Barrier coatings are used to protect sensitive materials from damaging influences such as oxygen or moisture that can degrade long-term product performance. Recent advances in barrier technology include coatings that cost less than typical foil laminate and multi-layer structures involving both liquid and vacuum coating. The goal is to produce coatings that can be applied to flexible materials with barrier properties comparable to glass.
There are also barrier coatings that repel water and/or oil or protect surfaces from corrosion, flame or chemicals, often in conjunction with barrier coatings and hard coats. Considering just oxygen and moisture barriers, some commonly used metrics can clarify the issues. Oxygen barrier or oxygen transmission rate (OTR) is typically measured with units of cc O2/m2/day. Moisture degrades the performance of most coated oxygen barriers, so it is important to document the humidity level used to test the OTR. Moisture vapor barrier or transmission rate, known as MVTR, is typically measured with units of g H2O/m2/day. In both cases, a lower rate is better, and is often expressed as a 10-x barrier level. A low 0.1 or 10-1 barrier may be acceptable for food packaging applications, while a high 0.0001 or 10-4 to 10-6 barrier may be necessary when protecting organic, light-emitting diode (OLED) devices or other sensitive materials.
Aqueous dispersions of clay platelets in binders are often used to enhance the barrier of packaging films such as biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), biaxially oriented nylon (BON), or polylactic acid (PLA). The micron-sized platelets have a high aspect ratio (width-to-thickness) of up to ~10,000:1. The platelets are oriented and stacked into a brick-like pattern when coated and dried, creating a tortuous path for gas molecules, which provides effective barrier performance in a thin layer (0.2 – 0.5 microns dry) with good strength and flexibility. Clay platelets are only one example of new structures being developed.
Since water vapor and oxygen molecules are extremely small, they can easily pass through even microscopic defects in barrier coatings. Higher barriers are typically created through alternating multi-layer constructions. The materials used for such coatings are normally layers of inorganic oxides and organic materials. Each layer pair is called a dyad. The inorganic materials are particularly impermeable and the organic ones are good for providing a smooth surface and filling imperfections. Newer approaches using only multi-layer solution coatings are also being developed that avoid the vacuum deposition requirements and cost of inorganic oxides.
Minimal contamination and uniform coating thickness are also very important to delivering the best barrier possible. Carestream’s clean, high-precision multi-layer coating technology is ideally suited to overcome these challenges and deliver optimal performance. Carestream has more than a century of in-depth knowledge of coating and manufacturing, complemented by a core competency in commercializing new products. Customers can access this knowledge and speed time to market using new materials and new multi-layer structures.