Styrene-based thermoplastic elastomer compositions, articles containing the same, and medical dispensing plugs

Abstract

The present invention provides a styrene-based thermoplastic elastomer composition with excellent leakage resistance, and a medical injection stopper using the same. [Solution] A styrene-based thermoplastic elastomer composition comprising (a) 72-95% by mass of a styrene-based hydrogenated block copolymer and (b) 28-5% by mass of a polypropylene-based polymer (where the sum of (a) styrene-based hydrogenated block copolymer and (b) polypropylene-based polymer is 100% by mass), wherein (a) styrene-based hydrogenated block copolymer has one or more peaks in the ranges of molecular weight 220,000-330,000 and molecular weight 80,000-190,000, respectively.

Description

Technical Field

[0001] The present invention relates to a styrenic thermoplastic elastomer composition. More specifically, it relates to a styrenic thermoplastic elastomer composition that can be suitably used as a material for medical infusion stoppers, articles using the same, and medical infusion stoppers.

Background Art

[0002] For rubber compositions for manufacturing medical rubber stoppers, compositions mainly composed of various synthetic rubbers are used. Among these, butyl rubber has been put into practical use as a material suitable for rubber stoppers because of its high gas barrier properties against gases such as oxygen and water vapor. Among medical rubber stoppers, medical infusion stoppers can easily handle liquid substances, and thus are widely used in, for example, blood transfusion bags, infusion containers, chemical solution containers, blood circuits for hemodialysis, and peritoneal dialysis solution bags.

[0003] Medical infusion stoppers are required to have performance such as liquid leakage resistance, puncture resistance, and resealability. However, medical infusion stoppers made of vulcanized rubber such as the above-mentioned butyl rubber have problems such as elution of sulfur compounds and amine compounds in the rubber component, and the man-hours required for the vulcanization process. Therefore, it has been proposed to use a thermoplastic elastomer composition instead of conventional vulcanized rubber as a material for medical infusion stoppers (for example, Patent Documents 1, 2, etc.).

[0004] For example, in Patent Document 1, it has been reported that by using a styrenic thermoplastic elastomer such as styrene - ethylene - propylene - styrene copolymer (SEPS), styrene - ethylene - ethylene - propylene - styrene copolymer (SEEPS), etc. having a weight average molecular weight of 150,000 to 350,000, liquid leakage prevention and permanent strain resistance (compression set resistance) against heat compression are improved.

[0005] Furthermore, Patent Document 2 proposes that by using a styrene-based thermoplastic elastomer such as a styrene-isoprene-butadiene-styrene hydrogenated block copolymer, which has at least one of two peaks and peak shoulders in the range of 250,000 to 350,000 and the range of 100,000 to 150,000, a medical rubber stopper with excellent needle-stick properties and good leak-proof sealing and sterilization stability can be realized. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-019750 [Patent Document 2] Japanese Patent Publication No. 2012-025944 [Overview of the project] [Problems that the invention aims to solve]

[0007] As mentioned above, various styrene-based thermoplastic elastomers suitable for use as medical injection stoppers have been proposed, but there was still room for improvement in terms of leak resistance. In particular, liquid sometimes seeped out from the gap between the needle and the injection stopper when the needle was inserted into it, so improvement in leak resistance was needed.

[0008] Therefore, the object of the present invention is to provide a styrene-based thermoplastic elastomer composition with excellent resistance to liquid leakage, and a medical injection stopper using the same. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have found that the above problems can be solved by a specific thermoplastic elastomer composition.

[0010] In other words, the embodiments of the present invention are as follows. [1] (a) Styrene-based hydrogenated block copolymer 72-95% by mass; and (b) Polypropylene polymer 28-5% by mass; (Here, the sum of (a) styrene-based hydrogenated block copolymer and (b) polypropylene-based polymer is 100% by mass.) A styrene-based thermoplastic elastomer composition containing, The (a) styrene-based hydrogenated block copolymer is Molecular weights of 220,000 to 330,000, and Molecular weight: 80,000-190,000 A styrene-based thermoplastic elastomer composition having one or more peaks in each of the following ranges. [2] The (a) styrene-based hydrogenated block copolymer is Molecular weight is 20,000 to 40,000 The styrene-based thermoplastic elastomer composition according to [1], further having one or more peaks in the range. [3] The (a) styrene-based hydrogenated block copolymer is (a-1) A styrene-based hydrogenated block copolymer having one or more peaks in the molecular weight range of 220,000 to 330,000 and in the molecular weight range of 20,000 to 40,000, (a-2) A styrene-based hydrogenated block copolymer having one or more peaks in the molecular weight range of 80,000 to 190,000, A styrene-based thermoplastic elastomer composition according to [2], comprising: [4] The styrene-based thermoplastic elastomer composition according to [3], wherein the (a-2) styrene-based hydrogenated block copolymer is contained in a proportion of 12 to 65% by mass with respect to the total amount of the (a-1) styrene-based hydrogenated block copolymer and the (a-2) styrene-based hydrogenated block copolymer. [5] (c) The styrene-based thermoplastic elastomer composition according to [1], further comprising a hydrogenated petroleum resin. [6] (d) The styrene-based thermoplastic elastomer according to [1], further comprising a non-aromatic rubber softener. [7] (e) The styrene-based thermoplastic elastomer according to [1], further comprising a silicone compound. [8] An article containing the styrenic thermoplastic elastomer composition according to any one of [1] to [7]. [9] A medical infusion stopper made of the styrenic thermoplastic elastomer composition according to any one of [1] to [7].

Advantages of the Invention

[0011] According to the present invention, a styrenic thermoplastic elastomer composition excellent in liquid leakage resistance can be provided. In particular, it is possible to suppress the leakage from the gap between the needle and the infusion stopper when the infusion stopper is punctured with a needle. Therefore, the styrenic thermoplastic elastomer composition of the present invention can be suitably used as a material for medical infusion stoppers. Further, since the styrenic thermoplastic elastomer composition of the present invention has excellent liquid leakage resistance characteristics, it can also be suitably used as a material for articles other than medical infusion stoppers, for example, articles such as prefilled syringe gaskets, connecting rubber tubes, packings, etc.

Brief Description of the Drawings

[0012] [Figure 1] It is a conceptual diagram for explaining a method of calculating the enthalpy of fusion from a second melting curve. [Figure 2] It is a conceptual diagram for explaining a liquid leakage resistance test.

