[DESCRIPTION] [Invention Title]

ASPHALT COMPOSITION HAVING IMPROVED MECHANICAL PROPERTY AND ANTI-AGING PROPERTY AND METHOD OF PREPARING THE SAME [Technical Field]

The present invention relates to an asphalt composition having improved mechanical properties and anti-aging performance and a method of preparing the same, and, more particularly, to a method of providing asphalt cement, which has superior mechanical properties, including penetration or ductility, and also has improved storage stability, by mixing asphalt or bitumen with a polymer at a predetermined ratio and selectively adding an additive. [Background Art]

Typically, asphalt is classified into various types depending on production methods and production regions. Further, asphalt is largely divided into natural asphalt, which occurs naturally, and petroleum asphalt, which is produced from crude oil. At present, petroleum asphalt accounts for most of the asphalt which is produced and used domestically, but natural asphalt is sometimes imported and used. In general, petroleum asphalt, which is bituminous material obtained from the bottom of a Vacuum distillation tower during the purification of crude oil, or which results from the oxidation of such bituminous material, is chiefly used for road pavement, construction materials, coating, and other industrial purposes. The quality of the asphalt is greatly affected by the properties of crude oil. Hence, the use of inappropriate crude oil leads to asphalt having poor quality. Further, because asphalt is very sensitive to change in temperature, it should be prepared such that it is suitable for the climatic properties of the region in which it is used. For example, asphalt, which has good quality at a high temperature (60 ⁰ C), maiy have poor quality at room temperature (15°C) or a low temperature (4°C). Therefore, it is very important to select and use asphalt that is suitable for the climatic

conditions of the region. Furthermore, to improve the quality of the asphalt, many additives, including hydrocarbons, have been employed, but satisfactory improvement effects have not been attained thereby.

These days, research into the improvement of the quality of asphalt through the addition of material, including a polymer modifier, is being intensively and extensively conducted. In US Patent Nos. 3,985,694 and 4,130,516, asphalt is added with a polymer, such as polyolefin or styrene-butadiene rubber, to thus improve the properties thereof, but there is a problem in that adhesion at room temperature (15°C) is not improved. In addition, US Patent No. 5,221,703 discloses a method of preparing an asphalt/polymer composition having improved properties thanks to the use of oil and a polymer modifier, such as styrene-butadiene rubber. In this patent, the polymer modifier and the oil are added, thereby improving properties including viscosity. In particular, although properties at a low temperature (4°C) may be improved, there is little or no effect of improvement on adhesion at room temperature (15°C) or on anti-aging performance, indicating the ability to maintain quality upon storage at high temperatures. That is, in the case where styrene-butadiene-based polymer modifiers are stored at high temperatures for long periods of time, oxidation or deterioration may occur, undesirably resulting in degraded properties. Therefore, not only improvement of the properties, but also prevention of degradation in the properties due to long storage, that is, improvement of anti-aging performance, are becoming increasingly important issues. [Disclosure]

[Technical Problem]

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide an asphalt composition having superior adhesion at room temperature, in particular, having greatly improved anti-aging performance.

[Technical Solution]

One aspect of the present invention, which was devised to accomplish the above object, pertains to a method of preparing an asphalt composition having improved mechanical properties and anti-aging performance, comprising mixing, at 110~220°C, 90-99.9 wt% of asphalt or bitumen (component A) having viscosity of 100-1,000,000 poise (at 60°C) and penetration of 5-400 ditnm (1/10 mm) (at 25°C) with 0.1-10 wt% of one or more polymers (component B) selected from the group consisting of a styrene polymer having a weight average molecular weight of 50,000-2,000,000 and having a styrene content of 20-50 wt%, ethylene methacrylate, ethylene propylene rubber or ethyl vinyl acetate random copolymer, having a weight average molecular weight of 50,000-1 ,000,000 and having an ethylene content of 40-99.7 wt%, and an isoprene polymer having a weight average molecular weight of 50,000-1,000,000.

