Thermoplastic compositions of polyetheretherketones having improved tribological material properties and use thereof

Abstract

A thermoplastic component may include a matrix component (A) and a filler component (B). The matrix component (A) may include a polyetheretherketone and the filler component (B) may include inorganic particles and carbon-containing particles. The overall composition may include equal or different portions, as filler component (B), of hydrophobic silicon dioxide, carbon fibres, titanium dioxide particles, graphite particles, and a particulate lubricant selected from divalent metallic sulfides and alkaline earth metal sulfates.

Claims

1. A thermoplastic composition, comprising: (A) a matrix component comprising polyetheretherketones; and (B) a filler component, wherein a content of the polyetheretherketones is from 30 to 95 wt. % based on a total weight of the thermoplastic composition, and wherein the polyetheretherketone comprises a structural element of the following formula (I): ##STR00003## having Melt Volume-flow Rate (MVR) of from 10 to 90 cm.sup.3/10 min determined at 400 C., load 2.16 kg, in a capillary having a length of 8 mm and a diameter of 2.095 mm, inlet angle 180, and wherein the filler component (B) comprises from 5 to 70 wt. % of inorganic and carbon-containing particles based on a total weight of the thermoplastic composition, and comprises, based on a total weight of the thermoplastic composition, from 1 to 20 wt. % of hydrophobic silicon dioxide, from 1 to 20 wt. % of carbon fibers, from 1 to 20 wt. % of titanium dioxide particles, from 1 to 20 wt. % of graphite particles, and from 1 to 20 wt. % of a particulate lubricant comprising a divalent metallic sulfide and/or alkaline earth metal sulfate, wherein the total weight of the thermoplastic composition is 100 wt. %, wherein the thermoplastic composition is suitable for at least one lubricant-free tribological application, and wherein the hydrophobic silicon dioxide has a particle size distribution D50 of from 2 to 5 m, and a D100 of less than 150 m, the particle size distribution having been determined according to ISO 13320 with dry-dispersed particles.

2. The composition of claim 1, comprising, as the filler component (B), from 2 to 20 wt. % of the hydrophobic silicon dioxide, from 2 to 20 wt. % of the carbon fibers, from 1 to 15 wt. % of the particulate lubricant, from 2 to 20 wt. % of the graphite particles, and from 1 to 15 wt. % of the titanium dioxide particles, and wherein the total weight of the thermoplastic composition is 100 wt. %.

3. The composition of claim 1, comprising from 30 to 81 wt. % of the polyetheretherketones comprising the polyetheretherketone structural element of the formula (I), from 5 to 15 wt. % of the hydrophobic silicon dioxide, from 2 to 8 wt. % of the particulate lubricant, from 5 to 15 wt. % of the graphite particles, from 2 to 8 wt. % of the titanium dioxide particles, and from 5 to 15 wt. % of the carbon fibers, wherein the total weight of the thermoplastic composition is 100 wt. %.

4. The composition of claim 1, comprising from 30 to 73.5 wt. % of polyetheretherketones comprising the polyetheretherketone structural element of the formula (I), from 7.5 to 12.5 wt. % of the hydrophobic silicon dioxide, from 2 to 8 wt. % of the particulate lubricant, from 7.5 to 12.5 wt. % of the graphite particles, from 2 to 8 wt. % of the titanium dioxide particles, and from 7.5 to 12.3 wt. % of the carbon fibers, wherein the total weight of the thermoplastic composition is 100 wt. %.

5. The composition of claim 1, wherein the carbon fibers have a fiber length of from 15 to 555 m.

6. The composition of claim 1, wherein the hydrophobic silicon dioxide has a carbon content of from 1 to 2 wt. % determined according to ISO 3262-20, based on the silicon dioxide.

7. The composition of claim 1, wherein the titanium dioxide particles have a bimodal particle size distribution.

8. The composition of claim 1, wherein the graphite particles have a particle size distribution D50 of from 5 to 15 m, and a D100 of less than 50 m, the particle size distribution having been determined according to ISO 13320 with dry-dispersed particles.

9. The composition of claim 1, wherein the particulate lubricant is ZnS and has a particle size distribution having a D.sub.50 of from 500 to 1000 nm and a D.sub.90 of less than 20 m.

10. A process for producing the thermoplastic composition of claim 1, the process comprising: (i) producing a first masterbatch by mixing, in an extruder, of polyetheretherketone containing structural elements of the formula (I): ##STR00004## with hydrophobic silicon dioxide at an elevated temperature, and at a vacuum pressure of from 1000 to 5 mbar absolute, to obtain the first masterbatch; feeding the first masterbatch into a base feed, and feeding carbon fibers in downstream to obtain the thermoplastic composition.

