Resin composition and molded article

Abstract

To provide a resin composition from which a molded article having short measuring time, a low coefficient of dynamic friction to a metal member, and has a limit PV value to a resin member can be provided, and a molded article.SOLUTION: A resin composition contains, with respect to (A) 100 pts.mass of a polyacetal resin, (B) 0.3-2.5 pts.mass of an aliphatic acid metal salt which contains calcium and / or magnesium and has an aliphatic group having 10 to 50 carbon atoms, and (C) 0.3-2.5 pts.mass of aliphatic acid full ester, wherein a mass ratio of (B) to (C) is 0.5 or more and less than 5.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a resin composition and a molded product.

Background Art

[0002] Polyacetal resins are used in a wide range of applications as plastics having excellent mechanical properties, electrical properties, and chemical properties such as chemical resistance. Here, in order to further enhance the functionality of polyacetal resins, blending various additives has been studied. For example, Patent Document 1 discloses a polyacetal resin composition comprising a polyacetal resin, a predetermined fatty acid diester compound, a predetermined fatty acid monoester compound, a fatty acid, and a fatty acid metal salt.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in order to impart slidability to a polyacetal resin, a fatty acid ester may be blended. However, it has been found that the fatty acid ester has good slipperiness and the metering time becomes long. As a result of studies by the present inventors, it was considered to blend a fatty acid metal salt in order to shorten the metering time. However, it has been found that when a fatty acid metal salt is blended, the coefficient of kinetic friction with respect to a metal member increases or the limiting PV value with respect to a resin member decreases. An object of the present invention is to solve the above problems, and to provide a resin composition capable of providing a molded product having a short metering time, a low coefficient of kinetic friction with respect to a metal member, and a high limiting PV value with respect to a resin member, and a molded product. [Means for solving the problem]

[0005] Based on the above problems, the inventors conducted investigations and found that the above problems were solved by using a fatty acid full ester as the fatty acid ester, using a fatty acid metal salt with a sufficiently long aliphatic chain as the fatty acid metal salt, and precisely adjusting the ratio of the two. Specifically, the above problem was solved by the following means. <1> (A) Per 100 parts by mass of polyacetal resin, (B) 0.3 to 2.5 parts by mass of a fatty acid metal salt containing calcium and / or magnesium and having an aliphatic group having 10 to 50 carbon atoms, (C) Contains 0.3 to 2.5 parts by mass of fatty acid ester, A resin composition in which the mass ratio of (B) / (C) is 0.5 or more and less than 5. <2> The fatty acid metal salt (B) includes a fatty acid metal salt having a linear aliphatic group with 12 to 36 carbon atoms. <1> The resin composition described above. <3> The aforementioned fatty acid full ester (C) contains 1 to 4 ester groups in one molecule. <1> or <2> The resin composition described above. <4> The fatty acid full ester (C) has a linear aliphatic group having 10 to 50 carbon atoms. <1> ~ <3> A resin composition as described in any one of the following. <5> The fatty acid metal salt (B) comprises a fatty acid metal salt having a linear aliphatic group having 12 to 36 carbon atoms, and the fatty acid full ester (C) contains 1 to 4 ester groups in one molecule and has a linear aliphatic group having 10 to 50 carbon atoms. <1> The resin composition described above. <6> In a thrust-type friction and wear test conducted on carbon steel S45C using a cylindrical thrust test specimen formed from the aforementioned resin composition, the coefficient of dynamic friction at a surface pressure of 4.9 MPa was 0.15 or less, with a linear velocity of 10 cm / s and the surface pressure increasing from 3 kg every 3 minutes. <1> ~ <5> A resin composition as described in any one of the following. <7> Regarding test specimens formed from the aforementioned resin composition into cylindrical thrust test specimens, in a thrust-type friction and wear test conducted at a linear velocity of 10 cm / s with the surface pressure increased from 3 kg every 3 minutes, the limiting PV value is 29 MPa·cm / s or higher, compared to test specimens formed from polyamide 6 into similar cylindrical thrust test specimens. <1> ~ <6> A resin composition as described in any one of the following. <8> <1> ~ <7> A molded article formed from any one of the resin compositions described in that one. [Effects of the Invention]

[0006] The present invention makes it possible to provide a resin composition and molded articles that have a short weighing time, a low coefficient of dynamic friction with respect to metal members, and a high limit PV value with respect to resin members. [Modes for carrying out the invention]

[0007] 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, 2022 shall apply.

