Polyacetal resin composition and sliding member

Abstract

The present invention relates to a polyalkene resin composition and a sliding member. The present invention aims to provide a polyalkene resin composition and a sliding member which maintain the appearance of a molded product, have little mold contamination during molding, and have excellent friction / abrasion properties. This is achieved by a polyalkene resin composition containing at least: (A) 100 parts by mass of a polyalkene resin, (B) 0.01 to 1 parts by mass of a hindered phenol-based antioxidant, (C) 0.3 to 5 parts by mass of a silicone oil, (D) 0.1 to 1.0 parts by mass of calcium carbonate, and (E) 0.02 to 0.2 parts by mass of a fatty acid, the aforementioned (D) calcium carbonate being light calcium carbonate having an average particle diameter of 1 µm or less and being uncoated, and the aforementioned (E) fatty acid being a fatty acid having a carbon number of 12 or more and 30 or less.

Description

[0001] This application is a divisional application of the application filed on April 10, 2020, with application number 202080027849.1 and invention title "Polyacetal Resin Composition and Sliding Member". Technical Field

[0002] This invention relates to polyacetal resin compositions and sliding components. Background Technology

[0003] Polyacetal resin (also known as polyoxymethylene resin, abbreviated as POM resin) has balanced mechanical properties, excellent friction / wear resistance, chemical resistance, heat resistance, and electrical properties, and is therefore widely used in the automotive, electrical / electronic products and other fields.

[0004] However, the required properties in the aforementioned fields are becoming increasingly sophisticated. As one example, there is a strong demand to improve the basic sliding properties, such as the coefficient of friction and wear, while maintaining the excellent surface smoothness of polyacetal resins.

[0005] To meet these requirements, methods for adding fluoropolymers and polyolefins to polyacetal resins are known. However, fluoropolymers and polyolefins lack compatibility with polyacetal resins. Therefore, the following situations may occur: these resins separate from the polyacetal resin and peel off from the surface of the molded article, or precipitates may form on the mold during molding.

[0006] Furthermore, methods are known to add lubricants such as fatty acids, fatty acid esters, silicone oils, and various mineral oils to polyacetal resins. However, the following issues may arise: during molding, the polyacetal resin may separate from the lubricant, leading to leakage of the lubricant, which can impair extrusion and molding processability. Additionally, if the lubricant leaks onto the surface of the molded part, it can also damage the appearance of the molded part.

[0007] To address these issues, a polyacetal resin composition has been proposed, which is made by adding and mixing polyethylene wax, polyethylene resin, and silicone oil with a specific kinematic viscosity to a polyacetal resin (see, for example, Patent Document 1).

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2008-19430 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] However, even with the polyacetal resin composition described in Patent Document 1, there is room for further improvement regarding issues such as lubricant seepage, deterioration of the appearance of the molded product due to peeling off the surface of the molded sheet, and mold deposits during molding.

[0013] The purpose of this invention is to provide a polyacetal resin composition and a sliding component that maintain the appearance of the molded article, minimize mold contamination during molding, and have excellent friction / wear properties.

[0014] Solution for solving the problem

[0015] In order to achieve the above-mentioned objectives, the inventors conducted in-depth research and found that by using polyacetal resin as the matrix and adding specific amounts of hindered phenolic antioxidants, silicone oil, untreated light calcium carbonate with a specific particle size, and specific fatty acids, the above objectives can be achieved, thus completing the present invention.

[0016] 1. A polyacetal resin composition comprising at least:

[0017] (A) 100 parts by weight of polyacetal resin

[0018] (B) Hindered phenolic antioxidants: 0.01 parts by weight or more and 1 part by weight;

[0019] (C) Silicone oil, 0.3 parts by weight or more and 5 parts by weight or less.

[0020] (D) Calcium carbonate, 0.1 parts by weight or more and 1.0 parts by weight or less, and

[0021] (E) Fatty acids, 0.02 parts by weight or more and 0.2 parts by weight or less.

[0022] The aforementioned (D) calcium carbonate is light calcium carbonate with an average particle size of less than 1 μm and without surface treatment.

[0023] The aforementioned (E) fatty acids are fatty acids with 12 or more carbon atoms and less than 30 carbon atoms.

[0024] 2. A sliding member comprising the polyacetal resin composition described in 1 above.

