Resin composition, pellets, and molded article

Abstract

Provided are a resin composition, pellets, and a molded article. The resin composition includes a polyacetal resin (A), a silicone resin (B) having a weight-average molecular weight of 800,000 or more, and a silicone oil (C) having a weight-average molecular weight of less than 100,000, wherein the mass ratio (B) / (C) of the silicone resin (B) to the silicone oil (C) is 10 / 90 to 90 / 10.

Description

Resin composition, pellets, and molded products

[0001] The present invention relates to a resin composition, a pellet, and a molded article, and more particularly to a resin composition containing a polyacetal resin as a main component.

[0002] Polyacetal resin is a plastic with excellent mechanical properties, electrical properties, and chemical properties such as chemical resistance, and is used in a wide range of applications. One known use of polyacetal resin is as a sliding member. As an example of using polyacetal resin as a sliding member, Patent Document 1 discloses a polyacetal resin composition containing 99.8 to 80 parts by weight of polyacetal, 0.1 to 20 parts by weight of polyethylene wax, and 0.1 to 5 parts by weight of silicone oil.

[0003] Japanese Patent Application Publication No. 04-224856

[0004] The resin composition described in Patent Document 1 is a material with excellent sliding properties. However, in recent years, even better sliding properties have been required. However, when the amount of sliding agent added is large, mold contamination during molding becomes a problem. The present invention aims to solve this problem, and aims to provide a resin composition, pellets, and molded articles that can provide molded articles with excellent sliding properties and little mold contamination.

[0005] In light of the above-mentioned problems, the present inventors conducted research and found that the above-mentioned problems could be solved by combining a silicone resin and a silicone oil of a predetermined molecular weight with a polyacetal resin. Specifically, the above-mentioned problems were solved by the following means. <1> A resin composition comprising a polyacetal resin (A), a silicone resin (B) having a weight-average molecular weight of 800,000 or more, and a silicone oil (C) having a weight-average molecular weight of less than 100,000, wherein the mass ratio of the silicone resin (B) to the silicone oil (C), (B) / (C), is 10 / 90 to 90 / 10. <2> The resin composition according to <1>, in which the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 10 parts by mass per 100 parts by mass of the polyacetal resin (A). <3> The resin composition according to <1>, in which the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 2 parts by mass per 100 parts by mass of the polyacetal resin (A). <4> Pellets of the resin composition according to any one of <1> to <3>. <5> A molded article formed from the resin composition according to any one of <1> to <3>. <6> A molded article formed from the pellets according to <4>.

[0006] According to the present invention, it is possible to provide a molded article having excellent sliding properties and a resin composition with little mold contamination, as well as pellets and a molded article.

[0007] 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 following present embodiment is an example for explaining the present invention, and the present invention is not limited to only this embodiment. Note that in this specification, the word "to" is used to mean that the numerical values ​​before and after it are included as lower and upper limits. In this specification, various physical property values ​​and characteristic values ​​are those at 23°C unless otherwise specified. When the measurement methods etc. described in the standards shown in this specification vary depending on the fiscal year, they are based on the standards as of January 1, 2023, unless otherwise specified.

[0008] The resin composition of this embodiment comprises a polyacetal resin (A), a silicone resin (B) having a weight-average molecular weight of 800,000 or more, and a silicone oil (C) having a weight-average molecular weight of less than 100,000, with the mass ratio of the silicone resin (B) to the silicone oil (C), (B) / (C), being 10 / 90 to 90 / 10. This configuration reduces mold contamination during molding, making it possible to provide molded articles with excellent sliding properties. Adding a silicone resin (B) having a weight-average molecular weight of 800,000 or more can improve the sliding properties of the resulting molded article. This is presumably because a high molecular weight silicone resin increases the dispersion diameter in the polyacetal resin, making it more likely for the silicone resin to appear on the surface of the molded article. However, it has been found that the use of a silicone resin with a high molecular weight is prone to mold contamination during molding. To address this issue, this embodiment adds a silicone oil (C) having a weight-average molecular weight of less than 100,000. That is, the silicone oil (C) having a weight-average molecular weight of less than 100,000 alone cannot achieve sufficient sliding properties, but by blending two kinds of silicone resins, it is possible to maintain excellent sliding properties while suppressing mold contamination.Furthermore, when using a high molecular weight silicone resin, the delamination of the obtained molded product tends to be poor, but this aspect can also be suppressed by using it in combination with the silicone oil (C) having a weight-average molecular weight of less than 100,000.Hereinafter, the details of this embodiment will be described.

