Resin composition, pellet, and molded article

Abstract

Provided are a resin composition, pellets, and a molded article. This resin composition contains 100 parts by mass of a polyacetal resin, 0.4-10 parts by mass of a silicone gum having a kinematic viscosity higher than 1,000,000 mm2 / s, and 0.5-10 parts by mass of a polyolefin-based lubricant. 25-80 mass% of the polyolefin-based lubricant is an oxidation-modified polyolefin-based lubricant.

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. In particular, there is a demand for resin compositions that can provide molded articles with a high PV limit and a low dynamic friction coefficient. The present invention aims to solve this problem by providing a resin composition, pellets, and molded articles that can provide molded articles with a high PV limit and a low dynamic friction coefficient.

[0005] The present inventors have conducted research to solve the above problems and have found that the above problems can be solved by blending a specific silicone gum and a polyolefin-based lubricant with a polyacetal resin. Specifically, the above problems have been solved by the following means: <1> 100 parts by mass of polyacetal resin and a kinematic viscosity of 1,000,000 mm ２A resin composition comprising: 0.4 to 10 parts by mass of a silicone gum having a viscosity of more than 1 / s; and 0.5 to 10 parts by mass of a polyolefin-based lubricant, wherein 25 to 80 mass% of the polyolefin-based lubricant is an oxidatively modified polyolefin-based lubricant. <2> A resin composition comprising a polyacetal resin, a silicone gum, and a polyolefin-based lubricant, wherein the resin composition is molded into a cylindrical thrust test piece, and domains containing the silicone compound observed with a laser microscope have an average length L of 8.0 μm or more and an average width W of 3.0 μm or less. <3> The kinematic viscosity of the silicone gum contained in the resin composition is 5,000,000 mm ２ <4> The resin composition according to <1>, wherein the kinematic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm / s or more. ２ / s or more. <5> The resin composition according to any one of <1> to <4>, wherein the polyolefin-based lubricant contained in the resin composition comprises an oxidatively modified polyolefin-based lubricant. <6> The resin composition according to any one of <1> to <5>, wherein the proportion of the oxidatively modified polyolefin-based lubricant in the polyolefin-based lubricant contained in the resin composition is 35 mass% or more. <7> The kinematic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm ２ / s or more, and a proportion of oxidatively modified polyolefin-based lubricant in the polyolefin-based lubricant contained in the resin composition is 35 mass% or more. <8> The resin composition according to any one of <1> to <7>, wherein the resin composition is molded into a cylindrical thrust test piece, and domains containing a silicone compound, when observed with a laser microscope, have an average length L of 8.0 μm or more and an average width W of 3.0 μm or less. <9> The kinematic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm ２ / s or more, and 35 mass% or more of the polyolefin-based lubricant is an oxidatively modified polyolefin-based lubricant. <10> The resin composition according to <2> or <8>, wherein the ratio L / W of the average length L to the average width W of the domains containing the silicone compound is 3.0 or more. <11> Pellets of the resin composition according to any one of <1> to <10>. <12> A molded article formed from the resin composition according to any one of <1> to <10>. <13> A molded article formed from the pellets according to <11>.

[0006] According to the present invention, it is possible to provide a resin composition capable of providing a molded article having a high PV limit value and a low dynamic friction coefficient, as well as pellets and a molded article.

[0007] 1 is an electron microscope photograph of a test piece of Example 4. FIG. 2 is an electron microscope photograph of a test piece of Comparative Example 7.

[0008] 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 ​​written 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.

[0009] The resin composition of the present embodiment comprises 100 parts by mass of polyacetal resin and a viscoelastic polymer having a kinematic viscosity of 1,000,000 mm ２ The resin composition is characterized by comprising 0.4 to 10 parts by mass of a silicone gum having a viscosity of more than 1 / s and 0.5 to 10 parts by mass of a polyolefin-based lubricant, wherein 25 to 80% by mass of the polyolefin-based lubricant is an oxidatively modified polyolefin-based lubricant. By adopting such a configuration, it is possible to provide a resin composition capable of providing a molded product having a high PV limit value and a low dynamic friction coefficient.

