Table of Contents
Introduction to the Process
Principle
Lamination is a surface finishing process in printing, also known as post-press coating, post-press lamination, or post-press film application. It involves covering the surface of printed products with a transparent plastic film (primarily BOPP and PET materials) of 0.012 to 0.020 mm thickness using a laminating machine, forming a paper-plastic composite product through adhesion.
Advantages
Enhanced Durability: Lamination enhances the durability of packaging by adding a protective film to paper boxes and gift boxes, effectively preventing scratches, stains, and other damage. This extends the packaging’s lifespan and ensures products remain undamaged during transport and storage.
Improved Visual Appeal: Lamination can significantly enhance the visual appeal of packaging. By choosing transparent or colored laminating materials, the packaging can appear more vibrant and attractive, capturing consumer attention and increasing product appeal.
Additional Design Space: Lamination offers extra design possibilities. Using materials with special effects or textures, such as matte or glossy finishes, can add unique and sophisticated elements to the packaging, enhancing the product’s perceived quality and value.
Working Methods and Process
The lamination process can be divided into wet lamination and pre-coating lamination based on the materials and equipment used. Wet lamination involves using a freshly applied adhesive, which can be solvent-based or emulsion-based. Pre-coating lamination uses a pre-coated film with heat-melting or solvent-evaporating adhesives.
Wet Lamination Process
Process Preparation: Proper preparation ensures smooth production and high efficiency. This involves checking printed materials, selecting plastic films, and preparing adhesives.
Film Installation: Cut the selected film to appropriate widths and install it on the laminating machine’s film feed mechanism, ensuring the film is smooth and uniformly tensioned.
Adhesive Coating: Adjust adhesive viscosity based on paper quality, ink thickness, drying tunnel temperature, and machine speed. Ensure even adhesive coating thickness.
Drying: The drying process removes solvents from the adhesive, retaining its solid content. The drying tunnel temperature should be between 40-60°C. Proper drying enhances bonding strength and prevents bubbling or delamination.
Adjusting Heat and Pressure: Set heat and pressure based on the ink layer’s thickness, paper quality, and climatic conditions. Maintain appropriate temperatures to prevent film deformation and ensure strong adhesion.
Controlling Machine Speed: Adjust machine speed according to heat and pressure requirements, ensuring optimal lamination quality.
Sample Testing: Conduct sample testing to ensure surface smoothness and absence of wrinkles or bubbles.
Trimming and Cutting: For pre-coated laminations, immediate cutting is necessary. For coated paper and cardboard, allow 24 hours before cutting to ensure strong bonding.
Pre-coating Lamination Process
The pre-coating lamination process omits the adhesive preparation, coating, and drying steps, simplifying the operation.
Classification of Lamination Films
Gloss Film: Includes BOPP and PET gloss films with high surface glossiness (≥100 degrees).
Scratch-resistant Gloss Film: Features scratch resistance, preventing surface damage.
Matte Film: Commonly used matte film with low glossiness (≤3 degrees).
Scratch-resistant Matte Film: Offers a metallic texture and moderate glossiness (3-6 degrees).
Touch Film: Provides a velvety texture and allows UV printing and hot stamping.
Holographic Film: Produces various holographic effects through embossing.
Common Adhesives for Lamination
Solvent-based Adhesives: Includes EVA, acrylic, polyurethane, polyester, styrene-butadiene rubber, and isobutylene rubber adhesives.
Alcohol-soluble Adhesives: Includes acrylic, polyurethane, and polyester adhesives.
Water-soluble Adhesives: Includes EVA, acrylic, polyurethane, and polyester adhesives.
Lamination Methods
Wet Lamination: Involves applying adhesive, combining the film with the substrate, and drying it in one process.
Dry Lamination: Adhesive is applied and dried before combining with the substrate in one machine.
Pre-coated Lamination: Adhesive is pre-applied and dried on the film before lamination, eliminating the need for adhesive application and drying on-site.
Impact of Lamination on Print Color and Solutions
Lamination enhances color brightness and contrast, potentially causing color shifts. To manage this:
New Standards: Brightness deviation should be within specified limits.
Sample Testing: Use sample tests to predict and adjust color shifts.
Simulation: Use transparent tape to simulate lamination effects.
Effect on Matte Film: Generally, colors appear redder and less saturated with matte lamination.
Common Issues and Solutions in Lamination
Blistering and Spotting
Causes: High paper moisture, improper adhesive concentration, excessive ink additives, dust on surfaces, uneven adhesive application.
Solutions: Dry printed products, adjust adhesive concentration, clean surfaces, and maintain uniform adhesive application.
Wrinkling of Printed Products
Causes: High paper moisture, uneven roller pressure, misaligned paper.
Solutions: Control environmental humidity, adjust roller pressure, align paper correctly.
Film Wrinkling
Causes: High temperatures, excessive film tension, fast lamination speed.
Solutions: Adjust temperature, tension, and lamination speed.
Curling During Processing
Causes: Moisture in paper, high environmental humidity, excessive film tension.
Solutions: Control humidity, adjust roller pressure and film tension.
Poor Adhesion
Causes: Undried ink layers, low pressure, high speed, low temperature.
Solutions: Extend drying time, increase pressure, adjust speed and temperature.
Surface Whitening
Causes: High environmental humidity, trapped moisture.
Solutions: Control temperature and humidity.
