JP2013253696A - Helical gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a helical gear which is small in a deformation amount before and after a gear rotation test, and can reduce an increase of a sound accompanied by the gear rotation test.SOLUTION: In a helical gear comprising a plurality of ribs having penetration holes which are formed in centers and teeth formed at external peripheries, and radially arranged in directions toward the external peripheries from the penetration holes, and flat-plate shaped webs arranged between the plurality of ribs, the helical gear is a molded body of a polyacetal resin composition which contains a polyacetal resin and whose tensile elasticity is 3,500 to 7,000 Mpa, a twisted angle is 5 to 30°, a tooth width is 1 to 20 mm, the thickness of the web is 1.5 to 6 mm, and the number of the ribs is 6 to 24.

Description

  The present invention relates to a helical gear.

  Polyacetal resin is excellent in the balance of mechanical strength, chemical resistance and slidability, and easy to process. Therefore, as typical engineering plastics, mechanical parts of electric and electronic equipment, automobile parts and It is used over a wide range centering on other mechanical parts. Among them, polyacetal resin is widely used as a gear (gear) application in various fields because it is excellent in frictional wear and repetitive impact and can be produced by injection molding. In recent years, the performance required for gears is that the amount of deformation before and after using the gear is small, and the generation of sound when using the gear is small.

  By the way, the helical gear, which is a kind of gear, is a gear in which the tooth traces form a spiral line. However, since it is a quiet gear with a high meshing rate, it is used mainly for printer parts. In recent years, with the increase in accuracy and speed of OA equipment such as printers and copiers, rotation angle transmission, which is one of the most important purposes, is transmitted to gears that transmit power and rotation of these OA equipment. There is a demand not only for ensuring a small error, but also for difficulty in deformation in order to maintain the small error. In other words, if the teeth are distorted by the load while the gear meshing is in progress, the transmission angle during rotation varies, and the rotation angle is not uniform, causing dynamic pitch irregularities. Therefore, the performance of the OA device cannot be fully exhibited (see, for example, Patent Document 1). Therefore, the gear material is required not only to enable high-precision molding so as to reduce the angle transmission error, but also to ensure high rigidity.

  Examples of a method for obtaining a highly rigid polyacetal resin composition include a method for changing the physical properties of the base resin (polyacetal resin) itself such as increasing the crystallinity, and a method for containing a filler in the composition (for example, Non-patent document 1). Among these, since there is a limit to the method for increasing the rigidity of the base resin itself, many methods have conventionally been employed in which various fillers are included in the polyacetal resin composition to change the rigidity. However, when various kinds of fillers are contained, the moldability of the composition is lowered, shrinkage anisotropy, shrinkage unevenness, and the like are caused, resulting in a drop in molding accuracy. Therefore, conventionally, the blending amount of a preferable filler in the polyacetal resin composition is set to 10% by mass or less (see, for example, Patent Document 2 and Non-Patent Document 2).

  Further, as another method for obtaining a gear that is highly rigid and difficult to deform from the resin composition, a shape balance is determined and partial pressure is applied during molding (for example, see Patent Document 3), or a thermosetting resin is used (for example, A method of performing double injection molding (see, for example, Patent Document 5) or the like has also been studied. Furthermore, in Patent Document 7, for example, a gear including a tooth portion, a shaft support portion, and a web, a circumferential rib is formed on the web, and a circumferential cross section of the web between the circumferential rib and the tooth portion. There has been proposed a gear having a substantially wavy shape.

  It has already been described as a publicly known matter that if the rigidity of the gear is insufficient, the angle transmission error becomes very large under the actual rotational speed and rotational torque, and the dynamic accuracy is lowered (for example, Patent Document 6). reference). At present, in order to obtain a gear with high dynamic accuracy, the influence of static accuracy is more dominant than the influence of the elastic modulus of the material (see, for example, Non-Patent Document 3). In addition, it has been described in the past that gears whose total phase difference of specific orders is kept low are less sensitive to torque fluctuations. (For example, refer to Patent Document 8).

JP-A-8-137156 JP-A-11-51154 JP 2002-235835 A JP-A-9-144848 JP 2001-336608 A JP 2002-235835 A JP 2001-336609 A JP 2007-298157 A

Published by Nikkan Kogyo Shimbun, Polyacetal Resin Handbook First Edition, 1st Edition, P64 Tenac Handbook, May 2002 edition, P167 Presentation material of the Japan Society for Mold Processing 2003, Research on rotation transmission accuracy of polyacetal resin gears

  However, the methods described in Patent Documents 3 to 5 have a problem that costs are increased such as the introduction of equipment and an increase in processes. Furthermore, the gear proposed in Patent Document 7 has a complicated shape, and there is a problem that costs such as a mold are required. Therefore, in place of these methods, there is a need for a method that is difficult to deform even when a load is applied to a helical gear by a gear rotation test or the like and that can reduce an increase in sound generated when meshing.

  In addition, the evaluation method defined in the current JIS B1702 (1976) clearly clarifies how a highly rigid material is evaluated to become a gear that can withstand high torque fluctuations. However, there is room for further study on what factors are affected by the torque fluctuation dependence of the gears.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a helical gear in which the amount of deformation before and after the gear rotation test is small and the increase in sound accompanying the gear rotation test can be reduced. To do.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that a helical gear having specific specifications is loaded when it is molded from a polyacetal resin composition having a specific tensile elastic modulus. However, the present inventors have found that the amount of deformation and the increase in sound can be reduced, leading to the present invention.

That is, the present invention is as follows.
[1] A plurality of ribs having a through hole formed in the center and a tooth portion formed on the outer periphery, and radially provided in a direction from the through hole to the outer periphery, and provided between the plurality of ribs A helical gear comprising a polyacetal resin, a molded article of a polyacetal resin composition containing a polyacetal resin and having a tensile elastic modulus of 3500 to 7000 MPa, a twist angle of 5 to 30 °, and a tooth A helical gear having a width of 1 to 20 mm, a web thickness of 1.5 to 6 mm, and a number of ribs of 6 to 24.
[2] The helical gear of [1], wherein the twist angle is 10 to 30 °.
[3] The helical gear of [1] or [2], wherein the tooth width is 7 to 20 mm.
[4] The helical gear according to any one of [1] to [3], wherein the thickness of the web is 1.8 to 6 mm.
[5] The helical gear according to any one of [1] to [4], wherein the number of the ribs is 8 to 24.
[6] The polyacetal resin composition contains a filler, the average particle diameter of the filler is more than 0.01 μm and less than 5 μm, and the ratio of the average major axis to the average minor axis of the filler particles is 30 or less. , [1] to [5] is a helical gear.
[7] The helical gear of [6], wherein the filler is calcium carbonate.
[8] The helical gear of [6] or [7], containing 5 to 120 parts by mass of the filler with respect to 100 parts by mass of the polyacetal resin.
[9] The helical gear of [6] or [7], containing 5 to 100 parts by mass of the filler with respect to 100 parts by mass of the polyacetal resin.

  According to the present invention, it is possible to provide a helical gear in which the amount of deformation before and after the gear rotation test is small and the increase in sound accompanying the gear rotation test can be reduced.

