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
1999-04-29
2001-03-13
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...
C525S232000, C525S240000
Reexamination Certificate
active
06201069
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a composition comprising polypropylene and a propylene-ethylene copolymer (hereinafter referred to as “polypropylene/propylene-ethylene copolymer composition”) and a process for producing the same. More particularly, this invention relates to a polypropylene/propylene-ethylene copolymer composition having an excellent balance among rigidity, toughness, impact resistance, etc., and to a process for producing the same.
BACKGROUND ART
Polypropylene resins have conventionally been used in a wide variety of fields because they are relatively inexpensive and have excellent properties. However, there has been a desire for an improvement in impact resistance, in particular, low-temperature impact resistance. Many techniques for eliminating this problem have been proposed so far. A generally employed technique is to produce a propylene block copolymer by firstly forming a propylene homopolymer ingredient and then incorporating an ethylene-propylene random copolymer ingredient. Compared to propylene polymers, propylene block copolymers are inferior in rigidity, hardness, and heat resistance although improved in impact resistance.
Among techniques which have been proposed for mitigating these drawbacks is a method in which the ratio of the melt flow rate of a first-stage polymer to that of a second-stage polymer is regulated as described in Unexamined Published Japanese Patent Application No. 5-117342. This method is in extensive use in various industrial fields such as the fields of motor vehicles and domestic electrical appliances.
However, even the above-described technique according to Unexamined Published Japanese Patent Application No. 5-117342 has still had an insufficient balance among rigidity, toughness, impact resistance, etc.
An object of the present invention is to provide a polypropylene/propylene-ethylene copolymer composition excellent in rigidity, toughness, and impact strength and to further provide a process for producing the same.
In view of the problems described above, the present inventors made intensive studies in order to obtain an improved balance between rigidity and toughness/impact resistance in propylene-ethylene block copolymers. As a result, it has been found that a polypropylene/propylene-ethylene copolymer composition excellent in rigidity, toughness, and impact strength is obtained by yielding a propylene-ethylene copolymer composition through two-stage polymerization in such a manner that a polypropylene having a tie molecule volume content (&bgr;) of 1.38% or higher is produced as a product of the first stage and a propylene-ethylene copolymer is yielded, in the second stage, around the polypropylene yielded in the first stage. The present invention has thus been completed.
DISCLOSURE OF THE INVENTION
That is, the invention for which a patent is claimed is as follows.
(1) A polypropylene/propylene-ethylene copolymer composition having a melt flow rate (ASTM D-1238; the same applies hereinafter) of from 1 to 80 g/10 min obtained through:
a first stage (polymerization step (I)) in which propylene is polymerized in the presence of a highly stereoregular catalyst and hydrogen to produce a propylene polymer having a melt flow rate in the range of from 15 to 99 g/10 min and a tie molecule volume content (&bgr;), as obtained from an oriented sample and defined by
&bgr;=(1−0.01
Xc
)
E
/(41−0.01
Xc·E
)
wherein Xc: degree of crystallization (%); and
E (GPa): modulus of elasticity, of 1.38% or higher in an amount of from 60 to 95% by weight based on the total amount of the composition to be finally obtained; and
a second stage (polymerization step (II)) in which ethylene and propylene are subsequently fed to the product of the first stage in such a proportion as to result in an ethylene content of from 20 to 80% by weight to produce a propylene-ethylene copolymer in an amount of from 5 to 40% by weight based on the total amount of the composition to be finally obtained.
(2) The polypropylene/propylene-ethylene copolymer composition as described in the above (1), wherein the common logarithm of the ratio of the melt flow rate of the propylene polymer obtained in polymerization step (I) (MFR (i)) to the melt flow rate of the propylene-ethylene copolymer obtained in polymerization step (II) (MFR (ii)), i.e., the common logarithm of MFR (i)/MFR (ii), is from 2 to 9.
(3) The polypropylene/propylene-ethylene copolymer composition as described in the above (1), wherein the common logarithm of the ratio of the melt flow rate of the propylene polymer obtained in polymerization step (I) (MFR (i)) to the melt flow rate of the propylene-ethylene copolymer obtained in polymerization step (II) (MFR (ii)), i.e., the common logarithm of MFR (i)/MFR (ii), is from 4 to 7.
(4) The polypropylene/propylene-ethylene copolymer composition as described in the above (1), which has a melt flow rate of from 20 to 30 g/10 min.
(5) The polypropylene/propylene-ethylene copolymer composition as described in the above (1), which has a melt flow rate of from 40 to 80 g/10 min.
(6) The polypropylene/propylene-ethylene copolymer composition as described in the above (1), wherein the propylene polymer is a propylene polymer which consists of repeating units represented by the following general formula (1) and has a number-average molecular weight of from 10,000 to 60,000, a density of from 0.90 to 0.92 g/cm
3
, and a tie molecule volume content (&bgr;) of 1.38% or higher.
(7) A process for producing a polypropylene/propylene-ethylene copolymer composition having a melt flow rate (ASTM D-1238; the same applies hereinafter) of from 1 to 80 g/10 min which comprises:
a first stage (polymerization step (I)) in which a highly stereoregular catalyst is used to polymerize propylene in the presence of the highly stereoregular catalyst and hydrogen to produce a propylene polymer having a melt flow rate in the range of from 15 to 99 g/10 min and a tie molecule volume content (&bgr;), as obtained from an oriented sample and defined by
&bgr;=(1−0.01
Xc
)
E
/(41−0.01
Xc·E
)
wherein Xc: degree of crystallization (%); and
E (GPa): modulus of elasticity, of 1.38% or higher in an amount of from 60 to 95% by weight based on the total amount of the composition to be finally obtained; and
a second stage (polymerization step (II)) in which ethylene and propylene are subsequently fed to the product of the first stage in such a proportion as to result in an ethylene content of from 20 to 80% by weight to produce a propylene-ethylene copolymer in an amount of from 5 to 40% by weight based on the total amount of the composition to be finally obtained.
BEST MODES FOR CARRYING OUT THE INVENTION
The present invention is explained in detail below.
The polymerization step (I) in the present invention is conducted in such a manner that the resultant propylene polymer has a melt flow rate (MFR (i)) in the range of from 15 to 99 g/10 min, preferably from 30 to 99 g/10 min, and a tie molecule volume content (&bgr;) of 1.38% or higher.
The value of &bgr; is determined according to the method proposed by Masaru Ishikawa et al. in
Polymer.,
Vol.37, No.24, 5375-5379(1996). Specifically, the following method was used.
To 100 parts by weight of a virgin polymer were added 0.1 part by weight of IRGANOX 1010 (tetrakis[methylene-3-(3′,5′-dibutyl-4′-hydroxyphenyl)propionate]methane) (manufactured by Ciba-Geigy Ltd.) as a phenolic heat stabilizer and 0.1 part by weight of calcium stearate. These ingredients were mixed together at room temperature for 2 minutes using a high-speed agitation type mixer (e.g., a Henschel mixer, trade name), and this mixture was granulated at 200° C. with an extrusion granulator having a screw diameter of 40 mm. Subsequently, the granules were heated with a pressing machine for 3 minutes under the conditions of a molten-resin temperature of 230° C. and 4 MPa, subsequently cooled for 3 minutes under the conditions of 30° C. and 14.8 MPa, and then taken out of the mold to obtain a compression-
Fukazawa Tooru
Kawazoe Shunji
Shimomura Yozo
Chisso Corporation
Leydig , Voit & Mayer, Ltd.
Nutter Nathan M.
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