Process for improving the flexural toughness of moldings

Abstract

Poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof are used in molding materials comprising polyoxymethylene or a copolymer containing a majority of oxymethylene units, for improving the flexural toughness of moldings formed from the molding materials.

Claims

1. A process for improving the flexural toughness of moldings formed from a molding material comprising: incorporating poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof into the molding material; and forming a molding from the molding material, wherein the molding has increased elongation at break compared to a molding without the poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane, or mixture thereof; the molding material comprising: an oxymethylene polymer mixture comprising: (B1.1). from 10 to 90% by weight of a polyoxymethylene homopolymer or a copolymer containing a majority of oxymethylene units, with a weight-average molar mass (Mw) in the range from above 60,000 to 200,000 g/mol, and (B1.2). from 10 to 90% by weight of a copolymer containing a majority of oxymethylene units, with a weight-average molar mass (Mw) in the range of 10,000 to 60,000 g/mol; and 40 to 70% by volume of sinterable pulverant metal, sinterable pulverant metal alloy, sinterable pulverant ceramic powders or mixtures thereof, based on the molding material; wherein, the copolymer in B1.2 is a polyoxymethylene copolymer, at least 90% by weight of which, based on the copolymer, is derived from trioxane and 1,3-dioxepane as monomers and butylal as regulator, with a proportion of 1,3-dioxepane, based on the copolymer, in the range from 1 to 30% by weight, and a proportion of butylal, based on the copolymer, in the range from 0.01 to 2.5% by weight, the % by weight being based on the copolymer and the molecular weights are determined by gel permeation chromatography or size exclusion chromatography; and, if B1.1 is a copolymer containing a majority of oxymethylene units, the copolymer in B1.1 is a polyoxymethylene copolymer, at least 90% by weight of which, based on the copolymer, is derived from trioxane and 1,3-dioxepane as monomers and butylal as regulator, with a proportion of 1,3-dioxepane, based on the copolymer, in the range from 1 to 30% by weight, and a proportion of butylal, based on the copolymer, in the range from 0.01 to 2.5% by weight, the % by weight being based on the copolymer and the molecular weights are determined by gel permeation chromatography or size exclusion chromatography; and wherein the copolymer in B1.2 has a polydispersity Mw/Mn in the range from 3 to 5.

2. The process according to claim 1, wherein the molding has improved elongation at break compared to a molding without the poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane, or mixture thereof.

3. The process according to claim 1, wherein the poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof are employed in an amount, based on the sum of polyoxymethylene or a copolymer containing a majority of oxymethylene units and poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof, of from 1 to 16% by weight.

4. The process according to claim 1, wherein the poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof is poly-1,3-dioxepane having a weight-average molecular weight of from 10,000 to 150,000 g/mol.

5. The process according to claim 1, wherein the weight-average molar mass (M.sub.W) of the polyoxymethylene copolymer (B1.2) is from 30,000 to 60,000 g/mol and/or the number-average molar mass (M.sub.n) is from 5,000 to 18,000 g/mol.

6. The process according to claim 1, wherein at least 90% by weight of component B1.1, based on the polymer, derive from trioxane and 1,3-dioxepane as monomers, with a proportion of 1,3-dioxepane, based on the polymer, in the range from 1 to 5% by weight.

7. The process according to claim 1, wherein at least 90% by weight of component B1.2, based on the polymer, derive from trioxane and optionally 1,3-dioxepane as monomers, with a proportion of 1,3-dioxepane, based on the polymer, in the range from 2.7 to 30% by weight.

8. The process according to claim 1, wherein the molding material after incorporation comprises A.) from 40 to 70% by volume of the sinterable pulverant metal or metal alloy or ceramic or mixture thereof; B.) from 30 to 60% by volume of a binder comprising the mixture of: B1.) from 50 to 97% by weight of the mixture of B1.1 and B1.2, based on the total amount of the component B; B2.) from 2 to 35% by weight of one or more polyolefins, based on the total amount of component B; B3.) from 1 to 40% by weight of the poly-1,3-dioxolane, poly-1,3-dioxepane or polytetrahydrofurane or mixtures thereof, based on the total amount of component B, the sum of B1.), B2.) and B3.) adding up to 100% by weight.

9. The process according to claim 1, wherein the weight-average molar mass (M.sub.W) of the polyoxymethylene copolymer is from 40,000 to 50,000 g/mol and/or the number-average molar mass (M.sub.n) is from 8,000 to 16,000 g/mol.

10. The process according to claim 1, wherein the number-average molar mass (M.sub.n) of the polyoxymethylene copolymer is from 10,000 to 14,000 g/mol.

