Propylenic copolymer, and its film

Details Propylenic copolymer, and its film Propylenic copolymer, and its film

1997-10-14

2003-11-18

Lu, Caixia (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S348100

Reexamination Certificate

active

06649725

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a propylenic copolymer and its film. More precisely, the invention relates to a binary random copolymer of propylene and ethylene, and to a film to be formed by sheeting the copolymer. As having an excellent low-temperature heat-sealing property, the copolymer and its film are favorably used as sealant layers of laminate films to be produced through lamination or co-extrusion. The invention also relates to a multi-layered film as produced by laminating or co-extruding a sealant layer of the propylenic random copolymer on at least one surface of a propylenic random copolymer substrate with good stiffness.
BACKGROUND OF THE INVENTION
As having good stiffness, transparency and moisture resistance, films such as biaxially-stretched films or T die-cast films of crystalline propylene polymers are widely used as wrapping films. Wrapping films are generally formed into bags through heat sealing, and the bags are closed also through heat sealing after having been charged with contents. Therefore, for such wrapping films, preferred are multi-layered films having a sealant layer of a resin with good heat-sealability at low-temperature on their one or both surfaces, to films of propylene homopolymers with poor heat-sealability at low-temperature.
In order to improve the heat-sealability at low-temperature of propylene resins to be used for sealant layers, various techniques have heretofore been developed for copolymerizing propylene with other olefin(s) such as ethylene or &agr;-olefins. However, most conventional techniques require copolymerization of propylene with a large amount of olefin(s) in order to make the resulting copolymers have good heat-sealability at low-temperature, resulting in that copolymers formed contain a large amount of unfavorable sticky side products which greatly lower the anti-blocking property of the copolymers. To solve this problem, known is a method of removing the sticky components by dissolving them in inert solvents. However, this method is still problematic in that the low-temperature-melting crystalline components that exist in the copolymers and are indispensable for the heat-sealability at low-temperature of the copolymers are also dissolved out of the copolymers, thus causing a condition in that the heat-sealability at low-temperature of the copolymers is worsened.
On the other hand, since the resins used for such heat-sealing layers are expensive, recently used are multi-laminate films having thinner heat-sealing layers that is surface layers and therefor having higher stiffness as a whole. In such multi-laminate films, a low-temperature heat-sealing property of them depends on not only resin characteristics of heat-sealing layers but also on that of substrate layers. Therefore, the resin characteristics of substrate layers also have been tried to be improved. For example, one attempt is to copolymerize propylene with ethylene, 1-butene or the like comonomer to give resin substrate layers, which, however, is still problematic in that the copolymerization greatly lowers the crystallinity of the resins formed and therefore the resins could not have good stiffness.
In addition to their good heat-sealability at low-temperature and high strength after heat sealing, films are further required to have good slipping and anti-blocking properties in the step of re-winding the films being produced, and also to have good outward appearance and good transparency. Moreover, desired are resins capable of being formed into high-quality films even in recent high-producible, large-scale sheeting machines and high-speed sheeting machines.
On the other hand, in general, wrapping films are formed into bags through heat sealing; then the bags are charged with contents and closed also through heat sealing, and thereafter final consumers open the sealed bags to take out the contents. Thus, the process from the sheeting of those wrapping films to the end of their role takes a long time. Therefore, wrapping films are required to maintain their good quality, especially impact resistance, for the necessary period of time and under ordinary temperature conditions. Unfortunately, however, no example is known at least at present capable of satisfactorily removing the unfavorable phenomena of wrapping films, such as the reduction in their impact resistance and the reduction in their transparency.
SUMMARY OF THE INVENTION
One object of the invention is to provide a propylenic random copolymer capable of being sheeted into films having good heat-sealability at low-temperature and good slipping and anti-blocking properties necessary for high-speed sheeting of the copolymer without interfering with the intrinsic good characteristics of polypropylene films.
Another object of the invention is to provide a multi-layered film capable of exhibiting extremely high stiffness and good heat-sealability at low-temperature that are well balanced to each other, without interfering as much as possible with the intrinsic good characteristics of polypropylene films.
We, the present inventors have assiduously studied in order to attain the above-mentioned objects of the invention and, as a result, have found that, when a propylenic copolymer (A) or (B) having the specific characteristics mentioned below and containing a reduced amount of sticky components is sheeted into films, the resulting films have good slipping and anti-blocking properties and have extremely excellent heat-sealability at low-temperature.
In addition, the inventors have further found that a multi-layered laminate film comprising a substrate layer of a propylenic random copolymer (C) having the specific characteristics mentioned below, and a surface layer of the propylenic copolymer (A) or (B) having the specific characteristics mentioned below, as formed at least on one surface of the substrate layer has extremely high stiffness and good heat-sealability at low-temperature that are well balanced to each other. On the basis of these findings, we have completed the present invention.
Specifically, the invention provides a propylenic copolymer and its film, and also a multi-layered laminate film comprising the copolymer film, which are as follows:
[1] A propylenic copolymer (A) of propylene and ethylene, which satisfies the following (1) to (3):
(1) The ethylene unit content (xa, wt. %) of the copolymer is from 3 to 10 wt. %.
(2) The relation between the boiling diethyl ether extraction (Ea, wt. %) of the copolymer and xa satisfies the following (I) or (II):
Ea≦
0.25
xa+
1.1(
xa=
3 to 6
wt.
%)  (I)
Ea≦
2.6(
xa=
6 to 10
wt.
%)  (II)
(3) The relation between the melting point (Tm, ° C.) of the copolymer as measured with a differential scanning calorimeter and xa satisfies the following (III) or (IV):
Tma≦
140(
xa=
3 to 5
wt.
%)  (III)
Tma≦
165−5
xa
(
xa=
5 to 10
wt.
%)  (IV)
[2] The propylene-ethylene copolymer (A) of [1], which further satisfies the following (4) and (5):
(4) The copolymer has a melt index (MIa, g/10 min) of from 4 to 12 g/10 min.
(5) The isotactic triad fraction (mma, mol %) in the PPP sequence of the copolymer, as measured in
13
C-NMR, is not smaller than 98.0 mol %.
[3] A film as formed by sheeting the propylenic random copolymer (A) of any one of [1] or [2].
[4] A film of a copolymer of propylene and ethylene, which satisfies the following (6) to (8):
(6) The ethylene unit content (xf, wt. %) of the copolymer composing the film is from 3 to 10 wt. %.
(7) The relation between the heat of fusion of the film as measured with a differential scanning calorimeter at 120° C. or lower (&Dgr;H120, J/g) and xf satisfies the following (V) or (VI):
&Dgr;
H
120≧14(
xf=
3 to 5
wt.
%)  (V)
&Dgr;
H
120≧5
xf
−11(
xf=
5 to 10
wt.
%)  (VI)
(8) The isotactic triad fraction (mmf, mol %) in the PPP sequence of the copolymer composing the film, as measured i

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