JPH0786166B2 - Polyacetal resin composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyacetal resin composition, and more particularly to a polyacetal resin composition which is a molded product having excellent screw biting property and excellent friction and wear characteristics.

[Prior Art] Generally, polyacetal is superior to metal in self-lubricating property, has low friction coefficient, good friction and wear characteristics, is light in weight, and has low noise during driving. It is extremely useful as a non-lubricated component. Its equilibrium water absorption is extremely small compared to nylon 6, 66, etc., so it has good dimensional stability, and its mechanical properties are not significantly degraded by water absorption, so its application is wide-ranging.

However, when viewed as sliding parts, the PV limit value is relatively low, so it is limited to low-load applications.

The limit PV value here is generally the limit of the load at which the bearing material melts or burns above a certain surface pressure P (kg / cm ² ) and peripheral speed (m / min). Indicates a value.
Therefore, the larger the limit PV value is, the better the friction and wear characteristics are, and the higher the load can be endured.

Therefore, in order to improve the friction and wear characteristics of polyacetal, it has been customary to add a lubricant such as molybdenum disulfide, graphite, fine powder of tetrafluoroethylene, oil or wax.

When a liquid lubricant such as oil or wax is added during molding, the oil or wax is impregnated in advance in an oil absorbent such as activated carbon or polynorbornene and then melt mixed.

[Problems to be Solved by the Invention] However, when molybdenum disulfide or graphite is used as a lubricant, not only the color of the resin is limited to black, but also when tetrafluoroethylene fine powder, oil or wax is used. In comparison, the effect of improving the friction and wear characteristics was not obtained.

Further, even if fine powder of tetrafluoroethylene is used, it is more effective as a lubricant than molybdenum disulfide and graphite, but it is inferior to oils and waxes and has a problem that it is expensive. . On the other hand, when oils and waxes are used, it is superior in terms of friction and wear characteristics,
When screw extrusion is attempted, there is a problem that the biteability of the screw is poor.

In addition, if activated carbon is used as the oil absorber in the method of impregnating oil or waxes into the oil absorber such as activated carbon or polynorbornene, the resin is limited to black, and the activated carbon has negative friction and wear characteristics. It was a factor. On the other hand, when polynorbornene is used as an oil absorber, polynorbornene has a double bond in the main chain and thus is inferior in heat resistance, and the polynorbornene elastomer itself has the same friction and wear characteristics as activated carbon. Or, there was a problem that it became a negative factor.

An object of the present invention is to provide a polyacetal resin composition which solves the above-mentioned problems, improves screw biting property, and has excellent friction and wear characteristics, and also has excellent mechanical strength. It is a thing.

[Means for Solving the Problems] That is, in the present invention, 100 parts by weight of polyacetal and 0.1 to 4 parts by weight of silicone oil are used, and the general formula is H ₁₇ C ₈ OOC (CH ₂ ) _n COOC ₈ H ₁₇ (however, n Is an integer of 4 to 8)
It is a polyacetal resin composition containing 0.5 to 8 parts by weight.

Incidentally, the polyacetal resin composition of the present invention has various forms, for example, pellets obtained by melt-kneading a mixture containing predetermined components in an extruder, and using the pellets A molded product formed into a predetermined shape such as a round bar, a tubular shape, or a plate shape by an injection molding machine, an extrusion molding machine, or the like, or a mixture containing predetermined components, which is not yet melted and solidified.

The polyacetal used in the present invention is a homopolymer CH ₂
-O _n, copolymers _{CH 2 -O n CH 2 -CH 2} -O
_The number average molecular weight is 20,000 to 100,000.

Further, the silicone oil used here has a structure of dimethylpolysiloxane and has a viscosity of 100 cSt (centistokes) or more, preferably 3000 cSt or more. These oils are added in an amount of 0.1 to 4 parts by weight with respect to 100 parts by weight of polyacetal, but if the amount is less than 0.1 parts by weight, a sufficient limiting PV value cannot be obtained. Further, if it exceeds 4 parts by weight, when injection molding is performed, delamination may occur or the screw may not bite. Addition of silicone oil to polyacetal has a remarkable effect on improving the limiting PV value in friction and wear characteristics, but does not provide sufficient effect on wear resistance.

On the other hand, another oil used in the present invention, that is, a compound represented by the general formula: H ₁₇ C ₈ OOC (CH ₂ ) _n COOC ₈ H ₁₇ (where n is an integer of 4 to 8) is dioctyl. Adipate, dioctyl pimelate, dioctyl sperate, dioctyl azelate, and dioctyl sebacate were mentioned, and it was recognized that the abrasion resistance was more effective than the improvement of the critical PV value.

