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
2000-10-10
2003-04-08
Fox, John (Department: 3753)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C604S408000
Reexamination Certificate
active
06545096
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat-resistant plastic sheet. Further, the present invention relates to an infusion bag formed by the heat-resistant plastic sheet, which has excellent transparency and flexibility, and which does not generate a significant number of insoluble fine particles in liquid contained in the bag.
BACKGROUND OF THE INVENTION
Requirements for a plastic medical vessels such as an infusion bag or a blood preservation bag are flexibility and transparency. In addition, heat resistance to high-pressure steam sterilization is required. Olefin polymers such as polyethylene or polypropylene, polyvinyl chlorides, ethylene-vinyl acetate copolymers, etc. have conventionally been used as a material for medical vessels. Of these, polyethylene has been particularly used as a material for an infusion bag, because of its excellent chemical resistance.
However, although low density polyethylene has relatively excellent flexibility and transparency, it has poor heat resistance because of its low softening point. For this reason, this kind of polyethylene does not withstand high-pressure steam sterilization, and is subject to deformation, whitening, blocking, and the like.
Conventional polyethylene vessels also have a problem relating to the generation of insoluble particles. The insoluble particles are particles that can be examined in an insoluble particle test in injection that is standardized in the Pharmacopeia of Japan (13
th
version). The particles also should be examined in a test of a plastic medical apparatus that is also standardized in the Pharmacopeia of Japan (13
th
version). Each test is used to determine the size and number of the particles in a liquid container. The former test is more strict than the latter test. An infusion bag should pass both tests to sell it in the market. The insoluble particles are believed to be contaminants eluted or degraded from the resin by the chemicals contained in the vessel.
As a technique for reducing such defects of polyethylene vessels various proposals have been made in which the material for forming a vessel is made of a multilayer sheet so as to have the three properties described above; i.e., flexibility, transparency and heat resistance (Japanese Patent No. 2550256, Japanese Patent Application Laid-open No. Sho 58-165866, Japanese Patent Application Laid-open No. Hei 6-209981, etc.). The bag disclosed in Japanese Patent No. 2550256 is made of a multilayer sheet of which inner and outer layers are made from a high density polyethylene as a main component, and an interlayer between the inner layer and the outer layer is made from a straight-chain low density polyethylene. The vessel disclosed in Japanese Patent Application Laid-open No. Sho 58-165866 is made of a multilayer sheet having an interlayer comprising a polymer such as ethylene-vinyl acetate copolymer or elastomer. Further, the vessel disclosed in Japanese Patent Application Laid-open No. Hei 6-209981 is made of a multilayer sheet having a straight-chain low density polyethylene as a first layer and a polymer composition comprising a high density polyethylene and a low density polyethylene as a second layer.
However, the multilayer sheet has a defect in that formation of a multilayer involves complicated layer-forming conditions, resulting in an increase in production costs. Because of this defect, a low-density polyethylene produced with a metallocene catalyst (hereinafter referred to as “M-LLDPE”) is recently noted as a material for forming a bag which has excellent flexibility and transparency. In addition, medical vessels using such a resin have been proposed (Japanese Patent Application Laid-open No. Hei 6-329848, Japanese Patent Application Laid-open No. Hei 9-99035, Japanese Patent Application Laid-open No. Hei 11-19183, etc.).
Alternatively, the medical vessel disclosed in Japanese Patent Application Laid-open No. Hei 9-99035 is formed from a multilayer sheet in which an inner layer or an interlayer comprises M-LLDPE having a density of 0.928 g/cm
3
or less and accordingly transparency and flexibility are improved. Further, in a medical vessel disclosed in Japanese Patent Application Laid-open No. Hei 11-19183, a wall of the vessel main body comprises a M-LLDPE layer having a density in a range of 0.921-0.925 g/cm
3
(M-LLDPE content is 60% or more in the layer and constitutes a main layer having 60% or more thickness) and, accordingly, in addition to transparency and flexibility, heat dimensional stability is improved.
The polymer composition disclosed in Japanese Patent Application Laid-open No. Hei 6-329848 is a blend of (I) a polymer composition comprising (A) 5-95 wt % of a C3-20 &agr;-olefin/ethylene copolymer having a density of 0.880-0.940 g/cm
3
and an intrinsic viscosity of 1.0-10.0 dl/g (at 135° C. in decalin) and (B) 5-95 wt % of a C3-20 &agr;-olefin/ethylene copolymer having a density of 0.910-0.96 g/cm
3
and an intrinsic viscosity of 0.5-2.0 dl/g (at 135° C. in decalin), each copolymer having specifically determined relationships between Tm(° C.) and density, melting tension and melt flow rate (MFR), and weight of soluble components and density, and (II) a low density polyethylene produced by a high pressure radical method and having an MFR of 0.1-50 g/10 min and satisfying a certain relationship between molecular weight distribution and MFR. The weight ratio of the polymer composition (I) to the low density polyethylene (II) is in a range of 99:1 to 60:40. A film formed by the polymer composition shows excellent transparency and heat-resistance.
However, although medical vessels made from the M-LLDPE have excellent transparency, heat resistance of the vessels is not sufficient resulting in frequent deformation due to heat when the vessels are sterilized at 115° C., which is a problem. Further, the medical vessel disclosed in Japanese Patent Application Laid-open No. Hei 9-99035, which uses a multilayer sheet, also has a defect in its forming process under complicated conditions, resulting in an increase in production costs.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an infusion bag which does not generate a significant number of fine particles in liquid contained in the bag, which has excellent transparency and flexibility, and which also has sufficient heat resistance so that deformation does not occur even when sterilization is carried out at 115° C.
SUMMARY OF THE INVENTION
As a result of extensive investigations to solve the above-mentioned problems, the inventors of the present invention have found that an infusion bag material which has good heat resistance, excellent transparency, impact resistance and flexibility and which does not generate a significant number of insoluble fine particles in liquid contained in the bag is obtained by appropriately combining three kinds of polyethylenes having different properties. These polyethylenes are a straight-chain polyethylene having a density of 0.928 g/cm
3
or more and produced using a metallocene catalyst, and which does not generate a significant number of insoluble fine particles in liquid contained in the bag and has excellent heat resistance; a low density polyethylene produced under high pressure having high viscosity in melting and good transparency; and a straight-chain polyethylene having a density of 0.91 g/cm
3
or less and produced using a metallocene catalyst and which has excellent flexibility and impact resistance.
That is, the present invention relates to a heat-resistant plastic sheet formed from a polymer composition containing 40-75% by weight, preferably 50-70% by weight, of (a) a straight-chain polyethylene having a density of 0.928 g/cm
3
or more and produced with a metallocene catalyst; 5-35% by weight, preferably 10-30% by weight, of (b) a low density polyethylene produced under high pressure; and 15-45% by weight, preferably 20-40% by weight, of (c) a straight-chain polyethylene having a density of 0.91 g/cm
3
or less and produced with a metalloc
Futagawa Hitoshi
Hama Yoshihisa
Honda Minoru
Ohmori Kenji
Fox John
Kubovcik & Kubovcik
Nipro Corporation
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