Patent Description:
Recently, there have been many changes in the material industry in addition to environmental issues. In particular, many efforts have been made to replace polyvinyl chloride, polycarbonate, and the like, which have been conventionally used, due to issues such as environmental hormones or disposal for materials used as medical or food containers. Particularly, there is a need to develop new materials in the field of medical transparent materials used for syringes and tube connectors that are used while storing liquids therein.

Meanwhile, polycarbonate, polymethyl methacrylate, polystyrene, polyacrylonitrile-styrene, and the like are commonly used as transparent resins. Polycarbonate has excellent impact strength and excellent transparency, but the processability thereof is poor, which makes it difficult to produce complex products, and chemical resistance is not excellent. Also, the use of polycarbonate is increasingly restricted due to bisphenol A used in the preparation of polycarbonate. In addition, polymethyl methacrylate has excellent optical characteristics, but the impact resistance and chemical resistance thereof are not excellent. Additionally, polystyrene and polyacrylonitrile-styrene are not excellent in impact resistance and chemical resistance. In addition, diene-based graft polymers have excellent impact resistance and excellent processability while achieving the balance therebetween, but the transparency thereof is not excellent.

Therefore, there is a demand for the development of a medical material excellent in all of transparency, impact resistance, chemical resistance, and processability.

<CIT> discloses a thermoplastic resin composition comprising a) a first graft copolymer and b) a second copolymer, and having a weight average molecular weight of <NUM> to <NUM>, wherein, as the a) first graft copolymer rubber latex, methyl methacrylate, styrene and acrylonitrile are used as raw material, wherein the rubber latex has an average particle diameter of <NUM>, and, as the b) second copolymer, methyl methacrylate, styrene and acrylonitrile are used as raw material.

<CIT> discloses a thermoplastic resin composition containing a rubber graft copolymer (A) and an acryl-aromatic vinyl-based copolymer (B), wherein a latex-type diene-based rubber polymer is prepared using <NUM> parts by mass of <NUM>,<NUM>-butadiene and <NUM> parts by mass of styrene.

The present invention is directed to providing a thermoplastic resin composition that achieves the balance among transparency, impact resistance, and processability and is capable of reducing the usage amount of a (meth)acrylate-based monomer to improve chemical resistance and gamma radiation resistance and reduce manufacturing costs. The present invention is also directed to providing a thermoplastic resin composition that can be used for medical purposes.

One aspect of the present invention provides a thermoplastic resin composition which includes: a graft copolymer including a rubber polymer including a first styrene-based monomer unit and a diene-based monomer unit in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM> and having an average particle diameter of <NUM> to <NUM>; a (meth)acrylate-based monomer unit grafted onto the rubber polymer; a second styrene-based monomer unit grafted onto the rubber polymer, and a non-grafted copolymer including a (meth)acrylate-based monomer unit and a second styrene-based monomer unit, wherein the weight ratio of the (meth)acrylate-based monomer unit to the second styrene-based monomer unit is <NUM> or less, and a weight-average molecular weight of the thermoplastic resin composition ranges from <NUM>,<NUM> to <NUM>,<NUM>/mol.

A thermoplastic resin composition of the present invention is not only excellent in transparency, impact resistance, processability, chemical resistance, and gamma radiation resistance but also capable of reducing the usage amount of a (meth)acrylate-based monomer, resulting in the reduction of manufacturing costs. Also, the thermoplastic resin composition can be used as a medical material.

In the present invention, an average particle diameter may be measured by a dynamic light scattering method, specifically, by using a Nicomp <NUM> instrument (manufactured by Particle Sizing Systems). In the present invention, an average particle diameter may refer to an arithmetic average particle diameter in the particle size distribution as measured by a dynamic light scattering method, that is, an average particle diameter based on a scattering intensity distribution.

In the present invention, an average particle diameter may be measured using a transmission electron microscope (TEM).

