Patent Application
20240240009
The present invention relates to a thermoplastic elastomer composition. The present invention also relates to a molded article made of the thermoplastic elastomer composition.
Thermoplastic elastomers are soft materials with rubber elasticity and have the same moldability and recyclability as thermoplastic resins. Thermoplastic elastomers are produced without a vulcanization process. Thermoplastic elastomers have been used in a wide variety of industrial fields such as automobile parts and medical parts in recent years. Among these, as medical parts need to be sanitary, thermoplastic elastomers that do not contain vulcanizing agents or vulcanization accelerators are widely used as substitutes for vulcanized rubber.
Certain types of thermoplastic elastomer compositions have been improved to have compression set equivalent to that of vulcanized rubber. Certain types of thermoplastic elastomer compositions have been improved in liquid-leakage sealing properties when used as plugs such as cap liners, packing, and rubber plugs. As one of such thermoplastic elastomer compositions, a thermoplastic elastomer composition has been proposed that uses a modified polypropylene-based resin having a specific structure and further contains a specific amount of a block copolymer and a hydrocarbon softener for rubber (see Patent Literature 1).
Furthermore, a thermoplastic elastomer using a styrene-based elastomer having multiple peaks or peak shoulders on the relatively low molecular weight side has been proposed (see Patent Literature 2) in which a molecular weight distribution of styrene-based elastomers is focused.
According to the inventor's detailed study, the thermoplastic elastomer composition described in above Patent Literature 1 still has insufficient compression set, as shown in Comparative Example 2 which will be described later and has not been reached the performance level required for conventional vulcanized rubber.
The thermoplastic elastomer composition described in above Patent Literature 2 also still has insufficient compression set, as shown in Comparative Examples 4 to 9 which will be described later and has not reached the performance level required for conventional vulcanized rubber.
An object of the present invention is to provide a thermoplastic elastomer composition that has both excellent compression set and moldability, and a molded article made of the thermoplastic elastomer composition.
The present inventors have discovered that a thermoplastic elastomer composition containing a styrene-based thermoplastic elastomer having a specific molecular weight distribution and a hydrocarbon group-grafted polypropylene can achieve both excellent compression set and moldability and solve the problems of the conventional technology.
The gist of the present invention resides in the following [1] to [12].
[1] A thermoplastic elastomer composition comprising the following component (A) and component (B).
The styrene-based thermoplastic elastomer has a peak top in the range of 360,000 or more and 600,000 or less in a differential molecular weight distribution diagram calculated in terms of styrene obtained by gel permeation chromatographic analysis of the styrene thermoplastic elastomer.
[2] The thermoplastic elastomer composition according to [1], wherein the component (A) is a styrene-based thermoplastic elastomer having the following molecular weight distribution.
The styrene-based thermoplastic elastomer has a peak top in the range of 400,000 or more and 600,000 or less in a differential molecular weight distribution diagram calculated in terms of styrene obtained by gel permeation chromatographic analysis of the styrene thermoplastic elastomer.
[3] The thermoplastic elastomer composition according to [2], wherein the component (A) is a styrene-based thermoplastic elastomer having the following molecular weight distribution.
The styrene-based thermoplastic elastomer has a peak Lp having a peak top in the range of 100,000 or more and 400,000 or less and a peak Hp having a peak top in the range more than 400,000 and 600,000 or less in a differential molecular weight distribution diagram calculated in terms of styrene obtained by gel permeation chromatographic analysis of the styrene thermoplastic elastomer.
[4] The thermoplastic elastomer composition according to any one of [1] to [3], further comprising the following component (C).
[5] The thermoplastic elastomer composition according to [4], wherein the content of the component (B) is 3% by mass or more and 30% by mass or less in a total of 100% by mass of the components (A), (B) and (C).
[6] The thermoplastic elastomer composition according to [4] or [5], wherein the content of the component (A) is 35% by mass or more and 65% by mass or less in a total of 100% by mass of the components (A) and (C).
[7] The thermoplastic elastomer composition according to any one of [1] to [6], having a compression set of 40% or less.
[8] The thermoplastic elastomer composition according to any one of [1] to [7], having a melt flow rate (230° C., load 5 kgf) of 0.5 g/10 minutes or more and 200 g/10 minutes or less.
[9] The thermoplastic elastomer composition according to any one of [1] to [8], having a Duro hardness A of 10 or more and 50 or less.
The thermoplastic elastomer composition according to any one of [1] to [9], further comprising the following component (D).
A molded article made of the thermoplastic elastomer composition according to any one of [1] to [10].
The molded article according to [11], wherein the molded article is a rubber stopper having a needle pricking part.
The thermoplastic elastomer composition of the present invention has both excellent compression set and moldability. Therefore, according to the thermoplastic elastomer composition of the present invention, a molded article having excellent compression set can be provided with good moldability.
The molded article of the present invention can be suitably used for rubber stoppers having a needle pricking part such as syringe gaskets, rubber stoppers for infusion bags and vial bottles, cap liners, packing, etc., which require liquid leak sealability.
Embodiments of the present invention will be described in detail below.
The following description is an example of the embodiment of the present invention, ant the present invention is not limited to the following description. The present invention can be modified and practiced in any manner that is consistent with the scope of the present invention.
In this specification, when numerical values or physical property values are expressed by using “to” with preceding and following numbers, it is to be understood that the preceding and following numbers are included.