It is a schematic diagram which shows an example of the helical gear of this invention, (a) is a top view, (b) is a bottom view. It is a schematic diagram of the helical gear shown in FIG. 1, (a) is a front view, (b) is A-A 'sectional drawing of (a).

  DESCRIPTION OF EMBODIMENTS Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. Further, the present invention is not limited to the present embodiment described below, and can be implemented with various modifications within the scope of the gist.

  1 and 2 are schematic views showing an example of a helical gear according to the present embodiment. FIG. 1A is a plan view, FIG. 1B is a bottom view, and FIG. FIG. 2B is a cross-sectional view taken along the line AA ′ in FIG. The helical gear 100 of the present embodiment has a through hole 110 formed in the center and a tooth portion 120 formed on the outer periphery, and a plurality of ribs provided radially in the direction from the through hole 110 to the outer periphery. 130 and a helical gear in a right-handed direction including a flat web 140 provided between a plurality of ribs, and a polyacetal resin composition containing a polyacetal resin and having a tensile elastic modulus of 3500 to 7000 MPa. The molded body has a twist angle of 5 to 30 °, a tooth width of 1 to 20 mm, a web thickness of 1.5 to 6 mm, and a number of ribs of 6 to 24. The module of the helical gear 100 is preferably 0.3-3, and the thickness of the rib 130 is preferably 1-5 mm. Furthermore, the tooth depth may be any of low teeth, normal teeth, and high teeth. The helical gear 100 includes an outer peripheral rim 150 on the outer peripheral portion thereof, and a tooth portion 120 is formed on the outer peripheral surface of the outer peripheral rim 150. The helical gear 100 includes a cylindrical inner peripheral rim 160 on the outer periphery of the through hole 110, and the through hole 110 is surrounded by a wall portion that is an inner wall of the inner peripheral rim 160. The helical gear 100 has a keyway 170 on the bottom surface (back surface). The key groove 170 is for fitting a shaft core (not shown) passed through the through hole 110 in order to rotate the helical gear 100, so that the shaft core is a helical gear. 100 is fixed.

  The helical gear 100 of the present embodiment preferably has a helix angle of 5 to 30 °, more preferably 10 to 30 °. When the twist angle is 5 ° or more, the above-described effects of the present invention are more sufficiently exhibited, and when the twist angle is 30 ° or less, molding such as injection molding becomes easy.

  The helical gear 100 of the present embodiment preferably has a tooth width of 1 to 20 mm, and more preferably 7 to 20 mm. When the tooth width is 1 mm or more, the above-described effects of the present invention are more sufficiently exerted, and when the tooth width is 20 mm or less, molding such as injection molding becomes easy.

  In the helical gear 100 of the present embodiment, the thickness of the web 140 is preferably 1.5 to 6 mm, and more preferably the thickness of the web 140 is 1.8 mm to 6 mm. When the thickness of the web 140 is 1.5 mm or more, the above-described effect according to the present invention is more sufficiently exerted, and when the thickness of the web 140 is 6 mm or less, cooling is performed in forming the helical gear 100. Time can be shortened and production efficiency is improved.

  The helical gear 100 of the present embodiment preferably has 6 to 24 ribs 130 and more preferably 8 to 24 ribs 130. When the number of the ribs 130 is 6 or more, the above-described effects of the present invention are more sufficiently exhibited, and when the number of the ribs 130 is 24 or less, thick ribs can be easily formed.

  As for the helical gear 100 of this embodiment, it is preferable in the module being 0.3-3. When the module of the helical gear 100 is 0.3 or more, the meshing rate is increased and the effect of noise reduction is obtained, and when it is 3 or less, the effect of molding sink is reduced.

  In the helical gear 100 of the present embodiment, the thickness of the rib 130 is preferably 1 to 5 mm. If the thickness of the rib 130 is 1 mm or more, the effect of improving the strength of the gear is obtained, and if it is 5 mm or less, the effect of reducing sink marks due to molding is obtained.

  The helical gear 100 of this embodiment is obtained by molding a polyacetal resin composition containing a polyacetal resin. About the helical gear 100 of this embodiment which has the above-mentioned specifications, the tensile elasticity modulus of the said polyacetal resin composition is 3500-7000 Mpa. The tensile elastic modulus is preferably 4000 to 6500 MPa, the upper limit is more preferably 6000, still more preferably 5000 MPa, and particularly preferably 4500 MPa. When the tensile elastic modulus is 3500 MPa or more, the above-described effect according to the present invention can be sufficiently exerted, and when the tensile elastic modulus is 7000 MPa or less, the deformation of the helical gear 100 is suppressed. Since it is not necessary to include a large amount of filler in the polyacetal resin composition, the problem that injection molding becomes difficult due to the decrease in fluidity and / or thermal stability of the composition does not occur.

  The tensile elastic modulus of the polyacetal resin composition is determined according to ISO9988-2 according to the conditions of cylinder temperature 205 ° C., injection pressure 60 MPa, injection time 15 seconds, cooling time 25 seconds, mold temperature 90 ° C. A test piece is obtained by injection molding, and the test piece is measured in accordance with ISO178.

  In order for the polyacetal resin composition to have the above-described tensile elastic modulus, the composition of the composition may be adjusted within the following range.

  First, examples of the polyacetal resin contained in the polyacetal resin composition according to this embodiment include a polyacetal homopolymer and a polyacetal copolymer. A polyacetal homopolymer is obtained by homopolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trioxane) or tetramer (tetraoxane) thereof, and is substantially composed only of oxymethylene units. . Polyacetal copolymers include formaldehyde monomers or cyclic oligomers of formaldehyde such as trimers (trioxane) and tetramers (tetraoxane), ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane and 1,4-butanediol. It is obtained by copolymerizing a cyclic ether such as a glycol such as formal or a cyclic formal of diglycol or a cyclic formal. The polyacetal copolymer may be a branched polyacetal copolymer obtained by copolymerizing a monofunctional glycidyl ether, or a polyacetal copolymer having a crosslinked structure obtained by copolymerizing a polyfunctional glycidyl ether. Furthermore, a polyacetal homopolymer having a block component obtained by polymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde in the presence of a compound having a functional group such as a hydroxyl group at both ends or one end, for example, polyalkylene glycol; , A compound having a functional group such as a hydroxyl group at both ends or one end, for example, a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trioxane) or a tetramer (tetraoxane) in the presence of hydrogenated polybutadiene glycol. It may be a polyacetal copolymer having a block component obtained by copolymerizing a cyclic ether and a cyclic formal. As described above, both the polyacetal homopolymer and the polyacetal copolymer can be used as the polyacetal resin according to the present embodiment. A polyacetal resin is used individually by 1 type or in combination of 2 or more types. Of these, polyacetal copolymers are preferred.

  When the polyacetal resin is a polyacetal copolymer of trioxane and a comonomer such as 1,3-dioxolane, generally, the copolymerization ratio of the comonomer is preferably 0.1 to 60 mol% with respect to 100 mol% of trioxane. More preferably, it is 0.1-20 mol%, More preferably, it is 0.13-10 mol%.

