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US-12624180-B2 - In-situ formation of low density thermoplastic polyurethane flexible foams

US12624180B2US 12624180 B2US12624180 B2US 12624180B2US-12624180-B2

Abstract

A reactive mixture and method for making a thermoplastic polyurethane (TPU) flexible foam having a predominantly open-cell structure (open-cell content of ≥50% by volume calculated on the total volume of the foam and measured according to ASTM D6226-10) and an apparent density below 200 kg/m 3 .

Inventors

  • Jan Vandenbroeck
  • Steve Andre Woutters
  • Rajesh Kumar Gajendran
  • Martino Dossi
  • Rene Alexander Klein
  • Mark Joseph Brennan

Assignees

  • HUNTSMAN INTERNATIONAL LLC

Dates

Publication Date
20260512
Application Date
20201109
Priority Date
20191112

Claims (16)

  1. 1 . An in-situ method for making a thermoplastic polyurethane (TPU) flexible foam having (i) an open-cell content of ≥50% by volume calculated on the total volume of the foam and measured according to ASTM D6226-10, (ii) a density below 200 kg/m 3 , measured according to ISO 845, (iii) a hardblock content in the range 15 up to 65%, and (iv) a trousers tear strength>100 N/m measured according to DIN 53356, said method comprising combining at an isocyanate index between 90 and 110 in situ at least following ingredients to form a reactive mixture: a) a polyisocyanate composition comprising at least 90% by weight difunctional isocyanate compounds calculated on the total weight of all isocyanate compounds in the polyisocyanate composition, b) an isocyanate reactive composition comprising at least 90 wt % difunctional isocyanate reactive compounds calculated on the total weight of all isocyanate reactive compounds in the isocyanate reactive composition and wherein said difunctional isocyanate reactive compounds are selected from at least one linear high molecular weight difunctional polyol having a molecular weight in the range 500-20000 g/mol and at least one low molecular weight difunctional chain extender having a molecular weight<500 g/mol, c) at least one polyurethane forming catalysts, d) a blowing agent composition wherein at least 90 wt % of the blowing agents are selected from physical blowing agents and/or non-reactive chemical blowing agents having no isocyanate reactive groups, wherein the amount of blowing agents is from 5 to 60 parts by weight per hundred weight parts isocyanate reactive compounds, e) at least one compound acting as a surfactant, and f) optionally further additives and wherein the reactive mixture contains less than 0.1 wt % water calculated on the total weight of the reactive mixture and wherein said in-situ method is selected from a moulding process, a free-rise spray process or a free-rise slabstock process.
  2. 2 . The method according to claim 1 wherein the isocyanate index is between 90 and 110.
  3. 3 . The method according to claim 1 wherein the TPU flexible foam has an open-cell content of ≥60% by volume calculated on the total volume of the foam and measured according to ASTM D6226-10.
  4. 4 . The method according to claim 1 wherein the physical blowing agents are selected from CO 2 , N 2 , or mixtures thereof.
  5. 5 . The method according to claim 1 wherein the blowing agent composition comprises >95 wt % physical blowing agents selected from CO 2 , N 2 , or mixtures thereof.
  6. 6 . The method according to claim 1 wherein the blowing agent composition comprises >95 wt % of physical blowing agents and/or non-reactive chemical blowing agents having no isocyanate reactive groups based on the total weight of the blowing agent composition and wherein the amount of blowing agents is from 5 to 60 parts by weight per hundred weight parts isocyanate reactive compounds.
  7. 7 . The method according to claim 1 wherein the reactive mixture comprises less than 0.075 wt % of water calculated on the total weight of the reactive mixture calculated on the total weight of the blowing agent composition.
  8. 8 . The method according to claim 1 wherein the physical blowing agents are selected from isobutene, methylformate, dimethyl ether, methylene chloride, acetone, t-butanol, argon, krypton, xenon, chloro fluoro carbons (CFCs), hydro fluoro carbons (HFCs), hydro chloro fluoro carbons (HCFCs), hydro fluoro olefins (HFO's), Hydro Chloro Fluoro Olefins (HCFO's), and hydrocarbons or mixtures thereof.
  9. 9 . The method according to claim 1 wherein the polyisocyanate composition contains at least 95 wt % 4,4′-diphenylmethane diisocyanates calculated on the total weight of the polyisocyanate composition.
  10. 10 . The method according to claim 1 wherein the polyisocyanate component in the polyisocyanate composition is an isocyanate-terminated prepolymer which is prepared by reaction of an excessive amount of the polyisocyanate having at least 85% of 4,4′-diphenylmethane diisocyanate with a difunctional polyol and wherein the NCO value of the isocyanate-terminated prepolymer is above 5 wt %.
  11. 11 . The method according to claim 1 wherein the high molecular weight difunctional polyols are selected from polyester diols, polyether polyols and/or polyester polyether polyols having a molecular weight in the range 500 g/mol up to 10000 g/mol.
  12. 12 . The method according to claim 1 wherein isocyanate reactive composition comprises at least 85 wt % difunctional polyols calculated on the total weight of the isocyanate reactive composition.
  13. 13 . The method according to claim 1 wherein the difunctional chain extenders have a molecular weight<500 g/mol and are selected from 1,6 hexanediol, 1,4-butanediol and/or ethylene glycol in an amount of 2-10 wt % calculated on the total weight of the isocyanate reactive composition.
