JPS59204637A - Rubber composition for base tread - Google Patents

Abstract

PURPOSE:The titled composition having low Mooney viscosity, small die swell, improved processing properties, providing a vulcanized material with low heat build-up, containing a specific rubber reinforced composition, consisting of components in a specific ratio. CONSTITUTION:A composition consisting of (A) a rubber reinforced composition wherein 5-100pts.wt. fine thin short fibers of thermo-plastic polymer containing -CONH- group in the polymer chain and the polymer is grafted onto the rubber through a precondensate of phenol-formaldehyde resin at the interfaces of the fibers, (B) natural and/or polyisoprene, (C) diene rubber except the component B, and (D) 35-45pts.wt. carbon black based on 100pts.wt. total amounts of the rubber components in such a way that an amount of the polymer in the component A is 1-15pts.wt. based on 100pts.wt. total amounts of the rubber components, total amounts of the rubber in the components A and B are 100- 50wt% based on total rubber components, providing a vulcanized material having >=60% impact resilience ratio designated by BS903.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a comb composition for base pellets that has a small Mooney viscosity (M L ) and die swell, has excellent processability, and has a vulcanizate with low heat generation.

In general, tires are required to have excellent maneuverability, durability, etc., and in particular, from the viewpoint of safety, they are required to have excellent anti-scratch properties on wet road surfaces. In response to the recent social demand for resource conservation, efforts are being made to develop tires with low rolling resistance, that is, tires with low energy loss, in order to reduce dynamic losses in tires. The energy loss consumed in a free-rotating tire varies depending on the structure of the tire, etc., but approximately 1/2 of the total energy loss is consumed in the trend section. Therefore, if the internal consumption of tread rubber is reduced, the energy loss during tire rolling is reduced, and a tire with low rolling resistance can be obtained.

Therefore, attempts have been made to modify the tread rubber to reduce energy loss. However, such modification of rubber tends to reduce wet skid resistance.

Improving transfer resistance and improving wet skid resistance are generally contradictory matters.

In order to achieve both of these goals, various improvements have been made to the tire structure. As for the ingenuity.

One example is to make the tread two-layered, consisting of a cap tread and a base tread. That is, the tread is made of two layers: a cap tread with good wet skid properties and a paste tread with low energy loss, thereby increasing the single-control wet skid properties of the tire as a whole and reducing energy loss.

Rubber for Base Trend is required to have low heat build-up. As the low heat generation rubber, natural rubber, in-prene rubber, ci-s 1.4'-polybutadiene rubber may be used alone, or these rubbers may be blended with carbon black. In order to achieve low heat build-up, it is possible to use a carbon blank with a large particle diameter and to reduce the amount of carbon blank blended, but these methods lower the elastic modulus and fatigue resistance of the rubber.

On the other hand, there is a method to make rubber highly elastic by blending short fibers of nylon or vinylon, but these short fibers do not adhere well to the rubber, so breakage tends to progress along the interface of the short fibers, and repeated elongation is difficult. The disadvantage is that the fatigue life at the bottom is short.

When adopting the cap/base method for passenger car tires, there are manufacturing technology problems that are not seen in large tires. Since the tread gauge is thin, it must be carefully extruded from the extruder to avoid edge breakage and to ensure good dimensional stability. Also, since the cap trend rubber and base trend rubber have different die swells, care must be taken when extruding multiple layers. These problems will be solved if the die swell of Base Trend rubber becomes smaller. If a large amount of highly reinforcing carbon blank is blended, the die swell will become smaller, but the heat generation will increase, so the die swell and low heat generation will be reduced. A way to be satisfied at the same time is still being discovered.

As a result of extensive research aimed at obtaining a vulcanizate for base treads with low heat build-up and low Mooney viscosity and die swell, the authors have developed a specific rubber compound used in the present invention. The present invention has been completed based on the discovery that the above object can be achieved by blending a reinforced rubber composition and blending each component in a constant ratio of e %.

In other words, the present invention provides a thermoplastic resin having -♂-Ni (- group) in the polymer molecule in the vulcanizable rubber 100 part.
-1: 5 to 100 parts by weight of fine short fibers of polymer are (l
Reinforced rubber composition (A) in which the polymer and the rubber capable of adding 4Iji tjJ are grafted at the interface of the fibers via an initial condensate of a phenol formaldehyde resin, natural rubber, polyester, etc. isoprene or a mixture of both (B), natural rubber and diene rubber excluding polyisoprene (C), and carbon black (D), and satisfies the following conditions (1) to Ov). The present invention relates to a rubber composition for pasted treads.

