A Brief Guide to Varnishing Machine

Last updated on 10 4 月, 2023
Reina
Uncategorized

Introduction

The varnishing process involves applying a layer of colorless transparent coating on the surface of printed materials, which, after leveling and drying, forms a thin and uniform transparent glossy layer on the surface of the printed materials. This process effectively enhances the glossiness, smoothness, water resistance, light resistance, and wear resistance of the products, serving to protect and beautify them while enhancing their practical value.

Working Principle

The principle of varnishing in printing mainly involves applying (or spraying, printing) a layer of colorless transparent coating on the surface of printed materials. After processes like leveling, drying, pressing, and curing, this layer of coating forms a thin and even transparent glossy layer on the surface of the printed materials. The principles include:

Selection of coating: Choose appropriate varnish based on the material, color, and desired glossiness of the printed materials. Common varnishes include oil-based, water-based, and UV-curable types.

Coating application: Use coating machines or other coating equipment to evenly apply the varnish on the surface of the printed materials. Control the thickness and uniformity of the coating during application to ensure the final glossy layer has a good appearance and performance.

Leveling: After the coating is applied to the surface of the printed materials, it needs some time for leveling. During leveling, the coating will automatically spread and flow on the surface of the printed materials to eliminate unevenness and traces.

Drying: After leveling, the coating needs to be dried. During drying, the solvent in the coating evaporates, causing the coating to gradually cure into a film. The drying temperature and time need to be adjusted according to the type of coating and the material of the printed materials.

Pressing: After the coating is dried, a pressing machine can be used to press the printed materials to enhance the smoothness and glossiness of the coating layer, and to increase the wear resistance and light resistance of the printed materials.

Forms of Varnishing

Coating Varnishing (Regular Varnishing)

Apply varnish oil directly onto the printed materials and dry it.

Features: Simple process, low cost, good varnishing effect.

Press Varnishing

After coating varnishing, use a pressing machine to roll and increase the surface glossiness.

Features: Relatively simple process, low cost, good varnishing effect.

UV Varnishing

Apply UV varnish oil on the surface of the printed materials, and cure it by UV irradiation.

Features: Non-volatile, energy-saving, glossy and sturdy film, corrosion-resistant, fast varnishing speed (up to 500m/min), suitable for online varnishing.

Composition and Classification of Varnishing Machines

Classification of Varnishing Machines

Water-based Varnishing Machine

Water-based varnishing: It uses water-based varnish for varnishing, which has characteristics such as high solid content, low viscosity, and non-toxicity. It also has good leveling and glossiness and can be diluted with water.

Wide applicability: Water-based varnishing machines are very suitable for the printing and processing of packaging materials in industries such as food and pharmaceuticals.

Good heat sealing: Water-based varnish has excellent heat sealing properties, and even when using cellosolve, it can achieve good heat sealing effects.

Strong wear resistance: Products processed with water-based varnish have good flatness and strong anti-curling ability, making them particularly suitable for packaging printed materials that require strong wear resistance. Especially in high-speed operation, such as cigarette labels, which need to withstand a lot of mechanical load, water-based varnish can meet the requirements of high transparency and wear resistance.

UV Varnishing Machine

High surface glossiness: UV varnishing machines can improve the surface glossiness of printed materials, making them have a more vivid and beautiful appearance.

Strong wear resistance: The surface of printed materials treated with UV varnishing machines forms a hard and wear-resistant transparent film layer, effectively enhancing the wear resistance of printed materials and making them more durable.

Fast curing speed: UV varnishing machines have a fast curing speed and can complete the varnishing process in a very short time, improving production efficiency.

Varnishing

Materials

Water-based Varnish

Water-based varnish refers to a liquid used to increase the glossiness, water resistance, and abrasion resistance of paper-printed products, applied either inline with a printing press or offline with a varnishing machine, with water as the carrier.

UV Varnish

UV varnish, also known as UV clear coat, is a transparent coating. After application on printed materials, it undergoes a transition from liquid to solid state through UV light exposure, providing durability against scratches and abrasions while presenting a glossy appearance. UV varnish mainly consists of UV curing resin, active diluents, photoinitiators, and other additives.

Varnishing Process and Procedure

Preparation

Firstly, identify the printed materials that require varnishing, typically selecting areas that need to highlight colors and patterns for varnishing treatment. Clean the printed materials to ensure the surface is free from dust, preventing any interference with the varnishing effect.

Selection of Varnishing Method:

Based on the requirements and characteristics of the printed materials, select an appropriate varnishing method. Common varnishing methods include UV varnishing, water-based varnishing, and solvent-based varnishing.

Preparation of Varnish

Choose the suitable varnish according to the selected varnishing method. Prepare or dilute the varnish as required, ensuring that the concentration and viscosity of the varnish are suitable for the varnishing needs of the printed materials.