Further, the above compound has 4 to 8 intermediate methylene groups in the structure of H ₁₇ C ₈ OOC (CH ₂ ) _n COOC ₈ H ₁₇ . Since the compatibility between the compound having 4 to 8 methylene groups and the polyacetal resin is moderate, the decrease in mechanical strength is relatively small, and the sliding surface moderately bleeds, contributing to wear resistance. To do. On the other hand, in the above compound, n
When it is 3 or less, the number of methylene groups is small and the compatibility with the polyacetal is good, so that it becomes a plasticizer for the polyacetal resin, and the mechanical strength is greatly reduced.

Further, since the compatibility is good, it is taken into the polyacetal and the amount of bleeding to the sliding surface is small, so that the contribution to the wear resistance is relatively small. That is, in the present invention, the general formula for abrasion resistance, which is difficult to obtain a sufficient effect with silicone oil, is represented by H ₁₇ C ₈ OOC (CH ₂ ) _n COOC ₈ H ₁₇ (where n is an integer from 4 to 8). It is complementary to the compound, and it is preferable to add 0.5 to 8 parts by weight to the polyacetal. If it is less than 0.5 parts by weight, sufficient abrasion resistance cannot be obtained, and if it exceeds 8 parts by weight, the screw biting property may deteriorate. Further, if the total weight of the above-mentioned oil added to the polyacetal exceeds 10 parts by weight, the mechanical properties will deteriorate, which is a practical problem.

The composition of the present invention can be obtained by kneading the above polyacetal resin and silicone oil with an ordinary extruder. The extrusion temperature in this extrusion molding and injection molding is 19
The range of 0 to 210 ° C is preferable. If extruded at a temperature lower than 190 ° C, the resin will be hard and will not easily penetrate into the screw. Also,
Extrusion at a temperature higher than 210 ° C is not suitable because the resin tends to burn or decompose.

The present invention can be carried out by using a filler, a reinforcing material, various additives and a coloring agent according to the purpose other than the above additives.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[Examples] Raw materials used in Examples and Comparative Examples are collectively shown below. Ultraform N2320 (manufactured by BASF) Silicone oil 100,000 cSt (manufactured by Toray Downing Silicone) Dioctyl sebacate (DOS) (Sanken Kako Co., Ltd.)
Dioctyl adipate (DOA) (Dahachi Chemical Co., Ltd.)
Manufacture) [Examples 1 to 5] The above raw materials were blended as shown in Examples of Table 1,
The mixture was supplied to a twin-screw extruder (PCM-45 manufactured by Ikegai Iron Works Co., Ltd.) and melt-kneaded to obtain pellets. Using the pellets, test pieces were prepared with an injection molding machine, and the limit PV value, thrust wear value, and bending strength of the obtained molded body were measured. The results are shown in Table 1.

The method of obtaining the limit PV value was measured by the Matsubara thrust test, the test piece was φ50 × 3t, the mating material S45C cylindrical shape (φ25.6 × φ
In 20), the surface pressure was increased by 10 kg / cm ² every 10 minutes, and the product of the pressure P and the speed V when the surface pressure could not be maintained was defined as the limit PV value.

The thrust wear amount was tested by using the same tester and test piece as above, with a surface pressure of 20 kg / cm ² and a speed of 15 m / min for 24 hours, and the weight difference before and after the test was used as the thrust wear amount.

[Comparative Examples 1 to 6] Specimens were prepared in the same manner as in Examples 1 to 4 except that the raw materials 1 to 3 were blended as in Comparative Examples 1 to 6 in Table 1 to prepare test pieces. The test was conducted. The results are shown in Table 1.
Shown in.

As can be seen from the composition and the measurement results shown in Table 1, in the examples, the limit PV value shows a certain value or more, and the thrust wear value also has a small value. Then, both values are clearly superior to only polyacetal from Comparative Example 1, and the one containing only silicone oil from Comparative Example 2 shows the same limit PV value as that of the Example, but the thrust wear value. Is inferior. Comparative Examples 3 and 6 show that when silicone oil or DOS is excessively blended, molding is possible but delamination occurs, or pellets do not bite into the screw and cannot be molded. In Comparative Examples 4 and 5, silicone oil is blended. It can be seen that the marginal PV value does not increase without it.

[Effect] As described above, according to the present invention, a compound represented by H ₁₇ C ₈ OOC (CH ₂ ) _n COOC ₈ H ₁₇ (where n is an integer from 4 to 8) is represented by the general formula. By blending both of the above, it is possible to obtain a polyacetal resin composition which is excellent in both physical properties such as a limiting PV value and abrasion resistance and further excellent in mechanical strength.

Claims (1)

[Claims] Claims: 1. 100 parts by weight of polyacetal and 0.1 to 4 parts by weight of silicone oil, and the general formula is H ₁₇ C ₈ OOC (CH ₂ ) _n COOC ₈ H ₁₇ (where n is an integer from 4 to 8). 0.5 of the compound
A polyacetal resin composition characterized by containing 8 to 8 parts by weight.