rubber available as Budene® 1254 from Goodyear Tire and Rubber Company 4) Natural rubber (cis 1,4-polyisoprene) 5) Rubber processing oil present in 9.4 parts in E-BSR and 5 parts in PBd, but the amount of E-SBR and PBd reported above is dry weight (without oil), and about 11 additional rubber processing Oil was added.

【0046】

6) Alkylaryl para-phenylenediamine type 7) Lone-Silica available as Z1165MP from Pourek Company, but with a BET area of about 165 and a DBP absorption of about 260-280 as reported.

【0047】

8) Bis-3-triethoxysilylpropyl) tetrasulfide (50% active) commercially available from Degussa as X50S. However, it was obtained as a 50/50 blend of tetrasulfide and N330 carbon black (thus considered to be 50% active).

【0048】

[Table 2]

<img file="JPH071908A_D0002.tif" />These properties of the rubber composition are such that the expected rolling resistance and traction for the tire with the tread of Sample X is superior to that of Sample Y referenced as a control in Example II below. ..

【0049】

[Example II]

Manufactured pneumatic tires as size 185/65 / R15 steel belted radial ply tires. It has a sulfur-cured rubber tread consisting of the type of rubber composition described as Test X in Example I.

【0050】

Tire Y had a tread of a blend of natural rubber and solution polymer, and was reinforced with about 60 phr of carbon black and contained about 10 phr of silica. This was used as a comparative example.

【0051】

Table 3 shows the tire test results compared with the control standardized to a value of 100.

【0052】

[Table 3]

<img file="JPH071908A_D0003.tif" />The higher values reported above for rolling resistance for tire X actually indicate improved or lower tire rolling resistance and improved fuel economy for vehicles.

【0053】

The higher wet skid values reported for tire X indicate greater tire tread resistance to towing and slipping under wet conditions.

【0054】

The higher wear resistance reported for tire X indicates lower tread wear, thus indicating a greater predictable tread life for tire X.

【0055】

Therefore, these examples show that the rolling resistance, wet skid resistance and wear resistance of the aforementioned tire X are significantly improved beyond the values of the control Y tire.

【0056】

Although some representative embodiments and details have been shown for purposes of illustration of the present invention, it will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and scope of the invention. Will.