JPH0477546A - Polyacetal resin composition - Google Patents

Abstract

PURPOSE:To obtain a polyacetal resin composition having excellent screw-biting performance, frictional and abrasion characteristics and mechanical properties by compounding specific amounts of silicone oil and a specific compound. CONSTITUTION:The objective composition is produced by compounding (A) 100pts.wt. of a polyacetal with (B) 0.1-4pts.wt. of a silicone oil having a viscosity of preferably >=3,000cst and (C) 0.5-8pts.wt. of a compound of formula ((n) is 4-8) (e.g. dioctyl adipate).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polyacetal resin composition, and more particularly to a polyacetal resin composition that has excellent screw penetration properties and can be formed into a molded article with excellent friction and wear properties.

[Prior art] In general, polyacetal has superior self-lubricating properties compared to metals, has a low coefficient of friction, has good friction and wear characteristics, is lightweight, and produces less noise during driving, so it is used for bearings, gears, rollers, cam guide rails, etc. Extremely useful as an oil-free part. Since it has an extremely low equilibrium water absorption rate compared to nylon 6.66, etc., it has good dimensional stability and the decrease in mechanical properties due to water absorption is extremely small, so its uses are wide-ranging.

However, when viewed as a sliding component, its limiting PV value is relatively low, so it is limited to low-impact applications.

Note that the limit PV value mentioned here generally means that the bearing material has a certain surface pressure P (kg/cm2) and circumferential speed (m/m1n).
) or above indicates the limit value of the load at which the material melts or seizes. Therefore, the larger the limit Pv value, the better the friction and wear characteristics and the ability to withstand high loads.

For this reason, in order to improve the friction and wear characteristics of polyacetal, lubricants such as molybdenum disulfide, graphite, tetrafluoroethylene fine powder, oil, wax, etc. have been added to the furnace material.

Furthermore, when a liquid lubricant such as oil or wax is added to the stratification, the oil or wax is impregnated in advance into an oil absorbing body such as activated carbon or polynorbornene, and then melted and mixed.

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

Furthermore, even if fine powder of ethylene tetrafluoride was used, it was more effective as a lubricant than molybdenum disulfide or graphite, but it was inferior to oils and waxes, and it was expensive. . On the other hand, the use of oils and waxes has excellent friction and wear properties, but
When screw extrusion was attempted, there was a problem in that the screw had poor penetration.

In addition, among methods of impregnating oil or wax into an oil absorbing material such as activated carbon or polynorbornene, if activated carbon is used as the oil absorbing material, the resin will be limited to black color, and activated carbon will have a disadvantage in terms of friction and wear properties. It was a factor. On the other hand, if polynorbornene is used as an oil absorber,
Polynorbornene has a double bond in its main chain, so it has poor heat resistance, and the polynorbornene elastomer itself has the same or more negative friction and wear characteristics as activated carbon. there were.

The object of the present invention is to solve the above-mentioned problems and provide a polyacetal resin composition that improves screw penetration and provides a molded product with excellent friction and wear properties as well as excellent mechanical strength. It is.

[Means for Solving the Problems] That is, the present invention includes 100 parts by weight of polyacetal, 0.1 to 4 parts by weight of silicone oil, and the general formula is H17C80.
0C(CH2)ncOOcBH17 (where n is 4 to
This is a polyacetal resin composition containing 0.5 to 8 parts by weight of a compound represented by the formula (an integer up to 8).

The polyacetal resin composition of the present invention has various forms, such as pellets obtained by melt-kneading a mixture of predetermined components in an extruder, and A molded body made into a predetermined shape such as a round bar, cylinder, plate, etc. using an injection molding machine, extrusion molding machine, etc.
Alternatively, it includes a mixture of predetermined components that has not yet been melted and solidified.

The polyacetal used in the present invention is a homopolymer-%
CH220+. , copolymer+CH2-〇+T+CH2-CH2-0+m, and has a number average molecular weight of 20,000 to 100°OOO.

Furthermore, the silicone oil used here has a dimethylpolysiloxane structure and a viscosity of 10,006 St.
(centistokes) or higher, especially 3000c
St or higher is preferable. These oils are added in O=1 to 4 parts by weight per 100 parts by weight of polyacetal, but if it is less than 0.1 part by weight, a sufficient limit Pv value cannot be obtained. Moreover, if the amount exceeds 4 parts by weight, delamination may occur during injection molding or the screw may not penetrate. Although the addition of silicone oil to polyacetal has a remarkable effect on improving the limit Pv value of friction and wear resistance, a sufficient effect on wear resistance cannot be obtained.

