Ionizing radiation-resistant thermoplastic resin composition, and molded product comprising same

Abstract

A thermoplastic resin composition of the present invention comprises a rubber-modified vinyl-based graft copolymer, a first aromatic vinyl-based copolymer, a second aromatic vinyl-based copolymer, and a polyalkylene glycol, wherein the first aromatic vinyl-based copolymer is a copolymer of methyl methacrylate, methyl acrylate, an aromatic vinyl-based monomer, and a monomer copolymerizable with the aromatic vinyl-based monomer, the second aromatic vinyl-based copolymer is a copolymer of an aromatic vinyl-based monomer and a monomer copolymerizable with the aromatic vinyl-based monomer, and the weight ratio of methyl methacrylate to methyl acrylate, in the first aromatic vinyl-based copolymer, is approximately 1:0.01 to approximately 1:0.2. The thermoplastic resin composition has excellent discoloration resistance, color, transparency, and the like even after irradiation with ionizing radiation.

Claims

1. A thermoplastic resin composition comprising: about 100 parts by weight of a base resin comprising about 10 wt % to about 50 wt % of a rubber-modified vinyl graft copolymer; about 30 wt % to about 70 wt % of a first aromatic vinyl copolymer; and about 5 wt % to about 40 wt % of a second aromatic vinyl copolymer; and about 0.001 to about 5 parts by weight of polyalkylene glycol, wherein the first aromatic vinyl copolymer is a copolymer of methyl methacrylate, methyl acrylate, an aromatic vinyl monomer and a monomer copolymerizable with the aromatic vinyl monomer, the second aromatic vinyl copolymer is a copolymer of an aromatic vinyl monomer and a monomer copolymerizable with the aromatic vinyl monomer, and the first aromatic vinyl copolymer comprises methyl methacrylate and methyl acrylate in a weight ratio of about 1:0.01 to about 1:0.2.

2. The thermoplastic resin composition according to claim 1, wherein the rubber-modified vinyl graft copolymer is prepared through graft polymerization of an aromatic vinyl monomer and a monomer copolymerizable with the aromatic vinyl monomer to a rubber polymer.

3. The thermoplastic resin composition according to claim 1, wherein the first aromatic vinyl copolymer is a copolymer of about 65 wt % to about 85 wt % of methyl methacrylate and methyl acrylate, about 10 wt % to about 30 wt % of the aromatic vinyl monomer, and about 1 wt % to about 10 wt % of the monomer copolymerizable with the aromatic vinyl monomer.

4. The thermoplastic resin composition according to claim 1, wherein the second aromatic vinyl copolymer is a copolymer of about 5 wt % to about 50 wt % of the aromatic vinyl monomer and about 50 wt % to about 95 wt % of the monomer copolymerizable with the aromatic vinyl monomer.

5. The thermoplastic resin composition according to claim 1, wherein the thermoplastic resin composition has a difference in yellow index (ΔYI) of about 4 or less, as calculated on a 3.2 mm thick specimen according to Equation 1:
ΔYI=YI.sub.1−YI.sub.0  [Equation 1] wherein YI.sub.0 is a yellow index (YI) of the specimen, as measured in accordance with ASTM D1925 before irradiation with gamma rays, and YI.sub.1 is a yellow index (YI) of the specimen, as measured in accordance with ASTM D1925 after the specimen is irradiated with 25 kGy gamma rays and left for 21 days.

6. The thermoplastic resin composition according to claim 1, wherein the thermoplastic resin composition has a luminosity (L*) of about 85 or more, an a* value of about −3 to about 4, and a b* value of about −3 to about 4, as measured on a 3.2 mm thick specimen in accordance with ASTM D2244 after the specimen is irradiated with 25 kGy gamma rays and left for 21 days.

7. The thermoplastic resin composition according to claim 1, wherein the thermoplastic resin composition has a transmittance of about 85% or more, as measured on a 3.2 mm thick specimen in accordance with ASTM D1003 after the specimen is irradiated with 25 kGy gamma rays and left for 21 days, and a haze of about 5% or less, as measured on a 3.2 mm thick specimen in accordance with ASTM D1003.

8. A molded product formed of the thermoplastic resin composition according to claim 1.

9. The molded product according to claim 8, wherein the molded product is an ionizing radiation resistant medical supply product.

Description

EXAMPLE

(1) Details of components used in Examples and Comparative Examples are as follows.

(2) (A) Rubber-Modified Vinyl Graft Copolymer

(3) A methyl methacrylate-acrylonitrile-butadiene-styrene graft copolymer (g-MABS) obtained through graft copolymerization of 55 wt % of polybutadiene rubber particles (average particle diameter (D50): 280 nm) and 45 wt % of methyl methacrylate, styrene and acrylonitrile (weight ratio: 72/21/7) was used.

(4) (B) First Aromatic Vinyl Copolymer

(5) (B1) A methyl methacrylate-styrene-acrylonitrile copolymer (MSAN, weight average molecular weight: 90,000 g/mol) obtained through polymerization of 74 wt % of methyl methacrylate (MMA) and methyl acrylate (Mac) (weight ratio (MMA:Mac) of 1:0.06), 22 wt % of styrene and 4 wt % of acrylonitrile was used.