(1) The thermoplastic polymer has a total of 10 rubber components.
1 to 15 parts by weight per 0 parts by weight.

(g) The proportion of rubber is such that the amount of gold between natural rubber or polyisoprene in component (A) and component (B) is 100 to 500.
0 to 50 parts by weight (iii) The amount of carbon blank is 35 to 45 parts by weight based on the total 100 parts by weight of the rubber components.

(1v) The vulcanized product of the composition has an impact modulus of 60 inches or more as defined in BS 903.

The rubber silk paraboloid for Pace Trend of this invention has a small Mooney viscosity MLl+4 (100°C), a swell ratio of 1.8 or less, and a vulcanizate ASTM D623 M
The heat generation ΔT according to ethod A is 25° C. or less, and the processability is excellent, and the vulcanizate has low heat generation.

In this invention, 5 to 100 parts by weight of fine staple fibers of a thermoplastic polymer having an -A-NH- group in the polymer molecule are superimposed on 100 parts of the vulcanizable rubber.

20 to 100 parts by weight of the good-sale material is embedded.

and) at the interface of the 11V fiber, the polymer and the vulcanizable rubber are the first J of the phenol formaldehyde resin.
It is necessary to blend a reinforcing rubber composition that is grafted via the υ1 condensate, and by doing so, it is possible to obtain a rubber composition that has excellent moldability despite the blending of polymer fibers. It is.

The vulcanizable rubbers mentioned above include natural rubber, cis-1,
4 polybutadiene, polyimprene, styrene-butadiene copolymer rubber, isoprene-isobutylene copolymer, and the like.

Among these rubbers, natural rubber is preferred.

The fine short fibers of the heat management polymer have a melting point of 19
Nylon 6, nylon 61, with a temperature of 0 to 235°C, a suitable temperature of 190 to 225°C, a particularly suitable temperature of 200 to 220°C.
0. Nylon 12. It is formed from polymer molecules such as nylon such as nylon 611 and nylon 612, polyurea such as polyhebutamethylene urea and polyundecamethylene urea, and polyurethane, or nylon, and has an average diameter of 0°05 to 0.8μ. It is embedded in vulcanizable rubber in the form of fine short fibers with seven circular cross sections, the shortest fiber length is preferably 1 μ or more, and molecules are arranged in the fiber axis direction.

Moreover, at the interface of the fibers mentioned above, the polymer? A thermoplastic polymer having a -CNH- group in its molecule and a vulcanizable rubber are grafted via an initial condensate of a formaldehyde resin.

The initial condensate of the phenol formaldehyde resin mentioned above may include an initial condensate of a resol type or novolac type phenol formaldehyde resin. Among these, an initial condensate of a novolak type phenol formaldehyde resin (hereinafter sometimes simply abbreviated as novolak) is preferred.

The above-mentioned novolac is a catalyst known per se.

For example, a soluble and fusible resin obtained by a condensation reaction of phenol such as phenol or bisphenols, 111, and formaldehyde (paraformaldehyde may also be used) using an acid such as sulfuric acid, hydrochloric acid, phosphoric acid, or sialic acid as a catalyst. It is a modified product (denatured product). 1 for example as novolak.

novolac type phenol formaldehyde initial condensate,
Novolac type lactam-bisphenol F-formaldehyde initial condensate, novolac type styrenated phenol-phenol-formaldehyde first condensate, etc. can be suitably used.

In the present invention, in the reinforced rubber composition used, a polymer embedded in a rubber that can be added (IAT) has a strong J structure of fine and short fibers of a thermoplastic polymer having 16NH groups in one molecule. At the interface of the short fibers, the thermoplastic polymer and the vulcanizable rubber are graft-bonded, preferably via a novolak.
Although the elastic modulus of the vulcanizate is high, the vulcanizate has low heat build-up, and it is possible to obtain a rubber silk parabolite for pace trends with low Mooney viscosity and small die swell.

