Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2002-05-17
2004-02-03
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S910000, C526S348000, C526S943000
Reexamination Certificate
active
06686055
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polypropylene composite film which is excellent not only in heat-sealing properties, such as low-temperature heat-sealing properties and heat-sealing strength and hot tack properties, but also in slip properties and blocking resistance.
BACKGROUND OF THE INVENTION
Crystalline polypropylene films are excellent in mechanical properties such as tensile strength, rigidity, surface hardness, impact strength and cold temperature resistance, optical properties such as gloss and transparency, and food hygienic properties such as non-toxicity and non-odorous property, and, therefore, they have been widely used for packaging of foods.
However, the crystalline polypropylene films are high in heat-sealable temperatures and they shrink when heated to the heat-sealing temperatures. Therefore, the crystalline polypropylene films are generally provided with heat-sealing layers.
The heat-sealing layer is required to have the following properties.
(1) The layer can be heat-sealed at a temperature considerably lower than that of the base layer (film of crystalline polypropylene);
(2) The layer is excellent in heat-sealing strength and is almost free from change of heat-sealing temperature with time;
(3) The layer is excellent in high bond strength to the substrate;
(4) The layer has transparency almost equal or higher than that of the base layer;
(5) The layer can be stored without blocking;
(6) The layer does not adhere to bag-making machines or fill packaging machines; and
(7) The layer has high scratch resistance.
For forming such heat-sealing layer, various polymers have been proposed. However, the conventional heat-sealing materials do not always satisfy all of these properties. For example, high- or low-density polyethylenes are poor in transparency, and ethylene-vinyl acetate copolymers or ethylene-&agr;-olefin copolymers are poor in blocking resistance and scratch resistance.
As ethylene-&agr;-olefin copolymers improved in the blocking resistance and the scratch resistance, ethylene-propylene copolymers have been proposed in Japanese Patent Publications No. 31478/1971 and No. 14343/1974. The ethylene-propylene copolymers have certainly excellent blocking resistance and scratch resistance and relatively good heat-sealing properties. Of such copolymers, an ethylene-propylene random copolymer is particularly excellent in the transparency and shows relatively good heat-sealing properties. However, the suitable heat-sealing temperature of the ethylene-propylene random copolymer proposed in the above Japanese Patent Publication No. 31478/1971 is higher than that of medium- or high-density polyethylenes by not lower than 10° C. Therefore, lowering of the suitable heat-sealing temperature of the copolymer has been desired.
As the ethylene component content in the copolymer becomes higher, the heat-sealing temperature (i.e., melting point) of this ethylene-propylene random copolymer lowers. Therefore, by increasing the ethylene component content in the copolymer, the improvement of low-temperature heat-sealing properties are realized. However, when the ethylene component content exceeds 10% by mol, the random copolymerizability of ethylene is reduced, leading to deterioration of the transparency. Besides, the blocking resistance and the scratch resistance are markedly lowered.
In place of the ethylene-propylene random copolymer, use of a copolymer of propylene and an &agr;-olefin of 4 or more carbon atoms has been also proposed as a material of a heat-sealing layer. For instance, Japanese Patent Laid-Open Publication No. 128781/1975 has proposed a copolymer of propylene and an &agr;-olefin of 4 to 10 carbon atoms, which is prepared in the presence of a titanium trichloride catalyst and contains 80 to 95% by weight (84.2 to 96.2% by mol when the &agr;-olefin is 1-butene) of a propylene component. However, the suitable heat-sealing temperature of the propylene-1-butene copolymer described in this publication is still high, i.e., 130° C. or higher. Thus, it cannot be said that the low-temperature heat-sealing properties are improved as compared with those of the above-mentioned ethylene-propylene random copolymer and that the change of the heat-sealing properties with time caused by storage or the like is small.
By increasing the content of the 1-butene component, the heat-sealing temperature (melting point) of the propylene/1-butene copolymer can be lowered as described in, for example, Japanese Patent Publication No. 25546/1986 and Japanese Patent Laid-Open Publication No. 114887/1978. In these Publications, a composite film using a propylene/1-butene copolymer having good heat-sealing properties and a biaxially oriented film using a propylene/1-butene copolymer having improved heat-sealing properties are disclosed.
These propylene/1-butene copolymers are able to show improved low-temperature heat-sealing properties by virtue of increase the content of the 1-butene component. However, the films made from the copolymers come to exhibit tackiness and are deteriorated in slip properties and blocking resistance at high temperatures.
Therefore, the propylene/1-butene copolymers are desired to be improved in hot tack properties. Moreover, these copolymers are also desired to be improved in the low-temperature heat-sealing properties to such degrees that they are suitable for high-speed packaging.
Accordingly, it has been desired to develop a polypropylene composite film which is excellent not only in heat sealing properties, such as low-temperature heat-sealing properties and heat-sealing strength, and hot tack properties, but also in transparency, scratch resistance, blocking resistance and slip properties.
OBJECT OF THE INVENTION
The present invention has been made under such circumstances as mentioned above, and it is an object of the invention to provide a polypropylene composite film which is excellent in heat-sealing properties and hot tack properties as well as in transparency, scratch resistance, blocking resistance and slip properties.
SUMMARY OF THE INVENTION
The polypropylene composite film of the present invention comprises:
(A) a crystalline polypropylene layer, and
(B) a propylene/1-butene random copolymer layer laminated on at least one surface of the crystalline polypropylene layer (A);
said propylene/1-butene random copolymer having the following properties:
(1) the copolymer contains 50 to 95% by mol of constituent units derived from propylene and 50 to 5% by mol of constituent units derived from 1-butene,
(2) the intrinsic viscosity, as measured in Decalin (decahydronaphthalene, E.I. duPont de Nemours & Co., Wilmington, Del.) at 135° C., is in the range of 0.1 to 5 dl/g,
(3) the molecular weight distribution (Mw/Mn), as determined by gel permeation chromatography (GPC), is not more than 3, and
(4) the parameter B value, which indicates randomness of the copolymerized monomer sequence distribution, is in the range of 1.0 to 1.5.
It is preferred that the parameter B value of the propylene/1-butene random copolymer (B) is in the range of 1.0 to 1.3 and the copolymer (B) further has, in addition to the above properties (1) to (4), the following properties:
(5) the melting point Tm, as measured by a differential scanning calorimeter, is in the range of 60 to 140° C., and the melting point Tm and the 1-butene constituent unit content M (% by mol) satisfy the following relation:
−2.6M+130
≦Tm≦−
2.3M+155
and
(6) the crystallinity C, as measured by X-ray diffractometry, and the 1-butene constituent unit content M (% by mol) satisfy the following relation:
C≧−
1.5M+75
The propylene/1-butene random copolymer (B) is prepared by copolymerizing propylene and 1-butene in the presence of an olefin polymerization catalyst comprising:
(a) a transition metal compound represented by the following formula (I):
wherein M is a transition metal of Group IVb, Vb or VIb of the periodic table,
R
1
and R
2
are each a hydrogen atom, a halogen atom, a hydrocarbon group of 1 to 20 carbon atoms, a halogenated hy
Kagami Mamoru
Sugi Masahiro
Tanaka Yasuo
Burns Doane , Swecker, Mathis LLP
Mitsui Chemicals Inc.
Tarazano D. Lawrence
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