APRIL 2013 | VOL. 12 NO. 4 | TAPPI JOURNAL 19 P roduction of lightweight coated paper (LWC) from deinked pulp (DIP) is a growing trend in the industry [1], with some mills using 100% DIP for the base paper [2]. Pilot studies have shown that it is possible to coat a paper made with large fractions of DIP; however, this may cause coating defects, such as streaks and scratches [3], especially with the blade coating process. Coating color optimization combined with film press (for LWC only) or latest technologies such as soft tip blade or curtain coating may help solve such problems. Also, specks in the base paper may be difficult to cover by the coat layer. In most cases, however, optical specifications of the final product are achievable by a combination of deinking and coating. A lower-quality base paper (containing more inks) can be used to reach similar brightness after coating, provided additional coat weight is applied or coating color with higher scattering power is used. Optical properties can be achieved by deinking the base paper and then com- pensating by coating, but the question remains about the best combination of deinking and coating that will lead to optimization of overall production cost. The optical characteristics of coated paper can be calcu- lated using a multilayer Kubelka-Munk approach [4–6]. It has been shown that considering coated paper as a stack of dis- tinct coating layers and paper layer leads to accurate predic- tions of brightness and opacity [7,8]. It is possible to take into account the impregnation of the base paper by the coating color through an additional mixing layer [9]. The multilayer Kubelka-Munk modeling requires identification of the optical characteristics of the coating layer itself; this can be deter- mined from reflectance measurements of coated and uncoat- ed paper, or coating layer deposited on a transparent film, and then using several numerical methods (e.g., [10,11]). The ef- fect of variable composition of DIP (in terms of fiber type, filler, and inks) on optical properties can be accurately pre- dicted thanks to the Kubelka-Munk mixing rules [12,13]. These methods have been successful in optimizing the formu- lation costs of coating colors for various coated paper and board grades [14,15]. The objective of this study was to find the most economical combination of deinking and coating processes to produce coated paper, with base paper formed from DIP. General optimization methods were developed to assess the effect of deinking and coating parameters on the optimum cost for coated paper production. The main target parameter for the cost optimization was the brightness of the coated paper. In addition, the evolution of mechanical properties of the coated paper as a function of deinking process yield and deposited coat weight was also modeled and used as an additional constraint. METHODS The production of DIP of different brightness was carried out on our deinking pilot plant (CTP; Grenoble, France). The fur- nish was a mixture of 30% old newsprint (ONP) and 70% old magazines (OMG). The deinking process used a drum pulper with alkaline chemistry and soap at 19% consistency for 20 min at 45°C; the chemistry was 0.35% sodium hydroxide, 0.6% soap (Serfax MT90 from Stephenson Group; Leeds, UK), 1.75% silicate, and 1% peroxide. The process also used fine screening (0.2 mm slots); two successive flotation steps (Ver- ticell from Kadant; Westford, MA, USA) at 1.2% consistency, 45°C, constant froth flow, and 300% air ratio; thickening with a vacuum filter (15% outlet consistency); screw press (30% outlet consistency); and high-speed dispersing (30% consis- tency, 70°C, specific energy of 60 kWh/ton). Pulp was sam- pled at four locations throughout the deinking line, for further making of handsheets: flotation inlet (“pulp.”), flotation 1 ac- cept (“flot.1”), after flotation 2 accept (“flot.2”), and after dis- persing (“disp.”). The deinking process differed from com- mon practice for LWC DIP. To limit the losses, there was no final washing. In addition, the dispersion step is usually per- Economics of coated paper production made from deinked pulp PATRICK HUBER, LAURENT LYANNAZ, AND BRUNO CARRÉ COATING PEER-REVIEWED ABSTRACT: The fraction of deinked pulp for coated paper production is continually increasing, with some mills using 100% deinked pulp for the base paper. The brightness of the coated paper made from deinked pulp may be reached through a combination of more or less extensive deinking, compensated by appropriate coating, to optimize costs overall. The authors proposed general optimization methods combined with Kubelka-Munk multilayer calcula- tions to find the most economical combination of deinking and coating process that would produce a coated paper made from DIP, at a given target brightness, while maintaining mechanical properties. Application: The methods and software can help papermakers find the least expensive combination of deink- ing and coating process to produce coated paper with targeted optical properties.