This invention relates to a bitumen composition suitable for road paving, waterproofing materials, adhesives and the like. In particular, it relates to a bitumen composition ideal for improving stability and strength, and a method of manufacture thereof as well as an asphalt composition comprising the bitumen composition.

Bitumen has hitherto been used in a wide variety of fields such as road paving and waterproofing. Styrene- butadiene-styrene block copolymers (SES) have generally been used as a reinforcing material for the bitumen. However, the stability of the SBS decreases when it is dispersed in the bitumen, and in particular/ at the storage temperatures applicable during commercial uses lot the order of 150 to 1.80ºC), the bitumen and SBS separate readily, so that there have been problems with the SBS floating up.

For this reason, there have, in the past, been proposals, when mixing in S3Ξ to reinforce the bitumen, to use, for example, sulphur, polyoxyethylene nonylphenol, peroxides, carbon black or aromatic-based oils as α stabiliser to stabilise the SBS in the bitumen.

However, when sulphur is added as a stabiliser there is an accompanying risk of the generation of hydrogen sulphide, and the use of polyoxyethylene nonylphenol should be avoided for reasons to do with environmental hormones {see Japanese Laid-open Patent 2O00-S3865) . Furthermore, organic peroxides carry the risk of decomposition and explosion when handled at high temperatures, and carbon black is expensive compared to bitumen, so that in practice it becomes prohibitive to supply the bitumen products to the market (see Japanese Laid-σpen Patent H10-237309) . The addition of aromatic- based oils can also improve stability by dissolving the styrene blocks in the SBS, but then Lhe improvement in elasticity which can be made manifest only through the presence of the styrene blocks can no longer be expected, and there are therefore problems in that it is difficult to obtain the expected strength in the bitumen products. There is a need for a technology to further improve both stability and strength of bitumen compositions. This invention intends to overcome the deficiencies in the prior art bitumen compositions, methods of manufacture thereof and asphalt compositions comprising such bitumen compositions. In particular, the aim of the present invention is to offer a bitumen composition suitable for road paving, waterproofing materials, adhesives and the like, and especially, a bitumen composition capable of improving stability and strength, and also a method of manufacture thereof as well as an asphalt composition comprising the bitumen composition. Accordingly, the present invention provides a bitumen composition characterised in that it contains 2 to less than 8% by weight of a styrene-butadiene-styrene block copolymer (SBS) and 0.3 to 3% by weight of a polycyclic diterpene comprising one or more carboxyl groups and having in its molecular formula 20 carbon atoms, and the remaining portion comprising bitumen. According to a further aspect, the present invention provides a method for manufacture of a bitumen composition characterised in that 2 to 8% by weight of styrene-butadiene-styrene block copolymer (SBS) and 0.3 to 3% by weight of a poiycyclic diterpene comprising one or more carboxyl groups and having in its molecular formula 20 carbon atoms, are mixed in bitumen at a temperature in the range of from 190 to 210°C.

According to a further aspect, the present invention provides an asphalt composition comprising a bitumen composition as described herein and filler and/or aggregate.

According to a further aspect, the present invention provides a method for manufacture of an asphalt composition characterised in that 2 to 8% by weight of styrene-butadiene-styrene block copolymer (SBS) and 0.3 to 3% by weight of a poiycyclic diterpene comprising one or more carboxyl groups and having in its molecular formula 20 carbon atoms, are mixed with bitumen and aggregate or filler at a temperature in -he range of from 190 to 210ºC.

Preferably, the poiycyclic diterpene is a rosin containing any one or more of abietic acid, dehydroabietic acid, neoabietic acid, pirr.aric acid, isopimaric acid and palustri.c acid.

Preferably, the bitumen composition contains 0.3 to 1% by weight of the poiycyclic diterpene.

Preferably, the bitumen composition comprises bitumen that contains not more than 5% by weight relative to the total weight of said bitumen composition of an aromatic- based oil. More preferably, the bitumen composition comprises bitumen that contains not more than 5% by weight relative to the total weight of said bitumen composition of an aromatic-based oil, wherein the aromatic-based oil is an extract obtained by solvent extraction of a solvent deasphalted oil obtained by deasphalting a vacuum distillation residual oil from a crude oil.

The bitumen composition of the present invention improves both storage stability by making the softening point difference between the top part and the bottom part of a container in a storage test not more than 3°C, and at the same time improves strength by making the DS value not less than 6000 (rotations/mm) , this value being a criterion for anti-rutting performance in road paving. The bitumen composition; the method of manufacture thereof; and the asphalt composition are described in detail below by way of preferred embodiments of the invention.