On the other hand, another type of oil used in the present invention, that is, a compound whose general formula is H17C800C(CH2)ncOOcsH17 (where n is an integer of 4 to 8), is dioctyl adipate, dioctyl adipate, dioctyl adipate, dioctyl aze. rate, 5 of dioctyl sebacate
It was recognized that this method had a remarkable effect on wear resistance rather than improving the critical PV value.

Furthermore, the above compound has 4 to 8 intermediate methylene groups in the structure 817C800C(CH2)ncOOcsHl,7. Since the compatibility between this compound having 4 to 8 methylene groups and the polyacetal resin is moderate, the decrease in mechanical strength is relatively small, and moderate oozing occurs on the sliding surface, contributing to wear resistance. do.

On the other hand, when n is 3 or less in the above compound, there are few methylene groups and the compound has good compatibility with polyacetal, so it becomes a plasticizer for the polyacetal resin, and its mechanical strength is greatly reduced.

Furthermore, due to its good compatibility, it is incorporated into the polyacetal and the amount of oozing out onto the sliding surface is small, so its contribution to wear resistance is relatively small. In other words, in the present invention, the general formula for wear resistance, which is difficult to obtain with silicone oil, is supplemented with a compound represented by H17CBOOC(CH2)ncOOcaH17 (where n is an integer from 4 to 8), and 0. Preferably, 5 to 8 parts by weight are added 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, screw penetration may deteriorate. Furthermore, if the total weight of the oil added to the polyacetal exceeds 10 parts by weight, the mechanical properties will deteriorate, causing a practical problem.

The composition of the present invention can be obtained by kneading the above polyacetal resin and silicone oil using a conventional extruder. The extrusion temperature in this extrusion molding and injection molding is 1
The temperature range is preferably from 90 to 210°C. If extruded at a temperature lower than 190°C, the resin will be hard and difficult to bite into the screw. Furthermore, extruding at a temperature higher than 210° C. is not appropriate because the resin tends to burn or decompose.

The present invention can also be carried out using fillers, reinforcing materials, various additives, and colorants in addition to the above-mentioned additives depending on the purpose.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Example] The raw materials used in the Examples and Comparative Examples are listed below. That is, ■ Ultraform N2320 (manufactured by BASF) ■
Silicone oil 100,000 C3t (Toshi, Dow Corning Silicone Co., Ltd. fR) ■ Dioctyl sebacate (DO8) (manufactured by Sanken Kako ■) ■ Dioctyl adipate (DOA) (manufactured by Oiri Kagaku ■) [Examples 1 to 5] The above raw materials ■ to ■ are blended as shown in the examples in Table 1,
The mixture was supplied to a twin-screw press (PCM-45, manufactured by Ikegai Tekko Co., Ltd.) and melted and kneaded to obtain a pellet. A test piece was made using an injection molding machine using this pellet, and the limit PV value, thrust wear value, and bending strength of the obtained molded product were measured. The results are shown in Table 1.

The limit PV value was determined using the Matsubara thrust test.
φ25.6Xφ20) with surface pressure of 10kg/c every 10 minutes.
The limit PV value was defined as the product of the pressure P and the speed ■ when the surface pressure could not be maintained by increasing the pressure by m2.

In addition, the thrust wear amount was measured using the same testing machine and test piece as above, surface pressure 20 kg/cm2, speed 15 m/min,
The test was conducted for 24 hours, and the difference in weight before and after the test was taken as the amount of thrust wear.

[Comparative Examples 1 to 6] Test pieces were prepared in exactly the same manner as in Examples 1 to 4, except that the various materials ■ to ■ were used in the compositions of Comparative Examples 1 to 6 in Table 1. A similar test was conducted. Table 1 shows the results.
Shown below.

As can be seen from the formulations and measurement results shown in Table 1 below, the limit Pv values in the examples are above a certain level,
Moreover, small values were obtained for thrust wear values. Comparative Example 1 shows that both values are clearly superior to polyacetal alone, and Comparative Example 2 shows that the product containing only silicone oil has the same limit Pv value as the example, but the thrust wear value. So it's inferior. Comparative Example 3.6 shows that when DO5 is blended in excess, molding is possible but delamination occurs, and the pellet does not dig into the screw, making molding impossible. Comparative Example 4.5 does not contain silicone oil. It can be seen that the limit Pv value does not become high.

[Effects] As described above, according to the present invention, by blending both silicone oil and a compound represented by the general formula H17CBOOC(CH2)ncOOc6H17 (where n is an integer from 4 to 8), the limit can be improved. It is possible to obtain a polyacetal resin composition that has excellent physical properties such as both Pv value and abrasion resistance, and also has excellent mechanical strength.

Claims (1)

[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_1_7C_8OOC(CH_2)_nCOOC_8
A polyacetal resin compound characterized by blending 0.5 to 8 parts by weight of a compound represented by H_1_7 (where n is an integer from 4 to 8).