Rubber composition

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a rubber composition, more specifically relates to a rubber composition suitable for use for a tire tread, sidewalls, or other rubber parts and having improved tensile strength, elongation, and abrasion resistance.

[0003] 2. Description of the Related Art

[0004] In recent years, improvements in various types of performance have been sought in the rubber compositions for automobile and other tires etc. Therefore, in tire tread rubber and the like, several types of polymers have been used by blending together. However, when these polymers are incompatible with each other, phase separated interfaces are present. In most cases, these interfaces become starting points for breakage and are believed to have a detrimental effect on the tensile strength, tear strength, abrasion resistance, etc. However, in tire and other rubber products, since the special process of vulcanization is included, it is not possible to apply as is the molecular design of the block copolymer for control of the phase structure as is normally done in rubber/resin blends or resin/resin blends. Therefore, the problem of the phase separation interface of rubber/rubber blends has not been sufficiently studied and no method for solving this problem had been found yet.

[0005] In the past, the decrease in the breaking strength due to the incompatibility of polymer blends obtained by blending block copolymers has not been sufficiently studied. Blending, into a blend of natural rubber (NR)/polybutadiene rubber (BR), a small amount of a block copolymer of polybutadiene (BR) and polyisoprene (IR) has only been described slightly in J. Apply. Polym. Sci., 49 (1993) and RCT. 66 (1993). However, the compositions of the block copolymers used in these references have insufficient compatibility with BR, and therefore, are not satisfactory in performance for practical use. Further, attempts have been made to add cis-BR into an incompatible polymer blend of cis-BR/SBR so as to improve the abrasion resistance, but the wet braking performance is decreased, and therefore, there is a limit to the amount of addition of cis-BR and there were consequently problems in practical use. In addition, except for the proposals made by the inventors of the present invention (Japanese Unexamined Patent Publication (Kokai) Nos. 7-188510, 8-134267, 8-193147, 8-193146, 8-193145, 8-283465, 8-302071, 10-007844, and 10-036465), examples of blending a block polymer into a rubber composition as a compatibilizing agent have not been known. The previous proposals by the present inventors did not clarify the relationship between the rubber component forming the matrix of the rubber composition and the molecular weight of the block polymer added. Later study resulted in clarification of this point and the present invention has been completed.

SUMMARY OF THE INVENTION

[0006] Accordingly, the object of the present invention is to provide a rubber composition capable of eliminating the, above-mentioned problems in the prior art and improving the tensile strength, elongation, abrasion resistance, etc. thereof.

[0007] In accordance with the present invention, there is provided a rubber composition comprising (i) an incompatible polymer blend comprising at least two diene rubbers selected from the group consisting of rubbers containing at least one conjugated diene monomer and optionally at least one aromatic vinyl monomer, such as natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), styrene-isoprene copolymer rubber (SIR) and styrene-isoprene-butadiene rubber (SIBR) and forming two incompatible polymer phases (A) and (B) and (ii) 0.1 to 20 parts by weight, based upon 100 parts by weight of the total polymer component including the block copolymer, of a block copolymer having at least two mutually incompatible blocks (a) and (b), the block (a) being compatible with the polymer phase (A) and being incompatible with the polymer phase (B) and the block (b) being compatible with the polymer phase (B) and incompatible with the polymer phase (A), and comprising at least one conjugated diene monomer (e.g., isoprene, butadiene) and, optionally, at least one aromatic vinyl monomer (e.g., styrene), wherein the molecular weights of the polymers forming the polymer phases (A) and (B) satisfy the following equations (I) and (II):

S

A

=Mw

30
(A)/Mw(a)≦1.2 (I)

S

B

=Mw

30
(B)/Mw(b)≦1.2 (II)

[0008] wherein

[0009] Mw30(A): molecular weight of the low molecular weight portion of the polymer forming the polymer phase (A),

[0010] Mw30(B): molecular weight of the low molecular weight portion of the polymer forming the polymer phase (B),

[0011] Mw(a): weight average molecular weight of block (a) of block copolymer, and

[0012] Mw(b): weight average molecular weight of block (b), of block copolymer.

