JP2006291034A - Asphalt composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an asphalt composition having high softening point, penetration rate, elongation and cohesive power and excellent processability. <P>SOLUTION: The asphalt composition contains 100 pts.wt. of asphalt and 0.5-25 pts.wt. of a block copolymer having an A-B-A structure composed of a vinyl aromatic hydrocarbon and a conjugated diene (B is conjugated diene block), having a vinyl aromatic hydrocarbon content [S] of 15-25 wt.% and a peak molecular weight [M] of 20-40 (unit: 10<SP>4</SP>), satisfying the formula 3[S]&le;[M]+40 and having a linear structure. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to an asphalt composition comprising a block copolymer of vinyl aromatic hydrocarbon and conjugated diene and asphalt.

Conventionally, asphalt compositions have been widely used in applications such as road pavement, waterproof sheets, sound insulation sheets, and roofing. At that time, many attempts have been made to improve the properties by adding various polymers to asphalt. Specific examples of the polymer include ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, rubber latex, block copolymer composed of conjugated diene and vinyl aromatic hydrocarbon (for example, Patent Documents 1 and 2). However, an asphalt composition in which an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer is added to asphalt is inferior in low-temperature characteristics, and is not preferable because cracks in winter occur. The elongation characteristics are also inferior, and therefore the caking strength (tenacity) is also inferior, and therefore the aggregate grasping characteristics are inferior. On the other hand, the asphalt composition to which a conventional block copolymer composed of a conjugated diene and a vinyl aromatic hydrocarbon is added is excellent in low-temperature characteristics, and has a characteristic such as excellent workability when made into a waterproof sheet with a low elastic modulus. However, the softening point, elongation, and cohesive force may be insufficient. For this reason, attempts have been made to improve by increasing the amount of addition of the block copolymer. When the addition amount is increased, the melt viscosity increases, and the workability of a waterproof sheet, road pavement, etc. is sacrificed. As described above, it is difficult for the asphalt composition to which each conventional polymer is added to satisfy simultaneously the high degree of softening point, penetration, elongation, cohesive force characteristics and processability required as its characteristics. It was.
Japanese Patent Publication No. 47-17319 JP-A-53-17618

  In order to solve the above-mentioned problems of the prior art, the present invention provides a softening point, penetration, elongation, and cohesive strength characteristics of an asphalt composition containing a block copolymer composed of a vinyl aromatic hydrocarbon and a conjugated diene and asphalt. In addition, intensive studies were conducted on improvement of workability. An object of the present invention is to provide an asphalt composition that is excellent in each of the above performances even if the amount of the block copolymer added to the asphalt is reduced.

In order to solve the above problems, the present inventors include an asphalt composition comprising 0.5 to 25 parts by weight of the following block copolymer (a) and 100 parts by weight of asphalt (b). The present inventors have found that the softening point, penetration, elongation, and cohesive force characteristics are high, and that the processability is excellent, and the present invention has been made.
In other words, the present invention
The block copolymer (a) comprises a polymer block mainly composed of at least two vinyl aromatic hydrocarbons and a polymer block mainly composed of at least one conjugated diene, and has the following characteristics (1) to (5): Is a block copolymer.
(1) The vinyl aromatic hydrocarbon content [S] is 15 to 25% by weight,
(2) The peak molecular weight [M] is 200 to 400,000
(3) The relation between the content [S] of the vinyl aromatic hydrocarbon and the peak molecular weight [M] (unit: 10,000) of the block copolymer is 3 [S] ≦ [M] +40
And
(4) A block copolymer having a linear structure.
That is, the block copolymer of the present invention is an asphalt composition that has high softening point, penetration, elongation, cohesive strength characteristics and excellent workability even when added in a smaller amount than conventional block copolymers.

  The asphalt composition of the present invention is excellent in each characteristic balance of softening point, penetration, elongation, cohesive force and processability. And even when a low amount of block copolymer is contained, an asphalt composition having a remarkably high softening point can be obtained, so that it is possible to reduce the use of expensive block copolymers and at the same time melt Since the viscosity does not increase, the processability is excellent. Furthermore, the time for kneading with asphalt can be shortened.

