Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-06-19
2002-06-25
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S346000, C428S220000, C428S910000
Reexamination Certificate
active
06410673
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ethylene-aromatic vinyl compound copolymer which has an aromatic vinyl compound content of from 0.5 to 10 mol % and which has a high transparency, a glass transition point represented by a specific formula and a high molecular weight, and a molded product, particularly a film, a sheet or a tube, employing such a copolymer and having high mechanical properties, melting point, etc.
BACKGROUND ART
Ethylene-styrene Copolymer
An ethylene-styrene copolymer employing a so-called Ziegler-Natta catalyst, is obtainable as a mixture with a homopolymer component such as polyethylene or polystyrene, and its compositional distribution is large, whereby it has problems with respect to transparency, mechanical properties, etc. Recently, styrene-ethylene copolymers obtainable by using a so-called homogeneous Ziegler-Natta catalyst system comprising a transition metal catalyst component and an organic aluminum compound, and methods for their production have been known.
JP-A-3-163088 and JP-A-7-53618 disclose a styrene-ethylene copolymer wherein no normal styrene chain exists, i.e. a pseudo random copolymer, which is obtainable by using a complex having a so-called constrained geometrical structure. Here, a normal St chain means a chain of head-to-tail bonding. Further, in the following, styrene may sometimes be represented by St. The pseudo random copolymer is defined to be a copolymer in which no head-to-tail styrene chain structure is contained, and phenyl groups in the alternating structure of styrene-ethylene present in this pseudo random copolymer, have no stereoregularity. Further, as no normal styrene chain exists, the content of styrene can not exceeds 50 mol %. Such a pseudo random copolymer is not sufficiently satisfactory with respect to the mechanical properties such as breaking strength or solvent resistance.
JP-A-6-49132 and Polymer Preprints, Japan, 42, 2292 (1993) disclose a method for producing a similar styrene-ethylene copolymer wherein no normal St chain exists, i.e. a so-called pseudo random copolymer, by means of a catalyst comprising a cross-linked metallocene type Zr complex and a co-catalyst.
According to Polymer Preprints, Japan, vol. 42, 2292 (1993), phenyl groups in the alternating structure of styrene-ethylene present in this pseudo random copolymer, have no substantial stereoregularity. Further, like the case of a complex having a constrained geometrical structure, as no normal styrene chain exists, the content of styrene can not exceed 50 mol %. The activity is also practically inadequate.
Further, recently, a styrene-ethylene copolymer close to an alternating copolymer having a stereoregularity has been reported which is obtainable under a cryogenic condition (−25° C.) by means of a specific crosslinked bisindenyl type Zr complex i.e. rac[ethylenebis(indenyl)zirconium dichloride]. (Macromol. Chem., Rapid Commun., vol. 17,745 (1996).)
However, from the disclosed 13C-NMR spectrum and from the description of the article, it is evident that in this copolymer, no head-to-tail styrene chain exists.
Further, if copolymerization is carried out at a polymerization temperature of at least room temperature by means of this complex, it is only possible to obtain a copolymer having a low styrene content and a low molecular weight.
Further, with styrene-ethylene copolymers obtained by using the foregoing respective catalyst systems, transparency is not good especially in a relatively low styrene content range. This is considered attributable to non uniformity of the compositional distribution, etc. of the copolymers, i.e. due to the fact that a component having a styrene content lower or higher than average, is present relatively abundantly.
WO98/09999 discloses a styrene-ethylene copolymer obtainable by means of a specific zirconocene complex {rac-dimethylsilylenebis(2-methyl,4-phenyl-1-indenyl)zirconium dichloride}. This copolymer has a wide molecular weight distribution and a large compositional distribution. The copolymer having a styrene content of about 10 mol % also contains a polyethylene component and thus is an opaque copolymer.
The present inventors have heretofore proposed a catalyst system for ethylene-styrene copolymerization and an ethylene-styrene copolymer as described below.
JP-A-9-309925 which is an application filed by the present inventors, discloses a novel ethylene-styrene copolymer having a styrene content of from 1 to 50 mol %, an isotactic stereoregularity in the styrene-ethylene alternating structure and an alternating index (value &lgr; in this specification) of the copolymer of at most 70, which is obtainable by using a polymerization catalyst comprising a zirconocene complex having an indenyl group crosslinked with an isopropylidene group, and a co-catalyst. The copolymer obtainable by this catalyst has good transparency and mechanical properties, but when it is attempted to obtain a copolymer having a styrene content of at most 10 mol %, it is difficult to obtain a copolymer having a high molecular weight required to have an inflation molding property or an adequate physical property as a molded product under a polymerization condition of at least about 30° C. at which the catalyst exhibits a practical activity.
EP-872492 discloses a method for producing an ethylene-styrene copolymer having an optional composition by using a zirconocene catalyst having, as a ligand, a benzoindenyl group having a crosslinked structure.
Film of an Ethylene-styrene Copolymer
A film is known which employs a so-called pseudo random ethylene-styrene copolymer having no head-to-tail styrene chain and no stereoregularity derived from styrene units. For example, U.S. Pat. No. 5,703,187 discloses a pseudo random copolymer having a styrene content of from 1.4 to 47 mol % obtained by using a so-called CGCT type catalyst, and a film employing it. JP-A-3-163088 and JP-7-53618 disclose pseudo random copolymers obtainable by means of a so-called CGCT type catalyst and films employing them. WO95/32095 discloses a (multi layer) shrinkable film employing a pseudo random copolymer obtainable by means of a similar CGCT type catalyst.
A copolymer obtained by means of a CGCT catalyst has a drawback that it is poor in the transparency in its application for a film, since it contains a copolymer component having a relatively large compositional distribution of the styrene content and a substantially lower (or higher) styrene content than an average styrene content, especially in the case of a copolymer having a styrene content of at most 20 mol %, particularly at most 10 mol %.
JP-A-10-60051 discloses an ethylene-styrene copolymer obtainable by means of a similar CGCT type catalyst, which is excellent in flexibility and elastic recovery and excellent in transparency and which has a styrene content of particularly preferably from 14 to 30 mol %. However, when the copolymer having a styrene content which is disclosed to be particularly preferred, is employed as a stretch film, the mechanical properties (particularly tensile strength, elastic modulus), the film-forming property and the packaging machine compatibility are not satisfactory, and the elastic modulus in the prescribed styrene content range is too low (the flexibility is too high) as a stretch film. Further, the prescribed glass transition temperature is too low especially in a range where the styrene content is at most 10 mol %. Therefore, it is inadequate with respect to the molding processability as a packaging film, particularly as a stretch packaging film, the softness when it is touched with a hand, and the touched feeling.
Stretch Packaging Film
For stretch packaging, a polyvinyl chloride type film is mainly employed, and an olefin type film made of low density polyethylene, an ethylene-vinyl acetate copolymer, linear low density polyethylene or polypropylene, is partly employed.
However, in recent years, with respect to a polyvinyl chloride film, elusion of a plasticizer contained, or combustion gas formed at the time of incineration has been r
Arai Toru
Nakajima Masataka
Naoe Takanori
Nishitoba Yukiko
Oda Takeshi
Denki Kagaku Kogyo Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Teskin Fred
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