JP7673426B2 - Styrenic thermoplastic elastomer composition - Google Patents

Description

The present invention relates to a styrene-based thermoplastic elastomer composition. The present invention also relates to a molded article and a syringe gasket made of this styrene-based thermoplastic elastomer composition.

The medical devices "disposable syringes" and "prefilled syringes" consist of a cylindrical syringe, an injection needle or administration device attached to the tip of the syringe, and a sealing part called a gasket. These medical devices are used to administer the medicinal liquid or injection liquid filled in the syringe by pushing the gasket in and sliding it inside the syringe. The gasket is made of vulcanized rubber or a styrene-based thermoplastic elastomer.

Conventionally, various efforts have been made to smoothly press the gasket and slide it inside the syringe.
For example, Non-Patent Document 1 describes coating the inner surface of a syringe and the surface of a gasket with silicone oil.
Furthermore, Patent Document 1 describes a gasket resin composition that contains a hydrogenated derivative of a styrene-isoprene block copolymer and/or a hydrogenated derivative of a styrene-isoprene-butadiene block copolymer in a specific blend ratio to prevent the occurrence of the pulsation phenomenon, as well as a rubber softener and a polyethylene resin.

Development of a prefilled syringe suitable for biopharmaceuticals with consideration for suppressing aggregation and material design Science & Technology ISBN978-4-86428-201-7

JP 2004-123977 A

Prefilled syringes are easy to use and already contain the drug solution, eliminating the need to prepare the drug on-site. This not only prevents bacterial infection, but also has many other advantages, such as shortening dispensing time. As a result, there is a demand for prefilled versions of various drugs from the perspective of improving the efficiency of treatment and preventing medical errors.

In addition, the market size of biopharmaceuticals is expanding year by year, and there are an increasing number of cases where a biopharmaceutical liquid is filled into a syringe and supplied as a prefilled syringe (PFS) formulation. Compared to conventional low-molecular-weight pharmaceuticals, many biopharmaceuticals are physically and chemically unstable and easily deteriorated, and it is known that silicone oil applied to the inner surface of a syringe or the surface of a gasket causes the protein components, which are the main components of biopharmaceuticals in PFS, to aggregate. From the viewpoint of preventing the impact of protein component aggregation on the efficacy and safety of biopharmaceuticals, there is a demand for a gasket material that can be smoothly pressed and slid inside the syringe without applying silicone oil to the inner surface of the syringe or the surface of the syringe gasket as in Non-Patent Document 1, i.e., a gasket material with excellent sliding properties.

The sliding properties of a gasket material are determined mainly by the following three elements (1) to (3), and the desired sliding properties can be obtained by controlling these elements.
(1) The sliding resistance value is appropriate.
(2) Does not produce pulsation.
(3) The time it takes for the sliding resistance value to stabilize is appropriate.
However, the gasket resin composition of Patent Document 1, for example the gasket resin composition corresponding to Example 2 of Patent Document 1, leaves room for improvement in terms of sliding properties, as shown in Comparative Example 1 below.

In view of the above circumstances, the present invention aims to provide a styrene-based thermoplastic elastomer composition that can produce molded articles with excellent liquid leakage sealing properties and sliding properties.

As a result of intensive research aimed at solving the above problems, the present inventors have found that by using a styrene-based thermoplastic elastomer composition containing a styrene-based thermoplastic elastomer, an ethylene-based polymer, and a vinyl alcohol-based copolymer and having a Duro hardness A of 40 to 80, a molded article having excellent liquid leakage sealing properties and sliding properties can be obtained, and have arrived at the present invention.
That is, the present invention has the following features.

[1] A styrene-based thermoplastic elastomer composition comprising the following components (A) to (C) and having a durometer hardness A of 40 to 80:
Component (A): Styrene-based thermoplastic elastomer Component (B): Ethylene-based polymer Component (C): Vinyl alcohol-based polymer

[2] The styrene-based thermoplastic elastomer composition according to [1], in which the content of component (C) is 8 to 35 mass% in a total of 100 mass% of components (A) to (C).

[3] The styrene-based thermoplastic elastomer composition according to [1] or [2], wherein the density of the ethylene-based polymer of the component (B) is 0.900 to 0.980 g/ ^cm3 .

[4] A molded article made of the styrene-based thermoplastic elastomer composition described in any one of [1] to [3].

[5] A syringe gasket made of the styrene-based thermoplastic elastomer composition described in any one of [1] to [3].

According to the present invention, there is provided a styrene-based thermoplastic elastomer composition which can produce a molded article having excellent liquid leakage sealing properties and sliding properties.
By using a syringe gasket made of the styrene-based thermoplastic elastomer composition of the present invention, it is possible to provide medical syringes such as "prefilled syringes" and "disposable syringes" that are easy to handle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments.
The following description is an example of an embodiment of the present invention, and the present invention is not limited to the contents of the following description as long as it does not exceed the gist of the present invention. The present invention can be modified in any way as long as it does not deviate from the gist of the present invention.
In the present invention, when "~" is used to express a value with a numerical value or physical property value before and after it, the values before and after it are included in the expression.

