The term glaze is often used when describing problems experienced with the offset printing process, usually concerning rubber rollers. In reality, the term can be used for a variety of conditions each of which has different causes and different symptoms and therefore, different remedies.
There is no debate that glaze needs to be removed. Hence, let’s first identify the types of glaze so that the correct remedy can be made. An incorrect solution obviously leads to wasted time and effort and a reduction in the user’s confidence in the product and the brand. A lose-lose situation.
Types of Glaze
Fundamentally, there are three types of glaze, imparted by:
1. Oxidised ink vehicle (varnish)
2. Calcium deposition
3. Dried gum glaze
Definition
The term glaze originates from the glassy or polished appearance a roller’s surface caused when the roller is coated with oxidised ink vehicle and dried gum. This retards the ability of the roller to transport an even film of ink. It happens due to reduced adhesion between the roller surface and the ink. Though this may be caused by a number of different reasons, the failure of the roller to transport ink is generically known as glaze.
When using aromatic free washes, if roller maintenance is less than an optimal, then oxidised ink vehicle slowly builds up in the pores on the roller surface. This compromises the hardness and transfer properties of the roller. Left unchecked, this then becomes the glaze. Once formed, the glaze can only be removed using either a strong oxygenated solvent (not wash) or using a specialised glaze removal paste.
Another very common cause of glaze is the deposition of a layer of insoluble calcium salts on the roller or blanket surface. These salts are hydrophilic and thus attract water to the roller surface, which in turn prevents or reduces the adhesion of ink. This thin layer of insoluble salts is often invisible; however, if the condition becomes severe, it may be observed as white powdery deposits. The sources of the calcium can be paper, water, and inks. Among it, some papers contain up to 30% calcium carbonate by weight as a filler, opacifier or whitening agent, the lower-cost magentas are known to contain high levels of calcium.
In severe condition, decalcification may also need to be carried out on bareback rubber rollers in the dampening system.
It needs to be understood clearly that these troublesome calcium salts are completely insoluble in pressroom solvents and require specialty cleaners to dissolve and remove them. As far as the existing solutions available in the market are concerned, the only water finished decalcifier offered is by TechNova.
Other than three most common causes of glaze as above, there are a few others, fewer common forms of glaze. For example:
Conclusion
Prevention is always better than cure and, therefore, after providing a remedy to the problem by identifying the type and source of the glaze and utilising an appropriate glaze removal product, the next step is to help the user identify the underlying cause of the problem and to suggest a counter-strategy. This may include the following:
Chris Searle
Chris Searle is the author of the article. He is an industrial chemist who has been working in graphic arts industry for over 30 years. Chris has been spearheading TechNova’s technological advances in chemical business for years, the objective has been to offer its customer with new solutions. He spends significant amount of time in India to work with team TechNova.
Avinash Kawadkar
The article is indigenised by Avinash Kawadkar who currently works for TechNova’s chemical business. He has been working in the graphic arts industry for over two decades in India as well as many overseas markets. He specialises in product application and manages business development portfolio.
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