JPH05306371A - Resin composition for gear - Google Patents

Abstract

PURPOSE:To provide a resin composition for a gear with required molding accuracy, heat distortion resistance, mechanical strength and injection moldability and enable the molding of the gear having abrasion resistance without damaging the opposite gear made of a synthetic resin. CONSTITUTION:The resin composition for a gear is obtained by blending 100 pts.wt. cross-linked polyphenylene sulfide resin, having 1400-15000P melt viscosity and prepared by cross-linking an uncross-linked polyphenylene sulfide having 350-3000P as polymerized melt viscosity with 10-50 pts.wt. unsintered polytetrafluoroethylene resin having >=10000 number-average molecular weight, 10-30 pts.wt. aromatic polyamide pulp and 30-80 pts.wt. zinc oxide whisker.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for gears used as a molding material for resin gears.

[0002]

2. Description of the Related Art Generally, gears made of synthetic resin are used in various fields such as audio equipment, copying machines, automobile parts, etc. Excellent polyacetal and nylon are known. These polyacetals and nylons are not sufficient in heat resistance and mechanical strength, and polyphenylene sulfide resin (hereinafter abbreviated as PPS resin) is also known as an engineering plastic excellent in this respect.

Such a PPS resin has a low glass transition point of 88 ° C., but by adding a reinforcing material such as glass fiber or carbon fiber, it is possible to prevent the mechanical strength from decreasing.
The composition containing these reinforcing materials has a heat resistance of more than 250 ° C.

[0004]

However, since the above-mentioned glass fiber and carbon fiber have a high hardness, when a gear is formed from PPS resin containing such a fiber reinforcing material, the gear is a partner with which it meshes. There is a problem that the tooth surface of the gear is scraped off, resulting in remarkable wear.

On the other hand, there are aromatic polyamide fibers (hereinafter referred to as aramid fibers), potassium titanate whiskers or zinc oxide whiskers as relatively soft fiber reinforcing materials, which are used in place of the high hardness fiber reinforcing materials. It is also possible.

However, with a PPS resin containing such a fiber reinforcing material, the molded gear does not have sufficient wear resistance, and the mating gear (made of synthetic resin) is scraped, that is, it has an attacking property. There is a problem. Further, if a gear is formed of a PPS resin containing a powdered filler such as aramid powder instead of the above fiber reinforcement, it is excellent in terms of damage to the mating gear but poor in wear resistance. There is.

The present invention solves the above-mentioned problems and provides a resin composition for gears with required molding accuracy, heat distortion resistance, mechanical strength and injection moldability, and damages a mating gear made of synthetic resin. Without wear and wear resistance,
An object of the present invention is to make it possible to form a gear that can stably transmit torque.

[0008]

In order to solve the above problems, in the present invention, 10 to 50 parts by weight of polytetrafluoroethylene resin and 10 to 3 parts of aromatic polyamide pulp are used with respect to 100 parts by weight of polyphenylene sulfide resin.
The composition of 0 parts by weight and 30 to 80 parts by weight of zinc oxide whiskers is used.

The polyphenylene sulfide resin may be a crosslinkable polyphenylene sulfide resin having a melt viscosity of 1400 to 15000 poise obtained by crosslinking an uncrosslinked polyphenylene sulfide resin having a melt viscosity of 350 to 3000 poise just after polymerization. The polytetrafluoroethylene resin may be an unsintered polytetrafluoroethylene resin having a number average molecular weight of 10,000 or more. The details will be described below.

First, the PPS resin in the present invention is represented by the following formula [Chemical formula 1].

[0011]

[Chemical 1]

As a typical example of the above PPS resin, there is a polymer represented by the following formula [Chemical formula 2].

[0013]

[Chemical 2]

This polymer is obtained by condensing Na ₂ S and p-dichlorobenzene in an amide solvent such as n-methylpyrrolidone or dimethylacetamide or a sulfone solvent such as sulfolane. It is supposed to be the polymerization of resin. This polymerized low molecular weight PP
By subjecting the S resin to a step such as heat treatment, it is possible to freely produce resins having any degree of polymerization, from those having no cross-linking in the resin to those having partial cross-linking. That is, a resin having the optimum melt viscosity characteristic for melt blending can be arbitrarily selected and used.