  The polymerization catalyst used when the polyacetal resin is obtained by polymerization is not particularly limited, but a cationically active catalyst such as Lewis acid, proton acid and ester or anhydride thereof is preferable. Examples of Lewis acids include boric acid, tin, titanium, phosphorus, arsenic and antimony halides. More specifically, boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, Examples thereof include phosphorus pentachloride, antimony pentafluoride, and complex compounds or salts thereof. However, the Lewis acid is not limited to these. Specific examples of the protonic acid, its ester or anhydride include perchloric acid, trifluoromethanesulfonic acid, perchloric acid-tertiary butyl ester, acetyl perchlorate, trimethyloxonium hexafluorophosphate, It is not limited. Among these polymerization catalysts, boron trifluoride; boron trifluoride hydrate; and a coordination complex compound of an organic compound containing an oxygen atom or a sulfur atom and boron trifluoride are preferable. Specific examples of such a polymerization catalyst include boron trifluoride diethyl ether and boron trifluoride di-n-butyl ether.

  The method for polymerizing the polyacetal resin is not particularly limited, but conventionally known methods such as US Pat. No. 3,027,352, US Pat. No. 3,803,094, German Patent No. 1161412, and German Patent Invention No. No. 1495228, German Patent No. 1720358, German Patent No. 3018898, JP-A-58-98322, JP-A-7-70267.

  As a polymerization method of the polyacetal resin, generally, bulk polymerization is exemplified, and either a batch type or a continuous type may be used. Examples of the polymerization apparatus used include a self-cleaning type extrusion kneader such as a kneader, a twin screw continuous extrusion kneader, and a twin screw paddle type continuous mixer. Molten monomer is supplied to the polymerization machine, and solid agglomerated polyacetal resin is obtained as the polymerization proceeds.

Since the polyacetal resin obtained as described above has a thermally unstable terminal portion (— (OCH ₂ ) _n —OH group), in order to improve its practicality, It is preferable to perform the decomposition removal treatment of the part, and it is more preferable to perform the decomposition removal treatment of the specific unstable terminal portion shown below. Specifically, the specific unstable terminal portion decomposition removal treatment (hereinafter, simply referred to as “unstable end portion removal treatment”) refers to at least one quaternary ammonium compound represented by the following general formula (1). In this method, heat treatment is performed in a state where the polyacetal resin is melted at a temperature not lower than the melting point of the polyacetal resin and not higher than 260 ° C. in the presence.

[R ¹ R ² R ³ R ⁴ N ⁺ ] _n X ⁻ⁿ (1)
Here, in the formula, R ¹ , R ² , R ³ and R ⁴ are each independently an unsubstituted alkyl group or substituted alkyl group having 1 to 30 carbon atoms; an aryl group having 6 to 20 carbon atoms; An aralkyl group in which at least one hydrogen atom of an unsubstituted alkyl group having 1 to 30 or a substituted alkyl group is substituted with an aryl group having 6 to 20 carbon atoms; or at least one hydrogen of an aryl group having 6 to 20 carbon atoms An alkylaryl group in which an atom is substituted with an unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted alkyl group, and the unsubstituted alkyl group or substituted alkyl group is linear, branched, or cyclic (ie, unsubstituted cycloalkyl Group or a substituted cycloalkyl group). The substituent of the substituted alkyl group is a halogen atom, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, or an amide group. In the unsubstituted alkyl group, aryl group, aralkyl group, and alkylaryl group, a hydrogen atom may be substituted with a halogen atom. n shows the integer of 1-3. X represents a hydroxyl group or an acid residue of a carboxylic acid having 1 to 20 carbon atoms, a hydrogen acid other than a hydrogen halide, an oxo acid, an inorganic thioacid, or an organic thioacid having 1 to 20 carbon atoms.

The quaternary ammonium compound is not particularly limited as long as it is represented by the general formula (1), but R ¹ , R ² , R ³ , and R ⁴ in the general formula (1) are each independently selected. The alkyl group having 1 to 5 carbon atoms or the hydroxyalkyl group having 2 to 4 carbon atoms is preferable, and at least one of R ¹ , R ² , R ³ , and R ⁴ is a hydroxyethyl group. Those are particularly preferred. Specifically, tetramethylammonium, tetoethylammonium, tetrapropylammonium, tetra-n-butylammonium, cetyltrimethylammonium, tetradecyltrimethylammonium, 1,6-hexamethylenebis (trimethylammonium), decamethylene-bis- ( Trimethylammonium), trimethyl-3-chloro-2-hydroxypropylammonium, trimethyl (2-hydroxyethyl) ammonium, triethyl (2-hydroxyethyl) ammonium, tripropyl (2-hydroxyethyl) ammonium, tri-n-butyl ( 2-hydroxyethyl) ammonium, trimethylbenzylammonium, triethylbenzylammonium, tripropylbenzylammonium, tri-n-butylbenzene Zirammonium, trimethylphenylammonium, triethylphenylammonium, trimethyl-2-oxyethylammonium, monomethyltrihydroxyethylammonium, monoethyltrihydroxyethylammonium, okdadecyltri (2-hydroxyethyl) ammonium, tetrakis (hydroxyethyl) ammonium, etc. Hydroxides of hydrochloric acid, odorous acid, hydrofluoric acid, etc .; sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, chloric acid, iodic acid, silicic acid, perchloric acid, chlorous acid, hypochlorous acid Oxo acid salts such as chlorosulfuric acid, amidosulfuric acid, disulfuric acid, tripolyphosphoric acid; thioic acid salts such as thiosulfuric acid; formic acid, acetic acid, propionic acid, butanoic acid, isobutyric acid, pentanoic acid, caproic acid, caprylic acid, capric acid Carboxylic acid salts such as benzoic acid and oxalic acid It is. Among these, hydroxide (X ⁿ⁻ = OH ⁻ ), sulfuric acid (X ⁿ⁻ = HSO ₄ ⁻ , SO ₄ ²⁻ ), carbonic acid (X ⁿ⁻ = HCO ₃ ⁻ , CO ₃ ²⁻ ), boric acid (X ⁿ⁻ = B (OH) ₄ ⁻ ), carboxylic acid salts are preferred. Among the carboxylates, formate, acetate, and propionate are particularly preferable.

  A quaternary ammonium compound is used individually by 1 type or in combination of 2 or more types. Further, in addition to the quaternary ammonium compound, amines such as ammonia and triethylamine, which are known decomposition accelerators for unstable terminals, may be used in combination.

The amount of the quaternary ammonium compound used in the heat treatment method is converted to the amount of nitrogen derived from the quaternary ammonium compound represented by the following formula (2) with respect to the total mass of the polyacetal resin and the quaternary ammonium compound. And it is preferable in it being 0.05-50 mass ppm, More preferably, it is 1-30 mass ppm.
P × 14 / Q (2)
Here, in the formula, P represents the concentration (mass ppm) of the quaternary ammonium compound relative to the polyacetal resin, 14 represents the atomic weight of nitrogen, and Q represents the molecular weight of the quaternary ammonium compound.

  If the amount of the quaternary ammonium compound added is less than 0.05 ppm by mass, the rate of decomposition and removal of unstable terminals tends to decrease, and if it exceeds 50 ppm by mass, after removal of unstable terminals The color tone of the polyacetal resin tends to deteriorate.