[0008] The resin composition of this embodiment is characterized by comprising (A) 100 parts by mass of polyacetal resin, (B) 0.3 to 2.5 parts by mass of fatty acid metal salt containing calcium and / or magnesium and having aliphatic groups having 10 to 50 carbon atoms, and (C) 0.3 to 2.5 parts by mass of fatty acid full ester, wherein the mass ratio of (B) / (C) is 0.5 or more and less than 5. By adopting this configuration, it becomes possible to provide a resin composition that can produce molded products with a short weighing time, a low coefficient of dynamic friction with respect to metal components, and a high limit PV value with respect to resin components. To impart sliding properties to polyacetal resin, it is conceivable to incorporate fatty acid esters. However, it was found that incorporating fatty acid esters made the resin composition prone to slipping during molding. In other words, although the sliding properties were excellent, the excessive slipperiness resulted in a longer metering time. A long metering time is undesirable from the standpoint of moldability. Therefore, the inventors conducted further investigations and found that slipping during molding could be suppressed by incorporating fatty acid metal salts. It was hypothesized that the fatty acid metal salts dispersed on the interior side of the polyacetal resin and provided an anchoring effect for the fatty acid esters, thereby suppressing slipping during molding. Furthermore, the inventors' investigations suggested that even with fatty acid metal salts, if the aliphatic group chain is short or the number of carbon atoms is small, the anchoring effect may be insufficient, potentially resulting in insufficient suppression of slipping when fatty acid esters are added. In addition, it was found that even with fatty acid metal salts, if zinc salts were used, the metering time would be longer. This was hypothesized to be because when fatty acid zinc was used, the skin layer of the polyacetal resin molded product became thicker, making it easier for the fatty acid zinc to come to the surface. In other words, it was hypothesized that during the molding of the resin composition, zinc fatty acid acts as a lubricant, and the frictional force Fc between the pellet and the cylinder wall is lower than the frictional force Fs between the pellet and the screw surface, thus increasing the metering time. Furthermore, even with fatty acid esters, by using full fatty acid esters and precisely adjusting the ratio of fatty acid metal salts to full fatty acid esters, it was possible to increase the limiting PV value of the resulting molded product relative to the resin component. Further details of the present invention will be described below.

[0009] <(A) Polyacetal resin> The resin composition of this embodiment contains a polyacetal resin. By including the polyacetal resin, a molded product with excellent sliding properties and mechanical strength can be obtained. The polyacetal resin used in this embodiment has an acetal structure -(-O-CRH-) n The polyacetal resin used in this embodiment is a polymer having a repeating structure of -(wherein R represents a hydrogen atom or an organic group), and usually has an oxymethylene group (-CH2O-) where R is a hydrogen atom as the main constituent unit. The polyacetal resin used in this embodiment may include not only acetal homopolymers consisting only of this repeating structure, but also copolymers (including block copolymers) and terpolymers that contain one or more constituent units other than the oxymethylene group, and may have not only a linear structure but also branched and crosslinked structures.

[0010] Other structural units besides the oxymethylene group include, for example, branched oxyalkylene groups having 2 to 10 carbon atoms, such as oxyethylene (-CH2CH2O-), oxypropylene (-CH2CH2CH2O-), and oxybutylene (-CH2CH2CH2CH2O-). Among these, branched oxyalkylene groups having 2 to 4 carbon atoms are preferred, and oxyethylene groups are particularly preferred. The content of such oxyalkylene structural units other than the oxymethylene group is preferably 0.1 mol% to 20 mol%, and more preferably 0.1 mol% to 15 mol% in the polyacetal resin.