The melt viscosity after polymerization is 3
It is preferably 50 to 3000 poise. For example, 3
Crosslinkable PP obtained by crosslinking PPS resin of less than 50 poise
Since S resin is inferior in mechanical strength, especially in flexibility, it is not suitable for use in a site where impact strength and toughness are required.
If it exceeds 000 poise, the creep resistance in a high temperature atmosphere is poor, and the heat resistance of the PPS resin is hindered from being used at high temperatures.

On the other hand, when a linear PPS resin is used,
Added polytetrafluoroethylene resin (hereinafter PT
(FE resin) is not fiberized and the filler aramid pulp is not crushed, so that the lubricity and wear resistance are reduced.

In order to crosslink the PPS resin after polymerization, it is treated by heat treatment or the like as in the above-mentioned crosslinking method.
Specifically, it is carried out by heating below the melting point in the presence of oxygen, or by adding a crosslinking agent or a branching agent. The preferable crosslinkable PPS resin thus obtained has a melt viscosity of 1400 to 15000 poise. This is because the crosslinkable PPS resin having a melt viscosity of less than 1400 poise has a low creep resistance in a high temperature range of 150 ° C. or higher,
Easier to plastically deform. Further, a crosslinkable PPS resin having a viscosity of more than 20,000 poise has a melt viscosity of 350 after polymerization.
Even when the porosity is up to 3000 poise, the moldability is remarkably inferior and the flexibility is also inferior, which is not preferable.

The PTFE resin used in the present invention may be used without any particular limitation on its molecular weight, but it is preferable that it has a number average molecular weight of 10,000 or more and is unbaked. This is because when a low-molecular weight PTFE resin is used, the melt viscosity becomes excessively low, and the difference in interfacial energy with the PPS resin becomes large, which may cause layer separation during melt blending or injection.

On the other hand, those having a molecular weight of 10,000 or more are preferable because they have a high melt viscosity and are unlikely to separate into layers during melt blending or injection. If unsintered PTFE resin is used, shear stress during injection promotes fiberization of the PTFE resin. Since the PTFE resin thus fiberized is uniformly dispersed in the matrix and strongly entangled with the aramid pulp described later,
Good friction and wear characteristics can be obtained.

The aromatic polyamide pulp (hereinafter referred to as aramid pulp) used in the present invention is not particularly limited as long as it is in a pulp form. For example, aramid fibers having a fiber length of 6 mm and a fiber diameter of 12 μm are crushed, It is feathered. This product is well wetted with the matrix PPS resin and shows an affinity, and the feather-like three-dimensional fine fibers of the pulp take up the PPS resin, and are further entangled with the tetrapot-shaped zinc oxide whiskers and the PTFE resin, Form a three-dimensional mesh structure. Further, since the fibers in the pulp are fine, there is almost no attack on the mating gear during sliding.

The aramid pulp on which such feather-like three-dimensional fine fibers are sufficiently formed has a large specific surface area, and specifically, one having a specific surface area of 3 m ² / g or more is preferable.
It is particularly preferably 5 m ² / g or more.

Since the zinc oxide whiskers used in the present invention are tetrapod-type needle-shaped crystals per unit of crystal, it is possible to prevent the loss of fine matrix. Further, in the needle-shaped whiskers, anisotropy occurs due to the flow of the resin at the time of injection, but since it is a three-dimensional whisker, the anisotropy is relaxed and the dimensional accuracy is good.
Further, since the zinc oxide whiskers have vibration damping characteristics, noise generated during driving can be suppressed.

The mixing ratios of the above raw materials are set within the predetermined ranges for the following reasons. That is, when the PTFE resin as the solid lubricant is less than 10 parts by weight with respect to 100 parts by weight of the PPS resin, the wear coefficient becomes large, and the torque transmission is hindered. On the other hand, when it exceeds 50 parts by weight, the strength is lowered and it cannot withstand a high load.

When the amount of aramid pulp, which is one of the reinforcing fillers, is less than 10 parts by weight with respect to 100 parts by weight of PPS resin, the abrasion resistance is significantly reduced. On the other hand, if the amount exceeds 50 parts by weight, fluidity is poor during melt blending or injection, and molding cannot be performed.