[0010] The silicone gum disperses in the polyacetal resin to form domains. This silicone gum is stretched by the flow of the resin during injection molding of the resin composition. The stretching of the silicone gum region improves the limiting PV value. However, if the silicone gum content is too high, other physical properties of the resulting molded product tend to be poor. On the other hand, the polyolefin-based lubricant contributes to improving the initial sliding properties. Furthermore, together with the silicone gum, it can improve the overall sliding properties and reduce the dynamic friction coefficient of the resulting molded product. However, it is believed that non-oxidized polyolefin-based lubricants tend to be present on the surface of the molded product and are easily removed from the molded product. In this embodiment, it is believed that this problem is solved by using at least an oxidized polyolefin-based lubricant. That is, it is believed that the oxidized polyolefin-based lubricant is compatible with the polyacetal resin and is present not only on the surface but also inside the molded product. Furthermore, it is believed that the non-oxidized polyolefin-based lubricant can be dragged along by the oxidized polyolefin-based lubricant, allowing it to be present not only on the surface but also inside the molded product. As a result, a molded product having a high PV limit value and a low dynamic friction coefficient can be obtained. The details of this embodiment will be described below.

[0011] <Polyacetal Resin> 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.

[0012] Examples of the oxyalkylene group having 2 to 6 carbon atoms include an oxyethylene group, an oxypropylene group, and an oxybutylene group.

[0013] 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 %.

[0014] 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.

[0015] 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 cm３ / 10 minutes or less is more preferable, ３ It is even more preferable that the time is 10 minutes or less.

[0016] 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.

[0017] The resin composition of the present 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, still more preferably 93% by mass or more, even more preferably 95% by mass or more, and still more preferably 97% by mass or more. ２ The resin composition of the present embodiment may contain only one type of polyacetal resin or two or more types of polyacetal resins. When two or more types of polyacetal resins are contained, the total amount is preferably within the above range.

[0018] <Kinematic viscosity 1,000,000mm ２ / s or more> The resin composition of this embodiment has a kinematic viscosity of 1,000,000 mm ２ It is preferable that the silicone gum contains a silicone gum having a viscosity of more than 1,000,000 mm / s. By containing such a silicone gum, the limit PV value of the obtained molded product can be increased. Silicone gum means a liquid silicone or silicone oil having a large molecular weight. In this embodiment, the molecular weight is defined by the kinematic viscosity. The kinematic viscosity used in this embodiment is 1,000,000 mm ２ The kinematic viscosity of silicone gums is greater than 5,000,000 mm / s. ２ / s or more, and 10,000,000 mm ２ / s or more, and more preferably 15,000,000 mm ２ / s or more, and more preferably 17,000,000 mm ２ / s or more, and more preferably 30,000,000 mm ２ / s or less, and 25,000,000 mm ２ / s or less, and more preferably 22,000,000 mm ２ / s or less. By setting the value to be equal to or greater than the lower limit, it is possible to maintain a high critical PV value. By setting the value to be equal to or less than the upper limit, it is possible to maintain a high critical PV value while suppressing mold contamination and delamination of the molded piece.

[0019] The resin composition of this embodiment has a kinematic viscosity of 1,000,000 mm ２ The composition may contain only one type of silicone gum having a viscosity of more than 1 / s, or may contain two or more types. When two or more types are contained, it is preferable that the kinematic viscosity of the mixture be within the above range. The kinematic viscosity is measured by measuring the viscosity of a toluene solution (0.1 g / L) of each silicone gum at 25°C using a cone-plate viscometer, and calculated from a calibration curve of the kinematic viscosity of the silicone oil and the viscosity of the toluene solution. As a measuring device, a cone-plate viscometer TVE-25L manufactured by Toki Sangyo Co., Ltd. can be used.

[0020] The silicone gum used in this embodiment is a compound having a structure linked by siloxane bonds. The silicone gum is preferably polyorganosiloxane, and is preferably —(Si(R) ２-O)-, and each R is preferably 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 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) ２ There may be two or more types of —O)—.