[Styrene-based thermoplastic elastomer composition]
The styrene-based thermoplastic elastomer composition of the present invention is characterized by containing the following components (A) to (C) and having a durometer hardness A of 40 to 80. It is preferable that the styrene-based thermoplastic elastomer composition of the present invention further contains the following component (D) in addition to the following components (A) to (C).
Component (A): Styrene-based thermoplastic elastomer Component (B): Ethylene-based polymer Component (C): Vinyl alcohol-based polymer Component (D): Hydrocarbon-based rubber softener

<Duro hardness A>
The lower limit of the durometer hardness A of the styrene-based thermoplastic elastomer composition of the present invention is usually 40 or more, preferably 45 or more, from the viewpoint of the engagement force with a syringe plunger and the sliding resistance. The upper limit of the durometer hardness A of the styrene-based thermoplastic elastomer composition of the present invention is usually 80 or less, preferably 75 or less, from the viewpoint of the assembling property of a molded product.
Here, the Durohardness A of the styrene-based thermoplastic elastomer composition of the present invention is the ISO hardness based on ISO 7619-1 as described in the Examples section below.
In contrast, the JIS hardness is about 5 points higher than the ISO hardness even if the hardness is the same. Therefore, the ISO durometer hardness A of the styrene-based thermoplastic elastomer composition of the present invention is 45 to 85, preferably 50 to 80, when converted into the JIS hardness.

The durometer hardness A of the styrene-based thermoplastic elastomer composition can be adjusted by controlling the blending ratio of components (A) to (D), as described later.

<Component (A): Styrene-based thermoplastic elastomer>
The styrene-based thermoplastic elastomer composition of the present invention contains a styrene-based thermoplastic elastomer. As the styrene-based thermoplastic elastomer, a block copolymer selected from the group consisting of a block copolymer having at least one polymer block P derived from a vinyl aromatic compound and at least one polymer block Q derived from a conjugated diene, and a block copolymer obtained by hydrogenating the block copolymer (hydrogenated block copolymer) can be used.

Polymer block P is a polymer block of a monomer mainly composed of a vinyl aromatic compound, while polymer block Q is a polymer block of a monomer mainly composed of a conjugated diene. Here, "mainly composed" means that the content in the block is 50 mol % or more.

The vinyl aromatic compound monomer constituting the polymer block P is not limited, but styrene derivatives such as styrene, α-methylstyrene, and chloromethylstyrene are preferred. Of these, it is preferred to use styrene as the main component. These may be used alone or in combination of two or more. The polymer block P may contain monomers other than the vinyl aromatic compound as raw materials.

The monomers constituting the polymer block Q are not limited, but are preferably butadiene alone, isoprene alone, a mixture of butadiene and isoprene, etc. These may be used alone or in combination of two or more. Note that the polymer block Q may contain monomers other than butadiene and isoprene as raw materials.

Furthermore, the polymer block Q may be a hydrogenated derivative in which the double bonds contained therein are hydrogenated after polymerization, i.e., a hydrogenated block copolymer. The hydrogenation rate of the polymer block Q is not limited, but is preferably 50 to 100% by mass, and more preferably 80 to 100% by mass. By hydrogenating the polymer block Q within the above range, the thermal stability and weather resistance stability tend to be improved. The same applies to the case in which the polymer block P uses a diene component as a raw material. The hydrogenation rate can be measured by ¹³ C-NMR.

The styrene unit content of the styrene thermoplastic elastomer is preferably 8 to 45% by mass. When the styrene unit content of the styrene thermoplastic elastomer is equal to or higher than the lower limit, bleeding out of the hydrocarbon rubber softener from the styrene thermoplastic elastomer composition can be suppressed. On the other hand, when the styrene unit content is equal to or lower than the upper limit, the hardness of the styrene thermoplastic elastomer can be suppressed from becoming too high. The styrene unit content of the styrene thermoplastic elastomer is more preferably 10 to 40% by mass.
The term "styrene unit content" is used to mean not only the content of styrene units but also the content of structural units in which an atom or atomic group other than a hydrogen atom is substituted on the aromatic ring of a styrene unit. The styrene unit content can be measured by ¹³ C-NMR.

The chemical structure of the copolymer having the polymer block P and polymer block Q in the styrene-based thermoplastic elastomer may be linear, branched, radial, or the like, but is preferably a block copolymer represented by the following formula (1) or (2).

