While loosing market share for much of the last three decades, solid board packaging still has a niche market in items such as fish boxes, etc. and is described below for the benefit of packaging students.


Solid fiberboard for case making is composed of 2 to 5 plies of board laminated together on a machine called a "paster". The multiple plies distinguish solid fiberboard from carton board which is just one ply produced on a board machine.


In any combination, solid board consists of one or more layers of container middles, normally with an outer liner of light weight laminating Kraft. In some instances a Kraft liner is also used on the underside of the board.

The total caliper of the board is determined by the number of plies and the caliper of each, and the outward appearance by the color of the Kraft liner. Standard container middles in use are 0.024" and 0.030" in caliper (610 and 762 microns) and the standard Kraft liner 0.00411 (70 microns). The variation in numbers and caliper of the various plies permits a range of solid boards of 0.038" to 0.10211 total caliper.

Further variation can be obtained by using 0.01511 (260 microns) wet strength Kraft and 0.02811 (700 microns) aquapruf middles, to product such as Aquapruf solid board. Water resistant adhesives are used in the lamination of this product.


The various plies are laminated on a paster which consists of a series of reel stands, glue applicators, a drying section and a slitting and cutting section. Schematics of the production process are shown below:

Reels: Reels held in position pre laminating.

Adhesive Application: Glue is applied to middles.

Pressing and Drying: The various plies are brought together.

Finishing: The laminated board is cut to required blank size.

Starch adhesive is used for laminating container middles to Kraft liners and silicate between plies of container middles. P V A is used when producing Aquapruf board. The application of too much adhesive will require a lower running rate. It is important at this stage that the board is held at the correct tension and the edges are aligned.

Pressing and Drying

After the liners and middles meet at the nip roll, they pass through a series of driven rolls, after which they are carried along under pressure through the curing section before leaving the combiner. The pressure section is between 20 to 50 feet in length and each set of rolls placed consecutively applies a higher degree of pressure, to ensure that the adhesive is not squeezed out along the edges of the board. To keep the board an even caliper between each set of rollers, the pressure rolls vary in diameter by approximately five thousandths of an inch, with the larger roll first, making each set of rolls pull just a little faster than those proceeding.


After leaving the pressure section, the board passes under tension to the rotary trimming and slitting knives which cut the board to the required case blank width. Trim from edges of the web is removed as a continuous strip, and is collected in scrap boxes for removal. The manufactured strips are then chopped to the required case blank length. Some pasters are equipped with duplex cut offs. Sheets are finally discharged from the paster where they are manually stacked at the take off. Manual methods are employed as the board sometimes warps precluding the use of automatic machinery. The take off operator also checks the quality of the blanks leaving the paster.

Schematic of Laminating Process


Most pasters can laminate 5 plies of board and will have 10 reel stands, thereby having a reserve reel for each ply for changeover during running.

One reel is fed from the top, the next from the bottom, thus causing the edges of the web to push against each other to prevent curling.

Kraft rolls would be placed at the two ends of the reel stand with the container middles in the center, in the same relative order in which they are combined into solid board.

Adhesive Application

The plies are pulled through the gluing and drying sections. Glue is applied by rolls before the plies are brought together at the nip. In making solid board, no adhesive is applied to the top or bottom liner. Generally, the adhesive is applied to the top and bottom of the first ply of container middles and to the bottom of each of the second and third plies when making five ply board.