The inventor has carried out intensive tests and research in order to overcome the above-mentioned problems and to manufacture bitumen compositions in such manner that they can exhibit the desired stability and strength. As a result, the inventor has discovered that, by adding a styrene-butadiene-styrene block copolymer (SBS) and a polycyclic diterpene comprising one or more carboxyl groups and having in its molecular formula 20 carbon atoms (resin acid) to bitumen with specified ranges of percentage by weight, it is possible to exhibit stability without the bitumen and SBS separating, and also that it is possible further to improve the strength of the bitumen composition itself. In more specific terns, and without wishing to be bound to a particular theory, it would appear that it is possible to bond the polycyclic diterpene onto the double bonds forming the butadiene blocks, by mixing the SBS with a resin acid, and that it is possible as a result to resolve the fact that styrene blocks agglomerate, so thai it is possible further to improve the stability of the bitumen's own composition ultimately obtained by application of this invention (referred to below as the bitumen composition of this invention) .

The styrene-butadiene-styrene block copolymer (SBS) is a so-called thermoplastic elastomer added to the bitumen. SBS is commercially available and is typically prepared by anionic polymerisation of styrene to form a first polymer block; continued anionic polymerisation but now with butadiene to form a second polymer block and either (i) coupling the thus formed living styrene- butadiene block copolymer with a coupling agent x to form a block copolymer of structure S-B-x-B-S, or (ii) continued anionic polymerisation with styrene to form a second styrene block. It will be appreciated that both methods of manufacture produce a styrene-butadiene- styrene block copolymer and for the purposes of this invention whenever reference is made to a styrene- butadiene-styrene block copolymer, this explicitly includes those block copolymers that have been manufactured using a coupling agent.

With this SBS the reduction in physical strength, chiefly the storage shear modulus of elasticity and kinetic viscosity, due to decomposition at the bitumen manufacturing temperature and the temperature of use and the processing temperature (of the order of 150 to 21OºC) is small, and it is a cheaper elastomer than the hydrogenated thermoplastic elastomers mentioned below. The SBS has a chemical structure in which a butadiene block is sandwiched between styrene blocks, and by attaching a polycyclic diterpene (resin acid) of carbon number 20 and having carboxyl groups to the double bonds forming this butadiene block, it becomes possible to improve the stability of the SBS in the bitumen composition, that is its tendency not to separate and float up, and ils performance.

In this invention, the properties and characteristics of the bitumen composition of this invention are optimally controlled by regulating the mixing ratio of the SBS that is to be mixed with the bitumen.

Bitumen is a material in which there is a very large variation in physical properties depending on temperature changes. In other words, bitumen is a material with a large susceptibility to temperature. Because of this, when moulding materials zo be used at normal temperatures, it is heated to approximately 100 to 200ºC and so nelted and rendered into fluid form, by which means it is possible to mould it into any shape. However, even when using bitumen at normal temperatures, the temperature of use varies according to the place of use and the season, and so the properties of the bitumen may vary and the specified performance may not be achieved.

With the bitumen comoosition of this invention, therefore, it is so arranged that SBS, which has a smaller variation in physical properties due to temperature changes than bitumen, that is it has a smaller temperature susceptibility, is added to and mixed with the bitumen to reduce the temperature susceptibility of the bitumen. Furthermore, in this invention the SBS is added and mixed in also from the standpoint of improving physical strength, because the SBS has a larger modulus of elasticity than bitumen at normal temperatures.

However, if the amount of SBS incorporated per the total weight of the bitumen composition of this invention is less than 2% by weight, in practice the degree of improvement in temperature susceptibility and enhancement of physical strength is inadequate, and problems will arise in that it is not possible to improve the temperature dependence of the bitumen's properties and characteristics, and it becomes difficult to obtain suitable properties and characteristics over a wide range of temperatures. On the other hand, if the amount of SBS incorporated exceeds 8% by weight, the viscosity of the bitumen composition ultimately obtained becomes too large, and this will also cause a considerable deterioration in workability when using it for paving roads. Also, if the amount of SBS incorporated exceeds 8% by weight, the thermal stability and the storage stability of the bitumen composition ultimately obtained deteriorate and it becomes difficult to obtain a uniform composition. For these reasons, the amount of SBS incorporated is made 2 to 8% by weight.

