JP2022151058A - Polyacetal resin composition, method for producing the same, and resin-made gear - Google Patents

Abstract

To provide a method for producing a polyacetal resin composition which is excellent in slidable characteristics, in particular, abrasion resistance, and is excellent in fatigue durability when applied to a gear.SOLUTION: There is provided a method for producing a polyacetal resin composition which includes, with respect to 100 pts.mass of (A) a polyacetal copolymer that is obtained by adding a basic inactivator (d) to a reaction product obtained by using trioxane as a main monomer (a) and cyclic ether and/or cyclic formal having one or more C-C bonds as a comonomer (b), using a predetermined heteropolyacid in a polymerization catalyst (c), and performing copolymerization, melt-kneading the reaction product, and inactivating a polymerization catalyst (c), (B) a predetermined modified olefinic polymer, (C) a predetermined alkylene glycol-based polymer, (D) a predetermined calcium carbonate, (E) a partial ester of a di- or higher and tetra- or lower polyhydric alcohol, and (F) an alpha olefin oligomer, in each predetermined amount.SELECTED DRAWING: None

Description

The present invention relates to a polyacetal resin composition, a method for producing the same, and a resin gear.

Polyacetal resin (also called polyoxymethylene resin, abbreviated as POM resin) has well-balanced mechanical properties and is excellent in friction/wear resistance, chemical resistance, heat resistance, electrical properties, etc. Therefore, it is widely used in fields such as automobiles and electric/electronic products. The properties required in this field are gradually becoming more sophisticated, and as one example, there is a demand for further improvements in sliding properties as well as general physical properties. Such sliding properties are anti-friction and wear properties, and in order to further improve such properties, POM resin compositions containing various additives have been proposed (see Patent Document 1).

Japanese Patent No. 5847261

By the way, gears generally have a function of transmitting rotational power through the meshing of the gears. When the gears rotate, high contact surface pressure is applied to the contact surfaces where the gears mesh with each other, so if the gears are used continuously for a long period of time, they will eventually become fatigued and damaged. Accordingly, gears are required to have not only friction and wear resistance, but also durability against fatigue.
Although the POM resin composition described in Patent Document 1 is excellent in sliding properties, there is room for further improvement as a material for resin gears.

The present invention has been made in view of the above-mentioned conventional problems, and the problem is to provide a polyacetal resin composition that has excellent sliding properties, particularly excellent wear resistance, and excellent fatigue durability when applied to gears. An object of the present invention is to provide a manufacturing method thereof and a resin gear.

One aspect of the present invention for solving the above problems is as follows.
(1) Trioxane as the main monomer (a) (80 to 99.9 mol% of all monomers), a cyclic ether and/or cyclic formal having at least one carbon-carbon bond as a comonomer (b), and a polymerization catalyst ( A basic deactivator (d) is added to the reaction product obtained by copolymerizing c) using a heteropolyacid represented by the following general formula (1), melt-kneaded, and the polymerization catalyst ( With respect to 100 parts by mass of the polyacetal copolymer (A) obtained by deactivating c),
(B) 0.5 parts by mass or more and 10 parts by mass or less of a modified olefin polymer obtained by modifying an olefin polymer with at least one selected from unsaturated carboxylic acids, unsaturated fatty acid anhydrides, and derivatives thereof; When,
(C) 0.01 parts by mass or more and 5 parts by mass or less of an alkylene glycol polymer having a primary amino group or a secondary amino group and a number average molecular weight of 400 or more and 500,000 or less;
(D) 0.1 parts by mass or more and 20 parts by mass or less of cubic calcium carbonate having a BET specific surface area of 15 m ² /g or less, an average particle size of 50 nm or more and 200 nm or less, and an untreated surface;
(E) 0.1 parts by mass or more and 10 parts by mass or less of a partial ester of a polyhydric alcohol having a valence of 2 or more and 4 or less;
(F) an alpha olefin oligomer of 0.1 parts by mass or more and 10 parts by mass or less;
A method for producing a polyacetal resin composition containing
H _m [M ¹ _x ·M ² _y O _Z ]·nH ₂ O General formula (1)
[In general formula ( ¹ ), M1 represents a central element consisting of one or two elements selected from P and Si. M2 represents one or ^more coordinating elements selected from W, Mo and V; x is an integer of 1 or more and 10 or less, y is an integer of 6 or more and 40 or less, z is an integer of 10 or more and 100 or less, m is an integer of 1 or more, and n is an integer of 0 or more and 50 or less. indicates ]

(2) A polyacetal resin composition produced by the method for producing a polyacetal resin composition according to (1) above.

(3) A resin gear formed by molding the polyacetal resin composition according to (2) above.

According to the present invention, it is possible to provide a polyacetal resin composition that has excellent sliding properties, particularly excellent wear resistance, and excellent fatigue durability when applied to gears, a method for producing the same, and a resin gear.