The thermoplastic elastomer composition of the present invention is characterized by containing the following component (A) and component (B).
The styrene-based thermoplastic elastomer has a peak top in the range of 360,000 or more and 600,000 or less in a differential molecular weight distribution diagram calculated in terms of styrene obtained by gel permeation chromatographic analysis of the styrene thermoplastic elastomer.
The mechanism by which the thermoplastic elastomer composition of the present invention can achieve both excellent compression set and moldability is considered to be as follows.
It is considered that a styrene-based thermoplastic elastomer having the above-mentioned unique molecular weight distribution can achieve both high moldability and low compression set.
On the other hand, a hydrocarbon group-grafted polypropylene is considered to have a low compression set because the crystal lamellae of polypropylene become stronger and plastic deformation of the matrix is less likely to occur.
Furthermore, the coexistence of the component (A) and the component (B) strongly acts as a cohesive interaction between domains and between matrices, and the lamellar structure that is the crystalline component of the component (B) is more likely to be firmly maintained. This results in excellent compression set.
In particular, when the component (A) is a styrene-based thermoplastic elastomer having the peaks Lp and Hp as described below, the component present in the peak Lp of the component (A) is moderately entangled with the component present in the peak Hp, and the viscosity of the polymer chain derived from the peak Hp component easily decreases in the molten state. This results in high moldability.
In addition, in the non-molten state, the entanglement of the polymer chains of the domain is increased by the component present in the peak Hp of component (A), resulting in low compression set.
The styrene-based thermoplastic elastomer of the component (A) has a peak top in the range of 360,000 or more and 600,000 or less in the differential molecular weight distribution diagram calculated in terms of styrene obtained by gel permeation chromatographic analysis of the styrene thermoplastic elastomer. It is preferable to have a peak top in the range of more than 400,000 and 600,000 or less, and it is more preferable to have a peak Lp having a peak top in the range of 100,000 or more and 400,000 or less, and a peak Hp having a peak top in the range of more than 400,000 and 600,000 or less.
Here, the peaks Lp and Hp do not include shoulder peaks or subpeaks having an intensity of 0.1 or less with respect to dw/dlogM of the most intense (highest) peak.
The shoulder peak generally refers to a small peak that exists on the tailing or leading of the main peak. The shoulder peak can be separated in the differential molecular weight distribution diagram of styrene-based thermoplastic elastomers by the Gauss-Newton method as a peak with its shoulder portion at the top.
The molecular weight distribution (PDI), peak top molecular weight, its dw/dlogM, the mass average molecular weight (Mw), and number average molecular weight (Mn) of the styrene-based thermoplastic elastomer described below are determined by gel permeation chromatography (hereinafter referred to as GPC). They are a polystyrene equivalent values measured under the following conditions, and the analysis range is a molecular weight of 10,000 or more.
The styrene-based thermoplastic elastomer of the component (A) may be a single styrene-based thermoplastic elastomer having the above mentioned molecular weight distribution, or a styrene-based thermoplastic elastomer as the component (A) having the above mentioned molecular weight distribution by mixing and using a plurality of styrene-based thermoplastic elastomers having different molecular weight distributions. However, it is preferable to manufacture a thermoplastic elastomer composition by blending a single styrene-based thermoplastic elastomer having the above mentioned molecular weight distribution, especially a single styrene-based thermoplastic elastomer having the above peak Lp and peak Hp, with the component (B) and the component (C) which will be described later. That is, by blending this single styrene-based thermoplastic elastomer with the component (B) and the component (C), which will be described later, to manufacture a thermoplastic elastomer composition, the entanglement of the component present at the peak Lp and the component present at the peak Hp of the component (A) is promoted, and the compression set tends to improve.
It is more preferable that component (A) has a peak top of peak Lp in the range of 150,000 or more and 300,000 or less, and a peak top of peak Hp in the range of 450,000 or more and 550,000 or less.
The ratio of the peak top molecular weight of peak Hp to the peak top molecular weight of peak Lp (peak top molecular weight of peak Hp/peak top molecular weight of peak Lp) is preferably 1.5 or more and 4 or less and more preferably 2 or more and 3.5 or less from the viewpoint of moldability and compression set.
The styrene-based thermoplastic elastomer may have peaks other than peak Lp and peak Hp. In such case, the peak top height other than peak Lp and peak Hp is preferably equal to or less than the lower of the peak top heights of peak Lp and peak Hp, and more preferably equal to or less than ½.
As the styrene-based thermoplastic elastomer of the component (A), 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.
The polymer block P is a polymer block of a monomer mainly consisting of a vinyl aromatic compound. The polymer block Q is a polymer block of a monomer mainly consisting of a conjugated diene. Here, “mainly” means that the content ratio in the block is 50 mol % or more.
The vinyl aromatic compounds of the monomer comprising the polymeric block P are not limited, but styrene derivatives such as styrene, α-methylstyrene, and chloromethylstyrene are preferred. Among these, styrene is preferred as the main component. One of these may be used alone, or two or more can be used in combination. The polymer block P may contain monomers other than vinyl aromatic compounds as raw materials.
The monomers constituting the polymeric block Q are not limited, but butadiene alone, isoprene alone, or a mixture of butadiene and isoprene is preferred. One of these can be used alone, or two or more can be used in combination. The polymer block Q may contain monomers other than butadiene and isoprene as raw materials.