[0021] When blending the silicone gum, it may be made into a masterbatch. An example of a resin used for the masterbatch is a polyacetal resin. The proportion of the silicone gum in the masterbatch is preferably 10% by mass or more, more preferably 20% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less.

[0022] The kinematic viscosity of the resin composition of this embodiment is 1,000,000 mm ２ The content of the silicone gum exceeding 1 / s is preferably 0.4 parts by mass or more, more preferably 0.6 parts by mass or more, and even more preferably 0.8 parts by mass or more, relative to 100 parts by mass of the polyacetal resin, and is preferably 10 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 2.5 parts by mass or less, even more preferably 1.8 parts by mass or less, and even more preferably 1.5 parts by mass or less. By setting the content to be equal to or greater than the above lower limit and equal to or less than the above upper limit, the sliding properties tend to be further improved. The resin composition of this embodiment has a kinematic viscosity of 1,000,000 mm ２ The composition may contain one or more silicone gums in an amount of more than 1 / s. When two or more types are contained, the total amount is preferably in the above range.

[0023] <Polyolefin-Based Lubricant> The resin composition of this embodiment contains a polyolefin-based lubricant. The inclusion of a polyolefin-based lubricant improves initial sliding properties and, together with the silicone gum, reduces the dynamic friction coefficient. The polyolefin-based lubricant is an olefin homopolymer or copolymer. Examples of polyolefin-based lubricants include polyethylene wax, polypropylene wax, and polyethylene propylene wax, with polyethylene wax being preferred. The polyolefin-based lubricant may be unmodified or modified. Examples of modified polyolefin-based lubricants include vinyl ester-modified polyolefin-based lubricants, acid-modified polyolefin-based lubricants, and oxidized polyolefin-based lubricants (oxidized and modified polyolefin-based lubricants), with the inclusion of an oxidized polyolefin-based lubricant being preferred. The oxidized polyolefin-based lubricant is easily mixed with the polyacetal resin and is dispersed evenly throughout the molded article, further improving the sliding properties of the resulting molded article.

[0024] The polyethylene wax may be composed of an ethylene homopolymer or an ethylene-α-olefin copolymer. Examples of the α-olefin as the ethylene copolymer include α-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, isobutylene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadecene, 1-octadecene, and 4-methyl-1-pentene. The content of ethylene units in the ethylene-α-olefin copolymer wax is preferably more than 50 mol%, more preferably 60 to 100 mol%. The polyethylene wax may be unmodified or modified. Examples of unmodified polyethylene waxes include Licowax (registered trademark) PE520, PE130, and PE190; Licocene (registered trademark) PE3101TP, PE4201, and PE5301; and Ceridust (registered trademark) 3620 and 3610, all of which are manufactured by Clariant Chemicals.

[0025] The polypropylene wax may be composed of a propylene homopolymer or a propylene-α-olefin copolymer. Examples of α-olefins used as propylene copolymers include α-olefins having 3 to 20 carbon atoms, such as ethylene, 1-butene, isobutylene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadecene, 1-octadecene, and 4-methyl-1-pentene. The content of propylene units in the propylene-α-olefin copolymer wax is preferably greater than 50 mol%, more preferably 60 to 100 mol%. The polypropylene wax may be unmodified or modified. Examples of unmodified polypropylene waxes include Licocene (registered trademark) PP6102, PP6502, PP7502, PP1302, PP1502, PP1602, PP2602, and PP3602 manufactured by Clariant Chemicals; and Ceridust (registered trademark) 6050M.

[0026] The resin composition of this embodiment preferably contains an oxidized polyolefin-based lubricant. By including an oxidized polyolefin-based lubricant, initial sliding properties can be further improved, and together with the silicone gum, the dynamic friction coefficient can be further reduced. The oxidized polyolefin-based lubricant can be obtained by oxidizing a corresponding unmodified polyolefin-based lubricant. In this embodiment, oxidized polyethylene wax is preferred. Examples of oxidized polyethylene wax include Licowax (registered trademark) PED521, PED522, and PED121 manufactured by Clariant Chemicals; Ceridust (registered trademark) 3715, and the like.