[0013] In accordance with the present invention, there is also provided a rubber composition, wherein 5 to 200 parts by weight, based upon 100 parts by weight of the block copolymer, of a polymer (α) compatible with the block (a) and the polymer phase (A) and/or a polymer (β) compatible with the block (b) and polymer phase (B) are further blended and the weight average molecular weights of the polymers (α) and (β) satisfy the following equations (III) and (IV):

S

α

=Mw
(α)/Mw(a)≦1.2 (III)

S

β

=Mw
(β)/Mw(b)≦1.2 (IV)

[0014] wherein

[0015] Mw(α): weight average molecular weight of polymer (α),

[0016] Mw(β): weight average molecular weight of polymer (β),

[0017] Mw(a): weight average molecular weight of block (a) of block copolymer, and

[0018] Mw(b): weight average molecular weight of block (b) of block copolymer.

[0019] In accordance with the present invention, there is further provided a rubber composition comprised of a block copolymer having at least two mutually incompatible blocks (a) and (b) and comprising at least one conjugated diene and, optionally, at least one aromatic vinyl monomer based upon 100 parts by weight of the same, 5 to 200 parts by weight of a polymer (α) compatible with the block (a) and/or a polymer (β) compatible with the block (b), the weight average molecular weights of the polymers (α) and (β) satisfying the following equations (III) and (IV):

S

α

=Mw
(α)/Mw(a)≦1.2 (III)

S

β

=Mw
(β)/Mw(b)≦1.2 (IV)

[0020] wherein

[0021] Mw(α): weight average molecular weight of polymer (α),

[0022] Mw(β): weight average molecular weight of polymer (β),

[0023] Mw(a): weight average molecular weight of block (a) of block copolymer, and

[0024] Mw(b): weight average molecular weight of block (b) of block copolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be better understood from the description set forth below with reference to the accompanying drawings, wherein

[0026]
FIG. 1 is a view of an example of a molecular weight distribution curve (integrated molecular weight curve) of molecular weights measured by GPC forming the basis for finding the molecular weights of the low molecular weight portions of the polymers of the polymer phases (A) and (B) of equations (I) and (II);

[0027] GPC Measurement Conditions

[0028] GPC: HLC-8020 made by Toso

[0029] Column: GMH-HR-H, 2

[0030] Temperature: 40° C.

[0031] Mobile phase: THF

[0032] Standard substance: 10 points used between standard polystyrene 1000 to 10,000,000

[0033] Approximation method: By tertiary method.

[0034] Preparation of polymer sample: 50 mg of the polymer was dissolved in 10 cc of THF. The mixture was stirred at room temperature for about 168 hours so as to dissolve. This was then filtered by a 0.5 micron filter (H25-5 made by Toso) to remove the insolubles. The result was used as the sample. The amount injected into the GPC was made 400 μl.

[0035]
FIG. 2 is a view of an integrated molecular weight curve obtained by converting the molecular weight distribution curve of FIG. 1, wherein Mw30(A) and Mw30(B) of equations (I) and (II) are found from the molecular weight of the cumulative area 30% as shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The present inventors found that the above-mentioned object can be achieved by compounding, into a rubber composition formed from at least two rubber phases comprising at least two incompatible rubbers, a block polymer comprising at least two incompatible blocks having molecular weights which are defined by two types of relationships with the molecular weights of the rubbers forming the two rubber phases.

[0037] The tire rubber composition according to the present invention can be obtained by blending (i) an incompatible polymer blend of two polymer phases (A) and (B) comprising at least two types of incompatible rubbers of NR, IR, BR, SBR, SIR, and SIBR, preferably in the weight ratio of (A)/(B) of 90/10 to 10/90, more preferably 85/15 to 15/85) and (ii) 0.1 to 20 parts by weight, preferably 1 to 15 parts by weight, based upon 100 parts by weight of the entire rubber component including a block copolymer, of the block copolymer having at least two blocks comprising monomers selected from isoprene, butadiene, and styrene, wherein the blocks (a) and (b) are mutually incompatible, the block (a) is compatible with the polymer phase (A) and incompatible with the polymer phase (B), and the block (b) is compatible with the polymer phase (B) and incompatible with the polymer phase (A), preferably the weight ratio of (a)/(b) of 80/20 to 20/80, more preferably 60/40 to 40/60, and wherein the molecular weights of the polymers forming the polymer phases (A) and (B) satisfy the equations (I) and (II). Note that SA and SB preferably are 0.1 to 1.2, more preferably 0.3 to 1.0.

