Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-08-20
2002-09-10
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S114000, C526S116000, C526S160000, C526S127000, C526S130000, C526S348300, C526S348600, C526S943000, C502S113000, C502S120000, C502S154000
Reexamination Certificate
active
06448356
ABSTRACT:
The present invention relates to an ethylene-&agr;-olefin copolymer. More particularly, the present invention relates to an ethylene-&agr;-olefin copolymer, of which the MFR, the MT, the density and the elution behavior in cross fractionation satisfy certain specific relational formulae. When the copolymer of the present invention is molded into a film, it is excellent in the molding stability, and it is possible to obtain a film which is excellent in transparency, gloss and drape and free from stickiness.
A copolymer of ethylene with an &agr;-olefin has been used in a large amount for various uses, particularly for bags, since a film obtained by blown-film extrusion of such a copolymer is excellent in mechanical properties such as tensile strength and impact strength. However, a film obtainable by blown-film extrusion of a copolymer of ethylene with an &agr;-olefin alone has had a problem that the transparency is inadequate in many uses.
On the other hand, an ethylene-&agr;-olefin copolymer produced by means of a metallocene catalyst has been proposed in recent years. The transparency of this copolymer is improved over the conventional ethylene-&agr;-olefin copolymer but is still inadequate, and its molecular weight distribution is so narrow that the bubble stability during molding is not good (JP-A-4-213309).
Under the circumstances, there has been a proposal to improve the molding characteristic of polyethylene by broadening the molecular weight distribution by a method of carrying out polymerization in multisteps (JP-A-3-23717) or carrying out polymerization by using two or more metallocene compounds in combination (JP-A-5-155932 and JP-A-60-35006), or a proposal of a method wherein a polyethylene prepared by a high pressure method is mixed to an ethylene-&agr;-olefin copolymer produced by means of a metallocene catalyst.
Further, International Patent Application WO93/08221 discloses a resin which is described to be excellent in the fluidity in spite of its narrow molecular weight distribution. However, even the resin disclosed in this application has had no adequate transparency, although it is better in fluidity and moldability to some extent than the former proposals.
Accordingly, it has been desired to develop an ethylene-&agr;-olefin copolymer which, when formed into a film, provides adequate transparency without impairing excellent mechanical properties and processability specific to an ethylene-&agr;-olefin copolymer.
The present inventors have conducted various studies to solve the above problems and as a result, have found that such problems can be solved by an ethylene-&agr;-olefin copolymer, of which the melt tension and the melt flow rate have a certain specific relation, and which satisfies a certain specific elution condition. The present invention has been accomplished on the basis of this discovery.
That is, the present invention provides an ethylene-&agr;-olefin copolymer which is a copolymer of ethylene with a C
3-20
&agr;-olefin and which satisfies the following conditions (a) to (c):
(a) the density (D) is from 0.850 to 0.950 g/cm
3
,
(b) the relation between the melt tension (MT) and the melt flow rate (MFR) at 190° C. satisfies the following formula (1):
log(MT)≧−0.91×log(MFR)+0.06 (1),
and
(c) the following three formulae (2), (3) and (4) are satisfied:
Tmax≦972D−813 (2)
logW
60
≦−0.114 Tmax+9.48 (3)
logW
90
≧0.0394 Tmax−2.95 (4)
where D is the density, Tmax is the elution peak temperature (°C.) by the cross fractionation measurement, W
60
is the weight percent (wt %) of a soluble copolymer content at 60° C. or lower, and W
90
is the weight ratio (wt %) of a soluble copolymer content at 90° C. or higher.
Preferred is the ethylene-&agr;-olefin copolymer wherein said condition (c) is such that the following formulae are satisfied:
Tmax≦972D−816 (2)′
logW
60
≦−0.114 Tmax+9.48 (3)
logW
90
≧0.0394 Tmax−2.81 (4)′
Particularly preferred is the ethylene-&agr;-olefin copolymer wherein the density (D) of said condition (a) is from 0.850 to 0.935 g/cm
3
.
Now, the present invention will be described in detail with reference to the preferred embodiments.
The copolymer of the present invention has a density (D) of from 0.850 to 0.950 g/cm
3
, preferably from 0.850 to 0.935 g/cm
3
(condition (a)). If the density is too low, the drape of the formed film product will be inadequate, and the processability by e.g. a bag-manufacturing machine will be poor, such being undesirable. On the other hand, if it is too high, no adequate transparency of the film will be secured.
Here, the density is one measured by a density gradient tube method after a strand obtained at the time of measuring the melt index is subjected to heat treatment at 100° C. for one hour and left to cool at room temperature for one hour.
Further, the copolymer of the present invention is required to satisfy a condition such that the relation between the melt tension (MT) and the melt flow rate (MFR) at 190° C. satisfies:
log(MT)≧−0.91×log(MFR)+0.06 (1)
preferably,
log(MT)≧−0.91×log(MFR)+0.12
more preferably,
log(MT)≧−0.91×log(MFR)+0.21
(condition (b)). If this relational formula is not satisfied, there will be a problem that during blown-film extrusion, the bubble is likely to be broken or swaying (the stability of the bubble can not be maintained).
It is particularly preferred that MFR of the copolymer is from 0.1 to 50 g/10 min. If MFR is too low, the fluidity at the time of melting tends to be inadequate, and the molded product tends to have surface roughness. On the other hand, if MFR is too high, the strength of the molded product tends to deteriorate, such being undesirable.
Here, MFR is one measured at 190° C. under a load of 2.16 kg in accordance with ASTMD 1238. The melt tension (MT) was measured by means of a capirograph manufactured by Kabushiki Kaisha Toyo Seiki Seisakusho under such conditions that the nozzle diameter was 2.095 mm&phgr;, the nozzle length was 8 mm, the flow-in angle was 180°, the temperature was 190° C., the extrusion rate was 1.0 cm/min, the withdrawing rate was 4.0 m/min, and the distance from the die outlet to the lower end of the V-pully of the tension detector, was 40 cm.
A particularly important point in the present invention is that the copolymer has the specific copolymer composition distribution while having a narrow molecular weight distribution. Such a copolymer composition distribution is characterized in that the maximum peak temperature (Tmax) in the elution curve by cross fractionation shifts to a relatively low side depending upon the density of the copolymer, and the amount of soluble components in a high temperature region is relatively large depending upon Tmax. Namely, in the present invention, the density (D), the temperature (Tmax) at the maximum peak position, the soluble content weight percentage at 60° C. or lower (W
60
) and the soluble content weight percentage at 90° C. or higher (W
90
) are required to satisfy the following three formulae simultaneously, for example, in order to attain excellent film-molding stability during blown-film extrusion for excellent transparency of the resulting film (condition (c)):
Tmax≦972D−813 (2)
logW
60
≦−0.114 Tmax+9.48 (3)
logW
90
≧0.0394 Tmax−2.95 (4)
preferably,
Tmax≦972D−816 (2)′
logW
60
≦−0.114 Tmax+9.48 (3)
logW
90
≧0.0394 Tmax−2.81 (4)′
If the above formulae are not satisfied, the stability of the bubble can not be maintained when such a resin is formed into a film by blown-film extrusion, and the resulting film tends to be poor in the transparency (haze) and in the drape, and the film surface tends to be sticky.
Here, the measurement by cross fractionation was carried out by means of a cross fra
Goto Yukitaka
Ishihama Yoshiyuki
Uehara Yumito
Lu Caixia
Mitsubishi Chemical Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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