A polycyclic diterpene comprising one or more carboxyl groups and having in its molecular formula 20 carbon atoms (resin acid) is incorporated, for example abietic acid, dehydroabietic acid, neoabietic acid, pimaric acid, isopimaric acid or palustric acid, but it is not limited to these. Any resin acid that falls under the definition of being a polycyclic diterpene comprising one or more carboxyl groups and having in i.ts molecular formula 20 carbon atoms may be incorporated. These polycyclic diterpenes are generally contained in rosins.

For rosins here it is possible to use gum rosins, wood rosins, tall oil rosins and so on. Depending on differences in place of origin, raw material and method of extraction, these rosins can be classified as gum rosins, wood rosins and so on. Rosins may be obtained as the residual component of steam distillation of pine resin. Rosin is typically a mixture of abietic acid, palustric acid, neoabietic acid, dehydroabietic acid, pimaric acid, sandaracopimaric acid, isopimaric acid, and so on. The rosin normally softens at about 80ºC and melts at 90 to 100ºC. Various resin acids such as abietic acid, dehydroabietic acid, dihydroabiettc acid, tetrahydroabietic acid, palustric acid, neoabietic acid and laevopimarj c acid are contained within the rosin, but these resin acids may also be refined and used individually.

In the examples described herein, gum rosin has been used as the polycyclic diterpene. Impurities were removed from this gum rosin by filtering raw tapped pine resin, after which the rosin was obtained by distillation, and separating out the terpene oil in the low boiling point component. In general this gum rosin contains 20 to 40% by weight of abietic acid, 15 to 25% by weight of neoabietic acid, 20 to 301 by weight of palustric acid, 3 to 8% by weight of pimaric acid, 1.0 to 20% by weight of isoplmaric acid and 3 to 8% by weight of dehydroabietic acid.

Also, instead of using the rosin as is, it is also possible to use one or more υf acids selected from abietic acid, dehydroabietic acid, aeoabietic acid, pimaric acid, isopimaric acid, palustric acid and so on.

The polycyclic diterpene is incorporated to the amount of 0.3 to 3% by weight relative to the total weight of the bitumen composition of this invention. If the amount of this polycyclic diterpene is less than 0.3% by weight, the stability of the bitumen composition is not sufficiently improved. On the other hand, if the amount of polycyclic diterpene exceeds 3% by weight, the cost of the bitumen composition increases without a further significant increase in stability. In other words, even if the amount of polycyclic diterpene exceeds 3% by weight, stability will not be improved significantly beyond this, yet it will be disadvantageous as regards raw material costs . Also, it is preferable if the polycyclic diterpene is incorporated within the range of 0.3 to 1% by weight relative to the total weight of the bitumen composition of this invention. By making the upper limit of the amount of polycyclic diterpene 1% by weight, it is possible to bring about an improvement in the stability of the bitumen composition of this invention while keeping the increase in raw material costs extremely low, and so it is possible to improve the effect on expenditure. Bitumen is a viscous, non-volatile product from crude oil. It usually consists of hydrocarbons and derivatives which may be aromatic and/or have long carbon chains. It Is commonly produced by refining processes after atmospheric or in vacuum distillation. . For raising the softening point of bitumen or when a bitumen having specific properties is to be produced the bitumen may be oxidized with an oxygen-containing gas to produce blown bitumen. Bitumen may be combined with aggregate or filler to provide asphalt. The term "asphalt" in the present description is used no describe a mixture comprising bitumen and aggregate or filler.

Typically, the bitumen may be a straight bitumen obtained as the residual oil from vacuum distillation of crude oil, deasphalted bitumen obtained by deasphalting, by means of propane or the like, of the vacuum distillation residual oil from crude oil., or an extract obtained by solvent extraction of solvent-deasphaited oil obtained by deasphalting, by means of propane or the like, of vacuum distillation residual oil from crude oil. In place of this extract, it is also possible to use an aromatic-based oil. The aromatic-based oil is typically as stipulated in JIS K6200 and will be a hydrocarbon- based process oil containing at least 35% by weight of aromatic hydrocarbons.

The bitumen is manufactured by any of the above- mentioned methods of vacuum distillation, blowing (a method of introducing air) or blending. In other words, the bitumen contains any one kind or more of propane- deasphalted bitumen, straight bitumen or extract.

