Presentation on Flexographic Printing Techniques.

1 Presentation on Flexographic Printing Techniques. At:- by:- Leslie D. Embury January 2010. The gwent Group of Companies Suppliers to Major Multinational Companies in :- The Automotive Industry. The Fuel Cell Industry. The Electro-ceramics Industry. The Pharmaceutical Industry. The Bio Science Industry. The Electronic Display Industry. and General Electronics. Large Area Printing The Application of Flexography for the Volume Printing of Electronics. Synopsis Flexography is an additive Printing process that has the potential to achieve the necessary resolution and precision for volume Printing of plastic electronics and OLED lighting. The Technology Strategy board funded the Accuflex project, this project is developing a Flexographic Printing system for volume production of high resolution plastic electronics, achieving fine line registration within large areas on continuous webs.

2 This will require improved control of the Printing process, particularly the plate (image carrier) technology; web handling and drying to create accurate fine line and precise features with the requisite inter layer registration that is essential for the use of these processes for the manufacture of sophisticated flexible displays, RFID, intelligent packaging, bio sensors, disposable electronics and intelligent textiles. The initial target products for Accuflex are large area lighting and conducting tracks for packaging, on tablet or blister packs. Accuflex A UK government funded project. The gwent Group.: Formulation of improved conducting inks. Timsons Ltd.: Press development include precision digital drive system on their T-Flex press. Tectonic Ltd.: On line inter unit registration measurement and full web inspection. Millennium Lasers Ltd.: on-line trimming.

3 Asahi plc.: Flexographic plate technology. Innovia Ltd.: Substrate technology, including biodegradable films. WCPC, Swansea University: Fundamental research in flexography, particularly on contoured and textured plates to address the demands of feature resolution and quality. Areas of Technology to be addressed. Machine registration. Ink formulation. Printing geometry. Substrate stability & surface parameters. Transfer plate development. Optical registration. Laser trim. Flexographic Printing Flexographic Printing Flexoprinting 10-60 meters per minute Flexographic Printing The TFlex 508. Flexographic Printing press is being used as a basic platform for Accuflex project due to its robust construction, high specification drive elements and adaptability Flexographic Printing Flexographic Printing Flexographic Printing Current Printing Techniques. The process of choice currently for deposition of conductive inks is screen Printing , which are typically demands high viscosity materials producing a thick film which have prolonged drying and curing times.

4 A variation being Stencil Printing . There are significant challenges in formulating materials for Flexographic Printing . Additionally, the system must compete with alterative possibilities. Direct Gravure. Ink Jet Direct Write. Subtractive Technologies. Screen Printing Fig 1 The basic screen print process Squeegee Screen mesh Paste Screen frame Substrate Emulsion Nest Screen Printing Printing speed: 60 -1500 sheets per hour High Definition Screens Screen with 500 mesh calendared fabric wire diameter 8 m line/space 20 m/20 m Material agglomeration Three particle agglomerate limits maximum particle size of powder to 12-15 m (assuming aperture of 45 m). Print Limitations 300 SDS 40 m 400UT 40 m V330 40 m C2090903R3 76% Pt Stencil Printing Electroformed apertures Positive advantage since no threads to reduce open area. Negative one direction only, without a dotting process.

5 Stencils 20 micron lines and spaces Speed of Printing 60-1500 sheets per hour Ink Jet Piezo-Electric Deposition Up to 24 meters/min for digital Printing Ink Jet Nano silvers printed 50 micron lines Using Current technology 30 50 m lines Ink Jet SEM of Ink Jetted GOX layer Glucose Biosensor response Ink Dispersion Equipment for flexo Ink Ink Requirements for Flexographic Printing The process demands low viscosity inks, the films deposited are thinner The solvents in the ink must be compatible with the plates. Increased flexibility is required and the drying times are significantly shorter. The initial demands are for conductive inks, this process requirement mean a fundamental rethink in formulation in terms of:- Particle size. Particle shape Solvent and Resin systems that can be used. Their development had led to a conductive ink which is capable of being printed by flexography Flexographic Printing Inks Raw Materials Selection Solvents and the roles they play in the formulation.