[0009] <Polyacetal Resin (A)> The resin composition of this embodiment contains a polyacetal resin. The type of the polyacetal resin is not particularly limited, and the polyacetal resin may be a homopolymer containing only divalent oxymethylene groups as structural units, or a copolymer containing divalent oxymethylene groups and divalent oxyalkylene groups having 2 to 6 carbon atoms as structural units.

[0010] Examples of the oxyalkylene group having 2 to 6 carbon atoms include an oxyethylene group, an oxypropylene group, and an oxybutylene group.

[0011] In the polyacetal resin, the proportion of oxyalkylene groups having 2 to 6 carbon atoms in the total number of moles of oxymethylene groups and oxyalkylene groups having 2 to 6 carbon atoms is not particularly limited, and may be 0.5 to 10 mol %.

[0012] To produce the polyacetal resin, trioxane is typically used as the main raw material. Furthermore, to introduce oxyalkylene groups having 2 to 6 carbon atoms into the polyacetal resin, cyclic formals or cyclic ethers can be used. Specific examples of cyclic formals include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3,5-trioxepane, and 1,3,6-trioxocane. Specific examples of cyclic ethers include ethylene oxide, propylene oxide, and butylene oxide. To introduce oxyethylene groups into the polyacetal resin, 1,3-dioxolane can be used as the main raw material. To introduce oxypropylene groups, 1,3-dioxane can be used as the main raw material. To introduce oxybutylene groups, 1,3-dioxepane can be used as the main raw material. In addition, it is preferable that the amount of hemiformal terminal groups, formyl terminal groups, and terminal groups unstable to heat, acid, or base is small in the polyacetal resin. ２ A formyl terminal group is represented by —CHO.

[0013] The polyacetal resin used in this embodiment has a melt volume rate (MVR) of 0.5 cm3 measured at a temperature of 190°C and a load of 2.16 kg in accordance with ISO 1133. ３ / 10 minutes or more is preferable, and 0.6 cm ３ / 10 minutes or more is more preferable, and 0.8 cm ３ / 10 minutes or more is more preferable, ３ / 10 minutes or more is more preferable, ３ By setting the MVR to the above lower limit or more, the productivity of the resin composition tends to be further improved.３ / 10 minutes or less is preferable, and 18 cm ３ / 10 minutes or less is more preferable, and 14 cm ３ / 10 minutes or less is more preferable, and 10 cm ３ / 10 minutes or less is more preferable, ３ It is even more preferable that the time is 10 minutes or less.

[0014] In addition to the above, the polyacetal resin may be the polyacetal resin described in paragraphs 0018 to 0043 of JP 2015-074724 A, the contents of which are incorporated herein by reference. The polyacetal resin used in this embodiment may be a recycled product (including recovered products, material recycled products, chemical recycled products, etc.), a rejected product, or a waste material from thermoplastic resin molding.

[0015] The resin composition of this embodiment preferably contains polyacetal resin in a proportion of 80% by mass or more of the resin composition, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 93% by mass or more, even more preferably 95% by mass or more, and even more preferably 97% by mass or more. Furthermore, all components other than the silicone resin (B) and the silicone oil (C) may be polyacetal resin. The resin composition of this embodiment may contain only one type of polyacetal resin, or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range.

[0016] <Silicone resin (B) having a weight-average molecular weight of 800,000 or more> The resin composition of this embodiment contains a silicone resin (B) having a weight-average molecular weight of 800,000 or more. By containing a silicone resin (B) having a weight-average molecular weight of 800,000 or more, it is possible to improve the sliding properties. In particular, it is possible to improve the limit PV value and reduce the dynamic friction coefficient.

[0017] The weight average molecular weight of the silicone resin (B) is preferably 850,000 or more, more preferably 900,000 or more, even more preferably 950,000 or more, and even more preferably 980,000 or more, and is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less, and may be 1,200,000 or less. By setting it to the lower limit or more, sliding properties tend to be further improved. On the other hand, by setting it to the upper limit or less, the effect of suppressing mold contamination and delamination of molded pieces tends to be further improved.