The polymer block Q may be a hydrogenated derivative obtained by hydrogenating the double bonds after polymerization, that is a hydrogenated block copolymer. The hydrogenation rate of the polymer block Q is not limited, but is preferably 50% or more and 100% or less by mass, and more preferably 80% or more and 100% or less by mass. By hydrogenating the polymer block Q within the above range, thermal stability and weathering stability tend to improve. The same applies to the case where the polymer block P uses a diene component as a raw material. The hydrogenation rate can be measured by 13C-NMR.
The styrene-based thermoplastic elastomer preferably has a styrene unit content of 8% or more and 45% or less by mass. When the styrene unit content of the styrene-based thermoplastic elastomer is at least the above lower limit, the bleeding out of the hydrocarbon softener for rubber from the thermoplastic elastomer composition can be suppressed. When the styrene unit content of the styrene-based thermoplastic elastomer is below the above upper limit, the hardness of the styrene-based thermoplastic elastomer can be prevented from becoming too high. The styrene unit content of the styrene-based thermoplastic elastomer is more preferably 10% or more and 40% or less by mass.
The term “styrene unit content” is used to include not only the content of styrene units, but also the content of component units in which atoms or atomic groups other than hydrogen atoms are substituted into the aromatic ring of the styrene unit. The styrene unit content can be measured by 13C-NMR.
The chemical structure of the copolymer having the polymer block P and the polymer block Q in the styrene-based thermoplastic elastomer may be linear, branched, radial, or the like. The styrene-based thermoplastic elastomer is preferably a block copolymer represented by the following formula (1) or (2).
Further, 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, heat resistance stability and weather resistance stability tend to be good.
(In the formula, P represents the polymer block P, and Q represents the polymer block Q. m represents an integer from 1 to 5. n represents an integer from 1 to 5.)
In the formula (1) or (2), m and n are preferably larger in terms of lowering the order-disorder transition temperature as a rubber-like polymer, but smaller in terms of ease of production and cost.
As block copolymer and/or hydrogenated block copolymer of styrene-based thermoplastic elastomer (hereinafter collectively referred to as “(hydrogenated) block copolymers”), the (hydrogenated) block copolymer represented by the formula (1) is more preferable than the (hydrogenated) block copolymer represented by the formula (2) because of its superior rubber elasticity.
The upper limit of the mass average molecular weight (Mw) of the styrene-based thermoplastic elastomer is not limited, but is usually 700,000 or less, preferably 600,000 or less, more preferably 500,000 or less. The lower limit of the mass average molecular weight (Mw) of styrene-based thermoplastic elastomers is not limited, but is usually 40,000 or more, preferably 60,000 or more, more preferably 100,000 or more. By controlling the mass average molecular weight of the styrene-based thermoplastic elastomer to be equal to or less than the above upper limit, moldability and appearance of the molded article can be maintained favorably. By controlling the mass average molecular weight of the styrene-based thermoplastic elastomer to be equal to or more than the above lower limit, it is possible to suppress bleeding out of the hydrocarbon softener for rubber from the thermoplastic elastomer composition and to reduce compression set.
The upper limit of the number average molecular weight (Mn) of the styrene-based thermoplastic elastomer is not limited, but is usually 600,000 or less, preferably 500,000 or less, and more preferably 400,000 or less. The lower limit of the number average molecular weight (Mn) of the styrene-based thermoplastic elastomer is not limited, but is usually 30,000 or more, preferably 50,000 or more, and more preferably 80,000 or more. By controlling the number average molecular weight of the styrene-based thermoplastic elastomer to be equal to or less than the above upper limit, moldability and appearance of the molded article can be maintained favorably. By controlling the number average molecular weight of the styrene-based thermoplastic elastomer to be equal to or more than the above lower limit, it is possible to suppress bleeding out of the hydrocarbon softener for rubber from the thermoplastic elastomer composition and to reduce compression set.
The method for producing the styrene-based thermoplastic elastomer is not particularly limited and may be any method as long as the above structure and physical properties can be obtained. For example, it can be obtained by block polymerization in an inert solvent using a lithium catalyst or the like. For the hydrogenation of the block copolymer, a known method such as hydrogenation in an inert solvent in the presence of a hydrogenation catalyst can be employed.
Among those described above, styrene-conjugated diene block copolymers and/or their hydrogenated products are preferred as styrene-based thermoplastic elastomers, and hydrogenated products in which the conjugated diene of the styrene-conjugated diene block copolymer is composed of one or more selected from isoprene and butadiene are suitable. The styrene-conjugated diene block copolymer and/or its hydrogenated product may have a polar group if necessary.
Examples of the styrene-conjugated diene block copolymer and/or its hydrogenated product include styrene-butadiene block copolymer and/or its hydrogenated product, styrene-butadiene-styrene block copolymer and/or its hydrogenated product, styrene-isoprene block copolymer and/or its hydrogenated product, styrene-isoprene-styrene block copolymer and/or its hydrogenated product, styrene-butadiene-isoprene block copolymer and/or its hydrogenated product, and styrene-isoprene-butadiene-styrene block copolymer and/or its hydrogenated product.
Examples of hydrogenated products of styrene-butadiene block copolymer include styrene-butadiene-butylene copolymer (SBB) and styrene-ethylene-butylene copolymer (SEB).