Embodiments for Carrying Out the Invention

[0013] <​​​​​​​​In this specification, the term "greater than or equal to" in relation to a numerical range means a certain number or greater than a certain number. For example, "20% or more" means 20% or greater than 20%. The term "less than or equal to" in relation to a numerical range means a certain number or less than a certain number. For example, "20% or less" means 20% or less than 20%. The symbol "~" in relation to a numerical range means a certain number, greater than a certain number and less than another certain number, or another certain number. Here, the other certain number is a number greater than a certain number. For example, "10~90%" means 10%, greater than 10% and less than 90%, or 90%. Furthermore, the upper and lower limits of a numerical range can be combined arbitrarily, and embodiments with such arbitrary combinations should be discernible. For example, from descriptions relating to the numerical range of a certain characteristic, such as "usually 10% or more, preferably 20% or more. On the other hand, usually 40% or less, preferably 30% or less," or "usually 10-40%, preferably 20-30%," it can be inferred that, in one embodiment, the numerical range of that characteristic is 10-40%, 20-30%, 10-30%, or 20-40%.

[0016] Except in the examples, or unless otherwise specified, all numerical values ​​used herein and in the claims should be understood to be modified by the term “approximately.” Without attempting to limit the application of the doctrine of equivalents to the claims, each numerical value should be interpreted in terms of significant figures and by applying common rounding methods.

[0017] [Styrene-based thermoplastic elastomer composition] The styrene-based thermoplastic elastomer composition of the present invention comprises (a) 72 to 95% by mass of a styrene-based hydrogenated block copolymer and (b) 28 to 5% by mass of a polypropylene polymer. Here, the sum of (a) the styrene-based hydrogenated block copolymer and (b) the polypropylene polymer is 100% by mass. In one embodiment, the styrene-based thermoplastic elastomer composition of the present invention may further contain (c) a hydrogenated petroleum resin, (d) a non-aromatic rubber softener, and (e) a silicone compound. The components constituting the styrene-based thermoplastic elastomer composition of the present invention will be described below.

[0018] (a) Styrene-based hydrogenated block copolymer The styrene-based thermoplastic elastomer composition of the present invention comprises (a) a styrene-based hydrogenated block copolymer. (a) The styrene-based hydrogenated block copolymer is obtained by hydrogenating a block copolymer of styrene units and a conjugated diene compound. (a) Examples of styrene-based hydrogenated block copolymers include block copolymers having structures such as ABA, BABA, and ABABA.

[0019] Examples of styrene units include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylstyrene, N,N-diethyl-p-aminoethylstyrene, vinyltoluene, and p-tertiary butylstyrene, and one or more of these can be used in combination. Among these, styrene is preferred.

[0020] The styrene unit may be a polymer block consisting solely of styrene units, or a copolymer block of styrene units and a conjugated diene compound. When the polymer block is a copolymer block, the content of structural units derived from styrene units in the polymer block may, from the viewpoint of moldability, be 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more, with the total sum of all structural units constituting polymer block A being 100% by mass. The distribution of structural units derived from the conjugated diene compound in the polymer block is not particularly limited and is arbitrary. Furthermore, when there are two or more polymer blocks derived from styrene units, they may have the same structure or they may have different structures.

[0021] Conjugated diene compounds are polymerizable monomers having a structure in which two carbon-carbon double bonds are connected by one carbon-carbon single bond. Examples of conjugated dienes include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, and chloroprene (2-chloro-1,3-butadiene), and one or more of these can be used in combination. Among these, 1,3-butadiene and isoprene are preferred.

[0022] When the polymer block of a conjugated diene compound is a polymer block mainly composed of isoprene, examples include a homopolymer block of isoprene, a copolymer block of isoprene and a conjugated diene other than isoprene, a copolymer block of isoprene and styrene units, and a copolymer block of isoprene, a conjugated diene other than isoprene, and styrene units. When the polymer block is a copolymer block, the content of structural units derived from isoprene in the polymer block may be, from the viewpoint of resistance to liquid leakage, usually 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more, with the total sum of all structural units constituting the polymer block being 100% by mass. The distribution of structural units derived from monomers other than isoprene in the polymer block is not particularly limited. (a) In a styrene-based hydrogenated block copolymer, when there are two or more polymer blocks B, they may have the same structure or they may have different structures.

[0023] In the present invention, (a) the styrene-based hydrogenated block copolymer includes structural units having a 1,4-microstructure among the structural units derived from isoprene. Here, microstructure refers to which position of carbon in isoprene is bonded to an adjacent structural unit. The 1,4-microstructure is shown in formula (1) below.

[0024] [ka]

[0025] In the above equation (1), R 1 and R 2 ∫ means adjacent structural units. In the present invention, (a) the hydrogenated block copolymer contains structural units having the above 1,4-microstructure in a proportion of typically 70 to 100% by mass, preferably 80 to 100% by mass, with the total amount of structural units derived from isoprene being 100% by mass.

[0026] The above characteristic (a2) is, 13From the spectrum measured using 1C-NMR, it can be calculated as the ratio of the sum of the signal intensity of saturated (hydrogenated) structural units derived from isoprene and having a 1,4-microstructure to the signal intensity of unsaturated (unhydrogenated) structural units derived from isoprene and having a 1,4-microstructure, relative to the signal intensity of all structural units derived from isoprene.

[0027] (a) The styrene-based hydrogenated block copolymer, from the viewpoint of miscibility and compatibility with (b) polypropylene polymers and other optional components described later, has its carbon-carbon double bonds, with the number of carbon-carbon double bonds before hydrogenation set at 100 mol%, typically 85 mol% or more, preferably 90 mol% or more, hydrogenated to become carbon-carbon single bonds. That is, the number of carbon-carbon double bonds remaining in (a) the styrene-based hydrogenated block copolymer is typically 15 mol% or less, preferably 10 mol% or less. The origin of the carbon-carbon double bonds in (a) the styrene-based hydrogenated block copolymer is not particularly limited, but is usually considered to originate from conjugated dienes such as isoprene. The above characteristics are 13 From spectra measured using 1C-NMR, the number of hydrogenated carbon-carbon single bonds (calculated from the signal intensity of saturated (hydrogenated) structural units derived from monomers containing all carbon-carbon double bonds) can be calculated as the ratio of the number of pre-hydrogenation carbon-carbon double bonds (calculated from the signal intensity of all pre-hydrogenation carbon-carbon double bonds) to the number of hydrogenated carbon-carbon single bonds (calculated from the signal intensity of saturated (hydrogenated) structural units derived from monomers containing all carbon-carbon double bonds).