The present invention will be specifically described below.
The block copolymer (a) used in the present invention is a block copolymer comprising a vinyl aromatic hydrocarbon and a conjugated diene.
The vinyl aromatic hydrocarbon content [S] in the block copolymer (a) used in the present invention is 15% by weight or more and 25% by weight or less based on the block copolymer. Since the content of the vinyl aromatic hydrocarbon in the block copolymer is in the above range, an asphalt composition excellent in each characteristic balance of softening point, penetration, elongation, cohesive force and workability can be obtained. From the viewpoint of balance such as softening point, penetration, elongation, cohesive force and workability, the content of vinyl aromatic hydrocarbon is preferably 17% by weight or more and 23% by weight or less.

The peak molecular weight [M] of the block copolymer (a) used in the present invention is 200,000 or more and 400,000 or less. When the peak molecular weight of the block copolymer is within the above range, an asphalt composition having good asphalt characteristics such as a softening point and excellent workability can be obtained even if the addition amount of the block copolymer is reduced. In view of the balance between asphalt characteristics and processability, the peak molecular weight of the block copolymer used in the present invention is preferably 220,000 or more and 350,000 or less.
In the present invention, the relationship between the vinyl aromatic hydrocarbon content [S] in the block copolymer (a) and the peak molecular weight [M] of the block copolymer (a) is 3 [S] ≦ [M] +40. It is. As the vinyl aromatic hydrocarbon content and peak molecular weight of the block copolymer are in the above ranges, the asphalt characteristics such as softening point and cohesive force are good.

The structure of the block copolymer (a) used in the present invention is a linear structure. Since the structure of the block copolymer is linear, an asphalt composition having an excellent balance of properties of softening point, penetration, elongation, cohesive force and processability can be obtained.
The viscosity of the block copolymer (a) used in the present invention is 12,000 poise or less when the shear rate ω = 1.22 × 10 ³ (sec ⁻¹ ) and the melting temperature is 180 ° C. Since the viscosity of the block copolymer is in the above range, an asphalt composition having excellent processability can be obtained.
The peak molecular weight of the block copolymer is determined by gel permeation chromatography (GPC) using a calibration curve obtained for a commercially available standard monodisperse polystyrene having a known molecular weight.

In the present invention, a linear block copolymer in which the polymer structure of the block copolymer is represented by the following general formula can be used.
(A-B) _n , A- (B-A) _n , B- (A-B) _m
(In the above formula, A is a polymer block mainly composed of vinyl aromatic hydrocarbons, and B is a polymer block mainly composed of conjugated dienes. The boundary between the A block and the B block is not always clearly distinguished. Also, n is 1 or more and m is an integer of 2 or more.) Among these, the A-B-A structure has each of softening point, penetration, elongation, cohesive force and workability. It is particularly preferable because of its excellent characteristic balance.

Examples of the vinyl aromatic hydrocarbon used in the present invention include styrene, o-methyl styrene, ρ-methyl styrene, α-methyl styrene, and styrene is particularly common. These may be used alone or in combination of two or more.
A conjugated diene is a diolefin having a pair of conjugated double bonds. Examples of conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene (ie, isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1, Examples include 3-pentadiene and 1,3-hexadiene. Of these, 1,3-butadiene and isoprene are particularly preferred. These may be used alone or in combination of two or more.

  There is no limitation in particular about the manufacturing method of the block copolymer used by this invention, A well-known method can be used. For example, it can be produced by anionic living polymerization using a polymerization initiator such as an organic alkali metal compound in a hydrocarbon solvent. Examples of hydrocarbon solvents include aliphatic hydrocarbons such as n-butane, isobutane, n-pentane, n-hexane, n-heptane, n-octane, alicyclic such as cyclohexane, cycloheptane, and methylcycloheptane Examples include hydrocarbons and aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene.

