Resin compositions, pellets, and molded articles

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

[Technical Field]

[0001] This invention relates to resin compositions, pellets, and molded articles. In particular, it relates to resin compositions having polyacetal resin as a main component. [Background technology]

[0002] Polyacetal resin is a plastic with excellent mechanical, electrical, and chemical properties, including chemical resistance, and is used in a wide range of applications. Furthermore, one known application 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 comprising 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. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 04-224856 [Overview of the project] [Problems that the invention aims to solve]

[0004] The resin composition described in Patent Document 1 above is a material with excellent sliding properties. However, in recent years, there has been a demand for even better sliding properties. In particular, there is a need for a resin composition that can provide molded products with a high PV limit value and a low coefficient of dynamic friction. The present invention aims to solve the aforementioned problems and to provide a resin composition, pellets, and molded articles that can provide molded articles with a high PV limit and a low coefficient of dynamic friction. [Means for solving the problem]

[0005] Based on the above problems, the inventors conducted research and found that the above problems can be solved by blending a predetermined silicone gum and a polyolefin-based lubricant with polyacetal resin. Specifically, the above problem was solved by the following means. <1> 100 parts by mass of polyacetal resin, Kinematic viscosity 1,000,000mm 2 0.4 to 10 parts by mass of silicone gum exceeding / s, It contains 0.5 to 10 parts by mass of a polyolefin-based lubricant, 25-80% by mass of the polyolefin-based lubricant is an oxidized polyolefin-based lubricant. Resin composition. <2> A resin composition comprising a polyacetal resin, silicone gum, and a polyolefin-based lubricant, The resin composition is molded into a cylindrical thrust test specimen, and the domains containing the silicone compound, as observed by 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. Resin composition. <3> The kinematic viscosity of the silicone gum contained in the resin composition is 5,000,000 mmHg. 2 It is greater than or equal to / s. <1> The resin composition described above. <4> The kinematic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm². 2 It is greater than or equal to / s. <1> ~ <3> A resin composition as described in any one of the following. <5> The resin composition contains a polyolefin-based lubricant that has been oxidized and modified. <1> ~ <4> A resin composition as described in any one of the following. <6> In the aforementioned resin composition, the proportion of oxidatively modified polyolefin lubricant is 35% by mass or more. <1> ~ <5> A resin composition as described in any one of the following. <7> The kinematic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm². 2 / s or greater, The resin composition according to any one of <1> to <6>, wherein in the polyolefin-based lubricant contained in the resin composition, the proportion of the oxidation-modified polyolefin-based lubricant is 35% by mass or more. <8> The resin composition according to any one of <1> to <7>, wherein when the resin composition is molded into a cylindrical thrust test piece, a domain containing a silicone compound observed by a laser microscope has an average length L of 8.0 µm or more and an average width W of 3.0 µm or less. <9> The silicone gum contained in the resin composition has a kinematic viscosity of 10,000,000 mm 2 / s or more, The resin composition according to any one of <1> to <8>, wherein 35% by mass or more of the polyolefin-based lubricant is an oxidation-modified polyolefin-based lubricant. <10> The resin composition according to <2> or <8>, wherein a ratio L / W of the average length L to the average width W of the domain containing the silicone compound is 3.0 or more. <11>A pellet 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 pellet according to <11>. Effects of the Invention

[0006] According to the present invention, it has become 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 a pellet and a molded article. Brief Description of the Drawings

[0007] [Figure 1] It is an electron micrograph of the test piece of Example 4. [Figure 2] It is an electron micrograph of the test piece of Comparative Example 7. Mode for Carrying Out the Invention

[0008] The following describes in detail embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment"). Note that the following embodiment is illustrative for explaining the present invention, and the present invention is not limited to this embodiment. In this specification, "~" is used to mean that the numbers before and after it are included as the lower and upper limits, respectively. In this specification, all physical properties and characteristic values ​​shall be those at 23°C unless otherwise specified. If the measurement methods, etc., described in the standards shown herein differ from year to year, unless otherwise specified, the standards as of January 1, 2023 shall apply.

