MVTR Barrier of Metallized PLA Films Sigma Technologies Int l A. Yializis PhD Presented By: Steven Yializis 1
What Is PLA PLA is a Natural Product Based on Plant Photosynthesis H 2 O + CO 2 + Light CH 2 O + O 2 CH 2 O Sugar Fermentation Lactic Acid PLA Poly Lactic Acid Lactic Acid (α-hydroxypropionic acid) Dimer Polymer
What is PLA PLA can be produced from many different sugars that are derived from various crops that t include Corn, Rice, Wheat, Sugarcane, Beets, Potatoes In the US Corn is the most abundant and lowest cost source of sugar Corn is processed in a wet milling process where starch is separated from fats, fiber, proteins, etc. Starch is reacted with enzymes to produce Dextrose (sugar) Dextrose is fermented and purified to produce Lactic Acid
PLA Polymer Films Since PLA is an aliphatic polyester formed by condensation of an acid with an alcohol it should not be confused with PET which is known also as polyester PLA PET The PLA polymer resin when formed into a polymer film is biaxially i oriented with the same MD and CMD stretch as PET, therefore a PET line can produce PLA with no efficiency loss
Basic Properties of PLA Films Clear polymer films High modulus Safe for Food Contact Resists degradation by oils and fats Good: for Aroma and Non Polar Solvents Barrier: Poor: Moisture vapor, Oxygen and CO 2 Low Flammability Low smoke generation (much lower than PET) Resists UV degradation Very Hydrophilic good breathability good printability Biodegradable Must first hydrolyze back to Lactic Acid Effective hydrolysis requires 60+ o C and 95%+RH
Barrier Properties of PLA Films POLYMER OTR (100sq.in) MVTR (100sq.in) PLA 35-45 15-25 BOPET 3-6 1-3 BOPP 150-180 0.5 0.8 NYLON 2-3 15-25 PLA films resemble Nylon6 when one looks at MVTR alone Unlike Nylon Metallized Films result in a poor metallized barrier
Metallized PLA MVTR Barrier Eldridge Mount (Converting Magazine Sept 8 2008) Reported that the best metallized moisture barrier value I have seen being about 3 gm/m^2/day (0.2 gm/100in^2/day) Celplast l who is a leading metallizer of PLA films, reports: For clear SiO2 Ceramis coated PLA Films, WVTR 7.75 gr/m2/24hrs - (0.5 grams/100 sq.in/24hrs) For Al Metallized Films MVTR as low as 3.7gr/m2/24hr (0.25 grams/100 sq.in/24hr) Sono-Tek Corp is reporting a coating of ultra-thin layer of clay nanoparticles to enhances PLA barrier properties A patent application by a major PLA film OEM is claiming metallized MVTR barrier of 1gr/m2/24hr using a polyolefin coating
BASIC REQUIREMENTS FOR PRODUCING A HIGH METALLIZED FILM BARRIER SUBSTRATE PROPERTIES Adequate Thermomechanical Stability To Allow Deposition of the Aluminum Layer with no Microcracking Substrate Surface Should be Free of Contaminants Low Molecular Weight Polymer LMW, Additives Loose Particles Surface Flatness: Apart of a Small number of Irregularities, Surface Microroughness Should be of the Same Order of Magnitude and the Barrier Layer Thickness Surface of Substrate Should Have Adequate Chemical Functionality to: Promote Adhesion Of Barrier Layer Maximize Crystal Nucleation
Can PLA Film Fulfill the Basic Requirements? YES PLA SUBSTRATE PROPERTIES Adequate Thermomechanical Stability To Allow Deposition of the Aluminum Layer with no Microcracking YES? Substrate Surface Should be Free of Contaminants Low Molecular Weight Polymer, Additives Loose Particles YES Surface Flatness: Apart of a Small number of Irregularities, Surface Microroughness Should be of the Same Order of Magnitude and the Barrier Layer Thickness YES Surface of Substrate Should Have Adequate Chemical Functionality to: Promote Adhesion Of Barrier Layer Maximize Crystal Nucleation Why Is the MVTR of Metallized PLA So Poor?
