JPH04311747A - Polypropylene-based resin composition - Google Patents

Abstract

PURPOSE:To obtain a composition suitable for food containers having excellent resistance by high-energy radiation and excellent transparency by blending a polypropylene-based resin with an ethylene-alpha-olefin copolymer and a dibenzylidene sorbitol-based compound. CONSTITUTION:100 pts.wt. resin mixture comprising (A) 95-99.5wt.% polypropylene-based resin and (B) 5-0.5wt.% ethylene-alpha-olefin copolymer having 0.910-0.940g/cm<3> density and 5-30 side chains based on 1,000 carbon atoms of main chain are blended with (C) 0.05-0.4 pt.wt. dibenzylidene sorbitol-based compound shown by the formula (R1 is H; R2 and R3 are H or CH3). 1-Butene or 4-methyl-1-pentene may be cited as the alpha-olefin of the component B and the component B has preferably 5-25g/10 minutes MFR.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a radiation-resistant polypropylene resin composition, and more specifically to radiation-resistant polypropylene resin compositions.
Polypropylene has excellent resistance to irradiation with high-energy radiation such as beams and electron beams, and has excellent transparency, making it suitable as a raw material for medical devices such as syringes and food packaging containers that are sterilized by radiation. The present invention relates to a resin composition.

0002

[Prior Art] In general, polypropylene resin is non-toxic and has excellent hygiene properties, and its molded products are transparent enough to allow the contents to be seen through, so it is widely used in food containers, medical instruments, etc. It's being used. Food containers, medical equipment, etc.
Due to the nature of its use, it is necessary to sterilize it before use, and conventional methods include injection, heat sterilization using steam,
Gas sterilization using ethylene oxide gas or sterilization using disinfectants such as hydrogen peroxide is performed.

[0003] In recent years, radiation sterilization methods that sterilize by irradiating radiation have been developed, and because they are superior in that they can be almost completely sterilized in a short period of time, they are widely used to sterilize food containers, medical instruments, etc. .

However, polypropylene resin has low durability against radiation, so when radiation sterilization is used for food containers, medical instruments, etc. that use polypropylene resin, decomposition and deterioration reactions of the polypropylene resin proceed.
The resin is also colored yellow and its transparency is impaired, and its physical properties such as mechanical strength are also significantly reduced, making the containers unusable.

[0005] Therefore, in order to prevent the physical properties of polypropylene resin from deteriorating due to radiation irradiation, methods of adding various stabilizers have been proposed. Specifically, (1) a method of blending a phenol-based, phosphorus-based, or sulfur-based compound as an additive (Japanese Unexamined Patent Publication No. 49-39637);
2) Method of blending hindered amine (JP-A-55-1)
9199) and (3) a method of blending an amorphous additive into a polypropylene resin with a narrow molecular weight distribution (US Pat. No. 4,274,932). In addition, as a method of blending specific resins and additives, (4)
A composition comprising a polypropylene resin and a specific ethylene-α-olefin copolymer (JP-A-2-215848), (5) a composition in which a dibenzylidene sorbitol compound having a specific substituent is added to a polypropylene resin (Japanese Patent Publication No. 61-57784).

[0006]

[Problems to be Solved by the Invention] Through these methods,
Although it is possible to prevent the physical properties of polypropylene resin from deteriorating due to radiation irradiation to some extent, various problems occur. For example, method (1) causes discoloration due to the additive, decrease in heat resistance, elution of the additive during use, etc., and is not practical. In method (2), there are problems such as the additive is toxic and its elution cannot be completely prevented, and the hindered amine bleeds onto the surface of the molded product over time. Furthermore, when only a hindered amine is added, the molecular weight decreases during molding, and the strength of the resulting molded product is significantly reduced. Further, although method (4) has no problems in terms of elution of additives or toxicity, it cannot be said that the transparency is sufficient. The disadvantage of method (5) is that the molded product, especially the molded product after irradiation with radiation, has a strong odor.

[0007] The present inventors have therefore found that when radiation irradiation is carried out, it is possible to maintain the physical properties of polypropylene resin, such as impact resistance, rigidity, and transparency, within a range that does not pose a practical problem, as well as to create a product that has little odor and is safe. We have conducted intensive research to develop a polypropylene resin composition that is also satisfactory from a sanitary standpoint.