[0028] (a) The content of structural units derived from styrene units in the styrene-based hydrogenated block copolymer is not particularly limited, but from the viewpoint of mechanical strength, it is preferably 5 to 60% by mass, more preferably 20 to 50% by mass, with the total sum of all structural units constituting the styrene-based hydrogenated block copolymer being 100% by mass.

[0029] (a) The styrene-based hydrogenated block copolymer has one or more peaks in the GPC differential curve (molecular weight distribution) measured by gel permeation chromatography (GPC method) in the ranges of molecular weight 220,000 to 330,000 and molecular weight 80,000 to 190,000. In the styrene-based thermoplastic elastomer composition of the present invention, by using a styrene-based hydrogenated block copolymer having two specific molecular weight peaks as described above, leakage can be suppressed, particularly leakage from the gap between the needle and the injection stopper when the needle is inserted into the injection stopper. The reason for this is not clear, but it is thought to be as follows. Specifically, when a needle is inserted into a stopper, a small gap is formed between the stopper and the needle due to the movement and vibration of the needle. The styrene-based hydrogenated block copolymer, which is a high molecular weight component with a molecular weight peak (Mp) of 220,000 to 330,000, exerts a force to push back the gap, while the styrene-based hydrogenated block copolymer, which is a low molecular weight component with a molecular weight peak (Mp) of 80,000 to 190,000, allows the resin to flexibly deform to fill the gap caused by the movement and vibration of the needle. As a result, it is thought that leakage will be less likely to occur even when a needle is inserted.

[0030] Furthermore, GPC differential curves can be measured under the following conditions. The system used is the LC-2000Plus high-performance liquid chromatography system from JASCO Corporation (a system including a degasser, PU-2080 liquid transfer pump, AS-2055 autosampler, CO-2065 column oven, and RI-2031 radioisotope detector). Two PLgel Mixed-D polystyrene-divinylbenzene copolymer columns from Agilent Technologies, Inc. are linked together and used as the column. Chloroform for high-performance liquid chromatography from Kanto Chemical Co., Ltd. is used as the mobile phase, and the procedure is performed under the following conditions: flow rate of 1.0 ml / min, column temperature of 40°C, sample concentration of 1 ml / ml, and sample injection volume of 100 microliters. The sample is prepared by adding 10 mg of the sample to 10 ml of chloroform used as the mobile phase, allowing it to stand at room temperature for dissolution, and then filtering it using a syringe filter "Captiva Econo Filter PTFE (trade name)" with a pore size of 0.45 μm from Agilent Technologies, Inc. Also, a calibration curve from the retention volume to the polystyrene-equivalent molecular weight can be created using commercially available standard polystyrene. It should be noted that appropriate selection should be made so that the measured values are interpolated in the calibration curve. In the examples described later, a standard polystyrene "EasiCal PS-1 (trade name)" from Agilent Technologies, Inc. (molecular weights of Plain Spatula A: 6870000, 841700, 152800, 28770, 2930; molecular weights of Hole-puncched Spatula B: 2348000, 327300, 74800, 10110, 580) was used. The analysis program can use "ChromNAV (trade name)" from JASCO Corporation. Regarding the theory of GPC and the actual measurement, reference can be made to reference books such as "Size Exclusion Chromatography, High Performance Liquid Chromatography of Polymers" published by Kyoritsu Shuppan Co., Ltd., author: Sadao Mori, first edition, first printing on December 10, 1991, and "Synthetic Polymer Chromatography" published by Ohmsha, Ltd., editors: Hajime Ohtani, Tatsuya Takasaki (the "崎" in Takasaki has "立" at the upper part), first edition, first printing on July 25, 2013.

[0031] In one embodiment of the present invention, (a) the styrene-based hydrogenated block copolymer preferably has one or more additional peaks in the molecular weight range of 20,000 to 40,000 in the molecular weight distribution. In addition to the above-mentioned molecular weight range, by being a styrene-based hydrogenated block copolymer with a molecular weight peak (Mp) in the range of 20,000 to 40,000, the liquid leakage property is further improved. That is, since the styrene-based hydrogenated block copolymer with a lower molecular weight component is included, the resin deforms more flexibly and adheres to the needle, and the gaps associated with the movement and vibration of the needle are filled, so it is considered that the effect of the liquid leakage property is exerted.

[0032] (a) The styrene-based hydrogenated block copolymer may be a bimodal styrene-based hydrogenated block copolymer having one or more peaks in the molecular weight range of 220,000 to 330,000 and one or more peaks in the molecular weight range of 80,000 to 190,000, or it may be a mixture of a styrene-based hydrogenated block copolymer having a peak in the molecular weight range of 220,000 to 330,000 and a styrene-based hydrogenated block copolymer having a peak in the molecular weight range of 80,000 to 190,000.

[0033] Furthermore, in one embodiment of the present invention, (a) the styrene-based hydrogenated block copolymer comprises (a-1) a styrene-based hydrogenated block copolymer having one or more peaks in the range of molecular weight 220,000 to 330,000 and molecular weight 20,000 to 40,000, and (a-2) a styrene-based hydrogenated block copolymer having one or more peaks in the range of molecular weight 80,000 to 190,000. In this case, the molecular weight distribution (ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) (Mw / Mn)) of (a) the styrene-based hydrogenated block copolymer is preferably 10 or less, more preferably 5 or less, even more preferably 2 or less, and may be 1 or more.

[0034] (a) When the styrene-based hydrogenated block copolymer is composed of (a-1) styrene-based hydrogenated block copolymer and (a-2) styrene-based hydrogenated block copolymer, from the viewpoint of resistance to liquid leakage, the (a-2) styrene-based hydrogenated block copolymer is preferably included in a proportion of 12 to 65% by mass, more preferably 15 to 45% by mass, and even more preferably 18 to 25% by mass, based on the total amount of (a-1) and (a-2).

[0035] The above-mentioned (a) styrene-based hydrogenated block copolymer used in the styrene-based thermoplastic elastomer composition of the present invention can be obtained, for example, by block polymerization in an inert solvent using a lithium catalyst or the like, as described in Japanese Patent Publication No. 40-23798. Hydrogenation of the block copolymer can be carried out in an inert solvent in the presence of a hydrogenation catalyst, as described in Japanese Patent Publication No. 42-8704, Japanese Patent Publication No. 43-6636, Japanese Unexamined Patent Publication No. 59-133203 and Japanese Unexamined Patent Publication No. 60-79005, etc. Styrene-based hydrogenated block copolymers having various molecular weight ranges as described above may be prepared by optimizing the manufacturing conditions, or they may be appropriately selected and used from commercially available (hydrogenated) block copolymers.