(6) (B2) A methyl methacrylate-styrene-acrylonitrile copolymer (MSAN, weight average molecular weight: 90,000 g/mol) obtained through polymerization of 74 wt % of methyl methacrylate (MMA) and methyl acrylate (Mac) (weight ratio (MMA:Mac) of 1:0.14), 22 wt % of styrene and 4 wt % of acrylonitrile was used.

(7) (B3) A methyl methacrylate-styrene-acrylonitrile copolymer (MSAN, weight average molecular weight: 90,000 g/mol) obtained through polymerization of 74 wt % of methyl methacrylate, 22 wt % of styrene and 4 wt % of acrylonitrile was used.

(8) (C) Second Aromatic Vinyl Copolymer

(9) A methyl methacrylate-styrene-acrylonitrile copolymer (MSAN, weight average molecular weight: 120,000 g/mol) obtained through polymerization of 74 wt % of methyl methacrylate, 21 wt % of styrene and 5 wt % of acrylonitrile was used.

(10) (D) Polyalkylene Glycol

(11) Polypropylene glycol (number average molecular weight (Mn): 2,000 g/mol) was used.

Examples 1 and 2 and Comparative Examples 1 and 2: Preparation of Thermoplastic Resin Composition

(12) According to compositions and amounts as listed in Table 1, (A) a rubber-modified vinyl graft copolymer, (B) a first aromatic vinyl copolymer, (C) a second aromatic vinyl copolymer and (D) polyalkylene glycol were mixed, followed by extrusion molding using a twin-screw type extruder (L/D=36, Φ=32) at 250° C. and preparation of a thermoplastic resin composition in pellet form using a pelletizer. The thermoplastic resin composition prepared in pellet form was dried in an oven at 80° C. for 2 hours, followed by injection molding using an injection molding machine (DHC 120WD, Dongshin Hydraulics Co., Ltd.) under conditions of a molding temperature of 250° C. and a mold temperature of 70° C., thereby preparing a specimen. The prepared specimen was evaluated as to the following properties and evaluation results are shown in Table 1.

(13) Property Evaluation

(14) (1) Discoloration resistance: A difference in yellow index (ΔYI) was calculated by the following Equation 1 by measuring yellow indices of a 3.2 mm thick specimen of a thermoplastic resin composition in accordance with ASTM D1925 before irradiation with gamma rays and after the specimen was irradiated with 25 kGy gamma rays and left for 21 days, respectively.
ΔYI=YI.sub.1−YI.sub.0  [Equation 1]

(15) wherein YI.sub.0 is a yellow index (YI) of the specimen, as measured in accordance with ASTM D1925 before irradiation with gamma rays, and YI.sub.1 is a yellow index (YI) of the specimen, as measured in accordance with ASTM D1925 after the specimen is irradiated with 25 kGy gamma rays and left for 21 days.

(16) (2) Color evaluation: Luminosity (L*), a* and b* were measured on a 3.2 mm thick specimen of a thermoplastic resin composition in accordance with ASTM D2244 before irradiation with gamma rays and after the specimen was irradiated with 25 kGy gamma rays and left for 21 days.

(17) (3) Transparency (unit: %): Transmittance (total light transmittance) and haze were measured on a 3.2 mm thick specimen of a thermoplastic resin composition in accordance with ASTM D1003 before irradiation with gamma rays and after the specimen was irradiated with 25 kGy gamma rays and left for 21 days.

(18) TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 1 2 (A) (wt %) 25 25 25 25 (B) (wt %) (B1) 55 — — 55 (B2) — 55 — — (B3) — — 55 — (C) (wt %) 20 20 20 20 (D) (parts by weight) 0.1 0.1 0.1 — Before Transmittance 91.2 91.2 91.3 91.3 irradiation (%) with γ-ray Haze (%) 2.5 2.1 2.8 2.7 YI 2.1 1.8 3.5 2.6 L* 96.0 95.9 96.1 96.1 a* −0.5 −0.5 −0.6 −0.6 b* 1.4 1.2 2.1 1.5 21 days after Transmittance 90.5 90.8 90.1 89.6 irradiation (%) with γ-ray Haze (%) 3.4 2.8 4.2 5.8 YI 5.2 4.3 7.8 8.0 L* 96.4 95.8 96.8 97.1 a* −0.1 −0.9 −0.1 −0.3 b* 3.2 2.6 4.6 5.0 ΔYI (before irradiation with 3.1 2.5 4.3 5.4 gamma ray/21 days after irradiation with gamma ray)

(19) From the results shown in Table 1, it could be seen that the thermoplastic resin compositions (Examples 1 and 2) according to the present invention had good properties in terms of discoloration resistance, color, and transparency even after irradiation with ionizing radiation.

(20) On the contrary, it could be seen that the thermoplastic resin composition of Comparative Example 1 prepared using the first aromatic vinyl copolymer (B3) not containing methyl acrylate (Mac) and the thermoplastic resin composition of Comparative Example 2 prepared without polyalkylene glycol suffered from deterioration in discoloration resistance, color, and transparency after irradiation with ionizing radiation.

(21) It should be understood that various modifications, changes, alterations, and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the present invention.