METHOD FOR PREPARING THERMOPLASTIC POLYURETHANE PELLETS

Abstract

The present invention relates to a method for manufacturing thermoplastic polyurethane pellets by means of reactive extrusion of: a long macrodiol with a molecular weight of 500 to 3000 g/mol; a diisocyanate; at least one chain extender comprising a dianhydrohexitol; and a polymerization catalyst. The invention also relates to the resulting thermoplastic polyurethane pellets.

Claims

1. A method for manufacturing thermoplastic polyurethane pellets by reactive extrusion, comprising: introducing, into an extruder, a macrodiol (a) of molar mass from 500 to 3000 g/mol, a diisocyanate (b), at least one chain extender (c) comprising a dianhydrohexitol and a polymerization catalyst (d), said compounds (a), (b), (c) and (d) being introduced into the extruder in liquid form; mixing the compounds (a), (b), (c) and (d) and polymerizing said mixture in the extruder; and extruding and cutting said polymerized mixture to form the thermoplastic polyurethane pellets.

2. The method as claimed in claim 1, wherein the ratio of the number of isocyanate functions to the number of hydroxyl functions is between 0.9 and 1.1, preferably between 0.95 and 1.05, more preferentially between 0.97 and 1.02 and even more preferentially equal to 1.

3. The method as claimed in claim 1, wherein the content by weight of rigid segments of the thermoplastic polyurethane is from 25% to 40%.

4. The method as claimed in claim 1, wherein the following are introduced into the extruder: from 60% to 75% by weight of long macrodiol (a); from 20% to 35% by weight of diisocyanate (b); and from 2% to 10% by weight of chain extender (c).

5. The method as claimed in claim 1, wherein the macrodiol (a) is chosen from polyether glycols, polyester glycols, polycarbonate glycols or mixtures thereof; the macrodiol (a) is preferably a polyether glycol.

6. The method as claimed in claim 1, wherein the dianhydrohexitol (c) is isosorbide.

7. The method as claimed in claim 1, wherein the reagents (a), (b), (c) and (d) are introduced simultaneously at the extruder feed end.

8. The method as claimed in claim 1, wherein the step of mixing and polymerizing is carried out at a temperature of between 200° C. and 250° C.

9. The method as claimed in claim 1, further comprising a step of drying the thermoplastic polyurethane pellets.

10. The method as claimed in claim 1, wherein an inert gas purge is carried out on the molten isosorbide before it is introduced into the extruder; an inert gas purge is preferably carried out on each of the reagents in the melt state.

11. A thermoplastic polyurethane pellet obtained by the method as defined in claim 1.

Description

EXAMPLES

[0039] Synthesis of the TPUs

[0040] The TPUs were produced by reactive extrusion starting from a long macrodiol, namely Terathane 1000 sold by Invista (polytetramethylene ether glycol, PTMEG, 1000 g/mol) or Bester 86 sold by Rohm and Haas (polyadipate, 1000 g/mol), from 4,4-diphenylmethane diisocyanate (MDI) and a chain extender, namely isosorbide for examples 1 to 4 according to the invention and 1,4-butanediol (BDO) for comparative examples 1 and 2. The proportions of each of the reagents expressed as weight percentage are indicated in table 1 below. Dibutyltin dilaurate (DBTDL) was used as catalyst at a concentration of 50 ppm.

TABLE-US-00001 TABLE 1 Comp. Comp. Ex. 1 Ex. 2 Ex. 1 Ex. 3 Ex. 4 Ex. 2 PTMEG 65 60 65 Polyadipate 65 60 65 MDI 28.1 30.8 30.05 28.1 30.8 30.05 BDO 4.95 4.95 Isosorbide 6.9 9.2 6.9 9.2

[0041] The various reagents were prepared in the following way before being introduced into the extruder. The macrodiol is kept stirred in a jacketed vessel regulated at 80° C. The MDI melted beforehand at 60° C. is also kept stirred in a jacketed vessel regulated at 80° C. The BDO is metered at room temperature. The isosorbide is melted and kept stirred in a jacketed vessel regulated at 65° C. For the isosorbide, three cycles of vacuum (approximately 400 mbar for 1 minute)/inert gas stream (1 minute at 1.5 bar) are carried out before maintaining the product under a stream of inert gas. The other products are degassed under inert gas stream and maintained under this stream during use. An input of inert gas is also introduced at the feed-end of the extruder with a permanent flow rate making it possible to prevent the introduction of oxygen into the extruder (flow rate=free volume of the extruder/minute).