Problem: Degradation of Al Layer in Contact with the PLA Polymer Aluminum Layer LA Will Cause Al to Microcrack and Corrode Hydrolyzed Monomeric Components Will cause Al to Microcrack PLA FILM Moisture During the MVTR Test Partially Hydrolyzed PLA Polymer Prior to Metallization Additional and PLA Polymer
Solution: Isolate the Al Metal Layer from the PLA Polymer Aluminum Layer Uniform Thickness, Thermo echanically Stable Polymer Layer PLA FILM
Polymer Coated PLA Most PLA OEMs and converters have concluded the PLA film must be coated in order to enhance the barrier properties of metallized Aluminum Key Properties of polymer coating Must be thin enough not to disqualify PLA as a compostable and renewable polymer film Uniform thickness to fully isolate the aluminum layer from the PLA Must Adhere to the PLA surface Thermomechanically stable High surface functionality to produce a good metallized layer
Coating of PLA Film Inline with Metallization 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 Processes That Can Be Performed on Wed Substrates Without the Use of Solvent and Water Vacuum Plasma Treatment Atmospheric Plasma Treatment and Grafting Vacuum Based Polymer Coatings
Polymer Multi Layer Coating Technology 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 Deposited onto the Surface of a Substrate and are Cured Using an Electron Beam Curtain Submicron Thick Coatings Can be Used to Change the Chemical and Thermomechanical Properties of Polymer Film Polymers Can be Deposited Inline with the Metallization Process
Polymer Deposition SOLID LIQUID GAS LIQUID
MONOMER DEPOSITION Operating Pressure: 0.5torr and below 100nm Thick Layers are Adequate for most Applications Deposition Speed: 200-1500+ft/min
RADIATION CURING: UV or Electron Beam E-Beam Operating Pressure: 10 mtorr or lower UV Operating Pressure: Atmospheric Pressure or Vacuum
2.5m Wide Production Machine Designed for Acrylate Coating, Metallization and other Specialty Products
Properties Of Different Polymer Coatings Broad Range of Monomer Chemistry: Free Radical Polymerizable Acrylates Cationically Polymerizable Materials Epoxies Vinyl monomers Clear Cea and Transparent spae Films Thickness as low as 5nm Anti-Stain Anti-flammable Anti-bacterial Chemical Sensing - Color Change Metal Chelating Color Heat Sealing UV Absorbing Ionically Conductive Electrically Dissipating Release
Historic Best Barrier Data To date with Different Barrier Materials BARRIER STACK MVTR (gr/m2/24hr) at 37C Polycarbonate/Acrylate/ ITO/ Acrylate 004± 0.04 ± 004 0.04 PET/Acrylate/SiO2/Acrylate y 0.03 ± 0.002 PET/Acrylate/Al/Acrylate 0.004± 0.005
PLA Barrier Structure Given the low-end packaging application of metallized PLA films and issues relating to added thickness of non compostable and renewable polymer materials, a thin acrylate undercoat with thickness of 0.1-0.2 0.2 mm is a realistic target (instead of Acrylate/Al/Acrylate) First Series of Experiments: (Aluminum OD=2.7) PLA/Al PLA/Plasma/Al PLA/Acrylate - PET/Acrylate (witness sample) PLA/Plasma/Acrylate - PET/Plasma/Acrylate (witness sample) Perform adhesion tests Control metallization trials show that Al bonds well to PLA films, although reaction with the hydrolyzed PLA surface causes Al to perhaps micro-crack crack and corrode Many Acrylate formulations failed to adhere to PLA, regardless of the level l of plasma treatment It appears that the hydrolyzed surface of the PLA has too high a quantity of low molecular weight species to allow it to bond with the acylate coatings, unless the acrylate is made to react with the PLA surface
MVTR of PLA Coated with Acrylate Polymer Layers of Different Chemistry ACRYLATE BARRIER STACK MVTR -37C CHEMISTRY DEPOSITED ON PLA (gr/m2/24hr) ± 0.002 A B Plasma/Al Plasma/Acrylate/Plasma/Al 2.20 0.25 COMMENTS Adhesion No Adhesion Plasma/Acrylate/Plasma/Al 0.50 No Adhesion C D Plasma/Al 220 2.20 Adhesion Plasma/Acrylate/Plasma/Al 0.33 No Adhesion Plasma/Al Plasma/Acrylate/Plasma/Al 2.20 0.39 Adhesion No Adhesion E* Plasma/Al Plasma/Acrylate/Plasma/Al * Designed to React with the PLA Polymer 2.00 0.15 Adhesion Good Adhesion
Conclusions Metallized Al adheres well to PLA films but has relatively poor moisture vapor barrier properties Many Acrylate polymer chemistries have poor adhesion to PLA regardless of level of plasma treatment, degree of cross linking and polymer thickness All acrylate polymer coatings improve the moisture vapor barrier of the metallized films by about an order of magnitude, even if some coatings have poor adhesion to the PLA film The barrier results suggest that key properties for an effective polymer coating include, uniform thickness, high surface energy and adequate thermomechanical properties to allow it to be metallized without damage This work was conducted in a narrow web development machine, higher barrier is expected in a production machine