At the end of this module, you will be able to:
- List the sheet properties that are enhanced by paper coating
- List the three main ingredient categories used in paper coating mixtures
- Describe the purpose of pigments, binders, and additives in coating mixtures
- Describe the functionality of the more common paper coating pigments and binders
- Identify and describe common coating additives
The following key questions are answered in this module:
Why are some paper and board grades coated?
Paper and board grades can be coated to enhance printability, visual properties (brightness, opacity, gloss), or functionality (ink holdout, glueability) of the sheet.
What does a typical paper or board coating mixture contain?
Some coating mixtures contain 10 or more ingredients. A typical print-grade coating formula might contain 83% pigment, 13% binder and 4% additives (by percent of dry weight). These ingredients are typically dispersed in water.
What is the purpose of pigments in coating mixtures?
Pigments used in paper and board coatings govern the final optical and printing properties of the sheet. They do this by providing brightness, whiteness, smoothness, and opacity.
Why do some coating mixtures smell like latex paint?
Latex can be used as a binder in coating mixtures and also in latex paints. Binders hold pigment particles to each other and to the sheet, help fill voids between pigment particles, and influence the viscosity and water retention of the solution.
Antifoamers and defoamers can be used to control foam in coating systems. What is the difference?
Antifoamers prevent foam from forming, whie defoamers help eliminate foam after it has formed.
Below is a transcript of the video sample provided for this module:
Binders can be natural or synthetic and they have three functions in paper coatings. One, to hold the pigment particles to each other and to the bay sheet. Two, to partially fill voids between the pigment particles and improve printability. And three, to affect the viscosity and water retention of the coating solution. Natural binders include starches and proteins from either animal and vegetable sources. They can be either grown specifically for the job or obtained as a byproduct. Starch is the most important natural binder used in paper coatings. Other natural binders are casein and soy polymer. Casein is derived from excess milk production and is the best of all binders when the quality is good. Unfortunately, quality is variable and so is availability.
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