[0036] (b) Polypropylene polymers The styrene-based thermoplastic elastomer composition of the present invention comprises (b) a polypropylene polymer. (b) The polypropylene polymer is a polymer mainly comprising structural units derived from propylene. Here, "mainly comprising structural units derived from propylene" means that the content of structural units derived from propylene is usually 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and typically 75 to 100% by mass.

[0037] (b) Examples of polypropylene polymers include propylene homopolymers and copolymers of propylene with one or more α-olefins (e.g., ethylene, 1-butene, 1-hexene, and 1-octene) (including block copolymers and random copolymers).

[0038] (b) In one preferred embodiment, the polypropylene polymer may be a resin mixture comprising (b1) a polypropylene polymer having a melting enthalpy of 20 to 85 J / g as measured by a differential scanning calorimeter and a melting point of 130°C to 155°C, and (b2) a polypropylene polymer having a melting enthalpy of 85 J / g as measured by a differential scanning calorimeter and a melting point of 155°C.

[0039] In this specification, (b) the enthalpy of fusion measured by differential scanning calorimeter of polypropylene polymers is calculated from the second melting curve (the melting curve measured during the final heating process) measured using a differential scanning calorimeter (DSC measuring device) in accordance with JIS K7121-1987, with a program that involves holding at 230°C for 5 minutes, cooling to -10°C at 10°C / min, holding at -10°C for 5 minutes, and heating to 230°C at 10°C / min. The melting point of (b) the polypropylene polymer is the peak top temperature of the melting peak with the highest peak top height of the second melting curve measured in the same manner. As a DSC measuring device, for example, a Diamond DSC type differential scanning calorimeter from PerkinElmer Japan Co., Ltd. can be used. A conceptual diagram of the method for calculating the enthalpy of melting from the second melting curve is shown (Figure 1). When performing the calculation, note that the melting peak appearing in the second melting curve of polypropylene polymers usually has a long, gradual tail on the low-temperature side; and the baseline should be drawn so that the straight line extending the high-temperature baseline to the low-temperature side and the straight line extending the low-temperature baseline to the high-temperature side coincide, as shown in Figure 1 of JIS K7121-1987, 9. How to Read DTA or DSC Curves.

[0040] The enthalpy of melting of component (b1), as measured by differential scanning calorimeter, is typically 85 J / g or less from the viewpoint of flexibility. On the other hand, from the viewpoint of mechanical strength and miscibility with component (a), it is typically 20 J / g or more, preferably 30 J / g or more, more preferably 40 J / g or more, and even more preferably 50 J / g or more.

[0041] The melting point of component (b1), as measured by differential scanning calorimeter, is typically 130°C or higher, preferably 135°C or higher, from the viewpoint of leak resistance. On the other hand, from the viewpoint of leak resistance, it is typically 155°C or lower, preferably 150°C or lower.

[0042] Examples of component (b1) include block copolymers of propylene and α-olefins in which the crystalline component is a random copolymer of propylene and α-olefins; block copolymers of propylene and α-olefins in which the crystalline component is a low stereoregularity propylene homopolymer; and random copolymers of propylene and α-olefins.

[0043] Examples of α-olefins that may be included in component (b1) include ethylene, 1-butene, 1-hexene, 1-octene, 1-decene, and 1-dodecene. In addition, one or more of these can be used as the α-olefin.

[0044] From the viewpoint of flexibility, the content of amorphous components in component (b1) may be typically 30% by mass or more (70% by mass or less of crystalline components), preferably 40% by mass or more (60% by mass or less of crystalline components). On the other hand, from the viewpoint of mechanical strength, it may be typically 90% by mass or less (10% by mass or more of crystalline components), preferably 80% by mass or less (20% by mass or more of crystalline components).

[0045] In this specification, the content of crystalline and amorphous components in polypropylene polymers is measured by the following method. Specifically, 1 g of polypropylene polymer is dissolved in 300 ml of boiling (para)xylene at 140°C under stirring. After dissolution, the mixture is kept at 140°C for another hour while continuing to stir, and then cooled to 100°C over 30 minutes. Next, the mixture is rapidly cooled to 23°C in a rapid cooling oil bath under agitation, left for another 20 minutes, and then the precipitate is naturally filtered using filter paper. The precipitate is defined as the crystalline component of the polypropylene polymer, and its mass is measured. Next, the filtrate is evaporated to dryness using an evaporator, then dried under reduced pressure at 120°C for 2 hours, and finally allowed to cool to room temperature. The obtained dry material is defined as the amorphous component of the polypropylene polymer, and its mass is measured.

[0046] In terms of balancing formability and mechanical strength, component (b1) may have a melt mass flow rate of preferably 5 to 50 g / 10 min, more preferably 10 to 40 g / 10 min, measured at 230°C and 21.18 N according to ASTM D1238.

[0047] The enthalpy of fusion of component (b2), as measured by differential scanning calorimeter, is greater than 85 J / g, preferably 90 J / g or higher, from the viewpoint of leakage resistance. There is no particular upper limit to the enthalpy of fusion. However, since it is a polypropylene polymer, the highest enthalpy typically available is probably around 120 J / g.

[0048] The melting point of component (b2), as measured by differential scanning calorimeter, is greater than 155°C, preferably 160°C or higher, from the viewpoint of maintaining mechanical strength in high-temperature environments. There is no particular upper limit to the melting point. However, since it is a polypropylene polymer, the melting point of those that are usually available will be at most around 167°C.

[0049] Examples of component (b2) include highly stereoregular propylene homopolymers; random copolymers of propylene and α-olefins with a very small content of structural units derived from α-olefins; block copolymers of propylene and α-olefins in which the crystalline component is a highly stereoregular propylene homopolymer; and block copolymers of propylene and α-olefins in which the crystalline component is a random copolymer of propylene and α-olefins, and in which the content of structural units derived from α-olefins in the crystalline component is very small.

[0050] Examples of α-olefins that may be included in component (b2) include ethylene, 1-butene, 1-hexene, 1-octene, 1-decene, and 1-dodecene. One or more of these can be used as the α-olefin.