If the amount of the other reinforcing filler zinc oxide whiskers is less than 30 parts by weight with respect to 100 parts by weight of the PPS resin, the strength is particularly poor and the gears are apt to cause tooth spillage. If it exceeds 70 parts by weight, it causes abrasive wear on a plastic or soft metal partner.

Here, the method of mixing the above-mentioned raw materials is as follows.
It is not particularly limited, and a method which is generally widely used, for example, a resin as a main component and other various raw materials are individually or after appropriately dry mixed by a mixer such as a Henschel mixer, a ball mill, a tumbler mixer, A method of supplying to an injection molding machine or a melt extrusion molding machine having a good melt mixing property, or performing melt mixing with a hot roll, a kneader, a Banbury mixer, a melt extruder or the like in advance may be used. Further, the molding method of the resin composition for gears of the present invention is not limited, and injection molding or other general-purpose methods can be adopted.

With respect to the composition containing the PPS resin as a main component of the present invention, oxidation prevention is provided within a range that does not deteriorate desired properties such as lubricity, abrasion resistance, and non-aggressiveness. Various additives such as an agent, a heat stabilizer, an ultraviolet absorber, a colorant, a flame retardant, an antistatic agent, and a crystallization accelerator can be blended.

[0028]

The resin composition for gears according to the present invention has the inherent heat resistance, weather resistance and injection moldability of the PPS resin, and the good lubricity of the PTFE resin, and the feather-like three-dimensional shape of aramid pulp. Since such fine fiber lumps incorporate PPS resin with good affinity and further entangle with tetrapod-shaped zinc oxide whiskers to form a three-dimensional network structure, they have wear resistance and do not damage the mating gear. Further, since there is no variation in strength due to the orientation of the fiber filler, stable mechanical strength is provided.

[0029]

EXAMPLES The raw materials used in Examples and Comparative Examples are collectively shown below. In addition, P ₁ is a melt viscosity after polymerization, P ₂ is a melt viscosity after crosslinking, and M is a number average molecular weight.

(1) Linear PPS resin (Kureha Chemical Industry Co., Ltd .: KPS- # 214, P ₁ = 1400 poise) (2) Crosslinkable PPS resin (Topren Co .: T-4 (2),
P ₁ = 700 poise, P ₂ = 1840 poise) (3) Crosslinkable PPS resin (K-4, P ₁ manufactured by Topren Co., Ltd.)
= 100 poise, P ₂ = 2000 poise) (4) PTFE resin (manufactured by Daikin Industries, Ltd.: M-12, M =
7000000) (5) PTFE resin (manufactured by Daikin Industries, Ltd .: Lubron L-
2, M = 30000) (6) Zinc oxide whiskers (manufactured by Matsushita Electric Industrial Co., Ltd.) (7) Aramid pulp (manufactured by Nippon Aramid Co .: Twaron-A)
R-1097pulp) (8) Potassium titanate fiber (Otsuka Chemical Co., Ltd .: Tismo D)
101) (9) Carbon fiber (manufactured by Toray Industries: trading card MLD-100) (10) Aramid fiber (manufactured by Teijin Ltd .: Conex Cut Fiber 1 mm) The ratios of the above raw materials (1) to (7) shown in Table 1. Blended with
After dry-mixing with a Henschel mixer, it is supplied to a melt extruder (PCM45 manufactured by Ikegai Co., Ltd.), and a cylinder temperature is 290.
Melt blending was carried out at a temperature of ℃ and a screw rotation speed of 100 rpm. After that, the cylinder temperature is 325 ° C and the injection pressure is 1000.
A predetermined test piece was prepared by applying an injection molding machine under the condition of kg / cm ² , and the bending strength, friction coefficient, specific wear amount, mating material damage property, tooth tip wear, mating gear damage degree of the obtained test piece were as follows. It was determined by the test method shown in.

Bending test Bending strength according to ASTM-D790 (10 g / cm ² ).
Was measured. The unit of bending strength is kgf / cm ²
And

Grinding wear test The friction coefficient, the specific wear amount, and the damage to the mating material were measured with an NTN thrust type friction wear tester.

