JP7688538B2 - Resin composition for molding gears, gear, and method for producing resin composition for molding gears - Google Patents

Description

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

Gears are widely used in engines and other devices as sliding members. In recent years, in order to reduce the weight of devices, the replacement of conventionally used metal gears with resin gears has been considered. When using resin as the gear material, crystalline resins are sometimes used because they can improve the wear resistance and strength of the resin gears produced. Representative crystalline resins used for gear applications include polyacetal (POM), polyamide (PA), and polyether ether ketone (PEEK).

Conventionally, aliphatic polyamides, which have excellent abrasion resistance and strength, have been used as polyamides, but aliphatic polyamides have a problem of poor dimensional stability due to their high water absorption. In recent years, therefore, semi-aromatic polyamides, which have low water absorption, have been developed and their application has been considered. For example, according to Patent Document 1, a resin cam gear material is made of a material in which 5 to 20 parts by weight of modified polyolefin is added to 100 parts by weight of polyamide, and the dicarboxylic acid units constituting the polyamide contain 60 to 100 mol % of terephthalic acid units, and the diamine units constituting the polyamide contain 60 to 100 mol % of 1,9-nonanediamine units and/or 2-methyl-1,8-octadiamine units, making it possible to provide a resin cam gear that has low water absorption and excellent durability and abrasion resistance.

JP 2006-152999 A

However, the gear shown in Patent Document 1 does not have sufficient torque resistance, making it difficult to use under conditions where a higher torque load is applied.

The present invention was made to solve the above problems, and aims to provide a plastic gear with excellent torque resistance.

That is, the present invention has the following aspects:

［式（１）中、
Ａｒ^１は、フェニレン基又はナフチレン基を表し、複数個のＡｒ^１は互いに同一でも異なっていてもよく、ｐは１０である。］
［４］ 前記変性ポリオレフィンが、酸変性ポリオレフィンである、前記［１］～［３］のいずれか一つに記載のギヤ成形用樹脂組成物。
［５］ 前記変性ポリオレフィンの、ＤＳＣ（示差走査熱量測定）により１０℃／分の冷却速度で測定された吸熱ピークが３０℃以上である、前記［１］～［４］のいずれか一つに記載のギヤ成形用樹脂組成物。
［６］ 前記［１］～［５］のいずれか一つに記載のギヤ成形用樹脂組成物から成形されたギヤ。
［７］ 前記ポリアミドと、前記変性ポリオレフィンとを混合することを含む、前記［１］～［５］のいずれか一つに記載のギヤ成形用樹脂組成物の製造方法。 [1] A resin composition for molding gears, comprising a resin in which a modified polyolefin is added to a polyamide,
The resin composition for use in molding gears has a fracture toughness value of 3.5 MPa·m ^1/2 or more after curing as determined by ASTM D5045.
[2] The resin composition for molding gears according to [1], comprising a resin in which the modified polyolefin is added in a ratio of 2 to 15 parts by mass per 100 parts by mass of the polyamide.
[3] The resin composition for molding gears according to [1] or [2] above, wherein the polyamide is a semi-aromatic polyamide having a structural unit represented by the following general formula (1):

[In formula (1),
Ar ¹ represents a phenylene group or a naphthylene group, a plurality of Ar ¹ 's may be the same or different, and p is 10.
[4] The resin composition for molding gears according to any one of [1] to [3], wherein the modified polyolefin is an acid-modified polyolefin.
[5] The resin composition for molding gears according to any one of [1] to [4], wherein the modified polyolefin has an endothermic peak of 30° C. or higher as measured by DSC (differential scanning calorimetry) at a cooling rate of 10° C./min.
[6] A gear molded from the resin composition for molding gears according to any one of [1] to [5] above.
[7] A method for producing the resin composition for molding gears according to any one of [1] to [5], comprising mixing the polyamide and the modified polyolefin.

