JPH0373309B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a plastic molded article that can be sterilized by radiation, and in particular provides a plastic molded article that can be expected to be applied to the food packaging field and the medical device field. [Prior Art] Polyolefins such as polypropylene and poly4-methyl-1-pentene can be used with syringes, forceps,
It is widely used in medical instruments such as clamps and pipettes, and food packaging materials such as containers, films, and packs. By the way, these instruments, containers, films, etc. used in the medical and food fields are usually sterilized to a considerable degree. Conventional sterilization treatments generally include boiling or gas (eg, ethylene oxide gas). However, with boiling sterilization, complete sterilization may not be expected depending on the type of bacteria, and with gas sterilization, there is a risk that toxic gas may remain inside the container or the cylinder of the syringe. Therefore, radiation sterilization, which allows complete sterilization and leaves no toxic substances behind, has been attracting attention in recent years. However, when polyolefin is irradiated with radiation, the resin decomposes and deteriorates, resulting in a decrease in mechanical strength, and the various compounding agents contained in the resin decompose, resulting in discoloration, which reduces the product value. You can see the phenomenon of dropping. This phenomenon is particularly fatal for medical and food applications. That is,
In medical and food applications where it is necessary to measure the amount of drug in a syringe or container, or to make the packaged food look beautiful, it is necessary to use a machine that is transparent or has a similar color so that the contents can be visually confirmed. Not only the decrease in the optical strength but also the occurrence of coloring are not desirable. However, although the conventionally commercially available polyolefins labeled as having radiation resistance have had a certain degree of reduction in mechanical strength, no problem has been found in preventing discoloration at all. [Problems to be Solved by the Invention] In view of the current situation, the present inventors have conducted intensive studies on polyolefin molded products that can prevent a decrease in mechanical strength and do not cause discoloration even when subjected to radiation sterilization. As a result, it was discovered that the objective could be achieved by blending a very small amount of a specific polybutadiene. [Means for Solving the Problems] That is, the present invention provides a plastic for radiation sterilization characterized by being made of a crystalline polyolefin containing 0.01 to 3% by weight of polybutadiene having a 1,2-vinyl structure as a main component. Regarding molded products. [Function] By the way, it is known to mix polybutadiene with polyolefin and irradiate it with radiation. Specifically, Japanese Patent Publication No. 45-23025 discloses a technique called a method for breaking bridges in crystalline polypropylene, which is characterized in that 5 to 40% by weight of polybutadiene is mixed with crystalline polypropylene and the mixture is irradiated with radiation. However, the technology disclosed here is
The purpose of this is to create bridges in polypropylene to improve its physical properties at high temperatures and its resistance to chemicals such as solvent resistance.For this purpose, the amount of polybutadiene blended is as high as 5 to 40% by weight, and The amount of radiation irradiated is usually extremely high, 5 to 50 Mrad. On the other hand, in the present invention, as will be described later, the amount of polybutadiene blended is extremely small at 3% by weight or less (this amount is on the same level as the amount of various stabilizers normally added to polyolefin), and it is also radioactive. The amount is also 5 Mrad
A low level, usually less than 2.5 Mrad, is sufficient. There is no mention or suggestion in the publication that plastic molded products can be sterilized with such low blending amounts and low radiation doses, with little change in mechanical properties and no coloration. According to the description in the same publication, it is merely shown that when the amount of the compound is small as in the present invention, bridge cracking will not occur unless a large amount of radiation is irradiated. Furthermore, the publication does not even suggest polybutadiene containing a 1,2-vinyl structure as the main component as in the present invention. Japanese Patent Publication No. 51-28114 discloses a packaging material made of a thermoplastic resin containing 5% by weight or more and a maximum of 100% by weight of polybutadiene having a 1,2-vinyl structure of 70% or more and a crystallinity of 10% or more. The main text describes ultraviolet irradiation. However, the polybutadiene disclosed in the publication does not contain a small amount of polyolefin as in the present invention. Furthermore, the purpose of ultraviolet irradiation is to cure the bridge by chipping, and to make it hard and brittle, which is completely different from the purpose of the present invention. In addition, regarding compositions of liquid polybutadiene and polyolefin, see Journal of Japan Rubber Association, Vol. 43, No. 1 (1970), pages 29-38, and Vol. 47, No. 10 (1974), 81
