Tech gyaan on paperboards

What is paperboard?
Paper and paperboard, by definition is a mat of interlaced network of cellulosic fibres. These fibres are bound together by an organic compound called lignin. The fibres are to be separated from lignin and re-organised to form a mat which is further calendered and coated to form smooth paper.  Usually, the mat up to 170gsm is termed as paper; above which is paperboard. 

In the process of formation of paperboard, pulping plays the major role in deciding the properties of the final product. Wood basically consists of Cellulose and Lignin, pulping is the process in which lignin is separated from Cellulose.

Pulping can be done either mechanically, by pressing the debarked wood logs against a rotating grindstone thereby softening and breaking of lignin bonds and separating the fibres; or chemically,  by cooking the wood chips in a digester to dissolve the lignin. The fibres derived mechanically are less dense than chemical pulp. Therefore, at a given grammage, the sheet is thicker. 

Furthermore, chemical pulping has lower yield as compared to mechanical process due to the fact that the non-cellulose constituents of the wood are removed. This results in a higher degree of inter-fibre bonding. Furthermore, the average fibre length of wood is longer in case of chemical pulping. The fibres are more flexible. These factors result in a stronger and more flexible sheet. 

Based on these pulp formation and processing techniques, there are four basic types of paperboards namely: white lined chipboard (WLC), solid bleached board or sulphate (SBB / SBS), folding boxboard (FBB) and coated unbleached Kraft board (CUK / SUB).

Among these, SBS and FBB are pure cellulose primary (virgin) boards whereas WLC and CUK are produced from partly recycled fibres. 

Solid bleached board (SBB / SBS)

SBS is considered as premium grades for packaging and graphical purposes in FMCG Industry (Typically high end personal care and cosmetic brands). Being a 100% virgin fibre board, SBS is preferred choice for food packaging applications like paper cups and liquid packaging. It is made up of bleached chemical pulp coated with mineral or synthetic pigments on top and sometimes on reverse side, thus this coated back makes it well suited for book covers and greeting cards which require back side printing. This grade of paperboard has high brightness, smoothness and superior surface and printing characteristics. It has surface brightness of 90% ISO. 

SBS is preferred grade when it comes to purity, good appearance and runnability of packaging material is required.

ITC has two pure SBS grades and one modified SBS grade in its product offerings: Pearl Propac, Optical Brightening Agent(OBA) Free ,Saphire Graphik is blue white and Carte Lumina which is a high whiteness board. Other grades available in Indian Market is Ultima, a blue white board.

Folding box board (FBB) 

This board comprises middle layers of mechanical pulp sandwiched between layers of bleached chemical pulp. The mechanical pulp at the centre makes the board stiffer as compared to SBS. The top and reverse sides of this board may be coated with mineral or synthetic pigments. As the bleached chemical pulp layer is translucent the reverse side of the board appears cream (or manila) in colour. However, if the mechanical pulp in the middle layers is given a mild chemical treatment, it becomes lighter in colour and this makes the reverse side colour lighter in shade.

The reverse side layer may be coated with a white mineral pigment coating, thus becoming a white back folding box board. Similar to SBS, FBB is produced from virgin fibres and is suitable for food packaging applications. It is considered ideal for cigarettes, cosmetics, pharmaceuticals and graphical applications. In India FBB is the primary grade of packaging substrate used by most of the companies.

ITC portfolio comprises of three grades of FBB namely: Cyber XL Pac, Cyber Premium and Saphire XL, blue white whereas other grade available is Tuffcote which is yellow white. 

Solid unbleached board (SUB / CUK) 

Exclusively made from unbleached chemical pulp, SUB is brown in colour. It can be coated with a white mineral pigment coating in order to make the surface white. Some part of unbleached chemical pulp may be replaced with recycled fibres. SUB is used where there is a high strength requirement in terms of puncture and tear resistance and good wet strength is required such as for bottle or as a base for liquid packaging.

White lined chipboard (WLC) (white back board / grey back board) 

WLC is widely used and manufactured board worldwide. It is also known as coated recycled board, grey back or duplex board. It comprises of 60-100% recycled fibres distributed across different layers. The middle plies, which are grey in colour, are made of recycled pulp recovered from mixed papers or carton waste. The top layer of bleached chemical pulp is coated with white mineral pigment. The layers between middle layer and top layer may comprise of bleached chemical pulp or mechanical pulp. The external appearance may be white by the use of bleached chemical pulp and, possibly, a white mineral pigment coating. The surface brightness of WLC is 80 to 85% ISO.

The recycled boards are thinner as they have a lower gsm:caliper ratio as compared to the virgin boards. 

The recycled paper manufacturing in India is dominated by regional players with ITC as the only national supplier in this category. ITC’s recycled board offerings again comprise of three products: Eco Natura, Eco Blanca and Neo White Bliss.

Key Properties of Paperboards

It has to be noted that paperboard quality depends on various parameters like 
·  GSM, Bulk & Calliper
·  Stiffness
·  Smoothness
·  Optical properties- Shade

The prices of a paperboard typically increase with increasing whiteness, bulk and cleanliness/hygiene. 

It has to be noted that grammage and caliper of paper or paperboard are unrelated parameters.

For instance, ITC’s FBB Cyber XL 200gsm board is 0.302 mm thick while 200gsm of Safire Graphik, ITC’s SBS, is 0.224mm thick.

The thickness and strength of a paperboard depends on the middle fibre layer. Denser the fibres, more the strength, higher the value of the board and thus higher will be the price.

Indian Players

Notable board producers in India include NR Agarwal (WLC), ITC (WLC, SBS and FBB), JK Paper (WLC), Gayatrishakti (WLC), Murli Industries (SBS, WLC and FBB), Rainbow (WLC) and West Coast (WLC). Besides these, there are many small mills in India exclusively producing WLC boards.