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US-20260125531-A1 - Silane Crosslinked Ethylene/a-Olefin Block Copolymer Bead Foam

US20260125531A1US 20260125531 A1US20260125531 A1US 20260125531A1US-20260125531-A1

Abstract

The present disclosure provides a process. The process includes (i) crosslinking pellets composed of a silane-grafted ethylene/α-olefin multi-block copolymer (Si-g-OBC) to a gel content from 10% to 80% to form crosslinked Si-g-OBC pellets; and (ii) foaming the crosslinked Si-g-OBC pellets to form crosslinked Si-g-OBC foam beads having a gel content from 10% to 80%.

Inventors

  • Yunfeng Yang
  • halyang Yu
  • Jozef J.I Van Dun
  • Miguel Alberto De Jesus Pristo

Assignees

  • DOW GLOBAL TECHNOLOGIES LLC

Dates

Publication Date
20260507
Application Date
20260106

Claims (14)

  1. 1 . A process comprising: (i) crosslinking pellets composed of a silane-grafted ethylene/α-olefin multi-block copolymer (Si-g-OBC) to a gel content from 10% to 80% to form crosslinked Si-g-OBC pellets; (ii) foaming the crosslinked Si-g-OBC pellets to form crosslinked Si-g-OBC foam beads having a gel content from 10% to 80%; and a density from 0.120 g/cc to 0.130 g/cc.
  2. 2 . The process of claim 1 comprising immersing the pellets of Si-g-OBC in water; and crosslinking the Si-g-OBC pellets to a gel content from 10% to 80%.
  3. 3 . The process of claim 1 comprising soaking the pellets of Si-g-OBC with a dibutyl tin solution; and catalytically crosslinking the Si-g-OBC pellets to a gel content from 10% to 80%.
  4. 4 . The process of any of claims 1-3 comprising crosslinking the pellets of Si-g-OBC to the gel content from 10% to 80% before the foaming.
  5. 5 . The process of any of claims 1-4 wherein the foaming comprises contacting the pellets of crosslinked Si-g-OBC with a blowing agent under foaming conditions; and forming the crosslinked Si-g-OBC foam beads.
  6. 6 . The process of any of claims 1-5 comprising forming crosslinked Si-g-OBC foam beads having (i) a density from less than 0.200 g/cc; (ii) a melting temperature from 117° C. to 121.5° C.; and (iii) a heat of fusion, ΔH in J/g, from 63 to 65.
  7. 7 . The process of any of claims 1-6 comprising sintering the crosslinked Si-g-OBC foam beads; and forming a sintered foam article.
  8. 8 . The process of claim 7 comprising forming a sintered foam article having (i) a hardness from 40.0 to 41.0 measured according to Asker C; (ii) a density from 0.190 g/cc to 0.210 g/cc; and (iii) a dynamic recovery ratio, measured at 1 min, from 87.0% to 100%.
  9. 9 . A foam bead comprising: crosslinked silane-grafted ethylene/α-olefin multi-block copolymer having a gel content from 10% to 80%; and a density from 0.120 g/cc to 0.130 g/cc.
  10. 10 . The foam bead of claim 9 comprising (i) a melting temperature from 117° C. to 121.5° C.; and (ii) a heat of fusion, ΔH in J/g, from 63 to 65.
  11. 11 . A sintered foam article comprising; foam beads composed of crosslinked silane-grafted ethylene/α-olefin multi-block copolymer having a gel content from 10% to 80%; and a density from 0.120 g/cc to 0.130 g/cc.
  12. 12 . The sintered foam article of claim 11 comprising (i) a hardness from 40.0 to 41.0 measured according to Asker C; (ii) a density from 0.190 g/cc to 0.210 g/cc; and (iii) a dynamic recovery ratio, measured at 1 min, from 87.0% to 100%.
  13. 13 . The process of claim 1 wherein the silane-grafted ethylene/α-olefin multi-block copolymer has a melt index from 0.1 g/10 min to 1.0 g/10 min.
  14. 14 . The process of claim 1 wherein the silane-grafted ethylene/α-olefin multi-block copolymer comprises from 0.1 wt % to 1.0 wt % silane, based on the total weight of the silane-grafted ethylene/α-olefin multi-block copolymer.