Propane-deasphalted bitumen uses propane or a mixture of propane and butane as the solvent for a vacuum distillation residual oil, and a so-called solvent- deasphaltcd bitumen is obtained by means of a deasphalting treatment. Also, apart from this propane- deasphalted bitumen, it is possible to αse, for example, straight bitumen or any bitumen such as blown bitumen. For this propane-deasphalted bitumen it is preferred to use one where, for example, the needle penetration at 25°C under the conditions of JlS K2207 is 8 (1/10 mm), the softening point is 66.5°C and the density at 15°C is 1028 kg/m ³ . Also, for the straight bitumen it is preferred to use one where, for example, the needle penetration aτ 25°C is 65 {1/10 mm), the softening point is 48.5°C and the density at 15°C is 1034 kq/m ³ .

Tho extract is typically an oil extracted during preparation of a heavy lubricating base oil as a refined oil by solvent extraction using a polar solvent, such as furfural. The feedstock to the solvent extraction process is typically a solvent-deasphalted oil obtained by deasphalting, using propane or the like, of a vacuum distillation residual oil from crude oil. It is preferred if the kinetic viscosity at 100ºC of the extract is 61.2 mm ² /s, its kinetic viscosity at 4OºC is 3970 mm ^? /s, and its density at 15°C is 976.4 kg/m ³ . In this connection, the amount of this extract is preferably not more than 5% by weight relative to τhc weight of the enti re bitumen composition of this invention. The reason for this is -hat if the amount of the extract exceeds 5% by weight, the strength of the bitumen composition is not improved to a degree that is preferred. When actually manufacturing the bitumen composition of this invention with the above-mentioned structure, the above mentioned bitumen is prepared first. This bitumen is a mixture of one or more kinds taken from straight bitumen, propane-deasphalted bitumen or extract. While maintaining the bxtumen at a temperature of approximately 195°C, 2 to 8% by weight of SBS is added, and then 0.3 to 3% by weight of the above-mentioned resin acid is added. Osing a homomixer, mixing and agitation are typically carried out for about 2 to 3 hours at a temperature of 190 to 210ºC and a speed of 1500 to 1600 rotations per minute. In this connection with regard to the mixing period, it is also possible to deviate from the range of 2 to 3 hours, but it is still necessary to do the mixing with the mixing temperature within the above-mentioned range of 190 to 210ºC. If the mixing temperature is less than 190°C, the stability of SBS in the bituiren composition doesn't improve sufficiently. Without wishing to be bound to a particular theory, it would appear that it becomes difficult to attach the polycyclic diterpene (resin acid) to the double bonds forming the butadiene bloc<: in the

SBS, and so it becomes difficult to improve the stability of the SBS in the bitumen composition, that is its tendency not to separate and float up in the bitumen, and thus performance. The bitumen and SBS as a result rray separate.

Also, if the mixing temperature is above 210ºC, the SBS itself may decompose and change in quality. It then becomes difficult to achieve the improvement in strength intended by addition and admixture of the SBS to the bitumen or to reduce (and so improve) the temperature susceptibility. The mixing temperature should therefore be limited to the above mentioned range.

The present invention will now be further illustrated with reference to the following Figures. Figure 1 shows the relationship of the complex modulus of elasticity G* and loss tangent (tan. δ) relative to the angular frequency ω in the bitumen composition.

Figure 2 is an oblique view showing schematically the measuring portion of a rheometer.

Figure 1 shows the relationship of the complex modulus of elasticity G* and loss tangent {tan δ) to the angular frequency ω in the bitumen composition. Sinusoidal vibrations are added to the bitumen composition with a constant strain, and the angular frequency ω is gradually increased. The complex modulus of elasticity G* and loss tangent (tan δ) are each measured relative to the angular frequency ω.

The complex modulus of elasticity G* stipulated in this invention can be measured by means of a rheometer. In specific terms, bitumen binder 1 as shown in Figure 2 is sandwiched between two parallel discs 2a and 2b. A sinusoidal strain of the specified frequency is applied to one disc 2a and the sinusoidal stress σ transmitted to the other disc 2b through the bitumen binder 1 is measured. The measurement conditions at this time are: diameter of discs 2a and 2b: 25 mm; thickness of bitumen binder 1: 1 mm; strain: 10%. The complex elastic modulus G* is obtained from Mathematical Formula 1 referred to herein below, on the basis of the results of these measurements, y in the Mathematical Formula 1 is the maximum strain applied to the disc 2a.

The loss tangent (tan δ) is an indicator of the amount of energy lost in the bitumen composition when a sinusoidal strain γ is applied to the bitumen composition.

When the loss tangent {tan δ) is large, it means that the energy loss when the strain is applied is large, in other words there is liable to be deformation and when the given strain is removed there is no return to the original shape. If the loss tangent (tan δ) is small, it means that the energy loss when the strain is applied is small, in other words there is not liable to be any deformation and when the given strain is removed the properties are such that there is a tendency to return to the original shape.