Varnishing Process

Apply the varnish evenly onto the surface of the printed materials using professional varnishing equipment (such as UV varnishing machines or water-based varnishing machines). While varnishing can be done manually, mechanical equipment (such as varnishing machines) is typically used to ensure uniform application and efficiency.

Drying

After applying the varnish, drying is necessary. The drying method depends on the type of varnish and the characteristics of the printed materials. For water-based varnish, natural drying or hot air drying methods are commonly used. For UV varnish, rapid curing drying is achieved by using ultraviolet light irradiation.

Curing (Specific to UV Varnishing)

If UV varnishing is chosen, curing is required after drying. After UV varnish is applied to the substrate, it undergoes a curing process where the varnish flows and enters the UV radiation zone for curing. The curing process involves a chemical cross-linking process, where unsaturated carbon-carbon double bonds in the prepolymers and monomers (liquid) receive energy from the photoinitiator and cross-link polymerize into a network structure of molecules (solid).

Quality Inspection

Conduct quality inspection on the completed varnished and cured printed materials to ensure the varnishing effect meets requirements and there are no issues such as missed spots, unevenness, or incomplete curing.

Packaging

After varnishing is completed, package the printed materials to protect the varnished surface from scratching or contamination.

Advantages of Varnishing Process

Enhanced Print Quality

Increased Gloss: The surface gloss of varnished prints is higher, resulting in brighter colors and clearer images, thus enhancing the overall quality of the prints.

Improved Durability: Varnished prints exhibit enhanced surface durability, effectively resisting daily wear and tear, thereby extending the lifespan of the prints.

Waterproof and Stain Resistant: Varnished prints demonstrate certain waterproof and stain-resistant properties after varnishing treatment, better maintaining the cleanliness and aesthetics of the prints.

Highlighted Visual Effects

Spot Varnishing: Through spot varnishing treatment, key information or images in prints can be emphasized, making the visuals more three-dimensional and vivid, attracting the audience’s attention.

Gloss Contrast: The contrast in gloss between varnished and unvarnished areas enhances visual impact, making the prints more attractive.

Energy-efficient and Effective: The varnishing process is simple and efficient, enabling rapid curing and reducing energy consumption and emissions.

Improved Production Efficiency

Rapid Curing: Varnish has strong affinity and adhesion with ink, enabling rapid curing and shortening the production cycle.

Reduced Scrap Rate: Varnishing treatment stabilizes print quality, reducing scrap rates caused by quality issues.

Wide Application

Various Print Materials: The varnishing process is suitable for various print materials such as book covers, posters, brochures, packaging, etc., with broad application prospects.

Different Materials: This process can be applied to a variety of materials including paper, plastic films, expanding the range of material choices for prints.

Applications of Varnishing Process

Book Binding

In the binding of high-end books, varnishing is used to enhance the glossiness and durability of the book covers. For example, the covers of some hardcover books are treated with UV varnishing, giving them a mirror-like gloss while also increasing the waterproof and dustproof properties of the books.

Cosmetic Packaging

Varnishing treatment in cosmetic packaging is primarily aimed at highlighting the product’s texture and brand image. The varnishing process can create a high gloss surface or special gloss effects such as pearlescent and holographic, thereby enhancing the product’s attractiveness. Additionally, varnishing treatment also improves the packaging’s durability and waterproofing, protecting the quality and appearance of the cosmetics.

Label Printing

In the field of label printing, varnishing is commonly used to enhance the labels’ durability and waterproofing. For example, on product labels, clothing tags, etc., varnishing treatment can make the surface smoother, more wear-resistant, and increase the labels’ waterproofing performance. Moreover, some labels requiring anti-counterfeiting measures also adopt varnishing treatment to enhance their anti-counterfeiting performance through special gloss effects.

Packaging Boxes

In the printing of packaging boxes, varnishing is indispensable. It not only enhances the glossiness of the box surface, making it more attractive but also provides waterproof and moisture-proof properties, protecting the products inside the packaging.

Business Cards

Business cards are essential items in business activities, and the varnishing process can be used in their production to make them look more professional and textured.

Common Problems and Solutions in Varnishing Process

Poor Gloss, Insufficient Brightness

Main Causes: (1) UV varnish with low viscosity, resulting in a thin coating layer; (2) Excessive dilution with non-reactive solvents such as ethanol; (3) Paper with high absorbency; (4) Fine mesh roller with insufficient ink supply. Solutions: Adjust the viscosity and coating amount of UV varnish accordingly based on the different paper conditions. For papers with strong absorption, a base oil layer can be applied beforehand.