Description

BACKGROUND The present disclosure relates to crosslinked ethylene-based polymer foams. Polyethylene foams are utilized in footwear components, such as midsole applications. Crosslinked ethylene-based polymers including ethylene vinyl acetate (EVA) copolymer and polyolefin elastomers have traditionally dominated the polyethylene foam market in footwear as they can easily be foamed with a chemical blowing agent. However, chemical blowing agents are known to produce unpleasant odors and contaminate molds. Such crosslinking chemical foaming process used in footwear industry is very labor intensive and thus alternative foaming technology with environmental and cost-saving process is pursued. Bead foaming technology, one type of physical foaming, is an alternative foaming method that enables automation. The advantages of bead foaming technology compared to chemical foaming include: no unpleasant odor, less contamination to molds, recyclability, and isotropic properties of parts. However, not all polymers are suitable for bead foaming technology. Crosslinked ethylene-based polymers to be used in bead foaming technology need to be of low density so they foam properly. Further, the polymers must remain stable at a high temperature, which is required to form a sintered foam structure, such as a foam midsole. The polymers also need to form a foam bead that does not shrink when subjected to a high temperature. Therefore, a crosslinked ethylene-based polymer composition that is of low density and remains stable at high temperatures is needed. The art recognizes the need for a crosslinked ethylene-based polymer composition that exhibits suitable density for foaming. The art also recognizes the need for a crosslinked ethylene-based polymer composition that forms a foam bead structure that does not shrink when subjected to a high temperature. SUMMARY The present disclosure provides a process. The process includes (i) crosslinking pellets composed of a silane-grafted ethylene/α-olefin multi-block copolymer (Si-g-OBC) to a gel content from 10% to 80% to form crosslinked Si-g-OBC pellets; and (ii) foaming the crosslinked Si-g-OBC pellets to form crosslinked Si-g-OBC foam beads having a gel content from 10% to 80%. The present disclosure also provides a foam bead formed from the present process. In an embodiment, the foam bead composed of crosslinked Si-g-OBC has a gel content of 10% to 80%; and the foam bead has a foam density of less than 0.200 g/cc. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 are photographs of cross-section of the sintered plaques of foamed beads for comparative samples and inventive examples. FIG. 2 provides Scanning Electron Microscope (SEM) images of cross-section views of sintered plaques of foam beads for comparative samples and inventive examples. FIG. 3 is a graph showing the recovery ratio of foam plaque thickness as a function of time for comparative samples and inventive examples. DEFINITIONS Any reference to the Periodic Table of Elements is that as published by CRC Press, Inc., 1990-1991. Reference to a group of elements in this table is by the new notation for numbering groups. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety (or its equivalent US version is so incorporated by reference) especially with respect to the disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure) and general knowledge in the art. The numerical ranges disclosed herein include all values from, and including, the lower and upper value. For ranges containing explicit values (e.g., 1 or 2; or 3 to 5; or 6; or 7). The range 1-7 includes subranges of 1 to 2; 2 to 6; 5 to 7; 3 to 7; 5 to 6; etc. Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percents are based on weight and all test methods are current as of the filing date of this disclosure. A “blowing agent” is a substance that is capable of producing a cellular structure in the composition via a foaming process. The terms “blend” or “polymer blend,” as used herein, is a blend of two or more polymers. Such a blend may or may not be miscible (not phase separated at molecular level). Such a blend may or may not be phase separated. Such a blend may or may not contain one or more domain configurations, as determined from transmission electron spectroscopy, light scattering, x-ray scattering, and other methods known in the art. The term “block copolymer” or “segmented copolymer” refers to a polymer comprising two or more chemically distinct regions or segments (referred to as “blocks”) joined in a linear manner, that is, a polymer comprising chemically differentiated units which are joined (covalently bonded) end-to-end with respect to polymerized functionality, rather than in pendent or grafted fashion. In an embodiment, the blocks differ in the amou