[0009] The resin composition of this embodiment comprises 100 parts by mass of polyacetal resin and a kinematic viscosity of 1,000,000 mm². 2 The present invention provides a resin composition comprising 0.4 to 10 parts by mass of silicone gum with a PV limit of over / 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. This configuration makes it possible to provide a resin composition that can produce molded products with a high PV limit and a low dynamic friction coefficient.

[0010] Silicone gum disperses in polyacetal resin to form domains. These silicone gums are then stretched by the resin flow during injection molding of the resin composition. The longer the silicone gum region is stretched, the higher the critical PV value becomes. However, if the silicone gum content is too high, other physical properties of the resulting molded article tend to be inferior. On the other hand, polyolefin-based lubricants contribute to improving initial sliding properties. Furthermore, together with silicone gum, they can improve overall sliding properties and lower the coefficient of dynamic friction of the resulting molded product. However, it is presumed that non-oxidized polyolefin-based lubricants tend to remain on the surface of the molded product and are prone to leaching out. In this embodiment, it is presumed that this problem is solved by using at least an oxidized polyolefin-based lubricant. That is, it is presumed that the oxidized polyolefin-based lubricant is compatible with polyacetal resin and is present not only on the surface of the molded product but also inside it. Furthermore, it is presumed that the non-oxidized polyolefin-based lubricant can also be made to exist not only on the surface of the molded product but also inside it, dragged along by the oxidized polyolefin-based lubricant. As a result, molded products with a high PV limit and a low coefficient of dynamic friction are obtained. The details of this embodiment will be described below.

[0011] <Polyacetal resin> The resin composition of this embodiment includes a polyacetal resin. The polyacetal resin is not particularly limited in type, and may be a homopolymer containing only divalent oxymethylene groups as constituent units, or a copolymer containing divalent oxymethylene groups and divalent oxyalkylene groups having 2 to 6 carbon atoms as constituent units.

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

[0013] In polyacetal resins, the proportion of oxyalkylene groups having 2 to 6 carbon atoms to the total number of moles of oxymethylene groups and oxyalkylene groups having 2 to 6 carbon atoms is not particularly limited and can be 0.5 to 10 mol%.

[0014] In order to produce the above polyacetal resin, trioxane is usually used as the main raw material. Further, for introducing oxyalkylene groups having 2 to 6 carbon atoms into a polyacetal resin, cyclic formals or cyclic ethers can be used. Specific examples of the cyclic formal include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3,5-trioxepane, 1,3,6-trioxocane, and the like. Specific examples of the cyclic ether include ethylene oxide, propylene oxide, butylene oxide, and the like. To introduce oxyethylene groups into a polyacetal resin, 1,3-dioxolane may be used as the main raw material; to introduce oxypropylene groups, 1,3-dioxane may be used as the main raw material; and to introduce oxybutylene groups, 1,3-dioxepane may be used as the main raw material. In addition, for polyacetal resins, it is preferable that the amounts of hemiformal terminal groups, formyl terminal groups, and terminal groups unstable to heat, acid and base are small. Here, the hemiformal terminal group is represented by -OCH2OH, and the formyl terminal group is represented by -CHO.

[0015] The polyacetal resin used in the present embodiment has a melt volume rate (MVR) measured in accordance with ISO 1133 under the conditions of a temperature of 190°C and a load of 2.16 kg of 0.5 cm 3 / 10 min or more is preferable, and 0.6 cm 3 / 10 min or more is more preferable, 0.8 cm 3 / 10 min or more is even more preferable, 1 cm 3 / 10 min or more is still more preferable, and 5 cm 3 / 10 min or more is even more particularly preferable. Setting the MVR to be not lower than the above lower limit tends to further improve the productivity of the resin composition. Further, the MVR of the polyacetal resin is 20 cm 3 / 10 min or less is preferable, 18 cm 3 / 10 min or less is more preferable, 14 cm 3 / 10 min or less is even more preferable, 10 cm 3 / More preferably it is 10 minutes or less, 8cm 3 It is even more preferable if it is 10 minutes or less.

[0016] In addition to the above, polyacetal resins described in paragraphs 0018 to 0043 of Japanese Patent Publication No. 2015-074724 can be used as polyacetal resins, and these contents are incorporated herein by reference. The polyacetal resin used in this embodiment may be recycled (including recovered products, material recycled products, chemical recycled products, etc.), rejected products, or scraps from thermoplastic resin molding.

