Novel Technology to Produce Ultra High Gloss Coated Paper, 2000 Coating Conference Proceedings

C. Wakai, H. Morii, H. Fujiwara--A novel process for production of coated paper was developed. The technology can be used on conventional double coating facilities. The precoating is usual pigment coating and the material used for the top coating is a newly developed synthetic polymer pigment. Emulsion of the polymer pigment is applied without binders and then metered. Although the coat weight of the top coating was less than 1 g/m 2 per side, the sheet gloss of uncalendered coated paper was around 70 % and after supercalendering it was around 90 %. Coated paper obtained by this technology can be printed on web offset presses because of its good blistering resistance caused by relatively low total coat weights. SEM (Scanning Electron Microscope) and AFM (Atomic Force Microscope) show existence of an even layer composed by the spherical polymer particles. INTRODUCTION Pigment coating is the technology to increase sheet properties and printing properties of printing paper such as sheet gloss, print gloss, pick strength and smoothness. To increase sheet gloss, calendering (supercalendering or hot soft-nip calendering) is usually used. With calendering, coated paper looses its bulk caused by the pressure under calendering. Cast coating is an alternative method to produce high gloss and high bulk paper. In this process, wet coating layer composed of pigments and binders contacts the mirror finished cast drum. One of the disadvantages of cast coating is its slow production speed. And it means high production cost. Several ideas have been suggested to produce high gloss paper using heated calender instead of cast drums [1-3]. Those technologies are based on coating of pigment / polymeric latex mixture or water-soluble polymer followed by calendering with heated calender. However, gloss development was not sufficient and the technologies do not seem to be commercially available. To produce high gloss paper only by conventional pigment coating, high coat weights must be necessary. In case of high basis weight coated paper, some cases 30 g/m 2 per side (or more) of coating color is applied by double or triple coating. Sheet gloss of such coated papers (usually basis weight is high) is high, and many cases over 80 %. Density and air resistances for such papers are also high because of high coat weights and calendering. If such paper is printed on a heat set web offset press, blistering is a big problem because of high air resistance. Consequently, it has been difficult to produce web offset grade with high sheet gloss and high basis weight through conventional pigment coating technology even if the productivity is good and production cost is reasonable. Therefore, development of a new technology has been required which we can produce high gloss, high bulk and low air resistance paper with. We found that a combination of conventional pigment coating and following synthetic pigment emulsion coating showed an extremely high potentiality to produce very high gloss paper. Conventional double coating system can be used for this technology. After supercalendering, sheet gloss of the paper obtained by this technology is over than 85 %, and many cases around 90 %, although the coat weight of the top emulsion coating is less than 1 g/m 2 per side. It means that the total coat weights are almost the same level as single coating. Because of relatively low coat weights, density of the coated paper is low and air resistance is low. One of the biggest advantages of the coated paper obtained by this technology is that ultra high gloss, high bulk, web offset grade can be produced.