Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-12-15
2003-04-22
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...
C526S943000, C526S158000, C526S129000, C526S352000, C526S348000, C525S240000
Reexamination Certificate
active
06552138
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyethylene type resin for flexible sealed containers and flexible sealed containers obtained therefrom.
TECHNICAL BACKGROUND
Because of their excellent transparency, flexibility, strength and moisture resistance, those sealed containers produced by injection-molding polyethylene are used widely as molded containers for preserving food.
In recent years, under the background of the necessity for preserving the contents of containers such as food at low temperatures, there is an increasingly great demand for those sealed containers which show a higher degree of flexibility than that of the conventional sealed containers.
As the material of such sealed containers, linear very low density polyethylene and high-pressure low density polyethylene are used utilizing those particular properties. However, it has been found that a problem arises when such polyethylene is blended with another resin or a plasticizer to improve its flexibility because the sealed containers obtained from such blended polyethylene will tend to have higher flexibility but become sticky and decline in slip properties.
For this reason, the inventor of the invention set a target of supplying a resin for flexible sealed containers that can provide sealed containers having higher flexibility than that of conventional sealed containers and yet excellent slip properties that are free of stickiness.
The present invention is intended to resolve such problem accompanied by conventional technology as described above. The purpose of the invention is to provide a resin for flexible sealed containers that can manufacture sealed containers which have higher flexibility than that of conventional sealed containers and exhibit unstickiness and excellent slip properties.
DISCLOSURE OF THE INVENTION
The resin for flexible sealed containers of the present invention is an ethylene/&agr;-olefin copolymer (A) comprising ethylene and an &agr;-olefin having 3 to 12 carbon atoms, with the said ethylene/&agr;-olefin copolymer (A) being a polyethylene resin which shows:
(1) Density ranging from 0.900 to 0.930 g/cm
3
;
(2) Melt flow rate ranging from 0.1 to 100 g/10 min.;
(3) Content of the component soluble in n-decane at normal temperature which ranges from 0.1 to 2 wt %;
(4) Molecular weight distribution (Mw/Mn) as measured by GPC which ranges from 1.5 to 3.5; and
(5) Olsen rigidity ranging from 500 to 3,500 g/cm
2
.
The resin for flexible sealed containers of the present invention is an ethylene/&agr;-olefin copolymer (A) comprising ethylene and an &agr;-olefin having 3 to 12 carbon atoms. This ethylene/&agr;-olefin copolymer (A) may be of a straight-chain type or a branched (short-chain/long-chain branched) type.
Specific examples of the &agr;-olefin having 3 to 12 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene and 1-dodecene. More preferable examples of the &agr;-olefin are those &agr;-olefins having 3 to 8 carbon atoms such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene.
Therefore, a more preferable ethylene/&agr;-olefin copolymer (A) is an ethylene/&agr;-olefin copolymer (A) comprising ethylene and an &agr;-olefin having 3 to 8 carbon atoms.
Preferable examples of the ethylene/&agr;-olefin copolymer (A) of the invention are ethylene/1-butene copolymer, ethylene/1-pentene copolymer, ethylene/1-hexene copolymer, ethylene/4-methyl-1-pentene copolymer and ethylene/1-octene copolymer.
This ethylene/&agr;-olefin copolymer (A) contains 65 to 99 wt %, preferably 70 to 98 wt %, more preferably 75 to 96 wt %, of the component unit derived from a ethylene and 1 to 35 wt %, preferably 2 to 30 wt %, more preferably 4 to 25 wt %, of the component unit derived from the &agr;-olefin having 3 to 12 carbon atoms.
The density of the ethylene/&agr;-olefin copolymer (A) is in a range of 0.900 to 0.930 g/cm
3
, preferably 0.900 to 0.920 g/cm
3
. The ethylene/&agr;-olefin copolymer (A) having density in this range makes the molding of sealed containers having adequate mechanical strength and flexibility possible.