[0017] The resin composition of this embodiment preferably contains polyacetal resin in a proportion of 80% by mass or more, 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, and the kinematic viscosity is 1,000,000 mmHg. 2 The components other than the silicone gum with a viscosity exceeding / s and the polyolefin-based lubricant may all be polyacetal resin. The resin composition of this embodiment may contain only one type of polyacetal resin, or it may contain two or more types. If it contains two or more types, it is preferable that the total amount is within the above range.

[0018] <Kinematic viscosity 1,000,000mm 2 / s Super Silicone Gum > The resin composition of this embodiment has a kinematic viscosity of 1,000,000 mm². 2 It is preferable to include a silicone gum with a kinematic viscosity greater than / s. Including such a silicone gum can increase the limiting PV value of the resulting molded article. Silicone gum refers to liquid silicone or silicone oil with 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 mm². 2The kinematic viscosity of silicone gum with a viscosity exceeding 1 / s is 5,000,000 mm². 2 Preferably, it should be 10,000,000 mm² or more. 2 It is more preferable that the value be 15,000,000 mm² or more. 2 It is even more preferable that the rate is 17,000,000 mm² or higher. 2 It is even more preferable that the speed is 30,000,000 mm or more. 2 Preferably, the rate is less than or equal to 25,000,000 mm 2 It is more preferable that the rate is less than or equal to / s, and 22,000,000 mm 2 It is even more preferable that the value be less than or equal to / s. By setting it above the lower limit, it becomes possible to maintain a high limit PV value. Also, by setting it below the upper limit, it is possible to maintain a high limit PV value while suppressing mold contamination and delamination of molded pieces.

[0019] The resin composition of this embodiment has a kinematic viscosity of 1,000,000 mm². 2 The mixture may contain only one type of silicone gum with a viscosity greater than / s, or it may contain two or more types. When two or more types are included, it is preferable that the kinematic viscosity of the mixture be within the above range. Kinematic viscosity is calculated 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 then using a calibration curve of the kinematic viscosity of the silicone oil and the viscosity of the toluene solution. As the measuring device, the TVE-25L cone plate type viscometer 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 a polyorganosiloxane, represented as -(Si(R)2-O)-, where R is independently a hydrogen atom, a hydrocarbon group, an -O-hydrocarbon group, or a hydroxyl group (however, at least one of R is a hydrocarbon group or an -O-hydrocarbon group). 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. The -(Si(R)2-O)- in the silicone gum may be of two types or more than two types.

[0021] When incorporating silicone gum, it may be prepared as a masterbatch. Polyacetal resin is an example of a resin used in the masterbatch. The proportion of silicone gum in the masterbatch is preferably 10% by mass or more, more preferably 20% by mass or more, preferably 60% by mass or less, and more preferably 50% by mass or less.

[0022] The kinematic viscosity of the resin composition of this embodiment is 1,000,000 mm². 2 The content of silicone gum with a viscosity of more than / s is preferably 0.4 parts by mass or more, more preferably 0.6 parts by mass or more, even more preferably 0.8 parts by mass or more, and also 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. Setting the content above the lower limit and below the upper limit tends to further improve sliding properties. The resin composition of this embodiment has a kinematic viscosity of 1,000,000 mm². 2 The product may contain only one type of silicone gum with a viscosity exceeding / s, or it may contain two or more types. If it contains two or more types, it is preferable that the total amount is within the above range.

[0023] <Polyolefin-based lubricant> The resin composition of this embodiment contains a polyolefin-based lubricant. By including the polyolefin-based lubricant, the initial sliding properties are improved, and together with the silicone gum, the coefficient of dynamic friction can be reduced. Polyolefin lubricants are homopolymers or copolymers of olefins. 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 polyolefin-based lubricants), and it is preferable that the lubricant contains an oxidized polyolefin-based lubricant. The oxidized polyolefin-based lubricant is easily mixed with the polyacetal resin, disperses evenly throughout the molded product, and further improves the sliding properties of the resulting molded product.