Incomplete Curing, Surface Tackiness

Main Causes: (1) Aging of UV lamps resulting in reduced intensity; (2) Prolonged storage time of UV varnish; (3) Excessive addition of non-reactive diluents; (4) Machine running at excessive speed. Solutions: Timely maintenance of equipment and replacement of lamps. Generally, the required radiation intensity for UV varnish curing should not be lower than 25mW/cm². Adding a certain amount of photoinitiators and photosensitizers, such as triethylamine, to accelerate curing speed. Adjusting the printing process.

Failure to Apply UV Varnish on the Surface of Printed Products

Main Causes: (1) UV varnish with low viscosity, resulting in a thin coating layer; (2) Excessive addition of ink setting agents or drying oils in ink; (3) Ink surface crystallization; (4) Excessive use of anti-stick materials (such as silicone oil, spray powder) on the ink surface; (5) Fine mesh coating roller. Solutions: For products requiring UV varnishing, corresponding measures must be taken during printing. Apply UV varnish appropriately thicker, if necessary, solve the problem by applying base oil or replacing special varnish.

White Spots and Pinholes in UV Varnish Coating

Main Causes: (1) Thin coating layer; (2) Fine mesh pattern of the roller; (3) Excessive addition of non-reactive diluents (such as ethanol); (4) Excessive dust on the surface of printed products. Solutions: Maintain cleanliness in the production environment and on the surface of printed products. Increase the thickness of the coating layer, and optionally add a small amount of leveling agent or wetting agent. It is better to use reactive diluents for dilution.

Thickening and Gelling of Varnish

Main Causes:

Prolonged storage time of varnish;

Varnish not stored away from light completely;

High storage temperature. Solutions: Pay attention to the effective shelf life of UV varnish, strictly store away from light, and maintain a storage temperature of 5-25°C.

Environmental Protection And Sustainability

To reduce environmental impact and promote sustainability, the following measures can be implemented:

Firstly, opt for environmentally friendly varnish materials:

Utilize eco-friendly varnish materials such as water-based varnish and UV-curable varnish. These materials are free from harmful solvents, have low volatile organic compound (VOC) emissions, and significantly reduce environmental pollution.
Develop and apply biodegradable varnish materials that can be decomposed by microorganisms under specific conditions, further lowering environmental pollution.

Secondly, optimize production processes:

Introduce advanced production technologies and equipment, such as UV curing technology, to enhance curing efficiency and reduce energy consumption and emissions.
Precisely control the amount of varnish used to avoid excessive usage, which can lead to waste and pollution.

Thirdly, strengthen waste gas treatment:

Install effective waste gas treatment equipment, such as VOCs recovery devices, to capture and treat the waste gases generated during the printing process, thereby reducing emissions.
Regularly inspect and maintain waste gas treatment equipment to ensure its efficient operation.

Fourthly, obtain green printing certifications:

Actively participate in and obtain green printing certifications, such as ISO 14001 Environmental Management System certification, to demonstrate the efforts and achievements of printing facilities in environmental protection.
Enhance the competitiveness of printing facilities through certifications and promote the development of green printing.

Lastly, research and develop new technologies and materials:

Invest resources in researching and exploring new eco-friendly technologies and materials, such as the application of nanotechnology in varnishing processes, to further improve environmental performance.
Keep abreast of industry trends and timely introduce and apply advanced eco-friendly technologies and materials.

Development Trends of Varnishing Process

Wide Application of Eco-friendly Materials: With the increasing global awareness of environmental protection, the varnishing process in printing is increasingly adopting eco-friendly materials such as water-based varnish and UV-curable varnish. These materials not only reduce environmental pollution but also provide excellent printing results and gloss.

Application of Digitalization and Automation Technologies: With the rapid development of digitalization and automation technologies, the varnishing process in printing has also witnessed new transformations. Digital workflows integrate prepress, printing, and post-press processing, enhancing production efficiency and reducing costs. Additionally, intelligent control systems monitor various parameters in real-time during production, ensuring stability and consistency in product quality.

Innovation in UV Curing Technology: The application of UV curing technology in the varnishing process is becoming increasingly widespread. Although traditional UV curing technology offers fast curing speeds and low energy consumption, it faces challenges such as high equipment costs and skill requirements for operators. Therefore, the latest UV curing technology improves curing efficiency, reduces energy consumption, and lowers skill requirements for operators by enhancing light sources, curing agents, and coating methods.

Application of Nanotechnology: The application of nanotechnology in the varnishing process enhances the surface quality and performance of printed products. Nanomaterials possess unique physical and chemical properties that significantly improve gloss, abrasion resistance, weather resistance, and other properties of the varnish layer. Through the application of nanotechnology, printed products not only look more aesthetically pleasing but also exhibit enhanced performance.

In summary, the varnishing process will continue to play a vital role in the printing industry. With the emergence of new materials and technologies, we look forward to seeing more environmentally friendly and efficient varnishing processes that bring innovative possibilities to printed products. Moreover, we anticipate the expansion of varnishing processes into more fields, adding brilliance to products across various industries.

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