[0027] In this embodiment, it is preferable that the lubricant contains an oxidized polyolefin-based lubricant and an unmodified polyolefin-based lubricant, and it is more preferable that the lubricant contains an oxidized polyethylene wax and an unmodified polyethylene wax.

[0028] The content of the oxidized polyolefin-based lubricant in the resin composition of this embodiment is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, even more preferably 40% by mass or more, even more preferably 45% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 74% by mass or less. By setting the content at or above the lower limit, the dynamic friction coefficient of the obtained molded article tends to be smaller. Furthermore, by setting the content at or below the upper limit, the PV limit value of the obtained molded article tends to be higher. The resin composition of this embodiment may contain only one type of oxidized polyolefin-based lubricant, or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range.

[0029] The molecular weight (viscosity method) of the polyolefin-based lubricant (oxidized polyolefin-based lubricant, unmodified polyolefin-based lubricant, etc.) is preferably 1,000 or more, more preferably 2,000 or more, and even more preferably 3,000 or more. For unmodified polyolefin-based lubricants, it is more preferably 4,500 or more, even more preferably 5,000 or more, and even more preferably 6,000 or more. By setting it to the above lower limit value or above, high sliding properties can be maintained without bleeding out from the molded product. Furthermore, the molecular weight (viscosity method) of the polyolefin-based lubricant is preferably 20,000 or less, more preferably 15,000 or less, even more preferably 10,000 or less, and even more preferably 8,000 or less. Setting it to the above upper limit value or below tends to further improve sliding properties. The molecular weight of the polyolefin-based lubricant is measured according to gel permeation chromatography (viscosity method). In the case where the resin composition of the present embodiment contains two or more polyolefin-based lubricants, the molecular weight is the weighted average value of the molecular weights of the respective polyolefin-based lubricants.

[0030] The content of the polyolefin-based lubricant in the resin composition of this embodiment is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, even more preferably 1.0 parts by mass or more, even more preferably 1.2 parts by mass or more, even more preferably 1.4 parts by mass or more, even more preferably 1.6 parts by mass or more, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 2.5 parts by mass or less. By setting the content to be above the lower limit and below the upper limit, the sliding properties tend to be further improved. The resin composition of this embodiment may contain only one type of polyolefin-based lubricant, or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range.

[0031] <Other Components> The resin composition of this embodiment may contain known additives and fillers within the scope of the present invention. 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, mold release agents, antistatic agents, ultraviolet absorbers, flame retardants, and flame retardant aids, which may be added as needed. The resin composition of this embodiment contains a polyacetal resin having a kinematic viscosity of 1,000,000 mm ２ The resin composition of this embodiment is adjusted so that the total of the silicone gum having a kinematic viscosity of more than 1,000,000 mm / s, the polyolefin-based lubricant, and other components blended as necessary is 100 mass %. ２ The total of the silicone gum and the polyolefin-based lubricant preferably accounts for 85% by mass or more of the resin composition, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may even account for 98% by mass or more.

[0032] <Other Embodiments> The resin composition of this embodiment is also a resin composition containing a polyacetal resin, a silicone gum, and a polyolefin-based lubricant. When the resin composition is molded into a cylindrical thrust-molded piece and observed with a laser microscope, it is preferable that the domains containing the silicone compound have an average length of 8.0 μm or more and an average width of (3.0) μm or less. The formation of thin, long domains containing the silicone compound in the molded article results in a molded article with a low dynamic friction coefficient and a high limiting PV value. It is preferable that 90% by mass or more of the domains be formed by the silicone compound. The average length of the domains is preferably 8.0 μm or more, more preferably 9.0 μm or more, even more preferably 10.0 μm or more, even more preferably 11.0 μm or more, and even more preferably 12.0 μm or more. It is also preferably 30.0 μm or less, more preferably 25.0 μm or less, and may be 20.0 μm or less, 15.0 μm or less, or 10.0 μm or less depending on the application. By setting the tensile strength at or above the lower limit, it is possible to maintain a high critical PV value, whereas by setting the tensile strength at or below the upper limit, it is possible to maintain a high critical PV value without a decrease in toughness as indicated by tensile elongation or Charpy impact value.