[0038] If the value of SA and the value of SB are more than 1.2, the block copolymer added while mixing the rubber component does not disperse well and the effect as a compatibilizing agent cannot be sufficiently exhibited.

[0039] Note that the molecular weights of the low molecular weight portions of the polymers forming the polymer phases (A) and (B) mean those found as values of molecular weights (i.e., Mw30(A) and Mw30(B)) corresponding to 30% of the cumulative area when converting the curve of the distribution of the molecular weight measured by GPC such as shown in FIG. 1 to the integrated molecular weight curve, as shown in FIG. 2. The GPC is measured by, for example, dissolving the polymer sample into THF, removing the insoluble gel component by a 0.5 micron filter, then calculating the molecular weight by an equation obtained from the amount of elution of standard polystyrene.

[0040] Further, it is possible to previously blend a block copolymer having at least two mutually incompatible blocks (a) and (b) and comprising a conjugated diene and/or aromatic vinyl monomer with a polymer (α) compatible with the block (a) and the polymer phase (A) and/or a polymer (β) compatible with the block (b) and the polymer phase (B), which satisfies the following equations (III) and (IV):

S

α

=Mw
(α)/Mw(a)≦1.2 (III)

S

β

=Mw
(β)/Mw(b)≦1.2 (IV)

[0041] wherein

[0042] Mw(α): weight average molecular weight of polymer (α),

[0043] Mw(β): weight average molecular weight of polymer (β),

[0044] Mw(a): weight average molecular weight of block (a) of block copolymer, and

[0045] Mw(b): weight average molecular weight of block (b) of block copolymer,

[0046] so as to improve the dispersion of the block copolymer during mixing of the rubber and obtain the better mechanical strength.

[0047] Note that Sα and Sβ are preferably 0.1 to 1.2, more preferably 0.3 to 1.0.

[0048] In particular, (α) should be added when the low molecular weight portion of the polymer forming the polymer phase (A) is small and (β) should be added when the low molecular weight portion of the polymer forming the polymer phase (B) is small. Therefore, even when the above equations (I) and/or (II) are not satisfied, it is possible to obtain the effect of the present invention by blending in the polymer (α) or (β).

[0049] Here, as the polymer (α) or (β), rubbers such as IR, BR, SBR, SIBR having a suitable molecular weight are preferable, but it is not limited to a rubber so long as the object of improving the dispersion at the time of mixing the block polymer is achieved without impairing the vulcanized physical properties of the rubber composition finally obtained. Other polymers may also be used.

[0050] The amount of the polymer (α) or (β) blended should be 5 to 200 parts by weight, preferably 20 to 100 parts by weight, based upon 100 parts by weight of the block copolymer. If the amount is less than 5 parts by weight, the anticipated effect is not manifested, while if more than 200 parts by weight, the elasticity or mechanical strength is decreased, and therefore, there is a detrimental effect on the physical properties or the Mooney viscosity of the starting rubber is decreased and handling becomes difficult.

[0051] The process of production of the block copolymer used in the present invention is not particularly limited, but, for example, this may be produced by polymerizing isoprene, butadiene, or styrene monomers in a hydrocarbon solvent using an organoactive metal as an initiator. As the organoactive metal, for example, an anionic polymerizable organoactive metal such as an organoalkali metal compound, organoalkali earth metal compound, or organolanthanoid based rare earth metal compound may be mentioned. Among these, an organoalkali metal compound is particularly preferable.

