Varying thicknesses of film at the end seal can cause sealing problems, especially at the transition point between two and four layers created by the fin seal, gussets, wrinkles and creases, as well at the corners. Applications of pressure and heat (if applicable) must be great enough to cause the sealant layer to flow into and seal off these voids. 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 first in a four-part series, will examine this process on horizontal flow wrappers; Part 2 considers these issues on vertical baggers.
Any impediment that disturbs the even flow of film can distort packages and cause leakers; a combination of factors is often to blame. To find the causes of these problems and fix them we recommend a comprehensive analysis, beginning with the film roll and following along sequentially as the film is unwound, formed, filled, and sealed.
Too much, too little, or uneven tension can cause wrinkles and creases.
- Make sure the film coming off the roll is properly centered, side-to-side, over the forming box.
- Check for bent rollers, worn bearings, or other impediments that can keep the rollers from turning freely.
- Make sure the power unwind and the film tension rollers are adjusted properly.
- Keep in mind that inadequate slip on the film creates extra tension that can cause wrinkles and creases.
Inconsistent product size and off-center positioning of the product in the ultimate package can create or exacerbate film wrinkles in the end seals. This is especially true with round or irregularly shaped products. Variances should be monitored and eliminated whenever possible.
Problems forming the fin seal or drawing the film tube through the wrapper can create unintended wrinkles and creases.
- Clean product contamination from the fin wheels.
- Check the fin wheels for wear or damage.
- On heat seal applications, make sure the fin wheels are not too hot.
- Make sure the fin wheels are set-up properly, to ensure film tube consistency and quality seals.
- Ensure that the serration pattern is optimally designed for drawing and sealing the film in use.
Damaged or improperly installed deck plates can twist the package and lead to undesired wrinkles and creases.
- Take care during frequent removal and reinstallation of deck plates—they may seem inconsequential but can be easily bent or otherwise damaged.
- Install deck plates properly, and avoid using screws that protrude and inhibit package movement.
As the film tube, with the product inside, moves toward the sealing and cutting head there are a few additional considerations:
- If tuckers are used, refine their adjustments to create smoother, more consistent folds.
- To ensure proper presentation of the film tube and product to the cutting and sealing head, adjust the end seal pause, or dwell, so that the crimpers move at the same or at a slightly faster speed than the film.
Vertical Adjustment of the Sealing Head
- The cutting and sealing head should be adjusted vertically so that the crimpers come together midway between the top and bottom of the package. Packages that get pulled upward or downward by the crimpers are more likely to develop wrinkles and creases.
Taking steps to minimize or eliminate end seal wrinkles and creases is an important step toward optimizing seal quality. Our next blog post, Part 2 of 4, will explore how to refine the package formation process on vertical baggers. The third and fourth installments in this series will review Machine Adjustment Procedures and Crimper and Sealing Jaw Designs that improve seal quality across multiple layers of film at the end seal.
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