Furthermore, the block copolymer represented by the following formula (1) or (2) is preferably a hydrogenated derivative (hydrogenated block copolymer). When the copolymer represented by the following formula (1) or (2) is a hydrogenated block copolymer, the heat resistance and weather resistance tend to be good.
P-(Q-P) _m (1)
(P-Q) _n (2)
(In the formula, P represents a polymer block P, Q represents a polymer block Q, m represents an integer of 1 to 5, and n represents an integer of 1 to 5.)

In formula (1) or (2), the larger the m and n, the lower the order-disorder transition temperature of the rubber-like polymer, but the smaller the m and n, the lower the cost and ease of production.

As for block copolymers and/or hydrogenated block copolymers of styrene-based thermoplastic elastomers (hereinafter collectively referred to as "(hydrogenated) block copolymers"), the (hydrogenated) block copolymer represented by formula (1) is more preferable than the (hydrogenated) block copolymer represented by formula (2) because of its superior rubber elasticity.

The upper limit of the weight average molecular weight of the styrene-based thermoplastic elastomer is not limited, but is usually 700,000 or less, preferably 600,000 or less, and more preferably 500,000 or less. The lower limit of the weight average molecular weight of the styrene-based thermoplastic elastomer is not limited, but is usually 40,000 or more, preferably 60,000 or more, and more preferably 90,000 or more. By setting the weight average molecular weight of the styrene-based thermoplastic elastomer to the above upper limit or less, it is possible to maintain good moldability and the appearance of the molded product. In addition, by setting the weight average molecular weight to the above lower limit or more, it is possible to suppress bleeding out of the hydrocarbon-based rubber softener from the styrene-based thermoplastic elastomer composition, and to appropriately roughen the surface of the styrene-based thermoplastic elastomer composition molded product, thereby reducing the sliding resistance.

The weight average molecular weight of the styrene-based thermoplastic elastomer is a value calculated in terms of polystyrene measured by gel permeation chromatography (hereinafter sometimes abbreviated as GPC) under the following conditions.
<Gel permeation chromatography (GPC) measurement conditions>
Equipment: Tosoh Corporation HLC-8120
Column: TSKgel Super H1000+H2000+H3000 manufactured by Tosoh Corporation
Detector: Differential refractive index detector (RI/built-in)
Solvent: Tetrahydrofuran Temperature: 40°C
Flow rate: 0.5mL/min Injection volume: 10μL
Concentration: 0.2% by mass
Calibration sample: Monodisperse polystyrene Calibration method: Polystyrene equivalent

The method for producing a styrene-based thermoplastic elastomer is not particularly limited, and may be any method that can obtain the above-mentioned structure and physical properties. For example, it can be obtained by block polymerization in an inert solvent using a lithium catalyst or the like. In addition, the hydrogenation (hydrogenation) of the block copolymer can be performed in an inert solvent in the presence of a hydrogenation catalyst or other known methods.

Among those described above, the styrene-based thermoplastic elastomer is preferably a styrene-conjugated diene block copolymer and/or a hydrogenated product thereof, and more preferably a hydrogenated product of the styrene-conjugated diene block copolymer in which the conjugated diene is one or more selected from isoprene and butadiene. The styrene-conjugated diene block copolymer and/or a hydrogenated product thereof may have a polar group as required.
Examples of the styrene-conjugated diene block copolymer and/or hydrogenated product thereof include styrene-butadiene block copolymer and/or hydrogenated product thereof, styrene-butadiene-styrene block copolymer and hydrogenated product thereof, styrene-isoprene block copolymer and/or hydrogenated product thereof, styrene-isoprene-styrene block copolymer and/or hydrogenated product thereof, styrene-butadiene-isoprene block copolymer and/or hydrogenated product thereof, styrene-isoprene-butadiene-styrene block copolymer and/or hydrogenated product thereof, styrene-isoprene-butadiene-styrene block copolymer and/or hydrogenated product thereof, and hydrogenated product thereof.

Examples of hydrogenated styrene-butadiene block copolymers include styrene-butadiene-butylene copolymers (SBB), styrene-ethylene-butylene copolymers (SEB), and styrene-ethylene-butylene copolymers (SEB).
An example of the hydrogenated styrene-butadiene-styrene block copolymer is styrene-ethylene-butylene-styrene copolymer (SEBS).
Examples of hydrogenated styrene-isoprene-styrene block copolymers include styrene-ethylene-propylene-styrene copolymer (SEPS).
An example of a hydrogenated product of a styrene-isoprene-butadiene-styrene block copolymer is a styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS).

Among these, from the viewpoint of tensile strength and compression set, styrene-ethylene-butylene-styrene copolymer (SEBS), which is a hydrogenated product of styrene-butadiene-styrene block copolymer, styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS), which is a hydrogenated product of styrene-isoprene-butadiene-styrene block copolymer, and styrene-ethylene-propylene-styrene copolymer (SEPS), which is a hydrogenated product of styrene-isoprene-styrene block copolymer, are preferred. These may be fully hydrogenated or partially hydrogenated.