Sliding conditions Peripheral speed: 128 m / min Surface pressure: 3.9 kg / cm ² Atmosphere: R.S. T dry mating material: SUS303 steel With respect to the unit of the above test results, the friction coefficient was expressed by a dimensionless number, and the specific wear amount was expressed by × 10 ^-10 cm ³ / kg · m. As for the mating material damage property, four-level evaluation was performed based on the following criteria according to the depth of sliding marks of the mating material SUS303 steel.

Evaluation Criteria ⊚: Wear depth ≦ 1 μm ◯: 1 μm <wear depth ≦ 5 μm Δ: 5 μm <wear depth ≦ 10 μm ×: 10 μm <wear depth Gear actual machine durability test A durability test was conducted using a precision resin gear strength tester.

Test conditions Test time: 200 hr Revolution: 470 rpm 350 rpm Torque: 4.5 to 5.5 kgf · cm Atmosphere: R.S. T. Drive gear: Each PPS gear (NTN Precision Resins Co .: PC
D47) Counter gear: polyacetal gear (PCD35 manufactured by Polyplastics Co., Ltd.) The tooth tip wear and the counter gear damage degree in the test results were evaluated according to the following criteria.

Evaluation criteria ⊚: wear depth ≦ 10 μm ◯: 10 μm <wear depth ≦ 50 μm Δ: 50 μm <wear depth ≦ 100 μm ×: 100 μm <wear depth

[0037]

[Table 1]

[Comparative Examples 1 to 8] The various raw materials (1) described above,
(4) Test pieces were prepared in exactly the same manner as in Examples 1 to 10 except that (6) to (10) were mixed in the proportions shown in Table 4, and evaluated in the same manner as in the above-mentioned test method. The results are also shown in Table 2.

[0039]

[Table 2]

As is clear from the results shown in Tables 1 and 2, Comparative Examples 2 and 3 in which aramid pulp was not used even if zinc oxide whiskers were used, and aramid fibers other than aramid pulp were used even when zinc oxide whiskers were used. Comparative Example 4 using No. 3, Comparative Example 5 using zinc oxide whiskers even if using aramid pulp, and all of them are inferior in abrasion resistance and have high damage to the other party.

Comparative Example 6 in which PTFE resin was not used even with zinc oxide whiskers and aramid pulp
Has a large friction coefficient and is poor in wear resistance. Furthermore,
Even if the four essential components in this invention are blended,
Comparative Example 7 containing a small amount of zinc oxide whiskers was inferior in abrasion resistance, and Comparative Example 8 containing an excessive amount of zinc oxide was inferior in damage to the other party.

On the other hand, Examples 1 to 10 in which the four essential components were blended in a predetermined ratio exhibited excellent physical properties. In particular, a crosslinkable PPS resin having a predetermined melt viscosity was used and the number average molecular weight was 7,000,000. The example 2 in which the high-molecular-weight PTFE was mixed was the most excellent in abrasion resistance. Further, comparing Example 2 and Example 4, it was found that the composition using the high-molecular weight PTFE resin has a lower friction coefficient and is excellent in wear resistance.

[0043]

As described above, according to the present invention, the PPS resin and the PTFE resin are used as the main materials, and the predetermined amount of the reinforcing material having a three-dimensional structure such as aramid pulp and zinc oxide whiskers is mixed. There is no variation in strength due to the orientation of the reinforcing material, dimensional accuracy by molding, heat distortion resistance, mechanical strength and injection moldability are satisfied, and the mating gear is not damaged,
Has wear resistance. Therefore, it can be said that it is the most suitable as a molding material for gear molding capable of stable torque transmission.

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area C08L 27:18 77:00)

Claims (3)

[Claims] 1. A polyphenylene sulfide resin 100.
10 parts by weight of polytetrafluoroethylene resin
A resin composition for gears, which comprises 50 parts by weight, 10 to 30 parts by weight of aromatic polyamide pulp and 30 to 80 parts by weight of zinc oxide whiskers. 2. The crosslinkable polyphenylene sulfide resin having a melt viscosity of 1400 to 15000 poise, which is obtained by crosslinking an uncrosslinked polyphenylene sulfide resin having a melt viscosity of 350 to 3000 poise just after polymerization, in the polyphenylene sulfide resin. Resin composition for gears. 3. The resin composition for gears according to claim 1, wherein the polytetrafluoroethylene resin is an unsintered polytetrafluoroethylene resin having a number average molecular weight of 10,000 or more.