CCK paper versus PCK paper
The graphic arts market is dominated by two paper based release liner solutions. The AWA global market study Pressure-sensitive Graphic Films 2016 shows, that Clay Coated Kraft papers (CCK) with a share of 44% and PE Coated papers (PCK) with a share of 40% are mostly used as release liner worldwide. Further release liner solutions for graphic art applications are Glassine/SCK paper with 12%, Films with 3% and other papers with 1%. The release liner solutions have to meet the graphic art market demands for good dimensional stability, high internal bond strength, high mechanical strength and excellent rigidity for manual handling.
The graphic art sector includes indoor advertising and branding, outdoor advertising and branding, vehicle graphics like car wrapping, road traffic and safety markings, shelf markers and architectural graphics. AWA reported for 2015 a global volume of 2,302 million square meters for pressure-sensitive graphic films. Key markets are North America and Europe with a common market share of 54%.
Wide adoption of CCK grades in Europe
When it comes to market adoption in US and European markets there are clear differences. In Europe, CCK grades hold a 77% market share according to the AWA Global European Release Liner Study 2016 with PE coated taking 20%. This compares to just 40% for CCK in the U.S. market (AWA Global North America Release Liner Study 2014) with PE Coated paper holding the best-seller position at 49%.
The North American market has traditionally relied on high quality graphic films such as polymeric calendared vinyl and cast vinyl. This is because historically CCK grades in the US have an open reverse side so there is no coating, which has a negative effect on the dimensional stability. This prompted operations to use PE Coated Papers, even for less critical applications, as they have had an advantage in terms of dimensional stability. This means they prevent problems with evenness and the formation of humidity bulges in composite laminates, especially in critical climate zones. In the USA: “It is worth noting that in the past,” Gunnar Sieber, Manager Product Group Release Liner at Sappi, says, “The image of CCK papers is not as good, because of no reverse side coating and the reduced dimensional stability. Siliconizers who were looking for a safe solution would be more likely to specify PE Coated paper.”
Enhanced performance of CCK paper in Europe
Compared to the US market CCK grades are mainly coated on the reverse side in Europe. During recent decades, companies like Sappi developed many enhancements of their CCK paper to improve the dimensional stability. As a result of this development, CCK paper became a strong release liner solution, even for high advanced applications. In addition CCK paper with functional reverse side coating like Sappi Sol from Sappi offers features like suitable smoothness for logo printing and retardation of moisture penetration. This even permits paper re-humidification with vapour or water film.
The latest enhancements deliver a wide range of performance benefits that will support a broad reach of market sectors. Combined with competitive price performance, the high quality results allow end users to confidently develop their services using this more advantageous release liner. Testing has shown that with appropriate humidity control in the lamination process for finished composite films/paper laminates, there is no formation of undesirable bumps in the paper. Its blocking effect against migrating contaminants prevents printing errors on the cover film and also minimises problems due to uncured silicone drips in the top film printing. Since the surface is coated on both sides, mechanical embossing effects (orange peel) on soft printing films are prevented while low hygro expansion makes it an excellent alternative to PE Coated.
Further advantages of CCK paper
“These advances expand the range of more critical applications for CCK papers,” Sieber comments. Traditionally, PE Coated carrier papers are used in areas where they are not always necessary. But with these improvements, PE papers can be replaced with dimensionally stable CCK papers like Sappi Sol in less critical applications. FSC and PEFC certified CCK papers offer improved sustainability as compared to PE papers as they are an easy recyclable paper-based grade compared to a plastic based one. Pulp sourced from FSC approved wood is used to produce the grades and their reduced silicone consumption results in significant cost savings and has a positive effect on the eco-balance. Another important disadvantage of PE Coated papers is that these carrier materials are not suitable for applications with high heat exposure, such as laser printing. Gunnar Sieber, says: “Compared to the European graphic art market, the U.S. market has more broadly adopted PE Coated grades as release liner. However, with all the improvements we have made in our CCK grades over the years, we believe they have much to offer as an alternative to PE Coated grades.”
CCK and PE: working together
CCK and PE Coated grades can also be combined to create hybrid liners. CCK with a PE Coated extruded reverse side offers good lay flat performance under critical climate conditions. This marries the siliconizing properties of the CCK coating with a strong moisture barrier extrusion layer on the reverse side.
Sieber adds, “The fact that the grades are made up from layers allows converters to combine them to achieve the best mix. Their excellent reverse stability allows converters to choose to use them on the open reverse side. In many applications, however, CCK paper alone is an efficient alternative to PE coated paper.”
Sieber concludes, “In Europe CCK papers have been in ongoing development during the past few years. As a result, CCK with reverse side coating has become better and better, making it a tried and tested grade of choice with a market share of more than 75%.
“It is only in harsh environmental conditions such as those with high humidity where PE Coated paper remains the premier option. Even with more challenging environments, a hybrid solution of CCK paper with PE coating on the reverse is becoming an increasingly popular option.”