The Effect of Bottle Shape on Shrink Quality
With the advent of full bottle shrink labels marketers have had a new world of packaging options open up to them. Never before has it been so easy for small producers to compete for attention on the shelf. Hand-in-hand with shrink labels' popularity has been the increasing complexity of the shape and design of containers.
When product managers or marketing teams decide on packaging, they often focus on uniqueness and customer appeal and do not put enough focus on possible production difficulties. The container shape chosen could make life difficult for the production person responsible for the quality of shrink on the finished package.
The easiest possible container shape for heat shrink labelling is a perfect cylinder. However, this ideal container shape is often eschewed for a more complex-and eye-catching-design, potentially causing problems during label shrinking. Let's explore some of the shape challenges you may encounter and how they affect shrinking:
Vertical Edges - i.e. square containers
Can cause local areas of distortion to the shrink label
Can cause label tearing on the edges
Can result in areas shielded from direct influence of the heat source
Changing Cross-Section - Where the label needs to shrink more in some areas than others
Can cause distortion of the label print
Can cause wrinkling in areas with smaller cross-section
Extreme changes can cause tearing or uneven shrinking
Tapers - Different from changing cross-section in that they are continuous or more pronounced in one direction
Can cause the label to preferentially shift in one direction when it is first heated, leading to incorrectpositioning
There are remedies for the problems listed above but there is not a generic fix. Each application must be considered carefully and often requires its own unique heat shrink solution. Some examples of techniques and tricks to get a successful shrink are outlined below:
Tacking - If a label has a tendency to shift during shrink, tacking is often necessary. Tacking involves locating a lock point on the bottle (a lip, crevice, or circumferential edge) and hitting that location with
heat before the rest of the bottle. This locks the label in place before the application of bulk heat shrinks the remainder of the label.
Spin - A bottle with sharp vertical edges will often preferentially shrink on the faces directly facing the heat. It is sometimes necessary in these cases to install devices that will spin the bottle as the heat is applied.
Preferential Heat - Bottles with very complex shapes will often require more heat in some sections of the bottle than others, to further activate the heat shrink label in those areas. This can lead to complex heat tunnel designs, additional heaters, heated air knives for increased heat impingement, and other advanced solutions to properly distribute the heat as required.
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