Polyacetal resin composition and medical device component

Abstract

To provide: a polyacetal resin composition that can suppress the amount of thermal decomposition by simultaneously inhibiting main chain decomposition due to an acid and terminal decomposition due to an onium salt during long-term storage; and a medical device component in which the resin composition is used.SOLUTION: The polyacetal resin composition contains a polyacetal resin, and a compound (A) represented by the structural formula (1) in the figure. The content of the compound (A) in the composition is 1-30 mass ppm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyacetal resin composition and a medical instrument part, and more particularly to a polyacetal resin composition and a medical instrument part that are resistant to thermal decomposition. [Background technology]

[0002] Polyacetal resin is a material with excellent rigidity, strength, toughness, sliding properties, and creep resistance, and is therefore used in a wide range of applications, including as a resin material for various mechanical parts in automobile parts, electrical and electronic parts, industrial parts, and medical devices.

[0003] It is known that polyacetal resins are decomposed by the action of heat, light, oxygen, acid, alkali, etc. In particular, it is known that acids decompose the main chain of polyacetal resins, and alkalis decompose the terminals, and such decomposition is further accelerated during thermal processing of polyacetal resins, leading to a deterioration in moldability and processability and an increase in the amount of low-boiling point compounds remaining in the final resin molded product.

[0004] It is also known that decomposition originating from the terminals can also occur at unstable hemiformal terminals. Therefore, it is common to stabilize such hemiformal terminals by esterifying them with acetic anhydride or the like. These ester groups are known to easily decompose into unstable terminals in the presence of alkali, so it is generally undesirable to allow alkali to be present in polyacetal resins.

[0005] In order to improve thermal stability, various techniques have been proposed. For example, disclosed techniques include adding an amine polymer, polyamide, and allantoin to a polyacetal resin (see Patent Document 1), adding a poly-β-alanine polymer and polyamide 6 / 66 / 610 to a polyacetal resin (see Patent Document 2), adding a nitrogen-containing hindered phenol compound and a formaldehyde scavenger to a polyacetal resin (see Patent Documents 3, 4, and 5), and adding a polycarboxylic acid hydrazide containing an aryl group to a polyacetal resin (see Patent Document 6). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2016 / 126514 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-256425 [Patent Document 3] Japanese Patent Application Publication No. 01-315455 [Patent Document 4] Japanese Patent Application Publication No. 06-179798 [Patent Document 5] Japanese Patent Application Publication No. 04-293952 [Patent Document 6] Japanese Patent Application Laid-Open No. 2005-312801 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been a demand for polyacetal resin compositions with reduced thermal decomposition, for use in advanced medical devices and the like. However, in general synthesis methods for polyacetal resins, onium salts are used as polymerization catalysts or terminal stabilization catalysts, and these onium salts remain in the resin even after washing and drying and gradually act as alkaline compounds, which may generate unstable terminals during long-term storage and generate starting points for thermal decomposition. Adding acidic compounds to neutralize these onium salts is conceivable, but there is a risk that the acidic compounds may cause decomposition originating from the main chain of the polyacetal resin, thereby accelerating the decomposition.

[0008] That is, conventionally known techniques have not been able to solve the problem that attempts to neutralize the remaining onium salt in order to suppress the amount of thermal decomposition end up promoting the decomposition instead, and there has been a demand for the development of a technique that can suppress thermal decomposition.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a polyacetal resin composition capable of suppressing the amount of thermal decomposition by simultaneously suppressing main chain decomposition by an acid and terminal decomposition by an onium salt during long-term storage, and a medical device part using the resin composition. [Means for solving the problem]

[0010] As a result of intensive research conducted by the present inventors to solve the above problems, it was discovered that by adding a predetermined amount of a compound that gradually generates an acid to a polyacetal resin, it is possible to neutralize an onium salt without causing main chain decomposition by the acid, and this led to the completion of the present invention.