  Examples of the polymerization initiator include aliphatic hydrocarbon alkali metal compounds, aromatic hydrocarbon alkali metal compounds, and organic aminoalkali metal compounds having anionic polymerization activity with respect to vinyl aromatic compounds and conjugated diene compounds. Examples of the alkali metal include lithium, sodium, and potassium. Suitable organic alkali metal compounds are aliphatic and aromatic hydrocarbon lithium compounds having 1 to 20 carbon atoms, and compounds containing one lithium in one molecule (monolithium compounds, dilithium compounds, trilithium compounds, Tetralithium compounds). Specifically, n-propyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, n-pentyllithium, n-hexyllithium, benzyllithium, phenyllithium, tolyllithium, diisopropenylbenzene and sec- A reaction product of butyllithium, a reaction product of divinylbenzene, sec-butyllithium and a small amount of 1,3-butadiene can be used. Furthermore, organolithium metal compounds disclosed in US Pat. No. 5,708,092, British Patent 2,241,239, US Pat. No. 5,527,753 and the like can also be used.

In the present invention, when an organic alkali metal compound is used as a polymerization initiator and a vinyl aromatic compound and a conjugated diene compound are copolymerized, a vinyl bond (1, 2 or 3, 4 bond) resulting from the conjugated diene compound incorporated in the polymer A tertiary amine compound or an ether compound can be added as an adjusting agent in order to adjust the content of and to adjust the random copolymerizability between the conjugated diene compound and the vinyl aromatic compound.
The tertiary amine compound is a compound of the general formula R1R2R3N (wherein R1, R2, and R3 are hydrocarbon groups having 1 to 20 carbon atoms or a tertiary amino group). For example, trimethylamine, triethylamine, tributylamine, N, N-dimethylaniline, N-ethylpiperidine, N-methylpyrrolidine, N, N, N ′, N′-tetramethylethylenediamine, N, N, N ′, N′— Tetraethylethylenediamine, 1,2-dipiperidinoethane, trimethylaminoethylpiperazine, N, N, N ′, N ″, N ″ -pentamethylethylenetriamine, N, N′-dioctyl-p-phenylenediamine and the like It is done.

  Examples of ether compounds include linear ether compounds and cyclic ether compounds. Examples of linear ether compounds include dimethyl ether, diethyl ether, diphenyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether and other ethylene glycol dialkyl ether compounds, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether And dialkyl ether compounds of diethylene glycol. Cyclic ether compounds include tetrahydrofuran, dioxane, 2,5-dimethyloxolane, 2,2,5,5-tetramethyloxolane, 2,2-bis (2-oxolanyl) propane, and alkyl ethers of furfuryl alcohol. Etc.

  In the present invention, the method of copolymerizing a vinyl aromatic compound and a conjugated diene compound using an organic alkali metal compound as a polymerization initiator may be batch polymerization, continuous polymerization, or a combination thereof. The polymerization temperature is usually 0 to 180 ° C, preferably 30 to 150 ° C. The time required for the polymerization varies depending on other conditions, but is usually within 48 hours, particularly preferably 0.1 to 10 hours. The polymerization atmosphere is preferably an inert gas atmosphere such as nitrogen gas. The polymerization pressure is not particularly limited as long as it is within a range sufficient to maintain the monomer and solvent in a liquid phase within the above polymerization temperature range. Furthermore, care must be taken so that impurities (water, oxygen, carbon dioxide, etc.) that inactivate the catalyst and living polymer do not enter the polymerization system.

In the present invention, a coupling reaction can be performed by adding a necessary amount of a bifunctional coupling agent at the end of the polymerization. Any known bifunctional coupling agent may be used and is not particularly limited. Examples thereof include dihalogen compounds such as dimethyldichlorosilane and dimethyldibromosilane, and acid esters such as methyl benzoate, ethyl benzoate, phenyl benzoate, and phthalates.
The block copolymer solution obtained as described above can remove the catalyst difference as needed, and can separate the block polymer from the solution. Solvent separation methods include, for example, a method in which a polar solvent that is a poor solvent for a block copolymer such as acetone or alcohol is added to the block copolymer solution to precipitate and recover the polymer, and a solution of the block copolymer is used. Examples thereof include a method in which the mixture is poured into hot water with stirring and the solvent is removed by steam stripping, or a method in which the solvent is distilled off by directly heating the block copolymer solution. In addition, stabilizers, such as various phenol type stabilizers, phosphorus type stabilizers, sulfur type stabilizers, and amine type stabilizers, can be added to the block copolymer of the present invention.