[0052] According to the present invention, it is possible to further blend low molecular weight polymers (for example, IR, BR, SBR, or SIBR) as parts of the polymers forming the polymer phases so as to satisfy the above equations (I) and (II). The amounts of the low molecular weight polymers blended are preferably 1 to 50 parts by weight, based upon 100 parts by weight of the rubber component, as a whole. If the amounts blended are too great, this leads to the decrease in the tensile strength etc., and therefore, this is not preferred.

[0053] The incompatible polymer blend comprising the polymer phases (A) and (B) used in the present invention is not particularly limited so long as two or more types of polymers selected from polymers containing conjugated dienes and/or aromatic vinyl monomers such as NR, IR, BR, SBR, are selected and constitute two incompatible polymer phases (A) and (B). Further, the block copolymer comprising the blocks (a) and (b) used in the present invention may be made any polymer provided with the above conditions. For example, a BR block, SBR block, IR block, SIR (i.e., styrene isoprene rubber) block, BIR (i.e., butadiene isoprene) block, SBIR (i.e., styrene butadiene isoprene) block, etc. may be suitably combined for use.

[0054] Representative examples of combinations of such incompatible polymers and block copolymers are as follows:

1TABLE IMatrix polymer (A)/(B)Block copolymer ((a)/(b))NR/SBR (wherein, amount ofIR/SBR (amount of vinyl ofvinyl of Bd part is notBd part not more than aboutmore than about 60 mol %)60 mol %) or SBR/SBR (amountof St about 20% by weight,amount of vinyl of Bd partabout 70 mol %)NR/BR (cis content not lessIR/SBR (amount of St aboutthan 90 mol %)20% by weight, amount ofvinyl of Bd part about 50mol %)

[0055] Of course, the present invention is not limited to the above examples.

[0056] The rubber composition according to the present invention may suitably use various conventional additives according to its application, for example, various reinforcing fillers generally used in the prior art such as carbon black and silica, softeners, antioxidant, wax, resin, vulcanization agent, vulcanization accelerator, vulcanization accelerator activator, etc. Further, blowing agent, low moisture plasticizer, short fibers, etc. may be used.

[0057] In blending the rubber composition according to the present invention, it is preferable to first mix the rubber (i.e., matrix rubber and block copolymer) and the additives other than, for example, vulcanization agent and vulcanization accelerator according to an ordinary method, then blend them. Of course, even if some of these ingredients are separately mixed, the resultant mixture, needless to say, falls in the technical scope of the present invention so long as the object of the present invention is not impaired. Further, the blending may be carried out in any means used in the past.

[0058] The rubber composition of the present invention may be vulcanized by a general method. The amount of the above additives blended may be the general amounts. Further, the vulcanization conditions may be made the general conditions.

EXAMPLES

[0059] The present invention will be further illustrated with reference to Examples, but the present invention is of course by no means limited in scope by these Examples.

Standard Examples 1 to 6, Examples 1 to 12, and Comparative Examples 1 to 7

[0060] The ingredients of the formulations of Tables II to IV, Table V, and Table VI (parts by weight) (wherein the characteristics of the polymers used as the phase (A) and phase (B) are shown in Table VII, the characteristics of the block polymers are shown in Table VIII, and the characteristics of the polymers (α) and (β) are shown in Table IX) were mixed in 1.5 liter Bambury mixers for 4 minutes, then the vulcanization accelerators and sulfur were mixed with the mixtures by 8-inch test-use roll mill to obtain the rubber compositions. These rubber compositions were press vulcanized at 160° C. for 20 minutes to prepare the desired test pieces which were then subjected to various tests and measured in physical properties. The physical properties of the vulcanates obtained were as shown in Tables II, III and IV.

[0061] Mixing Method

[0062] The mixing methods used in the Examples and the Comparative Examples were all according to the following mixing specifications:

[0063] 1) Rotor speed: 60 rpm

[0064] 2) Temperature adjustment: 50° C.