According to the present invention, it is possible to provide a resin composition for molding gears, which can be used to produce resin gears having excellent torque resistance.
Furthermore, according to the present invention, it is possible to provide a gear having excellent torque resistance, which is molded using the resin composition for molding gears as a molding material.

1 is a graph plotting the fracture toughness values of the resin compositions of Comparative Example 1 and Examples 1 to 4 and the gear fracture torque values of each resin composition. 1 is a DSC curve showing endothermic peaks of MH7020 and MH5020 used as modifiers in the examples. FIG. 2 is a schematic diagram showing the shape of a test piece used in a fracture toughness test. 1 is a photographed image of a gear manufactured in an embodiment.

The following describes embodiments of the resin composition for molding gears, the gear, and the method for manufacturing the resin composition for molding gears of the present invention.

<Resin composition for gear molding>
A resin composition for gear molding according to an embodiment (hereinafter, may be simply referred to as a "resin composition") is a resin composition for gear molding containing a resin in which a modified polyolefin is added to a polyamide, and the resin composition for gear molding after curing has a fracture toughness value of 3.5 MPa·m ^1/2 or more as determined by ASTM D5045.

As shown in the examples described later, the inventors have found that there is a very high correlation between the fracture toughness value of a cured resin composition and the torque resistance of a gear obtained from the resin composition.
According to an embodiment of the resin composition, the fracture toughness value of the cured resin composition as determined by ASTM D5045 is 3.5 MPa·m ^1/2 or more, it is possible to manufacture a gear having improved torque resistance. The resin composition can be suitably used as a gear molding resin composition used for molding gears.

The fracture toughness value of the cured resin composition for molding gears, as determined by ASTM D5045, can be measured by the following fracture toughness test.

(Fracture toughness test)
Using the resin composition to be measured as the molding material, a molded product was obtained using an injection molding machine under injection conditions of a mold temperature of 120°C, injection pressure of 100 MPa, injection time of 2 seconds, and cooling time of 20 seconds. A cut was then made using a precision cutter and cutter to obtain the following test pieces as specified in ASTM D5045.
Test piece: ISO test piece type A [see Figure 3, 80 mm x 10 mm x 4 mm (B = 4 mm, W = 10 mm, W/B = 2.5)] with a notch within the specified range (notch depth a = 0.45W to 0.55W).
The obtained test pieces are subjected to the following test method in the following test environment in accordance with ASTM D5045, and the fracture toughness value is calculated based on the following formula (see FIG. 3 for each item. Pmax is the maximum load of the bending SS (Stress-Strain) curve).
Equipment used: Tensilon Bending speed: 10 mm/sec
Test method: Three-point bending (SENB; Single edge notch bending)
Test environment: Temperature 23°C, humidity 50% RH

The fracture toughness value of the resin composition for molding gears after curing in the fracture toughness test is 3.5 MPa·m ^1/2 or more, preferably 4.0 MPa·m ^1/2 or more, more preferably 5.0 MPa·m ^1/2 or more, and even more preferably 5.5 MPa·m ^1/2 or more.
It is preferable that the fracture toughness value is equal to or greater than the above lower limit, since the torque resistance of the gear is improved.

The upper limit of the fracture toughness value of the cured resin composition for molding a gear in the fracture toughness test is not particularly limited, but may be, for example, 10 MPa·m ^1/2 or less, 9 MPa·m ^1/2 or less, or 8 MPa·m ^1/2 or less.

The lower limit and the upper limit of the fracture toughness value of the resin composition for molding a gear after curing can be freely combined. An example of the numerical range of the fracture toughness value in the fracture toughness test of the resin composition for molding a gear after curing may be 3.5 MPa·m ^1/2 or more and 10 MPa·m ^1/2 or less, 4.0 MPa·m ^1/2 or more and 9 MPa·m ^1/2 or less, 5.0 MPa·m ^1/2 or more and 8 MPa·m ^1/2 or less, or 5.5 MPa·m ^1/2 or more and 8 MPa·m ^1/2 or less.