<Method for producing polyacetal resin composition>
In the method for producing the polyacetal resin composition of the present embodiment, trioxane is used as the main monomer (a) (80 to 99.9 mol% of all monomers), and at least one carbon-carbon bond cyclic ether and / or cyclic formal is used as a comonomer (b), and a basic deactivator (d) is added to a reaction product obtained by copolymerizing using a heteropolyacid represented by the following general formula (1) as a polymerization catalyst (c), (B) an unsaturated carboxylic acid, an acid anhydride of an unsaturated fatty acid and these 0.5 parts by mass or more and 10 parts by mass or less of a modified olefin polymer obtained by modifying an olefin polymer with at least one selected from derivatives, and (C) a primary amino group or a secondary amino group, 0.01 parts by mass or more and 5 parts by mass or less of an alkylene glycol polymer having a number average molecular weight of 400 or more and 500,000 or less, and (D) a BET specific surface area of 15 m ² /g or less and an average particle diameter of 50 nm or more. 0.1 parts by mass or more and 20 parts by mass or less of calcium carbonate that is 200 nm or less, has an untreated surface, and is cubic, and (E) 0.1 parts by mass of a partial ester of a polyhydric alcohol having a valence of 2 or more and 4 or less. It is characterized by containing 10 parts by mass or less and (F) 0.1 parts by mass or more and 10 parts by mass or less of alpha olefin oligomer.
H _m [M ¹ _x ·M ² _y O _Z ]·nH ₂ O General formula (1)
[In general formula ( ¹ ), M1 represents a central element consisting of one or two elements selected from P and Si. M2 represents one or ^more coordinating elements selected from W, Mo and V; x is an integer of 1 or more and 10 or less, y is an integer of 6 or more and 40 or less, z is an integer of 10 or more and 100 or less, m is an integer of 1 or more, and n is an integer of 0 or more and 50 or less. indicates ]

In the method for producing the polyacetal resin composition of the present embodiment, by adding predetermined amounts of the components (B) to (F) to 100 parts by mass of the polyacetal copolymer (A), sliding properties, particularly resistance A polyacetal resin composition having excellent abrasion resistance and excellent fatigue durability when applied to gears can be obtained. From the above Patent Document 1, it is considered that the components (B) to (F) mainly contribute to the excellent sliding properties. On the other hand, excellent fatigue durability when applied to gears cannot be realized only by adding components (B) to (F), so polyacetal copolymer (A) obtained by a predetermined manufacturing method is thought to have contributed. However, since it is difficult to specify the structure and properties of the (A) polyacetal copolymer, it is not clear how the (A) polyacetal copolymer contributes. In any case, the polyacetal copolymer (A) obtained by a predetermined manufacturing method and the components (B) to (F) are combined to improve sliding characteristics and fatigue durability when applied to gears. It is thought that
First, each component used in the production method of the present embodiment will be described below.

[(A) Polyacetal Copolymer]
In the present embodiment, (A) the polyacetal copolymer has trioxane as the main monomer (a) (80 to 99.9 mol% of all monomers), and has at least one carbon-carbon bond. A basic deactivator (d) is added to a reaction product obtained by copolymerizing formal as a comonomer (b) and using a heteropolyacid represented by the following general formula (1) as a polymerization catalyst (c). , melt-kneading to deactivate the polymerization catalyst (c).

(main monomer (a))
Trioxane is used as main monomer (a). Trioxane is a cyclic trimer of formaldehyde, and is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst, and is used after being purified by a method such as distillation. Trioxane used for polymerization is preferably one in which impurities such as water and methanol are reduced as much as possible.

(comonomer (b))
Cyclic ethers and/or cyclic formals containing at least one carbon-carbon bond are used as comonomers (b). Typical examples of compounds used as comonomer (b) include 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, ethylene oxide, propylene oxide, epichlorohydrin and the like. mentioned. Among them, 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, and ethylene oxide are preferred in view of polymerization stability.
Furthermore, in addition to the main monomer (a) and the comonomer (b), as a third comonomer component, a known modifier such as a branching agent is added to the extent that the performance of the resulting polyacetal resin composition is not significantly reduced. A comonomer may also be added in combination.

In the present embodiment, the amount of the compound selected from cyclic ethers and/or cyclic formals used as the comonomer (b) is 0.1 to 20 mol% as a proportion of all monomers (total amount of main monomer and comonomer). preferably 0.2 to 10 mol %. If the amount of comonomer (b) is less than 0.1 mol %, unstable terminal portions of the crude polyacetal copolymer formed by polymerization may increase, resulting in poor stability. If the amount of comonomer exceeds 20 mol %, the resulting copolymer may become soft and lower in melting point.

