JP2695459B2 - Radiation resistant polypropylene resin composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radiation resistant polypropylene resin composition, and more particularly to irradiation of radiation, particularly high energy radiation such as γ rays, X rays and electron rays. The present invention relates to a polypropylene resin composition having excellent transparency and excellent transparency.

[Problems to be Solved by Conventional Techniques and Inventions] Generally, polypropylene-based resins have excellent hygiene properties, and molded articles thereof have translucency that allows the contents to be transparent. Widely used for etc. Due to the nature of its application, food containers, medical equipment, etc., must be sterilized before use. Conventionally, heat sterilization using steam, gas sterilization using ethylene oxide gas, sterilization with hydrogen peroxide, etc. Is being carried out.

In recent years, a radiation sterilization method has been developed in which sterilization is performed by irradiating with radiation, and it is excellent in that it can be almost completely sterilized in a short time, and therefore it is widely used for sterilization of food containers, medical instruments and the like. However, polypropylene resins have low resistance to radiation, so when the radiation sterilization method is applied to food containers and medical instruments that use polypropylene resins, decomposition and deterioration reactions proceed, causing yellowing and becoming transparent. Properties are impaired, and physical properties such as mechanical strength are significantly reduced,
Those containers and the like cannot be used.

Therefore, a method of adding various stabilizers has been proposed in order to prevent the deterioration of the physical properties of the polypropylene resin due to the irradiation of radiation. Specifically, (1) a method of blending a phenol-based, phosphorus-based or sulfur-based compound (JP-A-49)
-39637), (2) a method of blending a hindered amine (JP-A-55-19199), and (3) a method of blending a polypropylene resin having a narrow molecular weight distribution with an amorphous additive (US Patent No. No. 4274932) and the like.

These methods can prevent deterioration of the physical properties of the polypropylene resin due to radiation irradiation to some extent, but have various problems. For example, the method (1) is not practical because it causes discoloration, deterioration of heat resistance, elution of additives, and the like.
The method (2) has problems such as elution of a toxic substance and hindered amine bleeding over the surface of the molded product over time. Furthermore, addition of the hindered amine alone causes a decrease in molecular weight during molding, resulting in a marked decrease in strength of the resulting molded product.

Therefore, the present inventors can maintain the physical properties of polypropylene resin such as impact resistance, rigidity, and transparency when radiation is applied, in a range that does not hinder practical use, and also in terms of safety and hygiene. We have conducted intensive studies to develop a satisfactory polypropylene resin composition.

[Means for solving the problem]

As a result, the specific ethylene of polypropylene resin
It was found that the resin composition obtained by blending the α-olefin copolymer in a certain range is stable against irradiation with radiation and has desired physical properties.

The present invention has been completed based on such findings. That is, the present invention relates to (a) polypropylene resin 95 to 99.5
%, And (b) a density of 0.910 to 0.940 g / cm ³ , and an ethylene-α-olefin copolymer having from 5 to 30 side chain groups per 1000 carbon atoms in the main chain, 5 to 0.5% by weight. The present invention provides a radiation-resistant polypropylene-based resin composition comprising:

In the present invention, the polypropylene resin used as the component (a) is not particularly limited, and various resins can be used. Specifically, propylene homopolymer, propylene-ethylene copolymer, propylene-α-
It is an olefin copolymer or a mixture thereof.
The copolymer is not particularly limited, and may be irregular, alternating, block or graft copolymer. The α-olefin in the propylene-α-olefin copolymer is 1
-Butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and the like can be mentioned.

Further, the molecular weight of the polypropylene resin is not particularly limited, but generally, the number average molecular weight is 20,000 to 100,
000, especially 50,000 to 80,000 are preferable.

The present invention uses the above-mentioned polypropylene resin as the component (a) and the ethylene-α-olefin copolymer as the component (b). Here, the ethylene-α-olefin copolymer is
Density 0.910 to 0.940 g / cm ³ , preferably 0.915 to 0.930 g / cm ^3.
And the number of side chain alkyl groups (number of short chain branches) per 1000 carbon atoms in the main chain is 5 to 30, preferably 5 to 20. The α-olefin in this ethylene-α-olefin copolymer is not particularly limited and various ones can be used. For example, propylene, 1-butene, 4-methyl-1-pentene, 1-octene and the like can be mentioned.

The ethylene-α-olefin copolymer, which is the component (b) of the composition of the present invention, is what is called linear low-density polyethylene (LLDPE), and its properties should satisfy the above conditions. For example, the sag is not particularly limited, but those having a melt florate (MFR) of 0.6 to 30 g / 10 minutes, particularly 5 to 25 g / 10 minutes are preferable.