  The unstable end portion removal treatment of the polyacetal resin is achieved by performing a heat treatment in a state where the polyacetal resin is melted at a temperature not lower than the melting point of the polyacetal resin and not higher than 260 ° C. The apparatus used for this heat treatment is not particularly limited, but it is preferable to perform heat treatment using an extruder, a kneader or the like. In addition, formaldehyde generated by decomposition is removed under reduced pressure. The addition method of the quaternary ammonium compound is not particularly limited, and examples thereof include a method of adding it as an aqueous solution in the step of deactivating the polymerization catalyst, and a method of spraying the polyacetal resin powder produced by the polymerization. Whichever addition method is used, it may be added in the step of heat-treating the polyacetal resin, and may be poured into an extruder. Alternatively, when the filler or pigment is blended into the polyacetal resin composition using an extruder or the like, the compound may be attached to the resin pellet, and the unstable terminal portion may be removed in the subsequent blending step.

  The unstable terminal portion removal treatment may be performed after the polymerization catalyst in the polyacetal resin obtained by polymerization is deactivated or may be performed without deactivating the polymerization catalyst. The polymerization catalyst deactivation treatment is not particularly limited, but a representative example is a method of neutralizing and deactivating the polymerization catalyst in a basic aqueous solution such as amines. In addition, without deactivating the polymerization catalyst, heating in an inert gas atmosphere at a temperature below the melting point of the polyacetal resin, reducing the polymerization catalyst by volatilization removal, and then performing the unstable end portion removal treatment. It is an effective method.

  By performing the unstable terminal portion removal treatment, it is possible to obtain a polyacetal resin excellent in thermal stability and having almost no unstable terminal portion.

  From the viewpoint of suppressing deformation of the helical gear 100, the polyacetal resin composition according to the present embodiment preferably contains a filler. The smaller the particle diameter, and the smaller the average aspect ratio (L / D), which is the ratio of the average major axis (L) to the average minor axis (D) of the particle, the smaller the filler is on the surface of the helical gear 100. It is preferable because shrinkage can be suppressed and molding accuracy can be improved. Specifically, from the relationship between the dispersibility of the filler and the molding accuracy, the average particle size of the filler is preferably greater than 0.01 μm and less than 5 μm, and the average aspect ratio is preferably 30 or less. It is more preferable to satisfy both of these. More preferably, a filler having an average particle size of more than 0.01 μm and less than 4 μm and an average aspect ratio of less than 10, particularly preferably an average particle size of more than 0.01 μm and less than 3 μm and an average aspect ratio of less than 2 It is a filler.

Here, in this specification, the particle shape and size of the filler use the definition of Heywood, and in the plan view of the particle, the shortest distance between the two parallel lines in contact with the particle outline (periphery) is the shortest diameter and longest distance. Is measured as the major axis. The average particle diameter, average long diameter, average short diameter, and average aspect ratio are defined as follows when Ni fillers having a long diameter Li and a short diameter di exist in a unit volume.
Average particle diameter = Average major axis = ΣLi ² Ni / ΣLiNi
Average minor axis = Σdi ² Ni / ΣdiNi
Average aspect ratio L / D = (ΣLi ² Ni / ΣLiNi) / (Σdi ² Ni / ΣdiNi)

  More specifically, the filler to be measured was sampled using a scanning electron microscope (SEM), and a particle image was taken at a magnification of 1,000 to 50,000 times using this, and was randomly selected. Each length is measured and determined from a minimum of 100 filler particles.

  The filler according to this embodiment is not particularly limited as long as it is a known filler, and broadly includes organic fillers and inorganic fillers.

  As the organic filler, a hydrocarbon-based fine organic filler having a high melting point or glass transition point is preferable as compared with the polyacetal resin. Specific examples thereof include fine powder and fine particles such as epoxy resin, melamine resin, urea resin, acrylic resin, phenol resin, fluororesin, saturated or unsaturated polyester resin, aliphatic or aromatic polyamide resin, polyphenylene ether resin, and the like. And fine powder and fine particles of super engineer plastic resin such as liquid crystal polymer resin, polyetherketone resin, polyimide resin, and polysulfone resin. The organic filler may be a low molecular weight resin powder and fine particles, or may be a high molecular weight or crosslinked resin powder and fine particles. Further, the resin obtained by polymerization may have a shape and particle diameter as described above by mechanical treatment such as pulverization. An organic filler is used individually by 1 type or in combination of 2 or more types.

  Examples of inorganic fillers include carbon black, carbon nanotubes, silica, quartz powder, glass beads, glass powder, calcium silicate, aluminum silicate, kaolin, talc, clay, diatomaceous earth, silicates represented by wollastonite, and iron oxide. , Titanium oxide, alumina, metal oxides typified by zinc oxide, calcium sulfate, metal sulfates typified by barium sulfate, calcium carbonate, magnesium carbonate, carbonates typified by dolomite, others, silicon carbide, silicon nitride , Boron nitride, various metal powders, mica, glass flakes, glass balloons, silica balloons, shirasu balloons, metal balloons, stainless steel, aluminum, titanium, copper, brass and other metal particles. An inorganic filler is used individually by 1 type or in combination of 2 or more types.

  From the standpoint that the particle size can be reduced and the particle size distribution is narrow, preferred inorganic fillers are carbon black, carbon nanotubes, silica, quartz powder, glass beads, glass powder, calcium silicate, aluminum silicate, kaolin, talc, clay, diatomaceous earth. , Iron oxide, titanium oxide, alumina, zinc oxide, calcium carbonate, magnesium carbonate, boron nitride, mica, and glass flakes. More preferably, carbon black, carbon nanotube, silica, glass beads, glass powder, aluminum silicate, kaolin, talc, clay, zinc oxide, calcium carbonate, boron nitride, mica, and more preferably carbon black, carbon nanotube, silica , Kaolin, talc, zinc oxide and calcium carbonate, particularly preferably calcium carbonate.

  The filler according to this embodiment may be subjected to a surface treatment with a known surface treatment agent in order to improve the affinity with the resin. Examples of the surface treatment agent include silane coupling agents such as aminosilane and epoxysilane, titanate coupling agents, fatty acids (saturated fatty acids and unsaturated fatty acids), alicyclic carboxylic acids, resin acids, and metal soaps. However, these surface treatment agents also cause a reduction in the rigidity of the helical gear 100. From this viewpoint, the amount of the surface treatment agent added to the filler is preferably 3% by mass or less, more preferably 2% by mass or less. More preferably, it is substantially not surface-treated.

  In addition, when the filler is an inorganic filler, the inorganic filler can be used either surface-treated or unsurface-treated, but the surface of the molding surface is smooth and has mechanical characteristics. In some cases, a surface-treated product is preferable. The surface treatment agent used for the surface treatment of the inorganic filler may be a conventionally known one, and examples thereof include various coupling treatment agents such as silane, titanate, aluminum, and zirconium. More specifically, N- (2-aminoethyl) -3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyl tristearoyl titanate, diisopropoxyammonium ethyl acetate, n-butyl zirconate Is mentioned.

  From the viewpoint of mechanical properties, the filler content in the helical gear 100 obtained by molding the polyacetal resin composition according to this embodiment is 5 to 120 parts by mass with respect to 100 parts by mass of the polyacetal resin. Preferably there is. When the content of the filler is 5 parts by mass or more, the above-described effect due to the addition of the filler can be more effectively exhibited, and deformation due to shrinkage is further suppressed. Moreover, it exists in the tendency for a moldability and durability to become further favorable because content of a filler is 120 mass parts or less.

