POLYMER COMPOSITION BASED ON POLY(METH)ACRYLIMIDE FOR TRIBOLOGICAL APPLICATIONS

Abstract

Polymer compositions are made based on imidated polyalkyl (meth)acrylate, especially imidated polymethyl methacrylate. The polymer composition includes a polymer matrix A and at least one tribological additive B, especially selected from organic or inorganic solid hardening particles. The polymer compositions and formed articles made thereof exhibit low friction coefficients and high wear resistance even at elevated temperatures. They can advantageously be used in tribological application, in replacement of high-performance materials, such as polyether ether ketone (PEEK).

Claims

1. A polymer composition for tribological applications, comprising: a polymer matrix A, which comprises at least one poly(meth)acrylimide, and at least one tribological additive B, selected from the group consisting of organic particulate fillers B1, inorganic particulate fillers B2 and reinforcing fibers B3, wherein the at least one poly(meth)acrylimide comprises: i) from 1 to 95 wt.-%, based on a total weight of the poly(meth)acrylimide, units of formula I ##STR00006## ii) from 1 to 70 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula II ##STR00007## iii) from 1 to 20 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula III ##STR00008## and iv) from 0 to 15 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula IV ##STR00009## wherein R.sup.1 and R.sup.2 are, independently from each other, hydrogen or C.sub.1-C.sub.6 alkyl; R.sup.3 is hydrogen, C.sub.1-C.sub.18-alkyl, C.sub.5-C.sub.8-cycloalkyl, C.sub.6-C.sub.10-aryl, or C.sub.6-C.sub.10-aryl-C.sub.1-C.sub.4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of C.sub.1-C.sub.4-alkyl, C.sub.1-C.sub.4-alkoxy and halogen; and R.sup.4 is C.sub.1-C.sub.18-alkyl, C.sub.5-C.sub.8-cycloalkyl, C.sub.6-C.sub.10-aryl, or C.sub.6-C.sub.10-aryl-C.sub.1-C.sub.4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of C.sub.1-C.sub.4-alkyl, C.sub.1-C.sub.4-alkoxy and halogen.

2. The polymer composition according to claim 1, comprising, in each case based on a total weight of the polymer composition: from 50 to 97 wt.-%, of the polymer matrix A; from 3 to 30 wt.-%, of the at least one tribological additive B; from 0 to 5 wt.-%, of at least one lubricant C; from 0 to 20 wt.-%, of one or more further component D.

3. The polymer composition according to claim 1, wherein the polymer matrix A comprises at least 50 wt.-%, based on the polymer matrix A, of the at least one poly(meth)acrylimide.

4. The polymer composition according to claim 1, wherein the at least one poly(meth)acrylimide comprises at least 5 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula (I) ##STR00010## in which R.sup.1 and R.sup.2 are, independently from each other, hydrogen or C.sub.1-C.sub.6 alkyl; and R.sup.3 is hydrogen, C.sub.1-C.sub.18-alkyl, C.sub.5-C.sub.8-cycloalkyl, C.sub.6-C.sub.10-aryl, or C.sub.6-C.sub.10-aryl-C.sub.1-C.sub.4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of C.sub.1-C.sub.4-alkyl, C.sub.1-C.sub.4-alkoxy and halogen.

5. The polymer composition according to claim 1, wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are methyl.

6. The polymer composition according to claim 1, wherein the at least one tribological additive B comprises at least one organic particulate filler B1, wherein the organic particulate filler B1 is selected from the group consisting of polymer particles having a L/D ratio in a range from 1 to 3 and a particle diameter in a range of 1 to 100 ?m, and wherein the polymer particles essentially consist of a polymer selected from the group consisting of polyphenylene sulfone, polytetrafluoroethylene, perfluoroalkoxy alkane polymers, tetrafluoroethylene/ethylene copolymers; and high molecular weight polyolefins.

7. The polymer composition according to claim 1, wherein the tribological additive B is selected from the group consisting of polytetrafluoroethylene particles, graphite, boron nitride, molybdenum disulfide, tungsten disulfide, silicon nitride, silicon carbide, boron carbide, calcium carbonate, titanium dioxide, silicon dioxide, cerium dioxide, aluminum oxide, copper particles, silver particles, carbon fibers, glass fibers, and aramid fibers.

8. The polymer composition according to claim 1, wherein the polymer composition comprises from 0.5 to 5 wt.-%, based on the total polymer composition, at least one liquid lubricant C, selected from silicon oils.