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

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

[0026] The resin composition of this embodiment preferably contains an oxidized polyolefin-based lubricant. Including an oxidized polyolefin-based lubricant further improves the initial sliding properties and, together with the silicone gum, can further reduce the coefficient of dynamic friction. Oxidized polyolefin lubricants can be obtained by oxidizing a corresponding unmodified polyolefin lubricant. In this embodiment, oxidized polyethylene wax is preferred. Examples of polyethylene oxide waxes include Licowax® PED521, PED522, and PED121 from Clariant Chemicals, and Ceridust® 3715.

[0027] In this embodiment, it is preferable to include an oxidized polyolefin-based lubricant and an unmodified polyolefin-based lubricant, and more preferably to include an oxidized polyethylene wax and an unmodified polyethylene wax.

[0028] The content of the oxidatively modified polyolefin 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 also preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 74% by mass or less. Setting it above the lower limit tends to make the dynamic friction coefficient of the resulting molded article smaller. Conversely, setting it below the upper limit tends to make the PV limit value of the resulting molded article larger. The resin composition of this embodiment may contain only one type of oxidatively modified polyolefin lubricant, or it may contain two or more types. When two or more types are included, it is preferable that the total amount is within the above range.

[0029] The molecular weight (viscosity method) of polyolefin-based lubricants (oxidized polyolefin-based lubricants, unmodified polyolefin-based lubricants, 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 even more preferably 4,500 or more, even more preferably 5,000 or more, and even more preferably 6,000 or more. By setting it above the lower limit, high sliding performance can be maintained without bleed-out from the molded product. Furthermore, the molecular weight (viscosity method) of polyolefin-based lubricants 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 below the upper limit tends to further improve sliding performance. The molecular weight of polyolefin lubricants is measured according to gel permeation chromatography (viscosity method). In this embodiment, if the resin composition contains two or more polyolefin-based lubricants, the molecular weight shall be the weighted average value of the molecular weights of each polyolefin-based lubricant.

[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 part 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 also 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. Setting the content above the lower limit and below the upper limit tends to further improve sliding properties. The resin composition of this embodiment may contain only one type of polyolefin-based lubricant, or it may contain two or more types. When two or more types are included, it is preferable that the total amount is within the above range.

[0031] <Other ingredients> The resin composition of this embodiment may contain known additives and fillers, to the extent that they do not impair the objectives of the present invention. Examples of additives and fillers that can be used in this embodiment include, as needed, known thermoplastic polymers other than polyacetal resin, acid-modified polymers, weathering agents, formaldehyde scavengers, inorganic particles, antioxidants (hindered amine-based, hindered phenol-based, etc.), heat stabilizers, colorants, nucleating agents, plasticizers, fluorescent whitening agents, mold release agents, antistatic agents, ultraviolet absorbers, flame retardants, and flame retardant enhancers. The resin composition of this embodiment is a polyacetal resin with a kinematic viscosity of 1,000,000 mm². 2 The silicone gum with a viscosity of over / s, the polyolefin-based lubricant, and other components added as needed are adjusted to a total of 100% by mass. The resin composition of this embodiment has a kinematic viscosity of 1,000,000 mm². 2 Preferably, the total of the silicone gum with a viscosity of more than / s and the polyolefin-based lubricant 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 also account for 98% by mass or more.

[0032] <Other forms> The resin composition of this embodiment is also 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 molded piece, and it is preferable that the domains containing the silicone compound, as observed by a laser microscope, have an average length of 8.0 μm or more and an average width of 3.0 μm or less. By forming such thin and long domains containing the silicone compound in the molded product, a molded product with a low coefficient of dynamic friction and a high limit PV value can be obtained. It is preferable that 90% or more of the domains are 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, even more preferably 12.0 μm or more, and also preferably 30.0 μm or less, more preferably 25.0 μm or less, and depending on the application, it may be 20.0 μm or less, 15.0 μm or less, or 10.0 μm or less. Setting it above the lower limit allows for maintaining a high limit PV value. Setting it below the upper limit allows for maintaining a high limit PV value without a decrease in toughness as indicated by tensile elongation or Charpy impact value.