The gear molding resin composition of the embodiment includes both the pre-cured and post-cured states. The gear of the embodiment can be formed using the cured gear molding resin composition (the cured product of the gear molding resin composition).

The gear of the embodiment is molded from the gear molding resin composition of the embodiment that satisfies the above fracture toughness value, and therefore has excellent torque resistance.

The torque resistance of a gear can be measured by the torque value (breaking torque) at which the gear breaks when a torque is applied to the gear. The gear torque resistance test for measuring the breaking torque of the gear of this embodiment and its preferred value will be described later.

The fracture toughness value of the resin composition for molding gears after curing can be adjusted by, for example, selecting the type of polyamide and controlling the compounding ratio of polyamide to modified polyolefin, making it possible to obtain a resin composition for molding gears having a suitable fracture toughness value after curing.

In addition, by using a semi-aromatic polyamide having a structural unit represented by the following general formula (1), the fracture toughness value of the resin composition for molding gears after curing can be easily improved.

Details about the preferred blend ratios of polyamide and modified polyolefin are provided below.

A resin in which a modified polyolefin is added to a polyamide can contain a polyamide and a modified polyolefin, and may also contain a reaction product between a polyamide and a modified polyolefin.

<Polyamide>
The polyamide is preferably a semi-aromatic polyamide from the viewpoint of reducing water absorption. The semi-aromatic polyamide can be obtained as a polymer of an aliphatic diamine and an aromatic dicarboxylic acid.

As the polyamide according to the embodiment, a semi-aromatic polyamide having a structural unit represented by the following general formula (1) is preferred.

[In formula (1),
Ar ¹ represents a phenylene group or a naphthylene group, and a plurality of Ar ¹ 's may be the same or different.
p is an integer of 10 to 11, and multiple p's may be the same or different.

More preferably, in the general formula (1), Ar ¹ represents a phenylene group or a naphthylene group, a plurality of Ar ^{1 s} may be the same or different, and p may be 10.

The phenylene group of Ar ¹ may be a 1,4-phenylene group or a 1,3-phenylene group.The naphthylene group of Ar ¹ may be a 2,6-naphthylene group or a 2,7-naphthylene group.

More preferably, in the general formula (1), Ar ¹ represents a 1,4-phenylene group and p may be 10.

In the polyamide, the content of the structural unit represented by the general formula (1) is preferably 40% or more, more preferably 80% or more, and even more preferably 90% or more, relative to the total number of all structural units in the polyamide (100%).

In the polyamide, the content of the structural unit represented by the general formula (1), in which Ar ¹ represents a phenylene group or a naphthylene group, a plurality of Ar ^1s may be the same or different, and p is 10, is preferably 40% or more, more preferably 80% or more, and even more preferably 90% or more, based on the total number of all structural units in the polyamide (100%).

In the polyamide, the content of the structural unit represented by the general formula (1), in which Ar ¹ represents a 1,4-phenylene group and p is 10, is preferably 40% or more, more preferably 80% or more, and even more preferably 90% or more, relative to the total number (100%) of all structural units in the polyamide.

In the gear molding resin composition of the embodiment, the content ratio of the polyamide to the total mass (100 mass%) of the gear molding resin composition may be 50 mass% or more, 50 to 99.5 mass%, 70 to 98.5 mass%, 80 to 97 mass%, or 80 to 95 mass%. However, in the gear molding resin composition, the polyamide, modified polyolefin, and other optional components are contained in such a way that the total content (mass%) of them does not exceed 100 mass%.

<Modified polyolefin>
The polyolefin in the modified polyolefin is not particularly limited, but is preferably a thermoplastic elastomer. Examples of the modified polyolefin include copolymers of ethylene and/or propylene and α-olefin monomers, and ethylene-α-olefin copolymers are preferred. Examples of the α-olefin include α-olefins having preferably 4 to 20 carbon atoms, more preferably 4 to 10 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 1-octene, and 1-decene.

