MXPA99006069A - Polypropylene compositions with a high content of heavy mineral fillers suited for coating metal pipes - Google Patents

Abstract

Polypropylene composition comprising by weight (A) 60-90%of at least one heavy mineral filler having a specific weight greater than or equal to 3;(B) 0.1-4%of a filler compatibilizer;and (C) 10-40%of a heterophasic polyolefin composition containing rubber. Said composition has an MIL ranging from 0.5 to 10 g/10 min, elongation at break greater than 100 to 800%, and flexural modulus ranging from 100 to less than 3000 MPa.

Description

POLYPROPYLENE COMPOSITIONS WITH HIGH CONTENT OF HEAVY MINERAL FILLERS FILLED FOR REVERSE METAL TUBES DESCRIPTIVE MEMORY The present invention relates to polyolefin compositions with a high content of heavy mineral fillers, particularly suitable for coating metal tubes by means of extrusion coating processes. It is well known that polyolefins, and particularly propylene polymers, can be used successfully to coat the outer surface of metal tubes that are used in pipes designed for liquid and gaseous fluids. In fact, propylene polymers make it possible to obtain coatings with high corrosion resistance and optimum mechanical properties. However, in cases where already coated pipes are used in marine pipelines, there is often a need for additional external layers of heavy materials, particularly concrete, in order to prevent said pipes from floating. For example, polyolefin compositions, which optionally contain elastomeric polymers, and have a specific gravity high are described in the European patent application EP-A-673966. The polyolefin compositions described in the aforementioned patent application are suitable for coating and achieving good weight balance, corrosion resistance, and high mechanical properties, thus eliminating the possible adhesion of layers of other heavy materials, such as concrete. , which can break and are sometimes difficult to apply to tubes. Now there is a need for materials, which compared with known materials, provide better mechanical properties while having a high weight and are resistant to corrosion. In particular, there is a need for a material with high elongation at break, good elasticity and high impact strength. In response to the aforementioned needs, the improved polyolefin compositions of the Applicant have thermoplastic and elastomeric properties, contain high amounts of heavy mineral fillers, are easy to apply to the outer surface of the metal tubes, allow the application of a or multiple layers, and possess the aforementioned balance of properties. Multilayer coatings may consist of layers of plastic materials with different properties, such as expandable plastic. It has been noted that in order to obtain the required results, the compositions must contain a limited maximum amount of one elastomeric copolymer so that the compositions adhere to the tube to which they are applied; on the other hand, if the amount of the elastomeric copolymer is very low, the desired balance of the mechanical properties is not obtained. Then, the polyolefin compositions which are the subject of the present invention consist of: (A) 60% -90%, preferably 65% -90%, most preferably 75% -85% by weight of at least one heavy mineral filler having a specific gravity greater than or equal to 3, such as BaSO, or zirconium silicates; (B) 10-40%, preferably 10-35%, most preferably 15-25% by weight of a heterophasic polyolefin composition (with thermoplastic and elastomeric properties); and (C) a compatibilizer for fillers in amounts ranging from 0.1% to 4%, preferably 0.2% -2% by weight with respect to the weight of the components (A) + (B); said composition (B) comprising (in percent by weight): 1) 30-60% of a propylene homopolymer fraction of more than 80% soluble in xylene at room temperature, or a copolymer of propylene with ethylene and / or a C4-C10 α-olefin, which contains more than 80% propylene, and which is more than 80% insoluble in xylene at room temperature (Fraction 1o); 2) 40-70% of a fraction of an ethylene copolymer with propylene and / or C4-C10 α-olefin, and optionally smaller amounts of a diene; said copolymer containing from 15 to 70% ethylene, and being soluble in xylene at room temperature (Fraction 2o); and 3) 0-30%, with respect to the sum of the fractions (1o) and (2o), of a fraction of copolymer containing ethylene, said fraction insoluble in xylene at room temperature (Fraction 3o). Said compositions have a flow index (ASTM D 1238, condition L, MIL) varying from 0.5 to 10 g / 10 minutes, preferably from 0. 7 to 6 g / 10 minutes, elongation at break (ASTM D 638) of more than 100% to 800%, preferably 120 to 550%, and a flexural modulus (ASTM D 790) of 100 to less than 3,000 MPa, preferably 100 to 2700 MPa. The solubility and insolubility of the polymers of the present invention are defined as soluble or insoluble fractions in xylene at room temperature, ie, around 25 ° C (see note 1). The aforementioned compositions can be easily applied to the outer surface of the metal tubes through extrusion techniques known in the art, since they have a sufficiently high viscosity in the molten state, and therefore can withstand stresses to those that are subject during the traditional coating procedures without fractures of the molten material. In order to obtain optimum adhesion to the surface of the tube, it is preferable that before the application of the compositions of the invention, said surface is coated with a layer of a molten composition. hot type of the type commonly used in the art (such as the one based on polypropylene grafted with maleic anhydride). Preferably, the heterophasic composition (B) has a propylene content in the copolymers of Fraction 1o ranging from 90 to 99% by weight. The polymer fraction insoluble in xylene in said Fraction 1st, preferably ranges from 85% to 99% in the case of homopolymers, and 85% to 95% in the case of copolymers. Examples of the aforementioned C4-C10 α-olefins present in composition (B) are 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-ketene. The preferred comonomer is 1-butene. When the diene is present in the composition (B) it preferably varies from 1 to 10%, most preferably 2.5-7% by weight with respect to the total weight of Fraction 2o. Some examples of dienes are butadiene, 1,4-hexadiene, 1,5-hexadiene, and 5-ethylidene-2-norbomeno. When present, said Fraction (3o) preferably exceeds 1% by weight, most preferably from 1 to 25% by weight with respect to the sum of the fractions (1o) and (2o). Preferably, the content of ethylene in the Fraction (3o) is at least 75% by weight, most preferably 80% by weight, based on the total weight of the Fraction (3o). The comonomers in the copolymer of Fraction (3o) are preferably the same as those of the copolymer of Fraction (2o). An example of a copolymer contained in Fraction (3o) is a copolymer linear semicrystalline of ethylene and propylene, a specific example is that of a linear low density polyethylene (LLDPE). The aforementioned heterophasic composition can be prepared by mixing the fractions (1o), (2o), and optionally (3o) in the melting state, i.e. at temperatures higher than their softening or melting point, and more preferably by the sequential polymerization in one or more stages in the presence of a highly stereospecific Ziegler-Natta catalyst. In particular, the catalyst system used consists of (a) a solid catalyst component containing a titanium compound and an electron donor compound, both supported on magnesium chloride, and (b) an Al-trialkyl compound and a donor compound of electrons The above sequential polymerization process for the production of the heterophasic composition consists of at least two stages, in the first stage, the propylene is polymerized to form the Fraction (1o), and in the subsequent steps the mixtures of ethylene with propylene and / or said C4-C10 α-olefin and optional diene are polymerized to form the Fraction (2o), and optionally the Fraction (3 °). The polymerization processes are carried out in the liquid, gas, or liquid / gas phase. The reaction temperature in the different polymerization steps may be the same or different, and generally ranges from 40 ° to 90 ° C, preferably from 50 ° to 80 ° C for the production of the Fraction (1o), and from 40 ° to 60 ° C for the production of Fraction (2 °) and optionally the Fraction (3 °).