(Polymerization catalyst (c))
In the present embodiment, a heteropolyacid represented by the following general formula (1) is used as the polymerization catalyst (c) in the production of the polyacetal copolymer as described above.
H _m [M ¹ _x ·M ² _y O _Z ]·nH ₂ O General formula (1)

In formula ( ¹ ), M1 represents a central element consisting of one or two elements selected from P and Si. M2 represents one or ^more coordinating elements selected from W, Mo and V; x is an integer of 1 or more and 10 or less, y is an integer of 6 or more and 40 or less, z is an integer of 10 or more and 100 or less, m is an integer of 1 or more, and n is an integer of 0 or more and 50 or less. indicates

Specific examples of the heteropolyacid include phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadate, phosphomolybdenum tungstovanadate, phosphotungstovanadic acid, silicotungstic acid, silicomolybdic acid, silicomolyb Dotungstic acid, silicon molybdenum tungstic tovanadic acid, and the like. Above all, considering the stability of polymerization and the stability of the heteropolyacid itself, the heteropolyacid is preferably at least one of silicomolybdic acid, silicotungstic acid, phosphomolybdic acid and phosphotungstic acid.

In this embodiment, the amount of the heteropolyacid used varies depending on the type of the heteropolyacid, and can be changed appropriately to control the polymerization reaction. It is in the range of up to 100 ppm (hereinafter referred to as mass/mass ppm), preferably 0.1 to 50 ppm. Also, very strongly acting heteropolyacids such as phosphomolybdic acid, phosphotungstic acid, etc., are sufficient in amounts of 0.1 to 10 ppm. The fact that copolymerization is possible even with such a small amount of catalyst minimizes undesirable reactions such as main chain decomposition and depolymerization of the polymer due to the catalyst, and unstable formate terminal groups (-O-CH=O) , hemiacetal end groups (--O--CH ₂ --OH) and the like are effectively suppressed, and it is also economically advantageous.

In order to carry out the reaction uniformly, it is desirable to dilute the polymerization catalyst with an inert solvent that does not adversely affect the polymerization, and add it to the main monomer (a) and/or comonomer (b) before use. Examples of the inert solvent include low molecular weight carboxylic acids having 1 to 10 carbon atoms such as formic acid, acetic acid, propionic acid and butyric acid, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, -Methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 3-methyl-1-butanol, 1-hexanol, etc. are obtained by condensation of low molecular weight alcohols having 1 to 10 carbon atoms. Ester: Low molecular weight ketones having 1 to 10 carbon atoms such as acetone, 2-butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, methyl isobutyl ketone and methyl-t-butyl ketone are preferred. but not limited to these. Considering industrial availability, methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, 2-butanone, methyl isobutyl ketone and the like are most preferable. The polymerization catalyst is dissolved in the inert solvent preferably at a concentration of 1 to 30% by weight/weight, but is not limited thereto. In addition, a predetermined amount of the polymerization catalyst is previously mixed with a partial amount or the whole amount of any one or more of the above-mentioned main monomer (a), comonomer (b), molecular weight modifier, etc., and this solution is polymerized. A method of adding to the system to carry out polymerization is also preferred.

[Preparation of copolymer]
In the present embodiment, the crude polyacetal copolymer can be prepared by polymerization using the same equipment and method as for the conventionally known copolymerization of trioxane. That is, any of a batch system, a continuous system, and a semi-continuous system can be used, and the general method is to use a liquid monomer and obtain a polymer in the form of solid particles as the polymerization progresses. As the polymerization apparatus used in the present embodiment, a reaction vessel with a stirrer that is generally used in a batch system can be used, and as a continuous system, a co-kneader, a twin-screw continuous extrusion mixer, and a twin-screw paddle type can be used. A continuous mixer and other continuous polymerization apparatuses such as trioxane that have been proposed so far can be used, and two or more types of polymerization machines can be used in combination.

The polymerization method is not particularly limited. The resulting mixture can be supplied to a polymerization apparatus together with trioxane as the main monomer (a) to carry out a copolymerization reaction. This makes it possible to reduce the required amount of catalyst, and as a result, it is advantageous for obtaining a polyacetal copolymer that emits less formaldehyde, and is a more suitable polymerization method. The polymerization temperature is in the temperature range of 60-120°C.

In the present embodiment, when the main monomer (a) and comonomer (b) are polymerized to prepare a polyacetal copolymer, a known chain transfer agent, such as a low molecular weight methylal, is used to adjust the degree of polymerization. It is also possible to add linear acetals and the like.

In addition, the polymerization reaction is desirably carried out in a state in which impurities having active hydrogen, such as water, methanol, formic acid, etc., are substantially absent, for example, in a state in which each of these is 10 ppm or less. It is desirable to use trioxane, cyclic ethers and/or cyclic formals prepared to contain as little as possible as main monomers and comonomers.

Next, deactivation of the polymerization catalyst by addition of a basic deactivator will be described.

