RU2181130C2 - Bitumen compositions and their production process - Google Patents

Abstract

FIELD: road-building materials. SUBSTANCE: process involves blowing of bitumen blend with oxygen-containing gas, bitumen blend including bitumen with penetration rate less than 300 dmm (according to procedure ASTM D5 at 25 C) and thermoplastic rubber in amount less than 3% of the total weight of blend. Bitumen blends of invention, which show good low-temperature characteristics, are applied for pavements. Employed rubber has formula A(AB)_m or (AB)_nX, wherein block A represents predominantly block of poly(monovinylaromatic hydrocarbon) with up to 10% of a comonomer, block B represents predominantly block of poly(conjugated diene) with up to 10% of a comonomer, X residue of multivalent linking reagent, n and m integers equal to or greater than 1. Block copolymer can also be hydrogenized. EFFECT: improved working characteristics. 4 cl, 1 tbl, 4 ex

Description

 This invention relates to bituminous compositions, a method for their preparation and a method of use in asphalt mixtures for road surfaces.

 Bitumen is used as a binder for road asphalt mixtures and is constantly being improved to meet the ever-increasing demands placed on it by, for example, road builders. Typically, bitumen serves well in road asphalt, but the ever-increasing flow of heavy cargo carried leads to premature wear of a large number of roads with the formation of furrows and cracks on the surface. The appearance of cracks is a serious defect in the asphalt road, as it allows water to reach lower layers of the road surface, where it causes rapid destruction, which speeds up the need for early repairs. An increase in bitumen content in asphalt or the use of softer grades of bitumen improves the asphalt resistance to cracking at low temperatures, but increases the risk of excess furrows at higher temperatures, since the mixture becomes significantly softer. Conversely, resistance to the appearance of furrows can be improved by reducing the amount of bitumen in the asphalt mixture or by using harder varieties of bitumen with a loss of resistance to cracking, as the mixture becomes less ductile.

 Based on the foregoing, it is clear that it would be very advantageous to develop a durable bitumen composition that meets the modern requirement for crack resistance, i.e. bituminous composition having both a good characteristic at low temperatures and good resistance to furrowing at high temperature.

 It is known that the low temperature properties of bitumen can be improved by mixing them with a polymer. However, when this modification is carried out in hard bitumen, bitumen and polymer incompatibility are usually observed, leading to slightly improved or not completely improved properties at low temperatures and relatively low aging.

 Also known from WO 94/16019 is a method for producing industrial and roofing bitumen by blowing a bitumen / polymer mixture. However, it turned out that these bitumen compositions are not suitable for use in road construction due to their high softening temperature and relatively high penetration.

 The subject of this invention is a bitumen composition suitable for use in road construction, having both a good low-temperature characteristic and good resistance to furrow formation at high temperature and an additionally improved character of changes in properties during aging.

 It has been unexpectedly discovered that such a bitumen composition can be obtained by treating the bitumen mixture with a partial blowing method.

Thus, this invention relates to a method for producing a bitumen composition for an asphalt paving mixture, comprising purging with an oxygen-containing gas a mixture that comprises bitumen having a penetration of at least 300 dmm (as measured by ASTM D at 25 ^{° C.} ), and thermoplastic rubber, which is present in an amount of less than 5% (wt.) based on the total weight of the mixture.

 It is suitable if the thermoplastic rubber is present in an amount of less than 3% (wt.), Preferably in the range of 1 to 3% (wt.), Based on the total weight of the mixture.

The bitumen used in this method has a penetration of 300 dmm (in accordance with the measurement according to ASTM D 5 at 25 ^o C).

It is suitable if the bitumen has a penetration of less than 250 dmm, preferably less than 200 dmm (as measured by ASTM D 5 at 25 ^{° C.} ).

 The purge is carried out with an oxygen-containing gas such as air or pure oxygen. The use of air is preferred.

It is suitable to carry out the process in accordance with this invention at a temperature in the range from 200 to 280 ^o C.

Preferably, the process in accordance with this invention is carried out at a temperature in the range of 210 to 260 ^{° C.} , more preferably in the range of 230 to 250 ^° C.

 The process in accordance with this invention can be carried out at ambient pressure or at elevated pressure. However, it will usually be conducted at ambient pressure.

 It is suitable to carry out the process of the present invention for a period of time of less than 4 hours, preferably less than 3 hours, more preferably less than 2.5 hours.

 The mixture includes thermoplastic rubber. The mixture may include one or more thermoplastic rubbers of various types. However, only one type of thermoplastic rubber is preferred.