In this invention, the proportion of fine short fibers of the thermoplastic polymer having -A-NH- groups in the polymer molecules grafted and embedded in the vulcanizable rubber is A reinforced rubber composition containing 5 to 100 parts by weight of said fibers per 100 parts by weight is used.

Particularly, in the present invention, vulcanizable rubber grafted to the thermoplastic polymer via a novolac applied to the interface of the fibers with respect to the weight of fine short fibers of the thermoplastic polymer embedded in the vulcanizable rubber. Weight percentage of rubber (vulcanizable rubber/fine short fibers of thermoplastic polymer)
The graft ratio represented by 3 to 25 weight ratio, especially 5 to 20
It is preferable that the thermoplastic polymer forming the fiber and the vulcanizable rubber are graft-bonded, preferably via a novolac, so as to have a weight ratio.

The reinforced rubber composition according to the present invention having the above-mentioned percentage characteristics is, for example, vulcanizable rubber and a weight per minute of 20,000.
A thermoplastic polymer having less than 0 -CNH- groups in the polymer molecule, and 90.2 to 5xi parts of novolac type phenol formaldehyde based on 100 parts by weight of the total amount of these rubbers and thermoplastic polymer. The condensate and the formaldehyde donor body are kneaded at a temperature above the melting point of the thermoplastic polymer and below 270°C, and the resulting kneaded product is kneaded □11.). When the proportion of rubber is 5 to 100 parts by weight of the polymer, the ratio of rubber and thermoplastic polymer in the mixed material is 18 parts by weight per 100 parts by weight of rubber. If the plastic polymer exceeds 5 parts by weight, add additional vulcanizable rubber to the mixer if necessary to provide 5 to 100 parts by weight of thermoplastic polymer per 100 parts by weight of total rubber. After further kneading at a temperature above the melting point of the thermoplastic polymer and below 270°C,
A 1L product can be produced by extruding at a temperature above the melting point of the thermoplastic polymer and below 270° C. and stretching the extrudate at a temperature below the melting point of the thermoplastic polymer.

As the formaldehyde donor, a compound that generates formaldehyde upon heating is used. For example, as a formaldehyde donor.

Hexamethylenetetramine, acetaldehyde ammonia: (CH3GHNH2)3+ parapolmaldehyde,
Examples include α-polyoxymethylene, polyvalent methylolmelamine derivatives, oxazolidine derivatives, polyvalent methylolated acetylene urea, and the like.

In said method, the novolak and formaldehyde donor described above are used, and the vulcanizable rubber, a thermoplastic polymer having 16NH groups in the polymer molecule, the novolak and the formaldehyde donor are mixed as described above. The vulcanizable rubber and the thermoplastic polymer are graft-bonded via the novolak, and the thermoplastic polymer is finely dispersed in the vulcanizable rubber (the particle size of the dispersed thermoplastic polymer is usually 1 to 2 μm). It is.

) can be uniformly dispersed.

In addition, in the above method, by stretching the extrudate, the thermoplastic polymer in the vulcanizable rubber of the resulting reinforced rubber composition undergoes molecular orientation of the fibers and converts into a fibrous structure, resulting in a fine structure with high strength. They become short fibers.

A reinforced rubber composition obtained by the above method.

Force 1Xe ′i′iT Egg rubber 5 per 100 parts
~100 parts by weight of a thermoplastic polymer having an -NH- group is contained in the polymer molecule, the thermoplastic polymer is fine short fibers, and the thermoplastic polymer and vulcanizable rubber are present at the interface of the fibers. are graft-bonded via novolac.

The rubber composition for Base Trend of the present invention comprises the above-mentioned reinforced rubber composition (A), a mixture of both natural rubber and polyimblene (B), a diene rubber excluding natural rubber and polyisoprene (C), and Carbon black (1
)).

Examples of the diene rubber (C) include cis-1,4 polybutadiene, styrene-butadiene copolymer rubber, isoprene-inbutylene copolymer, and the like.

Carbon black has a particle diameter of 90 mμ or less, dibutyl phthalate (DBP) oil absorption of 70 g/100
g or more is preferably used. Examples of carbon blanks include HAF, FF, FF, and F.

() Various carbon blacks such as PE, SAF, ISA, F', and SRF are used.

