JP2009079077A - Rubber composition for tire, cap tread and tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire that affords a tire exhibiting an enhanced friction coefficient on a frozen road surface and excellent abrasion resistance on a dry road surface, a cap tread formed of the rubber composition, and a tire manufactured using the cap tread. <P>SOLUTION: The rubber composition for a tire comprises a diene rubber, at least 25 pts.mass and at most 55 pts.mass, based on 100 pts.mass of the diene rubber, of a glass bead, at least 5 pts.mass and at most 200 pts.mass, based on 100 pts.mass of the diene rubber, of carbon black, and at least 0.1 pt.mass and at most 15 pts.mass, based on 100 pts.mass of the diene rubber, of an ultrafine particle of zinc oxide, wherein the carbon black has an iodine adsorption number of at least 100 mg/g and at most 300 mg/g and the ultrafine particle of zinc oxide has an average particle size of at most 200 nm. The cap tread is formed of the rubber composition. The tire is manufactured using the cap tread. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a tire rubber composition, a cap tread, and a tire, and in particular, can improve a coefficient of friction on an icy road surface, and can produce a tire having excellent wear resistance on a dry road surface. The present invention relates to a rubber composition for tires, a cap tread formed from the rubber composition, and a tire manufactured using the cap tread.

  Conventionally, when a vehicle travels on an icy road surface, a spike tire has been used and a chain is attached to the tire. However, mounting of spike tires and chains on tires causes environmental problems such as generation of dust and damage to dry road surfaces, so the development of cap treads that do not require the mounting of spikes or chains has become an urgent issue. .

  In view of this, a studless tire has been developed as a tire for traveling on an icy road surface in which generation of dust and damage to a dry road surface are suppressed (see, for example, Patent Document 1).

Studless tires are devised in terms of material and design because the coefficient of friction is significantly reduced on icy road surfaces and becomes slippery compared to dry road surfaces. For example, as a rubber composition for a studless tire, a rubber composition containing a diene rubber excellent in low temperature characteristics has been developed.
JP 63-297106 A JP 2003-55505 A

  However, since the friction coefficient on the icing road surface of the studless tire is not sufficient as compared with the spike tire, it has been desired to develop a tire rubber composition capable of improving the friction coefficient on the icing road surface. Needless to say, it is desirable that the tire has excellent wear resistance on dry road surfaces from the viewpoint of suppressing the generation of dust.

  In view of the above circumstances, an object of the present invention is to improve a coefficient of friction on an icing road surface and to produce a tire having excellent wear resistance on a dry road surface. An object of the present invention is to provide a cap tread formed from the rubber composition and a tire manufactured using the cap tread.

  The present invention relates to a diene rubber, 25 to 55 parts by weight of glass beads with respect to 100 parts by weight of the diene rubber, and 5 to 200 parts by weight of carbon with respect to 100 parts by weight of the diene rubber. Black and ultrafine zinc oxide in an amount of 0.1 to 15 parts by mass with respect to 100 parts by mass of the diene rubber, and the iodine adsorption amount of the carbon black is from 100 mg / g to 300 mg / g The rubber composition for tires has an average particle diameter of ultrafine zinc oxide of 200 nm or less.

  In the tire rubber composition of the present invention, the diene rubber is preferably composed of at least one selected from the group consisting of natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber and butadiene rubber. .

  Moreover, in the rubber composition for tires of this invention, it is preferable that the particle size of a glass bead exists in the range of 50 micrometers or more and 200 micrometers or less.

  Moreover, this invention is the cap tread formed using said rubber composition for tires.

  Furthermore, this invention is a tire manufactured using said cap tread.

  ADVANTAGE OF THE INVENTION According to the present invention, a rubber composition for a tire that can improve a coefficient of friction on an icing road surface and can produce a tire having excellent wear resistance on a dry road surface, formed from the rubber composition The cap tread made and the tire manufactured using the cap tread can be provided.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<Diene rubber>
Examples of the diene rubber used in the rubber composition for tires of the present invention include natural rubber (NR), polyisoprene synthetic rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), and acrylonitrile butadiene rubber. (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), and the like can be used. These diene rubbers may be used alone or in combination of two or more.

  Among these, from the viewpoint of improving the friction coefficient on the frozen road surface, the diene rubber used in the tire rubber composition of the present invention includes natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, and butadiene rubber. It is preferable to use at least one selected from the group consisting of

<Glass beads>
As the glass beads used in the tire rubber composition of the present invention, for example, those generally used in plastics or metal abrasives can be used. By blending such glass beads, the friction coefficient on the ice road surface is increased by increasing the roughness of the surface of the cap tread when the tire tread of the tire is formed using the tire rubber composition of the present invention. Can be improved.