Examples of hydrogenated products of styrene-butadiene-styrene block copolymer include styrene-ethylene-butylene-styrene copolymers (SEBS).
Examples of hydrogenated products of styrene-isoprene-styrene block copolymer include styrene-ethylene-propylene-styrene copolymer (SEPS).
Examples of hydrogenated products of styrene-isoprene-butadiene-styrene block copolymer include styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS).
Among these, from the viewpoint of tensile strength and compression set, styrene-ethylene-butylene copolymer (SEB) which is a hydrogenated product of styrene-butadiene block copolymer, 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 completely hydrogenated or partially hydrogenated.
It is also possible to use a commercially available styrene-based thermoplastic elastomer. As a commercially available product, an appropriate product can be selected and used from the “Tuftec (registered trademark)” series manufactured by Asahi Kasei Corporation.
The styrene-based thermoplastic elastomer may be used alone or in combination of two or more different in physical properties, block structure, or hydrogenation or non-hydrogenation, etc.
The thermoplastic elastomer composition of the present invention contains polypropylene grafted with a hydrocarbon group as the component (B). Hydrocarbon group-grafted polypropylene is considered to provide a low compression set because the polypropylene crystal lamellae become strong, making plastic deformation of the matrix less likely to occur. Hydrocarbon group-grafted polypropylene is obtained by graft-modifying a propylene-based resin with a diene compound.
The propylene-based resin used as a raw material for the component (B) is specifically a propylene homopolymer or random copolymer, and examples thereof include crystalline polymers. As the propylene copolymer, one containing 75% by mass or more of propylene units is preferable because it maintains the characteristics of polypropylene, such as crystallinity, rigidity, and chemical resistance.
Monomers copolymerizable with propylene constituting the propylene copolymer used as a raw material for the component (B) include α-olefins having 2 or 4 to 12 carbon atoms such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene or the like; cyclic olefins such as cyclopentene, norbornene, and tetracyclo[6,2,11,8,13,6]-4-dodecene or the like; dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene or the like; vinyl monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methylstyrene, vinyltoluene, and divinylbenzene or the like. These compounds may be used alone or in combination of two or more. Among these, ethylene and 1-butene are preferred because they are inexpensive and easy to handle.
Only one type of raw material propylene-based resin may be used, or two or more types may be used.
Examples of diene compounds that can be used for graft modification of the above raw material propylene-based resin include conjugated diene compounds such as butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4-hexadiene or the like. These compounds may be used alone or in any combination and ratio of two or more. Among these, butadiene and isoprene are preferred, and isoprene is particularly preferred.
Any method may be used for modification to obtain component (B). For example, it can be produced by the method described in JP2015-98542 A. Other examples include a method of irradiating the polypropylene-based resin with radiation, or a method of melt-mixing a polypropylene-based resin, a diene compound, and a radical generator. Among these, a method of melt-mixing a polypropylene-based resin, a diene compound, and a radical generator is preferred because it does not require expensive apparatus and can produce modified polypropylene at low cost.
Apparatuses for reacting a propylene-based resin, a diene compound, and a radical generator include kneading apparatuses such as rolls, co-kneaders, Banbury mixers, Brabenders, extruders such as single-screw extruders, and twin-screw extruders; horizontal agitators such as twin-axis surface renewal devises, and two-axis multi-disc devices; and a vertical agitators such as double helical ribbon agitators or the like. Among these, it is preferable to use a kneading apparatus, and an extruder is particularly preferable from the viewpoint of productivity.
There are no particular restrictions on the order or method of mixing and kneading (stirring) the propylene-based resin, the diene compound, and the radical generator. After mixing the polypropylene-based resin, the diene compound, and the radical generator, the mixture may be melt-kneaded (stirred). After melt-kneading (stirring) the propylene-based resin, the diene compound or the radical generator may be mixed simultaneously or separately, all at once or in portions. The propylene-based resin and either the diene compound or the radical generator may be melt-kneaded (stirred), and then the other of the diene compound and the radical generator may be added and melt-kneaded (stirred).
The temperature of the kneader (stirrer) is preferably 130° C. or higher and 300° C. or lower because the propylene-based resin melts and does not thermally decompose. The kneading (stirring) time is generally preferably 1 minute of more and 60 minutes or less.
The shape and size of the hydrocarbon group-grafted polypropylene thus obtained are not limited, and may be in the form of pellets.
The blending ratio of the diene compound to the polypropylene-based resin is not particularly limited. The blending ratio of the diene compound to 100 parts by mass of the propylene-based resin is usually 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and usually 30 parts by mass or less, preferably 10 parts by mass or less, more preferably 5 parts by mass or less.
Together with the diene compound, one or more monomers copolymerizable with the diene compound, such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, acrylic acid metal salt, methacrylic acid metal salt, acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate or the like, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate or the like, may be used.
The radical generator is not particularly limited, but peroxides and azo compounds or the like can be used. Specific examples thereof include diacyl peroxides such as diperoxide and dilauroyl peroxide or the like, dialkyl peroxides such as dicumyl peroxide, tert-butylcumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, α,α′-bis(tert-butylperoxy-m-isopropyl)benzene, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane or the like, alkyl peroxy esters such as tert-butyl peroxybenzoate, tert-butyl peroxy isobutyrate, tert-butyl peroxy pivalate, and cumyl peroxy pivalate or the like, peroxy carbonates such as tert-butyl peroxy isopropyl carbonate, tert-butylperoxy 2-ethylhexyl carbonate, and tert-amylperoxyisopropyl carbonate or the like, peroxyketals such as 1,1-bis(tert-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl 4,4-bis(tert-butylperoxy)valerate, and 2,2-bis(tert-butylperoxy)butane or the like, azo compounds such as azobisisobutyronitrile, and dimethyl azoisobutyrate or the like.