The modified polyolefin is preferably an acid-modified polyolefin.
The modified polyolefin may have, in the molecule, functional groups imparted by the acid modification, such as a carboxyl group, a carboxylic anhydride group, an ester group, a metal carboxylate group, a carboxylic acid imide group, a carboxylic acid amide group, etc. When the modified polyolefin has, for example, the functional groups exemplified above, it is possible to increase compatibility with the polyamide and improve mechanical properties such as fracture toughness.

The acid modification is preferably a modification with a carboxylic acid or an anhydride thereof. The carboxylic acid may be a saturated carboxylic acid or an unsaturated carboxylic acid, and is preferably an unsaturated dicarboxylic acid. Examples of the carboxylic acid include maleic acid, fumaric acid, succinic acid, phthalic acid, acrylic acid, and methacrylic acid, and it is more preferable that the modification is with maleic acid or an anhydride thereof.

By using a modified polyolefin, the fracture toughness value of the resin composition for molding gears after curing can be improved. Preferably, by using an acid-modified polyolefin, the fracture toughness value of the resin composition for molding gears after curing can be further improved.

In the gear molding resin composition of the embodiment, the content of the modified polyolefin relative to the total mass (100 mass%) of the gear molding resin composition may be 50 mass% or less, may be 0.5 to 50 mass%, may be 1.5 to 30 mass%, may be 2 to 20 mass%, or may be 3 to 15 mass%.

The above-mentioned numerical ranges of the polyamide content ratio and the numerical ranges of the modified polyolefin content ratio can be freely combined. As an example of a gear molding resin composition of the embodiment, a composition in which the polyamide content ratio is 50 to 99.5 mass% and the modified polyolefin content ratio is 0.5 to 50 mass% relative to the total mass (100 mass%) of the gear molding resin composition is exemplified.

In the gear molding resin composition of the embodiment, the modified polyolefin is preferably added in a ratio of 1 to 30 parts by mass, more preferably 2 to 15 parts by mass, even more preferably 3 to 12 parts by mass, still more preferably 3 to 7 parts by mass, and particularly preferably 4 to 7 parts by mass, relative to 100 parts by mass of the polyamide.
The resin composition for molding gears, in which the modified polyolefin is added to the polyamide in the above ratio, tends to have improved fracture toughness after curing, and the gear molded from the resin composition for molding gears also tends to have improved torque resistance and durability.

The structure of the modified polyolefin may be linear or branched.

The endothermic peak of the modified polyolefin measured by DSC (differential scanning calorimetry) using a differential scanning calorimeter (e.g., DSC-60 Plus, manufactured by Shimadzu Corporation) at a cooling rate of 10°C/min is preferably 30°C or higher, more preferably 30 to 45°C, and even more preferably 35 to 42°C.
The term "endothermic peak measured by DSC (differential scanning calorimetry) at a cooling rate of 10° C./min" means the temperature at the apex of the endothermic peak.

The endothermic peak can be measured as the freezing point of the modified polyolefin. It is presumed that a modified polyolefin having a high endothermic peak value has, for example, a low degree of branching in the branched chain and tends to be closer to a linear chain. By using a modified polyolefin having an endothermic peak value equal to or greater than the lower limit above, it is possible to improve the durability of a gear molded from a resin composition for molding gears. The durability of the gear can be measured, for example, by the following durability test.