  Next, the asphalt of the component (b) used in the present invention is a by-product (petroleum asphalt) during petroleum refining. Or the thing obtained as a natural product (natural asphalt) or the thing which mixed these and petroleum etc. can be mentioned, The main component is what is called bitumen (bitumen). Specifically, straight asphalt, semi-blown asphalt, blown asphalt, tar, pitch, cutback asphalt added with oil, asphalt emulsion, and the like can be used. These may be mixed and used. The asphalt preferable in the present invention is straight asphalt having a penetration of 30 to 300, preferably 40 to 200, more preferably 45 to 150. In the asphalt composition of the present invention, the blending ratio of the block copolymer is 0.5 to 25 parts by weight, preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight with respect to 100 parts by weight of asphalt. .

  In this invention, arbitrary additives can be mix | blended as needed. For example, inorganic fillers such as calcium carbonate, magnesium carbonate, talc, silica, alumina, titanium oxide, glass fiber and glass beads, organic reinforcing agents such as organic fiber and coumarone indene resin, organic peroxides, inorganic peroxides, etc. Crosslinkers, titanium white, carbon black, pigments such as carbon black, iron oxide, dyes, flame retardants, antioxidants, UV absorbers, antistatic agents, lubricants, paraffinic process oils, naphthenic process oils, aromatic process oils, Softeners / plasticizers such as paraffin, organic polysiloxane, mineral oil, tackifying resins such as coumarone indene resin and terpene resin, polyolefin resins such as atactic polypropylene and ethylene-ethyl acrylate copolymer, low molecular weight vinyl Aromatic thermoplastic resin, natural rubber, polyisopropylene Rubber, ethylene-propylene rubber, chloroprene rubber, acrylic rubber, isoprene-isobutylene rubber, and styrene-butadiene block copolymers or hydrogenated products thereof other than the present invention, styrene-isoprene block copolymers or hydrogenated products thereof Synthetic rubbers such as sulfur, vulcanizing agents such as sulfur, vulcanization aids, other extenders, or mixtures thereof. In particular, when the asphalt composition of the present invention is used for road paving, it is usually used by mixing with minerals such as crushed stone, sand, slag and the like.

The method for mixing the asphalt composition of the present invention is not particularly limited, and it is prepared by heating and kneading with, for example, the above-mentioned various additives, for example, with a hot melting kettle, a kneader, a Banbury mixer, an extruder or the like. However, it is preferably carried out at a temperature of 160 to 200 ° C. (usually around 180 ° C.), and the stirring time is preferably 30 minutes to 6 hours, more preferably 2 to 3 hours. The stirring speed may be selected as appropriate depending on the apparatus to be used, but is usually 100 to 8,000 rpm.
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

In Examples and Comparative Examples, the properties of the block copolymer and the physical properties of the asphalt composition were measured as follows.
1. Various copolymers 1-1) Styrene content The styrene content was measured using an ultraviolet spectrophotometer (UV-2450, manufactured by Shimadzu Corporation).
1-2) Peak molecular weight The peak molecular weight was measured by GPC [apparatus, manufactured by Shimadzu Corporation], tetrahydrofuran was used as a solvent, and measurement conditions were performed at a temperature of 40 ° C. The peak molecular weight was determined using a calibration curve (created using the peak molecular weight of standard polystyrene) determined from measurement of commercially available standard polystyrene.
1-3) Viscosity The viscosity of the block copolymer is measured with a capillograph [device is Toyo Seiki Seisakusho Co., Ltd.], and the measurement conditions are shear rate ω = 1.22 × 10 ³ (sec ⁻¹ ), temperature 180. Performed at ° C.