Another aspect of the present invention, which was devised to accomplish the above object, pertains to an asphalt composition having improved mechanical properties and anti-aging performance, comprising 90-99.9 wt% of asphalt or bitumen (component A) having viscosity of 100-1,000,000 poise (at 60°C) and penetration of 5-400 dmm (1/10 mm) (at 25°C); and

0.1-10 wt% of one or more polymers (component B) selected from the group consisting of a styrene polymer having a weight average molecular weight of 50,000-2,000,000 and having a styrene content of 20-50 wt%, ethylene methacrylate, ethylene propylene rubber or ethyl vinyl acetate random copolymer, having a weight average molecular weight of 50,000-1 ,000,000 and having an ethylene content of 40-99.7 wt%, and an isoprene polymer having a weight average molecular weight of 50,000-1,000,000.

[Advantageous Effects]

According to the present invention, an asphalt composition prepared by adding conventional asphalt with a polymer is superior in mechanical properties, including viscosity,

softening point, and ductility, and undergoes little change in ductility even upon high-temperature storage, and thus may have considerably improved anti-aging performance and storage stability. Therefore, the asphalt composition may be directly applied to road pavement, and as well, the composition is reprocessed into an emulsified state and then may be widely applied to road pavement or as an industrial waterproof material. [Description of Drawings]

FIG. 1 shows the process of measuring the penetration of asphalt cement; FIG. 2 shows the process of measuring the ductility of asphalt cement; and FIG. 3 shows the process of evaluating the degree of aging of asphalt cement. [Best Mode]

Hereinafter, a detailed description will be given of the present invention. As mentioned above, the asphalt composition according to the present invention is characterized in that asphalt or bitumen (component A) is mixed with one or more polymers (component B). Also, one or more components selected from among a) free sulfur, b) an aromatic hydrocarbon compound having an aromatic content of 80 wt% or more, and c) a stabilizer may be further added, if necessary.

The asphalt (component A), which is the primary component of the asphalt composition of the present invention, is not particularly limited, as long as it has viscosity of

100-1,000,000 poise (at 6O ⁰ C) and penetration of 5-400 dmm (1/10 mm) (at 25°C) according to the ASTM standard. The asphalt includes various types of straight-run asphalt produced from crude oil, straight-run asphalt diluted with a diluent selected from among paraffinic, aromatic, naphthanic hydrocarbons and mixtures thereof, and oxidized straight-run asphalt.

Further, specific asphalt, other than petroleum asphalt, including coal tar pitch or Trinidad asphalt, may be included. More preferably, the use of asphalt, which has a flash point of at least 230°C (COC type, ASTM D-92) and in which the asphaltene content is 2-40 wt%

(analysis method: ASTM D 4142), is effective.

The asphalt is contained in the composition of the present invention in an amount of 90-99.9 wt%. In the case where the amount of asphalt falls outside the above range, problems, in which performance improvement effects are insignificant or flexibility is decreased, may occur.

Used as the secondary component of the asphalt composition of the present invention, the polymer functions as a polymer modifier to improve the quality of asphalt. The polymer modifier is typically classified into (1) thermoplastic polymer, (2) natural and synthetic rubber, (3) thermoplastic rubber, and (4) thermosetting polymer. The modifier may be applied depending on the mechanical properties that are desired to be improved. That is, to improve the quality at high temperatures, polyolefm resin may be used. Furthermore, to improve the quality both at high temperatures and at low temperatures, rubber is used. In this case, particularly useful is a styrene polymer having high compatibility with asphalt.

The polymer used in the present invention specifically includes a styrene polymer having a weight average molecular weight of 50,000-2,000,000 and having a styrene content of 20-50 wt%, ethylene methacrylate, ethylene propylene rubber or ethyl vinyl acetate random copolymer, having a weight average molecular weight of 50,000-1,000,000 and having an ethylene content of 40-99.7 wt%, or an isoprene polymer having a weight average molecular weight of 50,000-1,000,000, which may be used alone or in mixtures of two or more thereof. Preferably, the polymer may be contained in the composition of the present invention in an amount of 0.1-10 wt%. hi the case where the amount of the polymer falls outside the above range, problems related to insignificant performance improvement effects or no additional improvement effects occur.