 Although a wide range of thermoplastic rubbers may be suitable for use in accordance with this invention, preferred thermoplastic rubbers include optionally hydrogenated block copolymers that include at least two end blocks of a poly (monovinyl aromatic hydrocarbon) and at least one central block poly (conjugated diene).

Preferably, the constituents of the block copolymer are selected from the group consisting of constituents of formula A (BA) _m or (AB) _n X, where A is a block of poly (monovinyl aromatic hydrocarbon) and up to 10% comonomer, and B is a block of poly (conjugated) diene) and up to 10% of the other comonomer, X represents the remainder of the polyvalent binder component, n represents an integer ≥1, preferably ≥2, and m represents an integer ≥1, preferably m is 1.

 More preferably, blocks A are blocks of poly (styrene) and up to 10% of another comonomer, and blocks B are blocks of poly (butadiene) or poly (isoprene) and up to 10% of another comonomer. Polyvalent binder reagents for use in this invention include reagents commonly known in the art.

 The corresponding blocks A and B can be obtained mainly from monovinyl aromatic hydrocarbon monomer and conjugated diene monomer, which can be mixed with other structurally similar or structurally unrelated comonomers, for example, when using monovinyl aromatic hydrocarbon monomer as the main component and small amounts ( up to 10%) of other monomers, or using butadiene mixed with isoprene or with small amounts of styrene.

 More preferably, the copolymers contain blocks of pure poly (styrene), pure poly (isoprene) or pure poly (butadiene), of which poly (isoprene) blocks or poly (butadiene) blocks can be selectively hydrogenated to the highest residual unsaturation of 20%, preferably equal to less than 5%. Most preferably, the block copolymer used has an ABA structure, where A has an apparent molecular weight in the range of 3,000 to 100,000, and preferably in the range of 5,000 to 40,000, and B has an apparent molecular weight in the range of 10,000 to 250,000, and preferably in the range of 40,000 to 200,000. The initially obtained poly (conjugated diene) blocks typically contain from 5 to 50% (mol.) Vinyl groups formed by 1,2 polymerization of conjugated diene molecules, and preferably the vinyl content is from 10 to 25%.

 A complete block copolymer for use in accordance with this invention typically contains polymerized monovinyl aromatic hydrocarbon monomers in an amount of from 10 to 60% (wt.) And preferably from 15 to 45% (wt.).

 The apparent molecular weight of the entire block copolymer will typically be in the range of 15,000 to 350,000, and preferably in the range of 40,000 to 250,000.

 As examples of suitable pure block copolymers, KRATON G-1651, KRATON G-1654, KRATON G-1657, KRATON G-1650, KRATON G-1701, KRATON D-1101, KRATON D-1102, KRATON D-1107 can be mentioned , KRATON D-1111, KRATON D-1116, KRATON D-1117, KRATON D-1118, KRATON D-1122, KRATON D-1135X, KRATON D-1184, KRATON D-1144X, KRATON D-1300X, KRATON D-4141 and KRATON D-4158 {KRATON trade name).

 Bitumen may be a residue obtained by distilling a technical oil, a cracking residue, a residue obtained by purging a technical oil, or residues obtained by distilling a technical oil, or extracts of technical oils, and bitumen is obtained from propane bitumen, butane bitumen, pentane bitumen or mixtures thereof. Other suitable bitumens are bitumens comprising mixtures of the aforementioned bitumen with fillers (flow improvers), such as oil extracts, for example aromatic extracts, distillates or residues.

It is suitable if the bitumen used has a softening point in the range of 35 to 65 ^{° C.} , preferably in the range of 42 to 58 ^{° C.} (as measured by ASTM D 36).

 A very unexpected and advantageous aspect of this method is that bitumen compositions can be obtained under moderate conditions without the need for a bitumen purge catalyst. Thus, the process of the invention is suitably carried out in the absence of a bitumen purge catalyst.

 The thermoplastic rubbers mentioned above are preferably unvulcanized thermoplastic rubbers. The use of unvulcanized thermoplastic rubbers in accordance with this invention has the advantage that bituminous compositions with advantageous properties can be obtained without the need for a vulcanizing reagent.

As will be appreciated by the skilled person, the mixture of bitumen and thermoplastic rubber is heated before the purge process. A mixture of bitumen and thermoplastic rubber is usually preheated in such a way as to set the initial temperature of the mixture in the range from 160 to 220 ^o C.