[0065] 3) Charging specifications:

[0066] 0′ . . . rubber ingredients (matrix rubber, block copolymer)

[0067] 1′ . . . carbon black in half amount, zinc white, stearic acid

[0068] 2′30″ . . . carbon black in half amount, antioxidant, wax

[0069] 3′30″ . . . raising and lowering of ram (cleaning ram portion)

[0070] 4′00″ . . . discharge

[0071] The “yes” in the compatibility section of Tables II, III and IV indicates a compatible relationship, while the “no” indicates an incompatible relationship.

2TABLE IIStandardComp. Ex.Comp.Ex. 11Ex. 2Ex. 1phase (A) polymer NR-250454545phase (B) polymer SBR50454545Block polymer BP-1—10——BP-2——10—BP-3———10CompatibilityBlock (a) ⇄ block (b)—NoNoNoBlock (a) ⇄ phase (A)—YesYesYespolymerBlock (a) ⇄ phase (B)—NoNoNopolymerBlock (b) ⇄ phase (A)—NoNoNopolymerBlock (b) ⇄ phase (B)—YesYesYespolymerRelation with molecularweightSA = Mw30 (A)/Mw (a)—1.81.70.8SB = Mw30 (B)/Mw (b)—1.20.60.6Physical properties ofrubber compositionTensile strength (MPa)23.223.524.026.3Elongation (%)370378380418Abrasion resistance100102101120index (index)

[0072]

3

TABLE III

Standard
Standard
Standard

Ex. 2
Ex. 3
Ex. 4

phase (A) polymer NR-1
80
—
—

NR-2
—
80
—

NR-3
—
—
80

phase (B) polymer BR
20
20
20

Physical properties of

rubber composition

Tensile strength (MPa)
29.9
28.1
26.6

Elongation (%)
568
578
579

Abrasion resistance index
100
100
100

(index)

Times to breakage in
2195900
2320300
2342100

fatigue test

Comp. Ex. 3
Comp. Ex. 4
Ex. 2

phase (A) polymer NR-2
78
78
78

phase (B) polymer BR
19
19
19

Block polymer BP-4
3
—
—

BP-5
—
3
—

BP-6
—
—
3

Compatibility

Block (a) ⇄ block (b)
No
No
No

Block (a) ⇄ phase (A) polymer
Yes
Yes
Yes

Block (a) ⇄ phase (B) polymer
No
No
No

Block (b) ⇄ phase (A) polymer
No
No
No

Block (b) ⇄ phase (B) polymer
Yes
Yes
Yes

Relation with molecular weight

SA = Mw30 (A)/Mw (a)
1.7
1.7
0.9

SB = Mw30 (B)/Mw (b)
0.7
0.3
0.3

Physical properties of rubber

composition

Tensile strength (MPa)
28.4
28.3
30.6

Elongation (%)
581
580
586

Abrasion resistance index
101
102
106

(index)

Times to breakage in fatigue
2310000
2298700
3212400

test

Comp. Ex. 5
Ex. 3

phase (A) polymer NR-1
78
—

NR-3
—
78

phase (B) polymer BR
19
19

Block polymer BP-5
—
3

BP-6
3
—

Compatibility

Block (a) ⇄ block (b)
No
No

Block (a) ⇄ phase (A) polymer
Yes
Yes

Block (a) ⇄ phase (B) polymer
No
No

Block (b) ⇄ phase (A) polymer
No
No

Block (b) ⇄ phase (B) polymer
Yes
Yes

Relation with molecular weight

SA = Mw30 (A)/Mw (a)
1.3
1.2

SB = Mw30 (B)/Mw (b)
0.3
0.3

Physical properties of rubber

composition

Tensile strength (MPa)
29.9
29.1

Elongation (%)
572
599

Abrasion resistance index (index)
102
107

Times to breakage in fatigue test
2188800
3400200

[0073]

4

TABLE IV

Standard
Comp. Ex.