(Gear durability test)
A metal master gear serving as a drive gear and a resin gear to be tested are meshed and placed in a power absorbing gear operation test machine as specified in JIS B 1759.
The test machine is operated under the following conditions: load torque of 8 Nm, rotation speed of 1000 rpm, no lubrication, temperature of 23°C, and humidity of 50% RH, and the total number of rotations until the resin gear breaks is measured. In this durability test, the "breakage" of the resin gear is defined as a state in which the resin gear during operation is photographed with a high-speed camera and a crack of a size (approximately 0.5 mm) or more that can be visually confirmed is generated in at least a part of the resin gear in the image. If the total number of rotations until the resin gear breaks is ¹⁰⁵ or more, the durability can be evaluated as good.
The shape and material of the metal master gear and the shape of the resin gear to be tested can be those described in the Examples.

(Other ingredients)
The resin composition for molding gears of the present embodiment may contain other components that do not fall under the category of polyamides, modified polyolefins, or reaction products thereof, within the scope that does not impair the effects of the present invention.

Examples of the other components include fillers, additives, and resins that do not fall into either the polyamide or modified polyolefin categories (hereinafter sometimes referred to as "other resins").
These other components may be used alone or in combination of two or more.

The filler may be a fibrous filler or a granular filler. The filler may be an inorganic filler or an organic filler.

Examples of additives include stabilizers, release agents, antioxidants, heat stabilizers, UV absorbers, antistatic agents, surfactants, flame retardants and colorants.

Other examples of resins include thermoplastic resins such as polyester, polyphenylene sulfide, polyether ketone, polycarbonate, polyphenylene ether, polyetherimide, and fluororesin; and thermosetting resins such as phenolic resin, epoxy resin, polyimide resin, and cyanate resin.

As another aspect, the following embodiments of the resin composition for molding gears are exemplified as <1> to <3>.
<1> A resin composition for molding a gear, comprising a resin in which a modified polyolefin is added to a polyamide, wherein the fracture toughness value of the resin composition for molding a gear after curing is 3.5 MPa m ^1/2 or more as determined by ASTM D5045;
The polyamide is a semi-aromatic polyamide having a structural unit represented by the general formula (1), in which Ar ¹ represents a 1,4-phenylene group and p is 10, and the modified polyolefin is a modified polyolefin modified with maleic acid or anhydride thereof.

<2> The resin composition for molding gears described in <1> contains a resin to which the modified polyolefin is added in a ratio of 2 to 15 parts by mass per 100 parts by mass of the polyamide.

<3> The gear molding resin composition according to <1> or <2>, wherein the modified polyolefin has an endothermic peak of 30°C or higher as measured by DSC (differential scanning calorimetry) at a cooling rate of 10°C/min.

Gear
The gear of the embodiment is molded from the resin composition for gear molding of the above embodiment. An example of the gear of the embodiment is a resin gear molded from the resin composition for gear molding of the above embodiment.

In another aspect, the gear of the embodiment includes a resin in which a modified polyolefin is added to a polyamide, and the resin has a fracture toughness value of 3.5 MPa·m ^1/2 or more as determined by ASTM D5045. Examples of the polyamide and the modified polyolefin include those exemplified in the above-mentioned gear molding resin composition.

In one embodiment, there is provided a method for producing a gear, the method including molding the gear from the resin composition for gear molding of the above embodiment. The gear includes a resin in which a modified polyolefin is added to a polyamide, and the resin has a fracture toughness value of 3.5 MPa·m ^1/2 or more as determined by ASTM D5045.

The method for molding the resin composition for gear molding into a gear is not particularly limited, but melt molding is preferred, and examples of such methods include extrusion molding, T-die molding, blow molding, and injection molding. By selecting a molding method according to the shape of the gear, etc., the resin composition for gear molding can be molded into the desired gear shape.

The type of gear is not particularly limited, and examples include spur gears, helical gears, racks, internal gears, worm gears, worm wheel gears, bevel gears, hypoid gears, etc.

The gear of the embodiment is molded from the gear molding resin composition of the embodiment, and therefore has excellent torque resistance. The gear's breaking torque, which is an index of torque resistance, can be measured by the following torque resistance test. The higher the breaking torque value, the better the torque resistance of the gear. Gear destruction includes cases where at least a part of the gear is chipped, deformed, broken, or cracked.

