Why Multi-layer Film Delamination? What Can We do?

In daily life, the packaging bags commonly used for various foods and daily necessities are mostly composite bags. They are made of multiple film layers, and due to various factors, composite bags can delaminate.

So, why do composite bags delaminate? How should we address the issue of film delamination?

In this article, we will explore these questions in detail.

What is Film Delamination?

Film delamination refers to the separation of the layers in the multi-layer plastic pouch, which can compromise its integrity and functionality. This can be caused by poor adhesive quality, improper lamination process, or exposure to extreme conditions like heat or moisture.

Reasons for film delamination?

The lamination plastic bags are made from multi-layer films bonded with adhesive, several reasons can lead to film delamination:

• 1, Material suitability:
  Many people assume that all bags are the same, but this is not true. Different content requires specific bag material structures.
  For instance, items that undergo high-temperature sterilization require a PP inner layer and retortable adhesive.
  Conversely, products stored in the refrigerator at low temperatures may require different films.
  Using the wrong material for your products can lead to film delamination.
• 2, Lamination Technology:
  Expertise in the lamination process, along with machine parameters and the amount of material used, significantly influences the effectiveness of the lamination.

  For instance, if the coating amount of adhesive is too low or too thick, or if the coating is uneven, the bond strength between each layer of the composite film may be compromised.
  This poor adhesion increases the likelihood of film delamination, especially when compared to seals created with high heat sealing strength.

• 3, Aging Time:
  After the lamination process, the laminated film must be placed in an aging room for a specific period to allow the adhesive to cure and ensure a strong bond between the layers.
  If this curing time is insufficient, it can result in film delamination.
• 4, Moisture and Humidity:
  Goods are stored in a high-moisture and humidity environment that exceeds the maximum limits of the bags.
  Excess moisture can weaken the bond between layers, leading to separation, particularly in such humid conditions.
• 5, Temperature Changes:
  Extreme temperatures can cause expansion and contraction, stressing the bonds and resulting in film delamination.

Solutions to Address Film Delamination

Film delamination is completely unacceptable in flexible packaging, as it poses significant risks such as food spoilage, leakage of contents, and damage to brand reputation and sales.

To address and improve film delamination, we can implement better material selection, enhance adhesive quality, optimize processing conditions, and conduct thorough quality control throughout the manufacturing process.

• Material Selection:
  1. Choose the appropriate material structure for plastic bags.
     For food that requires retort processing, use PP film or metallic film with high-temperature resistance.
     Incorporate moisture-resistant materials or coatings to protect against humidity.
  2. Use adhesives specifically formulated for the materials being bonded to improve compatibility and adhesion strength.
     Differentiate between normal, pasteurization (boiling sterilization), and retort methods.
• Lamination Process Control:
  Monitor heat sealing and peel strength of the plastic bags, maintaining strict control over the lamination process.
  Conduct thorough testing for adhesion strength and resistance to environmental factors throughout the manufacturing process.
• Aging Time Control:
  Regulate the aging time of the laminated film to ensure it meets the required specifications.
• Storage Condition:
  Optimize storage and transportation conditions to minimize temperature fluctuations, ensuring goods are stored under suitable conditions.
• Design Considerations:
  Design plastic bags to minimize stress points and enhance their structural integrity.

How to Improve Film Delamination After Heat Sealing

The heat sealing quality of composite packaging bags is a crucial factor for packaging manufacturers in maintaining product quality.
How can we improve the film delamination after packaging bag heat sealing?

• The type, thickness, and quality of heat seal layer materials have a decisive impact on heat sealing strength.

  Commonly used heat seal materials for composite packaging include CPE, CPP, EVA, hot melt adhesives, and other ion-type resin co-extruded or blended modified films.

  The thickness of heat seal materials typically ranges from 20 to 80 μm, although in special cases, it can reach 100 to 200 μm.

  For the same type of heat seal material, the heat sealing strength increases with thickness.

  For retort pouches, the heat sealing strength is generally required to reach 40 to 50 Newtons, meaning the thickness of the heat seal material should be above 60 to 80 μm.