11. The process of claim 10, wherein the first masterbatch is produced at a vacuum pressure of from 300 to 100 mbar absolute.

12. The process of claim 10, wherein (i) the elevated temperature is from 380 to 450 C., and/or (ii) a second masterbatch is produced at a temperature of from 380 to 450 C., in an extruder, and/or (iii) the thermoplastic composition is produced at a temperature of from 380 to 450 C.

13. A process for producing a shaped article, the process comprising: (a) injection molding comprising one- to multi-component injection molding, (b) fused deposition modelling or fused filament fabrication, (c) pressing, (d) extruding and/or co-extruding, optionally with calendering or film blowing, and/or (e) material-removing, the thermoplastic material of claim 1.

14. A process for influencing tribology, the process comprising: contacting with a machine element the thermoplastic material of claim 1 as component in at least one lubricant-free tribological application.

15. The process of claim 10, wherein the hydrophobic silicon dioxide comprises hydrophobic fumed silicon dioxide.

Description

(1) FIG. 1 shows, in a rising load test at a pressure of 4 MPa with speed increasing stepwise, the coefficients of friction of inventive example 1 and of a commercial material, WG 101 from Victrex (CompEx 2). The details of the rise are given in the descriptive text for Table 2. The lower coefficients of friction of the shaped article according to the invention are clearly apparent.

(2) It is particularly advantageous that components made of the compositions according to the invention do not cause any adaptation problems at all after a change in speed. Friction very rapidly settles at a new constant value, it being essential that the fiction does not fluctuate, i.e. does not show transient behaviour. This is particularly advantageous since changes in running speed, for example in a concentric runner bearing, i.e. the speed of rotation, does not result in any additional stresses in other components, i.e., for example, large jumps in torque that affect the axis of a concentric bearing.

(3) Materials: PEEK: polyetheretherketone from Evonik with different MVR SiO.sub.2: fumed silica, hydrophobized, carbon content 1.2% by weight (ISO 3262-20); particle diameter (dry-dispersed) D.sub.50 3.13 m, D.sub.100<80 m ZnS: particle size (wet-dispersed) D.sub.50 0.80 m, D.sub.90<5 m Carbon fibres: Sigrafil C C6-4.0/240-T190 Graphite particles: particle size (dry-dispersed) D50 9.3 m, D100<35 m TiO.sub.2: particle diameter (dry-dispersed) D (mode, max) 350 nm, D (bimod, max) 3.5 m; surface-modified with Si, Zr and Al

EXAMPLE 1: Composition Based on PEEK with MVR 34 cm.SUP.3./10 min (test weight 2.16 kg/400 C.)

EXAMPLE 2: Composition Based on PEEK with MVR 72 cm.SUP.3./10 MIN (Test Weight 2.16 kg/400 C.)

Production of the Thermoplastic Composition in a Twin-Screw Extruder

(4) Masterbatch 1: 80% by weight of PEEK and 20% by weight of SiO.sub.2, extruded (melt temperature 439 C., housing temperature 390 C.), with employment of a vacuum pressure for devolatilization of about 300 to 100 mbar absolute (at the position of addition of silica).

(5) Masterbatch 2: 60% by weight of PEEK, 20% by weight of TiO.sub.2 and 20% by weight of zinc sulfide (melt temperature 428 C., housing temperature 390 C.).

(6) 50% by weight of masterbatch 1 and 25% by weight of masterbatch 2 were fed together into the base feed of the extruder (5% by weight of the respective PEEK); 10% by weight of graphite and 10% by weight of carbon fibres were successively fed in downstream. The melt temperature was 439 C. and the housing temperature 390 C. The product is pelletized at the end of the extrusion.

(7) Thus, the compositions according to the invention from the examples comprise 60% by weight of PEEK, 10% by weight of SiO.sub.2 particles, 5% by weight of ZnS particles, 10% by weight of graphite particles, 5% by weight of TiO.sub.2 particles and 10% by weight of carbon fibres.

(8) A comparative example (CompEx 1) comprises 60% by weight of PEEK (VESTAKEEP 2000, product from Evonik), 10% by weight of ZnS particles, 10% by weight of graphite particles, 10% by weight of TiO.sub.2 particles and 10% by weight of carbon fibres.

(9) A further comparative example (CompEx 2) is WG101, a commercial product from Victrex. Test specimens: The pellets were injection-moulded into plaques; the dimensions of the plaques were a thickness of 4 mm and an area of 50 mm*50 mm.

(10) The test specimens were machined as cubic blocks. They have a test area of 44 mm.sup.2 with a length of 10 mm. The fibres were aligned essentially in the test plane; the vectors of frictional force and the vector of fibre alignment were orthogonal to one another.

