Polypropylene composition and process for producing the same

Details Polypropylene composition and process for producing the same Polypropylene composition and process for producing the same

1999-10-15

2001-08-07

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

Reexamination Certificate

active

06271310

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a polypropylene composition which has high melt tension, a high crystallization temperature, and high thermal stability and which provides a molded article having excellent transparency, excellent resistance to whitening by impact or bending, and low molding shrinkage, as well as to a process for producing the composition.
BACKGROUND ART
Polypropylene has excellent mechanical properties, chemical resistance, and other properties, and is very useful in view of balance against economy. Therefore, polypropylene is widely applied to a variety of molding techniques. However, moldability of polypropylene with respect to techniques such as blow molding, expansion molding, and extrusion molding is insufficient due to low melt tension and low crystallization temperature. In addition, high-speed production of a molded object through other molding techniques is limited.
Although a crystalline propylene homopolymer has high rigidity, its impact resistance has a problem remained, particularly at low temperature. In order to mitigate this drawback, there has been proposed a composition produced by forming a crystalline propylene homopolymer and subsequently forming an ethylene-propylene copolymer (a so-called block copolymer). Although the composition has improved impact resistance as compared to the case of a crystalline propylene homopolymer, the block polymer still has drawbacks such as being highly prone to whitening by impact or bending; low transparency; and large molding shrinkage.
In view of the foregoing, an object of the present invention is to provide a polypropylene composition having high melt tension, a high crystallization temperature, and excellent thermal stability and providing a molded article having excellent transparency, reduced molding shrinkage, and excellent resistance to whitening by impact or bending to mitigate the above drawbacks. Another object of the present invention is to provide a process for producing the composition.
DISCLOSURE OF THE INVENTION
The present inventors have conducted earnest studies to solve the above problems, to thereby attain the present invention.
Accordingly, in a first mode of the present invention, there is provided a polypropylene composition comprising 0.01-5 parts by weight of an olefin (co) polymer (a), 100 parts by weight of a propylene homopolymer (b), and 28-300 parts by weight of an ethylene-propylene copolymer (c), wherein the product, ([&eegr;]
RC
/[&eegr;]
PP
)×(W
PP
/W
RC
), of the ratio of the intrinsic viscosity of the ethylene-propylene copolymer (c) to that of the propylene homopolymer (b) represented by [&eegr;]
RC
/[&eegr;]
PP
and the ratio of the weight of propylene homopolymer (b) to that of the ethylene-propylene copolymer (c) represented by W
PP
/W
RC
falls within the range of 0.2-3.0;
the olefin (co)polymer (a) having an intrinsic viscosity as measured in tetralin at 135° C. and represented by [&eegr;]
E
of 15-100 dl/g;
the propylene homopolymer (b) having an intrinsic viscosity as measured in tetralin at 135° C. and represented by [&eegr;]
PP
of 0.2-15 dl/g; and
the ethylene-propylene copolymer (c) having an intrinsic viscosity as measured in tetralin at 135° C. and represented by [&eegr;]
RC
of 0.2-10 dl/g.
In a second mode of the present invention, there is provided a polypropylene composition as described in the first mode, wherein the ratio of the ethylene-propylene copolymer (c) to the propylene homopolymer (b) is 50-300 parts by weight/100 parts by weight; the ratio of the melt flow rate of the propylene homopolymer (b) to that of the ethylene-propylene copolymer (c) represented by MFR
PP
/MFR
RC
is 0.3-4; and the product represented by ([&eegr;]
RC
/[&eegr;]
PP
)×(W
PP
/W
RC
) falls within the range of 0.2-2.0.
In a third mode of the present invention, there is provided a polypropylene composition as described in the first mode, wherein the ratio of the ethylene-propylene copolymer (c) to the propylene homopolymer (b) is 28-67 parts by weight/100 parts by weight; the ratio represented by [&eegr;]
RC
/[&eegr;]
PP
is 0.7-1.2; and the product represented by ([&eegr;]
RC
/[&eegr;]
PP
)×(W
PP
/W
RC
) falls within the range of 1.0-3.0.
In a fourth mode of the present invention, there is provided a process for producing a polypropylene composition comprising the steps of:
forming 0.01-5 parts by weight of an olefin (co)polymer having an intrinsic viscosity as measured in tetralin at 135° C. and represented by [&eegr;]
E
of 15-100 dl/g (a) through (co)polymerization of ethylene or a mixture of ethylene and the other olefin;
forming 100 parts of a propylene homopolymer having an intrinsic viscosity as measured in tetralin at 135° C. and represented by [&eegr;]
RC
of 0.2-15 dl/g (b) through homopolymerization of propylene; and
forming 28-300 parts by weight of an ethylene-propylene copolymer having an intrinsic viscosity as measured in tetralin at 135° C. and represented by [&eegr;]
RC
of 0.2-10 dl/g (c) through copolymerization of a mixture of ethylene and propylene, wherein the above steps are performed in the presence of a catalyst for producing polyolefin comprising a transition metal compound catalyst component containing at least a titanium compound, an organometallic compound of a metal selected from the group consisting of metals belonging to Group 1, Group 2, Group 12, and Group 13, and an optional electron donor, and the product, ([&eegr;]
RC
/[&eegr;]
PP
)×(W
PP
/W
RC
), of the ratio of the intrinsic viscosity of the ethylene-propylene copolymer (c) to that of the propylene homopolymer (b) represented by [&eegr;]
RC
/[&eegr;]
PP
and the ratio of the weight of propylene homopolymer (b) to that of the ethylene-propylene copolymer (c) represented by W
PP
/W
RC
falls within the range of 0.2-3.0.
In a fifth mode of the present invention, there is provided a process for producing a polypropylene composition as described in the fourth mode, wherein the organometallic compound is used in an amount of 0.01-1,000 mol per mol of transition metal atoms and the optional electron donor is used in an amount of 500 mol or less per mol of transition metal atoms.
In a sixth mode of the present invention, there is provided a process for producing a polypropylene composition as described in any one of the fourth mode and the fifth mode, comprising the steps of:
preliminarily polymerizing propylene and subsequently forming the olefin (co)polymer (a) through polymerization to thereby preliminarily activate a catalyst;
forming the propylene homopolymer (b); and
subsequently forming the ethylene-propylene copolymer (c).
In a seventh mode of the present invention, there is provided a process for producing a polypropylene composition as described in the sixth mode, comprising the steps of:
forming the olefin (co)polymer (a) through polymerization to thereby preliminarily activate a catalyst;
addition-polymerizing propylene; and
subsequently forming the propylene homopolymer (b).
BEST MODE FOR CARRYING OUT THE INVENTION
The modes for carrying out the present invention will next be described.
First of all, definitions of the notation shown in the description and mutual relations to the components of the polypropylene composition are described.
The polypropylene composition of the present invention comprises the following components:
a small amount of polypropylene (B) formed though a preliminary polymerization step (i);
an olefin (co)polymer (a) formed through a preliminary activation step for a catalyst (ii) (referred to as “polyethylene (A)” when the olefin (co)polymer is particularly polyethylene);
a small amount of polypropylene (D) formed through an addition polymerization step (iii);
polypropylene (b) formed through a homopolymerization step for propylene (iv) among the main (co)polymerization steps; and
an ethylene-propylene copolymer (c) form

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