[0033] The average domain width is preferably 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. The average domain width is preferably 3.0 μm or less, more preferably 2.8 μm or less, even more preferably 2.5 μm or less, even more preferably 2.3 μm or less, and even more preferably 2.0 μm or less. The ratio L / W, where L is the average domain length and W is the average domain width, is preferably 3.0 or more, more preferably 3.5 or more, even more preferably 3.8 or more, and even more preferably 4.0 or more. By setting L / W at or above the lower limit, the limit PV value can be maintained at a higher value. The upper limit of L / W is not particularly specified, but a value of 20 or less is practical. The domains are mainly formed by mixing a polyacetal resin having a kinematic viscosity of 1,000,000 mm ２ This can be achieved by blending a silicone gum having a viscosity of more than 1 / s and a polyolefin-based lubricant in a predetermined amount. Furthermore, this can be achieved by blending a predetermined amount of an oxidatively modified polyolefin-based lubricant. Of course, it goes without saying that the domains may be formed by other methods. The preferred range of the resin composition in the other forms described above is the same as the preferred range of the resin composition of this embodiment described first in this specification.

[0034] <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 0.30 or less, more preferably 0.29 or less, even more preferably 0.24 or less, even more preferably 0.23 or less, and even more preferably 0.20 or less when molded into a cylindrical thrust-molded piece. The lower limit is, for example, practically 0.01 or more. Such a dynamic friction coefficient is mainly determined when the polyacetal resin has a dynamic viscosity of 1,000,000 mm ２The coefficient of dynamic friction is achieved by blending a silicone gum having a coefficient of friction of more than 1 / s and a polyolefin-based lubricant in a predetermined amount. The coefficient of dynamic friction is measured as described in the Examples section below.

[0035] The resin composition of this embodiment has a contact area of ​​2 cm ２ When measured at a temperature of 23°C according to the thrust ring friction and wear test specified in JIS K7218 Method A, the limiting PV value (MPa cm / s) is preferably 14.0 MPa cm / s or more, more preferably 15.0 MPa cm / s or more, even more preferably 15.5 MPa cm / s or more, even more preferably 16.0 MPa cm / s or more, and even more preferably 16.5 MPa cm / s or more. There is no particular upper limit, but 50.0 MPa cm / s or less is practical. The limiting PV value is measured as described in the examples below.

[0036] <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 and fed into an extruder for melt-kneading to obtain a pellet-shaped resin composition; (2) a method in which some of the components constituting the resin composition are fed into an extruder through a main feed port 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 then these pellets are mixed to obtain a resin composition having a predetermined composition. In this embodiment, it is preferable to prepare a masterbatch of the silicone gum before melt-kneading it with the remaining components. Examples of kneading machines include a kneader, a Banbury mixer, and an extruder. The various conditions and equipment for mixing and kneading are not particularly limited and may be appropriately selected from conventionally known conditions. Kneading is preferably performed at a temperature above the melting point of the polyacetal resin, specifically above the melting temperature of the polyacetal resin (generally 180°C or higher).

[0037] <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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 1. Raw Materials The raw materials shown in Table 1 below were used.

[0043] In Table 1 above, POM is an abbreviation for polyacetal resin.

[0044] 2. Examples 1 to 9 and Comparative Examples 1 to 10 <Production of Resin Compositions (Pellets)> The components shown in Table 1 were melt-kneaded in the proportions shown in Tables 2 to 5 (proportions of each component are in parts by mass) using a twin-screw extruder (manufactured by Ikegai Corporation, PCM-30, screw system 30 mm) under conditions of a screw rotation speed of 120 rpm and a cylinder set temperature of 190°C, and then extruded into strands and cut with a pelletizer to produce pellets of the resin compositions.

