Improved pressure sensitive bituminous compositions

Abstract: A pressure sensitive bituminous composition having improved tack and adhesiveness, comprising: (1) from about 50 to about 87% of a bituminous component; from about 1 to about 15% of a thermoplastic block copolymer, M₁, of the A-B-A type, preferably styrene-butadiene-styrene; (3) from about 1 to about 10% of a block copolymer, M₂, of the A-B type, preferably styrene-butadiene; and (4) from about 5 to about 50% of a fumed silica. The fumed silica is an active ingredient which absorbs excess oil and improves the tack and adhesiveness of the final composition.

Description: The present invention relates to novel pressure sensitive bituminous compositions which are especially useful in the preparation of articles requiring self-adhesive properties based on bituminous compositions and which are cold applicable. The compositions, according to the present invention, as defined in claim 1, comprise at least a bituminous component, two different polymeric components and a fumed silica and exhibit improved tack and adhesiveness. Compositions consisting of a bituminous component, thermoplastic polymer component, and various fillers are known in the art. They can be applied in the production of products such as below grade waterproofing, water-resistant membranes for road application, and in roofing membranes. Such compositions, however, typically require the use of solvent based bitumen mastics or application with hot bitumen, which require additional equipment not readily available to the average individual. Heretofore fillers have been admixed with bituminous and thermoplastic polymer compositions as inactive ingredients used for decreasing cost and extending the composition. Commonly used fillers include limestone, dolomite, fly ash and silica sand, e.g. For instance U.S. Patent Number 4,196,115 to Bresson discloses an asphalt composition with at least two different copolymers derived from a conjugated diene and a monovinyl aromatic and fillers such as silicates and carbonates, e.g. and mineral aggregates such as sand, chat, pebbles or rock. These fillers play no role as an active ingredient of the composition and are therefore considered as a minor component. The present invention addresses the current need for a cold applicable bituminous composition for roofing and paving materials with improved tack and adhesiveness. The inventive composition replaces the need for hot bituminous adhesives which create hazardous fumes, as well as requiring expensive equipment, and also reduces the release of volatile organic compounds (voc's) into the atmosphere found in cold application cements. The present invention incorporates the use of fumed silica as an active ingredient in the bituminous composition. The use of fumed silica improves the composition in several areas not indicated in the prior art. As an active ingredient, the fumed silica promotes the retention of oils in the composition that, if not retained, reduce the adhesive characteristics of the bituminous composition. The interactive nature of the fumed silica promotes increased tack and adhesion of the bituminous composition. Adhesion to various substrates such as aluminum, galvanized metal, wood, and masonry is enhanced by the fumed silica. The performance (adhesion, slipping) of the present inventive composition on vertical angles at high temperatures is markedly improved over similar compositions that exclude the use of fillers or use a nonactive filler (e.g., limestone, silica sand and fly ash). The present invention relates to a pressure sensitive bituminous composition as defined in claim 1, which exhibits excellent adhesiveness and tack. Specifically, the novel pressure sensitive bituminous composition as defined in claim 1, comprises by weight from 50 to 87% of a bituminous component; from 1 to 15% of a thermoplastic A-B-A type block copolymer, M 1 ; from 1 to 10% of a thermoplastic A-B type block copolymer, M 2 , such that the percentage of M 1 and M 2 in combination is at least about 3%; and at least 5% fumed silica. A preferred pressure sensitive bituminous composition comprises at least 61% of a bituminous component; from 5 to 10% of a thermoplastic A-B-A type block copolymer, M 1 ; from 2 to 3% of a thermoplastic A-B type block copolymer, M 2 ; and from 20 to 30% fumed silica. A most preferred pressure sensitive bituminous composition comprises at least 62% of a bituminous component; from 7 to 8% of a thermoplastic A-B-A type block copolymer, M 1 ; from 2.1 to 2.4% of a thermoplastic A-B type block copolymer, M 2 ; and from 23 to 27% fumed silica, said fumed silica having preferably an average particle diameter less than or equal to about 0.1 µm. A most suitable A-B-A type block copolymer is available from Shell under the trade designation RP6400. A most suitable A-B type block copolymer is also available from Shell under the trade designation DX1118. The features and advantages of the present invention are meant to be illustrative rather than exhaustive. Further advantages