As the styrene-based thermoplastic elastomer, commercially available products can be used. Examples of commercially available products include the "Kraton (registered trademark)" G series manufactured by Kraton Polymer Japan Co., Ltd., the "TAIPOL (registered trademark)" and "VECTOR (registered trademark)" series manufactured by TSRC, and the "Septon (registered trademark)" series manufactured by Kuraray Co., Ltd.

A single type of styrene-based thermoplastic elastomer may be used, or two or more types with different physical properties, block structures, hydrogenation, etc. may be mixed and used.

<Component (B): Ethylene-Based Polymer>
The styrene-based thermoplastic elastomer composition of the present invention contains an ethylene-based polymer as component (B). By blending component (B) in the styrene-based thermoplastic elastomer composition, the sliding resistance can be controlled to be low.

The ethylene polymer may be any known polymer, and may be a homopolymer of ethylene or a copolymer of ethylene with an α-olefin or other monomer.

Specific examples of ethylene-based polymers include low-density polyethylene (LDPE), high-density polyethylene (HDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE), and ethylene-propylene copolymers.

The ethylene polymer contained in the styrene-based thermoplastic elastomer composition of the present invention preferably has a density of 0.900 to 0.980 g/ ^cm3 as measured according to JIS K7112, from the viewpoint of achieving both liquid leakage sealing properties and sliding properties. The lower limit of the density of the ethylene polymer is more preferably 0.940 g/ ^cm3 or more. Meanwhile, the upper limit is more preferably 0.970 g/ ^cm3 or less.
It is believed that by setting the density of the ethylene polymer contained in the styrenic thermoplastic elastomer composition of the present invention within the above range, it is possible to provide a styrenic thermoplastic elastomer composition that is less likely to deform after high-pressure steam sterilization, is less likely to leak liquid, and has low sliding resistance.

The melt flow rate (MFR) of the ethylene polymer is preferably 1.0 g/10 min or more, more preferably 2.0 g/10 min or more, and is preferably 100 g/10 min or less, more preferably 80 g/10 min or less. When the MFR of the ethylene polymer is within the above range, the compression set, sliding resistance, and appearance after high-pressure steam sterilization of a molded article made of the styrene-based thermoplastic elastomer composition of the present invention tend to be excellent.
Here, the MFR of the ethylene polymer is a value measured according to JIS K7210-1 or JIS K6922-2 under conditions of a temperature of 190° C., a load of 21.2 N, and a time of 10 minutes.

Ethylene-based polymers are available as commercial products. Commercially available products include the "Novatec (registered trademark)" series manufactured by Japan Polyethylene Corporation, the "Creolex (registered trademark)" series manufactured by Asahi Kasei Corporation, and the "Yumerit series" manufactured by Ube Maruzen Polyethylene Co., Ltd., and can be appropriately selected and used.

Only one type of ethylene polymer may be used, or two or more types with different physical properties, copolymer component compositions, structures, etc. may be mixed and used.

<Component (C): Vinyl Alcohol Polymer>
As the vinyl alcohol-based polymer of component (C) contained in the styrene-based thermoplastic elastomer composition of the present invention, a vinyl alcohol-based copolymer which is a copolymer of vinyl alcohol with ethylene, butylene or other monomers can be suitably used, and an ethylene-vinyl alcohol-based copolymer is preferred.

Ethylene-vinyl alcohol copolymers are resins obtained by saponifying copolymers of ethylene and vinyl ester monomers (ethylene-vinyl ester copolymers), and are water-insoluble thermoplastic resins. Ethylene-vinyl alcohol copolymers are primarily composed of structural units derived from ethylene and vinyl alcohol structural units, and contain a small amount of vinyl ester structural units that remain unsaponified.

Specific examples of ethylene-vinyl alcohol copolymers include ethylene-vinyl alcohol copolymer resin (EVOH) and modified ethylene-vinyl alcohol resin.

The ethylene unit content of the ethylene-vinyl alcohol copolymer is preferably 10 to 70 mol%, more preferably 20 to 60 mol%, as measured based on ISO 14663.

From the viewpoints of heat resistance and sliding properties, the vinyl alcohol polymer such as an ethylene-vinyl alcohol copolymer preferably has a density measured by a dry density method at 23°C of 1.00 to 1.40 g/ ^cm3 , more preferably 1.10 to 1.30 g/ ^cm3 .

The melt flow rate (MFR) of the vinyl alcohol polymer such as an ethylene-vinyl alcohol copolymer is preferably 0.5 g/10 min or more, and more preferably 1.0 g/10 min or more, from the viewpoints of sliding resistance and appearance after high-pressure steam sterilization, and is preferably 50 g/10 min or less, and more preferably 30 g/10 min or less.
The MFR of the vinyl alcohol polymer is a value measured under conditions of a temperature of 210° C., a load of 21.2 N, and a time of 10 minutes.