(Gear torque resistance test)
A metal master gear serving as a drive gear and a resin gear to be tested are meshed and placed in a power absorbing gear operation test machine as specified in JIS B 1759.
The test machine is operated at a rotation speed of 1000 rpm, under lubricant-free conditions, at a temperature of 23°C, and at a humidity of 50% RH, and the load torque on the plastic gear is started from 2 N·m and increased by 1 N·m every 3 minutes. The plastic gear during operation is photographed with a high-speed camera, and the load torque at which a crack or chipped tooth of a size larger than that visible to the naked eye (about 0.5 mm) occurs in at least a part of the plastic gear in the image is defined as the breaking torque.
The shape and material of the metal master gear and the shape of the resin gear to be tested can be those described in the Examples.

The value of the breaking torque measured by the torque resistance test of the gear of the embodiment may be 9 N·m or more, may be 9 to 30 N·m, may be 11 to 20 N·m, or may be 13 to 17 N·m.

The gear of the embodiment has good torque resistance, so it may be used under conditions where the torque applied to the gear is 9 N·m or more, or may be used under conditions of 9 to 30 N·m, or may be used under conditions of 11 to 20 N·m, or may be used under conditions of 13 to 17 N·m.

As another aspect, the following embodiment of the gear is illustrated.
<4> A gear molded from the resin composition for gear molding according to any one of <1> to <3>, wherein the gear has a breaking torque value of 9 N·m or more as measured by the torque resistance test.

<Method for producing resin composition for gear molding>
The method for producing a resin composition for molding a gear according to the embodiment includes mixing the polyamide and the modified polyolefin. According to the method for producing a resin composition for molding a gear according to the embodiment, the resin composition for molding a gear according to the embodiment can be produced. Examples of the polyamide and the modified polyolefin include those exemplified in the above-mentioned resin composition for molding a gear.

The mixing method is known, and for example, the polyamide, the modified polyolefin, and other components, if necessary, can be melt-kneaded to obtain the gear molding resin composition of the embodiment.

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

<Raw materials>
Base resin: Polyamide PA10T (a semi-aromatic polyamide having a structural unit represented by the general formula (1) in which Ar ¹ represents a 1,4-phenylene group and p is 10)
PA9T (Kuraray, N1000: semi-aromatic polyamide having a structural unit represented by the general formula (1) in which Ar ¹ represents a 1,4-phenylene group and p is 9)

Modifier: Modified polyolefin MH7020 (maleic anhydride modified ethylene-butene copolymer manufactured by Mitsui Chemicals)
MH5020 (Maleic anhydride modified ethylene-butene copolymer, manufactured by Mitsui Chemicals)

<Measurement>
(Measurement of the freezing point of the modifier)
Using a differential scanning calorimeter (DSC-60 Plus, manufactured by Shimadzu Corporation), the sample was cooled at a temperature decreasing rate of 10° C./min, the position of the endothermic peak was confirmed, and the temperature at the apex of the endothermic peak was measured.

(Fracture toughness test)
Using the resin compositions obtained in the Examples and Comparative Examples as molding materials, molded articles were obtained using an injection molding machine under injection conditions of a mold temperature of 120°C, an injection pressure of 100 MPa, an injection time of 2 seconds, and a cooling time of 20 seconds. Cutting was then performed using a precision cutter and cutter to obtain the following test pieces as specified in ASTM D5045.
Test piece: ISO test piece type A [see Figure 3, 80 mm x 10 mm x 4 mm (B = 4 mm, W = 10 mm, W/B = 2.5)] with a notch within the specified range (notch depth a = 0.45W to 0.55W).
The obtained test pieces were subjected to the following test method in the following test environment in accordance with ASTM D5045, and the fracture toughness value was calculated based on the following formula (see FIG. 3 for each item. Pmax is the maximum load of the bending SS (Stress-Strain) curve).
Equipment used: Tensilon Bending speed: 10 mm/sec
Test method: Three-point bending (SENB; Single edge notch bending)
Test environment: Temperature 23°C, humidity 50% RH