  The filler content in the polyacetal resin composition is 5 to 120 parts by mass with respect to 100 parts by mass of the polyacetal resin from the viewpoint of suppressing the deformation amount before and after the gear rotation test and the increase in sound accompanying the gear rotation test. More preferably, it is 5-100 mass parts, More preferably, it is 10-100 mass parts, Most preferably, it is 20-100 mass parts.

  When the polyacetal resin composition contains an appropriate additive as required, the helical gear 100 obtained by molding the polyacetal resin composition is further excellent in thermal stability. A suitable example of the additive is at least one selected from an antioxidant, a polymer or compound having formaldehyde-reactive nitrogen, a formic acid scavenger, a weathering (light) stabilizer, a release agent, and a lubricant. . The additive is preferably contained in the polyacetal resin composition in an amount of 0.01 to 10 parts by mass with respect to 100 parts by mass of the polyacetal resin.

  As the antioxidant, a hindered phenol antioxidant is preferable. Specifically, for example, n-octadecyl-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) -propionate, n-octadecyl-3- (3′-methyl-5′-) t-butyl-4′-hydroxyphenyl) -propionate, n-tetradecyl-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) -propionate, 1,6-hexanediol-bis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate], 1,4-butanediol-bis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) ) -Propionate], triethylene glycol-bis- [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) -propionate], pentaerythritol tetrakis Methylene-3- (3 ', 5'-di -t- butyl-4'-hydroxyphenyl) propionate], and methane. Preferably, triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate] and pentaerythritol tetrakis [methylene-3- (3 ′, 5′-di-t -Butyl-4'-hydroxyphenyl) propionate] methane. These antioxidants are used alone or in combination of two or more.

  Examples of polymers or compounds having formaldehyde-reactive nitrogen include nylon resins such as nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, nylon 12, and polymers thereof. Examples thereof include nylon 6 / 6-6 / 6-10 and nylon 6 / 6-12. Other examples include acrylamide and derivatives thereof, and copolymers of acrylamide and derivatives thereof with other vinyl monomers. More specifically, acrylamide and derivatives thereof with other vinyl monomers are converted into metal alcoholates. And a poly-β-alanine copolymer obtained by polymerization in the presence of. Examples of other polymers or compounds having formaldehyde-reactive nitrogen include amide compounds, amino-substituted triazine compounds, adducts of amino-substituted triazine compounds and formaldehyde, condensates of amino-substituted triazine compounds and formaldehyde, urea, urea Examples include derivatives, hydrazine derivatives, imidazole compounds, and imide compounds.

  Specific examples of the amide compound include polycarboxylic acid amides such as isophthalic acid diamide and anthranilamides. Specific examples of the amino-substituted triazine compound include 2,4-diamino-sym-triazine, 2,4,6-triamino-sym-triazine, N-butylmelamine, N-phenylmelamine, N, N-diphenylmelamine, N , N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sym-triazine), acetoguanamine (2,4-diamino-6-methyl-sym-triazine), 2,4-diamino-6-butyl -Sym-triazine is mentioned. Specific examples of the adduct of an amino-substituted triazine compound and formaldehyde include N-methylol melamine, N, N′-dimethylol melamine, and N, N ′, N ″ -trimethylol melamine. Specific examples of condensates with formaldehyde include melamine / formaldehyde condensates, and examples of urea derivatives include N-substituted urea, urea condensates, ethylene urea, hydantoin compounds, and ureido compounds. Specific examples of substituted urea include methylurea, alkylenebisurea, and aryl substituted urea substituted with a substituent such as an alkyl group, etc. Specific examples of urea condensates include condensates of urea and formaldehyde. Specific examples of hydantoin compounds include hydantoin, 5,5-di Specific examples of ureido compounds include allantoin, specific examples of hydrazine derivatives include hydrazide compounds, and specific examples of hydrazide compounds include dicarboxylic acids. More specifically, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, speric acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide Dihydrazide, phthalic acid dihydrazide, 2,6-naphthalenedicarbodihydrazide, etc. Specific examples of imide compounds include succinimide, glutarimide, and phthalimide. It is below.

  These polymers or compounds having formaldehyde-reactive nitrogen atoms are used alone or in combination of two or more.

  Examples of the formic acid scavenger include the above-mentioned amino-substituted triazine compounds, condensates of amino-substituted triazine compounds and formaldehyde, for example, melamine / formaldehyde condensates. Examples of other formic acid scavengers include alkali metal or alkaline earth metal hydroxides, inorganic acid salts, carboxylate salts, and alkoxides. More specifically, sodium, potassium, magnesium, calcium or barium hydroxides, carbonates, phosphates, silicates, borates, carboxylates and layered double hydroxides of the above metals may be mentioned.

  The carboxylic acid in the carboxylate is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, and these carboxylic acids may be substituted with a hydroxyl group. Specific examples of saturated or unsaturated aliphatic carboxylates include calcium dimyristate, calcium dipalmitate, calcium distearate, (myristic acid-palmitic acid) calcium, (myristic acid-stearic acid) calcium, ( (Palmitic acid-stearic acid) calcium is mentioned, and among them, calcium dipalmitate and calcium distearate are preferable.

Examples of the layered double hydroxide include hydrotalcites represented by the following general formula (3).
[(M ²⁺ ) _1-X (M ³⁺ ) _X (OH) ₂ ] _X ⁺ [(A ⁿ⁻ ) _{x / n} · mH ₂ O] _X ⁻ (3)
Here, in the formula, M ²⁺ is a divalent metal, M ³⁺ is a trivalent metal, A ^n-C n-valent (n is an integer of 1 or more) denotes an anion of, X is, 0 <X ≦ 0. It is a number in the range of 33, and m is a positive number.

In the general formula (3), examples of M ²⁺ include Mg ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , and Zn ²⁺ . Examples of M ³⁺ include Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Co ³⁺ and In ³⁺ . Examples of A ^{n- is, OH -, F -, Cl} -, Br -, NO 3 -, CO 3 2-, SO 4 2-, Fe (CN) 6 3-, CH 3 COO -, oxalic acid ion And salicylic acid ions, and CO ₃ ²⁻ and OH ⁻ are particularly preferable. Specific examples of the hydrotalcite represented by the general formula (3) include natural hydrotalcite represented by Mg _0.75 Al _0.25 (OH) ₂ (CO ₃ ) _0.125 · 0.5H ₂ O, Mg _4.5 Al Examples thereof include synthetic hydrotalcite represented by ₂ (OH) ₁₃ CO ₃ .3.5H ₂ O, Mg _4.3 Al ₂ (OH) _12.6 CO _{3 and the} like.

  These formic acid scavengers are used singly or in combination of two.

  The weather resistance (light) stabilizer is preferably one or more selected from the group consisting of benzotriazole-based and oxalic acid anilide-based UV absorbers and hindered amine-based light stabilizers.