[0008]

[Means for Solving the Problems] The present invention provides (a) a polypropylene resin of 95 to 99.5% by weight, (b) a density of 0.910 to 0.940 g/cm3, and 1000 carbon atoms in the main chain. A dibenzylidene sorbitol compound represented by the formula [I] is added to 100 parts by weight of a resin mixture consisting of 5 to 0.5% by weight of an ethylene-α-olefin copolymer having 5 to 30 side chain groups per copolymer. , 0.05
The above problem was solved by developing a radiation-resistant polypropylene resin composition characterized by containing ~0.4 parts by weight.

[Chemical 2]

The polypropylene resin used in the present invention is not particularly limited, and various types can be used. Specifically, it is a propylene homopolymer, a propylene-ethylene copolymer, a propylene-α-olefin copolymer, or a mixture thereof. The copolymer is not particularly limited and may be a random, alternating, block or graft copolymer. The α-olefin in the above propylene-α-olefin copolymer includes 1-butene, 1-
Examples include pentene, 1-hexene, 4-methyl-1-pentene, and the like. The melt flow rate (MFR) of these polypropylene resins is 0.5 to 80 g/10 minutes (
230°C).

[0010] The ethylene-α-olefin copolymer has a density of 0.910 to 0.940 g/cm3, preferably 0.
．． 915 to 0.930 g/cm3, 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 copolymerization is not particularly limited and various types can be used. For example, 1-butene, 4-methyl-1-pentene, 1-
Examples include octene (excluding propylene).

[0011] The ethylene-α-olefin copolymer is
It is so-called linear low-density polyethylene (LLDPE), and its properties are not particularly limited as long as it satisfies the above conditions, but melt fluorate (MFR)
(190℃) is 0.6 to 30g/10 minutes, especially 5 to 25
g/10 minutes is preferred.

[0012] The dibenzylidene sorbitol compound is
Generally represented by the above formula [I], the one used in the present invention is where R1 is H, and R2 and R3 are H or CH
3 (both H, one H and the other CH3, both C
H3).

In Japanese Patent Publication No. 61-57784, in order to reduce the odor after radiation irradiation, R1 and R2 are alkyl groups, and R3 is hydrogen. However, it was found that even with the method disclosed in the above publication, the odor of the molded product after irradiation with radiation cannot be avoided.

[0014] The present invention is applicable to R1, which was conventionally considered to be unfavorable.
By combining a dibenzylidene sorbitol compound in which is hydrogen with the above-mentioned so-called linear low-density polyethylene, a polypropylene resin composition that is transparent, has no color loss, and produces molded products with little odor has been developed.

The composition of the present invention contains 95 to 99.5% by weight of the above-mentioned polypropylene resin and 5 to 0.5% by weight of the ethylene-α-olefin copolymer, preferably 96 to 99% by weight of the polypropylene resin and 0.05 to 0.4 parts by weight of a dibenzylidene sorbitol compound is blended to 100 parts by weight of a mixture containing 4 to 1% by weight of an ethylene-α-olefin copolymer.

In the polypropylene resin composition of the present invention, when the proportion of the ethylene-α-olefin copolymer in the resin mixture is less than 0.5% by weight, the resulting composition is The impact resistance after irradiation is significantly reduced, making it unusable. Moreover, when it is added in an amount exceeding 5% by weight, transparency is lost and it becomes impossible to use it for applications such as medical instruments and food containers that require seeing through the contents.

On the other hand, the addition ratio of the dibenzylidene sorbitol compound is 0.05 parts by weight per 100 parts by weight of the resin mixture.
If it is less than 0.4 parts by weight, a sufficient transparency improvement effect cannot be obtained, and if it exceeds 0.4 parts by weight, deposits will be generated on the mold during molding, which will be mixed on the product surface, increasing the defective rate and reducing productivity. may be significantly damaged.

In addition to the above-mentioned components, the resin composition of the present invention may optionally contain an antioxidant, an ultraviolet absorber, an ultraviolet stabilizer,
Appropriate amounts of pigments, dispersants, neutralizing agents, etc. can be added. Specifically, 2,6-di-t-butyl-p-methylphenol, n-octadecyl-3-(4
-Hydroxy-3,5-di-t-butylphenyl)propionate, tetrakis[methylene-3(3,5-di-
t-Butyl-4-hydroxyphenyl) propionate] Phenolic antioxidants such as methane, pentaerythritol tetrakis (β-laurylthiopropionate)
, sulfur-based antioxidants such as dilaurylthiopropionate.