(Gear torque resistance test)
A metal master gear [material: S45C, carburized, quenched and tempered (surface hardening treatment), gear shape: spur gear, module 1, pressure angle 20°, number of teeth 67, tooth width 15 mm, addendum coefficient 0, number of straddling teeth 23.079 (number of straddling teeth 8)] was meshed with a resin gear obtained in the examples or comparative examples [gear shape: spur gear, module 1, number of teeth 48, tooth width 8 mm, addendum coefficient 0, straddling tooth thickness 16.909 (number of straddling teeth 6)] as a driving gear and installed in a power absorbing gear operation test machine specified in JIS B 1759.
The test machine was operated at a rotation speed of 1000 rpm, under lubricant-free conditions, at a temperature of 23° C., and at a humidity of 50% RH, and the load torque on the resin gear was started from 2 N·m and increased by 1 N·m every 3 minutes. The resin gear during operation was photographed with a high-speed camera, and the load torque at the point when a crack or chipped tooth of a size larger than that visible to the naked eye (about 0.5 mm) occurred in at least a part of the resin gear in the image was defined as the breaking torque.

(Gear durability test)
A metal master gear [material: S45C, carburized, quenched and tempered (surface hardening treatment), gear shape: spur gear, module 1, pressure angle 20°, number of teeth 67, tooth width 15 mm, addendum coefficient 0, number of straddling teeth 23.079 (number of straddling teeth 8)] was meshed with a resin gear obtained in the examples or comparative examples [gear shape: spur gear, module 1, number of teeth 48, tooth width 8 mm, addendum coefficient 0, straddling tooth thickness 16.909 (number of straddling teeth 6)] as a driving gear and installed in a power absorbing gear operation test machine specified in JIS B 1759.
The test machine was operated under the conditions of a load torque of 8 N m on the plastic gear, a rotation speed of 1000 rpm, no lubrication, a temperature of 23° C., and a humidity of 50% RH, and the total number of rotations until the plastic gear broke was measured and evaluated according to the following criteria. Note that "breakage" of the plastic gear in this durability test was defined as a state in which the plastic gear during operation was photographed with a high-speed camera, and a crack of a size visible to the naked eye (about 0.5 mm) or more was generated in at least a part of the plastic gear in the image.
AA: The total number of rotations until the resin gear broke was 2.5×10 ⁵ or more, and the durability was very good.
A: The total number of rotations until the resin gear broke was 1.0×10 ⁵ or more, and the durability was good.
B: The total number of rotations until the resin gear broke was less than 1.0 x ¹⁰⁵ times.

<Production of resin composition>
[Examples 1 to 6, Comparative Examples 1 to 4]
Polyamide and modified polyolefin were mixed in the parts by mass shown in Table 1, and melt-kneaded while degassing in a twin-screw extruder. The resulting kneaded product was discharged in the form of strands through a circular nozzle (discharge port), and then pelletized with a strand cutter to obtain resin compositions of the examples and comparative examples in the form of pellets.
For each of the resulting resin compositions, the above-mentioned fracture toughness test was carried out in accordance with ASTM D5045 to determine the fracture toughness value.

<Gear Manufacturing>
The pellets of each resin composition of the Examples and Comparative Examples were used as the molding material and injection molded under the injection conditions of a mold temperature of 120°C, an injection pressure of 120 MPa, an injection time of 6 seconds, and a cooling time of 25 seconds to produce the resin gears of the Examples and Comparative Examples, with a gear shape of spur gear, module 1, number of teeth 48, tooth width 8 mm, addendum coefficient 0, and straddling tooth thickness 16.909 (number of straddling teeth 6). The shape of the produced resin gear is shown in FIG.
For each of the gears obtained in the examples and comparative examples, torque resistance and durability tests were carried out.

