Cause and Countermeasures for Sealing Failures in Packaging Machines |Troubleshooting for Packaging Defects
There are various types of packaging machines, but the mechanism used to close the bag is common, in that it is sealed by heat.
“Sealing Failure” is the most frequent problem in the sealing process.
Status and causes of the trouble are on a case-by-case basis, but they are often caused not by the machines themselves, but by machine adjustments.
This section explains typical examples of seal failures and the countermeasures.
What is the seal failure of the packaging machine?
Food packaging in Japan began in the 1960s and has been evaluated as the world’s top-class accuracy due to advance of technology.
However, problems such as seal failure cannot be eliminated.
There are various types of seal failure, such as incomplete sealing, wrinkles or scratches, product in seal and so on.
Not only will the loss of products decrease profitability, but in modern times when food safety and thorough hygiene management are required, the defective products immediately lead to a negative image of consumers, which has a major impact on product sales.
Cause and Countermeasures for Sealing Failures of Packaging Machines
When a machine malfunction occurs, we tend to regard it as “a machine malfunction,” but there are many cases in which the problem is solved by adjustment of settings and maintenance of the packaging machine.
Plastic film for food packaging has a difference in thickness and material, so if the setting of the packaging machine is not appropriate for that, sealing failure will occur.
The main causes are the following 4 types.
- Improper sealing temperature: Unbonded area remains, shrinks, edge breaks
- Insufficient sealing time: Unbonded parts remain, making the bag easy to break open.
- Insufficient cleaning of sealed parts: Possible scratches or product contamination
- Sealing failure caused by static electricity: wrinkles, contents are attracted inward
Improper sealing temperature
There are many types of plastic films, and if they are not used at the proper temperature according to the material or thickness, unevenness or shrinkage will occur at the sealed point, which may cause sealing failure.
Features of typical food-use film materials are as follows.
|LDPE (low-density polyethylene)||LDPE (low-density polyethylene) is excellent in moisture resistance, water resistance, acid resistance, heat sealability, but is weak in oil resistance, organic solvent resistance, and heat resistance.|
|CPP (cast polypropylene)||CPP (cast polypropylene) is superior to LDPE in terms of moisture barrier property, transparency, and strength. Flexibility and impact resistance are weak.|
|OPP (biaxially oriented polypropylene)||OPP (biaxially oriented polypropylene) is excellent in tensile strength, moisture barrier property, and transparency, but is unsuitable for long-term storage.|
|KOP (polyvinylidene chloride coated OPP)||KOP (polyvinylidene chloride coated OPP) is excellent in gas barrier property, moisture barrier property, flavor retention property, etc.|
|PET (polyester)||PET (polyester) is excellent in cold resistance and heat resistance, and it is suitable for frozen foods and retort pouches.
It has good flavor preservability and is suitable for packing coffee, spice, etc.
Insufficient sealing time
Higher bag-making speed is required to improve working efficiency. However, if time of sealing is insufficient, sealing failure is likely to occur.
The most frequent problem is the peeling of the seal. If sealing time is insufficient with a high temperature, the seal may be broken.
In addition, because the sealing strength becomes weaker, it tends to burst due to impact even if it appears to be sealed.
As a countermeasure, we can expect to improve the sealing performance by increasing the heat-resistant temperature difference between the film on the printed surface and the sealant surface for welding, and by choosing a box-motion-type machine with a longer sealing period, instead of a rotary motion type that is superior in terms of speed but that can not have sufficient sealing strength.
Insufficient cleaning of sealer
In the inspection of seal packaging conducted by JIS, “product in seal” is one of the causes that are considered to be defective.
This is a problem that foreign matter enters into the seal part, and it is often caused by the scrap of the film material due to insufficient maintenance.
Also, residues of the material can cause scratches of bags, so it is necessary to thoroughly clean the sealer parts.
As a maintenance method, check that there is no film debris on the heat seal area at the end of work, and wipe it off.
It is also important to check the consumption of the cutter blade and apply grease.
Damages to Teflon tape and conveyor belts can also lead to improper sealing, so replace them as soon as they are damaged.
Seal failure caused by static electricity
Seal failure may be caused by static electricity.
If static electricity is not sufficiently removed in the process of making bags, the film material may stick each other and cause wrinkles.
In particular, when making bags with a vertical packing machine, wrinkles are likely to occur, and the contents stick to the inside of the bag even during the filling process, causing poor sealing and poor appearance.
(here for the vertical pillow packaging machine)
The methods to prevent this are to use the static eliminator at an effective timing, such as during storage where dust is easily attached, when the machine forms cylindrical shape with forming tube, or just before sealing.
Film materials are easily affected by the static electricity, so it is a prerequisite to keep them from accumulating it at all times.
Other Packaging Defects and Countermeasures
Other defective packaging problems are those that occur in the packaging machine.
As with sealing failures, many of these failures are caused by improper machine settings and maintenance.
This section explains the types of packaging defects that are likely to occur and how to deal with them.
- Wrinkles: Film wrinkles caused by tension failure during lamination
- Edge Breakage: Breakage of the end seal area that is likely to occur due to seal temperature or pressure
- Scratches: Longitudinal scratches caused by friction with foreign objects
- Seal waving: Seal deformation caused by heat shrinkage of the material
“Lamination” is a process for improving durability by laminating film and film to enhance moisture resistance, light-shielding, gas barrier, etc.
A trouble that is likely to occur at the take-up area during lamination processing is a wrinkle.
The cause of wrinkling is unevenness in tension when laminating film, which can lead to thin pressure, curl, uneven expansion and contraction, etc.
Tightening wrinkles not only lead to loss of material, but also lead to defective products during inspections after bag making.
To prevent this, it is necessary to set the tension properly and adjust the balance of the take-up shaft.
If the sealing temperature is too high or the sealing pressure is too high, “edge breakage” is likely to occur.
This is particularly likely to occur in OPP and CPP, and the film is cut off at the boundary between the sealed part and the inside of the bag because the material in the seal part melts unnecessarily.
Also, if the film is connected, the film may discolor or shrink, which may cause the contents to leak out of the damaged parts as well as appearance problems.
To avoid edge-breakage, the proper thermal and sealing pressure and sealing time for the material must be observed.
Generation of scratches
There are several causes of scratches on food packaging film.
First of all, it is generated in the film production line, but it is contaminated with air or foreign matter, or scratches that enter during processing, such as lamination or vapor deposition.
In the bag-making operation process, scratches in the longitudinal direction may occur due to rubbing with film deposits or foreign matter, which is particularly likely to occur when the film material is PE.
In addition to thorough cleaning of the seal, changing the sealant to the PP system may eliminate this problem.
Seal part waving
This is mainly a problem that occurs with OPP-based films.
Since the OPP type has a property that it easily expands and contracts when heat is applied, this may cause the sealed part of the seal to wavy.
This is called “wavy” sealing failure, which not only poses a problem with the appearance, but also prevents the packaging machine from moving smoothly.
The solution is to increase the temperature difference between the base film and the sealant.
Another countermeasure is to set the sealing temperature lower and reduce the speed.
The film used varies depending on the type and content of the food.
Some films are made by laminating a variety of materials, so it is important to note that problems may occur depending on the setting of the packaging machine.
Settings that match your films, such as temperature, pressure, and time, can be said to reduce loss and waste, resulting in a more efficient operation.