Method for producing expanded thermoplastic polymers with controlled density

Abstract

A method for producing expanded thermoplastic polymeric (eTP) material and tuning the density of the eTP during the process of producing said eTP wherein the density of the eTP material can be decreased by increasing the partial pressure of the at least one gas which is soluble in the TP material and/or by increasing the total pressure during the charging step.

Claims

1. A method for producing expanded thermoplastic polyurethane (eTPU) material from a non-expanded thermoplastic polyurethane (TPU) material, said method comprising at least following steps: determining a final density for the eTPU material before expanding the TPU material; placing the TPU material in an autoclave and closing the autoclave; heating the autoclave to a temperature between 150-185 C.; increasing internal pressure in the autoclave to a total pressure having a value in the range 50-250 bar by introducing at least one soluble gaseous fluid which has a solubility of >10 mg gaseous fluid/g TPU and at least one insoluble gaseous fluid which has solubility <0.0001 mg gaseous fluid/g TPU, wherein the at least one soluble gaseous fluid is introduced before introducing the at least one insoluble gaseous fluid (charging step); allowing the non-expanded TPU material to reach a saturation state (saturation step), maintaining an iso-thermal and iso-bar state during the saturation step for only about 5 minutes; decreasing the total pressure in the autoclave to a value in the range 0-20 bar such that the TPU material expands to form the eTPU material (expansion step) wherein during the charging step, the partial pressure of the at least one soluble gaseous fluid is in a range of 30 bar up to 100 bar and is 10 up to 90% of the total pressure, and wherein during the charging step, the partial pressure of the at least one soluble gaseous fluid and/or the total pressure are chosen based on the final density of the eTPU.

2. The method according to claim 1, wherein the non-expanded TPU material is in the form of pellets, sheets or any other shape.

3. The method according to claim 1, wherein the at least one soluble gaseous fluid is selected from CO.sub.2, H.sub.2S, acetone, methyl ethyl ketone (MEK), propane, butane and/or pentane, or any combination of these.

4. The method according to claim 1, wherein the at least one insoluble gaseous fluid is selected from N.sub.2, O.sub.2, H.sub.2, CH.sub.4, He, Chloro Fluoro Carbons (CFC), Hydro Chloro Fluoro Carbons (HCFC), Hydro Chloro Fluoro Olefins (HCFO), Hydro Fluoro Olefins (HFO), (cyclo)-alkanes or any combination of these.

5. The method according to claim 1, wherein an additional gas comprising a Hydro Chloro Fluoro Carbon, a Chloro Fluoro Carbon, a Hydro Chloro Fluoro Olefin, a Hydro Fluoro Olefin, a (cyclo)-alkane or a noble gas is introduced into the autoclave during the charging step.

6. The method according to claim 1, wherein the temperature within the autoclave is within the range 170-180 C.

7. The method according to claim 1, wherein the TPU material is in the form of pellets having an average diameter from 0.2 to 10 mm.

8. The method according to claim 1, wherein the step of allowing the TPU material to reach a saturation state is performed at controlled pressure and temperature within the autoclave until blowing agent saturated TPU material is achieved.

9. The method according to claim 1, wherein during the charging step the partial pressure of the soluble gaseous fluid is increased to 100 bar and the total pressure in the autoclave is in the range of 100-200 bar.

10. The method according to claim 1, wherein during the charging step the partial pressure of the soluble gaseous fluid is increased to a range of 75-100 bar and the total pressure in the autoclave is in the range of 100-150 bar.

11. The method according to claim 1, wherein during the charging step the partial pressure of the soluble gaseous fluid is increased to a range of 0-100 bar and the total pressure in the autoclave is in the range of 100-200 bar.

Description

FIGURES

(1) FIG. 1 illustrates an autoclave set up and process steps to achieve expanded polymer particles according to the invention.

(2) FIG. 2 illustrates the effect of altering the total pressure in the autoclave wherein the partial pressure of CO.sub.2 is kept constant at 30 bar on the density of the achieved eTP material.

(3) FIG. 3 illustrates the effect of altering the partial pressure of CO.sub.2 in the autoclave wherein the total pressure is 130 bar on the density of the achieved eTP material.

EXAMPLES

(4) FIG. 1 illustrates an autoclave set up and process steps to achieve expanded polymer particles according to the invention.