[0025] The effects of the invention

[0026] According to the present invention, a polyacetal resin composition with excellent friction / wear properties, and consequently good appearance of the molded article and good performance in mold contamination during molding can be provided. Detailed Implementation

[0027] The following describes specific embodiments of the present invention in detail. However, the present invention is not limited to any of the following embodiments. Within the scope of the purpose of the present invention, it can be implemented with appropriate modifications.

[0028] <Polyacetal Resin Composition>

[0029] The polyacetal resin composition of the present invention is characterized in that it contains at least: (A) polyacetal resin, (B) hindered phenolic antioxidant, (C) silicone oil, (D) light calcium carbonate, and (E) fatty acid.

[0030] (A) Polyacetal Resin

[0031] As for (A) the polyacetal resin, either a polyacetal homopolymer or a polyacetal copolymer whose main chain is mostly composed of oxymethylene chains can be used. Alternatively, a substance obtained by crosslinking or graft copolymerizing polyacetal using known methods can be used as the matrix resin. Furthermore, there are no particular restrictions on the degree of polymerization, etc., as long as it can be molded.

[0032] (B) Hindered Phenolic Antioxidants

[0033] There are no particular limitations on the (B) hindered phenolic antioxidants that can be used in this invention. Examples include: monocyclic hindered phenolic compounds (e.g., 2,6-di-tert-butyl-p-cresol, etc.), polycyclic hindered phenolic compounds linked by hydrocarbon groups or sulfur-containing groups (e.g., 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-methylenebis(2,6-di-tert-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butidene bis(3-methyl-6-tert-butylphenol), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 4,4'-thiobis( 3-Methyl-6-tert-butylphenol, etc.; hindered phenolic compounds having ester or amide groups (e.g., n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenyl)propionate, n-octadecyl-2-(4'-hydroxy-3',5'-di-tert-butylphenyl)propionate, 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylphenylpropionate], etc.). 2,4,8,10-tetraoxaspiro[5.5]undecane, 2-tert-butyl-6-(3'-tert-butyl-5'-methyl-2'-hydroxybenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-dihydrocinnamoamide), N,N'-ethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], N,N'-tetramethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], N,N'-Hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], N,N'-Ethylenebis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionamide], N,N'-Hexamethylenebis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionamide], N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, N,N'-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionyl]hydrazine, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate, 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate, etc.

[0034] In this invention, at least one or more of these antioxidants may be used.

[0035] In this invention, the content of the hindered phenolic antioxidant (B) relative to 100 parts by weight of the polyacetal resin (A) is 0.01 parts by weight or more and 1 part by weight or less, preferably 0.02 parts by weight or more and 0.5 parts by weight or less.

[0036] (B) When the amount of antioxidant in the formulation is low, the antioxidant properties are insufficient. Compared to short-term oxidative degradation at high temperatures during molding and processing, or long-term oxidative degradation under normal temperature conditions, the stability of (A) polyacetal resin is easily compromised, making it undesirable. Furthermore, when the stability of (A) polyacetal resin components is insufficient and deteriorates, it can also adversely affect the sliding properties. On the other hand, (B) when the amount of antioxidant in the formulation is excessive, it can sometimes also impair the mechanical properties of the resulting resin composition.

[0037] (C) Silicone Oil

[0038] There are no particular restrictions on the types of silicone oils (C). For example, polydimethylsiloxane, polymethylphenylsiloxane, etc., represented by the structure of the following formula (1) are known.

[0039]

[0040] In formula (1), R is basically methyl, but some of its components can be alkyl, phenyl, haloalkyl, halophenyl, etc.

[0041] In this invention, two or more silicone oils with different structures or viscosities can be mixed and used, or thickening materials, solvents, etc. can be added to the silicone oil to adjust the viscosity.

[0042] In this invention, the amount of silicone oil (C) is 0.3 parts by weight or more and 5 parts by weight or less relative to 100 parts by weight of polyacetal resin (A). When the amount of silicone oil (C) is low, the improvement effect on the friction / wear characteristics, which is the objective of this invention, becomes insufficient, and therefore is not preferred. On the other hand, when the amount of silicone oil (C) is excessive, mold contamination may occur during molding, and peeling and wear of the self-material during sliding on the surface of the molded part may occur in the sliding component, which is also not preferred.