[0051] From the viewpoint of moldability, component (b2) may have a melt mass flow rate of preferably 5 to 80 g / 10 min, more preferably 10 to 65 g / 10 min, measured at 230°C and 21.18 N according to ASTM D1238.

[0052] (b) In embodiments in which a mixture of component (b1) and component (b2) is used as the polypropylene polymer, the mixing ratio of component (b1) and component (b2) may be, from the viewpoint of leakage resistance and flexibility, typically 5 to 95% by mass of component (b1) and 95 to 5% by mass of component (b2), preferably 10 to 90% by mass of component (b1) and 90 to 10% by mass of component (b2), more preferably 20 to 80% by mass of component (b1) and 80 to 20% by mass of component (b2). Here, the sum of component (b1) and component (b2) is 100% by mass.

[0053] The blending ratio of (a) styrene-based hydrogenated block copolymer and (b) polypropylene-based polymer in the thermoplastic resin is typically 72-95% by mass for component (a) and 28-5% by mass for component (b), preferably 78-90% by mass for component (a) and 22-10% by mass for component (b), from the viewpoint of leakage resistance and flexibility. Here, the total of component (a) and component (b) is 100% by mass.

[0054] (c) Hydrogenated petroleum resin The styrene-based thermoplastic elastomer composition of the present invention may further contain (c) hydrogenated petroleum resin. (c) Hydrogenated petroleum resin is an unsaturated hydrocarbon compound produced by the decomposition of naphtha, etc., or an unsaturated hydrocarbon compound such as terpenes contained in plant essential oils such as turpentine oil, and is a hydrogenated polymer of an unsaturated hydrocarbon compound with a large number of carbon atoms (usually about 4 to 20 carbon atoms). In other words, in this specification, (c) hydrogenated petroleum resin includes hydrogenated plant essential oil resins such as hydrogenated terpene resins.

[0055] (c) Unsaturated hydrocarbon compounds used as monomers for hydrogenated petroleum resins are typically aliphatic unsaturated hydrocarbon compounds and / or aromatic unsaturated hydrocarbon compounds.

[0056] Examples of aliphatic unsaturated hydrocarbon compounds include 1-butene, 2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene, 1-heptene, 2-heptene, 3-heptene, 1,3-pentadiene, cyclopentadiene (cyclopenta-1,3-diene), methylcyclopentadiene, ethylcyclopentadiene, 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), dicyclopentadiene (tricyclo[5.2.1.02,6]deca-3,8-diene), and one or more oligomers thereof.

[0057] Examples of aromatic unsaturated hydrocarbon compounds include styrene, α-methylstyrene, β-methylstyrene, 4-methylstyrene, vinylxylene, indene, methylindene, ethylindene, and one or more oligomers thereof.

[0058] As the unsaturated hydrocarbon compound, one or a mixture of two or more of these can be used.

[0059] Hydrogenation of polymers of unsaturated hydrocarbon compounds can be carried out by known methods, for example, by treatment with a hydrogenation catalyst in an inert solvent. (c) The hydrogenation rate of hydrogenated petroleum resin (the ratio of the number of carbon-carbon single bonds to the number of carbon-carbon double bonds in the petroleum resin before hydrogenation) is usually 80 mol% or more, preferably 90 mol% or more, and more preferably 95 mol% or more.

[0060] (c) The softening point of hydrogenated petroleum resin may be preferably 130°C or higher, more preferably 135°C or higher, from the viewpoint of suppressing bleeding during sterilization. On the other hand, from the viewpoint of melt-kneadability when manufacturing thermoplastic elastomer compositions, it may be preferably 300°C or lower, more preferably 200°C or lower. The softening point is measured according to JIS K2207-1996 6.4 Softening point test method (ring-ball method).

[0061] (c) The amount of hydrogenated petroleum resin added is usually 0.5 to 20 parts by mass, preferably 2 to 16 parts by mass, and more preferably 4 to 14 parts by mass, with the total amount of component (a) and component (b) being 100 parts by mass, from the viewpoint of flexibility and resistance to liquid leakage.

[0062] (d) Non-aromatic rubber softeners The styrene-based thermoplastic elastomer composition of the present invention may further contain (d) a non-aromatic rubber softener. (d) The non-aromatic rubber softener is a non-aromatic mineral oil (hydrocarbon compound derived from petroleum, etc.) or synthetic oil (synthetic hydrocarbon compound). The non-aromatic rubber softener is usually liquid, gel-like, or gum-like at room temperature. Here, "non-aromatic" means, in the case of mineral oil, that it is not classified as aromatic in the following classification (the number of aromatic carbon atoms is less than 30%). In the case of synthetic oil, it means that aromatic monomers are not used.

[0063] Mineral oils used as rubber softeners are mixtures of one or more of the following: paraffin chains, naphthenic rings, and aromatic rings. Those with 30-45% of the naphthenic ring carbons are called naphthenic, those with 30% or more of the aromatic carbons are called aromatic, and those that do not belong to either naphthenic or aromatic, and where the number of carbons in the paraffin chains accounts for 50% or more of the total carbons, are called paraffinic.

[0064] (d) Examples of non-aromatic rubber softeners include paraffinic mineral oils such as linear saturated hydrocarbons, branched saturated hydrocarbons, and derivatives thereof; naphthenic mineral oils; and synthetic oils such as hydrogenated polyisobutylene, polyisobutylene, and polybutene. Among these, paraffinic mineral oils are preferred from the viewpoint of compatibility, and paraffinic mineral oils with a small number of aromatic carbon atoms are more preferred. Also, from the viewpoint of ease of handling, those that are liquid at room temperature are preferred. (d) One or more of these can be used as non-aromatic rubber softeners.

[0065] (d) From the viewpoint of compatibility and ease of handling, the non-aromatic rubber softener may preferably have a dynamic viscosity of 20 to 1000 cSt at 37.8°C. Also from the viewpoint of ease of handling, the pour point may preferably be -10 to -15°C. Furthermore, from the viewpoint of safety, the flash point (COC) may preferably be 170 to 300°C.

[0066] (d) The amount of non-aromatic rubber softener added is usually 110 parts by mass or more, preferably 120 parts by mass or more, more preferably 125 parts by mass or more, and even more preferably 130 parts by mass or more, with the total amount of component (a) and component (b) being 100 parts by mass, from the viewpoint of leak resistance, flexibility, and miscibility with each component of the styrene-based thermoplastic elastomer composition. On the other hand, from the viewpoint of increasing leak resistance, flexibility, mechanical strength, and sliding properties, and maintaining good fitability of the injection stopper, it is usually 250 parts by mass or less, preferably 220 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 180 parts by mass or less.