(5) The process steps to achieve expanded polymer particles according to an embodiment of the invention are summarized below: Heat-up the autoclave (1) till the required process-temperature. Autoclave (1): electrically heated tubular steel container, V=1.7 liter, 75 mm diameter, horizontally positioned. Position the TPU-material (3) in the centre of the autoclave. Close-off the autoclave. Pressurize with a (compressed) gaseous fluid which is soluble in the TP material (5a) and then close-off the supply. Increase internal pressure by means of compressed gaseous fluid which has a low solubility or which is not soluble in the TP material (5b) till the desired total pressure is reached. Maintain an iso-thermal & iso-bar state for short period (e.g. 5 minutes) to allow the TP material to absorb the gaseous fluid which is soluble in the TP material (to obtain saturated TP material (4) with gaseous fluid (5a). Induce a fast pressure-drop to ambient pressure (for example max. 2 seconds) to produce expanded TP material (7). Open the autoclave. Remove the (foamed) beads out of the autoclave. The resulting (foamed) eTPU material is left to stabilise under ambient temperature- & pressure-conditions prior to the density-measurement.

(6) Example 1 Illustrating the Effect of Altering the Total Pressure

(7) FIG. 2 illustrates the effect of altering the total pressure in the autoclave wherein the partial pressure of CO.sub.2 is kept constant at 30 bar on the density of the achieved eTP material.

(8) The process steps to achieve expanded polymer particles according to example 1 are as follows: Heat-up the pressure-vessel (1) till the required temperature (170-180-185 C.). Position 30 g Avalon A87P 6001 DP UV (dried) in the centre of the autoclave. Close-off the autoclave. Pressurize till 30 bar with (compressed) CO.sub.2, followed by the close-off of the CO.sub.2-supply. Increase internal pressure by means of compressed N.sub.2 till the desired total pressure is reached (70-130 bar). Maintain an iso-thermal & iso-bar state for 5 minutes. Induce a fast pressure-drop to ambient pressure (max. 2 seconds). Open the autoclave. Remove the (blown) beads out of the autoclave. The resulting eTPU material (beads) are left to stabilise under ambient temperature-& pressure-conditions prior to the density-measurement.

(9) An increase in total pressure from 70 bar towards 130 bar significantly reduces the density of the final eTPU bead. Apart from total (gas) pressure, final bead-density is also influenced by the temperature used during the pressurisation process. The usable temperature-range depends on the composition of the TP, and at all times needs to be lower than the melting temperature of the TP. Typically a higher process-temperature contributes to a lower bead-density, up to the point that the TP starts to melt and starts to lose its ability to retain the gas inside during the decrease in pressure (expansion-step).

(10) Example 2 Illustrating Effect of Altering the Partial Pressure of CO.sub.2 in the Autoclave

(11) FIG. 3 illustrates the effect of altering the partial pressure of CO.sub.2 in the autoclave wherein the total pressure is 130 bar on the density of the achieved eTP material.

(12) The process steps to achieve expanded polymer particles according to example 2 are as follows: Heat-up the pressure-vessel till the required temperature (170-180-185 C.). Position 30 g Avalon A87P 6001 DP UV (dried) in the centre of the autoclave. Close-off the autoclave. Pressurize till the desired CO.sub.2 partial pressure (0-50 bar) using (compressed) CO.sub.2, followed by the close-off of the CO.sub.2-supply. Increase internal pressure by means of compressed N.sub.2 till the total pressure of 130 bar is reached. Maintain an iso-thermal & iso-bar state for 5 minutes. Induce a fast pressure-drop to ambient pressure (max. 2 s). Open the autoclave. Remove the (blown) beads out of the autoclave. The resulting eTPU material (beads) are left to stabilise under ambient temperature-& pressure-conditions prior to the density-measurement.

(13) While keeping the combined pressures of soluble and insoluble fluids constant (at 130 bar), but altering the level (partial-pressure) of the soluble fluid, one can see that the final density of the eTPU (bead) decreases when the level of the soluble fluid increases. Since the changes of partial gas-pressure of the soluble fluid on density are much more linear (FIG. 3) than changes in the total pressure (while keeping the temperature constant), this is a more accurate way to control the final density of the eTP.

(14) Controlling the density of the eTP by means of (partial) pressure-control is preferred over temperature-control, since it can be done more homogeneous & instantaneous.