- Described on page 88. However, the composition shown here is EPM (ethylene propylene rubber),
Liquid polybutadiene is added to improve the peroxide crosslinking of atactic polypropylene, and its amount is as high as 5% by weight or more, which is completely different from the idea aimed at by the present invention. As described above, conventionally known compositions of polyolefin and polybutadiene are intended for radiation crosslinking or peroxide crosslinking, and as a matter of course, polybutadiene contains many rubber-like substances, and the amount of polybutadiene blended is much larger than that of the present invention. Furthermore, the amount of radiation exposure is also high. On the other hand, the present invention shows that when a small amount of a specific polybutadiene is added, not only does it exhibit good radiation resistance under radiation sterilization conditions, but it also exhibits an excellent hue with no coloration, which could not be achieved with conventional stabilizer formulations. This is an inventive concept that is completely different from conventional examples, and cannot be conceived from these conventional examples. The polybutadiene blended into the polyolefin in the present invention is a polybutadiene having a 1,2-vinyl structure as a main component. But the whole thing is 1,2
- Polybutadiene need not be of vinyl structure, but may contain a small amount of polybutadiene of 1,4-cis or 1,4-trans structure, specifically less than 30 mol% of the total, preferably 20
It may be contained in an amount of mol% or less, particularly 10 mol% or less. If polybutadiene mainly has a 1,4-structure, it is impossible to prevent a decrease in mechanical strength even if it is applied to the present invention. Moreover, the polybutadiene does not have only a butadiene monomer component as a constituent component, but may also contain a small amount of a comonomer component. Such comonomer components include styrene, α-methylstyrene, (meth)acrylate, acrylonitrile, and vinyl chloride monomers. Moreover, the polymer chain terminal may be modified with a hydroxyl group or a carboxyl group, if necessary. Polybutadiene can be used in either solid or liquid state, but liquid polybutadiene, which is liquid at room temperature, is most preferable because it has good dispersibility when mixed with polyolefin, and its effect can be achieved with a small amount of blending. . The liquid polybutadiene usually has a number average molecular weight (n) of about 300 to about 10,000, preferably about 500 to about 5,000, particularly about 800 to about 3,000. Note that the amount of 1,2-vinyl structure in polybutadiene is determined by infrared absorption spectroscopy by D.Morero et al. [Chim.e.Ind. (Milan), 41, 758
(1959)]. Basically, any crystalline polyolefin may be used, including ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, and
- a homopolymer or a copolymer of α-olefin such as methyl-1-pentene, 3-methyl-1-pentene, 1-hexene, 1-dodecene, or the above α-olefin;
- olefins and small amounts of other comonomer components such as styrene, acrylonitrile, vinyl chloride,
Examples include copolymers with (meth)acrylic acid esters, blends with the above or other thermoplastic resins, block copolymers, and graft copolymers. Among these, polypropylene, poly-1-butene, poly-4-
Polyolefins having tertiary carbon such as methyl-1-pentene show the effects of the present invention more clearly. The blending ratio of polybutadiene to polyolefin is approximately 0.01 to 3% by weight, preferably 0.01 to 3% by weight.
2% by weight, more preferably in the range of 0.05 to 1% by weight. If the content is less than the lower limit, the above-mentioned effects of improving radiation resistance and coloring prevention will not be seen.
If the amount exceeds 3% by weight, the original properties of the polyolefin will be impaired, and when used for radiation sterilization, deterioration will be accelerated and mechanical properties will tend to decrease, as well as weather resistance and heat aging resistance. Various known methods can be used to blend polyolefin with polybutadiene, such as mixing the two with a V-blender, ribbon blender, Henschel mixer, or tumbler blender, or after mixing with the blender,
There are methods of melt-kneading and granulating or pulverizing using a single-screw extruder, multi-screw extruder, kneader, Banbury mixer, etc. The mixture of polyolefin and polybutadiene thus obtained is then processed into a single-screw extruder, a vented extruder, a two-screw extruder, a three-screw extruder, a conical two-screw extruder, a co-kneader, and a platen extruder. Extrusion molding, injection molding, and blow molding are performed using a caterer, mixtruder, twin-screw conical screw extruder, planetary screw extruder, gear type extruder, screwless extruder, etc., to obtain a plastic molded product in the desired shape. Plastic molded products are irradiated for sterilization. The radiation dose irradiated for sterilization treatment is in the range of more than 0 and less than 5 Mrad, preferably in the range of 0.1 to 3 Mrad, and is often
Less than 2.5 Mrad. In particular, when used in food applications, most radiation doses are in the range of 1 Mrad or less, and when used in medical applications, a radiation dose of 2 to 2.5 Mrad is suitable. Radiation includes alpha, beta, and gamma rays from radioactive isotopes, and electron beam accelerators such as van de Graac type electron beam accelerators.