The polymer may be used in the form of either a solid or a latex. In the present invention, with the goal of improving both mechanical properties and anti-aging performance, it

is preferred that a polymer composed of very small particles be mixed with asphalt.

Specifically, when the polymer is used in a solid form, the polymer should be ground into very small particles using a high-speed shearing Mixer, such as a homogenizer, after having been added to asphalt. Thus, if the solid polymer is ground to a size as small as possible before it is added to the asphalt, the period of time required for mixing the polymer with the asphalt may be decreased.

On the other hand, in the case of the polymer in a latex form, since it already has a very small particle size and thus is present in a state of being mixed with water, such a polymer may be used in a manner such that it is mixed with asphalt, and then only water is removed. In this case, water may be removed through various methods known in the art. Furthermore, when the styrene polymer in a latex form is mixed with asphalt, water may be removed through evaporation by heat.

In the present invention, in the case where the styrene polymer is used in a latex form, it preferably has a solid content of 5-70 wt% and a molecular weight of 50,000-2,000,000 g/mol. In the case where the isoprene polymer is used in a latex form, it preferably has a solid content of 30-70 wt% and a molecular weight of 50,000-1,000,000 g/mol.

In the present invention, the mixing of the asphalt or bitumen (component A) and the polymer (component B) may be effectively conducted at 110~220°C, in consideration of the capabilities of mixing and oxidation of the above two components. Further, to more improve the mechanical properties of the asphalt/polymer composition, 1-10 wt% of hydrocarbon having an aromatic content of 80 wt% or more, and

0.01-5 wt% of free sulfur may be separately or simultaneously added before or after the addition of the polymer. This mixing is preferably conducted at 110~220°C, and more preferably at 130~200°C. The individual mixing procedures may be conducted via stirring while the mixing time is controlled in the range from 10 min to 10 hours depending on need.

In the case where the polymer in a latex form, which includes water and solid mixed together, is mixed with asphalt, water may evaporate and boil over during the mixing. Such a boil-over phenomenon is considered to occur because too large an amount of the latex is mixed within a short time. Thus, it is necessary to control the amount of the latex to be mixed. The polymer within the latex is preferably added at a rate of 0.1—1.0 wt%, based on the asphalt, per hour, and more preferably 0. l~0.5 wt%, based on the asphalt, per hour.

In addition to the free sulfur and aromatic hydrocarbon compound, the additive may include a stabilizer. When the asphalt/polymer composition according to the present invention is stored at high temperatures, the properties thereof may be degraded due to oxidation and deterioration. As such, this problem may be overcome using an appropriate stabilizer for the composition of the present invention. Specific examples of the stabilizer include an amine compound including N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine or N-isopropyl-N- phenyl-p-phenylenediarnine, a phosphite compound including tris(2,4-di-t- butylphenyl)phosphite, a phenol compound including 2-methyl-4,6-bis[(octylthio)- methyl]phenol, and a propionate compound including pentaerythrityl-tetrakis[3-(3,5-di-tert- butyl-4-hydroxyphenyl)-propionate], which may be used alone or in mixtures of two or more thereof.

The stabilizer is preferably used in an amount of 0.001-1 wt% based on the amount of asphalt or bitumen. In the case where the amount of the stabilizer falls outside the above range, the improvement effects on aging are insignificant, and no additional improvement effects occur.

The properties of the asphalt composition thus prepared may be evaluated through conventional standard tests. The evaluation items are given in Table 1 below.

TABLE l

In the present invention, the degree of improvement on anti-aging performance is evaluated by measuring properties before and after storage, in particular, by measuring ductility after thin film oven test, ASTM D- 1754. That is, in the case where the difference in properties before and after storage is small, anti-aging performance is evaluated to be superior.