Each of the above components, (1) the thermoplastic polymer (short fiber);
The amount of (ti) rubber is 1 to 15 parts by weight, preferably 2 to 15 parts by weight, based on the total 190 parts by weight of the rubber components, and the proportion of (ti) rubber is the same as that of natural rubber or polyisoprene in component (A) and (B). ) The total amount of ingredients is 100 to 50it %
(iii) The amount of carbon blank is 35 to 45 parts by weight based on 100 parts by weight of the rubber component in total,
(iv) The vulcanized product of the composition has an impact modulus of 60 or more as defined in B5903. It is blended to satisfy each condition.

If the amount of the thermoplastic polymer is less than the lower limit, a rubber composition with a small Mooney viscosity and die swell and a high rebound modulus of the vulcanizate cannot be obtained, and if the amount of the thermoplastic polymer is more than the upper limit, the composition Mooney viscosity and dice swell tend to increase. When the blending ratio of natural rubber or polyisoprene is outside the above range, the heat generation properties of the vulcanizate tend to deteriorate. If the amount of carbon black is less than the lower limit, the rebound modulus of the vulcanizate will be small, and if the amount of carbon blank is more than the upper limit, the viscosity and die swell of the rubber composition will increase, causing heat generation of the vulcanizate. gender tends to worsen. Indeed, if the impact modulus of the vulcanizate is outside the above range, it is not suitable as a rubber composition for base treads.

The rubber composition of the present invention is produced by mixing the above-mentioned components using a kneading machine such as a Banbury mixer or a roll.
It can be obtained by kneading at ~180°C for about 1 to 60 minutes.

Additives such as a vulcanizing agent are blended into the rubber composition of the present invention.

Vulcanizing agents include known vulcanizing agents, such as sulfur.

Organic peroxidants, sulfur-containing compounds, etc. can be used. There are no particular restrictions on the method of blending the vulcanizing agent into the rubber composition, and any known blending method can be employed. Along with the vulcanizing agent, reinforcing agents such as white carbon, activated calcium carbonate, ultrafine magnesium silicate, istyrene resin, coumaron indene resin, phenolic resin, lignin, modified melamine resin, and 15 oil resins,
Fillers such as various grades of calcium carbonate, basic magnesium carbonate, clay, zinc white, diatomaceous earth, Heigo rubber, powdered rubber, ebonite powder, aldehydes, ammonias, aldehydes/amines, guanidines, thioureas, thiazoles vulcanization accelerators such as thiurams, dithiocarbamates, xanthates, vulcanization accelerators such as metal oxides and fatty acids, amines/aldehydes, amines/ketones, amines, phenols, imidazoles.

The composition can be prepared by adding sulfur-containing or sulfur-containing anti-aging agents, naphthene-based aromatic process oils, etc. within a range that does not impair the effects of the present invention.

In particular, it is preferable to mix 1 to 30 parts by weight of process oil with respect to 100 parts by weight of rubber in the rubber composition of the present invention.

The rubber composition for base treads of the present invention can be used in place of conventionally known rubber compositions for base treads.

It can be used together with other tire components (cap trends, sidewalls, chafers, rims, beads, etc.) as tire components for passenger cars, buses, trucks, airplanes, etc.

Examples and comparative examples are shown below. In the following description, "part" indicates "heavy" part.

if), Colx parabolic Tsumoney viscosity MLl+4
(100℃) is measured according to JTSK6300,
The swell ratio was determined using a capillary rheometer.
/ 1-]-2+I+, #I 71111. #I, tensile modulus of the vulcanizate measured at an extrusion temperature of 10 °C and a shear rate of 360 scc.

Tensile strength and hardness are determined according to J I 5K6301, and rebound modulus is determined according to B S 903 using a Danronop trip meter. 1 heat generation ΔT is determined according to ASTM D623 Met, bod.
Each was measured according to A.

Example] Natural rubber (NFL') 10 o Shin 1 (and N-
1.0 part of (3-methacryloylkagisi 2-hydroxypropyl)-1ri'-p-phenylenediamine (Tsunocran 2G-1, manufactured by Shinko Ouchi) was added.

After 1 minute of stranding, 6-nylon (product name: 103OB, manufactured by Ube Industries, Ltd., melting point 22: LC, molecular weight 30000)
50 parts were added and kneaded for 4 minutes. During this time, the temperature inside the mixer rose to 230'C and the 6-nylon melted.

