A New Dielectrophoretic Coating Process for Depositing Thin Uniform Coatings on Films and Fibrous Surfaces

Transcription

1 A New Dielectrophoretic Coating Process for Depositing Thin Uniform Coatings on Films and Fibrous Surfaces by Angelo Yializis Ph.D., Xin Dai Ph.D. Sigma Technologies International Tucson, AZ USA

2 SIGMA TECHNOLOGIES Surface Functionalization Technologies and Equipment Vacuum Plasma Treaters Atmospheric Plasma Treater Multifunctional Coatings Specialty Materials New Product Areas Polymer Films: High Barrier Films for Packaging, biomedical, Flexible Display and Photovoltaic Applications Radiant Barriers: Metallized/coated Films and Non Woven Membranes Functional Textiles: Filters, Medical, Protective Fabrics, Functional Apparel, Heat Management, Agricultural Specialty Pigments: Nanoflake Aluminum pigments, Transparent Ag and ITO Nanoflakes

3 FUNCTIONALIZING WEB SURFACES USING DRY TECHNOLOGIES Sigma Has Been Working For Several Years to Develop Process and Equipment Technologies To Functionalize Surfaces Without Solvents and Water Incentives Environmentally Friendly Processes No Hazardous Waste Low Energy Consumption Small Real Estate Footprint Has Developed Two Processes That Can Be Used to Coat Polymer Films and Porous and Fibrous Materials Without the Use of Solvent and Water A Vacuum Based Polymer Coating Procces A Novel Atmospheric Technology Using A Dielectrophoretic Coating Process

4 DryFab TM Nanolayer Technology For Functionalizing Web Surfaces Sigma has Developed an 100% Solids Dry Coating Process: No Solvents which Require Recovery No Hazardous Waste for Disposal No Primers, Surfactants and Adhesion Promoters Replaced by Inline Plasma Treatment Monomers are Injected onto a Fabric At Supersonic Speed Forming Nanothick Layers that are Cured Using an Electron Beam Curtain Nanocoatings Change the Chemical Properties of the Fabric with no Effect on Weight, Porosity, Breathability, Hand, Mechanical Strength etc Given that Solvent and Water are not Used, It is Possible to Treat Half Way into the Fabric Single Fabric Layer can have two Different Functional Surfaces

5 IN-VACUUM PML COATING PROCESS SOLID LIQUID GAS LIQUID

6 PML Coating Components Monomer Tank Electron Beam Monomer Evaporator and Nozzle UV Lamp VACUUM POLYMER COATING CHAMBER

7 Polymer Nano-Layers on Polypropylene Film Uncoated Sub Micron Coating Color Coating

8 Dielectrophoretic (DEP) Coating Utilizing Ultrasonic Atomization The DryFab Process is a Vacuum Based Process Deposition of functional nanothick 100% solids coatings is virtually impossible using conventional coating techniques The challenge becomes even greater when coating fibrous materials such as paper, foam, and woven and non woven textiles Sigma has developed a proprietary dielectrophoretic (DEP) coating process that allows the deposition of nanothick functional coatings using radiation curable monomers (100% solids) Environmentally Friendly (no water or solvents) Energy Efficient Economical

9 Dielectrophoretic Forces (a) A liquid of dielectric constant k2>k1 is drawn in to the high field region (b) The liquid is expelled away from the non uniformity

10 Dielectrophoretic Tunable Lens (a) Two liquid layers, (b) Droplet forming with voltage application, (c) Stable state a t a certain voltage level, (d) In a relaxed state with no voltage press%20ren%20liquid%20lens.pdf

11 Micro Dielectrophoretic Extractor Scanning Electron Microscope picture of dielectrophoresis electrodes inside a channel

12 Dielectrophoretic Effect on Coated Fibers

13 Dielectrophoretic Effect on Liquids and Solids The dielectrophoretic force is present when materials with different dielectric constant exist in non uniform electric fields. The dielectrophoretic force is independent of polarity so it can be present with both DC and AC fields Liquids and particles are attracted to regions of stronger electric field when their dielectric constant is higher that that of the surrounding medium When the dielectric constant is lower that that of the surrounding medium the motion is toward a lower field region