  Moreover, content of the glass bead used for the rubber composition for tires of this invention is 25 to 55 mass parts with respect to 100 mass parts of said diene rubber. When the glass bead content is less than 25 parts by mass with respect to 100 parts by mass of the diene rubber, the rubber composition for tires of the present invention is contained under the ultrafine zinc oxide having an average particle size of 200 nm or less, which will be described later. There is no improvement in the coefficient of friction on the icing road surface of the tire cap tread formed using the object. Further, when the content of the glass beads exceeds 55 parts by mass with respect to 100 parts by mass of the diene rubber, the resistance to the dry road surface of the tire cap tread formed by using the rubber composition for tires of the present invention. There is no improvement in wear.

  Moreover, as the glass beads used in the rubber composition for tires of the present invention, it is preferable to use those having a particle diameter of 50 μm or more and 200 μm or less. When the particle size of each glass bead is less than 50 μm, there is a tendency that the friction coefficient on the ice road surface of the tire cap tread formed using the tire rubber composition of the present invention is not improved, and 200 μm In the case of exceeding the above, there is a tendency that an improvement in wear resistance on the dry road surface of the cap tread of the tire formed using the tire rubber composition of the present invention is not observed. Here, the particle size of the glass beads means the length of the longest straight line (major axis) among straight lines connecting two arbitrary points on the periphery of each glass bead.

As the glass beads, it is preferred to use those with silicon dioxide (SiO ₂₎ principal component (including 50 wt% or higher).

<Carbon black>
As the carbon black used in the tire rubber composition of the present invention, conventionally known carbon blacks can be used. For example, SAF, ISAF, HAF, FEF and the like can be used alone or in combination of two or more. .

  Here, content of carbon black used for the rubber composition for tires of the present invention is 5 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the diene rubber. When the carbon black content is less than 5 parts by mass, the reinforcing effect associated with the blending of carbon black cannot be obtained, and when it exceeds 200 parts by mass, the processability of the tire rubber composition of the present invention is deteriorated. .

  Moreover, the iodine adsorption amount of carbon black used for the rubber composition for tires of the present invention is 100 mg / g or more and 300 mg / g or less. When the iodine adsorption amount of carbon black is less than 100 mg / g, improvement in wear resistance on the dry road surface of a tire cap tread formed using the rubber composition for tire of the present invention is not observed, and 300 mg When it exceeds / g, the processability of the tire rubber composition of the present invention deteriorates, and the rolling resistance of the tire cap tread formed using the tire rubber composition of the present invention also tends to deteriorate.

  The iodine adsorption amount of carbon black is measured based on JIS K 6217: 2001.

<Ultrafine zinc oxide>
As the ultrafine zinc oxide used in the tire rubber composition of the present invention, zinc oxide particles having an average particle diameter of 200 nm or less can be used. Here, the average particle diameter is obtained by calculating the average value of the diameters with the length of the longest straight line (major axis) among the straight lines connecting any two points on the periphery of each zinc oxide particle as the diameter. Can do.

  Here, the content of ultrafine zinc oxide used in the tire rubber composition of the present invention is 0.1 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the diene rubber. When the content of ultrafine zinc oxide is less than 0.1 parts by mass, there is no effect of blending ultrafine zinc oxide, and when the content exceeds 15 parts by mass, the tire rubber composition of the present invention is used. There is no improvement in wear resistance on the dry road surface of the tire cap tread.

<Other ingredients>
In the tire rubber composition of the present invention, in addition to the above components, for example, oils, waxes, anti-aging agents, stearic acid, zinc white, sulfur and vulcanization accelerators commonly used in the tire industry Various components such as these may be appropriately blended.

  Here, conventionally known oil can be used as the oil, for example, process oil, vegetable oil, or a mixture thereof can be used. As the process oil, for example, paraffinic process oil, naphthenic process oil, aromatic process oil, or the like can be used. Examples of vegetable oils include castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, sesame oil, sesame oil, olive oil Sunflower oil, palm kernel oil, cocoon oil, jojoba oil, macadamia nut oil, safflower oil, tung oil, and the like can be used.

  Moreover, as a wax, a conventionally well-known thing can be used, for example, Onouchi Shinsei Chemical Co., Ltd. sun knock wax etc. can be used.