[0067] (e) Silicone compounds The styrene-based thermoplastic elastomer composition of the present invention may further contain (e) a silicone compound. Examples of the silicone compound include polysiloxanes such as silicone oil and silicone gum (also called silicone rubber); a copolymer of siloxane and another monomer, or a silicone copolymer which is a reaction product obtained by bonding siloxane and another polymer; and so on. Polysiloxane is a polymer compound having a linear structure consisting of siloxane bonds, and among silicones, oily ones are called silicone oil, and rubbery ones are called silicone gum (or silicone rubber).

[0068] Examples of polysiloxanes include dimethylpolysiloxane, diphenylpolysiloxane, methylphenylpolysiloxane, and modified versions thereof. Examples of modified versions include vinyl-modified silicones in which some of the methyl or phenyl groups of the above polysiloxane are replaced with vinyl groups, hydrogen polysiloxanes replaced with hydrogen atoms, alkyl-modified silicones replaced with alkyl groups, higher fatty acid ester-modified silicones replaced with higher fatty acid ester groups, fluorine-modified silicones replaced with fluorine atoms or alkyl fluorides, polyether-modified silicones replaced with polyether groups, amino-modified silicones replaced with groups having amino groups, carbinol-modified silicones replaced with hydroxylalkyl groups, epoxy-modified silicones replaced with groups having oxirane rings, carboxy-modified silicones replaced with groups having carboxyl groups, and so on.

[0069] Among the above, silicone-modified polypropylene and silicone-modified polyethylene, which have silicone bonds introduced into polypropylene or polyethylene, can be preferably used. For example, these are available as the BY27 series silicone concentrate from DuPont-Toray Specialty Materials and GENIOPLAST PELLETS from Asahi Kasei Wacker Silicone Co., Ltd.

[0070] The (e) silicone compound used in the present invention preferably has a kinematic viscosity of 500,000 cSt or more at 25°C, and more preferably 1,000,000 cSt or more, from the viewpoint of both hardness and leak resistance. In this specification, kinematic viscosity refers to the value measured in accordance with JIS Z 8803:2011.

[0071] The (e) silicone compounds described above exhibit less change in kinematic viscosity with respect to temperature changes compared to petroleum-based oils, and their viscosity does not decrease even when the temperature is raised, making them difficult to disperse in other materials. From the viewpoint of uniformly dispersing high-viscosity silicone compounds, it is preferable to use a masterbatch that has been pre-mixed with other resins. There are no particular restrictions on the other resin when the (e) silicone compound is used as the masterbatch, but in the styrene-based thermoplastic elastomer composition of the present invention, polypropylene is preferred. There are no particular restrictions on the mixing ratio of the (e) silicone compound and the other resin (polypropylene) when using a masterbatch, but it is preferably in the range of 1:9 to 9:1 by mass, and more preferably 3:7 to 7:3. Examples include BY27-001 (a 50:50 composition of dimethyl silicone and polypropylene) manufactured by DuPont-Toray Specialty Materials, Ltd., and SB-001P (a 50:50 composition of high molecular weight silicone and polypropylene) manufactured by Riken Vitamin Co., Ltd.

[0072] (e) The amount of silicone compound to be blended is usually 0.5 parts by mass or more, preferably 1 part by mass or more, and more preferably 1.5 parts by mass or more, with the total amount of component (a) and component (b) being 100 parts by mass, from the viewpoint of leak resistance, flexibility, and miscibility with each component of the styrene-based thermoplastic elastomer composition. On the other hand, from the viewpoint of increasing leak resistance, flexibility, mechanical strength, and sliding properties, and maintaining good fit of the injection stopper, it is usually 5 parts by mass or less, preferably 4 parts by mass or less, and more preferably 3.5 parts by mass or less.

[0073] (f) Talc The styrene-based thermoplastic elastomer composition of the present invention preferably further comprises (f) talc. From the viewpoint of enabling its use as a material for medical injection plugs used in blood transfusion bags, infusion containers, drug solution containers, blood circuits for hemodialysis, and peritoneal dialysis fluid bags, (f) talc is preferably one that conforms to the standards stipulated in the Pharmaceutical Affairs Law. From the viewpoint of enabling its use as a material for injection plugs in food packaging, (f) talc is preferably one that conforms to the standards stipulated in the Food Sanitation Law.

[0074] (f) In accordance with JIS R1629:1997 for talc, the 50% diameter value (median diameter D50) in the volume-based integrated fraction of the particle size distribution measured by laser diffraction-scattering method may be 1 to 40 μm, preferably 2 to 30 μm, from the viewpoint of leakage resistance and dimensional stability.

[0075] (f) The amount of talc is not particularly limited as it is an optional component, but from the viewpoint of resistance to liquid leakage and dimensional stability, it is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more, with the total amount of component (a) and component (b) being 100 parts by mass. On the other hand, from the viewpoint of flexibility and mechanical strength, it is preferably 50 parts by mass or less, more preferably 35 parts by mass or less, even more preferably 20 parts by mass or less, and most preferably 15 parts by mass or less.

[0076] The 15-second hardness value of the styrene-based thermoplastic elastomer composition of the present invention, measured according to JIS K 6253:2012, is preferably 10 to 40, more preferably 15 to 35, from the viewpoint of leakage resistance.

[0077] The styrene-based thermoplastic elastomer composition of the present invention may optionally contain components other than components (a) and (b), and components (c) to (f), to the extent that they do not contradict the objectives of the present invention. For example, it may further contain optional components such as softeners or plasticizers, heat stabilizers, light stabilizers, ultraviolet absorbers, crystal nucleating agents, antiblocking agents, sealing agents, mold release agents (e.g., stearic acid and silicone oil), lubricants such as polyethylene wax, colorants, pigments, inorganic fillers other than component (f) (e.g., alumina, calcium carbonate, mica, valustonite, and clay), blowing agents (organic and inorganic), and flame retardants (e.g., hydrated metal compounds, red phosphorus, polyammonium phosphate, antimony compounds, and silicon). The amount of the optional component is not particularly limited as it is an optional component, but it may be 20 parts by mass or less, 10 parts by mass or less, 5 parts by mass or less, or about 0.1 to 5 parts by mass per 100 parts by mass of the resin component (components (a), (b), and (c)).