11. The process according to claim 5, wherein the M.sub.W/M.sub.n ratio of the polyoxymethylene copolymer is in the range from 3.5 to 4.5.

12. The process according to claim 1, wherein at least 90% by weight of component B1.1, based on the polymer, derive from trioxane and 1,3-dioxepane as monomers, with a proportion of 1,3-dioxepane, based on the polymer, in the range 2 to 3.5% by weight.

13. The process according to claim 1, wherein at least 90% by weight of component B1.1, based on the polymer, derive from trioxane and 1,3-dioxepane as monomers, with a proportion of 1,3-dioxepane, based on the polymer, in the range from 2.5 to 3% by weight.

14. The process according to claim 1, wherein at least 90% by weight of component B1.2, based on the polymer, derive from trioxane and 1,3-dioxepane as monomers, with a proportion of 1,3-dioxepane, based on the polymer, in the range from 2.8 to 20% by weight.

15. The process according to claim 1, wherein at least 90% by weight of component B1.2, based on the polymer, derive from trioxane and 1,3-dioxepane as monomers, with a proportion of 1,3-dioxepane, based on the polymer, in the range from 3 to 17% by weight.

16. The process according to claim 1, wherein the sinterable pulverant metal, sinterable pulverant metal alloy, sinterable pulverant ceramic powders, or mixture thereof is a stainless steel metal powder.

17. The process according to claim 16, wherein the stainless steel metal powder has a particle size distribution of D.sub.50 in the range from 10 to 15 m.

18. The process according to claim 1, wherein the poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixture thereof is poly-1,3-dioxepane or poly-1,3-dioxolane.

19. The process according to claim 18, wherein the poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixture thereof is poly 1-3-dioxepane.

20. The process according to claim 19, wherein the poly-1,3-dioxepane is present in an amount of 9.6-16% by weight, based on the molding material.

21. The process according to claim 20, wherein poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof is a stainless steel metal powder with a particle size distribution of D.sub.50 in the range from 10 to 15 m.

22. A process for improving the flexural toughness of moldings comprising providing a molding formed from molding materials comprising a mixture comprising from 10 to 90% by weight of a polyoxymethylene homo- or copolymer with a weight-average molar mass (M.sub.W) in the range from above 60,000 to 200,000 g/mol as component B1.1 and from 10 to 90% by weight of a polyoxymethylene copolymer with a weight average molar mass (M.sub.W) in the range from 10,000 to 60,000 g/mol, as component B1.2, comprising: incorporating poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane or mixtures thereof in the molding material; and forming a molding from the molding material; wherein the molding has increased elongation at break compared to moldings without the poly-1,3-dioxepane, poly-1,3-dioxolane, polytetrahydrofurane, or mixture thereof; wherein the molding material is filled with sinterable pulverant metal, metal alloy, ceramic powders, or mixtures thereof; wherein the component B1.1 has a polydispersity M.sub.w/M.sub.n in the range from 3 to 5.

23. The process according to claim 22, wherein the molding material after incorporation comprises A.) from 40 to 70% by volume of the sinterable pulverant metal or metal alloy or ceramic powder or mixtures thereof; B.) from 30 to 60% by volume of a binder comprising the mixture of: B1.) from 50 to 97% by weight of the mixture of B1.1 and B1.2, based on the total amount of the component B; B2.) from 2 to 35% by weight of one or more polyolefins, based on the total amount of component B; B3.) from 1 to 40% by weight of the poly-1,3-dioxolane, poly-1,3-dioxepane or polytetrahydrofurane or mixtures thereof, based on the total amount of component B, the sum of B1.), B2.) and B3.) adding up to 100% by weight.

24. A molding material comprising A.) from 40 to 70% by volume of a sinterable pulverant metal or a sinterable pulverant metal alloy or a sinterable pulverant ceramic or mixtures thereof; B.) from 30 to 60% by volume of a binder comprising the mixture of: B1.) from 50 to 97% by weight of a mixture, comprising from 10 to 90% by weight of a polyoxymethylene homo- or copolymer with a weight-average molar mass (M.sub.W) in the range from above 60,000 to 200,000 g/mol as component B1.1; and from 10 to 90% by weight of a polyoxymethylene copolymer with a weight average molar mass (M.sub.W) in the range from 10,000 to 60,000 g/mol, as component B1.2; based on the total amount of the component B; B2.) from 2 to 35% by weight of one or more polyolefins, based on the total amount of component B; B3.) from 1 to 40% by weight of poly-1,3-dioxolane, poly-1,3-dioxepane or polytetrahydrofurane or mixtures thereof, based on the total amount of component B, the sum of B1.), B2.) and B3.) adding up to 100% by weight; wherein component B1.1 has a polydispersity M.sub.w/M.sub.n in the range from 3 to 5.