[0043] (D) Light Calcium Carbonate

[0044] The polyacetal resin composition of the present invention contains (D) light calcium carbonate. To improve surface hardness and machinability, it is known to blend inorganic powders relative to the polyacetal resin. Besides calcium carbonate, known inorganic powders include magnesium carbonate, talc, silica, clay, kaolin, diatomaceous earth, perlite, bentonite, feldspar, carbon, and silica. However, considering the sliding properties and hardness with the target material, light calcium carbonate is used as the inorganic powder in this invention as a sliding component.

[0045] (D) Light calcium carbonate can be manufactured simply through chemical synthesis, and there are no particular restrictions on particle shape, etc. It can be used alone or in combination with two or more.

[0046] (D) The average particle size of the light calcium carbonate is 1 μm or less, preferably 500 nm or less, and more preferably 200 nm or less. If the average particle size is too large, the surface of the molded article becomes uneven, and the increased surface roughness may damage the sliding material, so it is not preferred.

[0047] It should be noted that, in this specification, particle size refers to the arithmetic mean of the major and minor diameters of the target particles measured using a Hitachi High-Technologies Corporation scanning electron microscope S3000H at 30,000x magnification. Additionally, in this specification, average particle size refers to the arithmetic mean of the particle sizes of 100 samples.

[0048] There is no particular limitation on the lower limit of the average particle size. In order to prevent secondary aggregation of the polyacetal resin composition, the average particle size of (D) light calcium carbonate is preferably 50 nm or more.

[0049] In this invention, the amount of (D) light calcium carbonate in the blend is 0.1 parts by weight or more and 1.0 parts by weight or less relative to 100 parts by weight of (A) polyacetal resin. When the amount of (D) light calcium carbonate with an average particle size of 1 μm or less is low, the improvement effect on the friction / wear characteristics, which is the objective of this invention, may become insufficient, and therefore is not preferred. On the other hand, when the amount of (D) light calcium carbonate with an average particle size of 1 μm or less is excessive, the wear of the material itself will increase, and therefore is not preferred. Furthermore, the surface of the molded article becomes uneven, and the increased surface roughness may damage the material being slid against; this is also not preferred.

[0050] The (D) light calcium carbonate used in this invention does not undergo "surface treatment" which involves reacting various coupling agents such as silane coupling agents, fatty acids, etc., with the particle surface to modify the particle surface in order to impart functionality to the particles.

[0051] (D) When light calcium carbonate is surface-treated, an increase in bulk density is observed after surface treatment. Therefore, it is assumed that the particles will further aggregate through surface treatment. As a result, when melt-blending with resin, the deterioration of tribological properties and appearance caused by the deterioration of the dispersion of light calcium carbonate particles in the resin compared to the case without surface treatment is not preferred.

[0052] (E) Fatty Acids

[0053] The (E) fatty acids used in this invention are higher fatty acids with a carboxyl group bonded to one end of an aliphatic hydrocarbon group, and have a total number of carbon atoms of 12 to 30. The aliphatic hydrocarbon group constituting the fatty acid can be straight or branched, and can be saturated or unsaturated.

[0054] These fatty acids can be used alone or in combination of two or more. Examples of (E) fatty acids include lauric acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, eicosanoic acid, benzyl acid, tetracosanoic acid, ceric acid, linoleic acid, beeswax acid, oleic acid, transoleic acid, cetene acid, erucic acid, brassinolic acid, linoleic acid, linolenic acid, arachidonic acid, and stearylene acid.

[0055] (E) The aliphatic hydrocarbon groups of fatty acids can be replaced by functional groups such as hydroxyl groups.

[0056] The amount of (E) fatty acid in this invention is 0.02 parts by mass or more and 0.2 parts by mass or less relative to 100 parts by mass of (A) polyacetal resin. When the amount of (E) fatty acid is too low, peeling may occur on the surface of the molded sliding member, which is undesirable. On the other hand, when the amount of (E) fatty acid is excessive, mold contamination during molding and peeling may occur on the surface of the molded part in the sliding member may occur, which is also undesirable.

[0057] Other Ingredients

[0058] The polyacetal resin composition of the present invention may also contain other components as needed. For example, as stabilizers, one or more of the following can be included: hydroxides of alkali metals or alkaline earth metals, inorganic salts, carboxylates, etc.

