Self-healing Slide-Ring Material paint makes fine scratches disappear on mobile phones, laptops, other surfaces

Nissan Motor Co., Ltd.

Ideal for mobile phone applications, laptop cases, and similar devices that suffer continual minor scratching and abrasion in pocket, backpack, and purse, Slide Ring Material (SRM) paint is able to heal about 80% of surface abrasions by itself, almost immediately. The coating is already commercialized in Japan. The product comprises polymer chains that freely slide through the cross-linked molecules, forming a supramolecular network. When disturbed by minor abrasions, the cross-linked molecules retain mobility and the coating redistributes its tension to “slide” back into place along the polymer chains, erasing the abrasion. Chemically, the coating is an oleophilic polyrotaxane. Its solubility and ability to react with curing agents make it highly applicable to coating resins. In operation, the paint resists cracking and peeling, offers improved elasticity and impact resistance, and is unsusceptible to fouling and adhesion.

Unlike conventional coatings, SRM consists of polymer chains on which slide molecular rings. These rings are the functional and cross-linking sites for the molecules. When the molecules are disturbed (by abrasion, for example) they retain enough mobility that the tension across the cross-linked supramolecular network soon tugs the coating back into place, effectively erasing the abrasion. More extensive abrasions can take a week to self-repair.

Slide-Ring Material (SRM) is particularly useful for coating products that require marring resistance, such as metal surfaces; resinous formed articles; wood products such as stairs, floor, furniture and the like; and similar products and surfaces.

It dramatically improves on the marring qualities of polycarbonate and acrylic plate in such physical properties as hardness, weatherability, stain resistance, and solvent resistance. SRM differs from UV– or EB-curable paints or silica-based paint in that the harder they are, they exhibit inferior adhesion to the substrate and a tendency to crack because of strain during hardening and shrinkage owing to an increased crosslinking density. When softer paints and coatings are used, chipping and cracking does not occur, but the softer coating is also inferior in weatherability and stain resistance.

SRM overcomes these difficulties by using an oleophilic polyrotaxane whose linear molecule and cyclic molecule are provided with hydrophilic modification groups. The linear molecule pierces the cyclic molecule. Blocking groups at both end terminals of the linear molecule prevent the cyclic molecule from leaving. The resulting material is amenable to use as a curable, solvent-based topcoating material that is able to form a film having excellent marring resistance in which cracks form only with great difficulty.

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