Ex. 5
6
Ex. 4
Ex. 5

phase (A) polymer NR-1
60
58
55
57.85

NR-2
—
—
—
—

phase (B) polymer BR
40
39
39
39

Block polymer BP-7
—
3
3
3

Polymer (α) α-1
—
—
3
—

α-2
—
—
—
0.15

α-3
—
—
—
—

α-4
—
—
—
—

Polymer (β) β-1
—
—
—
—

Compatibility

Block (a) ⇄ block (b)
—
No
No
No

Block (a) ⇄ phase (A)
—
Yes
Yes
Yes

polymer

Block (a) ⇄ phase (B)
—
No
No
No

polymer

Block (b) ⇄ phase (A)
—
No
No
No

polymer

Block (b) ⇄ phase (B)
—
Yes
Yes
Yes

polymer

Polymer (α) ⇄ block (a)
—
—
Yes
Yes

Polymer (α) ⇄ phase
—
—
Yes
Yes

(A) polymer

Polymer (β) ⇄ block (b)
—
—
—
—

Polymer (β) ⇄ phase (B)
—
—
—
—

polymer

Relation with molecular

weight

SA = Mw30 (A)/Mw (a)
—
2.2
2.2
2.2

SB = Mw30 (B)/Mw (b)
—
0.3
0.3
0.3

Sα = Mw (α)/Mw (a)
—
—
0.7
1

Sβ = Mw (β)/Mw (b)
—
—
—
—

Rate of polymers (α) and
—
—
100
5

(β) added/wt % (to block

polymer)

Physical properties of

rubber composition

Tensile strength (MPa)
27.9
28.3
29.2
28.7

Elongation (%)
550
560
588
575

Abrasion resistance
100
102
110
103

index (index)

Comp.

Ex. 6
Ex. 7
Ex. 8
Ex. 7

phase (A) polymer NR-1
55
52
55
55

NR-2
—
—
—
—

phase (B) polymer BR
39
39
39
39

Block polymer BP-7
3
3
3
3

Polymer (α) α-1
—
—
—
—

α-2
3
6

α-3
—
—
3
—

α-4
—
—
—
3

Polymer (β) β-1
—
—
—
—

Compatibility

Block (a) ⇄ block (b)
No
No
No
No

Block (a) ⇄ phase (A)
Yes
Yes
Yes
Yes

polymer

Block (a) ⇄ phase (B)
No
No
No
No

polymer

Block (b) ⇄ phase (A)
No
No
No
No

polymer

Block (b) ⇄ phase (B)
Yes
Yes
Yes
Yes

polymer

Polymer (α) ⇄ block (a)
Yes
Yes
Yes
Yes

Polymer (α) ⇄ phase
Yes
Yes
Yes
Yes

(A) polymer

Polymer (β) ⇄ block (b)
—
—
—
—

Polymer (β) ⇄ phase (B)
—
—
—
—

polymer

Relation with molecular

weight

SA = Mw30 (A)/Mw (a)
2.2
2.2
2.2
2.2

SB = Mw30 (B)/Mw (b)
0.3
0.3
0.3
0.3

Sα = Mw (α)/Mw (a)
1
1
1.2
1.4

Sβ = Mw (β)/Mw (b)
—
—
—
—

Rate of polymers (α) and
100
200
100
100

(β) added/wt % (to block

polymer)

Physical properties of

rubber composition

Tensile strength (MPa)
29.7
28.5
28.8
28.4

Elongation (%)
585
588
577
562

Abrasion resistance
108
103
105
102

index (index)

Stand-

ard Ex.