When the above-mentioned complex modulus of elasticity G* is measured, the loss tangent (tan δ) is calculated from the phase difference δ of the sinusoidal strain y for the specified angular frequency applied to one disc and the sinusoidal stress σ transmitted to the other disc through the bitumen composition.

The above mentioned complex modulus of elasticity G* and loss tangent (tan δ) may also be measured on the basis of "AO 62 Dynamic Shear Rheometer Test Method", a method shown in "IIo≤o Chosa - Shi ken -ho Benran" [Handbook of Methods of Investigating and Testing Pavement), edited by Nihon Doro Kyokai [Japan Road Association] . Tn this connection, the example of Figure 1 shows the complex modulus of activity G* and loss tangent (tan δ} when applying a sinusoidal strain of 10% at 60ºC to a bitumen composition which contained 4.5% by weight of SBS, 0.75% by weight of gum rosin and a remaining part comprised of bitumen. Also, as regards the mixing temperature when preparing the bitumen composition, different instances at 180ºC, 185°C and 190ºC were used as samples. In particular, at an actual site of road paving works, when laying a bitumen composition on the road together with aggregate (crushed rocks, sand, etc.), i.e. an asphalt composition, the paving surface is made flat by applying heavy machinery {rollers, etc.) or man power, and it is necessary to ensure improvement of the drive feel for road traffic, prevention of trip hazards for pedestrians, and prevention of the occurrence of puddle areas. In making the paved surface flat, the work is done in such a way that a large force is applied slowly to the paved surface, so that a so-called "ironing out" is done.

At this tirpe, because the asphalt composition is subject to vibrations at a low angular frequency ω, a higher tan δ under such a low angular frequency ω makes the asphalt composition more prone to deformation, with a lower recovery strength. This is appropriate from the standpoint of workability on site, that is in making it easier to form a flat road.

The sample with a mixing temperature of 19OºC showed a tendency for the tan δ at a low angular frequency ω to increase more than the other cases. In contrast, with a mixing temperature of 185°C or less, there was a tendency for the tan δ at a low angular frequency ω to be lower. For this reason, from the standpoint of workability it is evidently preferable to make the mixing temperature not less than 190°C. It is also preferable if the complex modulus of elasticity G* is small in the domain of low angular frequencies ω. In particular, when compacting and flattening the asphalt composition, a load is applied to the asphalt composition in the low angular frequency ω domain, but at this time workability is improved if it is far softer, or to put it another way, the lower the modulus of elasticity. Looking also from the standpoint of such a complex modulus of elasticity, the sample with a mixing temperature of 190ºC, compared with the others, showed a tendency for the complex modulus of elasticity G* at a low angular frequency ω to become lower. In contrast, in the case of a mixing temperature of 185°C or lower, the trend was for the complex modulus of elasticity G* at a low angular frequency ω to become higher, and for the workability to deteriorate. As regards workability, therefore, it is evident that the mixing temperature should preferably be made r.ot less than 190ºC.

The bitumen composition and asphalt composition of this invention produced by effecting the method of manufacture mentioned above can be finished off in a stable state and also without the bitumen and SBS separating.

Without wishing to be bound by a particular theory, it would appear that the reason for this is that the styrene blocks making up the SBS have the characteristic of trying to agglomerate with the other styrene blocks in the SBS, but in this invention it is possible to attach the polycyclic diterpene (resin acid) of carbon number 20 and having carboxyl groups to the double bonds forming the butadiene block. In particular, by virtue of the resin acid attaching in proximity to the styrene blocks, the present inventor believes that the bulky resin acid acts on the styrene blocks and, therefore, it becomes possible to resolve the agglomeration of the styrene blocks. By resolving the agglomeration of the styrene blocks, it becomes possible to ensure adequate stability without the SBS separating within the bitumen.