14 Dielectrophoretic Web Coating Utilizing Ultrasonic Atomization The coating process is composed of three separate and independent steps 1. Atmospheric plasma treatment station: used to increase surface energy and provide covalent bonding with the monomer coating 2. Ultrasonic coating module: used to apply thin coatings of radiation cured monomers and monomer mixtures with nanoparticles 3. Dielectrophoretic (DEP) station: used to spread the coating on the surface using an electro-hydrodynamic force The DEP effect acts upon the liquid monomer with a force that can be controlled by the application of an electromagnetic field on the coated surface The DEP process can be so effective, that a relatively viscous liquid deposited on one surface of a non woven material can be driven to coat the fibers in bulk of the material as well as the opposite surface

15 Dielectrophoretic Coating Process UV or e-beam Cure Substrate Substrate Substrate Atmospheric Plasma or Other Electromagnetic Field

16 Surface Activation with Plasma at Atmospheric Pressure Sigma in 1999 Introduced the First Commercial Atmospheric Plasma (ATP) System for Large Scale Web Substrates Technology Awards from the Association of Laminators, and Coaters (AIMCAL) and the Environmental Protection Authority (EPA) Application of Atmospheric Plasma Treatment Include Fabrics and Fibers Polymer Films Paper Powders Metal and Glass Surfaces

17 Atmospheric Plasma Can Be Used to Treat A Broad Range of Substrates Plasma Treater on a Foil Slitter Display Applications Treatment of Flat Solid Substrates Carpet Treatment Computer Applications Atmospheric Plasma Treater on BOPP line

18 Dielectrophoretic Coating of a Hydrophobic Non-Woven Membrane Plasma Treat Coat Apply DP Force

19 Dielectrophoretic Fabric Coating Utilizing Ultrasonic Atomization The coating module consists of a series of ultrasonic spray nozzles Such coating system is particularly effective when coating fibrous surfaces with 100% solids in conjunction nano-particle additives Ultrasonic atomization of water and solvent based coatings can also be effective using less solvent than conventional roll coating equipment Micro-droplet formation leads to water/solvent evaporation during the coating step, reducing drying time The DEP station can also be used with conventional coating equipment - DEP equipment may be retrofitted into existing coating lines to enhance coating performance

20 Ulrtasonic Spay System Used to Coat Large Area Web Substrates Multiple ultrasonic nozzles may be used to coat large scale webs The monomer flow through each nozzle can be independently controlled Each nozzle has integrated gas flow to direct the atomized flow

21 Dielectrophoretic Coating Line ULTRASONIC DIELECTROPHORETIC COATING SYSTEM WITH RADIATION CURE Ultrasonic Atomization Dielectrophoretic Treatment Station Plasma Treatment Station Unwind Rewind e-beam or UV Cure

22 Dielectrophoretic Coating of a Hydrophilic Porous Material with a Hydrophobic UV Curable Monomer Control - Uncoated Surface Coated Surface + UV Cure Coated Surface +Dielectrophoretic Force + UV Cure

23 Advantages of the DEP Based Coating Processes Coating process has all the advantages of conventional 100% solid radiation curable coatings Can be tuned to have no significant effect on the mechanical properties and feel of porous substrates Can be used to treat one or both sides of a porous substrate with same or different functionalities. This is not possible with conventional wet coating processes Can utilize functional monomers mixed with nanoparticles (eg SiO 2, Al 2 O 3, TiO 2 ). Plasma treatment promotes bonding of the coating to virtually any substrate Lower material costs Zero emission of Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) Energy consumption and occupied space is a small fraction of wet processes

24 Material and Coating Properties Broad Range of Monomer Chemistries that include: Free Radical Polymerizable Acrylates Cationically Polymerizable Materials Epoxies Vinyl monomers Clear and Transparent Films Anti-Stain Anti-flammable Anti-bacterial Chemical Sensing - Color Change Color Heat Sealing Ionically Conductive Electrically Dissipating Release

25 Summary The plasma assisted ultrasonic and dielectrophoretic based coating process can be used to deposit nanothick functional coatings on various porous substrates The coatings can be made thin enough to functionalize the substrate with no significant effect on feel, hand or porosity and breathability of the coated material The process is environmentally friendly, and cost competitive with water/solvent based processes Coating formulations are virtually the same as those used in various protective coatings that utilize radiation cured chemistries and can include nanoparticle additives Unlike wet coating methods nanothick dielectrophoretic coatings can be limited only on one side of a porous substrates