In the present invention, a refractive index refers to an absolute refractive index of a material and is recognized as the ratio of the speed of electromagnetic radiation in free space to the speed of the radiation in the material, wherein the radiation may be visible light having a wavelength of <NUM> to <NUM>, specifically, visible light having a wavelength of <NUM>. A refractive index may be measured by a known method, i.e., by using an Abbe refractometer.

In the present invention, a refractive index may be measured at <NUM> with visible light having a wavelength of <NUM> using an Abbe refractometer after a graft copolymer and a non-grafted copolymer are cut to a thickness of <NUM>.

In the present invention, the weights of a rubber polymer, a diene-based monomer unit, a (meth)acrylate-based monomer unit, a first styrene-based monomer unit, and a second styrene-based monomer unit, which are included in a thermoplastic resin composition, may be measured by infrared (IR) spectroscopy. In this case, as an IR spectrometer, a Nicolet™ iS20 FTIR spectrometer (manufactured by Thermo Scientific) may be used.

In the present invention, the impact modifying part of a thermoplastic resin composition may refer to a part consisting of a rubber polymer and a monomer unit grafted onto the rubber polymer, and the matrix part of a thermoplastic resin composition may refer to a part excluding the impact modifying part and consisting of a monomer unit not grafted onto a rubber polymer in a graft copolymer and a monomer unit included in a non-grafted copolymer.

In the present invention, the weight-average molecular weight of a thermoplastic resin composition or a graft copolymer may be measured as a relative value with respect to a standard polystyrene (PS) sample by gel permeation chromatography (GPC) after the thermoplastic resin composition or graft copolymer is dissolved in acetone and then centrifuged to separate a supernatant and a precipitate, and the supernatant is dried, dissolved in tetrahydrofuran, and filtered.

Specifically, <NUM> of a thermoplastic resin composition or graft copolymer powder is dissolved in <NUM> of acetone while stirring for <NUM> hours and then centrifuged in a centrifuge (SUPRA <NUM> manufactured by Hanil Science Industrial) at <NUM>,<NUM> rpm and -<NUM> for <NUM> hours to separate a supernatant and a precipitate, and the supernatant is dried in a hot-air dryer set at <NUM> for <NUM> hours to obtain a dry solid. The obtained dry solid is dissolved at a concentration of <NUM> wt% in tetrahydrofuran and then filtered through a <NUM> filter, and then a weight-average molecular weight is measured as a relative value with respect to a standard PS sample by GPC.

Meanwhile, in the GPC measurement, the Agilent <NUM> series system may be used, and measurement conditions may be as follows.

In the present invention, the weight-average molecular weight of a non-grafted copolymer may be measured as a relative value with respect to a standard PS sample by GPC using tetrahydrofuran as an eluent.

In the present invention, a first styrene-based monomer unit may refer to a styrene-based monomer unit included in a rubber polymer, and a second styrene-based monomer unit may refer to a styrene-based monomer unit included in a thermoplastic resin composition, but not included in the rubber polymer.

In the present invention, each of the first and second styrene-based monomer units may be a unit derived from a styrene-based monomer. The styrene-based monomer may be one or more selected from the group consisting of styrene, α-methyl styrene, α-ethyl styrene, and p-methyl styrene, with styrene being preferred.

In the present invention, a (meth)acrylonitrile-based monomer unit may be a unit derived from a (meth)acrylonitrile-based monomer. The (meth)acrylonitrile-based monomer may be a C<NUM> to C<NUM> alkyl (meth)acrylate-based monomer, and the C<NUM> to C<NUM> alkyl (meth)acrylate-based monomer may be one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, <NUM>-ethylhexyl (meth)acrylate, and decyl (meth)acrylate, with methyl methacrylate being preferred.

In the present invention, an acrylonitrile-based monomer unit may be a unit derived from an acrylonitrile-based monomer. The acrylonitrile-based monomer may be one or more selected from the group consisting of acrylonitrile, methacrylonitrile, phenyl acrylonitrile, and α-chloroacrylonitrile, with acrylonitrile being preferred.