[0018] In this embodiment, the molecular weight of the silicone resin (B) is measured by the following method. The silicone in the silicone resin is extracted with dichloromethane. The extracted silicone is adjusted with 0.2% by mass of toluene eluent and allowed to stand at room temperature for 12 hours. The mixture is then filtered through a 0.45 μm membrane filter, and the filtrate is subjected to gel permeation chromatography (GPC) measurement. AQCUITY APC manufactured by Waters can be used for GPC measurement. When the resin composition of this embodiment contains two or more silicone resins (B), the Mw of the silicone resin (B) is taken as the Mw of the mixture. The same applies to the silicone oil (C).

[0019] The silicone resin (B) used in this embodiment is preferably a polyorganosiloxane, and is preferably —(Si(R) ２ -O)-, and each R is independently a hydrogen atom, a hydrocarbon group, an -O-hydrocarbon group, or a hydroxyl group (with the proviso that at least one of R is a hydrocarbon group or an -O-hydrocarbon group). Each R is preferably independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, an -O-hydrocarbon group having 1 to 6 carbon atoms, or a hydroxyl group, more preferably a hydrogen atom, a methyl group, an ethyl group, a phenyl group, a methoxy group, an ethoxy group, a phenoxy group, or a hydroxyl group, more preferably a hydrogen atom, a methyl group, or a methoxy group, and even more preferably a hydrogen atom or a methyl group. -(Si(R) ２The —O)— may be one type or two or more types.

[0020] The silicone resin (B) used in this embodiment is preferably a non-crosslinked silicone. The non-crosslinked silicone is a -(Si(R) ２ —O)—, and each R is independently —(Si(R′) ２ Examples include silicones that do not contain a structure represented by —O)— (each R′ independently forms a crosslinked structure with another moiety). R is the same as above, and the preferred range is also the same.

[0021] The silicone resin (B) used in this embodiment is preferably a linear silicone. The linear silicone is defined as -(Si(R) ２ Illustrative examples include compounds represented by the formula (I)—O)—, where each R is independently an atomic group containing no silicon atom and having 12 or less carbon atoms. R here has the same meaning as above, and the preferred range is also the same.

[0022] When blending the silicone resin (B), it may be made into a masterbatch. The resin used for the masterbatch is preferably a polyacetal resin. The proportion of the silicone resin (B) in the masterbatch is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 80% by mass or less, preferably 70% by mass or less, and more preferably 60% by mass or less.

[0023] The content of silicone resin (B) in the resin composition of this embodiment is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, relative to 100 parts by mass of polyacetal resin (A). Depending on the application, it may be 0.6 parts by mass or more, and preferably 9 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and even more preferably 0.9 parts by mass or less. Depending on the application, it may be 0.7 parts by mass or less. By setting it to the lower limit or more, sliding properties tend to be further improved. Furthermore, by setting it to the upper limit or less, the effect of suppressing mold contamination and delamination of molded pieces tends to be further improved. The resin composition of this embodiment may contain only one type of silicone resin (B), or may contain two or more types. When two or more types are contained, it is preferable that the total amount is within the above range.

[0024] <Silicone oil (C) having a weight-average molecular weight of less than 100,000> The resin composition of this embodiment contains silicone oil (C) having a weight-average molecular weight of less than 100,000. By using silicone oil (C) having a weight-average molecular weight of less than 100,000 in combination with silicone resin (B), it is possible to effectively suppress mold contamination and delamination while maintaining high sliding properties (particularly, limit PV value).

[0025] The weight average molecular weight of the silicone oil (C) is preferably 95,000 or less, more preferably 90,000 or less, and even more preferably 85,000 or less, and is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 35,000 or more. By setting it to the lower limit or more, sliding properties tend to be further improved. Furthermore, by setting it to the upper limit or less, the effect of suppressing mold contamination and delamination of molded pieces tends to be further improved.

[0026] The silicone oil (C) used in this embodiment is preferably an organosiloxane, and is preferably —(Si(R) ２-O)-, and each R is independently a hydrogen atom, a hydrocarbon group, an -O-hydrocarbon group, or a hydroxyl group (provided that at least one of R is a hydrocarbon group or an -O-hydrocarbon group). Each R is independently preferably a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, an -O-hydrocarbon group having 1 to 6 carbon atoms, or a hydroxyl group, more preferably a hydrogen atom, a methyl group, an ethyl group, a phenyl group, a methoxy group, an ethoxy group, a phenoxy group, or a hydroxyl group, more preferably a hydrogen atom, a methyl group, or a methoxy group, and even more preferably a hydrogen atom or a methyl group. -(Si(R)) in silicone oil (C) ２ The —O)— may be one type or two or more types.

