There is no one-size-fits-all solution for the design of crimpers and sealing jaws on horizontal flow wrappers and vertical baggers; they should be specified according to the packaging film, products, and conditions of your packaging operation.
This post, the last in our four-part series, reviews design options for crimpers and jaws. The optimal combination of serration patterns, materials, and special features can dramatically improve seal quality and productivity when sealing across extra film layers at the end seal.
Transitions on the end seal between varying thicknesses of film created by the fin seal, lap seal, gussets, and wrinkles make it more difficult to maintain the operating window necessary for quality seals:
Too little pressure leaves gaps, or leakers, at these transition zones.
Excess pressure can easily crush or split the end seal.
Overheating distorts the seal and can cause poor hot tack, where the film springs back open at transition zones or “moons,” before the seal can set.
The end results can be packages that fail to protect the product or have little appeal to consumers, as well as lost production time spent attempting to meet package quality standards.
Varying thicknesses of film at the end seal can cause sealing problems, especially at the transition points of multiple film layers created by the fin or lap seal, gussets, wrinkles, creases, and at the corners. Applications of pressure and heat must be great enough to cause the sealant layer to flow into and seal off these voids. However, excess pressure can easily crush or split the end seal, while overheating distorts the seal and can cause poor hot tack, where the film springs back open, or “moons,” before the seal can set.
The operating window for creating quality seals can be elusive, resulting in packages that leak, are distorted, and have little appeal to consumers.
An important step in troubleshooting these issues is to eliminate unintended wrinkles and creases. This post, the second in a four-part series, will examine this process on vertical baggers; Part 1 covered these issues on horizontal flow wrappers.
Any impediment that disturbs the even flow of film can distort packages and create leakers; a combination of factors is often to blame. To find the causes of these problems and fix them we recommend a comprehensive analysis of design, condition, and adjustment, beginning with the film roll and following along sequentially as the film is unwound, formed, filled, and sealed.
Film Contact with the Forming Collar
The wing of the forming collar should completely and evenly support the film as the flat web is formed into a tube. Too much, too little, or uneven tension can cause wrinkles and creases.
For heat seal applications, each packaging film structure has a Seal Initiation Temperature (SIT), at which the sealant layer is heated enough to flow into and seal off gaps in the end seal and provide a minimally acceptable seal, and a Maximum Temperature, beyond which the film distorts, fractures, or has inadequate hot tack (seal strength and integrity while the seal is still warm). The temperature range between the minimum and maximum is the film’s Operating Window.
For a number of reasons, regulating heat is not as straightforward as simply adjusting the temperature setting within the operating window for the film you are running.
♦ The sealing face of crimpers and sealing jaws is often hotter in the middle than at the ends, where heat dissipates more quickly. These inconsistencies are readily apparent in the thermal profile shown below: