JP2017031381A - Rubber composition for coating fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for coating a fiber for maintaining and enhancing mechanical properties while reducing heat generation property by blending carbon black having a specific colloidal property.SOLUTION: Carbon black having nitrogen adsorption specific surface area NSA of 90 m/g or less and compression DBP absorption amount (24M4) of 95 to 120 ml/100 g of 30 to 80 pts.mass are blended with 100 pts.mass of a diene rubber containing a natural rubber of 30 mass% or more and a styrene rubber of 10 to 50 mass% and a ratio of mode diameter Dst (nm) in a mass distribution curve of a Stokes diameter of an aggregate of the carbon black and half band width thereof ΔDst (nm), ΔDst/Dst is 0.65 or more and the NSA, (24M4) and Dst satisfy the following formula;(24M4)/Dst<0.0093×NSA-0.06.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a rubber composition for fiber coating, in which carbon black having specific colloidal characteristics is blended to maintain and improve mechanical characteristics while reducing exothermic properties.

  In recent years, in a pneumatic tire, a single carcass layer has been developed for the purpose of reducing the weight of the tire. In addition, a fiber reinforcing layer in which an organic fiber cord is coated with a rubber composition instead of a steel cord is increasingly used for a carcass layer or the like. As a rubber composition (fiber covering rubber composition) used for such a carcass layer (fiber reinforcing layer), even if it is a single layer, it has a high rigidity that can withstand a load or impact by forming a tire skeleton. It is required to have excellent adhesion to an embedded organic fiber cord.

  Further, for the purpose of reducing environmental load, it is required to further reduce rolling resistance in a pneumatic tire. Therefore, for example, the exothermic property of the rubber composition constituting the pneumatic tire is suppressed. In general, 60 ° C. tan δ by dynamic viscoelasticity measurement is used as an index of exothermic property of the rubber composition. The smaller the tan δ (60 ° C.) of the rubber composition, the smaller the exothermicity. Are known. As a method of reducing the tan δ (60 ° C.) of this rubber composition, for example, the amount of carbon black is reduced, the particle size of carbon black is increased, or a phenol-based thermosetting resin is added. However, in these methods, mechanical properties such as tensile breaking strength, tensile breaking elongation, and rubber hardness are lowered, and tire performance such as steering stability, wear resistance, and durability is lowered. There is.

  Here, in order to further reduce the rolling resistance of the pneumatic tire, the above-described carcass layer (fiber reinforcing layer), which is one of the components of the pneumatic tire, is also required to reduce the heat generation. As described above, the rubber composition for fiber coating that constitutes the layer (fiber reinforcing layer) is required to have higher rigidity and excellent adhesion to organic fiber cords. Even if the amount is reduced, the particle size of carbon black is increased, or even if a phenolic thermosetting resin is blended, sufficient low heat build-up cannot be obtained, or performance required as a fiber coating rubber composition ( There is a problem that high tensile breaking elongation and adhesion with fiber cords cannot be maintained. For this reason, it is required that the low exothermic property for reducing the environmental load, the adhesiveness as the fiber coating rubber composition, and the high hardness are both highly compatible.

  In recent years, it has also been studied to improve the performance of carbon black in order to improve mechanical properties such as hardness while further reducing rolling resistance. For example, Patent Document 1 discloses that a rubber composition has a low heat generation mainly by blending carbon black with adjusted specific surface area (BET specific surface area, CTAB specific surface area, iodine adsorption index IA), DBP structure value, Stokes diameter dst, and the like. It is proposed to make it. However, this rubber composition does not necessarily have sufficient effects of ensuring mechanical strength such as hardness, high tensile elongation at break, and adhesiveness. For example, for use as a fiber coating rubber composition, further improvement is required. It was done.

Special table 2004-519552 gazette

  An object of the present invention is to provide a rubber composition for fiber coating that maintains and improves mechanical properties while reducing exothermicity by blending carbon black having specific colloidal properties.

The rubber composition for fiber coating of the present invention that achieves the above-mentioned object is a nitrogen adsorption specific surface area N ₂ SA with respect to 100 parts by mass of a diene rubber containing 30% by mass or more of natural rubber and 10 to 50% by mass of styrene butadiene rubber. There 90m ² / g or less, the compression DBP absorption (24M4) with is blended 30-80 parts by weight of carbon black 95~120mL / 100g, mode diameter in the mass distribution curve of Stokes diameter of the aggregates of the carbon black Dst (Nm) and its half width ΔDst (nm) ratio ΔDst / Dst is 0.65 or more, and N ₂ SA, (24M4) and Dst satisfy the following formula (1): Rubber composition.
(24M4) / Dst <0.0093 × N ₂ SA−0.06 (1)
(Where Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and (24M4) is the compressed DBP absorption (mL / 100 g). is there.)

The rubber composition for fiber coating of the present invention has a nitrogen adsorption specific surface area N ₂ SA of 90 m ² / g with respect to 100 parts by mass of diene rubber containing 30% by mass or more of natural rubber and 10 to 50% by mass of styrene butadiene rubber. Hereinafter, carbon black satisfying the relationship of the above formula (1), with the compressed DBP absorption amount (24M4) being 95 to 120 mL / 100 g, the ratio ΔDst / Dst in the mass distribution curve of the Stokes diameter of the carbon black aggregate being 0.65 or more Since 30 to 80 parts by mass of the rubber composition is blended, the mechanical properties such as elongation at break, adhesiveness and rubber hardness can be maintained and improved while reducing tan δ (60 ° C.) of the rubber composition.

The Dst of the carbon black is preferably 160 nm or more. The N ₂ SA of carbon black is preferably not 50 m ² / g or more.

  In the fiber coating rubber composition of the present invention, it is preferable that butadiene rubber is contained in less than 40% by mass in 100% by mass of the diene rubber.

  The pneumatic tire using the fiber coating rubber composition of the present invention for the fiber reinforcing layer can maintain and improve steering stability and durability more than conventional levels while reducing rolling resistance and improving fuel efficiency. it can.

The carbon black ASTM grade is a graph showing the relationship between (24M 4) / Dst for N ₂ SA. For carbon black used in the textile coating rubber composition of the present invention, an example of a graph showing the relationship between (24M4) / Dst for N ₂ SA. Against the N ₂ SA of the carbon black used in Examples and Comparative Examples herein (24M4) is a graph showing the relationship between / Dst.

  In the fiber coating rubber composition of the present invention, the rubber component is a diene rubber, and necessarily includes natural rubber and styrene butadiene rubber. As the natural rubber and styrene butadiene rubber, rubbers usually used in tire rubber compositions can be used. The content of the natural rubber is 30% by mass or more, preferably 30 to 60% by mass in 100% by mass of the diene rubber. If the content of the natural rubber is less than 30% by mass, the desired effect of the present invention cannot be obtained sufficiently. The content of the styrene butadiene rubber is 10 to 50% by mass, preferably 20 to 30% by mass in 100% by mass of the diene rubber. If the content of the styrene butadiene rubber deviates from 10 to 50% by mass, the desired effect of the present invention cannot be obtained sufficiently.

  The rubber composition of the present invention preferably contains butadiene rubber in addition to natural rubber and styrene butadiene rubber. As the butadiene rubber, a rubber usually used in a tire rubber composition can be used. When butadiene rubber is included, the content thereof is less than 40% by mass, preferably 10 to 35% by mass in 100% by mass of the diene rubber. In addition to natural rubber and styrene butadiene rubber, rolling processability is improved by including butadiene rubber.

  The rubber composition of the present invention may contain a diene rubber other than natural rubber, styrene butadiene rubber and butadiene rubber. Examples of other diene rubbers include isoprene rubber and acrylonitrile-butadiene rubber. Of these, isoprene rubber is preferred. These diene rubbers can be used alone or as any blend.

The rubber composition for fiber coating of the present invention has a specific nitrogen adsorption specific surface area N ₂ SA and a compressed DBP absorption amount (24M4), and a mode diameter Dst and a half-value width thereof in a mass distribution curve of the Stokes diameter of the aggregate. The ratio of ΔDst ΔDst / Dst and the new carbon black in which the relationship between Dst / (24M4) and N ₂ SA is limited are blended to make tan δ (60 ° C.) of the rubber composition using carbon black having a large particle size. However, mechanical properties such as rubber hardness and breaking elongation are not deteriorated. The compounding amount of carbon black is 30 to 80 parts by mass, preferably 50 to 70 parts by mass with respect to 100 parts by mass of the diene rubber. The rubber hardness of a rubber composition will deteriorate that the compounding quantity of carbon black is less than 30 mass parts. On the other hand, when the blending amount of carbon black exceeds 80 parts by mass, tan δ (60 ° C.) increases and tensile elongation at break decreases. In addition, wear resistance deteriorates.

Carbon black used in the present invention, the nitrogen adsorption specific surface area N ₂ SA is 90m ² / g or less, preferably 50~90m ² / g, more preferably 55~85m ² / g. When N ₂ SA exceeds 90 m ² / g, tan δ (60 ° C.) increases. In this specification, N ₂ SA of carbon black shall be measured according to JIS K6217-7.

  Moreover, the compressed DBP absorption amount (24M4) of carbon black is 95 to 120 mL / 100 g, preferably 100 to 115 mL / 100 g. When the compressed DBP absorption is less than 95 mL / 100 g, tan δ (60 ° C.) increases and wear resistance decreases. Further, since the molding processability of the rubber composition is lowered and the dispersibility of the carbon black is deteriorated, the reinforcing performance of the carbon black cannot be sufficiently obtained. If the compressed DBP absorption exceeds 120 mL / 100 g, the tensile strength at break and the tensile elongation at break will deteriorate. In addition, workability deteriorates due to an increase in viscosity. The amount of compressed DBP absorption shall be measured using a compressed sample described in Appendix A according to JIS K6217-4.

The carbon black used in the present invention has the above-described nitrogen adsorption specific surface area N ₂ SA and compressed DBP absorption (24M4), and also relates to the mode diameter Dst and its half-value width ΔDst in the mass distribution curve of the Stokes diameter of the aggregate. Have the relationship.

  In the present invention, the ratio ΔDst / Dst of the half-value width ΔDst (nm) of the mass distribution curve to the mode diameter Dst (nm) in the mass distribution curve of Stokes diameter of the carbon black aggregate is 0.65 or more, preferably 0.8. 70 or more. Heat generation can be reduced by setting the ratio ΔDst / Dst to 0.65 or more. In the present specification, the mode diameter Dst in the mass distribution curve of the Stokes diameter of the aggregate refers to the mode diameter of the maximum frequency in the mass distribution curve of the Stokes diameter of the aggregate obtained by centrifugal sedimentation of carbon black. The half-value width ΔDst refers to the distribution width when the frequency is half the maximum point in the aggregate mass distribution curve. In the present invention, Dst and ΔDst are measured according to the method for obtaining the aggregate distribution by JIS K6217-6 disc centrifugal light sedimentation method.

In the fiber coating rubber composition of the present invention, the nitrogen adsorption specific surface area N ₂ SA, the compressed DBP absorption amount (24M4), and Dst satisfy the following formula (1).
(24M4) / Dst <0.0093 × N ₂ SA−0.06 (1)
(Where Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and (24M4) is the compressed DBP absorption (mL / 100 g). is there.)

Carbon black has N ₂ SA, compression DBP absorption and ratio ΔDst / Dst within the specified range as described above, and (24M4) / Dst and N ₂ SA satisfy the above formula (1), thereby providing rubber. Mechanical properties such as tensile strength at break, tensile elongation at break, rubber hardness, and wear resistance can be maintained and improved while reducing tan δ (60 ° C.) of the composition.

FIG. 1 is a graph showing the relationship between (24M4) / Dst and N ₂ SA for an ASTM grade which is a representative carbon black having an ASTM standard number. In FIG. 1, the horizontal axis represents N ₂ SA (m ² / g), and the vertical axis represents (24M4) / Dst (mL / 100 g / nm). As shown in FIG. 1, (24M4) / Dst of conventional standardized carbon black black is approximately represented by a linear line (dashed line in FIG. 1) with respect to N ₂ SA, and its slope is about 0.0093, intercept Is 0.0133.

On the other hand, in the carbon black used in the present invention, the upper limit of the aggregate characteristic ratio (24M4) / Dst with respect to N ₂ SA is limited by the formula (1). This boundary line (primary straight line in which the inequality sign of the formula (1) is equal) is shown by a solid line in FIG. In addition, carbon black used in the examples of the present specification is plotted with ◯ marks. The broken line in FIG. 2 is a linear straight line obtained from ASTM grade carbon black. When the aggregate characteristic ratio (24M4) / Dst and N ₂ SA satisfy this relationship, the tensile strength at break and the tensile elongation at break can be made excellent.

In the present invention, when the carbon black specified by the formula (1) has N ₂ SA, compressed DBP absorption (24M4), and ratio ΔDst / Dst in the above-mentioned range, tan δ (60 ° C.) of the rubber composition. It is possible to maintain and improve mechanical properties such as tensile strength at break, tensile elongation at break, rubber hardness, and wear resistance.

  The Dst of the carbon black used in the present invention is not particularly limited, but is preferably 160 nm or more, and preferably 170 nm or more. If Dst is less than 160 nm, the heat generation may be deteriorated.

  The carbon black having the above-described characteristics is, for example, feedstock introduction conditions in a carbon black production furnace, supply amount of all air, introduction amount of fuel oil and feedstock, reaction time (combustion from the last feedstock introduction position to reaction stoppage) The production conditions such as gas residence time) can be adjusted.

  In the present invention, as carbon black, both carbon black having the above-described characteristics and other carbon blacks can be used. At this time, the proportion of carbon black having specific colloidal characteristics exceeds 50% by mass, and the total amount of carbon black is 30 to 80 parts by mass with respect to 100 parts by mass of the diene rubber. Thus, the balance between tan δ and mechanical properties of the rubber composition can be adjusted by blending together other carbon blacks.

  Various additives generally used in tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, various inorganic fillers, various oils, anti-aging agents, plasticizers, etc. An additive can be blended, and such an additive can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for fiber coating of the present invention can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for fiber coating of the present invention can be suitably used for rubber constituting a fiber reinforcing layer (for example, carcass layer) of a pneumatic tire. As described above, the pneumatic tire using the fiber coating rubber composition of the present invention for the fiber reinforcing layer has low heat generation during running, so that it can reduce rolling resistance and improve fuel efficiency. At the same time, by improving the mechanical properties of the rubber composition, it is possible to maintain and improve the handling stability and durability beyond the conventional level.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

23 types of rubber compositions (Examples 1 to 12, Standard Example, Comparative Examples 1 to 10) were prepared using 11 types of carbon black (CB-1 to CB-11). Of these, 3 types of carbon black (CB-1 to CB-3) are commercially available grades, 8 types of carbon black (CB-4 to CB-11) are prototypes, and their colloidal characteristics are shown in Table 1. . In FIG. 3, the relationship between (24M4) / Dst and N ₂ SA of each of the carbon blacks CB-1 to CB-11 is plotted, and numbers for referring to the respective carbon blacks are attached. In FIG. 3, the solid line is a straight line when the equation (1) is made equal, and the broken line is a primary straight line corresponding to the ASTM grade of carbon black.

In Table 1, each abbreviation represents the following colloidal characteristics.
N ₂ SA: Nitrogen adsorption specific surface area measured based on JIS K6217-7 24M4: Compressed DBP absorption measured based on JIS K6217-4 (compressed sample) Dst: Based on JIS K6217-6 Mode diameter which is the maximum value of the mass distribution curve of the Stokes diameter of the aggregate measured by the disc centrifugal light sedimentation method. ΔDst: Stokes diameter of the aggregate measured by the disc centrifugal photoprecipitation method measured based on JIS K6217-6 The distribution width when the mass frequency is half the maximum point in the mass distribution curve (half width)
ΔDst / Dst: ratio ΔDst / Dst value • left side of equation (1) (24M4) / calculated value of Dst • right side of equation (1) 0.0093 × N ₂ SA−0.06 Success or failure of formula (1): When the left side <right side is true, it is indicated by ◯, and when it is not true, it is indicated by ×.

Moreover, in Table 1, carbon black CB1-CB3 represents the following commercial grades, respectively.
CB1: Niteron Carbon Corporation Niteron # 200IS, N339
・ CB2: Tokai Carbon Co., Ltd. Seest 300, N326
CB3: Niteron Carbon Corporation Niteron # 10N, N550

Production of carbon blacks CB4 to CB11 Using a cylindrical reactor, as shown in Table 3, carbon blacks CB4 to CB11 were produced by changing the total air supply amount, fuel oil introduction amount, raw material oil introduction amount, and reaction time. .

Preparation and Evaluation of Rubber Composition for Fiber Coating 23 kinds of rubbers having the composition shown in Tables 3 and 4 in which the above 11 kinds of carbon blacks (CB1 to CB11) were added in common with the compounding ingredients in Table 5 In preparing the compositions (Examples 1 to 12, Standard Examples and Comparative Examples 1 to 10), the components excluding sulfur and the vulcanization accelerator were weighed and kneaded in a 55 L kneader for 15 minutes, and then the master batch. Was released and cooled to room temperature. This master batch was subjected to a 55 L kneader, and sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition for fiber coating. In addition, the quantity of the compounding agent described in Table 5 was described in parts by mass with respect to 100 parts by mass of the rubber components (NR, SBR, and BR) described in Tables 3 and 4.

  About 23 types of obtained rubber compositions (unvulcanized | cured), peeling force and rubber | gum coverage were evaluated by the method shown below.

Peeling force The obtained unvulcanized rubber composition is processed into a rubber sheet having a thickness of 1.0 mm, and a fiber cord that is aligned without gaps is sandwiched between two rubber sheets. Sheets in which the fiber cords were arranged with no gaps on the vulcanized rubber sheet were laminated so that the directions of the fiber cords were the same, and vulcanized at 150 ° C. for 45 minutes to prepare vulcanized samples. The obtained vulcanized sample was heated in a constant temperature bath at 100 ° C. for 96 hours, and at that temperature, the fiber cord and the vulcanized rubber portion on both sides of the central rubber sheet were pulled in opposite directions (180 °). The peel force was measured. The obtained results are shown in the column of “peeling force” in Tables 3 and 4 as an index with the value of the standard example being 100. The larger the index value, the greater the peeling force, and the better the adhesion with the fiber cord.

Rubber coverage The rubber coverage on the surface of the fiber cord after the above peel test (area ratio of rubber adhered to the cord surface) was measured. The obtained results are shown in the “Rubber coverage” column of Tables 3 and 4 as an index with the value of the standard example being 100. The larger the index value, the larger the rubber coverage and the better the adhesion to the fiber cord.

  Further, the obtained 23 types of rubber compositions (unvulcanized) were each vulcanized at 160 ° C. for 20 minutes in molds of predetermined shapes to prepare test pieces, and the rubber hardness, Evaluation of tan δ at 60 ° C. and elongation at break were performed.

Hardness Using the obtained test piece, it was measured at a temperature of 25 ° C. with a durometer type A according to JIS K6253. The obtained results are shown in the “Hardness” column of Tables 3 and 4 as an index with the value of the standard example being 100. A larger index value means higher hardness.

Tan δ at 60 ° C
Based on JIS K6394, the obtained test piece was subjected to a loss tangent tan δ at a temperature of 60 ° C. under the conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. It was measured. The obtained results are shown in the column of “tan δ (60 ° C.)” in Tables 3 and 4, using the value of the standard example as 100. The smaller the index value, the lower the heat generation, and the lower the rolling resistance when made into a tire, which means better fuel efficiency.

Breaking Elongation A JIS No. 3 dumbbell-shaped test piece (thickness 2 mm) was punched out from the obtained test piece in accordance with JIS K6251 and the test was performed at a tensile speed of 500 mm / min, and the tensile breaking elongation was measured. The obtained results are shown in the column of “Elongation at break” in Tables 3 and 4 as an index with the value of the standard example as 100. The larger the index value, the higher the elongation at break, which means that the durability when made into a tire is excellent.