[0042] The TPUs were synthesized in a twin-screw extruder with a 26 mm diameter and a length equal to 50 times the diameter (50 D). The extruder consists of ten zones of length 5 D comprising a first unheated feed section and nine independent heating sections. The die is also heated independently. The screw profile used is a profile commonly used by those skilled in the art for the synthesis of TPUs.

[0043] The macrodiol, the chain extender, the MDI and the DBTDL are introduced in liquid form at the feed-end of the extruder, the total flow rate being equal to 10 kg/h. The rotation speed is fixed at 250 rpm. The residence time of the mixture in the extruder is from 1 minute and 10 seconds to 2 minutes, depending on the reaction conditions employed, and the temperature profile varies between 200 and 250° C.

[0044] The TPU rod formed at the die outlet is cooled in water and cut into pellets. The TPUs synthesized are subsequently dried at 100° C. for 2 h.

[0045] Coloration of the TPUs Synthesized

[0046] Table 2 below summarizes the coloration of the TPUs synthesized.

[0047] The coloration of the TPUs is determined on the pellets using a Konica Minolta CM-2300d spectrophotometer. 20 grams of pellets are placed in the measuring crucible. The CIELAB (L*, a*, b*) values are measured 5 times. The values indicated in table 2 below represent the mean of these 5 measurements.

TABLE-US-00002 TABLE 2 Comp. Comp. Ex. 1 Ex. 2 Ex. 1 Ex. 3 Ex. 4 Ex. 2 Coloration L* 41.0 46.7 45.7 44.3 39.3 39.4 a −0.53 −0.89 −1.62 −1.05 −0.91 1.80 b 5.45 8.26 8.37 6.97 8.15 7.83

[0048] It should be noted that in the CIELAB system, the higher the L* value, the lighter and brighter the color measured. Moreover, neutral colors correspond to a* values (scale ranging from red for positive values to green for negative values) and b* values (scale ranging from yellow for positive values to blue for negative values) that typically meet the conditions −1.5<a*<1 and 0<b*<7. In particular, at a constant b* value, a color having a positive a* value, even weakly positive, appears less neutral than a color having a weak but negative a* value.

[0049] Thus, the TPUs of examples 1 and 3 have more neutral hues than those of the TPUs of comparative examples 1 and 2 having an identical content of rigid segments. Moreover, even with a higher content of rigid segments, the hue of the TPUs of examples 2 and 4 have hues comparable to those of the TPUs of comparative examples 1 and 2.

[0050] Mechanical Properties of the TPUs Synthesized

[0051] Table 3 below summarizes the mechanical properties of the TPUs synthesized.

[0052] The elongation at break (A%) is determined on a Lloyd machine fitted with a 10 kN sensor with a pull rate of 300 mm/min.

[0053] The Shore A hardness is measured according to standard ISO 868:2003 which consists in determining the driving in of a penetrator standardized in this field, by application of a given force.

[0054] The abrasion resistance is measured according to standard ISO 4649:2010 which consists in measuring the loss of volume of a sample after displacement of 40 linear meters on standardized abrasive paper.

TABLE-US-00003 TABLE 3 Comp. Ex. 1 Ex. 2 Ex. 1 A % (%) >400 >400 >400 Hardness (ShA) 79 87 82 Abrasion (mm.sup.3) 61 63 80

[0055] All three of the TPUs of examples 1 and 2 and of comparative example 1 have an equivalent hardness and a comparable elongation at break of greater than 400%, which is sufficient for most applications, especially in overmolding. On the other hand, the TPUs of examples 1 and 2 have a better abrasion resistance compared to the TPU of comparative example 1.