The melting point of the vinyl alcohol polymer such as an ethylene-vinyl alcohol copolymer is preferably 80° C. or higher, more preferably 90° C. or higher, and even more preferably 120° C. or higher, from the viewpoint of the appearance after high-pressure steam sterilization. On the other hand, from the viewpoint of compatibility with components (A) and (B), the melting point of the vinyl alcohol polymer is preferably 220° C. or lower, and more preferably 210° C. or lower.
The melting point of the vinyl alcohol copolymer is a value measured by a DSC method at a temperature increase and decrease rate of 10° C./min.

The ethylene-vinyl alcohol copolymer used in the present invention may further contain structural units derived from the comonomers shown below, in addition to ethylene structural units and vinyl alcohol structural units (including unsaponified vinyl ester structural units). Examples of the comonomers include α-olefins such as propylene, isobutene, α-octene, α-dodecene, and α-octadecene; hydroxyl-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 3-buten-1,2-diol, and hydroxyl-containing α-olefin derivatives such as esters and acylations thereof; unsaturated carboxylic acids or salts thereof, partial alkyl esters, complete alkyl esters, nitriles, amides, or anhydrides; unsaturated sulfonic acids or salts thereof; vinyl silane compounds; vinyl chloride; and styrene.

Furthermore, ethylene-vinyl alcohol polymers that have been "post-modified" by urethanization, acetalization, cyanoethylation, oxyalkylenation, or the like can also be used.

Ethylene-vinyl alcohol copolymers are available as commercial products. Commercially available products include the "Soarnol (registered trademark)" series and "Soaresin (registered trademark)" series manufactured by Mitsubishi Chemical Corporation, and "Eval (registered trademark)" manufactured by Kuraray Co., Ltd., and can be appropriately selected and used.

The vinyl alcohol polymer may be used alone or in combination of two or more kinds having different physical properties, copolymer component compositions, structures, etc.
For example, the ethylene-vinyl alcohol copolymer used in the present invention may be a mixture of two or more different ethylene-vinyl alcohol copolymers, in which case the mixture may be one having a different ethylene content, a different degree of saponification, a different melt flow rate (MFR) (210°C, load 21.2N), different other copolymerization components, or a different degree of modification (for example, one having a different content of 1,2-diol structural units).

In the styrene-based thermoplastic elastomer composition of the present invention, the vinyl alcohol-based polymer of component (C) is preferably contained in an amount of 8 to 35 mass % when the total amount of components (A) to (C) is taken as 100 mass % from the viewpoints of sliding resistance and sheet appearance after high-pressure steam sterilization. From the viewpoint of sliding resistance, a larger amount of component (C) is desirable, while a smaller amount of component (C) is desirable from the viewpoint of appearance after high-pressure steam sterilization.

<Component (D): Hydrocarbon-based rubber softener>
The styrene-based thermoplastic elastomer composition according to a preferred embodiment of the present invention preferably contains, in addition to the above-mentioned components (A) to (C), a hydrocarbon-based rubber softener as component (D).

As the hydrocarbon-based rubber softener of component (D), a process oil such as a hydrocarbon-based oil is used. As the hydrocarbon-based oil, a process oil such as a paraffin-based or naphthene-based oil is used. Of these, a paraffin-based process oil is preferred because it effectively softens the styrene-based thermoplastic elastomer composition of the present invention.

As the hydrocarbon rubber softener of component (D), a commercially available product can be used. Examples of commercially available products include the "Nippon Oil Polybutene (registered trademark)" HV series manufactured by JX Nippon Oil & Energy Corporation, the "Diana (registered trademark) Process Oil" PW series manufactured by Idemitsu Kosan Co., Ltd., and the "Lucant (registered trademark)" series manufactured by Mitsui Chemicals, Inc., and any of these can be appropriately selected and used.

The hydrocarbon-based rubber softener of component (D) may be used alone or in a mixture of two or more types.

<Component content>
The styrene-based thermoplastic elastomer composition according to a preferred embodiment of the present invention contains component (D) in addition to components (A) to (C).
When the styrene-based thermoplastic elastomer composition of the present invention contains component (D), the content of component (A) is preferably 10 to 50 mass%, and more preferably 26 to 38 mass%, when the total amount of components (A) to (D) is taken as 100 mass%. The content of component (B) is preferably 10 to 25 mass%. The content of component (C) is preferably 5 to 20 mass%. The content of component (D) is preferably 5 to 50 mass%.
Furthermore, the content of component (A) is preferably 35 to 65% by mass when the total amount of components (A) and (D) is taken as 100% by mass.