[0011] That is, the present invention is as follows. [1] A polyacetal resin composition comprising a polyacetal resin and a compound (A) represented by the following structural formula (1): A polyacetal resin composition, characterized in that the content of the compound (A) in the composition is 1 to 30 ppm by mass. [ka] (In formula (1), R 1 , R2 represents a hydrocarbon group having 1 to 10 carbon atoms, R 3 represents hydrogen or a methyl group. [2] R of the compound (A) 3 is a hydrogen atom. [3] The polyacetal resin composition according to [1], wherein the compound (A) is methylene diacetate. [4] A medical instrument part, comprising the polyacetal resin composition according to any one of [1] to [3]. [5] The medical device component according to [4], which is an insulin pen-type injector or a powder inhaler. [6] Use of the polyacetal resin composition according to any one of [1] to [3] in a medical device part. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a polyacetal resin composition and a medical device part in which the amount of decomposition during thermal processing is suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the following description, and various modifications can be made within the scope of the gist thereof.

[0014] <Polyacetal resin composition> The polyacetal resin composition of the present embodiment contains a polyacetal resin and a compound (A) represented by the following structural formula (1). [ka] (In formula (1), R 1 , R 2 represents a hydrocarbon group having 1 to 10 carbon atoms, R 3 represents hydrogen or a methyl group.

[0015] The polyacetal resin composition of the present embodiment may be a composition consisting of only the compound (A) and the polyacetal resin, or may further contain other components within a range that does not impair the effects of the present invention. In this specification, the compound (A) represented by structural formula (1) may be simply referred to as the "compound".

[0016] (Compound (A)) The polyacetal resin composition of the present embodiment contains a compound (A) represented by the following structural formula (1). [ka] The compound (A) generates acid slowly, and therefore can neutralize the onium salt while suppressing main chain decomposition caused by the acid, thereby significantly reducing the amount of decomposition during thermal processing.

[0017] In the above formula (1), R 1 and R 2 is a hydrocarbon group having 1 to 10 carbon atoms, and examples thereof include an alkyl group, a halogenated alkyl group, and an aryl group. Examples of the alkyl group include alkyl groups having 1 to 10 carbon atoms, such as a methyl group and an ethyl group. The alkyl group may be linear or branched, or may have a cyclic structure. Examples of the halogenated alkyl group include a trichloromethyl group. Examples of the aryl group include a phenyl group, a methylphenyl group, a chlorophenyl group, and a naphthyl group. R 3 As the carbon atom, a hydrogen atom is more preferable from the viewpoint of further suppressing the amount of thermal decomposition.

[0018] Examples of the compound (A) include methylene diacetate, methylene butanoate ester, methylene dipivalate, methylene dibenzoate, ethylidene diacetate, ethylidene butanoate ester, ethylidene dipivalate, and ethylidene dibenzoate. From the viewpoint of further suppressing the amount of thermal decomposition, methylene diacetate, methylene butanoate ester, methylene dipivalate, or methylene dibenzoate is preferred, and methylene diacetate is more preferred. Two or more of the above compounds may be used in combination.

[0019] The content of the compound (A) in the resin composition of this embodiment is 30 ppm by mass or less, and preferably 10 ppm by mass or less, in the polyacetal resin composition. When the content is within this range, main chain decomposition by carboxylic acid generated by decomposition can be suppressed. The content of the compound (A) in the resin composition of this embodiment is preferably 1 ppm by mass or more in the polyacetal resin composition. By including the compound (A) in an amount of 1 ppm by mass or more, the onium salt neutralization effect in the composition can be maintained well, and decomposition of the main chain of the polyacetal resin can be suppressed.

[0020] The compound (A) may be produced by a reaction between an ester compound and / or an acid anhydride used in the process of producing a polyacetal resin, which will be described later, and formaldehyde present in the process. The compound (A) thus produced may be used as it is.

[0021] The compound (A) in the resin composition of this embodiment can be added in addition to the compound produced in the production process to adjust the content to the above-mentioned preferred range, or the compound produced in the production process can be reduced by the method described below to adjust the content to the above-mentioned preferred range.

[0022] The method for reducing the by-produced compound (A) is not particularly limited, but examples thereof include a reduction method comprising step (1) of removing formaldehyde under mild conditions, step (2) of removing an ester compound and / or an acid anhydride, and step (3) of removing compound (A).