Electron beams from Kotskucroft, Walton type electron beam accelerator, insulation transformer type electron beam accelerator, transformer type gas (oil) insulation type electron beam accelerator, cold cathode shock voltage type electron beam accelerator, linear filament type electron beam accelerator, etc. Ionizing radiation such as is preferred. But X
Lines can also be used. According to the present invention, it is possible to radiation sterilize plastic molded products without damaging their initial physical properties and appearance. However, in order to further improve the durability of plastic molded products after sterilization, polyolefin is usually used. Various additives may be used in combination. Various known compounds can be used as such compounding agents, but compounds consisting of thiocarboxylic acid esters, such as dilauryl thiodipropionate, distearyl thiodipropionate, and lauryl, are particularly preferred from the viewpoint of appearance after radiation sterilization treatment.・Mainly contains stearyl thiodipropionate, dimyristyl thiodipropionate, ditridecyl thiodipropionate, pentaerythritol tetra (tridecylthiopropionate), and small amounts of phenols, amines, and phosphorus. It is preferable to incorporate a system stabilizer. [Example] The content of the present invention will be explained in more detail with reference to preferred examples below, but the present invention is not limited to these examples unless otherwise specified. In addition, the structure and evaluation test of the molded article in each example is performed as follows. (1) Additive blending and granulation 0.1% by weight of calcium stearate and the additive formulations shown in Examples were dry mixed into polypropylene powder using a Henschel mixer. This mixture was added to a 20mm tube manufactured by Thermoplastics.
Pelletize using a φ extruder at 220°C and screw rotation speed of 60 rpm under _N2 purge. (2) Manufacture of molded products Hot press the obtained pellets at 200℃
10 minutes, then cold press for 3 minutes to a thickness of approximately 500μ
A film was prepared and cut to a width of 5 cm to measure the uniformity of radiation irradiation. (3) Evaluation method For each test piece group, physical property changes based on the irradiation dose rate and total irradiation dose were compared with a blank, and the elongation at break residual rate (EL residual rate), color difference (YI value), and viscosity change ( [η]: Measured at 135°C using decalin. Examples 1 to 4 and Comparative Examples 1 to 5 Using a polypropylene homopolymer (Mitsui Petrochemical Polypro J300), additives having the concentrations shown in Table 1 are blended and molded. This was subjected to gamma ray irradiation (2.5 Mrad) using a cobalt-60 source. The results are shown in Table 1.

〔Effect of the invention〕

As described above, according to the present invention, radiation sterilization can be performed without changing the initial physical properties (mechanical strength, etc.) or appearance (color, etc.) of plastic molded products, and therefore it is It is possible to provide plastic molded products that can be sterilized more safely and reliably than sterilization by boiling or gas. Furthermore, since it contains polybutadiene, it poses no hygiene or safety hazards, is transparent or has a similar hue, and is suitable for the food and medical fields where coloring is a problem.

Claims (1)

[Scope of Claims] 1. A plastic molded article for radiation sterilization characterized by being made of a crystalline polyolefin containing 0.01 to 3% by weight of polybutadiene having a 1,2-vinyl structure as a main component. 2. A plastic molded article for radiation sterilization according to claim 1, wherein the polybutadiene is liquid polybutadiene. 3. A plastic molded article for radiation sterilization according to claim 1 or 2, which uses polybutadiene having a 1,2-vinyl structure of 70 mol% or more. 4 The blending ratio of polybutadiene is 0.05 to 1% by weight
A plastic molded article for radiation sterilization according to any one of claims 1 to 3. 5. A plastic molded article for radiation sterilization according to any one of claims 1 to 4, wherein the polyolefin has tertiary carbon. 6. A plastic molded article for radiation sterilization according to any one of claims 1 to 5, wherein the plastic molded article is used in the food field or the medical field.