Fresh bottle labeling, also called "hot bottle" labeling, means labeling a blow-molded plastic bottle even before it has shrunk to its ultimate size.

The largest portion of blow-molded containers produced in the U.S. are made from high-density polyethylene (HDPE). When these hot containers drop from the mold cavities, they are bigger than their specified size, and in fact test as medium-density polyethylene. Twenty-four hours after molding, the HDPE container will have shrunk to its ultimate size. A density test will show that the product is made of high-density polyethylene.

Two types of manufacturers seek to label their plastic bottles while they are still hot. Plastic container manufacturers, who also decorate for their customers, seek to label their containers immediately after molding to avoid double handling of the containers. High-volume consumer products manufacturers who blow their own containers want to do the forming, labeling, filling and case-packing as a continuous operation for greatest efficiency.

In both of the above scenarios, the containers will shrink after the labels have been applied. This change in size puts stresses and challenges on both the label adhesive and the face stock.

Blow-molded, unfilled containers are frequently inflated with air to present a rigid surface for labeling. Sometimes containers are also screen-printed with UV inks during the labeling operation. Both of these operations compound the distortion of the containers. Another potential problem concerns the suggested inflation pressure for labeling unfilled containers—3 to 5 psi. Operators frequently feel "if a little is good, more will be better." Higher pressures than that recommended further increase the container's size. Heat generated by UV lamps will also soften the plastic and increase the container's exterior dimensions.

Many packagers of high viscosity products such as syrups and salad dressings heat their products prior to bottle filling in order to shorten the filling time. The introduction of a hot product into the HDPE container also softens the plastic and increases the size of the container in a fashion very similar to that of fresh bottle labeling.

In hot-fill situations, the manufacturer may be filling prelabeled containers or post-labeling the filled hot containers. The stresses exerted upon the labels are significant, yet different in each case. Who said labeling was a simple operation?

The challenges presented by fresh-bottle, hot-bottle, and hot-fill labeling are manageable once you understand the environment and select suitable materials. The pressure-sensitive adhesive, for instance, should have these characteristics:

• Heat resistance
• Strong bond to HDPE
• Initial tack just slightly lower than the ultimate bond
• Good cohesive strength

The label face stock should meet these requirements:

• Ability to stretch and/or contract (try vinyl or MDPE)
• High internal strength in machine direction
• Conformability

A third criterion, for fresh bottle labeling, is a good wipe-down action that insures intimate contact of the entire label surface with the plastic container.

Most suppliers of pressure-sensitive label materials have had experience with fresh-bottle labeling. They have developed stocks for these applications. The labelmaker can also take advantage of his supplier's technical expertise.

Fortunately, the obstacles, frustration, development and testing of fresh-bottle labeling technology are largely behind us. You can now benefit from the experience of those who pioneered this decoration technique.

Skip Heintzelman

Consulting Technical Editor

704/366-5204