[0023] In the above step (1), it is important to remove formaldehyde under mild conditions, such as at room temperature. Under heated conditions, the above-mentioned ester compound and / or acid anhydride react with formaldehyde, which actually increases the amount of compound (A). In addition, in this step, it is desirable to keep the formaldehyde concentration at 10 ppm by mass or less. By keeping the formaldehyde concentration at this level or less, the above-mentioned reaction in step (2) can be suppressed, and the increase in compound (A) can be suppressed. Specific methods include, but are not limited to, a method in which the terminal-stabilized polycetal resin powder is brought into contact with dry air or an inert gas at room temperature while being stirred; a method in which the terminal-stabilized polycetal resin is dispersed in hexane or the like to form a slurry, and nitrogen gas is bubbled through the dispersion; and a method in which the terminal-stabilized polycetal resin is dispersed in hexane or the like to form a slurry, and a formaldehyde scavenger is added to remove formaldehyde that can react with the ester compound and / or acid anhydride.

[0024] In the above step (2), it is important to remove the ester compound and / or acid anhydride under conditions below the melting point of the polyacetal resin. Under conditions above the melting point of the polyacetal resin, the polyacetal decomposes slightly, generating formaldehyde, which then initiates the reaction that produces the aforementioned compound (A). Furthermore, in this step, it is desirable to keep the amount of the ester compound and / or acid anhydride below 10 ppm by mass. By keeping the amount of the ester compound and / or acid anhydride below this level, the aforementioned reaction in step (3) can be suppressed, thereby suppressing the increase in compound (A). Specific methods include, but are not limited to, a method of heating the polyacetal resin to a temperature below the melting point of the polyacetal resin using a paddle dryer equipped with a heating mechanism, and a method of washing the ester compound and / or acid anhydride away using an organic solvent that can dissolve the ester compound and / or acid anhydride and has a low boiling point.

[0025] The step (3) of removing the compound (A) is not particularly limited, but examples thereof include a method using a dryer equipped with a heating and stirring mechanism, melt degassing using a melt kneader equipped with a vent port, etc. Melt degassing is more preferred because it can efficiently remove the compound (A) remaining inside the resin.

[0026] (Polyacetal resin) The polyacetal resin contained in the polyacetal resin composition of the present embodiment has repeating oxymethylene units (acetal structure) represented by (—CH 2 O—) as its main constituent units, and any known polyacetal resin can be used. The polyacetal resin contained in the polyacetal resin composition of the present embodiment may be a homopolymer consisting of only oxymethylene units, or may be a copolymer (including a block copolymer) or terpolymer containing structural units other than oxymethylene units. Furthermore, the polyacetal resin may have not only a linear structure but also a branched or crosslinked structure. The polyacetal resins may be used singly or in combination of two or more.

[0027] Furthermore, when the total amount of the polyacetal resin is taken as 100% by mass, the polyacetal resin preferably contains 30 to 100% by mass, more preferably 50 to 100% by mass, and even more preferably 70 to 100% by mass of polyacetal homopolymer.

[0028] The polyacetal resin can be produced by a known method. For example, polyacetal homopolymers can be obtained by homopolymerizing formaldehyde monomers or cyclic oligomers of formaldehyde, such as its trimer (trioxane) and tetramer (tetraoxane). The resulting polyacetal homopolymers can be stabilized by known methods (e.g., by reacting the polymerization terminals with ether groups or ester groups). The main chain of the polyacetal homopolymer is composed substantially of oxymethylene units, that is, it preferably contains 99% by mass or more of oxymethylene units.

[0029] In the polyacetal copolymer, the constituent unit (copolymer unit) other than the oxymethylene unit is preferably an oxyethylene unit (-CH2CH2O-). Such polyacetal copolymers can be obtained by copolymerizing formaldehyde monomers or cyclic oligomers of formaldehyde, such as its trimer (trioxane) and tetramer (tetraoxane), with cyclic oligomers such as ethylene oxide and 1,3-dioxolane. When obtaining polyacetal copolymers from trioxane and 1,3-dioxolane, the amount of 1,3-dioxolane used is preferably 0.1 to 60 mol%, more preferably 0.1 to 20 mol%, and even more preferably 0.13 to 10 mol%, per 100 mol% of trioxane. Furthermore, the obtained polyacetal copolymer can be stabilized by known methods (e.g., melting it with a quaternary ammonium compound to decompose unstable terminal moieties). The polyacetal copolymer preferably contains oxyethylene units in an amount of 1 to 10% by mass, more preferably 1 to 5% by mass, and even more preferably 1 to 3% by mass, of the entire main chain of the polymer.