and features of the present invention will become apparent while reviewing the detailed description of the invention. The pressure sensitive bituminous composition of the present invention comprises four ingredients (by weight): (1) 50 to 87% bituminous component; (2) 1 to 15% thermoplastic A-B-A type block copolymer (M 1 ); (3) 1 to 10% thermoplastic A-B type block copolymer (M 2 ); and (4) at least 5% fumed silica. The bituminous component is preferably a petroleum asphalt. Examples of suitable bituminous components include distillation or "straight-run" bitumens and blown bitumens. Suitable bituminous components are those having a penetration of from 250-450 (0.1mm) at 25°C as measured by ASTM D5. Preference is given to the use of bitumens having a penetration of from 300-400 (0.1mm) at 250C as measured by ASTM D5. In addition to the penetration parameter, suitable bituminous components have a total aromatic content from 45 to 75% by weight of the bitumen. Preferably, the bituminous component has an aromatic content of 45 to 50% and a polar aromatic content of 16 to 24% by weight of the bituminous component. The amount of bituminous component ranges from 50 to 87% by weight of the total composition. It is preferred that the bituminous component represents at least 61% by weight of the total composition and more preferably at least 62%. According to the invention, use is made of two different polymers, M 1 and M 2 each having a different function. Polymeric component M 1 serves to give the final composition an improved resistance to flow at higher temperatures, while polymeric component M 2 causes improved tack and improved adhesion to other materials. Polymeric component M 1 is a block copolymer of A-B-A type. Preferably, polymeric component M 1 has polystyrene end blocks A and a rubbery polybutadiene midblock B. However, other suitable A-B-A type block copolymers are described in U.S. Patent No. 3,978,014. These A-B-A type block copolymers have polymer blocks A which are the same or different thermoplastic non-elastomeric polymers prepared by polymerization of one or more monoalkenyl aromatics and at least one polymer block B which is an elastomeric polymer block prepared either by polymerization of one or more conjugated alkadienes or by copolymerization of one or more conjugated alkadienes with one or more monovinyl aromatics. Preferably, the average molecular weight of polymeric component M 1 is 150,000 to 200,000, with the most preferred average molecular weight being 175,000 to 180,000. A polymer composition which meets the above specifications and has been found to impart desired characteristics is available from Shell under the trade designation RP6400. RP6400 primarily consists of an A-B-A type (styrene-butadiene-styrene) block copolymer and a small portion of A-B type block copolymer and has an average molecular weight of 172,044, a solubility parameter of 7.8 to 8.8 and a crystallinity of 0.07% at 25°C. Copolymers that may be used as component M 2 according to the invention, must be of the A-B type in which block A represents a thermoplastic polymer block prepared by polymerization of one or more alkenyl aromatics and block B represents an elastomeric polymer block prepared either by polymerization of one or more conjugated alkadienes or by copolymerization of one or more conjugated alkadienes with one or more monovinyl aromatics. Preferably, polymeric component M 2 has one end block A of polystyrene and a rubbery polybutadiene block B and has an average molecular weight between 85,000 and 105,000, with the most preferred average molecular weight between 95,000 and 98,000. A copolymer which meets the specifications of component M 2 and has been found to impart the desired characteristics is available from Shell under the trade designation DX1118. DX1118 contains an A-B type block copolymer and has an average molecular weight of 96,688, a solubility parameter of 7.8 to 8.8 and a crystallinity of 0% at 25°C. The amount of block copolymer M 1 ranges from 1 to 15% by weight of the final composition. Preferably, the amount of block copolymer M 1 ranges from 5 to 10% by weight of the final composition and most preferably from 7 to 8%. The amount of block copolymer M 2 ranges from 1 to 10% by weight of the final composition. Preferably, the amount of block copolymer M 2 ranges from 2 to 3% by weight of the final composition and most preferably from 2.1 to 2.4%. The total amount of the two block copolymers M 1 and M 2 in the final composition should be at least 3% by weight of the final composition. Preferably, the total amount of the two block copolymers in the final composition ranges from 9.1 to 10.4% by weight of the final composition. The pressure sensitive bituminous composition according to the present invention further comprises a fumed silica. Fumed silicas typically have an average particle size ranging from 1.0 µm to less than 0.007 µm in diameter. Preferably, the average particle size of the fumed silica is less than 0.5 µm in diameter with an average particle size of less than