Storage Considerations for Printed Mylar Bags Before Use
Before you even think about filling them, how and where you store your printed mylar bags is a critical factor in preserving their integrity, ensuring they perform as expected, and protecting your brand’s image. Proper storage is not just about keeping them in a cupboard; it’s a deliberate process to safeguard against environmental factors that can degrade the material, compromise seals, and ruin the print quality. The primary considerations revolve around controlling temperature, humidity, light exposure, and physical handling to prevent the bags from becoming brittle, the prints from fading, or the layers from delaminating.
Let’s break down the science behind why these factors matter so much. Mylar is a brand name for BoPET (Biaxially-Oriented Polyethylene Terephthalate), a polyester film known for its excellent strength, and gas and moisture barrier properties. However, these properties can be undermined by improper storage conditions. The inks used in printing, whether flexographic or digital, are also susceptible to environmental stressors. Getting the storage right from the start ensures your investment in high-quality mylar bags printing pays off when the bags are finally put to use.
The Temperature and Humidity Sweet Spot
This is arguably the most important duo to control. Mylar itself is relatively stable, but extreme temperatures and moisture can wreak havoc on both the film and the seals.
Avoiding High Temperatures: You should store mylar bags in a cool, dry place with a consistent temperature ideally between 15°C and 25°C (59°F and 77°F). Prolonged exposure to temperatures above 35°C (95°F) can have several negative effects. The material can become more pliable than intended, potentially leading to deformation under the weight of stacked boxes. More critically, heat can cause the layers of the bag laminate to soften, increasing the risk of delamination—where the layers separate—which completely voids the barrier protection. For the printed graphics, heat can cause certain inks to soften or bleed, especially if bags are stacked and pressure is applied.
The Perils of Cold and Condensation: On the flip side, storing bags in an unheated warehouse where temperatures drop near or below freezing (0°C / 32°F) is equally risky. Cold makes the mylar film brittle. When you handle a cold bag, it’s far more susceptible to cracking, micro-tears, and pinholes that are invisible to the naked eye but will compromise the bag’s ability to hold a vacuum or block out oxygen. The biggest danger, however, comes when you bring cold bags into a warmer environment. Condensation will form on the surface, and if this moisture gets trapped between bags or, worse, in the seal area, it will prevent a proper heat seal later on, leading to seal failures.
Controlling Humidity: The target relative humidity (RH) for storage should be below 50-60%. High humidity is a silent killer for stored packaging. Moisture in the air can be absorbed by the bag’s material or settle on its surface, leading to:
- Ink Issues: Water-based inks can reactivate or smudge. Even solvent-based inks can experience problems like blocking, where the printed surfaces stick together and tear when separated.
- Metal Layer Corrosion: If your mylar bags have a metallic layer for light blocking (like transparent window bags), high humidity can cause this layer to oxidize or corrode over time, reducing its effectiveness.
- Mold and Mildew: While the bags themselves won’t mold, the cardboard cartons they are shipped in can, and this can transfer to the bags, creating an unhygienic and unprofessional appearance.
The following table summarizes the ideal and risky environmental conditions:
| Factor | Ideal Range | Risky Conditions | Potential Consequences |
|---|---|---|---|
| Temperature | 15°C to 25°C (59°F to 77°F) | Above 35°C (95°F) or Below 0°C (32°F) | Delamination, ink bleeding, brittleness, cracking, seal failure due to condensation. |
| Humidity (RH) | Below 50-60% | Above 70% RH | Ink smudging/blocking, corrosion of metallic layers, mold growth on packaging. |
Shielding from Light and Oxygen
Even before they are filled, your printed bags need protection from their two main adversaries: light and oxygen.
Light Exposure: Ultraviolet (UV) radiation from direct sunlight or even strong fluorescent lighting is a powerful degrader of polymers and pigments. Continuous exposure will cause the mylar film to yellow and become brittle over months or years. More immediately noticeable will be the fading or color-shifting of your vibrant prints. UV light breaks down the chemical bonds in dyes and pigments, causing your brand’s carefully chosen colors to look washed out and unprofessional. Always store mylar bags in their original shipping boxes or in dark, opaque containers, and keep them away from windows and direct light sources.
Oxidation: While mylar is an excellent oxygen barrier, the materials themselves can be subject to slow oxidative degradation when exposed to air over very long periods. This is a slow process, but for bags intended for long-term storage before use (e.g., over a year), it’s a factor. Keeping them sealed in their original plastic packaging until needed minimizes air exposure and is a best practice.
Physical Handling and Stacking Protocols
How you physically manage the bags during storage is just as important as the environment. The goal is to prevent physical damage that compromises the bag’s structure.
Proper Stacking: Boxes of mylar bags should be stacked neatly and evenly. Avoid stacking boxes too high, as the weight can crush the bags at the bottom of the stack, potentially causing the bags to fuse together (blocking) or crease permanently. These creases can become weak points and may interfere with the sealing jaws during filling. A good rule of thumb is to not exceed 5-6 boxes in a stack, depending on the size and weight of the boxes.
Avoiding Compression and Punctures: Never store heavy or sharp objects on top of boxes containing mylar bags. The pressure can force the bags to conform to the shape of underlying objects, and sharp edges can easily puncture or tear the film. Designate a specific, clean area for bag storage that is not a general-purpose storage zone for other equipment.
First-In, First-Out (FIFO): Implement a strict FIFO inventory system. Use the oldest stock of bags first. This rotation prevents any single batch from sitting in storage for an excessively long time, reducing the cumulative risk of environmental damage. Mark your boxes with the date of receipt to make this process easy.
Long-Term Storage vs. Short-Term Storage
The duration of storage dictates the level of precaution needed.
Short-Term (Less than 3 Months): For most businesses, this is the typical storage window. The key here is to get the basics right: a clean, dark, climate-controlled room (like an office or dedicated storage closet) is usually sufficient. Just ensure the bags are kept in their original boxes and away from potential contaminants.
Long-Term (3 Months to Several Years): This scenario requires a more rigorous approach. If you’re ordering a large bulk quantity to save on unit costs, you must invest in proper storage infrastructure. This means a warehouse or storage unit with active climate control (HVAC) to maintain stable temperature and humidity year-round. The bags should remain in their master shipping cases, which are preferably placed on pallets and kept away from walls to promote air circulation. For extreme long-term storage, you might even consider sealing the master cartons in larger plastic bags with desiccant packets to control any residual moisture.
By paying close attention to these storage considerations—controlling the environment, handling with care, and matching your practices to the storage duration—you ensure that your printed mylar bags arrive at the filling line in perfect condition, ready to provide the superior protection and professional appearance you paid for.