  Examples of benzotriazole ultraviolet absorbers include 2- (2′-hydroxy-5′-methyl-phenyl) benzotriazole and 2- (2′-hydroxy-3 ′, 5′-di-t-butyl-phenyl). ) Benzotriazole, 2- [2′-hydroxy-3 ′, 5′-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-3 ′, 5′-bis -(Α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (2′-hydroxy-4′-octoxyphenyl) benzotriazole. Examples of the oxalic acid alinide ultraviolet absorbers include 2-ethoxy-2′-ethyloxalic acid bisanilide, 2-ethoxy-5-tert-butyl-2′-ethyloxalic acid bisanilide, and 2-ethoxy. -3'-dodecyl oxalic acid bisanilide. In these, a benzotriazole type ultraviolet absorber is preferable, More preferably, 2- [2′-hydroxy-3 ′, 5′-bis- (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2 -(2'-hydroxy-3 ', 5'-di-t-butyl-phenyl) benzotriazole. These ultraviolet absorbers are used alone or in combination of two or more.

  Examples of hindered amine light stabilizers include N, N ′, N ″, N ′ ″-tetrakis- (4,6-bis- (butyl- (N-methyl-2,2,6,6-tetramethyl). Piperidin-4-yl) amino) -triazin-2-yl) -4,7-diazadecane-1,10-diamine, dibutylamine, 1,3,5-triazine, N, N′-bis (2,2,2) A polycondensate of 6,6, tetramethyl-4-piperidyl-1,6-hexamethylenediamine and N- (2,2,6,6, tetramethyl-4-piperidyl) butylamine, poly [{6- ( 1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6, tetramethyl-4-piperidyl) imino} hexamethylene { (2,2,6,6-tetramethyl-4-pi Lysyl) imino}], a condensation product of dimethyl succinate and 4-hydroxy-2,2,6,6, tetramethyl-1-piperidineethanol, bis (2,2,6,6-tetramethyl-decanoate) 1 (octyloxy) -4-piperidinyl) ester, 1,1-dimethylethyl hydroperoxide and octane, the reaction product bis (1,2,2,6,6-pentamethyl-4-piperidyl) [[3 5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] butyl malonate, methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate, bis (2,2,6, 6-tetramethyl-4-piperidyl) -sebacate, 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β, β, And a condensate with ', β',-tetramethyl-3,9- [2,4,8,10-tetraoxaspiro (5,5) undecane] diethanol, preferably bis (2,2, 6,6-tetramethyl-4-piperidyl) -sebacate, bis- (N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, 1,2,3,4-butanetetracarboxylic acid And 1,2,2,6,6-pentamethyl-4-piperidinol and β, β, β ′, β ′,-tetramethyl-3,9- [2,4,8,10-tetraoxaspiro (5, 5) Undecane] Condensates with diethanol These hindered amine light stabilizers are used alone or in combination of two or more.

  As the release agent and lubricant, for example, alcohol, fatty acid and fatty acid ester thereof, polyoxyalkylene glycol, olefin compound having an average polymerization degree of 10 to 500, and silicone are preferably used.

  The polyacetal resin composition according to the present embodiment may further contain known additives other than those described above as necessary within a range not impairing the object of the present invention. Specific examples of such additives include crystal nucleating agents, conductive materials, thermoplastic resins, thermoplastic elastomers, and pigments.

  Examples of the conductive agent include conductive carbon black, graphite, carbon nanotube, metal powder, or fiber.

  Examples of the thermoplastic resin include polyolefin resin, acrylic resin, styrene resin, polycarbonate resin, and uncured epoxy resin. In addition, modified products of these resins are also exemplified. Examples of the thermoplastic elastomer include polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers.

  As the pigment, a known pigment usually used for a polyacetal resin can be used as long as it does not interfere with the purpose of the present invention. Examples of such pigments include inorganic pigments, organic pigments, metallic pigments, and fluorescent pigments. As the inorganic pigment, those generally used for coloring a resin can be used. For example, zinc sulfide, titanium oxide, barium sulfate, titanium yellow, cobalt blue, combustion pigment, carbonate, phosphorus Examples thereof include acid salts, acetate salts, carbon black, acetylene black, lamp black, chlorinated carbon lead, basic lead sulfate, basic lead silicate, and metal sulfide. Organic pigments include, for example, condensed ouzo, inone, furothocyanine, monoazo, diazo, polyazo, azomethine, methine, indanthrone, pyranthrone, flavanthrone, benzenethrone, perinone Pigments based on azoind, isoindoline, isoindolinone, pyrrole pyrrole, quinophthalone, anthraquinone, heterocyclic, pennon, quinacridone, thioindico, berylene, dioxazine, and phthalocyanine.

  These pigments are used singly or in combination of two or more, but are usually used in combination of two or more in order to obtain the required color tone.

  The total pigment content in the helical gear 100 is preferably 0.005 to 5.0 parts by mass with respect to 100 parts by mass of the polyacetal resin. From the viewpoint of thermal stability of the polyacetal resin, the content is preferably 5.0 parts by mass or less.

  The MFR of the polyacetal resin composition according to the present embodiment is 1 to 110 g / 10 minutes from the viewpoint of easily obtaining the helical gear 100, but the deformation amount before and after the gear rotation test and the sound accompanying the gear rotation test From the viewpoint of further suppressing the increase in the amount, it is preferably 3 to 80 g / 10 minutes, and more preferably 6 to 40 g / 10 minutes. The MFR of the polyacetal resin composition is derived by converting the amount of effluent extruded at a heating cylinder temperature of 190 ° C. and a load of 2160 g per 10 minutes in accordance with the measurement method specified in Condition D of ISO 1133 (1997). Is done.

  Moreover, the suitable melting | fusing point of a polyacetal resin composition is 162 degreeC-173 degreeC from a viewpoint of the deformation | transformation amount before and behind a gear rotation test, and the increase suppression of the sound accompanying a gear rotation test, Preferably it is 167 degreeC-173 degreeC. Preferably it is 167 degreeC-171 degreeC. A polyacetal copolymer having a melting point of 167 ° C. to 171 ° C. can be obtained by using a comonomer of about 1.3 to 3.5 mol% with respect to trioxane.

  The polyacetal resin composition used to obtain the helical gear 100 of this embodiment is manufactured using a general extruder. Examples of the extruder include a single-screw or multi-screw kneading extruder, and among them, a twin-screw extruder provided with a decompression device is preferable. As a method for producing the polyacetal resin composition, a polyacetal resin, a filler, and, if necessary, an additive are supplied from a top feed port (main feed port) of an extruder as necessary, and melt kneaded. There is a method in which polyacetal is supplied from the top feed port of the extruder, filler and additive are supplied from the side feed port, and they are melt-kneaded. The latter method is preferred.

  A method for molding the polyacetal resin composition and obtaining the helical gear 100 of the present embodiment, which is the molded body, is not particularly limited, and the helical gear 100 may be a known molding method such as extrusion molding, Injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, molding of other materials, gas assist injection molding, firing injection molding, low pressure molding, ultra-thin injection molding (ultra-high-speed injection molding) or in-mold composite molding (Insert molding, outsert molding).