Although components (A), (B), and (D) are non-polar, component (C) is a polar resin. Therefore, by adding component (C) in an amount within the above-mentioned preferred range, desired properties can be obtained without impairing the strength of the styrene-based thermoplastic elastomer composition.
By setting the contents of components (A), (B), (C), and (D) within the above ranges, it is easy to obtain good flexibility, compression set, sliding resistance, and sheet appearance after high-pressure steam sterilization.

Regarding durometer hardness A, which particularly affects flexibility, by setting the combined content of components (B) and (C) in the range of 15 to 38 mass% when the combined amount of components (A) to (D) is taken as 100 mass%, durometer hardness A can be easily controlled in the range of 40 to 80.

The total content of components (A) to (C) in the thermoplastic elastomer composition is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more.
When component (D) is further used, the total content of components (A) to (D) in the thermoplastic elastomer composition is preferably 75 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more.

<Other ingredients>
The styrene-based thermoplastic elastomer composition according to a preferred embodiment of the present invention may contain components other than the above components (A) to (D) as necessary, provided that the object of the present invention is not impaired.

Other components that may be contained in the styrene-based thermoplastic elastomer composition of the preferred embodiment of the present invention include various fillers such as talc and calcium carbonate, various antiblocking agents, heat stabilizers, antioxidants, lubricants, crystal nucleating agents, colorants, resins other than components (A), (B), and (C), etc.

Preferred examples of the antioxidant include phenol-based antioxidants such as pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and 4,4',4"-[(2,4,6-trimethyl-1,3,5-benzenetriyl)tris(methylene)]tris[2,6-bis(1,1-dimethylethyl)phenol, phosphorus-based processing stabilizers such as tris(2,4-di-t-butylphenyl)phosphite, and hydroxylamine-based processing heat stabilizers such as oxidation products of alkylamines made from reduced beef tallow. When an antioxidant is used, the amount of the antioxidant is preferably 0.01 to 1.0 part by mass, more preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of component (A).

Examples of resins other than components (A), (B), and (C) that may be contained in the styrene-based thermoplastic elastomer composition of the preferred embodiment of the present invention include polyolefin resins other than components (B) and (C), polyester resins, polyamide resins, acrylic resins, polycarbonate resins, polyvinyl chloride resins, polyphenylene ether resins, polystyrene resins, liquid crystal resins, various elastomers (excluding those corresponding to component (A)), etc. The above-mentioned other resins may be contained alone or in combination of two or more.

When the styrene-based thermoplastic elastomer composition of the preferred embodiment of the present invention contains other resins besides components (A) to (C), in order to fully obtain the effects of containing components (A) to (C), the content of the other resins is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the total of components (A) to (D).

<Method of producing thermoplastic elastomer composition>
The styrene-based thermoplastic elastomer composition according to a preferred embodiment of the present invention is obtained as a solid material such as pellets by mechanically mixing the above-mentioned components (A) to (C), the component (D) which is blended as necessary, and other components by a known method, for example, a Henschel mixer, a V blender, or a tumbler blender, mechanically melt-kneading the mixture by a known method, and extruding the mixture through a die. For the mechanical melt-kneading, a general melt-kneading machine such as a Banbury mixer, various kneaders, or a single-screw or twin-screw extruder can be used.

[Application]
According to the styrene-based thermoplastic elastomer composition of the present invention, a molded article having excellent liquid leakage sealing property and sliding property can be obtained. The molded article made of the styrene-based thermoplastic elastomer composition of the present invention is particularly suitable for use as a sealing part (syringe gasket) called a gasket for a medical syringe, which is a medical instrument.

In this case, the material of the cylindrical syringe is often polypropylene, cyclic olefin polymer (COP), cyclic olefin copolymer (COC), or glass, but other materials may also be used. The styrene-based thermoplastic elastomer composition of the present invention exhibits excellent sliding properties even without applying silicone oil to the inner surface of the syringe or the surface of the gasket, but an appropriate amount of silicone oil may be applied to the inner surface of the syringe or the surface of the gasket.

The styrene-based thermoplastic elastomer composition of the present invention is suitably used for medical syringes, either "disposable syringes" or "prefilled syringes."
Methods for sterilizing medical syringes include high-pressure steam sterilization, ethylene oxide gas sterilization, electron beam sterilization, and gamma ray sterilization, and the styrene-based thermoplastic elastomer composition of the present invention can be suitably applied to any of these sterilization methods.
Since heat resistance is most required for high-pressure steam sterilization, in the examples described later, the applicability to high-pressure steam sterilization was evaluated based on the appearance of the sheet after high-pressure steam sterilization.

The styrene-based thermoplastic elastomer composition of the present invention can be used in gaskets that require excellent leak-tightness and sliding properties, such as medical syringe gaskets, but its uses are not limited to medical syringes. For example, it can also be suitably used in non-medical syringes, droppers, water jugs, bottle pumps, syringe-type feeders, gaskets for water guns, gaskets for cooking utensils, exterior moldings for automobiles, window wipers for automobiles, etc.