  Moreover, conventionally well-known things can be used as an anti-aging agent, For example, anti-aging agents, such as an amine type, a phenol type, an imidazole type, and a carbamic acid metal salt, can be used.

  Moreover, as stearic acid, a conventionally well-known thing can be used, for example, the stearic acid by Nippon Oil & Fat Co., Ltd. can be used.

  Moreover, as a zinc flower, a conventionally well-known thing can be used, for example, Mitsui Metal Mining Co., Ltd. zinc flower No. 1 etc. can be used.

  Moreover, conventionally well-known thing can be used as sulfur, for example, powder sulfur etc. by Tsurumi Chemical Co., Ltd. can be used.

  Further, as the vulcanization accelerator, conventionally known ones can be used. For example, sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde- A material containing at least one of ammonia-based, imidazoline-based, or xanthate-based vulcanization accelerators can be used. Examples of the sulfenamide system include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-tert-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl-2- Sulfenamide compounds such as benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, N, N-diisopropyl-2-benzothiazolesulfenamide, and the like can be used. Examples of the thiazole group include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, cyclohexylamine salt, 2- (2,4-dinitro). Thiazole compounds such as phenyl) mercaptobenzothiazole and 2- (2,6-diethyl-4-morpholinothio) benzothiazole can be used. Examples of thiurams include TMTD (tetramethylthiuram disulfide), tetraethylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram monosulfide, dipentamethylenethiuram tetrasulfide, dipentamethylenethiuram hexasulfide. Further, thiuram compounds such as tetrabutylthiuram disulfide and pentamethylenethiuram tetrasulfide can be used. Examples of thiourea compounds that can be used include thiourea compounds such as thiocarbamide, diethylthiourea, dibutylthiourea, trimethylthiourea, and diortolylthiourea. Examples of the guanidine-based compounds include guanidine-based compounds such as diphenylguanidine, diortolylguanidine, triphenylguanidine, orthotolylbiguanide, and diphenylguanidine phthalate. Examples of dithiocarbamate include zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc diamyldithiocarbamate, zinc dipropyldithiocarbamate , Complex salt of zinc pentamethylenedithiocarbamate and piperidine, zinc hexadecyl (or octadecyl) isopropyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate, piperidine pentamethylenedithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, diamyl Dithiocarbamate such as cadmium It can be used carbamic acid compounds. As the aldehyde-amine system or aldehyde-ammonia system, for example, an aldehyde-amine system or aldehyde-ammonia system compound such as an acetaldehyde-aniline reaction product, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde-ammonia reaction product, or the like is used. be able to. As the imidazoline-based compound, for example, an imidazoline-based compound such as 2-mercaptoimidazoline can be used. As the xanthate type, for example, a xanthate type compound such as zinc dibutylxanthate can be used. These vulcanization accelerators may be used alone or in combination of two or more.

<Tire>
The tire rubber composition of the present invention can be produced by mixing at least the above-mentioned diene rubber, glass beads, carbon black, and ultrafine zinc oxide by kneading.

  For example, a tire tread of a tire is formed by extruding the rubber composition for a tire of the present invention produced as described above in an unvulcanized state.

  Then, a green tire is produced by arranging tire members such as cap treads formed from the rubber composition for tires of the present invention at predetermined positions, and thereafter, rubber compositions constituting each member of the green tire are prepared. The tire of the present invention is manufactured by vulcanization or the like.

  FIG. 1 shows a schematic cross-sectional view of the upper left half of an example of the tire of the present invention. Here, the tire 1 extends inward in the tire radial direction from both ends of the cap tread 2a serving as a ground contact surface of the tire 1, a base tread 2b positioned inward in the tire radial direction of the cap tread 2a, and the base tread 2b. A pair of sidewalls 3 constituting the side surface of the tire 1 and a bead core 5 positioned at the inner end of each sidewall 3 are provided. A ply 6 is bridged between the bead cores 5 and 5, and a belt 7 is installed outside the ply 6 and inside the base tread 2b.

  For example, the ply 6 has an angle of, for example, 70 ° to 90 ° with respect to the tire equator CO (a virtual line obtained by rotating the center of the width of the outer peripheral surface of the tire 1 once in the circumferential direction of the outer peripheral surface of the tire 1). A plurality of cords can be formed from a rubber sheet embedded in the rubber composition. Further, the ply 6 is folded and locked around the bead core 5 from the base tread 2b through the sidewall 3 from the inner side to the outer side in the tire axial direction.

  The belt 7 can be formed from, for example, a rubber sheet in which a plurality of cords that form an angle of, for example, 40 ° or less with respect to the tire equator CO is embedded in the rubber composition.