or equal to about 0.1 µm being most preferred. A suitable fumed silica is available from Analytical Materials, Inc., located in Joplin, Missouri. This fumed silica is derived from a ferro-silicate alloy manufacturing process and is especially fine, with particles having an average diameter of 0.1 µm and a density of 160 to 192 kg/m 3 (10-12 pounds per cubic foot) and contains by weight 75-80% amorphous silicon dioxide and 20 to 25% metal oxides and inert fillers. The amount of the fumed silica used in the present invention represents at least 5% by weight of the final composition. The preferred amount of fumed silica to be used in the pressure sensitive bituminous composition ranges from 20 to 30% by weight of the final composition with 23 to 27% being most preferred. It has been found that use of the fumed silica imparts improved tack and adhesiveness to the bitumen-polymer compositions disclosed herein. Hence, the fumed silica, unlike the fillers used in polymer modified bitumen compositions heretofore, is an active, property enhancing ingredient. It has also been found that the fumed silica promotes the retention of oils in the composition which, if not retained, reduces the adhesive properties of the final composition. In summary, the preferred embodiments of the present invention are as follows: Percent by Weight of Final Composition Component Suitable Preferred Most Preferred Bituminous component 50-87 at least 61 at least 62 Copolymer (A-B-A), M 1 1-15 5-10 7-8 Copolymer (A-B), M 2 1-10 2-3 2.1-2.4 Fumed Silica at least 5 20-30 23-27 The inventive composition is conveniently made by first blending, by conventional methods, the two thermoplastic polymers, M 1 and M 2 , with the bituminous component at temperatures between 163 to 218°C (325-425°F). Next, the fumed silica is added to the thermoplastic polymer modified bitumen by mixing, preferably by paddle mixers, while the thermoplastic polymer modified bitumen is maintained above 163°C (325°F). The inventive composition may be used in several different roofing applications and on different carriers. For example, the composition may be used in conjunction with polyester or fiberglass reinforcements. The following example is presented to show a preferred embodiment of the invention. It is not intended to limit the scope or content of the disclosure or invention. The preferred composition includes by weight: (1) about 65.25% bitumen (2) about 7.5% M 1 thermoplastic polymer (RP6400) (3) about 2.25% M 2 thermoplastic polymer (DX1118) (4) about 25.0% fumed silica (Analytical Materials, Inc.) The present invention is illustrated by means of the following examples. EXAMPLE 1 A pressure sensitive bituminous composition was prepared by mixing 65.25% weight of a bitumen component having a penetration of 350 (O.lmm) at 25°C as measured by ASTM D5; 7.5% weight of M 1 thermoplastic polymer being a styrene-butadiene-styrene (SBS) block copolymer; 2.25% weight of M 2 thermoplastic polymer being a styrene-butadiene (SB) block copolymer; and 25.0% weight of fumed silica. The pressure sensitive bituminous composition above was applied to a polyester membrane at a rate of 0.508 to 0.635 mm (20-25 mils), having the dimensions of 2.54 cm (1 inch) by 15.24 cm (6 inches) and weighing 15 grams. Resistance to flow was measured by adhering the 2.54 cm (1 inch) by 15.24 cm (6 inch) strips to an aluminum panel with 20.7 kPa (3 lbs./sq. in.) of pressure for a thirty second time interval. Samples were placed vertically in a forced air oven maintained at 70°C for 7 days with no movement of the sample. This illustrates the adhesive characteristics and thermal stability of the preferred composition. Additional samples consisting of the same components comprised in the preferred composition, but replacing the fumed silica with inexpensive fillers used by those in the art (e.g., limestone, fly ash, and silica sand) were evaluated in the same manner as described above for the preferred composition. The results are given in the following table: HIGH TEMPERATURE ADHESION AND STABILITY Filler Type Percent Loading Result Time (Hours) No filler 0 Failure 4 Fumed Silica 20 Pass No movement after 14 days-test discontinued Fumed Silica 25 Pass No movement after 7 days-test discontinued Fumed Silica 30 Pass No movement after 7 days-test discontinued Dolomite 20 Failure 22-1/2 Dolomite 40 Failure 21-1/2 Limestone 20 Failure 3 Limestone 40 Failure 21 Silica Sand 20 Failure 45 Silica Sand 40 Failure 21 Fly Ash 20 Failure 20 Fly Ash 40 Failure 31 From the results, it is clear that the pressure sensitive bituminous compositions, according to the present invention, possess a more than adequate adhesion under the temperature and orientation as described above. In addition, the use of fumed silica is illustrated to be an active ingredient that promotes the stability and adhesiveness of the composition as contrasted with the inexpensive nonactive fillers known in the industry as extenders. The example and descriptions provided are meant to be a clear indication of the inventive composition.