[0027] When blending silicone oil (C), it may be made into a masterbatch. The resin used for the masterbatch is preferably a polyacetal resin. The proportion of silicone oil (C) in the masterbatch is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and is preferably 60% by mass or less, preferably 55% by mass or less, and more preferably 45% by mass or less.

[0028] The content of silicone oil (C) in the resin composition of this embodiment is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass or more, relative to 100 parts by mass of polyacetal resin (A). Depending on the application, it may be 0.3 parts by mass or more, and is preferably 9 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, even more preferably 0.6 parts by mass or less. Depending on the application, it may be 0.4 parts by mass or less. By setting it to be equal to or greater than the lower limit, the sliding properties tend to be further improved. Furthermore, by setting it to be equal to or less than the upper limit, the delamination suppression effect tends to be further improved. The resin composition of this embodiment may contain only one type of silicone oil (C), or may contain two or more types. When two or more types are contained, it is preferable that the total amount is within the above range.

[0029] <Blend of Silicone Resin (B) and Silicone Oil (C)> In the resin composition of this embodiment, the mass ratio of the silicone resin (B) to the silicone oil (C), (B) / (C), is 10 / 90 to 90 / 10. This configuration allows for a balanced improvement in sliding properties and suppression of mold contamination. The blend ratio of the silicone resin (B) to the silicone oil (C) is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and preferably 40 parts by mass or more, per 100 parts by mass of the total of the silicone resin (B) and the silicone oil (C). Depending on the application, etc., it may be 51 parts by mass or more, or even 55 parts by mass or more, and preferably 85 parts by mass or less, more preferably 80 parts by mass or less, and may be 75 parts by mass or less, or even 70 parts by mass or less, depending on the application, etc.

[0030] The weight average molecular weight of each of the silicone resin (B) and the silicone oil (C) is M ｗＢ , M ｗＣThe ratio M of the weight average molecular weight of the silicone resin (B) to the weight average molecular weight of the silicone oil (C) when ｗＢ / M ｗＣ is preferably 10 or more, and may be 20 or more, or even 40 or more, and is preferably 100 or less, and may be 50 or less, 30 or less, or even 15 or less. By setting it within the above range, the effects of the present invention tend to be more effectively exhibited.

[0031] In the resin composition of this embodiment, the total content of the silicone resin (B) and the silicone oil (C) is preferably more than 0.1 parts by mass and less than 10 parts by mass per 100 parts by mass of the polyacetal resin (A). By making the total content equal to or greater than the lower limit, the sliding properties tend to be further improved. Furthermore, by making the total content equal to or less than the upper limit, the effect of suppressing mold contamination and delamination of molded pieces tends to be further improved. The total content of the silicone resin (B) and the silicone oil (C) is, relative to 100 parts by mass of the polyacetal resin (A), more preferably 0.1 parts by mass or more, even more preferably 0.11 parts by mass or more, even more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, even more preferably 0.8 parts by mass or more, and preferably 9 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and even more preferably 1.5 parts by mass or less.

[0032] The resin composition of this embodiment may or may not contain a silicone compound having a weight average molecular weight of 100,000 or more and less than 800,000. An example of this embodiment is that the resin composition is substantially free of silicone compounds having a weight average molecular weight of 100,000 or more and less than 800,000. "Substantially free" means that the content of silicone compounds having a weight average molecular weight of 100,000 or more and less than 800,000 contained in the resin composition is less than 10% by mass of the total content of the silicone resin (B) and the silicone oil (C), preferably less than 5% by mass, more preferably less than 3% by mass, and may even be less than 1% by mass.

[0033] In the resin composition of the present embodiment, the total content of the polyacetal resin (A), the silicone resin (B), and the silicone oil (C) in the resin composition is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, still more preferably 98% by mass or more, still more preferably 99% by mass or more, and may be 100% by mass or less.

[0034] <Other Components> The resin composition of this embodiment may contain known additives and fillers as long as the object of the present invention is not impaired. Examples of additives and fillers that can be used in this embodiment include known thermoplastic polymers other than polyacetal resins, acid-modified polymers, weathering agents, formaldehyde scavengers, inorganic particles, antioxidants (hindered amines, hindered phenols, etc.), heat stabilizers, colorants, nucleating agents, plasticizers, fluorescent brighteners, release agents, antistatic agents, UV absorbers, flame retardants, and flame retardant aids. The resin composition of this embodiment is prepared so that the total of the polyacetal resin, silicone resin (B), silicone oil (C), and other components blended as needed is 100% by mass.

