Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-06-28
2002-05-28
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000, C524S847000
Reexamination Certificate
active
06395832
ABSTRACT:
The present invention relates to an elastomeric thermoplastic polyolefin composition. In particular, the present invention relates to compositions containing a broad molecular weight distribution propylene polymer.
Due to its mechanical and physical properties, the polymer composition of the present invention finds application above all in automotive field (e.g. bumpers and side strips).
Such a polyolefin composition has a good balance of mechanical properties, in particular improved balance of flexural modulus and IZOD impact strength even at low temperatures (e.g. at −30° C.).
In addition to the above properties the composition of the present invention is endowed with satisfactory optical properties. As required by the market, the composition shows low gloss values.
An added advantage, which is shown by the composition of the present invention, is that it presents a low value of coefficient of linear thermal expansion (CLTE). Said property imparts a higher dimensional stability to the articles produced with the polyolefin composition of the present invention.
Therefore an object of the present invention is a polyolefin composition comprising (percentage by weight):
(A) from 40 to 60%, preferably 40 to 55%, of a broad molecular weight distribution propylene polymer (component A) having a polydispersity index from 5 to 15 and melt flow rate of from 80 to 200 g/10 min (according to ASTM-D 1238, condition L); and
(B) from 40 to 60%, preferably 45 to 60%, of a partially xylene-soluble olefin polymer rubber (component B) containing at least 65% by weight of ethylene;
the IV
S
/IV
A
ratio between the intrinsic viscosity (IV
S
) of the portion soluble in xylene of the polyolefin composition at room temperature and the intrinsic viscosity (IV
A
) of component (A) ranging from 2 to 2.5, preferably from 2.1 to 2.4, both values of intrinsic viscosity being measured in tetrahydronaphthalene at 135° C.
The method for measuring the xylene-soluble content and polydispersity index are described hereinbelow. The room temperature means a temperature of about 25° C. in the present application.
The polyolefin composition of the present invention may further contain a mineral filler. When present, it is contained in an amount from about 0.5 to 3 parts by weight with respect to the sum of components (A) and (B).
The composition of the present invention typically has a melt flow rate of from 5 to 20 g/10 min. In addition, typically, it has a flexural modulus of from 650 to 1000 MPa, preferably from 700 to 1000 MPa. Preferably the coefficient of linear thermal expansion is up to 8° C.
−1
×10
−5
, more preferably from 5 to 8; notched IZOD resilience at −30° C. is typically of 15 KJ/m
2
or higher, preferably from 18 KJ/m
2
. Typically, gloss values are lower than 50‰. The methods for measuring the said properties are described hereinbelow.
Component (A) is a crystalline propylene homopolymer or a propylene copolymer with ethylene or C
4
-C
10
&agr;-olefin or a mixture thereof. Ethylene is the preferred comonomer. The comonomer content ranges preferably from 0.5 to 1.5% by weight, more preferably from 0.5 to 1% by weight.
A xylene-insoluble content at 25° C. of component (A) is typically greater than 90%, preferably equal to or greater than 94%.
Preferably, component (A) has a melt flow rate of from 80 to 150 g/10 min.
Component (A) approximately has a molecular weight distribution {overscore (M)}
w
/{overscore (M)}
n
, ({overscore (M)}
w
=weight average molecular weight and {overscore (M)}
n
=number average molecular weight, both measured by gel permeation chromatography) of from 8 to 30, more preferable from 8.5 to 25.
The olefin polymer rubber of component (B) used in the polyolefin composition of the present invention can be a poly(ethylene-co-C
3
-C
10
&agr;-olefin) or poly(ethylene-co-propylene-co-C
4
-C
10
&agr;-olefin) having an ethylene content preferably from 65 to 80% by weight. The latter contains about from 0.5 to 10% by weight of a C
4
-C
10
&agr;-olefin. The olefin polymer rubber can optionally further contain a diene, the content of which is preferably of from 1 to 10% by weight, more preferably from 1 to 5% by weight.
The olefin polymer rubber of component (B) is partially soluble in xylene at room temperature. The xylene-insoluble content is about 25-35% by weight, preferably 27-33% by weight.
The C
3
-C
10
&agr;-olefins useful in the preparation of component (B) described above include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene. Propylene and 1-butene are particularly preferred.
The mineral filler, when present, is preferably selected from talc, calcium carbonate, silica, conventional clays, wollastonite, diatomaceous earth, titanium oxide and zeolites. Preferably, the mineral filler is talc.
In addition to the mineral fillers discussed above, the polyolefin composition of the present invention may further contain conventional additives, for example, stabilizers, pigments, other fillers and reinforcing agents, e.g. carbon black and glass beads and fibers.
The polyolefin composition of the present invention can be prepared by way of a physical blend or chemical blend.
Preferably, the composition of the present invention is prepared directly in polymerization by sequential polymerization processes in a series of reactors based on the use of particular stereospecifc Ziegler-Natta catalysts, producing by polymerization a mixture of component (A) and component (B). Subsequently, the mineral filler is, optionally, added by blending, or in the final pelletization section of the industrial polymerisation plant.
The polymerization process is carried out in at least three consecutive stages, in the presence of particular stereopecific Ziegler-Natta catalysts, supported on a magnesium halide in active form. In particular, the broad molecular weight distribution propylene polymer of component (A) described above can be prepared by sequential polymerization in at least two stages and the olefin polymer rubber in the other stage(s).
Alternatively, the polyolefin composition of the present invention can be physically blended or admixed in any conventional mixing apparatus, such as an extruder or a Banbury mixer, by mixing components (A) and (B) and optionally further components. Components (B) and (A) are blended in the molten or softened state.
As previously mentioned, the polymerization stage can be carried out in at least three sequential steps, wherein components (A) and (B) are prepared in separate subsequent steps, operating in each step in the presence of the polymer formed and the catalyst used in the immediately preceding step. The catalyst is added only in the first step, however its activity is such that it is still active for all the subsequent steps. The order in which components (A) and (B) are prepared is not critical. However, it is preferred to produce component (B) after producing component (A).
The catalyst used for preparing component (A) is preferably characterized in that it is capable of producing propylene polymers having a xylene insoluble fraction at 25° C. greater than or equal to 90% by weight, preferably greater than or equal to 94%. Moreover, it has a sensitivity to molecular weight regulators high enough to produce propylene homopolymers having a melt flow rate in the range from 1 to 20 g/10 min and greater than 200 g/10 min.
Methods of preparing the broad molecular weight distribution propylene polymer of component (A) of the present invention are described in the European patent application 573 862.
The above said catalyst is used in all the steps of the polymerization process of the present invention for producing directly the sum of components (A) and (B).
Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in U.S. Pat. No. 4,399,054 and European patents 45977 and 395083.
The polymerization process can be carried out in continuous or in batch, according to known techniques and oper
Ferrari Paolo
Galetti Giovanni
Pelliconi Anteo
Baselltech USA Inc.
Nutter Nathan M.
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