[0059] In addition, as long as it does not impair the purpose / effect of the present invention, one or more common additives, such as dyes, pigments and other colorants, lubricants, release agents, antistatic agents, surfactants, or organic polymer materials, inorganic or organic fibrous, powdered, or plate-shaped fillers, may be added relative to the thermoplastic resin as needed.

[0060] <Method for manufacturing polyacetal resin compositions>

[0061] A melt-blending apparatus is used to manufacture the polyacetal resin composition of the present invention. There are no particular limitations on the melt-blending apparatus; any apparatus capable of melt-blending polyacetal resin with other components is preferred, especially one with a venting function. Examples include: a single-screw or multi-screw continuous extrusion mixer, a kneader, etc., with at least one vent hole.

[0062] As a method for manufacturing resin compositions, known methods commonly used in existing resin composition manufacturing methods can be used. For example, the following methods can be used: (1) mixing all the components constituting the composition and feeding them to an extruder for melt mixing to obtain a granular composition; (2) feeding 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 melting mixing to obtain a granular composition; (3) temporarily preparing granules with different compositions by extrusion or the like, and mixing the granules to adjust them to a specified composition.

[0063] In this invention, method (1) is preferred. For example, it is preferred to mix the components of the composition in an intermittent mixer, then supply the mixed raw material to an extruder, and perform melt mixing.

[0064] The melt-blending process is preferably carried out at a temperature range above the melting point of the polyacetal resin up to 260°C. Temperatures above 260°C result in polymer decomposition and degradation, which is not preferred.

[0065] <Sliding Member>

[0066] The sliding member of the present invention is constructed by comprising a resin molded body containing the above-described polyacetal resin composition. This sliding member not only exhibits excellent friction / wear characteristics but also good surface properties of the molded sheet, thus making it suitable for use in sliding components in fields such as AV, OA, measuring instruments, and conveying parts.

[0067] Example

[0068] The present invention will be specifically described below through examples, but the present invention is not limited thereto.

[0069] <Examples and Comparative Examples>

[0070] <Preparation of Polyacetal Resin Compositions>

[0071] The components listed in Tables 1 and 2 were mixed in the proportions listed in Tables 1 and 2 and melt-blended in a twin-screw extruder at 210°C to obtain granules of the polyacetal resin compositions of the Examples and Comparative Examples.

[0072] It should be noted that the various components used in the embodiments and comparative examples of the present invention recorded in Tables 1 and 2 are as described below.

[0073] (A) Polyacetal resin

[0074] (A-1) A polyacetal copolymer formed by copolymerizing 96.7% by mass of trioxane with 3.3% by mass of 1,3-dioxolane (melt index (measured at 190°C and 2160 g load): 9 g / 10 min)

[0075] (B) Hindered phenolic antioxidants

[0076] (B-1) Irganox245 (manufactured by BASF CORPORATION)

[0077] Triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate]

[0078] (C) Silicone oil

[0079] (C-1) SH200-60000CS (manufactured by Dow Corning Toray Co., Ltd.)

[0080] The kinematic viscosity at 25°C is 60,000 cSt (600 cm⁻¹). 2 / s)

[0081] (D) Calcium carbonate

[0082] (D-1) Brilliant-1500 (manufactured by Shiraishi Kogyo Co., Ltd.).

[0083] Light calcium carbonate with an average particle size of 150 nm and no surface treatment

[0084] (D-2) Whiton P-30 (manufactured by Toyo Fine Chemical Co., Ltd.)

[0085] Heavy calcium carbonate with an average particle size of 4.4 μm

[0086] (D-3) Vigot-15 (Made by Shiraishi Kogyo Co., Ltd.)

[0087] Light calcium carbonate with an average particle size of 150 nm and surface-treated with fatty acids

[0088] (E) fatty acids

[0089] (E-1) Stearic acid (carbon number: 18)

[0090] (E-2) Oleic acid (carbon number: 18)

[0091] (E-3) Lauric acid (carbon number: 12)

[0092] (E-4) Octanoic acid (carbon number: 8)

[0093] [Table 1]

[0094]

[0095] [Table 2]

[0096]

[0097] <Evaluation>

[0098] To evaluate the granular polyacetal resin compositions of the Examples and Comparative Examples, the tribological properties, appearance of the molded articles, and amount of mold residue during molding were evaluated. The results are shown in Tables 3 and 4.

