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EP-4140679-B1 - METHOD FOR DETACHING SUBSTRATES BONDED BY POLYURETHANE ADHESIVE

EP4140679B1EP 4140679 B1EP4140679 B1EP 4140679B1EP-4140679-B1

Inventors

  • Park, Gwanghyun
  • Nam, Arnold Yeonwoo

Dates

Publication Date
20260513
Application Date
20210824

Claims (8)

  1. A method for detaching two substrates bonded by a polyurethane adhesive, comprising the steps of: (1) treating a first substrate and a second substrate bonded by a polyurethane adhesive with a debonding agent comprising lactic acid, at least one surfactant and water at a temperature from 40°C to 90°C, and (2) separating the first substrate and the second substrate from the polyurethane adhesive, wherein lactic acid is present in the debonding agent in an amount of 1% to 60% by weight based on the weight of the debonding agent.
  2. The method according to claim 1, wherein the surfactant is a non-ionic surfactant.
  3. The method according to claim 1 or 2, wherein the treating temperature in step (1) is from 40°C to 80°C.
  4. The method according to any one of claims 1 to 3, wherein the first substrate is selected from thermoplastic polyurethane (TPU), polyamide (PA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), ethylene-vinyl acetate (EVA), weft-knitted fabric, warp-knitted fabric, woven fabric, non-woven fabric, braided fabric, leather and combination thereof.
  5. The method according to any one of claims 1 to 4, wherein the second substrate is selected from thermoplastic polyurethane (TPU), polyamide (PA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), ethylene-vinyl acetate (EVA), weft-knitted fabric, warp-knitted fabric, woven fabric, non-woven fabric, braided fabric, leather and combination thereof.
  6. The method according to any one of claims 1 to 5, wherein the first substrate and the second substrate are shoe parts selected from upper, midsole or outsole.
  7. The method according to claim 6, wherein the first substrate is an upper or outsole, and the second substrate is a midsole.
  8. Use of the method according to any one of claims 1 to 7 in recycling parts of shoes, preferably sport shoes.

Description

The present invention is directed to a method for detaching two substrates bonded by polyurethane adhesive, in particular for detaching shoe parts. In addition, the present invention relates to the use of the method in recycling parts of shoes. Bonding parts by polyurethane adhesives has found applications in various areas such as aeronautics, aerospace, electronics, automotive, construction, sports and packaging. Polyurethane adhesives can be used to bind various materials such as metals, polymers, ceramics, cork, rubbers, fabrics, etc. However, one of the drawbacks of polyurethane adhesive bonding is its "permanence" character as the bonds are not easy to detach. In most cases, the bonds cannot be detached without destroying the substrates. Nowadays, the large amount of production of widely used materials e.g. for shoes have created an increasing demand for recyclability, driven by economic and environmental reasons. Thus, the development of new technologies and processes for easy recycling and repairing adhesively bonded assemblies are becoming of great interest for the industry. If the adhesive bonds can be broken without damage of the parts, recycling will be much easier. In addition, from an environmentally friendly point of view, it is necessary to separate the bonds between the bonded substrates so that the different materials can be reused on a qualitatively high level. As recycling becomes a necessary and global issue, reversible adhesives or debonding on command of the adhesive bonds have been developed. For example, WO 01/30932 describes a process for the adhesive separation of adhesive bonds. The adhesive bond comprises a heat-softenable thermoplastic adhesive layer or a heat-cleavable thermoset adhesive layer and a primer layer, the primary layer containing nanoscale particles which can be heated by electromagnetic alternating fields. WO 01/28771 A1 describes a microwave-curable composition containing particles capable of absorbing microwaves with a Curie temperature which is higher than the curing temperature of the composition. US 2021/0037916 discloses articles of footwear and components for articles of footwear including a debondable adhesive matrix. The debondable adhesive matrix can allow for the bonding and debonding of two substrates in the article of footwear or component thereof. Another method for detaching two substrates bonded by a polyurethane adhesive is know from document GB 2 574 260 A. However, if used in high demanding applications such as shoes which require excellent adhesion portfolio in bonding strength, impact resistance and application easiness, the methods in prior art have drawbacks of increased cost of the adhesives, insufficient bonding strength and/or impact resistance. In addition, the prior art methods using special heating equipment also increase the cost and energy. In view of the existing problems in providing an alternative and/or improved method for detaching an adhesively bonded substrates, there is still need in the art for methods of detaching adhesively bonded substrates which is suitable for the application in industrial scale and obviate the need for cost-intensive treatments. The present invention is defined by a method for detaching two substrates bonded by a polyurethane adhesive, as defined in claim 1. In another aspect, the present invention relates to the use of the method as described herein in recycling the parts of shoes, preferably sport shoes. All percentages given herein in relation to the compositions or formulations relate to % by weight (wt%) relative to the total weight of the respective composition or formulation, if not explicitly stated otherwise. The present invention is based on the inventor's surprising finding that by using a debonding agent comprising lactic acid to treat polyurethane adhesively bonded substrates at a temperature from 40°C to 90°C, the detachment of the substrates from the adhesive can be well achieved. As the first step, the method for detaching substrates bonded by a polyurethane adhesive comprises the step of treating two substrates bonded by a polyurethane adhesive with a debonding agent comprising lactic acid at a temperature from 40°C to 90°C. As used herein, the term "treating" means that the debonding agent contacts at least the interface between the substrate(s) and the adhesive by conventional methods, such as immersing, brushing, spraying, etc. In one preferred embodiment, the two substrates bonded by an adhesive are immersed in the debonding agent. In one embodiment, the duration of the treatment of substrate(s) by the debonding agent is from 0.5 hour to 240 hours, preferably from 2 hours to 100 hours, and more preferably from 24 hours to 72 hours. The debonding agent comprises lactic acid, at least one surfactant and water. Lactic acid is present in the debonding agent in an amount of 1% to 60% by weight, preferably from 5% to 40% by weight based on the weight of the debonding agent. The debonding