9. The polymer composition according to claim 1, wherein the polymer composition comprises at least one further component D, selected from the group consisting of crosslinking agents, thermal stabilizers, UV absorbers, and impact modifiers.

10. The polymer composition according to claim 1, wherein the polymer matrix A exhibits a Vicat softening temperature of at least 130? C. determined according to ISO 306 (B50).

11. A process for producing a polymer composition according to claim 1, comprising: mixing the polymer matrix A and the at least one tribological additive B, and optionally further components C and/or D.

12. A formed article made of a polymer composition according to claim 1.

13. The formed article according to claim 12, wherein the formed article is utilized in or in form of pump casings, pump parts, transmission control equipment, chain guides, sliding bearings, ball bearings, sliding shoes, gear wheels, gear drives, rolls, pistons, piston rings, piston rods, clutches, brakes, seals, membranes, fittings, bushings, casings, valve casings, or valve parts.

14. A process for producing a formed article from the polymer composition according to claim 1 via injection molding or extrusion.

15. The process for producing a formed article according to claim 14, comprising: at least one step of crosslinking by exposing the polymer composition to radiation selected from the group consisting of beta radiation, gamma radiation, electron beam, x-ray radiation, and UV/Vis radiation.

16. The polymer composition according to claim 1, wherein the at least one poly(meth)acrylimide comprises: i) from 20 to 92 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula I; ii) from 2 to 60 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula II; iii) from 1 to 12 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula III; and iv) from 0 to 10 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula IV.

17. The polymer composition according to claim 1, comprising, in each case based on a total weight of the polymer composition: from 60 to 95 wt.-%, of the polymer matrix A; from 5 to 25 wt.-%, of the at least one tribological additive B; from 0 to 3 wt.-%, of at least one lubricant C; from 0 to 10 wt.-%, of one or more further component D.

18. The polymer composition according to claim 1, wherein the at least one poly(meth)acrylimide comprises at least 15 wt.-%, based on the total weight of the poly(meth)acrylimide, units of formula (I), in which R.sup.1 and R.sup.2 are, independently from each other, hydrogen or methyl.

Description

DESCRIPTION OF THE FIGURE

[0144] FIG. 1 shows the preparation of test pins from a standard tension rod (left picture) and the tribological testing using a pin-on-disc apparatus (right picture).

[0145] The invention is illustrated in more detail hereinafter using experimental examples and if appropriate comparative examples.

EXAMPLES

a. Components of Polymer Compositions

[0146] A1: Polymethyl methacrylimide (PMMI), prepared by reaction of polymethylmethacrylate with methylamine via reactive extrusion, wherein the polymer-analogous reaction, specifically the imidation, was carried out on a reactive extrusion system consisting of a reactive extruder with a highly effective mixing part and a vented extruder with two venting zones and attached vacuum lines. 10 kg per hour of a PMMA molding material were introduced into the reactive extruder. In the first part of the mixing zone, there is a feed point for liquids. 3000 g of methylamine per h were fed into this feed point as the reaction medium. The mean reaction time was 5 minutes at a temperature of 250? C. On completion of the reaction, the reaction mixture was decompressed in the vented extruder, the gaseous and volatile fractions were removed, and finally extrudates were made, cooled and cut to granules. The obtained PMMI A1 comprises about 90 wt.-% of unit according to formula I with R.sup.1, R.sup.2 and R.sup.3 being methyl. The PMMI A1 exhibits a melt volume rate (MVR) of about 1.7 cm.sup.3/10 min, determined according to ISO 1133, at 260? C. using 10 kg load, and a Vicat softening temperature of about 170? C., determined according to ISO 306 (B/50). [0147] A2 Polyetheretherketone PEEK, extruded rod made of Victrex? PEEK 450G (comparative material) [0148] B1: POLYMISTR? F5A, Solvay, polytetrafluoroethylene (PTFE) as tribological additive B1. [0149] C1: ACCUREL? Si755, from Evonik, 50 wt-% silicone oil based in polyamide PA6 as lubricant C.

b. Preparation of Polymer Compositions and Test Specimens

[0150] The compounding of the polymer compositions as given in table 1 was carried out on a co-rotating twin screw extruder (ZSK30) at a temperature in the range of 220? C. to 285? C. and a screw rotational speed of about 200 min.sup.?1. The raw materials were dried before extrusion so that a water content of less than 0.1 wt.-% was obtained. It was found that the melt is foaming at the nozzle outlet without pre-drying. A cooling metal plate was used for pelletizing. The pelletizer was cooled with compressed air.