[0033] The average width of the domain 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. Furthermore, the average width of the domain 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. When the average domain length is L and the average domain width is W, the ratio L / W is preferably 3.0 or higher, more preferably 3.5 or higher, even more preferably 3.8 or higher, and even more preferably 4.0 or higher. By keeping L / W above the lower limit, it becomes possible to maintain a higher critical PV value. There is no specific upper limit for L / W, but it is practical to keep it at 20 or lower. The above domain mainly involves polyacetal resin with a kinematic viscosity of 1,000,000 mmHg. 2 This is achieved by blending a silicone gum with a viscosity exceeding / s with a polyolefin-based lubricant in predetermined amounts. Furthermore, it can be achieved by blending an oxidatively modified polyolefin-based lubricant in predetermined amounts. Of course, it goes without saying that the above domains may be formed by other methods. The preferred range of the other forms of resin compositions described above is the same as the preferred range of the resin compositions of this embodiment described first in this specification.

[0034] <Physical properties of resin compositions> 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 when molded into a cylindrical thrust molded piece, 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. A practical lower limit is, for example, 0.01 or more. Such a dynamic friction coefficient is mainly due to the kinematic viscosity of the polyacetal resin at 1,000,000 mm². 2 This is achieved by blending silicone gum with a viscosity exceeding / s and a polyolefin-based lubricant in predetermined amounts. The coefficient of dynamic friction is measured according to the description in the examples below.

[0035] The resin composition of this embodiment has a contact area of ​​2 cm². 2 When measured at a temperature of 23°C according to the thrust ring friction wear test specified in JIS K7218 Method A, the limit PV value (MPa·cm / s) is preferably 14.0 MPa·cm / s or higher, more preferably 15.0 MPa·cm / s or higher, even more preferably 15.5 MPa·cm / s or higher, even more preferably 16.0 MPa·cm / s or higher, and even more preferably 16.5 MPa·cm / s or higher. There is no specific upper limit, but 50.0 MPa·cm / s or lower is practical. The limiting PV value is measured according to the example described below.

[0036] <Method for producing resin compositions> The resin composition of this embodiment can be easily prepared by known methods commonly used for preparing conventional thermoplastic resin compositions. For example, (1) a method of mixing all the components constituting the resin composition, supplying it to an extruder and melt-kneading it to obtain a pelletized resin composition; (2) a method of supplying a portion of the components constituting the resin composition from the main feed port of an extruder and the remaining components from the side feed port and melt-kneading them to obtain a pelletized resin composition; (3) a method of preparing pellets with different compositions by extrusion or the like, and then mixing these pellets to adjust them into a resin composition having a predetermined composition. In this embodiment, it is preferable to first prepare the silicone gum as a masterbatch and then melt-mix it with the remaining components. Examples of mixing machines include kneaders, Banbury mixers, and extruders. There are no particular restrictions on the various conditions and equipment for mixing and kneading; they can be appropriately selected from any conventionally known conditions. Mixing is preferably carried out at a temperature above the melting temperature of the polyacetal resin, specifically above the melting temperature of the polyacetal resin (generally 180°C or higher).

[0037] <Molded products> The molded articles of this embodiment are formed from the resin composition or pellets of this embodiment. The pellets obtained by pelletizing the resin composition of this embodiment are molded into molded articles by various molding methods. Alternatively, the resin composition, which has been melt-kneaded in an extruder, can be directly molded into molded articles without going through pellets. There are no particular restrictions on the shape of the molded product, and it can be appropriately selected according to the application and purpose of the molded product. Examples include plate-shaped, rod-shaped, sheet-shaped, film-shaped, cylindrical, annular, circular, elliptical, gear-shaped, polygonal, irregularly shaped, hollow, frame-shaped, box-shaped, and panel-shaped products. The molded product in this embodiment may be a finished product or a component.

[0038] The method for molding the molded product is not particularly limited, and conventionally known molding methods can be used. Examples include injection molding, injection compression molding, extrusion molding, shape extrusion, transfer molding, hollow molding, gas-assisted hollow 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 sliding members. Therefore, molded articles formed from the resin composition of this embodiment are preferably used as sliding members (sliding parts). Specific examples of sliding components include gears, rotating shafts, bearings, various gears, cams, end face materials for mechanical seals, valve seats for valves, sealing components such as V-rings, rod packings, piston rings, and rider rings, as well as sliding components such as the rotating shafts, rotating sleeves, pistons, impellers, and rollers of compressors, all aimed at achieving high quality as required in electrical and electronic equipment, office equipment, vehicles (automobiles), and industrial equipment.