[0035] <Physical Properties of Resin Composition> The resin composition of this embodiment preferably has excellent sliding properties. The resin composition of this embodiment preferably has a dynamic friction coefficient of 0.25 or less when molded into a cylindrical thrust test piece. A practical lower limit value is, for example, 0.01 or more. Such a small dynamic friction coefficient is mainly achieved by blending silicone oil (C) with the polyacetal resin (A). The dynamic friction coefficient is measured according to the description in the Examples below.

[0036] The resin composition of this embodiment was molded into a cylindrical thrust test piece with a contact area of ​​2 cm 2 When measured according to the thrust ring friction and wear test specified in JIS K7218 Method A at a temperature of 23°C, the limiting PV value (MPa cm / s) is preferably 16.0 MPa cm / s or more. There is no particular upper limit, but 50.0 MPa cm / s or less is practical. Such a high limiting PV value is mainly achieved by blending the silicone resin (B) with the polyacetal resin (A). The limiting PV value is measured as described in the examples below.

[0037] <Method for Producing Resin Composition> The resin composition of this embodiment can be easily prepared by a known method commonly used for preparing conventional thermoplastic resin compositions. For example, (1) a method in which all components constituting the resin composition are mixed, fed into an extruder, and melt-kneaded to obtain a pellet-shaped resin composition; (2) a method in which some of the components constituting the resin composition are fed through the main feed port of an extruder and the remaining components through a side feed port, and melt-kneaded to obtain a pellet-shaped resin composition; or (3) a method in which pellets with different compositions are prepared by extrusion or the like, and the pellets are mixed to prepare a resin composition having a predetermined composition. In this embodiment, it is preferable to prepare a masterbatch of the silicone resin (B) and / or silicone oil (C) (preferably the silicone resin (B)) and then melt-knead it with the remaining components. Examples of kneading machines include kneaders, Banbury mixers, extruders, etc. The various conditions and devices for mixing and kneading are not particularly limited and may be appropriately selected from any conventionally known conditions. The kneading is preferably carried out at a temperature at which the polyacetal resin melts or higher, specifically at a temperature at or higher than the melting point of the polyacetal resin (generally 180° C. or higher).

[0038] <Molded Article> The molded article of this embodiment is formed from the resin composition or pellets of this embodiment. The pellets obtained by pelletizing the resin composition of this embodiment are molded into a molded article by various molding methods. Alternatively, a resin composition melt-kneaded in an extruder can be directly molded into a molded article without going through pelletization. The shape of the molded article is not particularly limited and can be appropriately selected depending on the application and purpose of the molded article. Examples of the shape of the molded article include plate-like, plate-like, rod-like, sheet-like, film-like, cylindrical, ring-like, circular, elliptical, gear-like, polygonal, irregular-shaped, hollow, frame-like, box-like, and panel-like shapes. The molded article of this embodiment may be a finished product or a part.

[0039] The method for molding the molded article is not particularly limited, and any conventionally known molding method can be used, such as injection molding, injection compression molding, extrusion molding, profile extrusion, transfer molding, blow molding, gas-assisted blow molding, blow molding, extrusion blow molding, IMC (in-mold coating molding), rotational molding, multilayer molding, two-color molding, insert molding, sandwich molding, foam molding, and pressure molding.

[0040] The resin composition of this embodiment is preferably used for forming a sliding member. Therefore, a molded article formed from the resin composition of this embodiment is preferably used as a sliding member (sliding part). Specific examples of the sliding member include gears, rotating shafts, bearings, various gears, cams, end face materials for mechanical seals, valve seats for valves, V-rings, rod packings, piston rings, rider rings, and other sealing members, as well as rotating shafts, rotating sleeves, pistons, impellers, rollers, and other sliding members for compressors, which are intended to achieve the high quality required for electrical and electronic equipment, office equipment, vehicles (automobiles), industrial equipment, and the like.

[0041] The sliding member of this embodiment can be used as a sliding member in combination with not only another sliding member of this embodiment but also other resin sliding members, fiber-reinforced resin sliding members, and ceramic or metal sliding members.

