Achieving strength and productivity

By Brian Duffy, Senior Industry Development Manager, Board & Packaging Grades, and Brad Benz, Senior Industry Technical Consultant, Nalco Company

BRUSSELS, Dec. 12, 2011 (RISI) - In recent years, containerboard demand has been rebounding in the worldwide economic recovery and globalization of the market. Faster machine speeds, increased operating rates, and the demand for fiber to fulfill production capacity needs has been an ongoing challenge to the industry. This demand has caused fiber prices to escalate, especially recycled fiber such as OCC from recovery processes. Many producers are implementing plans around fiber reduction as it directly relates to manufacturing cost and selling prices. Additionally, management teams are discussing this every day in their plants. Having a well-managed chemical program and a well-run mechanical operation is a highly important and effective way to sustain the process of fiber reduction without compromising strength such as ECT or compression strength.

Moving to lighter weights, strength, and energy costs are critical drivers in the board and packaging market. However, achieving the desired end-product performance to satisfy demand while maintaining and improving production efficiency can be a difficult task.

Table 1 - Basis weights for key linerboard grades (Source: RISI International, 2007)

The "lightweighting" of containerboard

The shift to lighter basis weights for containerboard has been a compelling industry trend for the last 20 years. Since the adoption of Alternate Rule 41 in 1990, many users have opted for box compression standards as the preferred method for specifying their boxes. Several factors have significantly influenced this shift, including advances in manufacturing technology, shifts in fiber supply, supply chain considerations and sustainability awareness. Over time, basis weights have also been steadily declining for key linerboard grades, as illustrated in Table 1.

Achieving strength and reduced basis weight targets can be a challenge for any papermaker, especially when lower quality fibers are part of the furnish mix. Use of Nalco's patented METRIX^® technology program allows paperboard manufacturers to increase strength, lower basis weight, enhance production and improve sheet quality.

Variability in quality and supply of raw materials also presents significant challenges to paperboard manufacturers. Increasing refining to achieve strength often leads to reduced drainage, lower retention and higher energy costs. Increasing starch dosages may also be ineffective as fibers become saturated and additional starch cannot be retained.

Overuse of other cationic additives such as alum and coagulants may also cause the furnish to become cationically dispersed, affecting retention, sizing, system foam, and finished product quality. Nalco developed the multi-component METRIX retention, drainage, and pressability program to allow board manufacturers to simultaneously optimize basis weight, strength, caliper and sheet smoothness. For example, the METRIX technology program provides papermakers with the flexibility to increase strength, while at the same time reducing basis weight, increasing machine speed, improving sheet properties and lowering fiber and energy costs.

Over the past 10 years, Nalco has committed significant time and research investment into the continued development of METRIX technology. Currently, the 7th generation of this technology is being marketed, and the 8th generation will be available globally in late 2012.

Case study example

Mill Overview

Grade: LinerboardBasis weight produced: 35 and 42#/1000ft² (170 and 205 g/m²)Machine type: Single ply fourdrinierPress type: 1st Straight through, 2nd LNPProduction rate: 45 tons/hr Machine speed: 1,700-2,250 ft/min (518-686 m/min)Furnish: 65% OCC and 35% kraftWet-end chemistry: CAT PAM flocculant, thin & thick stock starch, rosin size & alum

pH: Acid

A linerboard manufacturer capable of producing 1,200 tons/day (1,091 tonnes/day) realized serial reductions in production. Most days averaged 1,030 tons (938 tonnes) which was due to a need for higher basis weight to meet quality specifications. Low production was most prevalent on 35# (170 g/m²) high performance linerboard and 42# (205 g/m²) linerboard. This integrated board mill was using a higher percentage of recycle fiber in comparison with unbleached kraft pulp, 65% and 35% respectively. Recycled fiber quality had also suffered over the years.

The thick stock Canadian standard freeness of recycled fiber had declined by 100 mL or greater from the facility's recycle plant. Lower freeness was making it increasingly difficult to achieve sheet quality parameters at nominal basis weight and target speed/production. On occasion, the paper machine in question was running at target speed, but rarely longer than one day. Several mechanical changes (refining, fourdrinier set-up, pressing, drying) contributed to minimal improvements in strength and speed. In addition, several wet end chemical trials (coagulant, flocculant, starch, silica, strength resin) achieved minimal to moderate benefit in quality parameters. To meet quality goals, the mill was forced to run 2-3 lb (0.9-1.4 kg) over standard basis weight on select grades for this paper machine. This manufacturer sold finished board on a manufactured square foot/meter basis. Therefore, running over target created several drawbacks which included increased fiber cost, slower machine speed, decreased production rates, and higher energy and unit cost per ton of linerboard produced.

To be continued ... Read Part II here.

Pulp & Paper International is FREE to qualified subscribers. Click here to find out more.