In the present invention, a diene-based monomer unit may be a unit derived from a diene-based monomer. The diene-based monomer unit may be one or more selected from the group consisting of <NUM>,<NUM>-butadiene, isoprene, chloroprene, and piperylene, with <NUM>,<NUM>-butadiene being preferred.

A thermoplastic resin composition according to an embodiment of the present invention includes: a graft copolymer including a rubber polymer including a first styrene-based monomer unit and a diene-based monomer unit in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM> and having an average particle diameter of <NUM> to <NUM>; a (meth)acrylate-based monomer unit grafted onto the rubber polymer; a second styrene-based monomer unit grafted onto the rubber polymer; and a non-grafted copolymer including a (meth)acrylate-based monomer unit and a second styrene-based monomer unit, wherein a weight ratio of the (meth)acrylate-based monomer unit to the second styrene-based monomer unit is <NUM> or less, and a weight-average molecular weight of the thermoplastic resin composition ranges from <NUM>,<NUM> to <NUM>,<NUM>/mol.

The inventors of the present invention have found that a thermoplastic resin composition excellent in transparency, impact resistance, processability, chemical resistance, and gamma radiation resistance is prepared by adjusting the composition and average particle diameter of a rubber polymer, the weight ratio of a second styrene-based monomer unit and a (meth)acrylate-based monomer unit included in a thermoplastic resin composition, and a weight-average molecular weight, and completed the present invention based on this finding.

When a rubber polymer includes only a diene-based monomer unit, to eliminate or minimize a difference in the refractive index between the impact modifying part and matrix part of a thermoplastic resin composition, an excessive amount of a (meth)acrylate-based monomer unit needs to be included in the matrix part. However, the (meth)acrylate-based monomer unit causes degradation of the chemical resistance of a thermoplastic resin composition and an increase in manufacturing costs due to the high cost of the monomer. In addition, a rubber polymer may not be prepared only using a styrene-based monomer. However, the rubber polymer according to the present invention includes not only a diene-based monomer unit but also a first styrene-based monomer unit to increase the refractive index of the rubber polymer, and accordingly, it is possible to include a small amount of a (meth)acrylate-based monomer unit in a matrix part. Therefore, the thermoplastic resin composition according to the present invention can minimize the problems such as degradation of chemical resistance and an increase in manufacturing costs which are caused by a (meth)acrylate-based monomer unit.

According to the embodiment of the present invention, the rubber polymer includes a first styrene-based monomer unit and a diene-based monomer unit in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>, and preferably, in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>. When the above-described condition is satisfied, it is possible to improve impact resistance and increase a refractive index, and thus the usage amount of a (meth)acrylate-based monomer unit can be reduced, and degradation of chemical resistance and an increase in manufacturing costs, which are caused by a (meth)acrylate-based monomer unit, can be minimized. However, when the content of the first styrene-based monomer unit is below the above-described range, chemical resistance and gamma radiation resistance may be substantially degraded. On the other hand, when the content of the first styrene-based monomer unit is above the above-described range, transparency and impact resistance may be substantially degraded.

Since the rubber polymer includes the diene-based monomer unit and the first styrene-based monomer unit in the above-described weight ratio, the refractive index thereof may be higher than that of a rubber polymer consisting of only a diene-based monomer. Specifically, the rubber polymer may have a refractive index of <NUM> to <NUM>, and preferably, <NUM> to <NUM>.

In addition, the rubber polymer included in the thermoplastic resin composition according to the embodiment of the present invention has an average particle diameter of <NUM> to <NUM>, and preferably, <NUM> to <NUM>. When the thermoplastic resin composition according to the embodiment of the present invention includes a rubber polymer having an average particle diameter below the above-described range, processability and impact resistance may be substantially degraded. On the other hand, when the thermoplastic resin composition includes a rubber polymer having an average particle diameter above the above-described range, surface gloss characteristics may be degraded. In addition, a case in which a rubber polymer is prepared by emulsion polymerization is not preferred because the latex stability of the rubber polymer is substantially degraded.

