Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-12-07
2001-06-05
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000, C422S026000, C422S028000, C426S521000
Reexamination Certificate
active
06242535
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hollow vessel for use for heat sterilization, made of a polyolefin resin. More specifically, the invention concerns a hollow vessel made of a polyolefin resin, which is superior in the transparency and in the impact strength, emits scarce unpleasant smell and maintains these characteristic properties at a high level, in particular for the transparency, even after the vessel has been subjected to a steam sterilization procedure, so that it can be used favorably for container of food product and medical goods and utensils.
BACKGROUND OF THE INVENTION
Hollow vessels made of a polyolefin resin, such as polypropylene resin, are, in general, superior in the stiffness, heat resistance and chemical resistance, nevertheless they reveal usually disadvantages of lower transparency and inferior impact resistance. For remedying these disadvantages, polyolefinic resins in which these inferior properties are improved have been brought into practical use. Proposals for such improved polyolefinic resins include, for example, a resin composition in which a linear polyethylene and an elastomer component are blended with a polypropylene resin (Japanese Patent Kokai Sho 61-98756 A), a resin composition in which a polymerization product of ethylene is blended with a polypropylene resin (Japanese Patent Kokai Hei 6-31796 A), a resin composition in which a polymerization product of 3-methylbutene-1 is blended with a polypropylene resin (Japanese Patent Kokai Hei 3-14852 A, corresponding to U.S. Pat. No. 5,286,540 and to EP 417319 A1) and a resin composition in which a specific nucleation enhancing agent is blended with a polypropylene resin (Japanese Patent Kokai Sho 60-127336, corresponding to EP 151741 A2).
Hollow vessels made of conventionally proposed polyolefin resins such as above have problems, that an improvement in the impact strength may accompany a decrease in the transparency and that an improvement in the transparency may cause unpleasant smell or may cause decrease in the impact strength. Moreover, it is also problematic that hollow vessels of prior art are subject to decrease in the transparency upon a heat sterilization with saturated steam, whereby visibility of the contents retained in the vessel, such as a drink or medical goods, is decreased and their state becomes unrecognizable.
When a nucleation enhancing agent is blended in the resin of the vessel for improving the transparency of the vessel, the productivity of the vessel becomes decreased due to high crystallization rate, in addition to an unfavorable consequence that such an additive may often cause emission of unpleasant smell and is not preferred for such hollow vessels. Especially, in the case of hollow vessels to be served for enclosing medical goods and food products therein, such problems as emission of smell and migration of the additive from the resin of the vessel into the contents thereof are the greatest defect. When a resin composition in which an ethylenic polymer is blended with a polypropylene resin for improving the impact strength is used as the material of the hollow vessel, an increase in the amount of the ethylenic polymer for increasing the impact strength will cause decrease in the transparency, so that hollow vessels having satisfactory properties may scarcely be reached.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a hollow vessel for heat sterilization made of a polyolefin resin, which is superior in the transparency and in the impact strength and causes scarce emission of smell and which preserves these superior properties, in particular, transparency, even after it has been subjected to a heat sterilization with steam.
The hollow vessel for heat sterilization according to the present invention is defined as follows:
(1) A hollow vessel for heat sterilization, made of a polyolefin resin having characteristic properties comprising
1) an underwater light transmittance of 70-99% resulting from determination of light transmission at a wave length of 450 nm for a resin specimen of a thickness of 0.5 mm which has been subjected to a heat sterilization treatment with steam at a temperature of 121° C. for 20 minutes,
2) a tensile elastic modulus of 200-700 MPa, determined according to ASTM D 638 for a resin specimen of a thickness of 0.5 mm which has been subjected to a heat sterilization treatment with steam at a temperature of 121° C. for 20 minutes,
3) a haze value difference &Dgr; Haze between the Haze
2
value and the Haze
1
value (Haze
2
−Haze
1
), of 1-20%, determined according to ASTM D 1330 for a resin specimen of a thickness of 0.5 mm respectively after and before the specimen has been subjected to a heat sterilization treatment with steam at a temperature of 121° C. for 20 minutes, and
4) a high-speed impact strength of 1.5-10 J, determined by an impact test at 0° C. as the total rupture energy required for rupturing a resin specimen having a thickness of 0.5 mm, a length of 9 cm and a width of 9 cm, which has been subjected to a heat sterilization treatment with steam at 121° C. for 20 minutes and is then held at 0° C. for 2 hours, wherein the impact test is carried out by settling the specimen by fastening it on a jig having a hole of 1 inch diameter and causing a rush probe having a semispherical rush top of 0.5 inch diameter to impinge onto the specimen at an impingement speed of 3 m/sec.
(2) A hollow vessel for heat sterilization as defined in the above (1), wherein the average number of repeats of an impact test of sample vessels withstood to the test without causing rupture is at least 5, wherein the impact test is carried out by subjecting ten hollow vessels, each having an internal volume of 270 ml and a wall thickness of 0.5 mm obtained by blow molding, to a heat sterilization treatment with steam at 121° C. for 20 minutes, maintaining them at 0° C. for 24 hours after they are filled with water and then causing them repeatedly to fall on a floor from a height of 1.8 m.
(3) A hollow vessel for heat sterilization as defined in the above (1) or (2), wherein the polyolefin resin comprises
(A) a polypropylene resin,
(B) an ethylene/&agr;-olefin random copolymer with the &agr;-olefin having at least three carbon atoms, the said random copolymer having a content of the structural unit of ethylene of 60-95 mole %, a density of 0.86-0.94 g/cm
3
and a melt flow rate, determined according to ASTM D 1238 at 190° C. under a load of 2.16 kg, of 0.01-50 g/10 min. and
(C) a propylene/ethylene/1-butene random copolymer which meets the three conditions 5) to 7) given below,
namely,
condition 5) that it comprises 50-90 mole % of propylene unit, 2-30 mole % of ethylene unit and 8-40 mole % of 1-butene unit and that the content of 1-butene unit is greater than the content of ethylene unit;
condition 6) that it has a melt flow rate, determined according to ASTM D 1238 at 230° C. under a load of 2.16 kg, of 0.01-50 g/10 min.; and
condition 7) that it has a molecular weight distribution expressed by Mw/Mn, determined by gel permeation chromatography (GPC), of 3 or less.
(4) A hollow vessel for heat sterilization made of a polyolefin resin composition comprising
(A) a polypropylene resin,
(B) an ethylene/&agr;-olefin random copolymer with the &agr;-olefin having at least three carbon atoms, the said random copolymer having a content of the structural unit of ethylene of 60-95 mole %, a density of 0.86-0.94 g/m
3
and a melt flow rate, determined according to ASTM D 1238 at 190° C. under a load of 2.16 kg, of 0.01-50 g/10 min. and
(C) a propylene/ethylene/1-butene random copolymer which meets the three conditions 5) to 7) given below, namely,
condition 5) that it comprises 50-90 mole % of propylene unit, 2-30 mole % of ethylene unit and 8-40 mole % of 1-butene unit and that the content of 1-butene unit is greater than the content of ethylene unit;
condition 6) that it has a melt flow rate, determined according to ASTM D 1238 at 230° C. under a load of 2.16 kg, of 0.01-50 g/10 min.; and
condition 7) that it has a mole
Kagami Mamoru
Maeda Seiki
Tanaka Yasuo
Mitsui Chemicals Inc.
Nutter Nathan M.
Sherman & Shalloway
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