TABLE-US-00001 TABLE 1 PMMI polymer compositions and comparative material A1 A2 B1 C1 Ex wt.-% wt.-% wt.-% wt.-% 1* 100 0 0 2 80 20 0 3 78 20 2 4 90 10 0 5 88 10 2 9* 100 *Comparative example

[0151] The polymer granulates obtained according to examples 1 to 5 were formed into tension rods according to DIN EN ISO 527, Typ 1A via injection molding. The injection molding was carried out using a Battenfeld 350 CD injection molding machine (melt temperature 285? C./mold temperature 120? C.). Talcum was added (about 10 g talcum to 3000 g polymer granulate) to the polymer granulate, if necessary.

c. Radiation Cross-Linking

[0152] The PMMI materials similar to examples 2 and 3 were additionally equipped with 10 wt % of an additive for radiation crosslinking. Said radiation crosslinking additive was tri-methylol-propane tri-methacrylate (TMPTMA) with low-density polyethylene (LDPE) as carrier material (35 wt % TMPTMA, 65 wt % LDPE).

[0153] Polymer granulates and tension rods of the following PMMI materials (summarized in Table 1A) were prepared as described above. These tension rods were exposed to electron beam irradiation, wherein the total radiation dose was 100 kGy, divided into three doses with 33.3 kGy each (Examples 7 and 8).

TABLE-US-00002 TABLE 1A PMMI polymer compositions for radiation TMPTMA A1 B1 C1 in LDPE Ex wt.-% wt.-% wt.-% wt.-% 7 72 18 0 10 8 70.5 17.5 2 10

d. Testing and Results

[0154] The tribological properties were evaluated using a pin-on-disc test setting following DIN ISO 7148-2 (2014), as illustrated in FIG. 1. The pin-on-disc tribological tests were carried out using a disc (outer diameter=110 mm, inner diameter=75 mm, thickness=7 mm) of hardened steel (100 Cr6) as sliding partner, wherein the following parameters were utilized: contact pressure p=4 N/mm.sup.2; sliding speed v=0.5 m/s; an average surface roughness of sliding partner (disc) R.sub.z=1.5 ?m. Test pins (4 mm?4 mm?7 mm) were prepared from the tension rods according to DIN EN ISO 527, Typ 1A (see FIG. 1). Test pins (4 mm?4 mm?7 mm) of PEEK comparative material A2 were milled out of the rod.

[0155] In the first test setting the tribological tests were carried out at ambient temperature of 23? C. without adjusting temperature of steel disc (table 2). In the second test setting the temperature of the steel disc was adjusted to 100? C. or 150? C. (table 3). The tribological pin-on-disc testing was carried out without external lubrication (dry).

[0156] The results for comparative materials polyethylene (PE), polyamide (PA), and polyoxymethylene (POM) were taken from literature, wherein similar pin-on-disc test setting were described. Further, in comparative example 9 commercially available tribological polyetheretherketone PEEK (material A2) was used.

[0157] Typical indicators for assessment of tribological properties are the coefficient of friction u and the wear coefficient k (also referred to as k-factor) The coefficient of friction u also represents a value for the fraction heat dissipated in the system. The wear coefficient k indicates the material loss and represents the material loss depending on glide path and contact pressure. Further, the friction-induced temperature rise was measured and given as TFR.

[0158] The coefficient of friction ? (also referred to as sliding friction coefficient or friction coefficient) is dimensionless and given as ratio of friction force F.sub.R to normal force F.sub.N:

[00001]$?=F_R/F_N$

[0159] The wear coefficient (k-factor) k in mm.sup.3/(N m) is given as:

[00002]$k=?I/\left(p.Math.v.Math.?t\right)$ [0160] with [0161] ?l linear wear in mm observed in the time interval ?t in s [0162] p contact pressure in N/mm.sup.2 [0163] v sliding speed in m/s

[0164] The test results were summarized in following tables 2 and 3, wherein the standard deviation ? of the measured values are given.