[0011] The method for producing the polyacetal resin used in this embodiment is arbitrary and can be any conventionally known method. For example, a polyacetal resin having an oxymethylene group and an oxyalkylene group having 2 to 4 carbon atoms as constituent units can be produced by copolymerizing a cyclic oligomer of an oxymethylene group, such as a trimer (trioxane) or tetramer (tetraoxane) of formaldehyde, with a cyclic oligomer containing an oxyalkylene group having 2 to 4 carbon atoms, such as ethylene oxide, 1,3-dioxolane, 1,3,6-trioxocan, or 1,3-dioxepane.

[0012] In particular, the polyacetal resin used in the present invention is preferably a copolymer of a cyclic oligomer such as trioxane or tetraoxane with ethylene oxide and / or 1,3-dioxolane, and especially preferably a copolymer of trioxane and 1,3-dioxolane. In this case, it is preferable that the total amount of ethylene oxide and / or 1,3-dioxolane is 1 to 20% by mass, relative to 80 to 99% by mass of the cyclic oligomer. The melt flow rate (MFR) of the polyacetal resin is optional, but according to ASTM-D1238, the value measured at 190°C under a 2.16 kg load is usually 1 g / 10 min or more, preferably 10 g / 10 min or more, more preferably 13 g / 10 min or more, even more preferably 20 g / 10 min or more, even more preferably 32 g / 10 min or more, even more preferably 35 g / 10 min or more, and even more preferably 40 g / 10 min or more. Furthermore, the MFR is usually 150 g / 10 min or less, preferably 100 g / 10 min or less, more preferably 70 g / 10 min or less, even more preferably 60 g / 10 min or less, and even more preferably 50 g / 10 min or less. When the resin composition of this embodiment contains two or more types of (A) polyacetal resins, it is preferable that the MFR of the mixture satisfies the above range.

[0013] The resin composition of this embodiment preferably contains (A) polyacetal resin in an amount of 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The upper limit is the amount in which the entire amount other than (B) fatty acid metal salt and (C) fatty acid full ester becomes polyacetal resin. The resin composition of this embodiment may contain only one type of (A) 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.

[0014] <(B) Fatty acid metal salts> The resin composition of the present embodiment contains (B) a fatty acid metal salt containing calcium and / or magnesium and having an aliphatic group with 10 to 50 carbon atoms in a proportion of 0.3 to 2.5 parts by mass with respect to 100 parts by mass of (A) polyacetal resin. Even if (C) fatty acid esters are blended by containing (B) fatty acid metal salts, the metering time can be shortened.

[0015] The (B) fatty acid metal salt used in the present embodiment is a calcium salt and / or a magnesium salt, and it is preferable to contain at least a calcium salt. Moreover, the (B) fatty acid metal salt used in the present embodiment has an aliphatic group with 10 to 50 carbon atoms, and the number of carbon atoms is preferably 12 or more, more preferably 14 or more, and preferably 36 or less, more preferably 28 or less, still more preferably 25 or less, and even more preferably 20 or less. The aliphatic group is preferably a linear aliphatic group. Further, the aliphatic group may have a hydroxyl group as a substituent. By having a hydroxyl group as a substituent, the metering time during molding of the obtained resin composition tends to be shorter. Also, the aliphatic group may be a saturated aliphatic group or an unsaturated aliphatic group, but a saturated aliphatic group is preferable. More specifically, examples of the fatty acid constituting the fatty acid metal salt include myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, henicosanoic acid, behenic acid, lignoceric acid, cerotic acid, and montanic acid, and fatty acids in which one of the hydrogen atoms of the aliphatic chain of these fatty acids is substituted with a hydroxyl group. Stearic acid and hydroxystearic acid are preferable. In the present embodiment, the (B) fatty acid metal salt is preferably calcium stearate, magnesium stearate, calcium hydroxystearate, or magnesium hydroxystearate, and more preferably calcium hydroxystearate or calcium stearate.