The composition of the present invention comprises 95 to 99.5% by weight of the above (a) polypropylene resin and 5 to 0.5% by weight of the above (b) ethylene-α-olefin copolymer, preferably (a) polypropylene resin 69 to 99% by weight and (b) ethylene-α
-Olefin copolymer 4 to 1% by weight is blended.

Here, if the blending ratio of the ethylene-α-olefin copolymer (b) is less than 0.5% by weight, the resulting composition has a significantly reduced impact resistance after irradiation with radiation and becomes unusable for practical use. If it exceeds 5% by weight, the transparency is significantly lowered, which is not preferable.

In addition to the above components, the resin composition of the present invention may optionally contain an antioxidant, an ultraviolet absorber, an ultraviolet stabilizer, a pigment,
An appropriate amount of dispersant, neutralizing agent, etc. can be added. Specifically, 2,6-di-t-butyl-p-methylphenol, n-outadecyl-3- (4-hydroxy-3,5-di-t-butylphenyl) propionate as an antioxidant,
Tetrakis [methylene-3 (3,5-di-t-butyl-4
-Hydroxyphenyl) propionate] methane and other phenolic antioxidants, pentaerythritol tetrakis (β-lauryl thiopropinate), and dilauryl thiopropinate and other sulfur-based antioxidants.

Further, as the ultraviolet absorber, 2-hydroxy-4-
Examples thereof include n-octoxybenzophenone; 2- (2'-hydroxy-3,5-di-t-butylphenyl) 5-chlorobenzotriazole.

Further, examples of the ultraviolet stabilizer include bis (2,2,6-tetramethyl-4-piperidyl) sebacate.

The addition amount of these should be such that physical properties of the resin composition after irradiation with radiation are not deteriorated and hygiene is not affected.

The resin composition of the present invention is the above-mentioned polypropylene resin,
By mixing a predetermined amount of an ethylene-α-olefin copolymer and an additive to be blended as necessary with a Henschel mixer or other kneading machine and uniformly dispersing them, the resulting mixture is melted and pelletized by an extruder. Obtainable.

〔Example〕

Next, the resin composition of the present invention was produced and compared with the conventional one.

Examples 1 to 3 Ethylene content (C _E ) 3.0 mol%, density 0.910 g / cm ³ , MA
A propylene polymer R25g / 10 min, density 0.916 g / cm ^3, the amount indicating the side chain groups (degree of branching) carbon atoms 1000 20 per one ethylenically 1-butene copolymer backbone in Table 1 Was mixed and kneaded in an extruder at 230 ° C. for 3 minutes in a nitrogen atmosphere to form pellets.

The pellets thus obtained were flat (130
× 130 × 2 mm) was molded.

Γ-ray irradiation (irradiation dose 2.5Mrad) for the obtained flat plate
The front and rear impact resistance and transparency were measured. Table 1 shows the results.

The impact resistance is determined by placing the flat plate on an iron plate with a hole of 50 mm in diameter, applying a 1/2 inch diameter impact core to this, dropping the load from the top, and setting the impact energy to the crack height. Represented.

Use a commercially available haze meter for ASTM D1003 transparency.
It measured according to.

Comparative Examples 1 to 3 In Examples 1 to 3, flat plates were obtained in the same manner as in the above Examples except that the blending amount of the ethylene-1-butene copolymer was changed to the amount shown in Table 1, and before and after gamma irradiation. The impact resistance and transparency were measured. Table 1 shows the results.

[Effects of the Invention] As described above, the polypropylene resin composition of the present invention has stable physical properties such as transparency and mechanical strength with respect to irradiation with radiation, and bleeding of additives and toxic decomposition products. It has no elution and is excellent in hygiene and safety.

Therefore, the radiation sterilization method can be safely and hygienically applied to various molded articles obtained from the resin composition of the present invention without deteriorating the physical properties.

Therefore, the resin composition of the present invention is very effectively used as a molding material for food containers, medical instruments and the like.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiromi Matsushita 3-2 Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Akira Kawasaki Plastics Research Laboratory, Waseda Electric Works Co., Ltd. (72) Masashi Uchida 3-chidori-cho, Kawasaki-ku, Kawasaki, Kanagawa ―2 Sho Dawa Co., Ltd. Kawasaki Plastic Research Institute

Claims (1)

(57) [Claims] 1. A polypropylene resin having a content of 95 to 99.5% by weight and a density of 0.910 to 0.940 g / cm ³ and having 5 to 30 side chain groups per 1000 carbon atoms in the main chain. A radiation resistant polypropylene resin composition, characterized in that it comprises 5 to 0.5% by weight of an ethylene-α-olefin copolymer.