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
1997-06-04
2001-05-01
Mullis, Jeffrey C. (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...
C525S269000, C525S270000, C525S323000
Reexamination Certificate
active
06225414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a propylene block copolymer. More particularly, it relates to a propylene block copolymer which is superior in flexibility, transparency and impact resistance at low temperature.
2. Description of the Related Arts
A crystalline propylene polymer (herein-after, referred to as simply as “propylene polymer”) has widely been used in the fields of films, sheets, containers, etc. because of excellent heat resistance and rigidity.
In the medical field such as infusion bag, etc. and food packaging field, materials having a good flexibility, transparency, impact resistance and heat resistance have recently been required. A propylene homopolymer is superior in heat resistance, but is inferior in flexibility, transparency and impact resistance at low temperature. A random copolymer of propylene and &agr;-olefin is superior in transparency, but is insufficient in impact resistance at low temperature and, therefore, use thereof is limited.
Some trials of improving the impact resistance using a propylene block copolymer have been made.
JP-A-56-084712 discloses a polypropylene block copolymer composed of a propylene ethylene copolymer block as a moiety A and a propylene ethylene copolymer block as a moiety B, characterized in that a melt flow index suitable for an air-cooling inflation method is from 0.01 to 0.3 g/10 minutes, an ethylene content of the moiety A is less than 20% by weight and an ethylene content of the moiety B is not less than 20% by weight. Specifically, a polymer polymerized by a solvent method is disclosed but is not sufficient in transparency. Namely, in Comparative Example of it, there is disclosed a composition having an ethylene content of the moiety A of 4.6% by weight, an ethylene content of the moiety B is 13.9% by weight and a content of the moiety B of 17.7% by weight. Although the transparency is improved by reducing the ethylene content, the impact strength at low temperature is insufficient.
JP-A-06-093061 discloses an ethylene-propylene block copolymer obtained by producing a polymer moiety (component A) which is mainly composed of propylene in the absence of an inert solvent, substantially, in a first step, and then producing an ethylene-propylene copolymer moiety (component B) in a gas phase in a second step, using a Ziegler-Natta catalyst. The ethylene content of the component (B) is from 20 to 50% by weight and the impact resistance at low temperature is good, but the transparency is insufficient.
The present inventors have intensively studied to solve drawbacks of the conventional ethylene-propylene block copolymer. As a result, the problems above can be solved by a specific block copolymer obtained by polymerizing in the absence of the solvent, substantially.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polypropylene block copolymer having a good transparency and improved impact resistance at low temperature.
According to the present invention, there is provided a polypropylene block copolymer obtained by producing an ethylene-propylene copolymer moiety as a component A having an ethylene content of 1.5 to 6.0% by weight in an amount of 40 to 85% by weight based on the total of components A and B, in the absence of an inert solvent, substantially, in a first step, with a Ziegler-Natta catalyst, and then producing an ethylene-propylene copolymer moiety as a component B having an ethylene content of 7 to 17% by weight in an amount of 15 to 60% by weight based on an amount of the total of components A and B in a gas phase in a second step, wherein the intrinsic viscosity ([&eegr;]B) of the component B is from 2.0 to 5.0 dl/g and the ratio ([&eegr;]B/[&eegr;]A) of the intrinsic viscosity ([&eegr;]B) of the component B to the intrinsic viscosity ([&eegr;]A) of the component A is within the range of 0.5 to 1.8.
Herein, this block copolymer composed of components A and B strictly means a composition composed of the components A and B because the greater part of the component A is not chemically bonded with the component B in the block copolymer. This composition is referred to as “block copolymer” in the present specification.
DETAILED DESCRIPTION OF THE INVENTION
The polypropylene block copolymer of the present invention is a block copolymer obtained by producing an ethylene-propylene copolymer moiety (component A) having an ethylene content of 1.5 to 6.0% by weight in the absence of an inert solvent, substantially, in a first step, with a Ziegler-Natta catalyst, and then producing an ethylene-propylene copolymer moiety (component B) having a different ethylene concentration in a gas phase in a second step.
The proportions of the component A and the component B are from 40 to 85% by weight and from 15 to 60% by weight based on the total weight of components A and B, respectively.
When the proportion of the component B is less than 15% by weight, the impact resistance at low temperature becomes poor. On the other hand, when it exceeds 60% by weight, the heat resistance decreases. In case of using for film applications, particularly, it is more preferred that the proportion of the component B is from 17 to 27% by weight from view point of the moldability.
In order to obtain the ethylene-propylene block copolymer wherein the proportion of the component B is from 17 to 27% by weight, it is possible to produce a block copolymer wherein the proportion of the component B is from 17 to 27% by weight in the polymerization step. It is also possible that an ethylene-propylene block copolymer wherein the proportion of the component B is from 27 to 60% by weight is produced by polymerization and only the component A obtained by carrying out the only first step polymerization may be added to the block copolymer in melt-kneading to adjust the proportion of the component B.
The ethylene content of the component A produced in the first step is from 1.5 to 6.0% by weight. When the ethylene content is less than 1.5% by weight, the flexibility is reduced. On the other hand, when it exceeds 6.0% by weight, the heat resistance is reduced. The ethylene content of 2.5 to 4.5% by weight is more preferred from the view point of a balance between the flexibility and heat resistance.
The ethylene content of the component B produced in the second step is from 7 to 17% by weight. When the ethylene content is less than 7% by weight, the impact resistance at low temperature is deteriorated. On the other hand, when it exceeds 17% by weight, the transparency is deteriorated. The ethylene content of 8 to 12% by weight is more preferred from the view point of a balance between the impact resistance at low temperature and transparency.
The intrinsic viscosity ([&eegr;]B) of the component B is from 2.0 to 5.0 dl/g, and the ratio ([&eegr;]B/[&eegr;]A) of the intrinsic viscosity ([&eegr;]B) of the component B to the intrinsic viscosity ([&eegr;]A) of the component A is from 0.5 to 1.8, in view of the transparency. When the [&eegr;]B is less than 2.0 dl/g, the proportion of a low-molecular weight component is increased and, therefore, it is not preferred. On the other hand, when it exceeds 5.0 dl/g, the fluidity and processability of the ethylene-propylene block copolymer become poor. The intrinsic viscosity of the [&eegr;]B) of the component B of the ethylene-propylene copolymer is preferably from 2.5 to 4.0 dl/g, in view of a balance between the inhibition of the low-molecular weight component and processability.
When the ratio of the [&eegr;]B to the [&eegr;]A ([&eegr;]B/[&eegr;]A ) is more than 1.8 or less than 0.5, the compatibility of the component A to the component B is deteriorated and the transparency is deteriorated. The ratio of the [&eegr;]B to the [&eegr;]A ([&eegr;]B/[&eegr;]A) is preferably from 0.8 to 1.5, in view of the transparency.
Moreover, the polypropylene block c
Kume Takanori
Shiratani Eisuke
Wakamatsu Kazuki
Birch Stewart Kolasch & Birch
Mullis Jeffrey C.
Sumitomo Chemical Company Limited
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