Propylene polymer, molded object thereof, and process for...

Details Propylene polymer, molded object thereof, and process for... Propylene polymer, molded object thereof, and process for...

2001-02-26

2004-10-05

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...

C526S170000, C526S943000, C526S351000, C526S348000, C526S901000

Reexamination Certificate

active

06800706

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a propylene polymer and its moldings, and also to a method for producing propylene polymers. Precisely, the invention relates to a propylene polymer of which the advantages are that its modulus of elasticity is well balanced with its melting point, that its low-temperature moldability and workability is good and that it has well-balanced mechanical strength; and relates to moldings obtained by molding the polymer; and also relates to a method for producing such propylene polymers. As having good low-temperature heat-sealability, good transparency, good scratch resistance and good mechanical strength, the propylene polymer of the invention is suitable to wrapping or packaging films.
BACKGROUND ART
Of polyolefins, polypropylene is inexpensive and has excellent physical properties, and its applications cover various fields including, for example, wrapping or packaging films, etc. For wrapping or packaging films, polypropylene must be modified to have improved low-temperature heat-sealability, as its melting point is relatively high. One general technique heretofore employed to meet the requirement comprises copolymerizing propylene with ethylene or with an &agr;-olefin having from 4 to 20 carbon atoms in the presence of a so-called Ziegler-Natta catalyst that comprises a titanium compound or a titanium compound held on a magnesium compound, and an organoaluminium compound.
However, it is known that the low-temperature heat-sealability of wrapping or packaging films of such a propylene-&agr;-olefin copolymer produced in that manner is not satisfactory though the transparency and the scratch resistance thereof are better than those of films of low-density polyethylene (Japanese Patent No. 268562, Japanese Patent Laid-Open Nos. 241439/1997, 255812/1990). If the &agr;-olefin content of the copolymer is increased so as to further improve the low-temperature heat-sealability of the copolymer, it involves some problems in that the composition distribution of the copolymer is broadened and the molecular weight thereof is lowered, and, as a result, the solvent-soluble content of the copolymer increases and the blocking resistance thereof is thereby lowered. Another problem is that the haze of the copolymer films increases, and the transparency thereof lowers.
On the other hand, it is reported that a metallocene catalyst is effective for producing polyolefins having a narrow molecular weight distribution (J. Polym. Sci., Polym. Chem., Ed. 23, 2117 (1985)). Having tried a metallocene catalyst, however, no one has succeeded in producing propylene polymers having well balanced low-temperature heat-sealability and mechanical strength. This is the current situation in the art.
The present invention is to provide a propylene polymer of which the advantages are that its modulus of elasticity is well balanced with its melting point, that its low-temperature moldability and workability is good and that it has well-balanced mechanical strength; and to provide moldings of the polymer and a method for producing the polymer.
DISCLOSURE OF THE INVENTION
We, the present inventors have assiduously studied so as to attain the above-mentioned object, and, as a result, have found that a propylene polymer of which the melting point and the enthalpy of fusion satisfy a specific relationship and of which the half-value width of the peak top of the elution curve obtained in programmed-temperature fractionation falls within a specific range attains the object. On the basis of this finding, we have completed the present invention. Specifically, the invention provides a propylene polymer and its moldings mentioned below, and provides a method for producing the propylene polymer also mentioned below.
1. A propylene polymer of which the heat of fusion &Dgr;H (J/g) and the melting point Tm (° C.) measured through differential scanning calorimetry satisfy the following relationship:
&Dgr;H≧0.45×Tm+22.
2. The propylene polymer of above 1, which has the following properties (1), (2) and (3):
(1) Its melting point Tm (° C.) measured through differential scanning calorimetry is 110≦Tm≦140;
(2) The half-value-width Th (° C.) of the peak top of its elution curve obtained in programmed-temperature fractionation is Th≦5;
(3) Its intrinsic viscosity [&eegr;] (dl/g) measured in a solvent of tetralin at 135° C. falls between 0.5 and 5.
3. The propylene polymer of above 2, of which the melting point Tm (° C.) measured through differential scanning calorimetry is 120≦Tm≦140.
4. The propylene polymer of above 2, of which the melting point Tm (° C.) measured through differential scanning calorimetry is 120≦Tm≦135.
5. The propylene polymer of any of above 1 to 4, which is a propylene homopolymer having an isotactic pentad fraction [mmmm] of from 65 to 85 mol %.
6. The propylene polymer of any of above 1 to 4, which is a propylene homopolymer having an isotactic pentad fraction [mmmm] of from 70 to 80 mol %.
7. A molding obtained by molding the propylene polymer of any of above 1 to 6.
8. A method for producing the propylene polymer of any of above 1 to 6, which comprises polymerizing propylene or propylene with ethylene and/or an &agr;-olefin having from 4 to 20 carbon atoms, in the presence of an olefin polymerization catalyst that contains (A) a transition metal compound of the Group 4 of the Periodic Table represented by the following general formula (1), and (B) at least one selected from (B-1) aluminiumoxy compounds and (B-2) ionic compounds capable of reacting with the transition metal compound to give cations:
wherein R
1
to R
11
, and X
1
and x
2
each independently represent a hydrogen atom, a halogen atom, a hydrocarbon group having from 1 to 20 carbon atoms, a halogen-containing hydrocarbon group having from 1 to 20 carbon atoms, a silicon-containing group, an oxygen-containing group, a sulfur-containing group, a nitrogen-containing group, or a phosphorus-containing group; R
3
and R
4
, and R
8
and R
9
may be bonded to each other to form a ring; y
1
is a divalent crosslinking group that crosslinks the two ligands, representing any of a hydrocarbon group having from 1 to 20 carbon atoms, a halogen-containing hydrocarbon group having from 1 to 20 carbon atoms, a silicon-containing group, a germanium-containing group, a tin-containing group, —O—, —CO—, —S—, —SO
2
—, —NR
12
—, —PR
12
—, —P(O)R
12
—, —BR
12
— or —AlR
12
—; R
12
represents a hydrogen atom, a halogen atom, a hydrocarbon group having from 1 to 20 carbon atoms, or a halogen-containing hydrocarbon group having from 1 to 20 carbon atoms; M
1
represents titanium, zirconium or hafnium.
9. A method for producing the propylene polymer of any of above 1 to 6, which comprises polymerizing propylene or propylene with ethylene and/or an &agr;-olefin having from 4 to 20 carbon atoms, in the presence of an olefin polymerization catalyst that contains (A) a transition metal compound of the Group 4 of the Periodic Table represented by the following general formula (2), and (B) at least one selected from (B-1) aluminiumoxy compounds and (B-2) ionic compounds capable of reacting with the transition metal compound to give cations:
wherein M
1
represents titanium, zirconium or hafnium; E
1
and E
2
each are a ligand selected from a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a substituted indenyl group, a heterocyclopentadienyl group, a substituted heterocyclopentadienyl group, an amido group, a phosphido group, a hydrocarbon group and a silicon-containing group, and they form a crosslinked structure via A
1
and A
2
, and they may be the same or different; X
3
represents a &sgr;-bonding ligand, and a plurality of X
3
's, if any, may be the same or different, and it may be crosslinked with other X
3
, E
1
, E
2
or Y
2
; Y
2
represents a Lewis base, and a plurality of Y
3
's, if any, may be the same or different, and it may be crosslinked with other Y
2
, E
1
, E
2
or X
3
; A
1
and A
2
each are a divalent cro

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