  Further, the tire 1 may be provided with a band (not shown) for suppressing the peeling of the belt 7 as necessary. Here, the band can be installed by, for example, a rubber sheet in which a plurality of cords are embedded in a rubber composition and spirally wound around the belt 7 substantially parallel to the tire equator CO.

  The tire 1 has a bead apex 8 extending outward in the tire radial direction from the bead core 5, and an inner liner 9 is installed inside the ply 6. Are covered with a side wall 3 and a clinch 4 extending inward in the tire radial direction from the side wall 3.

  In the above description, the case where the tire 1 shown in FIG. 1 is a tire for a passenger car has been described. However, the present invention is not limited to this, and various types of vehicles such as passenger cars, trucks, buses, heavy vehicles, etc. Can be applied to tires.

  However, when the cap tread 2a is formed from the rubber composition for tires of the present invention, the tire 1 of the present invention can improve the coefficient of friction on the icing road surface, and also has wear resistance on the dry road surface. Since the tire can be an excellent tire, the tire rubber composition of the present invention is preferably used for forming a cap tread of a studless tire.

<Preparation of unvulcanized rubber composition>
In accordance with the formulation shown in Table 1, components other than sulfur, vulcanization accelerator CZ and vulcanization accelerator D were kneaded for 5 minutes in a 1.7 liter closed Banbury mixer, and discharged when the temperature reached 150 ° C. The base kneaded rubber was used. Thereafter, sulfur, vulcanization accelerator CZ and vulcanization accelerator D were added to this base kneaded rubber and kneaded using an open roll, thereby allowing each of Examples 1 to 3 and Comparative Examples 1 to 3 to occur. An unvulcanized rubber composition was obtained.

  The numerical values shown in the rubber column of Table 1 represent the mixing ratio (mass ratio) of natural rubber and butadiene rubber, and the numerical values shown in the additive column of Table 1 are The amount of each additive when the amount of the rubber is 100 parts by mass is expressed in parts by mass.

(Note 1) Natural rubber: RSS # 3 grade (Note 2) Butadiene rubber: UBEPOL-BR150B manufactured by Ube Industries, Ltd.
(Note 3) Carbon black: Showa Black N220 manufactured by Showa Cabot Co., Ltd. (iodine adsorption amount: 119 mg / g)
(Note 4) Oil: Dyna Process Oil PS323 manufactured by Idemitsu Kosan Co., Ltd.
(Note 5) Wax: Sunnock wax manufactured by Ouchi Shinsei Chemical Co., Ltd. (Note 6) Anti-aging agent: Nocrack 6C (N-1,3-dimethylbutyl-N manufactured by Ouchi Shinsei Chemical Co., Ltd.) '-Phenyl-p-phenylenediamine)
(Note 7) Stearic acid: Stearic acid manufactured by NOF Corporation (Note 8) Zinc flower: Zinc flower No. 1 (average particle size: 290 μm) manufactured by Mitsui Kinzoku Mining Co., Ltd.
(Note 9) Glass beads: BZ-01 manufactured by AS ONE Co., Ltd. (particle size distribution 105-125 μm)
(Note 10) Ultrafine zinc oxide: Zincock Super F-2 (average particle size: 130 μm) manufactured by Hakusuitec Co., Ltd.
(Note 11) Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (Note 12) Vulcanization accelerator CZ: Noxeller CZ (N-cyclohexyl-2-benzothiazyl-sulfenamide) manufactured by Ouchi Shinsei Chemical Industries
(Note 13) Vulcanization accelerator D: Noxeller D (diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
<Friction test on ice>
A vulcanized rubber sheet was produced by vulcanizing each of the unvulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3 produced as described above at 170 ° C. for 10 minutes, From the vulcanized rubber sheet, rubber test pieces were prepared for Examples 1 to 3 and Comparative Examples 1 to 3.

Then, the rubber test piece produced as described above was pressed on the ice surface of −2 ° C. installed in the temperature-controlled room set at −5 ° C. with a pressure of ² kgf / cm ² and slipped at a speed of 20 km / h. Thus, the frictional force of each rubber test piece prepared from each of the unvulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3 was detected.