6 Polymer types and considerations. Functional Phases, Conductive powders. Flexographic Printing Inks Function and Selection of solvents Dissolve the selected resin system. Maintain printability. Control drying rate. Resin must remain fully dissolved during Printing and drying process. Generally several solvents are used with different boiling points and evaporation rates. Direct effect on the drying of the printed films. Flexographic Printing Inks Solvent Properties to Consider Solvents and diluent can be used. Solvents dissolve the resin, diluents do not. Solvents must remain in the ink formulation during drying process to maintain resin solubility. Combining solvents to give a blend gives the best drying properties to a printed ink. Drying is a wicking process that draws solvent from the printed ink film. Flexographic Printing Inks Function of the Resin Binder system to hold the particulates together.

7 Gives the final dried film strength and adhesion to a given substrate. Transfer process from photopolymer to the substrate. Flexographic Printing Inks Formulation Considerations for Resins. Many types of resins can be used. Resin type depends on the substrate and adhesion required. Resin must prefer to adhere to the substrate rather than the photopolymer, otherwise no transfer will take place. Resin type used will also depend on the types of solvents that can be used to dissolve it. Dielectric effect of the resin used will affect the electrical conductivity of the dried film. Shrinkage of the resin on drying will have an effect on the electrical conductivity. Solvent release of the resin on drying . Flexographic Printing Inks Functional Components Silver Powders Silver Flakes Carbon Powders Graphite Powders Silver Complexes Silver Metallo-Organics Flexographic Printing Inks Function of Conductive Powders Give final dried print electrical conductivity.

8 Particle size will also determine the rheology of the final ink. Flexographic Printing Inks Formulation Considerations for Conductive Powders Particle size. Particle size distribution. Tap density. Surface area. Flexographic Printing Inks Manufacturing of Silver Powders Chemical Precipitation. Coating of Powders. Processing of Powders. Manufacture of Flakes. Flexographic Printing Inks Effect of Silver Powder Coating Coatings are used to prevent agglomeration of the silver powder. Coating isolate each silver particle. Poor removal of the coating reduces conductivity. Solvents must be capable of removing the silver coating. Flexographic Printing Inks Selecting Silver Powder or Flake Powders Particle Size Distribution Flexographic Printing Inks Selecting Powder or Flake Typical Flake Particle Size Distribution Flexographic Printing Inks Nano-Silver Powder 30nm mono dispersed powder (25 -45nm).

9 Organic content minimised. No surfactants or dispersants added. Powder supplied wet in a solvent. Easier to disperse. PSD (SEM). D10 10nm D50 30nm D90 50nm Flexographic Printing Inks Selection of Silver Powder or Flake Flakes are flat platelets. Powders are spherical. Have greater overlap of Have less particle to particles when printed. particle contact. Generally give higher Generally give low conductivity in polymer conductivity in polymer formulations. systems. Wide range of flake sizes. Can be added to improve conductivity of flake formulations Functional Conductive Flexographic Inks Property Silver Ink Carbon Ink C2080815D1 C2090424D2. Ink Type Solvent Based Solvent Based Drying Requirement Forced air 60 70 c Forced air 60 70 c Viscosity @ 50s-1(typically) Pa s Pa s Volume Resistance Ohms/cm*. Maximum Print Speed** 30m/min 30m/min Flexographic Printing Inks Rheology of Conductive Flexographic Inks.

10 Carbon Flexo Ink C2080529D7 # Silver Flexo Ink C2080815D1# Viscosity Pa s Viscoaity Pa s 0. 0 50 100 150 200 250 300 350 400. Shear Rate s-1. 0 50 100 150 200 250 300 350 400. Shear Rate s-1. Trial Formulations All Silver powders and flakes have differing Tap Densities, and Surface areas. Silver Flakes range from g/cm3. Silver Powders range from g /cm3. Surface Area range from m2/g Require a Model formulation to be able to assess different Silver Powders and Flakes. Allows comparisons to be made between the performance of flakes and powders within the formulations. Volumetric Ratio's Allows the same volume of Silver to be added to the same volume of Resin in the formulation. Eliminates differences between the Tap Densities of different powders and flakes. Trial Formulations Product Code C2080605R4 C2080605R3 C2080605R2 C2080609R2 C2080609R1 C2080603R10. Volumetric Ratio :1 10:1 :1 7:1 6:1 5:1.