Then, using oxalic acid as a catalyst, phenol and paraformaldehyde are combined to form a state with a softening point of 106°C and a water content of 0.12. Weight, free phenol content,
Novolac-type phenol, which is a powder crystal with a weight of 13
Add 2.25 parts of formaldehyde initial condensate (manufactured by Asoichi Kasei Co., Ltd., black market name 550PL), and after mixing for 7 minutes,
Add 0.225 parts of hexamethylenetetramine, 2.
Knead for 5 minutes (temperature inside Banbury during this time is 230℃)
°C) After the graft reaction, it was dumped. The obtained crosstalk was measured with a nozzle inner diameter of 2 mm and a ratio of length to inner diameter (L/
D) 20+runφ extruder with 2 circular dies (H
The extrudate was extruded into a string at a die setting temperature of 2-35°C using a die set at 2-35°C, and the extrudate was placed in a funnel located vertically below the nozzle. The supplied cooling water flows through the funnel and into a cooling water storage vessel located vertically below the funnel, from where it is returned to the funnel by means of pumps and pipes. ), then passed through a guide roll, and was wound onto a bobbin at a speed of 35 m7 with a draft ratio of 0. This rolled material was vacuum dried at room temperature for one day and night to remove adhering water.

Approximately 500 of these rolls are bundled into a sheet (2rn thick).
m , jll 15 Q rn,m ), and roll gap Q , 2 m, m and temperature 60
A reinforced rubber composition (masterbatch) (sample 1) was obtained by roll rolling to a size of about 10 times with a pair of rolling rolls at a temperature of 1°C.

The compounding ingredients shown in Table 2 except for the vulcanization accelerator and sulfur were kneaded in a Banbury at 90°C + and 77 rpm to obtain a kneaded product, which is a rubber composition for paste red. The mixture was kneaded with a sulfur accelerator and sulfur using a 10-inch roll, rolled out into a 7-piece shape, and then placed in a mold and vulcanized to obtain a vulcanized product.

Vulcanization was performed at 145°C for 40 minutes. The results are summarized in Tables 1 and 2.

The reinforced rubber composition 22 obtained in Example 1 was mixed with benzene 20
0yd at room temperature to dissolve the rubber component in the reinforced rubber composition 1, and the returned slurry was centrifuged at room temperature to separate into a solution portion and a precipitate portion. After repeating the above operation seven times for the precipitated portion, the precipitated portion was dried to obtain nylon fibers.

This nylon fiber was dissolved in a mixed solvent of phenol and orndichlorobenzene at a ratio of 1:3 (weight ratio) and analyzed by IH nuclear magnetic resonance spectroscopy (NMR) (internal standard: tetramethylsilane). A methyl group and a methylene group originating from natural rubber, a methylene group adjacent to an aO group originating from 6-nylon, and a methylene group adjacent to an NH group.

For each peak of the methylene group adjacent to the NH group and the other three methylene groups, 6-
The graft ratio was calculated by determining the molar ratio of nylon and natural rubber.

In addition, the shape of the nylon fiber described in AfI is approximately 200%.
The size of the book was determined using a scanning microscope at 10,000x magnification. -The secret fibers were extremely thin short fibers with a circular cross section. The results are shown in Table 1.

Example 2 141 parts of ε-caglolactam and purity 8'' as a novolac. 55.6 parts of paraformaldehyde and 120 parts of paraformaldehyde
The reaction was carried out at ℃ for 5 hours to obtain an addition reaction solution containing an addition reaction product of ε-caprolactam and formaldehyde. Novolak was gradually added dropwise to a mixture of 9-caprolactam-pormaldehyde adduct and bisphenol F to cause a condensation reaction. A reinforced rubber composition (sample 2) was obtained in the same manner as in Example 1, except that a type lactam-bisphenol F-formaldehyde initial condensate was used; A rubber composition for Base Trend was obtained. The results are summarized in Tables 1 and 2.

