Propylene polymer

Details Propylene polymer Propylene polymer

2002-05-16

2004-06-29

Rabago, Roberto (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S348000, C526S160000

Reexamination Certificate

active

06756463

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to propylene polymers which are excellent in rigidity and heat resistance and have an appropriate melt tension and favorable molding processability and appearance.
2. Description of the Related Art
Because of having the characteristics of being excellent in rigidity, heat resistance, molding properties, transparency and chemical resistance, propylene polymers have attracted public attention and widely used for a number of purposes such as various industrial materials, various containers, daily necessities, films and fibers.
Metallocene catalysts with the use of metallocene transition metal compounds have been widely employed, since these catalysts generally have a high activity and propylene polymers obtained thereby are excellent in stereostructural properties. However, the propylene polymers produced by using metallocene catalysts have a disadvantage of having a small memory effect (ME) due to a narrow molecular weight distribution and thus showing a poor molding processability. ME is a value serving as an indication of the non-Newtonian properties of a resin. In general, a higher ME indicates the wider molecular weight distribution and a tendency toward the more favorable molding properties particularly owing to the effects of high-molecular weight components.
As a method of obtaining a propylene polymer having a large ME, there has been known a method wherein polymerization is performed by using a TiCl
3
-type catalyst or a specific Ziegler-Natta catalyst carrying magnesium. However, much cold xylene solubles (CXS) occur in this method, which brings about some problems of stickiness and worsening in rigidity and heat resistance. As techniques for improving ME by using metallocene-type catalysts, Japanese Patent Laid-Open No. 255812/1990 and ibid. No. 179776/1994 disclose methods of controlling molecular weight distribution by using two types of complexes (Hf and Zr), while International Patent Publication No. 2001-500176 proposes to broaden molecular weight distribution by using two types of Zr complexes having high stereoregularity. In case where the distribution is about 7 or lower, ME cannot be improved by these methods. Although ME can be improved thereby in a system having a larger molecular weight distribution value, no homogeneous mixture can be obtained, which results in a tendency that the molding appearance is worsened. It is therefore required to solve these problems. Japanese Patent Laid-Open No. 181343/2001 and ibid. No. 294609/2001 propose polymers having Mw/Mn ratios ranging from 6 to 50 and a process for producing the same. Although these polymers have high Mw/Mn ratios, MEs thereof are not so high. This is because these polymers contain less high-molecular weight components having relatively high molecular weight of 1,000,000 or more which are appropriate for improving ME. On the other hand, Japanese Patent Laid-Open No. 288220/2001 proposes single-peak polymers having Mw/Mn values of from 4 to 6. Although high molecular weight contributing to the improvement in ME can be achieved in this polymerization system, hydrogen is fed at once at the early stage and thus the polymerization is carried out in an almost hydrogen-free state as the hydrogen is consumed. As a result, there arises a problem that ME becomes higher in comparison with the Mw/Mn ratio and thus the appearance is worsened. It is therefore required to overcome this problem.
SUMMARY OF THE INVENTION
Considering the problems as discussed above, the present invention provides propylene polymers which are not only excellent in rigidity and heat resistance but also contain an appropriate amount of high-molecular weight components with little eluting components and have excellent molding processability.
According to the present invention, it has been found out that the above-described problems can be solved by providing a propylene polymer which is characterized by being excellent in stereoregularity, containing a small amount of low-molecular weight components and a small amount of CXS and yet having a large ME.
Accordingly, the propylene polymer of the present invention, which may be copolymerized with ethylene of 0 to 7% by weight, is characterized by comprising satisfying the following requirements:
(1) a melt flow rate (MFR) measured at 230° C. under a 2.16 kg load of from 0.1 to 1000 g/10 min;
(2) an isotactic triad fraction (mm) measured by
13
C—NMR of 99.0% or above;
(3) a Q value (i.e., the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn)) measured by gel permeation chromatography (GPC) of from 2.0 to 6.0;
(4) a relation between MFR measured at 230° C. under a 2.16 kg load and a memory effect (ME) measured at 190° C. at an orifice diameter of 1.0 mm satisfying the following formula (I):
1.75≧(
ME
)+0.26×log(
MFR
)≧1.40  (I);
and
(5) a relation of the cold xylene solubles at 23° C. (CXS, unit: % by weight) satisfying the following formula (II)
CXS≦
0.5×[
C
2]+0.2×log(
MFR
)+0.5  (II)
wherein [C2] represents the ethylene unit content (% by weight) in the polymer.
The present invention is also characterized in that the propylene polymer has been polymerized by using a metallocene catalyst.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides novel propylene polymers meeting with the physiological requirements (1) to (5) as described below.
Requirement (1): MFR
The propylene polymer according to the present invention has a melt flow rate (MFR) measured at 230° C. under a 2.16 kg load of from 0.1 to 1000 g/10 min. It is unfavorable from the viewpoint of the molding process that MFR is lower than 0.1, since the fluidity of the polymer is extremely worsened in this case. It is also unfavorable that MFR exceeds 1000, since the impact strength of the polymer is extremely lowered in this case.
It is preferable that the MFR ranges from 0.5 to 500. Favorable uses are restricted depending on the MFR level. In case of using in injection molding, it is favorable that MFR ranges from 10 to 300. In case of using in film-molding or sheet-molding, it is favorable that MFR ranges from 0.5 to 10, still preferably from 1.0 to 10.
To obtain a polymer having a low MFR, it is necessary to lessen the amount of hydrogen serving as a molecular weight controlling agent. In case of using hydrogen in a small amount, however, the ununiformity of active species as will be described hereinbelow can be hardly established, which makes it difficult to satisfy the relationship between ME and MFR according to the present invention.
Requirement (2): Stereoregularity
The propylene polymer according to the present invention has an isotactic triad fraction measured by
13
C—NMR in the propylene unit chain moiety made up of head-to-tail bonds (i.e., the ratio of propylene unit triads, in which propylene units are bonded to each other via head-to-tail bonds and the methyl branches in the propylene units are in the same direction, to arbitrary propylene unit triads in the polymer chain) of 99.0% or above, preferably 99.5% or above. The isotactic triad fraction will be sometimes referred to as mm fraction thereinafter.
This isotactic triad fraction (mm fraction) is a value which indicates that the stereostructure of methyl groups in the polypropylene molecular chain is isotactically regulate. A higher value means that the higher extent of the regulation. In case where this value is less than the lower limit as specified above, there arises a problem of poor heat resistance.
The
13
C—NMR spectrum can be measured by the following method. Namely, the
13
C—NMR spectrum is measured by completely dissolving a sample (350 to 500 mg) in a solvent prepared by adding about 0.5 ml of deuterated benzene which is a lock solvent to about 2.0 ml of o-dichlorobenzene in an NMR sample tube of 10 mm in diameter followed by the measurement by the proton complete decoupling method at 130° C. The measurement conditions are selected so as to give a

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