• The heat sealing temperature has the most direct impact on heat sealing strength.The melting temperatures of various materials determine the minimum heat sealing temperature for composite bags.

  During production, factors such as heat sealing pressure, bag-making speed, and the thickness of the composite substrate often require the actual heat sealing temperature to be higher than the melting temperature of the heat seal material.

  Lower heat sealing pressure necessitates a higher heat sealing temperature; similarly, faster machine speeds and thicker surface materials also require elevated sealing temperatures.

  If the heat sealing temperature is below the softening point of the heat seal material, no amount of increased pressure or extended sealing time will achieve a proper seal.

  Conversely, if the heat sealing temperature is too high, it can lead to excessive material flow, causing “root cutting” and significantly reducing both the heat sealing strength of the seal and the bag’s impact resistance.

• To achieve optimal heat sealing strength, a certain amount of pressure is essential.

  For lightweight packaging bags, the heat sealing pressure should be at least 2 kg/cm² and should increase accordingly with the overall thickness of the composite film.

  Insufficient heat sealing pressure can prevent proper fusion between the two layers of film, leading to weak seals or trapped air bubbles in the weld, resulting in inadequate sealing.

  However, it’s important to note that higher pressure is not always better; it should be applied in a way that does not damage the seal.

  At elevated heat sealing temperatures, the heat seal material is in a semi-molten state, and excessive pressure can force some of the adhesives out, causing the edges of the weld to become partially severed, which can make the seal brittle and reduce heat sealing strength.

• Heat sealing time is primarily determined by the speed of the bag-making machine.

  It is a key factor affecting both the strength and appearance of the seal.

  With the same heat sealing temperature and pressure, longer heat sealing times allow for a more thorough fusion of the heat seal layers, resulting in a stronger bond.

  However, excessively long heat sealing times can lead to wrinkling of the weld, negatively impacting the overall appearance.

• If the seal does not cool properly after heat sealing, it can affect not only the appearance and smoothness of the weld but also the heat sealing strength.

  The cooling process involves shaping the freshly molten seal under specific pressure and at a lower temperature to relieve stress concentrations.

  Insufficient pressure, poor water circulation, inadequate flow, high water temperature, or delayed cooling can all result in inadequate cooling, leading to reduced heat sealing strength.

• The more times the heat sealing occurs, the higher the heat sealing strength.

  The number of longitudinal heat seals is determined by the ratio of the effective length of the longitudinal sealing bar to the length of the bag.

  The number of transverse heat seals is dictated by the number of transverse sealing devices on the machine.

  For optimal heat sealing quality, it is recommended that the sealing occurs at least twice.

• For lamination films of the same structure and thickness, a higher interlayer peel strength correlates with greater heat sealing strength.

  In products with lower peel strength, weld failure often occurs when the layers of the composite film begin to delaminate at the weld, causing the inner heat seal layer to bear the destructive tensile force independently, thereby losing the reinforcing effect of the outer layer.

  This results in a significant reduction in the weld’s heat-sealing strength.

  Conversely, when the composite peel strength is higher, interlayer delamination at the weld is less likely, leading to a substantially higher measured heat sealing strength.

• If the filled products contaminate the seal, such as when some manufacturers use LDPE as the inner layer, they may find that the seal is prone to breaking when filling powdery substances.

  This occurs because LDPE does not have strong heat-sealing properties when contaminants are present. In such cases, it is necessary to either change the inner layer material or increase the thickness of the material to improve seal integrity.

How does KDW improve film delamination?

KDW’s products are shipped only after undergoing strict production and quality inspections.

Before shipping, all products are reviewed by the production, quality assurance, and sales departments, as well as the customer.

If delamination occurs during use, customers inform KDW sales personnel, who then gather details about the issue and analyze any returned delaminated samples.

KDW has its own laboratory, where our research and development and quality teams conduct experiments on the samples to identify potential causes.

We then implement targeted improvements and provide solutions, along with the results of our corrective actions.

KDW is committed to offering comprehensive after-sales service for all products, and we look forward to welcoming you to our company.