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This work examines the effect of coating pore structure on the evaporation behaviour of mineral oil, as a typical heatset web-offset ink solvent. Two different kinds of coating pigments are compared, a standard ground calcium carbonate (GCC) and a highly porous modified calcium carbonate (MCC) with fine intraparticle pores. The aim is to identify relevant pore structure parameters and their effect on the drying rate. Two internal stages of drying were identified for both structures : a rising drying rate period and a falling rate period. In the rising rate period, the effect of film tlow was of particular relevance for the case of GCC based structures : binder, filling the pore structure decreases the detail of geometry and thus reduces the film flow tendency, progressively depressing the drying rate. At the onset of the falling rate period the liquid phase is in the form of disconnected liquid clusters. Therefore, the diffusion resistance becomes a dominant factor. Because of the high permeability of MCC systems the evaporation rate proofed to be largely unsusceptible to the binder concentration. However, the GCC pigment systems exhibited an extended peak of the drying rate as a result of the increasing diffusion resistance with increasing binder content.

The effective thermal conductivity is an important element in understanding the thermal response to heating of a paper coating, e.g. during drying in heatset web-offset, and thus it not only affects the drying efficiency but also affects print quality detriments like web fluting. This study examines both the effective thermal conductivity of liquid-saturated ground calcium carbonate coating structures as well as the vaporisation behaviour from these structures. The liquids used for saturation were mineral oil and water in order to resemble ink and fountain solution, respectively, both of which are present in the traditional heatset web-offset process. The effective thermal conductivities of liquid-saturated coating structures are discussed in regard to the corresponding unsaturated systems by using a Lumped Parameter Model. It is shown that the liquid saturation has a dominant effect in determining the effective thermal conductivity. Since this effect is not fully captured by the model, other mechanisms like an apparent pigment–pigment connectivity increase by liquid bridging and the role of liquid in changing the contact resistance during the measurement of thermal conductivity are discussed. In addition, the transformation of three-dimensional structures to an equivalent two-dimensional modelling is evaluated. The vaporisation behaviour of mineral oil and water is studied by a thermogravimetric analysis. By following the changes in maximum evaporation temperatures and evaporation rates, the addition of binder is seen to lead to a reduction in the vaporisation rate of both liquids. Since there is little to no interaction between the liquids and the binder, the confinement caused by the geometry change induced by binder addition is identified as the mechanism resulting in elevated vapour pressure within the structure.

紙の着色コーティングの熱伝導度は，コーティングの構造内部での接続性や材料の配置に関係していることが明らかにされている。本研究において検討されるような炭酸カルシウムとラテックスバインダーとの場合には，湿潤状態でのバインダーと顔料との相対的な位置関係がコロイド的な相互作用により決まる。すなわち，これは分離と凝集の挙動であり，ほとんどの場合，枯渇凝集の形をとる。枯渇凝集においては，限界的用量のラテックスが加えられると顔料の充填が崩壊する。乾燥させると構造が固化することから，ラテックスバインダーは当初は顔料粒子間の接触点の中央に位置していることが分かる。炭酸カルシウム顔料を含む構造の熱伝導度は，充填密度，そして分散剤ポリマー（ポリアクリル酸）によって与えられる接続性によって決まる。ガラス転移温度（Tg）が低い場合，ラテックスは変形し押し出されるため微小孔を生成し，また伝熱経路がいっそう屈曲する。中間的な領域のTgのラテックスの場合，変形は減るので，接触点のみでの局所的な接続性となり，少添加量で最大限に熱伝導に寄与する。高添加量ではラテックスの絶縁特性が支配的になる。高いTgのラテックスは剛体球として挙動し，接触面積は全くないか，あっても少ない上，顔料接触点の間から押し出されるので，密な充填構造を作り熱伝導度は比較的高くなる。

Thermal conductivity of paper coatings is increasingly important in the performance of many printing processes, including traditional heatset web offset and thermal papers, as well as digital processes, such as electrophotography. This work studies the extension of a Modified Lumped Parameter Model, previously used successfully to describe talc coatings, to model the thermal conductivity–coating structure relationships of calcium carbonate (gcc: 60 wt% < 2 μm) coatings. A series of compact tablets were used to provide experimental values of thermal diffusivity and conductivity. The samples studied covered a range of latex binder addition levels, namely 0–25 parts, based on 100 parts pigment, of 0.2 μm styrene acrylate latex. Combining the observed thermal properties with knowledge of the pore structure changes induced by the latex addition, it is possible to establish initial correlation with the model, in which the connectivity of the structure is increased at low latex dose illustrating the initial increase in effective thermal conductivity. The practically hard sphere properties of the latex used, combined with the broad size distribution of the gcc, produce a disruptive packing effect as the dose level increases, such that the conductivity reflects a competition between the increasing connectivity provided by the latex versus the increasing relative pore size in the network structure. It is recognized that the fixed pigment volume in the model unit cell diverts from a true representation of the residual porosity. At the highest latex dose levels, the intrinsically less conducting properties of the latex begin to dominate.