How to Print on Mylar Bags

In recent years, mylar bags have become a popular packaging choice in industries such as food, cosmetics, and medicine. Their unique structure can effectively block light, oxygen and moisture, providing suitable storage conditions for the product. In order to achieve the combination of packaging functionality and brand display, many businesses will choose to print their own design on mylar bags, such as logo, product name and so on. This blog will introduce the structure of mylar bags, the common technology of printing on mylar bags and so on. We hope this will help you have a better understanding of printing on mylar bags.

Table of Contents

1. Overview of Mylar Bags
2. How to Print on Mylar Bags

2.1 Thermal Transfer Printing
2.2 Screen Printing
2.3 Offset Printing
2.4 Flexographic Printing
2.5 Gravure Printing
2.6 Digital Printing

3. Quality Inspection for Printed Mylar
4. FAQs about Printing on Mylar Bags

1. Overview of Mylar Bags

1.1 What is a Mylar Bag

• Mylar was originally a trademark registered by DuPont for its PET(Polyester Terephthalate) film. What is commonly known in the market as a “Mylar bag” actually refers to a high-performance composite bag with PET as the outer layer.
• A mylar bag is generally composed of three layers: 
  The outer layer is typically BOPET(Biaxially Oriented Polyethylene Terephthalate) film, offering exceptional abrasion resistance and excellent printing compatibility.
  The middle layer is either aluminum foil or metallized film, serving as the primary barrier layer.
  Aluminum foil provides near-complete protection against oxygen, moisture, and light, while metallized films offer enhanced—but not absolute—barrier performance compared to ordinary plastic films.
  The inner layer is a heat-sealing material such as PE(polyethylene), ensuring that the bag can be firmly sealed by heating.
• This composite structure enables mylar bags to surpass the functionality of ordinary plastic bags, making them widely used in fields with stringent storage requirements.

1.2 Why Choose Printing on Mylar Bags

• For businesses, printing on Mylar bags is a crucial step in realizing their commercial value and brand functionality. A well-designed and clearly printed Mylar bag can quickly capture the attention of consumers. The bag body can showcase the brand logo, product selling points, and attractive visual designs. Additionally, printing can provide essential product information, such as ingredient lists, usage instructions, and expiration dates.
• For individuals, printing on blank mylar bags is an operation with practical value and creative potential. Whether used for sealing homemade snacks or as a carrier for personalized souvenirs, the lightweight and waterproof properties of mylar bags make them an ideal choice. You can print your favorite patterns or meaningful words on the mylar bags, giving the items a unique personality and emotional value.

2. How to Print on Mylar Bags

There are many available printing techniques for printing on mylar bags. You can choose any method based on factors such as print volume and design patterns.

2.1 Thermal Transfer Printing

Thermal transfer is a relatively simple printing method, and the printed designs can exhibit excellent detail. However, it is not a particularly fast process and can be costly, making it less ideal for large-area designs.

• Step 1: You need to prepare a special transfer film. Transfer film is a transparent film pre-printed with the desired pattern. This pattern layer is composed of a special release coating.
• Step 2: Align the prepared transfer film precisely with the position where the mylar bag needs to be printed.
• Step 3: Start the thermal transfer equipment and use the heated stamping head on the equipment to gently press the transfer film. The ink on the transfer film will melt under the heat. At the same time, under pressure, the melted design will be completely transferred onto the surface of the mylar bag.
• Step 4: After the hot transfer process is completed, the equipment immediately enters the cooling and shaping stage. Through the cold pressing device, the film is forcibly cooled while maintaining the pressure, causing the hot melt adhesive layer to solidify rapidly.
• Step 5: Upon secure adhesion of the graphic layer, the carrier liner of the transfer film is automatically stripped and rewound by the peeling mechanism. You now have a uniquely designed mylar bag.

2.2 Screen Printing

Screen printing can achieve vibrant visual color effects. However, its production efficiency is relatively low, and it cannot well present the details of the design.

• Step 1: Select a suitable metal or nylon mesh fabric as the screen. Apply a layer of photosensitive glue evenly on the surface of the screen. After the photosensitive glue dries, cover the screen with a film with the required design and expose it for processing.
• Step 2: After exposure, the photosensitive emulsion in the screen areas corresponding to the film design (i.e., the areas intended for printing) remains uncured. During subsequent development, the uncured photosensitive emulsion in these areas is washed away, leaving the mesh openings in these areas open and unobstructed.
• Step 3: Secure the prepared screen properly and precisely place it over the area on the mylar bag that needs to be printed. Ensure that the screen is tightly adhered to the surface of the bag to avoid any misalignment.
• Step 4: Pour the ink onto one end of the screen and use a specialized scraper to move it uniformly from one end to the other. Where the scraper passes, the ink will flow through the open mesh of the screen and evenly spread onto the surface of the mylar bag, creating the corresponding design.
• Step 5: After the printing is complete, place the mylar bag in a ventilated area and wait for the ink to dry naturally. You can also use a drying device to accelerate the drying process.

2.3 Offset Printing

Offset printing can effectively print fine designs. However, its equipment and technology costs are relatively high, making it more suitable for large enterprises. Since mylar film is non-absorbent, offset printing ink dries relatively slowly.  To further reduce costs, most manufacturers will adopt the method of printing on the labels and then attaching them to the mylar bags.