In the thermoplastic resin composition according to the embodiment of the present invention, the weight ratio of the (meth)acrylate-based monomer unit to the second styrene-based monomer unit is <NUM> or less, and preferably, <NUM> to <NUM>. A case in which the weight ratio of the (meth)acrylate-based monomer unit to the second styrene-based monomer unit exceeds <NUM> means that an excessive amount of the (meth)acrylate-based monomer unit is included, and when the weight ratio of the (meth)acrylate-based monomer unit to the second styrene-based monomer unit exceeds <NUM>, the chemical resistance of the thermoplastic resin composition may be substantially degraded, and manufacturing costs may be increased by addition of an excessive amount of (meth)acrylate-based monomer. On the other hand, when the weight ratio of the (meth)acrylate-based monomer unit to the second styrene-based monomer unit is less than <NUM>, impact resistance may be degraded.

The thermoplastic resin composition according to the embodiment of the present invention has a weight-average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>/mol, and preferably, <NUM>,<NUM> to <NUM>,<NUM>/mol. The weight-average molecular weight refers to the weight-average molecular weight of a thermoplastic resin composition including a graft copolymer and a non-grafted copolymer to be described below, that is, a thermoplastic resin composition including an impact modifying part and a matrix part. When the weight-average molecular weight of the thermoplastic resin composition is below the above-described range, the chemical resistance of the thermoplastic resin composition may be degraded, and when above the above-described range, the processability of the thermoplastic resin composition may be degraded.

Meanwhile, the thermoplastic resin composition according to the embodiment of the present invention may include: the rubber polymer in an amount of <NUM> to <NUM> wt%; the (meth)acrylate-based monomer unit in an amount of <NUM> to <NUM> wt%; and the second styrene-based monomer unit in an amount of <NUM> to <NUM> wt%. Preferably, the thermoplastic resin composition includes: the rubber polymer in an amount of <NUM> to <NUM> wt%; the (meth)acrylate-based monomer unit in an amount of <NUM> to <NUM> wt%; and the second styrene-based monomer unit in an amount of <NUM> to <NUM> wt%. When the above-described condition is satisfied, a thermoplastic resin composition having improved properties in terms of impact resistance, chemical resistance, and processability can be prepared.

The thermoplastic resin composition according to the embodiment of the present invention may further include an acrylonitrile-based monomer unit to further improve chemical resistance. The acrylonitrile-based monomer unit may be included in an amount of <NUM> to <NUM> wt%, and preferably, <NUM> to <NUM> wt% to improve chemical resistance and minimize the occurrence of a yellowing phenomenon.

Meanwhile, the thermoplastic resin composition according to the embodiment of the present invention includes a graft copolymer and a non-grafted copolymer.

The graft copolymer may have a refractive index of <NUM> to <NUM>, and preferably, <NUM> to <NUM>. When the above-described range is satisfied, the refractive index of the graft copolymer is the same as or similar to that of the above-described rubber polymer, and thus the transparency of the graft copolymer can be further improved.

The refractive index of the graft copolymer and the refractive index of the non-grafted copolymer may differ by <NUM> or less, and it is preferable that the difference is <NUM>. When the above-described condition is satisfied, the thermoplastic resin composition can become more transparent.

A weight ratio of the graft copolymer and the non-grafted copolymer may be <NUM>:<NUM> to <NUM>:<NUM>, and preferably, <NUM>:<NUM> to <NUM>:<NUM>. When the above-described range is satisfied, processability can be further improved without degradation of impact resistance.

The graft copolymer includes a rubber polymer including a first styrene-based monomer unit and a diene-based monomer unit and having an average particle diameter of <NUM> to <NUM>, a (meth)acrylate-based monomer unit grafted onto the rubber polymer, and a second styrene-based monomer unit grafted onto the rubber polymer.

The graft copolymer may include a (meth)acrylate-based monomer unit and a second styrene-based monomer unit which are not grafted onto the rubber polymer.