2. Creation of block copolymer <Polymer 1>
Copolymerization was carried out by the following method using a stirrer having an internal volume of 10 L and a tank reactor with jacket.
After the reactor was sufficiently purged with nitrogen, 7000 cc of cyclohexane, 1.0 g of tetrahydrofuran, and 105 g of styrene as a monomer were charged into the reactor and adjusted to a temperature of 60 ° C., and then an n-butyllithium cyclohexane solution (7.2 g in pure content) was added. The styrene polymerization was started by addition. After the styrene was completely polymerized, 790 g of butadiene (1,3-butadiene) was continuously fed to the reactor at a constant rate over about 150 seconds, and the polymerization was continued. After the butadiene is completely polymerized, 105 g of styrene is further added as a monomer, methanol is added after completion of the reaction of styrene, and then octadecyl-3- (3,5-di-t-butyl-4- is used as a stabilizer. Hydroxyphenyl) propionate was added in an amount of 0.3% by weight based on the weight of the polymer to obtain a block copolymer (hereinafter referred to as polymer 1). Polymer 1 had a styrene content of 21% and a peak molecular weight of 340,000.

<Polymer 2>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. Other than changing the supply amount of n-butyllithium to 0.82 g, styrene supplied to the first stage to 110 g, butadiene supplied to the second stage to 780 g, and styrene supplied to the third stage to 110 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 2) had a styrene content of 22% and a peak molecular weight of 300,000.
<Polymer 3>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. Other than changing the supply amount of n-butyllithium to 0.81 g, changing styrene supplied to the first stage to 105 g, butadiene supplied to the second stage to 790 g, and styrene supplied to the third stage to 105 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 3) had a styrene content of 21% and a peak molecular weight of 250,000.

<Polymer 4>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. Other than changing the supply amount of n-butyllithium to 0.84 g, changing styrene supplied to the first stage to 90 g, butadiene supplied to the second stage to 820 g, and styrene supplied to the third stage to 90 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 4) had a styrene content of 18% and a peak molecular weight of 290,000.
<Polymer 5>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. Other than changing the supply amount of n-butyllithium to 0.92 g, styrene supplied to the first stage to 80 g, butadiene supplied to the second stage to 840 g, and styrene supplied to the third stage to 80 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 5) had a styrene content of 16% and a peak molecular weight of 210,000.

<Polymer 6>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. Other than changing the supply amount of n-butyllithium to 0.75 g, changing styrene supplied to the first stage to 120 g, butadiene supplied to the second stage to 760 g, and styrene supplied to the third stage to 120 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 6) had a styrene content of 24% and a peak molecular weight of 480,000.
<Polymer 7>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. Other than changing the supply amount of n-butyllithium to 0.82 g, changing styrene supplied to the first stage to 130 g, butadiene supplied to the second stage to 740 g, and styrene supplied to the third stage to 130 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 7) had a styrene content of 26% and a peak molecular weight of 280,000.

<Polymer 8>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. The supply amount of n-butyllithium is changed to 0.83 g, styrene supplied to the first stage is changed to 105 g, butadiene supplied to the second stage is changed to 790 g, and styrene supplied to the third stage is changed to 105 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 8) had a styrene content of 21% and a peak molecular weight of 220,000.
<Polymer 9>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. The supply amount of n-butyllithium is changed to 0.83 g, styrene supplied to the first stage is changed to 70 g, butadiene supplied to the second stage is changed to 860 g, and styrene supplied to the third stage is changed to 70 g. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 9) had a styrene content of 14% and a peak molecular weight of 300,000.
<Polymer 10>
The amount of monomers and the like supplied to the reactor was changed, and a copolymer was obtained in the same manner as in Polymer 1. Other than changing the supply amount of n-butyllithium to 0.91 g, 90 g of styrene supplied to the first stage, 820 g of butadiene supplied to the second stage, and 90 g of styrene supplied to the third stage. Polymerization was carried out in the same manner. The resulting block copolymer (hereinafter referred to as polymer 10) had a styrene content of 18% and a peak molecular weight of 180,000.