[0078] In one embodiment, the styrene-based thermoplastic elastomer composition of the present invention may not contain any resins other than components (a) to (c). In one embodiment, the styrene-based thermoplastic elastomer composition of the present invention may not contain any softeners or plasticizers other than component (d). In one embodiment, the styrene-based thermoplastic elastomer composition of the present invention may not contain any release agents or anti-blocking agents other than component (e). In one embodiment, the styrene-based thermoplastic elastomer composition of the present invention may not contain inorganic fillers other than component (f). In one embodiment, the styrene-based thermoplastic elastomer composition of the present invention may not contain any one or more substances selected from the following: resins other than components (a) to (c), softeners or plasticizers other than components (d) and (e), heat stabilizers, light stabilizers, ultraviolet absorbers, nucleating agents, antiblocking agents, sealing agents, mold release agents (e.g., stearic acid), lubricants such as polyethylene wax, colorants, pigments, inorganic fillers other than component (f) (e.g., alumina, calcium carbonate, mica, valustonite, and clay), blowing agents (organic and inorganic), and flame retardants (e.g., hydrated metal compounds, red phosphorus, ammonium polyphosphate, antimony compounds, and silicon).

[0079] [Method for producing styrene-based thermoplastic elastomer compositions] The styrene-based thermoplastic elastomer composition of the present invention can be obtained by adding components (a) and (b), and any optional components to be used as desired, simultaneously or in any order, and then melt-kneading them using any melt-kneader at a temperature of typically 120 to 240°C, preferably 140 to 200°C.

[0080] Examples of melting and mixing machines include batch mixers such as pressure kneaders and mixers; extrusion mixers such as single-screw extruders, co-rotating twin-screw extruders, and opposite-rotating twin-screw extruders; and calender roll mixers. These may be used in any combination.

[0081] The resulting resin composition can be pelletized by any method and then molded into any article by any method. Pelletization can be carried out by methods such as hot cutting, strand cutting, and underwater cutting. Examples of molding methods include injection molding, extrusion molding, and blow molding.

[0082] [Goods] The articles of the present invention include the styrene-based thermoplastic elastomer composition of the present invention. Examples of articles of the present invention include medical injection plugs, and transfusion bags, infusion containers, drug containers, blood circuits for hemodialysis, and peritoneal dialysis fluid bags containing the medical injection plugs; food packaging injection plugs, and food packaging containers and bags containing the food packaging injection plugs; and further, injection plugs other than medical injection plugs and food packaging injection plugs, containers containing the injection plugs, pre-filled syringe gaskets, connecting rubber tubes, and packings. [Examples]

[0083] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0084] <Evaluation Test Method> (1) Leakage resistance 1 Using the styrene-based thermoplastic elastomer composition described later, a cylindrical test specimen with a diameter of 22 mm and a height of 5.6 mm was prepared by injection molding at a temperature of 220°C and an injection pressure of 150 MPa. Next, 500 ml of distilled water was placed inside a polypropylene fitting unit with a volume of 1000 ml, an inner diameter of 18 mm at the opening, and a neck length of 8 mm, where the inner diameter of the neck portion was constant. The test specimen and the fitting unit were then secured together with tape to prevent water leakage (see Figure 2). Subsequently, a 3.6 mm diameter plastic needle (JY-ND323L (product name) from JMS Co., Ltd.) was inserted into the test specimen, and the fitting unit with the test specimen attached was inverted. It was then left in this state at a temperature of 23°C and a relative humidity of 50% for 2 hours. After that, the plastic needle was removed, and a visual inspection was performed for 1 minute to determine whether or not water leakage occurred from the test specimen. The same test was repeated 5 times, and the number of times no water leakage occurred was recorded. Furthermore, the amount of water leaked was calculated by taking the average amount per leak from the total amount leaked over all five leaks (by dividing by the natural number 5).

[0085] (2) Leakage resistance 2 The procedure was the same as in Test (2) Leakage Resistance 1 described above, except that after inserting the needle into the test specimen, it was left in an environment of 23°C and 50% relative humidity for 24 hours before being removed.

[0086] The styrene-based thermoplastic elastomer composition of the present invention may preferably have no water leakage in the above test (1) Leakage Resistance 1 for 4 or 5 times, more preferably 5 times. The amount of water leakage may preferably be less than 0.2 g, more preferably 0 g (no water leakage). Furthermore, the styrene-based thermoplastic elastomer composition of the present invention may preferably have no water leakage in the above test (2) Leakage Resistance 2 for 4 or 5 times, more preferably 5 times. The amount of water leakage may preferably be less than 2.0 g, more preferably less than 0.2 g.

[0087] (3) Hardness Using the styrene-based thermoplastic elastomer composition described later, a 6.3 mm thick press sheet was prepared and used as a test specimen. In accordance with JIS K 6253:2012, the 15-second hardness value of a Type A durometer was measured using the above test specimen. The preferred hardness range is 20 to 35.

[0088] (4) MFR The styrene-based thermoplastic elastomer composition described below was used for measurement under conditions of 230°C and 10 kg, in accordance with JIS K 7112. The measurement results are shown in Table 3. The preferred MFR range is 1 to 30.

[0089] (5) Mechanical properties (tensile strength, 100% modulus, and tensile elongation) Using the styrene-based thermoplastic elastomer composition described later, a 1 mm thick press sheet conforming to JIS K 6251-2010 was prepared by extrusion molding. A No. 3 dumbbell punched out from the press sheet was used as a test specimen, and measurements were taken under conditions of a tensile speed of 500 mm / min. The measurement results are shown in Table 3. Furthermore, the preferred tensile strength is 3.0 MPa or higher, more preferably 5.0 MPa or higher; the preferred 100% modulus is 0.5 MPa, more preferably 1.0 MPa; and the preferred tensile elongation is 150% or higher, more preferably 200% or higher.

[0090] (6) Compression set (Compression set at room temperature and high temperature) Using the styrene-based thermoplastic elastomer composition described later, cylindrical press sheets with a thickness of 6.3 mm were prepared in accordance with JIS K 6262-2003 and used as test specimens. A compressive strain equivalent to 25% of the thickness was applied to the test specimens, and they were held at 23°C for 22 hours. After releasing the strain, the compression set rate (%) was measured after 1 hour. In addition, after holding at 70°C for 22 hours and releasing the strain, the compression set rate (%) was measured after 1 hour. The measurement results are shown in Table 3. Furthermore, the preferred range of compression set after holding at 23°C for 22 hours is 20% or less, more preferably 15% or less. Also, the preferred range of compression set after holding at 70°C for 22 hours is 70% or less, more preferably 60% or less.