These radical generators can be appropriately selected depending on the type and MFR of the raw material polypropylene-based resin, the type of the diene compound, and reaction conditions or the like. The radical generator may be used alone or in any combination and ratio of two or more.
The amount of the radical generator to be added is not particularly limited. The amount of the radical generator to be added is usually 0.001 pats by mass or more and 20 parts by mass or less, preferably 0.005 parts by mass or more and 10 parts by mass or less, more preferably 0.01 parts by mass or more and 5 parts by mass or less, and even more preferably 0.05 parts by mass or more and 4 parts by mass or less, with respect to 100 parts by mass of the polypropylene-based resin.
The melt flow rate (MFR) of the component (B) is preferably 1.0 g/10 minutes or more, more preferably 2.0 g/10 minutes or more, and preferably 200 g/10 minutes or less, more preferably 100 g/10 minutes or less. When the MFR of the component (B) is within the above range, a molded article made of the thermoplastic elastomer composition of the present invention tends to have excellent compression set and appearance.
The MFR of the component (B) is a value measured by method according to ISO 1133-1 (2011) or JIS K7210-1 under the conditions of temperature of 230° C., load of 2.16 kg, and 10 minutes.
The component (B) can be obtained as a commercial product. As a commercially available product, an appropriate one can be selected and used from the “PP processability improvement material” series manufactured by Kaneka Corporation and the “Waymax (registered trademark)” series manufactured by Japan Polypropylene Corporation, or the like.
Only one type of the component (B) may be used, or two or more types of components having different physical properties and structures or the like may be used as a mixture.
The thermoplastic elastomer composition of the present invention may contain a hydrocarbon softener for rubber as the component (C).
As the hydrocarbon softener for rubber as the component (C), process oil such as hydrocarbon oil is used. As the hydrocarbon oil, paraffinic, naphthenic, and other process oils are used. Among these, paraffinic process oil is preferred because it effectively softens the thermoplastic elastomer composition of the present invention.
A kinematic viscosity at 40° C. of the hydrocarbon softener for rubber is not particularly limited. The kinematic viscosity is preferably 20 centistokes or more and more preferably 50 centistokes or more from the viewpoint of hygiene of the eluted fine particles and bleed-out. The kinematic viscosity is preferably 800 centistokes or less and more preferably 600 centistokes or less from the viewpoint of moldability.
A flash point (COC method) of the hydrocarbon softener for rubber is preferably 200° C. or higher and more preferably 250° C. or higher.
It is also possible to use a commercially available product as the hydrocarbon softener for rubber as the component (C). Commercially available products include the “Nisseki Polybutene (registered trademark)” HV series manufactured by ENEOS 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. These can be appropriately selected and used.
The hydrocarbon softener for rubber of the component (C) may be used alone or in combination of two or more.
The thermoplastic elastomer composition of the present invention preferably contains the component (A), a styrene-based thermoplastic elastomer, as a main component. The term “main component” as used herein means that the proportion (mass) of the styrene-based thermoplastic elastomer in the entire composition is the largest.
From the viewpoint of rubber elasticity, the content of the component (A) in the thermoplastic elastomer composition of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more based on the total of 100% by mass of the component (A), the component (B), and the optionally used component (C). On the other hand, from the viewpoint of heat resistance, the content of the component (A) is preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 60% by mass or less.
The content of the component (B) is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more based on the total of 100% by mass of the component (A), the component (B), and the optionally used component (C). When it is above this lower limit, the effect of the diene compound used for graft modification of the component (B) is maximized, and low compression set tends to be easily obtained. On the other hand, the upper limit of the content of the component (B) is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. When it is less than this upper limit, the molded article becomes moderately soft, and therefore a low compression set tends to be easily obtained.
When the thermoplastic elastomer composition of the present invention contains the component (C), from the viewpoint of flexibility and moldability of the molded article, the content of the component (C) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more based on the total of 100% by mass of the components (A), (B) and (C). On the other hand, from the viewpoint of oil bleeding, the upper limit of the content of the component (C) is preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 60% by mass or less.
When the thermoplastic elastomer composition of the present invention contains the component (C), the content of the component (A) is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more based on the total of 100% by mass of the component (A) and the component (C) from the viewpoint of oil bleeding. On the other hand, from the viewpoint of fluidity, the content of the component (A) is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, and particularly preferably 65% by mass or less.
The thermoplastic elastomer composition of the present invention may contain a polyphenylene ether-based resin composition as the component (D).
The polyphenylene ether-based resin composition refers to one whose main component is polyphenylene ether-based resin. The term “main component” as used herein means that the proportion of the amount (mass) of the polyphenylene ether-based resin in the entire composition is the largest.
Known polyphenylene ether-based resins can be used as the polyphenylene ether-based resin contained in the polyphenylene ether-based resin composition. Specific examples include poly(2,6-dimethyl-1,4-phenylene ether), poly(2-methyl-6ethyl-1,4-phenylene ether), poly(2,6-diphenyl-1,4-phenylene ether), poly(2-methyl-6-phenyl-1,4-phenylene ether), and poly(2,6-dichloro-1,4-phenylene ether) or the like.