• Step 1: Prepare the printing plate. Through exposure and development, oil-attracting and water-attracting areas are formed on aluminum plates.
• Step 2: During the printing process, the printing plate first comes into contact with the water roller, making the non-design areas wet. Then it contacts the ink roller, where the ink only adheres to the design areas.
• Step 3: The ink on the printing plate first transfers to the rubber roller. The rubber roller is elastic and can adapt to the unevenness of different surfaces.
• Step 4: The rubber roller comes into contact with the label, transferring the ink completely to the surface of the label.
• Step 5: Then these labels are attached to the mylar bags. This approach can balance both printing quality and practicality.

2.4 Flexographic Printing

Flexographic printing is cost-effective and enables fast production. Therefore, it is one of the common methods for large-scale printing on mylar bags.

• Step 1: Create a relief printing plate. Using a photosensitive polymer, the design part will form a raised surface while the non-design part will be flat. Then, install the relief plate on the printing equipment.
• Step 2: Prepare the ink. The anilox roller can precisely control the amount of ink and transfer it to the raised areas.
• Step 3: Install the mylar film at the feed end of the equipment. After starting the equipment, the mylar film will be transported forward at a constant speed. When passing over the relief plate, the relief plate gently presses against the bag, transferring the ink to the surface of the mylar film.
• Step 4: And the mylar film must pass through a drying or UV curing device to cure the ink before proceeding to bag-making processing.

2.5 Gravure Printing

Gravure printing effectively highlights design details and is the preferred method for high-quality printing. However, the production cost for making the plates is high, and the process takes a long time. Therefore, it is more suitable for the production of large quantities of standardized products.

• Step 1: Make the gravure plate. The production process of gravure printing plates requires precision machining, typically employing electronic engraving or laser engraving techniques. The surface of the plate is engraved or corroded to form countless microscopic cells. The depth and volume of the cells determine the amount of ink transferred and the tonal value of the print.
• Step 2: Install the gravure plate on the printing equipment. After starting the equipment, the ink will be evenly applied to the surface of the gravure plate, ensuring that all the cells are filled with ink.
• Step 3: The scraper will closely adhere to the surface of the printing plate, removing the excess surface ink and leaving only the ink in the cells. This prevents the excess ink from affecting the printing quality.
• Step 4: Uniformly transfer the mylar film into the equipment. Through high-pressure application, the cells on the gravure plate are brought into close contact with the mylar film. The ink will be completely transferred onto the surface of the mylar film, forming a clear design.
• Step 5: After the printed mylar film undergoes drying treatment, the ink will be fully cured before proceeding to bag-making processing.

2.6 Digital Printing

Digital printing is a highly flexible printing method that can be carried out on mylar bags. It does not require the creation of traditional printing plates. The process is simple and suitable for small batches and personalized customization.

• Step 1: Prepare the design file in advance. Import the design file into the digital printing equipment and set the printing parameters, such as color, size, and so on.
• Step 2: Place the Mylar bag on the printing platform of the equipment and secure its position to prevent any movement during printing.
• Step 3: Start the digital printer. The device directly prints design information from electronic files onto the mylar bag using inkjet or electrostatic imaging.
• Step 4: After the printing is completed, perform drying treatment according to the type of ink to ensure the ink is firmly adhered.

3. Quality Inspection for Printed Mylar 

It is essential to conduct quality inspections on the printed mylar bags or mylar films. Before commencing the mass production, you can first carry out partial printing and then conduct quality inspections on it. And for the mylar bags that have already been printed in batches, sampling tests can also be conducted according to the contents of the following suggestions.

• Print Defect Check: Check whether there are issues such as misregistration, omission, or dirt spots on the mylar bag/film.
• Color Verification: Use a color density meter or compare with standard Pantone colors to ensure color accuracy.
• Dimension Specs: Check whether the size and design position of the mylar bag meet the expected specifications.
• Ink Adhesion Test: Press the standard tape firmly onto the printed surface and then quickly remove it to evaluate the level of ink detachment.
• Barrier Property Verification: For products with high barrier requirements, it is necessary to check whether the printed materials still meet the established oxygen permeability or water vapor permeability standards.
• Food Safety Tests: If the mylar bag is used for food packaging, it is necessary to conduct a third-party test to ensure that the printing ink components comply with relevant food safety regulations.

4. FAQs about Printing on Mylar Bags

4.1 Can I print on mylar bags with a standard home inkjet or laser printer?

Direct printing is not recommended. The properties of mylar itself cause ordinary printer ink to stain and not dry. You need to use a dedicated thermal transfer device or digital printer to print directly on mylar bags. However, you can print the design on the label first, and then stick it onto the mylar bag.

4.2 Will printing affect the performance of the mylar bag?

No, it won't. The printing is only done on the surface of the outermost PET film. The ink layer is extremely thin and will not damage the crucial aluminum foil barrier layer in the middle. Therefore, it does not affect the core protective performance at all.

4.3 Does the Mylar bag have an odor after printing?

The newly printed products may have a slight smell of ink, which will dissipate after ventilation. If the smell is strong and pungent, it may indicate the use of inferior ink. In such cases, it is recommended to ask the supplier to provide relevant safety certifications.

Summary

By printing on mylar bags, you can make the product packaging more attractive. Moreover, this is also one of the effective ways to promote the brand image. Each printing method has its own advantages and disadvantages, and you need to weigh them according to your own needs. We hope this blog can enhance your understanding of printing on mylar bags.

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