3. Preparation of Asphalt Composition In Examples 1-5 and Comparative Examples 6-10, asphalt compositions were produced in the following manner. 500 g of straight asphalt 60-80 [manufactured by Shin Nippon Oil Co., Ltd.] was put into a 750 ml metal can, and the metal can was sufficiently immersed in an oil bath at 180 ° C. Next, a predetermined amount of the hydrogenated diene copolymer was charged into the molten asphalt little by little while stirring. After complete charging, the asphalt composition was prepared by stirring for 90 minutes at a rotational speed of 5000 rpm.

4). Characteristics of asphalt composition 4-1) Softening point (ring and ball method)
The softening point of the composition was measured according to JIS-K 2207. When a sample is packed in a specified ring, supported horizontally in water, a 3.5 g sphere is placed in the center of the sample, and the liquid temperature is increased at a rate of 5 ° C / min, the sample is circulated by the weight of the sphere. The temperature when touching the bottom plate of the table was measured.
4-2) Melt viscosity Measured with a Brookfield viscometer at 180 ° C.
4-3) Degree of penetration According to JIS-K 2207, the length of the prescribed needle entering the sample kept at 25 ° C. in a constant temperature water bath for 5 seconds was measured.
4-4) Elongation According to JIS-K 2207, after pouring a sample into a form and making it into a specified shape, keeping it at 15 ° C. in a constant temperature water bath, and then pulling the sample at a rate of 5 cm / min, The distance stretched before the sample was cut was measured.
4-5) Toughness, Tenacity In accordance with the method stipulated by the Japan Road Association, the surface of a metal hemisphere with a diameter of 2 cm is turned down and buried in an asphalt sample in an aluminum container with a diameter of 5 cm and a depth of 2.7 cm, and a temperature of 25 ° C. When the sample was pulled out at a speed of 50 cm / min, the load applied to the hemisphere was recorded on the vertical axis, and the displacement was recorded on the horizontal axis.

[Examples 1 to 5, Comparative Examples 6 to 10]
Polymers 1 to 10 were used as the block copolymer, and the addition amount of the block copolymer was set to 3.5% to obtain an asphalt composition. The characteristics are shown in Table 1.

  The asphalt composition of the present invention can be used in the fields of road pavement, roofing / waterproof sheet, and sealant, and has a remarkably high softening point, elongation, and cohesive strength even when a low amount of block copolymer is contained. Since an asphalt composition having excellent processability is obtained, it can be suitably used particularly in the field of road paving.

Claims (3)

An asphalt composition comprising 0.5 to 25 parts by weight of a block copolymer of vinyl aromatic hydrocarbon and conjugated diene (a) and 100 parts by weight of asphalt (b), wherein the component (a) comprises at least two components A block copolymer comprising a polymer block mainly composed of vinyl aromatic hydrocarbons and a polymer block mainly composed of at least one conjugated diene, and having the following characteristics (1) to (4).
(1) The vinyl aromatic hydrocarbon content [S] is 15 to 25% by weight,
(2) The peak molecular weight [M] is 200 to 400,000
(3) The relation between the content [S] of the vinyl aromatic hydrocarbon and the peak molecular weight [M] (unit: 10,000) of the block copolymer is 3 [S] ≦ [M] +40
And
(4) A block copolymer having a linear structure. The asphalt composition according to claim 1, wherein the viscosity of the component (a) is 12,000 poise or less at a shear rate ω = 1.22 x 10 ³ (sec ^-1 ) and a melting temperature of 180 ° C. object. The asphalt composition according to claim 1 or 2, wherein the component (a) is a block copolymer having the following polymer structure.
A-B-A
(However, A is a polymer block mainly composed of vinyl aromatic hydrocarbons, and B is a polymer block mainly composed of conjugated dienes.)