[0042] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

[0043] 1. Raw materials The following raw materials were used:

[0044] 2. Examples 1 to 6 and Comparative Examples 1 to 6 <Production of Resin Composition (Pellets)> The components shown in Table 1 were uniformly mixed in the proportions shown in Table 2 (proportions of each component are in parts by mass) using a Super Mixer manufactured by Kawada Manufacturing Co., Ltd. The resulting mixture was melt-shear mixed using a vented twin-screw extruder with a screw diameter of 30 mm ("PCM30" manufactured by Ikegai Corporation) at a cylinder temperature of 190°C, a screw rotation speed of 120 rpm, and a discharge rate of 10 kg / hour to produce pellets of the resin composition.

[0045] <Dynamic Friction Coefficient> Cylindrical thrust test specimens were molded from the pellets obtained above using a 32 mm screw SE-30DUZ manufactured by Sumitomo Heavy Industries, Ltd. under conditions of a cylinder temperature of 195°C and a mold temperature of 80°C. A thrust friction and wear test was performed on the obtained cylindrical thrust test specimens to measure the dynamic friction coefficient. An EFM-3-G manufactured by A&D Co., Ltd. was used for the thrust test. For the cylindrical thrust test specimens, a linear velocity of 10 cm / s was used to test a polyacetal resin specimen, with the surface pressure increased every 3 minutes to 3 kg, 5 kg, and 10 kg, with the surface pressure increasing by 5 kg after 5 kg. Focusing on the dynamic friction coefficient under low surface pressure (load 3 kg, surface pressure 0.15 MPa), where differences in the dynamic friction coefficient due to formulation are likely to occur, the average value of the dynamic friction coefficient over 3 minutes was recorded and evaluated.

[0046] <Limit PV Value> The pellets obtained above were injection molded using an SE30DUZ (manufactured by Sumitomo Heavy Industries, Ltd.) with a screw diameter of 32 mm at a cylinder temperature of 195° C. and a mold temperature of 80° C., and a thrust wear test was carried out using a cylindrical thrust test piece. A thrust friction wear test was carried out on the cylindrical thrust test piece at a linear velocity of 10 cm / s, with the surface pressure being increased every 3 minutes by 3 kg, 5 kg, and 10 kg, with the surface pressure increasing by 5 kg from 5 kg onwards, and the product of the surface pressure and the velocity one step below at which the test piece was fused due to frictional heat was taken as the limit PV value (unit: MPa cm / s).

[0047] <Delamination> The resin composition obtained above was molded using an SE-30DUZ molder manufactured by Sumitomo Heavy Industries, Ltd. at a cylinder temperature of 215°C, a mold temperature of 80°C, and an injection speed of 30 mm / s to prepare test pieces of 40 mm x 100 mm x 2 mm. Delamination was evaluated as follows. A and B represent practical levels. A: 3 cm or less and less than 5 cm from the gate B: 5 cm or more and less than 7 cm from the gate C: 7 cm or more from the gate

[0048] <Mold Contamination> The resin composition obtained above was continuously molded for 500 shots using a SE7MII molding machine manufactured by Sumitomo Heavy Industries, Ltd., with a cylinder temperature of 230°C and a teardrop-shaped mold set at a mold temperature of 40°C. The condition of the mold was then checked. Evaluation was carried out by five experts and judged by majority vote. A and B represent practical levels. A: No mold deposits at all, extremely good mold contamination suppression effect B: Some mold deposits present, but good mold contamination suppression effect (inferior to A above) C: Much mold deposits present, poor mold contamination suppression effect (inferior to B above)

[0049]

[0050] As is clear from the above results, the molded article obtained from the resin composition of the present embodiment had excellent sliding properties. Furthermore, mold contamination was also suppressed.

Claims

1. A resin composition comprising a polyacetal resin (A), a silicone resin (B) having a weight-average molecular weight of 800,000 or more, and a silicone oil (C) having a weight-average molecular weight of less than 100,000, wherein the mass ratio of the silicone resin (B) to the silicone oil (C), (B) / (C), is 10 / 90 to 90 / 10.

2. A resin composition according to claim 1, wherein the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 10 parts by mass per 100 parts by mass of the polyacetal resin (A).

3. The resin composition according to claim 1, wherein the total content of the silicone resin (B) and the silicone oil (C) is 0.5 parts by mass or more and less than 2 parts by mass per 100 parts by mass of the polyacetal resin (A).

4. Pellets of the resin composition according to any one of claims 1 to 3.

5. A molded article formed from the resin composition according to any one of claims 1 to 3.

6. A molded article formed from the pellets of claim 4.

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