(Basic deactivator (d))
The type and method of addition of the basic deactivator are not particularly limited, but the basic deactivator is added to the crude polyacetal copolymer as it is without washing the crude polyacetal copolymer, and melt-kneaded. By doing so, it is preferable that it can serve for deactivation of the polymerization catalyst and stabilization of the unstable terminal of the crude polyacetal copolymer. Specifically, the basic deactivator is a carbonate, hydrogen carbonate or carboxylate of an alkali metal element or an alkaline earth metal element, or a hydrate thereof, and an amino group or a triazine ring-containing triazine ring having a substituted amino group. It is preferable to include at least one selected from compounds.

Furthermore, when carbonates, hydrogen carbonates or carboxylates of alkali metal elements or alkaline earth metal elements or hydrates thereof are used, the finally obtained composition has a particularly low amount of formaldehyde generated. value and is more preferable. Specifically, it more preferably contains at least one selected from sodium formate, sodium acetate, sodium carbonate, sodium hydrogen carbonate, disodium succinate, sodium laurate, sodium palmitate, sodium stearate and calcium stearate. .

In the present embodiment, the above-mentioned basic deactivators may be of one kind, or may be used in combination. I do not care.

After such polymerization and deactivation treatment, separation and recovery of unreacted monomers, drying and the like are further carried out by conventionally known methods, if necessary.

Next, the components (B) to (F) used in this embodiment will be explained below.

[(B) Modified olefin polymer obtained by modifying an olefin polymer with at least one selected from unsaturated carboxylic acids, unsaturated fatty acid anhydrides and derivatives thereof]
In the present specification, the modified olefin polymer is also referred to as "(B) component". In the polyacetal resin composition according to the present embodiment, by containing the component (B), the sliding properties are excellent. Conversely, when the polyacetal resin composition contains an olefinic polymer other than the component (B), the sliding properties are poor.

The olefin polymer (before modification) used in component (B) includes homopolymers of α-olefins such as ethylene, propylene, butene, hexene, octene, nonene, decene, and dodecene, and two or more of these. Random, block or graft copolymers consisting of these, and non-conjugated diene components such as 1,4-hexadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 2,5-norbornadiene, butadiene, isoprene, piperylene, etc. Conjugated diene components, α,β-unsaturated acids such as acrylic acid and methacrylic acid, derivatives such as esters thereof, aromatic vinyl compounds such as acrylonitrile, styrene, α-methylstyrene, vinyl esters such as vinyl acetate, and vinyl methyl Examples include random, block or graft copolymers containing at least one comonomer component such as vinyl ethers such as ethers and derivatives of these vinyl compounds, and the degree of polymerization, the presence or absence of side chains and branches, and the like. It does not matter what the degree, copolymer composition ratio, etc. are.

Examples of olefin polymers include high pressure polyethylene, medium and low pressure polyethylene, gas phase ethylene-α-olefin copolymer, LLDPE, polypropylene, polybutene, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer. polymers, ethylene-ethyl acrylate copolymers, ethylene-butyl acrylate copolymers, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, and the like. Preferred are polyethylene, ethylene-methyl acrylate copolymer and ethylene-ethyl acrylate copolymer.

The component (B) used in the present embodiment includes the above olefin-based polymer, acrylic acid, methacrylic acid, maleic acid, citraconic acid, itaconic acid, tetrahydrophthalic acid, nadic acid, methylnadic acid, and allylsuccinic acid. and unsaturated carboxylic anhydrides such as maleic anhydride, citraconic anhydride, itaconic anhydride, tetrahydrophthalic anhydride, nadic anhydride, methyl nadic anhydride, allyl succinic anhydride, and these It is modified with at least one selected from the group consisting of derivatives and the like.

Preferred component (B) has a melt flow rate (MFR) of 0.01 to 100 g/10 min, more preferably 0.1 to 50 g/10 min, and particularly preferred. are those with an MFR of 0.2 to 30 g/10 min. The melt flow rate (MFR) was measured according to ISO 1133.

Specific examples of preferred component (B) include maleic anhydride-modified polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, and the like. Among them, it is preferable that the component (B) contains polyethylene modified with maleic anhydride, because the sliding properties of the molded product obtained by molding the polyacetal resin composition are enhanced.

As a modification method thereof, an olefinic polymer and at least one compound selected from the group consisting of unsaturated carboxylic acids, their anhydrides, and derivatives thereof are treated in a solution or molten state with an appropriate organic peroxide. A method of heating and reacting in the presence of a radical initiator such as a substance is preferable, but it is not particularly limited to this. The blending amount of both components is suitably 0.1 to 20 parts by mass, preferably 0.1 to 10 parts by mass, per 100 parts by mass of the olefinic polymer. If the effective amount of the compound in the olefinic polymer modified with such a compound is too low, the affinity between components (A) and (B) may be insufficient; In this case, physical properties to be improved such as sliding properties may be deteriorated.

