Analysis of the Impact of "Fish Eyes" on Custom Product Packaging

During the trade process of plastic packaging, many procurement professionals tend to focus primarily on material, thickness, and unit price when searching for plastic bag manufacturers. In fact, many detailed issues are also worth their attention, and one such issue is the presence of "fish eyes" in plastic bags.

For customers seeking brand effect, fish eyes are not only a visual flaw but also a nightmare for the printing process. As a plastic factory with over ten years of experience, we understand that the quality of a plastic bag is determined not just by its load-bearing capacity, but also by its microscopic-level cleanliness and flatness. This article will deeply analyze the root causes of fish eyes and share how we achieve "fish-eye-free" high-transparency film production through technical means.

1. What are "Fish Eyes"? Why Do They Make Your Logo Printing Look Cheap?
In the professional terminology of plastic bag manufacturers, fish eyes typically refer to small granular protrusions formed on the film surface during the blown film process, caused by incomplete resin modification or the mixing of unmelted high-molecular-weight components into the raw material.

• The Culprit of Printing "White Spots": When performing fine gravure printing or flexo printing, the printing roller contacts the plastic surface through the ink film. If fish eye protrusions exist on the film surface, the printing roller will slightly "jump" at that point, preventing uniform ink coverage around the fish eye. The final result: countless tiny "white rings" or uneven color patches appear on your carefully designed brand logo, severely affecting visual communication.

• Stress Concentration Leading to Breakage Risk: From a mechanical perspective, fish eyes are weak points for stress concentration. For heavy-duty packaging bags requiring frozen storage or long-distance transportation, fish eyes are prone to puncturing or tearing. This is a hidden quality risk.

2. Four "Deep-Zone" Causes of Fish Eyes
To solve the fish eye problem, one must operate with surgical precision. In our laboratory, we classify the causes into four points:

• Mismatch in Melt Flow Index (MFI) of Raw Materials: Many manufacturers mix large amounts of cheap off-grade materials into the main resin to reduce costs. These materials have extremely wide molecular weight distributions, and some ultra-high-molecular-weight components cannot fully melt at normal extrusion temperatures. These "stubborn molecules" eventually become fish eyes on the film.

• Insufficient Screw Shear Force: The extruder screw is the core of the factory. Worn or old equipment has reduced shearing action on the plastic melt, failing to fully separate agglomerated polymer molecular chains.

• Compromise on Mesh Count of Filter Screens: To pursue high output, many plastic bag factories choose filter screens with smaller mesh counts (e.g., 80 mesh) because larger mesh openings reduce back pressure and increase output speed. The consequence: tiny impurities and unmelted components pass directly through the filter screen, turning into thousands of fish eyes.

• Thermal Degradation in "Dead Zones": If the die head of the blown film machine has an unreasonable design with flow dead zones, the plastic melt will stagnate there for a long time and undergo thermal degradation (carbonization), periodically detaching and mixing into new material, forming black or yellow fish eyes.

3. How We Solve It: Factory Standardization Process for "Fish-Eye-Free" Production
As a plastic bag manufacturer with an almost obsessive pursuit of quality, we have established the following vertical control system to ensure that every roll of film delivered to customers has "mirror-grade" quality:

• 100% Virgin Brand Resin Commitment: We insist on cooperating with internationally renowned brands and strictly prohibit the addition of off-grade materials of unknown origin in high-performance packaging bags. This ensures molecular weight regularity from the source.

• Automated 3-Layer Co-extrusion Technology: Through three-layer co-extrusion, we can optimize physical properties, heat-seal properties, and appearance properties in separate layers. For example, adding high-toughness material to the middle layer while focusing the inner and outer layers on high flatness significantly dilutes the probability of fish eyes.

• High-Mesh Automatic Screen Changer System: We use multi-layer composite filter screens of 120 mesh or higher, equipped with a hydraulic automatic screen changer. This means we can maintain high melt purity at all times without stopping the machine. Although this increases power consumption and filtration loss, the payoff is nearly zero-defect printing performance in the finished product.

• Regular "Deep Spa" for the Die Head: Our technical team thoroughly cleans the flow channels of the extrusion system every two weeks to ensure no carbon deposits remain.

4. Conclusion: Choose a Partner Who Understands Your "Brand Pain Points"
The market in 2026 is no longer an era where "any bag will sell." Against the backdrop of globally escalating consumer aesthetic standards, the attention to detail in a plastic bag often represents the rigor of a brand.

We are not just a plastic bag manufacturer; we are the guardian of your brand's visual identity. If you are suffering from fish eyes, printing ghosting, or uneven tensile strength, please feel free to contact our technical team. We are happy to provide free material diagnosis and customize a "high-cleanliness" packaging solution tailored for you. You can confidently choose to trust our company, Shinloong Mae.