Examples of sequential polymerization processes are described in the European patent applications EP-A-472946 and EP-A-400333. By way of example, the heterophasic composition has values of MIL 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 polymerization process; as an alternative, said heterophasic composition can be subjected to a chemical viscosity breaking process performed in the presence of the appropriate viscosity breaking agents, such as peroxides. Said viscosity breaking chemical process is carried out according to the known methods. Among the aforementioned compositions, those which are particularly suitable for the preparation of compositions of the present invention are polyolefin compositions (B ') containing (in weight percent): 1) 30-50% of said Fraction (1) °) (Fraction 1); 2) 50-70% of said Fraction (2 °) wherein the amount of ethylene in the copolymer is less than 40%, preferably 20 to 38% (Fraction 2o); and 3) 0-20% of said Fraction (3 °) (Fraction 3). In said composition (B ') the weight percent of the sum of the Fractions (2o) and (3o) with respect to the total composition varies from 50 to 90%, preferably 65 to 80%, and the weight ratio (3) / (2) is less than 0.4, preferably 0.08 to 0.3. By way of example, the total amount of ethylene in the heterophasic composition (B ') ranges from 15 to 35% by weight. Other examples of the aforementioned compositions (B) that can be used in the present invention are the polyolefin (B ") compositions containing (in weight percent): I) 40-60% of said Fraction (1 o) ( Fraction 1), II) 40-60% of said Fraction (2o) wherein the amount of ethylene in the copolymer varies from 40% to 70% (Fraction II), and III) 0-25% of said Fraction (3 °) (Fraction III) By way of example, the total ethylene content polymerized in said composition (B ") varies from 20% to 60% by weight. The molecular weight of the different fractions of the composition (B ") (determined by the measurement of the intrinsic viscosity in tetrahydronaphthalene at 135 ° C) varies depending on the nature of the components, and the total melt index of the composition In particular, the intrinsic viscosity preferably remains between the following limits: -0.5-3 dl / g per Fraction (I), and -2-8 dl / g per Fraction (II) plus fraction (lll). of heterophasic polyolefin (B ') (B ") are set forth respectively in the aforementioned applications of European Patent EP-A-0472946 and EP-A-400 333.