Ex. 9
Ex. 10
6
Ex. 11
Ex. 12

phase (A) polymer NR-1
58
56
—
—
—

NR-2
—
—
60
58
57.4

phase (B) polymer BR
38
38
40
39
39

Block polymer BP-6
—
—
—
3
3

Block polymer BP-7
3
3
—
—
—

Polymer (α) α-1
—
—
—
—
—

α-2
—
2
—
—
0.6

α-3
—
—
—
—
—

α-4
—
—
—
—
—

Polymer (β) β-1
1
1
—
—
—

Compatibility

Block (a) ⇄ block (b)
No
No
—
No
No

Block (a) ⇄ phase (A)
Yes
Yes
—
Yes
Yes

polymer

Block (a) ⇄ phase (B)
No
No
—
No
No

polymer

Block (b) ⇄ phase (A)
No
No
—
No
No

polymer

Block (b) ⇄ phase (B)
Yes
Yes
—
Yes
Yes

polymer

Polymer (α) ⇄ block (a)
—
Yes
—
—
Yes

Polymer (α) ⇄ phase
—
Yes
—
—
Yes

(A) polymer

Polymer (β) ⇄ block (b)
Yes
Yes
—
—
—

Polymer (β) ⇄ phase (B)
Yes
Yes
—
—
—

polymer

Relation with molecular

weight

SA = Mw30 (A)/Mw (a)
2.2
2.2
—
0.9
0.9

SB = Mw30 (B)/Mw (b)
0.3
0.3
—
0.3
0.3

Sα = Mw (α)/Mw (a)
—
1.0
—
—
0.6

Sβ = Mw (β)/Mw (b)
0.3
0.3
—
—
—

Rate of polymers (α) and
33
100
—
—
20

(β) added/wt % (to block

polymer)

Physical properties of

rubber composition

Tensile strength (MPa)
28.4
30
26.8
27.7
29.8

Elongation (%)
570
590
520
566
602

Abrasion resistance
103
107
100
101
111

index (index)

[0074]

5

TABLE V

NR/SBR Blend Formulation (Parts by Weight)

Rubber component
100

Carbon black (N339)*1
50

Zinc white
3

Stearic acid
2

Antioxidant (6C)*2
3

Wax
2

Vulcanization accelerator (NS)*3
1

Sulfur
1.7

*1: Seast KH, made by Tokai Carbon Co.

*2: Santoflex 13, made by Flexis Co.

*3: Santocure NS, made by Flexis Co.

[0075]

6

TABLE VI

NR/BR Blend Formulation (Parts by Weight)

Rubber component
100

Carbon black (N110)*1
50

Zinc white
5

Stearic acid
2

Antioxidant (6C)*2
3

Vulcanization accelerator (NS)*3
1.2

Sulfur
1

*1: Diablack I (made by Mitsubishi Chemical)

*2: Santoflex 13 (made by Flexis Co.)

*3: Santocure NS (made by Flexis Co.)

[0076]

7

TABLE VII

Characteristics of Polymers Used as Phase (A)

and Phase (B)

Overall (MW)
30% (Mw)

NR-1*1
7.57 × 105
3.9 × 105

NR-2*2
1.19 × 106
2.6 × 105

NR-3*3
4.65 × 105
1.8 × 105

SBR*4
3.72 × 105
1.9 × 105

BR*5
3.51 × 105
1.1 × 105

(Note)

*1: Masticated natural rubber RSS #3. Masticated by 8-inch roll mill at 80° C. for 3 minutes.

*2: Notural rubber SMR-L

*3: Masticated natural rubber RSS #3. Masticated by 8-inch roll mill at 80° C. for 15 minutes.

*4: NS 114 (SBR made by Nippon Zeon)

*5: BR 1220 (BR made by Nippon Zeon)

[0077]

8

TABLE VIII

Characteristics of Block Polymer

Block (a)
Block (b)

Microstructure
Mw
Microstructure
Mw

BP-1
Polyisoprene
1.48 ×
SBR (St = 18 wt %,
1.61 ×

(cis/trans/vn =
105
Vn = 11 mol %)
105

77/16/7)

BP-2
Polyisoprene
1.52 ×
SBR (St = 18 wt %,
3.12 ×

(cis/trans/vn =
105
Vn = 11 mol %)
105

77/16/7)

BP-3
Polyisoprene
3.10 ×
SBR (St = 18 wt %,
3.21 ×

(cis/trans/vn =
105
Vn = 11 mol %)
105

77/16/7)

BP-4
Polyisoprene
1.51 ×
SBR (St = 19 wt %,
1.47 ×

(cis/trans/vn =
105
Vn = 46 mol %)
105

77/16/7)

