Roll-to-roll method and system for micro-replication of a pattern of large relief three-dimensional microstructures
View Patent ↗A method and system referred to as PALM (Patterning by Adhesive of Large Relief Three-Dimensional Microstructures) with large reliefs exceeding 1 μm and being as large as 100 μm. The microstructures can be either deterministic (such as microprisms), or random (such as diffusers), the first obtained by copying an original supermaster, and latter obtained by copying a laser speckle pattern. The master process entails copying a supermaster into the form of the microstructure constituting a pattern on the patterning cylinder (called a drum), to be then continuously multiplied in the PALM system, in a continuous roll-to-roll web process. The latter method, together with the related system, is the subject of this invention. The rolls continuously repeat the master pattern, copying by adhesive with large viscosity on acrylic (hybrid) as well as by a monolithic process. The monolithic process can be accomplished using temperature and pressure, or by UV-cured polymerization. Therefore, the invention comprises three alternative processes: one, hybrid (adhesive on acrylic), and two monolithic ones. In the PALM (hybrid) process, an epoxy is wet-coated on film substrates such as polycarbonate (PC), polyester (PET), (PE), or other flexible material. The adhesive, in liquid form, is applied to the substrate by a self-metered coating sub-process. In the present invention, the adhesive is used for forming the microstructure pattern. The microstructure pattern is replicated from a master roll or image drum onto a coating roll.
1. A method for replicating three dimensional microstructures from a master pattern of microstructures onto a continuous rolling substrate band of a flexible planar material having a width, an image surface, which was coated with curable coating liquid, and a reverse surface comprising the steps of:
providing an apparatus comprising an image drum having said master pattern of microstructures on a peripheral surface, an idler roll, a nip roll positioned in proximate parallel relation to said image drum, a source of ultraviolet radiation;
transferring the continuous rolling substrate band of flexible planar material around said idler roll;
bringing the image surface of the flexible planar material to the peripheral surface of the image drum at an entry point;
providing a puddle of curable coating liquid between and in contact with the image surface and the peripheral surface of the image drum at the location of the entry point;
applying pressure to the reverse surface of the flexible planar material across the width thereof to penetrate the coating liquid between the image surface and the peripheral surface of the image drum into the microstructures of the peripheral surface of the image drum,
wherein the pressure at the nip roll is p=(T/lr)=(T entry e −fθ lr), where p is the pressure, T is an actuation force, l is a length of the image drum, r is a radius of the image drum, and θ is a selected angle in the direction of motion to the image drum;
substantially curing the coating liquid prior to the image surface reaching an exit point and retaining on the image surface an impression of the microstructures on the peripheral surface of the image drum; and
separating the substantially cured coating liquid on the image surface of the flexible planar material from the peripheral surface of the image drum at the exit point.
2. The method of claim 1 , wherein the continuous rolling substrate band is wrapped on the image drum through the selected angle from 5 degree to 70 degree prior to reaching said nip roll.
3. The method of claim 2 , wherein the continuous rolling substrate band is wrapped on the image drum through the selected angle exceeding 90 degree beyond said nip roll.