The contents of the container sealed with a gasket made of the styrene-based thermoplastic elastomer composition of the present invention may be liquid, powder, solid, gel-like substance, gas, etc., but the styrene-based thermoplastic elastomer composition of the present invention is particularly suitable for medical syringes filled with medicines.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples as long as it does not exceed the gist of the invention. The various manufacturing conditions and evaluation result values in the following examples are meant as preferred upper or lower limit values in the embodiments of the present invention, and the preferred range may be a range defined by a combination of the above-mentioned upper or lower limit values and the values of the following examples or values between the examples.

[raw materials]
The raw materials used in the following Examples and Comparative Examples are shown below.

Component (A): Styrene-based thermoplastic elastomer A-1: Styrene-ethylene-propylene-styrene copolymer (SEPS)
Septon (registered trademark) 2005, manufactured by Kuraray Co., Ltd.
Styrene unit content: 20% by mass
Weight average molecular weight (Mw): 295,000
A-2: Styrene-ethylene-propylene-styrene copolymer (SEPS)
Septon (registered trademark) 2006, manufactured by Kuraray Co., Ltd.
Styrene unit content: 35% by mass
Weight average molecular weight (Mw): 276,000
A-3: Styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS)
Septon (registered trademark) 4077, manufactured by Kuraray Co., Ltd.
Styrene unit content: 30% by mass
Weight average molecular weight (Mw): 381,000
A-4: Styrene-ethylene-butylene-styrene copolymer (SEBS)
Kraton Corporation: Product name: Kraton (registered trademark) G1651HU
Styrene unit content: 33% by mass
Weight average molecular weight (Mw): 264,000

Component (B): Ethylene-based polymer B-1: High-density polyethylene manufactured by Asahi Kasei Corporation, product name Creolex (registered trademark) T701A
MFR: 12g/10min (Measurement conditions: 190°C, load 21.2N (JIS K7210-1))
Density: 0.966g/ ^cm3
B-2: High density polyethylene manufactured by Japan Polyethylene Corporation, product name Novatec HD (registered trademark) HJ492
MFR: 20g/10min (Measurement conditions: 190°C, load 21.2N (JIS K6922-2))
Density: 0.958g/ ^cm3
B-3: High density polyethylene manufactured by Japan Polyethylene Corporation, product name Novatec HD (registered trademark) HM160
MFR: 5 g/10 min (measurement conditions: 190°C, load 21.2 N (JIS K6922-2))
Density: 0.953g/ ^cm3
B-4: Low-density polyethylene, manufactured by Japan Polyethylene Corporation, product name Novatec LD (registered trademark) LC607K
MFR: 8.0 g/10 min (measurement conditions: 190°C, load 21.2 N (JIS K6922-2))
Density: 0.919g/ ^cm3

Component (C): Vinyl alcohol polymer C-1: Ethylene-vinyl alcohol copolymer resin (EVOH)
Manufactured by Mitsubishi Chemical Corporation Product name: Soarnol (registered trademark) H4815B
Ethylene unit content: 48 mol%
MFR: 15g/10min (measurement conditions: 210°C, load 21.2N)
Density: 1.12g/ ^cm3
Melting point: 158°C
C-2: Ethylene-vinyl alcohol copolymer resin (EVOH)
Manufactured by Mitsubishi Chemical Corporation, product name: Soarnol (registered trademark) A4412B
Ethylene unit content: 44 mol%
MFR: 12g/10min (measurement conditions: 210°C, load 21.2N)
Density: 1.14g/ ^cm3
Melting point: 164°C
C-3: Modified ethylene vinyl alcohol resin, manufactured by Mitsubishi Chemical Corporation, product name Soaresin (registered trademark) SG931
MFR: 15g/10min (measurement conditions: 210°C, load 21.2N)
Density: 1.14g/ ^cm3
Melting point: 95°C

Component (D): Hydrocarbon-based rubber softener (hydrocarbon-based oil)
D: Product name: Diana Process Oil (registered trademark) PW90 manufactured by Idemitsu Kosan Co., Ltd.

Component (E): Polypropylene-based polymer (for comparison)
E: Product name: Novatec PP (registered trademark) FA3KM, manufactured by Japan Polypropylene Corporation
MFR: 10g/10min (Measurement conditions: 230℃, load 21.2N (JIS K7210))
Density: 0.900g/ ^cm3

[Examples 1 to 15 and Comparative Examples 1 to 7]
<Preparation of pellets made of styrene-based thermoplastic elastomer composition>
The raw materials of Examples 1 to 15 and Comparative Examples 1 to 5 shown in Tables 1 and 2 were mixed in the amounts (parts by mass) listed.
100 parts by mass of the obtained mixture and 0.1 part by mass of tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane (Irganox (registered trademark) 1010 manufactured by BASF Japan Ltd.) were fed into a co-rotating twin-screw extruder ("TEM26-SS" manufactured by Toshiba Machine Co., Ltd., cylinder diameter opening 26 mm) at a rate of 20 kg/hour, melt-kneaded at 200°C, extruded from a die in the form of strands, and then cut to obtain pellets consisting of a styrene-based thermoplastic elastomer composition.
In Comparative Examples 6 and 7, purchased pellets of Components C-1 and C-2 were used to prepare the following sheets.

