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
2002-08-02
2004-06-01
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...
C525S192000, C525S193000, C525S197000, C525S240000
Reexamination Certificate
active
06743863
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin composition comprising ethylene-based polymers excellent in environmental stress cracking resistance (hereinafter referred to as ESCR) and stiffness without imperfections or gel, excellent in moldability, and suitable for blow molding to produce e.g. cans and bottles, and for extrusion molding to produce pipes, and a process for its production.
2. Discussion of Background
In recent years, higher performance has become required for polyethylene as its application and demand increases. For example, physical properties required for polyethylene for blow molding or for extrusion molding may be good ESCR, high stiffness due to high density, good moldability, etc.
Generally speaking, the polyethylene having lower density, or higher intrinsic viscosity and higher molecular weight leads better ESCR property of the resin composition. However, when the value of polymer density is lowered, the mechanical strength of the composition is lowered as well as stiffness. When the polyethylene has high value of intrinsic viscosity or high molecular weight, the composition is poorly flowable to cause the problem of molding. Thus, improving ESCR of the resin composition in control of the density of the polymers and increasing the stiffness of resin composition, are against each other. Likewise, improving ESCR of the composition in control of the molecular weight of the polymers and improving the moldability of the composition, are against each other.
Heretofore, as a method of producing a polyethylene having a broad molecular weight distribution to be used for blow molding, a method of producing a polyethylene having a high molecular weight and a polyethylene having a low molecular weight in more than two consecutive polymerization steps has been considered, and various methods have been proposed as multi-step polymerization methods. Generally speaking, a polyethylene obtained by a two-step polymerization method is excellent in the balance of stiffness and ESCR, as compared with a polyethylene obtained by a single step polymerization method. For example, according to the method described in JP-A-64-79204 or JP-A-2-155906, it is disclosed that an &agr;-olefin is copolymerized in order to control the stiffness of the polyethylene, and the balance between the stiffness and environmental stress cracking resistance (ESCR) can be remarkably improved by incorporating the &agr;-olefin so that the content of the &agr;-olefin in the higher molecular weight polymer is higher than the content of the &agr;-olefin in the lower molecular weight polymer.
However, the product obtained by such a two-step polymerization method has disadvantages that generally, the bonding strength at a pinch-off portion of the blow molded articles is small, and the swelling ratio is small. As a means to overcome such disadvantages of the two-step polymerization method, a three-step polymerization method has been proposed in, for example, JP-A-58-138719, JP-A-59-227913, JP-A-64-79204, JP-B-59-10724, JP-B-62-61057, JP-B-3-29805 and JP-B-4-14686. In the method described in these publications, three components having different molecular weights are produced in each step. However, as pointed out in JP-B-4-14686, there is a problem that the balance of stiffness and ESCR tends to be poor, although the swelling ratio of the obtained polyethylene can be improved. Further, in the three-step polymerization method as proposed by such prior art, generally in addition to the lower molecular weight component and the high molecular weight component produced by normal two-step polymerization, a small amount of an ultrahigh molecular weight component is produced as a third component, and consequently, a polyethylene containing a small amount of a polymer having such a very high molecular weight tends to form imperfections or gel.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a resin composition comprising ethylene-based polymers excellent in ESCR and stiffness without imperfections or gel, and excellent in moldability, and a process for producing such a resin composition.
The present inventors have conducted extensive studies to solve the above-mentioned difficult problems and establish a resin composition comprising ethylene-based polymers suitable for blow molding or extrusion molding, and a process for its production, and, as a result, have found that by combining three types of polymers having specific structures which are not ultrahigh molecular weight components, at specific contents, and further by setting the difference in molecular weight (evaluated by an intrinsic viscosity) between component (B) and component (C) among the three types not to be so large, and differentiating the contents of &agr;-olefins in the two components, all of the above-mentioned requirements can be satisfied and the object of the present invention can be realized. The present invention has been accomplished on the basis of these discoveries.
Thus, the present invention provides a resin composition comprising the following components (A), (B) and (C), wherein the content of component (A) is from 10 to 90 wt %, component (B):component (C)=from 10:1 to 1:5 (weight ratio), the intrinsic viscosity [&eegr;] is in the range from 0.17 to 0.40 m
3
/kg, and the density is in the range from 935 to 968 kg/m
3
:
Component (A): a homopolymer of ethylene or a copolymer of ethylene having an &agr;-olefin content of from 0 to 0.5 wt %, and an intrinsic viscosity [&eegr;] of from 0.035 to 0.17 m
3
/kg,
Component (B): a homopolymer of ethylene or a copolymer of ethylene having an &agr;-olefin content of from 0 to 0.5 wt %, and an intrinsic viscosity [&eegr;] of from 0.2 to 1.0 m
3
/kg, and
Component (C): a copolymer of ethylene having an &agr;-olefin content of from 0.7 to 15 wt %, and an intrinsic viscosity [&eegr;] of from 0.2 to 1.0 m
3
/kg.
The present invention also provides a process for producing a resin composition comprising ethylene-based polymers, which comprises carrying out
step (a): a step of producing from 10 to 90 wt %, based on the total amount of polymerized polymers, of a homopolymer of ethylene or a copolymer of ethylene having an &agr;-olefin content of from 0 to 0.5 wt %, and an intrinsic viscosity [&eegr;] of from 0.035 to 0.17 m
3
/kg, at a temperature of from 70 to 110° C.,
step (b): a step of producing a homopolymer of ethylene or a copolymer of ethylene having an &agr;-olefin content of from 0 to 0.5 wt %, and an intrinsic viscosity [&eegr;] of from 0.2 to 1.0 m
3
/kg, at a temperature of from 40 to 90° C., and
step (c): a step of producing a copolymer of ethylene having an &agr;-olefin content of from 0.7 to 15 wt %, and an intrinsic viscosity [&eegr;] of from 0.2 to 1.0 m
3
/kg, at a temperature of from 30 to 80° C., in an optional order, by using a catalyst which comprises a solid catalyst component (E) containing at least titanium, magnesium and a halogen, and an organic aluminum compound, wherein the three-step polymerization is carried out so that the ratio of amount of polymerized polymers in steps (b) and (c) becomes step (b):step (c)=from 10:1 to 1:5 (weight ratio), to produce a resin composition having an intrinsic viscosity [&eegr;] of from 0.17 to 0.4 m
3
/kg and a density of from 935 to 968 kg/m
3
.
The present invention further provides a process for producing a resin composition comprising ethylene-based polymers, which comprises carrying out
step (a): a step of producing from 10 to 90 wt %, based on the total amount of polymerized polymers, of a homopolymer of ethylene or a copolymer of ethylene having an &agr;-olefin content of from 0 to 0.5 wt %, and an intrinsic viscosity [&eegr;] of from 0.035 to 0.17 m
3
/kg, at a temperature of from 70 to 100° C.,
step (b): a step of producing a homopolymer of ethylene or a copolymer of ethylene having an &agr;-olefin content of from 0 to 0.5 wt %, and an intrinsic
Iida Masashi
Iizuka Tetsuya
Kawahara Masao
Nishitani Katsutoshi
Takemori Toshifumi
Maruzen Petrochemical Co. Ltd.
Nutter Nathan M.
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