[0040] The sliding members of this embodiment can be used not only with other sliding members of this embodiment, but also in combination with other resin sliding members, fiber-reinforced resin sliding members, ceramic or metal sliding members. [Examples]

[0041] The present invention will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate, as long as they do not depart 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 other reasons, measurements can be taken using other instruments with equivalent performance.

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

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

[0044] 2. Examples 1-9, Comparative Examples 1-10 <Manufacturing of resin compositions (pellets)> Each component shown in Table 1 was melt-mixed in the proportions shown in Tables 2 to 5 (the proportion of each component is in parts by mass) using a twin-screw extruder (Ikegai Co., Ltd., PCM-30, 30mm screw system) under the conditions of a screw rotation speed of 120 rpm and a cylinder set temperature of 190°C. The mixture was then extruded into strands and cut with a pelletizer to produce pellets of the resin composition. Note that the values ​​in the "Silicone Gum B-1" column in Tables 2 to 5 represent the amount of "silicone gum" itself derived from the "POM masterbatch".

[0045] <Manufacturing of cylindrical thrust test specimens> Using a Sumitomo Heavy Industries, Ltd. SE-30DUZ, the 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 produce cylindrical thrust test specimens (JIS K7218 method, size: outer). diameter It was molded to a size of 25.6mm (inner diameter 20.0mm) x 15.0mm (height).

[0046] <Average domain length and width> Cylindrical thrust specimens were used to measure the average length and width of the domains. The surfaces of the cylindrical thrust specimens were prepared by ultrasonic cleaning with ethanol to remove any impurities. Brightness images of the cylindrical thrust specimen surfaces were 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 capturing the luminance image and the image analysis method are shown below.

[0047] <<Conditions for capturing luminance images>> A hybrid laser microscope (OPTELICS HYBRID L7 (product name)) manufactured by Lasertec Corporation was used for brightness imaging. The imaging field of view was set to four locations, with the area directly above the gate as the reference point (0°), and around 90°, 180° (weld line on the opposite side of the gate), and 270°. A 20x objective lens was used. For the laser microscope's light source during imaging, a lamp was selected with a brightness of 200 and a light intensity of 100%. The resolution was set to 0.24 μm, and imaging was performed using the confocal function. The obtained luminance image was processed using automatic surface correction and a 5x5 median filter on the device to obtain the analysis image.

[0048] <<Image Analysis>> For image analysis of the photographs used to calculate the average length and width, we used image analysis software (WinROOF 2018 (product name)) manufactured by Mitani Corporation. For all domains shown in the photographs, the length, width, and average value of each domain were automatically calculated. All image analysis was performed using the image analysis software mentioned above, following the procedure below. First, the analysis image obtained under the above conditions was loaded into the image analysis software described above, and after being converted to a monochrome image, scale calibration was performed. The method used was to use the "manual calibration" function, aligning the line with the 100 μm scale bar located at the bottom of the luminance image, and entering 100 μm as the actual size value. Next, all areas except the area of ​​approximately 30 μm × 740 μm at the bottom of the captured image, including the analysis conditions section, were selected using a rectangular ROI, and the selected area was cropped to extract the image region. For setting the boundary processing method of the rectangular ROI, the box mode selected was "Cut and process at boundary". Next, a region of interest (ROI) area was selected, and thresholds for brightness were set using discriminant analysis. Specifically, to distinguish between the "area to be measured" and the "area not to be measured" based on the thresholds, pixels with a brightness of 200 or higher were selected, and a closing process was performed. The closing process was repeated twice. After performing the above process, pixels with brightness values ​​within the range of the two thresholds specified in the binarization process (200-255) and an area of ​​0.525 μm² were selected. 2 The collection of pixels with a number of pixels greater than or equal to the specified value was used as the subject of measurement. For the obtained measurement target image, "Skeleton Length" and "Diagonal Width" were selected from the "Shape Features" function, and the length and width of the binarized selected region were calculated. The above analysis was performed on 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 of view (4) to obtain the average length and average width of the domain. "Skeleton Length" represents the length of the free curve, and "Diagonal Width" represents the shortest distance between two lines parallel to the absolute maximum length when the figure is enclosed by two lines. The average value of the skeletal length obtained by the above method corresponds to the average length of the domain, and the average value of the diagonal width corresponds to the width of the domain.