In the present embodiment, component (B) is preferably contained in an amount of 0.5 parts by mass or more and 10 parts by mass or less, and may be contained in an amount of 2 parts by mass or more and 7 parts by mass or less per 100 parts by mass of component (A). more preferred. If the amount of component (B) is less than 0.5 parts by mass in the obtained polyacetal resin composition, the amount of frictional wear may increase, which is not preferable. If the amount of component (B) is more than 10 parts by mass, mechanical properties may deteriorate, which is not preferable.

[(C) Alkylene glycol-based polymer having a primary amino group or a secondary amino group and a number average molecular weight of 400 or more and 500,000 or less]
In this specification, the alkylene glycol-based polymer is also referred to as "component (C)". In the polyacetal resin composition according to the present embodiment, by containing the component (C), the sliding properties are excellent.

The alkylene glycol-based polymer having a primary amino group or secondary amino group, which is the component (C), is a homopolymer or copolymer of ethylene glycol, propylene glycol, or tetramethylene glycol, and A polymer having a primary or secondary amino group in Further, it may be a slightly modified polymer such as an ester with a fatty acid or an ether with an aliphatic alcohol. Examples thereof include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymers composed of these constituent units having at least one aminopropyl or aminooctyl group.

The type of polymer is not particularly limited, but if the alkylene glycol polymer is a slightly modified polymer such as forming an ester with a fatty acid or an ether with an aliphatic alcohol, the polyacetal resin composition It is preferable in that the sliding property of a molded product obtained by molding an object is enhanced.

Component (C) has a number average molecular weight of 400 to 500,000, preferably 400 to 100,000, and more preferably 1,000 to 6,000. This is because the blending of component (C) improves the dispersibility of component (B) in the polyacetal resin, but if the number average molecular weight of component (C) is less than 400, component (A) or component (B) This is because if the number average molecular weight exceeds 500,000, the melt viscosity becomes high and it becomes difficult to disperse it in the polyacetal resin.

The blending amount of component (C) is 0.01 parts by mass or more and 5 parts by mass or less, more preferably 0.1 parts by mass or more and 4 parts by mass or less, relative to component (A), and 0.3 parts by mass. It is more preferably 1 part or more and 3 parts by mass or less, and particularly preferably 1 part or more and 2 parts by mass or less. Above all, when the amount of component (C) to be blended is 1 part by mass or more, it is preferable in that the sliding properties of a molded article formed by molding the polyacetal resin composition can be greatly improved. If the amount of component (C) is less than 0.01 part by mass, the effect of improving the sliding properties of the molded product cannot be sufficiently obtained, and if it exceeds 5 parts by mass, the mechanical properties are undesirably lowered.

[(D) Cubic calcium carbonate having a BET specific surface area of 15 m ² /g or less, an average particle size of 50 nm or more and 200 nm or less, and an untreated surface]
In this specification, the said calcium carbonate is also called "(D)component." In the polyacetal resin composition according to the present embodiment, by containing the component (D), the sliding properties are excellent.
Conventionally, it has been known to use an inorganic filler as a component of a polyacetal resin composition in order to improve the sliding properties of a resin molded product. As inorganic fillers, calcium carbonate, potassium titanate, barium carbonate, talc, wollastonite, mica, zinc oxide and the like are known. However, in this embodiment, calcium carbonate is an essential component. Even if an inorganic filler other than calcium carbonate, which is the component (D), is included as an inorganic filler, the surface properties of the molded product cannot be said to be superior to the case where the component (D) is included. I don't like it.

The BET specific surface area of component (D) is 15 m ² /g or less. In this specification, the BET specific surface area refers to the specific surface area (surface area per unit mass) obtained from the adsorption amount at the time of completion of the monomolecular layer obtained by the BET formula using nitrogen as a reference gas. The measurement method is specified in ASTM D-3037. If the BET specific surface area exceeds 15 m ² /g, the molded product obtained by molding the polyacetal resin composition has poor surface properties and sliding properties, which is not preferable.

Component (D) has an average particle size of 50 nm or more and 200 nm or less, more preferably 80 nm or more and 170 nm or less. In the present specification, the particle size is an arithmetic operation of the major axis and the minor axis when the major axis and the minor axis of the target particle are measured by magnifying observation at 30,000 times using a scanning electron microscope S3000H manufactured by Hitachi High-Tech Co., Ltd. shall mean the average value. Further, in this specification, the average particle size means the arithmetic average value of the particle sizes of 100 samples. If the average particle size is less than 50 nm, there is a possibility of secondary aggregation in the product, which is not preferable. If the average particle size exceeds 200 nm, the surface properties and It is not preferable in that the sliding property is inferior.

The component (D) has no surface treatment. If the surface of the component (D) is treated, the wear resistance of the molded product obtained by molding the polyacetal resin composition is inferior, which is not preferable.

As used herein, the term "surface untreated" means that the surface of calcium carbonate particles is not treated with a surface treatment agent such as an epoxy compound, isocyanate compound, titanate compound, or silane compound.