(11) For determination of the tribological properties, block-on-ring and pin-on-disc tests were conducted; test specimens had identical dimensions:

(12) Measurement was effected at different speeds (v=0.5, 1, 2, 3 and 4 m/s) and with different contact pressures (pressure loads) (p=1, 2, 4, 8 and 10 MPa). After a running-in phase, the testing phase commenced. The block was formed from the test material; the ring and disc are made of steel (100Cr6H). The wear rate was measured by determining the loss of mass. The measurements were conducted at different temperatures without use of lubricants.

(13) Coefficients of friction (COF, friction value) and wear rate W.sub.s [10.sup.6 mm.sup.3/Nm] were determined. The calculation of the wear rate is based on the loss of mass of the test specimen according to the formula: W.sub.s=(m)/tF.sub.n, where m is the loss of mass, p the density of the test material, the sliding speed and t the test duration. F.sub.n is the contact force of the test specimen.

(14) The values in Tables 1a to 1d were found at 23 C. on the block-on-ring test bench. The run-in phase was 2 h, the testing phase 20 h. The steel ring had a roughness depth (Rz) of 2 m and an arithmetic average roughness (roughness, Ra) of 0.2 m.

(15) TABLE-US-00001 TABLE 1a Coefficients of friction with a contact pressure of 1 MPa as a function of sliding speed, 23 C. Coefficient of friction; 1 MPa 0.5 m/s 1 m/s 2 m/s 3 m/s 4 m/s Example 1 0.24-0.26 0.2-0.21 0.16-0.17 0.12-0.14 0.07-0.08 Example 2 0.26-0.28 0.25-0.26 0.17-0.18 0.13-0.14 0.11-0.12 CompEx 2 0.31-0.32 0.32-0.34 0.38-0.39 0.31-0.32 0.24-0.25

(16) The coefficients of friction of Inventive Examples 1 and 2 are lower than those of the commercial Victrex WG101 product. Moreover, there was a distinct decrease in the coefficients of friction of Inventive Examples 1 and 2 with increasing sliding speed, whereas the coefficients of friction of CompEx 2 actually increase starting from a speed of 0.5 m/s up to a speed of 2 m/s.

(17) TABLE-US-00002 TABLE 1b Coefficients of friction with a contact pressure of 2 MPa as a function of sliding speed, 23 C. Coefficient of friction; 2 MPa 0.5 m/s 1 m/s 2 m/s 3 m/s 4 m/s Example 1 0.18-0.19 0.14-0.15 0.13-0.14 0.08-0.09 0.06-0.07 Example 2 0.26-0.27 0.18-0.19 0.1-0.11 0.07-0.08 0.03-0.04 CompEx 2 0.48-0.49 0.46-0.47 0.35-0.36 0.27-0.28 0.27-0.28

(18) There is a further decrease in the low coefficients of friction of Inventive Examples 1 and 2 with increasing speed and increased contact pressure of 2 MPa.

(19) TABLE-US-00003 TABLE 1c Coefficients of friction at a contact pressure of 4 MPa as a function of sliding speed Coefficient of friction; 4 MPa 0.5 m/s 1 m/s 2 m/s 3 m/s 4 m/s Example 1 0.22-0.23 0.14-0.15 0.11-0.12 0.17-0.18 0.16-0.17 Example 2 0.17-0.18 0.12-0.14 0.08-0.09 0.1-0.11 0.04-0.05 CompEx 2 0.47-0.49 0.35-0.37 0.27-0.28 0.23-0.24 0.21-0.22

(20) There is a continuous further decrease in the coefficient of friction of Inventive Example 2 with increasing speed even at a further-increased contact pressure of 4 MPa. For the composition of Example 1, a minimum in the coefficient of friction is found at a speed of 2 m/s.

(21) TABLE-US-00004 TABLE 1d Coefficients of friction at a contact pressure of 8 MPa as a function of sliding speed Coefficient of friction; 8 MPa 0.5 m/s 1 m/s 2 m/s 3 m/s 4 m/s Example 1 0.17-0.19 0.16-0.17 0.12-0.14 0.08-0.09 0.07-0.08 Example 2 0.22-0.23 0.18-0.19 0.15-0.16 0.1-0.11 0.08-0.09 CompEx 2 0.43-0.44 0.33-0.35 0.24-0.26 0.17-0.18 0.16-0.17

(22) The coefficients of friction of Inventive Example 1 are lower than those of Example 2. There is a continuous further decrease in both coefficients of friction with increasing speed at a further-increased contact pressure of 8 MPa. Example 1 has similarly good coefficients of friction at 8 MPa as at 2 MPa.