Example 3 As novolac, 1412 parts of phenol and concentration 35
1,041 parts of styrene was gradually added dropwise to a mixture of phenol and 40.3 parts of hydrochloric acid, and the mixture was mixed at 130°C for 2 hours to styrenate the phenol. 1. The reaction mixture was distilled under reduced pressure (180°C,
40 hours) to obtain styrenated phenol, and to the total amount of this styrenated phenol, 1426 parts of formalin and 4 parts of formalin were added.
Add 87 parts of 0% sodium hydroxide and heat at 80℃ for 5 minutes.
Formaldehyde is added (methylolation) to the styrenated phenol by mixing for a period of time, and the total amount of the addition reaction product is
Add 1653 parts of phenol and 123 parts of shiulic acid,
Styrenated phenol with a softening point of 73°C (ring and ball method) obtained by condensation reaction of methylolated styrenated phenol and phenol at 00°C for 2 hours and vacuum distillation (100→180°C, 40 light HP) from the reaction mixture. Example 1 except that a phenol-phenol-formaldehyde initial condensate was used.
A reinforced rubber composition (Sample 3) was obtained in the same manner as in Example 2, and a rubber composition for Base Trend was obtained in the same manner as in Example 2, except that this reinforced rubber composition was used. The results are summarized in Tables 1 and 2.

Example 4 A reinforced rubber composition (sample 4) was prepared in the same manner as in Example 1, except that the amount of 6-nylon added to the natural rubber was changed to 100.
This reinforced rubber composition was used to obtain a rubber composition for paste red having the formulation shown in Table 2. The results are summarized and shown in Tables 1 and 2.

Example 5 A reinforced rubber composition (Sample 5) was prepared in the same manner as in Example 1, except that the amount of 6-nylon added to the natural rubber was changed to 20 parts. A rubber composition for Base Trend having the formulation shown in the table was obtained. The results are summarized in Tables 1 and 2.

Examples 6 to 8 Other than changing the blending ratio of each component as shown in Table 2,
A rubber composition for Base Trend was obtained in the same manner as in Example 1. The results are summarized in Table 2.

Examples 9 to 12 Example 1 except that the type of carbon blank to be blended was changed
It was carried out in the same way. The results are summarized and shown in Table 2.

Comparative Example 1 A plate composition for Pace Trend was obtained in the same manner as in Example 1, except that the reinforcing rubber composition was not used and the proportions of each component were changed as shown in Table 2. The results are summarized in Table 2.

Table 1 Note that the fiber length of the nylon fibers embedded in each of the reinforced rubber compositions of Samples 1 to 5 is approximately 200μ or less (
(by calculation).

(IE]) on: Bolibutage 7 (UBEPO
L-BR100.

(Note 2) SBR: Styrene-butadiene copolymer rubber (FEB, T ('-1500, manufactured by Japan Synthetic Rubber Co., Ltd.) (Note 3) N-330 nide] A, F' , particle size 30
ml, DBP oil absorption 110 n+j! /100
'1fN-440: FF, /r 38 mμ,
rr 757d/100 fN-550:
FEF, /r 41mμ, /r 12
2 mA/100 fi'N-660:C, PF,,
o 84mμ, rt 81mA/10
0fN-770: SRF, II 71 mμ,
〃76 td/1001i' (Note 4) Other compounding agents: 3 parts, stearic acid: 2 parts.

Anti-aging agent N-phenyl-N'-improvir-p
- 1 part of phenylenediamine, 0.8 part of vulcanization accelerator N-oxy/diethylenebenzothiazyl-2-sulfenamide.

Sulfur 1.5 parts Patent applicant: Ube Industries, Ltd.

Claims (1)

[Claims] 100 parts by weight of vulcanizable rubber contains -N in the polymer molecule.
Fine shorts (,4Q
ljl, , 3 to 1.001 parts is embedded, and at the interface of the knee II, the polymer and the vulcanizable rubber are grafted via an initial condensate of a phenol formaldehyde resin. Reinforced rubber composition (
Δ), natural rubber, polyisoprene or a mixture of both (
B) A base trend comprising a diene rubber (C) excluding natural rubber and polyimprene, and carbon black (D>), and satisfying the following conditions (1) to Ov). Rubber composition for use. (1) The amount of the thermoplastic polymer is 10 in total of the rubber component.
The amount is 1 to 15 parts by weight relative to 0 parts by weight. (11) The proportion of rubber is (A) b The total amount of natural rubber or polyisoprene and (B) component per minute is 10'
0-50 weight section. (iiD The amount of carbon blank is the total amount of rubber components 1
Weight at 35-45 parts by weight to 00 parts by weight. (IV) The vulcanized product of the a acid has an impact modulus of 60% or more as defined in BS 903.