The compatibilizers for the aforementioned fillers are preferably selected, for example, from stearic acid derivatives, such as inorganic stearates and stearamides, such as Ca and Zn. Other different examples of filler compatibilizers of stearic acid derivatives are those of polypropylene grafted with maleic anhydride or with other grafting compounds containing the carboxylic groups, and systems based on peroxides and alkoxysilanes substituted with vinyl. The compositions of the present invention can be prepared by known techniques for the preparation of polyolefin polymer blends with fillers. For example, it is possible to use Banbury, Buss, or Brabender mixers at temperatures that vary from 180 ° C to 260 ° C. The following examples are for the purpose of illustrating but not limiting the present invention. The methods used to obtain the information related to the properties mentioned in the examples and in the description are listed below.

Property Method Fusion index (MIL) ASTM-D 1238, Condition Solubility in xylene See note 1 Flexure modulus (FM) ASTM D 412 Resistance to tension at 23 ° C ASTM D 638 Effort to relax at 23 ° C ASTM D 638 Lengthening rupture at 23 ° C ASTM D 638 Elongation at relaxation at 23 ° C ASTM D 638 Density BS 4370 Impact resistance with ASTM D 256 slot Note l Determination of the percentage soluble in xylene: a solution of the sample is prepared in xylene at a concentration of 1% by weight, while the sample is kept under stirring in xylene for 1 hour at 135 ° C. After stirring, the contents are allowed to cool to 95 ° C, after the solution is poured into a bath at 25 ° C, and left to stand for 20 minutes without stirring, and for another 10 minutes stirring. The solution is then filtered, and acetone is added to a portion of the filtrate in order to obtain precipitation of the dissolved polymer. The polymer obtained is coated, washed, dried and finally weighed in order to determine the percentage soluble in xylene.

Components used in the examples and in the comparative examples The following heterophasic compositions (B) (i) - (iii) are obtained through sequential polymerization in the presence of a highly stereospecific and highly relaxed Ziegler-Natta catalyst based on MgCl 2. . - Heterophasic composition (i) containing a MIL of 0.6 g / 10 min including (in parts and in percent by weight): 1) 33 parts of a crystalline propylene copolymer with 4.3% ethylene; the copolymer contains about 9% of a fraction soluble in xylene at 25 ° C, and having an intrinsic viscosity of [?] of 1.5 dl / g; 2) 61 parts of an ethylene / propylene amorphous copolymer copolymer, containing 30% ethylene, fully soluble in xylene at 25 ° C, and with an intrinsic viscosity of [?] Of 3.2 dl / g; and 3) 6 parts of an ethylene / propylene copolymer linear essential copolymer totally insoluble in xylene at 25 ° C. -Elastomeric compound (II) having a MIL of 0.8 g / 10 min including (in parts and percent by weight): I. 40 parts of a propylene crystalline homopolymer containing a 97.5% xylene insoluble fraction, and MIL of 9 g / 10 min; II. 47 parts of an amorphous ethylene / propylene copolymer copolymer, containing 50% ethylene, fully soluble in xylene at 25 ° C, and with an intrinsic viscosity of [?] Of 3.7 dl / g; Y lll. 13 parts of a linear ethylene / propylene copolymer essential copolymer, totally insoluble in xylene at 25 ° C. Elastomeric composition (iii) having a MIL of 10.5 g / 10 min including (in weight percent): -67% of a propylene glyph copolymer containing 3% ethylene, and has MIL of 32 g / 10min; -27% of an ethylene / copolymer propylene copolymer soluble in xylene at 25 ° C containing 55% ethylene, and has an intrinsic viscosity [?] Of 2.35 dl / g; and -6% of an ethylene / propylene copolymer copolymer Soluble in xylene at 25 ° C. -Polymer (v): a propylene copolymer including (by weight) 3.5% ethylene, and 6% 1-butane, with a MIL of 5.5 g / 10 min, and a melting point of 132 ° C (determined by the DSC). -Polypropylene (v) and (vi): crystalline propylene homopolymers containing 96% of a fraction insoluble in xylene at room temperature, and having a MIL of 6 and 10 g / 10 respectively. Irganox B 225: 50% by weight of pentacritritol-tetrakis [3 (3,5-di-tert-butyl-4-hydroxyphenyl)] propionate, (Irganox 1010) + 50% by weight of bisphosphate (2,4-di) -tert-butylphenyl) (Irgafos 168), marketed by Ciba-Geigy.