Composition and Classification of Laminating Machines
Components
Adhesive Section: Equipped with adjustment mechanisms for adhesive application.
Drying Section: Includes infrared lamps and fans for adhesive drying.
Heat Press Section: Critical for adhesion, consisting of rollers with adjustable temperature and pressure.
Types of Laminating Machines
Wet Lamination Machines: Include adhesive application, drying, heat pressing, and film rewinding sections.
Pre-coating Lamination Machines: Simplify the process by pre-coating the film with adhesive.
Discussion on the Environmental Impact of Lamination
As environmental awareness deepens and relevant industry laws and regulations continue to improve, the printing industry must also keep pace with these developments, adjusting its practices to meet green and sustainable printing requirements.
Current Pollution Problems
The in-line lamination process uses a large amount of organic solvents, which have several drawbacks. The adhesives used contain benzene solvents, which are harmful to human health, potentially causing leukemia and skin allergies with a latency period. Prolonged exposure to these environments can lead to acute and subacute benzene poisoning.
The complexity of the in-line lamination process involves blending adhesives, applying adhesive coatings, and drying. Increasing concentrations of organic solvents can easily lead to fires due to static electricity generated by the film materials.
Residual harmful substances in products can negatively impact consumer health. Benzene and alcohol compounds are highly volatile, and while most evaporate during and shortly after the lamination process, some residues remain and can volatilize over time, contaminating the consumer environment and posing health risks.
In China, 80% of paper fibers are sourced from recycled materials, including waste paper, trimmings, etc. If lamination, particularly in-line lamination, is widely used and the paper cannot be separated from the plastic film, these laminated paper products cannot be recycled, leading to economic losses and resource wastage.
Countermeasures
Eliminate in-line lamination technology and use pre-coated film processes
Pre-coated film technology is an advanced, environmentally friendly lamination process that is poised to replace in-line lamination. It involves pre-applying hot-melt adhesive to BOPP (biaxially oriented polypropylene) film, which, upon reheating and pressing, securely bonds the film. This method is already used in pharmaceutical and food packaging.
Advantages of pre-coated film
No toxic gas emissions during production, improving the work environment and eliminating fire hazards.
Simplifies the lamination process, improving quality and efficiency. It enhances color saturation and clarity without harmful residues, avoiding common issues like bubbling, delamination, and curling.
Safe for use in book covers, food packaging, tobacco, alcohol, and pharmaceuticals, posing no threat to consumer health.
Develop new materials to enhance recyclability and environmental friendliness
To meet rising standards for print quality and market demand, the lamination industry must adjust its structure to reduce environmental impact.
Adhesive requirements:
-Adhesives must not contain toxic organic solvents like benzene, toluene, xylene, or halogenated hydrocarbons.
-Benzene, toluene, and xylene content in adhesives must be less than 1000 mg/kg, with benzene content below 100 mg/kg.
-Halogenated hydrocarbon content (measured as dichloroethane) must be less than 1000 mg/kg.
Strict adherence to international standards in raw material selection is essential. Safe, non-toxic adhesives like Nubond Instant, which does not contain harmful isocyanates, can be used. Environmentally friendly water-based adhesives like XS-109, suitable for food-grade paper containers, and XS-101, used for high-transparency and brightness applications, are recommended.
Standardize operational procedures
To prevent fires in lamination workshops, particularly those using in-line adhesive processes, strict operational norms are essential. Fire hazards are most likely to occur above the adhesive tray due to static electricity generated during film stretching and cutting.
Fire prevention measures:
-Ensure good grounding for machinery, preferably using a ring-shaped grounding network. Handle adhesives and solvents gently to avoid sparks from metal containers. Install self-sensing static eliminators on equipment.
-Increase humidity around the lamination machine using humidifiers or by sprinkling water, reducing static electricity accumulation.
-Maintain good ventilation to lower the concentration of volatile substances.
-Enforce strict no-smoking policies, avoid open flames, and ensure operators wear anti-static clothing and shoes.
As environmental awareness, health consciousness, and business philosophies evolve, outdated technologies will be replaced. The lamination process must move toward “non-toxic, harmless, green” methods, and Chinese enterprises should proactively address these environmental challenges responsibly.
Application Cases and Product Demonstrations
-Book and magazine covers, brochures, and commemorative albums
-Postcards, calendars, and maps
-Color boxes, card boxes, and fine boxes
-Shopping bags, envelopes, and business cards
-Hang tags, cards, and labels
Future Trends in Lamination
In developed countries, the lamination market is saturated, with many large printing and packaging companies owning their own lamination equipment. However, emerging markets in Asia, South America, and the Middle East are growing rapidly.
Future Trends Analysis
-Technological innovation: Advances like nanotechnology will improve scratch resistance and cleanliness of lamination films.
-Environmental requirements: The demand for eco-friendly materials and equipment will increase. Water-based lamination technologies will replace traditional solvent-based methods.
-Automation and intelligence: Lamination machines will become more automated and intelligent, enhancing production efficiency and quality while reducing labor costs.
-Personalized demand: Customized lamination machines will meet the diverse needs of different industries and customers.
-International cooperation: Global collaboration will drive technological and market advancements in the lamination industry.
In conclusion, the lamination process will continue to innovate and evolve. As environmental awareness and technology advance, the lamination industry will face broader prospects and opportunities.