  The helical gear 100 of the present embodiment has a small deformation amount before and after the rotation test, and a small increase in sound accompanying the gear rotation test. The reason for this is that by adjusting the tensile modulus of the polyacetal resin composition that is the raw material of the helical gear 100 to 3500 to 7000 MPa, the entire gear and the deformation amount for each tooth with respect to the load applied to the gear are reduced. It is presumed that the tooth undergoes less fatigue due to rotation, and as a result, it becomes easier to maintain the tooth profile before the rotation test. However, the factor is not limited to this. In addition, the helical gear 100 according to the present embodiment is inherently small in sound generation due to the meshing of the gear due to its shape.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said this embodiment. The present invention can be variously modified without departing from the gist thereof. For example, the size and shape of the helical gear of the present invention are not limited to those shown in FIGS. 1 and 2, and the helical gear 100 of the present embodiment is in the right twist direction. Of course, the left-handed direction may be used.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention more concretely, this invention is not limited at all by these.
The evaluation and measurement methods in the following examples and comparative examples are as follows.

<Tensile modulus>
Using an injection molding machine (trade name “SH-75”) manufactured by Sumitomo Heavy Industries, Ltd., cylinder temperature 205 ° C., injection pressure 60 MPa, injection time 15 seconds, cooling time 25 seconds, mold temperature 90 ° C. Under the conditions, a test piece for evaluation was obtained from the polyacetal resin composition in accordance with ISO9988-2, and the tensile modulus of the test piece was measured in accordance with ISO178.

<Production of helical gear>
Using an injection molding machine (trade name “SH-75”) manufactured by Sumitomo Heavy Industries, Ltd., conditions of cylinder temperature 200 ° C., injection pressure 60 MPa, injection time 15 seconds, cooling time 25 seconds, mold temperature 80 ° C. A helical gear having a right twist direction, a pitch circle diameter of 80 mm, a module 1, and a rib thickness of 1.5 mm was manufactured. In each of the examples and the comparative examples, the helical angle of the helical gear, the tooth width, the web thickness, and the number of ribs are as shown in Table 1, and the points other than the above are shown in FIGS. The shape is the same as that of the gear.

<Deformation before and after the gear rotation test>
For the helical gear obtained as described above, a gear meshing test was performed under the following conditions using a gear meshing rotation measuring machine (manufactured by Toshiba Corporation). Regarding the gear accuracy before and after the test, a gear accuracy measuring device (manufactured by Osaka Seimitsu Co., Ltd.) was used to measure tooth profile errors and tooth trace errors in 90 teeth at 4 teeth in accordance with JIS B1702-1: 1998. Then, the amount of change was obtained. It was determined that the larger the numerical value (total difference) of the change amount of the tooth profile error and the change amount of the tooth trace error, the greater the deformation amount of the helical gear.
Torque: 2 Nm, rotation speed: 500 rpm, measurement temperature: 23 ° C., time: 24 hours, mating gear: module 1, pitch circle diameter 80 mm, counterclockwise torsion opposite to that of the example, and a metal screw with the same helix angle gear

<Evaluation of sound generated during gear rotation test>
For the helical gear obtained as described above, a gear meshing test was performed under the following conditions using a gear meshing rotation measuring machine (manufactured by Toshiba Corporation). The sound pressure level [dBA] generated by the engagement immediately after the start of the test (indicated as “front” in Table 2) and immediately before the end (indicated as “after” in Table 2) is 80 cm away from the helical gear. A sound level meter (manufactured by Lion) was installed at the above position. The difference in sound pressure level between immediately after the start of the test and immediately before the end was determined. It was determined that the increase in sound was suppressed as the difference in sound pressure level was smaller.
Torque: 2 Nm, rotation speed: 500 rpm, measurement temperature: 23 ° C., time: 24 hours, mating gear: module 1, pitch circle diameter 80 mm, metal helical gear with the same helix angle as the embodiment

<Measurement of average particle diameter and average aspect ratio of filler>
First, a filler sample for microscopic observation was prepared using a fine coater manufactured by JEOL Ltd. under a coating condition of 30 mA for 60 seconds. Subsequently, the shape of the filler in the sample was observed under the conditions of an acceleration voltage of 9.00 kV and an applied current of 10.0 μA using a scanning electron microscope manufactured by JEOL Ltd. Was coated on the substrate. Observation was carried out under the following conditions using the following apparatus, and the average particle diameter and average aspect ratio (ratio of average major axis to average minor axis) were determined.

[raw materials]
<Polyacetal resin (a-1)>
A biaxial self-cleaning type polymerization machine (L / D = 8) with a jacket capable of passing a heating medium was adjusted to 80 ° C., 4 kg / hour of trioxane, and 1,3-dioxolane as a comonomer was 42. 8 g / hour (1.3 mol% with respect to 100 mol% of trioxane) and 2.35 × 10 ⁻³ mol of methylal as a chain transfer agent were continuously added with respect to 1 mol of trioxane. Further, boron trifluoride di-n-butyl etherate as a polymerization catalyst was continuously added to the polymerization machine in an amount of 1.5 × 10 ⁻⁵ mol with respect to 1 mol of trioxane to carry out polymerization. The polyacetal copolymer discharged from the polymerization machine was put into a 0.1% aqueous solution of triethylamine to deactivate the polymerization catalyst. After filtering the deactivated polyacetal copolymer of the polymerization catalyst, 100 parts by mass of the polyacetal copolymer contains choline formate (triethyl-2-hydroxyethylammonium formate) as a quaternary ammonium compound. 1 part by mass of the aqueous solution was added and mixed uniformly, and then dried at 120 ° C. The added amount of choline formate is adjusted by adjusting the concentration of choline formate in the aqueous solution containing the added choline formate, and converted to the amount of nitrogen represented by the above formula (2). To 20 ppm by mass. The dried polyacetal copolymer is supplied to a vented twin screw extruder, and 0.5 parts by mass of water is added to 100 parts by mass of the melted polyacetal copolymer in the extruder, and the extruder set temperature is 200 ° C. The unstable end portion was decomposed and removed under the condition of a residence time of 7 minutes in the extruder. The polyacetal copolymer with the unstable terminal portion decomposed was devolatilized under a condition of a vent vacuum of 20 Torr, extruded as a strand from the die portion of the extruder, and pelletized. The polyacetal resin (aa-1) thus obtained had a melting point of 169.5 ° C. and an MFR of 30 g / 10 minutes.

Subsequently, the polyacetal resin (a) was changed in the same manner as above except that the amount of methylal as a chain transfer agent was changed from 2.35 × 10 ⁻³ mol to 1.52 × 10 ⁻³ mol with respect to 1 mol of trioxane. -3) was obtained. The polyacetal resin (a-3) thus obtained had a melting point of 169.1 ° C. and an MFR of 8 g / 10 minutes.
And 35 mass parts of polyacetal resin (aa-1) and 65 mass parts of polyacetal resin (a-3) were mixed, and polyacetal resin (a-1) was obtained.

<Polyacetal resin (a-2)>
The same procedure as in the production of polyacetal resin (aa-1) except that the amount of 1,3 dioxolane added was changed from 42.8 g / hour to 128.3 g / hour (3.9 mol% relative to 100 mol% of trioxane). The polyacetal resin (a-2) was obtained. The polyacetal resin (a-2) thus obtained had a melting point of 164.5 ° C. and an MFR of 30 g / 10 minutes.

