METHOD FOR PRODUCING THREE DIMENSIONAL FOAM ARTICLES

Abstract

A process for making a three dimensional foam article of non-uniform shape employs a two-stage nitrogen autoclave process and a pre-form which has a non-uniform cross- section in at least one dimension.

Claims

1-44. (canceled)

45. A process for making a three dimensional foam article of non-uniform shape comprising the steps of: (a) providing a pre-form comprising a polymer in a pressure vessel; (b) subjecting the pre-form to at least one inert gas at a pressure higher than atmospheric in order to drive gas into the pre-form; (c) raising the temperature of the pre-form to or above its softening point, wherein steps (b) and (c) can take place in any order or simultaneously; (d) reducing the pressure to a pressure higher than atmospheric pressure but lower than the pressure of step (b) and then cooling the pre-form to below its softening point to result in a partially expanded article; (e) transferring said article to a second vessel and heating it to a temperature above its softening point under a pressure of inert gas or air; and (f) reducing the pressure whilst maintaining the temperature at or above the softening point of the polymer, in order to expand the partially expanded article to form a foamed article; wherein the cross-section of the polymer pre-form in at least one dimension is non-uniform.

46. The process as claimed in claim 45 wherein the polymer pre-form is cross-linked before step (a).

47. The process as claimed in claim 46 wherein the cross-linking is carried out by irradiation.

48. The process as claimed in claim 45 wherein the pre-form comprises one or more thermoplastic resins.

49. The polymer as claimed in claim 48 wherein one or more of the thermoplastic resins is a thermoplastic elastomer (TPE).

50. The process as claimed in claim 45 wherein the pre-form includes a coagent to modify the crosslinking behaviour of the polymer.

51. The process as claimed in claim 45 wherein the pre-form is injection moulded.

52. The process as claimed in claim 51 wherein the pre-form is injection moulded using an overmoulding, insert moulding, twin or multi-shot injection or co-injection process.

53. The process as claimed in claim 45 wherein the pre-form is compression moulded.

54. The process as claimed in claim 45 wherein the pre-form is produced using an additive manufacturing or 3D printing process.

55. The process as claimed in claim 45 wherein the pre-form is extruded or co-extruded.

56. The process as claimed in claim 45 wherein the pre-form is a 2.5D shape.

57. The process as claimed in claim 45 wherein the foamed article is a 2.5D shape.

58. The process as claimed in claim 45 wherein the polymer pre-form is a 3D shape.

59. The process as claimed in claim 45 wherein the foamed article is a 3D shape.

60. The process as claimed in any one of claims 45 to 59, additionally comprising the step of preparing the pre-form for step (a).

61. The process as claimed in claim 45, wherein the shape of the foamed article has substantially the same form as the shape of the pre-form.

62. The process as claimed in claim 45 wherein the foamed article has a density of less than 300 kg/m.sup.3.

63. The process as claimed in claim 45 wherein the foamed article is subjected to a secondary process to produce a second 3D shape.

64. The process as claimed in claim 63 wherein the secondary process is selected from a group consisting of a thermal process, thermoforming and compression moulding.

65. The process as claimed in claim 45 wherein the foamed article is a midsole for a shoe.

66. The process as claimed in claim 45 in which in step (b) the pressure is from 20 to 1000 bar.

67. The process as claimed in claim 45 wherein the cross-section of the polymer pre-form in at least two dimensions is non-uniform.

68. The process as claimed in claim 45 wherein the cross-section of the polymer pre-form in at least three dimensions is non-uniform.

69. A foamed article produced by the process as claimed in claim 45.

Description

EXAMPLES The following examples are illustrative of preferred embodiments of the invention only.

Example 1

[0038] A polyether block amide (PEBA) polymer, Pebax 5533 from Arkema, was compounded with an irradiation crosslinkable additive to produce a crosslinkable PEBA material. The crosslinkable PEBA material was then injection moulded into the form of a football boot sole plate using the standard injection moulding conditions recommended by the Pebax 5533 manufacturer. The injection moulded sole plate was then subjected to gamma irradiation in order to crosslink the PEBA material. After irradiation the injection moulding was slightly darker in colour but showed no obvious change in dimensions.

