Weather resistant polyoxymethylene compositions

Abstract

The present invention relates to a composition comprising a) at least one polyoxymethylene (A) having terminal OH-groups of more than 15 mmol/kg, b) at least one coupling agent (B), c) one or more hindered amine light stabilizer (C) having a molecular weight ranging from 500 to 1000 g/mol, and d) optionally at least one reinforcing fiber (D).

Claims

1. A composition comprising a) at least one polyoxymethylene (A) having terminal OH-groups of more than 20 mmol/kg, the at least one polyoxymethylene being present in the composition in an amount ranging from 55 wt. % up to 95 wt. %, b) at least one coupling agent (B) comprising a polyisocyanate, c) one or more hindered amine light stabilizer(s) (C) having a molecular weight ranging from 500 to 1000 g/mol, and d) optionally at least one reinforcing fiber (D).

2. A composition according to claim 1, wherein at least 50%, of the terminal groups of the at least one polyoxymethylene (A) are hydroxyl groups.

3. A composition according to claim 1, wherein the at least one coupling agent (B) is an organic diisocyanate.

4. A molding composition according to claim 1, wherein the at least one polyoxymethylene (A) has a MVR ranging from 20 to 100 cm.sup.3/10 min determined according to ISO 1133 at 190 C. and 2.16 kg.

5. A composition according to claim 1, wherein the at least one polyoxymethylene (A) has a content of terminal hydroxyl groups of at least 40 mmol/kg.

6. A composition according to claim 1, wherein the one or more hindered amine light stabilizers (C) has an antioxidant moiety.

7. A composition according to claim 1, wherein the one or more hindered amine light stabilizers (C) has two or more sterically hindered amine groups.

8. A composition according to claim 1, wherein the one or more hindered amine light stabilizers (C) comprises at least one tertiary amine moiety.

9. A composition according to claim 1, wherein the one or more hindered amine light stabilizers (C) has a melting point ranging from 110 to 200 C.

10. A composition according to claim 1, wherein the one or more hindered amine light stabilizers (C) comprises a di-tert-butyl phenol moiety.

11. A composition according to claim 1, wherein the one or more hindered amine light stabilizers (C) is Bis(1,2,2,6,6-penta methyl-4-piperidinyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate.

12. Method for producing a molding composition comprising melt mixing the composition as defined in claim 1.

13. Molded article obtained by molding a composition according to claim 1.

14. A composition according to claim 1, wherein the composition contains the at least one reinforcing fiber.

15. A composition according to claim 14, wherein the at least one reinforcing fiber comprises glass fibers, the glass fibers provided with a sizing, the sizing comprising a silane, the at least one reinforcing fiber being present in the composition in an amount from about 7% by weight to about 45% by weight.

16. A composition comprising a) a polyoxymethylene polymer having terminal OH-groups of more than 15 mmol/kg, the polyoxymethylene polymer being present in the composition in an amount from about 55 wt % to about 95 wt %; b) a coupling agent comprising a polyisocyanate; c) a hindered amine light stabilizer having a molecular weight ranging from 500 to 1,000 g/mol, the hinder amine light stabilizer comprising Bis(1,2,2,6,6-penta methyl-4-piperidinyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate; and d) glass fibers being present in the composition in an amount from about 5% by weight to about 50% by weight, the glass fibers including a sizing, the sizing comprising a silane.

Description

EXAMPLES

(1) The following components were used in the Examples of Table 1: POM 0: MVR 8 cm.sup.3/10 min; Polyoxymethylene with a content of 3.4 wt.-% dioxolane comonomer; portion of terminal OH groups: 20-25 mmol/kg; melting point 165 C. POM 1: MVR 39 cm.sup.3/10 min.; polyoxymethylene with a content of 3.4 wt. % dioxolane comonomer; portion of terminal OH groups: 54-80 mmol/kg; melting point 165 C. B: Methylenediphenyl-4,4-diisocyanate (MDI) C: reinforcing fiber (NEG ECS 03 T-651H); sized glass fiber D: additives (antioxidants, stabilizers, nucleating agents) D1: Tinuvin 144 from BASF (light stabilizer of the hindered amine class), MW 685 g/mol

(2) All components beside the glass fiber were mixed together. For the compounding a ZSK 25MC, (Werner&Pfleiderer, Germany) was used (zone temperature 190 C., melt temperature about 210 C.). The glass fiber was added using a downstream feeding unit at a suitable position. The screw configuration with kneading elements was chosen so that effective thorough mixing of the components took place during the reactive extrusion as well as an optimal glass fiber length was obtained.

(3) The testing of the prepared molding compositions was performed according to the following standards:

(4) MVR (190 C.; 5 kg): ISO 1133;

(5) Charpy notched impact strength: determined at 23 C. according to ISO 179-1/1eA(CNI);

(6) Elongation at break, stress at break and tensile modulus have been determined according to ISO 527;

(7) Portion of terminal OH groups in POM has been determined as described in K. Kawaguchi, E. Masuda, Y. Tajima, Journal of Applied Polymer Science, Vol. 107, 667-673 (2008).

(8) Melting point of polyoxymethylene (POM) has been determined with Differential Scanning calorimetry (DSC); heating rate 10 K/min according to ISO 11357-1, -2, -3.

(9) Flow properties were measured using the length of a spiral injection moulded under defined conditions (melt temperature: 205 C., tool temperature: 90 C., coil thickness; 2 mm, injection pressure: 800 bar/1000 bar/1200 bar).