EXAMPLES 1-5, AND COMPARATIVE EXAMPLES 1C-3C The materials indicated in Table 1 are fed into the Buss 200 mixer. The mineral filler is barium sulfate (p.p.:4.4). The aforementioned materials are extruded in the mixer Buss at a temperature of 230 ° C. In addition, part of the obtained composition is used in an extrusion test using a single screw extruder with a flat die at a temperature of around 190 ° C, thus obtaining a homogeneous extruded product, and without material fracture problems molten. The results prove that the composition is suitable for the use of tube coating processes by means of extrusion. In order to determine the mechanical properties, another portion of the composition is used for the preparation of specimens of 120mm x 120mm x 3mm, by injection molding at 230 ° C. The value and density MIL, and the mechanical characteristics of the aforementioned compositions are shown in table 2.

TABLE 1 TABLE 2 1) The specimen does not break.

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. A polyolefin composition comprising: A) 60% -90% by weight of at least one heavy mineral filler with a specific gravity greater than or equal to 3; B) 10-40% by weight of a heterophasic polyolefin composition; and C) A compatibilizer for fillers in amouranging from 0.1% to 4% by weight with respect to the weight of the compone(A) + (B); said composition (B) is characterized in that it includes (in percent by weight): 1o) 30-60% of a propylene homopolymer fraction with an insolubility in xylene at room temperature greater than 80%, or a copolymer of propylene with ethylene and / or a C4-C10 α-olefin, which contains more than 80% propylene, and has an insolubility in xylene at room temperature greater than 80% (Fraction 1o); 2o) 40-70% of a fraction of ethylene copolymer with propylene and / or a C4-C10 α-olefin, and optional minor amouof diene; said copolymer contains from 15 to 70% ethylene, and is soluble in xylene at room temperature (Fraction 2o); and 3 °) 0-30%, with respect to the sum of the fractions (1o) and (2 °), of a fraction of copolymer containing ethylene, said fraction insoluble in xylene at room temperature (Fraction 3 °) .

2. - The composition according to claim 1, further characterized in that the compatibilizer is selected from the stearic acid derivatives.

3. - The polyolefin composition according to claim 1, further characterized in that the composition (B) contains (in percent by weight): 1) 30-50% of said Fraction (1 °); 2) 50-70% of said Fraction (2o) wherein the amount of ethylene in the copolymer is less than 40%, preferably 20 to 38%; and 3) 0-20% of said Fraction (3 °).

4. - The polyolefin composition according to claim 1, further characterized in that the composition (B) contains (in percent by weight): I) 40-60% of said Fraction (1o); II) 40-60% of said Fraction (2o), wherein the amount of ethylene in the copolymer varies from 40% to 70%; and III) 0-25% of said Fraction (3 °).

5. The composition according to claim 1, further characterized in that the heavy mineral filler (A) is BaS? 4, or silicates of Zr.

6. - The use of the compositions according to claim 1, for coating the outer surface of the metal tubes through the extrusion.

7. - Metal tubes whose external surface is coated with a layer of compositions according to claim 1.