Polyphenylene ether-based resin compositions also include polyphenylene ether copolymers such as copolymers of 2,6-dimethylphenol and other phenols (for example, 2,3,6-trimethylphenol and 2-methyl-6-butylphenol), and polymer alloys with polystyrene.
Among them, poly(2,6-dimethyl-1,4-phenylene ether), and copolymer of 2,6-dimethylphenol and 2,3,6-trimethylphenol are preferred, and poly(2,6-dimethyl-1,4-phenylene ether) is particularly preferred.
From the viewpoint of compression set, the polyphenylene ether-based resin composition of the component (D) is preferably blended in an amount of 1 part by mass or more and 20 parts by mass or less based on the total of 100 parts by mass of the component (A), the component (B), and the optionally used component (C).
Commercially available products of the component (D) include, for example, “lupiace (registered trademark)” manufactured by Mitsubishi Engineering-Plastics Corporation and “Xyron (registered trademark)” manufactured by Asahi Kasei Corporation.
The thermoplastic elastomer composition of the preferred embodiment of the present invention may contain other components other than the above-mentioned components (A) to (D) as necessary, as long as the object of the present invention is not impaired.
Other components include various fillers such as talc and calcium carbonate, various antiblocking agents, heat stabilizers, antioxidants, lubricants, crystal nucleating agents, coloring agents, and resins other than the components (A), (B), and (D).
For examples of antioxidants, phenolic antioxidants such as tetrakis [3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionic acid]pentaerythritol and 4,4′,4″-[(2,4,6-trimethyl-1,3,5-benzentriyl)tris(methylene)]tris[2,6-bis(1,1-dimethylethyl)phenol, phosphorus processing stabilizers such as tris(2,4-di-t-butylphenyl) phosphite, and hydroxylamine processing heat stabilizers such as oxidation products of alkylamines made from reduced beef tallow are preferred.
When using an antioxidant, the blending amount is preferably 0.01% by mass or more and 1.0% by mass or less and more preferably 0.05% by mass or more and 0.5% by mass or less based on the total of 100% by mass of the component (A), the component (B), and the optionally used component (C).
Resins other than the components (A), (B), and (D) that may be contained in the thermoplastic elastomer composition of the preferred embodiment of the present invention include styrene-based elastomers other than the component (A), polyolefin resins other than the component (B), polyester resins, polyamide resins, acrylic resins, polycarbonate resins, polyvinyl chloride resins, polystyrene resins, liquid crystal resins, various elastomers (excluding those falling under the component (A)), and the like. The other resins mentioned above may contain only one type or two or more types.
When the thermoplastic elastomer composition of the preferred embodiment of the present invention contains resins other than the components (A), (B), and (D), in order to fully obtain the effect of containing the component (A), the component (B), and the optionally used component (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 based on a total of 100 parts by mass of the component (A), the component (B), and the optionally used component (C).
The thermoplastic elastomer composition of the preferred embodiment of the present invention can be obtained as a solid material such as a pellet by mechanically mixing the above-mentioned component (A), component (B) and the optionally used component (C), component (D), and other components using a known method such as a Henschel mixer, a V-blender, or a tumbler blender, and then mechanically melt-kneading by a known method and extruding through a die. For the mechanical melt-kneading, general melt-kneaders such as a Banbury mixer, various kneaders, and a single-screw or twin-screw extruder can be used.
The thermoplastic elastomer composition of the present invention has both excellent compression set and moldability by containing the component (A) and the component (B), and the optionally used component (C) and component (D). The thermoplastic elastomer composition of the present invention preferably has the following physical properties.
In the present invention, the melt flow rate (MFR) measured at 230° C. and a load of 2.16 kgf (21 N) or 5 kgf (49 N) with reference to ISO 1133-1 (2011) is used as an indicator of a moldability of the thermoplastic elastomer composition.
In order to obtain excellent moldability, it is preferable that the melt flow rate (5 kgf) of the thermoplastic elastomer composition of the present invention is 0.5 g/10 minutes or more and 200 g/10 minutes or less. When the MFR of the thermoplastic elastomer composition is 0.5 g/10 minutes or more, the fluidity tends to be good. It is preferable from the viewpoint of heat resistance that the MFR of the thermoplastic elastomer composition is 200 g/10 minutes or less. From the viewpoint of fluidity, the MFR of the thermoplastic elastomer composition is more preferably 1 g/10 minutes or more. From the viewpoint of heat resistance, the MFR of the thermoplastic elastomer composition is more preferably 150 g/10 minutes or less, and even more preferably 100 g/10 minutes or less.
The thermoplastic elastomer composition of the present invention preferably has a compression set (recovery rate) of 40% or less, more preferably 35% or less, and even more preferably 30% or less, as determined as follows. Since the compression set is 40% or less, it has recovery properties close to those of vulcanized rubber, and is suitable for liquid-leakage resistance and sealing properties.