<Preparation of styrene-based thermoplastic elastomer composition sheet>
The obtained pellets were fed into an in-line screw type injection molding machine (IS130GN manufactured by Toshiba Machine Co., Ltd.) and injection molded under conditions of an injection pressure of 50 MPa, a cylinder temperature of 220°C, and a mold temperature of 40°C to obtain a sheet of the styrene-based thermoplastic elastomer composition having a thickness of 2 mm.
Using this styrene-based thermoplastic elastomer composition sheet, the performance of the syringe gasket was evaluated for the following evaluation items (1) to (4). The evaluation results are shown in Tables 1 and 2.

(1) Flexibility (Durohardness A, Durohardness D)
The durometer hardness A (type A durometer) was measured based on ISO 7619-1, or the durometer hardness D (type D durometer) was measured based on ISO 868-2003.

(2) Compression set Compression set (CS) was measured according to ISO 815-1. For use as a syringe gasket, the compression set is preferably 60% or less.

(3) Sliding resistance <Preparation of polypropylene sheet>
Assuming a syringe cylinder, Novatec PP (registered trademark) FA3KM manufactured by Nippon Polypropylene was fed into an in-line screw type injection molding machine (IS130GN manufactured by Toshiba Machine Co., Ltd.) and injection molded under conditions of an injection pressure of 50 MPa, a cylinder temperature of 220°C, and a mold temperature of 40°C to obtain a polypropylene sheet with a thickness of 2 mm.
<Measurement of sliding resistance>
The styrene-based thermoplastic elastomer composition sheet was pulled by a tensile tester while the corners of the styrene-based thermoplastic elastomer composition sheet were abutted against the polypropylene sheet at an angle of 60° using a tool, and the maximum test force when the surface of the polypropylene sheet was aligned at a speed of 100 mm/min was measured. The measurement was performed four times. It is preferable that the average value of the four maximum test forces is 4.0 N or less.

(4) Appearance of Sheet after High Pressure Steam Sterilization A styrene-based thermoplastic elastomer composition sheet was placed in a high pressure steam sterilizer and subjected to high pressure steam sterilization at 121°C for 30 minutes. The appearance and dimensions of the sheet after sterilization were compared with those of the sheet before sterilization and evaluated according to the following criteria.
◎: No change 〇: Some change △: Change ×: Large change

[Discussion]
The following can be seen from Tables 1 and 2.
The sheets obtained from the styrene-based thermoplastic elastomer compositions of Examples 1 to 15 were favorable in the evaluation results of Durograde hardness A, compression set, sliding resistance value, and sheet appearance after high-pressure steam sterilization, and are suitable as syringe gasket moldings.
Comparative Example 1 did not contain component (C) and therefore had high sliding resistance.
Comparative Example 2 has a high durometer A of 85 and is therefore unsuitable for use as a gasket.
Comparative Example 3 had a low durometer A of 36, and therefore had high sliding resistance.
Comparative Examples 4 and 5 had high sliding resistance because the propylene polymer of component (E) was used instead of the ethylene polymer of component (B).
Comparative Examples 6 and 7 were prepared using the vinyl alcohol polymer (C) alone, and were unsuitable for use as a gasket due to their high hardness.

Claims (3)

A syringe gasket made of a styrene-based thermoplastic elastomer composition containing the following components (A) to (D), having a durometer hardness A of 40 to 80, and when the total amount of components (A) to (D) is taken as 100 mass%, the content of component (A) is 10 to 50 mass%, the content of component (B) is 10 to 25 mass%, the content of component (C) is 5 to 20 mass%, and the content of component (D) is 5 to 50 mass%.
Component (A): Styrene-based thermoplastic elastomer Component (B): Ethylene-based polymer selected from one or more of low-density polyethylene (LDPE), high-density polyethylene (HDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE), and ethylene-propylene copolymer Component (C): Vinyl alcohol-based polymer different from component (A) Component (D): Hydrocarbon-based rubber softener The syringe gasket according to claim 1, wherein the content of the component (C) in the styrene-based thermoplastic elastomer composition is 8 to 35 mass% in a total of 100 mass% of the components (A) to (C). The syringe gasket according to claim 1 or ² , wherein the density of the ethylene polymer of component (B) is 0.900 to 0.980 g/cm3.