Compositions – X-ray or neutron shield
Reexamination Certificate
2000-02-11
2002-11-26
Toomer, Cephia D. (Department: 1714)
Compositions
X-ray or neutron shield
C524S115000, C524S116000, C524S120000, C523S136000
Reexamination Certificate
active
06485657
ABSTRACT:
This application is a 371 of PCT/JP99/03111, filed Jun. 10, 1998.
TECHNICAL FIELD
The present invention relates to a new gamma-ray stabilizer and a thermoplastic polymer composition containing said stabilizer. More specifically the present invention is concerned with a new gamma-ray stabilizer having following advantages: the stabilizer can effectively protect a thermoplastic polymer (hereinafter referred to as “thermoplastic resin” in some cases or a molded product thereof against properties deterioration and yellowing when the thermoplastic polymer or the molded product undergoes gamma-ray irradiation; the incidences of decomposition reaction, foreign matter formation and color tone deterioration are few on molding processing of a thermoplastic resin which has been compounded with said gamma-ray stabilizer; and further the incidences of such various defects are also low in the molded product formed from the composition containing said gamma-ray stabilizer. The present invention is also concerned with a thermoplastic resin composition containing said gamma-ray stabilizer in a specific amount; and a molded product formed from said composition.
BACKGROUND ART
Medical apparatuses and supplies which are made of aromatic polyearbonate (hereinafter referred to simply as “polycarbonate”) and many other thermoplastic resins are extensively used in the field of medical care. For example, because polycarbonate is a thermoplastic polymer having excellent characteristics in transparency, sanitation, dimensional stability, strength against impact, heat resistance and others, it is used for producing packaging materials for syringes and surgical instruments, artificial organs such as artificial lungs and kidneys, and various medical apparatuses such as surgical instruments and medical operation devices.
One of the most important required performances in such medical applications is the stability against various sterilization treatments. One of these sterilization methods is sterilization by gamma-ray irradiation. Compared with the conventional treatment by ethylene oxide or treatment by steam in an autoclave, this method provides less expensive dry sterilization at a lower temperature, and has come to find a wide application in recent years.
However, for example, when polycarbonate or its molded product is sterilized by gamma-ray irradiation, inherent transparence and clarity of the polycarbonate are extremely damaged, and the polycarbonate is yellowed and discolored in such a degree that the user feels uncomfortable; this problem is yet to be solved.
Many additives have been studied so far to prevent yellowing of the thermoplastic resin or molded products thereof due to gamma-ray irradiation For example, use of an alcohol such as aliphatic diol or polyol, a hindered phenol, or the like is disclosed in JP-A 60-192759 (JP-A means Japanese unexamined patent publication), while the use of a polyol such as polypropylene glycol is disclosed in JP-A 62-135556. Furthermore, the use of a specific polycarboxylic acid or acetal of benzaldehyde is mentioned in JP-A 2-132147. In addition, it is reported that an epoxy compound, a sulfur-containing compound, a boron compound and so forth have the effect of preventing yellowing due to gamma-ray irradiation.
However, these additives have problems as follows: a thermoplastic resin (e.g. polycarbonate) composition to which such a compound has been added does not have sufficient yellowing preventive effect; the properties of the resin composition are deteriorated when a sufficient amount of the compound is added for ensuring satisfactory effects; and the method of the addition to the thermoplastic resin is restricted due to the lack of sufficient heat resistance of the additive itself. Furthermore, there are other problems, that is, depending on the compound, when the gamma-ray irradiation is performed in a deoxygenated atmosphere, the same level of yellowing preventing effect as in the air cannot be achieved; or conversely, when gamma-ray irradiation is performed in the air, the yellowing preventing effect is small.
On the other hand, a method of using an organic halogen compound as a gamma-ray stabilizer is also known. For example, a method of using a bromine compound such as a tetrabromobisphenol A-type polycarbonate oligomer is disclosed in JP-A 2-129261, and a method of using a, nuclear bromine-substituted phthalic acid derivative is disclosed in JP-A 5-179127. Further, JP-A 5-214233 describes polyol compounds having halogen-substituted phenyl structures as a terminal group. These methods of using halogen compounds provide effective means for preventing yellowing whether gamma-ray irradiation is carried out in the air or in a deoxygenated atmosphere; however, these methods have disadvantages that environmental pollution problems arise when the resins containing the halogen compound or the products manufactured therefrom are discarded because of halogen atoms contained therein.
Furthermore, JP-A 5-132552 discloses the use of a polycarbonate which contains a p-hydroxybenzyl alcohol having hydrocarbyl group or hydrocarbyloxy group as an end cap agent. However, the production of this end capped polycarbonate resin requires a complicated manufacturing process, and the physical properties of the polymer itself are lowered by the use of a large amount of the end cap agent in order to enhance the yellowing prevention effect; these problems remain to be solved.
In addition, JP-A 8-225732 and European Patent Publication No. 384110 disclose compositions containing a benzyl compound as a gamma-ray stabilizer.
The composition containing a gamma-ray stabilizer of a prior art exhibits some effect in the prevention of yellowing of a thermoplastic resin (polyearbonate) caused by gamma-ray irradiation; however, when a molded product is produced by using such a composition, defects such as foaming, the occurrence of turbid spots or the generation of black foreign matters will appear in the molded products if molding is continued for a long period of time, for example, one to two days.
Especially, when an injection molding machine, which has been developed to improve the production efficiency of molded products, particularly a hot runner-type molding machine is used, the above-mentioned defects become more extreme.
PROBLEMS TO BE SOLVED BY THE INVENTION
The first object of the present invention is to provide a new gamma-ray stabilizer having the following advantages when added to a thermoplastic resin or a molded product thereof:
1) yellowing caused by gamma-ray irradiation during sterilization process is extremely little,
2) no lowering of physical properties nor generation of defects are observed on molding processing,
3) no deterioration of hue is detected even when the resin is held at a high temperature on molding processing,
4) the elution of the stabilizer is not observed at a steam treatment,
5) there are no problems when discarded, and so forth,
and thereby capable of giving a thermoplastic resin composition useful for medical apparatuses, medical supplies and medical materials.
The second object of the present invention is to provide a highly stable thermoplastic polymer composition containing said new gamma-ray stabilizer.
The third object of the present invention is to provide a polycarbonate molded product prepared by injection molding from said composition.
The fourth object of the present invention is to provide medical materials, especially a molded product of a jacket case for an artificial dialyzer which is prepared by injection molding from the said highly stable thermoplastic polymer composition.
Still further objects of the present invention will become clear from the following descriptions.
MEANS FOR SOLVING THE PROBLEMS
The present inventors zealously pursued investigations to solve said problems and found that, when at least one kind of benzyl compound (A) having a specific chemical structure is compounded with at least one kind of pentaerythritol phosphorous ester (B) having a spirocyclic structure at a specific quantitative ratio, and the obtaine
Funakoshi Wataru
Kanda Tetsuo
Kondo Fumitaka
Sasaki Katsushi
Sughrue & Mion, PLLC
Teijin Limited
Toomer Cephia D.
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