The component (D) is cubic. Here, the cubic shape includes not only a regular hexahedral cube, but also a hexahedron that is almost a cube, although it cannot be said to be a perfect cube. If the shape of the component (D) is not cubic, such as irregular shape, the molded product obtained by molding the polyacetal resin composition has poor surface properties and sliding properties, which is not preferable. In this specification, whether or not the component (D) has a cubic shape is confirmed by, for example, burning the product at 500° C. for 3 hours and observing the residue with an electron microscope.

Component (D) is added in an amount of 0.1 part by mass or more and 20 parts by mass or less, more preferably 0.1 part by mass or more and 1 part by mass or less based on component (A). If the amount of component (D) is less than 0.1 parts by mass, the amount of frictional wear may increase, and if it exceeds 20 parts by mass, the surface properties may deteriorate, which is not preferable.

[(E) Partial Ester of Dihydric to Tetravalent Polyhydric Alcohol]
In this specification, the partial ester of the polyhydric alcohol is also referred to as "component (E)". In the polyacetal resin composition according to the present embodiment, by containing the component (E), the surface properties and sliding properties are excellent.

BACKGROUND ART Conventionally, it has been known to use a lubricant as a component of a polyacetal resin composition. In addition, as lubricants, mineral oils, hydrocarbons, fatty acids, fatty alcohols, fatty esters composed of fatty acids and fatty alcohols, partial esters and/or full esters of polyhydric alcohols, esters of carboxylic acids and inorganic acids, fatty acids and amine compounds, metal soaps, natural waxes, silicones and their derivatives, substituted diphenyl ethers, and the like. However, in this embodiment, both the partial ester as the (E) component and the alpha olefin oligomer as the (F) component described later are essential constituents. Even if a lubricant other than the components (E) and (F) is contained as a lubricant, the surface properties cannot be said to be as excellent as in the present embodiment, which is not preferable.

Specific examples of the component (E) include glycerin monostearate, glycerin distearate, glycerin monobehenate, pentaerythritol monostearate and the like. Regarding the partial ester as the component (E), if the ester is not a partial ester, it is not preferable in that the molded product obtained by molding the polyacetal resin composition has poor surface properties and sliding properties.

Component (E) is added in an amount of 0.1 to 10 parts by mass, more preferably 0.5 to 2 parts by mass, based on component (A). If the amount of component (E) is less than 0.1 parts by mass, frictional wear may increase, and if it exceeds 10 parts by mass, bleeding may occur, which is not preferable.

[(F) Alpha Olefin Oligomer]
In this specification, the oligomer is also referred to as "(F) component". In the polyacetal resin composition according to the present embodiment, by including the component (F), the sliding properties are excellent.

Component (F) is added in an amount of 0.1 to 10 parts by mass, more preferably 1 to 5 parts by mass, relative to component (A). If the amount of component (F) is less than 0.1 part by mass, there is a possibility that the molded product obtained by molding the polyacetal resin composition will have poor sliding properties. It is not preferable because it may

[Other stabilizers and additives]
The polyacetal resin composition according to the present embodiment can further add various known stabilizers to reinforce stability. Moreover, in order to improve the physical properties according to the intended use, various known additives may be added.

Additives include various colorants, mold release agents, nucleating agents, antistatic agents, other surfactants, heterogeneous polymers (other than the above-mentioned graft copolymers), and the like. In addition, within a range that does not significantly reduce the performance of the composition targeted by the present embodiment, fibrous, powdery, granular, plate-like fillers such as inorganic, organic, and metal are used alone or in combination. You can also

[Preparation of polyacetal resin composition]
The polyacetal resin composition according to the present embodiment can be easily prepared by a known method generally used as a conventional resin composition preparation method. For example, (1) a method of mixing all the components that make up the composition, feeding this to an extruder and melt-kneading to obtain a pellet-like composition, (2) a method of obtaining a pellet-like composition, A method of obtaining a composition in the form of pellets by supplying the remaining components from the main feed port of the extruder and melt-kneading them from the side feed port. It is also possible to adopt a method of adjusting the composition to a predetermined composition.

<Polyacetal resin composition>
The polyacetal resin composition of the present embodiment is produced by the method for producing a polyacetal resin composition described above. Therefore, it has excellent sliding properties and excellent fatigue durability when applied to gears. The polyacetal resin composition of the present embodiment is excellent in fatigue durability when applied to gears, but is not limited to gears, and can be applied to members similar to gears that require fatigue durability. good.

<Resin gear>
The resin gear of this embodiment is formed by molding the polyacetal resin composition described above. Similar to the polyacetal resin composition of the present embodiment, the resin gear of the present embodiment has excellent sliding properties and excellent fatigue durability.

The method for molding a resin gear using the polyacetal resin composition according to this embodiment is not particularly limited, and various methods known in the technical field can be employed. For example, the polyacetal resin composition according to the present embodiment is put into an extruder, melt-kneaded and pelletized, and the pellets are put into an injection molding machine equipped with a predetermined mold and injection molded. can be done.