[0016] The content of (B) fatty acid metal salt in the resin composition of this embodiment is 0.3 parts by mass or more, preferably 0.4 parts by mass or more, more preferably 0.5 parts by mass or more, may be 0.6 parts by mass or more, or may be 0.9 parts by mass or more, per 100 parts by mass of polyacetal resin. Setting it above the lower limit tends to further improve the effect of suppressing slipping during molding when used in combination with (C) fatty acid full ester. Furthermore, the content of (B) fatty acid metal salt is 2.5 parts by mass or less, preferably 2.2 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.8 parts by mass or less, even more preferably 1.5 parts by mass or less, and may be 1.1 parts by mass or less, per 100 parts by mass of polyacetal resin. Setting it below the upper limit tends to further improve the effect of suppressing discoloration when heat is applied to the molded product. The resin composition of this embodiment may contain only one type of (B) fatty acid metal salt, or it may contain two or more types. When it contains two or more types, it is preferable that the total amount is within the above range.

[0017] The resin composition of this embodiment may contain fatty acid metal salts other than (B) fatty acid metal salt (for example, zinc stearate, etc.) to the extent that it does not depart from the spirit of this embodiment. However, in this embodiment, it is preferable that it is substantially free of fatty acid metal salts other than (B) fatty acid metal salt. Substantially free of fatty acid metal salts other than (B) fatty acid metal salt means that the content of fatty acid metal salts other than (B) fatty acid metal salt is 10% by mass or less of the content of (B) fatty acid metal salt, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0018] <(C) Fatty Acid Full Ester> The resin composition of this embodiment contains (A) 100 parts by mass of polyacetal resin and (C) 0.3 to 2.5 parts by mass of fatty acid ester. The inclusion of (C) fatty acid ester improves the sliding properties of the resulting molded product and increases the limit PV value for the resin member. (C) fatty acid full esters are compounds having one or more ester bonds in their molecules. (C) fatty acid full esters are usually compounds obtained by the reaction of the COOH of a fatty acid and the OH of an alcohol, and usually do not contain free COOH derived from the fatty acid or free OH derived from the alcohol in their molecules. By using (C) fatty acid full esters, the limit PV value for resin members can be made higher. In this embodiment, when using commercially available (C) fatty acid full esters, it is possible that some compounds may contain unreacted free COOH derived from the fatty acid and free OH derived from the alcohol, within a range that is normally acceptable to those skilled in the art. Furthermore, the number of ester groups in one molecule of (C) fatty acid full ester is preferably 1 to 4, more preferably 1 to 3, even more preferably 1 or 2, and most preferably 1. The molecular weight of the (C) fatty acid full ester is preferably 300 to 2000. In particular, when the (C) fatty acid full ester has one ester group, the molecular weight is preferably 300 to 800; when the (C) fatty acid full ester has two ester groups, the molecular weight is preferably 300 to 800; when the (C) fatty acid full ester has two ester groups, the molecular weight is preferably 300 to 1000; when the (C) fatty acid full ester has three ester groups, the molecular weight is preferably 500 to 1200; and when the (C) fatty acid full ester has four ester groups, the molecular weight is preferably 800 to 2000.

[0019] Furthermore, the (C) fatty acid full ester used in this embodiment preferably has an aliphatic group having 10 to 50 carbon atoms, but the number of carbon atoms is preferably 12 or more, more preferably 14 or more, preferably 36 or less, more preferably 28 or less, even more preferably 25 or less, and even more preferably 20 or less. The aliphatic group is preferably a linear aliphatic group. Furthermore, the aliphatic group may be a saturated aliphatic group or an unsaturated aliphatic group, but a saturated aliphatic group is preferred. More specifically, examples of fatty acids that make up (C) fatty acid full ester include myristic acid, pentadecyl acid, palmitic acid, margaric acid, stearic acid, arachidic acid, henicosyl acid, behenic acid, lignoceric acid, cerotic acid, and montanic acid, with stearic acid being preferred. Specific examples of fatty acid full ester (C) include stearyl stearate, glycol distearate, pentaerythritol tetrastearate, and triglyceride stearate, more preferably stearyl stearate, pentaerythritol tetrastearate, and triglyceride stearate, and even more preferably stearyl stearate.