(10) Weatherability Testing:

(11) The test plaques of the resin formulations were exposed to ultraviolet light and heat in a Xenon arc weatherometer, operated to automotive test procedure SAE J 1960. The primary conditions of the test are as follows:

(12) TABLE-US-00001 Light Dark Cycle Cycle Irradiance [W/m.sup.2] 0.55 Black Panel Temperature [ C.] 70 38 Relative Humidity [%] 50 95 Cycle Time [h] 40 Minutes of Light with no spray; 20 Minutes of Light with front specimen spray; 60 Minutes of Light with no spray; 60 Minutes of Dark with back specimen spray.

(13) The Xenon arc weatherometer is of the water-cooled, controlled irradiance type. Amount of exposure is measured in terms of the total irradiation the test plaques receive, expressed in kilojoules per square meter. The degree of color change is determined by instrumentally measuring the color of the exposed specimens versus the unexposed specimens. The degree of color change is quantified as the total color difference (Delta E), calculated for the illuminant, expressed in CIELab units, in accordance with ASTM D-224. Samples are measured at various increments of irradiation accumulated by the test plaques.

(14) TABLE-US-00002 TABLE 1 Molding compositions A B C D D1 % by % by % by % by % by Example Type weight weight weight weight weight 1 (inventive) POM 1 73.59 0.5 25 0.81 0.1 2 (comparative) POM 1 74.19 0 25 0.81 0 3 (comparative) POM 0 73.69 0.5 25 0.81 0 4 (comparative) POM 0 74.19 0 25 0.81 0

(15) TABLE-US-00003 TABLE 2 Mechanical properties of molding compositions Example 1 2 3 4 MVR (190 C./5 kg) 16.6 26.6 4.1 6.2 Tensile Modulus [MPa] 9500 9300 9350 9100 Stress at break (5 mm/min.) 158 126 150 130 [MPa] Elongation at break 3.0 2.1 3.3 2.5 (5 mm/min.)[%] Notched Charpy Charpy 11.2 7.8 12.1 8 Impact Strength [kJ/m.sup.2] Impact Strength [kJ/m.sup.2] 66 39 67 47 Flow path length [mm] 420/ 480/ 240/ 270/ 800 bar/1000 bar/1200 bar 490/490 560/630 280/330 310/360

(16) TABLE-US-00004 TABLE 3 Molding compositions A B C D E % by % by % by % by % by Examples weight weight weight type weight weight 5 (comparative) 90.24 0 9.76 0 6 89.41 0.4 9.76 D1 0.4 0.03 7 (comparative) 89.41 0.4 9.76 D2 0.4 0.03 8 (comparative) 89.41 0.4 9.76 D3 0.4 0.03

(17) The following components are used in Table 3: A: Molding composition from Example 3 B: Tinuvin 234 from BASF (ultraviolet light absorber) C: Color concentrate based on POM, containing 20, 8% Elftex TP, 1,13% additives (E) D1: Tinuvin 144 from BASF (light stabilizer of the hindered amine class), MW 685 g/mol D2: Tinuvin 770 from BASF (light stabilizer of the hindered amine class), MW 481 g/mol D3: Hostavin N30 (light stabilizer of the hindered amine class), MW>1500 g/mol E: additives (antioxidants, nucleating agents)

(18) TABLE-US-00005 TABLE 4 UV performance of molding composition after weatherability testing according to SAE J 1960, 2500 kJ/m.sup.2, washed Examples 5 6 7 8 (comparative) (inventive) (comparative) (comparative) DL* 1.37 1.04 1.07 1.45 Da* 0.08 0.06 0.12 0.06 Db* 0.13 0.48 0.72 0.35 DE* 1.38 1.15 1.29 1.50

(19) TABLE-US-00006 TABLE 5 Molding compositions A B C D E F G % by % by % by % by % by % by % by Examples weight weight weight weight type weight weight weight 9 72.0 24.7 0.48 1.73 E1 0.39 0.3 0.4 10 72.19 24.7 0.48 1.73 E1 0.2 0.3 0.4 11 72.79 24.7 0.48 1.73 0.3 12 72.39 24.7 0.48 1.73 0.3 0.4

(20) The following components are used in Table 5: A: POM 0, MVR 8 cm.sup.3/10 min; Polyoxymethylene with a content of 3.4 wt.-% dioxolane comonomer; portion of terminal OH groups: 20-25 mmol/kg; melting point: 165 C. B: reinforcing fiber (NEG ECS 03 T-651H); sized glass fiber C: Methylenediphenyl-4,4-diisocynate (MDI) D: Elftex TP, ex Cabot Corporation E1: Tinuvin 144 (light stabilizer of the hindered amine class), MW 685 g/mol F: additives (antioxidants, nucleating agents) G: Tinuvin 234 ex BASF (2-[2-hydroxy-3,5-di-(1,1-dimethylbenzyl)]-2H-benzotriazole)

(21) TABLE-US-00007 TABLE 6 Mechanical properties of molding compositions: Example 9 10 11 12 MVR (190 C./5 kg) 5.1 5.1 4.8 5.2 Tensile Modulus [MPa] 9250 9170 9310 9250 Stress at break (5 mm/min.) 138 138 137 138 [MPa] Elongation at break 2.8 2.9 2.9 3.0 (5 mm/min.)[%] Notched Charpy Charpy 10.4 9.8 10.1 10.1 Impact Strength [kJ/m.sup.2] Impact Strength [kJ/m.sup.2] 56.7 55.5 55.7 55.7