Meanwhile, the transparency of the graft copolymer may be determined by the refractive index of a shell including the rubber polymer and the monomer units grafted onto the rubber polymer. Also, the refractive index of the shell may be adjusted by a mixing ratio of the monomer units. That is, the refractive indices of the rubber polymer and the shell need to be similar to each other, and it is preferable that the refractive indices thereof are the same. Accordingly, the refractive index of the rubber polymer included in the graft copolymer and the refractive index of the monomer units grafted onto the rubber polymer may differ by <NUM> or less, and it is preferable that the difference is <NUM>. When the above-described condition is satisfied, the thermoplastic resin composition can become more transparent.

The graft copolymer may include the rubber polymer in an amount of <NUM> to <NUM> wt%, and preferably, <NUM> to <NUM> wt%. When the above-described range is satisfied, excellent impact resistance can be exhibited, and grafting is sufficiently performed in the preparation of the graft copolymer, and thus the graft copolymer can achieve excellent transparency.

The rubber polymer includes the first styrene-based monomer unit and the diene-based monomer unit in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>, and preferably, in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM>. When the above-described condition is satisfied, it is possible to improve impact resistance and increase a refractive index, and thus the usage amount of a (meth)acrylate-based monomer unit can be reduced, degradation of chemical resistance and an increase in manufacturing costs, which are caused by a (meth)acrylate-based monomer unit, can be minimized. However, when the content of the first styrene-based monomer unit is below the above-described range, chemical resistance and gamma radiation resistance may be substantially degraded. On the other hand, when the content of the first styrene-based monomer unit is above the above-described range, transparency and impact resistance may be substantially degraded.

The graft copolymer may include the (meth)acrylate-based monomer unit in an amount of <NUM> to <NUM> wt%, and preferably, <NUM> to <NUM> wt%. When the above-described range is satisfied, the graft copolymer can achieve excellent transparency.

The graft copolymer may include the second styrene-based monomer unit in an amount of <NUM> to <NUM> wt%, and preferably, <NUM> to <NUM> wt%. When the above-described range is satisfied, the graft copolymer can achieve excellent processability.

The graft copolymer may further include an acrylonitrile-based monomer unit to further improve chemical resistance. The acrylonitrile-based monomer unit may be included in an amount of <NUM> wt% or less, and preferably, <NUM> to <NUM> wt% to improve chemical resistance and minimize the occurrence of a yellowing phenomenon.

The graft copolymer may have a weight-average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>/mol, and preferably, <NUM>,<NUM> to <NUM>,<NUM>/mol. When the above-described range is satisfied, the chemical resistance and processability of the thermoplastic resin composition can be further improved.

In order to prepare the rubber polymer of the graft copolymer so that the rubber polymer has the above-described conditions, emulsion polymerization is preferably used.

The non-grafted copolymer includes a non-grafted copolymer including a (meth)acrylate-based monomer unit and a second styrene-based monomer unit.

The non-grafted copolymer may include the (meth)acrylate-based monomer unit in an amount of <NUM> to <NUM> wt%, and preferably, <NUM> to <NUM> wt%. When the above-described range is satisfied, a thermoplastic resin composition having improved transparency can be prepared.

The non-grafted copolymer may include the second styrene-based monomer unit in an amount of <NUM> to <NUM> wt%, and preferably, <NUM> to <NUM> wt%. When the above-described condition is satisfied, a thermoplastic resin composition having improved processability can be prepared.

The non-grafted copolymer may further include an acrylonitrile-based monomer unit to further improve chemical resistance. The acrylonitrile-based monomer unit may be included in an amount of <NUM> wt% or less, and preferably, <NUM> to <NUM> wt% to improve chemical resistance and minimize the occurrence of a yellowing phenomenon.

The non-grafted copolymer may have a weight-average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>/mol, and preferably, <NUM>,<NUM> to <NUM>,<NUM>/mol. When the above-described range is satisfied, the chemical resistance and processability of the thermoplastic resin composition can be further improved.