<Polyacetal resin (a-3)>
The same procedure as in the production of the polyacetal resin (aa-1) except that the amount of methylal as a chain transfer agent was changed from 2.35 × 10 ⁻³ mol to 1.52 × 10 ⁻³ mol with respect to 1 mol of trioxane. Thus, a polyacetal resin (a-3) was obtained. The polyacetal resin (a-3) thus obtained had a melting point of 169.1 ° C. and an MFR of 8 g / 10 minutes.

<Filler>
(B-1) Calcium carbonate (light calcium carbonate), trade name “Brilliant-15” manufactured by Shiraishi Kogyo Co., Ltd., average particle size 0.20 μm, average aspect ratio 1.0
(B-2) Talc, manufactured by Nippon Talc Co., Ltd. (surface untreated), average particle size 3 μm, average aspect ratio 20
(B-3) wollastonite, average particle size 4 μm, average aspect ratio 30
(B-4) Glass fiber, manufactured by Nippon Electric Glass Co., Ltd., average fiber diameter (particle diameter) 13 μm, average aspect ratio 200

[Examples 1-9, Comparative Examples 1-6]
100 parts by mass of polyacetal resin (a-1) and 0.3 parts by mass of triethylene glycol-bis- [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) -propionate] as an antioxidant Then, 0.15 parts by mass of calcium distearate as a formic acid scavenger was uniformly mixed using a Henschel mixer. The obtained mixture and the filler (b-1) having a predetermined mass part shown in Table 1 were separately supplied from the main feed port of a 30 mm vented twin screw extruder set at 200 ° C. and L / D = 30. The pellets of the polyacetal resin composition were manufactured by melt kneading at a screw rotation speed of 100 rpm. A helical gear was obtained from the obtained pellet as shown in <Preparation of helical gear>. Table 1 shows the helical gear twist angle, tooth width, web thickness, and number of ribs. The obtained helical gears were evaluated for the tensile elastic modulus, the amount of deformation before and after the gear rotation test (static accuracy), and the sound generated during the gear rotation test, by the measurement methods described above. The results are shown in Table 2.

[Examples 10 and 11, Comparative Example 7]
Except having changed the kind and content of a filler as shown in Table 1, it carried out similarly to Example 1, and manufactured the pellet of the polyacetal resin composition. A helical gear was obtained from the obtained pellets in the same manner as in Example 1 except that the twist angle, tooth width, web thickness, and number of ribs were changed as shown in Table 1. The obtained helical gears were evaluated for the tensile modulus, the amount of deformation before and after the gear rotation test (static accuracy), and the sound generated during the gear rotation test by the above-described measurement methods. The results are shown in Table 2.

[Examples 12 and 13]
A pellet of the polyacetal resin composition was produced in the same manner as in Example 1 except that the polyacetal resin (a-1) was replaced with the polyacetal resin shown in Table 1. A helical gear was obtained from the obtained pellets in the same manner as in Example 1. The obtained helical gears were evaluated for the tensile elastic modulus, the amount of deformation before and after the gear rotation test (static accuracy), and the sound generated during the gear rotation test, by the measurement methods described above. The results are shown in Table 2.

  The helical gear of the present invention has a mechanical property balance inherent in the polyacetal resin and suppresses the amount of deformation before and after the gear rotation test and the increase in sound accompanying the gear rotation test. It can be suitably used in the field of gears for mechanical parts in various fields such as electrical and electronic industries.

  DESCRIPTION OF SYMBOLS 100 ... Helical gear, 110 ... Through-hole, 120 ... Tooth part, 130 ... Rib, 140 ... Web.

That is, the present invention is as follows.
[1] A plurality of ribs having a through hole formed in the center and a tooth portion formed on the outer periphery, and radially provided in a direction from the through hole to the outer periphery, and provided between the plurality of ribs is a flat web and, is provided with a helical gear, a molded body of reportage Li acetal resin composition to contain one or more of the polyacetal resin selected from the group consisting of polyacetal homopolymer and polyacetal copolymer A helical gear having a twist angle of 5 to 30 °, a tooth width of 1 to 20 mm, a thickness of the web of 1.5 to 6 mm, and a number of ribs of 8 to 24.
[2] The helical gear of [1], wherein the polyacetal homopolymer includes a polyacetal homopolymer obtained by homopolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde.
[3] The helical gear of [1], wherein the polyacetal copolymer includes a polyacetal homopolymer obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde and a cyclic ether or cyclic formal.
[4] The polyacetal copolymer is a polyacetal homopolymer having a block component obtained by polymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde in the presence of a compound having a functional group at both ends or one end, or both ends. Or a polyacetal copolymer having a block component obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde with a cyclic ether or cyclic formal in the presence of a compound having a functional group at one end. A helical gear.
[ 5 ] The helical gear according to any one of [1] to [4], wherein the twist angle is 10 to 30 °.
[ 6 ] The helical gear according to any one of [1] to [5], wherein the tooth width is 7 to 20 mm.
[ 7 ] The helical gear according to any one of [1] to [ 6 ], wherein the thickness of the web is 1.8 to 6 mm .
[8 ] The polyacetal resin composition contains a filler, the average particle diameter of the filler is more than 0.01 μm and less than 5 μm, and the ratio of the average major axis to the average minor axis of the filler particles is 30 or less. , [1] to [ 7 ], a helical gear.
[ 9 ] The helical gear of [ 8 ], wherein the filler is calcium carbonate.
[ 10 ] The helical gear of [ 8 ] or [ 9 ], containing 5 to 120 parts by mass of the filler with respect to 100 parts by mass of the polyacetal resin.
[ 11 ] The helical gear of [ 8 ] or [ 9 ], containing 5 to 100 parts by mass of the filler with respect to 100 parts by mass of the polyacetal resin.

Claims (9)

A plurality of ribs that have a through hole formed in the center and teeth formed on the outer periphery, and are provided radially from the through hole to the outer periphery, and a flat plate provided between the plurality of ribs A helical gear comprising a web-shaped web,
A molded article of a polyacetal resin composition containing a polyacetal resin and having a tensile modulus of 3500 to 7000 MPa, a twist angle of 5 to 30 °, a tooth width of 1 to 20 mm, and a thickness of the web of 1.5 to 6 mm, A helical gear having 6 to 24 ribs.   The helical gear according to claim 1, wherein the twist angle is 10 to 30 °.   The helical gear according to claim 1 or 2, wherein the tooth width is 7 to 20 mm.   The helical gear according to any one of claims 1 to 3, wherein the thickness of the web is 1.8 to 6 mm.   The helical gear according to any one of claims 1 to 4, wherein the number of the ribs is 8 to 24.   The polyacetal resin composition contains a filler, the average particle diameter of the filler is more than 0.01 μm and less than 5 μm, and the ratio of the average major axis to the average minor axis of the filler particles is 30 or less. The helical gear as described in any one of 1-5.   The helical gear according to claim 6, wherein the filler is calcium carbonate.   The helical gear according to claim 6 or 7, comprising 5 to 120 parts by mass of the filler with respect to 100 parts by mass of the polyacetal resin.   The helical gear according to claim 6 or 7, wherein the filler is contained in an amount of 5 to 100 parts by mass with respect to 100 parts by mass of the polyacetal resin.

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