[0045] <Production of Cylindrical Thrust Test Piece> Using an SE-30DUZ manufactured by Sumitomo Heavy Industries, Ltd., pellets of the polyacetal resin composition obtained above were injection molded at a cylinder temperature of 200°C and a mold temperature of 80°C to form a cylindrical thrust test piece (JIS K7218 method, size: outer diameter 25.6 mm × inner diameter 20.0 mm × height 15.0 mm).

[0046] <Average length and width of domains> A cylindrical thrust test specimen was used to measure the average length and width of the domains. The surface of the cylindrical thrust test specimen was prepared by ultrasonic cleaning using ethanol to remove any impurities. A brightness image of the surface of the cylindrical thrust test specimen was obtained using a laser microscope, and the average length and width of the domains formed from the silicone compound were evaluated using image analysis software. The conditions for taking the brightness image and the method for image analysis are shown below.

[0047] <<Brightness Image Photography Conditions>> A hybrid laser microscope (OPTELICS HYBRID L7 (product name)) manufactured by Lasertec Corporation was used to photograph the brightness image. The photographing field was set at four positions: directly above the gate as the reference (0°), 90°, 180° (weld line on the anti-gate side), and near the 270° position, and a 20x objective lens was used. A lamp was selected as the light source for the laser microscope during photography, with a brightness of 200 and a light intensity of 100%. The resolution was set to 0.24 μm, and photography was performed using the confocal function. The obtained brightness image was subjected to automatic surface correction and median filter 5 × 5 processing on the device, and an analysis image was created.

[0048] <<Image Analysis>> Image analysis of the photographs used to calculate the average length and average width was performed using image analysis software (WinROOF 2018 (product name)) manufactured by Mitani Corporation. The length and width of each domain, as well as their average values, were automatically calculated for all domains in the photograph. All image analysis was performed using the above-mentioned image analysis software, following the procedure below. First, the analysis image obtained under the above conditions was loaded into the above-mentioned image analysis software, converted into a monochrome image, and the scale was calibrated. The "manual calibration" function was used to align the line with the 100 μm scale bar at the bottom of the luminance image, and 100 μm was entered as the actual size. Next, a rectangular ROI was used to select all areas except for the approximately 30 μm x 740 μm area at the bottom of the photograph, including the analysis condition field above. The selected area was then clipped to extract the image area. The box mode, which sets the border processing method for the rectangular ROI, was set to "cut at the boundary and process." Next, the ROI range was selected, and a threshold value for brightness was set using discriminant analysis. Specifically, in order to distinguish between the "portion to be measured" and the other "portion not to be measured" based on the threshold value, pixels with a luminance of 200 or more were selected and then a closing process was performed. The number of closing processes was set to 2. After performing the above process, pixels with a luminance value within the range of the two threshold values ​​(200-255) specified in the binarization process and an area of ​​0.525 μm were selected. ２The above-mentioned set of pixels was the subject of measurement. For the resulting image to be measured, "skeleton length" and "diagonal width" were selected from the "shape feature" function, and the length and width of the binarized selected region were calculated. The above analysis was performed for the four specified fields of view, and the average values ​​for each field of view automatically calculated by the image analysis software were added together and divided by the number of fields (4) to determine the average length and average width of the domain. Note that "skeleton length" refers to the length of the free-form curve, and "diagonal width" refers to the shortest distance between two lines parallel to the absolute maximum length when the figure is sandwiched between them. The average skeleton length calculated using the above method corresponds to the average length of the domain, and the average diagonal width corresponds to the domain width.

[0049] Electron microscope photographs of Example 4 and Comparative Example 7 are shown in Figures 1 and 2, respectively. It can be seen that elongated domains are formed in Example 4, whereas no elongated domains are formed in Comparative Example 7.

[0050] <Dynamic friction coefficient (surface pressure 4.9 MPa)> Cylindrical thrust test pieces of the resin composition were subjected to a thrust friction and wear test against carbon steel S45C at a linear velocity of 10 cm / s, with the surface pressure increased by 5 kg every 3 minutes from 3 kg, 5 kg, and 10 kg. Focusing on the dynamic friction coefficient under high surface pressure (load 100 kg, surface pressure 4.9 MPa), where differences in the dynamic friction coefficient due to formulations are likely to occur, the average value of the dynamic friction coefficient over 3 minutes was recorded. The results are shown in Tables 2 to 5 below.