[0039] The crosslinked injection moulding was placed on a tray in a high pressure autoclave and subjected to an atmosphere of nitrogen gas at 400 bar and 165 C. until the polymer was fully saturated with the gas. The pressure was then reduced to 170 bar, to nucleate a cell structure, before the autoclave was cooled to ambient temperature. Once at ambient temperature the remaining pressure was released and the gas containing injection moulding was removed from the high pressure autoclave. At this stage, the injection moulding was noticeably lighter in colour, because of the nucleated cell structure, and showed a 4% increase in dimensions.

[0040] The partially expanded injection moulding was placed in a freezer at 40 C. overnight to minimise any gas loss prior to expansion. The following day the injection moulding was allowed to return to room temperature before being placed on a tray in a lower pressure autoclave. The injection moulding was then heated to a uniform temperature of 167 C., under a pressure of 14 bar of nitrogen, before the pressure was released to atmospheric pressure, allowing the moulding to expand to form the foamed part.

[0041] In spite of the large variations in the thickness of the injection moulding, the expansion of the football boot sole plate was essentially uniform in all directions. The linear expansion ratio was 2.350.15, which equates to a final foam density of 80 kg/m.sup.3.

Example 2

[0042] A polyether block amide (PEBA) polymer, Pebax 5533 from Arkema, was compounded with an irradiation crosslinkable additive to produce a crosslinkable PEBA material.

[0043] The crosslinkable PEBA material was then injection moulded into the form of 1/2.5 scale running shoe midsole pre-forms, left and right foot, using the standard injection moulding conditions recommended by the Pebax 5533 manufacturer. The 1/2.5 scale pre-form dimensions were calculated to give the required dimension of the expanded midsole at the target density of 70 kg/m.sup.3. The injection moulded pre-forms were then subjected to gamma irradiation in order to crosslink the PEBA material. After irradiation the injection mouldings were slightly darker in colour but showed no obvious change in dimensions.

[0044] The crosslinked injection mouldings were placed in pairs on a tray in a high pressure autoclave and subjected to an atmosphere of nitrogen gas at 270 bar and 165 C. until the polymer was fully saturated with the gas. The pressure was then reduced to 150 bar, to nucleate a cell structure, before the autoclave was cooled to ambient temperature. Once at ambient temperature the remaining pressure was released and the gas containing mouldings were removed from the high pressure autoclave. At this stage, the mouldings were noticeably lighter in colour, because of the nucleated cell structure. The mouldings had also flattened slightly and showed a small (<2%) increase in dimensions.

[0045] The partially expanded mouldings were placed in a freezer at 40 C. to minimise any gas loss prior to expansion. Prior to expansion, the injection mouldings were allowed to return to room temperature before being placed, in pairs, on a tray in a lower pressure autoclave. The pairs of mouldings were then heated to a uniform temperature of 167 C., under a pressure of 14 bar of nitrogen, before the pressure was released to atmospheric pressure, allowing the mouldings to expand to form the foamed midsoles.

[0046] The expansion of the running shoe midsoles was essentially uniform in all directions. The linear expansion ratio was 2.40.1, which equates to a final foam density of 73 kg/m.sup.3.

Comparative Example

[0047] Crosslinked PEBA running shoe midsole pre-forms were prepared as described in Example 2. As previously, the injection mouldings were slightly darker in colour after irradiation but showed no obvious change in dimensions. The crosslinked injection mouldings were placed in pairs on a tray in a high pressure autoclave and subjected to an atmosphere of nitrogen gas at 270 bar and 165 C. until the polymer was fully saturated with the gas. The pressure was then reduced to atmospheric pressure, to allow the mouldings to expand to form the foamed midsoles, and the autoclave was then cooled to ambient temperature. Once at ambient temperature the mouldings were removed from the high pressure autoclave.

[0048] Unlike in Example 2, the mouldings had not expanded to their full dimensions and had become distorted. However, the mouldings were noticeably lighter in colour, which indicates that some degree of nucleation and cell growth had occurred during the process. The linear expansion ratio was only 1.10.15, which equates to a final foam density of 700 kg/m.sup.3.

[0049] All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.

[0050] The disclosures in UK patent application number 1409248.0, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.