Furthermore, the melt flow rate of the ethylene/&agr;-olefin copolymer (A) is in a range of 0.1 to 100 g/10 min., preferably 1 to 90 g/10 min., more preferably 10 to 80 g/10 min. The use of the ethylene/&agr;-olefin copolymer (A) showing the melt flow rate in the above range enables injection-molding to be carried out efficiently and containers retaining high mechanical strength to be molded.
Moreover, the content (W) of the component soluble in n-decane at normal temperature is in a range of 0.1 to 2 wt %, preferably 0.1 to 1.0 wt %.
The content (W) of the component soluble in n-decane can be defined by the following formula:
W (%)=[(Weight of component soluble in n-decane)/(total weight of components soluble and insoluble in n-decane)]×100
It means that as the content of the component soluble in n-decane decreases, the composition distribution of the ethylene/&agr;-olefin copolymer (A) becomes narrower. It is desirable that the content of the component soluble in n-decane is in the above range because if the content of the component soluble in n-decane is in the above range, the content of the low molecular weight component which causes stickiness is very low, enabling moldings having excellent slip properties to be obtained.
Furthermore, the ethylene/&agr;-olefin copolymer (A) shows a molecular weight distribution (Mw/Mn: Mw=weight average molecular weight; Mn=number average molecular weight) being in a range of 1.5 to 3.5, preferably 1.5 to 3.0, as measured by gel permeation chromatography (GPC). The use of the ethylene/&agr;-olefin copolymer (A) showing a molecular weight distribution being in the above range makes the manufacture of containers exhibiting low stickiness possible.
Furthermore, in the invention, the Olsen rigidity of the ethylene/&agr;-olefin copolymer (A) is in a range of 500 to 3,500 g/cm
2
, preferably 500 to 3,000 g/cm
2
. The moldings obtained from this resin show excellent flexibility because its Olsen rigidity is in the above range.
Those moldings also have excellent Izod impact strength and do normally not fail in Izod impact strength test.
The ethylene/&agr;-olefin copolymer (A) of the invention preferably shows a relationship between melt tension MT (g) at 190° C. and melt flow rate MFR (g/10 min.) as represented by:
MT>2.2×MFR
−0.84
(i)
The ethylene/&agr;-olefin copolymer (A) of the invention preferably shows a relationship between content W (wt %) of the component soluble in decane at room temperature and density d (g/cm
3
) as represented by:
When MFR ≦10 g/10 min.,
W<80×exp(−100(d −0.88))+0.1 (ii-a)
When MFR >10 g/10 min.,
W<80×(MFR−9)
0.26
×exp(−100(d−0.88))+0.1 (ii-b)
The ethylene/&agr;-olefin copolymer (A) of the present invention preferably shows a relationship between temperature Tm (° C.) at the highest peak in the endothermic curve as measured with a differential scanning calorimeter (DSC) and density (d) as represented by:
Tm<400d−248 (iii)
The ethylene/&agr;-olefin copolymer (A) of the invention most preferably shows the relationships as represented by (i), (ii-a) or (ii-b), and (iii) above simultaneously.
The ethylene/&agr;-olefin copolymer (A) of the invention much more preferably shows additionally a relationship between flow index FI (1/sec) as defined in terms of the shear rate at which the shear stress at 190° C. of the molten polymer reaches 2.4×10
6
dyne/cm
2
and melt flow rate MFR (g/10 min) which is represented by:
FI>75×MFR (iv)
Such ethylene/&agr;-olefin copolymer (A) can be manufactured, for example, by copolymerizing ethylene and &agr;-olefin in the presence of an olefin polymerization catalyst comprising a compound (a) of a transition metal in Group IV of the Periodic Table which contains the cyclopentadienyl skeleton, an organo-aluminum oxy compo
Choi Ling-Siu
Mitsui Chemicals Inc.
Wu David W.
LandOfFree
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