Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1997-03-27
1999-10-26
Smith, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
502120, 526127, 5261242, 526348, 5263482, 5263483, 5263484, 5263485, 5263486, 526352, C08F 402, C08F 1002
Patent
active
059730838
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of The Invention
The present invention relates to a high density ethylene polymer and a method for producing the same. More particularly, the present invention is concerned with a high density ethylene polymer which is advantageous in that it has not only excellent mechanical properties, such as high impact resistance and high stiffness, but also excellent moldability, such as high melt flowability, and a method for producing the same.
2. Prior Art
High density ethylene polymers have been put into a wide variety of practical uses in the form of molded articles produced by various molding methods. For example, as a representative method for obtaining a molded film, there can be mentioned an inflation method in which a high density ethylene polymer is melted and the resultant molten polymer is extruded through a die while blowing air into the molten polymer being extruded, to thereby inflate the molten polymer extrudate. Further, as examples of methods for producing molded articles having desired shapes, there can be mentioned a blow molding method in which a high density ethylene polymer in the molten state is introduced into the cavity of a mold to form a molten polymer mass in the cavity. Air is blown into the molten polymer mass in the mold cavity, thereby causing the molten polymer mass to be expanded and pressed onto the inner wall of the cavity. Also an injection molding method is known in which a high density ethylene polymer in the molten state is injected under pressure into the cavity of a mold to fill the cavity.
To all of these various molding methods for high density ethylene polymers, it is common that a melt-molding operation be performed in which a high density ethylene polymer is melted by heating and the resultant molten polymer is molded. Therefore, the behavior of the high density ethylene polymer at heat-melting, i.e., melt properties, are extremely important in molding the high density ethylene polymer.
Especially in the injection molding method, melt properties, especially melt flowability, of a high density ethylene polymer are crucially important for achieving a satisfactory molding.
In the present invention, the term "melt flowability" means a property corresponding to the extrusion load at extrusion of a molten resin through an extruder. As examples of indices which can be used as a yardstick for melt flowability, there can be mentioned M.sub.I, H.sub.MI and M.sub.IR.
In the present invention, M.sub.I means an MFR (melt flow rate) as measured at 190.degree. C. under a load of 2.16 kg. H.sub.MI means an MFR as measured at 190.degree. C. under a load of 21.6 kg. M.sub.IR means the ratio of H.sub.MI to M.sub.I, that is, H.sub.MI /M.sub.I.
In general, with respect to each of M.sub.I, H.sub.MI and M.sub.IR, the larger the value, the higher the melt flowability.
However, in practice, the desired properties of a polymer as a molding material vary depending on the molding method employed. Therefore, which index can be suitably used as a yardstick for melt flowability varies depending on the molding method employed. For example, in the injection molding method, for surely obtaining a molded product having high impact resistance, there is a tendency to use a high density ethylene polymer having a narrow molecular weight distribution. In general, a high density ethylene polymer having a narrow molecular weight distribution has a small M.sub.IR, so that, as an index for melt flowability, M.sub.I and H.sub.MI are mainly used.
Conventionally, a high density ethylene polymer for use in the injection molding method has generally been produced by a polymerization using a Ziegler-Natta catalyst, which contains titanium, or using a chromium-containing catalyst. However, in general, a high density ethylene polymer produced by using such a conventional catalyst tends to have a broad molecular weight distribution, and it has been impossible to render a molecular weight distribution narrower than a certain breadth. In order to solve this problem, it has been attempt
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Idehara Tsutomu
Matsushita Fumio
Yamaguchi Fumihiko
Asahi Kasei Kogyo Kabushiki Kaisha
Smith Edward J.
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