[0020] The content of (C) fatty acid full ester in the resin composition of this embodiment is 0.3 parts by mass or more, 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 even more preferably 0.9 parts by mass or more, per 100 parts by mass of (A) polyacetal resin. Setting it above the lower limit allows for a shorter weighing time. Furthermore, the content of (C) fatty acid full ester is 2.5 parts by mass or less, preferably 2.0 parts by mass or less, more preferably 1.8 parts by mass or less, even more preferably 1.6 parts by mass or less, even more preferably 1.4 parts by mass or less, and even more preferably 1.2 parts by mass or less, per 100 parts by mass of (A) polyacetal resin. Setting it below the upper limit tends to further improve the effect of improving weighing stability during molding. The resin composition of this embodiment may contain only one type of (C) fatty acid ester, or it may contain two or more types. When it contains two or more types, it is preferable that the total amount is within the above range.

[0021] The resin composition of this embodiment may contain fatty acid esters other than (C) fatty acid full ester (for example, monoglyceride stearate) to the extent that it does not depart from the spirit of this embodiment. However, in this embodiment, it is preferable that the composition is substantially free of fatty acid esters other than (C) fatty acid full ester. Substantially free of fatty acid esters other than (C) fatty acid full ester means that the content of fatty acid esters other than (C) fatty acid full ester is 10% by mass or less of the content of (C) fatty acid full ester, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0022] In the resin composition of this embodiment, the mass ratio of (B) fatty acid metal salt to (C) fatty acid full ester ((B) / (C) mass ratio) is 0.5 or higher, preferably 0.6 or higher, more preferably 0.8 or higher, and even more preferably 0.9 or higher. Setting it to be above the lower limit allows for a shorter weighing time. Furthermore, the mass ratio of (B) / (C) is less than 5, preferably 4 or lower, more preferably 3 or lower, even more preferably 2 or lower, even more preferably 1.5 or lower, and even more preferably 1.2 or lower. Setting it to be below the upper limit allows for a smaller coefficient of dynamic friction with respect to the metal member.

[0023] <Other ingredients> The resin composition of this embodiment may contain known additives and fillers, provided that the objectives of the present invention are not impaired. Specific examples of additives and fillers that can be used in this embodiment include known thermoplastic polymers, antioxidants, formaldehyde scavengers, antistatic agents, ultraviolet absorbers, light stabilizers, carbon fibers, glass fibers, glass flakes, talc, mica, calcium carbonate, potassium titanate whiskers, and the like. The total content of these components is preferably 10% by mass or less of the resin composition.

[0024] <Physical properties of the resin composition> In this embodiment, the resin composition, when used in a thrust friction and wear test on a cylindrical thrust test specimen against carbon steel S45C, with the surface pressure increased every 3 minutes from 3 kg at a linear velocity of 10 cm / s, preferably has a dynamic friction coefficient of 0.15 or less at a surface pressure of 4.9 MPa, more preferably 0.14 or less, even more preferably 0.13 or less, and even more preferably 0.12 or less. A practical lower limit is, for example, 0.01 or more. Such a dynamic friction coefficient is mainly achieved by blending (B) fatty acid metal salts and (C) fatty acid full esters. The resin composition of this embodiment, when used to form a cylindrical thrust test specimen, exhibits a thrust-type friction and wear test performed at a linear velocity of 10 cm / s, increasing the surface pressure from 3 kg every 3 minutes, compared to a similar cylindrical thrust test specimen made of polyamide 6. In this test, the limiting PV value is preferably 29 MPa·cm / s or higher, more preferably 30 MPa·cm / s or higher, even more preferably 35 MPa·cm / s or higher, and even more preferably greater than 49 MPa·cm / s. The upper limit of the limiting PV value is practically set to, for example, 100 MPa·cm / s or less. Such a limiting PV value is mainly achieved by incorporating (C) fatty acid full ester. The coefficient of dynamic friction and the limit PV value are measured according to the examples described below.

[0025] <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 composition, (2) a method of supplying a portion of the components constituting the composition from the main feed port of the extruder and the remaining components from the side feed port and melt-kneading them to obtain a pelletized composition, or (3) a method of preparing pellets with different compositions by extrusion or the like, and then mixing the pellets to adjust them to a predetermined composition.

[0026] 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).

[0027] <Molded products> The molded articles of this embodiment are formed from the resin composition of this embodiment. Pelletized from the resin composition of this embodiment are then molded into molded articles using 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 the pellet stage. 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.

[0028] 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.

[0029] 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.

[0030] 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]

[0031] 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.

