Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-07-24
2001-09-04
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06284820
ABSTRACT:
The present invention relates to bituminous compositions modified with new polyolefinic materials and particularly suitable for applications either of road surfacing type or building waterproofing.
It is known that bitumens employed for these applications are modified by mixing with modifying materials in order to suitably improve the properties. In the non-modified state, in fact, bitumens are easily processable and show good impermeability, but their resistance to ageing is poor and their elastic characteristics are inadequate.
In particular, materials suitable for modifying bitumens must be able to increase the softening temperature and the resistance to elastic failure at high temperatures without negatively affecting the properties at low temperatures and the processability.
Furthermore, the modifying materials must show a good compatibility degree with bitumen, in order to avoid or at least to limit the arising of segregation phenomena between the bitumen phase and the modifying phase, phenomena which could cause a premature worsening of the properties of the material. It has to be kept in mind with regard to this that the compatibility degree modifier-bitumen is not easily foreseeable because of the complex structure and chemical composition of the bitumen and for the variability depending on the starting crude material and production process.
Known modifiers for bitumen are for example homopolymer or copolymer atactic polypropylenes (A-PP), ethylene-propylene rubber (EPR) or ethylene-propylene-ethylidenenorbornene rubber (EPDM), ethylene-vinylacetate copolymer (EVA) or ethylene methylmethacrylate copolymer (EMA) and styrene copolymers such as styrene-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS).
Among these, atactic polypropylenes generally show good blendability with bitumens and improve the properties of these at low temperatures, with a slight increase of the elastic recovery, but they contribute little to increase the softening temperature and the penetration. EVA and EMA copolymers show a good blendability with bitumens and contribute to increase the softening and properties at the penetration, with fair elastic recovery and properties at the low temperatures. EPR or EPDM rubbers in many cases causes insufficiently high softening temperatures and furthermore show blending difficulties with bitumens because of their high viscosity.
SBS and SIS styrene copolymers give the bitumen elasticity at the low temperatures, but they yield bituminous compositions that are not very resistant to penetration at temperatures higher than 50-60° C.; the resistance to ageing is also limited because of the vulnerability of the unsaturated groups to the degrading action of light and atmospheric agents as well as cross-linking phenomena of the product itself.
Also known is the use of mixtures of different modifiers to modify bitumens, these mixtures being used to balance the effects of single components. European patent application EP-A-204157, for example, describes modifiers which comprise an ethylene-propylene elastomeric copolymer and optionally A-PP and/or polyethylene and/or isotactic polypropylene and/or EVA. Mixtures of modifiers described in U.S. Pat. No. 4,829,109 comprise on the contrary an ethylene-propylene copolymer, an ethylene-terpolymer, a high density polyethylene and, optionally, an EVA copolymer.
It has now been found that it is possible to obtain bituminous compositions which are particularly suitable for applications either of road surfacing type or building waterproofing using new ethylene copolymers as modifiers. The bituminous compositions obtained are particularly interesting in that they combine good elastic properties, resistance to penetration and softening together with an effective resistance to ageing.
The bituminous compositions of the present invention comprise bitumen and copolymers of ethylene with propylene and/or alpha-olefins CH
2
═CHR, wherein R is an alkyl radical having 2-10 carbon atoms, characterized by the following properties:
i. solubility in pentane at 25° C. higher than 90%;
ii. melting enthalpy lower than 20 J/g;
iii. content of propylene or alpha-olefin units in form of triads comprised between 4 and 50% of the propylene or alpha-olefin, with at least 70% of said triads having isotactic structure;
iv. values of the product r
1
·r
2
of the reactivity ratio of ethylene, r
1
, and propylene or alpha-olefin, r
2
, comprised between 0.4 and 1;
v. intrinsic viscosity higher than or equal to 1.5 dl/g and preferably comprised between 1.5 and 3.5 included.
The values of the melting enthalpy indicated under ii. correspond to a restricted crystallinity degree. The characteristic described under iv. indicates a random distribution of the ethylene and propylene units and/cr of the units deriving from alpha-olefins in sections of the chain having copolymeric structure.
The combination of characteristics from i. to v. gives the copolymers of the invention valuable elasto-plastic properties; in particular, it is possible to reach a tensile strength higher than 3-4 MPa and tension set values (200%, 1 min., 25° C.) lower than 30% on the non vulcanized product.
Copolymers of the invention generally contain between 35 and 85% by mole of ethylene, between 15 and 65% by mole of propylene and/or alpha-olefins, and between 0 and 10% by mole of units deriving from dienes or polyenes. Preferably, the ethylene content is comprised between 45 and 75% by mole and the propylene and/or alpha-olefins content is comprised between 25 and 55% by mole.
The content of units from diene or polyene is generally comprised between 0 and 10% by mole, preferably between 0.5 and 2% by mole.
Preferably the copolymers have an intrinsic viscosity comprised between 1.5 and 3.5 inclusive, more preferably between 1.5 and 2.5 inclusive.
Copolymers used as modifiers in this bituminous compositions of the invention are prepared by polymerization of mixtures of ethylene with propylene and/or an alpha-olefin CH
2
═CHR, optionally in the presence of a diene or polyene, with chiral catalysts obtained from metallocene derivatives of zirconium, such as ethylene-bis(tetrahydroindenyl)zirconium, dichloride or dimethylsilanylene-bis-(tetrahydroindenyl)-zirconium dichloride, and tetraisobutyl-alumoxane.
The preparation of the copolymers is carried out by copolymerization of mixtures of monomers, working in liquid phase consisting of propylene and/or alpha-olefin at a temperature comprised between about 40 and 50° C.
Useful alpha-olefins CH
2
═CHR, are for example 1-butene, 1-pentene, 4-methyl-l-pentene, 1-hexene, 1-octene, 1-dodecene. Suitable dienes or polyenes are preferably selected from linear non-conjugated diolefins, such as 1,4-hexadiene, or bridged cyclic diolefins such as 5-ethylidene-2-norbornene.
For bitumens used in the compositions of the invention the materials indicated as bitumens or asphalt bitumens are meant, as described in Kirk-Othmer, “Encyclopedia of Chemical Technology”, 3rd Edition, Vol 3, page 84, the two first paragraphs. Examples of bitumens are those from direct distillation (also called “Straight Run”, SR bitumens) and those deriving from visbreaking (see C. Giavarini, P. De Filippis and F. Del Manso, Intnl. Symposium Chemistry of bitumens, Roma, 1991, vol I, page 314).
The preparation of the bituminous compositions of the invention can be carried out according to the known blending techniques for the mixing of bitumens with polymeric modifiers.
In one preferred method the modifiers are mixed in the preheated bitumen, at temperatures higher than the melting point of the components of the mixture. Depending on the viscosity of the bitumen and modifiers, a more or less high shear mixing apparatus are used in such a way to obtain an effective dispersion of the modifiers in the bitumen. It is possible, for example, to use a Silverson L4R mixer, according to the process described in the Examples. The mixing can also be carried out in two steps, by first preparing a bitumen/modifier masterbatch having a low content of bitumen and thereafter mixin
Albizzati Enrico
Braga Vittorio
Galimberti Maurizio
Martini Emilio
Cave LLP Bryan
Montell Technology Company BV
Mulcahy Peter D.
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