Rod Urqhart outlines how the PRINT lab is helping wine label producers
In the last article I mentioned that the PRINT lab had done a significant amount of work for the wine industry of late, and in talking to one of our friendly clients, he suggested that this story should be told.
(In fact, everyone I know connected with the wine industry is friendly - perhaps that is one of the side benefits of the product).By far the most common problem is the phenomenon of labels blistering and creasing after being applied to the surface of wine bottles. When the label goes on, the job looks to be fine, but at some time later, the labels distort and blister.
Whilst this may not be the end of the world for those who consume the contents of the wine bottle, the wine producer is justifiably not happy unless the entire package is presented to the customer at its optimum, and the poor old printer, the paper supplier, and even the bottle manufacturer and bottling company, cop the complaints for a problem that is essentially out of their individual control.
In summary, the effect is a combination of interactions between the paper from which the label is made, the label application process, the surface contours of the bottle to which it is applied, and the influence of moisture.
As we all know, paper swells when wet, and unless the paper label is firmly affixed to the glass bottle it will be free to do just that. Thus an important step is to know how closely the label follows the surface contours of the bottle.
The surface of the glass from which the bottle is made is seldom perfectly smooth, which is an unavoidable artifact of the manufacturing process of the bottles, and depressions in the surface of the glass require that the label bridge the ‘dimple’.
The adhesive on the back of the label will stick tightly to the glass surface when in is in immediate contact, but over the top of a depression there will be a small void underneath the label where the adhesive does not fully touch the glass.
If moisture can be transmitted through the label it can condense on the surface of the glass, particularly in the areas where the depression in the glass forms a cavity. This is especially true for white wines that are served chilled, but can equally occur when bottles are slightly colder than the atmosphere into which they are introduced (from a cellar to the table for example).
We all know that when paper is exposed to moisture, the cellulose fibres in the paper core will want to expand, but where a piece of paper is prevented from expanding by being glued tightly to a surface no differences in formation will be visible.
However, over the area of a depression in the glass, the paper is not restrained and can swell, forming a blister.
Here is a micrograph of a blister:
Here is the glass surface underneath with the paper label removed:
Note that the adhesive has not stuck to the depression in the glass.
The problem is obviously exacerbated by the design of larger labels that expose the label to more potential dimples in the glass.
In order to avoid the problem, obviously the simplest answer would be to use only bottles that are perfectly smooth - however, this is not an option as the commercially available bottles from all manufacturers have some surface imperfections arising from the process by which they are formed.
With regard to the aspect of the label application process, it must be the objective to get the label backing adhesive to contact all areas of the glass as completely as possible, and to try to get the adhesive to the bottom of the dimples in the glass. To the best of my knowledge, the bottlers always try to do just that, and although their technique is outside of my area of expertise, I would assume that a soft applicator roll at maximum pressure would be required.
Moisture-resistant
From the label side, the major contribution to avoidance would be from the best moisture-resistant label possible.
Going back a few years, wine labels were mostly printed on cast coated stocks, and were varnished to give a glossy result, a combination that gave very good resistance to the ingress of moisture. However, fashions change, and labels are now often being designed on matt papers, and even uncoated stocks, that are often not sealed in any way, and are thus porous. This trend has effectively given rise to the rash of complaints that have arisen in the past couple of years as such labels will allow moisture transmission.
Printers and paper suppliers can only act within the specifications given by their customers, and so it is those customers themselves that can help stamp out the problem by making sure that the designers of their labels understand the dynamics that I have just described, and so do not generate label designs that are almost guaranteed to fail.
I would strongly recommend that labels not cover large areas of the bottle, and that labels be varnished, with a matt coating if that sort of finish is desired, as in addition to the moisture seal, such varnishes provide good abrasion resistance to the label.
This way we can stop worrying about the aesthetics of the wine bottle label, and simply enjoy the contents.