The types of raw materials used in Tables 3 and 4 are shown below.
NR: natural rubber, RSS # 3 manufactured by VON BUNDIT
-SBR: Styrene butadiene rubber, Nippon Zeon Corporation NIPOL 1502
-BR: Butadiene rubber, manufactured by Nippon Zeon Co., Ltd. NIPOL BR 1220
CB1 to CB11: carbon black shown in Table 1 above

The types of raw materials used in Table 5 are shown below.
・ Oil: Showa Shell Sekiyu Extract 4 S
・ Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. ・ Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
・ Vulcanization accelerator: Nouchira DZ-G manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. (sulfur content 95.24% by weight)

  As is apparent from Tables 3 to 4, the rubber compositions for fiber coating of Examples 1 to 12 maintain and improve the hardness, tan δ (60 ° C.), elongation at break, peeling force, and rubber coverage more than conventional levels. It was confirmed.

As is clear from Table 3, the rubber composition of Comparative Example 1 has a compression DBP absorption amount (24M4) of carbon black CB-2 of less than 95 mL / 100 g and does not satisfy the formula (1). Is inferior. The rubber composition of Comparative Example 2 is inferior in peeling force and hardness because the compressed DBP absorption amount (24M4) of carbon black CB-3 is less than 95 mL / 100 g and does not satisfy the formula (1). The rubber composition of Comparative Example 3 is inferior in elongation at break because carbon black CB-4 does not satisfy the formula (1). The rubber composition of Comparative Example 4 has an inferior elongation at break because the compressed DBP absorption amount (24M4) of carbon black CB-9 is less than 95 mL / 100 g and does not satisfy the formula (1). Since the rubber composition of Comparative Example 5 has a nitrogen adsorption specific surface area N ₂ SA of carbon black CB-10 of more than 90 m ² / g and does not satisfy the formula (1), the elongation at break is poor. The rubber composition of Comparative Example 6 has a poor tan δ (60 ° C.) because the nitrogen adsorption specific surface area N ₂ SA of carbon black CB-11 exceeds 90 m ² / g.

  As is apparent from Table 4, the rubber composition of Comparative Example 7 has a proportion of natural rubber in 100% by mass of diene rubber less than 30% by mass and a proportion of styrene butadiene rubber in excess of 50% by mass. Further, the elongation at break and the rubber coverage are inferior. The rubber composition of Comparative Example 8 is inferior in hardness because it does not contain styrene butadiene rubber. The rubber composition of Comparative Example 9 is inferior in hardness and peel strength because the blending amount of carbon black CB-8 with respect to 100 parts by mass of the diene rubber is less than 30 parts by mass. The rubber composition of Comparative Example 10 is inferior in breaking elongation because the blending amount of carbon black CB-8 with respect to 100 parts by mass of the diene rubber is more than 80 parts by mass.

Claims (5)

The nitrogen adsorption specific surface area N ₂ SA is 90 m ² / g or less and the compressed DBP absorption (24M4) is 95 with respect to 100 parts by mass of diene rubber containing 30% by mass or more of natural rubber and 10-50% by mass of styrene butadiene rubber. A blend of 30 to 80 parts by mass of ~ 120 mL / 100 g of carbon black and a ratio ΔDst / Dst of the mode diameter Dst (nm) and its half-value width ΔDst (nm) in the Stokes diameter mass distribution curve of the carbon black aggregate Is a rubber composition for fiber coating, wherein N ₂ SA, (24M4) and Dst satisfy the following formula (1):
(24M4) / Dst <0.0093 × N ₂ SA−0.06 (1)
(Where Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and (24M4) is the compressed DBP absorption (mL / 100 g). is there.)   The rubber composition for fiber coating according to claim 1, wherein the Dst is 160 nm or more. The rubber composition for fiber coating according to claim 1 or 2, wherein the N ₂ SA is 50 m ² / g or more.   The rubber composition for fiber coating according to any one of claims 1 to 3, wherein the butadiene rubber is contained in an amount of less than 40% by mass with respect to 100 parts by mass of the diene rubber.   The pneumatic tire which coat | covered the fiber cord with the fiber coating composition in any one of Claims 1-4.

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