According to the present invention, the asphalt/polymer composition or the asphalt/polymer/stabilizer composition including the stabilizer may be directly applied to road pavement. Furthermore, the invented composition is reprocessed into an emulsified state, and may thus be used for roεid pavement or as industrial waterproof material. [Mode for Invention]

Below, the present invention is more specifically described through the following examples, but the scope of the present invention is not limited thereto. In the following examples and comparative examples, the amounts of respective materials were represented by weight based on the total weight of asphalt/polymer/stabilizer.

Comparative Example 1

A composition comprising 100% asphalt having penetration of 70 (at 25°C) according to the ASTM standard, produced through distillation using Middle Eastern crude oil, was prepared and measured for penetration, softening point, viscosity, PI (Penetration Index), and ductility at room temperature before and after heating. The results are shown in Table 2 below.

Comparative Example 2

A composition, comprising 100% asphalt having penetration of 72 (at 25°C) according to the ASTM standard, produced through distillation using Chinese crude oil, instead of Middle Eastern crude oil, was prepared and measured for the same properties as in Comparative Example 1. The results are shown in Table 2 below.

Comparative Example 3

A composition, comprising 100% asphalt having penetration of 85 (at 25°C) according to the ASTM standard, produced through distillation using Chinese crude oil, was prepared and measured for the same properties as in Comparative Example 1. The results are shown in Table 2 below.

Comparative Example 4 A composition, comprising 100% asphalt having penetration of 35 (at 25 ⁰ C) according

to the ASTM standard, produced through distillation using Chinese crude oil, was prepared and measured for the same properties as in Comparative Example 1. The results are shown in Table 2 below.

Comparative Example 5

99 wt% of the asphalt produced in Comparative Example 3 was added with 1 wt% of natural asphalt in a reactor at 180°C, and then stirred for 1 hour, thus preparing an asphalt composition.

Comparative Example 6

91 wt% of the asphalt produced in Comparative Example 4 was added with 9 wt% of hydrocarbon having 91% aromatic content in a reactor at 150°C, and then stirred for 1 hour, thus preparing an asphalt composition.

Comparative Example 7

91 wt% of the asphalt produced in Comparative Example 4 was added with 9 wt% of hydrocarbon having 82% aromatic content in a reactor at 150 ⁰ C, and then stirred for 1 hour, thus preparing an asphalt composition.

Comparative Example 8

91 wt% of the asphalt produced in Comparative Example 4 was added with 9 wt% of hydrocarbon having 66% aromatic content in a reactor at 150 ⁰ C, and then stirred for 1 hour, thus preparing an asphalt composition.

Example 1

99.5 wt% of the asphalt produced in Comparative Example 1 was added with 0.5 wt% of ethylene methacrylate, having an average molecular weight of 150,000 g/mol, and then stirred at 150°C for 2 hours, thus preparing an asphalt composition according to the present invention.

Example 2

99.5 wt% of the asphalt produced in Comparative Example 1 was mixed with 0.5 wt% of ethylene propylene rubber, having an average molecular weight of 200,000 g/mol, at 150°C, and then stirred for 2 hours, thus preparing an asphalt composition according to the present invention.

Example 3

99.5 wt% of the asphalt produced in Comparative Example 1 was mixed with 0.5 wt% of ethylenevinylacetate, having an average molecular weight of 350,000 g/mol, and then stirred at 150 ⁰ C for 2 hours, thus preparing an asphalt composition according to the present invention.

Example 4

99.6 wt% of trie asphalt produced in Comparative Example 1 was added with 0.4 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 1,000,000 g/mol and containing 23% styrene, and then stirred in a reactor at 18O ⁰ C for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 5

99.6 wt% of trie asphalt produced in Comparative Example 1 was added with 0.4 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 50,000 g/mol and containing 23 wt% styrene, in a reactor at 18O ⁰ C, and then stirred for 1 hour, thus preparing an

asphalt composition according to the present invention.