In addition, the resin gear of the present embodiment can be formed by molding the polyacetal resin composition according to the present embodiment into a plate-like or rod-like shape, and then performing general molding such as cutting.

The types of gears to which the resin gear of the present embodiment can be applied are not particularly limited. Gears, straight bevel gears, spiral bevel gears, zerol bevel gears, screw gears, cylindrical worm gears, and the like.

EXAMPLES The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the following examples.

<(A) Preparation of polyacetal copolymer>
[Polyacetal Copolymers A-1 to A-4]
A continuous twin-screw polymerization machine was used as a polymerization reactor. This polymerization machine has a jacket for passing a medium for heating or cooling on the outside, and two rotating shafts with many paddles for stirring and propelling are provided in the longitudinal direction inside. ing. A heat medium at 80°C is passed through the jacket of the twin-screw polymerizer, and while the two rotating shafts are rotated at a constant speed, trioxane as the main monomer (a) and A mixture of 1,3-dioxolane (3.3% by weight relative to total monomers) and 1500 ppm by weight of methylal as a chain transfer agent (relative to total monomers) was continuously fed. Then, a polymerization catalyst (methyl formate solution) shown in Table 1 was continuously added to the mixed solution in an amount shown in Table 1 with respect to all the monomers to carry out copolymerization. In Table 1, the amount of polymerization catalyst added is the mass ratio (unit: ppm) to the total of all monomers. Thereafter, the crude polyacetal copolymer was discharged from a discharge port provided at the other end of the polymerization machine, and a basic deactivator shown in Table 1 was added to deactivate the polymerization catalyst. In Table 1, the amount of basic deactivator is the mass ratio (unit: ppm) to the crude polyacetal copolymer. Then, 0.3 parts by mass of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] is added as an antioxidant, and a twin-screw extruder with a vent is used. The mixture was melted and kneaded at a temperature of 220° C. and a vacuum degree of 5 mmHg at the vent, and extruded. Polyacetal copolymers (A-1 to A-4) were obtained through the above steps. The melt flow rate (MFR) of each polyacetal copolymer was measured according to ISO 1133 using a measuring device: Melt Indexer L202 (manufactured by Takara Thermistor Co., Ltd.) at a load of 2.16 kg and a temperature of 190 ° C. .

[Polyacetal Copolymer A'-1]
Boron trifluoride is used as a catalyst in a gaseous state, and the polyacetal copolymers A-1 to A-4 and the above-mentioned polyacetal copolymers A-1 to A-4 are used until the crude polyacetal copolymer is discharged from a discharge port provided at the other end of the polymerization machine. did the same. The discharged reaction product was rapidly passed through a crusher and added to an aqueous solution containing 0.05% by mass of triethylamine at 60° C. to deactivate the catalyst. Furthermore, by separating, washing and drying, a crude polyacetal copolymer was obtained. Next, with respect to 100 parts by mass of this crude polyacetal copolymer, 3% by mass of a 5% by mass triethylamine aqueous solution, pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate ] was added in an amount of 0.3% by mass, and melt-kneaded at 210° C. in a twin-screw extruder to remove unstable portions to obtain a polyacetal copolymer related to polyacetal copolymer A′-1.

<Preparation of polyacetal resin composition>
After preblending the (A) component obtained in <(A) Preparation of polyacetal copolymer> and the following components (B) to (F) in the proportions shown in Table 2 (unit: parts by mass), one vent Throw into the main feed port of a twin-screw extruder with a 30 mm diameter port and melt and mix (extrusion conditions: L / D = 35, extrusion temperature = 200 ° C., screw rotation speed = 120 rpm, vent vacuum = -700 mmHg, discharge amount = 12 kg/hr) to prepare a composition in the form of pellets.

(B) Modified olefin polymer (B-1) Maleic anhydride-modified low-density polyethylene (LDPE) (product name: Toughmer MM6850, manufactured by Mitsui Chemicals, Inc.)
(B-2) Maleic anhydride-modified ethylene-ethyl acrylate copolymer (EEA) (product name: HPR AR2011, manufactured by DuPont Mitsui Polychemicals Co., Ltd.)
(C) Alkylene glycol polymer having a primary amino group or secondary amino group and a number average molecular weight of 400 or more and 500,000 or less (C-1) Amine-modified polyethylene glycol (PEG) at both ends (product name : Chemistat Y-400, number average molecular weight: 4,000, manufactured by Sanyo Chemical Industries Co., Ltd.)
(D) Cubic calcium carbonate having a BET specific surface area of 15 m ² /g or less, an average particle size of 50 nm or more and 200 nm or less, and an untreated surface (D-1) A BET specific surface area of 11.5 m ² /g, average particle size of 150 nm, surface untreated, cubic calcium carbonate (product name: Brilliant 1500, colloidal calcium carbonate, manufactured by Shiraishi Kogyo Co., Ltd.)
(E) Partial ester of polyhydric alcohol (E-1) Glycerin monostearate (product name: Rikemal S100, manufactured by Riken Vitamin Co., Ltd.)
(F) Alpha Olefin Oligomer (F-1) Alpha Olefin Oligomer (Product name: Lucant HC600, manufactured by Mitsui Chemicals, Inc.)