BP-5
Polyisoprene
1.49 ×
SBR (St = 19 wt %,
3.22 ×

(cis/trans/vn =
105
Vn = 46 mol %)
105

77/16/7)

BP-6
Polyisoprene
3.01 ×
SBR (St = 19 wt %,
3.21 ×

(cis/trans/vn =
105
Vn = 46 mol %)
105

77/16/7)

BP-7
Polyisoprene
1.80 ×
SBR (St = 19 wt %,
3.22 ×

(cis/trans/vn =
105
Vn = 46 mol %)
105

77/16/7)

(Note) BP-1 to BP-7 were obtained by 2-stage polymerization by butyl lithium initiator in n-hexane solvent.

[0078]

9

TABLE IX

Characteristics of Polymers Used as

(α) and (β)

Microstructure
Mw

α-1
Polyisoprene (cis/trans/vn = 77/16/7)
1.2 × 105

α-2
Polyisoprene (cis/trans/vn = 77/16/7)
1.8 × 105

α-3
Polyisoprene (cis/trans/vn = 77/16/7)
2.2 × 105

α-4
Polyisoprene (cis/trans/vn = 77/16/7)
2.5 × 105

β-1
SBR (St = 19 wt %, Vn = 46 mol %)
1.0 × 105

(Notes) α-1 to α-4 and β-1 were obtained by polymerization in organic solvents using organometallic compounds as initiators.

[0079] The physical properties evaluated in the above Examples were measured by the following methods:

[0080] Tensile strength (Mpa): Measured according to JIS K6251.

[0081] Elongation (%): Measured according to JIS K6251.

[0082] Abrasion resistance test: Measured using a Lambourn abrasion tester at conditions of a slip rate of 25% and a load of 5 kg. The results are shown indexed to the formulation of the corresponding Standard Examples as 100 (abrasion resistance index). The larger the figure, the better the abrasion resistance shown.

[0083] Times to breakage in fatigue test: Shown by number of times to breakage of a JIS No. 3 dumbbell shaped sample after being given repeated deformation at a cycle rate of 400 rpm at an elongation stress of 100% (average for four tests).

[0084] The incompatibility of polymers was judged by the following method:

[0085] 1) The incompatibility of the polymer phases (A) and (B) of the polymer blend was judged by vulcanizing the polymer blend, preparing ultrathin slice samples by the freezing method, then dyeing these in a gas phase with a benzene solution of osmium tetraoxide at room temperature for about 15 hours. The presence of phase (a) separated structure was examined by observation through a transmission type electron microscope at magnifications of about 5000 to 10,000.

[0086] 2) The incompatibility of the blocks (a) and (b) of the block copolymer was judged by preparing samples in the same way as above from the block copolymer in the unvulcanized state, then observing them through a transmission type electron microscope at a magnification of about 60,000 to examine the presence of a phase separated structure.

[0087] 3) The incompatibility of the blocks of the block copolymer and the polymer phases of the polymer blend was judged by separating polymerizing and preparing the polymers corresponding to the polymers constituting the blocks, mixing these with the matrix polymers, vulcanizing them, then proceeding in the same way as above to prepare samples for observation through an electron microscope and observing these at magnifications of about 5000 to 10,000 to examine the presence of phase separated structures.

[0088] In addition, the compatibilities and incompatibilities may be decided by judging the presence of bimodal or not from the temperature dependence curve of tan δ or by judging the presence of plurality of glass transition temperatures or not of the blend polymers can be observed by DSC measurement and further may be judged by an optical microscope if the phase separated structure reaches as much as several dozen microns. Among these, the above direct observation by an electron microscope is the most sensitive method.

[0089] As explained above and as shown in Examples 1 to 12, the rubber compositions according to the present invention are improved in mechanical strength such as tensile strength, elongation, abrasion resistance, and fatigue resistance compared with the rubber compositions of Comparative Examples 1 to 7.

Number	Date	Country	Kind
11050710	Feb 1999	JP
2000-41396	Feb 2000	JP

	Number	Date	Country
Parent	09506443	Feb 2000	US
Child	10335922	Jan 2003	US

Rubber composition

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