The present invention also provides a bitumen composition that can be prepared by any of the processes described above. It is suitable if such a bitumen composition has a penetration of less than 100 dmm, preferably less than 7.5 mm (as measured by ASTM D 5 at 25 ^{° C.} ), a softening temperature in the range of 60 to 90 ^{° C.} , preferably in the range of 65 to 75 ^o C (as measured by ASTM D 36) and contains less than 3% (wt.), Preferably from 1 to 3% (wt.), Of any of the above thermoplastic rubbers - based on the total weight of bitumen composition. Such a bituminous composition is very desirable since it exhibits both a good characteristic at low temperature and good resistance to furrowing at high temperature.

 Fillers such as carbon black, silica and calcium carbonate, stabilizers, antioxidants, pigments and solvents are known to be useful in bitumen compositions and can be incorporated into compositions of this invention at concentrations known in the art.

 The invention will be further illustrated by the following Examples.

EXAMPLES
Example 1
The mixture is prepared on the basis of bitumen with a penetration of 10 (in accordance with the measurement according to the methodology of ASTM D 5 at 25 ^o C), non-naphthenic bitumen produced by the industry, which is obtained from technical distillation. Bitumen has a penetration index of 0.5 and a softening point of 44 ^{° C.} (as measured by ASTM D 36). To this bitumen, 2% (wt.) Of the block copolymer is added based on the weight of the whole mixture. The block copolymer used is a hydrogenated block copolymer of a polystyrene-polybutadiene-polystyrene structure with a styrene content of 30% (wt.) And a number average molecular weight of 103,000, as measured by the GPC method with polystyrene standard. The ethylene unsaturation of the polymer is reduced to less than 1% of the initial unsaturation by hydrogenation.

The mixture is prepared by mixing bitumen and a block copolymer at a temperature of 180 ^° C. Then the mixture of bitumen and block copolymer thus obtained is purged with air in a purge vessel at a temperature of 220 ^{° C.} for 2 hours. The main properties of the composition of oxidized bitumen are presented in the Table.

Example 2
The comparative purging process is carried out according to the method of Example 1 with the difference that thermoplastic rubber is not added to bitumen. The main properties of oxidized bitumen are presented in the Table.

 The bitumen composition thus obtained is subjected to a rolling thin film test in a thermostat (Rolling Thin film Oven Test - RTFOT) (test in accordance with ASTM D 2572). The main properties of the bitumen composition after such an aging experiment are presented in the lower part of the Table.

Example 3
The comparative purge process is carried out in a manner similar to that described in Example 1, with the difference that the block copolymer is added to the bitumen after it is purged. The main properties of the composition of oxidized bitumen are presented in the Table.

Example 4
The process is carried out in a manner similar to that described in Example 1, with the difference that 1% (wt.) Block copolymer is added to bitumen based on the total weight of the mixture. The main properties of the composition of oxidized bitumen are presented in the Table.

 The main properties of the bitumen composition after the RTFOT aging experiment are presented in the lower part of the Table.

 From the results presented in Table 1, it can be seen that according to the method of the present invention (Examples 1 and 4), a solid bitumen composition with predominant low-temperature ductility can be obtained, as shown by the Fraass tensile strength (measured by IP 80 method), while as a method that is beyond the scope of the present invention (examples 2 and 3), solid bitumen products with less advantageous properties are obtained.

 In addition, from Examples 2 and 4 it is seen that this bitumen composition is more stable against oxidation.

Claims (5)

1. A method of producing a bitumen composition for use in an asphalt mixture for paving, comprising purging with an oxygen-containing gas a mixture that includes bitumen having a penetration of less than 300 dmm (as measured by ASTM D 5 at 25 ^{° C.} ), and thermoplastic rubber, which is present in an amount of less than 3 wt. % based on the total weight of the mixture, in which the thermoplastic rubber includes an optionally hydrogenated block copolymer containing at least two end blocks of a poly (monovinyl aromatic hydrocarbon) and at least one central block of a poly (conjugated diene), in which the block copolymer has the formula A (AB) _m or (AB) _n X, where A is mainly a block of poly (monovinyl aromatic hydrocarbon) and up to 10% comonomer, B is mainly a block of poly (conjugated diene) and up to 10% of another comonomer, X represents the remainder of the polyvalent binder reagent, n is an integer ≥ 1 and m is an integer ≥ 1.  2. The method according to p. 1, in which the mixture is purged with air. 3. The method according to p. 1 or 2, in which a temperature in the range of 210 - 260 ^o C.  4. The method according to PP. 1-3, in which blocks A are blocks of poly (styrene) and up to 10% of another comonomer and B-blocks are blocks of poly (butadiene) or poly (isoprene) and up to 10% of another comonomer.  5. Bitumen composition, which can be obtained by the method defined in any one of paragraphs. 1-4. Priority on points:
11/28/1995 - according to paragraphs 1-5.

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