TABLE-US-00003 TABLE 2 Tribological results (pin disc system, p = 4 N/mm.sup.2, v = 0.5 m/s, R.sub.z = 1.5 ?m, ambient temperature, 23? C.) T.sub.FR ? T.sub.FR k ?.sub.k ? ?? Material ? C. 10.sup.?6 mm.sup.3/(N m) Ex. 1* 70 9 6373 1315 0.40 0.021 Ex. 2 36 3 3.50 0.37 0.19 0.004 Ex. 3 31 2 66.2 11.7 0.22 0.011 Ex. 7*** 38 3 12.1 6.7 0.04 0.007 Ex. 8*** 31 1 67.1 13.9 0.04 0.005 Ex. 9* (PEEK) 75 2 11.5 0.45 0.06 0.006 PE** n.a. n.a. 40 8 0.3 0.05 POM** n.a. n.a. 15 1 0.4 0.05 PA 66** n.a. n.a. 9.8 1.8 0.55 0.05 R.sub.z = 3.2 ?m *Comparative example **Comparative benchmark materials, wherein the results were taken from K?nkel, R., Auswahl und Optimierung von Kunststoffen f?r tribologisch beanspruchte Systeme, Dissertation FAU Erlangen, 2005. The values from pin-on-disc testing utilizing test conditions are similar as described above, differences are mentioned ***Subsequently subjected to electron beam irradiation for cross-linking (total dose = 100 kGy)

TABLE-US-00004 TABLE 3 Tribological results (pin disc system, p = 4 N/mm.sup.2, v = 0.5 m/s, R.sub.z = 1.5 ?m) T T.sub.FR ? T.sub.FR k ?k ? ?? Material ? C. ? C. 10.sup.?6 mm.sup.3/(N m) Ex. 1* 100 120 10 7750 340 0.47 0.02 Ex. 2 100 85 4 1.9 0.7 0.13 0.01 Ex. 3 100 85 6 0.6 0.4 0.15 0.01 Ex. 7*** 100 90 3 1.14 0.43 0.16 0.006 Ex. 8*** 100 82 3 1.04 0.30 0.16 0.015 Ex. 9* (PEEK) 100 108 4 17.1 1.5 0.41 0.015 Ex. 2 150 140 4 0.75 0.16 0.15 0.006 Ex. 3 150 139 9 1.07 0.26 0.16 0.025 Ex. 9* 150 179 8 40.3 6.7 0.41 0.021 POM** 80 n.a. n.a. 5.7 1.9 0.60 0.17 PA 66** 80 n.a. n.a. 8.6 2.7 0.70 0.15 R.sub.z = 3.2 ?m *Comparative example **Comparative benchmark materials, wherein the results were taken from literature. The values from pin-on-disc testing utilizing test conditions are similar as described above, differences are mentioned. Results for POM and PA were taken from K?nkel, R., Auswahl und Optimierung von Kunststoffen f?r tribologisch beanspruchte Systeme, Dissertation FAU Erlangen, 2005. ***Subsequently subjected to electron beam irradiation for cross-linking (total dose = 100 kGy)

[0165] It was found that the inventive polymer composition according to examples 2 (80 PMMI/20 PTFE) and 3 (78 PMMI/20 PTFE/2 ACCUREL? Si755) showed improved or similar performance than the comparative systems PE, PA, POM and even tested PEEK standard material (example 9) at ambient temperature (23? C.). Here specific wear rate <4.Math.10.sup.?6 mm.sup.3/(N m) and friction coefficient of ?0.2 were observed for the inventive material.

[0166] The tribological properties of inventive polymer compositions were very even more improved at elevated temperatures (100? C. or 150? C.). Here typical wear rates <1?2.Math.10.sup.?6 mm.sup.3/(N m) and fiction coefficients <0.15 were observed for the inventive polymer compositions, which are significantly lower than the values of the benchmark comparative systems and tested PEEK standard material (example 9).

[0167] The e-beam radiation results in improvement of friction coefficient ? (examples 7 and 8 compared to examples 2 and 3) at ambient temperature and improvement of wear rate k at elevated temperatures (example 7 compared to example 2).

[0168] Furthermore, mechanical properties were determined using 5 tension rods for each test, after condition at 23? C., 50% relative humidity: [0169] elongation at break, tensile modulus, and tensile strength (ultimate tensile strength or tensile strength at break), all according to ISO 527-1:2012 [0170] Charpy impact strength according to ISO 179, and [0171] Charpy notch impact strength according to ISO 179 1eA.

[0172] The results are summarized in table 4.

TABLE-US-00005 TABLE 4 Results of mechanical testing Tensile Elongation Tensile strength Charpy at break modulus at break Charpy notched Ex % MPa MPa kJ/m.sup.2 kJ/m.sup.2 1* 3.0 4000 80.0 20.0 2 2.6 3751 62.1 22.0 1.4 3 3.7 3557 46.9 15.0 1.7 4 2.7 3946 68.1 26.4 1.5 5 4.4 3832 55.0 20.2 1.5