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

Furthermore, as an ultraviolet stabilizer, bis(2,2
, 6-tetramethyl-4-piperidyl) sebacate, and the like.

[0021] The amount of these additives should be such that the physical properties of the resin composition after radiation irradiation are not deteriorated and the sanitary aspects are not affected.

The resin composition of the present invention is prepared by kneading the above-mentioned polypropylene resin, ethylene-α-olefin copolymer, dibenzylidene sorbitol compound, and a predetermined amount of additives added if necessary, using a Henschel mixer or other kneading device. It can be obtained by mixing and uniformly dispersing the mixture in a machine, and then melting and pelletizing it in an extruder.

[0023]

[Example] Next, a resin composition of the present invention was produced and compared with a conventional composition. (Examples 1 to 5) Ethylene content (CE) 3.0 mol%, density 0.910 g/cm3, MFR (230°C)
25g/10min propylene copolymer and density 0.91
6g/cm3, the number of side chain groups (degree of branching) is 1 carbon atom in the main chain
20 pieces per 000 pieces of ethylene-1-butene copolymer [MFR6.0g/10 minutes (190°C)] (LLDPE
) and a dibenzylidene sorbitol compound in the amounts shown in Table 1, which were melt-kneaded in an extruder at 230° C. under a nitrogen atmosphere for 3 minutes to form pellets. The obtained pellets were flat plated (130°C) at 200°C using an injection molding machine.
mm x 130 mm: thickness 2 mm and 1.5 mm). The obtained flat plate was irradiated with gamma rays (irradiation dose 2.
The impact resistance (2 mm thickness), transparency (1.5 mm thickness), and odor were measured around 5 Mrad). The results are shown in Table 1. The impact resistance was determined by placing the flat plate on a steel plate with a hole of 50 mm in diameter, applying a 1/2 inch diameter striking core to it, and dropping a load from the top to determine the impact energy at the crack height. It was expressed as follows. Transparency was measured according to ASTM D 1003 using a commercially available haze meter. The odor was determined by a sensory test. After irradiation, the molded product was placed in a desiccator and left at room temperature for 24 hours.
The desiccator was opened, the odor was smelled, and the odor was rated on a four-point scale, with the highest being 4.

(Comparative Examples 1 to 6) Comparative Examples 1 to 4 are the same as Example 1 above, except that the amounts of the ethylene-1-butene copolymer and dibenzylidene sorbitol compound were changed to the amounts shown in Table 1. A flat plate was obtained in the same manner as above, and the impact resistance and transparency before and after irradiation with gamma rays were measured. In Comparative Examples 5 and 6, flat plates were obtained in the same manner as in Example 1 except that the propylene polymerized resin used in the Examples was used as the resin mixture, and the impact resistance before and after γ-ray irradiation was measured. These results are shown in Table 1.

[0025]

[Table 1]

PP: Propylene polymer LLDPE: Ethylene-1-butene copolymer DBS: Dibenzylidene sorbitol A: R1 = H, R2 = H, R3 = HB: R1 =
H, R2 = CH3, R3 = CH3C: R1 = C
2 H5, R2 = H, R3 = C2 H5D: R1
=CH3, R2 =H, R3 =CH3 In Comparative Example 2, there was white powder adhering to the mold during injection molding, which was transferred to the surface of the molded product, and the resin adhered to the mold, increasing the defective rate of the product. .

[0027]

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 when irradiated with radiation, and also prevents bleeding of additives and elution of toxic decomposition products. It has excellent hygiene, safety, etc. Therefore, for various molded products obtained using the resin composition of the present invention, without deterioration of physical properties,
Furthermore, radiation sterilization can be applied safely and hygienically. Therefore, the resin composition of the present invention can be used extremely effectively as a molding material for food containers, medical instruments, and the like.

Claims (1)

[Claims] Claim 1: (a) Polypropylene resin 95-99.
5% by weight and (b) density 0.910-0.940g/
cm3 and the number of side chain groups per 1000 carbon atoms in the main chain is 5 to 0.5% by weight of an ethylene-α-olefin copolymer 100
A radiation-resistant polypropylene resin composition, characterized in that 0.05 to 0.4 parts by weight of a dibenzylidene sorbitol compound represented by the following formula [I] is blended with respect to parts by weight. [Chemical formula 1]