[0032] 1.Raw materials The raw materials shown in Table 1 were used. [Table 1]

[0033] 2. Examples 1-8, Comparative Examples 1-10 <Manufacturing of resin compositions (pellets)> Each component shown in Tables 2 to 5 was uniformly mixed in the proportions (parts by mass) shown in Tables 2 to 5 using a Super Mixer manufactured by Kawada Manufacturing Co., Ltd. The resulting mixture was melt-shear mixed using a vented single-screw extruder with a screw diameter of 40 mm (Tanabe Plastics Machinery Co., Ltd. "VS-40") at a cylinder temperature of 190°C, a screw rotation speed of 60 rpm, and a discharge rate of 18 kg / hour to produce resin composition pellets.

[0034] <Weighing time> Using a Sumitomo Heavy Industries SE-30DUZ injection molding machine, the maximum metering time (in seconds) displayed on the monitor was recorded when molding 20 thrust rings for each sample at a cylinder temperature of 190°C and a mold temperature of 80°C. The screw rotation speed during metering was 150 rpm and the back pressure was 5 MPa. In Comparative Example 8, the screw did not retract even after 300 seconds of weighing time had elapsed, so the molding process was abandoned and weighing was deemed impossible. The results are shown in Tables 2-5 below.

[0035] <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.

[0036] <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.

[0037] [Table 2]

[0038] [Table 3]

[0039] [Table 4]

[0040] [Table 5]

[0041] As is clear from the above results, the resin composition of the present invention was able to provide molded articles with short weighing times, low dynamic friction coefficients with respect to metal members, and high limiting PV values ​​with respect to resin members (Examples 1-8). In contrast, when (B) fatty acid metal salts were not included, or when they were included but in small amounts (Comparative Examples 1, 2, 7), the weighing time became longer. Also, even when fatty acid metal salts were included, the weighing time became longer when the length of the aliphatic group was short (Comparative Example 10). On the other hand, when (C) fatty acid full esters were not included (Comparative Examples 4, 5), or when (C) fatty acid full esters were included but in small amounts (Comparative Example 3), the limiting PV value was low. Also, even when fatty acid esters were included, if they were not fatty acid full esters (C) (Comparative Example 9), the limiting PV value was low.

Claims

1. (A) Per 100 parts by mass of polyacetal resin, (B) 0.3 to 2.5 parts by mass of a fatty acid metal salt containing calcium and / or magnesium and having an aliphatic group having 10 to 50 carbon atoms, (C) Contains 0.3 to 2.5 parts by mass of fatty acid ester, A resin composition for injection molding in which the mass ratio of (B) / (C) is 0.5 or more and less than 5.

2. The resin composition according to claim 1, wherein the fatty acid metal salt (B) comprises a fatty acid metal salt having a linear aliphatic group having 12 to 36 carbon atoms.

3. The resin composition according to claim 1, wherein the fatty acid full ester (C) contains 1 to 4 ester groups in one molecule.

4. The resin composition according to claim 1, wherein the fatty acid full ester (C) has a linear aliphatic group having 10 to 50 carbon atoms.

5. The fatty acid metal salt (B) includes a fatty acid metal salt having a linear aliphatic group with 12 to 36 carbon atoms. The resin composition according to claim 1, wherein the fatty acid full ester (C) contains 1 to 4 ester groups in one molecule and has a linear aliphatic group having 10 to 50 carbon atoms.

6. The resin composition according to any one of claims 1 to 5, wherein, in a thrust friction wear test performed on carbon steel S45C with a test piece formed from the resin composition into a cylindrical thrust test piece, the coefficient of dynamic friction at a surface pressure of 4.9 MPa is 0.15 or less at a linear velocity of 10 cm / s and the surface pressure is increased from 3 kg every 3 minutes.

7. The resin composition according to any one of claims 1 to 5, wherein, in a thrust friction and wear test performed on a test specimen formed from the resin composition into a cylindrical thrust test specimen, with the surface pressure increased from 3 kg every 3 minutes at a linear velocity of 10 cm / s, the limiting PV value is 29 or higher, compared to a test specimen formed from polyamide 6 into a similar cylindrical thrust test specimen.

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