[0051] <Limit PV Value (MPa cm / s)> A thrust friction and wear test was performed on a cylindrical thrust test piece of the resin composition against a polyamide 6 test piece at a linear velocity of 10 cm / s, with the surface pressure increased by 3 kg, 5 kg, and 10 kg every 3 minutes, and then by 5 kg thereafter. 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). The results are shown in Tables 2 to 5 below.

[0052]

[0053]

[0054]

[0055]

[0056] In the table above, "C2 ratio" refers to the ratio (unit: mass %) of the oxidized polyolefin-based lubricant to the total amount of polyolefin-based lubricant in each resin composition. As is clear from the above results, molded articles formed from the resin composition of the present invention had low dynamic friction coefficients and high limiting PV values ​​(Examples 1 to 9). In contrast, when the silicone gum content was low (Comparative Example 1), the sliding properties were poor. When no oxidized polyolefin-based lubricant was present, or when the content was low even if the oxidized polyolefin-based lubricant was present (Comparative Examples 3, 5, and 10), and even when no polyolefin-based lubricant was present (Comparative Examples 6 and 9), the PV limit was low. Furthermore, when the content of the oxidized polyolefin-based lubricant was high (Comparative Examples 2 and 4), the PV limit was low. On the other hand, when silicone oil was used instead of silicone gum (Comparative Examples 7 and 8), the PV limit was even lower. Furthermore, when silicone was not present (Comparative Example 9), the PV limit was particularly low.

Claims

1. 100 parts by mass of polyacetal resin and a kinetic viscosity of 1,000,000 mm ２ A resin composition comprising: 0.4 to 10 parts by mass of a silicone gum having a viscosity of more than 1 / s; and 0.5 to 10 parts by mass of a polyolefin-based lubricant, wherein 25 to 80 mass % of the polyolefin-based lubricant is an oxidatively modified polyolefin-based lubricant.

2. A resin composition comprising a polyacetal resin, a silicone gum, and a polyolefin-based lubricant, wherein the resin composition is molded into a cylindrical thrust test piece, and domains containing the silicone compound observed with a laser microscope have an average length L of 8.0 μm or more and an average width W of 3.0 μm or less.

3. The kinetic viscosity of the silicone gum contained in the resin composition is 5,000,000 mm ２ The resin composition according to claim 1, wherein the molecular weight is 1 / s or more.

4. The kinetic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm ２ The resin composition according to claim 1 or 2, wherein the molecular weight is 1 / s or more.

5. The resin composition according to claim 2, wherein the polyolefin-based lubricant contained in the resin composition includes an oxidatively modified polyolefin-based lubricant.

6. A resin composition according to claim 1 or 5, wherein the proportion of oxidatively modified polyolefin-based lubricant in the polyolefin-based lubricant contained in the resin composition is 35 mass% or more.

7. The kinetic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm ２ / s or more, and a ratio of the oxidatively modified polyolefin-based lubricant in the polyolefin-based lubricant contained in the resin composition is 35 mass % or more. The resin composition according to claim 1 , 8. The resin composition according to claim 7, wherein the resin composition is molded into a cylindrical thrust test piece and the domains containing the silicone compound observed with a laser microscope have an average length L of 8.0 μm or more and an average width W of 3.0 μm or less.

9. The kinetic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm ２ The resin composition according to claim 2, wherein the polyolefin-based lubricant has a molecular weight of 1000 or more and 35 mass % or more of the polyolefin-based lubricant is an oxidatively modified polyolefin-based lubricant.

10. The resin composition according to claim 2 or 8, wherein the ratio L / W of the average length L to the average width W of the domains containing the silicone compound is 3.0 or more.

11. Pellets of the resin composition according to claim 1, 3, 5, 7, 8 or 9.

12. A molded article formed from the resin composition according to claim 1, 3, 5, 7, 8 or 9.

13. A molded article formed from the pellets of claim 11.

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