Hereinafter, exemplary embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, it should be understood that the present invention can be implemented in various forms, and that the exemplary embodiments are not intended to limit the present invention thereto.

A monomer mixture consisting of <NUM> wt% of styrene and <NUM> wt% of <NUM>,<NUM>-butadiene was subjected to emulsion polymerization to prepare styrene/butadiene rubber polymer latex having an average particle diameter of <NUM> and a refractive index of <NUM>.

<NUM> parts by weight of methyl methacrylate, <NUM> parts by weight of styrene, <NUM> parts by weight of acrylonitrile, <NUM> parts by weight of ion exchanged water, <NUM> parts by weight of sodium oleate, <NUM> parts by weight of t-dodecyl mercaptan, <NUM> parts by weight of ethylenediamine tetraacetate, <NUM> parts by weight of sodium formaldehyde sulfoxylate, <NUM> parts by weight of ferrous sulfate, and <NUM> parts by weight of cumene hydroperoxide were homogeneously mixed to prepare a liquid mixture.

A reactor containing <NUM> parts by weight of the styrene/butadiene rubber polymer latex was heated to <NUM>, and polymerization was performed while continuously adding the liquid mixture for <NUM> hours. After the continuous addition was terminated, the reactor was heated to <NUM>, aging was performed for an hour, and the polymerization was terminated to obtain graft copolymer latex.

The graft copolymer latex was coagulated with calcium chloride, washed, dehydrated, and dried to obtain graft copolymer powder A-<NUM> having a refractive index of <NUM> and a weight-average molecular weight of <NUM>,<NUM>/mol.

A reactor containing <NUM> parts by weight (based on solid content) of the styrene/butadiene rubber polymer latex was heated to <NUM>, and polymerization was performed while continuously adding the liquid mixture for <NUM> hours. After the continuous addition was terminated, the reactor was heated to <NUM>, aging was performed for an hour, and the polymerization was terminated to obtain graft copolymer latex.

<NUM>,<NUM>-butadiene was subjected to emulsion polymerization to prepare butadiene rubber polymer latex having an average particle diameter of <NUM> and a refractive index of <NUM>.

A reactor containing <NUM> parts by weight of the butadiene rubber polymer latex was heated to <NUM>, and polymerization was performed while continuously adding the liquid mixture for <NUM> hours. After the continuous addition was terminated, the reactor was heated to <NUM>, aging was performed for an hour, and the polymerization was terminated to obtain graft copolymer latex.

The graft copolymer latex was coagulated with calcium chloride, washed, dehydrated, and dried to obtain graft copolymer powder A-<NUM> having a refractive index of <NUM> and a weight-average molecular weight of <NUM>,<NUM>/mol. The graft copolymer powder A-<NUM> became opaque due to a difference in refractive index between the butadiene rubber polymer and a hard copolymer grafted onto the butadiene rubber polymer, and therefore, the refractive index thereof was not measured.

A liquid mixture including <NUM> parts by weight of methyl methacrylate, <NUM> parts by weight of styrene, <NUM> parts by weight of acrylonitrile, <NUM> parts by weight of toluene, and <NUM> parts by weight of n-octyl mercaptan was continuously added to a reactor for an average polymerization time of <NUM> hours. In this case, a polymerization temperature was maintained at <NUM>. The polymerization solution continuously discharged from the reactor was heated in a preheating bath, and unreacted monomers and a solvent were volatilized in a volatilization tank. Subsequently, the resulting polymer was extruded using a polymer transfer pump extruder while maintaining a temperature of <NUM>, thereby preparing a non-grafted copolymer pellet B-<NUM> having a refractive index of <NUM> and a weight-average molecular weight of <NUM>,<NUM>/mol.

Graft copolymer powder and a non-grafted copolymer pellet were homogeneously mixed in contents shown in Tables <NUM> to <NUM> below to prepare a thermoplastic resin composition.

