Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-11-28
2002-06-18
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S068000, C524S069000, C524S070000, C524S071000
Reexamination Certificate
active
06407152
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the preparation of asphalt polymer compositions through the use of a multi-component crosslinking system incorporating a thiopolymer and at least one other crosslinking component.
BACKGROUND OF THE INVENTION
The use of bitumen (asphalt) compositions in preparing aggregate compositions (bitumen +rock) useful as road paving material is complicated by at least three factors, each of which imposes a serious impediment to providing an acceptable product. First, the bitumen compositions must meet certain performance criteria or specifications in order to be considered useful for road paving. For example, to ensure acceptable performance, state and federal agencies issue specifications for various bitumen applications including specifications for use as road pavement. Performance standards and properties relating to asphalt cements are set forth in various standards of the American Society for Testing and Materials (ASTM) and the American Associate of State Highway and Transportation Officials (AASHTO). Current Federal Highway Administration specifications designate a bitumen (asphalt) product, for example, AC-20R (“R” meaning rubber modified), as meeting defined parameters relating to properties such as viscosity, toughness, tenacity and ductility. Each of these parameters define an important feature of the bitumen composition and compositions failing to meet one or more of these parameters may well render that composition unacceptable for use as road pavement material. Table 1 sets forth the properties of various grades of asphalt cement (AC) as determined in accordance with AASHTO M-226 (Specification for Viscosity-Graded Asphalt Cement).
TABLE 1
Properties of Various Asphalt Grades
TEST
AASHTO M-226
AC 2.5
AC 5
AC 10
AC 20
AC 30
AC 40
Viscosity @140° F., poise
250 + 50
500 + 100
1000 + 200
2000 + 400
3000 + 600
4000 + 800
(AASHTO T-202)
Viscosity @275° F.; cSt,
125
175
250
300
350
400
minimum (AASHTO T-201)
Pen. @77° F.; minimum
220
140
80
60
50
40
AASHTO t-49)
Flash Point, COC
325
350
425
450
450
450
Minimum ° F.
Ductility After TFOT
100
100
75
50
40
25
(AASHTO T-179)
@77° F., 5 cm/min,
minimum
Viscosity After TFOT
1000
2000
4000
8000
12000
16000
(AASHTO T-179)
@140° F., poise
minimum
AR1000
AR2000
AR4000
AR8000
AR16000
Viscosity @140° F., poise
1000 + 250
2000 + 500
4000 + 1000
8000 + 2000
16000 + 4000
(AASHTO T-202)
Viscosity @275° F., cSt
140
200
275
400
500
minimum (AASHTO T-201)
Pen. @77° F., minimum
65
40
25
20
20
(AASHTO T49)
Percent of Original
B
40
45
50
52
Pen. @77° F., minimum
Ductility @77° F.,
100
100
75
75
75
minimum, 5 cm/min
Conventional bitumen compositions frequently cannot meet all of the requirements of a particular specification simultaneously and, if these specifications are not met, damage to the resulting road can occur, including permanent deformation, thermally induced cracking and flexural fatigue. This damage greatly reduces the effective life of paved roads.
In this regard, it has long been recognized that the properties of conventional bitumen compositions can be modified by the addition of other substances, such as polymers. A wide variety of polymers have been used as additives in bitumen compositions. For example, copolymers derived from styrene and conjugated dienes, such as butadiene or isoprene, are particularly useful, since these copolymers have good solubility in bitumen compositions and the resulting modified-bitumen compositions have good Theological properties.
It is also known that the stability of polymer-bitumen compositions can be increased by the addition of crosslinking agents such as sulfur, frequently in the form of elemental sulfur. It is believed that the sulfur chemically couples the polymer and the bitumen through sulfide and/or polysulfide bonds. The addition of extraneous sulfur is required to produce the improved stability, even though natural bitumens naturally contain varying amounts of native sulfur.
Thus, U.S. Pat. No. 4,145,322, issued Mar. 20, 1979 to Maldonado et al., discloses a process for preparing a bitumen-polymer composition consisting of mixing a bitumen, at 266°-446° F. (130°-230° C.), with 2 to 20% by weight of a block copolymer, having an average molecular weight between 30,000 and 300,000, with the theoretical formula S
x
—B
y
, in which S corresponds to styrene structure groups and B corresponds to conjugated diene structure groups, and x and y are integers. The resulting mixture is stirred for at least two hours, and then 0.1 to 3% by weight of sulfur relative to the bitumen is added and the mixture agitated for at least 20 minutes. The preferred quantity of added sulfur cited in this patent is 0.1 to 1.5% by weight with respect to the bitumen. The resulting bitumen-polymer composition is used for road coating, industrial coating, or other industrial applications.
U.S. Pat. No. 4,130,516, issued Dec. 19, 1978 to Gagle et al., discloses an asphalt (bitumen) polymer composition obtained by hot-blending asphalt with 3 to 7% by weight of elemental sulfur and 0.5 to 1.5% by weight of a natural or synthetic rubber, preferably a linear, random butadiene/styrene copolymer. U.S. Pat. No. 3,803,066, issued Apr. 9, 1974 to Petrossi, also discloses a process for preparing a rubber-modified bitumen by blending rubber, either natural or synthetic, such as styrene/butadiene rubber, with bitumen at 293°-365°F. (145°-185° C.), in an amount up to 10% by weight based on the bitumen, then adjusting the temperature to 257°-320° F. (125°-160°C.), and intimately blending into the mix an amount of sulfur such that the weight ratio of sulfur to rubber is between 0.3 and 0.9. A catalytic quantity of a free-radical vulcanization-accelerator is then added to effect vulcanization. This patent recites the critical nature of the sulfur to rubber ratio, and teaches that weight ratios of sulfur to rubber of less than 0.3 gives modified bitumen of inferior quality.
Although polymer-modified bitumen compositions are known, these previously described compositions are not necessarily useful for road paving applications. For example, mixing NorthWest paving asphalt having an initial viscosity of 682 poise at 140° F. (60° C.) with 3.6 weight percent Kraton®-4141, a commercially available styrene-butadiene tri-block copolymer which contains 29 weight percent plasticizer oil, and 0.25% sulfur gives a modified-asphalt composition with a viscosity of 15,000 poise at 140° F. (60° C.). This viscosity, however, greatly exceeds the acceptable viscosity range set by the widely used AC-20R specification for paving asphalt. This specification, issued by the Federal Highway Administration, requires bitumen compositions to have a viscosity in the range of 1600-2400 poise at 140° F. (60° C.). Thus, the modified bitumen compositions produced by the procedures of U.S. Pat. No. 4,145,322 using Kraton®-4141 would be unacceptable for use in road paving under the AC-20R specification.
A second factor complicating the use of bitumen compositions involves the viscosity stability of such compositions under storage conditions. In this regard, bitumen compositions are frequently stored for up to 7 days or more before being used and, in some cases, the viscosity of the composition can increase so much that the bitumen composition is unusable for its intended purpose. On the other hand, a storage stable bitumen composition would provide for only minimal viscosity increases and, accordingly, after storage it can still be employed for its intended purpose.
A third factor complicating the use of bitumen compositions involves the use of volatile solvents in such compositions. Specifically, while such solvents have been heretofore proposed as a means to fluidize bitumen-polymer compositions containing relatively small amounts of sulfur which compositions are designed as coatings (Maldonado et al., U.S. Pat. No. 4,242,246), environmental concerns restrict the use of volatile solvents in such compo
Butler James R.
Kelly Kevin P.
Fina Technology, Inc.
Jackson William D.
Szekely Peter
LandOfFree
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