Example 6

99.48 wt% of the asphalt produced in Comparative Example 1 was mixed with 0.4 wt% of a sryrene-butadiene polymer, having a weight average molecular weight of 1,000,000 g/mol and containing 23 wt% styrene, in a reactor at 180°C, stirred for 1 hour, further added with 0.02 wt% of free sulfur, stirred for 30 min, and then mixed with 0.1 wt% of pentaerythrityl-tetrakis[3- (3,5-di-tert-butyl-4-hydroxyphenyl)propionate] for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 7

99 wt% of the asphalt produced in Comparative Example 2 was added with 1 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 400,000 g/mol and containing 23% styrene, and then stirred at 13O ⁰ C for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 8

98.99 wt% of the asphalt prepared in Comparative Example 2 was added with 1 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 400,000 g/mol and containing 23% styrene, and with 0.01% of free sulfur, and then stirred at 140°C for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 9

97 wt% of the asphalt of Comparative Example 2 was mixed with 2 wt% of a styrene- butadiene polymer, having a weight average molecular weight of 400,000 g/mol and containing

23% styrene, stirred for 1 hour, further added with 1 wt% of free sulfur, and then stirred at 130°C for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 10 99.2 wt% of the asphalt composition prepared in Comparative Example 6 was added with 0.8 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 400,000 g/mol and containing 23% styrene, and then stirred at 13O ⁰ C for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 11

98 wt% of the asphalt composition prepared in Comparative Example 6 was added with 2 wt% of an isoprene polymer, having a weight average molecular weight of 100,000 g/mol, and then stirred at 12O ⁰ C for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 12

99 wt% of the composition prepared in Comparative Example 6 was added with 1 wt% of an isoprene polymer, having a weight average molecular weight of 700,000 g/mol, and then stirred at 150 ⁰ C for 1 hour, thus preparing an asphalt composition according to the present invention.

Example 13

99.6 wt% of the asphalt of Comparative Example 1 was added with 0.3 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 1,000,000 g/mol and containing 23% styrene, stirred at 18O ⁰ C for 1 hour, and then further added with 0.1 wt% of an

isoprene polymer having a weight average molecular weight of 300,000 g/mol, thus preparing an asphalt composition according to the present invention.

Example 14 99.59 wt% of the asphalt of Comparative Example 1 was added with 0.4 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 1,000,000 g/mol and containing 23% styrene, stirred at 180°C for 1 hour, further added with 0.01 wt% of phenylenediamine-based N-isopropyl-N'-phenyl-p-phenylenediamine, and then mixed for 30 min, thus preparing an asphalt composition according to the present invention.

Example 15

99.58 wt% of the asphalt of Comparative Example 1 was added with 0.3 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 1,000,000 g/mol and containing 23% styrene, stirred at 180 ⁰ C for 1 hour, further added with 0.1 wt% of an isoprene polymer, having a weight average molecular weight of 300,000 g/mol, furthermore added with 0.02 wt% of phenylenediamine-based N-isopropyl-N'-phenyl-p-phenylenediamine, and then mixed for 30 min, thus preparing an asphalt composition according to the present invention.

Example 16 To 99 wt% of the asphalt of Comparative Example 1, 0.8 wt% of a styrene-butadiene polymer in a latex form, having a weight average molecular weight of 1,000,000 g/mol and containing 23% styrene, was added at a rate of 0.5 wt% per hour, after which the mixture was stirred at 200°C for 1 hour, added with 0.1 wt% of an isoprene polymer having a weight average molecular weight of 300,000 g/mol and further with 0.1 wt% of phenylenediamine-based N- isopropyl-N'-phenyl-p-phenylenediamine, and then mixed for 30 min, thus preparing an asphalt

composition according to the present invention.

Example 17

90 wt% of asphalt having penetration of 350, produced from Chinese crude oil, was added with 8 wt% of a styrene-butadiene polymer, having a weight average molecular weight of 400,000 g/mol and containing 23% styrene, stirred at 200°C for 2 hours, further added with 1 wt% of an isoprene polymer having a weight average molecular weight of 200,000 g/mol and then with 0.5 wt% of N-isopropyl-N'-phenyl-p-phenylenediamine and 0.5 wt% of tris(2,4-di-t- butylphenyl)phosphite, and then mixed for 30 min, thus preparing an asphalt composition according to the present invention.