The above evaluation results are shown in Table 1. Figure 1 shows a graph plotting the fracture toughness values of the resin compositions of Comparative Example 1 and Examples 1 to 4 and the fracture torque values of the gears of each resin composition.

As shown in FIG. 1 and Table 1, it can be seen that there is a very high correlation between the fracture toughness value of the cured resin composition and the fracture torque value (torque resistance) of the corresponding gear.
In addition, with regard to the toughness of the cured resin composition, items such as tensile elongation and tensile strength that are generally thought of, no correlation was confirmed with the gear's breaking torque value (torque resistance).

From this, it is evident that the resin compositions of the examples, which have a fracture toughness value after curing of 3.5 MPa·m ^1/2 or more as determined by ASTM D5045, make it possible to manufacture gears with improved torque resistance.
It was shown that by using the fracture toughness value as an index, it is possible to provide a gear resin composition suitable as a gear molding material. It was also shown that by using a resin composition with an improved fracture toughness value, it is possible to manufacture a gear with improved torque resistance.

In addition, the resin compositions of Examples 1 to 6, which used polyamide PA10T as the base resin, had improved fracture toughness values compared to the resin compositions of Comparative Examples 3 and 4, which used polyamide PA9T.

In addition, the resin compositions of Examples 1 to 6, in which modified polyolefin was added as a modifier, had improved fracture toughness values compared to the resin composition of Comparative Example 1, in which no modified polyolefin was added.

Figure 2 shows DSC curves showing the endothermic peaks of MH7020 and MH5020 used as modifiers. Figure 2 also shows the temperatures (freezing points) of the endothermic peaks of MH7020 and MH5020.

Focusing further on the relationship between the type of modifier and the durability of the gear, a comparison of Example 2 and Example 5 (containing 5% by mass of modifier) in Table 1, and a comparison of Example 3 and Example 6 (containing 10% by mass of modifier) show that Examples 2 and 3, in which MH7020 (endothermic peak: 39°C) was added as a modifier, had better gear durability than Examples 5 and 6, in which MH5020 (endothermic peak: 13°C) was added.
This indicates that the addition of a modified polyolefin having an endothermic peak of 30°C or higher as measured by DSC (differential scanning calorimetry) is more effective in improving gear durability than the addition of a modified polyolefin that does not satisfy the regulations.

The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to each embodiment, but is limited only by the scope of the claims.

Claims (6)

A resin composition for molding gears, comprising a resin in which a modified polyolefin is added to a polyamide,
The polyamide is a semi-aromatic polyamide having a structural unit represented by the following general formula (1):
the modified polyolefin is an acid-modified polyolefin,
The resin contains 3 to 15 parts by mass of the modified polyolefin added to 100 parts by mass of the polyamide,
The resin composition for use in molding gears has a fracture toughness value of 3.8 MPa·m ^1/2 or more after curing, as determined by ASTM D5045.

[In formula (1),
Ar ¹ represents a phenylene group or a naphthylene group, a plurality of Ar ¹ 's may be the same or different, and p is 10. 2. The resin composition for molding gears according to claim 1 , wherein the modified polyolefin has an endothermic peak of 30° C. or higher as measured by DSC (differential scanning calorimetry) at a cooling rate of 10° C./min. The resin composition for molding gears according to claim 1 or 2, wherein the modified polyolefin is a thermoplastic elastomer. The resin composition for molding gears according to any one of claims 1 to 3, wherein the acid-modified polyolefin is a polyolefin modified with a carboxylic acid or an anhydride thereof. A gear molded from the resin composition for molding gears according to any one of claims 1 to 4 . The method for producing the resin composition for molding gears according to any one of claims 1 to 4 , comprising mixing the polyamide and the modified polyolefin.

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