(23) The values in Table 2 are rising load tests; they were found at 23 C. on the block-on-ring test bench. Without a running-in phase, sliding speed increased stepwise beginning at 0.5 m/s (10 h), 1 m/s (7.5 h), 2 m/s (5 h), 3 m/s (5) to 4 m/s (2.5 h). The steel ring had a roughness depth (Rz) of 2 m and an arithmetic average roughness (roughness, Ra) of 0.2 m.

(24) TABLE-US-00005 TABLE 2 Wear rates as a function of contact pressure with an increase in speed from 0.5 m/s to 4 m/s Wear rate [10.sup.6 mm.sup.3/Nm] 1 MPa 2 MPa 4 MPa 8 MPa Example 1 0.51-0.53 0.45-0.47 0.32-0.34 0.28-0.29 Example 2 0.23-0.25 0.25-0.26 0.35-0.37 0.26-0.27 CompEx 2 0.73-0.75 0.72-0.73 0.65-0.66 0.32-0.34

(25) The wear rates of Inventive Examples 1 and 2 are lower than those of Victrex WG101. In addition, there is a distinct and continuous decrease in the wear rates of Inventive Example 1 with increasing contact pressure.

(26) FIG. 1 shows the rising load experiments for test specimens from Example 1 and CompEx 2 at a contact pressure of 4 MPa; the measurements of the coefficient of friction were found at 20 C.

(27) The values in Tables 3a and 3b were found at 23 C. and 100 C. on the pin-on-disc test bench. The test phase was 5000 m. The steel ring had a roughness depth (Rz) of 5 m and an arithmetic average roughness (roughness, Ra) of 0.4 m.

(28) TABLE-US-00006 TABLE 3a Pin-on-disc, wear rate at 1 m/s Wear rate [10.sup.6 mm.sup.3/Nm] 4 MPa 10 MPa Example 1 25 C. 4.91 1.5 Example 2 25 C. 2.5 1.08 Example 1 100 C. 2.77 1.03 Example 2 100 C. 2.43 1.07

(29) TABLE-US-00007 TABLE 3b Pin-on-disc, coefficient of sliding friction at 1 m/s Coefficient of friction 4 MPa 10 MPa Example 1c 25 C. 0.23 0.07 Example 2b 25 C. 0.12 0.09 Example 1c 100 C. 0.05 0.05 Example 2b 100 C. 0.08 0.03

(30) There is a distinct decrease in the wear rate and coefficients of friction of the inventive examples under elevated contact pressure and even with increasing temperature.

(31) The values in Tables 4a, 4b, 5a and 5b were found at 25 C. on the block-on-ring test bench. The steel ring had an arithmetic average roughness (roughness, Ra) of 0.1 m-0.2 m.

(32) TABLE-US-00008 TABLE 4a Wear rates compared to the material of the KS slide bearing (EP 1511625 B2, sample PEEK 6) Wear rate [10.sup.6 mm.sup.3/Nm].sup.1 Conditions 1 MPa; 3 m/s 1 MPa; 4 m/s 3 MPa; 1 m/s 5 MPa; 1 m/s Example 1 0.59 0.87 0.32 0.84 CompEx 1 0.91 1.62 0.33 1.98

(33) It is apparent from these tests too that the components made from the compositions according to the invention are advantageous over the prior art. More particularly, these tests show the advantageous use of SiO.sub.2 particles in tribological applications. In these tests, this is manifested particularly at high load pressure or high speed.

(34) TABLE-US-00009 TABLE 5a Wear rates, block-on-ring, as a function of the quotient of pressure load and speed (p/v [MPa * s/m]) Wear rate [10.sup.6 mm.sup.3/Nm].sup.1 Ratio 1 MPa: 2 m/s 1 MPa: 4 m/s 3 MPa: 2 m/s 4 MPa: 2 m/s Example 1 0.9 0.6 0.3 0.3 CompEx 1 1.5 3.1 2.8 2.2

(35) TABLE-US-00010 TABLE 5b Coefficients of friction, block-on-ring, as a function of the quotient of pressure load and speed (p/v [MPa * s/m]) Coefficient of friction Ratio 1 MPa: 2 m/s 1 MPa: 4 m/s 3 MPa: 2 m/s 4 MPa: 2 m/s Example 1 0.27 0.18 0.12 0.09 CompEx 1 0.28 0.25 0.31 0.17

(36) The wear rates and coefficients of friction are lower across the board than those of the prior art. This likewise clearly shows the advantageous effect of the addition of SiO.sub.2 particles in the polymer component of a tribological system.