In this connection, it becomes possible to identify the storage stability according to whether or not the bitumen composition is stable. The storage stability can be confirmed by charging and sealing bitumen composition (approx. 250 g) up to a depth of 12 cm into an aluminium cylinder can of internal diameter 5.2 cm and height 13 cm, and heating for 48 hours at 170°C. Then the softening points of the top 4 cm and the bottom 4 cm of the bitumen composition inside the aluminium cylinder arc measured. Measurement of the softening points may be based on the method shown in JIS K2207. Evaluation of the stability is made through the absolute value of the difference between the softening points of the top part and the bottom part. If it is assumed that the storage stability is good whenever the absolute differential as regards these softening points is not more than 3.0°C, the bitumen composition of this invention can always restrict the softening point differential to 3°C or less. Also, the bitumen composition of this invention produced by effecting the method of manufacture mentioned above can improve the strength. The strength of this bitumen composition is assessed from the DS value on the basis of the wheel-tracking test described in "Hoso Hyoka - Shiken-ho Benran" [Handbook of Methods of Evaluating and Testing Pavement] , edited by Ninon Doro Kyokai [Japan Road Association] . This DS value can be obtained from the undermentioned Formula (2), and so can be obtained from the number of rotations of tyre travel in the period from 45 minutes to 60 minutes relative to the amount of deformation {nan) of the bitumen composition in the period from 45 minutes to 60 minutes. The higher this DS value, the less the amount of deformation of the bitumen composition, and so the more resistant the material is to rutting, which means its strength is higher.

(2) OS value (rev/mm) =

No. of tyre passes in the period from 45 min to 60 min (rev} Anount of deformation ir. the period from 45 i_in to 60 tr.in

In the bitumen composition of this invention, in particular if extract is restricted to not more than 5% by weight, it becomes possible, in mixtures with aggregate of dense granularity (maximum grain size of aggregate 13 min) as used on general road paving, to regulate more or less the above-mentioned DS value to not less than 6000 (rotations/minute} . In this connection, the point has been made in "Hoso Hyoka - Shiken-ho Benran" [Handbook of Methods of Evaluating and Testing Pavement] , edited by Nihon Doro Kyokai [Japan Road Association] that if the DS value is not less than 6000 (rotations/minute) , virtually no problems will arise as regards the strength aspect, of the bitumen composition.

On the basis of this Invention it is therefore possible to achieve an improvement in storage stability, owing to the fact that the softening point difference is made not more than 3.0ºC, and also, at the sane time, an improvement in strength, owing to the fact that the DS value is made not less than 6000 (rotations/minute) . The bitumen composition of this invention when mixed with aggregate, i.e. the asphalt composition of the invention, is especially suitable for road paving, but use of the bitumen composition is not limited to this and the bitumen composition is of course capable of being used for waterproofing materials, adhesives and so on. Example 1

The invention is explained in detail below by means of the following experiments. As shown in Table 1, 4.5% by weight of SBS was added to bitumen which contained at least any one kind taken from straight bitumen, propane- deasphalted bitumen (PDA) and extract, while maintaining the temperature at about 195°C.

For the SBS, a styrene-butadiene-styrene block copolymer was used in which the bromine number was 220 (g/100 g: JIS K0070), ^he molecular weight was approximately 150000 and the amount of styrene was 32% by mass and in which the amount of styrene block copolymer present on both terminals of the elastomer molecules was 16% by mass . The bitumen compositions shown by Comparative

Experiments 1 to 6 in which acid A (straight chain) was mixed therein were prepared, along with Experiments 1 to 5, in which rosin B was mixed in, Experiment 6, in which rosin C was mixed in, Experiment 7, in which abietic acid was mixed in, and Experiment 8, in which dehydroabietic acid was mixed in. In each of these bitumen compositions of the Experiments and Comparative Experiments, the proportions of straight bitumen, propane-deasphalted bitumen (PDA) and extract in the blend were such as to make ~he needle penetration 40 to 50.

The acid A referred to here was a mixture comprised of 7% by weight of monomer acid of straight-chain carbon number 18, 76% by weight of dimer acid of carbon number 36 and 7% by weight of trimer acid of carbon number 54, with acid number 190 (mgK0H/g: JIS K0070) and iodine number 110 (g/100g: JIS K0070) . The average molecular weight was approximately 590. Rosin B was a disproportionated gum rosin with acid number 156 {rrgKOH/g: JI3K0070) and softening point 77.0ºC (JIS K2207) . Rosin C was a tall oil rosin with acid number 170 {mgKOH/g: JISK0070) , saponification number 178 (mgKOH/g: JlS K0070) ar.d softening point 77.0ºC (JIS K2207) .