  14. 14 . The method according to claim 1 , said method comprising at least the steps of: i. pre-mixing the ingredients b) up to e) and optionally f), and then ii. mixing the polyisocyanate composition with the composition obtained in step i) in situ to form a reactive mixture, and iii. allowing the reactive mixture obtained in step ii) to foam to obtain the TPU flexible foam.
  15. 15 . The method according to claim 1 wherein the TPU flexible foam has a trousers tear strength >250N/m measured according to DIN 53356.
  16. 16 . The method according to claim 1 wherein the TPU flexible foam has a trousers tear strength >500N/m measured according to DIN 53356.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is the National Phase of International Application PCT/EP2020/081438 filed Nov. 9, 2020 which claims priority to EP Provisional App. No. 19208441.6 filed Nov. 12, 2019. The noted applications are incorporated herein by reference. FIELD OF INVENTION The present invention relates to processes for forming low density thermoplastic polyurethane foams, more in particular thermoplastic flexible foams having a predominantly open-cell structure and preferably having elastomeric properties. The present invention further relates to reactive mixtures for making the low density thermoplastic foams according to the invention. The present invention relates to thermoplastic low density polyurethane foams with a predominantly open-cell structure, a hard-block content in the range 15 up to 65%, an apparent density<200 kg/m3 measured according to ISO 845 and improved mechanical properties such as tear strength. BACKGROUND OF THE INVENTION Conventional flexible polyurethane foams with an open-cell structure are typically produced using isocyanate reactive compounds with a functionality higher than 2 in order to have stability during foaming and to achieve the required mechanical properties. It is known that the use of isocyanate reactive compounds with a functionality higher than 2 will give rise to a cross-linked polyurethane matrix. Furthermore, most of these foams are chemically blown using water, giving rise to urea-hard-blocks with a degradation temperature lower or close to its melt temperature. These two traits of conventional flexible polyurethane foams render them thermoset materials rather than thermoplastic which means that conventional (typically water blown) flexible polyurethane foams cannot be melted after service life and recycled like a thermoplastic material. Typically, this type of conventional flexible polyurethane foams are usually shredded and bonded together to make low quality foam products after their service life. U.S. Pat. No. 3,769,245 discloses the production of a thermoplastic polyurethane (TPU) foam using dicarboxylic acids as (chemical) blowing agent. High density foams are obtained (400 kg/m3) having an amide hard-block structure. CN10592461 describes thermoplastic polyurethane (TPU) which can be used to produce closed-cell extruded TPU foams (also referred to as expanded TPU or eTPU) with high density and heat resistance. The process starts from TPU pellets and a cellular structure is attained using a foam extrusion process which involves melt-processing of the TPU pellets. The density of the expanded TPU foam in CN10592461 is in the range between 400 and 600 kg/m3. Furthermore, the technology for producing these eTPUs gives closed-cell foams thereby limiting their application in several fields. Expanding TPU to form eTPU is also a cumbersome process with several intermediate processes requiring excess energy. Furthermore, current state of the art conventional low density (e.g. having densities below 100 kg/m3) flexible polyurethane foams with a predominant open-cell structure have a rather low tear strength, typically in the range 150-250 N/m. To solve above problems, there is a need to produce low density (being below 200 kg/m3) flexible polyurethane foams having a predominantly open-cell structure and improved mechanical properties such as tear strength which can be melted and recycled after their service life thereby significantly increasing their rework, recycling possibilities and application field. Aim of the Invention The ultimate goal would be to achieve a low density polyurethane flexible foam which is polymerized and blown in-situ, andhaving a predominantly open-cell structure (at least 50% open-cell content), andhaving an apparent density below 200 kg/m3 measured according to ISO 845, andthermally recyclable (e.g. via extrusion) to a material having a TPU matrix similar or identical to TPU materials made using state of the art TPU manufacturing processes, andmelt reprocessable after its service-life It is a further object of the present invention to develop a reactive mixture and a method for making flexible polyurethane foams having a predominantly open-cell structure and significant improved mechanical properties such as tear strength which are easily melt-reprocessable and recyclable after service life (use). Definitions and Terms In the context of the present invention the following terms have the following meaning: 1) “NCO value” or “isocyanate value” as referred to herein is the weight percentage of reactive isocyanate (NCO) groups in an isocyanate, modified isocyanate or isocyanate prepolymer compound.2) The “isocyanate index” or “NCO index” or “index” as referred to herein is the ratio of NCO-equivalents to the sum of equivalents of isocyanate-reactive hydrogen atoms present in a formulation, given as a percentage: [NCO]×100[active⁢ hydrogen]⁢(%)In other words, the NCO-index expresses the percentage of isocyanate a