Physical properties of the thermoplastic resin compositions according to Examples and Comparative Examples were measured by methods described below, and results thereof are shown in Tables <NUM> to <NUM>.

<NUM> parts by weight of each of the thermoplastic resin compositions according to Examples and Comparative Examples, <NUM> parts by weight of a lubricant, and <NUM> parts by weight of an antioxidant were homogeneously mixed, and then the resulting mixture was extruded using a twin-screw extrusion kneader whose cylinder temperature was <NUM> to prepare a pellet. A physical property of the pellet was measured by a method described below, and results thereof are shown in Tables <NUM> to <NUM>.

The pellet prepared in Experimental Example <NUM> was injection-molded to prepare a specimen. Physical properties of the specimen were measured by methods described below, and results thereof are shown in Tables <NUM> to <NUM> below.

In the above equation, L<NUM>, a<NUM>, and b<NUM> are the L, a, and b values measured in the CIE LAB color coordinate system after a specimen irradiated with gamma rays was stored for <NUM> days, and L<NUM>, a<NUM>, and b<NUM> are the L, a, and b values measured in the CIE LAB color coordinate system for a specimen not irradiated with gamma rays.

Referring to Tables <NUM> to <NUM>, in the case of Examples <NUM> to <NUM> which used styrene/butadiene rubber polymers prepared by polymerizing <NUM> to <NUM> wt% of styrene and <NUM> to <NUM> wt% of <NUM>,<NUM>-butadiene, all of processability, transparency, impact resistance, chemical resistance, and gamma radiation resistance were excellent. However, in the case of Comparative Example <NUM> which used a styrene/butadiene rubber polymer prepared by polymerizing <NUM> wt% of styrene and <NUM> wt% of <NUM>,<NUM>-butadiene, chemical resistance and gamma radiation resistance were substantially degraded compared to those of Examples <NUM> to <NUM>.

In the case of Comparative Example <NUM> which used a styrene/butadiene rubber polymer prepared by polymerizing <NUM> wt% of styrene and <NUM> wt% of <NUM>,<NUM>-butadiene, transparency and impact resistance were substantially degraded compared to those of Examples <NUM> to <NUM>.

Meanwhile, in the case of Comparative Example <NUM> in which the weight-average molecular weight of a thermoplastic resin composition was <NUM>,<NUM>/mol, molding was not performed during injection processing due to the excessively high weight-average molecular weight. Therefore, the evaluation of physical properties was not possible.

In the case of Comparative Example <NUM> which used a butadiene rubber polymer having an average particle diameter of <NUM>, transparency was substantially degraded.

In the case of Comparative Example <NUM> which used a styrene/butadiene rubber polymer having an average particle diameter of <NUM>, impact resistance was substantially degraded.

In the case of Comparative Examples <NUM> and <NUM> in which the weight-average molecular weight of a thermoplastic resin composition was <NUM>,<NUM>/mol, chemical resistance was substantially degraded.

In the case of Comparative Example <NUM> in which the weight ratio of a (meth)acrylate-based monomer unit to a second styrene-based monomer unit was about <NUM>, transparency, chemical resistance, and gamma radiation resistance were substantially degraded.

Claim 1:
A thermoplastic resin composition comprising:
a graft copolymer including a rubber polymer including a first styrene-based monomer unit and a diene-based monomer unit in a weight ratio of <NUM>:<NUM> to <NUM>:<NUM> and having an average particle diameter, as measured by dynamic light scattering as disclosed in the specification, of <NUM> to <NUM>,
a (meth)acrylate-based monomer unit grafted onto the rubber polymer,
a second styrene-based monomer unit grafted onto the rubber polymer; and
a non-grafted copolymer including a (meth)acrylate-based monomer unit and a second styrene-based monomer unit,
wherein the weight ratio of the (meth)acrylate-based monomer unit to the second styrene-based monomer unit is <NUM> or less, and
a weight-average molecular weight of the thermoplastic resin composition, as measured as disclosed in the specification, ranges from <NUM>,<NUM> to <NUM>,<NUM>/mol.