In the Constituent rows in Table 1, the numerals in the table all show % by weight. Comparative Example 1 was an instance where the extract in the bitumen was made 12% by weight. Comparative Example 2 was an instance where the extract in rhe bitumen was made 8% by weight. Comparative Example 3 was an instance where the extract in the bitumen was made 6 % by weight . Comparative Examples 4 to 6 were instances where the extract in the bitumen was made 4% by weight. In the case of Comparative Examples 1 to 4, all had 0.3% by weight of acid A (straight chain) . Comparative Example 5 had 0% by weight of acid A (straight chain). Comparative Example 6 was a mixture with 0.5% by weight of acid A (straight chain) . In the case of Examples of Embodiment 1 to 5, instead of the acid A (straight chain) which was mixed in Comparative Examples 1 to G, rosin B was added. In these Examples of Embodiment 1 to 5, the proportion of rosin B contained varied in each case. Experiments was mixed with 0.75 by weight of rosin C, Experiment 7 with 0.75% by weight of abietic acid, and Experiment 8 with 0.75% of dehydroabietic acid.

The manufacturing conditions for all compositions were mixing and agitation for about 2 hours with a mixing temperature of 195ºC and a homomixer speed of 3500 rotations per minute. The amount manufactured was 1.8 kg in all cases.

Table 1 also shows the results of the measurement of properties for each of the Comparative Examples and Examples of Embodiment manufactured. The properties measured were needle penetration (1/10 mm), softening point (ºC), viscosity at 18OºC (mPa.s), storage stability, and DS value. In the case of needle penetration, data were taken for 25°C measured under the conditions of JIS K2207. For the softening point, measurements were also made under the conditions of JIS K2207. The viscosity was measured under the conditions of JPI-5S-54-99 "Bitumen - Method for Testing Viscosity using a Rotating Viscometer". The measurement temperature was 180ºC and measurements were undertaken at 20 spindle rotations/minute using a spindle SC4-21.

In the case of the storage stability, the bitumen composition of this invention (approx. 250 g) was injected and sealed up to a depth of 12 cm In an aluminium cylinder can of internal diameter 5.2 cm and height 13 cm, and heated for 48 hours at 170ºC. Then the softening points of the top 4 cm and the bottom 4 cm of the bitumen composition inside the aluminium cylinder were measured in accordance with JI3 K2207. Table 1 shows the absolute value of the differential value between the softening points of the top part and the bottom part, that is the absolute softening-point differential.

The DS value was measured on the basis of a wheel tracking test. For this DS value an asphalt composition blend of each bitumen composition together with an aggregate mixture of dense granularity (13) was used. Test pieces in sheet form measuring 30 cm vertically, 30 cm horizontally and with a depth of 5 cm were prepared with the bitumen composition at 5.6% by weight, and the tests were carried out on the basis of the procedure defined in "Hoso Hyoka - Shiken-ho Benran" [Handbook of Methods of Evaluating and Testing Pavement] , edited by Nihon Doro Kyokai [Japan Road Association] . Japanese xOdds have been confirmed by experiment to reach a temperature of about 60ºC in places in summer. Under these conditions, when cars pass over them, flow deformation and rutting occur. A wheel tracking test is a test designed to confirm experimentally the degree to which this rutting occurs. It is a test carried out in order to evaluate the dynamic stability which is an indicator of flow-resistance properties in paving materials. Specifically, a tyre to which a specified load has been applied is run backwards and forwards over the experimental sample (test piece) for 1 hour in a constant temperature tank maintained at 6OºC, and the amount of deformation is measured. The DS value is calculated on the basis of the above-mentioned Mathematical Formula (2) from the amount of deformation in the period from 45 minutes to 60 minutes from the start of the test. In Table 1 given above, first of all the trend of

Comparative Examples 1 to 4 shows that the DS value improves as the extract is reduced. However, reducing the extract showed a tendency for the absolute value of the difference between, the softening point of the top part and the softening point of the bottom part to increase. In Comparative Example 4 in particular, the extract was reduced to 4% by weight, but as a result, whilst the DS value was improved to 7875 (rotations per minute) , the absolute softening-point differential deteriorated to 19.9ºC. Also, as shown by Comparative Examples 5 and 6, if the extract is reduced to 4% by weight, it means that even if acid A, that is the proportion of carboxyl groups contained, is increased or reduced, it is not possible to improve the storage stability. In Experiment 1, in addition to making the proportion of extract contained 4% by weight, 0.3% by weight of rosin B was incorporated, and it was evident that it was possible not only to improve the DS value up to more than 70C0 (rotations per minute) but it was also possible to reduce drastically the softening-point absolute differential and to improve both strength and stability. Similarly, in the case of Examples of Embodiment 2 to 5, it was evident that by setting rosin B at, respectively, 0.6% by weight, 0.75% by weight, 1% by weight and 1.5% by weight, it became possible to maintain the CS value at net less than 7000 (rotations per minute) while keeping the softening-point absolute differential to not more than 1.3ºC, and it was possible to improve both strength and stability. However, with regard to the storage stability, even when increasing the amount of rosin B added, it could be seen that there was not much change in the softening-point absolute differential. It is thought that even if in excess of 3% by weight of rosin B were added, there would be virtually no change in the softening-point absolute differential. In Experiment 6, in addition to reducing the proportion of extract contained to 4% by weighτ, 0.75% by weight of rosin C was added, but here too the DS value and the absolute differential of softening points were both good. Also, in the cases of Experiment 7 where abietic acid alone was added as the resin acid and