[Evaluation of Gear Fatigue Characteristics]
≪Molding conditions: gear molding≫
The pellet-shaped resin composition obtained under the above production conditions was molded using an injection molding machine (NEX500) manufactured by Nissei Plastic Industry Co., Ltd. with a cylinder temperature of 200 ° C., a mold temperature of 80 ° C., and an injection speed of 20 mm. /s, a holding pressure of 120 MPa, and a cooling time of 8 seconds to obtain a spur gear having a module of 1, 54 teeth, and a face width of 10 mm.
≪Gear durability test≫
The spur gear obtained in the above <<molding condition: gear molding>> was set in a small gear fatigue tester manufactured by Ono Sokki Co., Ltd. by meshing gears of the same material. One gear was the driving side and the other gear was the driven side. Next, the gear on the drive side was rotated at a torque of 10 N/m and a rotation speed of 300 rpm, and the total number of rotations until the gear broke was measured. Table 3 shows the measurement results.

[Evaluation of friction coefficient]
≪Molding conditions: Cylindrical specimen molding≫
Using an injection molding machine (αS50i-A) manufactured by Fanuc Co., Ltd., the pellet-shaped resin composition obtained under the above manufacturing conditions was molded at a cylinder temperature of 200° C., a mold temperature of 80° C., and an injection speed of 10 mm. /s, a holding pressure of 70 MPa, and a cooling time of 10 seconds to obtain a cylindrical test piece having an inner diameter of 20.0 mm, an outer diameter of 25.6 mm, and a height of 15.0 mm.
≪Abrasion test≫
Cylindrical test pieces obtained in the above «Molding conditions: Cylindrical test piece molding» were set in EFM-3-EN manufactured by Orientec Co., Ltd. by combining the same materials. One cylindrical test piece was used as the drive side, and the other as the fixed side. Next, it was rotated under conditions of a surface pressure of 0.06 MPa and a linear velocity of 15 cm/s, the frictional force was detected by a load cell, and the dynamic friction coefficient was calculated from the average value for one hour from 23 hours after the start of the test. Table 3 shows the calculation results.

From Table 3, it can be seen that in all of Examples 1 to 5, the total number of rotations until the gear fractures is greater than in Comparative Example 1, and the fatigue durability of the gear is excellent. Further, in Examples 1 to 5 and Comparative Example 1, the coefficient of friction was the same value.
From the above, it can be seen that the polyacetal resin compositions of Examples 1 to 5 are excellent in sliding properties and excellent in fatigue durability when applied to gears.

Claims (3)

Trioxane as the main monomer (a) (80 to 99.9 mol% of all monomers), at least one carbon-carbon cyclic ether and / or cyclic formal as comonomer (b), polymerization catalyst (c) A basic deactivator (d) is added to a reaction product obtained by copolymerization using a heteropolyacid represented by the following general formula (1), followed by melt-kneading to obtain the polymerization catalyst (c). With respect to 100 parts by mass of the polyacetal copolymer (A) obtained by deactivation,
(B) 0.5 parts by mass or more and 10 parts by mass or less of a modified olefin polymer obtained by modifying an olefin polymer with at least one selected from unsaturated carboxylic acids, unsaturated fatty acid anhydrides, and derivatives thereof; When,
(C) 0.01 parts by mass or more and 5 parts by mass or less of an alkylene glycol polymer having a primary amino group or a secondary amino group and a number average molecular weight of 400 or more and 500,000 or less;
(D) 0.1 parts by mass or more and 20 parts by mass or less of cubic calcium carbonate having a BET specific surface area of 15 m ² /g or less, an average particle size of 50 nm or more and 200 nm or less, and an untreated surface;
(E) 0.1 parts by mass or more and 10 parts by mass or less of a partial ester of a polyhydric alcohol having a valence of 2 or more and 4 or less;
(F) an alpha olefin oligomer of 0.1 parts by mass or more and 10 parts by mass or less;
A method for producing a polyacetal resin composition containing
H _m [M ¹ _x ·M ² _y O _Z ]·nH ₂ O General formula (1)
[In general formula ( ¹ ), M1 represents a central element consisting of one or two elements selected from P and Si. M2 represents one or ^more coordinating elements selected from W, Mo and V; x is an integer of 1 or more and 10 or less, y is an integer of 6 or more and 40 or less, z is an integer of 10 or more and 100 or less, m is an integer of 1 or more, and n is an integer of 0 or more and 50 or less. indicates ] A polyacetal resin composition produced by the method for producing a polyacetal resin composition according to claim 1 . A resin gear formed by molding the polyacetal resin composition according to claim 2 .