Description

EXAMPLES

(1) Production of the POM Oligomers and Polymers

(2) Laboratory-scale polymerization was carried out in a process which simulates the circulatory tray process. The monomers and the regulator were heated to 80 C. in open iron or aluminum reactors, with magnetic stirring. The mixture here was a transparent liquid. At a juncture t=0, an initiator solution was injected, composed of HClO.sub.4 in butyldiglyme, having a proton concentration which is typically 0.05 ppm relative to the monomers, or correspondingly higher for the POM containing higher amounts of comonomer. When polymerization was successful, the mixture became cloudy within a short time (induction period typically in the region of a few seconds to one minute) and the polymer precipitated.

(3) Post-Treatment of Raw Poly(Oxymethylene)

(4) The raw poly(oxymethylene) is milled to a fine powder and sprayed with a 0.01 wt.-% Sodium-glycerophosphate and 0.05 wt.-% Sodiumtetraborate aqueous buffer solution.

(5) Viscosity Measurements

(6) Rotational rheology measurements were performed using a SR2 rotationrheometer from Rheometric Scientific. The plate dimensions were set at diameter of 25 mm and a plate-spacing of 0.8-1 mm. Measurements were performed at 190 C. and a time of 15 min. A frequency-sweep measurement was performed, and the complex viscosity at a frequency of 10 rad/s is recorded on the second sweep.

(7) Capillary rheology measurements were performed using a Gttfert-Rheograph 2003 equipped with a capillary length of 30 mm and radius of 0.5 mm. The measurement was performed at 190 C. and a shear frequency sweep from 57 to 115201 1/s was measured.

(8) Molar Mass Determination

(9) The molar masses of the polymers were determined via size-exclusion chromatography in an SEC apparatus. This SEC apparatus was composed of the following combination of separating columns: a preliminary column of length 5 cm and diameter 7.5 mm, a second linear column of length 30 cm and diameter 7.5 mm. The separating material in both columns was PL-HFIP gel from Polymer Laboratories. The detector used comprised a differential refractometer from Agilent G1362 A. A mixture composed of hexafluoroisopropanol with 0.05% of potassium trifluoroacetate was used as eluent. The flow rate was 0.5 ml/min, the column temperature being 40C. 60 microliters of a solution at a concentration of 1.5 g of specimen per liter of eluent were injected. This specimen solution had been filtered in advance through Millipor Millex GF (pore width 0.2 micrometers). Narrowly distributed PMMA standards from PSS (Mainz, Del.) with molar masses M from 505 to 2 740 000 g/mol were used for calibration.

(10) Three-Point Bending Test

(11) Unnotched charpy bars with dimensions (1048 mm) were injected after processing the buffered polymer on a DSM mini-extruder. The polymer was extruded twice for 2 min each using a screw-speed of 80 rpm. These bars used as test specimens to determine the flexural modulus as well as the stress and elongation at break in flexural tension were using an ISO 178:2010 test. The flex-rate was set at 2 mm/min. The tests were performed at room temperature (23 C.).

(12) Components Used in the Molding Material Compositions:

(13) High molecular weight (HMW) POM: This POM is produced with 0.35% by weight butylal content. The number average molecular weight is 23000 g/mol, the weight average molecular weight 94000 g/mol. The ratio M.sub.W/M.sub.n is 4.2, the viscosity at 10 rad/s is 200 Pa.Math.s and the MFI is 42 to 43 cm.sup.3/10 min. The proportion of butandiol formal comonomer was 2.7% by weight, based on the polymer. Initiator concentration was 0.05 ppm, based on the monomers.

(14) Oligomeric POM: the oligomeric POM has a butylal concentration of 4.5 wt-%, a butandiol formal content of 2.7 wt-% (with respect to the monomer concentration), using 0.05 ppm of catalyst. The number average molecular weight was 4700 g/mol, the weight average molecular weight 11000 g/mol. The ratio M.sub.W/M.sub.n was 3.8, the viscosity at 10 rad/s 0.1 Pa.Math.s.

(15) Intermediate molecular weight (IMW) POM: This POM is produced with 1 wt % butylal content, butandiol formal content a 20 wt % (with respect to the monomer concentration) and a 0.2 ppm catalyst concentration. The number average molecular weight is 12000 g/mol, the weight average molecular weight is 34000 g/mol. The ratio of M.sub.w/M.sub.n is 2.9, the viscosity at 10 rad/s is 3.6 Pa.Math.s.

(16) PolyBUFO: polybutandiol formal with weight-average molecular weight from 30 000 to 60 000 g/mol.