And according to the following formula (1), for each of the rubber test pieces formed using the unvulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3, the friction index on ice is calculated. Calculated. The results are shown in the column of friction index on ice in Table 1. The larger the value in the column of friction index on ice in Table 1, the greater the friction coefficient on the ice surface.
(Friction index on ice) = 100 × (each frictional force of rubber test pieces formed using the unvulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3) / (Unadded of Comparative Example 1) Friction force of rubber test piece formed using vulcanized rubber composition) (1)
<Abrasion resistance test>
Each of the unvulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3 produced as described above was molded into the shape of a tire cap tread, and the molded cap tread was formed into another tire. A green tire was produced by installing together with the member. And the tire for test of 195 / 65R15 size was produced by vulcanizing the produced green tire. Here, the production of the test tire was performed for each of the cases where the unvulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were used.

  Next, after running a domestic FF vehicle equipped with each of the above test tires for 8000 km, the groove depth of the tire cap tread was measured, and the travel distance per 1 mm of the decrease in the groove depth was calculated.

And according to following formula (2), about each of the tire for a test produced using the unvulcanized rubber composition of Examples 1-3 and comparative examples 1-3, an abrasion resistance index is given. Calculated. The results are shown in the column of wear resistance index in Table 1. It shows that it is excellent in abrasion resistance, so that the numerical value of the column of abrasion resistance index of Table 1 is large.
(Abrasion resistance index) = 100 × (reduction amount per 1 mm of groove depth of each cap tread formed using the unvulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 3 Traveling distance) / (traveling distance per 1 mm of groove depth reduction of cap tread formed using the unvulcanized rubber composition of Comparative Example 1) (2)
<Evaluation results>
As shown in Table 1, 3 parts by mass of ultrafine zinc oxide having an average particle size of 130 μm and 50 parts by mass of carbon black having an iodine adsorption amount of 119 mg / g with respect to 100 parts by mass of a mixed rubber of natural rubber and butadiene rubber In addition, when the unvulcanized rubber composition of Examples 1 to 3 in which the content of the glass beads is within the range of 25 parts by mass or more and 55 parts by mass or less with respect to 100 parts by mass of the mixed rubber is used. It was confirmed that both the on-ice friction index and the wear resistance index were high.

  In addition, the unvulcanized rubber composition of Comparative Example 1 containing no glass beads has both an on-ice friction index and an abrasion resistance index as compared with the unvulcanized rubber compositions of Examples 1 to 3. It showed a low value.

  In addition, the unvulcanized rubber composition of Comparative Example 2 containing no ultrafine zinc oxide had an on-ice friction index comparable to that of the unvulcanized rubber compositions of Examples 1 to 3, but the wear resistance. The index was low.

  Further, the unvulcanized rubber composition of Comparative Example 3 having a glass bead content of 60 parts by mass with respect to 100 parts by mass of a mixed rubber of natural rubber and butadiene rubber had a high friction index on ice. However, the wear resistance index was significantly low.

  From the above results, when the tire cap tread was produced using the unvulcanized rubber compositions of Examples 1 to 3, the friction coefficient on the icing road surface could be improved, and on the dry road surface, Since it is considered that a tire having excellent wear resistance can be obtained, it is considered that the unvulcanized rubber compositions of Examples 1 to 3 are preferably used for a tire, particularly a cap tread of a studless tire.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  ADVANTAGE OF THE INVENTION According to the present invention, a rubber composition for a tire that can improve a coefficient of friction on an icing road surface and can produce a tire having excellent wear resistance on a dry road surface, formed from the rubber composition The cap tread made and the tire manufactured using the cap tread can be provided.

It is typical sectional drawing of the upper left half of an example of the tire of this invention.

Explanation of symbols

  1 tire, 2a cap tread, 2b base tread, 3 sidewall, 4 clinch, 5 bead core, 6 ply, 7 belt, 8 bead apex, 9 inner liner.

Claims (5)

A diene rubber, 25 to 55 parts by weight of glass beads with respect to 100 parts by weight of the diene rubber, and 5 to 200 parts by weight of carbon black with respect to 100 parts by weight of the diene rubber. And 0.1 to 15 parts by mass of ultrafine zinc oxide with respect to 100 parts by mass of the diene rubber,
The iodine adsorption amount of the carbon black is 100 mg / g or more and 300 mg / g or less,
A rubber composition for tires, wherein the ultrafine zinc oxide has an average particle size of 200 nm or less.   The tire rubber according to claim 1, wherein the diene rubber is at least one selected from the group consisting of natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber and butadiene rubber. Composition.   The tire rubber composition according to claim 1 or 2, wherein the glass beads have a particle size in a range of 50 µm to 200 µm.   A cap tread formed using the rubber composition for tires according to claim 1.   A tire manufactured using the cap tread according to claim 4.

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