[0030] The melt flow rate (MFR) of the polyacetal resin of this embodiment is preferably 1 to 50 g / 10 min from the viewpoint of achieving both fluidity and strength. The MFR can be measured in accordance with ISO 1133-1 at 190°C and under a load of 2.16 kg.

[0031] In this embodiment, the content of the polyacetal resin in 100% by mass of the polyacetal resin composition is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0032] The polyacetal resin composition of this embodiment may contain any conventionally known additives as long as the effects of the present invention are not impaired. For example, the composition may contain known additives such as a formic acid scavenger, a weather stabilizer, a release agent, a lubricant, a conductive agent, a thermoplastic resin, a thermoplastic elastomer, an inorganic or organic filler, a pigment, or a dye. These additives may be used alone or in combination of two or more.

[0033] The polyacetal resin composition of the present embodiment can be produced, for example, by a known melt-kneading method. For example, the polyacetal resin and the compound may be mixed in a stirrer such as a Henschel mixer and then supplied to a single-screw or twin-screw melt-kneading device (extruder) for melt-kneading. Alternatively, the polyacetal resin may be supplied from the upstream of a single-screw or twin-screw extruder and brought to a molten state, and then the compound may be supplied downstream and melt-kneaded.

[0034] <Molded bodies, medical device parts> The molding method for the polyacetal resin composition of the present embodiment is not particularly limited, and examples thereof include known molding methods such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, molding with other materials, gas-assisted injection molding, foam injection molding, low-pressure molding, ultra-thin-wall injection molding (ultra-high-speed injection molding), in-mold composite molding (insert molding, outsert molding), and melt-blow molding.

[0035] The shape of the molded article is not particularly limited, and examples thereof include injection molded articles (including outsert molded articles and insert molded articles), fibers / nonwoven fabrics, sheets / films, and profile extrusion articles.

[0036] The uses of the molded article are not particularly limited, and it can be suitably used, for example, for mechanical parts such as gears, cams, sliders, levers, shafts, bearings and guides, automobile interior parts such as door parts, seat belt parts, combination switch parts and switches, and in particular for medical device parts such as mechanical parts for insulin pen-type injectors and powder inhalers, and infusion pump cocks.

[0037] The polyacetal resin composition of this embodiment contains a specific amount of compound (A), which can suppress main chain decomposition caused by carboxylic acid produced by decomposition. Furthermore, the compound (A) gradually decomposes and neutralizes the onium salt, thereby suppressing main chain decomposition caused by heat. As a result, the polyacetal resin composition of this embodiment can highly suppress the amount of formaldehyde generated both in an inert gas environment and in air, making it suitable for use in medical device components. [Example]

[0038] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0039] The raw material components used in the examples and comparative examples are as follows: (1) Polyacetal resin: (POM-1) Polyacetal copolymer (MFR=25) obtained by polymerizing trioxane and 1,2-dioxolane (POM-2) Polyacetal homopolymer (MFR=23.5) obtained by polymerizing formaldehyde The MFR value was measured in accordance with ISO 1133-1 using a MELT INDEXER manufactured by Toyo Seiki Seisakusho Co., Ltd., at a cylinder temperature of 190°C and a load of 2.16 kg. The POM-2 used contained 200 mass ppm of methylene diacetate, a by-product of the production process. (POM-3) Polyacetal homopolymer (MFR=21.9) obtained by polymerizing formaldehyde The MFR value was measured in accordance with ISO 1133-1 using a MELT INDEXER manufactured by Toyo Seiki Seisakusho Co., Ltd., at a cylinder temperature of 190°C and a load of 2.16 kg. POM-3 contained 50 mass ppm of methylene diacetate, a by-product of the production process, 65 mass ppm of unreacted acetic anhydride, and 1000 mass ppm of formaldehyde, and was used in a powder state before being melted and kneaded.

[0040] (2) Compound (Compound 1) Methylene diacetate (manufactured by Combi-Blocks) (Compound 2) Ethylidene diacetate (Tokyo Chemical Industry Co., Ltd.) (Compound 3) Methylene dibenzoate (Tokyo Chemical Industry Co., Ltd.) (Compound 4) Acetic acid (Tokyo Chemical Industry Co., Ltd.)