Referring to ISO815-1, six test pieces having a diameter of 29 mm obtained by punching out a plate obtained by injection molding the thermoplastic elastomer composition of the present invention are stacked and the original thickness (t0) is measured. Thereafter, it is compressed by 25% using a compression device and a spacer (thickness t1), and heat treatment is performed in a gear oven maintained at 70° C. for 22 hours. Thereafter, immediately after taking it out of the oven, the test piece is taken out from the compression device under an environment of 23° C. and 50% RH and released from compression, and its thickness (t2) is measured 30 minutes later.
The compression set is calculated according to the formula below.
The thermoplastic elastomer composition of the present invention preferably has a hardness of 10 or more and 50 or less when measured using Duro hardness A (type A durometer) after 15 seconds by stacking three plates obtained by injection molding with reference to ISO 7619-1. When the Duro hardness A of the thermoplastic elastomer composition is 50 or less, compression set tends to be good. When the Duro hardness A of the thermoplastic elastomer composition is 10 or more, it is preferred for ease of assembly. From the viewpoint of assemblability, the Duro hardness A of the thermoplastic elastomer composition is more preferably 15 or more, and even more preferably 20 or more. From the viewpoint of liquid-leakage resistance and compression set, the Duro hardness A of the thermoplastic elastomer composition is more preferably 40 or less, even more preferably 35 or less, and particularly preferably 30 or less.
From the viewpoint of liquid-leakage resistance, the thermoplastic elastomer composition of the present invention preferably has a compression set (recovery rate) of 40% or less and a duro hardness A of 40 or less, more preferably has a compression set (recovery rate) of 35% or less and a duro hardness A of 35 or less, even more preferably has a compression set (recovery rate) of 30% or less and a duro hardness A of 35 or less, and particularly preferably has a compression set (recovery rate) of 30% or less and the duro hardness A of 30 or less.
The thermoplastic elastomer composition of the present invention can be used as a molded article by various molding methods. In particular, it is preferable to form a molded article by injection molding the thermoplastic elastomer composition of the present invention. The molding conditions for injection molding are as follows.
The molding temperature when injection molding the thermoplastic elastomer composition is usually 150° C. or higher and 300° C. or lower, and preferably 180° C. or higher and 280° C. or lower. The injection pressure is usually 5 MPa or more and 100 MPa or less, and preferably 10 MPa or more and 80 MPa or less. The mold temperature is usually 0° C. or higher and 80° C. or lower, and preferably 20° C. or higher and 60° C. or lower.
The thermoplastic elastomer composition of the present invention can be applied to rubber stoppers having needle pricking part such as syringe gaskets, infusion bag rubber stoppers, rubber stoppers for vials, etc. cap liners, and packing or the like, which require liquid-leakage sealing properties. Its uses are not limited to medical use. For example, it is suitably used for non-medical syringes, droppers, water pitchers, bottle pumps, syringe-type feeders, gaskets for water guns, gaskets for cooking utensils, exterior moldings for automobiles, window wipers for automobiles, and the like.
As mentioned above, the molded article of the present invention made of the thermoplastic elastomer composition of the present invention has excellent compression set and excellent liquid-leakage sealing properties, and is therefore particularly useful as a rubber stopper having a needle pricking part.
A rubber stopper having a needle pricking part as an embodiment of the molded article of the present invention will be described below with reference to
However, the rubber stopper according to the present invention is not limited to those shown in
The rubber stopper 10 shown in
In this rubber stopper 10, the needle pricking parts are composed of a needle pricking part 11 having a large diameter and needle pricking parts 12 to 14 having a small diameter provided at equal intervals around the needle pricking part 11.
In this way, by having the needle pricking part 11 and the needle pricking parts 12 to 14 with different diameters, it is possible to insert needles with different diameters. For example, a needle made of plastic and having a large diameter of an infusion set can be inserted into the large diameter of needle pricking part 11. The small diameter needle pricking parts 12 to 14 can be used for mixing for injecting a medicinal solution or to be inserted a needle made of metal having a small diameter.
The rubber stopper 20 shown in
The rubber stopper 30 shown in
The rubber stopper 40 shown in
The rubber stopper 50 shown in
Now, specific embodiments of the present invention will be described in further detail with reference to examples. The present invention is not limited to the following examples as long as the present invention is within the gist thereof.
The values of various production conditions and evaluation results in the following examples are to be understood as preferred upper or lower limit values of embodiments of the present invention, and preferred ranges may be a range defined by a combination of the upper or lower limit value and a value of an example described below or by a combination of values of examples described below.
In the following, the physical properties and characteristics of the styrene-based thermoplastic elastomer, thermoplastic elastomer composition, and molded product thereof were evaluated by the following method.
The molecular weights were measured by gel permeation chromatography (GPC) under the following conditions, converted to polystyrene, and a differential molecular weight distribution diagram was prepared. The analysis range was defined as a molecular weight of 10,000 or more.
The MFR of the thermoplastic elastomer composition was measured at 230° C. and a load of 2.16 kgf (21 N) or 5 kgf (49 N) referring to ISO 1133-1 (2011).
The pellets of the thermoplastic elastomer composition were supplied to an in-line screw type injection molding machine (IS130GN manufactured by Toshiba Machine Co., Ltd.), and injection molding was carried out under the conditions for a cylinder temperature of 190° C. or higher and 210° C. or lower (However, in Example 4, since d-1 was used, the cylinder temperature was 220° C. or higher and 270° C. or lower.), a mold temperature of 30° C. or higher and 50° C. or lower, an injection time of 2 seconds or more and 10 seconds or less, and a cooling time of 10 seconds or more and 40 seconds or less to obtain a sheet of the thermoplastic elastomer composition having a wall thickness of 2 mm.