[0049] Electron microscope images of Example 4 and Comparative Example 7 are shown in Figures 1 and 2, respectively. In Example 4, elongated domains are formed, whereas in Comparative Example 7, elongated domains are not formed.

[0050] <Coefficient of dynamic friction (surface pressure 4.9 MPa)> For cylindrical thrust test specimens of resin compositions, a thrust-type friction and wear test was conducted against carbon steel S45C at a linear velocity of 10 cm / s, increasing the surface pressure by 3 kg, 5 kg, and 10 kg every 3 minutes (5 kg after 5 kg). Focusing on the dynamic friction coefficient under high surface pressure (load 100 kg, surface pressure 4.9 MPa), where differences in dynamic friction coefficient due to formulation are likely to occur, the average value of the dynamic friction coefficient over 3 minutes was recorded. The results are shown in Tables 2-5 below.

[0051] <Limited PV value (MPa·cm / s)> For cylindrical thrust test specimens of resin compositions, a thrust-type friction and wear test was performed on polyamide 6 specimens at a linear velocity of 10 cm / s, increasing the surface pressure by 3 kg, 5 kg, and 10 kg every 3 minutes, with subsequent increases of 5 kg. The product of the surface pressure and velocity at the next lower pressure level where fusion occurred due to frictional heat was defined as the critical PV value (unit: MPa·cm / s). The results are shown in Tables 2-5 below.

[0052] [Table 2]

[0053] [Table 3]

[0054] [Table 4]

[0055] [Table 5]

[0056] In the table above, "C2 ratio" refers to the proportion (in mass %) of oxidized polyolefin lubricant in the total amount of polyolefin lubricant in each resin composition. As is clear from the above results, molded articles formed from the resin composition of the present invention had a low coefficient of dynamic friction and a high limit PV value (Examples 1-9). In contrast, when the silicone gum content was low (Comparative Example 1), the sliding properties were inferior. When oxidatively modified polyolefin lubricants were not present, or when they were present in small amounts (Comparative Examples 3, 5, and 10), and even when polyolefin lubricants were not present at all (Comparative Examples 6 and 9), the PV limit value was low. Furthermore, when the content of oxidatively modified polyolefin lubricants was high (Comparative Examples 2 and 4), the PV limit value 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, the PV limit was particularly low when silicone was not included (Comparative Example 9).

Claims

1. 100 parts by mass of polyacetal resin, 0.4 to 10 parts by mass of silicone gum, It contains 0.5 to 10 parts by mass of a polyolefin-based lubricant, The resin composition is such that 25 to 80% by mass of the polyolefin-based lubricant is an oxidatively modified polyolefin-based lubricant. The kinematic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm². ２ A resin composition having a coefficient of / s or higher.

2. A resin composition comprising a polyacetal resin, silicone gum, and a polyolefin-based lubricant, The resin composition is injection molded under conditions of a cylinder temperature of 200°C and a mold temperature of 80°C to form a cylindrical thrust test specimen as specified by JIS K7218, and when the surface of the cylindrical thrust test specimen is observed with a laser microscope, the observed domains containing the silicone compound have an average length L of 8.0 μm or more and an average width W of 3.0 μm or less. The kinematic viscosity of the silicone gum contained in the resin composition is 10,000,000 mm². ２ A resin composition having a coefficient of / s or higher.

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

4. The resin composition according to claim 1 or 3, wherein the proportion of oxidatively modified polyolefin lubricant in the polyolefin lubricant contained in the resin composition is 35% by mass or more.

5. The resin composition according to claim 4, wherein the resin composition is injection molded under conditions of a cylinder temperature of 200°C and a mold temperature of 80°C to form a cylindrical thrust test specimen as specified by JIS K7218, and when the surface of the cylindrical thrust test specimen is observed with a laser microscope, the observed domains containing the silicone compound have an average length L of 8.0 μm or more and an average width W of 3.0 μm or less.

6. The resin composition according to claim 2, 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.

7. Pellets of the resin composition according to claim 1 or 3.

8. A molded article formed from the resin composition according to claim 1 or 3.

9. A molded article formed from the pellets described in claim 7.

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