[0041] <Examples 1 to 5, Comparative Examples 1 to 5, 8, and 9> The polyacetal resin and each compound were mixed in the amounts shown in Table 1, and then fed into a twin-screw extruder (PCM30 manufactured by Ikegai Corporation), melt-kneaded at a screw rotation speed of 60 rpm and a cylinder temperature setting of 200°C, and then pelletized to obtain the resin composition of each sample. The polyacetal resin used in all samples was the aforementioned POM-1. For Comparative Example 1, no compound was added, and only the polyacetal resin was supplied and pelletized under the above conditions. The resulting pellets were dried for 3 hours using a hot air dryer at a temperature of 80°C.

[0042] [Table 1]

[0043] Example 6 The polyacetal resin used was the aforementioned POM-3, which contained 50 ppm by mass of methylene diacetate by-product from the production process, 65 ppm by mass of unreacted acetic anhydride, and 1000 ppm by mass of formaldehyde. The formaldehyde content was reduced to 9 ppm by mass by applying dry air while stirring at room temperature. The mixture was then heated to 130°C using a paddle dryer, reducing the acetic anhydride content to 3 ppm by mass. The mixture was then dried for 10 hours using a hot air dryer at 80°C, reducing the methylene diacetate content to 27 ppm by mass. The mixture was then pelletized using a kneader.

[0044] <Comparative Example 6> The polyacetal resin composition used was the above-mentioned POM-2 containing 200 mass ppm of methylene diacetate, a by-product of the production process, and was dried for 10 hours using a hot air dryer at a temperature of 80°C.

[0045] <Comparative Example 7> The polyacetal resin used was the aforementioned POM-3 containing 50 ppm by mass of methylene diacetate by-produced in the production process, 65 ppm by mass of unreacted acetic anhydride, and 1000 ppm by mass of formaldehyde, which was dried for 10 hours using a hot air dryer at a temperature of 80°C, and then pelletized using a kneader.

[0046] <Evaluation> The samples obtained in the examples and comparative examples were measured and evaluated as follows. The results are shown in Table 2.

[0047] (1) Amount of thermal decomposition The amount of thermal decomposition of the polyacetal resin composition was measured using a thermogravimetric analyzer (TGA) (Thermo plus EVO2 manufactured by Rigaku). Measurement was carried out at 200°C for 100 minutes, and the amount of thermal weight loss (wt%) was calculated. The thermal weight loss was measured under two conditions: under a nitrogen atmosphere and under air, and both results are shown in Table 1. The smaller this value, the more the amount of thermal decomposition is suppressed, which is preferable.

[0048] (2) Amount of Compound in Resin Composition 2g of each resin composition sample and 10g of purified water were placed in a sealed container and heated in an oven at 37°C for 24 hours. After returning to room temperature, the pellets and solution were separated by natural filtration, and the solution was analyzed by GC (apparatus: Shimadzu GC-2014ATF-SPL, column: Shimadzu GLC SH-PolarWax) to determine the amount of compound eluted into the solution. The amount of compound in the resin was expressed as the amount of compound (ppm by mass) relative to the polyacetal resin.

[0049] [Table 2]

[0050] From Table 2, it was found that the samples of the resin compositions of the Examples were able to reduce the amount of thermal decomposition, particularly in air, compared to the samples of the resin compositions of the Comparative Examples. [Industrial Applicability]

[0051] The polyacetal resin composition of the present invention can be suitably used in fields such as automobile interiors and medical equipment, where a reduction in volatile organic compounds is required.

Claims

1. A polyacetal resin composition comprising a polyacetal resin and a compound (A) represented by the following structural formula (1): A polyacetal resin composition, characterized in that the content of the compound (A) in the composition is 1 to 30 ppm by mass. 【Chemical 1】 (In formula (1), R １ , R ２ represents a hydrocarbon group having 1 to 10 carbon atoms, R ３ represents hydrogen or a methyl group.

2. R of the compound (A) ３ The polyacetal resin composition according to claim 1, wherein is a hydrogen atom.

3. The polyacetal resin composition according to claim 1, wherein the compound (A) is methylene diacetate.

4. A medical device part comprising the polyacetal resin composition according to any one of claims 1 to 3.

5. 5. A medical device part according to claim 4, characterized in that it is an insulin pen injector or a powder inhaler.

6. Use of the polyacetal resin composition according to any one of claims 1 to 3 in a medical device part.

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