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
2002-04-22
2004-04-06
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...
C525S195000, C525S240000
Reexamination Certificate
active
06716924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparing an ethylene polymer composition, particles of ethylene polymer composition and a film obtained from the particles of ethylene polymer composition. More particularly, the invention relates to a process for preparing an ethylene polymer composition of excellent particle morphology, which comprises polymerizing ethylene with high activity through two-step polymerization using a specific catalyst, particles of ethylene polymer composition which have excellent particle morphology, scarcely suffer sintering and are capable of efficiently undergoing subsequent processes, and a film obtained from the particles of ethylene polymer composition and having small gauge-variation and excellent tear strength.
BACKGROUND OF THE INVENTION
Ethylene polymers, such as homopolyethylene, a linear low-density ethylene polymer (LLDPE) and an ethylene &agr;-olefin copolymer, are excellent in transparency, mechanical strength, etc., and hence they have been widely used for films and the like.
For preparing such ethylene polymers, various processes have been heretofore known, and it is known that the ethylene polymers can be prepared with high polymerization activity by the use of, as a polymerization catalyst, a Ziegler catalyst containing a titanium catalyst component composed of titanium, magnesium, a halogen, and optionally, an electron donor. It is also known that especially when a solid titanium catalyst component obtained from a halogen-containing magnesium compound that is prepared as a liquid compound, a liquid titanium compound and an electron donor is used as the titanium catalyst component, the ethylene polymers can be prepared with high activity.
By the way, if it becomes possible to polymerize ethylene and an &agr;-olefin with much higher activity in the preparation of the ethylene polymers, not only the productivity is enhanced, but also the amount of a catalyst residue based on the polymer, particularly the amount of halogen, is decreased, and hence problems, such as mold rusting in the molding process, can be solved. On this account, a process for preparing an ethylene polymer, in which ethylene and an &agr;-olefin can be polymerized with much higher activity, has been desired.
As a process for polymerizing ethylene with high activity, there has been recently proposed, for example, a process wherein an ethylene polymerization catalyst containing a solid titanium catalyst component obtained by contacting a liquid magnesium compound, a liquid titanium compound and an organosilicon compound having no active hydrogen (Japanese Patent Laid-Open Publication No. 328514/1997) or a process wherein an olefin polymerization catalyst containing an aluminum compound selected from a reaction product of aluminosiloxane, aluminum alkyl and calixarene and a reaction product of aluminum alkyl and cyclodextrin, a halogen-containing magnesium compound and a titanium compound (Japanese Patent Laid-Open Publication No. 53612/1998), and preparation of polymers of excellent particle morphology using these catalysts has been proposed.
Under such circumstances, establishment of a process for more efficiently preparing an ethylene polymer industrially has been strongly desired. Immediately after the polymerization, an ethylene polymer is usually obtained in the form of a powder irrespective of the polymerization type such as slurry polymerization or gas phase polymerization, and it is desirable to prepare an ethylene polymer having excellent fluidity, containing no finely powdered particles and having excellent particle morphology, namely, an ethylene polymer having a narrow particle size distribution. The ethylene polymer having excellent particle morphology has various advantages such as an advantage that it can be used as it is without pelletization, depending upon the purpose. In addition, development of an ethylene polymer scarcely having tackiness at high temperatures, that is, scarcely suffering sintering, has been strongly desired.
OBJECT OF THE INVENTION
The present invention has been made under such circumstances as described above, and it is an object of the invention to provide a process for preparing an ethylene polymer composition in which ethylene and an &agr;-olefin can be polymerized with high activity and an ethylene polymer composition having excellent particle morphology, scarcely suffering sintering and having excellent moldability can be efficiently prepared. It is another object of the invention to provide particles of ethylene polymer composition which have excellent moldability, scarcely suffer sintering and have a small particle size distribution and to provide a film obtained from the particles of ethylene polymer composition and having small gauge-variation and excellent tear strength.
SUMMARY OF THE INVENTION
The process for preparing an ethylene polymer composition according to the invention is a process comprising:
(I) a step of polymerizing ethylene or ethylene and another &agr;-olefin to prepare an ethylene polymer (i) having an &agr;-olefin content of not more than 30% by weight and an intrinsic viscosity [&eegr;] of at least 1.5 times the intrinsic viscosity of the following ethylene polymer (ii) and ranging from 1 to 12 dl/g, and
(II) a step of polymerizing ethylene or ethylene and another &agr;-olefin to prepare an ethylene polymer (ii) having an &agr;-olefin content of not more than 15% by weight and an intrinsic viscosity [&eegr;] of 0.3 to 3 dl/g,
said steps (I) and (II) using an ethylene polymerization catalyst containing a solid titanium catalyst component obtained by contacting (a) a liquid magnesium compound with (b) a liquid titanium compound in the presence of (c) an organosilicon compound or an organosilicon aluminum compound,
wherein the step (II) is carried out in the presence of the ethylene polymer (i) obtained in the step (I) or the step (I) is carried out in the presence of the ethylene polymer (ii) obtained in the step (II), to prepare an ethylene polymer composition having an intrinsic viscosity [&eegr;] of 1 to 6 dl/g and a density of not less than 0.94 g/cm
3
.
In the process for preparing an ethylene polymer composition according to the invention, the step (I) and the step (II) are preferably carried out by slurry polymerization.
The particles of ethylene polymer composition according to the invention are prepared by the above process, comprise an ethylene polymer composition having a melt flow rate, as measured at 190° C. in accordance with ASTM D 1238E, of 0.0001 to 0.5 g/10 min and a molecular weight distribution (Mw/Mn) of 20 to 45, and have:
a particle size distribution index, as determined by the following formula, of 1.1 to 2.0,
Particle size distribution index={square root over (Polymer D
84
/Polymer D
16
)}
wherein Polymer D
16
is a particle diameter obtained when 16% by weight of the whole particles of ethylene polymer composition can be sieved, and Polymer D
84
is a particle diameter obtained when 84% by weight of the whole particles of ethylene polymer composition can be sieved,
a bulk density of 0.30 to 0.45 g/ml, and
a fluidity index of 45 to 90.
When the particles of ethylene polymer composition obtained by the invention are applied to film use, the resulting film has small gauge-variation and excellent tear strength.
The film according to the invention is obtained from the particles of ethylene polymer composition and has small gauge-variation and excellent tear strength.
DETAILED DESCRIPTION OF THE INVENTION
The process for preparing an ethylene polymer composition, the particles of ethylene polymer composition and the film obtained from the particles of ethylene polymer composition according to the invention are described in detail hereinafter.
The meaning of the term “polymerization” used herein is not limited to “homopolymerization” but may comprehend “copolymerization”. Also the meaning of the term “polymer” used herein is not limited to “homopolymer” but may comprehend “copolymer”.
Process for Preparing Ethylene Poly
Funabara Yasuo
Tsutsui Toshiyuki
Yashiki Tsuneo
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