(17) Metal powder: stainless steel metal powder (stainless steel 17-4 PH with typical powder particle size distribution, D.sub.50 in the range from 10 to 15 m, D.sub.90<30 m).

(18) Different molding materials were prepared using high molecular weight (HMW) POM, oligomeric POM, intermediate molecular weight (IMW) POM and PolyBUFO.

(19) First Test Series

(20) Comparative example C1 uses only high molecular weight POM. Comparative example 2 uses a mixture of high molecular weight POM and oligomeric POM. Example 1, according to the present invention, uses high molecular weight POM, oligomeric POM and polyBUFO.

(21) The amounts in the different compositions are listed in the following Table 1.

(22) TABLE-US-00001 Example C1 C2 1 Component 1 High High MW POM High MW POM molecular weight (MW) POM Loading Component 100 60 50.4 1 (wt %) Component 2 PolyBUFO Oligomeric POM PolyBUFO Loading Component 40 9.6 2 (wt %) Component 3 Oligomeric POM Loading Component 40 3 (wt %)

(23) The compositions listed in Table 1 were used as a binder for preparing molding materials filled with metal powder (17-4 PH). The metal constitutes 91.27 wt-% of the total weight. The remaining weight/volume is that of the binder. The wt-% in Table 1 refers to the respective binder without added metal powder. The mixing of binder material a metal powder is performed in a kneading apparatus.

(24) Afterwards, unnotched sharpy bars as indicated above were prepared from the metal filled molding materials.

(25) The viscosity and the mechanical properties of the various molding materials are compared in the following Table 2.

(26) TABLE-US-00002 Example C1 C2 1 Viscosity measured at 82 69.4 72 11520 l/rad (Pa .Math. s) Flexural modulus 7571 3373 3804 (MPa) Elongation at break 0.33 0.15 0.5 (%)

(27) As it is evident from the results of Table 2, by including oligomeric POM to high molecular weight POM, the viscosity can be reduced to a significant extent, when compared to a composition containing high molecular weight POM, see the results of examples C2 and C1. When a combination of high molecular weight POM, oligomeric POM and polyBUFO is employed according to example 1, the viscosity remains nearly identical to that of comparative composition C2. The flexural modulus is, however, increased when compared to comparative example C2. The elongation at break is furthermore significantly increased when compared to comparative example C2.

(28) Examples C2 and 1 show that the addition of the poly (1,3-dioxepane) has not affected the stiffness much but the toughness is improved, since the gradient in the initial part of the stress-strain curve is similar but the area under the stress-strain curve has been distinctly increased in example 1.

(29) Thus, the results of Table 2 show that in a POM molding material having a suitable viscosity for injection-molding, the addition of polyBUFO (poly-1,3-dioxepane) leads to an improved flexural toughness, increasing the flexural modulus and increasing the elongation of break, without adversely affecting the viscosity.

(30) Second Test Series

(31) Further different compositions as shown in Table 3 were evaluated. As in the first test series, the mechanical properties of the metal filled (91.27 wt-%) molding materials were measured.

(32) TABLE-US-00003 TABLE 3 Conc. Conc. Conc. Comp. 1 Comp. 2 Comp. 3 Example Component 1 (wt %) Component 2 (wt %) Component 3 (wt %) 2 HMW POM 90.4 PolyBUFO 9.6 3 HMW POM 84.8 PolyBUFO 15.2 4 HMW POM 84 PolyBUFO 16 5 HMW POM 70 Oligomeric 30 POM 6 HWM POM 60 Oligomeric 40 POM 7 HMW POM 40.4 Oligomeric 40 PolyBUFO 9.6 POM 8 HWM POM 50 Oligomeric 40 PolyBUFO 10 POM 9 HWM POM 45 Oligomeric 40 PolyBUFO 15 POM 10 IMW POM 100 11 IMW POM 90 HMW POM 10 12 IMW POM 80 HMW POM 20 13 IMW POM 80 HMW POM 10 PolyBUFO 10 14 IMW POM 80 HMW POM 4 PolyBUFO 16

(33) Table 4 shows the results for these materials:

(34) TABLE-US-00004 TABLE 4 Flexural Flexural stress Elongation Viscosity at break at break Example at 115 1/rad (MPa) (%) 2 1641 12.93 4.43 3 1230 10.11 3.07 4 1346 10.05 3.27 5 826 18.47 0.17 6 1005 18.77 0.21 7 779 16.85 0.82 8 812 11.14 1.3 9 719 8.19 1.34 10 480 11 0.21 11 607 11.71 0.2 12 791 16.08 0.21 13 694 6.48 0.94 14 744 3.7 0.58

(35) By employing the PolyBUFO, the flexural elongation at break could be improved significantly, leading to an improved flexural toughness.