[0099] Friction and Wear Characteristics

[0100] Granules of the polyacetal resin compositions used in the examples and comparative examples were molded into cylindrical test pieces (outer diameter: 25.6 mm, inner diameter: 20 mm, height: 15 mm) under the following conditions.

[0101] Using this test piece, the friction and wear characteristics were evaluated under the following conditions, and the dynamic friction coefficient and wear ratio at the end of the test were determined. The test was conducted at 23℃ in an atmosphere of 50% RH.

[0102] [Evaluation Method]

[0103] Test method: Suzuki friction and wear test

[0104] Test apparatus EFM-3-EN (manufactured by ORIENTEC CORPORATION)

[0105] Test conditions and materials: Cylindrical test pieces made of polyacetal resin as described above.

[0106] (Product name: DURACON (registered trademark) M90-44, manufactured by Polyplastics Co., Ltd.)

[0107] Surface pressure: 0.06 MPa

[0108] Speed: 15cm / second

[0109] Test duration: 24 hours

[0110] [Experimental piece molding conditions A]

[0111] Molding machine: FANUC ROBOSHOT α-S50iA (manufactured by FANUC Corporation)

[0112] Molding conditions: Barrel temperature (°C) Nozzle - C1 - C2 - C3

[0113] 200℃ - 200℃ - 180℃ - 170℃

[0114] Injection pressure: 60 MPa

[0115] Injection speed: 0.4 m / min

[0116] Mold temperature 80 (°C)

[0117] Appearance of Molded Products

[0118] Using the polyacetal resin composition granules from the examples and comparative examples, test pieces (80mm × 80mm × 1mm; side gate 2mm × 1mm) were similarly molded under the above-described test piece molding conditions A.

[0119] [Evaluation Method]

[0120] For the 10 molded sheets obtained, the surface of the molded sheets was visually inspected. The appearance was judged according to the following criteria based on the number of sheets with observed fuzzing or peeling on the surface.

[0121] 0: No fuzzing or peeling was found on the surface of any of the molded sheets.

[0122] 1: In two or fewer molded sheets, fuzzing or peeling was observed on the surface.

[0123] 2: Among three or more molded sheets, fuzzing or peeling is confirmed on the surface.

[0124] Mold contamination during molding

[0125] Using the polyacetal resin composition granules from the examples and comparative examples, molded into mold fouling test pieces (33mm × 23mm × 1mmt) under the following condition B.

[0126] [Evaluation Method]

[0127] After 5000 shots of continuous molding, visually inspect the surface of the mold cavity inside the mold and visually determine the amount of adhering material based on the following criteria.

[0128] 0: No attachments detected at all

[0129] 1: The attached material was slightly confirmed.

[0130] 2: Attached material was identified in the whole.

[0131] [Experimental piece molding conditions B]

[0132] * Molding machine: FANUC ROBOSHOT S-2000i 50B (FANUC Corporation)

[0133] * Molding conditions: Barrel temperature (°C) Nozzle - C1 - C2 - C3

[0134] 205℃ 215℃ 205℃ 185℃

[0135] Injection pressure: 40 MPa

[0136] Injection speed: 1.5 m / min

[0137] Mold temperature 80 (°C)

[0138] The evaluation results are shown below.

[0139] [Table 3]

[0140]

[0141] [Table 4]

[0142]

[0143] As shown above, the resin composition of the present invention not only has good friction / wear properties, but also has good performance in terms of the appearance of the molded article and mold contamination during molding.

Claims

1. A polyacetal resin composition comprising at least: (A) 100 parts by weight of polyacetal resin (B) Hindered phenolic antioxidants: 0.01 parts by weight or more and 1 part by weight; (C) Silicone oil, 0.3 parts by weight or more and 5 parts by weight or less. (D) Calcium carbonate, 0.1 parts by weight or more and 1.0 parts by weight or less, and (E) Fatty acids, 0.02 parts by weight or more and 0.2 parts by weight or less. The (D) calcium carbonate is a light calcium carbonate with an average particle size of less than 1 μm and without surface treatment. The (E) fatty acid is a fatty acid with 12 or more carbon atoms and less than 18 carbon atoms.

2. A sliding member comprising the polyacetal resin composition of claim 1.

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