[0091] <Ingredients used> (a) Styrene-based hydrogenated block copolymer (a-1-1) Styrene-butadiene-styrene hydrogenated block copolymer (styrene content: 32% by mass) "TAIPOL-6151 (product name)" from Taiwan Synthetic Rubber Co., Ltd. (TSRC), peak value of molecular weight distribution: 260,000). (a-1-2) Styrene-ethylene-ethylene-propylene-styrene hydrogenated block copolymer (styrene content 30% by mass) "SEPTON 4055 (product name)" manufactured by Kuraray Co., Ltd., with peak molecular weight distribution values ​​of 28,000 and 280,000).

[0092] (a-2-1) Styrene-ethylene-ethylene-propylene-styrene hydrogenated block copolymer (styrene content 30% by mass) "SEPTON 4033 (product name)" manufactured by Kuraray Co., Ltd., with a peak molecular weight distribution of 90,000). (a-2-2) Styrene-ethylene / butylene-styrene hydrogenated block copolymer (styrene content 32% by mass) "SEPTON 4044 (product name)" manufactured by Kuraray Co., Ltd., peak value of molecular weight distribution 173,000).

[0093] (b) Polypropylene polymers (b-1) Propylene homopolymer "J106MG (product name)" from Prime Polymer Co., Ltd.

[0094] (c) Hydrogenated petroleum resin: (c-1) Hydrogenated petroleum resin "iMarp P-140 (product name)" from Idemitsu Kosan Co., Ltd. Softening point 140℃.

[0095] (d) Non-aromatic rubber softeners: (d-1) Diana Process Oil PW-380 (product name), a linear saturated hydrocarbon paraffin oil from Idemitsu Kosan Co., Ltd. Dynamic viscosity at 37.8°C: 380 cSt; pour point: -15°C; flash point: 300°C.

[0096] (e) Silicone compounds (e-1) DuPont-Toray Specialty Materials' silicone masterbatch "BY27-001 (product name)" (a 50:50 (mass ratio) composition of dimethyl silicone and polypropylene with a kinematic viscosity of 1 million cSt or more at 25°C).

[0097] (f) Talc: (f-1) Talc "Crown Talc JS (product name)" from Matsumura Sangyo Co., Ltd. The median diameter D50 is 10 μm.

[0098] <Examples 1-18> The formulations shown in Table 1 were melt-kneaded using a co-rotating twin-screw extruder with an L / D ratio of 57 and a cylinder diameter of 45 mm, under conditions of a die outlet resin temperature of 200°C and a screw rotation speed of 200 rpm, to obtain styrene-based thermoplastic elastomer compositions. Each of the obtained styrene-based thermoplastic elastomer compositions was subjected to the evaluation tests (1) to (3) described above. The evaluation results are shown in Tables 1 and 2.

[0099] [Table 1]

[0100] [Table 2]

[0101] As is clear from Tables 1 and 2, in styrene-based thermoplastic elastomer compositions (Examples 1 to 16) in which two styrene-based hydrogenated block copolymers with molecular weight peaks within a specific range are used as component (a), and the blending ratio of component (a) to component (b) is within a specific range, the leakability is significantly improved. Furthermore, it can be seen that the hardness is within a desirable range. In contrast, even when two styrene-based hydrogenated block copolymers with molecular weight peaks within a specific range are used in combination as component (a), and even when the proportion of component (a) is too low in the styrene-based thermoplastic elastomer composition (Example 17), or conversely, when the proportion of component (a) is too high in the styrene-based thermoplastic elastomer composition (Example 18), no improvement in leakability is observed. Furthermore, the hardness also falls outside the desirable range.

[0102] Of the styrene-based thermoplastic elastomer compositions of Examples 1 to 16, which showed improvement in leak resistance, the styrene-based thermoplastic elastomer compositions of Examples 1 to 11 were subjected to the evaluation tests (4) to (6) described above. The evaluation results are shown in Table 3.

[0103] [Table 3]

[0104] As is clear from Table 3, styrene-based thermoplastic elastomer compositions (Examples 1 to 11) that use two styrene-based hydrogenated block copolymers with molecular weight peaks within a specific range as component (a), and in which the blending ratio of component (a) to component (b) is within a specific range, show significantly improved leak resistance and good hardness, as well as satisfying the various properties required when used as a material for medical injection stoppers.

Claims

1. (a) Styrene-based hydrogenated block copolymer 72 to 95% by mass; and (b) Polypropylene polymer 28-5% by mass; (Here, the sum of (a) styrene-based hydrogenated block copolymer and (b) polypropylene-based polymer is 100% by mass.) A styrene-based thermoplastic elastomer composition containing, The (a) styrene-based hydrogenated block copolymer is Molecular weight is 220,000 to 330,000, and Molecular weight: 80,000 to 190,000 A styrene-based thermoplastic elastomer composition having one or more peaks in each of the following ranges.

2. The (a) styrene-based hydrogenated block copolymer is Molecular weight is 20,000 to 40,000 The styrene-based thermoplastic elastomer composition according to claim 1, further having one or more peaks in the range.

3. The (a) styrene-based hydrogenated block copolymer is (a-1) A styrene-based hydrogenated block copolymer having one or more peaks in the range of molecular weight 220,000 to 330,000 and molecular weight 20,000 to 40,000, (a-2) A styrene-based hydrogenated block copolymer having one or more peaks in the molecular weight range of 80,000 to 190,000, A styrene-based thermoplastic elastomer composition according to claim 2, comprising:

4. The styrene-based thermoplastic elastomer composition according to claim 3, wherein the (a-2) styrene-based hydrogenated block copolymer is contained in a proportion of 12 to 65% by mass relative to the total amount of the (a-1) styrene-based hydrogenated block copolymer and the (a-2) styrene-based hydrogenated block copolymer.

5. (c) The styrene-based thermoplastic elastomer composition according to claim 1, further comprising a hydrogenated petroleum resin.

6. (d) The styrene-based thermoplastic elastomer according to claim 1, further comprising a non-aromatic rubber softener.

7. (e) The styrene-based thermoplastic elastomer according to claim 1, further comprising a silicone compound.

8. An article comprising the styrene-based thermoplastic elastomer composition according to any one of claims 1 to 7.

9. A medical dispensing stopper comprising the styrene-based thermoplastic elastomer composition according to any one of claims 1 to 7.

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