Experiment 8 where dehydroabietic acid alone was added as the resin acid, the DS value and the absolute differential of softening points were again both good. On the basis of the results of Examples of Embodiment 6 to 8, even in cases where the type of resin acid is varied, the DS value is maintained at a high level and the storage stability can be improved by addition of abietic acid or dehydroabietic acid alone.

So, on the basis of the results of Table 1, it is shown that the aims can be realised if, in order to iπprove both the DS value and the absolute value of the softening point differential, the extract is set at not more than 5% by weight and resin acid is added within the range 0.3 to 3% by weight. From the results of Table 1 it can be seen that, with the same amount of SBS in the blend, if the softening point after completion of the preparation of the bitumen composition (after manufacture) becomes lower, the storage stability becomes higher. This is thought to be because, in a system wi~h the same thermoplastic elastomer blended in the same amount, if the softening point after completion of preparation of the bj tumen composition is lower, the polycyclic diterpene (resin acid) of carbon number 20 and having carboxyl groups attaches to the double bonds forming the butadiene blocks in the SBS, and the stability is thus improved. Example 2

Table 2 shows the results of experiments to verify whether the expected function and effect of the invention were displayed when using sLyrcne-ethylene-butylene- styrene (SEBS) and styrene-isoprene-styrene (SIS) instead of the SBS. In these verification experiments, the manufacturing conditions for the bitumen compositions were the same as in Table 1 given above. Also, the amounts of SBS, SEBS and SIS added were all made 4.3% by weight, and the needle penetration, softening point and viscosities at 150ºC and 18OºC (mPa.s) were measured.

In Table 2, Rl and R? show examples of using SBS. Sample Rl was an instance of adding no gum rosin, and was a comparative example. In contrast, sample R2 was an example in which 0.75% by weight of gum rosin had been added, and corresponded to an example of the invention.

When comparing the properties of these two samples Rl and R2, the softening point in sample R2 was much lower than for sample R1. By addition of gum rosin the stability improved . In contrast, samples S1 and S2 were examples of using SEBS instead of SBS.

For the SEBS, hydrogen was attached to the double bonds in the butadiene blocks of SBS, and so a styrene- ethylene-butylene-styrene block copolymer (SEBS) was used in which the bromine number was 5 (g/100 g: JIS K0070) , the molecular weight was approximately 150000 and the amount of styrene was 30% by mass and in which the amount of the styrene block copolymer present on both terminals of the elastomer molecules was 15% by mass. Sample Sl was an instance of adding no gum rosin, and sample S2 was an example in which 1% by weight of gum rosin had been added. When comparing ^he properties of these two samples Sl and S2, in neither was thore hardly any change in softening point and so it could be shown that the effect of improving stability is not manifested by adding gum rosin.

Samples Pl to P6 also show examples with SIS added instead of SBS.

For the SIS, a styrene-isoprene-styrene block copolymer (SIS) was used in which the bromine number was 220 (g/100 g: JIS K0070), the molecular weight was approximately 220000 and the amount of styrene was 15% by mass and in which the amount of the styrene block copolymer present on both terminals of the elastomer molecules was 7.5% by mass. Pi to P3 were examples relating to addition of guru rosin, but there was virtually no change in softening point regardless of the amount of gum rosin added or whether or not any was added. Also, P4 to P6 were examples relating to addition of tall oil rosin, but there was virtually no change in softening point regardless of the amount of tall oil rosin added or whether or not any was added. Therefore, in this SIS, the effect of improving stability is not manifested by adding the rosin. In other words, the invention is one which exhibits the effect of improving stability by adding SBS, and it is evident that the requisite effect cannot be exhibited if using SF.BS or SIS instead of SBS. Only SBS, with butadiene blocks sandwiched between styrene blocks, can effect an improvement in its own stability, by attaching a resin acid to the double bonds forming the butadiene blocks, but SEBS and SiS cannot attach the resin acid and, as a result, cannot bring about an improvement in stabi lity.