Referring to ISO815-1, six test pieces having a diameter of 29 mm obtained by punching out a sheet obtained by injection molding the thermoplastic elastomer composition were stacked and the original thickness (t0) was measured. Thereafter, it was compressed by 25% using a compression device and a spacer (thickness t1), and heat treatment was performed in a gear oven maintained at 70° C. for 22 hours. Thereafter, immediately after taking it out of the oven, the test piece was taken out from the compression device under an environment of 23° C. and 50% RH and released from compression, and its thickness (t2) was measured 30 minutes later. The compression set was calculated according to the formula below.
Referring to ISO 7619-1, three sheets obtained by injection molding were stacked and the hardness was measured after 15 seconds using Duro hardness A (type A durometer).
The raw materials used in the following Examples and Comparative Examples are shown below.
The molecular weights of the peak Lp and peak Hp of the component (A) below are as shown in Table 1.
45.0 parts by mass of a-1 the styrene-based thermoplastic elastomer as component (A), 10.0 parts by mass of b-1 the hydrocarbon group-grafted polypropylene as component (B), and 45.0 parts by mass of c-1 hydrocarbon softener for rubber as component (C) were mixed to obtain a mixture. To 100 parts by mass of the obtained mixture, 0.1 part by mass of tetrakis [3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionic acid]pentaerythritol (manufactured by Adeka Corporation, product name: Adekastab (registered trademark) AO60) was added as an antioxidant, and the mixture was fed into a co-directional twin-screw extruder (“TEM26-SS” manufactured by Toshiba Machine Co., Ltd., cylinder diameter 26 mm) at a rate of 10 kg/hour or more and 20 kg/hour or less. The mixture was melt-kneaded at 180° C. or higher and 220° C. or lower, and extruded into a strand from a die. Thereafter, it was cut to obtain a thermoplastic elastomer composition in the form of pellets. This thermoplastic elastomer composition was evaluated according to (2) to (4) above. The results are shown in Table 1.
A mixture was obtained in the same manner as in Example 1, except that the formulation was changed as shown in Tables 1 and 2, and an antioxidant was added and kneaded in the same manner to obtain a pellet-shaped thermoplastic elastomer composition. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Tables 1 and 2.
A mixture was obtained in the same manner as in Example 1, except that the formulation was changed as shown in Table 1. To 100 parts by mass of the obtained mixture, 0.1 part by mass of tetrakis[3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionic acid]pentaerythritol (manufactured by Adeka Corporation, product name: Adekastab (registered trademark) AO60) was added as an antioxidant was added and the mixture was fed into a co-directional twin-screw extruder (“TEM26-SS” manufactured by Toshiba Machine Co., Ltd., cylinder diameter 26 mm) at a rate of 10 kg/hour or more and 20 kg/hour or less. The mixture was melt-kneaded at 230° C. or higher and 270° C. or lower, and extruded into a strand from a die. Thereafter, it was cut to obtain a thermoplastic elastomer composition in the form of pellets. Then, evaluation was performed in the same manner as in Example 1. The result is shown in Table 1.
The following can be seen from Tables 1 and 2.
The thermoplastic elastomer compositions of Examples 1 to 12 had good evaluation results for both compression set and moldability.
Comparative Example 1 was a thermoplastic elastomer composition obtained in the same manner as Example 1 except that a-2 having only a peak corresponding to peak Lp with respect to the component (A) was used, and had a high compression set.
Comparative Example 2 was a thermoplastic elastomer composition obtained using a-5, which had two peaks corresponding to peak Lp for the component (A), and had a high compression set.
Comparative Example 3 was a thermoplastic elastomer composition obtained by using high density polyethylene of other resin x-3 instead of the component (B), and had a high compression set.
Comparative Example 4 was a thermoplastic elastomer composition obtained by using a-5 having two peaks corresponding to peak Lp with respect to the component (A) and propylene homopolymer of other resin x-1 instead of the component (B), and had a high compression set.
Comparative Example 5 was a thermoplastic elastomer composition obtained by using propylene homopolymer of other resin x-1 instead of the component (B), and had a high compression set.
Comparative Example 6 was a thermoplastic elastomer composition obtained by using a-5 having two peaks corresponding to peak Lp with respect to the component (A) and propylene homopolymer of other resin x-2 instead of the component (B), and had a high compression set.
Comparative Example 7 was a thermoplastic elastomer composition obtained by using a-5 and a-7 having three peaks corresponding to peak Lp with respect to the component (A) and propylene homopolymer of other resin x-2 instead of the component (B), and had high compression set.
Comparative Examples 8 and 9 were thermoplastic elastomer compositions obtained by using a-6 and a-7 with respect to the component (A) and propylene homopolymer of other resin x-2 instead of the component (B), and had high compression set.
Comparative Examples 10 to 12 were thermoplastic elastomer compositions obtained in the same manner as Example 1, except that propylene homopolymer of other resin x-2 was used instead of the component (B), and had high compression set.
Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various changes can be made without departing from the spirit and scope of the present invention.
This application is based on Japanese Patent Application No. 2021-134245 filed on Aug. 19, 2021, which is incorporated by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-134245 | Aug 2021 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/030123 | Aug 2022 | WO |
| Child | 18444354 | US |