Example 18

98 wt% of the asphalt of Comparative Example 1 was added with 1.3 wt% of a styrene- butadiene polymer, having a weight average molecular weight of 400,000 g/mol and containing 23% styrene, stirred at 180°C for 2 hours, mixed with 0.3 wt% of an isoprene polymer having a weight average molecular weight of 200,000 g/mol, and then further mixed with 0.1 wt% of N- isopropyl-N'-phenyl-p-phenylenediamine, 0.1 wt% of tris(2,4-di-t-butylphenyl)phosphite, 0.1 wt% of 2-methyl-4,6-bis-[(octylthio)-methyl]phenol, and 0.1 wt% of pentaerythrityl-tetrakis[3- (3,5-di-tert-butyl-4-hydroxyphenyl)-propionate], thus preparing an asphalt composition according to the present invention.

Example 19

90.5 wt% of the asphalt produced in Comparative Example 4 was added with 9 wt% of hydrocarbon, having 82% aromatic content, stirred at 180°C for 1 hour, added with 0.5 wt% of a styrene-butadiene polymer, having an average molecular weight of 1,000,000 g/mol and

containing 23 wt% styrene, and then stirred for 1 hour, thus preparing an asphalt composition according to the present invention.

The properties, including penetration, softening point, and ductility, before and after heating the thin film, of the asphalt compositions of Comparative Examples 1~8 and Examples 1 — 19 were measured. The results are shown in Table 2 below.

TABLE 2

*PI (Penetration Index): Index for evaluation of temperature susceptibility by measuring penetration at 15 ⁰ C, 25°C, 30°C. Temperature susceptibility is decreased in inverse proportion to an increase in the above numerical index (quality is evaluated to be superior when the numerical index is low). PI = [20*(l-25A)]/(l+50A) (wherein A is a gradient in the relationship between temperature and penetration)

The asphalt, which is mainly used both at domestic and abroad, is classified into AP-5 asphalt, having penetration of 60-80, and AP-3 asphalt, having penetration of 80-100, depending on the penetration grade, determined by measuring hardness of asphalt at 25 ⁰ C. In this case, since the quality of the asphalt is greatly affected by the properties of the crude oil, the asphalt produced from specific crude oil is limited in quality. For example, asphalt having low penetration has high viscosity but has poor ductility. In contrast, asphalt having high penetration has low viscosity but good ductility. Thus, there is a limitation in improving the quality of the penetration-graded asphalt produced from crude oil.

However, in the present invention, as is apparent from Table 2, the polymer was used, and the stabilizer was selectively used, and thereby viscosity, softening point, and PI, which represents a temperature susceptibility, were improved while the penetration grade of various types of crude oil was maintained at the same level. In particular, ductility before and after thin film oven test was confirmed to be remarkably improved. Further, compared to compositions containing no free sulfur, the composition containing free sulfur was improved in softening point and viscosity, but ductility was not improved. Furthermore, although the addition of ethylenevinylacetate led to improved quality, improvement effects on ductility were lower than when the styrene polymer and the isoprene polymer were separately or simultaneously used. Moreover, when the composition including the asphalt and the polymer is mixed with the appropriate stabilizer, resistance to aging may be increased, the results of which may be confirmed in the following comparative example and examples. To evaluate anti-aging

performance, the composition was stored at a high temperature (12O ⁰ C) for a long period of time, and then the property before and after storage, in particular, ductility after thin film oven test, was measured. The results are shown in Table 3 below.

TABLE 3

In Examples 4, 6, 15 and 16, in which the asphalt, the polymer and the stabilizer were mixed, ductility was not greatly changed even upon storage at high temperatures for 10 days, thereby exhibiting remarkably improved anti-aging performance and storage stability.

From the above results, the method of the present invention can be seen to enable the improvement .of the quality of various types of asphalt. In particular, adhesion evaluated by measuring ductility (at 15°C, ASTM Dl 13) is proved to be drastically improved. Further, in addition to the ductility, the mechanical properties of asphalt, including penetration, softening point, and PI, may be seen to be improved.