Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-06-17
2002-10-08
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S461000, C525S088000, C525S089000, C525S240000
Reexamination Certificate
active
06461703
ABSTRACT:
The present invention concerns polyolefin compositions with a high content of heavy mineral fillers, particularly suited for coating metal pipes by way of extrusion coating processes. It is known that polyolefins, and particularly propylene polymers, can be used satisfactorily to coat the outside surface of metal pipes to be used for pipelines designed for liquid and gaseous fluids.
In fact, propylene polymers allow one to obtain coatings with high corrosion resistance and optimum mechanical properties.
However, in cases where the pipes thus coated are to be used for marine pipelines there is often the need for additional external layers of heavy materials, particularly concrete, in order to keep said pipelines from floating.
For example, polyolefin compositions, optionally containing elastomeric polymers, having a high specific weight are described in European patent application EP-A-673966.The polyolefin compositions described in the above mentioned patent application are suitable for coating displaying a good balance of weight, corrosion resistance, and high mechanical properties, rendering unnecessary the further addition of layers of other heavy materials, such as concrete, that are subject to breaking and at times are difficult to apply to the pipes.
The need has now been found for materials that compared to the materials already known provide better mechanical properties while having high weight and being corrosion resistant. In particular, the need is for a material with high elongation at break, good elasticity and impact strength.
In response to the above mentioned needs, the Applicant perfected polyolefin compositions having thermoplastic and elastomeric properties, containing high quantities of heavy mineral fillers, easy to apply to the outside surface of metal pipes, allowing the application of single or multiple layers, and possessing the above mentioned balance of properties.
The multi-layer coatings can comprise layers of plastic materials with different properties, such as expanded plastics.
It has been noticed that in order to obtain the required results the compositions must contain a limited maximum quantity of an elastomeric copolymer in order for the compositions to adhere to the pipe to which they are applied; on the other hand, if the quantity of elastomeric copolymer is too low, the desired balance of mechanical properties is not obtained.
Therefore, object of the present invention are polyolefin compositions comprising:
(A) 60%-90%, preferably 65%-90%, more preferably 75%-85% by weight of at least one heavy mineral filler having a specific weight greater than or equal to 3, such as BaSO
4
, or zirconium silicates;
(B) 10-40%, preferably 10-35%, more preferably 15-25% by weight of a heterophasic polyolefin composition (having thermoplastic and elastomeric properties); and
(C) a compatibilizer for fillers in quantities ranging from 0.1% to 4%, preferably 0.2%-2% by weight with respect to the weight of components (A)+(B);
said composition (B) comprising (weight percentage):
1) 30-60% of a propylene homopolymer fraction, said fraction being more that 80% insoluble in xylene at ambient temperature, or a copolymer of propylene with ethylene and/or a C
4
-C
10
&agr;-olefin, containing more than 80% propylene, and being more than 80% insoluble in xylene at ambient temperature (Fraction 1°);
2) 40-70% of a fraction of a copolymer of ethylene with propylene and/or a C
4
-C
10
&agr;-olefin, and optionally minor quantities of a diene; said copolymer containing from 15to 70% of ethylene, and being soluble in xylene at ambient temperature (Fraction 2°); and
3) 0-30%, with respect to the sum of Fractions (1°) and (2°), of a copolymer fraction containing ethylene, said fraction being insoluble in xylene at ambient temperature (Fraction 3°).
Said compositions have a flow index (ASTM D1238, condition L, MIL) ranging from 0.5 to 10 g/10 minutes, preferably from 0.7 to 6 g/10 minutes, elongation at break (ASTM D 638) from over 100% to 800%, preferably from 120 to 550%, and flexural modulus (ASTM D 790) from 100 to less than 3,000 MPa, preferably from 100 to 2700 MPa.
The solubility and insolubility of the polymers of the present invention are defined as fractions soluble or insoluble in xylene at ambient temperature, i.e., around 25° C. (see note 1). The above mentioned compositions can easily be applied to the exterior surface of metal pipes by using extrusion techniques known in the art, because they have a sufficiently high viscosity in the molten state, and therefore can withstand the tensions to which they are subjected during traditional coating processes without melt fracture.
In order to obtain an optimum adhesion to the pipe surface, it is preferable that prior to the application of the compositions of the invention said surface be coated with a layer of a hot melt composition of the type commonly used in the art (such as one based of polypropylene grafted with maleic anhydride).
Heterophasic composition (B) preferably has a propylene content in the copolymers of Fraction 1° ranging from 90 to 99% by weight. The polymer fraction insoluble in xylene in said Fraction 1° more preferably ranges from 85 to 99% in the case of homopolymers, and from 85 to 95% in the case of copolymers.
Examples of the above mentioned C
4
-C
10
&agr;-olefins present in composition (B) are 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-octene. The preferred comonomer is 1-butene.
When present, the diene in composition (B) preferably ranges from 1 to 10%, more preferably 2.5-7% by weight with respect to the total weight of Fraction 2°. Examples of dienes are butadiene, 1,4-hexadiene, 1,5-hexadiene, and 5-ethylidene-2-norbornene.
When present, said Fraction (3°) preferably exceeds 1% by weight, more preferably ranging from 1 to 25% by weight with respect to the sum of Fractions (1°) and (20°). Preferably the content of ethylene in Fraction (3°) is at least 75% by weight, more preferably 80% by weight, with respect to the total weight of Fraction (3°). The comonomers in the copolymer of Fraction (3°) are preferably the same as those of the copolymer of Fraction (2°). An example of copolymer comprised in Fraction (3°) is an essentially linear semicrystalline copolymer of ethylene with propylene, a specific example of which is linear low density polyethylene (LLDPE).
The above mentioned heterophasic composition can be prepared by blending Fractions (1°), (2°), and optionally (3°) in the molten state, that is to say at temperatures greater than their softening or melting point, or more preferably by sequential polymerization in one or more stages in the presence of a highly stereospecific Ziegler-Natta catalyst. In particular, the catalyst system used comprises (a) a solid catalytic component containing a titanium compound and an electron-donor compound, both supported on magnesium chloride, and (b) an Al-trialkyl compound and an electron-donor compound.
The above mentioned sequential polymerization process for the production of the heterophasic composition comprises at least two stages, where in the first stage the propylene is polymerized to form Fraction (1°), and in the subsequent stages mixtures of ethylene with propylene and/or said C
4
-C
10
&agr;-olefin, and optionally diene, are polymerized to form Fraction (2°), and optionally Fraction (3°). The polymerization processes are carried out in liquid, gaseous, or liquid/gas phase. The reaction temperature in the various stages of polymerization can be equal or different, and generally ranges from 40° to 90° C., preferably from 50° to 80° C. for the production of Fraction (1°), and from 40° to 60° C. for the production of Fraction (2°) and optionally Fraction (3°).
Examples of sequential polymerization processes are described in European patent applications EP-A-472946and EP-A-400333.
As a way of example, the heterophasic composition has MIL values ranging from 0.1 to 20 g/10 min, preferably from 0.2 to 15 g/10 min. The heterophasic composition with said melt index values can be obtained directly during the polymerizat
Basell Poliolefine Italia S.p.A.
Hon Sow-Fun
Pyon Harold
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