Claims: A pressure sensitive bituminous composition having improved adhesiveness and tack comprising: (a) from 50 to 87% of a bituminous component having a penetration rate between 250 and 450 (0.1mm) at 25°C and a total aromatic content from 45 to 75% of the bituminous component; (b) from 1 to 15% of a first block copolymer M 1 of the A-B-A type in which the two A blocks are the same or different thermoplastic non-elastomeric polymer blocks prepared by polymerization of one or more monoalkenyl aromatics and in which the polymer block B is an elastomeric polymer block prepared either by polymerization of one or more conjugated alkadienes or by copolymerization of one or more conjugated alkadienes with one or more monovinyl aromatics; (c) from 1 to 10% of a second block copolymer M 2 , of the A-B type in which block A represents a thermoplastic polymer block prepared by polymerization of one or more alkenyl aromatics and block B represents an elastomeric polymer block prepared either by polymerization of one or more conjugated alkadienes or by copolymerization of one or more conjugated alkadienes with one or more monovinyl aromatics, such that the percentage of said first block copolymer M 1 and said second block copolymer M 2 in combination is at least 3%; and (d) at least 5% of a fumed silica, wherein all percentages are weight percent and the sum of all constituents is 100%. The composition of claim 1 wherein the constituents (a) to (d) are contained in the following amounts Constituent Weight-% (a) at least 61 (b) 5-10 (c) 2-3 (d) 20-30 The composition of claim 1 wherein the constituents (a) to (d) are contained in the following amounts Constituent Weight-% (a) at least 62 (b) 7-8 (c) 2.1-2.4 (d) 23-27 The composition of claim 1 wherein the constituents (a) to (d) are contained in the following amounts Constituent Weight-% (a) about 65.25 (b) about 7.5 (c) about 2.25 (d) about 25 The composition of any of the preceding claims wherein said bituminous component (a) has a penetration rate of 300 to 400 (0.1 mm) at 25°C. The composition of any of the preceding claims wherein said total aromatic content in (a) consists of an aromatic content of 45 to 50% and a polar aromatic content of 16 to 24% by weight of said bituminous component (a). The composition of any of the preceding claims wherein said first block copolymer M 1 has an average molecular weight from 150,000 to 200,000, preferably from 175,000 to 180,000. The composition of any of the preceding claims wherein said second block copolymer M 2 has an average molecular weight from 85,000 to 105,000, preferably from 95,000 to 98,000. The composition of any of the preceding claims wherein the percentage of said first block copolymer M 1 and second block copolymer M 2 in combination is from 9.1 to 10.4% by weight of the final composition. The composition of any of the preceding claims wherein said fumed silica (d) has an average particle size below 0.5 µm in diameter, preferably about 0.1 µm or below. The composition of any of the preceding claims wherein said first block copolymer M 1 has polystyrene end blocks A and a rubbery polybutadiene mid block B, and said second block copolymer M 2 has a polystyrene block A and a polybutadiene block B.

Inventors: MITCHELL GRANT D, MITCHELL, GRANT D.
Applicants: TAMKO ROOFING PROD INC, TAMKO ROOFING PRODUCTS, INC.
Application year: 1992
Main classification: C09J195
IPC codes: C08K3, E04D5, C09J195, C08L95